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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Photon energy and polarization-dependent electronic structure of Cr-doped Bi 2 Se 3

In this article, we report a comparative study of the electronic structure of Cr-doped and pristine Bi 2 Se 3 . Circular dichroism and photon-energy-dependent angle-resolved photoemission experiments were performed. Even though the surface states seen on the Cr-doped samples are gapped, they exhibit strong circular dichroism, for which we provide its origin in accordance with the nontrivial band structure of the bulk. We note the surface electronic structure measurements with linear and circular polarized light show signatures that the orbital composition of the surface states is changed with Cr doping. Our observations not only provide further spectroscopic information about topological materials, but also promotes an alternative experimental tool to control their spin-orbital texture.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Orientational analysis of atomic pair correlations in nanocrystalline indium oxide thin films

The application of grazing-incidence total X-ray scattering (GITXS) for pair distribution function (PDF) analysis using >50 keV X-rays from synchrotron light sources has created new opportunities for structural characterization of supported thin films with high resolution. Compared with grazing-incidence wide-angle X-ray scattering, which is only useful for highly ordered materials, GITXS/PDFs expand such analysis to largely disordered or nanostructured materials by examining the atomic pair correlations dependent on the direction relative to the surface of the supporting substrate. A characterization of nanocrystalline In 2 O 3 -derived thin films is presented here with in-plane-isotropic and out-of-plane-anisotropic orientational ordering of the atomic structure, each synthesized using different techniques. The atomic orientations of such films are known to vary based on the synthetic conditions. Here, an azimuthal orientational analysis of these films using GITXS with a single incident angle is shown to resolve the markedly different orientations of the atomic structures with respect to the planar support and the different degrees of long-range order, and hence, the terminal surface chemistries. It is anticipated that orientational analysis of GITXS/PDF data will offer opportunities to extend structural analyses of thin films by providing a means to qualitatively determine the major atomic orientation within nanocrystalline and, eventually, non-crystalline films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Enhancing Diagnosis through AI-driven Analysis of Reflectance Confocal Microscopy

Reflectance Confocal Microscopy (RCM) is a non-invasive imaging technique used in biomedical research and clinical dermatology. It provides virtual high-resolution images of the skin and superficial tissues, reducing the need for physical biopsies. RCM employs a laser light source to illuminate the tissue, capturing the reflected light to generate detailed images of microscopic structures at various depths. Recent studies explored AI and machine learning, particularly CNNs, for analyzing RCM images. Our study proposes a segmentation strategy based on textural features to identify clinically significant regions, empowering dermatologists in effective image interpretation and boosting diagnostic confidence. This approach promises to advance dermatological diagnosis and treatment.

Yoon, Hong-Jun↗
DOE OSTI2020

Mesoscale simulations of High Burnup Fuel Fragmentation: Applying phase-field modeling to understand high burnup fuel fragmentation during loss of coolant accident conditions

During a loss-of-coolant accident (LOCA) in a nuclear power plant, a rapid increase in temperature is experienced in the fuel. In commercial light water reactors (LWRs), the high burnup structure (HBS) forms in regions of the UO 2 fuel where local burnup is high, characterized by smaller grain sizes and large, overpressurized bubbles. During a LOCA transient, fuel in the HBS region is susceptible to fine fragmentation, where the fuel breaks up into micron-size fragments (sometimes referred to as pulverization). To better understand the mechanisms behind this phenomenon, mesoscale computational modeling using the Idaho National Laboratory code Marmot has been employed to simulate the process of HBS formation and response to a LOCA transient. The process of complete and partial HBS formation was demonstrated in prototypical LWR conditions. The simulated HBS microstructures from these simulations were passed to a phase-field model of fracture. To provide a more direct comparison with experiments, a set of experiments conducted by Studsvik on fine fragmentation/pulverization during LOCA conditions was simulated using the BISON fuel performance code. The temperature profiles from the BISON simulations were passed to a phase-field model to determine the gas bubble pressure as a function of time. These pressure histories were used in a phase-field model of fracture to determine under what conditions and in which types of bubbles fine fragmentation was likely to occur.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1969

Fine-line sensitivity for holographic interferograms

Improvement in sensitivity of holography, the technique of lensless interferometry, is obtained by enhancing the higher-order structure in the interferogram. By using the light diffracted into higher orders than the first, phase sensitivity is increased over the first order sensitivity by a factor equal to the order number used.

Heflinger, L. O.↗
NASA NTRS1977

Structure-property relationships in oxide-dispersed iron-beryllia alloys

Two BeO dispersed iron alloys containing about 2.5 and 5.5 v/o dispersoid were produced by attritting, internally oxidizing, and extruding dilute, prealloyed Fe-Be powders. As-extruded alloys were given various thermomechanical treatments involving room temperature swaging and annealing above and below the allotropic transformation temperature. The elevated temperature rupture strengths were measured and correlated with changes in structure; strengthening trends were examined in the light of proposed models for such strengthening. The results obtained showed that the elevated temperature strength was determined by the oxide interparticle spacing (IPS) in recrystallized material and IPS as well as prior deformation in swaged specimens. In fact, a parametric correlation was found between rupture strength values in the longitudinal direction with prestrain during swaging. The overall pattern in strength and microstructural observations were more consistent with a strength-stored energy (substructure) dependence than a strength-grain shape (grain aspect ratio) relation.

Wolf, S.↗
NASA NTRS1977

The distribution of ammonia and its photochemical products on Jupiter

Altitude profiles of ammonia and its photochemical products are generated in the light of measurements of the Jovian temperature structure, eddy transport coefficient, improved chemical scheme, and rate constants. Realistic limits are placed on the concentration of hydrazine which may participate in the recycling of ammonia on Jupiter. The maximum hydrazine-ice production rate is calculated to be about 1.3 mg/sq m per Jovian day. The distribution of nitrogen gas is presented with and without supersaturation of hydrazine. The nitrogen mixing ratio near the ammonia cloud top is estimated to be in the range between 10 to the -9th and 10 to the -11th power. An appreciable latitudinal variation in the ammonia concentration is expected.

Atreya, S. K.↗
NASA NTRS1977

Interaction of the surfaces of the moon and Mercury with their exospheric atmospheres

A model of atmosphere-surface interactions on the moon and on Mercury is presented. This model rejects the traditional assumption that the atmospheric particle source is a 'saturated' absorbed surface layer of gas and instead assumes that interaction is with solid atoms bound in a lattice structure so that most collisions with the light atmospheric particles are free-free rather than free-bound. The energy accommodation per collision for He and H is dominated by first-order interaction terms and is generally less than 0.1 per collision. It follows that estimated thermal escape is drastically reduced for the light atoms on both bodies. Thus the model requires much reduced solar wind collection efficiencies for protons and alpha particles. Some peculiarities of the Mercury He and H atmospheres might possibly be explained by the nature of the gas-surface coupling.

Shemansky, D. E.↗
NASA NTRS1978

Composite bolometers for submillimeter wavelengths

The fabrication and optimization of composite submillimeter wave bolometers with metal film absorbing elements and doped Ge thermometers are described. Performance characteristics are given for 4 x 4-mm bolometers designed for operation at both He-4 and He-3 temperatures. The performance expected from such bolometers when they are optimized for various values of background loading is calculated. Current dependent noise, which can arise from any of several sources, is included in the analysis. This can make it impossible to reach the background fluctuation noise limit. Feed structures for these bolometers which employ Winston light concentrators are described.

Nishioka, N. S.↗
NASA NTRS1976

The status of cometary science

The problem of determining the chemical composition and physical structure of comet nuclei are discussed in light of recent analytical improvements. The development of radio and infrared techniques, improved sensing equipment, and the ability to conduct observations in space using satellites or skylabs are highlighted. The studies of two major comets, Kohoutek and West 1975n, are presented as examples of the utilization of these improved analytic tools.

Whipple, F. L.↗
NASA NTRS1985

Ripple Ring Basins on Ganymede and Callisto

The unusual morphology of the Valhalla multiple or ripple-ring basin in Callisto was totally unexpected in light of the morphologies of large impact structures on the terrestrial planets. Two other ripple-ring basins (RRB's), Asgard and a smaller structure near the crater Adlinda are also described. Several additional RRB's were found on Callisto, an example of which is shown. A previously unrecognized RRB on Ganymede was also found. An image and geologic sketch map of this RRB are shown. Morphometric and positional data for all known RRB's are given.

Croft, S. K.↗
NASA NTRS1986

Very extended infrared emission at the center of M51 - The role of star formation

Low surface brightness 10 micron emission has been detected in M51 extending more than 1 arcmin, or 3 kpc, in RA. The emission has roughly uniform brightness and originates from dust in a region that is prominent visually and centered on the nucleus. Complementary near-infrared scans, which are dominated by the light from red stars, also show notable structure from hot dust. The dust is heated predominately by young stars, although a nonthermal source and, to a lesser extent, red stars may power the emission at the nucleus. Simple starburst models imply that the star formation rate per square parsec in the extended infrared-disk is at least two to three orders of magnitude higher than in the solar neighborhood.

Telesco, C. M.↗
NASA NTRS1987

Coronagraph for astronomical imaging and spectrophotometry

A coronagraph designed to minimize scattered light in astronomical observations caused by the structure of the primary mirror, secondary mirror, and secondary support structure of a Cassegrainian telescope is described. Direct (1:1) and reducing (2.7:1) imaging of astronomical fields are possible. High-quality images are produced. The coronagraph can be used with either a two-dimensional charge-coupled device or photographic film camera. The addition of transmission dispersing optics converts the coronagraph into a low-resolution spectrograph. The instrument is modular and portable for transport to different observatories.

Vilas, Faith↗
NASA NTRS1989

LOX/Hydrocarbon Combustion Instability Investigation

The LOX/Hydrocarbon Combustion Instability Investigation Program was structured to determine if the use of light hydrocarbon combustion fuels with liquid oxygen (LOX) produces combustion performance and stability behavior similar to the LOX/hydrogen propellant combination. In particular methane was investigated to determine if that fuel can be rated for combustion instability using the same techniques as previously used for LOX/hydrogen. These techniques included fuel temperature ramping and stability bomb tests. The hot fire program probed the combustion behavior of methane from ambient to subambient temperatures. Very interesting results were obtained from this program that have potential importance to future LOX/methane development programs. A very thorough and carefully reasoned documentation of the experimental data obtained is contained. The hot fire test logic and the associated tests are discussed. Subscale performance and stability rating testing was accomplished using 40,000 lb. thrust class hardware. Stability rating tests used both bombs and fuel temperature ramping techniques. The test program was successful in generating data for the evaluation of the methane stability characteristics relative to hydrogen and to anchor stability models. Data correlations, performance analysis, stability analyses, and key stability margin enhancement parameters are discussed.

Jensen, R. J.↗
NASA NTRS1989

Light scattering instrumentation for micro gravity research

The analysis of light scattered from an ensemble of particles has long been a preferred method for characterizing their physical properties. Instrumentation to perform the measurements which forms the basis for such analysis is available in many forms based upon a variety of different experimental techniques. A system is presented which is singularly applicable for making many types of measurements in a microgravity environment. The commercial version of this device, the DAWN-F, has been used in many labs throughout the world to perform analyses of particular importance for both research and production. Light scattering theory is reviewed and the structure and function of the system is described.

Wyatt, Philip J.↗
NASA NTRS1990

Design of aircraft wings subjected to gust loads - A system reliability approach

A method for system reliability-based design of aircraft wing structures is presented. A wing of a light commuter aircraft designed for gust loads according to the FAA regulations is compared with one designed by system reliability optimization. It is shown that system reliability optimization has the potential of improving dramatically the safety and efficiency of new designs. The reasons for the differences between the deterministic and reliability-based designs are explained.

Yang, J. S.↗
NASA NTRS1991

High-Gain AlxGa1-xAs/GaAs Transistors For Neural Networks

High-gain AlxGa1-xAs/GaAs npn double heterojunction bipolar transistors developed for use as phototransistors in optoelectronic integrated circuits, especially in artificial neural networks. Transistors perform both photodetection and saturating-amplification functions of neurons. Good candidates for such application because structurally compatible with laser diodes and light-emitting diodes, detect light, and provide high current gain needed to compensate for losses in holographic optical elements.

Kim, Jae-Hoon↗