Correlation properties of black-body radiation in the context of the electron cyclotron emission of a magnetized plasma

Summary The quest for the cause of the anomalously large heat transport in magnetically confined thermonuclear plasmas has motivated detailed studies of fluctuations of various plasma parameters and, among others, of the electron temperature fluctuations. For an optically thick plasma the fluctuations of the electron cyclotron emission, ECE, are proportional to the electron temperature fluctuations up to a critical frequency where this ceases to be true. For the ultimate purpose of recovering, by correlation analysis, the actual plasma temperature fluctuations from the fluctuations of the measured radiation at frequencies above the critical, the mutual correlation properties of two ECE beams are analyzed and a criterion is obtained to decide when the thermal radiation fluctuations are uncorrelated and hence ignorable. The author of this paper has agreed to not receive the proofs for correction.     

Warm Inflation and Scalar Perturbations of the Metric

A second-order expansion for the quantum fluctuations of the matter field was considered in the framework of the warm inflation scenario. The friction and Hubble parameters were expanded by means of a semiclassical approach. The fluctuations of the Hubble parameter generates fluctuations of the metric. These metric fluctuations produce an effective term of curvature. The power spectrum for the metric fluctuations can be calculated on the infrared sector.     

Eccentricity fluctuations are not the only source of elliptic flow fluctuations in a multiphase transport model

Sources of event-by-event elliptic flow fluctuations in relativistic heavy-ion collisions are investigated in a multiphase parton transport model(AMPT).Besides the well-known initial eccentricity fluctuations,several other sources of elliptic flow dynamical fluctuations are identified.One is fluctuations in initial parton configurations at a given eccentricity.Configuration fluctuations are found to be as important as eccentricity fluctuations in elliptic flow development.A second is quantum fluctuations in parton-parton interactions during system evolution.A third is fluctuations caused by hadronization and final-state hadronic scatterings.The magnitudes of these fluctuations are investigated relative to the eccentricity fluctuations and the average elliptic flow magnitude.The fluctuations from the latter two sources are found to be negative.The results may have important implications for the interpretation of elliptic flow data.     

Effect of density fluctuations on the expansion of the universe far from the singularity

The effect of fluctuations in the density of matter on the expansion of the universe far from the singularity is analyzed on the basis of a model with a three-dimensional space which is homogeneous and isotropie on the average. The fluctuations reduce the gravitational effect, retarding the expansion. This effect of the fluctuations increases as the expansion proceeds and can strongly affect the expansion velocity. An equation is derived for the age of the universe on the basis of this model. The age is expressed in terms of observable quantities: the Hubble constant and the acceleration parameter. It is shown that fluctuations lead to an increase in this age. It is concluded that fluctuations must be taken into account in studying the expansion of the observable universe.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 7–11, January, 1977.     

Observation of the coherence between the plasma density fluctuations in the core and at the edge of the plasma column in the L-2M stellarator

Results are presented from the measurements of the radial coherence between the plasma density fluctuations in the core and at the edge of the plasma column in the L-2M stellarator. It is found that the radial coherence between these fluctuations is fairly high: the coherence coefficient attains a value of higher than 0.5 for the spectral wavelet components with frequencies lying in the range from several kilohertz to 30 kHz. The statistical characteristics of density fluctuations are also studied. It is shown that the power distribution function of the plasma density fluctuations in the plasma core differs from Gaussian.     

Fluctuations in the Curie-Weiss version of the random field Ising model

The fluctuations of the order parameter in the Curie-Weiss version of the Ising model with random magnetic field are computed. Away from criticality or at first-order critical points they have a Gaussian distribution with random (i. e.,sample-dependent) mean, thermal fluctuations contributing in same order as the fluctuations of the field; at second- or higher-order critical points, non-Gaussian sample-dependent distributions appear, and the fluctuations of the fields are enhanced, dominating over the thermal ones.     

On the Physical Origin of Long-Ranged Fluctuations in Fluids in Thermal Nonequilibrium States

Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations.     

Instability of flatspace and the origin of conformal fluctuations

It is shown that conformal fluctuations in the metric can be initiated by the vacuum fluctuations of a scalar field with mass greater than the Planck mass. Flatspace is unstable against such fluctuations.     

On the slow dynamics of density fluctuations near the colloidal glass transition

Slow dynamics of density fluctuations near the colloidal glass transition is discussed from a new viewpoint by numerically solving a nonlinear stochastic diffusion equation for the density fluctuations recently proposed by one of the present authors (MT). The effects of spatial heterogeneities on the dynamics of density fluctuations are then investigated in an equilibrium system. The spatial heterogeneities are generated by the nonlinear density fluctuations, while in a nonequilibrium system they are described by a nonlinear deterministic equation for the average number density. The dynamics of equilibrium density fluctuations is thus shown to be quite different from that of nonequilibrium ones, leading to a logarithmic decay followed by less distinct α- and β-relaxation processes. Received 9 March 2002 and Received in final form 19 September 2002     

On the kinetic theory of Brownian motion

The influence of fluctuations on the kinetic processes of Brownian motion is investigated. We consider fluctuations for which the correlation time is comparable with the relaxation time of the distribution function. Taking such large scale fluctuations into account is shown to lead to a change of the diffusion coefficient and to the appearance of additional correlations in the motions of Brownian particles. An expression is obtained for the correlation function of a Langevin source in the diffusion equation taking into account the contribution of large scale fluctuations.     

Noise power fluctuations and the masking of sine signals

This article is concerned with fluctuations in noise power and with the role that such fluctuations play in the masking of sine signals by noise. Several measures of noise fluctuations are discussed: the fourth moment of the waveform, the fourth moment of the envelope, and the crest factor. Relationships among these quantities are found for cases of equal-amplitude random-phase noise and Rayleigh-distributed-amplitude noise. Of particular interest is a special non-Gaussian noise called low-noise noise in which the fluctuations are small by any of our measures. The results of frozen-noise masking experiments are reported, where the noise waveform was fixed for all stimulus presentations. In separate experiments, equal-amplitude random-phase Gaussian noise, with typical fluctuations, and low-noise noise, with almost no fluctuations were used. The data show that for a noise bandwidth less than the critical bandwidth, the masked threshold is about 5 dB lower for low-noise noise than for Gaussian noise. When the noise bandwidth is larger than the critical bandwidth, the masked threshold is the same for both kinds of noise. It is concluded that noise power fluctuations increase masked threshold by about 5 dB and that filtering by the auditory system reintroduces fluctuations into broadband low-noise noise.     

Measurement of temperature fluctuations and anomalous transport in the SINP tokamak

Temperature fluctuations have been measured in the edge region of the SINP tokamak. We find that these fluctuations have a comparatively high level (30–40%) and a broad spectrum. The temperature fluctuations show a quite high coherence with density and potential fluctuations and contribute considerably to the anomalous particle flux.     

Effect of Anisotropy Fluctuations on the Piezomagnetic Properties of Magnetostrictive Ferromagnets

The effect of the angular and amplitude anisotropy fluctuations in an uniaxial magnetostrictive ferromagnet on its piezomagnetic parameters is examined. It is shown that the increase of the angular anisotropy fluctuations decreases the piezomagnetic parameters of the ferromagnet, while the increase of the amplitude anisotropy fluctuations increases these parameters.     

On the energetics of transversal and longitudinal fluctuations of atomic magnetic moments

By constrained spin-density functional calculations we estimate the relative role of the longitudinal and transversal fluctuations of the magnetic moments in the series of 3d metals (bcc Fe, hcp and fcc Co, and fcc Ni) for weak excitations from the ferromagnetic ground state. It is shown that the importance of longitudinal fluctuations strongly varies from relatively small in bcc Fe to large in fcc Ni. This means that a consistent adiabatic treatment of the low-energy spin fluctuations should include independent longitudinal fluctuations.     

On the low-frequency limit of the Schönfeld pulse 1/f law

On the basis of propositions of the common fluctuation theory, peculiarities of small fluctuations in real physical systems with limited sizes are analyzed. It is established that small fluctuations should necessarily be divided into two types of fluctuations: “small” and “very small”. It is shown that the damping process of “small” fluctuations has relaxation character, while the damping process of “very small” fluctuations is of random character, i.e., it represents a random rectangular signal. The probability density of “very small” fluctuations is shown to be Gaussian. The agreement of the obtained results with experimental data acquired from semiconductor-based devices is analyzed. A relation between the generation–recombination noise and phonon number fluctuations in semiconductors is studied. On the basis of this consideration it is shown that the Schönfeld pulse spectrum preserves its well-known 1/f form only in the range of intermediate frequencies; at lower frequencies the spectrum gets saturated. An expression for the low-frequency limit of Schönfeld pulse 1/f law is obtained.     

Reducing the linewidth of an atom laser by feedback

A continuous atom laser will almost certainly have a linewidth dominated by the effect of the atomic interaction energy, which turns fluctuations in the condensate atom number into fluctuations in the condensate frequency. These correlated fluctuations mean that information about the atom number could be used to reduce the frequency fluctuations, by controlling a spatially uniform potential. We show that feedback based on a physically reasonable quantum nondemolition measurement of the atom number of the condensate in situ can reduce the linewidth enormously.     

Fluctuations of the intersubband splitting energy and the potential well shape of two-dimensional electrons in the quantum Hall effect regime

Recombination radiation and inelastic light scattering spectra of 2D electrons are studied simultaneously in structures with a single GaAs quantum well in the quantum Hall effect regime. It is found that the intensity of intersubband inelastic light scattering (the SDE mode) at the filling factor ν = 2 exhibits fluctuations in phase with fluctuations of the photoluminescence intensity of 2D electrons of the ground subband. It is shown that, simultaneously with fluctuations of the scattered light and recombination radiation intensities, the spectral positions of these lines change stepwise by 0.3–0.5 meV. The jumps found in the spectral positions of lines are observed only in narrow intervals of magnetic fields corresponding to the quantum Hall effect and are presumably associated with zero-point fluctuations (Casimir-Lifshits force).     

On the magnitude of the local moment in the Anderson model

Consideration of the self-consistent coupling between transverse spin fluctuations and charge fluctuations at the impurity provides an understanding of the magnetic atom's susceptibility law which reduces to that appropriate for a spin one half only in the symmetric configuration at low temperatures.     

A study of the character of the phase transition to the superconducting phase by the renormalization group method

This study deals with phase transitions in magnetic systems when spin fluctuations and electronphonon interaction exchange enhancement occur. It is shown that in this context fluctuations play a substantial role and determine the character of the first-order phase transition that is close to a second-order transition.     

Intermittency of the density fluctuations and its influence on the radial transport in the boundary of J-TEXT

To improve the understanding of the turbulence intermittency,a detailed investigation of the intermittency of the density fluctuations has been performed in the boundary of J-TEXT.The intermittency of the density fluctuations and its influence on the radial transport are reported.The probability distribution functions of the density fluctuations are not scale-invariant,being inconsistent with the self-organized criticality hypothesis.The underlying dynamics of the intermittency are detected using the quiet-time statistical method.The probability distribution function of the quiet times shows double-power-law regions,indicating the existence of correlations between the successive burst events.