3,997 research outputs found

    Triggering with the LHCb calorimeters

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    on behalf of the LHCb collaborationInternational audienc

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

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    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) SiO2_{2} particles to those obtained with increasing fraction of 30 eV SiO2_{2} particles. Our results show that there is an energy interval - between 12 and 15 eV per condensing SiO2_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-}SiO2_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(O1/2_{1/2})4_{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 (‚ąľ\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

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

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    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

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    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
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