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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Death throes of massive stars

The data regarding the optical outburst in the case of the formation of a type II supernova are incomplete in the sense that supernovae are invariably discovered at or shortly after peak optical intensity so only the decline from maximum brightness has been recorded in any detail. The possibility of an observation of the preceding part of the optical intensity curve, would be greatly facilitated if the occurrence of a supernova could be predicted on the basis of the presupernova behavior of the star. It is shown that neutrino emission in the final stages of nuclear burning could, in principle, provide such a warning, though the current limitations are severe. The reported results are based on a study of the final stages of evolution of a 15-solar mass star.

Sofia, S.↗
NASA NTRS1984

Rodent CNS neuron development: Timing of cell birth and death

Data obtained from a staged series of single paired injections of tritiated thymidine to pregnant Wistar rats or C57B16/j mice on selected embryonic days and several postnatal times are reported. All injected specimens were allowed to come to term, each litter culled to six pups and specimens were sacrificed on PN28, with fixation and embedding for paraffin and plastic embedding. The results are derived from serial paraffin sections of PN28 animals exposed to autoradiographic processing and plotted with respect to heavily labelled cell nuclei present in the selected brain stem nuclei and sensory ganglia. Counts from each time sample/structure are totalled and the percentage of cells in the total labelled population/structure represented by each injection time interval plotted.

Keefe, J. R.↗
NASA NTRS1986

SN 1985f - Death of a Wolf-Rayet star

The optical spectrum of SN 1985f has been analyzed, and the supernova ejecta is shown to contain approximately 5 or more solar masses of oxygen and very little hydrogen. It is suggested that the explosion resulted from the pair instability supernova of a WO Wolf-Rayet star of about 50 solar masses, and that the optical luminosity of the supernova is powered by the radioactive decay of Co-56 synthesized in the explosion. As calculated from the rate of the optical emission decay, the explosion occurred about 350 days before its discovery in February, 1985. It is believed that some of the oxygen-rich supernova remnants may also have been produced by explosions of WO stars.

Begelman, M. C.↗
NASA NTRS1989

Reflections on human error - Matters of life and death

The last two decades have witnessed a rapid growth in the introduction of automatic devices into aircraft cockpits, and eleswhere in human-machine systems. This was motivated in part by the assumption that when human functioning is replaced by machine functioning, human error is eliminated. Experience to date shows that this is far from true, and that automation does not replace humans, but changes their role in the system, as well as the types and severity of the errors they make. This altered role may lead to fewer, but more critical errors. Intervention strategies to prevent these errors, or ameliorate their consequences include basic human factors engineering of the interface, enhanced warning and alerting systems, and more intelligent interfaces that understand the strategic intent of the crew and can detect and trap inconsistent or erroneous input before it affects the system.

Wiener, Earl L.↗
NASA NTRS1992

Transient nucleation induction time from the birth-death equations

For the set of finite-difference equations of Becker-Doering an exact formula for the induction time, which is expressed in terms of rapidly convergent sums, is presented. The form of the result is particularly amenable for analytical study, and the latter is carried out to obtain approximations of the exact expression in a rigorous manner and to assess its sensitivity to the choice of the nucleation model. The induction time is found to be governed by two main nucleation parameters, the normalized barrier height, and the number of molecules in the critical cluster. The ratio of these two parameters provides an assessment of the importance of discreteness effects. The exact expression is studied in both the continuous and the asymptotic limits. The accuracy of the Zeldovich equation, which is produced in the continuous limit, is discussed for several nucleation models.

Shneidman, Vitaly A.↗
NASA NTRS1992

Gamma-ray bursts as the death throes of massive binary stars

We propose that gamma-ray bursts are created in the mergers of double neutron star binaries and black hole neutron star binaries at cosmological distances. Two different processes provide the electromagnetic energy for the bursts: neutrino-antineutrino annihilation into electron-position pairs during the merger, and magnetic flares generated by the Parker instability in a postmerger differentially rotating disk. In both cases, an optically thick fireball of size less than or approximately equal to 100 km is initially created, which expands ultrarelativistically to large radii before radiating. The scenario is only qualitative at this time, but it eliminates many previous objections to the cosmological merger model. The strongest bursts should be found close to, but not at the centers of, galaxies at redshifts of order 0.1, and should be accompanied by bursts of gravitational radiation from the spiraling-in binary which could be detected by LIGO.

Narayan, Ramesh↗
NASA NTRS1992

Detecting surface roughness effects on the atmospheric boundary layer via AIRSAR data: A field experiment in Death Valley, California

The part of the troposphere influenced by the surface of the earth is termed the atmospheric boundary layer. Flow within this layer is influenced by the roughness of the surface; rougher surfaces induce more turbulence than smoother surfaces and, hence, higher atmospheric transfer rates across the surface. Roughness elements also shield erodible particles, thus decreasing the transport of windblown particles. Therefore, the aerodynamic roughness length (z(sub 0)) is an important parameter in aeolian and atmospheric boundary layer processes as it describes the aerodynamic properties of the underlying surface. z(sub 0) is assumed to be independent of wind velocity or height, and dependent only on the surface topography. It is determined using in situ measurements of the wind speed distribution as a function of height. For dry, unvegetated soils the intensity of the radar backscatter (sigma(sup 0)) is affected primarily by surface roughness at a scale comparable with the radar wavelength. Thus, both wind and radar respond to surface roughness variations on a scale of a few meters or less. Greeley showed the existence of a correlation between z(sub 0) and sigma(sup 0). This correlation was based on measurements over lava flows, alluvial fans, and playas in the southwest deserts of the United States. It is shown that the two parameters behave similarly also when there are small changes over a relatively homogeneous surface.

Blumberg, Dan G.↗
NASA NTRS1994

Proposed law of nature linking impacts, plume volcanism, and Milankovitch cycles to terrestrial vertebrate mass extinctions via greenhouse-embryo death coupling

A greenhouse-physiological coupling killing mechanism active among mammals, birds, and reptiles has been identified. Operating via environmental thermal effects upon the maternal core-skin blood flow critical to the survival and development of embryos, it reduces the flow of blood to the uterine tract. Today, during hot summers, this phenomena kills embryos on a vast, global scale. Because of sensitivity of many mammals to modern heat, a major modern greenhouse could reduce population numbers on a global scale, and potentially trigger population collapses in the more vulnerable parts of the world. In the geological past, the killing mechanism has likely been triggered into action by greenhouse warming via impact events, plume volcanism, and Earth orbital variations (Milankovitch cycles). Earth's biosphere is maintained and molded by the flow of energy from the solar energy source to Earth and on to the space energy sink (SES). This SES energy flow maintains Earth's biosphere and its living components, as open, intermediate, dissipative, nonequilibrium systems whose states are dependent upon the rate of energy flowing through them. Greenhouse gases such as CO2 in the atmosphere influence the SES energy flow rate. Steady-state flow is necessary for global ecological stability (autopoiesis). Natural fluctuations of the C cycle such as rapid releases of CO2 from the mantle, or oceans, disrupt steady-state SES flow. These fluctuations constantly challenge the biosphere; slowdown of SES energy flow drives it toward thermodynamical equilibrium and stagnation. Fluctuations induced by impact event, mantle plume volcanism, and Milankovitch cycles can grow into structure-breaking waves triggering major perturbations of Earth's C cycle and mass extinctions. A major C cycle perturbation involves readjustment of the outer physiochemical spheres of the Earth: the atmosphere, hydrosphere, and lithosphere; and by necessity, the biosphere. A greenhouse, one manifestation of a major C cycle perturbation, is the most dangerous natural phenomenon that life on Earth can experience. Greenhouse conditions existed during the KT mass extinctions of 65 m.y. ago, and the Pleistocene-Holocene (P-H) mammalian extinctions of 10,000-12,000 yr ago. Coupling climatology to reproductive physiology via effects of ambient air temperature upon uterine blood flow to developing embryos accounts for the extinctions via established physiological principles.

Mclean, D. M.↗
NASA NTRS1994

The one hundredth year of Rudolf Wolf's death: Do we have the correct reconstruction of solar activity?

In the one hundred years since Wolf died, little effort has gone into research to see if improved reconstructions of sunspot numbers can be made. We have gathered more than 349,000 observations of daily sunspot group counts from more than 350 observers active from 1610 to 1993. Based upon group counts alone, it is possible to make an objective and homogeneous reconstruction of sunspot numbers. From our study, it appears that the Sun has steadily increased in activity since 1700 with the exception of a brief decrease in the Dalton Minimum (1795-1823). The significant results here are the greater depth of the Dalton Minimum, the generally lower activity throughout the 1700's, and the gradual rise in activity from the Maunder Minimum to the present day. This solar activity reconstruction is quite similar to those Wolf published before 1868 rather than the revised Wolf reconstructions after 1873 which used geomagnetic fluctuations.

Hoyt, Douglas V.↗
NASA NTRS1998

The Synchrotron Shock Model Confronts a "Line of Death" in the BATSE Gamma-Ray Burst Data

The synchrotron shock model (SSM) for gamma-ray burst emission makes a testable prediction: that the observed low-energy power-law photon number spectral index cannot exceed -2/3 (where the photon model is defined with a positive index: $dN/dE \propto E{alpha}$). We have collected time-resolved spectral fit parameters for over 100 bright bursts observed by the Burst And Transient Source Experiment on board the {\it Compton Gamma Ray Observatory}. Using this database, we find 23 bursts in which the spectral index limit of the SSM is violated, We discuss elements of the analysis methodology that affect the robustness of this result, as well as some of the escape hatches left for the SSM by theory.

Preece, Robert D.↗
NASA NTRS1999

Infrared Space Observatory (ISO) Key Project: the Birth and Death of Planets

This program was designed to continue to analyze observations of stars thought to be forming protoplanets, using the European Space Agency's Infrared Space Observatory, ISO, as one of NASA Key Projects with ISO. A particular class of Infrared Astronomy Satellite (IRAS) discovered stars, known after the prototype, Vega, are principal targets for these observations aimed at examining the evidence for processes involved in forming, or failing to form, planetary systems around other stars. In addition, this program continued to provide partial support for related science in the WIRE, SOFIA and Space Infrared Telescope Facility (SIRTF) projects, plus approved ISO supplementary time observations under programs MCREE1 29 and VEGADMAP. Their goals include time dependent changes in SWS spectra of Long Period Variable stars and PHOT P32 mapping experiments of recognized protoplanetary disk candidate stars.

Stencel, Robert E.↗
NASA NTRS1999

Life and Death on Mars and Earth

Failure to discover life on Mars has led a great many experts to conclude that it must be hiding. Where? The likeliest hiding places are deep beneath the surface, where geothermal heat could permit liquid water. In this the search for life on Mars parallels the search for water on Mars. Liquid water has been, at least on occasion, a geologically significant presence on the surface. Channels were cut and plains dissected. This water is now hidden, in all likelihood having drained to the base of the porous regolith, where it fills possibly frozen aquifers. Presumably any surviving biota has followed the water from the surface to its hiding places in the deep. Accordingly, we have extended our environmental impact assessment of the environmental hazards posed by large asteroid and comet impacts to Mars, and compare its case to Earth's. In particular, we address the continuous habitability of surface and subsurface environments.

Zahnle, K. J.↗
NASA NTRS1998

Life and death in the microcirculation: a role for angiotensin II

OBJECTIVE: Angiotensin II (ANGII) plays a critical role in the maintenance of the microcirculation and in the anatomical loss of microvessels (rarefaction) that occurs in low renin forms of hypertension and in animals fed a high-salt diet. Elevations in sodium intake can trigger a series of hemodynamic and hormonal responses culminating in a substantial rarefaction of small arterioles and capillaries in both normal and reduced renal mass hypertensive rats. METHODS: Immunohistochemistry, Northern blot, and reverse transcription-polymerase chain reaction (RT-PCR) analysis of microdissected blood vessels were used to localize ANGII receptors in the microcirculation. Chronic infusion of ANGII and other physiologic and pharmacologic manipulations of the reninangiotensin system in rats was combined with morphologic and mathematical analysis of the network architecture. RESULTS: We have shown that rarefaction of the microcirculation can cause an increase in total peripheral resistance, reduced tissue perfusion, decreased oxygen delivery, and impaired organ function. Although the mechanisms by which this occurs are not well understood, a number of key observations point to a role for the renin-angiotensin system in this effect. First, ANGII infused systemically at subpressor levels, or locally into the skeletal muscle interstitium, can induce significant microvessel growth. Second, localization of ANGII receptor proteins by immunohistochemistry and Western blotting and RNA localization by RT-PCR confirm the presence of AT1 receptors, which are growth-stimulatory, and AT2 receptors, which are growth-inhibitory in the microcirculation. Third, maintenance of ANGII at normal levels during periods of hypertension or high-salt diet completely eliminates rarefaction. CONCLUSIONS: Taken together, these results support the hypothesis that ANGII acting through AT1- and AT2-receptor mechanisms modulate vessel density during high-salt diet and hypertension.

Review↗
NASA NTRS2009

From Research to Flight: Surviving the TRL Valley of Death for Robotic and Human Exploration

Fundamental research is critical to taking the next giant leap in the scientific exploration of space. NASA should be pushing the envelope and asking "what if?" .. Technology push enables new capabilities. When NASA began, everything was enabling. .. Technology pull is often required to meet current mission requirements. Technology management requires more than issuing NRAs and overseeing contracts. Continuous assessment, peer review, and system systems studies are vital to credible TRL advancement. A strategy for taking technology R&D to new heights will lead to discoveries at far-reaching destinations..

Johnson, Les↗
NASA NTRS2010

Positrons in the Galaxy: Their Births, Marriages and Deaths

High energy (approximately GeV) positrons are seen within cosmic rays and observation of a narrow line at 511 keV shows that positrons are annihilating in the galaxy after slowing down to approximately keV energies or less. Our state of knowledge of the origin of these positrons, of the formation of positronium 'atoms', and of the circumstances of their annihilation or escape from the galaxy are reviewed and the question of whether the two phenomena are linked is discussed.

Skinner, Gerald K.↗
NASA NTRS2018

Preventing Premature Death in the M&S Lifecycle: Lessons Learned from Resurrection and Modernization of a Space System Contamination Model

Models and simulations (M&S) are often developed to meet specific needs and unique requirements for a particular situation. Once the M&S is implemented for a specific case and questions are answered, the M&S may go dormant until a similar need arises again at a later time, perhaps months to years later. Possible modification of the M&S may be required, and issues may arise if the M&S is not well documented, captured, or available. This can severely limit the useful life of the M&S and hinder future development or enhancements. This situation occurred with an M&S tool that had been developed to determine the impact to space system performance due to the presence of molecular contaminant films accumulating on key spacecraft surfaces. The challenges and issues encountered when resurrecting, executing, and modernizing the tool will be presented as a case study. To stay ahead of tomorrow’s challenges, resources to create M&S tools must be utilized efficiently. Lessons learned from this case study will aid M&S developers and users in planning for proper maintenance, transfer, and capture of key M&S tools and knowledge to avoid increased cost, increased development time, and wasted resources for projects relying on M&S.

Seasly, Elaine↗