346 research outputs found


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    In my thesis we have addressed the issue of the first order description of generic stationary axisymmetric black holes in supergravity. To this the end we extended the extend the Hamilton-Jacobi formalism from mechanical models, whose degrees of freedom depend on just one variable, to field theories where the degrees of freedom depend on two or more variables. This problem was addressed and developed in generality in field theory, but not much was known in the context of gravitational field theories. An important issue in this thesis was to apply such extended formalism to the study of black holes. We have worked with the so-called De Donder-Weyl-Hamilton-Jacobi (DWHJ) theory, which is the simplest extension of the classical Hamilton-Jacobi approach in mechanics. One important difference with respect to the case of classical mechanics consists in the replacement of the Hamilton principal function S, directly related to the fake-superpotential of static black holes, with a Hamilton principal 1-form, which is a covariant vector Si. The application of this formalism to the description of axisymmetric solutions black holes required working out the general form of the principal functions Sm associated with the corresponding effective 2D sigma-model in the DWHJ setting. We have also given a characterization of the general properties of such solutions with respect to the global symmetry group of the effective 2D sigma-model which describes them. This was done by introducing, aside from the Nöther charge matrix, a further characteristic constant matrix Qψ, in the Lie algebra of G(3), the global symmetry properties of affine solutions 2D model, associated with the rotational motion of the black hol

    Practical Algorithms for Multicast Support in Input Queues Switches

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    Abstract — This paper deals with multicast flow support in N × N Input Queued switch architectures. A practical approach to support multicast traffic is presented, assuming that O(N) queues are available at each input port. The focus is on dynamic queueing policies, where, at each input port, multicast flows are assigned to one among the available queues when flows become active: flows are assigned to queues according to switch queue status and, possibly, to flow information. We discuss queueing assignments, scheduling algorithms and flow activity definition models. We explain why dynamic queueing disciplines may outperform static policies, and we show that, even in the most favorable conditions for static policies, they provide comparable performance. I

    Interest-based cooperative caching in multi-hop wireless networks

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    Abstract—New communication protocols, as WiFi Direct, are now available to enable efficient Device-to-Device (D2D) communications in wireless networks based on portable devices. At the same time, new network paradigms, as Content-Centric-Networking (CCN), allow a communication focused on the content and not its location within the network, enabling a flexible location for the content, which can be cached in the nodes across the network. In such context, we consider a multi-hop wireless network adopting CCN-like cooperative caching, in which each user terminal acts also as a caching node. We propose an interestbased insertion policy for the caching, based on the concept of “social-distance ” borrowed by online recommendation systems, to improve the performance of the overall network of caches; the main idea is to store only the contents which appear to be of interest for the local user. We show that our proposed scheme outperforms other well-known insertion policies, that are oblivious of such social-distance, in terms of cache hit probability and access delays. I