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941.
Anne Henry Stefano Leone Franziska C. Beyer Henrik Pedersen Olof Kordina Sven Andersson Erik Janzén 《Physica B: Condensed Matter》2012,407(10):1467-1471
The growth of thick epitaxial SiC layers needed for high-voltage, high-power devices is investigated with the chloride-based chemical vapor deposition. High growth rates exceeding 100 μm/h can be obtained, however to obtain device quality epilayers adjustments of the process parameters should be carried out appropriately for the chemistry used. Two different chemistry approaches are compared: addition of hydrogen chloride to the standard precursors or using methyltrichlorosilane, a molecule that contains silicon, carbon and chlorine. Optical and electrical techniques are used to characterize the layers. 相似文献
942.
PS Salmon JW Drewitt DA Whittaker A Zeidler K Wezka CL Bull MG Tucker MC Wilding M Guthrie D Marrocchelli 《J Phys Condens Matter》2012,24(41):415102
The structure of GeO(2) glass was investigated at pressures up to 17.5(5)?GPa using in situ time-of-flight neutron diffraction with a Paris-Edinburgh press employing sintered diamond anvils. A new methodology and data correction procedure were developed, enabling a reliable measurement of structure factors that are largely free from diamond Bragg peaks. Calibration curves, which are important for neutron diffraction work on disordered materials, were constructed for pressure as a function of applied load for both single and double toroid anvil geometries. The diffraction data are compared to new molecular-dynamics simulations made using transferrable interaction potentials that include dipole-polarization effects. The results, when taken together with those from other experimental methods, are consistent with four densification mechanisms. The first, at pressures up to ??5?GPa, is associated with a reorganization of GeO(4) units. The second, extending over the range from ??5 to 10?GPa, corresponds to a regime where GeO(4) units are replaced predominantly by GeO(5) units. In the third, as the pressure increases beyond ~10?GPa, appreciable concentrations of GeO(6) units begin to form and there is a decrease in the rate of change of the intermediate-range order as measured by the pressure dependence of the position of the first sharp diffraction peak. In the fourth, at about 30?GPa, the transformation to a predominantly octahedral glass is achieved and further densification proceeds via compression of the Ge-O bonds. The observed changes in the measured diffraction patterns for GeO(2) occur at similar dimensionless number densities to those found for SiO(2), indicating similar densification mechanisms for both glasses. This implies a regime from about 15 to 24?GPa where SiO(4) units are replaced predominantly by SiO(5) units, and a regime beyond ~24?GPa where appreciable concentrations of SiO(6) units begin to form. 相似文献
943.
944.
The compacting of a column of grains has been studied using a one-dimensional Ising model with long range directed interactions
in which down and up spins represent orientations of the grain having or not having an associated void. When the column is
not shaken (zero “temperature”) the motion becomes highly constrained and under most circumstances we find that the generator
of the stochastic dynamics assumes an unusual form: many eigenvalues become degenerate, but the associated multi-dimensional
invariant spaces have but a single eigenvector. There is no spectral expansion and a Jordan form must be used. Many properties
of the dynamics are established here analytically; some are not. General issues associated with the Jordan form are also taken
up. 相似文献
945.
946.
Andersson Barison Caroline Werner Pereira da Silva Francinete Ramos Campos Fabio Simonelli Cesar Antonio Lenz Antonio Gilberto Ferreira 《Magnetic resonance in chemistry : MRC》2010,48(8):642-650
A simple methodology for the determination of the fatty acid composition of edible oils through 1H NMR is proposed. The method is based on the fact that all fatty acid chains are esterified to a common moiety, glycerol, and the quantification is done directly in the 1H NMR spectra through the relationship between the areas of a characteristic signal of each fatty acid and a signal of the glycerol moiety, without the use of mathematical equations. The methodology was successfully applied to determine the fatty acid composition of several edible oils, with equivalent results to those given by the AOAC Official method by gas chromatography. Its main advantages are simplicity and the lack of need for sample pre‐treatment such as derivatization or extraction. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
947.
Eugenia H.O. Valença Anita H.O. Souza Alaide H.A. Oliveira Silvio L. Valença Roberto Salvatori Maria I.R. Gonçalves Luiz A. Oliveira-Neto Alana D. Barros Ualisson N. Nascimento Carla R.P. Oliveira Daniela F. Cardoso Valdinaldo A. Melo Manuel H. Aguiar-Oliveira 《Journal of voice》2012,26(5):673.e13-673.e19
948.
A k‐cycle with a pendant edge attached to each vertex is called a k‐sun. The existence problem for k‐sun decompositions of Kv, with k odd, has been solved only when k = 3 or 5. By adapting a method used by Hoffmann, Lindner, and Rodger to reduce the spectrum problem for odd cycle systems of the complete graph, we show that if there is a ‐sun system of ( odd) whenever lies in the range and satisfies the obvious necessary conditions, then such a system exists for every admissible . Furthermore, we give a complete solution whenever k is an odd prime. 相似文献
949.
950.
Anita Quye David Littlejohn Richard A. Pethrick Robert A. Stewart 《Polymer Degradation and Stability》2011,96(7):1369-1376
Cellulose nitrate was one of the first semi-synthetic plastics to be commercially exploited and as such many museums contain a large number of artefacts illustrating the versatility of this plastic for the creation of a wide variety of functional and aesthetic artefacts. Conservators find themselves faced with the challenge of preserving these ageing artefacts which are showing evidence of significant degradation. The challenge is enhanced by artefacts of similar age and type exhibiting different degrees of degradation. This paper reports the analytical study of selected historical artefacts to explore the origins of these differences. A connection between the durability of the artefacts and the quality of the original synthetic process is identified, indicating the influence of inherent chemical factors on stability. The major contributory factors determining degradation appear to be the sulphate content remaining from the stabilization process and the rate of loss of the camphor plasticizer. A simple swab test is proposed to aid the identification of artefacts which are potentially susceptible to degradation. The test involves analysis of swab extracts by ion chromatography to reveal the presence of oxalate, which is indicative of cellulose nitrate chain scission. 相似文献