26,606 research outputs found

    Two Aspects of the Mott-Hubbard Transition in Cr-doped V_2O_3

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    The combination of bandstructure theory in the local density approximation with dynamical mean field theory was recently successfully applied to V2_2O3_3 -- a material which undergoes the f amous Mott-Hubbard metal-insulator transition upon Cr doping. The aim of this sh ort paper is to emphasize two aspects of our recent results: (i) the filling of the Mott-Hubbard gap with increasing temperature, and (ii) the peculiarities of the Mott-Hubbard transition in this system which is not characterized by a diver gence of the effective mass for the a1ga_{1g}-orbital.Comment: 2 pages, 3 figures, SCES'04 conference proceeding

    Independent Orbiter Assessment (IOA): Analysis of the life support and airlock support subsystems

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    The results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. This report documents the independent analysis results corresponding to the Orbiter Life Support System (LSS) and Airlock Support System (ALSS). Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. The LSS provides for the management of the supply water, collection of metabolic waste, management of waste water, smoke detection, and fire suppression. The ALSS provides water, oxygen, and electricity to support an extravehicular activity in the airlock

    Scaling properties of the redshift power spectrum: theoretical models

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    We report the results of an analysis of the redshift power spectrum PS(k,μ)P^S(k,\mu) in three typical Cold Dark Matter (CDM) cosmological models, where μ\mu is the cosine of the angle between the wave vector and the line-of-sight. Two distinct biased tracers derived from the primordial density peaks of Bardeen et al. and the cluster-underweight model of Jing, Mo, & B\"orner are considered in addition to the pure dark matter models. Based on a large set of high resolution simulations, we have measured the redshift power spectrum for the three tracers from the linear to the nonlinear regime. We investigate the validity of the relation - guessed from linear theory - in the nonlinear regime PS(k,μ)=PR(k)[1+βμ2]2D(k,μ,σ12(k)), P^S(k,\mu)=P^R(k)[1+\beta\mu^2]^2D(k,\mu,\sigma_{12}(k)), where PR(k)P^R(k) is the real space power spectrum, and β\beta equals Ω00.6/bl\Omega_0^{0.6}/b_l. The damping function DD which should generally depend on kk, μ\mu, and σ12(k)\sigma_{12}(k), is found to be a function of only one variable kμσ12(k)k\mu\sigma_{12}(k). This scaling behavior extends into the nonlinear regime, while DD can be accurately expressed as a Lorentz function - well known from linear theory - for values D>0.1D > 0.1. The difference between σ12(k)\sigma_{12}(k) and the pairwise velocity dispersion defined by the 3-D peculiar velocity of the simulations (taking r=1/kr=1/k) is about 15%. Therefore σ12(k)\sigma_{12}(k) is a good indicator of the pairwise velocity dispersion. The exact functional form of DD depends on the cosmological model and on the bias scheme. We have given an accurate fitting formula for the functional form of DD for the models studied.Comment: accepted for publication in ApJ;24 pages with 7 figures include

    Deriving the Nonlinear Cosmological Power Spectrum and Bispectrum from Analytic Dark Matter Halo Profiles and Mass Functions

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    We present an analytic model for the fully nonlinear power spectrum P and bispectrum Q of the cosmological mass density field. The model is based on physical properties of dark matter halos, with the three main model inputs being analytic halo density profiles, halo mass functions, and halo-halo spatial correlations, each of which has been well studied in the literature. We demonstrate that this new model can reproduce the power spectrum and bispectrum computed from cosmological simulations of both an n=-2 scale-free model and a low-density cold dark matter model. To enhance the dynamic range of these large simulations, we use the synthetic halo replacement technique of Ma & Fry (2000a), where the original halos with numerically softened cores are replaced by synthetic halos of realistic density profiles. At high wavenumbers, our model predicts a slope for the nonlinear power spectrum different from the often-used fitting formulas in the literature based on the stable clustering assumption. Our model also predicts a three-point amplitude Q that is scale dependent, in contrast to the popular hierarchical clustering assumption. This model provides a rapid way to compute the mass power spectrum and bispectrum over all length scales where the input halo properties are valid. It also provides a physical interpretation of the clustering properties of matter in the universe.Comment: Final version to appear in the Astrophysical Journal 544 (2000). Minor revisions; 1 additional figure. 25 pages with 6 inserted figure
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