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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Guidance to Design Grain Boundary Mobility Experiments with Molecular Dynamics and Phase-Field Modeling

Quantitative phase-field modeling can play an important role in designing experiments to measure the grain boundary (GB) mobility. In this work, molecular dynamics (MD) simulation is employed to determine the GB mobility using Cu bicrystals. Two grain configurations are considered: a shrinking circular grain and a half loop grain. The results obtained from the half loop configuration approaches asymptotically to that obtained from the circular configuration with increasing half loop width. We then verify the phase- field model by directly comparing to the MD simulation results, obtaining excellent agreement. Next, this phase-field model is used to predict the behavior in a common experimental setup that utilizes a half loop grain configuration in a bicrystal to measure the GB mobility. With a 3D simulation, we identify the two critical times within the experiments to reach an accurate value of the GB mobility. We use a series of 2D simulations to investigate the impact of the notch angle on these two critical times and we identify an angle of 60? as an optimal value. We also show that if the notch does not have a sharp tip, it may immobilize the GB migration indefinitely.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Interpreting anomalies observed in oxide semiconductor TFTs under negative and positive bias stress

Oxide semiconductor thin-film transistors can show anomalous behavior under bias stress. Two types of anomalies are discussed in this paper. The first is the shift in threshold voltage (V{sub TH}) in a direction opposite to the applied bias stress, and highly dependent on gate dielectric material. We attribute this to charge trapping/detrapping and charge migration within the gate dielectric. We emphasize the fundamental difference between trapping/detrapping events occurring at the semiconductor/dielectric interface and those occurring at gate/dielectric interface, and show that charge migration is essential to explain the first anomaly. We model charge migration in terms of the non-instantaneous polarization density. The second type of anomaly is negative V{sub TH} shift under high positive bias stress, with logarithmic evolution in time. This can be argued as electron-donating reactions involving H{sub 2}O molecules or derived species, with a reaction rate exponentially accelerated by positive gate bias and exponentially decreased by the number of reactions already occurred.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Study of meridional flow using Ca-K line profiles during solar cycles 22 and 23

The analysis of Ca-K line spectra as a function of solar latitude and integrated over longitudes taken during the period of 1989-2011 indicates that the K{sub 1} width attains maximum amplitude at various latitude belts at different phases of the solar cycle. The FWHM of the K{sub 1} distribution at different latitudes shows that its width varies by about 30% for the equatorial belt (<30°) and 11% for the polar region (>70°) latitudes. Interestingly, the K{sub 1} width varies by ∼6% only in the 40-60° latitude belts during the solar cycle. The analysis of cross-correlation coefficients of the K{sub 1} width between the 35° latitude and other latitude belts as a function of phase differences indicates that the activity representing toroidal field shifted at a uniform rate of about 5.1 m s{sup –1} in the northern hemisphere from mid-latitudes toward the equator. In the southern hemisphere, activity shifted at a faster rate, ∼14 m s{sup –1}, in the beginning of the cycle and the speed decreased with time, yielding an average speed of 7.5 m s{sup –1} toward the equator. The shift of activity in the higher latitude belts showed complex behavior, indicating poleward and equatorward migration. These findings, especially the fewer variations in mid-latitude belts as compared to polar regions, asymmetry in the speed of the shift in the activity in both hemispheres, and complex variation in the direction of the shift in the activity representing poloidal fields in mid-latitude belts, will have an important implication on the modeling of the solar dynamo.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

Polymer Coatings Reduce Electro-osmosis

Poly(ethylene glycol) film controls electrostatic potential. Electro-osmosis in quartz or glass chambers reduced or reversed by coating inside surface of chambers with monomacromolecular layers of poly(ethylene glycol). Stable over long times. Electrostatic potential across surface of untreated glass or plastic chamber used in electro-phoresis is negative and attracts cations in aqueous electrolyte. Cations solvated, entrains flow of electrolyte migrating toward cathode. Electro-osmotic flow interferes with desired electrophoresis of particles suspended in electrolyte. Polymer coats nontoxic, transparent, and neutral, advantageous for use in electrophoresis.

Herren, Blair J.↗
NASA NTRS1998

The Impact of FU Orionis Outbursts and the Solar Nebula

Protostellar systems are variable on many timescales. One of the most dramatic forms of variability known to occur in low mass stellar systems is the FU Orionis outburst (Herbig 1977). Throughout a typical outburst lasting several decades, system luminosities may be a hundred times what is typical of the quiesent state. FU Orionis outburst events are thought to have significant impact on the thermal structure of the protosolar nebula; their existence has been used to explain features in the meteoritic record from thermally induced homogenization to the formation of chondrules. Until recently, the magnitude of the likely effect from such outbursts has been largely speculative due to the lack of a detailed understanding of the outburst mechanism. Recent numerical models (Bell\& Lin 1994) have demonstrated the viability of the observational hypothesis (Hartmann\& Kenyon 1985) that the radiation observed during outburst is emitted by a luminous circumstellar disk transporting mass at a thousand times the quiesent rate. Light curves and color and line width evolution observed in FU Orionis systems are naturally explained by time dependent outbursting model disks (Bell et al. 1995). The radial temperature structure and shape of the disk during outburst derived from these models may be used to calculate the outburst's expected impact on primitive material at various radii throughout the disk. In this review, we will begin by discussing what is known about the FU Orionis outburst phenomenon from recent observations and theory including statistically deduced outburst timescales and observed peak temperatures. Unless covered by another author, we will discuss the evidence which suggests that outburst radiation is emitted by a circumstellar disk rather than by the star and will briefly review the thermal instability as a mechanism for outburst. We will then report on recent work which investigates the likely heating of solar nebula material due to FU Orionis outbursts including the following effects: (1) heating of the planet forming region by direct radiation from the hot inner nebula; (2) heating by the diffuse radiation field of a coccooning envelope; and (3) time-dependent penetration of the increased luminosity from the above sources into the optically thick nebula. Some of this work is currently in progress. The potential effects on condensation and migration in the nebula and the thermal processing of solids will be evaluated.

Bell, Robbins↗
NASA NTRS1998

Influence of gravity and light on the developmental polarity of Ceratopteris richardii fern spores

The polarity of germinating single-celled spores of the fern Ceratopteris richardii Brogn. is influenced by gravity during a time period prior to the first cellular division designated a "polarity-determination window". After this window closes, control of polarity is seen in the downward (with respect to gravity) migration of the nucleus along the proximal face of the spore and the subsequent downward growth of the primary rhizoid. When spores are germinated on a clinostat the direction of nuclear migration and subsequent primary rhizoid growth is random. However, in each case the direction of nuclear migration predicts the direction of rhizoid elongation. Although it is the most obvious movement, the downward migration is not the first movement of the nucleus. During the polarity-determination window, the nucleus moves randomly within a region centered behind the trilete marking. While the polarity of many fern spores has been reported to be controlled by light, spores of C. richardii are the first documented to have their polarity influenced by gravity. Directional white light also affects the polarity of these spores, but this influence is slight and is secondary to that of gravity.

Non-NASA Center↗
NASA NTRS2024

Alaska Ecological Conservation II: Using NASA Earth Observations to Identify Recent Changes in Vegetation Phenology and Its Impacts on Caribou Calving and Migration

Caribou are known for their long-distance migrations from wintering grounds to specified calving zones. Notably, the Western Arctic Herd (WAH) is the largest caribou herd in Northwestern Alaska that exhibits this behavior. These calving zones are highly predictable, and research suggests that calving and the availability of high-quality vegetation are correlated. We partnered with the U.S. National Park Service in Northwestern Alaska to use Terra and Aqua Moderate Resolution Imaging Spectroradiometer(MODIS)and Harmonized Landsat and Sentinel-2 (HLS) imagery to derive Normalized Difference Vegetated Index (NDVI) values and assess vegetation phenology in calving zones from 2000 –2024. Our partners seek to understand if observed changes in caribou migration patterns and calving events correlate with shifts in the availability of nutrient-rich vegetation. Our results showed spatial variations of highly vegetated zones and annual shifts in the timing and length of growing seasons. While limitations existed in the MODIS and HLS datasets, we demonstrated feasibility using National Aeronautics and Space Administration (NASA)Earth observations for NDVI analysis over the study region. Using location data, our results may further research into caribou calving behaviors.

NDVI↗
DOE OSTI2018

Women in Science: Fermilab computing analyst Margherita Vittone-Wiersma

With February 11 marking the International Day of Women and Girls in Science, female physicists, engineers and computer scientists from CERN and Fermilab share their experiences of building careers in science. Margherita Vittone-Wiersma came to Fermilab as a physicist in February 1985. Together with a group of researchers from Italy's Institute of Nuclear Physics, she began a new experiment called E687. But she soon learned that she preferred working on data acquisition and the many methods to store and access the huge amount of data coming out of science experiments. What was once mere megabytes of data is now terabytes of information - and experimental physicists need to be able to retrieve stored data and monitor data coming from the detectors in real-time. "It's been an incredible change in scale of the amount of data that is handled by computers and has to be analyzed by the physicists," she says. Margherita migrated from physics to her new role in computing through lots of hands-on learning and classes in different programming languages and software development offered at Fermilab. She officially joined the lab's computing division in 1989. "It's a great experience to work with the physicists," she says. Together physicists and computing experts iterate over tools "to make sure that everything is working the way they expect. It's very rewarding." Credits: Video production - Fermilab Creative Services Music Copyright: Universal Production Music Astral Light Chevalier Idea originally conceived by Tanya Levshina, Fermilab and Maria Dimou, CERN.

99 GENERAL AND MISCELLANEOUS↗
NASA NTRS2021

Widespread Megaripple Activity Across the North Polar Ergs of Mars

The most expansive dune fields on Mars surround the northern polar cap where various aeolian bedform classes are modified by wind and ice. The morphology and dynamics of these ripples, intermediate-scale bedforms (termed megaripples and transverse aeolian ridges (TARs)), and sand dunes reflect information regarding regional boundary conditions. We found that populations of polar megaripples and larger TARs are distinct in terms of their morphology, spatial distribution, and mobility. Whereas regionally-restricted TARs appeared degraded and static in long-baseline observations, polar megaripples were not only widespread but migrating at relatively high rates (0.13± 0.03 m/Earth year) and possibly more active than other regions on Mars. This high level of activity is somewhat surprising since there is limited seasonality for aeolian transport due to surficial frost and ice during the latter half of the martian year. A comprehensive analysis of an Olympia Cavi dune field estimated that the advancement of megaripples, ripples, and dunes avalanches accounted for ~1%, ~10%, and ~100%, respectively, of the total aeolian system’s sand fluxes. This included dark-toned ripples that migrated the average equivalent of 9.6±6 m/yr over just 22 days in northern summer - unprecedented rates for Mars. While bedform transport rates are some of the highest yet reported on Mars, the sand flux contribution between the different bedforms does not substantially vary from equatorial sites with lower rates. Seasonal off-cap sublimation winds and summer-time polar storms are attributed as the cause for the elevated activity, rather than cryospheric processes. Plain Language Summary “Megaripples” are distinct wind-driven bedforms that occur on the surface of Earth and Mars, often with sizes between that of smaller ripples and larger dunes. Recent work has found the thin martian atmosphere can mobilize some coarse-grained megaripples, overturning prior notions that these were static relic landforms from a past climate. We mapped megaripples and adjacent bedforms across the north polar sand seas, the most expansive collection of dune fields on Mars. Megaripples were found to be widespread across the region and migrating at relatively high rates relative to other sites on Mars that are at lower latitudes. This enhanced activity is likely related to the greater sand fluxes found for neighboring dunes which are driven by summer-time seasonal winds when polar ice is sublimating. In contrast, other megaripples appear to be stabilized, a likely result of inter-granular ice within low wind areas.

Matthew Chojnacki↗
NASA NTRSDate not supplied

Cloud-Based Time Series Analysis of Extremes: Use Cases and Applications

"Extreme weather events, such as hurricanes, tornadoes, floods, droughts, heatwaves, and blizzards, can cause widespread damage, disrupting ecosystems, agricultural production, and economies. The frequency and intensity of these events have been increasing, likely due to climate change, raising concerns and the need for more accurate analysis and predictions. NASA's Goddard Earth Sciences Data and Information Services Center (GES DISC) has migrated its long-term historical datasets, including precipitation data from MERRA-2 reanalysis, GLDAS land data assimilation, and IMERG satellite observations, to the cloud. This cloud-stored data enables scientists and researchers to utilize cloud computing for advanced modeling and forecasting of extreme weather events, eliminating the need to download large datasets. In this presentation, we will provide an overview of the cloud-based data and services managed by GES DISC; demonstrate methods for accessing and analyzing time series data stored in the cloud; and compare results across various datasets to address critical questions related to extreme precipitation. We will present use cases including: 1. Determining the average total precipitation in California during January and February from 2000 to 2024, and identifying anomalous precipitation in 2021. 2. Calculating the 10, 20, 50, and 100-year return periods for maximum daily rainfall based on 25 years of historical precipitation data (2000-2024) for Maryland.

time series↗
DOE OSTI2018

Pathways Following Electron Injection: Medium Effects and Cross-Surface Electron Transfer in a Ruthenium-Based, Chromophore–Catalyst Assembly on TiO 2

Interfacial dynamics following photoexcitation of the water oxidation assembly [((PO 3 H 2 ) 2 bpy) 2 Ru II (bpy-bimpy)Ru II (tpy)(OH 2 )] 4+ , -[Ru a II –Ru b II –OH 2 ] 4+ , on nanocrystalline TiO 2 electrodes, starting from either -[Ru a II –Ru b II –OH 2 ] 4+ or -[Ru a II –Ru b III –OH 2 ] 5+ , have been investigated. Transient absorption measurements for TiO 2 –[Ru a II –Ru b II –OH 2 ] 4+ in 0.1 M HPF 6 or neat trifluoroethanol reveal that electron injection occurs with high efficiency but that hole transfer to the catalyst, which occurs on the electrochemical time scale, is inhibited by local environmental effects. Back electron transfer occurs to the oxidized chromophore on the microsecond time scale. Photoexcitation of the once-oxidized assembly, TiO 2 –[Ru a II –Ru b III –OH 2 ] 5+ , in a variety of media, generates -[Ru a III –Ru b III –OH 2 ] 6+ . The injected electron randomly migrates through the surface oxide structure reducing an unreacted -[Ru a II –Ru b III –OH 2 ] 5+ assembly to -[Ru a II –Ru b II –OH 2 ] 4+ . In a parallel reaction, -[Ru a III –Ru b III –OH 2 ] 6+ formed by electron injection undergoes proton loss giving -[Ru a II –Ru b IV $=$O] 4+ with possible conversion to -[Ru a II –Ru b II –OH 2 ] 4+ by an electrolyte-mediated reaction. In the following slow step, re-equilibration on the surface occurs either by reaction with added Fe III/II or by cross-surface electron transfer between spatially separated -[Ru a II –Ru b IV $=$O] 4+ and -[Ru a II –Ru b II –OH 2 ] 4+ assemblies to give -[Ru a II –Ru b III –OH 2 ] 5+ with a half-time of t 1/2 ~ 68 μs. Finally, these results and analyses show that the transient surface behavior of the assembly and cross-surface reactions play important roles in producing and storing redox equivalents on the surface that are used for water oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Methylammonium Lead Tribromide Single Crystal Detectors towards Robust Gamma-Ray Photon Sensing

In recent years, hybrid perovskite single crystalline solid-state detectors have shown promise in γ-ray spectroscopy. Here, the γ-ray photon induced electrical pulses are investigated, which are produced by perovskite solid-state detectors made with the commonly used methylammonium lead tribromide crystals with chlorine incorporation. Under low electric field detector operation, slow pulses generated by γ-rays with average rise times of 65 µs are observed, which decreases to 20 µs when a higher electrical field of 500 V cm -1 is applied. However, the baseline becomes noisy quickly, which prevents collection of clean pulses for spectra construction. Further, by systematically measuring the temperature dependence and current–voltage characteristics, such instability is attributed to the local ion migration under electrical field creating a fluctuating dark noise, which presents a major challenge in perovskite γ-ray detector technologies. It is demonstrated that cycling the bias between positive and negative polarity can stabilize the detector, allowing for longer periods of pulse accumulation for generating energy resolved spectra with resolutions of ≈35% at 59.6 keV and ≈25% at 662 keV at room temperature. The study indicates that the main limiting factors of perovskite-based γ-ray detectors are slow rise times and bias instability. Finally, these challenges must be properly addressed to achieve reproducible, high-resolution γ-ray detection.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Water Infiltration and Solute Transport in An Unsaturated Underground Porous Environment - 18442

Water flow and contaminant transport in an unsaturated porous medium are studied by solving the Richards equation for the moisture movement and the convective-dispersive transport of contaminant by using the software HYDRUS 1D for prescribed head condition at the top boundary of a soil layer: a single peak and two peaks of finite duration. While the moisture migration is solved separately, the contaminant transport is coupled to moisture movement. Due to unsaturated nature of the medium the downward water flux in the soil shows vertical variation. The movement of contaminant concentration disturbance is slowed down as it moves downwards. For two separated head peaks in time, the two concentration peaks merge into one and this tendency takes place faster for larger sorption coefficient. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Investigating PID Shunting in Polycrystalline CIGS Devices via Multi-Scale, Multi-Technique Characterization

We investigated potential-induced degradation (PID) in CuIn 1-x Ga x Se 2 (CIGS) mini-modules stressed in the laboratory. Small cores were removed from the modules and were subjected to analysis. We completed a proof-of-concept correlative study relating cathodoluminescence to sodium content via time-of-flight secondary-ion mass spectrometry imaging. By comparing one-dimensional depth profile results and three-dimensional tomography results on stressed and unstressed CIGS mini-modules, we can see that PID in CIGS results from sodium migration through absorber, most likely via grain boundaries. Potassium concentration distributions show little change when adding a voltage bias to a temperature and humidity stress. This suggests doping with other large alkali ions, such as cesium and rubidium, rather than sodium can increase the PID resistance of CIGS modules.

14 SOLAR ENERGY↗
DOE OSTI2016

Determination of grain boundary mobility during recrystallization by statistical evaluation of electron backscatter diffraction measurements

One of the key aspects influencing microstructural design pathways in metallic systems is grain boundary motion. The present work introduces a method by means of which direct measurement of grain boundary mobility vs. misorientation dependence is made possible. The technique utilizes datasets acquired by means of serial electron backscatter diffraction (EBSD) measurements. The experimental EBSD measurements are collectively analyzed, whereby datasets were used to obtain grain boundary mobility and grain aspect ratio with respect to grain boundary misorientation. The proposed method is further validated using cellular automata (CA) simulations. Single crystal aluminium was cold rolled and scratched in order to nucleate random orientations. Subsequent annealing at 300 °C resulted in grains growing, in the direction normal to the scratch, into a single deformed orientation. Growth selection was observed, wherein the boundaries with misorientations close to Σ7 CSL orientation relationship (38° 〈111〉) migrated considerably faster. The obtained boundary mobility distribution exhibited a non-monotonic behavior with a maximum corresponding to misorientation of 38° ± 2° about 〈111〉 axes ± 4°, which was 10–100 times higher than the mobility values of random high angle boundaries. Correlation with the grain aspect ratio values indicated a strong growth anisotropy displayed by the fast growing grains. The observations have been discussed in terms of the influence of grain boundary character on grain boundary motion during recrystallization. - Highlights: • Statistical microstructure method to measure grain boundary mobility during recrystallization • Method implementation independent of material or crystal structure • Mobility of the Σ7 boundaries in 5N Al was calculated as 4.7 × 10{sup –8} m{sup 4}/J ⋅ s. • Pronounced growth selection in the recrystallizing nuclei in Al • Boundary mobility values during recrystallization 2–3 orders of magnitude larger vis-à-vis curvature driven motion.

36 MATERIALS SCIENCE↗
DOE OSTI2016

IR-Live: fabrication of a low-cost plastic microfluidic device for infrared spectromicroscopy of living cells

Water is a strong mid-infrared absorber, which has hindered the full exploitation of label-free and non-invasive infrared (IR) spectromicroscopy techniques for the study of living biological samples. To overcome this barrier, many researchers have built sophisticated fluidic chambers or microfluidic chips wherein the depth of the liquid medium in the sample compartment is limited to 10 μm or less. We report an innovative and simple way to fabricate plastic devices with infrared transparent view-ports enabling infrared spectromicroscopy of living biological samples; therefore the device is named “IR-Live”. Advantages of this approach include lower production costs, a minimal need to access a micro-fabrication facility, and unlimited mass or waste exchange for the living samples surrounding the view-port area. We demonstrate that the low-cost IR-Live in combination with microfluidic perfusion techniques enables long term (>60 h) cell culture, which broadens the capability of IR spectromicroscopy for studying living biological samples. To illustrate this, we first applied the device to study protein and lipid polarity in migrating REF52 fibroblasts by collecting 2-dimensional spectral chemical maps at a micrometer spatial resolution. Then, we demonstrated the suitability of our approach to study dynamic cellular events by collecting a time series of spectral maps of U937 monocytes during the early stage of cell attachment to a bio-compatible surface.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

EVIDENCE OF AN ASTEROID ENCOUNTERING A PULSAR

Debris disks and asteroid belts are expected to form around young pulsars due to fallback material from their original supernova explosions. Disk material may migrate inward and interact with a pulsar's magnetosphere, causing changes in torque and emission. Long-term monitoring of PSR J0738–4042 reveals both effects. The pulse shape changes multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead us to postulate that we are witnessing an encounter with an asteroid or in-falling debris from a disk.

79 ASTRONOMY AND ASTROPHYSICS↗