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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Development and evaluation of integrated infrared arrays for astronomical applications

The status of a technology program to evaluate existing infrared detector arrays, and to develop improved ones for low background astronomical applications, is described. For applications such as the Shuttle Infrared Telescope Facility, arrays that cover as much of the 1-1000 micron range as possible are of interest. Low background test results for a 2 x 64 Si:Bi charge-injection-device, and 1 x 20 InSb charge-coupled-device arrays, are included. As a result of the present testing, improved, astronomy-optimized extrinsic silicon arrays in both linear and area formats are planned. Efforts to develop accumulation mode MOSFETs specifically for liquid helium temperatures, and cryogenic amplifier and multiplexer circuits, are discussed.

Mccreight, C. R.↗
NASA NTRS1983

The oblique whistler instability in the earth's foreshock

The linear Vlasov stability properties of electron velocity distributions, similar to those observed in the upstream foreshock region in association with obliquely propagating whistler waves at approximately 1 Hz, are studied. These distributions are modeled by a sum of bi-Maxwellians with drift speeds parallel to the magnetic field B. Such distributions are found to be stable to modes with wavevectors k parallel to B but unstable to whistler waves propagating obliquely to the magnetic field. The frequencies and wavelengths of these unstable modes agree well with those of whistlers observed upstream of the earth's bow shock. The free energy source driving the instability is a region of positive parallel slope at large pitch angles (about 85 deg) and intermediate energies (about 20 eV), probably corresponding to solar wind electrons magnetostatically reflected from the magnetic ramp of the bow shock. The whistlers grow via electromagnetic Landau resonance with this free energy source.

Sentman, D. D.↗
NASA NTRS1983

Chemical characteristics and origin of H chondrite regolith breccias

Petrologic data and contents of Ag, Bi, Cd, Co, Cs, Ga, In, Rb, Se, Te, Tl and Zn-trace elements spanning the volatility/mobility range-in light and dark portions of H chondrite regolith breccias and L chondrite fragmental breccias are reported. The chemical/petrologic characteristics of H chondrite regolith breccias differ from those of nonbrecciated chondrites or fragmental breccias. Petrologic characteristics and at least some trace element contents of H chondrite regolith breccias reflect primary processes; contents of the most volatile/mobile elements may reflect either primary or secondary processing, possibly within layered H chondrite parent object(s). Chemical/petrologic differences existed in different regions of the parent(s). Regoligh formation and gardening and meteoroid compaction were not so severe as to alter compositions markedly.

Lipschutz, M. E.↗
NASA NTRS1983

Stratospheric sulfuric acid fraction and mass estimate for the 1982 volcanic eruption of El Chichon

The stratospheric sulfuric acid fraction and mass for the 1982 volcanic eruptions of El Chichon are investigated using data from balloon soundings at Laramie (41 deg N) and in southern Texas (27-29 deg N). The total stratospheric mass of these eruptions is estimated to be approximately 8 Tg about 6.5 months after the eruption with possibly as much as 20 Tg in the stratosphere about 45 days after the eruption. Observations of the aerosol in Texas revealed two primary layers, both highly volatile at 150 C. Aerosol in the upper layer at about 25 km was composed of an approximately 80 percent H2SO4 solution while the lower layer at approximately 18 km was composed of a 60-65 percent H2SO4 solution aerosol. It is calculated that an H2SO4 vapor concentration of at least 3 x 10 to the 7th molecules/cu cm is needed to sustain the large droplets in the upper layer. An early bi-modal nature in the size distribution indicates droplet nucleation from the gas phase during the first 3 months, while the similarity of the large particle profiles 2 months apart shows continued particle growth 6.5 months after the explosion.

Hofmann, D. J.↗
NASA NTRS1982

Integrated infrared detector arrays for low-background applications

Advanced infrared detector and detector array technology is being developed and characterized for future NASA space astronomy applications. Si:Bi charge-injection-device arrays have been obtained, and low-background sensitivities comparable to that of good discrete detectors have been measured. Intrinsic arrays are being assessed, and laboratory and telescope data have been collected on a monolithic InSb CCD array. For wavelengths longer than 30 microns, improved Ge:Ga detectors have been produced, and steps have been taken to prove the feasibility of an integrated extrinsic germanium array. Other integrated arrays and cryogenic components are also under investigation.

Mccreight, C. R.↗
NASA NTRS1983

In situ trace element microanalysis

The use of particle-track-radiography and X-ray- fluorescence techniques in the in situ measurement of trace (less than 1000 ppm) elements in single mineral phases of polished sections is surveyed, and examples of their application to ordinary, carbonaceous and enstatite chondrites are provided. Radiographic methods surveyed include fission-track radiography (for U, Th, and Pu-244), alpha radiography using nuclear reactions (for Li and B), alpha autoradiography (for Bi and Pb), and beta autoradiography (for several elements in synthetic or biological samples). Two X-ray-fluorescence methods are compared: (1) photon-induced X-ray emission (PIXE), and (2) the potential use of synchrotron radiation. The latter is shown to allow much greater sensitivity than current PIXE technology and a much broader range of elements than particle-track radiography: the ppm analysis of 10-micron grains for all elements heavier than Na. These advantages are seen as balancing the high cost of accelerator use.

Burnett, D. S.↗
NASA NTRS1982

Directional solidification of alloys in systems containing a liquid miscibility gap

The problem considered is the unidirectional growth of alloys close to monotectic composition and within the miscibility gap when the direction of gravity is down the temperature gradient (solidification upwards) or up the temperature gradient (solidification downwards). The systems Al-In and Al-Bi are taken as examples. With solidification upwards it is shown that bulk liquid composition adjusts to that of the monotectic while in the reverse situation, the bulk liquid gradually rises. In the former case it is possible to grow aligned fibrous structures of monotectic composition but in the latter the microstructures are irregular and globular.

Grugel, R. N.↗
NASA NTRS1983

Improved fabrication techniques for infrared bolometers

Ion implantation and sputter metallization are used to produce ohmic electrical contacts to Ge:Ga chips. The method is shown to give a high yield of small monolithic bolometers with very little low-frequency noise. It is noted that when one of the chips is used as the thermometric element of a composite bolometer it must be bonded to a dielectric substrate. The thermal resistance of the conventional epoxy bond is measured and found to be undesirably large. A procedure for soldering the chip to a metallized portion of the substrate in such a way as to reduce this resistance is outlined. An evaluation is made of the contribution of the metal film absorber to the heat capacity of a composite bolometer. It is found that the heat capacity of a NiCr absorber at 1.3 K can dominate the bolometer performance. A Bi absorber possesses significantly lower heat capacity. A low-temperature blackbody calibrator is built to measure the optical responsivity of bolometers. A composite bolometer system with a throughput of approximately 0.1 sr sq cm is constructed using the new techniques. The noise in this bolometer is white above 2.5 Hz and is slightly below the value predicted by thermodynamic equilibrium theory.

Lange, A. E.↗
NASA NTRS1983

Siderophile, lithophile and mobile trace elements in the lunar meteorite Allan Hills 81005

The content of trace elements (siderophile Co, Au, As, Sb, Ga; chalcophile/mobile Se, Te, Bi, In, Ag, Zn, Tl, Cd; lithophile Rb, Cs, U) is investigated to ascertain whether the meteorite is of lunar origin. Five elements reflect lunar crustal processes, whereas the remaining 11 siderophile and mobile elements suggest 1.4 + or - 0.5 percent micrometeorite admixture or enrichment by thermal redistribution on the moon. It is found that the impact launching of ALH A81005 to the earth was not attended by substantial shock loading. A Martian origin for severely shocked SNC meteorites is therefore considered plausible.

Verkouteren, R. M.↗
NASA NTRS1984

Inversion algorithms for the microwave remote sensing of soil moisture. Experiments with swept frequency microwaves

Two experiments were performed employing swept frequency microwaves for the purpose of investigating the reflectivity from soil volumes containing both discontinuous and continuous changes in subsurface soil moisture content. Discontinuous moisture profiles were artificially created in the laboratory while continuous moisture profiles were induced into the soil of test plots by the environment of an agricultural field. The reflectivity for both the laboratory and field experiments was measured using bi-static reflectometers operated over the frequency ranges of 1.0 to 2.0 GHz and 4.0 to 8.0 GHz. Reflectivity models that considered the discontinuous and continuous moisture profiles within the soil volume were developed and compared with the results of the experiments. This comparison shows good agreement between the smooth surface models and the measurements. In particular the comparison of the smooth surface multi-layer model for continuous moisture profiles and the yield experiment measurements points out the sensitivity of the specular component of the scattered electromagnetic energy to the movement of moisture in the soil.

Hancock, G. D.↗
NASA NTRS1984

Astronomical application of IR CID technology

A portable microcomputer data system was developed to test a 2 x 64-element Si:Bi charge injection device (CID) infrared detector array on the Lick Observatory Shane telescope. An existing 0.5 m spectrograph was used for the tests after modification, and a spectral resolution of 1000 was achieved. Slow device response, due to the low background conditions in the spectrograph were shown. Astronomical data were later obtained, and a device read noise on the order of a few hundred electrons was achieved. The signal to noise ratios of the resulting spectra were about a factor of five lower than what could have been achieved with discrete photoconductive detectors. It is concluded that the CID array is competitive for applications in backgrounds lower than those used in the tests.

Rank, D. M.↗
NASA NTRS1984

Assessment of Thematic Mapper Band-to-band Registration by the Block Correlation Method

The design of the Thematic Mapper (TM) multispectral radiometer makes it susceptible to band-to-band misregistration. To estimate band-to-band misregistration a block correlation method is employed. This method is chosen over other possible techniques (band differencing and flickering) because quantitative results are produced. The method correlates rectangular blocks of pixels from one band against blocks centered on identical pixels from a second band. The block pairs are shifted in pixel increments both vertically and horizontally with respect to each other and the correlation coefficient for each shift position is computed. The displacement corresponding to the maximum correlation is taken as the best estimate of registration error for each block pair. Subpixel shifts are estimated by a bi-quadratic interpolation of the correlation values surrounding the maximum correlation. To obtain statistical summaries for each band combination post processing of the block correlation results performed. The method results in estimates of registration error that are consistent with expectations.

Card, D. H.↗
NASA NTRS1984

A cryogenically cooled, multidetector spectrometer for infrared astronomy

A liquid helium-cooled, 24 detector grating spectrometer was developed and used for low resolution astronomical observations in the 5 to 14 micron spectral range. The instrument operated on the 91 cm Kuiper Airborne Observatory, the 3 m IRTF (Mauna Kea), the 3 m Shane telescope Observatory, the 3 m Shane telescope (Lick Observatory), and the 152 cm NASA and University of Arizona telescope. The detectors are discrete Si:Bi photoconductors with individual metal oxide semiconductor field effect transistor preamplifiers operating at 4 K. The system uses a liquid helium-cooled slit, order-sorter filter, collimator mirror, grating, and camera mirror arranged in a Czerny-Turner configuration with a cold stop added between the collimator mirror and the grating. The distances between components are chosen so that the collimator mirror images the secondary mirror of the telescope onto the cold stop, thus providing a very effective baffle. Scattered radiation is effectively reduced by using liquid helium-cooled, black baffles to divide the spectrometer into three separate compartments. The system noise-equivalent flux density, when used on the 152 cm telescope from 8 to 13 microns with a resolving power of 50, is 4.4 x 10 to the minus 17th power W/sq cm micron square root of Hz. The main applications are for measuring continuum radiation levels and solid state emission and absorption features in regions of star and planet formation.

Witteborn, F. C.↗
NASA NTRS1983

Enstatite chondrites - Trace element clues to their origin

Three EH and three EL chondrites have been subjected to RNAA analysis for 20 trace elements, and interelement correlations were examined in order to assess the effects of nebular fractionation and metamorphism. The refractory siderophiles Ir, Os, and Re correlate with the normal siderophiles Ni, Pd, Au, Sb, and Ge, in ELs but not in EHs. The two element groups presumably condensed on separate phases at first, but concentrated in metal during metabolism. Volatiles are consistently more depleted in ELs than EHs. Strong correlations are found for In-Tl, Tl-Bi, and Zn-Cd-In, which are equally consistent with predicted condensation curves for the solar nebula and with volatilization curves for artificially heated Abee. The three factors accounting for 93 percent of variance reflect volatile, siderophile, and chalcophile behavior.

Hertogen, J.↗
NASA NTRS1984

Chemical studies of L chondrites. III - Mobile trace elements and Ar-40/Ar-39 ages

Radiochemical neutron activation analysis has been used to determine the content of the mobile trace elements Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Se, Te, Tl, and Zn, in L4-6 chondrites with undisturbed Ar-40 release patterns or patterns showing some 4.4-4.6 Gyr plateau disturbance that indicates some shock-induced loss. The mean concentrations are significantly lower in 16 chondrites with disturbed patterns than in 4 with undisturbed ones, consistent with shock-induced mobilization. Significantly lower mean concentrations of nearly all trace elements in 26 strongly shocked chondrites than in 14 mildly shocked ones indicate loss in shock-formed FeS-Fe eutectic and/or by means of vaporization during cooling of shock-heated collisional debris.

Huston, T. J.↗
NASA NTRS1984

Fatigue in Composite Materials

The deformation and failure behavior of graphite/epoxy tubes under biaxial loading was investigated. The increase of basic understanding of and provide design information for the bi-axial response of graphite/epoxy composites to fatigue loads are considered.

Source record↗
NASA NTRS1984

SPAR X Technical Report for Experiment 76-22 Directional Solidification of Magnetic Composites

The effects of gravity on Bridgman-Stockbarger directional solidification of off-eutectic Bi/MnBi were studied in reduced gravity aboard the SPAR X flight and compared to normal-gravity investigations and previous eutectic Bi/MnBi SPAR flight experiments. The directional solidification of off-eutectic Bi/MnBi results in either a dendritic structure connected with local cooperative growth or a coupled low volume fraction faceted/non faceted aligned rod eutectic whose Mn macrosegregation, MnBi rod size, interrod spacing, and thermal and magnetic properties are sensitive functions of the solidification processing conditions. Two hypoeutectic and two hypereutectic samples were solidified during 605 sec of furnace travel, with an initial 265 sec low-gravity interval. Comparison Earth-gravity samples were solidified in the same furance assembly under identical processing conditions. Macrosegregation in the low-g samples was consistent with a metastable increase in Mn solubility in the Bi matrix, in partial agreement with previous Bi/MnBi SPAR findings of MnBi volume reduction.

Bethin, J.↗