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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

A Study of autunite dissolution in the presence of Shewanella oneidensis MR1 and different bicarbonate concentrations - 15736

Remediation of uranium at Hanford Site 300 area via tripolyphosphate injections could sequester uranium (VI) in an insoluble form, creating different types of uranium phosphate minerals like autunite. The factors that influence the dissolution of such minerals come into question. Bacteria can play a significant role in the dissolution of minerals and the formation of secondary minerals. Formed autunite, as a phosphorus-containing mineral, can attract bacteria to liberate phosphorus, meeting their nutrient requirements and causing uranium release back into the environment. Previous studies have been conducted under aerobic conditions. This research was extended to investigate the stability of the autunite mineral under anaerobic conditions pertaining to the Hanford Site, and to study the effect of facultative anaerobic bacteria on the uranium (VI) release from autunite. Objectives: - Evaluate bacterial interactions with uranium (VI) by focusing on facultative anaerobic bacteria, Shewanella Oneidensis MR1. - Study the effect of bacteria on the dissolution of the uranyl phosphate solid phases created as a result of sodium tripolyphosphate injections into the subsurface at the Hanford 300 Area. - Evaluate the role of anaerobic bacteria as one of the factors affecting the outcome of environmental remediation. Experimental Approach: - 16 crimp-sealed bottles were prepared with 50 ml of media solution and 90 mg (4.4 mM of uranium VI) Ca-autunite mineral obtained from Hanford site. Bottles were inoculated with Shewanella Oneidensis MR1 strains when autunite was equilibrated with the media solutions. Bacteria was obtained from Pacific Northwestern National Laboratory (PNNL). - Solution media preparation: 20 mM NaHepes buffer: pH=7, 10 mM Lactate plus bicarbonate in four concentrations (0, 3, 5 and 10 of KHCO{sub 3}) and a bacteria-free control. Samples were taken from the supernatant solutions of the experimental and control bottles. Wet and dry digestion was performed until a white solid residue was acquired. Dilution was made on solid samples for KPA analysis to determine concentration of U (VI) as function of time. The results suggests that in the absence of HCO{sub 3}{sup -} there was a decrease in the of uranium (VI) concentration due to metal reducing bacteria Shewanella Oneidensis MR1, but for higher concentrations of HCO{sub 3}{sup -}, there is no significant difference in uranium (VI) reduction before and after inoculation with bacteria. - Although bottles were sealed, there is an hypothesis that it was oxygen restricted but not strictly performed under anaerobic conditions. For that matter there is a reason to repeat the experiment using the glove box to understand the uranium (VI) reduction mechanism and behavior of bacteria with oxic/anoxic interfaces. Conclusions: - Higher bicarbonate concentrations might interfere with uranium (VI) reduction by anaerobic bacteria. - It is necessary to reduce time of sampling before the inoculation and prolong sampling time after inoculation. - It might be necessary to increase concentration of lactate. Future Work: - Conduct experiment in strictly anaerobic conditions by using the glove box and evaluate if further reduction of uranium (VI) is obtained in the presence of carbonates (HCO{sub 3}{sup -}). - Finalize analysis of calcium and phosphorous via ICP instrument.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Dynamic interplay between uranyl phosphate precipitation, sorption, and phase evolution

We report that natural examples demonstrate uranyl-phosphate minerals can maintain extremely low levels of aqueous uranium in groundwaters due to their low solubility. Thus, greater understanding of the geochemical factors leading to uranyl phosphate precipitation may lead to successful application of phosphate-based remediation methods. However, the solubility of uranyl phosphate phases varies over >3 orders of magnitude, with the most soluble phases typically observed in lab experiments. To understand the role of common soil/sediment mineral surfaces in the nucleation and transformation of uranyl phosphate minerals under environmentally relevant conditions, we carried out batch experiments with goethite and mica at pH 6 in mixed electrolyte solutions ranging from 1–800 μM U and 1–800 μM P. All experiments ended with uranium concentrations below the USEPA MCL for U, but with 2–3 orders of magnitude difference in uranium concentrations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Geochemical Modeling of F Area Seepage Basin Composition and Variability

From the 1950s through 1989, the F Area Seepage Basins at the Savannah River Site (SRS) received low level radioactive wastes resulting from processing nuclear materials. Discharges of process wastes to the F Area Seepage Basins followed by subsequent mixing processes within the basins and eventual infiltration into the subsurface resulted in contamination of the underlying vadose zone and downgradient groundwater. For simulating contaminant behavior and subsurface transport, a quantitative understanding of the interrelated discharge-mixing-infiltration system along with the resulting chemistry of fluids entering the subsurface is needed. An example of this need emerged as the F Area Seepage Basins was selected as a key case study demonstration site for the Advanced Simulation Capability for Environmental Management (ASCEM) Program. This modeling evaluation explored the importance of the wide variability in bulk wastewater chemistry as it propagated through the basins. The results are intended to generally improve and refine the conceptualization of infiltration of chemical wastes from seepage basins receiving variable waste streams and to specifically support the ASCEM case study model for the F Area Seepage Basins. Specific goals of this work included: (1) develop a technically-based 'charge-balanced' nominal source term chemistry for water infiltrating into the subsurface during basin operations, (2) estimate the nature of short term and long term variability in infiltrating water to support scenario development for uncertainty quantification (i.e., UQ analysis), (3) identify key geochemical factors that control overall basin water chemistry and the projected variability/stability, and (4) link wastewater chemistry to the subsurface based on monitoring well data. Results from this study provide data and understanding that can be used in further modeling efforts of the F Area groundwater plume. As identified in this study, key geochemical factors affecting basin chemistry and variability included: (1) the nature or chemistry of the waste streams, (2) the open system of the basins, and (3) duration of discharge of the waste stream types. Mixing models of the archetype waste streams indicated that the overall basin system would likely remain acidic much of the time. Only an extended periods of predominantly alkaline waste discharge (e.g., >70% alkaline waste) would dramatically alter the average pH of wastewater entering the basins. Short term and long term variability were evaluated by performing multiple stepwise modeling runs to calculate the oscillation of bulk chemistry in the basins in response to short term variations in waste stream chemistry. Short term (1/2 month and 1 month) oscillations in the waste stream types only affected the chemistry in Basin 1; little variation was observed in Basin 2 and 3. As the largest basin, Basin 3 is considered the primary source to the groundwater. Modeling showed that the fluctuation in chemistry of the waste streams is not directly representative of the source term to the groundwater (i.e. Basin 3). The sequence of receiving basins and the large volume of water in Basin 3 'smooth' or nullify the short term variability in waste stream composition. As part of this study, a technically-based 'charge-balanced' nominal source term chemistry was developed for Basin 3 for a narrow range of pH (2.7 to 3.4). An example is also provided of how these data could be used to quantify uncertainty over the long term variations in waste stream chemistry and hence, Basin 3 chemistry.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1999

Renal Stone Risk During Space Flight

Space flight produces a number of metabolic and physiological changes in the crewmembers exposed to microgravity. Following launch, body fluid volumes, electrolyte levels, and bone and muscle undergo changes as the human body adapts to the weightless environment. Changes in the urinary chemical composition may lead to the potentially serious consequences of renal stone formation. Previous data collected immediately after space flight indicate changes in the urine chemistry favoring an increased risk of calcium oxalate and uric acid stone formation (n = 323). During short term Shuttle space flights, the changes observed include increased urinary calcium and decreased urine volume, pH and citrate resulting in a greater risk for calcium oxalate and brushite stone formation (n = 6). Results from long duration Shuttle/Mir missions (n = 9) followed a similar trend and demonstrated decreased fluid intake and urine volume and increased urinary calcium resulting in a urinary environment saturated with the calcium stone-forming salts. The increased risk occurs rapidly upon exposure to microgravity, continues throughout the space flight and following landing. Dietary factors, especially fluid intake, or pharmacologic intervention can significantly influence the urinary chemical composition. Increasing fluid intake to produce a daily urine output of 2 liters/day may allow the excess salts in the urine to remain in solution, crystals formation will not occur and a renal stone will not develop. Results from long duration crewmembers (n = 2) who had urine volumes greater than 2.5 L/day minimized their risk of renal stone formation. Also, comparisons of stone-forming risk in short duration crewmembers clearly identified greater risk in those who produced less than 2 liters of urine/day. However, hydration and increased urine output does not correct the underlying calcium excretion due to bone loss and only treats the symptoms and not the cause of the increased urinary salts. Dietary modification and promising pharmacologic treatments may also be used to reduce the potential risk for renal stone formation. Potassium citrate is being used clinically to increase the urinary inhibitor levels to minimize the development of crystals and the growth of renal stones. Bisphosphonates are a class of drugs recently shown to help in patients with osteoporosis by inhibiting the loss of bones in elderly patients. This drug could potentially prevent the bone loss observed in astronauts and thereby minimize the increase in urinary calcium and reduce the risk for renal stone development. Results of NASA's renal stone risk assessment program clearly indicate that exposure to microgravity changes the urinary chemical environment such that there is an increased risk for supersaturation of stone-forming salts, including calcium oxalaie and brushite. These studies have indicated specific avenues for development of countermeasures for the increased renal stone risk observed during and following space flight. Increased hydration and implementation of pharmacologic countermeasures should largely mitigate the in-flight risk of renal stones.

Whitson, Peggy A.↗
DOE OSTI2015

Influence of edaphic and management factors on the diversity and abundance of ammonia‐oxidizing thaumarchaeota and bacteria in soils of bioenergy crop cultivars

Summary Ammonia‐oxidizing thaumarcheota ( AOA ) and ammonia‐oxidizing bacteria ( AOB ) differentially influence soil and atmospheric chemistry, but soil properties that control their distributions are poorly understood. In this study, the ammonia monooxygenase gene ( amoA ) was used to identify and quantify presumptive AOA and AOB and relate their distributions to soil properties in two experimental fields planted with different varieties of switchgrass ( P anicum virgatum ), a potential bioenergy feedstock. Differences in ammonia oxidizer diversity were associated primarily with soil properties of the two field sites, with pH displaying significant correlations with both AOA and AOB population structure. Percent nitrogen (%N), carbon to nitrogen ratios (C : N), and pH were also correlated with shifts nitrifier population structure. N itrosotalea ‐like and N itrosospira cluster II populations were more highly represented in acidic soils, whereas populations affiliated with N itrososphaera and N itrosospira cluster 3 A .1 were relatively more abundant in alkaline soils. AOA were the dominant functional group in all plots based on quantitative polymerase chain reaction and high‐throughput sequencing analyses. These data suggest that AOA contribute significantly to nitrification rates in carbon and nitrogen rich soils influenced by perennial grasses.

Bertagnolli, Anthony D.↗
DOE OSTI2019

Top-Down Analysis of Proteins in Low Charge States

The impact of charging methods on the dissociation behavior of intact proteins in low charge states is investigated using HCD and 193 nm UVPD. Low charge states are produced for seven different proteins using the following four different methods: (1) proton transfer reactions of ions in high charge states generated from conventional denaturing solutions; (2) ESI of proteins in solutions of high ionic strength to enhance retention of folded native-like conformations; (3) ESI of proteins in high pH solutions to limit protonation; and (4) ESI of carbamylated proteins. Comparison of sequence coverages, degree of preferential cleavages, and types and distribution of fragment ions reveals a number of differences in the fragmentation patterns depending on the method used to generate the ions. More notable differences in these metrics are observed upon HCD than upon UVPD. The fragmentation caused by HCD is influenced more significantly by the presence/absence of mobile protons, a factor that modulates the degree of preferential cleavages and net sequence coverages. Carbamylation of the lysines and the N-terminus of the proteins alters the proton mobility by reducing the number of proton-sequestering, highly basic sites as evidenced by decreased preferential fragmentation C-terminal to Asp or N-terminal to Pro upon HCD. UVPD is less dependent on the method used to generate the low charge states and favors non-specific fragmentation, an outcome which is important for obtaining high sequence coverage of intact proteins. .

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Hydrogen bonds are a primary driving force for de novo protein folding

The protein-folding mechanism remains a major puzzle in life science. Purified soluble activation-induced cytidine deaminase (AID) is one of the most difficult proteins to obtain. Starting from inclusion bodies containing a C-terminally truncated version of AID (residues 1–153; AID 153 ), an optimized in vitro folding procedure was derived to obtain large amounts of AID 153 , which led to crystals with good quality and to final structural determination. Interestingly, it was found that the final refolding yield of the protein is proline residue-dependent. The difference in the distribution of cis and trans configurations of proline residues in the protein after complete denaturation is a major determining factor of the final yield. A point mutation of one of four proline residues to an asparagine led to a near-doubling of the yield of refolded protein after complete denaturation. It was concluded that the driving force behind protein folding could not overcome the cis -to- trans proline isomerization, or vice versa , during the protein-folding process. Furthermore, it was found that successful refolding of proteins optimally occurs at high pH values, which may mimic protein folding in vivo . It was found that high pH values could induce the polarization of peptide bonds, which may trigger the formation of protein secondary structures through hydrogen bonds. It is proposed that a hydrophobic environment coupled with negative charges is essential for protein folding. Combined with our earlier discoveries on protein-unfolding mechanisms, it is proposed that hydrogen bonds are a primary driving force for de novo protein folding.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Structure and conformational dynamics of Clostridioides difficile toxin A

Clostridioides difficile toxin A and B (TcdA and TcdB) are two major virulence factors responsible for diseases associated with C. difficile infection (CDI). Here, we report the 3.18-Å resolution crystal structure of a TcdA fragment (residues L843–T2481), which advances our understanding of the complete structure of TcdA holotoxin. Our structural analysis, together with complementary single molecule FRET and limited proteolysis studies, reveal that TcdA adopts a dynamic structure and its CROPs domain can sample a spectrum of open and closed conformations in a pH-dependent manner. Furthermore, a small globular subdomain (SGS) and the CROPs protect the pore-forming region of TcdA in the closed state at neutral pH, which could contribute to modulating the pH-dependent pore formation of TcdA. A rationally designed TcdA mutation that trapped the CROPs in the closed conformation showed drastically reduced cytotoxicity. Taken together, these studies shed new lights into the conformational dynamics of TcdA and its roles in TcdA intoxication.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Quantifying Drivers of Methane Hydrobiogeochemistry in a Tidal River Floodplain System

The influence of coastal ecosystems on global greenhouse gas (GHG) budgets and their response to increasing inundation and salinization remains poorly constrained. In this study, we have integrated an uncertainty quantification (UQ) and ensemble machine learning (ML) framework to identify and rank the most influential processes, properties, and conditions controlling methane behavior in a freshwater floodplain responding to recently restored seawater inundation. Our unique multivariate, multiyear, and multi-site dataset comprises tidal creek and floodplain porewater observations encompassing water level, salinity, pH, temperature, dissolved oxygen (DO), dissolved organic carbon (DOC), total dissolved nitrogen (TDN), partial pressure of carbon dioxide (pCO 2 ), nitrous oxide (pN 2 O), methane (pCH 4 ), and the stable isotopic composition of methane (δ 13 CH 4 ). Additionally, we incorporated topographical data, soil porosity, hydraulic conductivity, and water retention parameters for UQ analysis using a previously developed 3D variably saturated flow and transport floodplain model for a physical mechanistic understanding of factors influencing groundwater levels and salinity and, therefore, CH 4 . Principal component analysis revealed that groundwater level and salinity are the most significant predictors of overall biogeochemical variability. The ensemble ML models and UQ analyses identified DO, water level, salinity, and temperature as the most influential factors for porewater methane levels and indicated that approximately 80% of the total variability in hourly water levels and around 60% of the total variability in hourly salinity can be explained by permeability, creek water level, and two van Genuchten water retention function parameters: the air-entry suction parameter α and the pore size distribution parameter m. These findings provide insights on the physicochemical factors in methane behavior in coastal ecosystems and their representation in local- to global-scale Earth system models.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1991

Growth and maintenance of an embryogenic cell culture of daylily (Hemerocallis) on hormone-free medium

Callus cultures of the diploid daylily (Hemerocallis) clone Autumn Blaze' were initiated and maintained in hormone-containing nutrient medium. At various times (from 6 weeks to 1 year) after being initiated, hormone-derived cultures were evaluated for their ability to be maintained and to multiply on hormone-free medium at low pH (between pH 4 and 4.5). Cultures had to be exposed to hormone-containing medium for at least 12 weeks before they could be maintained on hormone-free medium at low pH. The transition to maintainability on low pH hormone-free medium included the production of many aberrant embryonal forms ( neomorphs'). However, all hormone-derived cultures tested consisted entirely of preglobular stage proembryos (PGSPs) after 12-24 weeks on low pH hormone-free medium. PGSP cultures have been maintained and multiplied as such for over 1 year on low pH hormone-free medium. PGSPs continue their development into various somatic embryo stages when cultured on hormone-free medium buffered at pH 5.8. The production of well-formed somatic embryos was greatly enhanced when PGSPs were plated on activated charcoal impregnated filter papers that were placed on top of the agar surface. The gross morphology and histology of the PGSPs and stages of somatic embryo development are presented. The work shows that the ability of hormone-free medium at low pH to permit PGSP multiplication without development into later stages of embryo development is not restricted to carrot.

Non-NASA Center↗
NASA NTRS1999

Changes in cytosolic pH within Arabidopsis root columella cells play a key role in the early signaling pathway for root gravitropism

Ratiometric wide-field fluorescence microscopy with 1',7'- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF)-dextran demonstrated that gravistimulation leads to rapid changes in cytoplasmic pH (pHc) in columella cells of Arabidopsis roots. The pHc of unstimulated columella cells in tiers 2 and 3, known sites of graviperception (E.B. Blancaflor, J.B. Fasano, S. Gilroy [1998] Plant Physiol 116: 213-222), was 7.22 +/- 0.02 pH units. Following gravistimulation, the magnitude and direction of pHc changes in these cells depended on their location in the columella. Cells in the lower side of tier 2 became more alkaline by 0.4 unit within 55 s of gravistimulation, whereas alkalinization of the cells on the upper side was slower (100 s). In contrast, all cells in tier 3 acidified by 0.4 pH unit within 480 s after gravistimulation. Disrupting these pHc changes in the columella cells using pHc modifiers at concentrations that do not affect root growth altered the gravitropic response. Acidifying agents, including bafilomycin A1, enhanced curvature, whereas alkalinizing agents disrupted gravitropic bending. These results imply that pHc changes in the gravisensing cells and the resultant pH gradients across the root cap are important at an early stage in the signal cascade leading to the gravitropic response.

NASA Discipline Plant Biology↗
DOE OSTI2013

The ordinary life of the γ-ray emitting narrow-line Seyfert 1 galaxy PKS 1502+036

In this paper, we report on multifrequency observations of the γ-ray emitting narrow-line Seyfert 1 galaxy PKS 1502+036 performed from radio to γ-rays during 2008 August–2012 November by Fermi -Large Area Telescope (LAT), Swift (X-ray Telescope and Ultraviolet/Optical Telescope), Owens Valley Radio Observatory, Very Long Baseline Array (VLBA) and Very Large Array. No significant variability has been observed in γ-rays, with 0.1–100 GeV flux that ranged between (3–7) × 10 –8 ph cm –2 s –1 using 3-month time bins. The photon index of the LAT spectrum (Γ = 2.60 ± 0.06) and the apparent isotropic γ-ray luminosity (L0.1-100 GeV = 7.8 × 10 45 erg s –1 ) over 51 months are typical of a flat spectrum radio quasar. The radio spectral variability and the one-sided structure, in addition to the observed γ-ray luminosity, suggest a relativistic jet with a high Doppler factor. In contrast to SBS 0846+513, the VLBA at 15 GHz did not observe superluminal motion for PKS 1502+036. Despite having the optical characteristics typical of a narrow-line Seyfert 1 galaxy, radio and γ-ray properties of PKS 1502+036 are found to be similar to those of a blazar at the low end of the black hole mass distribution for blazars. As a result, this is in agreement with what has been found in the case of the other γ-ray emitting narrow-line Seyfert 1 SBS 0846+513.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Nutrient limitation shapes functional traits of mycorrhizal fungi and phosphorus-cycling bacteria across an elevation gradient

In nutrient-limited high-elevation ecosystems, plants rely on arbuscular mycorrhizal (AM) fungi to provide mineral phosphorus (P) in the form of phosphate (PO43-). AM fungi gather these nutrients from phosphorus-cycling bacteria (PCBs) that can mineralize PO43- from organic matter and solubilize mineral-bound P. How climate, soil factors, and nutrient limitation influence AM fungi and PCB assembly remains unclear. We collected soil from montane meadows across a 1,000-m elevation gradient on three replicate mountainsides and analyzed AM fungal marker genes, P-cycling genes from shotgun metagenomes, and edaphic measurements. High-elevation soils had nearly 50-fold less soil PO₄³⁻ and 60% more AM fungal hyphae than low-elevation soils. AM fungal turnover was linked to changes in pH, organic carbon, and PO₄³-. The composition of 198 P-cycling genes was influenced by the AM fungal community structure. Drivers of individual PCB functional genes, including pH and organic carbon, varied with gene phylogeny. We found a trade-off in P-cycling strategies across elevation: P-rich, low-elevation soils supported root-colonizing AM fungi and organic P-mineralizing bacteria. P-poor, high-elevation soils were dominated by stress-tolerant AM fungi and mineral P-solubilizing bacteria. Our results suggest that AM fungi and PCB community turnover across elevation are both shaped by pH, organic carbon, and P availability. With continued climate warming, the structure and function of mountaintop ecosystems might shift to resemble lower elevations, disrupting long-established and specialized microbial assemblages, with consequences for P-cycling dynamics and the total P available to plant communities.IMPORTANCEPhosphorus (P) limits plant productivity in high-elevation ecosystems, yet the microbial networks that mobilize P, including arbuscular mycorrhizal (AM) fungi and phosphorus-cycling bacteria (PCBs), remain under-characterized in these nutrient-poor soils. We show that across a 10,00-m elevation gradient, AM fungi and P-cycling gene assemblages shift predictably with pH, organic carbon, and phosphate availability. Higher elevations, with less available P, select for stress-tolerant AM fungal taxa and PCB strategies geared toward mineral solubilization, while low-elevation sites favor root colonization by AM fungi and organic P mineralization. These results suggest that nutrient limitation can constrain microbial community assembly in consistent ways across landscapes. High mountain soils are low in P and rely on a network of underground AM fungi and PCB to deliver nutrients to plants. This study shows how those underground relationships reorganize with elevation and how climate change could collapse long-standing microbial strategies by pushing high-elevation ecosystems toward lowland conditions. As soils warm and dry, the microbial scaffolding that supports alpine plant life may become increasingly unstable.

arbuscular mycorrhizal fungi↗
NASA NTRS1992

Purification and characterization of a casein kinase 2-type protein kinase from pea nuclei

Almost all the polyamine-stimulated protein kinase activity associated with the chromatin fraction of nuclei purified from etiolated pea (Pisum sativum L.) plumules is present in a single enzyme that can be extracted from chromatin by 0.35 molar NaCl. This protein kinase can be further purified over 2000-fold by salt fractionation and anion-exchange and casein-agarose column chromatography, after which it is more than 90% pure. The purified kinase has a specific activity of about 650 nanomoles per minute per milligram protein in the absence of polyamines, with either ATP or GTP as phosphoryl donor. Spermidine can stimulate its activity fourfold, with half-maximal activation at about 2 millimolar. Spermine and putrescine also stimulate activity, although somewhat less effectively. This kinase has a tetrameric alpha 2 beta 2 structure with a native molecular weight of 130,000, and subunit molecular weights of 36,000 for the catalytic subunit (alpha) and 29,000 for the regulatory subunit (beta). In western blot analyses, only the alpha subunit reacts strongly with polyclonal antibodies to a Drosophila casein kinase II. The pea kinase can use casein and phosvitin as artificial substrates, phosphorylating both the serine and threonine residues of casein. It has a pH optimum near 8.0, a Vmax of 1.5 micromoles per minute per milligram protein, and a Km for ATP of approximately 75 micromolar. Its activity can be almost completely inhibited by heparin at 5 micrograms per milliliter, but is relatively insensitive to concentrations of staurosporine, K252a, and chlorpromazine that strongly antagonize Ca(2+) -regulated protein kinases. These results are discussed in relation to recent findings that casein kinase 2-type kinases may phosphorylate trans-acting factors that bind to light-regulated promoters in plants.

NASA Program Space Biology↗
DOE OSTI2021

Understanding tungsten erosion during inter/intra-ELM periods in He-dominated JET-ILW plasmas

Tungsten erosion was quantified during inter/intra-ELM periods in He-dominated JET-ILW plasmas by optical emission spectroscopy. The intra-ELM tungsten sputtering in helium plasmas, which dominates the total W source, prevails by a factor of about 4 over inter-ELM sputtering in the investigated ELM frequency range from 90 Hz–120 Hz. He ions are mainly responsible for the W erosion during the ELMs in He plasmas. The strong in/out asymmetry of the ELM-induced W erosion is observed in He plasmas even at high ELM frequencies beyond 100 Hz. In Ohmic/L-mode plasmas and during the H-mode inter-ELM plasma phases both He 2+ and Be 2+ ionic species are major contributors to the W erosion. Their contribution depends on the electron temperature in the divertor: for T e > 15 eV both species cause significant W sputtering, for T e < 15 eV, B e 2+ ions are solely responsible for the W erosion. Tungsten erosion during in both inter and intra-ELM periods in He-dominated plasmas are significantly larger than in deuterium plasmas. It is 15–25 times larger during the inter-ELM phase and in L-mode discharges at T e = 25–30 eV. On the other hand, the ELM-induced W source is by a factor of 3 larger than in D plasmas.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Effect of pH and calcium on short-term NO3- fluxes in roots of barley seedlings

The effect of pH and Ca2+ on net NO3- uptake, influx, and efflux by intact roots of barley (Hordeum vulgare L.) seedlings was studied. Seedlings were induced with NO3- or NO2-. Net NO3- uptake and efflux, respectively, were determined by following its depletion from, and accumulation in, the external solution. Since roots of both uninduced and NO2(-)-induced seedlings contain little internal NO3- initial net uptake rates are equivalent to influx (M. Aslam, R.L. Travis, R.C. Huffaker [1994] Plant Physiol 106: 1293-1301). NO3-, uptake (influx) by these roots was little affected at acidic pH. In contrast, in NO3(-)-induced roots, which accumulate NO3-, net uptake rates decreased in response to acidic pH. Under these conditions, NO3- efflux was stimulated and was a function of root NO3- concentration. Conversely, at basic pH, NO3- uptake by NO3- and NO2(-)-induced and uninduced roots decreased, apparently because of the inhibition of influx. Calcium had little effect on NO3- uptake (influx) by NO2(-)-induced roots at either pH 3 or 6. However, in NO3(-)-induced roots, lack of Ca2+ at pH 3 significantly decreased net NO3- uptake and stimulated efflux. The results indicate that at acidic pH the decrease in net NO3- uptake is due to the stimulation of efflux, whereas at basic pH, it is due to the inhibition of influx.

Non-NASA Center↗
DOE OSTI2022

Electrochemical techniques and mechanisms for the corrosion of metals and alloys in sub- and supercritical aqueous systems

Corrosion has become a decisive factor hindering supercritical water technologies' long-cycle, safe implementation. Electrochemical experiments performed in supercritical aqueous systems can capture essential, real-time information about the micro/nanoscale processes of corrosion and their kinetics. As a starting point, this paper first summarizes the critical chemical properties of supercritical aqueous systems and analyzes their role in determining the duality of corrosion mechanisms (whether electrochemical or chemical micro-processes predominate). Next, it reviews the available electrochemical techniques such as pH sensors, electrochemical noise measurements, and related applications for quantitatively elaborating the corrosion issues in supercritical aqueous systems. With thick and heavy colors, a series of mechanistic models, such as the mixed potential model and the coupled environment models were introduced from the fundamental theories to the related applications, which have been applied widely in ambient and subcritical aqueous systems and exhibit great values and potential to be employed in high-density supercritical water environments. The passivity, depassivation, and passivity breakdown of metals and alloys in terms of the Point Defect Model (PDM) were also successfully implemented and discussed. Further, the newly built SCW_PDM describes the film growth kinetics at the atomic level of metals and alloys in supercritical water and is being developed to quantitatively analyze and resolve a series of corrosion issues such as the passivity breakdown and the stress corrosion cracking that occur in supercritical aqueous systems. This review is helpful by promoting the development of the electrochemical corrosion theory in supercritical aqueous systems and by identifying corrosion prevention and control methods for the safe implementation of relevant supercritical water technologies.

36 MATERIALS SCIENCE↗