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Coupling Methods (coupling + methods)

Distribution by Scientific Domains

Engineering	33%

Selected Abstracts

Comparison of Coupling Methods for Linking Between Reactor and Feature Scales

CHEMICAL VAPOR DEPOSITION, Issue 1-3 2010
Jonathan Jilesen
Abstract Currently there are two main methods used for coupling macroscopic reactor-scale and microscopic feature-scale models in multi-scale CVD simulation. These methods differ in the plane selected for coupling. With one method, coupling occurs at a source plane offset from the deposition surface, while in the other method coupling occurs on the deposition surface itself. The two methods also have different feature-scale modeling techniques associated with them. A Monte Carlo (MC) technique is used for the source plane-coupling method, while a ballistic transport technique is used for the deposition surface-coupling method. In this study a multi-scale code with a ballistic feature-scale model is modified so that both coupling methods can be applied, allowing for direct comparison of the two coupling methods. [source]

Coupling of mesh-free methods with finite elements: basic concepts and test results

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2006
T. Rabczuk
Abstract This paper reviews several novel and older methods for coupling mesh-free particle methods, particularly the element-free Galerkin (EFG) method and the smooth particle hydrodynamics (SPH), with finite elements (FEs). We study master,slave couplings where particles are fixed across the FE boundary, coupling via interface shape functions such that consistency conditions are satisfied, bridging domain coupling, compatibility coupling with Lagrange multipliers and hybrid coupling methods where forces from the particles are applied via their shape functions on the FE nodes and vice versa. The hybrid coupling methods are well suited for large deformations and adaptivity and the coupling procedure is independent of the particle distance and nodal arrangement. We will study the methods for several static and dynamic applications, compare the results to analytical and experimental data and show advantages and drawbacks of the methods. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Toward accurate hybrid prediction techniques for cavity flow noise applications

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009
W. De Roeck
Abstract A large variety of hybrid computational aeroacoustics (CAA) approaches exist differing from each other in the way the source region is modeled, in the way the equations are used to compute the propagation of acoustic waves in a non-quiescent medium, and in the way the coupling between source and acoustic propagation regions is made. This paper makes a comparison between some commonly used numerical methods for aeroacoustic applications. The aerodynamically generated tonal noise by a flow over a 2D rectangular cavity is investigated. Two different cavities are studied. In the first cavity (L/D=4, M=0.5), the sound field is dominated by the cavity wake mode and its higher harmonics, originating from a periodical vortex shedding at the cavity leading edge. In the second cavity (L/D=2, M=0.6), shear-layer modes, due to flow-acoustic interaction phenomena, generate the major components in the noise spectrum. Source domain modeling is carried out using a second-order finite-volume large eddy simulation. Propagation equations, taking into account convection and refraction effects, are solved using high-order finite-difference schemes for the linearized Euler equations and the acoustic perturbation equations. Both schemes are compared with each other for various coupling methods between source region and acoustic region. Conventional acoustic analogies and Kirchhoff methods are rewritten for the various propagation equations and used to obtain near-field acoustic results. The accuracy of the various coupling methods in identifying the noise-generating mechanisms is evaluated. In this way, this paper provides more insight into the practical use of various hybrid CAA techniques to predict the aerodynamically generated sound field by a flow over rectangular cavities. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Chemistry of ,-hydroxymethylserine: problems and solutions,

JOURNAL OF PEPTIDE SCIENCE, Issue 11 2008
Marcin Stasiak
Abstract Further improvements related to the synthesis of peptides containing HmS are presented. Efficient synthetic protocols have been developed to synthesize "difficult" sequences containing a C -terminal HmS residue, MeA,HmS or consecutive HmS. Preparative methods for orthogonal N - and/or C -protected HmS(Ipr) derivatives are described. Their compatibility with standard solution or solid-phase peptide chemistry protocols allows synthetic flexibility toward HmS-containing peptides. In the synthesis of the sterically hindered dipeptides with the C -terminal HmS(Ipr) residue, HATU proves the highest efficiency, as compared with the fluoride and PyBroP/DMAP coupling methods. The HATU method also outperforms the fluoride activation in the solid-phase assembly of HmS homosequence. Specific protocols are described to overcome an undesired cyclization to diketopiperazines that occurs during the removal of Fmoc from dipeptides with the C -terminal HmS(Ipr) or HmS residues, thus precluding their C , N elongation. The successful protocols involve: (i) the 2 + 1 condensation using mixed anhydride activation yielding the desired product with the highest optical integrity or (ii) use of the 2-chlorotrityl resin as a solid support sterically suppressing the undesired cleavage due to diketopiperazine formation. The latter approach allows the mild conditions of peptide cleavage from solid support, preserving the isopropylidene protection and minimizing the undesired N , O -acyl migration that was observed under prolonged acid treatment used for cleaving the HmS peptide from the Wang resin. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source]

An O(n2) bound for the relaxation time of a Markov chain on cladograms

RANDOM STRUCTURES AND ALGORITHMS, Issue 1 2002
Jason Schweinsberg
Abstract A cladogram is an unrooted tree with labeled leaves and unlabeled internal branchpoints of degree 3. Aldous has studied a Markov chain on the set of n -leaf cladograms in which each transition consists of removing a random leaf and its incident edge from the tree and then reattaching the leaf to a random edge of the remaining tree. Using coupling methods, Aldous showed that the relaxation time (i.e., the inverse of the spectral gap) for this chain is O(n3). Here, we use a method based on distinguished paths to prove an O(n2) bound for the relaxation time, establishing a conjecture of Aldous. © 2002 John Wiley & Sons, Inc. Random Struct. Alg., 20, 59,70, 2002 [source]