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See detailConstant Envelope MIMO-OFDM Precoding for Low Complexity Large-Scale Antenna Array Systems
Domouchtsidis, Stavros UL; Tsinos, Christos UL; Chatzinotas, Symeon UL et al

in IEEE Transactions on Wireless Communications (2020)

Herein, we consider constant envelope precoding in a multiple-input multiple-output orthogonal frequency division multiplexing system (CE MIMO-OFDM) for frequency selective channels. In CE precoding the ... [more ▼]

Herein, we consider constant envelope precoding in a multiple-input multiple-output orthogonal frequency division multiplexing system (CE MIMO-OFDM) for frequency selective channels. In CE precoding the signals for each transmit 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 (PS) and nonlinear power amplifiers, which are key for the feasibility of large-scale antenna array systems because of their low cost and power consumption. The CE precoding problem is firstly formulated as a least-squares problem with a unit modulus constraint and solved using an algorithm based on coordinate descent. The large number of optimization variables in the case of the MIMO-OFDM system motivates the search for a more computationally efficient solution. To tackle this, we reformulate the CE precoding design into an unconstrained nonlinear least-squares problem, which is solved efficiently using the Gauss-Newton algorithm. Simulation results underline the efficiency of the proposed solutions and show that they outperform state of the art techniques. [less ▲]

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See detailDevelopment and Validation of the Revised Multicultural Ideology Scale in Germany and Luxembourg
Stogianni, Maria UL; Berry, John; Grigoryev, Dmitry et al

E-print/Working paper (2020)

A revised version of the Multicultural Ideology Scale (rMCI; Berry 2020; Berry et al., 1977) is currently being developed to measure endorsement of multiculturalism in different cultural contexts. The ... [more ▼]

A revised version of the Multicultural Ideology Scale (rMCI; Berry 2020; Berry et al., 1977) is currently being developed to measure endorsement of multiculturalism in different cultural contexts. The current study, which is part of this cross-cultural research project, presents the first assessment of the rMCI scale in the German language. The measure aims to cover several attitudinal dimensions of multiculturalism, relevant to the integration of different ethnocultural groups: Cultural Maintenance, Equity/Inclusion, Social interaction, Essentialistic Boundaries, Extent of Differences, and Consequences of Diversity. Two independent datasets were acquired from Germany (N = 382) and Luxembourg (N = 148) to estimate the factor structure of the rMCI using different confirmatory factor analysis techniques. The findings suggest that a 4-factor solution, including Cultural Maintenance, Equity/Inclusion, Social interaction, and Consequences of Diversity, was the best fit for the data. Most of these subscales demonstrated adequate psychometric properties (internal consistency, convergent, and discriminant validity). The 4-factor model of the rMCI was partially invariant across the two ethnic groups and full measurement invariance was established across gender. [less ▲]

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See detailMOTIVAID: Motivationally and digitally enhanced development by self-insight
Grund, Axel UL

Speeches/Talks (2020)

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See detailCan citizen science complement official data sources that serve as evidence-base for policies and practice to improve water quality?
König, Ariane UL; Pickar, Karl Arthur UL; Stankiewicz, Jacek UL et al

in Statistical Journal of the IAOS (2020), vol. Pre-Press

Addressing environmental issues in policy making requires recognising these issues as part of a complex socio-ecological system. The evidence base for such policies and associated monitoring and ... [more ▼]

Addressing environmental issues in policy making requires recognising these issues as part of a complex socio-ecological system. The evidence base for such policies and associated monitoring and implementation measures, as well as related official indicators, statistics and environmental accounts are receiving increasing attention. This paper explores the potential of citizen science as a non-traditional source of data to complement the current data production process for evidence-based policy-making, using pollution of surface waters and its effect on associated ecosystems as an example. The paper develops a framework that helps to explore the official data production process in relation to different purposes of environmental policies. This highlights different challenges that the current official data production process sees itself confronted with in relation to the different purposes of the policies and associated monitoring regimes. These questions are explored with reference to the case of evidence-based policy making on water quality of surface freshwater in the EU, with a focus on Luxembourg. The analysis is based on extensive documentary analysis and literature review, as well as a series of interviews and participatory workshops with various stakeholders, and first results of a pilot project work with engaged citizen volunteers to solicit data on water quality with a focus on its nutrient content. On this basis, this paper argues that citizen science has the clear potential to meaningfully contribute both to the evidence base for policy and practice, as well as to an improved governance process. [less ▲]

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See detailLow-light image enhancement of permanently shadowed lunar regions with physics-based machine learning
Moseley, Ben; Bickel, Valentin; Lopez-Francos, Ignacio et al

in Low-light image enhancement of permanently shadowed lunar regions with physics-based machine learning (2020, December)

Finding water(-ice) on the Moon is key to enabling a sustainable human presence on the Moon and beyond. There is evidence that water-ice is abundant in and around the Moon’s Permanently Shadowed Regions ... [more ▼]

Finding water(-ice) on the Moon is key to enabling a sustainable human presence on the Moon and beyond. There is evidence that water-ice is abundant in and around the Moon’s Permanently Shadowed Regions (PSRs), however, direct visual detection has not yet been possible. Surface ice or related physical features could potentially be directly detected from high-resolution optical imagery, but, due to the extremely low-light conditions in these areas, high levels of sensor and photon noise make this very challenging. In this work we generate high-resolution, low-noise optical images over lunar PSRs by using two physics-based deep neural networks to model and remove CCD-related and photon noise in existing low-light optical imagery, potentially paving the way for a direct water-ice detection method. [less ▲]

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See detailUn inventaire du patrimoine après une épidémie de démolitions?
Pauly, Michel UL

Article for general public (2020)

plaidoyer pour l'introduction d'une procédure d'urgence dans le projet de loi 7473 afin d'éviter des démolitions en masse avant la finalisation de l'inventaire des monuments historiques

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See detailTHIS TIME IS REALLY DIFFERENT: FLIGHT-TO-SAFETY AND THE COVID-19 CRISIS
Löwen, Celina; Kchouri, Bilal UL; Lehnert, Thorsten UL

E-print/Working paper (2020)

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See detailPublicly provided healthcare and migration
Mahe, Clotilde UL

in Economics and Human Biology (2020), 39

Publicly provided healthcare has received growing attention. Debates have been fuelled by evidence on improved health and reduced poverty, and concerns over adverse labour market effects; concerns that ... [more ▼]

Publicly provided healthcare has received growing attention. Debates have been fuelled by evidence on improved health and reduced poverty, and concerns over adverse labour market effects; concerns that are, to date, only supported by mixed empirical findings. This article examines whether publicly provided healthcare influences the decision to migrate. The spatial and temporal variation in the expansion of a non-contributory health insurance programme in Mexico, combined with the panel dimension and the timing of household survey data allows causal identification of the effect of increased coverage on migration. Difference-in-differences estimates reveal that accessing healthcare for free raises internal migration. The effect on international migration, costlier by nature, is statistically insignificant. Potential mechanisms include better health, the alleviation of financial constraints and a greater propensity to work. Results point to the relevance of including household members who have migrated in assessing the impacts of social health policies. They suggest that publicly provided healthcare could have multiplier effects on economic development and welfare by enabling labour force detachment of working-age members in affiliated households. [less ▲]

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See detailPhase transition for the volume of high-dimensional random polytopes
Bonnet, Gilles; Kabluchko, Zakhar; Turchi, Nicola UL

in Random Structures and Algorithms (2020)

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See detailAR4OER: A Semantic Platform for Open Educational Augmented Reality Resources
Grevisse, Christian UL; Martins Gomes, Carina; Rothkugel, Steffen UL

in Proceedings of the 2020 IEEE International Symposium on Multimedia (2020, December)

Tablet computers are gaining in presence in modern-day classrooms, enabling the use of a variety of apps for purposes such as note-taking or assessment. Augmented Reality (AR) experiences in the classroom ... [more ▼]

Tablet computers are gaining in presence in modern-day classrooms, enabling the use of a variety of apps for purposes such as note-taking or assessment. Augmented Reality (AR) experiences in the classroom, made possible by current hardware, permit new ways of interaction and visualization, as well as increase student motivation and engagement. They also overcome the need for potentially expensive hardware required for experiments in certain scientific domains. The movement of Open Educational Resources (OER) has enabled the sharing of heterogeneous learning resources. Their retrieval can be improved by enriching their metadata using Semantic Web technologies. In this paper, we present AR4OER, a semantic platform for heterogeneous AR experiences provided as OER. We showcase four AR scenarios from different school subjects. These scenarios can be integrated through a lose coupling in third-party apps. Apart from describing how this integration works, we demonstrate how a note-taking app can benefit from these scenarios. [less ▲]

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See detailPrivacy-Preserving Logistic Regression as a Cloud Service Based on Residue Number System
Cortés-Mendoza, Jorge; Tchernykh, Andrei; Babenko, Mikhail et al

in Voevodin, Vladimir; Sobolev, Sergey (Eds.) 6th Russian Supercomputing Days, Moscow 21-22 September 2020 (2020, December)

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See detailA hybrid MGA-MSGD ANN training approach for approximate solution of linear elliptic PDEs
Dehghani, Hamidreza UL; Zilian, Andreas UL

E-print/Working paper (2020)

We introduce a hybrid "Modified Genetic Algorithm-Multilevel Stochastic Gradient Descent" (MGA-MSGD) training algorithm that considerably improves accuracy and efficiency of solving 3D mechanical problems ... [more ▼]

We introduce a hybrid "Modified Genetic Algorithm-Multilevel Stochastic Gradient Descent" (MGA-MSGD) training algorithm that considerably improves accuracy and efficiency of solving 3D mechanical problems described, in strong-form, by PDEs via ANNs (Artificial Neural Networks). This presented approach allows the selection of a number of locations of interest at which the state variables are expected to fulfil the governing equations associated with a physical problem. Unlike classical PDE approximation methods such as finite differences or the finite element method, there is no need to establish and reconstruct the physical field quantity throughout the computational domain in order to predict the mechanical response at specific locations of interest. The basic idea of MGA-MSGD is the manipulation of the learnable parameters’ components responsible for the error explosion so that we can train the network with relatively larger learning rates which avoids trapping in local minima. The proposed training approach is less sensitive to the learning rate value, training points density and distribution, and the random initial parameters. The distance function to minimise is where we introduce the PDEs including any physical laws and conditions (so-called, Physics Informed ANN). The Genetic algorithm is modified to be suitable for this type of ANN in which a Coarse-level Stochastic Gradient Descent (CSGD) is exploited to make the decision of the offspring qualification. Employing the presented approach, a considerable improvement in both accuracy and efficiency, compared with standard training algorithms such classical SGD and Adam optimiser, is observed. The local displacement accuracy is studied and ensured by introducing the results of Finite Element Method (FEM) at sufficiently fine mesh as the reference displacements. A slightly more complex problem is solved ensuring the feasibility of the methodology [less ▲]

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See detailOpinion Statement ECJ-TF 2/2020 on the ECJ Decision of 3 March 2020 in Vodafone Magyarország Mobil Távközlési Zrt. (Case C-75/18) on Progressive Turnover Taxes
García Prats, Alfredo; Haslehner, Werner UL; Heydt, Volker et al

in European Taxation (2020), 60(12), 555-564

This CFE Opinion Statement discusses the decision of the Grand Chamber of the ECJ in Vodafone. The Court held that the imposition of the Hungarian progressive turnover-based tax on the telecommunications ... [more ▼]

This CFE Opinion Statement discusses the decision of the Grand Chamber of the ECJ in Vodafone. The Court held that the imposition of the Hungarian progressive turnover-based tax on the telecommunications sector did not infringe the EU fundamental freedoms or article 401 of the VAT Directive (2006/112), and that the question regarding the prohibition of State aid was inadmissible. Vodafone is especially important in respect of the current debate regarding turnover-based digital services taxes. [less ▲]

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See detailSensitivity Analysis on Regularity Based Driver Advisory Systems
Laskaris, Georgios; Seredynski, Marcin; Viti, Francesco UL

in 2020 IEEE 23rd International Conference on Intelligent Transportation Systems (ITSC) (2020, December)

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See detailScience of Science: Connecting Multidisciplinary Studies of Research, Higher Education, and Society
Dusdal, Jennifer UL; Akbaritabar, Aliakbar; Kosmützky, Anna

Book published by Frontiers (2020)

Marked by expanding and diverse forms of collaboration and competition, the investigation of contemporary developments in higher education and science systems need additional attention. Therefore, this ... [more ▼]

Marked by expanding and diverse forms of collaboration and competition, the investigation of contemporary developments in higher education and science systems need additional attention. Therefore, this research topic provides a forum for multidisciplinary exchange of pioneering research ideas and dialogues as well as complementary research that contribute to the field of knowledge, and aspires to support innovative, cutting-edge, and policy relevant research at the nexus of higher education research and science studies (HERSS), bibliometrics, scientometrics, and computational social sciences –traditionally separate communities focusing either on small scale and in-depth case studies or on large-scale “big data” research. Researchers bringing together the aforementioned scientific communities can be classified as important bridge-builders to bolster the growing research and current initiatives in the field of Science of Science between diverse scientific communities and the wider public. Especially sociology with its ambition to pair classic and innovative theoretical approaches with new methods to analyze and to qualitatively interpret quantitative “big data” with machine learning algorithms initiates a fascinating and promising approach to interlink the still separate scientific communities in favor of a more holistic understanding of Science of Science. In this Research Topic -as part of the Lecture Series: Science of Science in the Spotlight at the University of Luxembourg- we invite members of these diverse scientific communities and researchers who are working at the intersection as “translators” to present their latest research. We aim to promote and provide evidence-based insights into the drivers of multidisciplinary and international research and innovation, networks, and collaboration, including higher education developments, scientific knowledge production (e.g. publications, citations, patents), science capacity-building, research evaluation, policy reforms, cultural and societal change processes, and institutions and organizations as well as scientists’ geographical mobility, gender inequalities and career paths in science, and of migrant scientists. Furthermore, we want to stimulate debate on theoretical in-depth context knowledge and innovative methodological approaches (for example social network analysis and machine learning algorithms), and on data acquisition and analysis -long identified as an important research gap in Science of Science. The aim of this research topic is to consolidate common themes and research interests to maintain and improve collaborations among researchers with different academic backgrounds and expertise from a wide range of disciplines. We welcome contributions that address the aforementioned topics and encourage to combine theory-driven, empirically-rich, multidisciplinary, historical, and comparative research, including informed and evidence-based interpretations of research results that illustrate the importance of the topic for researchers, policymakers, funding agencies, university managers, and other public research organizations. [less ▲]

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See detailWireless Edge Caching: Modeling, Analysis, and Optimization
Vu, Thang Xuan UL; Bastug, Ejder; Chatzinotas, Symeon UL et al

Book published by Cambridge University Press (2020)

Understand both uncoded and coded caching techniques in future wireless network design. Expert authors present new techniques that will help you to improve backhaul, load minimization, deployment cost ... [more ▼]

Understand both uncoded and coded caching techniques in future wireless network design. Expert authors present new techniques that will help you to improve backhaul, load minimization, deployment cost reduction, security, energy efficiency and the quality of the user experience. Covering topics from high-level architectures to specific requirement-oriented caching design and analysis, including big-data enabled caching, caching in cloud-assisted 5G networks, and security, this is an essential resource for academic researchers, postgraduate students and engineers working in wireless communications. [less ▲]

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See detailEvaluating Pretrained Transformer-based Models on the Task of Fine-Grained Named Entity Recognition
Lothritz, Cedric UL; Allix, Kevin UL; Veiber, Lisa UL et al

in Proceedings of the 28th International Conference on Computational Linguistics (2020, December)

Named Entity Recognition (NER) is a fundamental Natural Language Processing (NLP) task and has remained an active research field. In recent years, transformer models and more specifically the BERT model ... [more ▼]

Named Entity Recognition (NER) is a fundamental Natural Language Processing (NLP) task and has remained an active research field. In recent years, transformer models and more specifically the BERT model developed at Google revolutionised the field of NLP. While the performance of transformer-based approaches such as BERT has been studied for NER, there has not yet been a study for the fine-grained Named Entity Recognition (FG-NER) task. In this paper, we compare three transformer-based models (BERT, RoBERTa, and XLNet) to two non-transformer-based models (CRF and BiLSTM-CNN-CRF). Furthermore, we apply each model to a multitude of distinct domains. We find that transformer-based models incrementally outperform the studied non-transformer-based models in most domains with respect to the F1 score. Furthermore, we find that the choice of domains significantly influenced the performance regardless of the respective data size or the model chosen. [less ▲]

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See detailDouble-Graded Quantum Superplane
Bruce, Andrew UL; Duplij, Steven

in Reports on Mathematical Physics (2020), 86(3), 383-400

A ℤ2 × ℤ2-graded generalisation of the quantum superplane is proposed and studied. We construct a bicovariant calculus on what we shall refer to as the double-graded quantum superplane. The ommutation ... [more ▼]

A ℤ2 × ℤ2-graded generalisation of the quantum superplane is proposed and studied. We construct a bicovariant calculus on what we shall refer to as the double-graded quantum superplane. The ommutation rules between the coordinates, their differentials and partial derivatives are explicitly given. Furthermore, we show that an extended version of the double-graded quantum superplane admits a natural Hopf -algebra structure. [less ▲]

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See detailAge, Intentions and the Implicit Role of Out-Selection Factors of International Migration
Beine, Michel UL

E-print/Working paper (2020)

In this paper, I propose to isolate the role of age as a self-selection factor of international migration. The role of age is estimated on intended emigration rather than on observed outcomes of migration ... [more ▼]

In this paper, I propose to isolate the role of age as a self-selection factor of international migration. The role of age is estimated on intended emigration rather than on observed outcomes of migration, using individual measures of intended emigration drawn from a large-scale survey conducted by Gallup. I find evidence that age has a monotonic negative effect on desired emigration for the working-age population. The estimations point to a very robust effect, suggesting that an additional year of age decreases the probability of intended emigration by about 0.5%. This effect is steady over different periods of time and for most types of countries of origin. The results contrast with previous evidence obtained on observed outcomes of migration, suggesting that out-selection factors interact with age and shape the demographic profile of migrants. [less ▲]

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