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991.
Joachim Naumann 《Mathematical Methods in the Applied Sciences》2006,29(16):1883-1906
This paper is concerned with the equations of non‐stationary motion in 3D of heat‐conducting incompressible viscous fluids with temperature‐dependent viscosity. The conservation of internal energy includes the usual dissipation term. We prove the existence of a ‘weak solution with defect measure’ to the system of PDEs under consideration. Our method of proof is based on a regularization of the equations of conservation of momentum. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
992.
The mode hopping phenomenon induced by optical feedback in single-mode microchip Nd:YAG lasers is presented. With optical feedback, mode hopping strongly depends on two factors: the ratio of external cavity length to intra-cavity length, and initial gains of the two hopping modes, When external cavity length equals an integral multiple of intracavity length, there is almost no mode hopping. However, if the external cavity length does not equal an integral multiple of intra-cavity length, mode hopping occurs. The ratio of external cavity length to intra-cavity length determines the position of two-mode hopping, The initial gains of the two hopping modes determine the corresponding peak values and oscillating periods of them in the intensity modulation curves. 相似文献
993.
A detailed theoretical study of the low-temperature lattice specific heat of Ni-based dilute alloys has been carried out.
Lattice Green’s function method has been used to calculate the local density of states of substitutional impurities and lattice
specific heat in different alloys. The resonance condition has been investigated for possible occurrence of resonance modes.
Except in NiCr and NiMn, low-frequency resonance modes have been obtained in all the alloys. However, no localized mode was
obtained. The impurity-induced increase in lattice specific heat is explained on the basis of the obtained resonance modes.
The calculation shows an excellent agreement with the measured lattice specific heat in these alloys 相似文献
994.
The paper consists of two parts. In the first part, we propose a procedure to estimate local errors of low order methods applied
to solve initial value problems in ordinary differential equations (ODEs) and index 1 differential-algebraic equations (DAEs).
Based on the idea of defect correction we develop local error estimates for the case when the problem data is only moderately
smooth. Numerical experiments illustrate the performance of the mesh adaptation based on the error estimation developed in
this paper. In the second part of the paper, we will consider the estimation of local errors in context of stochastic differential
equations with small noise.
AMS subject classification (2000) 65L06, 65L80, 65L50, 65L05 相似文献
995.
G. Montambaux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):377-383
The stability of a Charge Density Wave (CDW) in a one-dimensional ring pierced by a Aharonov-Bohm flux is studied in a mean-field
picture. It is found that the stability depends on the parity of the number N of electrons. When the size of the ring becomes as small as the coherence length , the CDW gap increases for even N and decreases for odd N. Then when N is even, the CDW gap decreases with flux but it increases when N is odd. The variation of the BCS ratio with size and flux is also calculated. We derive the harmonics expansion of the persistent
current in a presence of a finite gap.
Received: 16 September 1997 / Received in final form: 12 November 1997 / Accepted: 13 November 1997 相似文献
996.
对液氮温度下六方相GaN和掺Mg的P型GaN薄膜的拉曼谱进行了对比研究。除对两个样品中主晶格振动模进行了对比分析外,着重讨论了位于247 cm-1的散射峰的产生机制。结果表明GaN:Mg的谱中该峰的散射强度随温度升高先增大再减小,在500K以上消失且对样品重新降温到78K观察此峰不再出现,因此认为它是缺陷产生的振动模。而GaN样品中经同样加热降温的过程此峰仍然存在,说明两个样品中该峰的产生机制不同。此外,在GaN:Mg的谱中还观察到Mg诱导的局域振动模。 相似文献
997.
998.
Michael F. Shlesinger 《Journal of statistical physics》1984,36(5-6):639-648
Dielectric relaxation in amorphous materials is treated in a defect-diffusion model where relaxation occurs when a mobile defect, such as a vacancy, reaches a frozen-in dipole. The random motion of the defect is assumed to be governed by a fractal time stochastic process where the mean duration between defect movements is infinite. When there are many more defects than dipoles, the Williams-Watts decaying fractional exponential relaxation law is derived. The argument of the exponential is related to the number of distinct sites visited by the random walk of the defect. For the same reaction dynamics but with more traps than walkers, an algebraically decaying relaxation is found. 相似文献
999.
制备了Bi7Ti4NbO21,Bi4Ti3O12及Nb掺杂Bi4Ti3O12(Nb-Bi4Ti3O12)层状结构铁电陶瓷材料.结合Nb-Bi 4Ti3O12的介电温谱和 退极化实验结果,研究了Bi7Ti4NbO21的晶体结构 对其介电、压电性能的影响 .高分辨透射电镜结果表明,在Bi7Ti4NbO21中, 沿着c轴方向,(Bi2Ti3O10)2-和(BiTiNbO7)2-两个类钙钛矿层分别 与(Bi2O2)2+层叠加堆积而成.这种晶体结构决定了Bi7Ti4NbO21的 介电温谱在668℃和845℃出现介 电双峰.结合极化样品的退化实验分析,说明材料在这两个温度附近发生了铁电—铁电相变 、铁电—顺电相变,分别是(Bi2Ti3O10)2-< /sup>和(BiTiNbO7)2-层状 结构发生微观结构相变的结果.在退极化过程中,由于受热时钙钛矿层内空位引起的缺陷偶 极子的定向排列受到破坏,引起材料部分退极化,表现为300℃热处理后Bi7Ti 4NbO 21的压电活性降低了10%,显示了室温下材料的压电性能来源于自发极化的固有电 偶极子和缺陷偶极子的共同贡献. 相似文献
1000.
Giovanna Longhi Sergio Abbate Claudio Zagano Giovanni Botto Laure Ricard-Lespade 《Theoretical chemistry accounts》1992,82(3-4):321-337
Summary The system consisting of two Morse oscillators coupled via either a potential or a kinetic quadratic term is considered. The corresponding classical equations of motion have been numerically integrated and the initial conditions have been systematically analyzed in the regime of low total excitation energy of the system. Particular attention was paid to the full characterization of an intermediate type of motion, herein called transition mode, which appears at total energy values in between those typical of normal modes and those where local and normal modes coexist. A previously proposed perturbative approach (Jaffé C, Brumer P (1980) J Chem Phys 73:5646) is reanalyzed and compared with the results of numerical experiments, with the purpose of lending further support to the existence of transition modes. 相似文献