Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “visible light”

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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Radius and limb darkening of Titan from speckle imaging

The radius R of Titan is determined from ground-based, visible light observations using a two-dimensional speckle imaging technique. The value of R is found to depend on the limb-darkening exponent alpha, which is used in modeling the observed disk, and it is determined that the probable range extends from R values of 2680 + or - 100 km for alpha of 0.6 to 2900 + or - 100 km for alpha of 1.3. This range is in agreement with Voyager 1 and Pioneer Saturn observations. It is suggested that spatial resolution may be doubled by using a grid of 256 x 256 pixels at the time the image is digitized, and that further improvements are possible with speckle-reduction techniques under development.

Nisenson, P.↗
NASA NTRS1981

Photoelectric array detectors for use at XUV wavelengths

The characteristics of photoelectric detector systems for use at visible-light, ultraviolet, and X-ray wavelengths are briefly reviewed in the context of the needs of the Spacelab solar-physics facilities. Photoelectric array detectors for use at XUV wavelengths between 90 and 1500 A are described, and their use in the ESA Grazing-Incidence Solar Telescope (GRIST) facility is discussed.

Timothy, J. G.↗
NASA NTRS1981

Photoassisted carbon dioxide reduction and formation of twoand three-carbon compounds

The photoassisted reduction of aqueous carbon dioxide in the presence of naturally occurring minerals is investigated as a possible abiotic precursor of photosynthesis. Aqueous carbon dioxide saturated suspensions or surfaces of the minerals nontronite, bentonite, anatase, wolframite, molybdenite, minium, cinnabar and hematite were irradiated with high-pressure mercury lamps or sunlight. Chemical analyses reveal the production of formic acid, formaldehyde, methanol and methane, and the two and three-carbon compounds glyoxal (CHOCHO) and malonaldehyde (CH2(CHO)2). It is suggested that such photosynthetic reactions with visible light in the presence of semiconducting minerals may provide models for prebiological carbon and nitrogen fixation in both oxidized and reduced atmospheres.

Halmann, M.↗
NASA NTRS1984

Silicone Cerenkov-Radiator Material

Dyes enhance visible output. Three fluorescent dyes combine to increase output of silicone material that normally has low yield of visible Cerenkov radiation by converting large amount of available ultraviolet photons into visible light.

Balasubrahmanyan, V.↗
NASA NTRS1983

The association of radio noise storm enhancements with the appearance of additional material in the corona

Visible light observations of the corona have been combined with radioheliograph observations at metric wavelengths to examine the dynamic behavior of the corona during and after noise storm onsets and enhancements. For the period studied, the occurrence of such radio events is systematically associated with the addition of coronal material in the vicinity of the radio source. Some of the events correspond to mass ejection transients, but they more frequently represent merely a brightening, which grows in 1 hour or less with the coronal region and remains dense and stable for several hours.

Kerdraon, A.↗
NASA NTRS1982

High-resolution spectroscopy with the multi-anode microchannel array detector systems

The results of a series of high-resolution spectroscopic observations undertaken with a linear (1 x 1024)-pixel visible-light Multi-Anode Microchannel Array (MAMA) detector on the Coudespectrograph of the 2.2-meter telescope at the Mauna Kea Observatory and on the vacuum spectrograph of the McMath Solar telescope at the Kitt Peak National Observatory are described. In addition, the two-dimensional MAMA detector systems with (16 x 1024)-pixel, (24 x 1024)-pixel, and (256 x 1024)-pixel formats which are now being readied for use in a series of ground-based, balloon, and sounding-rocket observing programs are briefly described.

Timothy, J. G.↗
NASA NTRS1983

Variability of antarctic sea ice and changes in carbon dioxide

Available data for antarctic sea ice is examined for the presence of long terms trends which could signal a decrease in the total ice amount being brought on by atmospheric warming due to increased CO2 concentrations. The Nimbus 5 electrically scanning microwave radiometer derived ice concentrations from 1972-1976, after which the scanning multifrequency microwave radiometer on the Nimbus 7 spacecraft was used from 1978-1981. Additionally, ship reports, IR data from the NOAA 5 radiometer, and the Landsat visible light scanner were considered. The data were digitized for analyses, which covered seasonal, year-to-year, trends over several years, and interannual seasonal variations. The total ice amplitude varied by 30 pct annually, and decreases in one area corresponded to increases in ice in others. No particular long-term trends were observed, and it is suggested that the satellite ice coverage data be extended in time in order to uncover any trends that extend beyond 9 yr.

Zwally, H. J.↗
NASA NTRS1982

Modelling the neutral gas environment of comets with special application to P/Halley

A technique has been developed which allows relatively accurate modelling of cometary gas production from nothing more than a visible light curve. Application to P/Halley suggests that the production rate of parent molecules will be about 2.6 x 10 to the 29th/second on March 10, 1986, for example. The uncertainties and intrinsic limitations in this approach are outlined. The theory is then extended to predictions of abundance of other gaseous species, and a photometric model of these gases is provided.Combined with the dust model of Divine (1981), preliminary predictions of the luminance of P/Halley, as seen in any direction from inside the coma or outside, can be provided for in the 3000-7000 A wavelength range.

Newburn, R. L., Jr.↗
NASA NTRS1984

Measurements of stratospheric NO2 from the Solar Mesosphere Explorer satellite. I - An overview of the results

The visible light spectrometer on board the Solar Mesosphere Explorer spacecraft measures stratospheric NO2 in the 20-40 km altitude region and provides accurate daytime NO2 density profiles with nearly complete latitudinal coverage over an extended period of time. The instrument and data analysis are discussed in detail, and NO2 results for winter/spring 1982 are presented and compared to current theoretical models. Agreement with other measurements is good, and comparison with NOx models indicates that although the overall agreement is acceptable, improvements in the models are required before good agreement is reached at all latitudes. The data indicate that NO2 has a strong memory of the physical conditions present in the stratosphere over a time period of several days.

Mount, G. H.↗
NASA NTRS1984

Type II bursts, shock waves, and coronal transients - The event of 1980 June 29, 0233 UT

The metric Type-II solar burst event of June 29, 1980, is characterized on the basis of spatially resolved radioheliograph observations obtained at Culgoora, Australia, and visible-light observations obtained with the coronograph/polarimeter of the SMM satellite. The data are presented in images, diagrams, and graphs and discussed in detail. The Type-II emission is found to arise in the dense moving material behind the transient loops, which have sky-plane width 0.5 solar radius and line-of-sight depth 0.1-0.4 solar radius. A faint arc observed moving ahead of the transient loops at about 900 km/sec and not associated with the Type-II burst is attributed to a shock front, and the compression ratio and Alfven Mach number of the enhanced-density region are estimated as n2/n1 = 1.3-3 and M(A) = 1.2-3. The ambient material at 3 solar radii is determined to have Alfven speed 250-625 km/sec and magnetic-field strength 50-120 mG. The total mass of the event is calculated as 700 Tg; the total magnetic energy of the loops is (1.5-15) x 10 to the 29th ergs.

Gary, D. E.↗
NASA NTRS1984

The evaluation of a deformable diffraction grating for a stigmatic EUV spectroheliometer

A second toroidal replica grating was found to have an aspect ratio within 10% of the desire value. The aspect ratio of replica toroidal gratings is coming out somewhat low. Whether this is caused by some relaxation in the epoxy or some residual error in the setup when the replication is made from the deformable submaster grating will be determined. The first imaging tests at EUV wavelengths near 500 A were carried out. The initial results are most encouraging with blur sizes of the order of, or less than, 40 microns. Further focussing and additional photographic tests will be carried out, and preparations made for the first photoelectric measurements of the image quality using the (256 x 1024)-pixel MAMA detection system. The visible-light (256 x 1024)-pixel MAMA detector tube has completed initial evaluation.

Timothy, J. G.↗
NASA NTRS1984

The development and test of ultra-large-format multi-anode microchannel array detector systems

The specific tasks that were accomplished with each of the key elements of the multi-anode microchannel array detector system are described. The modes of operation of position-sensitive electronic readout systems for use with high-gain microchannel plates are described and their performance characteristics compared and contrasted. Multi-anode microchannel array detector systems with formats as large as 256 x 1024 pixels are currently under evaluation. Preliminary performance data for sealed ultraviolet and visible-light detector tubes show that the detector systems have unique characteristics which make them complementary to photoconductive array detectors, such as CCDs, and superior to alternative pulse-counting detector systems employing high-gain MCPs.

Timothy, J. G.↗
NASA NTRS1985

Physics and design of advanced IR bolometers and photoconductors

The state-of-the-art in photoconductors and bolometers is reviewed, centering on the materials development and concepts of extrinsic Si and Ge devices. It is suggested that in the field of 2-D detector arrays the hybrid circuits containing a photoconductor or a photodiode array, bonded with In solder to a switched MOS readout device with up to 60 x 60 elements, will produce superior performance. Other systems discussed include charge-coupled devices, developed for visible-light imaging and adapted to IR imaging, and charge-injection devices, a monolithic combination of a standard photoconductor and a metal-insulator-semiconductor capacitor. Finally, it is pointed out that a nonequilibrium theory of bolometer noise demonstrates the possibility of reducing the traditionally accepted noise limits by 60 percent for Johnson noise and 30 percent for the noise from phonons in the thermal link of the bolometer.

Haller, E. E.↗
NASA NTRS1985

Flammability Limits of Gases Under Low Gravity Conditions

The purpose of this combustion science investigation is to determine the effect of zero, fractional, and super gravity on the flammability limits of a premixed methane air flame in a standard 51 mm diameter flammability tube and to determine, if possible, the fluid flow associated with flame passage under zero-g conditions and the density (and hence, temperature) profiles associated with the flame under conditions of incipient extinction. This is accomplished by constructing an appropriate apparatus for placement in NASA's Lewis Research Center Lear Jet facility and flying the prescribed g-trajectories while the experiment is being performed. Data is recorded photographically using the visible light of the flame. The data acquired is: (1) the shape and propagation velocity of the flame under various g-conditions for methane compositions that are inside the flammable limits, and (2) the effect of gravity on the limits. Real time accelerometer readings for the three orthogonal directions are displayed in full view of the cameras and the framing rate of the cameras is used to measure velocities.

Strehlow, R. A.↗
NASA NTRS1985

The LAMAR telescope module for high throughput imaging and spectroscopy

Kirkpatrick-Baez mirror assemblies for the LAMAR experiment of the Space Shuttle are described. The aperture is 20 cm x 30 cm and the distance from the front of the mirror to the focal plane is 3.4 m. The reflectors are made from 1.8 mm gold coated float glass. A prototype brassboard mirror was constructed with only one-third of the plates. Its angular resolution is 35 arcsec (HPW) in visible light. X-ray tests over small areas indicate very little scattering. The fabrication technique is applicable to larger mirror systems such as those of XMM. The use of flatter material for the reflectors results in better angular resolution.

Gorenstein, P.↗
NASA NTRS1985

The August 1984 eclipse of 22 Vulpeculae

Observations are reported of the newly discovered eclipsing binary 22 Vul (G3 IB-II+B9), in and around the 1984 eclipse. IUE satellite and ground-based photometric observations are included. The depth of total eclipse of the hot component was 0.05 mag in the V band, 0.14 in B, and 0.35 in U. Time of mideclipse is now established at JD1445942.3 (1984 August 29.8) plus-or-minus 0.2 day, with an eclipse duration of 9.8 plus-or-minus 0.2 days. The period is 249.115 plus-or-minus 0.024 days. The ingress and egress phases, lasting only about one day in visible light, last a week or more at some UV wavelengths and are not symmetrical.

Parsons, S. B.↗
NASA NTRS1984

Performance characteristics of multi-anode microchannel array detector systems

The multi-anode microchannel arrays (MAMAs) are state-of-the-art, pulse-counting, photoelectric array detectors designed specifically for use in space astrophysics instruments. The present paper provides a description of recent progress related to the development of ultraviolet and visible-light versions of the MAMA detectors, taking into account a comparison of the operating characteristics of these devices with those of photoconductive array detectors, such as the CCDs. Attention is given to MAMA detector system design parameters, the operating characteristics of MAMAs and CCDs, MAMA performance characteristics, and future developments.

Timothy, J. G.↗