Application of the heat-kernel method to the constituent quark model at finite temperature

The heat-kernel method is applied to the constituent quark model. We calculate the effect of thermal quark fluctuations on the meson action and the resulting quark condensate and ππ-scattering amplitude at finite temperature. The quarks produce a chiral phase transition only by their effect on the mesonic coupling constants. The s-wave isospin zero ππ-scattering amplitude diverges near the phase transition showing the necessity for a more sophisticated treatment of meson fluctuations.     

Propagation characteristics of laser beams with amplitude modulations and phase fluctuations in apertured fractional Fourier transforming system

The apertured fractional Fourier transforming system is introduced and applied to treat the propagation of Gaussian beams with amplitude modulations and phase fluctuations. Based on the treatment that a rectangular function can be expanded into an approximate sum of complex Gaussian functions with finite numbers, the analytical expressions for the mutual intensity distribution of laser beams with amplitude modulations and phase fluctuations passing through the apertured fractional Fourier transforming system are obtained. Some numerical simulations are illustrated for their propagation properties.     

Thermodynamic limitation on the conversion of heat into coherent radiation

From the thermodynamical point of view there is the possibility of supplying a small amount of the energy of coherent radiation from a thermal reservoir. This possibility is attributed to the finite flow of entropy of light which is coherent but shows amplitude and/or phase fluctuations even if the radiation field consists of only a single mode.     

步进累加方法的实践

本文由理论与实验证明步进累加方法本质上是一种狭带的带通滤波的选择接收方法。其线型为类sinc函数。累加的结果与累加次数有关。对单脉冲后步进累加在一定次数以后即趋近饱和。对类回波的接收则出现极大值。只有在弱耦合体系中且offset选择在化学位移处才能得到所谓化学位移滤波。最后讨论实验条件及应用例子。     

Spatial filtering of wall pressure fluctuations beneath a turbulent boundary layer

Methods of experimental spatial filtering of wall pressure fluctuations beneath a turbulent boundary layer are developed with the aim of obtaining information on the wave number-frequency spectrum. The spatial filtering of the pressure field components by wave-vector filters is studied. The method of spatial filtering of pressure fluctuations by an acoustic array, i.e., a periodic structure with a finite number of elementary transducers, is analyzed. The relation between the wave number characteristic of the acoustic array and the wave number spectrum of the amplitude distribution of transducer’s local sensitivity is determined. Quantitative estimates are obtained for the sensitivity of the array to the wave number spectrum of turbulent boundary-layer pressures, which is necessary for measuring the wall pressure fluctuations in a turbulent boundary layer by wave-vector filters.     

Properties of the quantum universe in quasistationary states and cosmological puzzles

Old and new puzzles of cosmology are reexamined from the point of view of the quantum theory of the universe developed here. It is shown that in the proposed approach the difficulties of the standard cosmology do not arise. The theory predicts the observed dimensions of the non-homogeneities of matter density and the amplitude of fluctuations of the cosmic background radiation temperature in the Universe and points to a new quantum mechanism of their origin. The large-scale structure in the Universe is explained by the growth of non-homogeneities which arise from primordial quantum fluctuations due to the finite width of the quasistationary states. The theory allows one to obtain the value of the deceleration parameter, which is in good agreement with the recent SNe Ia measurements. It explains the large value of the entropy of the Universe and describes other parameters. Received: 30 July 2001 / Published online: 8 February 2002     

Exactly solvable toy model for the pseudogap state

We present an exactly solvable toy model which describes the emergence of a pseudogap in an electronic system due to a fluctuating off-diagonal order parameter. In one dimension our model reduces to the fluctuating gap model (FGM) with a gap that is constrained to be of the form , where A and Q are random variables. The FGM was introduced by Lee, Rice and Anderson [Phys. Rev. Lett. 31, 462 (1973)] to study fluctuation effects in Peierls chains. We show that their perturbative results for the average density of states are exact for our toy model if we assume a Lorentzian probability distribution for Q and ignore amplitude fluctuations. More generally, choosing the probability distributions of A and Q such that the average of vanishes and its covariance is , we study the combined effect of phase and amplitude fluctuations on the low-energy properties of Peierls chains. We explicitly calculate the average density of states, the localization length, the average single-particle Green's function, and the real part of the average conductivity. In our model phase fluctuations generate delocalized states at the Fermi energy, which give rise to a finite Drude peak in the conductivity. We also find that the interplay between phase and amplitude fluctuations leads to a weak logarithmic singularity in the single-particle spectral function at the bare quasi-particle energies. In higher dimensions our model might be relevant to describe the pseudogap state in the underdoped cuprate superconductors. Received 15 March 2000     

Background fluctuations in the GPS-microlab-1 ionospheric radio sounding experiment

We analyze the spectra of the phase and amplitude fluctuations of radio signals recorded in the course of four ionospheric radio-sounding sessions at altitudes from 70 to 120 km. Our study is aimed at determining the sources of these fluctuations. Comparing the statistical properties of fluctuations measured at two wavelengths with theoretical calculations, we conclude that only the low-frequency part of background fluctuations is of ionospheric origin, while the high-frequency fluctuations are caused by noise of the measuring system. The amplitude fluctuations are more informative in the high-frequency region, since they are mainly due to ionospheric irregularities. We discuss the possibility of separation of the components of amplitude fluctuations caused by ionospheric irregularities and the irregularities of the neutral atmosphere in the case of sounding at the altitudes at which those components have comparable values. It is shown that this problem cannot be solved by dispersion and extrapolation methods, which are used for separation of the regular ionospheric and atmospheric components of the amplitude and phase variations of radio signals. A. N. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp. 511–523, June 1999.     

Stochastic Resonance in a Bistable System Subject to Dichotomous Noise

The stochastic resonance phenomenon in a bistable system subject to Markov dichotomous noise (DN) is investigated. Based on the adiabatic elimination and the two-state theories, the explicit expressions for the signal-to-noise ratio (SNR) and the spectral power amplification (SPA) have been obtained. It is shown that two peaks can occur on the curve of SNR versus the intensity of the DN. Moreover, the SNR is a non-monotonic function of the correlation time of the DN. The SPA varies non-monotonously with the strength of the DN. The dependence of the SNR on the frequency and the amplitude of the external periodic signal are discussed. The effect of the external frequency and the correlation time of the DN on the SPA are analyzed.     

On the impact of large amplitude pairing fluctuations on nuclear spectra

The influence of large amplitude pairing fluctuations is investigated in the framework of beyond mean field symmetry conserving configuration mixing calculations. In the numerical application the finite range density dependent Gogny force is used. We investigate the nucleus ⁵⁴Cr with particle number and angular momentum projected wave functions considering the axial quadrupole deformation and the pairing gap degree of freedom as generator coordinates. We find that the effects of the pairing fluctuations increase with the excitation energy and the angular momentum. The self-consistency in the determination of the basis states plays an important role.     

The Structure of Stratospheric Irregularities According to Radio-Occultation Data Obtained using Satellite-to-Satellite Paths

We analyze the possibility of monitoring density or temperature fluctuations in the stratosphere based on data of amplitude radio-occultation measurements at centimeter waves using satellite-to-satellite paths. Comparison of the experimental spectra of amplitude fluctuations with the theoretical spectra calculated for a model containing both strongly anisotropic irregularities and an isotropic Kolmogorov turbulence shows that the amplitude fluctuations of radio waves in the stratosphere are mainly contributed by anisotropic irregularities which correspond to the model of saturated internal gravity waves. The efficiency of the radio occultation technique for the global remote monitoring of internal waves in the stratosphere is demonstrated.     

Energy diffusion in hard-point systems

We investigate the diffusive properties of energy fluctuations in a one-dimensional diatomic chain of hard-point particles interacting through a square-well potential. The evolution of initially localized infinitesimal and finite perturbations is numerically investigated for different density values. All cases belong to the same universality class which can be also interpreted as a Levy walk of the energy with scaling exponent γ=3/5. The zero-pressure limit is nevertheless exceptional in that normal diffusion is found in tangent space and yet anomalous diffusion with a different rate for perturbations of finite amplitude. The different behaviour of the two classes of perturbations is traced back to the “stable chaos" type of dynamics exhibited by this model. Finally, the effect of an additional internal degree of freedom is investigated, finding that it does not modify the overall scenario.     

Giant stress fluctuations at the jamming transition

We study the stress response to a steady imposed shear rate in a concentrated suspension of colloidal particles. We show that, in a small range of concentrations and shear rates, stress exhibits giant fluctuations. The amplitude of these fluctuations obeys a power-law behavior, up to the apparition of a new branch of flow, leading to an excess of high amplitude fluctuations which exhibit a well-defined periodicity.     

Nucleus-nucleus collisions: Intrinsic motion with external correlations

A consistent treatment of the relative and intrinsic motion which goes beyond the mean-field approach allows to include the fluctuations of the time-dependent mean field for the intrinsic as well as for the relative motion. Starting with the v. Neumann equation for the total density matrix, we derive a modified equation for the intrinsic many-body density matrix. This equation is used to obtain the quantum kinetic equations for the one-body density matrix and the two-body correlator. In the time-dependent single-particle basis, the occupation numbers change in time due to a collision term originating from residual two-body interactions which account for equilibration, and due to the fluctuations of the external mean field. The relations to TDHF with collision term are discussed. Special attention is paid to the conditions for a diabatic evolution of the single-particle states and to finite size effects which play an important role to make two-body collisions operative in finite nuclei.     

Dust acoustic shock wave generation due to dust charge variation in a dusty plasma

In a dusty plasma, the non-adiabaticity of the charge variation on a dust grain surface results in an anomalous dissipation. Analytical investigation shows that this results in a small but finite amplitude dust acoustic (DA) wave propagation which is described by the Korteweg-de Vries-Burger equation. Results of the numerical investigation of the propagation of large-amplitude dust acoustic stationary shock wave are presented here using the complete set of non-linear dust fluid equations coupled with the dust charging equation and Poisson equation. The DA waves are of compressional type showing considerable increase of dust density, which is of significant importance in astrophysical context as it leads to enhanced gravitational attraction considered as a viable process for star formation. The DA shock transition to its far downstream amplitude is oscillatory in nature due to dust charge fluctuations, the oscillation amplitude and shock width depending on the ratioω _pd/V_ch and other plasma parameters Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.     

Generalized ramsey scheme for precision spectroscopy of ultracold atoms and ions: Inclusion of a finite laser line width and spontaneous relaxation of the atomic levels

Ramsey schemes with pulses of different lengths and with a composite pulse have been analyzed taking into account a finite width of the laser line and spontaneous relaxation of atomic levels. The optimal parameters of pulses corresponding to the maximum suppression of the excitation-related shift and the maximum resonance amplitude have been found for both schemes. According to the numerical results, spontaneous relaxation of the atomic levels and a finite width of the laser line must be taken into account in the calculation of the optimal parameters of the excitation pulses. The Ramsey scheme with a composite pulse is less sensitive to fluctuations of the Rabi frequency than the scheme with pulses of different lengths.     

具有有限温度的热克尔态

利用热场动力学方法，提出了具有有限温度的热克尔态，研究了这些态的量子统计性质及其与温度的关系，讨论了这些态中场振幅的涨落与压缩性质．对于热化的场，还提出了热压缩的定义，并对热克尔态，讨论了温度对热压缩的影响     

On the appearance of a system of ring vortices in the mixing layer of axially symmetric turbulent jets under acoustic action

The shadow visualization method is applied to study the process of loss of stability of the mixing layer of a subsonic axially symmetric turbulent jet under longitudinal internal action of saw-tooth sound waves of finite amplitude. Such action leads to the formation of a system of ring vortices in the mixing layer at the frequency of its intrinsic instability. The interaction of the vortices can be accompanied by sound emission. A similar phenomenon is also observed in turbulent jets for small supercritical pressure fluctuations on a nozzle.