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At least 955 records · Page 53

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NASA NTRS1977

The interior structure of Jupiter (Consequences of Pioneer 10 data)

Models of the Jovian interiors based on theoretical equations of state of hydrogen and helium supported by a few experimental points and on observed parameters such as oblateness, gravitational coefficients, heat emission, magnetic fields, are discussed. The models fall into three categories: (1) those that assume a uniform and rather low H2/He ratio throughout the planet; (2) those in which this ratio is solar and thus higher; and (3) those that take into account the lack of complete miscibility of the two elements in the condensed state. It appears now also that within the limits of error the planet is in a hydrostatic equilibrium. The large heat emission and the need for an efficient source of internal heat are confirmed, but the results do not indicate which one of the various possible mechanisms is favored, although new evolutionary models suggest that the primordial heat may be insufficient. A new red spot has been discovered. Finally, the presence of a highly eccentric and inclined magnetic field poses new problems related to the pattern of internal convection and to the possibility of a north-south asymmetry of the interior. Further analysis of the available data may throw additional light on these questions.

Smoluchowski, R.↗

NASA NTRS1977

Equations and closure methods

Basic differential equations governing compressible turbulent boundary layer flow are reviewed, including conservation of mass and energy, momentum equations derived from Navier-Stokes equations, and equations of state. Closure procedures were broken down into: (1) simple or zeroth-order methods, (2) first-order or mean field closure methods, and (3) second-order or mean turbulence field methods.

Source record↗

NASA NTRS1978

Monte Carlo simulation of the classical two-dimensional one component plasma

Monte Carlo simulation, lattice dynamics in the harmonic approximation, and solution of the hypernetted chain equation were used to study the classical two-dimensional one component plasma. The system consists of a single species of charged particles immersed in a uniform neutralizing background. The particles interact via a l/r potential, where r is the two dimensional separation. Equations of state were calculated for both the liquid and solid phases. Results of calculation of the thermodynamic functions and one and two particle correlation functions are presented.

Gann, R. C.↗

NASA NTRS1978

Gamma-ray lines from neutron stars as probes of fundamental physics

The detection of gamma-ray lines produced at the surface of neutron stars will serve to test both the strong and gravitational interactions under conditions unavailable in terrestrial laboratories. Observation of a single redshifted gamma-ray line, combined with an estimate of the mass of the star will serve as a strong constraint on allowable equations of state of matter at supernuclear densities. Detection of two redshifted lines arising from different physical processes at the neutron star surface can provide a test of the strong principle of equivalence. Expected fluxes of nuclear gamma-ray lines from accreting neutron stars were calculated, including threshold, radiative transfer and redshift effects. The most promising probes of neutron star structure are the deuterium formation line and the positron annihilation line. Detection of sharp redshifted gamma-ray lines from X-ray sources such as Cyg X-1 would argue strongly in favor of a neutron star rather than black hole identification for the object.

Brecher, K.↗

NASA NTRS1977

Hot gas in clusters of galaxies

Radio and X-ray observations are discussed which seem to favor the presence of a hot intracluster gas in rich clusters of galaxies. On the assumption that the X-rays are produced by thermal bremsstrahlung, a temperature of the order of 100 million K and a density of a few thousandths per cu cm are computed for the intracluster gas. Theories on the origin and dynamics of this gas are reviewed, and the discovery of an iron line in the spectrum of the Perseus cluster is taken as strong evidence for thermal emission from a hot intracluster gas. Effects of and on the intracluster gas are considered, particularly the formation of radio-tail galaxies due to ram pressure on the galaxies in rich clusters, stripping of interstellar gas from the galaxies, and heating of the intracluster gas by the galaxies. It is concluded that the intracluster gas: (1) originated partially in primordial matter that collapsed into the clusters and partially in gas lost from the galaxies, (2) is in static or almost static equilibrium in the clusters, and (3) either is tightly bound or has an equation of state corresponding to a gamma value of less than 5/3.

Lea, S. M.↗

NASA NTRS1977

A block iterative finite element algorithm for numerical solution of the steady-state, compressible Navier-Stokes equations

An iterative method for numerically solving the time independent Navier-Stokes equations for viscous compressible flows is presented. The method is based upon partial application of the Gauss-Seidel principle in block form to the systems of the nonlinear algebraic equations which arise in construction of finite element (Galerkin) models approximating solutions of fluid dynamic problems. The continuous cubic element on triangles is employed for function approximation. Computational results for a free shear flow at Re = 1000 indicate significant achievement of economy in iterative convergence rate over finite element and finite difference models which employ the customary time dependent equations and symptotic time marching procedure to steady solution. Numerical results are in excellent agreement with those obtained for the same test problem employing time marching finite element and finite difference solution techniques.

Cooke, C. H.↗

NASA NTRS1978

Superdense neutron matter

A relativistic theory of high-density matter is presented which takes into account the short-range interaction due to the exchange of spin-2 mesons. An equation of state is derived and used to compute neutron-star properties. The prediction of the theory for the values of maximum mass and moment of inertia for a stable neutron star are 1.75 solar masses and 1.68 by 10 to the 45th power g-sq cm, in very good agreement with the presently known observational bounds. The corresponding radius is found to be 10.7 km. It is found that the inclusion of the spin-2 interaction reduces the disagreement between the relativistic and nonrelativistic theories in their predictions of masses and moments of inertia.

Canuto, V.↗

NASA NTRS1977

Impact-induced energy partitioning, melting, and vaporization on terrestrial planets

The reported investigation was conducted in connection with the desirability to obtain information regarding the response of a solidified planetary surface to the primary impact of a meteoroid whose dimensions are small compared to that of the planet. The investigation is an extension of studies conducted by Ahrens and O'Keefe (1977) concerned with a calculation via finite-difference techniques of the entire flow field, the energy partitioning, and the quantity of melt and vapor produced upon impact of an iron object on a gabbroic anorthosite half-space at 15 km/sec. The assumptions used in these calculations are summarized. Calculations based on an equation of state for the low- and high-pressure mineral assemblage of gabbroic anorthosite, initial density 2.94 g/cu cm are considered. An algorithm is formulated for the description of the phase transformation upon shock loading. It is shown that the relative volume of melt and the equivalent volume of shock-induced vapor is proportional to the meteoroid kinetic energy (at high speeds) using the similarity scaling of projectile and target properties as suggested by Dienes and Walsh (1970).

Okeefe, J. D.↗

NASA NTRS1977

Thermal conductivity of steam in the critical region

The thermal conductivity of fluids exhibits an anomalous enhancement in a large range of densities and temperatures around the critical point. We formulate an equation for the thermal conductivity that connects the anomalous behavior in the vicinity of the critical point with the normal behavior of the thermal conductivity away from the critical point. The critical thermal conductivity enhancement is related to the anomalous behavior of the isothermal compressibility which in turn is represented by a scaled equation of state. The method is used to analyze experimental thermal conductivity data in the critical region of steam.

Basu, R. S.↗

NASA NTRS1978

Neutron stars

Quantum-mechanical processes associated with the presence of high magnetic fields and the effect of such fields on the evolution of neutron stars are reviewed. A technical description of the interior of a neutron star is presented. The neutron star-pulsar relation is reviewed and consideration is given to supernovae explosions, flux conservation in neutron stars, gauge-invariant derivation of the equation of state for a strongly magnetized gas, neutron beta-decay, and the stability condition for a neutron star.

Canuto, V.↗

NASA NTRS1978

Viscosity of nitrogen near the critical point

The formulation of a quantitative description of the critical enhancement in the shear viscosity of fluids near the gas-liquid critical point is considered. The critical point is a point of marginal thermodynamic stability. In the vicinity of the critical point, large-scale density fluctuations are present in the fluid. The critical enhancement of the transport properties is related to the correlation length. The correlation length is related to the compressibility, thus providing consistency between the equations for the transport properties and the equation of state in the critical region. The critical region parameters for nitrogen are presented in a table. It is found that the critical viscosity enhancement observed by Zozulya and Blagoi (1974) for nitrogen is consistent with current theoretical predictions

Basu, R. S.↗

NASA NTRS1979

Measurement of post-shock temperatures in aluminum and stainless steel

Until recently experimental measurements of post-impact temperatures have been obtained only for metals at high pressures. Our aim has been to develop a technique for measuring post-shock temperatures in a variety of materials, including metals and silicates, at pressures in the range of 5 to 50 GPa, providing further insight into the shock process in these substances and additional constraints to available equation of state data. This paper describes the method we have developed, and its application to the determination of post-shock temperatures in aluminum-2024 and stainless steel-304.

Raikes, S. A.↗

NASA NTRS1980

Volume-energy parameters and turbulent-flow density fluctuations

Volume-energy relations determined from an equation of state were used to group many sets of heat transfer data for liquids and gases, including the near-critical region. The volume - Gibbs energy parameter grouped these data better than did such other parameters as enthalpy, temperature, or internal energy.

Hendricks, R. C.↗

NASA NTRS1979

Possible observational constraints on the mass-radius relation of neutron stars

The effect of gravitational redshift on the blackbody radii, as deduced from the tails of X-ray bursts, is considered. Observed values of blackbody radii put an upper limit to the mass and constrain the mass-radius relations of neutron stars. Possible consequences for the equation of state of high-density matter are briefly discussed.

Van Paradijs, J.↗

NASA NTRS1979

Lightman-Eardley instabilities and accretion disk thickening

After reviewing the role of Compton scattering in accretion disks around black holes, it is discussed whether Lightman-Eardley (LE) secular instabilities can trigger and maintain Pringle-Rees (PR) thermal instabilities. The radiative-transfer-equation and equation-of-state criteria for LE stability in alpha-viscosity-law disk models and dynamic viscosity criteria for more general situations is derived. On the basis of these considerations the LE instability is insufficient for inducing PR instabilities and hot thick inner regions important in accretion-disk models of compact hard X-ray sources. The density thinning due to radial velocity gradients in the accretion flow is suggested as a more likely and satisfactory mechanism.

Stoeger, W. R.↗

NASA NTRS1979

Thermodynamic properties of nitrogen gas from sound velocity measurements

Thermodynamic properties of nitrogen gas have been calculated from 80 K to 350 K and at pressures to 10 bar from sound velocity measurements and existing P-V-T data using multiproperty fitting techniques. These new data are intended to improve existing predictive capability of the equation of state in the low density region needed for use with the NASA-Langley National Transonics Facility.

Younglove, B. A.↗

NASA NTRS1980

Calculations of the evolution of the giant planets

Evolutionary calculations are presented for spherically symmetric protoplanetary configurations with a homogeneous solar composition and with masses of 1000, 1500, 28,500 and 42,000 solar masses. Recent improvements in equation-of-state and opacity calculations are incorporated. Sequences start as subcondensations in the solar nebula with densities of 10 to the -10th to 10 to the -11th g/cu cm, evolve through a hydrostatic phase lasting 100 thousand to 10 million years, undergo dynamic collapse due to dissociation of molecular hydrogen, and regain hydrostatic equilibrium with densities of about 1 g/cu cm. The nature of the objects at the onset of the final phase of cooling and contraction is discussed and compared with previous calculations.

Bodenheimer, P.↗

NASA NTRS1981

Investigation of air solubility in jet A fuel at high pressures

The solubility and density properties of saturated mixtures of fuels and gases were measured. The fuels consisted of Jet A and dodecane, the gases were air and nitrogen. The test range included pressures of 1.03 to 10.34 MPa and temperatures of 298 to 373 K. The results were correlated successfully, using the Soave equation of state. Over this test range, dissolved gas concentrations were roughly proportional to pressure and increased slightly with increasing temperature. Mixture density was relatively independent of dissolved gas concentration.

Rupprecht, S. D.↗