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At least 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53 Mn- 53 Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53 Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53 Cr/ 52 Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53 Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53 Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.

58 GEOSCIENCES↗
DOE OSTI2015

Stereotactic Body Radiation Therapy for Non-Small Cell Lung Cancer Tumors Greater Than 5 cm: Safety and Efficacy

Purpose: The purpose of this study was to determine outcomes of patients with node-negative medically inoperable non-small cell lung cancer (NSCLC) whose primary tumors exceeded 5 cm and were treated with stereotactic body radiation therapy (SBRT). Methods and Materials: We surveyed our institutional prospective lung SBRT registry to identify treated patients with tumors >5 cm. Treatment outcomes for local control (LC), locoregional control (LRC), disease-free survival (DFS), and overall survival (OS) were assessed by Kaplan-Meier estimates. Toxicities were graded according to Common Terminology Criteria for Adverse Events version 4. Mean pretreatment pulmonary function test values were compared to mean posttreatment values. Results: From December 2003 to July 2014, 40 patients met study criteria. Median follow-up was 10.8 months (range: 0.4-70.3 months). Median age was 76 years (range: 56-90 years), median body mass index was 24.3 (range: 17.7-37.2), median Karnofsky performance score was 80 (range: 60-90), and median Charlson comorbidity index score was 2 (range: 0-5). Median forced expiratory volume in 1 second (FEV1) was 1.41 L (range: 0.47-3.67 L), and median diffusion capacity (DLCO) was 47% of predicted (range: 29%-80%). All patients were staged by fluorodeoxyglucose-positron emission tomography/computed tomography staging, and 47.5% underwent mediastinal staging by endobronchial ultrasonography. Median tumor size was 5.6 cm (range: 5.1-10 cm), median SBRT dose was 50 Gy (range: 30-60 Gy) in 5 fractions (range: 3-10 fractions). Eighteen-month LC, LRC, DFS, and OS rates were 91.2%, 64.4%, 34.6%, and 59.7%, respectively. Distant failure was the predominant pattern of failure (32.5%). Three patients (7.5%) experienced grade 3 or higher toxicity. Mean posttreatment FEV1 was not significantly reduced (P=.51), but a statistically significant absolute 6.5% (P=.03) reduction in DLCO was observed. Conclusions: Lung SBRT for medically inoperable node-negative NSCLC with primary tumors larger than 5 cm is safe and provides excellent local control with limited toxicity. The predominant pattern of failure in this population was distant failure.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Enhanced strength and electrical conductivity of ultrafine-grained Al-Mg-Si alloy processed by hydrostatic extrusion

Highlights: • Al-Mg-Si alloy was subjected to hydrostatic extrusion combined with aging treatment. • UFG Al-Mg-Si alloy with UTS of 332 MPa and conductivity of 58% IACS was obtained. • Precipitation process depended on applied strains and crystallographic texture. • Strengthening effect was achieved by UFG structure and needle-like β″ precipitates. • Precipitation of β″ and spherical β′/β particles at GB provided high conductivity. - Abstract: The effect of hydrostatic extrusion combined with an artificial aging on microstructure, mechanical and electrical properties of 6101 Al-Mg-Si alloy was investigated. It has been shown that such thermo-mechanical treatment is an effective method for producing of long wires with an ultrafine-grained microstructure (grain size of 300–400 nm) and enhanced ultimate tensile strength (> 330 MPa) and electrical conductivity (up to 58% IACS). The mechanical behavior of 6101 Al-Mg-Si alloy depended strongly on applied strains by hydrostatic extrusion and crystallographic texture. Higher accumulative strain accelerated the precipitation kinetics but decreased the age hardening response. The double fiber <100> and <111> texture was observed for hydrostatically extruded samples. The <001> grains with homogenously distributed needle-like β″ precipitates provided precipitation strengthening of material while <111> grains resulted in more efficient grain boundary strengthening. Quantitative microstructure characterization allowed adjusting physical model to estimate the electrical conductivity and compare it with experimental data. The high conductivity was provided mainly by decomposition of solid solution due to precipitation of needle-like β″ precipitates in the grain interior and spherical β′ or β particles located at grain boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2025

E-scooter safety: How attitudinal factors influence risky behavior among shared e-scooter riders

In recent years, e-scooter usage for short-distance trips has grown rapidly. This surge in e-scooter use, combined with the high exposure of e-scooter riders to accident risk, has sparked concerns regarding e-scooter safety. Despite some studies focusing on e-scooter safety, little is known about how attitudinal factors lead e-scooter riders to engage in risky riding behaviors. In this paper, we developed a survey-based empirical model to identify the attitudinal factors influencing engagement in risky behaviors among e-scooter users. We used survey data collected from 420 shared e-scooter users in Chicago in 2022. The survey showed that 47.7% of respondents had experienced at least one collision or fall-off while riding e-scooters. We employed the Partial Least Squares Structural Equation Model (PLS-SEM) to examine the relationships between latent attitudinal factors and risky behavior engagement. Moreover, we conducted Permutation Multi-group Analysis (PMGA) to assess the moderating effect of socio-demographic factors within the estimated model. The findings suggest that riders’ unsafe riding attitude and riding confidence are the most influential factors shaping their risky behavior engagement. In addition, accident experience, infrastructure suitability, perceived enjoyment, traffic risk perception, and operational risk perception are among the other significant predictors. Among socio-demographic factors, gender, age, education, and car use frequency significantly influence riders’ engagement in risky behaviors. The results highlight the importance of infrastructure suitability and accident experience in analyzing e-scooter users’ riding behavior. The developed model advances our understanding of factors contributing to e-scooter riders’ risky behavior engagement. The findings offer valuable insights for policymakers and e-scooter vendors aiming to mitigate e-scooter users’ accident risk. Specifically, we recommend three safety countermeasures: (1) safety training programs to encourage a safer attitude, (2) practice-based initiatives to enhance riding confidence, and (3) infrastructure improvements, especially the expansion of bike lanes.

E-scooter↗
DOE OSTI2014

CHARACTERIZING A DRAMATIC ΔV ∼ –9 FLARE ON AN ULTRACOOL DWARF FOUND BY THE ASAS-SN SURVEY

We analyze a ΔV ∼ –9 magnitude flare on the newly identified M8 dwarf SDSS J022116.84+194020.4 (hereafter SDSSJ0221) detected as part of the All-Sky Automated Survey for Supernovae. Using infrared and optical spectra, we confirm that SDSSJ0221 is a relatively nearby (d ∼ 76 pc) M8 dwarf with strong quiescent Hα emission. Based on kinematics and the absence of features consistent with low-gravity (young) ultracool dwarfs, we place a lower limit of 200 Myr on the age of SDSSJ0221. When modeled with a simple, classical flare light curve, this flare is consistent with a total U-band flare energy E{sub U} ∼ 10{sup 34} erg, confirming that the most dramatic flares are not limited to warmer, more massive stars. Scaled to include a rough estimate of the emission line contribution to the V band, we estimate a blackbody filling factor of ∼10%-30% during the flare peak and ∼0.5%-1.6% during the flare decay phase. These filling factors correspond to flare areas that are an order of magnitude larger than those measured for most mid-M dwarf flares.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The gMOSS: the galaxy survey and galaxy populations of the large homogeneous field

ABSTRACT We present the gMOSS (Galaxies of Medium-band One-meter Schmidt telescope Survey) catalogue of ∼19 000 galaxies in 20 filters (4 broad-band SDSS and 16 medium-band filters). We observed 2.386 deg2 on the central part of the HS47.5-22 field with the 1-m Schmidt telescope of the Byurakan Astrophysical Observatory. The gMOSS is a complete flux-limited sample of galaxies with a threshold magnitude of r SDSS ≤ 22.5 AB. From photometric measurements with 16 medium-band filters and u SDSS, we get spectral energy distributions for each object in the field, which are used for further analysis. Galaxy classification and photometric redshift estimation based on spectral template matching with zebra software. The obtained redshift accuracy is σNMAD < 0.0043. Using the SED-fitting cigale code, we obtained the main properties of the stellar population of galaxies, such as rest-frame (u − r)res colour, stellar mass, extinction, and mass-weighted age with a precision of 0.16 ± 0.07 mag, 0.14 ± 0.04 dex, 0.27 ± 0.1 mag, and 0.08 ± 0.04 dex, respectively. Using a dust-corrected colour–mass diagram, we divided the full sample into populations of red and blue galaxies and considered the dependencies between stellar mass and age. Throughout cosmic time, red sequence galaxies remain older and more massive than blue cloud galaxies. The star formation history of a complete subsample of galaxies selected in the redshift range 0.05 ≤ z ≤ 0.015 with <$\mathrm{log} M \mathrm{\gt }_\mathrm{[M_\odot ]}$>8.3 shows an increase in the SFRD up to z ∼ 3, under the results obtained in earlier studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Molecular dynamics simulations of dislocations in TlBr crystals under an electrical field

TlBr crystals have superior radiation detection properties; however, their properties degrade in the range of hours to weeks when an operating electrical field is applied. To account for this rapid degradation using the widely-accepted vacancy migration mechanism, the vacancy concentration must be orders of magnitude higher than any conventional estimates. The present work has incorporated a new analytical variable charge model in molecular dynamics (MD) simulations to examine the structural changes of materials under electrical fields. Our simulations indicate that dislocations in TlBr move under electrical fields. As a result, this discovery can lead to new understanding of TlBr aging mechanisms under external fields.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Collapsing cloud models for Bok globules

The dynamic collapse of rotating gas clouds is calculated for a wide range of initial conditions. Properties of cloud models are compared with observed radio and optical properties of Bok globules, to test the hypothesis that globules undergo collapse and to determine parameters which are not easily observed. Five of the six globules studied are consistent with collapse models. It is inferred that these objects have masses of about 100 solar masses and ages smaller than their free-fall times. Inferred initial densities are much larger than minimum densities for gravitational collapse, suggesting that collapse is initiated by strong external compression or that globules are fragments of larger condensed clouds. Values inferred for the (C-13)O/H2 ratio are smaller than previous estimates and depend strongly on cloud density.

Villere, K. R.↗
NASA NTRS2006

Compositional Pathways and Capillary Effects during Early-stage Isothermal Precipitation in a Nondilute Ni-Al-Cr Alloy

For a Ni-5.2 Al-14.2 Cr at.% alloy with moderate solute supersaturations, the compositional pathways, as measured with atom-probe tomography, during early to later stage y'(LI2)-precipitation (R = 0.45-10 nm), aged at 873 K, are discussed in light of a multi-component coarsening model. Employing nondilute thermodynamics, detailed model analyses during quasistationary coarsening of the experimental data establish that the y/y' interfacial free-energy is 22- 23+/-7 mJ/sq m. Additionally, solute diffusivities are significantly slower than model estimates. Strong quantitative evidence indicates that an observed y'-supersaturation of Al results from the Gibbs-Thomson effect, providing the first experimental verification of this phenomenon. The Gibbs-Thomson relationship, for a ternary system, as well as differences in measured phase equilibria with CALPHAD assessments, are considered in great detail.

Sudbrack, Chantal K.↗
NASA NTRS2010

Highly Siderophile Elements as Tracers for the Subcontinental Mantle Evolution Beneath the Southwestern USA: The San Carlos and Kilbourne Hole Peridotite Xenoliths Revisited

Peridotite xenoliths from San Carlos, Arizona, and Kilbourne Hole, New Mexico, have been studied since the 1970 s to give insights into melting and metasomatism in the subcontinental mantle beneath the southwestern USA. More recently, the highly siderophile elements (HSE; Os, Ir, Ru, Rh, Pt, Pd, and Re) and the included Re-Os isotope system have been established as powerful tools for the study of mantle processes because of their range in compatibility during mantle melting and their siderophile and chalcophile geochemical behavior. Model aluminachron Re-Os ages for San Carlos and Kilbourne Hole, as well as for the nearby Dish Hill and Vulcan's Throne sites, give consistent depletion ages of around 2.2 Ga. This age can be interpreted as a single large scale mantle melting event linked to crustal formation and continental growth under the southwestern USA. Highly siderophile elements, however, may be added to depleted peridotites via melt-rock interaction, especially the more incompatible and hence mobile Pt, Pd, and Re. This may result in overprinting of the signature of melt extraction, thus abating the usefulness of Re-Os mantle extraction model ages. A comprehensive characterization of the suite of mantle xenoliths from the SW USA in terms of HSE concentrations is thus necessary to re-assess the Re-Os system for dating purposes. San Carlos peridotites are depleted to moderately fertile, as indicated by their bulk Al2O3 contents between 0.66 wt% and 3.13 wt%. Bulk Os-187/Os-188 in San Carlos peridotites range from 0.1206 to 0.1357. In contrast, Kilbourne Hole peridotites tend to be more fertile with Al2O3 between 2.11 and 3.78 wt%, excluding one extremely depleted sample with 0.30 wt% Al2O3, and have Os-187/Os-188 between 0.1156 and 0.1272, typical for mantle peridotites. No large fractionation between the more compatible HSE Os, Ir, and Ru are observed. The more incompatible HSE Re, Pd, and to a minor extent, Pt, however, are depleted in a number of samples by factors of up to 4 for Pt, 6 for Pd, and 20 for Re, compared to primitive mantle estimates. This is in agreement with previous studies from the same locales, which demonstrated the presence of different populations of mantle xenoliths having undergone various degrees of melt extraction. The depletion of the more incompatible elements (Re, Pd, and Pt) also suggests that the HSE budgets of the SW USA peridotites were primarily established by extraction of basaltic melt, and reflect only minor influence from later episodes of metasomatism. Model Re-Os ages obtained from San Carlos and Kilbourne Hole xenoliths may thus reflect ages of crustal formation and mantle depletion in the SW USA region.

vanAcken, D.↗
DOE OSTI2016

The development of explosions in axisymmetric ab initio core-collapse supernova simulations of 12–25 M{sub ⊙} STARS

We present four ab initio axisymmetric core-collapse supernova simulations initiated from 12, 15, 20, and 25 M{sub ⊙} zero-age main sequence progenitors. All of the simulations yield explosions and have been evolved for at least 1.2 s after core bounce and 1 s after material first becomes unbound. These simulations were computed with our Chimera code employing RbR spectral neutrino transport, special and general relativistic transport effects, and state-of-the-art neutrino interactions. Continuing the evolution beyond 1 s after core bounce allows the explosions to develop more fully and the processes involved in powering the explosions to become more clearly evident. We compute explosion energy estimates, including the negative gravitational binding energy of the stellar envelope outside the expanding shock, of 0.34, 0.88, 0.38, and 0.70 Bethe (B ≡ 10{sup 51} erg) and increasing at 0.03, 0.15, 0.19, and 0.52 B s{sup −1}, respectively, for the 12, 15, 20, and 25 M{sub ⊙} models at the endpoint of this report. We examine the growth of the explosion energy in our models through detailed analyses of the energy sources and flows. We discuss how the explosion energies may be subject to stochastic variations as exemplfied by the effect of the explosion geometry of the 20 M{sub ⊙} model in reducing its explosion energy. We compute the proto-neutron star masses and kick velocities. We compare our results for the explosion energies and ejected {sup 56}Ni masses against some observational standards despite the large error bars in both models and observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Research applications of primary biodiversity databases in the digital age

Our world is in the midst of unprecedented change-climate shifts and sustained, widespread habitat degradation have led to dramatic declines in biodiversity rivaling historical extinction events. At the same time, new approaches to publishing and integrating previously disconnected data resources promise to help provide the evidence needed for more efficient and effective conservation and management. Stakeholders have invested considerable resources to contribute to online databases of species occurrences. However, estimates suggest that only 10% of biocollections are available in digital form. The biocollections community must therefore continue to promote digitization efforts, which in part requires demonstrating compelling applications of the data. Our overarching goal is therefore to determine trends in use of mobilized species occurrence data since 2010, as online systems have grown and now provide over one billion records. To do this, we characterized 501 papers that use openly accessible biodiversity databases. Our standardized tagging protocol was based on key topics of interest, including: database(s) used, taxa addressed, general uses of data, other data types linked to species occurrence data, and data quality issues addressed. We found that the most common uses of online biodiversity databases have been to estimate species distribution and richness, to outline data compilation and publication, and to assist in developing species checklists or describing new species. Only 69% of papers in our dataset addressed one or more aspects of data quality, which is low considering common errors and biases known to exist in opportunistic datasets. Globally, we find that biodiversity databases are still in the initial stages of data compilation. Novel and integrative applications are restricted to certain taxonomic groups and regions with higher numbers of quality records. Continued data digitization, publication, enhancement, and quality control efforts are necessary to make biodiversity science more efficient and relevant in our fast-changing environment.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1993

The Acraman impact structure: Estimation of the diameter by the ejecta layer thickness

The big role of gigantic craters formation in geological history of the Earth was established by the example of the K/T boundary event. The discovery of the iridium anomaly in the sedimentary rocks of Vendian in the western part of Ukrainian shield allows to suppose its origin in connection with the great impact of that time. The only big impact structure of that age is the Acraman Crater in south-eastern part of Australia. The Acraman Crater is presented by deeply eroded structure, original diameter of which it is difficult to determine. By geological and morphological data the Acraman Crater is presented by an inner ring 30 km in diameter, an intermediate ring 90 km in diameter, and an outer ring about 150-160 km in diameter.

Gurov, E. P.↗
DOE OSTI2023

Cannibals in the thick disk II. Radial-velocity monitoring of the young α -rich stars

Determining ages of stars for reconstructing the history of the Milky Way remains one of the most difficult tasks in astrophysics. This involves knowing when it is possible to relate the stellar mass with its age and when it is not. The young α-rich (YAR) stars present such a case in which we are still not sure about their ages because they are relatively massive, implying young ages, but their abundances are α-enhanced, which implies old ages. We report the results from new observations from a long-term radial-velocity-monitoring campaign complemented with high-resolution spectroscopy, as well as new astrometry and seismology of a sample of 41 red giants from the third version of APOKASC, which includes YAR stars. The aim is to better characterize the YAR stars in terms of binarity, mass, abundance trends, and kinematic properties. The radial velocities of HERMES, APOGEE, and Gaia were combined to determine the binary fraction among YAR stars. In combination with their mass estimate, evolutionary status, chemical composition, and kinematic properties, it allowed us to better constrain the nature of these objects. We found that stars with M < 1 M ⊙ were all single, whereas stars with M > 1 M ⊙ could be either single or binary. This is in agreement with theoretical predictions of population synthesis models. Studying their [C/N], [C/Fe], and [N/Fe], trends with mass, it became clear that many YAR stars do not follow the APOKASC stars, favoring the scenario that most of them are the product of mass transfer. Our sample further includes two likely undermassive stars, that is to say of such as low mass that they cannot have reached the red clump within the age of the Universe, unless their low mass is the signature of mass loss in previous evolutionary phases. These stars do not show signatures of currently being binaries. Both YAR and undermassive stars might show some anomalous APOGEE abundances for the elements N, Na, P, K, and Cr; although, higher-resolution optical spectroscopy might be needed to confirm these findings. Considering the significant fraction of stars that are formed in pairs and the variety of ways that makes mass transfer possible, the diversity in properties in terms of binarity, and chemistry of the YAR and undermassive stars studied here implies that most of these objects are likely not young.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Estimation of split renal function using different volumetric methods: inter- and intraindividual comparison between MRI and CT

Purpose: This study aims to determine whether contrast-enhanced (CE)-magnetic resonance imaging (MRI) is comparable to CE-computed tomography (CT) for estimation of split renal function (SRF). For this purpose, two different kidney volumetry methods, the renal cortex volumetry (RCV) and modified ellipsoid volume (MELV), are compared for both acquisition types (CT vs. MRI) with regard to accuracy and reliability, subsequently referred to as RCV{sub CT}/RCV{sub MRI} and MELV{sub CT}/MELV{sub MRI}. Methods: This retrospective study included 29 patients (18 men and 11 women; mean age 62.8 ± 12.4 years) who underwent CE-MRI and CE-CT of the abdomen within a period of 3 months. Two independent readers (R1/R2) performed RCV and MELV in all datasets with corresponding semiautomated software tools. RCV was performed with datasets in the arterial phase and MELV in the venous phase. Statistics were calculated using one-way ANOVA, two-tailed Student’s t test, Pearson´s correlation, and Bland–Altman plots with p ≤ 0.05 being considered statistically significant. Results: In all datasets, SRF was almost identical for both volumetry methods with a mean difference of < 1%. Bland–Altman analysis comparing RCV in CT and MRI showed very good agreement for R1/R2. Interreader agreement was strong for RCV{sub CT} and good for RCV{sub MRI} (r = 0.89; r = 0.69). MELV{sub CT/MRI} interreader agreement was only moderate (r = 0.54; r = 0.50) with a high range of values. Intrareader agreement was excellent for all measurements, except MELV{sub MRI} which showed a high mean bias and range of values (RCV{sub CT}: r = 0.93, RCV{sub MRI}: r = 0.98, MELV{sub CT}: r = 0.89, MELV{sub MRI}: r = 0.54). Conclusion: Renal volumetric estimates of SRF are almost as accurate and reliable with CE-MRI as with CE-CT using RCV method. In distinction, the calculation of SRF using MELV was inferior to RCV with respect to accuracy and reliability. Thus, RCV method is recommended to estimate SRF, primarily using CT datasets. However, RCV with MRI datasets for kidney volumetry allows for comparable accuracy and reliability while sparing patients and healthy donors of unnecessary radiation exposure.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Organic photolysis reactions in tropospheric aerosols: effect on secondary organic aerosol formation and lifetime

This paper presents the first modeling estimates of the potential effect of gas- and particle-phase organic photolysis reactions on the formation and lifetime of secondary organic aerosols (SOAs). Typically only photolysis of smaller organic molecules (e.g., formaldehyde) for which explicit data exist is included in chemistry–climate models. Here, we specifically examine the photolysis of larger molecules that actively partition between the gas and particle phases. The chemical mechanism generator GECKO-A is used to explicitly model SOA formation from α-pinene, toluene, and C 12 and C 16 n-alkane reactions with OH at low and high NO x . Simulations are conducted for typical mid-latitude conditions and a solar zenith angle of 45° (permanent daylight). The results show that after 4 days of chemical aging under those conditions (equivalent to 8 days in the summer mid-latitudes), gas-phase photolysis leads to a moderate decrease in SOA yields, i.e., ~15 % (low NO x ) to ~45 % (high NO x ) for α-pinene, ~15 % for toluene, ~25 % for C 12 n-alkane, and ~10 % for C 16 n-alkane. The small effect of gas-phase photolysis on low-volatility n-alkanes such as C 16 n-alkane is due to the rapid partitioning of early-generation products to the particle phase, where they are protected from gas-phase photolysis. Minor changes are found in the volatility distribution of organic products and in oxygen to carbon ratios. The decrease in SOA mass is increasingly more important after a day of chemical processing, suggesting that most laboratory experiments are likely too short to quantify the effect of gas-phase photolysis on SOA yields. Our results also suggest that many molecules containing chromophores are preferentially partitioned into the particle phase before they can be photolyzed in the gas phase. Given the growing experimental evidence that these molecules can undergo in-particle photolysis, we performed sensitivity simulations using an empirically estimated SOA photolysis rate of J SOA = 4 × 10 &minus;4 J NO 2 . Modeling results indicate that this photolytic loss rate would decrease SOA mass by 40–60 % for most species after 10 days of equivalent atmospheric aging at mid-latitudes in the summer. It should be noted that in our simulations we do not consider in-particle or aqueous-phase reactions which could modify the chemical composition of the particle and thus the quantity of photolabile species. The atmospheric implications of our results are significant for both the SOA global distribution and lifetime. GEOS-Chem global model results suggest that particle-phase photolytic reactions could be an important loss process for SOA in the atmosphere, removing aerosols from the troposphere on timescales of less than 7 days that are comparable to wet deposition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Quantifying subsurface parameter and transport uncertainty using surrogate modelling and environmental tracers

Here, we combine physics-based groundwater reactive transport modelling with machine-learning techniques to quantify hydrogeological model and solute transport predictive uncertainties. We train an artificial neural network (ANN) on a dataset of groundwater hydraulic heads and 3 H concentrations generated using a high-fidelity groundwater reactive transport model. Using the trained ANN as a surrogate model to reproduce the input–output response of the high-fidelity reactive transport model, we quantify the posterior distributions of hydrogeological parameters and hydraulic forcing conditions using Markov chain Monte Carlo calibration against field observations of groundwater hydraulic heads and 3 H concentrations. We demonstrate the methodology with a model application that predicts Chlorofluorocarbon-12 (CFC-12) solute transport at a contaminated field site in Wyoming, United States. Our results show that including 3 H observations in the calibration dataset reduced the uncertainty in the estimated permeability field and infiltration rates, compared to calibration against hydraulic heads alone. However, predictive uncertainty quantification shows that CFC-12 transport predictions conditioned to the parameter posterior distributions cannot reproduce the field measurements. We found that calibrating the model to hydraulic head and 3 H observations results in groundwater mean ages that are too large to explain the observed CFC-12 concentrations. The coupling of the physics-based reactive transport model with the machine-learning surrogate model allows us to efficiently quantify model parameter and predictive uncertainties, which is typically computationally intractable using reactive transport models alone.

58 GEOSCIENCES↗
DOE OSTI2016

Elevated blood lead and cadmium levels associated with chronic infections among non-smokers in a cross-sectional analysis of NHANES data

Background: Experimental animal studies, in vitro experiments, and clinical assessments have shown that metal toxicity can impair immune responses. We analyzed data from a United States representative National Health and Nutrition Examination Survey (NHANES) to explore associations between chronic infections and elevated blood concentrations of lead and cadmium among non-smoking NHANES participants. Methods: NHANES data from 1999 to 2012 were examined and weighted to represent the United States population. Multivariable logistic regression was used to estimate adjusted odds ratios (AOR) and 95 % confidence intervals (CI) for heavy metal associations with seropositivity for Helicobacter pylori, Toxoplasma gondii, and Hepatitis B virus (HBV) infections. Results: Available 2-year survey cycles for infection seroprevalence varied by pathogen, from 1 to 7 cycles. Available sample size, disease seroprevalence, and participant age range also varied by pathogen of interest. After controlling for demographic characteristics and general health condition, an elevated blood lead level above the survey population median was significantly associated with seropositivity for all three pathogens (AORs = 1.2–1.5). In addition, an elevated blood cadmium level above the median was significantly associated with HBV (AOR = 1.5; 95 % CI = 1.2–2.0) and H. pylori (AOR = 1.5; 95 % CI = 1.2–1.7) seropositivity. Age-specific analyses for H. pylori and T. gondii indicated stronger associations among children under 13 years of age, particularly for lead exposure and H. pylori seropositivity, and weaker associations among those over 35 years of age. Conclusions: The results of this cross-sectional human health survey suggest that the immunological effects of lead and cadmium toxicity may be associated with an increased susceptibility to chronic infections.

54 ENVIRONMENTAL SCIENCES↗