23,085 research outputs found
Analysis of changes in leg volume parameters, and orthostatic tolerance in response to lower body negative pressure during 59 days exposure to zero gravity Skylab 3
The cardiovascular responses of the Apollo crewmen associated with postflight evaluations indicate varying decrements of orthostatic tolerance. The postflight changes indicate a slightly diminished ability to the cardiovascular system to function effectively against gravity following exposure to weightlessness. The objective of the Skylab LBNP experiments (M092) was to provide information about the magnitude and time course of the cardiovascular changes associated with prolonged periods of exposure to weightlessness. This report details the equipment, signal processing and analysis of the leg volume data obtained from the M092 experiment of the Skylab 3 Mission
Tripropellant combustion process
The addition of small amounts of hydrogen to the combustion of LOX/hydrocarbon propellants in large rocket booster engines has the potential to enhance the system stability. Programs being conducted to evaluate the effects of hydrogen on the combustion of LOX/hydrocarbon propellants at supercritical pressures are described. Combustion instability has been a problem during the development of large hydrocarbon fueled rocket engines. At the higher combustion chamber pressures expected for the next generation of booster engines, the effect of unstable combustion could be even more destructive. The tripropellant engine cycle takes advantage of the superior cooling characteristics of hydrogen to cool the combustion chamber and a small amount of the hydrogen coolant can be used in the combustion process to enhance the system stability. Three aspects of work that will be accomplished to evaluate tripropellant combustion are described. The first is laboratory demonstration of the benefits through the evaluation of drop size, ignition delay and burning rate. The second is analytical modeling of the combustion process using the empirical relationship determined in the laboratory. The third is a subscale demonstration in which the system stability will be evaluated. The approach for each aspect is described and the analytical models that will be used are presented
Heat transfer and pressure distributions at M equals 8 on 0.029 scale models of the Viking entry vehicle
An investigation in the Langley Research Center Mach-8 Variable Density Hypersonic Tunnel was made of the pressure distributions and heat transfer rate distributions on two 0.029 scale Viking Entry Vehicle models. Comparable ranges of test Reynolds number were exercised for the two tests between run conditions around 4 million and conditions of about 1.6 million. At angles of attack less than 20 degrees the pressure ratio distribution referenced to stagnation pressure appeared invariant with Reynolds number. Increasing angle of attack results in a flatter distribution of both the windward and leeward pressure distributions; in addition, the stagnation point shifted into the windward plane. A subsequent rise in the heating rate profile on the leeward side with further increase in angle of attack is attributed to boundary layer natural transition to turbulent flow. Schlieren photographs were taken for flow field visualization and to correct model angle of attack
Rippled Cosmological Dark Matter from Damped Oscillating Newton Constant
Let the reciprocal Newton 'constant' be an apparently non-dynamical
Brans-Dicke scalar field damped oscillating towards its General Relativistic
VEV. We show, without introducing additional matter fields or dust, that the
corresponding cosmological evolution averagely resembles, in the Jordan frame,
the familiar dark radiation -> dark matter -> dark energy domination sequence.
The fingerprints of our theory are fine ripples, hopefully testable, in the FRW
scale factor; they die away at the General Relativity limit. The possibility
that the Brans-Dicke scalar also serves as the inflaton is favorably examined.Comment: RevTex4, 12 pages, 5 figures; Minor revision, References adde
Buoyant Venus station mission feasibility study for 1972 and 1973 launch opportunities. Volume 3 - Configuration definition. Part 1 - Configuration Final report
Configuration definitions for buoyant Venus station missions for 1972 - 1973 launch perio
Neutron Star Properties with Hyperons
In the light of the recent discovery of a neutron star with a mass accurately
determined to be almost two solar masses, it has been suggested that hyperons
cannot play a role in the equation of state of dense matter in
-equilibrium. We re-examine this issue in the most recent development of
the quark-meson coupling model. Within a relativistic Hartree-Fock approach and
including the full tensor structure at the vector-meson-baryon vertices, we
find that not only must hyperons appear in matter at the densities relevant to
such a massive star but that the maximum mass predicted is completely
consistent with the observation.Comment: Minor correction
Integrability of the N-body problem in (2+1)-AdS gravity
We derive a first order formalism for solving the scattering of point sources
in (2+1) gravity with negative cosmological constant. We show that their
physical motion can be mapped, with a polydromic coordinate transformation, to
a trivial motion, in such a way that the point sources move as time-like
geodesics (in the case of particles) or as space-like geodesics (in the case of
BTZ black holes) of a three-dimensional hypersurface immersed in a
four-dimensional Minkowskian space-time, and that the two-body dynamics is
solved by two invariant masses, whose difference is simply related to the total
angular momentum of the system.Comment: 15 pages, LaTeX, no figure
Chern-Simons Modification of General Relativity
General relativity is extended by promoting the three-dimensional
gravitational Chern-Simons term to four dimensions. This entails choosing an
embedding coordinate v_\mu -- an external quantity, which we fix to be a
non-vanishing constant in its time component. The theory is identical to one in
which the embedding coordinate is itself a dynamical variable, rather than a
fixed, external quantity. Consequently diffeomorphism symmetry breaking is
hidden in the modified theory: the Schwarzschild metric is a solution;
gravitational waves possess two polarizations, each traveling at the velocity
of light; a conserved energy-momentum (pseudo-) tensor can be constructed. The
modification is visible in the intensity of gravitational radiation: the two
polarizations of a gravity wave carry intensities that are suppressed/enchanced
by the extension.Comment: 19 pages, added references, an addition in section
Radiatively Induced Lorentz and CPT Violation in Electrodynamics
In a nonperturbative formulation, radiative corrections arising from Lorentz
and CPT violation in the fermion sector induce a definite and nonzero
Chern-Simons addition to the electromagnetic action. If instead a perturbative
formulation is used, an infinite class of theories characterized by the value
of the Chern-Simons coefficient emerges at the quantum level.Comment: 4 page
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