7,408 research outputs found
Rat body size, composition and growth at hypo- and hypergravity
The effects of hypergravity (centrifugation) on body composition were investigated. Hypogravitational and hypergravitational aspects were reflected in the research effort. A list of publications is provided
Performance analysis of advanced spacecraft TPS
The analysis on the feasibility for using metal hydrides in the thermal protection system of cryogenic tanks in space was based on the heat capacity of ice as the phase change material (PCM). It was found that with ice the thermal protection system weight could be reduced by, at most, about 20 percent over an all LI-900 insulation. For this concept to be viable, a metal hydride with considerably more capacity than water would be required. None were found. Special metal hydrides were developed for hydrogen fuel storage applications and it may be possible to do so for the current application. Until this appears promising further effort on this feasibility study does not seem warranted
Transit Thermal Control Design for Galileo Entry Probe for Planet Jupiter
A totally passive design was completed for the thermal control of the Galileo entry probe during its transit to the planet Jupiter. The design utilizes radio isotope heater units, multilayer insulation blankets and a thermal radiator in conjunction with a design conductance support structure to achieve both the required storage and critical initial planet atmosphere entry temperatures. The probe transit thermal design was completed and verified based on thermal vacuum testing of a prototype probe thermal test model
Improved molecular sorbent trap for high-vacuum systems
Closed cycle refrigeration loop in which trays holding molecular sorbent are made to serve as cooling baffles improves the performance of high vacuum systems. High performance is obtained with almost no decrease in pumping speed
Null Cones in Lorentz-Covariant General Relativity
The oft-neglected issue of the causal structure in the flat spacetime
approach to Einstein's theory of gravity is considered. Consistency requires
that the flat metric's null cone be respected, but this does not happen
automatically. After reviewing the history of this problem, we introduce a
generalized eigenvector formalism to give a kinematic description of the
relation between the two null cones, based on the Segre' classification of
symmetric rank 2 tensors with respect to a Lorentzian metric. Then we propose a
method to enforce special relativistic causality by using the naive gauge
freedom to restrict the configuration space suitably. A set of new variables
just covers this smaller configuration space and respects the flat metric's
null cone automatically. In this smaller space, gauge transformations do not
form a group, but only a groupoid. Respecting the flat metric's null cone
ensures that the spacetime is globally hyperbolic, indicating that the Hawking
black hole information loss paradox does not arise.Comment: groupoid nature of gauge transformations explained; shortened, new
references, 102 page
Null Cones and Einstein's Equations in Minkowski Spacetime
If Einstein's equations are to describe a field theory of gravity in
Minkowski spacetime, then causality requires that the effective curved metric
must respect the flat background metric's null cone. The kinematical problem is
solved using a generalized eigenvector formalism based on the Segr\'{e}
classification of symmetric rank 2 tensors with respect to a Lorentzian metric.
Securing the correct relationship between the two null cones dynamically
plausibly is achieved using the naive gauge freedom. New variables tied to the
generalized eigenvector formalism reduce the configuration space to the
causality-respecting part. In this smaller space, gauge transformations do not
form a group, but only a groupoid. The flat metric removes the difficulty of
defining equal-time commutation relations in quantum gravity and guarantees
global hyperbolicity
Light Cone Consistency in Bimetric General Relativity
General relativity can be formally derived as a flat spacetime theory, but
the consistency of the resulting curved metric's light cone with the flat
metric's null cone has not been adequately considered. If the two are
inconsistent, then gravity is not just another field in flat spacetime after
all.
Here we discuss recent progress in describing the conditions for consistency
and prospects for satisfying those conditions.Comment: contribution to the Proceedings of the 20th Texas Symposium on
Relativistic Astrophysics; 3 pages, 1 figur
Two force component measuring device Patent
Development of two force component measuring devic
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