Critical state theory for nonparallel flux line lattices in type-II superconductors

Coarse-grained flux density profiles in type-II superconductors with non-parallel vortex configurations are obtained by a proposed phenomenological least action principle. We introduce a functional $C[H(x)]$, which is minimized under a constraint of the kind $J$ belongs to $Delta$ for the current density vector, where $Delta$ is a bounded set. This generalizes the concept of critical current density introduced by C. P. Bean for parallel vortex configurations. In particular, we choose the isotropic case ($Delta$ is a circle), for which the field penetration profiles $H(x,t)$ are derived when a changing external excitation is applied. Faraday's law, and the principle of minimum entropy production rate for stationary thermodynamic processes dictate the evolution of the system. Calculations based on the model can reproduce the physical phenomena of flux transport and consumption, and the striking effect of magnetization collapse in crossed field measurements.Comment: The compiled TeX document length is 10 pages. Two figures (one page each) are also included The paper is accepted for publication in Phys. Rev. Let

Reduction of optical crosstalk in SiPMs due to coupled light guides and investigation of other properties demonstrated with the SensL MicroFJ-60035-TSV

The optical coupling of light guides to Silicon Photomultipliers (SiPMs) influences the probability for optical crosstalk. Measurements of the crosstalk probability and the relative gain of 122 SiPMs of type SensL MicroFJ-60035-TSV are presented. Semi-conductor photo sensors have replaced photo multiplier tubes in numerous applications featuring single-photon resolution, insensitivity to magnetic fields, higher robustness and enhanced photo detection efficiency at lower operation voltage and lower costs. Light guides are used to increase the comparably small photo sensitive area of SiPMs. Their optical coupling changes the surface conditions of the sensor and influences the probability for crosstalk photons to leave the sensor without inducing secondary breakdowns. This study compares properties of sensors that are optically coupled to light guides with bare sensors, operated at nominal bias voltage. It demonstrates, that the optical coupling to a light guide significantly reduces the crosstalk probability of the measured sensors

Latin Americans and Caribbeans in Europe. A cross-country analysis

With the beginning of the 21st century, there has been an acceleration of migratory flows from Latin America and the Caribbean (LAC) to Europe. As a result, and despite the negative impact of the economic crisis, 4.6 million Latin American and Caribbean immigrants reside in Europe, half of them in Spain. This article analyses the recent evolution of these migratory flows, their territorial distribution, and their demographic profiles according to the 2011 European census data disseminated by a new tool -the Census Hub- implemented by the European Statistical System. The analysis shows the existence of a high LAC immigrant concentration in Spain and in certain European cities, a marked young and feminized demographic profile, a great variety of educational levels and a different insertion in each European labour market, although many LAC immigrants work in low-skill occupations, being overqualified and underemployed in most of the countries

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum