20,765 research outputs found

    Technology requirements for future Earth-to-geosynchronous orbit transportation systems. Volume 1: Executive summary

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    Technologies including accelerated technology that are critical to performance and/or provide cost advantages for future space transportation systems are identified. Mission models are scoped and include priority missions, and cargo missions. Summary data, providing primary design concepts and features, are given for the SSTO, HLLV, POTV, and LCOTV vehicles. Significant system costs and total system costs in terms of life cycle costs in both discounted and undiscounted dollars are summarized for each of the vehicles

    Technology requirements for future Earth-to-geosynchronous orbit transportation systems. Volume 3: Appendices

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    Technological requirements and forecasts of rocket engine parameters and launch vehicles for future Earth to geosynchronous orbit transportation systems are presented. The parametric performance, weight, and envelope data for the LOX/CH4, fuel cooled, staged combustion cycle and the hydrogen cooled, expander bleed cycle engine concepts are discussed. The costing methodology and ground rules used to develop the engine study are summarized. The weight estimating methodology for winged launched vehicles is described and summary data, used to evaluate and compare weight data for dedicated and integrated O2/H2 subsystems for the SSTO, HLLV and POTV are presented. Detail weights, comparisons, and weight scaling equations are provided

    On the structure of large N cancellations in baryon chiral perturbation theory

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    We show how to compute loop graphs in heavy baryon chiral perturbation theory including the full functional dependence on the ratio of the Delta--nucleon mass difference to the pion mass, while at the same time automatically incorporating the 1/N cancellations that follow from the large-N spin-flavor symmetry of baryons in QCD. The one-loop renormalization of the baryon axial vector current is studied to demonstrate the procedure. A new cancellation is identified in the one-loop contribution to the baryon axial vector current. We show that loop corrections to the axial vector currents are exceptionally sensitive to deviations of the ratios of baryon-pion axial couplings from SU(6) values

    BARYON-BARYON INTERACTIONS IN LARGE N_C CHIRAL PERTURBATION THEORY

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    Interactions of two baryons are considered in large NCN_C chiral perturbation theory and compared to the interactions derived from the Skyrme model. Special attention is given to a torus-like configuration known to be present in the Skyrme model.Comment: 18 pages, REVTEX, 8 uuencoded PS figures appende

    1/N_c Expansion of the Heavy Baryon Isgur-Wise Functions

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    The 1/N_c expansion of the heavy baryon Isgur-Wise functions is discussed. Because of the contracted SU(2N_f) light quark spin-flavor symmetry, the universality relations among the Isgur-Wise functions of \Lambda_b to \Lambda_c and \Sigma_b^{(*)} to \Sigma_c^{(*)} are valid up to the order of 1/N_c^2.Comment: 7 pages, latex, no figures, to appear in Phys. Rev.

    HIV testing and informed consent - ethical considerations

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    One of the authors (T.J.) was invited by the AIDS Advisory Group to form a widely representative committee to recommend ethical guidelines concerning the extent to which HIV testing should receive informed consent. This paper presents and argues for the recommended guidelines. The question is considered with regard to a number of distinct purposes of HIV testing: the care of a patient; research; blood, tissue and organ donation; and the protection of third parties, including the health care worker. We contend that in each case there is no good reason for the requirement of informed consent to be significantly waived
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