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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Statistical Perspectives on Stratospheric Transport

Long-lived tropospheric source gases, such as nitrous oxide, enter the stratosphere through the tropical tropopause, are transported throughout the stratosphere by the Brewer-Dobson circulation, and are photochemically destroyed in the upper stratosphere. These chemical constituents, or "tracers" can be used to track mixing and transport by the stratospheric winds. Much of our understanding about the stratospheric circulation is based on large scale gradients and other spatial features in tracer fields constructed from satellite measurements. The point of view presented in this paper is different, but complementary, in that transport is described in terms of tracer probability distribution functions (PDFs). The PDF is computed from the measurements, and is proportional to the area occupied by tracer values in a given range. The flavor of this paper is tutorial, and the ideas are illustrated with several examples of transport-related phenomena, annotated with remarks that summarize the main point or suggest new directions. One example shows how the multimodal shape of the PDF gives information about the different branches of the circulation. Another example shows how the statistics of fluctuations from the most probable tracer value give insight into mixing between different regions of the atmosphere. Also included is an analysis of the time-dependence of the PDF during the onset and decline of the winter circulation, and a study of how "bursts" in the circulation are reflected in transient periods of rapid evolution of the PDF. The dependence of the statistics on location and time are also shown to be important for practical problems related to statistical robustness and satellite sampling. The examples illustrate how physically-based statistical analysis can shed some light on aspects of stratospheric transport that may not be obvious or quantifiable with other types of analyses. An important motivation for the work presented here is the need for synthesis of the large and growing database of observations of the atmosphere and the vast quantities of output generated by atmospheric models.

Sparling, L. C.↗
DOE OSTI2025

Artificial intelligence for advanced functional materials: exploring current and future directions

This perspective addresses the topic of harnessing the tools of artificial intelligence (AI) for boosting innovation in functional materials design and engineering as well as discovering new materials for targeted applications in energy storage, biomedicine, composites, nanoelectronics or quantum technologies. It gives a current view of experts in the field, insisting on challenges and opportunities provided by the development of large materials databases, novel schemes for implementing AI into materials production and characterization as well as progress in the quest of simulating physical and chemical properties of realistic atomic models reaching the trillion atoms scale and with near ab initio accuracy.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Two-dimensional electrostatic turbulence with variable density and pressure

Large-scale turbulence transverse to a uniform dc magnetic field is considered from the point of view of a two-fluid model of an electrostatic plasma of variable density. An approximation motivated by 'geostrophic' techniques of dynamic meteorology is introduced. It is argued that the inverse cascade phenomenon should persist in the presence of variable pressure and density.

Montgomery, D.↗
NASA NTRS1981

Infrared-temperature variability in a large agricultural field

Dunnigan Agro-Meteorological Experiment airborne thermal scanner images of a large varying-terrain barley field are acquired and analyzed. Temperature variability that may occur within instantaneous fields of view (IFOV) is defined (coefficient of variation: standard deviation/mean temperature in degrees C), and the percentage of the area within various IFOV's within + or - 1, 2, 3, and 5 degrees of the mean is determined. With the exception of very rugged terrain, over 80% of the area within 4, 16, 65 and 258 ha cells was at temperatures within + or - 3 C of the mean cell temperature. Remote measurements of field temperature appeared to be slightly influenced by pixel size in the range 4 ha to 259 ha, and the area percentage within any pixel which contributes within + or - 1, 2, 3, and 5 degrees C of the mean, is nominally the same. In conclusion, no great advantage is found in utilizing a small IFOV instead of a large one for remote sensing of crop temperature.

Millard, J. P.↗
NASA NTRS1987

Information retrieval from holographic interferograms: Fundamentals and problems

Holographic interferograms can contain large amounts of information about flow and temperature fields. Their information content can be very high because they can be viewed from many different directions. This multidirectionality, and fringe localization add to the information contained in the fringe pattern if diffuse illumination is used. Additional information, and increased accuracy can be obtained through the use of dual reference wave holography to add reference fringes or to effect discrete phase shift or hetrodyne interferometry. Automated analysis of fringes is possible if interferograms are of simple structure and good quality. However, in practice a large number of practical problems can arise, so that a difficult image processing task results.

Vest, Charles M.↗
NASA NTRS1985

Fundamental study of flow field generated by rotorcraft blades using wide-field shadowgraph

The vortex trajectory and vortex wake generated by helicopter rotors are visualized using a wide-field shadowgraph technique. Use of a retro-reflective Scotchlite screen makes it possible to investigate the flow field generated by full-scale rotors. Tip vortex trajectories are visible in shadowgraphs for a range of tip Mach number of 0.38 to 0.60. The effect of the angle of attack is substantial. At an angle of attack greater than 8 degrees, the visibility of the vortex core is significant even at relatively low tip Mach numbers. The theoretical analysis of the sensitivity is carried out for a rotating blade. This analysis demonstrates that the sensitivity decreases with increasing dimensionless core radius and increases with increasing tip Mach number. The threshold value of the sensitivity is found to be 0.0015, below which the vortex core is not visible and above which it is visible. The effect of the optical path length is also discussed. Based on this investigation, it is concluded that the application of this wide-field shadowgraph technique to a large wind tunnel test should be feasible. In addition, two simultaneous shadowgraph views would allow three-dimensional reconstruction of vortex trajectories.

Parthasarathy, S. P.↗
NASA NTRS2009

Prominence Structure and Dynamics

Nonerupting prominences are not dull, static objects. Rather, they are composed of fine-scale blobs and threads that are highly dynamic, often appearing to travel in opposite directions on adjacent tracks (denoted counterstreaming). Because the plasma is largely constrained to travel along the magnetic field, these cool, dense features can serve as tracers of the prominence magnetic structure, a valuable resource in view of the long-standing difficulty of observing the coronal field. Conversely, greater understanding of the fundamental magnetic geometry of filament channels can provide important constraints on the physical processes governing the accumulation, support, motion, and eruption of the cool plasma. Despite over a century of detailed observations, large gaps remain in our knowledge of filament channel/plasma formation and evolution. Resolving these issues will shed light on the physics of coronal heating, helicity transport throughout the solar cycle, and the origins of eruptive activity on the Sun. I will discuss the leading models for the magnetic and plasma structure, and outline how new observations and theory /modeling could solve long-standing uncertainties regarding this majestic solar phenomenon.

Karpen, Judy T.↗
DOE OSTI2024

Spinning metasurface stack for spectro-polarimetric thermal imaging

Spectro-polarimetric imaging in the long-wave infrared (LWIR) region plays a crucial role in applications from night vision and machine perception to trace gas sensing and thermography. However, the current generation of spectro-polarimetric LWIR imagers suffers from limitations in size, spectral resolution, and field of view (FOV). While meta-optics-based strategies for spectro-polarimetric imaging have been explored in the visible spectrum, their potential for thermal imaging remains largely unexplored. In this work, we introduce an approach for spectro-polarimetric decomposition by combining large-area stacked meta-optical devices with advanced computational imaging algorithms. The co-design of a stack of spinning dispersive metasurfaces along with compressive sensing and dictionary learning algorithms allows simultaneous spectral and polarimetric resolution without the need for bulky filter wheels or interferometers. Our spinning-metasurface-based spectro-polarimetric stack is compact (<10×10×10cm) and robust, and it offers a wide field of view (20.5°). We show that the spectral resolving power of our system substantially enhances performance in machine learning tasks such as material classification, a challenge for conventional panchromatic thermal cameras. Our approach represents a significant advance in the field of thermal imaging for a wide range of applications including heat-assisted detection and ranging (HADAR).

Optics↗
NASA NTRS1986

Small-scale eruptive filaments on the quiet sun

A study of a little known class of eruptive events on the quiet sun was conducted. All of 61 small-scale eruptive filamentary structures were identified in a systematic survey of 32 days of H alpha time-lapse films of the quiet sun acquired at Big Bear Solar Observatory. When fully developed, these structures have an average length of 15 arc seconds before eruption. They appear to be the small-scale analog of large-scale eruptive filaments observed against the disk. At the observed rate of 1.9 small-scale eruptive features per field of view per average 7.0 hour day, the rate of occurence of these events on the sun were estimated to be greater than 600 per 24 hour day.. The average duration of the eruptive phase was 26 minutes while the average lifetime from formation through eruption was 70 minutes. A majority of the small-scale filamentary sturctures were spatially related to cancelling magnetic features in line-of-sight photospheric magnetograms. Similar to large-scale filaments, the small-scale filamentary structures sometimes divided opposite polarity cancelling fragments but often had one or both ends terminating at a cancellation site. Their high numbers appear to reflect the much greater flux on the quiet sun. From their characteristics, evolution, and relationship to photospheric magnetic flux, it was concluded that the structures described are small-scale eruptive filaments and are a subset of all filaments.

Hermans, Linda M.↗
NASA NTRS1976

Planetary magnetospheres: A comparative view

There are eight large bodies in the solar system about which definite statements regarding the existence or nonexistence of a magnetic field of internal origin can now be made. Of these bodies (Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, and the Earth's Moon), only Venus and the Moon have negligible surface magnetic fields. By negligible is meant that the magnetic fields are so weak that they do not sensibly perturb the local solar wind. The other bodies provide an interesting zoo of magnetic field configurations and attendant charged particle behavior. Six of these bodies have magnetic fields, and two do not. Furthermore, of those which have magnetic fields, it appears that only that of Mars is ineffective in accelerating charged particles.

Dessler, A. J.↗
NASA NTRS1998

Conjugate Observations of Optical Aurora with POLAR Satellite and Ground Based Imagers in Antarctica

Operation of the ultraviolet imager on the POLAR satellite permits the observation of Aurora Borealis in daylight during northern summer. With optical imagers in the Automatic Geophysical Observatories (AGO-s) large regions of the oval of Aurora Australis can be observed simultaneously during the southern winter polar night. This opportunity permits conducting a systematic study of the properties of auroras on opposite ends of the same field line. It is expected that simultaneously observed conjugate auroras occurring on closed field lines should be similar to each other in appearance because of the close connection between the two hemispheres through particle scattering and mirroring processes. On open or greatly distorted field lines there is no a priori expectation of similarity between conjugate auroras. To investigate the influence of different IMF conditions on auroral behavior we have examined conjugate data for periods of southward IMF. Sudden brightening and subsequent poleward expansions are observed to occur simultaneously in both hemispheres. The POLAR data show that sudden brightening are initiated at various local time regions. When the local time of this region is in the field of view of the AGO station network then corresponding brightening is also found to occur in the southern hemisphere. Large features such as substorm induced westward propagation and resulting auroral brightening seem to occur simultaneously on conjugate hemispheres. The widely different view scales make it difficult to make unique identification of individual auroral forms in the POLAR and in the ground based data but in a general sense the data is consistent with conjugate behavior.

Mende, S. H.↗
DOE OSTI2020

The Single-Volume Scatter Camera

The multi-institution Single-Volume Scatter Camera (SVSC) collaboration led by Sandia National Laboratories (SNL) is developing a compact, high-efficiency double-scatter neutron imaging system. Kinematic emission imaging of fission-energy neutrons can be used to detect, locate, and spatially characterize special nuclear material. Neutron-scatter cameras, analogous to Compton imagers for gamma ray detection, have a wide field of view, good event-by-event angular resolution, and spectral sensitivity. Existing systems, however, suffer from large size and/or poor efficiency. We are developing high-efficiency scatter cameras with small form factors by detecting both neutron scatters in a compact active volume. This effort requires development and characterization of individual system components, namely fast organic scintillators, photodetectors, electronics, and reconstruction algorithms. In this presentation, we will focus on characterization measurements of several SVSC candidate scintillators. The SVSC collaboration is investigating two system concepts: the monolithic design in which isotropically emitted photons are detected on the sides of the volume, and the optically segmented design in which scintillation light is channeled along scintillator bars to segmented photodetector readout. For each of these approaches, we will describe the construction and performance of prototype systems. We will conclude by summarizing lessons learned, comparing and contrasting the two system designs, and outlining plans for the next iteration of prototype design and construction.

Manfredi, Juan↗
DOE OSTI2021

HAT-P-68b: A Transiting Hot Jupiter around a K5 Dwarf Star

We report the discovery by the ground-based Hungarian-made Automated Telescope Network (HATNet) survey of the transiting exoplanet HAT-P-68b, which has a mass of 0.724 ± 0.043 M {sub J}, and radius of 1.072 ± 0.012 R {sub J}. The planet is in a circular P = 2.2984 day orbit around a moderately bright V = 13.937 ± 0.030 magnitude K-dwarf star of mass 0.673{sub −0.014}{sup +0.020} M {sub ⊙}, and radius 0.6726 ± 0.0069 R {sub ⊙}. The planetary nature of this system is confirmed through follow-up transit photometry obtained with the Fred L. Whipple Observatory (FLWO) 1.2 m telescope, high-precision radial velocities measured using Keck I/High Resolution Echelle Spectrometer (HIRES), FLWO 1.5 m/Tillinghast Reflector Echelle Spectrograph (TRES), and Observatoire de Haute-Provence (OHP) 1.9 m/Sophie, and high-spatial-resolution speckle imaging from WIYN 3.5 m/DSSI. HAT-P-68 is at an ecliptic latitude of +3° and outside the field of view of both the NASA Transiting Exoplanet Survey Satellite primary mission and the K2 mission. The large transit depth of 0.036 mag (r band) makes HAT-P-68b a promising target for atmospheric characterization via transmission spectroscopy.

47 OTHER INSTRUMENTATION↗
NASA NTRS1990

Kinetic instability associated with spherical shell distribution of cometary pickup ions

The stability of ion shell distribution is an interesting and important issue in view of the fact that it is stable under perturbations propagating parallel to the ambient magnetic field, despite large amount of free energy it contains. It was found, however, that if the shell distribution of ions has a sufficient amount of drift speed with respect to the solar wind hydromagnetic waves, it can become unstable. The obliquely propagating hydromagnetic instability associated with the ion shell distribution was recently discovered. This letter presents the unified stability analysis of the ion shell distribution, under what condition the drift-induced instability of the type first discussed by Gary and Sinha (1989), and the oblique hydromagnetic instability discussed by Wu and Yoon (1990) are excited, and how the two types of instabilities are related.

Yoon, Peter H.↗
NASA NTRS1998

Hard X-ray Observation of Cygnus X-1 By the Marshall Imaging X-ray Experiment (MIXE2)

The second generation of the Marshall Imaging X-ray Experiment (MIXE2) was flown from Fort Sumner, New Mexico on May 7-8, 1997. The experiment consists of coded-aperture telescope with a field of view of 1.8 degrees (FWHM) and an angular resolution of 6.9 arcminutes. The detector is a large (7.84x10(exp 4) sq cm) effective area microstrip proportional counter filled with 2.0x10(exp5) Pascals of xenon with 2% isobutylene. We present MIXE2 observation of the 20-80keV spectrum and timing variability of Cygnus X-1 made during balloon flight.

Minamitani, Takahisa↗
NASA NTRS2000

Design and Plans for a Wide-Field Imaging Interferometry Testbed

Future scientific observatories for NASA will utilize interferometry to image astronomical sources. Interferometry is particularly needed in the far-infrared and sub-millimeter because the long wavelength drives large baselines in order to achieve reasonable spatial resolution. However, the requirement to cover a wide field of view with interferometry has not been demonstrated. Because of this, we have been funded by NASA to develop a testbed for demonstrating wide field imaging interferometry that will also allow us to evaluate the system issues associated with this type of observatory. This paper will describe the drivers for this testbed, the design of this testbed, and the actual tests and algorithms we plan to run and demonstrate.

Feinberg, Lee D.↗
NASA NTRS2009

Xenia Mission: Spacecraft Design Concept

The proposed Xenia mission will, for the first time, chart the chemical and dynamical state of the majority of baryonic matter in the universe. using high-resolution spectroscopy, Xenia will collect essential information from major traces of the formation and evolution of structures from the early universe to the present time. The mission is based on innovative instrumental and observational approaches: observing with fast reaction gamma-ray bursts (GRBs) with a high spectral resolution. This enables the study of their (star-forming) environment from the dark to the local universe and the use of GRBs as backlight of large-scale cosmological structures, observing and surveying extended sources with high sensitivity using two wide field-of-view x-ray telescopes - one with a high angular resolution and the other with a high spectral resolution.

Hopkins, R. C.↗
NASA NTRS1996

Astrometric Detection of Extrasolar Planets: Results of a Feasibility Study with the Palomar 5 Meter Telescope

The detection of extrasolar planets around stars like the Sun remains an important goal of astronomy. We present results from Palomar 5 m observations of the open cluster NGC 2420 in which we measure some of the sources of noise that will be present in an astrometric search for extrasolar planets. This is the first time that such a large aperture has been used for high-precision astrometry. We find that the atmospheric noise is 150 micro-arcsec hr(exp 1/2) across a 90 sec field of view and that differential chromatic refraction (DCR) can be calibrated to 128 micro-arcsec for observations within 1 hr of the meridian and 45 deg of zenith. These results confirm that a model for astrometric measurements can be extrapolated to large apertures. We demonstrate, based upon these results, that a large telescope achieves the sensitivity required to perform a statistically significant search for extra solar planets. We describe an astrometric technique to detect planets, the astrometric signals expected, the role of reference stars, and the sources of measurement noise: photometric noise, atmospheric motion between stars, sky background, instrumental noise, and DCR. For the latter, we discuss a method to reduce the noise further to 66 micro-arcsecond for observations within 1 hr of the meridian and 45 deg of zenith. We discuss optimal lists of target stars taken from the latest Gliese & Jahreiss catalog of nearby stars with the largest potential astrometric signals, declination limits for both telescope accessibility and reduced DCR, and galactic latitude limits for a sufficiant number of reference stars. Two samples are described from which one can perform statistically significant searches for gas giant planets around nearby stars. One sample contains 100 "solar class" stars with an average stellar mass of 0.82 solar mass; the other maximizes the number of stars, 574, by searching mainly low-mass M stars. We perform Monte Carlo simulations of the statistical significance of the expected results by using measured and estimated noise quantities. We show the semimajor axis parameter spaces that are searched for each star and how an increase in the length of the observing program expands these spaces. The search over semimajor axis parameter space relates to the theory of gas giant planet formation.

Pravdo, Steven H.↗