核连续态之间的直接辐射俘获跃迁

本文推导了计算跃迁到连续终态的直接辐射俘获截面公式,跃迁振幅包括两项,分别对应势阱散射-势阱散射跃迁与势阱散射-复合核散射跃迁.以¹¹B(p,γ₁₉)为例的数值计算表明,在合理的参数范围内,仅仅考虑直接俘获机制就有可能给出这一反应实验结果的一些主要特征,并且上述两项的贡献为同一数量级.还讨论了结果的物理意义.     

光散射谱作为研究半导体材料的探针

本文讨论了半导体材料激发的光散射谱,主要包括传导电子和空穴的单粒子跃迁;具有各种施主态和受主态的束缚电子和空穴的跃迁;杂质和缺陷的局域化振动和电子振动跃迁以及诸如等离子体子散射的集体激发。     

光散射谱作为研究半导体材料的探针

本文讨论了半导体材料激发的光散射谱,主要包括传导电子和空穴的单粒子跃迁;具有各种施主态和受主态的束缚电子和空穴的跃迁;杂质和缺陷的局域化振动和电子振动跃迁以及诸如等离子体子散射的集体激发。     

关于超Raman效应中散射强度的计算

本文根据辐射的量子理论,对超Raman散射强度进行了计算。从理论上直接断言:所有具有振动红外活性的Raman介质都同时具有振动超Raman活性。由于偶极跃迁几率只对反Stokes超Raman散射线有贡献,所以反Stokes线与Stokes线的强度公式不对称,前者含有更丰富的频谱。并且对于低波数频移,即使在室温条件下,两者也几乎有同数量级的强度。最后讨论了超Raman散射中的共振效应。 关键词：     

n维氢原子的散射态

研究了n维氢原子的散射态性质．给出了精确的按“k/2π标度”归一化的散射态的精确解波函数及相移表达式，讨论了相移的解析性质，获得了束缚-连续跃迁矩阵元的解析计算公式．普通氢原子(n=3)散射态的有关结果作为特例包含在本文的一般结论之中． 关键词： n维氢原子 散射态 精确解 相移 束缚-连续跃迁矩阵元     

新环形库仑势的束缚连续跃迁矩阵元

利用新环形库仑势的归一化的束缚态径向波函数和按“k/2π标度”归一化的散射态径向波函数,本文给出了新环形库仑势的任意幂次的束缚连续跃迁矩阵元的通项表达式.为了简化高幂次的束缚连续跃迁矩阵元的计算,我们还推导出了不同幂次的束缚连续跃迁矩阵元之间所满足的递推关系,并提出了计算径向波函数微商的矩阵元的计算办法.本文结果可广泛的用于原子与分子的散射问题特别是环形分子的散射问题之中.     

球型量子点中的电子拉曼散射

研究了球型半导体量子点中的电子拉曼散射.讨论了初态为导带全满,价带全空时的电子跃迁过程,给出了电子拉曼散射的跃迁选择定则。通过计算GaAs和CdS材料球型量子点中电子及空穴参与拉曼散射的微分散射截面,分别比较了电子和空穴的不同影响,发现电子对拉曼散射的贡献要远大于空穴的贡献;当选取不同量子点半径时,拉曼散射微分散射截面变化也非常明显;量子点尺寸不变的条件下,改变入射光子能量,可以发现,微分散射截面随入射光子能量增大而减小。     

漫反射各向异性散射介质内的温度热流场

本文采用射线踪迹结合节点分析法和谱带模型,研究了漫反射不透明边界下吸收、发射、各向异性散射介质内的热辐射传递过程。考虑介质辐射能的入射和散射方向,导出漫反射、不透明边界、各向异性散射介质的辐射传递系数。在辐射平衡的情况下,考察了表面发射率和散射反照率对介质内辐射热流和温度场的影响。研究表明,介质不透明边界处存在温度跃迁现象,而且,内界面发射率越大,相应界面温度跃迁越小。     

黄昆对物理学的贡献

黄昆是晶格动力学的奠基人和权威,声子物理学科开拓者。他是多声子光跃迁和多声子无辐射跃迁理论学科的开创者,是“极化激元”概念的最早阐述者。他的姓氏也与晶格振动长波唯象方程、X光漫散射理论联系在一起。在多年离开科研第一线后,黄昆70岁还建立了半导体超晶格光学声子的“黄－朱模型”。本文简要介绍黄昆先生在科学研究领域的几项主要贡献。     

基于微观IBM对电子-核散射及核电磁性质的研究(I) BE理论方案

从价核子自由度出发构造出核跃迁电荷/电流密度算符,采用Dyson玻色子展开技术给出了获取核玻色子形式跃迁电荷/电流密度有效算符的一种微观方法(BE方法).利用微观相互作用玻色子模型(IBM)提供的波函数可在玻色子态空间中求出核跃迁电荷/电流密度,结合电子-核散射以及核电磁跃迁的形式理论,建立了可研究电子-核散射各种形状因子,微分散射截面以及核约化跃迁几率、电磁多极矩、核态g因子等物理量的理论方案.在一种微观sdIBM-2框架下,结合现有理论方案,初步计算了     

Signature of a type-a glass transition and intrinsic confinement effects in a binary glass-forming system

We study dynamically highly asymmetric binary mixtures comprised of small methyl tetrahydrofuran (MTHF) molecules and polystyrene. Combined use of dielectric spectroscopy, ^{2}H nuclear magnetic resonance, incoherent quasielastic neutron scattering, and depolarized dynamic light scattering allows us to selectively probe the dynamics of the components in a broad dynamic range. It turns out that the mixtures exhibit two glass transitions in a wide concentration range although being fully miscible on a macroscopic scale. In between both glass transition temperatures, the dynamics of the small molecules show strong confinement effects, e.g., a crossover from Vogel-Fulcher to Arrhenius behavior of the time constants. Moreover, the dynamical behavior of small molecules close to the slow matrix is consistent with mode coupling theory predictions for a type-A glass transition, which was expected from recent theoretical and simulation studies in comparable systems.     

Coherent X-ray radiation generated by a beam of relativistic electrons in a single crystal under conditions of multiple scattering

The dynamic theory of the coherent X-ray radiation of a divergent beam of relativistic electrons generated in a single-crystal wafer under conditions of the multiple scattering of incident particles is developed. Radiation cross sections are averaged over the divergent beam of rectilinear trajectories of electrons. Expressions describing the spectral-angular characteristics of parametric X-ray radiation and diffracted transition radiation under conditions of multiple scattering are obtained. Conditions under which the contribution of diffracted brehmsstrahlung can be disregarded are shown, and the spectral-angular characteristics of parametric X-ray radiation and diffracted transition radiation are calculated numerically for such conditions.     

Viscosity of a liquid crystal near the nematic-smectic A phase transition

We report the results of an x-ray scattering study where both the dynamic and the static properties of a liquid crystal (8OCB) near the nematic-smectic A phase transition were probed. The static, time-averaged data show the gradual formation of smectic layers in the nematic phase, and we find that the smectic order correlation length parallel to the molecular axis diverges with the critical exponent nu( parallel )=0.70(4) at the transition. The literature value is nu( perpendicular )=0.58 for the perpendicular direction. By x-ray photon correlation spectroscopy, we find that the viscosity coefficient eta(3) shows critical, diverging behavior at the phase transition with a critical exponent x=0.95(5). This contradicts previous light scattering work (x=0.50), but is in good agreement with the theoretical prediction x=3nu( parallel )-2nu( perpendicular ) by Hossain et al.     

Pressure dependence of fragile-to-strong transition and a possible second critical point in supercooled confined water

By confining water in nanopores of silica glass, we can bypass the crystallization and study the pressure effect on the dynamical behavior in deeply supercooled state using neutron scattering. We observe a clear evidence of a cusplike fragile-to-strong (FS) dynamic transition. Here we show that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS transition. Identification of this end point with the possible second critical point is discussed.     

Phase diagrams of a nonequilibrium mixed spin-1/2 and spin-2 Ising ferrimagnetic system under a time-dependent oscillating magnetic field

We present phase diagrams for a nonequilibrium mixed spin-1/2 and spin-2 Ising ferrimagnetic system on a square lattice in the presence of a time dependent oscillating external magnetic field. We employ the Glauber transition rates to construct the mean-field dynamical equations. The time variation of the average magnetizations and the thermal behavior of the dynamic magnetizations are investigated, extensively. The nature (continuous or discontinuous) of the transitions is characterized by studying the thermal behaviors of the dynamic magnetizations. The dynamic phase transition points are obtained and the phase diagrams are presented in two different planes. Phase diagrams contain paramagnetic (p) and ferrimagnetic (i) phases, and one coexistence or mixed phase region, namely the i+p, that strongly depend on interaction parameters. The system exhibits the dynamic tricritical point and the reentrant behaviors.     

Characterization of the drastic increase in molecular mobility of a deformed amorphous polymer

Original experiments of dynamic mechanical analysis and small angle x-ray scattering on a deformed amorphous polymer below its glass transition temperature are reported. The mechanical treatment reveals high mobility zones induced by shearing and leads to a drastic increase in the molecular mobility of the system. These domains are evidenced by small angle x-ray scattering measurements, and their geometrical characteristics are independent of the applied deformation. An experimental procedure is proposed to determine an apparent activation energy associated with high mobility domains. The energy values obtained for intermediate modes rise from the beta to the alpha relaxation ones.     

Parametric x-ray radiation along the velocity of relativistic electron in a Bragg scattering geometry

Based on the dynamic scattering theory, forward parametric x-ray radiation (FPXR) of a relativistic electron is investigated in a single crystal plate in a Bragg scattering geometry. Analytical expressions for the spectral-angular distribution of FPXR and transition radiation (TR) including the crystal surface orientation with respect to a system of diffracting atomic planes are derived, which allow one to identify the conditions under which a contribution from FPXR is considerable even in the case of a thick absorbing crystal. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–56, June, 2007.     

Spin-orbit interaction and two-dimensional weak localization in a carbon matrix with cobalt nanoclusters

The magnetic-field dependence of the magnetoresistive effect in carbon fibers that contain cobalt nanoclusters and exhibit effects of weak localization at low temperatures (T < 45 K) is investigated on the metal side of the dielectric-metal transition. The carbon fibers are prepared by heat treatment of carboxylated cellulose after the substitution of cobalt cations for protons of COOH groups. It is found that, under conditions of two-dimensional weak localization at temperatures below 10 K, the carbon fibers possess an alternating magnetoresistance due to spin-orbit scattering of electrons by cobalt nanoclusters. The time of phase breaking of the wave function and the time of spin-orbit scattering are determined from a comparison of the experimental and theoretical magnetic-field dependences of the electrical resistance.     

Dynamical heterogeneity close to the jamming transition in a sheared granular material

The dynamics of a bidimensional dense granular packing under cyclic shear is experimentally investigated close to the jamming transition. Measurement of multipoint correlation functions are produced. The self-intermediate scattering function, displaying slower than exponential relaxation, suggests dynamic heterogeneity. Further analysis of four point correlation functions reveal that the grain relaxations are strongly correlated and spatially heterogeneous, especially at the time scale of the collective rearrangements. Finally, a dynamical correlation length is extracted from a spatiotemporal pattern of mobility. Our experimental results open the way to a systematic study of dynamic correlation functions in granular materials.     

Dynamic phase transitions in the kinetic mixed spin-1/2 and spin-5/2 Ising model under a time-dependent oscillating magnetic field

We calculate the dynamic phase transition (DPT) temperatures and present the dynamic phase diagrams in the kinetic mixed spin-1/2 and spin-5/2 Ising model under the presence of a time-dependent oscillating external magnetic field. We employ the Glauber transition rates to construct the set of mean-field dynamic equations. The time variation of the average magnetizations and the thermal behavior of the dynamic magnetizations are investigated, extensively. The nature (continuous or discontinuous) of the transitions is characterized by studying the thermal behaviors of the dynamic magnetizations. The DPT points are obtained and the phase diagrams are presented in two different planes. Phase diagrams contain four fundamental phases and three coexistence or mixed phases, which strongly depend on interaction parameters. The phase diagrams are discussed and a comparison is made with the results of the other mixed spin Ising systems.