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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Observational Constraint on the Radius and Oblateness of the Lunar Core‐Mantle Boundary

Lunar laser ranging (LLR) data and Apollo seismic data analyses, revealed independent evidence for the presence of a fluid lunar core. However, the size of the lunar fluid core remained uncertain by _55 km (encompassing two contrasting 2011 Apollo seismic data analyses). Here we show that a new description of the lunar interior's dynamical model provides a determination of the radius and geometry of the lunar core-mantle boundary (CMB) from the LLR observations. We compare the present day lunar core oblateness obtained from LLR analysis with the expected hydrostatic model values, over a range of previously expected CMB radii. The findings suggest a core oblateness (f(c) = (2.2 ± 0.6) x 10(exp 14)) that satisfies the assumption of hydrostatic equilibrium over a tight range of lunar CMB radii (R(CMB) = 381 ± 12 km). Our estimates of a presently-relaxed lunar CMB translates to a core mass fraction in the range of 1.59 - 1.77% with a present-day Free Core Nutation (FCN) within (367±100) years.

Moon↗
NASA NTRS1998

Influence of gravity on cardiac performance

Results obtained by the investigators in ground-based experiments and in two parabolic flight series of tests aboard the NASA KC-135 aircraft with a hydraulic simulator of the human systemic circulation have confirmed that a simple lack of hydrostatic pressure within an artificial ventricle causes a decrease in stroke volume of 20%-50%. A corresponding drop in stroke volume (SV) and cardiac output (CO) was observed over a range of atrial pressures (AP), representing a rightward shift of the classic CO versus AP cardiac function curve. These results are in agreement with echocardiographic experiments performed on space shuttle flights, where an average decrease in SV of 15% was measured following a three-day period of adaptation to weightlessness. The similarity of behavior of the hydraulic model to the human system suggests that the simple physical effects of the lack of hydrostatic pressure may be an important mechanism for the observed changes in cardiac performance in astronauts during the weightlessness of space flight.

NASA Discipline Cardiopulmonary↗
NASA NTRS1992

Glomerular hemodynamic alterations during acute hyperinsulinemia in normal and diabetic rats

Treatment of insulin dependent diabetes invariably requires exogenous insulin to control blood glucose. Insulin treatment, independent of other factors associated with insulin dependent diabetes, may induce changes that affect glomerular function. Due to exogenous delivery of insulin in insulin dependent diabetes entering systemic circulation prior to the portal vein, plasma levels of insulin are often in excess of that observed in non-diabetics. The specific effects of hyperinsulinemia on glomerular hemodynamics have not been previously examined. Micropuncture studies were performed in control (non-diabetic), untreated diabetic and insulin-treated diabetic rats 7 to 10 days after administration of 65 mg/kg body weight streptozotocin. After the first period micropuncture measurements were obtained, 5 U of regular insulin (Humulin-R) was infused i.v., and glucose clamped at euglycemic values (80 to 120 mg/dl). Blood glucose concentration in non-diabetic controls was 99 +/- 6 mg/dl. In control rats, insulin infusion and glucose clamp increased nephron filtration rate due to decreases in both afferent and efferent arteriolar resistance (afferent greater than efferent) resulting in increased plasma flow and increased glomerular hydrostatic pressure gradient. However, insulin infusion and glucose clamp produced the opposite effect in both untreated and insulin-treated diabetic rats with afferent arteriolar vasoconstriction resulting in decreases in plasma flow, glomerular hydrostatic pressure gradient and nephron filtration rate. Thromboxane A2 (TX) synthetase inhibition partially decreased the vasoconstrictive response due to acute insulin infusion in diabetic rats preventing the decrease in nephron filtration rate.(ABSTRACT TRUNCATED AT 250 WORDS).

NASA Discipline Cardiopulmonary↗
NASA NTRS1972

Composite overwrapped metallic tanks

Work is reported for fabricating and testing the fiberglass overwrapped titanium pressure vessel for cryogenic service. Difficulties encountered in the tank liner fabrication phase involved explosive forming, vacuum annealing, chemical milling and electron beam welding. While each of these processes and the nondestructive test methods employed are normally considered to be individually reliable, the combination of poor material together with fabrication and development reversals prevented the full achievement of the desired end results. Eight tanks plus a prototype and tool proofing article were produced. Six of the vessels failed during the hydrostatic sizing operation. One of the remaining tanks was hydrostatically pressurized to burst and the other was pressurized repeatedly at 75 F from 100 psi to the operating pressure until failure occurred. As a result, it is not possible to draw firm conclusions as to the true value of the design concept due to the problems encountered in the program.

Caudill, C. L.↗
NASA NTRS1972

Development of boron epoxy rocket motor chambers.

A 71 cm diameter 74 cm length boron/epoxy composite rocket motor chamber was designed based on the geometric configuration of the JPL Applications Technology Satellite titanium alloy apogee motor chamber. Because analyses showed large stress concentrations in the domes, the configuration was modified using the same basic constraints for openings and attachments. The rocket motor chamber was then fabricated by filament winding with boron/epoxy tape and hydrostatically tested to failure at 264 N/sq cm, 57.2 N/sq cm above the design value. Two more rocket motor chambers were fabricated with the same basic constraints, but shortened to 57.6 cm for a smaller propellant load. The first of these short chambers failed in proof because of filament winding fabrication difficulties. The second chamber was successfully fabricated and passed the hydrostatic proof test.

Jensen, W. M.↗
NASA NTRS1974

Intrathoracic and venous pressure relationships during responses to changes in body position

Simultaneous end-expiratory pressures, referred to midthoracic level, in the superior and abdominal venae cavae, pericardial space, and right and left heart, were recorded without thoracotomy in three anesthetized dogs during sudden changes from supine to vertical head-up or head-down body positions. Intrathoracic and dependent great vein pressures referred to midchest level (sixth thoracic vertebra) decreased and showed simple hydrostatic gradients in either vertical position. However, a discontinuity in the large vein hydrostatic gradient occurred just distal to the superior margin of the thorax in either body position and was resumed again above this level. It is concluded that, just as the cerebrospinal fluid and intraperitoneal pressures minimize the effects of gravitational and inertial forces on the cerebral and visceral circulations, the pericardial and pleural pressures have a similar role for the heart proper.

Avasthey, P.↗
NASA NTRS1975

Means and methods of physical conditioning of man in long space flights

Methods of prophylaxis for disorders caused predominantly by reduction or absence of hydrostatic blood pressure in weightlessness and in experimental stimulation of it (readjustment of the watersalt metabolism, relative dehydration, disruption of competence of the cardiovascular system with respect to orthostatic loads, etc.), are adequately substantiated. Two theoretically possible approaches to prophylaxis of this type of disorder are examined: The use of methods of simulation of the effect of hydrostatic blood pressure in flight and the decrease in the gravitational redistribution of blood to the lower part of the body in the postflight period. In particular, the method of negative pressure in the lower region of the body gave favorable results. A significant decrease in orthostatic disorders after completion of such experiments was achieved by use of g-suits or other types of special clothing.

Stepantsov, V. I.↗
NASA NTRS1974

Calculations of the early evolution of Jupiter

The evolution of the protoplanet Jupiter is followed, using a hydrodynamic computer code with radiative energy transport. Jupiter is assumed to have formed as a subcondensation in the primitive solar nebula at a density just high enough for gravitational collapse to occur. The initial state has a density of 0.0015 nanograms per cu cm and a temperature of 43 K; the calculations are carried to an equilibrium state where the central density reaches 0.5 g per cu cm and the central temperature reaches 25,000 K. During the early part of the evolution the object contracts in quasi-hydrostatic equilibrium; later on hydrodynamic collapse occurs, induced by the dissociation of hydrogen molecules. After dissociation is complete, the planet regains hydrostatic equilibrium with a radius of a few times the present value. Further evolution beyond this point is not treated here; however the results are consistent with the existence of a high-luminosity phase shortly after the planet settles into its final quasi-static contraction.-

Bodenheimer, P.↗
NASA NTRS1974

Depth of immersion as a determinant of the natriuresis of water immersion

The current study was undertaken to further assess the contribution of an immersion-induced hydrostatic pressure gradient on the redistribution of blood volume. The rate of sodium excretion by seated subjects was significantly increased by water immersion up to the chest and neck compared to waist immersion and controls. These results are consistent with the hypothesis that whereas immersion to the level of the diaphragm merely cancels the intravascular hydrostatic pressure gradient by providing an identical external gradient, immersion above the diaphragm level results in increased water pressure which tends to favor a shift in blood volume from the lower extremities.

Epstein, M.↗
NASA NTRS1976

Cardiorespiratory deconditioning with static and dynamic leg exercise during bed rest

Results are presented for an experimental study designed to compare the effects of heavy static and dynamic exercise training during 14 days of bed rest on the cardiorespiratory responses to submaximal and maximal exercise performed by seven healthy men aged 19-22 yr. The parameters measured were submaximal and maximal oxygen uptake, minute ventilation, heart rate, and plasma volume. The results indicate that exercise alone during bed rest reduces but does not eliminate the reduction in maximal oxygen uptake. An additional positive hydrostatic effect is therefore necessary to restore maximal oxygen uptake to ambulatory control levels. The greater protective effect of static exercise on maximal oxygen uptake is probably due to a greater hydrostatic component from the isometric muscular contraction. Neither the static nor the dynamic exercise training regimes are found to minimize the changes in all the variables studied, thereby suggesting a combination of static and dynamic exercises.

Stremel, R. W.↗
NASA NTRS1977

A review of the thermonuclear runaway model of a nova outburst

Kraft's (1963) model for a nova outburst caused by a thermonuclear runaway in the hydrogen-rich matter accreted onto the white dwarf in a binary system is reviewed. Hydrostatic and hydrodynamic studies of this phenomenon are summarized, analyses of shock ejection based on hydrodynamic computer codes are discussed, and one specific hydrodynamic code is outlined. Results obtained with this code are presented and evaluated for an initial model containing a white dwarf with a hydrogen-rich envelope of 0.0001 to 0.001 solar mass in hydrostatic and thermal equilibrium. It is shown that an implicit hydrodynamic computer code is required in order to study the thermonuclear-runaway phenomenon. The early evolution of three models with different intrinsic luminosities is illustrated, and enhancement of CNO nuclei at the bottom of the hydrogen-rich envelope is investigated. It is suggested that the concentration of C-13, N-15, and O-17 should be greatly enhanced in nova ejecta.

Sparks, W. M.↗
NASA NTRS1977

Radio and EUV observations of a coronal hole

Current ideas and modeling assumptions concerning the structure of the transition region and corona are summarized. Observations of a specific coronal hole are reported which were made with the EUV spectroheliometer aboard Skylab and with high-resolution radio telescopes in Australia and West Germany. Theoretical EUV line intensities and radio brightness temperatures are calculated, and an attempt is made to analyze the observations on the basis of standard one-dimensional plane-parallel hydrostatic-equilibrium models for the transition region and corona. It is found that any given standard model predicts either higher radio brightnesses or lower EUV line intensities than are observed. Several potential problem areas are examined in order to resolve this conflict. It is concluded that a model involving departures from hydrostatic equilibrium, varying conductive flux, mass outflow, as well as effects of thermal diffusion and nonequilibrium ionization should be investigated in more detail.

Dulk, G. A.↗
NASA NTRS1978

Internal friction Q factor measurements in lunar rocks

In order to better interpret recently reported values for the variation of seismic Q as a function of depth below the lunar surface, we have developed apparatus and made laboratory measurements of Q as a function of hydrostatic pressure, temperature and frequency. Our measurements of the Q associated with shear deformations have demonstrated that the large difference in Q between well outgassed and volatile rich rocks persists to pressures corresponding to a depth of at least 50 km. Here we report new measurements of Q as a function of temperature, on the development of techniques to measure the Q associated with extensional deformations under hydrostatic pressure, on the derivation of theoretical relations between our laboratory Q values and the attenuation coefficient of seismic waves, and on the development of a model for mechanism of adsorption.

Tittmann, B. R.↗
NASA NTRS1978

Possible flyby measurements of Galilean satellite interior structure

Flyby encounters of the Galilean satellites from a Jupiter orbiter spacecraft could yield information about the second-degree gravity harmonics of these satellites. The expected values of these harmonics have been calculated for a range of plausible interior models in hydrostatic equilibrium. Because the satellites respond to comparable perturbations from rotation and tides, an independent test of hydrostatic equilibrium is feasible. For Io and Ganymede, the expected measurement accuracy from a nominal encounter should make possible an excellent discrimination from the ensemble of interior models. For Europa, a qualitative distinction between near-uniform and centrally condensed models seems feasible. Only for Callisto is the proposed experiment of marginal value.

Hubbard, W. B.↗
NASA NTRS1978

Dynamics of the quiescent solar corona

An analytical model for the quiescent inhomogeneous solar corona is developed on the basis of the hypothesis that looplike structures are the basic coronal building blocks. By assuming that quiescent loop structures observed in X-rays are in hydrostatic equilibrium, it is demonstrated that such loops must have their temperature maximum located near their apex and that substantial nonradiative energy deposition must occur along most of their length. The calculations yield a unique relation among loop temperature, pressure, and size, which fits the X-ray observations of quiescent structures well and is consistent with the initial assumption of hydrostatic equilibrium. The results suggest that the coronal loops visible in X-rays represent a relatively steady-state equilibrium of the confined plasmas and that fluctuations in such quantities as the local heating rate can lead to dynamically unstable states in which the loop plasma does not attain a temperature sufficient for X-ray emission. A parameterization of various proposed coronal heating theories is also developed within the context of the analytical model.

Rosner, R.↗
NASA NTRS1978

Soft X-ray structure of the Perseus cluster of galaxies

A 0.5-1.5-keV X-ray image of the Perseus cluster of galaxies was obtained with a focusing telescope system aboard a sounding rocket. The source consists of a region of diffuse emission plus a superposed central source in the vicinity of NGC 1275 smaller than 4 arcmin in diameter that accounts for one-quarter of the total intensity within a radius of 25 arcmin. The results for the diffuse source are consistent with the isothermal-hydrostatic picture in which the hot gas has a core radius of 17 arcmin and is approximately symmetric about NGC 1275. Several isothermal-hydrostatic models are considered which relate the size and temperature of the diffuse X-ray source with the core radius of the galaxies and their velocity dispersion. Fixing the velocity dispersion at values measured by Chincarini and Rood (1971) requires the core radius of the galaxies to be 28 + or - 9 arcmin, which is larger than present measurements. Conversely, fixing the core radius of the galaxies at 8 arcmin requires a smaller velocity dispersion or a condition in which the velocity distribution is anisotropic. Upper limits on the intrinsic X-ray absorption of the central source place the bulk of its X-ray emission beyond the nuclear region of NGC 1275.

Gorenstein, P.↗
NASA NTRS1979

A luminosity-temperature relation for cluster X-ray sources

Luminosity-temperature (L-T) relations are derived for a self-gravitating isothermal gas sphere and for an isothermal gas sphere in hydrostatic equilibrium with the total mass of a cluster of galaxies. The relationships are compared with X-ray data for 13 clusters of galaxies. The L-T relation for the self-gravitating isothermal gas sphere is found to predict X-ray luminosities that are considerably larger than those observed, and the corresponding model is ruled out. It is shown, however, that the L-T relation for the isothermal gas sphere in hydrostatic equilibrium with total cluster mass is consistent with X-ray observations for reasonable choices of the ratio between central density and confining-mass density. Core radii or gas temperatures are predicted for five of the 13 clusters considered.

Henry, P.↗