极性晶体膜中强耦合激子的性质

在强耦合极化子模型基础上,采用Lee-Low-Pines(LLP)变分法研究了极性晶体膜中激子与表面光学(SO)声子强耦合、与体纵光学(LO)声子弱耦合体系的性质.讨论了极性晶体膜中激子的诱生势与膜厚度和温度的变化关系.结果表明:激子的诱生势不仅与电子-空穴间距离有关,而且与极性晶体膜厚度有关,同时温度对激子诱生势的影响十分显著.     

晶格振动对激子运动的影响

在本文中用Haga研究极化子时提出的微扰法讨论晶格振动对激子运动的影响。把作者过去的工作推广到电子和空穴质量不相等的普遍情形。在忽略反冲效应中不同波矢的声子之间的相互作用时,导出了激子的基态能量、有效质量、约化质量和内部势能。指出:激子的有效质量和电子、空穴与声子的相互作用有关;激子的约化质量不仅和电子、空穴与声子的相互作用有关,而且还和电子空穴质量比有关;激子形成自陷态的条件并非由电子、空穴与声子相互作用的大小,而是由电子、空穴质量比决定。形成激子自陷的条件是电子、空穴质量比0.261<μ_e/μ_h<3.83。在μ_e/μ_h<0.261或μ_e/μ_h>3.83的情形,激子极化晶体中并不形成自陷态。 关键词：     

准二维强耦合激子有效质量的温度依赖性

采用Tokuda改变的线性组合算符法和改进的Lee-Low-Pines变换法,研究了温度对量子阱中电子(空穴)与界面光学(IO)声子强耦合又与体纵光学(LO)声子弱耦合激子的有效质量的影响.结果表明,由电子(空穴)-体纵光学声子弱耦合所产生的激子有效质量(Mex*-LO)随量子阱宽N的增加而增大、随电子与空穴间相对距离P的增加而先增大后缓慢减小再趋于稳定,温度T对Mex*-LO及其随N和P变化的规律产生显著影响.同时,Mex*-LO)随T的变化也强烈的受到量子尺寸效应的影响;由电子(空穴)-界面光学声子强耦合所产生的激子有效质量Mcx*-IO随N的增加而减小,随T的升高而增大、随p的增加而先增大后缓慢减小再趋于稳定,但丁对Mex-IO随N和p变化的规律无明显影响.     

极性晶体膜中强耦合激子的极化子效应和温度依赖性

采用线性组合算符和变分方法研究了极性晶体膜中激子与表面光学（SO）声子强耦合、与体纵光学（LO）声子弱耦合体系的性质,推导出了激子诱生势的表达式,并以AgBr晶体为例进行了数值计算.结果表明：激子的诱生势不仅与电子-空穴间距离有关,而且温度与极性晶体膜厚度对激子诱生势的影响也十分显著.     

极性晶体膜中强耦合激子的极化子效应和温度依赖性

采用线性组合算符和变分方法研究了极性晶体膜中激子与表面光学(SO)声子强耦合、与体纵光学(LO)声子弱耦合体系的性质,推导出了激子诱生势的表达式,并以AgBr晶体为例进行了数值计算.结果表明:激子的诱生势不仅与电子-空穴间距离有关,而且温度与极性晶体膜厚度对激子诱生势的影响也十分显著.     

SO和LO声子对GaAs-Ga1-xAlxAs量子阱中激子束缚能的影响

本文考虑了电—声子耦合作用,应用么正变换方法计算了GaAs-Ga1-xAlxAs量子阱中的激子束缚能;得到了激子束缚能随阱宽变化的曲线。当考虑激子声子相互作用后,激子相对于电子极化子和空穴极化子的第一子带底的束缚能小于相应的裸激子的束缚能量。     

温度和极化子效应对准二维强耦合激子基态的影响

采用Huybrechts线性组合算符和Lee-Low-Pines变换法研究了温度和极化子效应对量子阱中激子与界面光学声子强耦合又与体纵光学声子弱耦合体系基态的影响,推导出激子基态的诱生势和基态能量的移动的表达式. 以AgCl/AgBr量子阱为例进行了数值计算,结果表明,由激子-界面光学声子强耦合所产生的激子基态的诱生势和基态能量的移动随温度的升高而增大,而由激子-体纵光学声子弱耦合所产生的激子基态的诱生势和基态能量的移动随温度的升高而减小. 关键词： 量子阱 强耦合激子 极化子效应 温度依赖性     

表面磁极化子的回旋共振性质

在磁场中有不少的极性晶体,电子和体纵光学声子的耦合弱,而与表面光学声子的耦合强。本文讨论电子和体纵光学声子耦合弱,与表面光学声子耦合强时对表面磁极化子的性质的影响。采用改进了的线性组合算符法导出了磁场中表面极化子的回旋共振频率和回旋共振质量,对AgCl晶体进行了数值计算。结果表明,磁场中表面极化子的回旋共振频率和回旋共振质量随磁场的增加而增加。     

温度和极化子效应对准二维强耦合激子基态的影响

采用Huybrechts线性组合算符和Lee-Low-Pines变换法研究了温度和极化子效应对量子阱中激子与界面光学声子强耦合又与体纵光学声子弱耦合体系基态的影响，推导出激子基态的诱生势和基态能量的移动的表达式. 以AgCl/AgBr量子阱为例进行了数值计算，结果表明，由激子-界面光学声子强耦合所产生的激子基态的诱生势和基态能量的移动随温度的升高而增大，而由激子-体纵光学声子弱耦合所产生的激子基态的诱生势和基态能量的移动随温度的升高而减小.     

极性晶体中表面极化子的温度效应

有不少的极性晶体,电子与体纵光学声子的耦合弱,但与表面光学声予的耦合强.本文讨论电子和体纵光学声子耦合弱,与表面光学声子耦合强时对表面极化子的温度特性的影响,用线性组合算符法研究表面极化子的振动频率、诱生势和有效质量的温度依赖性.对AgBr晶体进行了数值计算,结果表明极化子的振动频率,诱生势和有效质量随温度的升高而减小.     

孤立波在一维复合颗粒链中传播特性的模拟研究

采用分子动力学方法模拟研究了孤立波在重轻颗粒相间排列的一维复合颗粒链中的传播特性.结果发现,在轻重颗粒的质量比较大或较小时,散射作用较弱,颗粒的速度和孤立波的速度衰减较慢.在轻重颗粒的质量比为中等时,散射作用较强,颗粒的速度和孤立波的速度衰减较快.孤立波在通过重-轻颗粒界面时,存在有增速效应,可以提高孤立波的传播速度.并且,轻重颗粒的质量比越小增速效应越强.在散射作用和增速效应的共同作用下,改变轻重颗粒的质量比可以调控孤立波在重-轻颗粒链中的传播时间.     

炸药水下爆炸能量输出特性试验研究

为了解炸药水中爆炸能量的输出特性,特别是冲击波能随距离的衰减规律,对有效比冲能进行了研究。经过理论推导发现,传统的有效比冲能计算公式仍然满足相似律。TNT炸药水下爆炸试验结果表明,炸药的有效比冲能、比气泡能和总能量的测量结果与经验公式计算结果吻合较好。通过对试验结果进行分析,拟合得到了有效比冲能随距离变化的趋势线。对比经验公式结果,发现在小药量试验中冲击波能随距离的衰减更明显。     

Propagation of solitary waves in channels of decreasing depth

The changes which occur in a right-going solitary wave as it travels a channel of decreasing depth are discussed. In addition to the changes in the solitary wave, we have found through a judicious use of the conservation laws two secondary structures (a shelf and a reflection). Each of these structures is small with respect to the solitary wave, though the mass flux associated with each is of the same order as that of the solitary wave. Of interest is that the amplitude of the reflected wave does not satisfy Green's law. But rather, the amplitude of the reflected wave is constant along left-going characteristics. This finding allows us to satisfy the mass flux conservation laws to leading order and establishes the perturbed Korteweg-deVries equation as a consistent approximation for the right-going profile.     

Acoustic waves in random fields

The effect of space- and time-dependent random mass density, velocity, and pressure fields on frequencies and amplitudes of acoustic waves is considered by means of the analytical perturbative method. The analytical results, which are valid for weak fluctuations and long wavelength sound waves, reveal frequency and amplitude alteration, the effect of which depends on the type of random field. In particular, the effect of a random mass density field is to increase wave frequencies. Space-dependent random velocity and pressure fields reduce wave frequencies. While space-dependent random fields attenuate wave amplitudes, their time-dependent counterparts lead to wave amplification. In another example, sound waves that are trapped in the vertical direction but are free to propagate horizontally are affected by a space-dependent random mass density field. This effect depends on the direction along which the field is varying. A random field, which varies along the horizontal direction, does not couple vertically standing modes but increases their frequencies and attenuates amplitudes. These modes are coupled by a random field which depends on the vertical coordinate, but the dispersion relation remains the same as in the case of the deterministic medium.     

Nonrelativistic wave functions in relativistic physics

We explore the validity of using nonrelativistic wave functions for lightly-bound states in relativistic situations. This is shown to be acceptable for scattering problems, but not necessarily for those involving a decay. In the latter case the wave function would need to have special properties. These do not occur for a deuteron-like wave function but do occur for a positronium-like system, the crucial features being that positronium is bound by zero mass exchange.     

Nonequilibrium processes in condensed media. Part 2. Structural instability induced by shock loading

In the first part of the work, we described our concept of shock wave processes, which is based on nonlocal nonequilibrium transport theory, and an associated mathematical elastoplastic wave model that allows for inertial properties, structural changes, and variation in mechanical properties of solid-state materials under shock loading. In the second part of the work, it is demonstrated that the energy exchange between the scales of dynamic deformation is defined by the relation between the characteristics measurable in real time: the mesoscale mass velocity variation and the mass velocity defect due to loss of the energy expended in structure formation. An internal criterion is found for the transition of a dynamically deformed material to structural instability.     

脉冲管制冷机中惯性管的数值模拟研究

本文利用Fluent软件对惯性管进行数值模拟,计算采用二维层流的数值模型,得到惯性管入口处质量流量与压力波之间的相位及惯性管内部的压力波幅值和质量流量幅值的变化,给出不同频率及惯性管尺寸对惯性管入口处压力波与质量流量之间的相位的影响.通过分析并计算得到脉冲管冷端质量流量,进行设计计算.     

Effects of a reverse shock wave on neutrino oscillations in a new supernova model

It is known that in supernova explosions, there might be a reverse shock wave in addition to the forward shock wave during the explosion phase, when the mass of supernova is in a certain range. In this paper, we propose to add the reverse shock wave to the previous supernova model, in which only the forward shock wave was included,and thus obtain a new model. By analyzing the resonance condition as well as the density jump in the new model and using the Landau-Zener method, an expression for the crossing probability in high density matter(PH) is given.We proceed to study how PH varies with time and with neutrino energy when both the reverse shock wave and the forward shock wave are considered. From comparison with the previous results, where only the effects of the forward shock wave were considered, it is clear that the reverse shock wave brings significant changes to PH.     

Nonlinear Wave Propagation in a Disordered Medium

In this paper we consider the problem of solitary wave propagation in a weakly disordered potential. Through a series of careful numerical experiments we have observed behavior which is in agreement with the theoretical predictions of Kivshar et al., Bronski, and Gamier. In particular we observe numerically the existence of two regimes of propagation. In the first regime the mass of the solitary wave decays exponentially, while the velocity of the solitary wave approaches a constant. This exponential decay is what one would expect from known results in the theory of localization for the linear Schrödinger equation. In the second regime, where nonlinear effects dominate, we observe the anomalous behavior which was originally predicted by Kivshar et al. In this regime the mass of the solitary wave approaches a constant, while the velocity of the solitary wave displays an anomalously slow decay. For sufficiently small velocities (when the theory is no longer valid) we observe phenomena of total reflection and trapping.     

Mass change of dielectric media induced by propagation of electromagnetic waves

It has been experimentally confirmed that an electromagnetic wave carries momentum and thus exerts forces on dielectrics. Combining wave-particle duality with the theory of relativity, it was shown in the present work that the electromagnetic wave also increases the mass of the dielectric medium through which the incident wave propagates. The change in the mass density of the medium, or the mass density of the electromagnetic wave in the medium, was found to be proportional to the energy density of the incident wave. At an absolute temperature T, the mass density of the black body radiation was shown to be proportional to T⁴. “Weighing” the light wave in a glass fiber provides a novel technique to study the particle nature of electromagnetic waves in dielectric media.