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See detailEfficient 3D transfer operators based on numerical integration
Bussetta, Philippe ULg; Boman, Romain ULg; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2015), 102(3-4), 892-929

This paper deals with data transfer between two meshes as it happens in a finite element context when a remeshing has to be performed. We propose a finite-volume-based data transfer method for an ... [more ▼]

This paper deals with data transfer between two meshes as it happens in a finite element context when a remeshing has to be performed. We propose a finite-volume-based data transfer method for an efficient remeshing of three-dimensional solid mechanics problems. The originality of this transfer method stems from a linear reconstruction of the fields to be transferred on an auxiliary finite volume mesh, a fast computation of the transfer operator and the application to the complete remeshing of 3D problems. This procedure is applicable to both nodal values and discrete fields defined at quadrature points. In addition, a data transfer method using mortar elements is presented. The main improvement made to this second method comes from a fast computation of mortar elements. These two data transfer methods are compared with the simplest transfer method, which consists of a classical interpolation. After some academic examples, we present 2D forging and 3D friction stir welding applications. [less ▲]

Detailed reference viewed: 23 (2 ULg)
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See detailEfficient access pricing and endogenous market structure
Gautier, Axel ULg

Poster (2010, May)

We investigate how a regulatory mechanism can influence the nature of competition in a network industry. In the downstream market, the seller of a differentiated retail product competes with an incumbent ... [more ▼]

We investigate how a regulatory mechanism can influence the nature of competition in a network industry. In the downstream market, the seller of a differentiated retail product competes with an incumbent firm. The incumbent firm is also the owner of the essential input. The regulator may or may not observe the cost of the entrant. To maximize social welfare the regulator specifies the access charge that the entrant must pay to the incumbent, and the retail prices. The optimal access charge is a uniform price that respects the criteria of transparency and non-discrimination that are imposed by the competition and regulation directives in most countries. We derive new formulas for retail and access prices adhering to the traditional Ramsey rule. Since the competing firm takes the decision to enter following the choice of the regulatory regime, the nature of the retail market competition is endogenous [less ▲]

Detailed reference viewed: 15 (1 ULg)
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See detailEfficient ALE mesh management for 3D quasi-Eulerian problems
Boman, Romain ULg; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2012), 92(10), 857-890

In computational solid mechanics, the ALE formalism can be very useful to reduce the size of finite element models of continuous forming operations such as roll forming. The mesh of these ALE models is ... [more ▼]

In computational solid mechanics, the ALE formalism can be very useful to reduce the size of finite element models of continuous forming operations such as roll forming. The mesh of these ALE models is said to be quasi-Eulerian because the nodes remain almost fixed—or almost Eulerian—in the main process direction, although they are required to move in the orthogonal plane in order to follow the lateral displacements of the solid. This paper extensively presents a complete node relocation procedure dedicated to such ALE models. The discussion focusses on quadrangular and hexahedral meshes with local refinements. The main concern of this work is the preservation of the geometrical features and the shape of the free boundaries of the mesh. With this aim in view, each type of nodes (corner, edge, surface and volume) is treated sequentially with dedicated algorithms. A special care is given to highly curved 3D surfaces for which a CPU-efficient smoothing technique is proposed. This new method relies on a spline surface reconstruction, on a very fast weighted Laplacian smoother with original weights and on a robust reprojection algorithm. The overall consistency of this mesh management procedure is finally demonstrated in two numerical applications. The first one is a 2D ALE simulation of a drawbead, which provides similar results to an equivalent Lagrangian model yet is much faster. The second application is a 3D industrial ALE model of a 16-stand roll forming line. In this case, all attempts to perform the same simulation by using the Lagrangian formalism have been unsuccessful. [less ▲]

Detailed reference viewed: 53 (15 ULg)
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See detailAn efficient algorithm for the provision of a day-ahead modulation service by a load aggregator
Mathieu, Sébastien ULg; Ernst, Damien ULg; Louveaux, Quentin ULg

in Proceedings of the 4th European Innovative Smart Grid Technologies (ISGT) (2013, October)

This article studies a decision making problem faced by an aggregator willing to offer a load modulation service to a Transmission System Operator. This service is contracted one day ahead and consists in ... [more ▼]

This article studies a decision making problem faced by an aggregator willing to offer a load modulation service to a Transmission System Operator. This service is contracted one day ahead and consists in a load modulation option, which can be called once per day. The option specifies the range of a potential modification on the demand of the loads within a certain time interval. The specific case where the loads can be modeled by a generic tank model is considered. Under this assumption, the problem of maximizing the range of the load modulation service can be formulated as a mixed integer linear programming problem. A novel heuristic-method is proposed to solve this problem in a computationally efficient manner. This method is tested on a set of problems. The results show that this approach can be orders of magnitude faster than CPLEX without significantly degrading the solution accuracy. [less ▲]

Detailed reference viewed: 134 (34 ULg)
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See detailAn efficient algorithm to perform multiple testing in epistasis screening
Van Lishout, François ULg; Mahachie John, Jestinah ULg; Gusareva, Elena ULg et al

in BMC Bioinformatics (2013), 14

Background: Research in epistasis or gene-gene interaction detection for human complex traits has grown over the last few years. It has been marked by promising methodological developments, improved ... [more ▼]

Background: Research in epistasis or gene-gene interaction detection for human complex traits has grown over the last few years. It has been marked by promising methodological developments, improved translation efforts of statistical epistasis to biological epistasis and attempts to integrate different omics information sources into the epistasis screening to enhance power. The quest for gene-gene interactions poses severe multiple-testing problems. In this context, the maxT algorithm is one technique to control the false-positive rate. However, the memory needed by this algorithm rises linearly with the amount of hypothesis tests. Gene-gene interaction studies will require a memory proportional to the squared number of SNPs. A genome-wide epistasis search would therefore require terabytes of memory. Hence, cache problems are likely to occur, increasing the computation time. In this work we present a new version of maxT, requiring an amount of memory independent from the number of genetic effects to be investigated. This algorithm was implemented in C++ in our epistasis screening software MBMDR-3.0.3. We evaluate the new implementation in terms of memory efficiency and speed using simulated data. The software is illustrated on real-life data for Crohn's disease. Results: In the case of a binary (affected/unaffected) trait, the parallel workflow of MBMDR-3.0.3 analyzes all gene-gene interactions with a dataset of 100,000 SNPs typed on 1000 individuals within 4 days and 9 hours, using 999 permutations of the trait to assess statistical significance, on a cluster composed of 10 blades, containing each four Quad-Core AMD Opteron Processor 2352 2.1 GHz. In the case of a continuous trait, a similar run takes 9 days. Our program found 14 SNP-SNP interactions with a multiple-testing corrected p-value of less than 0.05 on real-life Crohn's disease data. Conclusions: Our software is the first implementation of the MB-MDR methodology able to solve large-scale SNP-SNP interactions problems within a few days, without using much memory, while adequately controlling the type I error rates. A new implementation to reach genome-wide epistasis screening is under construction. In the context of Crohn's disease, MBMDR-3.0.3 could identify epistasis involving regions that are well known in the field and could be explained from a biological point of view. This demonstrates the power of our software to find relevant phenotype-genotype higher-order associations. [less ▲]

Detailed reference viewed: 58 (17 ULg)
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See detailAn Efficient Algorithm to Perform Multiple Testing in Epistasis Screening
Van Lishout, François ULg; Cattaert, Tom ULg; Mahachie John, Jestinah ULg et al

Conference (2011, December 13)

Background: Research in epistasis or gene-gene interaction detection for human complex traits has grown exponentially over the last few years. It has been marked by promising methodological developments ... [more ▼]

Background: Research in epistasis or gene-gene interaction detection for human complex traits has grown exponentially over the last few years. It has been marked by promising methodological developments, improved translation efforts of statistical epistasis to biological epistasis and attempts to integrate different omics information sources into the epistasis screening to enhance power. The quest for gene-gene interactions poses severe multiple-testing problems. In this context, the maxT algorithm is one technique to control the false-positive rate. However, the memory needed by this algorithm rises linearly with the amount of hypothesis tests. In main-effects detection, this is not a problem since the memory required is thus proportional to the number of SNPs. In contrast, gene-gene interaction studies will require a memory proportional to the squared amount of SNPs. A genome wide epistasis would therefore require terabytes of memory. Hence, cache problems are likely to occur, increasing the computation time. Methods: In this work we present a new version of maxT, requiring an amount of memory independent from the number of genetic effects to be investigated. This algorithm was implemented in C++ in our epistasis screening software MB-MDR-2.6.2 and compared to MB-MDR's first implementation as an R-package (Calle et al., Bioinformatics 2010). We evaluate the new implementation in terms of memory efficiency and speed using simulated data. The software is illustrated on real-life data for Crohn's disease. Results: The sequential version of MBMDR-2.6.2 is approximately 5,500 times faster than its R counterparts. The parallel version (tested on a cluster composed of 14 blades, containing each 4 quad-cores Intel Xeon CPU E5520@2.27 GHz) is approximately 900,000 times faster than the latter, for results of the same quality on the simulated data. It analyses all gene-gene interactions of a dataset of 100,000 SNPs typed on 1000 individuals within 4 days. Our program found 14 SNP-SNP interactions with a p-value less than 0.05 on the real-life Crohn’s disease data. Conclusions: Our software is able to solve large-scale SNP-SNP interactions problems within a few days, without using much memory. A new implementation to reach genome wide epistasis screening is under construction. In the context of Crohn's disease, MBMDR-2.6.2 found signal in regions well known in the field and our results could be explained from a biological point of view. This demonstrates the power of our software to find relevant phenotype-genotype associations. [less ▲]

Detailed reference viewed: 59 (25 ULg)
See detailEfficient algorithmic approach for mixed lubrication in cold rolling
STEPHANY, A.; Ponthot, Jean-Philippe ULg; COLLETTE, C. et al

in Proceedings of AMPT 2003, Advances in Materials and Processing Technologies (2003)

Detailed reference viewed: 7 (1 ULg)
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See detailEfficient algorithmic approach for mixed-lubrication in cold rolling
Stephany, A.; Ponthot, Jean-Philippe ULg; Collette, C. et al

in Journal of Materials Processing Technology (2004), 153(1), 307-313

A model of cold rolling taking into account lubrication in mixed mode was developed. The main objective is to obtain a numerical tool that permits us to optimise a mill configuration from the lubrication ... [more ▼]

A model of cold rolling taking into account lubrication in mixed mode was developed. The main objective is to obtain a numerical tool that permits us to optimise a mill configuration from the lubrication point of view. It means that lubricant viscosity but also roll diameter and roughness, rolling diagrams, etc could be modified to improve stability and efficiency of the mill. A modified slab method is solved iteratively and is coupled with a sophisticated tribological model. A general calculation of the modified Reynolds equation is presented in order to evaluate the fluid pressure for any piezoviscosity law. The coupling is made through the calculation of fluid thickness and friction along the roll bite. The evolution of the cylinder/strip contact area due to the asperity crushing along the roll bite is also considered. A parametric study has been undertaken in order to determine the influence of various process parameters on friction and lubricant flow. Applications to industrial cases obtained from Cockerill Sambre plant will show the applicability of the method. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailEfficient Algorithms for Large-Scale Topology Discovery
Donnet, Benoît ULg; Raoult, Philippe; Friedman, Timur et al

in ACM SIGMETRICS International Conference on Measurement and Modeling of Computer Systems (2005, June)

There is a growing interest in discovery of internet topology at the interface level. A new generation of highly distributed measurement systems is currently being deployed. Unfortunately, the research ... [more ▼]

There is a growing interest in discovery of internet topology at the interface level. A new generation of highly distributed measurement systems is currently being deployed. Unfortunately, the research community has not examined the problem of how to perform such measurements efficiently and in a network-friendly manner. In this paper we make two contributions toward that end. First, we show that standard topology discovery methods (e.g., skitter) are quite inefficient, repeatedly probing the same interfaces. This is a concern, because when scaled up, such methods will generate so much traffic that they will begin to resemble DDoS attacks. We measure two kinds of redundancy in probing (intra- and inter-monitor) and show that both kinds are important. We show that straightforward approaches to addressing these two kinds of redundancy must take opposite tacks, and are thus fundamentally in conflict. Our second contribution is to propose and evaluate Doubletree, an algorithm that reduces both types of redundancy simultaneously on routers and end systems. The key ideas are to exploit the tree-like structure of routes to and from a single point in order to guide when to stop probing, and to probe each path by starting near its midpoint. Our results show that Doubletree can reduce both types of measurement load on the network dramatically, while permitting discovery of nearly the same set of nodes and links. [less ▲]

Detailed reference viewed: 20 (0 ULg)
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See detailEfficient and Resilient Overlay Topologies over Ad Hoc Networks
Calomme, Sandrine; Leduc, Guy ULg

in Lecture Notes in Computer Science (2007, September), 4725

We discuss what kind of overlay topology should be pro-actively built before an overlay routing protocol enters a route search process on top of it. The basic overlay structures we study are the K-Nearest ... [more ▼]

We discuss what kind of overlay topology should be pro-actively built before an overlay routing protocol enters a route search process on top of it. The basic overlay structures we study are the K-Nearest Neighbours overlay topologies, connecting every overlay node to its K nearest peers. We introduce a family of optimizations, based on a pruning rule. As flooding is a key component of many route discovery mechanisms in MANETs, our performance study focusses on the delivery percentage, bandwidth consumption and time duration of flooding on the overlay. We also consider the overlay path stretch and the overlay nodes degree as respective indicators for the data transfer transmission time and overlay resilience. We finally recommend to optimize the K-Nearest Neighbours overlay topologies with the most selective pruning rule and, if necessary, to set a minimal bound on the overlay node degree for improving resilience. [less ▲]

Detailed reference viewed: 64 (2 ULg)
Peer Reviewed
See detailEfficient and robust simulation of tissue differentiation in fracture healing
Gerisch, Alf; Geris, Liesbet ULg

in Proceedings of the European Conference on Mathematical and Theoretical Biology (2005)

Detailed reference viewed: 2 (0 ULg)
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See detailAn efficient automata approach to some problems on context-free grammars
Bouajjani, Ahmed; Esparza, Javier; Finkel, Alain et al

in Information Processing Letters (2000), 74(5-6), 221-227

Book and Otto (1993) solve a number of word problems for monadic string-rewriting systems using an elegant automata-based technique. In this note we observe that the technique is also very interesting ... [more ▼]

Book and Otto (1993) solve a number of word problems for monadic string-rewriting systems using an elegant automata-based technique. In this note we observe that the technique is also very interesting from a pedagogical point of view, since it provides a uniform solution to several elementary problems on context-free languages. [less ▲]

Detailed reference viewed: 29 (0 ULg)
Peer Reviewed
See detailEfficient biochemical monitoring and survival assessment after an acute myocardial infarction
Albert, Adelin ULg; Chapelle, Jean-Paul ULg; Heusghem, C. et al

in Clinical Chemistry (1984), 5(abstr suppl.1), 187

Detailed reference viewed: 3 (0 ULg)
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See detailAn efficient biphasic synthesis of polymer-grafted reduced graphite oxide based nanocomposites
Vuluga, Daniela ULg; Thomassin, Jean-Michel ULg; Molenberg, Isabel et al

Conference (2011, June 01)

Detailed reference viewed: 51 (6 ULg)
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See detailAn efficient biphasic synthesis of polymer-grafted reduced graphite oxide based nanocomposites
Vuluga, Daniela ULg; Thomassin, Jean-Michel ULg; Molenberg, Isabel et al

Poster (2011, March 03)

Detailed reference viewed: 26 (4 ULg)