弹簧摆运动的研究

由初值用差分递推方法模拟弹簧摆的运动,把小球的运动分为横向和径向两个方向,经过研究得出:初始摆角的增大会影响径向的周期运动规律,而劲度系数的变化会影响横向的周期运动规律,大的劲度系数也会对径向周期振动的幅度造成起伏,选择小的摆角和合适的劲度系数可以近似地使小球在横向和径向两个方向上都作周期性运动,且两个方向上运动的耦合影响都很小.     

On the theory of light and atomic backscattering in the Bose-Einstein condensate of a dilute gas

A semiclassical theory of light scattering from a Bose-Einstein condensate of a dilute gas is developed. It is shown that the results of theoretical calculations are in qualitative agreement with the data obtained from recent experiments on the observation of atoms scattered in the backward direction with respect to the direction of a pump laser beam. It is demonstrated that there can arise a field that propagates in the backward direction and whose intensity exceeds the intensity of conventional Rayleigh scattering.     

Instability of oscillations in the flow moving through a random medium as the counterpart of the localization of waves in a passive random medium

This paper deals with waves propagating in a one-dimensional flow moving through a randomly layered medium. The flow velocity is assumed to be greater than the group velocity of the waves in the reference system of the flow. As a result, in the laboratory reference system, all the waves propagate in a single direction. Amplitudes of these waves moving through a randomly inhomogeneous medium are growing exponentially. This effect is analogous to the wave localization phenomenon in a randomly inhomogeneous passive medium. The only difference is that the wave propagation in a passive medium is described by the boundary value problem, while all the oscillations in a medium with flow propagate in a single direction and hence the corresponding problem is formulated in the form of the initial value Cauchy problem. In the former case exponentially decreasing solutions are realized in the direction of the wave incidence, while in the latter case (as in the case of parametric resonances) the exponentially increasing solutions are realized.     

Computer study of the physical properties of a copper film on a heated graphene surface

The structural, kinetic, and mechanical properties of a copper film deposited on single-layer and two-layer graphenes have been studied in a molecular-dynamics model in the temperature range 300 K ≤ T ≤ 3300 K. The film sizes are reduced in the “zigzag” direction more slowly than in the “armchair” direction. The differences have been found to appear in the behavior of copper atoms on single-layer and two-layer graphenes with increasing temperature. Copper atoms on the two-layer graphene have higher horizontal mobility over entire temperature range. However, Cu atoms on the single-layer graphene become more mobile in the vertical direction beginning from a temperature of ～1500 K. The stress tensor components of the copper film characterizing the action of forces on the horizontal areas have a sharp extremum at T = 1800 K in the case of the single-layer graphene and are characterized by quite smooth behavior in the case of the two-layer graphene.     

Effect of the electric field on the shape of a bubble in a conducting liquid

Technical Physics - It is found that a bubble in a conducting liquid is stretched in the direction of the electric field. Expressions are derived for the extension coefficient of the bubble as a...     

Influence of a magnetic field on the light-induced ion drift

It is shown that the velocity component transverse to the radiation propagation direction can arise in the light-induced ion drift (LIID) after applying an external magnetic field to a weakly ionized gas. It is predicted that the projection of the ion drift velocity onto the radiation direction changes its sign with an increase in the magnetic field, resulting in the anomalous LIID.     

Stress effect on the magnetization process in Ni-Cu-Zn ferrite in a weak field

The effect of stress on the magnetization process for Ni-Cu-Zn ferrite was studied by the measurement of the nonsaturated hysteresis loop under external applied stress. A weak field was applied to estimate the effect of stress during the reversal magnetization process. The experimental results show that the nonreversible reversal magnetization process is affected considerably by the compressive stress in the applied field from 0.20 to 0.84 Oe. The compressive stress acts as positive field to impede the nonreversible process which takes place during the reversal magnetization process. The tensile stress had a counter effect but the effect was too small. Stress perpendicular to detecting direction seems to exhibit an effect opposite to that of parallel stress. The sample was toroidal to estimate the differencein the effect of stress between detecting direction and radial direction perpendicular to the detecting direction. The effect of stress in the detecting direction is larger than in the radial direction for the Ni-Cu-Zn ferrite with negative magnetostriction.     

On the polarization characteristics of Cherenkov radiation from a dielectric screen

The Cherenkov effect is a well-known phenomenon and its properties are widely used in many fields of physics. However, some features of the polarization characteristics of Cherenkov radiation that appears when charged particles pass near azimuthally asymmetric, finite dielectric targets are still poorly studied. This problem is solved in this work. The polarization characteristics of Cherenkov radiation in the case of a rectangular dielectric screen are analyzed using the Stokes approach. Owing to the azimuthal asymmetry of the target, radiation acquires an elliptic polarization whose rotation direction and inclination angle depend both on the direction of radiation propagation and on the dielectric properties of a substance. The results demonstrate that the Cherenkov effect can be used to create sources of elliptically polarized radiation with the controlled direction of polarization rotation.     

新型偏振风成像干涉仪中偏振化方向对调制度和干涉强度的影响研究

简要论述了新型偏振风成像干涉仪的原理;分析了偏振风成像干涉仪的各光学部件的偏振化方向对调制度和干涉强度的影响;给出了起偏器的偏振化方向、干涉仪两臂λ/4波片及出射位置处λ/4波片的光轴取向偏离理想方向时干涉仪调制度和干涉强度的理论表达式;采用计算机模拟分别给出了调制度随各偏角变化的曲面图及风速、温度反演误差随各偏角变化的曲线图;给出了温度精度为5K、风速精度为20m/s时偏振化方向的误差容限.该研究对新型偏振风成像干涉仪的研究、研制提供了一定的理论依据和实践指导,对高层大气光学被动探测以及空间探测、对地观测都具有科学意义和应用前景.     

Interaction of a magnetic vortex with the probe field of a magnetic force microscope

The interaction of a magnetic vortex in a circular ferromagnetic nanoparticle with the probe field of a magnetic force microscope (MFM) is theoretically investigated. In the calculations, the probe field is approximated by the point dipole field. The rigid magnetic vortex model is used to describe the vortex state of magnetization. It is found that the effect of the probe field on the rigid magnetic vortex shell is similar to the effect of a uniform magnetic field parallel to the particle plane. The effect of the Z component of the probe field on the core of the vortex results in mutual probe-vortex attraction or repulsion. It is shown that the magnetization direction of the core of the vortex in the MFM probe field can be changed without a change in the shell vorticity direction.     

Influence of the divergence of a light beam on the characteristics of collinear diffraction

Two types of anisotropic collinear diffractions of light on a diffraction grating are theoretically investigated, including that where the light is scattered forward in the direction of the incident radiation and that where the light is scattered backward in the direction toward the incident radiation. For both types, two-dimensional transfer functions are calculated, and the character of their transformation upon variation of the light wavelength and the period of the diffraction grating is analyzed. The dependence of the integrated diffraction efficiency and transmission band of diffraction filters on the divergence angle of the light beam is studied.     

Interaction of a Surface Acoustic Wave with a Two-dimensional Electron Gas

When a surface acoustic wave （SAW） propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coemcient is ~alculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is strongly dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.     

Interaction of a Surface Acoustic Wave with a Two-dimensional Electron Gas

When a surface acoustic wave (SAW) propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is strongly dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.     

Determination of the direction to a source of antineutrinos via inverse beta decay in Double Chooz

To determine the direction to a source of neutrinos (and antineutrinos) is an important problem for the physics of supernovae and of the Earth. The direction to a source of antineutrinos can be estimated through the reaction of inverse beta decay. We show that the reactor neutrino experiment Double Chooz has unique capabilities to study antineutrino signal from point-like sources. Contemporary experimental data on antineutrino directionality is given. A rigorous mathematical approach for neutrino direction studies has been developed. Exact expressions for the precision of the simple mean estimator of neutrinos’ direction for normal and exponential distributions for a finite sample and for the limiting case of many events have been obtained.     

Electron in the field of a classical and a quantized plane wave traveling in the same direction

The Dirac equation is solved exactly for an electron interacting with a quantized and a classical plane wave traveling in the same direction. It is shown that in a certain sense the system can be regarded as consisting of noninteracting quasiparticles.     

Reversal of the dipole vortex in a negative index of refraction material

When a small particle is illuminated by a circularly polarized laser beam, the induced electric dipole moment rotates in a plane. The flow lines of the emitted electromagnetic energy are the field lines of the Poynting vector. When the particle is embedded in a dielectric, these field lines have a vortex structure, and the rotation in the vortex has the same orientation as the rotation direction of the dipole. We show that when the embedding medium is a negative index of refraction material, the direction of rotation in the vortex is reversed.     

光在双轴晶体表面的反射与折射

介绍了光在双轴晶体表面反射、折射问题的求解方法.用该方法可以方便精确地计算晶体任意取向下光从任意方向入射时折射光的折射率、偏振态、波矢方向、能流方向. 推导了反射光、折射光的振幅和能量的计算公式. 并以KTP晶体为例，给出了数值计算的结果. 关键词： 双轴晶体 双折射 菲涅耳公式 布儒斯特角     

Approach flow direction effects on the cross-flow induced vibrations of a square array of tubes

Water tunnel experiments were conducted on a square array of tubes with a pitch ratio of 1·5. The array could be rotated about an axis perpendicular to the direction of flow so that the effects of incident flow direction on cross-flow tube response could be studied. Constant Strouhal number vorticity response was observed over a range of orientations with some Strouhal number dependence on orientation angle. While incident flow direction was found to have some effect on the fluid-elastic stability threshold, no dramatic changes, such as occurred for triangular arrays, were found. Experiments were also conducted to determine the stability behaviour of a single flexible tube in otherwise rigid arrays.     

应用熔石英棒相位共轭镜的LD泵浦激光MOPA系统

 用熔石英棒作为相位共轭镜材料,在LD泵浦的激光MOPA系统中实现了在 100和400 Hz下的受激布里渊散射相位共轭。实验测得重复频率100 Hz时双通放大后的x和y方向的光束质量平方因子分别为1.74和1.66,最大反射率达到24.33% ,脉冲宽度从60 ns压缩到31.34 ns。重复频率400 Hz时双通放大后的x和y方向的光束质量平方因子分别为2.10和2.12,脉冲宽度从56.69 ns压缩到28.84 ns。     

Spontaneous Emission of a Polarized Atom in a Medium Between Two Parallel Mirrors

Using the photon closed orbit theory, the spontaneous emission rate of a polarized atom in a medium between two parallel mirrors is derived and calculated. It is found that the spontaneous emission rate of a polarized atom between the mirrors is related to the atomic position and the polarization direction. The results show that in the vicinity of the mirror, the variation of the spontaneous emission rate depends crucially on the atomic polarization direction. With the increase of the polarization angle, the oscillation in the spontaneous emission rate becomes decreased. For the polarization direction parallel to the mirror plane, the oscillation is the greatest; while for the perpendicular polarization direction, the oscillation is nearly vanished. The agreement between our result and the quantum electrodynamics result suggests the correctness of our calculation. This study further verifies that the atomic spontaneous emission process can be effectively controlled by changing the polarization orientation of the atom.