Regularities in penetration of electromagnetic waves through metallic magnetic films

Penetration of millimeter electromagnetic waves through permalloy films under magnetic resonance conditions is studied experimentally and theoretically. Measurements are taken on film samples from 40 to 200 nm in thickness in a frequency range from 26 to 38 GHz. Magnetic resonance, antiresonance, and spin-wave resonance are observed. The resonance spectrum is reconstructed. The Gilbert damping constant is determined for a series of films. It is shown that the damping constant decreases upon an increase in the film thickness. The resonance line profile is calculated, and the dependences of resonance line amplitude and width on experimental conditions and material parameters of the film are determined.     

亚波长周期性各向异性金属薄膜的等离子体共振特性

 基于各向异性模型,运用全矢量的3维时域有限差分法（FDTD）,研究了在外磁场作用下,亚波长周期性各向异性金属薄膜的表面等离子体共振机制和特性,即由周期性穿孔形成的局域波导共振和由周期性结构引起的光子晶体共振效应。研究发现:当薄膜厚度一定时,两种等离子体共振模式都会随着外磁场的增大而向短波方向移动;而当外磁场一定、薄膜变厚时,周期结构因素引起的共振传输峰向长波方向转移,波导共振传输峰向短波方向转移;通过调控外加磁场的大小或方向可控制光通过金属薄膜的增强传输效应。     

Analysis of the sandwich piezoelectric ultrasonic transducer in coupled vibration

The coupled vibration of the sandwich piezoelectric transducer with a large cross-section is analyzed using an approximate analytic method. The resonance frequency equations of the transducer are derived and the effect of the geometrical dimensions on the resonance frequency is studied. It is illustrated that when the radial vibration in the transducer is considered, the vibration of the sandwich transducer becomes more complex. Apart from the longitudinal resonance frequency, the radial resonance frequency can also be obtained. For comparison, numerical methods are also used to simulate the coupled vibration; the resonance frequency and the vibrational displacement distribution are computed. Compared with one-dimensional longitudinal theory, the radial dimensions of the transducer are no longer limited because the coupled vibration is considered. Compared with numerical methods, the physical meaning of the analytic method is concise. It is illustrated that the resonance frequencies obtained from the coupled resonance frequency equations are in good agreement with those from numerical methods, and they are in better agreement with the measured results than those from one-dimensional theory. Since the radial and the coupled vibration are considered in the analysis, more resonance frequencies can be obtained. Therefore, using the coupled resonance frequency equations, the sandwich transducer with multifrequency or wide frequency bandwidth can be designed and used in ultrasonic cleaning, ultrasonic sonochemistry and other applications.     

Coherent stochastic resonance in the case of two absorbing boundaries

The coherent stochastic resonance is observed and studied with a multistep periodic signal in a continuous medium having two absorbing boundaries. The general features of this process are exhibited. The universal features at the resonance point are demonstrated. The kinetic behaviors around the resonance point are also presented.     

Pitchfork bifurcation and vibrational resonance in a fractional-order Duffing oscillator

The pitchfork bifurcation and vibrational resonance are studied in a fractional-order Duffing oscillator with delayed feedback and excited by two harmonic signals. Using an approximation method, the bifurcation behaviours and resonance patterns are predicted. Supercritical and subcritical pitchfork bifurcations can be induced by the fractional-order damping, the exciting high-frequency signal and the delayed time. The fractional-order damping mainly determines the pattern of the vibrational resonance. There is a bifurcation point of the fractional order which, in the case of double-well potential, transforms vibrational resonance pattern from a single resonance to a double resonance, while in the case of single-well potential, transforms vibrational resonance from no resonance to a single resonance. The delayed time influences the location of the vibrational resonance and the bifurcation point of the fractional order. Pitchfork bifurcation is the necessary condition for the double resonance. The theoretical predictions are in good agreement with the numerical simulations.     

Study on guided-mode resonance characteristic of multilayer dielectric grating with broadband and wide using-angle

Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resonance is very important. In this paper the characteristics of guided-mode resonance in multilayer dielectric grating are studied with the aim of better understanding the physical process of guided-mode resonance and designing a broadband multilayer dielectric grating with no guided-mode resonance. By employing waveguide theory, all guided-wave modes appearing in multilayer dielectric grating are found, and the incident conditions, separately, corresponding to each guided-wave mode are also obtained. The electric field enhancement in multilayer dielectric grating is shown obviously. Furthermore, from the detailed analyses on the guided-mode resonance conditions, it is found that the reduction of grating period would effectively avoid the appearing of guided-mode resonance. And the expressions for calculating maximum periods, which ensure that no guided-mode resonance occurs in the requiring broad angle or wavelength range, are first reported. The above results calculated by waveguide theory and Fourier mode method are compared wit each other, and they are coincident completely. Moreover, the method that relies on waveguide theory is more helpful for understanding the guided-mode resonance excited process and analyzing how each parameter affects the characteristic of guided-mode resonance. Therefore, the effects of multilayer dielectric grating parameters, such as period, fill factor, thickness of grating layer, {\it et al.}, on the guided-mode resonance characteristic are discussed in detail based on waveguide theory, and some meaningful results are obtained.     

Time dependence of resonance scattering

The process of resonance scattering is studied in a time dependent approach. A formulation is given where one can see the time dependence of the prompt potential scattering and the delayed resonance scattering. It is shown that the usual expression for the resonance scattering is obtained in an experiment where the detectors are sensitive during a long time. Switching off the detectors after some time comparable to the life time of the resonance yields considerable modifications of the cross section: a broadening of the resonance and oscillations are observed in this case.     

Resonant scattering of photon by electron in the presence of the pulsed laser field

The scattering of photon by electron in the presence of the field of the low-intensity circularly-polarized pulsed laser wave is analyzed at a laser pulse duration that is significantly greater than the characteristic oscillation time. The conditions for the resonance process in which the intermediate particle is located in the vicinity of the mass surface are determined. The existence of three resonance ranges is demonstrated. The first one corresponds to the resonance of direct diagram, and two ranges correspond to the resonance of exchange diagram via electron and positron intermediate states. The conditions under which only the resonance of the direct diagram takes place are determined, and the probability of such process is calculated. It is demonstrated that the resonance probability can be significantly greater than the probability of the Compton effect in the absence of the external field.     

Analysis of the phase tunneling time for cold neutrons through a neutron interference filter

Explicit expressions are obtained for the energy dependence of the particle transmission coefficient and phase tunneling time through two rectangular barriers near resonance. The resonance half-width and the phase tunneling time for neutrons in resonance are calculated.     

Estimation of sea bottom parameters from the angle-frequency resonances of the reflection coefficient

The resonance structure of the frequency response is used for the determination of sea bottom properties. The behavior of the resonance characteristics is investigated in the plane of two different bottom parameters for a fixed angle of incidence. The features of the behavior of the resonance structure characteristics are used to develop the procedure for evaluating the parameters of a layered sea bottom. With the proposed procedure, the parameters of a layered sea bottom are determined from model data in which an error is artificially introduced. The efficiency of the bottom parameter determination is shown to increase when several characteristics of the resonance structure are used simultaneously.     

Diversity-induced resonance with two different kinds of time delays

The phenomena of diversity-induced resonance in a coupled bistable system are investigated numerically and analytically when two different characteristic time delays are considered, i.e., the feedback time delay and the coupling time delay. By applying the mean-field approximation, the theoretical analysis of the spectral amplification factor is derived. It is shown that both of the time delays can induce periodic resonance. The feedback time delay can induce a damping oscillation in resonance at each multiple of the driving period. The feedback strength can reduce the resonance. While there exists an optimal value of the coupling strength at which the resonance can reach its maximum.     

Adiabatic theory of particle trapping due to Coulomb crossing of one-dimensional betatron resonance

In the presence of space charge forces, synchrotron oscillations result in periodic modulation of the space charge tune shift, periodic crossing of betatron resonances, and particle trapping in resonance islands. The trapping effect for one-dimensional resonance is considered using classical perturbation theory and the “frozen core” approach to calculation of space charge forces. The beam losses and emittance growth are analyzed for arbitrary order resonance; the numerical results are given for the third-order resonance. The text was submitted by the authors in English.     

Monopole Excitation of the Nucleon in a Relativistic Three-Quark Model

The densities and form factors of the proton andthe Roper monopole excitedstate resonance are calculatedusing a relativistic three-quark model. Small currentquark masses are used with the three-body Dirac equation solved in hypercentralapproximation. A QCD-based three-body potential,proportional to a minimum string length between thethree quarks, is used for confinement. The calculatedelectric form factor for the proton reproduces closelya dipole fit to the data. The proton density is morecompact than is the Roper resonance density. The centraldensity of the proton is about five times that for the Roper resonance. The hyperradial nodein the Roper resonance composite three-quark wavefunction shows up as a node in the transition densitybetween the proton and the Roper resonance. This node also causes the calculated transition formfactor to be larger than either the proton or Roperresonance form factors, all evaluated at the same valueof momentum transfer. The Roper resonance form factor is smaller than the proton form factor, asexpected, indicative of the Roper resonance being a morediffuse system than the proton.     

双稳系统随机共振的反馈控制

将双稳系统的输出反馈到输入端再作用于系统,提出了采用反馈来控制随机共振的方法.以典型双稳系统为对象,并以信噪比和功率谱放大率作为度量随机共振效应的可观察变量,分别研究了采用线性或非线性反馈函数所产生的随机共振现象.理论分析和数值仿真结果表明随机共振是可控制的.该方法特别适用于系统参数固定或难以改变的系统. 关键词： 双稳系统 随机共振 反馈控制 共振效应     

基于硅基光子器件的Fano共振研究进展

硅基光子技术的发展为新型微纳光学功能器件和片上系统提供了高可靠、高精度的实现手段.采用硅基光子技术构建的具有连续(准连续)模式微腔与离散模式的微腔耦合产生的Fano共振现象得到了广泛关注.Fano共振光谱在共振波长附近具有不对称且尖锐的谐振峰,传输光的强度在共振波长附近从0突变为1,该机制可显著提高硅基光开关、探测器、传感器,以及光非互易性全光信号处理的性能.本综述分析了Fano共振的一般数学表述,总结了当前硅基光子微腔耦合产生Fano共振的理论模型研究现状,讨论了不同类型硅光器件实现Fano共振的方法,比较各种方案优劣及适用场合,梳理了Fano共振在全光信号处理方面的应用研究情况.最后探讨存在的一些问题及未来可能的相关研究方向.     

磁性多层薄膜中交换各向异性研究

采用铁磁共振理论研究了自旋阀体系中交换各向异性场和两铁磁薄膜厚度对体系性质的影响,得到系统色散关系的解析表达式.研究表明:体系中存在的交换各向异性场H_E对声学模和光学模的共振场均有影响(其对声学模的影响较大).而且还发现声学模共振场随A,B层铁磁薄膜厚度的变化关系依赖于系统中交换各项异性场的强弱;相反,光学模共振场随两铁磁层厚度的增加始终增强.     

金复合纳米微粒的消光特性

基于Mie光散射理论,研究了金壳介质芯的金复合纳米球壳微粒在光散射与吸收中的消光特性.对微粒增大时的多极子特性以及内半径变动时共振峰的移动作了计算和分析,证实了共振峰位置随内外半径比增大而增大的规律.还对纯金纳米微粒的多极子特性作了计算,并讨论了总消光效率中散射和吸收各自的贡献.     

超声波作用下泡群的共振声响应

从球状泡群气泡动力学方程出发, 考虑泡群间次级声辐射的影响, 得到了声场中两泡群共同存在时气泡振动的动力学方程, 并以此为基础探讨声波驱动下双泡群振动系统的共振响应特征. 由于泡群间气泡间的相互作用, 系统存在低频共振和高频共振现象, 两不同共振频率的数值与泡群内气泡的本征频率相关. 泡群内气泡的本征频率又受到初始半径、泡群大小和泡群内气泡数量的影响. 气泡自由振动和驱动声波的耦合激起泡群内气泡的受迫振动, 气泡初始半径、气泡数密度和驱动声波频率等都会影响泡群内气泡的振动幅值和初相位. 关键词： 气泡群 共振 声响应 超声空化     

Towards transport theory of hadron gases

An important role of hadron resonances for determining the characteristics of hadron gases is argued. A kinetic theory model of hadron gas is developed. A classical, nonquantum, distribution function of a resonance is defined with the help of the profile function being an analogue of the mass shell delta function of stable particles. The Boltzmann equation is generalized to include the resonance decay and resonance formation processes. To determine the unknown profile function, the transition rates are assumed to satisfy the bilateral normalization or the detailed balance condition. The profile function is expressed through the resonance formation cross section and the decay width. The H-theorem is proved, and it is shown that the form of the equilibrium distribution function of a resonance coincides with that of a stable particle. Macroscopic equilibrium characteristics are studied. Significance of the resonance mass smearing effect is demonstrated.     

具有固有频率涨落的记忆阻尼线性系统的随机共振

研究了在内噪声、外噪声(固有频率涨落噪声)及周期激励信号共同作用下具有指数型记忆阻尼的广义Langevin方程的共振行为.首先将其转化为等价的三维马尔可夫线性系统,再利用Shapiro-Loginov公式和Laplace变换导出系统响应一阶矩和稳态响应振幅的解析表达式.研究发现,当系统参数满足Routh-Hurwitz稳定条件时,稳态响应振幅随周期激励信号频率、记忆阻尼及外噪声参数的变化存在"真正"随机共振、传统随机共振和广义随机共振,且随机共振随着系统记忆时间的增加而减弱.数值模拟计算结果表明系统响应功率谱与理论结果相符.