15,100 research outputs found

    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 Hall Effect on the Hyperbolic Plane

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    In this paper, we study both the continuous model and the discrete model of the Quantum Hall Effect (QHE) on the hyperbolic plane. The Hall conductivity is identified as a geometric invariant associated to an imprimitivity algebra of observables. We define a twisted analogue of the Kasparov map, which enables us to use the pairing between KK-theory and cyclic cohomology theory, to identify this geometric invariant with a topological index, thereby proving the integrality of the Hall conductivity in this case.Comment: AMS-LaTeX, 28 page

    Twisted K-theory and finite-dimensional approximation

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    We provide a finite-dimensional model of the twisted K-group twisted by any degree three integral cohomology class of a CW complex. One key to the model is Furuta's generalized vector bundle, and the other is a finite-dimensional approximation of Fredholm operators.Comment: 26 pages, LaTeX 2e, Xypic; main theorem improve

    Primary transit of the planet HD189733b at 3.6 and 5.8 microns

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    The hot Jupiter HD 189733b was observed during its primary transit using the Infrared Array Camera on the Spitzer Space Telescope. The transit depths were measured simultaneously at 3.6 and 5.8 microns. Our analysis yields values of 2.356 +- 0.019 % and 2.436 +- 0.020$ % at 3.6 and 5.8 microns respectively, for a uniform source. We estimated the contribution of the limb-darkening and star-spot effects on the final results. We concluded that although the limb darkening increases by ~0.02-0.03 % the transit depths, and the differential effects between the two IRAC bands is even smaller, 0.01 %. Furthermore, the host star is known to be an active spotted K star with observed photometric modulation. If we adopt an extreme model of 20 % coverage with spots 1000K cooler of the star surface, it will make the observed transits shallower by 0.19 and 0.18 %. The difference between the two bands will be only of 0.01 %, in the opposite direction to the limb darkening correction. If the transit depth is affected by limb darkening and spots, the differential effects between the 3.6 and 5.8 microns bands are very small. The differential transit depths at 3.6 and 5.8 microns and the recent one published by Knutson et al.(2007) at 8 microns are in agreement with the presence of water vapour in the upper atmosphere of the planet. This is the companion paper to Tinetti et al. (2007b), where the detailed atmosphere models are presented.Comment: 6 pages, 4 figures, Astrophysical Journal 675. Accepted Nov 21, 20007, to appear on March 10, 200

    Simulation model of a twin-tail, high performance airplane

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    The mathematical model and associated computer program to simulate a twin-tailed high performance fighter airplane (McDonnell Douglas F/A-18) are described. The simulation program is written in the Advanced Continuous Simulation Language. The simulation math model includes the nonlinear six degree-of-freedom rigid-body equations, an engine model, sensors, and first order actuators with rate and position limiting. A simplified form of the F/A-18 digital control laws (version 8.3.3) are implemented. The simulated control law includes only inner loop augmentation in the up and away flight mode. The aerodynamic forces and moments are calculated from a wind-tunnel-derived database using table look-ups with linear interpolation. The aerodynamic database has an angle-of-attack range of -10 to +90 and a sideslip range of -20 to +20 degrees. The effects of elastic deformation are incorporated in a quasi-static-elastic manner. Elastic degrees of freedom are not actively simulated. In the engine model, the throttle-commanded steady-state thrust level and the dynamic response characteristics of the engine are based on airflow rate as determined from a table look-up. Afterburner dynamics are switched in at a threshold based on the engine airflow and commanded thrust
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