SEARCH · Search NASA
Results for “aging”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The ice age ecologist: testing methods for reserve prioritization during the last global warming: Reserve selection and the ice age ecologist
We play the role of an ice age ecologist (IAE) charged with conserving biodiversity during the climate changes accompanying the last deglaciation. We develop reserve-selection strategies for the IAE and check them against rankings based on modern data. Three reserve-selection strategies are developed. (1) Abiotic: the IAE uses no information about species–climate relationships, instead maximizing the climatic and geographic dispersion of reserves. (2) Species distribution models (SDMs): the IAE uses boosted-regression trees calibrated against pollen data and CCSM3 palaeoclimatic simulations from 21 to 15 ka bp to predict modern taxon distributions, then uses these as input to the Zonation reserve-ranking program. (3) Rank-and-regress: regression models are used to identify climatic predictors of zonation rankings. All strategies are assessed against a Zonation ranking based on modern pollen distributions. Analysis units are ecoregions and grid cells. The abiotic strategy has a negative or no correlation between predicted and actual rankings. The SDM-based strategy fares better, with a significantly positive area-corrected correlation (r= 0.474, P < 0.001) between predicted and actual rankings. Predictive ability drops when grid cells are the analysis unit (r= 0.217, P = 0.058). Predictive ability for the rank-and-regress strategy is similar to the SDM results. For the IAE, SDMs improve the predictive ability of reserve-selection strategies. However, predictive ability is limited overall, probably due to shifted realized niches during past no-analogue climates, new species interactions as species responded individually to climate change, and other environmental changes not included in the model. Twenty-first-century conservation planning also faces these challenges, and is further complicated by other anthropogenic impacts. The IAE's limited success does not preclude the use of climate scenarios and niche-based SDMs when developing adaptation strategies, but suggests that such tools offer at best only a rough guide to identifying possible areas of future conservation value.
Structural relaxation and aging scaling in the Coulomb and Bose glass models
We employ Monte Carlo simulations to study the relaxation properties of the two-dimensional Coulomb glass in disordered semiconductors and the three-dimensional Bose glass in type-II superconductors in the presence of extended linear defects. We investigate the effects of adding non-zero random on-site energies from different distributions on the properties of the correlation-induced Coulomb gap in the density of states (DOS) and on the non-equilibrium aging kinetics highlighted by the density autocorrelation functions. Here, we also probe the sensitivity of the system’s equilibrium and non-equilibrium relaxation properties to instantaneous changes in the density of charge carriers in the Coulomb glass or flux lines in the Bose glass.
2023 SRNL Aging and Lifetimes Report: Tritium Aging of Welded and Additively Manufactured Austenitic Stainless Steels
This report documents work performed in fiscal year 2023 at Savannah River National Laboratory (SRNL) collaborating with Sandia National Laboratories in support of the Aging and Lifetimes program. This work supports Gas Transfer Systems (GTS) design by measuring the mechanical behavior of structural materials used in GTS. Data on properties in relevant conditions are crucial for GTS lifetime assessments and predictions. To simulate relevant conditions, SRNL, in concert with the Savannah River Site, thermally pre-charges test specimens with tritium and stores them at -80°C to allow the tritium decay product, helium-3, to build up while limiting tritium diffusion. According to test plans based on how much helium-3 has accumulated, specimens are removed from storage and tested. Results from mechanical testing provide an empirical basis for GTS design as well as insight to how these structural materials degrade in a tritium environment.
Radiation ages and gas-retention ages of carbonaceous chondrites and of unequilibrated ordinary chondrites
Radiation and gas retention ages of chondrites from mass spectrometry of helium, neon, and argon
Radiation ages and gas-retention ages of carbonaceous chondrites and unequilibrated ordinary chondrites.
Radiation and gas retention ages of carbonaceous and unequilibrated ordinary chondrites from primordial inert gases determinations by mass spectrometry
Rb-Sr ages of igneous rocks from the Apollo 14 mission and the age of the Fra Mauro formation.
Internal Rb-Sr isochrons were determined on four basaltic rocks and on a basaltic clast from a breccia from the Fra Mauro landing site. An internal isochron was determined for rock 12004 and yielded a value in agreement with previous results for basaltic rocks from the Apollo 12 site. The crystallization ages for Apollo 14 basalts are only 0.2 to 0.3 AE older than were found for mare basalts from the Sea of Tranquility. Assuming these leucocratic igneous rocks to be representative of the Fra Mauro site, it follows that there were major igneous processes active in these regions, and presumably throughout the highlands, at times only slightly preceding the periods at which the maria were last flooded.
Rb-Sr age of a Luna 16 basalt and the model age of lunar soils.
An internal isochron was determined on a small basalt fragment (sample B-1) returned from the Luna 16 mission, which yields an age of 3.42 plus or minus 0.8 b.y. and a low initial Sr87/Sr86 value. A comparison is made of the data from four lunar missions to mare sites which shows that the last period of major flooding of the mare basins is confined to a narrow time interval of only 0.55 b.y. The direct evidence of major lunar magmatic activity appears to be confined to the interval from 3.1 to 4.0 b.y. The Sr87/Sr86 values for all mare basalts are extremely primitive and lie in a rather narrow range. A diagram is given for initial Sr87/Sr86 as a function of time for all lunar rocks.
Cosmic ray exposure ages of Apollo 17 samples and the age of Tycho
Cosmic ray exposure data for Apollo 17 samples and quantitative photogeologic data are presented which support the hypothesis that the Central Cluster unit and the Bright Mantle at the Apollo 17 landing site are related to impact of ejecta from the crater Tycho, lying about 2000 km to the southwest. The exposure ages point to a site-wide event 96 m.y ago, which included emplacement of the Bright Mantle and Central Cluster units.
Are Noachian-age ridged plains (Nplr) actually Early Hesperian in age?
The Nplr ridged plains studied are quite thin (less than 150 m, with some less than 90 m) based on the smallest surviving craters from the different preserved crater retention surfaces. The thinness of the Nplr ridged plains permits craters from older surfaces to show through, leading to a greater total crater count than actually applies to the ridged-plains component of those surfaces. It is found that the ridged-plains mapped as Noachian-age Nplr actually resurfaced older Noachian cratered terrain in the Early Hesperian, creating crater retention surfaces of N(1) equals (25,000 +/- 3000) in the Memnonia and Argyre regions.
Implications of early Hesperian ages for presumed Noachian age volcanic flows on Mars
Volcanic resurfacing has been important in Martian history. Major common-age resurfacing events are recorded in the cumulative frequency curves for the highland/lowland transition zone in eastern Mars and elsewhere. Most obvious in all these regions is a major resurfacing at the early hesperian (EH) time of ridged plains (unit Hr) eruption in Lunae Planum and elsewhere. This event seems to have occurred with greater or lesser efficiency in nearly all terrains studied: ridged plains, knobby terrain, smooth plains, and adjacent cratered terrain. Volcanic processes have apparently dominated all other sources of resurfacing (aeolian, periglacial, impact, fluvial) throughout all Martian history.
Calendar and PHEV Cycle Life Aging of High-Energy, Lithium-Ion Cells Containing Blended Spinel and Layered-Oxide Cathodes
One hundred seven commercially available, off-the-shelf, 1.2-Ah cells were tested for calendar life and CS cycle- and CD cycle-life using the new USABC PHEV Battery Test Manual. Here, the effects of temperature on calendar life, on CS cycle life, and on CD cycle life; the effects of SOC on calendar life and on CS cycle life; and the effects of rest time on CD cycle life were investigated. The results indicated that the test procedures caused performance decline in the cells in an expected manner, calendar < CS cycling < CD cycling. In some cases, the kinetic law changed with test type, from linear-with-time to about t2. Additionally, temperature was found to stress the cells more than SOC, causing increased changes in performance with increasing temperature.
Compression Testing of Aged Low Density Flexible Polyurethane Foam.
Abstract not provided.
X-ray diffraction, differential scanning calorimetry and evolved gas analysis of aged plutonium tetrafluoride (PuF4)
A 30 year-old PuF4 sample consisting of brown powder (PuF4-b) and pink granules (PuF4-p) was analyzed. X-ray difraction shows the bulk is comprised of three compounds: PuF4, PuO2, and PuF4·1.6H2O. Broadening of PuF4 XRD peaks suggests possible a-damage. After annealing at 650 °C, crystalline PuF4 and PuO2 remain. Thermogravimetric analysis and diferential scanning calorimetry—with simultaneous evolved gas analysis—of the separated PuF4-p and PuF4-b components reveal a distinct sequence of reactions. Dehydration occurs between~90 and 300 °C. Exothermic annealing of the a-damage occurs in two stages: at 350–355 °C and at 555–558 °C. Hydrofuoric acid, fuorine and helium desorb during the frst exotherm. Above 700 °C, PuF4 reacts with PuO2, resulting in oxygen release and mass loss.
Temporal evolution of a model Co-Al-W superalloy aged at 650 °C and 750 °C
Not Available