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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The role of extraterrestrial phenomena in extinction

In the several years since the Alvarez report of anomalously high iridium concentrations at the Cretaceous-Tertiary boundary, evidence for the involvement of meteorite impacts in biological extinction has increased dramatically. Much more research will be needed, however, before meteorite impact is established as a general causal factor in extinction. Of ever greater long-term interest is the possibility that other extraterrestrial forces have had important influences on the evolution of life. To recognize the effects of such forces, it will be necessary to coordinate the research of astronomy and paleontology so that testable predictions can be formulated. It is possible that known, systematic changes in the Solar System or Galaxy have had effects on global biology and that these effects have been preserved in the paleontological record.

Non-NASA Center↗
NASA NTRS1987

Mass extinction: a commentary

Four neocatastrophist claims about mass extinction are currently being debated; they are that: 1, the late Cretaceous mass extinction was caused by large body impact; 2, as many as five other major extinctions were caused by impact; 3, the timing of extinction events since the Permian is uniformly periodic; and 4, the ages of impact craters on Earth are also periodic and in phase with the extinctions. Although strongly interconnected the four claims are independent in the sense that none depends on the others. Evidence for a link between impact and extinction is strong but still needs more confirmation through bed-by-bed and laboratory studies. An important area for future research is the question of whether extinction is a continuous process, with the rate increasing at times of mass extinctions, or whether it is episodic at all scales. If the latter is shown to be generally true, then species are at risk of extinction only rarely during their existence and catastrophism, in the sense of isolated events of extreme stress, is indicated. This is line of reasoning can only be considered an hypothesis for testing. In a larger context, paleontologists may benefit from a research strategy that looks to known Solar System and Galactic phenomena for predictions about environmental effects on earth. The recent success in the recognition of Milankovitch Cycles in the late Pleistocene record is an example of the potential of this research area.

Review, Tutorial↗
NASA NTRS1987

Theoretical constraints on oxygen and carbon dioxide concentrations in the Precambrian atmosphere

Simple (one-dimensional) climate models suggest that carbon dioxide concentrations during the Archean must have been at least 100-1000 times the present level to keep the Earth's surface temperature above freezing in the face of decreased solar luminosity. Such models provide only lower bounds on CO2, so it is possible that CO2 levels were substantially higher than this and that the Archean climate was much warmer than today. Periods of extensive glaciation during the early and late Proterozoic, on the other hand, indicate that the climate at these times was relatively cool. To be consistent with climate models CO2 partial pressures must have declined from approximately 0.03 to 0.3 bar around 2.5 Ga ago to between 10(-3) and 10(-2) bar at 0.8 Ga ago. This steep decrease in carbon dioxide concentrations may be inconsistent with paleosol data, which implies that pCO2 did not change appreciably during that time. Oxygen was essentially absent from the Earth's atmosphere and oceans prior to the emergence of a photosynthetic source, probably during the late Archean. During the early Proterozoic the atmosphere and surface ocean were apparently oxidizing, while the deep ocean remained reducing. An upper limit of 6 x 10(-3) bar for pO2 at this time can be derived by balancing the burial rate of organic carbon with the rate of oxidation of ferrous iron in the deep ocean. The establishment of oxidizing conditions in the deep ocean, marked by the disappearance of banded iron formations approximately 1.7 Ga ago, permitted atmospheric oxygen to climb to its present level. O2 concentrations may have remained substantially lower than today, however, until well into the Phanerozoic.

Review, Tutorial↗
NASA NTRS1986

Community living long before man: fossil and living microbial mats and early life

Microbial mats are layered communities of bacteria that form cohesive structures, some of which are preserved in sedimentary rocks as stromatolites. Certain rocks, approximately three and a half thousand million years old and representing the oldest known fossils, are interpreted to derive from microbial mats and to contain fossils of microorganisms. Modern microbial mats (such as the one described here from Matanzas, Cuba) and their fossil counterparts are of great interest in the interpretation of early life on Earth. Since examination of microbial mats and stromatolites increases our understanding of long-term stability and change, within the global environment, such structures should be protected wherever possible as natural science preserves. Furthermore, since they have existed virtually from the time of life's origin, microbial mats have developed exemplary mechanisms of local community persistence and may even play roles in the larger global environment that we do not understand.

NASA Discipline Exobiology↗
NASA NTRS1987

Metabolism of proteinoid microspheres

The literature of metabolism in proteinoids and proteinoid microspheres is reviewed and criticized from a biochemical and experimental point of view. Closely related literature is also reviewed in order to understand the function of proteinoids and proteinoid microspheres. Proteinoids or proteinoid microspheres have many activities. Esterolyis, decarboxylation, amination, deamination, and oxidoreduction are catabolic enzyme activities. The formation of ATP, peptides or oligonucleotides is synthetic enzyme activities. Additional activities are hormonal and inhibitory. Selective formation of peptides is an activity of nucleoproteinoid microspheres; these are a model for ribosomes. Mechanisms of peptide and oligonucleotide syntheses from amino acids and nucleotide triphosphate by proteinoid microspheres are tentatively proposed as an integrative consequence of reviewing the literature.

Non-NASA Center↗
NASA NTRS1987

Metabolism of proteinoid microspheres

The literature of metabolism in proteinoids and proteinoid microspheres is reviewed and criticized from a biochemical and experimental point of view. Closely related literature is also reviewed in order to understand the function of proteinoids and proteinoid microspheres. Proteinoids or proteinoid microspheres have many activities. Esterolysis, decarboxylation, amination, deamination, and oxidoreduction are catabolic enzyme activities. The formation of ATP, peptides or oligonucleotides is synthetic enzyme activities. Additional activities are hormonal and inhibitory. Selective formation of peptides is an activity of nucleoproteinoid microspheres; these are a model for ribosomes. Mechanisms of peptide and oligonucleotide syntheses from amino acids and nucleotide triphosphate by proteinoid microspheres are tentatively proposed as an integrative consequence of reviewing the literature.

Non-NASA Center↗
NASA NTRS1986

Molecular selection in a unified evolutionary sequence

With guidance from experiments and observations that indicate internally limited phenomena, an outline of unified evolutionary sequence is inferred. Such unification is not visible for a context of random matrix and random mutation. The sequence proceeds from Big Bang through prebiotic matter, protocells, through the evolving cell via molecular and natural selection, to mind, behavior, and society.

Review, Tutorial↗
NASA NTRS1995

Diagnosis and management of baroreflex failure

Baroreflex failure has a range of presentations, varying from the acute onset of a hypertensive crisis to a chronically volatile blood pressure and heart rate with hypertensive surges in response to stress, punctuated by periods of normal or even low blood pressure during rest. Differentiating this syndrome from other causes of labile hypertension is essential in devising effective treatment.

Review, Tutorial↗
NASA NTRS1999

Engineering plants for spaceflight environments

The conversion efficiency of radiation into biomass and yield has steadily increased for centuries because of continued improvement in both plant genetics and environmental control. Considerable effort has gone into improving the environment for plant growth in space, but work has only begun to engineer plants for spaceflight. Genetic manipulation offers tremendous potential to improve our ability to study gravitational effects. Genetic manipulation will also be necessary to build an efficient regenerative life support system. We cannot fully characterize plant response to the spaceflight environment without understanding and manipulating their genetic composition. Identification and selection of the existing germplasm is the first step. There are thousands of cultivars of each of our major crop plants, each specifically adapted to a unique environment on our planet. Thousands of additional lines are held in national germplasm collections to maintain genetic diversity. Spaceflight imposes the need to tap this diversity. Existing lines need to be evaluated in the environment that is characteristic of closed-system spaceflight conditions. Many of the plant growth challenges we confront in space can be better solved through genetic change than by hardware engineering. Ten thousand years of plant breeding has demonstrated the value of matching genetics with the environment. For example, providing continuous light can increase plant growth in space, but this often induces calcium deficiencies because Ca is not supplied by guttation during a dark period. This deficiency cannot be eliminated through increased root-zone and foliar Ca applications. It can be solved, in wheat, through genetic selection of lines that do not have the deficiency. Subsequent comparison of lines with and without the Ca deficiency has also helped us understand the nature of the problem.

Non-NASA Center↗
NASA NTRS1999

Microgravity cultivation of cells and tissues

In vitro studies of cells and tissues in microgravity, either simulated by cultivation conditions on earth or actual, during spaceflight, are expected to help identify mechanisms underlying gravity sensing and transduction in biological organisms. In this paper, we review rotating bioreactor studies of engineered skeletal and cardiovascular tissues carried out in unit gravity, a four month long cartilage tissue engineering study carried out aboard the Mir Space Station, and the ongoing laboratory development and testing of a system for cell and tissue cultivation aboard the International Space Station.

Review, Tutorial↗
NASA NTRS1999

An overview of vertebrate mineralization with emphasis on collagen-mineral interaction

The nucleation, growth, and development of mineral crystals through their interaction principally with collagen in normal bone and calcifying tendon have been elaborated by applying a number of different techniques for analysis of the inorganic and organic constituents of these tissues. The methods have included conventional and high voltage electron microscopy, electron diffraction, microscopic tomography and 3D image reconstruction, and atomic force microscopy. This summary presents results of these studies that have now characterized the size, shape, and aspects of the chemical nature of the crystals as well as their orientation, alignment, location, and distribution with respect to collagen. These data have provided the means for understanding more completely the formation and strength of the collagen-mineral composite present in most vertebrate calcifying tissues and, from that information, a basis for the adaptation of such tissues under mechanical constraints. In the context of the latter point, other data are given showing effects on collagen in bone cell cultures subjected to the unloading parameters of spaceflight. Implications of these results may be particularly relevant to explaining loss of bone by humans and other vertebrate animals during missions in space, during situations of extended fracture healing, long-term bedrest, physical immobilization, and related conditions. In a broader sense, the data speak to the response of bone and mineralized vertebrate tissues to changes in gravitational loading and applied mechanical forces in general.

Non-NASA Center↗
NASA NTRS1997

The ethylene signal transduction pathway in Arabidopsis

The gaseous hormone ethylene is an important regulator of plant growth and development. Using a simple response of etiolated seedlings to ethylene as a genetic screen, genes involved in ethylene signal transduction have been identified in Arabidopsis. Analysis of two of these genes that have been cloned reveals that ethylene signalling involves a combination of a protein (ETR1) with similarity to bacterial histidine kinases and a protein (CTR1) with similarity to Raf-1, a protein kinase involved in multiple signalling cascades in eukaryotic cells. Several lines of investigation provide compelling evidence that ETR1 encodes an ethylene receptor. For the first time there is a glimpse of the molecular circuitry underlying the signal transduction pathway for a plant hormone.

NASA Discipline Plant Biology↗
NASA NTRS1998

Psychosocial issues affecting crews during long-duration international space missions

Psychosocial issues can negatively impact on crew performance and morale during long-duration international space missions. Major psychosocial factors that have been described in anecdotal reports from space and in studies from analog situations on Earth include: 1) crew heterogeneity due to gender differences, cultural issues, and work experiences and motivations; 2) language and dialect variations; and 3) task versus supportive leadership roles. All of these factors can lead to negative sequelae, such as intra-crew tension and cohesion disruptions. Specific sequelae that can result from single factors include subgrouping and scapegoating due to crew heterogeneity; miscommunication due to major or subtle language differences; and role confusion, competition, and status leveling due to inappropriate leadership role definition. It is time to conduct research exploring the impact of these psychosocial factors and their sequelae on space crews during actual long-duration international space missions.

Non-NASA Center↗
NASA NTRS1998

Nutrition, endocrinology, and body composition during space flight

Space flight induces endocrine changes that perturb metabolism. This altered metabolism affects both the astronauts' body composition and the nutritional requirements necessary to maintain their health. During the last 25 years, a combination of studies conducted on Skylab (the first U.S. space laboratory), U.S. Shuttle flights, and Soviet and Russian flights provides a range of data from which general conclusions about energy and protein requirements can be drawn. We have reviewed the endocrine data from those studies and related it to changes in body composition. From these data it appears that protein and energy intake of astronauts are similar to those on Earth. However, a combination of measures, including exercise, appropriate diet, and, potentially, drugs, is required to provide the muscle health needed for long duration space flight.

Flight Experiment↗
NASA NTRS1995

Pathophysiology of immobilization osteoporosis

The reduction of gravity-related forces on the skeleton creates a type of osteoporosis that is unique because its severity is dependent on the mechanical stress bearing function of the skeleton as well as the length of time that the forces are absent or reduced. Bones that bear weight under normal conditions are more affected than bones that normally do not bear weight. The cytokine environment and the cells in the affected bones are altered in time so that stem cells produce fewer new cells and the differentiated cells tend to be less active. These alterations in the local environment of the affected parts appear to resemble those of age- and disease-associated systemic forms of osteoporosis. The osteoporosis produced as a result of the loss of normal activity however, appears to be at least partially reversible through remobilization, strenuous exercise, and--possibly in the future--cytokine therapy.

Non-NASA Center↗
NASA NTRS1997

Clinical utility of T-wave alternans

Electrical alternans represents a variation in the morphology of electrocardiographic complexes on an every-other-beat basis in an ABABAB... pattern. Apparent electrical alternans associated with pericardial effusion results from rotation of the heart in the pericardial sac, and not true alternation in electrical conduction patterns. In contrast, true electrical alternans results from an alternation in electrical conduction patterns in the heart itself. Repolarization alternans is true electrical alternans associated with the ST segment and T wave of the electrocardiogram (ECG). Here we will focus on T-wave alternans (TWA) and its association with susceptibility to ventricular tachyarrhythmias. Electrical alternans was reported in the literature as early as 1909. Historically, electrical alternans has been regarded as a fairly rare electrocardiographic abnormality. Case reports of electrical alternans have been associated with a variety of disease states, including acute ischemia, Prinzmetal's angina, a variety of electrolyte abnormalities, and the long QT syndrome. Interestingly, patients born with the prolonged QT syndrome have a very high incidence of sudden cardiac death at an early age. Schwartz and Malliani showed that patients with the prolonged QT syndrome who do not demonstrate alternans at rest, may evidence alternans during stress such as emotional excitement. Thus, over the years electrical alternans has been associated anecdotally with conditions associated with an increased risk of ventricular arrhythmias. In 1948, Kalter reviewed the world literature on electrical alternans and found a total of 41 reported cases. In addition, he reviewed clinical ectrocardiograms from 6059 patients and found five new cases (incidence of less than 1 in 1000 patients). Interestingly, he found a very high mortality, 62%, associated with this condition. Despite the clinical associations reported in the literature, the consensus view of electrical alternans until recent years has been that alternans is an electrocardiographic curiosity rarely encountered in clinical practice which, when identified, does not have specific clinical significance.

Review, Tutorial↗
NASA NTRS1997

Dissecting global diversity patterns: examples from the Ordovician Radiation

Although the history of life has been characterized by intermittent episodes of radiation that can be recognized in global compilations of biodiversity, it does not necessarily follow that these episodes are caused by processes that occurred uniformly around the world. Major diversity increases could be generated by the cumulative effects of different mechanisms operating simultaneously at several geographic or environmental scales. The purpose of this review is to describe ongoing research on the manifestations, at several scales, of the Ordovician Radiation, which was among the most extensive intervals of diversification in the history of life. Through much of the period, diversity was concentrated most heavily near regions of active mountain building and volcanism; differences in diversity patterns from continent to continent, and among regions within continents, reflect this overprint. While this suggests a linkage of the Radiation and tectonic activity, this is by no means the only mediating agent. Outcrop-based research in North America has demonstrated that tectonic activity was detrimental to some biotic elements, in contrast to its effects on other organisms. Moreover, in the Great Basin of North America where the local stratigraphic record is of particularly high quality, biotic transitions characteristic of the period occurred far more rapidly than observed in global compilations of diversity, suggesting that the global rate of transition may represent the aggregate sum of transitions that occurred abruptly, but at different times, around the world. Finally, it has been demonstrated that, in concert with an increase in average age, the environmental and geographic ranges of Ordovician genera both increased significantly through the period, indicating a role for intrinsic factors in producing Ordovician biotic patterns.

Non-NASA Center↗