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Rodney Loudon 《物理学进展》2013,62(66):243-280
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. 相似文献
3.
A.-S. F. Obada G. M. Abd Al-Kader 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):189-198
The nonlinear extensions of the single-mode squeezed vacuum and
squeezed coherent states are studied. We have constructed the
nonlinear squeezed states (NLSS's) realization of
SU(1,1) Lie algebra. Two cases of this realization are
considered for unitary and non-unitary deformation operator
function. The nonlinear squeezed coherent states (NLSCS's)
are defined and special cases of these states are obtained.
Some nonclassical properties of these states are discussed. The
s-parameterized characteristic function and various moments are
calculated. The Glauber second-order coherence function is
calculated. The squeezing properties of the NLSCS's are studied.
Analytical and numerical results for the quadrature component
distributions for the NLSCS's are presented. A generation scheme for
NLSCS's using the trapped ions centre-of-mass motion approach is
proposed. 相似文献
4.
The characteristics and principles of multilevel trigger systems of the ATLAS and CMS detectors are considered. Calorimeter algorithms for particle identification are described. The parameters of the trigger chambers used for muon track identification are presented. Methods for designing custom processors based on custom integrated circuits and programmable arrays are described. The parameters of the trigger systems of the ATLAS and CMS detectors are compared. 相似文献
5.
Electronic stopping powers for 0. 05-10 MeV protons in a group of organic materials are systematically calculated. The calculations are based on Ashley's dielectric model, and an evaluation approach of optical energy loss function is incorporated into Ashley's model because no experimental optical data are available for most of the organic materials under consideration. The Barkas-effect correction and Bloch correction are included. The proton stopping powers for the considered organic materials except for mylar in the energy range from 0.05 to 10 MeV are presented for the first time. The results may be useful for studies of various radiation effects in these materials and for space research. 相似文献
6.
N. V. Studenichnik 《Acoustical Physics》2002,48(1):110-117
Experimental data on the volume and surface prereverberation are presented. The main prereverberation features and parameters are considered, and the mechanism and theory of the phenomenon are discussed. The range dependences of the prereverberation times are analyzed for different ocean regions and for distances from 180 to 1500 km. Quantitative data on the prereverberation times are presented. The widths of the scattering diagrams are estimated for the underwater and surface sound channels. 相似文献
7.
G. L. Depoorter 《Optics & Laser Technology》1976,8(2):65-67
Construction details are given for a non-coaxial Marx-bank driver system for optical excitation of organic dye lasers. Coaxial flashlamps are used. The electrical characteristics of the driver system are discussed and performance characteristics for Rhodamine 6G are given. The system performs well for visible dyes. 相似文献
8.
Gamal M. Abd Al-Kader 《中国物理》1999,8(10):754-767
Much attention is given for the squeezed coherent states (SCS's) superposition. The s-parameterized charactristic function (CF) for the output field with the superposition of SCS's as input field is given. The s-parameterized quasiprobabilty distribution function (QDF) for the output field with superposition of SCS's as input state are investigated. Various moments are calculated by using the s-parameterized CF for that field. The Glauber second-order coherence function is calculated. The quadrature squeezing for the output field are discussed. Some QDF's of the output fields are plotted as functions of the interaction time. Phase properties of the superpostion of SCS's are studied. The s-parameterized phase distributions obtained by integrating the s-parameterized QDF over radial variable are illustrated. 相似文献
9.
The system of partial differential equations for moving optical solitons in fiber Bragg gratings are studied. The traveling wave reductions are used to look for solutions of the system of equations. The compatibility conditions for the overdetermined system of equations are analyzed and discussed. Periodic and solitary waves in optical fiber gratings are found and illustrated. 相似文献
10.
Balance equations are established for steady-state nonlinear electronic transport in the presence of an electric field both for a single quasi 1D-heterostructure and for a multi-quantum-wire superlattice. The carrier-impurity scatterings and carrierphonon scatterings have been taken into account. The general equations for determining the resistivities are obtained and the Ohmic mobility formula are given. The density-density correlation functions for the wire structures are also studied in some detail. 相似文献
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Elastic Waves in Generalized Thermo-Piezoelectric Transversely Isotropic Circular Bar Immersed in Fluid 下载免费PDF全文
In this paper, a mathematical model is developed to study the wave propagation
in an infinite, homogeneous, transversely isotropic thermo-piezoelectric solid
bar of circular cross-sections immersed in inviscid fluid. The present study is based
on the use of the three-dimensional theory of elasticity. Three displacement potential
functions are introduced to uncouple the equations of motion and the heat and
electric conductions. The frequency equations are obtained for longitudinal and flexural
modes of vibration and are studied based on Lord-Shulman, Green-Lindsay and
Classical theory theories of thermo elasticity. The frequency equations of the coupled
system consisting of cylinder and fluid are developed under the assumption of perfect-slip
boundary conditions at the fluid-solid interfaces, which are obtained for longitudinal
and flexural modes of vibration and are studied numerically for PZT-4 material
bar immersed in fluid. The computed non-dimensional frequencies are compared
with Lord-Shulman, Green-Lindsay and Classical theory theories of thermo elasticity
for longitudinal and flexural modes of vibrations. The dispersion curves are drawn
for longitudinal and flexural modes of vibrations. Moreover, the dispersion of specific
loss and damping factors are also analyzed for longitudinal and flexural modes of
vibrations. 相似文献
13.
Phase transitions for systems with diperiodic symmetry are discussed. Direct group-theoretical methods are employed to obtain a list of possible commensurate lower-symmetry phases (subgroups) which are induced by a single order parameter. The lower-symmetry phases for all 80 diperiodic space groups are given, along with specific details of the group-subgroup relationships. Results for the 17 two-dimensional space groups are also contained in our list. The renormalization-group Hamiltonian densities for the diperiodics are calculated. The 12 densities listed constitute the complete set of densities which may arise in the diperiodic space groups. Critical properties for the diperiodics can thus be obtained from analysis of these densities. 相似文献
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In this paper the conservation theorems of the constrained Birkhoffian systems are
studied by using the method of integrating factors. The differential equations of
motion of the system are written. The definition of integrating factors is given
for the system. The necessary conditions for the existence of the conserved quantity
for the system are studied. The conservation theorem and its inverse for the system
are established. Finally, an example is given to illustrate the application of the
results. 相似文献
16.
The corrections to in the standard model are calculated for arbitrary light fermions f. The relevant analytical results are listed in a form that is appropriate for practical applications, and numerical results
for integrated cross sections are discussed. The corresponding QED corrections are generally of the order of some per mille
for arbitrary energies. The weak corrections to are negligible below the electroweak scale, reach the percent level at a few hundred GeV, and grow to about at 2 TeV. The weak corrections to and production have a shape similar to the one for , but they are larger by factors of about 1.4 and 3, respectively.
Received: 18 December 1998 / Revised version: 1 March 1999 / Published online: 18 June 1999 相似文献
17.
A.L. Crosbie R.L. Dougherty H.V. Kothari 《Journal of Quantitative Spectroscopy & Radiative Transfer》1977,18(1):69-91
An exact formulation is presented for a nongray two-dimensional, finite, planar, absorbing-emitting medium in radiative equilibrium. The absorption coefficient consists of an array of equal intensity, nonoverlapping bands or lines. Rectangular, triangular, exponential, Doppler and Lorentz shapes are specifically considered. Exact expressions are obtained for a medium subjected to collimated and diffuse radiation. The integral equations are linearized by the narrow-band approximation. The solution for the cosine-varying, collimated, monochromatic radiation model is used to construct the solutions for other boundary conditions. The two-dimensional equations are reduced to one-dimensional equations by the method of separation of variables. Results for the diffuse case are presented for several spatial variations. 相似文献
18.
The three-dimensional vibrational problem for the isolated van der Waals complex formed by the Li+ cation with the N2 molecule is solved by the variational method. The potential energy and dipole moment surfaces are calculated using different basis sets of atomic functions and different approaches for taking electron correlation into account. The anharmonic effects caused by the interaction of vibrational degrees of freedom of the complex are consistently considered for the first time. The energy levels of three-dimensional vibrational states are determined. The frequency shift of the N2 molecule vibration upon complexation and the fundamental transition intensity for this vibration in the complex are calculated. The frequencies and intensities for a number of spectral transitions between the states associated with excitation of low-frequency modes are determined. The average values of geometrical parameters and their variances are calculated for the ground state and excited vibrational states of the complex. 相似文献
19.
Tiwari G. N. Singh Dinesh Tolpadi S. K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1976,4(1):62-65
The dispersion relations and cut-off frequencies for the appropriate modes existing inside the relativistically moving lossy isotropic plasma waveguide are studied and are found to depend on waveguide dimensions, plasma-parameters and the drift velocity of plasma medium. The field as well as power flow are also studied in detail and it is found that the fields as well as power flow for TE modes are unchanged while for TM modes they are modified depending on the drift velocity of the plasma medium. The results are compared with those obtained for the case of lossless relativistically moving and lossy stationary plasma waveguides. 相似文献
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Low-amplitude Screening-photovoltaic Spatial Solitons in Biased Photovoltaic Photorefractive Crystals 总被引:1,自引:0,他引:1
1 Introduction Photorefractivespatialsolitonshaveattractedgreatattentioninthepastyears[1~ 11] .Theyhavebecomeoneofconsiderablesubjectsinphotorefractivenonlinearoptics .Uponillumination ,photorefractivematerialscansetupspace chargefieldincrystals,whichwilli… 相似文献