141,596 research outputs found

    Transition Temperature of a Uniform Imperfect Bose Gas

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    We calculate the transition temperature of a uniform dilute Bose gas with repulsive interactions, using a known virial expansion of the equation of state. We find that the transition temperature is higher than that of an ideal gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a is the S-wave scattering length, and K_0 is a constant given in the paper. This disagrees with all existing results, analytical or numerical. It agrees exactly in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe

    Convective flow during dendritic growth

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    A review is presented of the major experimental findings obtained from recent ground-based research conducted under the SPAR program. Measurements of dendritic growth at small supercoolings indicate that below approximately 1.5 K a transition occurs from diffusive control to convective control in succinonitrile, a model system chosen for this study. The key theoretical ideas concerning diffusive and convective heat transport during dendritic growth are discussed, and it is shown that a transition in the transport control should occur when the characteristic length for diffusion becomes larger than the characteristic length for convection. The experimental findings and the theoretical ideas discussed suggest that the Fluid Experiment System could provide appropriate experimental diagnostics for flow field visualization and quantification of the fluid dynamical effects presented here

    Gamma-Rays Produced in Cosmic-Ray Interactions and the TeV-band Spectrum of RX J1713.7-3946

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    We employ the Monte Carlo particle collision code DPMJET3.04 to determine the multiplicity spectra of various secondary particles (in addition to π0\pi^0's) with γ\gamma's as the final decay state, that are produced in cosmic-ray (pp's and α\alpha's) interactions with the interstellar medium. We derive an easy-to-use γ\gamma-ray production matrix for cosmic rays with energies up to about 10 PeV. This γ\gamma-ray production matrix is applied to the GeV excess in diffuse Galactic γ\gamma-rays observed by EGRET, and we conclude the non-π0\pi^0 decay components are insufficient to explain the GeV excess, although they have contributed a different spectrum from the π0\pi^0-decay component. We also test the hypothesis that the TeV-band γ\gamma-ray emission of the shell-type SNR RX J1713.7-3946 observed with HESS is caused by hadronic cosmic rays which are accelerated by a cosmic-ray modified shock. By the χ2\chi^2 statistics, we find a continuously softening spectrum is strongly preferred, in contrast to expectations. A hardening spectrum has about 1% probability to explain the HESS data, but then only if a hard cutoff at 50-100 TeV is imposed on the particle spectrum.Comment: 3 pages; 4 figures; Contribution to the First GLAST Symposium, Standord, 200

    Universality and itinerant ferromagnetism in rotating strongly interacting Fermi gases

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    We analytically determine the properties of three interacting fermions in a harmonic trap subject to an external rotation. Thermodynamic quantities such as the entropy and energy are calculated from the third order quantum virial expansion. By parameterizing the solutions in the rotating frame we find that the energy and entropy are universal for all rotations in the strongly interacting regime. Additionally, we find that rotation suppresses the onset of itinerant ferromagnetism in strongly interacting repulsive three-body systems.Comment: 5 pages with 3 figure

    Localization Transition in Incommensurate non-Hermitian Systems

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    A class of one-dimensional lattice models with incommensurate complex potential V(θ)=2[λrcos(θ)+iλisin(θ)]V(\theta)=2[\lambda_r cos(\theta)+i \lambda_i sin(\theta)] is found to exhibit localization transition at ∣λr∣+∣λi∣=1|\lambda_r|+|\lambda_i|=1. This transition from extended to localized states manifests in the behavior of the complex eigenspectum. In the extended phase, states with real eigenenergies have finite measure and this measure goes to zero in the localized phase. Furthermore, all extended states exhibit real spectrum provided ∣λr∣≥∣λi∣|\lambda_r| \ge |\lambda_i|. Another novel feature of the system is the fact that the imaginary part of the spectrum is sensitive to the boundary conditions {\it only at the onset to localization}
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