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At least 685 records · Page 38

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NASA NTRS1986

Development of composite facets for the surface of a space-based solar dynamic concentrator

An account is given of the composite fabrication techniques envisioned for the production of mirror-quality substrates furnishing the specular reflectance required for the NASA Space Station's solar dynamic concentrator energy system. The candidate materials were graphite fiber-reinforced glass, aluminum, and polymer matrices whose surfaces would be coated with thin metal layers and with atomic oxygen degradation-inhibiting protective coatings to obtain the desired mirror surface. Graphite-epoxy mirror substrate samples have been found to perform satisfactorily for the required concentrator lifetime.

Ayers, Schuyler R.↗

NASA NTRS1987

Stress concentration around a part-through hole weakening a laminated plates

A quasi-three-dimensional-elasticity type theory, based on the assumptions of transverse inextensibility and layerwise constant shear-angle, is presented, in the context of an assumed quadratic displacement potential energy approach, for analyzing an edge-loaded laminated plate weakened by the presence of a part-through hole. Numerical results, obtained using the C-deg-type triangular finite element, indicate the existence of severe cross-sectional warping in the vicinity of the hole and plate boundaries. Furthermore, the three-dimensional nature of the stress concentration factor in the neighborhood of the hole boundary is clearly exhibited. Besides, very high stress concentration factors are found in the layer weakened by the part-through hole. The numerical results presented should serve as bench-mark solutions for future comparisons.

Chaudhuri, Reaz A.↗

NASA NTRS1988

Relating Nimbus-7 37 GHz data to global land-surface evaporation, primary productivity and the atmospheric CO2 concentration

Global observations at 37 GHz by the Nimbus-7 SMMR are related to zonal variations of land surface evaporation and primary productivity, as well as to temporal variations of atmospheric CO2 concentration. The temporal variation of CO2 concentration and the zonal variations of evaporation and primary productivity are shown to be highly correlated with the satellite sensor data. The potential usefulness of the 37-GHz data for global biospheric and climate studies is noted.

Choudhury, B. J.↗

NASA NTRS1988

Mass spectrometer for measurements of relative ion concentrations in plasmas

A mass spectrometer which can be used to measure relative ion concentrations in a multiion component plasma has been designed for use in a strong (1-4-kG) uniform magnetic field. The spectrometer features an acceleration region which accelerates thermal ions through a series of three tantalum electrodes at a 30 deg angle to the B field, and a collection region in which ions are selectively collected, depending on the size of their gyroradii, by a cylindrical collector. Relative ion concentrations are determined from measurements of the collector current as a function of accelerating voltage. Results obtained using this instrument in a Q-machine device operated with a two-ion (Cs+/K+) component plasma are presented.

Suszcynsky, David M.↗

NASA NTRS1988

Estimating sea ice concentration from satellite passive microwave data and a physical model

Sea ice remote sensing and estimation of concentrations of each of several ice types from passive microwave satellite data is described. The approach is based on the Kalman filter; it incorporates surface temperature, ice advection, and ice deformation data derived from drifting buoys and uses the whole temporal microwave record to make a smoothed estimate of ice concentration. The method allows resolution of previously ambiguous surface types. An example using time histories of two SMMR measurements to resolve the fractional areas of four surface types: open water, first-year, second-year and older multiyear ice is shown.

Rothrock, D. A.↗

NASA NTRS1989

Domed Fresnel lens concentrator technology for space application

Over the past three years, NASA Lewis and Entech, Inc. have been investigating the use of high efficiency refractive photovoltaic concentrators for use in space. The design currently under investigation uses a square domed Fresnel lens to focus light on a GaAs concentrator cell. A prismatic cell cover, which directs light away from the front contacts and thus eliminates metalization losses, is applied to the top of the GaAs cell to further enhance array efficiency. The latest experimental results based on testing the GaAs cell/prism cover assembly at standard and operating conditions are presented.

Piszczor, Michael F., Jr.↗

NASA NTRS1989

The 25 percent-efficient GaAs Cassegrainian concentrator cell

Very high-efficiency GaAs Cassegrainian solar cells have been fabricated in both the n-p and p-n configurations. The n-p configuration exhibits the highest efficiency at concentration, the best cells having an efficiency eta of 24.5 percent (100X, AM0, temperature T = 28 C). Although the cells are designed for operation at this concentration, peak efficiency is observed near 300 suns (eta = 25.1 percent). To our knowledge, this is the highest reported solar cell efficiency for space applications. The improvement in efficiency over that reported at the previous SPRAT conference is attributed primarily to lower series resistance and improved grid-line plating procedures. Using previously measured temperature coefficients, researchers estimate that the n-p GaAs cells should deliver approximately 22.5 percent efficiency at the operating conditions of 100 suns and T = 80 C. This performance exceeds the NASA program goal of 22 percent for the Cassegrainian cell. One hundred Cassegrainian cells have been sent to NASA as deliverables, sixty-eight in the n-p configuration and thirty-two in the p-n configuration.

Hamaker, H. C.↗

NASA NTRS1988

Airborne in-situ spectral characterization and concentration estimates of fluorescent organics as a function of depth

The primary purpose of many in-situ airborne light scattering experiments in natural waters is to spectrally characterize the subsurface fluorescent organics and estimate their relative concentrations. This is often done by shining a laser beam into the water and monitoring its subsurface return signal. To do this with the proper interpretation, depth must be taken into account. If one disregards depth dependence when taking such estimates, both their spectral characteristics and their concentrations estimates can be rather ambiguous. A simple airborne lidar configuration is used to detect the subsurface return signal from a particular depth and wavelength. Underwater scatterometer were employed to show that in-situ subsurface organics are very sensitive to depth, but they also require the use of slow moving boats to cover large sample areas. Also, their very entry into the water disturbs the sample it is measuring. The method described is superior and simplest to any employed thus far.

Tittle, R. A.↗

NASA NTRS1989

An integrating matrix formulation for buckling of rotating beams including the effects of concentrated masses

The integrating matrix technique of computational mechanics is extended to include the effects of concentrated masses. The stability of a flexible rotating beam with discrete masses is analyzed to determine the critical rotational speeds for buckling in the inplane and out-of-plane directions. In this problem, the beam is subjected to compressive centrifugal forces arising from steady rotation about an axis which does not pass through the clamped end of the beam. To determine the eigenvalues from which stability is assessed, the differential equations of motion are solved numerically by combining the extended integrating matrix method with an eigenanalysis. Stability boundaries for a discrete mass representation of a uniform beam are shown to asymptotically approach the stability boundaries for the corresponding continuous mass beam as the number of concentrated masses is increased. An error in the literature is also noted for the discrete mass problem concerning the behavior of the critical rotational speed for inplane buckling as the radius of rotation of the clamped end of the beam is reduced.

Lakin, William D.↗

NASA NTRS1988

Variability of surface pigment concentrations in the South Atlantic Bight

A time sequence of surface pigment images of the South Atlantic Bight (SAB), derived from the Nimbus 7 CZCS for the period between November 1978 and October 1979, was correlated with in situ observations of hydrographic parameters, fresh-water discharge, sea level, coastal winds, and currents in order to couple physical processes and the spatial and temporal variability of the surface pigment fields. A definite seasonal modulation of the surface pigment fields was found, with the concentrations in the Georgia Bight being highest in summer, and those north of Cape Romain highest in winter. This phase difference was found to be the result of variations in wind fields, Gulf Stream-shelf interactions, and fresh-water discharge patterns. At some locations (e.g., near Charleston) the alongshore band of high pigment concentrations increased in width throughout the year; at other locations (near Jacksonville), the alongsore band exhibited a minimum width in the summer and a maximum width in the fall of 1979.

Mcclain, Charles R.↗

NASA NTRS1988

Investigation of stress concentration factor - Stress intensity factor interaction for flaws in filleted rods

To predict the fatigue life of machine parts which contain flaws in regions of stress concentration, the engineer needs to treat a series of crack sizes and/or shapes quickly and economically. In this paper the stress intensity factor distributions for circular surface flaws in the roots of fillets in rods loaded by remote tension are presented and examined. The examination reveals insight into the interaction of cracks with other stress concentrating discontinuities, and based on this it is suggested that weight function methods used in conjunction with known crack solutions may provide needed, efficient stress intensity factor prediction methods for such three-dimensional geometries.

Springfield, C. W., Jr.↗

NASA NTRS1988

Temperature coefficients for concentrator cells at various electron and proton fluence levels

Data are presented on the Isc, Voc and Pmax temperature coefficients for several small concentrator solar cells. The cells are AlGaAs (1.72 eV), GaAs, silicon and InGaAs (1.1 eV) concentrator cells operating at 6.25 and 100 times AM0. The temperature range covered was 25 to 100 C. Cells were irradiated with 1-MeV electrons and 37-MeV protons, and data are presented at different fluence levels.

Curtis, Henry B.↗

NASA NTRS1988

Effects of Cobalt Concentration on the Relative Resistance to Octahedral and Cube Slip in Nickel-Base Superalloys

Compression yielding tests were performed at 760 C on crystals of the Ni base superalloys Rene 150 and a modified MAR-M247, both having two different Co concentrations. For both alloy bases, increasing Co concentration was shown to decrease the critical resolved shear stress for octahedral slip, but to have little effect on that for cube slip. The results suggest that decreasing complex stacking fault energy in the gamma-prime with increasing Co could account for the observed effects.

Bobeck, Gene E.↗

NASA NTRS1989

An intercomparison of measurement systems for vapor and particulate phase concentrations of formic and acetic acids

During June 1986, eight systems for measuring vapor phase and four for measuring particulate phase concentrations of formic acid (HCOOH) and acetic acid (CH3COOH) were intercompared in central Virginia. HCOOH and CH3COOH vapors were sampled by condensate, mist, Chromosorb 103 GC resin, NaOH-coated annular denuders, NaOH-impregnated quartz filters, K2CO3 and NaCO3-impregnated cellulose filters, and Nylasorb membranes. Atmospheric aerosol was collected on Teflon and Nuclepore filters using both hi-vol and lo-vol systems to measure particulate phase concentrations. Performances of the mist chamber and K2CO3-impregnated filter techniques were evaluated using zero air and ambient air spiked with HCOOH(g) and CH3COOH(g), and formaldehyde from permeation sources. The advantages and drawbacks of these methods are reported and discussed.

Keene, William C.↗

NASA NTRS1990

Concentrating Gaseous Contaminants For Monitoring

Apparatus concentrates contaminants outgassing from specimens in vacuum and passes concentrated contaminants to gas-chromatography/mass-spectrometry system for analysis. Cold wall of collection chamber adsorbs gases from specimen in isothermal cell. When wall heated, plate desorbs gases so they can be analyzed. Collection chamber maintained at low pressure throughout adsorption and desorption process. Determines whether candidate materials for use in vacuum environments generate harmful substances.

Mahone, William C.↗

NASA NTRS1990

Experiment K-6-11. Actin mRNA and cytochrome c mRNA concentrations in the tricepts brachia muscle of rats

It is well known that some skeletal muscles atrophy as a result of weightlessness (Steffen and Musacchia 1986) and as a result of hindlimb suspension (Tischler et al., 1985, Thomason et al., 1987). Because the content of protein is determined by the rates of protein synthesis and degradation, a decrease in protein synthesis rate, or an increase in the protein degradation, or changes in both could produce the atrophy. Indeed, an increased protein degradation (Tischler et al., 1985) and a decreased protein synthesis (Thomason et al., 1988) have been observed in skeletal muscles of suspended hindlimbs of rats. Any decrease in protein synthesis rate could be caused by decreases in mRNA concentrations. Such decreases in the concentration and content of alpha-actin mRNA and cytochrome c mRNA have been noted in skeletal muscles of hindlimb suspended rats (Babij and Booth, 1988). From these findings researchers hypothesized that alpha-actin mRNA and cytochrome c mRNA would decrease in the triceps brachia muscle of Cosmos 1887 rats.

Booth, F. W.↗

NASA NTRS1990

Investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data

The effects of ice surface melt on microwave signatures and errors in the calculation of sea ice concentration are examined, using active and passive microwave data sets from the Marginal Ice Zone Experiment aircraft flights in the Fram Strait region. Consideration is given to the possibility of using SAR to supplement passive microwave data to unambiguously discriminate between open water areas and ponded floes. Coincident active multichannel microwave radiometer and SAR measurements of individual floes are used to describe the effects of surface melt on sea ice concentration calculations.

Cavalieri, Donald J.↗

NASA NTRS1989

Observations of winter polynyas and fractures using NOAA AVHRR TIR images and Nimbus-7 SMMR sea ice concentration charts

The validity of the daily sea ice concentration charts obtained from Nimbus-7 SMMR data is tested against thermal IR NOAA AVHRR-4 images with a 1.1 x 1.1 km resolution. Polynyas and fractures recorded in both data sets are compared for the same times over the same areas. Although the coarser resolution of SMMR data leads to a loss of detail, it is found that the ice concentration charts provide valuable data on openings in the ice. The SMMR data on the location, orientation, and size of polynyas and fractures are shown to be in good agreement with the AVHRR data. Also, the results suggest that the location and orientation of plynyas and fractures are related to the direction of surface winds.

Dey, B.↗