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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Surface Melting Over the Greenland Ice Sheet Derived From Enhanced Resolution Passive Microwave Brightness Temperatures (1979–2019)

Surface melting is a major component of the Greenland ice sheet surface mass balance, and it affects sea level rise through direct runoff and the modulation of ice dynamics and hydrological processes, supraglacially, englacially and subglacially. Passive microwave (PMW) brightness temperature observations are of paramount importance in studying the spatial and temporal evolution of surface melting due to their long temporal coverage (1979–present) and high temporal resolution (daily). However, a major limitation of PMW datasets has been the relatively coarse spatial resolution, which has historically been of the order of tens of kilometers. Here, we use a newly released PMW dataset (37 GHz, horizontal polarization) made available through a NASA “Making Earth System Data Records for Use in Research Environments” (MeASUREs) program to study the spatiotemporal evolution of surface melting over the Greenland ice sheet at an enhanced spatial resolution of 3.125 km. We assess the outputs of different detection algorithms using data collected by automatic weather stations (AWSs) and the outputs of the Modèle Atmosphérique Régional (MAR) regional climate model. We found that sporadic melting is well captured using a dynamic algorithm based on the outputs of the Microwave Emission Model of Layered Snowpack (MEMLS), whereas a fixed threshold of 245 K is capable of detecting persistent melt. Our results indicate that, during the reference period from 1979 to 2019 (from 1988 to 2019), surface melting over the ice sheet increased in terms of both duration, up to 4.5 (2.9) d per decade, and extension, up to 6.9 % (3.6 %) of the entire ice sheet surface extent per decade, according to the MEMLS algorithm. Furthermore, the melting season started up to 4.0 (2.5) d earlier and ended 7.0 (3.9) d later per decade. We also explored the information content of the enhanced-resolution dataset with respect to the one at 25 km and MAR outputs using a semi-variogram approach. We found that the enhanced product is more sensitive to local-scale processes, thereby confirming the potential of this new enhanced product for monitoring surface melting over Greenland at a higher spatial resolution than the historical products and for monitoring its impact on sea level rise. This offers the opportunity to improve our understanding of the processes driving melting, to validate modeled melt extent at high resolution and, potentially, to assimilate these data in climate models.

Surface melting↗
DOE OSTI2015

Sclerostin antibody treatment improves fracture outcomes in a Type I diabetic mouse model

Type 1 diabetes mellitus (T1DM) patients have osteopenia and impaired fracture healing due to decreased osteoblast activity. Further, no adequate treatments are currently available that can restore impaired healing in T1DM; hence a significant need exists to investigate new therapeutics for treatment of orthopedic complications. Sclerostin (SOST), a WNT antagonist, negatively regulates bone formation, and SostAb is a potent bone anabolic agent. To determine whether SOST antibody (SostAb) treatment improves fracture healing in streptozotocin (STZ) induced T1DM mice, we administered SostAb twice weekly for up to 21 days post-fracture, and examined bone quality and callus outcomes at 21 days and 42 days post-fracture (11 and 14 weeks of age, respectively). Here we show that SostAb treatment improves bone parameters; these improvements persist after cessation of antibody treatment. Markers of osteoblast differentiation such as Runx2, collagen I, osteocalcin, and DMP1 were reduced, while an abundant number of SP7/osterix-positive early osteoblasts were observed on the bone surface of STZ calluses. These results suggest that STZ calluses have poor osteogenesis resulting from failure of osteoblasts to fully differentiate and produce mineralized matrix, which produces a less mineralized callus. SostAb treatment enhanced fracture healing in both normal and STZ groups, and in STZ + SostAb mice, also reversed the lower mineralization seen in STZ calluses. Micro-CT analysis of calluses revealed improved bone parameters with SostAb treatment, and the mineralized bone was comparable to Controls. Additionally, we found sclerostin levels to be elevated in STZ mice and β-catenin activity to be reduced. Consistent with its function as a WNT antagonist, SostAb treatment enhanced β-catenin activity, but also increased the levels of SOST in the callus and in circulation. Lastly, our results indicate that SostAb treatment rescues the impaired osteogenesis seen in the STZ induced T1DM fracture model by facilitating osteoblast differentiation and mineralization of bone.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1993

Toward large eddy simulation of turbulent flow over an airfoil

The flow field over an airfoil contains several distinct flow characteristics, e.g. laminar, transitional, turbulent boundary layer flow, flow separation, unstable free shear layers, and a wake. This diversity of flow regimes taxes the presently available Reynolds averaged turbulence models. Such models are generally tuned to predict a particular flow regime, and adjustments are necessary for the prediction of a different flow regime. Similar difficulties are likely to emerge when the large eddy simulation technique is applied with the widely used Smagorinsky model. This model has not been successful in correctly representing different turbulent flow fields with a single universal constant and has an incorrect near-wall behavior. Germano et al. (1991) and Ghosal, Lund & Moin have developed a new subgrid-scale model, the dynamic model, which is very promising in alleviating many of the persistent inadequacies of the Smagorinsky model: the model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model has been remarkably successful in prediction of several turbulent and transitional flows. We plan to simulate turbulent flow over a '2D' airfoil using the large eddy simulation technique. Our primary objective is to assess the performance of the newly developed dynamic subgrid-scale model for computation of complex flows about aircraft components and to compare the results with those obtained using the Reynolds average approach and experiments. The present computation represents the first application of large eddy simulation to a flow of aeronautical interest and a key demonstration of the capabilities of the large eddy simulation technique.

Choi, Haecheon↗
NASA NTRSDate not supplied

Analog Environments for Venus Aerosol Instrument and Mission Concept Testing

The most common hypothesis discussed for life on Venus is a habitat in the dense, persistent clouds, which are primarily sulfuric acid with a secondary water component. Although Earth lacks a complete Venus analog environment, several partial analogs exist which can inform our understanding of the requirements for cloud habitability as well as serving as potential testbeds for future Venus instruments or missions. Earth’s tropospheric clouds have larger particles, more water, and shorter lifetimes than Venus’s; however, they have a partial overlap in pressure and temperature, and are our only example of an airborne habitat.They can inform how particle residence time and microbial generation time constrain habitable atmospheric regions. On the biological side, this includes available nutrients and energy, environmental stressors such as radiation, osmotic potential and acidity, and time spent in protective but inactive forms (endospores, cysts, akinetes); on the physical side, gravity, air density and viscosity, thermal lofting, gravity waves, scavenging due to precipitation, and other airflow dynamics, as well as effective particle radius and electrical charge. They can also enable sampling strategy tests for airborne life detection, ranging from10 2 to10 8 viable cells/mL (10 -3 to 10 -9 cells/particle). Conversely, Earth's stratospheric sulfate layer lacks an active microbial presence, and is at a colder and less dense altitude but has partially analogous values in terms of H2SO4 and water concentration, particle size, and number density. These aerosols are accessible to aircraft and high-altitude balloons. Even more accessible potential analogs include sea spray, which overlaps with the smaller (haze) particle sizes and densities at Venus and contains trace organic constituents; marine fog, which at higher densities can match Venus’s larger (Mode 2) particle properties and contains a range of trace compounds including ammonia, phosphates, sulfates, and nitrates; and spray from acidic hydrothermal systems, which can cover a wide variety of sizes, densities, and chemical compositions. These analogs could improve the development of Venus cloud sampling instruments or sondes, including field tests of material compatibility, particle capture efficiency, and analysis sensitivity.

Analog↗
NASA NTRS1979

Positions and identifications of galactic X-ray sources

A catalog of compact Galactic X-ray sources with precise positions is presented together with a large bibliography. The catalog provides available X-ray, optical, and radio data for the 96 compact Galactic sources that have been identified and contains the most precise of the available optical, X-ray, or radio positions, the maximum and minimum published intensities, references to finding charts, and a comprehensive referenced list of X-ray, optical, and radio characteristics. The catalog also includes X-ray sources in the Magellanic clouds as well as all unidentified hard (greater than 2 keV) compact sources with an error radius of less than 60 arcsec and a Galactic latitude of less than 10 deg (absolute value). The sources list includes 14 X-ray Doppler or eclipsing binaries, seven or eight other X-ray pulsators, 23 transients or X-ray novae, 15 persistent bright bulge sources, seven X-ray sources associated with globular clusters, nine bursters, seven Galactic Center sources, and 18 other identified sources.

Bradt, H. V.↗
NASA NTRS2006

Evaluating Trichloroethylene Degradation Using Differing Nano- and Micro-Scale Iron Particles

Trichioroethylene, or TCE, is a central nervous system depressant and possible carcinogen, as well as a persistent groundwater pollutant. TCE exists in the aquifer either as free product in the form of a dense non-aqueous phase liquid (DNAPL) or as a dissolved-phase constituent. It is only slightly soluble in water, so dissolution of the contaminant is a long-term process and in-situ remediation is difficult. To remedy this, NASA and the University of Central Florida developed Emulsified Zero-Valent Iron, or EZVI. The emulsion droplet contains ZVI particles and water encapsulated by an oil/surfactant membrane, and effectively penetrates to degrade DNAPL-phase TCE. To maximize the efficiency of this process, several commercially available ZVIs of radically different particle sizes and morphologies both in emulsion and as neat (unemulsified) metal were evaluated for relative effectiveness at TCE degradation.

Berger, Cristina M.↗
DOE OSTI2023

Midwinter Dry Spells Amplify Post‐Fire Snowpack Decline

Abstract Increasing wildfire and declining snowpacks in mountain regions threaten water availability. We combine satellite‐based fire detections with snow seasonality classifications to examine fire activity in California's seasonal and ephemeral snow zones. We find a nearly tenfold increase in fire activity during 2020–2021 versus 2001–2019. Accumulation season broadband snow albedo declined 25%–71% at two burned sites (2021 and 2022) according to in‐situ data relative to un‐burned conditions, with greater declines associated with increased burn severity. By enhancing snowpack susceptibility to melt, both decreased snow albedo and canopy drove midwinter melt during a multi‐week dry spell in 2022. Despite similar meteorological conditions in December–February 2013 and 2022–linked to persistent high pressure weather regimes–minimal melt occurred in 2013. Post‐fire snowpack differences are confirmed with satellite measurements. With growing geographical overlap between wildfire and snow, our findings suggest California's snowpack is increasingly vulnerable to the compounding effects of dry spells and wildfire.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Emulating the Android Boot Process

Critical vulnerabilities continue to be discovered in the boot process of Android smartphones used around the world. The entire device's security is compromised if boot security is compromised, so any weakness presents undue risk to users. Vulnerabilities persist, in part, because independent security analysts lack access and appropriate tools. In response to this gap, we implemented a procedure for emulating the early phase of the Android boot process. This work demonstrated feasibility and utility of emulation in this space. By using HALucinator, we derived execution context and data flow, as well as incorporated peripheral hardware behavior. While smartphones with shared processors have substantial code overlap regardless of vendor, generational changes can have a significant impact. By applying our approach to older and modern devices, we learned interesting characteristics about the system. Such capabilities introduce new levels of introspection and operation understanding not previously available to mobile researchers.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

2024 OES-Environmental 2024 State of the Science Report, Chapter 1: Marine Renewable Energy and Ocean Energy Systems-Environmental

For many countries, marine renewable energy (MRE) is the most recent entry into their renewable energy portfolio. MRE involves the generation of energy from the movement of seawater including tides, waves, and persistent ocean currents, as well as from the gradients of temperature and salinity in the oceans. Some countries also include energy generation from the open waters of large rivers as part of MRE. Each MRE resource requires a different type of device to harvest that energy, placed in the appropriate portion and depth of the ocean or large river and secured to the seabed either by weight or by anchors. At full scale, these devices are large; Figure 1.1 puts the size of these devices in the context of other technologies and well-known landmarks for scale. The MRE devices generally represent the largest devices available.

16 TIDAL AND WAVE POWER↗
NASA NTRS2008

Monitoring the Black Hole Binary GRS 1758-258 with INTEGRAL and RXTE

The microquasar GRS 1758-258 is one of only three persistent black hole binaries that spend most of their time in the hard spectral state, the other two being Cyg X-l and 1E 1741.7-2942. It therefore provides the rare opportunity for an extensive long term study of this important black hole state which is associated with strong variability and radio jet emission. INTEGRAL has been monitoring the source since the first Galactic Center Deep Exposure season in spring 2003 during two 2-3 months long Galactic Center viewing epochs each year, amounting to 11 epochs including spring of 2008. With the exception of the last epoch quasi-simultaneous RXTE monitoring observations are available as well. Here we present an analysis of the epoch averaged broad band spectra which display considerable long term variability, most notably the occurrence of two soft/off states, extreme examples for the hysteretic behavior of black hole binaries. The hard source spectrum and long exposures allow us to extend the analysis for several epochs to approximately 800 keV using PICsIT data and address the question of the presence of a non-thermal Comptonization component.

Pottschmidt, Katja↗
NASA NTRS2014

Investigation of Unsteady Flow Field in a Low-Speed One and a Half Stage Axial Compressor: Effects of Tip Gap Size On the Tip Clearance Flow Structure at Near Stall Operation - Part 2

The primary focus of this paper is to investigate the effect of rotor tip gap size on how the rotor unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor at near stall operation (for example, where maximum pressure rise is obtained). A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at this flow condition with both a small and a large tip gaps. The numerically obtained flow fields at the small clearance matches fairly well with the available initial measurements obtained at the Johns Hopkins University with 3-D unsteady PIV in an index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. The numerical results are also compared with previously published measurements in a low speed single stage compressor (Maerz et al. [2002]). The current study shows that, with the smaller rotor tip gap, the tip clearance vortex moves to the leading edge plane at near stall operating condition, creating a nearly circumferentially aligned vortex that persists around the entire rotor. On the other hand, with a large tip gap, the clearance vortex stays inside the blade passage at near stall operation. With the large tip gap, flow instability and related large pressure fluctuation at the leading edge are observed in this one and a half stage compressor. Detailed examination of the unsteady flow structure in this compressor stage reveals that the flow instability is due to shed vortices near the leading edge, and not due to a three-dimensional separation vortex originating from the suction side of the blade, which is commonly referred to during a spike-type stall inception. The entire tip clearance flow is highly unsteady. Many vortex structures in the tip clearance flow, including the sheet vortex system near the casing, interact with each other. The core tip clearance vortex, which is formed with the rotor tip gap flows near the leading edge, is also highly unsteady or intermittent due to pressure oscillations near the leading edge and varies from passage to passage. For the current compressor stage, the evidence does not seem to support that a classical vortex breakup occurs in any organized way, even with the large tip gap. Although wakes from the IGV influence the tip clearance flow in the rotor, the major characteristics of rotor tip clearance flows in isolated or single stage rotors are observed in this one and a half stage axial compressor.

Unsteady↗
DOE OSTI2017

Sources of price dispersion in U.S. residential solar installations

Prices of solar PV have dropped dramatically, by half in just the past 6 years. But looking simply at prices paid today, there is considerable heterogeneity. For systems installed in 2014, the 10-90 percentile range for the observed $/W spans nearly a factor of 2. This apparent price dispersion raises policy relevant questions, such as: why are consumers paying more than they need to? And would better-informed consumers increase the social benefits of solar PV? This paper analyzes price dispersion in U.S. residential PV installations between 2008 and 2014. Focusing on the most commonly used metric in previous studies of price dispersion, we use the quarterly coefficient of variation (CV) as our measure of price dispersion. We find higher levels of price dispersion in our data (0.22) than the average of 55 previous studies we reviewed (0.16). We also find that price dispersion has been persistent; it has remained above 0.15 since 2000 with no trend over that period. If anything, price dispersion has been increasing recently during the period for which we have complete data, 2008-14. Econometric analysis of the factors affecting price dispersion supports theories from the economic literature focusing on access to information and the costs and benefits of consumer search. Factors that increase the consumer payoffs of investing time in searching for information—system size and the value of solar— are associated with lower levels of price dispersion. Factors that reduce the costs of search—neighbors who have recently installed solar and having third-party quotes available—are also associated with less price dispersion. These results provide support for the importance of public efforts to enhance access to price information, e.g. by supporting private sector price quote providers. The results also point to the particular need for information in nascent markets for PV in which access to the experience of neighbors is not available.

14 SOLAR ENERGY↗
NASA NTRS1987

The terminal area simulation system. Volume 2: Verification cases

The numerical simulation of five case studies are presented and are compared with available data in order to verify the three-dimensional version of the Terminal Area Simulation System (TASS). A spectrum of convective storm types are selected for the case studies. Included are: a High-Plains supercell hailstorm, a small and relatively short-lived High-Plains cumulonimbus, a convective storm which produced the 2 August 1985 DFW microburst, a South Florida convective complex, and a tornadic Oklahoma thunderstorm. For each of the cases the model results compared reasonably well with observed data. In the simulations of the supercell storms many of their characteristic features were modeled, such as the hook echo, BWER, mesocyclone, gust fronts, giant persistent updraft, wall cloud, flanking-line towers, anvil and radar reflectivity overhang, and rightward veering in the storm propagation. In the simulation of the tornadic storm a horseshoe-shaped updraft configuration and cyclic changes in storm intensity and structure were noted. The simulation of the DFW microburst agreed remarkably well with sparse observed data. The simulated outflow rapidly expanded in a nearly symmetrical pattern and was associated with a ringvortex. A South Florida convective complex was simulated and contained updrafts and downdrafts in the form of discrete bubbles. The numerical simulations, in all cases, always remained stable and bounded with no anomalous trends.

Proctor, F. H.↗
DOE OSTI2018

Metabolism and Evolution of a Biofuel-Producing Microbial Coculture

Specialized features of individual microbial species can be combined in coculture to produce useful fuels and chemicals. Cocultures can also be used to address how microbes cooperate in nature through metabolic interactions but with a level of experimental control that is not possible in natural systems. However, the challenge of maintaining stable microbial relationships and the limited assays available for studying single strains in consortia has impeded progress in characterizing and implementing synthetic communities. In this project, my lab developed a stable and highly reproducible H 2 biofuel-producing coculture between fermentative Escherichia coli and phototrophic Rhodopseudomonas palustris . In this coculture each species provides or 'cross-feeds' a nutrient that the other requires for growth. My lab used this coculture along with mathematical modeling to uncover basic principles governing mutualistic interactions between microbes, including (i) the potential for cross-fed nutrients to alternatively act as toxins depending on the level to which they are produced, (ii) how mutualistic cross-feeding can establish and persist in nutrient-deprived environments where the highest biofuel yields were observed, and (iii) the potential for competition between mutualistic partners for a cross-fed nutrient when that nutrient holds value for both species involved. In using ethanol-producing Zymomonas mobilis in place of E. coli in the coculture, my lab also discovered that Z. mobilis can use N 2 gas as a nitrogen source, with potential cost-savings for the industrial production of cellulosic ethanol.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

WATCHDOG: A COMPREHENSIVE ALL-SKY DATABASE OF GALACTIC BLACK HOLE X-RAY BINARIES

With the advent of more sensitive all-sky instruments, the transient universe is being probed in greater depth than ever before. Taking advantage of available resources, we have established a comprehensive database of black hole (and black hole candidate) X-ray binary (BHXB) activity between 1996 and 2015 as revealed by all-sky instruments, scanning surveys, and select narrow-field X-ray instruments on board the INTErnational Gamma-Ray Astrophysics Laboratory, Monitor of All-Sky X-ray Image, Rossi X-ray Timing Explorer, and Swift telescopes; the Whole-sky Alberta Time-resolved Comprehensive black-Hole Database Of the Galaxy or WATCHDOG. Over the past two decades, we have detected 132 transient outbursts, tracked and classified behavior occurring in 47 transient and 10 persistently accreting BHs, and performed a statistical study on a number of outburst properties across the Galactic population. We find that outbursts undergone by BHXBs that do not reach the thermally dominant accretion state make up a substantial fraction (∼40%) of the Galactic transient BHXB outburst sample over the past ∼20 years. Our findings suggest that this “hard-only” behavior, observed in transient and persistently accreting BHXBs, is neither a rare nor recent phenomenon and may be indicative of an underlying physical process, relatively common among binary BHs, involving the mass-transfer rate onto the BH remaining at a low level rather than increasing as the outburst evolves. We discuss how the larger number of these “hard-only” outbursts and detected outbursts in general have significant implications for both the luminosity function and mass-transfer history of the Galactic BHXB population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Interactions between cumulus convection and its environment as revealed by the MC3E sounding array

This study attempts to understand interactions between midlatitude convective systems and their environments through a heat and moisture budget analysis using the sounding data collected from the Midlatitude Continental Convective Clouds Experiment (MC3E) in central Oklahoma. Distinct large-scale structures and diabatic heating and drying profiles are presented for cases of weaker and elevated thunderstorms as well as intense squall line and supercell thunderstorm events during the campaign. The elevated cell events were nocturnal convective systems occurring in an environment having low convective available potential energy (CAPE) and a very dry boundary layer. In contrast, deeper convective events happened during the morning into early afternoon within an environment associated with large CAPE and a near-saturated boundary layer. As the systems reached maturity, the diagnosed diabatic heating in the latter deep convective cases was much stronger and of greater vertical extent than the former. Both groups showed considerable diabatic cooling in the lower troposphere, associated with the evaporation of precipitation and low-level clouds. The horizontal advection of moisture also played a dominant role in moistening the lower troposphere, particularly for the deeper convective events, wherein the near surface southeasterly flow allows persistent low-level moisture return from the Gulf of Mexico to support convection. The moisture convergence often was present before these systems develop, suggesting a strong correlation between the large-scale moisture convergence and convection. As a result, sensitivity tests indicated that the uncertainty in the surface precipitation and the size of analysis domain mainly affected the magnitude of these analyzed fields rather than their vertical structures.

54 ENVIRONMENTAL SCIENCES↗