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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.

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At least 595 records · Page 33

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NASA NTRS1981

DC calibration of the strain sensitivity of a single mode optical fiber interferometer

The strain sensitivity of an optical fiber interferometer developed for the detection of pulsed ultrasonic waves in solids was calibrated. Light from the output ends of both fibers was superimposed to form an interference fringe pattern that was interrogated in the far field to give a signal proportional to the differential optical fiber path length. Strain sensitivity is determined by comparing data obtained by clamping and bending the bar at different lengths to simple cantilever beam theory. A minimum theoretical detectable strain of less than 10 to the minus 10th power is indicated.

Claus, R. O.↗

NASA NTRS1982

Current economic and sensitivity analysis for ID slicing of 4 inch and 6 inch diameter silicon ingots for photovoltaic applications

The economics and sensitivities of slicing large diameter silicon ingots for photovoltaic applications were examined. Current economics and slicing add on cost sensitivities are calculated using variable parameters for blade life, slicing yield, and slice cutting speed. It is indicated that cutting speed has the biggest impact on slicing add on cost, followed by slicing yield, and by blade life as the blade life increases.

Roberts, E. G.↗

NASA NTRS1982

A medium sensitivity X-ray survey using the Einstein Observatory - The log N-log S relation for extragalactic X-ray sources

The paper presents results of an X-ray survey of about 50 sq deg of the high galactic latitude sky at sensitivities in the range of 7 x 10 to the -14 to 5 x 10 to the -12 ergs/sq cm/s. The number-flux relation is derived for the extragalactic population to yield a best-fit power-law slope of 1.53 + or - 0.16, and the content of the sample is analyzed in terms of types of sources, appearing to be significantly different from the content of similar samples selected at higher fluxes. The medium sensitivity sample of extragalactic sources is dominated by active galactic nuclei, while samples selected at higher fluxes and higher energies are dominated by clusters of galaxies. Thus, the number-flux relation for extragalactic sources may be interpreted to a first approximation as the sum of the two different distributions with flatter and steeper slopes describing clusters and AGNs, respectively.

Maccacaro, T.↗

NASA NTRS1982

Predicting radiation sensitivity of polymers

Recently two independent applications have emerged for highly radiation-sensitive polymers: as resists for production of microelectronic circuitry and as materials to record the tracks of energetic nuclear particles. The relief images used for masking in resist materials are generated by radiation-induced differential dissolution rates, whereas the techniques used in recording nuclear particle tracks employ differential etching processes, that is, development by a chemical etchant that actually degrades the polymer. It is found that the sensitivity of materials to these very different processes is related to their gamma-ray scission efficiency. This correlation provides a predictive capability.

Osullivan, D.↗

NASA NTRS1982

Sensitivity of the boundary layer energy fluxes to forcing parameters in a simple climate model

Winter and summer surface temperatures and time-averaged boundary layer energy fluxes are calculated by utilizing the Saltzman-Ashe parameterization for boundary layer fluxes in a two-level static model. The results are found to agree with observed patterns. Within the framework of this simple model, sensitivity analyses of the time-averaged boundary layer energy fluxes are conducted. Based on these results some of the forcing parameters (such as the subsurface temperature, cloud cover, surface albedo, etc.) are arranged in a hierarchical order of importance. A generalized method of sensitivity analysis is also suggested.

Rao, M. S.↗

NASA NTRS1982

Gravity receptors in a microcrustacean water flea - Sensitivity of antennal-socket setae in Daphnia magna

Gravity receptors of Dephnia magna were discovered on the basal segment of the swimming antennae and were shown to respond to upward water currents that pass the animal as it sinks between swimming strokes. Sensitivity of the gravity perceiving mechanism was tested by subjecting daphnids to a series of five decreasingly dense aqueous solutions (neutral density to water) in darkness (to avoid visual cues). Three-dimensional, video analysis of body position (pitch, yaw and roll) and swimming path (hop and sink, vertical and horizontal patterns) revealed a gradual threshold that occurred near a density difference between the animal and its environment of less than 0.25%. Because daphnids do not sink but continue to slide after stroking in the increased density solutions, gravity perception appears to occur during a vertical swing of the longitudinal body axis to the vertical plane, about their center of gravity, and, thereby, implies a multidirectional sensitivity for the antennal-socket setae.

Meyers, D. G.↗

NASA NTRS1983

Sensitivity studies with a coupled ice-ocean model of the marginal ice zone

An analytical coupled ice-ocean model is considered which is forced by a specified wind stress acting on the open ocean as well as the ice. The analysis supports the conjecture that the upwelling dynamics at ice edges can be understood by means of a simple analytical model. In similarity with coastal problems it is shown that the ice edge upwelling is determined by the net mass flux at the boundaries of the considered region. The model is used to study the sensitivity of the upwelling dynamics in the marginal ice zone to variation in the controlling parameters. These parameters consist of combinations of the drag coefficients used in the parameterization of the stresses on the three interfaces atmosphere-ice, atmosphere-ocean, and ice-ocean. The response is shown to be sensitive to variations in these parameters in that one set of parameters may give upwelling while a slightly different set of parameters may give downwelling.

Roed, L. P.↗

NASA NTRS1983

Sensitivity of model calculations to uncertain inputs, with an application to neutron star envelopes

A method is given for determining the sensitivity of certain types of calculations to the uncertainties in the input physics or model parameters; this method is applicable to problems that involve solutions to coupled, ordinary differential equations. In particular the sensitivity of calculations of the thermal structure of neutron star envelopes to uncertainties in the opacity and equation of state is examined. It is found that the uncertainties in the relationship between the surface and interior temperatures of a neutron star are due almost entirely to the imprecision in the values of the conductive opacity in the region where the ions form a liquid; here the conductive opacity is, for the most part, due to the scattering of electrons from ions.

Epstein, R. I.↗

NASA NTRS1985

Calculating Closed-Loop Sensitivity to Parameter Variations

Performance sensitivity calculated by back substitution. Original Lyapunov equation differentiated two times with respect to parameter p. Each differential turns out to yield Lyapunov equation for first and second derivatives with respective to parameter p of steady-state covariance of state variables. Derivatives desired closed-loop performance sensitivities.

Schaechter, D. B.↗

NASA NTRS1983

A helicopter flight investigation of roll-control sensitivity, damping and cross coupling in a low altitude lateral maneuvering task

A helicopter in-flight simulation was conducted to determine the effects of variations in roll damping, roll sensitivity, and pitch and roll rate cross-coupling on helicopter flying qualities in a low altitude maneuver. The experiment utilized the UH-1H helicopter in-flight simulator, which is equipped with the V/STOLAND avionics system. The response envelope of this vehicle allowed simulation of configurations with low to moderate damping and sensitivity. A visual, low level slalom course was set up, consisting of constant speed and constant altitude S-turns around the 1000 ft makers of an 8000 ft runway. Results are shown in terms of Cooper-Harper pilot ratings, pilot commentary, and statistical and frequency analyses of the lateral characteristics. These results show good consistency with previous ground simulator results and are compared with existing flying qualities criteria.

Corliss, L. D.↗

NASA NTRS1984

Climate sensitivity with a seasonal cycle energy balance model

The sensitivity of climate which may have a local maximum as the ice cap passes through a midlatitude region where the atmosphere's transport efficiency varies strongly with latitude is examined. This behavior, found in a two level primitive equations climate model forced with annual mean insolation, was reproduced in an energy balance model (EBM) by making the diffusion coefficient a function of latitude. The two level seasonally varying EBM was applied and the global mean surface temperature vs. solar constant for this model are shown and two regions of enhanced sensitivity appear. The snowcover distributions around the year for three cases are shown.

Suarez, M. J.↗

NASA NTRS1983

Purging sensitive science instruments with nitrogen in the STS environment

Potential contamination of extremely sensitive science instruments during prelaunch, launch, and earth orbit operations are a major concern to the Galileo and International Solar Polar Mission (ISPM) Programs. The Galileo Program is developing a system to purify Shuttle supplied nitrogen gas for in-flight purging of seven imaging and non-imaging science instruments. Monolayers of contamination deposited on critical surfaces can degrade some instrument sensitivities as much as fifty percent. The purging system provides a reliable supply of filtered and fried nitrogen gas during these critical phases of the mission when the contamination potential is highest. The Galileo and ISPM Programs are including the system as Airborne Support Equipment (ASE).

Lumsden, J. M.↗

NASA NTRS1984

Effects of Shuttle bay environment on UV sensitive photographic film - Instrumentation for Get-Away-Special

An account is given of a Get-Away-Special experiment flown on Space Shuttles 7 and 8 investigating the effect of the space environment on Shumann emulsions. Shumann emulsions, having low gelatin content and no protective gelatin overcoating, are useful detectors of ultraviolet radiation shorter than 2200 angstroms but are extremely sensitive to environmental conditions and handling. The instrument required no interface with the Shuttle. It was turned on by an aneroid switch at an altitude of 50,000 feet. After that, its operation was controlled completely by a CMOS digital controller. Each hour, two temperatures and one voltage were read and stored in a CMOS programmable read only memory. At intervals, valves were opened and closed to expose SO 652 film strips of three sensitivities to the cargo bay environment for various time periods. The design and operation of the instrument package is described.

Kreplin, R. W.↗

NASA NTRS1984

A position-sensitive germanium detector for gamma-ray astronomy

The critical problem in high-resolution cosmic gamma-ray spectroscopy in the energy range from 0.02 to 10 MeV is the limited spectral sensitivity of the detectors used. This results from the small effective area of the detectors and the high background noise due to induced radioactivity and scattering in the detectors' high-energy particle environment. The effective area can be increased by increasing the number of detectors, but this becomes prohibitive because of the size and expense of the resulting instrument. We have taken a new approach: a segmented large-volume germanium gamma-ray detector which can effectively discriminate against internal background yet maintain the high spectral resolution and efficiency of conventional coaxial Ge detectors. To verify this concept, a planar detector divided into two segments has been fabricated and laboratory measurements agree well with Monte Carlo calculations. A large coaxial detector which will be divided into five segments is being built using the techniques developed for the planar detector. Monte Carlo calculations show that the sensitivity (minimum detectable flux) of the segmented coaxial detector is a factor of 2-3 better than conventional detectors because of the reduction in the internal background.

Varnell, L. S.↗

NASA NTRS1984

Maintenance of contamination sensitive surfaces on board long-term space vehicles

In the current age, highly sensitive instruments are being flown on spacecraft, and questions of contamination have become important. The present investigation is concerned with the available approaches which can provide long-term protection for contamination sensitive surfaces. Aspects and sources of spacecraft contamination are examined, taking into account materials outgassing, particulates, propulsion system interaction, overboard venting, man-made and cosmic debris, and atomic oxygen/ambient atmosphere interaction. Suitable protection approaches provided by current technology are discussed, giving attention to aperture covers, a possibility for a retractable cover design, gaseous purges, options for prolonging the lifetime of the thermal control system, and plume shields. Some new possibilities considered are related to an early warning system for excessive amounts of contamination, a molecular/wake shield, and the use of atomic oxygen.

Phillips, A.↗

NASA NTRS1984

Sensitivity analysis of limit state functions for probability-based plastic design

The evaluation of the total probability of a plastic collapse failure P sub f for a highly redundant structure of random interdependent plastic moments acted on by random interdepedent loads is a difficult and computationally very costly process. The evaluation of reasonable bounds to this probability requires the use of second moment algebra which involves man statistical parameters. A computer program which selects the best strategy for minimizing the interval between upper and lower bounds of P sub f is now in its final stage of development. The relative importance of various uncertainties involved in the computational process on the resulting bounds of P sub f, sensitivity is analyzed. Response sensitivities for both mode and system reliability of an ideal plastic portal frame are shown.

Frangopol, D. M.↗

NASA NTRS1984

Sensitivities of projected 1980 photovoltaic system costs to major system cost drivers

The sensitivity of projected 1990 photovoltaic (PV) system costs to major system cost drivers was examined. It includes: (1) module costs and module efficiencies; (2) area related balance of system (BOS) costs; (3) inverter costs and efficiencies; and (4) module marketing and distribution markups and system integration fees. Recent PV system cost experiences and the high costs of electricity from the systems are reviewed. The 1990 system costs are projected for five classes of PV systems, including four ground mounted 5-MWp systems and one residential 5-kWp system. System cost projections are derived by first projecting costs and efficiencies for all subsystems and components. Sensitivity analyses reveal that reductions in module cost and engineering and system integration fees seem to have the greatest potential for contributing to system cost reduction. Although module cost is clearly the prime candidate for fruitful PV research and development activities, engineering and system integration fees seem to be more amenable to reduction through appropriate choice of system size and market strategy. Increases in inverter and module efficiency yield significant benefits, especially for systems with high area related costs.

Zimmerman, L. W.↗

NASA NTRS1985

Sensitivity of an energy balance climate model with predicted snowfall rates

A snowfall parameterization and a polar-ice-sheet model are developed and applied to the two-level zonally averaged seasonal energy-balance climate model of Held and Suarez (1979), and sensitivity experiments involving changes in insolation are performed both with and without ice sheets. The results are presented in tables and graphs, and the hydrological-cycle response to insolation changes is found to be similar to that predicted by global-circulation models employing prescribed precipitation levels, with a somewhat higher sensitivity in the snow line. The area covered by ice sheets in the ice-sheet models is shown to be greater than that covered by permanent snow in the models without ice sheets, an effect attributed to lower surface temperatures over the ice. It is inferred that an increase in the solar constant can cause increased high-latitude precipitation but not an ice age.

Bowman, K. P.↗