Propagation of Waves Through Cylindrical Bore in a Cubic Micropolar Generalized Thermoelastic Medium

The article deals with the propagation of axial symmetric cylindrical surface waves in a cylindrical bore through a micropolar thermoelastic medium of infinite extent possessing cubic symmetry. The theories of generalized thermoelasticity developed by Lord and Shulman and Green and Lindsay are used to study the problem. The frequency equations, connecting the phase velocity with the wave number, radius of bore, and other material parameters for empty and liquid-filled bores are derived. Some special cases have been deduced. The numerical results obtained have been illustrated graphically to understand the behavior of the phase velocity and attenuation coefficient versus the wave number.     

Interaction of Counter-propagating Elliptically Polarized Light Waves in Isotropic Nonlinear Media

Abstract

The nonlinear interaction of elliptically polarized counter-propagating waves in an isotropic transparent medium is analysed. Self-induced changes in the polarization of the counter-propagating light waves, are described. Using these results, a new type of modulator giving self-induced rotation of the polarization ellipse (SIRPE) is studied. The transmission of counter-propagating waves in the SIRPE modulator is shown to exhibit saturation with increase in light intensity and to be a multiple-valued function of the light intensity.     

The Piezoelectric Potential of a Screw Dislocation in a Cubic Medium

An exact and closed-form solution is found for the electric potential generated by a screw dislocation in a cubic piezoelectric medium. The governing equations for the antiplane elastic deformation coupled with the in-plane electric field are formulated in terms of the elastic displacement and the electric potential, and a general solution is obtained. The complex logarithm function is exploited to find the electric potential around the screw dislocation. It is found that the equipotential lines are straight lines passing through the dislocation which is a singular point. Two cubic piezoelectric crystals (Bismuth Germanate and Bismuth Germanium Oxide) are used to illustrate the angular variation of the electric potential around the dislocation. It is concluded that a two-term Fourier series representation is an excellent approximation for Bismuth Germanate, but it is not good enough for Bismuth Germanium Oxide.     

Probing Sound Speed of an Optically-Trapped Bose Gas with Periodically Modulated Interactions by Bragg Spectroscopy

A Bose–Einstein condensate (BEC) with periodically modulated interactions (PMI) has emerged as a novel kind of periodic superfluid, which has been recently experimentally created using optical Feshbach resonance. In this paper, we are motivated to investigate the superfluidity of a BEC with PMI trapped in an optical lattice (OL). In particular, we explore the effects of PMI on the sound speed and the dynamical structure factor of the model system. Our numerical results, combined with the analytical results in both the weak-potential limit and the tight-binding limit, have shown that the PMI can strongly modify the sound speed of a BEC. Moreover, we have shown that the effects of PMI on the sound speed can be experimentally probed via the dynamic structure factor, where the excitation strength toward the first Bogoliubov band exhibits a marked difference from the non-PMI one. Our predictions of the effects of PMI on the sound speed can be tested using the Bragg spectroscopy.     

Magneto-thermoelastic Response in a Functionally Graded Isotropic Unbounded Medium Under a Periodically Varying Heat Source

This paper deals with the problem of magneto-thermoelastic interactions in a functionally graded isotropic unbounded medium due to the presence of periodically varying heat sources in the context of linear theory of generalized thermoelasticity with energy dissipation (TEWED) and without energy dissipation (TEWOED) having a finite conductivity. The governing equations of generalized thermoelasticity (GN model) for a functionally graded material (FGM) under the influence of a magnetic field are established. The Laplace–Fourier double transform technique has been used to get the solution. The inversion of the Fourier transform has been done by using residual calculus, where poles of the integrand are obtained numerically in a complex domain by using Leguerre’s method and the inversion of the Laplace transformation is done numerically using a method based on a Fourier series expansion technique. Numerical estimates of the displacement, temperature, stress, and strain are obtained for a hypothetical material. The solution to the analogous problem for homogeneous isotropic materials is obtained by taking a suitable non-homogeneous parameter. Finally, the results obtained are presented graphically to show the effect of a non-homogeneous, magnetic field and damping coefficient on displacement, temperature, stress, and strain.     

Reflection of Plane Waves in a Semiconducting Medium under Photothermal Theory

In this paper photothermal theory was used to study the reflection of waves at the surface of a semi-infinite semiconconducting medium. Using the harmonic wave method, the reflection coefficient ratios were obtained analytically under coupled thermoelastic theory and plasma theory for an incident CI wave, which is one coupled thermoelastic plasma wave and an incident rotational wave. The variations of the amplitude of reflection coefficient ratios with the angle of incidence are shown graphically for silicon. Effects of the thermal frequency, the thermoelastic coupling parameter, and the thermoelectric coupling parameter were given by numerical results. Also, the energy ratios for reflected waves were computed to check the numerical results.     

基于增益调度的结构振动分布式反馈控制

使用多传感器和驱动器控制简支板的振动.传感器和驱动器局部连接组成独立的闭环.在仿真中分别采用了点力驱动器和压电陶瓷驱动器.以极小化系统的总动能为目标,使用同步扰动方法对结构振动的分布式反馈增益进行最优调度.仿真结果表明,所提出的方法可以有效地抑制结构振动.     

Generation of Picosecond Pulses by Lasers with Distributed Feedback at a Wavelength of 1064 nm

Technical Physics Letters - The mode of generation of picosecond optical pulses in the spectral range near 1064 nm by semiconductor lasers with distributed feedback and active region based on an...     

Light-induced Distributed Feedback in a Quasi-waveguide Thin-film Laser: Theory and Experiment

Abstract

The results of theoretical and experimental investigations of the quasi-waveguide laser system with light-induced distributed feedback (DFB) are given. The DFB theory in the system is developed. The threshold and spectral angular characteristics of operation are calculated. Frequency-tuneable operation of the system in single-mode and multimode regimes have been investigated.     

Spectrum of a Micromaser with Kerr Nonlinearity

Abstract

We analyse the spectrum of a micromaser with a Kerr-type nonlinearity in its cavity. We show that the intracavity Kerr nonlinearity has significant effects on the spectrum leading to narrowing of the subnatural linewidth and frequency-shifts.     

Mechanical/Thermal Sources in a Micropolar Thermoelastic Medium Possessing Cubic Symmetry without Energy Dissipation

The present problem is concerned with the study of the deformation of a thermoelastic micropolar solid possessing cubic symmetry under the influence of various sources acting on the plane surface. The analytic expressions of displacement components, microrotation, force stress, couple stress, and temperature distribution are obtained in the physical domain for the Green and Nagdhi (G–N) theory of thermoelasticity by applying the integral transforms. A numerical inversion technique has been applied to obtain the solution in the physical domain. The numerical results are presented graphically for a particular material.     

具有三次曲线解的Kolmogorov三次系统的极限环

本文研究一类具有过原点的三次曲线解的Kolmogorov三次系统。首次给出并证明了一种简化的等价系统,得到了此系统既不位于坐标轴也不位于三次曲线解上的奇点的精确表达式。证明了在一定条件下存在极限环,而且至少存在三个极限环,并给出了数值例子。     

Analytical Solution for the Propagation of Shock Waves in a Rotating Medium: Power Series Solution

Journal of Engineering Physics and Thermophysics - In this study an approximate analytical solution is obtained for the propagation of a cylindrical shock wave in a rotating perfect gas. The flow...     

非线性光学活性分子的线性电光效应

报道了反射型电光调制法研究６种偶氮化合物的线性电光效应,分析了给体－受体强度、掺杂浓度对线性电光系数的影响。结果表明,掺杂偶氮化合物４－「２－羟乙基苯甲氨基」－４－硝基偶氮苯的极化聚合物薄膜具有较强的线性电光效应,其线性电光系数随参杂浓度的增大而增大。     

一类具有线性分母的有理插值样条的逼近问题

对被插函数f(t)∈c^3[t0,tm],讨论了一类具有线性分母的有理插值函数的逼近性质,证明了插值误差系数的有界性和其对参数的双重对称性。     

Self-Focusing of Rayleigh Waves and Lamb Waves with a Linear Phased Array

A simple idea for self-focusing of a linear array has been extended to Rayleigh and Lamb waves. The self-focusing procedure first measures the backscattered signals for a first transmission by a single element of the array. A cross-correlation technique is used to determine the time-of-flight differences of the backscattered signals received by the elements of the array. These time delays are used to adjust the times of excitation of the elements for transmission focusing on the defect. Using the differences in arrival time once more, the backscattered signals after transmission focusing are aligned for reception focusing. Experimental results demonstrate the ability to self-focus on single defects. For multiple defects, the technique has been extended to focus on the defect that produces the largest backscattered signal.