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Rotation Functions (rotation + function)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Two simple and efficient displacement-based quadrilateral elements for the analysis of composite laminated plates

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2004
Y. X. Zhang
Abstract Two simple 4-node 20-DOF and 4-node 24-DOF displacement-based quadrilateral elements named RDKQ-L20 and RDKQ-L24 are developed in this paper based on the first-order shear deformation theory (FSDT) for linear analysis of thin to moderately thick laminates. The deflection and rotation functions of the element sides are obtained from Timoshenko's laminated composite beam functions. Linear displacement interpolation functions of the standard 4-node quadrilateral isoparametric plane element and displacement functions of a quadrilateral plane element with drilling degrees of freedom are taken as in-plane displacements of the proposed elements RDKQ-L20 and RDKQ-L24, respectively. Due to the application of Timoshenko's laminated composite beam functions, convergence can be ensured theoretically for very thin laminates. The elements are simple in formulation, and shear-locking free for extremely thin laminates even with full integration. A hybrid-enhanced procedure is employed to improve the accuracy of stress analysis, especially for transverse shear stresses. Numerical tests show that the new elements are convergent, not sensitive to mesh distortion, accurate and efficient for analysis of thin to moderately thick laminates. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Cluster analysis for phasing with molecular replacement: a feasibility study

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2009
Andreas Buehler
Molecular replacement can fail to find a solution, namely a unique orientation and position of a search model, even when many search models are tested under various conditions. Simultaneous use of the results of these searches may help in the solution of such difficult structures. A closeness between the peaks of several calculated rotation functions may identify the model orientation. The largest and most compact cluster of such peaks usually corresponds to models which are oriented similarly to the molecule under study. A search for the optimal translation may be more problematic and both individual translation functions and straightforward cluster analysis in the space of geometric parameters such as rotation angles and translation vectors may give no result. An improvement may be obtained by performing cluster analysis of the peaks of several translation functions in phase-set space. In this case, the Fourier maps computed using the observed structure-factor magnitudes and the phases calculated from differently positioned models are compared. Again, as a rule, the largest and the most compact cluster corresponds to the correct solution. The result of the updated procedure is no longer a single search model but an averaged Fourier map. [source]

Likelihood-enhanced fast translation functions

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2005
Airlie J. McCoy
This paper is a companion to a recent paper on fast rotation functions [Storoni et al. (2004), Acta Cryst. D60, 432,438], which showed how a Taylor-series expansion of the maximum-likelihood rotation function leads to improved likelihood-enhanced fast rotation functions. In a similar manner, it is shown here how linear and quadratic Taylor-series expansions and least-squares approximations of the maximum-likelihood translation function lead to likelihood-enhanced translation functions, which can be calculated by FFT and which are more sensitive to the correct translation than the traditional correlation-coefficient fast translation function. These likelihood-enhanced translation targets for molecular-replacement searches have been implemented in the program Phaser using the Computational Crystallography Toolbox (cctbx). [source]

Preliminary X-ray crystallographic analysis of 2-methylcitrate synthase from Salmonella typhimurium

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 4 2010
Sagar Chittori
Analysis of the genomic sequences of Escherichia coli and Salmonella typhimurium has revealed the presence of several homologues of the well studied citrate synthase (CS). One of these homologues has been shown to code for 2-methylcitrate synthase (2-MCS) activity. 2-MCS catalyzes one of the steps in the 2-methylcitric acid cycle found in these organisms for the degradation of propionate to pyruvate and succinate. In the present work, the gene coding for 2-MCS from S. typhimurium (StPrpC) was cloned in pRSET-C vector and overexpressed in E. coli. The protein was purified to homogeneity using Ni,NTA affinity chromatography. The purified protein was crystallized using the microbatch-under-oil method. The StPrpC crystals diffracted X-rays to 2.4,Å resolution and belonged to the triclinic space group P1, with unit-cell parameters a = 92.068, b = 118.159, c = 120.659,Å, , = 60.84, , = 67.77, , = 81.92°. Computation of rotation functions using the X-ray diffraction data shows that the protein is likely to be a decamer of identical subunits, unlike CSs, which are dimers or hexamers. [source]