22 research outputs found
Railway Timetable Stability Analysis Using Stochastic Max-Plus Linear Systems
No full textStability and robustness of a railway timetable are essential properties for punctual and reliable operations. Timetable performance evaluation is therefore an important aspect in the timetable design process. In particular, the stability and recoverability properties of a timetable with respect to daily process time variations must be well analysed. The timetable must be able to recover from primary delays due to stochastic process times and it must be robust against secondary delays due to train interactions. This paper presents a stability analysis approach based on stochastic max-plus linear system theory. Stochastic counterparts of well-established concepts from the deterministic max-plus stability analysis are proposed, like timetable stability and realizability. General probability distributions can be used to model the primary stochastic behaviour of process times, while delay propagation due to timetable and infrastructure constraints are computed from the stochastic recursive system equations. Recently developed powerful algorithms can be utilized to analyse and improve large-scale stochastic systems, and to establish the amount of stochastic variations that a timetable can absorb without external control.Transport and PlanningCivil Engineering and Geoscience
On the convergence to equilibria of a sequence defined by an implicite scheme
No full textWe present numerical implicit scheme based on a geometric approach to the study of the convergence of solutions of gradient-like systems given in [2]. Depending on the globality of the induced metric, we can prove the convergence of these algorithms. Dedicated to the memory of Ezzeddine ZAHROUNI 1. Notation For a riemannian manifold (M, g) of dimension N we denote ·, · g the scalar product dened on each tangent space. The induced norm is denoted · g (or · when there is no risk of confusion) For a local system of coordinates on M , g ij will denote the coecient of the matrix dening the scalar product above. Let us recall that a C 1 curve x : [0, 1] → M is called a geodesic between x(0) and x(1) i it is a critical point of the functional L(γ) = 1 0 ||γ (t)|| g dt restricted to the C 1-curves γ : [0, 1] → M such that γ(0) = x(0) and γ(1) = x(1). For a dierentiable function f : M → R and p ∈ M we denote ∇ g f (p) the unique element of the tangent space T p M to M at p such that ∀u ∈ T p M, ∇ g f (p), u g = df (p).u 2. A implicit numerical scheme and main result of the paper Let us consider (M, g) a complete connected non compact riemaniann manifold and E a smooth real function. Associated to E, it is quite natural to consider the following gradient system (1)Ẋ(t) + ∇ g E(X(t)) = 0. In the paper [11] the authors Merlet & Pierre consider the situation when (M, g) is the standard R N with its natural euclidian structure and prove the convergence of a sequence dened by an implicit scheme associated to (1). It is quite natural to extend the scheme there introduced to the case of more general manifolds. Such insights were initially considered in [12] provided (M, g) is a submanifold of R N. However the specic case of the backward Euler scheme was not considered in this paper under the intrinsic point of view, i.e. the backward scheme is constructed ex post in [12], considering the embedded situation. Here we try to focus on the The rst author wishes to thanks the organizers of ICAAM 2019 in Hammamet, Tunisia, where this work was initiated. The second author wishes to thanks CNAM, France where this work was partially completed
On the convergence to equilibria of a sequence defined by an implicite scheme
No full textWe present numerical implicit scheme based on a geometric approach to the study of the convergence of solutions of gradient-like systems given in [2]. Depending on the globality of the induced metric, we can prove the convergence of these algorithms. Dedicated to the memory of Ezzeddine ZAHROUNI 1. Notation For a riemannian manifold (M, g) of dimension N we denote ·, · g the scalar product dened on each tangent space. The induced norm is denoted · g (or · when there is no risk of confusion) For a local system of coordinates on M , g ij will denote the coecient of the matrix dening the scalar product above. Let us recall that a C 1 curve x : [0, 1] → M is called a geodesic between x(0) and x(1) i it is a critical point of the functional L(γ) = 1 0 ||γ (t)|| g dt restricted to the C 1-curves γ : [0, 1] → M such that γ(0) = x(0) and γ(1) = x(1). For a dierentiable function f : M → R and p ∈ M we denote ∇ g f (p) the unique element of the tangent space T p M to M at p such that ∀u ∈ T p M, ∇ g f (p), u g = df (p).u 2. A implicit numerical scheme and main result of the paper Let us consider (M, g) a complete connected non compact riemaniann manifold and E a smooth real function. Associated to E, it is quite natural to consider the following gradient system (1)Ẋ(t) + ∇ g E(X(t)) = 0. In the paper [11] the authors Merlet & Pierre consider the situation when (M, g) is the standard R N with its natural euclidian structure and prove the convergence of a sequence dened by an implicit scheme associated to (1). It is quite natural to extend the scheme there introduced to the case of more general manifolds. Such insights were initially considered in [12] provided (M, g) is a submanifold of R N. However the specic case of the backward Euler scheme was not considered in this paper under the intrinsic point of view, i.e. the backward scheme is constructed ex post in [12], considering the embedded situation. Here we try to focus on the The rst author wishes to thanks the organizers of ICAAM 2019 in Hammamet, Tunisia, where this work was initiated. The second author wishes to thanks CNAM, France where this work was partially completed
Google Scholar as a source for citation and impact analysis for a non-ISI indexed medical journal
No full textIt is difficult to determine the influence and impact of journals which are not covered by the ISI databases and Journal Citation Report. However, with the availability of databases such as MyAIS (Malaysian Abstracting and Indexing System), which offers sufficient information to support bibliometric analysis as well as being indexed by Google Scholar which provides citation information, it has become possible to obtain productivity, citation and impact information for non-ISI indexed journals. The bibliometric tool Harzing's Publish and Perish was used to collate citation information from Google scholar. The study examines article productivity, the citations obtained by articles and calculates the impact factor of Medical Journal of Malaysia (MJM) published between 2004 and 2008. MJM is the oldest medical journal in Malaysia and the unit of analysis is 580 articles. The results indicate that once a journal is covered by MyAIS it becomes visible and accessible on the Web because Google Scholarindexes MyAIS. The results show that contributors to MJM were mainly Malaysian (91) and the number of Malaysian-Foreign collaborated papers were very small (28 articles, 4.8). However, citation information from Google scholar indicates that out of the 580 articles, 76.8 (446) have been cited over the 5-year period. The citations were received from both mainstrean foreign as well as Malaysian journals and the top three citors were from China, Malaysia and the United States. In general more citations were received from East Asian countries, Europe, and Southeast Asia. The 2-yearly impact factor calculated for MJM is 0.378 in 2009, 0.367 in 2008, 0.616 in 2007 and 0.456 in 2006. The 5-year impact factor is calculated as 0.577. The results show that although MJM is a Malaysian journal and not ISI indexed its contents have some international significance based on the citations and impact score it receives, indicating the importance of being visible especially in Google scholar
Melamine-Based Microporous Organic Framework Thin Films on an Alumina Membrane for High-Flux Organic Solvent Nanofiltration
No full textMicroporous polymer frameworks have attracted considerable attention to make novel separation layers owing to their highly porous structure, high permeability, and excellent molecular separation. This study concerns the fabrication and properties of thin melamine-based microporous polymer networks with a layer thickness of around 400 nm, supported on an α-alumina support and their potential use in organic solvent nanofiltration. The modified membranes show excellent solvent purification performances, such as n-heptane permeability as high as 9.2 L m−2 h−1 bar −1 in combination with a very high rejection of approximately 99 % for organic dyes with molecular weight of ≥457 Da. These values are higher than for the majority of the state-of-the-art membranes. The membranes further exhibit outstanding long-term operation stability. This work significantly expands the possibilities of using ceramic membranes in organic solvent nanofiltration.OLD ChemE/Organic Materials and Interface
Comparing the Performance of Organic Solvent Nanofiltration Membranes in Non-Polar Solvents
No full textOrganic solvent nanofiltration (OSN) is gradually expanding from academic research to industrial implementation. The need for membranes with low and sharp molecular weight cutoffs that are able to operate under aggressive OSN conditions is increasing. However, the lack of comparable and uniform performance data frustrates the screening and membrane selection for processes. Here, a collaboration is presented between several academic and industrial partners analyzing the separation performance of 10 different membranes using three model process mixtures. Membrane materials range from classic polymeric and thin film composites (TFCs) to hybrid ceramic types. The model solutions were chosen to mimic cases relevant to today's industrial use: relatively low molar mass solutes (330–550 Da) in n-heptane, toluene, and anisole.OLD ChemE/Organic Materials and InterfacesChemE/Advanced Soft Matte
MIL-53(Al) and NH<sub>2</sub>-MIL-53(Al) modified α-alumina membranes for efficient adsorption of dyes from organic solvents
No full text To the best of our knowledge, for the first time MIL-53(Al) and NH 2 -MIL-53(Al) modified α-alumina membranes are investigated for the adsorption of organic dyes from organic solvents. These new, modified membranes show excellent adsorption of high concentrations of Rose Bengal dye in methanol and isopropanol solutions. </p
111 Can early introduction of specialized palliative care limit intensive care, emergency and hospital admissions in patients with severe and very severe COPD? A pilot randomized study
No full textP134 Inclusion of patients with severe or very severe COPD in a randomised controlled trial on early specialised palliative care: a difficult challenge
No full textFinite Volumes for Complex Applications VIII - Methods and Theoretical Aspects [electronic resource] : FVCA 8, Lille, France, June 2017 /
No full textThis first volume of the proceedings of the 8th conference on "Finite Volumes for Complex Applications" (Lille, June 2017) covers various topics including convergence and stability analysis, as well as investigations of these methods from the point of view of compatibility with physical principles. It collects together the focused invited papers comparing advanced numerical methods for Stokes and Navier–Stokes equations on a benchmark, as well as reviewed contributions from internationally leading researchers in the field of analysis of finite volume and related methods, offering a comprehensive overview of the state of the art in the field. The finite volume method in its various forms is a space discretization technique for partial differential equations based on the fundamental physical principle of conservation, and recent decades have brought significant advances in the theoretical understanding of the method. Many finite volume methods preserve further qualit ative or asymptotic properties, including maximum principles, dissipativity, monotone decay of free energy, and asymptotic stability. Due to these properties, finite volume methods belong to the wider class of compatible discretization methods, which preserve qualitative properties of continuous problems at the discrete level. This structural approach to the discretization of partial differential equations becomes particularly important for multiphysics and multiscale applications. The book is a valuable resource for researchers, PhD and master’s level students in numerical analysis, scientific computing and related fields such as partial differential equations, as well as engineers working in numerical modeling and simulations.PART 1. Invited Papers. Chi-Wang Shu, Bound-preserving high order finite volume schemes for conservation laws and convection-diffusion equations.-E.D. Fernandez-Nieto, Some geophysical applications with finite volume solvers of two-layer and two-phase systems.-Thierry Gallouet, Some discrete functional analysis tools.-Yuanzhen Cheng, Alina Chertock and Alexander Kurganov, A Simple Finite-Volume Method on a Cartesian Mesh for Pedestrian Flows with Obstacles -- PART 2. Franck Boyer and Pascal Omnes, Benchmark on discretization methods for viscous incompressible flows. Benchmark proposal for the FVCA8 conference : Finite Volume methods for the Stokes and Navier-Stokes equations.-Louis Vittoz, Guillaume Oger, Zhe Li, Matthieu De Leffe and David Le Touze, A high-order Finite Volume solver on locally refined Cartesian meshes.-Daniele A. Di Pietro and Stella Krell, Benchmark session : The 2D Hybrid High-Order method.-Jerome Droniou and Robert Eymard, Benchmark: two Hybrid M imetic Mixed schemes for the lid-driven cavity.-Eric Chenier, Robert Eymard and Raphaele Herbin, Results with a locally refined MAC scheme - benchmark session.-Sarah Delcourte and Pascal Omnes, Numerical results for a discrete duality finite volume discretization applied to the Navier-Stokes equations.-Franck Boyer and Stella Krell and Flore Nabet, Benchmark session : The 2D Discrete Duality Finite Volume Method.-P.-E. Angeli, M.-A. Puscas, G. Fauchet and A. Cartalade, FVCA8 benchmark for the Stokes and Navier-Stokes equations with the TrioCFD code – benchmark session.-PART 3. Theoretical Aspects of Finite Volumes. Franc¸oise Foucher, Moustafa Ibrahim and Mazen Saad, Analysis of a Positive CVFE Scheme For Simulating Breast Cancer Development, Local Treatment and Recurrence.-Christoph Erath and Dirk Praetorius, Céa-type quasi-optimality and convergence rates for (adaptive) vertexcentered FVM.-Helene Mathis and Nicolas Therme, Numerical convergence for a diffusive limit of the Goldstein-Taylor system on bounded domain.-Florian De Vuyst, Lagrange-Flux schemes and the entropy property.-Caterina Calgaro and Meriem Ezzoug, -stability of IMEX-BDF2 finite volume scheme for convection diffusion equation.-Raphaele Herbin, Jean-Claude Latche and Khaled Saleh, Low Mach number limit of a pressure correction MAC scheme for compressible barotropic flows.-T. Gallouet, R. Herbin, J.-C. Latche and K. Mallem, Convergence of the MAC scheme for variable density flows.-J. Droniou, J. Hennicker, R. Masson, Uniform-in-time convergence of numerical schemes for a two-phase discrete fracture model.-Claire Chainais-Hillairet, Benoıt Merlet and Antoine Zurek, Design and analysis of a finite volume scheme for a concrete carbonation model.-Rita Riedlbeck, Daniele A. Di Pietro, and Alexandre Ern, Equilibrated stress reconstructions for linear elasticity problems with application to a posteriori error analysis.-Patricio Farrell and Alexander Linke, Uniform Second Order Convergence of a Complete Flux Scheme on Nonuniform 1D Grids.-J. Droniou and R. Eymard, The asymmetric gradient discretisation method.-Robert Eymard and Cindy Guichard, DGM, an item of GDM.-Claire Chainais-Hillairet, Benoıt Merlet and Alexis F. Vasseur, Positive lower bound for the numerical solution of a convection-diffusion equation.-Franc¸ois Dubois, Isabelle Greff and Charles Pierre, Raviart Thomas Petrov Galerkin Finite Elements.-Naveed Ahmed, Alexander Linke, and Christian Merdon, Towards pressure-robust mixed methods for the incompressible Navier-Stokes equations.-Thierry Goudon, Stella Krell and Giulia Lissoni, Numerical analysis of the DDFV method for the Stokes problem with mixed Neumann/Dirichlet boundary conditions.-J. Droniou, R. Eymard, T. Gallouet, C. Guichard and R. Herbin, An error estimate for the approximation of linear parabolic equations by the Gradient Discretization Method.-M. Bessemoulin-Chatard, C. Chainais-Hillairet, and A. Jungel, Uniform estimates for approximate solutions of the bipolar driftdiffusion system.-Abdallah Bradji, Some convergence results of a multi-dimensional finite volume scheme for a time-fractional diffusion-wave equation.-Nina Aguillon and Franck Boyer, Optimal order of convergence for the upwind scheme for the linear advection on a bounded domain.-Matus Tibensky, Angela Handlovicova, Numerical scheme for regularised Riemannian mean curvature flow equation.-Ahmed Ait Hammou Oulhaj, A finite volume scheme for a seawater intrusion model.-Clement Cances and Flore Nabet, Finite volume approximation of a degenerate immiscible two-phase flow model of Cahn-Hilliard type.-Clement Cances, Claire Chainais-Hillairet and Stella Krell, A nonlinear Discrete Duality Finite Volume Scheme for convection-diffusion equations.-Wasilij Barsukow, Stationarity and vorticity preservation for the linearized Euler equations in multiple spatial dimensions.-Jan Giesselmann and Tristan Pryer, Goal-oriented error analysis of a DG scheme for a second gradient elastodynamics model.-Alain Prignet, Simplified model for the clarinet and numerical schemes -- Author Index.This first volume of the proceedings of the 8th conference on "Finite Volumes for Complex Applications" (Lille, June 2017) covers various topics including convergence and stability analysis, as well as investigations of these methods from the point of view of compatibility with physical principles. It collects together the focused invited papers comparing advanced numerical methods for Stokes and Navier–Stokes equations on a benchmark, as well as reviewed contributions from internationally leading researchers in the field of analysis of finite volume and related methods, offering a comprehensive overview of the state of the art in the field. The finite volume method in its various forms is a space discretization technique for partial differential equations based on the fundamental physical principle of conservation, and recent decades have brought significant advances in the theoretical understanding of the method. Many finite volume methods preserve further qualit ative or asymptotic properties, including maximum principles, dissipativity, monotone decay of free energy, and asymptotic stability. Due to these properties, finite volume methods belong to the wider class of compatible discretization methods, which preserve qualitative properties of continuous problems at the discrete level. This structural approach to the discretization of partial differential equations becomes particularly important for multiphysics and multiscale applications. The book is a valuable resource for researchers, PhD and master’s level students in numerical analysis, scientific computing and related fields such as partial differential equations, as well as engineers working in numerical modeling and simulations
