![]() Bordas, Stéphane ![]() Report (2016) Detailed reference viewed: 508 (12 UL)![]() Bordas, Stéphane ![]() ![]() Report (2018) Detailed reference viewed: 2382 (215 UL)![]() Agathos, Konstantinos ![]() ![]() Scientific Conference (2016, May) Detailed reference viewed: 254 (20 UL)![]() ; ; et al in Construction and Building Materials (2018), 188 Foamed concrete has been widely used in infrastructure construction and poses new challenges to design and modelling. This paper investigates the behaviour of foamed concrete with the help of X-ray ... [more ▼] Foamed concrete has been widely used in infrastructure construction and poses new challenges to design and modelling. This paper investigates the behaviour of foamed concrete with the help of X-ray Computed Tomography (XCT), which is capable of characterising the microstructure of foamed concrete. An in situ compressive test-XCT scan is carried out to observe the failure mechanism of foamed concrete by XCT when subjected to compression load. A meso-scale simulation based on XCT images is conducted to simulate the behaviour of foamed concrete. An algorithm that directly reconstructs the meso-scale model from XCT images is developed. The experimental and numerical results show that foamed concrete exhibits a significant change in mechanical behaviour; it is less brittle compared to the response of dense samples. However, the reduction in the level of brittleness is accompanied by a significant decrease in compressive strength. Failure development inside samples is successfully captured by the XCT scan and the meso-scale modelling. The topology of foamed structures, in particular the chain of interconnected pores, influences the failure mechanism of foamed concrete. The combination of XCT scan and meso-scale modelling provides a comprehensive framework to understand the mechanical behaviour of foamed concrete. [less ▲] Detailed reference viewed: 161 (2 UL)![]() Querol, Jorge ![]() ![]() ![]() Poster (2021, April 19) The new phase of space exploration involves a growing number of human and robotic missions with varying communication and service requirements. Continuous, maximum coverage of areas where activities are ... [more ▼] The new phase of space exploration involves a growing number of human and robotic missions with varying communication and service requirements. Continuous, maximum coverage of areas where activities are concentrated and orbiting missions (single spacecraft or constellations) around the Earth, Moon or Mars will be particularly challenging. The standardization of the 5G Non-Terrestrial Networks (NTN) has already begun [1], and nothing prevents 5G from becoming a common communications standard supporting space resource missions [2]. The 5G Space Communications Lab (5G-SpaceLab) is an interdisciplinary experimental platform, funded by the Luxembourg Space Agency and is part of the Space Research Program of SnT. The lab allows users to design and emulate realistic space communications and control scenarios for the next-generation of space applications. The capabilities of the 5G-SpaceLab testbed combine the experience of different disciplines including space communications, space and satellite mission design, and space robotics. The most relevant include the demonstration of SDR 5G NTN terminals including NB-IoT, emulation of space communications channel scenarios (e.g. link budget, delay, Doppler…), small satellite platform and payload design and testing, satellite swarm flight formation, lunar rover and robotic arm control and AI-powered telerobotics. Earth-Moon communications is one of the scenarios demonstrated in the 5G-SpaceLab. Bidirectional communication for the teleoperation of lunar rovers for near real-time operations including data collection and sensors feedback will be tested. AI-based approaches for perception and control will be developed to overcome communication delays and to provide safer, trustworthy, and efficient remote control of the rovers. [1] 3GPP Release 17 Timeline. [Online]. Available: https://www.3gpp.org/release-17 [2] Nokia, Nokia selected by NASA to build first ever cellular network on the Moon. [Online]. Available: https://www.nokia.com/about-us/news/releases/2020/10/19/nokia-selected-by-nasa-to-build-first-ever-cellular-network-on-the-moon/ [less ▲] Detailed reference viewed: 473 (59 UL)![]() ; ; Bordas, Stéphane ![]() Scientific Conference (2023, June 06) Fractional powers of the Laplacian operator are important tools in the modeling and study of non-local phenomena. Several numerical challenges arise from the discretization of these operators due to their ... [more ▼] Fractional powers of the Laplacian operator are important tools in the modeling and study of non-local phenomena. Several numerical challenges arise from the discretization of these operators due to their non-local nature. For example, a direct discretization via finite element methods can lead to dense and possibly large linear systems. One way to circumvent this density is by using a rational scheme combined with a finite element method. In this talk we describe a novel local a posteriori estimator for the finite element discretization error measured in the L2 norm that can be used to perform adaptive mesh refinement. This estimator is adapted from the strategy introduced by Bank and Weiser and can be used with any rational approx- imation scheme such as best uniform rational approximations or schemes based on the Dunford–Taylor formula. Especially, our estimator preserves the locality and robustness of the Bank–Weiser estimator and preserves the parallel nature of rational approximations. In addition, oour method can be combined with an estimator for the rational approximation error to obtain a more complete description of the discretization errors. Finally, we use an implementation in the FEniCSx finite element software to demonstrate the performances of our method on several numerical experiments including three–dimensional prob- lems. [less ▲] Detailed reference viewed: 28 (0 UL)![]() Bulle, Raphaël ![]() ![]() in Computer Methods in Applied Mechanics and Engineering (2023), 407 We develop a novel a posteriori error estimator for the L2 error committed by the finite ele- ment discretization of the solution of the fractional Laplacian. Our a posteriori error estimator takes ... [more ▼] We develop a novel a posteriori error estimator for the L2 error committed by the finite ele- ment discretization of the solution of the fractional Laplacian. Our a posteriori error estimator takes advantage of the semi–discretization scheme using a rational approximation which allows to reformulate the fractional problem into a family of non–fractional parametric problems. The estimator involves applying the implicit Bank–Weiser error estimation strategy to each parametric non–fractional problem and reconstructing the fractional error through the same rational approximation used to compute the solution to the original fractional problem. We provide several numerical examples in both two and three-dimensions demonstrating the effectivity of our estimator for varying fractional powers and its ability to drive an adaptive mesh refinement strategy. [less ▲] Detailed reference viewed: 108 (11 UL)![]() ; Lygidakis, Charilaos ![]() in Journal of Hypertension (2018, October) Objectives: In this study, we review the evidence and discuss how the digitalization affects the CHWs programs for tackling non-communicable diseases (NCDs) in low-and-middle income countries (LMICs ... [more ▼] Objectives: In this study, we review the evidence and discuss how the digitalization affects the CHWs programs for tackling non-communicable diseases (NCDs) in low-and-middle income countries (LMICs). Methods: We conducted a review of literature covering two databases: PubMED and Embase. A total of 97 articles were abstracted for full text review of which 21 are included in the analysis. Existing theories were used to construct a conceptual framework for understanding how digitalization affects the prospects of CHW programs for NCDs. Results: We identified three benefits and three challenges of digitalization. Firstly, it will help improve the access and quality of services, notwithstanding its higher establishment and maintenance costs. Secondly, it will add efficiency in training and personnel management. Thirdly, it will leverage the use of data generated across grass-roots platforms to further research and evaluation. The challenges posed are related to funding, health literacy of CHWs, and systemic challenges related to motivating CHWs. More than 60 digital platforms were identified, including mobile based networking devices (used for behavioral change communication), Web-applications (used for contact tracking, reminder system, adherence tracing, data collection, and decision support), videoconference (used for decision support) and mobile applications (used for reminder system, supervision, patients’ management, hearing screening, and tele-consultation). Conclusion: The digitalization efforts of CHW programs are afflicted by many challenges, yet the rapid technological penetration and acceptability coupled with the gradual fall in costs constitute encouraging signals for the LMICs. Both CHWs interventions and digital technologies are not inexpensive, but they may provide better value for the money. [less ▲] Detailed reference viewed: 178 (0 UL)![]() Garcia Santa Cruz, Beatriz ![]() ![]() in Bildverarbeitung für die Medizin 2022. Informatik aktuell. Springer Vieweg, Wiesbaden. (2022, April 05) Detailed reference viewed: 45 (3 UL)![]() Distler, Verena ![]() Bachelor/master dissertation (2017) Detailed reference viewed: 68 (15 UL)![]() Distler, Verena ![]() ![]() in Proceedings of the 2018 CHI Conference on Human Factors in Computing Systems (2018, April) Autonomous vehicles have the potential to fundamentally change existing transportation systems. Beyond legal concerns, these societal evolutions will critically depend on user acceptance. As an emerging ... [more ▼] Autonomous vehicles have the potential to fundamentally change existing transportation systems. Beyond legal concerns, these societal evolutions will critically depend on user acceptance. As an emerging mode of public transportation [7], Autonomous mobility on demand (AMoD) is of particular interest in this context. The aim of the present study is to identify the main components of acceptability (before first use) and acceptance (after first use) of AMoD, following a user experience (UX) framework. To address this goal, we conducted three workshops (N=14) involving open discussions and a ride in an experimental autonomous shuttle. Using a mixed-methods approach, we measured pre-immersion acceptability before immersing the participants in an on-demand transport scenario, and eventually measured post-immersion acceptance of AMoD. Results show that participants were reassured about safety concerns, however they perceived the AMoD experience as ineffective. Our findings highlight key factors to be taken into account when designing AMoD experiences. [less ▲] Detailed reference viewed: 133 (15 UL)![]() ; ; et al in Pimienta, P M (Ed.) 10th World Congress on Computational Mechanics (WCCM 2012) (2012) Detailed reference viewed: 289 (1 UL)![]() ; ; et al in Bordas, Stéphane; Kerfriden, P (Eds.) 2nd International Conference on the Extended Finite Element Method (2011) Detailed reference viewed: 122 (0 UL)![]() ; ; Bordas, Stéphane ![]() in Oliver, J; Jirasek, M; Allix, O (Eds.) et al Computational Modeling of Fracture and Failure of Materials and Structures. Proceedings of CFRAC 2011 (2011) During the last years the use of error estimators which measure the error in a quantity of interest defined by the analyst, instead of the energy norm, have become increasingly popular as they provide an ... [more ▼] During the last years the use of error estimators which measure the error in a quantity of interest defined by the analyst, instead of the energy norm, have become increasingly popular as they provide an error indicator for goal oriented adaptivity procedures. In this paper we propose an a posteriori recovery-based error estimation procedure which considers the stress intensity factor K typical of singular problems as the quantity of interest in finite element (FE) approximations. In general, error estimators in quantities of interest have been based on residual techniques and, although recovery techniques have been often preferred when considering the error in energy norm due to their robustness and simplicity, so far, there is no available procedure which considers an equilibrated recovery technique that can be used in standard FE frameworks. In [1] a standard SPR recovery technique is used to obtain an error measure of the J-integral, which is closely related to the value of the SIF. However, it does not consider any equilibrium constraints or the singularity near the crack tip, thus the obtained recovered stress field is not well suited for this kind of problems. The technique proposed herein relies on the enhanced superconvergent patch recovery technique presented in [2] to evaluate highly accurate recovered stress fields of the primal and dual problems, which are then used to obtain a sharp error estimate. The primal problem is simply the problem under analysis. To formulate the dual problem we consider the linear interaction integral representing K to obtain the applied loads of the dual FE approximation to solve. The high accuracy of the recovered stress fields for both the primal and dual solutions is obtained by decomposing the raw stress field obtained from the finite element approximations into singular and smooth parts, and enforcing the fulfilment of boundary and internal equilibrium equations. The results indicate an accurate estimation of the error in K for benchmark problems with exact solution. [less ▲] Detailed reference viewed: 138 (1 UL)![]() ; ; Bordas, Stéphane ![]() in International Journal for Numerical Methods in Engineering (2011), 86(2), 249-268 Fracture modelling using numerical methods is well-advanced in 2D using techniques such as the extended finite element method (XFEM). The use of meshless methods for these problems lags somewhat behind ... [more ▼] Fracture modelling using numerical methods is well-advanced in 2D using techniques such as the extended finite element method (XFEM). The use of meshless methods for these problems lags somewhat behind, but the potential benefits of no meshing (particularly in 3D) prompt continued research into their development. In methods where the crack face is not explicitly modelled (as the edge of an element for instance), two procedures are instead used to associate the displacement jump with the crack surface: the visibility criterion and the diffraction method. The visibility criterion is simple to implement and efficient to compute, especially with the help of level set coordinates. However, spurious discontinuities have been reported around crack tips using the visibility criterion, whereas implementing the diffraction method in 3D is much more complicated than the visibility criterion. In this paper, a tying procedure is proposed to remove the difficulty with the visibility criterion so that crack tip closure can be ensured while the advantages of the visibility criterion can be preserved. The formulation is based on the use of level set coordinates and the element-free Galerkin method, and is generally applicable for single or multiple crack problems in 2D or 3D. The paper explains the formulation and provides verification of the method against a number of 2D crack problems. [less ▲] Detailed reference viewed: 131 (3 UL)![]() Bourantas, Georgios ![]() in Journal of Computational Physics (2009), 228 The aim of the present paper is the development of an efficient numerical algorithm for the solution of magnetohydrodynamics flow problems for regular and irregular geometries subject to Dirichlet ... [more ▼] The aim of the present paper is the development of an efficient numerical algorithm for the solution of magnetohydrodynamics flow problems for regular and irregular geometries subject to Dirichlet, Neumann and Robin boundary conditions. Toward this, the meshless point collocation method (MPCM) is used for MHD flow problems in channels with fully insulating or partially insulating and partially conducting walls, having rectangular, circu- lar, elliptical or even arbitrary cross sections. MPC is a truly meshless and computationally efficient method. The maximum principle for the discrete harmonic operator in the mesh- free point collocation method has been proven very recently, and the convergence proof for the numerical solution of the Poisson problem with Dirichlet boundary conditions have been attained also. Additionally, in the present work convergence is attained for Neumann and Robin boundary conditions, accordingly. The shape functions are constructed using the Moving Least Squares (MLS) approximation. The refinement procedure with meshless methods is obtained with an easily handled and fully automated manner. We present results for Hartmann number up to 105 . The numerical evidences of the proposed meshless method demonstrate the accuracy of the solutions after comparing with the exact solution and the conventional FEM and BEM, for the Dirichlet, Neumann and Robin boundary con- ditions of interior problems with simple or complex boundaries. [less ▲] Detailed reference viewed: 120 (1 UL)![]() Bommaraveni, Srikanth ![]() Scientific Conference (2019, November 03) Edge caching has received much attention as an effective solution to face the stringent latency requirements in 5G networks due to the proliferation of handset devices as well as data-hungry applications ... [more ▼] Edge caching has received much attention as an effective solution to face the stringent latency requirements in 5G networks due to the proliferation of handset devices as well as data-hungry applications. One of the challenges in edge caching systems is to optimally cache strategic contents to maximize the percentage of total requests served by the edge caches. To enable the optimal caching strategy, we propose an Active Learning approach (AL) to learn and design an accurate content request prediction algorithm. Specifically, we use an AL based Query-by-committee (QBC) matrix completion algorithm with a strategy of querying the most informative missing entries of the content popularity matrix. The proposed AL framework leverage's the trade-off between exploration and exploitation of the network, and learn the user's preferences by posing queries or recommendations. Later, it exploits the known information to maximize the system performance. The effectiveness of proposed AL based QBC content learning algorithm is demonstrated via numerical results. [less ▲] Detailed reference viewed: 91 (14 UL)![]() Bommaraveni, Srikanth ![]() ![]() ![]() Scientific Conference (2020, October 08) Edge caching is a promising technology to facethe stringent latency requirements and back-haul trafficoverloading in 5G wireless networks. However, acquiringthe contents and modeling the optimal cache ... [more ▼] Edge caching is a promising technology to facethe stringent latency requirements and back-haul trafficoverloading in 5G wireless networks. However, acquiringthe contents and modeling the optimal cache strategy is achallenging task. In this work, we use an active learningapproach to learn the content popularities since it allowsthe system to leverage the trade-off between explorationand exploitation. Exploration refers to caching new fileswhereas exploitation use known files to cache, to achievea good cache hit ratio. In this paper, we mainly focus tolearn popularities as fast as possible while guaranteeing anoperational cache hit ratio constraint. The effectiveness ofproposed learning and caching policies are demonstratedvia simulation results as a function of variance, cache hitratio and used storage. [less ▲] Detailed reference viewed: 90 (7 UL)![]() Sprumont, François ![]() Doctoral thesis (2017) Travel behaviour analysis is a complex task because of the myriad of determinants influencing decision makers. The commuting trip constitutes an important travel purpose, but is not the dominant one ... [more ▼] Travel behaviour analysis is a complex task because of the myriad of determinants influencing decision makers. The commuting trip constitutes an important travel purpose, but is not the dominant one. Because of its spatial and temporal concentration, the commuting flow is an ideal target for mobility management measures aiming at decreasing its negative externalities. Nevertheless, commuting travels are done in the frame of a more complex activity-travel chain, and some choices, whether on the short term (e.g. commuting mode choice) or in the longer term (e.g. where to live, buy a car) are done considering an ensemble of trips. Our research hypothesis is that workplace relocation, or more generally an event that strongly affects travellers’ trip chains, induces different and interrelated responses. Our research aim is to gain insight into this complex decision-making process, in order to better understand its relation with transport policy measures. [less ▲] Detailed reference viewed: 217 (19 UL)![]() Eisenbart, Boris ![]() ![]() ![]() in Proceedings of 19th International Conference on Engineering Design (2013) Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. The IFM framework intends to support ... [more ▼] Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. The IFM framework intends to support interdisciplinary collaboration of designers, by linking the different functional modelling perspectives, which are prominent in the different disciplines. The presented analysis aims to answer the question, which particular adaptations are required, in order to enable and improve the application of the IFM framework across disciplines. The paper presents a comparison of the framework with established functional approaches proposed in literature. It is shown, in which ways the specific contents addressed in the individual steps of the reviewed functional approaches can be mapped onto corresponding views in the IFM framework. The findings suggest that the IFM framework is interoperable with the reviewed functional approaches without necessitating fundamental changes. Furthermore, specific potentials for the improvement of its applicability across disciplines are derived. Finally, the paper discusses specific adaptations of the IFM framework, in order to improve its applicability. [less ▲] Detailed reference viewed: 113 (9 UL) |
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