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At least 469 records · Page 26

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NASA NTRS1978

Characterization of oriented cracks with differential strain analysis

Linear strain of a rock sample as a function of hydrostatic pressure can be measured with a precision of 2 millionths. Such high-precision data for three orthogonal directions allow calculation of the distribution function for the porosity due to cracks' closing completely at a given pressure. Such data for at least six independent directions yield the zero-pressure strain tensor due to cracks' closing completely at a given pressure. The principal values and axes of this tensor distribution function provide information about the orientation of cracks as a function of closure pressure. The mathematical basis for the technique is developed, and the technique is illustrated with differential strain data for two samples, the Westerly (Rhode Island) granite and the Twin Sisters (Washington) dunite. Strain-tensor calculations reveal that each of these samples has a different type of anisotropic crack distribution.

Siegfried, R.↗

NASA NTRS1977

Design considerations in mechanical face seals for improved performance. II - Lubrication

The importance of sealing technology in the U.S. industrial chemical-orientated society in regard to maintenance and environmental contamination is pointed out. It is stated that seal performance (leakage, life) is directly related to seal lubrication, which is a mechanism not well understood. Current thinking in regard to seal lubrication is reviewed, the effect of energy dissipation in the thin lubricating film separating the sealing faces is pointed out, and the results of vaporization due to heating are illustrated. Also, hydrodynamic lubrication is reviewed, and an inherent tendency for the seal to operate with angular misalignment is pointed out. Recent work on hydrostatic effects is summarized and the conditions for seal instability are discussed. Four different modes of seal lubrication are postulated with the mode type being a strong function of speed and pressure.

Ludwig, L. P.↗

NASA NTRS1978

Line formation in the solar chromosphere. I - The C II resonance lines observed with OSO 8

The temperature structure of the upper chromosphere is investigated using center-to-limb measurements of the C II resonance lines at 1335 A from the University of Colorado spectrometer aboard OSO 8. Spectrum synthesis of these lines shows them to be extremely sensitive to the temperature and the physical extent of the 20,000 K plateau proposed by Vernazza et al (1973). Hydrostatic equilibrium models of the quiet chromosphere are computed to obtain theoretical spectra of the Lyman lines and continuum as well as the center-to-limb behavior of the C II lines. Good agreement is found with observations for a plateau at 16,500 K with about 25% more material than that of Vernazza et al.

Lites, B. W.↗

NASA NTRS1978

Effect of gravitational and inertial forces on vertical distribution of pulmonary blood flow

Vertical distribution of pulmonary blood flow (VDPBF) was studied, using radioactive microsphere emboli, in dogs without thoracotomy in the right decubitus position during exposure to lateral accelerations of 1, 2, 4, and 6 G. At all levels of force environment studied, an inverse linear relationship was observed between vertical height in the thorax and pulmonary blood flow (ml/min/ml lung tissue) with a decrease in flow to the most dependent region of the lung despite large increases in intravascular pressures at this site. Changes in blood flow were smallest at the mid-lung level, the hydrostatic 'balance point' for vascular and pleural pressures. These force environment-dependent changes in VDPBF are not readily explainable by the Starling resistor analog. Gravity-dependent regional differences in pleural and associated interstitial pressures, plus possible changes in vascular tone resulting from inadequate aeration of blood in the most dependent regions of the lung, probably also affect VDPBF.

Chevalier, P. A.↗

NASA NTRS1978

Photochemistry and dynamics of the ozone layer

The paper presents a broad review of the photochemical and dynamic theories of the ozone layer. The two theories are combined into the MIT three-dimensional dynamic-chemical quasi-geostrophic model with 26 levels in the vertical spaced in logarithmic pressure coordinates between the ground and 72-km altitude. The chemical scheme incorporates the important odd nitrogen, odd hydrogen, and odd oxygen chemistry, but is simplified in the sense that it requires specification of the distributions of NO2, OH and HO2. The prognostic equations are the vorticity equation, the perturbation thermodynamic equation, and the global mean and perturbation continuity equations for ozone; diagnostic equations include the hydrostatic equation, the balance condition, and the mass continuity equation. The model is applied to the investigation of the impact of supersonic aircraft on the ozone layer.

Prinn, R. G.↗

NASA NTRS1978

Stellar model chromospheres. VIII - 70 Ophiuchi A /K0 V/ and Epsilon Eridani /K2 V/

Model atmospheres for the late-type active-chromosphere dwarf stars 70 Oph A and Epsilon Eri are computed from high-resolution Ca II K line profiles as well as Mg II h and k line fluxes. A method is used which determines a plane-parallel homogeneous hydrostatic-equilibrium model of the upper photosphere and chromosphere which differs from theoretical models by lacking the constraint of radiative equilibrium (RE). The determinations of surface gravities, metallicities, and effective temperatures are discussed, and the computational methods, model atoms, atomic data, and observations are described. Temperature distributions for the two stars are plotted and compared with RE models for the adopted effective temperatures and gravities. The previously investigated T min/T eff vs. T eff relation is extended to Epsilon Eri and 70 Oph A, observed and computed Ca II K and Mg II h and k integrated emission fluxes are compared, and full tabulations are given for the proposed models. It is suggested that if less than half the observed Mg II flux for the two stars is lost in noise, the difference between an active-chromosphere star and a quiet-chromosphere star lies in the lower-chromospheric temperature gradient.

Kelch, W. L.↗

NASA NTRS1978

Mars topography harmonics and geophysical implications

The paper describes an improved model of Martian global topography which has been obtained by fitting a sixteenth-degree harmonic series to occultation, radar, spectral, and photogrammetric measurements. Empirical elevation data based on photographic data are used to supplement the observations in areas without data. Values for the mean radius, the mean density, and the displacement of the center of the figure from the center of mass are presented. The reported geometric flattening is too great and the reported dynamic flattening is too small for Mars to be homogeneous and hydrostatic. Maps of the data distribution, global topography, and Bouguer gravity anomaly are interpreted in terms of a crustal thickness map which is consistent with gravity, topography, and recent preliminary Viking seismic results.

Bills, B. G.↗

NASA NTRS1978

Ortho- and para-hydrogen in dense clouds, protoplanets, and planetary atmospheres

If ortho- and para-hydrogen achieve a thermal ratio on dynamical time scales in a molecular hydrogen cloud, then the specific heat is high enough in the temperature range 35-70 K to possibly induce hydrodynamic collapse. The ortho-para ratio in many interstellar cloud fragments is expected to meet this condition. The same may have been true for the primitive solar nebula. Detailed hydrodynamic and hydrostatic calculations are presented that show the effects of the assumed ortho-para ratio on the evolution of Jupiter during its protoplanetary phase. Some possible consequences of a thermalized ortho-para ratio in the atmospheres of the giant planets are also discussed.

Decampli, W. M.↗

NASA NTRS1978

Vertical temperature and density patterns in the Arctic mesosphere analyzed as gravity waves

Three series of rocket soundings including pitot soundings, grenade soundings, and paired pitot-grenade soundings, were conducted from high latitude sites during winter. Temperature and wind profiles and one density profile were observed independently to obtain the thermodynamic structure, the wind structure, and thus their interdependence in the mesosphere. Temperature profiles from all soundings in each series were averaged, and a smooth curve (or series of smooth curves) drawn through the points. A hydrostatic atmosphere based on the average, measured temperature profile was computed, and deviations from the mean atmosphere were analyzed in terms of gravity wave theory. The vertical wavelengths of the deviations were 10-20 km, and the wave amplitudes slowly increased with height. The experimental data were matched by calculated gravity waves having a period ranging between 15 and 80 minutes and horizontal wavelengths of 60 to 280 km. The interpretation is generally consistent with the results of others who have studied gravity-acoustic waves in the atmosphere. The wind measurements are consistent with the thermodynamic measurements. The results also suggest that gravity waves traveled from east to west with a horizontal phase velocity of approximately 60 m/sec.

Eberstein, I. J.↗

NASA NTRS1977

The multiple nesting of mesoscale, submesoscale, and nonhydrostatic microscale numerical models for a case of mesocyclogenesis and severe storm development

A fundamental approach involving the integration of two different numerical models over several different spatial mesh lengths is considered. Model I is a hydrostatic, incompressible, and adiabatic primitive (Newtonian) equation set with no boundary layer forcing, i.e., surface heat or moisture flux or external frictional stresses. Typically this model is initialized from conventional radiosonde data and run for a 12-15 hour forecast period over a 40 km horizontal mesh. If phase I of the tornado developmental processes develops, the data is 'frozen' in space and time, interpolated to a 20 km mesh, and integrated for a shorter time period (3 hours) with a shorter time step. Model II is a nonhydrostatic compressible 18-level complement of model I. If model II indicates the development of the intensification of phase V dynamical processes, the data is frozen and interpolated to finer mesh lengths until the tornadic circulation system is approximated

Kaplan, M. L.↗

NASA NTRS1978

Cloud containment by a flux of particles

It is generally believed that relatively dense gas clouds must be present in the broad-line-emitting regions of Seyfert galaxies and quasars. A possible mechanism for the containment of these dense clouds is investigated in which momentum transfer from a flux of particles produces the hydrostatic equilibrium. Using a slab geometry and requiring ionization, energy, and force balance at each point in the cloud, the physical conditions are determined as a function of position in the cloud. The calculation describes equally well the confinement by ram pressure of a cloud moving rapidly through a thin gas. An important result is that the initial relative velocity of the incident particles and the cloud must be at least 20,000 km/s in the absence of a magnetic field parallel to its surface.

Rowe, D.↗

NASA NTRS1978

Magnetohydrodynamic models of coronal transients in the meridional plane. I - The effect of the magnetic field

The propagation of coronal transients through the lower corona in the meridional plane is studied on the basis of numerical solutions of the time-dependent MHD equations of motion. The importance of the topology of the initial coronal magnetic field is demonstrated by considering two configurations: one which is essentially radial (open), and another which is essentially parallel to the solar surface (closed). The effect of coronal field magnitude is investigated by using values for the beta parameter of 1 and 0.1 at the coronal base. The consequences of including radiative losses and of varying the polytropic index are also considered. The solar event is simulated by a step-function increase in the pressure at the base of an initially hydrostatic atmosphere by a factor of 5, lasting for a period of 5 min.

Steinolfson, R. S.↗

NASA NTRS1978

An elastic-perfectly plastic analysis of the bending of the lithosphere at a trench

A number of authors have modeled the flexure of the lithosphere at an oceanic trench using a thin elastic plate with a hydrostatic restoring force. In some cases good agreement with observed topography is obtained but in other cases the slope of the lithosphere within the trench is greater than that predicted by the elastic theory. In this paper the bending of a thin plate is considered using an elastic-perfectly plastic rheology. It is found that the lithosphere behaves elastically seaward of the trench, but that plasticity decreases the radius of curvature within the trench. The results are compared with a number of observed trench profiles. The elastic-perfectly plastic profiles are in excellent agreement with those profiles that deviate from elastic behavior.

Turcotte, D. L.↗

NASA NTRS1979

Estimating tropical cyclone outer surface winds from satellite microwave data

Warm temperature anomalies over tropical cyclones are sensed by the 55.45 GHz channel of the Nimbus 6 Scanning Microwave Spectrometer. Radial brightness temperature gradients are related to radial surface pressure gradients through the hydrostatic and radiative transfer equations. Surface wind speeds outside of the radius of maximum wind are calculated from the pressure gradients and compared with observations.

Kidder, S. Q.↗

NASA NTRS1978

Metallurgical analysis of skylab M552 and M557 samples

The anomalous microstructures on the basis of phase equilibria, liquid/liquid phase separation, and liquid/solid segregation for the Skylab M557 and M552 flight samples were studied. All of the unknown diffraction spectra have been identified. The previously unknown crystal structure of the Zn3Sb2 phase the M577B Experiment was determined. Previously unreported effects due to the near-absence of the hydrostatic pressure head are documented for the M557C samples.

Larson, D. J., Jr.↗

NASA NTRS1979

Determination of tropical cyclone surface pressure and winds from satellite microwave data

An approach to the problem of deducing wind speed and pressure around tropical cyclones is presented. The technique, called the Surface Wind Inference from Microwave data (SWIM technique, uses satellites microwave sounder data to measure upper tropospheric temperature anomalies which may then be related to surface pressure anomalies through the hydrostatic and radiative transfer equations. Surface pressure gradients outside of the radius of maximum wind are estimated for the first time. Future instruments may be able to estimate central pressure with + or - 0/1 kPa accuracy.

Kidder, S. Q.↗

NASA NTRS1979

The promise of space processing

The long exposure to a virtually zero-gravity environment is a truly unique situation that cannot be duplicated or even approximated for any length of time on earth. The topics discussed are: (1) low gravity; (2) atmospheric effects; (3) potential advantages of materials processing in space; (4) the absence of buoyancy-driven convection; (5) the absence of hydrostatic pressure; (6) the absence of sedimentation and buoyancy; (7) containerless processing; and (8) ultrahigh vacuum processing.

Source record↗

NASA NTRS1978

X-ray analysis of a polar plume

Polar plumes have been detected in X-rays with the Skylab S-054 experiment. Observations of one well-observed plume are analyzed and the plasma pressure is determined. An isothermal model in hydrostatic equilibrium is found to require unacceptably low temperatures. A hydrodynamic model is proposed which is consistent with earlier white light and EUV observations. Calculations indicate that the total outward mass flux in polar plumes is comparable to that in high speed solar wind streams expected from a polar coronal hole.

Ahmad, I. A.↗