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See detailA co-located partitions strategy for parallel CFD-DEM couplings
Pozzetti, Gabriele UL; Besseron, Xavier UL; Rousset, Alban UL et al

E-print/Working paper (in press)

In this work, a new partition-collocation strategy for the parallel execution of CFD–DEM couplings is investigated. Having a good parallel performance is a key issue for an Eulerian-Lagrangian software ... [more ▼]

In this work, a new partition-collocation strategy for the parallel execution of CFD–DEM couplings is investigated. Having a good parallel performance is a key issue for an Eulerian-Lagrangian software that aims to be applied to solve industrially significant problems, as the computational cost of these couplings is one of their main drawback. The approach presented here consists in co-locating the overlapping parts of the simulation domain of each software on the same MPI process, in order to reduce the cost of the data exchanges. It is shown how this strategy allows reducing memory consumption and inter-process communication between CFD and DEM to a minimum and therefore to overcome an important parallelization bottleneck identified in the literature. Three benchmarks are proposed to assess the consistency and scalability of this approach. A coupled execution on 280 cores shows that less than 0.1% of the time is used to perform inter-physics data exchange. [less ▲]

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See detailHigher Education and the Exponential Rise of Science: Competition and Collaboration
Powell, Justin J W UL

in Scott, Robert; Buchmann, Marlis (Eds.) Emerging Trends in the Social and Behavioral Sciences (in press)

How we collaborate and compete to find solutions to the problems and challenges of our age vastly impacts our individual and group success and well-being. Interdependent, the institutions of education and ... [more ▼]

How we collaborate and compete to find solutions to the problems and challenges of our age vastly impacts our individual and group success and well-being. Interdependent, the institutions of education and science have dramatically expanded. Today, scientists in nearly all countries contribute to our shared stores of knowledge, with research universities the driving force behind unexpected pure exponential growth in scientific production. Competition—regional, national, organizational, and individual—has become more potent—with performance measures, comparative indicators, and formal evaluations continuously generated and used in decision-making. Simultaneously, collaboration across institutional, disciplinary, organizational, and cultural boundaries expands the possibilities of discovery and produces the most influential science. Competition and collaboration at the nexus of higher education and science demand enhanced attention as they shape the future of scientific innovation and production, with its understudied yet increasingly incontrovertible effects on individuals and societies. [less ▲]

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See detailSimultaneous finite element analysis of circuit-integrated piezoelectric energy harvesting from fluid-structure interaction
Ravi, Srivathsan; Zilian, Andreas UL

in Mechanical Systems & Signal Processing (2019), 114

Flow-driven piezoelectric energy harvesting is a strongly coupled multiphysics phenomenon that involves complex three-way interaction between the fluid flow, the electromechanical effect of the ... [more ▼]

Flow-driven piezoelectric energy harvesting is a strongly coupled multiphysics phenomenon that involves complex three-way interaction between the fluid flow, the electromechanical effect of the piezoelectric material mounted on a deformable substrate structure and the controlling electrical circuit. High fidelity computational solution approaches are essential for the analysis of flow-driven energy harvesters in order to capture the main physical aspects of the coupled problem and to accurately predict the power output of a harvester. While there are some phenomenological and numerical models for flow-driven harvesters reported in the literature, a fully three-dimensional strongly coupled model has not yet been developed, especially in the context of flow-driven energy harvesting. The weighted residuals method is applied to establish a mixed integral equation describing the incompressible Newtonian flow, elastic substrate structure, piezoelectric patch, equipotential electrode and attached electric circuit that form the multiphysics fluid-structure interaction problem. A monolithic numerical solution method is derived that provides consistent and simultaneous solution to all physical fields as well as to fluid mesh deformation. The approximate solution is based on a mixed space-time finite element discretization with static condensation of the auxiliary fields. The discontinuous Galerkin method is utilized for integrating the monolithic model in time. The proposed solution scheme is illustrated in the example of a lid driven cavity with a flexible piezoelectric bottom wall, demonstrating quantification of the amount of electrical energy extractable from fluid flow by means of a piezoelectric harvester device. The results indicate that in order to make reliable predictions on the power output under varying operational states, the realization of strong multiphysics coupling is required for the mathematical model as well as the numerical solution scheme to capture the characteristics of flow-driven energy harvesters. [less ▲]

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See detailReductions of elliptic curves
Perucca, Antonella UL

in Proceedings of the Roman Number Theory Association (2019), 4

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See detailStriking a balance between competitiveness and social fairness: what can we expect from the European Pillar of Social Rights?
Muñoz, Susana UL

in Chiocchetti, Paolo; Allemand, Frédéric (Eds.) Competitiveness and Solidarity in the European Union: Interdisciplinary Perspectives (2019)

The solemnly proclaimed European Pillar of Social Rights provides a meaningful response to the process of building a deeper, fairer European Union in the aftermath of the crisis. This chapter aims to ... [more ▼]

The solemnly proclaimed European Pillar of Social Rights provides a meaningful response to the process of building a deeper, fairer European Union in the aftermath of the crisis. This chapter aims to provide a critical assessment of the nature, scope, rationale, purpose, content and effectiveness of the Pillar in the light of its potential contribution to foster social fairness and competitiveness in the EU. The Pillar complements and develops the EU’s social acquis and reinforces standards which may provide a fairer and more socially-balanced competitiveness in the EU. Progress has been made, but further efforts are needed to build a sense of common purpose to strengthen the social foundations of the Union. [less ▲]

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See detailSocial Change for Sustainable Localized Food Sovereignty. Convergence between Prosumers and Ethical Entrepreneurs.
Reckinger, Rachel UL

in Sociologia del Lavoro (2018), 152(4),

Recently, some resourceful community-driven initiatives for local food production and retail have arisen in Luxembourg, where low organic agricultural rates are paradoxically paired with high consumer ... [more ▼]

Recently, some resourceful community-driven initiatives for local food production and retail have arisen in Luxembourg, where low organic agricultural rates are paradoxically paired with high consumer demands. This niche of social innovators is combining agro-ecology with circular economy practices. Four cases of alternative food networks are of interest – studied with qualitative interviews and participant observation. One has been established since the 1980s with 200 employees, partly in social insertion measures. The more recent and smaller initiatives are characterized by a cooperative governance, a community-supported agricultural outlook, hands-on workshops and time-banks, all enabled by social media. These initiatives are more radical in their agro-ecological or permaculture practices, focusing on regenerative land use without relying on imports and fostering the integration of consumers with varying degrees of prosumer involvement, as a politicized step further than mere (possibly industrialized) organic production. [less ▲]

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See detailEducational assessment and its prospects in the 21st century
Greiff, Samuel UL

Speeches/Talks (2018)

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See detailHITECS: A UML Profile and Analysis Framework for Hardware-in-the-Loop Testing of Cyber Physical Systems
Shin, Seung Yeob UL; Chaouch, Karim UL; Nejati, Shiva UL et al

in Proceedings of ACM/IEEE 21st International Conference on Model Driven Engineering Languages and Systems (MODELS’18) (2018, October)

Hardware-in-the-loop (HiL) testing is an important step in the development of cyber physical systems (CPS). CPS HiL test cases manipulate hardware components, are time-consuming and their behaviors are ... [more ▼]

Hardware-in-the-loop (HiL) testing is an important step in the development of cyber physical systems (CPS). CPS HiL test cases manipulate hardware components, are time-consuming and their behaviors are impacted by the uncertainties in the CPS environment. To mitigate the risks associated with HiL testing, engineers have to ensure that (1) HiL test cases are well-behaved, i.e., they implement valid test scenarios and do not accidentally damage hardware, and (2) HiL test cases can execute within the time budget allotted to HiL testing. This paper proposes an approach to help engineers systematically specify and analyze CPS HiL test cases. Leveraging the UML profile mechanism, we develop an executable domain-specific language, HITECS, for HiL test case specification. HITECS builds on the UML Testing Profile (UTP) and the UML action language (Alf). Using HITECS, we provide analysis methods to check whether HiL test cases are well-behaved, and to estimate the execution times of these test cases before the actual HiL testing stage. We apply HITECS to an industrial case study from the satellite domain. Our results show that: (1) HITECS is feasible to use in practice; (2) HITECS helps engineers define more complete and effective well-behavedness assertions for HiL test cases, compared to when these assertions are defined without systematic guidance; (3) HITECS verifies in practical time that HiL test cases are well-behaved; and (4) HITECS accurately estimates HiL test case execution times. [less ▲]

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See detailEnabling Model Testing of Cyber-Physical Systems
Gonzalez Perez, Carlos Alberto UL; Varmazyar, Mojtaba UL; Nejati, Shiva UL et al

in Proceedings of ACM/IEEE 21st International Conference on Model Driven Engineering Languages and Systems (MODELS’18) (2018, October)

Applying traditional testing techniques to Cyber-Physical Systems (CPS) is challenging due to the deep intertwining of software and hardware, and the complex, continuous interactions between the system ... [more ▼]

Applying traditional testing techniques to Cyber-Physical Systems (CPS) is challenging due to the deep intertwining of software and hardware, and the complex, continuous interactions between the system and its environment. To alleviate these challenges we propose to conduct testing at early stages and over executable models of the system and its environment. Model testing of CPSs is however not without difficulties. The complexity and heterogeneity of CPSs renders necessary the combination of different modeling formalisms to build faithful models of their different components. The execution of CPS models thus requires an execution framework supporting the co-simulation of different types of models, including models of the software (e.g., SysML), hardware (e.g., SysML or Simulink), and physical environment (e.g., Simulink). Furthermore, to enable testing in realistic conditions, the co-simulation process must be (1) fast, so that thousands of simulations can be conducted in practical time, (2) controllable, to precisely emulate the expected runtime behavior of the system and, (3) observable, by producing simulation data enabling the detection of failures. To tackle these challenges, we propose a SysML-based modeling methodology for model testing of CPSs, and an efficient SysML-Simulink co-simulation framework. Our approach was validated on a case study from the satellite domain. [less ▲]

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See detailTUNA: TUning Naturalness-based Analysis
Jimenez, Matthieu UL; Cordy, Maxime UL; Le Traon, Yves UL et al

in 34th IEEE International Conference on Software Maintenance and Evolution, Madrid, Spain, 26-28 September 2018 (2018, September 26)

Natural language processing techniques, in particular n-gram models, have been applied successfully to facilitate a number of software engineering tasks. However, in our related ICSME ’18 paper, we have ... [more ▼]

Natural language processing techniques, in particular n-gram models, have been applied successfully to facilitate a number of software engineering tasks. However, in our related ICSME ’18 paper, we have shown that the conclusions of a study can drastically change with respect to how the code is tokenized and how the used n-gram model is parameterized. These choices are thus of utmost importance, and one must carefully make them. To show this and allow the community to benefit from our work, we have developed TUNA (TUning Naturalness-based Analysis), a Java software artifact to perform naturalness-based analyses of source code. To the best of our knowledge, TUNA is the first open- source, end-to-end toolchain to carry out source code analyses based on naturalness. [less ▲]

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See detailAssessment of the suitability of gravel wash mud as raw material for the synthesis of an alkali-activated binder
Thapa, Vishojit Bahadur UL; Waldmann, Danièle UL; Wagner, Jean-Frank et al

in Applied Clay Science (TOP10 Journal in Mineralogy) (2018), 161(C), 110-118

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of ... [more ▼]

Gravel wash mud (GWM), a waste product from gravel mining was dried and processed into a fine powder to be activated by different concentrations of sodium hydroxide (NaOH) solutions for the synthesis of an alkali-activated binder. The GWM powders were thermally treated at five different calcination temperatures 550, 650, 750, 850 and 950°C. The characterisation of the raw material comprises the particle size distribution (PSD) by laser granulometry, the chemical and mineralogical composition by X-ray fluorescence and X-ray diffraction analysis respectively, and simultaneous thermal analysis. The performance of the alkali-activated binders was examined using compression strength tests and the microstructure was observed using scanning electron microscopy (SEM). The GWM was classified as an aluminosilicate raw material with kaolinite and illite as main clay minerals. Furthermore, a mean particle size around 6.50μm was determined for the uncalcined and calcined GWM powders. The SEM images of the developed binders showed the formation of a compact microstructure, however, relatively low strengths were achieved. This preliminary study highlights an example of an aluminosilicate prime material, which shows very promising chemical and mineralogical characteristics, but its suitability for alkaline activation without further additives was not confirmed as far as performance-based criteria are considered. [less ▲]

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See detailOn the impact of tokenizer and parameters on N-gram based Code Analysis
Jimenez, Matthieu UL; Cordy, Maxime UL; Le Traon, Yves UL et al

Scientific Conference (2018, September)

Recent research shows that language models, such as n-gram models, are useful at a wide variety of software engineering tasks, e.g., code completion, bug identification, code summarisation, etc. However ... [more ▼]

Recent research shows that language models, such as n-gram models, are useful at a wide variety of software engineering tasks, e.g., code completion, bug identification, code summarisation, etc. However, such models require the appropriate set of numerous parameters. Moreover, the different ways one can read code essentially yield different models (based on the different sequences of tokens). In this paper, we focus on n- gram models and evaluate how the use of tokenizers, smoothing, unknown threshold and n values impact the predicting ability of these models. Thus, we compare the use of multiple tokenizers and sets of different parameters (smoothing, unknown threshold and n values) with the aim of identifying the most appropriate combinations. Our results show that the Modified Kneser-Ney smoothing technique performs best, while n values are depended on the choice of the tokenizer, with values 4 or 5 offering a good trade-off between entropy and computation time. Interestingly, we find that tokenizers treating the code as simple text are the most robust ones. Finally, we demonstrate that the differences between the tokenizers are of practical importance and have the potential of changing the conclusions of a given experiment. [less ▲]

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See detailLes blockchains en 50 questions: comprendre le fonctionnement et les enjeux de cette technologie innovante
Dumas, J.-G.; Lafourcade, P.; Tichit, A. et al

Book published by Dunod - 1er (2018)

Depuis l’apparition de bitcoin, les innovations liées à la blockchain sont en plein essor. Ce livre tente d'expliquer le fonctionnement de cette technologie innovante mais aussi ses applications au ... [more ▼]

Depuis l’apparition de bitcoin, les innovations liées à la blockchain sont en plein essor. Ce livre tente d'expliquer le fonctionnement de cette technologie innovante mais aussi ses applications au travers de 50 questions comme: • Qu’est-ce qu’une blockchain ? • Quel est le lien entre le bitcoin et les blokchains ? • Qui sont les mineurs et que font-ils ? • Quelle est aujourd’hui la part des cryptomonnaies dans l’économie mondiale ? • Qu’est-ce qu’un smart contract (contrat intelligent) ? • Peut-on faire une blockchain sans bloc ? • Comment les blockchains vont-elles révolutionner le monde ? Voici quelques-unes des questions dont vous trouverez les réponses dans ce livre [less ▲]

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See detailResource Allocation and Relay Selection for Multi-User OFDM-Based Cooperative Networks with SWIPT
Gautam, Sumit UL; Lagunas, Eva UL; Chatzinotas, Symeon UL et al

Scientific Conference (2018, August)

In this paper, we investigate resource allocation and relay selection in a two-hop relay-assisted multi-user network, where the end users support Simultaneous Wireless Information and Power Transfer ... [more ▼]

In this paper, we investigate resource allocation and relay selection in a two-hop relay-assisted multi-user network, where the end users support Simultaneous Wireless Information and Power Transfer (SWIPT). In particular, we consider single source assisted by a set of spatially distributed relays able to amplify-and-forward orthogonal frequency division multiplexing (OFDM) signals carrying both data and power at the same time. The users are assumed to implement a power splitting technique where the received signal is orthogonally split in two streams of different power levels, where one signal stream is sent to the power harvesting module while the other is converted to baseband for information decoding. We aim at optimizing the users’ power splitting ratios as well as the relay, carrier and power assignment so that the end-users’ sum-rate is maximized subject to transmitted and harvested power constraints. Such joint optimization is combinatorial in nature with a non-convex structure. Therefore, we present a sub-optimal low complex solution based on the harmonic mean of the two-hop relay channel coefficients. Simulation results reveal that the proposed algorithm provides significant performance gains in comparison with a semi-random resource allocation and relay selection approach. [less ▲]

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See detailTapping the Potential of Diverse Founding Teams for Firm Growth: The Role of New Venture Activities
Tryba, Anne UL; Patzelt, Holger; Breugst, Nicola

Scientific Conference (2018, August)

Detailed reference viewed: 22 (0 UL)