Spiral wave drift in an electric field and scroll wave instabilities

I present the numerical computation of speed and direction of the drift of a spiral wave in an excitable medium in the presence of an electric field. In contrast to earlier results, the drift speed presents a strong variation close to the parameter value where the drift speed component along the field changes direction. Using a simple phenomenological model and results from a numerical linear stability analysis of scroll waves, I show this behavior can be attributed to a resonance of the meander modes with the translation modes of the spiral wave. Extending this phenomenological model to scroll waves also clarifies the link between the drift and long wavelength instabilities of scroll waves.Comment: Phys Rev E accepte

Stabilization of vortex beams in Kerr media by nonlinear absorption

We elaborate a new solution for the problem of stable propagation of transversely localized vortex beams in homogeneous optical media with self-focusing Kerr nonlinearity. Stationary nonlinear Bessel-vortex states are stabilized against azimuthal breakup and collapse by multiphoton absorption, while the respective power loss is offset by the radial influx of the power from an intrinsic reservoir. A linear stability analysis and direct numerical simulations reveal a region of stability of these vortices. Beams with multiple vorticities have their stability regions too. These beams can then form robust tubular filaments in transparent dielectrics as common as air, water and optical glasses at sufficiently high intensities. We also show that the tubular, rotating and speckle-like filamentation regimes, previously observed in experiments with axicon-generated Bessel beams, can be explained as manifestations of the stability or instability of a specific nonlinear Bessel-vortex state, which is fully identified.Comment: Physical Review A, in press, 9 pages, 6 figure

Kinetics of non-ionic surfactant adsorption at a fluid-fluid interface from a micellar solution

The kinetics of non-ionic surfactant adsorption at a fluid-fluid interface from a micellar solution is considered theoretically. Our model takes into account the effect of micelle relaxation on the diffusion of the free surfactant molecules. It is shown that non-ionic surfactants undergo either a diffusion or a kinetically limited adsorption according to the characteristic relaxation time of the micelles. This gives a new interpretation for the observed dynamical surface tension of micellar solutions.Comment: 4 page

Pattern formation by kicked solitons in the two-dimensionnal Ginzburg-Landau medium with a transverse grating

We consider the kick-induced mobility of two-dimensional (2D) fundamental dissipative solitons in models of lasing media based on the 2D complex Ginzburg-Landau (CGL) equation including a spatially periodic potential (transverse grating). The depinning threshold is identified by means of systematic simulations, and described by means of an analytical approximation, depending on the orientation of the kick. Various pattern-formation scenarios are found above the threshold. Most typically, the soliton, hopping between potential cells, leaves arrayed patterns of different sizes in its wake. In the laser cavity, this effect may be used as a mechanism for selective pattern formation controlled by the tilt of the seed beam. Freely moving solitons feature two distinct values of the established velocity. Elastic and inelastic collisions between free solitons and pinned arrayed patterns are studied too.Comment: 15 pages, 20 figures (with 41 sub-figures

Properties of massive stars in four clusters of the VVV survey

The evolution of massive stars is only partly understood. Observational constraints can be obtained from the study of massive stars located in young massive clusters. The ESO Public Survey VISTA Variables in the Via Lactea (VVV) discovered several new clusters hosting massive stars. We present an analysis of massive stars in four of these new clusters. Our aim is to provide constraints on stellar evolution and to better understand the relation between different types of massive stars. We use the radiative transfer code CMFGEN to analyse K-band spectra of twelve stars with spectral types ranging from O and B to WN and WC. We derive the stellar parameters of all targets as well as surface abundances for a subset of them. In the Hertzsprung-Russell diagram, the Wolf-Rayet stars are more luminous or hotter than the O stars. From the log(C/N) - log(C/He) diagram, we show quantitatively that WN stars are more chemically evolved than O stars, WC stars being more evolved than WN stars. Mass loss rates among Wolf-Rayet stars are a factor of 10 larger than for O stars, in agreement with previous findings.Comment: paper accepted in New Astronom

The CMS detector magnet

CMS (Compact Muon Solenoid) is a general-purpose detector designed to run in mid-2005 at the highest luminosity at the LHC at CERN. Its distinctive features include a 6 m free bore diameter, 12.5 m long, 4 T superconducting solenoid enclosed inside a 10,000 tonne return yoke. The magnet will be assembled and tested on the surface by the end of 2003 before being transferred by heavy lifting means to a 90 m deep underground experimental area. The design and construction of the magnet is a `common project' of the CMS Collaboration. It is organized by a CERN based group with strong technical and contractual participation by CEA Saclay, ETH Zurich, Fermilab Batavia IL, INFN Geneva, ITEP Moscow, University of Wisconsin and CERN. The return yoke, 21 m long and 14 m in diameter, is equivalent to 1.5 m of saturated iron interleaved with four muon stations. The yoke and the vacuum tank are being manufactured. The indirectly-cooled, pure- aluminium-stabilized coil is made up from five modules internally wound with four layers of a 20 kA mechanically reinforced conductor. The contracts for the conductor and the outer cryogenics have just been awarded, and the remaining coil parts, including winding, are being tendered worldwide in industry. The project is described, with emphasis on the present status. (13 refs)

Compressive Raman imaging with spatial frequency modulated illumination

We report a line scanning imaging modality of compressive Raman technology with spatial frequency modulated illumination using a single pixel detector. We demonstrate the imaging and classification of three different chemical species at line scan rates of 40 Hz

Large scale EPR correlations and cosmic gravitational waves

We study how quantum correlations survive at large scales in spite of their exposition to stochastic backgrounds of gravitational waves. We consider Einstein-Podolski-Rosen (EPR) correlations built up on the polarizations of photon pairs and evaluate how they are affected by the cosmic gravitational wave background (CGWB). We evaluate the quantum decoherence of the EPR correlations in terms of a reduction of the violation of the Bell inequality as written by Clauser, Horne, Shimony and Holt (CHSH). We show that this decoherence remains small and that EPR correlations can in principle survive up to the largest cosmic scales.Comment: 5 figure

El tiempo en un geólogo

Uno de los mayores aportes de la Geología a la cultura universal es haber dado dimensión al tiempo geológico. Se analiza los conceptos de tiempo relativo ytiempo absoluto, y se da cuenta de diversos métodos ideados por lo geólogos para establecer la edad de la Tierra y de las rocas que la conforman. Se discutefinalmente un caso real de determinación de edad de formación de ciertas rocas en Aysén, resaltando algunas de las dificultades que para ello se debe enfrentary resolver.