Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “events”

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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Relativistic electron events in interplanetary space

Review of relativistic electron events observed in interplanetary space. The different types of event are identified and illustrated. The relationships between solar X-ray and radio emissions and relativistic electrons are examined, and the relevance of the observations to solar flare acceleration models is discussed. A statistical analysis of electron spectra, the electron/proton ratio and propagation from the flare site to the earth is presented. A model is outlined which can account for the release of electrons from the sun in a manner consistent with observations of energetic solar particles and electromagnetic solar radiation.

Simnett, G. M.↗
NASA NTRS1974

Solar particle events with anomalously large relative abundance of He-3

Experimental results are reported on three energetic particle events with extremely high abundance of He-3. The measurements were taken onboard the OGO-5 satellite. It was shown that the abundance of protons relative to He nuclei were significantly low in these events. Not more than four H-2 and three H-3 were detected during the entire period under study compared to 1110 H-3 nuclei. The limitations these observations place on theoretical models are discussed to explain He-3 flares.

Serlemitsos, A. T.↗
NASA NTRS1974

Solar energetic particle event with He-3/He-4 greater than 1

An unusual solar event involving the detection of a He-3/He-4 ratio of about 1.5 was observed with the aid of the cosmic-ray telescopes of OGO-V on May 28, 1969. A theory dealing with the production of H-2, H-3, and He-3 in solar events is considered together with the conditions which would have to be satisfied in order to explain the observed very high helium isotope ratio in terms of the theory.

Balasubrahmanyan, V. K.↗
NASA NTRS1975

Solar particle events with anomalously large relative abundance of He-3

Energetic particle data are presented from a series of solar flares with a relative abundance of He-3 much higher than that of any previous events. The abundance of protons relative to He nuclei was significantly low in these events; not more than four H-2 and three H-3 were detected during the entire period under study, compared with 1110 He-3 nuclei. Results from these experiments are compared with data available from other investigations, and the limitations the former observations place on theoretical models to explain He-3-rich flares are discussed.

Serlemitsos, A. T.↗
NASA NTRS1976

Influence of a solar proton event on stratospheric ozone

Ozone depletion in the stratosphere associated with the solar proton event of August 4, 1972, was observed with the backscattered ultraviolet experiment on the Nimbus 4 satellite. An abrupt ozone decrease in the 75-80 deg N zone of about 0.002 atm-cm above 4 mb was observed to persist throughout the month of August. A decrease was noted in the 55-65 deg N zone on days 219 and 220, but recovery occurred on day 221. Thereafter, a more gradual decrease was observed. The equatorial zone also showed gradual decrease after day 218, but these were not uniquely distinguished from seasonal variations. The observed change in total ozone following the event was -0.003 atm-cm for the 75-80 deg N zone, corresponding to a 1.3 percent reduction in the 0.305 atm-cm zonal average, but within the 0.019 atm-cm standard deviation. Above the 10 mb surface in the 75-80 deg N zone however, a decrease of 0.004 atm-cm may be compared with a standard deviation of 0.001 atm-cm.

Heath, D. F.↗
NASA NTRS1975

Uranium lines in the spectra of peculiar A stars - A search for recent r-process events

Uranium wavelengths in the spectra of Ap stars are studied to see if they give any indication of a recent r-process event. It is concluded that there is no credible evidence for an admixture of uranium-235 in these stars, which would imply such an event. The evidence, though negative, is badly confused by blending of lines, and a final judgement must wait for an observational clarification of the situation.

Cowley, C. R.↗
NASA NTRS1975

Solar cosmic ray events at large radial distances from the sun

The cosmic ray telescopes on Pioneer 10 and 11 are used to examine solar cosmic ray events out to a distance about 5 AU from the sun. A detailed error analysis of the cosine fit to the anisotropy is presented. The anisotropy and intensity time characteristics during solar events are discussed as a function of radial distance.

Zwickl, R.↗
NASA NTRS1976

Preliminary report on the CTS transient event counter performance through the 1976 spring eclipse season

The transient event counter (TEC), senses and counts transients having a voltage rise of greater than five volts in three separate wire harnesses: the attitude control harness, the solar array instrumentation harness and the solar array power harness. The operational characteristics of TEC are defined and the preliminary results obtained through the first 90 days of operation including the spring 1976 eclipse season are presented. The results show that the Communications Technology Satellite was charged to the point where discharges occurred. The discharge induced transients did not cause any anomalous events in spacecraft operation. The data indicate that discharges can occur at any time during the day without preference to any local time quadrant. The number of discharges occurring in the one second sample interval are greater than anticipated. The compilation and review of the data is continuing.

Stevens, N. J.↗
NASA NTRS1976

On flares, substorms, and the theory of impulsive flux transfer events

Solar flares and magnetospheric substorms are discussed in the context of a general theory of impulsive flux transfer events (IFTE). IFTE theory, derived from laboratory observations in the Double Inverse Pinch Device (DIPD), provides a quantitative extension of 'neutral sheet' theories to include nonsteady field line reconnection. Current flow along the reconnection line increases with magnetic flux storage. When flux build-up exceeds the level corresponding to a critical limit on the current, instabilities induce a sudden transition in the mode of conduction. The resulting IFTE, indifferent to the specific modes and instabilities involved, is the more energetic, the lower the initial resistivity. It is the more violent, the greater the resulting resistivity increase and the faster its growth. Violent events can develop very large voltage transients along the reconnection line. Persistent build-up promoting conditions produce relaxation oscillations in the quantity of flux and energy stored (build-up-IFTE cycles). It is difficult to avoid the conclusion: flares and substorms are examples of IFTE.

Bratenahl, A.↗
NASA NTRS1977

Coronal plasma parameters in a long-duration X-ray event observed by Skylab

Physical conditions in the solar coronal X-ray-emitting plasma are analyzed for an event observed by the S-056 X-ray telescope on Skylab in August 1973. The event was located at the west limb and consisted of a series of high looplike structures that underwent dramatic changes in structure and intensity for more than 50 hours. A total X-ray energy (8 to 20 A) of about 5 by 10 to the 28th power erg is obtained by integrating over the lifetime and is shown to be equivalent to that reported previously for a 'typical' flare. It is found that a first major peak in total X-ray flux and thermal energy density was due to an increase in temperature, a major secondary peak in these parameters corresponded to the time of maximum in density, and conductivity energy losses near maximum intensity were much greater than radiative losses. Models dealing with sources of heating and energy balance are evaluated.

Vorpahl, J. A.↗
NASA NTRS1977

Physical conditions in the solar corona during flarelike events

Soft X-ray images of the sun obtained with the S-056 telescope aboard Skylab are used to investigate physical conditions in the X-ray-emitting coronal plasma during flarelike events. Temporal and spatial variations in the density and temperature of the main X-ray source during a flare are determined along with the total radiative energy emitted by an observed loop system. Models for heat sources and energy balance are analyzed, radiative as well as conductive energy losses are computed, and an attempt is made to develop a self-consistent model of the observed X-ray event. It is concluded that: (1) loop tips constitute the source of the maximum X-ray flux; (2) conductive losses exceed radiative losses by several orders of magnitude; (3) energy (and possibly new matter) is added at loop tips; and (4) the most intense X-ray structures are located in areas where the magnetic field has a small radius of curvature and the axis of a loop sequence changes direction.

Vorpahl, J. A.↗
NASA NTRS1977

Solar proton event - Influence on stratospheric ozone

Large-scale reductions in the ozone content of the middle and upper stratosphere over the polar cap regions were associated with the major solar proton event of 4 August 1972. This reduction, which was determined from measurements with the backscattered ultraviolet experiment on the Nimbus 4 satellite, is interpreted as being due to the catalytic destruction of ozone by odd-nitrogen compounds (NOx) produced by the event.

Heath, D. F.↗
NASA NTRS1977

Preliminary report on the CTS transient event counter performance through the 1976 spring eclipse season

The transient event counter is described, defining its operational characteristics, and presenting the preliminary results obtained through the first 90 days of operation including the Spring 1976 eclipse season. The results show that the CTS was charged to the point where discharges have occurred. The discharge induced transients have not caused any anomalous events in spacecraft operation. The data indicate that discharges can occur at any time during the day without preference to any local time quadrant. The number of discharges occurring in the 1 sec sample interval are greater than anticipated.

Stevens, N. J.↗
NASA NTRS1977

Summary of the CTS Transient Event Counter data after one year of operation

The environmental charging of satellite surfaces during geomagnetic substorms is the apparent cause of a significant number of anomalous events occurring on geosynchronous satellites since the early 1970's. Electromagnetic pulses produced in connection with the differential charging of insulators can couple into the spacecraft harness and cause electronic switching anomalies. An investigation conducted to determine the response of the spacecraft surfaces to substorm particle fluxes makes use of a harness transient detector. The harness transient detector, called the Transient Event Counter (TEC) was built and integrated into the Canadian-American Communications Technology Satellite (CTS). A description of the TEC and its operational characteristics is given and the obtained data are discussed. The data show that the satellite surfaces appear to be charged to the point that discharges occur and that the discharge-induced transients couple into the wire harnesses.

Stevens, N. J.↗
NASA NTRS1977

Coronal mass-ejections-kinematics of the 19 December 1973 event

A detailed description of the observed kinematics of the coronal disturbance of December 19, 1973, is presented along with inferences about the temperatures, densities, magnetic fields, and electric currents within the event. This disturbance consisted of the eruption of a previously quiescent prominence, an associated ejection of coronal material, and the destruction of a large coronal streamer. Observations of the prominence and the corona with a scanning spectroheliometer and a white-light coronagraph aboard Skylab before, during, and after the prominence eruption are discussed, and the temperature and density in the eruptive prominence are traced as the prominence rose to a height of 3 solar radii over 7 hr. The results obtained are shown to reinforce previous arguments that the material comprising the bulk of the mass ejected from the corona in transient events arises from the low corona rather than from the eruptive prominence, which may accompany the coronal mass ejection.

Schmahl, E.↗
NASA NTRS1978

Evolution of the coronal and transition-zone plasma in a compact flare - The event of 1973 August 9

X-ray and extreme ultraviolet observations of a compact flare were analyzed to determine the relative importance of radiation, thermal conduction, and 'evaporation' in the evolution of the temperature and density structure of the plasma. In the event studied (1973 August 9), the electron density was relatively high (5 x 10 to the eleventh to 1 x 10 to the twelfth) and radiation was evidently an important energy-loss and cooling mechanism. The light curves of ultraviolet lines formed at temperatures between 10 to the fifth to 10 to the seventh K indicate a time-varying emission measure gradient, and hence temperature gradient, during the flare. Radiative instability evidently played an important role in determining the steepness of these gradients during the rise and fall phases, and caused strong downward motions of material during the cooling phase. Toward the end of the event, the coronal electron density decreased and the temperature gradient relaxed toward that expected from a conduction-dominated plasma. For this flare, evaporative cooling did not appear to be a significant factor.

Underwood, J. H.↗
NASA NTRS1979

Hydrogen over helium enhancement in successive solar flare particle events from the same active region

An analysis of all of the identified solar-flare-associated energetic particle events in the 1972-1975 period observed with instruments aboard the IMP 7 and IMP 8 satellites has revealed at least eight occasions when more than one particle-producing flare occurred within the same McMath active plage region during its transit of the visible solar disk. A strong tendency for second flares to produce hydrogen over helium (p/alpha) enhanced energetic particle fluxes when compared with the first flare in the 1.8-10.0 MeV per nucleon range emerged in these multiflare regions. The p/alpha enhancement is apparently transient, and for flares separated by at least about 100 hours the p/alpha ratio tends toward its preflare value. It is suggested that the substrate plasma in an active region may be enriched prior to a flare in elements heavier than hydrogen and the composition may not be significantly altered during subsequent acceleration, escape, and propagation. Thus, the preflare history of the active region must be added to the list of factors influencing observed solar-particle-event composition.

Briggs, P. R.↗
NASA NTRS1979

Characteristics of the inverted-V event

An attempt is made to determine the origin of the inverted-V precipitating electrons and mechanisms that could create the inverted-V structure. The energy and pitch angle structures are compared with predictions from several theories that have been proposed to explain the origin of inverted-V events. Data from the AE-D satellite indicate that the origin of the inverted-V precipitating electrons is in the magnetosphere, the most probable regions being the plasma sheet and the neutral sheet. The energy and pitch angle distributions show that electrons are trapped between the mirror points and the electric field potential. The observations suggest that field-aligned precipitating electrons have been heated, probably when they were accelerated by the parallel electric field. Qualitatively, the detailed structures of the inverted-V events favor the theory of anomalous resistivity.

Lin, C. S.↗