Thermodynamics of Quantum Collisions

Doctoral thesis (2021)

In this thesis, we show how the thermodynamic concepts of heat and work arise at the level of a quantum collision. We consider the collision of a particle travelling in space, described by a wave packet ... [more ▼]

In this thesis, we show how the thermodynamic concepts of heat and work arise at the level of a quantum collision. We consider the collision of a particle travelling in space, described by a wave packet, with a fixed system having internal energy states. Our main finding is that the energy width of the wave packet, which can be narrow or broad with respect to the system energies, plays a crucial role in identifying energy exchanges due to collisions as heat or work. While heat is generated by narrow wave packets effusing with thermal momenta, work is generated by fast and broad wave packets. We compare our results with models of repeated interactions, which despite being inspired by quantum collisions, still present shortcomings when used as a basis for a thermodynamic theory. We show how these difficulties are circumvented by a proper application of quantum scattering theory. [less ▲]

Mining App Lineages: A Security Perspective

Doctoral thesis (2021)

Direct inter-app code invocation in Android apps and its evolution: The Android ecosystem offers different facilities to enable communication among app components and across apps to ensure that rich ... [more ▼]

Direct inter-app code invocation in Android apps and its evolution: The Android ecosystem offers different facilities to enable communication among app components and across apps to ensure that rich services can be composed through functionality reuse. At the heart of this system is the Inter-component communication (ICC) scheme, which has been largely studied in the literature. Less known in the community is another powerful mechanism that allows for direct inter-app code invocation which opens up for different reuse scenarios, both legitimate or malicious. In this dissertation, we expose the general workflow for this mechanism, which beyond ICCs, enables app developers to access and invoke functionalities (either entire Java classes, methods or object fields) implemented in other apps using official Android APIs. We experimentally showcase how this reuse mechanism can be leveraged to “plagiarize" supposedly-protected functionalities. Typically, we could leverage this mechanism to bypass security guards that a popular video broadcaster has placed for preventing access to its video database from outside its provided app. We further contribute with a static analysis toolkit, named DICIDer, for detecting direct inter-app code invocations in apps. An empirical analysis of the usage prevalence and evolution of this reuse mechanism is then conducted. [less ▲]

Digital History als ‚experimental space‘: Handels- und Transportnetzwerke in Gallien und Germanien sowie die Transportverbindung zwischen Mosel und Saône

Doctoral thesis (2021)

This dissertation consists of two parts. In the first part, the focus lies on the study of trade and transport networks in the Gaulish and German provinces during the Roman Empire based on inscriptions ... [more ▼]

This dissertation consists of two parts. In the first part, the focus lies on the study of trade and transport networks in the Gaulish and German provinces during the Roman Empire based on inscriptions. Different approaches are used to tackle this topic, e.g. networks between different people and families, organisations and cities. The results show that networks between merchants or merchant families likely existed with the aim of securing and improving one’s own position in the business world. The networks between organisations show the close connection of these organisations among themselves and to the social and political elite. The spatial networks emphasize the important role of Lyon and show long-range connections of the merchants. The second part focuses on the reconstruction of the roman road between upper Saône and Moselle with the help of ancient, medieval and modern sources as well as digital methods like least cost path analysis. The results show that the road between Corre, Escles and Portieux is the most likely candidate, but it is also possible that other options existed. The dissertation is also part of the Doctoral Doctoral Training Unit ‚Digital History & Hermeneutics‘. One of the basic ideas of the DTU was a critical reflection on the epistemological and methodological challenges of doing historical research in the digital age and a critical and self-reflexive use of these new digital tools and technologies. Especially during the first part of the study, it became evident, that the fragmented nature of the sources leads to several problems when using the new digital methods and tools. This applies even more to Ancient History. The dealing with these problems became another important aspect of the dissertation. There is no point in denying the chances the digital turn and that it will change today’s academia landscape. They can be useful in historic research, but at the same time, they are still a journey into the unknown. It is of the utmost importance to keep a critical mindset towards the new developments, methods and tools. Detailed knowledge of the sources and especially their shortcomings is key. This also applies to their communication and to the documentation of the research process since digital methods can quickly produce impressive-looking results. Furthermore, not only methodological knowledge is required but, especially and probably even more importantly, methodological awareness. [less ▲]

Load bearing mechanisms of headed stud shear connections in profiled steel sheeting transverse to the beam

Doctoral thesis (2021)

Composite steel-concrete floor solutions have become popular in the design of buildings thanks to the efficient combination of high tensile strength and ductility of steel with reinforced concrete ... [more ▼]

Composite steel-concrete floor solutions have become popular in the design of buildings thanks to the efficient combination of high tensile strength and ductility of steel with reinforced concrete elements in compression. To ensure the longitudinal shear transfer between the downstand steel beam and the concrete slab in composite beams, headed stud shear connections are generally employed with profiled steel sheeting transverse to the supporting beam. However, whilst the steel deck enhances the bending resistance of the slab, the performance of the shear connection decreases. Based on the evaluation of a large database of push-out tests carried out in the last 40 years, several design models have been proposed in the last decades to predict the resistance of studs but none of them provides safe and reliable results. This is related to the fact that the proposed design equations do not always consider appropriately the actual resistance mechanisms activated in the shear connection. Also, as the failure modes are typically observed at high displacements, no information on the resistance components at lower displacements is given. Therefore, a deep investigation on the sequence of the load bearing resistance mechanisms of headed stud shear connections was performed with the support of an experimental campaign of 21 full scale push-out tests and numerical simulations. From the analysis of the experimental results, it was seen that all the samples experienced rib punching at low displacements followed by concrete pull-out failure or stud rupture. The influence of several structural parameters was also assessed by comparing different test series. It was found that 200 mm wide recess and slab depth have a minor impact on the performance of the connection. Instead, the addition of waveform rebars increased the resistance by 26% as well as the slip capacity whereas the different position of the wire mesh did not show an important influence. To investigate specifically the behaviour of the shear connections, the distribution of the compressive stresses in the rib and the plastic hinges developed in the stud connector were evaluated by means of a validated finite element model. From the outcomes of the experimental and numerical study, three main load bearing phases were distinguished. At low displacements (Phase 1), the concrete is not damaged until the typical cone crack initiates at the edge of the rib and the stud deforms in bending. Subsequently (Phase 2), while the cracks propagate, the internal forces in the rib redistribute and the resistance is governed by the bearing stresses of the concrete in front of the connector. At large displacements (Phase 3), the front side of the concrete rib is highly damaged whereas the tension stresses in the stud increases significantly due to pulling forces. For further slips, this can lead to concrete pull-out or stud rupture as confirmed by the experimental studies. These insights were taken as a basis for the development of three respective mechanical models: cantilever model, modified strut and tie model (MSTM), and strut and tie model (STM). Whilst the first considers the system as a cantilever beam, the other two reproduce the concrete as a system of compression struts and the steel sheeting was modelled as tie elements. All the resistance functions were analytically derived in consideration of the experimental and numerical results in order to estimate the capacity of the shear connection at different displacements. As the STM focuses on the behaviour at large deformations, only the first two models were considered to predict the actual capacity of the shear connection. The design resistance of these two proposed models was finally calibrated according to the statistical procedure of EN 1990. [less ▲]

Implications of Blockchain-Based Smart Contracts on Contract Law

Doctoral thesis (2021)

DEVELOPMENT OF A MULTIPLEX DIGITAL PCR STRATEGY FOR SENSITIVE PREANALYTIC CHARACTERIZATION OF DNA AND ITS APPLICATION IN MOLECULAR PATHOLOGY

Doctoral thesis (2021)

REFERENCE MEASUREMENTS AND SIMULATIONS OF STATIC AND DYNAMIC CHARACTERISTICS OF PRESTRESSED CONCRETE BRIDGES UNDER OUTDOOR CONDITIONS FOR STRUCTURAL HEALTH MONITORING

Doctoral thesis (2021)

Today’s traffic infrastructure, including its engineering structures such as bridges, is stressed not only by natural ageing and corrosion but also by fatigue. The fatigue of material is accelerated by ... [more ▼]

Today’s traffic infrastructure, including its engineering structures such as bridges, is stressed not only by natural ageing and corrosion but also by fatigue. The fatigue of material is accelerated by the steadily growing traffic volume and heavier vehicles. Many bridges were built after World War 2 using the prestressed concrete construction method that emerged at that time. Some bridges are close to the end of the planned service life and show damage such as spalling, cracking and corrosion. In addition, some bridges have not yet reached the end of their planned service life and already exhibit damage. These bridges require special attention and control, knowing that this issue is highly safety and cost relevant at the same time. Structural Health Monitoring (SHM) of bridges aims to detect and localise damage as early as possible to take countermeasures to reach at least the planned service life or even more. Therefore, control systems are needed to support the engineers in addition to the visual bridge inspection. Permanent control systems can allow real time controlling of the bridge behaviour but generate high effort and cost. One approach in SHM is damage detection based on stiffness changes. Damage can alter both the static and modal properties of a structure. It leads to a loss of stiffness and, consequently, to greater static deflection and, in dynamics, to a decrease of eigenfrequencies. A prerequisite for early damage detection is essential information about the bridge structure, best knowledge and understanding of the individual bridge behaviour already in the undamaged state to track changes. This information can be obtained with experiments on a bridge and, in parallel, by simulation with a Finite Element (FE) model. In the next step, the FE model is updated to the measurements so that the reference state of the structure is well matched. The aim of the simulation is not the ultimate load bearing analysis, but the simulation of changes in the deflection line, eigenfrequencies, mode shapes and in the best case, also in the static or dynamic flexibility matrix and even better stiffness matrix due to damage. For this purpose, recurring measurements and simulations are compared with the initial measurements. If changes in the properties occur, model updating can be used to detect, localise and quantify damage. For the described approach, the detection and localisation of damage depend on the best possible reference state’s characteristics acquisition. The most commonly used construction method for bridges is prestressed concrete. Therefore, the main focus of this work is the recording of the undamaged reference state of a post tensioning bridge beam. The test object was a 26 m long prestressed concrete T-beam, which was saved before the demolition of the real bridge. It was subsequently installed outdoors on the campus of the University of Luxembourg as a simple supported real size test beam. Since the changes in static and dynamic system properties are not only due to damage but can also occur, for example, as a result of temperature fluctuations, the work focuses as well on the recording and assessment of influences arising from bearing and real environmental conditions in the undamaged reference state. For the temperature acquisition, the tests were carried out over around 2 years. Moreover, the influence of bearing conditions was tested by three interchangeable movable bearing types. The reference condition was recorded by static, quasi-static and dynamic tests. Throughout the observation period, the temperature and deflection of the bridge were continuously measured at different positions. For the deflection measurements, a commercial system was used that requires contact with the bridge. In addition, two new non-contact measurement approaches were tested. One is a camera-based system and the other is a laser-based system. The laser-based measurement method was improved during the recordings and tested by a second laser based system at the beam. Through the various tests, the deflections, eigenfrequencies and mode shapes of the bridge were determined. With the information of the experimental part, an FE model was created and best fitted to the reference state. The FE model consists mainly of solid elements. For a future model updating, a special FE model was created, offering a slice-by-slice adjustment of the beam stiffness. The model was used to perform static deformation and modal analysis. Then, the static and dynamic flexibility matrix was calculated and compared based on the experimental and numerical results. Finally, and in view of the subsequent artificial damage of the beam, damage scenarios are proposed based on the calculated cracking moment. [less ▲]

Large Scale Parallel Simulation For Extended Discrete Element Method

Doctoral thesis (2020)

Numerical models are commonly used to simulate or model physical processes such as weather forecasts, fluid action, rocket trajectory, building designs, or biomass combustion. These simulations are ... [more ▼]

Numerical models are commonly used to simulate or model physical processes such as weather forecasts, fluid action, rocket trajectory, building designs, or biomass combustion. These simulations are immensely complex and require a hefty amount of time and computation, making it impossible to run on a standard modern laptop in a reasonable and fair period. This research work targets large-scale and parallel simulations of DEM and DEM-CFD couplings using high-performance computing techniques and optimizations. This thesis aims to analyze, contribute, and apply the DEM approach using the XDEM multi-Physics toolbox to physical processes that have been reluctant to be used due to their required computational resources and time. The first step of this work is to analyze and investigate the performance bottlenecks of the XDEM software. Therefore, the latter has been profiled and some critical parts as the contact detection were identified as the main bottlenecks of the software. A benchmark has also been set up to assess each bottleneck part’s performance using a baseline case. This step is crucial as it defines the general guidelines to follow in optimizing any application in general. A complete framework has been developed from scratch and aims to test and compare several contact detection algorithms and implementations. The framework, which also has a parallel version, has been used to select an appropriate algorithm and implementation for the XDEM software. The link-cell approach, combined with a new Verlet list concept, proved to be the best option for significantly reducing the contact detection part’s computational time. The Verlet buffer concept developed during this thesis takes the particle flow regime into account when selecting the skin margin to enhance the algorithm’s efficiency further. In order to target the high-performance computers for large-scale simulations, a full hybrid distributed-shared memory parallelization has been introduced by adding a fine-grain OpenMP implementation layer to the existing MPI approach. A shared memory parallelization allows taking full advantage of personal workstations with modern CPU architecture. On the other hand, a hybrid approach is one of the best ways to fully exploit the computing node capacities of our modern CPU clusters that mainly have a NUMA architecture. Macro-benchmarking performance analysis showed that we could entirely exploit 80% (speed-up) of 85 computing nodes representing 2380 cores on the ULHPC supercomputer. Finally, a life-size biomass combustion furnace is developed and used as an application test to demonstrate the complex and heavy cases that the XDEM software can accommodate at this time. The furnace is the combustion chamber of a 16 MW geothermal steam super-heater, partoftheEnelGreenPower"Cornia2." powerplant located in Italy. It proves that DEM, in general, and XDEM in particular, can be used for real case applications that discourage users due to their complexity and especially the time required to deliver the outcome results. [less ▲]

Spice of life. How can we explore and measure the quality of life of children facing life-limiting conditions? Results and challenges of the MOSAIK study in Belgium.

Doctoral thesis (2020)

Taxation, Data and Destination - An Analysis of the Compatibility of a Digitalized Destination-Based Corporate Tax and a Destination-Based Cash-Flow Tax with International and EU Tax and Data Protection Law Frameworks

Doctoral thesis (2020)

The digitalized economy poses challenges and issues to traditional corporate taxation that require modifications in the way companies are taxed under international tax law. The thesis discusses two tax ... [more ▼]

The digitalized economy poses challenges and issues to traditional corporate taxation that require modifications in the way companies are taxed under international tax law. The thesis discusses two tax proposals to face some of the main issues, such as the intangibility of business assets and operations, the lack of physical presence of businesses in market jurisdictions, as well as non-taxation under both corporate income tax and value added tax in these jurisdictions. One of the tax proposals is the destination-based cash-flow tax that has been elaborated on mainly in economic literature. The other proposal has been drafted by the author and is named "digitalized destination-based corporate tax". The thesis analyzes the business and legal context in which the two taxes would operate: beyond the testing of the two model taxes against several digitalized business models, the relevant legal frameworks known in taxation and composed by double taxation conventions, EU law and WTO law are analyzed. Moreover, considering that the place of destination is determined by reference to the place of customers or users, corporate taxpayers likely need to collect and process (personal) data of these third parties in order to determine their place of tax liability. Thus, the thesis also examines potential data protection law interferences. [less ▲]

Pressure Sensing with Nematic Liquid Crystal and Carbon Nanotube Networks

Doctoral thesis (2020)

The study of colloidal dispersions of nanoparticles in liquid crystals (LCs) is well known. In most of the works, the particles are mixed into the LC to form suspensions with well-dispersed particles ... [more ▼]

The study of colloidal dispersions of nanoparticles in liquid crystals (LCs) is well known. In most of the works, the particles are mixed into the LC to form suspensions with well-dispersed particles. However, when nanoparticles are physically connected to form networks, the overall macroscopic properties of the ensemble are directly linked to the specific properties of the nanoparticles. Carbon nanotubes (CNTs) are excellent electrical conductors possessing extremely high aspect ratio, which results in a very low concentration threshold needed to obtain percolation. Therefore, they form conductive networks with extremely small amounts of CNTs. Another advantage of carbon nanotubes is their capability to transport large current densities without damage by electromigration, maintaining a stable resistance, and having scattering-less paths across several microns. Moreover, the electromechanical properties of CNTs make them an ideal candidate in pressure sensing technology. The doctoral thesis presented here describes two different approaches to integrate and utilise CNTs in an LC matrix. In the first case, we show that a variety of nanoparticles that are dispersed in LC can be attracted and assembled onto a LC defect line generated in a predetermined location, thereby creating a vertical interconnect of nanoparticles. The second consists of CNT sheets mechanically drawn from a CNT forest and an LC cell is then built on top, and the second consists of a template-based assembly of dispersed CNTs onto defect lines in LCs. In this case, we study the electrical and optical properties of CNT sheets in the presence and absence of liquid crystals based on their DC electrical characterization with distributed electrical contacts. Finally, we discuss how these two approaches can be used to successfully fabricate pressure-sensing devices. The pressure response in both these sensors is achieved based on the change in resistance of the CNTs, induced by the structural variations under the external applied pressure. Both the pressure sensors developed here are easy to fabricate, cost-effective, and recoverable owing to the elasticity and softness of the LC. [less ▲]

Recycling of gravel wash mud for manufacturing CO2-reduced cement

Doctoral thesis (2020)

The present research project “CO2REDCEM” is carried out at the Laboratory of Solid Structures (LSS) of the University of Luxembourg, in close collaboration with Luxembourgish industrial partners (Cimalux ... [more ▼]

The present research project “CO2REDCEM” is carried out at the Laboratory of Solid Structures (LSS) of the University of Luxembourg, in close collaboration with Luxembourgish industrial partners (Cimalux S.A., Carrières Feidt S.A. and Contern S.A.). This project aims at reducing the generation of CO2 emissions during cement production by minimisation of the use of cement clinker or its complete replacement by new binder compositions and concepts, containing novel material resources derived from local unused industrial waste products. Such a potential raw material is gravel wash mud (GWM), which occurs as a waste product from gravel mining. This clayey mud is collected from a sludge reservoir, located in the North West of Luxembourg. Currently, this waste product is landfilled without any further use. However, this prime material offers very promising properties, which require a thorough characterisation and verification before its revalorisation as a viable supplementary cementitious material (SCMs). Reusing or recycling of waste elements into goods has been among the greatest ambitions of our and earlier generations, and it will take a more important role in the future economy. One primary goal of this project is to replace the “end-of-life” concept of gravel wash mud by reusing it as new raw material. This endeavour will bring double benefit to environment as the waste is prevented from landfilling, and it is revalorised as a prime resource in another system.This research work shares the outcomes from the assessment of the performance of the prime material GWM within the following binder concepts and binder reaction mechanisms: • The use of gravel wash mud (GWM) powders as a precursor material for the synthesis of alkali-activated binders: A “cementless” binder is synthesised by alkaline activation of processed and calcined GWM powders. The mitigation of the CO2 emissions is achieved by the calcination process of the clayey gravel wash mud, which requires less thermal energy and thus lower energy consumption than for cement clinker production. • Substitution of Ordinary Portland Cement (OPC) by calcined GWM powders: Cement and concrete mixtures are prepared based on partial replacement of Portland cement by calcined GWM powders. This study presents the investigations on the involved reaction mechanisms (pozzolanic and cementitious hydration reactions), the optimal mixture configurations and the optimal material treatment processes. • The development of lime-Metakaolin-GWM binder concepts: Mixtures without cement are developed using GWM and other constituents, classified as industrial by-products. This research includes the mineralogical and microstructural characterisation of the constituents, the understanding of the reaction mechanism, and the optimisation of the mixtures to enhance the performance of the novel cementitious products. This thesis allowed to assess the performance of the waste product GWM as a valid pozzolanic prime material and to understand the requirements on physical, chemical and mineralogical characteristics of any potential raw material to ensure its permissibility as an alternative supplementary cementitious material (SCM). [less ▲]

Boosting Automated Program Repair for Adoption By Practitioners

Doctoral thesis (2020)

Automated program repair (APR) attracts a huge interest from research and industry as the ultimate target in automation of software maintenance. Towards realizing this automation promise, the research ... [more ▼]

Automated program repair (APR) attracts a huge interest from research and industry as the ultimate target in automation of software maintenance. Towards realizing this automation promise, the research community has explored various ideas and techniques, which are increasingly demonstrating that APR is no longer fictional. Although literature techniques constantly set new records in fixing a significant fraction of defects within well-established benchmarks, we are not aware of large-scale adoption of APR in practice. Meanwhile, open-source and commercial organizations have started to reflect on the potential of integrating some automated steps in the software development cycle. Actually, the current practice has several development settings that use a number of tools to automate and systematize various tasks such as code style checking, bug detection, and systematic patching. Our work is motivated by this fact. We advocate that systematic and empirical exploration of the current practice that leverage tools to automate debugging tasks would provide valuable insights for rethinking and boosting the APR agenda towards its acceptability by developer communities. We have identified three investigation axes in this dissertation. First, mining software repositories towards understanding code change properties that could be valuable to guide program repair. Second, analyzing communication channels in software development in order to assess to what extent they could be relevant in a real-world program repair scenario. Third, exploring generic concepts of patching in the literature for establishing a common foundation for program repair pipelines that can be integrated with industrial settings. This dissertation makes the following contributions to the community: • An empirical study of tool support in a real development setting providing concrete insights on the acceptance, stability and the nature of bugs being fixed by manually-craft patches vs tool-supported patches and manifests opportunities for improving automated repair techniques. • A novel information retrieval based bug localization approach that learns how to compute the similarity scores of various types of features. • An automated mining strategy to infer fix pattern that can be integrated to automated program repair pipelines. • A practical bug report driven program repair pipeline. [less ▲]

Tertium non datur: Various aspects of value-added (VA) models used as measures of educational effectiveness

Doctoral thesis (2020)

Value-added (VA) models are used as measures of educational effectiveness which aim to find the “value” that has been added by teachers or schools to students’ achievement, independent of students’ ... [more ▼]

Value-added (VA) models are used as measures of educational effectiveness which aim to find the “value” that has been added by teachers or schools to students’ achievement, independent of students’ backgrounds. Statistically speaking, teacher or school VA scores are calculated as the part of an outcome variable that cannot be explained by the covariates that are in the VA model (i.e., the residual). Teachers or schools are classified as effective (or ineffective) if they have a positive (or negative) effect on students’ achievement compared to a previously specified norm value. Although VA models have gained popularity in recent years, there is a lack of consensus concerning various aspects of VA scores. The present dissertation aims at shedding light on these aspects, including the state of the art of VA research in the international literature, covariate choice, and model selection for the estimation of VA scores. In a first step, a systematic literature review was conducted, in which 370 studies from 26 countries were classified, focusing on methodological issues (Study 1 of the present dissertation). Results indicated no consensus concerning the applied statistical model type (the majority applied a linear regression, followed by multilevel models). Concerning the covariate choice, most studies used prior achievement as a covariate, cognitive and/or motivational student data were hardly considered, and there was no consensus on the in- or exclusion of students’ background variables. Based on these findings, it was suggested that VA models are better suited to improve the quality of teaching than for accountability and decision-making purposes. Secondly, based on one of the open questions resulting from Study 1 (i.e., covariate choice), the aim of Study 2 was to systematically compare different covariate combinations in the estimation of school VA models. Based on longitudinal data from primary school students participating in the Luxembourg School Monitoring Programme in Grades 1 and 3, three covariate sets were found to be essential when calculating school VA scores with math or language achievement as dependent variables: prior language achievement, prior math achievement, and students’ sociodemographic and sociocultural background. However, the evaluation of individual schools’ effectiveness varied widely depending on the covariate set that was chosen, casting further doubt on the use of VA scores for accountability purposes. Thirdly, the aim of Study 3 was to investigate statistical model selection, as Study 1 showed no consensus on which model types are most suitable for the estimation of VA scores, with the majority of studies applying linear regression or multilevel models. These classical linear models, along with nonlinear models and different types of machine learning models were systematically compared to each other. Covariates were kept constant (based on the results from Study 2) across models. Multilevel models led to the most accurate prediction of students’ achievement. However, as school VA scores varied depending on specific model choices and as these results can be only generalized for a Luxembourgish sample, it was suggested for future research that the model selection process should be made transparent and should include different specifications in order to obtain ranges of potential VA scores. In conclusion, all three studies imply that the application of VA models for decision-making and accountability should be critically discussed and that VA scores should not be used as the only measure for accountability or high-stakes decisions. In addition, it can be concluded that VA scores are more suitable for informative purposes. Thus, the findings from the present dissertation prepare the ground for future research, where schools with stable high VA scores can be part of further investigations (both qualitatively and quantitatively) to study their pedagogical strategies and learn from them. [less ▲]

A newform theory for Katz modular forms

Doctoral thesis (2020)

In this thesis, a strong multiplicity one theorem for Katz modular forms is studied. We show that a cuspidal Katz eigenform which admits an irreducible Galois representation is in the level and weight old ... [more ▼]

In this thesis, a strong multiplicity one theorem for Katz modular forms is studied. We show that a cuspidal Katz eigenform which admits an irreducible Galois representation is in the level and weight old space of a uniquely associated Katz newform. We also set up multiplicity one results for Katz eigenforms which have reducible Galois representation. [less ▲]

Immersions of surfaces into SL(2,C) and into the space of geodesics of Hyperbolic space

Doctoral thesis (2020)

This thesis mainly treats two developments of the classical theory of hypersurfaces inside pseudo-Riemannian space forms. The former - a joint work with Francesco Bonsante - consists in the study of ... [more ▼]

This thesis mainly treats two developments of the classical theory of hypersurfaces inside pseudo-Riemannian space forms. The former - a joint work with Francesco Bonsante - consists in the study of immersions of smooth manifolds into holomorphic Riemannian space forms of constant curvature -1 (including SL(2,C) with a multiple of its Killing form): this leads to a Gauss-Codazzi theorem, it suggests an approach to holomorphic transitioning of immersions into pseudo-Riemannian space forms, a trick to construct holomorphic maps into the PSL(2,C)-character variety, and leads to a restatement of Bers theorem. The latter - a joint work with Andrea Seppi - consists in the study of immersions of n-manifolds inside the space of geodesics of the hyperbolic (n+1)-space. We give a characterization, in terms of the para-Kahler structure of this space of geodesics, of the Riemannian immersions which turn out to be Gauss maps of equivariant immersions into the hyperbolic space. [less ▲]

van der Waals Dispersion Interactions in Biomolecular Systems: Quantum-Mechanical Insights and Methodological Advances

Doctoral thesis (2020)

Intermolecular interactions are paramount for the stability, dynamics and response of systems across chemistry, biology and materials science. In biomolecules they govern secondary structure formation ... [more ▼]

Intermolecular interactions are paramount for the stability, dynamics and response of systems across chemistry, biology and materials science. In biomolecules they govern secondary structure formation, assembly, docking, regulation and functionality. van der Waals (vdW) dispersion contributes a crucial part to those interactions. As part of the long-range electron correlation, vdW interactions arise from Coulomb-coupled quantum-mechanical fluctuations in the instan- taneous electronic charge distribution and are thus inherently many-body in nature. Common approaches to describe biomolecular systems (i.e., classical molecular mechanics) fail to capture the full complexity of vdW dispersion by adapting a phenomenological, atom-pairwise formalism. This thesis explores beyond-pairwise vdW forces and the collectivity of intrinsic electronic behav- iors in biomolecular systems and discusses their role in the context of biomolecular processes and function. To this end, the many-body dispersion (MBD) formalism parameterized from density-functional tight-binding (DFTB) calculations is used. The investigation of simple molecular solvents with particular focus on water gives insights into the vdW energetics and electronic response properties in liquids and solvation as well as emergent behavior for coarse-grained models. A detailed study of intra-protein and protein–water vdW interactions highlights the role of many-body forces during protein folding and provides a funda- mental explanation for the previously observed “unbalanced” description and over-compaction of disordered protein states. Further analysis of the intrinsic electronic behaviors in explicitly solvated proteins indicates a long-range persistence of electron correlation through the aque- ous environment, which is discussed in the context of protein–protein interactions, long-range coordination and biomolecular regulation and allostery. Based on the example of a restriction enzyme, the potential role of many-body vdW forces and collective electronic behavior for the long-range coordination of enzymatic activity is discussed. Introducing electrodynamic quantum fluctuations into the classical picture of allostery opens up the path to a more holistic view on biomolecular regulation beyond the traditional focus on merely local structural modifications. Building on top of the MBD framework, which describes vdW dispersion within the interatomic dipole-limit, a practical extension to higher-order terms is presented. The resulting Dipole- Correlated Coulomb Singles account for multipolar as well as dispersion-polarization-like contri- butions beyond the random phase approximation by means of first-order perturbation theory over the dipole-coupled MBD state. It is shown that Dipole-Correlated Coulomb Singles become particularly relevant for relatively larger systems and can alter qualitative trends in the long-range interaction under (nano-)confinement. Bearing in mind the frequent presence of confinement in biomolecular systems due to cellular crowding, in ion channels or for interfacial water, this so-far neglected contribution is expected to have broad implications for systems of biological relevance. Ultimately, this thesis introduces a hybrid approach of DFTB and machine learning for the accu- rate description of large-scale systems on a robust, albeit approximate, quantum-mechanical level. The developed DFTB-NN rep approach combines the semi-empirical DFTB Hamiltonian with a deep tensor neural network model for localized many-body repulsive potentials. DFTB- NN rep provides an accurate description of energetic, structural and vibrational properties of a wide range of small organic molecules much superior to standard DFTB or machine learning. Overall, this thesis aims to extend the current view of complex (bio)molecular systems being governed by local, (semi-)classical interactions and develops methodological steps towards an advanced description and understanding including non-local interaction mechanisms enabled by quantum-mechanical phenomena such as long-range correlation forces arising from collective electronic fluctuations. [less ▲]

End-to-end Signal Processing Algorithms for Precoded Satellite Communications

Doctoral thesis (2020)

The benefits of full frequency reuse in satellite communications consist of increased spectral efficiency, physical layer security, enhanced coverage, and improved Quality of Service. This is possible due ... [more ▼]

The benefits of full frequency reuse in satellite communications consist of increased spectral efficiency, physical layer security, enhanced coverage, and improved Quality of Service. This is possible due to novel digital signal processing techniques for interference mitigation as well as signal predistortion in non-linear high-performance amplifiers. Advanced linear precoding and symbol-level precoding can jointly address the signal processing demands in the next-generation satellite communications. The real-time signal precoding increases the computational complexity handled at the gateway, thus requiring low-complexity high-performance algorithms to be developed. Additionally, extensive in-lab and field tests are required to increase the technology readiness level and industrial adaption rate. In this thesis, we focus on low-complexity precoding design and in-lab validations. We study the state-of-the-art linear and symbol-level precoding techniques and multi-user MIMO test-beds available in the literature. First, we present a novel low-complexity algorithm for sum power minimization precoding design. This technique allows to reduce transmitted power in a multi-beam satellite system and improves the quality of the received signal at user terminals. Next, we demonstrate an FPGA accelerated high-throughput precoding design. The FPGA precoding design is scalable for a different number of beams in the systems and operates in a real-time processing regime using a commercially available software defined radio platform. One of the highlights of this research is the creation of a real-time in-lab precoding test-bed. The test-bed consists of a DVB-S2X precoding enabled gateway prototype, a MIMO channel emulator, and user terminals. By using the radio frequency for transmitting and receiving the precoded signals, we can test the performance of different precoding techniques in realistic scenarios and channel impairments. We demonstrate an end-to-end symbol-level precoded real-time transmission, in which user terminals can acquire and decode the precoded signals showing an increase in performance and throughput. The in-lab validations confirm numerical results conducted alongside in this work. [less ▲]

Argument Acceptance and Commitment in Formal Argumentation

Doctoral thesis (2020)

Instruction Coverage for Android App Testing and Tuning

Doctoral thesis (2020)

For many people, mobile apps have already become an indispensable part of modern life. Apps entertain, educate, assist us in our daily routines and help us connect with others. However, the advanced ... [more ▼]

For many people, mobile apps have already become an indispensable part of modern life. Apps entertain, educate, assist us in our daily routines and help us connect with others. However, the advanced capabilities of modern devices running the apps and sensitive user data make mobile devices also an attractive attack target. To get access to sensitive data, adversaries tend to conceal malicious functionality in freely distributed legitimately-looking apps. The problem of low-quality and malicious apps, spreading at an enormous scale, is especially relevant for one of the biggest software repositories – Google Play. The Android apps distributed through this platform undergo a validation process by Google. However, that is insufficient to confirm their good nature. To identify dangerous apps, novel frameworks for testing and app analysis are being developed by the Android community. Code coverage is one of the most common metrics for evaluating the effectiveness of these frameworks, and it is used as an internal metric to guide code exploration in some of them. However, when analyzing apps without source code, the Android community relies mostly on method coverage since there are no reliable tools for measuring finer-grained code coverage in 3rd-party Android app testing. Another stumbling block for testing frameworks is the inability to test an app exhaustively. While code coverage measurement can indicate an improvement in testing, it is neither possible to reach 100% coverage nor to identify the maximum reachable coverage value for the app. Despite testing, the app still contains high amounts of not executed code, which makes it impossible to confirm the absence of potentially malicious code in the part of the app that has not been tested. The existing static debloating approaches aim at app size minimization rather than security and simply debloat not reachable code. However, there is currently no approach to debloat apps based on dynamic analysis information, i.e. to cut out not-executed code. In this dissertation, we solve these two problems by, first, proposing an efficient approach and a tool to measure code coverage at the instruction level, and second, a dynamic binary shrinking methodology for deleting not executed code from the app. We support our solutions by the following contributions: - An instrumentation approach to measure code coverage at the instruction level. Our technique instruments smali representation of Android bytecode to allow code coverage measurement at the finest level. - An implementation of the instrumentation approach. ACVTool is a self-contained package containing 4K lines of Python code. It is publicly available and can be integrated into different testing frameworks. - An extensive empirical evaluation that shows the high reliability and versatility of our approach. ACVTool successfully executes on 96.9% of apps from our dataset, introduces a negligible instrumentation time and runtime overheads, and its results are complaint to the results of JaCoCo (source code coverage) and Ella (method coverage) tools. - A detailed study on the influence of code coverage metric granularity on automated testing. We demonstrate the usefulness of ACVTool for automated testing techniques that rely on code coverage data in their operation. - A dynamic debloating approach based on ACVTool instruction coverage. We propose Dynamic Binary Shrinking System, a novel methodology created to shrink 3rd-party Android apps towards observed benign functionality on executed code. - An implementation of the dynamic debloating technique incorporated into the ACVCut tool. The tool demonstrates the viability of the Dynamic Shrinking System on two examples. It allows us to cut out not executed code and, thus, provide 100% instruction coverage on explored app behaviors. [less ▲]

Scalable Control of Asynchronous Boolean Networks

Doctoral thesis (2020)

Direct cell reprogramming has been garnering attention for its therapeutic potential for treating the most devastating diseases characterised by defective cells or a deficiency of certain cells. It is ... [more ▼]

Direct cell reprogramming has been garnering attention for its therapeutic potential for treating the most devastating diseases characterised by defective cells or a deficiency of certain cells. It is capable of reprogramming any kind of abundant cells in the body into the desired cells to restore functions of the diseased organ. It has shown promising benefits for clinical applications, such as cell and tissue engineering, regenerative medicine and drug discovery. A major obstacle in the application of direct cell reprogramming lies in the identification of effective reprogramming factors. Experimental approaches are usually laborious, time-consuming and enormously expensive. Mathematical modelling of biological systems paves the way to study mechanisms of biological processes and identify therapeutic targets with computational reasoning and tools. Among several modelling frameworks, Boolean networks have apparent advantages. They provide a qualitative description of biological systems and thus evade the parametrisation problem, which often occurs in quantitative models. In this thesis, we focus on the identification of reprogramming factors based on asynchronous Boolean networks. This problem is equivalent to the control of asynchronous Boolean networks: finding a subset of nodes, whose perturbations can drive the dynamics of the network from the source state (the initial cell type) to the target attractor (the desired cell type). Before diving into the control problems, we first develop a near-optimal decomposition method and use this method to improve the scalability of the decomposition-based method for attractor detection. The new decomposition-based attractor detection method can identify all the exact attractors of the network efficiently, such that we can select the proper attractors corresponding to the initial cell type and the desired cell type as the source and target attractors and predict the key nodes for the conversion. Depending on whether the source state is given or not, we can have two control problems: source-target control and target control. We develop several methods to solve the two problems using different control strategies. All the methods are implemented in our software CABEAN. Given a control problem, CABEAN can provide a rich set of realistic solutions that manipulate the dynamics in different ways, such that biologists can select suitable ones to validate with biological experiments. We believe our works can contribute to a better understanding of the regulatory mechanisms of biological processes and greatly facilitate the development of direct cell reprogramming. [less ▲]

JOINT DESIGN OF USER SCHEDULING AND PRECODING IN WIRELESS NETWORKS: A DC PROGRAMMING APPROACH

Doctoral thesis (2020)

These scenarios are of relevance and are already being considered in current and upcoming standards including 4G and 5G. This thesis begins by presenting the necessity of the joint design of scheduling ... [more ▼]

These scenarios are of relevance and are already being considered in current and upcoming standards including 4G and 5G. This thesis begins by presenting the necessity of the joint design of scheduling and precoding for the aforementioned scenario in detail in chapter 1. Further, the coupled nature of scheduling and precoding that prevails in many other designs is discussed. Following this, a detailed survey of the literature dealing with the joint design is presented. In chapter 2, the joint design of scheduling and precoding in the unicast scenario for multiuser MISO downlink channels for network functionality optimization considering sum-rate, Max-min SINR, and power. Thereafter, different challenges in terms of the problem formulation and subsequent reformulations for different metrics are discussed. Different algorithms, each focusing on optimizing the corresponding metric, are proposed and their performance is evaluated through numerical results. In chapter 3, the joint design of user grouping, group scheduling, user scheduling, and precoding is considered for MGMC. Differently to chapter 2, the optimization of a novel metric called multicast energy efficiency (MEE) is considered. This new paradigm for joint design in MGMC poses several additional challenges that can not be dealt with by the design in chapter 2. Therefore, towards addressing these additional challenges, a novel algorithm is proposed for MEE maximization and its efficacy is presented through simulations. In chapters 2 and 3, the joint design is considered within a given transmit slot and temporal design is not considered. In chapter 4, the joint design scheduling and precoding are considered over a block of multiple time slots for a unicast scenario. Differently to single slot design, the multi-slot joint design facilitates to address users' latency directly in terms of time slots. Noticing this, joint design across multiple slots is considered with the objective of minimizing the number of slots to serve all the users subject to users' QoS and latency constraints. Further, this multi-slot joint design problem is modeled as a structured group sparsity problem. Finally, by rendering the problem as a DC, high-quality stationary points are obtained through an efficient CCP based algorithm. In chapter 5, the joint scheduling and precoding schemes proposed in previous chapters are applied to satellite systems. Finally, The thesis concludes with the main research findings and the identification of new research challenges in chapter 6. [less ▲]

Problems in nonequilibrium fluctuations across scales: A path integral approach

Doctoral thesis (2020)

In this thesis we study stochastic systems evolving with Markov jump processes. In a first work we discuss different representations of the stochastic evolution: the master equation, the generalized ... [more ▼]

In this thesis we study stochastic systems evolving with Markov jump processes. In a first work we discuss different representations of the stochastic evolution: the master equation, the generalized Langevin equation, and their path integrals. The description is used to derive the generating functions for out of equilibrium observables, together with the typical approximation techniques. In a second work the path integral is used to enforce thermodynamic consistency across scales. The description of identical units with all-to-al interactions is reduced from a micro- to a meso- to a macroscopic level. A suitable scaling of the dynamics and of the thermodynamic observables allows to preserve the thermodynamical structure at the different levels. In a third work we focus on the large deviation properties of chemical networks. The path integral allows to compute the dominant trajectories that constitute macroscopic fluctuations. For bi-stable systems the existence of multiple macroscopic contributions results in a phase transition for the macroscopic current. In a fourth work we study the response of such chemical currents to external perturbations. Out of equilibrium the system can display negative differential response, a feature that offers different strategies to minimize external or internal disturbances. Finally, in a fifth work, we start from a quantum system where part of the system can be traced out to act as multiple reservoirs at different temperatures. Using the Schwinger-Keldysh contour and Green's functions we can obtain the generating function for the different parts of the hamiltonian. The statistics of thermodynamic observables is accessible even in the strong coupling regime, while the semi-classical approximation is in agreement with the classical counterpart. [less ▲]

Analysis, Detection, and Prevention of Cryptographic Ransomware

Doctoral thesis (2020)

Cryptographic ransomware encrypts files on a computer system, thereby blocks access to victim’s data, until a ransom is paid. The quick return in revenue together with the practical difficulties in ... [more ▼]

Cryptographic ransomware encrypts files on a computer system, thereby blocks access to victim’s data, until a ransom is paid. The quick return in revenue together with the practical difficulties in accurately tracking cryptocurrencies used by victims to perform the ransom payment, have made ransomware a preferred tool for cybercriminals. In addition, exploiting zero-day vulnerabilities found in Windows Operating Systems (OSs), the most widely used OS on desktop computers, has enabled ransomware to extend its threat and have detrimental effects at world-wide level. For instance, WannaCry and NotPetya have affected almost all countries, impacted organizations, and the latter alone caused damage which costs more than $10 billion. In this thesis, we conduct a theoretical and experimental study on cryptographic ransomware. In the first part, we explore the anatomy of a ransomware, and in particular, analyze the key management strategies employed by notable families. We verify that for a long-term success, ransomware authors must acquire good random numbers to seed Key Derivation Functions (KDFs). The second part of this thesis analyzes the security of the current anti-ransomware approaches, both in academic literature and real-world systems, with the aim to anticipate how such future generations of ransomware will work, and in order to start planning on how to stop them. We argue that among them, there will be some which will try to defeat current anti-ransomware; thus, we can speculate over their working principles by studying the weak points in the strategies that six of the most advanced anti-ransomware currently implements. We support our speculations with experiments, proving at the same time that those weak points are in fact vulnerabilities and that the future ransomware that we have imagined can be effective. Next, we analyze existing decoy strategies and discuss how they are effective in countering current ransomware by defining a set of metrics to measure their robustness. To demonstrate how ransomware can identify existing deception-based detection strategies, we implement a proof-of-concept decoy-aware ransomware that successfully bypasses decoys by using a decision engine with few rules. We also discuss existing issues in decoy-based strategies and propose practical solutions to mitigate them. Finally, we look for vulnerabilities in antivirus (AV) programs which are the de facto security tool installed at computers against cryptographic ransomware. In our experiments with 29 consumer-level AVs, we discovered two critilcal vulnerabilities. The first one consists in simulating mouse events to control AVs, namely to send them mouse “clicks” to deactivate their protection. We prove that 14 out of 29 AVs can be disabled in this way, and we call this class of attacks Ghost Control. The second one consists in controlling whitelisted applications, such as Notepad, by sending them keyboard events (such as “copy-and-paste”) to perform malicious operations on behalf of the malware. We prove that the anti-ransomware protection feature of AVs can be bypassed if we use Notepad as a “puppet” to rewrite the content of protected files as a ransomware would do. Playing with the words, and recalling the cat-and-mouse game, we call this class of attacks Cut-and-Mouse. In the third part of the thesis, we propose a strategy to mitigate cryptographic ransomware attacks. Based on our insights from the first part of the thesis, we present UShallNotPass which works by controlling access to secure randomness sources, i.e., Cryptographically Secure Pseudo-Random Number Generator (CSPRNG) Appliction Programming Interfaces (APIs). We tested UShallNotPass against 524 real-world ransomware samples, and observe that UShallNotPass stops 94% of them, including WannaCry, Locky, CryptoLocker and CryptoWall. Remarkably, it also nullifies NotPetya, the offspring of the family which so far has eluded all defenses. Next, we present NoCry, which shares the same defense strategy but implements an improved architecture. We show that NoCry is more secure (with components that are not vulnerable to known attacks), more effective (with less false negatives in the class of ransomware addressed) and more efficient (with minimal false positive rate and negligible overhead). To confirm that the new architecture works as expected, we tested NoCry against a new set of 747 ransomware samples, of which, NoCry could stop 97.1%, bringing its security and technological readiness to a higher level. Finally, in the fourth part, we present the potential future of the cryptographic ransomware. We identify new possible ransomware targets inspired by the cybersecurity incidents occurred in real-world scenarios. In this respect, we described possible threats that ransomware may pose by targeting critical domains, such as the Internet of Things and the Socio-Technical systems, which will worrisomely amplify the effectiveness of ransomware attacks. Next, we looked into whether ransomware authors re-use the work of others, available at public platforms and repositories, and produce insecure code (which might enable to build decryptors). By methodically reverse-engineering malware executables, we have found that, out of 21 ransomware samples, 9 contain copy-paste code from public resources. From this fact, we recall critical cases of code disclosure in the recent history of ransomware and, reflect on the dual-use nature of this research by arguing that ransomware are components in cyber-weapons. We conclude by discussing the benefits and limits of using cyber-intelligence and counter-intelligence strategies that could be used against this threat. [less ▲]

AN NLP-BASED FRAMEWORK TO FACILITATE THE DERIVATION OF LEGAL REQUIREMENTS FROM LEGAL TEXTS

Doctoral thesis (2020)

Information systems in several regulated domains (e.g., healthcare, taxation, labor) must comply with the applicable laws and regulations. In order to demonstrate compliance, several techniques can be ... [more ▼]

Information systems in several regulated domains (e.g., healthcare, taxation, labor) must comply with the applicable laws and regulations. In order to demonstrate compliance, several techniques can be used for assessing that such systems meet their specified legal requirements. Since requirements analysts do not have the required legal expertise, they often rely on the advisory of legal professionals. Hence, this paramount activity is expensive as it involves numerous professionals. Add to this, the communication gap between all the involved stakeholders: legal professionals, requirements analysts and software engineers. Several techniques attempt to bridge this communication gap by streamlining this process. A promising way to do so is through the automation of legal semantic metadata extraction and legal requirements elicitation from legal texts. Typically, one has to search legal texts for the relevant information for the IT system at hand, extract the legal requirements entailed by these legal statements that are pertinent to the IT system, and validate the conclusiveness and correctness of the finalized set of legal requirements. Nevertheless, the automation of legal text processing raises several challenges, especially when applied to IT systems. Existing Natural Language Processing (NLP) techniques are not built to handle the peculiarities of legal texts. On the one hand, NLP techniques are far from perfect in handling several linguistic phenomena such as anaphora, word sense disambiguation and delineating the addressee of the sentence. Add to that, the performance of these NLP techniques decreases when applied to foreign languages (other than English). On the other hand, legal text is far from being identical to the formal language used in journalism. We note that the most prominent NLP techniques are developed and tested against a selection of newspapers articles. In addition, legal text introduces cross-references and legalese that are paramount to proper legal analysis. Besides, there is still some work to be done concerning topicalization, which we need to consider for the relevance of legal statements. Existing techniques for streamlining the compliance checking of IT systems often rely on code-like artifacts with no intuitive appeal to legal professionals. Subsequently, one has no practical way to double-check with legal professionals that the elicited legal requirements are indeed correct and complete regarding the IT system at hand. Further, manually eliciting the legal requirements is an expensive, tedious and error-prone activity. The challenge is to propose a suitable knowledge representation that can be easily understood by all the involved stakeholders but at the same time remains cohesive and conclusive enough to enable the automation of legal requirements elicitation. In this dissertation, we investigate to which extent one can automate legal processing in the Requirements Engineering context. We focus exclusively on legal requirements elicitation for IT systems that have to conform to prescriptive regulations. All our technical solutions have been developed and empirically evaluated in close collaboration with a government entity. [less ▲]

Discursive Input/Output Logic: Deontic Modals, and Computation

Doctoral thesis (2020)

Staging the Nation in an Intermediate Space: Cultural Policy in Luxembourg and the State Museums (1918-1974)

Doctoral thesis (2020)

Cultural policy has been analysed from various perspectives, ranging from sociology over cultural studies to political science. Historians have also been interested in cultural policy, but they have ... [more ▼]

Cultural policy has been analysed from various perspectives, ranging from sociology over cultural studies to political science. Historians have also been interested in cultural policy, but they have barely reflected on a theoretical framework. In addition, cultural policy has not been thoroughly researched in Luxembourg. The present thesis aims to contribute to this gap and examines how national cultural policy in Luxembourg evolved from the 1920s to the early 1970s. It investigates the presence of the national idea in cultural policy, and possible tensions and connections between the idea of the nation and the use or inclusion of foreign cultural references. Drawing on the concept of Zwischenraum (intermediate space) coined by the historian Philip Ther, the study considers Luxembourg as a nationalised intermediate space with the tensions that this status entails. Furthermore, it investigates how the State Museums, particularly the history section, evolved in the cultural policy context. To analyse the evolution of cultural policy, three interconnected aspects are considered: structures, actors and discourses. Three main periods are considered in a chronological fashion: the interwar period marked by efforts of nation-building and an increasingly interventionist state; the Nazi occupation of Luxembourg (1940-1944), when the idea of an independent nation-state was turned into its opposite; the post-war period until the early 1970s, subdivided into an immediate post-war period marked by restitution and reconstruction, and the 1950s and the 1960s characterised by a state-administrator and a conservative cultural policy. These periods, however, are not always neatly separable and reveal continuities. For each period, the State Museums are analysed in their cultural policy context: from their construction in the age of nation-building, over their ambiguous situation during Nazi occupation, to their new missions in the post-war period. [less ▲]

From Secure to Usable and Verifiable Voting Schemes

Doctoral thesis (2020)

Elections are the foundations of democracy. To uphold democratic principles, researchers have proposed systems that ensure the integrity of elections. It is a highly interdisciplinary field, as it can be ... [more ▼]

Elections are the foundations of democracy. To uphold democratic principles, researchers have proposed systems that ensure the integrity of elections. It is a highly interdisciplinary field, as it can be studied from a technical, legal or societal points of view. While lawyers give a legal framework to the voting procedures, security researchers translate these rules into technical properties that operational voting systems must satisfy, notably privacy and verifiability. If Privacy aims to protect vote-secrecy and provide coercion-resistance to the protocol, Verifiability allows voters to check that their vote has been taken into account in the general outcome, contributing to the assurance of the integrity of the elections. To satisfy both properties in a voting system, we rely on cryptographic primitives such as encryption, signatures, commitments schemes, or zero-knowledge proofs, etc. Many protocols, paper-based or electronic-based, have been designed to satisfy these properties. Although the security of some protocols, and their limits, have been analysed from a technical perspective, the usability has often been shown to have very low rates of effectiveness. The necessary cryptographic interactions have already shown to be one contributor to this problem, but the design of the interface could also contribute by misleading voters. As elections typically rarely happen, voters must be able to understand the system they use quickly and mostly without training, which brings the user experience at the forefront of the designed protocols. In this thesis, the first contribution is to redefine privacy and verifiability in the context of tracker-based verifiable schemes. These schemes, using a so-called tracking number for individual verification, need additional user steps that must be considered in the security evaluation. These security definitions are applied to the boardroom voting protocol F2FV used by the CNRS, and the e-voting protocol Selene, both use a tracker-based procedure for individual verifiability. We provide proofs of security in the symbolic model using the Tamarin prover. The second contribution is an implementation of the Selene protocol as a mobile and a web application, tested in several user studies. The goal is to evaluate the usability and the overall user experience of the verifiability features, as well as their understanding of the system through the evaluation of mental models. The third contribution concerns the evaluation of the voters' understanding of the coercion mitigation mechanism provided by Selene, through a unique study design using game theory for the evaluation of voters. Finally, the fourth contribution is about the design of a new voting scheme, Electryo, that is based on the Selene verification mechanisms but provides a user experience close to the standard paper-based voting protocols. [less ▲]

Analyzing and Improving Very Deep Neural Networks: From Optimization, Generalization to Compression

Doctoral thesis (2020)

Learning-based approaches have recently become popular for various computer vision tasks such as facial expression recognition, action recognition, banknote identification, image captioning, medical image ... [more ▼]

Learning-based approaches have recently become popular for various computer vision tasks such as facial expression recognition, action recognition, banknote identification, image captioning, medical image segmentation, etc. The learning-based approach allows the constructed model to learn features, which result in high performance. Recently, the backbone of most learning-based approaches are deep neural networks (DNNs). Importantly, it is believed that increasing the depth of DNNs invariably leads to improved generalization performance. Thus, many state-of-the-art DNNs have over 30 layers of feature representations. In fact, it is not uncommon to find DNNs with over 100 layers in the literature. However, training very DNNs that have over 15 layers is not trivial. On one hand, such very DNNs generally suffer optimization problems. On the other hand, very DNNs are often overparameterized such that they overfit the training data, and hence incur generalization loss. Moreover, overparameterized DNNs are impractical for applications that require low latency, small Graphic Processing Unit (GPU) memory for operation and small memory for storage. Interestingly, skip connections of various forms have been shown to alleviate the difficulty of optimizing very DNNs. In this thesis, we propose to improve the optimization and generalization of very DNNs with and without skip connections by reformulating their training schemes. Specifically, the different modifications proposed allow the DNNs to achieve state-of-the-art results on several benchmarking datasets. The second part of the thesis presents the theoretical analyses of DNNs without and with skip connections based on several concepts from linear algebra and random matrix theory. The theoretical results obtained provide new insights into why DNNs with skip connections are easy to optimize, and generalize better than DNNs without skip connections. Ultimately, the theoretical results are shown to agree with practical DNNs via extensive experiments. The third part of the thesis addresses the problem of compressing large DNNs into smaller models. Following the identified drawbacks of the conventional group LASSO for compressing large DNNs, the debiased elastic group least absolute shrinkage and selection operator (DEGL) is employed. Furthermore, the layer-wise subspace learning (SL) of latent representations in large DNNs is proposed. The objective of SL is learning a compressed latent space for large DNNs. In addition, it is observed that SL improves the performance of LASSO, which is popularly known not to work well for compressing large DNNs. Extensive experiments are reported to validate the effectiveness of the different model compression approaches proposed in this thesis. Finally, the thesis addresses the problem of multimodal learning using DNNs, where data from different modalities are combined into useful representations for improved learning results. Different interesting multimodal learning frameworks are applied to the problems of facial expression and object recognition. We show that under the right scenarios, the complementary information from multimodal data leads to better model performance. [less ▲]

A Systems biology approach to elucidate the contribution of alpha-synuclein to early in vitro phenotypes of Parkinson’s disease

Doctoral thesis (2020)

Although Parkinson's disease (PD was first described more than two hundred years ago, the clinical treatment options remain limited to symptom alleviation. Consequently, understanding the underlying ... [more ▼]

Although Parkinson's disease (PD was first described more than two hundred years ago, the clinical treatment options remain limited to symptom alleviation. Consequently, understanding the underlying molecular mechanisms is vital for the development of new therapeutic strategies. Most cases of PD are associated with toxic aggregations of the alpha-synuclein (α-syn) protein. However, the physiological and pathological mechanisms of α-syn aggregation are not entirely understood. One main reason for this knowledge gap is the lack of models that properly recapitulate the pathology in a human-midbrain-like context. Organoid models have emerged as an attractive model system that covers key aspects of in vivo tissue and organ complexity. Here, we present an optimized organoid protocol, which recapitulates features of the human midbrain. These human midbrain organoids (hMOs) present reduced levels of cell death in the core, while exhibiting reduced variability and increased viability. Their smaller size also allowed the implementation of a time-efficient image analysis technique. By using the protocol mentioned above, we generated hMOs from patient-derived induced pluripotent stem cells (iPSCs harboring a triplication of the SNCA gene (3xSNCA. 3xSNCAexhibited twice the levels of α-syn protein compared to wild type (WT) hMOs. Transcriptionalanalysis of 3xSNCA hMOs showed upregulation of PD- and SNCA-associated genes, as wellas transcriptional deregulations in neurogenesis, cell death, proliferation, and synapse formation. The analysis of cellular phenotypes in patient-specific hMOs supported these genetic observations. 3xSNCA hMOs presented reduced proliferation, cell death and reduced synapse count in mature organoids. Furthermore, 3xSNCA hMOs showed a reduced total number of neurons and impaired astrocytic differentiation. In addition, analysis of transcriptional and metabolomic data showed deregulation in metabolic pathways. To further analyze and explain our results, we used the latest human metabolic reconstruction (Recon3D) to generate an in silico model. The results presented here are a systematic analysis of patient-specific phenotypes in midbrain organoids from individuals with a triplication in the SNCA gene, which represent a starting point for further approaches to develop therapies. [less ▲]

For a New Hermeneutics of Practice in Digital Public History: Thinkering with memorecord.uni.lu

Doctoral thesis (2020)

This thesis is built upon an experimental study of doing digital public history. I aim to study the digital interferences of the digital component on the historiographic operation as a whole. While the ... [more ▼]

This thesis is built upon an experimental study of doing digital public history. I aim to study the digital interferences of the digital component on the historiographic operation as a whole. While the fields of digital and public history are advancing fast with abundant work on development and application of new methodologies, tools and approaches, the discipline of history is still lagging behind in terms of theoretical reflection on the new practices emerging from it. Researchers have been exploring alternative forms of source criticism, storytelling and publications for years now, yet the greatest attention still goes to the outputs, while little criticism, if any, is devoted to the process of doing digital work. By building and analysing a digital public history platform, this research aims to make a contribution in this direction. To do so, the research takes a fully hands-on approach and offers an evaluation of digital methods that to great extent emerge from practice and the researcher’s first-hand experience with the digital. The empirical study consisted of investigating memories of Italian and Portuguese immigrants in Luxembourg through the establishment of a collaboratively shaped digital memory platform. The process of building the Memorecord platform, activating the crowdsourcing through social media and analysing the born-digital data originated from this collection informed the theoretical reflection of this thesis. While in the more practical layer, hands-on work and collaboration were highlighted, from the more speculative layer, the main theoretical contribution verse on the hybridisation of old and practices and capacities synthesized in the emergence of a hermeneutics of practice, derived from the heuristics gesture of creative and playful experimentation, (i.e. thinkering) around the digital tools and methods. This specific hermeneutical approach may function as a visibility broker, assisting historians in the process of unveiling the unspoken and implicit aspects of historical inquiry in the digital age. Hermeneutics of practice, hence, should facilitate the identification of the digital interferences we encounter throughout the research process and improve the researcher’s readiness to face the new research conditions placed by the digital component. If a new style of reasoning of/about/in/within digital and digital public history should be stabilised, hermeneutics of practice could become an important procedure to ensure historical objectivity in 21st Century. [less ▲]

Hilbert modular forms modulo p of partial weight one and unramifiedness of Galois representations

Doctoral thesis (2020)

This thesis studies Hilbert modular forms of arbitrary weight with coefficients over a finite field of characteristic p. In particular, we compute the action on geometric q- expansions attached to these ... [more ▼]

This thesis studies Hilbert modular forms of arbitrary weight with coefficients over a finite field of characteristic p. In particular, we compute the action on geometric q- expansions attached to these forms of Hecke operators, including at places dividing p as constructed by Emerton, Reduzzi and Xiao. As an application, we prove that the Galois representation attached to a Hilbert cuspidal eigenform mod p, which has parallel weight 1 at a place P dividing p, is unramified at P. [less ▲]

MOMENT AND LONGITUDINAL RESISTANCE FOR COMPOSITE BEAMS BASED ON STRAIN LIMITED DESIGN METHOD

Doctoral thesis (2020)

The bending and longitudinal shear design of composite beams of steel and concrete follows often the plastic design method, which is a simplification based on rectangle stress blocks. The application of ... [more ▼]

The bending and longitudinal shear design of composite beams of steel and concrete follows often the plastic design method, which is a simplification based on rectangle stress blocks. The application of the plastic design method requires cross-section to have enough rotation capacity allowing most parts of the critical cross-section reach plastic at failure. There are different types of compact composite beams, such as the slim-floor beams. For them, the neutral axis position often gets deeper at failure, which reduces the rotation capacity and brings questions to the bending resistance and longitudinal shear design according to the plastic design resistance. For a composite beam with deep neutral axis position, advanced numerical methods such as strain-limited design and FEM simulations can provide more accurate results than the plastic cross-section resistance. However, they are challenging to perform for general design engineers. In this work, simplified non-linear strain-limited design approaches, a strain-limited design software "SL.com" and an Abaqus add-in "CivilLab" have been developed to simplify the numerical calculations. They have also been applied in other chapters of this work to check the conventional plastic design results and to provide simplified design rules through parametric studies. With full shear connection, a deep neutral axis position in composite beam under sagging bending may cause an important part of the steel section not to reach plastic at concrete failure. In this case, plastic bending resistance calculated based on rectangle stress blocks can result in an overestimation of the resistance and therefore leads to unsafe design. Thus, according to EN1994-1-1 [22], a reduction factor β on plastic bending resistance (Mpl,Rd) needs to be applied for cross-sections with steel grade S420 and S460 and the relative compression zone height (zpl/h) is over 0.15. However, with the developments in industry as well as the second generation of Eurocode, this reduction factor still needs to be updated to consider new types of composite beams and wider ranges of steel grades. While the conventional plastic design method has its limitations and only applicable when the beam cross-section has enough rotation capacity to allow full plastic development, the more advanced strain-limited numerical calculation and FEM can be used for a much wider range regardless of the position of the neutral axis. The investigations in this dissertation through comparing the plastic bending resistance with advanced numerical calculation results, have confirmed that besides the cross-sections with high steel grades (S420, S460), also certain cross-sections with lower steel grades can have an overestimated plastic bending moment resistance. At least this effect is more important for compact cross-section types such as slim-floor sections or composite beams with asymmetrical structural steel profiles or with a small concrete slab effective width. Therefore vast amount of parametric studies based on strain-limited method and FEM have been developed to check the topics, such as limitation of plastic design methods for different types of composite beams. Furthermore new reduction β functions on Mpl,Rd for engineering practice considering much wider variates of composite beam cross-sections have been deviated. For the design with partial shear connection, the partial shear diagram developed based on plastic analysis has been widely used. As discussed above, the plastic design may not be suitable when the position of neutral axis is too deep, similar problems can occur for the partial shear diagram. This problem is especially significant for slim-floor beams, for which due to the compact cross-section, the relative compression zone height (zpl/h) is usually much higher than conventional composite beams. Thus the limitation of using the partial shear diagram for slim-floor beams is provided, and additional simplified engineering design rules are proposed. Plastic development inside the cross-section increases the longitudinal shear force in the plastic zones, furthermore with ductile shear connectors and respecting the minimum degree of shear connection, the non-linear redistribution of longitudinal shear force allows equal distance arrangement of shear connectors by the conventional design. For which, the full plastic development of the cross-section allowing plastic bending moment resistance and ductile shear connectors allowing non-linear longitudinal shear force distribution are the two fundamental conditions. The deep neutral axis position brings questions directly to the first assumption, as full plastic development of crosssection may not be able to reach. Thus the impact of a deep neutral axis position in the composite beams on longitudinal shear force distribution has been analysed. For which, the influence of plastic development inside beam cross-sections on longitudinal shear force with full shear interaction is theoretically explained. The different stages of nonlinear distribution of longitudinal shear force due to shear connectors are investigated through FEM parametric studies. Based on the theoretical and numerical calculation, the design suggestions of composite beams with deep neutral axis position are given. [less ▲]

JUDICIAL ACCOUNTABILITY IN EGYPT: CONVERGENCE BETWEEN WESTERN LAWS AND ISLAMIC JURISPRUDENCE

Doctoral thesis (2020)

Energy-efficient Mobile Crowdsensing Solutions for Smart Cities

Doctoral thesis (2020)

This thesis proposes energy-efficient mobile crowdsensing (MCS) solutions for smart cities. Specifically, it focuses on sensing and communications processes in distributed computing paradigms and complex ... [more ▼]

This thesis proposes energy-efficient mobile crowdsensing (MCS) solutions for smart cities. Specifically, it focuses on sensing and communications processes in distributed computing paradigms and complex urban dynamics in city-wide scenarios. MCS is a data collection paradigm that has gained significant attention in recent years and has become appealing for urban sensing. MCS systems rely on contributions from mobile devices of a large number of participants or a crowd. Smartphones, tablets, and wearable devices are deployed widely and already equipped with a rich set of sensors, making them an excellent source of information. Mobility and intelligence of humans guarantee higher coverage and better context awareness if compared to traditional sensor networks. At the same time, individuals may be reluctant to share data for devices’ battery drain and privacy concerns. For this reason, MCS frameworks are specifically designed to include incentive mechanisms and address privacy concerns. Despite the growing interest in the research community, MCS solutions still need a more in-depth investigation and categorization on many aspects that span from sensing and communication to system management and data storage. This Ph.D. thesis focuses not only on sustainable MCS solutions to challenging problems in urban environments but also on a comprehensive study aiming to clarify concepts, aspects, and inconsistencies in existing literature from a global perspective. Specifically, this manuscript proposes the following contributions: • Present the MCS paradigm as a four-layered architecture divided into application, data, communication, and sensing layers, proposing novel taxonomies related to each layer. The detailed taxonomy aims to shed light on the current landscape, covering all MCS aspects and allowing for a simple and clear classification of applications, methodologies, and architectures. • A significant improvement of the previously developed simulation environment CrowdSenSim by implementing a set of novel features. The novelties include easy-to-use city-wide street networks, more realistic pedestrian mobility models, and real battery drain measurements over several other features. • An analysis of energy efficiency that poses the basis for sustainable MCS data collection frameworks (DCFs). It includes both a theoretical methodology to assess different DCFs and real energy measurements conducted in a laboratory, simulated in large scale urban environments. • A study that exploits crowdsensed data for a learning-driven estimation of local businesses’ attractiveness in cities to show how MCS systems can support urban planning. • A novel efficient edge data centers deployment in real urban environments based on human mobility and traffic generated from mobile devices. The citizens’ mobility is developed by feeding CrowdSenSim with crowdsensed data. [less ▲]

ESSAYS ON ASSET PRICING AND MARKET AUCTIONS

Doctoral thesis (2020)

Smart Electrical and Thermal Energy Supply for Nearly Zero Energy Buildings

Doctoral thesis (2020)

The European Union (EU) intends to reduce the greenhouse gas emissions to 80-95 % below 1990 levels by 2050. To achieve this goal, the EU focuses on higher energy efficiency mainly within the building ... [more ▼]

The European Union (EU) intends to reduce the greenhouse gas emissions to 80-95 % below 1990 levels by 2050. To achieve this goal, the EU focuses on higher energy efficiency mainly within the building sector and a share of renewable energy sources (RES) of around 30 % in gross final energy consumption by 2030. In this context, the concept of nearly zero-energy buildings (nZEB) is both an emerging and relevant research area. Balancing energy consumption with on-site renewable energy production in a cost-effective manner requires to develop suitable energy management systems (EMS) using demandside management strategies. This thesis develops an EMS using certainty equivalent (CE) economic model predictive control (EMPC) to optimally operate the building energy system with respect to varying electricity prices. The proposed framework is a comprehensive mixed integer linear programming model that uses suitable linearised grey box models and purely data-driven model approaches to describe the system dynamics. For this purpose, a laboratory prototype is available, which is capable of covering most building-relevant types of energy, namely thermal and electrical energy. Thermal energy for space heating, space cooling and domestic hot water is buffered in thermal energy storage systems. A dual source heat pump provides thermal energy for space heating and domestic hot water, whereas an underground ice storage covers space cooling. The environmental energy sources of the heat pump are ice storage or wind infrared sensitive collectors. The collectors are further used to regenerate the ice storage. Photovoltaic panels produce electrical energy which can be stored in a battery storage system. The electrical energy system is capable of selling and buying electricity from the public power grid. The laboratory test bench interacts with a virtual building model which is integrated into the building simulation software TRNSYS Simulation Studio. The EMS prototype is tested and validated on the basis of various simulations and under close to real-life laboratory conditions. The different test scenarios are generated using the typical day approach for each season. [less ▲]

Generalized Langevin equations and memory effects in non-equilibrium statistical physics

Doctoral thesis (2020)

The dynamics of many-body complex processes is a challenge that many scientists from various fields have to face. Reducing the complexity of systems involving a large number of bodies in order to reach a ... [more ▼]

The dynamics of many-body complex processes is a challenge that many scientists from various fields have to face. Reducing the complexity of systems involving a large number of bodies in order to reach a simple description for observables captur- ing the main features of the process is a difficult task for which different approaches have been proposed over the past decades. In this thesis we introduce new tools to describe the coarse-grained dynamics of arbitrary observables in non-equilibrium processes. Following the projection operator formalisms introduced first by Mori and Zwanzig, and later on by Grabert, we first derive a non-stationary Generalized Langevin Equation that we prove to be valid in a wide spectrum of cases. This includes in particular driven processes as well as explicitly time-dependent observ- ables. The equation exhibits a priori memory effects, controlled by a so-called non- stationary memory kernel. Because the formalism does not provide extensive infor- mation about the memory kernel in general, we introduce a set of numerical meth- ods aimed at evaluating it from Molecular Dynamics simulation data. These proce- dures range from simple dimensionless estimations of the strength of the memory to the determination of the entire kernel. Again, the methods introduced are very general and require as input a small number of quantities directly computable from numerical of experimental timeseries. We finally conclude this thesis by using the projection operator formalisms to derive an equation of motion for work and heat in dissipative processes. This is done in two different ways, either by using well-known integral fluctuation theorems, or by explicitly splitting the dynamics into adiabatic and dissipative parts. [less ▲]

Hatt oder si? Genuszuweisung bei weiblicher Personenreferenz im Luxemburgischen und Moselfränkischen

Doctoral thesis (2020)

In Luxembourgish and Moselle Franconian, as well as in various other German, Swiss German and Dutch dialects, it is possible to assign the feminine and neuter genders to female individuals. The neuter ... [more ▼]

In Luxembourgish and Moselle Franconian, as well as in various other German, Swiss German and Dutch dialects, it is possible to assign the feminine and neuter genders to female individuals. The neuter gender of female first names is strongly grammaticalized in both Luxembourgish and Moselle Franconian, so that they mostly trigger the neuter gender on their targets (e.g. definite articles, personal pronouns). At the same time, the use of the neuter gender is not limited to the use of female first names. Rather, personal pronouns can also be used in reference to female appellatives, female kinship terms, and combinations of a female first name with a last name. Moreover, gender assignment is determined by socio-pragmatic factors (e.g. age, familiarity) and shows a high degree of variation in some reference contexts. The aim of the present study is to provide a first major empirical and comprehensive presentation of this phenomenon in both varieties, taking into account different socio-pragmatic factors and various reference contexts. The results are based on quantitative elicited data retrieved from an online survey and audio recordings collected by means of the Luxembourgish language app Schnëssen, as well as qualitative data from structured interviews involving different descriptive tasks. The collection of the data was undertaken at different localities in the area under investigation. While it was found that the use of neuter in Moselle Franconian is more closely tied to the personal relationship between the speaker and the referent, it is partly possible in Luxembourgish to refer to female public figures using neuter forms. Additionally, an apparent-time analysis for Luxembourgish makes it possible to identify differences between the different age groups of the speakers. It becomes apparent that there is a tendency for younger speakers to prefer neutral gender assignment in variable reference contexts. This also applies to exophoric reference contexts to female individuals without a given reference noun, in which neuter seems to become prevalent as a sort of default gender. [less ▲]

Blockchain-enabled Traceability and Immutability for Financial Applications

Doctoral thesis (2020)

The dissertation explores the efficacy of exploiting the transparency and immutability characteristics of blockchain platforms in a financial ecosystem. It elaborates on blockchain technology employing a ... [more ▼]

The dissertation explores the efficacy of exploiting the transparency and immutability characteristics of blockchain platforms in a financial ecosystem. It elaborates on blockchain technology employing a succinct approach, which serves as the foundation to comprehend the contributions of the present research work. The dissertation gives a verified mathematical model, derived using Nash equilibrium, to function as a framework for blockchain governance. The work elucidates the design, implementation and evaluation of a management plane to monitor and manage blockchain-based decentralized applications. The dissertation also solves the problem of data privacy by the development and evaluation of a management plane for differential privacy preservation through smart contracts. Further, the research work discusses the compliance of the privacy management plane to GDPR using a permissioned blockchain platform. The dissertation is a pioneer in conducting an implementation-based, comparative and an exploratory analysis of tokenization of ethical investment certificates. The dissertation also verifies the utility of blockchain to solve some prevalent issues in social finance. It accomplishes this through the development and testing of a blockchain-based donation application. A qualitative review of the economic impact of blockchain-based micropayments has also been conducted. The discussion on the economic impact also includes a proposition for extending the access of blockchain-based financial services to the underbanked and unbanked people. The work concludes with a hypothetical model of a financial ecosystem, depicting the deployment of the major contributions of this dissertation. [less ▲]

Inkjet-printed piezoelectric films for transducers

Doctoral thesis (2020)

Lead zirconate titanate (PZT) thin films are a popular choice for piezoelectric devices such as microelectromechanical systems, micro-pumps, micro-mirrors or energy harvesters. Various fabrication ... [more ▼]

Lead zirconate titanate (PZT) thin films are a popular choice for piezoelectric devices such as microelectromechanical systems, micro-pumps, micro-mirrors or energy harvesters. Various fabrication techniques exist for the deposition of PZT in the form of thin films. Physical vapor deposition (PVD) methods are particularly cost-intensive, as they require vacuum conditions and expensive infrastructure. Fabrication costs can be decreased by the use of chemical solution deposition (CSD), where the metal precursors are dispersed in a solvent medium and coated onto a substrate. Thermal treatments convert the liquid precursor into a functional solid film. Spin coating is a conventional coating technique allowing for the deposition of homogeneous layers over large-area substrates. However, it is inherently wasteful, as most of the precursor material is spun off the substrate in the coating process. In addition, as spin coating results in complete coverage of the substrate, layer patterning requires lithography, which adds up extra steps and costs to the overall process. Inkjet printing is an additive manufacturing technique that has the potential to address both of these issues, thus further decreasing manufacturing costs and the associated ecological footprint. The working principle of inkjet printing can be described as the deposition of individual ink droplets at digitally determined locations on the substrate surface, which then merge into a continuous film. Inkjet printing is compatible with CSD processing of PZT thin films, as demonstrated by the previous works in the field. However, the adaptation of standard CSD processing for inkjet printing comes with several challenges, which have to be considered to obtain state-of-the-art functional PZT layers. In the present work, we explore several issues related to the processing of PZT thin films by inkjet printing and we provide possible solutions to address them, in a way that had not been described yet by the state of the art. In particular, we describe a novel strategy that uses inkjet-printed alkanethiolate-based self-assembled monolayers for direct patterning of PZT thin films on platinized silicon. Then, we present a systematic study of the pyrolysis step of the process, which enabled us to print dense and textured layers with state-of-the-art electrical properties. We also developed a proof-of-concept piezoelectric energy harvesting device based on inkjet-printed PZT films. Finally, we unveil a comparative study where we identified an alternative solvent for CSD processing of PZT thin films. [less ▲]

The impartiality and independence of arbitrators in international commercial arbitration

Doctoral thesis (2020)

A Real-World Flexible Job Shop Scheduling Problem With Sequencing Flexibility: Mathematical Programming, Constraint Programming, and Metaheuristics

Doctoral thesis (2020)

In this work, the online printing shop scheduling problem is considered. This challenging real scheduling problem, that emerged in the nowadays printing industry, corresponds to a flexible job shop ... [more ▼]

In this work, the online printing shop scheduling problem is considered. This challenging real scheduling problem, that emerged in the nowadays printing industry, corresponds to a flexible job shop scheduling problem with sequencing flexibility that includes several complicating specificities such as resumable operations, periods of unavailability of the machines, sequence-dependent setup times, partial overlapping between operations with precedence constraints, fixed operations, among others. In the present work, a mixed integer linear programming model, a constraint programming model, and heuristic methods such as local search and metaheuristics for the minimization of the makespan are presented. Modeling the problem is twofold. On the one hand, the problem is precisely defined. On the other hand, the capabilities and limitations of a commercial software for solving the models are analyzed. Numerical experiments show that the commercial solver is able to optimally solve only a fraction of the small-sized instances when considering the mixed integer linear programming formulation. While considering the constraint programming formulation of the problem, medium-sized instances are optimally solved, and feasible solutions for large-sized instances of the problem are found. Ad-hoc heuristic methods, such as local search and metaheuristic approaches that fully exploit the structure of the problem, are proposed and evaluated. Based on a common representation scheme and neighborhood function, trajectory and populational metaheuristics are considered. Extensive numerical experiments with large-sized instances show that the proposed metaheuristic methods are suitable for solving practical instances of the problem; and that they outperform the half-heuristic-half-exact off-the-shelf constraint programming solver. Numerical experiments with classical instances of the flexible job shop scheduling problem show that the introduced methods are also competitive when applied to this particular case. [less ▲]

LehrerInnenprofessionalisierung in einer digitalen, videogestützten Lernumgebung

Doctoral thesis (2020)

The sustainable use of digital media and the conception of effective task designs are relevant aspects for the learning outcome in the training of future teachers. To model professional action competence ... [more ▼]

The sustainable use of digital media and the conception of effective task designs are relevant aspects for the learning outcome in the training of future teachers. To model professional action competence, video-supported learning opportunities are increasingly used today to train professional perception and reflexive confrontation with new knowledge, convictions and experiences from teaching. So far, however, there is a lack of empirical studies that systematically take into account effective design elements of innovative learning environments for the promotion of reflexive practice, such as blended learning, social video learning and ePortfolio [less ▲]

Fatigue and fracture of rubber: Accelerated and experimentally validated phase-field damage models

Doctoral thesis (2020)

Rubbers behave very particularly. Anyone who has stretched a rubber band knows that large elastic deformations over 400% can be attained with a minimal force. In order to utilize the full potential of the ... [more ▼]

Rubbers behave very particularly. Anyone who has stretched a rubber band knows that large elastic deformations over 400% can be attained with a minimal force. In order to utilize the full potential of the material and to improve the performance of a product, it is imperative to accurately model the material's failure. This thesis focuses on the development, experimental validation and application of a fatigue damage model for rubber. Cohesive zone models or nodal enrichment strategies, which treat cracks as sharp discontinuities, require a priori knowledge of the crack path or are limited in their ability to handle complex crack phenomena like branching and coalescence. On the other hand, the results of standard continuum damage models are affected by the mesh size. Phase-field damage models avoid sharp discontinuities by adding a smooth damage process zone to the crack. The width of this zone is controlled by a length scale parameter. Because of this pure continuum description, the mentioned complex phenomena are simulated without additional effort. Furthermore, the introduction of the length scale ensures mesh-independence during strain softening. Despite these advantages, phase-field models to describe the failure of rubber parts are still limited. Firstly, most published works focus only on monotonic loading. Fatigue damage of rubber has never been considered in a phase-field model. Secondly, the computational burden is too large so that only examples with limited practical relevance can be simulated. Thirdly, there is insufficient experimental validation in the literature and the process of parameter identification is not adequately addressed. For instance, the selection of the length scale parameter is often arbitrary. This thesis collects three works that have been presented to the scientific community in an effort to overcome the mentioned problems. Because the fracture resistance of rubbers is a function of the loading rate, the first work presents a rate-dependent phase-field damage model for rubber and finite strains. Rate-dependency is considered in the constitutive description of the bulk as well as in the damage driving force. All the material parameters are identified from experiments. Particular attention is paid to the length scale parameter, which is calibrated by means of local strain measurements close to the crack tip obtained via digital image correlation. The second work extends the phase-field damage model so that fatigue failure can be predicted. For this purpose, an additional fatigue damage source depending on an accumulated load history variable is introduced. The thermodynamical consistency is demonstrated by measuring the energy storage and dissipation of the various model components. Dedicated fatigue experiments are conducted in order to identify additional (fatigue) parameters. The extended model reproduces Woehler curves and Paris theory for fatigue crack growth. Using explicit and implicit cycle jump schemes, the third work focuses on the reduction of the computation time. A finite number of load cycles is simulated and the results for the next cycles are extrapolated. By alternating simulations and jumps until the component failure is reached, the total number of simulated cycles is significantly reduced, with respect to the full simulations. As the size of the cycle jump governs the acceleration of the simulations, but also the numerical stability, an adaptive cycle jump scheme for the implicit acceleration framework is proposed. Consequently, no manual adjustment of the step size is necessary. Additional experiments validate both the numerical model and the identified material parameters. Finally, the fatigue phase-field damage model is used in two industry-relevant examples demonstrating how this technology creates immediate benefits in product development. [less ▲]

Essays in risk and experimental finance

Doctoral thesis (2020)

Cultural identity and values in intergenerational movement: The multicultural case of the Grand-Duchy of Luxembourg

Doctoral thesis (2020)

Migration flows have led to an increase in questions about the multiple cultural influences on individuals. The resulting demographic changes raise in many host societies essential questions related to ... [more ▼]

Migration flows have led to an increase in questions about the multiple cultural influences on individuals. The resulting demographic changes raise in many host societies essential questions related to national belonging, and thus to cultural identity and value systems. While migrating to a new cultural environment, migrant individuals face several challenges and they have to negotiate several developmental tasks using self-regulatory strategies, with correspondingly different psychological outcomes. These issues become even more important in a country such as Luxembourg with a high migrant proportion (47%; Statec, 2019). Little is still known about how second-generation adults who have grown up in immigrant families negotiate the double cultural identity, and about their value profiles compared to the local populations of the country of origin and receiving country. Four diverse subsamples were used out of the broader IRMA project pool, depending on the different objectives of the four studies. In total, N = 506 participants from three cultural subgroups ( LU natives, PT migrants in Luxembourg & PT natives in Portugal) participated in the quantitative part of the IRMA project ( LuN: n = 179; PtM: n = 209 & PtN: n = 118), and N = 20 took part in the qualitative part (n = 10 PtM dyads & n = LuN dyads). Study 1 highlighted the importance of the migration experience as a life-disruptive event that has impacts on individual and family cultures, as well as value systems during the life of migrant families. Study 2, looking specifically at PT migrant families, found a generational gap in terms of adult children’s higher attachment to the receiving culture as well as stronger tendencies towards a compatible identity orientation compared to their respective parents. However, the qualitative part of Study 2 revealed ambivalent feelings about double cultural belonging amongst the Portuguese second-generation adult children. Study 3 therefore focused on the latter and identified four ways of dealing with double cultural frames - blended, alternated, separated (Phinney & Devich-Navarro, 1997) - and expanded the model by identifying a fourth cluster of ambivalent cultural identity. In addition, the survey analyzed how their cultural identity profiles enabled them to achieve personally or socially meaningful goals and values. Blended biculturals used mainly primary regulatory control strategies, which were linked to the most positive psychological outcomes (higher self-esteem & well-being, and low acculturation stress). The ambivalent cluster was the least successful in terms of psychological outcomes (low self-esteem & well-being, and high acculturative stress) using both primary and secondary compensatory regulatory strategies. Study 4, an intercultural comparison between two family generations – one adult child and two elder parents – within three different cultural subgroups – LuN, PtM and PtN – aimed to better disentangle the effects of family, culture and immigration, and thus investigate the different cultural influences and messages reflected in the processes of transmission of values and value profiles. Overall, findings of Study 4 revealed the existence of an intergenerational gap between elder parents and their respective adult children; the presence of a cultural gap between the three cultural subgroups studied, which could be explained by both culture of origin and migration, with specifically an acculturation gap in the sub-sample of Portuguese migrants; and a moderate relative intergenerational transmission across cultures. The latter thus allows for a certain cultural persistence and continuity of a society and its cultural system (Trommsdorff et al., 2004) while allowing for cultural flexibility over generations that could be important for family identity and beneficial for well-being far more than a mere exact reproduction of values over generations (Barni & Donato, 2018). [less ▲]

OPTICAL DEFECT SPECTROSCOPY IN CUINS2 THIN FILMS AND SOLAR CELLS

Doctoral thesis (2020)

Pure-sulphide Cu(In,Ga)S2 solar cells have reached certified power conversion efficiency as high as 15.5 %. While this record performance has been achieved by growing the semiconducting absorber at very ... [more ▼]

Pure-sulphide Cu(In,Ga)S2 solar cells have reached certified power conversion efficiency as high as 15.5 %. While this record performance has been achieved by growing the semiconducting absorber at very high temperature with a copper deficient composition, all other previous records were based on chalcopyrite films deposited under Cu excess. Still, this world record is far from the theoretical power conversion achievable in single junction solar cell for this semiconductor (about 30 %), which has a tunable band gap between 1.5 and 2.4 eV. This thesis aims to gain insight into the optoelectronic properties of this semiconductor, particularly CuInS2, looking at their variation as a function of the deposition temperature and of the absorber composition. The investigations are carried out mainly by photoluminescence (PL) spectroscopy, which allows to measure the quasi Fermi level splitting (QFLS), that is an upper limit of the maximum open circuit voltage (VOC) an absorber is capable of. PL spectroscopy is used to get insights onto the electronic defects as well, both the shallow ones, which contribute to the doping, and the deep ones, which enhance non-radiative recombination. By increasing the Cu content in the as-grown compositions, the morphology and microstructure of the thin films improve, as they show larger grains and less structural defects than films deposited with Cu deficiency. The composition affects the QFLS as well, which is significantly higher for sample deposited under Cu excess, in contrast to the observations in selenide chalcopyrite. The increment of the process temperature leads to an improvement of the QFLS too, although absorbers grown in Cu deficiency are less influenced, likely because of a lower sodium content in the high-temperature glass used as substrate. The QFLS increase correlates with the lowering of a deep defect related band, which manifests itself with a peak maximum at around 0.8 eV in room temperature PL spectra. In literature, the low efficiencies exhibited by Cu(In,Ga)S2–based solar cells are often attributed to interface problems at the p-n junction, i.e. at the absorber-buffer layer interface. In this work, the comparison of the QFLS and VOC of pure sulphides CIGS with those measured on selenides clearly points out that the lower efficiencies exhibited by the former are caused also by the intrinsic lower optoelectronic quality of Cu(In,Ga)S2 films. To shed light on the electronic structure, high quality CuInS2 films are deeply investigated by means of low temperature PL. Four shallow defects are detected: one shallow donor at about 30 meV from the conduction band and three shallow acceptors at about 105, 145 and 170 meV from the valence band. The first of these acceptors dominates the band edge luminescence of sample grown with composition close to the stoichiometry, whereas the second deeper acceptor is characteristic of absorbers deposited in Cu rich regime. The deepest of these acceptors seems to be present over a wide range of compositions, although its luminescence is observable only for slight Cu-poor samples with sodium incorporation during the deposition. The quality of the examined films allows the observations of phonon coupling of these shallow defects for the first time in this semiconductor. All these observations on shallow defects and their phonon coupling behaviour allowed to revise the defect model for this semiconductor. The findings of this thesis reveal the strong similarity of the shallow defects structure with selenium based compounds. On the other hand, the presence of deep defects in CuInS2 strongly limits the optoelectronic quality of the bulk material, causing the gap in power conversion efficiencies compared to low-band gap Cu(In,Ga)Se2 solar cells, which show efficiencies above 23%. [less ▲]

On the practical security of white-box cryptography

Doctoral thesis (2020)

Cryptography studies how to secure communications and information. The security of a cryptosystem depends on the secrecy of the underlying key. White-box cryptography explores methods to hide a ... [more ▼]

Cryptography studies how to secure communications and information. The security of a cryptosystem depends on the secrecy of the underlying key. White-box cryptography explores methods to hide a cryptographic key into some software deployed in the real world. Classical cryptography only assumes that the adversary accesses the target cryptographic primitive in a black-box manner in which she can only observe or manipulate the input and output of the primitive, but cannot know or tamper with its internal details. The gray-box model further allows an adversary to exploit key- dependent sensitive information leaked from the execution of physical implementations. All sorts of side-channel attacks exploit some physical information leakage, such as the power consumption of the device. The white-box model considers the worst-case scenario in which the adversary has complete control over the software and its execution environment. The goal of white-box cryptography is to securely implement a cryptographic primitive against such a powerful adversary. Although the scientific community has proposed some candidate solutions to build white-box cryptography, all have proven ineffective. Consequently, this problem has remained open for almost two decades since the concept was introduced. The continuous growth in market demand and the emerging potential applications have driven the industry to deploy secretly-designed proprietary solutions. Al- though this paradigm of achieving security through obscurity contradicts the widely accepted Kerckhoffs' principle in cryptography, this is currently the only option for white-box cryptography. Security experts have reported how gray-box attacks could be used to extract keys from several publicly available white-box implementations. In a gray-box attack, the adversary adapts side-channel analysis techniques to the white-box context, i.e., to target computation traces made of noise-free run- time information instead of the noisy physical leakage. Gray-box attacks are generic since they do not require any a priori knowledge of the implementation and hence avoid costly reverse engineering. Some non-publicly scrutinized industrial white- box schemes in the market are believed to be under the threat of gray-box attacks. This thesis focuses on the analysis and improvement of gray-box attacks and the associated countermeasures for white-box cryptography. We first provide an in- depth analysis of why gray-box attacks are capable of breaking the classical white- box design which is based on table encodings. Next, we introduce a new gray-box at- tack named linear decoding analysis and show that linearly encoding sensitive information is insufficient to protect the cryptographic software. Afterward, we describe how to combine state-of-the-art countermeasures to resist gray-box attacks and comprehensively elaborate on the (in)effectiveness of these combined countermeasures in terms of computation complexity. Finally, we introduce a new attack technique that exploits the data-dependency of the targeted implementation to substantially lower the complexity of the existing gray-box attacks on white-box cryptography. In addition to the theoretical analyses and new attack techniques introduced in this thesis, we report some attack experiments against practical white-box implementations. In particular, we could break the winning implementations of two consecutive editions of the well-known WhibOx white-box cryptography competition. [less ▲]

Demountable composite beams: Analytical calculation approaches for shear connections with multilinear load-slip behaviour

Doctoral thesis (2020)

The work carried out throughout the thesis focused on the behaviour of demountable composite beams in order to facilitate the integration of steel-concrete composite construction into the concept of ... [more ▼]

The work carried out throughout the thesis focused on the behaviour of demountable composite beams in order to facilitate the integration of steel-concrete composite construction into the concept of circular economy. There are several hindrances in the way of reuse when considering traditional composite structures. One of them is the method that the current construction practice applies for connecting the concrete deck to the steel beam. The traditionally applied welded studs are advantageous in the terms of structural performance; however, they do not provide the ability of dismounting. In order to overcome this issue, different demountable shear connection types were investigated that use pretensioned bolted connections. The investigations included laboratory experiments in the means of push-out tests and full-scale beam-tests. The experiments were complemented by numerical simulations and parametric studies. The experiments showed that the developed shear connections have highly a nonlinear load-slip behaviour. When these types of connections are applied in a composite beam, the nonlinearity of the shear connection causes a nonlinear load-deflection response already in the elastic phase. Analytical equations were derived for the description of the elastic properties of composite beams with nonlinear shear connection. For the calculation of the elastic deflections an iterative procedure was developed. This method is capable of capturing the nonlinear load-deflection response. With the developed iterative method, the elastic deflections can be determined with a similar accuracy by using spreadsheet calculations as by using nonlinear finite element simulations. Due to the highly nonlinear behaviour of the tested shear connections the basic assumptions of Eurocode 4 for the determination of the plastic moment resistance of composite beams with partial shear connection are not valid anymore. The code does not enable the use of equidistant shear connector spacing and the design needs to be conducted using fully elastic analysis. This would make the use of demountable shear connections complicated and uneconomic. In the face of these issues, the probability of the practical application of demountable and reusable composite structures would be very low. On the other hand, experiments and numerical simulations show that composite beams can develop plasticity even if a non-ductile shear connection is applied. In order to overcome these issues, a new calculation method was developed for the prediction of the plastic moment resistance of demountable composite beams. A simplified method was proposed based on the developed procedure by defining an effective shear resistance for the demountable shear connections. The effective shear resistance allows the current calculation method to be extended for demountable shear connections. In this way, the benefits of composite construction can be maintained while providing the possibility of reuse. [less ▲]