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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Supercooled spin liquid state in the frustrated pyrochlore Dy 2 Ti 2 O 7

A “supercooled” liquid develops when a fluid does not crystallize upon cooling below its ordering temperature. Instead, the microscopic relaxation times diverge so rapidly that, upon further cooling, equilibration eventually becomes impossible and glass formation occurs. Classic supercooled liquids exhibit specific identifiers including microscopic relaxation times diverging on a Vogel–Tammann–Fulcher (VTF) trajectory, a Havriliak–Negami (HN) form for the dielectric function ε(ω,T), and a general Kohlrausch–Williams–Watts (KWW) form for time-domain relaxation. Recently, the pyrochlore Dy 2 Ti 2 O 7 has become of interest because its frustrated magnetic interactions may, in theory, lead to highly exotic magnetic fluids. However, its true magnetic state at low temperatures has proven very difficult to identify unambiguously. Here, we introduce high-precision, boundary-free magnetization transport techniques based upon toroidal geometries and gain an improved understanding of the time- and frequency-dependent magnetization dynamics of Dy 2 Ti 2 O 7 . We demonstrate a virtually universal HN form for the magnetic susceptibility χ(ω,T), a general KWW form for the real-time magnetic relaxation, and a divergence of the microscopic magnetic relaxation rates with the VTF trajectory. Low-temperature Dy 2 Ti 2 O 7 therefore exhibits the characteristics of a supercooled magnetic liquid. Lastly, one implication is that this translationally invariant lattice of strongly correlated spins may be evolving toward an unprecedented magnetic glass state, perhaps due to many-body localization of spin.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Phylogenetically resolving epidemiologic linkage

The use of phylogenetic trees in epidemiological investigations has become commonplace, but their epidemiological interpretation has not been systematically evaluated. Here, we use an HIV-1 within-host coalescent model to probabilistically evaluate transmission histories of two epidemiologically linked hosts. Previous critique of phylogenetic reconstruction has claimed that direction of transmission is difficult to infer, and that the existence of unsampled intermediary links or common sources can never be excluded. The phylogenetic relationship between the HIV populations of epidemiologically linked hosts can be classified into six types of trees, based on cladistic relationships and whether the reconstruction is consistent with the true transmission history or not. We show that the direction of transmission and whether unsampled intermediary links or common sources existed make very different predictions about expected phylogenetic relationships: (i) Direction of transmission can often be established when paraphyly exists, (ii) intermediary links can be excluded when multiple lineages were transmitted, and (iii) when the sampled individuals’ HIV populations both are monophyletic a common source was likely the origin. Inconsistent results, suggesting the wrong transmission direction, were generally rare. In addition, the expected tree topology also depends on the number of transmitted lineages, the sample size, the time of the sample relative to transmission, and how fast the diversity increases after infection. Typically, 20 or more sequences per subject give robust results. Moreover, we confirm our theoretical evaluations with analyses of real transmission histories and discuss how our findings should aid in interpreting phylogenetic results.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Conserved epitope on influenza-virus hemagglutinin head defined by a vaccine-induced antibody

Circulating influenza viruses evade neutralization in their human hosts by acquiring escape mutations at epitopes of prevalent antibodies. A goal for next-generation influenza vaccines is to reduce escape likelihood by selectively eliciting antibodies recognizing conserved surfaces on the viral hemagglutinin (HA). The receptor-binding site (RBS) on the HA “head” and a region near the fusion peptide on the HA “stem” are two such sites. We describe here a human antibody clonal lineage, designated CL6649, members of which bind a third conserved site (“lateral patch”) on the side of the H1-subtype, HA head. A crystal structure of HA with bound Fab6649 shows the conserved antibody footprint. The site was invariant in isolates from 1977 (seasonal) to 2012 (pdm2009); antibodies in CL6649 recognize HAs from the entire period. In 2013, human H1 viruses acquired mutations in this epitope that were retained in subsequent seasons, prompting modification of the H1 vaccine component in 2017. The mutations inhibit Fab6649 binding. We infer from the rapid spread of these mutations in circulating H1 influenza viruses that the previously subdominant, conserved lateral patch had become immunodominant for individuals with B-cell memory imprinted by earlier H1 exposure. We suggest that introduction of the pdm2009 H1 virus, to which most of the broadly prevalent, neutralizing antibodies did not bind, conferred a selective advantage in the immune systems of infected hosts to recall of memory B cells that recognized the lateral patch, the principal exposed epitope that did not change when pdm2009 displaced previous seasonal H1 viruses.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

The contribution of black carbon to global ice nucleating particle concentrations relevant to mixed-phase clouds

Significance The Earth’s climate is affected by the radiative properties of clouds. In clouds containing both supercooled water droplets and ice particles (mixed-phase clouds), cloud lifetime and albedo are affected by the presence of ice nucleating particles (INP). After decades of research, the importance of black carbon (BC) as an INP remains unresolved. In this work, we determined the contribution of BC to INP concentrations ([INP]) from real-world wildfires and prescribed burns. We found that BC does not contribute significantly to [INP] in near-field biomass burning plumes. These results were applied as parameterizations to global climate model output. Combined with previous work on diesel-engine exhaust, we find that BC does not contribute significantly to global [INP] relevant to mixed-phase clouds.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Revisiting particle dry deposition and its role in radiative effect estimates

Wet and dry deposition remove aerosols from the atmosphere, and these processes control aerosol lifetime and thus impact climate and air quality. Dry deposition is a significant source of aerosol uncertainty in global chemical transport and climate models. Dry deposition parameterizations in most global models were developed when few particle deposition measurements were available. However, new measurement techniques have enabled more size-resolved particle flux observations. We combined literature measurements with data that we collected over a grassland in Oklahoma and a pine forest in Colorado to develop a dry deposition parameterization. We find that relative to observations, previous parameterizations overestimated deposition of the accumulation and Aitken mode particles, and underestimated in the coarse mode. These systematic differences in observed and modeled accumulation mode particle deposition velocities are as large as an order of magnitude over terrestrial ecosystems. As accumulation mode particles form most of the cloud condensation nuclei (CCN) that influence the indirect radiative effect, this model-measurement discrepancy in dry deposition alters modeled CCN and radiative forcing. We present a revised observationally driven parameterization for regional and global aerosol models. Using this revised dry deposition scheme in the Goddard Earth Observing System (GEOS)-Chem chemical transport model, we find that global surface accumulation-mode number concentrations increase by 62% and enhance the global combined anthropogenic and natural aerosol indirect effect by −0.63 W m −2 . Our observationally constrained approach should reduce the uncertainty of particle dry deposition in global chemical transport models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

GHB analogs confer neuroprotection through specific interaction with the CaMKIIα hub domain

Ca 2+ /calmodulin-dependent protein kinase II alpha subunit (CaMKIIα) is a key neuronal signaling protein and an emerging drug target. The central hub domain regulates the activity of CaMKIIα by organizing the holoenzyme complex into functional oligomers, yet pharmacological modulation of the hub domain has never been demonstrated. Here, using a combination of photoaffinity labeling and chemical proteomics, we show that compounds related to the natural substance γ-hydroxybutyrate (GHB) bind selectively to CaMKIIα. By means of a 2.2-Å x-ray crystal structure of ligand-bound CaMKIIα hub, we reveal the molecular details of the binding site deep within the hub. Furthermore, we show that binding of GHB and related analogs to this site promotes concentration-dependent increases in hub thermal stability believed to alter holoenzyme functionality. Selectively under states of pathological CaMKIIα activation, hub ligands provide a significant and sustained neuroprotection, which is both time and dose dependent. This is demonstrated in neurons exposed to excitotoxicity and in a mouse model of cerebral ischemia with the selective GHB analog, HOCPCA (3-hydroxycyclopent-1-enecarboxylic acid). Together, our results indicate a hitherto unknown mechanism for neuroprotection by a highly specific and unforeseen interaction between the CaMKIIα hub domain and small molecule brain-penetrant GHB analogs. This establishes GHB analogs as powerful tools for investigating CaMKII neuropharmacology in general and as potential therapeutic compounds for cerebral ischemia in particular.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Drying of tundra landscapes will limit subsidence-induced acceleration of permafrost thaw

We used a model for permafrost hydrology informed by detailed measurements of soil ice content to better understand the potential risk of abrupt permafrost thaw triggered by melting ground ice, a key open question associated with permafrost response to a warming Arctic. Our spatially resolved simulations of a well-characterized site in polygonal tundra near Utqiaġvik, Alaska, agree well with multiple types of observations in the current climate. Projections indicate 63 cm of bulk subsidence from 2006 to 2100 in the strong-warming Representative Concentration Pathway 8.5 climate. Permafrost thaw as measured by the increase in active layer thickness (ALT)—the thickness of the soil layer that thaws each summer—is accelerated by subsidence, but the effect is relatively small. The ALT increases from the current-day value of approximately 50 cm to approximately 180 cm by 2100 when subsidence is included compared to about 160 cm when it is neglected. In these simulations, previously identified positive feedbacks between subsidence and thaw are self-limiting on decadal time frames because landscape runoff and increasing evapotranspiration result in drier tundra with weaker surface/atmosphere coupling. These results for a tundra site that is representative of large swathes of the Alaska North Slope suggest that subsidence is unlikely to lead to abrupt thaw over large areas. However, subsidence does have significant effects on the hydrology of polygonal tundra. Specifically, subsidence increases landscape runoff, which helps maintain streamflow in the face of increased evapotranspiration but also causes drier tundra conditions that could have deleterious effects on sensitive Arctic wetland ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Self-terminating, heterogeneous solid–electrolyte interphase enables reversible Li–ether cointercalation in graphite anodes

Ether solvents are suitable for formulating solid-electrolyte interphase (SEI)-less ion-solvent cointercalation electrolytes in graphite for Na-ion and K-ion batteries. However, ether-based electrolytes have been historically perceived to cause exfoliation of graphite and cell failure in Li-ion batteries. In this study, we develop strategies to achieve reversible Li–solvent cointercalation in graphite through combining appropriate Li salts and ether solvents. Specifically, we design 1M LiBF 4 1,2-dimethoxyethane (G1), which enables natural graphite to deliver ~91% initial Coulombic efficiency and >88% capacity retention after 400 cycles. We captured the spatial distribution of LiF at various length scales and quantified its heterogeneity. The electrolyte shows self-terminated reactivity on graphite edge planes and results in a grainy, fluorinated pseudo-SEI. The molecular origin of the pseudo-SEI is elucidated by ab initio molecular dynamics (AIMD) simulations. The operando synchrotron analyses further demonstrate the reversible and monotonous phase transformation of cointercalated graphite. Our findings demonstrate the feasibility of Li cointercalation chemistry in graphite for extreme-condition batteries. The work also paves the foundation for understanding and modulating the interphase generated by ether electrolytes in a broad range of electrodes and batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Extreme elevational migration spurred cryptic speciation in giant hummingbirds

The ecoevolutionary drivers of species niche expansion or contraction are critical for biodiversity but challenging to infer. Niche expansion may be promoted by local adaptation or constrained by physiological performance trade-offs. For birds, evolutionary shifts in migratory behavior permit the broadening of the climatic niche by expansion into varied, seasonal environments. Broader niches can be short-lived if diversifying selection and geography promote speciation and niche subdivision across climatic gradients. To illuminate niche breadth dynamics, we can ask how “outlier” species defy constraints. Of the 363 hummingbird species, the giant hummingbird (Patagona gigas) has the broadest climatic niche by a large margin. To test the roles of migratory behavior, performance trade-offs, and genetic structure in maintaining its exceptional niche breadth, we studied its movements, respiratory traits, and population genomics. Satellite and light-level geolocator tracks revealed an >8,300-km loop migration over the Central Andean Plateau. This migration included a 3-wk, ~4,100-m ascent punctuated by upward bursts and pauses, resembling the acclimatization routines of human mountain climbers, and accompanied by surging blood-hemoglobin concentrations. Extreme migration was accompanied by deep genomic divergence from high-elevation resident populations, with decisive postzygotic barriers to gene flow. The two forms occur side-by-side but differ almost imperceptibly in size, plumage, and respiratory traits. The high-elevation resident taxon is the world’s largest hummingbird, a previously undiscovered species that we describe and name here. The giant hummingbirds demonstrate evolutionary limits on niche breadth: when the ancestral niche expanded due to evolution (or loss) of an extreme migratory behavior, speciation followed.

Science & Technology - Other Topics↗
DOE OSTI2024

Peripheral positions encode transport specificity in the small multidrug resistance exporters

In secondary active transporters, a relatively limited set of protein folds have evolved diverse solute transport functions. Because of the conformational changes inherent to transport, altering substrate specificity typically involves remodeling the entire structural landscape, limiting our understanding of how novel substrate specificities evolve. In the current work, we examine a structurally minimalist family of model transport proteins, the small multidrug resistance (SMR) transporters, to understand the molecular basis for the emergence of a novel substrate specificity. We engineer a selective SMR protein to promiscuously export quaternary ammonium antiseptics, similar to the activity of a clade of multidrug exporters in this family. Using combinatorial mutagenesis and deep sequencing, we identify the necessary and sufficient molecular determinants of this engineered activity. Using X-ray crystallography, solid-supported membrane electrophysiology, binding assays, and a proteoliposome-based quaternary ammonium antiseptic transport assay that we developed, we dissect the mechanistic contributions of these residues to substrate polyspecificity. We find that substrate preference changes not through modification of the residues that directly interact with the substrate but through mutations peripheral to the binding pocket. Our work provides molecular insight into substrate promiscuity among the SMRs and can be applied to understand multidrug export and the evolution of novel transport functions more generally.

Science & Technology - Other Topics↗
DOE OSTI2020

Airborne Release Fractions from Surrogate Nuclear Waste Fires Containing Lanthanide Nitrates and Depleted Uranium Nitrate in 30% Tributyl Phosphate in Kerosene

Airborne contaminants from fires containing nuclear waste represent significant health hazards and shape the design and operation of nuclear facilities. Much of the data used to formulate DOE-HDBK-3010-94, “Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear Facilities,” from the U.S. Department of Energy, were taken over 40 years ago. The objectives of this study were to reproduce experiments from Pacific Northwest Laboratories conducted in June 1973 employing current aerosol measurement methods and instrumentation, develop an enhanced understanding of particulate formation and transport from fires containing nuclear waste, and provide modeling and experimental capabilities for updating current standards and practices in nuclear facilities. A special chamber was designed to conduct small fires containing 25 mL of flammable waste containing lutetium nitrate, ytterbium nitrate, or depleted uranium nitrate. Carbon soot aerosols showed aggregates of primary particles ranging from 20 to 60 nm in diameter. In scanning electron microscopy, ~200-nm spheroidal particles were also observed dispersed among the fractal aggregates. The 200-nm spherical particles were composed of metal phosphates. Airborne release fractions (ARFs) were characterized by leaching filter deposits and quantifying metal concentrations with mass spectrometry. The average mass-based ARF for 238 U experiments was 1.0 × 10 -3 with a standard deviation of 7.5 × 10 -4 . For the original experiments, DOE-HDBK-3010-94 states, “Uranium ARFs range from 2 × 10 -4 to 3 × 10 -3 , an uncertainty of approximately an order of magnitude.” Therefore, current measurements were consistent with DOE-HDBK-3010-94 values. ARF values for lutetium and ytterbium were approximately one to two orders of magnitude lower than 238 U. Furthermore, metal nitrate solubility may have varied with elemental composition and temperature, thereby affecting ARF values for uranium surrogates (Yb and Lu). In addition to ARF data, solution boiling temperatures and evaporation rates can also be deduced from experimental data.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Experimental Study on Heat Transfer and Pressure Drop of In-House Synthesized Graphene Oxide Nanofluids

In this work, first, graphene oxide nanosheets were synthesized in-house according to the modified Hummers method, and these nanosheets were used to prepare graphene oxide nanofluids at two concentrations. Then the thermo-physical properties of nanofluids characterized using X-ray diffraction analysis, a scanning electron microscope, and UV-Vis spectrophotometry. The particle size distribution was investigated using dynamic light scattering. Then, a fundamental study was conducted on the thermal-hydraulic characteristics of graphene oxide nanofluids flowing through a straight copper tube. An experimental setup was developed to find the heat transfer characteristics and pressure drop of nanofluids in the test section consisting of a copper tube with constant heat flux. The flow regimes and associated pressure drop and heat transfer characteristics at varying flow rate were investigated at three different heat flux conditions of 7.4, 9.1, and 12.6 kW/m 2 . Due to the increase in viscosity, flowrate and Reynolds number decreased from 0.01 wt.% to 0.1 wt.% of graphene oxide nanofluids at constant pump frequency. Experimental data obtained for water was validated with the findings from the literature, and the correlations were formulated for the Nusselt number and Reynolds number by considering the multiple regression analysis. The convective heat transfer coefficient for graphene oxide at 0.01 wt.% was higher when compared to graphene oxide at 0.1 wt.% and water. Finally, the variation of Nusselt number with the heat flux and velocity was insignificant.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Second International Workshop on Ambient Pressure X-ray Photoelectron Spectroscopy

The Second International Workshop on Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) was held at Lawrence Berkeley National Laboratory (LBNL) in Berkeley, CA, from December 7-9, 2015. It brought together more than 100 participants from 17 countries. The workshop followed the inaugural meeting at the French synchrotron SOLEIL in December 2014, which was organized by François Rochet. The strong interest in these workshops reflects the growth of the APXPS community over the last decade, with instruments now operational at more than 12 synchrotrons around the world (see SRN, Vol. 27, No. 2, pp. 14–23 (2014)), and a steady increase in the number of laboratory instruments. Finally, APXPS has established itself as an important method for the investigation of surfaces and interfaces under in situ and operando conditions, including liquid/vapor and liquid/solid interfaces.

36 MATERIALS SCIENCE↗