Unpinning the spiral waves by using parameter waves

The spiral waves anchored to heterogeneous areas are more difficult to control and eliminate than freely rotating ones in homogenous mediums.To eliminate pinned spiral waves,the resistant force should be provided to resist the pinning force.Other than advection field,we introduce parametric wave to play the role of providing resistant force.It is found that the parametric wave with large enough amplitude and proper frequency can unpin and eliminate the spiral wave successfully.The capability of parametric wave in providing resistant force is dependent on its amplitude and frequency sensitively.On the basis of parametric wave,the dependence of pinning force on the size and level of heterogeneity is further confirmed.

CALCULATION OF SECOND PHASE PARTICLE-GRAIN BOUNDARY INTERACTION RANGE

On the basis of the grain boundary equation by HeUman and corresponding analysis of Worner, this article deals with the interaction range between the second-phase particle （SPP） and grain boundary （GB） as viewed from the applicability of grain boundary equation. Also, a new expression describing the interaction range has been derived, which solves the problem in theory that the interaction range between SPP and GB can only be qualitatively analyzed previously. It is shown that given the interaction position between SPP and GB, the interaction range can be quantitatively determined by use of this expression.

Towards high degree of c-axis orientation in MgB_(2) bulks

The paper presents fabrication and characterization of spark plasma sintered textured(001) MgB_(2)with a record degree of orientation of about 40% and 16% by high-energy ultra-sonication and slip casting in high magnetic field(12 T) and 0 T magnetic field, respectively.Structural characterization was performed by X-ray diffraction, and electron microscopy. The analysis revealed unexpected preferred orientation also in the MgO secondary phase due to the epitaxial growth of(111) MgO on(001) MgB_(2). The influence of oriented microstructure on the superconducting characteristics expressed by critical current density(J_(c)), irreversibility field(H_(irr)), and on the pinning properties were assessed. High anisotropy versus sample orientation in applied magnetic field, H, was observed for J_(c), Hirr, pinning activation energy(U^(*))extracted from relaxation measurements. The zero-field critical current, J_(c0)and F_(p),maxare weakly or not dependent on the direction of H,while the other indicated parameters are significantly influenced. Results enable control of superconducting parameters by further optimization of microstructure through MgB_(2) texturing as a novel and viable strategy for development of bulk MgB2with enhanced properties when taking advantage of its anisotropy.

Modeling Study of the Particle Pinning Effect on the Grain Boundary Movement

In this work,based on the classical grain boundary (GB) formula and the principle of work-energy conversion,a new physically-based model has been developed to predict the particle pinning force concerning the interaction between second phase particles (SPPs) and the moving GB.The effect of particles pinning on the GB movement is analyzed.The modeling results can be applied to quantitatively determine the critical numbers of SPPs required for complete pining the grain growth,such as the critical SPPs number of the unit GB area,the critical number for single grain stagnation,the critical volume fraction of particles at a given particle size.Theoretical predictions are in good agreement with the experimental results by Gladman.

A review of thickness-induced evolutions of microstructure and superconducting performance of REBa2Cu3O7-δ coated conductor

The research and development of high temperature superconducting （HTS） films, especially ReBa2Cu3- O7-δ （REBCO or RE123; RE=Y, Gd, or other rare earths） yttrium-based coated conductors, has generated widespread interest for the potential applications of the second generation superconducting films. In view of commercialization, however, the maximum superconducting currents for coated conductors should be increased further. Unfortunately, it has been frequently observed that the average critical current density Jc decreases with an increase in film thickness. The thickness effect is still a hurdle for largescale production, especially in pulsed laser deposition and metal organic deposition processes. An engineering current of more than 1 000 A/cm is desired owing to the high cost of 2G superconducting materials. The present work attempts to review the evolution of various issues subject to the thickness effect, including the microstructure, epitaxial texture, surface roughness, pinning force, oxygen deficiency, residual stress, copper-rich layers, and segregation of elements. Furthermore, recent progress in enhancing the performance of superconductors especially in terms of critical current density is illustrated, such as the use of heavy doping. Further understanding of the thickness effect is extremely important for large-scale commercial development of the second generation high temperature superconductors.

EFFECT OF MAGNETIC NANOPARTICLES ON THE MECHANICAL PROPERTIES OF TYPE-II SUPERCONDUCTORS

In this paper, the effect of magnetic nanoparticles on the mechanical properties of a type-II superconductor is investigated both theoretically and numerically. Magnetic part of the pinning force associated with the interaction between a finite-size spheroidal magnetic inclusion and an Abrikosov vortex is calculated in the London approximation. It is found that the size and shape of magnetic nanoparticles result in different enhancements of vortex pinning in large-k type-II superconductors. Meanwhile, the screening current induced by a magnetic spheroid suffer the action of Lorentz force, which will lead to prestress in the superconductor, so further numerical calculations are needed to explore the interaction between the spheroidal magnetic particle and superconductor. The distribution of displacement, stress and strain in the superconductor are finally obtained. It is shown that different sizes and shapes of nanoparticles also can change the distributions of these quantities.