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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 91 records · Page 5
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NASA NTRS2013

Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies

The amount of metals in the Intracluster Medium (ICM) in rich galaxy clusters exceeds that expected based on the observed stellar population by a large factor. We quantify this discrepancy--which we term the "cluster elemental abundance paradox"--and investigate the required properties of the ICM-enriching population. The necessary enhancement in metal enrichment may, in principle, originate in the observed stellar population if a larger fraction of stars in the supernova-progenitor mass range form from an initial mass function (IMF) that is either bottom-light or top-heavy, with the latter in some conflict with observed ICM abundance ratios. Other alternatives that imply more modest revisions to the IMF, mass return and remnant fractions, and primordial fraction, posit an increase in the fraction of 3-8 solar mass stars that explode as SNIa or assume that there are more stars than conventionally thought--although the latter implies a high star formation efficiency. We discuss the feasibility of these various solutions and the implications for the diversity of star formation, the process of elliptical galaxy formation, and the nature of this hidden source of ICM metal enrichment in light of recent evidence of an elliptical galaxy IMF that, because it is skewed to low masses, deepens the paradox.

Lowenstein, Michael↗
NASA NTRS2013

Saturn's F Ring Core: Calm in the Midst of Chaos

The long-term stability of the narrow F Ring core has been hard to understand. Instead of acting as "shepherds", Prometheus and Pandora together stir the vast preponderance of the region into a chaotic state, consistent with the orbits of newly discovered objects like S/2004S6. We show how a comb of very narrow radial locations of high stability in semimajor axis is embedded within this otherwise chaotic region. The stability of these semimajor axes relies fundamentally on the unusual combination of rapid apse precession and long synodic period which characterizes the region. This situation allows stable "antiresonances" to fall on or very close to traditional Lindblad resonances which, under more common circumstances, are destabilizing. We present numerical integrations of tens of thousands of test particles over tens of thousands of Prometheus orbits that map out the effect. The stable antiresonance zones are most stable in a subset of the region where Prometheus first-order resonances are least cluttered by Pandora resonances. This region of optimum stability is paradoxically closer to Prometheus than a location more representative of "torque balance", helping explain a longstanding paradox. One stable zone corresponds closely to the currently observed semimajor axis of the F Ring core. While the model helps explain the stability of the narrow F Ring core, it does not explain why the F Ring material all shares a common apse longitude; we speculate that collisional damping at the preferred semimajor axis (not included in the current simulations) may provide that final step. Essentially, we find that the F Ring core is not confined by a combination of Prometheus and Pandora, but a combination of Prometheus and precession.

Planetary Rings↗
NASA NTRS2018

Is Water Necessary for Life?

The universality of water as the solvent for life is usually justified by its role in supporting the rich organic chemistry. It has been pointed out, however, that even richer synthetic chemistry is possible in other organic solvents. Does it mean that water is not necessary for life? Here, other, essential criteria for solvent for life that have not been sufficiently considered are discussed. In biological systems, complex molecules are not only constantly synthesized but also degraded. Solvent-mediated degradation is essential for regulating cell content, preventing overcrowding and allowing for recycling organic material. Achieving a balance between synthetic and degradative processes is facile in water, but not in many other organic liquids. Thus, the so-called “water paradox” according to which water is both necessary to life and toxic to biopolymer synthesis might not be paradoxical at all. The machinery of life is based on non-covalent interactions that do not involve making or breaking chemical bonds. Their strength needs to be properly tuned. If they are too weak, there might be undesired response to natural fluctuations of physical or chemical parameters. If they are too strong, the kinetics and energetics of cellular processes could adversely influenced. The solvent must allow for balancing these interactions, which provides strong, universal constraints on the medium for life. Water influences non-covalent interactions mainly by two mechanisms. First, it reduces strong, electrostatic interactions between molecules, chemical groups or atoms carrying electric charge or dipole. Second, it induces the hydrophobic effect, the tendency to remove non-polar (hydrophobic) molecules and groups from direct contact with aqueous solution and, instead, interact with each other. In living systems, the hydrophobic effect is largely responsible for self-organization of molecules to more complex structures, such as aggregation of lipid molecules to form biological membranes and protein folding. Water exists as stable liquid in a large temperature range, and the hydrophobic effects are a consequence of the temperature insensitivity of essential properties of its liquid state. In summary, water accomplishes an amazing feat – it reduces strong interactions between dissolved species and simultaneously increases the strength of weak interactions, bringing all of them to the right range. Once we consider not only synthetic capabilities but also other required traits of the solvent for life, no viable alternative to water is currently known.

Life↗
NASA NTRS2021

Forest Cover Correlation with Population Trends of the Eastern Towhee in the Mid-Eastern U.S.

The Eastern Towhee (Pipilo erythrophthalmus) is a large, ground-nesting sparrow-like bird in the Eastern United States that has shown dramatic population declines over the last 50 years. This species lives year-round in the southeastern U.S., but individuals from the northeastern U.S. migrate south in the winter and overlap with southeastern residents. The Eastern Towhee is one of the fastest-declining bird species in the eastern U.S. In this study, we compare Eastern Towhee population trends during the breeding season with winter population trends over the last three decades. Paradoxically, this species is significantly increasing in Maryland, West Virginia, New Jersey, Virginia, and Delaware during the winter, but decreasing during the summer. Using the national Breeding Bird Survey dataset, we show that the Eastern Towhee populations have been declining roughly at a rate of -11.58% in Maryland, -9.51% in West Virginia, -37.95% in New Jersey, -11.22% in Virginia, and -16.96% in Delaware per year from 1984-2015. But the populations have been increasing during winter roughly at a rate of 0.62% in Maryland, 0.05% in West Virginia, 0.33% in New Jersey, 0.08% in Virginia, and 0.51% in Delaware per year from 1984-2019, using the Christmas Bird Count. We explore a variety of hypotheses to explain this paradox, including a northward range shift in association with climate change, as well as changes in habitat availability. Our study documents how the natural world is changing in complex ways due to many stressors and will help understand how to conserve the Eastern Towhee.

Meklit Mesfin↗
NASA NTRS1971

Criteria for electrically heated temperature probes in flames.

Measurement techniques proposed by Gilbert and Lobdell (1953) and Rein and O'Laughlin (1967) are considered, giving attention to an apparent paradox. The criteria under which the assumptions made for the measurement techniques apply are specified. If sensors of different diameters are tested and the resultant plots of the parameter ?S' vs the wire temperature intersect below the abscissa, the considered measurement techniques are not applicable.

Miller, I. M.↗
NASA NTRS1973

Skylab and solar exploration

Review of some of the findings concerning solar structure, energy production, and heat transport obtained with the aid of the manned Skylab space station observatory launched on May 14, 1973. Among the topics discussed are the observation of thermonuclear fusion processes which cannot be simulated on earth, the observation of short-wave solar radiation not visible to observers on earth, and the investigation of energy-transport processes occurring in the photosphere, chromosphere, and corona. An apparent paradox is noted in that the cooler chromosphere is heating the hotter corona, seemingly in defiance of the second law of thermodynamics, thus suggesting that a nonthermal mechanism underlies the energy transport. Understanding of this nonthermal mechanism is regarded as an indispensable prerequisite for future development of plasma systems for terrestrial applications.

Von Puttkamer, J.↗
NASA NTRS1974

The formation of the moon

Supporting evidence for the fission hypothesis for the origin of the moon is offered. The maximum allowable amount of free iron now present in the moon would not suffice to extract the siderophiles from the lunar silicates with the observed efficiency. Hence extraction must have been done with a larger amount of iron, as in the mantle of the earth, of which the moon was once a part, according to the fission hypothesis. The fission hypothesis gives a good resolution of the tektite paradox. Tektites are chemically much like products of the mantle of the earth; but no physically possible way has been found to explain their production from the earth itself. Perhaps they are a product of late, deep-seated lunar volcanism. If so, the moon must have inside it some material with a strong resemblance to the earth's mantle.

O'Keefe, J. A., III↗
NASA NTRS1977

Flutter of an elastic plate under tension

The problem of flutter of a tensioned elastic plate is reconsidered on a model of two-dimensional aerodynamic flow over a one-dimensional, infinitely wide plate. The purpose is to clarify the effect of variations in plate bending stiffness on the flutter of a plate under a given tension, and vice versa. On the basis that the flutter mode for the one-dimensional infinitely wide plate is essentially the first plate natural mode for subsonic and low supersonic Mach numbers, and that the dynamic pressure required for flutter is proportional to the square of the first natural mode frequency, it is shown that the membrane paradox disappears for Mach numbers 0 and 1.3, so that reduced bending stiffness reduces the dynamic pressure required for flutter.

Dowell, E. H.↗
NASA NTRS1978

New lunar microcrater evidence against a time varying meteoroid flux

An attempt to measure the relative times of formation of 25 microcraters on lunar rock 60015 is discussed which was carried out as part of a study of the flux of interplanetary dust and possible time variations of that flux over periods of 1000 to 1 million yr. The data obtained could indicate that the formation rate of 100-micron-sized pits was lower in the past as compared with the formation rate of micron-sized pits, that the flux of particles forming 100-micron-sized pits may have varied relative to that of particles forming micron-sized pits, or that 100-micron-sized pits are forming now at a higher rate, relative to the formation rate of accretionary disks, than in the past. The last suggestion is shown to be almost untenable, and the overall results are found to lead to a logical paradox. It is concluded that the attempt probably failed and that the reason for failure raises serious questions regarding the use of lunar rock surfaces as meteoroid detectors.

Hartung, J. B.↗
NASA NTRS1979

Temperature anisotropy of the Jovian sulfur nebula

The apparent paradox between the reported observation of a 3-eV gyration energy of Jupiter's ionized sulfur nebula and its observed thickness is discussed. An observation of the thickness of the cloud taken nearly edge-on is presented and shown to imply a large bounce-averaged anisotropy of the sulfur in temperature. These observations are used to construct a self-consistent model of the sulfur nebula in which the sulfur ions are injected by Io as ions and remain sufficiently collisionless in the magnetosphere to maintain the anisotropy for a time longer than a characteristic diffusion time. It is also shown that the proton-electron plasma is collisionally thermalized and provides an adequate means of tapping the rotational energy of the planet to provide the power radiated in the sulfur lines.

Eviatar, A.↗
NASA NTRS1980

Applications of liquid state physics to the earth's core

New results derived for application to the earth's outer core using the modern theory of liquids and the hard-sphere model of liquid structure are presented. An expression derived in terms of the incompressibility and pressure is valid for a high-pressure liquid near its melting point, provided that the pressure is derived from a strongly repulsive pair potential; a relation derived between the melting point and density leads to a melting curve law of essentially the same form as Lindemann's law. Finally, it is shown that the 'core paradox' of Higgins and Kennedy (1971) can occur only if the Gruneisen parameter is smaller than 2/3, and this constant is larger than this value in any liquid for which the pair potential is strongly repulsive.

Stevenson, D. J.↗
NASA NTRS1980

A Lagrangian mean theory of wave, mean-flow interaction with applications to nonacceleration and its breakdown

A review is given of new Lagrangian mean theory of wave transport. Attention is focused on the so-called 'nonacceleration' theorem, and it is shown that such a theorem arises naturally in the Lagrangian mean framework. Also discussed is a simple example of the Stokes drift, a concept which is central to nonacceleration. The Lagrangian mean theory substantially simplifies and unifies the understanding of wave driving in cases where nonacceleration is violated because of wave transience and dissipation. Moreover, the theory has given new insights in one particular case, that of Rossby gravity wave, mean-flow interaction. These insights have successfully explained some hitherto unresolved paradoxes in the theory of the quasi-biennial oscillation of zonal wind in the equatorial stratosphere. Some brief remarks are also made concerning some of the outstanding difficulties of the theory in need of future investigation.

Dunkerton, T.↗
NASA NTRS1980

The meteorite-asteroid connection - The infrared spectra of eucrites, shergottites, and Vesta

Infrared reflectance spectra have been obtained for the meteorites Shergotty and Allan Hills (ALHA) 77005, a unique achondrite apparently related to the shergottites. Comparisons with the reflectance spectra of eucrites and asteroid 4 Vesta indicate that the surface of Vesta is covered with eucrite-like basalts and that, if shergottite-like basalts are present on the surface of Vesta, they must be a minor rock type. The paradox that both the eucrite and shergottite parent bodies should presently exist is examined. The preferred solution is that both eucrites and shergottites are derived from Vesta, and that this asteroid is compositionally and isotopically heterogeneous; however, other possible solutions cannot be ruled out.

Feierberg, M. A.↗
NASA NTRS1980

Current understanding of the physics of type III solar radio bursts

One of the most exciting plasma physics investigations of recent years has been connected with the understanding of a new strong turbulent plasma state excited by propagating electron beams. This new state is initiated on the linear level by parametric instabilities (OTS, modulational, etc.) and results in a very dynamic state composed of collective clusters of modes called solitons, cavitons, spikons, etc. Introduction of these concepts into the classic beam-plasma interaction problem has rendered quasi-linear and weak turbulence theories inapplicable over most of the interesting parameter range, and helped explain many paradoxes connected with the propagation of beams in the laboratory and space. Following a brief review of these nonlinear notions, the means by which their application to type III solar radiobursts has revolutionized understanding of their propagation, radioemission and scaling properties and has guided the in situ observations towards a more complete understanding are demonstrated. A particular burst (May 16, 1971) is analyzed in detail and compared with numerical predictions.

Papadopoulos, K.↗
NASA NTRS1980

Changes in cardiac output and tibial artery flow during and after progressive LBNP

A 3.0 MHz Pulsed Doppler velocity meter (PD) was used to determine blood velocities in the ascending aorta from the suprasternal notch before, during and after progressive 5 min stages of lower body negative pressure (LBNP) in 7 subjects. Changes in stroke volume were calculated from the systolic velocity integrals. A unique 20 MHz PD was used to estimate bloodflow in the posterior tibial artery. With -20 torr mean stroke volume fell 11% and then continued to decline by 48% before LBNP was terminated. Mean tibial flow fell progressively with LBNP stress, due to an increase in reverse flow component and a reduction in peak forward flow and diameter. Stroke volume increased and heart rate fell dramatically during the first 15 sec of recovery. The LBNP was terminated early in 2 subjects because of vasovagal symptons (V). During V the stroke volume rose 86% which more than compensated for the drop in heart rate. This implies that V is accompanied by a paradoxical increase in venous return and that the reduction in HR is the primary cardiovascular event. During the first 15 sec of recovery these 2 subjects had a distinctive marked rise to heart rate reminiscent of the Bainbridge reflex.

Source record↗
NASA NTRS1981

Conceptual design and analysis of orbital cryogenic liquid storage and supply systems

A wide variety of orbital cryogenic liquid storage and supply systems are defined in NASA and DOD long-range plans. These systems include small cooling applications, large chemical and electrical orbit transfer vehicles and supply tankers. All have the common requirements of low-g fluid management to accomplish gas-free liquid expulsion and efficient thermal control to manage heat leak and tank pressure. A preliminary design study was performed to evaluate tanks ranging from 0.6 to 37.4 cu m (22 to 1320 cu ft). Liquids of interest were hydrogen, oxygen, methane, argon and helium. Conceptual designs were generated for each tank system and fluid dynamic, thermal and structural analyses were performed for Shuttle compatible operations. Design trades considered the paradox of conservative support structure and minimum thermal input. Orbital performance and weight data were developed, and a technology evaluation was completed.

Eberhardt, R. N.↗