Symmetry analysis and exact solutions of modified Brans-Dicke cosmological equations

We perform a symmetry analysis of modified Brans-Dicke cosmological equations and present exact solutions. We discuss how the solutions may help to build models of cosmology where, for the early universe, the expansion is linear and the equation of state just changes the expansion velocity but not the linearity. For the late universe the expansion is exponential and the effect of the equation of state on the rate of expansion is just to change the constant Hubble parameter.Comment: LaTeX2e source file, 14 pages, 7 reference

Comment on ``Phase ordering in chaotic map lattices with conserved dynamics''

Angelini, Pellicoro, and Stramaglia [Phys. Rev. E {\bf 60}, R5021 (1999), cond-mat/9907149] (APS) claim that the phase ordering of two-dimensional systems of sequentially-updated chaotic maps with conserved ``order parameter'' does not belong, for large regions of parameter space, to the expected universality class. We show here that these results are due to a slow crossover and that a careful treatment of the data yields normal dynamical scaling. Moreover, we construct better models, i.e. synchronously-updated coupled map lattices, which are exempt from these crossover effects, and allow for the first precise estimates of persistence exponents in this case.Comment: 3 pages, to be published in Phys. Rev.

Linear Temperature Variation of the Penetration Depth in YBCO Thin Films

We have measured the penetration depth $\lambda(T)$ on $\rm YBa_{2}Cu_{3}O_{7}$ thin films from transmission at 120, 330 and 510~GHz, between 5 and 50~K. Our data yield simultaneously the absolute value and the temperature dependence of $\lambda(T)$. In high quality films $\lambda(T)$ exhibits the same linear temperature dependence as single crystals, showing its intrinsic nature, and $\lambda(0)=1750\,{\rm \AA}$. In a lower quality one, the more usual $T^2$ dependence is found, and $\lambda(0)=3600\,{\rm \AA}$. This suggests that the $T^2$ variation is of extrinsic origin. Our results put the $d$-wave like interpretation in a much better position.Comment: 12 pages, revtex, 4 uuencoded figure

Cosmology and the Hubble Constant: On the Megamaser Cosmology Project (MCP)

The Hubble constant Ho describes not only the expansion of local space at redshift z ~ 0, but is also a fundamental parameter determining the evolution of the universe. Recent measurements of Ho anchored on Cepheid observations have reached a precision of several percent. However, this problem is so important that confirmation from several methods is needed to better constrain Ho and, with it, dark energy and the curvature of space. A particularly direct method involves the determination of distances to local galaxies far enough to be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear supermassive black holes. The goal of this article is to describe the relevance of Ho with respect to fundamental cosmological questions and to summarize recent progress of the the `Megamaser Cosmology Project' (MCP) related to the Hubble constant.Comment: 10 pages, 7 postscript figures (8 ps files), IAU Symposium 287, uses iaus.cl

Magnetic patterning of (Ga,Mn)As by hydrogen passivation

We present an original method to magnetically pattern thin layers of (Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the hole density, and thereby locally suppress the carrier-mediated ferromagnetic phase. The sample surface is thus maintained continuous, and the minimal structure size is of about 200 nm. In micron-sized ferromagnetic dots fabricated by hydrogen passivation on perpendicularly magnetized layers, the switching fields can be maintained closer to the continuous film coercivity, compared to dots made by usual dry etch techniques

Universal conductance fluctuations in epitaxial GaMnAs ferromagnets: structural and spin disorder

Mesoscopic transport measurements reveal a large effective phase coherence length in epitaxial GaMnAs ferromagnets, contrary to usual 3d-metal ferromagnets. Universal conductance fluctuations of single nanowires are compared for epilayers with a tailored anisotropy. At large magnetic fields, quantum interferences are due to structural disorder only, and an unusual behavior related to hole-induced ferromagnetism is evidenced, for both quantum interferences and decoherence. At small fields, phase coherence is shown to persist down to zero field, even in presence of magnons, and an additional spin disorder contribution to quantum interferences is observed under domain walls nucleation.Comment: 15 pages, 4 figure

The Universe out of an Elementary Particle?

We consider a model of an elementary particle as a 2 + 1 dimensional brane evolving in a 3 + 1 dimensional space. Introducing gauge fields that live in the brane as well as normal surface tension can lead to a stable "elementary particle" configuration. Considering the possibility of non vanishing vacuum energy inside the bubble leads, when gravitational effects are considered, to the possibility of a quantum decay of such "elementary particle" into an infinite universe. Some remarkable features of the quantum mechanics of this process are discussed, in particular the relation between possible boundary conditions and the question of instability towards Universe formation is analyzed

Particle Image Velocimetry (PIV) measurements in a water film, application to a tire rolling through a puddle

International audienceA measurement method based on Particle Image Velocimetry with refraction of the laser sheet at a win-dow/water interface is proposed for the measurement of the velocity field of a water flow formed by a tire moving inside a water puddle. This study focuses of the feasibility and repeatability of this optical measurement method. The characterization of the optical properties of the measurement technique defines the integration effect in height of the measurement method. The analysis of the overall features of the flow is focused on two main zones in front and around the tire. The flow inside the first zone is defined by a characteristic velocity of the water displaced in an area located in front of the tire ; in the second zone a characteristic velocity representative of the flow in the vicinity of the shoulder of the tire is also defined. Correlations of both characteristic velocities with the car speed and water film height are established. New and worn tires were tested in this work

Classification of SD-OCT Volumes using Local Binary Patterns: Experimental Validation for DME Detection

International audienceThis paper addresses the problem of automatic classification of Spectral Domain OCT (SD-OCT) data for automatic identification of patients with Diabetic Macular Edema (DME) versus normal subjects. Optical Coherence Tomography (OCT) has been a valuable diagnostic tool for DME, which is among the most common causes of irreversible vision loss in individuals with diabetes. Here, a classification framework with five distinctive steps is proposed and we present an extensive study of each step. Our method considers combination of various pre-processings in conjunction with Local Binary Patterns (LBP) features and different mapping strategies. Using linear and non-linear classifiers, we tested the developed framework on a balanced cohort of 32 patients. Experimental results show that the proposed method outperforms the previous studies by achieving a Sensitivity (SE) and Specificity (SP) of 81.2% and 93.7%, respectively. Our study concludes that the 3D features and high-level representation of 2D features using patches achieve the best results. However, the effects of pre-processing is inconsistent with respect to different classifiers and feature configurations

Subitizing with Variational Autoencoders

Numerosity, the number of objects in a set, is a basic property of a given visual scene. Many animals develop the perceptual ability to subitize: the near-instantaneous identification of the numerosity in small sets of visual items. In computer vision, it has been shown that numerosity emerges as a statistical property in neural networks during unsupervised learning from simple synthetic images. In this work, we focus on more complex natural images using unsupervised hierarchical neural networks. Specifically, we show that variational autoencoders are able to spontaneously perform subitizing after training without supervision on a large amount images from the Salient Object Subitizing dataset. While our method is unable to outperform supervised convolutional networks for subitizing, we observe that the networks learn to encode numerosity as basic visual property. Moreover, we find that the learned representations are likely invariant to object area; an observation in alignment with studies on biological neural networks in cognitive neuroscience