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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.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Payload crew activity planning integration. Task 2: Inflight operations and training for payloads

The primary objectives of the Payload Crew Activity Planning Integration task were to: (1) Determine feasible, cost-effective payload crew activity planning integration methods. (2) Develop an implementation plan and guidelines for payload crew activity plan (CAP) integration between the JSC Orbiter planners and the Payload Centers. Subtask objectives and study activities were defined as: (1) Determine Crew Activity Planning Interfaces. (2) Determine Crew Activity Plan Type and Content. (3) Evaluate Automated Scheduling Tools. (4) Develop a draft Implementation Plan for Crew Activity Planning Integration. The basic guidelines were to develop a plan applicable to the Shuttle operations timeframe, utilize existing center resources and expertise as much as possible, and minimize unnecessary data exchange not directly productive in the development of the end-product timelines.

Hitz, F. R.↗
NASA NTRS1976

Development of solar active regions

The birth, growth, and decay of solar active regions are described. The appearance of active regions in different atmospheric layers is examined, and the coronal extension of active regions is considered. The use of Skylab soft X-ray and extreme UV observations for studying the complex loop structure of active regions in the solar corona and the sensitive reactions of the upper atmospheric layers to newly emerging flux is explained. It was found that well developed active regions are much bigger in the corona than in the underlying sunspot groups and plages, and that many of the active regions are connected with others through systems of magnetic field lines, occasionally visible in soft X-rays. These interconnections, which may survive several solar rotations, indicate bigger complexes on the sun than one individual active region.

Svestka, Z.↗
NASA NTRS1982

Solar irradiance variations and solar activity

A mean value for the 1 AU total solar irradiance of 1368.2 W/sq m and a downward trend of 0.05% per year were derived from measurements by the Active Cavity Radiometer Irradiance Monitor (ACRIM) experiment on the Solar Maximum Mission during 1980. Distinct temporary solar irradiance decreases associated with solar activity maxima were observed with a series of nine dips from April to October recurring at fairly regular intervals averaging 24 days. The decreases correlate inversely with sunspot area, 2800-MHz flux, and Zurich sunspot number. Dominant periods common to the irradiance and sunspot area power spectra link the irradiance decreases to sunspot flux deficit in solar active regions. Evidence of significant total irradiance modulation by facular flux excess is cited. A persistent radiative cycle of active regions consistent with the ACRIM irradiance results and the morphology of solar active regions was found. The pattern of regularly recurrent active region maxima between April and October suggests an asymmetry in solar activity generation during this period.

Willson, R. C.↗
NASA NTRS1983

The quiescent chromospheres and transition regions of active dwarf stars - What are we learning from recent observations and models?

Progress in understanding active dwarf stars based on recent IUE, Einstein, and ground-based observations is reviewed. The extent of magnetic field control over nonflare phenomena in active dwarf stars is considered, and the spatial homogeneity and time variability of active dwarf atmospheres is discussed. The possibility that solar like flux tubes can explain enhanced heating in active dwarf stars in examined, and the roles of systematic flows in active dwarf star atmospheres are considered. The relation between heating rates in different layers of active dwarf stars is summarized, and the mechanism of chromosphere and transition region heating in these stars are discussed. The results of one-component and two-component models of active dwarf stars are addressed.

Linsky, J. L.↗
NASA NTRS1985

Magnetospheric impulse response for many levels of geomagnetic activity

The temporal relationship between the solar wind and magnetospheric activity has been studied using 34 intervals of high time resolution IMP 8 solar wind data and the corresponding AL auroral activity index. The median values of the AL index for each interval were utilized to rank the intervals according to geomagnetic activity level. The linear prediction filtering technique was then applied to model magnetospheric response as measured by the AL index to the solar wind input function VB(s). The linear prediction filtering routine produces a filter of time-lagged response coefficients which estimates the most general linear relationship between the chosen input and output parameters of the magnetospheric system. It is found that the filters are composed of two response pulses speaking at time lags of 20 and 60 min. The amplitude of the 60-min pulse is the larger for moderate activity levels, while the 20-min pulse is the larger for strong activity levels. A possible interpretation is that the 20-min pulse represents magnetospheric activity driven directly by solar wind coupling and that the 60-min pulse represents magnetospheric activity driven by the release of energy previously stored in the magnetotail. If this interpretation is correct, the linear filtering results suggest that both the driven and the unloading models of magnetospheric response are important facets of a more comprehensive response model.

Bargatze, L. F.↗
NASA NTRS1987

A study of methods to predict and measure the transmission of sound through the walls of light aircraft. Numerical method for analyzing the optimal performance of active noise controllers

An optimal active noise controller is formulated and analyzed for three different active noise control problems. The first problem formulated is the active control of enclosed or partially enclosed harmonic sound fields where the noise source strengths and enclosure boundary description are known. The enclosure boundary is described by either pressure, velocity, or impedance boundary conditions. The second problem formulated is the active control of the free field power radiated from a distributed noise source with a known time harmonic surface velocity. The third problem formulated is the active control of enclosed or partially enclosed harmonic sound field where the noise source strengths of enclosure boundary description may not be known. All three formulations are derived using an indirect boundary element technique. Formulation and verification of an indirect boundary element method is presented. The active noise controller formulations for enclosures are capable of analyzing systems with generalized enclosure shapes, point noise sources, and/or locally reacting impedance boundary conditions. For each formulation, representative results of optimal active noise controller case studies are presented, and some general conclusions are drawn.

Mollo, Christopher G.↗
NASA NTRS1987

Distribution of flares on the sun - Superactive regions and active zones of 1980-1985

The author analyzed coordinates of energetic solar flares observed with the hard X-ray burst spectrometer during the period from February 1980 through August 1985. A small number of 'superactive regions' produced the majority of the major flares during this period. There exist active zones, in which the flare occurrence rate is much higher. Two active zones are in the northern hemisphere, and two are in the southern hemisphere. The longitudinal separation of the two active zones in the same hemisphere is about 180 deg, but tha active zones of the southern hemisphere are misaligned from those of the northern hemisphere by about 80 deg. The rotation period of the active zones is 26.75 d. Active zones last several years or longer. There is a hint of active centers rotating at a period of 23.7 d.

Bai, Taeil↗
NASA NTRS1988

Crew activities, science, and hazards of manned missions to Mars

The crew scientific and nonscientific activities that will occur at each stage of a mission to Mars are examined. Crew activities during the interplanetary flight phase will include simulations, maintenance and monitoring, communications, upgrading procedures and operations, solar activity monitoring, cross-training and sharpening of skills, physical conditioning, and free-time activities. Scientific activities will address human physiology, human psychology, sociology, astronomy, space environment effects, manufacturing, and space agriculture. Crew activities on the Martian surface will include exploration, construction, manufacturing, food production, maintenance and training, and free time. Studies of Martian geology and atmosphere, of the life forms that may exist there, and of the Martian moons will occur on the planet's surface. Crew activities and scientific studies that will occur in Mars orbit, and the hazards relevant to each stage of the mission, are also addressed.

Clark, Benton C.↗
NASA NTRS1992

Continual expansion of the active-region corona observed by the Yohkoh Soft X-ray Telescope

We have found from the observations of the Yohkoh Soft X-ray Telescope (SXT) that the corona above active regions expands occasionally, and almost continually in the cases of 'active' active regions. The key to this discovery has been a movie representation of the Yohkoh SXT data, which, for the first time, provides adequate sampling and continuity for this purpose. The movies show ubiquitous expansions above the active regions, with velocities in the range of a few to a few tens km/s. The expansion appears to preserve the overall structure of the active-region corona. This finding of almost continual expansion of the active-region corona may affect some of the basic ideas concerning active regions, as well as those of the mass-loss from the Sun and Sunlike stars.

Uchida, Yutaka↗
NASA NTRS1992

Activated transport in AMTEC electrodes

Transport of alkali, metal atoms through porous cathodes of alkali metal thermal-to-electric converter (AMTEC) cells is responsible for significant reducible losses in the electrical performance of these cells. Experimental evidence for activated transport of metal atoms at grain surfaces and boundaries within some AMTEC electrodes has been derived from temperature dependent studies as well as from analysis of the detailed frequency dependence of ac impedance results for other electrodes, including thin, mature molybdenum electrodes which exhibit transport dominated by free molecular flow of sodium gas at low frequencies or dc conditions. Activated surface transport will almost always exist in parallel with free molecular flow transport, and the process of alkali atom adsorption/desorption from the electrode surface will invariably be part of the transport process, and possibly a dominant part in some cases. The temperature dependence of the diffusion coefficient of the alkali metal through the electrode in several cases provides an activation energy and preexponential, but at least two activated processes may be operative, and the activation parameters should be expected to depend on the alkali metal activity gradient that the electrode experiences. In the case of Pt/W/Mn electrodes operated for 2500 hours, limiting currents varied with electrode thickness, and the activation parameters could be assigned primarily to the surface/grain boundary diffusion process.

Williams, R. M.↗
NASA NTRS1993

Optical fiber sensor having an active core

An optical fiber is provided. The fiber is comprised of an active fiber core which produces waves of light upon excitation. A factor ka is identified and increased until a desired improvement in power efficiency is obtained. The variable a is the radius of the active fiber core and k is defined as 2 pi/lambda wherein lambda is the wavelength of the light produced by the active fiber core. In one embodiment, the factor ka is increased until the power efficiency stabilizes. In addition to a bare fiber core embodiment, a two-stage fluorescent fiber is provided wherein an active cladding surrounds a portion of the active fiber core having an improved ka factor. The power efficiency of the embodiment is further improved by increasing a difference between the respective indices of refraction of the active cladding and the active fiber core.

Egalon, Claudio Oliveira↗
NASA NTRS1994

Solar activity variations in midlatitude thermospheric meridional winds

Upper thermospheric meridional wind data at midlatitudes and for low magnetic activity are examined for solar activity variations following an analysis scheme suggested by a Coordinated Analysis of the Thermosphere workshop. Wind data from incoherent scatter, Fabry-Perot, and F2 peak heights show decreasing diurnal amplitudes with increasing solar activity during all seasons, except for Saint Santin data, which show a slight increase in summer. Equivalent winds from F2 peak height data have strong decreases in diurnal amplitude in all seasons. The coupled thermosphere ionosphere model and thermosphere ionosphere global circulation model predictions of diurnal amplitude, while differing considerably in magnitude, also show decreasing amplitudes during all seasons except summer, while the HWM90 empirical model amplitudes increase slightly with solar activity during all seasons. The diurnal mean wind trends with solar activity are fairly weak, except for Millstone Hill incoherent scatter radar, which shows a shift from strong southward to near zero or northward wind with increasing activity. Model results for the mean generally fall within the band of measurements. Near midnight, most of the data also show that the typically southward winds weaken with increasing solart activity in all seasons except summer, when results are mixed. There are significant differences between the trends and between absolute values for the various data sets and models which need further investigation.

Hedin, A. E.↗
NASA NTRS1995

Interplanetary planar magnetic structures associated with expanding active regions

Planar magnetic structures are interplanetary objects whose magnetic field cannot be explained by Parker's solar wind model. They are characterized by two-dimensional structure of magnetic field that are highly variable and parallel to a plane which is inclined to the ecliptic plane. They appeared independently of interplanetary compression, solar flares, active prominences nor filament disappearances, but the sources often coincided with active regions. On the other hand, it has been discovered by the Yohkoh Soft X-ray telescope that active-region corona expand outwards at speeds of a few to a few tens of km/s near the Sun. The expansions occurred repeatedly, almost continually, even in the absence of any sizable flares. In the Yohkoh Soft X-ray images, the active-region corona seems to expand out into interplanetary space. Solar sources of interplanetary planar magnetic structures observed by Sakigake were examined by Yohkoh soft X-ray telescope. During a quiet period of the Sun from January 6 to November 11, 1993, there found 5 planar magnetic structures according to the criteria (absolute value of Bn)/(absolute value of B) less than 0.1 for planarity and (dB)/(absolute value of B) greater than 0.7 for variability of magnetic field, where Bn, dB, and the absolute value of B are field component normal to a plane, standard deviation, and average of the magnitude of the magnetic field, respectively. Sources of 4 events were on low-latitude (less than 5 degrees) active regions from which loop-like structures were expanding. The coincidence, 80%, is extremely high with respect to accidental coincidence, 7%, of Sakigake windows of solar wind observation with active regions. The last source was on loop-like features which seemed to be related with a mid-latitude (20 degrees) active region.

Nakagawa, Tomoko↗
NASA NTRS1998

Assessment of Uncertainty in the Determination of Activation Energy for Polymeric Materials

An assessment of the experimental uncertainty in obtaining the kinetic activation energy from thermogravimetric analysis (TGA) data is presented. A neat phenolic resin, Borden SC1O08, was heated at three heating rates to obtain weight loss vs temperature data. Activation energy was calculated by two methods: the traditional Flynn and Wall method based on the slope of log(q) versus 1/T, and a modification of this method where the ordinate and abscissa are reversed in the linear regression. The modified method produced a more accurate curve fit of the data, was more sensitive to data nonlinearity, and gave a value of activation energy 75 percent greater than the original method. An uncertainty analysis using the modified method yielded a 60 percent uncertainty in the average activation energy. Based on this result, the activation energy for a carbon-phenolic material was doubled and used to calculate the ablation rate In a typical solid rocket environment. Doubling the activation energy increased surface recession by 3 percent. Current TGA data reduction techniques that use the traditional Flynn and Wall approach to calculate activation energy should be changed to the modified method.

Darby, Stephania P.↗
NASA NTRS1999

Active Control of Inlet Noise on the JT15D Turbofan Engine

This report presents the key results obtained by the Vibration and Acoustics Laboratories at Virginia Tech over the year from November 1997 to December 1998 on the Active Noise Control of Turbofan Engines research project funded by NASA Langley Research Center. The concept of implementing active noise control techniques with fuselage-mounted error sensors is investigated both analytically and experimentally. The analytical part of the project involves the continued development of an advanced modeling technique to provide prediction and design guidelines for application of active noise control techniques to large, realistic high bypass engines of the type on which active control methods are expected to be applied. Results from the advanced analytical model are presented that show the effectiveness of the control strategies, and the analytical results presented for fuselage error sensors show good agreement with the experimentally observed results and provide additional insight into the control phenomena. Additional analytical results are presented for active noise control used in conjunction with a wavenumber sensing technique. The experimental work is carried out on a running JT15D turbofan jet engine in a test stand at Virginia Tech. The control strategy used in these tests was the feedforward Filtered-X LMS algorithm. The control inputs were supplied by single and multiple circumferential arrays of acoustic sources equipped with neodymium iron cobalt magnets mounted upstream of the fan. The reference signal was obtained from an inlet mounted eddy current probe. The error signals were obtained from a number of pressure transducers flush-mounted in a simulated fuselage section mounted in the engine test cell. The active control methods are investigated when implemented with the control sources embedded within the acoustically absorptive material on a passively-lined inlet. The experimental results show that the combination of active control techniques with fuselage-mounted error sensors and passive control techniques is an effective means of reducing radiated noise from turbofan engines. Strategic selection of the location of the error transducers is shown to be effective for reducing the radiation towards particular directions in the farfield. An analytical model is used to predict the behavior of the control system and to guide the experimental design configurations, and the analytical results presented show good agreement with the experimentally observed results.

Smith, Jerome P.↗
NASA NTRS1999

Aeronautics and Space Report of the President: Fiscal Year 1998 Activities

The National Aeronautics and Space Act of 1958 directed the annual Aeronautics and Space Report to include a "comprehensive description of the programmed activities and the accomplishments of all agencies of the United States in the field of aeronautics and space activities during the preceding calendar year. In recent years, the reports have been prepared on a fiscal year (FY) basis, consistent with the budgetary period now used in programs of the Federal Government. This year's report covers activities that took place from October 1, 1997, through September 30, 1998. The activities of agencies included are NASA, the Department of Defense, The Federal Aviation Administration, the Department of Commerce, the Department of the Interior, the Federal Communications Commission, the Department of Agriculture, the National Science Foundation, the Department of State, the Department of Energy, the Smithsonian Institution, the Arms Control and Disarmament Agency, the Environmental Protection Agency, and the U.S. Information Agency. Appendices cover the U.S. Government Spacecraft Record, World Record of Space Launches Successful in Attaining Earth Orbit or Beyond , Successful Launches to Orbit on U.S. Launch Vehicles, October 1, 1997-September 30, 1998, U.S. and Russian Human Space Flights, 1961-September 30, 1998, U.S. Space Launch Vehicles, Space Activities of the U.S. Government-Historical Budget Summary, Space Activities of the U.S. Government-Budget Authority in Equivalent FY 1998 Dollars, Federal Space Activities Budget, Federal Aeronautics Budget, and a glossary

Source record↗
NASA NTRS2003

Effect Of Simulated Microgravity On Activated T Cell Gene Transcription

Studies of T lymphocytes under the shear stress environment of clinorotation have demonstrated an inhibition of activation in response to TCR mediated signaling. These results mimic those observed during space flight. This work investigates the molecular signaling events of T lymphocyte activation with clinorotation. Purified human T lymphocytes and the T cell clone Jurkat exhibit an uncoupling of signaling as mediated through the TCR. Activation of the transcription factor AP-1 is inhibited while activation of NFAT occurs. NFAT dephosphorylation and activation is dependent on sustained Ca(++) influx. Alternatively, AP-1, which consists of two transcription factors, jun and fos, is activated by PKC and Ras mediated pathways. TCR signaling is known to be dependent on cytoskeletal rearrangements, in particular, raft aggregation is critical. Raft aggregation, as mediated through GM, crosslinking, overcomes the inhibition of T lymphocyte activation with clinorotation, indicating that the block is occurring upstream of raft aggregation. Clinorotation is shown to have an effect similar to a weak TCR signal.

Morrow, Maureen A.↗
NASA NTRS2003

Fluid shear stress inhibits TNF-alpha-induced apoptosis in osteoblasts: a role for fluid shear stress-induced activation of PI3-kinase and inhibition of caspase-3

In bone, a large proportion of osteoblasts, the cells responsible for deposition of new bone, normally undergo programmed cell death (apoptosis). Because mechanical loading of bone increases the rate of new bone formation, we hypothesized that mechanical stimulation of osteoblasts might increase their survival. To test this hypothesis, we investigated the effects of fluid shear stress (FSS) on osteoblast apoptosis using three osteoblast cell types: primary rat calvarial osteoblasts (RCOB), MC3T3-E1 osteoblastic cells, and UMR106 osteosarcoma cells. Cells were treated with TNF-alpha in the presence of cyclohexamide (CHX) to rapidly induce apoptosis. Osteoblasts showed significant signs of apoptosis within 4-6 h of exposure to TNF-alpha and CHX, and application of FSS (12 dyne/cm(2)) significantly attenuated this TNF-alpha-induced apoptosis. FSS activated PI3-kinase signaling, induced phosphorylation of Akt, and inhibited TNF-alpha-induced activation of caspase-3. Inhibition of PI3-kinase, using LY294002, blocked the ability of FSS to rescue osteoblasts from TNF-alpha-induced apoptosis and blocked FSS-induced inhibition of caspase-3 activation in osteoblasts treated with TNF-alpha. LY294002 did not, however, prevent FSS-induced phosphorylation of Akt suggesting that activation of Akt alone is not sufficient to rescue cells from apoptosis. This result also suggests that FSS can activate Akt via a PI3-kinase-independent pathway. These studies demonstrate for the first time that application of FSS to osteoblasts in vitro results in inhibition of TNF-alpha-induced apoptosis through a mechanism involving activation of PI3-kinase signaling and inhibition of caspases. FSS-induced activation of PI3-kinase may promote cell survival through a mechanism that is distinct from the Akt-mediated survival pathway. Copyright 2002 Wiley-Liss, Inc.

Non-NASA Center↗