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921.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献
922.
B. Szafran P. S
p J. Adamowski S. Bednarek 《Physica E: Low-dimensional Systems and Nanostructures》2003,18(4):523-529
We present a theoretical study of the charging spectra in natural and artificial atoms. We apply a model electrostatic potential created by a homogenously charged sphere. This model potential allows for a continuous passage from the Coulomb potential of the nucleus to parabolic confinement potential of quantum dots. We consider electron systems with N=1,…,10 electrons with the use of the Hartree–Fock method. We discuss the qualitative similarities and differences between the chemical potential spectrum of electron systems bound to nucleus and confined in quantum dots. 相似文献
923.
V. A. Burov I. M. Grishina O. I. Lapshenkina S. A. Morozov O. D. Rumyantseva E. G. Sukhov 《Acoustical Physics》2003,49(6):627-637
In the ultrasonic diagnostics of small-size neoplasms of biological tissues at the earliest stage of their development, an efficient way to eliminate the distorting influence of high-contrast or large inhomogeneities of the biological medium is to apply the iterative technique. A simple approach is proposed, which makes it possible with only two iteration steps to achieve an efficient focusing of the tomograph array. At the first step, the unknown distribution of the large-scale inhomogeneities of sound velocity and absorption over the scatterer is reconstructed, where the large-scale inhomogeneities are those whose size exceeds several wavelengths. At the second step, the fine structure of the scatterer is reconstructed against the large-scale background, which can be performed with a high accuracy owing to the evaluation of the background at the first step. The possibility of simultaneous reconstruction of the large-scale and fine structures by the noniterative Grinevich-Novikov algorithm is considered as an alternative. This algorithm reconstructs in an explicit form two-dimensional refractive-absorbing acoustic scatterers of almost arbitrary shape and strength. Taking into account the effects of multiple scattering, this algorithm provides resolution of the fine structure almost as good as that achieved in reconstructing the same structure against an undistorting homogeneous background. The results of numerical simulations of both algorithms are presented. 相似文献
924.
925.
926.
Geerk J. Linker G. Meyer O. Politis C. Ratzel F. Smithey R. Strehlau B. Xiong G. C. 《Zeitschrift für Physik B Condensed Matter》1987,67(4):507-511
Thin superconducting films of La1.8Sr0.2CuO4 have been prepared by magnetron sputter deposition and subsequent temperature treatment. The composition of the films has been determined by Rutherford backscattering and the structure by thin film X-ray diffraction. The onset of superconductivity was about 32 K and the midpoint near 28 K. Defect production in the films by He ion bombardment revealed a drasticT
c
reduction with a sensitivity similar to that observed in the Chevrel phases. Oxygen implantation and subsequent annealing led to an enhancement of theT
c
onset. 相似文献
927.
928.
A new grid‐free upwind relaxation scheme for simulating inviscid compressible flows is presented in this paper. The non‐linear conservation equations are converted to linear convection equations with non‐linear source terms by using a relaxation system and its interpretation as a discrete Boltzmann equation. A splitting method is used to separate the convection and relaxation parts. Least squares upwinding is used for discretizing the convection equations, thus developing a grid‐free scheme which can operate on any arbitrary distribution of points. The scheme is grid free in the sense that it works on any arbitrary distribution of points and it does not require any topological information like elements, faces, edges, etc. This method is tested on some standard test cases. To explore the power of the grid‐free scheme, solution‐based adaptation of points is done and the results are presented, which demonstrate the efficiency of the new grid‐free scheme. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
929.
We consider a splitting finite-difference scheme for an initial-boundary value problem for a two-dimensional nonlinear evolutionary
equation. The problem is split into nonlinear and linear parts. The linear part is also split into locally one-dimensional
equations. We prove the convergence and stability of the scheme in L
2 and C norms.
Printed in Lietuvos Matematikos Rinkinys, Vol. 45, No. 3, pp. 413–434, July–September, 2005. 相似文献
930.