5,011 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
Transition probabilities in OH A 2 sigma + - X 2 pi i: Bands with v prime = 0 and 1, v double prime = 0 to 4
Experimental results for relative vibrational band transition probabilities for v prime = 0 and 1, and v double prime = 0 to 4 in the A-X electronic system of OH are presented. The measurements, part of a larger set involving v prime = 0 to 4 and v double prime = 0 to 6, were made using spectrally dispersed laser-induced fluorescence (LIF) in the burnt gases of a flame. These Einstein coefficients will be useful in dynamics experiments for quantitative LIF determinations of OH radical concentrations in high v double prime
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
Cosmological perturbation spectra from SL(4,R)-invariant effective actions
We investigate four-dimensional cosmological vacuum solutions derived from an
effective action invariant under global SL(n,R) transformations. We find the
general solutions for linear axion field perturbations about homogeneous
dilaton-moduli-vacuum solutions for an SL(4,R)-invariant action and find the
spectrum of super-horizon perturbations resulting from vacuum fluctuations in a
pre big bang scenario. We show that for SL(n,R)-invariant actions with n>3
there exists a regime of parameter space of non-zero measure where all the
axion field spectra have positive spectral tilt, as required if light axion
fields are to provide a seed for anisotropies in the microwave background and
large-scale structure in the universe.Comment: 8 pages, 3 figures, revtex plus epsf, minor typos corrected, version
to appear in Physical Review
Noise characteristics of the O-1 airplane and some approaches to noise reduction
A brief study of the O-1A airplane to determine possible means for reducing the aircraft aural detection distance was conducted. This effort involved measuring the noise signature of the basic airplane, devising methods to attenuate the noise, and then estimating the effect of several selected modifications on the aural detection distance of the aircraft. A relatively simple modification utilizing a 6.5 ft diameter, six-blade propeller and including a muffler having a volume of 0.725 cu ft is indicated to reduce the aural detection distance of the O-1 aircraft from about 6 miles at an altitude of 1,000 ft and 2 to 3 miles at an altitude of 300 ft to approximately half these values. The flyover noise data suggest that routing the exhaust stacks up and over the wing would provide immediate noise reduction of about 5 dB with an attendant reduction in detection distance. Furthermore, all these studies confirm the work of other investigators that the 1/3 octave band (center frequency=125 cps) is the most critical in reducing aural detection distance
Kinematic Constraints on Formation of Bound States of Cosmic Strings - Field Theoretical Approach
Superstring theory predicts the potential formation of string networks with
bound states ending in junctions. Kinematic constraints for junction formation
have been derived within the Nambu-Goto thin string approximation. Here we test
these constraints numerically in the framework of the Abelian-Higgs model in
the Type-I regime and report on good agreement with the analytical predictions.
We also demonstrate that strings can effectively pass through each other when
they meet at speeds slightly above the critical velocity permitting bound state
formation. This is due to reconnection effects that are beyond the scope of the
Nambu-Goto approximation.Comment: 6 pages, 12 eps figures - matches the published versio
Dynamical Stability of Witten Rings
The dynamical stability of cosmic rings, or vortons, is investigated for the
particular equation of state given by the Witten bosonic model. It is found
that there exists a finite range of the state parameter for which the vorton
states are actually stable against dynamical perturbations. Inclusion of the
electromagnetic self action into the equation of state slightly shrinks the
stability region but otherwise yields no qualitative difference. If the Witten
bosonic model represents a good approximation for more realistic string models,
then the cosmological vorton excess problem can only be solved by assuming
either that strings are formed at low energy scales or that some quantum
instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP
R-94/1
Collisions of strings with Y junctions
We study the dynamics of Nambu--Goto strings with junctions at which three
strings meet. In particular, we exhibit one simple exact solution and examine
the process of intercommuting of two straight strings, in which they exchange
partners but become joined by a third string. We show that there are important
kinematical constraints on this process. The exchange cannot occur if the
strings meet with very large relative velocity. This may have important
implications for the evolution of cosmic superstring networks and non-abelian
string networks.Comment: 4 pages, 1 figure, uses revtex 4. Clarifying comments added to
correct a conceptual error, reference updated. Version accepted by Phys Rev
Letters, with additional references and minor change
Anisotropic String Cosmology at Large Curvatures
We study the effect of the antisymmetric tensor field on the
large curvature phase of string cosmology. It is well-known that a
non-vanishing value of leads to an anisotropic expansion of the spatial
dimensions. Correspondingly, in the string phase of the model, including
corrections, we find anisotropic fixed points of the evolution,
which act as regularizing attractors of the lowest order solutions. The
attraction basin can also include isotropic initial conditions for the scale
factors. We present explicit examples at order for different values
of the number of spatial dimensions and for different ans\"{a}tze for .Comment: 16 pages, Latex, 2 figure
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