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See detailMachine Learning Force Fields: Recent Advances and Remaining Challenges
Poltavskyi, Igor UL; Tkatchenko, Alexandre UL

in Journal of Physical Chemistry Letters (2021)

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See detailHybrid A/D Precoding for Downlink Massive MIMO in LEO Satellite Communications
Qiang, Xiaoyu; You, Li; Li, Ke-Xin et al

in 2021 IEEE International Conference on Communications Workshops (ICC Workshops) (2021, July 09)

In this paper, we develop hybrid analog/digital precoding based on the fully-connected architecture for massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite communications (SATCOM ... [more ▼]

In this paper, we develop hybrid analog/digital precoding based on the fully-connected architecture for massive multiple-input multiple-output (MIMO) low earth orbit (LEO) satellite communications (SATCOM), by exploiting the statistical channel state information (CSI) at the transmitter. The hybrid precoder design is formulated as an energy efficiency (EE) maximization problem by considering both continuous and discrete phase shift networks for implementing the analog precoder. The resulting optimization problem is nonconvex and difficult to solve. To that end, first, we apply a closed-form tight upper bound to approximate the ergodic rate. Then, we adopt Dinkelbach's algorithm and the iteratively weighted minimum mean-square error (WMMSE) method to obtain the fully digital precoders. After that, the alternating minimization and inexact majorization-minimization (MM) algorithms are utilized to compute the hybrid precoders. Simulation results show that the proposed algorithmic solutions achieve significant performance gains when compared to existing literature ones, especially in the case where the discrete phase shift network is employed for analog precoding. [less ▲]

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See detailAnimal Law: Why do we need to work across disciplines?
Bobrowicz, Katarzyna UL

Presentation (2021, July 08)

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

Doctoral thesis (2021)

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

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

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See detailTopological Defect-Guided Regular Stacking of Focal Conic Domains in Hybrid-Aligned Smectic Liquid Crystal Shells
Noh, Junghyun; Lagerwall, Jan UL

in Crystals (2021), 11(8), 913

We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase ... [more ▼]

We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at the thinnest and thickest points, respectively. On cooling from N to SmA, the symmetry axis connecting the defects gradually reorients from blackalong gravity to perpendicular to it, reversibly and continuously, if the LC and aqueous phase are density matched at the N-SmA transition. This suggests reduced density near the defects---reflecting a local reduction in order---under the strong confinement with antagonistic boundary conditions. In the SmA phase, a regular array of focal conic domains (FCDs) develops, templated in position and orientation by the +1 defect at the thinnest point. Around this defect, a single complete toroidal FCD always develops, surrounded by incomplete FCDs. In contrast to similar FCD arrangements on flat aqueous interfaces, this is a stable situation, since the two +1 defects are required by the spherical topology. Our results demonstrate how the topological defects of LC shells can be used to template complex self-organized structures. blackWith a suitable adaption of the LC chemistry, shells might serve as a basis for producing solid particles with complex yet highly regular morphologies. [less ▲]

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See detail"Getting on the same page" - How participants' reading aloud from an interactive tabletop facilitates joint game participation
Heuser, Svenja UL; Arend, Béatrice UL; Sunnen, Patrick UL

Scientific Conference (2021, July 01)

This paper addresses how adult participants in a multiparty serious game-activity (ORBIT project, see Sunnen et al. 2018) at an interactive tabletop (ITT) use reading aloud (Heuser et al. 2020) to co ... [more ▼]

This paper addresses how adult participants in a multiparty serious game-activity (ORBIT project, see Sunnen et al. 2018) at an interactive tabletop (ITT) use reading aloud (Heuser et al. 2020) to co-facilitate joint accessibility to interactionally relevant text information about the unfamiliar game they are engaging in. These so called ‘written informings’ displayed on the horizontal interface are designed to serve as a game-manual. Since the activity is new to the participants, they rely on these informings in order to jointly accomplish the game. We consider participants’ reading aloud as an interactional practice for participating in the interaction and getting each other ‘on the same page’. By verbalizing and thereby also emphasizing specific (parts of the) text at a specific point in the interaction, participants make written informings from the ITT interactionally relevant and mutually accessible within the group. [less ▲]

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See detailTaming Reflection: An Essential Step Toward Whole-program Analysis of Android Apps
Sun, Xiaoyu; Li, Li; Bissyande, Tegawendé François D Assise UL et al

in ACM Transactions on Software Engineering and Methodology (2021), 30(3), 1-36

Android developers heavily use reflection in their apps for legitimate reasons. However, reflection is also significantly used for hiding malicious actions. Unfortunately, current state-of-the-art static ... [more ▼]

Android developers heavily use reflection in their apps for legitimate reasons. However, reflection is also significantly used for hiding malicious actions. Unfortunately, current state-of-the-art static analysis tools for Android are challenged by the presence of reflective calls which they usually ignore. Thus, the results of their security analysis, e.g., for private data leaks, are incomplete, given the measures taken by malware writers to elude static detection. We propose a new instrumentation-based approach to address this issue in a non-invasive way. Specifically, we introduce to the community a prototype tool called DroidRA, which reduces the resolution of reflective calls to a composite constant propagation problem and then leverages the COAL solver to infer the values of reflection targets. After that, it automatically instruments the app to replace reflective calls with their corresponding Java calls in a traditional paradigm. Our approach augments an app so that it can be more effectively statically analyzable, including by such static analyzers that are not reflection-aware. We evaluate DroidRA on benchmark apps as well as on real-world apps, and demonstrate that it can indeed infer the target values of reflective calls and subsequently allow state-of-the-art tools to provide more sound and complete analysis results. [less ▲]

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See detailSecure Transmission in Cell-Free Massive MIMO With RF Impairments and Low-Resolution ADCs/DACs
Zhang, Xianyu; Liang, Tao; An, Kang et al

in IEEE Transactions on Vehicular Technology (2021), 70(9, Sept. 2021), 8937-8949

This paper considers the secure transmission in a cell-free massive MIMO system with imperfect radio frequency (RF) chains and low-resolution analog-to-digital converters (ADCs) and digital-to-analog ... [more ▼]

This paper considers the secure transmission in a cell-free massive MIMO system with imperfect radio frequency (RF) chains and low-resolution analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) at both access points (APs) and legitimate users, where an active eavesdropper attempts to wiretap the confidential data. The Gaussian RF impairment model (GRFIM) and additive quantization noise model (AQNM) are used to evaluate the impacts of the RF impairments and low resolution ADCs/DACs, respectively. The analytical results of the linear minimum mean square error (MMSE) channel estimation show that there is nonzero floor on the estimation error with respect to the RF impairments, ADC/DAC precision and the pilot power of the eavesdropper which is different from the conventional case with perfect transceiver. Then, a tractable closed-form expression for the ergodic secrecy rate is obtained with respect to key system parameters, such as the antenna number per AP, the AP number, user number, quality factors of the ADC/DAC and the RF chain, pilot signal power of the eavesdropper, etc. Moreover, a compensation algorithm between the imperfect RF components and the inexpensive coarse ADCs/DACs is also presented. Finally, numerical results are provided to illustrate the efficiency of the achieved expressions and the devised algorithm, and show the effects of RF impairments and low resolution ADC/DAC on the secrecy performance. [less ▲]

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See detailRepeatability and precision of different static deflection measurements on a real bridge-part under outdoor conditions in view of damage detection
Kebig, Tanja UL; Nguyen, Viet Ha UL; Bender, Michél et al

in Cunha, A.; Caetano, E. (Eds.) Proceedings of the 10th International Conference on Structural Health Monitoring of Intelligent Infrastructure, SHMII 10 (2021, July)

A large number of concrete bridges show increasing damage due to corrosion and fatigue. The traditional visual inspection and subsequent assessment of concrete bridges is carried out regularly by an ... [more ▼]

A large number of concrete bridges show increasing damage due to corrosion and fatigue. The traditional visual inspection and subsequent assessment of concrete bridges is carried out regularly by an experienced engineer. This type of inspection can be time-consuming, costly and leading to errors. Hence, there is a great interest in complementary, alternative and easy-to-implement methods for condition monitoring of bridges. The University of Luxembourg tested different approaches on a part of a real bridge. Various tests were performed in the healthy reference state, e.g. loading tests with a movable test load according to today’s standards. The measurements in the reference state were repeated several times under outdoor conditions to monitor and document the real temperature influence. Displacement transducers were set up in the vertical and horizontal directions. Simultaneously, a new approach was used for determining the deflection with a laser-based system, that measured the displacements in the bridge’s longitudinal direction by an oblique reflector panel under a well-defined angle. The data gained from the laser-based measurement system were compared to the data from classical displacement transducers. In general, the comparison of the two measuring systems shows quite similar results. [less ▲]

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See detail𝑘-Pareto Optimality for Many-Objective Genetic Optimization
Ruppert, Jean; Aleksandrova, Marharyta UL; Engel, Thomas UL

Poster (2021, July)

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See detailMoral Principles: Hedged, Contributory, Mixed
Knoks, Aleks UL

in Knoks, Aleks (Ed.) Deontic Logic and Normative Systems, 15th International Conference, DEON 2020/2021 (2021, July)

It's natural to think that the principles expressed by the statements "Promises ought to be kept" and "We ought to help those in need" are defeasible. But how are we to make sense of this defeasibility ... [more ▼]

It's natural to think that the principles expressed by the statements "Promises ought to be kept" and "We ought to help those in need" are defeasible. But how are we to make sense of this defeasibility? On one proposal, moral principles have hedges or built-in unless clauses specifying the conditions under which the principle doesn't apply. On another, such principles are contributory and, thus, do not specify which actions ought to be carried out, but only what counts in favor or against them. Drawing on a defeasible logic framework, this paper sets up three models: one model for each proposal, as well as a third model capturing a mixed view on principles that combines them. It then explores the structural connections between the three models and establishes some equivalence results, suggesting that the seemingly different views captured by the models are closer than standardly thought. [less ▲]

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See detailUnlinkable Updatable Hiding Databases and Privacy-Preserving Loyalty Programs
Damodaran, Aditya Shyam Shankar UL; Rial, Alfredo UL

in Proceedings on Privacy Enhancing Technologies (2021, July), 2021(3), 95-121

Loyalty programs allow vendors to profile buyers based on their purchase histories, which can reveal privacy sensitive information. Existing privacy friendly loyalty programs force buyers to choose ... [more ▼]

Loyalty programs allow vendors to profile buyers based on their purchase histories, which can reveal privacy sensitive information. Existing privacy friendly loyalty programs force buyers to choose whether their purchases are linkable. Moreover, vendors receive more purchase data than required for the sake of profiling. We propose a privacy-preserving loyalty program where purchases are always unlinkable, yet a vendor can profile a buyer based on her purchase history, which remains hidden from the vendor. Our protocol is based on a new building block, an unlinkable updatable hiding database (HD), which we define and construct. HD allows the vendor to initialize and update databases stored by buyers that contain their purchase histories and their accumulated loyalty points. Updates are unlinkable and, at each update, the database is hidden from the vendor. Buyers can neither modify the database nor use old versions of it. Our construction for HD is practical for large databases. [less ▲]

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See detailOn the Impact of Sample Duplication in Machine Learning based Android Malware Detection
Zhao, Yanjie; Li, Li; Wang, Haoyu et al

in ACM Transactions on Software Engineering and Methodology (2021), 30(3), 1-38

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See detailGeneralized Chern numbers based on open system Green's functions
Farias, Maria Belen UL; Groenendijk, Solofo; Schmidt, Thomas UL

in New Journal of Physics (2021), 23

We present an alternative approach to studying topology in open quantum systems, relying directly on Green's functions and avoiding the need to construct an effective non-Hermitian (nH) Hamiltonian. We ... [more ▼]

We present an alternative approach to studying topology in open quantum systems, relying directly on Green's functions and avoiding the need to construct an effective non-Hermitian (nH) Hamiltonian. We define an energy-dependent Chern number based on the eigenstates of the inverse Green's function matrix of the system which contains, within the self-energy, all the information about the influence of the environment, interactions, gain or losses. We explicitly calculate this topological invariant for a system consisting of a single 2D Dirac cone and find that it is half-integer quantized when certain assumptions about the self-energy are made. Away from these conditions, which cannot or are not usually considered within the formalism of nH Hamiltonians, we find that such a quantization is usually lost and the Chern number vanishes, and that in special cases, it can change to integer quantization. [less ▲]

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See detailSurface anchoring mediates bifurcation in nematic microflows within cylindrical capillaries
Paul, Steffen; Eric, Stellamanns; Sengupta, Anupam UL

in Physics of Fluids (2021), 33(072005), 072005-1-072005-13

Capillary microflows of liquid crystal phases are central to material, biological and bio-inspired systems. Despite their fundamental and applied significance, a detailed understanding of the stationary ... [more ▼]

Capillary microflows of liquid crystal phases are central to material, biological and bio-inspired systems. Despite their fundamental and applied significance, a detailed understanding of the stationary behavior of nematic liquid crystals (NLC-s) in cylindrical capillaries is still lacking. Here, using numerical simulations based on the continuum theory of Leslie, Ericksen, and Parodi, we investigate stationary NLC flows within cylindrical capillaries possessing homeotropic (normal) and uniform planar anchoring conditions. By considering the material parameters of the flow-aligning NLC, 5CB, we report that instead of the expected, unique director field monotonically approaching the alignment angle over corresponding Ericksen numbers (dimensionless number capturing viscous vs elastic effects), a second solution emerges at a threshold flow rate (or applied pressure gradient). We demonstrate that the onset of the second solution, a nematodynamic bifurcation yielding distinct director configurations at the threshold pressure gradient, can be controlled by the surface anchoring and the flow driving mechanism (pressure-driven or volume-driven). For homeotropic surface anchoring, this alternate director field orients against the alignment angle in the vicinity of the capillary center; while in the uniform planar case, the alternate director field extends throughout the capillary volume, leading to reduction of the flow speed with increasing pressure gradients. While the practical realization and utilization of such nematodynamic bifurcations still await systematic exploration, signatures of the emergent rheology have been reported by the authors previously within microfluidic environments, under both homeotropic and planar anchoring conditions. [less ▲]

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See detailThe sense of belonging in the context of migration and active ageing: The case of multicultural Luxembourg
Albert, Isabelle UL; Bemtgen, Nadia; Hoffmann, Martine et al

Scientific Conference (2021, July)

Migration is a life-changing transition and the establishment of new bonds in the receiving country constitutes an important developmental task. While feelings of belonging are closely linked to ... [more ▼]

Migration is a life-changing transition and the establishment of new bonds in the receiving country constitutes an important developmental task. While feelings of belonging are closely linked to subjective well-being, the feeling of not fitting in might be related to social exclusion and loneliness. Though social isolation is not bound to specific groups and ages, older migrants might be at a particular risk as recent studies suggest. The present study is part of the project PAN-VAL on active ageing in Luxembourg, financed by the Ministry of Family and Integration. Here, we focus on social embeddedness vs. social isolation of migrants and non-migrants living in the multicultural context of Luxembourg. Our aim is to identify facilitators and obstacles to participation in social activities, focusing in particular on the role of "sense of belonging" of older people to their place and country of residence. Applying a mixed-methods design, we will first focus on a national sample of N=1000 migrants and non-migrants 50+ living in Luxembourg who are asked about their family and friendship networks, leisure activities, sense of belonging to different entities (such as their neighborhood, municipality and country of residence) as well as their feelings of social isolation and loneliness. Secondly, we will draw on qualitative interviews in four selected municipalities contrasting active vs. non-active older migrants vs. non-migrants, exploring in more depth their experiences of belonging and social embeddedness. Results will be discussed in a life-span perspective, considering different developmental trajectories to belonging as a fundamental need of human beings. [less ▲]

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