不同掺杂的钇系-123薄膜磁通特性

我们在磁场中分别测量了最佳掺杂的YBa2Cu3O7-δ、钙0．2掺杂的Y1-xCaxBa2Cu3O7-δ及钙0．5掺杂的Pr1-xCaxBa2Cu3O7-δ薄膜的电阻温度关系．利用最近Zhang et al.[Phys．Rev．B71（2005），052502]提出的热激活能的分析方法对薄膜的磁通特性进行了分析、比较与讨论．     

三维不可压缩Euler方程的H1(R~3)轴对称解

在适当的初值条件下，对三维不可压缩Ｅｕｌｅｒ方程组，我们证明了Ｈ１（Ｒ３）轴对称解的存在性．     

Accuracy of a deterministic particle method for Navier-Stokes equations

The accuracy of a deterministic particle method in approximating the solution of the Navier-Stokes equations is investigated. The convective part is solved using a classical vortex method for inviscid fluids, and an iterative procedure is added to improve the interpolation of the vorticity function. In our examples the vorticity is radially symmetric. For a regular initial data, a discrete quadratic error on the velocity and the vorticity is considered. Otherwise, for a singular initial data, the exact and computed angular moments of the vorticity are compared.     

Numerical simulation of an isolated vortex and shear flow interaction

A numerical solution for the Navier-Stokes equations in the unbounded region is considered for the interaction of an isolated vortex and shear flow. A Chebyshey collocation method in space and finite-difference method for temporal discretization are used. The results of the numerical experiments for the interaction are discussed. It is shown that shear flow can both increase and decrease the vortex dissipation rate.     

A method for predicting unsteady potential flow about an aerofoil

A new model is presented for the calculation of the incompressible, inviscid flow around an arbitrary aerofoil undergoing unsteady motion. The technique was developed from the steady flow algorithm of Leishman and Galbraith¹ in which use was made of a linear distribution of panel vorticity. The procedure is in the same class as that of Basu and Hancock² but, because of the particular approach to the manner of specifying the shed vorticity, only a set of linear simultaneous equations needs be solved, unlike the method of Reference 2, complicated by the necessary solution of a quadratic. A brief history of unsteady flow modelling is given in the introduction, followed by the mathematical details of the current method. Results are presented and discussed for a number of cases which clearly illustrate relevant characteristics of unsteady flow.     

Probing the discrete motion of vortices with rf excitations

In this work we present experimental results on the rectification of vortices in a superconductor/ferromagnet system under a high frequency drive. The two-dimensional pinning landscape, induced by the stray fields of the ferromagnetic template, has no intrinsic asymmetry. Nevertheless, an asymmetric potential is artificially induced by an applied dc bias. The experimental results unambiguously show a biased, discrete motion of the vortices in the periodic potential at frequencies above 10 MHz. This synchronized motion is very sensitive to the external applied field. Increasing temperature leads to a reduction of the pinning potential, which in turn results in a lower ac power needed to drive the vortex lattice.     

Vortex motion in high-Tc films and a micropattern-induced phase transition

A micropattern-induced transition in the mechanism of vortex motion and vortex mobility is observed in high-T_c thin films. The competition between the anomalous Hall effect and the guidance of vortices by rows of microholes (antidots) lead to a sudden change in the direction of vortex motion that is accompanied by a change in the critical current density and microwave losses. The latter effect demonstrates the difference in vortex mobility in different phases of vortex motion in between and within the rows of antidots.     

Enhanced pinning of superconducting vortices at circular magnetic dots in the magnetic-vortex state

Low-temperature magnetic force microscopy (LT-MFM) was used to study the distribution of superconducting vortices in Nb above a square array of 1 μm-sized circular ferromagnetic dots in a magnetic-vortex state. The force that the MFM tip exerts on the individual vortex in the depinning process was used to estimate the spatial modulation of the pinning potential. It was found, that the superconducting vortices which are preferably located on top of the Py dots experience a pinning force, about 15 times stronger as compared to the pinning force in the pure Nb film. This strong pinning exceeds the repulsive interaction between the superconducting vortices and allows vortex clusters to be located above the dots.     

Research on flux-flow oscillators induced different types of pinning potentials

We have studied dynamics of Josephson vortices in strongly coupled long Josephson junctions stack, such as an intrinsic Josephson junction, by numerical simulations based on coupled sine–Gordon equations considering a periodic pinning potential. In this report, we investigate flux-flow oscillators induced two types of pinning potentials. One is magnetic periodic pinning potential, the other is periodic bias currents. Our results demonstrate that the periodic pinning potential can develop the generated power of flux-flow oscillator in certain condition.