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41.
S. Loridant G. LucazeauT. Le Bihan 《Journal of Physics and Chemistry of Solids》2002,63(11):1983-1992
A high-pressure structural study of SrCeO3 has been performed at room temperature by Raman spectroscopy and X-ray diffraction up to 32 and 45 GPa, respectively. A first-order reversible phase transition is observed at about 12 GPa in both techniques. A second weak structural change, taking place between 18 and 25 GPa, can be suspected from Raman data. The increase in the number of Raman bands and diffraction lines is an indication that the symmetry is lowered and the compound does not evolve towards the ideal cubic perovskite structure. A Rietveld analysis of X-ray data was performed for the low-pressure phase and the atomic positions and the cell lattice parameters variations are reported in this paper. The volume compressibility derived from Raman modes (5.6×10−12 Pa−1), involving mainly bond-stretching for each type of polyhedron, is found to be close to the one obtained from volume cell variations measured by X-ray diffraction (7.9×10−12 Pa−1). 相似文献
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B. Tatischeff M. P. Comets Y. Le Bornec N. Willis B. Bonin J. C. Lugol B. Mayer Y. Terrien R. Beurtey A. Boudard J. M. Durand P. Fassnacht F. Hibou 《Zeitschrift für Physik A Hadrons and Nuclei》1987,328(2):147-149
Some evidence is presented for a narrow peak at 1969±2 MeV (FWHM=9±2 MeV) in the missing mass spectrum of the3He(p, d) reaction, with 3 standard deviations. The nature of this state, the mass of which is below the NN threshold, is discussed in connection with structures found in other experiments. 相似文献
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Arielle Milliet Georges Sozzi Henri E. Audier 《Journal of mass spectrometry : JMS》1992,27(7):787-794
Radical cations derived from the ethers ROCH2CH2OR′ (R, R′ = H, CH3, C25) were studied, since β-distonic oxonium ions are often prepared from ionized ethers of glycol. The first step in the fragmentation is a 1,5-transfer of an α-hydrogen to oxygen of a terminal alkoxy group leading to a δ-distonic oxonium ion. This step is thermo-neutral and reversible in the ROCH2CH2OH radical cations and exothermic and irreversible in the dialkyl ether radical cations. Depending on R and R,′ these δ-distonic oxonium ions fragment by three reactions: the loss of an alcohol or a water molecule, the formation of a β-distonic oxonium ion ˙CH2CH2O(H)+R and a 1,4-H migration between carbon atoms. Competition between these processes is discussed. 相似文献
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Chepoi showed that every breadth first search of a bridged graph produces a cop-win ordering of the graph. We note here that Chepoi's proof gives a simple proof of the theorem that G is bridged if and only if G is cop-win and has no induced cycle of length four or five, and that this characterization together with Chepoi's proof reduces the time complexity of bridged graph recognition. Specifically, we show that bridged graph recognition is equivalent to (C4,C5)-free graph recognition, and reduce the best known time complexity from O(n4) to O(n3.376). 相似文献
50.
The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two‐dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier–Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献