116 research outputs found

    1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-

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    Using a known result by Falk et al. for the 1/m_b^2 correction to the dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry in this decay. Employing an up-to-date range of values for the non-perturbative parameter \lambda_1, we find that the correction is much smaller than it should have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear in Physical Review D. The complete postscript file is also available from URL ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g

    Global value chains and human development: a class-relational framework

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    Global Value Chain proponents argue that regional and human development can be achieved through ‘strategic coupling’ with transnational corporations. This argument is misleading for two reasons. First, GVC abstracts firm-firm and firm-state relations from their class-relational basis, obscuring fundamental developmental processes. Second, much GVC analysis promotes linear conceptions of development. This article provides a class-relational framework for GVC analysis. The formation and functioning of GVCs and the developmental effects associated with them are products of histories of evolving and often conflictive, class relations. A study of export horticulture in North East Brazil provides empirical support for these arguments

    Two photon decays of heavy vector mesons, BBγγB^{*}\to B\gamma \gamma,DDγγD^{*}\to D\gamma \gamma, and the possible determination of the gB(D)B(D)πg_{B^{*}(D^{*})B(D)\pi} and gB0B0γg_{{B^{*}}^0B^0\gamma} couplings

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    We study the novel decays BBγγB^{*}\to B\gamma\gamma and DDγγD^{*}\to D\gamma \gamma using the framework of the Heavy Meson Chiral Lagrangian (HMχ\chiL) to leading order in chiral perturbation theory. The branching ratios of these decays are expressed in terms of the strong gB(D)B(D)πg_{B^{*}(D^{*})B(D)\pi} and the electromagnetic gB(D)B(D)γg_{B^{*}(D^*)B(D)\gamma} couplings, thus providing a possible tool for their determination. In the charm case, using the experimentally determined ratios (D0,+Dπ)/(D0,+Dγ),({D^*}^{0,+}\to D\pi)/({D^*}^{0,+}\to D\gamma), we are able to express the branching ratio as a function of the strong coupling only. We thus find 1.6×106<Br(D0D0γγ)<3.3×1051.6\times 10^{-6}<{\rm Br} ({D^{*}}^{0}\to D^0\gamma\gamma)<3.3\times 10^{-5} for 0.25<g<1,0.25<g<1, where gg is the strong coupling of HMχ\chiL. In the beauty sector, the Br(B0B0γγ){\rm Br}({B^{*}}^{0} \to B^0 \gamma\gamma) which we estimate to be in the 10710510^{-7}-10^{-5} range is a function of both gBBπg_{B^{*}B\pi} and gBBγ.g_{B^{*}B\gamma}. Its behaviour does not afford an unambiguous determination of these couplings except for the region of high gg values like g>0.6.g>0.6. The expected two-photon differential distributions are presented for both B0B0γγ{B^{*}}^{0} \to B^0 \gamma\gamma and D0D0γγ,{D^{*}}^{0}\to D^0\gamma\gamma, for different values of the couplings involved.Comment: 22 pages, LaTeX, 5 ps-figures (uses subfigure.sty). Accepted by Phys. Rev.

    Cadophora margaritata sp. nov. and other fungi associated with the longhorn beetles Anoplophora glabripennis and Saperda carcharias in Finland

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    Symbiosis with microbes is crucial for survival and development of wood-inhabiting longhorn beetles (Coleoptera: Cerambycidae). Thus, knowledge of the endemic fungal associates of insects would facilitate risk assessment in cases where a new invasive pest occupies the same ecological niche. However, the diversity of fungi associated with insects remains poorly understood. The aim of this study was to investigate fungi associated with the native large poplar longhorn beetle (Saperda carcharias) and the recently introduced Asian longhorn beetle (Anoplophora glabripennis) infesting hardwood trees in Finland. We studied the cultivable fungal associates obtained from Populus tremula colonised by S. carcharias, and Betula pendula and Salix caprea infested by A. glabripennis, and compared these to the samples collected from intact wood material. This study detected a number of plant pathogenic and saprotrophic fungi, and species with known potential for enzymatic degradation of wood components. Phylogenetic analyses of the most commonly encountered fungi isolated from the longhorn beetles revealed an association with fungi residing in the Cadophora-Mollisia species complex. A commonly encountered fungus was Cadophora spadicis, a recently described fungus associated with wood-decay. In addition, a novel species of Cadophora, for which the name Cadophora margaritata sp. nov. is provided, was isolated from the colonised wood.Peer reviewe

    A Prototype Representation to Approximate White Matter Bundles with Weighted Currents

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    International audienceQuantitative and qualitative analysis of white matter fibers resulting from tractography algorithms is made difficult by their huge number. To this end, we propose an \textit{approximation scheme} which gives as result a more concise but at the same time exhaustive representation of a fiber bundle. It is based on a novel computational model for fibers, called \textit{weighted currents}, characterised by a metric that considers both the pathway and the anatomical locations of the endpoints of the fibers. Similarity has therefore a twofold connotation: geometrical and related to the connectivity. The core idea is to use this metric for approximating a fiber bundle with a set of weighted prototypes, chosen among the fibers, which represent ensembles of similar fibers. The weights are related to the number of fibers represented by the prototypes. The algorithm is divided into two steps. First, the main modes of the fiber bundle are detected using a \textit{modularity based clustering} algorithm. Second, a \textit{prototype fiber selection} process is carried on in each cluster separately. This permits to explain the main patterns of the fiber bundle in a fast and accurate way
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