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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

Baseline Vector Repeatability at the Sub-Millimeter Level Enabled by Radio Interferometer Phase Delays of Intra-Site Baselines

We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very-long-baseline interferometry (VLBI) observations rather than dedicated short-baseline experiments. An analysis of phase delay observables at X band from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24-hr VLBI sessions since 2019 yields weighted root-mean-square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N–WETTZELL enable an investigation of sources of error at the sub-millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the Up estimates of this baseline vector when atmospheric delays were estimated. Although the sub-millimeter repeatability has been achieved for the baseline vector WETTZ13N–WETTZELL, we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step toward the goal of global geodesy at the 1 mm level.

geodetic VLBI↗
DOE OSTI2023

Quantifying Burst Repeatability for Godiva IV

The minimum resolvable relative change in the neutron source emission of Godiva IV between bursts, i.e., burst repeatability, was quantified using a combination of activation monitors and a resistance temperature detector (RTD). Measurements support changes in the neutron source emission between bursts can be determined with a precision of 2.7%. The measurements were performed during a series of twelve Godiva IV bursts and were a collaborative effort between Los Alamos National Laboratory, Sandia National Laboratories, and Pacific Northwest National Laboratory. Gold, iron, nickel, and sulfur activation monitors were positioned in a sample holder in the central cavity of Godiva IV for each burst. The RTD is part of the Godiva burst diagnostic system and is in a fixed location in the safety block of Godiva IV. It is used to determine the temperature rise of the burst, i.e., the difference between the maximum temperature recorded during the burst and the initial temperature prior to the burst. Differences in either the specific activity of the activation monitor reactions, or the temperature rise can be used to determine the relative change in the neutron source emission for separate bursts, but historic results have proven that each method is susceptible to various sources of biases which generally cannot be isolated using a single method. We address this issue by applying both measurement methods and analyzing the correlation between them. The results presented in this work will be used to support future experiments with Godiva IV at the National Criticality Experiments Research Center (NCERC).

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

T-Toxin Virulence Genes: Unconnected Dots in a Sea of Repeats

In 1970 a corn disease epidemic ravaged fields in the United States to great economic loss. The outbreak was caused by a never-before seen, supervirulent strain of the fungal pathogen Cochliobolus heterostrophus. This was a plant disease epidemic, however, the current COVID-19 pandemic of humans is a stark reminder that novel, highly virulent, pathogens evolve with devastating consequences, no matter what the host-animal, plant, or other organism.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1962

LOW-ALTITUDE REPEATER SATELLITES

The new perspective that is forced upon us by the Space Age is oddly evident in the title of this paper. The key adjective is "low-altitude," evoking, perhaps, a picture of objects flying just above the rooftops. In the strange new realm of space, however, we are using a different order of measurement. The low-altitude satellites that I shall discuss will be moving in orbits anywhere from a few hundred to more than ten thousand miles above the Earth.

Low altitude↗
NASA NTRS2004

An L-band SAR for repeat pass deformation measurements on a UAV platform

We are proposing to develop a miniaturized polarimetric L-band synthetic aperture radar (SAR) for repeatpass differential interferometric measurements of deformation for rapidly deforming surfaces of geophysical interest such as volcanoes or earthquakes that is to be flown on a unmanned aerial vehicle (UAV or minimally piloted vehicle (MPV).

repeat pass interferometry↗
DOE OSTI2021

Repeated freeze-thaw cycles increase extractable, but not total, carbon and nitrogen in a Maine coniferous soil

Northeastern North America has been experiencing warmer winters with reduced snow accumulation, with more frequent winter freeze-thaw cycles. We conducted a laboratory experiment to investigate how increased frequency of freeze-thaw cycles (FTC) would alter soil C and N availability. Organic (O) and mineral (B) horizon soils were collected from a coniferous forest in Maine, processed to exclude roots, and then frozen in the laboratory (-10 °C) with one (FTC-1), two (FTC-2), or six (FTC-6) thaw periods. Soils were analyzed for extractable inorganic ammonium (NH4-N), water extractable organic carbon (WEOC), carbon dioxide flux (respiration), and total C and N. Extractable NH4-N increased following FTC, for both horizons. WEOC in O horizons had a lower SUVA254, indicating a stronger microbial influence (i.e., microbial cell lysis) in these soils after FTC. Respiration in O horizon soils decreased post-incubation and did not differ between FTC and Control soils. In the B horizon, however, FTC soils showed greater respiration than Control soils, suggesting that the newly available nutrients may have stimulated microbial activity. In contrast to these results, total C and N remained unaltered by FTC, presumably because the FTC disturbances represented mostly a translocation of C and N from one pool into another, and losses due to respiration were too small to significantly influence the large TC and TN pools. The effect of FTC on NH4-N did not change with FTC frequency, suggesting that a single FTC is sufficient to alter both C and N availability and quality, and that additional FTC may not have a significant further effect. This study provides fresh insights on how organic and mineral soils might respond to increased freeze-thaw frequency in winter.

Patel, Kaizad F.↗