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1.
In situ high pressure energy dispersive X-ray diffraction measurements on the layered perovskite-like manganate Ca3Mn2O7 powder under pressures were performed by using the diamond anvil cell with synchrotron radiation. The results show that the structure of layered perovskite-like manganate Ca3Mn2O7 is unstable under pressure due to the easy compression of NaCl-type blocks. The structure of Ca3Mn2O7 underwent two phase transitions under pressures in the range of 0-35 GPa. One was at about 1.3 GPa with the crystal structure changing from tetragonal to orthorhombic. The other was at about 9.5 GPa with the crystal structure changing from orthorhombic back to another tetragonal. 相似文献
2.
A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3(l00) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy
electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface.
The relationship between the second-order nonlinear optical susceptibilities and the superlattice structure was systematically
studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities
of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk
BaTiO3 crystal. The mechanism of the enhancement of the second-order optical nonlinearity was discussed by taking into account the
stress-induced lattice distortion and polarization enhancement. 相似文献
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4.
Duanwei He Fuxiang Zhang Xiangyi Zhang Ming Zhang Riping Liu Yingfan Xu Wenkui Wang 《中国科学A辑(英文版)》1998,41(4):405-410
C3N4 crystals with the size of several micrometers have been synthesized from C3N4H4 in the presence of nickel-based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400°C
for 10 min. Scanning electron microscopy, energy-disperse X-ray analysis, and X-ray diffraction were used to examine the grown
crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures
and high temperatures is suggested. 相似文献
5.
Mariya Ishteva Lieven De Lathauwer P.-A. Absil Sabine Van Huffel 《Numerical Algorithms》2009,51(2):179-194
An increasing number of applications are based on the manipulation of higher-order tensors. In this paper, we derive a differential-geometric
Newton method for computing the best rank-(R
1, R
2, R
3) approximation of a third-order tensor. The generalization to tensors of order higher than three is straightforward. We illustrate
the fast quadratic convergence of the algorithm in a neighborhood of the solution and compare it with the known higher-order
orthogonal iteration (De Lathauwer et al., SIAM J Matrix Anal Appl 21(4):1324–1342, 2000). This kind of algorithms are useful for many problems.
This paper presents research results of the Belgian Network DYSCO (Dynamical Systems, Control, and Optimization), funded by
the Interuniversity Attraction Poles Programme, initiated by the Belgian State, Science Policy Office. The scientific responsibility
rests with its authors. Research supported by: (1) Research Council K.U.Leuven: GOA-Ambiorics, CoE EF/05/006 Optimization
in Engineering (OPTEC), (2) F.W.O.: (a) project G.0321.06, (b) Research Communities ICCoS, ANMMM and MLDM, (3) the Belgian
Federal Science Policy Office: IUAP P6/04 (DYSCO, “Dynamical systems, control and optimization”, 2007–2011), (4) EU: ERNSI.
M. Ishteva is supported by a K.U.Leuven doctoral scholarship (OE/06/25, OE/07/17, OE/08/007), L. De Lathauwer is supported
by “Impulsfinanciering Campus Kortrijk (2007–2012)(CIF1)” and STRT1/08/023. 相似文献
6.
Yousong Gu Yongping Zhang Xiangrong Chang Zhongzhuo Tian Nanxian Chen Dongxia Shi Xiufang Zhang Lei Yuan 《中国科学A辑(英文版)》2000,43(2):185-198
C3N4 films have been synthesized on both Si and Ft substrates by microwave plasma chemical vapor deposition (MPCVD) method. X-ray
spectra were calculated for single phase α-C3N4 and β-C3N4 respectively. The experimental X-ray spectra of films deposited on both Si and Pt substrates showed all the strong peaks
of α-C3N4 and β-C3N4 so the films are mixtures of α-C3N4 and β-C3N4. The N/C atomic ratio is in the range of 1.0–2.0. X-ray photoelectron spectroscopy (XPS) analysis indicated that the binding
energy of Is and N ls are 286.2 eV and 399.5 eV respectively, corresponding to polarized C-N bond. Fourier transform infrared
absorption (FT-IR) and Raman spectra support the existence of C-N covalent bond in the films. Nano-indentation hardness tests
showed that the bulk modulus of a film deposited on Pt is up to 349 GPa 相似文献
7.
Hongnian Li Yabo Xu Shining Bao Haiyang Li Peimo He Haijie Qian Fengqin Liu Yibulaxi Kuirexi 《中国科学A辑(英文版)》2000,43(11):1189-1194
K3C60, single crystal film was prepared on the cleaved (111) surface of C60, single crystal. Synchrotron radiation angle-resolved photoemission spectra were measured at normal emission with sample temperature at × 150K. Up to four subpeaks of LUMO-derived band were observed. These sub-peaks exhibit distinct energy dispersions which resemble in general the theoretical ones calculated for K3C60 at low temperature with the so-called one-dimensional disordered structure. But there is large deviation of experimental sub-band intervals from the theoretical values. This result is meaningful for the studies of the physical properties of alkali-doped C60 solids, e.g. the mechanism for superconductivity. 相似文献
8.
Let Z2 denote a cyclic group of 2 order and Z22 = Z2 ×Z2 the direct product of groups. Suppose that (M, Φ) is a closed and smooth manifold M with a smooth Z22 -action whose fixed point set is the disjoint union of two real projective spaces with the same dimension. In this paper, the authors give a sufficient condition on the fixed data of the action for (M, Φ) bounding equivariantly. 相似文献
9.
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Xiangyi Zhang Jingwu Zhang Fuxiang Zhang Wen Yu Duanwei He Liming Cao Jianhua Zhao Riping Liu Yingfan Xu Wenkui Wang 《中国科学A辑(英文版)》1999,42(4):407-413
The formation of nanocrystalline Fe73.5 Cu1Nb3Si13.5 B9 alloy by annealing an amorphous Fe73.5Cu1Nb3Si13.5B9 alloy at a temperature of 823 K under pressures in the range of 1–5 GPa is investigated by using X-ray diffraction, electron
diffraction, and transmission electron microscopy. The high pressure experiments are carried out in belt-type pressure apparatus.
Experimental results show that the initial crystalline phase in these annealed alloys is a-Fe solid solution (named a-Fe phase
below), and high pressure has a great influence on the crystallization process of the a-Fe phase. The grain size of the a-Fe
phase decreases with the increase of pressure (P). The volume fraction of the a-Fe phase increases with increasing the pressure
as the pressure is below 2 GPa, and then decreases (Pδ2 GPa). The mechanism for the effects of the high pressure on the crystallization
process of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy is discussed
Project supported by the National Natural Science Foundation of China (Grant No. 19674070) and the Natural Science Foundation
of Hebei Province. 相似文献
11.
Nguyen Quang Do Thong 《K-Theory》1993,7(5):429-441
The well-known formula of Riemann-Hurwitz gives the change of genuses in ann-fold covering of compact connected Riemann surfaces. In Iwasawa theory, there existp-adic analogues which give the change of certain ±-invariants in ap-extension ofCM number fields. Using functorial and arithmetical properties ofK
3, we extend such Riemann-Hurwitzp-adic formulas to non-CM fields, assuming some restrictive hypotheses on the capitulation ofK
2. 相似文献
12.
Lα (0 α 1) is a class of infinitely divisible distributions defined by restricting the measure in the Levy-Khinchin formula to a special form. When α = 1, Lα is just the classical class L. Several properties for Lα classes, which are similar to the most important properties for the class L, are established. Also, a conjecture of Wolfe about unimodality of some Lα distributions is disproved by giving a counterexample. 相似文献
13.
Alexander Nenashev 《K-Theory》2005,34(3):219-232
We interpret the Steinberg symbols xi,j(a) as homotopies contracting the elementary matrices ei,j(a), the latters being represented by certain arcs in a simplicial model of the K-theory. We further prove the Steinberg relations for these homotopies. This provides an explicit map from K2 of a ring, defined classically as ker(St(R) → GL(R)), to π2 of the G-construction assigned to R. Though the two groups are known to be isomorphic, a certain work is to be done to prove that this explicit map is an isomorphism.
Mathematics Subject Classification 1991: Primary 19B99, 19D99; secondary 18E10, 18F25. 相似文献
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ComplexK-theory ofBSL3(Z) andBSt3(Z) are computed. We first study a Brown-Peterson (BP) version of Soulé's arguments. Then we consider complexK-theory by using a Conner-Floyd type theorem. 相似文献
16.
For a local field F the finite subgroups of K2 F are expressed by a class of special elements of finite order, which makes a famous theorem built by Moore, Carroll, Tate
and Merkurjev more explicit and also disproves a conjecture posed by Browkin. 相似文献
17.
Frans Keune 《K-Theory》1989,2(5):625-645
For any prime p, the p-primary part of the tame and the wild kernel of a number field F is described in terms of ideal class groups of p-power cyclotomic extensions of F. 相似文献
18.
This paper presents a method to get improved bounds for norms of exceptional v ’ s in computing the group K2 0F, where F is a quadratic imaginary field, and as an application we show that
相似文献
19.
Li-ping Feng Zheng-tang Liu Qi-jun LiuAuthor vitae 《Journal of computational science》2011,2(3):299-303
Electronic, chemical bonding and optical properties of tetragonal SrHfO3 were investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The optimized equilibrium lattice parameters of tetragonal SrHfO3 are in good agreement with experimental values. Band structure, densities of states (DOS), charge densities and molecular-orbital bonding structure of tetragonal SrHfO3 have been obtained. The band structure shows that tetragonal SrHfO3 has direct band gap. The DOS and charge densities indicate that bonding between Hf and O is mainly covalent due to Hf 5d and O 2p hybridization and that bonding between Sr and O is mainly ionic. The complex dielectric function, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of tetragonal SrHfO3 have been predicted. The imaginary and real parts of the calculated complex dielectric functions are consistent with the experimental observations. 相似文献