Angular dependent vortex pinning mechanisms in YBCO coated conductors and thin films

We present a comparative study of the angular dependent critical current density in YBa2Cu3O7 films deposited on IBAD MgO and on single crystal MgO and SrTiO3 substrates. We identify three angular regimes where pinning is dominated by different types of correlated and uncorrelated defects. We show that those regimes are present in all cases, indicating that the pinning mechanisms are the same, but their extension and characteristics are sample dependent, reflecting the quantitative differences in texture and defect density. In particular, the more defective nature of the films on IBAD turns into an advantage as it results in stronger vortex pinning, demonstrating that the critical current density of the films on single crystals is not an upper limit for the performance of the IBAD coated conductors.Comment: 14 pages, 3 figures. Submitted to AP

Analysis of tumour ecological balance reveals resource-dependent adaptive strategies of ovarian cancer.

BACKGROUND:Despite treatment advances, there remains a significant risk of recurrence in ovarian cancer, at which stage it is usually incurable. Consequently, there is a clear need for improved patient stratification. However, at present clinical prognosticators remain largely unchanged due to the lack of reproducible methods to identify high-risk patients. METHODS:In high-grade serous ovarian cancer patients with advanced disease, we spatially define a tumour ecological balance of stromal resource and immune hazard using high-throughput image and spatial analysis of routine histology slides. On this basis an EcoScore is developed to classify tumours by a shift in this balance towards cancer-favouring or inhibiting conditions. FINDINGS:The EcoScore provides prognostic value stronger than, and independent of, known risk factors. Crucially, the clinical relevance of mutational burden and genomic instability differ under different stromal resource conditions, suggesting that the selective advantage of these cancer hallmarks is dependent on the context of stromal spatial structure. Under a high resource condition defined by a high level of geographical intermixing of cancer and stromal cells, selection appears to be driven by point mutations; whereas, in low resource tumours featured with high hypoxia and low cancer-immune co-localization, selection is fuelled by aneuploidy. INTERPRETATION:Our study offers empirical evidence that cancer fitness depends on tumour spatial constraints, and presents a biological basis for developing better assessments of tumour adaptive strategies in overcoming ecological constraints including immune surveillance and hypoxia

Plasma resonance at low magnetic fields as a probe of vortex line meandering in layered superconductors

We consider the magnetic field dependence of the plasma resonance frequency in pristine and in irradiated Bi$_2$Sr$_2$CaCu$_2$O$_8$ crystals near $T_c$. At low magnetic fields we relate linear in field corrections to the plasma frequency to the average distance between the pancake vortices in the neighboring layers (wandering length). We calculate the wandering length in the case of thermal wiggling of vortex lines, taking into account both Josephson and magnetic interlayer coupling of pancakes. Analyzing experimental data, we found that (i) the wandering length becomes comparable with the London penetration depth near T$_{c}$ and (ii) at small melting fields ($< 20$ G) the wandering length does not change much at the melting transition. This shows existence of the line liquid phase in this field range. We also found that pinning by columnar defects affects weakly the field dependence of the plasma resonance frequency near $T_c$.Comment: RevTex, 4 pages, 2 PS figures, Submitted to Phys. Rev.

Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments

We present an experimental study of thermally activated flux creep in a superconducting ring-shaped epitaxial YBCO film as well as a new way of analyzing the experimental data. The measurements were made in a wide range of temperatures between 10 and 83 K. The upper temperature limit was dictated by our experimental technique and at low temperatures we were limited by a crossover to quantum tunneling of vortices. It is shown that the experimental data can very well be described by assuming a simple thermally activated hopping of vortices or vortex bundles over potential barriers, whereby the hopping flux objects remain the same for all currents and temperatures. The new procedure of data analysis also allows to establish the current and temperature dependencies of the flux-creep activation energy U, as well as the temperature dependence of the critical current Ic, from the flux-creep rates measured at different temperatures. The variation of the activation energy with current, U(I/Ic), is then used to reconstruct the profile of the potential barriers in real space.Comment: 12 pages, 13 Postscript figures, Submitted to Physical Review

Magnetic field and field orientation dependence of the critical current density in Bi-2212 round wires and other HTS conductors

The authors have performed measurements of the magnetic field dependence of the critical current density J{sub c} of Bi-2212/Ag round wire produced by isothermal melt processing. In contrast to the case for flat tape, there is very little dependence of J{sub c} on the direction of the magnetic field as it is rotated normal to the wire axis, which is the direction of the nominal current flow. However, when the angle of the magnetic field direction is rotated from normal to the wire axis to parallel to that axis, J{sub c} at 64 K and 0.2 T increases by more than a factor of four. Again, this is in contrast to the results observed for Bi-2212/Ag and Bi-2223/Ag flat tapes, which show no anisotropy under similar experimental conditions. They can explain these differences in angular anisotropy by referring to the microstructure of these two conductor types, which have distinctly different types of grain alignment. They discuss the general behavior of the dependence of J{sub c} on the orientation of a magnetic field for high temperature superconductors

Flux pinning enhancement in ferromagnetic and superconducting thin-film multilayers

Flux pinning in high-temperature superconductors such as YBa2Cu3O7−xYBa2Cu3O7−x (YBCO) in the past has been accomplished by pinning the vortex cores. We demonstrate magnetic-domain-induced flux pinning of the magnetic flux of vortices in a ferromagnet-superconductor bilayer consisting of CoPt grown on YBCO, where the ferromagnet has uniaxial perpendicular magnetic anisotropy and a random domain structure. We observe an improvement of the critical current due to magnetic pinning at temperatures close to the transition temperature. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71072/2/APPLAB-82-5-778-1.pd