4,906 research outputs found

    Causal Propagators for Algebraic Gauges

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    Applying the principle of analytic extension for generalized functions we derive causal propagators for algebraic non-covariant gauges. The so generated manifestly causal gluon propagator in the light-cone gauge is used to evaluate two one-loop Feynman integrals which appear in the computation of the three-gluon vertex correction. The result is in agreement with that obtained through the usual prescriptions.Comment: LaTex, 09 pages, no figure

    Schwinger's Principle and Gauge Fixing in the Free Electromagnetic Field

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    A manifestly covariant treatment of the free quantum eletromagnetic field, in a linear covariant gauge, is implemented employing the Schwinger's Variational Principle and the B-field formalism. It is also discussed the abelian Proca's model as an example of a system without constraints.Comment: 8 pages. Format PTPtex. No figur

    GCN-based reinforcement learning approach for scheduling DAG applications

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    Applications in various fields such as embedded systems or High-Performance-Computing are often represented as Directed Acyclic Graphs (DAG), also known as taskgraphs. DAGs represent the data flow between tasks in an application and can be used for scheduling. When scheduling taskgraphs, a scheduler needs to decide when and on which core each task is executed, while minimising the runtime of the schedule.This paper explores offline scheduling of dependent tasks using a Reinforcement Learning (RL) approach. We propose two RL schedulers, one using a Fully Connected Network (FCN) and another one using a Graph Convolutional Network (GCN). First, we detail the different components of our two RL schedulers and illustrate how they schedule a task. Then, we compare our RL schedulers to a Forward List Scheduling (FLS) approach based on two different datasets. We demonstrate that our GCN-based scheduler produces schedules that are as good or better than the schedules produced by the FLS approach in over 85% of the cases for a dataset with small taskgraphs. The same scheduler performs very similar to the FLS scheduler (at most 5% degradation) in almost 76% of the cases for a more challenging dataset

    Coasting cosmologies with time dependent cosmological constant

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    The effect of a time dependent cosmological constant is considered in a family of scalar tensor theories. Friedmann-Robertson-Walker cosmological models for vacumm and perfect fluid matter are found. They have a linear expansion factor, the so called coasting cosmology, the gravitational "constant" decreace inversely with time; this model satisfy the Dirac hipotesis. The cosmological "constant" decreace inversely with the square of time, therefore we can have a very small value for it at present time.Comment: 7 pages, latex file (ijmpal macro), accepted for publication in Int. Mod. Phys.

    Bopp-Podolsky black holes and the no-hair theorem

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    Bopp-Podolsky electrodynamics is generalized to curved space-times. The equations of motion are written for the case of static spherically symmetric black holes and their exterior solutions are analyzed using Bekenstein's method. It is shown the solutions split-up into two parts, namely a non-homogeneous (asymptotically massless) regime and a homogeneous (asymptotically massive) sector which is null outside the event horizon. In addition, in the simplest approach to Bopp-Podolsky black holes, the non-homogeneous solutions are found to be Maxwell's solutions leading to a Reissner-Nordstr\"om black hole. It is also demonstrated that the only exterior solution consistent with the weak and null energy conditions is the Maxwell's one. Thus, in light of energy conditions, it is concluded that only Maxwell modes propagate outside the horizon and, therefore, the no-hair theorem is satisfied in the case of Bopp-Podolsky fields in spherically symmetric space-times.Comment: 9 pages, updated to match published versio

    Demandas de pesquisas tecnologicas para a fruticultura Cearense.

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    bitstream/CNPAT/7913/1/doc56.pd

    Perfil tecnico-economico dos perimetros irrigados das bacias do Curu e Baixo Acarau

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    bitstream/CNPAT/7902/1/doc80.pd

    An analysis of cosmological perturbations in hydrodynamical and field representations

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    Density fluctuations of fluids with negative pressure exhibit decreasing time behaviour in the long wavelength limit, but are strongly unstable in the small wavelength limit when a hydrodynamical approach is used. On the other hand, the corresponding gravitational waves are well behaved. We verify that the instabilities present in density fluctuations are due essentially to the hydrodynamical representation; if we turn to a field representation that lead to the same background behaviour, the instabilities are no more present. In the long wavelength limit, both approachs give the same results. We show also that this inequivalence between background and perturbative level is a feature of negative pressure fluid. When the fluid has positive pressure, the hydrodynamical representation leads to the same behaviour as the field representation both at the background and perturbative levels.Comment: Latex file, 18 page
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