Measurements in Situ and Spectral Analysis of Wind Flow Effects on Overhead Transmission Lines

In the paper an important issue of vibrations of the transmission line in real conditions was analyzed. Such research was carried out by the authors of this paper taking into account the cross-section of the cable being in use on the transmission line. Analysis was performed for the modern ACSR high voltage transmission line with span of 213.0 m. The purpose of the investigation was to analyze the vibrations of the power transmission line in the natural environment and compare with the results obtained in the numerical simulations. Analysis was performed for natural and wind excited vibrations. The numerical model was made using the Spectral Element Method. In the spectral model, for various parameters of stiffness, damping and tension force, the system response was checked and compared with the results of the accelerations obtained in the situ measurements. A frequency response functions (FRF) were calculated. The credibility of the model was assessed through a validation process carried out by comparing graphical plots of FRF functions and numerical values expressing differences in acceleration amplitude (MSG), phase angle differences (PSG) and differences in acceleration and phase angle total (CSG) values. Particular attention was paid to the hysteretic damping analysis. Sensitivity of the wave number was performed for changing of the tension force and section area of the cable. The next aspect constituting the purpose of this paper was to present the wide possibilities of modelling and simulation of slender conductors using the Spectral Element Method. The obtained results show very good accuracy in the range of both experimental measurements as well as simulation analysis. The paper emphasizes the ease with which the sensitivity of the conductor and its response to changes in density of spectral mesh division, cable cross-section,tensile strength or material damping can be studied.     

Vibrational relaxation and line widths in liquids dephasing by intermolecular forces

A theory of vibrational relaxation in liquids is presented in which the vibrations are loosely coupled to a bath or lattice of molecular translations and rotations by intermolecular forces. Using the second-order perturbation expressions familiar from magnetic resonance the secular contribution to the line width is calculated. Different coupling paths are considered and expressions given for the line widths in a liquid mixture in terms of number densities and diffusion coefficients valid when reorientation is slow and translation diffusional.     

Prediction of vibrations induced by underground railway traffic in Beijing

This paper examines the problem of subway induced vibrations on line 4 of Beijing metro, which is currently under construction and is planned to pass in close proximity of the Physics Laboratory of Beijing University. The laboratory has a lot of equipment that is very sensitive to traffic induced vibrations and future operation of metro line 4 is a matter of concern. Hence, it is important to study the influence of subway induced vibrations inside the laboratory and to propose a viable solution to mitigate the vibrations. In this paper, the tunnel north of Chengfulu station is modelled using a coupled periodic FE-BE model and the free-field response due to moving trains is predicted. In addition, vibration measurements have been performed on the site of the Physics Laboratory to estimate the existing vibration levels due to road traffic. The predicted and measured vibrations are superimposed to assess the vibrations due to the combined effect of road and railway traffic in the vicinity of the Physics Laboratory. Apart from the numerical investigations, vibration measurements have also been performed on a similar site at line 1 of Beijing metro to substantiate the estimated results on metro line 4. Finally, it is studied how the vibrations can be controlled using a floating slab track, which is widely used as an effective measure of vibration isolation in tunnels. The efficiency of a 7.9 Hz floating slab track as a vibration countermeasure is assessed in this paper. This study demonstrates the applicability of the numerical model for the relevant assessment of subway induced vibrations and its use to study the performance of different track structures in the tunnel.     

Grain Boundary Resistivity and Electrically Induced Grain Boundary Migration (EIGM) in Metallic Bamboo Microstructures

As VLSI conductor line dimensions continue to decrease, electrotransport properties increasingly effect device lifetimes. Grain boundaries are intimately linked to these processes, providing paths of varying diffusivity, and as mobile defects themselves. Haessner et al. [6] make a challenging finding in experiments with thin gold films: based on calorimetric data, in order to account for the velocity of grain boundaries migrating in high electric current densities, the force on the atoms of a grain boundary would have to be two orders of magnitude larger than what the accepted theory for bulk ions predicts. The failure is attributed to the simplicity of the model which does not account for possible variations of the resistivity and effective valance charge that could occur in the vicinity of a grain boundary. In this paper, expressions are developed for the electron wind force on the atoms near grain boundaries, and they are written in terms of thermodynamic variables: the boundary specific volume expansion and specific resistivity. The enhancement of the wind force of the boundary atoms over the bulk wind force is calculated using published data. This model allows for more than an order of magnitude enhancement in gold, and Haessner's observation is rationalized.     

混合型光纤喇曼放大器增益和带宽的研究

混合型色散补偿光纤喇曼放大器由普通G652光纤和色散补偿光纤(DCF)组成,包括:DCF +G652、G652 +DCF和 G652+DCF +G652。讨论了它们的工作原理.使用FRA-OptiAmplifier4.0软件对其进行了优化设计,最佳结构为G652 +DCF.它可补偿光纤网络的色散,扩展通信波长范围.1427 nm的喇曼激光器作为激发源,用Q8384光谱分析仪测量了光纤的喇曼增益谱和小信号放大光谱,混合型色散补偿光纤喇曼放大器在S带和C带具有88 nm的增益带宽,这增加了光纤通信网络的传输通道.     

传递过程的统一描述

提出了传递公理,即任何形式的传递过程都是在相应基本强度量差推动下,基本广延量的流动过程;基本广延量的传递过程也同时是与之对应的能和(火用)的传递过程。定义了热力学流密度和热力学力的数学表达式,在传递公理的基础上,利用能和(火用)的普遍化表达式,分别建立了三类广延量的传递定律。利用传递定律,结合广延量的平衡方程,导出了传递方程的普遍化表达式。     

Diffraction and channeling in nanotubes

A theory of the interaction of fast charged particles and gamma rays with nanotubes with different helicity is developed. Analytical expressions are obtained for the potential and the electron density of a nanotube taking account of the anisotropic thermal vibrations of the atoms. A system of equations determining the quantum states of the transverse motion of relativistic electrons, positrons, and x-ray photons in a superlattice consisting of nanotubes is formulated, and methods for solving this system are developed. Calculations of the soft x-ray Bragg reflection coefficients of a superlattice are performed in the two-wave approximation of the dynamical theory of diffraction.     

The time-local view of nonequilibrium statistical mechanics. II. Generalized Langevin equations

On a semiphenomenological level, generalized Langevin equations are usually obtained by adding a random force (RF) term to macroscopic deterministic equations assumed to be known. Here this procedure is made rigorous by conveniently redefining the RF, which is shown to be colored noise weakly correlated with the observables at earlier times due to the finite lifetime of microscopic events. Corresponding fluctuation-dissipation theorems are derived. Explicit expressions for the spectral density of the fluctuations are obtained in a particularly simple form, with the deviation of the line shape from the Lorentzian being related most explicitly to the spectral density of the RF. Well-known low-frequency expressions and the Einstein relation of (generalized) Brownian motion theory are modified so as to include lifetime effects. New sum rules are obtained relating dissipative quantities to contour integrals (in the complex frequency domain) over spectral densities or corresponding response functions. The Heisenberg dynamics of a complete set of macroobservables is shown to be equivalent to a generalized Orstein-Uhlenbeck stochastic process which is a non-Markovian process due to the lifetime effects.     

AN ANALYTICAL APPROACH TO DETERMINING THE DYNAMIC CHARACTERISTICS OF A CYLINDRICAL SHELL WITH CLOSING CRACKS

The paper is devoted to developing mathematical models of the elastic oscillations of a cylindrical shell with surface closing cracks. The respective forms of shell vibrations have been chosen to represent various types of damage of the shell. In the case of dispersed and single-surface damage, the transverse shell vibrations are simulated. The cycle of vibrations is assumed to be subdivided into two parts, in one of them the damaged surface fibers are compressed so closing the cracks and negating their influence. For the second part, the cracks are open, so their influence is taken into account. The problem is solved in a piecewise linear with different frequencies and amplitudes at each vibrations cycle interval. The vibration parameters are calculated by means of Relay's energy conservation method and are represented by analytical expressions, the system being assumed to be conservative. The functions determining the vibration process are decomposed by a Fourier analysis using the averaged frequency, the coefficients of the resulting series being obtained as analytical expressions. Vibrodiagnostic functions, which enable the geometrical parameters of the cracks to be determined depending on the geometry of the shell and type of damage, have been plotted.     

Scan-based near-field acoustical holography and partial field decomposition in the presence of noise and source level variation

Practical holography measurements of composite sources are usually performed using a multireference cross-spectral approach, and the measured sound field must be decomposed into spatially coherent partial fields before holographic projection. The formulations by which the latter approach have been implemented have not taken explicit account of the effect of additive noise on the reference signals and so have strictly been limited to the case in which noise superimposed on the reference signals is negligible. Further, when the sound field is measured by scanning a subarray over a number of patches in sequence, the decomposed partial fields can suffer from corruption in the form of a spatially distributed error resulting from source level variation from scan-to-scan. In the present work, the effects of both noise included in the reference signals, and source level variation during a scan-based measurement, on partial field decomposition are described, and an integrated procedure for simultaneously suppressing the two effects is provided. Also, the relative performance of two partial field decomposition formulations is compared, and a strategy for obtaining the best results is described. The proposed procedure has been verified by using numerical simulations and has been applied to holographic measurements of a subsonic jet.     

近距离牛顿反平方定律实验检验进展

为了统一描述自然界的四种基本相互作用,科学家提出了很多理论模型,其中很多理论认为牛顿反平方定律在近距离下会发生偏离,或存在其他的非牛顿引力作用,而理论的正确与否需要高精度的实验检验.国际上很多研究组在不同间距下采用不同的技术对反平方定律进行了高精度的实验检验,本文重点介绍华中科技大学引力中心采用密度调制法分别在亚毫米与微米范围进行的实验研究进展.在亚毫米范围采用精密扭秤技术,在对牛顿引力进行双补偿、抑制电磁干扰后,结合零实验与非零实验结果,在作用程为70—300μm区间对Yukawa形式的破缺给出国际上精度最高的限制.在微米范围采用悬臂梁作为弱力传感器,通过测量金球和密度调制吸引质量间水平力的变化来检验非牛顿引力是否存在,实验结果不需进行Casimir力和静电力背景扣除,是此间距下不依赖于Casimir力和静电力理论计算模型的两个结果之一.     

Radiation force on absorbing targets and power measurements of a high intensity focused ultrasound (HIFU) source

Based on the analytic expressions for the radiated field of a circular concave piston given by Hasegawa et al.,an integral for calculation of the radiation force on a plane absorbing target in a spherically focused field is derived.A general relation between acoustic power P and normal radiation force Fn is obtained under the condition of kr 1.Numerical computation is carried out by using the symbolic computation program for practically focused sources and absorbing circular targets.The results show that,for a given source,there is a range of target positions where the radiation force is independent of the target's position under the assumption that the contribution of the acoustic field behind the target to the radiation force can be neglected.The experiments are carried out and confirm that there is a range of target positions where the measured radiation force is basically independent of the target's position even at high acoustic power (up to 700 W).It is believed that when the radiation force method is used to measure the acoustic power radiated from a focused source,the size of the target must be selected in such a way that no observable sound can be found in the region behind the target.     

Influence of isovector pairing and particle-number projection effects on spectroscopic factors for one-pair like-particle transfer reactions in proton-rich even-even nuclei

Isovector neutron-proton(np) pairing and particle-number fluctuation effects on the spectroscopic factors(SF) corresponding to one-pair like-particle transfer reactions in proton-rich even-even nuclei are studied. With this aim, expressions of the SF corresponding to two-neutron stripping and two-proton pick-up reactions, which take into account the isovector np pairing effect, are established within the generalized BCS approach, using a schematic definition proposed by Chasman. Expressions of the same SF which strictly conserve the particle number are also established within the Sharp-BCS(SBCS) discrete projection method. In both cases, it is shown that these expressions generalize those obtained when only the pairing between like particles is considered. First, the formalism is tested within the Richardson schematic model. Second, it is applied to study even-even proton-rich nuclei using the single-particle energies of a Woods-Saxon mean-field. In both cases, it is shown that the np pairing effect and the particle-number projection effect on the SF values are important, particularly in N =Z nuclei, and must then be taken into account.     

Vibrations in Magnet/Superconductor Levitation Systems

The problem of a small magnet levitating above a very thin superconducting disc in the Meissner state is analysed. The dipole-dipole interaction model is employed to derive analytical expressions for the interaction energy, levitation force, magnetic stiffness and frequency of small vibrations about the equilibrium position in two different configurations, i.e. with the magnetic moment parallel and perpendicular to the superconductor. The results show that the frequency of small vibrations decreases with the increasing levitation height for a particular radius of the superconducting disc, which is in good agreement with the experimental results. However, the frequency increases monotonically up to saturation by increasing the radius of the disc for a particular height of the magnet. In addition, the frequency of vibrations is higher when the system is in the vertical configuration than that when the system is in the horizontal configuration.     

Transient stimulated raman scattering in crystals during motion of populations of vibrational states

Transient stimulated Raman scattering (SRS) in crystals is analyzed taking into account the motion of populations of vibrational states under the action of subpicosecond (shorter than the dephasing time) pump pulses. Analytic expressions describing the dynamics of excitation of vibrations in SRS are derived. It is found that for a small wavelength of SRS interaction and high intensities of pump radiation observed for femtosecond SRS in crystals, avalanche excitation of vibrations can be responsible for SRS suppression. It is shown that when phase matching of Stokes-anti-Stokes parametric coupling in transient SRS is ensured, it is possible to elevate the efficiency of frequency conversion under conditions of motion of populations of vibrational states; this explains recent successful results in the experimental implementation of femtosecond SRS in crystals pumped by a Bessel beam.     

Energy of the frequency-elastic effect in solids

A decrease in the frequency of skeletal vibrations (frequency-elastic effect) has been measured using Raman spectroscopy, and the stretching of backbone interatomic bonds in polyethylene molecules under elastic tensile loading of oriented polyethylene fibers has been measured using X-ray diffraction. It has been found that there are differences in the sign and magnitude of the changes in the zero-point energy and the work of the external force. The energy of the frequency-elastic effect has been explained in terms of the influence exerted by the initial (before loading) anharmonic stretching of backbone bonds and the force of anharmonic pressure, with the separation of the anharmonic (potential) component of the zero-point energy of the solid. A change in the frequency of vibrations corresponds to a change in the harmonic component of the zero-point energy. The loading with an external force causes a redistribution of the zero-point energy components. An energy analysis of the loaded quantum anharmonic oscillator has confirmed the conclusion regarding the mechanism of energy transfer and revealed that, under loading, there is a redistribution of the average values of the kinetic and potential components of the internal energy of the oscillator.     

Study on forward stimulated Brillouin scattering in a backward pumped fiber Raman amplifier

Strong multi-order forward stimulated Brillouin scattering (SBS) has been observed in the backward pumped S-band distributed fiber Raman amplifier (FRA) with tunable narrow signal source (less than 100 MHz) when the pump power of FRA reached the SBS threshold. This does not obey the theory that only weak backward SBS lines exist according to the conservation of energy and momentum and the wave vector selected rule. This is because the sound waveguide characteristic weakens the wave vector rule, and the forward transmitted sound waveguide Brillouin scattering lines are generated and amplified in FRA.When the pump power is further increased, 11 orders of SBS lines and comb-like profile are observed. For the excited line, the frequency is 197.2296 THz and the power is 0 dBm. The even order SBS lines are stronger than odd order SBS lines, the power of the 2nd and 4th order SBS lines is 1.75 dBm, which is 16 dB higher than that of the 1st and 3rd order SBS lines. The odd order SBS lines are named BrillouinRayleigh scattering lines.     

Analytical representations for the transient admittance of a plate vibrating in a medium

Flexural vibrations of a plate contacting on one side with an ideal compressible liquid are considered. The plate is driven by a harmonic force uniformly distributed along a straight line. The transient admittance of the plate as a function of the distance from the line of the force application is shown to be representable as a sum of an integer function and an integer function multiplied by a logarithmic function. A procedure for determining the power series expansions of these functions is described, and the initial terms of the expansions are derived. The approximations formed by these initial terms and the asymptotic expansion at infinity are compared with the results of numerical calculations for several particular values of the parameters. Vibrations of a liquid with an impedance load at its surface are considered as an auxiliary problem, and, in the framework of this problem, the initial terms of the power series expansions of the integer functions, which appear in the expression for the transient admittance, are determined. The expansions obtained make it possible to raise the speed of the admittance calculations near the points of application of the driving force.     

A novel technique for measurement of self-generated magnetic fields and the plasma density in laser produced plasmas from the Faraday rotation using two color probes

Diagnostic information about the self-generated magnetic fields (SGMF) generated in laser produced plasmas is normally obtained by measuring the Faraday rotation angle (FRA) of a linearly polarized laser probe beam passing through the plasma. Simultaneous recording of the corresponding interferogram is required to get the density information necessary for estimating the magnetic field. The problem with this method is that the visibility of the fringes in the interferogram can be poor, and the SGMF cannot be calculated in the regions where the interference fringes are not observable. In this paper, we propose a new method to obtain the density distribution and the SGMF from two simultaneous measurements of FRA using two probe beams of different colors, which allows one to calculate the SGMF without the need of interferometry.     

On the meaning of the nuclear reaction durations,measured by means of the blocking effect

The expressions for the duration of the nuclear reaction and the compound-nucleus lifetime at a range of strongly over- lapping resonances are generalized. It is shown how the interpretation of the measurements by means of the shadow (blocking) effect is changed when the non-exponential compound-nucleus decay is taken into account. A new method is proposed for obtaining information on the resonance density and width from the measured compound-nucleus lifetimes with the utilization of the optical-statistical analysis.