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See detailProceedings of the BIVEC-GIBET Transport Research Days 2013
Hesse, Markus UL; Caruso, Geoffrey UL; Gerber, Philippe et al

Book published by University Press (2013)

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See detailProcess analysis in thermal process engineering with high-performance computing using the example of grate firing
Peters, Bernhard UL; Rousset, Alban UL; Besseron, Xavier UL et al

in Process analysis in thermal process engineering with high- performance computing using the example of grate firing (in press)

Biomass as a renewable energy source continues to grow in popularity to reduce fossil fuel consumption for environmental and economic benefits. In the present contribution, the combustion chamber of a 16 ... [more ▼]

Biomass as a renewable energy source continues to grow in popularity to reduce fossil fuel consumption for environmental and economic benefits. In the present contribution, the combustion chamber of a 16 MW geothermal steam super-heater, which is part of the Enel Green Power "Cornia 2" power plant, is being investigated with high-performance computing methods. For this purpose, the extended discrete element method (XDEM) developed at the University of Luxembourg is used in a high-performance computing environment, which includes both the moving wooden bed and the combustion chamber above it. The XDEM simulation platform is based on a hybrid four-way coupling between the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). In this approach, particles are treated as discrete elements that are coupled by heat, mass, and momentum transfer to the surrounding gas as a continuous phase. For individual wood particles, besides the equations of motion, the differential conservation equations for mass, heat, and momentum are solved, which describe the thermodynamic state during thermal conversion. The consistency of the numerical results with the actual system performance is discussed in this paper to determine the potentials and limitations of the approach. [less ▲]

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See detailProcess Reference Model "IT Grundschutz"
Asselborn, Jean-Claude; Dagorn, Nathalie; Niederkorn, Philippe et al

Report (2006)

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See detailProcess Reference Model "Mehari"
Asselborn, Jean-Claude; Dagorn, Nathalie; Niederkorn, Philippe et al

Report (2006)

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See detailProgramming the material point method in Julia
Sinaie, Sina; Nguyen, Viet Ha UL; Nguyen, Chi Thanh et al

in Advances in Engineering Software (2017), 105

This article presents the implementation of the material point method (MPM) using Julia. Julia is an open source, multi-platform, high-level, high-performance dynamic programming language for technical ... [more ▼]

This article presents the implementation of the material point method (MPM) using Julia. Julia is an open source, multi-platform, high-level, high-performance dynamic programming language for technical computing, with syntax that is familiar to Matlab and Python programmers. MPM is a hybrid particle-grid approach that combines the advantages of Eulerian and Lagrangian methods and is suitable for complex solid mechanics problems involving contact, impact and large deformations. We will show that a Julia based MPM code, which is short, compact and readable and uses only Julia built in features, performs much better (with speed up of up to 8) than a similar Matlab based MPM code for large strain solid mechanics simulations. We share our experiences of implementing MPM in Julia and demonstrate that Julia is a very interesting platform for rapid development in the field of scientific computing. [less ▲]

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See detailProject Advanced Discretisaztion Methods
Farina, Sofia UL

Presentation (2019, February 01)

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See detailProjection-based reduction of fluid-structure interaction systems using monolithic space-time modes
Zilian, Andreas UL; Dinkler, D.; Vehre, A.

in Computer Methods in Applied Mechanics & Engineering (2009), 198(47-48), 3795-3805

The focus of this work is the development of reduced models for engineering applications in complex bidirectional fluid-structure interaction. In the simultaneous solution procedure, velocity variables ... [more ▼]

The focus of this work is the development of reduced models for engineering applications in complex bidirectional fluid-structure interaction. In the simultaneous solution procedure, velocity variables are used for both fluid and solid, and the whole set of model equations is discretized by a stabilized time-discontinuous space-time finite element method. Flexible structures are modeled using a three-dimensional continuum approach in a total Lagrangian setting considering large displacements and rotations. In the flow domain the incompressible Navier-Stokes equations describe the Newtonian fluid. A continuous finite element mesh is applied to the entire spatial domain, and the discretized model equations are assembled in a single set of algebraic equations, considering the two-field problem as a whole. The continuous fluid-structure mesh with identical orders of approximation for both solid and fluid in space and time automatically yields conservation of mass, momentum and energy at the fluid-structure interface. A mesh-moving scheme is used to adapt the nodal coordinates of the fluid space-time finite element mesh to the structural deformation. The computational approach for strongly coupled fluid-structure interaction is used to create suitable reduced models of generic nonlinear problems. Reduction is performed with monolithic projection-based space-time modes, ensuring strong coupling of fluid and structure in the reduced model. The contribution discusses results using proper orthogonal decomposition (POD) for determination of monolithic space-time modes in the reduction of fluid-structure systems. © 2009 Elsevier B.V. All rights reserved. [less ▲]

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See detailThe provision of urban green space and its accessibility: Spatial data effects in Brussels
Le Texier, Marion UL; Schiel, Kerry UL; Caruso, Geoffrey UL

in PLoS ONE (2018), 13(10), 0204684

Urban green space (UGS) has many environmental and social benefits. UGS provision and access are increasingly considered in urban policies and must rely on data and indicators that can capture variations ... [more ▼]

Urban green space (UGS) has many environmental and social benefits. UGS provision and access are increasingly considered in urban policies and must rely on data and indicators that can capture variations in the distribution of UGS within cities. There is no consensus about how UGS, and their provision and access, must be defined from different land use data types. Here we identify four spatial dimensions of UGS and critically examine how different data sources affect these dimensions and our understanding of their variation within a city region (Brussels). We compare UGS indicators measured from an imagery source (NDVI from Landsat), an official cadastre-based map, and the voluntary geographical information provided by OpenStreetMap (OSM). We compare aggregate values of provision and access to UGS as well as their spatial distribution along a centrality gradient and at neighbourhood scale. We find that there are strong differences in the value of indicators when using the different datasets, especially due to their ability to capture private and public green space. However we find that the interpretation of intra-urban spatial variations is not affected by changes in data source. Centrality in particular is a strong determinant of the relative values of UGS availability, fragmentation and accessibility, irrespective of datasets. [less ▲]

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See detailPublic Transport in the Era of ITS: ITS Technologies for Public Transport
Monzon, Andres; Hernandez, Sara; Martinez, Andres et al

in Gentile, Guido; Klaus, Noekel (Eds.) Public Transport in the Era of ITS (2016)

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See detailPublic Transport in the Era of ITS: The Role of Public Transport in Sustainable Cities and Regions
Rosello, Xavier; Langeland, Anders; Viti, Francesco UL

in Public Transport in the Era of ITS (2016)

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See detailQuadratic Surface Lyapunov Functions in Global Stability Analysis of Saturation Systems
Goncalves, Jorge UL

in Proceedings of the American Control Conference (2001)

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See detailQuadratic Surface Lyapunov Functions in the Analysis of Feedback Systems with Double Integrators and Saturations
Goncalves, Jorge UL

in Proceedings of the 10th IEEE Mediterranean Conference on Control and Automation (2002)

Many systems like servo systems, satellites, harddisks, and CD players, can be modeled as linear systems with a single integrator and a saturation. Many times, such systems are controlled with a PI ... [more ▼]

Many systems like servo systems, satellites, harddisks, and CD players, can be modeled as linear systems with a single integrator and a saturation. Many times, such systems are controlled with a PI controller resulting in a feedback interconnection with a double integrator and a saturation. In this paper, we propose a loop transformation that results in bounded operators so that classical analysis tools like mu􀀀-analysis or IQCs can be applied. In order to show boundedness of all operators, we use quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2 􀀀-gain less than gamma > 0 􀀀. We show that for many of such systems, the L2 􀀀-gain is non-conservative in the sense that this is approximately equal to the lower bound obtained by replacing the saturation with a constant gain of . [less ▲]

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See detailQualifying and Measuring Transparency: A Medical Data System Case Study
Spagnuelo, Dayana; Bartolini, Cesare UL; Lenzini, Gabriele UL

in Computers and Security (2020)

Transparency is a data processing principle enforced by the GDPR but purposely left open to interpretation. As such, the means to adhere to it are left unspecified. Article 29 Working Party provides ... [more ▼]

Transparency is a data processing principle enforced by the GDPR but purposely left open to interpretation. As such, the means to adhere to it are left unspecified. Article 29 Working Party provides practical guidance on how to interpret transparency, however there are no defined requirements nor ways to verify the quality of the implementation of transparency. We address this problem. We discuss and define applicable metrics for transparency, propose how measurement can be conducted in an operative system, and suggest a practical way in which these metrics can be interpreted in order to increase confidence that transparency is realised in a system. [less ▲]

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See detailQuantifying partial observability in network sensor location problems
Viti, Francesco UL; Rinaldi, Marco; Corman, Francesco

Scientific Conference (2013)

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See detailQuantitative Assignment of Reaction Directionality in a Multicompartmental Human Metabolic Reconstruction
Haraldsdottir, Hulda UL; Thiele, Ines UL; Fleming, Ronan MT UL

in Biophysical Journal (2012), 102(8), 17031711

Reaction directionality is a key constraint in the modeling of genome-scale metabolic networks. We thermodynamically constrained reaction directionality in a multicompartmental genome-scale model of human ... [more ▼]

Reaction directionality is a key constraint in the modeling of genome-scale metabolic networks. We thermodynamically constrained reaction directionality in a multicompartmental genome-scale model of human metabolism, Recon 1, by calculating, in vivo, standard transformed reaction Gibbs energy as a function of compartment-specific pH, electrical potential, and ionic strength. We show that compartmental pH is an important determinant of thermodynamically determined reaction directionality. The effects of pH on transport reaction thermodynamics are only seen to their full extent when metabolites are represented as pseudoisomer groups of multiple protonated species. We accurately predict the irreversibility of 387 reactions, with detailed propagation of uncertainty in input data, and manually curate the literature to resolve conflicting directionality assignments. In at least half of all cases, a prediction of a reversible reaction directionality is due to the paucity of compartment-specific quantitative metabolomic data, with remaining cases due to uncertainty in estimation of standard reaction Gibbs energy. This study points to the pressing need for 1), quantitative metabolomic data, and 2), experimental measurement of thermochemical properties for human metabolites. [less ▲]

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See detailQuasi-dynamic traffic assignment with spatial queueing, control and blocking back
Smith, Mike; Huang, Wei; Viti, Francesco UL et al

in Transportation Research. Part B, Methodological (2019)

This paper introduces a steady-state, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queueing delays and explicit bounds on queue storage ... [more ▼]

This paper introduces a steady-state, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queueing delays and explicit bounds on queue storage capacities. The model is a quasi-dynamic model. The link model at the heart of this quasi-dynamic equilibrium model is a spatial queueing model, which takes account of the space taken up by queues both when there is no blocking back and also when there is blocking back. The paper shows that if this quasi-dynamic model is utilised then for any feasible demand there is an equilibrium solution, provided (i) queue storage capacities are large or (ii) prices are used to help impose capacity restrictions; the prices either remove queueing delays entirely or just reduce spatial queues sufficiently to ensure that blocking back does not occur at equilibrium. Similar results, but now involving the P0 control policy (introduced in Smith (1979a, 1987)) and two new variations of this policy (i.e., the spatial P0 control policy, and the biased spatial P0 control policy) are obtained. In these results, the control policies allow green-times to vary in response to prices as well as spatial queueing delays. These three policies are also tested on a small simple network. In these tests, the biased spatial version of P0 is much the best in reducing equilibrium delays (on this simple network). The paper further illustrates how the spatial queueing model works on simple networks with different merge models; it is demonstrated that equilibrium may be prevented by certain (fixed ratio) merge models. It is also shown in this case that equilibrium may be imposed on just the controlled area itself by a variety of (merge model, gating strategy) combinations. Opportunities for developing such combined gating and merging control strategies are finally discussed. [less ▲]

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See detailQuasicontinuum methods for planar beam lattices (abstract)
Beex, Lars UL; Kerfriden, Pierre; Heaney, Claire et al

Scientific Conference (2015, July)

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See detailQuizbot: Exploring Formative Feedback with Conversational Interfaces
Vijayakumar, Bharathi UL; Höhn, Sviatlana UL; Schommer, Christoph UL

in Vijayakumar, Bharathi; Höhn, Sviatlana; Schommer, Christoph (Eds.) Proceedings of the (2018)

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See detailRandomised controlled non-inferiority trial of primary care-based facilitated access to an alcohol reduction website: cost-effectiveness analysis
Hunter, Rachael; Wallace, Paul; Struzzo, Pierluigi et al

in BMJ Open (2017), 7(11),

Objectives To evaluate the 12-month costs and quality-adjusted life years (QALYs) gained to the Italian National Health Service of facilitated access to a website for hazardous drinkers compared with a ... [more ▼]

Objectives To evaluate the 12-month costs and quality-adjusted life years (QALYs) gained to the Italian National Health Service of facilitated access to a website for hazardous drinkers compared with a standard face-to-face brief intervention (BI). Design Randomised 1:1 non-inferiority trial. Setting Practices of 58 general practitioners (GPs) in Italy. Participants Of 9080 patients (>18 years old) approached to take part in the trial, 4529 (49·9%) logged on to the website and 3841 (84.8%) undertook online screening for hazardous drinking. 822 (21.4%) screened positive and 763 (19.9%) were recruited to the trial. Interventions Patients were randomised to receive either a face-to-face BI or access via a brochure from their GP to an alcohol reduction website (facilitated access). Primary and secondary outcome measures The primary outcome is the cost per QALY gained of facilitated access compared with face-to-face. A secondary analysis includes total costs and benefits per 100 patients, including number of hazardous drinkers prevented at 12 months. Results The average time required for the face-to-face BI was 8 min (95% CI 7.5 min to 8.6 min). Given the maximum time taken for facilitated access of 5 min, face-to-face is an additional 3 min: equivalent to having time for another GP appointment for every three patients referred to the website. Complete case analysis adjusting for baseline the difference in QALYs for facilitated access is 0.002 QALYs per patient (95% CI −0.007 to 0.011). Conclusions Facilitated access to a website to reduce hazardous drinking costs less than a face-to-face BI given by a GP with no worse outcomes. The lower cost of facilitated access, particularly in regards to investment of time, may facilitate the increase in provision of BIs for hazardous drinking. Trial registration number NCT01638338;Post-results. [less ▲]

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