1,541 research outputs found
The COLD-SAT Experiment for Cryogenic Fluid Management Technology
Future national space transportation missions will depend on the use of cryogenic fluid management technology development needs for these missions. In-space testing will be conducted in order to show low gravity cryogenic fluid management concepts and to acquire a technical data base. Liquid H2 is the preferred test fluid due to its propellant use. The design of COLD-SAT (Cryogenic On-orbit Liquid Depot Storage, Acquisition, and Transfer Satellite), an Expendable Launch Vehicle (ELV) launched orbital spacecraft that will perform subcritical liquid H2 storage and transfer experiments under low gravity conditions is studied. An Atlas launch vehicle will place COLD-SAT into a circular orbit, and the 3-axis controlled spacecraft bus will provide electric power, experiment control, and data management, attitude control, and propulsive accelerations for the experiments. Low levels of acceleration will provide data on the effects that low gravity might have on the heat and mass transfer processes used. The experiment module will contain 3 liquid H2 tanks; fluid transfer, pressurization and venting equipment; and instrumentation
The Gluon Spin in the Chiral Bag Model
We study the gluon polarization contribution at the quark model
renormalization scale to the proton spin, , in the chiral bag model. It
is evaluated by taking the expectation value of the forward matrix element of a
local gluon operator in the axial gauge . It is shown that the confining
boundary condition for the color electric field plays an important role. When a
solution satisfying the boundary condition for the color electric field, which
is not the conventionally used but which we favor, is used, the has a
positive value for {\it all} bag radii and its magnitude is comparable to the
quark spin polarization. This results in a significant reduction in the
relative fraction of the proton spin carried by the quark spin, which is
consistent with the small flavor singlet axial current measured in the EMC
experiments.Comment: Corrections to figure
The solid surface combustion space shuttle experiment hardware description and ground-based test results
The Lewis Research Center is developing a series of microgravity combustion experiments for the Space Shuttle. The Solid Surface Combustion Experiment (SSCE) is the first to be completed. SSCE will study flame spreading over thermally thin fuels (ashless filter paper) under microgravity conditions. The flight hardware consists of a combustion chamber containing the sample and a computer which takes the data and controls the experiment. Experimental data will include gas-phase and solid-phase temperature measurements and motion pictures of the combustion process. Flame spread rates will be determined from the motion pictures
Long Hours, Uneasy Feelings : Parliamentary Work in Denmark, Finland and Sweden
A correction has been published: Parliamentary Affairs, Volume 75, Issue 3, July 2022, Page 576, https://doi.org/10.1093/pa/gsab034Politicians' work pressure is gaining more attention in parliamentary studies. To participate in the discussion about governing under pressure, this article offers an interdisciplinary approach to investigate how representatives navigate within a flexible, limitless work culture. This article presents a new inquiry to re-examine contemporary political agency by combining cultural studies theories with empirical insights in Nordic countries. By analysing 52 semi-structured interviews with MPs in Denmark, Finland and Sweden, the study finds that politics attracts people who want to change the world, but these attributes may initiate a vicious cycle, taking the form of psychological strain.Peer reviewe
Parton distributions in a constituent quark scenario
A simple picture of the constituent quark as a composite system of point-like
partons is used to construct the unpolarized and polarized parton distributions
by a convolution between constituent quark momentum distributions and
constituent quark structure functions. We achieve good agreement with
experiments in the unpolarized, as well as, in the polarized case. When our
results are compared with similar calculations using non-composite constituent
quarks, the accord with the experiments of the present scheme is impressive. We
conclude that DIS data are consistent with a low energy scenario dominated by
composite constituents of the nucleon.Comment: 4 pages; latex using espcrc1.sty; 4 postscript figures; Invited talk
at the Workshop ``Nucleon '99'', Frascati; Italy 7-9 June 1999. Submitted to
Nuc. Phys.
Instantaneous flowrate measurements in high-pressure liquid flows
A new flowmeter suitable for high-pressure flows and with a prompt dynamic response is presented. It is constituted by two pressure transducers installed on the monitored high-pressure pipe at a fixed distance one from the other, together with a low-pressure flowmeter that provides a time-averaged flowrate. The measurement algorithm consists of an ordinary differential equation obtained by combining the mass conservation partial differential equation and the momentum balance one applied to the considered piece of pipe comprised between the two pressure transducers. Due to the absence of a master instrument that can be employed as reference to verify the consistency of the measured flowrate, the flowmeter accuracy has been demonstrated by means of numerical models of various hydraulic components, rigorously validated through pressure measurements. The flow ripple of gear pumps has been measured, as well as the flowrate entering a Common Rail injector. For all these cases, the measured flowrate and the one obtained by means of the numerical model are in very good agreement, leading to a robust validation of the presented measurement device
Nucleon and delta masses in QCD
Using the positivity of the path integral measure of and defining a
structure for the quark propagator in a background field according to the
fluxon scenario for confinement, we calculate and compare the correlators for
nucleon and delta. From their shape we elucidate about the origin of their mass
difference, which in our simplified scenario is due to the tensor structure in
the propagator. This term arises due to a dynamical mechanism which is
responsible simultaneously for confinement and spontaneous chiral symmetry
breaking. Finally we discuss, by comparing the calculated correlators with the
Lehmann representation, the possibility that a strong CP and/or P violation
occurs as a consequence of a specific mechanism for confinement.Comment: Latex, FTUV/92-2
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