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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Improved modeling of GPS selective availability

Selective Availability (SA) represents the dominant error source for stand-alone users of the Global Positioning System (GPS). Even for DGPS, SA mandates the update rate required for a desired level of accuracy in realtime applications. As was witnessed in the recent literature, the ability to model this error source is crucial to the proper evaluation of GPS-based systems. A variety of SA models were proposed to date; however, each has its own shortcomings. Most of these models were based on limited data sets or data which were corrupted by additional error sources. A comprehensive treatment of the problem is presented. The phenomenon of SA is discussed and a technique is presented whereby both clock and orbit components of SA are identifiable. Extensive SA data sets collected from Block 2 satellites are presented. System Identification theory then is used to derive a robust model of SA from the data. This theory also allows for the statistical analysis of SA. The stationarity of SA over time and across different satellites is analyzed and its impact on the modeling problem is discussed.

Braasch, Michael S.↗
NASA NTRS1994

The moist available energy of a conditionally unstable atmosphere. Part 2: Further analysis of GATE data

The generalized convective available potential energy (GCAPE) observed during GARP Atlantic Tropical Experiment (GATE) has been analyzed using the Lagrangian algorithm of Lorenz, as modified by Randall and Wang. The effects of ice are included and are discussed in an Appendix. A high positive correlation is found between the rate of GCAPE production by large-scale processes and the observed precipitation rate, and a negative correlation between the GCAPE itself and the precipitation rate. The observed time rate of change of the GCAPE is much smaller than the rate of GCAPE production by large-scale processes.

Wang, Junyi↗
NASA NTRS1994

Convective available potential energy in the environment of oceanic and continental clouds: Correction and comments

In 1980, Zipser and LeMone estimated the convective available potential energy (CAPE) for the Thunderstorm Project cumulonimbus environment to be about 3000 J per kg. By assuming the most adiabat reported by Byers and Braham (1949) to be that of an undilute parcel rather than a reference moist adiabat, a significant error was introduced. On the basis of recent calculations made under similar conditions in Oklahoma and Florida, CAPE is now estimated to be considerably lower. These lower CAPE estimates shed doubt on the suggestion that differences in CAPE account for differences in the vertical velocities in convective updrafts over land and over the ocean.

Lucas, Christopher↗
NASA NTRS1995

TOGA COARE Satellite data summaries available on the World Wide Web

Satellite data summary images and analysis plots from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), which were initially prepared in the field at the Honiara Operations Center, are now available on the Internet via World Wide Web browsers such as Mosaic. These satellite data summaries consist of products derived from the Japanese Geosynchronous Meteorological Satellite IR data: a time-size series of the distribution of contiguous cold cloudiness areas, weekly percent high cloudiness (PHC) maps, and a five-month time-longitudinal diagram illustrating the zonal motion of large areas of cold cloudiness. The weekly PHC maps are overlaid with weekly mean 850-hPa wind calculated from the European Centre for Medium-Range Weather Forecasts (ECMWF) global analysis field and can be viewed as an animation loop. These satellite summaries provide an overview of spatial and temporal variabilities of the cloud population and a large-scale context for studies concerning specific processes of various components of TOGA COARE.

Chen, S. S.↗
NASA NTRS1995

System-Availability And Resource-Allocation Program

ACARA analyzes availability, life-cycle cost, and scheduling of resources. Uses statistical Monte Carlo method to simulate capacity states of system as well as failure and repair of components. Failures of components modeled mathematically by use of combination of exponential and Weibull probability distributions. Schedules replacement of components to optimize performance of system. Made to comply with any constraints on production of components, capacities of resupply vehicles, spares kept on site, crews, and/or equipment. Written in APL2.

Viterna, L. A.↗
NASA NTRS1995

Electronic availability of microgravity experiments safety and integration requirements documents

This follow-on to NASA Contractor Report 195447, Microgravity Experiments Safety and Integration Requirements Document Tree, provides the details for accessing the systems that contain the official, electronic versions of the documents initially researched in NASA Contractor Report 195447. The data in this report serves as a valuable information source for the NASA Lewis Research Center Project Documentation Center (PDC), as well as for all developers of space experiments. The PDC has acquired the hardware, software, ID's, and passwords necessary to access most of these systems and is now able to provide customers with current document information as well as immediate delivery of available documents in either electronic or hard copy format.

Hogan, Jean M.↗
NASA NTRS1996

ERS-1 SAR monitoring of ice growth on shallow lakes to determine water depth and availability in north west Alaska

Images taken by the ERS-1 synthetic aperture radar (SAR) were used to identify and to differentiate between the lakes that freeze completely to the bottom and those that do not, on the North Slope, in northwestern Alaska. The ice thickness at the time each lake froze completely is determined with numerical ice growth model that gives a maximum simulated thickness of 2.2 m. A method combining the ERS-1 SAR images and numerical ice growth model was used to determine the ice growth and the water availability in these regions.

Jeffries, Martin↗
NASA NTRS1997

Containerless Liquid to Solid Nucleation Pathways in Two Representative Grades of Commercially Available Zirconium

Experimental measurements were conducted to determine the solid metal nucleation pathways of radiatively cooling, molten zirconium spheres of two different commercially available purity grades in a high-vacuum, high-temperature electrostatic levitator. The ensemble distribution of maximum undercooling temperatures was interpreted using Poisson statistics to determine the temperature dependence of the solid metal nucleation rate. For a sample of nominally 99.95% pure zirconium, the results are consistent with heterogeneous solid metal nucleation either on static catalyst particles at least approx. 30 nm diameter or on a surface coating. For a sample of nominally 99% pure zirconium, however, it appears that heterogeneous solid metal nucleation occurred either on a polydispersion of approx. 10 nm (mean diameter) static catalyst particles or on dynamic catalyst particles that precipitated from a solution that became supersaturated as the melt cooled.

Rulison, A. J.↗
NASA NTRS1999

Electron Induced Scintillation Testing of Commercially Available Optical Fibers for Space Flight

A test to verify the performance of several commercial and military optical fibers available on the market today was conducted, via usage of an electron accelerator, to monitor radiation induced scintillation or luminescence. The test results showed that no significant effects could be detected with the PMT system used, above a noise floor of 50 photons/sec that were due to optical fiber scintillation. Although some data appeared to show events taking place, noise scan results have correlated these events to arcing inside the electron accelerator facility. This test was to simply characterize for space flight, which optical fiber candidates were the largest scintillators among the eighteen optical fiber candidates tested.

Ott, Melanie N.↗
NASA NTRS1999

One GigaSample Per Second Data Acquisition using Available Gate Array Technology

A new National Aeronautics and Space Administration instrument forced demanding requirements upon its altimeter digitizer system. Eight-bit data would be generated at a rate of one billion samples per second. NASA had never before attempted to capture such high-speed data in the radiation, low-power, no-convective-cooling, limited-board-area environment of space. This presentation describes how the gate array technology available at the time of the design was used to implement this one gigasample per second data acquisition system

Wagner, K.W.↗
NASA NTRS1999

Spice Products Available to The Planetary Science Community

This paper presents the availability of SPICE products to the Planetary Science Community. The topics include: 1) What Are SPICE Data; 2) SPICE File Types; 3) SPICE Software; 4) Examples of What Can Be Computed Using SPICE Data and Software; and 5) SPICE File Avalability.

Acton, Charles↗
NASA NTRS2001

Publicly Available Numerical Codes for Modeling the X-ray and Microwave Emissions from Solar and Stellar Activity

We have posted numerical codes on the Web for modeling the bremsstrahlung x-ray emission and the a gyrosynchrotron radio emission from solar and stellar activity. In addition to radiation codes, steady-state and time-dependent Fokker-Planck codes are provided for computing the distribution and evolution of accelerated electrons. A 1-D hydrodynamics code computes the response of the stellar atmosphere (chromospheric evaporation). A code for modeling gamma-ray line spectra is also available. On-line documentation is provided for each code. These codes have been developed for modeling results from the High Energy Solar Spectroscopic Imager (HESSI) along related microwave observations of solar flares. Comprehensive codes for modeling images and spectra of solar flares are under development. The posted codes can be obtained on NASA/Goddard's HESSI Web Site at http://hesperia.gsfc.nasa.gov/hessi/modelware.htm. This work is supported in part by the NASA Sun-Earth Connection Program.

Holman, Gordon D.↗
NASA NTRS1996

Operational Characteristics of Two Commercially Available Personal Cooling Vests

Personal thermoregulatory systems which provide chest cooling are used in the industrial and aerospace environments to alleviate thermal stress. However, little information is available regarding the physiologic and circulatory changes produced by routine operation of these systems. The objectives of this study were to compare the effectiveness of two passive cooling vests, and to measure the body temperature and circulatory changes produced by each cooling vest configuration. A Life Enhancement Technologies, (LET) ice vest garment and a Steele, Inc. vest were used to cool the chest region of 11 male subjects (25 to 55 yr) in this study. Calf, forearm and finger blood flows were measured using a tetrapolar impedance rheograph. The subjects, seated in an upright position at normal room temperature (approximately 21 C) were tested for 60 min. with the cooling system operating at its maximum cooling capacity. Blood flows were recorded continuously using a computer data acquisition system with a sampling frequency of 250 Hz. Oral, right and left ear temperatures and cooling system parameters were logged manually every 5 min. Arm, leg, chest and rectal temperatures; heart rate; respiration; and an activity index were recorded continuously on a U.F.I., Inc. Biolog ambulatory monitor. No significant differences were found in either the oral or ear temperature responses to the two vests. However, the rectal and mean skin temperatures at the end of the cooling period were both significantly lower (P less than 0.05), approximately 0.2 and 1.9 C, respectively for the LET vest than for the Steele garment. These data show that different vest configurations may produce different thermal responses in healthy male subjects which should be considered in the use of these cooling garments.

Ku, Yu-Tsuan E.↗
NASA NTRS1997

Operational Characteristics of Four Commercially Available Personal Cooling Vests

Personal thermoregulatory systems which provide chest cooling are used in the industrial and aerospace environments to alleviate thermal stress. However, little information is available regarding the physiologic and circulatory changes produced by routine operation of these systems. The objectives of this study were to compare the effectiveness of two passive and two active cooling vests, and to measure the body temperature and circulatory changes produced by each cooling vest configuration. The MicroClimate Systems and the Life Enhancement Tech(LET) lightweight liquid cooling vests, the Steele Vest and LET's Zipper Front Garment were used to cool the chest region of 11 male and 10 female subjects (25 to 55 yr.) in this study. Calf, forearm and finger blood flows were measured using a tetrapolar impedance rheograph. The subjects, seated in an upright position at normal room temperature (approx.21 C), were tested for 60 min. with the cooling system operated at its maximum cooling capacity. Blood flows were recorded continuously using a computer data acquisition system with a sampling frequency of 250 Hz. Oral, right and left ear temperatures and cooling system parameters were logged manually every 5 min. Arm, leg, chest and rectal temperatures; heart rate; respiration; and an activity index were recorded continuously on a URI Inc. Biolog ambulatory monitor. In general, the male and female subjects' rectal and ear temperature responses to cooling were similar for all vest configurations tested. Oral temperatures during the recovery period were significantly (P<0.05) lower than during the control period, approx.0.2 - 0.5 C, for both men and women wearing any of the four different garments. The corresponding car temperatures were significantly (P<0.05) decreased approx.0.2 - 0.3 C by the end of the recovery period. Compared to the control period, no significant differences were found in rectal temperatures during cooling and recovery periods. These results show that all vest configurations elicit a similar thermal response in both male and female subject groups. However, subject population variance was rather large and may have masked differences between the vests. One vest may prove more effective than another for a given individual, and experience is the only means of determining this.

Ku, Yu-Tsuan E.↗
NASA NTRS2002

Advanced Measurement Systems Available to PIWG Members

It was developed advanced measurement technologies to meet NASA goals: reduce design cycle time, reduce emission, reduce testing time, increase safety. The technology are saving money. This technology are available now for technology transfer: optical diagnostics, the film technology and MEMS devices.

Anderson, Robert↗
NASA NTRS1947

Summary of Available Data Relating to Reynolds Number Effects on the Maximum Lift Coefficients of Swept-Back Wings

The available foreign and American data relating to Reynolds number effects on the maximum lift coefficients of swept-back wings are summarized and discussed. The data show that at low Reynolds numbers (below about 2.0 x 10(exp 6)) higher maximum lift coefficients were measured in most cases for moderately swept-back wings than for unswept wings of similar plan form; at high Reynolds numbers, however, increasing sweepback resulted in decreasing maximum lift coefficients. A smaller rate of increase of the maximum lift coefficient with Reynolds number was measured for the swept-back wings than for similar unswept wings in the critical range of Reynolds number. Increasing the Reynolds number resulted in decreases in the maximum lift coefficients of the two wings of approximately triangular plan form that were investigated.

Sweberg, Harold H.↗
NASA NTRS1985

NMR characterization of functional groups: 9--isomer ratios of available chloromethylstyrene mixtures

From the assignments of the 1H and 13C 11.7 tesla NMR spectra of available mixtures of m- and p-chloromethylstyrene, the proportion of the meta and para compounds are easily determined. For these materials from two common commercial sources, proportions of 72 and 28% and 68 and 32% were found. These concentrations are substantially different from the often assumed 60 and 40% for the meta and para compounds, respectively. The influence of this difference on the desired properties of copolymers made from such mixtures is discussed. An alternative quantitative procedure for determining the chloromethyl group isomer ratios is also described which employs silver trifluoroacetate in acetone displacement of chloride and 19F NMR examination of the resulting ester mixture with a 2.3 tesla spectrometer.

Polystyrenes/analysis/chemistry↗