61,725 research outputs found

    Performance characteristics of a thermionic converter with a /110/ tungsten emitter and a collector of niobium with trace amounts of tungsten and niobium carbide on the surface

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    Comparison of thermionic tungsten /110/ converter performances with niobium collectors and nickel collectors at various emitter, collector and cesium reservoir temperature

    Characteristics of a thermionic converter with a chloride vapor deposited tungsten emitter /110/ and a collector of molybdenum deposited on niobium

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    Performance characteristics of parallel plane, variable spaced thermionic converter with tungsten emitter and molybdenum-niobium collecto

    Characteristics of a thermionic converter with a chloride vapor deposited tungsten emitter /110/ and a nickel collector

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    Thermionic coverter with chloride vapor deposited tungsten emitter and nickel collecto

    Lattice Ï•4\phi^4 theory of finite-size effects above the upper critical dimension

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    We present a perturbative calculation of finite-size effects near TcT_c of the ϕ4\phi^4 lattice model in a dd-dimensional cubic geometry of size LL with periodic boundary conditions for d>4d > 4. The structural differences between the ϕ4\phi^4 lattice theory and the ϕ4\phi^4 field theory found previously in the spherical limit are shown to exist also for a finite number of components of the order parameter. The two-variable finite-size scaling functions of the field theory are nonuniversal whereas those of the lattice theory are independent of the nonuniversal model parameters.One-loop results for finite-size scaling functions are derived. Their structure disagrees with the single-variable scaling form of the lowest-mode approximation for any finite ξ/L\xi/L where ξ\xi is the bulk correlation length. At TcT_c, the large-LL behavior becomes lowest-mode like for the lattice model but not for the field-theoretic model. Characteristic temperatures close to TcT_c of the lattice model, such as Tmax(L)T_{max}(L) of the maximum of the susceptibility χ\chi, are found to scale asymptotically as Tc−Tmax(L)∼L−d/2T_c - T_{max}(L) \sim L^{-d/2}, in agreement with previous Monte Carlo (MC) data for the five-dimensional Ising model. We also predict χmax∼Ld/2\chi_{max} \sim L^{d/2} asymptotically. On a quantitative level, the asymptotic amplitudes of this large -LL behavior close to TcT_c have not been observed in previous MC simulations at d=5d = 5 because of nonnegligible finite-size terms ∼L(4−d)/2\sim L^{(4-d)/2} caused by the inhomogeneous modes. These terms identify the possible origin of a significant discrepancy between the lowest-mode approximation and previous MC data. MC data of larger systems would be desirable for testing the magnitude of the L(4−d)/2L^{(4-d)/2} and L4−dL^{4-d} terms predicted by our theory.Comment: Accepted in Int. J. Mod. Phys.

    Business strategy and firm performance: the British corporate economy, 1949-1984

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    There has been considerable and ongoing debate about the performance of the British economy since 1945. Empirical studies have concentrated on aggregate or industry level indicators. Few have examined individual firms’ financial performance. This study takes a sample of c.3000 firms in 19 industries and identifies Britain’s best performing companies over a period of 35 years. Successful companies are defined as a) those that survive as independent entities, b) that outperform peer group average return to capital for that industry, and c) that outperform other firms in the economy according to return on capital relative to industry average. Results are presented as league tables of success and some tentative explanations offered concerning the common strategies of successful firms. A broader research agenda for British business history is suggested

    Quasideterminants

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    The determinant is a main organizing tool in commutative linear algebra. In this review we present a theory of the quasideterminants defined for matrices over a division algebra. We believe that the notion of quasideterminants should be one of main organizing tools in noncommutative algebra giving them the same role determinants play in commutative algebra.Comment: amstex; final version; to appear in Advances in Mat

    Universal scaling behavior at the upper critical dimension of non-equilibrium continuous phase transitions

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    In this work we analyze the universal scaling functions and the critical exponents at the upper critical dimension of a continuous phase transition. The consideration of the universal scaling behavior yields a decisive check of the value of the upper critical dimension. We apply our method to a non-equilibrium continuous phase transition. But focusing on the equation of state of the phase transition it is easy to extend our analysis to all equilibrium and non-equilibrium phase transitions observed numerically or experimentally.Comment: 4 pages, 3 figure

    Tunable Holstein model with cold polar molecules

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    We show that an ensemble of polar molecules trapped in an optical lattice can be considered as a controllable open quantum system. The coupling between collective rotational excitations and the motion of the molecules in the lattice potential can be controlled by varying the strength and orientation of an external DC electric field as well as the intensity of the trapping laser. The system can be described by a generalized Holstein Hamiltonian with tunable parameters and can be used as a quantum simulator of excitation energy transfer and polaron phenomena. We show that the character of excitation energy transfer can be modified by tuning experimental parameters.Comment: 5 pages, 3 figures (accepted in as a Rapid Communication in Phys.Rev.A
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