270 research outputs found

### Vanishing of the upper critical field in Bi_2Sr_2CaCu_2O_{8+\delta} from Landau-Ott scaling

We apply Landau-Ott scaling to the reversible magnetization data of
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ published by Y. Wang et al. [\emph{Phys.
Rev. Lett. \textbf{95} 247002 (2005)}] and find that the extrapolation of the
Landau-Ott upper critical field line vanishes at a critical temperature
parameter, T^*_c, a few degrees above the zero resistivity critical
temperature, T_c. Only isothermal curves below and near to T_c were used to
determine this transition temperature. This temperature is associated to the
disappearance of the mixed state instead of a complete suppression of
superconductivity in the sample.Comment: 3 figure

### Transition to a Superconductor with Insulating Cavities

An extreme type II superconductor with internal insulating regions, namely
cavities, is studied here. We find that the cavity-bearing superconductor has
lower energy than the defect-free superconductor above a critical magnetic
induction $B^*$ for insulating cavities but not for metallic ones. Using a
numerical approach for the Ginzburg-Landau theory we compute and compare free
energy densities for several cavity radii and at least for two cavity
densities, assuming a cubic lattice of spherical cavities.Comment: 7 pages, 4 figures, to be published in Europhysics Letter

### The ground states of the two-component order parameter superconductor

We show that in presence of an applied external field the two-component order
parameter superconductor falls in two categories of ground states, namely, in
the traditional Abrikosov ground state or in a new ground state fitted to
describe a superconducting layer with texture, that is, patched regions
separated by a phase difference of $\pi$. The existence of these two kinds of
ground states follows from the sole assumption that the total supercurrent is
the sum of the two individual supercurrents and is independent of any
consideration about the free energy expansion. Uniquely defined relations
between the current density and the superfluid density hold for these two
ground states, which also determine the magnetization in terms of average
values of the order parameters. Because these ground state conditions are also
Bogomolny equations we construct the free energy for the two-component
superconductor which admits the Bogomolny solution at a special coupling value.Comment: 5 page

### Critical vortex line length near a zigzag of pinning centers

A vortex line passes through as many pinning centers as possible on its way
from one extremety of the superconductor to the other at the expense of
increasing its self-energy. In the framework of the Ginzburg-Landau theory we
study the relative growth in length, with respect to the straight line, of a
vortex near a zigzag of defects. The defects are insulating pinning spheres
that form a three-dimensional cubic array embedded in the superconductor. We
determine the depinning transition beyond which the vortex line no longer
follows the critical zigzag path of defects.Comment: 8 pages, 25 figures with low resolution option, 1 table. To be
published in Eur. Phys. Jour.

### Three-dimensional Ginzburg-Landau simulation of a vortex line displaced by a zigzag of pinning spheres

A vortex line is shaped by a zigzag of pinning centers and we study here how
far the stretched vortex line is able to follow this path. The pinning center
is described by an insulating sphere of coherence length size such that in its
surface the de Gennes boundary condition applies. We calculate the free energy
density of this system in the framework of the Ginzburg-Landau theory and study
the critical displacement beyond which the vortex line is detached from the
pinning center.Comment: Submitted to special issue of Prammna-Journal of Physics devoted to
the Vortex State Studie

### Lyapunov exponent in the Vicsek model

The well-known Vicsek model describes the flock dynamics of self-propelled
agents. Surprisingly, a direct measure of the chaotic behavior of such systems
is missing. Here, we discuss the kinetic phase transition present in Vicsek
systems in light of the largest Lyapunov exponent, which is numerically
computed by following the dynamical evolution in tangent space. As
discontinuities in the neighbors weighting factor hinder the computations, we
propose a continuous form of the model. Our results about chaotic regime
reinforce the idea that the Lyapunov exponent is also a phase transition
indicator.Comment: 7 pages, 16 equations, 6 figure

### Threefold onset of vortex loops in superconductors with a magnetic core

A magnetic inclusion inside a superconductor gives rise to a fascinating
complex of {\it vortex loops}. Our calculations, done in the framework of the
Ginzburg-Landau theory, reveal that {\it loops always nucleate in triplets}
around the magnetic core. In a mesoscopic superconducting sphere, the final
superconducting state is characterized by those confined vortex loops and the
ones that eventually spring to the surface of the sphere, evolving into {\it
vortex pairs} piercing through the sample surface.Comment: 6 pages, 6 figures (low resolution), latex2

### Mediterranean dietary pattern and cancer risk in the EPIC cohort

Background: Although several studies have investigated the association of the Mediterranean diet with overall mortality or risk of specific cancers, data on overall cancer risk are sparse. Methods: We examined the association between adherence to Mediterranean dietary pattern and overall cancer risk using data from the European Prospective Investigation Into Cancer and nutrition, a multi-centre prospective cohort study including 142 605 men and 335 873. Adherence to Mediterranean diet was examined using a score (range: 0–9) considering the combined intake of fruits and nuts, vegetables, legumes, cereals, lipids, fish, dairy products, meat products, and alcohol. Association with cancer incidence was assessed through Cox regression modelling, controlling for potential confounders. Results: In all, 9669 incident cancers in men and 21 062 in women were identified. A lower overall cancer risk was found among individuals with greater adherence to Mediterranean diet (hazard ratio=0.96, 95% CI 0.95–0.98) for a two-point increment of the Mediterranean diet score. The apparent inverse association was stronger for smoking-related cancers than for cancers not known to be related to tobacco (P (heterogeneity)=0.008). In all, 4.7% of cancers among men and 2.4% in women would be avoided in this population if study subjects had a greater adherence to Mediterranean dietary pattern. Conclusion: Greater adherence to a Mediterranean dietary pattern could reduce overall cancer risk

### The association of education with body mass index and waist circumference in the EPIC-PANACEA study

Abstract Background To examine the association of education with body mass index (BMI) and waist circumference (WC) in the European Prospective Investigation into Cancer and Nutrition (EPIC). Method This study included 141,230 male and 336,637 female EPIC-participants, who were recruited between 1992 and 2000. Education, which was assessed by questionnaire, was classified into four categories; BMI and WC, measured by trained personnel in most participating centers, were modeled as continuous dependent variables. Associations were estimated using multilevel mixed effects linear regression models. Results Compared with the lowest education level, BMI and WC were significantly lower for all three higher education categories, which was consistent for all countries. Women with university degree had a 2.1 kg/m2 lower BMI compared with women with lowest education level. For men, a statistically significant, but less pronounced difference was observed (1.3 kg/m2). The association between WC and education level was also of greater magnitude for women: compared with the lowest education level, average WC of women was lower by 5.2 cm for women in the highest category. For men the difference was 2.9 cm. Conclusion In this European cohort, there is an inverse association between higher BMI as well as higher WC and lower education level. Public Health Programs that aim to reduce overweight and obesity should primarily focus on the lower educated population.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

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