A cell-centred finite volume approximation for second order partial derivative operators with full matrix on unstructured meshes in any space dimension

Finite volume methods for problems involving second order operators with full diffusion matrix can be used thanks to the definition of a discrete gradient for piecewise constant functions on unstructured meshes satisfying an orthogonality condition. This discrete gradient is shown to satisfy a strong convergence property on the interpolation of regular functions, and a weak one on functions bounded for a discrete $H^1$ norm. To highlight the importance of both properties, the convergence of the finite volume scheme on a homogeneous Dirichlet problem with full diffusion matrix is proven, and an error estimate is provided. Numerical tests show the actual accuracy of the method

Facet-Based Browsing in Video Retrieval: A Simulation-Based Evaluation

In this paper we introduce a novel interactive video retrieval approach which uses sub-needs of an information need for querying and organising the search process. The underlying assumption of this approach is that the search effectiveness will be enhanced when employed for interactive video retrieval. We explore the performance bounds of a faceted system by using the simulated user evaluation methodology on TRECVID data sets and also on the logs of a prior user experiment with the system. We discuss the simulated evaluation strategies employed in our evaluation and the effect on the use of both textual and visual features. The facets are simulated by the use of clustering the video shots using textual and visual features. The experimental results of our study demonstrate that the faceted browser can potentially improve the search effectiveness

A unified approach to Mimetic Finite Difference, Hybrid Finite Volume and Mixed Finite Volume methods

We investigate the connections between several recent methods for the discretization of anisotropic heterogeneous diffusion operators on general grids. We prove that the Mimetic Finite Difference scheme, the Hybrid Finite Volume scheme and the Mixed Finite Volume scheme are in fact identical up to some slight generalizations. As a consequence, some of the mathematical results obtained for each of the method (such as convergence properties or error estimates) may be extended to the unified common framework. We then focus on the relationships between this unified method and nonconforming Finite Element schemes or Mixed Finite Element schemes, obtaining as a by-product an explicit lifting operator close to the ones used in some theoretical studies of the Mimetic Finite Difference scheme. We also show that for isotropic operators, on particular meshes such as triangular meshes with acute angles, the unified method boils down to the well-known efficient two-point flux Finite Volume scheme

Swelling of phospholipid floating bilayers: the effect of chain length

The equilibrium distance between two lipid bilayers stable in bulk water and in proximity of a substrate was investigated. Samples consisted of a homogeneous lipid bilayer, floating near an identical bilayer deposited on the hydrophilic surface of a silicon single crystal. Lipids were saturated di-acyl phosphocholines, with the number of carbon atoms per chain, n, varying from 16 to 20. The average and r.m.s. positions of the floating bilayer were determined by means of neutron specular reflectivity. Samples were prepared at room temperature (i.e. with the lipids in the gel phase) and measurements performed at various temperatures so that the whole region of transition from gel to fluid phase was explored. Data have been interpreted in terms of competition between the interbilayer potential and membrane fluctuations and used to estimate the bending rigidity of the bilayer

Accurate measurement of Cn2 profile with Shack-Hartmann data

The precise reconstruction of the turbulent volume is a key point in the development of new-generation Adaptive Optics systems. We propose a new Cn2 profilometry method named CO-SLIDAR (COupled Slope and scIntillation Detection And Ranging), that uses correlations of slopes and scintillation indexes recorded on a Shack-Hartmann from two separated stars. CO-SLIDAR leads to an accurate Cn2 retrieval for both low and high altitude layers. Here, we present an end-to-end simulation of the Cn2 profile measurement. Two Shack-Hartmann geometries are considered. The detection noises are taken into account and a method to subtract the bias is proposed. Results are compared to Cn2 profiles obtained from correlations of slopes only or correlations of scintillation indexes only.Comment: 10 pages, 8 figures, SPIE Conference "Astronomical Telescopes and Instrumentation" 2012, Amsterdam, paper 8447-19

H-convergence and numerical schemes for elliptic equations

We study the convergence of two coupled numerical schemes, which are a discretization of a so-called elliptic-hyperbolic system. Only weak convergence properties are proved on the discrete diffusion of the elliptic problem, and an adaptation of the H-convergence method gives a convergence property of the elliptic part of the scheme. The limit of the approximate solution is then the solution of an elliptic problem, the diffusion of which is not in the general case the H-limit of the discrete diffusion. In a particular case, a kind of weak limit is then obtained for the hyperbolic equation

Finite volume schemes for two phase flow in porous media

The system of equations obtained from the conservation of multiphasic fluids in porous media is usually approximated by finite volume schemes in the oil reservoir simulation setting. The convergence properties of these schemes are only known in a few simplified cases. The aim of this paper is to present some new results of convergence in more complex cases. These results are based on an adaptation of the H-convergence notion to the limit of discrete approximates

Securing coherence rephasing with a pair of adiabatic rapid passages

Coherence rephasing is an essential step in quantum storage protocols that use echo-based strategies. We present a thorough analysis on how two adiabatic rapid passages (ARP) are able to rephase atomic coherences in an inhomogeneously broadened ensemble. We consider both the cases of optical and spin coherences, rephased by optical or radio-frequency (rf) ARPs, respectively. We show how a rephasing sequence consisting of two ARPs in a double-echo scheme is equivalent to the identity operator (any state can be recovered), as long as certain conditions are fulfilled. Our mathematical treatment of the ARPs leads to a very simple geometrical interpretation within the Bloch sphere that permits a visual comprehension of the rephasing process. We also identify the conditions that ensure the rephasing, finding that the phase of the optical or rf ARP fields plays a key role in the capability of the sequence to preserve the phase of the superposition state. This settles a difference between optical and rf ARPs, since field phase control is not readily guaranteed in the former case. We also provide a quantitative comparison between $\pi$-pulse and ARP rephasing efficiencies, showing the superiority of the latter. We experimentally verify the conclusions of our analysis through rf ARP rephasing sequencies performed on the rare-earth ion-doped crystal Tm$^{3+}$:YAG, of interest in quantum memories.Comment: 24 pages, 7 figure

Ferrocene- and Fullerene[60]- Containing Liquid-Crystalline Materials

This paper shows the versatility of ferrocene and fullerene for the design of thermotropic liquid-crystalline materials: i) the electrochemical properties of the ferrocene-ferrocenium system were exploited to design redox-active metallomesogens (1 and 2); ii) ferrocene-containing side-chain liquid-crystalline polysiloxane (3) and polymethacrylates (5 and 6) were synthesized by grafting a mesomorphic vinylferrocene monomer (4) onto commercially available polysiloxane and by free-radical polymerization of mesomorphic methacrylate-ferrocene monomers (7 and 8), respectively; iii) a first-generation ferrocene-containing liquid-crystalline dendrimer (9) was synthesized; and iv) liquid-crystalline fullerene (10) and mixed fullerene-ferrocene (11) derivatives were obtained by functionalizing the C60 core with a twin cholesterol moiety

Pour un renouvellement du débat sur la validation des modèles en Sciences de Gestion à partir du test de l'Argument transcendantal

International audienceLa validation des modélisations en sciences de gestion est un sujet délicat dans la mesure où elles n'adoptent pas toutes le même positionnement épistémologique. Certains travaux s'appuient sur une perspective résolument hypothético-déductive et se livrent au test de la réfutabilité des propositions, dans la lignée des écrits de Karl POPPER. D'autres auteurs font le choix du constructiviste qui interdit un tel critère de validation. Est-ce à dire, dans ces cas, qu'il n'est pas possible d'envisager un critère universel de validité des recherches en gestion ? Dans certaines modélisations, il est recommandé de valider les modèles sur la base de leur utilité pratique pour les acteurs de terrain. Mais se contenter d'un tel critère priverait la gestion de tout statut scientifique en la réduisant à une ingénierie, certes d'une grande utilité. C'est pourquoi le recours à un critère supplémentaire qui repose sur l'examen critique des représentations du chercheur et de celles qu'il prête aux acteurs modélisés, s'avère indispensable. Dans ce texte, nous adaptons le test philosophique de l'Argument transcendantal qui consiste à vérifier la cohérence entre les présupposés du discours scientifique et celui-ci pour en faire un outil de validation et de discussion des modélisations en Sciences de Gestio