969 research outputs found

    Self-dual Ginzburg-Landau vortices in a disk

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    We study the properties of the Ginzburg-Laundau model in the self-dual point for a two-dimensional finite system . By a numerical calculation we analyze the solutions of the Euler-Lagrange equations for a cylindrically symmetric ansatz. We also study the self-dual equations for this case. We find that the minimal energy configurations are not given by the Bogomol'nyi equations but by solutions to the Euler Lagrange ones. With a simple approximation scheme we reproduce the result of the numerical calculation.Comment: 8 pages, 4 figures, RevTex macro

    Three-dimensionality in quasi-two dimensional flows: recirculations and barrel effects

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    A scenario is put forward for the appearance of three-dimensionality both in quasi-2D rotating flows and quasi-2D magnetohydrodynamic (MHD) flows. We show that 3D recirculating flows and currents originate in wall boundary layers and that, unlike in ordinary hydrodynamic flows, they cannot be ignited by confinement alone. They also induce a second form of three-dimensionality with quadratic variations of velocities and current across the channel. This scenario explains both the common tendency of these flows to two-dimensionality and the mechanisms of the recirculations through a single formal analogy covering a wide class of flow including rotating and MHD flows. These trans-disciplinary effects are thus active in atmospheres, oceans or the cooling blankets of nuclear fusion reactors.Comment: 6 pages, 1 Figur

    Decentralized Markets versus Central Control: A Comparative Study

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    Multi-Agent Systems (MAS) promise to offer solutions to problems where established, older paradigms fall short. In order to validate such claims that are repeatedly made in software agent publications, empirical in-depth studies of advantages and weaknesses of multi-agent solutions versus conventional ones in practical applications are needed. Climate control in large buildings is one application area where multi-agent systems, and market-oriented programming in particular, have been reported to be very successful, although central control solutions are still the standard practice. We have therefore constructed and implemented a variety of market designs for this problem, as well as different standard control engineering solutions. This article gives a detailed analysis and comparison, so as to learn about differences between standard versus agent approaches, and yielding new insights about benefits and limitations of computational markets. An important outcome is that "local information plus market communication produces global control"

    Proportionele aansprakelijkheid, omkeringsregel, bewijslastverlichting en eigen schuld: een inventarisatie van de stand van zaken

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    In het arrest Fortis/Bourgonje van 24 december 2010 over de aansprakelijkheid van de bank als vermogensbeheerder bevestigt de Hoge Raad dat aan de proportionele benadering uit het arrest Nefalit/Karamus een breder toepassingsbereik toekomt dan alleen de werkgeversaansprakelijkheid. Anderzijds wordt benadrukt dat het bij deze benadering om een uitzondering gaat, en wordt de toepassing door het hof op het voorliggende geval afgewezen. Dat roept de vraag op wanneer proportionele aansprakelijkheid wel, en wanneer niet een toelaatbare oplossing is. Uit de rechtspraak over dit onderwerp blijkt de nauwe verwevenheid met andere leerstukken zoals het bewijs van causaal verband, de omkeringsregel en de ‘eigen schuld’ van artikel 6:101 BW. Wie zoekt naar algemene lijnen voor de toepasselijkheid van het ene dan wel het andere leerstuk, moet concluderen dat de rechtspraak van de Hoge Raad de nodige vragen open laat. In dit artikel wordt de stand van zaken geïnventariseerd en worden enkele suggesties gedaan voor een nadere systematisering van dit terrein

    Geometrical dependence of decoherence by electronic interactions in a GaAs/GaAlAs square network

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    We investigate weak localization in metallic networks etched in a two dimensional electron gas between 25 25\:mK and 750 750\:mK when electron-electron (e-e) interaction is the dominant phase breaking mechanism. We show that, at the highest temperatures, the contributions arising from trajectories that wind around the rings and trajectories that do not are governed by two different length scales. This is achieved by analyzing separately the envelope and the oscillating part of the magnetoconductance. For T≳0.3 T\gtrsim0.3\:K we find \Lphi^\mathrm{env}\propto{T}^{-1/3} for the envelope, and \Lphi^\mathrm{osc}\propto{T}^{-1/2} for the oscillations, in agreement with the prediction for a single ring \cite{LudMir04,TexMon05}. This is the first experimental confirmation of the geometry dependence of decoherence due to e-e interaction.Comment: LaTeX, 5 pages, 4 eps figure

    Inelastic Multiple Scattering of Interacting Bosons in Weak Random Potentials

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    We develop a diagrammatic scattering theory for interacting bosons in a three-dimensional, weakly disordered potential. We show how collisional energy transfer between the bosons induces the thermalization of the inelastic single-particle current which, after only few collision events, dominates over the elastic contribution described by the Gross-Pitaevskii ansatz.Comment: 5 pages, 3 figures, very close to published versio

    Quantum oscillations in mesoscopic rings and anomalous diffusion

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    We consider the weak localization correction to the conductance of a ring connected to a network. We analyze the harmonics content of the Al'tshuler-Aronov-Spivak (AAS) oscillations and we show that the presence of wires connected to the ring is responsible for a behaviour different from the one predicted by AAS. The physical origin of this behaviour is the anomalous diffusion of Brownian trajectories around the ring, due to the diffusion in the wires. We show that this problem is related to the anomalous diffusion along the skeleton of a comb. We study in detail the winding properties of Brownian curves around a ring connected to an arbitrary network. Our analysis is based on the spectral determinant and on the introduction of an effective perimeter probing the different time scales. A general expression of this length is derived for arbitrary networks. More specifically we consider the case of a ring connected to wires, to a square network, and to a Bethe lattice.Comment: 17 pages, 7 eps figure

    Quantum criticality near the Stoner transition in a two-dot with spin-orbit coupling

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    We study a system of two tunnel-coupled quantum dots, with the first dot containing interacting electrons (described by the Universal Hamiltonian) not subject to spin-orbit coupling, whereas the second contains non-interacting electrons subject to spin-orbit coupling. We focus on describing the behavior of the system near the Stoner transition. Close to the critical point quantum fluctuations become important and the system enters a quantum critical regime. The large-NN approximation allows us to calculate physical quantitites reliably even in this strongly fluctuating regime. In particular, we find a scaling function to describe the crossover of the quasiparticle decay rate between the renormalized Fermi liquid regime and the quantum critical regime.Comment: 19 pages, 5 figure
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