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See detailCentralized or not Centralized? Topology Analysis of the XRP Ledger
Tumas, Vytautas UL; Rivera, Sean UL; Magoni, Damien et al

Scientific Conference (2022, October 12)

XRP is one of the oldest, well-established cryptocurrencies. Despite the popularity of XRP, little is known about its underlying peer-to-peer network. The structural properties of a network impact its ... [more ▼]

XRP is one of the oldest, well-established cryptocurrencies. Despite the popularity of XRP, little is known about its underlying peer-to-peer network. The structural properties of a network impact its efficiency, security and robustness. We aim to close the knowledge gap by providing a detailed analysis of the XRP overlay network. In this paper we examine the graph-theoretic properties of the XRP Network topology and its temporal characteristics. We crawl the XRP Network over two months and collect 1,290 unique network snapshots. We uncover a small group of nodes that act as a networking backbone. In addition, we observe a high network churn, with a third of the nodes changing every five days. Our findings have strong implications for the resilience and safety of the XRP Ledger. [less ▲]

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See detailConcept of an Active Debris Removal 2-step capturing system for small satellites in Low Earth Orbit
Hubert Delisle, Maxime UL; Martinez Luna, Carol UL; Yalcin, Baris Can UL et al

Scientific Conference (2022, October 12)

Space debris brings up two main critical issues: not only a non-sustainable space environment for satellite missions, with orbit saturation, but also the creation of an unsafe place for human-related ... [more ▼]

Space debris brings up two main critical issues: not only a non-sustainable space environment for satellite missions, with orbit saturation, but also the creation of an unsafe place for human-related space missions. Despite being extremely challenging, catching autonomously and harmlessly an uncooperative object tumbling at high velocity demand reliability, compliance, and robustness. Grasping an object in microgravity means having control during the impact, but also keeping the link between the chaser satellite and the debris secure enough to handle the deorbiting phase. Supposing that the GNC installed tackles the synchronization with the debris rotation, so that only a linear translation is necessary to capture, three main problems can occur. The first problem can occur at the impact between the servicer and the debris. Due to the motion-reaction law, the debris could be pushed away if the capturing system does not prevent that motion. Besides, a high stiffness of the system, added to an unexpected strong impact, could damage either the servicer and/or the debris, resulting in a mission failure. Moreover, the need for a secure attach is required to go-on with the deorbit phase without losing the debris. That’s why, thanks to the fruitful collaboration between industry and academia (Spacety Luxembourg - SpaceR research group at the University of Luxembourg), a cutting-edge concept of a two-step capturing mechanism is being designed. Data analysis of trackable objects in LEO reveals an abundant number of CubeSat-shaped satellites, that future constellations might also take advantage of. Consequently, the concept presented is focusing on capturing these, at their end of life. A first ‘soft capture’ ensures that the debris is received softly while dampening any vibrations generated. A gecko-inspired adhesive surface will first receive the debris, preventing it from being pushed away. The property of such dry adhesive is that they do not require a high preload to stick to the surface, while having a very strong adhesion. To absorb most of the vibrations or movements due to the first impact, a compliant mechanism will be integrated behind the adhesive part. To that extent, if the alignment is not perfect, the system has some degrees of freedom, so that no damage can be generated. This compliant and sticky system would prevent the first main two issues of capturing an uncooperative target in microgravity. Then, a ‘hard capture’ secures the debris so that it would be deorbited without being released on the way. This part of the system would either gently squeeze the debris, using controlled adhesive flexible arms, or encircle it, and would be designed in compliance of ESA guidelines for demise. A two-step capturing mechanism is here proposed, taking advantage of bio-inspired dry adhesive technology, and compliant mechanisms, while having ESA guidelines in mind. Bringing the advantage of removing a vast range of objects in orbit, it also allows a reliable capturing, removing risks of generating more debris. Later works would bring attention to architecture that would fit more than a box shape. [less ▲]

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See detailMindfulness extends the trans-contextual model for autonomous motivation in physical education and leisuretime
Hutmacher, Djenna; Eckelt, Melanie; Bund, Andreas UL et al

in International Journal of Environmental Research and Public Health (2022), 19(20),

Mindfulness is assumed to foster the ability to consistently act in line with one’s authentic self; a skill which has been found to enhance students’ autonomous motivated behavior in the educational ... [more ▼]

Mindfulness is assumed to foster the ability to consistently act in line with one’s authentic self; a skill which has been found to enhance students’ autonomous motivated behavior in the educational context. However, evidence regarding how mindfulness can be integrated into existing conceptual frameworks such as the trans-contextual model is scarce. Therefore, the present study aimed to evaluate the role of mindfulness in students’ autonomous motivation in the school and leisure time contexts. Overall, N = 1877 students (M = 14.74 years, SD = 2.63) indicated their self-reported mindfulness, their perceived need for support in physical education, their autonomous motivation during physical education and leisure time, as well as their perceived behavioral control, attitude, subjective norm, and intention toward physical activity. Physical activity was additionally measured physiologically for n = 240 students using accelerometers. Path model analyses revealed that the inclusion of mindfulness substantially improved the trans-contextual model fit. Perceived autonomy support positively predicted mindfulness, which, in turn, predicted autonomous motivation in physical education and leisure time, attitude, subjective norm, and perceived behavioral control. Furthermore, mediation analyses revealed the significant indirect effects of mindfulness on physiological and self-reported physical activity. Based on these results, mindfulness can be considered a key factor in fostering students’ motivation to become physically active. [less ▲]

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See detailLocality of spontaneous symmetry breaking and universal spacing distribution of topological defects formed across a phase transition
Del Campo Echevarria, Adolfo UL; Gómez-Ruiz, Fernando Javier; Zhang, Hai-Qing

in Physical Review. B (2022)

The crossing of a continuous phase transition results in the formation of topological defects with a density predicted by the Kibble-Zurek mechanism (KZM). We characterize the spatial distribution of ... [more ▼]

The crossing of a continuous phase transition results in the formation of topological defects with a density predicted by the Kibble-Zurek mechanism (KZM). We characterize the spatial distribution of pointlike topological defects in the resulting nonequilibrium state and model it using a Poisson point process in arbitrary spatial dimensions with KZM density. Numerical simulations in a one-dimensional φ4 theory unveil short-distance defect-defect corrections stemming from the kink excluded volume, while in two spatial dimensions, our model accurately describes the vortex spacing distribution in a strongly coupled superconductor indicating the suppression of defect-defect spatial correlations. [less ▲]

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See detailRole of boundary conditions in the full counting statistics of topological defects after crossing a continuous phase transition
Gómez-Ruiz, Fernando J.; Subires, David; Del Campo Echevarria, Adolfo UL

in Physical Review. B, Condensed Matter and Materials Physics (2022)

In a scenario of spontaneous symmetry breaking in finite time, topological defects are generated at a density that scales with the driving time according to the Kibble-Zurek mechanism (KZM). Signatures of ... [more ▼]

In a scenario of spontaneous symmetry breaking in finite time, topological defects are generated at a density that scales with the driving time according to the Kibble-Zurek mechanism (KZM). Signatures of universality beyond the KZM have recently been unveiled: The number distribution of topological defects has been shown to follow a binomial distribution, in which all cumulants inherit the universal power-law scaling with the quench rate, with cumulant rations being constant. In this work, we analyze the role of boundary conditions in the statistics of topological defects. In particular, we consider a lattice system with nearest-neighbor interactions subject to soft antiperiodic, open, and periodic boundary conditions implemented by an energy penalty term. We show that for fast and moderate quenches, the cumulants of the kink number distribution present a universal scaling with the quench rate that is independent of the boundary conditions except for an additive term, which becomes prominent in the limit of slow quenches, leading to the breaking of power-law behavior. We test our theoretical predictions with a one-dimensional scalar theory on a lattice. [less ▲]

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See detailEugenia, incarnée par Marina Hands, dans Actrice de Pascal Rambert : le corps d’une mourante comme figuration de la Dame Blanche
Deregnoncourt, Marine UL

in Laforêt, Carole; Raimbault, Nicole (Eds.) Les femmes et leur corps (2022, October 10)

Soit cette description physique de l’actrice franco-britannique Marina Hands par Éric Ruf (Administrateur Général de la Comédie-Française depuis 2014) : Marina est une jeune femme très belle, mais elle a ... [more ▼]

Soit cette description physique de l’actrice franco-britannique Marina Hands par Éric Ruf (Administrateur Général de la Comédie-Française depuis 2014) : Marina est une jeune femme très belle, mais elle a une beauté très singulière. Elle ne correspond en rien au canon. Elle a des épaules des nageuses est-allemandes, elle a des bras longs comme des kilomètres, elle est massive, elle a une drôle de tronche avec des pommettes extrêmement saillantes. Elle n’a pas une beauté classique. Nous avons conclu ainsi notre exposé au 10ème colloque orléanais consacré aux sorcières. En vue de contribuer humblement et d’apporter modestement notre pierre à l’édifice du prochain congrès intitulé : « Femmes des lumières et de l'ombre. Les Femmes et leur Corps », nous entendons, par le biais de cette nouvelle communication, prolonger notre réflexion initiale sur Marina Hands en nous axant plus particulièrement, cette fois-ci, sur le corps de cette comédienne au miroir de son interprétation d’Eugenia dans Actrice de Pascal Rambert. Tout d’abord, en quoi le corps de Marina Hands peut-il être défini comme « masculin » et quels en sont, non seulement, les enjeux, mais aussi, les implications sur son jeu d’actrice ? C’est précisément ce que nous entendons aborder, par la suite, avec le rôle d’Eugenia, protagoniste autour de laquelle se construit l’action d’Actrice de Pascal Rambert. Pourquoi le corps d’Eugenia, mourante, peut-il être perçu comme une figuration de la Dame Blanche, messagère de la mort, et comment Pascal Rambert, renforce-t-il cette idée en construisant un requiem, par un dispositif scénographique singulier ? C’est spécifiquement à ces trois questions centrales auxquelles cette présentation souhaite répondre [less ▲]

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See detailRace and gender homophily in collaborations and citations
Kozlowski, Diego UL; Larivière, Vincent; Sugimoto, Cassidy R. et al

Scientific Conference (2022, October 09)

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See detail„Ich will mein altes Leben zurück“ – Einblicke in die veränderten Beziehungen, Aktivitäten und das Wohlbefinden luxemburgischer Kinder in der Pandemie
Kirsch, Claudine UL; Neumann, Sascha

in Diskurs Kindheits- und Jugendforschung (2022)

The Covid-19 pandemic has changed children's lives. This paper presents the changes during the pandemic of children’s well-being, relationships and everyday activities from the perspective of six to ... [more ▼]

The Covid-19 pandemic has changed children's lives. This paper presents the changes during the pandemic of children’s well-being, relationships and everyday activities from the perspective of six to twelve-year-olds in Luxembourg. The data draw on interviews carried out in 2020 and standardised surveys in 2020 and 2021. The results show that all children were affected by the pandemic but experienced it differently. Many children expressed fears and worries right at the beginning of the pandemic and these emotions intensified over time. Their leisure time activities shifted from more outside to more domestic activities during the pandemic which in our view corresponds to an intermediate “domestication of childhood”. The survey in the summer of 2021 confirms that many of these changes remained or intensified. [less ▲]

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See detailCross-Border Labour market in the Greater Region SaarLorLux
Pigeron-Piroth, Isabelle UL

Presentation (2022, October 07)

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See detailRESOURCE MANAGEMENT TECHNIQUES FOR FLEXIBLE BROADBAND SATELLITE COMMUNICATION SYSTEMS
Abdu, Tedros Salih UL

Doctoral thesis (2022)

The application of Satellite Communications (SatCom) has recently evolved from providing simple Direct-To-Home television (DTHTV) to enable a range of broadband internet services. Typically, it offers ... [more ▼]

The application of Satellite Communications (SatCom) has recently evolved from providing simple Direct-To-Home television (DTHTV) to enable a range of broadband internet services. Typically, it offers services to the broadcast industry, the aircraft industry, the maritime sector, government agencies, and end-users. Furthermore, SatCom has a significant role in the era of 5G and beyond in terms of integrating satellite networks with terrestrial networks, offering backhaul services, and providing coverage for the Internet of Things (IoT) applications. Moreover, thanks to the satellite's wide coverage area, it can provide services to remote areas where terrestrial networks are inaccessible or expensive to connect. Due to the wide range of satellite applications outlined above, the demand for satellite service from user terminals is rapidly increasing. Conventionally, satellites use multi-beam technology with uniform resource allocation to provide service to users/beams. In this case, the satellite's resources, such as power and bandwidth, are evenly distributed among the beams. However, this resource allocation method is inefficient since it does not consider the heterogeneous demands of each beam, which may result in a beam with a low demand receiving too many resources while a beam with a high demand receiving few resources. Consequently, we may not satisfy some beam demands. Additionally, satellite resources are limited due to spectrum regulations and onboard batteries constraint, which require proper utilization. Therefore, the next generation of satellites must address the above main challenges of conventional satellites. For this, in this thesis, novel advanced resource management techniques are proposed to manage satellite resources efficiently while accommodating heterogeneous beam demands. In the above context, the second and third chapters of the thesis explore on-demand resource allocation methods with no precoding technique. These methods aim to closely match the beam traffic demand by using the minimum transmit power and utilized bandwidth while having tolerable interference among the beams. However, an advanced interference mitigation technique is required in a high interference scenario. Thus, in the fourth chapter of the thesis, we propose a combination of resource allocation and interference management strategies to mitigate interference and meet high-demand requirements with less power and bandwidth consumption. In this context, the performance of the resource management method for systems with full precoding, that is, all beams are precoded; without precoding, that is, no precoding is applied to any beams; and with partial precoding, that is, some beams are precoded, is investigated and compared. Thanks to emerging technologies, the next generation of satellite communication systems will deploy onboard digital payloads; thus, advanced resource management techniques can be implemented. In this case, the digital payload can be configured to change the bandwidth, carrier frequency, and transmit power of the system in response to heterogeneous traffic demands. Typically, onboard digital payloads consist of payload processors, each operating with specific power and bandwidth to process each beam signal. There are, however, only a limited number of processors, thus requiring proper management. Furthermore, the processors consume more energy to process the signals, resulting in high power consumption. Therefore, payload management will be crucial for future satellite generation. In this context, the fifth chapter of the thesis proposes a demand-aware onboard payload processor management method, which switches on the processors according to the beam demand. In this case, for low demand, fewer processors are in-use, while more processors become necessary as demand increases. Demand-aware resource allocation techniques may require optimization of large variables. Consequently, this may increase the computational time complexity of the system. Thus, the sixth chapter of the thesis explores the methods of combining demand-aware resource allocation and deep learning (DL) to reduce the computational complexity of the system. In this case, a demand-aware algorithm enables bandwidth and power allocation, while DL can speed up computation. Finally, the last chapter provides the main conclusions of the thesis, as well as the future research directions. [less ▲]

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See detailA discussion on international interdisciplinary collaborations. Working at the European level
Schafer, Valerie UL

Presentation (2022, October 06)

Roundtable related to interdisciplinary and international collaborations

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See detailA Secure Authentication Protocol for Cholesteric Spherical Reflectors using Homomorphic Encryption
Arenas Correa, Monica Patricia UL; Bingol, Muhammed Ali; Demirci, Huseyin UL et al

in Lecture Notes in Computer Science (2022, October 06), 13503

Sometimes fingerprint-like features are found in a material. The exciting discovery poses new challenges on how to use the features to build an object authentication protocol that could tell customers and ... [more ▼]

Sometimes fingerprint-like features are found in a material. The exciting discovery poses new challenges on how to use the features to build an object authentication protocol that could tell customers and retailers equipped with a mobile device whether a good is authentic or fake. We are exactly in this situation with Cholesteric Spherical Reflectors (CSRs), tiny spheres of liquid crystals with which we can tag or coat objects. They are being proposed as a potential game-changer material in anti-counterfeiting due to their unique optical properties. In addition to the problem of processing images and extracting the minutiæ embedded in a CSR, one major challenge is designing cryptographically secure authentication protocols. The authentication procedure has to handle unstable input data; it has to measure the distance between some reference data stored at enrollment and noisy input provided at authentication. We propose a cryptographic authentication protocol that solves the problem, and that is secure against semi-honest and malicious adversaries. We prove that our design ensures data privacy even if enrolled data are leaked and even if servers and provers are actively curious. We implement and benchmark the protocol in Python using the Microsoft SEAL library through its Python wrapper PySEAL. [less ▲]

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See detailDie Uni Luxemburg vernetzt kluge Köpfe für die Nachkriegszeit
Ganschow, Inna UL; Weisbrodt, Sebastian; During, Marten UL et al

Article for general public (2022)

"Am Campus Belval sollen die Forschenden aus der Ukraine durch das LURN (Luxembourg Ukrainian Researcher Network) ein interdisziplinäres Netzwerk aufbauen, also Forschende außerhalb ihres Fachgebiets ... [more ▼]

"Am Campus Belval sollen die Forschenden aus der Ukraine durch das LURN (Luxembourg Ukrainian Researcher Network) ein interdisziplinäres Netzwerk aufbauen, also Forschende außerhalb ihres Fachgebiets kennenlernen. Zusätzlich sollen sie Berührungspunkte mit der luxemburgischen Forschungslandschaft bekommen." [less ▲]

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See detailRecent Developments and Overview of the Country and Practitioners Reports
Cole, Mark David UL

in European Data Protection Law Review (2022), 8(3), 386-390

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See detailMinimizing Supervision for Vision-Based Perception and Control in Autonomous Driving
Robinet, François UL

Doctoral thesis (2022)

The research presented in this dissertation focuses on reducing the need for supervision in two tasks related to autonomous driving: end-to-end steering and free space segmentation. For end-to-end ... [more ▼]

The research presented in this dissertation focuses on reducing the need for supervision in two tasks related to autonomous driving: end-to-end steering and free space segmentation. For end-to-end steering, we devise a new regularization technique which relies on pixel-relevance heatmaps to force the steering model to focus on lane markings. This improves performance across a variety of offline metrics. In relation to this work, we publicly release the RoboBus dataset, which consists of extensive driving data recorded using a commercial bus on a cross-border public transport route on the Luxembourgish-French border. We also tackle pseudo-supervised free space segmentation from three different angles: (1) we propose a Stochastic Co-Teaching training scheme that explicitly attempts to filter out the noise in pseudo-labels, (2) we study the impact of self-training and of different data augmentation techniques, (3) we devise a novel pseudo-label generation method based on road plane distance estimation from approximate depth maps. Finally, we investigate semi-supervised free space estimation and find that combining our techniques with a restricted subset of labeled samples results in substantial improvements in IoU, Precision and Recall. [less ▲]

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