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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Investigating rapid alpha-decay induced aging of 238 PuO 2 by Raman Spectroscopy

Investigating alpha-decay induced aging in PuO 2 is useful in nuclear forensics; helping to determine the time since last calcination. This was previously investigate by monitoring the damage to 240 PuO 2 over the course of a few years. The rate of alpha-decay induced aging has long been assumed to scale only with the decay rate of other isotopes without direct verification. This article reports the first alpha-decay aging study of 238 PuO 2 by Raman spectroscopy. Contrary to the expected 10 days for 238 PuO 2 to reach steady state based on 240 PuO 2 studies, the alpha aging curve reached an approximate steady state ∼24–30 h after laser annealing. While the cause of the order of magnitude decrease is unknown, it is speculated that dynamic annealing could contribute to the differences in rate of induced aging. The Raman spectra of annealed and aged 238 PuO 2 matched the expected features in 239 PuO 2 and 240 PuO 2 spectra; showing no formation of new stable chemical species in the material such as secondary Pu oxide phases (e.g., Pu 4 O 9 ). In conclusion, results indicate that 238 Pu could be leveraged for rapid alpha-decay aging studies to characterize alpha-decay induced features and better understand matrix temperatures and the annealing of Frankel pair defects.

Actinide↗
DOE OSTI2018

Mechanical behavior and texture development of over-aged and solution treated Al-Cu-Mg alloy during multi-directional forging

The effects of initial heat treatments, i.e. solution treating and over ageing, on deformation behavior of an age hardenable Al-Cu-Mg alloy, including mechanical properties and texture evolution, during multi-directional forging (MDF) are investigated. Hardness measurements, electron back scatter diffraction (EBSD) maps, and differential scanning calorimetry (DSC) are carried out. Mechanical behaviors of the alloy in terms of compressive stress and hardness test after MDF are investigated. In both solution treated and over-aged alloys, the compressive stress during MDF shows an increase up to the second pass, and by further straining the flow stress is decreased. However, shear and deformation bands are formed in both solution treated and over-aged alloys, the density of these instabilities in the solution treated alloy is higher than that in over-aged alloy. In the solution treated alloy, not only large particles induce deformation bands, but also the dynamically formed GPB zones/Cu-Mg co-clusters. Texture analysis shows that the shear component of C {001}<110> (Φ{sub 1} = 90°, Φ = 0°, Φ{sub 2} = 45°) is developed with 18 mrd during MDF of the over-aged alloy. In the solution treated alloy, due to the high density of deformation bands and different microchemistry of the matrix in comparison with that of the over-aged alloy, the Copper type texture component {112}<111> (Φ{sub 1} = 90°, Φ = 35°, Φ{sub 2} = 45°) is developed with 11 mrd.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Metabolic brain networks in aging and preclinical Alzheimer's disease

Metabolic brain networks can provide insight into the network processes underlying progression from healthy aging to Alzheimer's disease. We explore the effect of two Alzheimer's disease risk factors, amyloid-β and ApoE ε4 genotype, on metabolic brain networks in cognitively normal older adults (N = 64, ages 69–89) compared to young adults (N = 17, ages 20–30) and patients with Alzheimer's disease (N = 22, ages 69–89). Subjects underwent MRI and PET imaging of metabolism (FDG) and amyloid-β (PIB). Normal older adults were divided into four subgroups based on amyloid-β and ApoE genotype. Metabolic brain networks were constructed cross-sectionally by computing pairwise correlations of metabolism across subjects within each group for 80 regions of interest. We found widespread elevated metabolic correlations and desegregation of metabolic brain networks in normal aging compared to youth and Alzheimer's disease, suggesting that normal aging leads to widespread loss of independent metabolic function across the brain. Amyloid-β and the combination of ApoE ε4 led to less extensive elevated metabolic correlations compared to other normal older adults, as well as a metabolic brain network more similar to youth and Alzheimer's disease. This could reflect early progression towards Alzheimer's disease in these individuals. Altered metabolic brain networks of older adults and those at the highest risk for progression to Alzheimer's disease open up novel lines of inquiry into the metabolic and network processes that underlie normal aging and Alzheimer's disease.

Neurosciences & Neurology↗
DOE OSTI2024

Adhesion and Contact Aging of Acrylic Pressure-Sensitive Adhesives to Swollen Elastomers

Fluid-infused (or swollen) elastomers are known for their antiadhesive properties. The presence of excess fluid at their surface is the main contributor to limiting contact formation and minimizing adhesion. Despite their potential, the mechanisms for adhesion and contact aging to fluid-infused elastomers are poorly understood beyond contact with a few materials (ice, biofilms, glass). This study reports on adhesion to a model fluid-infused elastomer, poly(dimethylsiloxane) (PDMS), swollen with silicone oil. The effects of oil saturation, contact time, and the opposing surface are investigated. Specifically, adhesion to two different adherents with comparable surface energies but drastically different mechanical properties is investigated: a glass surface and a soft viscoelastic acrylic pressure-sensitive adhesive film (PSA, modulus ~25 kPa). Adhesion between the PSA and swollen PDMS [with 23% (w/w) silicone oil] retains up to 60% of its value compared to contact with unswollen (dry) PDMS. In contrast, adhesion to glass nearly vanishes in contact with the same swollen elastomer. Adhesion to the PSA also displays stronger contact aging than adhesion to glass. Contact aging with the PSA is comparable for dry and unsaturated PDMS. Moreover, load relaxation when the PSA is in contact with the PDMS does not correlate with contact aging for contact with the dry or unsaturated elastomer, suggesting that contact aging is likely caused by chain interpenetration and polymer reorganization within the contact region. Closer to full saturation of the PDMS with oil, adhesion to the PSA decreases significantly and shows a delay in the onset of contact aging that is weakly correlated to the poroelastic relaxation of the elastomer. Additional confocal imaging suggests that the presence of a layer of fluid trapped at the interface between the two solids could explain the delayed (and limited) contact aging to the oil-saturated PDMS.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Landscape Age as a Major Control on the Geography of Soil Weathering

Global-scale models of rock-derived nutrient availability often assume that physical erosion drives soils toward an approximate “steady state” over geologic timescales. By definition, steady-state models do not represent landscape age—that is, the time elapsed since soil formation is initiated by major erosional or depositional events. We hypothesize that this steady-state assumption has large consequences on estimates of soil fertility because landscape age can mediate the retention of mobile elements in soil, particularly in low-relief landscapes and humid climates. We quantified the effect of landscape age on soil fertility by estimating Na retention in soils across the United States and explicitly resolving landscape age in regions that experienced significant deposition or glacial retreat after the Last Glacial Maximum (LGM). We then used a simple one-compartment model to simulate soil formation and weathering, comparing predictions that incorporated landscape age with those based on the steady-state assumption. We found that soils formed in LGM deposits in low-relief, humid settings generally retain 10 times more Na than soils formed outside of LGM deposits. Furthermore, the model that accounted for landscape age outperformed a steady-state model across the United States and increased globally averaged estimates of Na retention by 17%. These results reinforce the idea that landscape age is a major control on weathering and should not be ignored in simulations of nutrient cycling.

58 GEOSCIENCES↗
DOE OSTI2022

Short term treatment with a cocktail of rapamycin, acarbose and phenylbutyrate delays aging phenotypes in mice

Pharmaceutical intervention of aging requires targeting multiple pathways, thus there is rationale to test combinations of drugs targeting different but overlapping processes. In order to determine if combining drugs shown to extend lifespan and healthy aging in mice would have greater impact than any individual drug, a cocktail diet containing 14 ppm rapamycin, 1000 ppm acarbose, and 1000 ppm phenylbutyrate was fed to 20-month-old C57BL/6 and HET3 4-way cross mice of both sexes for three months. Mice treated with the cocktail showed a sex and strain-dependent phenotype consistent with healthy aging including decreased body fat, improved cognition, increased strength and endurance, and decreased age-related pathology compared to mice treated with individual drugs or control. The severity of age-related lesions in heart, lungs, liver, and kidney was consistently decreased in mice treated with the cocktail compared to mice treated with individual drugs or control, suggesting an interactive advantage of the three drugs. This study shows that a combination of three drugs, each previously shown to enhance lifespan and health span in mice, is able to delay aging phenotypes in middle-aged mice more effectively than any individual drug in the cocktail over a 3-month treatment period.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

THE AGES OF HIGH-MASS X-RAY BINARIES IN NGC 2403 AND NGC 300

We have examined resolved stellar photometry from HST imaging surrounding 18 high-mass X-ray binary (HMXB) candidates in NGC 300 and NGC 2403 as determined from combined Chandra/HST analysis. We have fit the color-magnitude distribution of the surrounding stars with stellar evolution models. All but one region in NGC 300 and two in NGC 2403 contain a population with an age between 20 and 70 Myr. One of the candidates is the ultraluminous X-ray source in NGC 2403, which we associate with a 60 {+-} 5 Myr old population. These age distributions provide additional evidence that 16 of these 18 candidates are HMXBs. Furthermore, our results suggest that the most common HMXB age in these galaxies is 40-55 Myr. This preferred age is similar to observations of HMXBs in the Small Magellanic Cloud, providing new evidence of this formation timescale, but in higher metallicity populations. We suggest that this preferred HMXB age is the result of the fortuitous combination of two physical effects. First, this is the age of a population when the greatest rate of core-collapse events should be occurring, maximizing neutron star production. Second, this is the age when B stars are most likely to be actively losing mass. We also discuss our results in the context of HMXB feedback in galaxies, confirming HMXBs as a potentially important source of energy for the interstellar medium in low-mass galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A BAYESIAN APPROACH TO DERIVING AGES OF INDIVIDUAL FIELD WHITE DWARFS

We apply a self-consistent and robust Bayesian statistical approach to determine the ages, distances, and zero-age main sequence (ZAMS) masses of 28 field DA white dwarfs (WDs) with ages of approximately 4-8 Gyr. Our technique requires only quality optical and near-infrared photometry to derive ages with <15% uncertainties, generally with little sensitivity to our choice of modern initial-final mass relation. We find that age, distance, and ZAMS mass are correlated in a manner that is too complex to be captured by traditional error propagation techniques. We further find that the posterior distributions of age are often asymmetric, indicating that the standard approach to deriving WD ages can yield misleading results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Not-so-simple stellar populations in the intermediate-age Large Magellanic Cloud star clusters NGC 1831 and NGC 1868

Using a combination of high-resolution Hubble Space Telescope/Wide-Field and Planetary Camera-2 observations, we explore the physical properties of the stellar populations in two intermediate-age star clusters, NGC 1831 and NGC 1868, in the Large Magellanic Cloud based on their color-magnitude diagrams. We show that both clusters exhibit extended main-sequence turn offs. To explain the observations, we consider variations in helium abundance, binarity, age dispersions, and the fast rotation of the clusters' member stars. The observed narrow main sequence excludes significant variations in helium abundance in both clusters. We first establish the clusters' main-sequence binary fractions using the bulk of the clusters' main-sequence stellar populations ≳ 1 mag below their turn-offs. The extent of the turn-off regions in color-magnitude space, corrected for the effects of binarity, implies that age spreads of order 300 Myr may be inferred for both clusters if the stellar distributions in color-magnitude space were entirely due to the presence of multiple populations characterized by an age range. Invoking rapid rotation of the population of cluster members characterized by a single age also allows us to match the observed data in detail. However, when taking into account the extent of the red clump in color-magnitude space, we encounter an apparent conflict for NGC 1831 between the age dispersion derived from that based on the extent of the main-sequence turn off and that implied by the compact red clump. We therefore conclude that, for this cluster, variations in stellar rotation rate are preferred over an age dispersion. For NGC 1868, both models perform equally well.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The panchromatic Hubble Andromeda Treasury. V. Ages and masses of the year 1 stellar clusters

We present ages and masses for 601 star clusters in M31 from the analysis of the six filter integrated light measurements from near-ultraviolet to near-infrared wavelengths, made as part of the Panchromatic Hubble Andromeda Treasury (PHAT). We derive the ages and masses using a probabilistic technique, which accounts for the effects of stochastic sampling of the stellar initial mass function. Tests on synthetic data show that this method, in conjunction with the exquisite sensitivity of the PHAT observations and their broad wavelength baseline, provides robust age and mass recovery for clusters ranging from ∼10{sup 2} to 2 × 10{sup 6} M {sub ☉}. We find that the cluster age distribution is consistent with being uniform over the past 100 Myr, which suggests a weak effect of cluster disruption within M31. The age distribution of older (>100 Myr) clusters falls toward old ages, consistent with a power-law decline of index –1, likely from a combination of fading and disruption of the clusters. We find that the mass distribution of the whole sample can be well described by a single power law with a spectral index of –1.9 ± 0.1 over the range of 10{sup 3}-3 × 10{sup 5} M {sub ☉}. However, if we subdivide the sample by galactocentric radius, we find that the age distributions remain unchanged. However, the mass spectral index varies significantly, showing best-fit values between –2.2 and –1.8, with the shallower slope in the highest star formation intensity regions. We explore the robustness of our study to potential systematics and conclude that the cluster mass function may vary with respect to environment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The metallicity spread and the age-metallicity relation of ω Centauri

ω Centauri is a peculiar globular cluster formed by a complex stellar population. To investigate it, we studied 172 stars belonging to the five SGBs that we can identify in our photometry, in order to measure their [Fe/H] content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs have a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several subpopulations. We were able to identify at least six of them based on their mean [Fe/H] content. These metallicity-based subpopulations are seen to varying extents in each of the five SGBs. Taking advantage of the age sensitivity of the SGB, we showed that, first of all, at least half of the subpopulations have an age spread of at least 2 Gyr. Then, we obtained an age-metallicity relation that is the most complete to date for this cluster. Interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations with different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they can be assumed to be two independent primordial objects, or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Declines in Pneumonia and Meningitis Hospitalizations in Children Under 5 Years of Age After Introduction of 10-Valent Pneumococcal Conjugate Vaccine in Zambia, 2010–2016

Background: Pneumococcus is a leading cause of pneumonia and meningitis. Zambia introduced a 10-valent pneumococcal conjugate vaccine (PCV10) in July 2013 using a 3-dose primary series at ages 6, 10, and 14 weeks with no booster. We evaluated the impact of PCV10 on meningitis and pneumonia hospitalizations. Methods: Using hospitalization data from first-level care hospitals, available at the Ministry of Health, and from the largest pediatric referral hospital in Lusaka, we identified children aged <5 years who were hospitalized with pneumonia or meningitis from January 2010–December 2016. We used time-series analyses to measure the effect of PCV10 on monthly case counts by outcome and age group (<1 year, 1–4 years), accounting for seasonality. We defined the pre- and post-PCV10 periods as January 2010–June 2013 and July 2014–December 2016, respectively. Results: At first-level care hospitals, pneumonia and meningitis hospitalizations among children aged <5 years accounted for 108 884 and 1742 admissions in the 42 months pre-PCV10, respectively, and 44 715 and 646 admissions in the 30 months post-PCV10, respectively. Pneumonia hospitalizations declined by 37.8% (95% confidence interval [CI] 21.4–50.3%) and 28.8% (95% CI 17.7–38.7%) among children aged <1 year and 1–4 years, respectively, while meningitis hospitalizations declined by 72.1% (95% CI 63.2–79.0%) and 61.6% (95% CI 50.4–70.8%), respectively, in these age groups. In contrast, at the referral hospital, pneumonia hospitalizations remained stable and a smaller but significant decline in meningitis was observed among children aged 1–4 years (39.3%, 95% CI 16.2–57.5%). Conclusions: PCV10 introduction was associated with declines in meningitis and pneumonia hospitalizations in Zambia, especially in first-level care hospitals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Measuring M31 globular cluster ages and metallicities using both photometry and spectroscopy

ABSTRACT The ages and metallicities of globular clusters play an important role not just in testing models for their formation and evolution but also in understanding the assembly history of their host galaxies. Here, we use a combination of imaging and spectroscopy to measure the ages and metallicities of globular clusters in M31, the closest massive galaxy to our own. We use the strength of the near-infrared calcium triplet spectral feature to provide a relatively age-insensitive prior on the metallicity when fitting stellar population models to the observed photometry. While the age–extinction degeneracy is an issue for globular clusters projected on to the disc of M31, we find generally old ages for globular clusters in the halo of M31 and in its satellite galaxy NGC 205 in line with previous studies. We measure ages for a number of outer halo globular clusters for the first time, finding that globular clusters associated with halo substructure extend to younger ages and higher metallicities than those associated with the smooth halo. This is in line with the expectation that the smooth halo was accreted earlier than the substructured halo.

Usher, Christopher (ORCID:0000000273837106)↗
DOE OSTI2025

Interplay between aging and rejuvenation in spin glasses

Aging in a single-crystal spin glass (Cu 0.92 ⁢Mn 0.08 ) has been measured using ac susceptibility techniques over a temperature range of 0.3–0.8𝑇 𝑔 . In these studies, traditional aging experiments (or “quench” aging protocols) are compared to aging curves constructed from finite-cooling-rate curves. By comparing the growth rates of spin glass order between the two types of aging curves, it is determined that quantitative comparisons between protocols that are taken by quenching and protocols using a finite cooling rate are not possible without a deeper understanding of the interplay between aging and rejuvenation. Finally, we then demonstrate that the data presented indicate that rejuvenation, rather than cumulative aging, is the cause of the discrepancies between the two growth rates.

dynamical phase transitions↗
DOE OSTI2010

Revisit of cosmic age problem

We investigate the cosmic age problem associated with 9 extremely old globular clusters in M31 galaxy and 1 very old high-z quasar automatic plate-measuring machine 08279+5255 at z=3.91. These 9 globular clusters have not been used to study the cosmic age problem in the previous literature. By evaluating the age of the Universe in the {Lambda} cold dark matter model with the observational constraints from the Type Ia supernovae, the baryon acoustic oscillations, the cosmic microwave background, and the independent H{sub 0} measurements, we find that the existence of 5 globular clusters and 1 high-z quasar are in tension (over 2{sigma} confidence level) with the current cosmological observations. So if the age estimates of these objects are correct, the cosmic age puzzle still remains in the standard cosmology. Moreover, we extend our investigations to the cases of the interacting dark energy models. It is found that although the introduction of the interaction between dark sectors can give a larger cosmic age, the interacting dark energy models still have difficulty to pass the cosmic age test.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Detection of diffusion limited oxidation in thermally aged ethylene propylene rubber cable insulation material

The lifetime prediction of electrical cable insulation in nuclear power plants (NPPs) is primarily based on accelerated aging. Polymeric insulation exposed to accelerated aging at high temperatures may demonstrate diffusion limited oxidation (DLO) where oxygen within the material is consumed faster than can be supplied by diffusion from the surrounding air. This situation leads to equilibrium oxidation at the exposed surfaces and limited oxidation away from the surfaces. Therefore, DLO results in a heterogeneously aged material which can lead to underestimation of lifetime for in-service cable insulation. In this study, the presence of inhomogeneous aging caused by DLO was evaluated on cross-sectioned cable insulation specimens made of ethylene propylene rubber (EPR). The studies were performed on thermally aged specimens (165 °C, 1 day and 165 °C, 16 days) using local measurement techniques including nanoindentation, micro-Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) - energy dispersive spectroscopy (EDS). All the results indicate some degree of heterogenous aging, with 165 °C, 16 days, aging demonstrating highest degree of oxidative degradation on the inside edges presumably caused due to copper catalyzed oxidation.

Pallaka, Madhusudhan Reddy↗
DOE OSTI2018

Dielectric Response of Cross-Linked Polyethylene (XLPE) Cable Insulation Material to Radiation and Thermal Aging

This work seeks dielectric indicators of the aged state of cross-linked polyethylene (XLPE) that has been simultaneously irradiated and thermally aged. The XLPE samples studied here were of the same material formulation as XLPE insulation found in RSCC I46-0021 instrumentation cable, formed into tapes with dimensions approximately 20 × 0.7 × 100 mm 3 . Aging was conducted by suspending the samples from a rack within an oven and subsequently exposing oven and samples to gamma radiation. Samples were aged at 60, 90, and 115 °C, with gamma-radiation dose rates from 0 to 450 Gy/h with total received doses from 0 to 216 kGy. The dielectric spectra of these samples were measured over the frequency range 1 Hz to 1 MHz using custom electrodes and a Novocontrol dielectric spectrometer before dielectric breakdown strength was measured on the same samples. Dielectric loss tangent was observed to increase as a function of dose, dose rate and exposure time for XLPE samples exposed as described above. Dielectric loss tangent did not, however, show sensitivity to thermal aging for the range of temperatures studied. Dielectric breakdown strength initially increased as the material oxidized, then decreased for more extreme aging, due to chain scission. It is concluded that dielectric loss tangent is a promising indicator of XLPE aging due to gamma radiation exposure.

dielectric losses, dielectric breakdown, cable ins↗
DOE OSTI2025

Matrix Diffusion Controls Mountain Hillslope Groundwater Ages and Inferred Storage Dynamics

Groundwater age distributions provide fundamental insights on coupled water and biogeochemical processes in mountain watersheds. Field-based studies have found mixtures of young and old-aged groundwater in mountain catchments underlain by bedrock; yet, the processes that dictate these groundwater age distributions are poorly understood. In this work, we use the coupled ParFlow-CLM integrated hydrologic and EcoSLIM particle tracking models to simulate groundwater age distributions on a lower montane hillslope in the East River Watershed, Colorado (USA). We develop a convolution-based approach to propagate fracture-matrix diffusion processes to the EcoSLIM advection-dominated age distributions. We compare observed 3 H and 4 He concentrations from two groundwater wells against model predictions that have varying advective transport times and matrix diffusion magnitudes. Based on a Monte Carlo analysis that considers uncertain matrix and fracture parameters, we find that matrix diffusion is needed to jointly predict 3 H and 4 He observations at both wells. The advection-dominated age distributions lack adequate mixing of young and old-aged water to capture the observed co-occurrence of 3 H and 4 He. The model scenario that best matches the 3 H, 4 He, and water level observations when considering both advective flowpath and matrix diffusion mixing processes has a dynamic bedrock groundwater reservoir that is susceptible to considerable storage losses during low-snow periods. This dynamic groundwater system amplifies the need to assimilate deeper bedrock groundwater into watershed hydro-biogeochemical predictions. This work further highlights the importance of considering matrix diffusion when interpreting environmental tracers in bedrock groundwater systems.

54 ENVIRONMENTAL SCIENCES↗