4,752 research outputs found
Space-suit carbon dioxide absorption system: A concept
Partial pressure of carbon dioxide within a space suit is maintained at safe levels by regenerating carbon dioxide with potassium hydroxide solution on board spacecraft or by portable units
Advanced Extravehicular Protective Systems (AEPS) study
A description is given of life support subsystem concepts for advanced extravehicular protective systems (AEPS) intended for use on future orbital, lunar surface, and Mars surface missions in the late 1970's and 1980's. Primary interest was centered around the thermal control and carbon dioxide control subsystems because they offer the greatest potential for total weight savings. Emphasis was placed on the generation of regenerable subsystem concepts; however, partially regenerable and expendable concepts were also considered. Previously conceived and developed subsystem concepts were included in the study. Concepts were evaluated on the basis of subsystem weight and volume, and subsystem contribution to parent vehicle weight and volume, which included spares, regeneration equipment, expendables, expandables storage penalty, power penalty, and process heating or cooling penalty. Results are presented showing total weight and volume penalty as a function of total mission extravehicular activity (EVA) hours, and showing EVA weight and volume as a function of EVA duration. Subsystem concepts are recommended for each life support function, and secondary concepts which should be developed are also identified
Regenerable thermal control and carbon dioxide control techniques for use in advanced extravehicular protective systems
The most promising closed CO2 control concept identified by this study is the solid pellet, Mg(OH2)2 system. Two promising approaches to closed thermal control were identified. The AHS system uses modular fusible heat sinks, with a contingency evaporative mode, to allow maximum EVA mobility. The AHS/refrigerator top-off subsystem requires an umbilical to minimize expendables, but less EVA time is used to operate the system, since there is no requirement to change modules. Both of these subsystems are thought to be practical solutions to the problem of providing closed heat rejection for an EVA system
Constraints on string networks with junctions
We consider the constraints on string networks with junctions in which the
strings may all be different, as may be found for example in a network of
cosmic superstrings. We concentrate on three aspects of junction
dynamics. First we consider the propagation of small amplitude waves across a
static three-string junction. Then, generalizing our earlier work, we determine
the kinematic constraints on two colliding strings with different tensions. As
before, the important conclusion is that strings do not always reconnect with a
third string; they can pass straight through one another (or in the case of
non-abelian strings become stuck in an X configuration), the constraint
depending on the angle at which the strings meet, on their relative velocity,
and on the ratios of the string tensions. For example, if the two colliding
strings have equal tensions, then for ultra-relativistic initial velocities
they pass through one another. However, if their tensions are sufficiently
different they can reconnect. Finally, we consider the global properties of
junctions and strings in a network. Assuming that, in a network, the incoming
waves at a junction are independently randomly distributed, we determine the
r.m.s. velocities of strings and calculate the average speed at which a
junction moves along each of the three strings from which it is formed. Our
findings suggest that junction dynamics may be such as to preferentially remove
the heavy strings from the network leaving a network of predominantly light
strings. Furthermore the r.m.s. velocity of strings in a network with junctions
is smaller than 1/\sqrt{2}, the result for conventional Nambu-Goto strings
without junctions in Minkowski spacetime.Comment: 12 pages, 6 figures. Version to appear in PRD. (2 new references and
slightly extended discussion in section VII
Reheating and gravitino production in braneworld inflation
We consider the constraints that can be imposed on a wide class of Inflation
models in modified gravity scenarios in which the Friedmann equation is
modified by the inclusion of terms, where is the total energy
density. In particular we obtain the reheating temperature and gravitino
abundance associated with the end of inflation. Whereas models of chaotic
inflation and natural inflation can easily avoid the conventional gravitino
overproduction problem, we show that supersymmetric hybrid inflation models
(driven by both F and D-terms) do not work in the dominated era. We
also study inflation driven by exponetial potentials in this modified
background, and show that the gravitino production is suppressed enough to
avoid there being a problem, although other conditions severely constrain these
models.Comment: 24page
Topological defects in extended inflation
The production of topological defects, especially cosmic strings, in extended inflation models was considered. In extended inflation, the Universe passes through a first-order phase transition via bubble percolation, which naturally allows defects to form at the end of inflation. The correlation length, which determines the number density of the defects, is related to the mean size of bubbles when they collide. This mechanism allows a natural combination of inflation and large scale structure via cosmic strings
Research approaches to alleviation of airport-community noise
Airport-community noise reduction problem
On the reliability of inflaton potential reconstruction
If primordial scalar and tensor perturbation spectra can be inferred from
observations of the cosmic background radiation and large-scale structure, then
one might hope to reconstruct a unique single-field inflaton potential capable
of generating the observed spectra. In this paper we examine conditions under
which such a potential can be reliably reconstructed. For it to be possible at
all, the spectra must be well fit by a Taylor series expansion. A complete
reconstruction requires a statistically-significant tensor mode to be measured
in the microwave background. We find that the observational uncertainties
dominate the theoretical error from use of the slow-roll approximation, and
conclude that the reconstruction procedure will never insidiously lead to an
irrelevant potential.Comment: 16 page LaTeX file with eight postscript figures embedded with epsf;
no special macros neede
Reconstructing the Inflaton Potential
A review is presented of recent work by the authors concerning the use of
large scale structure and microwave background anisotropy data to determine the
potential of the inflaton field. The importance of a detection of the
stochastic gravitational wave background is emphasised, and some preliminary
new results of tests of the method on simulated data sets with uncertainties
are described. (Proceedings of ``Unified Symmetry in the Small and in the
Large'', Coral Gables, 1994)Comment: 13 pages, uuencoded postscript file with figures included (LaTeX file
available from ARL), FERMILAB-Conf 94/189
Noise study of single stage compressor rotor-stator interaction
Study made of noise radiation from rotor-stator interaction in axial-flow compressors. The collected data were reduced to the form of radiation patterns and frequency spectra. These data show how the radiation patterns are affected by the relative number of rotor blades and stator vanes
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