Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Search”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

A search of the SAS-2 data for pulsed gamma-ray emission from radio pulsars

Data from the SAS-2 high energy gamma ray experiment were examined for pulsed emission from each of 75 radio pulsars which were viewed by the instrument and which have sufficiently well defined period and period derivative information from radio observations to allow for gamma ray periodicity searches. When gamma ray arrival times were converted to pulsar phase using the radio reference timing information, two pulsars, PSR 1747-46 and PSR 1818-04, showed positive effects, each with a probability less than 0.0001 of being a random fluctuation in the data for that pulsar. These are in addition to PSR 0531+21 and PSR 0833-45, previously reported. The results of this study suggest that gamma-ray astronomy has reached the detection threshold for gamma ray pulsars and that work in the near future should give important information on the nature of pulsars.

Ogelman, H. B.↗
NASA NTRS1975

Soft X-ray search of centre of Cygnus Loop

Equipment on the Copernicus satellite has been used to search for evidence of a compact object in the center of the Cygnus Loop supernova remnant. Rocket measurements reported by Rappaport et al. (1973) indicate that a central object exists. However, the study conducted with the aid of the satellite was negative. This negative result could indicate that the X-ray source was simply not in its high-intensity mode at the time of observation, or could arise because the source is at some other location in the Loop.

Snyder, W. A.↗
NASA NTRS1975

Search for continuous X-ray emission from NP 0532

A search for continuous X-ray emission from the pulsar NP 0532 has been performed using lunar occultations and high temporal resolution. No increase in the nonpulsed phase of the flux from the Crab Nebula was observed when NP 0532 was exposed. The result is used to establish an upper limit of 4.7 million K (99% confidence) on the surface temperature of the neutron star.

Wolff, R. S.↗
NASA NTRS1975

Search for extreme ultraviolet radiation from selected stars

Results are reported for a search for EUV radiation between 140 and 430 A from selected objects which was conducted with a rocket-borne EUV filter photometer. The candidate objects included the bright planetary nebula NGC 2392 and the stars gamma Gem, alpha CMa, omicron-prime CMa, and gamma-2 Vel. Upper limits (2-sigma level) to the flux near 200 A are determined for the five objects, and estimates of the expected 200-A helium-continuum flux are derived for two of the stars on the basis of the hot-corona model. It is found that the calculated upper limits are at least two orders of magnitude higher than plausible flux estimates based on the hot-corona model. However, it is noted that uncertainties in the flux estimates are great enough to make the upper limits useful.

Riegler, G. R.↗
NASA NTRS1976

Search for correlation between geomagnetic disturbances and mortality

A search is conducted for a possible correlation between solar activity and myocardial infarction and stroke in the United States. A statistical analysis is performed using data on geomagnetic activity and the daily U.S. mortality due to coronary heart disease and stroke for the years 1962 through 1966. None of the results are found to yield any evidence of a correlation. It is concluded that correlations claimed by Soviet workers between geomagnetic activity and the incidence of various human diseases are probably not statistically significant or probably are not due to a causal relation between geomagnetic activity and disease.

Lipa, B. J.↗
NASA NTRS1976

A search for optical counterparts of nine galactic X-ray sources

Results of a photographic and spectrophotometric search to a limiting B magnitude of approximately 18.5 for the optical counterparts of nine galactic X-ray sources with good positions are reported. The sources included in this survey are 3U 1709-23, 1728-16, 1728-24, 1758-20, 1758-25, 1811-17, 1813-14, 1837+04, 1908+00. Optical candidates for six of these sources are discussed, including blue objects which may be the optical counterparts of 1709-23 and 1728-16, a distant B star near 1908+00, and a very unusual strong-emission-line object which is probably associated with 1728-24 (GX 2+5). Coordinates, magnitudes, colors, spectral data, and finding charts are presented.

Davidsen, A.↗
NASA NTRS1975

A search for X rays from UV Ceti flare stars

A search of the MIT/OSO-7 data has been made for evidence of X-ray emission from flares of UV Ceti flare stars. Observations from McDonald Observatory have been used to identify the times of optical flares. The only instance of coincident coverage occurred on 1974, January 21, UT at 03:43:26 GMT for a flare of YZ CMi with a u magnitude increment of 0.86. No radio coverage of this particular event was obtained. Upper limits (3 sigma) of 0.8, 1.0, and 0.7 photons/sq cm sec on the observed X-ray flux have been set for the energy ranges greater than 15, greater than 3, and 1-10 keV, respectively.

Crannell, C. J.↗
NASA NTRS1975

A search for solar flare positrons

The detection of solar gamma-ray line emission and observations of the isotopes H2, H-3, and He-3 in solar cosmic rays provide direct evidence for the occurrence of high energy nuclear reactions in solar flare events. Appreciable numbers of other reaction products, including positrons with energies near about 1 MeV, should also be produced in such events. We have searched for positrons in the 0.16-1.6 MeV energy interval during 5 H-3 rich solar particle events. Based on calculations of positron and He-3 production at the sun, and using a simplified model of interplanetary propagation, we might expect comparable fluences of positrons and He-3 to be observed. Summing over these 5 events, we find the 0.16 to 1.6 MeV positron fluence to be a maximum of about 10% of the He-3 fluence with more tnan 1 MeV/nuc. This suggests that other processes, such as preferential trapping by the solar magnetic field, may be important.

Mewaldt, R. A.↗
NASA NTRS1975

Search for a particle with a long interaction length

A search has been carried out for a long-lived particle having an interaction length lambda sub m equals 300 to 2000 gm/sq cm in air. Such a particle, called the mandela, has been proposed to explain an anomalous energy spectrum of particles observed near sea level with a shallow spectrometer. Data taken at mountain altitude with a deep spectrometer has been examined for compatibility with the existence of the mandela. Although data tend to favor the mandela hypothesis the results are not conclusive and appear to be explainable by conventional means.

Barrowes, S. C.↗
NASA NTRS1976

The search for life in the solar system

The search for extraterrestrial life in the solar system is reviewed in the light of present knowledge about the physical state of the planets. Arguing that all life in the universe is based on carbon chemistry, the carbon abundance in the solar system is discussed along with the composition of the planets, the presence of organic compounds (particularly amino acids) in meteorites, and the existence of complex organic compounds in interstellar space. Prospects for life in the solar system are evaluated by eliminating most of the bodies as potential biological habitats on the basis of temperature and lack of an atmosphere. Bodies eliminated in this manner include the moon, most of the other satellites, Mercury, Venus, the asteroids, and the giant planets. It is shown that the outlook for life on Titan is uncertain, but that Mars fulfills the minimum conditions for a life-bearing planet. Theories on the Martian surface environment are reviewed, the problem of the lack of water on Mars is examined, and the possibility of climatic changes is considered. The Viking mission is briefly noted.

Horowitz, N. H.↗
NASA NTRS1976

Search for X-ray emission from Nova Cygni 1975

A search for X-rays from Nova Cygni 1975 was carried out before, during, and after the time of optical maximum. No X-rays were detected over the spectral range 0.1-50 keV. On the basis of these results a strong upper limit of .0001 has been placed on the ratio of X-ray to optical luminosity for this nova, consistent with effective temperatures of about 10,000 K. If Nova Cygni 1975 is a virgin nova, its low mass exchange rate would imply that any associated X-ray emission would not be detectable by present techniques.

Hoffman, J. A.↗
NASA NTRS1976

Inverse atmospheric radiative transfer problems - A nonlinear minimization search method of solution

The paper studies the inversion of the radiative transfer equation describing the interaction of electromagnetic radiation with atmospheric aerosols. The interaction can be considered as the propagation in the aerosol medium of two light beams: the direct beam in the line-of-sight attenuated by absorption and scattering, and the diffuse beam arising from scattering into the viewing direction, which propagates more or less in random fashion. The latter beam has single scattering and multiple scattering contributions. In the former case and for single scattering, the problem is reducible to first-kind Fredholm equations, while for multiple scattering it is necessary to invert partial integrodifferential equations. A nonlinear minimization search method, applicable to the solution of both types of problems has been developed, and is applied here to the problem of monitoring aerosol pollution, namely the complex refractive index and size distribution of aerosol particles.

Fymat, A. L.↗
NASA NTRS1976

Ballistic trajectories for Mercury Orbiter missions using optimal Venus flybys, a systematic search

The considered approach, which has been previously studied by Hollenbeck et al. (1973) makes use of a Venus gravity assist. The search for ideal trajectories for Mercury Orbiter missions involves a determination of trajectories with the lowest possible Mercury approach speed. Ideal Venus-to-Mercury transfers and opportunities are discussed. The second part of the reported investigation is concerned with the determination of suitable trajectories for the trip from earth to Venus. On the basis of the obtained data it appears that the best ten trajectories can deliver spacecraft from a low of 720 kg to a high of 1230 kg to orbits with 500 km periapse and 24 hr periods. The corresponding flight times are 790 days and 1243 days.

Bender, D. F.↗
NASA NTRS1976

Search for radiation from the 2 pi 1/2, J = 5/2 state of interstellar CH

The note reports results of an unsuccessful search for the four hyperfine transitions in the cited rotational state of interstellar CH, which was performed using a 25.6-m radio telescope equipped with a traveling-wave maser radiometer. The frequency interval covered ranged from 4677 to 4850 MHz; the sources observed were W3 Cont, W51, Orion A, and IRC+10216. It is shown that the lines in the present excited state cannot be expected to be observed if the state is populated according to thermodynamic equilibrium at the kinetic temperature of the medium. The possibility is considered of detecting thermally excited CH in a more compact region and of detecting excited-state CH maser lines. It is concluded that no strong CH maser lines exist for the frequencies and sources covered.

Sume, A.↗
NASA NTRS1976

Search for the Viking 2 landing site

The search for the landing site of Viking 2 is reviewed, emphasizing the characteristics of the various candidate sites and reasons for rejecting unsuitable sites. It is shown that the B3 site in Utopia Planitia was selected because the B latitude band (40 to 50 deg N) was of the highest scientific interest, the site appeared to be smoothed by uniform mantling, and the additional data analysis and acquisition required to land at any other site could have resulted in a landing delay and significant additional operational complexity. It is tentatively concluded that the Viking 2 lander rests in a deflation hollow.

Masursky, H.↗
NASA NTRS1976

A search for slowly varying radio continuum emission from UV Ceti stars

The paper presents results of a search conducted at the Arecibo Observatory for variable 430-MHz emission from the active flare stars EQ Peg, YZ CMi, and AD Leo. No statistically significant evidence for slowly varying emission is found to a level of 0.05 Jy for AD Leo, 0.018-0.021 Jy for YZ CMi, and 0.009-0.018 Jy for EQ Peg. Upper limits of about 10 trillion K are determined for the brightness temperature of active radio regions on these stars at the time of the observations.

Spangler, S. R.↗
NASA NTRS1976

A search of the SAS-2 data for pulsed gamma-ray emission from radio pulsars

Data from the SAS-2 high-energy (above 35 MeV) gamma-ray experiment have been examined for pulsed emission from each of 75 radio pulsars which were viewed by the instrument and which have sufficiently well-defined period and period-derivative information from radio observations to allow for gamma-ray periodicity searches. When gamma-ray arrival times were converted to pulsar phase using the radio reference timing information, two pulsars, PSR 1747-46 and PSR 1818-04, showed positive effects, each with a probability of less than 1 part in 10,000 of being a random fluctuation in the data for that pulsar. These are in addition to PSR 0531+21 and PSR 0833-45, previously reported. The results of this study suggest that gamma-ray astronomy has reached the detection threshold for gamma-ray pulsars and that work in the near future should give important new information on the nature of pulsars.

Ogelman, H.↗
NASA NTRS1976

A search for radio emission from ionized hydrogen in M15

A sensitive search at 3.6 cm for thermal emission from ionized gas in the globular cluster M15 (NGC 7078) reveals no emission greater than the experimental error, which is 0.003 Jy. Based on this flux-density limit, the mass of ionized gas within 3 pc of the cluster center is less than 26 solar masses. This result suggests that the ionized-gas content of M15, which contains an intense X-ray source, is not greatly enhanced compared with similar globular clusters without known X-ray sources. This mass limit is an order of magnitude greater than the amount of gas required to produce the X-ray flux by accretion onto massive black holes.

Klein, M. J.↗