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991.
992.
After a survey of the solid–liquid transition, driven by phonon–phonon interactions, attention is next focussed on two phase transitions caused by electron–phonon interactions. These are (i) the Barden–Cooper–Schrieffer pure metal superconducting transition and (ii) the original Peierls instability. These have closely similar forms for the respective transition temperatures, both being related to energy gaps. Spin–phonon interactions are then discussed in relation to spin-Peierls materials. Finally, magnon–magnon interactions are treated in the context of the ferromagnetic–paramagnetic transition in the itinerant electron systems Fe, Co and Ni. Heuristic and phenomenological arguments, plus of course experiment, provide the basis for the conclusions drawn here. 相似文献
993.
994.
Durga Prasad Ojha 《Phase Transitions》2013,86(4):469-482
Molecular alignment of some biphenyl derivatives likes 4'-Nitro-2-biphenylamine (NBPA), 4-Acetyl-3'-chlorobiphenyl (ACBP) and 4-Acetyl-3'-florobiphenyl (AFBP) has been examined. The CNDO/2 method has been employed to compute the net atomic charge and atomic dipole-moment components at each atomic centre. Configurational energy has been computed using a modified Rayleigh- Schrodinger perturbation method at an interval of 0.1 A° in translation and 1° in rotation, and corresponding probabilities have been calculated using MB-statistics. A comparative study of molecular parameters like the total energy, the binding energy and the total dipole moment etc., has been made. On the basis of the stacking and the in-plane interaction energy calculations, all the possible geometrical arrangements between molecular pairing have been obtained. The investigation suggests that a strong intermolecular interaction energy between a pair of NBPA molecules, and the specific minimum energy configuration, determines the alignment of molecules with respect to one another. An attempt has been made to correlate the liquid crystalline properties exhibited by this class of molecules, and thereby develop a molecular model for the liquid crystallinity. 相似文献
995.
The longitudinal ultrasonic velocity (V) and attenuation at a frequency of 10?MHz, as well as magnetization and resistivity, have been measured in the single-phase polycrystalline La1– x Sr x FeO3 (x?=?1/3, 0.4, 0.45). Upon cooling down from high temperature, a slight softening in V and dramatic stiffening are observed in all samples, and this stiffening is coincided with a big attenuation peak. The relative increase of V is proportional to the Sr concentration, which implies that this anomaly is strongly correlated with Fe4+. However, no obvious changes in magnetic and electric properties are found at this temperature range. The analysis suggests that this feature may be caused by the Jahn–Teller effect of Fe4+ and correspond to the formation of short-range charge-ordering state. 相似文献
996.
997.
The three-dimensional Thomas-Fermi (TF) model is used to simulate the variation of the d + d → t + p cross-section at low impact energies, when the target deuterium nucleus is embedded in metallic or insulator environments.
The comparison of the computational results to recent experiments demonstrates that even though the TF model can explain some
increase in the low-energy cross-section for metallic host, a full explanation of the experimental results is still lacking.
Possible reasons for the disagreement are discussed. 相似文献
998.
J.-P. Nguenang T. Njassap Njassap T. C. Kofané 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):539-545
A quintic complex Ginzburg-Landau equation is derived from a Landau-Lifshitz-Gilbert equation and is used to describe the
magnetization dynamics in a one-dimensional uni-axial ferromagnet. Trough the use of suitable approximations, we derive the
magnetic solitary wave excitations solutions which have pulse-like shapes. Subsequent numerical simulations reveal domain
wall propagation. 相似文献
999.
A. H. Moudden 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):173-183
Several structures for off-stoichiometric beryllium diboride dicarbide Be1−xB2C2 have been designed, and their properties studied from first-principles density functional methods. Among the most stable
phases examined, the layered hexagonal structures are shown to exhibit various features in the electronic properties and in
the lattice dynamics reminiscent of the superconducting magnesium diboride and alkaline earth-intercalated graphites. For
substoichiometric composition x ∼ 1/3, the system is found metallic with a moderately strong electron-phonon coupling through a predominant contribution
arising from high frequency streching modes modulating the σ-bonding of the B-C network, and a weaker contribution at medium frequency range of the phonon spectra, arising from the intercalent
motion coupled to the π-bonding states. Further, anharmonicities emerging from the proximity of the Fermi level to the σ-band edge, contributes to reduce the phonon softening hence stabilizing the structure. All these effects appear to combine
favourably to produce a high temperature phonon-superconductivity. 相似文献
1000.
The existing experimental data on the d(n, p)nn and d(p, n)pp cross-sections in the forward direction are reviewed in terms of the Dean sum rule. It is shown that the measurement of the
ratio of the charge exchange on the deuteron to that on the proton might, if taken together with other experimental data,
allow a direct construction of the np → np scattering amplitude in the backward direction with few ambiguities.
Communicated by T. Hennino 相似文献