Search NASA⌕ Search

SEARCH · Search NASA

Results for “stack”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Mechanically-stacked tandem solar cells with GaAsP on GaP and silicon

Preliminary results are encouraging for the achievement of high conversion efficiencies using a GaAsP top solar cell mechanically stacked on a conventional silicon solar cell. A realistic maximum of 29.4 percent is suggested when both the top and bottom solar cells are state of the art. Practical system efficiencies greater than 25 percent are attainable in the near future with the use of a state of the art bottom solar cell.

Negley, Gerald H.↗
NASA NTRS1987

Systolic arrays and stack decoding

The application of systolic priority queues to the sequential stack decoding algorithm is discussed in a review of the work of K. Yao and C. Y. Chang. Using a systolic array architecture, one can significantly improve the performance of such algorithms at high signal-to-noise ratios.

Shahshahani, M.↗
NASA NTRS1987

Satellite power using magnetically suspended flywheel stack

Research activities with magnetically suspended flywheels are reported. The purpose of the effort is to critically examine and further the development of all the key technologies which impact the inertial energy storage system. The results presented discuss the concept of a magnetically suspended flywheel as it applies to a 500 Watt-hour energy storage system. The proposed system is currently under hardware development and is based upon two pancake magnetic bearings arranged in a vertical stack.

Kirk, James A.↗
NASA NTRS1987

Effect of ship-stack effluents on cloud reflectivity

Under stable meteorological conditions the effect of ship-stack exhaust on overlying clouds was detected in daytime satellite images as an enhancement in cloud reflectivity at 3.7 micrometers. The exhaust is a source of cloud-condensation nuclei that increases the number of cloud droplets while reducing droplet size. This reduction in droplet size causes the reflectivity at 3.7 micrometers to be greater than the levels for nearby noncontaminated clouds of similar physical characteristics. The increase in droplet number causes the reflectivity at 0.63 micrometer to be significantly higher for the contaminated clouds despite the likelihood that the exhaust is a source of particles that absorb at visible wavelengths. The effect of aerosols on cloud reflectivity is expected to have a larger influence on the earth's albedo than that due to the direct scattering and absorption of sunlight by the aerosols alone.

Coakley, James A., Jr.↗
NASA NTRS1988

Stacked-Disk Combustor

Materials chosen for strength rather than thermal conductivity. Stacked washerlike disks accommodate built-in coolant passages while providing combustion zone of ideal shape. Fuel flows through coolant passages where preheated before entering combustion zone through passages in disks. Eight coolant passages in cross section, although number in particular application determined by required rate of flow of fuel and pressure drop. Combustion chamber operates for greater efficiency at pressures and temperatures higher than those of conventional tube-wall combustion chamber.

Ingle, Walter B.↗
NASA NTRS1988

Stacked Metal Silicide/Silicon Far-Infrared Detectors

Selective doping of silicon in proposed metal silicide/silicon Schottky-barrier infrared photodetector increases maximum detectable wavelength. Stacking layers to form multiple Schottky barriers increases quantum efficiency of detector. Detectors of new type enhance capabilities of far-infrared imaging arrays. Grows by molecular-beam epitaxy on silicon waferscontaining very-large-scale integrated circuits. Imaging arrays of detectors made in monolithic units with image-preprocessing circuitry.

Maserjian, Joseph↗
NASA NTRS1988

Effects of operating parameters on PAFC stack performance

This work was performed to assess actual relationships of phosphoric acid fuel cell voltage responses obtained from subscale cells with air-cooled and full size cells in stacks as a function of operating parameters. Key relationships were verified and found to be in agreement with the Nerst equation. An empirical equation was developed to predict cell voltages as a function of the measureable parameters.

Le, M. T.↗
NASA NTRS1988

Satellite power using a magnetically suspended flywheel stack

Research activities with magnetically suspended flywheels are reported. The purpose of the effort is to critically examine and further the development of all the key technologies which impact the inertial energy storage system. The results presented discuss the concept of a magnetically suspended flywheel as it applies to a 500 Watt-hour energy storage system. The proposed system is currently under hardware development and is based upon two pancake magnetic bearings arranged in a vertical stack.

Kirk, James A.↗
NASA NTRS1988

Predicted and observed effects of stacking sequence and delamination size on instability-related delamination growth

A three-dimensional, geometrically nonlinear finite element analysis was used to calculate strain-energy release rate distributions for several laminates which exhibited instability-related delamination growth. Two stacking sequences, (0/90/90/0)6 and (90/0/0/90)6 were considered. The specimens were fabricated with a double layer of 0.013 mm Kapton film located between the fourth and fifth plies, thereby simulating a delamination. Initial delamination sizes were 30, 40, or 60 mm in diameter. The static strain corresponding to delamination growth was determined experimentally. Comparison of the analytical and experimental results indicated that delamination growth was governed by the magnitude of GI.

Whitcomb, John D.↗
NASA NTRS1989

The correlation between the temperature dependence of the CRSS and the formation of superlattice-intrinsic stacking faults in the nickel-base superalloy PWA 1480

The PWA 1480 nickel-base superalloy is known to exhibit a unique minimum in the critical resolved shear stress (CRSS) at about 400 C. This paper reports an observation of a deformation mechanism whose temperature dependence correlates exactly with the reduction in the CRSS. It was found that, after monotonic or cyclic deformation of PWA 1480 at 20 C, the deformation substructures typically contain high density of superlattice-intrinsic stacking faults (S-ISFs) within the gamma-prime precipitates. As the temperature of deformation is increased, the density of S-ISFs is reduced, until finally no faults are observed after deformation in the range from 400 to 705 C. The reduction in the fault density corresponds exactly to the reduction in the CRSS, and the temperature at which the fault density is zero corresponds with the minimum in the CRRS. Two possible mechanisms related to the presence of the S-ISFs in the alloy are considered.

Milligan, Walter W.↗
NASA NTRS1990

Microstrip subarray with coplanar and stacked parasitic elements

A parasitic subarray configuration combining the coplanar and stacked geometries is proposed and studied. It is numerically shown that a two-layer cross offers a gain enhancement of several decibels compared with either the coplanar cross or the two-layer electromagnetically coupled antenna. Preliminary experimental results appear to be in agreement with this estimate.

Lee, K. F.↗
NASA NTRS1991

Stacking Oxygen-Separation Cells

Simplified configuration and procedure developed for assembly of stacks of solid-electrolyte cells separating oxygen from air electrochemically. Reduces number of components and thus reduces probability of such failures as gas leaks, breakdown of sensitive parts, and electrical open or short circuits. Previous, more complicated version of cell described in "Improved Zirconia Oxygen-Separation Cell" (NPO-16161).

Schroeder, James E.↗
NASA NTRS1991

Stacked-Gate FET's For Analog Memory Elements

Three-terminal, double-stacked-gate field-effect transistor (FET), developed as analog memory element. Particularly suited for use as synapse with variable connection strength in electronic neural network. Provides programmable, nonvolatile resistive connection, somewhat in manner of porous-gate FET described in "Porous-Floating-Gate Field-Effect Transistor" (NPO-17532). Resembles commercial erasable programmable read-only memory (EPROM) device, except for thickness of layers of silicon dioxide electrically isolating gates. Either p-channel or n-channel device.

Thakoor, Anilkumar P.↗
NASA NTRS1991

Laterally stacked Schottky diodes for infrared sensor applications

Laterally stacked Schottky diodes for infrared sensor applications are fabricated utilizing porous silicon having pores. A Schottky metal contract is formed in the pores, such as by electroplating. The sensors may be integrated with silicon circuits on the same chip with a high quantum efficiency, which is ideal for IR focal plane array applications due to uniformity and reproducibility.

Lin, True-Lon↗
NASA NTRS1991

The mechanisms and temperature dependence of superlattice stacking fault formation in the single-crystal superalloy PWA 1480

The mechanism of the formation of superlattice staking faults in the single-crystal nickel-base superalloy PWA 1480 was investigated by observing deformation microstructures in the superalloy single crystals in the temperature range 20-1100 C. Results showed that, in addition to superlattice stacking faults observed after slow strain rate deformation at temperatures from 700 to 950 C, a high-density of superlattice staking faults formed after deformation at 200 C and below. The mechanisms of fault formation, which are different in the high- and the low-temperature regimes, are discussed.

Milligan, Walter W.↗
NASA NTRS1992

An Extention of the Raman-lidar Technique to Measure the Velocity and Temperature of the Atmospheric Emission Jets from Stacks

If a Raman lidar possesses a proper spatial resolution sufficient for acquiring profiles of return signals across an emission jet, then the difference in number densities of nitrogen molecules within the jet and outside it will cause a dip in the lidar return signal from nitrogen. Experimentation showed that the Raman lidar technique can accurately measure the velocity and temperature of atmospheric emission from smoke stacks.

Arshinov, Yu. F.↗
NASA NTRS1992

Optimization of laminated stacking sequence for buckling load maximization by genetic algorithm

The use of a genetic algorithm to optimize the stacking sequence of a composite laminate for buckling load maximization is studied. Various genetic parameters including the population size, the probability of mutation, and the probability of crossover are optimized by numerical experiments. A new genetic operator - permutation - is proposed and shown to be effective in reducing the cost of the genetic search. Results are obtained for a graphite-epoxy plate, first when only the buckling load is considered, and then when constraints on ply contiguity and strain failure are added. The influence on the genetic search of the penalty parameter enforcing the contiguity constraint is studied. The advantage of the genetic algorithm in producing several near-optimal designs is discussed.

Le Riche, Rodolphe↗