An interferometric method for determining the mean refractive indices of highly birefringent fibres

An interferometric method with its mathematical derivation is suggested to determine the mean refractive indices and birefringence of highly birefringent fibres using multiple-beam Fizeau fringes in transmission. The application of this method depends on measuring the cross-sectional area of the fibre and the area enclosed under the fringe shift. It is very difficult to measure the area enclosed under the fringe shift in case of highly birefringent fibres, as these fibres have a relatively large optical path difference and a bad connection with the surrounding medium fringe. This difficulty is solved using the suggested method. Poly(aryel ether ether ketone) (PEEK) and poly(ethylene 2,6-naphthalene-dicarboxylate) (PEN) were used as applied examples of highly birefringent fibres for the suggested method. The refractive indices and birefringence of polypropylene fibre with draw ratio 4 are determined using the suggested and conventional methods. The results of the two methods are compared and it is found to be in agreement with the previously published data. The diffraction of He–Ne laser beam was used to determine the mean value of cross-sectional areas of fibres. Microinterferograms and tables are given for illustrations.     

Acoustic sounding of the thermal and velocity structure characteristics with allowance for the turbulent attenuation

A method of simultaneous acoustic sounding of vertical profiles of the thermal and velocity structure parameters with allowance for the turbulent sound attenuation is suggested in the present work. A closed iterative algorithm that implements the suggested method is described, and results of its application for processing of measurements with the Zvuk-2 three-component Doppler sodar are given. It is demonstrated that the thermal, velocity, and acoustic refractive index structure characteristics obtained are in good agreement with the data available from the literature. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 84–90, November, 2008.     

Optimum conditions for the generation of the second harmonic of intense laser radiation

A generalized approximation of strong interactions of waves is suggested for the theoretical analysis of second-harmonic generation under conditions of self-action. On the basis of the method suggested, approximate solutions for the efficiency of second-harmonic generation are obtained with regard to the influence of higher nonlinearities, depletion of pumping radiation, and linear phase mismatch. The effects of the phase mismatch and the spatial distribution of the amplitude of the fundamental harmonic on the efficiency of second harmonic generation by intense laser radiation is analyzed. The results obtained with the approximate method developed are shown to be in good agreement with known experimental data and numerical calculations. Optimum conditions for second harmonic generation are determined in a wide range of laser radiation intensity and at different spatial distributions of the fundamental harmonic amplitude.     

雷达发射机的冷却及热设计优化分析

论述了雷达发射机的冷却和热设计的原则,分析了雷达发射机的常用冷却方法的特点及适用场合。针对目前的雷达发射机热设计现状,从设计思想、热设计的层次和冷却方法等方面提出改进意见,对雷达发射机的热设计方法的优化进行了有益的探讨。     

Identification of overlapping optical lines in molecular spectra by means of the coherent population trapping of quantum levels

A new method of molecular beam spectroscopy with the ultrahigh resolution is theoretically suggested. This method is based on the phenomenon of the coherent population trapping of molecular levels and allows the identification of the overlapping optical lines in complex spectra (typical for polyatomic molecules), even when frequency intervals between the centers of given lines are less than their natural line widths. The theoretical analysis is carried out on the basis of the Schrödinger equation for the three-level molecular A-system interacting with the two-frequency laser radiation. The conditions of the practical realization and possible applications of the suggested spectroscopy method are discussed.     

Measurement of the spectral dispersion curves of low birefringence polymer fibres

A method is suggested to overcome the difficulties of measuring the spectral dispersion of low birefringence fibres, that produce small optical path difference, δ<3λ, where δ is the optical path difference and λ is the wavelength of light used. This method depends on variable wavelength interferometry (VAWI). The suggested method is used to measure the spectral dispersion of birefringence of polypropylene fibre with a draw ratio 4 (low birefringence fibre). This method is also used to measure the spectral dispersion of birefringence of a polyester staple from ICI (high birefringence fibre). Also, the conventional VAWI method is used to measure the spectral dispersion of this fibre to confirm the results obtained by the suggested method. Microinterferograms are given for illustration.     

Reduced adiabatic hyperspherical basis in the Coulomb three-body bound state problem

A new version of the adiabatic hyperspherical approach (AHSA) is suggested which has significant advantages for the calculation of three-body states with total angular momentumJ> 0. The binding energies of all bound states of mesic molecules with normal parity are calculated by the suggested method. Comparison with results of variational calculations and the fast convergence of the method confirm its high efficiency.     

A statistical derivation of the density of final states for the exciton model

A new method for the derivation of the density of final states in the nuclear equilibration process, based on the Darwin-Fowler method of statistical physics, is suggested. This method is generally valid for an arbitrary energy level scheme and includes the Pauli principle. When it is applied to the equidistant-spacing energy level scheme, the results are very close to those derived by Oblo?inský et al.     

The Bethe ansatz for the six-vertex model with rotated boundary conditions

A method is suggested for derivation of the Bethe ansatz equations for the six-vertex model on a square lattice rotated at an arbitrary angle with respect to the coordinate axes. The method is based on the random walk representation for configurations of the model. The equations for the ice model on the rotated lattice are derived and some numerical results are obtained.     

On the theory of the combined ME-TDPAC method

A theoretical analysis of the combined ME-TDPAC method suggested in [1,2] is presented. General expressions are given for the radiation intensity time dependence and for the shape of the emission spectrum in the limit of an unbounded observation time. In addition, a detailed analysis is carried out for the special case of a polycrystalline⁵⁷Fe source and it is shown strictly that determination of the electric field gradient sign by this method is impossible.     

Finite-gap Solutions of the Fuchsian Equations

We find a new class of Fuchsian equations, with algebro-geometric solutions associated to a hyperelliptic curve. A method for calculating its arithmetic genus and branching points is suggested. Numerous examples are given.     

Finite-element method in the space-time domain for nonstationary electrodynamics

A new numerical method for solving problems of nonstationary electrodynamics is suggested that uses integro-differential equations and finite-element representation of fields. Examples of numerical calculations are given.     

白光彩色联合变换相关实验中的分通道方法

提出了在彩色联合变换相关中, 使用光栅对彩色图像进行分通道处理的方法, 讨论了实现此方法对光源、滤色片的限制, 并基于此讨论提出了一种使用三色光栅图像编码的分通道解决方法。实验的结果表明, 这种方法不但降低了对光源的限制, 而且对取向不同的功率谱也便于进行分通道并行处理, 包括并行地使用零级功率谱进行彩色图像的仅形状相关。     

An approximate analytical solution of the radiative transfer equation in hydrometeors accounting for scattering effects

An iterative method for the radiative transfer equation solution is suggested for the scattering hydrometeors. The method allows to find the layer scattering indicatrix. The method is shown to be more general as compared with the four-flux theory or the perturbation method and differs strongly from these ones because even in the case of the first iteration it gives the results which are very close to ones obtained by numerical methods for all rain scattering angles.     

Nakajima-Zwanzig's generalized master equation: Evaluation of the kernel of the integro-differential equation

A method is presented, which allows the exact elimination of the projection operator from the kernel of the Nakajima-Zwanzig generalized master equation without using perturbational expansions. Expressions for kernels of generalized master equations using several frequently occuring types of projection operators are derived explicitly. The application of this method for the exact derivation of generalized master equations describing the coherent and the coupled coherent and incoherent exciton motion is proposed. As another application, the derivation of the Smoluchowski equation is suggested.     

Method of solving the inverse problem of chemical kinetics for catalytic reactions in which each step involves main reactants

A new method is suggested for solving the inverse problem of chemical kinetics. This method provides means to derive, from unsteady-state experimental data, the rate constants of catalytic reactions in which each step involves at least one main reactant. Examples of applying this method to two- and three-step reactions are presented.     

On the calculation of the reaction matrix in finite nuclei

A method is suggested for calculating the reaction matrix in finite nuclei from any local or non-local potential. It employs a harmonic oscillator Pauli operator and purely kinetic particle states. Particle and hole states are properly orthogonalized. Bare reaction matrix elements to be used in shell-model calculations for A = 18 nuclei are given as sample results. They are based on the soft-core Reid potential.     

Nowcasting Avalanches as Earthquakes and the Predictability of Strong Avalanches in the Olami-Feder-Christensen Model

Nowcasting earthquakes, suggested recently as a method to estimate the state of a fault and hence the seismic risk, is based on the concept of natural time. Here, we generalize nowcasting to a prediction method the merits of which are evaluated by means of the receiver operating characteristics. This new prediction method is applied to a simple (toy) model for the waiting (natural) time of the stronger earthquakes, real seismicity, and the Olami-Feder-Christensen earthquake model with interesting results revealing acceptable to excellent or even outstanding performance.     

Determination of the optical and geometrical properties of fibres having skin–core structure

A method is suggested to determine both the refractive index and the transverse sectional shape and area of fibres, having skin–core structure, at the same time for the same region of the fibre. The method depends on using a fibre rotator device attached with Pluta polarizing interference microscope, to record the variation of the fibre thickness at each angle of rotation. Nylon 6 fibres having skin–core structure were used in this study. Beck-line method was used to determine the refractive index of the skin for light vibrating parallel and perpendicular to the fibre axis. To confirm the results of the suggested method, the optical microscope was used to determine the transverse sectional shapes of bundles of nylon 6 fibres. The mean refractive indices of the skin and core of nylon 6 fibres were determined. Microinterferograms are given for illustration.     

Use of the variational principle with the aim of determining oscillations in the extended X-ray absorption fine structure

A method of determining the smooth and oscillating components of extended X-ray absorption fine structure spectra is developed. The form of a functional that is minimized by the desired smooth function is suggested, and a series of EXAFS spectra is analyzed. A way of solution optimization is proposed. The results of applying the method to experimental spectra are reported.