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At least 307 records · Page 17
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DOE OSTI2016

MAGNETIC CYCLES IN A DYNAMO SIMULATION OF FULLY CONVECTIVE M-STAR PROXIMA CENTAURI

The recent discovery of an Earth-like exoplanet around Proxima Centauri has shined a spot light on slowly rotating fully convective M-stars. When such stars rotate rapidly (period ≲20 days), they are known to generate very high levels of activity that is powered by a magnetic field much stronger than the solar magnetic field. Recent theoretical efforts are beginning to understand the dynamo process that generates such strong magnetic fields. However, the observational and theoretical landscape remains relatively uncharted for fully convective M-stars that rotate slowly. Here, we present an anelastic dynamo simulation designed to mimic some of the physical characteristics of Proxima Centauri, a representative case for slowly rotating fully convective M-stars. The rotating convection spontaneously generates differential rotation in the convection zone that drives coherent magnetic cycles where the axisymmetric magnetic field repeatedly changes polarity at all latitudes as time progress. The typical length of the “activity” cycle in the simulation is about nine years, in good agreement with the recently proposed activity cycle length of about seven years for Proxima Centauri. Comparing our results with earlier work, we hypothesis that the dynamo mechanism undergoes a fundamental change in nature as fully convective stars spin down with age.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1970

Investigation of an Optimum Detection Scheme for a Star-Field Mapping System

An investigation was made to determine the optimum detection scheme for a star-field mapping system that uses coded detection resulting from starlight shining through specially arranged multiple slits of a reticle. The computer solution of equations derived from a theoretical model showed that the greatest probability of detection for a given star and background intensity occurred with the use of a single transparent slit. However, use of multiple slits improved the system's ability to reject the detection of undesirable lower intensity stars, but only by decreasing the probability of detection for lower intensity stars to be mapped. Also, it was found that the coding arrangement affected the root-mean-square star-position error and that detection is possible with error in the system's detected spin rate, though at a reduced probability.

Aldridge, M. D.↗
NASA NTRS1973

Entry environmental simulation testing of REI-Mullite TPS

Glassy fibrous mullite coatings exhibit noncatalytic surface characteristics which limit surface temperature rise under certain convective heat flux conditions. Thermal conductivity design curves provide good agreement with test results. The inclusion of shine-in effects results in improved accuracy of transient temperature gradient predictions for the materials.

Florence, D. E.↗
NASA NTRS1973

LAGEOS mission analyses

Two error sources are found to be compatible and significant for the parameters affecting the LAGEOS mission. The first error source is the uncertainty in the gravity model, and the second error source is the radiation pressure which includes direct radiation, albedo radiation, and earth shine. Retrograde orbits increase the number of passes per day over the tracking stations at the expense of also increasing the number of time gaps when no station is observing. It is shown that relativistic effects are significant and must be included in orbit computation and determination systems for this mission. If station locations are known only to one meter, the error in the satellite orbits is comparable with solar pressure induced errors.

Squires, R. K.↗
NASA NTRS1973

Mars - The intermediate between earth and moon

The present work represents a summary of the state of our knowledge concerning the chief physical characteristics of Mars as deduced from existing observational and theoretical evidence. Two main geological provinces are distinguished on Mars: areas of rough terrain and dense cratering, and smooth areas comparable to lunar maria. A thermal model for the Martian poles which takes into account convective transport would indicate that the CO2 frost over the north pole is not permanent, lasting about 420 days with the water frost lasting the remaining 267 days of the Martian year. The meandering appearance of Martian rift valleys are cracks probably produced, as also in the case of lunar rilles, by stresses, perhaps in solidifying lava of impact origin, and not by erosional river beds. Data indicate a strong absorption in the thin Martian atmosphere. The atmospheric blue and violet cap around a Martian pole in winter is interpreted as a 'blue clearing' of the atmosphere increasing transparency so that surface detail of higher albedo shines through in the blue.

Opik, E. J.↗
NASA NTRS1974

Thermal conductivity measurements on Mullite and Silica REI for the Space Shuttle - Complementary guarded hot plate and radical outflow measurements

The materials studied are described along with the apparatus and the experimental techniques employed. The results of the measurements involving two REI Silica materials and a Mod 1 B REI Mullite are listed in a table. Measurements were conducted at unusually high temperature differences to detect 'shine-through' radiation transparency. Photographs are presented of the high-temperature guarded hot plate assembly.

Brazel, J. P.↗
NASA NTRS1978

Inexpensive, portable, integrating solar energy meter

Silicon-cell insolometer automatically measures and totals amount of energy available in sunlight falling on the earth at specific location over selected period of time. Device incorporates single silicon solar cell as sensing element and relies on principle that short-circuit current from solar cell is directly proportional to amount of light that shines on cell.

Masters, R. M.↗
NASA NTRS1975

Automatic visual inspection system for microelectronics

A system for automatically inspecting an integrated circuit was developed. A device for shining a scanning narrow light beam at an integrated circuit to be inspected and another light beam at an accepted integrated circuit was included. A pair of photodetectors that receive light reflected from these integrated circuits, and a comparing system compares the outputs of the photodetectors.

Micka, E. Z.↗
NASA NTRS1978

Physical properties of solar chromospheric plages. III - Models based on Ca II and Mg II observations

Solar plages are modeled using observations of both the Ca II K and the Mg II h and k lines. A partial-redistribution approach is employed for calculating the line profiles on the basis of a grid of five model chromospheres. The computed integrated emission intensities for the five atmospheric models are compared with observations of six regions on the sun as well as with models of active-chromosphere stars. It is concluded that the basic plage model grid proposed by Shine and Linsky (1974) is still valid when the Mg II lines are included in the analysis and the Ca II and Mg II lines are analyzed using partial-redistribution diagnostics.

Kelch, W. L.↗
NASA NTRS1980

Resonant Doppler velocimeter

A technique is presented for visualizing and quantitatively measuring velocity, temperature, and pressure by shining a single frequency laser beam into a gaseous flow which is seeded with an atomic species. The laser is tuned through the absorption frequencies of the seeded species and the absorption profile is detected by observing fluorescence as the atoms relax back to the ground state. The flow velocity is determined by observing the Doppler shift in the absorption frequency. Spectroscopic absorption line broadening mechanisms furnish information regarding the static temperature and pressure of the moving gas. Results of experiments conducted in the free stream and in the bow shock of a conical model mounted in a hypersonic wind tunnel indicate that the experimental uncertainties in the measurement of average values for the velocity, temperature and pressure of the flow are 0.1, 5 and 10 percent respectively.

Zimmermann, M.↗
NASA NTRS1982

Resonant Doppler velocimetry in supersonic nitrogen flow

The development of the Resonant Doppler Velocimeter (RDV) is discussed. It is a new nonintrusive laser technique for flow diagnosis. The RDV technique is applied to supersonic nitrogen flow with sodium atoms as tracer particles. The measurements are achieved by shining a tunable single frequency laser beam into the flow. The resonant absorption spectrum of the seeded species is determined by observing the fluorescence signal intensity as a function of excitation wavelength. By comparing the peak absorption wavelength with a reference frequency marker, the flow velocity along the excitation beam can be obtained through the Doppler shift relation. By fitting the spectrum with a theoretical line profile, the static temperature and pressure of the flow an be determined.

Cheng, S. W. S.↗
NASA NTRS1981

Structure of the sunspot penumbra

An exceptionally highly resolved sunspot photograph is presented which reveals the fine-scale structure of the photospheric penumbra down to 0.2 arcsec. The photograph was taken through a glass filter in a 170-A FWHM band centered on 4660 A on the 65-cm vacuum Gregorian telescope at Big Bear Solar Observatory during practically perfect seeing. The photograph reveals the penumbra to be full of extremely fine-scale fibril structures, with apparent widths near the resolution limit. The three-dimensional structure of the photospheric penumbra is seen to be similar to that of the chromospheric penumbra and superpenumbra, with dark fibrils arching above a lower brighter structure and many of the bright fibrils representing portions of wider bright structures shining through the narrow spaces between the elevated dark fibrils. Thus, in contrast to previous pictures, much of the dark component of the photospheric penumbra is not physically analogous to the intergranular dark lanes in the normal photosphere.

Moore, R. L.↗
NASA NTRS1983

Results of thermal environment measurements on the thermal cannister experiment and get away special enclosure

Because the OSS-1 pallet contained a variety of instruments with irregular surface geometry and properties which limited predictability, the total absorbed flux on thermal canister radiators was measured to determine heat rejection capability. The instrumentation and sensor cup design and locations for the thermal canister experiment are illustrated. Graphs show flux sensor history in hot and coal orbits. Kapton erosion is also considered. Results show that the flux levels measured in all STS attitudes are higher than predictions. In cold and moderate attitudes, flight results are a factor of two to three higher than predicts. In hot attitude, much better agreement occurred. It is concluded that in cold or moderate attitudes other sources may be contributing to added inputs (albedo, Earth shine, shuttle background). In hot attitude, smaller differences could be attributed to coatings assumptions or calculation uncertainty.

Ollendorf, S.↗
NASA NTRS1983

The Voyager mission to Uranus and beyond

On 24 January 1986 the Voyager 2 probe will approach within 82,000 km of the cloud tops of the planet Uranus, obtaining our first closeup pictures of this giant outer planet as well as amassing large quantities of data from the ten other onboard experiments. Closeups of the five presently known Uranian satellites will be transmitted back over a distance of 20 AU with a one-way light-time of two and three-quarter hours. The narrow, elliptical, inclined rings of Uranus will be probed both by the imaging subsystem and by the photopolarimeter detecting the light of stars shining through this diffuse necklace.

Kerridge, S. J.↗
NASA NTRS1984

Laser pulse detection method and apparatus

A sensor is described for detecting the difference in phase of a pair of returned light pulse components, such as two components of a light pulse of an optical gyro. In an optic gyro, the two light components have passed in opposite directions through a coil of optical fiber, with the difference in phase of the returned light components determining the intensity of light shining on the sensor. The sensor includes a CCD (charge coupled device) that receives the pair of returned light components to generate a charge proportional to the number of photons in the received light. The amount of the charge represents the phase difference between the two light components. At a time after the transmission of the light pulse and before the expected time of arrival of the interfering light components, charge accumulating in the CCD as a result of reflections from components in the system, are repeatedly removed from the CCD, by transferring out charges in the CCD and dumping these charges.

Goss, W.↗
NASA NTRS1983

Skylab observations of the solar C I multiplets at 1560- and 1657-A

Skylab spectrograph profile observations of the solar C I multiplets are presented, and the profile variations from center to limb and at various heights above the quiet solar limb are noted. These lines are of interest both because they are formed in the midchromosphere, thereby providing checks and constraints on chromospheric models, and because they are sensitive to the magnitude of the nonthermal microvelocities included in theoretical calculations. The present observations are compared with the C I profiles calculated by Shine et al (1978), discussing the many inconsistencies that emerge, notably between the observed and computed 1560/1657-A ratio and in the center-to-limb and above-the-limb variations of the integrated intensity. The multiplet central cores are discussed in terms of several microturbulent velocity structures.

Roussel-Dupre, D.↗
NASA NTRS1983

Summary of NASA Langley's pilot scan behavior research

The present investigation is concerned with the information acquired in a series of basic studies designed to obtain an understanding of the pilot's scanning behavior. In the studies, use was made of an oculometer system which operates by shining a beam of collimated infrared light at the subject's eyes. A number of oculometer software modifications have been made to make the oculometer user-friendly and versatile. Scanning is found to be a subconscious conditioned activity. The conditioned activity of scanning is different for each pilot. There are also slight variations between test runs for the same conditions for the same pilot. This indicates that scanning is situation dependent. Attention is given to the rate of information transfer, the possibility that scanning can be disrupted, the visual approach look-point, and workload sensitive measures.

Spady, A. A., Jr.↗
NASA NTRS1985

Spectral evolution of gamma-rays from adiabatically expanding sources in dense clouds

The excess of antiprotons (P) observed in cosmic ray was attributed to their production in supernova (SN) envelopes expanding in dense clouds. While creating P, gamma rays are also produced and these clouds would shine as gamma-ray sources. The evolution of the gamma-ray spectrum is calculated for clouds of r sub H = 10.000 and 100.000/cu cm.

Stephens, S. A.↗