半导体激光器的M2因子可以小于1

根据Porras的非傍轴矢量矩理论,对双异质结半导体激光器的光束质量进行了研究.结果表明,在有源层厚度d_a远小于波长λ的条件下,半导体激光器的M²因子可以小于1,并且没有下限.     

Top Quark Chromomagnetic Dipole Moment in the Littlest Higgs Model with T-Parity

The littlest Higgs model with T-parity, which is called LHT model, predicts the existence of the new particles, such as heavy top quarks, heavy gauge bosons, and mirror fermions. We calculate the one-loop contributions of these new particles to the top quark chromomagnetic dipole moment (CMDM) ΔK. We find that the contribution of the LHT model is one order of magnitude smaller than the standard model prediction value.     

基于不稳定核基本性质测量的原子核结构研究

精密激光谱学是通过测量核素原子光谱的超精细结构和同位素移位来研究原子核的基本性质,为原子核自旋、磁矩、电四极矩及电荷均方根半径的确定提供了一种模型独立的测量方式。这些原子核基本性质的测量,能够比较精确地描述原子核微观结构的演化。近年来,随着放射性束流装置的发展,产生远离β-稳定线的丰中子/丰质子核素成为可能,也进一步促进了高分辨和高灵敏度的激光谱技术更加广泛的应用。简单介绍了基于放射性核素超精细结构的激光谱学测量原理,并通过几个经典实例来回顾近年来激光谱学在原子核奇特结构研究领域的独特贡献。主要通过分析几个重要核区原子核的基本性质,结合大尺度壳模型、ab initio理论、密度泛函理论等,来探索丰中子核中展现出来的一些新的奇特现象,如晕结构、幻数演化、形状共存等。High-precision laser spectroscopy technique is used to determine the ground state properties of exotic nuclei by probing its electronic hyperfine structure and isotope shift. It provides a model-independent measurement of nuclear spin, magnetic moment, electric quadrupole moment and charge radii. These nuclear parameters can be used to investigate the nuclear structure evolution and the nuclear shapes. With the development of accelerators and isotope separators, exotic isotopes far from β stability became accessible experimentally, which enhanced the capability of the laser spectroscopy technique being applied in the field of nuclear physics. A brief introduction to experimental principle is given, followed by a review of several typical examples for the experimental investigations in the different regions of nuclear chart. This aims to demonstrate the contributions of ground state properties measurement by using laser spectroscopy technique to the nuclear structure study of exotic isotopes. This discussion involves several different nuclear theory models in order to interpret the exotic phenomena observed in the neutron-rich isotopes, such as halo structure, shell evolution, shape coexistence and so on.     

Persistent currents in a lattice correlated electron ring with a magnetic impurity

The behavior of charge and spin persistent currents in an integrable lattice ring of strongly correlated electrons with a magnetic impurity is exactly studied. Our results manifest that the oscillations of charge and spin persistent currents are similar to the ones, earlier obtained for integrable continuum models with a magnetic impurity. The difference is due to two (instead of one) Fermi velocities of low-lying excitations. The form of oscillations in the ground state is “saw-tooth”-like, generic for any multi-particle coherent one-dimensional models. The integrable magnetic impurity introduces net charge and spin chiralities in the generic integrable lattice system, which determine the initial phase shifts of charge and spin persistent currents. We show that the magnitude of the charge persistent current in the generic Kondo situation does not depend on the parameters of the magnetic impurity, unlike the (magneto)resistivity of transport currents. Received 30 January 2003 / Received in final form 12 March 2003 Published online 11 April 2003 RID="a" ID="a"e-mail: zvyagin@fy.chalmers.se     

定轴转动带电体的远区磁场分布

类比定轴转动刚体转动惯量以及电偶极子电场的计算方法，得出定轴转动带电体的磁矩及其远区磁场分布。     

Cell image recognition with radial harmonic Fourier moments

Various types of moments have been utilized to recognize image patterns in a number of applications. Multi-distortion invariant－radial harmonic Fourier moments were investigated in the recognition of cell smear images. Image recognition experiments showed that radial harmonic Fourier moments are not only highly concentrated image features but also have a good property of antidistortion and antinoise. They may be used in fast and accurate automatic cell recognition.     

Extended Hydrodynamics from Enskog’s Equation for a Two-Dimensional System General Formalism

Balance equations are derived from Enskog’s kinetic equation for a two-dimensional system of hard disks using Grad’s moment expansion method. This set of equations constitute an extended hydrodynamics for moderately dense bi-dimensional fluids. The set of independent hydrodynamic fields in the present formulations are: density, velocity, temperature and also—following Grad’s original idea—the symmetric and traceless pressure tensor p _ij and the heat flux vector q ^k . An approximation scheme similar in spirit to one made by Grad in his original work is made. Once the hydrodynamics is derived it is used to discuss the nature of a simple one-dimensional heat conduction problem. It is shown that, not too far from equilibrium, the nonequilibrium pressure in this case only depends on the density, temperature and heat flux vector. PACS: 51.10.+y, 05.20.Jj, 44.10.+i, 05.70.Ln     

几种二阶矩模型模拟湍流旋流燃烧的比较

本文对几种二阶矩湍流反应模型,包括统一二阶矩模型、只考虑温度脉动的二阶矩模型、只考虑浓度脉动关联的二阶矩模型、及同时考虑温度脉动和浓度脉动关联的二阶矩模型,进行了比较。将上述模型加入到FLUENT6.0软件平台上,模拟了不同旋流数下甲烷-空气的旋流燃烧。模拟结果和实验结果进行了比较,探讨了各关联量大小及其对时平均反应率的影响。结果表明,统一二阶矩湍流反应模型具有最好的模拟效果。其原因是,各种关联矩中,化学反应率系数与浓度间的脉动关联最重要。