2,055 research outputs found

    NECAP 4.1: NASA's Energy Cost Analysis Program thermal response factor routine

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    A thermal response factor is described and calculation sequences and flowcharts for RESFAC2 are provided. RESFAC is used by NASA's (NECAP) to calculate hourly heat transfer coefficients (thermal response factors) for each unique delayed surface. NECAP uses these response factors to compute each spaces' hourly heat gain/loss

    Chiral Magnetism of the Nucleon

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    We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons, pions and delta resonances as explicit degrees of freedom. We point out that the usual powercounting applied so far to this problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified powercounting and compare the resulting chiral extrapolation function to available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here are consistent with the Pade fit ansatz introduced by the Adelaide group a few years ago.Comment: 30 pages, Latex, 7 figure

    Thermal Dileptons from Quark and Hadron Phases of an Expanding Fireball

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    A fireball model with time evolution based on transport calculations is used to examine the dilepton emission rate of an ultra-relativistic heavy-ion collision. We assume a transition from hadronic matter to a quark-gluon plasma at a critical temperature T_C between 130-170 MeV. We include thermal corrections to the hadronic spectra below T_C and use perturbation theory above T_C. The sensitivity of the spectra with respect to the freeze-out temperature, the initial fireball temperature and the critical temperature is investigated.Comment: 14 pages, 5 figures; paragraph and one figure added; version to appear in Eur. Phys. J.

    Comment on "Surprises in threshold antikaon-nucleon physics"

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    It has recently been claimed by Oller et al. [PRL 95 (2005) 172502] that the DEAR kaonic hydrogen data can be reconciled with K^- p scattering data in a chiral unitary approach. In this comment we demonstrate that the proposed solution violates fundamental principles of scattering theory.Comment: 1 page, 1 figur

    Note on finite temperature sum rules for vector and axial-vector spectral functions

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    An updated analysis of vector and axial-vector spectral functions is presented. The resonant contributions to the spectral integrals are shown to be expressible as multiples of 4 pi^2 f_pi^2, encoding the scale of spontaneous chiral symmetry breaking in QCD. Up to order T^2 this behavior carries over to the case of finite temperature.Comment: 10 pages, 2 figure

    Hire Education: Mastery, Modularization and the Workforce Revolution

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    This new research identifies online competency-based learning as the solution to shifting demands for specialized workforce skills and the front runner for disrupting higher education

    Chiral extrapolations of nucleon properties from lattice QCD

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    We report on recent work about the study of quark mass dependence of nucleon magnetic moments and axial-vector coupling constant. We examine the feasibility of chiral effective field theory methods for the extrapolation of lattice QCD data obtained at relative large pion masses down to the physical values.Comment: 5pages, LaTeX, 3 figures, uses World Scientific style file; presented at PANIC 02, Osak

    Model for dilepton rates from a fireball

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    We calculate the dilepton emission rate from a fireball created in an ultra-relativistic heavy-ion collision. For the partonic phase, we complement the perturbative results by a phenomenological approach based on lattice QCD results, whereas in the hadronic phase temperature and finite baryon density effects on the spectral function are considered. The resulting rates are compared to data from CERES/NA45.Comment: 4 pages, 3 figures. Talk given at 15th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (QM2001), Stony Brook, New York, 15-20 Jan 200
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