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排序方式: 共有121条查询结果,搜索用时 31 毫秒
1.
T.M. Mishonov N. Chéenne D. Robbes J.O. Indekeu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):291-296
The generation of harmonics of the voltage response is considered when an AC current is applied through a superconducting
film above Tc. It is shown that almost at all temperatures the mechanism of the temperature oscillations created by the AC current and
the temperature dependence of the resistance dominates over the isothermal nonlinear electric conductivity. Only in a narrow
critical region close to Tc the latter is essential for the generation of the harmonics. A detailed investigation of harmonics generation provides an
accurate method for measuring the thermal boundary conductance between the film and the insulating substrate. The critical
behaviour of the third harmonic will give a new method for the determination of the lifetime of metastable Cooper pairs above
Tc. The comparison of the calculated fifth harmonics of the voltage with the experiment is proposed as an important test for
the applicability of the employed theoretical models.
Received 8 September 2001 相似文献
2.
3.
The properties of fluctuations in space in or outside thermal equilibrium are obtained by solving hierarchies of equations derived either from the Liouville or the Master equation. In particular we study the one-, two-, etc., time correlation functions that describe the spatial and temporal behavior of the fluctuations in space. Explicit solutions are obtained for a dilute gas. The Langevin approach is briefly discussed. Our results are compared with those obtained in the extensive literature, which is reviewed in some detail. 相似文献
4.
H. Shigematsu 《Journal of statistical physics》1993,71(5-6):981-1002
Fluctuation of the average spin for one-dimensional Ising spins with nearest neighbor interactions are studied. The distribution function for the average spin is calculated for a finite volume, finite temperature, and finite magnetic field. As the volume increases and the temperature diminishes at zero magnetic field, there are two limits in which the probability distribution shows quite different behaviors: in the thermodynamic limit as the volume goes to infinity for finite temperature, small deviations of the fluctuations are described by a Gaussian distribution, and in the limit as the temperature vanishes for a finite volume, the ground states are realized with probability one. The crossover between these limits is analyzed via a ratio of the correlation length to the volume. The helix-coil transition in a polypeptide is discussed as an application. 相似文献
5.
Gueroui Z Freyssingeas E Place C Berge B 《The European physical journal. E, Soft matter》2003,11(1):105-108
We observed fluctuations of elongated DNA molecules by fluorescence microscopy. The molecules are fixed at both ends and undulate.
Mode analysis of the thermally excited undulations of the labeled DNA molecules gives access to the spectral density of the
amplitude fluctuations. From these measurements we estimate the tension acting on the DNA molecules. We found the forces to
be within the entropic elasticity range of a typical DNA molecule (measured on the single-molecule level).
Received: 11 November 2002 / Accepted: 12 May 2002 / Published online: 4 June 2003
RID="a"
ID="a"Present address: Center for Studies in Physics and Biology, Rockefeller University, 1230 York Avenue, New York, NY 10021, USA. e-mail: zoherg@rockefeller.edu 相似文献
6.
R. Menegotto Costa L. Mendon?a Ferreira V. N. Vieira P. Pureur J. Schaf 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):107-113
We have studied experimentally the electrical magneto-conductivity near the
superconducting transition of YBa2Cu3O7-δ, YBa2
(Cu2.95Zn0.05)O7-δ and Y(Ba1.75Sr0.25)Cu3O7-δ polycrystalline samples. The measurements were performed in magnetic fields ranging from 0 to 400 Oe applied parallel to
the current orientation. The results show that the resistive transition of these systems proceeds in two stages. The pairing
transition occurs at the bulk critical temperature Tc, where superconductivity is stabilized within small and homogeneous regions of the
sample generically called grains. The regime of approach to the zero resistance state reveals the occurrence of a coherence
transition at a lower temperature Tc0. This transition is related to the connective nature of the granular samples and is controlled by fluctuations of the
order-parameter phase of individual grains. Our experiments show that the Zn-doping, besides depressing the pairing critical
temperature, strongly enlarges the temperature range dominated by effects related to the coherence transition. The substitution
of Ba by Sr causes only a small reduction of Tc, but also enhances significantly the effects related to the grain
coupling phenomenology. In general, our results indicate that these impurity substitutions in YBa2Cu3O7-δ produce or magnify the granularity at a microscopic level, enhancing the effects of phase fluctuations in the conductivity
near the transition. 相似文献
7.
Detrended fluctuation analysis (DFA) is a scaling method commonly used for detecting long-range correlations in non-stationary time series. The DFA method uses a trend based on polynomial fitting to extract and quantify fluctuations at different time scales. Basically, such procedure acts as a (non-dynamical) high-pass filter that removes time series components below a given time scale. As an alternative to the polynomial fitting approach, this paper proposes a DFA method based on well-known high-pass filters (e.g., Butterworth, elliptic, etc.). Numerical results show that the proposed DFA approach yields results similar to traditional DFA method. Maybe, the main advantage of the proposed DFA method is that efficient implementations of high-pass filters are available commercially. 相似文献
8.
9.
The recently discovered properties of the I-confinement Regime are explained as resulting from the excitation of a heavy particle mode. The theoretically predicted mode phase velocity in the direction of the electron diamagnetic velocity and the induced confinement of impurities at the edge of the plasma column have been confirmed by the experiments. The direction of the mode phase velocity is consistent with that (opposite) of the spontaneous rotation in the plasma core. The mode is of the “ion-mixing” type, in that it does not produce any electron transport across the fields and it involves significant poloidal magnetic field fluctuations. 相似文献
10.
Fluctuations induced extinction and stochastic resonance effect in a model of tumor growth with periodic treatment 总被引:1,自引:0,他引:1
We investigate a stochastic model of tumor growth derived from the catalytic Michaelis-Menten reaction with positional and environmental fluctuations under subthreshold periodic treatment. Firstly, the influences of environmental fluctuations on the treatable stage are analyzed numerically. Applying the standard theory of stochastic resonance derived from the two-state approach, we derive the signal-to-noise ratio (SNR) analytically, which is used to measure the stochastic resonance phenomenon. It is found that the weak environmental fluctuations could induce the extinction of tumor cells in the subthreshold periodic treatment. The positional stability is better in favor of the treatment of the tumor cells. Besides, the appropriate and feasible treatment intensity and the treatment cycle should be highlighted considered in the treatment of tumor cells. 相似文献