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71.
E. V. Kholopov 《Journal of Structural Chemistry》2003,44(2):175-179
The paper considers instability of a symmetric linear ion chain against a spontaneous distortion that orders ions of opposite charge without a multiple change in the spacing. Transverse deformation in dense chains is observed. The dipolar interaction responsible for 3D ordering of similar structures of Cu—O chains in yttrium perovskites has been assessed. The superclose ion packing in Cu—O chains is explained by the existence of an oriented hole orbital in the electronic structure of bivalent copper. The possible role of this orbital as an additional degree of freedom leading to thermodynamic singularities at intermediate temperatures below the tetra–ortho transition temperature has been investigated. 相似文献
72.
Drevensek Olenik I Kocevar K Musevic I Rasing T 《The European physical journal. E, Soft matter》2003,11(2):169-175
Brewster-angle reflection ellipsometry and surface optical
second harmonic generation were used to study the growth of
4'-n-octyl-4-cyanobiphenyl
(8CB) films evaporated in air onto polymeric and quartz glass
substrates. The layer-by-layer growth of the films terminates
after formation of two distinctive interfacial layers. Both of
these two layers are polar and tilted. In the first layer the
molecules lie nearly flat on the surface, while in the second
layer they point on average about 50° toward the surface normal.
The dipole moment of the second layer has a lower magnitude and
an opposite direction with respect to the dipole moment of the
first layer. 相似文献
73.
S.A. Blundell M.D. Núñez-Regueiro 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):453-456
From the recently determined structure of the delafossite YCuO2.5, we argue that the Cu-O network has nearly independent Δ chains but with different interactions between the s = 1/2 spins. Motivated by this observation, we study the Δ chain for different ratios of the base-base and base-vertex interactions,
J
bb/J
bv. By exact diagonalization and extrapolation, we show that the elementary excitation spectrum is the same for total spins
S
tot = 0 and 1, but not for S
tot = 2, and has a gap only in the interval 0.4874(1) ⩽ J
bb/J
bv ⩽ 1.53(1). The gap, known to be dispersionless for J
bb = J
bv, is found to acquire increasing k-dependence as J
bb/J
bv moves away from unity.
Received 29 October 2002 / Received in final form 14 January 2003 Published online 6 March 2003
RID="a"
ID="a"e-mail: sblundell@cea.fr
RID="b"
ID="b"e-mail: nunezreg@lps.u-psud.fr 相似文献
74.
“调配问题”的动态规划模型与计算 总被引:1,自引:0,他引:1
本给出了调配问题的动态规划模型与计算,该表征更具一般化,且便于计算机计算。 相似文献
75.
O.V. Borisov F. Hakem T.A. Vilgis J.-F. Joanny A. Johner 《The European physical journal. E, Soft matter》2001,6(1):37-47
We present a scaling theory for the adsorption of a weakly charged polyelectrolyte chain in a poor solvent onto an oppositely
charged surface. Depending on the fraction of charged monomers and on the solvent quality for uncharged monomers, the globule
in the bulk of the solution has either a spherical conformation or a necklace structure. At sufficiently high surface charge
density, a chain in the globular conformation adsorbs in a flat pancake conformation due to the Coulombic attraction to the
oppositely charged surface. Different adsorption regimes are predicted depending on two screening lengths (the Debye screening
length monitored by the salt concentration and the Gouy-Chapman length monitored by the surface charge density), on the degree
of ionization of the polymer and on the solvent strength. At low bulk ionic strength, an increase in the surface charge density
may induce a transition from an adsorbed necklace structure to a uniform pancake due to the enhanced screening of the intra-chain
Coulombic repulsion by the counterions localized near the surface.
Received 12 April 2001 相似文献
76.
77.
Z.Q. Li D.X. Zhang X.H. Zhang Y.Q. Gao X.J. Liu E.Y. Jiang 《Physics letters. A》2007,370(5-6):512-516
The charge ordering characteristics in Y0.5Ca0.5MnO3 manganite, prepared by sol–gel process, have been investigated experimentally. It is found that the superlattice diffractions appear in the electron diffraction patterns recorded at low temperatures, while only basic Brag diffraction spots can be observed when temperature is higher than 300 K. This provides direct evidence for the existence of charge ordering in Y0.5Ca0.5MnO3. The magnetization and specific heat measurements indicate the charge ordering temperature of Y0.5Ca0.5MnO3 is 290 K, around which both the magnetization and specific heat reveal anomalous behaviors. We also observed that the MnO bond length changed remarkably and the effective number of carriers reduced prominently with decreasing temperature around charge ordering temperature through transform infrared spectra measurements. 相似文献
78.
CAO Zhen-Bin DUAN Yi-Shi 《理论物理通讯》2009,51(1):110-114
Generally, open string boundary conditions play a nontrivial role in string theory. For example, in the presence of an antisymmetric tensor background field, they will lead the spacetime coordinates noncommutative. In this paper, we mainly discuss how to build up a generalized Dirichlet normal ordered product of open bosonic string embedding operators that satisfies both the equations of motion and the generalized Dirichlet boundary conditions at the quantum level in the presence of an antisymmetric background field, as the generalized Neumann case has already been discussed in the literature. Further, we also give a brief check of the consistency of the theory under the newly introduced normal ordering. 相似文献
79.
Banach空间中微分方程解的存在与唯一性 总被引:6,自引:0,他引:6
在一般Banach空间中,作者讨论了微分方程的初值问题u=f(t,u),u(0)=x0.在比文[6]中弱Carathodory条件更弱的情况下,不仅放宽了[6]中的一个重要不等式条件,还去掉了另一与之相关的不等式限制,仍获得了初值问题解的存在与唯一性及解的迭代逼近.对周期边值问题也获得了类似结果. 相似文献
80.
B. G. Bhaskaran 《Queueing Systems》1986,1(1):103-127
Given conditions, which concern the infinitesimal parameters of two birth and death processes, the processes are constructed on the same probability space such that one process is almost surely larger than the other. Application is made to M/M/s queueing systems. Stochastic comparisons of queue length and virtual waiting time in two M/M/s systems are obtained. 相似文献