Search NASA⌕ Search

SEARCH · Search NASA

Results for “Burst Map”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Experimental Investigation of Current Sheet Instabilities

Configuration space instabilities of propagating current sheets were studied in order to better understand acceleration mechanisms in pulsed plasma thrusters. Experiments were carried out in a parallel plate accelerator with argon as propellant. Propagating current sheets were visualized using fast framing cameras with inter-frame delays ranging between 0.05 - 2 microsecond. Schlieren photography using a pulse-burst Nd:YAG laser was used to image electron density gradients in the discharge. Magnetic field probes were used to map the magnetic field topology during the evolution of the discharge. Pressure probes were used to monitor axial pressure gradients. Emission spectroscopy was used to estimate the electron temperature in the arc. The motivation for applying all of these diagnostics was to gain an understanding of what parameters influence the macroscopic stability of a propagating current sheet. Since a stable current sheet is required for any effective snowplow-type of accelerator, an understanding of the processes which can cause current sheets to break apart into filaments is essential for the design of future pulsed plasma thrusters.

Markusic, Thomas E.↗
NASA NTRS1996

Forearm training attenuates sympathetic responses to prolonged rhythmic forearm exercise

We previously demonstrated that nonfatiguing rhythmic forearm exercise at 25% maximal voluntary contraction (12 2-s contractions/min) evokes sympathoexcitation without significant engagement of metabolite-sensitive muscle afferents (B.A. Batman, J.C. Hardy, U.A. Leuenberger, M.B. Smith, Q.X. Yang and L.I. Sinoway. J. Appl. Physiol. 76: 1077-1081, 1994). This is in contrast to the sympathetic nervous system responses observed during fatiguing static forearm exercise where metabolite-sensitive afferents are the key determinants of sympathetic activation. In this report we examined whether forearm exercise training would attenuate sympathetic nervous system responses to rhythmic forearm exercise. We measured heart rate, mean arterial blood pressure (MAP), muscle sympathetic nerve activity (microneurography), plasma norepinephrine (NE), and NE spillover and clearance (tritiated NE kinetics) during nonfatiguing rhythmic forearm exercise before and after a 4-wk unilateral forearm training paradigm. Training had no effect on forearm mass, maximal voluntary contraction, or heart rate but did attenuate the increase in MAP (increase in MAP: from 15.2 +/- 1.8 before training to 11.4 +/- 1.4 mmHg after training; P < 0.017), muscle sympathetic nerve activity (increase in bursts: from 10.8 +/- 1.4 before training to 6.2 +/- 1.1 bursts/min after training; P < 0.030), and the NE spillover (increases in arterial spillover: from 1.3 +/- 0.2 before training to 0.6 +/- 0.2 nmol.min-1.m-2 after training, P < 0.014; increase in venous spillover: from 2.0 +/- 0.6 before training to 1.0 +/- 0.5 nmol.min-1.m-2 after training, P < 0.037) seen in response to exercise performed by the trained forearm. Thus forearm training reduces sympathetic responses during a nonfatiguing rhythmic handgrip paradigm that does not engage muscle metaboreceptors. We speculate that this effect is due to a conditioning-induced reduction in mechanically sensitive muscle afferent discharge.

NASA Discipline Musculoskeletal↗
NASA NTRS1990

The Lunar Observer Radio Astronomy Experiment (LORAE)

The paper proposes to place a simple low-frequency dipole antenna on board the Lunar Observer (LO) satellite. LO will orbit the moon in the mid-1990's, mapping the surface at high resolution and gathering new geophysical data. In its modest concept, LORAE will collect crucial data on the radio interference environment while on the near-side (to aid in planning future arrays) and will monitor bursts of emission from the sun and the Jovian planets. LORAE will also be capable of lunar occultation studies of greater than 100 of the brightest sources, gathering arcminute resolution data on sizes and measuring source fluxes. A low resolution all-sky map below 10 MHz, when combined with data from the Gamma-Ray Observatory, will uniquely determine the density of Galactic cosmic ray electrons and the strength of the Galaxy's magnetic field. LORAE also will be able to measure the density of the moon's ionosphere.

Burns, Jack O.↗
NASA NTRS2010

Terrestrial Gamma-Ray Flashes (TGFs)

This slide presentation reviews the observation of Terrestrial Gamma Ray Flashes (TGFs) by Gamma-Ray Telescopes. These were: (1) BATSE /Compton Observatory, (2) Solar Spectroscopic Imager, (3) AGILE Gamma-ray Telescope, and (4) Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope. It contains charts which display the counts over time, a map or the TGFs observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). and a map showing the latitude and longitude of 85 of the TGFs observed by the Fermi GBM.

Fishman, Gerald J.↗
NASA NTRS1982

VLA observations of the evolution of a solar burst source structure at 6 centimeter wavelength

Evolutionary changes in the total intensity and polarization structure of a 6 cm radio burst source have been observed with the VLA, over time scales ranging from 10 s to several minutes. This burst was associated with a 2B/M1 flare observed on 1980 May 14. The 6 cm burst consisted of a gradual phase of 30 minutes duration and a strong impulsive phase of duration less than two minutes. Synthesized maps of total intensity and polarization were obtained with spatial resolution of 2 x 3 arcsec and with temporal resolutions of five minutes during the gradual phase and 10 s during the impulsive phase. The sequence of polarization maps suggests a complex magnetic field structure undergoing rapid changes. Most importantly, they show the development of two bipolar regions or quadrupole structure just prior to the impulsive energy release.

Velusamy, T.↗
NASA NTRS2001

The 1998-2000 SHADOZ (Southern Hemisphere ADditional OZonesondes) Tropical Ozone Climatology: Ozonesonde Precision, Accuracy and Station-to-Station Variability

As part of the SAFARI-2000 campaign, additional launches of ozonesondes were made at Irene, South Africa and at Lusaka, Zambia. These represent campaign augmentations to the SHADOZ database described in this paper. This network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere ADditional OZonesondes (SHADOZ) project and established from operational sites, provided over 1000 profiles from ozonesondes and radiosondes during the period 1998-2000. (Since that time, two more stations, one in southern Africa, have joined SHADOZ). Archived data are available at: http://code9l6.gsfc.nasa.gov/Data-services/shadoz>. Uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in stratospheric ozone profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column-integrated total ozone from sondes with total ozone from the Earth-Probe/TOMS (Total Ozone Mapping Spectrometer) satellite and ground-based instruments; (3) possible biases from station-to-station due to variations in ozonesonde characteristics. The key results are: (1) Ozonesonde precision is 5%; (2) Integrated total ozone column amounts from the sondes are in good agreement (2-10%) with independent measurements from ground-based instruments at five SHADOZ sites and with overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS-sonde offsets and in groundbased-sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave-one pattern in total and tropospheric ozone, but not in stratospheric ozone.

Witte, J. C.↗
NASA NTRS1976

Advances in gamma-ray burst astronomy

The paper reviews the current status of observational research into the highly puzzling problem of cosmic gamma-ray bursts. Up to now there is no convincing temporal or spatial correlation with any known celestial processes or objects. The typical burst source strength is somewhere between 10 to the 26th power ergs and 10 to the 52nd power ergs. A list of 39 confirmed and 9 unconfirmed cosmic gamma-ray bursts observed by satellite is given, showing times of occurrence and in some cases, the size in erg per square centimeter. Several approaches to the problem of source object identification are discussed: (1) accumulation of observation statistics with their present poor resolution and research for correlative phenomena, (2) mapping out celestial source distributions with moderate resolution in order to search for galactic or other anisotropies in direction or to look for repeating source regions, and (3) very high-accuracy localization of the source directions of one or several bursts in order to pinpoint a tiny fraction of the celestial sphere for correlative radio, optical and X-ray studies. Planned future instrumentation for deep space probes and multiple-balloon studies is described.

Cline, T. L.↗
NASA NTRS1987

Supernovae and the interstellar medium

Repeated supernovae from an OB association will, in a few 10s of Myr, create a cavity of coronal gas in the interstellar medium, with radius greater than 100 pc, surrounded by a dense expanding shell of cool interstellar gas. Such a cavity will likely burst through the gas layer of a disk galaxy. Such holes and 'supershells' have been observed in optical and H I radio emission maps of the Galaxy and other nearby galaxies. The gas swept up in supershell is likely to become gravitationally unstable, providing a mechanism for propagating star formation that may be particularly effective in irregular galaxies.

Mccray, Richard↗
NASA NTRS2004

High Resolution Digital Elevation Models of Pristine Explosion Craters

In order to effectively capture a realistic terrain applicable to studies of cratering processes and landing hazards on Mars, we have obtained high resolution digital elevation models of several pristine explosion craters at the Nevada Test Site. We used the Airborne Terrain Mapper (ATM), operated by NASA's Wallops Flight Facility to obtain DEMs with 1 m spacing and 10 cm vertical errors of 4 main craters and many other craters and collapse pits. The main craters that were mapped are Sedan, Scooter, Schooner, and Danny Boy. The 370 m diameter Sedan crater, located on Yucca Flat, is the largest and freshest explosion crater on Earth that was formed under conditions similar to hypervelocity impact cratering. As such, it is effectively pristine, having been formed in 1962 as a result of a controlled detonation of a 100 kiloton thermonuclear device, buried at the appropriate equivalent depth of burst required to make a simple crater. Sedan was formed in alluvium of mixed lithology and subsequently studied using a variety of field-based methods. Nearby secondary craters were also formed at the time and were also mapped by ATM. Adjacent to Sedan and also in alluvium is Scooter, about 90 m in diameter and formed by a high-explosive event. Schooner (240 m) and Danny Boy (80 m) craters were also important targets for ATM as they were excavated in hard basalt and therefore have much rougher ejecta. This will allow study of ejecta patterns in hard rock as well as engineering tests of crater and rock avoidance and rover trafficability. In addition to the high resolution DEMs, crater geometric characteristics, RMS roughness maps, and other higher-order derived data products will be generated using these data. These will provide constraints for models of landing hazards on Mars and for rover trafficability. Other planned studies will include ejecta size-frequency distribution at the resolution of the DEM and at finer resolution through air photography and field measurements, correlation of ejecta size and composition with radar and visible-thermal IR remote sensing signatures, and comparison of these results with similar measurements of Mars. The final DEMs, ancillary data sets, and derived data products will be made available to the community.

T G Farr↗
NASA NTRS1992

Microwave spectroscopy of the active sun

In studies of solar active regions and bursts, the ability to obtain spatially resolved radio spectra (brightness temperature spectra) opens a whole new range of possibilities for study of the solar corona. For active regions, two-dimensional maps of brightness temperature over a wide range of frequencies allows one to determine temperature, column density, and magnetic field strength over the entire region in a straightforward, unambiguous way. For flares, the time-dependent electron energy distribution, number of accelerated electrons, and magnetic field strength and direction can be found. In practice, obtaining complete radio images at a large number of frequencies is a significant technical challenge, especially while keeping costs down. Our instrument at Owens Valley Radio Observatory provided the starting point for a modest attempt at meeting this goal. We proposed to build three additional, very low-cost 2-m antennas which, when combined with our existing two 27-m dishes, expands the array to 5 elements. This modest increase in number of solar dedicated antennas, from 2 to 5, increases our maximum number of physical baselines from 1 to 10 and allows the instrument to do true imaging of solar microwave sources, both bursts and active regions. Combined with the technique of frequency synthesis, the new array has up to 450 effective baselines, giving imaging capability that approaches that of a sub-arrayed VLA. The prototype antenna design was finalized and the antenna was put into operation in Nov. 1989.

Hurford, Gordon↗
NASA NTRS1988

VLF bursts in the night ionosphere of Venus - Effects of the magnetic field

The occurrence rate of bursts at 0.1, 0.73, 5.4, and 30 kHz in the night ionosphere of Venus and factors controlling these bursts are examined. It is found that orientation has little effect on the occurrence rates but that the field strength has a strong effect. A contour map of the 100 Hz occurrences is shown to be similar to earlier maps at higher frequencies which have been corrected for altitude dependence.

Russell, C. T.↗
NASA NTRS2010

Flow, Aurora and PI2 Associations Observed by Themis

It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of sub storm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to sub storm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I suggest that the results strongly support flow-burst driven models of magnetospheric activity. I discuss further the association of flow bursts and Pi2 pulsations, and discuss the possibility of using Pi2 waveforms to infer midtail reconnection dynamics

Kepko, E. I.↗
NASA NTRS1994

The Compton Gamma Ray Observatory

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.↗
NASA NTRS1996

Electron Densities in Solar Flare Loops, Chromospheric Evaporation Upflows, and Acceleration Sites

We compare electron densities measured at three different locations in solar flares: (1) in Soft X-Ray (SXR) loops, determined from SXR emission measures and loop diameters from Yohkoh Soft X-Ray Telescope maps (n(sub e, sup SXR) = (0.2-2.5) x 10(exp 11)/ cu cm); (2) in chromospheric evaporation upflows, inferred from plasma frequency cutoffs of decimetric radio bursts detected with the 0.1-3 GHz spectrometer Phoenix of ETH Zuerich (n(sub e, sup upflow) = (0.3-11) x 10(exp 10)/cu cm; and (3) in acceleration sites, inferred from the plasma frequency at the separatrix between upward-accelerated (type III bursts) and downward-accelerated (reverse-drift bursts) electron beams [n(sub e, sup acc) = (0.6-10) x 10(exp 9)/cu cm]. The comparison of these density measurements, obtained from 44 flare episodes (during 14 different flares), demonstrates the compatibility of flare plasma density diagnostics with SXR and radio methods. The density in the upflowing plasma is found to be somewhat lower than in the filled loops, having ratios in a range n(sub e, sup upflow)/n(sub e, sup SXR) = 0.02-1.3, and a factor of 3.6 higher behind the upflow front. The acceleration sites are found to have a much lower density than the SXR-bright flare loops, i.e., n(sub e, sup acc)/n(sub e, sup SXR) = 0.005- 0.13, and thus must be physically displaced from the SXR-bright flare loops. The scaling law between electron time-of-flight distances l' and loop half-lengths s, l'/s = 1.4 +/- 0.3, recently established by Aschwanden et al. suggests that the centroid of the acceleration region is located above the SXR-bright flare loop, as envisioned in cusp geometries (e.g., in magnetic reconnection models).

Aschwanden, Markus J.↗
NASA NTRS1983

Observations of H-alpha and microwave brightening caused by a distant solar flare

Synthesized maps with integration times of 10 and 30 sec, based on the observation of three subflares at 6 cm and H-alpha 6563 A, indicate that most of the 6 cm burst emission originated in 10-15 arcsec features coincident with, or adjacent to, H-alpha flare kernels. During the onset of one of the subflares, 6 cm emission was discovered in a loop stretching over 100,000 km from the primary flare site in association with H-alpha flare-like brightness at the remote footpoint of the loop. Assuming a primary flare site origin for the energy of the distant brightening, about 4 x 10 to the 24th ergs/sec propagated along the connecting magnetic loop at a velocity of more than 6000 km/sec. It is suggested that the energy may have been carried by electrons originating in the high energy tail of the electron thermal velocity distribution, escaping from the primary flare site.

Kundu, M. R.↗
NASA NTRS1978

Processing laser velocimeter high-speed burst counter data

The statistical calculations of the mean and potential bias errors are considered with respect to their applicability to the randomly sampled velocity data obtained from a laser velocimeter. Techniques for displaying the resulting data in the form of arrow plots, flow streamline plots, and contour maps are also discussed. A description is presented of the operation of a new hardware interface between the signal processing electronics and the computer. The interface has been constructed to make it possible to use recently developed data processing techniques for obtaining turbulent power spectra from laser velocimeter data. Additional capabilities which were built into the interface allow the measurement of the velocity vector for each particle passing through the laser velocimeter sample window. By processing the data with extended versions of the turbulent power spectra techniques, cross spectra, interactions between velocity magnitude fluctuations, and flow angle fluctuations may be investigated.

Meyers, J. F.↗
NASA NTRS1985

The Pioneer Venus extended mission

A history of the Pioneer Venus Orbiter is given, as well as a presentation of the ongoing and future missions (through reentry in 1992). General characteristics of Venus including atmospheric and ionospheric data are reviewed. Development of the Pioneer program and studies including comet detection, gamma ray bursts, composition and structure of the atmosphere, ionosphere, clouds, and solar wind are discussed. Planned observations of Halley's Comet in 1986 and of past observations of the Comet Enke are examined in detail. Maps and diagrams illustrate the studies and observations of this extended mission. Specification of the spacecraft as well as details of its orbits are given.

Craig, R. A.↗