Search results for "Decomposition"
showing 10 items of 766 documents
On the implementation of weno schemes for a class of polydisperse sedimentation models
2011
The sedimentation of a polydisperse suspension of small rigid spheres of the same density, but which belong to a finite number of species (size classes), can be described by a spatially one-dimensional system of first-order, nonlinear, strongly coupled conservation laws. The unknowns are the volume fractions (concentrations) of each species as functions of depth and time. Typical solutions, e.g. for batch settling in a column, include discontinuities (kinematic shocks) separating areas of different composition. The accurate numerical approximation of these solutions is a challenge since closed-form eigenvalues and eigenvectors of the flux Jacobian are usually not available, and the characte…
A Flux-Split Algorithm Applied to Relativistic Flows
1998
The equations of RFD can be written as a hyperbolic system of conservation laws by choosing an appropriate vector of unknowns. We give an explicit formulation of the full spectral decomposition of the Jacobian matrices associated with the fluxes in each spatial direction, which is the essential ingredient of the techniques we propose in this paper. These techniques are based on the recently derived flux formula of Marquina, a new way to compute the numerical flux at a cell interface which leads to a conservative, upwind numerical scheme. Using the spectral decompositions in a fundamental way, we construct high order versions of the basic first-order scheme described by R. Donat and A. Marqu…
Multiresolution based on weighted averages of the hat function I: Linear reconstruction techniques
1998
In this paper we analyze a particular example of the general framework developed in [A. Harten, {\it SIAM J. Numer. Anal}., 33 (1996) pp. 1205--1256], the case in which the discretization operator is obtained by taking local averages with respect to the hat function. We consider a class of reconstruction procedures which are appropriate for this multiresolution setting and describe the associated prediction operators that allow us to climb up the ladder from coarse to finer levels of resolution. In Part I we use data-independent (linear) reconstruction techniques as our approximation tool. We show how to obtain multiresolution transforms in bounded domains and analyze their stability with r…
Weighted ENO interpolation and applications
2004
Abstract Data-dependent interpolatory techniques such as essentially non-oscillatory (ENO) technique [J. Comput. Phys. 71 (1987) 231] have long been used as a reconstruction process in multiresolution schemes. In this work we analyze the weighted ENO (WENO) technique introduced by Liu et al. in the context of conservation laws [J. Comput. Phys. 115 (1994) 200] and improved by Jiang and Shu [J. Comput. Phys. 126 (1996) 202], and apply it to the compression of images, using multiresolution techniques.
Fictitious Domain Methods for the Numerical Solution of Two-Dimensional Scattering Problems
1998
Fictitious domain methods for the numerical solution of two-dimensional scattering problems are considered. The original exterior boundary value problem is approximated by truncating the unbounded domain and by imposing a nonreflecting boundary condition on the artificial boundary. First-order, second-order, and exact nonreflecting boundary conditions are tested on rectangular and circular boundaries. The finite element discretizations of the corresponding approximate boundary value problems are performed using locally fitted meshes, and the discrete equations are solved with fictitious domain methods. A special finite element method using nonmatching meshes is considered. This method uses …
Evolution of the optimal catalytic systems for the oxidative dehydrogenation of ethane: The role of adsorption in the catalytic performance
2022
Three samples that correspond to the evolution of optimal catalytic systems for the oxidative dehydrogenation of ethane have been synthesized and compared in terms of catalytic behavior and adsorption properties: (i) vanadium oxide supported on alumina, (ii) Sn-promoted NiO, and (iii) multicomponent MoVTeNbO with the M1 structure. The main difference in catalytic performance lies in the extent of the overoxidation of the ethylene formed, following the order VOx/Al2O3 > NiSnOx > MoVTeNb-M1. Accordingly, the selectivity to ethylene at medium and high ethane conversion follows the order MoVTeNb-M1 > NiSnOx > VOx/Al2O3. These results are confirmed by the relative reaction rates observed for the…
Programmable opticaldigital processor for rank order and morphological filtering
1995
A flexible hybrid opto-electronic processor for rank-order and morphological filtering is presented. The system is based on the shadow-casting convolver architecture, and the threshold decomposition concept. It provides the possibility of programming the input image and structuring element at video rate. The possibilities of the processor are experimentally demonstrated.
A gradient-based decomposition approach to optimize pressure path and counterpunch action in Y-shaped tube hydroforming operations
2008
International audience; In tube hydroforming, the concurrent actions of pressurized fluid and mechanical feeding allows obtaining tube shapes characterized by complex geometries such as different diameters sections and/or bulged zones. Main process parameters are material feeding history (i.e., the punches velocity history), internal pressure path during the process, and (in T- or Y-shaped tube hydroforming) counterpunch action. What is crucial, in such processes, is the proper design of operative parameters aimed to avoid defects (for instance underfilling or ductile fractures). Actually, the design of tube hydroforming operations is mainly aimed to prevent bursting or buckling occurrence …
Der austausch des cyclopentadienylliganden im methylcyclopentadienyl-mangantricarbonyl
1981
Abstract The exchange of the cyclopentadienyl ring in methylcyclopentadienylmanganese(I) tricarbonyl by methy-substituted benzenes in the presence of aluminium halide leads to [arene-Mn(CO) 3 ] + -ions. The reaction conditions have been optimised; in addition to the yield the purity of the complexes has been determined in some detail. After mild decomposition the arenes were analysed by GLC. Pure [arene-Mn(CO) 3 ] + -ions can be isolated with benzene, toluene, m - and o -xylene.
No carrier-added nucleophilic aromatic radiofluorination using solid phase supported arenediazonium sulfonates and 1-(aryldiazenyl)piperazines
2012
Abstract This Letter concerns the investigation of a solid phase based method for no carrier-added nucleophilic [ 18 F]fluorination of aromatic compounds via de-diazofluorination. Initial screening of reaction conditions was conducted using soluble analogues, that is, substituted benzenediazonium tosylates and 1-(phenyldiazenyl)piperazines in solution. This was followed by translation of the principle conditions to solid phase bound analogues. A variety of substituted aryldiazonium cations were immobilised using a sulfonate functionalised ion exchange resin and labelled with [ 18 F]fluoride ion by Balz–Schiemann like thermal decomposition in the presence of no carrier-added [ 18 F]fluoride …