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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

The Discrepancy Between Measured and Modeled Downwelling Solar Irradiance at the Ground: Dependence on Water Vapor

Moderate resolution spectra of the downwelling solar irradiance at the around in north central Oklahoma were measured during the Department of Energy Atmospheric Radiation Measurement Program Intensive Observation Period in the fall of 1997. Spectra obtained under cloud-free conditions were compared with calculations using a coarse resolution radiative transfer model to examine the dependency of model-measurement bias on water vapor. It was found that the bias was highly correlated with water vapor and increased at a rate of 9 W/sq m per cm of water. The source of the discrepancy remains undetermined because of the complex dependencies of other variables, most notably aerosol optical depth, on water vapor.

Pilewskie, P.↗
NASA NTRS2000

The Discrepancy Between Measured and Modeled Downwelling Solar Irradiance at the Ground: Dependence on Water Vapor

Moderate resolution spectra of the downwelling solar irradiance at the ground in north central Oklahoma were measured during the Department of Energy Atmospheric Radiation Measurement Program Intensive Observation Period in the fall of 1997. Spectra obtained under-cloud-free conditions were compared with calculations using a coarse resolution radiative transfer model to examine the dependency of model-measurement bias on water vapor. It was found that the bias was highly correlated with water vapor and increased at a rate of 9 Wm per cm of water. The source of the discrepancy remains undetermined because of the complex dependencies of other variables, most notably aerosol optical depth, on water vapor.

Pilewski, P.↗
NASA NTRS2000

The Discrepancy Between Measured and Modeled Downwelling Solar Irradiance at the Ground: Dependence on Water Vapor

Moderate resolution spectra of the downwelling solar irradiance at the ground in north central Oklahoma were measured during the Department of Energy Atmospheric Radiation Measurement Program Intensive Observation Period in the fall of 1997. Spectra obtained under cloud-free conditions were compared with calculations using a coarse resolution radiative transfer model to examine the dependency of model-measurement bias on water vapor. It was found that the bias was highly correlated with water vapor and increased at a rate of 9 Wm(exp -2) per cm of water. The source of the discrepancy remains undetermined because of the complex dependencies of other variables, most notably aerosol optical depth, on water vapor.

Pilewskie, P.↗
NASA NTRS2001

Distributed Spacecraft Control Architectures

A fundamental issue for estimation and control of distributed systems such as formation flying spacecraft is the information exchange architecture. In centralized schemes, each subordinate need only share its measurement data with a central hub, and the subordinates depend on the center to direct their actions. In decentralized schemes, all nodes participate in the data exchange, so that each has the same in by formation as the center, and may thereby self-direct the same action that the center would have commanded, assuming all share a common goal. This talk compares and contrasts the centralized and decentralized schemes in the context of autonomously maintaining a distributed satellite formation.

Carpenter, James Russell↗
NASA NTRS1992

Heating of H II regions with application to the Galactic center

The heating and thermal equilibrium of photoionized gas is reviewed. Photon-heating mechanisms (UV photoionization heating, grain photoelectric heating, and X-ray heating) either fail to provide the required heating rates or else require that the ionization state of the gas is very high. Specific application to the Galactic center observations show that the total heating power required to maintain the gas at the derived temperatures, using the observed emission measure in the bar and the temperature distribution derived from the radio recombination lines, is about 7 x 10 exp 6 solar luminosities, comparable to the bolometric luminosity of the central source as measured by the FIR flux from grains. Thus, the cooling emission from this hot gas, if LTE-derived temperatures are correct, would supply a major fraction of the bolometric and ionizing luminosity inferred from the ionized gas in the central 1 pc cavity and the dust and neutral gas in the surrounding torus.

Maloney, Philip R.↗
NASA NTRS1999

Chemical Abundances of the Planetary Nebula IC 4634 and Its Central Star

We have measured the spectral line intensities of the metal poor planetary nebula IC 4634. Using a photo-ionization model calculation, we try to fit the the optical and UV region spectra, i.e., Hamilton Echelle and IUE observations. From direct images, one expects complicated density variations, but the model predicts a range in densities that may be smaller than actually exist. We find N(sub epsilon) approximates 5000 /cubic meter. In spite of the geometrical complexity of the S shaped double-lobed structure, the simple photoionization model with a spherical symmetry can fit most emission lines, fairly well. The derived chemical composition has been compared with previous estimates and also with the Sun - The metallicity in IC 4634 appears to be lower than in the Sun or the average planetary nebula. The most likely temperature of the central ionizing source of IC 4634 appears to be about 55,000 K. We find a central star mass of about 0.55 Solar Mass from comparison with theoretical evolutionary tracks.

Hyung, S.↗
NASA NTRS1993

Infrared spectroscopic measurements relevant to atmospheric remote sensing

SF6 is a synthetic chemical which is used in many industrial applications and as a meteorological tracer. This paper describes determinations of spectral absorption coefficients k-nu of SF6 measured in the central Q-branches of the nu(3)-fundamental at 947/cm at various temperature-pressure combinations representing tangent heights in solar-occultation experiments or layers in the atmosphere. Spectral data were also obtained for C2H4 and NH3 fundamental bands. Measurements were made with the Doppler-limited spectral resolution of a tunable diode laser spectrometer with a cryogenically cooled absorption cell, described by Varanasi and Chudamani (1992).

Varanasi, Prasad↗
NASA NTRS2005

Warm Molecular Gas Traced with CO J = 7 --> 6 in the Galaxy's Central 2 Parsecs: Dynamical Heating of the Circumnuclear Disks

We present an 11" resolution map of the central 2 pc of the Galaxy in the CO J = 7 --> 6 rotational transition. The CO emission shows rotation about Sgr A* but also evidence for noncircular turbulent motion and a clumpy morphology. We combine our data set with available CO measurements to model the physical conditions in the disk. We find that the molecular gas in the region is both warm and dense, with T approx. 200-300 K and n(sub H2) approx. (5-7) x 10(exp 4) cm(exp -3). The mass of warm molecular gas we measure in the central 2 pc is at least 2000 M(solar), about 20 times the UV-excited atomic gas mass, ruling out a UV heating scenario for the molecular material. We compare the available spectral tracers with theoretical models and conclude that molecular gas is heated with magnetohydrodynamic shocks with v approx. 10-20 km s(exp -1) and B approx. 0.3- 0.5 mG. Using the conditions derived with the CO analysis, we include the other important coolants, neutral oxygen and molecular hydrogen, to estimate the total cooling budget of the molecular material. We derive a mass-to-luminosity ratio of approx. 2-3 M(solar)(L(solar)exp -1), which is consistent with the total power dissipated via turbulent decay in 0.1 pc cells with v(sub rms) approx. 15 kilometers per second. These size and velocity scales are comparable to the observed clumping scale and the velocity dispersion. At this rate, the material near Sgr A* is dissipating its orbital energy on an orbital timescale and cannot last for more than a few orbits. Our conclusions support a scenario in which the features near Sgr A* such as the circumnuclear disk and northern arm are generated by infalling clouds with low specific angular momentum.

galatic nuclei↗
NASA NTRS2015

Estimating Viscoelastic Deformation Due to Seasonal Loading

Scientists have been making summer-­‐time geodetic measurements in south central Alaska for decades to estimate the rate at which a continental-­‐ocean terrane is accreting to the North American continent. Southern Alaska has big earthquakes every century and large, rapidly changing glaciers. In the last decade, primarily as part of the EarthScope Plate Boundary Observatory project, continuous GPS measurements have recorded the response of sites such as the near-­‐coastal geodetic site, AB35 to competing processes: uplift and movement to the northwest due to tectonic forces and the response of the solid Earth to seasonal and longer-­‐term changes in the cryosphere (snow and ice) surrounding the site. Which process causes the largest displacements of the site? Figure 1 (Blewitt, Nevada Geodetic Lab, 2015) shows the Northward, Eastward, and Upward motion of AB35 between 2007 and 2015. The site is moving rapidly to the north and west reflecting the tectonic convergence of site toward interior Alaska but there is small wiggle on the North component reflecting seasonal displacements of the site associated with snow loading and unloading. However, the Up component, shows a large seasonal signal due to snow loading in the winter (down) and ice and snow melting in the warmer months (site goes up). Between 2007 and the present, the site position is slowly moving upward, due to tectonic forcing but probably associated with longer-­‐ term ice melting as well. We are using the CIG finite element modeling (FEM) program Pylith to estimate the surface displacements and stresses associated with seasonal loading changes (top figure and Figure 2 far right) for water year 2012, 2011.8 - 2012.8) and the longer-­‐term retreat of the surrounding glaciers.

Alaska↗
NASA NTRS1994

Summertime tropospheric ozone distributions over central and eastern Canada

Ozone measurements were obtained between the surface and the 6-km altitude on aircraft flights over central and eastern Canada during the summer 1990 NASA Global Tropospheric Experiment Arctic Boundary Layer Expedition (GTE/ABLE 3B). Tropospheric O3 budgets for these regions were observed to be highly variable and significantly impacted by long-range transport and regional scale air mass modification processes. For example, integrated O3 abundance below 5-km altitude averaged 40% and 30% greater in air masses influenced by anthropogenic sources and biomass burning, respectively, than in background (polar) air. Conversely, aged air transported from subtropical areas of the Pacific at times reduced O3 abundance in this height interval by up to 20%. Though intrusion of anthropogenic air was infrequent during the experiment period, the influence of biomass-burning emissions was particularly notable as two thirds of the flights sampled air influenced by plumes from fires burning in Alaska and western Canada. The impinging pollution, both natural and anthropogenic, not only elevated O3 levels directly but also was a source of reactive nitrogen (and nonmethane hydrocarbons) which generally increases the tropospheric lifetime of O3 via moderation of photochemical destruction rates.

Anderson, B. E.↗
NASA NTRS1997

Prediction and measurement of direct-normal solar irradiance: A closure experiment

Direct-Normal Solar Irradiance (DNSI), the total energy in the solar spectrum incident on a plane perpendicular to the Sun's direction on a unit area at the earth's surface in unit time, depends only on the atmospheric extinction of sunlight without regard to the details of extinction-whether absorption or scattering. Here the authors describe a set of closure experiments performed in north-central Oklahoma, wherein measured atmospheric composition is input to a radiative transfer model, MODTRAN-3, to predict DNSI, which is then compared to measured values. Thirty six independent comparisons are presented; the agreement between predicted and measured values falls within the combined uncertainties in the prediction (2%) and measurement (0.2%) albeit with a slight bias ((approximately) 1% overprediction) that is independent of the solar zenith angle. Thus these results establish the adequacy of current knowledge of the solar spectrum and atmospheric extinction as embodied in MODTRAN-3 for use in climate models. An important consequence is the overwhelming likelihood that the atmospheric clear-sky absorption is accurately described to within comparable uncertainties.

Halthore, R. N.↗
NASA NTRS2005

Eta Carinae: What We have learned recently with HST/STIS, VLT/UVES and VLTI: What We Might Learn with VLT/VLTI across the 2008/9 Minimum

Eta Carinae, the LBV that we have learned to love and hate, has revealed many clues of its character over the past seven years by studies with HST and VLT. Based upon X-Ray, optical and IR observations, Eta Carinae is convincingly a massive binary system that uniquely has major nebular ejecta that are connected with historical outbursts. We have successhlly followed the stellar and nebular changes over the 5.5 year cycle, especially with STIS and RXTE, and across the spectroscopic minimum in 2003.5 with STIS, CHANDRA, RXTE, FUSE, and VLT/UVES. The HST/STIS high spatial resolution, combined with appropriate spectral resolving powers from 1150 to 10300 A, has revealed much about the Central Source and especially the spatially resolved extended stellar atmosphere and the ejecta, known as the Homunculus. Indeed the neutral, dusty outer Homunculus, ejected in the 1840s, envelops the newly discovered ionized Little Homunculus, ejected in the 1890s. In line of sight, multiple hot clumps, both ionized and neutral, are seen in absorption and provide much information on the physical conditions of these massive ejecta. Against the nebular-scattered starlight, wind and nebular absorptions provide views at different angles from line of sight. The VLT/UVES studies from 2002 through 2004 provided very important time-sampled spectra of both the star as seen directly and as seen by the SE lobe viewing the polar region of the star. The VLTI 2.2 micron measures of the central source are consistent with a prolate spheroid with its axis extending along the axis of the Homunculus. This is consistent with the noticeably larger wind mass and higher terminal velocity along the axis of the Homunculus compared to that measured in line of sight at about 45 degrees from the polar axes. We understand the system to be a massive primary with an O or WR companion in a very highly elliptical orbit. The spectroscopic minimum occurs during periastron, when the greatly extended primary atmosphere and wind bottles up the ionizing uv radiation of the companion star. This transient drop in uv photons leads to recombination of much of the wind structure and of the nearby ejecta. Doubly-ionized elements (iron, neon, argon, vanadium) recombine to singly ionized forms and extended structures on the scales of below 0.03 arcseconds to an arcsecond change, appear, or disappear. With the loss of the STIS on HST, ground-based observations, especially with high spatial-resolution facilities, including the VLT and VLTI will be key to further studies across the minimum centered on 2009.0. Now is the time to plan for these studies.

Gull, Theodore R.↗
NASA NTRS2004

The Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) Experiment

NASA has developed an Earth Observing System (EOS) consisting of a series of satellites designed to study global change from space. The EOS flagship is the EOS TERRA satellite, launched in December 1999, equipped with five unique sensors to monitor and study the Earth s heat budget and many of the key controlling variables governing the Earth's climate system. CLAMS, the Chesapeake Lighthouse and Aircraft Measurements for Satellites field campaign was conducted from NASA Wallops Flight Facility and successfully executed over the middle Atlantic eastern seaboard from July 10 August 2, 2001. CLAMS is primarily a shortwave closure experiment designed to validate and improve EOS TERRA satellite data products being derived from three sensors: CERES (Clouds and Earth's Radiant Energy System), MISR (Multi-angle Imaging Spectro-Radiometer) and MODIS (MODerate Resolution Imaging Spectroradiometer). CLAMS is jointly sponsored by the CERES, MISR and MODIS instrument teams and the NASA GEWEX Global Aerosol Climatology Project (GACP). CLAMS primary objectives are to validate satellite-based retrievals of aerosol properties and vertical profiles of radiative flux, temperature and water vapor. Central to CLAMS measurement strategy is the Chesapeake Lighthouse, a stable sea platform located in the Atlantic Ocean, 13 miles east of Virginia Beach near the mouth of the Chesapeake Bay and the site of an ongoing CERES Ocean Validation Experiment (COVE). Six research aircraft were deployed to make detailed measurements of the atmosphere and ocean surface in the vicinity of COVE, over the surrounding ocean, over nearby NOAA buoys and over a few land sites. The measurements are used to validate and provide ground truth for simultaneous products being derived from TERRA data, a key step toward an improved understanding and ability to predict changes in the Earth's climate. One of the two CERES instruments on-board TERRA was programmed for Rotating Azimuth Plane Scans (RAPS) during CLAMS, increasing the CERES coverage over COVE by a factor of 10. Nine coordinated aircraft missions and numerous additional sorties were flown under a variety of atmospheric conditions and aerosol loadings. On one golden day, July 17, all six aircraft flew coordinated patterns, vertically stacked between 100 ft and 65,000 ft over the COVE site as the TERRA satellite orbited overhead. A summary of CLAMS measurement campaign and a description of the platforms and measurements is given.

Smith, William L., Jr.↗
NASA NTRS1978

Escort: A data acquisition and display system to support research testing

Primarily designed to acquire data at steady state test conditions, the system can also monitor slow transients such as those generated in moving to a new test condition. The system configuration makes use of a microcomputer at the test site which acts as a communications multiplexer between the measurement and display devices and a centrally located minicomputer. A variety of measurement and display devices are supported using a modular approach. This allows each system to be configured with the proper combination of devices to meet the specific test requirements, while still leaving the option to add special interfaces when needed. Centralization of the minicomputer improves utilization through sharing. The creation of a pool of minis to provide data acquisition and display services to a variable number of running tests also offers other important advantages.

Miller, R. L.↗
NASA NTRS2000

Populations of High-Luminosity Density-Bounded HII Regions in Spiral Galaxies? Evidence and Implications

In this paper we present evidence that the H II regions of high luminosity in disk galaxies may be density bounded, so that a significant fraction of the ionizing photons emitted by their exciting OB stars escape from the regions. The key piece of evidence is the presence, in the Ha luminosity functions (LFs) of the populations of H iI regions, of glitches, local sharp peaks at an apparently invariant luminosity, defined as the Stromgren luminosity Lstr), LH(sub alpha) = Lstr = 10(sup 38.6) (+/- 10(sup 0.1)) erg/ s (no other peaks are found in any of the LFs) accompanying a steepening of slope for LH(sub alpha) greater than Lstr This behavior is readily explicable via a physical model whose basic premises are: (a) the transition at LH(sub alpha) = Lstr marks a change from essentially ionization bounding at low luminosities to density bounding at higher values, (b) for this to occur the law relating stellar mass in massive star-forming clouds to the mass of the placental cloud must be such that the ionizing photon flux produced within the cloud is a function which rises more steeply than the mass of the cloud. Supporting evidence for the hypothesis of this transition is also presented: measurements of the central surface brightnesses of H II regions for LH(sub alpha) less than Lstr are proportional to L(sup 1/3, sub H(sub alpha)), expected for ionization bounding, but show a sharp trend to a steeper dependence for LH(sub alpha) greater than Lstr, and the observed relation between the internal turbulence velocity parameter, sigma, and the luminosity, L, at high luminosities, can be well explained if these regions are density bounded. If confirmed, the density-bounding hypothesis would have a number of interesting implications. It would imply that the density-bounded regions were the main sources of the photons which ionize the diffuse gas in disk galaxies. Our estimates, based on the hypothesis, indicate that these regions emit sufficient Lyman continuum not only to ionize the diffuse medium, but to cause a typical spiral to emit significant ionizing flux into the intergalactic medium. The low scatter observed in Lstr, less than 0.1 mag rms in the still quite small sample measured to date, is an invitation to widen the data base, and to calibrate against primary standards, with the aim of obtaining a precise, approx. 10(exp 5) solar luminosity widely distributed standard candle.

Beckman, J. E.↗
NASA NTRS1972

Dynamical in-orbit behavior of the Radio Astronomy Explorer satellite

Onboard sensors and associated ground based processing systems are used to maintain a well stabilized attitude for the RAE 1 in its near circular earth orbit despite the satellite's four extremely long and flexible antenna booms. Boom tip deflection pictures and central hub orientation measurements show that large boom vibrations and major attitude stability problems anticipated prior to launch have not materialized.

Walden, H.↗
NASA NTRS1973

Further considerations of spallation effects

Trapped photon and cosmic ray effects on spallation in the UK-5 (hard X ray telescope) central crystal were measured. Both low dose and high dose effects were considered. Decay results are presented in tables.

Dyer, C.↗