失调望远镜型激光发射系统设计方法的研究

用高斯光束ｑ参数变化法设计失调望远镜型激光发射系统的数学模型，并运用计算机模拟设计软件设计出一种可省去内调焦镜的激光发射系统。     

Influence of negative ion element impurities on laser induced damage threshold of HfO2 thin film

Negative ion element impurities breakdown model in HfO₂ thin film was reported in this paper. The content of negative ion elements were detected by glow discharge mass spectrum analysis (GDMS); HfO₂ thin films were deposited by the electron-beam evaporation method. The weak absorption and laser induced damage threshold (LIDT) of HfO₂ thin films were measured to testify the negative ion element impurity breakdown model. It was found that the LIDT would decrease and the absorption would increase with increasing the content of negative ion element. These results indicated that negative ion elements were harmful impurities and would speed up the damage of thin film.     

Magnetoimpedance effect in Nanoperm alloys

The influence of isothermal annealing (1 h at 600 °C in Ar atmosphere) on the soft magnetic properties and magnetoimpedance (MI) effect has been studied in ribbons of the following Nanoperm alloys: Fe₉₁Zr₇B₂, Fe₈₈Zr₈B₄, Fe₈₇Zr₆B₆Cu₁ and Fe₈₀Zr₁₀B₁₀. A maximum MI ratio of about 27% was measured for the nanocrystalline alloy Fe₈₇Zr₆B₆Cu₁ at a driving frequency of 0.2 MHz. The thermal annealing led to magnetic softening for this alloy, while a hardening is observed for the Fe₈₀Zr₁₀B₁₀ alloy.     

The effects of nonlinear couplings and external magnetic field on the thermal entanglement in a two-spin-qutrit system

We investigate the effects of nonlinear couplings and external magnetic field on the thermal entanglement in a two-spin-qutrit system by applying the concept of negativity. It is found that the nonlinear couplings favor the thermal entanglement creating. Only when the nonlinear couplings ∣K∣ are larger than a certain critical value does the entanglement exist. The dependence of the thermal entanglement in this system on the magnetic field and temperature is also presented. The critical magnetic field increases with the increasing nonlinear couplings constant ∣K∣. And for a fixed nonlinear couplings constant, the critical temperature is independent of the magnetic field B.     

Microwave properties of composites with glass coated amorphous magnetic microwires

The complex permittivity and permeability of composites filled with Fe-based microwires are measured in a coaxial line at frequencies from 0.01 to 10 GHz.The samples under study consist of closely packed wire sections with various orientations relative to wave vector. The composites, where the wires are collinear to the coaxial axis, are found to be low permeable. Their permittivity has frequency dispersion governed by the length of the wire and its linear impedance. The middle section of the wire has higher impedance than that of the end sections where the regular domain structure is distorted. Magnetic bias parallel to the wire axis affects the linear impedance and parameters of dielectric absorption of a composite, the effect is proportional to bias strength. The samples of a coil-type structure, where the wires are wound around the coaxial axis, display the intensive magnetic absorption attributed to the domain wall motion. The absorption takes place in the megahertz band, at microwaves the permeability is close to unity. The microwave properties of diluted composites filled with randomly oriented permeable wires are discussed.     

Classical magnetostriction of nickel in high magnetic field

A simple model is proposed as a possible explanation for the checkerboard pattern of modulations in the hole density observed in recent tunneling experiments on underdoped cuprates. Two assumptions are made; first, an enhanced hole density near the acceptor dopants and secondly short range correlations in the positions of these dopants caused by their electrostatic and anisotropic elastic interactions. Together these can lead to a structure factor in qualitative agreement with experiment.     

On fixed points of stratified maps

Nielsen fixed point theory deals with the fixed point sets of self maps on compact polyhedra. In this note, we shall extend it to stratified maps, to consider fixed points on (noncompact) strata. The extension was motivated by our recent work on the braid forcing problem in which the deleted symmetric products are indispensable. The stratified viewpoint is theoretically as natural as the equivariant Nielsen fixed point theory, while it can be more tractable computationally and more flexible in applications. This work was partially supported by an NSFC grant and a BMEC grant.     

Simple infinite-dimensional quotients of the group C-algebras ofcertain discrete 6-dimensional nilpotent groups

We study here the simple infinite-dimensional quotients of the group C^*-algebras of two discrete6-dimensional nilpotent groups H_6,1 and H_6,2 as the higher-dimensional analogues of the irrational rotation algebras. P Milnes and S. Walters, jointly and individually, have studied the lower-dimensional cases in a series of papers, and also have started the study of some other 6-dimensional groups. For G = H_6,1 or H_6,2, we can determine the crossed product presentations for the simple quotients of C^* (G), and matrix representations for those arising from non-faithful representations of the groups. The isomorphism classifications of these quotients are obtained using K-theoretic tools, namely, the K-groups and the range of trace on K₀. This marks the first use of K-theory in the classification of quotients for 6-dimensional groups.     

An Evolution Principle and the Existence of Entropy. ODE Case

We formulate a basic principle, called evolution principle, and show that in the case of an underdetermined ODE it is equivalent to other existing principles, which are the entropy principle and Carathéodory's inaccessibility axiom. In a forthcoming paper we shall formulate the same principle in the PDE case. Received May 20, 1997     

First order in the plaquette expansion

The plaquette expansion, a general non-perturbative method for calculating the properties of lattice Hamiltonian systems, is analytically investigated at the first non-trivial order for an arbitrary system. At this level the approximation describes systems with either a bounded or an unbounded spectrum, depending on simple inequalities formed from the first four cumulants. The analysis yields analytic forms for the ground state energy, mass gaps and density of states in the thermodynamic limit. An exact form for the resolvent oeprator is given for a finite number of sites, as well as the asymptotic form in the thermodynamic limit.