外加交变电场对光折变基频空间电荷场瞬态特性的影响

利用“跳跃模型”讨论外加交变电场（包括正弦和方波电场）对光折变基频空间电荷建立的影响,给出了空间电荷场基频分量随时间、外加交流电场振幅频率等变化的通解表达式。发现基频空间电荷场虎部和实部的振荡频率分别是外加交流电场振荡频率的两倍和一倍。当外加交变电场频率较大时光折变光栅是相移型的。这和基于“带导模型”给出的数值结果相符。     

Effects of the insulated magnetic field and oblique incidence of electrons on the multipactor in MILO

The theoretical analysis and actual performance of the single-surface multipactor discharge model in the presence of a magnetic field are conducted through simulations. The effects of the magnitude of the insulated magnetic field and the oblique incidence of electrons on the multipactor are analysed. The results show that the multipactor susceptibility region shrinks gradually as the magnetic field increases when the electron cyclotron frequency is close to the RF frequency of the electric field. As a result, the evolution of the multipactor discharge will reach saturation earlier and become saturated at a higher level than the case when the magnetic field is absent, but the change of evolution and saturation as the insulated magnetic field increases is not obvious.     

Dynamic control of the entanglement in the presence of the time-varying field

The interactions between a two-level atom and a field with a time-varying frequency have been investigated. The two typical cases, the frequency of the field varying with time in the forms of sine and rectangle, have been considered. The dynamic behavior of the atom-field entanglement is investigated numerically as function of time. A number of novel phenomena are discovered and discussed. The sine modulation of the field frequency can help to realize and stabilize the degree of the atom-field entanglement at high level. The influence of the rectangular frequency modulated field on the atom-field entanglement indicates that the entanglement is more sensitive to the detuning than the correlation between different Rabi oscillations. Not only the sine field frequency modulation but also the rectangular field frequency modulation is favorable to improve, enhance and stabilize the degree of the atom-field entanglement.     

微波大气击穿阈值的理论研究

本文通过对使用有效场强(或均方根场强)得到的微波大气击穿阈值表达式进行讨论, 指出其推导中所做的假设及这些假设应用到微波大气击穿过程中存在的问题. 然后分别使用解析理论和数值模拟对微波大气击穿过程中的有效电子温度变化过程和击穿阈值进行研究, 并将其与直流电场进行比较. 分析发现在高气压下, 电子能量转移频率高, 有效电子温度随电场大幅振荡, 由于电离频率随有效电子温度的增长率大于电子能量损失随有效电子温度的增长率, 因此在高气压时, 微波大气击穿阈值低于使用有效场强的击穿阈值. 通过大量分析, 给出了理论推导和数值模拟得到的微波大气击穿阈值拟合表达式.     

Influence of an electric field on the magnetoabsorption in a field of resonant laser radiation

The frequency dependence of the coefficient of interband magnetoabsorption of a weak electromagnetic wave propagating in a constant electric field and in a field of resonant laser radiation at a frequency equal to the cyclotron frequency (infrared magnetic resonance) is calculated. The specific features observed in interband absorption of the electromagnetic wave in a uniform electric field are considered for the case in which the frequency of laser radiation is equal to the confinement frequency in a parabolic quantum well (infrared quantum-well resonance).     

Effect of the Bloch-Siegert shift on the frequency responses of Rabi oscillations in the case of nutation resonance

The dynamics of a two-level spin system dressed by bichromatic radiation is studied under the conditions of double resonance when the frequency of one (microwave) field is equal to the Larmor frequency of the spin system and the frequency of the other (radio-frequency) field ω_rf is close to the Rabi frequency ω₁ in a microwave field. It is shown theoretically that Rabi oscillations between dressed-spin states with the frequency ? are accompanied by higher-frequency oscillations at frequencies nω_rf and nω_rf ± ?, where n = 1, 2,.... The most intense among these are the signals corresponding to n = 1. The counter-rotating (antiresonance) components of the RF field give rise to a shift of the dressed-state energy, i.e., to a frequency shift similar to the Bloch-Siegert shift. In particular, this shift is manifested as the dependence of the Rabi-oscillation frequency ? on the sign of the detuning ω₁ ? ω_rf from resonance. In the case of double resonance, the oscillation amplitude is asymmetric; i.e., the amplitude at the sum frequency ω_rf + ? increases, while the amplitude at the difference frequency ω_rf ? ? decreases. The predicted effects are confirmed by observations of the nutation signals of the electron paramagnetic resonance (EPR) of E′₁ centers in quartz and should be taken into account to realize qubits with a low Rabi frequency in solids.     

Frequency dependence of the coercive field and the internal bias field in ferroelectric thin films

The dependences of the coercive field and the internal bias field on the switching field frequency for lead zirconate titanate and lead titanate thin films are experimentally studied over a wide temperature range. It is shown that, as the frequency increases, the coercive field and the bias field in these films increase at the rate dependent on the temperature and the substrate used.     

The role of the polarization of a nonresonance external harmonic field in the dynamics of a nonautonomous spin oscillator

The results of an analysis of the action of a nonresonance external harmonic electromagnetic field on a quantum oscillator whose active medium is a two-level spin system, i.e. spin oscillator are briefly presented. The role of external field polarization in the dynamics of a nonautonomous spin oscillator is demonstrated. For the circular polarization of a nonresonance external field the shift of oscillation frequency of the spin oscillator is observed. For the linear polarization of a nonresonance external field the specific feature of spin oscillator synchronization at the third overtone of external field frequency is observed, along with an oscillation frequency shift.     

电声子相互作用对半导体超晶格动力学局域化的影响

本文用单带模型分别研究了直流外场和交流外场作用下，电声子相互作用对半导体超晶格的动力学局域化性质的影响。结果表明：电声子相互作用会破坏电子的动力学局域化。对同一声子频率，电声子相互作用的强度越大，电子越快被散射；当声子频率等于直流场的布洛赫频率或交流场频率时，初始局域在某一格点的电子被迅速地散射到其他格点上去，亦即光声子共振场会严重破坏电子的动力学局域化性质。     

超声辐照及辐照环境对液体中流场分布特性的影响

研究了超声辐照下液体中声压场分布,模拟了流场分布的特性,模拟结果与利用粒子成像测速仪得到的实验结果相符。进一步研究了声学参数及容器几何环境对流场分布的影响。研究发现,增大超声功率和频率可使流场速度变大:在30~60W范围内,超声功率与流场中最大流速间存在线性关系;在频率为100~472kHz范围内,流场速度大小随频率的升高而增加:在层流区,流速与频率的平方成正比;在湍流区,流速与频率的1/2次方成正比。进一步研究发现,随着换能器到容器壁间距离的增加,流场速度减小。      

频率变化的光场对双光子过程中量子纠缠的调控

运用量子信息熵理论研究了二能级原子与频率随时间变化的相干态光场作用的双光子过程中纠缠度演化,主要讨论了光场频率随时间作正弦调制和脉冲调制两种情况下,纠缠随时间的演化特性. 当光场频率随时间作正弦调制时,原子与光场的纠缠度明显增大,并保持高纠缠度. 通过改变光场频率调制的频率β和振幅α,发现原子与光场纠缠度的演化过程对调制的振幅更加敏感. 当光场频率随时间作脉冲调制时,在纠缠度最大值处开始加脉冲比在最小值处加脉冲能够更快、更容易实现原子与光场纠缠度的提高和稳定. 脉冲调制的突变使 关键词： 纠缠 场熵 相干态 双光子Jaynes-Cummings模型     

Estimation of the action of lunisolar tides on the electric field in the atmospheric surface layer

The average amplitude of the vertical electric field strength in the atmospheric surface layer at the frequencies of lunisolar tides has been estimated. The special feature of the problem of estimation of the amplitude E_z at the frequencies of tides is related to the necessity of using a long time series of experimental data which is related to the frequency range of tidal variations and to the necessary frequency resolution. The signal amplitude at the frequencies of tides has been estimated by using the radio engineering method of quadrature correlation receiver. Experimental data on the electric field in the atmospheric surface layer over the range of lunisolar tides obtained at different stations of Hydrometeorological Service have been analyzed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 69–73, August, 2007.     

The effect of ceramic vases on the acoustics of old Greek orthodox churches

The effect of resonators on the acoustics of orthodox churches was studied. Empty bottles of commercial refreshment were used as resonators. A total number of 480 resonators having the same resonant frequency, were placed inside a church, in steps of 100 resonators each time, and the impulse response of the church was measured and analyzed in 1/1 and 1/3 octave band analysis. The effect of resonators is rather poor. An amplification of sound in the near field of resonators was observed as well as a small attenuation of the sound level in the reverberant part of the field in the resonant frequency and near to a higher overtone. A remarkable increase of C80 and D50 at resonant frequency was also observed.     

The effect of a magnetic field on the crossover from the linear to quadratic frequency dependence of phononless hopping conductivity in disordered systems

The effect of an external magnetic field on the frequency dependence of phononless hopping conductivity in disordered system is studied. The dependence of the low-temperature phononless conductivity on the applied magnetic field is established. It is shown that in the limit of a strong magnetic field, the frequency of the transition (crossover) from linear to quadratic frequency dependence of phononless conductivity grows logarithmically with the value of a magnetic field.     

非线性啁啾频率对势阱产生正负电子对的增强

用计算量子场论方法研究了非线性啁啾频率对势阱中正负电子对产生的增强效应。研究了由静态势阱和动态势阱组成的组合势阱中产生的正负电子对的密度、产额和能谱等性质随着啁啾参数的变化,分析了组合势阱的频谱和瞬时束缚态。发现非线性啁啾效应对低频区域比较敏感,与固定频率情况相比可以使粒子数增加2～3倍。与组合势阱相比,非线性啁啾效应对单个振荡势阱更敏感。在低频下单个振荡的势阱中正负电子对产额可提高多个数量级。这是因为在低频下单个振荡的势阱中,主要通过量子隧穿过程产生的正负电子对数目非常低。非线性啁啾效应增加了高频场成分,提高了多光子过程和动力学辅助机制。由于高频抑制作用,所以非线性啁啾效应对高频区域粒子的增量不大,甚至会抑制正负电子对的产生。     

Ultrawide frequency linewidth of the permeability spectra of FeCoN thin film sputtered on the flexible substrate

Analysis shows that it is possible to make use of dispersed magnetic ripple fields to obtain a wide frequency linewidth of permeability spectra of soft magnetic thin films. As-sputtered FeCoN thin film sputtered on flexible Kapton substrate is studied as an example. It has ultrawide frequency linewidths of its resonance peaks in the permeability spectra, compared to its counterpart deposited on Si substrate. The frequency linewidth of FeCoN on Kapton substrate decreases with external magnetic field, showing a different field dependence from that of FeCoN on Si substrate. The ultrawide frequency linewidth and its decrease with external magnetic field are ascribed to the dispersed magnetic ripple fields caused by the flexible substrate. This work shows that the flexible substrate is effective in obtaining a wide frequency linewidth of the permeability spectra of soft magnetic thin films.     

Stability of capillary waves with arbitrary symmetry on the surface of a jet in a longitudinal electric field periodically varying with time

The Mathieu differential equation for the evolution of the amplitudes of arbitrarily symmetric capillary waves (with arbitrary azimuthal numbers) propagating over the surface of a incompressible dielectric cylindrical liquid jet is analyzed. The jet is placed in a time-periodic uniform electric field that is parallel to the symmetry axis of the jet unperturbed by the wave flow. It is found that the time-varying electric field pressure parametrically builds up both axisymmetric waves on the jet surface, flexural waves, and flexural deformation waves. At a fixed frequency of the external field, waves with different wavelengths and symmetries (different azimuthal numbers) may build up simultaneously in the main demultiplication resonance, as well as in secondary and tertiary resonances. The parametric buildup of flexural deformation waves has a threshold relative to the external field frequency: it takes place at the field frequency exceeding a certain value depending on the jet radius and physicochemical properties of the liquid.     

The effect of domain wall motion on the nondiagonal impedance component in amorphous wires with circular magnetic anisotropy

The effect of the domain wall motion on the nondiagonal impedance component in amorphous ferromagnetic wires with circular anisotropy was theoretically studied. The frequency spectrum of the electromotive force (emf) induced in the pick-up coil wound around the wire is analyzed. For sufficiently small amplitudes of the ac current passing in the wire, the emf frequency equals doubled frequency of the current. For the ac current amplitudes exceeding certain threshold value, all even harmonics appear in the frequency spectrum of the signal. The emf strongly depends on the longitudinal component of the applied magnetic field at any value of the ac current amplitude. These results can be important for developing frequency transducers controlled by magnetic field.     

基于行波管螺旋导电面模型的空间电荷场研究

通过分析行波管螺旋导电面模型中的电磁场，给出了色散和耦合阻抗计算公式，并深入研究了非线性理论中的空间电荷降低因子.结果表明，螺旋导电面模型相对理想导电圆筒中的空间电荷降低因子在较高频段变化不大.空间电荷降低因子的变化反映了螺旋线外电磁场对电子注的作用，同样的慢波结构，较高频率的电磁场应有较大的影响.因此，使用螺旋导电面模型在较高频段计算空间电荷降低因子是不合适的. 关键词： 行波管 非线性 螺旋导电面 空间电荷降低因子 色散 耦合阻抗     

The influence of frequency redistribution on the transfer of gyroresonant photons in the atmospheres of compact stars: Monte-Carlo analysis

We numerically model the frequency redistribution of gyroresonant photons in a plane-parallel semi-infinite plasma atmosphere of a compact star by means of the Monte-Carlo method. We calculate the mean frequency shift and the mean number of scatterings for photons leaving the atmosphere as functions of the optical depth at emission, plasma temperature, and magnetic field strength. The probability of the escape of cyclotron-radiation photons from the atmosphere as a function of their optical depth at birth is calculated. The influence of the frequency redistribution effects on the spectrum of emergent radiation is studied.