Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Flux Measurement”

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 NTRS1979

A small helium-cooled infrared telescope for Spacelab 2

A helium cooled telescope of 15 cm aperture is being designed and constructed jointly by the University of Arizona, the Smithsonian Astrophysical Observatory and the Marshall Space Flight Center for high sensitivity infrared astronomical observations from Spacelab 2. A focal plane array of ten detectors provide a total field of view of 3 deg and cover the wavelength regions 4.5-8.5, 6-7, 9-16, 18-30 and 80-120 microns. A highly redundant all sky survey will be conducted by repeated scanning of the sky during many orbits of the spacecraft. High redundancy will allow discrimination among variable and constant celestial sources and several types of variable nearby sources. The principal astronomical result of the survey will be the absolute flux measurement of low surface brightness, large scale celestial infrared emissions but it will also extend existing IR sky surveys by a factor of 10 in point source sensitivity. The experiment will also make significant engineering measurements of contaminants in the Shuttle environment, test the technology of storage and utilization of large quantities of superfluid helium in space and test mechanical designs for future infrared telescopes for the Space Shuttle.

Gautier, T. N., III↗
NASA NTRS1979

Charged dust in the outer planetary magnetospheres. I - Physical and dynamical processes

Typical interplanetary grains (Brownlee types) and the physical and dynamical processes associated with their entry into the Jovian magnetosphere are discussed. The charging and subsequent distribution of interplanetary dust grains entering the magnetosphere as well as the basic aspects of orbital dynamics of charged grains are examined. Results showed that all negatively charged fragments are strongly attracted towards the planet by the radial corotational electric field, while some are stably trapped, suggesting that the sudden enhancement by about two orders of magnitude of the interplanetary dust flux, measured at 30 Jupiter radii by Pioneer 10, is a combination of these two results. The similarity in brightness asymmetries between the Jovian and Saturnian satellites leads to the expectation that Saturn's magnetic moment and spin are parallel with the limit of plasma corotational lying between satellites Rhea and Iapetus.

Hill, J. R.↗
NASA NTRS1979

Discovery of a soft X-ray flux from AN Ursae Majoris

During November 1975, the soft X-ray detectors on the SAS 3 satellite scanned across AN Ursae Majoris, a star very similar to AM Herculis in its unusual optical properties. A soft (0.1-0.4 keV) X-ray flux averaging 2.8 x 10 to the -11th erg/sq cm-sec was detected from AN UMa, as had been anticipated by analogy with AM Her. Folding the X-ray flux measurement with the known binary period reveals an X-ray light curve with approximately 100% modulation, and thereby secures the identification of the X-ray source as AN UMa. Unlike the case in AM Her, the X-ray minimum in AN UMa occurs midway between optical linear-polarization peaks.

Hearn, D. R.↗
NASA NTRS1980

The HD 200775/NGC 7023 complex - A question of reddening

The separation of the observed reddening of HD 200775 into intrinsic and interstellar components is rediscussed in the light of new surface-brightness data for NGC 7023, the reflection nebula surrounding HD 200775. Appropriate correction for the nebular contribution to reported ultraviolet flux measurements of HD 200775 leads to new values due to dust reddening: E(B-V) sub D = 0.44, and due to intrinsic reddening: E(B-V) sub I = 0.13-0.26. The newly derived extinction curve for HD 200775 is characterized by an abnormally weak interstellar 2200 A absorption feature, and the deduced nebular brightness in the far-ultraviolet is consistent either with dust in NGC 7023 having a relatively high albedo (a approximately equal to 0.6) and a nearly isotropic phase function (g approximately equal to 0.2), or with low albedo dust (a approximately equal to 0.3) with a forward-throwing phase function (g approximately equal to 0.6).

Witt, A. N.↗
NASA NTRS1980

Cold dense photoionized universes

This investigation employs a computer code, initially constructed for modeling the evolution of a hot dense intergalactic medium (IGM), to study some properties of a cold dense IGM photoionized by QSOs. Within the observational constraints set by flux measurements in the far-ultraviolet, night sky brightness, and hard X-ray region, and the optical depth limits on various QSO spectra, it determines some allowable scenarios for a range of QSO spectral indices (alpha) and cutoff energies. With H(0) = 50 km/s-Mpc, closure density of an IGM (composed of H and He in their cosmic ratio) is possible only if alpha is greater than or equal to 0.1, a circumstance not likely to prevail; the most probable value, alpha = -0.7, implies an upper limit density about 0.35 of closure, which is somewhat larger than previous estimates. These estimates are substantially independent of whether or not QSOs produce the observed diffuse extragalactic X-ray background; such QSO spectral details are critical, however, in determining the ionization of heavy elements that are expected to contaminate a pure primeval plasma.

Sherman, R. D.↗
NASA NTRS1980

The 20-micron brightness temperature of the unilluminated side of Saturn's rings

Observations of the 20-micron brightness temperature of the unilluminated (north) side of Saturn's rings are presented and discussed in terms of models of B ring heating. Observations centered on the B ring ansae were made at 19.8 microns by the 3-m IR telescope facility on Mauna Kea during a period when the unilluminated side of the rings could be observed from earth. Flux measurements indicate a 20-micron brightness temperature of 56 + or - 1 K, in agreement with that measured at 45 microns by Pioneer 11. Under the assumptions that the emission of the Cassini division is negligible and that the ring brightness temperature is close to the actual temperature, it is shown that the brightness temperature can be accounted for by heating by the disk of Saturn, and is proportional to the sine of the Saturnicentric declination of the sun.

Tokunaga, A. T.↗
NASA NTRS1981

Grand unification and possible matter-antimatter domain structure in the universe

The theory and basic concepts for the development of a matter-antimatter domain cosmology are outlined within the framework of the grand unified gauge theory paradigm. It is shown how spontaneous CP symmetry breaking leads to such a domain sturcture in the universe. Astrophysical data such as the cosmic gamma-ray background spectrum, cosmic-ray p flux measurements, and galaxy clustering are found to favor this point of view. Future tests of this form of big-bang cosmology are suggested and discussed, including tests using deep underwater cosmic ray neutrino detectors.

Stecker, F. W.↗
NASA NTRS1981

Fluorescence equilibrium in the ultraviolet spectra of Comets Seargent (1978 m) and Bradfield (1979 l)

Detailed fluorescence calculations for OH including the Swings effect were performed. These calculations were used to reproduce the high resolution spectra of Comets Seargent and Bradfield taken with IUE. The calculations also provide the OH fluorescence efficiencies (g factors), as a function of heliocentric radial velocity, which are needed to derive OH abundances from measured fluxes. A close examination of the spectra shows no sign of the corresponding emission bands of OD allowing upper limits to be placed on the ratio N(OD)/N(OH). Preliminary attempts to reproduce the CO+ band structure by fluorescence are discussed.

Donn, B.↗
NASA NTRS1980

QSO evolution and the intergalactic medium

A model is developed of a cold, photoionized intergalactic medium in which only discrete, evolving sources (quasars) produce the observed extragalactic hard X-ray background. Constraints on the model are imposed by observed optical depth limits to various redshifts, far UV and visible flux measurements, X-ray background and source counts in the region 2-6 keV, and it makes use of results of the Palomar Bright Quasar Survey and the Braccesi Quasar survey to obtain expressions for the quasar evolution function, absolute luminosity, present number density and switch-on redshift. Results of computer modeling reveal an intergalactic medium with a density with respect to closure less than 0.35, temperature of 16,000 K and fractional ion abundances of approximately 0.000001 for H I and 0.001 for He II, under the assumption of a Hubble constant of 50 km/sec per Mpc. In addition, spectral indices of -0.4 and -1.3 are obtained for the regions of the emission spectrum above and below 4 x 10 to the 18th Hz.

Sherman, R. D.↗
NASA NTRS1980

The collective excitation of g-modes in the sun

Oscillations of the solar interior (linear g-modes) may be strongly driven by the collective influence of all the modes upon the nuclear reactions in the core. This heretofore neglected effect could couple the modes, reduce the effective amplitudes near the center, and spatially concentrate most of the oscillation energy into just a portion of the radiative interior. If operating at sufficient strength, this can reverse the conventional conclusion, drawn from single mode calculations, that almost all solar g-modes are damped. Furthermore, it would put the theory into rough harmony with three otherwise troubling observations: (1) the 'low' neutrino flux measured by Davis (1978), (2) the high correspondence found by Wolff (1976) between recurrence periods in solar activity and the rotational beat periods of g-modes, and (3) the fluctuations in the sun's diameter which imply g-mode activity at high angular harmonics (Hill and Caudell 1979). A nonlinear expression is derived for the local rate of work done on an array of oscillation modes by the nuclear reactions. Three additional tests of the model are suggested.

Wolff, C. L.↗
NASA NTRS1981

The ultraviolet spectrum of Herbig-Haro Object 1

Continuum and emission line fluxes for HH 1 in the range of 1200-1300 A have been determined using IUE spectra, and it is found that the luminosity of HH 1 in this wavelength interval is slightly larger than 1 solar luminosity, or 20 times greater than for the wavelength range 3200-11,000 A. If averaged over intervals of 100 A, it is shown that the UV continuum rises almost monotonically toward shorter wavelengths over the entire interval 1300-3000 A. The UV continuum energy distribution cannot be explained by a T Tauri stellar continuum that is scattered by dust. Emission line identifications and flux measurements strongly confirm the statement that the high-ionization emission lines are too strong to be explained by shock-wave models derived from the emission line spectrum in the interval 3700-11,000 A. A possible explanation for this fact is discussed.

Boehm, K. H.↗
NASA NTRS1981

The aerodynamics of bodies in a rarefied ionized gas with applications to spacecraft environmental dynamics

The objectives are to provide a parametric description of the electrostatic interaction of a mesosonic, collisionless plasma with conducting bodies on the order of 1 to 10 Debye lengths in size, and to extend this description to the satellite-ionospheric interaction, where possible. Experimental findings include: the wake of the geometrically complex body appears to be a linear superposition of the wakes of its simple geometric components; and vector ion flux measurements show converging ion streams at the wake axis and direct evidence of ion streams deflected from the wake axis by the positive space charge potential associated with the axial ion peak. The extension to the satellite-ionospheric interaction utilizes qualitative scaling and indicates that similar, but smaller amplitude, wake structures may be expected for small or highly charged bodies. However, for large bodies at small potentials, the structure may be diffused by the thermal ion motion and the dispersion resulting for space charge potentials.

Stone, N. H.↗
NASA NTRS1982

Thermal coupling of a heat flux sensor

The conditions of thermal coupling were investigated in relationship to the development of sensors for local thermal flux measurements of component surfaces. The dependence of the transfer function on heat conductivity coefficient of the measured object and the influence of the contact resistance at the sensor boundaries are discussed in terms of known results and investigations.

Kaiser, E.↗
NASA NTRS1981

Neutron star binaries, pulsars and burst sources

Unresolved issues involving neutron star binaries, pulsars, and burst sources are described. Attention is drawn to the types of observations most likely to resolve them. Many of these observations are likely to be carried out during the next decade by one or more missions that have been approved or proposed. Flux measurements with an imaging detector and broad-band spectroscopic studies in the energy range 30-150 keV are discussed. The need for soft X-ray and X-ray observations with an instrument which has arcminute angular resolution and an effective area substantially greater than of ROSAT or EXOSAT is also discussed.

Lamb, F. K.↗
NASA NTRS1981

First detection of nonflare microwave emissions from the coronae of single late-type dwarf stars

Results are presented of a search for nonflare microwave radiation from the coronae of nearby late-type dwarf stars comparable to the sun: single stars without evidence for either a large wind or circumstellar envelope. The observing program consisted of flux measurements of six stars over a 24-h period with the VLA in the C configuration at a wavelength of 6 cm with 50 MHz bandwidth. Positive detections at 6 cm were made for Chi 1 Ori (0.6 mJy) and the flare star UV Cet (1.55 mJy), and upper limits were obtained for the stars Pi 1 UMa, Xi Boo A, 70 Oph A and Epsilon Eri. It is suggested that Chi 1 Ori, and possibly UV Cet, represent the first detected members of a new class of radio sources which are driven by gyroresonance emission, i.e. cyclotron emission from nonrelativistic Maxwellian electrons.

Gary, D. E.↗
NASA NTRS1981

The rigidity dependence of cosmic ray solar modulation

Continuous particle flux measurements above rigidity thresholds of 1.2, 2.2, 5.5 and 11 GV were made by using the thresholds of two Cerenkov detectors aboard the ISEE-3 spacecraft. The ISEE-3 was launched in August 1978, near the beginning of the current solar cycle's heavy modulation phase, and the data presented represent the first direct measurement made at these energies with such a long time base. The measured long term modulation rigidity spectrum is compared with other data and with the spectrum of Forbush decreases, and it is found that the agreement between electron and positively charged particle results must be considered a constraint on cosmic ray modulation models involving the mechanism of gradient and curvature drift in the interplanetary magnetic field.

Evenson, P.↗
NASA NTRS1982

X-ray observations of Abell 2218 and implications for the Sunyaev-Zel'dovich effect

The Einstein Observatory was used to obtain a high-resolution X-ray image and an X-ray flux measurement of the galaxy cluster Abell 2218. The combined system of intracluster medium and galaxies is modeled as a gas in hydrostatic equilibrium in a common gravitational potential with an isothermal galaxy component. This model is then fitted in the least-squares sense to the X-ray surface brightness distribution and to the optically determined galaxy surface density profile to determine model parameters. The gas is found to be nominally isothermal, moderately dense, and very hot (10-30 keV); these conditions are consistent with the Sunyaev-Zel'dovich effect, i.e., the diminution in the cosmic microwave background radiation intensity in the direction of this cluster. It is noted that the considerable imprecision inherent in the method of distance measurement based on the combination of microwave measurements with X-ray and optical data makes it impossible to make a definitive statement about the distance to Abell 2218.

Boynton, P. E.↗
NASA NTRS1982

Surface composition and radius of Hyperion

New spectrophotometric data for Hyperion in the region 1.5-2.6 microns obtained in 1981 confirm the presence of water ice bands reported by Cruikshank (1980). The bands are now shown with sufficient clarity to permit improved comparisons with other ice-bearing satellites of Jupiter and Saturn and with laboratory samples. Comparisons with Ganymede and Rhea are shown, and Hyperion is found to differ from both satellites in terms of depth and width of the water ice bands. The sense of the difference is the same as noted earlier from broadband infrared photometry, but the physical cause is not fully understood. The effective radius of Hyperion (considered circular in cross section) derived from a 20-micron flux measurement and a revised value of V(1,0) = 4.62 is r = 140 + or - 19 km. This result is in better accord with both preliminary and refined values of the radius derived from Voyager images; the Voyager result supersedes that deduced from infrared observations.

Cruikshank, D. P.↗