Unifying Practical Uncertainty Representations: II. Clouds

There exist many simple tools for jointly capturing variability and incomplete information by means of uncertainty representations. Among them are random sets, possibility distributions, probability intervals, and the more recent Ferson's p-boxes and Neumaier's clouds, both defined by pairs of possibility distributions. In the companion paper, we have extensively studied a generalized form of p-box and situated it with respect to other models . This paper focuses on the links between clouds and other representations. Generalized p-boxes are shown to be clouds with comonotonic distributions. In general, clouds cannot always be represented by random sets, in fact not even by 2-monotone (convex) capacities.Comment: 30 pages, 7 figures, Pre-print of journal paper to be published in International Journal of Approximate Reasoning (with expanded section concerning clouds and probability intervals

Multi-spectroscopic investigation of the structure of single-wall carbon nanotubes

We present a multispectroscopic structural study of various nanotube samples with different tube diameters. We determine for each sample the mean bundle and tube diameter as well as the tube diameter distribution. The possibility to work on SWNT of various structural characteristics opens new opportunities to correlate the nanotube structure and their physical properties.Comment: Conf\'{e}rence : 8 au 15 mars 200

Nanotube-based systems for broadband optical limiting: towards an operational system

Nanotube-based systems are good candidates for optical limiting against broadband laser pulses. We explore new routes to improve their limiting performances. We show that the diameter of the nanotubes is a key factor to control the performances. On the other hand, we demonstrate that chemically modified nanotubes can be mixed with organic chromophores, leading to high performance composite limiting systems which are particularly efficient in the nanosecond regime due to the cumulative effects of nonlinear scattering and multiphoton absorption

Optohydrodynamics of soft fluid interfaces : Optical and viscous nonlinear effects

Recent experimental developments showed that the use of the radiation pressure, induced by a continuous laser wave, to control fluid-fluid interface deformations at the microscale, represents a very promising alternative to electric or magnetic actuation. In this article, we solve numerically the dynamics and steady state of the fluid interface under the effects of buoyancy, capillarity, optical radiation pressure and viscous stress. A precise quantitative validation is shown by comparison with experimental data. New results due to the nonlinear dependence of the optical pressure on the angle of incidence are presented, showing different morphologies of the deformed interface going from needle-like to finger-like shapes, depending on the refractive index contrast. In the transient regime, we show that the viscosity ratio influences the time taken for the deformation to reach steady state

Credible Autocoding of Convex Optimization Algorithms

The efficiency of modern optimization methods, coupled with increasing computational resources, has led to the possibility of real-time optimization algorithms acting in safety critical roles. There is a considerable body of mathematical proofs on on-line optimization programs which can be leveraged to assist in the development and verification of their implementation. In this paper, we demonstrate how theoretical proofs of real-time optimization algorithms can be used to describe functional properties at the level of the code, thereby making it accessible for the formal methods community. The running example used in this paper is a generic semi-definite programming (SDP) solver. Semi-definite programs can encode a wide variety of optimization problems and can be solved in polynomial time at a given accuracy. We describe a top-to-down approach that transforms a high-level analysis of the algorithm into useful code annotations. We formulate some general remarks about how such a task can be incorporated into a convex programming autocoder. We then take a first step towards the automatic verification of the optimization program by identifying key issues to be adressed in future work

Numerical simulation of flow interaction between stationary and downstream elastically mounted cylinders at low reynolds numbers

The vortex-induced vibration phenomenon can occur as a result of the action of wind on bridges, slender buildings, chimneys and energy transmission cables besides the action of water flow on pipelines and risers, among others. Despite the simplicity of the geometry of the circular cylinders, the uniform flow around them is very complex and important, since it may induce unsteady forces on structures associated with vortex shedding. This paper describes the study of two circular cylinders in tandem arrangement subject to bidimensional uniform laminar flows at low Reynolds numbers. The numerical model Ifeinco, which is based on the finite element method and uses a partitioned scheme that considers twoway interaction of fluid flow and structure, has been employed in the analysis. The fluid flow model uses a semi-implicit two-step Taylor-Galerkin method to discretize the Navier-Stokes equations whereas the arbitrary Lagrangean-Eulerian formulation to follow the cylinder motion. This movement has been described by the one DOF dynamic equation for the transverse direction discretized in time by the implicit Newmark method. Both cylinders are immersed in water and the downstream one is elastically mounted in transversal direction. Firstly, stationary cylinders in tandem arrangement for Re = 100 are analysed for L/D from 1.5 to 6.0. Results of lift and drag coefficients and Strouhal number are compared with other numerical results and good agreement is found. These analyses show that the vortex shedding occurs for both cylinders for gaps L/D > 4.0 and the wake behind the downstream cylinder is formed by the combination of vortex shed of both cylinders. Secondly, numerical simulations considering downstream elastically mounted cylinder for L/D = 5.25 are analysed for Reynolds numbers ranging from 100 to 140. It shows that the resonance occurred for Reynolds numbers between 115 and 120, unlike the range obtained for a single cylinder, from 102 to 113, submitted to the same conditions. Furthermore, the maximum dimensionless amplitude of oscillation is 0.721 for Re = 118, which is much higher than the one of the single cylinder (0.422 for Re = 103). The interaction between cylinders changes the Strouhal number in relation to the one of the single cylinder; because of this, there are differences between the lock-in regions

Evaluation qualitative macroscopique et microscopique du grasset chez un modèle expérimental d'arthrose canine 90 jours après section du ligament croisé crânial

La transection du ligament croisé crânial (CCLT) est une méthode couramment admise d'induction expérimentale d'arthrose (OA) au niveau du grasset chez le chien. Le but principal de cette étude était d'évaluer qualitativement les lésions d'arthrose induites par la CCLT par macroscopie et histologie 90 jours après chez 21 jeunes femelles de race beagle. Les lèvres de la trochlée fémorale présentaient le plus haut score ostéophytique tandis que la patelle présentait le plus bas et celui du condyle fémoral médial était supérieur à celui du condyle latéral. Les lésions méniscales ont été observées uniquement sur le ménisque médial de 5 genoux opérés. Les lésions macroscopiques du cartilage (stade de fibrillation) ont été notées dans un ordre de fréquence décroissant sur les condyles tibiaux médial et latéral, le condyle fémoral latéral, la trochlée fémorale, le condyle fémoral médial et enfin la patelle. L'examen histologique a révélé que la couche superficielle du cartilage était fibrillée et discontinue. La plupart des cellules étaient rondes et disposées tangentiellement à la surface. Dans les zones transitionnelle et profonde, quelques chondrocytes étaient modérément hypertrophiques et des amas de chondrocytes ont été uniquement observés dans la couche profonde. Concernant la membrane synoviale, un épaississement du mésothélium et une importante densité de collagène ont été notés et le rapport des épaisseurs mésothélium/fibres était entre 1/0.15 et 1/0.10 sur les genoux opérés et 1/0.05 sur les genoux témoins. Les images fournies ici pourront servir de références pour des travaux ultérieurs portant notamment sur les thérapies contre l'arthrose

Possibilistic information fusion using maximal coherent subsets (LFA 2007)

National audienceWhen multiple sources provide information about the same badly known quantity, aggregating them into a coherent and interpretable synthesis is often a tedious problem, especially when some conflict is present. In this paper, we propose and explore a fusion method using the notion of maximal coherent subsets (often used in logic) on quantitative possibility distributions. This methods result, a fuzzy belief structure, is then used to extract useful information about sources or to build a final synthetic possibility distribution.Lorsque plusieurs sources fournissent de l'information à propos d'une même quantité mal connue, en faire une synthèse cohérente et interprétable est souvent un problème difficile, surtout en présence de conflit entre les sources. Dans cet article, nous proposons et étudions une méthode de fusion basée sur la théorie des possibilités et sur la notion de sous-ensembles maximaux cohérents, une notion souvent utilisée dans le raisonnement logique. Cette méthode, dont le résultat final est une fonction de croyance floue, est ensuite utilisée aussi bien pour extraire de l'information utile sur les sources que pour construire une distribution synthétique finale