Topological transitions in superconductor nanomembranes under a strong transport current

The topological defects, vortices in bulk superconductors (SCs) and phase slips in low-dimensional SCs are known to lead to the occurrence of a finite resistance. We report on a topological transition between the both types of topological defects under a strong transport current in an open SC nanotube with a submicron-scale inhomogeneity of the normal-to-the-surface component of the applied magnetic field. When the magnetic field is orthogonal to the axis of the nanotube, which carries the transport current in the azimuthal direction, the phase-slip regime is characterized by the vortex/antivortex lifetime ∼ 10−14 s versus the vortex lifetime ∼ 10−11 s for vortex chains in the half-tubes, and the induced voltage shows a pulse as a function of the magnetic field. The topological transition between the vortex-chain and phase-slip regimes determines the magnetic-field–voltage and current–voltage characteristics of curved SC nanomembranes to pursue high-performance applications in advanced electronics and quantum computing

Co2 efflux, co2 concentration and photosynthetic refixation in stems of Eucalyptus globulus (Labill.)

Research PaperIn spite of the importance of respiration in forest carbon budgets, the mechanisms by which physiological factors control stem respiration are unclear. An experiment was set up in a Eucalyptus globulus plantation in central Portugal with monoculture stands of 5-year-old and 10-year-old trees. CO2 efflux from stems under shaded and unshaded conditions, as well as the concentration of CO2 dissolved in sap [CO2 *], stem temperature, and sap flow were measured with the objective of improving our understanding of the factors controlling CO2 release from stems of E. globulus. CO2 efflux was consistently higher in 5-year-old, compared with 10-year-old, stems, averaging 3.4 versus 1.3 mmol m22 s21, respectively. Temperature and [CO2 *] both had important, and similar, influences on the rate of CO2 efflux from the stems, but neither explained the difference in the magnitude of CO2 efflux between trees of different age and size. No relationship was found between efflux and sap flow, and efflux was independent of tree volume, suggesting the presence of substantial barriers to the diffusion of CO2 from the xylem to the atmosphere in this species. The rate of corticular photosynthesis was the same in trees of both ages and only reduced CO2 efflux by 7%, probably due to the low irradiance at the stem surface below the canopy. The younger trees were growing at a much faster rate than the older trees. The difference between CO2 efflux from the younger and older stems appears to have resulted from a difference in growth respiration rather than a difference in the rate of diffusion of xylemtransported CO

Numerical simulation of spray coalescence in an eulerian framework : direct quadrature method of moments and multi-fluid method

The scope of the present study is Eulerian modeling and simulation of polydisperse liquid sprays undergoing droplet coalescence and evaporation. The fundamental mathematical description is the Williams spray equation governing the joint number density function f(v, u; x, t) of droplet volume and velocity. Eulerian multi-fluid models have already been rigorously derived from this equation in Laurent et al. (2004). The first key feature of the paper is the application of direct quadrature method of moments (DQMOM) introduced by Marchisio and Fox (2005) to the Williams spray equation. Both the multi-fluid method and DQMOM yield systems of Eulerian conservation equations with complicated interaction terms representing coalescence. In order to validate and compare these approaches, the chosen configuration is a self-similar 2D axisymmetrical decelerating nozzle with sprays having various size distributions, ranging from smooth ones up to Dirac delta functions. The second key feature of the paper is a thorough comparison of the two approaches for various test-cases to a reference solution obtained through a classical stochastic Lagrangian solver. Both Eulerian models prove to describe adequately spray coalescence and yield a very interesting alternative to the Lagrangian solver

Relativistic positioning: four-dimensional numerical approach in Minkowski space-time

We simulate the satellite constellations of two Global Navigation Satellite Systems: Galileo (EU) and GPS (USA). Satellite motions are described in the Schwarzschild space-time produced by an idealized spherically symmetric non rotating Earth. The trajectories are then circumferences centered at the same point as Earth. Photon motions are described in Minkowski space-time, where there is a well known relation, Coll, Ferrando & Morales-Lladosa (2010), between the emission and inertial coordinates of any event. Here, this relation is implemented in a numerical code, which is tested and applied. The first application is a detailed numerical four-dimensional analysis of the so-called emission coordinate region and co-region. In a second application, a GPS (Galileo) satellite is considered as the receiver and its emission coordinates are given by four Galileo (GPS) satellites. The bifurcation problem (double localization) in the positioning of the receiver satellite is then pointed out and discussed in detail.Comment: 16 pages, 9 figures, published (online) in Astrophys. Space Sc

Electromagnetic transitions of the helium atom in superstrong magnetic fields

We investigate the electromagnetic transition probabilities for the helium atom embedded in a superstrong magnetic field taking into account the finite nuclear mass. We address the regime \gamma=100-10000 a.u. studying several excited states for each symmetry, i.e. for the magnetic quantum numbers 0,-1,-2,-3, positive and negative z parity and singlet and triplet symmetry. The oscillator strengths as a function of the magnetic field, and in particular the influence of the finite nuclear mass on the oscillator strengths are shown and analyzed.Comment: 10 pages, 8 figure

A Real-Space Full Multigrid study of the fragmentation of Li11+ clusters

We have studied the fragmentation of Li11+ clusters into the two experimentally observed products (Li9+,Li2) and (Li10+,Li) The ground state structures for the two fragmentation channels are found by Molecular Dynamics Simulated Annealing in the framework of Local Density Functional theory. Energetics considerations suggest that the fragmentation process is dominated by non-equilibrium processes. We use a real-space approach to solve the Kohn-Sham problem, where the Laplacian operator is discretized according to the Mehrstellen scheme, and take advantage of a Full MultiGrid (FMG) strategy to accelerate convergence. When applied to isolated clusters we find our FMG method to be more efficient than state-of-the-art plane wave calculations.Comment: 9 pages + 6 Figures (in gzipped tar file

Time-Independent Gravitational Fields

This article reviews, from a global point of view, rigorous results on time independent spacetimes. Throughout attention is confined to isolated bodies at rest or in uniform rotation in an otherwise empty universe. The discussion starts from first principles and is, as much as possible, self-contained.Comment: 47 pages, LaTeX, uses Springer cl2emult styl