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At least 613 records · Page 34

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NASA NTRS1971

A discussion of the ground-based radio observations

It is reasserted that the Gum nebula is not a single nebula but appears to be composed of several different entities. All the surveys of the southern sky in the continuum, recombination line, H I, and OH were considered. The large amount of high frequency radio emission from the small nebula is noted. The outer part of the Gum nebula has not been seen in any radio observations so far. Only the inner part has been observed to date. It is not justifiable to work out any parameters for the whole nebula by taking an average over the whole solid angle subtended by the big nebula. There appears to be a large difference in density between the small nebula and the big one.

Kerr, F. J.↗

NASA NTRS1977

Interpretation of observed cosmic microwave background radiation

It is argued that the 'surface of last scattering' of the observed microwave background radiation corresponds to the distribution of dust in galaxies or protogalaxies with a temperature of about 110 K at the epoch corresponding to Z roughly equal to 40. This is in contrast with the plasma temperature of over 3,000 K at an earlier epoch (Z greater than about 1,000), as given by the canonical model of big bang cosmologies. In view of this, the claim that the microwave background radiation lends strong support to hot big bang cosmologies is without foundation.

Alfven, H.↗

NASA NTRS1978

Local precision nets for monitoring movements of faults and large engineering structures

Along Bocono Fault were installed local high precision geodetic nets to observe the possible horizontal crustal deformations and movements. In the fault area there are few big structures which are also included in the mentioned investigation. In the near future, measurements shall be extended to other sites of Bocono Fault and also to the El Pilar Fault. In the same way and by similar methods high precision geodetic nets are applied in Venezuela to observe the behavior of big structures, as bridges and large dams and of earth surface deformations due to industrial activities.

Henneberg, H. G.↗

NASA NTRS1979

Helium synthesis, neutrino flavors, and cosmological implications

The problem of the production of helium in big bang cosmology is re-examined in the light of several recent astrophysical observations. These data, and theoretical particle physics considerations, lead to some important inconsistencies in the standard big bang model and suggest that a more complicated picture is needed. Thus, recent constraints on the number of neutrino flavors, as well as constraints on the mean density (openness) of the universe, need not be valid.

Stecker, F. W.↗

NASA NTRS1980

Helium synthesis, neutrino flavors, and cosmological implications

The problem of the production of helium in the big bang is reexamined in the light of several recent astrophysical observations. These data, and theoretical particle-physics considerations, lead to some important inconsistencies in the standard big-bang model and suggest that a more complicated picture is needed. Thus, recent constraints on the number of neutrino flavors, as well as constraints on the mean density (openness) of the universe, need not be valid.

Stecker, F. W.↗

NASA NTRS1982

Phase transitions and dynamics of the universe

The restoration of symmetry at grand unification in a closed contracting Robertson-Walker universe could slow down and halt the contraction, causing the universe to bounce and avoid the singular state or the big crunch. During subsequent expansion the symmetry is broken and the universe reverts back to its present state. A scenario is presented whereby the present entropy of the substance is created through a series of such bounces along with three possible initial states. The monopole, horizon, and flatness difficulties faced in ordinary Big Bang models are also solved by the model presented.

Petrosian, V.↗

NASA NTRS1982

Constraints on the density of baryons in the Universe

It is shown that it is possible to obtain a lower bound on the ratio of baryons to photons in the Universe, E, from Big Bang nucleosynthesis through the use of He-3 and deuterium, and that this limit is consistent with the Li-7 abundance. It is shown that this limit places very narrow bounds on the allowed value for E, thus tightly constraining the neutrino limits to no more than four species. The derived constraints are that E must be between 1.5 x 10 to the -10 and 7 x 10 to the -9 with a best fit between 3 and 6 x 10 to the -10. With reference to dark matter, the derived baryon density for Big Bang nucleosynthesis corresponds very closely with the implied density of matter in binaries and small groups of galaxies, implying that nonbaryonic matter is not dominant by a large factor on scales as large as binaries and small groups of galaxies.

Schramm, D. N.↗

NASA NTRS1982

Nuclear constraints on the age of the universe

A review is made of how one can use nuclear physics to put rather stringent limits on the age of the universe and thus the cosmic distance scale. The age can be estimated to a fair degree of accuracy. No single measurement of the time since the Big Bang gives a specific, unambiguous age. There are several methods that together fix the age with surprising precision. In particular, there are three totally independent techniques for estimating an age and a fourth technique which involves finding consistency of the other three in the framework of the standard Big Bang cosmological model. The three independent methods are: cosmological dynamics, the age of the oldest stars, and radioactive dating. This paper concentrates on the third of the three methods, and the consistency technique.

Schramm, D. N.↗

NASA NTRS1983

Spatial reasoning to determine stream network from LANDSAT imagery

In LANDSAT imagery, spectral and spatial information can be used to detect the drainage network as well as the relative elevation model in mountainous terrain. To do this, mixed information of material reflectance in the original LANDSAT imagery must be separated. From the material reflectance information, big visible rivers can be detected. From the topographic modulation information, ridges and valleys can be detected and assigned relative elevations. A complete elevation model can be generated by interpolating values for nonridge and non-valley pixels. The small streams not detectable from material reflectance information can be located in the valleys with flow direction known from the elevation model. Finally, the flow directions of big visible rivers can be inferred by solving a consistent labeling problem based on a set of spatial reasoning constraints.

Haralick, R. M.↗

NASA NTRS1983

Nuclear constraints on the age of the universe

Schramm, D. N.↗

NASA NTRS1985

Sulfur cycling and metabolism of phototrophic and filamentous sulfur bacteria

Phototrophic sulfur bacteria taken from different habitate (Alum Rock State Park, Palo Alto salt marsh, and Big Soda Lake) were grown on selective media, characterized by morphological and pigment analysis, and compared with bacteria maintained in pure culture. A study was made of the anaerobic reduction of intracellular sulfur globules by a phototrophic sulfur bacterium (Chromatium vinosum) and a filamentous aerobic sulfur bacterium (Beggiatoa alba). Buoyant densities of different bacteria were measured in Percoll gradients. This method was also used to separate different chlorobia in mixed cultures and to assess the relative homogeneity of cultures taken directly or enriched from natural samples (including the purple bacterial layer found at a depth of 20 meters at Big Soda Lake.) Interactions between sulfide oxidizing bacteria were studied.

Guerrero, R.↗

NASA NTRS1988

Primordial lithium - New reaction rates, new abundances, new constraints

Newly measured nuclear reaction rates for H-3(alpha, gamma)Li-7 (higher than previous values) and Li-7(p, alpha)He-4 (lower than previous values) are shown to increase the Li-7 yield from big band nucleosynthesis for lower baryon-to-photon ratio (less than about 4 x 10 to the 10th). Recent revisions in the He-3(alpha, gamma)Be-7 and the D(p, gamma)He-3 rates enhance the high (greater than 4 x 10 to the 10th) Li-7(Be) production. New, independent determinations of Li abundances in extreme population II stars are in excellent agreement with the work of Spites and give continued confidence in the use of Li-7 in big bang baryon density determinations.

Kawano, Lawrence↗

NASA NTRS1989

Primordial lithium and the standard model(s)

The results of new theoretical work on surface Li-7 and Li-6 evolution in the oldest halo stars are presented, along with a new and refined analysis of the predicted primordial Li abundance resulting from big-bang nucleosynthesis. This makes it possible to determine the constraints which can be imposed on cosmology using primordial Li and both standard big-bang and stellar-evolution models. This leads to limits on the baryon density today of 0.0044-0.025 (where the Hubble constant is 100h km/sec Mpc) and imposes limitations on alternative nucleosynthesis scenarios.

Deliyannis, Constantine P.↗

NASA NTRS1989

Cosmology and the weak interaction

The weak interaction plays a critical role in modern Big Bang cosmology. Two of its most publicized comological connections are emphasized: big bang nucleosynthesis and dark matter. The first of these is connected to the cosmological prediction of neutrine flavors, N(sub nu) is approximately 3 which in now being confirmed. The second is interrelated to the whole problem of galacty and structure formation in the universe. The role of the weak interaction both for dark matter candidates and for the problem of generating seeds to form structure is demonstrated.

Schramm, David N.↗

NASA NTRS1990

A VLSI decomposition of the deBruijn graph

A new Viterbi decoder for convolutional codes with constraint lengths up to 15, called the Big Viterbi Decoder, is under development for the Deep Space Network. It will be demonstrated by decoding data from the Galileo spacecraft, which has a rate 1/4, constraint-length 15 convolutional encoder on board. Here, the mathematical theory underlying the design of the very-large-scale-integrated (VLSI) chips that are being used to build this decoder is explained. The deBruijn graph B sub n describes the topology of a fully parallel, rate 1/v, constraint length n+2 Viterbi decoder, and it is shown that B sub n can be built by appropriately wiring together (i.e., connecting together with extra edges) many isomorphic copies of a fixed graph called a B sub n building block. The efficiency of such a building block is defined as the fraction of the edges in B sub n that are present in the copies of the building block. It is shown, among other things, that for any alpha less than 1, there exists a graph G which is a B sub n building block of efficiency greater than alpha for all sufficiently large n. These results are illustrated by describing a special hierarchical family of deBruijn building blocks, which has led to the design of the gate-array chips being used in the Big Viterbi Decoder.

Collins, O.↗

NASA NTRS1989

Weak bump quasars

The recent emphasis on big bumps dominating the UV continuum of quasars has obscured the facts that bump properties vary widely and that there are objects in which no such component is evident. As part of a survey of quasar continuum spectra, a class of quasars is identified in which the optical-UV continuum big bump feature appears to be weak or absent, relative to both IR and X-ray. These weak bump quasars are otherwise normal objects and constitute a few percent of the quasar population.

Mcdowell, Jonathan C.↗

NASA NTRS1990

The Cosmic Background Explorer

The Cosmic Background Explorer (CBE), NASA's cosmological satellite which will observe a radiative relic of the big bang, is discussed. The major questions connected to the big bang theory which may be clarified using the CBE are reviewed. The satellite instruments and experiments are described, including the Differential Microwave Radiometer, which measures the difference between microwave radiation emitted from two points on the sky, the Far-Infrared Absolute Spectrophotometer, which compares the spectrum of radiation from the sky at wavelengths from 100 microns to one cm with that from an internal blackbody, and the Diffuse Infrared Background Experiment, which searches for the radiation from the earliest generation of stars.

Gulkis, Samuel↗

NASA NTRS1991

Oxygen production on Mars: A figure-of-merit approach

A new approach is described toward evaluating the overall system performance in space missions; the objective is to demonstrate a new quantitative tool that can effectively synthesize and display the big picture. It considers a large number of individual components and factors that influence the big picture. The approach was found to be valuable in evaluating various options that must be considered in choosing one or more final ones. The application is especially suited to evaluate missions that consider ISRU. The Figure-of-Merit (FoM) can be different for different missions. In fact, it should be different for different priorities. Simple mass at launch, mass at the moment of departure from LEO, the payback time, the mass returned to LEO, the overall life-cycle costs, etc. are possible indicators of the FoM. After mentioning all of these possible definitions, the FoM for various historical missions will be presented. The FoM of a simple Mars Sample Return (MSR) mission is next presented. It is shown that the FoM is not only higher for missions employing ISRU, but that even among ISRU missions, several mundane propellant combinations are more desirable than the highest-performance propellants.

Preiss, Bruce↗