9,690 research outputs found

    Quintic threefolds and Fano elevenfolds

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    The derived category of coherent sheaves on a general quintic threefold is a central object in mirror symmetry. We show that it can be embedded into the derived category of a certain Fano elevenfold. Our proof also generates related examples in different dimensions.Comment: V1: 12 pages. V2: added reference to work of Iliev and Manivel. V3: persistent sign error corrected. Other minor changes following referee's suggestions. To appear in Crell

    Stochastic pumping of heat: Approaching the Carnot efficiency

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    Random noise can generate a unidirectional heat current across asymmetric nano objects in the absence (or against) a temperature gradient. We present a minimal model for a molecular-level stochastic heat pump that may operate arbitrarily close to the Carnot efficiency. The model consists a fluctuating molecular unit coupled to two solids characterized by distinct phonon spectral properties. Heat pumping persists for a broad range of system and bath parameters. Furthermore, by filtering the reservoirs' phonons the pump efficiency can approach the Carnot limit

    Quantum effects in thermal conduction: Nonequilibrium quantum discord and entanglement

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    We study the process of heat transfer through an entangled pair of two-level system, demonstrating the role of quantum correlations in this nonequilibrium process. While quantum correlations generally degrade with increasing the temperature bias, introducing spatial asymmetry leads to an intricate behavior: Connecting the qubits unequally to the reservoirs one finds that quantum correlations persist and increase with the temperature bias when the system is more weakly linked to the hot reservoir. In the reversed case, linking the system more strongly to the hot bath, the opposite, more natural behavior is observed, with quantum correlations being strongly suppressed upon increasing the temperature bias

    Noncommutative differential calculus for Moyal subalgebras

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    We build a differential calculus for subalgebras of the Moyal algebra on R^4 starting from a redundant differential calculus on the Moyal algebra, which is suitable for reduction. In some cases we find a frame of 1-forms which allows to realize the complex of forms as a tensor product of the noncommutative subalgebras with the external algebra Lambda^*.Comment: 13 pages, no figures. One reference added, minor correction

    Youth and old age in America

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    Maine Yankee Nuclear Power Plant: A Technological Utopia in Retrospect

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    The Maine Yankee nuclear power plant, built in 1968 and closed in 1996, provides a revealing case study of the rise and fall of the nuclear power industry in the United States. At its inception, the plant generated a great outpouring of optimistic superlatives promising electricity “too cheap to meter” and a solution to Maine’s longstanding energy problems. Its promoters envisioned a technological utopia for Maine communities based on cheap and efïŹcient energy, and based on these promising prospects, the town of Wiscasset welcomed the plant. This article traces the changes in public thinking that led to statewide referenda on the question of nuclear power in 1980, 1982, and 1987, and it highlights the anti-utopian fears that fueled these campaigns. Howard Segal is a professor of history specializing in history of technology at the University of Maine, having joined the faculty there in 1986. His publications include Technological Utopianism in American Culture (1985); Future Imperfect: The Mixed Blessings of Technology in America (1994); Technology in America: A Brief History (1989); and Recasting the Machine Age: Henry Ford’s Village Industries (2001).His current research involves a history of high-tech technological utopias in America
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