ATLAS prospects for beyond the Standard Model searches

We discuss how ATLAS has been preparing for the analysis of the first fb-1 of good data at 14 TeV in view of discovering new physics beyond the Standard Model. We show some ideas developed for understanding the backgrounds and we present as realistic as possible estimates of the reach of the experiment

Coherent acoustic vibration of metal nanoshells

Using time-resolved pump-probe spectroscopy we have performed the first investigation of the vibrational modes of gold nanoshells. The fundamental isotropic mode launched by a femtosecond pump pulse manifests itself in a pronounced time-domain modulation of the differential transmission probed at the frequency of nanoshell surface plasmon resonance. The modulation amplitude is significantly stronger and the period is longer than in a gold nanoparticle of the same overall size, in agreement with theoretical calculations. This distinct acoustical signature of nanoshells provides a new and efficient method for identifying these versatile nanostructures and for studying their mechanical and structural properties.Comment: 5 pages, 3 figure

Theoretical profiles of the Mg + resonance lines perturbed by collisions with He

International audienceThe effects of collision broadening by He are central to understanding the opacity of cool stellar atmospheres. Aims. DZ white dwarfs show metal lines which are, in many cases, believed to come from some rocky material, a remnant of a former exoplanetary system. The analysis of the Mg + resonance lines is a valuable method to determine the chemical abundances in these systems. Methods. Unified profiles of the strongest of the UV lines of Mg + have been calculated in the semi-classical approach using very recent ab initio potential energies. Results. We present the first theoretical line profile calculations of the resonance lines of Mg + that have been perturbed by helium in physical conditions of atmospheres in helium-rich white dwarfs with metal traces

Phase transitions between single- and double-layered smectic structures in binary mixtures of cyano-mesogens

Binary mixtures of mesogens which exhibit respectively single-layered (A 1), double layered (A2) and partially double layered (A d) smectic phases show abrupt A2-A1 or A2-Ad transitions as a function of concentration. Double layered structures imply the formation of dimerized entities and the possibility of dimerization is discussed in terms of the amphiphilic nature of the molecules in the binary mixture (symmetrical and dissymmetrical polar mesogens). The results are analysed with respect to the thermal stability of the A 2 phase when defects are introduced in the polar interface by adding non-polar symmetrical mesogens.Des mélanges binaires de mésogènes présentant respectivement des phases smectiques monocouches (A1), bicouches (A2) et partiellement bicouches (Ad) permettent de mettre en évidence en fonction de la concentration des transitions brusques A2-A1 ou A 2-Ad. La structure bicouche implique un processus de dimérisation des entités mésogènes qui est discuté en fonction du caractère amphipathique des molécules (molécules polaires symétriques et dissymétriques). La stabilité de la phase bicouche est également analysée lorsque l'on introduit une perturbation au niveau de l'interface polaire par adjonction de molécules non polaires

Barometric pumping of a fractured porous medium

International audienceBarometric pumping plays a crucial role in the release of trace gases from fractured porous media to the atmosphere, and it requires a rigorous and complete modeling in order to go beyond the approximate schemes available in the literature. Therefore, a coupled set of convection and convection-diffusion equations for a slightly compressible fluid in unsteady conditions should be solved. The numerical methodology is presented, and it is applied to conditions close to the ones of the Roselend Natural Laboratory (France). The precision of the code is assessed and the mechanism of barometric pumping is explained. The usual schematization by simple vertical fractures is shown to be only qualitative. Finally, barometric pumping is shown to be efficient in a narrow range of parameter values; its efficiency is a decreasing function of the matrix porosity and of the fracture density

Phylogeny, biogeography and diversification patterns of side-necked turtles (Testudines: Pleurodira)

Pleurodires or side-necked turtles are today restricted to freshwater environments of South America, Africa– Madagascar and Australia, but in the past they were distributed much more broadly, being found also on Eurasia, India and North America, and marine environments. Two hypotheses were proposed to explain this distribution; in the first, vicariance would have shaped the current geographical distribution and, in the second, extinctions constrained a previously widespread distribution. Here, we aim to reconstruct pleurodiran biogeographic history and diversification patterns based on a new phylogenetic hypothesis recovered from the analysis of the largest morphological dataset yet compiled for the lineage, testing which biogeographical process prevailed during its evolutionary history. The resulting topology generally agrees with previous hypotheses of the group and shows that most diversification shifts were related to the exploration of new niches, e.g. littoral or marine radiations. In addition, as other turtles, pleurodires do not seem to have been much affected by either the Cretaceous– Palaeogene or the Eocene–Oligocene mass extinctions. The biogeographic analyses highlight the predominance of both anagenetic and cladogenetic dispersal events and support the importance of transoceanic dispersals as a more common driver of area changes than previously thought, agreeing with previous studies with other non-turtle lineages.Fil: Ferreira, Gabriel S.. Universidade de Sao Paulo; Brasil. Senckenberg Centre For Human Evolution And Palaeoenvironment; Alemania. Universität Tübingen; AlemaniaFil: Bronzati Filho, Mario. Bayerische Staatssammlung für Paläontologie und Geologie; AlemaniaFil: Langer, Max C.. Universidade de Sao Paulo; BrasilFil: Sterli, Juliana. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Quotient Categories and Phases

We study properties of a category after quotienting out a suitable chosen group of isomorphisms on each object. Coproducts in the original category are described in its quotient by our new weaker notion of a 'phased coproduct'. We examine these and show that any suitable category with them arises as such a quotient of a category with coproducts. Motivation comes from projective geometry, and also quantum theory where they describe superpositions in the category of Hilbert spaces and continuous linear maps up to global phase. The quotients we consider also generalise those induced by categorical isotropy in the sense of Funk et al.Comment: Fixed typos, added discussion of isotropy, expanded introductio

Structure bicouche des mésophases SA et SB du 4-cyanobutoxybenzylidene-4-octylaniline

In order to analyze the mesomorphic behavior of molecules containing a highly dipolar endgroup mechanically decoupled from the rigid moiety, the 4-cyanobutoxybenzylidene-4-octylaniline was synthesized. The first observations made (polarizing microscopy, differential scanning calorimetry, and X-ray diffraction) suggest the présence of two smectic mesophases, of B and A type respectively. The structure of these would correspond to double layers : in each sub-layer, the molecular arrangement would be of the ferro-type, and the stacking of the sub-layers would be of the antiferro-type. However, it is impossible to definitely specify the spatial extension of the order described, on the basis of the experimental data obtained so far.Pour analyser le comportement mésomorphe de molécules contenant un groupe fortement dipolaire découplé mécaniquement du tronçon rigide, nous avons synthétisé le 4-cyanobutoxybenzylidène-4-octylaniline. Les premières observations (microscope polarisant, enthalpimétrie différentielle, diffraction des rayons X) indiquent la présence de deux mésophases smectiques, l'une de type B et l'autre de type A. Celles-ci auraient une structure bicouche : dans chaque sous-couche, les molécules seraient arrangées de manière ferro- et les sous-couches, elles-mêmes, seraient superposées de manière antiferro- . Cependant, les données expérimentales obtenues ne permettent pas encore de se prononcer définitivement sur l'étendue spatiale de ce type d'ordre