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101.
Gravity distorts the circular contours found for small‐angle neutron scattering data from azimuthally symmetric scattering systems when taken at long wavelength and with large wavelength spreads. The resolution is calculated for a Debye–Scherrer ring and compared with results from measurements taken on a sample of opal. 相似文献
102.
T. Hagen B. Langwallner 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2006,86(1):63-70
We study the one‐dimensional equations governing the formation of viscous fluid fibers in forced elongation when inertia enters the dominant balance. Even though it has been known for a long time that quite weak inertial forces suffice to suppress the onset of draw resonance, we shall give quantitatively more precise results than those reported before in the context of linear stability analysis. In addition, we shall demonstrate by numerical simulation that these findings remain valid in the nonlinear regime. 相似文献
103.
104.
The reinitialization, which is required to regularize the level set function, can be computationally expensive and hence is a determining factor for the overall efficiency of a level set method. However, it often has a significantly adverse impact on the accuracy of the level set solution. This short note is meant to shed light on the efficiency and accuracy issues of the reinitialization process. Using just one clearly defined level set propagation test case with an analytical solution the solutions obtained using a recently proposed efficient lower‐order constrained reinitialization (CR) scheme and standard low‐ and high‐order reinitialization schemes are juxtaposed to evidence the superiority of the novel CR formulation. It is shown that maintaining the location of the zero level set during the reinitialization is crucial for the accuracy and that the displacement caused by standard high‐order reinitialization schemes clearly outweighs the benefit of the high‐order smoothing of the level set function. Finally, results of a three‐dimensional problem are concisely reported to demonstrate the general applicability of the CR scheme. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
105.
Carlos A. Iglesias 《High Energy Density Physics》2005,1(1):42-51
It is shown that a quantum kinetic theory approach to line broadening, extended to stationary non-equilibrium states, yields corrections to the standard electron impact widths of isolated lines that depend on the population of the radiator internal levels. A consistent classical limit from a general quantum treatment of the perturbing electrons also introduces corrections to the isolated line widths. Both effects are essential in preserving detailed-balance relations. Preliminary analysis indicates that these corrections may resolve existing discrepancies between theoretical and experimental widths of isolated lines. An experimental test of the results is proposed. 相似文献
106.
The finite volume method with exact two‐phase Riemann problems (FIVER) is a two‐faceted computational method for compressible multi‐material (fluid–fluid, fluid–structure, and multi‐fluid–structure) problems characterized by large density jumps, and/or highly nonlinear structural motions and deformations. For compressible multi‐phase flow problems, FIVER is a Godunov‐type discretization scheme characterized by the construction and solution at the material interfaces of local, exact, two‐phase Riemann problems. For compressible fluid–structure interaction (FSI) problems, it is an embedded boundary method for computational fluid dynamics (CFD) capable of handling large structural deformations and topological changes. Originally developed for inviscid multi‐material computations on nonbody‐fitted structured and unstructured grids, FIVER is extended in this paper to laminar and turbulent viscous flow and FSI problems. To this effect, it is equipped with carefully designed extrapolation schemes for populating the ghost fluid values needed for the construction, in the vicinity of the fluid–structure interface, of second‐order spatial approximations of the viscous fluxes and source terms associated with Reynolds averaged Navier–Stokes (RANS)‐based turbulence models and large eddy simulation (LES). Two support algorithms, which pertain to the application of any embedded boundary method for CFD to the robust, accurate, and fast solution of FSI problems, are also presented in this paper. The first one focuses on the fast computation of the time‐dependent distance to the wall because it is required by many RANS‐based turbulence models. The second algorithm addresses the robust and accurate computation of the flow‐induced forces and moments on embedded discrete surfaces, and their finite element representations when these surfaces are flexible. Equipped with these two auxiliary algorithms, the extension of FIVER to viscous flow and FSI problems is first verified with the LES of a turbulent flow past an immobile prolate spheroid, and the computation of a series of unsteady laminar flows past two counter‐rotating cylinders. Then, its potential for the solution of complex, turbulent, and flexible FSI problems is also demonstrated with the simulation, using the Spalart–Allmaras turbulence model, of the vertical tail buffeting of an F/A‐18 aircraft configuration and the comparison of the obtained numerical results with flight test data. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
107.
Manually defined distance restraints can be useful during structure refinement, particularly in low‐resolution refinement where the additional restraints are needed to maintain appropriate stereochemical geometry. A large number of restraints are often required when refining macromolecular structures. Currently, restraint definition requires manual editing of a text file, which can be a daunting task when working with a large number of restraints. ResDe (Restraint Definer) is a suite of Python‐based tools that allows the user to quickly define and edit restraints using the PyMOL graphical interface. 相似文献
108.
Kirill S. Napolskii Ilya V. Roslyakov Andrey A. Eliseev Andrei V. Petukhov Dmytro V. Byelov Natalia A. Grigoryeva Wim G. Bouwman Alexey V. Lukashin Kristina O. Kvashnina Andrey P. Chumakov Sergey V. Grigoriev 《Journal of Applied Crystallography》2010,43(3):531-538
A quantitative analysis of long‐range order in the self‐organized porous structure of anodic alumina films has been performed on the basis of a microradian X‐ray diffraction study. The structure is shown to possess orientational order over macroscopic distances larger than 1 mm. At the same time, the interpore positional order is only short‐range and does not extend over more than ∼10 interpore distances. These positional correlations are mostly lost gradually rather than at the domain boundaries, as suggested by the divergence of the peak width for the higher‐order reflections. In the direction of the film growth the pores have a very long longitudinal self‐correlation length of the order of tens of micrometres. 相似文献
109.
Pseudo‐Kossel lines are cones of Bragg reflections that contain information on the structure of single crystals. Nevertheless, they are not used in structure determination. The feasibility of obtaining a data set of structure factor amplitudes from a pseudo‐Kossel line pattern measurement is presented in this paper. The experimental setup shown allows the detection of almost the complete cone pattern around the sample. The measurement process is significantly simpler than data collection with a conventional four‐circle diffractometer. The extraction of structural information from the measured pattern completely separates from the data collection phase. The process consists of three main steps: determining the crystal lattice from the geometry of the cones, calculating the integrated intensities belonging to each reflection and finally solving/refining the structure in the usual manner. As an example, the pseudo‐Kossel line pattern of a C60 single crystal was recorded and analysed. The extracted single‐crystal data set, fitted with the face‐centred cubic structure of C60, yielded R = 4.5% and Rw = 7.7%. The advantages and drawbacks of this method compared with conventional single‐crystal measurements are discussed. Two variants of the detection process in the method are also compared. 相似文献
110.
A novel approach to the development of a code for the solution of the time-dependent two-dimensional Navier–Stokes equations is described. The code involves coupling between the method of lines (MOL) for the solution of partial differential equations and a parabolic algorithm which removes the necessity of iterative solution on pressure and solution of a Poisson-type equation for the pressure. The code is applied to a test problem involving the solution of transient laminar flow in a short pipe for an incompressible Newtonian fluid. Comparisons show that the MOL solutions are in good agreement with the previously reported values. The proposed method described in this paper demonstrates the ease with which the Navier–Stokes equations can be solved in an accurate manner using sophisticated numerical algorithms for the solution of ordinary differential equations (ODEs). 相似文献