Current-voltage dependencies of heterogeneous semiconductor systems

Computed current-voltage (J–V) dependencies of heterogeneous (powder) semiconductor systems reveal an anomalous dependence between the constant-voltage current J and the uncompensated donor (acceptor) concentration N. Over a range of N(N₁ < n < N₂) of approximately one decade, J decreases by as much as four decades with increasing N. For N > N₂, the grain Schottky barrier thickness d is less than the grain half-width l/2, the grain surface potential V_s is almost independent of N and the J–V dependence is superlinear. For N₁ < N < N₂, d > l/2, V_s decreases linearly with N, J increases strongly with decreasing N and the J–V dependence is superlinear. For N < N₁, d > l/2. V_s ? V_th ( = kT/q) and J ∝ NV. The phenomenon is used to account for some observed J–V dependencies with column II-chalcogenide and ZnO powder semiconductor systems (electro-optic displays, electrophotographic receptors and heterogeneous catalysts).     

Long-wavelength excitations in a Bose gas at zero temperature

The long-wavelength excitations in a simple model of a dilute Bose gas at zero temperature are investigated from a purely microscopic viewpoint. The role of the interaction and the effects of the condensate are emphasized in a dielectric formulation, in which the response functions are expressed in terms of regular functions that do not involve an isolated single-interaction line nor an isolated single-particle line. Local number conservation is incorporated into the formulation by the generalized Ward identities, which are used to express the regular functions involving the density in terms of regular functions involving the longitudinal current. A perturbation expansion is then developed for the regular functions, producing to a given order in the perturbation expansion an elementary excitation spectrum without a gap and simultaneously response functions that obey local number conservation and related sum rules.Explicit results to the first order beyond the Bogoliubov approximation in a simple one-parameter model are obtained for the elementary excitation spectrum ω_k, the dynamic structure function $\text{S}$(k, ω), the associated structure function $\text{S}$_m(k), and the one-particle spectral function $\text{A}$(k, ω), as functions of the wavevector k and frequency ω. These results display the sharing of the gapless spectrum ω_k by the various response functions and are used to confirm that the sum rules of interest are satisfied. It is shown that ω_k and some of the $\text{S}$_m(k) are not analytic functions of k in the long wavelength limit. The dynamic structure function $\text{S}$(k, ω) can be conveniently separated into three parts: a one-phonon term which exhausts the f sum rule, a backflow term, and a background term. The backflow contribution to the static structure function $\text{S}$₀(k) leads to the breakdown of the one-phonon Feynman relation at order k³. Both $\text{S}$(k, ω) and $\text{A}$(k, ω) display broad backgrounds because of two-phonon excitations. Simple arguments are given to indicate that some of the qualitative features found for various physical quantities in the first-order model calculation might also be found in superfluid helium.     

A majorization theorem for the number of distinct outcomes in n independent trials

This paper is concerned with the probability distribution of the number of distinct outcomes k in N repetitions of an experiment. It is shown that the majorization of probability vectors implies the majorization of the distribution and expectation of k.     

Applications of variational principles in finite elasticity

Summary For some equilibrium states of a finitely deformed elastic body, variational principles can be used to provide bounds on overall quantities of physical interest. The principles are applied to the problem of the allaround finite extension of a plane sheet with a circular hole, and accurate estimates for the stress resultant at the outer edge are obtained for various extensions. The finite extension and torsion of an elastic cylinder is considered and bounds on the strain energy per unit length are obtained for an elliptical cylinder of neo-Hookean material with axes in the ratios of 2:1 and 4:1. The bounds lead to reliable estimates for the twisting moment and axial force.

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Zusammenfassung Für gewisse Gleichgewichtszustände eines endlich deformierten elastischen Körpers können Variationsprinzipien verwendet werden, um Schranken für globale Grössen von physikalischem Interesse zu erhalten. Die Prinzipien werden auf das Problem der allseitigen endlichen Extension einer ebenen Scheibe mit kreisförmigem Loch angewendet, und es werden für verschiedene Extensionen gute Abschätzungen der Resultierenden am Aussenrand gewonnen. Ferner wird die endliche Zug- und Torsionsverformung eines elastischen Zylinders betrachtet, und es werden Schranken für die Verformungsenergie je Längeneinheit für einen elliptischen Zylinder aus Neo-Hookeschem Material für die Achsenverhältnisse 2:1 und 4:1 erhalten. Die Schranken liefern zuverlässige Schätzungen für das Torsionsmoment und die Axialkraft.

     

Truncation of the nuclear shell-model space using spectral strength distribution

A procedure, based on spectral distribution methods, is introduced to truncate a large shell-model matrix and to renormalize the matrix for the effects of the truncation. The basis states are selected depending on their contribution in the ground-state region and the renormalization is achieved by requiring that the strength distributions of each configuration in the truncated space to have the same widths as those in the full space. The calculation starts with a given effective Hamiltonian in the original space without having to introduce any free parameters due to truncation. Tests against full shell-model calculations in the ds shell are performed for energy levels of ²⁸Si and for electromagnetic transitions in the (ds)⁶T = 0 space.     

大麦抽穗期的遗传分析

本文对8×8大麦品种双列杂交的F_1和F_2的抽穗期进行了遗传分析,结果:(1)抽穗期性状在F_1双列试验中,W_r/V_r回归系数b(0.8399)与单位斜率1无显著差异,表明符合加性-显性遗传模型,在F_2中,b=0.2768,显著不同于1,存在上位效应。去阵列8后,对F_2双列资料重新检验,发现由此获得的亚双列系统符合模型(b=0.8230).W_r/V_r分析表明,F_1与F_2世代间阵列位置有变动,但阵列2,3在两个世代中均据回归线的上部.W_r+V_r与Y_r间的相关测定均为负相关,表明抽穗期晚一般由显性基因效应控制.(2)抽穗期F_1和F_2的广义遗传力为97％与98％,狭义遗传力为87％与69％.在F_1为0.59,表明抽穗期晚为部分显性.F_2却大于1,示有超显性特点;H_2/4H_1值都小于0.25,说明全部有关座位上,平均地说,显隐性等位基因频率不相等.F_1值为负值,表明所有亲本所携带的隐性基因比显性基因要多. (3)抽穗期一般配合力效应为负向的有小将,早熟3号和永2830.特殊配合力存在较大负向优势的杂交组合中,必含小将、早熟三号和永2830三个早熟品种之一为杂交亲本.     

Level density in large spectroscopic spaces

Statistical spectroscopy methods are used to calculate level densities for one-body Hamiltonians in the space of 440 single particle states. Comparisons are made with combinatorial counting and Fermi gas model. Possibilities to arrive at a more realistic level density formula including two-body effects are discussed.