新型长周期光纤光栅的横向负载特性及其偏振相关性研究

发现高频CO2激光脉冲写入的长周期光纤光栅谐振波长的横向负载特性具有较强的负载方向相关性,而损耗峰幅值的横向负载特性的方向相关性较弱.不同圆周方向的横向负载对谐振波长偏振相关性的影响差异较大,但对损耗峰幅值偏振相关性的影响差异较小.利用横向负载引起双折射进而导致光栅的光学主轴旋转的相关理论,合理解释了该长周期光纤光栅独特的横向负载特性及其偏振相关性.     

自然地面背景下红外目标检测算法

为了快速准确地检测出以地面物体为背景的红外序列图像中的目标,结合小波变换的特点及其应用于图像边缘检测的优点,提出了一种基于小波技术的图像预处理算法。该方法利用图像边缘在目标识别中的重要作用,讨论了基于小波变换的图像边缘检测方法,并结合地面背景红外图像自身的特点,大大地提高了单帧的检测概率。     

Axiomatic Geometric Formulation of Electromagnetism with Only One Axiom: The Field Equation for the Bivector Field <Emphasis Type="Italic">F</Emphasis> with an Explanation of the Trouton-Noble Experiment

In this paper we present an axiomatic, geometric, formulation of electromagnetism with only one axiom: the field equation for the Faraday bivector field F. This formulation with F field is a self-contained, complete and consistent formulation that dispenses with either electric and magnetic fields or the electromagnetic potentials. All physical quantities are defined without reference frames, the absolute quantities, i.e., they are geometric four-dimensional (4D) quantities or, when some basis is introduced, every quantity is represented as a 4D coordinate-based geometric quantity comprising both components and a basis. The new observer-independent expressions for the stress-energy vector T(n) (1-vector), the energy density U (scalar), the Poynting vector S and the momentum density g (1-vectors), the angular momentum density M (bivector) and the Lorentz force K ((1-vector) are directly derived from the field equation for F. The local conservation laws are also directly derived from that field equation. The 1-vector Lagrangian with the F field as a 4D absolute quantity is presented; the interaction term is written in terms of F and not, as usual, in terms of A. It is shown that this geometric formulation is in a full agreement with the Trouton-Noble experiment.     

The Difference Between the Standard and The Lorentz Transformations of the Electric and the Magnetic Fields

In this paper it is shown by using the Clifford algebra formalism that the usual Lorentz transformations of the three-dimensional (3D) vectors of the electric and magnetic fields E and B (which will be named as standard transformations (ST)) are different than the Lorentz transformations (LT) of well-defined quantities from the 4D spacetime. This difference between the ST and the LT is obtained regardless of the used algebraic objects (1-vectors or bivectors) for the representation of the electric and magnetic fields in the usual observer dependent decompositions of F. The LT correctly transform the whole 4D quantity, e.g., E_f : F · γ₀, whereas the ST are the result of the application of the LT only to the part of E_f, i.e., to F, but leaving γ₀ unchanged. The new decompositions of F in terms of 4D quantities that are defined without reference frames, i.e., the absolute quantities, are introduced and discussed. It is shown that the LT of the 4D quantities representing electric and magnetic fields correctly describe the motional electromotive force (emf) for all relatively moving inertial observers, whereas it is not the case with the ST of the 3D E and B.     

对《二维六角形晶格伊辛模型的重正化群解》一文的进一步计算

针对《二维六角形晶格伊辛模型的重正化群解》一文中有关〈V〉0的计算进行了修正,给出了新的重正化群的变换、重正化群的线性化变换矩阵以及临界指数.     

中国优秀物理学家的杰出代表——葛庭燧

回顾介绍了葛庭燧院士的生平和他在科学研究、人才培养方面所作出的贡献,展示了他的高尚情操,分析了他取得卓著成就的原因.     

Intrinsic Localized Spin-Wave Modes in an Anisotropic Ferromagnet with Dzyaloshinsky-Moriya Interaction

The existence and properties of intrinsic localized spin-wave modes in a ferromagnetic XXZ spin chain with Dzyaloshinsky-Moriya interaction are investigated analytically in the semiclassical limit. The model Hamiltonian is quantized by introducing the Dyson-Maleev transformation and the coherent state representation is chosen as the basic representation of the system. By making use of the method of multiple scales combined with a quasidiscreteness approximation, the equation of motion for the coherent-state amplitude is reduced to the nonlinear Schrödinger equation. It is shown that a bright intrinsic localized spin-wave mode whose eigenfrequency lies below the bottom of the magnon frequency band can exist in the ferromagnetic system. We also show that the system can produce a dark intrinsic localized spin-wave mode, i.e., nonpropagating kink, whose eigenfrequency is below the upper of the magnon frequency band. In addition, we find that the introduction of the Dzyaloshinsky-Moriya interaction changes wave numbers in the Brillouin-zone corresponding to the appearance of intrinsic localized spin-wave modes.     

大功率高温超导滤波器的设计与功率测试

本文在双面YBCO高温超导薄膜上设计并制备了两节大功率超导滤波器,根据滤波器功率承载能力与最大电流密度之间的关系,减小电流密度和分散电流密度的分布是提高功率承载能力的关键.本文采用增加超导谐振器尺寸、优化几何结构及改进馈线耦合方式的方法,设计了两节2 GHz频段梭型谐振器结构的滤波器.设计及测量结果显示了馈线结构及谐振器几何尺寸优化程度对超导滤波器功率承载能力有不同程度的影响,说明了在大功率超导滤波器设计中应选用无结点间隙耦合式馈线以抑制电流密度的聚集.采用优化后的谐振器结构制备的梭型两节超导滤波器经测试功率承载能力为2 W.超导滤波器的尺寸为25×12 mm LaAlO3基片,中心频率2.022 GHz,相对带宽为2.4%.同时给出了超导滤波器功率测试的结构和方法.     

太赫兹GaAs肖特基混频二极管高频特性分析

在太赫兹波段,存在几种新的高频效应会限制混频二极管的高频特性.应用热电子发射理论和隧道理论,研究了外延层肖特基二极管的高频特性,并以截止频率为品质因数对二极管进行优化设计.研究表明,当二极管工作频率大于等离子频率时,二极管相当于一个电容,失去了混频性能;提高基底掺杂浓度可以减小基底等离子共振效应;外延层等离子频率非常重要并且在研究外延层等离子共振效应时必须考虑传输时间效应;减小阳极直径、减小外延层厚度、提高外延层掺杂浓度可以提高二极管的工作频率.这对太赫兹波段室温混频器件的研制具有重要的参考价值.     

Effects of the structural order of canthaxanthin on the Raman scattering cross section in various solvents: A study by Raman spectroscopy and ab initio calculation

In this work,we measure the Raman scattering cross sections(RSCSs) of the carbon-carbon(CC) stretching vibrational modes of canthaxanthin in benzene,acetone,n-heptane,cyclohexane,and m-xylene.It is found that the absolute RSCS of CC stretching mode of canthaxanthin reaches a value of 10 24 cm 2 ·molecule 1 ·sr 1 at 8×10 5 M,which is 6 orders of magnitude larger than general RSCS(10 30 cm 2 ·molecule 1 ·sr 1),and the RSCSs of canthaxanthin in various solvents are very different due to the hydrogen bond.A theoretical interpretation of the magnetic experimental results is given,which is introduced in a qualitative nonlinear model of coherent weakly damped electron-lattice vibration in the structural order of polyene chains.In addition,the optimal structure and the bond length alternation(BLA) parameter of canthaxanthin are calculated using quantum chemistry calculation(at the b3lyp/6-31g(d,p) level of theory).The theoretical calculations are in good agreement with the experimental results.Furthermore,the combination of Raman spectroscopy and the quantum chemistry calculation study would be a quite suitable method of studying the structures and the properties of the π-conjugated systems.