10,690 research outputs found

    Universal scaling relations in molecular superconductors

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    Scaling relations between the superconducting transition temperature TcT_{\rm c}, the superfluid stiffness ρs\rho_{\rm s} and the normal state conductivity σ0(Tc)\sigma_0(T_{\rm c}) are identified within the class of molecular superconductors. These new scaling properties hold as TcT_{\rm c} varies over two orders of magnitude for materials with differing dimensionality and contrasting molecular structure, and are dramatically different from the equivalent scaling properties observed within the family of cuprate superconductors. These scaling relations place strong constraints on theories for molecular superconductivity.Comment: 4 pages, 4 figure

    Unconventional Quantum Critical Points

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    In this paper we review the theory of unconventional quantum critical points that are beyond the Landau's paradigm. Three types of unconventional quantum critical points will be discussed: (1). The transition between topological order and semiclassical spin ordered phase; (2). The transition between topological order and valence bond solid phase; (3). The direct second order transition between different competing orders. We focus on the field theory and universality class of these unconventional quantum critical points. Relation of these quantum critical points with recent numerical simulations and experiments on quantum frustrated magnets are also discussed.Comment: 28 pages, 6 figures. Review article for Int. J. Mod. Phys.

    Balancing Local Order and Long-Ranged Interactions in the Molecular Theory of Liquid Water

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    A molecular theory of liquid water is identified and studied on the basis of computer simulation of the TIP3P model of liquid water. This theory would be exact for models of liquid water in which the intermolecular interactions vanish outside a finite spatial range, and therefore provides a precise analysis tool for investigating the effects of longer-ranged intermolecular interactions. We show how local order can be introduced through quasi-chemical theory. Long-ranged interactions are characterized generally by a conditional distribution of binding energies, and this formulation is interpreted as a regularization of the primitive statistical thermodynamic problem. These binding-energy distributions for liquid water are observed to be unimodal. The gaussian approximation proposed is remarkably successful in predicting the Gibbs free energy and the molar entropy of liquid water, as judged by comparison with numerically exact results. The remaining discrepancies are subtle quantitative problems that do have significant consequences for the thermodynamic properties that distinguish water from many other liquids. The basic subtlety of liquid water is found then in the competition of several effects which must be quantitatively balanced for realistic results.Comment: 8 pages, 6 figure

    Study and development of a mathematical analysis for the performance assessment of space communication system parameters

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    Electronic computer program user manual for optimum design of space communication syste

    User's manual for COPTRAN, a method of optimum communication system design

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    User manual for COPTRAN /communication system optimization program translator

    Digital adaptive controllers for VTOL vehicles. Volume 1: Concept evaluation

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    A digital self-adaptive flight control system was developed for flight test in the VTOL approach and landing technology (VALT) research aircraft (a modified CH-47 helicopter). The control laws accept commands from an automatic on-board guidance system. The primary objective of the control laws is to provide good command-following with a minimum cross-axis response. Three attitudes and vertical velocity are separately commanded. Adaptation of the control laws is based on information from rate and attitude gyros and a vertical velocity measurement. The final design resulted from a comparison of two different adaptive concepts--one based on explicit parameter estimates from a real-time maximum-likelihood estimation algorithm, the other based on an implicit model reference adaptive system. The two designs were compared on the basis of performance and complexity

    COPTRAN - A method of optimum communication systems design

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    Single set of mathematical expressions describes system cost and probability of error of data transmission in terms of four basic parameters in the link equation. A Lagrange multiplier sets up equations whose solutions yield the optimum values for system design considerations and weight and cost values

    Digital adaptive controllers for VTOL vehicles. Volume 2: Software documentation

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    The VTOL approach and landing test (VALT) adaptive software is documented. Two self-adaptive algorithms, one based on an implicit model reference design and the other on an explicit parameter estimation technique were evaluated. The organization of the software, user options, and a nominal set of input data are presented along with a flow chart and program listing of each algorithm
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