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1.
We study a current shot noise in a macroscopic insulator based on a two-dimensional electron system in GaAs in a variable range hopping (VRH) regime. At low temperature and in a sufficiently depleted sample a shot noise close to a full Poissonian value is measured. This suggests an observation of a finite-size effect in shot noise in the VRH conduction and demonstrates a possibility of accurate quasiparticle charge measurements in the insulating regime. 相似文献
2.
S. Maslowski 《Optical and Quantum Electronics》1973,5(4):275-284
This paper offers a review of the contributions of German research groups in the field of fibre-optical communications until now. Since the latest publications are also taken into account which in part are not yet printed, a survey is given at the same time of current activities in this field in Germany. 相似文献
3.
A. Ghosh S.K. Adhikari 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):31-36
The solutions of a renormalized BCS equation are studied in three space dimensions in s, p and d waves for finite-range separable
potentials in the weak to medium coupling region. In the weak-coupling limit, the present BCS model yields a small coherence
length and a large critical temperature, , appropriate for some high- materials. The BCS gap, , and specific heat as a function of zero-temperature condensation energy are found to exhibit potential-independent universal scalings. The
entropy, specific heat, spin susceptibility and penetration depth as a function of temperature exhibit universal scaling below
in p and d waves.
Received: 18 July 1997 / Revised: 8 September 1997 / Accepted: 29 September 1997 相似文献
4.
The thermal instability of a layer of Rivlin-Ericksen elastico-viscous fluid in porous medium acted on by a uniform magnetic field is considered. For stationary convection, Rivlin-Ericksen elastico-viscous fluid behaves like a Newtonian fluid. The magnetic field is found to have stabilizing effect whereas medium permeability has destabilizing effect. The magnetic field introduces oscillatory modes in the system, A sufficient condition for the non-existence of overstability is also obtained. 相似文献
5.
V. V. Zharov A. N. Lyalin O. V. Karban’ P. A. Perevozchikov N. N. Samartseva G. N. Konygin S. I. Leesment 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(5):804-808
The atomic force method (AFM) was used to study the processes of repair in the sclera tissue within the grafting zone of a
nanostructured biomaterial in a rabbit. The use of the nanostructured placenta has been shown to speed up the penetration
of a graft into the sclera and to induce the formation of new connective-tissue structures. Differences have been revealed
in the structure of mature and newly-formed collagen fibrils. 相似文献
6.
We study the existence conditions for the thermodynamic limit in the chain of BBGKY equations for the equilibrium correlation functions of a charged plasma. It is shown that in order for the thermodynamic limit to exist the charge of the plasma cannot increase faster than the surface area of the plasma. When this condition is satisfied the equilibrium correlation functions of the charged plasma are asymptotically identical to the correlation functions of a neutral plasma in a self-consistent electrostatic field, which depends only on the one-particle correlation functions. For a plasma which is uniform everywhere except in a thin surface region, this field is found in explicit form. For a plasma occupying an infinite half-space, the problem is equivalent to a neutral plasma near a charged wall.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, 11–16, February, 1987. 相似文献
7.
V. S. Barashenkov L. P. Grachev I. I. Esakov B. F. Kostenko K. V. Khodataev M. Z. Yur’ev 《Technical Physics》2000,45(10):1265-1270
Results are presented from studies of a high-pressure electrodeless breakdown in air at the focus of a standing wave in a high-Q quasi-optical two-mirror resonator pumped by single microwave pulses. In the experiment, the breakdown occurred at the front of the pulse of the resonator field. The breakdown field substantially exceeded the critical level and, under fixed conditions, showed a scatter from pulse to pulse. It is shown that the experimentally found excess in the threshold breakdown field over the critical level is due to the fact that the resonator field increases as a discharge plasmoid forms during breakdown and that the appearance of an electron initiating breakdown in a gas is a random event. 相似文献
8.
S. Gershman A. Belkind 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,60(3):661-672
A phenomenological picture of a pulsed electrical discharge in gas bubbles
in water is produced by combining electrical, spectroscopic, and imaging
characterization methods. The discharge is generated by applying 1 m\mu s
pulses of 5 to 20 kV between a needle and a disk electrode submerged in
water. An Ar gas bubble surrounds the tip of the needle electrode. Imaging,
electrical characteristics, and time-resolved optical emission spectroscopic
data suggest a fast streamer propagation mechanism and the formation of a
plasma channel in the bubble. Comparing the electrical and imaging data for
consecutive pulses applied to the bubble at a frequency of 1 Hz indicates
that each discharge proceeds as an entirely new process with no memory of
the previous discharge aside from the presence of long-lived chemical
species, such as ozone and oxygen. Imaging and electrical data show the
presence of two discharge events during each applied voltage pulse, a
forward discharge near the beginning of the applied pulse depositing charge
on the surface of the bubble and a reverse discharge removing the
accumulated charge from the water/gas interface when the applied voltage is
turned off. The pd value of ~ 300–500 torr cm, the 1 μs long pulse duration, low repetition rate, and unidirectional character of
the applied voltage pulses make the discharge process here unique compared
to the traditional corona or dielectric barrier discharges. 相似文献
9.
D. Chakraborty 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):263-269
We consider a class of inhomogeneous media known as composite media that is often encountered in experimental sciences, and
investigate the persistence probability of a random walker in such a system. Analytical and numerical results for the crossover
time scales are obtained for a composite system with two homogeneous components and three homogeneous components respectively. 相似文献
10.
The capacity and the dielectric loss tangent of a Gd x Mn1–xSe (x ≤ 0.2) solid solution have been measured in the frequency range 1–300 kHz without a magnetic field and in a magnetic field of 8 kOe in the temperature range 100–450 K, and the magnetic moment of the solid solution has been measured in a field of 8.6 kOe. The magnetocapacity effect and the change in the magnetocapacity sign have been observed in room temperature in the paramagnetic region. A correlation of the changes in the dielectric permittivity and the magnetic susceptibility with temperature has been revealed. The magnetocapacity is described using the model with orbital electron ordering and the Maxwell–Wagner model. 相似文献
11.
Moessbauer data have been obtained for a series of organotin anions. The spectra of these anions in solution show the presence of two species, a singlet in the tin(IV) region and a doublet in the tin(II) region. The crystal structure of triphenyltin anion with potassium in 18-crown-6 as the cation has been determined. The Moessbauer spectrum of this sample is a doublet in the tin(II) region. 相似文献
12.
Focusing in microlenses close to a wavelength in diameter 总被引:4,自引:0,他引:4
Light focused from air into a spherical microlens is affected by diffraction at the lens surface as its diameter approaches the wavelength of light. Through an extension of Mie theory, we show that a converging wave that is incident upon a Si microlens with a diameter less than approximately 4lambda creates a spot as much as 25% smaller than predicted with vector diffraction theory. Si microlenses only a wavelength in diameter are shown to be virtually insensitive to variations in the maximum illumination angle, and changes in index of refraction are not found to cause the proportional changes in spot size that would be expected from vector diffraction theory. 相似文献
13.
E. N. Argyres C. G. Papadopoulos M. T. M. van Kessel R. H. P. Kleiss 《The European Physical Journal C - Particles and Fields》2009,61(3):495-518
We show how to transform a d-dimensional Euclidean path integral in terms of two (Cartesian) fields to a path integral in terms of polar field variables.
First we present a conjecture that states how this transformation should be done. Then we show that this conjecture is correct
in the case of two toy models. Finally the conjecture will be proven for a general QFT model with two fields. 相似文献
14.
15.
《Magnetic resonance imaging》1999,17(1):29-36
The hippocampus plays a central role in the generation and propagation of seizures in patients with complex partial seizures. Hippocampal sclerosis (HS) is a common structural abnormality in patients with refractory epilepsy. The aim of this study was to quantify diffusion in the hippocampus in patients with epilepsy to evaluate the diffusion changes associated with HS. We scanned 20 subjects (14 patients and 6 controls) with a 1.5T magnetic resonance (MR) system using a cardiac-gated, navigated spin-echo diffusion-weighted sequence. Hippocampal ADC measurements were performed on maps of the ADC measured in three orthogonal directions labeled x, y, and z. The mean ADC (ADCav) and an anisotropy index (AI) were calculated. Hippocampi which fulfilled the MR criteria for HS had a higher ADCav (p < 0.001) and a lower AI (p = 0.04) than normal appearing hippocampi in patients and hippocampi in controls. These results imply a loss of structural organization in sclerotic hippocampi and an expansion of the extracellular space. Quantitative measurements of diffusion can be used as an independent parameter for the identification and characterization of abnormal hippocampi in epilepsy. 相似文献
16.
It is shown that bulk semiconductors exhibit strongly asymmetric Fano-type resonance profiles in magnetoabsorption processes
involving the formation of hot electron-hole pairs (EHPs) and accompanied by the scattering of the EHPs by defects. This result
is valid for transitions to electronic states with large Landau quantum numbers, when the Coulomb interaction plays a small
role. The physical reason for such a sharp change in the magnetoabsorption coefficient as compared with the expected result
for the ordinary density of states in a quantizing magnetic field is that the electronic excitations are quasi-one-dimensional.
The form of the resonance absorption is in good qualitative agreement with the experimental data.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 619–622 (25 April 1996) 相似文献
17.
18.
The behavior of large-scale circulation appearing against the background of Rayleigh-Bénard turbulent convection in rectangular
cavities of various geometries (from a thin layer to a cubic cell) has been experimentally investigated. It has been shown
that the regimes of large-scale circulation with spontaneous reversals separated by long periods of quasistationary circulation
appear both in a limited range of the Rayleigh number and in a limited range of the aspect ratio, which determines the ratio
of the thickness of a cell to the side in the circulation plane. A regime without reversals is established in a thick layer,
whereas a regime characterized by numerous changes in the direction of circulation, which are not separated by intervals with
the stable direction of the large-scale flow, arises in a thin layer. The spectra of oscillations of the amplitude of large-scale
circulation have been analyzed. It has been shown that a dominant frequency appears in the spectrum of oscillations of the
cubic cell. 相似文献
19.
We consider the generation of squeezed light in the process of degenerate downconversion in a quasi-phase-matched periodically poled nonlinear medium. The squeezing in the downconverted mode is analyzed for different orders of quasi-phase matching and for phase-mismatch parameter as well as varying pump input powers. The results show that a high degree of squeezing and high powers can be obtained for well-matched interactions. 相似文献
20.
W. M. Kloet 《Few-Body Systems》1998,24(2-3):193-199
The various terms present in the unitarity relation for elastic and inelastic nucleon-nucleon scattering are studied in a
three-body model. Because of the three-body dynamics one can determine a special interference term contributing to the total
cross section. This interference term can be positive or negative. The explicit calculation of this term may serve as a check
on three-body calculations. It also provides a measure of the actual importance of three-body dynamics in a particular model.
Received July 7, 1997; revised January 16, 1998; accepted for publication January 26, 1998 相似文献