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At least 739 records · Page 41

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NASA NTRS1985

The depths of the mare basalt source region

Chemical data for the parental magmas of the nine known VLT Array I pyroclastic glasses show statistically significant trends due to olivine (approximately Fo83) control during their formation by partial melting. The compositional scatter is largely due to compositional variations in the source regions on the + or - 1 percent level. This compositional scatter is small when one considers that the scale of the source region is up to 1000 km, but is sufficient to make positive identification of the residual phase(s) in the source regions difficult. Nevertheless, when the effects of the scatter are properly modeled, it is relatively clear that olivine is the residual phase in the source region. Hence these data and additional constraints indicate that the source regions are at shallow depths in the moon.

Binder, A. B.↗

NASA NTRS1985

A method of rapidly obtaining concentration-depth profiles from X-ray diffraction

A broadened diffraction peak, or intensity band, is observed in the case diffraction from a nonhomogeneous phase in which the variations in compositions result in a range of lattice spacings. An intriguing aspect regarding the relationship between the X-ray diffraction band and the composition-depth profile is the hypersensitivity of the intensity band to the shape of the profile. A number of investigators have sought to use this sensitivity to construct high-precision profiles. Difficulties encountered are related to complications due to intensity broadening, and prohibitive computational requirements. Simulation techniques have provided the most accurate interpretation of the intensity band. However, the involved calculations have been prohibitively long. The present study discusses a technique which has simple computational requirements and is as accurate and flexible as the simulation techniques.

Wiedemann, K. E.↗

NASA NTRS1986

Gravitational microlensing at large optical depth

A large number of numerical models of gravitational microlensing by stars in the lensing galaxy have been calculated, and properties of the models are described. The expected light intensity variations are more rapid when optical depth to microlensing is large, but the time scale is a few years in the best cases, and much longer in a typical case. However, microlensing introduces considerable scatter, up to two or three orders of magnitude, to the intensity of macroimages expected at any given time, and this may considerably complicate the analysis of the observed lenses. It is shown that macroimage is surrounded with a faint 'halo' made of a large number of microimages from individual stars with average surface brightness falling off as R to the -4th. It is also shown that a high surface mass density of continuously distributed matter may affect very strongly properties of microlensing, making possible very large declines in observed intensity, up to two or three orders of magnitude.

Paczynski, B.↗

NASA NTRS1986

Effects of multiple scattering on time- and depth-resolved signals in airborne lidar systems

A semianalytic Monte Carlo radiative transfer model (SALMON) is employed to probe the effects of multiple-scattering events on the time- and depth-resolved lidar signals from homogeneous aqueous media. The effective total attenuation coefficients in the single-scattering approximation are determined as functions of dimensionless parameters characterizing the lidar system and the medium. Results show that single-scattering events dominate when these parameters are close to their lower bounds and that when their values exceed unity multiple-scattering events dominate.

Punjabi, A.↗

NASA NTRS1986

Latitude and depth variation of solar rotation

New measurements of frequencies of various modes of acoustic waves trapped within the sun are reported for degrees up to 98 which allow the convective envelope to be isolated. For degrees between 20 anad 98, no evidence is found that internal rotation differs significantly with depth or latitude from the rotation of surface magnetic field patterns. Modes covering a wide latitude range have systematically lower frequencies than those confined near the equator, indicating the existence of a structural asymmetry within the sun.

Duvall, T. L., Jr.↗

NASA NTRS1987

Depth Gauge for Liquids Under High Pressure

Piezoelectric element mounted in hole drilled in high-pressure plug. Transducer used to measure depth of liquid when pressure in vessel high. New configuration transmits ultrasonic vibration directly into liquid, enhancing signal strength, accuracy, and range, yet piezoelectric element protected from high-pressure liquid.

Zuckerwar, A. J.↗

NASA NTRS1987

A prediction model of the depth-of-discharge effect on the cycle life of a storage cell

Cycle life requirements are very high for batteries used in aerospace applications in low Earth orbit. The data base required to establish confidence in a particular cell design is thus both extensive and expensive. Reliable accelerated cycle life testing and performance decay modeling represent attractive alternatives to real-time tests of cycle life. In light of certain long-term cycle life test results, this paper examines a very simple performance decay model developed earlier. Application of that model to available data demonstrates a rigid relationship between a battery's expected cycle life and the depth of discharge of cycling. Further, modeling analysis of the data suggests that a significantly improved cycle life can be obtained with advanced components, materials, and designs; and that cycle life can be reliably predicted from the results of accelerated testing.

Thaller, Lawrence H.↗

NASA NTRS1987

Atmospheric optical depth effects on angular anisotropy of plant canopy reflectance

The effects of varying atmospheric aerosol optical depth on the bidirectional reflectance distribution of vegetation canopies is investigated. The reflectance distributions of two pasture grass canopies and one soya bean canopy under different sky irradiance distributions were measured, and the data were analyzed in the visible and IR spectral bands. It is observed that, for the pasture grass canopies, the change in reflectance is due to the percentage of shadowed area viewed by the sensor, and for the soya bean, the specular reflection effect and increased diffuse irradiance penetration into the canopy cause reflectance changes. It is detected that the reflectivity for the soya bean canopy on a hazy day is lower than on a clear day; however, the opposite change is observed for the pasture grass. It is also detected that the normalized difference vegetation index values differ under clear and hazy conditions for the same vegetation canopy conditions.

Deering, Donald W.↗

NASA NTRS1987

Aerosol optical depth and planetary Albedo in the visible from the Solar Mesosphere Explorer

The Solar Mesosphere Explorer (SME) satellite has observed the visible sunlight scattered at the earth's limb since early 1982. By using a radiative-transfer model including multiple scattering and albedo effects, observations at 20 deg N latitude have been interpreted in terms of aerosol optical depth. The ratio of aerosol extinction to Rayleigh extinction at 431.8 nm shows a large increase after the eruption of El Chichon. A maximum ratio of 5 at 36 km and larger than 11 at 30 km occurred in the summer of 1982 followed by a decrease through 1983 and 1984. Aspects of the aerosol time evolution appear to be consistent with other observations and model predictions. Quantitative differences exist between inferred SME and lidar extinction coefficients, possibly due to the different wavelengths of the measurements and to the different scattering phase functions used in the two analyses. It is also shown that visible limb radiances provide information on the planetary albedo, which shows an increase from the equator to the poles with a maximum in the winter hemisphere and a minimum in the summer hemisphere.

Naudet, J. P.↗

NASA NTRS1988

Systematic variation of magnetic-field penetration depth in high-T(c) superconductors studied by muon spin relaxation

The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 Sr0.15 CuO4 in transverse external magnetic fields 1 is approximately 4kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

Uemura, Y. J.↗

NASA NTRS1987

A prediction model of the depth-of-discharge effect on the cycle life of a storge cell

Cycle life requirements are very high for batteries used in aerospace applications in low earth orbit. The data base required to establish confidence in a particular cell design is thus both extensive and expensive. Reliable accelerated cycle life testing and performance decay modeling represent attractive alternatives to real-time tests of cycle life. In light of certain long-term cycle life test results, this paper examines a very simple performance decay model developed earlier. Application of that model to available data demonstrates a rigid relationship between a battery's expected cycle life and the depth of discharge of cycling. Further, modeling analysis of the data suggests that a significantly improved cycle life can be obtained with advanced components, materials, and designs; and that cycle life can be reliably predicted from the results of accelerated testing.

Thaller, Lawrence H.↗

NASA NTRS1988

Dynamical effects on the core-mantle boundary from depth-dependent thermodynamical properties of the lower mantle

A common assumption in modeling dynamical processes in the lower mantle is that both the thermal expansivity and thermal conductivity are reasonably constant. Recent work from seismic equation of state leads to substantially higher values for the thermal conductivity and much lower thermal expansivity values in the deep mantle. The dynamical consequences of incorporating depth-dependent thermodynamic properties on the thermal-mechanical state of the lower mantle are examined with the spherical-shell mean-field equations. It is found that the thermal structure of the seismically resolved anomalous zone at the base of the mantle is strongly influenced by these variable properties and, in particular, that the convective distortion of the core-mantle boundary (CMB) is reduced with the decreasing thermal expansivity. Such a reduction of the dynamically induced topography from pure thermal convection would suggest that some other dynamical mechanism must be operating at the CMB.

Zhang, Shuxia↗

NASA NTRS1988

Nonlinear photorefractive response at high modulation depths

The response of photorefractive materials to sinusoidal intensity patterns of high modulation depths is considered. It is shown that the induced refractive-index response in this regime is highly nonlinear. Concise analytic expressions for the various nonlinear harmonics of the photorefractive response field are developed and compared with exact numerical solutions of the underlying charge-transport equations as well as with the results of previous theoretical models over a broad range of physical parameters. We show that the nonlinear response characteristics are strongly dependent on both the magnitude of applied electric fields and the relative concentrations of charge donor and acceptor sites in the material. For drift dominated recording, in particular, we determine analytically that in the limit of a minimal acceptor/donor ratio, the amplitudes of higher spatial harmonics of the response reach a maximum and eventually decay as functions of increasing applied field, whereas these amplitudes reach a nonzero limit in the case of a near-unity acceptor/donor ratio. Finally, we generalize our results to account for diffusion effects in an appended derivation.

Vachss, Frederick↗

NASA NTRS1987

Mars: Crustal pore volume, cryospheric depth, and the global occurrence of groundwater

It is argued that most of the Martian hydrosphere resides in a porous outer layer of crust that, based on a lunar analogy, appears to extend to a depth of about 10 km. The total pore volume of this layer is sufficient to store the equivalent of a global ocean of water some 500 to 1500 m deep. Thermal modeling suggests that about 300 to 500 m of water could be stored as ice within the crust. Any excess must exist as groundwater.

Clifford, Stephen M.↗

NASA NTRS1988

Inversion of the Solar Rotation Rate Versus Depth and Latitude

Three differential inversion techniques were used to compute the internal solar rotation rate from several sets of n-averaged frequency splittings. An iterative variation of the spectral expansion method; the optimal averaging kernel method; and a piecewise constant constrained least square method were used to invert the data. Each computation was carried out independently. While they present similar trends, each of the solutions differs in detail. A consistent feature in all the inversions is the disappearance of differential rotation below the base of the convection zone. Also, a strong differential signature in the deeper part of the convection zone is present in most of the solutions. A slow decrease of the rotation rate with depth for the equatorial and midlatitude curves is significant in the spectral expansion and the least square results but only marginally apparent in the averaging kernel results.

Korzennik, Sylvain G.↗

NASA NTRS1988

Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

Uemura, Y. J.↗

NASA NTRS1989

Nonaqueous chemical depth profiling of YBa2Cu3O(7-x)

A nonaqueous solution of Br in absolute ethanol (EtOH) has recently been reported to be effective at removing nonsuperconducting surface species from YBa2Cu3O(7-x) films, leaving the surface close to the ideal stoichiometry. This same etchant is shown here to be an effective bulk etchant in chemical depth profiling through 1-micron-thick films. The Cu remains in the 2 + oxidation state and the stoichiometry, as determined by X-ray photoelectron spectroscopy, is close to ideal and nearly constant throughout the profile, indicating the absence of any large preferential etching effects. The reaction of YBa2Cu3O(7-x) films with HF/EtOH, HCl/EtOH, and I/EtOH solutions is also reported.

Vasquez, R. P.↗

NASA NTRS1990

Borescope With Large Depth Of Focus

Modification of commercial borescope yields clear, glare-free images of defects on inside of tube. Used to examine diverging wall of tube. Wall illuminated by light from fiber distinct from fused-fiber cable used for viewing. Viewing cable holds right-angle mirror at tip so it can look sideways. Image appears, magnified, on monitor. Instrument offers large depth of focus and therefore used in tubes of varying inside diameter.

Guirguis, Kamal S.↗