Evolution of basic equations for nearshore wave field

In this paper, a systematic, overall view of theories for periodic waves of permanent form, such as Stokes and cnoidal waves, is described first with their validity ranges. To deal with random waves, a method for estimating directional spectra is given. Then, various wave equations are introduced according to the assumptions included in their derivations. The mild-slope equation is derived for combined refraction and diffraction of linear periodic waves. Various parabolic approximations and time-dependent forms are proposed to include randomness and nonlinearity of waves as well as to simplify numerical calculation. Boussinesq equations are the equations developed for calculating nonlinear wave transformations in shallow water. Nonlinear mild-slope equations are derived as a set of wave equations to predict transformation of nonlinear random waves in the nearshore region. Finally, wave equations are classified systematically for a clear theoretical understanding and appropriate selection for specific applications.     

Polarization changes and beam profile deformation of light during acousto-optic interaction in isotropic media

A spatial Fourier transform approach is proposed to investigate the effects of polarization changes and beam profile deformation of light during acousto-optic (AO) interaction in isotropic media. The behaviour of the total scattered optical fields inside the AO cell can be properly described by a vector wave equation of which the permittivity is perturbed by an acoustic wave propagating inside the medium. In the Bragg regime, using a spatial Fourier transform approach, two coupled differential equations can be derived from the wave equation to depict AO interaction in the spatial frequency domain. Analytic solutions, which comprise the effects of changing polarization, beam deformation and propagating diffraction, can be found from the coupled equations. Detailed numerical simulations, including Fourier transforming the incident light profile to calculate the spectra of the scattered light beams and, hence, their profiles in space using the inverse transform, are presented.     

Temperature dependence of the photonic bandgap and the orientational order parameter for a cholesteric photonic crystal

The reflection spectra of a cholesteric photonic crystal have been measured. The experimental spectra are described by a theoretical expression that follows from the analytical solution of the Maxwell equations. The photonic bandgap width Δν has been determined. The photonic bandgap width changes abruptly as the position of the diffraction band changes. The temperature dependence of the relative bandgap width Δν/ν₀ and the order parameter for a photonic crystal are described by Landau’s theory of phase transitions.     

Empirical determination of the random fraction in disordered channel

A new method of deriving the random fraction in a disordered channel : rom dechanneling experiments is described. In this method backscattering spectra obtained at two different doses are employed, with an assumption on the dose dependence of the defect concentration. The method is applied to the experimental data for B-implanted Si and it is found that the obtained random fraction is similar to the result of the diffusion calculation made by the present authors. The depth profiles of defects are also obtained and compared with the result of theoretical calculations.     

Wave processes in media with hysteretic nonlinearity. Part I

Two phenomenological models of hysteretic equations of state for media with imperfect elasticity are described and compared. On the basis of these equations, a theoretical study of nonlinear effects caused by the acoustic wave propagation in an unbounded medium is performed. The profiles, parameters, and spectra of waves are determined. The distinctive features of nonlinear wave processes in such media are revealed, so that these features can be used to choose the appropriate hysteretic equation of state for analytically describing the experimental data.     

Eikonal approximation of dynamical diffraction equations for X-ray beams with two-dimensional curvature of the wave front. I. Basic formulas

Taking into account the second derivatives of amplitudes with respect to the coordinate perpendicular to the diffraction plane, the eikonal approximation of dynamical diffraction equations for X-ray beams with two-dimensional curvature is presented. The diffracted field outside the crystal, in vacuum is described by the corresponding eikonal approximation of the parabolic equation of diffraction. The corresponding eikonal equations and complete integrals are obtained in case of a perfect crystal. A method is described, by which the eikonals and trajectories inside the crystal as well as in vacuum, outside the crystal, satisfying the given boundary conditions, can be obtained. This method allows to describe diffraction using sufficiently general assumptions on the incident wave front and for the non-plane entrance and exit surfaces of the crystal.     

Determination of diffusion profiles in thin film couples by means of x-ray-diffraction

An x-ray method for the determination of concentration profiles in thin film diffusion couples is presented. This method is based on the theory of Fourier analysis of x-ray diffraction profiles which is generalized to polycrystalline samples showing nonuniform lattice parameter. A Fourier synthesis of the concentration spectrum is possible when the influences of the particle size and the strain in the sample as well as the instrumental function are eliminated from the measured diffraction profile. This can be done by means of reference profiles obtained from layers of the diffusion components. Absorption of the radiation in the sample is negligible when diffusion couples of symmetrical sandwich structure are used. The method is tested experimentally in the system Au-Cu.     

Time-dependent behavior of a pulsed high power xenon flashlamp. Application to the Mega-Joule laser pumping

A numerical model has been developed for studying the time-dependent behavior of cylindrical high power xenon flashlamp. The equations of local energy conservation and mass conservation are solved using the finite volume method to give plasma parameters such as radial temperature profiles, instantaneous emission spectra, pressure, velocity, arc conductance, etc. In a first approximation the plasma is described under local thermodynamic equilibrium, LTE. The results are given as a function of time over the pulse and for several nodes in the cross section. Then the detailed spectral and temporal calculations of the output radiation from xenon flashlamp and radiation efficiencies are provided.     

Investigation of Fe-Mg-Alloys Produced by Ion Implantation

Iron and magnesium are insoluble elements with each other and there is no phase diagram. However, it is possible to produce artificial alloys by ion implantation, in this study by iron implantation into magnesium. Samples are investigated by conversion electron Moessbauer spectroscopy, Auger electron spectroscopy and x-ray diffraction. While at low doses gaussian shaped iron profiles and paramagnetic doublets as Mössbauer spectra are obtained, the iron concentration reaches at the highest dose 90 at.-% in maximum and the Mössbauer spectrum shows a dominant ferromagnetic fraction. The x-ray diffraction pattern let conclude that a dilated α-iron lattice is formed. Microhardness of all samples is clearly increased due to the implantation.     

非均匀反射体全息光栅的数值研究

本文运用矩阵方法详细分析了非均匀反射式全息光栅衍射特性.把全息光栅内部的折射率调制分布看作是一种空间非均匀折射率调制分布,在此基础上进行了数值计算,详细分析了几个影响其衍射性质的因子.基于该方法的数值模拟结果与耦合波理论和以前的实验结果能较好地符合.     

声表面波在声栅上的反常Bragg衍射

本文讨论了在考虑基片各向异性因素时,声表面波在声栅上的Bragg衍射现象。理论分析时,将有关波式和不同模式之间的差别唯象地以它们对应的相速不同来表征之,而不具体讨论这些波式或模式的偏振特性。在分析时,与讨论声-光反常Bragg衍射情形一样采用二波近似,但不借助于引入对应于极化矢量那样的量,而直接由栅区声速分布给出各波式之间的耦合系数。由此而得出的“反常Bragg衍射”公式,与声-光情形下采用极化矢量概念给出的公式一一对应。由这些公式计算的结果,与实验结果良好地符合。 关键词：     

Spectral localization of arbitrarily shaped regions of interest (SLASH) using single voxel signals

A method for obtaining localized spectra from arbitrarily shaped regions of interest is described. When a sample consists of homogeneous compartments or domains, spectra localized in each compartment can be obtained from signals of single voxels with regular shapes by solving a set of simultaneous linear equations. Experimental demonstrations on a phantom and on human brain in vivo for a two compartment, two voxel case are presented. The issue of signal-to-noise ratio is also discussed.     

Method of Coupled Waves in the Theory of Diffraction of Light by Elastic Waves in Crystals

Diffraction of light by elastic waves in crystals is described by the method of coupled waves in a form different from that used by other researchers. The difference is determined by the treatment of two pairs of orthogonal coordinate systems whose principal axes are oriented along the directions of phase and energy transfer of two optical waves interacting on a sound wave. Due to this, the equations of coupled waves assume the most compact form, which was previously unknown for crystals. These equations are easily solved by the conventional methods in terms of quasi-plane waves and also admit of a wider class of solutions for bounded interaction regions. Two different diffraction regimes are compared in the present work, namely, the transmission and reflection diffraction. It is indicated that the suggested approach allows one to refine the parameters that define the efficiency of diffraction of light by elastic waves in crystals.     

Deducing 1D concentration profiles from EPR imaging: a new approach based on the concept of virtual components and optimization with the genetic algorithm

Application of the genetic algorithm (GA) in conjunction with the concept of virtual components (VC) to determine 1D concentration profiles from EPRI spectra (images) is described. In this approach the concentration profile is expressed as the superposition of virtual components described by analytical functions of the Gaussian and Boltzmann type. The method was implemented in the computer program ACon, which allows for fully automated profile extraction via the nonlinear least-squares fitting of experimental images. The parametric sensitivity of the GA internal parameters such as population size, probabilities of the crossover, mutation and elitist retention to the search space was investigated in detail in order to find their optimal settings. The customized genetic algorithm was evaluated using simulated and experimental test data sets and its performance was compared with the Monte Carlo approach.     

On the Diffraction of a Pulsed Wave by a Slit

A new interpretation of the pulsed wave diffraction by a slit is given. The interpretation is based on the representation of the diffraction within the framework of a new method of local oscillation frequencies. The method is used to analyze the radiation field structure described in terms of the Laplace-Beltrami wave equation and the Einstein equations for weak gravitational fields in a curved space. It is found that, under assumptions corresponding to the method of local-oscillation frequencies, the energy-conservation law breaks down in the radiation field defined by the Einstein equations. An analysis of transverse structure of radiation in the far-field zone using the Laplace-Beltrami wave equation yielded results that agree satisfactorily with the known results of experimental and theoretical studies.     

Difference equation solutions for non-steady-state diffusion of charged particles in solids

The hopping transport of charged particles through a solid is described by means of difference equations based on the concept of classical thermal motion over discrete energy barriers. Homogeneous electric fields and concentration gradients are considered to be the driving forces for transport. Transient and steady-state currents are derived, and the concentration profiles are obtained for the mobile charged defect species. For the case of a slab geometry the discreteness of the potential barriers leads to a nonlinear dependence of current on voltage in the high electric field limit, with a more rapid increase of current with voltage than would be expected from an extrapolation of the low field linear dependence. The field-dependent relaxation of a non-steady-state defect concentration profile to the corresponding steady-state profile can be nearly exponential in the limit of large fields. Tracer distributions for the cases of semi-infinite and unbounded diffusion mediums are likewise affected appreciably in the high field limit. The velocity of the peak is increased over that obtained by linear extrapolation from the low field limit. It is concluded that the combination of high electric fields with the natural microscopic discreteness of a solid-state diffusion medium can result in readily observable nonlinear electric field effects which increase approximately exponentially with the atomic separation distances of the discrete barriers in hopping transport. Some of this nonlinear behavior can be retained in differential equations derived from the difference equations by means of Taylor series expansions of the carrier concentration with respect to position.     

The influences of ZnO doping concentration on structure and photorefractive properties of Zn:Fe:LiNbO3 crystals grown by TSSG method

In this paper, LiNbO₃ crystals doped with same concentration of Fe₂O₃ and with different concentration of ZnO have been grown by the top-seeded-solution-growth (TSSG) method. Their IR transmittance spectra, UV-vis absorption spectra, lattice constants, and Curie temperature were measured. In two-wave coupling experiments, writing and erasure time constants, and maximum diffraction efficiency of the crystals were measured and compared with those of congruent LiNbO₃ (CLN) crystals doped with same ions. The crystals grown by TSSG method show shorter writing time, erasure time, and lower diffraction efficiency than the CLN crystals. The influences of ZnO doping concentration on photorefractive properties are studied.     

Formation of holographic diffraction gratings in photoresist

The exposure-development process for the fabrication of holographic diffraction gratings for integrated optics in the positive photoresist Shipley AZ-1350 is theoretically and experimentally investigated. An analysis of the light intensity distribution is carried out, taking into account the reflectivity at the photoresist-substrate interface and the attenuation in the photoresist for two holographic exposure arrangements. The influence of the exposure energy, the development time for a fixed concentration of the developer and the initial photoresist thickness are described. Various grating profiles are calculated for photoresist films, coated on matched and reflective substrates. Scanning electron micrographs demonstrate very good agreement between the actual and calculated gratings profiles.     

Analysis of colonic autofluorescence spectra using multivariate curve resolution alternating least squares

Autofluorescence （AF） spectra of colonic normal and adenocarcinoma tissues are measured under excitation of 337 nm and analyzed by multivariate curve resolution alternating least squares （MCR-ALS） method using non-negativity constraint. Collagen, nicotinamide adenine dinucleotide hydrate （NADH） and elastin are identified as the main contributing biomedical components. Fisher＇s discrminant anlysis （FDA） on the concentration profiles of the principle components （PCs） shows acceptable sensitivity, specificty and accuracy for discrminanting the adenocarcinoma tissues from the normal tissues. MCR-ALS is a powerful tool for characterzing the spectra profiles of the main biochemical components in neoplasm transformation.     

Axisymmetric Electric Waves of Periodic Waveguide Systems for Relativistic Microwave Electronics

We consider the use of one-dimensional integral equations of the second kind for calculation of axisymmetric waves in hollow and open periodic axisymmetric waveguide systems. Methods of discriminating between the fundamental and additional spectra of the problem are proposed. It is shown that the applicability range of this method can be extended considerably. In particular, a special transformation of the integration variable permits one to include waveguides with nonsmooth wall profiles in the applicability range of the method.