Perturbation approach to plasma oscillations

It is shown that the complete spectrum, continuous as well as discrete, and corresponding eigenfunctions of the Vlasov operator can be obtained by a single perturbation procedure from the purely continuous spectrum and corresponding eigenfunctions of the free-streaming operator. In addition we present an alternative definition of the eigenfunctions and show that the problem of normalizing the continuous eigenmodes is thus solved automatically.     

An analysis of acoustic oscillations in dust plasma structures

Low-frequency oscillations in the density of dust particles, which are spontaneously excited in the standing plasma column of a dc glow discharge in neon, were experimentally studied. The longitudinal waves were monitored by a special visualization technique, and the dust sound oscillation characteristics were determined and analyzed using specially developed algorithm and data processing software. It was established that the longitudinal waves propagate from anode to cathode, the frequency and wavevector of the dust sound oscillations being dependent on the discharge current, gas pressure, particle density in the dust cloud, and spatial coordinates. Two-dimensional (2D) fields of the main wave characteristics were studied using an original algorithm. The possible mechanisms of excitation of the dust sound oscillations is discussed. The experimental spatial distributions of the wave parameters are compared to the patterns obtained within the framework of various theoretical models.     

The Lund fragmentation process for a multi-gluon string according to the area law

The Lund area law describes the probability for the production of a set of colourless hadrons from an initial set of partons, in the Lund string fragmentation model. It was derived from classical probability concepts but has later been interpreted as the result of gauge invariance in terms of the Wilson gauge loop integrals. In this paper {we will present a general method to implement the area law for a multi-gluon string state}. In this case the world surface of the massless relativistic string is a geometrically bent (1+1)-dimensional surface embedded in the (1+3)-dimensional Minkowski space. The partonic states are in general given by a perturbative QCD cascade and are consequently defined only down to a cutoff in the energy-momentum fluctuations. We will show that our method defines the states down to the hadronic mass scale inside an analytically calculable scenario. We will then show that there is a differential version of our process which is closely related to the generalized rapidity range , which has been used as a measure on the partonic states. We identify as the area spanned between the directrix curve (the curve given by the parton energy-momentum vectors laid out in colour order, which determines the string surface) and the average curve (to be called the -curve) of the stochastic X-curves (curves obtained when the hadronic energy-momentum vectors are laid out in rank order). Finally {we show that from the X-curve corresponding to a particular stochastic fragmentation situation it is possible to reproduce the directrix curve} (up to one starting vector and a set of sign choices, one for each hadron). This relationship provides an analytical formulation of the notion of parton–hadron duality. The whole effort is made in order to get a new handle to treat the transition region between where we expect perturbative QCD to work and where the hadronic features become noticeable. Received: 3 July 2001 / Published online: 31 August 2001     

Real-time kadanoff-baym approach to plasma oscillations in a correlated electron Gas

A nonequilibrium Green's functions approach to the collective response of correlated Coulomb systems at finite temperatures is presented. It is shown that solving Kadanoff-Baym-type equations of motion for the two-time correlation functions including the external perturbing field allows one to compute the plasmon spectrum with collision effects in a systematic and consistent way. The scheme has a "built-in" sum-rule preservation and is simpler to implement numerically than the equivalent equilibrium approach based on the Bethe-Salpeter equation.     

Nonlinear radial oscillations of encapsulated microbubbles subject to ultrasound: the effect of membrane constitutive law

The nonlinear radial oscillations of bubbles that are encapsulated in an elastic shell are investigated numerically subject to three different constitutive laws describing the viscoelastic properties of the shell: the Mooney-Rivlin (MR), the Skalak (SK), and the Kelvin-Voigt (KV) models are used in order to describe strain-softening, strain-hardening and small displacement (Hookean) behavior of the shell material, respectively. Due to the isotropic nature of the acoustic disturbances, the area dilatation modulus is the important parameter. When the membrane is strain softening (MR) the resonance frequency decreases with increasing sound amplitude, whereas the opposite happens when the membrane is strain hardening (SK). As the amplitude of the acoustic disturbance increases the total scattering cross section of a microbubble with a SK membrane tends to decrease, whereas that of a KV or a MR membrane tends to increase. The importance of strain-softening behavior in the abrupt onset of volume pulsations, that is often observed with small insonated microbubbles at moderately large sound amplitudes, is discussed.     

纳米氦液滴-超低温化学研究装置

成功研制了新一代纳米氦液滴实验装置．氦液滴是由高压的高纯氦气通过超低温的脉冲阀绝热膨胀形成的,通过调节连接在超低温氦冷头上的脉冲阀的温度(10～30 K)及脉冲阀内氦气的背景压力(10～40 atm),氦液滴的大小在包含103到105个氦原子间连续可调,和传统的连续氦液滴束源比较起来,脉冲束源的强度提高了一个量级以上,提供了一个和商品化脉冲激光器结合使用,研究超低温条件下超流体氦中的化学反应动力学的机会．通过研究氦液滴中包裹的CH₃I分子的光解动力学来对仪器的性能进行测试,利用离子速度影像技术研究了超低温纳米氦液滴中包裹的CH₃I分子在252 nm下的光解动力学,光解产物甲基通过(2+1)共振增强多光子电离并运用离子影像进行检测,结果表明光解产物的平动能及角分布被氦原子环境有效的弛豫．也证实了运用脉冲氦液滴束源研究衰减光谱的可行性,通过对氦液滴中掺杂苯的衰减光谱的研究,还发现小于3%的衰减信号都可以被检测到,表明所研制的脉冲氦液滴束的稳定性及检测器的灵敏度都是很高的．     

Remarks to the standard scheme (theory) of neutrino oscillations. Corrected scheme of neutrino oscillations

In the standard theory of neutrino oscillations, it is supposed that physically observed neutrino states ν _e , ν_μ, ν_τ, have no definite masses, that they are initially produced as a mixture of the ν₁, ν₂, ν₃ neutrino states (i.e., they are produced as a wave packet), and that neutrino oscillations are the real ones. Then, this wave packet must decompose at a definite distance into constituent parts and neutrino oscillations must disappear. It was shown that these suppositions lead to violation of the law of energy and momentum conservation. An alternative scheme of neutrino oscillations obtained within the framework of particle physics has been considered, where the above mentioned shortcomings are absent, the oscillations of neutrinos with equal masses are the real ones, and the oscillations of neutrinos with different masses are the virtual ones. Expressions for probabilities of neutrino transitions (oscillations) in the alternative (corrected) scheme are given. The text was submitted by the author in English.     

应用质心运动定理一例

利用质心运动定理方便地求出了沿放在光滑水平面上圆弧槽运动的小球相对惯性参照系的运动轨迹。     

Spectral manifestation of collective plasma oscillations quasi-resonant to eigenfrequencies of individual nanoparticles in a silver Island film

A doublet is revealed in the light extinction spectrum of a thin silver island film and the explanation of its nature is proposed. Based on the electron microscopy data, it is found that the doublet cannot be formed only by intrinsic resonances of individual islands. Because of interisland interactions, light can excite collective fields localized near the film. Resonant frequencies of these localized modes depend on the size, concentration, and arrangement of individual islands, whose plasma oscillation frequencies differ only slightly from one another.     

Relation between particle sizes and concentration in undiluted and diluted blood plasma according to light scattering data

Bulletin of the Lebedev Physics Institute - The article is devoted to the study of dilution effect on the blood plasma particle concentrations and sizes, obtained by dynamic light scattering...     

Viscous hydrodynamic model of non-linear plasma oscillations in two-dimensional conduction channels and application to the detection of terahertz signals

In the Dyakonov-Shur detector the plasma resonance in a short channel High Electron Mobility Transistor is used for the resonant tunable detection of terahertz radiation. We derived a viscous hydrodynamic model with temperature dependent transport coefficients for the gated conduction channel. We evaluated the detector response function and obtained the quality factor of the plasma resonance.     

利用有效势能曲线对轨迹的分析与数值模拟

采用中心力的有效势能对一个力学问题进行分析,得出了物体运动的规律和特性,并且采用数值模拟直观地显示了物体运动的轨迹,其结果与有效势能曲线一致.