Theory of infra-red and optical spectra of antiferromagnets

The contributions of magnons to the optical properties of antiferromagnets having the rutile structure are discussed. The properties considered are electric-dipole active two-magnon absorption in the infra-red, and magnon sidebands on sharp-line exciton transitions in the visible. The discussion is based on a thorough treatment of the properties of excitons and magnons in the antiferromagnetically ordered state. The site-group and space-group symmetries of the magnetic excitations are derived and the selection rules for electric and magnetic dipole transitions are determined. The occurrence of magnetic Davydov splittings of the excitons is investigated, and their symmetry properties throughout the Brillouin zone are derived. The functional dependences of exciton energy on wave vector are calculated. Applications of the theory are made to experimental results on excitons and magnons in MnF₂, FeF₂ and CoF₂.

The possible mechanisms for two-magnon and magnon-sideband absorption are discussed, and the influence of crystal symmetry on these mechanisms is described. The two-magnon state responsible for electric-dipole absorption is identified and selection rules for electric-dipole activity are presented. A spin Hamiltonian for the two-magnon process is set up and used to derive expressions for absorption coefficients for electric vector parallel and perpendicular to the crystal c-axis. Comparison with experiment for MnF₂ yields numerical values for the parameters of the basic coupling mechanism. The exciton-magnon states which give rise to magnon-sideband absorption are explicitly constructed and electric-dipole selection rules are derived for all possible types of sideband. Spin Hamiltonians for the various magnonsideband absorption processes are presented and used to derive expressions for sideband shapes. The results are applied to the experimental spectra for MnF₂ and FeF₂ and the sideband shapes in MnF₂ are calculated numerically. The sideband shapes observable in emission spectra are also briefly discussed.     

外电场下BN分子的结构及性质

采用QCISD方法研究了BN基态分子在不同场强条件下的稳定构型及激发态性质。分析了外电场对BN分子键长、总能量、能级、谐振频率和红外谱强度以及对BN分子前10个激发态的激发能、振子强度等的影响。结果表明随着正向电场的逐渐增大, BN分子键长先减小后增大;分子总能量则先增大后减小;分子电偶极矩 增大;费米能级和能隙均减小。谐振频率及红外谱强度均随正向电场的增大而增大。由基态到第1激发态的波长减小,激发能增大,而基态至第2-10激发态的波长增大而激发能减小。     

外电场下BN分子的结构及性质

采用QCISD方法研究了BN基态分子在不同场强条件下的稳定构型及激发态性质。分析了外电场对BN分子键长、总能量、能级、谐振频率和红外谱强度以及对BN分子前10个激发态的激发能、振子强度等的影响。结果表明随着正向电场的逐渐增大, BN分子键长先减小后增大;分子总能量则先增大后减小;分子电偶极矩μ增大;费米能级和能隙均减小。谐振频率及红外谱强度均随正向电场的增大而增大。由基态到第1激发态的波长减小,激发能增大,而基态至第2－10激发态的波长增大而激发能减小。     

Successive oscillatory fields at radio to optical frequencies

The methods of separated or successive oscillatory fields (often called Ramsey methods) are described for radio, microwave and optical coherent radiation. The methods are initially described qualitatively. The quantitative theories of the methods are also given. For a two-level system at radio frequencies exact expressions for the transition probability amplitudes for an arbitrary number of successive oscillatory regions can be found in terms of products of successive transformation matrices. The expressions are greatly simplified if the oscillatory-field regions are very short. If there are only two oscillatory-field regions the situation is similar to a Young's two-slit interference pattern except that the two paths are separated in spin space rather than normal space. Some results from more than two oscillatory regions are discussed. The extensions of the methods and the theories to optical frequencies are described. The advantages and disadvantages of the methods are given as are the many extensions of the method beyond the original concept.I am honored to write an article in celebration of the sixtieth birthday of Herbert Walther. He has established one of the world's best atomic-physics laboratories and has made great contributions to physics, ranging from precision spectroscopy and laser cooling to measurements of fundamental atomic and quantum properties. He has also been a helpful consultant, adviser, and friend to many of us in the field. Happy birthday!!     

体内(in Vivo)NMR研究

本文综述了体内(in Vivo)核磁共振波谱技术的目前概况,简要介绍了这一技术的基本原理。对空间定位技术进行了重点评述,并给出了分类表。同时讨论了化学位移对空间定位精确的影响,介绍了提高定位精确度的实验方法。列举了空间定位波谱技术在生命科学研究中的应用,给出了大量的参考文献。     

NON-LINEAR STEADY STATE VIBRATIONS OF BEAMS EXCITED BY VORTEX SHEDDING

In this paper the non-linear vibrations of beams excited by vortex-shedding are considered. In particular, the steady state responses of beams near the synchronization region are taken into account. The main aerodynamic properties of wind are described by using the semi-empirical model proposed by Hartlen and Currie. The finite element method and the strip method are used to formulate the equation of motion of the system treated. The harmonic balance method is adopted to derive the amplitude equations. These equations are solved with the help of the continuation method which is very convenient to perform the parametric studies of the problem and to determine the response curve in the synchronization region. Moreover, the equations of motion are also integrated using the Newmark method. The results of calculations of several example problems are also shown to confirm the efficiency and accuracy of the presented method. The results obtained by the harmonic balance method and by the Newmark methods are in good agreement with each other.     

Worldwide business opportunities in fiber optic communications

The world market for fiber optic intelligence transmission systems is forecast through I990 and segmented according to the geographical regions of production and demand. The total world market forecast is also segmented according to end-industry application. Fiber optic component markets are forecast and price trends are reviewed. The most significant future developments in components are discussed. The major business opportunities are outlined and the possible threats to development of a viable market are reviewed.     

光在两单轴晶体间界面的反射和透射

根据位相匹配条件和应该满足的边界方程,在光轴取向任意的条件下,得到了光在两单轴晶体界面的反射和折射的理论表达式,给出了更普遍的公式计算光能量损失以及两束折射光的能量比。数值模拟表明所得结果满足能量守恒,光轴的取向和入射角大小对晶体中折射的o光、e光的能量比有重大影响,但是对反射率影响很小。只要知道了晶体的有关参数及入射条件,利用所给表达式可以计算各光束光能量比,为晶体器件特性研究提供了有力的工具。由于对光轴取向和入射角度没有任何限制,公式具有普遍性。     

Cosmic rays of the highest energies

The article describes the study of cosmic rays above 10 19 eV. Following a brief introduction, the reasons for the current interest in this topic are discussed. The methods used to measure the properties of the very rare ultrahigh-energy cosmic rays are explained and the current data described. The data lead to an enigma and the many theories proposed to explain it are summarized. The properties and potential of new detectors are outlined.     

Effective responses of nonlinear elliptic cylindrical composites

The higher-order dielectric responses of composites composed of weakly nonlinear elliptic cylindrical inclusions randomly embedded in linear media are investigated. The general formulae for effective DC coefficients are newly derived by the average field method up to the ninth order and then applied to analyze the effects of inclusion shapes on the effective response. The results are directly transformed to the quasi-static AC response of the composites under the sinusoidal external electric field with fundamental and third harmonic frequencies. The more general relationships between the effective DC and AC coefficients are established up to the seventh order and third harmonic, which are applicable to all weakly nonlinear isotropic composites.     

Formulation of Zeeman modulation as a signal filter

The Bloch equation containing a Zeeman modulation field is solved analytically by treating the Zeeman modulation frequency as a perturbation. The absorption and dispersion signals at both 0 degrees and 90 degrees modulation phase are obtained. The solutions are valid to first order in the modulation frequency, but are otherwise valid for any value of modulation amplitude or microwave amplitude. A first order treatment of modulation frequency is shown to be a valid approximation over a wide range of typical experimental EPR conditions. The solutions derived from the Bloch equation suggest that the effect of over-modulation on first and second harmonic EPR spectra can be formulated as a mathematical filter that smoothes and broadens the under-modulated signal. The only adjustable filter parameter is a width that is equivalent to the applied peak-to-peak modulation amplitude. The true spin-spin and spin-lattice relaxation rates are completely determined from the under-modulated spectrum. The filters derived from the analytic solutions of the Bloch equation in the linear limit of modulation frequency are tested against numerical solutions of the Bloch equation that are valid for any modulation frequency to show their applicability. The filters are further tested using experimental EPR spectra. Experimental under-modulated spectra are mathematically filtered and compared with the experimental over-modulated spectra. The application of modulation filters to STEPR spectra is explored and limitations are discussed.     

Measurement of the quark and gluon fragmentation functions in Z^0 hadronic decays

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse and longitudinal components of the total hadronic cross section are evaluated from the measured fragmentation functions. They are found to be and respectively. The strong coupling constant is calculated from in next-to-leading order of perturbative QCD, giving Including non-perturbative power corrections leads to The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, The fragmentation functions and multiplicities in and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated. Received: 12 September 1997 / Published online: 19 October 1998     

Nonplanar double layers in plasmas with opposite polarity dust

Nonplanar (cylindrical and spherical) double layers (DLs) in a four-component dusty plasma (composed of inertial positively and negatively charged dust, Boltzmann electrons and ions) are studied by employing the reductive perturbation method. The modified Gardner equation describing the nonlinear propagation of the dust-acoustic (DA) waves is derived, and its nonplanar double layer solutions are numerically analyzed. The parametric regimes for the existence of the DLs, which are found to be associated with positive potential only, are obtained. The basic features of nonplanar DA DLs, which are found to be different from planar ones, are also identified. The implications of our results to different space and laboratory dusty plasma situations, where opposite polarity dust are observed, are discussed.     

Electrostatic solitons in unmagnetized hot electron-positron-ion plasmas

Linear and nonlinear electrostatic waves in unmagnetized electron-positron-ion (e-p-i) plasmas are studied. The electrons and positrons are assumed to be isothermal and dynamic while ions are considered to be stationary to neutralize the plasma background only. It is found that both upper (fast) and lower (slow) Langmuir waves can propagates in such a type of pair (e-p) plasma in the presence of ions. The small amplitude electrostatic Korteweg-de Vries (KdV) solitons are also obtained using reductive perturbation method. The electrostatic potential hump structures are found to exist when the temperature of the electrons is larger than the positrons, while the electrostatic potential dips are obtained in the reverse temperature conditions for electrons and positrons in e-p-i plasmas. The numerical results are also shown for illustration. The effects of different ion concentration and temperature ratios of electrons and positrons, on the formation of nonlinear electrostatic potential structures in e-p-i plasmas are also discussed.     

Dispersion properties of electron acoustic waves in degenerate and non‐degenerate quantum plasmas

The longitudinal response functions are used to generalize the dispersion properties of electron acoustic waves (EAWs) in the presence of quantum recoil, for isotropic, non‐relativistic, degenerate/non‐degenerate plasmas. In order to study the EAWs, the constituents of non‐degenerate (thermal) plasma are considered to be of two groups of electrons having different number density and temperature, namely the cold electrons and the hot electrons. Similarly in degenerate (Fermi) plasma the two population of electrons are considered to be the thinly populated and the thickly populated electrons. The sparsely populated electrons are termed as cold electrons while the densely populated ones are termed as hot electrons. The ions are stationary which form the neutralizing background. The absorption coefficients for Landau damping with the inclusion of the quantum recoil in both plasmas are calculated and discussed. The results are discussed in the context of laser‐produced plasma.     

折射混合望远物镜的设计、制作及实验

介绍了用以取代传统双胶合望远镜的混合单透镜的设计方法,结合设计实例详细介绍了折衍混合单透镜的制作过程及实验结果,并对实际成像效果进行了分析。首次给出了反映折衍混合系统成像性能的图片,它们对混合光学系统及其应用的研究具有重要的参考价值和指导意义     

Worldwide business opportunities in fiber optic communications

Abstract

The world market for fiber optic intelligence transmission systems is forecast through I990 and segmented according to the geographical regions of production and demand. The total world market forecast is also segmented according to end-industry application. Fiber optic component markets are forecast and price trends are reviewed. The most significant future developments in components are discussed. The major business opportunities are outlined and the possible threats to development of a viable market are reviewed.     

Note on the stochastic theory of a self-catalytic chemical reaction. II

The general results of article I on the stochastic representation of the macroscopic stationary state of a self-catalytic chemical system are applied to a step-by-step chemical reaction. The relaxation times to the quasi-stationary state and to the final stationary state are computed by evaluating the first two non-trivial eigenvalues of the transition matrix. The previous results of Oppenheim, Shuler and Weiss are confirmed, precised and extended. The critical and subcritical cases are treated by the same method.     

Spin-Wave Excitations in Anisotropic Kondo Lattice Model

The spin-wave excitations in anisotropic Kondo lattice model are studied using the spin Green's function. Both the ferromagnetic and antiferromagnetic cases are considered. The equations to determine the spectrum of low-energy excitations are given. The anisotropy gaps are obtained, and the long-wavelength and strong-coupling limits are analyzed.