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51.
In this paper, a projection method is presented for solving the flow problems in domains with moving boundaries. In order to track the movement of the domain boundaries, arbitrary‐Lagrangian–Eulerian (ALE) co‐ordinates are used. The unsteady incompressible Navier–Stokes equations on the ALE co‐ordinates are solved by using a projection method developed in this paper. This projection method is based on the Bell's Godunov‐projection method. However, substantial changes are made so that this algorithm is capable of solving the ALE form of incompressible Navier–Stokes equations. Multi‐block structured grids are used to discretize the flow domains. The grid velocity is not explicitly computed; instead the volume change is used to account for the effect of grid movement. A new method is also proposed to compute the freestream capturing metrics so that the geometric conservation law (GCL) can be satisfied exactly in this algorithm. This projection method is also parallelized so that the state of the art high performance computers can be used to match the computation cost associated with the moving grid calculations. Several test cases are solved to verify the performance of this moving‐grid projection method. Copyright © 2004 John Wiley Sons, Ltd. 相似文献
52.
Marcelo Goncalves Hnnicke Edson Massayuki Kakuno Cesar Cusatis Irineu Mazzaro 《Journal of Applied Crystallography》2004,37(3):451-454
A standard procedure cannot be used to detect a back‐diffracted X‐ray beam (h‐beam) at a diffraction angle of 90° (back‐diffraction) because the detector will intercept the incident beam. A new method is proposed in which a silicon single crystal simultaneously back‐diffracts and detects the variation of the photon counting rate when the crystal is in and out of the X‐ray back‐diffraction condition. The detected intensity shows the inverted diffraction profile; that is, a dip in the photon counting rate due to the photons that are being back‐diffracted. The experimental results presented here show such a dip, referred to here as the anti‐h peak or the inverted rocking curve (IRC), for different situations. 相似文献
53.
Philip J. Withers Mark R. Daymond Michael W. Johnson 《Journal of Applied Crystallography》2001,34(6):737-743
Much of crystallography is concerned with the accurate location of the centre of diffraction peak profiles. Simple analytical expressions are derived for estimating the precision of diffraction peak location that can be achieved for Gaussian diffraction peaks with a flat background, in terms of the standard deviation, integrated intensity and peak height (H) to background (B) ratio. Two formulations are derived using standard methods: one for the case of very low background, the other for significant backgrounds. It is found that in cases of significant background, peak position is less well determined by a factor of [1+2(21/2)B/H]1/2 compared with the case of no background. The applicability of the expression has been demonstrated by Monte Carlo simulation of Gaussian profiles and by the analysis of real data collected at a large number of neutron and synchrotron sources, largely as part of the VAMAS TWA20 project. While the solution is presented for Gaussian peak shapes, it is believed to be approximately correct for a wide range of other common diffraction peak shapes (Lorentzian, Voigtian etc.). The method is applied to the assessment of the variation in optimal measuring time as a function of the depth of the gauge volume for residual strain scanning measurements. 相似文献
54.
Arthur J. Schultz Mads Ry Vogel Jrgensen Xiaoping Wang Ruth L. Mikkelson Dennis J. Mikkelson Vickie E. Lynch Peter F. Peterson Mark L. Green Christina M. Hoffmann 《Journal of Applied Crystallography》2014,47(3):915-921
The intensity of single‐crystal Bragg peaks obtained by mapping neutron time‐of‐flight event data into reciprocal space and integrating in various ways is compared. These methods include spherical integration with a fixed radius, ellipsoid fitting and integration of the peak intensity, and one‐dimensional peak profile fitting. In comparison to intensities obtained by integrating in real detector histogram space, the data integrated in reciprocal space result in better agreement factors and more accurate atomic parameters. Furthermore, structure refinement using integrated intensities from one‐dimensional profile fitting is demonstrated to be more accurate than simple peak‐minus‐background integration. 相似文献
55.
T. H. Simm P. J. Withers J. Quinta da Fonseca 《Journal of Applied Crystallography》2014,47(5):1535-1551
The broadening of diffraction peaks representing different families of grain orientations has been measured for a number of deformed metals: austenitic stainless steel 316, nickel 200 and the titanium alloy Ti‐6Al‐4V. These measurements have been compared with predictions that explain differences in broadening in terms of the contrast factor of dislocations via two different approaches. This was done in order to understand the effect the contrast factor has on the results of diffraction peak profile analysis methods and the cause of broadening anisotropy. An approach that considers all grains and orientations to behave similarly was found to be unsuccessful in explaining the large variations of broadening in different peaks. These variations can be explained, and errors reduced, by adopting an approach that uses a polycrystal plasticity model. However, if the plasticity based approach is used to solely calculate changes in the contrast factor, it only partly explains changes in broadening. Instead, factors such as variations in the dislocation density and crystallite size in different orientations, the number of dislocations that are mobile, and the number of edge and screw dislocations need consideration. The way to incorporate these additional factors is difficult, but their contribution to broadening anisotropy can be as important as that of the contrast factor. 相似文献
56.
In nuclear spectroscopy by crystal diffraction, peak sharpness and low count rate make the jitter of the goniometer angle a limit to resolution. A device that uses the photon detection to trigger the reading of the angle allows information to be preserved, notwithstanding noise. A Bayesian analysis is applied to estimate the centre of the diffraction peak, without binning the recorded angles. 相似文献
57.
Owing to the relatively low intensity of diffraction and resulting low contrast topographic images, and also the richly detailed domain structure, it can be difficult to extract individual mosaic domains (size and shape) for protein crystals. Here, orthogonal projection was tested and found to be a superior approach over previous methods to extract mosaic domain information from a fine‐sliced topographic sequence of images. The topographic sequence was collected at room temperature from a lysozyme crystal with a low mosaicity. Orthogonal projection can be applied to image sequences that are spatially invariant and composed of linearly additive image formation processes. The domains were determined by using a particle swarm optimizer to fit Gaussians to the integrated intensity profile of the reflection as a function of angle, although any basis function could have been used. This optimization method was more amenable to automation and converged to the global minimum more efficiently. The number of domains can normally be determined by visually inspecting the integrated intensity profile; this only needs to be done once for each crystal, because the number of domains remains constant during collection, and not for each reflection. The results can be used to provide a picture of the internal structure of the crystal and may be useful to aid in the improvement of crystal growth techniques. 相似文献
58.
A method for simply identifying the X‐ray diffraction peak broadening caused by tilt and twist distributions through analysis of their hkl dependence is proposed. The development of a new general formulation for the hkl‐dependence analysis is presented. This makes the hkl‐dependence analysis generally applicable to any material with any type of crystal structure. It also makes it possible to analyze the hkl dependence of broadening in terms of whole profile shapes, which improves the reliability of the analysis. Another advantage of the formulation is that the analysis procedures for broadening due to both tilt and twist distributions can be derived in a straightforward manner from the same general version. Owing to these advantages, the method is applicable to GaN‐based epitaxial films. The method for twist distributions is experimentally demonstrated using GaN epitaxial films on sapphire substrates. 相似文献
59.
Luciano Gonç alves Noleto Manuel N. D. Barcelos Jr. & Antonio C. P. Brasil Jr. 《advances in applied mathematics and mechanics.》2013,5(2):194-211
This work presents a moving mesh methodology based on the solution
of a pseudo flow problem. The mesh motion is modeled as a pseudo Stokes
problem solved by an explicit finite element projection method. The mesh
quality requirements are satisfied by employing a null divergent velocity
condition. This methodology is applied to triangular unstructured meshes
and compared to well known approaches such as the ones based on diffusion
and pseudo structural problems. One of the test cases is an airfoil with
a fully meshed domain. A specific rotation velocity is imposed as the
airfoil boundary condition. The other test is a set of two cylinders
that move toward each other. A mesh quality criterion is employed to
identify critically distorted elements and to evaluate the performance
of each mesh motion approach. The results obtained for each test case
show that the pseudo-flow methodology produces satisfactory meshes
during the moving process. 相似文献
60.
《Analytical letters》2012,45(18):3457-3471
Abstract Induced peak phenomenon in capillary zone electrophoresis with electrochemiluminescence detection for chiral separation of racemic phenylalanine mixture employing sulfated‐β‐cyclodextrin as chiral selector and acetonitrile as organic additive in the separation buffer was observed. Various experimental parameters influencing the intensity and the position of the induced peak were systematically investigated to find out the truth of the induced peak. Based on the experimental evidence, a reasonable mechanism involved in the formation of the induced peak was proposed. We found out the induced peak resulted from physical interactions between the components in the separation buffer and the injected sample during the electromigration process rather than chemical complexation interactions. Furthermore, suggestions to avoid the appearance of induced peak in capillary zone electrophoresis with electrochemiluminescence detection for chiral separations were presented. 相似文献