1,970 research outputs found

    New analysis of semileptonic B decays in the relativistic quark model

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    We present the new analysis of the semileptonic B decays in the framework of the relativistic quark model based on the quasipotential approach. Decays both to heavy D^{(*)} and light \pi(\rho) mesons are considered. All relativistic effects are systematically taken into account including contributions of the negative-energy states and the wave function transformation from the rest to moving reference frame. For heavy-to-heavy transitions the heavy quark expansion is applied. Leading and subleading Isgur-Wise functions are determined as the overlap integrals of initial and final meson wave functions. For heavy-to-light transitions the explicit relativistic expressions are used to determine the dependence of the form factors on the momentum transfer squared. Such treatment significantly reduces theoretical uncertainties and increases reliability of obtained predictions. All results for form factors, partial and total decay rates agree well with recent experimental data and unquenched lattice calculations. From this comparison we find the following values of the Cabibbo-Kobayashi-Maskawa matrix elements: |V_{cb}|=(3.85\pm0.15\pm 0.20)*10^{-2} and |V_{ub}|=(3.82\pm0.20\pm0.20)*10^{-3}, where the first error is experimental and the second one is theoretical.Comment: 25 pages, 11 figure

    Backhaul For Low-Altitude UAVs in Urban Environments

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    Unmanned Aerial Vehicles (UAVs) acting as access points in cellular networks require wireless backhauls to the core network. In this paper we employ stochastic geometry to carry out an analysis of the UAV backhaul performance that can be achieved with a network of dedicated ground stations. We provide analytical expressions for the probability of successfully establishing a backhaul and the expected data rate over the backhaul link, given either an LTE or a millimeter-wave backhaul. We demonstrate that increasing the density of the ground station network gives diminishing returns on the performance of the UAV backhaul, and that for an LTE backhaul the ground stations can benefit from being colocated with an existing base station network

    Coverage Analysis for Low-Altitude UAV Networks in Urban Environments

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    Wireless access points on unmanned aerial vehicles (UAVs) are being considered for mobile service provisioning in commercial networks. To be able to efficiently use these devices in cellular networks it is necessary to first have a qualitative and quantitative understanding of how their design parameters reflect on the service quality experienced by the end user. In this paper we set up a scenario where a network of UAVs operating at a certain height above ground provide wireless service within coverage areas shaped by their directional antennas. We provide an analytical expression for the coverage probability experienced by a typical user as a function of the UAV parameters.Comment: Under Submissio
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