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Obtained Structures (obtained + structure)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Structures and energies of D -galactose and galabiose conformers as calculated by ab initio and semiempirical methods

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2003
Majda Rahal-Sekkal
Abstract Optimized geometries and total energies of some conformers of ,- and ,- D -galactose have been calculated using the RHF/6-31G* ab initio method. Vibrational frequencies were computed at the 6-31G* level for the conformers that favor internal hydrogen bonding, in order to evaluate their enthalpies, entropies, Gibbs free energies, and then their structural stabilities. The semiempirical AM1, PM3, MNDO methods have also been performed on the conformers GG, GT, and TG of ,- and ,- D -galactose. In order to test the reliability of each semiempirical method, the obtained structures and energies from the AM1, PM3, and MNDO methods have been compared to those achieved using the RHF/6-31G* ab initio method. The MNDO method has not been investigated further, because of the large deviation in the structural parameters compared with those obtained by the ab initio method for the galactose. The semiempirical method that has yielded the best results is AM1, and it has been chosen to perform structural and energy calculations on the galabiose molecule (the disaccharides constituted by two galactose units , 1,4 linked). The goal of such calculations is to draw the energy surface maps for this disaccharide. To realize each map, 144 different possible conformations resulting from the rotations of the two torsional angles , and , of the glycosidic linkage are considered. In each calculation, at each increment of , and ,, using a step of 30° from 0 to 330°, the energy optimization is employed. In this article, we report also calculations concerning the galabiose molecule using different ab initio levels such as RHF/6-31G*, RHF/6-31G**, and B3Lyp/6-31G*. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 806,818, 2003 [source]

Space fullerenes: a computer search for new Frank,Kasper structures

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010
Mathieu Dutour Sikiri
A Frank,Kasper structure is a 3-periodic tiling of the Euclidean space by tetrahedra such that the vertex figure of any vertex belongs to four specified patterns with, respectively, 20, 24, 26 and 28 faces. Frank,Kasper structures occur in the crystallography of metallic alloys and clathrates. A new computer enumeration method has been devised for obtaining Frank,Kasper structures of up to 20 cells in a reduced fundamental domain. Here, the 84 obtained structures have been compared with the known 27 physical structures and the known special constructions by Frank,Kasper,Sullivan, Shoemaker,Shoemaker, Sadoc,Mosseri and Deza,Shtogrin. [source]

Room temperature gas sensor based on porous silicon/metal oxide structure

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2007
V. M. Arakelyan
Abstract N-type TiO2,x and In2O3 · SnO2 thin films were deposited onto p-type porous silicon layer which was formed by common electrochemical anodization. The current-voltage characteristics of obtained structures and sensitivity to different concentrations of hydrogen in air were studied. Measurements were carried out at room temperature. As shown results of measurements, an exponential growth of the current in forward branch of the current-voltage characteristics of the device made of TiO2,xlayer was detected. Higher sensitivity to hydrogen of the TiO2,x -porous silicon sensor in comparison to structure made of In2O3 · SnO2 film was detected at room temperature (without preheating of work body of the sensor). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Self-assembled honeycomb polycarbonate films deposited on polymer piezoelectric substrates and their applications

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2005
Edward Bormashenko
Abstract Self-assembled honeycomb polycarbonate films were deposited on polymer piezoelectric (poled polyvinylidene fluoride) substrates under a fast dip-coating process. Ordered structures with micro-scaled pores dispersed in the polycarbonate matrix were obtained, demonstrating two-dimensional (2D) hexagonal packing. A theoretical model explaining the self-assembling process is proposed. Fabricated structures have a potential as 2D tunable photonic crystals. Photonic bandgap location was estimated. Visible-IR transmittance spectrum of the self-assembled films was studied with a FT-IR spectrometer. Diffraction properties of the honeycomb patterns were investigated. High transparency of the components makes possible IR optics applications of obtained structures. Copyright © 2005 John Wiley & Sons, Ltd. [source]