1,292 research outputs found

    Part III, Free Actions of Compact Quantum Groups on C*-Algebras

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    We study and classify free actions of compact quantum groups on unital C*-algebras in terms of generalized factor systems. Moreover, we use these factor systems to show that all finite coverings of irrational rotation C*-algebras are cleft

    On the efficiency of heat engines at the micro-scale and below

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    We investigate the thermodynamic efficiency of sub-micro-scale heat engines operating under the conditions described by over-damped stochastic thermodynamics. We prove that at maximum power the efficiency obeys for constant isotropic mobility the universal law η=2ηC/(4ηC)\eta=2\,\eta_{C}/(4-\eta_{C}) where ηC\eta_{C} is the efficiency of an ideal Carnot cycle. The corresponding power optimizing protocol is specified by the solution of an optimal mass transport problem. Such solution can be determined explicitly using well known Monge--Amp\`ere--Kantorovich reconstruction algorithms. Furthermore, we show that the same law describes the efficiency of heat engines operating at maximum work over short time periods. Finally, we illustrate the straightforward extension of these results to cases when the mobility is anisotropic and temperature dependent.Comment: 5 pages; revised version including the derivation of the efficiency and of the corresponding optimal protocols in the presence of anisotropic temperature dependent mobilit

    On the origin of temperature dependence of interlayer exchange coupling in metallic trilayers

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    We study the influence of collective magnetic excitations on the interlayer exchange coupling (IEC) in metallic multilayers. The results are compared to other models that explain the temperature dependence of the IEC by mechanisms within the spacer or at the interfaces of the multilayers. As a main result we find that the reduction of the IEC with temperature shows practically the same functional dendence in all models. On the other hand the influence of the spacer thickness, the magnetic material, and an external field are quite different. Based on these considerations we propose experiments, that are able to determine the dominating mechanism that reduces the IEC at finite temperatures.Comment: 8 pages, 7 figures, accepted for PR

    Mechanism of temperature dependence of the magnetic anisotropy energy in ultrathin Cobalt and Nickel films

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    Temperature dependent FMR-measurements of Ni and Co films are analysed using a microscopic theory for ultrathin metallic systems. The mechanism governing the temperature dependence of the magnetic anisotropy energy is identified and discussed. It is reduced with increasing temperature. This behavior is found to be solely caused by magnon excitations.Comment: 3 pages, 4 figures III Joint European Magnetic Symposia, San Sebastian, Spai

    Teaching Case: Design and Development of a Special Population Resource Connection Database

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    Connecting people with resources is a common activity. However, special situations have unique data needs. Without the appropriate leadership and tools to manage the data, the connections may never take place. This case examines the data needs associated with providing resources and social connections for families having a member with a special need. The case provides a realistic scenario that can be used in a systems analysis and design, database development, or graduate-level management information systems course. The case focuses on developing a database to provide a support system for connecting caregivers of loved ones having special needs with people in similar circumstances, volunteers, and social and employment opportunities. Two assignment options are provided, allowing instructors to select an assignment based on course material coverage. Suggested assignments include the development of process modeling diagrams such as a data flow or swimlane diagrams and database design and development artifacts
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