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See detailSOCIAL CLAUSES IN OUTSOURCING PROCESSES. SOCIAL RIGHTS VERSUS ECONOMIC FREEDOMS IN THE PRISM OF THE MULTILEVEL LEGAL ORDER
Marchi, Giulia UL

Doctoral thesis (2020)

The aim of the thesis is to study the different provisions included in the notion of social clause and offer an in-depth and systematic analysis of some types of social clauses in the Italian and European ... [more ▼]

The aim of the thesis is to study the different provisions included in the notion of social clause and offer an in-depth and systematic analysis of some types of social clauses in the Italian and European Union legal order, their characteristics, their regulation, and the legal interests that are aimed at protecting, as well as their classification in the multilevel legal order. This study is preliminary for the assessment on the legitimacy of such clauses in relation to economic freedoms. Indeed, the application of social clauses is one of the fields in which the contrast between fundamental social rights and economic freedoms emerges most clearly and in relation to which some differences occur in the reconciliation of interests made by the Courts at national and EU level. The most relevant distinction for this research relies on the classification developed by Italian scholars, who, on the basis of contents and interests protected by social clauses, usually distinguish between equal treatment or first-generation social clauses and rehiring or second-generation social clauses. Also the nature of the procurement contract, public or private, may condition the judgment on the legitimacy of social clauses with regard to economic freedoms, due to the different regulations applicable in the two fields and the tension between the protection of competition and social objectives, which historically characterizes the action of the public administration in the field of public procurements. The thesis investigates the legislation and the case law concerning the first- and second-generation social clauses, both statutory and contractual, at European and Italian level, with reference to public and private procurements. From this study, it is clear that there are problems of effectiveness and applicability concerning first- and second-generation social clauses, as well as of conflicting interests: social clauses may hinder the competition, negatively condition the entrepreneur’s freedom to conduct a business, affect the entrepreneurs’ freedom of association, and, therefore, risk to contrast with the constitutional and European provisions protecting those freedoms. In this reasoning, the different levels of protection and the importance recognised to social rights and economic freedoms in the Italian and European Union legal systems, the legal framework generated by their interaction, and the type of balancing in the two legal orders must be considered. In the search for a reasonable balance between economic freedoms and social rights, the thesis explores whether the various interests protected by the different types of social clauses can fall within that notion of employment protection which constitutes an overriding reason relating to the public interest justifying a limitation of the economic freedoms and investigates to what extent the prevention of unfair competition and social dumping, the protection of workers’ rights and employment stability can justify a restriction of fundamental economic freedoms. In conclusion, the aim of the study is to investigate if it is possible to achieve a fair balance between opposing interests, social rights, on the one hand, and economic freedoms and free competition, on the other, and comprehend how the interests contrasting with them in relation to the case of social clauses can be balanced. [less ▲]

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See detailNational Banking Law in the European Single Supervisory Mechanism
Voordeckers, Olivier UL

Doctoral thesis (2020)

In 2013, the European Central Bank acquired the competence to apply national banking law in a direct manner to banks established in the euro area, as part of its supervisory competence under the Single ... [more ▼]

In 2013, the European Central Bank acquired the competence to apply national banking law in a direct manner to banks established in the euro area, as part of its supervisory competence under the Single Supervisory Mechanism. This marks the first instance of direct administration of national law by a European institution. The thesis scrutinises the salient features as well as the strengths and weaknesses of this new administrative system in the landscape of European Union law. [less ▲]

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See detailPERFORMANCE EVALUATION AND MODELLING OF SAAS WEB SERVICES IN THE CLOUD
Ibrahim, Abdallah Ali Zainelabden Abdallah UL

Doctoral thesis (2020)

This thesis studies the problem of performance evaluation and assurance of communications and services quality in cloud computing. The cloud computing paradigm has significantly changed the way of doing ... [more ▼]

This thesis studies the problem of performance evaluation and assurance of communications and services quality in cloud computing. The cloud computing paradigm has significantly changed the way of doing business. With cloud computing, companies and end-users can access the vast majority of services online through a virtualized environment. The main three services typically consumed by cloud users are Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). Cloud Services Providers (CSPs) deliver cloud services to cloud customers on a pay-per-use model while the quality of the provided services is defined using Service Level Agreements (SLAs). Unfortunately, there is no standard mechanism which exists to verify and assure that delivered services satisfy the signed SLA agreement in an automatic way, which impedes the possibility to measure accurately the Quality of Service (QoS). In this context, this thesis aims at offering an automatic framework to evaluate the QoS and SLA compliance of Web Services (WSs) offered across several CSPs. Yet unlike other approaches, the framework aims at quantifying in a fair and by stealth way the performance and scalability of the delivered WS. By stealthiness, it refers to the capacity of evaluating a given Cloud service through multiple workload patterns that makes them indistinguishable from regular user traffic from the provider point of view. This thesis work is motivated by recent scandals in the automotive sector, which demonstrate the capacity of solution providers to adapt to the behavior of their product when submitted to an evaluation campaign to improve the performance results. The framework defines a set of Common performance metrics handled by a set of agents within customized clients for measuring the behavior of cloud applications on top of a given CSP. Once modeled accurately, the agent behavior can be dynamically adapted to hide the true nature of the framework client to the CSP. In particular, the following contributions are proposed: • A new framework of performance metrics for communication systems of cloud computing SaaS. The proposed framework evaluates and classifies in a fair and stealth way the performance and scalability of the delivered WS across multiple CSPs. • Analysis of the performance metrics for the cloud SaaS Web Service (WS) by analyzing all the possible metrics which could be used to evaluate and monitor the behavior of the cloud applications. • Benchmarking the cloud SaaS applications and web services by using referenced benchmarking tools and frameworks. • Modeling the SaaS WS by providing a set of Gaussian models. These models can be used to help the other researchers to generate data representing the CSP’s behavior under a high load and under the normal usage in just a couple of minutes without any experiments. • A novel optimization model to obfuscate the testing from the CSP and to achieve stealthiness. The optimization process relies on meta-heuristic and machine learning algorithms, such as Genetic Algorithm and Gaussian Process Regression accordingly. • A virtual QoS aggregator and SLA checker which takes care of evaluating the QoS and SLA compliance of the WS offered across the considered CSPs. • Ranking multiple CSPs based on multi-criteria decision analysis. [less ▲]

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See detailExperimentelle Untersuchungen und analytischen Modellierung von adiabaten Siedevorgängen in Naturumlaufsystemen
Haag, Michel UL

Doctoral thesis (2020)

Modern nuclear reactors increasingly use passive safety systems to ensure the integrity of the containment in the event of an accident. Natural circulation systems allow passive heat removal from the ... [more ▼]

Modern nuclear reactors increasingly use passive safety systems to ensure the integrity of the containment in the event of an accident. Natural circulation systems allow passive heat removal from the containment to the environment. One of their disadvantages is that instabilities develop as soon as evaporation occurs in the system. This thesis investigates instabilities in two-phase natural circulation systems. After comprehensive literature review on existing test facilities, the first part of this work presents experimental investigations on the stability behaviour of natural circulation systems. To conduct these investigations, the INTRAVIT test facility was designed and constructed at the University of Luxembourg. INTRAVIT offers both a high degree of flexibility in the design of the pipelines and the advantage of a direct, electrically controllable heat supply. Two measurement campaigns were carried out. During the first campaign, the influence of the heating tube inclination angle on the instabilities was investigated at constant riser pipe length. During the second measurement campaign, the influence of the riser pipe length and the influence of the flow resistance in the downcomer pipe were investigated at a constant inclination angle of the heating tube. For these investigations, temperatures, mass flow and the distribution of void in the riser pipe were analysed. In addition, pressure response during the instabilities was measured to investigate the pressure shocks caused by water hammering. The second part of this work develops an analytical model to decribe evaporation processes in adiabatic pipes. The model consists of several sub models that calculate the interfacial surface density and the evaporation rate as a function of the flow pattern. An integrated nucleation model calculates the onset of the evaporation. The derived model was implemented in the system code ATHLET. Experiments from the INTRAVIT measurement campaigns were then modelled using the new evaporation model as well as the standard evaporation model. Both were compared with the measurement data. The design and construction of the INTRAVIT test facility is a foundation for future research on instabilities in natural circulation systems. Moreover, a new evaporation model is presented, which can easily be adapted and refined by modifying individual sub models. [less ▲]

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See detailMachine Learning-based Methods for Driver Identification and Behavior Assessment: Applications for CAN and Floating Car Data
Jafarnejad, Sasan UL

Doctoral thesis (2020)

The exponential growth of car generated data, the increased connectivity, and the advances in artificial intelligence (AI), enable novel mobility applications. This dissertation focuses on two use-cases ... [more ▼]

The exponential growth of car generated data, the increased connectivity, and the advances in artificial intelligence (AI), enable novel mobility applications. This dissertation focuses on two use-cases of driving data, namely distraction detection and driver identification (ID). Low and medium-income countries account for 93% of traffic deaths; moreover, a major contributing factor to road crashes is distracted driving. Motivated by this, the first part of this thesis explores the possibility of an easy-to-deploy solution to distracted driving detection. Most of the related work uses sophisticated sensors or cameras, which raises privacy concerns and increases the cost. Therefore a machine learning (ML) approach is proposed that only uses signals from the CAN-bus and the inertial measurement unit (IMU). It is then evaluated against a hand-annotated dataset of 13 drivers and delivers reasonable accuracy. This approach is limited in detecting short-term distractions but demonstrates that a viable solution is possible. In the second part, the focus is on the effective identification of drivers using their driving behavior. The aim is to address the shortcomings of the state-of-the-art methods. First, a driver ID mechanism based on discriminative classifiers is used to find a set of suitable signals and features. It uses five signals from the CAN-bus, with hand-engineered features, which is an improvement from current state-of-the-art that mainly focused on external sensors. The second approach is based on Gaussian mixture models (GMMs), although it uses two signals and fewer features, it shows improved accuracy. In this system, the enrollment of a new driver does not require retraining of the models, which was a limitation in the previous approach. In order to reduce the amount of training data a Triplet network is used to train a deep neural network (DNN) that learns to discriminate drivers. The training of the DNN does not require any driving data from the target set of drivers. The DNN encodes pieces of driving data to an embedding space so that in this space examples of the same driver will appear closer to each other and far from examples of other drivers. This technique reduces the amount of data needed for accurate prediction to under a minute of driving data. These three solutions are validated against a real-world dataset of 57 drivers. Lastly, the possibility of a driver ID system is explored that only uses floating car data (FCD), in particular, GPS data from smartphones. A DNN architecture is then designed that encodes the routes, origin, and destination coordinates as well as various other features computed based on contextual information. The proposed model is then evaluated against a dataset of 678 drivers and shows high accuracy. In a nutshell, this work demonstrates that proper driver ID is achievable. The constraints imposed by the use-case and data availability negatively affect the performance; in such cases, the efficient use of the available data is crucial. [less ▲]

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See detailThe ALMA-Yactul Ecosystem: A Holistic Approach for Student-centered Integration of Learning Material
Grevisse, Christian UL

Doctoral thesis (2020)

Digital learning resources play a key role in technology enhanced learning, yet their organization poses a challenge to both learners and teachers. Students are confronted with an ever-growing amount of ... [more ▼]

Digital learning resources play a key role in technology enhanced learning, yet their organization poses a challenge to both learners and teachers. Students are confronted with an ever-growing amount of available resources in an open, heterogeneous corpus. Finding relevant learning material for a given context or task, such as an exercise, is non-trivial, especially for novices in a complex domain, who often lack specific search skills. In addition, there is often no direct link between the learning material and the task at hand, and the constant interruption of the task in order to search for resources may have an impact on the cognitive load. Moreover, from the perspective of teachers and instructional designers, authoring high-quality learning material is a time-intensive task. Hence, reusing the authored material in multiple contexts would be beneficial. This dissertation addresses these issues by proposing the ALMA-Yactul ecosystem, a holistic approach for student-centered integration of learning material. Learners can benefit from scaffolding support to retrieve learning material relevant to their current context at a fine-grained level and across the boundaries of individual courses. This integration is showcased in multiple applications and domains, such as a plugin for an Integrated Development Environment or an enhanced sketchnoting app. While the former provides novices in computer programming the necessary tools to scaffold the search for heterogeneous documents on fine-grained syntactical elements, the latter allows for suggesting further information while taking notes in class. In both cases, it is not necessary for learners to leave their current study environment. To implicitly link learning resources and tasks, Semantic Web technologies such as ontologies are used to annotate documents. For this purpose, an extensible and lightweight modular domain ontology for programming languages has been created. While the main study domain in this work is computer science with a special focus on programming, the transferability of the proposed approach to other domains is demonstrated through multiple examples. Furthermore, to foster the active engagement of students in the learning process, Yactul, a game-based platform for continuous active learning has been developed. Apart from its use in the classroom, the platform also provides formative assessment to the individual learner by keeping track of her performance on a per-concept basis. Yactul activities are a key element in the ecosystem, both benefitting from and contributing to the integration of learning material. Finally, teachers are assisted in semantically enhancing their resources through semi-automatic annotation support within popular authoring tools. A Knowledge Graph-based approach is employed for core concept identification. Apart from analysing the usage of this ecosystem and evaluating the user satisfaction in university courses, an experiment with high school pupils lacking prior knowledge in programming yielded positive results with respect to the proposed scaffolding support. [less ▲]

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See detailCommercial Radio Stations and their Dispositif. Transnational and Intermedial Perspectives on Radio Luxembourg and Europe n°1 in the Long Sixties.
Legay, Richard UL

Doctoral thesis (2020)

Commercial radio stations Radio Luxembourg (French and English services) and Europe n°1 are the focal point of this work. They were popular institutions in Western Europe throughout the Long Sixties (1958 ... [more ▼]

Commercial radio stations Radio Luxembourg (French and English services) and Europe n°1 are the focal point of this work. They were popular institutions in Western Europe throughout the Long Sixties (1958-1974) working across media and broadcasting transnationally. This thesis postulates the existence of an overarching dispositif of commercial radio stations that enabled them to operate on various dimensions and differentiated them from other broadcasters. The research conducted in this thesis leans on various historical sources (i.e. institutional archives, maps, radio programmes, magazines) to analyse the dispositif through three main lenses. The first lens focuses on the appropriation and representation by the stations of a transnational broadcasting space, thanks to institutional archives and maps. The second inquires into the construction of a soundscape of commercial radio and identifies its key features by a close study and thick description of recordings as source material. Magazines - namely Salut les Copains and Fabulous 208 - are the core sources of the third lens, which studies the intermedial and intertextual entanglements of Europe n°1 and Radio Luxembourg with other media. This thesis relies on various scales and multiple dimensions of radio - such as its materiality, content, significance, and commercialism - to conduct an historical analysis on a particularly diverse source material. Building on the empirical results obtained throughout the research, this thesis shows the relevance of the dispositif concept to encompass and explains the transnational and intermedial nature of commercial radio stations. By doing so, the thesis contributes to current calls in media history to look beyond national and single-medium borders. [less ▲]

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See detailGegenkulturelle Tendenzen im postdramatischen Theater
Nonoa, Koku Gnatuloma UL

Doctoral thesis (2020)

Aufgrund ihrer verwandten Störstrategien sind Hermann Nitsch und Christoph Schlingensief wie „zwei Zwillingsbrüder“ zu betrachten, die individualisierte Künstlerpersönlichkeiten aufweisen. Sie sind zudem ... [more ▼]

Aufgrund ihrer verwandten Störstrategien sind Hermann Nitsch und Christoph Schlingensief wie „zwei Zwillingsbrüder“ zu betrachten, die individualisierte Künstlerpersönlichkeiten aufweisen. Sie sind zudem von der institutionskritischen Inszenierung theatraler, körperzentrierter Präsenz und Erfahrung des Realen bis zur Fusionierung ritueller, religiöser und politischer Elemente verwandt und sehr gute compagnons de route. Diese Publikation widmet sich der Analyse des Theaters als Kunst bzw. Ästhetik kultureller Selbstreflexion und Selbstveränderung in Nitschs und Schlingensiefs postdramatischen Inszenierungs- sowie Störstrategien im Spannungsfeld von Religion, Politik und Theater. [less ▲]

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See detailEssays on Networks, Information Economics, and Dynamic Games of Populism and Conflict
Hakobyan, Zaruhi UL

Doctoral thesis (2020)

This thesis focuses on developing tools and models for studying strategic interaction among agents in dynamics games. This dissertation consists of one pure theory paper and two applied theory papers. The ... [more ▼]

This thesis focuses on developing tools and models for studying strategic interaction among agents in dynamics games. This dissertation consists of one pure theory paper and two applied theory papers. The first chapter develops a general result in differential games. This is an area for studying strategic interactions when agents are forward-looking and calculate their future strategic interactions. The second and third chapters deal with the problem of strategic interactions under incomplete information, in the context of networks. In the second chapter, the analytical tools for linking up strategic actions with the evolution of a network are developed. The last chapter extends the second chapter by recommending network-manager strategies that can lead to welfare-improving network evolution under incomplete information. The thesis presents the first studies to propose a search and matching mechanism of network friends in an environment of incomplete information, higher-order beliefs, and evolutionary dynamics. [less ▲]

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See detailRethinking agricultural cooperatives in Kyrgyzstan: towards a postcapitalist approach to cooperation in postsocialism (and beyond) (and beyond)
Cima, Ottavia UL

Doctoral thesis (2020)

In the last three decades, community-based approaches have gained large acclamation worldwide as a way to promote sustainable and inclusive development but also, in ex-socialist countries in Central and ... [more ▼]

In the last three decades, community-based approaches have gained large acclamation worldwide as a way to promote sustainable and inclusive development but also, in ex-socialist countries in Central and Eastern Europe and the Former Soviet Union, as a way to support the postsocialist “transition” towards market economy. International donors have attempted to establish formal institutions for cooperation in local communities; among these, service cooperatives have promised a democratic and market-fit alternative to socialist collective farms. Kyrgyzstan’s liberalised economy after its independence from the Soviet Union in 1991 has been a fertile ground for experiments with models of institutionalised cooperation – including agricultural cooperatives. However, today the dominant framing considers most cooperatives in the country as failed and explains this apparent failure with some forms of historically inherited negative attitude towards cooperation. This research aims to provide an alternative reading of agricultural cooperatives in Kyrgzystan in order to generate affects more positive than the feelings of failure and inadequacy produced by the dominant framing. I thus focus on the promotion of agricultural cooperatives in rural Kyrgyzstan by international actors and on how local communities reinterpret and renegotiate a formal institution for cooperation promoted by external actors. I thereby illustrate how international actors uphold a specific model of cooperatives – as a tool on a prescribed route towards a teleological fantasy of development – and how local actors incorporate, and thereby reframe, this model in their everyday practices. I do this through an ethnographic engagement with villagers in Pjak, in the North-East of the country, and in particular with the practices and representations that emerge in relation to a local cooperative, Ak-Bulut. My analysis represents an entry point for rethinking not only cooperatives but also well-established economic theories and models – not only in Kyrgyzstan or in other ex-socialist countries in CEE and the FSU, but globally. The focus on cooperative promotion, indeed, opens to a broader reflection on how communities and individuals locally rearticulate global processes of neoliberalisation and marketisation. I thus interrogate the ways in which hegemonic discourses on the economy, development and modernity produce particular kinds of subjectivities and affects and the consequences of this on material inequalities; simultaneously, I explore the room for individual agency – for resistance and contestation – that emerges from the discontinuities of these hegemonic discourses. As a way to reinforce and expand this agency, I propose a renewed approach – a postcapitalist, postfantasmatic and relational one – to cooperatives and cooperation in postsocialism that invites to assume an open, anti-essentialist stance to engage with communities in the here and now. This approach, I argue, is relevant (and indeed needed) also for other contexts globally, especially in the present context of rising nationalist and authoritarian forces. [less ▲]

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See detailSYMBOL LEVEL PRECODING TECHNIQUES FOR HARDWARE AND POWER EFFICIENT WIRELESS TRANSCEIVERS
Domouchtsidis, Stavros UL

Doctoral thesis (2020)

Large-scale antennas are crucial for next generation wireless communication systems as they improve spectral efficiency, reliability and coverage compared to the traditional ones that are employing ... [more ▼]

Large-scale antennas are crucial for next generation wireless communication systems as they improve spectral efficiency, reliability and coverage compared to the traditional ones that are employing antenna arrays of few elements. However, the large number of antenna elements leads to a big increase in power consumption of conventional fully digital transceivers due to the one Radio Frequency (RF) chain / per antenna element requirement. The RF chains include a number of different components among which are the Digital-to-Analog Converters (DACs)/Analog-to-Digital Converters (ADCs) that their power consumption increases exponential with the resolution they support. Motivated by this, in this thesis, a number of different architectures are proposed with the view to reduce the power consumption and the hardware complexity of the transceiver. In order to optimize the transmission of data through them, corresponding symbol level precoding (SLP) techniques were developed for the proposed architectures. SLP is a technique that mitigates multi-user interference (MUI) by designing the transmitted signals using the Channel State Information and the information-bearing symbols. The cases of both frequency flat and frequency selective channels were considered. First, three different power efficient transmitter designs for transmission over frequency flat channels and their respective SLP schemes are considered. The considered systems tackle the high hardware complexity and power consumption of existing SLP techniques by reducing or completely eliminating fully digital RF chains. The precoding design is formulated as a constrained least squares problem and efficient algorithmic solutions are developed via the Coordinate Descent method. Next, the case of frequency selective channels is considered. To this end, Constant Envelope precoding in a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing system (CE MIMO-OFDM) is considered. In CE MIMO-OFDM the transmitted signals for each antenna are designed to have constant amplitude regardless of the channel realization and the information symbols that must be conveyed to the users. This facilitates the use of power-efficient components, such as phase shifters and non-linear power amplifiers. The precoding problem is firstly formulated as a least-squares problem with a unit-modulus constraint and solved using an algorithm based on the coordinate descent (CCD) optimization framework and then, after reformulating the problem into an unconstrained non-linear least squares problem, a more computationally efficient solution using the Gauss-Newton algorithm is presented. Then, CE MIMO-OFDM is considered for a system with low resolution DACs. The precoding design problem is formulated as a mixed discrete- continuous least-squares optimization one which is NP-hard. An efficient low complexity solution is developed based also on the CCD optimization framework. Finally, a precoding scheme is presented for OFDM transmission in MIMO systems based on one-bit DACs and ADCs at the transmitter’s and the receiver’s end, respectively, as a way to reduce the total power consumption. The objective of the precoding design is to mitigate the effects of one-bit quantization and the problem is formulated and then is split into two NP hard least squares optimization problems. Algorithmic solutions are developed for the solution of the latter problems, based on the CCD framework. [less ▲]

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See detailThe low-dimensional algebraic cohomology of infinite-dimensional Lie algebras of Virasoro-type
Ecker, Jill Marie-Anne UL

Doctoral thesis (2020)

In this doctoral thesis, the low-dimensional algebraic cohomology of infinite-dimensional Lie algebras of Virasoro-type is investigated. The considered Lie algebras include the Witt algebra, the Virasoro ... [more ▼]

In this doctoral thesis, the low-dimensional algebraic cohomology of infinite-dimensional Lie algebras of Virasoro-type is investigated. The considered Lie algebras include the Witt algebra, the Virasoro algebra and the multipoint Krichever-Novikov vector field algebra. We consider algebraic cohomology, meaning we do not put any constraints of continuity on the cochains. The Lie algebras are considered as abstract Lie algebras in the sense that we do not work with particular realizations of the Lie algebras. The results are thus independent of any underlying choice of topology. The thesis is self-contained, as it starts with a technical chapter introducing the definitions, concepts and methods that are used in the thesis. For motivational purposes, some time is spent on the interpretation of the low-dimensional cohomology. First results include the computation of the first and the third algebraic cohomology of the Witt and the Virasoro algebra with values in the trivial and the adjoint module, the second algebraic cohomology being known already. A canonical link between the low-dimensional cohomology of the Witt and the Virasoro algebra is exhibited by using the Hochschild-Serre spectral sequence. More results are given by the computation of the low-dimensional algebraic cohomology of the Witt and the Virasoro algebra with values in general tensor-densities modules. The study consists of a mix between elementary algebra and algorithmic analysis. Finally, some results concerning the low-dimensional algebraic cohomology of the multipoint Krichever-Novikov vector field algebra are derived. The thesis is concluded with an outlook containing possible short-term goals that could be achieved in the near future as well as some long-term goals. [less ▲]

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See detailDeep Pattern Mining for Program Repair
Liu, Kui UL

Doctoral thesis (2019)

Error-free software is a myth. Debugging thus accounts for a significant portion of software maintenance and absorbs a large part of software cost. In particular, the manual task of fixing bugs is tedious ... [more ▼]

Error-free software is a myth. Debugging thus accounts for a significant portion of software maintenance and absorbs a large part of software cost. In particular, the manual task of fixing bugs is tedious, error- prone and time-consuming. In the last decade, automatic bug-fixing, also referred to as automated program repair (APR) has boomed as a promising endeavor of software engineering towards alleviating developers’ burden. Several potentially promising techniques have been proposed making APR an increasingly prominent topic in both the research and practice communities. In production, APR will drastically reduce time-to-fix delays and limit downtime. In a development cycle, APR can help suggest changes to accelerate debugging. As an emergent domain, however, program repair has many open problems that the community is still exploring. Our work contributes to this momentum on two angles: the repair of programs for functionality bugs, and the repair of programs for method naming issues. The thesis starts with highlighting findings on key empirical studies that we have performed to inform future repair approaches. Then, we focus on template-based program repair scenarios and explore deep learning models for inferring accurate and relevant patterns. Finally, we integrate these patterns into APR pipelines, which yield the state of the art repair tools. The dissertation includes the following contributions: • Real-world Patch Study: Existing APR studies have shown that the state-of-the-art techniques in automated repair tend to generate patches only for a small number of bugs even with quality issues (e.g., incorrect behavior and nonsensical changes). To improve APR techniques, the community should deepen its knowledge on repair actions from real-world patches since most of the techniques rely on patches written by human developers. However, previous investigations on real-world patches are limited to statement level that is not sufficiently fine-grained to build this knowledge. This dissertation starts with deepening this knowledge via a systematic and fine-grained study of real-world Java program bug fixes. • Fault Localization Impact: Existing test-suite-based APR systems are highly dependent on the performance of the fault localization (FL) technique that is the process of the widely studied APR pipeline. However, APR systems generally focus on the patch generation, but tend to use similar but different strategies for fault localization. To assess the impact of FL on APR, we identify and investigate a practical bias caused by the FL step in a repair pipeline. We propose to highlight the different FL configurations used in the literature, and their impact on APR systems when applied to the real bugs. Then, we explore the performance variations that can be achieved by “tweaking” the FL step. • Fix Pattern Mining: Fix patterns (a.k.a. fix templates) have been studied in various APR scenarios. Particularly, fix patterns have been widely used in different APR systems. To date, fix pattern mining is mainly studied in three ways: manually summarization, transformation inferring and code change action statistics. In this dissertation, we explore mining fix patterns for static bugs leveraging deep learning and clustering algorithms. • Avatar: Fix pattern based patch generation is a promising direction in the APR community. Notably, it has been demonstrated to produce more acceptable and correct patches than the patches obtained with mutation operators through genetic programming. The performance of fix pattern based APR systems, however, depends on the fix ingredients mined from commit changes in development histories. Unfortunately, collecting a reliable set of bug fixes in repositories can be challenging. We propose to investigate the possibility in an APR scenario of leveraging code changes that address violations by static bug detection tools. To that end, we build the Avatar APR system, which exploits fix patterns of static analysis violations as ingredients for patch generation. • TBar: Fix patterns are widely used in patch generation of APR, however, the repair performance of a single fix pattern is not studied. We revisit the performance of template-based APR to build comprehensive knowledge about the effectiveness of fix patterns, and to highlight the importance of complementary steps such as fault localization or donor code retrieval. To that end, we first investigate the literature to collect, summarize and label recurrently-used fix patterns. Based on the investigation, we build TBar, a straightforward APR tool that systematically attempts to apply these fix patterns to program bugs. We thoroughly evaluate TBar on the Defects4J benchmark. In particular, we assess the actual qualitative and quantitative diversity of fix patterns, as well as their effectiveness in yielding plausible or correct patches. • Debugging Method Names: Except the issues about semantic/static bugs in programs, we note that how to debug inconsistent method names automatically is important to improve program quality. In this dissertation, we propose a deep learning based approach to spotting and refactoring inconsistent method names in programs. [less ▲]

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See detailDEVELOPING INDIVIDUAL-BASED GUT MICROBIOME METABOLIC MODELS FOR THE INVESTIGATION OF PARKINSON’S DISEASE-ASSOCIATED INTESTINAL MICROBIAL COMMUNITIES
Baldini, Federico UL

Doctoral thesis (2019)

The human phenotype is a result of the interactions of environmental factors with genetic ones. Some environmental factors such as the human gut microbiota composition and the related metabolic functions ... [more ▼]

The human phenotype is a result of the interactions of environmental factors with genetic ones. Some environmental factors such as the human gut microbiota composition and the related metabolic functions are known to impact human health and were put in correlation with the development of different diseases. Most importantly, disentangling the metabolic role played by these factors is crucial to understanding the pathogenesis of complex and multifactorial diseases, such as Parkinson’s Disease. Microbial community sequencing became the standard investigation technique to highlight emerging microbial patterns associated with different health states. However, even if highly informative, such technique alone is only able to provide limited information on possible functions associated with specific microbial communities composition. The integration of a systems biology computational modeling approach termed constraint-based modeling with sequencing data (whole genome sequencing, and 16S rRNA gene sequencing), together with the deployment of advanced statistical techniques (machine learning), helps to elucidate the metabolic role played by these environmental factors and the underlying mechanisms. The first goal of this PhD thesis was the development and deployment of specific methods for the integration of microbial abundance data (coming from microbial community sequencing) into constraint-based modeling, and the analysis of the consequent produced data. The result was the implementation of a new automated pipeline, connecting all these different methods, through which the study of the metabolism of different gut microbial communities was enabled. Second, I investigated possible microbial differences between a cohort a Parkinson’s disease patients and controls. I discovered microbial and metabolic changes in Parkinson’s disease patients and their relative dependence on several physiological covariates, therefore exposing possible mechanisms of pathogenesis of the disease.Overall, the work presented in this thesis represents method development for the investigation of before unexplored functional metabolic consequences associated with microbial changes of the human gut microbiota with a focus on specific complex diseases such as Parkinson’s disease. The consequently formulated hypothesis could be experimentally validated and could represent a starting point to envision possible clinical interventions. [less ▲]

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See detailIMPROVEMENT OF THE LOAD-BEARING CAPACITY OF DRY-STACKED MASONRY
Chewe Ngapeya, Gelen Gael UL

Doctoral thesis (2019)

Mortar bonded masonry is one of the oldest construction technics traditionally used around the world. However, dry-stacked masonry (DSM) is a competitive system that confers significant assets to masonry ... [more ▼]

Mortar bonded masonry is one of the oldest construction technics traditionally used around the world. However, dry-stacked masonry (DSM) is a competitive system that confers significant assets to masonry in the sense that, concisely, it saves construction time, requires less skill labourers and ease the construction as well as the de-construction. Despite all this major benefits, the current use of DSM is hindered by the geometric imperfections of the block units and the lack of adapted design codes. Indeed, the block geometric imperfections, i.e. the bed-joint roughness and the height difference, cause a significant uneven load-distribution in DSM, which generally leads to a premature cracking and a drop of the wall compressive strength. On the other hand, the lack of adapted design codes entail significant safety hazards in the construction of such masonry walls. In view of the foregoing, through systematic numerical, experimental and analytical investigations, the present thesis aims to analyse the impacts of the block bed-joint imperfections on the mechanical response of DSM axially loaded. Furthermore, the current thesis aims to develop a strategy to overcome the block geometric imperfections and alleviate its impacts on the load-bearing capacity of DSM. Finally, the present thesis intends to develop a design model for predicting the load-bearing capacity of DSM, while taking into account the effects of the block geometric imperfections for a safe design. First of all, at the beginning of the research project, a new dry-stacked masonry block is designed and labelled ‘M-Block’. The impact of the bed-joint roughness and the block height variation on the stress distribution in a DSM is analysed through numerical modelling. It is shown that the block height difference yields five potential load cases that block units may suffer upon the axial compression of a DSM wall. Accordingly, it is also shown that a nominal DSM wall can exhibit different load percolation paths and different damages. Further, a strategy is presented to overcome the bed-joint imperfections, increase the actual contact area in the bed-joints and ultimately improve the load-bearing capacity of DSM, by adding a material layer (the ‘contact layer’) on the raw DSMb. The capacity of the contact layer to increase the actual contact and level the stress distribution was first investigated through numerical models then evidenced through experimental tests on masonry triplets. The contact layer was also investigated for improving the load-bearing capacity of dry-stacked masonry, with satisfactory results obtained on wallets tested in the lab. As the finite element modelling is cumbersome and the experimental investigations onerous and laborious, an analytical model has then been developed for predicting the load-bearing capacity of DSM. A statistical modelling has been developed for determining a factor δh, which stands for the reduction of the nominal section of a DSM generated by the block height variation. Experimental tests were also performed on masonry triplets for measuring the ultimate actual contact in the bed-joints and defining a factor δr, which stands for the reduction of the nominal contact area generated by the block bed-joint roughness. The two defined parameters were then exploited to establish the design model that takes into account the block imperfections in the prediction of the load-bearing capacity of DSM. The design model was shown quite well capable of predicting the load-bearing capacity of DSM with a mean accuracy of 93% - 106% and a standard deviation of 12% - 10%. [less ▲]

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See detailEssays on Demographic Change and Economic Performance
Iong, Ka Kit UL

Doctoral thesis (2019)

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See detailAssessment of Fundamental Motives
Dörendahl, Jan UL

Doctoral thesis (2019)

Motivation, that is, the orientation of the momentary execution of life towards a positively evaluated target state (Rheinberg & Vollmeyer, 2012), is one of the most important psychological constructs ... [more ▼]

Motivation, that is, the orientation of the momentary execution of life towards a positively evaluated target state (Rheinberg & Vollmeyer, 2012), is one of the most important psychological constructs related to success in various life domains such as school, work or family life (Pellegrino & Hilton, 2013). To be able to provide guidance to people and to support them in achieving success in these life domains, it is essential to identify those motivational aspects that are relevant for the respective life domain and to make them assessable. Here, motivational aspects that are inherent in a person, such as motives or goals, are promising candidates. Both constructs can be defined as explicit cognitive representations of desirable end states (Brandstätter, Schüler, Puca, & Lozo, 2013; Karoly, 1999). However, motives and goals are distinguished at the level of abstraction, that is, goals are a concrete representation of more abstract motives (Elliot & Church, 1997). In order to broaden our understanding in the assessment of motives and goals that are of relevance for education and work as two of the most important life domains, three studies were conducted in the context of the presented dissertation. In Paper 1, we revised the theory of Fundamental Motives (Havercamp, 1998; Reiss & Havercamp, 1998) and developed a time- and cost-efficient questionnaire to assess them in research settings. Fundamental Motives are a self-contained framework of 16 motives considered to be relevant for people in their everyday lives. The framework is appealing as it provides an approach to narrow down the plethora of motives to those relevant in a variety of life domains. In addition, the framework is already used extensively in coaching for work and other areas of life (Reyss & Birkhahn, 2009). First, an initial item pool was successively refined into 16 scales with three items each (named 16 motives research scales; 16mrs) across two samples with a total sample size of N = 569 representative for the German population with respect to age, sex and education. Second, we used another representative sample (N = 999) to validate the questionnaire and explore its nomological network. Results support the reliability and validity of the 16mrs for the assessment of Fundamental Motives. Investigations of the nomological network indicate, that Fundamental Motives represent aspects of personality that are different from the Big Five personality traits (e.g., Costa & McCrae, 1992) and cover motivational aspects beyond the well-established Power, Achievement, Affiliation, Intimacy, and Fear motives (Heckhausen & Heckhausen, 2010). Paper 2 was based on the results of Study 1, since we applied the framework of Fundamental Motives, as measured by the 16mrs constructed in Study 1, to the life domain of work. In coaching in work contexts, Fundamental Motives have been used extensively, not least because of their fine-grained level of abstraction that allows for a straightforward interpretation by the client. By investigating how the satisfaction of fine-grained motives supplied by characteristics of the workplace (i.e., need-supply fit) contribute to job satisfaction, we further validated the framework itself. At the same time were able to gain more detailed insights into how need-supply fit impacts job satisfaction, compared to broader motive or value clusters. To this end, we used the representative sample from Study 1 (N = 999) and selected all working people (n = 723). We applied polynomial regression in combination with response surface analysis (e.g., Edwards & Parry, 1993), which allows to simultaneously investigate how different levels of Fundamental Motives on the one hand and different levels of supply to satisfy these motives at the workplace on the other contribute to job satisfaction. We found that job satisfaction was highest when the level of supply by the workplace exceeded the level of the motive for Social Acceptance, Status, Autonomy, Sex, and Retention motives. When a high level of the motive and a high level of supply met, job satisfaction was highest for Curiosity, Idealism, and Social Participation motives. When the supplies fell short compared to the level of the motive, job satisfaction was negatively affected by the need-supply fit of Social Acceptance, Status, Sex, Retention, Curiosity, and Idealism motives. The results can be used in coaching and career development to uncover potential causes of low job satisfaction and provide guidance to clients on how to enhance their job satisfaction. In Paper 3, we shifted the focus to education as another major life domain. Here, achievement motivation has been identified as one of the major driving forces for progression and success (Schiefele & Schaffner, 2015). On a more concrete level compared to achievement motivation, Achievement Goals have been established as students’ cognitive representations of desired and undesired end states in educational achievement contexts (Elliot & Thrash, 2002; Hulleman, Schrager, Bodmann, & Harackiewicz, 2010). These goals typically focus on mastery, that is learning as much as possible, and performance, that is outperforming others or avoiding being outperformed. So far, Achievement Goals have been mostly conceptualized as domain-specific (Bong, 2001). Although this assumption is supported by previous studies, research on the processes operating behind the domain- specificity is scarce. The dimensional comparisons theory (Möller & Marsh, 2013) has introduced dimensional comparisons as a potential process operating behind the domain- specificity. Dimensional comparisons describe intrapersonal comparisons of characteristics in a domain with characteristics in another domain for the sake of self-evaluation. Previous investigations indicated that dimensional comparison processes are involved in the formation of the domain-specificity of important educational constructs, such as Self-Concept or Test Anxiety. Consequently, our aim in study 3 was to investigate, if dimensional comparison processes operate in the formation of the domain-specificity of Achievement Goals. To this end, we used a sample of N = 381 German ninth and tenth grade students in six German highest-track schools. Results indicate that dimensional comparison processes impact the domain specificity of Achievement Goals. Thus, the results extend our understanding of the domain specificity of Achievement Goals and simultaneously add to the validity of the dimensional comparison theory. In conclusion, the presented scientific work adds to the assessment of motives and goals that are crucially important in various life domains, but especially in work and educational settings. The contributions of this dissertation to the existing literature include (1) the revision of a comprehensive motivational framework (Paper 1), (2) the development and validation of a questionnaire based on this revised framework (Papers 1 & 2), (3) important assessment related insights concerning Achievement Goals in educational settings (Paper 3), and (4) practical implications for coaching and interventions in work and educational settings as two of the most important life domains (Papers 2 & 3). [less ▲]

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See detailEssays in Financial Stability
Gabriele, Carmine UL

Doctoral thesis (2019)

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See detailGraph-based Algorithms for Smart Mobility Planning and Large-scale Network Discovery
Changaival, Boonyarit UL

Doctoral thesis (2019)

Graph theory has become a hot topic in the past two decades as evidenced by the increasing number of citations in research. Its applications are found in many fields, e.g. database, clustering, routing ... [more ▼]

Graph theory has become a hot topic in the past two decades as evidenced by the increasing number of citations in research. Its applications are found in many fields, e.g. database, clustering, routing, etc. In this thesis, two novel graph-based algorithms are presented. The first algorithm finds itself in the thriving carsharing service, while the second algorithm is about large graph discovery to unearth the unknown graph before any analyses can be performed. In the first scenario, the automatisation of the fleet planning process in carsharing is proposed. The proposed work enhances the accuracy of the planning to the next level by taking an advantage of the open data movement such as street networks, building footprints, and demographic data. By using the street network (based on graph), it solves the questionable aspect in many previous works, feasibility as they tended to use rasterisation to simplify the map, but that comes with the price of accuracy and feasibility. A benchmark suite for further research in this problem is also provided. Along with it, two optimisation models with different sets of objectives and contexts are proposed. Through a series of experiment, a novel hybrid metaheuristic algorithm is proposed. The algorithm is called NGAP, which is based on Reference Point based Non-dominated Sorting genetic Algorithm (NSGA-III) and Pareto Local Search (PLS) and a novel problem specific local search operator designed for the fleet placement problem in carsharing called Extensible Neighbourhood Search (ENS). The designed local search operator exploits the graph structure of the street network and utilises the local knowledge to improve the exploration capability. The results show that the proposed hybrid algorithm outperforms the original NSGA-III in convergence under the same execution time. The work in smart mobility is done on city scale graphs which are considered to be medium size. However, the scale of the graphs in other fields in the real-world can be much larger than that which is why the large graph discovery algorithm is proposed as the second algorithm. To elaborate on the definition of large, some examples are required. The internet graph has over 30 billion nodes. Another one is a human brain network contains around 1011 nodes. Apart of the size, there is another aspect in real-world graph and that is the unknown. With the dynamic nature of the real-world graphs, it is almost impossible to have a complete knowledge of the graph to perform an analysis that is why graph traversal is crucial as the preparation process. I propose a novel memoryless chaos-based graph traversal algorithm called Chaotic Traversal (CHAT). CHAT is the first graph traversal algorithm that utilises the chaotic attractor directly. An experiment with two well-known chaotic attractors, Lozi map and Rössler system is conducted. The proposed algorithm is compared against the memoryless state-of-the-art algorithm, Random Walk. The results demonstrate the superior performance in coverage rate over Random Walk on five tested topologies; ring, small world, random, grid and power-law. In summary, the contribution of this research is twofold. Firstly, it contributes to the research society by introducing new study problems and novel approaches to propel the advance of the current state-of-the-art. And Secondly, it demonstrates a strong case for the conversion of research to the industrial sector to solve a real-world problem. [less ▲]

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See detailDeep Neural Networks for Personalized Sentiment Analysis with Information Decay
Guo, Siwen UL

Doctoral thesis (2019)

People have different lexical choices when expressing their opinions. Sentiment analysis, as a way to automatically detect and categorize people’s opinions in text, needs to reflect this diversity. In ... [more ▼]

People have different lexical choices when expressing their opinions. Sentiment analysis, as a way to automatically detect and categorize people’s opinions in text, needs to reflect this diversity. In this research, I look beyond the traditional population-level sentiment modeling and leverage socio-psychological theories to incorporate the concept of personalized modeling. In particular, a hierarchical neural network is constructed, which takes related information from a person’s past expressions to provide a better understanding of the sentiment from the expresser’s perspective. Such personalized models can suffer from the data sparsity issue, therefore they are difficult to develop. In this work, this issue is addressed by introducing the user information at the input such that the individuality from each user can be captured without building a model for each user and the network is trained in one process. The evolution of a person’s sentiment over time is another aspect to investigate in personalization. It can be suggested that recent incidents or opinions may have more effect on the person’s current sentiment than the older ones, and the relativeness between the targets of the incidents or opinions plays a role on the effect. Moreover, psychological studies have argued that individual variation exists in how frequently people change their sentiments. In order to study these phenomena in sentiment analysis, an attention mechanism which is reshaped with the Hawkes process is applied on top of a recurrent network for a user-specific design. Furthermore, the modified attention mechanism delivers a functionality in addition to the conventional neural networks, which offers flexibility in modeling information decay for temporal sequences with various time intervals. The developed model targets data from social platforms and Twitter is used as an example. After experimenting with manually and automatically labeled datasets, it can be found that the input formulation for representing the concerned information and the network design are the two major impact factors of the performance. With the proposed model, positive results have been observed which confirm the effectiveness of including user-specific information. The results reciprocally support the psychological theories through the real-world actions observed. The research carried out in this dissertation demonstrates a comprehensive study of the significance of considering individuality in sentiment analysis, which opens up new perspectives for future research in the area and brings opportunities for various applications. [less ▲]

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See detailTOWARDS A MODELLING FRAMEWORK WITH TEMPORAL AND UNCERTAIN DATA FOR ADAPTIVE SYSTEMS
Mouline, Ludovic UL

Doctoral thesis (2019)

Self-Adaptive Systems (SAS) optimise their behaviours or configurations at runtime in response to a modification of their environments or their behaviours. These systems therefore need a deep ... [more ▼]

Self-Adaptive Systems (SAS) optimise their behaviours or configurations at runtime in response to a modification of their environments or their behaviours. These systems therefore need a deep understanding of the ongoing situation which enables reasoning tasks for adaptation operations. Using the model-driven engineering (MDE) methodology, one can abstract this situation. However, information concerning the system is not always known with absolute confidence. Moreover, in such systems, the monitoring frequency may differ from the delay for reconfiguration actions to have measurable effects. These characteristics come with a global challenge for software engineers: how to represent uncertain knowledge that can be efficiently queried and to represent ongoing actions in order to improve adaptation processes? To tackle this challenge, this thesis defends the need for a unified modelling framework which includes, besides all traditional elements, temporal and uncertainty as first-class concepts. Therefore, a developer will be able to abstract information related to the adaptation process, the environment as well as the system itself. Towards this vision, we present two evaluated contributions: a temporal context model and a language for uncertain data. The temporal context model allows abstracting past, ongoing and future actions with their impacts and context. The language, named Ain’tea, integrates data uncertainty as a first-class citizen. [less ▲]

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See detailPATHOGENIC ROLE OF PARKINSON’S DISEASE-ASSOCIATED MIRO1 MUTATIONS IN THE MITOCHONDRIAL-ENDOPLASMIC RETICULUM INTERPLAY
Berenguer, Clara UL

Doctoral thesis (2019)

Parkinson´s disease (PD) is a chronic neurodegenerative disorder, in which only 5-10% of the cases are caused by genetic mutations. One of the main pathological hallmarks of PD is the loss of midbrain ... [more ▼]

Parkinson´s disease (PD) is a chronic neurodegenerative disorder, in which only 5-10% of the cases are caused by genetic mutations. One of the main pathological hallmarks of PD is the loss of midbrain dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of diseased brains. These DA neurons require large amounts of energy for the maintenance of their pace-making activity and their complex dendritic and axonal arborizations, features that force them to rely on a fully functional mitochondrial network. In this regard, mitochondrial dyshomeostasis is a central factor in PD pathophysiology. Mitochondria are considered the powerhouse of the cells, and they are extremely dynamic organelles that are distributed throughout the entire neuronal body to meet the cellular energy demands. The maintenance of mitochondrial function requires their interaction with other cellular organelles, in particular, the endoplasmic reticulum (ER). Overwhelming evidence indicates that the mitochondrial-ER interface is a potential target of growing importance for the investigation of PD. Several PD-related proteins were found to be involved in the structural maintenance and signaling regulation of mitochondrial-ER contact sites (MERCs). In recent years, myriad studies have identified the mitochondrial GTPase Miro1 as a crucial player in PD pathology. Miro1 protein is not only an adaptor for mitochondrial transport, but also acts as a cytosolic calcium sensor and as an ubiquitination target for the mitochondrial quality control machinery. Moreover, Miro1 can localize to MERCs, where it functions as a regulator of the calcium exchange between both organelles. To date, no genetic link between Miro1 and PD has been identified, and the influence of Miro1 in the regulation of MERCs within the context of neurodegeneration is still underestimated. This current study explored the damaging effect of novel PD-associated heterozygous mutations in RHOT1, the gene encoding Miro1 protein, in a diseased genetic background. We first obtained skin fibroblasts from the affected PD patients harboring Miro1 mutations, which we further differentiated into iPSC-derived neurons. The characterization of the mutations in both patient-derived cellular models unveiled important impairments in mitochondrial calcium homeostasis and sensitivity to calcium stress, associated with alterations in the abundance and functionality of the MERCs. Consequently, downstream pathways to these mechanisms were affected, such as autophagy flux and mitochondrial clearance. From our results, we can conclude that PD-associated mutant Miro1 leads to crucial alterations in MERCs, consequently affecting downstream mechanisms such as calcium homeostasis and mitophagy. These dysregulations might lead to an increased sensitivity to stress and finally cell death. Our findings strongly support the key role of MERCs in the progress of neurodegeneration and establish RHOT1 as a rare genetic risk factor in PD. [less ▲]

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See detailModeling Parkinson's disease using human midbrain organoids
Monzel, Anna Sophia UL

Doctoral thesis (2019)

With increasing prevalence, neurodegenerative disorders present a major challenge for medical research and public health. Despite years of investigation, significant knowledge gaps exist, which impede the ... [more ▼]

With increasing prevalence, neurodegenerative disorders present a major challenge for medical research and public health. Despite years of investigation, significant knowledge gaps exist, which impede the development of disease-modifying therapies. The development of tools to model both physiological and pathological human brains greatly enhanced our ability to study neurological disorders. Brain organoids, derived from human induced pluripotent stem cells (iPSCs), hold unprecedented promise for biomedical research to unravel novel pathological mechanisms of a multitude of brain disorders. As brain proxies, these models bridge the gap between traditional 2D cell cultures and animal models. Owing to their human origin, hiPSC-derived organoids can recapitulate features that cannot be modeled in animals by virtue of differences in species. Parkinson’s disease (PD) is a human-specific neurodegenerative disorder. The major manifestations are the consequence of degenerating dopaminergic neurons (DANs) in the midbrain. The disease has a multifactorial etiology and a multisystemic pathogenesis and pathophysiology. In this thesis, we used state-of-the-art technologies to develop a human midbrain organoid (hMO) model with a great potential to study PD. hMOs were generated from iPSC-derived neural precursor cells, which were pre-patterned to the midbrain/hindbrain region. hMOs contain multiple midbrain-specific cell types, such as midbrain DANs, as well as astrocytes and oligodendrocytes. We could demonstrate features of neuronal maturation such as myelination, synaptic connections, spontaneous electrophysiological activity and neural network synchronicity. We further developed a neurotoxin-induced PD organoid model and set up a high-content imaging platform coupled with machine learning classification to predict neurotoxicty. Patient-derived hMOs display PD-relevant pathomechanisms, indicative of neurodevelopmental deficits. hMOs as novel in vitro models open up new avenues to unravel PD pathophysiology and are powerful tools in biomedical research. [less ▲]

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See detailFeldtest und dynamische Simulation der außenliegenden Wandtemperierung
Schmidt, Christoph Wilhelm UL

Doctoral thesis (2019)

The present work deals in detail with two new, thermally active components for building renovation, namely the external wall tempering (aWT) and the external air tempering (aLT). With the help of these ... [more ▼]

The present work deals in detail with two new, thermally active components for building renovation, namely the external wall tempering (aWT) and the external air tempering (aLT). With the help of these two components, existing buildings can be thermally activated as part of an energetic refurbishment. The installation of the two components is minimally invasive from the outside. Due to the position of the active layer in the wall structure, the use of very low fluid temperatures is possible (low-exergy approach). Initially the theoretical principles for both components were developed and presented in accordance with standard literature for thermoactive component systems. Then characteristic values for the evaluation of the components (efficiency and utilisation rates) were developed and based on the theoretical principles, implementation concepts for both components were subsequently developed. Finally, a large-scale implementation of the two components could be realized on a facade. The aim of the implementation was not only to present the "feasibility" of the componentes but also to generate measurement data for the following considerations. In the course of its development, some sources of error could be identified and a multiplicity of realizations were obtained. For example, for warranty reasons a compromise had to be made regarding the thickness of the plaster for plastering the capillary tube mats. Overall, both components were successfully implemented and put into operation. In coordination to the implementation the system costs of both components were determined. Here, similar values were achieved in the implementation as determined within the framework of sample planning (~70 €/m²). With the help of the measurement data from the field test areas of the two components and two laboratory test benches, suitable modelling approaches could now be developed, verified and finally validated. Then stationary as well as transient measurements were carried out and compared and a good agreement between modelling and measurements could be determined. The comparison between idealized modelling and real-life components, which are under the influence of the (partly not unambiguously attributable) environmental conditions, causes difficulties. For the aWT, a maximum useful heat flow of around 60 W/m² in over-compensatory heating mode was determined. The useful heat flow is defined as the heat flow from the tempering level into the interior of the building. In a low-exergy operating mode, however, ~15 W/m² is more likely. For such external components, the time constants are also relevant; for the aWT these are in the daily range, with dead times of 3-4 hours. At the same time, the thermal activation of the existing structure can make it usable as a storage mass. However, since validated simulation models are available after completion of the measurements, potential estimates and further considerations can be made at simulation level. The simulation studies carried out on the building level show the potential, but also the important "sticking points" of the components. In summary, it can be stated that the aWT is more suitable for binary operation than a kind of base load tempering. Again, the pump power requirement in relation to the thermal input must be taken into account for long running times. The lower the heating requirement of a building, the more likely it is that the aWT can also be used as a independent system. When considering the aWT alone, control strategies adapted to the inertia of the aWT are the key to high cover shares. The combination of aLT and aWT was found to be very suitable for the complete heating of a building. Here, the simulation achieves high cover ratios with low flow temperatures and simple control strategies. Thus the feasibility of the ideas was shown, realistic system costs were determined and the basics were created on model level in order to investigate the further interesting aspects of the components by means of simulations and on the basis of the field test areas. [less ▲]

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See detailOptimization assisted Designing Mechanical Elements for Direct Metal Laser Sintering
Cao, Thanh Binh UL

Doctoral thesis (2019)

The common question that many mechanical engineers have tried to answer is “how to maximize strength and working reliability of parts during designs while being able to minimize the parts’ weights?” The ... [more ▼]

The common question that many mechanical engineers have tried to answer is “how to maximize strength and working reliability of parts during designs while being able to minimize the parts’ weights?” The associated solutions attach the design methods, which need to be de-veloped to build up the parts. The better solutions are the more reliable and lighter parts could be built up. Hence, the fewer negative impacts on the environment could be yielded and the closer distance we could step towards the more sustainable future. Under the influences of the Fourth Industrial Revolution, many optimization methods have been being developed, aimed at supporting engineers on figuring out the above question. Despite having substantial developments in recent years, both the optimization methods and its applications in the mechanical design field are still far from being fully exploited. To evaluate the potential use of the methods, specific product developments are essentially considered and investigated. The Thesis work particularly dealt with the investigations of the optimization assisted design methods, employed to develop structures of some mechanical elements. These constructed elements were expected to have higher performance than those traditionally designed and were able to be practically produced. For gradually studying and evaluating the processes of design, it was proposed to divide the work into the five separating phases. Within the initial phase, the first scheme of the optimization assisted design was theoretically investigated. Such a scheme was relied on the combination of topology optimization and lattice optimization and was considered in association with the redesigning process of a motorcycle frame. The frame was selected for this starting phase due to the convenient definition of the design volume subjected to the optimizations. By handling the investigations in dealing with (i) the first resonance frequency, (ii) the mass, (iii) the buckling load factor, and (iv) the equivalent stress of the newly designed frame and those of the original one, the potential use of the design approach was revealed. In addition, the investigations pointed out that further studies are essentially taken place to search for more appropriate ways to apply this approach to design novel complex structures. During the next three consecutive phases, the more complicate optimization schemes were proposed and studied. The schemes were composed of three optimization steps, including free shape optimization, topology optimization, as well as lattice optimization. The studies were handled in conjunction with the processes of innovating the hydrogen valve structure, which holds the unexposed design space. Different novel configurations were developed for the valve within these phases, targeting the reduction of mass, the prolongation of fatigue life, as well as the structural compatibility of the designed valves with DMLS. In addition, the design of a test channel for the valve performed via the use of a fatigue based approach was also introduced in one of the three phases. It was aimed at providing a mean to detect multiple early valve’s damages. All of the built structures were then virtually evaluated to point out the effectiveness of the design works. Within the last phase, experimental tests were proposed to carry out. In this phase, the best possible valve structure was selected and was subjected to produce by DMLS along with post-machining afterwards. Upon completion of the fabrications, the in-house fatigue tests were tak-en place for the produced valves until damages or reaching 2E5 cycles. The obtained data of the tests provided further evidence to support the theoretical studies demonstrated in the first four phases. [less ▲]

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See detailEpistemic Nonconceptualism. Nonconceptual Content and the Justification of Perceptual Beliefs
Orlando, Andy UL

Doctoral thesis (2019)

The questions whether the content of perception is nonconceptual and, if so, whether it can serve as the justificatory basis for perceptual beliefs have been at the epicentre of wide-ranging debates in ... [more ▼]

The questions whether the content of perception is nonconceptual and, if so, whether it can serve as the justificatory basis for perceptual beliefs have been at the epicentre of wide-ranging debates in recent philosophy of mind and epistemology. The present dissertation will set out to answer these matters. It will be argued that the content of perception is not necessarily conceptual, i.e. a specific understanding of nonconceptual content will be laid out and defended. Starting from the presentation and criticism of conceptualism, it will be concluded that the arguments brought forth against nonconceptualism can successfully be met. A specific version of nonconceptualism will be developed on this basis and will serve as the necessary framework for the remainder of the discussion. Flowing from these arguments, this specific version of nonconceptualism will be taken to task by clarifying, analysing and specifying its epistemological commitments and options. Several problem sets will have to be introduced and evaluated, such as the divide between externalists and internalists, the phenomena surrounding epistemic defeaters and examinations pertaining to reasoning, specifically whether experiences could be the output states of inferential processes. These reflections will not only provide a more in-depth investigation of some of the most pressing epistemological questions surrounding nonconceptual content, but will also allow for a seamless transition into the problem of which specific epistemological theory best bears out the epistemological role of nonconceptual content. Specifically, disjunctivism, capacity approaches and phenomenal conservatism will be assessed as to their capacity to vindicate nonconceptual content. Phenomenal conservatism will be identified as the theory that best integrates nonconceptualism. While phenomenal conservatism will thus be defended, the closing sections of the present dissertation will mainly focus on questions surrounding rationality. Indeed, if perception and/ or perceptual experiences could be classified as rational, or more accurately put, if arguments pertaining to the evaluability of a perceptual experience’s aetiology are tenable, it can reasonably be asked whether phenomenal conservatism can satisfactorily meet this challenge. Ultimately, it will be concluded that there is room for a specific notion of nonconceptual content as the justificatory basis for basic perceptual beliefs. [less ▲]

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See detailSix regards sur la master-classe de piano : phénoménologie et sémiotique de la rencontre musicale
Kim, Seong Jae UL

Doctoral thesis (2019)

In this thesis, I suggest new ways of grasping the affective dimension of musical experience that which traditional semiotics and musicology take little into account. Inspired by a dynamistic modelling ... [more ▼]

In this thesis, I suggest new ways of grasping the affective dimension of musical experience that which traditional semiotics and musicology take little into account. Inspired by a dynamistic modelling approach –which developed from the 1960s and since then has been influential in the domain of semiolinguistic disciplines–, I sketch out the fluctuating phases of semiogenesis within the field of piano masterclasses. The term ‘semiogenesis’ here, is taken in a broad sense, encompassing any deployment of sign-forms, either vague or articulated, diffused or well-defined. Such forms are conceived as being strained between expressiveness and normativity. They are also valorized in that they call the subject to participate in his or her own ‘lines of life’ which, in turn, may come to exist by those forms. A piano masterclass is given by a genuine master to highly accomplished students, both who truly testify to their own lives, to their own ways of ethical feeling, in the search for a unique musical praxis. In recent years, the field of masterclass has begun to attract the attention of the scientific community, especially in areas related to musical teaching and experience, such as psychology, aesthetics and epistemology or even sociology. Yet it is still suboptimal that most of the problems adopted in these frameworks incorporate nothing or so little in terms of the metamorphosis of sensitivity and the play of musical feeling in the characterization of their research objects. Nevertheless, the field of piano masterclass seems to be a particularly interesting and promising object of research in that the horizon of affect is preeminent in all the semiotic activities tied to it. Thus, I have attended several masterclasses in order to closely follow the praxis of the musicians (e.g., active and passive participation in masterclasses, audiovisual recordings, interviews, conversations and debates on music, etc.), in the spirit of making all its genetic depth to the semiotic activity, by approaching it under the perspective of an encountering and an orientation of musical sensibilities. One of the main tasks of my approach in the designing of the descriptions of this particular musical praxis consists in understanding the acoustic, gestural and linguistic phenomena, as giving birth to semiogenetic conditions of the constitution of a musical meaning. In this way, it is a fundamentally descriptive method, inspired by philosophical (Shaftesbury, Kierkegaard, Wittgenstein, Merleau-Ponty) and semiotic (Peirce, Saussure) minds, which joins the semiotic preoccupation from the very initial levels of a microgenesis, and by promoting it immediately into a hermeneutical and existential phenomenology. The perceptive and semiogenetic issues of musical sensitivity allow us to remodel the notion of a musical motive, understood both as a motive-of-praxis and as an existential-motive. I tried to grasp the idea of a certain listening of the musical praxis by finding there a constant passage between an ethical perception, and the search –through the playing of the music and its motives–, for a musical personality engaged in the musical praxis. Such conceptions on motive and personality proved to be fruitful to the extent that they make it possible to suggest a certain ethic of musical feeling, without reducing it to a skill, a psychology or a ritual. I have thus managed to redefine the notion of a musical ‘sign’ by playing up on the 'motival' horizon of this semiotic activity, understood – in the formal and sensitive nature of musical practices– as participation (i.e., desire and commitment to participate) to a certain regime of human existence. In this way, I believe to be paving the way for a new conception of musical praxis, which interweaves aesthetics and ethics. The thesis thus addresses these problems by casting six successive contemplations on it: Piano Masterclass; Feeling, Knowing and Doing; Field and Form; Motive and Form; Lines of Life; Enchantment. [less ▲]

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See detailThe influence of socio-economic status on the risk of being overweight or underweight in adolescents in Luxembourg
Residori, Caroline UL

Doctoral thesis (2019)

Factors indicating risks for future health and processes pertaining to the development of illnesses have come into the focus of social research. Ecological human development models and life course ... [more ▼]

Factors indicating risks for future health and processes pertaining to the development of illnesses have come into the focus of social research. Ecological human development models and life course approaches to illness and health provide a theoretical understanding of the fundamental causes of ill health and the different spheres, which influence health. The sociological understanding of the stratification of society by (socio-economic) status constitutes the theoretical backdrop for understanding uneven distributions of health resources and health strains. Socio-economic health inequalities are observed in many countries including very wealthy countries such as Luxembourg. Social-psychological perspectives on processes of social cognition and social comparison in combination with theories on collective health lifestyles and beliefs highlight the processes through which social stratification is embodied into health inequalities, even in wealthy contexts. The theoretical model of the pathways through which socio-economic status influences health that underlies this thesis draws on all of the aforementioned disciplinary perspectives. Differentiating between objective and subjective conceptions of socio-economic status seems particularly important in wealthy contexts and is therefore also part of the theoretical model that underlies this thesis. As foundations for adult health and illness are laid during childhood and youth, socio-economic inequalities during these life phases can be all the more consequential and it is crucial to investigate and understand them thoroughly. While results on socio-economic health inequalities from empirical studies for childhood and adulthood are consistent across different health domains, results for adolescence are less consistent and vary for different health domains, different conceptions of socio-economic status and different national and regional contexts. Considering the lack of studies and literature on socio-economic health inequalities among adolescents in Luxembourg and using overweight and underweight as examples, this thesis empirically investigates socio-economic health inequalities among adolescents in Luxembourg. The 5 research questions of this thesis focus on the prevalence of overweight and underweight, the influence of socio-economic status on them, the distinct influences of objective and subjective socio-economic status on overweight and underweight, the influence of socio-economic status on additional weight-related health concerns and the relations between health relevant factors and socio-economic status. The method used for the empirical investigation is a statistical analysis of data collected in Luxembourg in the context of the Health Behaviour in School-Aged Children (HBSC) study between 2006 and 2014. Descriptive statistical analyses are used for the presentation of the epidemiology of overweight and underweight, while logistic regression and hierarchical logistic regression are used for the analysis of the influence of socio-economic status on overweight, underweight, weight-related health concerns and health relevant factors. The results of the statistical analysis and their interpretation reveal that overweight and underweight are equally crucial health concerns as both affects around 14% of adolescents in Luxembourg. An inverse relation between socio-economic status and overweight and underweight is observed. An increase in socio-economic status is on one hand associated with a decrease in the risk of being overweight, but on the other hand, it is associated with an increase in the risk of being underweight. The influences of objective and subjective socio-economic status on overweight and three health relevant factors are confirmed to be distinct and independent from each other. The differentiation between objective and subjective socio-economic status is thus relevant for health inequalities among adolescents in Luxembourg. The relations between socio-economic status and the weight-related health concerns body image and weight reduction behaviour are opposite in direction when the effects of overweight and underweight are held constant in the models. Although an increase in socio-economic status is associated with a decrease in the risk of having a negative body image, it is also associated with an increase in the risk of engaging in weight reduction behaviour among adolescents in Luxembourg. One psycho-social and five behavioural health relevant factors are related to overweight and these relations tie in with the theoretical model. The statistical relations observed between health relevant factors and underweight are more complex and need further empirical and theoretical investigation. Based on the discussed results, this thesis concludes that the theoretical model aids the understanding of health inequalities among adolescents in Luxembourg, but applies differently to different health concerns and needs to take potential inverse effects of socio-economic status into account. This thesis contributes to the scientific knowledge through the identification of underweight as an important health concern among adolescents in wealthy countries and through the confirmation of the relevance of the differentiation between objective and subjective socio-economic status for health inequalities in adolescents. The implications of the results for policy and prevention should be an increased awareness of the need to target prevention programmes to specific risk groups and the need to take the risk of underweight into account by shifting the focus from the prevention of overweight to the encouragement of heathy behaviour. [less ▲]

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See detailTowards an understanding of the language–integration nexus: a qualitative study of forced migrants’ experiences in multilingual Luxembourg
Kalocsanyiova, Erika UL

Doctoral thesis (2019)

This cumulative thesis offers insights into the under-researched area of linguistic integration in multilingual societies. It is a collection of four papers that seek to address key questions such as: How ... [more ▼]

This cumulative thesis offers insights into the under-researched area of linguistic integration in multilingual societies. It is a collection of four papers that seek to address key questions such as: How can people’s existing language resources be validated and used to aid language learning? What are the politics of language and integration in settings of complex linguistic diversity? What role do language ideologies play in their creation and/or perception? What types of individual trajectories emerge? The research reported here is grounded in the Luxembourgish context, which represents an important European focal point for exploring the dynamics of linguistic integration. Taking a qualitative approach informed by linguistic ethnography (Copland & Creese 2015; Pérez-Milans 2016; Rampton 2007a; Rampton et al. 2015; Tusting & Maybin 2007), this work focuses on the language learning and integration experiences of five men who, fleeing war and violence, sought international protection in the Grand Duchy of Luxembourg. Building on theories of multilingual communication (Canagarajah & Wurr 2011), translanguaging (Creese & Blackledge 2010; García & Li Wei 2014) and receptive multilingualism (ten Thije et. al. 2012), the first paper of this thesis considers the affordances of multilingual learning situations in classroom-based language training for forced migrants. The second paper moves on to scrutinise the instrumental and integrative dimensions of language (Ager 2001), as articulated and perceived by the research participants. It exposes the vagueness and contradictory logics of linguistic integration as currently practiced, and throws light on how people with precarious immigration status interpret, experience and act upon ideologies surrounding language and integration (cf. Cederberg 2014; Gal 2006; Kroskrity 2004; Stevenson 2006). The third paper, likewise, directs attention to the controversies and potential unwarranted adverse effects of current linguistic integration policies. Through juxtaposing the trajectories of two forced migrants – who shared similar, multi-layered linguistic repertoires (Blommaert & Backus 2013; Busch 2012, 2017) – this part of the thesis elucidates the embodied efforts, emotions, and constraints inherent in constructing a new (linguistic) belonging in contemporary societies. Taken together, these papers illustrate and expand the discussion about the language–integration nexus. Additionally, by bringing into focus multilingual realities and mobile aspirations, they seek to provide a fresh impetus for research, and contribute to the creation of language policies that recognise a larger range of communicative possibilities and forms of language knowledge (cf. Ricento 2014; Flubacher & Yeung 2016). The thesis also makes a methodological contribution, by demonstrating the value of cross-language qualitative research methods in migration and integration research. It includes a detailed discussion of the complexities of researching in a multilingual context (Holmes et al. 2013; Phipps 2013b), as well as a novel inquiry into the interactional dynamics of an interpreter-mediated research encounter (fourth paper). [less ▲]

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See detailThe impact of macro-substrate on micropollutant degradation in activated sludge systems
Christen, Anne UL

Doctoral thesis (2019)

Wastewater treatment plants are designed as a first barrier to reduce xenobiotic emission into rivers. However, they are not sufficient enough to fully prevent environmental harm of emerging substances in ... [more ▼]

Wastewater treatment plants are designed as a first barrier to reduce xenobiotic emission into rivers. However, they are not sufficient enough to fully prevent environmental harm of emerging substances in the water body. Therefore, advanced treatment processes are currently being investigated but their implementation is cost-intensive. The optimisation of the activated sludge treatment to enhance biological micropollutant removal could reduce operating costs and material. Although the impact of operational parameters, such as sludge retention time and hydraulic retention time on the xenobiotic removal have been investigated, the influence of the macro-substrate composition and load on micropollutant elimination causes a high degree of uncertainty. This study focuses on the latter by analysing 15 municipal wastewater treatment plants, where variations in load and composition of the macro-substrate were expected. Assuming that macro-substrate shapes the biomass and triggers their activity, the impact of macro-substrate composition and load on xenobiotic degradation by microorganisms was analysed. It was hypothesised that on the one hand, a high dissolved organic carbon concentration might lead to enhanced xenobiotic degradation for certain substances due to a high microbial activity. The latter is assumed to be caused by a high labile dissolved organic carbon portion and the tendency for a shorter sludge retention time. On the other hand, a low dissolved organic carbon concentration, probably containing a predominant recalcitrant substrate portion, tends to a longer sludge retention time. Consequently, slow-growing and specialised microorganisms may develop, able to degrade certain xenobiotics. As a second question, the contribution of the autotrophic biomass to xenobiotic degradation was tested by inhibiting the autotrophic microorganisms during the degradation test. To additionally test the hypothesis, the impact of a readily biodegradable substrate (acetate) on the xenobiotic degradation was tested and the sensitivity of the fluorescence signal of tryptophan was used to analyse the impact of tryptophan on xenobiotic degradation. Degradation tests focusing on the removal of macro-substrate and micropollutants within 18 hours incubation in the OxiTop® system were performed. The OxiTop® system is known as fast and easy method for organic matter analysis in the wastewater. To assess the macro-substrate composition prior to and after the degradation test, three characterisation methods were applied. Firstly, to determine the labile and the rather recalcitrant portion in the dissolved organic carbon, absorbance was measured at 280 nm and further analysed. This was verified by the characterisation of both portions based on the oxygen consumption measurements. Secondly, to analyse the organic matter concerning its fluorescent properties, excitation-emission scans were run and analysed using the parallel factor analysis approach. Lastly, the chromophoric and fluorescent organic matter was separated via size-exclusion chromatography to investigate the macro-substrate composition. Micropollutant elimination efficiency was followed by measuring initial and final concentrations of the targeted substances using liquid chromatography tandem-mass spectrometry and calculating pseudo-first-order degradation rates. To distinguish between the contribution of the heterotrophic biomass and the total biomass on xenobiotic degradation, allylthiourea was added to inhibit the autotrophic biomass. No significant composition changes of the chromophoric macro-substrate were observed. A higher initial dissolved organic carbon concentration led to higher chromophoric and fluorescent properties. The same was found for the degraded dissolved organic carbon amount and the loss of signal within the chromophoric and fluorescent portions. Variations in the macro-substrate load or rather concentration were tracked. Derived from the oxygen consumption measurements, a prominent labile and non-chromophoric portion was present at higher dissolved organic carbon levels, impacting the microbial activity. However, a characterisation of the non-chromophoric macro-substrate composition was not done within the study. Regarding the micropollutant removal, varying elimination rates were observed. For 4 out of 17 substances, distinct degradation dynamics were found, suggesting a possible impact of the present macro-substrate load. However, no overall impact of the macro- substrate on xenobiotic removal was observed. Atenolol, bezafibrate and propranolol showed a negative correlation with the initial dissolved organic carbon concentration, meaning higher degradation rates at a lower substrate load. This might indicate the presence of specialised microorganisms and a higher microbial diversity. Furthermore, inhibition studies using allylthiourea suggest a contribution of the autotrophic biomass to xenobiotic degradation. Sulfamethoxazole showed a positive trend with the initial dissolved organic carbon concentration, possibly indicating co-metabolic degradation of sulfamethoxazole by the autotrophic and heterotrophic biomass. Thus, it seemed that the removal efficiencies of sulfamethoxazole benefited from higher substrate loads. With respect to the short term experiments with acetate, higher degradation efficiencies were observed for several substances in the presence of acetate. Ketoprofen and bezafibrate showed in all tested wastewaters enhanced removal efficiencies. The tryptophan test indicated the presence of tryptophan in wastewater, but no clear contribution to the xenobiotic degradation was seen. The presented findings substantially contribute to the understanding of the influencing parameters on xenobiotic degradation in activated sludge systems. By using the OxiTop® application for xenobiotic degradation tests, an easy and fast method was established. Absorbance and fluorescence measurements proved to be a sufficient method for characterisation and biodegradability estimation of organic matter, which could be further applied as online measurements on wastewater treatment plants. Thus, the current study will serve as a base for future work investigating the influencing parameters on the xenobiotic degradation pathways and focusing on the optimisation of the biological and advanced treatment process to overcome current limitations. [less ▲]

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See detailThe Development and Utilization of Scenarios in European Union Energy Policy
Scheibe, Alexander UL

Doctoral thesis (2019)

Scenarios are a strategic planning tool, which essentially enables decision-makers to identify future uncertainties and to devise or adjust organizational strategies. Increasingly, scenario building has ... [more ▼]

Scenarios are a strategic planning tool, which essentially enables decision-makers to identify future uncertainties and to devise or adjust organizational strategies. Increasingly, scenario building has been applied as a planning instrument by public policymakers. At the European Union (EU) level, scenarios are widely used in various policy areas and for different purposes. However, the development and utilization of scenarios in policymaking as well as their concrete impact on the decision process remain an under-explored research field. The academic literature focuses on scenarios in the business domain, where they are a well-established strategic planning component. In public policy, however, the development and use of scenarios conceivably differ from the private sector. In the case of the EU, the potential impact of its distinctive multi-stakeholder and multi-level policymaking environment on the development of scenarios is not sufficiently accounted for in the literature. Moreover, it is uncertain how scenarios are situated in the wider EU political context. This thesis seeks to explain how scenarios are developed and utilized in the EU’s policymaking process. To that end, an institutionalized scenario development exercise from the Union’s energy policy (the Ten-Year Network Development Plan, TYNDP) is investigated as a case study. Drawing from empirical evidence primarily based on elite interviews, the research applies a qualitative-interpretative research framework that combines the analytical concepts of policy networks, epistemic communities, and strategic constructivism. The combination facilitates the design of a theoretical model of inner and outer spheres in EU energy policymaking, accounting for both the role of scenarios in policymaking and the impact of political goals on their development. The research concludes that the wider EU political context of the outer sphere shapes the development of scenarios in the inner sphere and determines how they are utilized in the policymaking process. The expectations of political actors frame the technical expertise in the scenario development process. With regard to the application of scenarios in wider public policy, the research demonstrates that the closer the scenario building is to the decision-making process, the stronger the political impact on the scenarios is likely to be. This is because political actors and decision-makers seek to align the scenario outcomes to their respective preferences. [less ▲]

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See detailEssays on Monetary Economics and Asset Pricing
Weber, Fabienne UL

Doctoral thesis (2019)

This dissertation consists of three chapters based on three applied theory papers, which all use microfoundations to study mechanisms behind asset prices in the context of monetary policy and financial ... [more ▼]

This dissertation consists of three chapters based on three applied theory papers, which all use microfoundations to study mechanisms behind asset prices in the context of monetary policy and financial stability. Market Fragility and the Paradox of the Recent Stock-Bond Dissonance. The objective of this study is to jointly explain stock prices and bond prices. After the Lehman-Brothers collapse, the stock index has exceeded its pre-Lehman-Brothers peak by 36% in real terms. Seemingly, markets have been demanding more stocks instead of bonds. Yet, instead of observing higher bond rates, paradoxically, bond rates have been persistently negative after the Lehman-Brothers collapse. To explain this paradox, we suggest that, in the post-Lehman-Brothers period, investors changed their perceptions on disasters, thinking that disasters occur once every 30 years on average, instead of disasters occurring once every 60 years. In our asset-pricing calibration exercise, this rise in perceived market fragility alone can explain the drop in both bond rates and price-dividend ratios observed after the Lehman-Brothers collapse, which indicates that markets mostly demanded bonds instead of stocks. Time-Consistent Welfare-Maximizing Monetary Rules. The objective of this study is to jointly explain capital prices, bond prices and money supply/demand. We analyze monetary policy from the perspective that a Central Bank conducts monetary policy serving the ultimate goal of maximizing social welfare, as dictated by a country's constitution. Given recent empirical findings that many households are hand-to-mouth, we study time-consistent welfare-maximizing monetary-policy rules within a neoclassical framework of a cash-in-advance economy with a liquidity-constrained good. The Central Bank performs open-market operations buying government bonds in order to respond to fiscal shocks and to productivity shocks. We formulate the optimal policy as a dynamic Stackelberg game between the Central Bank and private markets. A key goal of optimal monetary policy is to improve the mixture between liquidity constrained and non-liquidity constrained goods. Optimal monetary responses to fiscal shocks aim at stabilizing aggregate consumption fluctuations, while optimal monetary responses to productivity shocks allow aggregate consumption fluctuations to be more volatile. Jump Shocks, Endogenous Investment Leverage and Asset Prices: Analytical Results. The objective of this study is to jointly model leveraging and stock prices in an environment with rare stock-market disaster shocks. Financial intermediaries invest in the stock market using household savings. This investment leveraging, and its extent, affects stock price movements and, in turn, stock-price movements affect investment leveraging. If the price mechanism is unable to absorb a rare stock-market disaster, then with leverage ratios of 20 or more, financial intermediaries can go bankrupt. We model the interplay between leverage ratios and stock prices in an environment with rare stock-market disaster shocks. First we introduce dividend shocks that follow a Poisson jump process to an endowment economy with pure exchange between two types of agents: (i) shareholders of financial intermediaries that invest in the stock market ("experts"), and (ii) savers, who deposit their savings to financial intermediaries (households). Under the assumption that the households and the so called "experts" both have logarithmic utility, we obtain a closed-form solution for the endowment economy. This closed-form solution serves as a guide for numerically solving the model with recursive Epstein-Zin preferences in continuous-time settings. In our extension we introduce production based on capital investments, but with adjustment costs for investment changes. Jump shocks directly hit the productive capital stock, but the way they influence stock returns of productive firms passes through the leveraging channel, which is endogenous. The production economy also has endogenous growth, and investment adjustment costs partly influence the model's stability properties. Importantly, risk has an endogenous component due to leveraging, and this endogenous-risk component influences growth opportunities, bridging endogenous cycles with endogenous growth. This chapter is part of a broader project on financial stability. Future extensions will include an evaluation of the Basel II-III regulatory framework in order to assess their effectiveness and their impact on growth performance. [less ▲]

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See detailCONFIDENCE-BASED DECISION-MAKING SUPPORT FOR MULTI-SENSOR SYSTEMS
Neyens, Gilles UL

Doctoral thesis (2019)

We live in a world where computer systems are omnipresent and are connected to more and more sensors. Ranging from small individual electronic assistants like smartphones to complex autonomous robots ... [more ▼]

We live in a world where computer systems are omnipresent and are connected to more and more sensors. Ranging from small individual electronic assistants like smartphones to complex autonomous robots, from personal wearable health devices to professional eHealth frameworks, all these systems use the sensors’ data in order to make appropriate decisions according to the context they measure. However, in addition to complete failures leading to the lack of data delivery, these sensors can also send bad data due to influences from the environment which can sometimes be hard to detect by the computer system when checking each sensor individually. The computer system should be able to use its set of sensors as a whole in order to mitigate the influence of malfunctioning sensors, to overcome the absence of data coming from broken sensors, and to handle possible conflicting information coming from several sensors. In this thesis, we propose a computational model based on a two layer software architecture to overcome this challenge. In a first layer, classification algorithms will check for malfunctioning sensors and attribute a confidence value to each sensor. In the second layer, a rule-based proactive engine will then build a representation of the context of the system and use it along some empirical knowledge about the weaknesses of the different sensors to further tweak this confidence value. Furthermore, the system will then check for conflicting data between sensors. This can be done by having several sensors that measure the same parameters or by having multiple sensors that can be used together to calculate an estimation of a parameter given by another sensor. A confidence value will be calculated for this estimation as well, based on the confidence values of the related sensors. The successive design refinement steps of our model are shown over the course of three experiments. The first two experiments, located in the eHealth domain, have been used to better identify the challenges of such multi-sensor systems, while the third experiment, which consists of a virtual robot simulation, acts as a proof of concept for the semi-generic model proposed in this thesis. [less ▲]

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See detailFrom Persistent Homology to Reinforcement Learning with Applications for Retail Banking
Charlier, Jérémy Henri J. UL

Doctoral thesis (2019)

The retail banking services are one of the pillars of the modern economic growth. However, the evolution of the client’s habits in modern societies and the recent European regulations promoting more ... [more ▼]

The retail banking services are one of the pillars of the modern economic growth. However, the evolution of the client’s habits in modern societies and the recent European regulations promoting more competition mean the retail banks will encounter serious challenges for the next few years, endangering their activities. They now face an impossible compromise: maximizing the satisfaction of their hyper-connected clients while avoiding any risk of default and being regulatory compliant. Therefore, advanced and novel research concepts are a serious game-changer to gain a competitive advantage. In this context, we investigate in this thesis different concepts bridging the gap between persistent homology, neural networks, recommender engines and reinforcement learning with the aim of improving the quality of the retail banking services. Our contribution is threefold. First, we highlight how to overcome insufficient financial data by generating artificial data using generative models and persistent homology. Then, we present how to perform accurate financial recommendations in multi-dimensions. Finally, we underline a reinforcement learning model-free approach to determine the optimal policy of money management based on the aggregated financial transactions of the clients. Our experimental data sets, extracted from well-known institutions where the privacy and the confidentiality of the clients were not put at risk, support our contributions. In this work, we provide the motivations of our retail banking research project, describe the theory employed to improve the financial services quality and evaluate quantitatively and qualitatively our methodologies for each of the proposed research scenarios. [less ▲]

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See detailTowards Optimal Real-Time Bidding Strategies for Display Advertising
Du, Manxing UL

Doctoral thesis (2019)

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See detailDevelopment of an innovative U-shaped steel-concrete composite beam solution: Experimental and numerical studies on the mechanical behaviour
Turetta, Maxime UL

Doctoral thesis (2019)

An innovative solution of steel-concrete composite beam was developed taking into consideration the fire situation and the construction stage. The beam is composed of a U-shaped steel part connected to a ... [more ▼]

An innovative solution of steel-concrete composite beam was developed taking into consideration the fire situation and the construction stage. The beam is composed of a U-shaped steel part connected to a reinforced concrete part. In the construction phase, the beam is supporting the slab and constitutes a formwork for the reinforced concrete part. The U-shaped beam withstands the construction loads without any temporary propping system. When casting concrete, the steel beam is filled at the same time as the slab, this allows considerable time-saving on site. In exploitation stage, the beam behaves as a steel-concrete composite beam. The connection between the two materials is made by welded headed studs on the lower part of the U-shaped beam. In fire situations, the composite beam satisfies conventional fire stability durations due to the longitudinal reinforcements inside the concrete downstand part with sufficient covers. A literature review focuses on modern solutions that fulfils the criteria of the thesis is performed in order to develop an innovative solution optimised. In construction stage, the U-shaped steel beam without restraints is prone to lateral torsional buckling instability. In order to characterise the stability of the beam, a full-scale test is carried out at the Laboratory of the University of Luxembourg. The test clearly showed the lateral torsional buckling of the steel beam. The test results are compared to numerical simulations and analytical studies. A parametrical study, covering 200 geometrical configurations of the U-shaped beam, is carried out to validate the use of the curve "b" for the design of the steel beam for lateral torsional buckling according to Eurocodes 3. In the exploitation phase, once the concrete hardens, the beam has a steel-concrete composite behaviour provided by the shear connection between the two materials. For manufacturing reasons, the connection is located in a zone where the concrete is subjected to tension forces induced by the bending of the beam. The concrete in this zone is potentially cracked, thus the efficiency of the connection and therefore the mechanical steel-concrete composite behaviour is investigated. Another test is therefore carried out in the Laboratory of the University of Luxembourg, this time the specimen tested is made of concrete and steel. The failure mode is a shear mechanism of the composite beam at very large displacements. However, the beam specimen exhibited a real steel-concrete composite behaviour with high ductility, the connection is therefore very efficient. The test results are compared to numerical simulations in order to validate the finite element model developed. From numerical results and test results, an analytical method, based on EN 1994-1-1, is proposed to find the bending resistant of this composite beam by taking into account the partial yield of the side plates of the U-shaped steel section. A global analytical design method is proposed for the developed solution based on the Eurocodes with additional considerations and constructional guidelines. [less ▲]

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See detailLiquid Metals and Liquid Crystals Subject to Flow: From Fundamental Fluid Physics to Functional Fibers
Honaker, Lawrence William UL

Doctoral thesis (2019)

Technology over the past few decades has pushed strongly towards wearable technology, one such form being textiles which incorporate a functional component. There are several ways to produce polymer ... [more ▼]

Technology over the past few decades has pushed strongly towards wearable technology, one such form being textiles which incorporate a functional component. There are several ways to produce polymer fibers on both laboratory and industrial scales, but the implementation of these techniques to spin fibers incorporating a functional heterocore has proven challenging for certain combinations of materials. In general, fiber spinning from polymer solutions, regardless of the method, is a multifaceted process with concerns in chemistry, materials science, and physics, both from fundamental and applied standpoints, requiring balancing of flow parameters (interfacial tension, viscosity, and inertial forces) against solvent extraction. This becomes considerably more complicated when multiple interfaces are present. This thesis explores the concerns involved in the spinning of fibers incorporating functional materials from several standpoints. Firstly, due to the importance of interfacial forces in jet stability, I present a microfluidic interfacial tensiometry technique for measuring the interfacial tension between two immiscible fluids, assembled using glass capillary microfluidics techniques. The advantage of this technique is that it can measure the interfacial tension without reliance on sometimes imprecise external parameters and data, obtaining interfacial tension measurements solely from experimental observations of the deformation of a droplet into a channel and the pressure needed to induce the same. Using the knowledge gained from both microfluidic device assembly and the interfacial tension, I then present the wet spinning of polymer fibers using a glass capillary spinneret. This technique uses a polymer dope flowed along with a coagulation bath tooled to extract solvent, leaving behind a continuous polymer fiber. We were able to spin both pure polymer fibers and elastomer microscale fibers containing a continuous heterocore of a liquid crystal, with the optical properties of the liquid crystal maintained within the fiber. While we were not able to spin fibers of a harder polymer containing a continuous core, either liquid crystalline or of a liquid metal, I present analysis of why the spinning was unsuccessful and analysis that will lead us towards the eventual spinning of such fibers. [less ▲]

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See detailLe jugement par défaut dans l'espace judiciaire européen
Richard, Vincent Jérôme UL

Doctoral thesis (2019)

French judges regularly refuse to enforce foreign judgements rendered by default against a defendant who has not appeared. This finding is also true for other Member States, as many European regulations ... [more ▼]

French judges regularly refuse to enforce foreign judgements rendered by default against a defendant who has not appeared. This finding is also true for other Member States, as many European regulations govern cross-border enforcement of decisions rendered in civil and commercial matters between Member States. The present study examines this problem in order to understand the obstacles to the circulation of default decisions and payment orders in Europe. When referring to the recognition of default judgments, it would be more accurate to refer to the recognition of decisions made as a result of default proceedings. It is indeed this (default) procedure, more than the judgment itself, which is examined by the exequatur judge to determine whether the foreign decision should be enforced. This study is therefore firstly devoted to default procedures and payment order procedures in French, English, Belgian and Luxembourgish laws. These procedures are analysed and compared in order to highlight their differences, be they conceptual or simply technical in nature. Once these discrepancies have been identified, this study turns to private international law in order to understand which elements of the default procedures are likely to hinder their circulation. The combination of these two perspectives makes it possible to envisage a gradual approximation of national default procedures in order to facilitate their potential circulation in the European area of freedom, security and justice. [less ▲]

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See detailLA QUESTION DE L’AUTEUR DANS LES ROMANS DE JEAN ROUAUD : VARIATIONS SUR LA PRÉSENCE ET L’ABSENCE
AGUIAR, Jean Roger Marcellin

Doctoral thesis (2019)

Cette thèse traite de la présence de l’auteur dans les romans de Jean Rouaud. Chez lui, la place accorder à l’auteur dans le déchiffrement du sens du texte est une donnée importante. Elle s’inscrit dans ... [more ▼]

Cette thèse traite de la présence de l’auteur dans les romans de Jean Rouaud. Chez lui, la place accorder à l’auteur dans le déchiffrement du sens du texte est une donnée importante. Elle s’inscrit dans la mouvance de certains écrivains actuels qui s’autorisent une intrusion dans la fiction pour poser leurs problèmes personnels, mais aussi ceux auxquels a été confronté l’auteur durant la période structuraliste. En effet, la littérature des trente dernières années témoigne du retour de l’auteur au sein de la fiction, après sa fameuse disparition. Retour qui se fait avec la présence fictionnelle d’un personnage-auteur inventé par l’écrivain. Une telle pratique impose la considération des résultats actuels des recherches sur la présence de l’auteur dans les fictions contemporaines, à savoir le déplacement de l’auteur dans la fiction. Ce travail est donc une réponse à la présence de Jean Rouaud dans la diégèse. Présence qui s’inscrit dans une perspective de définition de la littérature, selon Rouaud. [less ▲]

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See detailMotivation and self-regulation
Grund, Axel UL

Postdoctoral thesis (2019)

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See detailParliamentary involvement in EU affairs during treaty negotiations in a historical comparative perspective: the cases of the Austrian, Finnish and Luxembourgish parliaments
Badie, Estelle Céline UL

Doctoral thesis (2019)

Until recently, studies on the Europeanisation of national parliaments mostly tended to focus on the evolution of their institutional capacities rather than on their actual behaviour in EU affairs. This ... [more ▼]

Until recently, studies on the Europeanisation of national parliaments mostly tended to focus on the evolution of their institutional capacities rather than on their actual behaviour in EU affairs. This thesis seeks to identify variations in behavioural patterns between the Austrian, Finnish and Luxembourgish legislatures. The historical comparative perspective bases mainly on political and societal similarities between the countries. Based on historical and Sociological Institutionalism, the thesis aims to analyse the evolution and motivations of parliamentary involvement in the field of European affairs over a period running from the negotiations on the Treaty establishing a Constitution for Europe until the Treaty on Stability, Coordination and Governance in the EMU. By including both institutional and motivational indicators, the objective consists of identifying the extent to which parliamentary involvement in EU matters has been challenged in the framework of EU treaties and intergovernmental treaties on the EMU. We address the following questions: What institutional and motivational factors influenced parliamentary involvement in EU affairs? What parliamentary initiatives have been taken to improve participation in EU affairs? In which direction did institutional change happen and who triggered it? The present thesis bases primarily on qualitative data, i.e. interviews with parliamentarians, civil servants from parliamentary administrations and parliamentary group collaborators. Thereby we aim to produce empirical in-depth knowledge on actual parliamentary behaviour in each studied country. Thus, the assessment of parliamentary involvement in EU affairs through the lenses of parliamentarians’ motivations and their institutional context helps to investigate the parliamentary “black box”. [less ▲]

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See detailAccess Control Mechanisms Reconsidered with Blockchain Technologies
Steichen, Mathis UL

Doctoral thesis (2019)

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See detailEntwicklung und Modellierung eines Hybrid-Solarmodulkollektor-basierten Wärmepumpensystems auf der Basis von CO2 Direktverdampfung in Mikrokanälen
Rullof, Johannes UL

Doctoral thesis (2019)

As early as the end of the 1970s, heat pumps in combination with glycol-based large-area combined radiation environmental heat absorbers were developed as evaporators which, in comparison to forced ... [more ▼]

As early as the end of the 1970s, heat pumps in combination with glycol-based large-area combined radiation environmental heat absorbers were developed as evaporators which, in comparison to forced convection-based air heat pumps, not only used ambient energy but also solar energy as an energy source. However, due to the falling oil prices after the oil crisis, this technology, which was for the most part not yet economical and moreover required large absorber surfaces, could not prevail. Due to the significant re-duction in the heating requirement of new buildings, nowadays much smaller absorber surfaces are needed in combination with a heat pump, which leads to a renewed interest in the combination of heat pumps and absorbers. Above all, the combination of thermal absorber, based on free convection and radiation, and photovoltaic (PV) in one module (PVT module), may be an alternative to forced convection-based air heat pumps. The use of solar energy as the heat source of the heat pump leads one to expect higher coef-ficients of performance by achieving higher evaporation temperatures than conventional forced convection-based air heat pumps. Numerous publications describe the market potential of solar hybrid modules with di-rect evaporation (PVT-direct module), and several theoretical studies describe con-structive approaches and related calculations. However, to date, there is still no practi-cal implementation of a PVT hybrid module in combination with a module-integrated direct evaporation of the natural refrigerant CO2 in microchannels. So far, no experi-mental studies on CO2-PVT-based heat pump systems with direct evaporation have been carried out by research institutions. Thus, the proof of the constructive and func-tional feasibility of a CO2-based PVT-direct module as well as the energetic feasibility of the PVT-based CO2 heat pump system is still a desideratum. The three objectives of this work can be summarized as follows: 1. Development and production of the PVT-direct module for the analysis of the constructional feasibility of the PVT-direct module 2. Experimental investigation of the PVT-direct module for the analysis of both the thermal and electrical functional feasibility of the PVT-direct module 3. Analysis of the energetic feasibility of the PVT-based CO2 heat pump system [less ▲]

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See detailInvestigation of the immune functions of DJ-1
Zeng, Ni UL

Doctoral thesis (2019)

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See detailIMPROVED DESIGN METHODS FOR THE BEARING CAPACITY OF FOUNDATION PILES
Rica, Shilton UL

Doctoral thesis (2019)

Pile foundations are often used for civil structures, both offshore and onshore, which are placed on soft soils. Nowadays, there are many different methods used for the prediction of the pile bearing ... [more ▼]

Pile foundations are often used for civil structures, both offshore and onshore, which are placed on soft soils. Nowadays, there are many different methods used for the prediction of the pile bearing capacity. However, the resulting design values are often different from the values measured at pile load field tests. A reason for this is that there are many pile installation effects and (unknown) soil conditions which influence the pile bearing capacity. Another problem is that for many pile load field tests in the past, the residual stresses at the pile after pile installation, have been ignored unfortunately. This ignoring leads to a measured tip bearing resistance which is lower than the real tip bearing resistance (capacity), and a measured pile shaft friction which is higher than the real pile shaft friction. The main aim of this thesis is, to come to a better understanding of the pile performance and especially the pile bearing capacity. In order to achieve this aim, many numerical loading simulations were computed for small displacements with the Finite Element Model Plaxis and many existing pile design methods have been studied. The pile installation process itself was modelled and simulated with the help of the material point method, MPM, which is able to handle large displacement numerical simulations. The used version of this MPM method was recently developed at the research institute Deltares in the Netherlands. The results from the MPM simulations showed that there is a big difference between the bearing capacity of a pre-installed pile (no installation effect are taken into account) and the bearing capacity of a pile where the installations effects are taken into account. This proves in a numerical way the importance of the pile installation effects on the pile bearing capacity. However, the MPM numerical simulations were done only for jacked piles. Therefore, impact piles, vibrated piles etc., were not simulated. For this reason, there is not a detailed numerical study for the effect of each installation method specific on the pile bearing capacity. The fact that the installation effects, in general, has an important influence on the pile bearing capacity was already proven by field tests and centrifuge tests, and has been published before by several authors. The performed numerical simulations show that during the loading and failure of a pile, a balloon shaped plastic zone develops around the pile tip, which is in fact the failure mechanism. A better understanding of this zone could lead to a better estimation of the pile tip bearing capacity because the size and position of this plastic zone are directly related to the pile tip bearing capacity. Therefore, this plastic zone has been studied for different soil and pile parameters. Also, the influence of each parameter has been studied and discussed. A similar balloon shaped plastic zone was found for both small and large displacement simulations. The tip bearing capacity of a pile is regarded to depend only on the soil in a certain zone around the pile tip. This zone is called the influence zone. The influence zone is found to be similar to the plastic zone of a pile tip. Therefore, the influence of a soft soil layer, near the influence zone of the pile tip, has also been studied. The numerical results have been validated with laboratory tests made by Deltares. The influence zone is roughly from 2 times the pile diameter, 𝐷, above the pile tip, to 5 or 6 times 𝐷 below the pile tip. Laboratory tests, using the direct shear test machine, have been performed in order to define the difference between the soil-pile friction angle and the soil-cone friction angle. The tests were done for different surface roughnesses and for three different sand types. The results were compared with the roughness of the sleeve of the Cone Penetration Test (CPT) apparatus. Based on the numerical simulations and the laboratory tests of Deltares, a new design method has been proposed for the estimation of the pile bearing capacity. This method has as main input value, the CPT results, therefore it is a CPT-based design method. The proposed method has been validated using pile field tests that were performed in Lelystad in the Netherlands. During this research, several axial and lateral pile field tests were performed at the West Coast of Mexico. Their results have been reported and discussed in the appendices. [less ▲]

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See detailDISSECTING GENETIC EPISTASIS IN FAMILIAL PARKINSON’S DISEASE USING A DIGENIC PATIENT-DERIVED STEM CELL MODEL
Hanss, Zoé UL

Doctoral thesis (2019)

Parkinson’s disease (PD) is the second most common neurodegenerative disorder worldwide. 10% of PD patients present a familial form of the disease implicating genetic mutations. A variability in terms of ... [more ▼]

Parkinson’s disease (PD) is the second most common neurodegenerative disorder worldwide. 10% of PD patients present a familial form of the disease implicating genetic mutations. A variability in terms of disease expressivity, severity and penetrance can be observed among familial cases. The idea that the classical one-gene one-trait model may not catch the full picture of genetic contribution to PD pathophysiology is increasingly recognized. Therefore, a polygenic model where multiple genes would influence the disease risk and the phenotypic traits in PD should be investigated. Mutations in PRKN, encoding the E3 ubiquitin-protein ligase Parkin, cause young onset autosomal recessive forms of PD. A variability in terms of clinical presentation and neuropathology have been observed in PD patients carrying mutations in Parkin. On the other hand, mutations in GBA were recently recognized as the most common genetic risk factor for developing PD. The incomplete penetrance of the disease in patients with GBA mutations may implicate other genetic factors. Therefore, it can be hypothesized that the interactions between common PD genes like PRKN and GBA can contribute to the phenotypic heterogeneity observed in PD cases. To explore this hypothesis, we generated patient-derived cellular models from several PD patients carrying pathogenic mutations in either both PRKN and GBA (triallelic models) or in only one of them (bi- or monoallelic models). We developed a novel strategy to gene edit the N370S mutation in GBA via CRISPR-Cas9, without interference with its respective pseudogene, which allows for the dissection of the role of GBA in the context of a PRKN mutation on an isogenic background. We identified a specific α-synuclein homeostasis in the triallelic model. The genetic and pharmacological rescue of GBA in the triallelic model modified the observed α-synuclein phenotype, proving the contribution of GBA to the observed phenotype. We then investigated whether Parkin was contributing to the phenotype. The modulation of Parkin function in the context of a GBA mutation induced a modification of the α-synuclein homeostasis. We therefore concluded that both PRKN and GBA are influencing α-synuclein homeostasis in the triallelic model. Nevertheless, the phenotypic outcome of the co-occurrence of these mutations was not additive nor synergistic. We therefore suggest the existence of an epistatic interaction between mutant GCase and Parkin that would underlie the clinical heterogeneity observed in PD patients carrying these mutations. [less ▲]

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See detailAssessment and Improvement of the Practical Use of Mutation for Automated Software Testing
Titcheu Chekam, Thierry UL

Doctoral thesis (2019)

Software testing is the main quality assurance technique used in software engineering. In fact, companies that develop software and open-source communities alike actively integrate testing into their ... [more ▼]

Software testing is the main quality assurance technique used in software engineering. In fact, companies that develop software and open-source communities alike actively integrate testing into their software development life cycle. In order to guide and give objectives for the software testing process, researchers have designed test adequacy criteria (TAC) which, define the properties of a software that must be covered in order to constitute a thorough test suite. Many TACs have been designed in the literature, among which, the widely used statement and branch TAC, as well as the fault-based TAC named mutation. It has been shown in the literature that mutation is effective at revealing fault in software, nevertheless, mutation adoption in practice is still lagging due to its cost. Ideally, TACs that are most likely to lead to higher fault revelation are desired for testing and, the fault-revelation of test suites is expected to increase as their coverage of TACs test objectives increase. However, the question of which TAC best guides software testing towards fault revelation remains controversial and open, and, the relationship between TACs test objectives’ coverage and fault-revelation remains unknown. In order to increase knowledge and provide answers about these issues, we conducted, in this dissertation, an empirical study that evaluates the relationship between test objectives’ coverage and fault-revelation for four TACs (statement, branch coverage and, weak and strong mutation). The study showed that fault-revelation increase with coverage only beyond some coverage threshold and, strong mutation TAC has highest fault revelation. Despite the benefit of higher fault-revelation that strong mutation TAC provide for software testing, software practitioners are still reluctant to integrate strong mutation into their software testing activities. This happens mainly because of the high cost of mutation analysis, which is related to the large number of mutants and the limitation in the automation of test generation for strong mutation. Several approaches have been proposed, in the literature, to tackle the analysis’ cost issue of strong mutation. Mutant selection (reduction) approaches aim to reduce the number of mutants used for testing by selecting a small subset of mutation operator to apply during mutants generation, thus, reducing the number of analyzed mutants. Nevertheless, those approaches are not more effective, w.r.t. fault-revelation, than random mutant sampling (which leads to a high loss in fault revelation). Moreover, there is not much work in the literature that regards cost-effective automated test generation for strong mutation. This dissertation proposes two techniques, FaRM and SEMu, to reduce the cost of mutation testing. FaRM statically selects and prioritizes mutants that lead to faults (fault-revealing mutants), in order to reduce the number of mutants (fault-revealing mutants represent a very small proportion of the generated mutants). SEMu automatically generates tests that strongly kill mutants and thus, increase the mutation score and improve the test suites. First, this dissertation makes an empirical study that evaluates the fault-revelation (ability to lead to tests that have high fault-revelation) of four TACs, namely statement, branch, weak mutation and strong mutation. The outcome of the study show evidence that for all four studied TACs, the fault-revelation increases with TAC test objectives’ coverage only beyond a certain threshold of coverage. This suggests the need to attain higher coverage during testing. Moreover, the study shows that strong mutation is the only studied TAC that leads to tests that have, significantly, the highest fault-revelation. Second, in line with mutant reduction, we study the different mutant quality indicators (used to qualify "useful" mutants) proposed in the literature, including fault-revealing mutants. Our study shows that there is a large disagreement between the indicators suggesting that the fault-revealing mutant set is unique and differs from other mutant sets. Thus, given that testing aims to reveal faults, one should directly target fault-revealing mutants for mutant reduction. We also do so in this dissertation. Third, this dissertation proposes FaRM, a mutant reduction technique based on supervised machine learning. In order to automatically discriminate, before test execution, between useful (valuable) and useless mutants, FaRM build a mutants classification machine learning model. The features for the classification model are static program features of mutants categorized as mutant types and mutant context (abstract syntax tree, control flow graph and data/control dependency information). FaRM’s classification model successfully predicted fault-revealing mutants and killable mutants. Then, in order to reduce the number of analyzed mutants, FaRM selects and prioritizes fault-revealing mutants based of the aforementioned mutants classification model. An empirical evaluation shows that FaRM outperforms (w.r.t. the accuracy of fault-revealing mutant selection) random mutants sampling and existing mutation operators-based mutant selection techniques. Fourth, this dissertation proposes SEMu, an automated test input generation technique aiming to increase strong mutation coverage score of test suites. SEMu is based on symbolic execution and leverages multiple cost reduction heuristics for the symbolic execution. An empirical evaluation shows that, for limited time budget, the SEMu generates tests that successfully increase strong mutation coverage score and, kill more mutants than test generated by state-of-the-art techniques. Finally, this dissertation proposes Muteria a framework that enables the integration of FaRM and SEMu into the automated software testing process. Overall, this dissertation provides insights on how to effectively use TACs to test software, shows that strong mutation is the most effective TAC for software testing. It also provides techniques that effectively facilitate the practical use of strong mutation and, an extensive tooling to support the proposed techniques while enabling their extensions for the practical adoption of strong mutation in software testing. [less ▲]

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See detailDynamical Modeling Techniques for Biological Time Series Data
Mombaerts, Laurent UL

Doctoral thesis (2019)

The present thesis is articulated over two main topics which have in common the modeling of the dynamical properties of complex biological systems from large-scale time-series data. On one hand, this ... [more ▼]

The present thesis is articulated over two main topics which have in common the modeling of the dynamical properties of complex biological systems from large-scale time-series data. On one hand, this thesis analyzes the inverse problem of reconstructing Gene Regulatory Networks (GRN) from gene expression data. This first topic seeks to reverse-engineer the transcriptional regulatory mechanisms involved in few biological systems of interest, vital to understand the specificities of their different responses. In the light of recent mathematical developments, a novel, flexible and interpretable modeling strategy is proposed to reconstruct the dynamical dependencies between genes from short-time series data. In addition, experimental trade-offs and optimal modeling strategies are investigated for given data availability. Consistent literature on these topics was previously surprisingly lacking. The proposed methodology is applied to the study of circadian rhythms, which consists in complex GRN driving most of daily biological activity across many species. On the other hand, this manuscript covers the characterization of dynamically differentiable brain states in Zebrafish in the context of epilepsy and epileptogenesis. Zebrafish larvae represent a valuable animal model for the study of epilepsy due to both their genetic and dynamical resemblance with humans. The fundamental premise of this research is the early apparition of subtle functional changes preceding the clinical symptoms of seizures. More generally, this idea, based on bifurcation theory, can be described by a progressive loss of resilience of the brain and ultimately, its transition from a healthy state to another characterizing the disease. First, the morphological signatures of seizures generated by distinct pathological mechanisms are investigated. For this purpose, a range of mathematical biomarkers that characterizes relevant dynamical aspects of the neurophysiological signals are considered. Such mathematical markers are later used to address the subtle manifestations of early epileptogenic activity. Finally, the feasibility of a probabilistic prediction model that indicates the susceptibility of seizure emergence over time is investigated. The existence of alternative stable system states and their sudden and dramatic changes have notably been observed in a wide range of complex systems such as in ecosystems, climate or financial markets. [less ▲]

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See detailIntegrity and Confidentiality Problems of Outsourcing
Pejo, Balazs UL

Doctoral thesis (2019)

Cloud services enable companies to outsource data storage and computation. Resource-limited entities could use this pay-per-use model to outsource large-scale computational tasks to a cloud-service ... [more ▼]

Cloud services enable companies to outsource data storage and computation. Resource-limited entities could use this pay-per-use model to outsource large-scale computational tasks to a cloud-service-provider. Nonetheless, this on-demand network access raises the issues of security and privacy, which has become a primary concern of recent decades. In this dissertation, we tackle these problems from two perspectives: data confidentiality and result integrity. Concerning data confidentiality, we systematically classify the relaxations of the most widely used privacy preserving technique called Differential Privacy. We also establish a partial ordering of strength between these relaxations and enlist whether they satisfy additional desirable properties, such as composition and privacy axioms. Tackling the problem of confidentiality, we design a Collaborative Learning game, which helps the data holders to determine how to set the privacy parameter based on economic aspects. We also define the Price of Privacy to measure the overall degradation of accuracy resulting from the applied privacy protection. Moreover, we develop a procedure called Self-Division, which bridges the gap between the game and real-world scenarios. Concerning result integrity, we formulate a Stackelberg game between outsourcer and outsourcee where no absolute correctness is required. We provide the optimal strategies for the players and perform a sensitivity analysis. Furthermore, we extend the game by allowing the outsourcer no to verify and show its Nash Equilibriums. Regarding integrity verification, we analyze and compare two verification methods for Collaborative Filtering algorithms: the splitting and the auxiliary data approach. We observe that neither methods provides a full solution for the raised problem. Hence, we propose a solution, which besides outperforming these is also applicable to both stage of the algorithms. [less ▲]

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See detailNumerical parametric study on minimum degree of shear connection in steel-concrete composite beams
Romero Guzman, Alfredo UL

Bachelor/master dissertation (2019)

In steel-concrete composite beams, the mechanical shear connectors are used to provide the shear transfer at the steel-concrete interface by connecting the concrete slab and the steel beam. Eurocode 4 (EN ... [more ▼]

In steel-concrete composite beams, the mechanical shear connectors are used to provide the shear transfer at the steel-concrete interface by connecting the concrete slab and the steel beam. Eurocode 4 (EN 1994-1-1), provides the design rules to achieve an adequate degree of shear connection. In recent years, revised rules have been proposed for the new generation of Eurocodes and research has been done to assess their suitability. The aim of this study is to complement previous studies and to evaluate the revised rules for minimum degree of shear connection of propped composite beams with ductile shear connectors and symmetric cross sections. First, a simple and comprehensive numerical model of a simply supported composite beam was developed in the finite element software ABAQUS and validated against previous numerical studies. Then, a parametric study was performed to evaluate the proposed rules on solid composite beams and composite beams with profiled steel sheeting for four span lengths (i.e. Lₑ= 6, 9, 12, and 15 m). For each span length, ten distinct configurations were analysed and each configuration was evaluated for five different degrees of shear connection (i.e. η= 0.20, 0.40, 0.60, 0.80, and 1.0). Thus, more than 200 simulations were completed in this parametric study. The results were post-processed and the suitability of the proposed rules was assessed in terms of end slip and midspan deflection at ULS and SLS respectively. The design rules led to adequate results in terms of midspan deflection. However, in some cases the end slip at ULS exceeded the 6 mm upper bound given in EN 1994-1-1 for ductile shear connectors. In order to properly identify and limit the end slip of the unsafe cases, the data from previous studies focusing on long span beams (i.e. 15m<Lₑ≤25m) was gathered with the results of the present study. Based on the assessment of the results, additional limitations to the revised rules were provided for the unsafe configurations. In these cases, the load level shall be limited by a reduction factor βₓ varying between 0.85 and 1, as a function of the plastic neutral axis depth to the overall height ratio (i.e. xₚₗ/h) and the composite to steel beam plastic bending resistance ratio (i.e. Mpl,Rd/Mpl,a,Rd). The effectiveness of this condition was re-evaluated and the results showed that more than 90% of the cases exhibited a maximum allowable end slip lower than 6 mm. Finally, a design proposal that accounts for the reduction factor βₓ was developed. [less ▲]

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See detailAnálisis empírico del comercio internacional a partir de la segunda mitad del siglo XX.
Kozlowski, Diego UL

Bachelor/master dissertation (2019)

The study of international trade is one of the classical research areas of the economic thought. Its empirical characterization, at the same time that it goes back in time, is today an application space ... [more ▼]

The study of international trade is one of the classical research areas of the economic thought. Its empirical characterization, at the same time that it goes back in time, is today an application space for new techniques, based on the intensive use of data. The increase in the availability of information curated for all countries allows exploring new analysis techniques. In turn, the multiple dimensions of the problem prevent a single analysis technique from capturing the entire phenomenon. The present work proposes to carry out various methodological proposals for the study of international trade, in such a way that together they allow obtaining a novel vision of the data. To do this, techniques widely used in other fields are tested on this particular subject, such as graph analysis and bayesian generative models. Aggregate trade between countries as well as the composition of the export baskets are considered. [less ▲]

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See detailIntegrative Network-Based Approaches For Modeling Human Disease
Ali, Muhammad UL

Doctoral thesis (2019)

The large-scale development of high-throughput sequencing technologies has allowed the generation of reliable omics data related to various regulatory levels. Moreover, integrative computational modeling ... [more ▼]

The large-scale development of high-throughput sequencing technologies has allowed the generation of reliable omics data related to various regulatory levels. Moreover, integrative computational modeling has enabled the disentangling of a complex interplay between these interconnected levels of regulation by interpreting concomitant large quantities of biomedical information (‘big data’) in a systematic way. In the context of human disorders, network modeling of complex gene-gene interactions has been successfully used for understanding disease-related dysregulation and for predicting novel drug targets to revert the diseased phenotype. Recent evidence suggests that changes at multiple levels of genomic regulation are responsible for the development and course of multifactorial diseases. Although existing computational approaches have been able to explain cell-type-specific and disease-associated transcriptional regulation, they so far have been unable to utilize available epigenetic data for systematically dissecting underlying disease mechanisms. In this thesis, we first provided an overview of recent advances in the field of computational modeling of cellular systems, its major strengths and limitations. Next, we highlighted various computational approaches that integrate information from different regulatory levels to understand mechanisms behind the onset and progression of multifactorial disorders. For example, we presented INTREGNET, a computational method for systematically identifying minimal sets of transcription factors (TFs) that can induce desired cellular transitions with increased efficiency. As such, INTREGNET can guide experimental attempts for achieving effective in vivo cellular transitions by overcoming epigenetic barriers restricting the cellular differentiation potential. Furthermore, we introduced an integrative network-based approach for ranking Alzheimer’s disease (AD)-associated functional genetic and epigenetic variation. The proposed approach explains how genetic and epigenetic variation can induce expression changes via gene-gene interactions, thus allowing for a systematic dissection of mechanisms underlying the onset and progression of multifactorial diseases like AD at a multi-omics level. We also showed that particular pathways, such as sphingolipids (SL) function, are significantly dysregulated in AD. In-depth integrative analysis of these SL-related genes reveals their potential as biomarkers and for SL-targeted drug development for AD. Similarly, in order to understand the functional consequences of CLN3 gene mutation in Batten disease (BD), we conducted a differential gene regulatory network (GRN)-based analysis of transcriptomic data obtained from an in vitro BD model and revealed key regulators maintaining the disease phenotype. We believe that the work conducted in this thesis provides the scientific community with a valuable resource to understand the underlying mechanism of multifactorial diseases from an integrative point of view, helping in their early diagnosis as well as in designing potential therapeutic treatments. [less ▲]

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See detailFirst-Principles High-Throughput Study of Linear and Nonlinear Optical Materials
Naccarato, Francesco UL

Doctoral thesis (2019)

Nonlinear optical (NLO) processes, such as second harmonic generation (SHG), play an important role in modern optics, especially in laser-related science and technology. They are at the core of a wide ... [more ▼]

Nonlinear optical (NLO) processes, such as second harmonic generation (SHG), play an important role in modern optics, especially in laser-related science and technology. They are at the core of a wide variety of applications ranging from optoelectronics to medicine. Among the various NLO materials, insulators are particularly important for second-order NLO properties. In particular, only crystals which are non-centrosymmetric can display a non-zero second-order NLO susceptibility. However, given the large number of requirements that a material needs to meet in order to be a good nonlinear optical material, the choice of compounds is drastically limited. Indeed, despite recent progress, a systematic approach to design NLO materials is still lacking. In this work, we conduct a first-principles high-throughput study on a large set of semiconductors for which we computed the linear and nonlinear susceptibility using Density Functional Perturbation Theory. For the linear optical properties, our calculations confirm the general trend that the refractive index is roughly inversely proportional to the band gap. In order to explain the large spread in the data distribution, we have found that two descriptors successfully describe materials with relatively high refraction index: (i) a narrow distribution in energy of the optical transitions which brings the average optical gap close to the direct band gap (ii) a large number of transitions around the band edge and/or high dipole matrix elements. For non-centrosymmetric crystals, we perform the calculation of the efficiency of SHG. We observe some materials with particularly high SHG, much stronger than the general relation with the linear refraction index through Miller’s rule predicts. We relate the value of Miller’s coefficient to geometric factors, i.e., how strongly the crystal deviates from a centrosymmetric one. We also identified interesting materials that show high optical responses for which it would be worth performing further analysis. [less ▲]

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See detailTHE INFLUENCE OF FAMILY OWNERSHIP ON M&AS AND INNOVATION
Issah, Abdul-Basit UL

Doctoral thesis (2019)

I draw from the concept of mixed gambles to investigate the socioemotional wealth trade-offs associated with high risk strategic decisions such as firm acquisition decisions of family firms. We contrast ... [more ▼]

I draw from the concept of mixed gambles to investigate the socioemotional wealth trade-offs associated with high risk strategic decisions such as firm acquisition decisions of family firms. We contrast the predictions from mixed gambles with those of the commonly used behavioural agency model (BAM). Our empirical results for a panel data set of large U.S. firms support the mixed gambles predictions and reject those derived from BAM. They reveal that family firms are more likely to engage in horizontal acquisitions than non-family firms and that the engagement of family firms in horizontal acquisitions is even higher when they are in a gain frame. [less ▲]

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See detailDie Entwicklung der Entfremdung vom Lernen in der unteren Sekundarstufe in Luxemburg: Der Beitrag differenzieller schulischer Lern- und Entwicklungsmilieus
Grecu, Alyssa Laureen UL

Doctoral thesis (2019)

This dissertation provides research on alienation from learning in differential learning and developmental milieus (vgl. Baumert/Stanat/Watermann 2006) within the strongly stratified educational system of ... [more ▼]

This dissertation provides research on alienation from learning in differential learning and developmental milieus (vgl. Baumert/Stanat/Watermann 2006) within the strongly stratified educational system of Luxembourg. Alienation from learning is defined as a student´s generalised negative orientation towards learning (Hascher/Hadjar 2018, S. 179) and collocates with severe consequences including school dropout (see Hascher/Hagenauer 2010, S. 220). The study focusses on the question of how the development of alienation from learning differs between the differential learning and developmental milieus within Luxembourgish secondary school tracks. The conceptual framework is based on the perspective of differential learning and developmental milieus (Baumert/Stanat/Watermann 2006), the theory of school culture (Helsper 2008; Kramer/Thiersch/Ziems 2015) and further culture sociological and resonance pedagogical approaches (Willis 1978; Beljan 2017). Combining research on school culture and research on school alienation, this works examines the interplay between school culture and individual students and its impact on alienation from learning. Conceptualized as a mixed method study, this research aims for a holistic picture on alienation from learning by combining quantitative and qualitative approaches. The quantitative part is based on a three-year panel study with students from all secondary school tracks (grade 7-9). Employing random effects models and growth curves models it investigated the degree and development of alienation from learning over time. Qualitative group discussions and interviews with classes (grade 7) and their teachers from the high-achieving and low-achieving school track (corresponding to grammar school and the lowest secondary school track) were conducted to research how schools´ specific demands contribute to alienation from learning. The method employed in the qualitative analysis was the sequence-analytical habitus reconstruction approach. Quantitative analysis reveals a moderate but increasing degree of alienation from learning in all secondary school tracks from grade 7 to 9. Therefore, alienation from learning develops similarly in all secondary school tracks. Students from the high-achieving ES-Track show the strongest degree of alienation from learning whereas students from the low-achieving Modulaire-Track show the lowest degree of alienation from learning. Qualitative analysis identifies the high-achieving and low-achieving secondary school tracks as differential learning and developmental milieus characterized by diverging educational demands and standards on the class level. Consequently, when students’ orientations conflict with the school´s demands and offers there is a high risk for them to develop alienation. Track-specific possibilities and risks were identified with regard to bonding and alienation. Strong achievement orientation, theoretical educational content and highly standardised educational settings may foster alienation from learning depending on the students´ individual competencies and orientations. [less ▲]

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See detailStudy of nanopulsed discharges for plasma-polymerization: experimental characterization and theoretical understanding of growth mechanisms in the deposition of functional polymer thin films
Loyer, François UL

Doctoral thesis (2019)

Plasma processes are highly versatile methods able to promote the formation of thin films from a vast variety of compounds thanks to the numerous energetic species they generate. Notably, plasma-enhanced ... [more ▼]

Plasma processes are highly versatile methods able to promote the formation of thin films from a vast variety of compounds thanks to the numerous energetic species they generate. Notably, plasma-enhanced chemical vapor deposition (PECVD) processes have already led to the simultaneous synthesis and deposition of a wide variety of organic functional materials. Reciprocally, the many reactive species composing the plasma induce a non-negligible number of side reactions, yielding altered chemistry compared to conventional polymerization processes. Therefore, there is a strong need for controlled methods promoting conventional polymerization pathway in plasma-based processes to increase their range of application. To this end, the atmospheric-pressure plasma-initiated chemical vapor deposition (AP-PiCVD) process was developed, differing from classical PECVD by its initiation source. AP-PiCVD relies on square-wave nanopulsed discharges with single ultra-short plasma on times (t_on ≈ 100 ns) and long plasma off-times (t_off = 0.1 – 100 ms) rather than alternative current sources yielding long and repeated discharges (t_on = 10 µs). Methacrylate monomers initiated by nanopulsed discharges highlighted a shift of growth mechanisms from classical PECVD pathways (plasma-polymerization) to conventional free-radical polymerization. Notably, the growth of polymer layers with an extremely high retention of the monomer’s chemistry and unprecedented molecular weights for an atmospheric-pressure plasma process is demonstrated at long plasma off-times. Moreover, a transition from gas phase to surface growth mechanisms is observed, allowing the deposition of conformal coatings similarly to low-pressure alternative chemical vapor deposition processes. A thorough investigation of the thin films’ chemistry confirms the conventional nature of the layers grown by AP-PiCVD and shed light upon the growth mechanisms in low-frequency nanosecond pulsed plasmas. While the on-time induces the formation of free radicals from the monomers’ fragmentation which are able to initiate and terminate the chain addition process, conventional polymerization mechanisms are strongly promoted during the off-time yielding linear polymer core. Interestingly, new insights on selective initiation mechanisms based on sacrificial functions for an enhanced control of the molecular fragmentation are put forward and discussed. The development of a model describing the kinetic of pulsed plasma was carried out and correlated with experimental observations, providing deeper understanding of the interaction between the gas phase and the surface. The extraction of important physical parameters for the description of the growth kinetics in AP-PiCVD is demonstrated and their significance discussed. Using the fundamental knowledge developed on nanosecond pulsed plasma-initiated polymerization mechanisms, thermoresponsive copolymer layers grown by AP-PiCVD are reported for the first time. The properties of the layers are evaluated and related to their chemistry, allowing the determination of an optimal co-monomers ratio to integrate both of their individual properties as a unique functional thin film. [less ▲]

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See detailMULTILINE HOLDING CONTROL AND INTEGRATION OF COOPERATIVE ITS
Laskaris, Georgios UL

Doctoral thesis (2019)

Transportation is an important sector of the global economy. The rapid urbanization and urban sprawl comes with continuous demand for additional transportation infrastructure in order to satisfy the ... [more ▼]

Transportation is an important sector of the global economy. The rapid urbanization and urban sprawl comes with continuous demand for additional transportation infrastructure in order to satisfy the increasing and variable demand. Public transportation is a major contributor in alleviating traffic congestion in the modern megacities and provide a sustainable alternative to car for accessibility. Public transport operation is inherently stochastic due to the high variability in travel times and passenger demand. This yields to disruptions and undesired phenomena such as vehicles arriving in platoons at stops. Due to the correlation between the headway between vehicles and passenger demand, bunching leads to long waiting time at stops, overcrowded vehicles, discomfort for the passengers and from the operators side poor management of available resources and overall a low of service of the system. The introduction of intelligent transport systems provided innovative applications in order to monitor the operation, collect data and react dynamically to any disruption of the transit system. Advanced Public Transport Systems extended the range of control strategies and their objectives beyond schedule adherence and reliance on historical data alone. Among strategies, holding is a thoroughly investigated and applicable control strategy. With holding, a vehicle is instructed to remain at a designated stop for an additional amount of time after the completion of dwell time, until a criterion is fulfilled. Depending on the characteristics of the line the criterion aim for schedule adherence or regularity or minimization of passenger costs and its components. So far, holding is used for regulating single line operation. Beyond single line, it has been used for transfer synchronization at transfer hubs and recently has been extended to regulate the operation on consecutive stops that are served by multiple lines. The first part of this dissertation is dedicated to real time holding control of multiple lines. A rule based holding criterion is formulated based on the passenger travel time that accounts for the passengers experiencing the control action. Total holding time is estimated based on the size of all passenger groups that interact. The formulated criterion can be applied on all different parts of trunk and branch network. Additionally, the criterion is coupled with a rule based criterion for synchronization and the decision between the two is taken based on the passenger cost. The criterion has been tested for different trunk and branch networks and compared with different control schemes and its performance has been assessed using regularity indices as well as passenger cost indicators for the network in total but also per passenger group. Finally, an analysis has been conducted in order to define under which network and demand configuration multiline control can be preferred over single line control. Results shown that under specific demand distributions multiline control can outperform single line control in network level. Continuously new technologies are introduced to transit operation. Recently, Cooperative Intelligent Transport Systems utilized in the form of Driver Advisory Systems (DAS) shown that can provide the same level of priority with transit signal priority without changing the time and the phases of a traffic light. However, until now the available DASs focus exclusively on public transport priority neglecting completely the sequence of the vehicles and the effects on the operation. In the second part of the dissertation, two widely used DASs are combined with holding in order to meet both the objective of reducing the number of stops at traffic signals and at the same time maintain regularity. Two hybrid controllers are introduced, a combination of two holding criteria and a combination of holding and speed advisory. Both controllers are tested using simulation in comparison to the independent application of the controllers and different levels of transit signal priority. The hybrid controllers can drastically reduce transit signal priority requests while they manage to achieve both objectives. [less ▲]

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See detailAttentional bias to body- and sexually-relevant stimuli
Czeluscinska-Peczkowska, Agnieszka UL

Doctoral thesis (2019)

Sexual dysfunctions and body image dissatisfaction in women have reached significant levels, with prevalence rates being currently estimated at 50% and 38%, respectively. The potential societal and health ... [more ▼]

Sexual dysfunctions and body image dissatisfaction in women have reached significant levels, with prevalence rates being currently estimated at 50% and 38%, respectively. The potential societal and health costs are considerable, as a negative body image is considered a high risk factor for the development and maintenance of eating disorders, and sexual dysfunctions can negatively impact overall well-being. Previous research has separately examined body image dissatisfaction and sexual functioning but research linking these two areas is missing. Study 1 demonstrated the significance of contextual body image in evaluating visual sexual images. Valence ratings of sexually explicit stimuli were found to be associated with sexual functioning level mediated by contextual body image: women, who rated sexually explicit pictures less positively scored lower on sexual functioning if they reported a more self-conscious focus and avoidance of the body in the context of sexual experiences. In Study 2 we were able to prove the relevance of new sexually-explicit images in evoking sexual arousal, which was reflected by evaluative judgements and psychophysiological indicators of arousal. Study 3 aimed to compare responses to sexual stimuli and stimuli related to body image dissatisfaction (images of own body) in participants with sexual dysfunctions (SD) and a healthy control (HC) group. Contrary to our expectations, women in the SD group looked significantly longer and more frequently at self-defined most satisfying than dissatisfying body parts when compared to HC participants. There were no significant group differences in gaze duration and frequency of sexually explicit images, but the women with SDs rated these stimuli as less positive, less arousing and expressed less motivation to keep looking at them. Furthermore, by inducing a positive or negative attention bias (AB) to own body parts we aimed at changing state body image satisfaction and state sexual arousal in response to sexually explicit video-clip. The proposed AB induction was not sufficient and did not affect body image and sexual experiences. Altogether, the findings from current study suggests that it visual attention and general arousal in response to sexual stimuli in women with SD is not disturbed but rather the process of evaluation. [less ▲]

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See detailCoopération, Sécurité, Paix et Développement durable : Quelle nouvelle stratégie des Systèmes d'Alerte précoce (SAP) de la troisième génération pour plus d'efficacité dans la prévention et gestion des conflits violents?
Nadialine, Biagui Alexandre UL

Doctoral thesis (2019)

The atrocities associated with the wars in the Balkans in the 1990s and the Rwandan genocide represent a critical period leading to the questioning of the relevance of Conflict Early Warning Systems (CEWS ... [more ▼]

The atrocities associated with the wars in the Balkans in the 1990s and the Rwandan genocide represent a critical period leading to the questioning of the relevance of Conflict Early Warning Systems (CEWS), which purpose consists in preventing violent conflicts. On the one hand, the supporters of these mechanisms are enthusiatic about the invaluable contributions of CEWS and the notion that these mechanisms are crucial in understanding the underlying causes and dynamics of violent conflicts in order to enable their prevention, resolution and peaceful transformation. The critics, on the other hand, believe that these mechanisms are incapable of fulfilling their assigned mission. Thus, in order to fully understand these mechanisms and to verify the validity of the argument supporting their modest contribution in the process of preventing violent conflicts, a large-scale literature review was undertaken. With regards to all generations of CEWS, from 1990 to 2016, the main objective consisted in identifying difficulties in the literature and recommendations for the improvement of these mechanisms. Considering that CEWS and response mechanisms interact constantly, identifying difficulties and recommendations related to response mechanisms for the same time period in the relevant literature was also a focus. In order to strengthen our investigation, a focus-group with CEWS practitioners was held in March 2018 in Senegal. With regard to the online literature review, a search strategy was set up. It allowed the exploration of several documents from a variety of sources. As for the focus-group, inclusion criteria for participant’s selection were also defined. On the one hand, 14504 documents were explored, of which 259 thoroughly reviewed, of which 153 were selected. In addition, 20 other so-called mixed documents, focusing on the main concepts of the thesis (5 documents per concept) were selected. On the other hand, 5 participants took part in the focus-group. As for the online literature review’s results, several types of difficulties and recommendations related to CEWS and response mechanisms were identified and divided into categories and sub-categories. Similarly, with regard to the focus-group’s results, several types of difficulties and recommendations related to CEWS and response mechanisms were identified and dispatched into the corresponding categories and sub-categories. Consequently, a compendium of difficulties and recommendations related to CEWS and response mechanisms from 1990 to 2016 was established. By associating the Maxqda software to the document and content analysis methods, the two types of data (review and empirical) were valorized through the principal of inference. A cross-analysis of these two types of data made it possible to invalidate and confirm the existence of certain failures, but also to confirm the persistence of several difficulties that CEWS and response mechanisms face. A critical analysis of these mechanisms has demonstrated that, despite their contributions and progress, much work is still to be done, especially when it comes to the collection and management of information for early warning purposes. Indeed, the failure to take into account a number of technical issues could have negative effects on the whole Collection-Verification-Transmission-Analysis-Referal process (CVTAR) and on the management of intra- or inter-state conflicts. Thus, with regard to the later, the geopolitical and geostrategic game dictating the outcome of international mediation degrades its image by promoting a distorted and selfish culture of violent conflicts prevention. As a result, such flaws have prompted the formulation of alternative and relevant strategies with the aim of optimazing the effectiveness of violent conflict prevention and management. In addition to theoretical and practical contributions, the provision of a product, currently under conceptualization, to a federal structure of CEWS and response mechanisms at the national level, promises an invaluable contribution to social unrests and/ or violent conflicts prevention, but also a transparent management of public affairs and the promotion of good governance. [less ▲]

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See detailRobotic Trajectory Tracking: Position- and Force-Control
Klecker, Sophie UL

Doctoral thesis (2019)

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a ... [more ▼]

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a freeform surface in a discontinuous manner. Next to resulting switching constraints, disturbances and uncertainties, the case of unknown robot models is addressed. In a second phase, once contact has been established between surface and end effector and the freeform path is followed, a desired force is applied. In order to react to changing circumstances, the manipulator needs to show the features of an intelligent agent, i.e. it needs to learn and adapt its behaviour based on a combination of a constant interaction with its environment and preprogramed goals or preferences. The robotic manipulator mimics the human behaviour based on bio-inspired algorithms. In this way it is taken advantage of the know-how and experience of human operators as their knowledge is translated in robot skills. A selection of promising concepts is explored, developed and combined to extend the application areas of robotic manipulators from monotonous, basic tasks in stiff environments to complex constrained processes. Conventional concepts (Sliding Mode Control, PID) are combined with bio-inspired learning (BELBIC, reinforcement based learning) for robust and adaptive control. Independence of robot parameters is guaranteed through approximated robot functions using a Neural Network with online update laws and model-free algorithms. The performance of the concepts is evaluated through simulations and experiments. In complex freeform trajectory tracking applications, excellent absolute mean position errors (<0.3 rad) are achieved. Position and torque control are combined in a parallel concept with minimized absolute mean torque errors (<0.1 Nm). [less ▲]

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See detailCreating better ground truth to further understand Android malware: A large scale mining approach based on antivirus labels and malicious artifacts
Hurier, Médéric UL

Doctoral thesis (2019)

Mobile applications are essential for interacting with technology and other people. With more than 2 billion devices deployed all over the world, Android offers a thriving ecosystem by making accessible ... [more ▼]

Mobile applications are essential for interacting with technology and other people. With more than 2 billion devices deployed all over the world, Android offers a thriving ecosystem by making accessible the work of thousands of developers on digital marketplaces such as Google Play. Nevertheless, the success of Android also exposes millions of users to malware authors who seek to siphon private information and hijack mobile devices for their benefits. To fight against the proliferation of Android malware, the security community embraced machine learning, a branch of artificial intelligence that powers a new generation of detection systems. Machine learning algorithms, however, require a substantial number of qualified samples to learn the classification rules enforced by security experts. Unfortunately, malware ground truths are notoriously hard to construct due to the inherent complexity of Android applications and the global lack of public information about malware. In a context where both information and human resources are limited, the security community is in demand for new approaches to aid practitioners to accurately define Android malware, automate classification decisions, and improve the comprehension of Android malware. This dissertation proposes three solutions to assist with the creation of malware ground truths. The first contribution is STASE, an analytical framework that qualifies the composition of malware ground truths. STASE reviews the information shared by antivirus products with nine metrics in order to support the reproducibility of research experiments and detect potential biases. This dissertation reports the results of STASE against three typical settings and suggests additional recommendations for designing experiments based on Android malware. The second contribution is EUPHONY, a heuristic system built to unify family clusters belonging to malware ground truths. EUPHONY exploits the co-occurrence of malware labels obtained from antivirus reports to study the relationship between Android applications and proposes a single family name per sample for the sake of facilitating malware experiments. This dissertation evaluates EUPHONY on well-known malware ground truths to assess the precision of our approach and produce a large dataset of malware tags for the research community. The third contribution is AP-GRAPH, a knowledge database for dissecting the characteristics of malware ground truths. AP-GRAPH leverages the results of EUPHONY and static analysis to index artifacts that are highly correlated with malware activities and recommend the inspection of the most suspicious components. This dissertation explores the set of artifacts retrieved by AP-GRAPH from popular malware families to track down their correlation and their evolution compared to other malware populations. [less ▲]

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See detailNumerische Untersuchung zur Strömungsentwicklung im passiven Flutsystem des Reaktordesigns Kerena
Kaczmarkiewicz, Nadine UL

Doctoral thesis (2019)

In case of a loss-of-coolant accident in a nuclear power plant, the passive gravity-driven core flooding system recovers the reactor’s water inventory so that the core is covered at all times. It is ... [more ▼]

In case of a loss-of-coolant accident in a nuclear power plant, the passive gravity-driven core flooding system recovers the reactor’s water inventory so that the core is covered at all times. It is essential to estimate, when passive flooding valves open, whether reverse flow occurs and to which extent this may delay flooding or even lead to initial mass displacement from the reactor to the flooding pools. Experimental investigations including passive safety systems of the KERENA-design are performed in a scaled-down facility. Such so-called integral tests are carried out with initial and boundary conditions of different design basis accidents. The behavior of the passive core flooding system is analyzed proofing the influence through other passive safety systems. Evidence is shown that a stable two-phase reverse flow occurs, due to incomplete condensation at the outlet of the emergency condenser and to adiabatic evaporation in the flooding line. The hydrostatic column is reduced during reverse flow but regained in all considered cases. As a result the onset of flooding is delayed only moderately. The influence on the flow development of the containment pressure, of the geometry of the flooding line, and of other peculiar boundary conditions of the considered experiments is discussed. Results from numerical simulations are presented and confirm the experimental results. The considered numerical model of the flooding system can predict fundamental phenomena governing the flow development in the flooding line with satisfactory accuracy. [less ▲]

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See detailCritical perspectives on plurilingual students' identity performance in sustainability education
Gorges, Anna UL

Doctoral thesis (2019)

The purpose of this critical video-ethnographic study is to gain new perspectives on how the open, dialogic structures in an alternative high school setting afford plurilingual adult students’ to take ... [more ▼]

The purpose of this critical video-ethnographic study is to gain new perspectives on how the open, dialogic structures in an alternative high school setting afford plurilingual adult students’ to take agency and the development of a positive student identity. With this goal, the study seeks to contribute to the research literature on plurilingual adult students and on nontraditional students learning about sustainability. The overarching question that guides this study is how does the figured world of multilingual sustainability education based on socioscientific issues mediate plurilingual adult students identities as competent science students? This study is multi-theoretical, multi-method, and multi-level, and as such, the manuscriptstyle dissertation presents several case studies of students as they participate in an interdisciplinary unit on sustainability. Situated in a superdiverse context, the data collection took place at an alternative high school, where students who dropped out of the traditional school system have the chance to get a leaving certificate. Data resources include video data, audio data, student artefacts, fieldnotes and photographs. Multimodal discourse analysis based on Gee (1996) was used to reveal the structures at the micro, meso and macro level that mediate learning for students in the alternative educational setting and afford them to make connections to their everyday lives. Three individual manuscripts examine three separate case studies regarding students’ use of transmodalling, students’ engagement in socio-scientific issues, and students’ perspectives on the holistic teaching and learning approaches in their school. Drawing on dialectic understandings of learning, the three case studies each illuminate holistic approaches to learning focusing on students’ multimodal means of expression, emotions and identity development that afford them with opportunities to take agency and create solidarity in the class and school community. This study concludes that dialogic pedagogy as space of possibilities mediates student’ development of identities as competent science learners, which has implications for their identities as agents positioned for transformative actions. [less ▲]

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See detailExtracting the spatio-temporal variations in the gravity field recovered from GRACE spatial mission: methods and geophysical applications
Prevost, Paoline Fleur UL

Doctoral thesis (2019)

Measurements of the spatio-temporal variations of Earth’s gravity field recovered from the Gravity Recovery and Climate Experiment (GRACE) mission have led to unprecedented insights into large spatial ... [more ▼]

Measurements of the spatio-temporal variations of Earth’s gravity field recovered from the Gravity Recovery and Climate Experiment (GRACE) mission have led to unprecedented insights into large spatial mass redistribution at secular, seasonal, and sub-seasonal time scales. GRACE solutions from various processing centers, while adopting different processing strategies, result in rather coherent estimates. However, these solutions also exhibit random as well as systematic errors, with specific spatial and temporal patterns in the latter. In order to dampen the noise and enhance the geophysical signals in the GRACE data, several methods have been proposed. Among these, methods based on filtering techniques require a priori assumptions regarding the spatio-temporal structure of the errors. Despite the large effort to improve the quality of GRACE data for always finer geophysical applications, removing noise remains a problematic question as discussed in Chapter 1. In this thesis, we explore an alternative approach, using a spatio-temporal filter, namely the Multichannel Singular Spectrum Analysis (M-SSA) described in Chapter 2. M-SSA is a data-adaptive, multivariate, and non-parametric method that simultaneously exploits the spatial and temporal correlations of geophysical fields to extract common modes of variability. We perform an M-SSA simultaneously on 13 years of GRACE spherical harmonics solutions from five different processing centers. We show that the method allows for the extraction of common modes of variability between solutions, and removal of the solution-specific spatio-temporal errors arising from each processing strategies. In particular, the method filters out efficiently the spurious North-South stripes, most likely caused by aliasing of the imperfect geophysical correction models of known phenomena. In Chapter 3, we compare our GRACE solution to other spherical harmonics solutions and to mass concentration (mascon) solutions which use a priori information on the spatio-temporal pattern of geophysical signals. We also compare performance of our M-SSA GRACE solution with respect to others by predicting surface displacements induced by GRACE-derived mass loading and comparing results with independent displacement data from stations of the Global Navigation Satellite System (GNSS). Finally, in Chapter 4 we discuss the possible application of a refined GRACE solution to answer debated post-glacial rebound questions. More precisely, we focus on separating the post-glacial rebound signal related to past ice melting and the present ice melting in the region of South Georgia. [less ▲]

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See detailFichte und der Skeptizismus
Motz, Oliver Tobias UL

Doctoral thesis (2019)

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See detailAutomated optimisation of stem cell-derived neuronal cell culture in three dimensional microfluidic device
Kane, Khalid UL

Doctoral thesis (2019)

This dissertation is a compilation of publications and manuscripts that aim 1) to integrate an automated platform optimised for long term in vitro cell culture maintenance for Parkinson’s disease, long ... [more ▼]

This dissertation is a compilation of publications and manuscripts that aim 1) to integrate an automated platform optimised for long term in vitro cell culture maintenance for Parkinson’s disease, long term live cell imaging and the handling of many cell lines, 2) to combine physics principles with imaging techniques to optimise the seeding of Matrigel embedded human neuroepithelial stem cells into a three-dimensional microfluidic device, and 3) to combine engineering principles with cell biology to optimise the design of a three-dimensional microfluidic system based on phaseguide technology. In the first publication manuscript, we investigated Matrigel as a surrogate extracellular matrix in three-dimensional cell culture systems, including microfluidic cell culture. The study aimed at understanding and characterising the properties of Matrigel. Using classical rheological measurements of Matrigel (viscosity versus shear rate) in combination with fluorescence microscopy and fluorescent beads for particle image velocimetry measurements (velocity profiles), the shear rates experienced by cells in a microfluidic device for three-dimensional cell culture was characterised. We discussed how the result of which helped to mechanically optimise the use of Matrigel in microfluidic systems to minimise the shear stress experienced by cells during seeding in a microchannel. The second manuscript proposes a methodology to passively control the flow of media in a three-dimensional microfluidic channel. We used the fluid dynamic concept of similitude to dynamically replicate cerebral blood flow in a rectangular cross-sectional microchannel. This similarity model of a target cell type and a simple fluid flow mathematical prediction model was used to iterate the most optimum dimensions within some manufacturing constraints to adapt the design of the OrganoPlate, a cell culture plate fully compatible with laboratory automation, which allowed its re-dimension to achieve over 24h of flow for the culture of human neuroepithelial stem cells into midbrain specific dopaminergic neurons. In the third publication manuscript, we propose an automated cell culture platform optimised for long-term maintenance and monitoring of different cells in three-dimensional microfluidic cell culture devices. The system uses Standard in Laboratory Automation or SiLA, an open source standardisation which allows rapid software integration of laboratory automation hardware. The automation platform can be flexibly adapted to various experimental protocols and features time-lapse imaging microscopy for quality control and electrophysiology monitoring to assess cellular activity. It was biologically validated by differentiating Parkinson’s disease patient derived human neuroepithelial stem cells into midbrain specific dopaminergic neurons. This system is the first example of an automated Organ-on-a-Chip culture and has the potential to enable a versatile array of in vitro experiments for patient-specific disease modelling. Finally, the fourth manuscript initiates the assessment of the neuronal activity of induced pluripotent stem cell derived neurons from Parkinson’s Disease patients with LRRK2-G2019S mutations and isogenic controls. A novel image analysis pipeline that combined semi-automated neuronal segmentation and quantification of calcium transient properties was developed and used to analyse neuronal firing activity. It was found that LRRK2-G2019S mutants have shortened inter-spike intervals and an increased rate of spontaneous calcium transient induction than control cell lines. [less ▲]

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See detailShear Transfer in Heavy Steel-Concrete Composite Columns with Multiple Encased Steel Profiles
Chrzanowski, Maciej UL

Doctoral thesis (2019)

The PhD Thesis is dealing with the shear transfer in heavy steel-concrete composite columns with multiple encased steel profiles. In the conducted research, a focus was placed on two aspects of shear ... [more ▼]

The PhD Thesis is dealing with the shear transfer in heavy steel-concrete composite columns with multiple encased steel profiles. In the conducted research, a focus was placed on two aspects of shear transfer: (1) local shear transfer at the steel-concrete interface and (2) global shear transfer between the embedded steel profiles. With reference to the current practice, gaps in the knowledge and in the available solutions have been identified. The development of a novel, easy-applicable and efficient type of shear connectors for an application in composite columns with one or multiple-encased steel profiles satisfies the improvement need to assure local shear transfer between steel and concrete materials. The novel type of flat shear connectors has a form of reinforcement bars welded to the flanges of steel profiles. Three main orientations, in accordance to the steel beam longitudinal axis, were investigated: 1) transversal, 2) longitudinal and 3) angled under 45° - V-shaped. The force transfer mechanism of the proposed shear connectors considers the usage of the external stirrups to anchorage the compression struts and bear the tensile forces. In parallel, the steel-concrete bond phenomenon was examined and analysed. In the consideration of the global shear transfer and in respect to the mechanical engineering model and behaviour of large composite columns with more than one embedded steel profile, the common practice so far is to assume a homogenous system with one stiffness and analyse it based on the Bernoulli beam theory. However, the results of the recent tests caused some doubts whether this approach is correct. The derivation away from the Bernoulli beam behaviour leads to a changed stiffness of the column and hence changed critical buckling load. An innovative hybrid conception has been proposed, where a transition towards the Vierendeel truss model embedded into the Timoshenko beam model is considered in order to govern the identified significant effects of shear deformation. Within this objective, big-scale beam/column members with two embedded steel profiles were examined in order to investigate an internal forces distribution and its bending and shear stiffness. A complex interaction between the materials and lack of knowledge regarding composite behaviour in columns with multiple encased steel profiles opens opportunities to develop novel systems and design methods. The described objectives are investigated experimentally and by the FE numerical simulations. As an outcome, an analytical model for the resistance of the developed novel shear connectors and innovative mechanical engineering model for the description of the structural behaviour, as well as effective stiffness, of a composite member with more than one embedded steel profile are given. [less ▲]

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See detailEmpirical Essays on Institutional Determinants of Firm Entry and Exit
Murmann Geb. Wagner, Simona Christine UL

Doctoral thesis (2019)

This thesis is a collection of three essays investigating unintended and non-obvious effects of economic policy changes and established institutional systems on firm entry and exit. The first essay ... [more ▼]

This thesis is a collection of three essays investigating unintended and non-obvious effects of economic policy changes and established institutional systems on firm entry and exit. The first essay investigates the effect of personal preferences of insolvency trustees and judges on insolvency outcomes in Germany. The second essay reveals that governmental wage setting through minimum wages will not only affect dependent employees but also self-employment. In the third essay, introduction of high-speed internet effects on firm entries and exits are analyzed. [less ▲]

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See detailMultiscale modeling of mitochondria
Garcia, Guadalupe Clara UL

Doctoral thesis (2019)

Life is based on energy conversion by which cells and organisms can adapt to the environment. The involved biological processes are intrinsically multiscale phenomena since they are based on molecular ... [more ▼]

Life is based on energy conversion by which cells and organisms can adapt to the environment. The involved biological processes are intrinsically multiscale phenomena since they are based on molecular interactions on a small scale leading to the emerging behavior of cells, organs and organisms. To understand the underlying regulation and to dissect the mechanisms that control system behavior, appropriate mathematical multiscale models are needed. Such models do not only offer the opportunity to test different hypothesized mechanisms but can also address current experimental technology gaps by zooming in and out of the dynamics, changing scales, coarse-graining the dynamics and giving us distinct views of the phenomena. In this dissertation substantial efforts were done to combine different computational modeling strategies based on different assumptions and implications to model an essential system of eukaryotic life -- the energy providing mitochondria -- where the spatiotemporal domain is suspected to have a substantial influence on its function. Mitochondria are highly dynamic organelles that fuse, divide, and are transported along the cytoskeleton to ensure cellular energy homeostasis. These processes cover different scales, in space and time, where on the more global scale mitochondria exhibit changes in their molecular content in response to their physiological context including circadian modulation. On the smaller scales, mitochondria show also faster adaptation by changing their morphology within minutes. For both processes, the relation between the underlying structure of either their regulating network or the spatial morphology and the functional consequences are essential to understand principles of energy homeostasis and their link to health and disease conditions. This thesis focuses on different scales of mitochondrial adaptation. On the small scales, fission and fusion of mitochondria are rather well established but substantial evidence indicates that the internal structure is also highly variable in dependence on metabolic condition. However, a quantitative mechanistic understanding how mitochondrial morphology affects energetic states is still elusive. In the first part of this dissertation I address this question by developing an agent-based dynamic model based on three-dimensional morphologies from electron microscopy tomography, which considers the molecular dynamics of the main ATP production components. This multiscale approach allows for investigating the emergent behavior of the energy generating mechanism in dependence on spatial properties and molecular orchestration. Interestingly, comparing spatiotemporal simulations with a corresponding space-independent approach, I found only minor space dependence in equilibrium conditions but qualitative difference in fluctuating environments and in particular indicate that the morphology provides a mechanism to buffer energy at synapses. On the more global scale of the regulation of mitochondrial protein composition, I applied a data driven approach to explore how mitochondrial activity is changing during the day and how food intake restrictions can effect the structure of the underlying adaptation process. To address the question if at different times of the day, the mitochondrial composition might adapt and have potential implications for function, I analyzed temporal patterns of hepatic transcripts of mice that had either unlimited access to food or were hold under temporal food restrictions. My analysis showed that mitochondrial activity exhibits a temporal activity modulation where different subgroups of elements are active at different time points and that food restriction increases temporal regulation. Overall, this thesis provides new insights into mitochondrial biology at different scales by providing an innovative computational modeling framework to investigate the relation between morphology and energy production as well as by characterizing temporal modulation of the regulatory network structure under different conditions. [less ▲]

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See detailZeit- und Zukunftskonzepte in Konrads von Würzburg "Trojanerkrieg"
Krämer, Charlotte UL

Doctoral thesis (2019)

Den Ausgangspunkt für diese Untersuchung zu Konrads von Würzburg „Trojanerkrieg“ – einem durch den Tod des Autors 1287 unvollendet gebliebenen Roman von mehr als 40.000 Versen, der als der am weitesten ... [more ▼]

Den Ausgangspunkt für diese Untersuchung zu Konrads von Würzburg „Trojanerkrieg“ – einem durch den Tod des Autors 1287 unvollendet gebliebenen Roman von mehr als 40.000 Versen, der als der am weitesten verbreitete deutschsprachige Antikenroman des Mittelalters gilt – bilden die Zeit- und Zukunftskonzepte der in der erzählten Welt physisch präsenten menschlichen Akteure: Was wissen sie über ihre Zukunft? Wie weit reicht die Zeitspanne, die sie aus ihrem jeweiligen Jetztpunkt antizipieren, in die Zukunft voraus, und welche Entwürfe eigenen Handelns schmieden sie? Wie gehen sie mit konkurrierenden Zukunftsmodellen um, insbesondere mit solchen, die die Möglichkeit eines alternativen Geschehensverlaufs eröffnen? Kurz: Wie stellt Konrad im „Trojanerkrieg“ das Verhältnis des handelnden Menschen zur eigenen Zukunft dar? Augenfällig ist das Spannungsfeld zwischen kausaler und finaler Handlungsmotivierung, in dem sich die Figuren in unterschiedlichen Geschehenszusammenhängen – als Eltern, Liebende oder Rächende – bewegen: Einerseits werden sie immer wieder mit Informationen über die Zukunft konfrontiert, die eigentlich außerhalb ihres „natürlichen“ Wissenshorizonts liegen und ihren Handlungsspielraum erweitern. Andererseits wird dieser von verschiedenen metaphysischen Mächten (wie etwa Gott, Glück und Zufall) eingeschränkt oder gar gänzlich nivelliert. Denn Konrad spielt im „Trojanerkrieg“ mit der Eigendynamik der fatalen Prozesse, die den Untergang der Trojaner vorbereiten: Anders etwa als den Protagonisten der volkssprachlichen Heldenepik gelingt es seinen Figuren nicht, Konflikte durch die Anwendung von Gewalt beizulegen – vielmehr entstehen dadurch neue Probleme. Als Alternative zur gewaltsamen Reaktion werden zukunftsorientiertere Handlungsstrategien diskutiert, wobei Konrad sich besonders für den Umschlagpunkt interessiert, an dem aus subjektiven Handlungsplänen eine Geschichte scheiternder Personenverbände entsteht, weil die Zukunftskonzepte der Figuren überwiegend über keine oder nur eine minimale soziale Ausdehnung verfügen. [less ▲]

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See detailNonlinear Observation and Control of a Lightweight Robotic Manipulator Actuated by Shape Memory Alloy (SMA) Wires
Quintanar Guzman, Serket UL

Doctoral thesis (2019)

In the last decade, the industry of Unmanned Aerial Vehicles (UAV) has gone through immense growth and diversification. Nowadays, we find drone based applications in a wide range of industries, such as ... [more ▼]

In the last decade, the industry of Unmanned Aerial Vehicles (UAV) has gone through immense growth and diversification. Nowadays, we find drone based applications in a wide range of industries, such as infrastructure, agriculture, transport, among others. This phenomenon has generated an increasing interest in the field of aerial manipulation. The implementation of aerial manipulators in the UAV industry could generate a significant increase in possible applications. However, the restriction on the available payload is one of the main setbacks of this approach. The impossibility to equip UAVs with heavy dexterous industrial robotic arms has driven the interest in the development of lightweight manipulators suitable for these applications. In the pursuit of providing an alternative lightweight solution for the aerial manipulators, this thesis proposes a lightweight robotic arm actuated by Shape Memory Alloy (SMA) wires. Although SMA wires represent a great alternative to conventional actuators for lightweight applications, they also imply highly nonlinear dynamics, which makes them difficult to control. Seeking to present a solution for the challenging task of controlling SMA wires, this work investigates the implications and advantages of the implementation of state feedback control techniques. The final aim of this study is the experimental implementation of a state feedback control for position regulation of the proposed lightweight robotic arm. Firstly, a mathematical model based on a constitutive model of the SMA wire is developed and experimentally validated. This model describes the dynamics of the proposed lightweight robotic arm from a mechatronics perspective. The proposed robotic arm is tested with three output feedback controllers for angular position control, namely a PID, a Sliding Mode and an Adaptive Controller. The controllers are tested in a MATLAB simulation and finally implemented and experimentally tested in various different scenarios. Following, in order to perform the experimental implementation of a state feedback control technique, a state and unknown input observer is developed. First, a non-switching observable model with unknown input of the proposed robotic arm is derived from the model previously presented. This model takes the martensite fraction rate of the original model as an unknown input, making it possible to eliminate the switching terms in the model. Then, a state and unknown input observer is proposed. This observer is based on the Extended Kalman Filter (EKF) for state estimation and sliding mode approach for unknown input estimation. Sufficient conditions for stability and convergence are established. The observer is tested in a MATLAB simulation and experimentally validated in various different scenarios. Finally, a state feedback control technique is tested in simulation and experimentally implemented for angular position control of the proposed lightweight robotic arm. Specifically, continuous and discrete-time State-Dependent Riccati Equation (SDRE) control laws are derived and implemented. To conclude, a quantitative and qualitative comparative analysis between an output feedback control approach and the implemented state feedback control is carried out under multiple scenarios, including position regulation, position tracking and tracking with changing payloads. [less ▲]

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See detailNumerical Modeling of air-gap membrane distillation
Cramer, Kerstin Julia UL

Doctoral thesis (2019)

Fresh water supply is a problem in large parts of the world and present on every continent. Many countries facing physical water scarcity, however, have access to the sea and lie in arid zones of the ... [more ▼]

Fresh water supply is a problem in large parts of the world and present on every continent. Many countries facing physical water scarcity, however, have access to the sea and lie in arid zones of the earth where solar energy is plentiful available. Membrane distillation (MD) describes an emerging desalination technology which has advantages when driven by solar energy or waste heat. In MD, seawater is thermally desalinated by generating a temperature gradient between hot salt water and produced fresh water which are separated by a membrane. In air-gap membrane distillation (AGMD) an insulating air-gap is introduced between membrane and distillate in order to minimize conductive losses. Despite its advantages, the permeate stream needs to be increased for large-scale application. To improve performance and energy efficiency, a detailed understanding of the highly coupled heat and mass transfer is crucial. However, for AGMD not many models exist and the existing models simplify the heat and mass transfer processes. The goal of this thesis is therefore to increase the understanding of the AGMD process and the predictive power of numerical models. A three-dimensional (3D) macro-scale model is developed with emphasis on the heat and mass transfer. It integrates aspects from multiphase flow modeling namely energy conservation over phase-change interfaces and the thermodynamic concept of moist air in the air-gap. Thereby, it computes the condensation mass flow independently from the evaporation mass flow, allowing to study the influence of convection on the heat and mass transfer in the air-gap. The model is accelerated for computation on graphical processing units (GPU). Employing the macro-scale model, a comparative analysis of the effects of module orientation on module performance and efficiency is performed. Vortexes in the air-gap are observed when using a module configuration where the hot feed flows below air-gap and membrane and the temperature gradient is opposing gravity. These vortexes lead to a significantly increased energy utilization also at low feed velocities. As the main advantage of AGMD is the reduction of heat losses, this configuration could bring further improvement. Furthermore, membrane transport properties are determined from high-resolution 3D membrane imaging combined with Lattice-Boltzmann simulation. Thereby, the 3D structure of membrane samples is obtained and porosity, tortuosity and permeability values are computed for the investigated membranes. Following the findings in the papers, further studies are suggested employing the modeling approaches developed in this thesis. [less ▲]

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See detailGeneration of midbrain organoids as a model to study Parkinson's disease
Smits, Lisa UL

Doctoral thesis (2019)

The study of 3D cell culture models not only bridges the gap between traditional 2D in vitro experiments and in vivo animal models, it also addresses processes that cannot be recapitulated by these ... [more ▼]

The study of 3D cell culture models not only bridges the gap between traditional 2D in vitro experiments and in vivo animal models, it also addresses processes that cannot be recapitulated by these traditional models. Therefore, it offers an opportunity to better understand complex biology, for instance brain development, where conventional models have not proven successful. The so{called brain organoid technology provides a physiologically relevant context, which holds great potential for its application in modelling neurological diseases. To obtain these highly specialised structures, resembling specifically key features of the human midbrain, we derived a human midbrain-specific organoid (hMO) system from regionally patterned neural stem cells (NSCs). The resulting neural tissue exhibited abundant neurons with midbrain dopaminergic neuron (mDAN) identity, as well as astroglia and oligodendrocyte di erentiation. Within the hMOs, we could observe neurite myelination and the formation of synaptic connections. Regular fire patterning and neural network synchronicity were determined by multielectrode array (MEA) recordings. In addition to electrophysiologically functional mDANs producing and secreting dopamine (DA), we also detected responsive neuronal subtypes, like GABAergic and glutamatergic neurons. To investigate Parkinson's disease (PD)-relevant pathomechanisms, we derived hMOs from PD patients carrying the LRRK2-G2019S mutation and compared them to healthy control hMOs. In addition to a reduced number and complexity of mDANs, we determined a signi cant increase of the stem cell marker FOXA2 in the patient-derived hMOs. This suggests a neurodevelopmental defect induced by a PD-specific mutation and emphasises the importance of advanced three-dimensional (3D) stem cell-based in vitro models. The in this thesis described hMOs are suitable to reveal PD{relevant phenotypes, thus constitute as a powerful tool for human-specific in vitro disease modelling of neurological disorders with a great potential to be utilised in advanced therapy development. [less ▲]

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See detailIl "Tieste" di Ugo Foscolo e l'estetica teatrale di Melchiorre Cesarotti. Per la storia e le implicazioni di un'inconciliabilità ideologica e filosofica
Scagnetti, Matteo Martino UL

Doctoral thesis (2019)

This work analyzes the tragedy written by Ugo Foscolo (1778-1827) at the end of his adolescence : Tieste. The drama has not been sufficiently studied yet, but presents various and important elements of ... [more ▼]

This work analyzes the tragedy written by Ugo Foscolo (1778-1827) at the end of his adolescence : Tieste. The drama has not been sufficiently studied yet, but presents various and important elements of interest. The idea of literature emerging from it is definitely new, and Tieste tries untrodden ways, incompatible with the dominant idea of tragedy at its epoch. Most of all, Tieste marks a rebellion against the aesthetic canons of Melchiorre Cesarotti (1730-1808), a well-known philosopher who had a deep influence in the theatrical field and who had established the standards of a good tragedy. Cesarotti’s parameters were still those of the Enlightenment, and imposed a moral message to every tragedy, whose characters should be rewarded or punished on the basis of their goodness or their wickedness. For Cesarotti, a character would have encountered an unfavourable fate only as a consequence of a moral crime. His virtue, instead, would have avoided any danger. In Foscolo, on the contrary, there is no providence, and the destiny of human beings doesn’t depend on their behaviour. Virtuous characters are powerless and succumb without even understanding why, while the evil tyrant triumphs, moved only by his sadism. The evil is ineffable and inexplicable, and Reason, which solves every problem in Cesarotti’s Weltanschauung, is now helpless and meaningless. Foscolo’s first tragedy therefore represents the transition from an Ancien Régime world view to the phantoms and the nightmares of the contemporary age, when no certitude is possible anymore. [less ▲]

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See detailEffective Testing Of Advanced Driver Assistance Systems Using Evolutionary Algorithms And Machine Learning
Ben Abdessalem (helali), Raja UL

Doctoral thesis (2019)

Improving road safety is a major concern for most car manufacturers. In recent years, the development of Advanced Driver Assistance Systems (ADAS) has subsequently seen a tremendous boost. The development ... [more ▼]

Improving road safety is a major concern for most car manufacturers. In recent years, the development of Advanced Driver Assistance Systems (ADAS) has subsequently seen a tremendous boost. The development of such systems requires complex testing to ensure vehicle’s safety and reliability. Performing road tests tends to be dangerous, time-consuming, and costly. Hence, a large part of testing for ADAS has to be carried out using physics-based simulation platforms, which are able to emulate a wide range of virtual traffic scenarios and road environments. The main difficulties with simulation-based testing of ADAS are: (1) the test input space is large and multidimensional, (2) simulation platforms provide no guidance to engineers as to which scenarios should be selected for testing, and hence, simulation is limited to a small number of scenarios hand-picked by engineers, and (3) test executions are computationally expensive because they often involve executing high-fidelity mathematical models capturing continuous dynamic behaviors of vehicles and their environment. The complexity of testing ADAS is further exacerbated when many ADAS are employed together in a self-driving system. In particular, when self-driving systems include many ADAS (i.e., features), they tend to interact and impact one another’s behavior in an unknown way and may lead to conflicting situations. The main challenge here is to detect and manage feature interactions, in particular, those that violate system safety requirements, hence leading to critical failures. In practice, once feature interaction failures are detected, engineers need to devise resolution strategies to resolve potential conflicts between features. Developing resolution strategies is a complex task and despite the extensive domain expertise, these resolution strategies can be erroneous and are too complex to be manually repaired. In this dissertation, in addition to testing individual ADAS, we focus on testing self-driving systems that include several ADAS. In this dissertation, we propose a set of approaches based on meta-heuristic search and machine learning techniques to automate ADAS testing and to repair feature interaction failures in self-driving systems. The work presented in this dissertation is motivated by ADAS testing needs at IEE, a world-leading part supplier to the automotive industry. In this dissertation, we focus on the problem of design time testing of ADAS in a simulated environment, relying on Simulink models. The main research contributions in this dissertation are: - A testing approach for ADAS that combines multi-objective search with surrogate models to guide testing towards the most critical behaviors of ADAS, and to explore a larger part of the input search space with less computational resources. - An automated testing algorithm that builds on learnable evolution models and uses classification decision trees to guide the generation of new test scenarios within complex and multidimensional input spaces and help engineers interpret test results. - An automated technique that detects feature interaction failures in the context of self-driving systems based on analyzing executable function models typically developed to specify system behaviors at early development stages. - An automated technique that uses a new many-objective search algorithm to localize and repair errors in the feature interaction resolution rules for self-driving systems. [less ▲]

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See detailComputational and symbolic analysis of distance-bounding protocols
Toro Pozo, Jorge Luis UL

Doctoral thesis (2019)

Contactless technologies are gaining more popularity everyday. Credit cards enabled with contactless payment, smart cards for transport ticketing, NFC-enabled mobile phones, and e-passports are just a few ... [more ▼]

Contactless technologies are gaining more popularity everyday. Credit cards enabled with contactless payment, smart cards for transport ticketing, NFC-enabled mobile phones, and e-passports are just a few examples of contactless devices we are familiar with nowadays. Most secure systems meant for these devices presume physical proximity between the device and the reader terminal, due to their short communication range. In theory, a credit card should not be charged of an on-site purchase if the card is not up to a few centimeters away from the payment terminal. In practice, this is not always true. Indeed, some contactless payment protocols, such as Visa's payWave, have been shown vulnerable to relay attacks. In a relay attack, a man-in-the-middle uses one or more relay devices in order to make two distant devices believe they are close. Relay attacks have been implemented also to bypass keyless entry and start systems in various modern cars. Relay attacks can be defended against with distance-bounding protocols, which are security protocols that measure the round-trip times of a series of challenge/response rounds in order to guarantee physical proximity. A large number of these protocols have been proposed and more sophisticated attacks against them have been discovered. Thus, frameworks for systematic security analysis of these protocols have become of high interest. As traditional security models, distance-bounding security models sit within the two classical approaches: the computational and the symbolic models. In this thesis we propose frameworks for security analysis of distance-bounding protocols, within the two aforementioned models. First, we develop an automata-based computational framework that allows us to generically analyze a large class of distance-bounding protocols. Not only does the proposed framework allow us to straightforwardly deliver computational (in)security proofs but it also permits us to study problems such as optimal trade-offs between security and space complexity. Indeed, we solve this problem for a prominent class of protocols, and propose a protocol solution that is optimally secure amongst space-constrained protocols within the considered class. Second, by building up on an existing symbolic framework, we develop a causality-based characterization of distance-bounding security. This constitutes the first symbolic property that guarantees physical proximity without modeling continuous time or physical location. We extend further our formalism in order to capture a non-standard attack known as terrorist fraud. By using our definitions and the verification tool Tamarin, we conduct a security survey of over 25 protocols, which include industrial protocols based on the ISO/IEC 14443 standard such as NXP's MIFARE Plus with proximity check and Mastercard's PayPass payment protocol. For the industrial protocols we find attacks, propose fixes and deliver security proofs of the repaired versions. [less ▲]

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See detailPROVABLE SECURITY ANALYSIS FOR THE PASSWORD AUTHENTICATED KEY EXCHANGE PROBLEM
Lopez Becerra, José Miguel UL

Doctoral thesis (2019)

Password-based Authenticated Key-Exchange (PAKE) protocols allow the establishment of secure communications despite a human-memorable password being the only secret that is previously shared between the ... [more ▼]

Password-based Authenticated Key-Exchange (PAKE) protocols allow the establishment of secure communications despite a human-memorable password being the only secret that is previously shared between the participants. After more than 25 years since the initial proposal, the PAKE problem remains an active area of research, probably due to the vast amount of passwords deployed on the internet as password-based still constitutes the most extensively used method for user authentication. In this thesis, we consider the computational complexity approach to improve the current understanding of the security provided by previously proposed PAKE protocols and their corresponding security models. We expect that this work contributes to the standardization, adoption and more efficient implementation of the considered protocols. Our first contribution is concerning forward secrecy for the SPAKE2 protocol of Abdalla and Pointcheval (CT-RSA 2005). We prove that the SPAKE2 protocol satisfies the so-called notion of weak forward secrecy. Furthermore, we demonstrate that the incorporation of key-confirmation codes in the original SPAKE2 results in a protocol that provably satisfies the stronger notion of perfect forward secrecy. As forward secrecy is an explicit requirement for cipher suites supported in the TLS handshake, we believe our results fill the gap in the literature and facilitate the adoption of SPAKE2 in the recently approved TLS 1.3. Our second contribution is regarding tight security reductions for EKE-based protocols. We present a security reduction for the PAK protocol instantiated over Gap Diffie-Hellman groups that is tighter than previously known reductions. We discuss the implications of our results for concrete security. Our proof is the first to show that the PAK protocol can provide meaningful security guarantees for values of the parameters typical in today's world. Finally, we study the relation between two well-known security models for PAKE protocols. Security models for PAKEs aim to capture the desired security properties that such protocols must satisfy when executed in the presence of an adversary. They are usually classified into i) indistinguishability-based (IND-based) or ii) simulation-based (SIM-based), however, controversy remains within the research community regarding what is the most appropriate security model that better reflects the capabilities that an adversary is supposed to have in real-world scenarios. Furthermore, the relation between these two security notions is unclear and mentioned as a gap in the literature. We prove that SIM-BMP security from Boyko et al. (EUROCRYPT 2000) implies IND-RoR security from Abdalla et al. (PKC 2005) and that IND-RoR security is equivalent to a slightly modified version of SIM-BMP security. We also investigate whether IND-RoR security implies (unmodified) SIM-BMP security. [less ▲]

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See detailALIGNED MULTI-WALL CARBON NANOTUBE SHEETS FOR LIQUID CRYSTAL DISPLAYS
Rahman, Md Asiqur UL

Doctoral thesis (2019)

The great interest in carbon nanotubes (CNTs) was triggered by their discovery by Iijima and has led to significant research efforts finding exceptional electrical and mechanical properties. The ... [more ▼]

The great interest in carbon nanotubes (CNTs) was triggered by their discovery by Iijima and has led to significant research efforts finding exceptional electrical and mechanical properties. The extraordinarily high anisotropy is not just limited to the shape of CNTs, but it is also reflected in their properties that show strong orientational dependence. However, a crucial step involves the incorporation of CNTs into macro-size devices while keeping the nanotubes perfectly aligned in a single direction with a high degree of nanotube straightness. It has been an additional challenge to produce CNT assemblies that meet all these requirements until Kaili Jiang et al introduced a solid state method to produce highly aligned multi-wall CNTs pulled from a forest. They reported that it is possible to pull continuous strings of nanotubes from vertically-aligned CNT forests, forming parallel arrays aligned along the pulling direction. Due to their high alignment, transparency, flexibility, conductivity and optical anisotropy, sheets formed by aligned CNTs are promising as optical polarizer, heaters, sensors, energy devices and aligning and electrodes layers in displays. The alignment of a liquid crystal (LC) on a CNT surface was first realized by Giusy Scalia et al. Later, Russel et al. showed that surfaces with aligned CNTs align LCs unidirectionally, followed by Fu et al. demonstrating that coated CNT sheets can also act as transparent electrodes for switching LC. Thus, aligned CNT sheets show promise as attractive multifunctional systems for LC displays, being able to simultaneously serve diverse functions by replacing both polyimide (PI) and indium tin oxide (ITO) layers, thus, minimizing costs and simplifying the fabrication process. The mechanical properties of CNTs offer also better performance than ITO when used on flexible substrates. However, the optical anisotropy of MWCNT sheets in the range of visible wavelengths remains almost unexplored. There is thus an urgent need to investigate and fundamentally understand the interaction of light with CNT sheets in order to accurately realize CNT-based liquid crystal optical devices. In LC displays, the modulation of light is based on the use of polarized light, and the introduction of an optically anisotropic layer can affect the modulation; thus, it is important to acquire fundamental knowledge on the interaction between aligned MWCNT sheets and light. We followed the technique reported by Kaili Jiang and Ray Baughman to produce highly aligned CNT sheets by pulling CNTs from a spinnable CNT forest. We further deposited the aligned CNT sheets on a glass substrate and characterized them in the visible wavelength range, finding that the aligned CNT sheets anisotropically absorb light. Furthermore, the linearly polarized light travelling through the CNT sheets is rotated and the polarization of the light is affected by the presence of even a single layer of CNTs. Moreover, the magnitude of rotation of polarization increases as the layer thickness increases. We performed theoretical investigations which closely fit the experimental data, suggests that the origin of the rotation is mainly due to the anisotropic absorption. However, other contributions, such as from birefringence, cannot be ruled out. By optical investigations, the dependence of the optical behavior on the thickness of CNTs was also established. Moreover, the average orientational order parameter of the CNT sheets was evaluated from the anisotropic absorption of aligned CNT sheets. A high value of orientational order parameter in CNT sheets is needed since the alignment of the CNT sheets translates to LC alignment. The order parameter of free-standing CNT sheets was found to be ~0.6; however, it decreases once deposited on a substrate. The adhesion between the CNT sheets and the substrate is an additional problem and was studied using different strategies correlating the adhesion to the final alignment of the CNTs on a substrate. Parts of this research effort were devoted to investigating CNT sheets on various polymer surfaces, leaving the surface of CNTs almost free from polymer, for a direct investigation of the LC alignment on the CNT graphitic surface. The general goal was to improve the adhesion while keeping the alignment of the CNTs intact as pulled from the forest. We found a tradeoff between the adhesion of the CNTs and their alignment on a substrate; however, achieving highly-ordered CNTs and perfect adhesion on the surface is an issue. A second approach was based on complete coverage of CNTs by coating the nanotube films with inorganic dielectric layers (SiO_2 or Al_2 O_3). We found that SiO_2 coating preserved the freely-suspended CNT alignment while improving the film flatness. These inorganic coatings help to obtain good electrical performance of LC in cells made with the CNT-based substrates. The alignment of the liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) in the cells was generally planar and unidirectional, with differences in the quality depending on the type of coating layer and on the value of the order parameter of the CNT sheets. We investigated both the uniformity of the LC alignment as well as the switching voltages and times and compared this to the performance of the LC in commercial cells. Integration of aligned CNTs with LC requires the understanding of the interactions of CNT layers with light to realize CNT devices. Aligned CNTs from forests can be obtained easily; sequentially depositing CNT layers, however, while maintaining control of the degree of alignment when integrating them into devices is an open issue. This work shows the occurrence of unexpected interactions with polarized light due to the intrinsic properties of CNTs and due to their alignment. By exploring and optimizing the optical performance of CNT sheets, through their orientational order, it can be possible to use them as optical films for producing, among other optical devices, variable rotation of polarization, polarizers and transparent electrodes that also can align LCs integrated into LCDs. [less ▲]

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See detailOptical investigation of voltage losses in high-efficiency Cu(In,Ga)Se2 thin-film solar cells
Wolter, Max UL

Doctoral thesis (2019)

The increases in power conversion efficiencies up to 23.35 % in thin-film Cu(In,Ga)Se2 (CIGS) solar cells in recent years can mainly be ascribed to the alkali post-deposition treatment (PDT). The latter ... [more ▼]

The increases in power conversion efficiencies up to 23.35 % in thin-film Cu(In,Ga)Se2 (CIGS) solar cells in recent years can mainly be ascribed to the alkali post-deposition treatment (PDT). The latter consists of an additional treatment step after absorber growth where alkali elements, such as sodium (Na) or rubidium (Rb), are injected into the absorber. While the beneficial effects of the alkali PDT, attributed partly to a reduction of voltage losses, are undeniable, it is not yet entirely clear what underlying mechanisms are responsible. To clarify the specific influence of the alkali PDT on the voltage of the CIGS solar cells, photoluminescence (PL) spectroscopy experiments were conducted on state-of-the-art CIGS absorbers having undergone different alkali PDTs. Photoluminescence allows the investigation of possible voltage losses on the absorbers through the analysis of optoelectronic quantities such as the absorption coefficient, the quasi-Fermi level splitting (QFLS), electronic defects, and potential fluctuations. Mainly due to a smooth surface and a band gap minimum inside the bulk, the PL spectra of state-of-the-art CIGS absorbers are distorted by interference fringes. To remove the interference fringes at room temperature, an experimental method, which revolves around the measurement of PL under varying angles, is developed in this thesis. In addition, to enable PL experiments even at low temperatures, an auxiliary polystyrene-based scattering layer is conceptualized and deposited on the surface of the absorbers. With the influence of the interference fringes under control, the quasi-Fermi level splitting can be measured on bare and CdS-covered absorbers. The results reveal an improvement of the QFLS in absorbers that contain Na with an additional increase being recorded in absorbers that also contain Rb. The improvement of the QFLS is present in both bare and CdS-covered absorbers, indicating that the beneficial effect of the alkali PDT is not only occurring on the surface but also inside the bulk. To identify possible origins of the QFLS increase, various PL-based experiments were performed. At room temperature, spatially-resolved PL measurements on the microscopic scale do not reveal any optoelectronic inhomogeneities in state-of-the-art CIGS absorbers. Defect spectroscopy at low temperatures also does not reveal the presence of deep-level trap states. Through temperature- and excitation-dependent PL experiments, a reduction of electrostatic potential fluctuations is observed in absorbers that contain Na with a stronger reduction witnessed in absorbers that contain Rb as well. The extraction of the absorption coefficient through PL measurements at room temperature reveals a reduction of band tails with alkali PDT that empirically correlates to the measured increase in the QFLS. This correlation might indicate that the band tails, through non-radiative recombination, may be the origin of the performance-limiting voltage losses. In combination with reports from literature, it is suggested that the beneficial effect of the light alkali PDT (Na) is mainly a doping effect i.e. an increase in the QFLS through an increase in the hole carrier concentration. The beneficial effect of the heavier alkali PDT (Rb) is attributed partly to a surface effect but mainly to a grain boundary effect, either through a reduction in band bending or a reduction of non-radiative recombination through tail states. Finally, the various voltage losses in state-of-the-art CIGS solar cells are compared to the best crystalline silicon device, revealing almost identical losses. This shows that the alkali PDT enables the fabrication of high-efficiency CIGS solar cells that show, in terms of voltage, identical performance. To bridge the gap between CIGS and the even better performing GaAs, the results of this thesis suggest that grain boundaries are crucial in this endeavour. [less ▲]

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See detailOptimization of logical networks for the modelling of cancer signalling pathways
De Landtsheer, Sébastien UL

Doctoral thesis (2019)

Cancer is one of the main causes of death throughout the world. The survival of patients diagnosed with various cancer types remains low despite the numerous progresses of the last decades. Some of the ... [more ▼]

Cancer is one of the main causes of death throughout the world. The survival of patients diagnosed with various cancer types remains low despite the numerous progresses of the last decades. Some of the reasons for this unmet clinical need are the high heterogeneity between patients, the differentiation of cancer cells within a single tumor, the persistence of cancer stem cells, and the high number of possible clinical phenotypes arising from the combination of the genetic and epigenetic insults that confer to cells the functional characteristics enabling them to proliferate, evade the immune system and programmed cell death, and give rise to neoplasms. To identify new therapeutic options, a better understanding of the mechanisms that generate and maintain these functional characteristics is needed. As many of the alterations that characterize cancerous lesions relate to the signaling pathways that ensure the adequacy of cellular behavior in a specific micro-environment and in response to molecular cues, it is likely that increased knowledge about these signaling pathways will result in the identification of new pharmacological targets towards which new drugs can be designed. As such, the modeling of the cellular regulatory networks can play a prominent role in this understanding, as computational modeling allows the integration of large quantities of data and the simulation of large systems. Logical modeling is well adapted to the large-scale modeling of regulatory networks. Different types of logical network modeling have been used successfully to study cancer signaling pathways and investigate specific hypotheses. In this work we propose a Dynamic Bayesian Network framework to contextualize network models of signaling pathways. We implemented FALCON, a Matlab toolbox to formulate the parametrization of a prior-knowledge interaction network given a set of biological measurements under different experimental conditions. The FALCON toolbox allows a systems-level analysis of the model with the aim of identifying the most sensitive nodes and interactions of the inferred regulatory network and point to possible ways to modify its functional properties. The resulting hypotheses can be tested in the form of virtual knock-out experiments. We also propose a series of regularization schemes, materializing biological assumptions, to incorporate relevant research questions in the optimization procedure. These questions include the detection of the active signaling pathways in a specific context, the identification of the most important differences within a group of cell lines, or the time-frame of network rewiring. We used the toolbox and its extensions on a series of toy models and biological examples. We showed that our pipeline is able to identify cell type-specific parameters that are predictive of drug sensitivity, using a regularization scheme based on local parameter densities in the parameter space. We applied FALCON to the analysis of the resistance mechanism in A375 melanoma cells adapted to low doses of a TNFR agonist, and we accurately predict the re-sensitization and successful induction of apoptosis in the adapted cells via the silencing of XIAP and the down-regulation of NFkB. We further point to specific drug combinations that could be applied in the clinics. Overall, we demonstrate that our approach is able to identify the most relevant changes between sensitive and resistant cancer clones. [less ▲]

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See detailSelf-Organizing Cellulose Nanorods: From the fundamental physical chemistry of self-assembly to the preparation of functional films
Honorato Rios, Camila UL

Doctoral thesis (2019)

Cellulose nanocrystals (CNCs), nanorods isolated by acid hydrolysis from cellulose sources, be- long to a selective type of functional biomaterials. The intriguing ability of these nanoparticles to self ... [more ▼]

Cellulose nanocrystals (CNCs), nanorods isolated by acid hydrolysis from cellulose sources, be- long to a selective type of functional biomaterials. The intriguing ability of these nanoparticles to self-organize and develop a chiral nematic liquid crystal phase when suspended in aqueous suspensions, is increasing interest regardless of the diverse range of research fields. Unfortu- nately (or fortunately, for this thesis), pristine CNCs are always disperse, with great variations in rod length within a single sample. Of particular interest is the fractionation of CNC rods by separation of the coexisting phases: isotropic phase from the liquid crystalline (LC) part. Since the aspect ratio is considered to be the critical parameter that dictates the particle fraction at which cholesteric-isotropic phase separation starts, it is expected that the high aspect ratio rods will separate from low aspect ratio rods, and this is indeed what I found in this thesis. By a systematic repetition of separation of phases, I could reach a quality of separation of long from short rods that is remarkable. The fractionation procedure was then improved by varying the equilibrium phase volume fraction at which the phases were separated, reducing with this new procedure the multiple separations from five cycles to only one. The onset of liquid crystallinity was drastically reduced in the long rod fraction and the decrease in the threshold for complete liquid crystallinity was even stronger. The mass fraction threshold at which gelation of the CNC suspension is triggered is not at all affected by the fractionation. Since gelation is a percolation phenomenon, the expectation was that also the onset of gelation would move to lower mass fractions, but this remained at about the same value. Together with the shift to lower mass fractions of the cholesteric liquid crystal phase formation we have thus opened access to a whole new range of the equilibrium phase diagram, where the full sample is cholesteric yet not gelled. I demonstrate that the critical parameter for inducing gelation is in fact not the fraction of CNC, but the concentration of counterions in the solution. This suggests that the gelation is more complex than direct percolation between individual CNC rods, and instead is related to loss of colloidal stability due to reduced electrostatic screening. I also show that the behavior of key parameters, such as the period of the helical modulation, so-called pitch, that is characteristic of the cholesteric phase, is very different in the range of phase coexistence compared to the range of complete liquid crystallinity. In addition, I found that the dependence of the pitch on CNC mass fraction has less to do with the size of the nanorods but rather than with the variation of effective volume fraction as a result of more rods in the suspension or higher counterion concentration. I corroborate this hypothesis by adding different amounts of salt to CNC suspensions of varying mass fraction such that the ion concentration is held constant, thereby tuning the pitch to the same value throughout the suspensions. In films prepared by drying CNC suspensions, the pitch can go down to a few hundred nanome- ters, resulting in circularly polarized colorful Bragg re ection of visible light. By working with the long-rod fraction we can absolutely obtain a highly-ordered monodomain structure that results in uniform color of films, with only one circular polarization re ected, as should be the case. While the study is carried out on CNCs, the implications go far beyond this particular nanoma- terial, revealing new challenges and opportunities in general liquid crystal and colloid physics, as well as in strategic research where fractionation and the drying of initially disperse populations of nanorods is desirable. [less ▲]

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See detailMathematical Histopathology and Systems Pharmacology of Melanoma
Albrecht, Marco UL

Doctoral thesis (2019)

Treated metastatic melanoma often becomes resistant and relapses whereby resistance mechanisms can be found at the level of biochemical, histological, and pharmacological data. By using this data in a ... [more ▼]

Treated metastatic melanoma often becomes resistant and relapses whereby resistance mechanisms can be found at the level of biochemical, histological, and pharmacological data. By using this data in a mathematical form, an integrative understanding of tumour progression can be gained that reveal the functionality of more complex and hidden recurrence mechanisms. The aims of this thesis were - to investigate how a new engineering concept on tumour growth, based on porous media theory, can be leveraged to support medicine and cancer biology research, - to identify suitable tests for cancer growth model validation, - to study how elements of biochemical cancer pathways are linked to the elements of physical growth, and - to establish a pharmacokinetics module for the melanoma cancer drug dabrafenib. The studied engineering concept is qualitatively suitable to represent late-stage metastatic melanoma in irregular fibrous tissue types, whereby all equations are tested for biological relevance and parametrisation. The framework allows modelling of tissue-specific growth, and the thesis shows that the simulated tumour can shift between compact growth with ECM displacement and invasive growth with ECM circumvention as a consequence of cell plasticity/viscosity change. This is unique among continuous models of tumour growth. However, the investigation also shows that the pressure-saturation relationships are not biologically motivated and can be replaced by a swelling polymer model which captures the water absorbing effect of glycans. The thesis addresses a biologically and computationally reasonable strategy to validate the tumour growth model as complete as possible. A suitable way to validate a part of the tumour growth model is using time course data of spheroid growth in hydrogels of different stiffness values. Spheroids generated from the LU451 melanoma cell line mainly grow due to ECM degradation, have a time-variant growth rate increasing with gel rigidity, and the confined environment renders the melanoma cell line drug-resistant upon dabrafenib dose escalation. This setting reveals the interplay between mechanical and biochemical development over time. The dependency between biological elements of cancer pathways and the mechanical elements of the engineering concept on tumour growth were clarified. Therefore, the literature on mechanoregulation has been reviewed and serves as a computational link between systems biology and physical oncology. Finally, the thesis provides preliminary steps and a concept toward a serious interdisciplinary methodology to understand tumour growth, although this cannot be considered a final model for any of the known melanoma growth settings. Additionally, the thesis provides a novel quantitative systems pharmacology approach to consider liver-enzyme-induction and drug-drug-interaction. The finding is that the potent dabrafenib metabolite desmethyl-dabrafenib accumulates with consequential efficacy loss in a confined tumour environment. [less ▲]

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