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See detailUsing Bayesian inference to recover the material parameters of a heterogeneous hyperelastic body
Hale, Jack UL; Farrell, Patrick; Bordas, Stéphane UL

Scientific Conference (2016)

We present a method for calculating a Bayesian uncertainty estimate on the recovered material parameters of a heterogeneous geometrically non-linear hyperelastic body. We formulate the problem in the ... [more ▼]

We present a method for calculating a Bayesian uncertainty estimate on the recovered material parameters of a heterogeneous geometrically non-linear hyperelastic body. We formulate the problem in the Bayesian inference framework [1]; given noisy and sparse observations of a body, some prior knowledge on the parameters and a parameter-to-observable map the goal is to recover the posterior distribution of the parameters given the observations. In this work we primarily focus on the challenges of developing dimension-independent algorithms in the context of very large inverse problems (tens to hundreds of thousands of parameters). Critical to the success of the method is viewing the problem in the correct infinite- dimensional function space setting [2]. With this goal in mind, we show the use of automatic symbolic differentiation techniques to construct high-order adjoint models [3], scalable maximum a posteriori (MAP) estimators, and efficient low-rank update methods to calculate credible regions on the posterior distribution [4]. [less ▲]

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See detailUsing Complex Problem Solving Simulations for General Cognitive Ability Assessment: the Genetics Lab Framework
Mayer, Hélène; Hazotte, Cyril; Djaghloul, Younes et al

in International Journal of Information Science and Intelligent System (2013), 2(4), 71-88

This paper presents the conception and operation of “the Genetics Lab,” a research platform designed for general intelligence measurement. This tool has been developed and refined to measure cognitive ... [more ▼]

This paper presents the conception and operation of “the Genetics Lab,” a research platform designed for general intelligence measurement. This tool has been developed and refined to measure cognitive skills of students in Luxembourg, Thanks to its generic and clear architecture, “the Genetics Lab” makes a major contribution by addressing technical weaknesses and flaws met with tools previously used to assess intelligence. This new platform can be used as groundwork for other evaluation solutions. In this paper, we explore in depth the main fields of e-assessment such as instructions, localized and multilingual content production and display, traces, and scoring. We also describe how the platform was put into action to create complex simulations and to make data collection resulting from the user’s test a flawless process. This paper is a continuation and extension of earlier work. [less ▲]

Detailed reference viewed: 125 (11 UL)
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See detailUsing mobile phone data for urban network state estimation
Derrmann, Thierry; Frank, Raphaël UL; Engel, Thomas UL et al

Scientific Conference (2018, June)

Detailed reference viewed: 73 (4 UL)
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See detailA UX Approach to Privacy and Security: the Impact of User, Contextual and System-Related Factors
Distler, Verena UL; Lallemand, Carine UL; Koenig, Vincent UL

in CHI Workshop Exploring Individual Diffferences in Privacy (2018, April)

This position paper lays out current and future studies which we conduct on the UX aspects of security and privacy, our goal being to understand which factors influence privacy-related decision-making. We ... [more ▼]

This position paper lays out current and future studies which we conduct on the UX aspects of security and privacy, our goal being to understand which factors influence privacy-related decision-making. We advocate using UX design methods in order to study interindividual differences, system-related and contextual factors involved in privacy and security attitudes and behaviors. These results will contribute to user-tailored and personalized privacy initiatives and guide the design of future technologies. [less ▲]

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See detailA UX Approach to Privacy and Security: the Impact of User, Contextual and System-Related Factors
Distler, Verena UL; Lallemand, Carine UL; Koenig, Vincent UL

in CHI Workshop Exploring Individual Diffferences in Privacy (2018, April)

This position paper lays out current and future studies which we conduct on the UX aspects of security and privacy, our goal being to understand which factors influence privacy-related decision-making. We ... [more ▼]

This position paper lays out current and future studies which we conduct on the UX aspects of security and privacy, our goal being to understand which factors influence privacy-related decision-making. We advocate using UX design methods in order to study interindividual differences, system-related and contextual factors involved in privacy and security attitudes and behaviors. These results will contribute to user-tailored and personalized privacy initiatives and guide the design of future technologies. [less ▲]

Detailed reference viewed: 254 (14 UL)
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See detailA variational formulation of dissipative quasicontinuum methods
Rokos, Ondrej; Beex, Lars UL; Peerlings, Ron et al

in International Journal of Solids and Structures (2016), 102-103

Lattice systems and discrete networks with dissipative interactions are successfully employed as meso-scale models of heterogeneous solids. As the application scale generally is much larger than that of ... [more ▼]

Lattice systems and discrete networks with dissipative interactions are successfully employed as meso-scale models of heterogeneous solids. As the application scale generally is much larger than that of the discrete links, physically relevant simulations are computationally expensive. The QuasiContinuum (QC) method is a multiscale approach that reduces the computational cost of direct numerical simulations by fully resolving complex phenomena only in regions of interest while coarsening elsewhere. In previous work (Beex et al., J. Mech. Phys. Solids 64, 154-169, 2014), the originally conservative QC methodology was generalized to a virtual-power-based QC approach that includes local dissipative mechanisms. In this contribution, the virtual-power-based QC method is reformulated from a variational point of view, by employing the energy-based variational framework for rate-independent processes (Mielke and Roub cek, Rate-Independent Systems: Theory and Application, Springer-Verlag, 2015). By construction it is shown that the QC method with dissipative interactions can be expressed as a minimization problem of a properly built energy potential, providing solutions equivalent to those of the virtual-power-based QC formulation. The theoretical considerations are demonstrated on three simple examples. For them we verify energy consistency, quantify relative errors in energies, and discuss errors in internal variables obtained for different meshes and two summation rules. [less ▲]

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See detailVibration of functionally graded material plates with cutouts & cracks in thermal environment
Rahimabadi, A. A.; Natarajan, S.; Bordas, Stéphane UL

in Key Engineering Materials (2013), 560

In this paper, the effect of a centrally located cutout (circular and elliptical) and cracks emanating from the cutout on the free flexural vibration behaviour of functionally graded material plates in ... [more ▼]

In this paper, the effect of a centrally located cutout (circular and elliptical) and cracks emanating from the cutout on the free flexural vibration behaviour of functionally graded material plates in thermal environment is studied. The discontinuity surface is represented independent of the mesh by exploiting the partition of unity method framework. A Heaviside function is used to capture the jump in the displacement across the discontinuity surface and asymptotic branch functions are used to capture the singularity around the crack tip. An enriched shear flexible 4-noded quadrilateral element is used for the spatial discretization. The properties are assumed to vary only in the thickness direction. The effective properties of the functionally graded material are estimated using the Mori-Tanaka homogenization scheme and the plate kinematics is based on the first order shear deformation theory. The influence of the plate geometry, the geometry of the cutout, the crack length, the thermal gradient and the boundary conditions on the free flexural vibration is numerically studied. © (2013) Trans Tech Publications, Switzerland. [less ▲]

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See detailVicinity Resource Cartography for Delay-Tolerant Networks: a Holistic Perspective
Sandulescu, Gabriel UL; Schaffer, Peter UL; Nadjm-Tehrani, Simin UL

in 2010 IFIP W IRELESS D AYS (2010)

In this paper we propose a distributed algorithm allowing nodes in delay-tolerant networks to construct vicinity resource maps based on past encounters. Our algorithm estimates the availability of the ... [more ▼]

In this paper we propose a distributed algorithm allowing nodes in delay-tolerant networks to construct vicinity resource maps based on past encounters. Our algorithm estimates the availability of the following resources: energy, buffer space, and bandwidth. We then show how a store-carry-forward scheme may benefit from having access to these resource estimates. While knowledge about resources available in the vicinity allows nodes to implement meaningful custodian election strategies, an evaluation of available bandwidth and contact time allows them to carry out adaptive queue management strategies. Thus, such strategies can be approached from a holistic perspective based on the availability of the three resources under consideration in node proximity.We validate our model separately in time-varying and space-varying environments. In addition to synthetic mobility models (random waypoint) we validate our resource estimation in a disaster area mobility model (using Bonn motion traces). We show that by using this information a routing protocol may dramatically improve its delivery rate and energy overhead while keeping delivery latency almost constant. [less ▲]

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See detailVirtual and smoothed finite elements: A connection and its application to polygonal/polyhedral finite element methods
Natarajan, Sundararajan; Bordas, Stéphane UL; Ooi, Ean Tat

in International Journal for Numerical Methods in Engineering (2015), 104(13), 1173-1199

We show both theoretically and numerically a connection between the smoothed finite element method (SFEM) and the virtual element method and use this approach to derive stable, cheap and optimally ... [more ▼]

We show both theoretically and numerically a connection between the smoothed finite element method (SFEM) and the virtual element method and use this approach to derive stable, cheap and optimally convergent polyhedral FEM.We show that the stiffness matrix computed with one subcell SFEM is identical to the consistency term of the virtual element method, irrespective of the topology of the element, as long as the shape functions vary linearly on the boundary. Using this connection, we propose a new stable approach to strain smoothing for polygonal/polyhedral elements where, instead of using sub-triangulations, we are able to use one single polygonal/polyhedral subcell for each element while maintaining stability. For a similar number of degrees of freedom, the proposed approach is more accurate than the conventional SFEM with triangular subcells. The time to compute the stiffness matrix scales with the O.dof s/1:1 in case of the conventional polygonal FEM, while it scales as O.dof s/0:7 in the proposed approach. The accuracy and the convergence properties of the SFEM are studied with a few benchmark problems in 2D and 3D linear elasticity. [less ▲]

Detailed reference viewed: 101 (2 UL)
See detailVirtual Coach Reaches Out To Me
Aleksic, Gabrijela UL

Conference given outside the academic context (2013)

Detailed reference viewed: 14 (0 UL)
See detailVirtual Coach Reaches Out To Me
Aleksic, Gabrijela UL

Conference given outside the academic context (2013)

Detailed reference viewed: 11 (1 UL)
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See detailThe virtual node polygonal element method for nonlinear thermal analysis with application to hybrid laser welding
Wu, SC; Peng, X; Zhang, WH et al

in International Journal of Heat & Mass Transfer (2013), 67

The nonlinear heat transfer process occurring during hybrid laser welding was simulated using the Virtual-node Polygonal Element (VPE) method within the framework of the Finite Element Method (FEM). To ... [more ▼]

The nonlinear heat transfer process occurring during hybrid laser welding was simulated using the Virtual-node Polygonal Element (VPE) method within the framework of the Finite Element Method (FEM). To achieve robustness in large-scale welding simulations, a dynamic mesh refinement with quadtree and octree data structures was used in the welding region. Accuracy, convergence and efficiency were verified by solving two and three dimensional problems. It is found that the present VPE can successfully simulate the hybrid laser welding process with good accuracy and convergence. The adaptive refined mesh box can synchronously move with the welding heat source, which dramatically reduces the number of field nodes. Compared with the standard FEM,the VPEM requires only approximately 42% of the total degrees of freedom used in standard FEM for the same accuracy. Furthermore, we compare the computational cost and accuracy of the method to that of the finite element method, the edge based virtual node polygonal element/virtual node method, the edge-based Smoothed Point Interpolation Meshless Method (ES-PIM), the edge-based Element (ES-PIM) the Element Free Galerkin (EFG) method and the Meshless Local Petrove-Galerkin Petrov-Galerkin (MLPG) method. Compared to all those methods, the proposed scheme is found competitive in terms of computational cost versus accuracy, and benefit from a simple implementation. © 2012 Elsevier B.V. All rights reserved. [less ▲]

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See detailVirtual-power-based quasicontinuum methods for discrete dissipative materials
Beex, Lars UL; Bordas, Stéphane UL

Scientific Conference (2016, June)

Detailed reference viewed: 74 (2 UL)
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See detailVirtual-power-based quasicontinuum methods for discrete dissipative materials
Beex, Lars UL

Scientific Conference (2016, June)

In this presentation, the formulation of the virtual-power-based QC framework will be outlined for an elastoplastic truss lattice. Subsequently, the framework is applied to an actual discrete material.

Detailed reference viewed: 55 (3 UL)
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See detailVisualizing Computer-Based Activity on Ambient Displays to Reduce Sedentary Behavior at Work
Brombacher, Hans; Ren, Xipei; Vos, Steven et al

in 32ND AUSTRALIAN CONFERENCE ON HUMAN-COMPUTER INTERACTION (2020)

Workplace health interventions have predominantly been designed around visualizations of physical activity data in the work routine. Yet, contextual factors, such as computer-based activity, appears to be ... [more ▼]

Workplace health interventions have predominantly been designed around visualizations of physical activity data in the work routine. Yet, contextual factors, such as computer-based activity, appears to be crucial to support healthier behaviors at work. In this research, we explore the effect of visualizing computer-based activity to prompt physical activity at work, through desktop-based ambient displays. Based on our prototypes Yamin and Apphia, we conducted an exploratory qualitative user study in a lab setting with office workers (N=16). Results showed that visualizing one’s computer-based activity could potentially increase the awareness, self-reflection, and social interactions for individuals to become physically active. With our findings, we discuss design implications for using computer activity data in a physical form as a motivational factor to encourage physically active workstyles. We present directions for future field studies to gain further insights on this topic. [less ▲]

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See detailViviane Reding on her action in the field of the information society and media (2004-2010)
Danescu, Elena UL

in Internet Histories: Digital Technology, Culture and Society (2020)

The following pages are taken from a long interview (more than eight hours of footage in total) that Viviane Reding granted us in 2015 in connection with the “Pierre Werner and Europe” research project ... [more ▼]

The following pages are taken from a long interview (more than eight hours of footage in total) that Viviane Reding granted us in 2015 in connection with the “Pierre Werner and Europe” research project. Drawing on more than 40 years’ experience in politics, Viviane Reding spoke about her career, the role of Luxembourg and Luxembourgers in the European integration process, and various key events in which she played a part. In these extracts, she discusses her role as a member of the first and second Barroso Commissions (2004-2009 and 2010-2014) and her efforts to help build an information and knowledge society in Europe, one that serves citizens and protects their rights and fundamental freedoms. Her achievements in this respect include capping mobile phone roaming charges (they were subsequently abolished in 2017), advocating for the introduction of a single emergency number (112) in all EU countries, launching the Europeana digital library, and spearheading a programme to use technological innovation for climate and energy solutions. She also describes the process of developing a Digital Agenda for Europe to improve the continent’s digital competitiveness compared with the United States, China and Japan – a complex and challenging task given the context of globalisation and the divergent interests of the various stakeholders (research, industry, consumers, etc.). Finally, she mentions the reform of personal data protection that she initiated (leading to the GDPR, adopted in April 2016). [less ▲]

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See detailA volume-averaged nodal projection method for the Reissner-Mindlin plate model
Ortiz-Bernardin, Alejandro; Köbrich, Philip; Hale, Jack UL et al

in Computer Methods in Applied Mechanics & Engineering (2018), 341

We introduce a novel meshfree Galerkin method for the solution of Reissner-Mindlin plate problems that is written in terms of the primitive variables only (i.e., rotations and transverse displacement) and ... [more ▼]

We introduce a novel meshfree Galerkin method for the solution of Reissner-Mindlin plate problems that is written in terms of the primitive variables only (i.e., rotations and transverse displacement) and is devoid of shear-locking. The proposed approach uses linear maximum-entropy approximations and is built variationally on a two-field potential energy functional wherein the shear strain, written in terms of the primitive variables, is computed via a volume-averaged nodal projection operator that is constructed from the Kirchhoff constraint of the three-field mixed weak form. The stability of the method is rendered by adding bubble-like enrichment to the rotation degrees of freedom. Some benchmark problems are presented to demonstrate the accuracy and performance of the proposed method for a wide range of plate thicknesses. [less ▲]

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See detailVulnerability Analysis of Cyber Physical Systems under False-Data injection and disturbance attacks
Gerard, Benjamin; Bezzaoucha, Souad UL; Voos, Holger UL et al

in Vulnerability Analysis of Cyber Physical Systems under False-Data injection and disturbance attacks (2018, September)

In the present paper, the problem of attacks on cyber-physical systems via networked control system (NCS) subject to unmeasured disturbances is considered. The geometric approach is used to evaluate the ... [more ▼]

In the present paper, the problem of attacks on cyber-physical systems via networked control system (NCS) subject to unmeasured disturbances is considered. The geometric approach is used to evaluate the security and vulnerability level of the controlled system. The presented work deals with the so-called false data injection attacks and shows how imperfectly known disturbances can be used to perform undetectable, or at least stealthy, attacks that can make the NCS vulnerable to attacks from malicious outsiders. A numerical example is given to illustrate the approach. [less ▲]

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See detailVulnerability analysis of network observability in link flow inference problems
Rinaldi, Marco UL; Viti, Francesco UL

Scientific Conference (2018, January)

Detailed reference viewed: 26 (0 UL)
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See detailA warmer world
van Dam, Tonie UL; Weigelt, Matthias UL; Jäggi, Adrian

in Pan European Networks: Science & Technology (2015), (14), 58-59

Detailed reference viewed: 250 (21 UL)