Triggering with the LHCb calorimeters

on behalf of the LHCb collaborationInternational audienc

Structural properties of silicon dioxide thin films densified by medium-energy particles

Classical molecular-dynamics simulations have been carried out to investigate densification mechanisms in silicon dioxide thin films deposited on an amorphous silica surface, according to a simplified ion-beam assisted deposition (IBAD) scenario. We compare the structures resulting from the deposition of near-thermal (1 eV) SiO$_{2}$ particles to those obtained with increasing fraction of 30 eV SiO$_{2}$ particles. Our results show that there is an energy interval - between 12 and 15 eV per condensing SiO$_2$ unit on average - for which the growth leads to a dense, low-stress amorphous structure, in satisfactory agreement with the results of low-energy ion-beam experiments. We also find that the crossover between low- and high-density films is associated with a tensile to compressive stress transition, and a simultaneous healing of structural defects of the {\em a-}SiO$_2$ network, namely three- and four-fold rings. It is observed, finally, that densification proceeds through significant changes at intermediate length scales (4--10 \AA), leaving essentially unchanged the ``building blocks'' of the network, viz. the Si(O$_{1/2}$)$_{4}$ tetrahedra. This latter result is in qualitative agreement with the mechanism proposed to explain the irreversible densification of amorphous silica recovered from high pressures ($\sim$ 15--20 GPa).Comment: 12 pages including 10 postscript figures; submitted to Phys. Rev. B; related publications can be found on web site http://www.centrcn.umontreal.ca/~lewi

SigTree: A Microbial Community Analysis Tool to Identify and Visualize Significantly Responsive Branches in a Phylogenetic Tree.

Microbial community analysis experiments to assess the effect of a treatment intervention (or environmental change) on the relative abundance levels of multiple related microbial species (or operational taxonomic units) simultaneously using high throughput genomics are becoming increasingly common. Within the framework of the evolutionary phylogeny of all species considered in the experiment, this translates to a statistical need to identify the phylogenetic branches that exhibit a significant consensus response (in terms of operational taxonomic unit abundance) to the intervention. We present the R software package SigTree, a collection of flexible tools that make use of meta-analysis methods and regular expressions to identify and visualize significantly responsive branches in a phylogenetic tree, while appropriately adjusting for multiple comparisons

Adsorption of a binary mixture of monomers with nearest-neighbour cooperative effects

A model for the adsorption of a binary mixture on a one-dimensional infinite lattice with nearest neighbour cooperative effects is considered. The particles of the two species are both monomers but differ in the repulsive interaction experienced by them when trying to adsorb. An exact expression for the coverage of the lattice is derived. In the jamming limit, it is a monotonic function of the ratio between the attempt frequencies of the two species, varying between the values corresponding to each of the two single species. This is in contrast with the results obtained in other models for the adsorption of particles of different sizes. The structure of the jamming state is also investigated.Comment: v2: Errors in the figures fixed; same text; 23 pages, 5 figures. Accepted for publication in Journal of Physics A: Mathematical and Genera

Tevatron Results

Recent results obtained by the CDF and D0 experiments at the Tevatron Run II are presented. A first part is dedicated to QCD physics where inclusive jet production, dijet azimuthal decorrelations and jet shapes measurements are reported. Electroweak physics is then discussed relating measurements of the W and Z bosons productions, of the forward-backward charge asymmetry in W production, of the W width and of the top quarks mass. The extensive Run II exploration program is finally approached reporting about searches for neutral supersymmetric Higgs bosons in multijet events and for sbottom quark from gluino decays

Pseudo-spectral methods for the spatial symplectic reduction of open systems of conservation laws

International audienceA reduction method is presented for systems of conservation laws with boundary energy flow. It is stated as a generalized pseudo-spectral method which performs exact differentiation by using simultaneously several approximation spaces generated by polynomials bases and suitable choices of port-variables. The symplecticity of this spatial reduction method is proved when used for the reduction of both closed and open systems of conservation laws, for any choice of collocation points (i.e. for any polynomial bases). The symplecticity of some more usual collocation schemes is discussed and finally their accuracy on approximation of the spectrum, on the example of the ideal transmission line, is discussed in comparison with the suggested reduction scheme