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991.
Underdoped manganites: Canted antiferromagnetic ordering or two-phase ferro-antiferromagnetic state?
E. L. Nagaev 《Journal of Experimental and Theoretical Physics》1998,87(6):1214-1220
We calculate the energy of charge-carrier-induced canted ordering in conducting layered antiferromagnetic systems with double
exchange. The quantum approach to the d-spins is used. In the jellium model the energy of the canted state is lower than the energies of both collinear ferro-and
antiferromagnetic states over a certain range of charge carrier densities, beginning with arbitrarily small densities. Nevertheless,
the canted state cannot be realized, because it is unstable against charge-carrier density fluctuations. The two-phase ferro-antiferromagnetic
state can play the role of an alternative to canting. The case of an intermediate electronic-impurity phase separation is
investigated.
Zh. éksp. Teor. Fiz. 114, 2225–2237 (December 1998)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
992.
The twisting power of chiral probes in nematics is interpreted in terms of a shape model, in which the surface elements of the solute molecules tend to align with the local director. The theoretical treatment is based on a previous approach, suitable for relating order parameters in nematics to molecular shape, and leads to the definition of a molecular pseudo-tensor whose orientational average determines the pitch and handedness of the helical macrostructures. Results of numerical calculations performed for distorted biphenyl and binaphthyl molecules are in agreement with the experimental results. 相似文献
993.
The orientational ordering of several liquid crystals containing a difluorosubstituted phenyl ring has been studied through the use of C-13 NMR. The fluorinated phenyl ring of these liquid crystals have Cs symmetry, so three order parameters are required to completely describe the ordering of this ring. All three of these order parameters have been calculated from carbon-fluorine dipolar coupling constants obtained from the carbon-fluorine splittings in the C-13 NMR spectra. Because of the complexity of the fluorine-coupled spectra, variable angle spinning (VAS) was used to resolve the carbon-fluorine splittings. In order to study the orientational ordering over wide ranges of temperature, we have developed an empirical correlation between the order parameter and the value of a carbon-fluorine dipolar coupling constant. This enabled us to study the change in the order parameter with temperature. The results of applying this method to several structurally similar liquid crystals containing the same type of difluorinated phenyl ring are presented. A comparison is made to a similar mono-fluorinated liquid crystal. 相似文献
994.
F. Máca 《Czechoslovak Journal of Physics》1993,43(9-10):941-945
We present the calculations of electronic structure and photoemission spectra for a lattice-matched Ag-Au(111) superlattice. The selfconsistent band structure exhibits a superlattice gap at about 1 eV below the Fermi level. A surface state is found in this gap and its dispersion properties are investigated. Its energy location is varied with location of surface terminating plane within the superlattice period. The calculated normal photoemission spectra explain well available experimental data. 相似文献
995.
A review of otoacoustic emissions 总被引:32,自引:0,他引:32
R Probst B L Lonsbury-Martin G K Martin 《The Journal of the Acoustical Society of America》1991,89(5):2027-2067
Otoacoustic emissions measured in the external ear canal describe responses that the cochlea generates in the form of acoustic energy. For the convenience of discussing their principal features, emitted responses can be classified into several categories according to the type of stimulation used to evoke them. On this basis, four distinct but interrelated classes can be distinguished including spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. The present review details the findings that have been described for each emission type according to this classification schema. Additionally, the known features of emitted responses are discussed for both normally hearing and hearing-impaired humans and experimental animals, and with respect to their potential clinical applications. The findings reviewed here clearly indicate that future studies of otoacoustic emissions will significantly increase our understanding of the basic mechanisms of cochlear function while, at the same time, provide a new and important clinical tool. 相似文献
996.
We summarize some recent results related to fluctuation-induced kinetics of diffusion-controlled processes. We show that kinetic behavior can be drastically changed due to fluctuation effects, spatial correlations between particles, and anomalous transport properties. In addition, we show that correlation-induced kinetics in some systems can govern the temporal evolution over the entire time domain. 相似文献
997.
998.
We investigate multiphoton states generated by high-gain optical parametric amplification of a single injected photon—polarization encoded as a qubit. The experimental configuration exploits the optimal phase-covariant cloning. The output state of the apparatus is found to exhibit the quantum superposition property of mesoscopic multiphoton assemblies involving about 300 photons. This work represents an experimental advance toward the test of several fundamental quantum processes in mesoscopic or macroscopic frameworks. 相似文献
999.
A numerical model for simulating nonlinear pulsed beams radiated by rectangular focused transducers, which are typical of
diagnostic ultrasound systems, is presented. The model is based on a KZK-type nonlinear evolution equation generalized to
an arbitrary frequency-dependent absorption. The method of fractional steps with an operator-splitting procedure is employed
in the combined frequency-time domain algorithm. The diffraction is described using the implicit backward finite-difference
scheme and the alternate direction implicit method. An analytic solution in the time domain is employed for the nonlinearity
operator. The absorption and dispersion of the sound speed are also described using an analytic solution but in the frequency
domain. Numerical solutions are obtained for the nonlinear acoustic field in a homogeneous tissue-like medium obeying a linear
frequency law of absorption and in a thermoviscous fluid with a quadratic frequency law of absorption. The model is applied
to study the spatial distributions of the fundamental and second harmonics for a typical diagnostic ultrasound source. The
nonlinear distortion of pulses and their spectra due to the propagation in tissues are presented. A better understanding of
nonlinear propagation in tissue may lead to improvements in nonlinear imaging and in specific tissue harmonic imaging.
Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 4, pp. 560–570.
This article was translated by the authors. 相似文献
1000.