5,963 research outputs found

    Phenomenological discussion of B→PVB\to P V decays in QCD improved factorization approach

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    Trying a global fit of the experimental branching ratios and CP-asymmetries of the charmless B→PVB\to PV decays according to QCD factorization, we find it impossible to reach a satisfactory agreement, the confidence level (CL) of the best fit is smaller than .1 %. This failure reflects the difficulty to accommodate several large experimental branching ratios of the strange channels. Furthermore, experiment was not able to exclude a large direct CP asymmetry in Bˉ0→ρ+π−\bar {B}^0\to\rho^+ \pi^-, which is predicted very small by QCD factorization. Proposing a fit with QCD factorization complemented by a charming-penguin inspired model we reach a best fit which is not excluded by experiment (CL of about 8 %) but is not fully convincing. These negative results must be tempered by the remark that some of the experimental data used are recent and might still evolve significantly.Comment: 8 pages, 2 figures (requires epsfig, psfrag),talk presented at the XXXVIIIth Rencontres de Moriond: Electroweak Interactions and Unified Theories,Les Arcs, France, March 15-22, 2003. To be published in the Proceeding

    Antisymmetrization of a Mean Field Calculation of the T-Matrix

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    The usual definition of the prior(post) interaction V(Vâ€Č)V(V^\prime ) between projectile and target (resp. ejectile and residual target) being contradictory with full antisymmetrization between nucleons, an explicit antisymmetrization projector A{\cal A} must be included in the definition of the transition operator, T≡Vâ€ČA+Vâ€ČAGV. T\equiv V^\prime{\cal A}+V^\prime{\cal A}GV. We derive the suitably antisymmetrized mean field equations leading to a non perturbative estimate of TT. The theory is illustrated by a calculation of forward α\alpha-α\alpha scattering, making use of self consistent symmetries.Comment: 30 pages, no figures, plain TeX, SPHT/93/14

    Entanglement and localization of wavefunctions

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    We review recent works that relate entanglement of random vectors to their localization properties. In particular, the linear entropy is related by a simple expression to the inverse participation ratio, while next orders of the entropy of entanglement contain information about e.g. the multifractal exponents. Numerical simulations show that these results can account for the entanglement present in wavefunctions of physical systems.Comment: 6 pages, 4 figures, to appear in the proceedings of the NATO Advanced Research Workshop 'Recent Advances in Nonlinear Dynamics and Complex System Physics', Tashkent, Uzbekistan, 200

    Characterising and modelling groundwater discharge in anagricultural wetland on the French Atlantic coast

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    Interaction between a wetland and its surrounding aquifer was studied in the Rochefort agricultural marsh (150 km<sup>2</sup>). Groundwater discharge in the marsh was measured with a network of nested piezometers. Hydrological modelling of the wetland showed that a water volume of 770,000 m<sup>3</sup> yr<sup>–1</sup> is discharging into the marsh, but that this water flux essentially takes place along the lateral borders of the wetland. However, this natural discharge volume represents only 20% of the artificial freshwater injected each year into the wetland to maintain the water level close to the soil surface. Understanding and quantifying the groundwater component in wetland hydrology is crucial for wetland management and conservation.</b></p> <p style='line-height: 20px;'><b>Keywords: </b>wetland, hydrology, groundwater, modelling, mars

    Detection of human bocavirus in children with Kawasaki disease

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    ABSTRACTHuman bocavirus (HboV) is an emerging virus that has been implicated as a cause of acute upper and lower respiratory tract infection in children. As no serological assay is available, PCR was used to screen nasopharyngeal, serum or stool samples from 16 patients with Kawasaki disease for HBoV nucleic acid. HBoV was identified by PCR in five (31.2%) patients, suggesting that this emerging virus may also play a pathogenic role in some cases of Kawasaki disease

    Magic traits drive the emergence of pathogens

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    An important branch of evolutionary biology strives to understand how divergent selection for an ecologically important trait can foster the emergence of new species specialized on different niches. Such ecological speciation is usually difficult to achieve because recombination between different subsets of a population that are adapting to different environments counteracts selection for locally adapted gene combinations. Traits pleiotropically controlling adaptation to different environments and reproductive isolation are therefore the most favourable for ecological speciation, and are thus called “magic traits”. We used genetic markers and cross-inoculations to show that pathogenicity-related loci are responsible for both host adaptation and reproductive isolation in emerging populations of Venturia inaequalis, the fungus causing apple scab disease. Because the fungus mates within its host and because the pathogenicity-related loci prevent infection of the non-host trees, host adaptation pleiotropically maintains genetic differentiation and adaptive allelic combinations between sympatric populations specific to different apple varieties. Such “magic traits” are likely frequent in fungal pathogens, and likely drive the emergence of new diseases.

    Emergence of novel fungal pathogens by ecological speciation: importance of the reduced viability of immigrants

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    Expanding global trade and the domestication of ecosystems have greatly accelerated the rate of emerging infectious fungal diseases, and host-shift speciation appears to be a major route for disease emergence. There is therefore an increased interest in identifying the factors that drive the evolution of reproductive isolation between populations adapting to different hosts. Here, we used genetic markers and cross-inoculations to assess the level of gene flow and investigate barriers responsible for reproductive isolation between two sympatric populations of Venturia inaequalis, the fungal pathogen causing apple scab disease, one of the fungal populations causing a recent emerging disease on resistant varieties. Our results showed the maintenance over several years of strong and stable differentiation between the two populations in the same orchards, suggesting ongoing ecological divergence following a host shift. We identified strong selection against immigrants (i.e. host specificity) from different host varieties as the strongest and likely most efficient barrier to gene flow between local and emerging populations. Cross-variety disease transmission events were indeed rare in the field and cross-inoculation tests confirmed high host specificity. Because the fungus mates within its host after successful infection and because pathogenicity-related loci prevent infection of nonhost trees, adaptation to specific hosts may alone maintain both genetic differentiation between and adaptive allelic combinations within sympatric populations parasitizing different apple varieties, thus acting as a ‘magic trait’. Additional intrinsic and extrinsic postzygotic barriers might complete reproductive isolation and explain why the rare migrants and F1 hybrids detected do not lead to pervasive gene flow across years

    Evidence for a vortex-glass transition in superconducting Ba(Fe0.9_{0.9}Co0.1_{0.1})2_{2}As2_{2}

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    Measurements of magneto-resistivity and magnetic susceptibility were performed on single crystals of superconducting Ba(Fe0.9_{0.9}Co0.1_{0.1})2_{2}As2_{2} close to the conditions of optimal doping. The high quality of the investigated samples allows us to reveal a dynamic scaling behaviour associated with a vortex-glass phase transition in the limit of weak degree of quenched disorder. Accordingly, the dissipative component of the ac susceptibility is well reproduced within the framework of Havriliak-Negami relaxation, assuming a critical power-law divergence for the characteristic correlation time τ\tau of the vortex dynamics. Remarkably, the random disorder introduced by the Fe1−x_{1-x}Cox_{x} chemical substitution is found to act on the vortices as a much weaker quenched disorder than previously reported for cuprate superconductors such as, e.g., Y1−x_{1-x}Prx_{x}Ba2_{2}Cu3_{3}O7−ή_{7-\delta}.Comment: 10 pages, 8 figure

    Ram pressure stripping and galaxy orbits: The case of the Virgo cluster

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    We investigate the role of ram pressure stripping in the Virgo cluster using N-body simulations. Radial orbits within the Virgo cluster's gravitational potential are modeled and analyzed with respect to ram pressure stripping. The N-body model consists of 10000 gas cloud complexes which can have inelastic collisions. Ram pressure is modeled as an additional acceleration on the clouds located at the surface of the gas distribution in the direction of the galaxy's motion within the cluster. We made several simulations changing the orbital parameters in order to recover different stripping scenarios using realistic temporal ram pressure profiles. We investigate systematically the influence of the inclination angle between the disk and the orbital plane of the galaxy on the gas dynamics. We show that ram pressure can lead to a temporary increase of the central gas surface density. In some cases a considerable part of the total atomic gas mass (several 10^8 M_solar) can fall back onto the galactic disk after the stripping event. A quantitative relation between the orbit parameters and the resulting HI deficiency is derived containing explicitly the inclination angle between the disk and the orbital plane. The comparison between existing HI observations and the results of our simulations shows that the HI deficiency depends strongly on galaxy orbits. It is concluded that the scenario where ram pressure stripping is responsible for the observed HI deficiency is consistent with all HI 21cm observations in the Virgo cluster.Comment: 29 pages with 21 figures. Accepted for publication in Ap

    Quantisations of piecewise affine maps on the torus and their quantum limits

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    For general quantum systems the semiclassical behaviour of eigenfunctions in relation to the ergodic properties of the underlying classical system is quite difficult to understand. The Wignerfunctions of eigenstates converge weakly to invariant measures of the classical system, the so called quantum limits, and one would like to understand which invariant measures can occur that way, thereby classifying the semiclassical behaviour of eigenfunctions. We introduce a class of maps on the torus for whose quantisations we can understand the set of quantum limits in great detail. In particular we can construct examples of ergodic maps which have singular ergodic measures as quantum limits, and examples of non-ergodic maps where arbitrary convex combinations of absolutely continuous ergodic measures can occur as quantum limits. The maps we quantise are obtained by cutting and stacking
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