1,313 research outputs found
Space vehicle thermal testing: Principles, practices and effectiveness
Component qualification and acceptance temperatures are derived from worst case thermal analyses and analytic uncertainty margin subject to certain specified temperature extremes. Temperature requirements are shown for equipment operation within specification and for survival and turn-on (need not operate within specification, but must not experience any degradation when returned to operational range). Temperature excursions for most equipment are seen to be 20 to 50 C above and below room temperature. Components without active electronics which are mounted outboard, such as solar arrays and antennas, are usually designed to withstand wider temperature excursions, particularly at the cold end. Batteries are tightly controlled at cold temperatures to increase life. Payload components such as extremely accurate clocks for precise navigation are controlled over a relatively narrow temperature range
Gas Requirements in Pressurized Transfer of Liquid Hydrogen
Of late, liquid hydrogen has become a very popular fuel for space missions. It is being used in such programs as Centaur and Saturn. Furthermore, hydrogen is the ideal working fluid for nuclear powered space vehicles currently under development. In these applications, liquid hydrogen fuel is generally transferred to the combustion chamber by a combination of pumping and pressurization. The pump forces the liquid propellant from the fuel tank to the combustion chamber; gaseous pressurant holds tank pressure sufficiently high to prevent cavitation at the pump inlet and to maintain the structural rigidity of the tank. The pressurizing system, composed of pressurant, tankage, and associated hardware can be a large portion of the total vehicle weight. Pressurant weight can be reduced by introducing the pressurizing gas at temperatures substantially greater than those of liquid hydrogen. Heat and mass transfer processes thereby induced complicate gas requirements during discharge. These requirements must be known to insure proper design of the pressurizing system. The aim of this paper is to develop from basic mass and energy transfer processes a general method to predict helium and hydrogen gas usage for the pressurized transfer of liquid hydrogen. This required an analytical and experimental investigation, the results of which are described in this paper
Solving for Micro- and Macro- Scale Electrostatic Configurations Using the Robin Hood Algorithm
We present a novel technique by which highly-segmented electrostatic
configurations can be solved. The Robin Hood method is a matrix-inversion
algorithm optimized for solving high density boundary element method (BEM)
problems. We illustrate the capabilities of this solver by studying two
distinct geometry scales: (a) the electrostatic potential of a large volume
beta-detector and (b) the field enhancement present at surface of electrode
nano-structures. Geometries with elements numbering in the O(10^5) are easily
modeled and solved without loss of accuracy. The technique has recently been
expanded so as to include dielectrics and magnetic materials.Comment: 40 pages, 20 figure
Apical endosomes isolated from kidney collecting duct principal cells lack subunits of the proton pumping ATPase.
Endocytic vesicles that are involved in the vasopressin-stimulated recycling of water channels to and from the apical membrane of kidney collecting duct principal cells were isolated from rat renal papilla by differential and Percoll density gradient centrifugation. Fluorescence quenching measurements showed that the isolated vesicles maintained a high, HgCl2-sensitive water permeability, consistent with the presence of vasopressin-sensitive water channels. They did not, however, exhibit ATP-dependent luminal acidification, nor any N-ethylmaleimide-sensitive ATPase activity, properties that are characteristic of most acidic endosomal compartments. Western blotting with specific antibodies showed that the 31- and 70-kD cytoplasmically oriented subunits of the vacuolar proton pump were not detectable in these apical endosomes from the papilla, whereas they were present in endosomes prepared in parallel from the cortex. In contrast, the 56-kD subunit of the proton pump was abundant in papillary endosomes, and was localized at the apical pole of principal cells by immunocytochemistry. Finally, an antibody that recognizes the 16-kD transmembrane subunit of oat tonoplast ATPase cross-reacted with a distinct 16-kD band in cortical endosomes, but no 16-kD band was detectable in endosomes from the papilla. This antibody also recognized a 16-kD band in affinity-purified H+ ATPase preparations from bovine kidney medulla. Therefore, early endosomes derived from the apical plasma membrane of collecting duct principal cells fail to acidify because they lack functionally important subunits of a vacuolar-type proton pumping ATPase, including the 16-kD transmembrane domain that serves as the proton-conducting channel, and the 70-kD cytoplasmic subunit that contains the ATPase catalytic site. This specialized, non-acidic early endosomal compartment appears to be involved primarily in the hormonally induced recycling of water channels to and from the apical plasma membrane of vasopressin-sensitive cells in the kidney collecting duct
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A Computer Model of the Neural Substrates of Classical Conditioning in the Aplysia
Uncertainties of the CJK 5 Flavour LO Parton Distributions in the Real Photon
Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real,
unpolarized photon, calculated in the CJK model being an improved realization
of the CJKL approach, have been recently presented. The results were obtained
through a global fit to the experimental F2^gamma data. In this paper we
present, obtained for the very first time in the photon case, an estimate of
the uncertainties of the CJK parton distributions due to the experimental
errors. The analysis is based on the Hessian method which was recently applied
in the proton parton structure analysis. Sets of test parametrizations are
given for the CJK model. They allow for calculation of its best fit parton
distributions along with F2^gamma and for computation of uncertainties of any
physical value depending on the real photon parton densities. We test the
applicability of the approach by comparing uncertainties of example
cross-sections calculated in the Hessian and Lagrange methods. Moreover, we
present a detailed analysis of the chi^2 of the CJK fit and its relation to the
data. We show that large chi^2/DOF of the fit is due to only a few of the
experimental measurements. By excluding them chi^2/DOF approx 1 can be
obtained.Comment: 28 pages, 8 eps figures, 2 Latex figures; FORTRAN programs available
at http://www.fuw.edu.pl/~pjank/param.html; table 10, figure 10 and section 6
correcte
Testing Color Evaporation in Photon-Photon Production of J/Psi at CERN LEP II
The DELPHI Collaboration has recently reported the measurement of J/Psi
production in photon-photon collisions at LEP II. These newly available data
provide an additional proof of the importance of colored c bar{c} pairs for the
production of charmonium because these data can only be explained by
considering resolved photon processes. We show here that the inclusion of color
octet contributions to the J/Psi production in the framework of the color
evaporation model is able to reproduce this data. In particular, the
transverse-momentum distribution of the J/Psi mesons is well described by this
model.Comment: 10 pages, 5 Figures, Revtex
Prospects for CP-violation searches in the future experiment with RF-separated K+/- beam at U-70
The first description of the experimental program "OKA" with RF-separated
K+/- beam at Protvino U-70 PS is presented. The parameters of the beam as well
as the potential for CP-violation searches are discussed.Comment: 8 pages, 6 figures, submitted to proceedings of International
Conference on CP Violation, Sep 18-22, 2000, Ital
Symmetry breaking effect on determination of polarized and unpolarized parton distributions
We perform a new extraction for unpolarized and polarized parton distribution
functions considering a flavor decompositions for sea quarks and applying very
recent deep inelastic scattering (DIS) and semi inclusive deep inelastic
scattering (SIDIS) data in the fixed flavor number scheme (FFNS) framework. In
the new symmetry breaking scenario the light quark and antiquark densities are
extracted separately and new parametrization forms are determined for them. The
heavy flavors contribution, including charm and bottom quarks, are also taken
to be account for unpolarized distributions.Comment: Talk presented at 16th International QCD Conference (QCD12),
Montpellier, France, July 2- 7, 2012. Submitted to Nuc. Phys. (Proc. Suppl.),
4 pages, 4 figure
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