SEARCH · Engineering Papers

Results for “arrival time”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS1983

Seismic velocity structure of the lunar mantle

The recently completed set of seismic arrival times from the Apollo lunar seismic network are inverted to estimate the average seismic velocities in three sections of the lunar mantle: two for the upper mantle and one for the middle mantle. The method used is a variation of the linearized least squares inversion where the inversion is accomplished in steps. The estimated average velocities in the upper mantle decrease from Vp = 7.74 km/sec and Vs = 4.49 km/sec in the section above 270-km depth to Vp = 7.46 km/sec and Vs = 4.25 km/sec in the section between 270- and 500-km depth, confirming the earlier finding of negative gradients based on seismic amplitude variations. The average velocities in the middle mantle between the depths of 500 km and 1000 km of Vp = 8.26 km/sec and Vs = 4.65 km/sec are significantly higher than those in the upper mantle, contradicting earlier estimates based on more limited data. The higher velocities may suggest initial melting of the moon down to at least 1000-km depth.

Nakamura, Y.↗

NASA NTRS1983

The period history of the X-ray pulsar in MSH 15-52

New and refined mesurements of the pulse period of the X-ray pulsar in the supernova remnant MSH 15-52 are presented. The data were obtained with the Monitor proportional Counter on board the HEAO 2 observatory. The period measurements were obtained by analyzing pulse arrival times determined by cross-correlating sample pulse profiles with a master template. The period history for the source and a representative 0.15 s X-ray light curve are shown. The X-ray measurements alone lead to a refined value of the period derivative of (1.5382 + or -0.0024) x 10 to the -12th s/s, while including the results of more recent radio observations leads to a value of (1.54029 + or -0.00095) x 10 to the -12th s/s. These results indicate a hard-point source surrounded by diffuse nebular emission.

Weisskopf, M. C.↗

NASA NTRS1984

Development of the L-1011 four-dimensional flight management system

The development of 4-D guidance and control algorithms for the L-1011 Flight Management System is described. Four-D Flight Management is a concept by which an aircraft's flight is optimized along the 3-D path within the constraints of today's ATC environment, while its arrival time is controlled to fit into the air traffic flow without incurring or causing delays. The methods developed herein were designed to be compatible with the time-based en route metering techniques that were recently developed by the Dallas/Fort Worth and Denver Air Route Traffic Control Centers. The ensuing development of the 4-D guidance algorithms, the necessary control laws and the operational procedures are discussed. Results of computer simulation evaluation of the guidance algorithms and control laws are presented, along with a description of the software development procedures utilized.

Lee, H. P.↗

NASA NTRS1985

A second catalog of gamma ray bursts: 1978 - 1980 localizations from the interplanetary network

Eighty-two gamma ray bursts were detected between 1978 September 14 and 1980 February 13 by the experiments of the interplanetary network (Prognoz 7, Venera 11 and 12 SIGNE experiments, Pioneer Venus Orbiter, International Sun-Earth Explorer 3, Helios 2, and Vela). Sixty-five of these events have been localized to annuli or error boxes by the method of arrival time analysis. The distribution of sources is consistent with isotropy, and there is no statistically convincing evidence for the detection of more than one burst from any source position. The localizations are compared with those of two previous catalogs.

Atteia, J. L.↗

NASA NTRS1985

Observation of an excess of cosmic ray muons of energies 2 TeV from the direction of Cygnus X-3

A high flux of muons from the Cygnus X-3 direction has been observed in NUSEX experiment at depths greater than 4600 hg/sq cm s.r. The excess muons show the 4.8 hour modulation in arrival time typical of this source. A study of this modulation was done in order to find the best value of the period and of the period derivative. The muon flux underground from NUSEX and SOUDAN (1800 hg/sq cm) experiments are used to determine the energy spectrum at sea level. The shape and the absolute intensities are found similar to those attributed to gamma rays responsible for production of air showers detected in direction of Cygnus X-3 in the energy range 10 to the 12th power to 10 to the 15th power eV.

Battistoni, G.↗

NASA NTRS1985

Observations of potential ultra high energy gamma-ray sources above 10(15) eV

The Haverah Park 50 m water-Cerenkov array has been used to examine a number of periodic sources for ultra high energy gamma-ray emission above 10 to the 15th power eV. The data, recorded between 1 Jan. 1979 and 31 Dec. 1984, feature a modest angular resolution of approx 3 deg with millisecond arrival time resolution post 1982. The sources investigated include the Crab pulsar, Her X-1, Au0115 + 63 and Geminga. All objects have been detected by workers in the TeV region, with varying degrees of confidence.

Lambert, A.↗

NASA NTRS1985

Search for bursts in air shower data

There have been reports in recent years of the possible observation of bursts in air shower data. If such events are truly of an astrophysical nature then, they represent an important new class of phemonenon since no other bursts have been observed above the MeV level. The spectra of conventional gamma ray bursts are unknown at higher energies but their observed spectra at MeV energies appear generally to exhibit a steepening in the higher MeV range and are thus unlikely to extrapolate to measurable fluxes at air shower energies. An attempt has been made to look for deviations from randomness in the arrival times of air showers above approx. 10 to the 14th power eV with a number of systems and results so far are presented here. This work will be continued for a substantial period of ime with a system capable of recording bursts with multiple events down to a spacing of 4 microns. Earlier data have also been searched for the possible association of air shower events with a glitch of the Vela pulsar.

Bruce, T. E. G.↗

NASA NTRS1985

Mini and super mini arrays for the study of highest energy cosmic rays

The chief difficulty in studying the highest energy cosmic rays is the extremely low intensity, only approximately 5 particles per sq km sr century above 10 to the 20th power eV. Instead of attacking the problem by assembling all of the available resources in one place, as has been done in the past, a way that the task can be performed at much less cost per unit sensitive area is suggested, by using numerous inexpensive mini arrays operating independently of each other. In addition to the quantities usually observed, each mini array will record shower particle arrival time distributions. At 10 to the 20th power eV the saving in cost per primary particle is estimated to be a factor of 10 or better, compared to methods now in use, even for mini arrays newly built from scratch for just this purpose.

Linsley, J.↗

NASA NTRS1985

Shower disc sampling and the angular resolution of gamma-ray shower detectors

As part of the design study for the new UHE gamma ray detector being constsructed at Haverah Park, a series of experiments using scintillators operated side-by-side in 10 to the 15th power eV air showers are undertaken. Investigation of the rms sampling fluctuations in the shower disc arrival time yields an upper limit to the intrinsic sampling uncertainty, sigma sub rms = (1.1 + or - 0.1)ns, implying an angular resolution capability 1 deg for an inter-detector spacing of approximately 25 m.

Lambert, A.↗

NASA NTRS1985

A new approach to evaluate gamma-ray measurements

Misunderstandings about the term random samples its implications may easily arise. Conditions under which the phases, obtained from arrival times, do not form a random sample and the dangers involved are discussed. Watson's U sup 2 test for uniformity is recommended for light curves with duty cycles larger than 10%. Under certain conditions, non-parametric density estimation may be used to determine estimates of the true light curve and its parameters.

Dejager, O. C.↗

NASA NTRS1985

Muon fluctuation studies of EAS 10(17) eV

Fluctuation studies need to compare a parameter which is sensitive to longitudinal fluctuations against a parameter which is insensitive. Cascade calculations indicate that the shower size parameter at Haverah Park, rho (500), and the muon density are insensitive while parameters that significantly reflect the longitudinal development of a particular extensive air shower (EAS) include the muon/water Cerenkov response ratio and the muon arrival time dispersion. This paper presents conclusions based on muon fluctuation studies of EAS measured between 1976 and 1981 at Haverah Park.

Blake, P. R.↗

NASA NTRS1985

The structure of the shower disk observed at Mt. Norikura

The structure of the EAS shower disk, the arrival time distribution of charged particles at the core of the small or middle size shower, is measured at Mt. Norikura in Japan. Four fast scintillation counters with an area of 0.25 sq m and a fast trigger system are added to the Mt. Norikura EAS array for the study.

Sasaki, H.↗

NASA NTRS1985

Structure of air shower disc near the core

The longitudinal structure of the air shower disk is studied by measuring the arrival time distributions of air shower particles for showers with electron size in the range 3.2 x 10 to the 5.5. power to 3.2 x 10 to the 7.5 power in the Akeno air-shower array (930 gcm squared atmospheric depth). The average FWHM as a parameter of thickness of air shower disk increases with core distances at less than 50m. AT the present stage, dependence on electron size, zenith angle and air shower age is not apparent. The average thickness of the air shower disk within a core distance of 50m could be determined by an electromagnetic cascade starting from the lower altitude.

Inoue, N.↗

NASA NTRS1985

Properties of 10 (18)-10 (19)eV EAS at far core distance

The properties of 10 to the 18th power - 10 to the 19th power eV EAS showers such as the electron lateral distribution, the muon lateral distribution ( 1Gev), the ratio of muon density to a electron density, the shower front structure and the transition effects in scintillator of 5cm thickness are investigated with the Akeno 4 sq km/20sq km array at far core distances between 500m and 3000m. The fluctuation of densities and arrival time increase rapidly at core distances greater than 2km.

Teshima, M.↗

NASA NTRS1985

Methods for roof-top mini-arrays

To test the idea of the Linsley effect mini array for the study of giant air showers, it is desirable to have a trigger that exploits the effect itself. In addition to the trigger, it is necessary to have a method for measuring the relative arrival times of the particle swarm selected by the trigger. Since the idea of mini arrays is likely to appeal to small research groups, it is desirable to try to design relatively simple and inexpensive methods, and methods that utilize existing detectors. Clusters of small detectors have been designed for operation in the local particle density realm where the probability of or = 2 particles per detector is small. Consequently, this method can discriminate pulses from each detector and thenceforth deal mainly with logic pulses.

Hazen, W. E.↗

NASA NTRS1985

Thickness of the particle swarm in cosmic ray air showers

The average dispersion in arrival time of air shower particles detected with a scintillator at an impact parameter r is described with accuracy 5-10% by the empirical formula sigma = Sigma sub to (1+r/r sub t) sup b, where Sigma sub to = 2.6 ns, r sub t = 30m and b = (1.94 + or - .08) (0.39 + or - .06) sec Theta, for r 2 km, 10 to the 8th power E 10 to the 11th power GeV, and Theta 60 deg. (E is the primary energy and theta is the zenith angle). The amount of fluctuation in sigma sub t due to fluctuations in the level of origin and shower development is less than 20%. These results provide a basis for estimating the impact parameters of very larger showers with data from very small detector arrays (mini-arrays). The energy of such showers can then be estimated from the local particle density. The formula also provides a basis for estimating the angular resolution of air shower array-telescopes.

Linsley, J.↗

NASA NTRS1984

Type III radio bursts in the interplanetary medium - The role of propagation

Interplanetary type III radio burst observations are analyzed in order to ascertain the role played by propagation effects between the true source and the observer. Large source altitudes are noted, together with an increasing angular size of sources with increasing angular distance from the sun's center. These and other observations furnish strong evidence for the theory that propagation effects, group delays, ducting and/or scattering significantly affect the observed heights, sizes, and brightness temperatures of interplanetary type III bursts. This would be true irrespective of whether the bursts are due to plasma radiation at the fundamental or at the harmonic, and the effects would extend to the arrival times of the radiation to a greater or lesser extent, depending on the path from the source to the observer.

Steinberg, J. L.↗

NASA NTRS1983

Gamma rays of 1-30 MeV from the Galactic Center Region

Preliminary results are reported for gamma rays from the Galactic Center Region at 1-30 MeV made with a balloon-borne double Compton scatter gamma ray telescope. The Compton scatter angle, energy, and arrival time of the incident gamma ray and direction of the Compton scattered secondary for downward-moving gamma rays were measured. The handling of the data is described, and the results of Monte Carlo simulation angular resolutions and absolute efficiencies for different zenith angles of incident gamma rays are given. A contour sky map of the weighted fluxes for a southern sky region is shown whose primary feature is a significant enhancement in the Galactic Center Region. It is concluded that several discrete sources contribute to broaden the maximum in the horizontal or RA direction. Less broadening is indicated along the galactic plane.

Oneill, T.↗