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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Frequency of light-flashes induced by Cerenkov radiation from heavy cosmic-ray nuclei

The expected frequency was calculated for light flashes induced in the dark-adapted eye by Cerenkov radiation from the flux of heavy nuclei that exists in space beyond the geomagnetic field. The expected frequency of light flashes depends on the threshold number of photons that must be absorbed in a rod cluster. The results of the calculation are presented as a curve of the mean frequency of light flashes versus the threshold number of absorbed photons. The results are not sensitive to variations in the path length from 5 to 15 grams per square centimeter of water-equivalent before the nucleus reaches the retina. Calculations were based on the fluxes and energy spectra of galactic cosmic ray nuclei of helium to iron, measured at a time of minimum solar modulation. The expected light flash frequencies induced by Cerenkov radiation are consistent with the frequencies reported by the astronauts on Apollo missions 11 through 14.

Madey, R.↗
NASA NTRS1975

Conspicuity of target lights: The influence of flash rate and brightness

The stimulus characteristics of lights that might aid a pilot to see and avoid, by alerting him to a potential threat were studied. The relative conspicuity of foveally equated, point-source, steady and flashing lights of several brightnesses, seen against a star background was examined. From the subject's viewpoint, these target lights could appear anywhere within a large (40 deg horizontal by 35 deg vertical) field of view. The lights appeared at random time intervals while the subject was periodically distracted by a simulated cockpit task. The results indicate that correct target detection increases and reaction time decreases with increased target intensity. Steady lights are missed more frequently and acquired more slowly than flashing lights, but no significant differences are found among the wide range of flash rates employed. The intensity of the light has a greater effect on both detection and reaction time to steady lights than to flashing lights. These results are compared with results of other researchers who used targets which appeared at fixed locations. The longest reaction times were recorded to lights which appeared either at the extremes or at the very center of the visual field.

Connors, M. M.↗
NASA NTRS1975

Light flashes observed by astronauts on Skylab 4

Two dedicated light flash observing sessions were conducted by one of the crewmen during the Skylab 4 mission. Analyses of his observations reveal a strong correlation between flash frequency and primary cosmic-ray flux, and an even stronger correlation between flash frequency and the South Atlantic Anomaly (SAA) region of the inner belt trapped radiation. Calculations indicate that an all-proton inner belt probably cannot produce the observed SAA flash rate, and they suggest that there may exist a previously unobserved inner belt flux of multiply charged nuclei.

Pinsky, L. S.↗
NASA NTRS1975

Apollo light flash investigations

The visual phenomenon of light flashes resulting from high energy, heavy cosmic rays penetrating the command module structure and crewmembers' eyes is investigated. Light flash events observed during dedicated sessions on Apollo 15, 16, 17 are described along with a Monte Carlo simulation of the exposure of an astronaut to cosmic radiation during a mission. Results of the Apollo Light Flash Moving Emulsion Detector experiment developed for Apollo 16 and 17 to obtain a direct record of incident cosmic ray particles are correlated with crewmembers' reports of light flashes.

W. Zachary Osborne↗
NASA NTRS1976

Quantitative observation of light flash sensations experiment MA-106

Light flashes caused by the interaction of cosmic particles with the visual apparatus have been observed by astronauts on all space missions since Apollo 11. This Apollo Soyuz Test Project experiment compared measurements of the observer's visual sensitivity with measurements of the ambient radiation environment and with the frequency and character of the flashes observed. The data obtained reveal a latitude dependence of the frequency of observed flashes. This distribution of flashes is correlated with the distribution of cosmic particles with stopping power greater than 15 keV/ micrometers in the eye. The interaction of dark adaptation, specific ionization, and range of particles in the retina as factors in the visualization of particle passage is discussed.

Budinger, T. F.↗
NASA NTRS1976

The structure of lightning flashes HF-UHF: 12 September 1975, Atlanta, Georgia

Simultaneous measurement of sferics at 3, 30, 139, and 295 MHz were made during thunderstorms. Wideband electronics and an analogue tape recorder continuously recorded the radiation from lightning with about 300 kHz of bandwidth. The data were obtained during the passage of a cold front. Flashing rate, burst rate and the structure of individual flashes were recorded. The record of a typical flash begins with a sudden burst of closely spaced pulses whose temporal structure is typical of the stepped leader, and ends in a large pulse suggestive of a first return stroke. The remainder of the flash consists of a sequence of pulses of varying amplitude separated by quiet periods of the order of milliseconds. The shape of these pulses and the temporal structure suggest that the first few large pulses are return strokes. Other discharges begin with widely spaced discrete pulses and resemble the preceding discharge less the leader and return stroke phase. The radiation exhibits a similar structure, at each of the frequencies monitored.

Levine, D. M.↗
NASA NTRS1977

Visual light flash observations on Skylab 4

Evaluation of light flashes observed in earth orbit establishes: (1) a strong correlation of very high flash rates with passage through the South Atlantic anomaly; (2) evidence for a predicted latitude effect; and (3) an increased flash rate outside the anomaly during a second observation period. Event rates and flash descriptions during South Atlantic anomaly passes indicate that there may be particles heavier than protons in the inner belt of trapped radiation.

Hoffman, R. A.↗
NASA NTRS1978

Char yield and flash-fire propensity of pyrolysis gases from materials

Comparison of the char yield after occurrence of a flash fire in the pyrolysis gases from various materials indicates that increased char yield appears to be associated with reduced flash-fire propensity for certain types of materials. For certain other materials, flash-fire propensity appears to be independent of char yield. The mechanisms of thermal decomposition and char formation may be more important factors in flash-fire propensity than the quantitative degree of char formation.

Hilado, C. J.↗
NASA NTRS1980

Thermonuclear-flash models for X-ray burst sources

Theoretical models for X-ray burst sources that invoke thermonuclear flashes in the surface layers of an accreting neutron star are discussed. Emphasis is placed on the studies by Joss (1978) and Joss and Li (1979) on the evolution of the helium-burning shell. Numerical calculations with regard to the mass accretion rate, core temperature of the neutron star and the sensitivity of the flash properties to the assumed mass and radius of the neutron star are considered. Attention is also given to the behavior of the surface luminosity following a thermonuclear flash, the decline from maximum X-ray luminosity, structure of the surface layers prior to and during the first helium-burning flash and the temporal evolution of the first X-ray burst.

Joss, P. C.↗
NASA NTRS1994

Flash heating is required to minimize sodium losses from chondrules

Chondrules were formed by high-temperature melting events, but do not always show Na depletion compared to CI chondrites, though extensive Na loss has been found in previous isothermal experiments. While Na loss can be prevented by high partial pressure of Na in the nebula, many people favor a flash-heating mechanism to reduce the Na loss from chondrule melts. To examine the validity of the flash-heating hypothesis, we have conducted a series of flash-heating experiments and observed Na loss rate under different conditions. Our results support the flash heating as a plausible heating mechanism to form chondrules.

Yu, Y.↗
NASA NTRS1993

Observations of upper atmospheric optical flashes recorded from an aircraft

Short-duration upper atmospheric optical flashes were recorded on the night of 8 July, 1993 (9 July UT) from the NASA DC-8 Airborne Laboratory flying over the American Midwest. All-sky video images from an intensified silicon intensified target (ISIT) camera revealed 19 upper atmospheric flashes occurring over a period of approximately 100 min. The flashes were similar in appearance to previously reported ground and shuttle-based video observations. Detailed analysis of 12 of the events yielded these parameters: (1) duration less than or equal to 17 ms; (2) brightness 10-50 kR, roughly that of bright aurorae; (3) terminal heights 30-100 km, with a mean of approximately 60 km; (4) horizontal extent 10-50 km; (5) emission volumes greater than 1000 cu km. The relative frequency of the optical flashes was (6) 1:200-1:400 compared to negative cloud-to-ground discharges and 1:20-1:40 compared to positive cloud-to-ground discharges.

Sentman, D. D.↗
NASA NTRS1993

Observations of Upper Atmospheric Optical Flashes Recorded From an Aircraft

Short-duration upper atmospheric optical flashes were recorded on the night of 8 July, 1993 (9 July UT) from the NASA DC-8 Airborne Laboratory flying over the American Midwest. All-sky video images from an intensified silicon intensified target (ISIT) camera revealed 19 upper atmospheric flashes occurring over a period of approximately 100 min. The flashes were similar in appearance to previously reported ground and shuttle-based video observations. Detailed analysis of 12 of the events yielded these parameters: (1) duration less than or = 17 ms; (2) brightness 10-50 kR, roughly that of bright aurorae; (3) terminal heights 30-100 km, with a mean of approximately 60 km; (4) horizontal extent 10-50 km; and (5) emission volume greater than 1000 km(sup 3). The relative frequency of the optical flashes was (6) 1:200-1:400 compared to negative cloud-to-ground discharges and 1:20-1:40 compared to positive cloud-to-ground discharges.

Sentman, D. D.↗
NASA NTRS2000

Global Lightning Variations Caused by Changes in Thunderstorm Flash Rate and by Changes in Number of Thunderstorms

Global lightning activity is highly variable on many time scales. This variability is attributable to changes in the flash rate per thunderstorm, the number of thunderstorms, or a combination. The TRMM Mission offers lightning observations from the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS) in space. Both are used to examine the response of these parameters to thermodynamic forcing of deep convection on the diurnal and annual time scales. On both time scales, the changes in the number of storms dominate the variations in total lightning activity. On the diurnal time scale, the mean flash rate appears to vary with cloud buoyancy, peaking in early afternoon and declining in late afternoon, but the contribution of number of thunderstorms is 2-3 times greater that the mean storm flash rate. On the annual time scale, almost all of the total lightning response is due to changes in the number of storms, with a negligible contribution from flash rate. Evidence is presented that the LIS/OTD 'area' is a meaningful objective identifier for a thunderstorm.

Williams, E. K.↗
NASA NTRS2000

Implementation of Self-Align Local Poly Interconnection on 0.25 Micron Flash Memory

For ETOX Flash technology. the self-aligned source module plays a critical role in minimizing cell size. For advanced Flash technology using the shallow-trench isolation (STI) scheme, however, it is difficult to form a stable source line. The Flash process in this experiment features an ETOX structure and with SIN spacer. Poly-Si (implanted poly) is used as the local interconnection material connecting the source line and was successfully implemented in the ETOX flash array in this paper.

C H Lee↗
NASA NTRS2007

OTD Observations of Continental US Ground Flashes Detected by NLDN

Lightning optical flash parameters (e.g., radiance, area, duration, number of optical groups, and number of optical events) derived from almost 5 yrs of Optical Transient Detector (OTD) data are compared with peak current and multiplicity observations derived from the US National Lightning Detection Networkm (NLDN). Despite the relatively low lightning geolocation accuracy afforded by OTD, a total of 48,870 NLDN cloud-to-ground (CG) flashes were correlated with OTD flashes, or about 10,000 CGs per year. The median values of the above OTD flash parameters for the 48,870 CGs were, respectively: 0.137 J/square meters/sr/micrometers, 313.7 square kilometers, 0.189 s, 4 optical groups per CG, and 8 optical events per CG. Invoking the multiplicity data, the median number of optical groups per stroke was 2.5, and the median number of optical events per stroke was 5.0. Median values of peak current for negative and positive CGs were -21.6 kA and 17.8 kA, respectively, and as expected, the negative CGs had a larger average multiplicity than the positive CGs. A statistical summary is provided for all CGs, for positive and negative CGs, and for CGs from different seasons. Standard two-distribution hypothesis tests were perfonned to intercompare the population means of the various lightning parameters. In particular, and to greater than the 99% confidence level, it was found that positive CGs are on average more radiant, of greater areal extent, and are longer lasting than negative CGs. Rankings from a complete set of hypothesis tests between CGs of different polarities and from different seasons are also provided. Most notably, wintertime positive CGs tend to be more radiant, of greater areal extent, and longer lasting than any other group of CGs (i.e., negative springtime CGs, positive summertime CGs, etc.).

Koshak, William J.↗
NASA NTRS2008

A Comparison of Lightning Flashes as Observed by the Lightning Imaging Sensor and the North Alabama Lightning Mapping Array

The Lightning Imaging Sensor (LIS) aboard the TRMM satellite has been collecting optical lightning data since November 1997. A Lightning Mapping Array (LMA) that senses VHF impulses from lightning was installed in North Alabama in the Fall of 2001. A dataset has been compiled to compare data from both instruments for all times when the LIS was passing over the domain of our LMA. We have algorithms for both instruments to group pixels or point sources into lightning flashes. This study presents the comparison statistics of the flash data output (flash duration, size, and amplitude) from both algorithms. We will present the results of this comparison study and show "point-level" data to explain the differences. AS we head closer to realizing a Global Lightning Mapper (GLM) on GOES-R, better understanding and ground truth of each of these instruments and their respective flash algorithms is needed.

Bateman, M. G.↗
NASA NTRS2010

Utilization of 3-D Imaging Flash Lidar Technology for Autonomous Safe Landing on Planetary Bodies

NASA considers Flash Lidar a critical technology for enabling autonomous safe landing of future large robotic and crewed vehicles on the surface of the Moon and Mars. Flash Lidar can generate 3-Dimensional images of the terrain to identify hazardous features such as craters, rocks, and steep slopes during the final stages of descent and landing. The onboard flight computer can use the 3-D map of terrain to guide the vehicle to a safe site. The capabilities of Flash Lidar technology were evaluated through a series of static tests using a calibrated target and through dynamic tests aboard a helicopter and a fixed wing aircraft. The aircraft flight tests were performed over Moon-like terrain in the California and Nevada deserts. This paper briefly describes the Flash Lidar static and aircraft flight test results. These test results are analyzed against the landing application requirements to identify the areas of technology improvement. The ongoing technology advancement activities are then explained and their goals are described.

Amzajerdian, Farzin↗
NASA NTRS2011

Summary of Almost 20 Years of Storm Overflight Electric Field, Conductivity, Flash Rates, and Electric Current Statistics

We determined total conduction currents and flash rates for around 900 high-altitude aircraft overflights of electrified clouds over 17 years. The overflights include a wide geographical sample of storms over land and ocean, with and without lightning, and with positive (i.e., upward-directed) and negative current. Peak electric field, with lightning transients removed, ranged from -1.0 kV m(sup -1) to 16. kV m(sup -1), with mean (median) of 0.9 kV m(sup -1) (0.29 kV m(sup -1)). Total conductivity at flight altitude ranged from 0.6 pS m(sup -1) to 3.6 pS m(sup -1), with mean and median of 2.2 pS m(sup -1). Peak current densities ranged from -2.0 nA m(sup -2) to 33.0 nA m(sup -2) with mean (median) of 1.9 nA m(sup -2) (0.6 nA m(sup -2)). Total upward current flow from storms in our dataset ranged from -1.3 to 9.4 A. The mean current for storms with lightning is 1.6 A over ocean and 1.0 A over land. The mean current for electrified shower clouds (i.e. electrified storms without lightning) is 0.39 A for ocean and 0.13 A for land. About 78% (43%) of the land (ocean) storms have detectable lightning. Land storms have 2.8 times the mean flash rate as ocean storms (2.2 versus 0.8 flashes min(sup -1), respectively). Approximately 7% of the overflights had negative current. The mean and median currents for positive (negative) polarity storms are 1.0 and 0.35 A (-0.30 and -0.26 A). We found no regional or latitudinal-based patterns in our storm currents, nor support for simple scaling laws between cloud top height and lightning flash rate.

Blakeslee, Richard J.↗