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At least 1,549 records · Page 86
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Comparison of Bimodal Ice Shapes on Full-Chord and Hybrid CRM Midspan Models

An ice shape database has been created to document ice accretions on a full-chord length and hybrid versions of a 65 percent scale size of the mid-span section of the Common Research Model resulting from an exposure to a Super-cooled Large Drop (SLD) icing cloud with a bimodal drop size distribution. The ice shapes created were documented with photographs, laser scanned surface measurements over a section of the model span, and measurement of the ice mass over the same section of each ice accretion. Drop distribution effects were evaluated by using the same IRT icing conditions except with either monomodal or bimodal drop distributions. Ice shapes resulting from the bimodal distribution as well as from monomodal distributions of identical cloud droplet Median Volume Diameter (MVD) were obtained and compared. Results indicated that the ice shapes resulting from the monomodal and bimodal drop size distributions have similar 2D Maximum Combined Cross Section, or MCCS, ice shape around the model leading edge region and equivalent ice mass measurement per unit span to within the IRT SLD cloud calibration uncertainty, as expected with this approach, but the bimodal distributions have distinctly larger ice feathers that extended further back on the chord of the model. For most test conditions, the overall size and shape of the main ice accretions compared well between the full-chord and hybrid models.

Icing↗
NASA NTRS1998

The Effect of Solution Parameters on Lysozyme Nucleation Rates and Crystal Quality

In the pursuit of strongly diffracting high quality macromolecule crystals of suitable volume, this study investigates how the formation of macromolecules in solution and their growth characteristics effect crystal volume and diffracting quality. We systematically investigated the effect of solution conditions on lysozyme nucleation rates and the volume of crystals produced. Batch crystallization plates were used in combination with a video microscope system to measure nucleation rates and crystal volume. As expected from classical nucleation theory, crystal numbers were found to increase with increases in temperature and supersaturation. Small changes in solution pH, at constant supersaturation values were found, however, to dramatically effect the number of crystals nucleated in the wells varying from 1000s to 10s in the pH range 4.0 to 5.2. Having optimized the conditions required to produce an appropriate number of crystals of a suitable volume for X-ray analysis, a large number of uniform crystals were produced under exactly the same conditions. In the X-ray analysis of more than 50 such crystals there was found a wide variation in crystal lattice parameters and data quality. The variation in X-ray quality crystal samples is thought to be related to the growth rate variation caused by growth rate dispersion seen in lysozyme crystal growth experiments.

Judge, R. A.↗
NASA NTRS2013

Discontinuity Detection for Analysis of Telerobot Trajectories

To identify spatial and temporal discontinuities in telerobot movement in order to describe the shift in operators control and error correction strategies from continuous control to move-and-wait strategies. This shift was studied under conditions of simulated increasingly time-delayed teleoperation. The ultimate goal is to determine if the time delay associated with the shift is invariant with independently imposed control difficulty. We expect this shift to manifest itself as changes in the number of discontinuity of movement path. We proposed an approach to spatial and temporal discontinuity detection algorithm for analysis of teleoperated trajectory in three dimensional space. The algorithm provides a simple and potentially objective method for detecting the discontinuity during telerobot operation and evaluating the difficulty of rotational coordinate condition in teleoperation.

Yeom, Kiwon↗
DOE OSTI2020

Duality and supersymmetry constraints on the weak gravity conjecture

Positivity bounds coming from consistency of UV scattering amplitudes are not always sufficient to prove the weak gravity conjecture for theories beyond Einstein-Maxwell. Additional ingredients about the UV may be necessary to exclude those regions of parameter space which are naïvely in conflict with the predictions of the weak gravity conjecture. In this paper we explore the consequences of imposing additional symmetries inherited from the UV theory on higher-derivative operators for Einstein-Maxwell-dilaton-axion theory. Using black hole thermodynamics, for a preserved SL(2, $\mathbb{R}$) symmetry we find that the weak gravity conjecture then does follow from positivity bounds. For a preserved O(d, d; $\mathbb{R}$) symmetry we find a simple condition on the two Wilson coefficients which ensures the positivity of corrections to the charge-to-mass ratio and that follows from the null energy condition alone. We find that imposing supersymmetry on top of either of these symmetries gives corrections which vanish identically, as expected for BPS states.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Exploring Material Solutions for Supercritical CO 2 Applications above 800 °C

There has been recent interest in exploring revolutionary supercritical CO 2 (sCO 2 ) power cycles, and this exploratory investigation was seeking materials with CO 2 compatibility at up to 1200 °C. Here, initial exposures were conducted at 0.1 and 2 MPa CO 2 for up to 1000 h at 900–1200 °C. As expected, specimens of Mo and W that might be used as matrix materials in cermets were rapidly attacked under these conditions. Even an alumina-forming FeCrAlMo alloy showed high mass gains in less than 100 h at 1200 °C due to the formation of Fe-rich oxide. However, at 900–1100 °C, more protective behavior was observed for FeCrAlMo specimens, with or without pre-oxidation, in 0.1 MPa CO 2 , but increased attack was observed in 2 MPa CO 2 . In contrast, most Ni-based alloys exposed at 900–1100 °C showed higher mass gains and thicker reaction products than formed in air. Thus, Ni-based alloys appear less compatible with CO 2 environments above 800 °C compared to lower temperatures. Low mass gains were observed for CVD SiC at 900–1200 °C, but MoSi 2 and Mo(Si,Al) 2 specimens did not form protective scales under these conditions at 1000 and 1100 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Influence of high-strain-rate compression and subsequent heat treatment on (TiNbZr) 89 (AlTa) 11 refractory high-entropy alloys: Dynamic-mechanical behavior and microstructural changes

This study explored the dynamic-mechanical behavior of a novel low-density (TiNbZr) 89 (AlTa) 11 refractory high-entropy alloy (RHEA) across strain rates ranging from 1.0×10 3 to 3.5×10 3 s –1 . A significant increase in the yield and ultimate compressive strengths with rising strain rates up to 3.0×10 3 s –1 was observed and attributed to enhanced dislocation activities and stress-induced microstructural transformations. The formation of the B2 phase and Zr 5 Al 3 precipitates was found to be crucial in bolstering the alloy strength at high strain rates. Beyond strain rates of 3.0×10 3 s –1 , a decrease in strength occurred due to thermal softening and strain localization. Microstructural analyses at 3.5×10 3 s –1 revealed grain refinement, the development of micro shear bands, and dislocation tangles, which were indicative of dynamic recrystallization. Besides, the findings also revealed that the post-dynamic compression heat treatment further enhanced the hardness and microstructural stability of the alloy. These results highlight the potential of the (TiNbZr) 89 (AlTa) 11 RHEA for applications requiring materials with high strength-to-weight ratios, particularly in dynamically loaded environments. It is expected that the results of this study will further advance our fundamental understanding of the behavior of RHEAs under extreme conditions, thereby opening new avenues for material innovation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Empirical Dynamic Modeling Reveals Complexity of Methane Fluxes in a Temperate Salt Marsh

Abstract Methane dynamics within salt marshes are complex because vegetation types, temperature, oscillating water levels, and changes in salinity and redox conditions influence CH 4 production, consumption, oxidation, and emissions. These non‐linear and complex interactions among variables affect the traditionally expected functional relationships and present challenges for interpreting and developing process‐based models. We employed empirical dynamic modeling (EDM) and convergent cross mapping (CCM) as a novel approach for characterizing seasonal/multiday and diurnal CH 4 dynamics by inferring causal variables, lags, and interconnections among multiple biophysical variables within a temperate salt marsh using 5 years of eddy covariance data. EDM/CCM is a nonparametric approach capable of quantifying the coupling between variables while determining time scales where variable interactions are the most relevant. We found that gross primary productivity, tidal creek dissolved oxygen, and temperature were important for seasonal/multiday dynamics (rho = 0.73–0.80), while water level was most important for diurnal dynamics during both the growing and dormancy phenoperiods (rho = 0.72 and 0.56, respectively). Lags for the top‐ranked variables (i.e., gross primary productivity, dissolved oxygen, temperature, water level) occurred between 1 and 5 weeks at the seasonal scale and 1–24 hr at the diurnal scale. The EDM had high prediction capabilities for intra‐/inter‐seasonal patterns and annual CH 4 sums but had limitations in representing large, infrequent fluxes. Results highlight the importance of non‐linearity, drivers, lag times, and interconnections among multiple biophysical variables that regulate CH 4 fluxes in tidal wetlands. This research introduces a novel approach to examining CH 4 fluxes, which will aid in evaluating current paradigms in wetlands and other ecosystems.

Environmental Sciences & Ecology↗
DOE OSTI2022

Tin removal by an annular surface wave plasma antenna in an extreme ultraviolet lithography source

Tin contamination of the collector mirror surface remains one of the crucial issues of EUV (Extreme Ultraviolet) sources, directly impacting the availability of the tool. Hydrogen plasma-based tin removal processes employ hydrogen radicals and ions to interact with tin deposits to form gaseous tin hydride (SnH 4 ), which can be removed through pumping. An annular surface wave plasma (SWP) source developed at the University of Illinois—Urbana Champaign is integrated into the cone and perimeter of the collection mirror for in situ tin removal. The SWP is characterized by high ion and radical densities, low electron temperature, and local generation where etching is needed. This method has the potential to significantly reduce downtime and increase mirror lifetime. Radical probe measurements show hydrogen radical densities in the order of 10 19 m -3 , while Langmuir probe measurements show electron temperatures of up to 6 eV and plasma densities on the order of 10 17–18 m -3 . The generated ions are essential to the tin cleaning and have sufficiently low energy to cause no damage to the collector capping layer. Tin etch rates of up to 270 nm/min were observed in a variety of experimental conditions, including various powers, pressures, flowrates, and temperatures. In conclusion, the high etch rates demonstrated in this study exceed the expected contamination rate of the EUV source.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

A MOOSE-Based Model for Fission Product Transport and Source Term Estimation for High-Temperature Gas-Cooled Reactors

Thanks to fuel elements containing tristructural isotropic (TRISO) particles combined with a low core power density and passive feedback mechanisms leading to modest temperature rises in the event of accidental events, high-temperature gas-cooled reactors (HTGRs) offer a high degree of reliability in terms of fission product retention. While the anticipated source term for HTGRs is expected to be very low, it is important to provide a quantitative estimate of radiological releases during nominal and accidental conditions. Here, we propose a computationally efficient mechanistic source term methodology relying on the Multiphysics Object Oriented Simulation Environment (MOOSE) for tracking fission product transport from TRISO particles up to the coolant pressure boundary, as well as modeling the transport and potential deposition of these nuclides inside the reactor coolant loop. The proposed computational scheme is applied to estimate source term inventories for a representative 10-MW(thermal) prismatic high-temperature microreactor and is qualitatively compared against known release fractions. In addition to providing an alternate analysis tool, this MOOSE model can help reactor designers quantify the influence of key design parameters relevant for studies of radiological dose consequences.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Engineering microalgal cell wall-anchored proteins using GP1 PPSPX motifs and releasing with intein-mediated fusion

AbstractHarnessing and controlling the localization of recombinant proteins is critical for advancing applications in synthetic biology, industrial biotechnology, and drug delivery. This study explores protein anchoring and controlled release inChlamydomonas reinhardtii, providing innovative tools for these fields. Using truncated variants of the GP1 glycoprotein fused to the plastic-degrading enzyme PHL7, we identified the PPSPX motif as essential for anchoring proteins to the cell wall. Constructs with increased PPSPX content exhibited reduced secretion but improved anchoring, pinpointing the potential anchor-signal sites of GP1 and highlighting the distinct roles of these motifs in protein localization. Building on the anchoring capabilities established with these glycomodules, we also demonstrated a controlled release system using a pH-sensitive intein derived from RecA fromMycobacterium tuberculosis. This intein efficiently cleaved and released PHL7 and mCherry that was fused to GP1 under acidic conditions, enabling precise temporal and environmental control. At pH 5.5, fluorescence kinetics demonstrated significant mCherry release from the pJPW4mCherry construct within 4 hours. In contrast, release was minimal under pH 8.0 conditions and negligible for the pJPW2mCherry (W2) control, irrespective of the pH. Additionally, bands on the Western blot at the expected size of mCherry also showed its efficient release from the mCherry::intein::GP1 fusion protein at pH 5.5. Conversely, at pH 8.0, no bands were detected. This anchor-release approach offers significant potential for drug delivery, biocatalysis, and environmental monitoring applications. By integrating glycomodules and pH-sensitive inteins, this study establishes a versatile framework for optimizing protein localization and release inC. reinhardtii, with broad implications for proteomics, biofilm engineering, and scalable therapeutic delivery systems.Graphical Abstract

Kang, Kalisa (ORCID:0009000619398129)↗
DOE OSTI2022

Perovskite solar cells can take the heat

Solar panels must endure extreme conditions during their service lifetime. There are few other products, let alone pristine semiconductor electronics, that are manufactured today and expected to withstand decades of abuse from full exposure to outdoor elements, including harsh ultraviolet sunlight, rain and hail, and daily and seasonal thermal cycles. Over the past decade, a new class of semiconductors, known as metal halide perovskites, has emerged, which constitutes the light-absorbing material in solar panels and has made incredible advancements, potentially taking photovoltaics in new directions. Perovskite materials have been touted as a potential game changer for solar energy production.

14 SOLAR ENERGY↗
DOE OSTI2020

IEA/HPT Annex 53 Advanced Cooling/Refrigeration Technologies Development – Task 1 Report

Air conditioning (AC) and refrigeration systems account for a large share of today’s global energy consumption, and this demand is expected to increase sharply over the next 50 years unless actions are taken to ameliorate the increase. The adoption of AC in developed countries increased rapidly in the twentieth century, and the twenty-first century is expected to see increased adoption in developing countries—especially those with hotter climates and large, growing populations, such as India, China, Brazil, and Middle Eastern and African nations. The International Energy Agency (IEA) projects that by 2050, AC energy consumption levels will increase by 4.3 times over the 2010 levels for non-Organization of Economic Coordination and Development (OECD) countries vs. only 1.5 times for OECD countries (Figure 1).

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Synthesis and Photonic Sintering of Proton Conducting Lanthanide Nickelates

Lanthanide nickelate perovskites are known proton conductors at intermediate temperatures (350-600°C). They are attractive targets for proton conducting fuel cells and electrolyzers due to their operational temperature range and their stability in the presence of CO 2 . These materials have the formula LNiO 3 , with the lanthanide L = La, Ce, Pr, Nd, or Sm. Sintering is challenging due to phase transformations that occur at lower temperatures than those required for sintering. In this project, a series of lanthanide nickelate perovskites was synthesized via both a precursor solid solution method and the glycine nitrate process. Powders derived from the precursor solid solution method for LaNiO 3 and NdNiO 3 were sintered at Utility Global Inc. at various temperatures utilizing fast photonic sintering. LaNiO 3 was successfully sintered while maintaining the perovskite phase. NdNiO 3 underwent a phase transformation at all the conditions tested. The stability of the perovskite phase decreases moving right across the lanthanides in the periodic table, while the expected proton conductivity increases. These results will inform further investigations into lanthanide nickelate perovskites toward the goal of producing a free-standing, sintered, proton-conducting membrane.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Time-Delay Cosmography: Spectroscopy of Galaxies in the Environment of the J1537 Lensed Quasar System

Due to their sufficient distances and prevalence, lensed quasars have been a key site for research in gravitational lensing. In particular, researchers are interested in constraining Hubble's constant by measuring time delays in the arrival times of multiply imaged quasars. However, a lens model will need to be created that accounts for not just the lensing galaxy, but also any perturbers nearby that could affect the light path. Here, the J1537-3010 lensed quasar environment is investigated, and redshifts of 62 targets have been identified using Gemini IRAF and RASCAL. The success rate is roughly 45% across all four masks, less than the expected 60%-70%. We expect that masking out a bad amplifier contributed to the lower redshift measurement rates, as well as potentially poor viewing conditions during observation. With these redshifts, flexion shifts can be measured to determine if the observed target should be included in the lens model. An accurate lens model is fundament al for constraining the measurements of the time-delays of the quasar images and, thereby, constraining measurements in Hubble’s constant.

Kharchilava, George V.↗
NASA NTRS1976

Electron parameter correlations in high-speed streams and heat flux instabilities

Statistical electron parameter correlations associated with high-speed streams are determined with the aim of identifying one or more locally active solar wind heat flux instabilities. Evidence that points toward local regulation of the heat flux at 1 AU is presented, and the results of a search for special signatures expected from the action of the Alfven, magnetosonic, and whistler flux instabilities are discussed. It is shown that under certain conditions, the whistler mode can be active in regulating the heat flux at 1 AU.

Feldman, W. C.↗
NASA NTRS1976

H2 molecules and the intercloud medium

The paper discusses expected column densities of H2 in the intercloud medium and the possible use of molecules as indicators of intercloud physical conditions. Molecule formation by the H(-) process and on graphite grains is treated, and it is shown that the Barlow-Silk hypothesis of a 1-eV semichemical hydrogen-graphite bond leads to a large enhancement of the intercloud molecule-formation rate. Rotational-excitation calculations are presented for both cloud and intercloud conditions which show, in agreement with Jura (1975), that the presently observed optically thin H2 absorption components are more likely to originate in cold clouds than in the intercloud medium.

Hill, J. K.↗
NASA NTRS1980

Evaluation of the cyclic behavior of aircraft turbine disk alloys, part 2

Several nickel-base aircraft turbine disk superalloys were evaluated at 650 C for resistance to fatigue crack initiation and propagation under cyclic and cyclic/dwell conditions. Controlled strain low cycle fatigue (LCF) and controlled load crack propagation tests were performed and results utilized to provide a direct comparison among the alloys. Tests were performed on selected alloys to evaluate the effects of hold times, mean stresses, stress-dwell cycle types, inert environment, and contractor test methods. At the lower total strain ranges of interest, the alloys exhibited generally increasing initiation life with increasing tensile strength for both cyclic (0.33 Hz) and cyclic/dwell (900-sec hold per cycle) conditions. Rank order of the alloys by LCF initiation life changed substantially at higher strain ranges, approaching the rank order expected from monotonic tensile ductilities. The effect of the 900 sec (15 min) hold time fatigue life varied significantly from alloy to alloy. Generally, the higher-strength, finer-grained alloys exhibited more significant reductions in fatigue life due to the dwell. The effects of mean strain were found to be negligible and the effects of mean stress were pronounced. At high strain ranges the mean stress was near zero and did not contribute to reduction in life. At low strain ranges, however, mean stresses were large and significant reductions in LCF lives occurred.

Cowles, B. A.↗
NASA NTRS1981

The Comet Halley handbook: An observer's guide

The orbit of Comet Halley is described as well as its expected physical behavior (brightness, tail lengths, coma diameters) in 1985-1986 during which time its preperihelion positon will allow better conditions for Northern Hemisphere observers. Southern Hemisphere observers will prefer post perihelion observation. Ephemeris data for 1981-1987 are presented in tables.

Yeomans, D. K.↗