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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The Shane-Wirtanen counts - Observer and time-dependent effects

In a recent paper, de Lapparent, Kurtz, and Geller (1986) announce the discovery of possible observer and time-dependent effects in the counts of galaxies in the Lick catalog and suggest that these effects may have distorted the galaxy correlation function calculated by Groth and Peebles (1986) from the Lick counts. In particular, they suggest that these effects may have introduced a break where none exists or may have diluted a break stronger than that seen by Groth and Peebles. The Lick counts have been reexamined and it is found that the observer and time-dependent effects are marginal and that they can have had only a negligible effect on the estimates of the correlation functions. Correlation functions have been calculated for each observer and time period separately and it is found that they all depart from the small-angle power law at about the expected scale. Further, the average of these correlation functions agrees extremely well with the average correlation function published by Groth and Peebles.

Groth, Edward J.↗
NASA NTRS1989

Analysis of radar images of the active volcanic zone at Krafla, Iceland: The effects of look azimuth biasing

The geomorphic expression of Mid-Ocean-Ridge (MOR) volcanism in a subaerial setting occurs uniquely on Earth in Iceland, and the most recent MOR eruptive activity has been concentrated in the Northeastern Volcanic Zone in an area known as Krafla. Within the Krafla region are many of the key morphologic elements of MOR-related basaltic volcanism, as well as volcanic explosion craters, subglacial lava shields, tectonic fissure swarms known as gjar, and basaltic-andesite flows with well developed ogives (pressure-ridges). The objective was to quantify the degree to which the basic volcanic and structural features can be mapped from directional SAR imagery as a function of the look azimuth. To accomplish this, the current expression of volcanic and tectonic constructs was independently mapped within the Krafla region on the E, W, and N-looking SAR images, as well as from SPOT Panchromatic imagery acquired in 1987. The initial observations of the E, W, and N images indicates that fresh a'a lava surfaces are extremely radar bright (rough at 3 cm to meter scales) independent of look direction; this suggests that these flows do not have strong flow direction related structures at meter and cm scales, which is consistent with typical Icelandic a'a lava surfaces in general. The basic impression from a preliminary analysis of the effects of look azimuth biasing on interpretation of the geology of an active MOR volcanic zone is that up to 30 percent of the diagnostic features can be missed at any given look direction, but that having two orthogonal look direction images is probably sufficient to prevent gross misinterpretation.

Garvin, J. B.↗
NASA NTRS1989

Small scale structure on cosmic strings

The current understanding of cosmic string evolution is discussed, and the focus placed on the question of small scale structure on strings, where most of the disagreements lie. A physical picture designed to put the role of the small scale structure into more intuitive terms is presented. In this picture it can be seen how the small scale structure can feed back in a major way on the overall scaling solution. It is also argued that it is easy for small scale numerical errors to feed back in just such a way. The intuitive discussion presented here may form the basis for an analytic treatment of the small scale structure, which argued in any case would be extremely valuable in filling the gaps in the present understanding of cosmic string evolution.

Albrecht, Andreas↗
NASA NTRS1990

Photometric and spectroscopic modeling of starspots on the RS Canum Venaticorum binary HD 26337

Results are presented on photometric and spectroscopic observations made in 1987-1988 on the rapidly rotating G5 subgiant in the single-lined RS CVn binary HD 26337. Results show the existence of a cool polar spot on HD 26337, which is rather long lived, persisting at least the nine years of the photometry observations. The polar spot contributes only insignificantly to the light curve amplitude, but is crucial for the overall brightness of the system. Evidence is also found for extremely rapid light curve shape variations on a time scale of only one or two rotation cycles. These changes could be modeled by rapidly decreasing a spot area.

Strassmeier, Klaus G.↗
NASA NTRS1990

Galactic H I and the interstellar medium in Ursa Major

Sensitive neutral hydrogen measurements have been made over a 100 square degree field in Ursa Major. The observations cover the area which has the least neutral hydrogen and probably the least interstellar matter of any direction in the sky. It is likely that this data set contains every line of sight that intersects a total H I column density of less than 6.5 x 10 to the 19th/sq cm. The smallest colum density is estimated to be 4.4 + or - 0.5 x 10 to the 19th/sq cm. Observations at 10 arcmin angular resolution reveal little structure that is not seen at 21 arcmin resolution, and it is believed that the estimates of the total H I column density are accurate on yet smaller angular scales. The lowest N(H I) area is also extremely deficient in H-alpha emission, and shows no evidence for significant amounts of H2.

Jahoda, Keith↗
NASA NTRS1992

Lidar measurements using large liquid mirror telescopes

It is a well accepted practice in the discussion of lidars to compare systems by a performance factor given by the product of the transmitter power and receiver aperture. This form of the performance factor reflects the two key parameters that determine the amount of photons recorded from a given range bin; the amount of transmitted photons and the probability of collecting a scattered photon. We are interested in studying the propagation and breaking of gravity waves typically generated in the lower atmosphere. To study these waves requires high temporal and spatial resolution, as they have frequencies as high as 500 mHz and generate turbulent structures with vertical scales of less than 25 m. In the 80 - 100 km region of the atmosphere these measurements are most efficiently obtained by using resonance scattering from sodium atoms deposited by meteors. However, in the 30 - 80 km region, the most efficient scattering arises from molecules (Rayleigh scattering). Since the atmospheric scale height is nominally 7 km, this scattering becomes extremely weak above 60 km. Furthermore, present laser technology limits the power available for Rayleigh-scattering experiments to about 0.5 - 50 W. The transmitter for the lidar system under development at the University of Western Ontario uses a two-beam transmitter to simultaneously measure density perturbations and temperature from both Rayleigh and resonance scattering.

Sica, R. J.↗
NASA NTRS1992

Utilization of space resources in the space transportation system

Utilization of space resources (i.e., raw materials obtained from nonterrestrial sources) has often been cited as a prerequisite for large-scale industrialization and habitation of space. While transportation of extremely large quantities of material from Earth would be costly and potentially destructive to our environment, vast quantities of usable resources might be derived from the Moon, the asteroids, and other celestial objects in a cost-effective and environmentally benign manner. The primary purpose of the parametric cost model developed as part of this study is to identify the factors that have the greatest influence on the economics of space resource utilization. In the near term, this information can be used to devise strategies for technology development so that capabilities developed will produce cost-effective results.

Simon, Michael C.↗
NASA NTRS1989

Low-order design and high-order simulation of active closed-loop control for aerospace structures under construction

Partially constructed/assembled structures in space are complicated enough but their dynamics will also be operating in closed-loop with feedback controllers. The dynamics of such structures are modeled by large-scale finite element models. The model dimension L is extremely large (approximately 10,000) while the numbers of actuators (M) and sensors (P) are small. The model parameters M(sub m) mass matrix, D(sub o) damping matrix, and K(sub o) stiffness matrix, are all symmetric and sparse (banded). Thus simulation of open-loop structure models of very large dimension can be accomplished by special integration techniques for sparse matrices. The problem of simulation of closed-loop control of such structures is complicated by the addition of controllers. Simulation of closed-loop controlled structures is an essential part of the controller design and evaluation process. Current research in the following areas is presented: high-order simulation of actively controlled aerospace structures; low-order controller design and SCI compensation for unmodeled dynamics; prediction of closed-loop stability using asymptotic eigenvalue series; and flexible robot manipulator control experiment.

Balas, Mark J.↗
NASA NTRS1994

New very large array maps of highly core-dominated BL Lacs: Testing unified schemes

We present high dyanamic range (greater than 10 000:1) Very Large Array (VLA) maps of four highly c ore-dominated BL Lacertae Objects (PKS 0735+178, OJ 287, 1219+285, and PKS 1413+135), all of which had been reported previously as being unresolved at dynamic ranges approximately 1000-3000:1. Three of the four possess low surface brightness kpc-scale structure, with extended power levels and morphologies reasonable for FR 1 radio galaxies. One, however (PKS 1413+135), possesses no extended structure at dynamic range 9600:1. Only one of the sources exhibits aligned Very Large Array (VLA) and VLBI structures, suggesting bends on approximately 100-1000 pc size scales for the other two. As these four have extremely high core-to-extended flux ratios (f approximately 30-5000), they provide an extreme test of unified schemes. By deriving minimum constraints for the beaming angles and Lorentz factors which are required to produce the degrees of core dominance seen, we find that the three extended radio sources are consistent with being beamed FR 1 radio galaxies. PKS 1413+135 remains an anomalous BL Lac Object for several reasons.

Perlman, Eric S.↗
NASA NTRS1995

Plume Particle Collection and Sizing from Static Firing of Solid Rocket Motors

Thermal radiation from the plume of any solid rocket motor, containing aluminum as one of the propellant ingredients, is mainly from the microscopic, hot aluminum oxide particles in the plume. The plume radiation to the base components of the flight vehicle is primarily determined by the plume flowfield properties, the size distribution of the plume particles, and their optical properties. The optimum design of a vehicle base thermal protection system is dependent on the ability to accurately predict this intense thermal radiation using validated theoretical models. This article describes a successful effort to collect reasonably clean plume particle samples from the static firing of the flight simulation motor (FSM-4) on March 10, 1994 at the T-24 test bed at the Thiokol space operations facility as well as three 18.3% scaled MNASA motors tested at NASA/MSFC. Prior attempts to collect plume particles from the full-scale motor firings have been unsuccessful due to the extremely hostile thermal and acoustic environment in the vicinity of the motor nozzle.

Sambamurthi, Jay K.↗
NASA NTRS1999

Melt Stabilization of PbSnTe in a Magnetic Field

Both the experimental observation and numerical simulation indicate that the Bridgman growth of PbSnTe under the microgravity environment in space is still greatly influenced by buoyancy-induced convection. The application of a magnetic field during the semiconductor growth can dampen the convective flow in the metal-like melt. However, for Bridgman growth of PbSnTe on earth (with either vertical or horizontal configuration), both experimental observation and numerical modeling suggest that even with a strong magnetic furnace (5-Tesla constant axial magnetic field), the convective flow in the melt still cannot be sufficiently suppressed to reach the diffusion-controlled level. In order to completely dampen the buoyancy-induced convection on earth, estimates based on scaling analysis indicate that for common experimental conditions, an extremely high magnetic field is required, far beyond the capacity of the experimental apparatus currently available. Therefore, it is proposed that only the combination of microgravity environment and magnetic damping will produce the desired diffusion-controlled growth state for this particular material. The primary objectives of this study are to provide a quantitative understanding of the complex transport phenomena during solidification of non-dilute binarys, to furnish a numerical tool for furnace design and growth condition optimization, to provide estimates of the required magnetic field strength for low gravity growth, and to assess the role of magnetic damping for space and earth control of the double-diffusive convection. As an integral part of a NASA research program, our numerical simulation supports both the flight and ground-based experiments in an effort to bring together a complete picture of the complex physical phenomena involved in the crystal growth process. For Bridgman growth of PbSnTe under microgravity (with both vertical and horizontal configurations), the simulations suggest that a moderate axial magnetic field of only a few kilo-Gauss in strength could effectively eliminate buoyancy-induced convection in the melt and control solute segregation. Therefore, this work confirms the idea that the combination of microgravity environment and the magnetic damping will indeed be sufficient to produce the desired diffusion-controlled growth state for PbSnTe.

Fripp, Archibald L.↗
NASA NTRS1997

Climate Variability in the Amundsen and Bellingshausen Seas

Satellite data reveal a 20% decline in sea ice extent in the Amundsen and Bellingshausen Seas in the two decades following 1973. This change is negatively correlated with surface air temperatures on the west side of the Antarctic Peninsula, which have increased -0.5 C / decade- since the mid-1940s, The recession was strongest during summer, when monthly average minima in 1991-92 removed much of the incipient multiyear ice over the continental shelf. This would have lowered the regional-mean ice thickness, impacting snow ice formation, brine production, and vertical heat flux. The northern ice edge contracted by 1 deg of latitude in all seasons from 1973-79 to 1987-93, returning toward mean conditions in 1993-95. The decline included multiyear cycles of several years in length, superimposed on high interannual variability. A review of atmospheric forcing shows winds consistent with mean and extreme ice extents, and suggests links to larger-scale circulation changes in the South Pacific. Historical ocean measurements are sparse in this sector, but mixed-layer depths and upper pycnoclines beneath the sea ice resemble those in the Weddell Sea. Weaker surface currents or changes in the upwelling of Circumpolar Deep Water on the continental shelf could have contributed to the anomaly persistence.

Jacobs, Stanley S.↗
NASA NTRS2001

Southern Ocean Climate and Sea Ice Anomalies Associated with the Southern Oscillation

The anomalies in the climate and sea ice cover of the Southern Ocean and their relationships with the Southern Oscillation (SO) are investigated using a 17-year of data set from 1982 through 1998. We correlate the polar climate anomalies with the Southern Oscillation index (SOI) and examine the composites of these anomalies under the positive (SOI > 0), neutral (0 > SOI > -1), and negative (SOI < -1) phases of SOL The climate data set consists of sea-level pressure, wind, surface air temperature, and sea surface temperature fields, while the sea ice data set describes its extent, concentration, motion, and surface temperature. The analysis depicts, for the first time, the spatial variability in the relationship of the above variables and the SOL The strongest correlation between the SOI and the polar climate anomalies are found in the Bellingshausen, Amundsen and Ross sea sectors. The composite fields reveal anomalies that are organized in distinct large-scale spatial patterns with opposing polarities at the two extremes of SOI, and suggest oscillating climate anomalies that are closely linked to the SO. Within these sectors, positive (negative) phases of the SOI are generally associated with lower (higher) sea-level pressure, cooler (warmer) surface air temperature, and cooler (warmer) sea surface temperature in these sectors. Associations between these climate anomalies and the behavior of the Antarctic sea ice cover are clearly evident. Recent anomalies in the sea ice cover that are apparently associated with the SOI include: the record decrease in the sea ice extent in the Bellingshausen Sea from mid- 1988 through early 199 1; the relationship between Ross Sea SST and ENSO signal, and reduced sea ice concentration in the Ross Sea; and, the shortening of the ice season in the eastern Ross Sea, Amundsen Sea, far western Weddell Sea, and the lengthening of the ice season in the western Ross Sea, Bellingshausen Sea and central Weddell Sea gyre over the period 1988-1994. Four ENSO episodes over the last 17 years contributed to a negative mean in the SOI (-0.5). In each of these episodes, significant retreats in the Bellingshausen/Amundsen Sea were observed providing direct confirmation of the impact of SO on the Antarctic sea ice cover.

Kwok, R.↗
NASA NTRS2004

Thermionic Emission of Single-Wall Carbon Nanotubes Measured

Researchers at the NASA Glenn Research Center, in collaboration with the Rochester Institute of Technology, have investigated the thermionic properties of high-purity, single-wall carbon nanotubes (SWNTs) for use as electron-emitting electrodes. Carbon nanotubes are a recently discovered material made from carbon atoms bonded into nanometer-scale hollow tubes. Such nanotubes have remarkable properties. An extremely high aspect ratio, as well as unique mechanical and electronic properties, make single-wall nanotubes ideal for use in a vast array of applications. Carbon nanotubes typically have diameters on the order of 1 to 2 nm. As a result, the ends have a small radius of curvature. It is these characteristics, therefore, that indicate they might be excellent potential candidates for both thermionic and field emission.

Landis, Geoffrey A.↗
NASA NTRS2010

Effect of Anatomical Modeling on Space Radiation Dose Estimates: A Comparison of Doses for NASA Phantoms and 5th, 50th, and 95th Percentile UF Hybrid Phantoms

The estimate of absorbed dose to individual organs of a space crewmember is affected by the geometry of the anatomical model of the astronaut used in the radiation transport calculation. For astronaut dosimetry, NASA currently uses the computerized anatomical male (CAM) and computerized anatomical female (CAF) stylized phantoms to represent astronauts in its operational radiation dose analyses. These phantoms are available in one size and in two body positions. In contrast, the UF Hybrid Adult Male and Female (UFHADM and UFHADF) phantoms have organ shapes based on actual CT data. The surfaces of these phantoms are defined by non-uniform rational B-spline surfaces, and are thus flexible in terms of body morphometry and extremity positioning. In this study, UFHADM and UFHADF are scaled to dimensions corresponding to 5th, 50th, and 95th percentile (PCTL) male and female astronauts. A ray-tracing program is written in Visual Basic 2008, which is then used to create areal density maps for dose points corresponding to various organs within the phantoms. The areal density maps, along with appropriate space radiation spectra, are input into the NASA program couplet HZETRN/BRYNTRN, and organ doses are calculated. The areal density maps selected tissues and organs of the 5th, 50th, and 95th PCTL male and female phantoms are presented and compared. In addition, the organ doses for the 5th, 50th, and 95th PCTL male and female phantoms are presented and compared to organ doses for CAM and CAF.

Bahadori, A.↗
NASA NTRS2012

On the Probability of Occurrence of Extreme Space Weather Events

By virtue of their rarity, extreme space weather events, such as the Carrington event of 1859, are difficult to study, their rates of occurrence are difficult to estimate, and prediction of a specific future event is virtually impossible. Additionally, events may be extreme relative to one parameter but normal relative to others. In this study, we analyze several measures of the severity of space weather events (flare intensity, coronal mass ejection speeds, Dst, and greater than 30 MeV proton fluences as inferred from nitrate records) to estimate the probability of occurrence of extreme events. By showing that the frequency of occurrence scales as an inverse power of the severity of the event, and assuming that this relationship holds at higher magnitudes, we are able to estimate the probability that an event larger than some criteria will occur within a certain interval of time in the future. For example, the probability of another Carrington event (based on Dst less than - 850 nT) occurring within the next decade is approximately 12%. We also identify and address several limitations with this approach. In particular, we assume time stationarity, and thus, the effects of long-term space climate change are not considered. While this technique cannot be used to predict specific events, it may ultimately be useful for probabilistic forecasting.

Riley, Pete↗
NASA NTRS2013

Herschel-ATLAS: A Binary HyLIRG Pinpointing a Cluster of Starbursting Protoellipticals

Panchromatic observations of the best candidate hyperluminous infrared galaxies from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z = 2.41 galaxies across an ≈100 kpc region-a cluster of starbursting protoellipticals. Via subarcsecond interferometric imaging we have measured accurate gas and star formation surface densities. The two brightest galaxies span ∼3 kpc FWHM in submillimeter/radio continuum and CO J = 4-3, and double that in CO J = 1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks-a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have Mdyn of several ×10(sup 11) solar Mass, and gas fractions of ∼40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star formation rates place them greater than or approx. equal to 5 × above the main sequence, which supposedly comprises large gas disks like these. Their high star formation efficiencies are difficult to reconcile with a simple volumetric star formation law. N-body and dark matter simulations suggest that this system is the progenitor of a B(inary)-type ≈10(sup 14.6) -solar mass cluster.

infrared: galaxies↗
NASA NTRS2014

ENSO Effect on East Asian Tropical Cyclone Landfall via Changes in Tracks and Genesis in a Statistical Model

Improvements on a statistical tropical cyclone (TC) track model in the western North Pacific Ocean are described. The goal of the model is to study the effect of El Nino-Southern Oscillation (ENSO) on East Asian TC landfall. The model is based on the International Best-Track Archive for Climate Stewardship (IBTrACS) database of TC observations for 1945-2007 and employs local regression of TC formation rates and track increments on the Nino-3.4 index and seasonally varying climate parameters. The main improvements are the inclusion of ENSO dependence in the track propagation and accounting for seasonality in both genesis and tracks. A comparison of simulations of the 1945-2007 period with observations concludes that the model updates improve the skill of this model in simulating TCs. Changes in TC genesis and tracks are analyzed separately and cumulatively in simulations of stationary extreme ENSO states. ENSO effects on regional (100-km scale) landfall are attributed to changes in genesis and tracks. The effect of ENSO on genesis is predominantly a shift in genesis location from the southeast in El Nino years to the northwest in La Nina years, resulting in higher landfall rates for the East Asian coast during La Nina. The effect of ENSO on track propagation varies seasonally and spatially. In the peak activity season (July-October), there are significant changes in mean tracks with ENSO. Landfall-rate changes from genesis- and track-ENSO effects in the Philippines cancel out, while coastal segments of Vietnam, China, the Korean Peninsula, and Japan show enhanced La Nina-year increases.

simulation↗