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See detailLaw, Order and Postwar Purge in the Grand Duchy of Luxembourg (1944 - 1955): Transitional Justice and Redistribution through the example of Justice, Gendarmerie and Police
Wingerter, Elisabeth UL

Doctoral thesis (2021)

The present doctoral thesis examines the strategies and redistributive effects of political purge in the Grand Duchy of Luxembourg after World War II. It examines in detail the judicial and administrative ... [more ▼]

The present doctoral thesis examines the strategies and redistributive effects of political purge in the Grand Duchy of Luxembourg after World War II. It examines in detail the judicial and administrative purge of justice personnel, magistrates, police officers and gendarmerie corps members, and the development of law and order in the 20th century. This study treats regulated purge measures as phenomena of transitional justice. In Luxembourg’s case, the transition in question is one of restorative and redistributive kind: The prewar sociopolitical order is largely restored, however, in the ranks of the state administrations, redistributive practices of purge have changed the internal order. The imperfect, yet initially quite severe judicial and administrative sanctions have laid the foundations for national myths and narratives that have for many years clouded the historical analysis of both the occupation and the postwar period. This happened through the redistribution of symbolic capital during the purge proceedings by classifying persons into “patriots” and “antipatriots”. The struggle of the “antipatriots” to regain their symbolic, financial and political capital after the war and their antagonism with the heterogeneous group of “patriots” often focused on perceived or real financial and professional disadvantages. While the redistribution of financial capital was gradually reversed in the postwar and efforts for reconciliation set in almost immediately after 1945, the redistribution of symbolic capital led to a social divide that was successively forgotten through the emergence of the master narrative of collective resistance. [less ▲]

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See detailSELECTION OF THE LIPID ACCUMULATOR MICROTHRIX PARVICELLA IN MUNICIPAL WASTEWATER TREATMENT PLANTS FOR SUBSEQUENT BIODIESEL PRODUCTION
Uwizeye, Marie Louise UL

Doctoral thesis (2021)

The current trend of more circular use of resources have driven the new practices in wastewater treatment that propose a transition from taking wastewater as just a waste to wastewater as a source of ... [more ▼]

The current trend of more circular use of resources have driven the new practices in wastewater treatment that propose a transition from taking wastewater as just a waste to wastewater as a source of resources. Thus, lipids accumulated by the microbial biomass represent a potentially important stock of resources for biodiesel production. Within this study, a lipid accumulating bacterium Microthrix parvicella (M. parvicella), was studied using a molecular biology approach (16S rRNA gene amplicon sequencing) and GC-MS/MS to identify its occurrence and its accumulated lipids and thus, their potential use for biodiesel production. [less ▲]

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See detailRAN Resource Slicing Mechanisms for Multiplexing of Multiple Services in 5G Downlink Wireless Networks
Korrai, Praveenkumar UL

Doctoral thesis (2021)

The fifth-generation (5G) of wireless networks majorly supports three categories of services, namely, enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLLC), and massive ... [more ▼]

The fifth-generation (5G) of wireless networks majorly supports three categories of services, namely, enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLLC), and massive machine-type communications. Every service has its own set of requirements such as higher data rates, lower latency in packet delivery, high reliability, and network energy-efficiency(EE) to support applications including ultra-high definition (UHD) video streaming, virtual reality (VR), autonomous vehicles, vehicular communications, smart farming, and remote-surgery, respectively. The existing one-size-fits-all services network model is not a viable option to support these services with stringent requirements. Therefore, accommodation of these different services on the same physical network while ensuring their distinct QoS requirements is a major challenge. To address this problem, a new concept called network slicing (NS) has emerged as a promising solution for the dynamic allocation of resources to wireless services with different QoS demands. The NS can be formed in both the radio access network (RAN) and core network (CN) parts. In this thesis, we concentrate on RAN resources slicing, and more specifically on challenges that reside in the assignment of limited radio resources to manage the distinct traffic demands occurring from a wide variety of users belonging to heterogeneous services. Specifically, we address the RAN optimization method for joint allocation of time, frequency, and space resources to the eMBB, URLLC, and mMTC users according to their traffic demands (i.e., queue status). Our work in this thesis can be broadly classified into three parts based on the objective function considered in the resource optimization problem: 1) sum-rate maximization, 2) power minimization, 3) EE maximization. In the first part of this thesis, we address an adaptive modulation coding (AMC) based resource allocation problem for dynamic multiplexing of URLLC and eMBB users on the shared resources of the OFDMA-based wireless downlink (DL) network. Specifically, we formulate the resource blocks (RBs) allocation problem as a sum-rate maximization problem subject to the minimum data rate constraint, the latency-related constraint, orthogonality, and reliability constraints. Furthermore, to allocate RBs and transmit power jointly to the users, we also formulate the AMC-based optimization problem to maximize the sum good-put of eMBB users subject to URLLC and eMBB users’ QoS constraints. Importantly, in this problem formulation, we consider a probabilistic constraint to incorporate CSI imperfections and a short-packet communication model for URLLC service. In the second part of this thesis, we formulate the joint RBs and transmit power allocation problem to minimize the transmit power consumption at the BS while guaranteeing the QoS constraints of eMBB, URLLC, and mMTC users and probabilistic constraint to incorporate CSI imperfection, respectively. Importantly, we consider mixed-numerology-based RB grid models to the users according to their queue status/traffic demand for satisfying their stringent requirements. Furthermore, different slicing strategies such as slice-aware (SA) and slice-isolation (SI) resource assignment mechanisms are considered for the efficient co-existence of URLLC, mMTC, and eMBB services on the same RAN infrastructure. The resulting problems in the first and second parts of the thesis are mixed-integer non-linear programming problems (MINLPs) which are intractable to solve. To provide solutions to these problems, we first transform the problems into more tractable using the AMC approximation functions, probabilistic to non-probabilistic conversion functions, Big-M theory, and difference of convex (DC) programming. Later, these transformed problems are solved using the successive convex approximation (SCA) based iterative algorithm. Our simulation results illustrate the performance of our proposed method compared to the baseline methods. Also, the simulation results show the effectiveness of the mixed-numerology-based RB grid model over the fixed numerology grid model and the performance of SA and SI resource slicing strategies in terms of achievable data rates, packet delivery latencies, and queue status, respectively. In the third part of this thesis, different from the first two parts, for the joint assignment of beams, RBs, and transmit power to eMBB and URLLC users, we formulate an EE maximization problem by considering resources scheduling, orthogonality, power-related constraints, and QoS constraints for different services. The resulting mixed-integer non-linear fractional programming problem (MINLFP) is intractable and difficult to solve. To provide a feasible solution, we first transform the formulated problem into a tractable form using fractional programming theory, approximation functions and later utilize the Dinklebach iterative algorithm, DC programming, and SCA to solve it. Finally, we compare the performance of the proposed method against baseline schemes through simulation results. In particular, we show the performance of RAN slicing mechanisms with the mixed and fixed-numerology-based RBs grid models in terms of achievable EE, packet latencies, data rates, total sum-rate, and computational complexity. The proposed algorithm outperforms the baseline schemes in terms of achieving higher data rates for eMBB users. The results also show the trade-off between the total achievable sum rate and EE of the network. The proposed method with mixed numerology grid delivers 20% of higher URLLC packets within 1 ms of latency. Besides, it achieves the lowest computation time than that with the fixed numerology grid. [less ▲]

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See detail5G AND BEYOND NETWORKS WITH UAV: TRAJECTORY DESIGN AND RESOURCE ALLOCATION
Tran Dinh, Hieu UL

Doctoral thesis (2021)

Over the past few years, unmanned aerial vehicle (UAV)-enabled wireless communications have attracted considerable attention from both academia and industry due to their high mobility, low cost, strong ... [more ▼]

Over the past few years, unmanned aerial vehicle (UAV)-enabled wireless communications have attracted considerable attention from both academia and industry due to their high mobility, low cost, strong light-of-sight communication links, and ease of deployment. Specifically, UAVs can be deployed to serve as aerial base stations (BSs), relays, power sources, etc., to support ground users (GUs) in various scenarios such as surveillance missions, search and rescue, crop monitoring, delivery of goods, data collection, emergency communications, secrecy communications, space-air-ground communications, etc. Despite many advantages, UAV-enabled communications are not without limitations. The limitations of UAVs have imposed technical restrictions on weight, size, and energy capability, thereby affecting the durability and performance of UAVs. The key goal of this dissertation is to propose and develop new frameworks and efficient optimization algorithms to solve novel challenging problems, facilitate the design and deployment of UAV-enabled communications. Consequently, these proposed algorithms can become one of the foundations for deploying UAVs in future wireless systems. Specifically, this dissertation investigates different UAV communication systems by addressing several important research problems through four emerging scenarios: 1) Design UAV trajectory based on traveling salesman problem with time window (TSPTW); 2) Full-duplex (FD) UAV relay-assisted emergency communications in Internet of Things (IoT) networks; 3) Backscatter- and cache-assisted UAV communications; and 4) Satellite- and cache-assisted UAV communications in 6G aerial networks. In the first scenario, we provide the coarse trajectory for the UAV based on TSPTW, which has not been investigated in UAV communications yet. Concretely, we propose two trajectory design algorithms based on TSPTW, namely heuristic algorithm and dynamic programming (DP)-based algorithm, and they are compared with exhaustive search and traveling salesman problem (TSP)-based methods. Based on the feasible path obtained from proposed algorithms, we minimize the total UAV’s energy consumption for each given path via a joint optimization of the UAV velocities in all hops. Simulation results show that the energy consumption value of DP is very close to that of the exhaustive algorithm with greatly reduced complexity. Based on this work, an efficient TSPTW-based algorithm can be used as an initialized trajectory for designing a joint problem of UAV trajectory and other communications factors (e.g., communication scheduling, transmit power allocation, time allocation), which are challenges. We then study the case of a FD UAV relaying system in IoT networks. Specifically, a UAV can be deployed as a flying base station (BS) to collect data from time-constrained IoT devices and then transfer it to a ground gateway (GW). Especially, the impact of latency constraint for the uplink (UL) and downlink (DL) transmission utilizing FD or half-duplex (HD) mode is investigated. Using the proposed system model, we aim to maximize the total number of served IoT devices subject to the maximum speed constraint of the UAV, total traveling time constant, UAV trajectory, maximum transmit power at the devices/UAV, limited cache size of the UAV, and latency constraints for both UL and DL. Next, we attempt to maximize the total throughput subject to the number of served IoT devices. The outcome of this work will motivate a new framework for UAV-aided communications in disaster or emergency communications. Next, a novel system model that considers SWIPT, backscatter and caching in UAV wireless networks is developed. Based on this model, we aim to maximize the system throughput by jointly optimizing the dynamic time splitting (DTS) ratio and the UAV’s trajectory with caching capability at the UAV. This is the first work that jointly considers wireless power transfer (WPT), caching, and BackCom in UAV communications, which provides a potential solution for a battery-free drone system that can fly for a long period in the sky to support the terrestrial communication systems. Finally, a novel system model for effective use of LEO satellite- and cache-assisted UAV communication is proposed and studied. Specifically, caching is provided by the UAV to reduce backhaul congestion, and the LEO satellite assists the UAV’s backhaul link. In this context, we aim to maximize the minimum achievable throughput per ground user (GU) by jointly optimizing cache placement, the UAV’s transmit power, bandwidth allocation, and trajectory with a limited cache capacity and operation time. The outcomes of this work can provide a new design framework for Satellite-UAV-terrestrial communications that includes two tiers, i.e., the backhaul link from satellite to UAV and the access link from UAV to ground users, which imposes new challenges and was not investigated before. [less ▲]

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See detailThe antioxidant glutathione as a regulator of natural killer cell immunity
Frias Guerra, Luana UL

Doctoral thesis (2021)

Natural killer (NK) cells are cytotoxic lymphocytes that belong to the innate branch of the immune system. Regulation of NK cell activity relies on the expression and engagement of a wide range of ... [more ▼]

Natural killer (NK) cells are cytotoxic lymphocytes that belong to the innate branch of the immune system. Regulation of NK cell activity relies on the expression and engagement of a wide range of inhibitory and activating receptors that detect signals arising from cells in distress. Besides their cytotoxic function, NK cells are effective producers of cytokines that participate in the regulation of other immune cells, such as dendritic cells and T cells. These innate lymphocytes control microbial infections and malignant cell growth, which are pathological conditions where reactive oxygen species (ROS) play a crucial role. ROS participate in cell signaling events and constitute important secondary messengers for immune cell proliferation and growth. However, when accumulated, their presence leads to oxidative stress due to their high reactivity against biomolecules. In order to ensure coordinated levels of ROS, cells are endowed of antioxidant systems that allow for ROS detoxification. One of the most important intracellular antioxidants is glutathione (GSH). Given the subset specificity of GSH regulation in immunity, we aimed to investigate the role of this antioxidant in NK cells. Using a genetic-based approach, through a flox-Cre system, we specifically abrogated GSH production in NK cells. Mutant mice had a reduced abundance of NK cells, when compared to controls. Furthermore, in vitro stimulation of NK cells with IL-15, showed that ablation of GSH production renders NK cells unable to proliferate and these cells were less cytotoxic. NK cells lacking GSH accumulated mitochondrial ROS, resulting in reduced mitochondrial fitness. This was paralleled by a general metabolic shutdown, and reduced mTOR and STAT5 signaling. In vivo, GSH and redox regulation were demonstrated to be key for NK cell-mediated regulation of T cells, in a viral model of lymphocytic choriomeningitis virus (LCMV). Moreover, in an experimental tumor model, deletion of GSH resulted in an NK cell intrinsic impairment of tumor dissemination and increased exhaustion. Taken together, our results indicate GSH as a key checkpoint for NK cell homeostasis and function. [less ▲]

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See detailINTERFACE OPEN-CIRCUIT VOLTAGE DEFICIT IN CU(IN,GA)S2 SOLAR CELL: CHARACTERIZATION, SIMULATION AND MITIGATION
Sood, Mohit UL

Doctoral thesis (2021)

Current commercial photovoltaic technologies are close to their practical limits, and enhancing their power conversion efficiency (PCE) requires a paradigm shift to tandem approaches. Tandem solar cells ... [more ▼]

Current commercial photovoltaic technologies are close to their practical limits, and enhancing their power conversion efficiency (PCE) requires a paradigm shift to tandem approaches. Tandem solar cells can exceed the single junction practical and thermodynamic limits. The desired top cell bandgap to enhance PCE of current photovoltaic technologies is ~1.6 1.7 eV. The bandgap tunability from 1.5 eV to 2.5 eV positions Cu(In,Ga)S2 as a prime top cell candidate for next generation low-cost tandem cells. However, they are limited by a low external open circuit voltage (VOC,ex). In this thesis, we have studied the interface recombination and found it to cause a difference between VOC,ex and internal open-circuit voltage (VOC,in) in Cu(In,Ga)S2 solar cell. We have introduced a quantifiable metric that has not been used before for Cu(In,Ga)S2, to evaluate VOC disparity in terms of “interface VOC deficit” defined as (VOC,in – VOC,ex). The temperature dependent current-voltage measurement allows to investigate the activation energy (Ea) of the dominating recombination path in the device, uncovering the cause of interface VOC deficit in Cu poor and Cu-rich Cu(In,Ga)S2 devices. We find that negative conduction band offset (CBO) at the absorber/buffer interface results in interface VOC deficit in Cu poor Cu(In,Ga)S2 devices. Although the interface VOC deficit can be reduced by replacing the buffer for favorable band alignment at the absorber/buffer interface, a substantial deficiency still exists. We observe that the CBO not only at the absorber/buffer interface but also at the buffer/i-layer interface leads to an interface VOC deficit in devices. This, in general, is not an issue in Cu(In,Ga)Se2 devices. By optimizing buffer and i-layer, we mitigate and overcome buffer/i-layer losses to get Cu poor Cu(In,Ga)S2 devices with consistently low interface VOC deficit. As a result, an in-house PCE of 15.1 % is achieved together with an externally certified PCE of 14 %. This is, by far, the best Cu(In,Ga)S2 device performance except for the record PCE device. In contrast, the interface VOC deficit and the interface recombination persists in Cu-rich Cu(In,Ga)S2 devices and is not resolved by alternative buffers. To identify the possible origin of the interface VOC deficit, we characterize two sister systems CuInS2 and CuInSe2, which offer reduced complexity due to Ga exclusion. The Cu-rich devices of these systems are also known to suffer from interface recombination, and for CuInSe2, it has been linked to the “200 meV” defect. However, the underlying mechanism of how this defect leads to interface recombination remains unknown. Through results obtained from photoelectron spectroscopic measurements, we exclude the possibility of two commonly evoked causes of interface recombination: negative CBO and Fermi-level pinning. Sulfur-based post-deposition treatments on KCN etched Cu-rich CuInS2 absorbers reveal near interface defects as a possible alternative cause of interface VOC deficit. The treatment increases the VOC,ex, which originates from improved Ea and interface VOC deficit in treated devices. The capacitance transient measurements further reveal that slow metastable defects are present in the untreated sample. The treated samples show that the slow transient is suppressed, suggesting the passivation of slow metastable defects. The treatment adapted to Cu rich CuInSe2 displays a reduction in the deep defect signature in admittance spectra, which explains the observed improvement in interface VOC deficit. This indicates that the defects near the absorber/buffer interface, acting as non-radiative recombination centers, as the source of interface VOC deficit. Finally, to understand how the defect leads to interface recombination, a new model based on near interface defects is offered using the holistic analysis and evaluation of the defect characteristics. We can reproduce an interface VOC deficit with all the signatures of an interface recombination-dominated device using numerical simulations. This model provides a solution for the consideration of interface recombination by defects distributed in a thin layer within the bulk absorber, an explanation beyond classical models. The near interface defect model finally explains why Cu rich chalcopyrite solar cells are limited in their VOC,ex despite a good VOC,in, which was not discovered before. The model thus forms a new third explanation for interface recombination signature in devices and is applicable to any device with highly recombinative defects near the interface. [less ▲]

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See detailA quasicontinuum approach towards mechanical simulations of periodic lattice structures
Chen, Li UL

Doctoral thesis (2021)

Thanks to the advancement of additive manufacturing, periodic metallic lattice structures are gaining more and more attention. A major attraction of them is that their design can be tailored to specific ... [more ▼]

Thanks to the advancement of additive manufacturing, periodic metallic lattice structures are gaining more and more attention. A major attraction of them is that their design can be tailored to specific applications by changing the basic repetitive pattern of the lattice, called the unit cell. This may involve the selection of optimal strut diameters and orientations, as well as the connectivity and strut lengths. Numerical simulation plays a vital role in understanding the mechanical behavior of metallic lattices and it enables the optimization of design parameters. However, conventional numerical modeling strategies in which each strut is represented by one or more beam finite elements yield prohibitively time­consuming simulations for metallic lattices in engineering­scale applications. The reasons are that millions of struts are involved, as well as that geometrical and material nonlinearities at the strut level need to be incorporated. The aim of this thesis is the development of multi­scale quasicontinuum (QC) frameworks to substantially reduce the simulation time of nonlinear mechanical models of metallic lattices. For this purpose, this thesis generalizes the QC method by a multi­field interpolation enabling amongst others the representation of varying diameters in the struts’ axial directions (as a consequence of the manufacturing process). The efficiency is further increased by a new adaptive scheme that automatically adjusts the model reduction whilst controlling the (elastic or elastoplastic) model’s accuracy. The capabilities of the proposed methodology are demonstrated using numerical examples, such as indentation tests and scratch tests, in which the lattice is modeled using geometrically nonlinear elastic and elastoplastic beam finite elements. They show that the multi­scale framework combines a high accuracy with substantial model reduction that are out of reach of direct numerical simulations. [less ▲]

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See detailEnhancing Photovoltaic Hosting Capacity in Distribution Grid via Grid Reconfigurations, PV Droops and Battery Inverter Control
Torchyan, Khachatur UL

Doctoral thesis (2021)

The EU 2030 climate and energy framework has set a mandatory goal to achieve a renewable energy share in the final energy demand of 32% by 2030. Moreover, in the final National Energy and Climate Plan ... [more ▼]

The EU 2030 climate and energy framework has set a mandatory goal to achieve a renewable energy share in the final energy demand of 32% by 2030. Moreover, in the final National Energy and Climate Plan (NECP) Luxembourg has defined its renewable generation share goal at 25% by 2030. Between 2018 and 2019, three times more photovoltaic (PV) panels were installed than in the previous years. To achieve the NECP target and to ensure further smooth integration of PV systems, the PV hosting capacity (HC) of the grid should be enhanced. This thesis discusses the common issues and current developments of HC enhancement and presents three HC enhancement techniques: grid reconfiguration and grid-code modification, extended current droop control and transformer loading control. First, the thesis analyzes the potential of grid reconfiguration in HC enhancement. For the analysis the grid configurations are divided into meshed and radial subsets. The grid reconfiguration analysis and HC calculation are done using pandapower and NetworkX library. The cross-influence and the location of DG are considered while determining the HC of the grid. The analysis shows that proper grid configuration selection is important as it can substantially increase the HC and decrease the average loading in the lines. Second, the impact of extended current droops on HC enhancement is investigated. In the designed extended current droops (Id(V ), Iq(V )), extra reactive power reserve is made available by changing the droop gain of the reactive current droop when the overvoltage is not cleared by the existing reactive power reserve. The simulations proved that the extended current droops are a viable grid reinforcement strategy which can not only regulate the voltage at the point of common coupling (PCC), but also relax the transformer loading and improve overall voltage and frequency stability. Additionally, oversizing of the inverter increases the reactive power reserve, which in turn lowers the voltage profile and decreases the amount of curtailed active power. Finally, two novel communication-less transformer overloading protection strategies based on a battery energy storage (BES): transformer protection droops (TPD) and direct loading control (DLC), are designed and compared. Both strategies force the PV inverters to curtail their active power output without relying on communication. The strategies have been tested on detailed models, where the total installed PV power varies between 0.9 to 2 times the transformer rating. The static and dynamic performance of the DLC is superior to the TPD control strategy. DLC is a robust control strategy. It can reduce the transformer loading by 41%, compared to the grid configuration without BES and bring the system to the steady-state within 700ms in the worst-case scenario. It also ensures to keep the system voltages within safe operational limits. It can be used as a backup active power curtailment solution in the cases of communication failure in centralized control. [less ▲]

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See detailAnalysis of flow induced texturing in complex fluids with Brillouin Rheology - a proof of concept
Lehr, Claudius Moritz UL

Doctoral thesis (2021)

The aim of this work is to study the flow induced texturing of molecules (complex fluids) in a shear field. This is done by measuring phonons with photons [1] in a commercially available rotational ... [more ▼]

The aim of this work is to study the flow induced texturing of molecules (complex fluids) in a shear field. This is done by measuring phonons with photons [1] in a commercially available rotational rheometer. The optical experimental method of transferring momentum and energy between phonons and photons is generally known as Inelastic Light Scattering (ILS) [2]. Brillouin Light Scattering (BLS) [3] has a quite small energy transfer compared to Raman spectroscopy [4] but with a high performance multi-pass Vernier tandem Fabry-Perot interferometer [5] and a sophisticated optical set-up, it is possible to achieve information about the texture (like entanglement of molecules) of complex fluids inside a rheometer gap while shearing. This can be acquired for any position in the sample, in contrast to the rheological experiments were an average over a whole sample is used. Here we successfully demonstrate an optical set-up that couples a BLS with rotational rheology in order to simultaneously measure the high-frequency longitudinal elastic modulus in a classical rheometer along with the zero-shear viscosity during the flow of complex fluids. BLS gives the possibility for contactless determination of local elastic properties, while the designed optical set-up is introduced as boundary conditions to control temperature gradients in the sample, and the position and dimension of the scattering volume. This method was tested for a range of temperatures, and well as for an applied shear field and different radial positions of the scattering volume in the sample using a plate-plate rheometer geometry. Measurements of a dilute polymer system suggest a homogeneous orientation of polymer molecules throughout the sample as soon as a critical shear rate has been reached at one spatial position. [less ▲]

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See detailQuantizations and moduli stacks of curves
Kalugin, Alexey UL

Doctoral thesis (2021)

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See detailPROCESS INNOVATION FOR SENSORS IN MOBILE APPLICATIONS BASED ON LASER ASSISTED METAL-POLYMER JOINING
Amne Elahi, Mahdi UL

Doctoral thesis (2021)

The laser joining of metals to polymers is currently an interesting research area thanks to the capability of developing lightweight structures. Considering their miscellaneous applications in the ... [more ▼]

The laser joining of metals to polymers is currently an interesting research area thanks to the capability of developing lightweight structures. Considering their miscellaneous applications in the automotive industry, aluminum and polyamide are chosen as the material combination for this study. There are three main challenges regarding laser joining of metals to polymers in general: significant difference between the melting points of the materials, adhesion at the interface, and the mechanical properties of the assembly. The first challenge is addressed by in-situ heating observation and temperature measurement during the joining process. Therefore, polyamide thermal pyrolysis is effectively avoided by optimizing the laser joining parameters and employing power modulation. The second one is studied by applying different surface treatments on the materials (laser-based and abrasive-based). The surfaces were tested by several characterization techniques before and after each surface treatment. The modification of the surface structure through an appropriate surface treatment leads to the improvement of wetting and adhesion between the melted polyamide and aluminum surface. Therefore, the alteration of a mixed failure (adhesive/cohesive) to a fully cohesive failure is the major step to enhance the mechanical properties of the assemblies. However, in the absence of bubbles, the structural modification of polyamide during the joining process is responsible for the failure. Energy-dispersive X-ray1 mapping and Time-of-Flight Secondary Ion Mass Spectrometry2 shows the physicochemical bonding between aluminum oxide and the polyamide at the interface. To further enhance the mechanical properties of the assemblies, the structure of the polyamide near the interface of metal/polymer is addressed. For this purpose, laser treatment of polyamide, post-heat treatment, and joining with different feed rates were implemented. Finally, the shear strength of approximately 45 MPa on average is achieved for the assembly of laser-polished aluminum laser-joined to the polyamide with 2 and 5 mm/s feed rate. [less ▲]

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See detailEffective Review in the Age of Information: The Case-study of Semi-automated Decision-making based on Schengen Information System
Demkova, Simona UL

Doctoral thesis (2021)

The speed with which the EU employs automation in large-scale informational cooperation is unparalleled by the attention devoted to the adjustment of the corresponding system of legal protection ... [more ▼]

The speed with which the EU employs automation in large-scale informational cooperation is unparalleled by the attention devoted to the adjustment of the corresponding system of legal protection. Illustrated with the case study of the Schengen Information System, yet as manifested across broader policy areas, the EU's determination to exploit the benefits of information technologies by rendering them ever smarter, fast and efficient, eventually puts to a test the Union’s fundamental values and principles. The technological progress affects not only the European constitutional promise of effective judicial protection but also of good administration. The drive to revolutionise decision-making takes a sway on the very act of deciding, rendering it an ever-more ‘automatised’ behaviour. Against this backdrop, the thesis addresses the research question: to what extent are supervisory authorities able to ensure effective protection to individuals against decisions taken based on large-scale informational cooperation, in light of the challenges arising from technological innovation, namely automation, for the exercise of effective review. The thesis offers a holistic assessment of the existing and novel challenges to effective account-giving and enforcement of individual rights in the EU multilevel system in view of contributing to the debate on the impacts of technological progress on the legal position of private persons. The assessment shows that ex post enforcement of rights is fundamentally weakened where established jurisdictional limits prevent addressing the multijurisdictional and cross-border conduct underpinning data-driven decision-making. Legal protection instead increasingly depends on the array of additional safeguards, including ex ante legal protection through the judicial authorisation or regular monitoring of the automated support systems. Their existence alone, however, does not uphold the constitutional promise of effective judicial protection. The quest to strengthen the available ex post review mechanisms needs to be addressed as the absolute priority in order to balance the magnitude of power exerted by means of automation on both public conduct and private lives. [less ▲]

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See detailESSAYS ON THE ECONOMICS OF INTERNATIONAL MIGRATION
Montes Viñas, Ana Cecilia UL

Doctoral thesis (2021)

The present dissertation consists of three main chapters of self-contained works about international human migration and migrant's integration in the host society. The first chapter introduces the general ... [more ▼]

The present dissertation consists of three main chapters of self-contained works about international human migration and migrant's integration in the host society. The first chapter introduces the general outline of the dissertation and briefly explains the research questions explored in each chapter. The second chapter studies the effect of migration networks and long-term cultural distance on migration flows. The main research question is whether the diaspora effect on migration flows is larger when the cultural distance between the country of origin and destination is large. We use an unbalanced panel database of bilateral migration flows data from 1960 to 2009 for about 175 sending countries to 32 destination countries. We proxy long-term cultural distance using ancestral distance, also called genetic distance. Based on the micro-founded gravity model for migration, we estimate the interaction between the diaspora size and ancestral distance using the Poisson Pseudo Maximum Likelihood (Santos Silva \& Tenreyro, 2006). We find evidence of a positive and significant interaction effect between the network effect and ancestral distance on international migration flows, however, this effect is small once we control for omitted unobserved determinants of migration flows. The third chapter studies the educational performance of the children of migrants in the United States of America. It pushes forward the hypothesis that misalignment between expectations and aspirations crucially affects the educational outcomes of immigrant young adults. It shows that the difference in school performance between migrant children and natives lies within the aspirations and expectations that migrant children form. This chapter uses the National Longitudinal Study of Adolescent to Adult Health (Add Health), a longitudinal database representative of American high schools that surveys adolescents between the grades 7-12 collected by the Carolina Population Center. The chapter shows that a positive difference between aspirations and expectations is a driving force for higher effort and better education outcomes of immigrant teenagers. This force resolves the well-known immigrant paradox. This result is specific to migrant children and does not hold for second-generation migrant pupils who appear quite acculturated to the USA context. In the fourth chapter, the relationship between financial aid and foreign education at the postgraduate level is evaluated. I use a sample of Colombian graduates who applied to a financial aid program that sponsors the completion of master's degrees abroad. It studies the case of a Scholarship-Loan program provided by the Colfuturo Foundation and the Administrative Department of Science, Technology, and Innovation (Colciencias). Students with an undergraduate degree can apply to receipt a fund of 50000 dollars to finance their post-graduate studies in any country in the world, with the condition to come back to Columbia. The characteristics of the selection process of the program allow the implementation of a Regression Discontinuity Design (RDD) to estimate the causal effect of the scholarship-loan program on the probability of completing studies abroad. Given Colfuturo’s selection process, the assignment of the fund is expected to be distributed quasi-randomly for the applicants around the vicinity of a cut-off point. This methodology allows for the estimation of the local average treatment effect (LATE) of the program. I employ the administrative records from the scholarship provider combined with internet sources. The results show that the scholarship-loan program is an effective tool to increase the probability of completing studies abroad by approximately 30 percentage points. The results are extremely robust across estimation methods. [less ▲]

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See detailFrom Tool to Experience: Establishing a User Experience Perspective on Digital Concept Mapping
Rohles, Björn UL

Doctoral thesis (2021)

Education today faces difficult challenges, particularly because the complexity of topics or problems is rising and requires that learners see connections across different domain boundaries. Consequently ... [more ▼]

Education today faces difficult challenges, particularly because the complexity of topics or problems is rising and requires that learners see connections across different domain boundaries. Consequently, learners and instructors need a systematic approach to build and assess structural knowledge, supporting them to work with complexity in the 21st century. Digital concept mapping is a promising method to address these challenges. Concept maps are graphical networks of concepts and links with a particular emphasis on explicit semantic relations. Digitalization of concept mapping offers a range of capabilities but also adds challenges of its own. As learners take on a simultaneous role of users, the question of how to purposefully design positive experiences in digital concept mapping becomes a key concern. A digital tool needs to be optimized to allow learners to focus on task-relevant aspects instead of investing cognitive resources into operating the tool. Furthermore, a digital tool can itself be a source of positive experiences, contributing to motivation and reaching the overall educational goals. With an insufficient focus on users, designers and researchers risk creating tools that do not adequately acknowledge the aforementioned impacts on education. The present dissertation argues that the notion of user experience (UX) is adequate for investigating and purposefully shaping learner experiences with concept maps. The dissertation addresses the following research question: How does a user experience-driven approach contribute to digital concept mapping? After a general introduction (Part I), the dissertation builds on eight studies in four main parts: defining objectives of user experience design for digital concept mapping (Part II), investigating user experience design for a digital concept mapping tool (Part III), identifying scoring approaches for concept map-based assessment (Part IV), and investigating the impact of user experience on digital concept mapping (Part V). It concludes with a general discussion (Part VI). Part II presents three studies. Chapter 2 describes a co-design study in four classes. It combined functionality-driven and experience-driven design and identified a requirements profile for a digital concept mapping tool. Chapter 3 describes a storytelling focus group study that identified the role, desired outcomes, and pain points of digital concept mapping in Luxembourgish secondary education. Chapter 4 describes an interview study that identified how digital concept mapping contributes to fulfilling psychological needs. Part III describes the user experience design of a digital concept mapping tool. Chapters 6, 7, 8, and 9 investigate and optimize user experience with a concept mapping tool, building on a combination of critical incidents, think-aloud, card-driven investigation of psychological needs, and interviews. In summary, these studies were able to optimize user experience in digital concept mapping. Part IV addresses the scoring of concept maps which was identified as a key challenge for instructors and researchers in Part II. Chapter 10 is a systematic literature review of criteria used to score concept maps, resulting in a comprehensive framework with three dimensions that define concept map scoring. Finally, Part V presents two studies measuring the impact of a user experience perspective on digital concept mapping. Chapter 11 investigates user experience, psychological needs, intention to use, and concept map scores. Psychological needs strongly determined positive user experience, but not universally across all needs. User experience strongly impacted intention to use. Furthermore, our results indicated the need for further research into the relation between user experience and scores. Chapter 12 presents work in progress on guidelines and a scoring rubric for the meaningful use of multimodal features (like color, shape, or line type) in digital concept mapping. The present dissertation contributes empirical results to establishing a user experience perspective by identifying functional and non-functional goals, contextual factors, desired outcomes, pain points, and functionalities and characteristics of digital concept mapping tools. Furthermore, it outlines how these requirements can be achieved with UX design. The dissertation also contributes theoretical and meta-analytical findings by proposing a profile of psychological needs for concept mapping and deriving a comprehensive framework of criteria used to score concept maps. Finally, the dissertation makes methodological contributions by demonstrating how humans can be systematically involved in shaping their experiences with digital concept maps. The dissertation also provides recommendations for future design and instruction. [less ▲]

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See detailSpinning Functional Fibers: An Interplay of Rheology, Miscibility & Crosslinking
Vats, Shameek UL

Doctoral thesis (2021)

Wearable technology in general has increasingly gained interest in the last few decades and textile with incorporated functional component constitute one form of it. There are multiple ways to produce ... [more ▼]

Wearable technology in general has increasingly gained interest in the last few decades and textile with incorporated functional component constitute one form of it. There are multiple ways to produce polymer fibers on both laboratory and industrial scales, and one of them is core–sheath electrospinning, which is a powerful method for producing advanced composite fibers. Liquid crystals (LCs), are materials that readily exhibit optical response to fluctua- tions and change in their immediate environment. By incorporating LC within polymer fibers through electrospinning, it is possible to create responsive LC-polymer fiber mats. However, incorporating a functional core has proven challenging for certain combinations of materials. This thesis explores and addresses some of the concerns involved in the coaxial electrospinning of fibers incorporating LCs from several standpoints. Firstly, the effect of solvents on the electrospinning process was systematically studied. Fol- lowing this, an optimum viscosity with pure and mixed solvents for successful electrospinning was identified and uniform fibers with different solvent combinations was produced. Using the knowledge gained, core-sheath electrospinning with LC as the core was carried out. One of the key findings of this work, the identification of a suitable means to reduce the interfacial tension between the core and sheath fluid to prevent break up of the jet and produce uniformly filled fibers, while at the same time avoiding complete mixing between core and sheath. These findings can be applied to any combination of core and sheath materials and should appeal to a large community of researchers. Eventually, to achieve the durability of the LC-functionalized electrospun fiber mats for use in wearable technology, the sheath polymer of the fiber were crosslinked after spinning. The resultant crosslinked fibers were easily manipulated by hand and even fully immersed in water without dissolving and without losing their functional LC core. [less ▲]

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See detailAdvanced Characterizations of Silica Surface in Rubber Compounds by Solid-State Nuclear Magnetic Resonance Spectroscopy
Yan, Chuanyu UL

Doctoral thesis (2021)

This thesis details the development, validation, and application of advanced solid-state nuclear Magnetic resonance spectroscopy (NMR) techniques for the characterization of the silica surface in raw ... [more ▼]

This thesis details the development, validation, and application of advanced solid-state nuclear Magnetic resonance spectroscopy (NMR) techniques for the characterization of the silica surface in raw materials and in rubber compounds. The performance of the quantitative techniques (29Si DP-CPMG, SVD and 29Si multiCP) and qualitative techniques (29Si CP-CPMG and {1H-29Si}-1H MCPi) are investigated using model and close-to-real life samples. The insights gained from this study are useful for the surface-specific characterization of silica and could offer clues for similar topics. [less ▲]

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See detailA Distributed Unmanned Aerial Vehicles Traffic Management System
Samir Labib, Nader UL

Doctoral thesis (2021)

The rapid adoption of Internet of Things (IoT) has encouraged the integration of new connected platforms such as Unmanned Aerial Vehicles (UAVs) to the ubiquitous network. UAVs promise a pragmatic ... [more ▼]

The rapid adoption of Internet of Things (IoT) has encouraged the integration of new connected platforms such as Unmanned Aerial Vehicles (UAVs) to the ubiquitous network. UAVs promise a pragmatic solution to the limitations of existing terrestrial IoT infrastructure as well as they bring new means of delivering services through a wide range of applications ranging from monitoring and surveillance to on-demand last-mile delivery and people transport. Owning to their potential, UAVs are expected to soon dominate the low-altitude airspace over populated cities. This introduces new research challenges such as the safe management of UAVs operation under high traffic demands. In response to this, industry proposed a handful of constructs for UAV Traffic Management (UTM), however due to their centralised approaches, they will inevitably face limitations in scalability and resilience with predicted traffic demands and advancement in UAV autonomy. In this context, the main objective of this work is to address the aforementioned problem by proposing a distributed UAV Traffic Management system (dUTM). This thesis, hence, investigates the validity of the above hypothesis by: (i) showing the performance insufficiency of centralised systems due to their inadequacy in efficiently optimising large UAV traffic, (ii) showing why a distributed system is favourable due to its characteristics of scalability and resilience, (iii) proposing a novel dUTM framework consisting of an airspace structure model, information exchange model and a traffic optimisation model that rely on distributed methods and approaches to intelligently handle highly dynamic and challenging traffic conditions. To this end, this manuscript contributes to scientific literature by proposing a novel way of structuring the uncontrolled, low-altitude airspace and introduces a model of the Class G airspace as a multi-weighted multilayer network of nodes and airways. Additionally the work presents a novel distributed multiobjective path planning algorithm incorporating a dynamic multi-criteria decision matrix allowing each UAV or agent to plan their path relying on local knowledge gained via digital stigmergy. The PhD thesis additionally contributes to existing state of the art by exploring the technical standardisation landscape and investigating synergies between research directions and standards developments, taking into consideration pressing inherit challenges of UAVs within IoT such as security, data protection and privacy. [less ▲]

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See detailAutomatic Analysis, Representation and Reconstruction of Textured 3D Human Scans
Saint, Alexandre Fabian A UL

Doctoral thesis (2021)

Various practical applications in computer vision are related to the human body. These involve representing and modelling the body shape, pose, clothing and appearance with mathematical and statistical ... [more ▼]

Various practical applications in computer vision are related to the human body. These involve representing and modelling the body shape, pose, clothing and appearance with mathematical and statistical tools requiring datasets of examples, representative of the variation in the data. Three-dimensional (3D) data is especially important as it allows to simulate the physical world directly, for example to analyse and lift ambiguities in other prevalent data modalities, such as images. However, existing datasets of 3D human scans show limitations in their size, diversity, quality or annotation. This reduces their applicability in tackling research questions around the 3D human body. Two particular applications of interest that remain unanswered are the estimation of body shape under clothing, and the completion of textured shape of missing or defective data. This thesis proposes three main contributions. First, 3DBodyTex, a dataset of 3D human scans, which complements alternative datasets with real scans, body and clothing scans, hundreds of subjects, high-resolution texture information, dense annotations and aligned body shapes under the clothing. The aim is to enable and facilitate new research possibilities with learning-based methods, in 3D or using derived modalities. Second, to build this dataset automatically from raw scans, multiple robust 3D processing methods are proposed. These involve pose estimation, pose fitting, tight body shape fitting, and body shape estimation under clothing. The proposed methods show competitive or improved results on existing benchmarks and new proposed benchmarks based on 3DBodyTex. In particular, an alternative method is proposed to estimate the body shape under clothing from a single scan. On independent benchmarks, it is competitive with, or better than, methods requiring a full time sequence of scans. Third, the task of shape and texture completion of 3D human scans is tackled. A new method is proposed that completes the shape and the texture sequentially, and automatically identifies the missing regions. In particular, partial convolutions are extended to texture images (UV maps) for inpainting the colour of a 3D scan using a convolutional neural network. A new benchmark, based on 3DBodyTex, is proposed for the evaluation. [less ▲]

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See detailVisualizing Visions: Re-viewing the seventeenth-century genre of constcamer paintings
Koeleman, Floor Anna UL

Doctoral thesis (2021)

Constcamer paintings or pictures of collections were created almost exclusively in Antwerp, and to a lesser extent in Brussels, in the seventeenth century. Until now, no attempt had been made to collect ... [more ▼]

Constcamer paintings or pictures of collections were created almost exclusively in Antwerp, and to a lesser extent in Brussels, in the seventeenth century. Until now, no attempt had been made to collect all known examples, partly because of the contemporary distribution of such works across collections throughout the Western world. Another difficulty in studying constcamer paintings is the great complexity of the rich variety of subjects, objects, and concepts on display in the images that combine many disciplines separated today. Advances in the field of computer science have made it possible to systematically collect, archive, and analyze artworks and associated information on a large scale. My digital approach to the genre aimed to determine what a constcamer painting is, in terms of form, content, and meaning. In addition to looking at pictorial features and cognitively identifying what we see, contextualization played a key role in achieving understanding. Pictorial, historical, social, cultural, and intellectual contexts served as the framework for interpretation. Special attention has been paid to the interplays between collecting and recollecting, art and science, and physical and metaphysical vision. This thesis argues that pictures of collections primarily lay claim to the active intellect to generate insights by uncovering the multitude of meanings embedded in the seventeenth-century genre. The examination of constcamer paintings through a dataset led to enhanced perception and highlighted the prominence of visuality in the transmission and acquisition of knowledge, both then and now. [less ▲]

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See detailPredictive Assistance for Security Risk Assessment
Bettaieb, Seifeddine UL

Doctoral thesis (2021)

In many domains such as healthcare and banking and most notably the Fintech industry, IT systems can be exposed to breaches or attacks and need to fulfill various requirements related to security to ... [more ▼]

In many domains such as healthcare and banking and most notably the Fintech industry, IT systems can be exposed to breaches or attacks and need to fulfill various requirements related to security to prevent such scenarios from happening while limiting any potential exposure. In order to demonstrate or establish that compliance, risk assessments are conducted to determine potential threats and vulnerabilities that a system might be exposed to, as well as potential security controls to implement in order to counter those breaches and fulfill the requirements.An important difficulty that analysts have to contend with during that process is sifting through a large number of vulnerabilities and security controls and determining which ones have a bearing on a given system. This challenge is often exacerbated by the scarce security expertise available in most organizations. In addition, risk assessments are conducted manually in a traditional approach and rely heavily on the expertise of available risk assessors. This turns manually eliciting the applicable vulnerabilities and controls into a lengthy, costly, tedious, and error-prone activity. Our goal is to develop an automated approach to provide decision support during that process by allowing the system to assist in the identification of vulnerabilities and security controls that are relevant to a particular context. Our approach, which is based on Machine Learning (ML), leverages historical data from security assessments performed over past systems in order to recommend applicable vulnerabilities and controls for a new system. Natural Language Processing (NLP) techniques are used in combination with ML to extract any useful information from those previous records e.g.: data from a project's internal and external environment including its scope, involved assets, collaborators,etc. We operationalize and empirically evaluate our approach using real historical data from the banking domain.The automation of such a process raises several challenges: Understanding the specifics of risk assessments is the first one and using the right tools to obtain the desired results is a second one. In fact, in addition to requiring the right data and features in combination with the proper ML techniques, existing NLP techniques are not built to handle the textual data in risk assessments with its technicalities or multilingualism. An additional challenge is to find a suitable knowledge representation for risk assessments that would enable the automation of decision-support while maintaining both cohesiveness and understandability from all involved stakeholders. In this dissertation, we investigate to which extent one can automatically provide recommendations during a risk assessment. We focus exclusively on Vulnerabilities and Security Controls. All our technical solutions have been developed and empirically evaluated in close collaboration with our industrial partner. [less ▲]

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See detailEssays on Human Capital, Inequality, and Income
Menta, Giorgia UL

Doctoral thesis (2021)

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See detailDevelopment of a Decision Support System for Incorporating Risk Assessments during the System Design of Microsatellites
Pandi Perumal, Raja UL

Doctoral thesis (2021)

The primary purpose of this research is to develop a decision support system for the early design of an optimal and reliable satellite while making the overall conceptual design process more efficient ... [more ▼]

The primary purpose of this research is to develop a decision support system for the early design of an optimal and reliable satellite while making the overall conceptual design process more efficient. Generally, a satellite design process begins with a mission definition followed by the functional design of the satellite system. Beyond this, the design goes through several iterations and eventually results in a detailed satellite system design. Only then does it make sense to feed in the piece-part information to estimate the reliability of the entire satellite system. Predicted reliability from this bottom-up method may sometimes be markedly lower than the requirements. In such case, the maturity of the design is brought down, and mitigation strategies need to be implemented to meet the reliability requirements. Consequently, introducing new or redundant parts as a mitigation approach can violate the previously satisfied requirements such as mass, power and cost. Furthermore, additional design iterations are needed until all the requirements are met. Therefore, this design approach is expensive, inefficient, and can be avoided if reliability is considered from the early design phase. However, the challenge is to simultaneously perform reliability analysis and system design as they are entirely different engineering disciplines. In this research, a decision support system: DESIRA is developed to bridge the gap between these two engineering disciplines and incorporate reliability assessments during the early design phase, thus resulting in a truly optimal satellite design. With its unique features such as Reliability Allocation, Reliability Growth, Multidisciplinary Design Optimization and Reliability-Based Multidisciplinary Design Optimization, DESIRA effectively aids the system design at each maturity level. [less ▲]

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See detailMuseum Meaning-making: Experience Design for Digital Cultural Heritage
Morse, Christopher UL

Doctoral thesis (2021)

Interactive technologies have created a ubiquity of digital arts and culture on the Web, offering visitors unprecedented access to museums around the world directly from their personal devices. Despite ... [more ▼]

Interactive technologies have created a ubiquity of digital arts and culture on the Web, offering visitors unprecedented access to museums around the world directly from their personal devices. Despite the enormous potential of these systems to facilitate education, cultural mediation, entertainment, or even interpersonal connection, research has demonstrated that users have difficulties deriving meaningful experiences from the digital museum visit due to a poor or incongruent user experience (UX). Among these challenges are a lack of integration between the online and on-site visit, as well as a disconnect from human-centered and participatory design methodologies increasingly embraced by contemporary museological practice. Insofar as museums are spaces of meaning-making, whether through aesthetic experiences, historical embodiment, or other phenomena, developing a deeper understanding of meaning and its implications for experience design in museum contexts may enhance the UX of museum technologies, particularly for the Web. Meaning has recently become an important conceptual focus of research in human-computer interaction (HCI), but additional work is necessary to connect theoretical advances in meaning-making to the cultural sector and to translate them into actionable design recommendations, which are the primary aims of the present work. This dissertation reports on five mixed-methods studies that address notions of meaningful design across three interrelated dimensions of UX analysis — the user, the system, and the context. For the purposes of this research, these dimensions have been adapted to the museum experience, thus becoming the (digital) visitor, (digital) cultural heritage, and the (digital) visit, respectively. The collection of studies contributes to a deeper understanding of meaning in and around museums through an analysis of museum memories, emerging information behaviors, public co-creation of digital technologies, and experience design strategies to bridge the on-site and online visit. While each study investigates individual facets of meaningful interaction between museums and their visitors, taken together they establish a fundamental interrelation, orienting designers and cultural professionals to embrace them as a coherent whole. The five studies presented in this work address individual dimensions of museum meaning and conclude with a framework of meaning to support museum experience design (MXD). The initial study provides insight on the (digital) visitor through an analysis of casual leisure information behaviors during navigation of an exploratory museum collections interface called rich-prospect (N = 30). The second is a co-creation study (N = 12) that introduces meaningful interaction through the design space of digital cultural heritage. The third study documents the #MuseumAtHome movement that emerged during the global COVID-19 pandemic, providing insights on meaningful design for the (digital) visit by integrating the on-site and online contexts. Finally, the fourth study combines an experience narrative analysis (N = 32) and a subsequent validation study (N = 354) on museum memories to establish a systematic understanding of the content of meaningful interaction in museums. This dissertation advances theory and practice in HCI by extending research on the psychology of meaningful interaction into a largely novel context, museum experience design. Each study contributes to a deeper understanding of the different facets of museum meaning-making and their relation to experience design, while the aggregate lays the groundwork for an integrated approach. The primary findings include new insights into the psychological factors of meaning in museum contexts, subsequent design recommendations for the online and on-site visit, and a suite of tools to support meaningful design in the cultural sector. [less ▲]

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See detailQuantum transport in topological condensed matter systems
Ekström, Carl Johan Ingvar UL

Doctoral thesis (2021)

Topology in condensed matter physics is a field that has exploded in the last two decades. With the realization of its importance, some previously unexplained observations can now be explained. With the ... [more ▼]

Topology in condensed matter physics is a field that has exploded in the last two decades. With the realization of its importance, some previously unexplained observations can now be explained. With the progress of time, many new topological phases of matter have been discovered, and topological materials have been shown to be fairly common in nature. Topological materials have further been shown to have properties that may be extremely useful for new technologies, such as spintronics and fault-tolerant quantum computation. The field is however, still evolving, and many properties of these materials are still unknown. In this thesis, we investigate how some of these types of materials react to applied external fields and the theories that can explain these observations. First, we investigate systems of coupled Majorana bound states. More specifically, we focus on the transport properties of the Majorana box and the T-junction in the presence of charging effects, overlap between the Majorana bound states, and multiple terminals connected to the system. To obtain the transport properties, we apply a master equation and calculate the current through the systems as biases are applied to the different terminals. By tuning the gate voltage, the transport is investigated in both the regime where sequential tunneling is dominating as well as the Coulomb blockaded regime, where cotunneling is the leading transport process. When sequential tunneling is dominating, the transport is mediated by both single electrons tunneling as well as processes that involve the creation and annihilation of Cooper pairs. In the Coulomb blockaded regime, transport is driven by cotunneling processes by transitions via virtual states. The results here show that four-terminal measurements can be a useful tool to characterize the properties of Majorana bound states with finite overlap and charging energy. Secondly, we study the optical activity of tilted nodal loop semimetals. The inherent Hall conductivity of topological materials makes the Kerr effect an excellent tool for investigating their properties. Here we first calculate the full conductivity tensor for a tilted nodal loop semimetal, where the tilt is in the $ k_{x} - k_{y} $ plane. The conductivity tensor allows us to calculate the Kerr effect. We study this both for a thin film and a bulk material and we fin, in general, that the Kerr effect is large, similar to other topological materials. Finally, we investigate electronic hydrodynamics in anomalous Hall insulators. First we derive the Navier-Stokes equations for topological materials and show that they are modified due to the Berry curvature. Secondly, we consider the flow in a narrow channel and the application of a small electric field. In this case, the Hall current can be neglected since it is much smaller than the longitudinal current. Flow in narrow channels conventionally leads to Poiseuille flow. However, as shown, the Berry curvature modifies the flow profile and shifts the maximum of the current profile towards one of the edges. Thirdly, we study the flow in an infinite geometry. In this case, it is shown that the Berry curvature induces whirlpools as well as causing an asymmetry in the profile of the electrical potential. Experimentally this can be observed by measuring the non-local resistance. [less ▲]

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See detailThe Experience of Security in Human-Computer Interactions: Understanding Security Perceptions Through the Concept of User Experience
Distler, Verena UL

Doctoral thesis (2021)

In traditional interactions that do not rely on technology, most people are able to assess risks to their privacy and security and understand how to mitigate these risks. However, risk assessment and ... [more ▼]

In traditional interactions that do not rely on technology, most people are able to assess risks to their privacy and security and understand how to mitigate these risks. However, risk assessment and mitigation is more challenging when interacting with technology, and people’s perceptions of security and privacy risks are not always aligned with reality. It is important for those who design technologies to understand how people perceive the security of technologies in order to avoid having their designs contribute to erroneous perceptions. Instead, interactions with technology should be deliberately designed to ensure that people do not over- or underestimate the security provided by the system. This dissertation contributes to a better understanding of users’ perceptions of security in human-computer interactions. It investigates which factors induce a perception of security and privacy risks and how user-centered design can influence these factors to deliberately design for or against perceived security. I use a mixed-methods approach to address these objectives, including a systematic literature review, empirical data collection with focus groups, expert co-creation sessions, user tests in a controlled environment and a quantitative survey experiment. The first research objective is to analyze how security and privacy researchers induce a perception of security and privacy risks with research participants. We conducted a systematic literature review and focused our analysis on study methods; risk representation; the use of prototypes, scenarios, and educational interventions; the use of deception to simulate risk; and types of participants. We discuss benefits and shortcomings of the methods, and identify key methodological, ethical, and research challenges when representing and assessing security and privacy risk. We also provide guidelines for the reporting of user studies in security and privacy. The second research objective is to explore the factors that contribute to the acceptance of privacy and security risks in situations where people need to weigh the potential advantages of a technology against its associated privacy or security risks. We conducted a series of focus groups and highlighted the reasons why people accept compromises to their privacy and security, finding that perceived usefulness and the fulfilment of the psychological needs for autonomy and control were important factors. Our results suggest potential links between technology acceptance models and user experience models in the context of privacy-relevant interactions. The third research objective is to design and evaluate examples of visible representations of security mechanisms, with a focus on encryption. We studied the effects of these visual and textual representations empirically to understand the impact of these visible security mechanisms on user experience, perceptions of security and users’ understanding of encryption. We addressed this question in a series of studies, both lab studies and online experiments. In a vignette experiment, we find that more complex descriptions of encryption can lead to a better understanding and higher perceived security when designed carefully. However, we find no effect of novel visualizations of encryption on user experience (UX), perceived security or understanding of encryption. The fourth objective is to explore how we might make the link from subjective experience to more secure behaviors. We introduce a new framework of security-enhancing friction design. The framework suggests helping users behave more securely by designing for moments of negative UX in security-critical situations while also ensuring that overall UX remains at an acceptable level to avoid disuse of secure technologies. Overall, this doctoral dissertation contributes to research in the field of human-computer interaction, and more specifically, usable privacy and security. It improves our understanding of the methods used by researchers in the field of usable privacy and security use to create a perception of risk, and the factors that make people accept or reject certain privacy trade-offs. This dissertation also makes contributions to helping researchers and creators of technology understand how their designs influence perceptions of security, UX and understanding of encryption. This enables them to design for or against a perception of security, depending on the actual level of security provided by the technology. Finally, we conceptualize security-enhancing friction, a framework that suggests helping users to behave more securely by designing for moments of negative UX. [less ▲]

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See detailCommunication Algorithms for 5G Internet of Things Systems via Satellites
Kodheli, Oltjon UL

Doctoral thesis (2021)

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See detailLearning How to Be Modern: An Ethnography of the Religious Education of L/liberal Jewish Talmud Torah Students in Luxembourg
Badder, Anastasia UL

Doctoral thesis (2021)

This dissertation is an ethnography of children and young people growing up Jewish in Luxembourg. It focuses on the students of a Talmud Torah class in a Liberal synagogue that, in recent years, has drawn ... [more ▼]

This dissertation is an ethnography of children and young people growing up Jewish in Luxembourg. It focuses on the students of a Talmud Torah class in a Liberal synagogue that, in recent years, has drawn increasing numbers of highly mobile, multilingual families from around the world. As these students learn how to be Jewish and carry on Jewish tradition, they simultaneously explore what it means to be modern and to be modern Jews. This process pushes them to confront a series of ambiguities and apparent paradoxes across the contexts of their everyday lives – in Talmud Torah, at home, and at school. Based on 31 months of fieldwork, this dissertation reveals the nuanced semiotic ideologies and competing visions of modernity that become visible through the lens of the students' Talmud Torah learning, including learning to read Hebrew, engaging with religious texts, and participating in ritual performance, and their school experiences. The students grapple with, navigate, and position themselves in relation to these different 'projects of modernity' as they work to make sense of and bring together the aims of Jewish continuity and liberal modernity and all that these entail. By exploring these processes, this dissertation aims to participate in the anthropological conversation about 'modernities' and 'the modern' as a project that is both embracing of the liberal, the secular, and inclusivity and can be powerfully normative, constraining, and exclusionary, and to encourage us as anthropologists and teachers to think about how we might leave open the possibility for nuance and alternative attachments, desires, goals, mobilities, and ways of being in the classroom and beyond. [less ▲]

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See detailOn the Maintenance of System User Interactive Tests
Rwemalika, Renaud UL

Doctoral thesis (2021)

Many companies rely on software testing to verify that their software products meet their requirements. As such, software testing is a keystone of the quality process. It offers means to assess that both ... [more ▼]

Many companies rely on software testing to verify that their software products meet their requirements. As such, software testing is a keystone of the quality process. It offers means to assess that both functional and technical requirements are met. However, scaling the number of tests while preserving their quality poses challenges, just as in any software artifact. This is particularly true in the case of complex tests interacting with the SUT through its Graphical User Interface (GUI), i.e. System User Interactive Test (SUIT). The problem becomes challenging because as the System Under Test (SUT) evolves, the SUIT suites need to adapt and conform to the evolved software. Indeed, because the user interface is a part of the system that tends to undergo rapid evolutions, SUITs are particularly prompt to break. As the first contribution of this dissertation, we aim to demonstrate the problem of test maintenance and overall improve the understanding of SUIT scripts evolution. To that end, we identify, collect and analyze test code changes across the evolution of an industrial test suite. We show that the problem of test maintenance is largely due to test fragility (most commonly performed changes are due to locator and synchronization issues) and bad practices (over 30% of keywords are duplicated). To further investigate the question of bad test code practices such as test clones, we perform a multivocal study to identify which bad practices, i.e. SUIT smells, are already studied in both industry and academia. This process yields a catalog of 35 test code smells. For 16 of them, we derive metrics to analyze their diffusion across tests as well as potential refactoring actions removing the test code smells. Through an empirical study including both industrial and open-source test suites, we show that test code smells are largely present in SUITs, potentially contributing to SUIT fragility and hindering the maintenance process. Interestingly, refactoring actions remain rare during the lifespan of the tests. Yet, symptoms tend to disappear as old tests are discarded and new ones are introduced. However, during the analysis of SUIT smells, we observe that bad practices impacting locators do not appear often in the test code. This observation contrasts with the analysis of the evolution of the SUIT presented in our first empirical study. This apparent contradiction arises from the limitation of property-based locators which rely on the structure of the representation layer of the SUT. Indeed, such approaches are sensitive to internal iso-functional changes occurring during the normal evolution of the SUT. To account for this limitation, we introduce a new way of expressing locators, HPath. Instead of relying on the internal representation of the presentation layer, HPath relies on the rendered characteristics of the GUI. Our results suggest that despite what is presented in the literature on locators, expressions relying on a smaller number of GUI elements to fully qualify a target do not necessarily lead to more robust locators. On the contrary, the choice of the GUI element properties seems to play a stronger role in the robustness to change. Overall, this dissertation provides insights into how SUITs evolve and shows that SUIT fragility plays a major role in the associated maintenance effort. It also proposes techniques that effectively facilitate SUIT maintenance with the early detection of sub-optimal patterns and the introduction of a locator representation more robust to SUT evolution. [less ▲]

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See detailAttaques et preuves de sécurité des protocoles d'échange de clés authentifiés
Sala, Petra UL

Doctoral thesis (2021)

The vast majority of communication on the Internet and private networks heavily relies on Public-key infrastructure (PKI). One possible solution, to avoid complexities around PKI, is to use Password ... [more ▼]

The vast majority of communication on the Internet and private networks heavily relies on Public-key infrastructure (PKI). One possible solution, to avoid complexities around PKI, is to use Password Authenticated Key-Exchange (PAKE) protocols. PAKE protocols enable a secure communication link between the two parties who only share a low-entropy secret (password). PAKEs were introduced in the 1990s, and with the introduction of the first security models and security proofs in the early 2000s, it was clear that PAKEs have a potential for wide deployment - filling the gap where PKI falls short. PAKEs' PKI-free nature, resistance to phishing attacks and forward secrecy are just some of the properties that make them interesting and important to study. This dissertation includes three works on various aspects of PAKEs: an attack on an existing PAKE proposal, an application of PAKEs in login (for password leak detection) and authentication protocols (HoneyPAKEs), and a security analysis of the J-PAKE protocol, that is used in practice, and its variants. In our first work, we provide an empirical analysis of the zkPAKE protocol proposed in 2015. Our findings show that zkPAKE is not safe against offline dictionary attacks, which is one of the basic security requirements of the PAKE protocols. Further, we demonstrate an implementation of an efficient offline dictionary attack, which emphasizes that, it is necessary to provide a rigorous security proof when proposing a new protocol. In our second contribution, we propose a combined security mechanism called HoneyPAKE. The HoneyPAKE construction aims to detect the loss of password files and ensures that PAKE intrinsically protects that password. This makes the PAKE part of the HoneyPAKE more resilient to server-compromise and pre-computation attacks which are a serious security threat in a client-server communication. Our third contribution facilitates the wider adoption of PAKEs. In this work, we revisit J-PAKE and simplify it by removing a non-interactive zero knowledge proof from the last round of the protocol and derive a lighter and more efficient version called sJ-PAKE. Furthermore, we prove sJ-PAKE secure in the indistinguishability game-based model, the so-called Real-or-Random, also satisfying the notion of perfect forward secrecy. [less ▲]

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See detailVerification of design models of cyber-physical systems specified in Simulink
Gaaloul, Khouloud UL

Doctoral thesis (2021)

Recent advances in cyber-physical systems (CPS) have allowed highly available and approachable technologies with interconnected systems between the physical assets and the computational software ... [more ▼]

Recent advances in cyber-physical systems (CPS) have allowed highly available and approachable technologies with interconnected systems between the physical assets and the computational software components. This has resulted in more complex systems with wider capabilities. For example, they can be applied in various domains such as safe transport, efficient medical devices, integrated systems, critical infrastructure control and more. The development of such critical systems requires advanced new models, algorithms, methods and tools to verify and validate the software components and the entire system. The verification of cyber-physical systems has become challenging: (1) The complex and dynamical behaviour of systems requires resilient automated monitors and test oracles that can cope with time-varying variables of CPS. (2) Given the wide range of existing verification and testing techniques from formal to empirical methods, there is no clear guidance as to how different techniques fare in the context of CPS. (3) Due to serious issues when applying exhaustive verification to complex systems, a common practice is needed to verify system components separately. This requires adding implicit assumptions about the operational environment of system components to ensure correct verification. However, identifying environment assumptions for cyber-physical systems with complex, mathematical behaviors is not trivial. In this dissertation, we focus on addressing these challenges. In this dissertation, we propose a set of effective approaches to verify design models of CPS. The work presented in this dissertation is motivated by ESAIL maritime micro-satellite system, developed by LuxSpace, a leading provider of space systems, applications and services in Luxembourg. In addition to ESAIL, we use a benchmark of eleven public-domain Simulink models provided by Lockheed Martin, which are representative of different categories of CPS models in the aerospace and defence sector. To address the aforementioned challenges, we propose (1) an automated approach to translate CPS requirements specified in a logic-based language into test oracles specified in Simulink. The generated oracles are able to deal with CPS complex behaviours and interactions with the system environment; (2) An empirical study to evaluate the fault-finding capabilities of model testing and model checking techniques for Simulink models. We also provide a categorization of model types and a set of common logical patterns for CPS requirements; (3) An automated approach to synthesize environment assumptions for a component under analysis by combining search-based testing, machine learning and model checking procedures. We also propose a novel technique to guide the test generation based on the feedback received from the machine learning process; and (4) An extension of (3) to learn more complex assumptions with arithmetic expressions over multiple signals and numerical variables. [less ▲]

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See detailFATIGUE LIFE OPTIMIZATION OF A HIGH-PRESSURE LOADED ALUMINUM VALVE BODY AND LEAKAGE INVESTIGATION FOR ELASTOMERIC SEALS AT LOW TEMPERATURE
Repplinger, Christian UL

Doctoral thesis (2021)

High-pressure hydrogen storage systems for fuel cell vehicles require a safe, compact, and light-weight design, especially the on-tank valves (OTV). These valves are directly connected to the high ... [more ▼]

High-pressure hydrogen storage systems for fuel cell vehicles require a safe, compact, and light-weight design, especially the on-tank valves (OTV). These valves are directly connected to the high-pressure tank and manage the filling process of gaseous hydrogen up to a nominal pressure of 700 bar, the storage of the high-pressurized gas in the tank, and the supply of the fuel cell. The OTV enclosure implements several different technical devices, which are mostly sealed with radial elastomeric O-rings within one complex aluminum valve body. This work’s first part analyzes and optimizes the fatigue life of the aluminum alloy (EN AW 6061 T6) OTV-body by defining the optimum autofrettage pressure before identifying the most significant effects influencing the sealing behavior of high-pressure loaded elastomeric O-rings at low temperatures in the second part. Both parts are of great benefit for safe product development considering the challenging technical requirements, such as a maximum pressure of 1050 bar and a temperature range of +85 °C to -60 °C, needed for the application of the OTV in a fuel cell vehicle. The aluminum valve body includes several channels and bore intersections which are pressure-loaded in operation. This complex untreated valve geometry does not achieve the technical requirements of 150 000 pressure cycles without a failure. Determining the optimum autofrettage pressure for this complex aluminum valve body enables an improvement of the lifetime for this internally highly pressurized component. The autofrettage process induces residual compressive stress after the release of a single static overload pressure, leading to plastic deformation at the inner wall, whereas the outer pulsating operating pressure range. Due to the complex geometry of the aluminum valve body, a detailed elastic-plastic finite element analysis is used to determine the optimum autofrettage pressure. Three load steps are simulated in a non-linear way based on experimental stress-strain curves. The FKM-guideline is used to assess fatigue life and crack initiation with detailed subsequent experimental verification. Even if small cracks occur, residual compressive stresses prohibit crack growth (non-propagating or dormant crack). This is analytically verified by fracture mechanical considerations (crack closure effect) and is proven via internal fatigue pressure testing up to 500 000 load cycles. Crack propagation is analyzed by optical inspections with a microscope, computer tomography, and numerical determination. The autofrettage process intentionally induces residual compressive stresses. Relaxation of these residual stresses due to cyclic loading in service would endanger the effectiveness of autofrettage and could ultimately lead to unexpected fatigue failure. Therefore, strain-controlled experiments up to 500 000 load cycles and amending non-linear finite element simulations are done for the aluminum alloy EN AW 6061 T6 to study potential cyclic stress relaxation in four-point bending tests after controlled single static plasticization for residual stress generation. The elastomeric O-ring seals must ensure functionality at high-pressure and a wide range of temperatures. The elastomeric material`s performance is especially limited at low temperatures. Geometrical and material effects are analyzed and assessed by numerical simulations and experiments. An accurate material model is necessary to present the complex material behavior and its influences on the sealing behavior. Therefore, an elastomeric seal material modeling guideline is developed to present the most significant effects. The mechanical material behavior of elastomers depends on time, temperature, and pressure. A thermo-rheologically simple (TRS) visco-hyperelastic material model is defined with the time-temperature superposition principle (TTSP) and used for the finite element simulations. This material model is validated with several material tests. The numerical analyses are especially useful in highlighting the individual influences of machining tolerances, different thermal expansion coefficients, limited recovery, and stress relaxation of the elastomer. The appearance of compressibility or volume swelling and their impacts on the sealing behavior are also explained. Experimental leakage tests are done for several O-ring dimensions from -60 °C to +23 °C up to a maximum pressure of 970 bar. The effect of machining tolerances and the necessity of a back-up ring are analyzed in a first test session. A second test session compares a relatively thin O-ring to a thicker one and investigates the sealing behavior of different geometries of the gland and the back-up ring. These geometrical design optimizations lead to a clear improvement of the sealing behavior. [less ▲]

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See detailStructuration of piezotronic junctions for ultrasensitive strain sensors
Joly, Raoul Joseph Adolphe UL

Doctoral thesis (2021)

The piezotronic effect relies on the creation of piezoelectric polarization charges mechanically induced within a piezoelectric semiconductor to modulate the carrier dynamics across electronic contact ... [more ▼]

The piezotronic effect relies on the creation of piezoelectric polarization charges mechanically induced within a piezoelectric semiconductor to modulate the carrier dynamics across electronic contact interfaces. The field of piezotronics is a relatively new area of study, based on a mechanical signal triggering, which is one of the most common kind of interactions between the environment and electronic systems. It started to draw a considerable attention in the early 2010’s, by reaching higher electromechanical sensitivities when compared to conventional methods of sensing. The rapidly spreading Internet-of-Things is accelerating Micro-ElectroMechanical Systems (MEMS) industry to deliver highly sensitive and miniaturized self-sensing sensors with low power consumption and cost-effective production process. Within this context, strain sensors based on the piezotronic effect appear as promising candidates to address these needs. However, several crucial questions remain unanswered or need to be refined, concerning the design and integration of piezotronic junctions with its fabrication process into microsystems or MEMS, the optimal configuration for strain sensing as well as noise studies for such systems. This PhD thesis proposes to rationalize the piezotronic effect for strain sensors and presents a novel microfabrication process integrating for the first time piezotronic strain sensors in millimetre-sized cantilevers on flexible polymeric substrates by means of maskless laser lithography. The atomic layer deposition (ALD) technique was used for the deposition of ZnO polycrystalline thin films on high work function metals to obtain Schottky junctions. However, such ZnO-based Schottky junctions by ALD have never been post-processed and integrated into a strain sensor. We propose to rationalize the ALD processing to obtain wurtzite polycrystalline zinc oxide thin films with a privileged (002) orientation and to make it compatible with microfabrication processing on polymer. The difficulties linked with the integration of inorganic thin films onto a polymeric substrate within the developed microfabrication process will be highlighted. We propose appropriate adjustments of the sensor’s design and the process flow. Pt/ZnO/Pt back-to-back Schottky diode junctions have been shaped in interdigitated microelectrodes to get piezotronic strain sensing on the clamp area of the cantilever structure. The conduction mechanisms occurring within the piezotronic strain microsensors have been thoroughly studied, based on the thermionic emission model. The developed electrical model will be detailed, emphasizing the presence of interface trap states and their prominent impact on the electrical characteristics. The piezotronic strain sensors’ transducing properties will be detailed as well by the mean of force spectroscopy, leading to the expected Schottky barrier height modulation by the piezotronic effect. Furthermore, we investigated for the first time the noise figure of within strain sensors based on the piezotronic effect. These new insights about noise amplitudes and origins are promising matter of optimization to improve the signal-to-noise ratio of the sensor. Within the last section of this work, we will detail the piezotronic strain sensors size miniaturization for integration in microcantilevers in a full-SU8 body. The miniaturization of our strain sensors makes them more prone for AFM (Atomic Force Microscopy) scanning probe operations on commercial machines, with the aim of greatly improving the sensitivity to small mechanical deformations. The approach taken for the microfabrication of these miniaturized sensors is based on a reversed processing by the mean of a sacrificial layer. This raised new difficulties in terms of metal adhesion and electrical contact continuity, which will be reported. The results obtained are highly promising and pave the way towards the processing of ultrasensitive strain microsensors on MEMS structures, as well as their great potential for AFM scanning probe operations. [less ▲]

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See detailThree Essays on the Role of Institutions in Labor Market Polarization
Pettinger, Maxime Dominique Eric UL

Doctoral thesis (2021)

This dissertation examines the impact of institutions on the distribution of jobs and wages, with a special focus on European countries. We are more specifically interested in labor market polarization, a ... [more ▼]

This dissertation examines the impact of institutions on the distribution of jobs and wages, with a special focus on European countries. We are more specifically interested in labor market polarization, a phenomenon which has notably been observed in the US between the 1980s and the 2010s. While wage polarization describes an increase in wages at both ends of the distribution relative to the middle, job polarization refers to an increase in the employment share of both low- and high-skill jobs relative to middle-skill jobs. A now standard explanation of this phenomenon is routine-biased technical change (RBTC). According to this approach, technical progress favors the substitution of machines --- and, indirectly, of high-skill workers --- for middle-skill labor, which leads in fine to the polarization of the distribution of earnings and jobs. While labor market polarization has also been observed in Europe, the intensity of this phenomenon depends on the country considered. Since developed economies have a similar access to technology, other determinants of the distribution of jobs and wages have to be considered to explain these cross-country differences. This dissertation considers institutions and demonstrates that a highly institutionalized labor market mitigates the twofold phenomenon of polarization. Institutions --- which are typically country-specific --- can thus partially explain cross-country differences in labor market polarization. This dissertation consists of three essays. In the first essay, we implement decomposition methods to show the impact of institutions on the wage structure. Our strategy makes use of the difference between the public and the private sector in terms of institutionalization of the wage-setting process. Decomposing the change in wage quantiles for both sectors and operating a between-sector comparison of the results for a set of European countries, we reach the conclusion that institutions are able to mitigate the RBTC-induced polarization of the wage structure. In the second essay, we develop a theoretical model based on the Acemoglu and Autor (2011) task-based framework. We contribute to this framework by including, in a Ricardian model of the labor market à la Acemoglu and Autor, an institutional device which mitigates wage polarization, based on the results of the first essay of this dissertation. While this device can be thought as unions operating in a centralized and coordinated bargaining regime, it is not restricted to this interpretation. Our model predicts that the institutions we consider, by mitigating wage polarization, have an anti-polarizing impact on the change in employment: while job polarization still follows skill-biased technical change, it is less pronounced in a highly institutionalized labor market. In the third and last essay, we test the predictions of the model presented in the second essay by empirically assessing the impact of institutions on job polarization. For each country studied in the first essay and for each year of the period 1992-2017, we build a measure of job polarization, based on the employment levels observed in selected, ranked and aggregated occupational categories. We then build a composite index of institutionalization and use panel cointegration techniques to estimate the long-run relationship between this index and each component of job polarization. Finally, we take into account both the reverse-causality problem implied by such a study and the potential delayed response of the variables by resorting on panel vector autoregressive models and structural impulse response analysis. Our results indicate that de-institutionalization fosters both components of job polarization, confirming the structural interpretation of the model introduced in the second essay. By combining different approaches and methods, this dissertation thus shows that the impact of technical change on the wage and occupational structure is mediated by country-specific institutional settings. Institutions do have an impact on labor market polarization, and can clearly be used to foster or inhibit this phenomenon. [less ▲]

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See detailTumour immune evasion is promoted by actin cytoskeleton-driven polarization of inhibitory signals to the immunological synapse
Wurzer, Hannah Gertrud Andrea UL

Doctoral thesis (2021)

Natural killer (NK) cells are innate immune cells that are the first line of defence against infection and malignant transformation. They have the ability to recognize and destroy virally infected or ... [more ▼]

Natural killer (NK) cells are innate immune cells that are the first line of defence against infection and malignant transformation. They have the ability to recognize and destroy virally infected or cancerous cells without the need for priming or activation and therefore represent a promising target for new immunotherapeutic approaches against cancer. For their anti-tumour function, NK cells rely on actin cytoskeleton remodelling, in particular during the formation of the lytic immunological synapse (IS) with prospective target cells. The IS is characterized by an extensive assembly of filamentous actin (F-actin) and polarization of the NK cell for directed delivery of lytic granules. However, the IS allows bi-directional exchange of information, and anti-tumour effector functions of NK cells are often impaired through inhibitory signals that are transmitted through killer immunoglobulin-like receptors (KIRs) or the CD94/NK group 2 member A (NKG2A) heterodimeric receptor. Moreover, resistant tumour cells can polarize their own actin cytoskeleton to the IS in a process called actin response, enforcing the formation of an evasion IS or actin response-IS (AR-IS). This PhD thesis focuses on the evaluation of associated resistance mechanisms that occur at the AR-IS, the conservation of these processes and their translation to in vivo models of cancer. For this purpose, individual cancer-NK cell conjugates were analysed by high-throughput imaging flow cytometry (IFC) to investigate the accumulation of F-actin at the IS and the distribution of inhibitory and activating ligands in relation to the IS. The AR was associated with a wider synaptic cleft, prominent recruitment of predominantly inhibitory ligands and inhibition of NK cell-induced target cell death. Further, the AR could also be applied to cytotoxic T lymphocyte (CTL) attack during antigen specific IS formation. To explore the in vivo relevance of the AR, modified murine cancer cell lines were established that allowed for the evaluation of impact of the AR on tumour progression, the tumour immune landscape, immune cell activation and exhaustion. Reduction of the actin response was associated with a reduction of tumour volume, enhanced infiltration of CTLs and NK cells and higher numbers of effector T cells. In summary, this study reports a novel, highly conserved immune-escape mechanism that exploits fast remodelling of the actin cytoskeleton of cancer cells to induce clustering of inhibitory ligands at the AR-IS and prevent NK cell activation. This AR is characterized by fine synaptic filopodia-like protrusions (SFPs) that are decorated with inhibitory ligands and probe the surface of the NK cell in addition to providing a steric hindrance for NK cell attachment to target cells. In our pre-clinical mouse model, we could demonstrate that a reduction of the AR results in the restoration of anti-tumour immunity. Understanding the mechanism that enables or initiates the AR and finding new ways to target this mechanism has the potential to improve cancer immunotherapy, especially for NK cell-based approaches. [less ▲]

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See detailEssays on the Economics of Forced Displacement and Conflict
Cömertpay, Rana UL

Doctoral thesis (2021)

In Chapter 1, we analyze the determinants of the internal mobility of refugees in Turkey. We track down this mobility relying on geolocalized mobile phone calls data and bring these measures to a micro ... [more ▼]

In Chapter 1, we analyze the determinants of the internal mobility of refugees in Turkey. We track down this mobility relying on geolocalized mobile phone calls data and bring these measures to a micro-founded gravity model in order to estimate the main drivers of refugee mobility across 26 regions in 2017. Our results show that the movements of refugees are sensitive to income differentials and contribute therefore to a more efficient allocation of labor across space. Comparing these findings with those of individuals with a non-refugee status, we find that refugees are more sensitive to variations of income at origin and to distance, while less responsive to changes in income at destination. These findings are robust to the way mobility is inferred from phone data and to the choice of the geographical unit of investigation. Further, we provide evidence against some alternative explanations of mobility such as the propensity to leave refugee camps, transit through Turkey, social magnet effects and sensitivity to agricultural business cycles. In Chapter 2, we exploit annual variations in the presence of refugees to approximate the resulting changes in diversity in the refugee-hosting areas across 23 countries in sub-Saharan Africa. We then assess the relationship between the refugee-corrected diversity indices and the likelihood of conflict between 2005 and 2016. In line with our theoretical framework, the refugee-corrected polarization exacerbates the risk of conflict. A one standard deviation increase in the polarization index raises the incidence of violent conflict by 5 percentage points. Such an effect corresponds to a 10 percent increase, at the mean. The opposite effect is found for the fractionalization index. Our results should not be interpreted as evidence that refugees per se impact the likelihood of violence. Indeed, we do not find any significant correlation between the number of refugees and the occurrence of conflict. Instead, our results point to the risk of conflict when refugees exacerbate ethnic polarization in the hosting communities. On the contrary, a situation where refugee flows raises the level of ethnic fractionalization is likely to see an attenuated risk of violence. This certainly calls for specific interventions in refugee-hosting and polarized communities. We also conduct additional analysis based on individual data and recent COVID-related protests. Results tend to support aggregate results. Refugee-corrected polarization raises the likelihood of experiencing physical assault and interpersonal crime by 2.7 resp. 4.2 percentage points, while no effect can be found for ethnic attachment and trust. Finally, the relevance of our results in the context of the COVID-19 pandemic is explored. In Chapter 3, we study the impact of independent media networks on political accountability during the Arab Spring across the Middle East and North Africa region. The study focuses on two major media networks in the Arab world: Al Jazeera and Al Arabiya. Political accountability is proxied using principally a measure of protests. Data on both political accountability measures and the media networks derive from the Arab Barometer surveys. The regional-level analysis is based on Jordan, Lebanon and Palestine due to data availability. The study uses regional ruggedness as an instrumental variable for the non-random use of independent media among individuals. Results are estimated using a Two-Stage least Squares (2SLS) regression analysis and indicate a positive and significant impact of independent media on political accountability. Several extensions are performed. First, the analysis is replicated for the impact of state media networks and results suggest a significant negative impact on participation to protests. Second, the impact of using independent media for public sector workers' participation to protests is compared with non-public workers. While a significant positive impact of using independent media is found among non-public workers, independent media among public workers seem not to affect their participation to protests. Some channels are tested using additional outcomes such as governmental trust, political alignment, signing petitions and general trust as proxies for political accountability. [less ▲]

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See detailDynamic Pricing Strategies in the Carsharing Business, Profit Maximization and Equity Considerations
Giorgione, Giulio UL

Doctoral thesis (2021)

In the last two decades the development of mobile technology and the ease of access to an internet connection helped the consolidation of the sharing economy paradigm. This new way of purchasing goods and ... [more ▼]

In the last two decades the development of mobile technology and the ease of access to an internet connection helped the consolidation of the sharing economy paradigm. This new way of purchasing goods and services differs from old traditional business models since it enables a shared use of resources in order to save money and generate profit. As an important player in the sharing economy, sharing mobility continues, nowadays, to shape urban mobility with the introduction of different modes of shared transport such as carsharing, bike sharing, ride sourcing, and other collective mobility services. Different stakeholders participate in the creation and exploitation of these new mobility services: governmental agencies, customers, and private companies. Each of them has a specific purpose that can affect and stir the benefit of sharing platforms. Focusing on the carsharing service, on the business side and on the user side, profit and customer satisfaction are usually the main goals even if, at times, both difficult to pursue together. Competition on today's landscape leaves little room for both established and less established businesses. Opportunities to increase corporate profit become scarcer and more refined systems to better manage carsharing operations are needed to guarantee commercial viability. Evaluating business models for carsharing is no trivial task. Several methods are used for assessing the quality of changes in some operations or to evaluate possible approaches. Combinatorial and stochastic optimization are used to answer decision-making problems in the case of deterministic or uncertain problems. The shortcoming of these approaches is that they are limited at solving problems related to fleet management or service planning as it is more difficult to have an overview in which multiple properties (e.g., demography, territorial distribution, specificity of the fleet, ...) of both supply and demand are considered. This happens because car sharing is a highly complex service that has many interdependent factors. Given this complexity, a more favorable approach to estimate the demand for the service - together with all its peculiarities - and to help operators in the decision-making process, is the simulation one. This criterion allows the interaction of multiple factors which, through functional relationships between the decision-making parameters of the supplier, can introduce indicators to evaluate the quality of the solutions that cannot be easily derived analytically. This dissertation focuses on a simulation-based approach that aims to create a decision support system for carsharing business. This decision support system aims to use demographic and land use data as input, once the provider's needs are known, and to return solutions regarding the optimization of the carsharing service. The development of this thesis is conceived from the point of view of the service provider, even if considerations regarding the equity of the various strategies proposed therein for the service customers constitute an integral and fundamental part of the construction of this system of support for decisions. In this manuscript, we discuss the introduction of different dynamic pricing strategies that aim to increase the profit of the carsharing service, along with other indicators such as the number of bookings and utilization time of vehicles. By developing different price models, the introduction of dynamic prices based on the quantity of vehicles present in the station at the time of booking is evaluated and the output of the implementation of a dynamic price based on the time of the day is examined. In the first part of this thesis, we discuss how it is possible to evaluate the quality of a carsharing service from the point of view of its members, focusing on how different strategies generate or can reduce inequalities due to different wages or purchasing powers. Furthermore, using data collected by a car-sharing company operating in Germany and the United Kingdom, Oply, we implement these same strategies in a scenario calibrated with real data. Finally, we propose a methodology for calibrating carsharing scenarios in an agent-based environment.Moreover, we use these scenarios to demonstrate how it is possible, once there is complete knowledge of the demand and the status of the offer, to attribute a certain price to a single booking that maximizes the profit of the service. The overall results show that the introduction of dynamic pricing strategies does not always benefit all segments of the population and that the goals of a carsharing company are not always compatible with those of its members. Furthermore, they show how it is possible to increase the profit of a carsharing company accordingly to its position on the market, whether it has a total knowledge of the territory or not, whether it is an established company or not yet fully established. As we will also see in the final chapter of this thesis, the product of this work does not consist only in a practical contribution aimed mostly at carsharing companies, but also in a scientific counterpart that outlines new research directions. [less ▲]

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See detailOptimal Motion Planning and Control with Safety Guarantees for Aerial Robots
Castillo López, Manuel UL

Doctoral thesis (2021)

Autonomous aerial robots are expected to revolutionize many industries, such as construction, transportation or even space exploration. However, to target an industry where different robots and humans are ... [more ▼]

Autonomous aerial robots are expected to revolutionize many industries, such as construction, transportation or even space exploration. However, to target an industry where different robots and humans are meant to share the same space our algorithms need to provide safety and efficiency guarantees. Navigating autonomously in these kind of environments poses a great challenge. We may face a significant number of obstacles, and we can only estimate where they are and where they are expected to be, but not exactly. Dealing with these uncertainties is a challenging problem in most robotics applications, including motion planning and control. During the last decade, major contributions have established the theoretical basis upon which optimal motion planning and control with safety guarantees can be achieved. However, they involve a high computational cost that scales exponentially with the number of obstacles, rendering a limited domain of robotic applications. The main contribution of this thesis provides an efficient, scalable and safe approximation to this problem, allowing its application to embedded systems with fast dynamics such as aerial robots. This thesis also includes an additional contribution that allow these methods to plan longer trajectories with a minimal computational footprint, allowing to better anticipate evasive maneuvers. These contributions have been validated mathematically, in simulation and in real-time operation on aerial robots, handling uncertain dynamic obstacles such as pedestrians. [less ▲]

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See detailStretching Directions in Cislunar Space: Stationkeeping and an Application to Transfer Trajectory Design
Muralidharan, Vivek UL

Doctoral thesis (2021)

The orbits of interest for potential missions are stable or nearly stable to maintain long-term presence for conducting scientific studies and to reduce the possibility of rapid departure. Near ... [more ▼]

The orbits of interest for potential missions are stable or nearly stable to maintain long-term presence for conducting scientific studies and to reduce the possibility of rapid departure. Near Rectilinear Halo Orbits (NRHOs) offer such stable or nearly stable orbits that are defined as part of the L1 and L2 halo orbit families in the circular restricted three-body problem. Within the Earth-Moon regime, the L1 and L2 NRHOs are proposed as long-horizon trajectories for cislunar exploration missions, including NASA's upcoming Gateway mission. These stable or nearly stable orbits do not possess well-distinguished unstable and stable manifold structures. As a consequence, existing tools for stationkeeping and transfer trajectory design that exploit such underlying manifold structures are not reliable for orbits that are linearly stable. The current investigation focuses on leveraging stretching direction as an alternative for visualizing the flow of perturbations in the neighborhood of a reference trajectory. The information supplemented by the stretching directions are utilized to investigate the impact of maneuvers for two contrasting applications; the stationkeeping problem, where the goal is to maintain a spacecraft near a reference trajectory for a long period of time, and the transfer trajectory design application, where rapid departure and/or insertion is of concern. Particularly, for the stationkeeping problem, a spacecraft incurs continuous deviations due to unmodeled forces and orbit determination errors in the complex multi-body dynamical regime. The flow dynamics in the region, using stretching directions, are utilized to identify appropriate maneuver and target locations to support a long lasting presence for the spacecraft near the desired path. The investigation reflects the impact of various factors on maneuver cost and boundedness. For orbits that are particularly sensitive to epoch time and possess distinct characteristics in the higher-fidelity ephemeris model compared to their CR3BP counterpart, an additional feedback control is applied for appropriate phasing. The effect of constraining maneuvers in a particular direction is also investigated for the 9:2 synodic resonant southern L2 NRHO, the current baseline for the Gateway mission. The stationkeeping strategy is applied to a range of L1 and L2 NRHOs, and validated in the higher-fidelity ephemeris model. For missions with potential human presence, a rapid transfer between orbits of interest is a priority. The magnitude of the state variations along the maximum stretching direction is expected to grow rapidly and, therefore, offers information to depart from the orbit. Similarly, the maximum stretching in reverse time, enables arrival with a minimal maneuver magnitude. The impact of maneuvers in such sensitive directions is investigated. Further, enabling transfer design options to connect between two stable orbits. The transfer design strategy developed in this investigation is not restricted to a particular orbit but applicable to a broad range of stable and nearly stable orbits in the cislunar space, including the Distant Retrograde Orbit (DROs) and the Low Lunar Orbits (LLO) that are considered for potential missions. Examples for transfers linking a southern and a northern NRHO, a southern NRHO to a planar DRO, and a southern NRHO to a planar LLO are demonstrated. [less ▲]

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See detailDesign and synthesis of novel benzoxazines to replace traditional reinforcing resins in rubber compounds
Trejo Machin, Acerina UL

Doctoral thesis (2021)

The mechanical performance of tires is controlled by many of the ingredients used in their production. Among them, novolac-type phenolic resins (PR) are petroleum-based materials commonly employed to ... [more ▼]

The mechanical performance of tires is controlled by many of the ingredients used in their production. Among them, novolac-type phenolic resins (PR) are petroleum-based materials commonly employed to reinforce rubber compounds. Even though overall performance is efficient, there is a growing societal need to develop alternatives to these resins as they are challenged by REACH regulations. Benzoxazine resins (Bz) are a new generation of materials that can be suitable for this purpose; they hold potential for improvement of both the mechanical properties and the sustainability of the rubber compounds. However, while PR have been extensively used and their interactions with tire compounds are well known, the use of benzoxazines in rubber compounds requires extensive studies and in-detail investigations. This thesis aims at filling this gap and designing benzoxazine resins that could be relevant alternatives to PR. For this purpose, novel sulfur containing dibenzoxazines were successfully synthesized and their interactions with rubber compounds were methodically investigated. Diphenolic compounds with either disulfide bonds (S‒S), or monosulfide bonds (‒S‒) were reacted with monoamines such as furfurylamine, a bio-based amine produced from agricultural byproducts. These partially bio-based original precursors, which were never reported before, exhibited polymerization behaviors that greatly fit the required conditions for rubber vulcanization. Indeed, the curing of these novel benzoxazine monomers occurred during rubber vulcanization, allowing the elaboration of reinforced materials at the molecular scale without detrimental side-reactions with the curing package. A fine investigation of the mechanical and thermal properties of the resulting rubber compounds indicated the reinforcing effect of these new resins at the macroscale. Therefore, the potential of each benzoxazine to act as a reinforcing resin was tested in real tire parts confirming the potential of Bz to be used as alternatives to PR resins in carbon-black filled compounds. In conclusion, the outcome of this thesis emphasizes that structural features of benzoxazines are a major parameter to be considered for their use in rubber reinforcement. Thanks to the knowledge generated, it was possible to develop novel benzoxazine resins capable of reinforcing rubber compounds in place of traditional phenolic resins. This study also paves the way to replace petroleum based resins by partially bio-based precursors, improving the sustainability of tire compounds. [less ▲]

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See detailEfficient Estimation with Non-Standard Sampling or Missing Endogenous Variables, and Conditional Density Modelling with Unobserved Copula-Connected Shocks
Kostyrka, Andreï UL

Doctoral thesis (2021)

In Chapter 1, it is shown how to use a smoothed empirical likelihood approach to conduct efficient semi-parametric inference in models characterised as conditional moment equalities when data are ... [more ▼]

In Chapter 1, it is shown how to use a smoothed empirical likelihood approach to conduct efficient semi-parametric inference in models characterised as conditional moment equalities when data are collected by variable probability sampling. Results from a simulation experiment suggest that the smoothed-empirical-likelihood-based estimator can estimate the model parameters very well in small to moderately sized stratified samples. In Chapter 2, a novel univariate conditional density model is proposed to decompose asset returns into a sum of copula-connected unobserved ‘good’ and ‘bad’ shocks. The novelty of this approach comes from two factors: correlation between unobserved shocks is modelled explicitly, and the presence of copula-connected discrete jumps is allowed for. The proposed framework is very flexible and subsumes other models, such as ‘bad environments, good environments’. The proposed model shows certain hidden characteristics of returns, explains investors’ behaviour in greater detail, and yields better forecasts of risk measures. The in-sample and out-of-sample performance of the proposed model is better than that of 40 popular GARCH variants. A Monte Carlo simulation shows that the proposed model recovers the structural parameters of the unobserved dynamics. This model is estimated on S&P 500 data, and time-dependent non-negative covariance between ‘good’ and ‘bad’ shocks with a leverage-like effect is found to be an essential component of the total variance. Asymmetric reaction to shocks is present almost in all characteristics of returns. The conditional distribution of returns seems to be very time-dependent with skewness both in the centre and tails. Continuous shocks are more important than discrete jumps for return modelling, at least at the daily frequency. In Chapter 3, the semi-parametric efficiency bound is derived for estimating finite-dimensional parameters identified via a system of conditional moment equalities when at least one of the endogenous variables (which can either be endogenous outcomes, or endogenous explanatory variables, or both) is missing for some individuals in the sample. An interesting result is obtained that if there are no endogenous variables that are not missing, i.e. all the endogenous variables in the model are missing, then estimation using only the validation subsample (the sub-sample of observations for which the endogenous variables are non-missing) is asymptotically efficient. An estimator based on the full sample is proposed, and it is shown that it achieves the semi-parametric efficiency bound. A simulation study reveals that the proposed estimator can work well in medium-sized samples and that the resulting efficiency gains (measured as the ratio of the variance of an efficient estimator based on the validation sample and the variance of our estimator) are comparable with the maximum gain the simulation design can deliver. [less ▲]

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See detailProbabilisitic limit theorems and the geometry of random fields
Notarnicola, Massimo UL

Doctoral thesis (2021)

The topics presented in this thesis lie at the interface of probability theory and stochastic geometry, with emphasis on the asymptotic study of geometric objects associated with Gaussian random fields ... [more ▼]

The topics presented in this thesis lie at the interface of probability theory and stochastic geometry, with emphasis on the asymptotic study of geometric objects associated with Gaussian random fields defined on manifolds. Such a research stream has been rapidly growing in past years, resulting in a number of developments focussing on local and global geometric quantities. Our principal aim is to discuss probabilistic methods allowing one to deal with the asymptotic fluctuations of volumes of zero sets (also called nodal sets) of Gaussian Laplace eigenfunctions as the eigenvalues diverge to infinity, with a particular focus on the models of Arithmetic Random Waves on the three-dimensional torus and Berry's Random Plane Wave on the two-dimensional Euclidean space. We prove universal variance estimates and non-Gaussian limit theorems for the zero sets of multiple independent Arithmetic Random Waves, complementing several related works in the literature. Our analysis for this builds on an abstract cancellation result applicable to the setting of Gaussian Laplace eigenfunctions on manifolds, yielding in particular a formal description of the so-called Berry's Cancellation Phenomenon observed in various models of random eigenfunctions. For the Berry Random Plane Wave, we prove spatial functional limit theorems for discretized and truncated versions of the nodal length indexed by rectangular domains. Such a contribution yields a basis for proving a fully general functional limit theorem for the nodal length and opens doors to a number of novel probabilistic limit theorems involving semi-local functionals of these nodal length processes. A common technique lying at the core of our arguments for dealing with these tasks is the asymptotic analysis of the Wiener-Itô chaos expansion in Hermite polynomials of such geometric quantities, often allowing one to reduce investigations on Wiener chaoses of lower order. In this context, we discuss properties of generalized Hermite polynomials with matrix arguments, appearing in multivariate statistics and the theory of zonal polynomials. We argue that this family of orthogonal polynomials is particularly effective for deducing chaotic expansions of random variables that are symmetric functionals in the eigenvalues of underlying Gaussian random matrices, notably appearing in different applications dealing with the geometry of random fields. We furthermore present a new characterization of matrix-Hermite polynomials as the eigenfunctions of a generalized Ornstein-Uhlenbeck semigroup on matrix spaces. The above mentioned probabilistic limit theorems originate from the systematic use of the Malliavin-Stein approach on Gaussian spaces, a collection of analytic statements allowing one to deduce probabilistic limit theorems by means of variational techniques. Such a series of results typically emerges from the combination of Stein's method for probabilistic approximations and Malliavin's infinite-dimensional differential calculus. At the end of this thesis, we present preliminary computations yielding variance estimates and Central Limit Theorems for certain non-linear functionals associated with the d-dimensional Berry Random field. Also, we discuss several aspects around optimal convergence rates within Gamma approximations of functionals of Gaussian fields. [less ▲]

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See detailMACHINE LEARNING FOR MIMO DETECTION AND EAVESDROPPING WITH SYMBOL-LEVEL PRECODING COUNTERMEASURES
Mayouche, Abderrahmane UL

Doctoral thesis (2021)

Multiple-input multiple-output (MIMO) technology is an integral part of many current wireless communication systems that can drastically improve the data rates and the spectral efficiency. One major ... [more ▼]

Multiple-input multiple-output (MIMO) technology is an integral part of many current wireless communication systems that can drastically improve the data rates and the spectral efficiency. One major performance limiting factor in MIMO communication is the inter-channel interference (ICI) that adversely affects the transmission's achievable rate, since the receiver has to deal with multiple interfering symbol streams that are transmitted concurrently through a channel subject to random noise and interference. In the case when the channel-state information (CSI) is known at the receiver, i.e., CSIR, it could be used by the latter to compensate for the undesired effects of ICI. Although the problem of symbol detection in MIMO systems -- where the knowledge of CSIR is available -- is a well studied problem with numerous classical detection methods, the complexity of optimal detection methods increase prohibitively in systems with large dimensions, making them impractical for real-time communication. The problem of signal detection in precoded MIMO channels without explicit knowledge of the CSIR is challenging and still being considered in recent research. In particular, this problem is a common occurrence in systems where CSI at the receiver is not available, e.g., time-division duplex (TDD) systems. In this thesis, we investigate the problem of multi-antenna signal detection in the case of a highly distorted received signal due to the ICI effects. The core idea of this thesis is to use pilot data, without explicitly estimating the CSI, to improve the detection performance at the receiver. Motivated by low-complexity signal detection and given the accessibility to pilot data, which form an integral part of communications systems, in this thesis, we propose ML based techniques for MIMO detection in systems where the downlink transmission is precoded using imperfect CSI at the transmitter. Firstly, in the context of a single-user MIMO system, we address the problem of MIMO detection when the received signals are highly distorted, i.e., the case where the signal distortion is caused by signals being precoded with a highly degraded CSI at the transmitter (CSIT). In this setting, we propose ML-based MIMO detectors robust to severe CSIT degradation. The second and third contributions relate to a downlink multi-user multiple-input single-output (MU-MISO) system, for which we propose ML-based detectors that are robust to inaccurate CSIT for uncoded and coded systems, respectively. Herein, the proposed ML detectors are presented as eavesdropping attacks, where, by using the proposed ML detectors, an eavesdropper (Eve) is able to learn the symbol detection function based on precoded pilots and to detect the transmitted symbols, intended for legitimate users, with high accuracy. To counteract these attacks, six symbol-level precoding (SLP)-based countermeasures are proposed with varying security, complexity, and power consumption trade-offs. Numerical results validate the effectiveness of the proposed ML-based detectors and the robustness to the harmful effects of ICI. [less ▲]

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See detailPlasma Initiated Chemical Vapour Deposition - from the Growth Mechanisms to Ultrathin Low-k Polymer Insulating Layers
Abessolo Ondo, Dominique UL

Doctoral thesis (2021)

Plasma-assisted approaches are broadly used in thin-film deposition, surface preparation and top-down fabrication. Particularly, plasma processes, which can operate at atmospheric pressure, have ensured ... [more ▼]

Plasma-assisted approaches are broadly used in thin-film deposition, surface preparation and top-down fabrication. Particularly, plasma processes, which can operate at atmospheric pressure, have ensured the simultaneous synthesis and deposition of numerous thin film compositions that have met multiple applications. Yet, the wide variety of reactive species composing plasmas induces a non-negligible amount of side reactions that result in a lack of regularity in polymeric materials compared to the ones formed by wet chemical polymerisation processes. The combination of ultrashort nanosecond plasma discharge (t_ON ≈ 100 ns) and long plasma OFF-time (t_OFF = 0.1 – 100 ms), for the initiation and propagation of the free-radical polymerisation reaction, was recently demonstrated to yield the formation of conventional polymer layers. Based on the current understanding of the process, i.e. significance of the plasma pulse frequency, this thesis aims at gaining a deeper insight in the influence of other important parameters. The nanosecond pulsed plasma deposition of low dielectric constant insulating thin films is studied. Providing additional dimensions to the characterisation, the dielectric layer’s properties such as the leakage current and the dielectric constant, allow to discriminate mechanisms that would not have been identified from other techniques. Hence, ensuring the further development of the fundamental understanding of the nanosecond pulsed plasma approach. From the nanosecond pulsed plasma deposition reaction of different tetra-organosiloxane compounds, the growth mechanisms driving the formation of insulating polymer layers are elucidated. For vinylic monomers, the plasma-induced polymerisation is demonstrated to be highly favour over plasma-state polymerisation at low plasma pulse frequency. This yields the excellent retention of the monomer structure and the prevalence of surface reactions, which are essential to obtain remarkable insulating properties. In addition to the significance of the monomer structure, the saturation ratio, i.e. the monomer partial pressure over its saturated vapour pressure (PM/Psat), is demonstrated as a key parameter of the thin film’s growth. While low P_M/P_sat values result in the prevalence of gas phase reactions, excessively high P_M/P_sat values lead to the formation of poorly reticulated and leaky polymer layers, when operating at low plasma pulse frequency. As such, three different regimes of growth are identified: the monomer deficient regime, the competition regime, and the energy deficient regime. Optimisation of saturation ratio ensures the formation of smooth and conformal low dielectric constant insulating thin films. Taking advantage on the understanding gained on the nanosecond pulsed plasma deposition of insulating polymer layers, the dielectric constant is tuned from the careful selection of the starting monomer compound. Several vinylic cyclo-siloxane and -silazane compounds are notably studied. Dielectric constant values as low as 2.8 are obtained from the monomer possessing the lowest polarisable bonds and the larger ring size, i.e. the 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotrisiloxane, while retaining a low leakage current density in the range of 10^-9 A/cm^2 at 20 V. [less ▲]

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See detailLaser Welding of Metals to Polymers Under the Special Influence of Surface Pretreatment on Interfacial Thermal Transfer
Alsayyad, Adham Ayman Amin UL

Doctoral thesis (2021)

Joining of metals to polymers is increasing among various industries because of its ability to produce lightweight hybrid products with tailored properties. Common joining methods, such as adhesive ... [more ▼]

Joining of metals to polymers is increasing among various industries because of its ability to produce lightweight hybrid products with tailored properties. Common joining methods, such as adhesive bonding and mechanical fastening, require adding a third material which might involve hazardous chemicals or add extra weight and stress concentration points to the component. On the other hand, Laser-Assisted Metal – Polymer joining (LAMP) is a contactless, rapid, highly precise and energy-efficient technique, that produces autogenous and miniaturized joints. It was already demonstrated that surface pretreatment prior to the welding process has a significant impact on the joint performance by modifying surface chemistry and topography, promoting chemical bonding and mechanical interlocking. This research aims at expanding the understanding of the effects of surface properties on the joint’s performance by investigating their influence on interfacial thermal transfer. While increased surface roughness of metallic partner is expected to improve LAMP joint performance by promoting mechanical interlocking, it is hypothesized that a smoother surface would improve the joint quality by enhancing the interfacial thermal transfer during the welding process, resulting in a larger area of molten polymer at the interface and a better joint performance. In this research, aluminum (Al1050) and titanium (Ti64) were joined with polyamide (PA6.6). Initially, laser welding parameters were optimized and kept constant during all surface pretreatments’ investigations. Preliminary surface pretreatments, using short-pulsed laser ablation and atmospheric plasma pretreatment, were conducted on Al1050 – PA6.6 to analyze the effects of surface composition and topography on joint quality and performance, and to optimize interfacial adhesion. Results show a correlation between increased surface oxidation and surface energy with improved interfacial adhesion and joint resistance to shear failure. Compared to plasma pretreated surfaces, laser ablation of metals results in a very rough surface which exhibits perfect wettability to both water and diiodomethane. This promotes mechanical interlocking and interfacial adhesion, resulting in a relatively stronger joint failing in a cohesive failure mode. Results confirm that an improvement of the assembly’s shear resistance to failure can certainly be achieved without an increase in surface roughness and interfacial interlocking, as observed in case of plasma pretreatment. Design of Experiments (DoE) techniques were utilized for both material combinations in order to optimize laser ablation process and to investigate the effects of pretreatment parameters on surface properties, interfacial thermal transfer, joint quality and resistance to failure. Laser ablation parameters influenced the surface topography with no significant effect on the surface composition, and all laser-ablated surfaces showed perfect wettability to both water and diiodomethane. While all ablated surfaces demonstrate cohesive failure mode, smoother ablated surfaces results in a better interfacial thermal transfer as indicated by the Thermal Contact Resistance (TCR) calculations and measurements, based on Cooper–Mikic–Yovanovich (CMY) model and layered Laser Flash Analysis (LFA) investigations, respectively. Results show that a smoother ablated surface results in better interfacial thermal transfer, melting a larger area of polymer which increases the joint quality and resistance to shear load. [less ▲]

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See detailThought, Language, and Reasoning. Perspectives on the Relation Between Mind and Language
Fraissler, Hannes UL

Doctoral thesis (2021)

This dissertation is an investigation into the relation between mind and language from different perspectives, split up into three interrelated but still, for the most part, self-standing parts. Parts I ... [more ▼]

This dissertation is an investigation into the relation between mind and language from different perspectives, split up into three interrelated but still, for the most part, self-standing parts. Parts I and II are concerned with the question how thought is affected by language while Part III investigates the scope covered by mind and language respectively. Part I provides a reconstruction of Ludwig Wittgenstein’s famous Private Language Argument in order to apply the rationale behind this line of argument to the relation between mind and language. This argumentative strategy yields the conclusion that reasoning – an important type of thought – is constitutively dependent on language possession and is therefore not available to non-linguistic creatures. This result is achieved by considering the preconditions for reasoning – given that it is a rule-governed activity – and eliminating competitors to language for providing reasoners with what it takes to reason. Part II provides a critical outlook on the wide and highly heterogeneous field of linguistic relativity theories. It is argued that no kind of linguistic relativity whatsoever follows from the conclusion of Part I – i.e., the claim that reasoning is constitutively dependent on having a language. While Part II does not provide a conclusive argument against the linguistic relativity hypothesis, it is argued that endorsement of linguistic relativity theories often rests on a mistaken assumption to the effect that language and culture are interwoven in a way which makes it impossible to separate culture and language, as well as their respective studies. This assumption is undermined by providing examples of languages which clearly predate their culture (Esperanto) or do not even have a culture at all (Klingon). So, the assumption that language and culture are inextricably intertwined is refuted by way of counterexample. Part III provides an in-depth examination of the Principle of Expressibility – prominently endorsed and formulated by John Searle – which claims that whatever can be thought can also be said. The domains of what can be thought and of what can be said are considered in set theoretic terms in order to determine whether one is contained in the other, so that everything we can think can also be adequately communicated. After thorough study of interpretative issues regarding the Principle of Expressibility and consideration of the most pressing potential counterexamples to the principle, we can conclude that we have good reason to believe in the truth of the Principle of Expressibility. In conclusion, the achieved results are related back to prominent positions in the discussion about thought and language which already make their appearance in the very beginning of this investigation. The final chapter of this dissertation reminds us that eminent figures in philosophy have often taken a wrongheaded perspective on the relation between language and thought, so that language has frequently appeared to be an impediment to thought. We can, however, confidently conclude that language, on the contrary, is by far our most apt means for thought and that reasoning would not even be possible without the resources language provides. [less ▲]

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See detailIntegrated multi-omic analyses of mobile genetic elements within a mixed microbial community
Martinez Arbas, Susana UL

Doctoral thesis (2021)

Microbial communities are ubiquitous, complex and dynamic systems that constantly adapt to changing environmental conditions, while playing important roles in natural environments, human health and ... [more ▼]

Microbial communities are ubiquitous, complex and dynamic systems that constantly adapt to changing environmental conditions, while playing important roles in natural environments, human health and biotechnological processes. Invasive mobile genetic elements (iMGE) are considered as important biotic components of microbial communities, in particular (bacterio)-phages and plasmids are some of the most abundant and diverse biological entities, which may influence community structure and dynamics. Microbial populations within naturally occurring communities are constantly interacting with each other. Ecological interactions between those populations can be generally classified as competitive and cooperative relationships. To date, extensive studies on biotic interactions, i.e. relationships between microbial hosts with iMGEs and between microbial populations, have been somewhat limited, thus restricting our understanding of microbial community dynamics. Fortunately, high-throughput multi-omics derived from microbiomes, i.e. metagenomics and metatranscriptomics, enables access to both functional -potential and -expression information of those biotic components. Combining longitudinal multi-omics data with mathematical frameworks allows us to model microbial community interactions and dynamics, unlike ever before. Here, I present a longitudinal integrated multi-omics analysis of biotic components within foaming activated sludge, spanning ~1.5 years to unravel i) iMGE-host dynamics and ii) ecological interactome. In the first part of this work, empirical host-iMGE CRISPR-based links in combination with mathematical modelling highlighted the importance of plasmids, relative to phages, in shaping community structure, while also showing that plasmids vastly outnumbered, and were more targeted via CRISPR-Cas systems, compared to their phage counterparts. In the second part of this work, mathematical modelling is used to provide ecological contexts for the relationships between microbial community members. In general, we observed a dynamic interactome, with higher cooperative interactions, despite these populations encoding highly similar functional potential. In summary, this work demonstrates the potential of longitudinal multi-omics in expanding our understanding of microbial community dynamics, which could be expanded to other microbial ecosystems and potentially lead to applications in human health and biotechnological processes. [less ▲]

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See detailFace-swap Deepfake Detection Using High-frequency Components
Mejri, Nesryne UL

Bachelor/master dissertation (2021)

Over the last years, very deceitful deepfakes applied to human visuals appeared on theInternet. Given their impressive visual quality, they are nowadays considered a potentialthreat for both individuals ... [more ▼]

Over the last years, very deceitful deepfakes applied to human visuals appeared on theInternet. Given their impressive visual quality, they are nowadays considered a potentialthreat for both individuals and organizations. Hence, researchers started investigatingthe flaws of deepfakes to develop automated tools capable of detecting forged content. Asa result, a wide range of deepfake detection methods has been introduced. In particular,deep learning based-approaches have shown impressive performance. Nevertheless, thesemethods are still not sufficiently robust as they usually consider only one type of artifact,either in the spatial or the frequency domain. In this context, this thesis proposes toleverage the high-frequency components extracted from color images jointly with theoriginal color information to detect unusual traces. It introduces an end-to-end trainablemodule that (a) extracts features from precomputed high-frequency components and (b)fuses them with RGB features. The deepfake detection framework not only exploitsthe high-frequency anomalies present in manipulated images but can also be integratedwith the majority of RGB-based deepfake detectors. Experimental results show thatthe proposed approach improves the performance of state-of-the-art networks, such asXceptionNet and EfficientNet, on a challenging deepfake dataset called Celeb-DF. [less ▲]

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See detailMehrsprachige Repertoires in kollaborativen Schreibinteraktionen
Stierwald, Mona UL

Doctoral thesis (2021)

Cette thèse examine la problématique du plurilinguisme et de la plurilitéracie individuelle dans des interactions portant sur des pratiques d'écriture collaborative. Le plurilinguisme et la plurilitéracie ... [more ▼]

Cette thèse examine la problématique du plurilinguisme et de la plurilitéracie individuelle dans des interactions portant sur des pratiques d'écriture collaborative. Le plurilinguisme et la plurilitéracie sont éclairées par les concepts de répertoires et de registres langagiers. Dans ce type d'interaction en face à face, deux ou plusieurs personnes se retrouvent au même endroit pour rédiger un document à partir d'idées partagées en menant une conversation à ce sujet. Il s'agit là de sonder les pratiques litéraciques d'étudiant-e-s plurilingues en études romanes de l'université Goethe de Francfort lorsqu'ils/elles formulent conjointement un texte académique dans une langue cible romane (en français ou en espagnol). Pour ce faire, cette recherche s'inscrit dans une approche qualitative mobilisant une pluralité de méthodologies et de courants théoriques inspirés principalement des recherches menées en sociolinguistique et de l'ethnographie comme la recherche action. Le recueil de données a eu lieu dans le cadre d'un séminaire de recherche-action au cours duquel les étudiant-e-s plurilingues ont réfléchi par écrit sur leurs propres répertoires langagiers et se sont réuni-e-s de manière interactive en groupes pour la rédaction de textes académiques. Les données résultantes ont été analysées par le biais d'une analyse de contenu qualitative et d'une analyse conversationnelle. En outre, des concepts venant des recherches sur le plurilinguisme et sur les processus d'écriture sont mobilisés a fin d'accéder à une vision holistique des dynamiques d'écriture collaborative. Cette recherche ouvre de nouvelles perspectives pour les recherches portant sur la plurilitéracie. D'un point de vue théorique, on voit comment la plurilitéracie structurelle peut être analysée à partir d'interactions portant sur l'écriture collaborative. D'un point de vue méthodologique, elle ouvre des voies de réflexion pour aiguiser la focalisation sur les processus d'interaction, les productions et leurs corrélations avec les parcours des individus impliqués. À cet égard, la relation entre l'ethnographie et l'analyse conversationnelle joue un rôle primordial. En fin, d'un point de vue didactique, il est significatif de voir comment dans les écrits universitaires le projet d'appropriation d'une langue cible peut aller de pair avec la prise en compte des ressources plurilingues. [less ▲]

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See detailComplex Networks in Manufacturing - Suitability and Interpretation
Omar, Yamila UL

Doctoral thesis (2021)

The fourth industrial revolution, and the associated digitization of the manufacturing industry, has resulted in increased data generation. Industry leaders aim to leverage this data to enhance ... [more ▼]

The fourth industrial revolution, and the associated digitization of the manufacturing industry, has resulted in increased data generation. Industry leaders aim to leverage this data to enhance productivity, boost innovation and generate new manners of competition. In this work, out of the many domains within the manufacturing sector, production will be explored. To this end, the mathematical tools of network science are utilized to characterize and evaluate production networks in terms of complex networks. In a manufacturing complex network, nodes represent workstations, and directed edges abstract the material flow that occurs among pairs of workstations. These types of complex networks are known as "material flow networks" and are used to study issues associated with manufacturing systems in the domain of production at the intra-enterprise level. While some research on the subject exists, this work will demonstrate that the use of complex networks to describe and evaluate manufacturing systems constitutes a nascent research field. In fact, the limited existing literature tackles a vast number of issues raising more questions than providing answers. This work aims to answer a number of those open questions. Firstly, which complex network metrics are suitable in the context of manufacturing networks will be determined. As a consequence, unsuitable metrics will be identified as well. To accomplish this, the flow underlying assumptions of popular complex network metrics is studied and compared to those of manufacturing networks. Furthermore, other existing complex network metrics with more appropriate underlying assumptions, but not yet explored in the context of manufacturing, are proposed and evaluated. Then, the appropriate interpretation of suitable complex network metrics in terms of Operations Research is provided. Finally, shortcomings of these metrics are highlighted to caution practitioners regarding their use in industrial settings. [less ▲]

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See detailOld and New Antiferroelectrics: Experimental Studies of Phase Transitions in Model Materials
Milesi-Brault, Cosme UL

Doctoral thesis (2021)

Antiferroelectrics are a subcategory of ferroic materials that display no spontaneous polarisation due to antiparallel ionic displacements. These materials undergo an electric field-induced transition to ... [more ▼]

Antiferroelectrics are a subcategory of ferroic materials that display no spontaneous polarisation due to antiparallel ionic displacements. These materials undergo an electric field-induced transition to a polar phase accompanied by the emergence of a spontaneous polarisation. As for ferroelectrics, heating up an antiferroelectric material above a certain temperature Tc will cause another phase transition towards a paraelectric phase. Antiferroelectricity is currently the subject of a renewed interest, mostly due to a rising need of new smart materials for applications such as energy storage, electrocaloric cooling or microelectronics. The most-studied antiferroelectric is lead zirconate PbZrO3perovskite. However, the understanding of its switching mechanism is still incomplete. In this work, we will first present our study on the sol-gel synthesis and characterisation of antiferroelectric polycrystalline thin films of canonical lead zirconate PbZrO3. We will notably highlight the realisation of an in-plane switching of our antiferroelectric samples grown on transparent substrates, as well as the optical observation of this switching through birefringence changes. On a more fundamental side, the oldest and best-known model of antiferroelectricity was defined by Kittel in 1951. No real unidimensional Kittel-like model material has, to our knowledge, been identified yet. We will detail our spectroscopic study of the lattice dynamics of francisite Cu3Bi(SeO3)2O2Cl which combines several inelastic scattering experiments. We will then discuss how this study proves that francisite is, to our knowledge, the best candidate of a material displaying a displacive antiferroelectric phase transition. [less ▲]

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See detailSteps Towards Semantic Code Search
Kim, Kisub UL

Doctoral thesis (2021)

Code search can be a core activity in software development for enhancing productivity. Developers commonly reuse existing source code fragments by searching for codebases available in local or global ... [more ▼]

Code search can be a core activity in software development for enhancing productivity. Developers commonly reuse existing source code fragments by searching for codebases available in local or global repositories. Code search helps developers ease the implementation by supplying code snippets to reuse or understand specific concepts deeper during software development by providing various code snippets for the same tasks. In addition, reading real-world examples (the results of code search) is helpful for developers to make programs more reliable, faster, or secure as the examples have been tested and reused by many other developers. However, it is getting more challenging as the codebases are becoming larger since the large codebase can derive too many code candidates. Thus, the research community has invested substantial efforts in developing new techniques, combining methods, and applying more extensive data to improve the performance and efficiency of code search. Despite the significant efforts made by researchers in the field, code search still has many open problems that the community needs to address, such as lack of benchmarks, vocabulary mismatch (between natural language and source code), and low extensibility on programming languages. Our work focuses on the open issues and the momentum of the domain on semantic code search, which considers the meaning of the user query rather than concerning the syntactic similarity that most other studies have approached. The thesis begins with exploring general issues on code search by conducting a systematic literature review. The survey organizes and classifies the code search approaches with various directions such as learning-based, feedback-driven, dynamic techniques. It reveals insights and new research directions. Given the research directions by the survey, we concentrate on alleviating the vocabulary mismatch problem between free-form text query and source code to improve the overall performance of code search first. To understand the free-form text query, we leverage crowd knowledge. The survey also discovered that there are only a few code-to-code approaches and investigation on crowd-knowledge indicated there exists demand, especially on finding semantically similar source code, i.e., source code that is syntactically different but performs the same functionality. Therefore, we go further, reformulating the user code query with real-world code snippets. This allows catching the semantics from the source code. Given the semantic information, a user can search for desired source code by using their code fragments. In this context, the present dissertation aims to explore semantic code search by contributing to the following three building blocks: Review of state-of-the-art: Despite the growing interest in code search, a comprehensive survey or systematic literature review on the field of code search remains limited. We conducted a large-scale systematic literature review on the internet-scale code search. Our objective in this study was to devise a grounded approach to understand the procedure for the code search approach. We built an operational taxonomy on top of each procedure to categorize the approaches and provide insights on the selection of various approaches. Our investigation on the open issues from the literature guide researchers and practitioners to future research directions. CoCaBu: Source code terms such as method names and variable types are often different from conceptual words mentioned in a search query. This vocabulary mismatch problem can make code search inefficient. We presented COde voCABUlary (CoCaBu), an approach to resolving the vocabulary mismatch problem when dealing with free-form code search queries. Our approach leverages common developer questions and the associated expert answers to augment user queries with the relevant but missing structural code entities to improve matching relevant code examples within large code repositories. To instantiate this approach, we built GitSearch, a code search engine, on top of GitHub and Stack Overflow Q&A data. Experimental results, collected via several comparisons against the state-of-the-art code search and existing online search engines such as Google, show that CoCaBu provides qualitatively better results. Furthermore, our live study on the developer community indicates that it can retrieve acceptable or attractive answers for their questions. FaCoY: Most existing approaches focus on serving user queries provided as natural language free-form input. However, there exists a wide range of use-case scenarios where a code-to-code approach would be most beneficial. For example, research directions in code transplantation, code diversity, patch recommendation can leverage a code-to-code search engine to find essential ingredients for their techniques. Given the wide range of use-case for code-to-code search, we propose FaCoY, a novel approach for statically finding code snippets that may be semantically similar to user input code. FaCoY implements a query alternation strategy: instead of directly matching code query tokens with code in the search space, FaCoY first attempts to identify other tokens, which may also be relevant in implementing the functional behavior of the input code. The experimental results show that FaCoY is more effective than all the existing online code-to-code search engines, and it can also be used to find semantic code clones (i.e., Type-4). Moreover, the results proved that FaCoY could be helpful in code/patch recommendation. [less ▲]

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See detailLes reconfigurations du politique et du religieux, au prisme de la sécularisation et du bioconservatisme : La Manif pour tous en France et le Family Day en Italie.
Durante, Raphaël UL

Doctoral thesis (2021)

Tensions between politics and religion lead to a very productive scope of investigation for those interested in contemporary democratic reconfigurations. In this context, this thesis will address two ... [more ▼]

Tensions between politics and religion lead to a very productive scope of investigation for those interested in contemporary democratic reconfigurations. In this context, this thesis will address two social phenomena located at the crossroads of political and religious considerations, in a comparative perspective: ‘La Manif pour tous’ - a movement opposing gay- marriage in France – and The Family Day – opposition movement to same-sex civil partnership in Italy. This study highlights the importance of the political and religious context in the structuring, the system of values and the impact of those so-called “anti-gender” movements, through a multidisciplinary approach bringing together conceptual tools from the social movement theory, religious sociology and political philosophy, but also through semi- structured interviews and attendee observations. The comparative perspective will indeed reveal a greater empowerment process for the French case, with more pronounced efforts to distance itself from traditional political and religious institutions. Despite this, this thesis will bring up a certain convergence of these movements towards the formation of a bio-conservative block, steeped in Christian anthropology but also scientific and legal considerations that challenge the principles of contemporary liberal democracies. The bio-conservative block shakes up the opposition between modern autonomy and religious heteronomy, and works on setting up and developing new political cleavages. [less ▲]

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See detailTopics in Computational Number Theory and Cryptanalysis - On Euclidean Lattices, Edwards Curves and Cryptographic Multilinear Maps
Notarnicola, Luca UL

Doctoral thesis (2021)

The content of this thesis is situated between number theory and cryptology. It contributes in several directions of mathematical cryptanalysis and arithmetic geometry, by the use of explicit and ... [more ▼]

The content of this thesis is situated between number theory and cryptology. It contributes in several directions of mathematical cryptanalysis and arithmetic geometry, by the use of explicit and computational methods in number theory. The thesis is divided into four main parts, describing four different works. The first part of this thesis treats cryptographic multilinear maps, introduced in the early 2000s, as extension of bilinear pairings on abelian varieties following a survey by Boneh and Silverberg (Contemp. Math. 2003). The difficulties of constructing efficient cryptographic multilinear maps from algebraic geometry led cryptographers to obtain multilinear maps from the notion of graded encoding systems, following the formalism of Garg, Gentry and Halevi (Eurocrypt 2013), backgrounded from ideas on fully homomorphic encryption. To this date, there are three candidate constructions. Their security however is rather poorly understood and many attacks have flourished over the past years. In this thesis, we consider the CLT13 Scheme, proposed by Coron, Lepoint and Tibouchi (Crypto 2013), constructing multilinear maps over the integers. A vulnerability of this scheme was detected by Gentry, Lewko and Waters (Crypto 2014), by exploiting the composite-ring structure of the plaintext space, enabling a simple two-dimensional lattice attack to reveal secret information. At the same time, the authors suggested a simple countermeasure to prevent this line of attack. By relying on high-dimensional lattice reduction, we design new cryptanalysis against CLT13, overriding the countermeasure of Gentry, Lewko and Waters by several orders of magnitude. Combined with the Cheon et al. attack (Eurocrypt 2015), we reveal all secret parameters of CLT13. By applying our cryptanalysis to concrete instantiations of CLT13-based construc- tions, certain parameter ranges are found unsecure. The second work presented in this thesis isolates the Hidden Lattice Problem as a more general problem appearing in several cryptographic scenarios, among which the Hidden Sub- set Sum Problem, studied by Nguyen and Stern (Crypto 1999). The Nguyen-Stern algorithm for the Hidden Subset Sum Problem builds on the use of orthogonal lattices, which have shown powerful in public-key cryptanalysis. After extending their algorithm to our more general setting, our main contribution is to present, based on duality in lattice theory, a new algorithm for the Hidden Lattice Problem, providing a competitive alternative to the cel- ebrated Nguyen-Stern orthogonal lattice attack. For both algorithms, we provide practical parameters, based on heuristic and rigorous studies of the geometry of the underlying lat- tices. The generality of our definition for the Hidden Lattice Problem allows encompassing multiple number-theoretic problems of cryptographic interest. For these problems, our new algorithm leads to a valuable alternative to the state-of-the-art algorithms. The third work presented in this thesis aims at extending the powerful cryptanalysis by Cheon et al. (Eurocrypt 2015) against the multiparty Diffie-Hellman protocol instantiated un- der the aforementioned CLT13 Scheme. To do so, we formulate, independently of the CLT- framework, a general problem on simultaneous diagonalization of special matrices of low- rank, which we call “incomplete”. Based on techniques from linear algebra, our major contri- bution is the design of efficient algorithms for this problem, providing explicit and practical parameters. We recognize that our algorithms also apply to solve the Approximate Common Divisor Problem based on the Chinese Remainder Theorem (CRT-ACD Problem). In partic- ular, our algorithms lead to quadratic improvements in the input length for the CRT-ACD Problem, and some cases of the Cheon et al. attack. The last work included in this thesis studies Edwards curves, a normal form for elliptic curves, first introduced by Edwards (Bull. Amer. Math. Soc. 2007). This model for elliptic curves has been proposed for elliptic-curve cryptography by the work of Bernstein and Lange (Asiacrypt 2007), by exploiting the efficient Edwards point arithmetic. Their work includes a construction of the Edwards model from the Weierstrass model. While not directly oriented towards cryptographic targets, our study of the Edwards model is of arithmetic-geometric nature. Our main contributions include abstract constructions for the Edwards model, an explicit generalization of the Bernstein-Lange construction, as well as general properties of geometric nature. From an analytic perspective, we complement our study with extensive computer calculations related to the ranks of rational elliptic curves in a family related to Ed- wards curves. Part of our statistical data is based on our extension of an algorithm involving L-functions and relying on the well-known Birch and Swinnerton-Dyer Conjecture for elliptic curves. [less ▲]

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See detailNomads’ Poetic Translingualism. Multiple voices, dialogical writing and space constructions in the work of Liliane Welch and Pierre Joris
Pauly Ep Hansen, Marie Anne UL

Doctoral thesis (2021)

In the past decades, multilingualism has developed into a highly researched topic in literary studies as well as in applied linguistics. Surprisingly, two Anglophone poets, Liliane Welch and Pierre Joris ... [more ▼]

In the past decades, multilingualism has developed into a highly researched topic in literary studies as well as in applied linguistics. Surprisingly, two Anglophone poets, Liliane Welch and Pierre Joris, originally from Luxembourg, have not been included in research despite the rich and manifold perspectives on languages that their work displays. They grew up and were educated in the multilingual environment of Luxembourg before they immigrated to North America while continuing to travel widely. For their writing, they rejected their earlier languages, Luxembourgish, French and German and opted for English as the language of their writing. These observations have motivated the overall research question: What multiple facets of translingualism does a nomadic approach of writing offer? Through close references to the work of Welch and Joris the study aims to investigate the impact of multiple languages on poetic writing, with a particular attention to poets’ linguistic meta-reflections and their positioning in relation to languages. The dissertation is divided into three parts with separate yet related research aims and objectives. Part I sets out the context of the research while it also enquires into the pertinence of associating literary and linguistic dimensions with important features of nomadic theory. The definition of research aims and objectives motivates the description of a concept-based inquiry. An extensive review of relevant studies highlights the international and interdisciplinary character of recent research on multilingualism while nomadism appears as a rich resource for thinking about what moving means for writers. Both areas thus significantly contribute to the description of conceptual and textual cornerstones, which ensure the coherence of the study as a whole. Concepts need not come as abstract ideas only; the palimpsest as conceptual metaphor proves a fitting tool to investigate layers of texts, thoughts and locations. It is a golden thread that all along the dissertation functions as reminder of transformative processes. A distinction between fact-oriented and poetic writing accounts for differences in focus in Parts II and III. Primary text resources in Part II comprise documentary and autobiographical writing as well as academic pieces. These texts help draw the poets’ itineraries, inquire into how they reconstruct former language experiences and develop key elements of a poetics for their creative writing. Gradually, the specificities of each poet’s conception of the role of language multiplicity emerges. Poetry as creative and imaginative work is at the centre of Part III, which scrutinizes texts for their various uses of translingualism in dialogical writing, in translational practices and in the creation of poetic spaces marked by superimposed voices, languages and texts. Among the outcomes of the study, a few points stand out. The elaboration of an interdisciplinary framework stresses the benefits of crossing disciplinary perspectives and negotiating between terminologies in different languages. Part II shows that, contrary to widespread beliefs, both poets reject the mother tongue as language for writing; moreover, they demonstrate the rich cognitive, self- constructive and creative potential that a new self-selected language holds. The fundamental role that nomads’ ongoing reading in several languages holds for translingual writing is another crucial point that both poets constantly demonstrate. Differences, however, appear in their understanding of language multiplicity in texts. While Welch aims at a unified language, Joris is in search of new forms of writing that transgress borders of languages and genres. The analysis of poems in Part III confirms these diverse orientations and underlines the relevance of a distinction between implicit and explicit forms of heterolingualism, which account for a highly diversified range of writing across languages. For a study of all forms, the palimpsest remains a powerful conceptual metaphor to investigate the articulation of languages. The examples show that only an in-depth analysis can bring to light the nature of interactions and indicate their relevance for studies of multilingualism outside the literary context. [less ▲]

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See detailUsing the Blockchain Technology for Trust Improvement of Processes in Logistics and Transportation
Imeri, Adnan UL

Doctoral thesis (2021)

This thesis address the general problem of safe and secure transport of dangerous goods (TDG). The TDG is very complicated to manage because of risk for the environment and human life. Currently, it ... [more ▼]

This thesis address the general problem of safe and secure transport of dangerous goods (TDG). The TDG is very complicated to manage because of risk for the environment and human life. Currently, it suffers from a lack of efficiency, trust, and t ransparency. In this thesis, we propose a novel method to specify the workflow aspects of TDG by considering all TDG process stages during its entire lifecycle. This method aims to facilitate the specifications of the TDG workflow management system that is entirely based on existing regulatory frameworks ensuring the compliance, trust, and transparency of all underlying processes. The proposed system design method is based on the so-called model-driven architecture (MDA) approach and enhancing it to consider blockchain properties. The first stage is the formal analysis of the process of TDG and its alignment with the regulatory frameworks. The proposed design method aims, at this stage, to allow the formal definition and verification of the design of the system with regard to the regulatory frameworks. The next stages of the method rely strongly on the model transformation that is a salient aspect of the proposed design method. Model transformation allows to automatically discover peer system components and authorized interactions. The last stage of the whole model transformations is the specification of digital twin profiles for all potential s t akeholders. All the interactions in the real world between stakeholders are transformed into interactions in the digital world, while the interactions with the environment are achieved through the use of IoT. The proposed approach enables interactions between components of the systems (digital twins, IoT devices, etc.) only if this is compliant with the regulatory framework. Thanks to blockchain technology, our design method allows improving trust and transparency in the process of TDG from the perspective of stakeholder collaborations. Smart contract technological capabilities are also a cornerstone of the proposed solution. This thesis also contributes to improving the semantic of smart contracts to capture supply chain management specifications as well as dangerous goods specificities in terms of t ransportation. Dynamic concepts related to the supply chain management of dangerous goods such as time-related and geographic constraints, digital certification, anomaly detection and multi-party smart contract, managing emergencies, and shared responsibility have been addressed at the level of the smart contract. In particular, this thesis proposes applying temporal logic for the formal specification and verification of smart contracts. This thesis proposes an integrated approach for blockchain and IoT to support the dynamic aspects in the supply chain of dangerous goods. Data collected from various IoT devices along the physical supply chain (goods, vehicles, country borders, etc.) are transmitted to the blockchain and further processed by the system following the workflow logic that was specified and automatically triggering related smart contracts and corresponding actions. The last contribution in this thesis is the implementation of a proof-of-concept system to validate the different aspects of the contribution, namely the design method, the trust and transparency assurance, and the automatic triggering of actions and information flows. [less ▲]

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See detailLeveraging Execution Logs to Support Model Inference and Software Testing
Messaoudi, Salma UL

Doctoral thesis (2021)

Many software engineering activities process the events contained in log files. However, before performing any processing activity, it is necessary to correctly parse the entries in a log file to retrieve ... [more ▼]

Many software engineering activities process the events contained in log files. However, before performing any processing activity, it is necessary to correctly parse the entries in a log file to retrieve the actual events recorded in the log. In the case of cyber-physical systems, execution logs are highly important because such systems integrate multiple third-party components where their source code is not always available. This limits the visibility of the system behavior to what is collected in the execution logs. The increasing amount of logs produced by cyber-physical systems calls for 1) more advanced techniques for accurate log parsing, 2) scalable model inference that will enabling efficient program comprehension and, 3) cost-effective software testing to ensuring the quality of complex soft- ware systems. [less ▲]

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See detailHOW TO MAKE MOTIVATION PERSIST: IMPROVING PHYSICAL ACTIVITY MOTIVATION IN YOUTH ACROSS THE SCHOOL AND LEISURE-TIME CONTEXT OVER TIME
Hutmacher, Djenna UL

Doctoral thesis (2021)

Worldwide, physical activity levels are decreasing over time and with age (Guthold et al., 2020), which is directly related to numerous physiological and psychological health issues (Poitras et al. 2016 ... [more ▼]

Worldwide, physical activity levels are decreasing over time and with age (Guthold et al., 2020), which is directly related to numerous physiological and psychological health issues (Poitras et al. 2016). In this regard, previous research has found that, predominantly, not the daily amount of sitting, but insufficient physical activity rates are related to higher mortality rates (Eklund et al., 2016; Van der Ploeg & Hillsdon, 2017). The purpose of the present thesis is therefore to investigate underlying factors, which are directly and indirectly related to and may foster physical activity behavior. For reasons of aiming at supporting most of children and adolescents, physical education provides a promising context to intervene. In this sense, one multi-theoretical framework, the trans-contextual model (Hagger et al., 2003), has been presented in order to investigate the transfer of motivation between the school and out-of-school context. Within this particular model, three propositions are given. First, (1) Hagger and Chatzisarantis (2016) claim that the students’ perceived support of autonomy by the physical education teacher is related to increased values of students’ autonomous motivation in physical education, which, in turn, (2) is related to autonomous motivation toward physical activity beyond the school context in leisure-time. Finally, (3) the authors suggest that autonomous motivation is related to the antecedents of the intention of getting physically active, namely attitude, subjective norm, and perceived behavioral control. In order to test and extend these assumptions, the perceived support of the three basic psychological needs for autonomy, competence, and relatedness (Deci & Ryan, 2000) by the physical education teacher, the different motivational regulation types in the physical education and leisure-time context, and the concepts of the theory of planned behavior (i.e., subjective norm, attitude, perceived behavioral control, intention, and physical activity behavior; Ajzen, 1991) were assessed. The analyses performed and results obtained are presented in three individual manuscripts, each addressing a unique research question. Within the first manuscript, the aim is to analyze the psychometric properties of our translated versions of the motivational regulation scales, the Revised Perceived Locus of Causality Scale (PLOC-R; Vlachopoulos et al., 2011) and the Behavioral Regulation in Exercise Questionnaire (BREQ-II; Markland & Tobin, 2004). In a second manuscript, the three different propositions of the trans-contextual model are tested in a longitudinal design via generalized linear mixed models, cross-lagged panels, and longitudinal mediation analyses. In a final step (manuscript three), a new yet already scientifically established concept, namely mindfulness, which has been found to be beneficial in classrooms (Zenner et al., 2014), is integrated into the trans-contextual model. As a purpose of the trans-contextual model is to foster autonomous motivation in physical education in order to increase overall physical activity, and as a recent meta-analysis has underlined the positive medium-sized impact of state mindfulness on autonomous motivation (Donald et al., 2020), a further aim of the present thesis was to implement mindfulness into the trans-contextual model. It is discussed that mindfulness may play a crucial role in the development of autonomous motivation, which may help to explain the link between mindfulness and the reduction of stress, negative affect, as well as the simultaneous promotion of well-being (Schneider et al., 2018), and the execution of a behavior. As an overarching aim of the present thesis is to discover important concepts, which are in the long term increasing overall physical activity rates of children and adolescents, the trans-contextual model, which unifies important concepts of the self-determination theory (SDT, Deci & Ryan, 1985) and the theory of planned behavior, is analyzed and extended by the concept of mindfulness in the third manuscript. More specifically, the support of autonomy, relatedness, competence, as well as the possibly beneficial impact of mindfulness, when being included into the trans-contextual model, was analyzed via path model analyses. Overall, promising results could be found for the psychometric properties of the motivational regulation questionnaires. Furthermore, partial scalar measurement invariance between the German and French version can be seen as confirmed. Thus, both translated questionnaire versions provide useful tools for further inter-cultural research in the exercise domain. Furthermore, the proposed directions of the trans-contextual model could be confirmed within a longitudinal format. We found that all three basic needs were distinctly important to be supported in physical education, as they were all found to be related to autonomous motivation. Autonomous motivation, in turn, was found to be bi-directionally related between both contexts, the school and out-of-school context, meaning that the promotion of autonomous motivation in either context might be beneficial. Finally, identified regulation was found to be directly related toward intention and intrinsic motivation to physical activity over time. Autonomous motivation was furthermore found to be related to subjective norm, perceived behavioral control, and attitude. With regard to the third manuscript, it was found that the path models including mindfulness into the trans-contextual model provided better model fit indices, compared to models without mindfulness. In addition, mindfulness was found to be positively predicted by the support of autonomy in class, while mindfulness statistically significantly predicted autonomous motivation in both contexts, namely for physical education and leisure-time physical activity. Furthermore, mindfulness was positively related to attitude, subjective norm, and perceived behavioral control. Overall, the presented results reveal that the trans-contextual model provides a strong conceptual framework, which helps to better understand the transfer of autonomous motivation beyond the school-context. Furthermore, it is discussed that, in order to promote autonomous motivation in students, further educational intervention programs should ideally rely on the four concepts of autonomy, relatedness, competence, and mindfulness support, which may, in turn, help to alleviate and redeem the diminishing physical activity rates across the globe. [less ▲]

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See detailPositive and Negative Emotions in Language Learning: Measurement, Interactions, and Nomological Network
Botes, E'louise UL

Doctoral thesis (2021)

This thesis investigates two emotion variables in the foreign language (FL) classroom, namely the negative emotion of Foreign Language Classroom Anxiety (FLCA) and the positive emotion of Foreign Language ... [more ▼]

This thesis investigates two emotion variables in the foreign language (FL) classroom, namely the negative emotion of Foreign Language Classroom Anxiety (FLCA) and the positive emotion of Foreign Language Enjoyment (FLE). FLCA is the unique situation-specific anxiety experienced by FL learners when confronted with the challenges of FL learning. FLE, in turn, is a broad positive emotion experienced when psychological needs are met during the course of FL learning. The dissertation examines three main themes regarding FLCA and FLE, namely (1) the psychometric measurement of the two emotion variables, (2) the relationship an interactions between FLCA and FLE, and (3) the broader nomological network of individual differences in FL learning. In Chapter 1, an overview of the development, definition, design, and measurement of FLCA and FLE is given. In addition, the current state of the literature regarding the relationship between FLCA and FLE and the broader nomological network is provided. This is followed by the five manuscripts that form the main body of the dissertation in Chapters 2 to 6. Papers 1 and 4 have already been published in peer-reviewed journals, whereas papers 2, 3, and 5 are currently under peer-review. The first empirical paper in this dissertation introduces the construct of FLCA by providing an extensive overview of the literature as well as a meta-analysis of FLCA and academic achievement. The paper addresses the research aim of examining the broader nomological network of the emotion variables and confirms the negative association between FLCA and academic achievement. The second paper follows with a second meta-analysis, this time with FLE at center stage. An overview of the literature regarding FLE is provided along with four individual meta-analyses of FLE and academic achievement, self-perceived achievement, willingness to communicate, and FLCA. The meta-analyses confirmed the positive association between FLE and academic achievement, self-perceived achievement and willingness to communicate. Furthermore, the negative association between FLCA and FLE found across the literature is confirmed. The paper contributes to the broader aim of examining the nomological network of the emotion variables. The third contribution investigated the measurement of FLE. The positive emotions variable was introduction to the research lexicon with an accompanying 21-item scale. The third paper attempted to develop a short-form of the 21-item scale and in the process uncover the factor structure underlying FLE. As a result, the third manuscript developed and validated a nine-item, three-factor hierarchical measure of FLE, which can be used with confidence in future studies. The third paper contributes to the overall aim of examining the measurement of the emotion variables. The fourth paper examined the broader nomological network of the two emotion variables by investigating the effect of multilingualism and self-perceived proficiency on FLCA and FLE. Previous research findings have theorized that a possible interaction effect may occur between the level of multilingualism and proficiency on emotions in the FL class. The study confirms an interaction effect of multilingualism and self-perceived proficiency on FLCA, but not FLE. The fourth manuscript contributes to the overall aim of examining the broader nomological network of FLCA and FLE. The fifth and final paper in the dissertation examined the complex interactions between FLCA and FLE on the perceived proficiency of an FL learner. Through the use of polynomial regression and response surface modelling, a three-dimensional model was rendered which visually depicted the complex non-linear interactions between FLCA and FLE. Furthermore, the relative ‘strengths’ of FLCA and FLE in the interaction effect could be examined with the negative impact of FLCA seeming to outweigh the positive impact of FLE in certain instances. Chapter 7 provides a general discussion of all papers included in the main body of the dissertation, as well as practical implications and limitations to the research. Lastly, chapter 8 provides additional manuscripts written during the course of my doctoral studies but which does not attempt to address the three main aims of the dissertation. [less ▲]

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See detailCharacterization of novel covalent and non-covalent drugs against K-Ras surrogate targets
Okutachi, Sunday Ojochegbe UL

Doctoral thesis (2021)

Mutations in the KRAS gene are associated with approximately 15% of all human cancers. This makes it one of the most frequently mutated oncogenes known. Whilst recent breakthroughs in Ras drug discovery ... [more ▼]

Mutations in the KRAS gene are associated with approximately 15% of all human cancers. This makes it one of the most frequently mutated oncogenes known. Whilst recent breakthroughs in Ras drug discovery have led to the FDA approval of the first direct and covalent inhibitor of the KRAS-G12C mutant, the majority of KRAS driven cancers are not G12C mutated. Furthermore, recent studies have identified resistance mechanisms against the new inhibitors. Consequently, research into other direct and indirect Ras inhibition strategies, as well as synergistic drug combination efforts are being vigorously pursued. In the first part of this thesis, I describe my contributions to the development and characterization of novel PDE6D inhibitors with activity against KRAS driven cancers. PDE6D is a trafficking chaperone of K-Ras that facilitates its dynamic localization to the plasma membrane. Although some progress had been made in identifying lead drug candidates against this protein, an Arl2 dependent PDE6D cargo ejection mechanism continues to hamper progress. We describe the development of Deltaflexin 1 and Deltaflexin 2, into which we engineered a ‘molecular spring’ to improve resilience to Arl2 ejection of PDE6D cargo. We show that these compounds selectively inhibit K-Ras membrane organization and exhibited K-Ras selective anti-proliferative effects against cancer cell lines from colon and breast tissues whilst blocking the 3D spheroid growth of lung and breast cancer cell lines. In the second part, I describe my main project, the identification of a novel covalent inhibitor of calmodulin (CaM) with anti-cancer activity in K-Ras mutated cancers named Calmirasone1. A relevance of the K-Ras/ CaM interaction for the promotion of cancer cell stemness has been previously suggested. We previously showed that the natural product Ophiobolin A (OphA) blocked K-Ras membrane organization in a CaM dependent manner and cancer cell spheroid formation. However, because of the broad toxicity of OphA, its suitability as a tool compound to further study this K-Ras/CaM associated stemness properties is limited. We have therefore characterized a set of benzazulenones with distant chemical similarity to OphA in a battery of assays. We identified Calmirasone1 which exhibits improved CaM affinity and a significantly lower unspecific toxicity relative to OphA. Furthermore, Calmirasone1 selectively blocked K-Ras membrane organization and inhibited the 3D spheroid growth of K-Ras dependent cancer cell lines. In the third part of this thesis, I assessed the synergistic potential of targeting CaM and protein phosphatase 2A (PP2A) in Ras-MAPK dependent cancer cell lines. PP2A is a tumor suppressor that catalyze the dephosphorylation of multiple targets in the cell. Using specific CaM inhibitors and PP2A agonists as well as the already clinically approved phenothiazines (PTZs), our results from this study suggests that synergistic targeting of CaM and PP2A improves anti-cancer effects and that PTZs combine CaM inhibitory and PP2A re-activating properties in their cancer killing activity. [less ▲]

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See detailThe Intra-Party Effects of Open List Design
Schmit, Dan UL

Doctoral thesis (2021)

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See detailChemical Vapor-Phase Deposition of Nanostructured Silver Layers
Wack, Sabrina Myriam UL

Doctoral thesis (2021)

Among the noble metals, silver (Ag) presents the lowest electrical resistivity at low thickness, the highest reflectance from visible to infrared spectra and the lowest thermal conductivity. Consequently ... [more ▼]

Among the noble metals, silver (Ag) presents the lowest electrical resistivity at low thickness, the highest reflectance from visible to infrared spectra and the lowest thermal conductivity. Consequently, it is used in a large range of applications, either as nanoparticle (NP) films, e.g. in devices based on localized surface plasmon resonance, or as continuous thin films for highly reflective optical mirrors or as infrared reflecting coatings. Although copper (Cu) is widely used in the field of microelectronics, Ag is a good candidate as a potential replacement of Cu for interconnects in integrated circuits (ICs) thanks to its lower residual stress and the absence of considerable increase of resistivity when downscaling. Among the non-line-of-sight vacuum deposition method, atomic layer deposition (ALD) is known for its ability to produce an accurate and precise thickness control giving uniform and conformal film growth thanks to the sequential and self-limiting surface reactions of precursors. However, the ALD of silver is still weakly understood, and the uniform deposition over large scale is often not demonstrated. It is also very challenging to obtain an ultra-thin continuous Ag films due to the growth mechanism leading to islands films rather than continuous layer. One part of this thesis work is dedicated to take advantage of the nanoparticle morphology and overcome the challenge of the good control of the morphology of Ag nanostructures on large-scale surfaces by an understanding of the growth mechanism. The uniformity of the deposition of silver NPs by plasma-enhanced ALD (PE-ALD) is quantified in terms of film morphology as well as chemical composition and crystalline structure over an 8-inch surface area. After a careful investigation of the PE-ALD parameters and their impact on the Ag deposition, we prove the self-saturated regime required for obtaining good control of the deposition and large-scale uniformity. An empirical model which explains the silver NPs growth mechanism correlated with the experimental results obtained is also proposed. This fine control of the Ag NP morphology opens the way for interesting applications requiring precise NP dimensions. The thesis also reports a new approach relying on an original two-step plasma-enhanced chemical vapor-phase deposition as an alternative process regime which might be more promising for obtaining the challenging continuous and highly conductive ultra-thin films deposition. After reviewing the influence of the deposition conditions, we prove that the first step provides a uniform new morphology made of compact Ag NPs that is usually not achieved at low thickness with CVD or ALD. Based on the experimental results obtained, a proposed model for the growth mechanism of this peculiar Ag morphology is discussed and suggests that the chemical reaction occurs not only on the surface but also in the gas phase. After the second step of plasma post-treatment of silver made of compact nanoparticles, the sintering of the Ag NPs enhances the electrical conductivity of silver films by increasing the connectivity between particles due to the presence of higher density of energetic radicals. This is highlighted by a rigorous investigation of the influence of the post-processing conditions on the film morphology and its electrical properties. Therefore, we manage to reach the electrical performances of silver films obtained by physical approaches, i.e. by achieving a critical thickness as low as 15 nm and an electrical conductivity of 3.9×10^5 S/cm for a 40-nm thick Ag film. The described method can also be extended to other noble metals, in particular copper and gold, for which the deposition using chemical vapor-based methods is a very active field. The two different processes developed in this work, i.e. standard PE-ALD and the novel two-step approach, are compared on complex substrates. The later path demonstrates a high film conformality on complex lateral high aspect ratio structures (LHAR with AR of 100), with better coverage than the one reported up to now for ALD of Ag. Moreover, the quasi-substrate-independency of silver films chemical-vapor phase deposited using both approaches confirms the weak influence of the underlayers known in the literature for Ag. On the other hand, we show that the study of the optical behavior of Ag films gives information about their morphology. Indeed, the presence of an absorbance visible peak is a signature of metallic NP morphology causing localized surface plasmon resonance. By following the film reflectivity spectrum of Ag NP films, a ‘continuous-like’ behavior understood by the Drude model is found at low wavelengths whereas higher wavelengths highlight a ‘particle-like’ behavior sticking to the oscillator model. This evolution of the optical properties is very similar for separated NPs using standard PE-ALD and film made of compact NPs obtained by the novel approach, except a stronger and broader absorbance peak typical for a film of aggregated NPs in the last case. On these compact NPs, a plasma post-processing gives strong increase of the infrared reflectance up to 97% and a strong decrease of near infrared transmittance as low as 3% for a 40-nm-thick film. Due to the wide ranges of applications of thin metal films, and the challenge to provide methods for conformal deposition, this work is interesting for the whole community of material scientists and could inspire many investigations. [less ▲]

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See detailA Republic of Alienists? A transnational perspective on psychiatric knowledge circulation across Europe (1843-1925)
Andersen, Eva UL

Doctoral thesis (2021)

The history of psychiatry has over the past decades been largely dominated by the production and re-production of national narratives in which different aspects of psychiatry are often associated with a ... [more ▼]

The history of psychiatry has over the past decades been largely dominated by the production and re-production of national narratives in which different aspects of psychiatry are often associated with a particular country or region. While this has left little room to consider the value of psychiatry’s less prominent developments, this persistent national tendency has also minimised the role and (in)direct contributions of foreign alienists on national and transnational developments across Europe. Numerous alienists in the nineteenth and early twentieth century strived towards the common goal of better patient care and treatment, and frequently communicated with each other in a variety of ways about these principals and the obstacles they faced. This begs the question if these shared ideals created an imagined or tangible Republic of Alienists, analogue to that of the Republic of Letters. This idea stands in contrast to nationally contained histories and creates the need for new representations of psychiatric knowledge development and its circulation. Transnational narratives can help to decentralise and open-up European historiography, and explore new avenues of the history of psychiatry. Via several case studies and by using concepts, theories and practices from the field of transnational history, the history of knowledge and digital history, I demonstrate the variety of ways through which knowledge was transported and able to circulate across Europe. Secondly, I illustrate that knowledge was built through peoples’ personal and professional networks and reputation, which were shaped by their involvement in various activities in the psychiatric community and through the rhetoric they used to communicate. Thirdly, I explain and highlight the many grey areas that existed in connection to the, not so straightforward, dissemination of psychiatric knowledge. Lastly, I demonstrate that forgotten or failed psychiatric knowledge forms as much a part of history as those facts, events and processes that have been identified as the most essential narratives. Combined, these outcomes demonstrate that there was not just one Republic of Alienists but that several existed in a variety of sizes and different degrees of authority. [less ▲]

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See detailLegal knowledge extraction in the data protection domain based on ontology design patterns
Leone, Valentina UL

Doctoral thesis (2021)

In the European Union, the entry into force of the General Data Protection Regulation (GDPR) has brought the domain of data protection to the fore-front, encouraging the research in knowledge ... [more ▼]

In the European Union, the entry into force of the General Data Protection Regulation (GDPR) has brought the domain of data protection to the fore-front, encouraging the research in knowledge representation and natural language processing (NLP). On the one hand, several ontologies adopted Semantic Web standards to provide a formal representation of the data protection framework set by the GDPR. On the other hand, different NLP techniques have been utilised to implement services addressed to individuals, for helping them in understanding privacy policies, which are notoriously difficult to read. Few efforts have been devoted to the mapping of the information extracted from privacy policies to the conceptual representations provided by the existing ontologies modelling the data protection framework. In the first part of the thesis, I propose and put in the context of the Semantic Web a comparative analysis of existing ontologies that have been developed to model different legal fields. In the second part of the thesis, I focus on the data protection domain and I present a methodology that aims to fill the gap between the multitude of ontologies released to model the data protection framework and the disparate approaches proposed to automatically process the text of privacy policies. The methodology relies on the notion of Ontology Design Pattern (ODP), i.e. a modelling solution to solve a recurrent ontology design problem. Implementing a pipeline that exploits existing vocabularies and different NLP techniques, I show how the information disclosed in privacy policies could be extracted and modelled through some existing ODPs. The benefit of such an approach is the provision of a methodology for processing privacy policies texts that overlooks the different ontological models. Instead, it uses ODPs as a semantic middle-layer of processing that different ontological models could refine and extend according to their own ontological commitments. [less ▲]

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See detailLiquid Crystal Shells: from Physics Mysteries, via Chemistry Challenges, to Biosensing Opportunities
Sharma, Anjali UL

Doctoral thesis (2021)

Liquid crystals (LCs) confined in a spherical geometry between two aqueous phases, i.e., a shell, exhibit unavoidable topological defects, real or virtual. In fact, the presence of defects, and their ... [more ▼]

Liquid crystals (LCs) confined in a spherical geometry between two aqueous phases, i.e., a shell, exhibit unavoidable topological defects, real or virtual. In fact, the presence of defects, and their configuration, on the shell are dictated by the LC alignment at the LC-water boundaries. With tangential alignment of the LC, we have a total of +2 defect strength on each interface, which can be distributed either over four +1/2 defects or a combination of +1 and +1/2 defects. In contrast, when the LC is radially aligned, the shell is defect free (but one can extrapolate the director field into a virtual point defect in the internal isotropic phase). The LC alignment can be tuned by adding a suitable solute in the aqueous phase.The vast majority of studies have used sodium dodecyl sulfate (SDS) for this purpose, with only a few studies employing other surfactants. We investigate various other surfactants with a positive and negative head group charge by varying alkyl chain length. Here, we focus on the minimum surfactant concentration required (below the critical micelle concentration (CMC)) for the stability of the shells as well as for ensuring the radial alignment. It turns out that surfactants at a low concentration do not necessarily impose radial alignment. However, they provide stability by decreasing the interfacial tension. Once the surfactant concentration is above the CMC, surfactant forms micelles in water. When these micelles are in the outer aqueous phase of the hybrid aligned shells, the LC alignment changes from hybrid to radial on cooling below the Krafft temperature (TK), below which the surfactant solubility is lower than CMC. Interestingly, on heating above TK, the LC alignment changes back to hybrid. It turns out that the adsorption and desorption of micelles as a result of changed solubility in water with temperature give rise to the change in the LC alignment. Next, we replace surfactant with lipids. We add lipids in the form of vesicles in the aqueous phase of pre-tangentially aligned LC shells. After some time these shells develop small spindle-shaped islands, and these islands merge and grow with time, and they even interact in intriguing ways across the LC, from the inside to the outside. After exploring various solutes in the aqueous phase, we change our LC phase from nematic to smectic A and C phases. In the smectic A phase, lunes on the shell occur due to the change in the shell cross section area from the inner to the outer interface. In this context, we present the first study on tangentially and hybrid aligned smectic C shells. The most studied LC mesogens in the shell geometry contain cyano and biphenyl groups. To test whether this is important, I also made shells with cyclohexane core mesogens. In contrast to the cyanobiphenyl-based LCs, this LC aligns radially regardless of solutes added into the aqueous phases. We investigate in detail and find that a cyano group at the terminal supports shell stability and while the aromatic rings in most LCs, for instance having a biphenyl core, give rise to the tangential alignment when in contact with surfactant-free water. [less ▲]

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See detailEnhancing Smart Grid Resilience and Reliability by Using and Combining Simulation and Optimization Methods
Antoniadis, Nikolaos UL

Doctoral thesis (2021)

Modern electrical grids include numerous digital technologies for producing, transmitting, distributing, and supplying electricity. The electrical grids that achieve the most reliable, efficient, and less ... [more ▼]

Modern electrical grids include numerous digital technologies for producing, transmitting, distributing, and supplying electricity. The electrical grids that achieve the most reliable, efficient, and less environmental impact operation using the above technologies combined with renewable energy sources are characterized as smart grids. The study of electricity networks aims at the continuous and uninterrupted production, transmission, and distribution of electricity under the safest operating conditions. Therefore, an electrical grid is designed and studied in a multifaceted way to highlight the weaknesses and reduce possible disturbances. One of the most critical disturbances that can occur in energy grids is overload. Overloads on an electrical system are dangerous, as they can cause overheating or an electric arc. Cables in an electrical grid have a maximum ampacity, i.e., current capacity, that can safely flow. If an excessive number of devices, such as electric vehicles, are connected to a circuit, the electrical current will overheat the cables. If the cable insulation melts, an electric arc can be generated and cause a fire in the overheating area, even inside a wall. In order to avoid overloads, fuses are installed in the circuits. If the current exceeds a specific value, the fuse is activated, drops, and opens the circuit, thus interrupting electricity flow. However, even if they are below the safety limits, sustained overloads could also damage the wires. Smart grid operators could change the state of each grid's fuse or could remotely curtail the over-producing/over-consuming users so that, with the minimum interruption, any potential overload could be prevented. Nevertheless, making the most appropriate decisions is a complicated decision-making task, mainly due to contractual and technical obligations. The present dissertation studies the overloading prevention problem in terms of smart grids' reliability and resilience and evaluates real-world topology in a Luxembourg city district. To this end, it suggests solution methods that can suggest optimal countermeasures to operators facing potential overloading incidents. Specifically, the dissertation has three main axes: The first axis regards the deterministic overloading prevention problem. Given the topology and the energy data of a microgrid at the current time, the potential overloading incidents are detected, and the optimal countermeasures are calculated for the next measurement interval. The grid operators can apply the proposed actions to recover the grid from the disturbance. Into the thesis, the problem is defined and formulated as a Multiobjective Mixed Integer Quadratically Constrained Program. The dissertation also suggests a solution method using a combinatorial optimization approach with a state-of-the-art exact solver. The second axis focuses on reliability analysis through simulation after a potential overloading incident. Smart grid operators would be of great use to ensure stability after a potential overload for a planning horizon, as the future electrical values are unknown. To evaluate the robustness of the topology reconfiguration after a disturbance, like an overload, reliability analysis through simulation is employed. The third axis proposes the single-stage stochastic overloading prevention problem. It differs from the deterministic problem as the optimal countermeasures are calculated for a measurement horizon, e.g., 24 h. The dissertation defines the corresponding single-stage stochastic program and proposes a simheuristic method to solve it. Overall, this thesis presents a fully-edge study on reliability optimization for smart grids to provide the appropriate countermeasures after a potential overloading disturbance. The present approach has been developed in collaboration with an industrial partner and evaluated on real-world topology. [less ▲]

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See detailLes enjeux des scissions transfrontalières au sein de l'Union européenne
Bernard, François Michel Béatrice UL

Doctoral thesis (2021)

Cross-border divisions represent an efficient restructuring method allowing competent economic actors to suppress potential negative synergies within a conglomerate or to reinforce a company’s share price ... [more ▼]

Cross-border divisions represent an efficient restructuring method allowing competent economic actors to suppress potential negative synergies within a conglomerate or to reinforce a company’s share price by correcting an asymmetry of information. Despite their protection by freedom of establishment and their partial harmonisation by the recent EU Directive 2019/2121, they remain largely unexplored and their effective implementation remains obscure. Furthermore, this kind of operation generates significant challenges in terms of stakeholder protection that need to be addressed in an adequate manner to avoid any leeway for abusive behaviors. The present research will propose a sophisticated solution to these challenges through a detailed analysis of the caselaw of the European Court of justice on freedom establishment and an extensive comparative exercise with (i) the existing EU regime applicable to cross-border divisions by incorporation and cross-border mergers, (ii) the cross-border division regimes existing under Belgian and Luxembourg company law and (iii) the German, Austrian and French domestic division regimes. [less ▲]

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See detailLes Règles du savoir-vivre dans le théâtre de Jean-Luc Lagarce : Une lecture ethnocritique et stylistique des œuvres dernières
Rodriguez Ép. Devaux, Alicia UL

Doctoral thesis (2021)

The purpose of this thesis is to propose an ethnocritical reading of the dramatic works of Jean-Luc Lagarce. It involves rereading the works of a writer consecrated by the Comédie Française and the ... [more ▼]

The purpose of this thesis is to propose an ethnocritical reading of the dramatic works of Jean-Luc Lagarce. It involves rereading the works of a writer consecrated by the Comédie Française and the Institution in an ethnocritical perspective which combines a poetics of literary texts with an ethnology of the symbolic in order to study the specific cosmologies present in the works. In order to do this, we propose to use a rhetorical and stylistic approach in order to illustrate the scriptural singularity demonstrated by the generic hybridity which is characteristic of his works and by forms of speech that are both highly “oralized” and very literary, in other words very “auralized”. We will pay particular attention to his last works: Juste la fin du monde, Les Règles du savoir-vivre dans la société moderne, J’étais dans ma maison et j’attendais que la pluie vienne et Le Pays lointain because of their emblematic and testamentary value. The first part of the thesis focuses on the rules, rituals and customs that are present in the works. The second part examines a third group of characters defined by Lagarce, as in addition to the living and the dead there are those who know they are going to die. These already-dead characters found in his works are liminary characters characterized by punctuation and typography that signifies a liminal space between two worlds: quotation marks, parentheses, dashes and italics invite us to explore the margins of the heterotopic theatre of Lagarce. The third part looks at the rules of creation in his final works that illustrate the processes of re-writing and hybridization between theatre, prose fiction and poetry. Our hypothesis is that as death drew closer, Lagarce saw each work as his last and each thus represents a rite of passage meant to insure that Lagarce will enjoy the recognition that he had not obtained while alive; each work is meant to guarantee his literary posterity through an “oeuvre-legenda” meant for his readers and that ended up by encountering spectators. [less ▲]

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See detailEncadrement des cryptomonnaies en droit pénal européen: réflexions sur la mise en réseau du droit
Jolly, Loren UL

Doctoral thesis (2021)

The project is to conduct an interdisciplinary research which follows a theoretical approach motivated by systems theory. This theory observes a dynamic within society which has consequences on ... [more ▼]

The project is to conduct an interdisciplinary research which follows a theoretical approach motivated by systems theory. This theory observes a dynamic within society which has consequences on sovereignty and which ends up in the development of fragmented legal frameworks. This change is observed through the example of the ecosystem of cryptocurrency developing its own functional rules and the reaction of the criminal justice system (especially through the anti-money laundering legal framework) which is used as means of social control upon the ecosystem. This has consequences not only on the legitimacy and on fundamental principles of criminal law but also on fundamental rights. The goal is to develop an autonomous legal order that would enable to address these issues. [less ▲]

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See detailEFFICIENT AND SCALABLE OPTIMIZATION ALGORITHMS FOR MULTIANTENNA SIGNAL PROCESSING
Arora, Aakash UL

Doctoral thesis (2021)

Multiantenna signal processing (MASP) is indispensable in many applications like wireless communications, radar, seismology, etc. Large-scale antenna arrays (LSAAs) are envisioned for future wireless ... [more ▼]

Multiantenna signal processing (MASP) is indispensable in many applications like wireless communications, radar, seismology, etc. Large-scale antenna arrays (LSAAs) are envisioned for future wireless communication systems to improve the range, power, and spectral efficiency (SE) of existing systems. Thus, for a practical multiantenna wireless communication system, efficient and scalable signal processing (SP) algorithms are essential to optimize system operations. In this thesis, we address several facets of such system optimization including beampattern matching, SE maximization among others. These are formulated as nonconvex optimization problems and the thesis proposes novel, efficient, and scalable optimization algorithms with theoretical convergence guarantees. We first consider the problem of transmit analog beamforming (or phase-only beamforming) design by solving a beampattern matching problem. We formulate variants of the unit-modulus/constant-modulus least-squares problem. To attempt at solving these NP-hard problems, we propose efficient and scalable algorithms based on different optimization frameworks including alternating minimization, majorization-minimization (MM), and cyclic coordinate descent (CCD). The proposed algorithms are theoretically shown to converge to a Karush–Kuhn–Tucker (KKT) point of the corresponding optimization problem while offering superior performance. We also provide a use case in satellite communications where a desired two-dimensional beampattern is approximated using a planar array by designing the analog beamforming system. Building on the previous problem, we consider a joint array design and beampattern matching perspective and formulate variants of sparse unit-modulus or sparse constant-modulus least-squares. The optimization problems are solved using combinations of different optimization frameworks such as variable projection/elimination, MM, and block/alternating MM. Next, we consider the problem of hybrid transceiver design for a single user point-to-point multiple-input multiple-output (MIMO) system employing LSAAs. We solve this problem based on the variable projection/elimination and MM frameworks. The proposed algorithms are shown to converge to a stationary point. We also study the applications of the proposed algorithms for hybrid precoding design for satellite communications. We then generalize convergence proofs from the earlier sections by providing a unified convergence proof for solving a generic block-structured optimization problem over nonconvex constraints. Finally, we consider the problem of localizing sources in the far-field of a spatio-temporal array formed by a single moving sensor along a known trajectory. We provide a novel signal model capturing the incoherency in the measurements sampled by the moving sensor. We establish different Cramér-Rao bounds for the considered system model by exploiting varying degrees of information, propose and study various direction of arrival (DOA) estimators. The thesis concludes by summarizing the main contributions and some open research problems. [less ▲]

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See detailTrans Narrative: Deutschsprachige Autobiografien von trans Personen
Artuso, Sandy Kathy UL

Doctoral thesis (2021)

Im Zentrum dieser Doktorarbeit steht ein Korpus von 67 Autobiografien, die zwischen 1984 und 2016 im deutschsprachigen Raum veröffentlicht wurden. Diese Arbeit verbindet Literaturwissenschaft und Trans ... [more ▼]

Im Zentrum dieser Doktorarbeit steht ein Korpus von 67 Autobiografien, die zwischen 1984 und 2016 im deutschsprachigen Raum veröffentlicht wurden. Diese Arbeit verbindet Literaturwissenschaft und Trans/Gender Studies, sie benutzt narratologische und queer-theoretische Werkzeuge, und setzt die Texte von trans Personen in den Mittelpunkt. Während immer die grundlegend narratologische Frage im Zentrum stand, wer denn spricht, wurde diese vermeintlich harmlos anmutende Frage jedoch immer mit einem kritischen Blick auf die Machtpositionen und Normativitätssysteme versehen, die intern und extern auf die Autobiografien wirken. So war es auch ein Ziel dieser Arbeit, die Bedeutung und Wertstellung von Autobiografien für trans Personen und ihre Communities zu erforschen, und gleichzeitig einen Einblick in die einzelnen Lebensgeschichten zu geben. [less ▲]

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See detailIdentifying and targeting metabolic vulnerabilities of IDH mutant gliomas
Cano Galiano, Andrés UL

Doctoral thesis (2021)

Diffuse gliomas are a group of central nervous system (CNS) tumors with a poor patient prognosis. Within these diffuse gliomas, isocitrate dehydrogenase (IDH) mutation defines the different tumor subtypes ... [more ▼]

Diffuse gliomas are a group of central nervous system (CNS) tumors with a poor patient prognosis. Within these diffuse gliomas, isocitrate dehydrogenase (IDH) mutation defines the different tumor subtypes and is considered to be an initiating event in gliomagenesis. IDH is a metabolic enzyme that in normal conditions mediates the conversion of isocitrate into α-ketoglutarate (α-KG), producing the reducing equivalent NADPH. IDH mutation (IDHm) leads to a neomorphic reaction where α-KG is consumed to generate the oncometabolite D-2-hydroxyglutarate (D-2HG), using NADPH as reducing agent. It has been reported that IDHm-dependent D-2HG synthesis has a direct impact on DNA and histone methylation, however the metabolic repercussions are not yet well defined. Due to the consumption of NADPH by IDHm reaction, some groups including us have hypothesized that IDHm cells may bear an imbalance of reducing equivalents, that may trigger a defective antioxidant defense. In the present study we made use of patient-derived cell lines and xenografts thereof as well as clinical samples in order to study the metabolic vulnerabilities of IDHm gliomas. In the first part of the thesis experimental data, we generated an integrative liquid chromatography-mass spectrometry (LCMS)-based proteomic-metabolomic characterization of IDHm metabolism. We made use of patients, cell lines and xenografts to address the direct effect of the mutation. We observed that IDHm gliomas have altered regulation of key processes in central carbon metabolism through glucose and glutamate processing as well as glutathione (GSH) metabolism and fatty acid production. In the second part of experimental data, we investigated the redox vulnerabilities of IDHm gliomas. Here we discovered that IDHm astrocytomas specifically upregulate cystathionine-γ-lyase (CSE) enabling them to synthesize GSH independently of NADPH. CSE is the only known enzyme capable of synthesizing cysteine. We found that genetic and chemical inhibition of CSE led to a decrease in cell viability upon cysteine restriction. Finally inhibition of CSE in vivo led to a delay in tumor growth rate. In conclusion, in the present PhD dissertation we expose a comprehensive study of the metabolic behavior of IDHm human gliomas, and we propose a novel therapeutic strategy that might improve patient prognosis, by inflicting oxidative damage to the tumor. [less ▲]

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See detailSpecification and Model-driven Trace Checking of Complex Temporal Properties
Boufaied, Chaima UL

Doctoral thesis (2021)

Offline trace checking is a procedure used to evaluate requirement properties over a trace of recorded events. System properties verified in the context of trace checking can be specified using different ... [more ▼]

Offline trace checking is a procedure used to evaluate requirement properties over a trace of recorded events. System properties verified in the context of trace checking can be specified using different specification languages and formalisms; in this thesis, we consider two classes of complex temporal properties: 1) properties defined using aggregation operators; 2) signal-based temporal properties from the Cyber Physical System (CPS) domain. The overall goal of this dissertation is to develop methods and tools for the specification and trace checking of the aforementioned classes of temporal properties, focusing on the development of scalable trace checking procedures for such properties. The main contributions of this thesis are: i) the TEMPSY-CHECK-AG model-driven approach for trace checking of temporal properties with aggregation operators, defined in the TemPsy-AG language; ii) a taxonomy covering the most common types of Signal-based Temporal Properties (SBTPs) in the CPS domain; iii) SB-TemPsy, a trace-checking approach for SBTPs that strikes a good balance in industrial contexts in terms of efficiency of the trace checking procedure and coverage of the most important types of properties in CPS domains. SB-TemPsy includes: 1) SB-TemPsy-DSL, a DSL that allows the specification of the types of SBTPs identified in the aforementioned taxonomy, and 2) an efficient trace-checking procedure, implemented in a prototype tool called SB-TemPsy-Check; iv) TD-SB-TemPsy-Report, a model-driven trace diagnostics approach for SBTPs expressed in SB-TemPsy-DSL. TD-SB-TemPsy-Report relies on a set of diagnostics patterns, i.e., undesired signal behaviors that might lead to property violations. To provide relevant and detailed information about the cause of a property violation, TD-SB-TemPsy-Report determines the diagnostics information specific to each type of diagnostics pattern. Our technological contributions rely on model-driven approaches for trace checking and trace diagnostics. Such approaches consist in reducing the problem of checking (respectively, determining the diagnostics information of) a property over an execution trace to the problem of evaluating an OCL (Object Constraint Language) constraint (semantically equivalent to ) on an instance (equivalent to ) of a meta-model of the trace. The results — in terms of efficiency of our model-driven tools—presented in this thesis are in line with those presented in previous work, and confirm that model-driven technologies can lead to the development of tools that exhibit good performance from a practical standpoint, also when applied in industrial contexts. [less ▲]

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See detailHigher education trajectories and social origin in Germany and the United States: A comparative sequence-analytical approach
Haas, Christina UL

Doctoral thesis (2021)

Students’ higher education trajectories as holistic educational processes are an underresearched aspect, particularly in the German context. This cumulative thesis fills this gap by investigating ... [more ▼]

Students’ higher education trajectories as holistic educational processes are an underresearched aspect, particularly in the German context. This cumulative thesis fills this gap by investigating students’ trajectories through bachelor’s degree courses in German and US higher education. In terms of methodology, it is based on a sequence-analytical approach using two student panel data sets (the German National Educational Panel Study (NEPS) and the US Beginning Postsecondary Students Longitudinal Study (BPS)) and comprises a literature review and three empirical research articles, each providing a different theoretical and conceptual angle. Higher education is a non-compulsory educational phase, implying students are granted more autonomy and more choice but also require more personal responsibility to plan a path through higher education. As such, it is assumed that parents’ cultural resources – defined here as higher education-specific knowledge – and economic resources shape students’ trajectories to enable them to proceed through their studies in a more continuous or linear way and prevent students from experiencing complex trajectories, such as delays, interruptions or detours. To begin with, the literature review, constructed as a narrative review with systematic elements, captured the state of research on higher education trajectories by reviewing peer-reviewed journal articles from a wide range of mainly higher education research journals. It revealed that this research area is rather heterogeneous and dominated by studies focusing on the United States. Research articles one and two employ similar research strategies – sequence analyses followed by cluster analyses. Stressing the relationship between parents’ resources and students’ trajectories, the first article concentrates exclusively on students in German research universities, whereas the second also considers students at universities of applied sciences. Overall, these studies reveal that the trajectories of students at the universities of applied sciences are more often linear, while the opposite applies to students at research universities and students of low social origin, pointing towards the hypothesised effect of parental resources. Furthermore, students of low social origin are more likely to follow a linear standard trajectory when studying at a university of applied sciences compared to at a research university. In the third paper, based on the premise that trajectories are systematically shaped by the institutional context of the higher education system, students’ trajectories in German and US higher education are compared, allowing to simultaneously a view on system-level characteristics and national idiosyncrasies. US higher education provides almost universal access, is very marketised and highly differentiated, thereby accommodating diverse demands and heterogeneous student groups. By contrast, German higher education, based on public funding and regulation, early ability tracking and low permeability, restricts access and provides an overall much less diversified study offering. Consequently, research article three revealed that students’ trajectories are overall less standardised in US higher education – but this differs greatly by higher education sector, whereas the trajectories of students in the (selective) research universities are overall more standardized. Furthermore, the social origin differences were quite pronounced in the United States, whereas the social origin effect was almost nonexistent for students in German higher education in this study (based on a different sequence-analytical approach). Remarkable, though, remains the finding that students’ trajectories are less linear at German research universities compared to the universities of applied sciences – even more so among students of low social origin – while US research universities facilitate linear trajectories. Overall, this dissertation provides an important contribution to the state of research on link between social origin, students’ trajectories and how this link is mediated by the institutional context of the respective higher education system. [less ▲]

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See detailDRY-STACKED INSULATION MASONRY BLOCKS BASED ON MISCANTHUS CONCRETE
Pereira Dias, Patrick UL

Doctoral thesis (2021)

The present dissertation entitled “Dry-stacked insulation masonry blocks based on Miscanthus concrete” is carried out at the University of Luxembourg and financed by CONTERN Lëtzebuerger Beton. The ... [more ▼]

The present dissertation entitled “Dry-stacked insulation masonry blocks based on Miscanthus concrete” is carried out at the University of Luxembourg and financed by CONTERN Lëtzebuerger Beton. The principal aim of this project is to valorise the sustainability in the construction sector and improve the circular economy by using Luxembourgish Miscanthus to produce a masonry block. The latter should include bearing and thermal properties. Besides, a dry-stacked system should be adopted. The imposed aims are reached by developing a masonry block based on two materials connected by a dovetail connection. Furthermore, a dry-stacked system is adopted using a horizontally and vertically tongue-groove system. The present research demonstrates the approach performed to achieve these goals. The process to reach the described aims is divided in five major steps. The first step consists of an analysis on the needed amount of mixture components with the aim of achieving the highest possible load-bearing capacity of concrete based on Miscanthus aggregates. It can be concluded that the variation of the amount of components affects the density, which has an increasing parabolic relation with the load-bearing capacity of the specimens. Furthermore, the long-term deformations considering shrinkage of Miscanthus concrete achieve in average 2350 𝜇𝑚/𝑚, which is the double of a lightweight concrete. However, comparing the long-term deformations of Miscanthus concrete with Hemp-concrete a benefit of at least 50 % can be considered. Secondly, a machine-learning tool is applied to predict the compressive strength by introducing the mixture components and avoiding the need of creating time-consuming and costly experimental tests. Furthermore, it is possible to analyse the impact of each individual component on the load-bearing capacity. This tool has the ability of optimising the mixture according to the needs in compressive strength. Next, a Miscanthus concrete mixture is used to manufacture rectangular masonry blocks and an analysis on their geometrical height and roughness imperfections is performed experimentally and numerically on the load-bearing capacity of walls and single masonry blocks. The roughness was investigated by measuring the contact surface. Accordingly, an exponential relation is identified between the applied compressive strength and the contact surface. The height imperfections show a low impact on the load-bearing capacity of the wall. This statement is also validated in the numerical calculation. Finally, an increase of the relation height to length of a wall reduces linearly the maximum achieved compressive strength. The next step consists of investigating the use of a Mycelium-Miscanthus composite for insulation purposes and analyse different properties. The scanning electron microscopic analysis allows investigating the bond between Mycelium and Miscanthus. It can be concluded that the Mycelium webs enter the Miscanthus fibre and holds in the way the specimen together. Furthermore, a density of 122 kg/m3 and a thermal conductivity of 0.09 W/mK is measured in this bio composite, which is higher than a conventional insulation material. Besides, a fire resistance of category EI15 according to EN13501-2:2003 is measured. These results show a promising capacity of this composite as a building insulation. The last phase of this project consists of creating an interaction between all the parts by applying the investigated material properties into one masonry block with a geometry able to be applied in a dry-stacked masonry wall. The latter is applied by introducing a horizontal and vertical tongue-groove system in the masonry block. This block is divided in two parts, a bearing and insulation material, which are connected by a dovetail connection. A sensitivity analysis is performed in the wall by varying different properties of the masonry block, such as the thickness of the bearing and the insulation part, the angle of the dovetail connection or the position of tongue-groove system. An increase of the width of the bearing part has an increasingly linear impact on the load-bearing capacity. However, an increase of the thickness of the insulation part does not show any impact on the maximum achieved compressive strength. Furthermore, the impact of the geometrical imperfections like height and roughness are analysed. Subsequently, the needed thickness of the masonry block is calculated based on the imposed thermal transmittance value. A total thickness of the masonry block of 77 cm was determined. Therefore, it can be concluded that the thermal conductivity of the insulation part has to be improved to reduce the needed thickness of the masonry block. Finally, this thesis assesses the use of Miscanthus fibres in a masonry block, which has a bearing and insulation capacity. Furthermore, the tongue-groove system of the masonry block and the low Young’s Modulus of the Miscanthus mixture allow its application in a dry-stacked wall in the construction sector. [less ▲]

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See detailMagnetoelectric thin-film composites for energy harvesting applications
Nguyen, Tai UL

Doctoral thesis (2021)

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See detailUnderstanding the role of colorectal cancer-associated bacteria in colorectal cancer
Ternes, Dominik UL

Doctoral thesis (2021)

Mounting evidence from 16S rRNA-based or metagenomic analyses suggests that dysbiosis, a state of pathological microbial imbalance, is prevalent in the gut of patients with CRC. Numerous microbial taxa ... [more ▼]

Mounting evidence from 16S rRNA-based or metagenomic analyses suggests that dysbiosis, a state of pathological microbial imbalance, is prevalent in the gut of patients with CRC. Numerous microbial taxa have been identified of which representative isolate cultures can interact with cancer cells, further triggering distinct disease pathways in animal models. Nevertheless, how these complex interrelationships of a dysbiotic microbiota may be involved in the pathogenesis of CRC remains a fundamental question and requires multifaceted mechanistic studies. This thesis moves beyond observational studies, it integrates novel experimental approaches for the study of the gut microbiome in colorectal cancer. It incorporates current knowledge in the field as well as interdisciplinary approaches. My work aims at contributing to an ecosystem-level mechanistic understanding of the CRC-associated microbiome in the initiation and progression of the disease. In detail, the objective of my work comprised an integrative approach of microbiome-CRC interaction studies. We revised current knowledge on, and studied the CRC-associated bacteria, in particular Fusobacterium nucleatum (Fn) and Gemella morbillorum (Gm). We assessed their direct and indirect effects on CRC cells, their interactions with immune cells, as well as their tumor-modulating potential in vitro, in silico, and in vivo. The results presented in this thesis comprise new findings on human microbial cross-talk of Fn with CRC. We identified formate as a potential fusobacterial oncometabolite, which enhanced cancer incidence and progression via increased cancer stemness signaling. Furthermore, we discovered immune-suppressive functions of Gm in the context of CRC. With my work in collaboration projects, I contributed to the development of two novel approaches in anti-cancer therapy: First, to the establishment of a personalized in vitro model (iHuMiX) for the study of microbe-host-immune interactions in anti-cancer therapy, and second, to the validation of an in silico workflow that uses metabolic rewiring strategies for network-based drug target predictions for CRC therapy. Taken together, this thesis work broadened the mechanistic understanding of CRC-associated microbes and it contributed to potential strategies for the development of an improved CRC therapy. [less ▲]

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See detailPopulismes et fabrique des droits économiques et sociaux dans le cadre des droits de l'Homme. Le Front national et l'Union démocratique du centre (1992-2013)
Albert, Frédéric UL

Doctoral thesis (2021)

Since the 1990’s, with the development of Europeanisation, globalisation and the installation of the neo-liberal paradigm, we observe in Europe the non-application of economic and social rights, despite ... [more ▼]

Since the 1990’s, with the development of Europeanisation, globalisation and the installation of the neo-liberal paradigm, we observe in Europe the non-application of economic and social rights, despite being aspired by the States of the human rights continent after the Second World War. At the same time, "national-populist" parties are gaining more and more support and are establishing themselves in the political landscape as a "right-wing third way", which would provide the answers that the governing parties do not seem to be able to find, in the context of an actual crisis of the welfare state. The aim of our research is to provide a comparative analysis of the discourses of the "Front National" in France, now Rassemblement National ("RN") and the "Union Démocratique du Centre" in Switzerland ("UDC/SVP") on economic and social rights, in order to confront them with the changes and public policies observed in our societies as a result of the neo-liberal paradigm. Using a cross-cutting analytical grid that identifies the characteristics of socio-economic discourse of a "national-populist" nature, this work is made up of numerous sources from both parties, studied over a period of twenty years : work that constitutes the boundaries between 1992, when the Maastricht Treaty developing the "European market" was signed, and 2013, with the start of negotiations for the signing of the transatlantic treaty opening the "European market" to the "US market". The research work is also based on original interviews with key figures from both parties and the creation of an online questionnaire aimed at elected representatives with responsibilities on a smaller scale (at regional level). Thus, the cross-referencing of our qualitative and quantitative data has enabled us to produce original results and to construct a new category of populist parties called : "national-populist parties opposed to human rights". Among other things, the latter develop in their socio-economic approach a will to defend economic and social rights but only for nationals, rejecting the universality of human rights. At the same time, they propose a hybrid form of capitalism with nuances between the "FN/RN" and the "UDC", combining a dose of protectionism but also a more or less sought-after integration into the "market". Furthermore, it is interesting to compare the discourses of a party outside government (the "RN") that has not yet participated in executive authority at the national level and a party associated with federal authority, the "UDC", both "inside and outside". Ultimately, in both cases, it is sovereignism and anchoring in so-called right-wing policies that seem to dominate the socio-economic DNA of the two populist parties studied. With the help of our research work, we can thus ask ourselves in what way does the "national-populist" discourse point to the failure of states on the human rights continent to implement economic and social rights as they intend ? [less ▲]

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See detailINTERFACIAL COVALENT CHEMICAL BONDING: TOWARDS THERMOREVERSIBLE ADHESION
Hassouna, Lilia UL

Doctoral thesis (2021)

Many industrial sectors like automotive and aeronautic industries are moving toward the use of multi-material devices and composite materials. Reversible adhesion becomes then increasingly important as it ... [more ▼]

Many industrial sectors like automotive and aeronautic industries are moving toward the use of multi-material devices and composite materials. Reversible adhesion becomes then increasingly important as it allows to structurally join dissimilar materials and keep them together during the material’s useful life, while allowing the easy repair of damaged parts or recycling of raw materials. One way to achieve this property is by thermoreversible covalent bonding based on Diels-Alder and its retro Diels-Alder reaction. This “click” reaction occurs between a diene and a dienophile to form an adduct at a certain temperature, then this adduct can be dissociated on command by simple heating. The investigation of the adduct dissociation via retro Diels-Alder reaction is key in understanding the adhesion reversibility based on these systems. In this work an already formed Diels-Alder adduct is synthesized then grafted on plasma polymer coatings or self assembled monolayers. These two different types of surfaces offer different environments for the molecules. Afterwards, a protocol for reaction monitoring based on TOF-SIMS spectroscopy was developed which allowed the determination of kinetic and thermodynamic parameters of the interfacial reaction on both surfaces. The effect of the adducts environment on the reaction was then elucidated by comparing the obtained values. Investigation of the same reaction in solution using 1H NMR spectroscopy confirmed the observations made on the effect of molecules immobilisation on the reaction. Essentially, the more the molecules are immobilized the lower is the energy barrier and the higher is the entropy contribution. Finally, the feasibility of interfacial adhesion based on this system was explored. [less ▲]

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See detailTaming Android App Crashes
Kong, Pingfan UL

Doctoral thesis (2021)

App crashes constitute an important deterrence for app adoption in the android ecosystem. Yet, Android app developers are challenged by the limitation of test automation tools to ensure that released apps ... [more ▼]

App crashes constitute an important deterrence for app adoption in the android ecosystem. Yet, Android app developers are challenged by the limitation of test automation tools to ensure that released apps are free from crashes. In recent years, researchers have proposed various automation approaches in the literature. Unfortunately, the practical value of these approaches have not yet been confirmed by practitioner adoption. Furthermore, existing approaches target a variety of test needs which are relevant to different sets of problems, without being specific to app crashes. Resolving app crashes implies a chain of actions starting with their reproduction, followed by the associated fault localization, before any repair can be attempted. Each action however, is challenged by the specificity of Android. In particular, some specific mechanisms (e.g., callback methods, multiple entry points, etc.) of Android apps require Android-tailored crash-inducing bug locators. Therefore, to tame Android app crashes, practitioners are in need of automation tools that are adapted to the challenges that they pose. In this respect, a number of building blocks must be designed to deliver a comprehensive toolbox. First, the community lacks well-defined, large-scale datasets of real-world app crashes that are reproducible to enable the inference of valuable insights, and facilitate experimental validations of literature approaches. Second, although bug localization from crash information is relatively mature in the realm of Java, state-of-the-art techniques are generally ineffective for Android apps due to the specificity of the Android system. Third, given the recurrence of crashes and the substantial burden that they incur for practitioners to resolve them, there is a need for methods and techniques to accelerate fixing, for example, towards implementing Automated Program Repair (APR). Finally, the above chain of actions is for curative purposes. Indeed, this "reproduction, localization, and repair" chain aims at correcting bugs in released apps. Preventive approaches, i.e., approaches that help developers to reduce the likelihood of releasing crashing apps, are still absent. In the Android ecosystem, developers are challenged by the lack of detailed documentation about the complex Android framework API they use to develop their apps. For example, developers need support for precisely identifying which exceptions may be triggered by APIs. Such support can further alleviate the challenge related to the fact that the condition under which APIs are triggered are often not documented. In this context, the present dissertation aims to tame Android crashes by contributing to the following four building blocks: Systematic Literature Review on automated app testing approaches: We aim at providing a clear overview of the state-of-the-art works around the topic of Android app testing, in an attempt to highlight the main trends, pinpoint the main methodologies applied and enumerate the challenges faced by the Android testing approaches as well as the directions where the community effort is still needed. To this end, we conduct a Systematic Literature Review (SLR) during which we eventually identified 103 relevant research papers published in leading conferences and journals until 2016. Our thorough examination of the relevant literature has led to several findings and highlighted the challenges that Android testing researchers should strive to address in the future. After that, we further propose a few concrete research directions where testing approaches are needed to solve recurrent issues in app updates, continuous increases of app sizes, as well as the Android ecosystem fragmentation. Locating Android app crash-inducing bugs: We perform an empirical study on 500 framework-specific crashes from an open benchmark. This study reveals that 37 percent of the crash types are related to bugs that are outside the crash stack traces. Moreover, Android programs are a mixture of code and extra-code artifacts such as the Manifest file. The fact that any artifact can lead to failures in the app execution creates the need to position the localization target beyond the code realm. We propose ANCHOR, a two-phase suspicious bug location suggestion tool. ANCHOR specializes in finding crash-inducing bugs outside the stack trace. ANCHOR is lightweight and source code independent since it only requires the crash message and the apk file to locate the fault. Experimental results, collected via cross-validation and in-the-wild dataset evaluation, show that ANCHOR is effective in locating Android framework-specific crashing faults. Mining Android app crash fix templates: We propose a scalable approach, CraftDroid, to mine crash fixes by leveraging a set of 28 thousand carefully reconstructed app lineages from app markets, without the need for the app source code or issue reports. We develop a replicative testing approach that locates fixes among app versions which output different runtime logs with the exact same test inputs. Overall, we have mined 104 relevant crash fixes, further abstracted 17 fine-grained fix templates that are demonstrated to be effective for patching crashed apks. Finally, we release ReCBench, a benchmark consisting of 200 crashed apks and the crash replication scripts, which the community can explore for evaluating generated crash-inducing bug patches. Documenting framework APIs' unchecked exceptions: We propose Afuera, an automated tool that profiles Android framework APIs and provides information on when they can potentially trigger unchecked exceptions. Afuera relies on a static-analysis approach and a dedicated algorithm to examine the entire Android framework. With Afuera, we confirmed that 26739 unique unchecked exception instances may be triggered by invoking 5467 (24%) Android framework APIs. Afuera further analyzes the Android framework to inform about which parameter(s) of an API method can potentially be the cause of the triggering of an unchecked exception. To that end, Afuera relies on fully automated instrumentation and taint analysis techniques. Afuera is run to analyze 50 randomly sampled APIs to demonstrate its effectiveness.Evaluation results suggest that Afuera has perfect true positive rate. However, Afuera is affected by false negatives due to the limitation of state-of-the-art taint analysis techniques. [less ▲]

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See detailUnderstanding multilingual pupils' translanguaging practices: a qualitative study in two primary schools in Luxembourg
Degano, Sarah UL

Doctoral thesis (2021)

Over the last decades, research in bilingual and trilingual schools has shown that translanguaging – the systematic alternation between two or more named languages – can promote children’s learning and ... [more ▼]

Over the last decades, research in bilingual and trilingual schools has shown that translanguaging – the systematic alternation between two or more named languages – can promote children’s learning and increase their opportunities to participate in class. Translanguaging can therefore provide more equitable access to the curriculum and address educational inequalities. To date, however, few translanguaging studies have researched older primary school children in multilingual schools. Similarly, few have explored the use of children’s non-linguistic resources in meaning-making processes. More recently, there has been an explicit call for a multimodal perspective on translanguaging, according to which translanguaging is conceptualised as the deployment of the semiotic repertoire. While multimodality studies have pointed out the potential of multimodal resources in education, there remains a paucity of empirical research that – with regard to more equitable educational practices – explores the pupils’ use of both multilingual and multimodal resources in class. With the aim of understanding what translanguaging means in two different multilingual primary schools, the present thesis addresses this issue. It presents a qualitative research on the ways in which multilingual fourth-graders in Luxembourg deploy and combine the resources of their semiotic repertoires to communicate and make meaning in interaction with their peers and teachers. The study was informed by the following questions – how is translanguaging practised in the classroom? How do pupils translanguage, drawing on their semiotic repertoire? How is translanguaging used to construct curricular meaning in interaction? I argue that the pupils’ translanguaging practices are interactively constructed because the ways in which they combine their multilingual and multimodal resources for communication and meaning-making in class reflect those of their teachers. Data was collected in two public primary schools in Luxembourg – one in the North, one in the East – from January to November 2018. This data took the form of observations, fieldnotes, video-recordings of lessons, semi-structured interviews with the pupils and the teachers, as well as stimulated recall interviews with the pupils. Over a duration of 130 hours, I observed and recorded four focal pupils of different language and education backgrounds as they deployed their semiotic repertoires in interaction with their teachers and peers in both Year 4 and at the beginning of Year 5. In order to explore how translanguaging was practiced in the classrooms, I conducted a thematic analysis of the 42 documents of field notes (analytic memos), totalling about 152,000 words. In addition, to investigate how the pupils combined the resources of their repertoires and drew on translanguaging to make meaning, I applied a multimodal interaction analysis and a sociocultural discourse analysis to 11 hours’ worth of video footage from 177 videos, ranging in length from 7 seconds to 24 minutes. The 13 hours’ worth of interview material were summarised by hand and served triangulation purposes. The study has shown that the pupils’ translanguaging practices were interactively constructed. Firstly, the translanguaging practices of the teachers and the pupils varied between school contexts. In both schools, the pupils learned French, German and/ or Luxembourgish, and regularly used several languages. However, while their translanguaging practices mainly involved shifts between German and Luxembourgish in the school in the East, they involved shifts between the three school languages as well as Portuguese in the school in the North. Secondly, all four focal pupils combined linguistic, extralinguistic and paralinguistic resources, but their semiotic combinations were influenced by the translanguaging practices of their teachers and, therefore, varied between schools and across year groups. In the school in the East, the focal pupils tended to deploy their semiotic repertoires more extensively in Year 5 than in Year 4; it was the other way around for the focal pupils in the school in the North. Thirdly, depending on their teachers’ translanguaging practices, the pupils orchestrated their multilingual and multimodal resources in complex ways to co-construct curricular meaning. They flexibly shifted between languages (e.g. school languages, home languages), modes (i.e. verbal mode of communication, non-verbal mode of communication) and modalities (e.g. speaking, singing), thereby combining different linguistic resources (e.g. English, French, German, Luxembourgish, Portuguese), extralinguistic resources (e.g. gaze, gesture, touch) and paralinguistic resources (e.g. intonation, sound effects, volume). The present study draws attention to the resourcefulness with which multilingual primary school pupils of different backgrounds can co-construct curricular meaning. It also emphasizes the role that teachers can play in constraining or supporting the pupils’ use of resources in class. This study has implications for teachers in that they can learn how important it is to allow pupils to use their own resources in class. It calls for professional development that will help teachers develop a translanguaging stance, that is the belief that pupils are able to leverage their semiotic repertoires to participate in class, make meaning and thereby access the curriculum. This is of particular importance for children of lower socio-economic status and with a migration background who continue to underperform. [less ▲]

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See detailENTRAINMENT OF DROPLETS FROM WATER POOLS
Ouallal, Mohammed UL

Doctoral thesis (2021)

The aim of this work is to study the phenomena of droplet entrainment from water pool. This phenomenon could be either a consequence of boiling or depressurization. In a bubble column, droplets are ... [more ▼]

The aim of this work is to study the phenomena of droplet entrainment from water pool. This phenomenon could be either a consequence of boiling or depressurization. In a bubble column, droplets are released from the surface of the pool by bubble burst (in bubbly flow regime) or by detachment from liquids sheets (in churn turbulent flow regime) depending on the hydrodynamics inside the pool. Eventually, these droplets will be entrained by the streaming gas (superficial gas velocity) or fall back due to gravity. Many experimental studies have been conducted, and several numerical simulations were performed for a better understanding of the phenomena of entrainment. Numerical simulation are a good tool to simulate an experiment due to limitations of data. To that end, CFD showed to be a good candidate to perform such a simulation, yet these it demand high computational performance and are time consuming. However, Lumped Parameter codes (LP) are widely used due to their simplicity and fast running. The number of correlations that quantify the entrainment previously developed based on empirical, semi-empirical and theoretical approaches are limited to a specific regime in the water pool, thermal hydraulic conditions or even to a specific geometry For this purpose, after an extensive study, an empirical correlation is proposed to cover the flow regimes from bubbly to churn turbulent, and could be applied to a wide range of geometries. The current correlation shows an increase until a maximum entrainment of about 2.10-4, corresponding to gas velocity of 0.05 m/s for bubbly flow regime, a slight decrease to 2.10-5, for the transition regime for superficial gas velocities up to 0.1 m/s, and a sharp increase as the superficial gas velocity goes up to 5 m/s The experimental database used to develop the present empirical correlation covers a broader range of boundary conditions, namely pressure [1 bar – 15 bar], water pool thermal condition [subcooled – boiling], vessel diameter[0.19m- 3.2 m], pool diameter [0.1 m – 1.4 m], superficial gas velocity up to 5.0 m/s and for soluble and insoluble aerosols. Therefore, the proposed empirical correlation aims to constitute an important tool to transfer the experimental results to reactor application. [less ▲]

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See detailInternationalisation and Multilingualism in Doctoral Education: Language Ideologies, Discourse and Positioning
Hofmann, Stephanie UL

Doctoral thesis (2021)

In light of the growing linguistic and cultural diversity among students and researchers, studies on multilingualism in higher education have been increasingly devoting attention to how students and ... [more ▼]

In light of the growing linguistic and cultural diversity among students and researchers, studies on multilingualism in higher education have been increasingly devoting attention to how students and academics use their plurilingual repertoire for writing academic texts. Framed by the internationalisation of higher education and its contributions towards a knowledge-based society and economy in Europe, little is known about how students and researchers conceptualise the role of the national language(s) and the linguistic repertoire(s) vis-à-vis English as the lingua franca. In particular, how academic actors negotiate voice when choosing a language for academic writing and publishing has not been closely examined. To rectify this lacuna, this study focuses on the linguistic processes of doctoral publications and outputs in the context of a multilingual university—the University of Luxembourg (UL), where next to English also German and French are official academic languages. In view of the increased usage of English for writing and publishing doctoral theses, questions arise about the mechanisms and preferences underlying doctoral researchers’ linguistic choices, and how such choices pertain to shifting academic norms. Thus, the overall aim of this exploratory study is to show how doctoral researchers in a multilingual research context—here, the University of Luxembourg—position themselves in relation to macrolevel discourses about language and academic success within their complex lingua-cultural and socio-economic setting. The data analysis is based on in-depth problemcentred interviews with five plurilingual doctoral researchers from China, Germany, Luxembourg and Russia. By applying discourse analysis to the interview transcripts, this thesis makes three substantial contributions to the research field. First, it reveals that despite the dominance of English, doctoral researchers continue to draw on their plurilingual repertoire as a resource for their research and writing processes, however, for different reasons, which are ideologically motivated. Second, the study shows that the choice for publishing in English is mostly based on shifts in academic norms that focus on economic imperatives, such as competition and hyper-performativity. Therefore, the prevalence of English and the pressure to publish in international journals seem to lead doctoral researchers towards limiting the use of the totality of their plurilingual repertoire for writing and publishing theses. And third, this research allows for a detailed understanding of underlying language ideologies of doctoral researchers in higher education. In particular, it gives insights into the value of the theoretical concepts of positioning and language ideology in discourse analysis for investigating the negotiation of voice. [less ▲]

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See detailLA KORA A LA CONFLUENCE DES CULTURES : UNE ETUDE DE LA TRANSMISSION D’UN OBJET CULTUREL DANS UN CONTEXTE TRANSCULTUREL CONTEMPORAIN
Ayegnon, Armel Benvide Osée UL

Doctoral thesis (2021)

The kora is a musical instrument of West African origin. Now played by several individuals who do not necessarily come from her native background, it has been transmitted from her endogenous cultural ... [more ▼]

The kora is a musical instrument of West African origin. Now played by several individuals who do not necessarily come from her native background, it has been transmitted from her endogenous cultural circle to other exogenous circles. We ourselves are kora players and belong to this exogenous circle. In our artistic journey and in our personal history, we have felt the need to produce a hybrid game. Thus, as an artist and researcher, our first objective of a doctoral thesis was to research hybridization processes from a so-called "traditional" repertoire and another called "modern". . Our academic career made us question these categorical qualifiers: "traditional", "modern". This questioning took place through the observation of the process of transmission of the kora. It was made from the very history of the instrument which cannot be dissociated from the history of the individuals and communities who adopted it. However, given the great diversity of the stories, it was necessary to think about setting up tools for collecting knowledge related to contexts and material and immaterial objects, relating to the kora. In order to achieve the primary goal we were pursuing, we finally directed this research towards proposing a method of approach to the study of transmission. There is therefore a dialectic between the object approached and the approach used in this research work. It is this dialectic that corresponds to the main objective of this work. Thus, this doctoral thesis aims to answer the following question: "How to think about the transmission of the kora" object-witness "of the meeting of cultures? "It is a double research focusing both on the transmission of the kora and on the means to study and realize this transmission. This research subsequently led to an applied anthropology and even cultural engineering project. This present writing is the summary of an academic adventure between practice and theory. [less ▲]

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See detailETHICAL PERSPECTIVES ON BIG DATA IN AGRI-FOOD: OWNERSHIP AND GOVERNANCE FOR SAFETY
Sapienza, Salvatore UL

Doctoral thesis (2021)

Big data are reshaping the way we interact with technology, thus fostering new applications to increase the safety-assessment of foods, a critical goal in the protec- tion of individuals’ right to health ... [more ▼]

Big data are reshaping the way we interact with technology, thus fostering new applications to increase the safety-assessment of foods, a critical goal in the protec- tion of individuals’ right to health and the flourishing of the food and feed market. An extraordinary amount of information, including real-time data available from multiple sources, is analysed using machine learning approaches aimed at detecting the existence or predicting the likelihood of future risks, thus reducing the inaccu- racy of risk assessment. Food business operators have to share the results of these analyses when applying to place on the market certain products, whereas agri-food safety agencies (including the European Food Safety Authority) are exploring new avenues to increase the accuracy of their evaluations by processing Big data. Such an informational endowment brings with it opportunities and risks correlated to the extraction of meaningful inferences from data. However, conflicting interests and tensions among the involved entities - the industry, food safety agencies, and con- sumers - hinder the finding of shared methods to steer the processing of Big data in a sound, transparent and trustworthy way. Taken together, a recent reform in the EU sectoral legislation, the lack of trust in the EU food safety system proved by the recent Fitness Check of the General Food Law Regulation and the presence of a considerable number of stakeholders highlight the need of ethical contributions aimed at steering the development and the deployment of Big data applications. At the same time, general Artificial Intelligence guidelines and charters published by European Union institutions and Member States have to be discussed in light of applied contexts, including the one at stake. This thesis aims to contribute to these goals by discussing what principles should be put forward when processing Big data in the context of agri-food safety-risk assessment. The research focuses on two narrow and interviewed topics - data ownership and data governance - by evaluating how the regulatory framework addresses the challenges raised by Big data analysis in these domains. To do so, it adopts a cross-disciplinary research methodology that keeps into account both the technological advances and the policy tools adopted in the European Union, while assuming an ethical perspective when exploring poten- tial solutions. The outcome of the project is a tentative Roadmap aimed to identify the principles to be observed when processing Big data in this domain and their possible implementations. [less ▲]

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See detailDATA PROTECTION BY DESIGN IN THE E-HEALTH CARE SECTOR: THEORETICAL AND APPLIED PERSPECTIVES
Bincoletto, Giorgia UL

Doctoral thesis (2021)

In the digital age, e-health technologies play a pivotal role in the processing of medical information. As personal health data represents sensitive information concerning a data subject, enhancing data ... [more ▼]

In the digital age, e-health technologies play a pivotal role in the processing of medical information. As personal health data represents sensitive information concerning a data subject, enhancing data protection and security of systems and practices has become a primary concern. In recent years, there has been an increasing interest in the concept of privacy by design (PbD), which aims at developing a product or a service in a way that it supports privacy principles and rules. In the European Union, Article 25 of the General Data Protection Regulation provides a binding obligation of implementing data protection by design (DPbD) technical and organisational measures. This thesis explores how an e-health system could be developed and how data processing activities could be carried out to apply data protection principles and requirements from the design stage. Currently, there is a lack of clarity and knowledge on the topic for developers, data controllers and stakeholders. The research attempts to bridge the gap between the legal and technical disciplines on DPbD by providing a set of guidelines for the implementation of the principle in the e-health care sector. The research is based on literature review, legal and comparative analysis, and investigation of the existing technical solutions and engineering methodologies. So, this thesis uses both legal comparison and the interdisciplinary method. The work can be differentiated by theoretical and applied perspectives. First, it critically conducts a legal analysis on the principle of PbD and it studies the DPbD legal obligation and the related provisions. Later, the research contextualises the rule in the health care field by investigating the applicable legal framework for personal health data processing. Moreover, the research focuses on the US legal system by conducting a comparative analysis since PbD is an international principle and in the US federal law there is a specific rule for the e-health care sector that mandates the implementation of technical and organisational safeguards. Adopting an applied perspective, the research investigates the existing technical methodologies and tools to design data protection and it proposes a set of comprehensive DPbD organisational and technical guidelines for a crucial case study, that is an Electronic Health Record system. [less ▲]

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See detailA Study of Hiring Discrimination Using Factorial Survey Experiments: Theoretical and Methodological Insights
Gutfleisch, Tamara Rebecca UL

Doctoral thesis (2021)

This dissertation provides new insights into the study of hiring discrimination related to three dimensions of inequality: gender, ethnicity, and unemployment. Scholars within sociology of work and labor ... [more ▼]

This dissertation provides new insights into the study of hiring discrimination related to three dimensions of inequality: gender, ethnicity, and unemployment. Scholars within sociology of work and labor economics widely agree that hiring discrimination based on these dimensions exists. However, the question of who is most affected beyond the classical look at single dimensions is less clear, as are the conditions under which hiring discrimination occurs. Focusing on young labor market entrants, I address these questions with two empirical studies using factorial survey experiments. First, I study how applicants’ gender and unemployment interactively shape recruiters’ hiring intentions in sex-segregated occupations. Second, I study the role of recruiter nationality in hiring discrimination against foreigners in Luxembourg. Moreover, while factorial surveys are increasingly applied in the study of hiring discrimination, they have been criticized for exhibiting low external validity. This dissertation empirically addresses how to overcome this criticism by improving the design of factorial surveys currently applied in employer studies. Specifically, I study whether designs based on real vacancies trigger more valid judgements compared to designs based on hypothetical vacancies. Overall, the findings of this dissertation support the relevance of hiring discrimination for labor market inequalities related to gender, ethnicity, and unemployment, but suggest that the mechanisms underlying hiring discrimination related to these dimensions are more nuanced. First, this dissertation suggests that occupational sex segregation might matter for how unemployment shapes recruiters’ hiring intentions towards men and women. Second, while foreign applicants might generally have better hiring chances if the recruiter is foreign, foreign applicants having the same nationality as the recruiter might benefit less from this situation. Finally, this dissertation provides first evidence that using hypothetical vacancies constitutes a valid approach to study recruiter decision-making within the limits of factorial surveys. [less ▲]

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