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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Nonlinear phase-space diffusion approach to turbulent organized structures

The study deals with the approximation of the effect of all velocity-increment moments on the spatial evolution of the pdf for maximally correlated structures by the effect of the second moment alone by assuming independence of separated length scales. The dependence of the two-point velocity statistics on length-scale or separation is found to be governed by the gradients of the stress, rather than of the velocity. This may provide a new approach for predicting the domain patterns observed in turbulent flows and a new means of characterizing or classifying different structures, namely, by their nonlinear diffusion coefficient.

Shen, Hubert H.↗
NASA NTRS1992

Ultrasonic evaluation of oxygen content, modulus, and microstructure changes in YBa2Cu3O(7-x) occurring during oxidation and reduction

Ultrasonic velocity measurement techniques were used to evaluate the effects of oxidation and reduction on the elastic properties, global microstructure and oxygen content of the YBa2Cu3O(7-x) ceramic superconductor for samples ranging from 70 to 90 pct of theoretical density. Bulk density, velocity, and elastic modulus generally increased with increasing oxygen content upon oxidation, and this behavior was reversible. Velocity image patterns were similar after oxidation and reduction treatments for a 90 pct. dense sample, although the velocity value at any given point on the sample was changed following the treatments. The unchanging pattern correlated with destructive measurements showing that the spatial pore distribution (fraction and size) was not measurably altered after the treatments. Changes in superconducting behavior, crystal structure, and grain structure were observed consistent with changes in oxygen content.

Roth, Don J.↗
NASA NTRS1993

Automated identification of OB associations in M31

A new identification of OB associations in M31 has been performed using the Path Linkage Criterion (PLC) technique of Battinelli (1991). We found 174 associations with a very small contamination (less than 5%) by random clumps of stars. The expected total number and average size of OB associations in the region of M 31 covered by our data set (Magnier et al. 1992) are approximately 280 and approximately 90 pc, respectively. M31 associations therefore have sizes similar to those of OB associations observed in nearby galaxies, so that we can consider them to be classical OB associations. This list of OB associations will be used for the study of the spatial distribution of OB associations and their correlation with other objects. Taking into account the fact that we do not cover the entire disk of M31, we extrapolate a total number of association in M31 of approximately 420.

Magnier, Eugene A.↗
NASA NTRS1999

Fuzzy Logic Enhanced Digital PIV Processing Software

Digital Particle Image Velocimetry (DPIV) is an instantaneous, planar velocity measurement technique that is ideally suited for studying transient flow phenomena in high speed turbomachinery. DPIV is being actively used at the NASA Glenn Research Center to study both stable and unstable operating conditions in a high speed centrifugal compressor. Commercial PIV systems are readily available which provide near real time feedback of the PIV image data quality. These commercial systems are well designed to facilitate the expedient acquisition of PIV image data. However, as with any general purpose system, these commercial PIV systems do not meet all of the data processing needs required for PIV image data reduction in our compressor research program. An in-house PIV PROCessing (PIVPROC) code has been developed for reducing PIV data. The PIVPROC software incorporates fuzzy logic data validation for maximum information recovery from PIV image data. PIVPROC enables combined cross-correlation/particle tracking wherein the highest possible spatial resolution velocity measurements are obtained.

Wernet, Mark P.↗
NASA NTRS1997

Antarctic Surface Temperatures Using Satellite Infrared Data from 1979 Through 1995

The large scale spatial and temporal variations of surface ice temperature over the Antarctic region are studied using infrared data derived from the Nimbus-7 Temperature Humidity Infrared Radiometer (THIR) from 1979 through 1985 and from the NOAA Advanced Very High Resolution Radiometer (AVHRR) from 1984 through 1995. Enhanced techniques suitable for the polar regions for cloud masking and atmospheric correction were used before converting radiances to surface temperatures. The observed spatial distribution of surface temperature is highly correlated with surface ice sheet topography and agrees well with ice station temperatures with 2K to 4K standard deviations. The average surface ice temperature over the entire continent fluctuates by about 30K from summer to winter while that over the Antarctic Plateau varies by about 45K. Interannual fluctuations of the coldest interannual variations in surface temperature are highest at the Antarctic Plateau and the ice shelves (e.g., Ross and Ronne) with a periodic cycle of about 5 years and standard deviations of about 11K and 9K, respectively. Despite large temporal variability, however, especially in some regions, a regression analysis that includes removal of the seasonal cycle shows no apparent trend in temperature during the period 1979 through 1995.

Comiso, Josefino C.↗
NASA NTRS2003

Stochastic Models of Tropical Rain-Rate Fields

Because of the extreme variability of rain rate in space and time and the difficulties with remote sensing methods of measuring rain rates, accurate determination of rainfall over large areas and time periods has long been a problem for hydrologists, meteorogists, and climatologists. A number of statistical models of rain have been developed in order to investigate the impact of rain variability on satellite remote sensing methods, validation of satellite rain products, and generation of rain maps with accompanying error estimates. These models may be useful in examining 'sub-grid scale' issues in representing precipitation in numerical mdoels. A stochastic model will first be described which can generate time-dependent high-resolution spatial rain fields with space and time correlations similar to those seen in rain data, as well as representing the presence of areas with zero rain rate and log-normally distributed rain rates where there is rain. A simpler model derived from this, formulated in the spectral domain, seems to imply fractal-like rain statistics at small scales when fit to rain data.

Bell, Thomas L.↗
NASA NTRS2005

Evolution of large shield volcanoes on Venus

We studied the geologic history, topographic expression, and gravity signature of 29 large Venusian shield volcanoes with similar morphologies in Magellan synthetic aperture radar imagery. While they appear similar in imagery, 16 have a domical topographic expression and 13 have a central depression. Typical dimensions for the central depression are 150 km wide and 500 m deep. The central depressions are probably not calderas resulting from collapse of a shallow magma chamber but instead are the result of a corona-like sagging of a previously domical volcano. The depressions all have some later volcanic filling. All but one of the central depression volcanoes have been post-dated by geologic features unrelated to the volcano, while most of the domical volcanoes are at the top of the stratigraphic column. Analysis of the gravity signatures in the spatial and spectral domains shows a strong correlation between the absence of post-dating features and the presence of dynamic support by an underlying plume. We infer that the formation of the central depressions occurred as a result of cessation of dynamic support. However, there are some domical volcanoes whose geologic histories and gravity signatures also indicate that they are extinct, so sagging of the central region apparently does not always occur when dynamic support is removed. We suggest that the thickness of the elastic lithosphere may be a factor in determining whether a central depression forms when dynamic support is removed, but the gravity data are of insufficient resolution to test this hypothesis with admittance methods.

Herrick, Robert R.↗
NASA NTRS2002

Method and apparatus for chemical and topographical microanalysis

A scanning probe microscope is combined with a laser induced breakdown spectrometer to provide spatially resolved chemical analysis of the surface correlated with the surface topography. Topographical analysis is achieved by scanning a sharp probe across the sample at constant distance from the surface. Chemical analysis is achieved by the means of laser induced breakdown spectroscopy by delivering pulsed laser radiation to the sample surface through the same sharp probe, and consequent collection and analysis of emission spectra from plasma generated on the sample by the laser radiation. The method comprises performing microtopographical analysis of the sample with a scanning probe, selecting a scanned topological site on the sample, generating a plasma plume at the selected scanned topological site, and measuring a spectrum of optical emission from the plasma at the selected scanned topological site. The apparatus comprises a scanning probe, a pulsed laser optically coupled to the probe, an optical spectrometer, and a controller coupled to the scanner, laser and spectrometer for controlling the operation of the scanner, laser and spectrometer. The probe and scanner are used for topographical profiling the sample. The probe is also used for laser radiation delivery to the sample for generating a plasma plume from the sample. Optical emission from the plasma plume is collected and delivered to the optical spectrometer so that analysis of emission spectrum by the optical spectrometer allows for identification of chemical composition of the sample at user selected sites.

Kossakovski, Dmitri A.↗
NASA NTRS2007

Simulation Studies of Forest Structure using 3D Lidar and Radar Models

The use of lidars and radars to measure forest structure attributes such as height and biomass are being considered for future Earth Observation missions. Large footprint lidar makes a direct measurement of the heights of scatterers in the illuminated footprint and can yield information about the vertical profile of the canopy. Synthetic Aperture Radar (SAR) is known to sense the canopy volume, especially at longer wavelengths and is useful for estimating biomass. Interferometric SAR (InSAR) has been shown to yield forest canopy height information. For example, the height of scattering phase retrieved from InSAR data is considered to be correlated with the three height and the spatial structure of the forest stand. There is much interest in exploiting these technologies separately and together to get important information for carbon cycle and ecosystem science. More detailed information of the electromagnetic radiation interactions within forest canopies is needed. And backscattering models can be of much utility here. As part of a NASA funded project to explore data fusion, a three-dimensional (3D) coherent radar backscattering model and a 3D lidar backscatter models were used to investigate the use of large footprint lidar, SAR and InSAR for characterizing realistic forest scenes. For this paper, we use stem maps and other forest measurements to develop a realistic spatial structure of a spruce-hemlock forest canopy found in Maine, USA. The radar and lidar models used measurements of the 3D forest scene as input and simulated the coherent radar backscattering signature and 1064nm energy backscatter, respectively. The relationships of backscatter derived forest structure were compared with field measurements. In addition, we also had detailed airborne lidar (Laser Imaging Vegetation Sensor, LVIS) data available over the stem map sites that was used to study the accuracies of tree height derived from modeled SAR backscatter and the scattering phase center retrieved from the simulated InSAR data will be compared with the height indices, or other structure parameters derived from the lidar data. These results will address the possible synergies between lidar and radar in data in terms of forest structural information.

Sun, Guoqing↗
NASA NTRS2008

ARMOR Dual-Polarimetric Radar Observations of Tornadic Debris Signatures

During the Super-Tuesday tornado outbreak of 5-6 February 2008, two EF-4 tornadoes occurred in Northern Alabama within 75 km range of the University of Alabama in Huntsville (UAH) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). This study will present an analysis of ARMOR radar-indicated dual-polarimetric tornadic debris signatures. The debris signatures were associated with spatially-confined large decreases in the copolar correlation coefficient (rho(hv)hv) that were embedded within broader mesocyclone "hook" signatures. These debris signatures were most obviously manifest during the F-3 to F-4 intensity stages of the tornado(s) and extended to altitudes of approximately 3 km. The rho(hv) signatures of the tornadic debris were the most easily distinguished relative to other polarimetric and radial velocity parameters (e.g., associated with large hail and/or the incipient mesocyclone). Based on our analysis, and consistent with the small number of studies found in the literature, we conclude that dual-polarimetric radar data offer at least the possibility for enhancing specificity and confidence in the process of issuing tornado warnings based only on radar detection of threatening circulation features.

Petersen, W. A,↗
NASA NTRS2013

United States Forest Disturbance Trends Observed Using Landsat Time Series

Disturbance events strongly affect the composition, structure, and function of forest ecosystems; however, existing U.S. land management inventories were not designed to monitor disturbance. To begin addressing this gap, the North American Forest Dynamics (NAFD) project has examined a geographic sample of 50 Landsat satellite image time series to assess trends in forest disturbance across the conterminous United States for 1985-2005. The geographic sample design used a probability-based scheme to encompass major forest types and maximize geographic dispersion. For each sample location disturbance was identified in the Landsat series using the Vegetation Change Tracker (VCT) algorithm. The NAFD analysis indicates that, on average, 2.77 Mha/yr of forests were disturbed annually, representing 1.09%/yr of US forestland. These satellite-based national disturbance rates estimates tend to be lower than those derived from land management inventories, reflecting both methodological and definitional differences. In particular the VCT approach used with a biennial time step has limited sensitivity to low-intensity disturbances. Unlike prior satellite studies, our biennial forest disturbance rates vary by nearly a factor of two between high and low years. High western US disturbance rates were associated with active fire years and insect activity, while variability in the east is more strongly related to harvest rates in managed forests. We note that generating a geographic sample based on representing forest type and variability may be problematic since the spatial pattern of disturbance does not necessarily correlate with forest type. We also find that the prevalence of diffuse, non-stand clearing disturbance in US forests makes the application of a biennial geographic sample problematic. Future satellite-based studies of disturbance at regional and national scales should focus on wall-to-wall analyses with annual time step for improved accuracy.

Masek, Jeffrey G.↗
NASA NTRS2017

Cosmic Infrared Background Fluctuations and Zodiacal Light

We performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR (near-infrared)background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution or from IRAC (Infrared Array Camera) observations of high-latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS (Cosmic Evolution Survey) field at low ecliptic latitude where the zodiacal light intensity varies by factors of approximately 2 over the range of solar elongations at which the field can be observed. We find that the white-noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales (greater than or approximately equal to 100 arcseconds) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large-scale power in the infrared background is not being caused by the zodiacal light.

cosmology: observations aEuro" diffuse radiation a↗
NASA NTRS2017

Scale Size-Dependent Characteristics of the Nightside Aurora

We have determined the spatiotemporal characteristics of the magnetosphere-ionosphere (M-I) coupling using auroral imaging. Observations at fixed positions for an extended period of time are provided by a ground-based all-sky imager measuring the 557.7 nanometer auroral emissions. We report on a single event of nightside aurora (at approximately 22 magnetic local time) preceding a substorm onset. To determine the spatiotemporal characteristics, we perform an innovative analysis of an all-sky imager movie (19 minutes duration, images at 3.31 hertz) that combines a two-dimensional spatial fast Fourier transform with a temporal correlation. We find a scale size-dependent variability where the largest scale sizes are stable on timescales of minutes while the small scale sizes are more variable. When comparing two smaller time intervals of different types of auroral displays, we find a variation in their characteristics. The characteristics averaged over the event are in remarkable agreement with the spatiotemporal characteristics of the nightside field-aligned currents during moderately disturbed times. Thus, two different electrodynamical parameters of the M-I coupling show similar behavior. This gives independent support to the claim of a system behavior that uses repeatable solutions to transfer energy and momentum from the magnetosphere to the ionosphere.

electrodynamical↗
DOE OSTI2018

Thermal Design of Hybrid Materials Produced via Ultrasonic Additive Manufacturing

Here, ultrasonic additive manufacturing (UAM) is a technique for producing three-dimensional components through the metallurgical bonding of successive layers of metal foil. Due to its ability to process at low temperatures, UAM is uniquely suited for building hybrid materials. In this study, AA6061+water hybrid blocks with varying water cavity sizes were produced and their thermal performances were measured. Nonoptimal processing parameters were used to understand the interaction between interlayer porosity and thermal diffusivity of bulk material containing both solid and liquid. Flash thermography was used to characterize the spatial distribution of thermal diffusivity for each part. The average thermal diffusivity was successfully compared to a simplified thermal resistor model. The spatial variation in thermal properties was also correlated to specific interlayer features and related back to interactions between process characteristics and the component geometry.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Single photon emission at 1.55 μm from charged and neutral exciton confined in a single quantum dash

We investigate charged and neutral exciton complexes confined in a single self-assembled InAs/InGaAlAs/InP quantum dash emitting at 1.55 μm. The emission characteristics have been probed by measuring high-spatial-resolution polarization-resolved photoluminescence and cross-correlations of photon emission statistics at T = 5 K. The photon auto-correlation histogram of the emission from both the neutral and charged exciton indicates a clear antibunching dip with as-measured g{sup (2)}(0) values of 0.18 and 0.31, respectively. It proves that these exciton complexes confined in single quantum dashes of InP-based material system can act as true single photon emitters being compatible with standard long-distance fiber communication technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Toddler home math environment: Triangulating multi-method assessments in a U.S. Sample

Introduction Current research has documented the home math environment (HME) of preschoolers and kindergarteners. Very few studies, however, have explored the number and spatial activities in which parents engage with children during their toddler years. Methods This study examined the HME of 157 toddlers using several methodologies, including surveys, time diaries, and observations of math talk. Further, it examined correlations within and across data sources to identify areas of convergence and triangulation, and correlated HME measures with measures of toddlers’ number and spatial skills. Results Findings showed that, in general, uses of different types of math activities, including both number and spatial, were intercorrelated within method. Across methods, there was high intercorrelation between the frequency of math activities reported on parent surveys and the diversity of types of math activities endorsed in time diary interviews. Parent math talk gleaned from semi-structured interviews functioned as a separate aspect of the HME; different types of math talk shared few intercorrelations with engagement in math activities as reported in either surveys or time diaries. Finally, several HME measures positively correlated with toddlers’ math skills. Discussion Given extant research demonstrating that both math activities and math talk predict children’s math skills, our results stress the need for multimethod studies that differentiate among these HME opportunities.

Miller, Portia↗
DOE OSTI2014

Optimally focused cold atom systems obtained using density-density correlations

Resonant absorption imaging is a common technique for detecting the two-dimensional column density of ultracold atom systems. In many cases, the system's thickness along the imaging direction greatly exceeds the imaging system's depth of field, making the identification of the optimally focused configuration difficult. Here we describe a systematic technique for bringing Bose-Einstein condensates (BEC) and other cold-atom systems into an optimal focus even when the ratio of the thickness to the depth of field is large: a factor of 8 in this demonstration with a BEC. This technique relies on defocus-induced artifacts in the Fourier-transformed density-density correlation function (the power spectral density, PSD). The spatial frequency at which these artifacts first appear in the PSD is maximized on focus; the focusing process therefore both identifies and maximizes the range of spatial frequencies over which the PSD is uncontaminated by finite-thickness effects.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Using 3D position sensitivity to reveal response non-uniformities in CdZnTe, TlBr, and CsPbBr 3 detectors

Position sensitivity enables the correction of response non-uniformities in room-temperature semiconductor detectors caused by crystal defects and other factors. It can also be used to pinpoint the exact location of crystal defects responsible for the response variations. This work describes a technique for revealing and visualizing the detector regions affecting the charge collection efficiency in CdZnTe (CZT), TlBr, and CsPbBr 3 detectors configured as position-sensitive virtual Frisch-grid (VFG) devices. The technique correlates the photopeak events in energy spectra with their spatial distributions inside the detectors using the position information. By selecting the events from narrow energy intervals within a photopeak, we can visualize the detector volumes with particular charge collection efficiencies, which, in turn, correlate with the locations of electrode and crystal defects. Here, we demonstrate this technique in several examples. Columnar structures in the volume plots (position distribution maps) are consistent with signal losses near or at the anode in selected samples of CZT and TlBr. Structures exhibiting a distinct depth dependence are consistent with grain boundaries or other crystal defects.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗