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At least 559 records · Page 31

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NASA NTRS1979

The kW power module evolution study: Executive summary

Using the Marshall Space Flight Center 25 kW Power Module (PM) reference design as a point of departure, the study defined evolutionary growth paths to 100 kW and above. A recommended development approach and initial configurations were described. Specific hardware changes from the reference design are recommended for the initial PM configuration to ensure evolutionary growth, improved replicability, and reduced cost. Certain functional changes are also recommended to enhance system capabilities.

Source record↗

NASA NTRS1979

Evolutional schemes for objects with active nuclei

The observational properties of quasistellar objects (QSO) reveal that they are extremely violent nuclei of distant galaxies, but the evolutionary stage of these galaxies is still undetermined. Various published attempts to classify QSO under different criteria - including the one based on the morphological type of the surrounding galaxy E- or S- are analyzed. There are evidences that radioactive quasars reside in E-, while radio-quiet quasars reside in both E- and S- systems. The latter may be evolutionary connected to Seyfert-like objects. A correlation between the nuclei activity level in systems of different morphological type and the relative amount of gas in them is noted. From the point of view of activity level and the duration of active stage of nuclei it is concluded that an interaction of galaxies with the intergalactic medium is of particular importance and must be most conspicuous in spheriodal systems of central regions of rich clusters, in tight groups and binary galaxies.

Komberg, B. V.↗

NASA NTRS1978

Bump Cepheids - The mass anomaly as an opacity effect

Nonlinear calculations of models for bump Cepheids indicate that most of the basic features of these stars can be reproduced well by models having normal to nearly normal evolutionary masses and normal helium abundances, if Carson's opacities are adopted. The trends of the properties of the models with various physical parameters are otherwise very similar to those obtained by other authors with the Los Alamos opacities (which have led to Cepheid masses of half the evolutionary masses). Difficulties with the resonance hypothesis of Simon and Schmidt as an explanation of the bump are discussed.

Sastri, V. K.↗

NASA NTRS1978

The REH theory of protein and nucleic acid divergence - A retrospective update

The random evolutionary hits (REH) theory of evolutionary divergence, originally proposed in 1972, is restated with attention to certain aspects of the theory that have caused confusion. The theory assumes that natural selection and stochastic processes interact and that natural selection restricts those codon sites which may fix mutations. The predicted total number of fixed nucleotide replacements agrees with data for cytochrome c, a-hemoglobin, beta-hemoglobin, and myoglobin. The restatement analyzes the magnitude of possible sources of errors and simplifies calculational methodology by supplying polynomial expressions to replace tables and graphs.

Holmquist, R.↗

NASA NTRS1979

Discovery of X-ray emission from two southern supernova remnants

Two soft X-ray sources positionally coincident with the supernova remnants PKS 1209-52 and RCW 103 have been discovered by using the A-2 experiment on HEAO 1. Their measured fluxes are, respectively, about 1.4 x 10 to the -10th erg/cm-sec (0.2-1.0 keV) and about 1.8 x 10 to the -10th erg/cm-sec (0.6-2.0 keV). Spectral data are used to derive physical parameters for each remnant. For PKS 1209-52 the parameters are suggestive of the remnant's being in an advanced evolutionary phase, with shock-heated interstellar material producing the soft X-ray emission. RCW 103, in contrast, is known from radio and optical data to be in an earlier evolutionary phase, and the soft X-ray flux is most likely due to emission originating in a reflected shock wave or in plasma evaporated from shock-heated interstellar clouds.

Tuohy, I. R.↗

NASA NTRS1979

Stellar evolution from the zero-age main sequence

A consistent set of 247 evolutionary sequences extending from the ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40, Z from 0.00001 to 0.10, and masses of 0.55 to 6.90 solar masses. Each sequence is started from a homogeneous ZAMS model, and almost all are evolved to the base of the red-giant branch. It is shown that: (1) the relative position of the main sequence can be determined as a function of composition; (2) theoretical luminosity functions can be derived from the relative evolutionary time scales; (3) a dip in luminosity sometimes occurs at the base of the red-giant branch and is most pronounced at larger Z values; (4) metal-poor stars evolve farther up along the main sequence before turning off toward the red-giant branch; and (5) the onset of helium burning halts the evolution across the Hertzsprung gap for the most massive and most metal-poor models, so that the star remains blue during its phase of core-helium burning.

Mengel, J. G.↗

NASA NTRS1979

25 kW power module evolution study

This paper presents a study of evolutionary growth concepts for the 25 kW power module to augment STS mission support future capabilities. The study aimed to establish user payload requirements, define evolution methods for system initial operational capability, and formulate a development program and conceptual designs. The payload requirements analysis focused on material processing in space, public services, and solar terrestrial observations; evolutionary system concepts were evaluated to derive the power module and system support requirements, and four reference orbits were used to construct the nominal program scenario. The mission accomodations analysis evaluated the capability of the nominal program scenario and associated power module concepts to meet user needs. Finally, the recommended modular design consisting of electric power, attitude control, thermal control, and command and data handling is described, and it is concluded that the 25 kW power module is a logical first step to support the near term NASA sortie and free-flyer mission requirements.

Overall, J. W., Jr.↗

NASA NTRS1980

From inanimate matter to living systems

Since the early part of this century, the Genesis account of the origin and evolution of life has been explained as an extrapolation of astronomical and geochemical processes. The essence of the answer to date is a protoreproductive protocell of much biochemical and cytophysical competance. The processes of its origin, molecular ordering, and its functions are described. A crucial understanding is that of the nonrandomness of evolutionary processes at all stages (with perhaps a minor statistical component). In this way, evolution conflicts with statistical randomness; the latter is a favorite assumption of both scientific and creationistic critics of the proteinoid theory. The principle contribution of the proteinoid theory to the understanding of general biology is to particularize the view that evolutionary direction is rooted in the shapes of molecules, in stereochemistry. After molecules of the right kind first assembled to protocells, life in its various stages of evolution was an inevitable consequence. It is molecules that continue to assemble as part of living process and, in the role of enzymes, continue to direct life cycle of the cell.

Fox, S. W.↗

NASA NTRS1980

Structure and evolution of Uranus and Neptune

Three-layer interior models of Uranus and Neptune with central rocky cores, mantles of water, methane, and ammonia (the 'ices'), and outer envelopes primarily composed of hydrogen and helium are presented. The models incorporate a new H2O equation of state based on experimental data which is considerably 'softer' than previous H2O equations of state. Corrections for interior temperatures approximately 5000 K are included in the models, and the thermal evolution of both planets is investigated using recent heat flow measurements. It is found that the evolutionary considerations are consistent with gravitational field data in supporting models with approximately solar abundances of 'ice' and 'rock'. Evolutionary considerations indicate that initial temperatures and luminosities for Uranus and Neptune were not substantially higher than the present value. Both planets apparently have relatively small approximately 1-2 earth masses) hydrogen-helium envelopes, with Neptune's envelope smaller than Uranus'. A monotonic trend is evident among the Jovian planets: all have central rock-ice cores of approximately 15 earth masses, but with hydrogen-helium envelopes which decrease in mass from Jupiter to Saturn to Uranus to Neptune.

Hubbard, W. B.↗

NASA NTRS1980

Vehicle expectations in air transportation for the year 2000

This paper is intended to provide an overview of the air transportation system for the year 2000 in terms of vehicle expectations. Emphasis is placed on civil air transportation with the time period approached from the standpoint of evolutionary changes for the near term and also with the assumption of more revolutionary changes for the far term. The view along the evolutionary path begins with a historical review of airline market growth and the impact that technologies have had on airplane designs. Projections of the life expectancy of existing, derivative, and new airplanes are examined in terms of their productivity and fuel efficiency in view of the present and projected fuel usage and availability. The factors influencing airline growth are outlined and some views on whether another new generation of subsonic airplanes are in the offing are given along with an assessment of the economic viability of an advanced commercial supersonic transport in terms of its higher speed, higher productivity, and higher fuel usage. With regard to revolutionary changes, major technology breakthroughs are assumed to occur at a specified date. As an example, the impact of a dramatic reduction in skin friction drag is examined in terms of its effect on the airplane configuration, its propulsion systems, it projected fuel usage, and the air transportation system in which it must operate.

Hearth, D. P.↗

NASA NTRS1980

Influence of a stellar wind on the evolution of a star of 30 solar masses

A coarse grid of theoretical evolutionary tracks was calculated for a 30 solar mass star to determine the role of mass loss in the evolution of the star during core He burning. The Cox-Stewart opacities were applied, and the rate of mass loss, criterion for convection, and initial chemical composition were taken into consideration. Using the Schwarzschild criterion, the star undergoes little mass loss during core He burning and remains a blue supergiant separated from main sequence stars on the H-R diagram. The stellar remnant consists of the original He core and may appear bluer than equally luminous main sequence stars; a variety of possible evolutionary tracks can be obtained for an initial solar mass of 30 with proper choices of free parameters.

Stothers, R.↗

NASA NTRS1980

The structure and evolution of X-ray clusters of galaxies

Einstein Observatory observations of the structures of nearby X-ray clusters of galaxies are discussed in relation to dynamic cluster evolution. Examples of Virgo-type clusters, in which cool and hot gas associated with cluster members are presented and variations in surface brightness profile and the location of the cluster center are used to classify the observed clusters. The types of clusters observed are interpreted in terms of dynamic cluster evolution, with Virgo-type clusters with broad, highly clumped emission and low velocity dispersion representing early evolutionary stages, clusters containing a cD galaxy formed as the cluster evolves, and clusters with dominant galaxies and Coma-type clusters representing an equilibrium stage. X-ray emission from poor clusters of galaxies is also considered, and similarities between the presumably collisionally formed cD galaxies in rich and poor clusters are noted. Finally, observations of distant clusters are discussed, and it is noted that their analysis will lead to a better determination of the evolutionary sequence.

Jones, C.↗

NASA NTRS1981

Einstein imaging observations of clusters of galaxies

X-ray observations suggest a broad division between clusters having a centrally-located, X-ray dominant galaxy characterized by a centrally-peaked X-ray emission, and clusters with a broader X-ray profile. Within these categories, such evolutionary indicators as X-ray temperature, vorticity dispersion, spiral fraction and central galaxy density may indicate the relative stages of evolution. X-ray imaging observations are presented for (1) the Virgo cluster, (2) other dynamically unevolved clusters, (3) double clusters which may be in an intermediate evolutionary stage, and (4) dynamically evolved clusters. The data are analyzed under the assumption of an isothermal X-ray gas which is gravitationally bound by galaxies and clusters.

Forman, W.↗

NASA NTRS1982

Concepts for large interferometers in space

Very high angular resolution can be achieved in optical and radio astronomy through interferometers in space. Evolutionary approaches and required technological advances are presented. In the optical region a phase-coherent array, (COSMIC) starting as a four-element linear array is discussed. Combining several modules results in greatly improved resolution with a goal of combining images to obtain a single field of view with 0.004 arcsecond resolution. The angular resolution, detail and temporal coverage of radio maps obtained by ground-based Very Long Interferometry (VLBI) can be greatly improved by placing one of the stations in earth orbit. An evolutionary program leading to a large aperture VLBI observatory in space is discussed.

Morgan, S. H.↗

NASA NTRS1983

From dwarfs to giants - Signposts of galaxy formation

A two-dimensional parametrization of galactic evolution from the primordial state involving mean surface density and velocity dispersion is presented. A dissipation diagram for large-scale structure is presented and its evolutionary significance explored while considering both the pancake and the hierarchical clustering models of galaxy formation. Gaseous dissipation is studied by assuming that individual clouds or turbulent elements of gas interact supersonically, producing strong shocks. It is found that many diverse properties of galaxies can be understood in terms of an evolutionary sequence operative during an early gas-rich protogalactic phase in which dissipation played a key role. Dwarf galaxies may be the fossilized link between primordial fluctuations and the giant galaxies observed today, relics of a past era of prolific galaxy formation.

Silk, J.↗

NASA NTRS1984

Interior structure of Uranus

Key measurements are discussed which are diagnostic of Uranus' interior structure and evolutionary history, and reviews their present status. Typical interior models have chondritic cores, but have the bulk of their mass in an envelope consisting of ice component, principally H2O. The total amount of free H2 in the planet cannot exceed approximately 1 to 2 earth masses. Measurements of the gravitational moments of Uranus are beginning to be accurate enough to constrain models, but are limited in utility by uncertainty in the rotation period. Discussed is evidence that the outermost planetary layers have a gravitationally significant quantity of denser material (ice component?) in addition to H2 and He. The He/H ratio and the deuterium abundance in the atmosphere may be diagnostic of the planet's previous evolutionary history. It is argued that the planet's interior is likely to now be at a temperature approximately 10(3) deg K. Uranus' interior with Neptune's in a number of ways, considering heat flow, degree of internal differentiation, and possible magnetic field.

Hubbard, W. B.↗

NASA NTRS1985

A survey of unified constitutive theories

The state of the art of time temperature dependent elastic viscoplastic constitutive theories which are based on the unified approach werre assessed. This class of constitutive theories is characterized by the use of kinetic equations and internal variables with appropriate evolutionary equations for treating all aspects of inelastic deformation including plasticity, creep, and stress relaxation. More than 10 such unified theories which are shown to satisfy the uniqueness and stability criteria imposed by Drucker's postulate and Ponter's inequalities are identified. The theories are compared for the types of flow law, kinetic equation, evolutionary equation of the internal variables, and treatment of temperature dependence. The similarities and differences of these theories are outlined in terms of mathematical formulations and illustrated by comparisons of theoretical calculations with experimental results which include monotonic stress-strain curves, cyclic hysteresis loops, creep and stress relaxation rates, and thermomechanical loops. Numerical methods used for integrating these stiff time temperature dependent constitutive equations are reviewed.

Chan, K. S.↗

NASA NTRS1985

On the nature of the companion to Van Biesbroeck 8

Results of the first numerical evolutionary calculations for very low-mass stars with ages up to the age of the Galaxy are presented. The calculations shed new light on the nature of the recently discovered object VB 8B, the companion to Van Biesbroeck's star no. 8, and support the identification of this object as a low-mass star in which hydrogen burning was never able to establish thermal equilibrium. For plausible ages of this binary stellar system, the mass of VB 8B is estimated to be in the range 0.04-0.08 solar mass. The object is supported primarily by degenerate electron pressure; its present values of central density and temperature are found to be 500-2000 g/cu cm and 1.0-1.5 million K. An orbital period of more than about 40 yr is predicted for the binary system. The presented evolutionary tracks are also applicable to the interpretation of observations of other very low-luminosity dwarfs.

Nelson, L. A.↗