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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Flare activity, sunspot motions, and the evolution of vector magnetic fields in Hale region 17244

The magnetic and dynamical circumstances leading to the 1B/M4 flare of November 5, 1980 are studied, and a strong association is found between the buildup of magnetic shear and the onset of flare activity within the active region. The development of shear, as observed directly in vector magnetograms, is consistent in detail with the dynamical history of the active region and identifies the precise location of the optical and hard-X-ray kernels of the flare emission.

Neidig, Donald F.↗
NASA NTRS1986

Evidence for coronal turbulence in a quiescent active region

The first evidence for nonthermal broadening of X-ray lines in a quiescent active region was based on a single observation of a limb active region by the Flat Crystal Spectrometer (FCS) on the SMM satellite, reported by Acton et al. (1981). With the renewal of SMM operations, the FCS has been used to further investigate this phenomenon. On April 28, 1984 a map of Mg XI resonance line profiles was made for a bright area in NOAA Active Region 4474 during a nonflaring period. The narrowest line profiles are consistent with the nominal instrumental width plus a thermal width equivalent to about 3 million K, the temperature derived from line ratios of O VIII, Ne IX, and Mg XI. The broadest line profiles are consistent with the instrumental width plus a thermal width equivalent to about 7 million K, but a substantial amount of plasma at this temperature would result in much greater flux in the FCS higher-temperature channels than was seen. If the excess width is attributed solely to plasma turbulence, the corresponding velocity would be about 40 + or - 10 km/s.

Saba, Julia L. R.↗
NASA NTRS1987

Effects of exercise and conditioning on clotting and fibrinolytic activity in men

Blood clotting and fibrinolytic activity in three groups of nonsmoking, nonobese, healthy men ranging from 19 to 59 years are studied. The groups consisted of (1) marathoners (men running more than 50 miles/week); (2) joggers (men running 5-15 miles/week; and (3) sedentary subjects (men who did not exercise routinely). It is observed that the rate of blood clotting is accelerated by exercise; marathoners had greater increases in fibrinolytic activity than the other two groups; and fibrin degradation products increased with exercise. The data reveal that the changes in clotting assays with exercise do not correlate with changes in whole blood lactate, blood pyruvate, or rectal temperatures. It is noted that the level of acceleration for fibrinolytic activity is directly related to the maximum aerobic capacity and work load of the individual, and that conditioning enhances the fibrinolytic response to exercise.

Ferguson, Earl W.↗
NASA NTRS1986

A conceptual design for a microwave active phased array SAR

The active phased array radar is well known for its assets of rapid electronic beam steering and adaptability to limited degrading influences. In a spaceborne synthetic aperture radar (SAR) application, therefore, it should be possible to provide for rapid beam control in the cross-track (variable incidence angle) and along-track (spot-light mode) directions, as well as allowing for possible relaxation of antenna structural requirements. A design study has been conducted at Stanford University for a conceptual spaceborne C-band SAR application operating in the early to mid-1990's time frame. This study was intended to identify principal design issues, as well as unique features associated with an active phased array antenna SAR. A hypothetical design is used to illustrate these issues. Some of this work should have generic application to space-based communications activities.

Gilchrist, Brian E.↗
NASA NTRS1987

Extended active space CASSCF/MRSD CI calculations of the barrier height for the reaction O + H2 yields OH + H

The convergence of the barrier height for the O + H2 yields OH + H reaction is studied as a function of the size of the active space in the CASSCF calculation and the size of the basis set. The basis set employed in this study is described. The sources of the differences between the POL-CI and MRSD-CI calculations for barrier height are examined. It is observed that the barrier height is rapidly convergent with respect to the expansion of the active space. The effects of adding active orbitals on the barrier height are investigated. The barrier height estimated from corrected MRSD-CI data is 12.4 kcal/mol.

Walch, Stephen P.↗
NASA NTRS1986

Energy balance in solar active regions - The dip of April, 1985

The presence of a solar active region affects the luminosity of the sun. Sunspots directly produce 'dips' in the total solar irradiance approximately proportionally to their projected area, while faculae produce excess energy. These effects were discovered during the solar maximum period of 1980, and the sunspot effect during solar minimum is examined. The 'dip' due to an active region in April, 1985, as observed in the total solar irradiance by the ACRIM instrument on the Solar Maximum Mission is examined. These data (obtained after the spacecraft repair in May, 1984) have simple variations, relative to those observed in 1980, because of the reduced level of activity approaching solar minimum. It is found that the PSI index of projected sunspot area as defined in 1980 appears to describe this 'dip' satisfactorily.

Hudson, H. S.↗
NASA NTRS1987

Activity associated with the solar origin of coronal mass ejections

Solar coronal mass ejections (CMEs) observed in 1980 with the HAO Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are compared with other forms of solar activity that might be physically related to the ejections. The solar phenomena checked and the method of association used were intentionally patterned after those of Munro et al.'s (1979) analysis of mass ejections observed with the Skylab coronagraph to facilitate comparison of the two epochs. Comparison of the results reveals that the types and degree of CME associations are similar near solar activity minimum and at maximum. For both epochs, most CMEs with associations had associated eruptive prominences, and the proportions of association of all types of activity were similar. A high percentage of association between SMM CMEs and X-ray long duration events is also found, in agreement with Skylab results. It is concluded that most CMEs are the result of the destabilization and eruption of a prominence and its overlying coronal structure, or of a magnetic structure capable of supporting a prominence.

Webb, D. F.↗
NASA NTRS1987

Intrusions in the active layer of channeled-substrate-planar laser diodes

Channeled-substrate-planar laser diodes from various wafers were observed to develop a node or dark spot in their near-field patterns after failure during lifetesting. 'Node' devices from each wafer were angle-lapped and stained in an attempt to uncover a physical mechanism for this common failure symptom. Optical microscopic examination of the beveled cross sections revealed that an intrusion, in the form of a spike at the tip of the zinc diffusion front, had penetrated into the active layer of these diodes. The node observed in the near-field pattern appears to be in a position correspondig to the location of the spike in the active region. In addition, cathodoluminescence measurements on other 'node' diodes revealed a dark line region approximately 2-micron-wide running parallel to and in the middle of the 5-micron contact stripe. It is believed that this dark line region is representative of an area of nonradiative recombination which occurs in the portion of the active layer containing the intrusion.

Slavin, S. E.↗
NASA NTRS1987

Comparison of active regions on the nucleus of Comet Halley

The images of the nucleus of Comet Halley returned by the Giotto spacecraft reveal a number of active regions on the surface, one of which is near the expected location of the rotation axis. This feature is larger and brighter than other source regions, suggesting that the mechanism which drives this source is also different. At this active region near the rotation pole the Sun is circumpolar for a significant portion of the solar encounter. Continuous solar insolation causes heating of the nucleus to greater depths and results in the unique properties of this source region. For example, the dust scattering in the antisolar regions around the nucleus is less from the polar region than from the region at the sunward end of the nucleus, consistent with spotty ejection of dusty mantle from the sunward tip and widespread activity in the polar region.

Reitsema, H. J.↗
NASA NTRS1987

Active layer model for wall-bounded turbulence

The active-layer model for wall-bounded turbulence hypothesizes that the nonlinear terms are large only in a thin layer near the wall, and hence the turbulence in the region outside the active inner layer can be modeled as a linear fluctuating flow driven by the active layer. This hypothesis is tested using data obtained from a direct simulation of turbulent channel flow. It is found that the nonlinear effects are the strongest near the wall with a maximum at around y sup + = 20 and, outside the near-wall region, these involve primarily the cascading mechanism leading to dissipation.

Landahl, M. T.↗
NASA NTRS1987

Mechanisms of active control in cylindrical fuselage structures

This paper summarizes ongoing efforts to understand and exploit active control techniques for low frequency noise suppression in aerospace applications. Analytical models are utilized in an effort to understand the mechanisms that govern noise transmission into acoustic spaces enclosed by lightweight structures and to examine the results of experimental implementations of active control schemes. Emphasis is placed on attaining global noise reductions using a minimum number of actuators rather than localized control over many subregions. This program has demonstrated the effect of synchrophasing and interface modal filtering, in limiting the modal density within the acoustic space, and how strong reactive effects may occur in two dimensional geometries. Finally, the performance of active control systems utilizing acoustic and vibration actuators is evaluated. Suppressions of 10 to 30 dB are demonstrated in practice, and performance is discussed in relation to the physical mechanisms and parameters of the system.

Silcox, R. J.↗
NASA NTRS1988

Activity in X-ray-selected late-type stars

A spectroscopic study has been conducted of nine X-ray bright late-type stars selected from two Einstein X-ray surveys: the Columbia Astrophysical Laboratory Survey (five stars) and the CFA Medium Sensitivity Survey (MSS; four stars). Spectral classes were determined and radial and V sin(i) velocities were measured for the stars. Four of the Columbia Survey stars were found to be new RS CVn-type binaries. The fifth Columbia survey star was found to be an active G dwarf star without evidence for binarity. None of the four MSS stars were found to be either binaries or optically active stars. Activity in these stars was assessed by measuring the excess emission in H-alpha and the Ca II IRT (8498, 8542) lines in comparison with inactive stars of similar spectral types. A correlation was found between X-ray luminosity and V sin(i) and H-alpha line excess. The measured excess line emission in H-alpha was also correlated with V sin(i) but not with the IRT line excess.

Takalo, Leo O.↗
NASA NTRS1988

Magnetic modulation of solar luminosity by photospheric activity

The behavior of slow changes in solar irradiance S is studied using measurements obtained with radiometers on the SMM and Nimbus 7 spacecraft. The general downtrend in the radiometer readings is examined by removing the influence of sunspot blocking and comparing the residual irradiance variations with changes in facular and network radiation as indicated by the He I 10830 and CaK indices. The time-integrated sunspot and facular contributions to irradiance variation and its implications for active region energetics are considered. The magnetic activity modulation of S over solar cycle 21 from daily data on sunspot blocking and the He I index are simulated, and this simulated irradiance variation is compared to radiometry since 1978. Other recent evidence for an irradiance modulation by magnetic activity is discussed.

Foukal, P.↗
NASA NTRS1988

Distribution of flares on the sun during 1955-1985 - 'Hot spots' (active zones) lasting for 30 years

The coordinates of 'major solar flares' observed during the period from January 1955 through August 1985 are analyzed. About 100 'superactive' regions (large, complex, active regions containing large sunspots) produced 46 percent of the major flares during the period. Superactive regions appeared more frequently in certain areas of the sun called 'hot spots' or 'active zones'. The synodic rotation periods of the northern and southern hemisphere hot spots were 26.72 d and 26.61 d, respectively. One of the two hot spots persisted through three solar cycles, and the other was active during cycles 19 and 21 but was dormant during cycle 20. These findings suggest that the mechanism producing hot spots must be stable for two or three solar cycles or longer.

Bai, Taeil↗
NASA NTRS1988

Production of the diffuse X-ray background spectrum by active galactic nuclei

This paper proposes a class of models in which the intensity and spectrum of the X-ray background radiation between 0.2 and 160 keV can be produced by active galactic nuclei. The key assumption of these models is that the spectra of active galactic nuclei are not described by a single power law. No evolution of the X-ray spectra of active galactic nuclei is required.

Schwartz, D. A.↗
NASA NTRS1984

Overview of the NASA/RECON educational, research, and development activities of the Computer Science Departments of the University of Southwestern Louisiana and Southern University

This document presents a brief overview of the scope of activities undertaken by the Computer Science Departments of the University of Southern Louisiana (USL) and Southern University (SU) pursuant to a contract with NASA. Presented are only basic identification data concerning the contract activities since subsequent entries within the Working Paper Series will be oriented specifically toward a detailed development and presentation of plans, methodologies, and results of each contract activity. Also included is a table of contents of the entire USL/DBMS NASA/RECON Working Paper Series.

Dominick, Wayne D.↗
NASA NTRS1988

High-resolution digital movies of emerging flux and horizontal flows in active regions on the sun

High-resolution observations of active regions in many wavelength bands obtained at the Vacuum Tower Telescope of NSO/Sunspot (Sacramento Peak) are presented. The SOUP tunable filter, HRSO 1024 x 1024 CCD camera, and a sunspot tracker for image stabilization were used. Subarrays of 512 x 512 pixels were processed digitally and recorded on videodisk in movie format. The movies with 0.5 to 1 arcsecond resolution of the following simultaneous observations were shown: green continuum, longitudinal magnetogram, Doppler velocity, Fe I 5576 A line center, H alpha wings, and H alpha line center. The best set of movies show a 90 x 90 arcsecond field-of-view of an active region at S29, W11. When viewed at speeds of a few thousand times real-time, the photospheric movies clearly show the active region fields being distorted by a remarkable combination of systematic flows and small eruptions of new flux. Flux emergence is most easily discovered in line center movies: an elongated dark feature appears first, followed soon after by bright points at one or both ends. A brief, strong upflow is seen when the dark feature first appears; downflow in the bright points persists much longer. The magnetic flux appears to increase gradually over this extended period. Some of the flux emergence events were studied in detail, with measurements of horizontal and vertical velocities and magnetic flux versus time within one footpoint of the loop.

Topka, K.↗
NASA NTRS1989

Active vibration control for flexible rotor by optimal direct-output feedback control

Experimental research tests were performed to actively control the rotor vibrations of a flexible rotor mounted on flexible bearing supports. The active control method used in the tests is called optimal direct-output feedback control. This method uses four electrodynamic actuators to apply control forces directly to the bearing housings in order to achieve effective vibration control of the rotor. The force actuators are controlled by an analog controller that accepts rotor displacement as input. The controller is programmed with experimentally determined feedback coefficients; the output is a control signal to the force actuators. The tests showed that this active control method reduced the rotor resonance peaks due to unbalance from approximately 250 micrometers down to approximately 25 micrometers (essentially runout level). The tests were conducted over a speed range from 0 to 10,000 rpm; the rotor system had nine critical speeds within this speed range. The method was effective in significantly reducing the rotor vibration for all of the vibration modes and critical speeds.

Nonami, Kenzou↗