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Sample records for active uvi reduction

  1. Kinetics of Microbial Reduction of Solid Phase U(VI)

    SciTech Connect

    Liu, Chongxuan; Jeon, Byong Hun; Zachara, John M.; Wang, Zheming; Dohnalkova, Alice; Fredrickson, Jim K.

    2006-10-01

    Sodium boltwoodite (NaUO2SiO3OH ?1.5H2O) was used to assess the kinetics of microbial reduction of solid phase U(VI) by a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. The bioreduction kinetics was studied with Na-boltwoodite in suspension or within alginate beads. Concentrations of U(VI)tot and cell number were varied to evaluate the coupling of U(VI) dissolution, diffusion, and microbial activity. Batch experiments were performed in a non-growth medium with lactate as electron donor at pH 6.8 buffered with PIPES. Microscopic and spectroscopic analyses with transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and laser-induced fluorescence spectroscopy (LIFS) collectively indicated that solid phase U(VI) was first dissolved and diffused out of grain interiors before it was reduced on bacterial surfaces and/or within the periplasm. The kinetics of solid phase U(VI) bioreduction was well described by a coupled model of bicarbonate-promoted dissolution of Na-boltwoodite, intraparticle uranyl diffusion, and Monod type bioreduction kinetics with respect to dissolved U(VI) concentration. The results demonstrated the intimate coupling of biological, chemical, and physical processes in microbial reduction of solid phase U(VI).

  2. U(VI) reduction to mononuclear U(VI) by desulfitobacterium spp.

    SciTech Connect

    Fletcher, K. E.; Boyanov, M. I.; Thomas, S. H.; Wu, Q.; Kemner, K. M.; Loffler, F. E.

    2010-06-15

    The bioreduction of U(VI) to U(IV) affects uranium mobility and fate in contaminated subsurface environments and is best understood in Gram-negative model organisms such as Geobacter and Shewanella spp. This study demonstrates that U(VI) reduction is a common trait of Gram-positive Desulfitobacterium spp. Five different Desulfitobacterium isolates reduced 100 {mu}M U(VI) to U(IV) in <10 days, whereas U(VI) remained soluble in abiotic and heat-killed controls. U(VI) reduction in live cultures was confirmed using X-ray absorption near-edge structure (XANES) analysis. Interestingly, although bioreduction of U(VI) is almost always reported to yield the uraninite mineral (UO{sub 2}), extended X-ray absorption fine structure (EXAFS) analysis demonstrated that the U(IV) produced in the Desulfitobacterium cultures was not UO{sub 2}. The EXAFS data indicated that the U(IV) product was a phase or mineral composed of mononuclear U(IV) atoms closely surrounded by light element shells. This atomic arrangement likely results from inner-sphere bonds between U(IV) and C/N/O- or P/S-containing ligands, such as carbonate or phosphate. The formation of a distinct U(IV) phase warrants further study because the characteristics of the reduced material affect uranium stability and fate in the contaminated subsurface.

  3. Abiotic reductive immobilization of U(VI) by biogenic mackinawite.

    PubMed

    Veeramani, Harish; Scheinost, Andreas C; Monsegue, Niven; Qafoku, Nikolla P; Kukkadapu, Ravi; Newville, Matt; Lanzirotti, Antonio; Pruden, Amy; Murayama, Mitsuhiro; Hochella, Michael F

    2013-03-05

    During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U(VI) reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe 1+x S, x = 0 to 0.11) to reduce U(VI) abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS, and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U(VI) indicate the formation of nanoparticulate UO2. This study suggests the relevance of sulfide-bearing biogenic minerals in mediating abiotic U(VI) reduction, an alternative pathway in addition to direct enzymatic U(VI) reduction.

  4. Reduction of U(VI) and Toxic Metals by Desulfovibrio Cytochrome c3

    SciTech Connect

    Wall, Judy D.

    2003-06-01

    The project, ''Reduction of U(VI) and toxic metals by Desulfovibrio cytochrome c3'', is designed to obtain spectroscopic information for or against a functional interaction of cytochrome c3 and uranium in the whole cells. That is, is the cytochrome c3 the uranium reductase? Our approach has been to start with purified cytochrome and determine any unique spectral disturbances during electron flow to U(VI). Then we will attempt to identify these signals emanating from cells actively reducing uranium. This project is being carried out in collaboration with Dr. William Woodruff at the Los Alamos National Laboratory where the spectral experiments are being carried out.

  5. Effects of Bacillus subtilis on the reduction of U(VI) by nano-Fe0

    NASA Astrophysics Data System (ADS)

    Ding, Congcong; Cheng, Wencai; Sun, Yubing; Wang, Xiangke

    2015-09-01

    The effects of Bacillus subtilis (B. subtilis, a typical model bacterium) on the reduction of U(VI) by nanoscale zero-valent iron (nano-Fe0) were investigated using batch techniques. The reaction products were analysed using spectroscopic techniques, and a kinetics model was developed to elucidate the mechanisms of U(VI) reduction by nano-Fe0. The presence of B. subtilis enhanced the U(VI) sorption rate at pH 3.5-9.5 but inhibited the reduction rate of U(VI) to U(IV) at pH > 4.5. According to the FTIR and XRD analysis, the reduction of U(VI) to U(IV) was inhibited due to the formation of inner-sphere surface complexes between the oxygen-containing functional groups of B. subtilis or extracellular polymeric substances with the Fe(II)/Fe(III) generated by nano-Fe0, which blocked electron transport from the Fe0 core to U(VI). Based on the EXAFS analysis, a fitting of U-Fe shell at ∼3.44 Å revealed inner-sphere bidentate complexes between uranyl and the oxide film of nano-Fe0. For the nano-Fe0 + B. subtilis system, the U-Fe shell (at ∼3.44 Å) and the U-C/P shell (at ∼2.90 Å) further indicated the formation of inner-sphere surface complexes. The kinetics model supported that U(VI) reduction was triggered by U(VI) sorption on the oxide shell of nano-Fe0. The XPS and XANES analyses showed that reductive precipitation was the main mechanism of U(VI) removal by nano-Fe0, whereas the sorption process dominated the removal of U(VI) in the presence of B. subtilis, which was further demonstrated by TEM images.

  6. Influence of Dynamical Conditions on the Reduction of UVI at the Magnetite-Solution Interface

    SciTech Connect

    Ilton, Eugene S.; Boily, Jean F.; Buck, Edgar C.; Skomurski, Frances N.; Rosso, Kevin M.; Cahill, Christopher L.; Bargar, John R.; Felmy, Andrew R.

    2010-01-14

    The heterogeneous reduction of UVI to UIV by ferrous iron is a potentially key process influencing the fate and transport of U in the environment. The reactivity of both sorbed and structural FeII has been studied for numerous substrates, including magnetite. The results from UVI-magnetite experiments have been variable, ranging from no reduction to clear evidence for the formation of UIV. In this contribution, we used XAS and high resolution (+cryogenic) XPS to study the interaction of UVI with nano-particulate magnetite. The results indicated that UVI was partially reduced to UV with no evidence of UIV. However, thermodynamic calculations indicated that mixed-valence U phases with average oxidation states below (V) should have been stable, indicating that the system was not in redox equilibrium. A reaction pathway that involves incorporation of U and stabilization of UV and UVI in secondary phases is invoked to explain the observations.

  7. Reduction of U(VI) Complexes by Anthraquinone Disulfonate: Experiment and Molecular Modeling

    SciTech Connect

    Ainsworth, C.C.; Wang, Z.; Rosso, K.M.; Wagnon, K.; Fredrickson, J.K.

    2004-03-17

    Past studies demonstrate that complexation will limit abiotic and biotic U(VI) reduction rates and the overall extent of reduction. However, the underlying basis for this behavior is not understood and presently unpredictable across species and ligand structure. The central tenets of these investigations are: (1) reduction of U(VI) follows the electron-transfer (ET) mechanism developed by Marcus; (2) the ET rate is the rate-limiting step in U(VI) reduction and is the step that is most affected by complexation; and (3) Marcus theory can be used to unify the apparently disparate U(VI) reduction rate data and as a computational tool to construct a predictive relationship.

  8. Characterization of U(VI) reduction in contaminated sediments with slow-degrading electron donor source

    NASA Astrophysics Data System (ADS)

    Wu, W.; Watson, D. B.; Zhang, G.; Mehlhorn, T.; Lowe, K.; Earles, J.; Phillips, J.; Kelly, S. D.; Boyanov, M.; Kemner, K. M.; Schadt, C.; Criddle, C. S.; Jardine, P. M.; Brooks, S. C.

    2011-12-01

    In order to select sustainable, high efficiency and cost effective electron donor source, oleate and emulsified vegetable oil (EVO) were tested uranium (VI) reduction in comparison with ethanol in microcosms using uranium contaminated sediments and groundwater from the US DOE Oak Ridge Integrated Field Research Challenge (ORIFRC) site. The effect of initial sulfate concentration on U(VI) reduction was also tested. Both oleate and EVO were effective electron donor sources for U(VI) reduction. Accumulation of acetate as a major product and the removal of aqueous U(VI) were observed and were associated with sulfate reduction. Both oleate and EVO supported U(VI) reduction but at slower rates with a comparable but slightly lower extent of reduction than ethanol. X-ray absorption near-edge spectroscopy (XANES) analysis confirmed reduction of U(VI) to U(IV). The extent of U(VI) reduction in solid phase was negatively influenced by aqueous calcium concentration. The majority of electrons of the three substrates were consumed by sulfate reduction, Fe(III) reduction, and methanogenesis. Initial U(VI) concentration in the aqueous phase increased with increased sulfate concentration (1 versus 5 mM), likely due to U(VI) desorption from the solid phase. At the higher initial sulfate concentration more U(VI) was reduced and fewer electrons were used in methanogenesis. Analysis of bacterial and archeal populations using 16S rRNA gene libraries showed a significant increase in Deltaproteobacteria after biostimulation. The microbial community structures developed with oleate and EVO were significantly distinct from those developed with ethanol. Bacteria similar to Desulforegula spp. was predominant for oleate and EVO degradation but were not observed in ethanol-amended microcosms. Known U(VI)-reducing bacteria in the microcosms amended with the three electron donor sources included iron(III) reducing Geobacter spp. but in lower abundances than sulfate-reducing Desulfovibrio spp. The

  9. Isotopic and geochemical tracers for U(VI) reduction and U mobility at an in situ recovery U mine

    DOE PAGES

    Basu, Anirban; Brown, Shaun T.; Christensen, John N.; ...

    2015-05-19

    In situ recovery (ISR) uranium (U) mining mobilizes U in its oxidized hexavalent form (U(VI)) by oxidative dissolution of U from the roll-front U deposits. Post-mining natural attenuation of residual U(VI) at ISR mines is a potential remediation strategy. Detection and monitoring of naturally occurring reducing subsurface environments are important for successful implementation of this remediation scheme. We used the isotopic tracers ²³⁸U/²³⁵U (δ²³⁸U), ²³⁴U/²³⁸U activity ratio, and ³⁴S/³²S (δ³⁴S), and geochemical measurements of U ore and groundwater collected from 32 wells located within, upgradient, and downgradient of a roll-front U deposit to detect U(VI) reduction and U mobility atmore » an ISR mining site at Rosita, TX, USA. The δ²³⁸U in Rosita groundwater varies from 0.61‰ to -2.49‰, with a trend toward lower δ²³⁸U in downgradient wells. The concurrent decrease in U(VI) concentration and δ²³⁸U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic ²³⁴U/²³⁸U activity ratio and δ³⁴S values may also be used to trace the mobility of the ore zone groundwater after mining has ended. These results support the use of U isotope-based detection of natural attenuation of U(VI) at Rosita and other similar ISR mining sites.« less

  10. Cassini UVIS Observations Show Active Saturn's Rings

    NASA Astrophysics Data System (ADS)

    Esposito, L.; Colwell, J. E.; UVIS Team

    2004-12-01

    The Cassini Ultraviolet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the NASA/ESA Cassini spacecraft. This spectrograph includes channels for extreme UV and far UV spectroscopic imaging, high speed photometry of stellar occultations, solar EUV occultation, and a hydrogen/deuterium absorption cell. We report our initial results from UVIS observations of Saturn's rings. Dynamic interactions between neutrals, ions, rings, moons and meteoroids produce a highly structured and time variable Saturn system Oxygen in the Saturn system dominates the magnetosphere. Observed fluctuations indicate close interactions with plasma sources. Stochastic events in the E ring may be the ultimate source. The spectral signature of water ice is seen on Phoebe and in Saturn's rings. Water ice is mixed non-uniformly with darker constituents. The high structure of the UV ring reflectance argues that collisional transport dominates ballistic transport in darkening the rings. Our preliminary results support the idea that rings are recycled fragments of moons: the current processes are more important than history and initial conditions. The spectra along the UVIS SOI radial scan indicate varying amounts of water ice. In the A ring, the ice fraction increases outward to a maximum at the outer edge. This large-scale variation is consistent with initially pure ice that has suffered meteoritic bombardment over the age of the Solar system (Cuzzi and Estrada 1998). We also see variations over scales of 1000 - 3000 km, which cannot be explained by this mechanism. Ballistic transport of spectrally neutral extrinsic pollutants from meteoroids striking the rings has a typical throw distance of 6000 km (Durisen et al 1989), too long to explain this finer structure. We propose a class of smaller renewal events, in which a small moon residing within the rings is shattered by an external impactor (Colwell and Esposito 1993, Barbara and Esposito 2002, Esposito and Colwell 2003). The

  11. Inhibition of U(VI) reduction by synthetic and natural pyrite.

    PubMed

    Yang, Zhuanwei; Kang, Mingliang; Ma, Bin; Xie, Jinglin; Chen, Fanrong; Charlet, Laurent; Liu, Chunli

    2014-09-16

    Reductive precipitation is an effective method of attenuating the mobility of uranium (U) in subsurface environments. The reduction of U(VI) by synthetic and naturally occurring pyrite was investigated at pH 3.0-9.5. In contrast to thermodynamic calculations that were used to predict UO2(s) precipitation, a mixed U(IV) and U(VI) product (e.g., U3O8/U4O9/U3O7) was only observed at pH 6.21-8.63 and 4.52-4.83 for synthetic and natural pyrite, respectively. Under acidic conditions, the reduction of UO2(2+) by surface-associated Fe(2+) may not be favored because the mineral surface is nearly neutral or not negative enough. At high pH, the sorption of negatively charged U(VI) species is not favored on the negatively charged mineral surface. Thus, the redox reaction is not favored. Trace elements generally contained within the natural pyrite structure can affect the reactivity of pyrite and lead to a different result between the natural and synthetic pyrite. Because UO2(s) is extremely redox-sensitive toward U(VI), the observed UO2+x(s) phase reduction product indicates a surface reaction that is largely controlled by reaction kinetics and pyrite surface chemistry. These factors may explain why most laboratory experiments have observed incomplete U(VI) reduction on Fe(II)-bearing minerals.

  12. Abiotic U(VI) Reduction by Sorbed Fe(II) on Natural Sediments

    SciTech Connect

    Fox, Patricia M.; Davis, James A.; Kukkadapu, Ravi K.; Singer, David M.; Bargar, John R.; Williams, Kenneth H.

    2013-09-15

    Laboratory experiments were performed as a function of aqueous Fe(II) concentration to determine the uptake and oxidation of Fe(II), and Fe(II)-mediated abiotic reduction of U(VI) by aquifer sediments from the Rifle IFRC field site in Colorado, USA. Mössbauer analysis of the sediments spiked with aqueous 57Fe(II) showed that 57Fe(II) was oxidized on the mineral surfaces to 57Fe(III) and most likely formed a nano-particulate Fe(III)-oxide or ferrihydrite-like phase. The extent of 57Fe oxidation decreased with increasing 57Fe(II) uptake, such that 100 % was oxidized at 7.3 μmol/g Fe and 52 % at 39.6 μmol/g Fe, indicating that the sediments had a finite capacity for oxidation of Fe(II). Abiotic U(VI) reduction was observed by XANES spectroscopy only when the Fe(II) uptake was greater than approximately 20 μmol/g and surface-bound Fe(II) was present. The level of U(VI) reduction increased with increasing Fe(II)- loading above this level to a maximum of 18 and 36 % U(IV) at pH 7.2 (40.7 μmol/g Fe) and 8.3 (56.1 μmol/g Fe), respectively in the presence of 400 ppm CO2. Greater U(VI) reduction was observed in CO2 free systems [up to 44 and 54 % at pH 7.2 (17.3 μmol/g Fe) and 8.3 (54.8 μmol/g Fe), respectively] compared to 400 ppm CO2 systems, presumably due to differences in aqueous U(VI) speciation. While pH affects the amount of Fe(II) uptake onto the solid phase, with greater Fe(II) uptake at higher pH, similar amounts of U(VI) reduction were observed at pH 7.2 and 8.3 for a similar Fe(II) uptake. Thus, it appears that abiotic U(VI) reduction is controlled primarily by Fe(II) concentration and aqueous U(VI) speciation. The range of Fe(II) loadings tested in this study are within the range observed in bioreduced sediments, suggesting that Fe(II)-mediated abiotic U(VI) reduction may indeed play a role in field settings.

  13. Sediment studies of the biological factors controlling the reduction of U(VI).

    SciTech Connect

    Lovley, derek, R.

    2004-08-04

    Studies were conducted primarily with sediments, both in laboratory incubations and in a field experiment, with supporting studies with pure cultures. To our knowledge the sediment studies were the first on microbial U(VI) reduction in actual uranium-contaminated subsurface sediments, under conditions that mimic those found in situ. Important findings included: (1) U(VI) reduction is a biotic process in subsurface sediments. (2) U(VI) reduction can be stimulated most effectively with the addition of acetate. Although it had been speculated that microbial U(VI) reduction might be capable of this type of environmental remediation ever since the discovery of microbial U(VI) reduction, this had not been previously demonstrated under environmentally relevant conditions. (3) U(VI) is reduced concurrently with Fe(III) and prior to sulfate reduction. U(VI) and Fe(III) reduction proceeded concurrently, accompanied by a dramatic enrichment in organisms in the Geobacteraceae. Sulfate-reducing microorganisms do not appear to be important components of the microbial community reducing U(VI) in these subsurface sediments. (4) Nitrate has important influences on U(VI) reduction. Nitrate inhibits the reduction of metals until nitrate is depleted. Fe(III)-reducing microorganisms such as Geobacter metallireducens and Desulfitobacterium species can oxidize Fe(II) with the reduction of nitrate which is an important consideration because our previous studies have demonstrated that freshly precipitated Fe(III) oxides can reoxidize U(IV) to U(VI). The discovery that G. metallireducens can ''run backwards'' and oxidize U(IV) when nitrate is present reveals another mechanism preventing precipitation of U(IV) in the presence of nitrate as well as potential novel strategy for removing uranium from the subsurface after a site has been remediated. (5) Importance of understanding Fe(III) forms available for microbial reduction. Fe(III) is orders of magnitude more abundant than U(VI) as an

  14. Reduction of U(VI) to U(IV) by indigenous bacteria in contaminated ground water

    NASA Astrophysics Data System (ADS)

    Abdelouas, A.; Lu, Yongming; Lutze, W.; Nuttall, H. E.

    1998-12-01

    We report on bio-catalyzed reduction and immobilization of U(VI) species (0.25 mg/l to 235 mg/l) in ground water in the presence of high concentrations of nitrate, sulfate and carbonate. We studied ground water from the uranium mill tailings site near Tuba City, Arizona (USA). Experiments with the ground water were conducted in the presence of the Navajo sandstone host rock. Uranium in solution is complexed by carbonate. Two indigenous denitrifying bacteria were identified Pseudomonas aeruginosa and P. stutzeri, and one sulfate reducing bacterium, Shewanella putrefaciens, also known as Fe(III)-reducer. S. putrefaciens can use U(VI) as an electron acceptor, instead of Fe(III). Ethanol was used as the organic carbon source. Microbially mediated reactions are sequential in the order of decreasing redox intensity. Metabolic reduction of nitrate to gaseous species (N 2, N 2O) was complete within 1 week at 16°C. The sulfate concentration remained constant. Some of the U(VI) coprecipitated with aragonite/calcite or was adsorbed on biomass during denitrification. Subsequently, the enzymatically catalyzed reduction of U(VI) to U(IV) was complete within 3 weeks but was accompanied by reduction of sulfate to sulfide. U(IV) precipitated as a uraninite solid solution (U, Ca)O 2, adhering to the bacteria. The final concentration in solution was ≤1 μg/l. U(VI) was not reduced by sulfide. Complexation of U(VI) by carbonate made its reduction by sulfide even slower than in pure water. The bio-catalyzed reaction is the faster process under the conditions given by the composition of the ground water.

  15. U(VI) Sorption and Reduction Kinetics on the Magnetite (111) Surface

    SciTech Connect

    Singer, David M.; Chatman, Shawn M.; Ilton, Eugene S.; Rosso, Kevin M.; Banfield, Jillian F.; Waychunas, Glenn A.

    2012-04-03

    Sorption of contaminants onto mineral surfaces is an important process that can restrict their transport in the environment. In the current study, uranium (U) uptake on magnetite (111) was measured as a function of time and solution composition (pH, [CO3]T, [Ca]) under continuous batch-flow conditions. We observed, in real-time and in situ, adsorption and reduction of U(VI) and subsequent growth of UO2 nanoprecipitates using atomic force microscopy (AFM) and newly developed batch-flow U LIII-edge grazing-incidence X-ray absorption spectroscopy near-edge structure (GI-XANES) spectroscopy. U(VI) reduction occurred with and without CO3 present, and coincided with nucleation and growth of UO2 particles. When Ca and CO3 were both present no U(VI) reduction occurred and the U surface loading was lower. In situ batch-flow AFM data indicated that UO2 particles achieved a maximum height of 4–5 nm after about 8 h of exposure, however, aggregates continued to grow laterally after 8 h reaching up to about 300 nm in diameter. The combination of techniques indicated that U uptake is divided into three-stages; (1) initial adsorption of U(VI), (2) reduction of U(VI) to UO2 nanoprecipitates at surface-specific sites after 2–3 h of exposure, and (3) completion of U(VI) reduction after ~6–8 h. U(VI) reduction also corresponded to detectable increases in Fe released to solution and surface topography changes. Redox reactions are proposed that explicitly couple the reduction of U(VI) to enhanced release of Fe(II) from magnetite. Although counterintuitive, the proposed reaction stoichiometry was shown to be largely consistent with the experimental results. In addition to providing molecular-scale details about U sorption on magnetite, this work also presents novel advances for collecting surface sensitive molecular-scale information in real-time under batch-flow conditions.

  16. Remediation of uranium contaminated soils with bicarbonate extraction and microbial U(VI) reduction

    USGS Publications Warehouse

    Philips , Elizabeth J.P.; Landa, Edward R.; Lovely, Derek R.

    1995-01-01

    A process for concentrating uranium from contaminated soils in which the uranium is first extracted with bicarbonate and then the extracted uranium is precipitated with U(VI)-reducing microorganisms was evaluated for a variety of uranuum-contaminated soils. Bicarbonate (100 mM) extracted 20–94% of the uranium that was extracted with nitric acid. The U(VI)-reducing microorganism,Desulfovibrio desulfuricans reduced the U(VI) to U(IV) in the bicarbonate extracts. In some instances unidentified dissolved extracted components, presumably organics, gave the extract a yellow color and inhibited U(VI) reduction and/or the precipitation of U(IV). Removal of the dissolved yellow material with the addition of hydrogen peroxide alleviated this inhibition. These results demonstrate that bicarbonate extraction of uranium from soil followed by microbial U(VI) reduction might be an effective mechanism for concentrating uranium from some contaminated soils.

  17. Role of U(VI) Reduction by Geobacter species

    SciTech Connect

    Lovely, Derrick

    2008-12-23

    Previous work had suggested that Acholeplasma palmae has a higher capacity for uranium sorption than other bacteria studied. Sorption studies were performed with cells in suspension in various solutions containing uranium, and results were used to generate uranium-biosorption isotherms. Results from this study showed that the U(VI) sorption capacity of G. uraniireducens was relatively similar in simple solutions, such as sodium chloride or bicarbonate. However, this ability to sorb uranium significantly decreased in groundwater. This suggested that certain chemicals present in the groundwater were inhibiting the ability of cell components of Geobacter to adsorb uranium. It was hypothesized that uranium removal would also be diminished in the bicarbonate solution. However, this did not seem to be the case, as uranium was as easily removed in the bicarbonate solution as in the sodium chloride solution.

  18. Elucidating Geochemical and Biogeochemical U(VI) Reduction Via Soil Sterilization at Oak Ridge, Tennessee

    NASA Astrophysics Data System (ADS)

    Bank, T. L.; Jardine, P. M.; Phelps, T. J.; Ginder-Vogel, M. A.; Fendorf, S. E.; Baldwin, M. E.

    2005-12-01

    The adsorption and reduction of U(VI) onto sterilized and nonsterilized soil from the Oak Ridge Reservation was studied to distinguish biogeochemical versus geochemical effects on metal reduction. The Oak Ridge soil under investigation is a saprolite sequence of interbedded weathered shale and limestone obtained at the capillary fringe with a pH near 7.6. Experiments were conducted on unaltered soils as well as subsamples of the soil that were pre-treated to remove free oxides and/or organic matter. Soils were sterilized by either steam sterilization at 1210C or by γ-irradiation using a Cobalt-60 source with a γ-ray dosage of 20kGy. Sterile and nonsterile U(VI) batch experiments were completed aerobically over a reaction time of 400 hours. The reactions were buffered using 25mM HEPES and NaHCO3. Initial U(VI) concentrations ranged from 0.5 to 10 ppm. The effects of sterilization on bacterial population, soil mineralogy, pH, ζ-potential, cation exchange capacity, redox potential, and soil organic matter (SOM) were identified. Sterilization by irradiation was >99.99% efficient and steam sterilization was approximately 99% efficient. Major mineralogy, soil pH, and clay mineral ζ-potential were unaffected by the sterilization techniques. The cation exchange capacity of the irradiated soils decreased from 40 to 30 cmolc/kg. Sterilization by irradiation caused some degradation of the SOM, as determined by UV-VIS, however the results were practically insignificant due to the small quantity of SOM in the Oak Ridge soil (<0.1%). The redox potential of the soil before and after sterilization is being tested. Results indicate that the removal of U(VI) from solution onto untreated soils was significantly increased in soil sterilized by γ-irradiation compared to nonsterilized soil and suggests that geochemical processes, rather than biogeochemical processes, controlled U(VI) sorption/reduction in these soils. Results of experiments completed using soils pre-treated with H2

  19. U(VI) reduction by diverse outer surface c-type cytochromes of Geobacter sulfurreducens.

    PubMed

    Orellana, Roberto; Leavitt, Janet J; Comolli, Luis R; Csencsits, Roseann; Janot, Noemie; Flanagan, Kelly A; Gray, Arianna S; Leang, Ching; Izallalen, Mounir; Mester, Tünde; Lovley, Derek R

    2013-10-01

    Early studies with Geobacter sulfurreducens suggested that outer-surface c-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain of G. sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surface c-type cytochromes of G. sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83% ± 10% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89% ± 10% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested that G. sulfurreducens requires outer-surface c-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors.

  20. U(VI) Reduction by Diverse Outer Surface c-Type Cytochromes of Geobacter sulfurreducens

    PubMed Central

    Leavitt, Janet J.; Comolli, Luis R.; Csencsits, Roseann; Janot, Noemie; Flanagan, Kelly A.; Gray, Arianna S.; Leang, Ching; Izallalen, Mounir; Mester, Tünde; Lovley, Derek R.

    2013-01-01

    Early studies with Geobacter sulfurreducens suggested that outer-surface c-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain of G. sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surface c-type cytochromes of G. sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83% ± 10% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89% ± 10% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested that G. sulfurreducens requires outer-surface c-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors. PMID:23934497

  1. Microbial reduction of U(VI) under alkaline conditions: implications for radioactive waste geodisposal.

    PubMed

    Williamson, Adam J; Morris, Katherine; Law, Gareth T W; Rizoulis, Athanasios; Charnock, John M; Lloyd, Jonathan R

    2014-11-18

    Although there is consensus that microorganisms significantly influence uranium speciation and mobility in the subsurface under circumneutral conditions, microbiologically mediated U(VI) redox cycling under alkaline conditions relevant to the geological disposal of cementitious intermediate level radioactive waste, remains unexplored. Here, we describe microcosm experiments that investigate the biogeochemical fate of U(VI) at pH 10-10.5, using sediments from a legacy lime working site, stimulated with an added electron donor, and incubated in the presence and absence of added Fe(III) as ferrihydrite. In systems without added Fe(III), partial U(VI) reduction occurred, forming a U(IV)-bearing non-uraninite phase which underwent reoxidation in the presence of air (O2) and to some extent nitrate. By contrast, in the presence of added Fe(III), U(VI) was first removed from solution by sorption to the Fe(III) mineral, followed by bioreduction and (bio)magnetite formation coupled to formation of a complex U(IV)-bearing phase with uraninite present, which also underwent air (O2) and partial nitrate reoxidation. 16S rRNA gene pyrosequencing showed that Gram-positive bacteria affiliated with the Firmicutes and Bacteroidetes dominated in the post-reduction sediments. These data provide the first insights into uranium biogeochemistry at high pH and have significant implications for the long-term fate of uranium in geological disposal in both engineered barrier systems and the alkaline, chemically disturbed geosphere.

  2. Reduction of U(VI) incorporated in the structure of hematite.

    PubMed

    Ilton, Eugene S; Pacheco, Juan S Lezama; Bargar, John R; Shi, Zhi; Liu, Juan; Kovarik, Libor; Engelhard, Mark H; Felmy, Andrew R

    2012-09-04

    U(VI) doped hematite was synthesized and exposed to two different organic reductants with E(0) of 0.23 and 0.70 V. A combination of HAADF-TEM and EXAFS provided evidence that uranium was incorporated in hematite in uranate, likely octahedral coordination. XPS indicated that structurally incorporated U(VI) was reduced to U(V), whereas non-incorporated U(VI) was reduced to U(IV). Specifically, the experiments indicate that U(V) was the dominant oxidation state of uranium in hematite around Eh -0.24 to -0.28 V and pH 7.7-8.6 for at least up to 5 weeks of reaction time. U(V), but not U(IV), was also detected in hematite at Eh +0.21 V (pH 7.1-7.3). The results support the hypothesis, based on previous experimental and theoretical work, that the stability field of U(V) is widened relative to U(IV) and U(VI) in uranate coordination environments where the coordination number of U is less than 8.

  3. Reduction of U(VI) Incorporated in the Structure of Hematite

    SciTech Connect

    Ilton, Eugene S.; Lazama Pacheco, Juan S.; Bargar, John R.; Shi, Zhi; Liu, Juan; Kovarik, Libor; Engelhard, Mark H.; Felmy, Andrew R.

    2012-09-04

    U(VI) doped hematite was synthesized and exposed to two different organic reductants with E0 of 0.23 and 0.70 V. A combination of HAADF-TEM and EXAFS provided evidence that uranium was incorporated in hematite in uranate, likely octahedral coordination. XPS indicated that structurally incorporated U(VI) was reduced to U(V), whereas adsorbed U(VI) was reduced to U(IV). Specifically, the experiments indicate that U(V) was the dominant oxidation state of uranium in hematite around Eh -0.24 to -0.28 V and pH 7.7-8.6 for at least up to 5 weeks of reaction time. U(V), but not U(IV), was also detected in hematite at Eh +0.21 V (pH 7.1-7.3). The results support the hypothesis, based on previous experimental and theoretical work, that the stability field of U(V) is widened relative to U(IV) and U(VI) in uranate coordination environments where the coordination number of U is less than 8.

  4. Metaproteomics Identifies the Protein Machinery Involved in Metal and Radionuclide Reduction in Subsurface Microbiomes and Elucidates Mechanisms and U(VI) Reduction Immobilization

    SciTech Connect

    Pfiffner, Susan M.; Löffler, Frank; Ritalahti, Kirsti; Sayler, Gary; Layton, Alice; Hettich, Robert

    2015-08-31

    The overall goal for this funded project was to develop and exploit environmental metaproteomics tools to identify biomarkers for monitoring microbial activity affecting U speciation at U-contaminated sites, correlate metaproteomics profiles with geochemical parameters and U(VI) reduction activity (or lack thereof), elucidate mechanisms contributing to U(VI) reduction, and provide remediation project managers with additional information to make science-based site management decisions for achieving cleanup goals more efficiently. Although significant progress has been made in elucidating the microbiology contribution to metal and radionuclide reduction, the cellular components, pathway(s), and mechanisms involved in U trans-formation remain poorly understood. Recent advances in (meta)proteomics technology enable detailed studies of complex samples, including environmental samples, which differ between sites and even show considerable variability within the same site (e.g., the Oak Ridge IFRC site). Additionally, site-specific geochemical conditions affect microbial activity and function, suggesting generalized assessment and interpretations may not suffice. This research effort integrated current understanding of the microbiology and biochemistry of U(VI) reduction and capitalize on advances in proteomics technology made over the past few years. Field-related analyses used Oak Ridge IFRC field ground water samples from locations where slow-release substrate biostimulation has been implemented to accelerate in situ U(VI) reduction rates. Our overarching hypothesis was that the metabolic signature in environmental samples, as deciphered by the metaproteome measurements, would show a relationship with U(VI) reduction activity. Since metaproteomic and metagenomic characterizations were computationally challenging and time-consuming, we used a tiered approach that combines database mining, controlled laboratory studies, U(VI) reduction activity measurements, phylogenetic

  5. Dynamic Succession of Groundwater Functional Microbial Communities in Response to Emulsified Vegetable Oil Amendment during Sustained In Situ U(VI) Reduction

    PubMed Central

    Zhang, Ping; Wu, Wei-Min; Van Nostrand, Joy D.; Deng, Ye; He, Zhili; Gihring, Thomas; Zhang, Gengxin; Schadt, Chris W.; Watson, David; Jardine, Phil; Criddle, Craig S.; Brooks, Scott; Marsh, Terence L.; Tiedje, James M.; Arkin, Adam P.

    2015-01-01

    A pilot-scale field experiment demonstrated that a one-time amendment of emulsified vegetable oil (EVO) reduced groundwater U(VI) concentrations for 1 year in a fast-flowing aquifer. However, little is known about how EVO amendment stimulates the functional gene composition, structure, and dynamics of groundwater microbial communities toward prolonged U(VI) reduction. In this study, we hypothesized that EVO amendment would shift the functional gene composition and structure of groundwater microbial communities and stimulate key functional genes/groups involved in EVO biodegradation and reduction of electron acceptors in the aquifer. To test these hypotheses, groundwater microbial communities after EVO amendment were analyzed using a comprehensive functional gene microarray. Our results showed that EVO amendment stimulated sequential shifts in the functional composition and structure of groundwater microbial communities. Particularly, the relative abundance of key functional genes/groups involved in EVO biodegradation and the reduction of NO3−, Mn(IV), Fe(III), U(VI), and SO42− significantly increased, especially during the active U(VI) reduction period. The relative abundance for some of these key functional genes/groups remained elevated over 9 months. Montel tests suggested that the dynamics in the abundance, composition, and structure of these key functional genes/groups were significantly correlated with groundwater concentrations of acetate, NO3−, Mn(II), Fe(II), U(VI), and SO42−. Our results suggest that EVO amendment stimulated dynamic succession of key functional microbial communities. This study improves our understanding of the composition, structure, and function changes needed for groundwater microbial communities to sustain a long-term U(VI) reduction. PMID:25862231

  6. Dynamic Succession of Groundwater Functional Microbial Communities in Response to Emulsified Vegetable Oil Amendment during Sustained In Situ U(VI) Reduction.

    PubMed

    Zhang, Ping; Wu, Wei-Min; Van Nostrand, Joy D; Deng, Ye; He, Zhili; Gihring, Thomas; Zhang, Gengxin; Schadt, Chris W; Watson, David; Jardine, Phil; Criddle, Craig S; Brooks, Scott; Marsh, Terence L; Tiedje, James M; Arkin, Adam P; Zhou, Jizhong

    2015-06-15

    A pilot-scale field experiment demonstrated that a one-time amendment of emulsified vegetable oil (EVO) reduced groundwater U(VI) concentrations for 1 year in a fast-flowing aquifer. However, little is known about how EVO amendment stimulates the functional gene composition, structure, and dynamics of groundwater microbial communities toward prolonged U(VI) reduction. In this study, we hypothesized that EVO amendment would shift the functional gene composition and structure of groundwater microbial communities and stimulate key functional genes/groups involved in EVO biodegradation and reduction of electron acceptors in the aquifer. To test these hypotheses, groundwater microbial communities after EVO amendment were analyzed using a comprehensive functional gene microarray. Our results showed that EVO amendment stimulated sequential shifts in the functional composition and structure of groundwater microbial communities. Particularly, the relative abundance of key functional genes/groups involved in EVO biodegradation and the reduction of NO3 (-), Mn(IV), Fe(III), U(VI), and SO4 (2-) significantly increased, especially during the active U(VI) reduction period. The relative abundance for some of these key functional genes/groups remained elevated over 9 months. Montel tests suggested that the dynamics in the abundance, composition, and structure of these key functional genes/groups were significantly correlated with groundwater concentrations of acetate, NO3 (-), Mn(II), Fe(II), U(VI), and SO4 (2-). Our results suggest that EVO amendment stimulated dynamic succession of key functional microbial communities. This study improves our understanding of the composition, structure, and function changes needed for groundwater microbial communities to sustain a long-term U(VI) reduction.

  7. Efficient sorption and reduction of U(VI) on zero-valent iron-polyaniline-graphene aerogel ternary composite.

    PubMed

    Chen, Lili; Feng, Shaojie; Zhao, Donglin; Chen, Shaohua; Li, Feifei; Chen, Changlun

    2017-03-15

    In this work, zero-valent iron-polyaniline-graphene aerogel composite (Fe-PANI-GA) was prepared and applied in the removal of U(VI) from aqueous solutions by batch sorption experiments. The experimental results showed that the Fe-PANI-GA composite had an excellent removal capacity for the removal of U(VI) in acidic solutions. The results also showed that the maximum removal capacity of the Fe-PANI-GA toward U(VI) was 350.47mg/g at pH 5.5. The sorption kinetics data were well-described by pseudo-second-order. The sorption isotherms of U(VI) fitted well with Langmuir isotherm and exhibited better removal efficiency with the increase of temperature. The thermodynamic parameters (ΔG, ΔS, ΔH) indicated that the sorption of U(VI) on the Fe-PANI-GA was an endothermic and spontaneous process. Moreover, removal mechanisms were studied based on the results of XRD, FTIR and XPS. Both U(VI) sorption and partially reductive precipitation of U(VI) to U(IV) contributed to the removal of U(VI) on Fe-PANI-GA. Therefore, Fe-PANI-GA was an economic and effective material for the removal of uranium from nuclear waste in practical application.

  8. Pilot-scale in situ bioremedation of uranium in a highly contaminated aquifer. 2. Reduction of u(VI) and geochemical control of u(VI) bioavailability.

    PubMed

    Wu, Wei-Min; Carley, Jack; Gentry, Terry; Ginder-Vogel, Matthew A; Fienen, Michael; Mehlhorn, Tonia; Yan, Hui; Caroll, Sue; Pace, Molly N; Nyman, Jennifer; Luo, Jian; Gentile, Margaret E; Fields, Matthew W; Hickey, Robert F; Gu, Baohua; Watson, David; Cirpka, Olaf A; Zhou, Jizhong; Fendorf, Scott; Kitanidis, Peter K; Jardine, Philip M; Criddle, Craig S

    2006-06-15

    In situ microbial reduction of soluble U(VI) to sparingly soluble U(IV) was evaluated at the site of the former S-3 Ponds in Area 3 of the U.S. Department of Energy Natural and Accelerated Bioremediation Research Field Research Center, Oak Ridge, TN. After establishing conditions favorable for bioremediation (Wu, et al. Environ. Sci. Technol. 2006, 40, 3988-3995), intermittent additions of ethanol were initiated within the conditioned inner loop of a nested well recirculation system. These additions initially stimulated denitrification of matrix-entrapped nitrate, but after 2 months, aqueous U levels fell from 5 to approximately 1 microM and sulfate reduction ensued. Continued additions sustained U(VI) reduction over 13 months. X-ray near-edge absorption spectroscopy (XANES) confirmed U(VI) reduction to U(IV) within the inner loop wells, with up to 51%, 35%, and 28% solid-phase U(IV) in sediment samples from the injection well, a monitoring well, and the extraction well, respectively. Microbial analyses confirmed the presence of denitrifying, sulfate-reducing, and iron-reducing bacteria in groundwater and sediments. System pH was generally maintained at less than 6.2 with low bicarbonate level (0.75-1.5 mM) and residual sulfate to suppress methanogenesis and minimize uranium mobilization. The bioavailability of sorbed U(VI) was manipulated by addition of low-level carbonate (< 5 mM) followed by ethanol (1-1.5 mM). Addition of low levels of carbonate increased the concentration of aqueous U, indicating an increased rate of U desorption due to formation of uranyl carbonate complexes. Upon ethanol addition, aqueous U(VI) levels fell, indicating that the rate of microbial reduction exceeded the rate of desorption. Sulfate levels simultaneously decreased, with a corresponding increase in sulfide. When ethanol addition ended but carbonate addition continued, soluble U levels increased, indicating faster desorption than reduction. When bicarbonate addition stopped

  9. Uranium isotopic fractionation factors during U(VI) reduction by bacterial isolates

    NASA Astrophysics Data System (ADS)

    Basu, Anirban; Sanford, Robert A.; Johnson, Thomas M.; Lundstrom, Craig C.; Löffler, Frank E.

    2014-07-01

    We experimentally determined the magnitude of uranium isotopic fractionation induced by U(VI) reduction by metal reducing bacterial isolates. Our results indicate that microbial U(VI) reduction induces isotopic fractionation; heavier isotopes (i.e., 238U) partition into the solid U(IV) products. The magnitudes of isotopic fractionation (expressed as ε = 1000‰ * (α-1)) for 238U/235U were 0.68‰ ± 0.05‰ and 0.99‰ ± 0.12‰ for Geobacter sulfurreducens strain PCA and strain IFRC-N, respectively. The ε values for Anaeromyxobacter dehalogenans strain FRC-W, strain FRC-R5, a novel Shewanella isolate, and Desulfitobacterium sp. strain Viet1 were 0.72‰ ± 0.15‰, 0.99‰ ± 0.12‰, 0.96‰ ± 0.16‰ and 0.86‰ ± 0.06‰, respectively. Our results show that the maximum ε values of ∼1.0‰ were obtained with low biomass (∼107 cells/mL) and low electron donor concentrations (∼500 μM). These results provide an initial assessment of 238U/235U shifts induced by microbially-mediated U(VI) reduction, which is needed as 238U/235U data are increasingly applied as redox indicators in various geochemical settings.

  10. Abiotic Reductive Immobilization of U(VI) by Biogenic Mackinawite

    SciTech Connect

    Veeramani, Harish; Scheinost, Andreas; Monsegue, Niven; Qafoku, Nikolla; Kukkadapu, Ravi K.; Newville, Mathew; Lanzirotti, Anthony; Pruden, Amy; Murayama, Mitsuhiro; Hochella, Michael F.

    2013-03-01

    During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in-situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U6+ reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe1+xS, x = 0 to 0.11) to reduce U6+ abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U6+ indicate the formation of nanoparticulate UO2. This study suggests the relevance of Fe(II) and sulfide bearing biogenic minerals in mediating abiotic U6+ reduction, an alternative pathway in addition to direct enzymatic U6+ reduction.

  11. Isotopic and geochemical tracers for U(VI) reduction and U mobility at an in situ recovery U mine

    SciTech Connect

    Basu, Anirban; Brown, Shaun T.; Christensen, John N.; DePaolo, Donald J.; Reimus, Paul W.; Heikoop, Jeffrey M.; Woldegabriel, Giday; Simmons, Ardyth M.; House, Brian M.; Hartmann, Matt; Maher, Kate

    2015-05-19

    In situ recovery (ISR) uranium (U) mining mobilizes U in its oxidized hexavalent form (U(VI)) by oxidative dissolution of U from the roll-front U deposits. Post-mining natural attenuation of residual U(VI) at ISR mines is a potential remediation strategy. Detection and monitoring of naturally occurring reducing subsurface environments are important for successful implementation of this remediation scheme. We used the isotopic tracers ²³⁸U/²³⁵U (δ²³⁸U), ²³⁴U/²³⁸U activity ratio, and ³⁴S/³²S (δ³⁴S), and geochemical measurements of U ore and groundwater collected from 32 wells located within, upgradient, and downgradient of a roll-front U deposit to detect U(VI) reduction and U mobility at an ISR mining site at Rosita, TX, USA. The δ²³⁸U in Rosita groundwater varies from 0.61‰ to -2.49‰, with a trend toward lower δ²³⁸U in downgradient wells. The concurrent decrease in U(VI) concentration and δ²³⁸U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic ²³⁴U/²³⁸U activity ratio and δ³⁴S values may also be used to trace the mobility of the ore zone groundwater after mining has ended. These results support the use of U isotope-based detection of natural attenuation of U(VI) at Rosita and other similar ISR mining sites.

  12. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; Jim Fredrickson; Ken Kemner; Shelly Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. ? Elucidate the controls on the rate and extent of contaminant reactivity. (2) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  13. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    SciTech Connect

    Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions.

  14. Electrochemical and spectroscopic evidence on the one-electron reduction of U(VI) to U(V) on magnetite

    SciTech Connect

    Yuan, Ke; Ilton, Eugene S.; Antonio, Mark R.; Li, Zhongrui; Cook, Peter J.; Becker, Udo

    2015-05-19

    Reduction of U(VI) to U(IV) on mineral surfaces has been considered as a one-step two electron process. However, stabilized U(V), with no evidence of U(IV), found in recent studies indicates U(VI) can undergo a one electron reduction to U(V) without further progression to U(IV). We investigated the mechanisms of uranium reduction by reducing U(VI) electrochemically on a magnetite electrode at pH 3.4 . The one electron reduction of U(VI) was first confirmed using the cyclic voltammetry method. Formation of nano-size uranium precipitates on the surface of magnetite at reducing potentials and dissolution of the solids at oxidizing potentials were observed by in situ electrochemical AFM. XPS analysis of the magnetite electrodes polarized in uranium solutions at voltages from 0.1 ~ 0.9 V (vs. Ag/AgCl) showed the presence of only U(V) and U(VI). The highest amount of U(V) relative to U(VI) was prepared at 0.7 V, where the longest average U–Oaxial distance of 2.05 ± 0.01 Å was evident in the same sample revealed by EXAFS analysis. The results demonstrate that the electrochemical reduction of U(VI) on magnetite only yields U(V), even at a potential of 0.9 V, which favors the one-electron reduction mechanism. U(V) did not disproportionate but stabilized on magnetite through precipitation of mixed-valence state U(VI)/U(V) solids.

  15. Reduction of U(VI) by Fe(II) in the presence of hydrous ferric oxide and hematite: effects of solid transformation, surface coverage, and humic acid.

    PubMed

    Jang, Je-Hun; Dempsey, Brian A; Burgos, William D

    2008-04-01

    Fe(II) was added to U(VI)-spiked suspensions of hydrous ferric oxide (HFO) or hematite to compare the redox behaviors of uranium in the presence of two different Fe(III) (oxyhydr)oxides. Experiments were conducted with low or high initial sorption density of U(VI) and in the presence or absence of humic acid (HA). About 80% of U(VI) was reduced within 3 days for low sorbed U(VI) conditions, with either hematite or HFO. The {Fe(3+)} in the low U(VI) experiments at 3 days, based on measured Fe(II) and U(VI) and the assumed presence of amorphous UO(2(s)), was consistent with control by HFO for either initial Fe(III) (oxyhydr)oxide. After about 1 day, partial re-oxidation to U(VI) was observed in the low sorbed U(VI) experiments in the absence of HA, without equivalent increase of dissolved U(VI). No reduction of U(VI) was observed in the high sorbed U(VI) experiments; it was hypothesized that the reduction required sorption proximity of U(VI) and Fe(II). Addition of 5mg/L HA slowed the reduction with HFO and had less effect with hematite. Mössbauer spectroscopy (MBS) of (57)Fe(II)-enriched samples identified the formation of goethite, hematite, and non-stoichiometric magnetite from HFO, and the formation of HFO, hydrated hematite, and non-stoichiometric magnetite from hematite.

  16. Microbial Community Changes in Response to Ethanol or Methanol Amendments for U(VI) Reduction

    SciTech Connect

    Vishnivetskaya, Tatiana A; Brandt, Craig C; Madden, Andrew; Drake, Meghan M; Kostka, Joel; Akob, Denise M.; Kusel, Kirsten; Palumbo, Anthony Vito

    2010-01-01

    Microbial community responses to ethanol, methanol and methanol + humics amendments in relationship to uranium bioremediation were studied in laboratory microcosm experiments using sediments and ground water from a uranium-contaminated site in Oak Ridge, Tennessee. Ethanol addition always resulted in uranium reduction at rate of 0.8-1.0 mol l-1 d-1 while methanol addition did so occasionally at rate 0.95 mol l-1 d-1. The type of carbon source added, the duration of incubation, and the sampling site influenced the bacterial community structure upon incubation. Analysis of 16S rRNA gene clone libraries indicated (1) bacterial communities found in ethanol- and methanol-amended samples with U(VI) reduction were similar due to presence of -Proteobacteria, and -Proteobacteria (members of the families Burkholderiaceae, Comamonadaceae, Oxalobacteraceae, and Rhodocyclaceae); (2) methanol-amended samples without U(VI) reduction exhibited the lowest diversity and the bacterial community contained 69.2-92.8% of the family Methylophilaceae; and (3) the addition of humics resulted in an increase of phylogenetic diversity of -Proteobacteria (Rodoferax, Polaromonas, Janthinobacterium, Methylophilales, unclassified) and Firmicutes (Desulfosporosinus, Clostridium).

  17. Biogeochemical controls on the product of microbial U(VI) reduction.

    PubMed

    Stylo, Malgorzata; Alessi, Daniel S; Shao, Paul PaoYun; Lezama-Pacheco, Juan S; Bargar, John R; Bernier-Latmani, Rizlan

    2013-01-01

    Biologically mediated immobilization of radionuclides in the subsurface is a promising strategy for the remediation of uranium-contaminated sites. During this process, soluble U(VI) is reduced by indigenous microorganisms to sparingly soluble U(IV). The crystalline U(IV) phase uraninite, or UO2, is the preferable end-product of bioremediation due to its relatively high stability and low solubility in comparison to biomass-associated nonuraninite U(IV) species that have been reported in laboratory and under field conditions. The goal of this study was to delineate the geochemical conditions that promote the formation of nonuraninite U(IV) versus uraninite and to decipher the mechanisms of its preferential formation. U(IV) products were prepared under varying geochemical conditions and characterized with X-ray absorption spectroscopy (XAS), scanning transmission X-ray microscopy (STXM), and various wet chemical methods. We report an increasing fraction of nonuraninite U(IV) species with decreasing initial U concentration. Additionally, the presence of several common groundwater solutes (sulfate, silicate, and phosphate) promote the formation of nonuraninite U(IV). Our experiments revealed that the presence of those solutes promotes the formation of bacterial extracellular polymeric substances (EPS) and increases bacterial viability, suggesting that the formation of nonuraninite U(IV) is due to a biological response to solute presence during U(VI) reduction. The results obtained from this laboratory-scale research provide insight into biogeochemical controls on the product(s) of uranium reduction during bioremediation of the subsurface.

  18. Modeling the inhibition of the bacteral reduction of U(VI) by beta-MnO2(s).

    PubMed

    Liu, Chongxuan; Zachara, John M; Fredrickson, James K; Kennedy, David W; Dohnalkova, Alice

    2002-04-01

    Pyrolusite (beta-MnO2(s)) was used to assess the influence of a competitive electron acceptor on the kinetics of reduction of aqueous uranyl carbonate by a dissimilatory metal-reducing bacterium (DMRB), Shewanella putrefaciens strain CN32. The enzymatic reduction of U(VI) and beta-MnO2(s) and the abiotic redox reaction between beta-MnO2(s) and biogenic uraninite (UO2(s)) were independently investigated to allow for interpretation of studies of U(VI) bioreduction in the presence of beta-MnO2(s). Uranyl bioreduction to UO2(s) by CN32 with H2 as the electron donor followed Monod kinetics, with a maximum specific reduction rate of 110 M/h/10(8) cells/mL and a half-saturation constant of 370 microM. The bioreduction rate of beta-MnO2(s) by CN32 was described by a pseudo-first-order model with respect to beta-MnO2(s) surface sites, with a rate constant of 7.92 x 10(-2) h(-1)/10(8) cells/mL. Uraninite that precipitated as a result of microbial U(VI) reduction was abiotically reoxidized to U(VI) by beta-MnO2(s), with concomitant reduction to Mn(II). The oxidation of biogenic UO2(s) coupled with beta-MnO2(s) reduction was well-described by an electrochemical model. However, a simple model that coupled the bacterial reduction of U(VI) and beta-MnO2(s) with an abiotic redox reaction between UO2(s) and beta-MnO2(s) failed to describe the mass loss of U(VI) in the presence of beta-MnO2(s). Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) revealed that the particle size and spatial distribution of the biogenic UO2(s) changed dynamically in systems with, as compared to without, beta-MnO2(s)). These observations suggested that the surface properties and localization of UO2(s) in relation to the cell and beta-MnO2(s) surfaces was an important factor controlling the abiotic oxidation of UO2(s) and, thus, the overall rate and extent of U(VI) bioreduction. The coupled model that was modified to account for the "effective" contact surface area between UO2

  19. Acceleration of Microbially Mediated U(VI) Reduction at a Uranium Mill Tailings Site, Colorado Plateau

    SciTech Connect

    Phil Long; Todd Anderson; Aaron Peacock; Steve Heald; Yun-Juan Chang; Dick Dayvault; Derek R. Lovley; C.T. Resch; Helen Vrionis; Irene Ortiz-Bernad; D.C. White

    2004-03-17

    A second field-scale electron donor amendment experiment was conducted in 2003 at the Old Rifle Uranium Mill Tailings Remedial Action (UMTRA) site in Rifle, Colorado. The objective of the 2003 experiment (done in collaboration with the U.S. Department of Energy's UMTRA Groundwater Project) was to test the hypothesis that amendment of increased concentration of electron donor would result in an increased export of electron donor down gradient which in turn would create a larger zone of down-gradient U(VI) bioreduction sustained over a longer time period relative to the 2002 experiment (Anderson et al. 2003). During the first experiment (2002), {approx}3 mM acetate was amended to subsurface over a period of 3 months in a 15m by 18m by 2.5m volume comprised of 3 upgradient monitoring wells, 20 injection wells, and 15 down-gradient monitoring wells. After an initial one-month phase of metal reduction, bioavailable oxidized Fe was consumed near the injection gallery and the dominant terminal electron accepting process became sulfate reduction, rapidly consuming the injected acetate. For the 2003 experiment, we amended sufficient acetate ({approx}10 mM) to consume available sulfate and export acetate down-gradient where bioavailable oxidized Fe was still present. Data from the experiment indicate that acetate was exported further down gradient, resulting in a larger zone of microbial U(VI) reduction than for the 2002 experiment. Geohydrologic, geochemical, and microbiological data collected during the course of both experiments enable assessment of relative importance of a number of factors controlling the experimental outcomes. Companion posters by Anderson et al. and White et al. provide additional results.

  20. Contribution of extracellular polymeric substances from Shewanella sp. HRCR-1 biofilms to U(VI) immobilization.

    PubMed

    Cao, Bin; Ahmed, Bulbul; Kennedy, David W; Wang, Zheming; Shi, Liang; Marshall, Matthew J; Fredrickson, Jim K; Isern, Nancy G; Majors, Paul D; Beyenal, Haluk

    2011-07-01

    The goal of this study was to quantify the contribution of extracellular polymeric substances (EPS) to U(VI) immobilization by Shewanella sp. HRCR-1. Through comparison of U(VI) immobilization using cells with bound EPS (bEPS) and cells with minimal EPS, we show that (i) bEPS from Shewanella sp. HRCR-1 biofilms contribute significantly to U(VI) immobilization, especially at low initial U(VI) concentrations, through both sorption and reduction; (ii) bEPS can be considered a functional extension of the cells for U(VI) immobilization and they likely play more important roles at lower initial U(VI) concentrations; and (iii) the U(VI) reduction efficiency is dependent upon the initial U(VI) concentration and decreases at lower concentrations. To quantify the relative contributions of sorption and reduction to U(VI) immobilization by EPS fractions, we isolated loosely associated EPS (laEPS) and bEPS from Shewanella sp. HRCR-1 biofilms grown in a hollow fiber membrane biofilm reactor and tested their reactivity with U(VI). We found that, when reduced, the isolated cell-free EPS fractions could reduce U(VI). Polysaccharides in the EPS likely contributed to U(VI) sorption and dominated the reactivity of laEPS, while redox active components (e.g., outer membrane c-type cytochromes), especially in bEPS, possibly facilitated U(VI) reduction.

  1. Réduction enzymatique de U(VI) dans des eaux souterraines

    NASA Astrophysics Data System (ADS)

    Abdelouas, Abdesselam; Lutze, Werner; Nuttall, Eric; Gong, Weiliang; Fritz, Bertrand; Crovisier, Jean-Louis

    1999-03-01

    The use of enzymatic reduction of U(VI) in remediation of groundwater contaminated with UCVI) is receiving considerable attention. Certain strains of bacteria can combine the oxidation of an organic compound to the reduction of U(VI) to U(IV), which precipitates as uraninite. In the present study, we tested the reduction of U(VI) in groundwaters with various origins and compositions. In all groundwaters U(VI) was reduced by sulfate reducing bacteria that had been activated by ethanol and trimetaphosphate. The reduction rate of U(VI) depends on sulfate concentration in water and the abundance of bacteria in the system. This work shows that bacteria capable of U(VI) reduction are ubiquitous in nature, and suggests the possibility of a large application of the enzymatic reduction of U(VI) for in situ clean up of groundwaters contaminated with uranium.

  2. Enhanced microbial reduction of Cr(VI) and U(VI) by different natural organic matter fractions

    NASA Astrophysics Data System (ADS)

    Gu, Baohua; Chen, Jie

    2003-10-01

    Although direct microbial reduction of Cr(VI) and U(VI) is known, few studies have examined the kinetics and the underlying mechanisms of the reduction of these contaminants by different natural organic matter (NOM) fractions in the presence or absence of microorganisms. In this study, NOM was found to chemically reduce Cr(VI) at pH 3, but the reduction rates were negligible at pH ˜7. The abiotic reduction of U(VI) by NOM was not observed, possibly because of the presence of small amounts of nitrate in the reactant solution. However, all NOM fractions, particularly the soil humic acid (HA), enhanced the bioreduction of Cr(VI) or U(VI) in the presence of Shewanella putrefaciens CN32. The reduction rates varied greatly among NOM fractions with different chemical and structural properties: the polyphenolic-rich NOM-PP fraction appeared to be the most reactive in abiotically reducing Cr(VI) at a low pH, but soil HA was more effective in mediating the microbial reduction of Cr(VI) and U(VI) under anaerobic, circumneutral pH conditions. These observations are attributed to an increased solubility and conformational changes of the soil HA with pH and, more importantly, its relatively high contents of polycondensed and conjugated aromatic organic moieties. An important implication of this study is that, depending on chemical and structural properties, different NOM components may play different roles in enhancing the bioreduction of Cr(VI) and U(VI) by microorganisms. Polycondensed aromatic humic materials may be particularly useful in mediating the bioreduction and rapid immobilization of these contaminant metals in soil.

  3. Influence of Mn oxides on the reduction of U(VI) by the metal-reducing bacterium Shewanella putrefaciens

    SciTech Connect

    Fredrickson, Jim K.; Zachara, John M.; Kennedy, David W.; Liu, Chongxuan; Duff, Martine C.; Hunter, David; Dohnalkova, Alice

    2002-09-16

    Dissimilatory metal-reducing bacteria (DMRB) enzymatically reduce Fe(III), Mn(III/IV), U(VI), and other polyvalent metals during anaerobic respiration. Previous investigations of the bacterial reduction of U(VI) in the presence of goethite (a-FeOOH) found that, in spite of potential competition as an electron acceptor, goethite had little impact on the bacterial reduction of U(VI) to insoluble U(IV). Mn(III/IV) oxides are also electron acceptors for DMRB but are stronger oxidants than Fe(III) oxides. Differences in the solubility of oxidized Mn and U challenges predictions of their biogeochemical behavior during redox cycling. The potential for Mn oxides to modify the biogeochemical behavior of U during reduction by a subsurface bacterium Shewanella putrefaciens CN32 was investigated using synthetic Mn(III/IV) oxides [pyrolusite ({beta}-MnO{sub 2}), bixbyite (Mn{sub 2}O{sub 3}) and K{sup +}-birnessite (K{sub 4}Mn{sub 14}O{sub 27} {center_dot} 8H{sub 2}O)]. In the absence of bacteria, pyrolusite and bixbyite oxidized biogenic uraninite (UO{sub 2}(s)) to soluble U(VI) species, with bixbyite being the most rapid oxidant. The Mn(III/IV) oxides lowered the bioreduction rate of U(VI) relative to rates in their absence, or in the presence of gibbsite [Al(OH){sub 3}] added as a non-redox reactive surface. Evolved Mn(II) increased with increasing initial U(VI) concentration in the biotic experiments, indicating that valence cycling of U facilitated the reduction of Mn(III/IV). Despite an excess of the Mn oxide, 43-100% of the initial U was bioreduced after extended incubation. Analysis of thin sections of bacterial-Mn oxide suspensions revealed that the reduced U resided in the periplasmic space of the bacterial cells. In the absence of Mn(III/IV) oxides, UO{sub 2}(s) accumulated as copius fine-grained particles external to the cell. These results indicate that the presence of Mn(III/IV) oxides may impede the biological reduction of U(VI) in subsoils and sediments?.

  4. Can microbially-generated hydrogen sulfide account for the rates of U(VI) reduction by a sulfate-reducing bacterium?

    SciTech Connect

    Boonchayaanant, Benjaporn; Gu, Baohua; Wang, Wei; Ortiz, Monica E; Criddle, Craig

    2010-01-01

    In situ remediation of uranium contaminated soil and groundwater is attractive because a diverse range of microbial and abiotic processes reduce soluble and mobile U(VI) to sparingly soluble and immobile U(IV). Often these processes are linked. Sulfate-reducing bacteria (SRB), for example, enzymatically reduce U(VI) to U(IV), but they also produce hydrogen sulfide that can itself reduce U(VI). This study evaluated the relative importance of these processes for Desulfovibrio aerotolerans, a SRB isolated from a U(VI)-contaminated site. For the conditions evaluated, the observed rate of SRB-mediated U(VI) reduction can be explained by the abiotic reaction of U(VI) with the microbially-generated H{sub 2}S. The presence of trace ferrous iron appeared to enhance the extent of hydrogen sulfide-mediated U(VI) reduction at 5 mM bicarbonate, but had no clear effect at 15 mM. During the hydrogen sulfide-mediated reduction of U(VI), a floc formed containing uranium and sulfur. U(VI) sequestered in the floc was not available for further reduction.

  5. Influence of dynamical conditions on the reduction of U(VI) at the magnetite-solution interface.

    PubMed

    Ilton, Eugene S; Boily, Jean-François; Buck, Edgar C; Skomurski, Frances N; Rosso, Kevin M; Cahill, Christopher L; Bargar, John R; Felmy, Andrew R

    2010-01-01

    The heterogeneous reduction of U(VI) to U(IV) by ferrous iron is believed to be a key process influencing the fate and transport of U in the environment. The reactivity of both sorbed and structural Fe(II) has been studied for numerous substrates, including magnetite. Published results from U(VI)-magnetite experiments have been variable, ranging from no reduction to clear evidence for the formation of U(IV). In this contribution, we used XAS and high resolution (+/-cryogenic) XPS to study the interaction of U(VI) with nanoparticulate magnetite. The results indicated that U(VI) was partially reduced to U(V) with no evidence of U(IV). However, thermodynamic calculations indicated that U phases with average oxidation states below (V) should have been stable, indicating that the system was not in redox equilibrium. A reaction pathway that involves incorporation and stabilization of U(V) and U(VI) into secondary phases is invoked to explain the observations. The results suggest an important and previously unappreciated role of U(V) in the fate and transport of uranium in the environment.

  6. Contribution of Extracellular Polymeric Substances from Shewanella sp. HRCR-1 Biofilms to U(VI) Immobilization

    SciTech Connect

    Cao, Bin; Ahmed, B.; Kennedy, David W.; Wang, Zheming; Shi, Liang; Marshall, Matthew J.; Fredrickson, Jim K.; Isern, Nancy G.; Majors, Paul D.; Beyenal, Haluk

    2011-06-05

    The goal of this study was to quantify the contribution of extracellular polymeric substances (EPS) in U(VI) immobilization by Shewanella sp. HRCR-1. Through comparison of U(VI) immobilization using cells with bound EPS (bEPS) and cells without EPS, we showed that i) bEPS from Shewanella sp. HRCR-1 biofilms contributed significantly to U(VI) immobilization, especially at low initial U(VI) concentrations, through both sorption and reduction; ii) bEPS could be considered as a functional extension of the cells for U(VI) immobilization and they likely play more important roles at initial U(VI) concentrations; and iii) U(VI) reduction efficiency was found to be dependent upon initial U(VI) concentration and the efficiency decreased at lower concentrations. To quantify relative contribution of sorption and reduction in U(VI) immobilization by EPS fractions, we isolated loosely associated EPS (laEPS) and bEPS from Shewanella sp. HRCR-1 biofilms grown in a hollow fiber membrane biofilm reactor and tested their reactivity with U(V). We found that, when in reduced form, the isolated cell-free EPS fractions could reduce U(VI). Polysaccharides in the EPS likely contributed to U(VI) sorption and dominated reactivity of laEPS while redox active components (e.g., outer membrane c-type cytochromes), especially in bEPS, might facilitate U(VI) reduction.

  7. U(VI) reduction at the nano, meso and meter scale: concomitant transition from simpler to more complex biogeochemical processes

    NASA Astrophysics Data System (ADS)

    Veeramani, H.; Hochella, M. F.

    2012-12-01

    Reduction of aqueous hexavalent U(VI) to the sparingly soluble nanoparticulate mineral uraninite [UO2] represents a promising strategy for the in situ immobilization of uranium in contaminated subsurface sediments and groundwater. Studies related to uranium reduction have been extensively carried out at various scales ranging from nano to meso to the meter scale with varying degrees of success. While nanoscale processes involving simple two-electron transfer reactions such as enzymatic microbial U(VI) reduction results in biogenic UO2 formation, mesoscale processes involving minerals and U(VI) are a step up in complexity and have shown varying results ranging from partial uranium reduction to the formation of mixed U(IV)/U(V) species. Although nano- and meso-scale biogeochemical processes have been helpful in predicting the contaminant dynamics at the meter scale, their occurrence is not necessarily apparent in soils and aquifers given the enormous volume of contaminated groundwater to be remediated, among other factors. The formation and long-term stability of biologically reduced uranium at the meter scale is also determined in addition by the complex interplay of aqueous geochemistry, hydrology, soil and sediment mineralogy and microbial community dynamics. For instance, indigenous subsurface microbes often encounter multiple electron acceptors in heterogeneous environments during biostimulation and can catalyze the formation of various reactive biogenic minerals. In such cases, abiotic interactions between U(VI) and reactive biogenic minerals is potentially important because the success of a remediation strategy is contingent upon the speciation of reduced uranium. This presentation will give an overview of uranium reduction ranging from simple nanoscale biological processes to increasingly complex meso and meter scale processes involving abiotic interactions between aqueous uranium and nano-biogenic minerals and the effect of mineralogy and aqueous

  8. Chemical reduction of U(VI) by Fe(II) at the solid-water interface using natural and synthetic Fe(III) oxides.

    PubMed

    Jeon, Byong-Hun; Dempsey, Brian A; Burgos, William D; Barnett, Mark O; Roden, Eric E

    2005-08-01

    Abiotic reduction of 0.1 mM U(VI) by Fe(II) in the presence of synthetic iron oxides (biogenic magnetite, goethite, and hematite) and natural Fe(III) oxide-containing solids was investigated in pH 6.8 artificial groundwater containing 10 mM NaHCO3. In most experiments, more than 95% of added U(VI) was sorbed to solids. U(VI) was rapidly and extensively (> or = 80%) reduced in the presence of synthetic Fe(III) oxides and highly Fe(II) oxide-enriched (18-35 wt % Fe) Atlantic coastal plain sediments. In contrast, long-term (20-60 d) U(VI) reduction was less than 30% in suspensions of six other natural solids with relatively low Fe(III) oxide content (1-5 wt % Fe). Fe(II) sorption site density was severalfold lower on these natural solids (0.2-1.1 Fe(II) nm(-2)) compared tothe synthetic Fe(lII) oxides (1.6-3.2 Fe(II) nm(-2)), which may explain the poor U(VI) reduction in the natural solid-containing systems. Addition of the reduced form of the electron shuttling compound anthrahydroquinone-2,6-disulfonate (AH2DS; final concentration 2.5 mM) to the natural solid suspensions enhanced the rate and extent of U(VI) reduction, suggesting that AH2DS reduced U(VI) at surface sites where reaction of U(VI) with sorbed Fe(II) was limited. This study demonstrates that abiotic, Fe(II)-driven U(VI) reduction is likely to be less efficient in natural soils and sediments than would be inferred from studies with synthetic Fe(III) oxides.

  9. Quantitative separation of monomeric U(IV) from UO2 in products of U(VI) reduction

    PubMed Central

    Alessi, Daniel S.; Uster, Benjamin; Veeramani, Harish; Suvorova, Elena I.; Lezama-Pacheco, Juan S.; Stubbs, Joanne E.; Bargar, John R.; Bernier-Latmani, Rizlan

    2012-01-01

    The reduction of soluble hexavalent uranium to tetravalent uranium can be catalyzed by bacteria and minerals. The end-product of this reduction is often the mineral uraninite, which was long assumed to be the only product of U(VI) reduction. However, recent studies report the formation of other species including an adsorbed U(IV) species, operationally referred to as monomeric U(IV). The discovery of monomeric U(IV) is important because the species is likely to be more labile and more susceptible to reoxidation than uraninite. Because there is a need to distinguish between these two U(IV) species, we propose here a wet chemical method of differentiating monomeric U(IV) from uraninite in environmental samples. To calibrate the method, U(IV) was extracted from known mixtures of uraninite and monomeric U(IV) and testted using X-ray absorption spectroscopy (XAS). Monomeric U(IV) was efficiently removed from biomass and Fe(II)-bearing phases by bicarbonate extraction, without affecting uraninite stability. After confirming that the method effectively separates monomeric U(IV) and uraninite, it is further evaluated for a system containing those reduced U species and adsorbed U(VI). The method provides a rapid complement, and in some cases alternative, to XAS analyses for quantifying monomeric U(IV), uraninite, and adsorbed U(VI) species in environmental samples. PMID:22540966

  10. Quantitative separation of monomeric U(IV) from UO2 in products of U(VI) reduction.

    PubMed

    Alessi, Daniel S; Uster, Benjamin; Veeramani, Harish; Suvorova, Elena I; Lezama-Pacheco, Juan S; Stubbs, Joanne E; Bargar, John R; Bernier-Latmani, Rizlan

    2012-06-05

    The reduction of soluble hexavalent uranium to tetravalent uranium can be catalyzed by bacteria and minerals. The end-product of this reduction is often the mineral uraninite, which was long assumed to be the only product of U(VI) reduction. However, recent studies report the formation of other species including an adsorbed U(IV) species, operationally referred to as monomeric U(IV). The discovery of monomeric U(IV) is important because the species is likely to be more labile and more susceptible to reoxidation than uraninite. Because there is a need to distinguish between these two U(IV) species, we propose here a wet chemical method of differentiating monomeric U(IV) from uraninite in environmental samples. To calibrate the method, U(IV) was extracted from known mixtures of uraninite and monomeric U(IV) and tested using X-ray absorption spectroscopy (XAS). Monomeric U(IV) was efficiently removed from biomass and Fe(II)-bearing phases by bicarbonate extraction, without affecting uraninite stability. After confirming that the method effectively separates monomeric U(IV) and uraninite, it is further evaluated for a system containing those reduced U species and adsorbed U(VI). The method provides a rapid complement, and in some cases alternative, to XAS analyses for quantifying monomeric U(IV), uraninite, and adsorbed U(VI) species in environmental samples.

  11. Influence of Reactive Transport on the Reduction of U(VI) in the Presence of Fe(III) and Nitrate: Implications for U(VI) Immobilization by Bioremediation / Biobarriers- Final Report

    SciTech Connect

    B.D. Wood

    2007-01-01

    Subsurface contamination by metals and radionuclides represent some of the most challenging remediation problems confronting the Department of Energy (DOE) complex. In situ remediation of these contaminants by dissimilatory metal reducing bacteria (DMRB) has been proposed as a potential cost effective remediation strategy. The primary focus of this research is to determine the mechanisms by which the fluxes of electron acceptors, electron donors, and other species can be controlled to maximize the transfer of reductive equivalents to the aqueous and solid phases. The proposed research is unique in the NABIR portfolio in that it focuses on (i) the role of flow and transport in the initiation of biostimulation and the successful sequestration of metals and radionuclides [specifically U(VI)], (ii) the subsequent reductive capacity and stability of the reduced sediments produced by the biostimulation process, and (iii) the potential for altering the growth of biomass in the subsurface by the addition of specific metabolic uncoupling compounds. A scientifically-based understanding of these phenomena are critical to the ability to design successful bioremediation schemes. The laboratory research will employ Shewanella putrefaciens (CN32), a facultative DMRB that can use Fe(III) oxides as a terminal electron acceptor. Sediment-packed columns will be inoculated with this organism, and the reduction of U(VI) by the DMRB will be stimulated by the addition of a carbon and energy source in the presence of Fe(III). Separate column experiments will be conducted to independently examine: (1) the importance of the abiotic reduction of U(VI) by biogenic Fe(II); (2) the influence of the transport process on Fe(III) reduction and U(VI) immobilization, with emphasis on methods for controlling the fluxes of aqueous species to maximize uranium reduction; (3) the reductive capacity of biologically-reduced sediments (with respect to re-oxidation by convective fluxes of O2 and NO3-) and

  12. Fe(III) Reduction and U(VI) Immobilization by Paenibacillus sp. Strain 300A, Isolated from Hanford 300A Subsurface Sediments

    SciTech Connect

    Ahmed, B.; Cao, B.; McLean, Jeffrey S.; Ica, Tuba; Dohnalkova, Alice; Istanbullu, Ozlem; Paksoy, Akin; Fredrickson, Jim K.; Beyenal, Haluk

    2012-11-07

    A facultative iron-reducing (Fe(III)-reducing) Paenibacillus sp. strain was isolated from Hanford 300A subsurface sediment biofilms that was capable of reducing soluble Fe(III) complexes (Fe(III)-NTA and Fe(III)-citrate) but unable to reduce poorly crystalline ferrihydrite (Fh). However, Paenibacillus sp. 300A was capable of reducing Fh in the presence of low concentrations (2 µM) of either of electron transfer mediators (ETMs) flavin mononucleotide (FMN) or anthraquinone-2,6-disulfonate (AQDS). Maximum initial Fh reduction rates were observed at catalytic concentrations (<10 µM) of either FMN or AQDS. Higher FMN concentrations inhibited Fh reduction, while increased AQDS concentrations did not. We found that Paenibacillus sp. 300A also could reduce Fh in the presence of natural ETMs from Hanford 300A subsurface sediments. In the absence of ETMs, Paenibacillus sp. 300A was capable of immobilizing U(VI) through both reduction and adsorption. The relative contributions of adsorption and microbial reduction to U(VI) removal from the aqueous phase were ~7:3 in PIPES and ~1:4 in bicarbonate buffer. Our study demonstrated that Paenibacillus sp. 300A catalyzes Fe(III) reduction and U(VI) immobilization and that these reactions benefit from externally added or naturally existing ETMs in 300A subsurface sediments.

  13. INVESTIGATION OF THE TRANSFORMATION OF URANIUM UNDER IRON-REDUCING CONDITIONS: REDUCTION OF UVI BY BIOGENIC FEII/FEIII HYDROXIDE (GREEN RUST)

    SciTech Connect

    O'Loughlin, Edward J.; Scherer, Michelle M.; Kemner, Kenneth M.

    2006-12-31

    The recent identification of green rusts (GRs) as products of the reduction of FeIII oxyhydroxides by dissimilatory iron-reducing bacteria, coupled with the ability of synthetic (GR) to reduce UVI species to insoluble UO2, suggests that biogenic green rusts (BioGRs) may play an important role in the speciation (and thus mobility) of U in FeIII-reducing environments. The objective of our research was to examine the potential for BioGR to affect the speciation of U under FeIII-reducing conditions. To meet this objective, we designed and executed a hypothesis-driven experimental program to identify key factors leading to the formation of BioGRs as products of dissimilatory FeIII reduction, to determine the key factors controlling the reduction of UVI to UIV by GRs, and to identify the resulting U-bearing mineral phases. The results of this research significantly increase our understanding of the coupling of biotic and abiotic processes with respect to the speciation of U in iron-reducing environments. In particular, the reduction of UVI to UIV by BioGR with the subsequent formation of U-bearing mineral phases may be effective for immobilizing U in suboxic subsurface environments. This information has direct applications to contaminant transport modeling and bioremediation engineering for natural or enhanced in situ remediation of subsurface contamination.

  14. Development of a biomarker for Geobacter activity and strain composition; Proteogenomic analysis of the citrate synthase protein during bioremediation of U(VI)

    PubMed Central

    Wilkins, Michael J.; Callister, Stephen J.; Miletto, Marzia; Williams, Kenneth H.; Nicora, Carrie D.; Lovley, Derek R.; Long, Philip E.; Lipton, Mary S.

    2011-01-01

    Summary Monitoring the activity of target microorganisms during stimulated bioremediation is a key problem for the development of effective remediation strategies. At the US Department of Energy's Integrated Field Research Challenge (IFRC) site in Rifle, CO, the stimulation of Geobacter growth and activity via subsurface acetate addition leads to precipitation of U(VI) from groundwater as U(IV). Citrate synthase (gltA) is a key enzyme in Geobacter central metabolism that controls flux into the TCA cycle. Here, we utilize shotgun proteomic methods to demonstrate that the measurement of gltA peptides can be used to track Geobacter activity and strain evolution during in situ biostimulation. Abundances of conserved gltA peptides tracked Fe(III) reduction and changes in U(VI) concentrations during biostimulation, whereas changing patterns of unique peptide abundances between samples suggested sample‐specific strain shifts within the Geobacter population. Abundances of unique peptides indicated potential differences at the strain level between Fe(III)‐reducing populations stimulated during in situ biostimulation experiments conducted a year apart at the Rifle IFRC. These results offer a novel technique for the rapid screening of large numbers of proteomic samples for Geobacter species and will aid monitoring of subsurface bioremediation efforts that rely on metal reduction for desired outcomes. PMID:21255372

  15. Development of a biomarker for Geobacter activity and strain composition; Proteogenomic analysis of the citrate synthase protein during bioremediation of U(VI).

    SciTech Connect

    Wilkins, Michael J.; Callister, Stephen J.; Miletto, Marzia; Williams, Kenneth H.; Nicora, Carrie D.; Lovely, Derek R.; Long, Philip E.; Lipton, Mary S.

    2011-01-01

    Monitoring the activity of target microorganisms during stimulated bioremediation is a key problem for the development of effective remediation strategies. At the U.S. Department of Energy’s Integrated Field Research Challenge (IFRC) site in Rifle, CO, the stimulation of Geobacter growth and activity via subsurface acetate addition leads to precipitation of U(VI) from groundwater as U(IV). Citrate synthase (gltA) is a key enzyme in Geobacter central metabolism that controls flux into the TCA cycle. Here, we utilize shotgun proteomic methods to demonstrate that the measurement of gltA peptides can be used to track Geobacter activity and strain evolution during in situ biostimulation. Abundances of conserved gltA peptides tracked Fe(III) reduction and changes in U(VI) concentrations during biostimulation, whereas changing patterns of unique peptide abundances between samples suggested sample-specific strain shifts within the Geobacter population. Abundances of unique peptides indicated potential differences at the strain level between Fe(III)-reducing populations stimulated during in situ biostimulation experiments conducted a year apart at the Rifle IFRC. These results offer a novel technique for the rapid screening of large numbers of proteomic samples for Geobacter species and will aid monitoring of subsurface bioremediation efforts that rely on metal reduction for desired outcomes.

  16. Development of a biomarker for Geobacter activity and strain composition; proteogenomic analysis of the citrate synthase protein during bioremediation of U(VI).

    PubMed

    Wilkins, Michael J; Callister, Stephen J; Miletto, Marzia; Williams, Kenneth H; Nicora, Carrie D; Lovley, Derek R; Long, Philip E; Lipton, Mary S

    2011-01-01

    Monitoring the activity of target microorganisms during stimulated bioremediation is a key problem for the development of effective remediation strategies. At the US Department of Energy's Integrated Field Research Challenge (IFRC) site in Rifle, CO, the stimulation of Geobacter growth and activity via subsurface acetate addition leads to precipitation of U(VI) from groundwater as U(IV). Citrate synthase (gltA) is a key enzyme in Geobacter central metabolism that controls flux into the TCA cycle. Here, we utilize shotgun proteomic methods to demonstrate that the measurement of gltA peptides can be used to track Geobacter activity and strain evolution during in situ biostimulation. Abundances of conserved gltA peptides tracked Fe(III) reduction and changes in U(VI) concentrations during biostimulation, whereas changing patterns of unique peptide abundances between samples suggested sample-specific strain shifts within the Geobacter population. Abundances of unique peptides indicated potential differences at the strain level between Fe(III)-reducing populations stimulated during in situ biostimulation experiments conducted a year apart at the Rifle IFRC. These results offer a novel technique for the rapid screening of large numbers of proteomic samples for Geobacter species and will aid monitoring of subsurface bioremediation efforts that rely on metal reduction for desired outcomes.

  17. Development of a biomarker for Geobacter activity and strain composition: Proteogenomic analysis of the citrate synthase protein during bioremediation of U(VI)

    SciTech Connect

    Wilkins, M.J.; Callister, S.J.; Miletto, M.; Williams, K.H.; Nicora, C.D.; Lovley, D.R.; Long, P.E.; Lipton, M.S.

    2010-02-15

    Monitoring the activity of target microorganisms during stimulated bioremediation is a key problem for the development of effective remediation strategies. At the US Department of Energy's Integrated Field Research Challenge (IFRC) site in Rifle, CO, the stimulation of Geobacter growth and activity via subsurface acetate addition leads to precipitation of U(VI) from groundwater as U(IV). Citrate synthase (gltA) is a key enzyme in Geobacter central metabolism that controls flux into the TCA cycle. Here, we utilize shotgun proteomic methods to demonstrate that the measurement of gltA peptides can be used to track Geobacter activity and strain evolution during in situ biostimulation. Abundances of conserved gltA peptides tracked Fe(III) reduction and changes in U(VI) concentrations during biostimulation, whereas changing patterns of unique peptide abundances between samples suggested sample-specific strain shifts within the Geobacter population. Abundances of unique peptides indicated potential differences at the strain level between Fe(III)-reducing populations stimulated during in situ biostimulation experiments conducted a year apart at the Rifle IFRC. These results offer a novel technique for the rapid screening of large numbers of proteomic samples for Geobacter species and will aid monitoring of subsurface bioremediation efforts that rely on metal reduction for desired outcomes.

  18. Reduction of U(VI) and Toxic Metals by Desulfovibrio Cytochrome C3

    SciTech Connect

    Wall, Judy D

    2013-04-11

    The central objective of our proposed research was twofold: 1) to investigate the structure-function relationship of Desulfovibrio desulfuricans (now Desulfovibrio alaskensis G20) cytochrome c3 with uranium and 2) to elucidate the mechanism for uranium reduction in vitro and in vivo. Physiological analysis of a mutant of D. desulfuricans with a mutation of the gene encoding the type 1 tetraheme cytochrome c3 had demonstrated that uranium reduction was negatively impacted while sulfate reduction was not if lactate were the electron donor. This was thought to be due to the presence of a branched pathway of electron flow from lactate leading to sulfate reduction. Our experimental plan was to elucidate the structural and mechanistic details of uranium reduction involving cytochrome c3.

  19. Development of U isotope fractionation as an indictor or U(VI) reduction in uranium plumes

    SciTech Connect

    Lundstrom, Craig; Johnson, Thomas

    2016-02-16

    This is the final report for a university research project that advanced development of a new technology for identifying chemical reduction of uranium contamination in groundwater at the Rifle Field Challenge site. Reduction changes mobile hexavalent uranium into immobile U(IV). The stable isotope ratio (238U/235U) measurements of U using multicollector ICP-mass spectrometry were performed to understand the chemical reduction and sorption processes during various field experiments. In addition laboratory experiments were performed to better understand the isotopic fractionations. The main objectives of this project were completed during the project period and two peer-reviewed articles were published to disseminate the information gained.

  20. Aqueous complexation reactions governing the rate and extent of biogeochemical U(VI) reduction

    SciTech Connect

    Kemner, K.M.; Kelly, S.D.; Brooks, Scott C.; Dong, Wenming; Carroll, Sue; Fredrickson, James K.

    2006-06-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments.

  1. Biogeochemical Modeling of In Situ U(VI) Reduction and Immobilization with Emulsified Vegetable Oil as the Electron Donor at a Field Site in Oak Ridge, Tennessee

    NASA Astrophysics Data System (ADS)

    Tang, G.; Parker, J.; Wu, W.; Schadt, C. W.; Watson, D. B.; Brooks, S. C.; Orifrc Team

    2011-12-01

    A comprehensive biogeochemical model was developed to quantitatively describe the coupled hydrologic, geochemical and microbiological processes that occurred following injection of emulsified vegetable oil (EVO) as the electron donor to immobilize U(VI) at the Oak Ridge Integrated Field Research Challenge site (ORIFRC) in Tennessee. The model couples the degradation of EVO, production and oxidation of long-chain fatty acids (LCFA), glycerol, hydrogen and acetate, reduction of nitrate, manganese, ferrous iron, sulfate and uranium, and methanoganesis with growth of multiple microbial groups. The model describes the evolution of geochemistry and microbial populations not only in the aqueous phase as typically observed, but also in the mineral phase and therefore enables us to evaluate the applicability of rates from the literature for field scale assessment, estimate the retention and degradation rates of EVO and LCFA, and assess the influence of the coupled processes on fate and transport of U(VI). Our results suggested that syntrophic bacteria or metal reducers might catalyze LCFA oxidation in the downstream locations when sulfate was consumed, and competition between methanogens and others for electron donors and slow growth of methanogen might contribute to the sustained reducing condition. Among the large amount of hydrologic, geochemical and microbiological parameter values, the initial biomass, and the interactions (e.g., inhibition) of the microbial functional groups, and the rate and extent of Mn and Fe oxide reduction appear as the major sources of uncertainty. Our model provides a platform to conduct numerical experiments to study these interactions, and could be useful for further iterative experimental and modeling investigations into the bioreductive immobiliztion of radionuclide and metal contaminants in the subsurface.

  2. Influence of Calcium on Microbial Reduction of Solid Phase Uranium (VI)

    SciTech Connect

    Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M.; Wang, Zheming

    2007-06-27

    The effect of calcium on microbial reduction of a solid phase U(VI), sodium boltwoodite (NaUO2SiO3OH ∙1.5H2O), was evaluated in a culture of a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1. Batch experiments were performed in a non-growth bicarbonate medium with lactate as electron donor at pH 7 buffered with PIPES. Calcium increased both the rate and extent of Na-boltwoodite dissolution by increasing its solubility through the formation of a ternary aqueous calcium-uranyl-carbonate species. The ternary species, however, decreased the rates of microbial reduction of aqueous U(VI). Laser-induced fluorescence spectroscopy (LIFS) and transmission electron microscopy (TEM) revealed that microbial reduction of solid phase U(VI) is a sequentially coupled process of Na-boltwoodite dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) to U(IV) that accumulated on bacterial surfaces/periplasm. The overall rates of microbial reduction of solid phase U(VI) can be described by the coupled rates of dissolution and microbial reduction that were both influenced by calcium. The results demonstrated that dissolved U(VI) concentration during microbial reduction was a complex function of solid phase U(VI) dissolution kinetics, aqueous U(VI) speciation, and microbial activity.

  3. Decrease of U(VI) Immobilization Capability of the Facultative Anaerobic Strain Paenibacillus sp. JG-TB8 under Anoxic Conditions Due to Strongly Reduced Phosphatase Activity

    PubMed Central

    Reitz, Thomas; Rossberg, Andre; Barkleit, Astrid; Selenska-Pobell, Sonja; Merroun, Mohamed L.

    2014-01-01

    Interactions of a facultative anaerobic bacterial isolate named Paenibacillus sp. JG-TB8 with U(VI) were studied under oxic and anoxic conditions in order to assess the influence of the oxygen-dependent cell metabolism on microbial uranium mobilization and immobilization. We demonstrated that aerobically and anaerobically grown cells of Paenibacillus sp. JG-TB8 accumulate uranium from aqueous solutions under acidic conditions (pH 2 to 6), under oxic and anoxic conditions. A combination of spectroscopic and microscopic methods revealed that the speciation of U(VI) associated with the cells of the strain depend on the pH as well as on the aeration conditions. At pH 2 and pH 3, uranium was exclusively bound by organic phosphate groups provided by cellular components, independently on the aeration conditions. At higher pH values, a part (pH 4.5) or the total amount (pH 6) of the dissolved uranium was precipitated under oxic conditions in a meta-autunite-like uranyl phosphate mineral phase without supplying an additional organic phosphate substrate. In contrast to that, under anoxic conditions no mineral formation was observed at pH 4.5 and pH 6, which was clearly assigned to decreased orthophosphate release by the cells. This in turn was caused by a suppression of the indigenous phosphatase activity of the strain. The results demonstrate that changes in the metabolism of facultative anaerobic microorganisms caused by the presence or absence of oxygen can decisively influence U(VI) biomineralization. PMID:25157416

  4. The effect of U(VI) bioreduction kinetics on subsequent reoxidation of biogenic U(IV)

    SciTech Connect

    Senko, John M.; Kelly, Shelly D.; Dohnalkova, Alice; Mcdonough, J. T.; Kemner, Kenneth M.; Burgos, William D.

    2007-10-01

    Microbially mediated in situ reduction of soluble U(VI) to insoluble U(IV) (as UO2) has been proposed as a means of preventing the migration of that radionuclide with groundwater, but preventing the oxidative resolubilization of U has proven difficult. We hypothesized that relatively slow rates of U(VI) bioreduction would yield larger UO2 precipitates that would be more resistant to oxidation than those produced by rapid U(VI) bioreduction. We manipulated U(VI) bioreduction rates by varying the density of Shewanella putrefaciens CN32 added to U(VI) containing solutions with lactate as an electron donor. Characterization of biogenic UO2 particles by extended X-ray absorption fine-structure spectroscopy and transmission electron microscopy revealed that UO2 nanoparticles formed by relatively slow rates of U(VI) reduction were larger and more highly aggregated than those formed by relatively rapid U(VI) reduction. UO2 particles formed at various rates were incubated under a variety of abiotically and biologically oxidizing conditions. In all cases, UO2 that was formed by relatively slow U(VI) reduction was oxidized at a slower rate and to a lesser extent than UO2 formed by relatively rapid U(VI) bioreduction, suggesting that the stability of UO2 in situ may be enhanced by stimulation of relatively slow rates of U(VI) reduction.

  5. Reduction of uranium by cytochrome c3 of Desulfovibrio vulgaris

    USGS Publications Warehouse

    Lovley, D.R.; Widman, P.K.; Woodward, J.C.; Phillips, E.J.P.

    1993-01-01

    The mechanism for U(VI) reduction by Desulfovibrio vulgaris (Hildenborough) was investigated. The H2-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome c3. Addition of cytochrome c3 back to the soluble fraction that had been passed over the cationic exchange column restored the U(VI)-reducing capacity. Reduced cytochrome c3 was oxidized by U(VI), as was a c-type cytochrome(s) in whole-cell suspensions. When cytochrome c3 was combined with hydrogenase, its physiological electron donor, U(VI) was reduced in the presence of H2. Hydrogenase alone could not reduce U(VI). Rapid U(VI) reduction was followed by a subsequent slow precipitation of the U(IV) mineral uraninite. Cytochrome c3 reduced U(VI) in a uranium-contaminated surface water and groundwater. Cytochrome c3 provides the first enzyme model for the reduction and biomineralization of uranium in sedimentary environments. Furthermore, the finding that cytochrome c3 can catalyze the reductive precipitation of uranium may aid in the development of fixed-enzyme reactors and/or organisms with enhanced U(VI)-reducing capacity for the bioremediation of uranium- contaminated waters and waste streams.

  6. Reduction of uranium by cytochrome c3 of Desulfovibrio vulgaris.

    PubMed Central

    Lovley, D R; Widman, P K; Woodward, J C; Phillips, E J

    1993-01-01

    The mechanism for U(VI) reduction by Desulfovibrio vulgaris (Hildenborough) was investigated. The H2-dependent U(VI) reductase activity in the soluble fraction of the cells was lost when the soluble fraction was passed over a cationic exchange column which extracted cytochrome c3. Addition of cytochrome c3 back to the soluble fraction that had been passed over the cationic exchange column restored the U(VI)-reducing capacity. Reduced cytochrome c3 was oxidized by U(VI), as was a c-type cytochrome(s) in whole-cell suspensions. When cytochrome c3 was combined with hydrogenase, its physiological electron donor, U(VI) was reduced in the presence of H2. Hydrogenase alone could not reduce U(VI). Rapid U(VI) reduction was followed by a subsequent slow precipitation of the U(IV) mineral uraninite. Cytochrome c3 reduced U(VI) in a uranium-contaminated surface water and groundwater. Cytochrome c3 provides the first enzyme model for the reduction and biomineralization of uranium in sedimentary environments. Furthermore, the finding that cytochrome c3 can catalyze the reductive precipitation of uranium may aid in the development of fixed-enzyme reactors and/or organisms with enhanced U(VI)-reducing capacity for the bioremediation of uranium-contaminated waters and waste streams. PMID:8285665

  7. Uranium Isotopic Fractionation Induced by U(VI) Adsorption onto Common Aquifer Minerals.

    PubMed

    Jemison, N E; Johnson, T M; Shiel, A E; Lundstrom, C C

    2016-11-15

    Uranium groundwater contamination due to U mining and processing affects numerous sites globally. Bioreduction of soluble, mobile U(VI) to U(IV)-bearing solids is potentially a very effective remediation strategy. Uranium isotopes ((238)U/(235)U) have been utilized to track the progress of microbial reduction, with laboratory and field studies finding a ∼1‰ isotopic fractionation, with the U(IV) product enriched in (238)U. However, the isotopic fractionation produced by adsorption may complicate the use of (238)U/(235)U to trace microbial reduction. A previous study found that adsorption of U(VI) onto Mn oxides produced a -0.2‰ fractionation with the adsorbed U(VI) depleted in (238)U. In this study, adsorption to quartz, goethite, birnessite, illite, and aquifer sediments induced an average isotopic fractionation of -0.15‰ with the adsorbed U(VI) isotopically lighter than coexisting aqueous U(VI). In bicarbonate-bearing matrices, the fractionation depended little on the nature of the sorbent, with only birnessite producing an atypically large fractionation. In the case of solutions with ionic strengths much lower than those of typical groundwater, less isotopic fractionation was produced than U(VI) solutions with greater ionic strength. Studies using U isotope data to assess U(VI) reduction must consider adsorption as a lesser, but significant isotope fractionation process.

  8. Measuring Substantial Reductions in Activity

    PubMed Central

    Schafer, Charles; Evans, Meredyth; Jason, Leonard A.; So, Suzanna; Brown, Abigail

    2015-01-01

    The case definitions for Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS), Myalgic Encephalomyelitis (ME), and chronic fatigue syndrome (CFS) each include a disability criterion requiring substantial reductions in activity in order to meet diagnostic criteria. Difficulties have been encountered in defining and operationalizing the substantial reduction disability criterion within these various illness definitions. The present study sought to relate measures of past and current activities in several domains including the SF-36, an objective measure of activity (e.g. actigraphy), a self-reported quality of life scale, and measures of symptom severity. Results of the study revealed that current work activities had the highest number of significant associations with domains such as the SF-36 subscales, actigraphy, and symptom scores. As an example, higher self-reported levels of current work activity were associated with better health. This suggests that current work related activities may provide a useful domain for helping operationalize the construct of substantial reductions in activity. PMID:25584524

  9. Characterization of microbial activities and U reduction in a shallow aquifer contaminated by uranium mill tailings.

    PubMed

    Elias, D A; Krumholz, L R; Wong, D; Long, P E; Suflita, J M

    2003-07-01

    A characterization of the Shiprock, NM, uranium mill tailing site focused on the geochemical and microbiological factors governing in-situ uranium-redox reactions. Groundwater and aqueous extracts of sediment samples contained a wide concentration range of sulfate, nitrate, and U(VI) with median values of 21.2 mM, 16.1 micro M, and 2.7 micro M, respectively. Iron(III) was not detected in groundwater, but a median value of 0.3 mM in sediment extracts was measured. Bacterial diversity down gradient from the disposal pile reflected the predominant geochemistry with relatively high numbers of sulfate- and nitrate-reducing microorganisms, and smaller numbers of acetogenic, methanogenic, nitrate-dependent Fe(II)-oxidizing, Fe(III)-reducing, and sulfide-oxidizing bacteria. In aquifer slurry incubations, nitrate reduction was always preferred and had a negative impact on sulfate-, Fe(III)-, and U-reduction rates. We also found that sulfate-reduction rates decreased sharply in the presence of clay, while Fe(III)-reduction increased with no clear impact on U reduction. In the absence of clay, iron and sulfate reduction correlated with concentrations of Fe(III) and sulfate, respectively. Rates of U(VI) loss did not correlate with the concentration of any electron acceptor. With the exception of Fe(III), electron donor amendment was largely unsuccessful in stimulating electron acceptor loss over a 2-week incubation period, suggesting that endogenous forms of organic matter were sufficient to support microbial activity. Our findings suggest that efforts to accelerate biological U reduction should initially focus on stimulating nitrate removal.

  10. Flavin reduction activates Drosophila cryptochrome.

    PubMed

    Vaidya, Anand T; Top, Deniz; Manahan, Craig C; Tokuda, Joshua M; Zhang, Sheng; Pollack, Lois; Young, Michael W; Crane, Brian R

    2013-12-17

    Entrainment of circadian rhythms in higher organisms relies on light-sensing proteins that communicate to cellular oscillators composed of delayed transcriptional feedback loops. The principal photoreceptor of the fly circadian clock, Drosophila cryptochrome (dCRY), contains a C-terminal tail (CTT) helix that binds beside a FAD cofactor and is essential for light signaling. Light reduces the dCRY FAD to an anionic semiquinone (ASQ) radical and increases CTT proteolytic susceptibility but does not lead to CTT chemical modification. Additional changes in proteolytic sensitivity and small-angle X-ray scattering define a conformational response of the protein to light that centers at the CTT but also involves regions remote from the flavin center. Reduction of the flavin is kinetically coupled to CTT rearrangement. Chemical reduction to either the ASQ or the fully reduced hydroquinone state produces the same conformational response as does light. The oscillator protein Timeless (TIM) contains a sequence similar to the CTT; the corresponding peptide binds dCRY in light and protects the flavin from oxidation. However, TIM mutants therein still undergo dCRY-mediated degradation. Thus, photoreduction to the ASQ releases the dCRY CTT and promotes binding to at least one region of TIM. Flavin reduction by either light or cellular reductants may be a general mechanism of CRY activation.

  11. Flavin reduction activates Drosophila cryptochrome

    PubMed Central

    Vaidya, Anand T.; Top, Deniz; Manahan, Craig C.; Tokuda, Joshua M.; Zhang, Sheng; Pollack, Lois; Young, Michael W.; Crane, Brian R.

    2013-01-01

    Entrainment of circadian rhythms in higher organisms relies on light-sensing proteins that communicate to cellular oscillators composed of delayed transcriptional feedback loops. The principal photoreceptor of the fly circadian clock, Drosophila cryptochrome (dCRY), contains a C-terminal tail (CTT) helix that binds beside a FAD cofactor and is essential for light signaling. Light reduces the dCRY FAD to an anionic semiquinone (ASQ) radical and increases CTT proteolytic susceptibility but does not lead to CTT chemical modification. Additional changes in proteolytic sensitivity and small-angle X-ray scattering define a conformational response of the protein to light that centers at the CTT but also involves regions remote from the flavin center. Reduction of the flavin is kinetically coupled to CTT rearrangement. Chemical reduction to either the ASQ or the fully reduced hydroquinone state produces the same conformational response as does light. The oscillator protein Timeless (TIM) contains a sequence similar to the CTT; the corresponding peptide binds dCRY in light and protects the flavin from oxidation. However, TIM mutants therein still undergo dCRY-mediated degradation. Thus, photoreduction to the ASQ releases the dCRY CTT and promotes binding to at least one region of TIM. Flavin reduction by either light or cellular reductants may be a general mechanism of CRY activation. PMID:24297896

  12. Long-term diffusion of U(VI) in bentonite: Dependence on density.

    PubMed

    Joseph, Claudia; Mibus, Jens; Trepte, Paul; Müller, Christa; Brendler, Vinzenz; Park, Dan M; Jiao, Yongqin; Kersting, Annie B; Zavarin, Mavrik

    2017-01-01

    As a contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over six years. Synthetic MX-80 model pore water was used as background electrolyte. Speciation calculations showed that Ca2UO2(CO3)3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3mm, 1.5mm, and 1mm into the clay plug at ρ=1.3, 1.6, and 1.9g/cm(3), respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uranium contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficients, De and Da, decreased with increasing dry density. The Da values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, Da values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. Some potential reasons for this behavior that were evaluated are changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time. By applying Archie's law and the extended Archie's law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). The results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.

  13. Long-term diffusion of U(VI) in bentonite: Dependence on density

    DOE PAGES

    Joseph, Claudia; Mibus, Jens; Trepte, Paul; ...

    2016-10-12

    As a contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over six years. Synthetic MX-80 model pore water was used as background electrolyte. Speciation calculations showed that Ca2UO2(CO3)3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3 mm, 1.5 mm, and 1 mm into the clay plug at ρ = 1.3, 1.6, and 1.9 g/cm3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uranium contained in the clay occurredmore » and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficients, De and Da, decreased with increasing dry density. The Da values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, Da values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. Some potential reasons for this behavior that were evaluated are changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time. By applying Archie's law and the extended Archie's law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). Finally, the results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.« less

  14. Periplasmic Cytochrome c(3) of Desulfovibrio vulgaris Is Directly Involved in H2-Mediated Metal but Not Sulfate Reduction

    SciTech Connect

    Elias, Dwayne A.; Suflita, Joseph M.; McInerney, Michael J.; Krumholz, Lee R.

    2004-01-01

    Kinetic parameters and the role of cytochrome c3 in sulfate, Fe(III), and U(VI) reduction were investigated in Desulfovibrio vulgaris Hildenborough. While sulfate reduction followed Michaelis-Menten kinetics (Km 220 uM), loss of Fe(III) and U(VI) was first-order at all concentrations tested. Initial reduction rates of all electron acceptors were similar for cells grown with H2 and sulfate, while cultures grown using lactate and sulfate had similar rates of metal loss but lower sulfate reduction activities. The similarities in metal, but not sulfate, reduction with H2 and lactate suggest divergent pathways. Respiration assays and reduced minus oxidized spectra were carried out to determine c-type cytochrome involvement in electron acceptor reduction. c-type cytochrome oxidation was immediate with Fe(III) and U(VI) in the presence of H2, lactate, or pyruvate. Sulfidogenesis occurred with all three electron donors and effectively oxidized the c-type cytochrome in lactate or pyruvate-reduced, but not H2-reduced cells. Correspondingly, electron acceptor competition assays with lactate or pyruvate as electron donors showed that Fe(III) inhibited U(VI) reduction, and U(VI) inhibited sulfate loss. However, sulfate reduction was slowed but not halted when H2 was the electron donor in the presence of Fe(III) or U(VI). U(VI) loss was still impeded by Fe(III) when H2 was used. Hence, we propose a modified pathway for the reduction of sulfate, Fe(III), and U(VI) which helps explain why these bacteria cannot grow using these metals. We further propose that cytochrome c3 is an electron carrier involved in lactate and pyruvate oxidation and is the reductase for alternate electron acceptors with higher redox potentials than sulfate.

  15. Periplasmic Cytochrome c3 of Desulfovibrio vulgaris Is Directly Involved in H2-Mediated Metal but Not Sulfate Reduction

    PubMed Central

    Elias, Dwayne A.; Suflita, Joseph M.; McInerney, Michael J.; Krumholz, Lee R.

    2004-01-01

    Kinetic parameters and the role of cytochrome c3 in sulfate, Fe(III), and U(VI) reduction were investigated in Desulfovibrio vulgaris Hildenborough. While sulfate reduction followed Michaelis-Menten kinetics (Km = 220 μM), loss of Fe(III) and U(VI) was first-order at all concentrations tested. Initial reduction rates of all electron acceptors were similar for cells grown with H2 and sulfate, while cultures grown using lactate and sulfate had similar rates of metal loss but lower sulfate reduction activities. The similarities in metal, but not sulfate, reduction with H2 and lactate suggest divergent pathways. Respiration assays and reduced minus oxidized spectra were carried out to determine c-type cytochrome involvement in electron acceptor reduction. c-type cytochrome oxidation was immediate with Fe(III) and U(VI) in the presence of H2, lactate, or pyruvate. Sulfidogenesis occurred with all three electron donors and effectively oxidized the c-type cytochrome in lactate- or pyruvate-reduced, but not H2-reduced cells. Correspondingly, electron acceptor competition assays with lactate or pyruvate as electron donors showed that Fe(III) inhibited U(VI) reduction, and U(VI) inhibited sulfate loss. However, sulfate reduction was slowed but not halted when H2 was the electron donor in the presence of Fe(III) or U(VI). U(VI) loss was still impeded by Fe(III) when H2 was used. Hence, we propose a modified pathway for the reduction of sulfate, Fe(III), and U(VI) which helps explain why these bacteria cannot grow using these metals. We further propose that cytochrome c3 is an electron carrier involved in lactate and pyruvate oxidation and is the reductase for alternate electron acceptors with higher redox potentials than sulfate. PMID:14711670

  16. UVIS CTE Monitor: Star Clusters

    NASA Astrophysics Data System (ADS)

    Noeske, Kai

    2010-09-01

    *** NOTE 2: 2ND CHANGE MAR 26 2011: VISIT 13 HAD FAILED. APPROVED FOR REPETITION. ****** NEW VISIT 14 IS IDENTICAL TO FORMER VISIT 13, WITH EXCEPTIONS THAT SOME SUBEXPOSURES ARE REMOVED. ****** SEE OBSERVING DESCRIPTION FOR DETAILS. ****** NOTE: THIS IS A CHANGED PHASE II PROPOSAL AFTER VISITS 1,2,7 HAD BEEN EXECUTED ****** CHANGES BECAME NECESSARY AFTER ANALYSIS OF INCOMING CALIBRATION DATA FROM 12379 AND 12348 ****** THIS REVISED PHASE II {submission 14FEB2011} ADDS THE EVALUATION OF CHARGE INJECTION***The changes amount to:1} dropping the 3rd epoch {August 2011} of external CTE monitoring {3 orbits}2} simplifying the CTE monitor observations in the second epoch {March 2011}, freeing up 1 orbit3} using the freed up orbits from 1} and 2}, together with two additional external orbits that we were granted, to thoroughly assess the data quality of charge - injected data under realistic observing setups.These charge-injected observations will be obtained during the 2nd epoch of the CTE monitor program, in the March 2011 window.------ Original Text prior to 14 Feb 2011 below this line -----------This program extends the Cycle 17 external CTE calibration {CAL/WFC3 ID 11924} program for WFC3/UVIS over Cycle 18. Targets are {i} the sparse cluster NGC 6791 observed in Cycle 17, to continue a consistent set of observations that allows to isolate the time evolution of the CTE, and {ii} a denser field in 47 Tuc {NGC 104}. The latter will provide data to measure the dependence of the CTE on field crowding. It will also provide a consistent comparison between the CTE evolution of WFC3/UVIS and that of ACS/WFC at the same time into the flight {1 year}, because ACS/WFC CTE data were based on 47 Tuc observations. Additional observations of 47 Tuc in the CVZ will provide a wide range of background levels to measure the background dependence of the UVIS CTE.Goals are {i} the continued monitoring of the time evolution of the WFC3/UVIS CTE, {ii} establishing the detector X

  17. Fate of Adsorbed U(VI) during Sulfidization of Lepidocrocite and Hematite

    PubMed Central

    2017-01-01

    The impact on U(VI) adsorbed to lepidocrocite (γ-FeOOH) and hematite (α-Fe2O3) was assessed when exposed to aqueous sulfide (S(-II)aq) at pH 8.0. With both minerals, competition between S(-II) and U(VI) for surface sites caused instantaneous release of adsorbed U(VI). Compared to lepidocrocite, consumption of S(-II)aq proceeded slower with hematite, but yielded maximum dissolved U concentrations that were more than 10 times higher, representing about one-third of the initially adsorbed U. Prolonged presence of S(-II)aq in experiments with hematite in combination with a larger release of adsorbed U(VI), enhanced the reduction of U(VI): after 24 h of reaction about 60–70% of U was in the form of U(IV), much higher than the 25% detected in the lepidocrocite suspensions. X-ray absorption spectra indicated that U(IV) in both hematite and lepidocrocite suspensions was not in the form of uraninite (UO2). Upon exposure to oxygen only part of U(IV) reoxidized, suggesting that monomeric U(IV) might have become incorporated in newly formed iron precipitates. Hence, sulfidization of Fe oxides can have diverse consequences for U mobility: in short-term, desorption of U(VI) increases U mobility, while reduction to U(IV) and its possible incorporation in Fe transformation products may lead to long-term U immobilization. PMID:28121137

  18. Fate of Adsorbed U(VI) during Sulfidization of Lepidocrocite and Hematite.

    PubMed

    Alexandratos, Vasso G; Behrends, Thilo; Van Cappellen, Philippe

    2017-02-21

    The impact on U(VI) adsorbed to lepidocrocite (γ-FeOOH) and hematite (α-Fe2O3) was assessed when exposed to aqueous sulfide (S(-II)aq) at pH 8.0. With both minerals, competition between S(-II) and U(VI) for surface sites caused instantaneous release of adsorbed U(VI). Compared to lepidocrocite, consumption of S(-II)aq proceeded slower with hematite, but yielded maximum dissolved U concentrations that were more than 10 times higher, representing about one-third of the initially adsorbed U. Prolonged presence of S(-II)aq in experiments with hematite in combination with a larger release of adsorbed U(VI), enhanced the reduction of U(VI): after 24 h of reaction about 60-70% of U was in the form of U(IV), much higher than the 25% detected in the lepidocrocite suspensions. X-ray absorption spectra indicated that U(IV) in both hematite and lepidocrocite suspensions was not in the form of uraninite (UO2). Upon exposure to oxygen only part of U(IV) reoxidized, suggesting that monomeric U(IV) might have become incorporated in newly formed iron precipitates. Hence, sulfidization of Fe oxides can have diverse consequences for U mobility: in short-term, desorption of U(VI) increases U mobility, while reduction to U(IV) and its possible incorporation in Fe transformation products may lead to long-term U immobilization.

  19. Bicarbonate impact on U(VI) bioreduction in a shallow alluvial aquifer

    NASA Astrophysics Data System (ADS)

    Long, Philip E.; Williams, Kenneth H.; Davis, James A.; Fox, Patricia M.; Wilkins, Michael J.; Yabusaki, Steven B.; Fang, Yilin; Waichler, Scott R.; Berman, Elena S. F.; Gupta, Manish; Chandler, Darrell P.; Murray, Chris; Peacock, Aaron D.; Giloteaux, Ludovic; Handley, Kim M.; Lovley, Derek R.; Banfield, Jillian F.

    2015-02-01

    Field-scale biostimulation and desorption tracer experiments conducted in a uranium (U) contaminated, shallow alluvial aquifer have provided insight into the coupling of microbiology, biogeochemistry, and hydrogeology that control U mobility in the subsurface. Initial experiments successfully tested the concept that Fe-reducing bacteria such as Geobacter sp. could enzymatically reduce soluble U(VI) to insoluble U(IV) during in situ electron donor amendment (Anderson et al., 2003; Williams et al., 2011). In parallel, in situ desorption tracer tests using bicarbonate amendment demonstrated rate-limited U(VI) desorption (Fox et al., 2012). These results and prior laboratory studies underscored the importance of enzymatic U(VI)-reduction and suggested the ability to combine desorption and bioreduction of U(VI). Here we report the results of a new field experiment in which bicarbonate-promoted uranium desorption and acetate amendment were combined and compared to an acetate amendment-only experiment in the same experimental plot. Results confirm that bicarbonate amendment to alluvial aquifer sediments desorbs U(VI) and increases the abundance of Ca-uranyl-carbonato complexes. At the same time, the rate of acetate-promoted enzymatic U(VI) reduction was greater in the presence of added bicarbonate in spite of the increased dominance of Ca-uranyl-carbonato aqueous complexes. A model-simulated peak rate of U(VI) reduction was ∼3.8 times higher during acetate-bicarbonate treatment than under acetate-only conditions. Lack of consistent differences in microbial community structure between acetate-bicarbonate and acetate-only treatments suggest that a significantly higher rate of U(VI) reduction in the bicarbonate-impacted sediment may be due to a higher intrinsic rate of microbial reduction induced by elevated concentrations of the bicarbonate oxyanion. The findings indicate that bicarbonate amendment may be useful in improving the engineered bioremediation of uranium in

  20. Bicarbonate Impact on U(VI) Bioreduction in a Shallow Alluvial Aquifer

    SciTech Connect

    Long, Philip E.; Williams, Kenneth H.; Davis, James A.; Fox, Patricia M.; Wilkins, Michael J.; Yabusaki, Steven B.; Fang, Yilin; Waichler, Scott R.; Berman, Elena S.; Gupta, Manish; Chandler, Darrell P.; Murray, Christopher J.; Peacock, Aaron D.; Giloteaux, L.; Handley, Kim M.; Lovley, Derek R.; Banfield, Jillian F.

    2015-02-01

    Field-scale biostimulation and desorption tracer experiments conducted in a uranium (U) contaminated, shallow alluvial aquifer have provided insight into the coupling of microbiology, biogeochemistry, and hydrogeology that control U mobility in the subsurface. Initial experiments successfully tested the concept that Fe-reducing bacteria such as Geobacter sp. could enzymatically reduce soluble U(VI) to insoluble U(IV) during in situ electron donor amendment (Anderson et al. 2003, Williams et al. 2011). In parallel, in situ desorption tracer tests using bicarbonate amendment demonstrated rate-limited U(VI) desorption (Fox et al. 2012). These results and prior laboratory studies underscored the importance of enzymatic U(VI)-reduction and suggested the ability to combine desorption and bioreduction of U(VI). Here we report the results of a new field experiment in which bicarbonate-promoted uranium desorption and acetate amendment were combined and compared to an acetate amendment-only experiment in the same experimental plot. Results confirm that bicarbonate amendment to alluvial aquifer desorbs U(VI) and increases the abundance of Ca-uranyl-carbonato complexes. At the same time, that the rate of acetate-promoted enzymatic U(VI) reduction was greater in the presence of added bicarbonate in spite of the increased dominance of Ca-uranyl-carbonato aqueous complexes. A model-simulated peak rate of U(VI) reduction was ~3.8 times higher during acetate-bicarbonate treatment than under acetate-only conditions. Lack of consistent differences in microbial community structure between acetate-bicarbonate and acetate-only treatments suggest that a significantly higher rate of U(VI) reduction the bicarbonate-impacted sediment may be due to a higher intrinsic rate of microbial reduction induced by elevated concentrations of the bicarbonate oxyanion. The findings indicate that bicarbonate amendment may be useful in improving the engineered bioremediation of uranium in aquifers.

  1. WFC3/UVIS Sky Backgrounds

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia; Anderson, Jay

    2012-06-01

    This report summarizes the on-orbit background levels present in WFC3/UVIS full-frame images. The results are based on nearly all standard readout images taken since the installation of WFC3 on HST in May 2009, with a relatively small number of exclusions e.g. images with obvious anomalous backgrounds (such as extended targets filling the field of view) or those taken with the quad filters (different bandpass in each amp). Comparisons are provided to estimates from the Exposure Time Calculator (ETC). We anticipate these results to be helpful in fine-tuning the level of post-flash required to achieve the optimum balance of charge transfter efficiency (CTE) loss mitigation versus noise penalty. Observers considering the use of post-flash should refer to the White Paper (MacKenty & Smith 2012) on the CTE WWW page (http://www.stsci.edu/hst/wfc3/ins_performance/CTE/).

  2. Mechanical investigation of U(VI) on pyrrhotite by batch, EXAFS and modeling techniques.

    PubMed

    Liu, Haibo; Zhu, Yuke; Xu, Bin; Li, Ping; Sun, Yubing; Chen, Tianhu

    2017-01-15

    The interaction mechanism of U(VI) on pyrrhotite was demonstrated by batch, spectroscopic and modeling techniques. Pyrite was selected as control group in this study. The removal of U(VI) on pyrite and pyrrhotite significantly decreased with increasing ionic strength from 0.001 to 0.1mol/L at pH 2.0-6.0, whereas the no effect of ionic strength was observed at pH >6.0. The maximum removal capacity of U(VI) on pyrite and pyrrhotite calculated from Langmuir model was 10.20 and 21.34mgg(-1) at pH 4.0 and 333K, respectively. The XPS analysis indicated the U(VI) was primarily adsorbed on pyrrhotite and pyrite and then approximately 15.5 and 9.8% of U(VI) were reduced to U(IV) by pyrrhotite and pyrite after 20 days, respectively. Based on the XANES analysis, the adsorption edge of uranium-containing pyrrhotite located between U(IV)O2(s) and U(VI)O2(2+) spectra. The EXAFS analysis demonstrated the inner-sphere surface complexation of U(VI) on pyrrhotite due to the occurrence of U-S shell, whereas the U-U shell revealed the reductive co-precipitates of U(VI) on pyrrhotite/pyrite with increasing reaction times. The surface complexation modeling showed that outer- and inner-surface complexation dominated the U(VI) removal at pH<4 and pH>5.0, respectively. The findings presented herein play a crucial role in the removal of radionuclides on iron sulfide in environmental cleanup applications.

  3. Growth of Desulfovibrio vulgaris when respiring U(VI) and characterization of biogenic uraninite.

    PubMed

    Zhou, Chen; Vannela, Raveender; Hyun, Sung Pil; Hayes, Kim F; Rittmann, Bruce E

    2014-06-17

    The capacity of Desulfovibrio vulgaris to reduce U(VI) was studied previously with nongrowth conditions involving a high biomass concentration; thus, bacterial growth through respiration of U(VI) was not proven. In this study, we conducted a series of batch tests on U(VI) reduction by D. vulgaris at a low initial biomass (10 to 20 mg/L of protein) that could reveal biomass growth. D. vulgaris grew with U(VI) respiration alone, as well as with simultaneous sulfate reduction. Patterns of growth kinetics and solids production were affected by sulfate and Fe(2+). Biogenic sulfide nonenzymatically reduced 76% of the U(VI) and greatly enhanced the overall reduction rate in the absence of Fe(2+) but was rapidly scavenged by Fe(2+) to form FeS in the presence of Fe(2+). Biogenic U solids were uraninite (UO2) nanocrystallites associated with 20 mg/g biomass as protein. The crystallite thickness of UO2 was 4 to 5 nm without Fe(2+) but was <1.4 nm in the presence of Fe(2+), indicating poor crystallization inhibited by adsorbed Fe(2+) and other amorphous Fe solids, such as FeS or FeCO3. This work fills critical gaps in understanding the metabolic utilization of U by microorganisms and formation of UO2 solids in bioremediation sites.

  4. A mutation in the uvi4 gene promotes progression of endo-reduplication and confers increased tolerance towards ultraviolet B light.

    PubMed

    Hase, Yoshihiro; Trung, Khuat Huu; Matsunaga, Tsukasa; Tanaka, Atsushi

    2006-04-01

    We have isolated and characterized a new ultraviolet B (UV-B)-resistant mutant, uvi4 (UV-B-insensitive 4), of Arabidopsis. The fresh weight (FW) of uvi4 plants grown under supplemental UV-B light was more than twice that of the wild-type. No significant difference was found in their ability to repair the UV-B-induced cyclobutane pyrimidine dimers, or in the amount of UV-B absorptive compounds, both of which are well-known factors that contribute to UV sensitivity. Positional cloning revealed that the UVI4 gene encodes a novel basic protein of unknown function. We found that the hypocotyl cells in uvi4 undergo one extra round of endo-reduplication. The uvi4 mutation also promoted the progression of endo-reduplication during leaf development. The UVI4 gene is expressed mainly in actively dividing cells. In the leaves of P(UVI4)::GUS plants, the GUS signal disappeared in basipetal fashion as the leaf developed. The total leaf blade area was not different between uvi4 and the wild-type through leaf development, while the average cell area in the adaxial epidermis was considerably larger in uvi4, suggesting that the uvi4 leaves have fewer but larger epidermal cells. These results suggest that UVI4 is necessary for the maintenance of the mitotic state, and the loss of UVI4 function stimulated endo-reduplication. Tetraploid Arabidopsis was hyper-resistant to UV-B compared to diploid Arabidopsis, suggesting that the enhanced polyploidization is responsible for the increased UV-B tolerance of the uvi4 mutant.

  5. Reduction of uranium by Desulfovibrio desulfuricans

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.

    1992-01-01

    The possibility that sulfate-reducing microorganisms contribute to U(VI) reduction in sedimentary environments was investigated. U(VI) was reduced to U(IV) when washed cells of sulfate-grown Desulfovibrio desulfuricans were suspended in a bicarbonate buffer with lactate or H2 as the electron donor. There was no U(VI) reduction in the absence of an electron donor or when the cells were killed by heat prior to the incubation. The rates of U(VI) reduction were comparable to those in respiratory Fe(III)-reducing microorganisms. Azide or prior exposure of the cells to air did not affect the ability of D. desulfuricans to reduce U(VI). Attempts to grow D. desulfuricans with U(VI) as the electron acceptor were unsuccessful. U(VI) reduction resulted in the extracellular precipitation of the U(IV) mineral uraninite. The presence of sulfate had no effect on the rate of U(VI) reduction. Sulfate and U(VI) were reduced simultaneously. Enzymatic reduction of U(VI) by D. desulfuricans was much faster than nonenzymatic reduction of U(VI) by sulfide, even when cells of D. desulfuricans were added to provide a potential catalytic surface for the nonenzymatic reaction. The results indicate that enzymatic U(VI) reduction by sulfate-reducing microorganisms may be responsible for the accumulation of U(IV) in sulfidogenic environments. Furthermore, since the reduction of U(VI) to U(IV) precipitates uranium from solution, D. desulfuricans might be a useful organisms for recovering uranium from contaminated waters and waste streams.

  6. Long-term diffusion of U(VI) in bentonite: Dependence on density

    SciTech Connect

    Joseph, Claudia; Mibus, Jens; Trepte, Paul; Muller, Christa; Brendler, Vinzenz; Park, Dan M.; Jiao, Yongqin; Kersting, Annie B.; Zavarin, Mavrik

    2016-10-12

    As a contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over six years. Synthetic MX-80 model pore water was used as background electrolyte. Speciation calculations showed that Ca2UO2(CO3)3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3 mm, 1.5 mm, and 1 mm into the clay plug at ρ = 1.3, 1.6, and 1.9 g/cm3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uranium contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficients, De and Da, decreased with increasing dry density. The Da values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, Da values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. Some potential reasons for this behavior that were evaluated are changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time. By applying Archie's law and the extended Archie's law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). Finally, the results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.

  7. Microbial reduction of uranium

    USGS Publications Warehouse

    Lovley, D.R.; Phillips, E.J.P.; Gorby, Y.A.; Landa, E.R.

    1991-01-01

    REDUCTION of the soluble, oxidized form of uranium, U(VI), to insoluble U(IV) is an important mechanism for the immobilization of uranium in aquatic sediments and for the formation of some uranium ores1-10. U(VI) reduction has generally been regarded as an abiological reaction in which sulphide, molecular hydrogen or organic compounds function as the reductant1,2,5,11. Microbial involvement in U(VI) reduction has been considered to be limited to indirect effects, such as microbial metabolism providing the reduced compounds for abiological U(VI) reduction and microbial cell walls providing a surface to stimulate abiological U(VI) reduction1,12,13. We report here, however, that dissimilatory Fe(III)-reducing microorganisms can obtain energy for growth by electron transport to U(VI). This novel form of microbial metabolism can be much faster than commonly cited abiological mechanisms for U(VI) reduction. Not only do these findings expand the known potential terminal electron acceptors for microbial energy transduction, they offer a likely explanation for the deposition of uranium in aquatic sediments and aquifers, and suggest a method for biological remediation of environments contaminated with uranium.

  8. A representative retinoid X receptor antagonist UVI3003 induced teratogenesis in zebrafish embryos.

    PubMed

    Zheng, Liang; Xu, Ting; Li, Daoji; Zhou, Junliang

    2015-03-01

    Retinoid X receptor (RXR) interfering activity has been detected in different water resources. To study RXR disruptor-induced toxicological effects on vertebrates, embryos of zebrafish (Danio rerio) were exposed to a representative RXR antagonist UVI3003. Results showed that the teratogenic index (LC50 /EC50 ) of UVI3003 was as high as 5.4. UVI3003 induced multiple malformations of embryos, including deformed fins, reduced brains, small jaws, bent tails and edema in hearts, the degree of which became more severe with increasing exposure concentration. Although no significant difference was observed in the hatching rates between the exposure group and control, the whole body length was significantly reduced by 6.5% and 8.9% when exposed to 200 and 300 µg l(-1) of UVI3003, respectively. The heart rate also significantly decreased by 8.8-50.2% during exposure. Further experiments revealed that the pharyngula stage was the most sensitive development phase in terms of embryo response to UVI3003. The results demonstrated severe teratogenicity of RXR antagonist in zebrafish embryos and provided important data for ecotoxicological evaluation of RXR antagonists.

  9. Analog VLSI system for active drag reduction

    SciTech Connect

    Gupta, B.; Goodman, R.; Jiang, F.; Tai, Y.C.; Tung, S.; Ho, C.M.

    1996-10-01

    In today`s cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to reduce costs. Even a 5% reduction in drag translates into estimated savings of millions of dollars in fuel costs. Drawing inspiration from the structure of shark skin, the authors are building a system to reduce drag along a surface. Our analog VLSI system interfaces with microfabricated, constant-temperature shear stress sensors. It detects regions of high shear stress and outputs a control signal to activate a microactuator. We are in the process of verifying the actual drag reduction by controlling microactuators in wind tunnel experiments. We are encouraged that an approach similar to one that biology employs provides a very useful contribution to the problem of drag reduction. 9 refs., 21 figs.

  10. Sorption of U(VI) to G. uraniireducens and A. palmae under Old Rifle Conditions

    NASA Astrophysics Data System (ADS)

    Leavitt, J.; Cabaniss, S.; Howe, K.; Comolli, L.; Long, P.; Stucker, V.

    2011-12-01

    Microbial reduction as a remediation method for uranium contaminated Department of Energy (DOE) sites has been explored with promising results. Although transport models have been improved to include variations in geochemical concentration, reductive microbial processes and adsorption of uranium to minerals, they do not incorporate the presence of microbes as possible sorption surfaces that may influence the overall transport of uranium. Our overall objective is to examine U(VI) sorption to biomass by determining partition coefficients between U(VI) and the microbial species of Geobacter uraniireducens and Acholeplasma palmae. Once these partition coefficients are obtained, they will be incorporated into a thermodynamic model with the geochemical parameters of the Old Rifle Site. Preliminary results indicate that U(VI) sorbs 1000X more strongly to bacteria under atmospheric pCO2 conditions than under 2% pCO2 conditions. U(VI) sorption to the surface of G. uraniireducens is 4X stronger than to the surface of A. Palmae and in high-DIC waters is comparable in strength to reported U(VI)-mineral surface sorption. While the concentration of G. uraniireducens during and after remediation results in relatively small sorption site density, the possibility persists that sorption to G. uraniireducens may retard uranium transport at the geochemical gradients which exist in nature.

  11. Saturn's variable thermosphere from Cassini/UVIS occultations

    NASA Astrophysics Data System (ADS)

    Koskinen, T. T.; Sandel, B. R.; Yelle, R. V.; Strobel, D. F.; Müller-Wodarg, I. C. F.; Erwin, J. T.

    2015-11-01

    We retrieved the density and temperature profiles in Saturn's thermosphere from 26 stellar occultations observed by the Cassini/UVIS instrument. These results expand upon and complement the previous analysis of 15 Cassini/UVIS solar occultations by Saturn's upper thermosphere. We find that the exospheric temperatures based on the stellar occultations agree with the solar occultations and range from 380 K to 590 K. These temperatures are also consistent with the recent re-analysis of the Voyager/UVS occultations. The retrieved density profiles support our earlier inference that the shape of the atmosphere at low pressures is consistent with a meridional trend of increasing temperatures with absolute latitude. This implies a high-latitude heat source, such as auroral heating, although the existing circulation models that include auroral heating still underestimate the equatorial temperatures by overestimating the meridional temperature gradient. This suggests either that the circulation models are somehow incomplete or there is some other heat source at low to mid latitudes that is relatively less efficient than high-latitude heating. We also find evidence for the expansion of the exobase by about 500 km between 2006 and 2011 near the equator, followed by possible contraction after 2011. The expansion appears to be caused by significant warming of the lower thermosphere that anti-correlates with solar activity and may be connected to changes in global circulation. Lastly, we note that our density profiles are in good general agreement with the Voyager/UVS data. In particular, the Voyager density profiles are most consistent with the Cassini/UVIS stellar occultations from late 2008 and early 2009 that roughly coincide in season with the Voyager flybys.

  12. Reduction kinetics of aqueous U(VI) in acidic chloride brines to uraninite by methane, hydrogen or C-graphite under hydrothermal conditions: Implications for the genesis of unconformity-related uranium ore deposits

    NASA Astrophysics Data System (ADS)

    Dargent, Maxime; Truche, Laurent; Dubessy, Jean; Bessaque, Gilles; Marmier, Hervé

    2015-10-01

    The formation of hydrothermal uranium ore deposits involves the reduction of dissolved U(VI)(aq) to uraninite. However, the nature of the reducing agent and the kinetics of such a process are currently unknown. These questions are addressed through dedicated experiments performed under conditions relevant for the genesis of unconformity-related uranium (URU) deposits. We tested the efficiency of the following potential reductants supposed to be involved in the reaction: H2, CH4, C-graphite and dissolved Fe(II). Results demonstrate the great efficiency of H2, CH4 and C-graphite to reduce U(VI)(aq) into uraninite in acidic chloride brines, unlike dissolved Fe(II). Times needed for H2 (1.4 bar), CH4 (2.4 bar) and C-graphite (water/carbon mass ratio = 10) to reduce 1 mM of U(VI)(aq) in an acidic brine (1 m LiCl, pH ≈ 1 fixed by HCl) to uraninite at 200 °C are 12 h, 3 days and 4 months, respectively. The effects of temperature (T) between 100 °C and 200 °C, H2 partial pressure (0.14, 1.4, and 5.4 bar), salinity (0.1, 1 and 3.2 m LiCl) and pH at 25 °C (0.8 and 3.3) on the reduction rate were also investigated. Results show that increasing temperature and H2 partial pressure increase the reaction rate, whereas increasing salinity or pH have the reverse effect. The reduction of uranyl to uraninite follows an apparent zero-order with respect to time, whatever the considered electron donor. From the measured rate constants, the following values of activation energy (Ea), depending on the nature of the electron donor, have been derived: EaC-graphite = 155 ± 3 kJ mol-1, EaCH4 = 143 ± 6 kJ mol-1, and EaH2 = 124 ± 15 kJ mol-1 at T < 150 °C and 32 ± 6 kJ mol-1 at T > 150 °C. An empirical relationship between the reaction rate, the hydrogen partial pressure, the uranyl speciation, and the temperature is also proposed. This allows an estimation of the time of formation of a giant U ore deposit such as McArthur River (Canada). The duration of the mineralizing event is

  13. U(VI) bioreduction with emulsified vegetable oil as the electron donor--microcosm tests and model development.

    PubMed

    Tang, Guoping; Wu, Wei-Min; Watson, David B; Parker, Jack C; Schadt, Christopher W; Shi, Xiaoqing; Brooks, Scott C

    2013-04-02

    We conducted microcosm tests and biogeochemical modeling to study U(VI) reduction in contaminated sediments amended with emulsified vegetable oil (EVO). Indigenous microorganisms in the sediments degraded EVO and stimulated Fe(III), U(VI), and sulfate reduction, and methanogenesis. Acetate concentration peaked in 100-120 days in the EVO microcosms versus 10-20 days in the oleate microcosms, suggesting that triglyceride hydrolysis was a rate-limiting step in EVO degradation and subsequent reactions. Acetate persisted 50 days longer in oleate- and EVO- than in ethanol-amended microcosms, indicating that acetate-utilizing methanogenesis was slower in the oleate and EVO than ethanol microcosms. We developed a comprehensive biogeochemical model to couple EVO hydrolysis, production, and oxidation of long-chain fatty acids (LCFA), glycerol, acetate, and hydrogen, reduction of Fe(III), U(VI) and sulfate, and methanogenesis with growth and decay of multiple functional microbial groups. By estimating EVO, LCFA, and glycerol degradation rate coefficients, and introducing a 100 day lag time for acetoclastic methanogenesis for oleate and EVO microcosms, the model approximately matched observed sulfate, U(VI), and acetate concentrations. Our results confirmed that EVO could stimulate U(VI) bioreduction in sediments and the slow EVO hydrolysis and acetate-utilizing methanogens growth could contribute to longer term bioreduction than simple substrates (e.g., ethanol, acetate, etc.) in the subsurface.

  14. Cassini UVIS Auroral Observations in 2016

    NASA Astrophysics Data System (ADS)

    Pryor, Wayne R.; Jouchoux, Alain; Esposito, Larry W.; Radioti, Aikaterini; Grodent, Denis; Gustin, Jacques; Gerard, Jean-Claude; Lamy, Laurent; Badman, Sarah; Bunce, Emma; Cecconi, Baptiste; Clarke, John T.; Crary, Frank; Dougherty, Michele; Dyudina, Ulyana A.; Kurth, William; Mitchell, Don; Nichols, Jonathan; Prange, Renee; Schippers, Patricia; Zarka, Philippe; Cassini UVIS Team

    2016-10-01

    In June of 2016, the Cassini Saturn orbiter began a series of high inclination orbits that will continue until September 2017 when the mission ends as Cassini enters the Saturn atmosphere. These orbits present excellent views of Saturn's polar regions suitable for auroral imaging at the closest distances to date, with the additional prospect of simultaneous particle and fields measurements within the sources of Saturn Kilometric Radiation (SKR) associated with ultraviolet auroral emissions and/or acceleration regions likely coinciding with them. We will present new Cassini Ultraviolet Imaging Spectrograph (UVIS) auroral images, spectra and movies obtained during the summer and fall of 2016 and put them in the context of auroral data collected since Cassini orbit insertion in 2004. Included in the new data will be UVIS south polar observations obtained simultaneously with Hubble Space Telescope observations of the north polar region on June 29, 2016 and August 19, 2016.

  15. Diffusion of U(VI) in Opalinus Clay: Influence of temperature and humic acid

    NASA Astrophysics Data System (ADS)

    Joseph, C.; Van Loon, L. R.; Jakob, A.; Steudtner, R.; Schmeide, K.; Sachs, S.; Bernhard, G.

    2013-05-01

    activation energy for the diffusion of U(VI) through Opalinus Clay of 10 kJ/mol was calculated. The observed increased Kd and De values for U(VI)aqueous at 60 °C compensated each other to almost equal values of the apparent diffusion coefficient Da at 25 and 60 °C. Hence, an elevated temperature of 60 °C does not impact the migration of U(VI) through OPA significantly.

  16. Ultraviolet Observations of Phoebe from the Cassini UVIS

    NASA Technical Reports Server (NTRS)

    Hendrix, Amanda R.; Hansen, Candice J.

    2007-01-01

    Observations of Saturn's distant moon Phoebe were made at far-ultraviolet (FUV) (1100-1900 A) and extreme-ultraviolet (EUV) (600-1100 A) wavelengths by the Cassini Ultraviolet Imaging Spectrograph (UVIS) during the Cassini spacecraft flyby on June 11, 2004. These are the first UV spectra of Phoebe and the first detection of water ice on a Solar System surface using FUV wavelengths. The characteristics of water ice in the FUV are presented, and Hapke models are used to interpret the spectra in terms of composition and grain size; the use of both areal and intimate mixing models is explored. Non-ice species used in these models include carbon, ice tholin, Triton tholin, poly-HCN and kerogen. Satisfactory disk-integrated fits are obtained for intimate mixtures of approx.10% H2O plus a non-ice species. Spatially resolved regions of higher (approx.20%) and lower (approx.5%) H2O ice concentrations are also detected. Phoebe does not display any evidence of volatile activity. Upper limits on atomic oxygen and carbon are 5 x 10(exp 11) and 2 x 10(exp 12) atoms/sq. cm, respectively, for solar photon scattering. The UVIS detection of water ice on Phoebe, and the ice amounts detected, are consistent with IR measurements and contribute to the evidence for a Phoebe origin in the outer Solar System rather than in the main asteroid belt.

  17. Ultraviolet observations of Phoebe from the Cassini UVIS

    NASA Astrophysics Data System (ADS)

    Hendrix, Amanda R.; Hansen, Candice J.

    2008-02-01

    Observations of Saturn's distant moon Phoebe were made at far-ultraviolet (FUV) (1100-1900 Å) and extreme-ultraviolet (EUV) (600-1100 Å) wavelengths by the Cassini Ultraviolet Imaging Spectrograph (UVIS) during the Cassini spacecraft flyby on June 11, 2004. These are the first UV spectra of Phoebe and the first detection of water ice on a Solar System surface using FUV wavelengths. The characteristics of water ice in the FUV are presented, and Hapke models are used to interpret the spectra in terms of composition and grain size; the use of both areal and intimate mixing models is explored. Non-ice species used in these models include carbon, ice tholin, Triton tholin, poly-HCN and kerogen. Satisfactory disk-integrated fits are obtained for intimate mixtures of ˜10% H 2O plus a non-ice species. Spatially resolved regions of higher ( ˜20%) and lower ( ˜5%) H 2O ice concentrations are also detected. Phoebe does not display any evidence of volatile activity. Upper limits on atomic oxygen and carbon are 5×10 and 2×10 atoms/cm, respectively, for solar photon scattering. The UVIS detection of water ice on Phoebe, and the ice amounts detected, are consistent with IR measurements and contribute to the evidence for a Phoebe origin in the outer Solar System rather than in the main asteroid belt.

  18. Comparing different Ultraviolet Imaging Spectrograph (UVIS) occultation observations using modeling of water vapor jets

    NASA Astrophysics Data System (ADS)

    Portyankina, Ganna; Esposito, Larry W.; Hansen, Candice; Aye, Klaus-Michael

    2016-10-01

    Motivation: On March 11, 2016 the Cassini UVIS observed its 6th star occultation by Enceladus' plume. This observation was aimed to determine variability in the total gas flux from the Enceladus' southern polar region. The analysis of the received data suggests that the total gas flux is moderately increased comparing to the average gas flux observed by UVIS from 2005 to 2011 [1]. However, UVIS detected variability in individual jets. In particular, Baghdad 1 is more collimated in 2016 than in 2005, meaning its gas escapes at higher velocity.Model and fits: We use 3D DSMC model for water vapor jets to compare different UVIS occultation observations from 2005 to 2016. The model traces test articles from jets' sources [2] into space and results in coordinates and velocities for a set of test particles. We convert particle positions into the particle number density and integrate along UVIS line of sight (LoS) for each time step of the UVIS observation using precise observational geometry derived from SPICE [3]. We integrate all jets that are crossed by the LoS and perform constrained least-squares fit of resulting modeled opacities to the observed data to solved for relative strengths of jets. The geometry of each occultation is specific, for example, during solar occultation in 2010 UVIS LoS was almost parallel to tiger stripes, which made it possible to distinguish jets venting from different tiger stripes. In 2011 Eps Orionis occultation LoS was perpendicular to tiger stripes and thus many of the jets were geometrically overlapping. Solar occultation provided us with the largest inventory of active jets - our model fit detects at least 43 non-zero jet contributions. Stellar occultations generally have lower temporal resolution and observe only a sub-set of these jets: 2011 Eps Orionis needs minimum 25 non-zero jets to fit UVIS data. We will discuss different occultations and models fits, including the most recent Epsilon Orionis occultation of 2016.[1] Hansen et al

  19. Reduction of bromate by granular activated carbon

    SciTech Connect

    Kirisits, M.J.; Snoeyink, V.L.; Kruithof, J.C.

    1998-07-01

    Ozonation of waters containing bromide can lead to the formation of bromate, a probable human carcinogen. Since bromate will be regulated at 10 {micro}g/L by the Stage 1 Disinfectants/Disinfection By-Products Rule, there is considerable interest in finding a suitable method of bromate reduction. Granular activated carbon (GAC) can be used to chemically reduce bromate to bromide, but interference from organic matter and anions present in natural water render this process inefficient. In an effort to improve bromate reduction by GAC, several modifications were made to the GAC filtration process. The use of a biologically active carbon (BAC) filter ahead of a fresh GAC filter with and without preozonation, to remove the biodegradable organic matter, did not substantially improve the bromate removal of the GAC filter. The use of the BAC filter for biological bromate reduction proved to be the most encouraging experiment. By lowering the dissolved oxygen in the influent to the BAC from 8.0 mg/L to 2.0 mg/L, the percent bromate removal increased from 42% to 61%.

  20. U(VI) behaviour in hyperalkaline calcite systems

    NASA Astrophysics Data System (ADS)

    Smith, Kurt F.; Bryan, Nicholas D.; Swinburne, Adam N.; Bots, Pieter; Shaw, Samuel; Natrajan, Louise S.; Mosselmans, J. Frederick W.; Livens, Francis R.; Morris, Katherine

    2015-01-01

    The behaviour of U(VI) in hyperalkaline fluid/calcite systems was studied over a range of U(VI) concentrations (5.27 × 10-5 μM to 42.0 μM) and in two high pH systems, young and old synthetic cement leachate in batch sorption experiments. These systems were selected to be representative of young- (pH 13.3) and old-stage (pH 10.5) leachate evolution within a cementitious geological disposal facility. Batch sorption experiments, modelling, extended X-ray absorption fine structure spectroscopy, electron microscopy, small angle X-ray scattering and luminescence spectroscopy were used to define the speciation of U(VI) across the systems of study. At the lowest concentrations (5.27 × 10-5 μM 232U(VI)) significant U removal was observed for both old and young cement leachates, and this was successfully modelled using a first order kinetic adsorption modelling approach. At higher concentrations (>4.20 μM) in the young cement leachate, U(VI) showed no interaction with the calcite surface over an 18 month period. Small angle X-ray scattering techniques indicated that at high U concentrations (42.0 μM) and after 18 months, the U(VI) was present in a colloidal form which had little interaction with the calcite surface and consisted of both primary and aggregated particles with a radius of 7.6 ± 1.1 and 217 ± 24 Å, respectively. In the old cement leachate, luminescence spectroscopy identified two surface binding sites for U(VI) on calcite: in the system with 0.21 μM U(VI), a liebigite-like Ca2UO2(CO3)3 surface complex was identified; at higher U(VI) concentrations (0.42 μM), a second binding site of undetermined coordination was identified. At elevated U(VI) concentrations (>2.10 μM) in old cement leachate, both geochemical data and luminescence spectroscopy suggested that surface mediated precipitation was controlling U(VI) behaviour. A focused ion beam mill was used to create a section across the U(VI) precipitate-calcite interface. Transmission electron

  1. Role of U(VI) Adsorption in U(VI) Reduction by Geobacter Species.

    SciTech Connect

    None, None

    2009-03-09

    Previous work had suggested that Acholeplasma palmae has a higher capacity for uranium sorption than other bacteria studied. Sorption studies were performed with cells in suspension in various solutions containing uranium and results were used to generate uranium-biosorption isotherms.

  2. EUV spectroscopy of the Venus dayglow with UVIS on Cassini

    NASA Astrophysics Data System (ADS)

    Gérard, J.-C.; Hubert, B.; Gustin, J.; Shematovich, V. I.; Bisikalo, D.; Gladstone, G. R.; Esposito, L. W.

    2011-01-01

    We analyze EUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus on 24 June 1999, a period of high solar activity level. Emissions from OI, OII, NI, CI and CII and CO have been identified and their disc average intensity has been determined. They are generally somewhat brighter than those determined from the observations made with the HUT spectrograph at a lower activity level, We present the brightness distribution along the foot track of the UVIS slit of the OII 83.4 nm, OI 98.9 nm, Lyman-ß + OI 102.5 nm and NI 120.0 nm multiplets, and the CO C-X and B-X Hopfield-Birge bands. We make a detailed comparison of the intensities of the 834 nm, 989 nm, 120.0 nm multiplets and CO B-X band measured along the slit foot track on the disc with those predicted by an airglow model previously used to analyze Venus and Mars ultraviolet spectra. This model includes the treatment of multiple scattering for the optically thick OI, OII and NI multiplets. It is found that the observed intensity of the OII emission at 83.4 nm is higher than predicted by the model. An increase of the O + ion density relative to the densities usually measured by Pioneer Venus brings the observations and the modeled values into better agreement. The calculated intensity variation of the CO B-X emission along the track of the UVIS slit is in fair agreement with the observations. The intensity of the OI 98.9 nm emission is well predicted by the model if resonance scattering of solar radiation by O atoms is included as a source. The calculated brightness of the NI 120 nm multiplet is larger than observed by a factor of ˜2-3 if photons from all sources encounter multiple scattering. The discrepancy reduces to 30-80% if the photon electron impact and photodissociation of N 2 sources of N( 4S) atoms are considered as optically thin. Overall, we find that the O, N 2 and CO densities from the empirical VTS3 model provide satisfactory

  3. UVIS 2.0: Ultraviolet Flats

    NASA Astrophysics Data System (ADS)

    Mack, J.

    2017-03-01

    Improved UV flat fields were delivered on February 23, 2016 for the four bluest WFC3 filters. These new reference files correct for sensitivity residuals in a crosshatch pattern on spatial scales of 50-100 pixels. The residuals are a result of in-flight temperature differences affecting the detector's spatial response, which was derived from ground test data at a warmer operating temperature. Photometry of white dwarf standards stepped across the UVIS detector shows a linear correlation between the flat field response and the measured flux residual, which is used to model the correction. With the 2016 flats, the photometric repeatability is now 3.0% peak-to-peak (0.7% rms) compared to 6.7% peak-to-peak (1.8% rms) with the original 2011 flats, excluding the left edge of the detector (x<300 pixels) in F275W where photometry is 1% higher than the rest of the frame. The UV filters have color terms of several percent, and the new chip-dependent calibration is intended to produce uniform count rate across the two chips for blue sources. When using the inverse sensitivity values delivered in February 2016, offsets in the UV count rate between chips of up to 2% are found for hot stars, and even more for cool stars. A revised calibration delivered in November 2016 corrects the offset for blue sources, allowing for more accurate drizzled data products when combining pixels from different UVIS chips.

  4. WFC3 UVIS Detector: Improved Flat Fields

    NASA Astrophysics Data System (ADS)

    Dahlen, Tomas; Mack, J.; Sabbi, E.; WFC3 Team

    2012-01-01

    We describe the improved flat field calibration for a set of UVIS broad-band filters that were delivered to MAST in August 2011. The total change peak-to-peak with respect to the previous pipeline flats ranges from 3.6% to 5.6%, increasing with wavelength. The flat-fields previously used in the pipeline were obtained during ground testing and contained a large reflection ghost (or flare) that affected 40% of the field. A simplified geometric model of the internal light reflections has been used to remove the flare from the ground flats. Residual low-frequency structures caused by differences in the ground-based and in-flight optical paths were then computed using photometry of Omega Centauri, observed at various roll angles and with large dithered steps. Furthermore, photometry in a range of apertures has been used to study the UVIS PSF in detail. For radii smaller than 0.4" (10 pixels) the PSF is strongly dependent on both the detector position and on the telescope focus at the time of observation. Therefore, the new pipeline flat fields have been normalized to "infinite" aperture by applying local aperture corrections to 10 pixels, making them more generally applicable.

  5. International Space Station (ISS) Risk Reduction Activities

    NASA Technical Reports Server (NTRS)

    Fodroci, Michael

    2011-01-01

    As the assembly of the ISS nears completion, it is worthwhile to step back and review some of the actions pursued by the Program in recent years to reduce risk and enhance the safety and health of ISS crewmembers, visitors, and space flight participants. While the ISS requirements and initial design were intended to provide the best practicable levels of safety, it is always possible to reduce risk -- given the determination and commitment to do so. The following is a summary of some of the steps taken by the ISS Program Manager, by our International Partners, by hardware and software designers, by operational specialists, and by safety personnel to continuously enhance the safety of the ISS. While decades of work went into developing the ISS requirements, there are many things in a Program like the ISS that can only be learned through actual operational experience. These risk reduction activities can be divided into roughly three categories: (1) Areas that were initially noncompliant which have subsequently been brought into compliance or near compliance (i.e., Micrometeoroid and Orbital Debris [MMOD] protection, acoustics) (2) Areas where initial design requirements were eventually considered inadequate and were subsequently augmented (i.e., Toxicity Level 4 materials, emergency hardware and procedures) (3) Areas where risks were initially underestimated, and have subsequently been addressed through additional mitigation (i.e., Extravehicular Activity [EVA] sharp edges, plasma shock hazards) Due to the hard work and cooperation of many parties working together across the span of nearly a decade, the ISS is now a safer and healthier environment for our crew, in many cases exceeding the risk reduction targets inherent in the intent of the original design. It will provide a safe and stable platform for utilization and discovery.

  6. Uranyl-chlorite sorption/desorption: Evaluation of different U(VI) sequestration processes

    NASA Astrophysics Data System (ADS)

    Singer, David M.; Maher, Kate; Brown, Gordon E., Jr.

    2009-10-01

    compositions, although it under-predicts U(VI) sorption by up to 10% at the highest U(VI) sorption loadings and at low pH in the CO 3-Ca-bearing system. After long-term exposure of chlorite to U(VI) under anaerobic conditions at 90 °C, XANES spectra of these samples indicate 25% U(IV) in the CO 3-Ca-free system and CO 3-bearing system samples, whereas no U(IV) was detected in the CO 3-Ca-bearing system sample. Analysis of the EXAFS spectra, TEM images, and EDS spectra indicated the presence of X-ray amorphous nanoparticulate UO 2. The presence of Ca in solution prohibited U(VI) reduction in our long-term sorption experiments.

  7. Enhanced U(VI) bioreduction by alginate-immobilized uranium-reducing bacteria in the presence of carbon nanotubes and anthraquinone-2,6-disulfonate.

    PubMed

    Wang, Weida; Feng, Yali; Tang, Xinhua; Li, Haoran; Du, Zhuwei; Yi, Aifei; Zhang, Xu

    2015-05-01

    Uranium-reducing bacteria were immobilized with sodium alginate, anthraquinone-2,6-disulfonate (AQDS), and carbon nanotubes (CNTs). The effects of different AQDS-CNTs contents, U(IV) concentrations, and metal ions on U(IV) reduction by immobilized beads were examined. Over 97.5% U(VI) (20 mg/L) was removed in 8 hr when the beads were added to 0.7% AQDS-CNTs, which was higher than that without AQDS-CNTs. This result may be attributed to the enhanced electron transfer by AQDS and CNTs. The reduction of U(VI) occurred at initial U(VI) concentrations of 10 to 100 mg/L and increased with increasing AQDS-CNT content from 0.1% to 1%. The presence of Fe(III), Cu(II) and Mn(II) slightly increased U(VI) reduction, whereas Cr(VI), Ni(II), Pb(II), and Zn(II) significantly inhibited U(VI) reduction. After eight successive incubation-washing cycles or 8 hr of retention time (HRT) for 48 hr of continuous operation, the removal efficiency of uranium was above 90% and 92%, respectively. The results indicate that the AQDS-CNT/AL/cell beads are suitable for the treatment of uranium-containing wastewaters.

  8. Influence of calcium on microbial reduction of solid phase uranium(VI).

    PubMed

    Liu, Chongxuan; Jeon, Byong-Hun; Zachara, John M; Wang, Zheming

    2007-08-15

    The effect of calcium on the dissolution and microbial reduction of a representative solid phase uranyl [U(VI)], sodium boltwoodite (NaUO(2)SiO(3)OH . 1.5H(2)O), was investigated to evaluate the rate-limiting step of microbial reduction of the solid phase U(VI). Microbial reduction experiments were performed in a culture of a dissimilatory metal-reducing bacterium (DMRB), Shewanella oneidensis strain MR-1, in a bicarbonate medium with lactate as electron donor at pH 6.8 buffered with PIPES. Calcium increased the rate of Na-boltwoodite dissolution and U(VI) bioavailability by increasing its solubility through the formation of a ternary aqueous calcium-uranyl-carbonate species. The ternary species, however, decreased the rates of microbial reduction of aqueous U(VI). Laser-induced fluorescence spectroscopy (LIFS) and transmission electron microscopy (TEM) collectively revealed that microbial reduction of solid phase U(VI) was a sequentially coupled process of Na-boltwoodite dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) to U(IV) that accumulated on bacterial surfaces/periplasm. Under studied experimental conditions, the overall rate of microbial reduction of solid phase U(VI) was limited by U(VI) dissolution reactions in solutions without calcium and limited by microbial reduction in solutions with calcium. Generally, the overall rate of microbial reduction of solid phase U(VI) was determined by the coupling of solid phase U(VI) dissolution, U(VI) aqueous speciation, and microbial reduction of dissolved U(VI) that were all affected by calcium.

  9. Iron Reduction and Radionuclide Immobilization: Kinetic, Thermodynamic and Hydrologic controls & Reaction-Based Modeling - Final Report

    SciTech Connect

    William D. Burgos

    2004-06-18

    Our research focused on (1) microbial reduction of Fe(III) and U(VI) individually, and concomitantly in natural sediments, (2) Fe(III) oxide surface chemistry, specifically with respect to reactions with Fe(II)and U(VI), (3) the influence of humic substances on Fe(III) and U(VI) bioreduction, and on U(VI) complexation, and (4) the development of reaction-based reactive transport biogeochemical models to numerically simulate our experimental results. We have continued our investigations on microbial reduction of Fe(III) oxides. Modeling our earlier experimental results required assumption of a hydrated surface for hematite, more reactive than predicted based on theoretical solubility (Burgos et al.2002). Subsequent studies with Shewanella putrefaciens and Geobacter sulfurreducens confirmed the rates of Fe(III) bioreduction depend on oxide surface area rather than oxide thermodynamic properties (Roden,2003a,b;2004; Burgos et al,2003). We examined the potential for bioreduction of U(VI) by Geobacter sulfurreducens in the presence of synthetic Fe(III) oxides and natural Fe(III) oxide-containing solids (Jeon et al,2004a,b) in which more than 95% of added U(VI) was sorbed to mineral surfaces. The results showed a significant portion of solid-associated U(VI) was resistant to both enzymatic and abiotic (Fe(II)-driven) reduction, but the rate and extent of bioreduction of U(VI) was increased due to the addition of anthraquinone-2,6-disulfonate (AQDS). We conducted long-term semicontinuous culture and column experiments on coupled Fe(III) oxide/U(VI) reduction. These experiments were conducted with natural subsurface sediment from the Oyster site in Virginia, whose Fe content and microbial reducibility are comparable to ORNL FRC sediments (Jeon et al, 2004b). The results conclusively demonstrated the potential for sustained removal of U(VI) from solution via DMRB activity in excess of the U(VI) sorption capacity of the natural mineral assemblages. Jang (2004) demonstrated

  10. Updated WFC3/UVIS Chip Dependent SYNPHOT/PYSYNPHOT Files

    NASA Astrophysics Data System (ADS)

    Deustua, S. E.

    2016-05-01

    The purpose of this ISR is to document the changes to WFC3/UVIS component files that are used with SYNPHOT and PYSYNPHOT as a result of the implementation of the detector dependent photometric calibration in February 2016.

  11. The adsorption behavior of U(VI) on granite.

    PubMed

    Fan, Q H; Hao, L M; Wang, C L; Zheng, Z; Liu, C L; Wu, W S

    2014-03-01

    The effects of pH, counter ions and temperature on the adsorption of U(VI) on Beishan granite (BsG) were investigated in the presence and absence of fulvic acid (FA) and humic acid (HA). The adsorption edge of U(VI) on BsG suggested that U(VI) adsorption was mainly controlled by ion exchange and outer-sphere complexation at low pH, whereas inner-sphere complex was the dominant adsorption species in the pH range of 4.0-9.0. Above pH 9.0, Na2U2O7 might play an important role in the rise of U(VI) adsorption again. Counter ions such as Cl(-), SO4(2-) and PO4(3-) can provoke U(VI) adsorption on BsG to some extent, which was directly correlated to the complexing ability of U(VI)-ligand. More noticeably, the large enhancement of U(VI) adsorption in the presence of phosphate can be attributed to the ternary complex formation (BsG-PO4-UO2), precipitation ((UO2)3(PO4)2(s)) and secondary phase (Na-autunite). Both FA and HA can slightly increase U(VI) adsorption at low pH, whereas they strongly inhibited U(VI) adsorption at high pH range. Artificial synthesized granite (AsG) prepared in the laboratory is impossible to use as an analogue of natural granite because of the large difference in the adsorption and surface properties.

  12. Simultaneous reduction of arsenic(V) and uranium(VI) by mackinawite: role of uranyl arsenate precipitate formation.

    PubMed

    Troyer, Lyndsay D; Tang, Yuanzhi; Borch, Thomas

    2014-12-16

    Uranium (U) and arsenic (As) often occur together naturally and, as a result, can be co-contaminants at sites of uranium mining and processing, yet few studies have examined the simultaneous redox dynamics of U and As. This study examines the influence of arsenate (As(V)) on the reduction of uranyl (U(VI)) by the redox-active mineral mackinawite (FeS). As(V) was added to systems containing 47 or 470 μM U(VI) at concentrations ranging from 0 to 640 μM. In the absence of As(V), U was completely removed from solution and fully reduced to nano-uraninite (nano-UO2). While the addition of As(V) did not reduce U uptake, at As(V) concentrations above 320 μM, the reduction of U(VI) was limited due to the formation of a trögerite-like uranyl arsenate precipitate. The presence of U also significantly inhibited As(V) reduction. While less U(VI) reduction to nano-UO2 may take place in systems with high As(V) concentrations, formation of trögerite-like mineral phases may be an acceptable reclamation end point due to their high stability under oxic conditions.

  13. Reductive immobilization of uranium(VI) by amorphous iron sulfide.

    PubMed

    Hua, Bin; Deng, Baolin

    2008-12-01

    Batch experiments were used to evaluate the reductive immobilization of hexavalent uranium (U(VI)) by synthesized, amorphous iron sulfide (FeS) in the anoxic environment. The tests were initiated by spiking 168.0 microM U(VI) to 0.18 g/L FeS suspensions under a CO2-free condition with pH varied from 5.99 to 10.17. The immobilization rate of U(VI) was determined by monitoring the changes of aqueous U(VI) concentration, and the reduction rate of U(VI) associated with FeS was determined by the difference between the total spiked U(VI) and the extractable amount of U(VI) by 25 mM NaHCO3 solution. The results showed that a rapid removal of U(VI) from the aqueous phase occurred within 1 h under all pH conditions accompanied by a simultaneous release of Fe(ll), whereas the reduction of U(VI) associated with FeS took hours to over a week for completion. The reduction rate was greatly increased with decreasing pH within the examined pH range. Product analysis by X-ray photoelectron spectroscopy showed the formation of U3O8/4O9/UO2, polysulfide, and ferric iron.

  14. Anaerobic bioremediation of hexavalent uranium in groundwater by reductive precipitation with methanogenic granular sludge.

    PubMed

    Tapia-Rodriguez, Aida; Luna-Velasco, Antonia; Field, Jim A; Sierra-Alvarez, Reyes

    2010-04-01

    Uranium has been responsible for extensive contamination of groundwater due to releases from mill tailings and other uranium processing waste. Past evidence has confirmed that certain bacteria can enzymatically reduce soluble hexavalent uranium (U(VI)) to insoluble tetravalent uranium (U(IV)) under anaerobic conditions in the presence of appropriate electron donors. This paper focuses on the evaluation of anaerobic granular sludge as a source of inoculum for the bioremediation of uranium in water. Batch experiments were performed with several methanogenic anaerobic granular sludge samples and different electron donors. Abiotic controls consisting of heat-killed inoculum and non-inoculated treatments confirmed the biological removal process. In this study, unadapted anaerobic granular sludge immediately reduced U(VI), suggesting an intrinsic capacity of the sludge to support this process. The high biodiversity of anaerobic granular sludge most likely accounts for the presence of specific microorganisms capable of reducing U(VI). Oxidation by O(2) was shown to resolubilize the uranium. This observation combined with X-ray diffraction evidence of uraninite confirmed that the removal during anaerobic treatment was due to reductive precipitation. The anaerobic removal activity could be sustained after several respikes of U(VI). The U(VI) removal was feasible without addition of electron donors, indicating that the decay of endogenous biomass substrates was contributing electron equivalents to the process. Addition of electron donors, such as H(2) stimulated the removal of U(VI) to varying degrees. The stimulation was greater in sludge samples with lower endogenous substrate levels. The present work reveals the potential application of anaerobic granular sludge for continuous bioremediation schemes to treat uranium-contaminated water.

  15. Redox Interactions of Tc(VII), U(VI), and Np(V) with Microbially Reduced Biotite and Chlorite.

    PubMed

    Brookshaw, Diana R; Pattrick, Richard A D; Bots, Pieter; Law, Gareth T W; Lloyd, Jonathan R; Mosselmans, J Fredrick W; Vaughan, David J; Dardenne, Kathy; Morris, Katherine

    2015-11-17

    Technetium, uranium, and neptunium are contaminants that cause concern at nuclear facilities due to their long half-life, environmental mobility, and radiotoxicity. Here we investigate the impact of microbial reduction of Fe(III) in biotite and chlorite and the role that this has in enhancing mineral reactivity toward soluble TcO4(-), UO2(2+), and NpO2(+). When reacted with unaltered biotite and chlorite, significant sorption of U(VI) occurred in low carbonate (0.2 mM) buffer, while U(VI), Tc(VII), and Np(V) showed low reactivity in high carbonate (30 mM) buffer. On reaction with the microbially reduced minerals, all radionuclides were removed from solution with U(VI) reactivity influenced by carbonate. Analysis by X-ray absorption spectroscopy (XAS) confirmed reductive precipitation to poorly soluble U(IV) in low carbonate conditions and both Tc(VII) and Np(V) in high carbonate buffer were also fully reduced to poorly soluble Tc(IV) and Np(IV) phases. U(VI) reduction was inhibited under high carbonate conditions. Furthermore, EXAFS analysis suggested that in the reaction products, Tc(IV) was associated with Fe, Np(IV) formed nanoparticulate NpO2, and U(IV) formed nanoparticulate UO2 in chlorite and was associated with silica in biotite. Overall, microbial reduction of the Fe(III) associated with biotite and chlorite primed the minerals for reductive scavenging of radionuclides: this has clear implications for the fate of radionuclides in the environment.

  16. Proposal for a modification of the UVI risk scale.

    PubMed

    Zaratti, Francesco; Piacentini, Rubén D; Guillén, Héctor A; Cabrera, Sergio H; Liley, J Ben; McKenzie, Richard L

    2014-07-01

    The standardisation of UV information to the public through the UV Index (UVI) has been hugely beneficial since its endorsement by multiple international agencies more than 10 years ago. It has now gained widespread acceptance, and UVI values are available throughout the world from satellite instruments, ground-based measurements, and from forecasts based on model calculations. These have been useful for atmospheric scientists, health professionals (skin and eye specialists), and the general public. But the descriptors and health messages associated with the UVI scale are targeted towards European skin types and UV regimes, and are not directly applicable to the population living closer to the equator, especially for those in the high-altitude Altiplano region of South America. This document arose from discussions at the Latin American Society of Photobiology and Photomedicine's Congress, which was held in Arequipa, Peru, in November 2013. A major outcome of the meeting was the Arequipa Accord, which is intended as a unifying document to ensure co-ordination of UV and health research decisions in Latin America. A plank of that agreement was the need to tailor the UVI scale to make it more relevant to the region and its population. Here we make some suggestions to improve the international applicability of the UVI scale.

  17. Analog VLSI for active drag reduction

    NASA Astrophysics Data System (ADS)

    Gupta, Vidyabhusan

    In today's cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to increase fuel efficiency which reduces these costs. Even a 1% reduction in drag can translate into estimated savings of tens of millions of dollars in annual fuel costs. Fluid mechanicists believe that microscopic vortex pairs impinging on the surface play an important role in turbulent transport that may cause large skin friction drag. The microscopic nature and unpredictable appearance of these structures has limited practical approaches to their control. With the advent of micromachining technology providing the ability to build mechanical structures with microscopic dimensions, the tools finally exist with which to detect and control the vortex structures. These sensors and actuators require control circuitry between them in order to build a complete system. We propose an analog VLSI system that can process information along a surface in a moving fluid with the goal of controlling actuators to minimize the surface shear stress. We obtain the information from the surface by using microsensors which measure the surface shear stress. The actuators interact with the fluid by moving up and down in an attempt to diminish the impact of the drag-inducing structures in the fluid. We have designed the fabricated an analog control system. We have tested the system in several different experiments to verify its effectiveness in providing a control signal that energizes an actuator. We also have studied the methodology for a completely integrated wafer-scale system.

  18. Dropout Prevention/Reduction Programs and Activities.

    ERIC Educational Resources Information Center

    Dade County Public Schools, Miami, FL.

    Seventeen activities or programs conducted in the Dade County (Florida) public elementary and secondary schools in order to reduce or prevent dropout are described in this resource guide. The programs activities include: (1) workshops to develop school-based dropout prevention programs; (2) "Students Working Intelligently to Combat High…

  19. Structural basis for the inhibition of AKR1B10 by the C3 brominated TTNPB derivative UVI2008.

    PubMed

    Ruiz, Francesc X; Crespo, Isidro; Álvarez, Susana; Porté, Sergio; Giménez-Dejoz, Joan; Cousido-Siah, Alexandra; Mitschler, André; de Lera, Ángel R; Parés, Xavier; Podjarny, Alberto; Farrés, Jaume

    2017-02-01

    UVI2008, a retinoic acid receptor (RAR) β/γ agonist originated from C3 bromine addition to the parent RAR pan-agonist 4-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid (TTNPB), is also a selective inhibitor of aldo-keto reductase family member 1B10 (AKR1B10). Thus, it might become a lead drug for the design of compounds targeting both activities, as an AKR1B10 inhibitor and RAR agonist, which could constitute a novel therapeutic approach against cancer and skin-related diseases. Herein, the X-ray structure of the methylated Lys125Arg/Val301Leu AKR1B10 (i.e. AKME2MU) holoenzyme in complex with UVI2008 was determined at 1.5 Å resolution, providing an explanation for UVI2008 selectivity against AKR1B10 (IC50 = 6.1 μM) over the closely related aldose reductase (AR, IC50 = 70 μM). The carboxylic acid group of UVI2008 is located in the anion-binding pocket, at hydrogen-bond distance of catalytically important residues Tyr49 and His111. The inhibitor bromine atom can only fit in the wider active site of AKR1B10, mainly because of the native Trp112 side-chain orientation, not possible in AR. In AKR1B10, Trp112 native conformation, and thus UVI2008 binding, is facilitated through interaction with Gln114. IC50 analysis of the corresponding Thr113Gln mutant in AR confirmed this hypothesis. The elucidation of the binding mode of UVI2008 to AKR1B10, along with the previous studies on the retinoid specificity of AKR1B10 and on the stilbene retinoid scaffold conforming UVI2008, could indeed be used to foster the drug design of bifunctional antiproliferative compounds.

  20. Annual waste reduction activities report. Issue 1

    SciTech Connect

    1991-03-18

    This report discusses the waste minimization activities for the Pinellas Plant. The Pinellas Plant deals with low-level radioactive wastes, solvents, scrap metals and various other hazardous materials. This program has realized cost savings through recycling and reuse of materials.

  1. The effect of temperature on the speciation of U(VI) in sulfate solutions

    SciTech Connect

    Rao, Linfeng; Tian, Guoxin

    2008-09-15

    Sulfate, one of the inorganic constituents that could be present in the nuclear waste repository, forms complexes with U(VI) and affects its migration in the environment. Results show that the complexation of U(VI) with sulfate is enhanced by the increase in temperature. The effect of temperature on the complexation and speciation of U(VI) in sulfate solutions is discussed.

  2. Kinetic Desorption and Sorption of U(VI) During Reactive Transport in a Contaminated Hanford Sediment

    SciTech Connect

    Qafoku, Nik; Zachara, John M.; Liu, Chongxuan; Gassman, Paul L.; Qafoku, Odeta; Smith, Steven C.

    2005-05-12

    Column experiments were conducted to investigate U(VI) desorption and sorption kinetics in a sand-textured, contaminated (22.7 µmol kg-1) capillary fringe sediment that had experienced long-term exposure to U(VI). The clay fraction mineralogy of the sediment was dominated by montmorillonite, muscovite, vermiculite, and chlorite. Saturated column experiments were performed under mildly alkaline/calcareous conditions representative of the Hanford site where uranyl–carbonate and calcium–uranyl–carbonate complexes dominate aqueous speciation. A U(VI) free solution was used to study U(VI) desorption in columns where different flow rates were applied. Uranium(VI) sorption was studied after the desorption of labile contaminant U(VI) using different U(VI) concentrations in the leaching solution. Strong kinetic behavior was observed for both U(VI) desorption and sorption. Although U(VI) is semi–mobile in mildly alkaline, calcareous subsurface environments, our results showed substantial U(VI) sorption, significant retardation during transport, and atypical breakthrough curves with extended tailing. A distributed rate model was applied to describe the effluent data and to allow comparisons between the desorption rate of contaminant U(VI) with the rate of short-term U(VI) sorption. Desorption was the slower process. Our results suggest that U(VI) release and transport in the vadose zone and aquifer system from which the sediment was obtained are kinetically controlled.

  3. REPEATED REDUCTIVE AND OXIDATIVE TREATMENTS ON GRANULAR ACTIVATED CARBON

    EPA Science Inventory

    Fenton oxidation and Fenton oxidation preceded by reduction solutions were applied to granular activated carbon (GAC) to chemically regenerate the adsorbent. No adsorbate was present on the GAC so physicochemical effects from chemically aggressive regeneration of the carbon coul...

  4. Effects of aqueous uranyl speciation on the kinetics of microbial uranium reduction

    NASA Astrophysics Data System (ADS)

    Belli, Keaton M.; DiChristina, Thomas J.; Van Cappellen, Philippe; Taillefert, Martial

    2015-05-01

    The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria. To determine the effects of aqueous uranyl speciation on uranium bioreduction kinetics, incubations and viability assays with Shewanella putrefaciens strain 200 were conducted over a range of pH and dissolved inorganic carbon (DIC), Ca2+, and Mg2+ concentrations. A speciation-dependent kinetic model was developed to reproduce the observed time series of total dissolved uranium concentration over the range of geochemical conditions tested. The kinetic model yielded the highest rate constant for the reduction of uranyl non-carbonate species (i.e., the 'free' hydrated uranyl ion, uranyl hydroxides, and other minor uranyl complexes), indicating that they represent the most readily reducible fraction of U(VI) despite being the least abundant uranyl species in solution. The presence of DIC, Ca2+, and Mg2+ suppressed the formation of more bioavailable uranyl non-carbonate species and resulted in slower bioreduction rates. At high concentrations of bioavailable U(VI), however, uranium toxicity to S. putrefaciens inhibited bioreduction, and viability assays confirmed that the concentration of non-carbonate uranyl species best predicts the degree of toxicity. The effect of uranium toxicity was accounted for by incorporating the free ion activity model of metal toxicity into the bioreduction rate law. Overall, these results demonstrate that, in the absence of competing terminal electron acceptors, uranium bioreduction kinetics can be predicted over a wide range of geochemical conditions based on the bioavailability and toxicity imparted on U(VI) by solution composition. These findings also imply that the concentration of uranyl non

  5. 29 CFR 4043.23 - Active participant reduction.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... EVENTS AND CERTAIN OTHER NOTIFICATION REQUIREMENTS Post-Event Notice of Reportable Events § 4043.23 Active participant reduction. (a) Reportable event. A reportable event occurs when the number of active...., facility shutdown or sale); and (2) The number of active participants at the date the reportable...

  6. 29 CFR 4043.23 - Active participant reduction.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... EVENTS AND CERTAIN OTHER NOTIFICATION REQUIREMENTS Post-Event Notice of Reportable Events § 4043.23 Active participant reduction. (a) Reportable event. A reportable event occurs when the number of active...., facility shutdown or sale); and (2) The number of active participants at the date the reportable...

  7. Evolution of the Microbial Community Structure and Iron Reduction Rate in a Column Biostimulation Experiment During the Transition From Iron to Sulfate Reduction

    NASA Astrophysics Data System (ADS)

    Jaffe, P. R.; Elbishlawi, H.; Hettich, R. L.; Kerkhof, L.; Komlos, J.; Kukkadapu, R. P.; Lipton, M. S.; Long, P. E.; McGuinness, L.; Moon, H.; Peacock, A. D.; Verberkmoes, N. C.; Williams, K. H.

    2007-12-01

    During the biostimulation of iron reducers for the purpose of concurrent biological reduction of U(VI), it has been postulated that iron reduction proceeds while bioavailable iron is present, after which the system switches to sulfate reduction if sulfate is present. Field experiments from the Rifle Integrated Field Challenge (IFC) site in Colorado showing that the onset of sulfate reduction has been associated with decreased removal of U(VI) from groundwater support this hypothesis. However, column experiments using sediments from the Rifle site and synthetic groundwater with comparable (7 mM) sulfate levels as in the field, showed that the onset of sulfate reduction occurred within a month with no negative effect on U(VI) reduction. Separate column experiments using low (9 uM) sulfate concentrations showed that iron reduction can be maintained for over 200 days with no indication of iron limitations. To address the discrepancy between field and column experiments, an experiment is being conducted to determine the activity of iron reducers before and after the onset of sulfate reduction. Since Fe(II) buildup is difficult to quantify in the presence of sulfate reduction, the sediments were augmented with Fe- 57 goethite. Minute changes in the Fe-57 goethite can be detected via Mössbauer spectroscopy. Ten columns (2.5 cm internal diameter and 15 cm in length), loaded with sediment from the Rifle site, have been set up and are being operated at 17 °C. Groundwater from the Rifle site, amended with 3mM acetate and 20 μM U(VI), is pumped through the columns at a rate of 0.035 ml/min. Column effluent concentrations are being monitored for acetate, Fe(II), U(VI), and sulfate. Columns are sacrificed at 10 day intervals and the sediment samples are analyzed for Fe(II), U(IV), and acid volatile sulfides using standard analytical procedures. Changes in Fe-57 goethite measured using Mössbauer spectroscopy during biostimulation of the native microorganisms at 10-day

  8. UVIS 2.0 Chip-dependent Inverse Sensitivity Values

    NASA Astrophysics Data System (ADS)

    Deustua, S. E.; Mack, J.; Bowers, A. S.; Baggett, S.; Bajaj, V.; Dahlen, T.; Durbin, M.; Gosmeyer, C.; Gunning, H.; Hammer, D.; Hartig, G.; Khandrika, H.; MacKenty, J.; Ryan, R.; Sabbi, E.; Sosey, M.

    2016-11-01

    We analyze 6 years of standard star observations acquired with the WFC3/UVIS imager between 2009 and 2015. Observations of the three white dwarf standard stars, GD 153, GD 71, and G191B2B were obtained at multiple dither positions near the center of the array and in all four-corner subarrays. Departing from previous practice, chip-dependent inverse sensitivities are computed at r=10 pixels (0.3962 arcsec) for the 42 full frame filters (excluding the 20 quad filters); and these data also provide encircled energy fractions as a function of filter. Chip-dependent inverse sensitivities differ on average by 3% from previous computations, primarily due to drizzling errors. UVIS2 science data are scaled to UVIS1 by the inverse sensitivity ratio so that only a single photflam value is needed for the full detector. We describe the UVIS 2.0 (chip-dependent) philosophy and discuss our results in the context of prior photometric calculations. An updated version of CALWF3 (version 3.3) is required to process the new chip-dependent solutions.

  9. UVIS 2.0: Chip-Dependent Flats

    NASA Astrophysics Data System (ADS)

    Mack, J.; Dahlen, T.; Sabbi, E.; Bowers, A. S.

    2016-03-01

    An improved set of flat fields was delivered to the HST archive on February 23, 2016 as part of the UVIS 2.0 photometric calibration. This new methodology treats the two UVIS chips as separate detectors when computing the flats and zeropoints. The most significant difference in the new flats is that each chip is now normalized by its median value, removing any inherent sensitivity offsets from the flats themselves. Instead, the new software (CALWF3 version 3.3) corrects for this effect by scaling the UVIS2 science extension by the sensitivity ratio between chips, as determined from observations of white dwarf standards. For the majority of filters, the maximum change in the flat field is less than 1%. For the UV filters, the flats are based on ground test data obtained in ambient conditions. These have been updated to correct for 3% sensitivity variations in a crosshatch pattern on scales of 50-100 pixels across both chips. To improve cosmetics in calibrated images, the new flats contain additional corrections for bad rows and columns and new data quality flags for slight vignetting in the outer corner of UVIS1 (amp A).

  10. Chromium Isotope Behaviour During Aerobic Microbial Reduction Activities

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Amor, K.; Porcelli, D.; Thompson, I.

    2014-12-01

    Microbial activity is a very important, and possibly even the dominant, reduction mechanism for many metals in natural water systems. Isotope fractionations during microbial metal reduction can reflect one major mechanism in metal cycling in the environment, and isotopic signatures can be used to identify and quantify reduction processes during biogeochemical cycling in the present environment as well as in the past. There are many Cr (VI)-reducing bacteria that have been discovered and isolated from the environment, and Cr isotopes were found to be fractionated during microbial reduction processes. In this study, Cr reduction experiments have been undertaken to determine the conditions under which Cr is reduced and the corresponding isotope signals that are generated. The experiments have been done with a facultative bacteria Pseudomonas fluorescens LB 300, and several parameters that have potential impact on reduction mechanisms have been investigated. Electron donors are important for bacteria growth and metabolism. One factor that can control the rate of Cr reduction is the nature of the electron donor. The results show that using citrate as an electron donor can stimulate bacteria reduction activity to a large extent; the reduction rate is much higher (15.10 mgˑL-1hour-1) compared with experiments using glucose (6.65 mgˑL-1ˑhour-1), acetate (4.88 mgˑL-1hour-1) or propionate (4.85 mgˑL-1hour-1) as electron donors. Groups with higher electron donor concentrations have higher reduction rates. Chromium is toxic, and when increasing Cr concentrations in the medium, the bacteria reduction rate is also higher, which reflects bacteria adapting to the toxic environment. In the natural environment, under different pH conditions, bacteria may metabolise in different ways. In our experiments with pH, bacteria performed better in reducing Cr (VI) when pH = 8, and there are no significant differences between groups with pH = 4 or pH = 6. To investigate this further, Cr

  11. Réduction de U(VI) par le fer métallique: application à la dépollution des eaux

    NASA Astrophysics Data System (ADS)

    Abdelouas, Abdesselam; Lutze, Werner; Nuttall, Eric; Gong, Weiliang

    1999-03-01

    We investigated the possibility of U(VI) reduction by zero-valent iron (Fe 0). We conducted batch experiments with granular iron and solutions containing 0.25 and 9.3 mg L -1 U(VI) at 24 °C. The solution pH ranges between 2 and 9. In all experiments uranium removal was complete within several hours to several days regardless of the pH value. The reduced uranium precipitated as poorly crystallized hydrated uraninite, UO 2. nH 2O. The reduction of U(VI) to U(IV) by Fe 0 was found to be the principal mechanism of U removal from the solution. Other mechanisms such as U(VI) sorption on the newly formed Fe(III) hydroxides are insignificant. These results show that zero-valent iron can be used to remediate U-contaminated waters from uranium mines and mill tailings sites, the pH of which usually ranges between 2 and 9.

  12. Kinetics of Abiotic Uranium(VI) Reduction by Sulfide

    NASA Astrophysics Data System (ADS)

    Hyun, S.; Davis, J. A.; Hayes, K. F.

    2010-12-01

    Uranium(VI) reduction is an important process affecting the radionuclide’s fate under sulfate reducing conditions. In this work, kinetics of abiotic U(VI) reduction by dissolved sulfide was studied using a batch reactor. The effects of solution pH, dissolved carbonate, Ca(II), U(VI), and S(-II) concentration on the reduction kinetics were tested. The ranges of these experimental variables were designed to cover the variation in groundwater chemistry observed at the Old Rifle uranium mill tailings site (Colorado, USA). Dissolved U concentration was monitored as a function of time using inductively coupled plasma-mass spectrometry to measure the rate of U(VI) reduction. Solid phase reduction products were identified using X-ray diffraction, transmission electron microscopy, and X-ray absorption spectroscopy. The results showed that changes in the experimental variables significantly affected U(VI) reduction kinetics by dissolved sulfide. U(VI) reduction occurred under circumneutral pH while no reduction was observed under alkaline conditions. The reduction rate was slowed by increased dissolved carbonate concentration. One solid phase reduction product was identified as nanoscale uraninite (UO2+x(s)). Thermodynamic modeling showed that the dissolved U(VI) aqueous species changed as a function of solution conditions correlated with the change in the reduction rate. These results show that U(VI) aqueous speciation is important in determining abiotic U(VI) reduction kinetics by dissolved sulfide. This study also illustrates the potential importance of dissolved sulfide in field-scale modeling of U reactive transport, and is expected to contribute to the understanding of long-term effects of biostimulation on U transport at the Rifle site.

  13. Effect of Phosphate on U(VI) Sorption to Montmorillonite: Ternary Complexation and Precipitation Barriers

    SciTech Connect

    Troyer, Lyndsay D.; Maillot, Fabien; Wang, Zheming; Wang, Zimeng; Mehta, Vrajesh; Giammar, Daniel; Catalano, Jeffrey G.

    2016-02-15

    Phosphate addition is a potential treatment method to lower the solubility of U(VI) in soil and groundwater systems by causing U(VI) phosphate precipitation as well as enhancing adsorption. Previous work has shown that iron oxide surfaces may facilitate the nucleation of U(VI) phosphate minerals and, that under weakly acidic conditions, phosphate also enhances U(VI) adsorption to such phases. Like iron oxides, clays are important reactive phases in the subsurface but little is known about the interaction of U(VI) and phosphate with these minerals. The effect of aqueous phosphate on U(VI) binding to Wyoming montmorillonite (SWy-2) in air-equilibrated systems was investigated. Equilibrium U(VI) uptake to montmorillonite was determined at pH 4, 6 and 8 at discrete initial phosphate concentrations between 0 and 100 μM. The observed behavior of U(VI) indicates a transition from adsorption to precipitation with increasing total uranium and phosphate concentrations at all pH values. At the highest phosphate concentration examined at each pH value, a barrier to U(VI) phosphate nucleation is observed. At lower concentrations, phosphate has no effect on macroscopic U(VI) adsorption. To assess the mechanisms of U(VI)-phosphate interactions on smectite surfaces, U(VI) speciation was investigated under selected conditions using laser-induced fluorescence spectroscopy (LIFS) and extended X-ray absorption fine-structure (EXAFS) spectroscopy. Samples above the precipitation threshold display EXAFS and LIFS spectral signatures consistent with the autunite family of U(VI) phosphate minerals. However, at lower U(VI) concentrations, changes in LIFS spectra upon phosphate addition suggest that U(VI)-phosphate ternary surface complexes form on the montmorillonite surface at pH 4 and 6 despite the lack of a macroscopic effect on adsorption. The speciation of solid-associated U(VI) below the precipitation threshold at pH 8 is dominated by U(VI)-carbonate surface complexes. This work

  14. CASSINI UVIS STELLAR OCCULTATION OBSERVATIONS OF SATURN's RINGS

    SciTech Connect

    Colwell, J. E.; Jerousek, R. G.; Pettis, D.; Bradley, E. T.; Esposito, L. W.; Sremcevic, M.

    2010-12-15

    The Cassini spacecraft's Ultraviolet Imaging Spectrograph (UVIS) includes a high-speed photometer (HSP) that has observed more than 100 stellar occultations by Saturn's rings. Here, we document a standardized technique applied to the UVIS-HSP ring occultation datasets delivered to the Planetary Data System as higher level data products. These observations provide measurements of ring structure that approaches the scale of the largest common ring particles ({approx}5 m). The combination of multiple occultations at different viewing geometries enables reconstruction of the three-dimensional structure of the rings. This inversion of the occultation data depends on accurate calibration of the data so that occultations of different stars taken at different times and under different viewing conditions can be combined to retrieve ring structure. We provide examples of the structure of the rings as seen from several occultations at different incidence angles to the rings, illustrating changes in the apparent structure with viewing geometry.

  15. Reaction of U-VI with titanium-substituted magnetite: Influence of Ti on U-IV speciation

    SciTech Connect

    Latta, Drew; Pearce, Carolyn I.; Rosso, Kevin M.; Kemner, Kenneth M.; Boyanov, Maxim I.

    2013-07-01

    Reduction of hexavalent uranium (UVI) to less soluble tetravalent uranium (UIV) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for UVI. Natural magnetites are often impure with titanium, and structural Fe3+ replacement by TiIV yields a proportional increase in the relative Fe2+ content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe2+/Fe3+ ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 xTixO4) reduce UVI to UIV. The UVI-Fe2+ redox reactivity was found to be controlled directly by R, but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where UVI was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25 0.53) results in the formation of UIV species that lack the bidentate U-O2-U bridges of uraninite. Extended x-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound UIV phase has a novel UIV-Ti binding geometry, different from the coordination of UIV in the mineral brannerite (UIVTi2O6). The observed UIV-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation UIV complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced UIV phase. The formation of the non-uraninite UIV-Ti phase appears to be controlled by availability of surface Ti sites, rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of UIV and suggests that further work to characterize the long-term stability of UIV phases formed in the presence of Ti is warranted.

  16. WFC3 TV2 Testing: UVIS Channel Glint

    NASA Astrophysics Data System (ADS)

    Brown, Thomas M.

    2007-10-01

    The UVIS spare detector (UVIS build 2) was housed in WFC3 during the most recent epoch of thermal vaccum ground testing. We scanned the chip gap with a HeNe laser, to look for scattering from any material in the CCD chip gap or the edges of the CCD chips themselves. Although we found no such scattering issues, we did find a significant glint problem involving reflection from the surface of the CCD to the CCD housing and back down to the CCD. The glint appears as a large streak, ~10,000 pixels in area, containing anywhere from 1% to 30% of the energy within the source itself, depending upon the wavelength and position of the source. Approximately 10% of the detector area leads to glint when a source is placed in that area. Although any one glint comprises a tiny fraction of the detector area, the glint sweeps over a large area as the source is moved, implying that approximately 15% of the detector could be significantly illuminated by glint when observing a crowded field. As a result, the UVIS detectors currently not installed in the instrument have been modified to mask the surfaces responsible for the glint, to avoid this issue on orbit.

  17. Active viscoelastic matter: from bacterial drag reduction to turbulent solids.

    PubMed

    Hemingway, E J; Maitra, A; Banerjee, S; Marchetti, M C; Ramaswamy, S; Fielding, S M; Cates, M E

    2015-03-06

    A paradigm for internally driven matter is the active nematic liquid crystal, whereby the equations of a conventional nematic are supplemented by a minimal active stress that violates time-reversal symmetry. In practice, active fluids may have not only liquid-crystalline but also viscoelastic polymer degrees of freedom. Here we explore the resulting interplay by coupling an active nematic to a minimal model of polymer rheology. We find that adding a polymer can greatly increase the complexity of spontaneous flow, but can also have calming effects, thereby increasing the net throughput of spontaneous flow along a pipe (a "drag-reduction" effect). Remarkably, active turbulence can also arise after switching on activity in a sufficiently soft elastomeric solid.

  18. Enhanced U(VI) release from autunite mineral by aerobic Arthrobacter sp. in the presence of aqueous bicarbonate

    SciTech Connect

    Katsenovich, Yelena P.; Carvajal, Denny A.; Wellman, Dawn M.; Lagos, Leonel E.

    2012-05-01

    The bacterial effect on U(VI) release from the autunite mineral (Ca[(UO2)(PO4)]2•3H2O) was investigated to provide a more comprehensive understanding of the important microbiological processes affecting autunite stability within subsurface bicarbonate-bearing environments. Experiments were performed in a culture of the Arthrobacter oxydans G975 strain, herein referred to as G975, a soil bacterium previously isolated from Hanford Site soil. 91 mg of autunite powder and 50 mL of phosphorous-limiting sterile media were amended with bicarbonate (ranging between 1 and 10 mM) in glass reactor bottles and inoculated with the G975 strain after the dissolution of autunite was at steady state. SEM observations indicated that G975 formed a biofilm on the autunite surface and penetrated the mineral cleavages. The mineral surface colonization by bacteria tended to increase concomitantly with bicarbonate concentrations. Additionally, a sterile culture-ware with inserts was used in non-contact dissolution experiments where autunite and bacteria cells were kept separately. The data suggest that G975 bacteria is able to enhance the release of U(VI) from autunite without direct contact with the mineral. In the presence of bicarbonate, the damage to bacterial cells caused by U(VI) toxicity was reduced, yielding similar values for total organic carbon (TOC) degradation and cell density compared to U(VI)-free controls. The presence of active bacterial cells greatly enhanced the release of U(VI) from autunite in bicarbonate-amended media.

  19. Enhanced U(VI) release from autunite mineral by aerobic Arthrobacter sp. in the presence of aqueous bicarbonate

    SciTech Connect

    Katsenovich, Yelena; Carvajal, Denny A.; Wellman, Dawn M.; Lagos, Leonel

    2012-04-20

    The bacterial effect on U(VI) leaching from the autunite mineral (Ca[(UO{sub 2})(PO{sub 4})]{sub 2} {center_dot} 3H{sub 2}O) was investigated to provide a more comprehensive understanding into important microbiological processes affecting autunite stability within subsurface bicarbonate-bearing environments. Experiments were performed in a culture of G975 Arthrobacter oxydans strain, herein referred to as G975, a soil bacterium previously isolated from Hanford Site soil. 91 mg of autunite powder and 50 mL of phosphorus-limiting sterile media were amended with bicarbonate ranging between 1-10 mM in glass reactor bottles and inoculated with G975 strain after the dissolution of autunite was at steady state. SEM observations indicated G975 formed a biofilm on the autunite surface and penetrated the mineral cleavages. The mineral surface colonization by bacteria tended to increase concomitantly with bicarbonate concentrations. Additionally, a sterile cultureware with inserts was used in non-contact bioleaching experiments where autunite and bacteria cells were kept separately. The data suggest the G975 bacteria is able to enhance U(VI) leaching from autunite without the direct contact with the mineral. In the presence of bicarbonate, the damage to bacterial cells caused by U(VI) toxicity was reduced, yielding similar values for total organic carbon (TOC) degradation and cell density compared to U(VI)-free controls. The presence of active bacterial cells greatly enhanced the U(VI) bioleaching from autunite in bicarbonate-amended media.

  20. Electromagnetic films as lightweight actuators for active noise reduction

    NASA Astrophysics Data System (ADS)

    Sachau, Delf; Kletschkowski, Thomas

    2006-03-01

    The increasing industrialization and markets across the globe do result in noise pollution that affects humans. In order to reduce the sound pressure level (SPL) of disturbing noise active noise control (also known as noise cancellation, active noise reduction (ANR) or anti-noise) is a good option. Herewith unwanted noise from a primary sound source can be reduced significantly by anti-noise generated from a secondary source: At present commercial active noise reduction systems are using moving-coil loudspeakers as actuators. These actuators need a quite large built-in volume and they are not lightweight. Therefore the industrial application of ANR in vehicles is limited. To reduce these difficulties the use of flat loudspeakers made of electromagnetic films seems to be a promising approach. It is a precondition for the use of such new technologies within an ANR- system to have a basic understanding of the dynamic systems behaviour and the sound transmission behaviour of such a lightweight active component: This paper describes the investigation of a flat panel speaker which is based on electrostatic loudspeaker technology. First of all the passive transmission properties have been measured in a test bed. The passive acoustic insulation has been analyzed and weak spots in the frequency response were discovered. Afterwards the flat panel speaker has been used as actuator in an ANR-System to support insulation at those frequencies. An adaptive filter (FxLMS) was adjusted to the panel and the reduction capabilities of a single-output system have been determined.

  1. The Composition and Structure of Enceladus' Plume from a Cassini UVIS Observation of a Solar Occultation

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Shemansky, D. E.; Esposito, L. W.; Stewart, I.; Hendrix, A. R.

    2010-12-01

    The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed an occultation of the sun by Enceladus’ water vapor plume on May 18, 2010. UVIS used its extreme ultraviolet (EUV) channel for this new observation, to detect absorptions in the wavelength range 55 to 110 nm. Molecular nitrogen and water vapor have absorptions in this range. The N2 b(3,0) line is at 97.2 nm, extinguishing the solar H Lyman gamma emission. Cassini’s Ion and Neutral Mass Spectrometer (INMS) detected a species with an atomic mass of 28 amu, which could be CO, C2H4 or N2 [1, 2]. Definitive UVIS detection of N2 was important to clear up this ambiguity, and this was an important goal of the observation, as the presence or lack of N2 is key to models of the geochemistry in the interior [3, 4, 5]. UVIS did not detect N2 and we set an upper limit for the column density of 3 x 10^13 cm^-2. The absorption features in the spectrum are best fit by a water vapor column density of 0.9 x 10^16 cm^-2. This column density is in family with previous UVIS measurements from stellar occultations in 2005 and 2007 at far ultraviolet wavelengths, suggesting that Enceladus’ activity has been stable for the last 5 years [6, 7]. We used fluctuations in the signal to probe the structure of the gas jets again, as was analyzed in the 2007 occultation of zeta Orionis [7]. Gas jets are correlated to the dust jets detected by Cassini’s Imaging Science Subsystem [8]. The path of the sun cut through the jets horizontally at an altitude above the limb of ~15 km at the closest point. The resolution of the solar occultation is higher than the stellar occultation, and collimation of the gas jets observed in the solar occultation is greater than estimated in 2007. The observed collimation allows us to derive a mach number of ~4 for the ratio of the vertical velocity in the jet to the thermal velocity of the plume gas. The new opportunity afforded by this solar occultation is used to further model the structure and

  2. Reduction of polygalacturonase activity in tomato fruit by antisense RNA.

    PubMed

    Sheehy, R E; Kramer, M; Hiatt, W R

    1988-12-01

    Polygalacturonase [PG; poly(1,4-alpha-D-galacturonide) glycanhydrolase; EC 3.2.1.15] is expressed in tomato only during the ripening stage of fruit development. PG becomes abundant during ripening and has a major role in cell wall degradation and fruit softening. Tomato plants were transformed to produce antisense RNA from a gene construct containing the cauliflower mosaic virus 35S promoter and a full-length PG cDNA in reverse orientation. The construct was integrated into the tomato genome by Agrobacterium-mediated transformation. The constitutive synthesis of PG antisense RNA in transgenic plants resulted in a substantial reduction in the levels of PG mRNA and enzymatic activity in ripening fruit. The steady-state levels of PG antisense RNA in green fruit of transgenic plants were lower than the levels of PG mRNA normally attained during ripening. However, analysis of transcription in isolated nuclei demonstrated that the antisense RNA construct was transcribed at a higher rate than the tomato PG gene(s). Analysis of fruit from transgenic plants demonstrated a reduction in PG mRNA and enzymatic activity of 70-90%. The reduction in PG activity did not prevent the accumulation of the red pigment lycopene.

  3. Blood pressure reduction following accumulated physical activity in prehypertensive

    PubMed Central

    Saxena, Yogesh; Gupta, Rani; Moinuddin, Arsalan; Narwal, Ravinder

    2016-01-01

    Context: Accumulated moderate physical activity (PA) for 30 min in a day is the only recommended treatment of prehypertension. Objective: We investigated autonomic modulation as a possible mechanism for the decrease in blood pressure (BP) during the rest periods in each 10 min session of PA. Design, Setting, and Participants: We conducted a single-blind randomized multi-arm control trial on 40 prehypertensive (pre-HT) young male adults. Methods: Participants were randomly divided by using random number table into four groups. Control (no intervention); Group 1 (walking at 50% of predicted VO2 peak); Group 2 (walking at 60% of predicted VO2 peak); Group 3 (walking at 70% of predicted VO2 peak). BP, heart rate variability (HRV), and heart rate recovery 1 min (HRR 1 min) were measured at baseline and during the rest period after each session of 10 min over 30 min of accumulated physical activity (PAcumm). Results: Significant diastolic BP (DBP) reduction (P < 0.001) was observed during the rest period after each session of PAcumm in intervention groups. An average reduction in DBP was more in pre-HT undertaking PAcumm at 70% of predicted VO2 Peak. Decrease in the mean value of low-frequency (LF) and LF/high-frequency ratio was observed following PAcumm in all intervention groups irrespective of the intensity of PA. No significant association of reduction of BP with HRV and HRR 1 s was observed. Conclusion: Reduction in BP was observed during the rest period after each 10 min session of PAcumm irrespective of the intensity of PA. Autonomic modulation does not seem to be the possible mechanism for the reduction in BP during the sessions. PMID:27843840

  4. The role of nanopores on U(VI) sorption and redox behavior in U(VI)-contaminated subsurface sediments

    SciTech Connect

    Xu, Huifang; Roden, Eric E.; Kemner, Kenneth M.; Jung, Hun-Bok; Konishi, Hiromi; Boyanov, Maxim; Sun, Yubing; Mishra, Bhoopesh

    2013-10-16

    Most reactive surfaces in clay-dominated sediments are present within nanopores (pores of nm dimension). The behavior of geological fluids and minerals in nanopores is significantly different from those in normal non-nanoporous environments. The effect of nanopore surfaces on U(VI) sorption/desorption and reduction is likely to be significant in clay-rich subsurface environments. Our research results from both model nanopore system and natural sediments from both model system (synthetic nanopore alumina) and sediments from the ORNL Field Research Center prove that U(VI) sorption on nanopore surfaces can be greatly enhanced by nanopore confinement environments. The results from the project provide advanced mechanistic, quantitative information on the physiochemical controls on uranium sorption and redox behavior in subsurface sediments. The influence of nanopore surfaces on coupled uranium sorption/desorption and reduction processes is significant in virtually all subsurface environments, because most reactive surfaces are in fact nanopore surfaces. The results will enhance transfer of our laboratory-based research to a major field research initiative where reductive uranium immobilization is being investigated. Our results will also provide the basic science for developing in-situ colloidal barrier of nanoporous alumina in support of environmental remediation and long term stewardship of DOE sites.

  5. Sulfate Reduction at a Lignite Seam: Microbial Abundance and Activity.

    PubMed

    Detmers, J.; Schulte, U.; Strauss, H.; Kuever, J.

    2001-10-01

    In a combined isotope geochemical and microbiological investigation, a setting of multiple aquifers was characterized. Biologically mediated redox processes were observed in the aquifers situated in marine sands of Tertiary age and overlying Quaternary gravel deposits. Intercalated lignite seams define the aquitards, which separate the aquifers. Bacterial oxidation of organic matter is evident from dissolved inorganic carbon characterized by average carbon isotope values between ?18.4 per thousand and ?15.7 per thousand (PDB). Strongly positive sulfur isotope values of up to +50 per thousand (CTD) for residual sulfate indicate sulfate reduction under closed system conditions with respect to sulfate availability. Both, hydrochemical and isotope data are thus consistent with the recent activity of sulfate-reducing bacteria (SRB). Microbiological investigations revealed the presence of an anaerobic food chain in the aquifers. Most-probable-number (MPN) determinations for SRB and fermenting microorganisms reached highest values at the interface between aquifer and lignite seam (1.5 x 103 cells/g sediment dry mass). Five strains of SRB were isolated from highest MPN dilutions. Spore-forming bacteria appeared to dominate the SRB population. Sulfate reduction rates were determined by the 35S-radiotracer method. A detailed assessment indicates an increase in the reduction rate in proximity to the lignite seam, with a maximum turnover of 8.4 mM sulfate/a, suggesting that lignite-drived compounds represent the substrate for sulfate reduction.

  6. Reductive activation of mitomycins A and C by vitamin C.

    PubMed

    Paz, Manuel M

    2013-06-01

    The anticancer drug mitomycin C produces cytotoxic effects after being converted to a highly reactive bis-electrophile by a reductive activation, a reaction that a number of 1-electron or 2-electron oxidoreductase enzymes can perform in cells. Several reports in the literature indicate that ascorbic acid can modulate the cytotoxic effects of mitomycin C, either potentiating or inhibiting its effects. As ascorbic acid is a reducing agent that is known to be able to reduce quinones, it could be possible that the observed modulatory effects are a consequence of a direct redox reduction between mitomycin C and ascorbate. To determine if this is the case, the reaction between mitomycin C and ascorbate was studied using UV/Vis spectroscopy and LC/MS. We also studied the reaction of ascorbate with mitomycin A, a highly toxic member of the mitomycin family with a higher redox potential than mitomycin C. We found that ascorbate is capable to reduce mitomycin A efficiently, but it reduces mitomycin C rather inefficiently. The mechanisms of activation have been elucidated based on the kinetics of the reduction and on the analysis of the mitosene derivatives formed after the reaction. We found that the activation occurs by the interplay of three different mechanisms that contribute differently, depending on the pH of the reaction. As the reduction of mitomycin C by ascorbate is rather inefficiently at physiologically relevant pH values we conclude that the modulatory effect of ascorbate on the cytotoxicity of mitomycin C is not the result of a direct redox reaction and therefore this modulation must be the consequence of other biochemical mechanisms.

  7. Discovery Of B Ring Propellers In Cassini UVIS, And ISS

    NASA Astrophysics Data System (ADS)

    Sremcevic, Miodrag; Stewart, G. R.; Albers, N.; Esposito, L. W.

    2012-10-01

    We present evidence for the existence of propellers in Saturn's B ring by combining data from Cassini Ultraviolet Imaging Spectrograph (UVIS) and Imaging Science Subsystem (ISS) experiments. We identify two propeller populations: (1) tens of degrees wide propellers in the dense B ring core, and (2) smaller, more A ring like, propellers populating the inner B ring. The prototype of the first population is an object observed at 18 different epochs between 2005 and 2010. The ubiquitous propeller "S" shape is seen both in UVIS occultations as an optical depth depletion and in ISS as a 40 degrees wide bright stripe in unlit geometries and dark in lit geometries. Combining the available Cassini data we infer that the object is a partial gap embedded in the high optical depth region of the B ring. The gap moves at orbital speed consistent with its radial location. From the radial separation of the propeller wings we estimate that the embedded body, which causes the propeller structure, is about 1.5km in size located at a=112,921km. The UVIS occultations indicate an asymmetric propeller "S" shape. Since the object is located at an edge between high and relatively low optical depth, this asymmetry is most likely a consequence of the strong surface mass density gradient. We estimate that there are possibly dozen up to 100 other propeller objects in Saturn's B ring. The location of the discovered body, at an edge of a dense ringlet within the B ring, suggests a novel mechanism for the up to now illusive B ring irregular large-scale structure of alternating high and low optical depth ringlets. We propose that this B ring irregular structure may have its cause in the presence of many embedded bodies that shepherd the individual B ring ringlets.

  8. Bioreduction of U(VI) in the presence of phosphate

    NASA Astrophysics Data System (ADS)

    Boyanov, M. I.; Mishra, B.; Latta, D. E.; Rui, X.; Kwon, M.-J.; Fletcher, K. E.; Loeffler, F. E.; O'Loughlin, E. J.; Kemner, K. M.

    2012-04-01

    Phosphate/phosphoryl moieties are ubiquitous in biological and environmental systems and can potentially affect the speciation of uranium during natural attenuation or stimulated bioremediation processes. The reactivity between U(VI) and phosphate has been studied extensively, but the significant influence of phosphate groups on the formation of reduced U(IV) species has only recently been recognized. We will compare and contrast the bioreduction of dissolved and solid-phase U(VI) by Gram-positive and Gram-negative metal-reducing bacteria (Shewanella, Anaeromyxobacter, Geobacter, and Desulfitobacterium) in the presence and absence of phosphate, from the perspective of solid-phase U speciation as determined by U L-edge x-ray absorption spectroscopy (XANES and EXAFS). In all cases examined, the presence of phosphate at concentrations of P/U > 1 led to the formation of reduced, inner-sphere complexed U(IV)-phosphate species that prevented the lowest-solubility U(IV) mineral uraninite (UO2) from forming over at least several months. In the absence of phosphate, nanoparticulate uraninite or complexed non-uraninite U(IV) species were observed (depending on the system and conditions), suggesting that the interplay between the chemical conditions at the location of electron transfer to U(VI) control the U(IV) product and subsequently the stability of reduced U. The importance of non-uraninite U(IV) species will be discussed in the context of their predominance in biostimulated sediments from the Oak Ridge field site in the United States.

  9. UVI Cyber-security Workshop Workshop Analysis.

    SciTech Connect

    Kuykendall, Tommie G.; Allsop, Jacob Lee; Anderson, Benjamin Robert; Boumedine, Marc; Carter, Cedric; Galvin, Seanmichael Yurko; Gonzalez, Oscar; Lee, Wellington K.; Lin, Han Wei; Morris, Tyler Jake; Nauer, Kevin S.; Potts, Beth A.; Ta, Kim Thanh; Trasti, Jennifer; White, David R.

    2015-07-08

    The cybersecurity consortium, which was established by DOE/NNSA’s Minority Serving Institutions Partnerships Program (MSIPP), allows students from any of the partner schools (13 HBCUs, two national laboratories, and a public school district) to have all consortia options available to them, to create career paths and to open doors to DOE sites and facilities to student members of the consortium. As a part of this year consortium activities, Sandia National Laboratories and the University of Virgin Islands conducted a week long cyber workshop that consisted of three courses; Digital Forensics and Malware Analysis, Python Programming, and ThunderBird Cup. These courses are designed to enhance cyber defense skills and promote learning within STEM related fields.

  10. A first principles investigation of electron transfer between Fe(II) and U(VI) on insulating Al- vs. semiconducting Fe-oxide surfaces via the proximity effect

    NASA Astrophysics Data System (ADS)

    Taylor, S. D.; Marcano, M. C.; Becker, U.

    2017-01-01

    This study investigates how the intrinsic chemical and electronic properties of mineral surfaces and their associated electron transfer (ET) pathways influence the reduction of U(VI) by surface-associated Fe(II). Density functional theory (DFT), including the Hubbard U correction to the exchange-correlation functional, was used to investigate sorption/redox reactions and ET mechanisms between Fe(II) and U(VI) coadsorbed on isostructural, periodic (0 0 1) surfaces of the insulator corundum (α-Al2O3) vs. the semiconductor hematite (α-Fe2O3). Furthermore, the coadsorbed Fe(II) and U(VI) ions are spatially separated from one another on the surfaces (⩾5.9 Å) to observe whether electronic-coupling through the semiconducting hematite surface facilitates ET between the adsorbates, a phenomenon known as the proximity effect. The calculations show that the different chemical and electronic properties between the isostructural corundum and hematite (0 0 1) surfaces lead to considerably different ET mechanisms between Fe(II) and U(VI). ET on the insulating corundum (0 0 1) surface is limited by the adsorbates' structural configuration. When Fe(II) and U(VI) are spatially separated and do not directly interact with one another (e.g. via an inner-sphere complex), U(VI) reduction by Fe(II) cannot occur as there is no physical pathway enabling ET between the adsorbates. In contrast to the insulating corundum (0 0 1) surface, the hematite (0 0 1) surface can potentially participate in ET reactions due to the high number of electron acceptor sites from the Fe d-states near the Fermi level at the hematite surface. The adsorption of Fe(II) also introduces d-states near the Fermi level as well as shifts unoccupied d-states of the Fe cations at the hematite surface to lower energies, making the surface more conductive. In turn, electronic coupling through the surface can link the spatially separated adsorbates to one another and provide distinct ET pathways for an electron from Fe

  11. Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments

    SciTech Connect

    Yin, Jun; Haggerty, Roy; Stoliker, Deborah L.; Kent, Douglas B.; Istok, Jonathan D.; Greskowiak, Janek; Zachara, John M.

    2011-04-05

    In the 300 Area of a U(VI)-contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real-time change of local groundwater chemistry.

  12. Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments

    NASA Astrophysics Data System (ADS)

    Yin, Jun; Haggerty, Roy; Stoliker, Deborah L.; Kent, Douglas B.; Istok, Jonathan D.; Greskowiak, Janek; Zachara, John M.

    2011-04-01

    In the 300 Area of a U(VI)-contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real-time change of local groundwater chemistry.

  13. Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments

    USGS Publications Warehouse

    Yin, Jun; Haggerty, Roy; Stoliker, Deborah L.; Kent, Douglas B.; Istok, Jonathan D.; Greskowiak, Janek; Zachara, John M.

    2011-01-01

    In the 300 Area of a U(VI)-contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real-time change of local groundwater chemistry.

  14. Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments

    USGS Publications Warehouse

    Yin, J.; Haggerty, R.; Stoliker, D.L.; Kent, D.B.; Istok, J.D.; Greskowiak, J.; Zachara, J.M.

    2011-01-01

    In the 300 Area of a U(VI)-contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real-time change of local groundwater chemistry. Copyright 2011 by the American Geophysical Union.

  15. Uranium Reduction by Clostridia

    SciTech Connect

    Francis, A.J.; Dodge, Cleveland J.; Gillow, Jeffrey B.

    2006-04-05

    The FRC groundwater and sediment contain significant concentrations of U and Tc and are dominated by low pH, and high nitrate and Al concentrations where dissimilatory metal reducing bacterial activity may be limited. The presence of Clostridia in Area 3 at the FRC site has been confirmed and their ability to reduce uranium under site conditions will be determined. Although the phenomenon of uranium reduction by Clostridia has been firmly established, the molecular mechanisms underlying such a reaction are not very clear. The authors are exploring the hypothesis that U(VI) reduction occurs through hydrogenases and other enzymes (Matin and Francis). Fundamental knowledge of metal reduction using Clostridia will allow us to exploit naturally occurring processes to attenuate radionuclide and metal contaminants in situ in the subsurface. The outline for this report are as follows: (1) Growth of Clostridium sp. under normal culture conditions; (2) Fate of metals and radionuclides in the presence of Clostridia; (3) Bioreduction of uranium associated with nitrate, citrate, and lepidocrocite; and (4) Utilization of Clostridium sp. for immobilization of uranium at the FRC Area 3 site.

  16. Reductive activation of Cr(Vi) by nitric oxide synthase.

    PubMed

    Porter, Ryan; Jáchymová, Marie; Martásek, Pavel; Kalyanaraman, B; Vásquez-Vivar, Jeannette

    2005-05-01

    Chromium(VI) is a recognized toxicant whose effects have been linked to its reduction to lower oxidation states. Although Cr(VI) is reduced by several systems, it is anticipated that its reduction by nitric oxide synthase (NOS) could have significant effects in endothelial and brain cells that express high constitutive levels of the enzyme. This possibility was examined by electron paramagnetic resonance that showed the formation of a stable Cr(V) species from NOS/Cr(VI). The formation of Cr(V) was calcium/calmodulin-independent indicating that Cr(VI) to Cr(V) reduction occurs at the flavin-containing domain of NOS. Accordingly, Cr(VI) reduction by the reductase domain of NOS and the chimera protein cytochrome-P450-reductase+tail-nNOS also generated Cr(V). Activation of tetrahydrobiopterin (BH(4))-free NOS with calcium/calmodulin diminished Cr(V) steady-state levels while increasing superoxide formation. Since SOD restored Cr(V) to control levels, this result was taken as evidence for a reaction between Cr(V) and superoxide. Supplementation of NOS with BH(4) cofactor not only failed to increase Cr(V) yields but generated superoxide and hydroxyl radical. Since the holoenzyme does not generate superoxide, this reaction indicated that Cr(V) mediates the oxidation of BH(4)-bound to the enzyme. In the presence of L-arginine, however, Cr(VI) neither enhances superoxide release nor inhibits NO formation from fully active NOS. This suggests that L-arginine protects BH(4) from Cr(V)-mediated oxidation. While Cr(V) was inactive toward NO, spin trapping experiments with 5-tert-butoxycarbonyl 5-methyl-1-pyrroline N-oxide and oxygen consumption measurements showed that Cr(V) reacts with superoxide by a one-electron-transfer mechanism to generate oxygen and Cr(IV). Thus, reduction of Cr(VI) to Cr(V) by NOS occurs in resting and fully active states. It is likely that the reaction between Cr(V) and superoxide influences the cytotoxic mechanisms of Cr(VI) in cells.

  17. U(VI) transport under the condition of water table fluctuations

    NASA Astrophysics Data System (ADS)

    Yin, J.; Haggerty, R.; Rockhold, M. L.; Kent, D. B.; Istok, J. D.; Zachara, J. M.

    2010-12-01

    U(VI) transport at the 300 Area Hanford IFRC site, WA appears to be strongly related to water table fluctuations resulting from rapid changes of Column River stage. In the “smear zone” (zone through which the water table sweeps) at the IFRC site, sediment can experience more than one saturation cycle every day. This unique phenomenon complicates the current understanding of U(VI) transport because the smear zone is likely a persistent source of long-term U(VI) contamination. In our study, two comparison column (4.28 cm × 44.4 cm) experiments are conducted to exam the U(VI) desorption affected by occasional, partially unsaturated conditions. In the experiment, one column remains saturated and the other one experiences three saturation-desaturation cycles. Less than 8 mm composite sediments collected from the Hanford IFRC site are packed into the column. TDRs and tensiometers are built into the column to measure both water contents and metric potentials at different depths. U-free synthetic ground water (SGW) is used to desorb U(VI) in both columns. In the experiment, both columns are initially saturated and SGW is injected in at a constant rate to desorb U(VI). Three stop flow events are embedded into desorption. Before each stop flow event, one of the columns is freely drained and the sediment represents the smear zone with the water table at the bottom of the column. After each stop flow, the column is re-saturated and regular desorption continues in both columns. During desorption and drainage, the pH in the effluent is continuously monitored. In addition, U(VI), major ions and alkalinity are measured in all samples. Previous studies show that aqueous U(VI) concentration increases due to the kinetic behavior of U(VI) desorption. If the column remains unsaturated during the stop flow, it is expected that the kinetic behavior of U(VI) will cause a much higher U(VI) concentration in less mobile pore water . Therefore, a lower U(VI) spike and a longer U(VI) tail

  18. Reduction of propeller noise by active noise control

    NASA Astrophysics Data System (ADS)

    Bschorr, O.; Kubanke, D.

    1992-04-01

    Active noise control, a method of cancelling noise by means of interference with a secondary anti-noise source, is now in full development. The first commercial application of this technique is in the case of active electronically controlled head sets. The next step will be the active noise cancellation in air ducts and in passenger cabins. The aim of this paper is to assess the possibilities of the anti-noise technique for reducing propeller noise. First, by a mathematical simulation the theoretical noise reduction on the ground was calculated and found to be promising for further investigations. In the case of the periodic engine and propeller noise, for example, with only a single anti-noise source, the noise foot prints of the lower propeller harmonics can be reduced by up to 10 dB. In laboratory tests the theoretical values will be confirmed experimentally. For cancellation of the periodic noise one can use synchronous anti-noise generators. Compared with the engine and propeller noise the reduction of jet noise by the anti-noise technique is much more difficult. Therefore a sensor and controlling unit are necessary because of the stochastic nature of jet noise. Since aircraft noise is a severe problem, all methods are to be considered.

  19. Thermodynamic Insight into the Solvation and Complexation Behavior of U(VI) in Ionic Liquid: Binding of CMPO with U(VI) Studied by Optical Spectroscopy and Calorimetry.

    PubMed

    Wu, Qi; Sun, Taoxiang; Meng, Xianghai; Chen, Jing; Xu, Chao

    2017-03-06

    The complexation of U(VI) with octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, denoted as L) in ionic liquid (IL) C4mimNTf2 was investigated by UV-vis absorption spectrophotometry and isothermal titration calorimetry. Spectro-photometric titration suggests that three successive complexes, UO2Lj(2+) (j = 1-3), formed both in "dry" (water content < 250 ppm) and "wet" (water content ≈ 12 500 ppm) ionic liquid. However, the thermodynamic parameters are distinctly different in the two ILs. In dry IL, the complexation strength between CMPO and U(VI) is much stronger, with stability constants of the respective complexes more than 1 order of magnitude higher than that in wet IL. Energetically, the complexation of U(VI) with CMPO in dry IL is mainly driven by negative enthalpies. In contrast, the complexation in wet IL is overwhelmingly driven by highly positive entropies as a result of the release of a large amount of water molecules from the solvation sphere of U(VI). Moreover, comparisons between the fitted absorption spectra of complexes in wet IL and that of extractive samples from solvent extraction have identified the speciation involved in the extraction of U(VI) by CMPO in ionic liquid. The results from this study not only offer a thermodynamic insight into the complexation behavior of U(VI) with CMPO in IL but also provide valuable information for understanding the extraction behavior in the corresponding solvent extraction system.

  20. uVis Studio: an integrated development environment for visualization

    NASA Astrophysics Data System (ADS)

    Pantazos, Kostas; Kuhail, Mohammad A.; Lauesen, Soren; Xu, Shangjin

    2013-01-01

    A toolkit facilitates the visualization development process. The process can be further enhanced by integrating the toolkits in development environments. This paper describes how the uVis toolkit, a formula-based visualiza- tion toolkit, has been extended with a development environment, called uVis Studio. Instead of programming, developers apply a Drag-Drop-Set-View-Interact approach. Developers bind controls to data, and the Studio gives immediate visual feedback in the Design Panel. This is a novel feature, called What-You-Bind-Is-What- You-Get. The Studio also provides Modes that allow developers to interact and view the visualization from the end-user's perspective without switching workspace, and Auto-Completion; a feature of the Property Grid that provides suggestions not only for the formula language syntax but also for the tables, the table elds and the relationships in the database. We conducted a usability study with six developers to evaluate if the Studio and its features enhance cognition and facilitate the visualization development. The results show that developers appreciated the Drag-Drop-Set- View-Interact approach, the What-You-Bind-Is-What-You-Get, the Auto-Completion and the Modes. Several usability problems were identified, and some suggestions for improvement include: new panels, better presentation of the Modes, and better error messages.

  1. WFC3 UVIS High-resolution Imaging Performance

    NASA Astrophysics Data System (ADS)

    Gilliland, R. L.; Rajan, A.

    2011-01-01

    The sharp and stable point spread function of HST and WFC3 allows for the detection of stellar companions at small offsets from target stars. Deep images obtained through six UVIS filters are used to assess this ability to detect faint companions of brighter targets. Analogous capabilities from the ground make use of Adaptive Optics and Speckle imaging. We contrast the capabilities of HST/WFC3 with several existing AO systems for imaging of V 12 stars for which detection of faint companions as close as possible is desired, and to a delta-magnitude of 10. The observations under comparison are motivated by high-resolution imaging applications for the Kepler Mission to constrain the existence of fainter background stars which, if eclipsing binaries, could mimic transits. The HST/WFC3 observations are found to be superior in the comparisons made to Keck, MMT and Palomar AO and WIYN Speckle systems in terms of delta-magnitude limits outside of about 0.3 arcseconds. In a metric of fraction of phase space that can be probed for delta-magnitude to 10 companions out to 2 arcsecs the UVIS imaging out performs all other approaches by a factor > 5.

  2. Reaction of U(VI) with titanium-substituted magnetite: influence of Ti on U(IV) speciation.

    PubMed

    Latta, Drew E; Pearce, Carolyn I; Rosso, Kevin M; Kemner, Kenneth M; Boyanov, Maxim I

    2013-05-07

    Reduction of hexavalent uranium (U(VI)) to less soluble tetravalent uranium (U(IV)) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for U(VI). Natural magnetites are often impure with titanium, and structural Fe(3+) replacement by Ti(IV) yields a proportional increase in the relative Fe(2+) content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe(2+)/Fe(3+) ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 - xTixO4) reduce U(VI) to U(IV). The U(VI)-Fe(2+) redox reactivity was found to be controlled directly by R but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where U(VI) was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25-0.53) results in the formation of U(IV) species that lack the bidentate U-O2-U bridges of uraninite. Extended X-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound U(IV) phase has a novel U(IV)-Ti binding geometry different from the coordination of U(IV) in the mineral brannerite (U(IV)Ti2O6). The observed U(IV)-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation U(IV) complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced U(IV) phase. The formation of the non-uraninite U(IV)-Ti phase appears to be controlled by availability of surface Ti sites rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of U(IV) and suggests that further work to characterize the long-term stability of U(IV) phases formed in the presence of Ti is warranted.

  3. Investigation of U(VI) adsorption in quartz-chlorite mineral mixtures.

    PubMed

    Wang, Zheming; Zachara, John M; Shang, Jianying; Jeon, Choong; Liu, Juan; Liu, Chongxuan

    2014-07-15

    A batch and cryogenic laser-induced time-resolved luminescence spectroscopy investigation of U(VI) adsorbed on quartz-chlorite mixtures with variable mass ratios have been performed under field-relevant uranium concentrations (5×10(-7) M and 5×10(-6) M) in pH 8.1 synthetic groundwater. The U(VI) adsorption Kd values steadily increased as the mass fraction of chlorite increased, indicating preferential sorption to chlorite. For all mineral mixtures, U(VI) adsorption Kd values were lower than that calculated from the assumption of component additivity possibly caused by surface modifications stemming from chlorite dissolution; The largest deviation occurred when the mass fractions of the two minerals were equal. U(VI) adsorbed on quartz and chlorite displayed characteristic individual luminescence spectra that were not affected by mineral mixing. The spectra of U(VI) adsorbed within the mixtures could be simulated by one surface U(VI) species on quartz and two on chlorite. The luminescence intensity decreased in a nonlinear manner as the adsorbed U(VI) concentration increased with increasing chlorite mass fraction-likely due to ill-defined luminescence quenching by both structural Fe/Cr in chlorite, and trace amounts of solubilized and reprecipitated Fe/Cr in the aqueous phase. However, the fractional spectral intensities of U(VI) adsorbed on quartz and chlorite followed the same trend of fractional adsorbed U(VI) concentration in each mineral phase with approximate linear correlations, offering a method to estimate of U(VI) concentration distribution between the mineral components with luminescence spectroscopy.

  4. Investigation of U(VI) Adsorption in Quartz-Chlorite Mineral Mixtures

    SciTech Connect

    Wang, Zheming; Zachara, John M.; Shang, Jianying; Jeon, Choong; Liu, Juan; Liu, Chongxuan

    2014-08-25

    A batch and cryogenic laser-induced time-resolved fluorescence spectroscopy investigation of U(VI) adsorbed on quartz-chlorite mixtures with variable mass ratios have been performed under field-relevant uranium concentrations (5x10-7 M and 5x10-6 M) in pH 8.1 synthetic groundwater. The U(VI) adsorption Kd values steadily increased as the mass fraction of chlorite increased, indicating preferential sorption to chlorite. For all mineral mixtures, U(VI) adsorption Kd values were lower than that calculated from the assumption of component additivity; The largest deviation occurred when the mass fractions of the two minerals were equal. U(VI) adsorbed on quartz and chlorite displayed characteristic individual fluorescence spectra that were not affected by mineral mixing. The spectra of U(VI) adsorbed within the mixtures could be simulated by one surface U(VI) species on quartz and two on chlorite. The fluorescence intensity decreased in a nonlinear manner as the adsorbed U(VI) concentration increased with increasing chlorite mass fraction – likely due to ill-defined fluorescence quenching by both structural Fe/Cr in chlorite, and trace amounts of solubilized and re-precipitated Fe/Cr in the aqueous phase. However, the fractional spectral intensities of U(VI) adsorbed on quartz and chlorite followed the same trend of fractional adsorbed U(VI) concentration in each mineral phase; approximate linear correlations in the quartz:chlorite mass ratio ranges of 0.0 - 0.2 and 0.2 - 1.0, offering a method to estimate of U(VI) concentration distribution between the mineral components.

  5. Active Clustering with Model-Based Uncertainty Reduction.

    PubMed

    Xiong, Caiming; Johnson, David M; Corso, Jason J

    2017-01-01

    Semi-supervised clustering seeks to augment traditional clustering methods by incorporating side information provided via human expertise in order to increase the semantic meaningfulness of the resulting clusters. However, most current methods are passive in the sense that the side information is provided beforehand and selected randomly. This may require a large number of constraints, some of which could be redundant, unnecessary, or even detrimental to the clustering results. Thus in order to scale such semi-supervised algorithms to larger problems it is desirable to pursue an active clustering method-i.e., an algorithm that maximizes the effectiveness of the available human labor by only requesting human input where it will have the greatest impact. Here, we propose a novel online framework for active semi-supervised spectral clustering that selects pairwise constraints as clustering proceeds, based on the principle of uncertainty reduction. Using a first-order Taylor expansion, we decompose the expected uncertainty reduction problem into a gradient and a step-scale, computed via an application of matrix perturbation theory and cluster-assignment entropy, respectively. The resulting model is used to estimate the uncertainty reduction potential of each sample in the dataset. We then present the human user with pairwise queries with respect to only the best candidate sample. We evaluate our method using three different image datasets (faces, leaves and dogs), a set of common UCI machine learning datasets and a gene dataset. The results validate our decomposition formulation and show that our method is consistently superior to existing state-of-the-art techniques, as well as being robust to noise and to unknown numbers of clusters.

  6. Active Clustering with Model-Based Uncertainty Reduction.

    PubMed

    Xiong, Caiming; Johnson, David M; Corso, Jason J

    2016-03-09

    Semi-supervised clustering seeks to augment traditional clustering methods by incorporating side information provided via human expertise in order to increase the semantic meaningfulness of the resulting clusters. However, most current methods are passive in the sense that the side information is provided beforehand and selected randomly. This may require a large number of constraints, some of which could be redundant, unnecessary, or even detrimental to the clustering results. Thus in order to scale such semi-supervised algorithms to larger problems it is desirable to pursue an active clustering method- i.e. an algorithm that maximizes the effectiveness of the available human labor by only requesting human input where it will have the greatest impact. Here, we propose a novel online framework for active semi-supervised spectral clustering that selects pairwise constraints as clustering proceeds, based on the principle of uncertainty reduction. Using a first-order Taylor expansion, we decompose the expected uncertainty reduction problem into a gradient and a step-scale, computed via an application of matrix perturbation theory and cluster-assignment entropy, respectively. The resulting model is used to estimate the uncertainty reduction potential of each sample in the dataset. We then present the human user with pairwise queries with respect to only the best candidate sample. We evaluate our method using three different image datasets (faces, leaves and dogs), a set of common UCI machine learning datasets and a gene dataset. The results validate our decomposition formulation and show that our method is consistently superior to existing state-of-the-art techniques, as well as being robust to noise and to unknown numbers of clusters.

  7. Long-Term International Space Station (ISS) Risk Reduction Activities

    NASA Technical Reports Server (NTRS)

    Forroci, Michael P.; Gafka, George K.; Lutomski, Michael G.; Maher, Jacilyn S.

    2011-01-01

    As the assembly of the ISS nears completion, it is worthwhile to step back and review some of the actions pursued by the Program in recent years to reduce risk and enhance the safety and health of ISS crewmembers, visitors, and space flight participants. While the initial ISS requirements and design were intended to provide the best practicable levels of safety, it is always possible to further reduce risk given the determination, commitment, and resources to do so. The following is a summary of some of the steps taken by the ISS Program Manager, by our International Partners, by hardware and software designers, by operational specialists, and by safety personnel to continuously enhance the safety of the ISS, and to reduce risk to all crewmembers. While years of work went into the development of ISS requirements, there are many things associated with risk reduction in a Program like the ISS that can only be learned through actual operational experience. These risk reduction activities can be divided into roughly three categories: Areas that were initially noncompliant which have subsequently been brought into compliance or near compliance (i.e., Micrometeoroid and Orbital Debris [MMOD] protection, acoustics) Areas where initial design requirements were eventually considered inadequate and were subsequently augmented (i.e., Toxicity hazard level-4 materials, emergency procedures, emergency equipment, control of drag-throughs) Areas where risks were initially underestimated, and have subsequently been addressed through additional mitigation (i.e., Extravehicular Activity [EVA] sharp edges, plasma shock hazards). Due to the hard work and cooperation of many parties working together across the span of more than a decade, the ISS is now a safer and healthier environment for our crew, in many cases exceeding the risk reduction targets inherent in the intent of the original design. It will provide a safe and stable platform for utilization and discovery for years to come.

  8. Propulsion Risk Reduction Activities for Nontoxic Cryogenic Propulsion

    NASA Technical Reports Server (NTRS)

    Smith, Timothy D.; Klem, Mark D.; Fisher, Kenneth L.

    2010-01-01

    The Propulsion and Cryogenics Advanced Development (PCAD) Project s primary objective is to develop propulsion system technologies for nontoxic or "green" propellants. The PCAD project focuses on the development of nontoxic propulsion technologies needed to provide necessary data and relevant experience to support informed decisions on implementation of nontoxic propellants for space missions. Implementation of nontoxic propellants in high performance propulsion systems offers NASA an opportunity to consider other options than current hypergolic propellants. The PCAD Project is emphasizing technology efforts in reaction control system (RCS) thruster designs, ascent main engines (AME), and descent main engines (DME). PCAD has a series of tasks and contracts to conduct risk reduction and/or retirement activities to demonstrate that nontoxic cryogenic propellants can be a feasible option for space missions. Work has focused on 1) reducing the risk of liquid oxygen/liquid methane ignition, demonstrating the key enabling technologies, and validating performance levels for reaction control engines for use on descent and ascent stages; 2) demonstrating the key enabling technologies and validating performance levels for liquid oxygen/liquid methane ascent engines; and 3) demonstrating the key enabling technologies and validating performance levels for deep throttling liquid oxygen/liquid hydrogen descent engines. The progress of these risk reduction and/or retirement activities will be presented.

  9. Propulsion Risk Reduction Activities for Non-Toxic Cryogenic Propulsion

    NASA Technical Reports Server (NTRS)

    Smith, Timothy D.; Klem, Mark D.; Fisher, Kenneth

    2010-01-01

    The Propulsion and Cryogenics Advanced Development (PCAD) Project s primary objective is to develop propulsion system technologies for non-toxic or "green" propellants. The PCAD project focuses on the development of non-toxic propulsion technologies needed to provide necessary data and relevant experience to support informed decisions on implementation of non-toxic propellants for space missions. Implementation of non-toxic propellants in high performance propulsion systems offers NASA an opportunity to consider other options than current hypergolic propellants. The PCAD Project is emphasizing technology efforts in reaction control system (RCS) thruster designs, ascent main engines (AME), and descent main engines (DME). PCAD has a series of tasks and contracts to conduct risk reduction and/or retirement activities to demonstrate that non-toxic cryogenic propellants can be a feasible option for space missions. Work has focused on 1) reducing the risk of liquid oxygen/liquid methane ignition, demonstrating the key enabling technologies, and validating performance levels for reaction control engines for use on descent and ascent stages; 2) demonstrating the key enabling technologies and validating performance levels for liquid oxygen/liquid methane ascent engines; and 3) demonstrating the key enabling technologies and validating performance levels for deep throttling liquid oxygen/liquid hydrogen descent engines. The progress of these risk reduction and/or retirement activities will be presented.

  10. Guided cobalamin biosynthesis supports Dehalococcoides mccartyi reductive dechlorination activity.

    PubMed

    Yan, Jun; Im, Jeongdae; Yang, Yi; Löffler, Frank E

    2013-04-19

    Dehalococcoides mccartyi strains are corrinoid-auxotrophic Bacteria and axenic cultures that require vitamin B12 (CN-Cbl) to conserve energy via organohalide respiration. Cultures of D. mccartyi strains BAV1, GT and FL2 grown with limiting amounts of 1 µg l(-1) CN-Cbl quickly depleted CN-Cbl, and reductive dechlorination of polychlorinated ethenes was incomplete leading to vinyl chloride (VC) accumulation. In contrast, the same cultures amended with 25 µg l(-1) CN-Cbl exhibited up to 2.3-fold higher dechlorination rates, 2.8-9.1-fold increased growth yields, and completely consumed growth-supporting chlorinated ethenes. To explore whether known cobamide-producing microbes supply Dehalococcoides with the required corrinoid cofactor, co-culture experiments were performed with the methanogen Methanosarcina barkeri strain Fusaro and two acetogens, Sporomusa ovata and Sporomusa sp. strain KB-1, as Dehalococcoides partner populations. During growth with H2/CO2, M. barkeri axenic cultures produced 4.2 ± 0.1 µg l(-1) extracellular cobamide (factor III), whereas the Sporomusa cultures produced phenolyl- and p-cresolyl-cobamides. Neither factor III nor the phenolic cobamides supported Dehalococcoides reductive dechlorination activity suggesting that M. barkeri and the Sporomusa sp. cannot fulfil Dehalococcoides' nutritional requirements. Dehalococcoides dechlorination activity and growth occurred in M. barkeri and Sporomusa sp. co-cultures amended with 10 µM 5',6'-dimethylbenzimidazole (DMB), indicating that a cobalamin is a preferred corrinoid cofactor of strains BAV1, GT and FL2 when grown with chlorinated ethenes as electron acceptors. Even though the methanogen and acetogen populations tested did not produce cobalamin, the addition of DMB enabled guided biosynthesis and generated a cobalamin that supported Dehalococcoides' activity and growth. Guided cobalamin biosynthesis may offer opportunities to sustain and enhance Dehalococcoides activity in contaminated

  11. Cassini UVIS highest resolution occultations of Saturn's rings

    NASA Astrophysics Data System (ADS)

    Sremcevic, Miodrag; Esposito, L. W.; Colwell, J.

    2013-10-01

    Since the beginning of the Cassini mission in 2004 the UVIS instrument has recorded >100 stellar occultations of Saturn's rings. Despite achieved radial resolutions of <1m true resolution is limited by the orbital motion of particles. These can move by almost 20m during a 1ms integration period, effectively smearing the ring profile. In order to achieve superior true resolution we designed a special type of observations, dubbed tracking occultations, where the spacecraft velocity projected onto the rings cancels the orbital motion of ring particles. The ring particles are thus nearly motionless in the field of view of UVIS instrument and essentially tracked. So far Cassini UVIS has recorded two "tracking" occultations of mid-A ring, one of the inner A ring, and one of the so called A ring ramp (a transition region between Cassini division and A ring). The occultations have at least 2m true resolution limited only by diffraction. The two mid-A ring occultations for the first time directly resolve the self-gravity (SG) Toomre like wakes. The SG wakes show as a train of opaque regions (tau>1.5) and nearly transparent gaps (tau<0.05). The observed opaque wakes can be as large as 200m, while transparent gaps are somewhat shorter (L<100m). The opaque and transparent regions are interspersed with material in an intermittent state (0.05

  12. Reduction of selenite to elemental selenium nanoparticles by activated sludge.

    PubMed

    Jain, Rohan; Matassa, Silvio; Singh, Satyendra; van Hullebusch, Eric D; Esposito, Giovanni; Lens, Piet N L

    2016-01-01

    Total selenium removal by the activated sludge process, where selenite is reduced to colloidal elemental selenium nanoparticles (BioSeNPs) that remain entrapped in the activated sludge flocs, was studied. Total selenium removal efficiencies with glucose as electron donor (2.0 g chemical oxygen demand (COD) L(-1)) at neutral pH and 30 °C gave 2.9 and 6.8 times higher removal efficiencies as compared to the electron donors lactate and acetate, respectively. Total selenium removal efficiencies of 79 (±3) and 86 (±1) % were achieved in shake flasks and fed batch reactors, respectively, at dissolved oxygen (DO) concentrations above 4.0 mg L(-1) and 30 °C when fed with 172 mg L(-1) (1 mM) Na2SeO3 and 2.0 g L(-1) COD of glucose. Continuously operated reactors operating at neutral pH, 30 °C and a DO >3 mg L(-1) removed 33.98 and 36.65 mg of total selenium per gram of total suspended solids (TSS) at TSS concentrations of 1.3 and 3.0 g L(-1), respectively. However, selenite toxicity to the activated sludge led to failure of a continuously operating activated sludge reactor at the applied loading rates. This suggests that a higher hydraulic retention time (HRT) or different reactor configurations need to be applied for selenium-removing activated sludge processes. Graphical Abstract Scheme representing the possible mechanisms of selenite reduction at high and low DO levels in the activated sludge process.

  13. Study of sorption-retarded U(VI) diffusion in Hanford silt/clay material

    SciTech Connect

    Bai, Jing; Liu, Chongxuan; Ball, William P.

    2009-10-15

    A diffusion cell method was developed to measure the effective aqueous diffusion coefficient for U(VI) under strictly controlled chemical conditions within the inter-particle pores of silt/clay sediment from the DOE Hanford site, WA. "Inward-flux” diffusion studies were conducted in which U(VI) concentrations in both aqueous and solid phases were measured as a function of distance into the cell under conditions of constant concentration at the cell boundaries. A sequential extraction method was developed to measure sorbed U(VI) content in the solid phase, while accounting for the non-negligible extractable background U(VI). U(VI) diffusion data were found to be consistent with a model that assumed that: 1) a single effective aqueous diffusion coefficient could be used to simulate the coupled diffusion of various aqueous U(VI) species, and 2) the local equilibrium assumption (LEA) is appropriate for modeling the effects of sorption under the given experimental conditions. An effective aqueous diffusion coefficient (De) of 1.6x10^-6 cm2/s was obtained under conditions of pH 8.0 and calcite saturation that are relevant to the subsurface conditions at some regions of the Hanford site. The developed experimental techniques provide a practical approach for measuring effective aqueous U(VI) diffusivity in sorptive porous media.

  14. Comparing approaches for simulating the reactive transport of U(VI) in ground water

    USGS Publications Warehouse

    Curtis, G.P.; Kohler, M.; Davis, J.A.

    2009-01-01

    The reactive transport of U(VI) in a well-characterized shallow alluvial aquifer at a former U(VI) mill located near Naturita, CO, was predicted for comparative purposes using a surface complexation model (SCM) and a constant K d approach to simulate U(VI) adsorption. The ground water at the site had U(VI) concentrations that ranged from 0.01 to 20 ??M, alkalinities that ranged from 2.5 to 18 meq/L, and a nearly constant pH of 7.1. The SCM used to simulate U(VI) adsorption was previously determined independently using laboratory batch adsorption experiments. Simulations obtained using the SCM approach were compared with simulations that used a constant K d approach to simulate adsorption using previously determined site-specific K d values. In both cases, the ground water flow and transport models used a conceptual model that was previously calibrated to a chloride plume present at the site. Simulations with the SCM approach demonstrated that the retardation factor varied temporally and spatially because of the differential transport of alkalinity and dissolved U(VI) and the nonlinearity of the U(VI) adsorption. The SCM model also simulated a prolonged slow decline in U(VI) concentration, which was not simulated using a constant K d model. Simulations using the SCM approach and the constant K d approach were similar after 20 years of transport but diverged significantly after 60 years. The simulations demonstrate the need for site-specific geochemical information on U(VI) adsorption to produce credible simulations of future transport. ?? 2009 Springer-Verlag.

  15. Physical activity, stress reduction, and mood: insight into immunological mechanisms.

    PubMed

    Hamer, Mark; Endrighi, Romano; Poole, Lydia

    2012-01-01

    Psychosocial factors, such as chronic mental stress and mood, are recognized as an important predictor of longevity and wellbeing. In particular, depression is independently associated with cardiovascular disease and all-cause mortality, and is often comorbid with chronic diseases that can worsen their associated health outcomes. Regular exercise is thought to be associated with stress reduction and better mood, which may partly mediate associations between depression, stress, and health outcomes. The underlying mechanisms for the positive effects of exercise on wellbeing remain poorly understood. In this overview we examine epidemiological evidence for an association between physical activity and mental health. We then describe the exercise withdrawal paradigm as an experimental protocol to study mechanisms linking exercise, mood, and stress. In particular we will discuss the potential role of the inflammatory response as a central mechanism.

  16. Highly active oxide photocathode for photoelectrochemical water reduction.

    PubMed

    Paracchino, Adriana; Laporte, Vincent; Sivula, Kevin; Grätzel, Michael; Thimsen, Elijah

    2011-06-01

    A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H(2) production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm(-2) at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

  17. Highly active oxide photocathode for photoelectrochemical water reduction

    NASA Astrophysics Data System (ADS)

    Paracchino, Adriana; Laporte, Vincent; Sivula, Kevin; Grätzel, Michael; Thimsen, Elijah

    2011-06-01

    A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H2 production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm-2 at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

  18. HST WFC3/UVIS: charge transfer efficiency monitoring and mitigation

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia M.; Sosey, Megan L.; Anderson, Jay; Gosmeyer, Catherine; Bourque, Matthew; Bajaj, Varun; Khandrika, Harish G.; Martlin, Catherine; Kozhurina-Platais, Vera; Sabbi, Elena; WFC3 Team

    2016-01-01

    The harsh low-earth orbit environment is known to damage CCD devices and the HST WFC3/UVIS camera is no exception. One consequence of the radiation damage is charge-transfer efficiency (CTE) loss over time. We summarize the level of the CTE losses, the effect on science data, and the pre- and post-observation mitigation options available. Among them is the pixel-based CTE correction, which has been incorporated into the HST automatic data processing pipeline. The pipeline now provides both standard and CTE-corrected data products; observers with older data can re-retrieve their images via the the Mikulski Archive for Space Telescopes (MAST) to obtain the new products.

  19. Antibacterial activity of silver bionanocomposites synthesized by chemical reduction route

    PubMed Central

    2012-01-01

    Background The aim of this study is to investigate the functions of polymers and size of nanoparticles on the antibacterial activity of silver bionanocomposites (Ag BNCs). In this research, silver nanoparticles (Ag NPs) were incorporated into biodegradable polymers that are chitosan, gelatin and both polymers via chemical reduction method in solvent in order to produce Ag BNCs. Silver nitrate and sodium borohydride were employed as a metal precursor and reducing agent respectively. On the other hand, chitosan and gelatin were added as a polymeric matrix and stabilizer. The antibacterial activity of different sizes of silver nanoparticles was investigated against Gram-positive and Gram-negative bacteria by the disk diffusion method using Mueller-Hinton Agar. Results The properties of Ag BNCs were studied as a function of the polymer weight ratio in relation to the use of chitosan and gelatin. The morphology of the Ag BNCs films and the distribution of the Ag NPs were also characterized. The diameters of the Ag NPs were measured and their size is less than 20 nm. The antibacterial trait of silver/chitosan/gelatin bionanocomposites was investigated. The silver ions released from the Ag BNCs and their antibacterial activities were scrutinized. The antibacterial activities of the Ag BNC films were examined against Gram-negative bacteria (E. coli and P. aeruginosa) and Gram-positive (S. aureus and M. luteus) by diffusion method using Muller-Hinton agar. Conclusions The antibacterial activity of Ag NPs with size less than 20 nm was demonstrated and showed positive results against Gram-negative and Gram-positive bacteria. The Ag NPs stabilized well in the polymers matrix. PMID:22967920

  20. Reduction of Uranium(VI) Phosphate during Growth of the Thermophilic Bacterium Thermoterrabacterium ferrireducens

    PubMed Central

    Khijniak, T. V.; Slobodkin, A. I.; Coker, V.; Renshaw, J. C.; Livens, F. R.; Bonch-Osmolovskaya, E. A.; Birkeland, N.-K.; Medvedeva-Lyalikova, N. N.; Lloyd, J. R.

    2005-01-01

    The thermophilic, gram-positive bacterium Thermoterrabacterium ferrireducens coupled organotrophic growth to the reduction of sparingly soluble U(VI) phosphate. X-ray powder diffraction and X-ray absorption spectroscopy analysis identified the electron acceptor in a defined medium as U(VI) phosphate [uramphite; (NH4)(UO2)(PO4) · 3H2O], while the U(IV)-containing precipitate formed during bacterial growth was identified as ningyoite [CaU(PO4)2 · H2O]. This is the first report of microbial reduction of a largely insoluble U(VI) compound. PMID:16204572

  1. Photocatalytic degradation and drug activity reduction of Chloramphenicol.

    PubMed

    Chatzitakis, A; Berberidou, C; Paspaltsis, I; Kyriakou, G; Sklaviadis, T; Poulios, I

    2008-01-01

    The photocatalytic degradation of Chloramphenicol, an antibiotic drug, has been investigated in aqueous heterogeneous solutions containing n-type oxide semiconductors as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. It was observed that, with TiO(2) P-25 as photocatalyst, quantitative degradation of the organic molecule occurs after 4h of illumination. During this time, the dechlorination of the substrate is complete, while the organic nitrogen was recovered in the form of nitrate and ammonium ions. The effect of temperature on the degradation rate of Chloramphenicol shows similar apparent activation energies for both TiO(2) P-25 and ZnO photocatalysts. The initial apparent photonic efficiency (zeta(0)) of the photo-oxidation and the mineralization under various experimental conditions have been calculated, while the Kirby-Bauer disc diffusion method showed a 100% reduction of the drug activity after 90 min of photocatalytic treatment.

  2. Active Vibration Reduction of the Advanced Stirling Convertor

    NASA Technical Reports Server (NTRS)

    Wilson, Scott D.; Metscher, Jonathan F.; Schifer, Nicholas A.

    2016-01-01

    Stirling Radioisotope Power Systems (RPS) are being developed as an option to provide power on future space science missions where robotic spacecraft will orbit, flyby, land or rove. A Stirling Radioisotope Generator (SRG) could offer space missions a more efficient power system that uses one fourth of the nuclear fuel and decreases the thermal footprint compared to the current state of the art. The Stirling Cycle Technology Development (SCTD) Project is funded by the RPS Program to developing Stirling-based subsystems, including convertors and controller maturation efforts that have resulted in high fidelity hardware like the Advanced Stirling Radioisotope Generator (ASRG), Advanced Stirling Convertor (ASC), and ASC Controller Unit (ACU). The SCTD Project also performs research to develop less mature technologies with a wide variety of objectives, including increasing temperature capability to enable new environments, improving system reliability or fault tolerance, reducing mass or size, and developing advanced concepts that are mission enabling. Active vibration reduction systems (AVRS), or "balancers", have historically been developed and characterized to provide fault tolerance for generator designs that incorporate dual-opposed Stirling convertors or enable single convertor, or small RPS, missions. Balancers reduce the dynamic disturbance forces created by the power piston and displacer internal moving components of a single operating convertor to meet spacecraft requirements for induced disturbance force. To improve fault tolerance for dual-opposed configurations and enable single convertor configurations, a breadboard AVRS was implemented on the Advanced Stirling Convertor (ASC). The AVRS included a linear motor, a motor mount, and a closed-loop controller able to balance out the transmitted peak dynamic disturbance using acceleration feedback. Test objectives included quantifying power and mass penalty and reduction in transmitted force over a range of ASC

  3. Active Vibration Reduction of the Advanced Stirling Convertor

    NASA Technical Reports Server (NTRS)

    Wilson, Scott D.; Metscher, Jonathan F.; Schifer, Nicholas A.

    2016-01-01

    Stirling Radioisotope Power Systems (RPS) are being developed as an option to provide power on future space science missions where robotic spacecraft will orbit, flyby, land or rove. A Stirling Radioisotope Generator (SRG) could offer space missions a more efficient power system that uses one fourth of the nuclear fuel and decreases the thermal footprint compared to the current state of the art. The Stirling Cycle Technology Development (SCTD) Project is funded by the RPS Program to developing Stirling-based subsystems, including convertors and controller maturation efforts that have resulted in high fidelity hardware like the Advanced Stirling Radioisotope Generator (ASRG), Advanced Stirling Convertor (ASC), and ASC Controller Unit (ACU). The SCTD Project also performs research to develop less mature technologies with a wide variety of objectives, including increasing temperature capability to enable new environments, improving system reliability or fault tolerance, reducing mass or size, and developing advanced concepts that are mission enabling. Active vibration reduction systems (AVRS), or "balancers", have historically been developed and characterized to provide fault tolerance for generator designs that incorporate dual-opposed Stirling convertors or enable single convertor, or small RPS, missions. Balancers reduce the dynamic disturbance forces created by the power piston and displacer internal moving components of a single operating convertor to meet spacecraft requirements for induced disturbance force. To improve fault tolerance for dual-opposed configurations and enable single convertor configurations, a breadboard AVRS was implemented on the Advanced Stirling Convertor (ASC). The AVRS included a linear motor, a motor mount, and a closed-loop controller able to balance out the transmitted peak dynamic disturbance using acceleration feedback. Test objectives included quantifying power and mass penalty and reduction in transmitted force over a range of ASC

  4. Modeling of Erythemal Dose Rate (UVI) and its Relationship to Column Ozone and Cloud Reflectivity

    NASA Astrophysics Data System (ADS)

    Herceg, D.; Minschwaner, K.

    2005-12-01

    Understanding the relationship between column ozone, cloud reflectivity, and surface ultraviolet has become an important issue in the last 25 years. We will show correlations between solar zenith angle, erythemal dose rate (UVI), cloud reflection, and column ozone, using ground based observation made at Socorro, New Mexico from 1997 to 2004. We will also use data retrieved from the Earth Probe TOMS satellite instrument which overpassed the observing site during the same time period. Through this correlation, we can take accurate ozone, and reflectivity data from satellites such as EP-TOMS and NIMBUS 7 to model past UVI trends dating back 25 years. Finally, we may then examine the trends in UVI, column ozone, and cloud reflectivity to understand the relationship of column ozone and cloud reflectivity to UVI.

  5. Laser spectroscopic studies of interactions of U(VI) withbacterial phosphate species

    SciTech Connect

    Knopp, Roger; Panak, Petra J.; Wray, Lewis A.; Renninger, NeilS.; Keasling, Jay D.; Nitsche, Heino

    2002-03-14

    We investigated the interactions of U(VI) with two bacterialphosphate species: Gram-positive B. sphaericus and Gram-negative P.aeruginosa. The Gram-positive B. sphaericus was investigated using Ramanspectroscopy and time-resolved laser-induced fluorescence spectroscopy(TRLFS). We found that living cells, spores, and intact heat-killed cellscomplexed U(VI) (pH 4.5) through phosphate groups bound to theirsurfaces, while decomposed cells released H2PO4- and precipitated U(VI)as UO2(H2PO4)2. TRLFS of U(VI) showed that Gram-negative P.aeruginosa-genetically engineered to accumulate polyphosphate,subsequently degrade it, and secrete phosphate-precipitated U(VI)quantitatively at pH 4.5. The same bacterial strain, not induced tosecrete phosphate, sorbed only a small amount of U(VI).

  6. Upscaling of U(VI) Desorption and Transport Using Decimeter-Scale Tanks

    SciTech Connect

    Rodriguez, Derrick

    2014-12-22

    Experimental work was used to validate modeling studies and develop multicontinuum models of U(VI) transport in a contaminated aquifer. At the bench scale, it has been shown that U(VI) desorption is rate-limited and that rates are dependent on the bicarbonate concentration. Two decimeter-scale experiments were conducted in order to help establish rigorous upscaling approaches that could be tested at the tracer test and plume scales.

  7. Uranium isotopes fingerprint biotic reduction.

    PubMed

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-05-05

    Knowledge of paleo-redox conditions in the Earth's history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth's crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

  8. Uranium isotopes fingerprint biotic reduction

    DOE PAGES

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; ...

    2015-04-20

    Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U),more » i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. In addition, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.« less

  9. Uranium isotopes fingerprint biotic reduction

    SciTech Connect

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-04-20

    Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. In addition, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

  10. Uranium isotopes fingerprint biotic reduction

    PubMed Central

    Stylo, Malgorzata; Neubert, Nadja; Wang, Yuheng; Monga, Nikhil; Romaniello, Stephen J.; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-01-01

    Knowledge of paleo-redox conditions in the Earth’s history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth’s crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium. PMID:25902522

  11. Treatment of activated carbon to enhance catalytic activity for reduction of nitric oxide with ammonia

    SciTech Connect

    Ku, B.J.; Rhee, H.K. . Dept. of Chemical Engineering); Lee, J.K.; Park, D. )

    1994-11-01

    Catalytic activity of activated carbon treated with various techniques was examined in a fixed bed reactor for the reduction of nitric oxide with ammonia at 150 C. Activated carbon derived from coconut shell impregnated with an aqueous solution of ammonium sulfate, further treated with sulfuric acid, dried at 120 C, and then heated in an inert gas stream at 400 C, showed the highest catalytic activity within the range of experimental conditions. The enhancement of catalytic activity of modified activated carbon could be attributed to the increase in the amount of oxygen function groups which increased the adsorption site for ammonia. Catalytic activity of activated carbons depended on the surface area and the oxygen content as well.

  12. Evaluating the effectiveness of active noise reduction in flight helmets

    NASA Astrophysics Data System (ADS)

    Forshaw, S. E.; Rylands, J. M.; Crabtree, R. B.

    1988-08-01

    The advent of high powered fixed- and rotary-wing aircraft and tracked armoured fighting vehicles has increased the level of noise to which crews are exposed. Active noise reduction (ANR) offers a means of increasing the attenuation at low and mid frequencies. It relies on sensing the sound inside a circumaural device and cancelling it by means of negative feedback through a miniature speaker inside the enclosed volume. This study was carried out to investigate laboratory procedures appropriate for measuring the effectiveness of ANR devices. The procedures were: ear-canal measurements using an acoustic test fixture (an objective procedure), and masked threshold and loudness balance tests (psycho-physical procedures). In addition, the effect of ANR on signal detection and speech reception was investigated. The results do not clearly permit one procedure to be recommended for the evaluation of ANR systems. Signal detection performance and speech intelligibility may be used, but the results are specific to the acoustic environment of the listener and the detection task or speech-system parameters of the evaluation. When the attenuation of the ANR system is measured objectively with a transducer inside the earmuff/ear-canal volume, the location of the transducer affects the observed ANR attenuations.

  13. The SIM Lite Astrometric Observatory: engineering risk reduction activity

    NASA Astrophysics Data System (ADS)

    Goullioud, Renaud; Dekens, Frank; Nemati, Bijan; An, Xin; Hovland, Larry

    2010-07-01

    The SIM Lite Astrometric Observatory is a mission concept for a space-borne instrument to perform micro-arcsecond narrow-angle astrometry to search 60 to 100 nearby stars for Earth-like planets, and to perform global astrometry for a broad astrophysics program. The main enabling technology development for the mission was completed during phases A & B. While the project is waiting for the results of the ASTRO2010 Decadal Survey to proceed into flight implementation, the instrument team is currently converting the developed technology onto flight-ready engineering models. These key engineering tasks will significantly reduce the implementation risks during the flight phases C & D of the mission. The main optical interferometer components, including the astrometric beam combiner (ABC), the fine steering mechanism (FSM), the path-length control and modulation optical mechanisms (POM & MOM), focal plane camera electronics (ATC & FTC), camera cooling cryo-heat pipe, and the siderostat mechanism are currently under development. Main assemblies are built to meet flight requirements and have been or will be subjected to flight qualification level environmental testing (random vibration and thermal cycling) and performance testing. The Spectral Calibration Development Unit (SCDU), a white light interferometer testbed has recently demonstrated how to perform the spectral calibration of the instrument. The Guide 2 Telescope testbed (G2T) has demonstrated the 50 micro-arcsecond angle monitoring capability required by SIM Lite to perform astrometry. This paper summarizes recent progress in engineering risk reduction activities.

  14. Discovery of B ring propellers in Cassini UVIS and ISS

    NASA Astrophysics Data System (ADS)

    Sremcevic, M.; Stewart, G.; Albers, N.; Esposito, L. W.

    2011-12-01

    One of the successes of the planetary ring theory has been the theoretical prediction of gravitational signatures of bodies embedded in the rings, and their subsequent detection in Cassini data. Bodies within the rings perturb the nearby ring material, and the orbital shear forms a two-armed structure -- dubbed a ``propeller'' -- which is centered at the embedded body. Although direct evidence of the present body or moonlet is still lacking, the observations of their propeller signatures has proved as an indispensable method to extend our knowledge about ring structure and dynamics. So far, propellers have been successfully detected within Saturn's A ring in two populations: a group of small and numerous propellers interior to the Encke gap forming belts, and by far less numerous but larger propellers exterior to Pan's orbit. Although there have been hints of propellers present within the B ring, or even C ring, their detection is less certain (e.g. neither has a single propeller been seen twice, nor has the ubiquitous two armed structure been observed). In this paper we present evidence for the existence of propellers in Saturn's B ring by combining data from Cassini Ultraviolet Imaging Spectrograph (UVIS) and Imaging Science Subsystem (ISS) experiments. A single object is observed for 5 years of Cassini data. The object is seen as a very elongated bright stripe (40 degrees wide) in unlit Cassini images, and dark stripe in lit geometries. In total we report observing the feature in images at 18 different epochs between 2005 and 2010. In UVIS occultations we observe the feature as an optical depth depletion in 14 out of 93 occultation cuts at corrotating longitudes compatible with imaging data. Combining the available Cassini data we infer that the object is a partial gap located at a=112,921km embedded in the high optical depth region of the B ring. The gap moves at Kepler speed appropriate for its radial location. Radial offsets of the gap locations in UVIS

  15. Enzymatic iron and uranium reduction by sulfate-reducing bacteria

    USGS Publications Warehouse

    Lovley, D.R.; Roden, E.E.; Phillips, E.J.P.; Woodward, J.C.

    1993-01-01

    The potential for sulfate-reducing bacteria (SRB) to enzymatically reduce Fe(III) and U(VI) was investigated. Five species of Desulfovibrio as well as Desulfobacterium autotrophicum and Desulfobulbus propionicus reduced Fe(III) chelated with nitrilotriacetic acid as well as insoluble Fe(III) oxide. Fe(III) oxide reduction resulted in the accumulation of magnetite and siderite. Desulfobacter postgatei reduced the chelated Fe(III) but not Fe(III) oxide. Desulfobacter curvatus, Desulfomonile tiedjei, and Desulfotomaculum acetoxidans did not reduce Fe(III). Only Desulfovibrio species reduced U(VI). U(VI) reduction resulted in the precipitation of uraninite. None of the SRB that reduced Fe(III) or U(VI) appeared to conserve enough energy to support growth from this reaction. However, Desulfovibrio desulfuricans metabolized H2 down to lower concentrations with Fe(III) or U(VI) as the electron acceptor than with sulfate, suggesting that these metals may be preferred electron acceptors at the low H2 concentrations present in most marine sediments. Molybdate did not inhibit Fe(III) reduction by D. desulfuricans. This indicates that the inability of molybdate to inhibit Fe(III) reduction in marine sediments does not rule out the possibility that SRB are important catalysts for Fe(III) reduction. The results demonstrate that although SRB were previously considered to reduce Fe(III) and U(VI) indirectly through the production of sulfide, they may also directly reduce Fe(III) and U(VI) through enzymatic mechanisms. These findings, as well as our recent discovery that the So-reducing microorganism Desulfuromonas acetoxidans can reduce Fe(III), demonstrate that there are close links between the microbial sulfur, iron, and uranium cycles in anaerobic marine sediments. ?? 1993.

  16. Effects of aqueous uranyl speciation on the kinetics of microbial uranium reduction

    DOE PAGES

    Belli, Keaton M.; DiChristina, Thomas J.; Van Cappellen, Philippe; ...

    2015-02-16

    The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria. In order to determine the effects of aqueous uranyl speciation on uranium bioreduction kinetics, incubations and viability assays with Shewanella putrefaciens strain 200 were conducted over a range of pH and dissolved inorganic carbon (DIC), Ca2+, and Mg2+ concentrations. A speciation-dependent kinetic model was developed to reproducemore » the observed time series of total dissolved uranium concentration over the range of geochemical conditions tested. The kinetic model yielded the highest rate constant for the reduction of uranyl non-carbonate species (i.e., the ‘free’ hydrated uranyl ion, uranyl hydroxides, and other minor uranyl complexes), indicating that they represent the most readily reducible fraction of U(VI) despite being the least abundant uranyl species in solution. In the presence of DIC, Ca2+, and Mg2+ is suppressed during the formation of more bioavailable uranyl non-carbonate species and resulted in slower bioreduction rates. At high concentrations of bioavailable U(VI), however, uranium toxicity to S. putrefaciens inhibited bioreduction, and viability assays confirmed that the concentration of non-carbonate uranyl species best predicts the degree of toxicity. The effect of uranium toxicity was accounted for by incorporating the free ion activity model of metal toxicity into the bioreduction rate law. These results demonstrate that, in the absence of competing terminal electron acceptors, uranium bioreduction kinetics can be predicted over a wide range of geochemical conditions based on the bioavailability and toxicity imparted on U(VI) by solution composition. Finally, these findings also imply

  17. Effects of aqueous uranyl speciation on the kinetics of microbial uranium reduction

    SciTech Connect

    Belli, Keaton M.; DiChristina, Thomas J.; Van Cappellen, Philippe; Taillefert, Martial

    2015-02-16

    The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria. In order to determine the effects of aqueous uranyl speciation on uranium bioreduction kinetics, incubations and viability assays with Shewanella putrefaciens strain 200 were conducted over a range of pH and dissolved inorganic carbon (DIC), Ca2+, and Mg2+ concentrations. A speciation-dependent kinetic model was developed to reproduce the observed time series of total dissolved uranium concentration over the range of geochemical conditions tested. The kinetic model yielded the highest rate constant for the reduction of uranyl non-carbonate species (i.e., the ‘free’ hydrated uranyl ion, uranyl hydroxides, and other minor uranyl complexes), indicating that they represent the most readily reducible fraction of U(VI) despite being the least abundant uranyl species in solution. In the presence of DIC, Ca2+, and Mg2+ is suppressed during the formation of more bioavailable uranyl non-carbonate species and resulted in slower bioreduction rates. At high concentrations of bioavailable U(VI), however, uranium toxicity to S. putrefaciens inhibited bioreduction, and viability assays confirmed that the concentration of non-carbonate uranyl species best predicts the degree of toxicity. The effect of uranium toxicity was accounted for by incorporating the free ion activity model of metal toxicity into the bioreduction rate law. These results demonstrate that, in the absence of competing terminal electron acceptors, uranium bioreduction kinetics can be predicted over a wide range of geochemical conditions based on the bioavailability and toxicity imparted on U(VI) by solution composition

  18. Biological reduction of uranium in groundwater and subsurface soil.

    PubMed

    Abdelouas, A; Lutze, W; Gong, W; Nuttall, E H; Strietelmeier, B A; Travis, B J

    2000-04-24

    Biological reduction of uranium is one of the techniques currently studied for in situ remediation of groundwater and subsurface soil. We investigated U(VI) reduction in groundwaters and soils of different origin to verify the presence of bacteria capable of U(VI) reduction. The groundwaters originated from mill tailings sites with U concentrations as high as 50 mg/l, and from other sites where uranium is not a contaminant, but was added in the laboratory to reach concentrations up to 11 mg/l. All waters contained nitrate and sulfate. After oxygen and nitrate reduction, U(VI) was reduced by sulfate-reducing bacteria, whose growth was stimulated by ethanol and trimetaphosphate. Uranium precipitated as hydrated uraninite (UO2 x xH2O). In the course of reduction of U(VI), Mn(IV) and Fe(III) from the soil were reduced as well. During uraninite precipitation a comparatively large mass of iron sulfides formed and served as a redox buffer. If the excess of iron sulfide is large enough, uraninite will not be oxidized by oxygenated groundwater. We show that bacteria capable of reducing U(VI) to U(IV) are ubiquitous in nature. The uranium reducers are primarily sulfate reducers and are stimulated by adding nutrients to the groundwater.

  19. Monitoring the WFC3/UVIS Relative Gain with Internal Flatfields

    NASA Astrophysics Data System (ADS)

    Fowler, J.; Baggett, S.

    2017-03-01

    The WFC3/UVIS gain stability has been monitored twice yearly. This project provides a new examination of gain stability, making use of the existing internal flatfield observations taken every three days (for the Bowtie monitor) for a regular look at relative gain stability. Amplifiers are examined for consistency both in comparison to each other and over time, by normalizing the B, C, and D amplifiers to A, and then plotting statistics for each of the three normalized amplifiers with time. We find minimal trends in these statistics, with a 0.02 - 0.2% change in mean amplifier ratio over 7.5 years. The trends in the amplifiers are well-behaved with the exception of the B/A ratio, which shows increased scatter in mean, median, and standard deviation. The cause of the scatter remains unclear though we find it is not dependent upon detector defects, filter features, or shutter effects, and is only observable after pixel flagging (both from the data quality arrays and outlier values) has been applied.

  20. Resupply Mechanism to a Contaminated Aquifer: A Laboratory Study of U(VI) Desorption from Capillary Fringe Sediments

    SciTech Connect

    Um, Wooyong; Zachara, John M.; Liu, Chongxuan; Moore, Dean A.; Rod, Kenton A.

    2010-09-15

    Contaminated capillary fringe sediments are believed to function as long term source of U(VI) to Hanford’s 300 Area groundwater uranium plume that discharges to the Columbia River. The deep vadose zone at this site experiences seasonal water table elevation and water compositional changes in response to Columbia River stage. Batch and column desorption experiments of U(VI) were performed on two mildly contaminated sediments from this system that vary in hydrologic position to ascertain their U(VI) release behavior and factors controlling it. Solid phase characterization of the sediments was performed to identify mineralogic and chemical factors controlling U(VI) desorption. The desorption behavior of U(VI) was different from the two sediments in spite of similar chemical and textural characteristics, and non-carbonate mineralogy. Adsorption strength and sorbed U(VI) lability was higher in the near-river sediment 11D. Inland sediment 39B displayed low sorbed U(VI) lability (~ 10%) and measurable solid-phase carbonate content. Kinetic desorption was observed that was attributed to regeneration of labile U(VI) in 11D, and carbonate mineral dissolution in 39B. The desorption reaction was best described as an equilibrium surface complexation reaction. The noted differences in desorption behavior appear to result from U(VI) contamination and hydrologic history, as well as sediment carbonate content. Insights are provided on the dynamic adsorption/desorption behavior of contaminants in linked groundwater-river systems.

  1. Proteome of Geobacter sulfurreducens in the presence of U(VI).

    PubMed

    Orellana, Roberto; Hixson, Kim K; Murphy, Sean; Mester, Tünde; Sharma, Manju L; Lipton, Mary S; Lovley, Derek R

    2014-12-01

    Geobacter species often play an important role in the in situ bioremediation of uranium-contaminated groundwater, but little is known about how these microbes avoid uranium toxicity. To evaluate this further, the proteome of Geobacter sulfurreducens exposed to 100 µM U(VI) acetate was compared to control cells not exposed to U(VI). Of the 1363 proteins detected from these cultures, 203 proteins had higher abundance during exposure to U(VI) compared with the control cells and 148 proteins had lower abundance. U(VI)-exposed cultures expressed lower levels of proteins involved in growth, protein and amino acid biosynthesis, as well as key central metabolism enzymes as a result of the deleterious effect of U(VI) on the growth of G. sulfurreducens. In contrast, proteins involved in detoxification, such as several efflux pumps belonging to the RND (resistance-nodulation-cell division) family, and membrane protection, and other proteins, such as chaperones and proteins involved in secretion systems, were found in higher abundance in cells exposed to U(VI). Exposing G. sulfurreducens to U(VI) resulted in a higher abundance of many proteins associated with the oxidative stress response, such as superoxide dismutase and superoxide reductase. A strain in which the gene for superoxide dismutase was deleted grew more slowly than the WT strain in the presence of U(VI), but not in its absence. The results suggested that there is no specific mechanism for uranium detoxification. Rather, multiple general stress responses are induced, which presumably enable Geobacter species to tolerate high uranium concentrations.

  2. Macroscopic and Microscopic Investigation of U(VI) and Eu(III) Adsorption on Carbonaceous Nanofibers.

    PubMed

    Sun, Yubing; Wu, Zhen-Yu; Wang, Xiangxue; Ding, Congcong; Cheng, Wencai; Yu, Shu-Hong; Wang, Xiangke

    2016-04-19

    The adsorption mechanism of U(VI) and Eu(III) on carbonaceous nanofibers (CNFs) was investigated using batch, IR, XPS, XANES, and EXAFS techniques. The pH-dependent adsorption indicated that the adsorption of U(VI) on the CNFs was significantly higher than the adsorption of Eu(III) at pH < 7.0. The maximum adsorption capacity of the CNFs calculated from the Langmuir model at pH 4.5 and 298 K for U(VI) and Eu(III) were 125 and 91 mg/g, respectively. The CNFs displayed good recyclability and recoverability by regeneration experiments. Based on XPS and XANES analyses, the enrichment of U(VI) and Eu(III) was attributed to the abundant adsorption sites (e.g., -OH and -COOH groups) of the CNFs. IR analysis further demonstrated that -COOH groups were more responsible for U(VI) adsorption. In addition, the remarkable reducing agents of the R-CH2OH groups were responsible for the highly efficient adsorption of U(VI) on the CNFs. The adsorption mechanism of U(VI) on the CNFs at pH 4.5 was shifted from inner- to outer-sphere surface complexation with increasing initial concentration, whereas the surface (co)precipitate (i.e., schoepite) was observed at pH 7.0 by EXAFS spectra. The findings presented herein play an important role in the removal of radionuclides on inexpensive and available carbon-based nanoparticles in environmental cleanup applications.

  3. Acceleration of Field-Scale Bioreduction of U(VI) in a Shallow Alluvial Aquifer: Temporal and Spatial Evolution of Biogeochemistry

    SciTech Connect

    Long, Phil

    2005-04-20

    Uranium mill tailings sites provide access to uranium-contaminated groundwater at sites that are shallow and low hazard, making it possible to address the following scientific objectives: (1) Determine the dominant electron accepting processes at field sites with long-term metal/rad contamination; (2) Define the biogeochemical transformations that may be important to either natural or accelerated bioremediation under field conditions; and (3) Examine the potential for using biostimulation (electron donor addition) to accelerate reduction of U(VI) to U(IV) at the field scale.

  4. Using Cassini UVIS Data to Constrain Enceladus' Libration State

    NASA Technical Reports Server (NTRS)

    Hurford, Terry A.; Helfenstein, P.; Hansen, C.

    2010-01-01

    Given the non-spherical shape of Enceladus, the satellite may experience gravitational torques that will cause it to physically librate as it orbits Saturn. Physical libration would produce a diurnal oscillation in the longitude of Enceladus' tidal bulge, which could have a profound effect on the diurnal stresses experienced by the surface of the satellite. Although Cassini ISS has placed an observational upper limit on Enceladus' libration amplitude, stall amplitude librations may have geologically significant consequences. For example, a physical libration will affect heat production along the tiger stripes as produced by tidal shear heating and a previous study has explored possible libration states that provided better matches to Cassini CIRS observations of heat along the tiger stripes. Cassini UVIS stellar occultations provided measurements of the column density of the Enceladus plume at two different points in Enceladus' orbit and find comparable column density values. This column density may be a reflection of the amount of the tiger stripe rifts in tension and able to vent volatiles and a physical libration will also affect the fraction of tiger stripe in tension at different points in the orbit. We have modeled the expected fraction of tiger stripes in tension under different libration conditions. Without libration the amount of tiger stripe rifts in tension at both paints in the orbit would not be comparable and therefore may not allow comparable amounts of volatiles to escape. However, we identify libration conditions that do allow comparable amounts of the tiger stripes to be in tension at each point in the orbit, which might lead to comparable column densities. The librations identified coincide with possible librations states identified in the earlier study, which used Cassini CIRS observations.

  5. Classification of F Ring Features Observed Using Cassini UVIS

    NASA Astrophysics Data System (ADS)

    Meinke, Bonnie K.; Esposito, L. W.; Albers, N.

    2009-09-01

    The Cassini Ultraviolet Imaging Spectrograph (UVIS) has observed 39 statistically significant F ring features in 103 occultations since July 2004. This work triples the number of features reported by Esposito et al. (2008). As the number of statistically significant features has grown, we are now able to classify them for the purposes of cataloging. We define three categories: moonlet, core, and icicle, which categorize the shapes of features seen to date in the occultation profiles of the F ring. With complete signal attenuation for a radial distance of 600 m, the feature observed in the Alp Leo Rev 9 occultation is the only moonlet observed. A myriad of icicles have been observed, which partially block stellar signal for 30 m to 1 km along the radial expanse of the occultation. The density enhancements responsible for such signal attenuations are likely due to transient clumping of material, evidence that aggregations of material are ubiquitous in the F ring. Finally, the large variety of core region shapes displays how even the general shape of the F ring is ever-changing due to continuous perturbations from internal and external objects. The core region of the F ring usually has a smooth U-shape to it, but particle-size segregation and narrow channeling of material lead to the core region taking the shape of Ws and Vs. These three categories show that F ring behavior is highly variable with time and space and that the locations of certain features correlate to proximity to Prometheus. Our lengthy observing campaign reveals possible states and possible causes of the observed structure. This research was supported by the Cassini Project.

  6. U(VI) Sequestration in Hydroxyapatite Produced by Microbial Glycerol 3-Phosphate Metabolism▿ †

    PubMed Central

    Shelobolina, Evgenya S.; Konishi, Hiromi; Xu, Huifang; Roden, Eric E.

    2009-01-01

    Previous studies have demonstrated the potential for removal of U(VI) from solution via precipitation of U(VI)-bearing calcium-phosphate (Ca-P) minerals coupled to microbial hydrolysis of glycerol phosphate compounds. We evaluated this process in circumneutral-pH groundwater from Area 2 of the U.S. Department of Energy Field Research Center at Oak Ridge National Laboratory. Area 2 groundwater contains high concentrations of dissolved calcium (ca. 4 mM), and thus, release of phosphate during glycerol phosphate metabolism has the potential to create conditions favorable for U(VI) sequestration in Ca-P minerals. Microbial enumeration and isolation studies verified the presence of aerobic and nitrate-reducing glycerol 3-phosphate (G3P)-metabolizing microorganisms in Area 2 sediments. Coprecipitation of U(VI) with Ca-P minerals coupled to microbial G3P hydrolysis was demonstrated in artificial groundwater under aerobic and nitrate-reducing conditions. Transmission electron microscopy analysis and mineral-washing experiments demonstrated that U(VI) was incorporated into the structure of the insoluble Ca-P mineral hydroxyapatite [Ca5(PO4)3OH]. Our results support the idea that U(VI) can be effectively removed from solution in contaminated aquifers through stimulation of microbial organophosphate metabolism. PMID:19633115

  7. Bioreduction of U(VI) and stability of immobilized uranium under suboxic conditions.

    PubMed

    Hu, Nan; Ding, De-xin; Li, Shi-mi; Tan, Xiang; Li, Guang-yue; Wang, Yong-dong; Xu, Fei

    2016-04-01

    In order to study the bioreduction of U(VI) and stability of immobilized uranium under suboxic conditions, microcosm were amended with ethanol, lactate and glucose, and incubated under suboxic conditions. During the incubation, total dissolved U in amended microcosms decreased from 0.95 mg/L to 0.03 mg/L. Pyrosequencing results showed that, the proportion of anaerobic microorganisms capable of reducing U(VI) under suboxic conditions was small compared with that under anoxic conditions; the proportion of aerobic and facultative anaerobic microorganisms capable of consuming the dissolved oxygen was large; and some of the facultative anaerobic microorganisms could reduce U(VI). These results indicated that different microbial communities were responsible for the bioreduction of U(VI) under suboxic and anoxic conditions. After the electron donors were exhausted, total dissolved U in the amended microcosms remained unchanged, while the U(VI)/U(IV) ratio in the solid phase of sediments increased obviously. This implied that the performance of bioreduction of the U(VI) can be maintained under suboxic condition.

  8. Determining Individual Mineral Contributions To U(VI) Adsorption In A Contaminated Aquifer Sediment: A Fluorescence Spectroscopy Study

    SciTech Connect

    Wang, Zheming; Zachara, John M.; Boily, Jean F.; Xia, Yuanxian; Resch, Charles T.; Moore, Dean A.; Liu, Chongxuan

    2011-05-15

    The adsorption and speciation of U(VI) was investigated on contaminated, fine grained sediment materials from the Hanford 300 area (SPP1 GWF) in simulated groundwater using cryogenic laser-induced U(VI) fluorescence spectroscopy combined with chemometric analysis. A series of reference minerals (montmorillonite, illite, Michigan chlorite, North Carolina chlorite, California clinochlore, quartz and synthetic 6-line ferrihydrite) was used for comparison that represents the mineralogical constituents of SPP1 GWF. Surface area-normalized Kd values were measured at U(VI) concentrations of 5x10-7 mol L-1 and 5x10-6 mol L-1, respectively, that displayed the following affinity series: 6-line-ferrihydrite > North Carolina chlorite ≈ California clinochlore > Michigan chlorite ≈ quartz > montmorillonite ≈ illite ≈ SPP1 GWF. Both time-resolved spectra and asynchronous two-dimensional (2D) correlation analysis of SPP1 GWF at different delay times indicated that two major adsorbed U(VI) species were present in the sediment that resembled U(VI) adsorbed on quartz and phyllosilicates. Simulations of the normalized fluorescence spectra confirmed that the speciation of SPP1 GWF was best represented by a linear combination of U(VI) adsorbed on quartz (90%) and phyllosilicates (10%). However, the fluorescence quantum yield for U(VI) adsorbed on phyllosilicates was lower than quartz and, consequently, its fractional contribution to speciation may be underestimated. Spectral comparison with literature data suggested that U(VI) exists primarily as inner-sphere U(VI) complexes with surface silanol groups on quartz while U(VI) on phyllosilicates was consistent with the formation of surface U(VI) tricarbonate complexes.

  9. Sorption and desorption of perchlorate and U(VI) by strong-base anion-exchange resins.

    PubMed

    Gu, Baohua; Ku, Yee-Kyoung; Brown, Gilbert M

    2005-02-01

    This study investigated the sorption affinity and capacity of six strong-base anion-exchange (SBA) resins for both uranium [U(VI)] and perchlorate (ClO4-) in simulated groundwater containing varying concentrations of sulfate (SO4(2-)). Additionally, desorption of U(VI) from spent resins was studied to separate U(VI) from resins with sorbed ClO4- for waste segregation and minimization. Results indicate that all SBA resins investigated in this study strongly sorb U(VI). The gel-type polyacrylic resin (Purolite A850) showed the highest sorption affinity and capacityfor U(VI) butwasthe least effective in sorbing ClO4-. The presence of SO4(2-) had little impact on the sorption of U(VI) but significantly affected the sorption of ClO4-, particularly on monofunctional SBA resins. A dilute acid wash was found to be effective in desorbing U(VI) but ineffective in desorbing ClO4- from bifunctional resins (Purolite A530E and WBR109). A single wash removed approximately 75% of sorbed U(VI) but only approximately 0.1% of sorbed ClO4- from the bifunctional resins. On the other hand, only 21.4% of sorbed U(VI) but approximately 34% of sorbed ClO4- was desorbed from the Purolite A850 resin. This study concludes that bifunctional resins could be used effectively to treatwater contaminated with ClO4- and traces of U(VI), and dilute acid washes could minimize hazardous wastes by separating sorbed U(VI) from ClO4- prior to the regeneration of the spent resin loaded with ClO4-.

  10. Enrichment of Members of the Family Geobacteraceae Associated with Stimulation of Dissimilatory Metal Reduction in Uranium-Contaminated Aquifer Sediments

    PubMed Central

    Holmes, Dawn E.; Finneran, Kevin T.; O'Neil, Regina A.; Lovley, Derek R.

    2002-01-01

    Stimulating microbial reduction of soluble U(VI) to insoluble U(IV) shows promise as a strategy for immobilizing uranium in uranium-contaminated subsurface environments. In order to learn more about which microorganisms might be involved in U(VI) reduction in situ, the changes in the microbial community when U(VI) reduction was stimulated with the addition of acetate were monitored in sediments from three different uranium-contaminated sites in the floodplain of the San Juan River in Shiprock, N.Mex. In all three sediments U(VI) reduction was accompanied by concurrent Fe(III) reduction and a dramatic enrichment of microorganisms in the family Geobacteraceae, which are known U(VI)- and Fe(III)-reducing microorganisms. At the point when U(VI) reduction and Fe(III) reduction were nearing completion, Geobacteraceae accounted for ca. 40% of the 16S ribosomal DNA (rDNA) sequences recovered from the sediments with bacterial PCR primers, whereas Geobacteraceae accounted for fewer than 5% of the 16S rDNA sequences in control sediments that were not amended with acetate and in which U(VI) and Fe(III) reduction were not stimulated. Between 55 and 65% of these Geobacteraceae sequences were most similar to sequences from Desulfuromonas species, with the remainder being most closely related to Geobacter species. Quantitative analysis of Geobacteraceae sequences with most-probable-number PCR and TaqMan analyses indicated that the number of Geobacteraceae sequences increased from 2 to 4 orders of magnitude over the course of U(VI) and Fe(III) reduction in the acetate-amended sediments from the three sites. No increase in Geobacteraceae sequences was observed in control sediments. In contrast to the predominance of Geobacteraceae sequences, no sequences related to other known Fe(III)-reducing microorganisms were detected in sediments. These results compare favorably with an increasing number of studies which have demonstrated that Geobacteraceae are important components of the

  11. Identification of proteins capable of metal reduction from the proteome of the Gram-positive bacterium Desulfotomaculum reducens MI-1 using an NADH-based activity assay

    SciTech Connect

    Otwell, Annie E.; Sherwood, Roberts; Zhang, Sheng; Nelson, Ornella D.; Li, Zhi; Lin, Hening; Callister, Stephen J.; Richardson, Ruth E.

    2015-01-01

    Metal reduction capability has been found in numerous species of environmentally abundant Gram-positive bacteria. However, understanding of microbial metal reduction is based almost solely on studies of Gram-negative organisms. In this study, we focus on Desulfotomaculum reducens MI-1, a Gram-positive metal reducer whose genome lacks genes with similarity to any characterized metal reductase. D. reducens has been shown to reduce not only Fe(III), but also the environmentally important contaminants U(VI) and Cr(VI). By extracting, separating, and analyzing the functional proteome of D. reducens, using a ferrozine-based assay in order to screen for chelated Fe(III)-NTA reduction with NADH as electron donor, we have identified proteins not previously characterized as iron reductases. Their function was confirmed by heterologous expression in E. coli. These are the protein NADH:flavin oxidoreductase (Dred_2421) and a protein complex composed of oxidoreductase FAD/NAD(P)-binding subunit (Dred_1685) and dihydroorotate dehydrogenase 1B (Dred_1686). Dred_2421 was identified in the soluble proteome and is predicted to be a cytoplasmic protein. Dred_1685 and Dred_1686 were identified in both the soluble as well as the insoluble (presumably membrane) protein fraction, suggesting a type of membrane-association, although PSORTb predicts both proteins are cytoplasmic. Furthermore, we show that these proteins have the capability to reduce soluble Cr(VI) and U(VI) with NADH as electron donor. This study is the first functional proteomic analysis of D. reducens, and one of the first analyses of metal and radionuclide reduction in an environmentally relevant Gram-positive bacterium.

  12. Iran’s Activities on Prevention, Treatment and Harm Reduction of Drug Abuse

    PubMed Central

    Saberi Zafarghandi, Mohammad Bagher; Jadidi, Mohsen; Khalili, Narjes

    2015-01-01

    Context: In the present review study, authors investigated Iran’s activities regarding prevention, abuse and harm reduction of drugs nationwide. The issue appears to be important in order to show the trend of activities in the country. Evidence Acquisition: In this report, authors gathered data from different Farsi/English peer review journals issued both in printed and online versions. These journals have been indexed in PubMed, ISI, ISC, SID, Magiran, UN, etc. These are among the most referred and cited databases. Results: Summarizing the data led to three distinguished sections: 1) drug supply reduction activities; 2) drug demand reduction activities; 3) harm reduction activities. Conclusions: As the results showed, the trend of activities was encouraging and some additional activities could be included to future programs relying on early-onset preventions. PMID:26870709

  13. Reduction of structural weight, costs and complexity of a control system in the active vibration reduction of flexible structures

    NASA Astrophysics Data System (ADS)

    Daraji, A. H.; Hale, J. M.

    2014-09-01

    This paper concerns the active vibration reduction of a flexible structure with discrete piezoelectric sensors and actuators in collocated pairs bonded to its surface. In this study, a new fitness and objective function is proposed to determine the optimal number of actuators, based on variations in the average closed loop dB gain margin reduction for all of the optimal piezoelectric pairs and on the modes that are required to be attenuated using the optimal linear quadratic control scheme. The aim of this study is to find the minimum number of optimally located sensor/actuator pairs, which can achieve the same vibration reduction as a greater number, in order to reduce the cost, complexity and power requirement of the control system. This optimization was done using a genetic algorithm. The technique may be applied to any lightly damped structure, and is demonstrated here by attenuating the first six vibration modes of a flat cantilever plate. It is shown that two sensor/actuator pairs, located and controlled optimally, give almost the same vibration reduction as ten pairs. These results are validated by comparing the open and closed loop time responses and actuator feedback voltages for various numbers of piezoelectric pairs using the ANSYS finite element package and a proportional differential control scheme.

  14. Active Flap Control of the SMART Rotor for Vibration Reduction

    NASA Technical Reports Server (NTRS)

    Hall, Steven R.; Anand, R. Vaidyanathan; Straub, Friedrich K.; Lau, Benton H.

    2009-01-01

    Active control methodologies were applied to a full-scale active flap rotor obtained during a joint Boeing/ DARPA/NASA/Army test in the Air Force National Full-Scale Aerodynamic Complex 40- by 80-foot anechoic wind tunnel. The active flap rotor is a full-scale MD 900 helicopter main rotor with each of its five blades modified to include an on-blade piezoelectric actuator-driven flap with a span of 18% of radius, 25% of chord, and located at 83% radius. Vibration control demonstrated the potential of active flaps for effective control of vibratory loads, especially normal force loads. Active control of normal force vibratory loads using active flaps and a continuous-time higher harmonic control algorithm was very effective, reducing harmonic (1-5P) normal force vibratory loads by 95% in both cruise and approach conditions. Control of vibratory roll and pitch moments was also demonstrated, although moment control was less effective than normal force control. Finally, active control was used to precisely control blade flap position for correlation with pretest predictions of rotor aeroacoustics. Flap displacements were commanded to follow specific harmonic profiles of 2 deg or more in amplitude, and the flap deflection errors obtained were less than 0.2 deg r.m.s.

  15. Using High Performance Computing to Understand Roles of Labile and Nonlabile U(VI) on Hanford 300 Area Plume Longevity

    SciTech Connect

    Lichtner, Peter C.; Hammond, Glenn E.

    2012-07-28

    Evolution of a hexavalent uranium [U(VI)] plume at the Hanford 300 Area bordering the Columbia River is investigated to evaluate the roles of labile and nonlabile forms of U(VI) on the longevity of the plume. A high fidelity, three-dimensional, field-scale, reactive flow and transport model is used to represent the system. Richards equation coupled to multicomponent reactive transport equations are solved for times up to 100 years taking into account rapid fluctuations in the Columbia River stage resulting in pulse releases of U(VI) into the river. The peta-scale computer code PFLOTRAN developed under a DOE SciDAC-2 project is employed in the simulations and executed on ORNL's Cray XT5 supercomputer Jaguar. Labile U(VI) is represented in the model through surface complexation reactions and its nonlabile form through dissolution of metatorbernite used as a surrogate mineral. Initial conditions are constructed corresponding to the U(VI) plume already in place to avoid uncertainties associated with the lack of historical data for the waste stream. The cumulative U(VI) flux into the river is compared for cases of equilibrium and multirate sorption models and for no sorption. The sensitivity of the U(VI) flux into the river on the initial plume configuration is investigated. The presence of nonlabile U(VI) was found to be essential in explaining the longevity of the U(VI) plume and the prolonged high U(VI) concentrations at the site exceeding the EPA MCL for uranium.

  16. Activity and Stability of Nanoscale Oxygen Reduction Catalysts

    SciTech Connect

    Shao-Horn, Yang

    2015-07-28

    Design of highly active and stable nanoscale catalysts for electro-oxidation of small organic molecules is of great importance to the development of efficient fuel cells. The amount and instability of Pt-based catalysts in the cathode limits the cost, efficiency and lifetime of proton exchange membrane fuel cells. We developed a microscopic understanding of the factors governing activity and stability in Pt and PtM alloys. Experimental efforts were focused on probing the size and shape dependence of ORR activity of Pt-based nanoparticles supported on carbon nanotubes. A microscopic understanding of the activity was achieved by correlating voltammetry and rotating ring disk electrodes to surface atomic and electronic structures, which were elucidated predominantly by high-resolution transmission electron microscopy (HRTEM), Scanning transmission electron microscopy energy dispersive X-ray Spectroscopy (STEM-EDS) and synchrotron X-ray absorption spectroscopy (XAS).

  17. Sustained Reduction of Cerebellar Activity in Experimental Epilepsy

    PubMed Central

    Rijkers, Kim; Moers-Hornikx, Véronique M. P.; Hemmes, Roelof J.; Aalbers, Marlien W.; Temel, Yasin; Vles, Johan S. H.; Hoogland, Govert

    2015-01-01

    Clinical and experimental evidence suggests a role for the cerebellum in seizure control, while no data are available on cerebellar activity between seizures. We hypothesized that interictal regional activity of the deep cerebellar nuclei is reduced in epilepsy and tested this in an animal model by using ΔFosB and cytochrome oxidase (COX) (immuno)histochemistry. The expression of these two markers of neuronal activity was analysed in the dentate nucleus (DN), interpositus nucleus (IN), and fastigial nucleus (FN) of the cerebellum of fully amygdala kindled rats that were sacrificed 48 hours after their last seizure. The DN and FN of kindled rats exhibited 25 to 29% less ΔFosB immunopositive cells than their respective counterpart in sham controls (P < 0.05). COX expression in the DN and FN of kindled animals was reduced by 32 to 33% compared to respective control values (P < 0.05). These results indicate that an epileptogenic state is characterized by decreased activity of deep cerebellar nuclei, especially the DN and FN. Possible consequences may include a decreased activation of the thalamus, contributing to further seizure spread. Restoration of FN activity by low frequency electrical stimulation is suggested as a possible treatment option in chronic epilepsy. PMID:26417599

  18. MOF catalysis of Fe(II)-to-Fe(III) reaction for an ultrafast and one-step generation of the Fe2O3@MOF composite and uranium(vi) reduction by iron(ii) under ambient conditions.

    PubMed

    Xiong, Yang Yang; Li, Jian Qiang; Yan, Chang Sheng; Gao, Heng Ya; Zhou, Jian Ping; Gong, Le Le; Luo, Ming Biao; Zhang, Le; Meng, Pan Pan; Luo, Feng

    2016-08-07

    Herein, we demonstrate that Zn-MOF-74 enables the ultrafast and one-step generation of the Fe2O3@MOF composite once Zn-MOF-74 contacts with FeSO4 solution. This unique reaction can be further applied in catalysis of U(vi) reduction by Fe(ii) under ambient conditions. The results provide a highly renovated strategy for U(vi) reduction by Fe(ii) just under ambient conditions, which completely subvert all established methods about U(vi) reduction by Fe(ii) in which O2- and CO2-free conditions are absolutely required.

  19. Sulfur Isotopes as Indicators of Bacterial Sulfate Reduction Processes Influencing Field Scale Uranium Bioremediation

    NASA Astrophysics Data System (ADS)

    Druhan, J. L.; Conrad, M. E.; Williams, K. H.; N'guessan, L.; Long, P. E.; Hubbard, S. S.

    2007-12-01

    An in-situ acetate amendment at a DOE Uranium Mill Tailings Remedial Action (UMTRA) site near Rifle, CO demonstrated successful reduction of aqueous U(VI), to less soluble U(IV) through stimulated microbial activity. U(VI) reduction rates were highest during iron reduction and decreased with the onset of sulfate reduction. However, sustained U(IV) attenuation was observed following subsequent termination of the acetate amendment. These findings illustrate the importance of the transition between iron and sulfate reducing conditions in stimulating bioreduction of uranium. The sulfur isotope compositions of sulfate and sulfide were measured through this transition in order to explore the utility of these data in tracking the extent of microbial sulfate reduction and to assess the stability of sulfide precipitates. Samples for isotopic analyses and aqueous measurements of sulfate, ferrous iron, U(VI) and acetate were collected in one background well and three monitoring wells down-gradient of the acetate injection. Results show an increase of up to 7‰ in the δ34S of sulfate at the onset of sulfate reduction, followed by a return to background δ34S values of -8‰ following cessation of the acetate amendment. The δ34S values of sulfide increased from roughly -20‰ at the onset of sulfate reduction to a maximum of -0.8‰ during peak sulfate removal, followed by a gradual return to values of roughly -28‰ upon cessation of the acetate amendment. These data present a unique perspective on the processes governing the bioreduction experiment in that the sulfate isotopes are a function of both transport and mixing processes, whereas the sulfide isotopes represent biogenic sulfide that is rapidly removed from the aqueous phase. Thus a comparable enrichment in sulfate isotopic data noted in the closest and furthest wells from the injection gallery suggest bioreduction in both of these locations, while a larger increase in sulfide isotopic values in the closest well

  20. Design Activity in the Software Cost Reduction Project.

    DTIC Science & Technology

    1986-08-18

    PM Physical Model S G System Generation SS Shared Services SU System Utilities . NOV M N 1600SEP A 0 JUL TOTAL 14000 MAAR cc 100 FEB :IESGN 0o 10000...iy---- .... ;’ TESTING Jan 78 Jan 79 Jan 80 Jan 81 Jan 82 Jan 83 Jan 84 Jan 85 M3ITH Fig. 7 - Shared services activities A F 0 U E C 1600 G B T...DISCUSSING 200M Jan 78 Jan 79 Jan 80 Jan 81 Jan 82 Jan 83 Jan 84 Jan 85 Fig 13 - Shared services design activities 5.~ S% 12 ......,ooU7 . . NRL REPORT 8974 A

  1. Transcription activation of a UV-inducible Clostridium perfringens bacteriocin gene by a novel sigma factor.

    PubMed

    Dupuy, Bruno; Mani, Nagraj; Katayama, Seiichi; Sonenshein, Abraham L

    2005-02-01

    Expression of the plasmid-encoded Clostridium perfringens gene for bacteriocin BCN5 was shown to depend in vivo and in vitro on the activity of UviA protein. UviA, also plasmid-encoded, proved to be an RNA polymerase sigma factor and was also partly autoregulatory. The uviA gene has two promoters; one provided a UviA-independent, basal level of gene expression while the stronger, UviA-dependent promoter was only utilized after the cell experienced DNA damage. As a result, BCN5 synthesis is induced by treatment with UV light or mitomycin C. UviA is related to a special class of sigma factors found to date only in Clostridium species and responsible for activating transcription of toxin genes in Clostridium difficile, Clostridium tetani, and Clostridium botulinum.

  2. Actively Controlled Landing Gear for Aircraft Vibration Reduction

    NASA Technical Reports Server (NTRS)

    Horta, Lucas G.; Daugherty, Robert H.; Martinson, Veloria J.

    1999-01-01

    Concepts for long-range air travel are characterized by airframe designs with long, slender, relatively flexible fuselages. One aspect often overlooked is ground induced vibration of these aircraft. This paper presents an analytical and experimental study of reducing ground-induced aircraft vibration loads using actively controlled landing gears. A facility has been developed to test various active landing gear control concepts and their performance. The facility uses a NAVY A6-intruder landing gear fitted with an auxiliary hydraulic supply electronically controlled by servo valves. An analytical model of the gear is presented including modifications to actuate the gear externally and test data is used to validate the model. The control design is described and closed-loop test and analysis comparisons are presented.

  3. Optimizing Estimated Loss Reduction for Active Sampling in Rank Learning

    DTIC Science & Technology

    2008-01-01

    ranging from the income level to age and her preference order over a set of products (e.g. movies in Netflix ). The ranking task is to learn a map- ping...learners in RankBoost. However, in both cases, the proposed strategy selects the samples which are estimated to produce a faster convergence from the...steps in Section 5. 2. Related Work A number of strategies have been proposed for active learning in the classification framework. Some of those center

  4. Atmospheric modelling for NOMAD-UVIS on board the ExoMars Trace Gas Orbiter mission

    NASA Astrophysics Data System (ADS)

    Dawson, D. G.; Patel, M. R.; Lewis, S. R.

    2012-09-01

    The Ultraviolet and Visible Spectrometer (UVIS) instrument development process requires the construction of an atmospheric model to provide synthetic UV transmission spectra. We discuss the requirements of the model to enable observational limits to be found, and the potential for certain atmospheric parameters to be further constrained.

  5. Characterization of U(VI) Sorption-Desorption Processes and Model Upscaling

    SciTech Connect

    Bai, Jing; Dong, Wenming; Ball, William P.

    2006-10-12

    The objectives of the overall collaborative EMSP effort (with which this project is associated) were to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties and to relate such characterization both to fundamental molecular-scale understanding and field-scale models of geochemistry and mass transfer. The research was intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to allow the development of approaches by which laboratory-developed geochemical models could be upscaled for defensible field-scale predictions of uranium transport in the environment. Within this broader context, objectives of the JHU-based project were to test hypotheses regarding the coupled roles of adsorption and impermeable-zone diffusion in controlling the fate and transport of U(VI) species under conditions of comparatively short-term exposure. In particular, this work tested the following hypotheses: (1) the primary adsorption processes in the Hanford sediment over the pH range of 7 to 10 are surface complexation reactions of aqueous U(VI) hydroxycarbonate and carbonate complexes with amphoteric edge sites on detrital phyllosilicates in the silt/clay size fraction; (2) macroscopic adsorption intensity (at given aqueous conditions) is a function of mineral composition and aquatic chemistry; and (3) equilibrium sorption and desorption to apply in short-term, laboratory-spiked pristine sediments; and (4) interparticle diffusion can be fully understood in terms of a model that couples molecular diffusion of uranium species in the porewater with equilibrium sorption under the relevant aqueous conditions. The primary focus of the work was on developing and applying both models and experiments to test the applicability of "local equilibrium" assumptions in the modeling interpretation of sorption retarded interparticle diffusion, as relevant to processes of U(VI

  6. Real-Time Active Cosmic Neutron Background Reduction Methods

    SciTech Connect

    Mukhopadhyay, Sanjoy; Maurer, Richard; Wolff, Ronald; Mitchell, Stephen; Guss, Paul

    2013-09-01

    Neutron counting using large arrays of pressurized 3He proportional counters from an aerial system or in a maritime environment suffers from the background counts from the primary cosmic neutrons and secondary neutrons caused by cosmic ray-induced mechanisms like spallation and charge-exchange reaction. This paper reports the work performed at the Remote Sensing Laboratory–Andrews (RSL-A) and results obtained when using two different methods to reduce the cosmic neutron background in real time. Both methods used shielding materials with a high concentration (up to 30% by weight) of neutron-absorbing materials, such as natural boron, to remove the low-energy neutron flux from the cosmic background as the first step of the background reduction process. Our first method was to design, prototype, and test an up-looking plastic scintillator (BC-400, manufactured by Saint Gobain Corporation) to tag the cosmic neutrons and then create a logic pulse of a fixed time duration (~120 μs) to block the data taken by the neutron counter (pressurized 3He tubes running in a proportional counter mode). The second method examined the time correlation between the arrival of two successive neutron signals to the counting array and calculated the excess of variance (Feynman variance Y2F)1 in the neutron count distribution from Poisson distribution. The dilution of this variance from cosmic background values ideally would signal the presence of man-made neutrons.2 The first method has been technically successful in tagging the neutrons in the cosmic-ray flux and preventing them from being counted in the 3He tube array by electronic veto—field measurement work shows the efficiency of the electronic veto counter to be about 87%. The second method has successfully derived an empirical relationship between the percentile non-cosmic component in a neutron flux and the Y2F of the measured neutron count distribution. By using shielding materials alone, approximately 55% of the neutron flux

  7. Reductions in Northeast Refining Activity: Potential Implications for Petroleum Product Markets

    EIA Publications

    2011-01-01

    This report is the Energy Information Administration's (EIA) initial effort to provide information and analysis on the potential impacts on petroleum product markets from reductions in Northeast petroleum refining activity.

  8. A process for the purification of organochlorine contaminated activated carbon: Sequential solvent purging and reductive dechlorination.

    PubMed

    Lee, Matthew; Cord-Ruwisch, Ralf; Manefield, Mike

    2010-03-01

    A system for the purification of organochlorine contaminated activated carbon is described. The system involves a continuous flow of aqueous ethanol to purge organochlorines from activated carbon. The organochlorine laden solvent is simultaneously treated with zero valent zinc as the bulk electron source, water as the proton source and the electron shuttle cyanocobalamin as a catalyst for reductive dechlorination. The system was characterised by performing batch reactions and extractions before being applied in a continuous flow system. In particular the ratio of water to ethanol in the system needed to be optimised. Water is needed for the reductive dechlorination reaction whilst it is not conducive to the extraction process. An 80% ethanolic solution was found to give optimal reductive dechlorination rates without compromising extraction of organochlorines from activated carbon. Of three electron shuttles evaluated cyanocobalamin was discovered to be the most relevant to the system with respect to reductive dechlorination rates and its ability to avoid absorption to activated carbon.

  9. Probing the interaction of U(vi) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy.

    PubMed

    Uribe, Eva C; Mason, Harris E; Shusterman, Jennifer A; Bruchet, Anthony; Nitsche, Heino

    2016-06-21

    The fundamental interaction of U(vi) with diethylphosphatoethyl triethoxysilane functionalized SBA-15 mesoporous silica is studied by macroscopic batch experiments and solid-state NMR spectroscopy. DPTS-functionalized silica has been shown to extract U(vi) from nitric acid solutions at or above pH 3. Extraction is dependent on pH and ionic strength. Single-pulse (31)P NMR on U(vi) contacted samples revealed that U(vi) only interacts with a fraction of the ligands present on the surface. At pH 4 the U(vi) extraction capacity of the material is limited to 27-37% of the theoretical capacity, based on ligand loading. We combined single pulse (31)P NMR on U(vi)-contacted samples with batch studies to measure a ligand-to-metal ratio of approximately 2 : 1 at pH 3 and 4. Batch studies and cross-polarization NMR measurements reveal that U(vi) binds to deprotonated phosphonate and/or silanol sites. We use (31)P-(31)P DQ-DRENAR NMR studies to compare the average dipolar coupling between phosphorus spins for both U(vi)-complexed and non-complexed ligand environments. These measurements reveal that U(vi) extraction is not limited by inadequate surface distribution of ligands, but rather by low stability of the surface phosphonate complex.

  10. Extracellular reduction of uranium via Geobacter conductive pili as a protective cellular mechanism.

    PubMed

    Cologgi, Dena L; Lampa-Pastirk, Sanela; Speers, Allison M; Kelly, Shelly D; Reguera, Gemma

    2011-09-13

    The in situ stimulation of Fe(III) oxide reduction by Geobacter bacteria leads to the concomitant precipitation of hexavalent uranium [U(VI)] from groundwater. Despite its promise for the bioremediation of uranium contaminants, the biological mechanism behind this reaction remains elusive. Because Fe(III) oxide reduction requires the expression of Geobacter's conductive pili, we evaluated their contribution to uranium reduction in Geobacter sulfurreducens grown under pili-inducing or noninducing conditions. A pilin-deficient mutant and a genetically complemented strain with reduced outer membrane c-cytochrome content were used as controls. Pili expression significantly enhanced the rate and extent of uranium immobilization per cell and prevented periplasmic mineralization. As a result, pili expression also preserved the vital respiratory activities of the cell envelope and the cell's viability. Uranium preferentially precipitated along the pili and, to a lesser extent, on outer membrane redox-active foci. In contrast, the pilus-defective strains had different degrees of periplasmic mineralization matching well with their outer membrane c-cytochrome content. X-ray absorption spectroscopy analyses demonstrated the extracellular reduction of U(VI) by the pili to mononuclear tetravalent uranium U(IV) complexed by carbon-containing ligands, consistent with a biological reduction. In contrast, the U(IV) in the pilin-deficient mutant cells also required an additional phosphorous ligand, in agreement with the predominantly periplasmic mineralization of uranium observed in this strain. These findings demonstrate a previously unrecognized role for Geobacter conductive pili in the extracellular reduction of uranium, and highlight its essential function as a catalytic and protective cellular mechanism that is of interest for the bioremediation of uranium-contaminated groundwater.

  11. ACTINIC MASK INSPECTION AT THE ALS: RISK REDUCTION ACTIVITIES FOR 2003

    SciTech Connect

    Barty, A; Levesque, R; Ayers, J; Liu, Y; Gullikson, E; Barale, P

    2004-01-05

    This document reports on risk reduction activities performed at the VNL during CY2003 as a part of the Lith-343 actinic inspection project funded by International SEMATECH. The risk reduction activities described in this document comprise deliverable items 3.1.3, 3.1.4, 3.1.5 and 3.1.6 of Amendment 6 to the VNL EUV mask blank technology transfer contract.

  12. Potential Impacts of Reductions in Refinery Activity on Northeast Petroleum Product Markets

    EIA Publications

    2012-01-01

    Potential Impacts of Reductions in Refinery Activity on Northeast Petroleum Product Markets is an update to a previous Energy Information Administration (EIA) report, Reductions in Northeast Refining Activity: Potential Implications for Petroleum Product Markets, released in December 2011. This update analyzes possible market responses and impacts in the event Sunoco's Philadelphia refinery closes this summer, in addition to the recently idled refineries on the East Coast and in the U.S. Virgin Islands.

  13. Reduction of interior sound fields in flexible cylinders by active vibration control

    NASA Technical Reports Server (NTRS)

    Jones, J. D.; Fuller, C. R.

    1988-01-01

    The mechanisms of interior sound reduction through active control of a thin flexible shell's vibrational response are presently evaluated in view of an analytical model. The noise source is a single exterior acoustic monopole. The active control model is evaluated for harmonic excitation; the results obtained indicate spatially-averaged noise reductions in excess of 20 dB over the source plane, for acoustic resonant conditions inside the cavity.

  14. Revealing the Origin of Activity in Nitrogen-Doped Nanocarbons towards Electrocatalytic Reduction of Carbon Dioxide.

    PubMed

    Xu, Junyuan; Kan, Yuhe; Huang, Rui; Zhang, Bingsen; Wang, Bolun; Wu, Kuang-Hsu; Lin, Yangming; Sun, Xiaoyan; Li, Qingfeng; Centi, Gabriele; Su, Dangsheng

    2016-05-23

    Carbon nanotubes (CNTs) are functionalized with nitrogen atoms for reduction of carbon dioxide (CO2 ). The investigation explores the origin of the catalyst's activity and the role of nitrogen chemical states therein. The catalysts show excellent performances, with about 90 % current efficiency for CO formation and stability over 60 hours. The Tafel analyses and density functional theory calculations suggest that the reduction of CO2 proceeds through an initial rate-determining transfer of one electron to CO2 , which leads to the formation of carbon dioxide radical anion (CO2 (.-) ). The initial reduction barrier is too high on pristine CNTs, resulting in a very high overpotentials at which the hydrogen evolution reaction dominates over CO2 reduction. The doped nitrogen atoms stabilize the radical anion, thereby lowering the initial reduction barrier and improving the intrinsic activity. The most efficient nitrogen chemical state for this reaction is quaternary nitrogen, followed by pyridinic and pyrrolic nitrogen.

  15. Uranium Biomineralization By Natural Microbial Phosphatase Activities in the Subsurface

    SciTech Connect

    Taillefert, Martial

    2015-04-01

    This project investigated the geochemical and microbial processes associated with the biomineralization of radionuclides in subsurface soils. During this study, it was determined that microbial communities from the Oak Ridge Field Research subsurface are able to express phosphatase activities that hydrolyze exogenous organophosphate compounds and result in the non-reductive bioimmobilization of U(VI) phosphate minerals in both aerobic and anaerobic conditions. The changes of the microbial community structure associated with the biomineralization of U(VI) was determined to identify the main organisms involved in the biomineralization process, and the complete genome of two isolates was sequenced. In addition, it was determined that both phytate, the main source of natural organophosphate compounds in natural environments, and polyphosphate accumulated in cells could also be hydrolyzed by native microbial population to liberate enough orthophosphate and precipitate uranium phosphate minerals. Finally, the minerals produced during this process are stable in low pH conditions or environments where the production of dissolved inorganic carbon is moderate. These findings suggest that the biomineralization of U(VI) phosphate minerals is an attractive bioremediation strategy to uranium bioreduction in low pH uranium-contaminated environments. These efforts support the goals of the SBR long-term performance measure by providing key information on "biological processes influencing the form and mobility of DOE contaminants in the subsurface".

  16. Biomineralization of U(VI) phosphate promoted by microbially-mediated phytate hydrolysis in contaminated soils

    NASA Astrophysics Data System (ADS)

    Salome, Kathleen R.; Beazley, Melanie J.; Webb, Samuel M.; Sobecky, Patricia A.; Taillefert, Martial

    2017-01-01

    The bioreduction of uranium may immobilize a significant fraction of this toxic contaminant in reduced environments at circumneutral pH. In oxic and low pH environments, however, the low solubility of U(VI)-phosphate minerals also makes them good candidates for the immobilization of U(VI) in the solid phase. As inorganic phosphate is generally scarce in soils, the biomineralization of U(VI)-phosphate minerals via microbially-mediated organophosphate hydrolysis may represent the main immobilization process of uranium in these environments. In this study, contaminated sediments were incubated aerobically in two pH conditions to examine whether phytate, a naturally-occurring and abundant organophosphate in soils, could represent a potential phosphorous source to promote U(VI)-phosphate biomineralization by natural microbial communities. While phytate hydrolysis was not evident at pH 7.0, nearly complete hydrolysis was observed both with and without electron donor at pH 5.5, suggesting indigenous microorganisms express acidic phytases in these sediments. While the rate of hydrolysis of phytate generally increased in the presence of uranium, the net rate of inorganic phosphate production in solution was decreased and inositol phosphate intermediates were generated in contrast to similar incubations conducted without uranium. These findings suggest uranium stress enhanced the phytate-metabolism of the microbial community, while simultaneously inhibiting phosphatase production and/or activity by the indigenous population. Finally, phytate hydrolysis drastically decreased uranium solubility, likely due to formation of ternary sorption complexes, U(VI)-phytate precipitates, and U(VI)-phosphate minerals. Overall, the results of this study provide evidence for the ability of natural microbial communities to liberate phosphate from phytate in acidic sediments, possibly as a detoxification mechanism, and demonstrate the potential utility of phytate-promoted uranium

  17. RFI Risk Reduction Activities Using New Goddard Digital Radiometry Capabilities

    NASA Technical Reports Server (NTRS)

    Bradley, Damon; Kim, Ed; Young, Peter; Miles, Lynn; Wong, Mark; Morris, Joel

    2012-01-01

    The Goddard Radio-Frequency Explorer (GREX) is the latest fast-sampling radiometer digital back-end processor that will be used for radiometry and radio-frequency interference (RFI) surveying at Goddard Space Flight Center. The system is compact and deployable, with a mass of about 40 kilograms. It is intended to be flown on aircraft. GREX is compatible with almost any aircraft, including P-3, twin otter, C-23, C-130, G3, and G5 types. At a minimum, the system can function as a clone of the Soil Moisture Active Passive (SMAP) ground-based development unit [1], or can be a completely independent system that is interfaced to any radiometer, provided that frequency shifting to GREX's intermediate frequency is performed prior to sampling. If the radiometer RF is less than 200MHz, then the band can be sampled and acquired directly by the system. A key feature of GREX is its ability to simultaneously sample two polarization channels simultaneously at up to 400MSPS, 14-bit resolution each. The sampled signals can be recorded continuously to a 23 TB solid-state RAID storage array. Data captures can be analyzed offline using the supercomputing facilities at Goddard Space Flight Center. In addition, various Field Programmable Gate Array (FPGA) - amenable radiometer signal processing and RFI detection algorithms can be implemented directly on the GREX system because it includes a high-capacity Xilinx Virtex-5 FPGA prototyping system that is user customizable.

  18. Speciation-dependent microbial reduction of uranium within iron-coated sands.

    PubMed

    Neiss, Jim; Stewart, Brandy D; Nico, Peter S; Fendorf, Scott

    2007-11-01

    Transport of uranium within surface and subsurface environments is predicated largely on its redox state. Uranyl reduction may transpire through either biotic (enzymatic) or abiotic pathways; in either case, reduction of U(VI) to U(IV) results in the formation of sparingly soluble UO2 precipitates. Biological reduction of U(VI), while demonstrated as prolific under both laboratory and field conditions, is influenced by competing electron acceptors (such as nitrate, manganese oxides, or iron oxides) and uranyl speciation. Formation of Ca-UO2-CO3 ternary complexes, often the predominate uranyl species in carbonate-bearing soils and sediments, decreases the rate of dissimilatory U(VI) reduction. The combined influence of uranyl speciation within a mineralogical matrix comparable to natural environments and under hydrodynamic conditions, however, remains unresolved. We therefore examined uranyl reduction by Shewanella putrefaciens within packed mineral columns of ferrihydrite-coated quartz sand under conditions conducive or nonconducive to Ca-UO2-CO3 species formation. The results are dramatic. In the absence of Ca, where uranyl carbonato complexes dominate, U(VI) reduction transpires and consumes all of the U(VI) within the influent solution (0.166 mM) over the first 2.5 cm of the flow field for the entirety of the 54 d experiment. Over 2 g of U is deposited during this reaction period, and despite ferrihydrite being a competitive electron acceptor, uranium reduction appears unabated for the duration of our experiments. By contrast, in columns with 4 mM Ca in the influent solution (0.166 mM uranyl), reduction (enzymatic or surface-bound Fe(III) mediated) appears absent and breakthrough occurs within 18 d (at a flow rate of 3 pore volumes per day). Uranyl speciation, and in particular the formation of ternary Ca-UO2-CO3 complexes, has a profound impact on U(VI) reduction and thus transport within anaerobic systems.

  19. Uranium(VI) reduction by nanoscale zero-valent iron in anoxic batch systems: The role of Fe(II) and Fe(III)

    SciTech Connect

    Yan, Sen; Chen, Yongheng; Xiang, Wu; Bao, Zhengyu; Liu, Chongxuan; Deng, Baolin

    2014-12-01

    The role of Fe(II) and Fe(III) on U(VI) reduction by nanoscale zerovalent iron (nanoFe0) was investigated using two iron chelators 1,10-phenanthroline and triethanolamine (TEA) under a CO2-free anoxic condition. The results showed U(VI) reduction was strongly inhibited by 1,10-phenanthroline and TEA in a pH range from 6.92 to 9.03. For instance, at pH 6.92 the observed U(VI) reduction rates decreased by 80.7% and 82.3% in the presence of 1,10-phenanthroline and TEA, respectively. The inhibition was attributed to the formation of stable complexes between 1,10-phenanthroline and Fe(II) or TEA and Fe(III). In the absence of iron chelators, U(VI) reduction can be enhanced by surface-bound Fe(II) on nanoFe0. Our results suggested that Fe(III) and Fe(II) probably acted as an electron shuttle to mediate the transfer of electrons from nanoFe0 to U(VI), therefore a combined system with Fe(II), Fe(III) and nanoFe0 can facilitate the U(VI) reductive immobilization in the contaminated groundwater.

  20. Comparison of U(VI) adsorption onto nanoscale zero-valent iron and red soil in the presence of U(VI)-CO3/Ca-U(VI)-CO3 complexes.

    PubMed

    Zhang, Zhibin; Liu, Jun; Cao, Xiaohong; Luo, Xuanping; Hua, Rong; Liu, Yan; Yu, Xiaofeng; He, Likai; Liu, Yunhai

    2015-12-30

    The influence of U(VI)-CO3 and Ca-U(VI)-CO3 complexes on U(VI) adsorption onto red soil and nanoscale zero-valent iron (NZVI) was investigated using batch adsorption and fixed-bed column experiments to simulate the feasibility of NZVI as the reactive medium in permeable- reactive barriers (PRB) for in situ remediation of uranium-contaminated red soils. The adsorption capacity (qe) and distribution constant (Kd) of NZVI and red soil decreased with increasing pH, dissolved carbonate and calcium concentrations, but the qe and Kd values of NZVI were 5-10 times higher than those of red soil. The breakthrough pore volume (PV) values increased with the decrease of pH, dissolved carbonate and calcium concentration; however, the breakthrough PV values of the PRB column filled with 5% NZVI were 2.0-3.5 times higher than the 100% red soil column. The U(VI)-CO3 complexes adsorbed onto the surface of red soil/NZVI (≡SOH) to form SO-UO2CO3(-) or SO-UO2 (CO3)2(3-). XPS and XRD analysis further confirmed the reduction of U(VI) to U(IV) and the formation of FeOOH on NZVI surfaces. The findings of this study are significant to the remediation of uranium-contaminated red soils and the consideration of practical U(VI) species in the natural environment.

  1. Enhanced activity and selectivity of carbon nanofiber supported Pd catalysts for nitrite reduction.

    PubMed

    Shuai, Danmeng; Choe, Jong Kwon; Shapley, John R; Werth, Charles J

    2012-03-06

    Pd-based catalyst treatment represents an emerging technology that shows promise to remove nitrate and nitrite from drinking water. In this work we use vapor-grown carbon nanofiber (CNF) supports in order to explore the effects of Pd nanoparticle size and interior versus exterior loading on nitrite reduction activity and selectivity (i.e., dinitrogen over ammonia production). Results show that nitrite reduction activity increases by 3.1-fold and selectivity decreases by 8.0-fold, with decreasing Pd nanoparticle size from 1.4 to 9.6 nm. Both activity and selectivity are not significantly influenced by Pd interior versus exterior CNF loading. Consequently, turnover frequencies (TOFs) among all CNF catalysts are similar, suggesting nitrite reduction is not sensitive to Pd location on CNFs nor Pd structure. CNF-based catalysts compare favorably to conventional Pd catalysts (i.e., Pd on activated carbon or alumina) with respect to nitrite reduction activity and selectivity, and they maintain activity over multiple reduction cycles. Hence, our results suggest new insights that an optimum Pd nanoparticle size on CNFs balances faster kinetics with lower ammonia production, that catalysts can be tailored at the nanoscale to improve catalytic performance for nitrite, and that CNFs hold promise as highly effective catalyst supports in drinking water treatment.

  2. Upscaling of U(VI) Desorption and Transport from Decimeter-Scale Heterogeneity to Plume-Scale Modeling

    SciTech Connect

    Curtis, Gary P.; Kohler, Matthias; Kannappan, Ramakrishnan; Briggs, Martin; Day-Lewis, Fred

    2015-02-24

    Scientifically defensible predictions of field scale U(VI) transport in groundwater requires an understanding of key processes at multiple scales. These scales range from smaller than the sediment grain scale (less than 10 μm) to as large as the field scale which can extend over several kilometers. The key processes that need to be considered include both geochemical reactions in solution and at sediment surfaces as well as physical transport processes including advection, dispersion, and pore-scale diffusion. The research summarized in this report includes both experimental and modeling results in batch, column and tracer tests. The objectives of this research were to: (1) quantify the rates of U(VI) desorption from sediments acquired from a uranium contaminated aquifer in batch experiments;(2) quantify rates of U(VI) desorption in column experiments with variable chemical conditions, and(3) quantify nonreactive tracer and U(VI) transport in field tests.

  3. The Effect of Variable Geochemical Conditions on the Reactive Transport of U(VI) in Small Scale Tracer Tests

    NASA Astrophysics Data System (ADS)

    Curtis, G. P.; Fox, P.; Kohler, M.; Davis, J. A.

    2005-12-01

    Small-scale tracer tests were conducted to evaluate the effect of variable geochemical conditions on the reactive transport of U(VI). The tracer tests were conducted in a shallow alluvial aquifer downgradient from a former uranium mill and a tailings disposal area near Naturita, CO. The U(VI) concentration in the groundwater at the tracer test site was approximately 5 μM, the alkalinity was 8.5 meq/L and the pH was approximately 7.1. Previous studies at the site demonstrated the U(VI) was most sensitive to the alkalinity and least sensitive to the pH values relative to the range of measured values. Uranium migration tests were conducted on a scale of 1-2.5 m and considered variable U(VI) and alkalinity and included Br as an inert tracer. The tracer tests demonstrated that the sediment readily released U(VI) even after many years of contact with the contaminated groundwater suggesting the U(VI) migration is controlled by adsorption reactions. Reactive transport simulations used a surface complexation model developed independently from laboratory bench scale studies to simulate adsorption. The reactive transport simulations gave good predictions of the observed breakthrough of U(VI) when the advection and dispersion parameters were fitted to Br breakthrough. Field studies also included several single well push-pull tests that were conducted at increased and decreased U(VI) and alkalinity values. Reactive transport simulations of these experiments will be presented and compared with the tracer tests simulations.

  4. Effect of 57Fe-goethite Amendment on Microbial Community Composition and Dynamics During the Transition from Iron to Sulfate Reduction

    NASA Astrophysics Data System (ADS)

    Moon, H.; McGuiness, L.; Kukkadapu, R. K.; Peacock, A.; Komlos, J.; Kerkhof, L.; Long, P. E.; Jaffe, P. R.

    2009-12-01

    Due to an increasing interest in microbial biostimulation for the purpose of U(VI) bioreduction, which proceeds via iron reduction, there is a growing need for a better understanding of the associated biogeochemical dynamics. This includes Fe(III) availability as well as the microbial community changes, including the activity of iron-reducers during the biostimulation period even after the onset of sulfate reduction. An up-flow column experiment was conducted with Old Rifle site sediments, where half of the columns had sediment that was augmented with 57Fe-goethite to track minute goethite changes after the onset of sulfate reduction, and to study the effects of increased Fe(III) levels on the overall biostimulation dynamics. The addition of the 57Fe-goethite did not delay the onset of sulfate reduction, but slightly suppressed the overall rate of sulfate reduction and hence acetate utilization. Mossbauer analyses confirmed that there was bioavailable iron present after the onset of sulfate reduction and that iron was still being reduced during sulfate reduction. Addition of the 57Fe-goethite to the sediment had a noticeable effect on the overall composition of the microbial population. 16S rRNA analyses of biostimulatd sediment using TRFLP showed that Geobacter sp. were still active and replicating after sulfate reduction had occurred for over 30 days. DNA fingerprints of the sediment-attached microbial communities were dominated by 5 TRFs, that comprised 25-57 % of the total profile. Augmentation of sediments with the 57Fe-goethite resulted in somewhat higher numbers of Geobacter-like species throughout the experiment, and during sulfate reduction slightly lower numbers of sulfate reducers. These columns also had a slightly improved U(VI) removal efficiency, which might be attributed to the higher Geobacter-like numbers.

  5. Influence of ammonium availability on expression of nifD and amtB genes during biostimulation of a U(VI) contaminated aquifer: implications for U(VI) removal and monitoring the metabolic state of Geobacteraceae

    SciTech Connect

    Mouser, Paula J.; N'Guessan, A. Lucie; Elifantz, Hila; Holmes, Dawn E.; Williams, Kenneth H; Wilkins, Michael J.; Long, Philip E.; Lovley, Derek R.

    2009-03-25

    The influence of ammonium availability on bacterial community structure and the physiological status of Geobacter species during in situ bioremediation of uranium-contaminated groundwater was evaluated. Ammonium concentrations varied by 2 orders of magnitude (<4 to 400 ?M) across the study site. Analysis of 16S rRNA sequences suggested that ammonium may have been one factor influencing the community composition prior to acetate amendment with Rhodoferax species predominating over Geobacter species with higher ammonium and Dechloromonas species dominating at the site with lowest ammonium. However, once acetate was added and dissimilatory metal reduction was stimulated, Geobacter species became the predominant organisms at all locations. Rates of U(VI) reduction appeared to be more related to acetate concentrations rather than ammonium levels. In situ mRNA transcript abundance of the nitrogen fixation gene, nifD, and the ammonium transporter gene, amtB, in Geobacter species indicated that ammonium was the primary source of nitrogen during uranium reduction. The abundance of amtB was inversely correlated to ammonium levels, whereas nifD transcript levels were similar across all sites examined. These results suggest that nifD and amtB expression are closely regulated in response to ammonium availability to ensure an adequate supply of nitrogen while conserving cell resources. Thus, quantifying nifD and amtB transcript expression appears to be a useful approach for monitoring the nitrogen-related physiological status of subsurface Geobacter species. This study also emphasizes the need for more detailed analysis of geochemical and physiological interactions at the field scale in order to adequately model subsurface microbial processes during bioremediation.

  6. Probing the interaction of U(VI) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy

    DOE PAGES

    Uribe, Eva C.; Mason, Harris E.; Shusterman, Jennifer A.; ...

    2016-05-30

    The fundamental interaction of U(VI) with diethylphosphatoethyl triethoxysilane functionalized SBA-15 mesoporous silica is studied by macroscopic batch experiments and solid-state NMR spectroscopy. DPTS-functionalized silica has been shown to extract U(VI) from nitric acid solutions at or above pH 3. Extraction is dependent on pH and ionic strength. Single-pulse 31P NMR on U(VI) contacted samples revealed that U(VI)only interacts with a fraction of the ligands present on the surface. At pH 4 the U(VI) extraction capacity of the material is limited to 27–37% of the theoretical capacity, based on ligand loading. We combined single pulse 31P NMR on U(VI)-contacted samples withmore » batch studies to measure a ligand-to-metal ratio of approximately 2 : 1 at pH 3 and 4. Batch studies and cross-polarization NMR measurements reveal that U(VI) binds to deprotonated phosphonate and/or silanol sites. We use 31P–31P DQ-DRENAR NMR studies to compare the average dipolar coupling between phosphorus spins for both U(VI)-complexed and non-complexed ligand environments. Furthermore, these measurements reveal that U(VI) extraction is not limited by inadequate surface distribution of ligands, but rather by low stability of the surface phosphonate complex.« less

  7. Uranium(VI) reduction by iron(II) monosulfide mackinawite.

    PubMed

    Hyun, Sung Pil; Davis, James A; Sun, Kai; Hayes, Kim F

    2012-03-20

    Reaction of aqueous uranium(VI) with iron(II) monosulfide mackinawite in an O(2) and CO(2) free model system was studied by batch uptake measurements, equilibrium modeling, and L(III) edge U X-ray absorption spectroscopy (XAS). Batch uptake measurements showed that U(VI) removal was almost complete over the wide pH range between 5 and 11 at the initial U(VI) concentration of 5 × 10(-5) M. Extraction by a carbonate/bicarbonate solution indicated that most of the U(VI) removed from solution was reduced to nonextractable U(IV). Equilibrium modeling using Visual MINTEQ suggested that U was in equilibrium with uraninite under the experimental conditions. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy showed that the U(IV) phase associated with mackinawite was uraninite. Oxidation experiments with dissolved O(2) were performed by injecting air into the sealed reaction bottles containing mackinawite samples reacted with U(VI). Dissolved U measurement and XAS confirmed that the uraninite formed from the U(VI) reduction by mackinawite did not oxidize or dissolve under the experimental conditions. This study shows that redox reactions between U(VI) and mackinawite may occur to a significant extent, implying an important role of the ferrous sulfide mineral in the redox cycling of U under sulfate reducing conditions. This study also shows that the presence of mackinawite protects uraninite from oxidation by dissolved O(2). The findings of this study suggest that uraninite formation by abiotic reduction by the iron sulfide mineral under low temperature conditions is an important process in the redistribution and sequestration of U in the subsurface environments at U contaminated sites.

  8. Key Factors Influencing Rates of Heterotrophic Sulfate Reduction in Active Seafloor Hydrothermal Massive Sulfide Deposits

    PubMed Central

    Frank, Kiana L.; Rogers, Karyn L.; Rogers, Daniel R.; Johnston, David T.; Girguis, Peter R.

    2015-01-01

    Hydrothermal vents are thermally and geochemically dynamic habitats, and the organisms therein are subject to steep gradients in temperature and chemistry. To date, the influence of these environmental dynamics on microbial sulfate reduction has not been well constrained. Here, via multivariate experiments, we evaluate the effects of key environmental variables (temperature, pH, H2S, SO42−, DOC) on sulfate reduction rates and metabolic energy yields in material recovered from a hydrothermal flange from the Grotto edifice in the Main Endeavor Field, Juan de Fuca Ridge. Sulfate reduction was measured in batch reactions across a range of physico-chemical conditions. Temperature and pH were the strongest stimuli, and maximum sulfate reduction rates were observed at 50°C and pH 6, suggesting that the in situ community of sulfate-reducing organisms in Grotto flanges may be most active in a slightly acidic and moderate thermal/chemical regime. At pH 4, sulfate reduction rates increased with sulfide concentrations most likely due to the mitigation of metal toxicity. While substrate concentrations also influenced sulfate reduction rates, energy-rich conditions muted the effect of metabolic energetics on sulfate reduction rates. We posit that variability in sulfate reduction rates reflect the response of the active microbial consortia to environmental constraints on in situ microbial physiology, toxicity, and the type and extent of energy limitation. These experiments help to constrain models of the spatial contribution of heterotrophic sulfate reduction within the complex gradients inherent to seafloor hydrothermal deposits. PMID:26733984

  9. U(VI) bioreduction with emulsified vegetable oil as the electron donor-Model application to a field test

    SciTech Connect

    Tang, Guoping; Watson, David B; Wu, Wei-min; Schadt, Christopher Warren; Parker, Jack C; Brooks, Scott C

    2013-01-01

    A one-time 2-hour emulsified vegetable oil (EVO) injection in a fast flowing aquifer decreased U discharge to a stream for over a year. Using a comprehensive biogeochemical model developed in the companion article based on microcosm tests, we approximately matched the observed acetate, nitrate, Fe, U, and sulfate concentrations, and described the major evolution trends of multiple microbial functional groups in the field test. While the lab-determined parameters were generally applicable in the field-scale simulation, the EVO hydrolysis rate constant was estimated to be an order of magnitude greater in the field than in the microcosms. The model predicted substantial biomass (sulfate reducers) and U(IV) accumulation near the injection wells and along the side boundaries of the treatment zone where electron donors (long-chain fatty acids) from the injection wells met electron acceptors (sulfate) from the surrounding environment. While EVO retention and hydrolysis characteristics were expected to control treatment longevity, modeling results indicated that electron acceptors such as sulfate may not only compete for electrons but also play a conducive role in degrading complex substrates and enhancing U(VI) reduction and immobilization. As a result, the spacing of the injection wells could be optimized for effective sustainable bioremediation.

  10. Observation of CI FUV emissions from the Venus thermosphere using Cassini-UVIS

    NASA Astrophysics Data System (ADS)

    Hubert, B. A.; Gerard, J. M.; Bisikalo, D. V.; Shematovich, V. I.; Gladstone, R.

    2011-12-01

    The Cassini spacecraft was launched on 15 October 1997. On its long journey to Saturn, the spacecraft took a gravitational assist to gain energy from Venus on 24 June 1999. The UVIS instrument on board Cassini obtained a series of FUV spectra during this flyby, while the solar F10.7 index was larger than 200 at Earth orbit. The UVIS instrument obtained ultraviolet spectra of Venus with a still unmatched spectral resolution of ~0.37 nm. We developed a least squares fit method able to extract the intensity of most of the emissions present in the instrument passband, that has already been used to quantify the CO Fourth Positive spectral system and oxygen emissions, among others. We identify several emissions of the carbon atom in the UVIS spectra, and estimate their intensity. In particular, we extract the intensity of the CI - 126.1, 156.1 and 165.7 nm multiplets, for every dayglow spectra recorded by UVIS along the Cassini track. These intensities are compared with a full radiative transfer modeling of these emissions, that includes the known photochemical sources of photons and resonant scattering of sunlight. The carbon density profile of the Venus thermosphere has never been directly measured and is taken from a photochemical model. We find a serious disagreement between observation and modeling that can be accounted for by applying a correction factor to the carbon column. This needed correction factor is found to increase monotonically as the solar zenith angle decreases, suggesting a possible photochemical origin to the disagreement, possibly involving the photochemistry of molecular oxygen to which the carbon density is highly sensitive.

  11. Boreal winter comparison of auroral images from Polar UVI and IMAGE FUV

    NASA Astrophysics Data System (ADS)

    Spann, J. F.; Germany, G.; Maddox, W.; Fillingim, M.; Parks, G.; Mende, S.

    2004-12-01

    Same-scene images made with Polar UVI and IMAGE FUV are compared for the boreal winter of 2000-2001. The results of the comparison are used to determine whether the use of both instruments could lead to a better evaluation of the average precipitation and total energy input than with either one individually. These results are a part of a broader investigation to quantitatively compare conjugate images using both instruments and to correlate observed asymmetries with solar wind and seasonal parameters.

  12. Effect of oxidation and catalytic reduction of trace organic contaminants on their activated carbon adsorption.

    PubMed

    Schoutteten, Klaas V K M; Hennebel, Tom; Dheere, Ellen; Bertelkamp, Cheryl; De Ridder, David J; Maes, Synthia; Chys, Michael; Van Hulle, Stijn W H; Vanden Bussche, Julie; Vanhaecke, Lynn; Verliefde, Arne R D

    2016-12-01

    The combination of ozonation and activated carbon (AC) adsorption is an established technology for removal of trace organic contaminants (TrOCs). In contrast to oxidation, reduction of TrOCs has recently gained attention as well, however less attention has gone to the combination of reduction with AC adsorption. In addition, no literature has compared the removal behavior of reduction vs. ozonation by-products by AC. In this study, the effect of pre-ozonation vs pre-catalytic reduction on the AC adsorption efficiency of five TrOCs and their by-products was compared. All compounds were susceptible to oxidation and reduction, however the catalytic reductive treatment proved to be a slower reaction than ozonation. New oxidation products were identified for dinoseb and new reduction products were identified for carbamazepine, bromoxynil and dinoseb. In terms of compatibility with AC adsorption, the influence of the oxidative and reductive pretreatments proved to be compound dependent. Oxidation products of bromoxynil and diatrizoic acid adsorbed better than their parent TrOCs, but oxidation products of atrazine, carbamazepine and dinoseb showed a decreased adsorption. The reductive pre-treatment showed an enhanced AC adsorption for dinoseb and a major enhancement for diatrizoic acid. For atrazine and bromoxynil, no clear influence on adsorption was noted, while for carbamazepine, the reductive pretreatment resulted in a decreased AC affinity. It may thus be concluded that when targeting mixtures of TrOCs, a trade-off will undoubtedly have to be made towards overall reactivity and removal of the different constituents, since no single treatment proves to be superior to the other.

  13. Gender-dependent reduction of spontaneous motor activity and growth in rats subjected to portacaval shunt.

    PubMed

    Conjeevaram, H S; Mullen, K D; May, E J; McCullough, A J

    1994-02-01

    Alterations in behavior are frequently described in rats subjected to portacaval shunt. Previous work has reported reduced spontaneous motor activity in various settings (nighttime, red light, decreased illumination) in this animal model. We investigated this phenomenon in rats of both genders subjected to portacaval shunt to determine whether our previously observed divergent growth patterns (males reduced, females unchanged) had any impact on the alterations in spontaneous motor activity in this model. Dietary intake, growth, motor activity and serum ammonia and amino acid concentrations were measured, in addition to final liver and spleen weights, in each animal after 3 to 4 wk of observation. Our results reconfirm the differential impact of portacaval shunt on growth in male (35% reduction p < 0.01) but not female rats (5% reduction, NS) compared with their respective-gender sham-operated controls. In addition, spontaneous motor activity was significantly reduced in male (congruent to 50%, p = 0.01) but not female rats subjected to portacaval shunt. The reduction of activity in male rats subjected to portacaval shunt did not correlate with any of the measured biochemical data or calculated nutritional/growth parameters. Thus we observed gender-dependent reduction in spontaneous motor activity after portacaval shunt in the rat. The mechanism for this phenomenon is unknown, but it is easily investigated with this reproducible model.

  14. Cryogenic Laser Induced Fluorescence Characterization of U(VI) in Hanford Vadose Zone Pore Waters

    SciTech Connect

    Wang, Zheming; Zachara, John M.; Yantasee, Wassana; Gassman, Paul L.; Liu, Chongxuan; Joly, Alan G.

    2004-11-01

    Ambient and liquid helium temperature laser-induced time-resolved uranyl fluorescence spectroscopy was applied to study the speciation of aqueous uranyl solutions containing carbonate and phosphate and two porewater samples obtained by ultra-centrifugation of U(VI)-contaminated sediments. The significantly enhanced fluorescence signal intensity and spectral resolution found at liquid helium temperature allowed, for the first time, direct fluorescence spectroscopic observation of the higher aqueous uranyl complexes with carbonate: UO2(CO3)22-, UO2(CO3)34- and (UO2)2(OH)3CO3-. The porewater samples were non-fluorescent at room temperature. However, at liquid helium temperature, both porewater samples displayed strong, well-resolved fluorescence spectra. Comparisons of the spectroscopic characteristics of the porewaters with those of the standard uranyl-carbonate complexes confirmed that U(VI) in the porewaters existed primarily as UO2(CO3)34-. A small amount of the dicalcium-urano-tricarbonate complex, Ca2UO2(CO3)3, was also observed that was consistent with thermodynamic calculation. The U(VI)-carbonate complex is apparently the mobile species responsible for the subsurface migration of U(VI), even though the majority of the in-ground U(VI) inventory at the site from which the samples were obtained exists as intragrain U(VI)-silicate precipitates.

  15. HST/WFC3: Evolution of the UVIS Channel's Charge Transfer Efficiency

    NASA Astrophysics Data System (ADS)

    Gosmeyer, Catherine; Baggett, Sylvia M.; Anderson, Jay; WFC3 Team

    2016-06-01

    The Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) contains both an IR and a UVIS channel. After more than six years on orbit, the UVIS channel performance remains stable; however, on-orbit radiation damage has caused the charge transfer efficiency (CTE) of UVIS's two CCDs to degrade. This degradation is seen as vertical charge 'bleeding' from sources during readout and its effect evolves as the CCDs age. The WFC3 team has developed software to perform corrections that push the charge back to the sources, although it cannot recover faint sources that have been bled out entirely. Observers can mitigate this effect in various ways such as by placing sources near the amplifiers, observing bright targets, and by increasing the total background to at least 12 electrons, either by using a broader filter, lengthening exposure time, or post-flashing. We present results from six years of calibration data to re-evaluate the best level of total background for mitigating CTE loss and to re-verify that the pixel-based CTE correction software is performing optimally over various background levels. In addition, we alert observers that CTE-corrected products are now available for retrieval from MAST as part of the CALWF3 v3.3 pipeline upgrade.

  16. Uranium Redox Transformations after U(VI) Coprecipitation with Magnetite Nanoparticles.

    PubMed

    Pidchenko, Ivan; Kvashnina, Kristina O; Yokosawa, Tadahiro; Finck, Nicolas; Bahl, Sebastian; Schild, Dieter; Polly, Robert; Bohnert, Elke; Rossberg, André; Göttlicher, Jörg; Dardenne, Kathy; Rothe, Jörg; Schäfer, Thorsten; Geckeis, Horst; Vitova, Tonya

    2017-02-21

    Uranium redox states and speciation in magnetite nanoparticles coprecipitated with U(VI) for uranium loadings varying from 1000 to 10 000 ppm are investigated by X-ray absorption spectroscopy (XAS). It is demonstrated that the U M4 high energy resolution X-ray absorption near edge structure (HR-XANES) method is capable to clearly characterize U(IV), U(V), and U(VI) existing simultaneously in the same sample. The contributions of the three different uranium redox states are quantified with the iterative transformation factor analysis (ITFA) method. U L3 XAS and transmission electron microscopy (TEM) reveal that initially sorbed U(VI) species recrystallize to nonstoichiometric UO2+x nanoparticles within 147 days when stored under anoxic conditions. These U(IV) species oxidize again when exposed to air. U M4 HR-XANES data demonstrate strong contribution of U(V) at day 10 and that U(V) remains stable over 142 days under ambient conditions as shown for magnetite nanoparticles containing 1000 ppm U. U L3 XAS indicates that this U(V) species is protected from oxidation likely incorporated into octahedral magnetite sites. XAS results are supported by density functional theory (DFT) calculations. Further characterization of the samples include powder X-ray diffraction (pXRD), scanning electron microscopy (SEM) and Fe 2p X-ray photoelectron spectroscopy (XPS).

  17. An Assessment of U(VI) removal from groundwater using biochar produced from hydrothermal carbonization.

    PubMed

    Kumar, Sandeep; Loganathan, Vijay A; Gupta, Ram B; Barnett, Mark O

    2011-10-01

    The ever-increasing growth of biorefineries is expected to produce huge amounts of lignocellulosic biochar as a byproduct. The hydrothermal carbonization (HTC) process to produce biochar from lignocellulosic biomass is getting more attention due to its inherent advantage of using wet biomass. In the present study, biochar was produced from switchgrass at 300 °C in subcritical water and characterized using X-ray diffraction, fourier transform infra-red spectroscopy, scanning electron micrcoscopy, and thermogravimetric analysis. The physiochemical properties indicated that biochar could serve as an excellent adsorbent to remove uranium from groundwater. A batch adsorption experiment at the natural pH (~3.9) of biochar indicated an H-type isotherm. The adsorption data was fitted using a Langmuir isotherm model and the sorption capacity was estimated to be ca. 2.12 mg of U g(-1) of biochar. The adsorption process was highly dependent on the pH of the system. An increase towards circumneutral pH resulted in the maximum adsorption of ca. 4 mg U g(-1) of biochar. The adsorption mechanism of U(VI) onto biochar was strongly related to its pH-dependent aqueous speciation. The results of the column study indicate that biochar could be used as an effective adsorbent for U(VI), as a reactive barrier medium. Overall, the biochar produced via HTC is environmentally benign, carbon neutral, and efficient in removing U(VI) from groundwater.

  18. Adsorption of U(VI) on sericite in the presence of Bacillus subtilis: A combined batch, EXAFS and modeling techniques

    NASA Astrophysics Data System (ADS)

    Sun, Yubing; Zhang, Rui; Ding, Congcong; Wang, Xiangxue; Cheng, Wencai; Chen, Changlun; Wang, Xiangke

    2016-05-01

    The effect of Bacillus subtilis (B. subtilis) on the adsorption of U(VI) onto sericite was investigated using batch, EXAFS and modeling techniques. The batch adsorption indicated that the increased adsorption of U(VI) on sericite + B. subtilis systems at pH < 5.0 was predominantly attributed to the formation of inner-sphere complexes between U(VI) and surface functional groups of B. subtilis, whereas the inhibited adsorption was observed at pH > 6.0 due to the combination of deprotonated carboxyl groups of B. subtilis with the hydroxyl of sericite. The slightly enhanced adsorption of U(VI) on sericite + B. subtilis with increasing CO2 contents at pH < 6.0 was ascribed to the electrostatic attraction between positively charged U(VI) species (UO22+ species) and negatively charged surface of sericite + B. subtilis, whereas the U(VI) adsorption sharply decreased at pH > 7.0 owing to electrostatic repulsion between negatively charged sericite + B. subtilis and negatively charged U(VI) species such as UO2(OH)3- or UO2(CO3)22- species. According to EXAFS analysis, the increased adsorption mechanism of U(VI) on sericite + B. subtilis at pH 4.0 was attributed to the formation of U-P shell, whereas the bidentate inner-sphere surface complexes was also observed at pH 7.0 due to the formation of U-C shell (2.92 Å) and/or U-Si/Al (3.18 Å) shell. Under the range of allowable error, the pH-dependent and isothermal adsorption of U(VI) on sericite + B. subtilis can be fitted by surface complexation modeling using ion exchange and surface complexation reaction by using equilibrium parameters obtained from each binary systems. These findings are important to understand the fate and transport of U(VI) on the mineral-bacteria ternary systems in the near-surface environment.

  19. Uranium(VI) Reduction by Nanoscale Zerovalent Iron in Anoxic Batch Systems

    SciTech Connect

    Yan, Sen; Hua, Bin; Bao, Zhengyu; Yang, John; Liu, Chongxuan; Deng, Baolin

    2010-11-17

    This study investigated the influences of pH, bicarbonate, and calcium on U(VI) adsorption and reduction by synthetic nanosize zero valent iron (nano Fe0) particles under an anoxic condition. The results showed that about 87.1%, 82.7% and 78.3% of U(VI) could be reduced within 96 hours in the presence of 10 mM bicarbonate at pHs 6.92, 8.03 and 9.03, respectively. The rates of U(VI) reduction and adsorption by nano Fe0, however, varied significantly with increasing pH and concentrations of bicarbonate and/or calcium. Solid phase analysis by X-ray photoelectron spectroscopy confirmed the formation of UO2 and iron (hydr)oxides as a result of the redox interactions between adsorbed U(VI) and nano Fe0. This study highlights the potential important role of groundwater chemical composition in controlling the rates of U(VI) reductive immobilization using nano Fe0 in subsurface environments.

  20. Microbial Reduction of Uranium under Iron- and Sulfate-reducing Conditions: Effect of Amended Goethite on Microbial Community Composition and Dynamics

    SciTech Connect

    Moon, Hee Sun; McGuinness, L.; Kukkadapu, Ravi K.; Peacock, Aaron D.; Komlos, John; Kerkhoff, Lee; Long, Philip E.; Jaffe, Peter R.

    2010-07-01

    There is a growing need for a better understanding of the biogeochemical dynamics involved in microbial U(VI) reduction due to an increasing interest in using biostimulation via electron donor addition as a means to remediate uranium contaminated sites. U(VI) reduction has been observed to be maximized during iron reducing conditions and to decrease upon commencement of sulfate reducing conditions. There are many unknowns regarding the impact of iron/sulfate biogeochemistry on U(VI) reduction. This includes Fe(III) availability as well as the microbial community changes, including the activity of iron-reducers during the uranium biostimulation period even after the onset of sulfate reduction. Up-flow column experiments were conducted with Old Rifle site sediments containing Fe-oxides, Fe-clays, and sulfate rich groundwater. Half of the columns had sediment that was augmented with small amounts of small-particle 57Fe-goethite to track continuously minute goethite changes, and to study the effects of increased Fe(III) levels on the overall biostimulation dynamics. The addition of the 57Fe-goethite did not delay the onset of sulfate reduction, but slightly suppressed the overall rate of sulfate reduction and hence acetate utilization, it did not affect the bacterial numbers of Geobacter-like species throughout the experiment, but did lower the numbers of sulfate reducers in the sediments. 57Fe-Mössbauer analyses (a 57Fe-specific technique) confirmed that there was bioavailable iron present after the onset of sulfate reduction and that iron was still being reduced during sulfate reduction. Addition of the 57Fe-goethite to the sediment had a noticeable effect on the overall composition of the microbial population. 16S rRNA analyses of biostimulated sediment using TRFLP (terminal restriction fragment length polymorphism) showed that Geobacter sp. (a known Fe-reducer) was still active and replicating during the period of significant sulfate reduction. DNA fingerprints of

  1. Altered biologic activities of commercial polychlorinated biphenyl mixtures after microbial reductive dechlorination.

    PubMed Central

    Mousa, M A; Ganey, P E; Quensen, J F; Madhukar, B V; Chou, K; Giesy, J P; Fischer, L J; Boyd, S A

    1998-01-01

    The reductive dechlorination of polychlorinated biphenyls (PCBs) by anaerobic bacteria has recently been established as an important environmental fate of these compounds. This process removes chlorines directly from the biphenyl ring with replacement by hydrogen, resulting in a product mixture in which the average number of chlorines per biphenyl is reduced. In this study, dechlorination of commercial PCB mixtures (Aroclors 1242 and 1254) by microorganisms eluted from PCB-contaminated sediments of the River Raisin (Michigan) and Silver Lake (Massachusetts) caused a depletion in the proportion of highly chlorinated PCB congeners and an accumulation of lesser-chlorinated congeners. Dechlorination occurred primarily at the meta and, to a much lesser extent, para positions of biphenyl. The concentrations of the coplanar congeners including 3,3',4,4',5-pentachlorobiphenyl, the most potent dioxinlike congener, were significantly lowered by reductive dechlorination. Microbial reductive dechlorination of commercial PCB mixtures caused a substantial reduction in biologic activities in several instances. It significantly lowered or eliminated the inhibitory effects of Aroclors on fertilization of mouse gametes in vitro. Similarly, the dechlorinated product mixtures had substantially lower ethoxyresorufin-O-deethylase induction potencies and showed less ability to induce activating protein 1 transcription factor activity as compared to the unaltered Aroclors. In other assays the same dechlorinated product mixtures demonstrated biologic activities similar to the nondechlorinated Aroclors, including the ability of PCB mixtures to stimulate insulin secretion and cause neutrophil activation. The data presented here establish that the biologic activities of commercial PCB mixtures are altered by microbial reductive dechlorination and that an assessment of their toxic potential requires an array of tests that include the different mechanisms associated with PCBs. Images Figure 2

  2. Identification of proteins capable of metal reduction from the proteome of the Gram-positive bacterium Desulfotomaculum reducens MI-1 using an NADH-based activity assay

    PubMed Central

    Otwell, A.E.; Sherwood, R.W.; Zhang, S.; Nelson, O.D.; Li, Z.; Lin, H.; Callister, S.J.; Richardson, R.E.

    2015-01-01

    Summary Understanding of microbial metal reduction is based almost solely on studies of Gram-negative organisms. In this study, we focus on Desulfotomaculum reducens MI-1, a Gram-positive metal reducer whose genome lacks genes with similarity to any characterized metal reductase. Using non-denaturing separations and mass spectrometry identification, in combination with a colorimetric screen for chelated Fe(III)-NTA reduction with NADH as electron donor, we have identified proteins from the D. reducens proteome not previously characterized as iron reductases. Their function was confirmed by heterologous expression in E. coli. Furthermore, we show that these proteins have the capability to reduce soluble Cr(VI) and U(VI) with NADH as electron donor. The proteins identified are NADH:flavin oxidoreductase (Dred_2421) and a protein complex composed of oxidoreductase FAD/NAD(P)-binding subunit (Dred_1685) and dihydroorotate dehydrogenase 1B (Dred_1686). Dred_2421 was identified in the soluble proteome and is predicted to be a cytoplasmic protein. Dred_1685 and Dred_1686 were identified in both the soluble as well as the insoluble protein fraction, suggesting a type of membrane-association, although PSORTb predicts both proteins are cytoplasmic. This study is the first functional proteomic analysis of D. reducens and one of the first analyses of metal and radionuclide reduction in an environmentally relevant Gram-positive bacterium. PMID:25389064

  3. Deriving the Structure and Composition of Enceladus’ Plume from Cassini UVIS Observations

    NASA Astrophysics Data System (ADS)

    Hansen, Candice; Esposito, Larry; Colwell, Josh; Hendrix, Amanda; Portyankina, Ganna; Shemansky, Don; West, Robert

    2015-11-01

    Cassini’s Ultraviolet Imaging Spectrograph (UVIS) has observed 4 stellar and one solar occultation by Enceladus’ water vapor plume. The July 2005 occultation observation established that water is the primary constituent of the plume [1], and allowed us to calculate the flux of water coming from the plume; the 2007 occultation showed super-sonic jets of gas imbedded within the plume [2]. The solar occultation observation set upper limits for N2 as a constituent of the plume and provided higher resolution data on the jets [3]. On 19 October 2011, epsilon and zeta Orionis were simultaneously occulted by the plume. The stars were in separate pixels on the detector, separated by 24 mrad, or ~20 km, with the lower altitude star (epsilon Orionis) 18 km above the limb at its closest point. The profile at two altitudes shows evidence for a new gas jet location, possibly between dust jet #50 and #51 identified in [4].Results from the assemblage of these data sets, with implications for the composition and vertical structure of the plume and jets, will be described. Gas being expelled from the “tiger stripe” fissures is largely on a vertical escape trajectory away from Enceladus. Upper limits are set for water vapor near the limb at latitudes well away from the south pole at 3 x 1015 cm-2. Upper limits are set for the amount of ethylene and H2 in the plume, two species of interest to the chemistry of the plume [5]. No hydrogen or oxygen emission features have been observed from Enceladus’ water vapor plume, in contrast to the purported plumes at Europa, probably due to the very different plasma environment at Saturn. Data have now been processed consistently for all occultations with slightly different results for water vapor supply to the Saturn magnetosphere than previously reported. Overall, eruptive activity has been steady to within ~20% from 2005 to 2011.References: [1] Hansen, C. J. et al., Science 311:1422 (2006). Hansen, C. J. et al., Nature 456:477 (2008

  4. Active Pt3Ni (111) Surface of Pt3Ni Icosahedron for Oxygen Reduction.

    PubMed

    Zhu, Jianbing; Xiao, Meiling; Li, Kui; Liu, Changpeng; Zhao, Xiao; Xing, Wei

    2016-11-09

    Highly active, durable oxygen reduction reaction (ORR) electrocatalysts are extremely important for fuel cell applications. Herein, we provide an efficient way to synthesis of activity Pt3M icosahedra by the one-pot hydrothermal method in the presence of glucosamine which can well adjust the reduction rate of Pt(4+) and efficiently control the morphology of final catalysts. Compared to Pt/C, the Pt3Ni icosahedra show 32-fold and 12-fold enhancement in specific and mass activity, respectively. Furthermore, robust durability was also observed in the accelerated durability test. Thus, this Pt3Ni icosahedron is found among the best Pt-based ORR catalysts, moreover, the findings also demonstrate how to mimic active extended surfaces in nanoscale.

  5. Reduction of Helicopter Blade-Vortex Interaction Noise by Active Rotor Control Technology

    NASA Technical Reports Server (NTRS)

    Yu, Yung H.; Gmelin, Bernd; Splettstoesser, Wolf; Brooks, Thomas F.; Philippe, Jean J.; Prieur, Jean

    1997-01-01

    Helicopter blade-vortex interaction noise is one of the most severe noise sources and is very important both in community annoyance and military detection. Research over the decades has substantially improved basic physical understanding of the mechanisms generating rotor blade-vortex interaction noise and also of controlling techniques, particularly using active rotor control technology. This paper reviews active rotor control techniques currently available for rotor blade vortex interaction noise reduction, including higher harmonic pitch control, individual blade control, and on-blade control technologies. Basic physical mechanisms of each active control technique are reviewed in terms of noise reduction mechanism and controlling aerodynamic or structural parameters of a blade. Active rotor control techniques using smart structures/materials are discussed, including distributed smart actuators to induce local torsional or flapping deformations, Published by Elsevier Science Ltd.

  6. Rice (Oryza sativa L.) roots have iodate reduction activity in response to iodine

    PubMed Central

    Kato, Shota; Wachi, Takanori; Yoshihira, Kei; Nakagawa, Takuya; Ishikawa, Akifumi; Takagi, Daichi; Tezuka, Aya; Yoshida, Hideharu; Yoshida, Satoshi; Sekimoto, Hitoshi; Takahashi, Michiko

    2013-01-01

    Although iodine is not an essential nutrient for higher plants, their roots take up and transport the element. However, the exact mechanisms involved in iodine uptake and metabolism in higher plants have yet to be elucidated. In this study, we compared two cultivars differing in iodine tolerance (“Nipponbare” and “Gohyakumangoku”) to increasing levels of I− and IO−3 in the root solutions of water-cultured rice (Oryza sativa L.). We found that IO−3 added to the root solutions was converted to I− in the presence of roots. Iodate reduction occurred over the course of several hours. Furthermore, the iodate reduction activity of “Nipponbare” (iodine-sensitive) and “Gohyakumangoku” (iodine-tolerant) roots increased after adding IO−3 or I−. The roots of barley and soybean also showed iodate reduction activity and the activity responded to iodine treatment either with IO−3 and I−. This study suggests that plant roots biologically reduce iodate to iodide and indicates that the iodate reduction activity of roots responds to external iodine conditions. PMID:23847633

  7. RADON REDUCTION TECHNIQUES FOR EXISTING DETACHED HOUSES - TECHNICAL GUIDANCE (THIRD EDITION) FOR ACTIVE SOIL DEPRESSURIZATION SYSTEMS

    EPA Science Inventory

    This technical guidance document is designed to aid in the selection, design, installation and operation of indoor radon reduction techniques using soil depressurization in existing houses. Its emphasis is on active soil depressurization; i.e., on systems that use a fan to depre...

  8. Vertical activity distribution of dissimilatory nitrate reduction in coastal marine sediments

    NASA Astrophysics Data System (ADS)

    Behrendt, A.; de Beer, D.; Stief, P.

    2013-05-01

    The relative importance of two dissimilatory nitrate reduction pathways, denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA), was investigated in intact sediment cores from five different coastal marine field sites. The vertical distribution of DEN activity was examined using the acetylene inhibition technique combined with N2O microsensor measurements, whereas NH4+ production via DNRA was measured with a recently developed gel probe-stable isotope technique. At all field sites, dissimilatory nitrate reduction was clearly dominated by DEN (> 59% of the total NO3- reduced) rather than by DNRA, irrespective of the sedimentary inventories of electron donors such as organic carbon, sulfide, and iron. Ammonium production via DNRA (8.9% of the total NO3- reduced) was exclusively found at one site with very high concentrations of total sulfide and NH4+ in the layer of NO3- reduction and below. Sediment from two field sites, one with and one without DNRA activity in the core incubations, was also used for slurry incubations. Now, in both sediments high DNRA activity was detected accounting for 37-77% of the total NO3- reduced. These contradictory results can be explained by enhanced NO3- availability for DNRA bacteria in the sediment slurries compared to the core-incubated sediments. It can be argued that the gel probe technique gives more realistic estimates of DNRA activity in diffusion-dominated sediments, while slurry incubations are more suitable for advection-dominated sediments.

  9. Identification of intrinsic catalytic activity for electrochemical reduction of water molecules to generate hydrogen.

    PubMed

    Shinagawa, Tatsuya; Takanabe, Kazuhiro

    2015-06-21

    Insufficient hydronium ion activities at near-neutral pH and under unbuffered conditions induce diffusion-limited currents for hydrogen evolution, followed by a reaction with water molecules to generate hydrogen at elevated potentials. The observed constant current behaviors at near neutral pH reflect the intrinsic electrocatalytic reactivity of the metal electrodes for water reduction.

  10. QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIPS FOR CHEMICAL REDUCTIONS OF ORGANIC CONTAMINANTS

    EPA Science Inventory

    Sufficient kinetic data on abiotic reduction reactions involving organic contaminants are now available that quantitative structure-activity relationships (QSARs) for these reactions can be developed. Over 50 QSARs have been reported, most in just the last few years, and they ar...

  11. Nickel-catalyzed reductive arylation of activated alkynes with aryl iodides

    PubMed Central

    Dorn, Stephanie C. M.; Olsen, Andrew K; Kelemen, Rachel E.; Shrestha, Ruja; Weix, Daniel J.

    2015-01-01

    The direct, regioselective, and stereoselective arylation of activated alkynes with aryl iodides using a nickel catalyst and manganese reductant is described. The reaction conditions are mild (40 °C in MeOH, no acid or base) and an intermediate organomanganese reagent is unlikely. Functional groups tolerated include halides and pseudohalides, free and protected anilines, and a benzyl alcohol. Other activated alkynes including an amide and a ketone also reacted to form arylated products in good yields. PMID:26028781

  12. Active breathing control (ABC): Determination and reduction of breathing-induced organ motion in the chest

    SciTech Connect

    Gagel, Bernd . E-mail: BGagel@UKAachen.de; Demirel, Cengiz M.P.; Kientopf, Aline; Pinkawa, Michael; Piroth, Marc; Stanzel, Sven; Breuer, Christian; Asadpour, Branka; Jansen, Thomas; Holy, Richard; Wildberger, Joachim E.; Eble, Michael J.

    2007-03-01

    Purpose: Extensive radiotherapy volumes for tumors of the chest are partly caused by interfractional organ motion. We evaluated the feasibility of respiratory observation tools using the active breathing control (ABC) system and the effect on breathing cycle regularity and reproducibility. Methods and Materials: Thirty-six patients with unresectable tumors of the chest were selected for evaluation of the ABC system. Computed tomography scans were performed at various respiratory phases starting at the same couch position without patient movement. Threshold levels were set at minimum and maximum volume during normal breathing cycles and at a volume defined as shallow breathing, reflecting the subjective maximal tolerable reduction of breath volume. To evaluate the extent of organ movement, 13 landmarks were considering using commercial software for image coregistration. In 4 patients, second examinations were performed during therapy. Results: Investigating the differences in a normal breathing cycle versus shallow breathing, a statistically significant reduction of respiratory motion in the upper, middle, and lower regions of the chest could be detected, representing potential movement reduction achieved through reduced breath volume. Evaluating interfraction reproducibility, the mean displacement ranged between 0.24 mm (chest wall/tracheal bifurcation) to 3.5 mm (diaphragm) for expiration and shallow breathing and 0.24 mm (chest wall) to 5.25 mm (diaphragm) for normal inspiration. Conclusions: By modifying regularity of the respiratory cycle through reduction of breath volume, a significant and reproducible reduction of chest and diaphragm motion is possible, enabling reduction of treatment planning margins.

  13. Influence of (calcium-)uranyl-carbonate complexation on U(VI) sorption on Ca- and Na-bentonites.

    PubMed

    Meleshyn, A; Azeroual, M; Reeck, T; Houben, G; Riebe, B; Bunnenberg, C

    2009-07-01

    The influence of uranyl-carbonate and calcium-uranyl-carbonate complexations on the kinetics of U(VI) (approximately 3.4 x 10(-3) mol L(-1)) sorption from NaNO3 and Ca(NO3)2 solutions on Na- and Ca-bentonites at circumneutral ambient conditions was investigated. Complexation of U(VI) in Ca2UO2(CO3)3(aq) aqueous species, dominating the U(VI) speciation in Ca(NO3)2 solution, reduces its adsorption on bentonite by a factor of 2-3 in comparison with that in (UO2)2CO3(OH)3- species, dominating in NaNO3 solution, within the studied period of time (21 days). As a result of the dissolution of accessory calcite, Ca2UO2(CO3)3(aq) can be formed in the initially Ca-free solution in contact with either Na- or Ca-bentonite. U(VI) adsorption on Na-bentonite is a factor of approximately 2 higher than that on Ca-bentonite for solutions with the Ca2UO2(CO3)3(aq) complex dominating aqueous U(VI) speciation. This favors use of Na-bentonite over that of Ca-bentonite in final disposal of radioactive waste. Furthermore, the observed strong correlation between U(VI) adsorption and Mg release as a result of montmorillonite dissolution indicates in agreement with previous findings that under the applied conditions U(VI) is adsorbed on the edge surface of montmorillonite, which is a major mineral phase of the studied clays.

  14. Reductive activation of mitomycin C by thiols: kinetics, mechanism, and biological implications.

    PubMed

    Paz, Manuel M

    2009-10-01

    The clinically used antitumor antibiotic mitomycin C requires a reductive activation to be converted to a bis-electrophile that forms several covalent adducts with DNA, including an interstrand cross-link which is considered to be the lesion responsible for the cytotoxic effects of the drug. Enzymes such as cytochrome P450 reductase and DT-diaphorase have traditionally been implicated in the bioreduction of mitomycin C, but recent reports indicate that enzymes containing a dithiol active site are also involved in the metabolism of mitomycin C. The reductive activation can also be effected in vitro with chemical reductants, but until now, mitomycin C was considered to be inert to thiols. We report here that mitomycin C can, in fact, be reductively activated by thiols. We show that the reaction is autocatalytic and that the end product is a relatively stable aziridinomitosene that can be trapped by adding several nucleophiles after the activation reaction. Kinetic studies show that the reaction is highly sensitive to pH and does not proceed or proceeds very slowly at neutral pH, an observation that explains the unsuccessful results on previous attempts to activate mitomycin C with thiols. The optimum pH for the reactions is around the pK(a) values of the thiols used in the activation. A mechanism for the reaction is hypothesized, involving the initial formation of a thiolate-mitomycin adduct, that then evolves to give the hydroquinone of mitomycin C and disulfide. The results presented here provide a chemical mechanism to explain how some biological dithiols containing an unusually acidic thiol group (deprotonated at physiological pH) participate in the modulation of mitomycin C cytotoxicity.

  15. Enhanced Activity and Stability of Pt catalysts on Functionalized Graphene Sheets for Electrocatalytic Oxygen Reduction

    SciTech Connect

    Kou, Rong; Shao, Yuyan; Wang, Donghai; Engelhard, Mark H.; Kwak, Ja Hun; Wang, Jun; Viswanathan, Vilayanur V.; Wang, Chong M.; Lin, Yuehe; Wang, Yong; Aksay, Ilhan A.; Liu, Jun

    2009-04-30

    Electrocatalysis of oxygen reduction using Pt nanoparticles supported on functionalized graphene sheets (FGSs) was studied. FGSs were prepared by thermal expansion of graphite oxide. Pt nanoparticles with average diameter of 2 nm were uniformly loaded on FGSs by impregnation methods. Pt-FGS showed a higher electrochemical surface area and oxygen reduction activity with improved stability as compared with commercial catalyst. Transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization suggest that the improved performance of Pt-FGS can be attributed to smaller particle size and less aggregation of Pt nanoparticles on the functionalized graphene sheets.

  16. Vibration reduction in helicopter rotors using an active control surface located on the blade

    NASA Technical Reports Server (NTRS)

    Millott, T. A.; Friedmann, P. P.

    1992-01-01

    A feasibility study of vibration reduction in a four-bladed helicopter rotor using individual blade control (IBC), which is implemented by an individually controlled aerodynamic surface located on each blade, is presented. For this exploratory study, a simple offset-hinged spring restrained model of the blade is used with fully coupled flap-lag-torsional dynamics for each blade. Deterministic controllers based on local and global system models are implemented to reduce 4/rev hub loads using both an actively controlled aerodynamic surface on each blade as well as conventional IBC, where the complete blade undergoes cyclic pitch change. The effectiveness of the two approaches for simultaneous reduction of the 4/rev hub shears and hub moments is compared. Conventional IBC requires considerably more power to achieve approximately the same level of vibration reduction as that obtained by implementing IBC using an active control surface located on the outboard segment of the blade. The effect of blade torsional flexibility on the vibration reduction effectiveness of the actively controlled surface was also considered and it was found that this parameter has a very substantial influence.

  17. Trend in the Catalytic Activity of Transition Metals for the Oxygen Reduction Reaction by Lithium

    SciTech Connect

    Dathar, Gopi Krishna Phani; Shelton Jr, William Allison; Xu, Ye

    2012-01-01

    Periodic density functional theory (DFT) calculations indicate that the intrinsic activity of Au, Ag, Pt, Pd, Ir, and Ru for the oxygen reduction reaction by Li (Li-ORR) forms a volcano-like trend with respect to the adsorption energy of oxygen, with Pt and Pd being the most active. The trend is based on two mechanisms: the reduction of molecular O{sub 2} on Au and Ag and of atomic O on the remaining metals. Step edges are found to be more active for catalyzing the Li-ORR than close-packed surfaces. Our findings identify important considerations in the design of catalyst-promoted air cathodes for nonaqueous Li-air batteries.

  18. Green synthesis of gold nanoparticles using aspartame and their catalytic activity for p-nitrophenol reduction

    NASA Astrophysics Data System (ADS)

    Wu, Shufen; Yan, Songjing; Qi, Wei; Huang, Renliang; Cui, Jing; Su, Rongxin; He, Zhimin

    2015-05-01

    We demonstrated a facile and environmental-friendly approach to form gold nanoparticles through the reduction of HAuCl4 by aspartame. The single-crystalline structure was illustrated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared (FTIR) results indicated that aspartame played a pivotal role in the reduction and stabilization of the gold crystals. The crystals were stabilized through the successive hydrogen-bonding network constructed between the water and aspartame molecules. Additionally, gold nanoparticles synthesized through aspartame were shown to have good catalytic activity for the reduction of p-nitrophenol to p-aminophenol in the presence of NaBH4.

  19. Conjugation of glutathione and other thiols with bioreductively activated mitomycin C. Effect of thiols on the reductive activation rate.

    PubMed

    Sharma, M; Tomasz, M

    1994-01-01

    Mitomycin C (MC), a clinically used natural antitumor agent, was shown to form three monoconjugates (11a-13a) and two bisconjugates (14a, 15a) with GSH upon reductive activation by rat liver microsomes, purified NADPH-cytochrome c reductase, or NADH-cytochrome c reductase or chemical reduction using H2/PtO2. Rat liver cytosol/NADH activated MC only at acidic pH (5.8), resulting in the formation of a single GSH-MC monoconjugate, 13a. The reductase responsible for cytosolic activation of MC to form this conjugate was DT-diaphorase. GSH itself did not reduce MC, and unreduced MC did not form conjugates with GSH. A moderate catalytic effect by glutathione S-transferase was demonstrated on the cytosol-activated reaction. Mercaptoethanol and N-acetylcysteine gave analogous sets of five MC-thiol conjugates under cytochrome c reductase or H2/PtO2 activation conditions. The structures of all 15 MC-thiol conjugates (five each with GSH, mercaptoethanol, and N-acetylcysteine, respectively) were determined, using 1H-NMR, UV, and mass spectroscopies, combined with analytical chemical and radiolabeling methods. The mechanism of formation of the conjugates features SN2 displacement of the carbamate of the reduced MC by GS-. The MC-GSH conjugates were noncytotoxic to the tumor cells tested. The conjugation of GSH with activated MC is likely to represent detoxication in mammalian cells. As another effect, GSH accelerates the rate of reduction of MC by "slow" reducing agents such as cytochrome c reductases and H2/PtO2. A mechanism is proposed to explain this effect, which involves further reduction of the initially formed MC semiquinone free radical by GSH.

  20. Effect of Subgrid Heterogeneity on Scaling Geochemical and Biogeochemical Reactions: A Case of U(VI) Desorption

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Shan, Huimei; Zachara, John M.

    2014-02-04

    The effect of subgrid heterogeneity in sediment properties on the rate of uranyl[U(VI)] desorption was investigated using a sediment collected from the US Department of Energy Hanford site. The sediment was sieved into 7 grain size fractions that each exhibited different U(VI) desorption properties. Six columns were assembled using the sediment with its grain size fractions arranged in different spatial configurations to mimic subgrid heterogeneity in reactive transport properties. The apparent rate of U(VI) desorption varied significantly in the columns. Those columns with sediment structures leading to preferential transport had much lower rates of U(VI) desorption than those with relatively homogeneous transport. Modeling analysis indicated that the U(VI) desorption model and parameters characterized from well-mixed reactors significantly over-predicted the measured U(VI) desorption in the columns with preferential transport. A dual domain model, which operationally separates reactive transport properties into two subgrid domains improved the predictions significantly. A similar effect of subgrid heterogeneity, albeit at a less degree, was observed for denitrification, which also occurred in the columns. The results imply that subgrid heterogeneity is an important consideration in extrapolating reaction rates from the laboratory to field.

  1. Suppression of oxygen reduction reaction activity on Pt-based electrocatalysts from ionomer incorporation

    SciTech Connect

    Shinozaki, Kazuma; Morimoto, Yu; Pivovar, Bryan S.; Kocha, Shyam S.

    2016-09-01

    The impact of Nafion on the oxygen reduction reaction (ORR) activity is studied for Pt/C and Pt-alloy/C catalysts using thin-film rotating disk electrode (TF-RDE) methods in 0.1 M HClO4. Ultrathin uniform catalyst layers and standardized activity measurement protocols are employed to obtain accurate and reproducible ORR activity. Nafion lowers the ORR activity which plateaus with increasing loading on Pt catalysts. Pt particle size is found not to have significant influence on the extent of the SA decrease upon Nafion incorporation. Catalysts using high surface area carbon (HSC) support exhibit attenuated activity loss resulting from lower ionomer coverage on catalyst particles located within the deep pores. The impact of metallic composition on the activity loss due to Nafion incorporation is also discussed.

  2. Neural Activity During Health Messaging Predicts Reductions in Smoking Above and Beyond Self-Report

    PubMed Central

    Falk, Emily B.; Berkman, Elliot T.; Whalen, Danielle; Lieberman, Matthew D.

    2011-01-01

    Objective The current study tested whether neural activity in response to messages designed to help smokers quit could predict smoking reduction, above and beyond self-report. Design Using neural activity in an a priori region of interest (a subregion of medial prefrontal cortex [MPFC]), in response to ads designed to help smokers quit smoking, we prospectively predicted reductions in smoking in a community sample of smokers (N = 28) who were attempting to quit smoking. Smoking was assessed via expired carbon monoxide (CO; a biological measure of recent smoking) at baseline and 1 month following exposure to professionally developed quitting ads. Results A positive relationship was observed between activity in the MPFC region of interest and successful quitting (increased activity in MPFC was associated with a greater decrease in expired CO). The addition of neural activity to a model predicting changes in CO from self-reported intentions, self-efficacy, and ability to relate to the messages significantly improved model fit, doubling the variance explained ( Rself−report2=.15,Rself−report+neuralactivity2=.35,Rchange2=.20). Conclusion: Neural activity is a useful complement to existing self-report measures. In this investigation, we extend prior work predicting behavior change based on neural activity in response to persuasive media to an important health domain and discuss potential psychological interpretations of the brain–behavior link. Our results support a novel use of neuroimaging technology for understanding the psychology of behavior change and facilitating health promotion. PMID:21261410

  3. Vertical activity distribution of dissimilatory nitrate reduction in coastal marine sediments

    NASA Astrophysics Data System (ADS)

    Behrendt, A.; de Beer, D.; Stief, P.

    2013-11-01

    The relative importance of two dissimilatory nitrate reduction pathways, denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA), was investigated in intact sediment cores from five different coastal marine field sites (Dorum, Aarhus Bight, Mississippi Delta, Limfjord and Janssand). The vertical distribution of DEN activity was examined using the acetylene inhibition technique combined with N2O microsensor measurements, whereas NH4+ production via DNRA was measured with a recently developed gel probe-stable isotope technique. At all field sites, dissimilatory nitrate reduction was clearly dominated by DEN (59-131% of the total NO3- reduced) rather than by DNRA, irrespective of the sedimentary inventories of electron donors such as organic carbon, sulfide, and iron. Highest ammonium production via DNRA, accounting for up to 8.9% of the total NO3- reduced, was found at a site with very high concentrations of total sulfide and NH4+ within and below the layer in which NO3- reduction occurred. Sediment from two field sites, one with low and one with high DNRA activity in the core incubations, was also used for slurry incubations. Now, in both sediments high DNRA activity was detected accounting for 37-77% of the total NO3- reduced. These contradictory results might be explained by enhanced NO3- availability for DNRA bacteria in the sediment slurries compared to the core-incubated sediments in which diffusion of NO3- from the water column may only reach DEN bacteria, but not DNRA bacteria. The true partitioning of dissimilatory nitrate reduction between DNRA and DEN may thus lie in between the values found in whole core (underestimation of DNRA) and slurry incubations (overestimation of DNRA).

  4. State anxiety reduction and exercise: does hemispheric activation reflect such changes?

    PubMed

    Petruzzello, S J; Landers, D M

    1994-08-01

    Acute bouts of aerobic exercise have been consistently associated with significant reductions in anxiety, but explanations for this effect remain elusive. The cerebral lateralization hypothesis predicts that anxiety reductions would be caused by a postexercise decrease in anterior right, relative to left, hemisphere activation. A sample of 19 right-handed males ran at 75% of their VO2max for 30 min on a treadmill. Electroencephalogram (EEG; F3, F4, T3, T4) and state anxiety were collected before and following exercise. Compared with preexercise, anxiety was significantly (P < 0.05) reduced at 10, 20, and 30 min postexercise. Preexercise EEG alpha asymmetry was significantly related to trait anxiety and also predicted a significant amount of variance (30%; P = 0.008) in postexercise anxiety reduction. From pre- to postexercise, the relative activation of the left frontal area increased with respect to the homologous right frontal site. Within-subject correlations for the change in anxiety with corresponding EEG changes were small but in line with theoretical predictions. It is concluded that the cerebral lateralization hypothesis remains tenable for explaining anxiety reductions associated with exercise.

  5. Highly active Pd-In/mesoporous alumina catalyst for nitrate reduction.

    PubMed

    Gao, Zhenwei; Zhang, Yonggang; Li, Deyi; Werth, Charles J; Zhang, Yalei; Zhou, Xuefei

    2015-04-09

    The catalytic reduction of nitrate is a promising technology for groundwater purification because it transforms nitrate into nitrogen and water. Recent studies have mainly focused on new catalysts with higher activities for the reduction of nitrate. Consequently, metal nanoparticles supported on mesoporous metal oxides have become a major research direction. However, the complex surface chemistry and porous structures of mesoporous metal oxides lead to a non-uniform distribution of metal nanoparticles, thereby resulting in a low catalytic efficiency. In this paper, a method for synthesizing the sustainable nitrate reduction catalyst Pd-In/Al2O3 with a dimensional structure is introduced. The TEM results indicated that Pd and In nanoparticles could efficiently disperse into the mesopores of the alumina. At room temperature in CO2-buffered water and under continuous H2 as the electron donor, the synthesized material (4.9 wt% Pd) was the most active at a Pd-In ratio of 4, with a first-order rate constant (k(obs) = 0.241 L min(-1) g(cata)(-1)) that was 1.3× higher than that of conventional Pd-In/Al2O3 (5 wt% Pd; 0.19 L min(-1) g(cata)(-1)). The Pd-In/mesoporous alumina is a promising catalyst for improving the catalytic reduction of nitrate.

  6. Effects of Extrinsic and Intrinsic Proton Activity on The Mechanism of Oxygen Reduction in Ionic Liquids

    NASA Astrophysics Data System (ADS)

    Zeller, Robert August

    Mechanisms for oxygen reduction are proposed for three distinct cases covering two ionic liquids of fundamentally different archetypes and almost thirty orders of magnitude of proton activity. Proton activity is treated both extrinsically by varying the concentration and intrinsically by selecting proton donors with a wide range of aqueous pKa values. The mechanism of oxygen reduction in ionic liquids is introduced by way of the protic ionic liquid (pIL) triethylammonium triflate (TEATf) which shares some similarities with aqueous acid solutions. Oxygen reduction in TEATf begins as the one electron rate limited step to form superoxide, O2 *-, which is then rapidly protonated by the pIL cation forming the perhydroxyl radical, HO2*. The perhydroxyl radical is further reduced to peroxidate (HO2-) and hydrogen peroxide in proportions in accordance with their pKa. The reaction does not proceed beyond this point due to the adsorption of the conjugate base triethylammine interfering with the disproportionation of hydrogen peroxide. This work demonstrates that this mechanism is consistent across Pt, Au, Pd, and Ag electrodes. Two related sets of experiments were performed in the inherently aprotic ionic liquid 1-butyl-2,3-dimethylimidazolium triflate (C4dMImTf). The first involved the titration of acidic species of varying aqueous pKa into the IL while monitoring the extent of oxygen reduction as a function of pKa and potential on Pt and glassy carbon (GC) electrodes. These experiments confirmed the greater propensity of Pt to reduce oxygen by its immediate and abrupt transition from one electron reduction to four electron reduction, while oxygen reduction on GC gradually approaches four electron reduction as the potentials were driven more cathodic. The potential at which oxygen reduction initiates shows general agreement with the Nernst equation and the acid's tabulated aqueous pKa value, however at the extremely acidic end, a small deviation is observed. The second set

  7. The reduction of rotorcraft power and vibration using optimally controlled active gurney flap

    NASA Astrophysics Data System (ADS)

    Bae, Eui Sung

    The main topic of the present study is the application of active control scheme for the reduction of rotorcraft main rotor power reduction and vibratory load. When the helicopter is operated near its flight boundary, the required power and vibratory loads rapidly increases which impose a limit on the helicopter operation. Various methods were proposed and studied in order to achieve performance improvement under such operating condition. The effect of active control scheme was examined for its impact on the performance improvement and vibration reduction in the present study. Numerical simulations are based on the UH-60A Blackhawk helicopter with an active Gurney flap spanning from 70%R to 80%R of the main rotor. For obtaining the aeroelastic response of the rotor blade, finite element method was used to represent elastic blade. The aerodynamic loads acting on the blade are provided by CFD based 2D lookup table. Prescribed wake model was used to resolve the induced inflow over the rotor disk. The unsteady aerodynamic behavior due to the higher harmonic actuation of active Gurney flap was resolved by the time-domain unsteady aerodynamic model. The first part of preliminary study covers parametric study using Gurney flap. Starting with simple rigid blade representation of the rotor blade, the effect of 1/rev Gurney flap actuation was examined on three different gross weights. The effect of active Gurney flap width, the chordwise location of active Gurney flap, the effect of unsteady aerodynamic model, and the effect of 2/rev actuation frequency were examined. The second part of preliminary study was conducted with the elastic blade model to include the effect of torsion dynamics. Performance improvement using active Gurney flap was examined for maximizing thrust capability at two flight speeds. 1/rev Gurney flap actuation increased the gross weight capability up to 1,000 lbs. Also, 1/rev actuation of Gurney flap increased maximum altitude limit of baseline rotor by 1

  8. Transport of U(VI) through sediments amended with phosphate to induce in situ uranium immobilization.

    PubMed

    Mehta, Vrajesh S; Maillot, Fabien; Wang, Zheming; Catalano, Jeffrey G; Giammar, Daniel E

    2015-02-01

    Phosphate amendments can be added to U(VI)-contaminated subsurface environments to promote in situ remediation. The primary objective of this study was to evaluate the impacts of phosphate addition on the transport of U(VI) through contaminated sediments. In batch experiments using sediments (<2 mm size fraction) from a site in Rifle, Colorado, U(VI) only weakly adsorbed due to the dominance of the aqueous speciation by Ca-U(VI)-carbonate complexes. Column experiments with these sediments were performed with flow rates that correspond to a groundwater velocity of 1.1 m/day. In the absence of phosphate, the sediments took up 1.68-1.98 μg U/g of sediments when the synthetic groundwater influent contained 4 μM U(VI). When U(VI)-free influents were then introduced with and without phosphate, substantially more uranium was retained within the column when phosphate was present in the influent. Sequential extractions of sediments from the columns revealed that uranium was uniformly distributed along the length of the columns and was primarily in forms that could be extracted by ion exchange and contact with a weak acid. Laser induced fluorescence spectroscopy (LIFS) analysis along with sequential extraction results suggest adsorption as the dominant uranium uptake mechanism. The response of dissolved uranium concentrations to stopped-flow events and the comparison of experimental data with simulations from a simple reactive transport model indicated that uranium adsorption to and desorption from the sediments was not always at local equilibrium.

  9. Electrically rechargeable anionically active reduction-oxidation electrical storage-supply system

    SciTech Connect

    Remick, R.J.; Ang, P.G.P.

    1984-11-27

    An electrically rechargeable anionically active reduction-oxidation electric storage-supply system and process is disclosed using a sodium or potassium sulfidepolysulfide anolyte reaction and an iodide-polyiodide, chloride-chlorine or bromide-bromine species catholyte reaction. The catholyte and anolyte are separated by an ion selective membrane permeable to positive sodium and potassium ions and substantially impermeable to negative bromide, chloride, iodide, sulfide and polysulfide ions. A flowing electrolyte system is disclosed with external electrolyte storage vessels. The apparatus and process provide an electrically rechargeable anionically active reduction-oxidation system in which the electrolytes may be maintained at near neutral or slightly basic pH, with virtually no parasitic side reactions upon charging, such as hydrogen or oxygen evolution, and the disclosed storage and supply system provides higher energy densities than referenced prior art systems.

  10. Synergy among manganese, nitrogen and carbon to improve the catalytic activity for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Wang, Hui; Ji, Shan; Key, Julian; Wang, Rongfang

    2014-04-01

    A highly active electrocatalyst for oxygen reduction reaction, manganese modified glycine derivative-carbon (Mn-CNx), is synthesized by a two-step carbonizing process. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy are used to characterize structure and morphology of the catalysts. Electrochemical tests show that Mn-CNx has higher catalytic activity for oxygen reduction reaction than CNx derived glycine and Mn modified Vulcan carbon. Moreover, the half-wave potential of Mn-CNx is only 12 mV lower than that of commercial Pt/C. Mn-CNx also has excellent durability to methanol crossover in alkaline solution, and thus provides a promising low cost, non-precious metal cathode catalyst for fuel cells.

  11. Enhanced Oxygen Reduction Activity In Acid By Tin-Oxide Supported Au Nanoparticle Catalysts

    SciTech Connect

    Baker,W.; Pietron, J.; Teliska, M.; Bouwman, P.; Ramaker, D.; Swider-Lyons, K.

    2006-01-01

    Gold nanoparticles supported on hydrous tin-oxide (Au-SnO{sub x}) are active for the four-electron oxygen reduction reaction in an acid electrolyte. The unique electrocatalytic of the Au-SnO is confirmed by the low amount of peroxide detected with rotating ring-disk electrode voltammetry and Koutecky-Levich analysis. In comparison, 10 wt % Au supported on Vulcan carbon and SnO{sub x} catalysts both produce significant peroxide in the acid electrolyte, indicating only a two-electron reduction reaction. Characterization of the Au-SnO{sub x} catalyst reveals a high-surface area, amorphous support with 1.7 nm gold metal particles. The high catalytic activity of the Au-SnO is attributed to metal support interactions. The results demonstrate a possible path to non-Pt catalysts for proton exchange membrane fuel cell cathodes.

  12. INVITED PAPER: Application of an active device for helicopter noise reduction in JAXA

    NASA Astrophysics Data System (ADS)

    Saito, Shigeru; Kobiki, Noboru; Tanabe, Yasutada

    2010-02-01

    Important issues in noise problems for current helicopters are described. An active tab (AT) was developed as a new active device for noise/vibration reduction under research cooperation between Japan Aerospace Exploration Agency (JAXA) and Kawada Industries, Inc. The wind tunnel test was conducted in order to investigate the effectiveness of the AT on the aeroacoustic characteristics of a helicopter. From the wind tunnel test, the capability of reducing blade vortex interaction (BVI) noise by an AT was verified. A new control law using instantaneous pressure change on a blade during BVI phenomena was introduced and applied to the wind tunnel testing. This new control law shows reasonable controllability for helicopter noise reduction. Furthermore, in order to analyze noise characteristics, the advanced computational fluid dynamics (CFD) code named JAXA_ov3d was developed in JAXA and extended to include CFD-CSD (computational structure dynamics) coupling by using the beam theory for blade deformation.

  13. Saturn's F ring as seen by Cassini UVIS: Kinematics and statistics

    NASA Astrophysics Data System (ADS)

    Albers, Nicole; Sremčević, Miodrag; Colwell, Joshua E.; Esposito, Larry W.

    2012-01-01

    We present a new orbital model of Saturn's F ring core based on 93 occultations by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Voyager radio and stellar occultations. We demonstrate that the core, despite its intrinsic variability, is well-described as an inclined, freely precessing ellipse. We find that post-fit residuals with a root-mean-square of 24 km are genuine, representing the well-known non-Keplerian features observed in the ring. Over the nearly 4 years of UVIS observations we find the residual variance to increase, coincident with the apse anti-alignment of Prometheus and F ring core in December 2009. This increase in dynamical F ring core temperature most likely reflects the ever-stronger perturbations by Prometheus. Our results are in good agreement with Earth-based and HST observations as well as Voyager imaging. Cassini UVIS stellar occultations resolve the F ring at unprecedented resolutions of a few meters and we identify the F ring core and inner and outer strands. We infer their normal optical depth and full width at half maximum (FWHM) and show that core and strands form distinct morphological groups. Typically, a strand is about ten times wider than the core (average FWHM is ˜10 km) while having a ten times smaller optical depth. Unlike in pre-Cassini occultations the F ring core displays significant optical depth with in some cases >3. In many cases we find a narrow optically thick component (˜ few km and τ > 0.5) embedded in the F ring core. Entertaining the possibility that this is the actual, "true" F ring core then UVIS results suggest that this "true" core is highly non-continuous. In addition, we report the detection of a previously unknown structure - dubbed the "secondary" as it visually resembles the F ring core. Its morphology is similar to that of the core in optical depth and FWHM and it displays individual opaque features. Despite its core-like appearance, we show that its kinematics is consistent with that of

  14. Winter Comparison of Auroral Images from Polar UVI and IMAGE FUV

    NASA Technical Reports Server (NTRS)

    Spann, James F.; Germany, Glynn; Maddox, Will

    2004-01-01

    Same-scene images made with Polar UVI and IMAGE Fuv are compared for the period between 2000 and 2001. The comparison indicates that the use of both instruments may lead to a better evaluation of the average precipitation than with either one individually. The evaluation of total energy input is however, not improved With use of both measurements. These results are a part of a larger investigation to quantitatively compare conjugate images using both instruments and to correlate observed asymmetries with solar wind and seasonal parameters.

  15. Sub-cm Particles in Saturn's Rings from VIMS, UVIS, and RSS occultations

    NASA Astrophysics Data System (ADS)

    Jerousek, Richard Gregory; Colwell, Josh E.; Hedman, Matthew M.; Marouf, Essam A.; Esposito, Larry W.; Nicholson, Philip D.; French, Richard G.

    2016-10-01

    Particles sizes in Saturn's rings roughly follow a truncated power law. One way to determine the governing parameters of the size distribution is through the analysis of differential optical depths (Zebker et al. 1983). Non-axisymmetric self-gravity wakes complicate this approach when optical depth measurements at different wavelengths are not made at same viewing geometry. Using occultations spanning a wide range of viewing angles and from multiple instruments onboard Cassini (the Ultraviolet Imaging Spectrograph (UVIS), the Visual and Infrared Mapping Spectrometer (VIMS), and the Radio Science Subsystem (RSS)), we forward-model the properties of the self-gravity wakes in Saturn's A and B rings while simultaneously constraining the parameters of the cm - sub-cm particle size distribution. In the absence of wakes, and in regions where particles smaller than ~ 8.86 mm are present, VIMS stellar occultations measure larger optical depths than UVIS stellar occultations due to the diffraction of 2.9 μm light out of the small (0.25 × 0.5 mrad) VIMS field of view compared with UVIS which measures shorter wavelength (0.15 μm) light over a much larger (6.4 × 6.0 mrad) field of view. This excess optical depth combined with RSS X-band (λ = 3.6 cm) optical depths provides a way to probe both the power law slope and the minimum particle size. In the A and B rings where self-gravity wakes are prevalent, we use the wake model of Colwell et al. (2006, 2007) with an additional free parameter representing the excess optical depth which would be measured through the gaps between opaque wakes, by VIMS compared to UVIS. In the B ring and inner A ring we find and absence of sub-cm particles and power law slopes of q ~ 2.8. In the trans-Encke region, where there are a multitude of satellite driven resonances, we find an increasing abundance of sub-cm particles as the outer edge of the A ring is approached. In the C Ring and the Cassini Division, where self-gravity wakes are absent

  16. Small particles and self-gravity wakes in Saturn's rings from UVIS and VIMS stellar occultations

    NASA Astrophysics Data System (ADS)

    Jerousek, Richard G.; Colwell, Joshua E.; Esposito, Larry W.; Nicholson, Philip D.; Hedman, Matthew M.

    2016-11-01

    The distribution of particle sizes in Saturn's rings roughly follows a truncated inverse power-law. Though it is well known that differential optical depths provide a way to probe the parameters of size distribution (i.e. Zebker et al. [1985] Icarus, 64, 531-548), the technique is complicated by the presence of self-gravity wakes which introduce a geometric dependence to the observed optical depth. Here we present a method of extracting information about the size distribution of the particles in the gaps between the self-gravity wakes. The Cassini Visual and Infrared Mapping Spectrometer (VIMS) occultations measure starlight at an effective wavelength of 2.9 μm falling onto a single pixel with angular dimensions 0.25 mrad × 0.5 mrad while Cassini Ultraviolet Imaging Spectrograph (UVIS) occultations measure starlight at a much smaller effective wavelength of 0.15 μm and over a field of view with larger angular dimensions of 6.0 mrad × 6.4 mrad. Starlight diffracted out of the VIMS pixel by particles smaller than 1.22λVIMS/2θ ∼8.86 mm, is not replaced by neighboring particles, while the UVIS instrument, with its larger field of view and smaller effective wavelength, collects all of the light diffracted by particles larger than 1.22λVIMS/2θ ∼0.025 mm. Consequently, measurements by VIMS overstate the optical depth in regions where sub-centimeter-sized particles are present. Using the rectangular cross section wake model of (Colwell et al. [2006], Geophys. Res. Lett., 33, L07201) and (Colwell et al. [2007] Icarus, 190, 127-144) with a new parameter to represent the excess VIMS optical depth not seen by UVIS, we combine VIMS and UVIS occultations for the first time for particle size analysis. We find a significant fraction of sub-cm particles only in the outermost portion of the A ring, and in the B1 region of the B ring. In the Trans-Encke region, we find a trend of increasing abundance of sub-cm particles as the outer edge of the A Ring is approached

  17. Modeling of the Enceladus water vapor jets for interpreting UVIS star and solar occultation observations

    NASA Astrophysics Data System (ADS)

    Portyankina, Ganna; Esposito, Larry W.; Aye, Klaus-Michael; Hansen, Candice J.

    2015-11-01

    One of the most spectacular discoveries of the Cassini mission is jets emitting from the southern pole of Saturn’s moon Enceladus. The composition of the jets is water vapor and salty ice grains with traces of organic compounds. Jets, merging into a wide plume at a distance, are observed by multiple instruments on Cassini. Recent observations of the visible dust plume by the Cassini Imaging Science Subsystem (ISS) identified as many as 98 jet sources located along “tiger stripes” [Porco et al. 2014]. There is a recent controversy on the question if some of these jets are “optical illusion” caused by geometrical overlap of continuous source eruptions along the “tiger stripes” in the field of view of ISS [Spitale et al. 2015]. The Cassini’s Ultraviolet Imaging Spectrograph (UVIS) observed occultations of several stars and the Sun by the water vapor plume of Enceladus. During the solar occultation separate collimated gas jets were detected inside the background plume [Hansen et al., 2006 and 2011]. These observations directly provide data about water vapor column densities along the line of sight of the UVIS instrument and could help distinguish between the presence of only localized or also continuous sources. We use Monte Carlo simulations and Direct Simulation Monte Carlo (DSMC) to model the plume of Enceladus with multiple (or continuous) jet sources. The models account for molecular collisions, gravitational and Coriolis forces. The models result in the 3-D distribution of water vapor density and surface deposition patterns. Comparison between the simulation results and column densities derived from UVIS observations provide constraints on the physical characteristics of the plume and jets. The specific geometry of the UVIS observations helps to estimate the production rates and velocity distribution of the water molecules emitted by the individual jets.Hansen, C. J. et al., Science 311:1422-1425 (2006); Hansen, C. J. et al, GRL 38:L11202 (2011

  18. An Overview of Cassini UVIS Icy Satellite Results So Far

    NASA Technical Reports Server (NTRS)

    Hendrix, A. R.; Hansen, C. J.

    2005-01-01

    The icy satellites of the Saturn system exhibit a remarkable amount of variability. From dark, battered Phoebe orbiting at 200 R(sub S) to black-and-white Iapetus, the wispy streaks of Dione, heavily cratered Tethys and Mimas, to potentially geologically active Enceladus, the extent of geological phenomena exhibited by these bodies is tremendous. Phoebe, Iapetus and Hyperion all orbit outside Saturn s magnetosphere, while Mimas, Enceladus, Dione Tethys and Rhea all orbit within the magnetosphere. Furthermore, Mimas, Enceladus, Tethys and Dione all orbit within the E-ring so the extent of exogenic effects on these icy satellites is wide-ranging. After 9 months in orbit around Saturn, we present UV results so far from Phoebe, Tethys, Dione, Iapetus, Mimas, Enceladus and Rhea. We expect that the UV signatures of these icy satellites are strongly influenced not only by their composition, but by external effects and magnetospheric environments.

  19. Reduction of the Radiating Sound of a Submerged Finite Cylindrical Shell Structure by Active Vibration Control

    PubMed Central

    Kim, Heung Soo; Sohn, Jung Woo; Jeon, Juncheol; Choi, Seung-Bok

    2013-01-01

    In this work, active vibration control of an underwater cylindrical shell structure was investigated, to suppress structural vibration and structure-borne noise in water. Finite element modeling of the submerged cylindrical shell structure was developed, and experimentally evaluated. Modal reduction was conducted to obtain the reduced system equation for the active feedback control algorithm. Three Macro Fiber Composites (MFCs) were used as actuators and sensors. One MFC was used as an exciter. The optimum control algorithm was designed based on the reduced system equations. The active control performance was then evaluated using the lab scale underwater cylindrical shell structure. Structural vibration and structure-borne noise of the underwater cylindrical shell structure were reduced significantly by activating the optimal controller associated with the MFC actuators. The results provide that active vibration control of the underwater structure is a useful means to reduce structure-borne noise in water. PMID:23389344

  20. Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

    NASA Technical Reports Server (NTRS)

    Sim, Ben W.; Potsdam, Mark; Kitaplioglu, Cahit; LeMasurier, Philip; Lorber, Peter; Andrews, Joseph

    2012-01-01

    A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

  1. Reduction of the radiating sound of a submerged finite cylindrical shell structure by active vibration control.

    PubMed

    Kim, Heung Soo; Sohn, Jung Woo; Jeon, Juncheol; Choi, Seung-Bok

    2013-02-06

    In this work, active vibration control of an underwater cylindrical shell structure was investigated, to suppress structural vibration and structure-borne noise in water. Finite element modeling of the submerged cylindrical shell structure was developed, and experimentally evaluated. Modal reduction was conducted to obtain the reduced system equation for the active feedback control algorithm. Three Macro Fiber Composites (MFCs) were used as actuators and sensors. One MFC was used as an exciter. The optimum control algorithm was designed based on the reduced system equations. The active control performance was then evaluated using the lab scale underwater cylindrical shell structure. Structural vibration and structure-borne noise of the underwater cylindrical shell structure were reduced significantly by activating the optimal controller associated with the MFC actuators. The results provide that active vibration control of the underwater structure is a useful means to reduce structure-borne noise in water.

  2. Boosting oxygen reduction/evolution reaction activities with layered perovskite catalysts.

    PubMed

    Chen, Dengjie; Wang, Jian; Zhang, Zhenbao; Shao, Zongping; Ciucci, Francesco

    2016-08-25

    Layered PrBaMn2O5+δ (H-PBM) was simply prepared by annealing pristine Pr0.5Ba0.5MnO3-δ in H2. The oxygen reduction/evolution reaction activities are remarkably enhanced by employing H-PBM. The improvement can be ascribed to the introduction of additional oxygen vacancies, an optimized eg filling of Mn ions, and the facile incorporation of oxygen into layered H-PBM.

  3. Effect of the mechanical activation on size reduction of crystalline acetaminophen drug particles

    PubMed Central

    Biazar, Esmaeil; Beitollahi, Ali; Rezayat, S Mehdi; Forati, Tahmineh; Asefnejad, Azadeh; Rahimi, Mehdi; Zeinali, Reza; Ardeshir, Mahmoud; Hatamjafari, Farhad; Sahebalzamani, Ali; Heidari, Majid

    2009-01-01

    The decrease in particle size may offer new properties to drugs. In this study, we investigated the size reduction influence of the acetaminophen (C8H9O2N) particles by mechanical activation using a dry ball mill. The activated samples with the average size of 1 μm were then investigated in different time periods with the infrared (IR), inductively coupled plasma (ICP), atomic force microscopy (AFM), and X-ray diffraction (XRD) methods. The results of the IR and XRD images showed no change in the drug structure after the mechanical activation of all samples. With the peak height at full width at half maximum from XRD and the Scherrer equation, the size of the activated crystallite samples illustrated that the AFM images were in sound agreement with the Scherrer equation. According to the peaks of the AFM images, the average size of the particles in 30 hours of activation was 24 nm with a normal particle distribution. The ICP analysis demonstrated the presence of tungsten carbide particle impurities after activation from the powder sample impacting with the ball and jar. The greatest reduction in size was after milling for 30 hours. PMID:20054432

  4. Stable platinum nanoclusters on genomic DNA-graphene oxide with a high oxygen reduction reaction activity.

    PubMed

    Tiwari, Jitendra N; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N; Kemp, K Christian; Le, Nhien H; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S

    2013-01-01

    Nanosize platinum clusters with small diameters of 2-4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA-graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA-graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA-graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries.

  5. Effects of pathogen reduction systems on platelet microRNAs, mRNAs, activation, and function.

    PubMed

    Osman, Abdimajid; Hitzler, Walter E; Meyer, Claudius U; Landry, Patricia; Corduan, Aurélie; Laffont, Benoit; Boilard, Eric; Hellstern, Peter; Vamvakas, Eleftherios C; Provost, Patrick

    2015-01-01

    Pathogen reduction (PR) systems for platelets, based on chemically induced cross-linking and inactivation of nucleic acids, potentially prevent transfusion transmission of infectious agents, but can increase clinically significant bleeding in some clinical studies. Here, we documented the effects of PR systems on microRNA and mRNA levels of platelets stored in the blood bank, and assessed their impact on platelet activation and function. Unlike platelets subjected to gamma irradiation or stored in additive solution, platelets treated with Intercept (amotosalen+ ultraviolet-A [UVA] light) exhibited significantly reduced levels of 6 of the 11 microRNAs, and 2 of the 3 anti-apoptotic mRNAs (Bcl-xl and Clusterin) that we monitored, compared with platelets stored in plasma. Mirasol (riboflavin+ UVB light) treatment of platelets did not produce these effects. PR neither affected platelet microRNA synthesis or function nor induced cross-linking of microRNA-sized endogenous platelet RNA species. However, the reduction in the platelet microRNA levels induced by Intercept correlated with the platelet activation (p < 0.05) and an impaired platelet aggregation response to ADP (p < 0.05). These results suggest that Intercept treatment may induce platelet activation, resulting in the release of microRNAs and mRNAs from platelets. The clinical implications of this reduction in platelet nucleic acids secondary to Intercept remain to be established.

  6. Effects of pathogen reduction systems on platelet microRNAs, mRNAs, activation, and function

    PubMed Central

    Osman, Abdimajid; Hitzler, Walter E.; Meyer, Claudius U.; Landry, Patricia; Corduan, Aurélie; Laffont, Benoit; Boilard, Eric; Hellstern, Peter; Vamvakas, Eleftherios C.

    2015-01-01

    Pathogen reduction (PR) systems for platelets, based on chemically induced cross-linking and inactivation of nucleic acids, potentially prevent transfusion transmission of infectious agents, but can increase clinically significant bleeding in some clinical studies. Here, we documented the effects of PR systems on microRNA and mRNA levels of platelets stored in the blood bank, and assessed their impact on platelet activation and function. Unlike platelets subjected to gamma irradiation or stored in additive solution, platelets treated with Intercept (amotosalen + ultraviolet-A [UVA] light) exhibited significantly reduced levels of 6 of the 11 microRNAs, and 2 of the 3 anti-apoptotic mRNAs (Bcl-xl and Clusterin) that we monitored, compared with platelets stored in plasma. Mirasol (riboflavin + UVB light) treatment of platelets did not produce these effects. PR neither affected platelet microRNA synthesis or function nor induced cross-linking of microRNA-sized endogenous platelet RNA species. However, the reduction in the platelet microRNA levels induced by Intercept correlated with the platelet activation (p < 0.05) and an impaired platelet aggregation response to ADP (p < 0.05). These results suggest that Intercept treatment may induce platelet activation, resulting in the release of microRNAs and mRNAs from platelets. The clinical implications of this reduction in platelet nucleic acids secondary to Intercept remain to be established. PMID:24749844

  7. Risk avoidance versus risk reduction: a framework and segmentation profile for understanding adolescent sexual activity.

    PubMed

    Hopkins, Christopher D; Tanner, John F; Raymond, Mary Anne

    2004-01-01

    The teen birthrate in the United States is twice that of other industrialized nations. Adolescents in the U.S. are among high-risk groups for HIV/AIDS and other sexually transmitted diseases. As a result, the Department of Health and Human Services changed its policy on the promotion of abstinence to teenagers from a focus on a risk reduction strategy to a focus on a risk avoidance strategy. In order to create more effective risk avoidance as well as risk reduction campaigns, this study proposes a framework to illustrate the distinction that teens make between spontaneous sexual activity and planned sexual activity, as well as those teens that make a commitment to abstinence versus abstinence by default. Furthermore, this study classifies teens into three behavior segments (abstemious, promiscuous and monogamous) and then assesses specific differences that exist within these groups relative to their attitudes and perceptions concerning abstinence, sexual activity, contraception, fear and norms. This change in focus from a risk reduction to a risk avoidance strategy has important implications for social marketing, public policy and marketing theory.

  8. Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction.

    PubMed

    Liang, Hai-Wei; Zhuang, Xiaodong; Brüller, Sebastian; Feng, Xinliang; Müllen, Klaus

    2014-09-17

    Development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the oxygen reduction reaction is of significance for many important electrochemical devices, such as fuel cells, metal-air batteries and chlor-alkali electrolysers. Here we report a highly active nitrogen-doped, carbon-based, metal-free oxygen reduction reaction electrocatalyst, prepared by a hard-templating synthesis, for which nitrogen-enriched aromatic polymers and colloidal silica are used as precursor and template, respectively, followed by ammonia activation. Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of nitrogen-doped carbons. Accordingly, the prepared catalysts show the highest oxygen reduction reaction activity (half-wave potential of 0.85 V versus reversible hydrogen electrode with a low loading of 0.1 mg cm(-2)) in alkaline media among all reported metal-free catalysts. Significantly, when used for constructing the air electrode of zinc-air battery, our metal-free catalyst outperforms the state-of the-art platinum-based catalyst.

  9. Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Liang, Hai-Wei; Zhuang, Xiaodong; Brüller, Sebastian; Feng, Xinliang; Müllen, Klaus

    2014-09-01

    Development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the oxygen reduction reaction is of significance for many important electrochemical devices, such as fuel cells, metal-air batteries and chlor-alkali electrolysers. Here we report a highly active nitrogen-doped, carbon-based, metal-free oxygen reduction reaction electrocatalyst, prepared by a hard-templating synthesis, for which nitrogen-enriched aromatic polymers and colloidal silica are used as precursor and template, respectively, followed by ammonia activation. Our protocol allows for the simultaneous optimization of both porous structures and surface functionalities of nitrogen-doped carbons. Accordingly, the prepared catalysts show the highest oxygen reduction reaction activity (half-wave potential of 0.85 V versus reversible hydrogen electrode with a low loading of 0.1 mg cm-2) in alkaline media among all reported metal-free catalysts. Significantly, when used for constructing the air electrode of zinc-air battery, our metal-free catalyst outperforms the state-of the-art platinum-based catalyst.

  10. Reduction of hexavalent chromium by Sphaerotilus natans a filamentous micro-organism present in activated sludges.

    PubMed

    Caravelli, Alejandro H; Giannuzzi, Leda; Zaritzky, Noemí E

    2008-08-15

    Wastewaters produced by various industries may contain undesirable amounts of hexavalent chromium (Cr(VI)), as chromate and dichromate, a hazardous metal affecting flora and animals of aquatic ecosystems as well as human health. One removal strategy comprises the microbial reduction of Cr(VI) to Cr(III), a less soluble chemical species that is less toxic than Cr(VI). In this work, the ability to reduce Cr(VI) of Sphaerotilus natans, a filamentous bacterium usually found in activated sludge systems, was evaluated. In aerobic conditions, S. natans was able to efficiently reduce Cr(VI) to Cr(III) from dichromate solutions ranging between 4.5 and 80 mg Cr(VI)l(-1) in the presence of a carbonaceous source. A simultaneous evaluation of the microbial respiratory activity inhibition was also carried out to analyze the toxic effect of Cr(VI). Cr(VI) reduction by S. natans was mathematically modeled; chromium(VI) reduction rate depended on both Cr(VI) concentration and active biomass concentration. Although it is known that S. natans removes heavy metal cations such as Cr(III) by biosorption, the ability of this micro-organism to reduce Cr(VI), which behaves as an oxyanion in aqueous solutions, is a novel finding. The distinctive capacity to reduce Cr(VI) to Cr(III) than remain soluble or precipitated becomes S. natans a potential micro-organism to decontaminate wastewaters.

  11. Mechanism of Uranium Reduction and Immobilization in Desulfovibrio vulgaris Biofilms.

    PubMed

    Stylo, Malgorzata; Neubert, Nadja; Roebbert, Yvonne; Weyer, Stefan; Bernier-Latmani, Rizlan

    2015-09-01

    The prevalent formation of noncrystalline U(IV) species in the subsurface and their enhanced susceptibility to reoxidation and remobilization, as compared to crystalline uraninite, raise concerns about the long-term sustainability of the bioremediation of U-contaminated sites. The main goal of this study was to resolve the remaining uncertainty concerning the formation mechanism of noncrystalline U(IV) in the environment. Controlled laboratory biofilm systems (biotic, abiotic, and mixed biotic-abiotic) were probed using a combination of U isotope fractionation and X-ray absorption spectroscopy (XAS). Regardless of the mechanism of U reduction, the presence of a biofilm resulted in the formation of noncrystalline U(IV). Our results also show that biotic U reduction is the most effective way to immobilize and reduce U. However, the mixed biotic-abiotic system resembled more closely an abiotic system: (i) the U(IV) solid phase lacked a typically biotic isotope signature and (ii) elemental sulfur was detected, which indicates the oxidation of sulfide coupled to U(VI) reduction. The predominance of abiotic U reduction in our systems is due to the lack of available aqueous U(VI) species for direct enzymatic reduction. In contrast, in cases where bicarbonate is present at a higher concentration, aqueous U(VI) species dominate, allowing biotic U reduction to outcompete the abiotic processes.

  12. Catalytic Activity of Platinum Monolayer on Iridium and Rhenium Alloy Nanoparticles for the Oxygen Reduction Reaction

    SciTech Connect

    Karan, Hiroko I.; Sasaki, Kotaro; Kuttiyiel, Kurian; Farberow, Carrie A.; Mavrikakis, Manos; Adzic, Radoslav R.

    2012-05-04

    A new type of electrocatalyst with a core–shell structure that consists of a platinum monolayer shell placed on an iridium–rhenium nanoparticle core or platinum and palladium bilayer shell deposited on that core has been prepared and tested for electrocatalytic activity for the oxygen reduction reaction. Carbon-supported iridium–rhenium alloy nanoparticles with several different molar ratios of Ir to Re were prepared by reducing metal chlorides dispersed on Vulcan carbon with hydrogen gas at 400 °C for 1 h. These catalysts showed specific electrocatalytic activity for oxygen reduction reaction comparable to that of platinum. The activities of PtML/PdML/Ir2Re1, PtML/Pd2layers/Ir2Re1, and PtML/Pd2layers/Ir7Re3 catalysts were, in fact, better than that of conventional platinum electrocatalysts, and their mass activities exceeded the 2015 DOE target. Our density functional theory calculations revealed that the molar ratio of Ir to Re affects the binding strength of adsorbed OH and, thereby, the O2 reduction activity of the catalysts. The maximum specific activity was found for an intermediate OH binding energy with the corresponding catalyst on the top of the volcano plot. The monolayer concept facilitates the use of much less platinum than in other approaches. Finally, the results with the PtML/PdML/Ir2Re electrocatalyst indicate that it is a promising alternative to conventional Pt electrocatalysts in low-temperature fuel cells.

  13. Adsorption characteristics of U(VI) on Fe(III)Cr(III) (oxy)hydroxides synthesized at different temperatures.

    PubMed

    Ahn, Hyangsig; Jo, Ho Young; Lee, Young Jae; Kim, Geon-Young

    2016-07-01

    In this study, the adsorption behavior of U(VI) on (oxy)hydroxides synthesized at different temperatures (25 and 75 °C) was investigated. Four (oxy)hydroxides were synthesized by drying slurries of Fe(III) and Fe(III)Cr(III) (oxy)hydroxide in a vacuum desiccator (25 °C) or in an oven (75 °C). Batch adsorption tests were conducted using the (oxy)hydroxides thus synthesized and groundwater containing uranium ions. In general, the U(VI) removal fraction significantly increased with increasing pH from 3 to 5, remained constant with increasing pH from 5 to 9, and decreased at pH greater than 9, regardless of the type of (oxy)hydroxides and solid-to-liquid ratio. The effect of pH on the U(VI) removal fraction was more significant at a low solid-to-liquid ratio. The oven-dried Fe(III) (oxy)hydroxide exhibited a U(VI) removal fraction lower than that of the vacuum-dried one, whereas the oven-dried Fe(III)Cr(III) (oxy)hydroxide exhibited a U(VI) removal fraction higher than that exhibited by the vacuum-dried one. X-ray photoelectron spectroscopy (XPS) analysis results indicated that the difference in the U(VI) removal fraction is attributed to the dissolution and precipitation of the Fe(III) (oxy)hydroxide during oven drying and dehydration of the Fe(III)Cr(III) (oxy)hydroxide during oven drying.

  14. Ag-Fe2O3 nanocomposites with enhanced catalytic activity for reduction of 4-nitrophenol

    NASA Astrophysics Data System (ADS)

    Liu, Shiben; Chen, Yingjie; Dong, Lifeng

    2016-07-01

    Hybrid nanostructures can be multifunctional and even possess enhanced properties. Ag-Fe2O3 nanocomposites and Ag nanoparticles (NPs) were fabricated and applied to catalyze the reduction of 4-nitrophenol. Compared with Ag NPs, Ag-Fe2O3 nanocomposites demonstrated enhanced catalytic activities. Furthermore, due to their magnetic properties, Ag-Fe2O3 nanocomposites could be easily separated from the reaction mixture and recycled through an external magnetic field. These findings will help us design hybrid nanostructures with catalytic activity and explore other potential applications of magnetic nanocomposites.

  15. Hexagonal 2H-MoSe2 broad spectrum active photocatalyst for Cr(VI) reduction

    PubMed Central

    Chu, Haipeng; Liu, Xinjuan; Liu, Baibai; Zhu, Guang; Lei, Wenyan; Du, Huigang; Liu, Junying; Li, Jianwei; Li, Can; Sun, Changqing

    2016-01-01

    To make full use of the solar energy, exploring broad spectrum active photocatalysts has become one of the core issues for photocatalysis. Here we report a novel hexagonal 2H-MoSe2 photocatalyst with ultraviolet (UV)-visible-near infrared (NIR) light response for the first time. The results indicate that the MoSe2 displays excellent photo-absorption and photocatalytic activity in the reduction of Cr(VI) under UV and visible even NIR light irradiation. MoSe2 synthesized at pH value of 2 achieves the highest Cr(VI) reduction rates of 99%, 91% and 100% under UV, visible and NIR light irradiation, respectively, which should be attributed to its comparatively higher light absorption, efficient charge separation and transfer as well as relatively large number of surface active sites. The excellent broad spectrum active photocatalytic activity makes the MoSe2 to be a promising photocatalyst for the effective utilization of solar energy. PMID:27734974

  16. The validation of an active control intervention for Mindfulness Based Stress Reduction (MBSR).

    PubMed

    MacCoon, Donal G; Imel, Zac E; Rosenkranz, Melissa A; Sheftel, Jenna G; Weng, Helen Y; Sullivan, Jude C; Bonus, Katherine A; Stoney, Catherine M; Salomons, Tim V; Davidson, Richard J; Lutz, Antoine

    2012-01-01

    Most of the extant literature investigating the health effects of mindfulness interventions relies on wait-list control comparisons. The current article specifies and validates an active control condition, the Health Enhancement Program (HEP), thus providing the foundation necessary for rigorous investigations of the relative efficacy of Mindfulness Based Stress Reduction (MBSR) and for testing mindfulness as an active ingredient. 63 participants were randomized to either MBSR (n = 31) or HEP (n = 32). Compared to HEP, MBSR led to reductions in thermal pain ratings in the mindfulness- but not the HEP-related instruction condition (η(2) = .18). There were significant improvements over time for general distress (η(2) = .09), anxiety (η(2) = .08), hostility (η(2) = .07), and medical symptoms (η(2) = .14), but no effects of intervention. Practice was not related to change. HEP is an active control condition for MBSR while remaining inert to mindfulness. These claims are supported by results from a pain task. Participant-reported outcomes (PROs) replicate previous improvements to well-being in MBSR, but indicate that MBSR is no more effective than a rigorous active control in improving these indices. These results emphasize the importance of using an active control condition like HEP in studies evaluating the effectiveness of MBSR.

  17. Enhancement of oxygen reduction reaction activities by Pt nanoclusters decorated on ordered mesoporous porphyrinic carbons

    SciTech Connect

    Sun-Mi Hwang; Choi, YongMan; Kim, Min Gyu; Sohn, Young-Jun; Cheon, Jae Yeong; Joo, Sang Hoon; Yim, Sung-Dae; Kuttiyiel, Kurian A.; Sasaki, Kotaro; Adzic, Radoslav R.; Park, Gu-Gon

    2016-03-08

    The high cost of Pt-based membrane electrode assemblies (MEAs) is a critical hurdle for the commercialization of polymer electrolyte fuel cells (PEFCs). Recently, non-precious metal-based catalysts (NPMCs) have demonstrated much enhanced activity but their oxygen reduction reaction (ORR) activity is still inferior to that of Pt-based catalysts resulting in a much thicker electrode in the MEA. For the reduction of mass transport and ohmic overpotential we adopted a new concept of catalyst that combines an ultra-low amount of Pt nanoclusters with metal–nitrogen (M–Nx) doped ordered mesoporous porphyrinic carbon (FeCo–OMPC(L)). The 5 wt% Pt/FeCo–OMPC(L) showed a 2-fold enhancement in activities compared to a higher loading of Pt. Our experimental results supported by first-principles calculations indicate that a trace amount of Pt nanoclusters on FeCo–OMPC(L) significantly enhances the ORR activity due to their electronic effect as well as geometric effect from the reduced active sites. Finally, in terms of fuel cell commercialization, this class of catalysts is a promising candidate due to the limited use of Pt in the MEA.

  18. Enhancement of oxygen reduction reaction activities by Pt nanoclusters decorated on ordered mesoporous porphyrinic carbons

    DOE PAGES

    Sun-Mi Hwang; Choi, YongMan; Kim, Min Gyu; ...

    2016-03-08

    The high cost of Pt-based membrane electrode assemblies (MEAs) is a critical hurdle for the commercialization of polymer electrolyte fuel cells (PEFCs). Recently, non-precious metal-based catalysts (NPMCs) have demonstrated much enhanced activity but their oxygen reduction reaction (ORR) activity is still inferior to that of Pt-based catalysts resulting in a much thicker electrode in the MEA. For the reduction of mass transport and ohmic overpotential we adopted a new concept of catalyst that combines an ultra-low amount of Pt nanoclusters with metal–nitrogen (M–Nx) doped ordered mesoporous porphyrinic carbon (FeCo–OMPC(L)). The 5 wt% Pt/FeCo–OMPC(L) showed a 2-fold enhancement in activities comparedmore » to a higher loading of Pt. Our experimental results supported by first-principles calculations indicate that a trace amount of Pt nanoclusters on FeCo–OMPC(L) significantly enhances the ORR activity due to their electronic effect as well as geometric effect from the reduced active sites. Finally, in terms of fuel cell commercialization, this class of catalysts is a promising candidate due to the limited use of Pt in the MEA.« less

  19. An ene reductase from Clavispora lusitaniae for asymmetric reduction of activated alkenes.

    PubMed

    Ni, Yan; Yu, Hui-Lei; Lin, Guo-Qiang; Xu, Jian-He

    2014-03-05

    A putative ene reductase gene from Clavispora lusitaniae was heterologously overexpressed in Escherichia coli, and the encoded protein (ClER) was purified and characterized for its biocatalytic properties. This NADPH-dependent flavoprotein was identified with reduction activities toward a diverse range of activated alkenes including conjugated enones, enals, maleimide derivative and α,β-unsaturated carboxylic esters. The purified ClER exhibited a relatively high activity of 7.3 U mg(prot)⁻¹ for ketoisophorone while a remarkable catalytic efficiency (k(cat)/K(m)=810 s⁻¹ mM⁻¹) was obtained for 2-methyl-cinnamaldehyde due to the high affinity. A series of prochiral activated alkenes were stereoselectively reduced by ClER furnishing the corresponding saturated products in up to 99% ee. The practical applicability of ClER was further evaluated for the production of (R)-levodione, a valuable chiral compound, from ketoisophorone. Using the crude enzyme of ClER and glucose dehydrogenase (GDH), 500 mM of ketoisophorone was efficiently converted to (R)-levodione with excellent stereoselectivity (98% ee) within 1h. All these positive features demonstrate a high synthetic potential of ClER in the asymmetric reduction of activated alkenes.

  20. Hexagonal 2H-MoSe2 broad spectrum active photocatalyst for Cr(VI) reduction.

    PubMed

    Chu, Haipeng; Liu, Xinjuan; Liu, Baibai; Zhu, Guang; Lei, Wenyan; Du, Huigang; Liu, Junying; Li, Jianwei; Li, Can; Sun, Changqing

    2016-10-13

    To make full use of the solar energy, exploring broad spectrum active photocatalysts has become one of the core issues for photocatalysis. Here we report a novel hexagonal 2H-MoSe2 photocatalyst with ultraviolet (UV)-visible-near infrared (NIR) light response for the first time. The results indicate that the MoSe2 displays excellent photo-absorption and photocatalytic activity in the reduction of Cr(VI) under UV and visible even NIR light irradiation. MoSe2 synthesized at pH value of 2 achieves the highest Cr(VI) reduction rates of 99%, 91% and 100% under UV, visible and NIR light irradiation, respectively, which should be attributed to its comparatively higher light absorption, efficient charge separation and transfer as well as relatively large number of surface active sites. The excellent broad spectrum active photocatalytic activity makes the MoSe2 to be a promising photocatalyst for the effective utilization of solar energy.

  1. Field-scale reduction of PCB bioavailability with activated carbon amendment to river sediments.

    PubMed

    Beckingham, Barbara; Ghosh, Upal

    2011-12-15

    Remediation of contaminated sediments remains a technological challenge because traditional approaches do not always achieve risk reduction goals for human health and ecosystem protection and can even be destructive for natural resources. Recent work has shown that uptake of persistent organic pollutants such as polychlorinated biphenyls (PCBs) in the food web is strongly influenced by the nature of contaminant binding, especially to black carbon surfaces in sediments. We demonstrate for the first time in a contaminated river that application of activated carbon to sediments in the field reduces biouptake of PCBs in benthic organisms. After treatment with activated carbon applied at a dose similar to the native organic carbon of sediment, bioaccumulation in freshwater oligochaete worms was reduced compared to preamendment conditions by 69 to 99%, and concentrations of PCBs in water at equilibrium with the sediment were reduced by greater than 93% at all treatment sites for up to three years of monitoring. By comparing measured reductions in bioaccumulation of tetra- and penta-chlorinated PCB congeners resulting from field application of activated carbon to a laboratory study where PCBs were preloaded onto activated carbon, it is evident that equilibrium sorption had not been achieved in the field. Although other remedies may be appropriate for some highly contaminated sites, we show through this pilot study that PCB exposure from moderately contaminated river sediments may be managed effectively through activated carbon amendment in sediments.

  2. Surface complexation modeling of U(VI) adsorption by aquifer sediments from a former mill tailings site at Rifle, Colorado

    SciTech Connect

    Hyun, S. P.; Fox, Patricia M.; Davis, James A.; Campbell, Kate M.; Hayes, Kim F.; Long, Philip E.

    2009-12-15

    U(VI) adsorption by two aquifer sediment samples was studied under oxic conditions as a function of pH, U(VI), Ca, and dissolved carbonate concentration. Background-A (BKG-A) sediment was collected upstream of a former uranium mill-tailings site at Rifle, Colorado, and Little Rusty Composite (LRC) was collected on site but with low U contamination. Batch adsorption experiments were performed using artificial groundwater solutions prepared to simulate the field groundwater composition in equilibrium with specific partial pressures of carbon dioxide. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8×10-8 to 10-5 M in [U(VI)]tot, 7.2 to 8.0 in pH, 3.0×10-3 to 6.0×10-3 M in [Ca2+], and 0.05 to 2.6% in partial pressure of carbon dioxide. The sediment was extracted with a dilute bicarbonate/carbonate solution to determine the background labile U(VI) already present in the sediment. A semi-empirical surface complexation model was developed to describe U(VI) adsorption using FITEQL4. The non-electrostatic, generalized composite surface complexation model successfully simulated U(VI) adsorption over the range of groundwater conditions at the Old Rifle site, using a two-site, two-reaction fitting scheme. The sensitivity of model parameters to background U(VI) concentration on the two samples was evaluated. U(VI) adsorption experiments were also performed using a sand fraction of BKG-A separated through repeated sonication and wet-sieving. Surface area normalized Kd for the bulk and sand fraction indicated similar reactivity for both. The surface complexation model developed in this work is expected to contribute to the prediction of fate and transport of U(VI) in the alluvial aquifer at the Old Rifle site, and to assist in the simulation of biostimulation field experiments performed at the site.

  3. Inhibition Mechanism of Uranyl Reduction Induced by Calcium-Carbonato Complexes

    NASA Astrophysics Data System (ADS)

    Jones, M. E.; Bargar, J.; Fendorf, S. E.

    2015-12-01

    Uranium mobility in the subsurface is controlled by the redox state and chemical speciation, generally as minimally soluble U(IV) or soluble U(VI) species. In the presence of even low carbonate concentrations the uranyl-carbonato complex quickly becomes the dominant aqueous species; they are, in fact, the primary aqueous species in most groundwaters. Calcium in groundwater leads to ternary calcium-uranyl-carbonato complexes that limit the rate and extent of U(VI) reduction. This decrease in reduction rate has been attributed to surface processes, thermodynamic limitations, and kinetic factors. Here we present a new mechanism for the inhibition of ferrous iron reduction of uranyl-carbonato species in the presence of calcium. A series of experiments under variable Ca conditions were preformed to determine the role of Ca in the inhibition of U reduction by ferrous iron. Calcium ions in the Ca2UO2(CO3)3 complex sterically prevent the interaction of Fe(II) with U(VI), in turn preventing the Fe(II)-U(VI) distance required for electron transfer. The mechanism described here helps to predict U redox transformations in suboxic environments and clarifies the role of Ca in the fate and mobility of U. Electrochemical measurements further show the decrease of the U(VI) to U(V) redox potential of the uranyl-carbonato complex with decreasing pH suggesting the first electron transfer is critical determining the rate and extent of uranium reduction.

  4. Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction

    SciTech Connect

    Lim, B.; Tao, J.; Jiang, M.; Camargo, P.H.C.; Cho, E.C.; Lu, X.; Zhu, Y.; Xia, Y.

    2009-06-05

    Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K{sub 2}PtCl{sub 4} with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst.

  5. Cassini UVIS Observations of the Io Plasma Torus. 4; Modeling Temporal and Azimuthal Variability

    NASA Technical Reports Server (NTRS)

    Steffl, A. J.; Delamere, P. A.; Bagenal, F.

    2008-01-01

    In this fourth paper in a series, we present a model of the remarkable temporal and azimuthal variability of the Io plasma torus observed during the Cassini encounter with Jupiter. Over a period of three months, the Cassini Ultraviolet Imaging Spectrograph (UVIS) observed a dramatic variaton in the average torus composition. Superimposed on this long-term variation, is a 10.07-hour periodicity caused by azimuthal variation in plasma composition subcorotating relative to System III longitude. Quite surprisingly, the amplitude of the azimuthal variation appears to be modulated at the beat frequency between the System III period and the observed 10.07-hour period. Previously, we have successfully modeled the months-long compositional change by supposing a factor of three increase in the amount of material supplied to Io's extended neutral clouds. Here, we extend our torus chemistry model to include an azimuthal dimension. We postulate the existence of two azimuthal variations in the number of superthermal electrons in the torus: a primary variation that subcorotates with a period of 10.07 hours and a secondary variation that remains fixed in System III longitude. Using these two hot electron variations, our model can reproduce the observed temporal and azimuthal variations observed by Cassini UVIS.

  6. Analysis of Dragon's Breath and Scattered Light Detector Anomalies on WFC3/UVIS

    NASA Astrophysics Data System (ADS)

    Fowler, Julia; Markwardt, Larissa; Bourque, Matthew; Anderson, Jay

    2017-02-01

    We summarize the examination of the light anomalies known as Dragon's Breath and Scattered Light for the UVIS channel of Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We present three methods for WFC3 users to help avoid these effects during observation planning. We analyzed all of the full-frame wide and long pass filters with exposure times ≥ 300 seconds, comprising ∼13% of WFC3/UVIS on-orbit data (∼20% of all full-frame data, and ∼35% of all full-frame ≥300 second exposures.) We find that stars producing Dragon's Breath peak at specific orientations to the detector and V-band magnitudes. The bulk of these stars fall along the vertical and horizontal edges, within ∼490 pixels of the image frame. The corners of the detector show significantly fewer instances of Dragon's Breath and Scattered Light, though still a few occurrences. Furthermore, matching stars outside the field of the image to V-band magnitude data from the Hubble Guide Star Catalog II (GSC-II) shows that stars causing the anomaly consistently peak around a V-band magnitude of 11.9 or 14.6, whereas the general trend of objects lying outside the field instead peaks around a magnitude of 16.5 within our exposure time and filter selection.

  7. WFC3/UVIS Dark Calibration: Monitoring Results and Improvements to Dark Reference Files

    NASA Astrophysics Data System (ADS)

    Bourque, M.; Baggett, S.

    2016-04-01

    The Wide Field Camera 3 (WFC3) UVIS detector possesses an intrinsic signal during exposures, even in the absence of light, known as dark current. A daily monitor program is employed every HST cycle to characterize and measure this current as well as to create calibration files which serve to subtract the dark current from science data. We summarize the results of the daily monitor program for all on-orbit data. We also introduce a new algorithm for generating the dark reference files that provides several improvements to their overall quality. Key features to the new algorithm include correcting the dark frames for Charge Transfer Efficiency (CTE) losses, using an anneal-cycle average value to measure the dark current, and generating reference files on a daily basis. This new algorithm is part of the release of the CALWF3 v3.3 calibration pipeline on February 23, 2016 (also known as "UVIS 2.0"). Improved dark reference files have been regenerated and re-delivered to the Calibration Reference Data System (CRDS) for all on-orbit data. Observers with science data taken prior to the release of CALWF3 v3.3 may request their data through the Mikulski Archive for Space Telescopes (MAST) to obtain the improved products.

  8. TITAN’S UPPER ATMOSPHERE FROM CASSINI/UVIS SOLAR OCCULTATIONS

    SciTech Connect

    Capalbo, Fernando J.; Bénilan, Yves; Yelle, Roger V.; Koskinen, Tommi T.

    2015-12-01

    Titan’s atmosphere is composed mainly of molecular nitrogen, methane being the principal trace gas. From the analysis of 8 solar occultations measured by the Extreme Ultraviolet channel of the Ultraviolet Imaging Spectrograph (UVIS) on board Cassini, we derived vertical profiles of N{sub 2} in the range 1100–1600 km and vertical profiles of CH{sub 4} in the range 850–1300 km. The correction of instrument effects and observational effects applied to the data are described. We present CH{sub 4} mole fractions, and average temperatures for the upper atmosphere obtained from the N{sub 2} profiles. The occultations correspond to different times and locations, and an analysis of variability of density and temperature is presented. The temperatures were analyzed as a function of geographical and temporal variables, without finding a clear correlation with any of them, although a trend of decreasing temperature toward the north pole was observed. The globally averaged temperature obtained is (150 ± 1) K. We compared our results from solar occultations with those derived from other UVIS observations, as well as studies performed with other instruments. The observational data we present confirm the atmospheric variability previously observed, add new information to the global picture of Titan’s upper atmosphere composition, variability, and dynamics, and provide new constraints to photochemical models.

  9. Spectroscopic studies of U(VI) sorption at the kaolinite-water interface. Final report

    SciTech Connect

    Thompson, H.A.; Parks, G.A.; Brown, G.E. Jr.

    1994-06-01

    Efficient use of U as a resource and safe handling, recycling and disposal of U-containing wastes require an understanding of the factors controlling the fate of U, where fate refers to the destination of U, typically expressed as an environmental medium or a process phase. The sorption process constitutes a change in elemental fate. Partitioning of an element from solution to a solid phase, or sorption, can be divided into three broad categories: adsorption, surface precipitation, and absorption. Extended X-ray absorption fine structure (EXAFS), a type of X-ray absorption spectroscopy (XAS), offers the possibility for distinguishing among different modes of sorption by characterizing the atomic environment of the sorbing element. In this study, the authors use EXAFS to determine the structure of U(VI) sorption complexes at the kaolinite-water interface. In Chapter One, they present an overview of selected aspects of U structural chemistry as a basis for considering the structural environment of U at the solid-water interface. To evaluate the utility of XAS for characterization of the structural environment of U(VI) at the solid-water interface, they have carried out an in-depth analysis of XAS data from U(VI)-containing solid and solution model compounds, which they describe in Chapter Two. In Chapter three, they consider sorption of U by kaolinite as a means of effecting the removal of U from surface collection pond waters on the Rocky Flats Plant site in northern Colorado.

  10. Molecular nitrogen and methane density retrievals from Cassini UVIS dayglow observations of Titan's upper atmosphere

    NASA Astrophysics Data System (ADS)

    Stevens, Michael H.; Evans, J. Scott; Lumpe, Jerry; Westlake, Joseph H.; Ajello, Joseph M.; Bradley, E. Todd; Esposito, Larry W.

    2015-02-01

    We retrieve number densities of molecular nitrogen (N2) and methane (CH4) from Titan's upper atmosphere using the UV dayglow. We use Cassini Ultraviolet Imaging Spectrograph (UVIS) limb observations from 800 to 1300 km of the N I 1493 Å and N II 1085 Å multiplets, both produced directly from photofragmentation of N2. UVIS N2 and CH4 densities are in agreement with measurements from Cassini's Ion Neutral Mass Spectrometer (INMS) from the same flyby if INMS densities are scaled up by a factor of 3.0 as reported in previous studies. Analysis of three Cassini flybys of Titan shows that (1) the CH4 homopause on Titan is between 900 and 1100 km, (2) upper atmospheric temperatures vary by less than 10 K over 6 h at the same geographic location and (3) from 1100 to 1700 local solar time temperatures also vary by less than 10 K. The capability of retrieving the global-scale composition from these data complements existing techniques and significantly advances the study of upper atmospheric variability at Titan and for any other atmosphere with a detectable UV dayglow.

  11. Cassini UVIS observations of Titan ultraviolet airglow intensity dependence with solar zenith angle

    NASA Astrophysics Data System (ADS)

    Royer, E. M.; Ajello, J. M.; Holsclaw, G. M.; West, R. A.; Esposito, L. W.; Bradley, E. T.

    2017-01-01

    The Cassini Ultraviolet Imaging Spectrometer (UVIS) observed the airglow (dayglow and nightglow) of Titan over a range of solar zenith angles (SZA) from 14 to 150° on five separate observations obtained between 2008 and 2012. The modeling of the solar cycle normalized UVIS observations indicates that a Chapman layer function provides a satisfactory fit to the intensity of the EUV and FUV airglow molecular emissions of the N2 Lyman-Birge-Hopfield band system (LBH a1Πg→X1>∑g+), the Carroll-Yoshino band system (c4'1>∑u+→X1>∑g+), and of several atomic multiplets of nitrogen (NI, II) as a function of SZA. This result shows that the strongest contribution to the Titan dayglow occurs by processes (photoelectrons and photodissociation) involving the solar EUV flux rather than magnetospheric particle precipitation that dominates emission excitation in the nightglow.

  12. Kinetics of uranium(VI) reduction by hydrogen sulfide in anoxic aqueous systems.

    PubMed

    Hua, Bin; Xu, Huifang; Terry, Jeff; Deng, Baolin

    2006-08-01

    Aqueous U(VI) reduction by hydrogen sulfide was investigated by batch experiments and speciation modeling; product analysis by transmission electron microscopy (TEM) was also performed. The molar ratio of U(VI) reduced to sulfide consumed, and the TEM result suggested that the reaction stoichiometry could be best represented by UO2(2+) + HS- = UO2+ S* + H+. At pH 6.89 and total carbonate concentration ([CO32-]T) of 4.0 mM, the reaction took place according to the following kinetics: -d[U(VI)]/dt = 0.0103[U(VI)][S2-]T0.54 where [U(VI)] is the concentration of hexavalent uranium, and [S2-]T is the total concentration of sulfide. The kinetics of U(VI) reduction was found to be largely controlled by [CO32-]T (examined from 0.0 to 30.0 mM) and pH (examined from 6.37 to 9.06). The reduction was almost completely inhibited with the following [CO32-]T and pH combinations: [(> or = 15.0 mM, pH 6.89); (> or = 4.0 mM, pH 8.01); and (> or = 2.0 mM, pH 9.06)]. By comparing the experimental results with the calculated speciation of U(VI), it was found that there was a strong correlation between the measured initial reaction rates and the calculated total concentrations of uranium-hydroxyl species; we, therefore, concluded that uranium-hydroxyl species were the ones being reduced by sulfide, not the dominant U-carbonate species present in many carbonate-containing systems.

  13. Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

    DOEpatents

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2010-08-03

    A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

  14. Catalytic activity of various pepsin reduced Au nanostructures towards reduction of nitroarenes and resazurin

    NASA Astrophysics Data System (ADS)

    Sharma, Bhagwati; Mandani, Sonam; Sarma, Tridib K.

    2015-01-01

    Pepsin, a digestive protease enzyme, could function as a reducing as well as stabilizing agent for the synthesis of Au nanostructures of various size and shape under different reaction conditions. The simple tuning of the pH of the reaction medium led to the formation of spherical Au nanoparticles, anisotropic Au nanostructures such as triangles, hexagons, etc., as well as ultra small fluorescent Au nanoclusters. The activity of the enzyme was significantly inhibited after its participation in the formation of Au nanoparticles due to conformational changes in the native structure of the enzyme which was studied by fluorescence, circular dichroism (CD), and infra red spectroscopy. However, the Au nanoparticle-enzyme composites served as excellent catalyst for the reduction of p-nitrophenol and resazurin, with the catalytic activity varying with size and shape of the nanoparticles. The presence of pepsin as the surface stabilizer played a crucial role in the activity of the Au nanoparticles as reduction catalysts, as the approach of the reacting molecules to the nanoparticle surface was actively controlled by the stabilizing enzyme.

  15. Enhanced catalytic activity of solid and hollow platinum-cobalt nanoparticles towards reduction of 4-nitrophenol

    NASA Astrophysics Data System (ADS)

    Krajczewski, Jan; Kołątaj, Karol; Kudelski, Andrzej

    2016-12-01

    Previous investigations of hollow platinum nanoparticles have shown that such nanostructures are more active catalysts than their solid counterparts towards the following electrochemical reactions: reduction of oxygen, evolution of hydrogen, and oxidation of borohydride, methanol and formic acid. In this work we show that synthesised using standard galvanic replacement reaction (with Co templates) hollow platinum nanoparticles exhibit enhanced catalytic activity also towards reduction of 4-nitrophenol by sodium borohydride in water. Unlike in the case of procedures involving hollow platinum catalysts employed so far to carry out this reaction it is not necessary to couple analysed platinum nanoparticles to the surface of an electrode. Simplification of the analyzed reaction may eliminate same experimental errors. We found that the enhanced catalytic activity of hollow Pt nanoparticles is not only connected with generally observed larger surface area of hollow nanostructures, but is also due to the contamination of formed hollow nanostructures with cobalt, from which sacrificial templates used in the synthesis of hollow Pt nanostrustures have been formed. Because using sacrificial templates is a typical method of synthesis of hollow metal nanostructures, formed hollow nanoparticles are probably often contaminated, which may significantly influence their catalytic activity.

  16. A modified oxic-settling-anaerobic activated sludge process using gravity thickening for excess sludge reduction

    PubMed Central

    Wang, Jun; Li, Shi-Yu; Jiang, Feng; Wu, Ke; Liu, Guang-Li; Lu, Hui; Chen, Guang-Hao

    2015-01-01

    Oxic-settling-anaerobic process (OSA) was known as a cost-effective way to reduce the excess sludge production with simple upgrade of conventional activated sludge process (CAS). A low oxidation-reduction potential (ORP) level was the key factor to sludge decay and lysis in the sludge holding tank of the OSA process. However, the ORP control with nitrogen purge or chemical dosing in the OSA process would induce extra expense and complicate the operation. Hence, in this study, a sludge holding tank using gravity thickening was applied to OSA process to reduce the excess sludge production without any ORP control. Results showed that the modified OSA process not only reduced the excess sludge production effectively but also improved the sludge settleability without affected the treatment capacity. The reduction of the excess sludge production in the modified OSA process resulted from interactions among lots of factors. The key element of the process was the gravity thickening sludge holding tank. PMID:26350761

  17. A modified oxic-settling-anaerobic activated sludge process using gravity thickening for excess sludge reduction

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Li, Shi-Yu; Jiang, Feng; Wu, Ke; Liu, Guang-Li; Lu, Hui; Chen, Guang-Hao

    2015-09-01

    Oxic-settling-anaerobic process (OSA) was known as a cost-effective way to reduce the excess sludge production with simple upgrade of conventional activated sludge process (CAS). A low oxidation-reduction potential (ORP) level was the key factor to sludge decay and lysis in the sludge holding tank of the OSA process. However, the ORP control with nitrogen purge or chemical dosing in the OSA process would induce extra expense and complicate the operation. Hence, in this study, a sludge holding tank using gravity thickening was applied to OSA process to reduce the excess sludge production without any ORP control. Results showed that the modified OSA process not only reduced the excess sludge production effectively but also improved the sludge settleability without affected the treatment capacity. The reduction of the excess sludge production in the modified OSA process resulted from interactions among lots of factors. The key element of the process was the gravity thickening sludge holding tank.

  18. Incorporation of Np(V) and U(VI) in carbonate and sulfate minerals crystallized from aqueous solution

    NASA Astrophysics Data System (ADS)

    Balboni, Enrica; Morrison, Jessica M.; Wang, Zheming; Engelhard, Mark H.; Burns, Peter C.

    2015-02-01

    The neptunyl Np(V)O2+ and uranyl U(VI)O22+ ions are soluble in groundwater, although their interaction with minerals in the subsurface may impact their mobility. One mechanism for the immobilization of actinyl ions in the subsurface is co-precipitation in low-temperature minerals that form naturally, or that are induced to form as part of a remediation strategy. Important differences in the crystal-chemical behavior of the Np(V) neptunyl and U(VI) uranyl ions suggest their behavior towards incorporation into growing crystals may differ significantly. Using a selection of low-temperature minerals synthesized in aqueous systems under ambient conditions, this study examines the factors that impact the structural incorporation of the Np(V) neptunyl and U(VI) uranyl ions in carbonate and sulfate minerals. Calcite (CaCO3), aragonite (CaCO3), gypsum (CaSO4·2H2O), strontianite (SrCO3), cerussite (PbCO3), celestine (SrSO4), and anglesite (PbSO4) were synthesized from aqueous solutions containing either 400-1000 ppm of U(VI) or Np(V) relative to the divalent cation present in the system. The synthetic products were investigated by inductively coupled plasma mass spectrometry, luminescence and time resolved luminescence spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Amongst the carbonate minerals, calcite significantly favors Np(V) incorporation over U(VI). U(VI) and Np(V) are incorporated in aragonite and strontianite in similar amounts, whereas cerussite did not incorporate either U(VI) or Np(V) under the synthesis conditions. The sulfate minerals weakly interact with the actinyl ions, relative to the carbonate minerals. Incorporation of U(VI) and Np(V) in celestine was observed at the level of a few tens of ppm; anglesite and gypsum did not incorporate detectable U(VI) or Np(V). Luminescence spectra of the uranyl incorporated in aragonite and strontianite are consistent with a uranyl unit coordinated by three bidentate CO32- groups

  19. Controlled reduction of red mud waste to produce active systems for environmental applications: heterogeneous Fenton reaction and reduction of Cr(VI).

    PubMed

    Costa, Regina C C; Moura, Flávia C C; Oliveira, Patrícia E F; Magalhães, Fabiano; Ardisson, José D; Lago, Rochel M

    2010-02-01

    In this work, controlled reduction of red mud with H(2) was used to produce active systems for two different environmental applications, i.e. the heterogeneous Fenton reaction and the reduction of Cr(VI). Mössbauer, powder X-ray diffraction, thermal analyses and scanning electron microscopy analyses showed that at different temperatures, i.e. 300, 400, 500 and 600 degrees C, H(2) reduces red mud to different phases, mainly Fe(3)O(4), Fe(0)/Fe(3)O(4) and Fe(0). These Fe phases are dispersed on Al, Si and Ti oxides present in the red mud and show high reactivity towards two environmental applications, i.e. the heterogeneous Fenton reaction and the reduction of Cr(VI). Reduction with H(2) at 400 degrees C showed the best results for the oxidation of the model dye methylene blue with H(2)O(2) at neutral pH due to the presence of the composite Fe(0)/Fe(3)O(4). The reduced red mud at 500-600 degrees C produced Fe(0) highly active for the reduction of Cr(VI) in aqueous medium. Another feature of these red mud based system is that after deactivation due to extensive use they can be completely regenerated by simple treatment with H(2).

  20. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    SciTech Connect

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; Mavrikakis, Manos; Xia, Younan

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.

  1. Thermal Noise Reduction of Mechanical Oscillators by Actively Controlled External Dissipative Forces

    NASA Technical Reports Server (NTRS)

    Liang, Shoudan; Medich, David; Czajkowsky, Daniel M.; Sheng, Sitong; Yuan, Jian-Yang; Shao, Zhifeng

    1999-01-01

    We show that the thermal fluctuations of very soft mechanical oscillators, such as the cantilever in an atomic force microscope (AFM), can be reduced without changing the stiffness of the spring or having to lower the environment temperature. We derive a theoretical relationship between the thermal fluctuations of an oscillator and an actively external-dissipative force. This relationship is verified by experiments with an AFM cantilever where the external active force is coupled through a magnetic field. With simple instrumentation, we have reduced the thermal noise amplitude of the cantilever by a factor of 3.4, achieving an apparent temperature of 25 K with the environment at 295K. This active noise reduction approach can significantly improve the accuracy of static position or static force measurements in a number of practical applications.

  2. Palladium-platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction.

    PubMed

    Wang, Xue; Choi, Sang-Il; Roling, Luke T; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A; Mavrikakis, Manos; Xia, Younan

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. These results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.

  3. Active sound reduction: A study of recent developments and some future possibilities

    NASA Astrophysics Data System (ADS)

    Lindqvist, E.

    1983-11-01

    It is suggested that active sound reduction is easiest to implement and most effective at low frequencies and in a duct rather than in a room or a free field. The prospects for success are considerably improved if the sound to be attenuated is periodic. Symmetry of the sound field can sometimes be exploited. The physical mechanisms of sound attenuation include reflection of sound by secondary sources, creation of higher order sources in order to reduce the energy radiated and conversion of acoustic energy. Active techniques can also be applied to prevent transmission of sound or vibrations from one sub-field to another. Microelectronics and digital filtering techniques are expected to greatly influence active sound attenuators.

  4. Why copper is preferred over iron for oxygen activation and reduction in haem-copper oxidases

    NASA Astrophysics Data System (ADS)

    Bhagi-Damodaran, Ambika; Michael, Matthew A.; Zhu, Qianhong; Reed, Julian; Sandoval, Braddock A.; Mirts, Evan N.; Chakraborty, Saumen; Moënne-Loccoz, Pierre; Zhang, Yong; Lu, Yi

    2016-11-01

    Haem-copper oxidase (HCO) catalyses the natural reduction of oxygen to water using a haem-copper centre. Despite decades of research on HCOs, the role of non-haem metal and the reason for nature's choice of copper over other metals such as iron remains unclear. Here, we use a biosynthetic model of HCO in myoglobin that selectively binds different non-haem metals to demonstrate 30-fold and 11-fold enhancements in the oxidase activity of Cu- and Fe-bound HCO mimics, respectively, as compared with Zn-bound mimics. Detailed electrochemical, kinetic and vibrational spectroscopic studies, in tandem with theoretical density functional theory calculations, demonstrate that the non-haem metal not only donates electrons to oxygen but also activates it for efficient O-O bond cleavage. Furthermore, the higher redox potential of copper and the enhanced weakening of the O-O bond from the higher electron density in the d orbital of copper are central to its higher oxidase activity over iron. This work resolves a long-standing question in bioenergetics, and renders a chemical-biological basis for the design of future oxygen-reduction catalysts.

  5. Enhanced Activity of Supported Ni Catalysts Promoted by Pt for Rapid Reduction of Aromatic Nitro Compounds

    PubMed Central

    Shang, Huishan; Pan, Kecheng; Zhang, Lu; Zhang, Bing; Xiang, Xu

    2016-01-01

    To improve the activities of non-noble metal catalysts is highly desirable and valuable to the reduced use of noble metal resources. In this work, the supported nickel (Ni) and nickel-platinum (NiPt) nanocatalysts were derived from a layered double hydroxide/carbon composite precursor. The catalysts were characterized and the role of Pt was analysed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) mapping, and X-ray photoelectron spectroscopy (XPS) techniques. The Ni2+ was reduced to metallic Ni0 via a self-reduction way utilizing the carbon as a reducing agent. The average sizes of the Ni particles in the NiPt catalysts were smaller than that in the supported Ni catalyst. The electronic structure of Ni was affected by the incorporation of Pt. The optimal NiPt catalysts exhibited remarkably improved activity toward the reduction of nitrophenol, which has an apparent rate constant (Ka) of 18.82 × 10−3 s−1, 6.2 times larger than that of Ni catalyst and also larger than most of the reported values of noble-metal and bimetallic catalysts. The enhanced activity could be ascribed to the modification to the electronic structure of Ni by Pt and the effect of exposed crystal planes. PMID:28335231

  6. Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal-nitrogen coordination.

    PubMed

    Strickland, Kara; Miner, Elise; Jia, Qingying; Tylus, Urszula; Ramaswamy, Nagappan; Liang, Wentao; Sougrati, Moulay-Tahar; Jaouen, Frédéric; Mukerjee, Sanjeev

    2015-06-10

    Replacement of noble metals in catalysts for cathodic oxygen reduction reaction with transition metals mostly create active sites based on a composite of nitrogen-coordinated transition metal in close concert with non-nitrogen-coordinated carbon-embedded metal atom clusters. Here we report a non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media. In situ X-ray absorption spectroscopy in conjunction with ex situ microscopy clearly shows nitrided carbon fibres with embedded iron particles that are not directly involved in the oxygen reduction pathway. Instead, the reaction occurs primarily on the carbon-nitrogen structure in the outer skin of the nitrided carbon fibres. Implications include the potential of creating greater active site density and the potential elimination of any Fenton-type process involving exposed iron ions culminating in peroxide initiated free-radical formation.

  7. Asymmetric reduction of activated alkenes using an enoate reductase from Gluconobacter oxydans.

    PubMed

    Richter, Nina; Gröger, Harald; Hummel, Werner

    2011-01-01

    A recombinant enoate reductase from Gluconobacter oxydans was heterologously expressed, purified, characterised and applied in the asymmetric reduction of activated alkenes. In addition to the determination of the kinetic properties, the major focus of this work was to utilise the enzyme in the biotransformation of different interesting compounds such as 3,5,5-trimethyl-2-cyclohexen-1,4-dione (ketoisophorone) and (E/Z)-3,7-dimethyl-2,6-octadienal (citral). The reaction proceeded with excellent stereoselectivities (>99% ee) as well as absolute chemo- and regioselectivity, only the activated C=C bond of citral was reduced by the enoate reductase, while non-activated C=C bond and carbonyl moiety remained untouched. The described strategy can be used for the production of enantiomerically pure building blocks, which are difficult to prepare by chemical means. In general, the results show that the investigated enoate reductase is a promising catalyst for the use in asymmetric C=C bond reductions.

  8. Highly active oxygen reduction non-platinum group metal electrocatalyst without direct metal–nitrogen coordination

    PubMed Central

    Strickland, Kara; Miner, Elise; Jia, Qingying; Tylus, Urszula; Ramaswamy, Nagappan; Liang, Wentao; Sougrati, Moulay-Tahar; Jaouen, Frédéric; Mukerjee, Sanjeev

    2015-01-01

    Replacement of noble metals in catalysts for cathodic oxygen reduction reaction with transition metals mostly create active sites based on a composite of nitrogen-coordinated transition metal in close concert with non-nitrogen-coordinated carbon-embedded metal atom clusters. Here we report a non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media. In situ X-ray absorption spectroscopy in conjunction with ex situ microscopy clearly shows nitrided carbon fibres with embedded iron particles that are not directly involved in the oxygen reduction pathway. Instead, the reaction occurs primarily on the carbon–nitrogen structure in the outer skin of the nitrided carbon fibres. Implications include the potential of creating greater active site density and the potential elimination of any Fenton-type process involving exposed iron ions culminating in peroxide initiated free-radical formation. PMID:26059552

  9. Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

    SciTech Connect

    Christ, J. M.; Neyerlin, K. C.; Wang, H.; Richards, R.; Dinh, H. N.

    2014-10-30

    The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 – C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resulting in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Lastly, greater than a 44% loss in ORR activity at 0.9V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities.

  10. Antidepressant activity of memory-enhancing drugs in the reduction of submissive behavior model.

    PubMed

    Knapp, Richard J; Goldenberg, Rachel; Shuck, Caroline; Cecil, Alicia; Watkins, Jeff; Miller, Cortland; Crites, Glenda; Malatynska, Ewa

    2002-04-05

    The present study tests the activity of nootropic drugs in a behavioral test linked to depression. This test measures the reduction of submissive behavior in a competition test as the relative success of two food-restricted rats to gain access to a feeder. Nootropic drugs tested include piracetam (2-oxo-1-pyrrolidineacetamide), aniracetam (1-(4-methoxybenzoyl)-2-pyrrolidinone), the Ampakine, Ampalex, 1-(quinoxalin-6-ylcarbonyl)piperidine, and analogs were compared to the antidepressants, fluoxetine ((+/-)-N-methyl-gamma-(4-[trifluoromethyl]phenoxy)-benzenepropanamine) and desimpramine (5H-dibenz[b,f]azepine-5-propanamine, 10,11-dihydro-N-methyl-, monohydrochloride), while the anxiolytic diazepam (7-chloro-1-methyl-5-phenyl-3H-1,4-benzodiazepin-2(1H)-one) served as a control. Drugs were given intraperitoneally for 3 weeks. The antidepressant and nootropic drugs reduced submissive behavior over time. The effect was dose dependent as measured for fluoxetine and Ampakines. The reduction of submissive behavior by Ampakines gradually faded after cessation of treatment and had a more rapid onset of activity (during the 1st week of treatment) than fluoxetine (after 2 weeks). The results suggest that Ampakines may have antidepressant activity. The potential of depression treatment with memory-enhancing drugs is hypothesized and the link between cognition and depression is discussed.

  11. Enhanced Activity of Supported Ni Catalysts Promoted by Pt for Rapid Reduction of Aromatic Nitro Compounds.

    PubMed

    Shang, Huishan; Pan, Kecheng; Zhang, Lu; Zhang, Bing; Xiang, Xu

    2016-06-04

    To improve the activities of non-noble metal catalysts is highly desirable and valuable to the reduced use of noble metal resources. In this work, the supported nickel (Ni) and nickel-platinum (NiPt) nanocatalysts were derived from a layered double hydroxide/carbon composite precursor. The catalysts were characterized and the role of Pt was analysed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) mapping, and X-ray photoelectron spectroscopy (XPS) techniques. The Ni(2+) was reduced to metallic Ni⁰ via a self-reduction way utilizing the carbon as a reducing agent. The average sizes of the Ni particles in the NiPt catalysts were smaller than that in the supported Ni catalyst. The electronic structure of Ni was affected by the incorporation of Pt. The optimal NiPt catalysts exhibited remarkably improved activity toward the reduction of nitrophenol, which has an apparent rate constant (Ka) of 18.82 × 10(-3) s(-1), 6.2 times larger than that of Ni catalyst and also larger than most of the reported values of noble-metal and bimetallic catalysts. The enhanced activity could be ascribed to the modification to the electronic structure of Ni by Pt and the effect of exposed crystal planes.

  12. Enhancing oxygen reduction reaction activity of Pt-shelled catalysts via subsurface alloying.

    PubMed

    Cheng, Daojian; Qiu, Xiangguo; Yu, Haiyan

    2014-10-14

    Despite remarkable efforts have been put into the field of Pt-shelled catalysts containing an atomically thin Pt surface layer for the oxygen reduction reaction (ORR) in the last decade, further development of new Pt-shelled catalysts is still necessary. Here, a new set of Pt-shelled catalysts by subsurface alloying with early transition metals such as Mn and Fe is predicted to be a good candidate for the ORR by using density functional theory (DFT) calculations. Trends in oxygen reduction activity of Pt-alloy catalysts are determined with calculations of oxygen binding by using the slab and cluster models. It is found that the subsurface alloys by the incorporation of submonolayer M (M = Mn and Fe) into Pt(111) in the slab model result in the enhancement of ORR activity, compared with the well-known Pt(111)-skin-M, pure Pt, and Pt3M alloy catalysts. For the cluster model, the Pt12Mn and Pt12Fe clusters are also found to be the optimal catalysts for the ORR. It is expected that this work can open up new opportunities for enhancing the ORR activity of Pt-alloy catalysts by subsurface alloying.

  13. Activity reductions in perirhinal cortex predict conceptual priming and familiarity-based recognition.

    PubMed

    Wang, Wei-Chun; Ranganath, Charan; Yonelinas, Andrew P

    2014-01-01

    Although it is well established that regions in the medial temporal lobes are critical for explicit memory, recent work has suggested that one medial temporal lobe subregion--the perirhinal cortex (PRC)--may also support conceptual priming, a form of implicit memory. Here, we sought to investigate whether activity reductions in PRC, previously linked to familiarity-based recognition, might also support conceptual implicit memory retrieval. Using a free association priming task, the current study tested the prediction that PRC indexes conceptual priming independent of contributions from perceptual and response repetition. Participants first completed an incidental semantic encoding task outside of the MRI scanner. Next, they were scanned during performance of a free association priming task, followed by a recognition memory test. Results indicated successful conceptual priming was associated with decreased PRC activity, and that an overlapping region within the PRC also exhibited activity reductions that covaried with familiarity during the recognition memory test. Our results demonstrate that the PRC contributes to both conceptual priming and familiarity-based recognition, which may reflect a common role of this region in implicit and explicit memory retrieval.

  14. Why copper is preferred over iron for oxygen activation and reduction in haem-copper oxidases.

    PubMed

    Bhagi-Damodaran, Ambika; Michael, Matthew A; Zhu, Qianhong; Reed, Julian; Sandoval, Braddock A; Mirts, Evan N; Chakraborty, Saumen; Moënne-Loccoz, Pierre; Zhang, Yong; Lu, Yi

    2017-03-01

    Haem-copper oxidase (HCO) catalyses the natural reduction of oxygen to water using a haem-copper centre. Despite decades of research on HCOs, the role of non-haem metal and the reason for nature's choice of copper over other metals such as iron remains unclear. Here, we use a biosynthetic model of HCO in myoglobin that selectively binds different non-haem metals to demonstrate 30-fold and 11-fold enhancements in the oxidase activity of Cu- and Fe-bound HCO mimics, respectively, as compared with Zn-bound mimics. Detailed electrochemical, kinetic and vibrational spectroscopic studies, in tandem with theoretical density functional theory calculations, demonstrate that the non-haem metal not only donates electrons to oxygen but also activates it for efficient O-O bond cleavage. Furthermore, the higher redox potential of copper and the enhanced weakening of the O-O bond from the higher electron density in the d orbital of copper are central to its higher oxidase activity over iron. This work resolves a long-standing question in bioenergetics, and renders a chemical-biological basis for the design of future oxygen-reduction catalysts.

  15. Impact of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Reaction Activity for Platinum Electrocatalysts

    DOE PAGES

    Christ, J. M.; Neyerlin, K. C.; Wang, H.; ...

    2014-10-30

    The impact of model membrane degradation compounds on the relevant electrochemical parameters for the oxygen reduction reaction (i.e. electrochemical surface area and catalytic activity), was studied for both polycrystalline Pt and carbon supported Pt electrocatalysts. Model compounds, representing previously published, experimentally determined polymer electrolyte membrane degradation products, were in the form of perfluorinated organic acids that contained combinations of carboxylic and/or sulfonic acid functionality. Perfluorinated carboxylic acids of carbon chain length C1 – C6 were found to have an impact on electrochemical surface area (ECA). The longest chain length acid also hindered the observed oxygen reduction reaction (ORR) performance, resultingmore » in a 17% loss in kinetic current (determined at 0.9 V). Model compounds containing sulfonic acid functional groups alone did not show an effect on Pt ECA or ORR activity. Lastly, greater than a 44% loss in ORR activity at 0.9V was observed for diacid model compounds DA-Naf (perfluoro(2-methyl-3-oxa-5-sulfonic pentanoic) acid) and DA-3M (perfluoro(4-sulfonic butanoic) acid), which contained both sulfonic and carboxylic acid functionalities.« less

  16. Activity reductions in perirhinal cortex predict conceptual priming and familiarity-based recognition

    PubMed Central

    Wang, Wei-chun; Ranganath, Charan; Yonelinas, Andrew P

    2013-01-01

    Although it is well established that regions in the medial temporal lobes are critical for explicit memory, recent work has suggested that one medial temporal lobe subregion – the perirhinal cortex (PRC) – may also support conceptual priming, a form of implicit memory. Here, we sought to investigate whether activity reductions in PRC, previously linked to familiarity-based recognition, might also support conceptual implicit memory retrieval. Using a free association priming task, the current study tested the prediction that PRC indexes conceptual priming independent of contributions from perceptual and response repetition. Participants first completed an incidental semantic encoding task outside of the MRI scanner. Next, they were scanned during performance of a free association priming task, followed by a recognition memory test. Results indicated successful conceptual priming was associated with decreased PRC activity, and that an overlapping region within the PRC also exhibited activity reductions that covaried with familiarity during the recognition memory test. Our results demonstrate that the PRC contributes to both conceptual priming and familiarity-based recognition, which may reflect a common role of this region in implicit and explicit memory retrieval. PMID:24157537

  17. Active Vibration Control for Helicopter Interior Noise Reduction Using Power Minimization

    NASA Technical Reports Server (NTRS)

    Mendoza, J.; Chevva, K.; Sun, F.; Blanc, A.; Kim, S. B.

    2014-01-01

    This report describes work performed by United Technologies Research Center (UTRC) for NASA Langley Research Center (LaRC) under Contract NNL11AA06C. The objective of this program is to develop technology to reduce helicopter interior noise resulting from multiple gear meshing frequencies. A novel active vibration control approach called Minimum Actuation Power (MAP) is developed. MAP is an optimal control strategy that minimizes the total input power into a structure by monitoring and varying the input power of controlling sources. MAP control was implemented without explicit knowledge of the phasing and magnitude of the excitation sources by driving the real part of the input power from the controlling sources to zero. It is shown that this occurs when the total mechanical input power from the excitation and controlling sources is a minimum. MAP theory is developed for multiple excitation sources with arbitrary relative phasing for single or multiple discrete frequencies and controlled by a single or multiple controlling sources. Simulations and experimental results demonstrate the feasibility of MAP for structural vibration reduction of a realistic rotorcraft interior structure. MAP control resulted in significant average global vibration reduction of a single frequency and multiple frequency excitations with one controlling actuator. Simulations also demonstrate the potential effectiveness of the observed vibration reductions on interior radiated noise.

  18. Hybrid feedforward-feedback active noise reduction for hearing protection and communication.

    PubMed

    Ray, Laura R; Solbeck, Jason A; Streeter, Alexander D; Collier, Robert D

    2006-10-01

    A hybrid active noise reduction (ANR) architecture is presented and validated for a circumaural earcup and a communication earplug. The hybrid system combines source-independent feedback ANR with a Lyapunov-tuned leaky LMS filter (LyLMS) improving gain stability margins over feedforward ANR alone. In flat plate testing, the earcup demonstrates an overall C-weighted total noise reduction of 40 dB and 30-32 dB, respectively, for 50-800 Hz sum-of-tones noise and for aircraft or helicopter cockpit noise, improving low frequency (<100 Hz) performance by up to 15 dB over either control component acting individually. For the earplug, a filtered-X implementation of the LyLMS accommodates its nonconstant cancellation path gain. A fast time-domain identification method provides a high-fidelity, computationally efficient, infinite impulse response cancellation path model, which is used for both the filtered-X implementation and communication feedthrough. Insertion loss measurements made with a manikin show overall C-weighted total noise reduction provided by the ANR earplug of 46-48 dB for sum-of-tones 80-2000 Hz and 40-41 dB from 63 to 3000 Hz for UH-60 helicopter noise, with negligible degradation in attenuation during speech communication. For both hearing protectors, a stability metric improves by a factor of 2 to several orders of magnitude through hybrid ANR.

  19. Mechanisms of Active Aerodynamic Load Reduction on a Rotorcraft Fuselage With Rotor Effects

    NASA Technical Reports Server (NTRS)

    Schaeffler, Norman W.; Allan, Brian G.; Jenkins, Luther N.; Yao, Chung-Sheng; Bartram, Scott M.; Mace, W. Derry; Wong, Oliver D.; Tanner, Philip E.

    2016-01-01

    The reduction of the aerodynamic load that acts on a generic rotorcraft fuselage by the application of active flow control was investigated in a wind tunnel test conducted on an approximately 1/3-scale powered rotorcraft model simulating forward flight. The aerodynamic mechanisms that make these reductions, in both the drag and the download, possible were examined in detail through the use of the measured surface pressure distribution on the fuselage, velocity field measurements made in the wake directly behind the ramp of the fuselage and computational simulations. The fuselage tested was the ROBIN-mod7, which was equipped with a series of eight slots located on the ramp section through which flow control excitation was introduced. These slots were arranged in a U-shaped pattern located slightly downstream of the baseline separation line and parallel to it. The flow control excitation took the form of either synthetic jets, also known as zero-net-mass-flux blowing, and steady blowing. The same set of slots were used for both types of excitation. The differences between the two excitation types and between flow control excitation from different combinations of slots were examined. The flow control is shown to alter the size of the wake and its trajectory relative to the ramp and the tailboom and it is these changes to the wake that result in a reduction in the aerodynamic load.

  20. Risk reduction activities for an F-1-based advanced booster for NASA's Space Launch System

    NASA Astrophysics Data System (ADS)

    Crocker, A. M.; Doering, K. B.; Cook, S. A.; Meadows, R. G.; Lariviere, B. W.; Bachtel, F. D.

    For NASA's Space Launch System (SLS) Advanced Booster Engineering Demonstration and/or Risk Reduction (ABEDRR) procurement, Dynetics, Inc. and Pratt & Whitney Rocketdyne (PWR) formed a team to offer a wide-ranging set of risk reduction activities and full-scale, system-level demonstrations that support NASA's goal of enabling competition on an affordable booster that meets the evolved capabilities of the SLS. During the ABEDRR effort, the Dynetics Team will apply state-of-the-art manufacturing and processing techniques to the heritage F-1, resulting in a low recurring cost engine while retaining the benefits of Apollo-era experience. ABEDRR will use NASA test facilities to perform full-scale F-1 gas generator and powerpack hot-fire test campaigns for engine risk reduction. Dynetics will also fabricate and test a tank assembly to verify the structural design. The Dynetics Team is partnered with NASA through Space Act Agreements (SAAs) to maximize the expertise and capabilities applied to ABEDRR.

  1. Effects of a TiC substrate on the catalytic activity of Pt for NO reduction.

    PubMed

    Chu, Xingli; Fu, Zhaoming; Li, Shasha; Zhang, Xilin; Yang, Zongxian

    2016-05-11

    Density functional theory calculations are used to elucidate the catalytic properties of a Pt monolayer supported on a TiC(001) substrate (Pt/TiC) toward NO reduction. It is found that the compound system of Pt/TiC has a good stability due to the strong Pt-TiC interaction. The diverse dissociation paths (namely the direct dissociation mechanism and the dimeric mechanism) are investigated. The transition state searching calculations suggest that NO has strong diffusion ability and small activation energy for dissociation on the Pt/TiC. For NO reduction on the Pt/TiC surface, we have found that the direct dissociation mechanisms (NO + N + O → NO2 + N and NO + N + O → N2 + O + O) are easier with a smaller dissociation barrier than those on the Pt(111) surface; and the dimeric process (NO + NO → (NO)2 → N2O + O → N2 + O + O) is considered to be dominant or significant with even a lower energy barrier than that of the direct dissociation. The results show that Pt/TiC can serve as an efficient catalyst for NO reduction.

  2. Atomic Ordering Enhanced Electrocatalytic Activity of Nanoalloys for Oxygen Reduction Reaction

    SciTech Connect

    Loukrakpam, Rameshwori; Shan, Shiyao; Petkov, Valeri; Yang, Lefu; Luo, Jin; Zhong, Chuan-Jian

    2013-10-01

    For oxygen reduction reaction (ORR) over alloy electrocatalysts, the understanding of how the atomic arrangement of the metal species in the nanocatalysts is responsible for the catalytic enhancement is challenging for achieving better design and tailoring of nanoalloy catalysts. This paper reports results of an investigation of the atomic structures and the electrocatalytic activities of ternary and binary nanoalloys, aiming at revealing a fundamental insight into the unique atomic-scale structure-electrocatalytic activity relationship. PtIrCo catalyst and its binary counterparts (PtCo and PtIr) are chosen as a model system for this study. The effect of thermochemical treatment temperature on the atomic-scale structure of the catalysts was examined as a useful probe to the structure-activity correlation. The structural characterization of the binary and ternary nanoalloy catalysts was performed by combining surface sensitive techniques such as XPS and 3D atomic ordering sensitive techniques such as high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis (HE-XRD/PDFs) and computer simulations. The results show that the thermal treatment temperature tunes the nanoalloy’s atomic and chemical ordering in a different way depending on the chemical composition, leading to differences in the nanoalloy’s mass and specific activities. A unique structural tunability of the atomic ordering in a platinum-iridium-cobalt nanoalloy has been revealed for enhancing greatly the electrocatalytic activity toward oxygen reduction reaction, which has significant implication for rational design and nanoengineering of advanced catalysts for electrochemical energy conversion and storage.

  3. A Computational Study of BVI Noise Reduction Using Active Twist Control

    NASA Technical Reports Server (NTRS)

    Fogarty, David E.; Wilbur, Matthew L.; Sekula, Martin K.

    2010-01-01

    The results of a computational study examining the effects of active-twist control on blade-vortex interaction (BVI) noise using the Apache Active Twist Rotor are presented. The primary goal of this activity is to reduce BVI noise during a low-speed descent flight condition using active-twist control. Rotor aeroelastic behavior was modeled using the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics code and the rotor noise was predicted using the acoustics code PSU-WOPWOP. The accuracy of the analysis was validated through comparisons with experimental acoustic data for the first generation Active Twist Rotor at an advance ratio of mu=0.14. The application of active-twist to the main rotor blade system consisted of harmonic actuation frequencies ranging from 2P to 5P, control phase angles from 0' to 360 , and tip-twist amplitudes ranging from 0.5 to 4.0 . The acoustic analysis was conducted for a single low-speed flight condition of advance ratio =0.14 and shaft angle-of-attack, c^=+6 , with BVI noise levels predicted on a flat plane of observers located 1.1 rotor diameters beneath the rotor. The results indicated reductions of up to 11dB in BVI noise using 1.25 tip-twist amplitude with negligible effects on 4P vertical hub shear.

  4. Activity Trends of Binary Silver Alloy Nanocatalysts for Oxygen Reduction Reaction in Alkaline Media.

    PubMed

    Wu, Xiaoqiang; Chen, Fuyi; Zhang, Nan; Lei, Yimin; Jin, Yachao; Qaseem, Adnan; Johnston, Roy L

    2017-02-02

    The electrocatalytic activity of Pt-based alloys exhibits a strong dependence on their electronic structures, but a relationship between electronic structure and oxygen reduction reaction (ORR) activity in Ag-based alloys is still not clear. Here, a vapor deposition based approach is reported for the preparation of Ag75 M25 (M = Cu, Co, Fe, and In) and Agx Cu100-x (x = 0, 25, 45, 50, 55, 75, 90, and 100) nanocatalysts and their electronic structures are determined by valence band spectra. The relationship of the d-band center and ORR activity exhibits volcano-shape behaviors, where the maximum catalytic activity is obtained for Ag75 Cu25 alloys. The ORR enhancement of Ag75 Cu25 alloys originates from the 0.12 eV upshift in d-band center relative to pure Ag, which is different from the downshift in the d-band center in Pt-based alloys. The activity trend for these Ag75 M25 alloys is in the order of Ag75 Cu25 > Ag75 Fe25 > Ag75 Co25 . These results provide an insight to understand the activity and stability enhancement of Ag75 Cu25 and Ag50 Cu50 catalysts by alloying.

  5. Low temperature equilibrium isotope fractionation and isotope exchange kinetics between U(IV) and U(VI)

    NASA Astrophysics Data System (ADS)

    Wang, Xiangli; Johnson, Thomas M.; Lundstrom, Craig C.

    2015-06-01

    Measurements of the uranium (U) isotope ratio 238U/235U provide an emerging redox proxy in environmental and paleoredox studies, but many key parameters concerning U isotope fractionation are still poorly constrained. Here we report the equilibrium isotopic fractionation between dissolved U(IV) and dissolved U(VI), and rates of isotope exchange between solid-phase U(IV) and dissolved U(VI). We conducted one experiment at high concentration [35 mM U(IV) and 32 mM U(VI)] and low pH (0.2) in hydrochloric acid media at room temperature to determine the equilibrium isotopic fractionation between dissolved U(IV) and dissolved U(VI). Isotopic equilibrium was reached in about 19 days under such experimental conditions. The equilibrium isotope fractionation was determined to be 1.64 ± 0.16‰, with U(IV) being enriched in 238U relative to U(VI). Applicability of the determined equilibrium fractionation is discussed. We also conducted a set of experiments to determine isotopic exchange rates between dissolved U(VI) and nanouraninite U(IV) under conditions closer to those in natural system, with lower concentrations and neutral pH. The exchange rate was found to conform to the rate law R = k[U(VI)]adsorbed, in which R is the isotopic exchange rate (μM day-1); k is the rate constant determined to be 0.21 day-1; and [U(VI)]adsorbed is the concentration of U(VI) adsorbed to nanouraninite (μM). Our results, combined with consideration of the variables controlling U(VI)-U(IV) contact in natural settings, indicate that the timescale for significant isotope equilibration varies depending on environmental conditions, mostly uranium concentrations. In natural uncontaminated sediments with low uranium concentrations, equilibration is expected to occur on a timescale of hundreds to thousands of years. In contrast, in U-contaminated aquifers with high U concentrations, significant equilibration could occur on timescales of weeks to years.

  6. Sulfidization of lepidocrocite and its effect on uranium phase distribution and reduction

    NASA Astrophysics Data System (ADS)

    Alexandratos, Vasso G.; Behrends, Thilo; Van Cappellen, Philippe

    2014-10-01

    Sulfidization of iron oxyhydroxides can be accompanied by a release of adsorbed uranium, thus enhancing the mobility of uranium in systems undergoing a shift in redox conditions. We investigated the phase distribution and redox state of uranium in batch experiments, in which lepidocrocite with adsorbed U(VI) was reacted with sulfide. The amount of added sulfide was varied in the experiments performed, at pH 8 and ionic strength of 0.1 M. Sulfide, when not added in excess, was removed from solution within less than 1 h of reaction time. Consumption of dissolved sulfide was accompanied by reduction of Fe(III) and formation of iron sulfide. Each addition of sulfide led to an instantaneous release of uranium into solution. This release is most likely caused by the exchange of hydroxide groups at the lepidocrocite surface by thiol groups which have a lower tendency to bind uranium. Along with the consumption of dissolved sulfide, part of the released uranium became reassociated with the solid phase. This can be explained by a reversal of the ligand exchange process at the solid surfaces. However, steady state concentrations of dissolved uranium remained higher than before sulfide addition, indicating that the product of lepidocrocite sulfidization has a lower affinity for uranium than the starting material. Reduction of U(VI) also contributed to the transfer of dissolved uranium back to the solid phase. X-ray absorption spectroscopy revealed that reduction of U(VI) occurred in all experiments. The extent of U(VI) reduction depended on sulfide addition, however, formation of UO2 occurred within a period of 48 h only when sulfide was added in excess. This suggests that the presence of dissolved sulfide is a prerequisite for fast reduction of U(VI) and formation of UO2. This would imply that the fast reaction of lepidocrocite with sulfide outcompetes reduction of U(VI) and, by this, kinetically inhibits the thermodynamically more favorable reduction of U(VI) to uraninite

  7. Targeting Reductions in Sitting Time to Increase Physical Activity and Improve Health.

    PubMed

    Keadle, Sarah K; Conroy, David E; Buman, Matthew P; Dunstan, David W; Matthews, Charles E

    2017-03-08

    New evidence suggests that reductions in sedentary behavior may increase physical activity and improve health. These findings point to new behavioral targets for intervention and new ways to think about intervening to increase overall physical activity in the population. This report provides a knowledge update reflecting the rapid accumulation of new evidence related to sedentary behavior and health among adults. Recent observational studies suggest that leveraging the time-inverse relationship between sedentary and active behaviors by replacing sitting with standing, light or moderate-intensity activity can have important health benefits, particularly among less active adults. Clinical studies are providing evidence of the probable physiologic mechanisms underlying these associations, as well as insights into the cardiometabolic impact of breaking up and reducing sedentary behavior. In contrast to the well-established behavioral theories that guide the development and dissemination of evidence-based interventions to increase moderate-vigorous intensity physical activity (MVPA), much less is known about how to reduce sedentary time in order to increase daily activities. It has become clear that the environmental, social and individual level-determinants for sedentary time are distinct from those linked to the adoption and maintenance of MVPA. As a result, novel intervention strategies that focus on sitting and lower intensity activities by leveraging the surrounding environment (e.g., workplace, school, home) as well as individual-level cues and habits of sedentary behavior are being tested to increase the potency of interventions designed to increase overall physical activity. Herein we summarize the solutions-oriented research across the behavioral research framework, with a focus on highlighting areas of synergy across disciplines and identifying gaps for future research.

  8. Vortex lattices and defect-mediated viscosity reduction in active liquids

    NASA Astrophysics Data System (ADS)

    Slomka, Jonasz; Dunkel, Jorn

    2016-11-01

    Generic pattern-formation and viscosity-reduction mechanisms in active fluids are investigated using a generalized Navier-Stokes model that captures the experimentally observed bulk vortex dynamics in microbial suspensions. We present exact analytical solutions including stress-free vortex lattices and introduce a computational framework that allows the efficient treatment of previously intractable higher-order shear boundary conditions. Large-scale parameter scans identify the conditions for spontaneous flow symmetry breaking, defect-mediated low-viscosity phases and negative-viscosity states amenable to energy harvesting in confined suspensions. The theory uses only generic assumptions about the symmetries and long-wavelength structure of active stress tensors, suggesting that inviscid phases may be achievable in a broad class of non-equilibrium fluids by tuning confinement geometry and pattern scale selection.

  9. Porous Dendritic Platinum Nanotubes with Extremely High Activity and Stability for Oxygen Reduction Reaction

    PubMed Central

    Zhang, Gaixia; Sun, Shuhui; Cai, Mei; Zhang, Yong; Li, Ruying; Sun, Xueliang

    2013-01-01

    Controlling the morphology of Pt nanostructures can provide opportunities to greatly increase their activity and stability. Porous dendritic Pt nanotubes were successfully synthesized by a facile, cost-effective aqueous solution method at room temperature in large scale. These unique structures are porous, hollow, hierarchical, and single crystalline, which not only gives them a large surface area with high catalyst utilization, but also improves mass transport and gas diffusion. These novel Pt structures exhibited significantly improved catalytic activity (4.4 fold) for oxygen reduction reaction (ORR) and greatly enhanced durability (6.1 fold) over that of the state-of-the-art commercial Pt/C catalyst. This work provides a promising approach to the design of highly efficient next-generation electrocatalysts. PMID:23524665

  10. New mechanistically based model for predicting reduction of biosolids waste by ozonation of return activated sludge.

    PubMed

    Isazadeh, Siavash; Feng, Min; Urbina Rivas, Luis Enrique; Frigon, Dominic

    2014-04-15

    Two pilot-scale activated sludge reactors were operated for 98 days to provide the necessary data to develop and validate a new mathematical model predicting the reduction of biosolids production by ozonation of the return activated sludge (RAS). Three ozone doses were tested during the study. In addition to the pilot-scale study, laboratory-scale experiments were conducted with mixed liquor suspended solids and with pure cultures to parameterize the biomass inactivation process during exposure to ozone. The experiments revealed that biomass inactivation occurred even at the lowest doses, but that it was not associated with extensive COD solubilization. For validation, the model was used to simulate the temporal dynamics of the pilot-scale operational data. Increasing the description accuracy of the inactivation process improved the precision of the model in predicting the operational data.

  11. Enhanced oxygen reduction activity and solid oxide fuel cell performance with a nanoparticles-loaded cathode.

    PubMed

    Zhang, Xiaomin; Liu, Li; Zhao, Zhe; Tu, Baofeng; Ou, Dingrong; Cui, Daan; Wei, Xuming; Chen, Xiaobo; Cheng, Mojie

    2015-03-11

    Reluctant oxygen-reduction-reaction (ORR) activity has been a long-standing challenge limiting cell performance for solid oxide fuel cells (SOFCs) in both centralized and distributed power applications. We report here that this challenge has been tackled with coloading of (La,Sr)MnO3 (LSM) and Y2O3 stabilized zirconia (YSZ) nanoparticles within a porous YSZ framework. This design dramatically improves ORR activity, enhances fuel cell output (200-300% power improvement), and enables superior stability (no observed degradation within 500 h of operation) from 600 to 800 °C. The improved performance is attributed to the intimate contacts between nanoparticulate YSZ and LSM particles in the three-phase boundaries in the cathode.

  12. The Origin of the Catalytic Activity of a Metal Hydride in CO2 Reduction.

    PubMed

    Kato, Shunsuke; Matam, Santhosh Kumar; Kerger, Philipp; Bernard, Laetitia; Battaglia, Corsin; Vogel, Dirk; Rohwerder, Michael; Züttel, Andreas

    2016-05-10

    Atomic hydrogen on the surface of a metal with high hydrogen solubility is of particular interest for the hydrogenation of carbon dioxide. In a mixture of hydrogen and carbon dioxide, methane was markedly formed on the metal hydride ZrCoHx in the course of the hydrogen desorption and not on the pristine intermetallic. The surface analysis was performed by means of time-of-flight secondary ion mass spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy, for the in situ analysis. The aim was to elucidate the origin of the catalytic activity of the metal hydride. Since at the initial stage the dissociation of impinging hydrogen molecules is hindered by a high activation barrier of the oxidised surface, the atomic hydrogen flux from the metal hydride is crucial for the reduction of carbon dioxide and surface oxides at interfacial sites.

  13. Simulating adsorption of U(VI) under transient groundwater flow and hydrochemistry: Physical versus chemical nonequilibrium model

    USGS Publications Warehouse

    Greskowiak, J.; Hay, M.B.; Prommer, H.; Liu, C.; Post, V.E.A.; Ma, R.; Davis, J.A.; Zheng, C.; Zachara, J.M.

    2011-01-01

    Coupled intragrain diffusional mass transfer and nonlinear surface complexation processes play an important role in the transport behavior of U(VI) in contaminated aquifers. Two alternative model approaches for simulating these coupled processes were analyzed and compared: (1) the physical nonequilibrium approach that explicitly accounts for aqueous speciation and instantaneous surface complexation reactions in the intragrain regions and approximates the diffusive mass exchange between the immobile intragrain pore water and the advective pore water as multirate first-order mass transfer and (2) the chemical nonequilibrium approach that approximates the diffusion-limited intragrain surface complexation reactions by a set of multiple first-order surface complexation reaction kinetics, thereby eliminating the explicit treatment of aqueous speciation in the intragrain pore water. A model comparison has been carried out for column and field scale scenarios, representing the highly transient hydrological and geochemical conditions in the U(VI)-contaminated aquifer at the Hanford 300A site, Washington, USA. It was found that the response of U(VI) mass transfer behavior to hydrogeochemically induced changes in U(VI) adsorption strength was more pronounced in the physical than in the chemical nonequilibrium model. The magnitude of the differences in model behavior depended particularly on the degree of disequilibrium between the advective and immobile phase U(VI) concentrations. While a clear difference in U(VI) transport behavior between the two models was noticeable for the column-scale scenarios, only minor differences were found for the Hanford 300A field scale scenarios, where the model-generated disequilibrium conditions were less pronounced as a result of frequent groundwater flow reversals. Copyright 2011 by the American Geophysical Union.

  14. Surface complexation modeling of U(VI) adsorption by aquifer sediments from a former mill tailings site at Rifle, Colorado.

    PubMed

    Hyun, Sung Pil; Fox, Patricia M; Davis, James A; Campbell, Kate M; Hayes, Kim F; Long, Philip E

    2009-12-15

    A study of U(VI) adsorption by aquifer sediment samples from a former uranium mill tailings site at Rifle, Colorado, was conducted under oxic conditions as a function of pH, U(VI), Ca, and dissolved carbonate concentration. Batch adsorption experiments were performed using <2 mm size sediment fractions, a sand-sized fraction, and artificial groundwater solutions prepared to simulate the field groundwater composition. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8 x 10(-8) to 10(-5) M in [U(VI)](tot), 7.2 to 8.0 in pH, 3.0 x 10(-3) to 6.0 x 10(-3) M in [Ca(2+)], and 0.05 to 2.6% in partial pressure of carbon dioxide. Surface area normalized U(VI) adsorption K(d) values for the sand and <2 mm sediment fraction were similar, suggesting a similar reactive surface coating on both fractions. A two-site two-reaction, nonelectrostatic generalized composite surface complexation model was developed and successfully simulated the U(VI) adsorption data. The model successfully predicted U(VI) adsorption observed from a multilevel sampling well installed at the site. A comparison of the model with the one developed previously for a uranium mill tailings site at Naturita, Colorado, indicated that possible calcite nonequilibrium of dissolved calcium concentration should be evaluated. The modeling results also illustrate the importance of the range of data used in deriving the best fit model parameters.

  15. Surface complexation modeling of U(VI) adsorption by aquifer sediments from a former mill tailings site at Rifle, Colorado

    USGS Publications Warehouse

    Hyun, S.P.; Fox, P.M.; Davis, J.A.; Campbell, K.M.; Hayes, K.F.; Long, P.E.

    2009-01-01

    A study of U(VI) adsorption by aquifer sediment samples from a former uranium mill tailings site at Rifle, Colorado, was conducted under oxic conditions as a function of pH, U(VI), Ca, and dissolved carbonate concentration. Batch adsorption experiments were performed using <2mm size sediment fractions, a sand-sized fraction, and artificial groundwater solutions prepared to simulate the field groundwater composition. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8 ?? 10-8 to 10-5 M in [U(VI)]tot, 7.2 to 8.0 in pH, 3.0 ?? 10-3 to 6.0 ?? 10 -3 M in [Ca2+], and 0.05 to 2.6% in partial pressure of carbon dioxide. Surface area normalized U(VI) adsorption Kd values for the sand and <2 mm sediment fraction were similar, suggesting a similar reactive surface coating on both fractions. A two-site two-reaction, nonelectrostatic generalized composite surface complexation model was developed and successfully simulated the U(VI) adsorption data. The model successfully predicted U(VI) adsorption observed from a multilevel sampling well installed at the site. A comparison of the model with the one developed previously for a uranium mill tailings site at Naturita, Colorado, indicated that possible calcite nonequilibrium of dissolved calcium concentration should be evaluated. The modeling results also illustrate the importance of the range of data used in deriving the best fit model parameters. ?? 2009 American Chemical Society.

  16. Aircraft panel with sensorless active sound power reduction capabilities through virtual mechanical impedances

    NASA Astrophysics Data System (ADS)

    Boulandet, R.; Michau, M.; Micheau, P.; Berry, A.

    2016-01-01

    This paper deals with an active structural acoustic control approach to reduce the transmission of tonal noise in aircraft cabins. The focus is on the practical implementation of the virtual mechanical impedances method by using sensoriactuators instead of conventional control units composed of separate sensors and actuators. The experimental setup includes two sensoriactuators developed from the electrodynamic inertial exciter and distributed over an aircraft trim panel which is subject to a time-harmonic diffuse sound field. The target mechanical impedances are first defined by solving a linear optimization problem from sound power measurements before being applied to the test panel using a complex envelope controller. Measured data are compared to results obtained with sensor-actuator pairs consisting of an accelerometer and an inertial exciter, particularly as regards sound power reduction. It is shown that the two types of control unit provide similar performance, and that here virtual impedance control stands apart from conventional active damping. In particular, it is clear from this study that extra vibrational energy must be provided by the actuators for optimal sound power reduction, mainly due to the high structural damping in the aircraft trim panel. Concluding remarks on the benefits of using these electrodynamic sensoriactuators to control tonal disturbances are also provided.

  17. RF probe recovery time reduction with a novel active ringing suppression circuit

    PubMed Central

    Peshkovsky, A.S.; Forguez, J.; Cerioni, L.; Pusiol, D.J.

    2005-01-01

    A simple Q-damper device for active probe recovery time reduction is introduced along with a straightforward technique for the circuit's component value optimization. The device is inductively coupled to a probe through a coupling transformer positioned away from the main coil, which makes the design independent of the coil type being used. The Q-damper is a tuned circuit, which is resonant at the same frequency as the probe and can be actively interrupted. When the circuit is interrupted, it is detuned and, thereby, is uncoupled from the probe, which operates normally. Turning the device on leads to re-coupling of the circuits and causes splitting of the probe's resonance line, which can be observed through its drive port. A resistance of an appropriate value is introduced into the Q-damper circuit, resulting in smoothing of the resonance splitting into one broad line, representing the coupled system's low-Q state, in which the energy stored in the main coil is efficiently dissipated. The circuit's component values are optimized by monitoring the shape of this low-Q state. Probe recovery time reduction by, approximately, an order of magnitude has been obtained with this device. Application of the device during an NQR experiment led to an increase in the signal-to-noise ratio by a factor of 4.9. PMID:16111906

  18. Classic Maya civilization collapse associated with reduction in tropical cyclone activity

    NASA Astrophysics Data System (ADS)

    Medina, M. A.; Polanco-Martinez, J. M.; Lases-Hernández, F.; Bradley, R. S.; Burns, S. J.

    2013-12-01

    In light of the increased destructiveness of tropical cyclones observed over recent decades one might assume that an increase and not a decrease in tropical cyclone activity would lead to societal stress and perhaps collapse of ancient cultures. In this study we present evidence that a reduction in the frequency and intensity of tropical Atlantic cyclones could have contributed to the collapse of the Maya civilization during the Terminal Classic Period (TCP, AD. 800-950). Statistical comparisons of a quantitative precipitation record from the Yucatan Peninsula (YP) Maya lowlands, based on the stalagmite known as Chaac (after the Mayan God of rain and agriculture), relative to environmental proxy records of El Niño/Southern Oscillation (ENSO), tropical Atlantic sea surface temperatures (SSTs), and tropical Atlantic cyclone counts, suggest that these records share significant coherent variability during the TCP and that summer rainfall reductions between 30 and 50% in the Maya lowlands occurred in association with decreased Atlantic tropical cyclones. Analysis of modern instrumental hydrological data suggests cyclone rainfall contributions to the YP equivalent to the range of rainfall deficits associated with decreased tropical cyclone activity during the collapse of the Maya civilization. Cyclone driven precipitation variability during the TCP, implies that climate change may have triggered Maya civilization collapse via freshwater scarcity for domestic use without significant detriment to agriculture. Pyramid in Tikal, the most prominent Maya Kingdom that collapsed during the Terminal Classic Period (circa C.E. 800-950) Rainfall feeding stalagmites inside Rio Secreto cave system, Yucatan, Mexico.

  19. Porous Silica-Coated Gold Nanorods: A Highly Active Catalyst for the Reduction of 4-Nitrophenol.

    PubMed

    Mohanta, Jagdeep; Satapathy, Smithsagar; Si, Satyabrata

    2016-02-03

    The successful coating of thin porous silica layers of various thicknesses [(10±1), (12±1), and (14±1) nm] on cetyl trimethylammonium bromide (CTAB) capped gold nanorods was achieved through a modified Stöber procedure. The resulting material was applied as a novel catalyst for the reduction of 4-nitrophenol. The catalytic activities of the gold nanorods increased up to eight times after coating with a layer of porous silica and the reaction followed a zero-order kinetics, having a rate constant as high as 2.92×10(-1) mol L(-1) min(-1). The spectral changes during the reduction reaction of 4-nitrophenol were observed within a very short span of time and a complete conversion to 4-aminophenol occured within 5-6 mins, including the induction period of ≈2 mins. The reusability of the catalyst was studied by running the catalytic reaction during five consecutive cycles with good efficiency without destroying the nanostructure. The methodology can be effectively applied to the development of composite catalysts with highly enhanced catalytic activity.

  20. Ti(3+)-Promoted High Oxygen-Reduction Activity of Pd Nanodots Supported by Black Titania Nanobelts.

    PubMed

    Yuan, Xiaotao; Wang, Xin; Liu, Xiangye; Ge, Hongxin; Yin, Guoheng; Dong, Chenlong; Huang, Fuqiang

    2016-10-04

    One-dimensional nanocrystals favoring efficient charge transfer have attracted enormous attentions, and conductive nanobelts of black titania with a unique band structure and high electrical conductivity would be interestingly used in electrocatalysis. Here, Pd nanodots supported by two kinds of black titania, the oxygen-deficient titania (TiO2-x) and nitrogen-doped titania (TiO2-x:N), were synthesized as efficient composite catalysts for oxygen-reduction reaction (ORR). These composite catalysts show improved catalytic activity with lower overpotential and higher limited current, compared to the Pd nanodots supported on the white titania (Pd/TiO2). The improved activity is attributed to the relatively high conductivity of black titania nanobelts for efficient charge transfer (CT) between Ti(3+) species and Pd nanodots. The CT process enhances the strong metal-support interaction (SMSI) between Pd and TiO2, which lowers the absorption energy of O2 on Pd and makes it more suitable for oxygen reduction. Because of the stronger interaction between Pd and support, the Pd/TiO2-x:N also shows excellent durability and immunity to methanol poisoning.

  1. RF probe recovery time reduction with a novel active ringing suppression circuit.

    PubMed

    Peshkovsky, A S; Forguez, J; Cerioni, L; Pusiol, D J

    2005-11-01

    A simple Q-damper device for active probe recovery time reduction is introduced along with a straightforward technique for the circuit's component value optimization. The device is inductively coupled to a probe through a coupling transformer positioned away from the main coil, which makes the design independent of the coil type being used. The Q-damper is a tuned circuit, which is resonant at the same frequency as the probe and can be actively interrupted. When the circuit is interrupted, it is detuned and, thereby, is uncoupled from the probe, which operates normally. Turning the device on leads to re-coupling of the circuits and causes splitting of the probe's resonance line, which can be observed through its drive port. A resistance of an appropriate value is introduced into the Q-damper circuit, resulting in smoothing of the resonance splitting into one broad line, representing the coupled system's low-Q state, in which the energy stored in the main coil is efficiently dissipated. The circuit's component values are optimized by monitoring the shape of this low-Q state. Probe recovery time reduction by, approximately, an order of magnitude has been obtained with this device. Application of the device during an NQR experiment led to an increase in the signal-to-noise ratio by a factor of 4.9.

  2. Reduction of beta-glucuronidase and nitroreductase activity by yoghurt in a murine colon cancer model.

    PubMed

    de Moreno de LeBlanc, A; Perdigón, G

    2005-04-01

    Yoghurt feeding inhibits induced colon cancer in mice. Several studies showed the immunomodulatory effect of yoghurt which can explain this inhibition. It is possible that yoghurt bacteria can also affect gut flora enzymes related to colon carcinogenesis as reported for other probiotics in different animal tumours. The aim of this work was to evaluate the role of yoghurt starter bacteria and their cell-free fermentation products on the reduction of procarcinogen enzyme activities (beta-glucuronidase and nitroreductase). Mice injected with 1,2-dimethylhydrazine (DMH) and fed with yoghurt were used for this study. Mice given milk or yoghurt supernatant (cell free extract) were used to evaluate if the yoghurt antitumour effect is due to the starter bacteria or other components released during fermentation, that could inhibit these enzymes. We determined that yoghurt by itself maintained enzymes activities similar or lower than non-treatment control group, and the enzyme activity was also lower than milk or yoghurt supernatant groups. DMH increased the activity of the enzymes. Mice injected with DMH and fed cyclically with yoghurt presented lower enzymes activities than the tumour control group. Feeding yoghurt decreased procarcinogenic enzyme levels in the large intestine contents of mice bearing colon tumour. The results of this study provide another mechanism by which yoghurt starter bacteria interact with the large intestine of the mice and prevent colon cancer.

  3. Tau reduction prevents Aβ-induced axonal transport deficits by blocking activation of GSK3β

    PubMed Central

    Xu, Jordan C.; Fomenko, Vira; Miyamoto, Takashi; Suberbielle, Elsa; Knox, Joseph A.; Ho, Kaitlyn; Kim, Daniel H.; Yu, Gui-Qiu

    2015-01-01

    Axonal transport deficits in Alzheimer’s disease (AD) are attributed to amyloid β (Aβ) peptides and pathological forms of the microtubule-associated protein tau. Genetic ablation of tau prevents neuronal overexcitation and axonal transport deficits caused by recombinant Aβ oligomers. Relevance of these findings to naturally secreted Aβ and mechanisms underlying tau’s enabling effect are unknown. Here we demonstrate deficits in anterograde axonal transport of mitochondria in primary neurons from transgenic mice expressing familial AD-linked forms of human amyloid precursor protein. We show that these deficits depend on Aβ1–42 production and are prevented by tau reduction. The copathogenic effect of tau did not depend on its microtubule binding, interactions with Fyn, or potential role in neuronal development. Inhibition of neuronal activity, N-methyl-d-aspartate receptor function, or glycogen synthase kinase 3β (GSK3β) activity or expression also abolished Aβ-induced transport deficits. Tau ablation prevented Aβ-induced GSK3β activation. Thus, tau allows Aβ oligomers to inhibit axonal transport through activation of GSK3β, possibly by facilitating aberrant neuronal activity. PMID:25963821

  4. Effect of microstructure of nitrogen-doped graphene on oxygen reduction activity in fuel cells.

    PubMed

    Zhang, Lipeng; Niu, Jianbing; Dai, Liming; Xia, Zhenhai

    2012-05-15

    The development of fuel cells as clean-energy technologies is largely limited by the prohibitive cost of the noble-metal catalysts needed for catalyzing the oxygen reduction reaction (ORR) in fuel cells. A fundamental understanding of catalyst design principle that links material structures to the catalytic activity can accelerate the search for highly active and abundant nonmetal catalysts to replace platinum. Here, we present a first-principles study of ORR on nitrogen-doped graphene in acidic environment. We demonstrate that the ORR activity primarily correlates to charge and spin densities of the graphene. The nitrogen doping and defects introduce high positive spin and/or charge densities that facilitate the ORR on graphene surface. The identified active sites are closely related to doping cluster size and dopant-defect interactions. Generally speaking, a large doping cluster size (number of N atoms >2) reduces the number of catalytic active sites per N atom. In combination with N clustering, Stone-Wales defects can strongly promote ORR. For four-electron transfer, the effective reversible potential ranges from 1.04 to 1.15 V/SHE, depending on the defects and cluster size. The catalytic properties of graphene could be optimized by introducing small N clusters in combination with material defects.

  5. Widespread reduction in sleep spindle activity in socially anxious children and adolescents.

    PubMed

    Wilhelm, Ines; Groch, Sabine; Preiss, Andrea; Walitza, Susanne; Huber, Reto

    2017-05-01

    Social anxiety disorder (SAD) is one of the most prevalent psychiatric diseases typically emerging during childhood and adolescence. Biological vulnerabilities such as a protracted maturation of prefrontal cortex functioning together with heightened reactivity of the limbic system leading to increased emotional reactivity are discussed as factors contributing to the emergence and maintenance of SAD. Sleep slow wave activity (SWA, 0.75-4.5 Hz) and sleep spindle activity (9-16 Hz) reflect processes of brain maturation and emotion regulation. We used high-density electroencephalography to characterize sleep SWA and spindle activity and their relationship to emotional reactivity in children and adolescents suffering from SAD and healthy controls (HC). Subjectively rated arousal was assessed using an emotional picture-word association task. SWA did not differ between socially anxious and healthy participants. We found a widespread reduction in fast spindle activity (13-16 Hz) in SAD patients compared to HC. SAD patients rated negative stimuli to be more arousing and these arousal ratings were negatively correlated with fast spindle activity. These results suggest electrophysiological alterations that are evident at an early stage of psychopathology and that are closely linked to one core symptom of anxiety disorders such as increased emotional reactivity. The role of disturbed GABAergic neurotransmission is discussed as an underlying factor.

  6. Microtubules Accelerate the Kinase Activity of Aurora-B by a Reduction in Dimensionality

    PubMed Central

    Noujaim, Michael; Bechstedt, Susanne; Wieczorek, Michal; Brouhard, Gary J.

    2014-01-01

    Aurora-B is the kinase subunit of the Chromosome Passenger Complex (CPC), a key regulator of mitotic progression that corrects improper kinetochore attachments and establishes the spindle midzone. Recent work has demonstrated that the CPC is a microtubule-associated protein complex and that microtubules are able to activate the CPC by contributing to Aurora-B auto-phosphorylation in trans. Aurora-B activation is thought to occur when the local concentration of Aurora-B is high, as occurs when Aurora-B is enriched at centromeres. It is not clear, however, whether distributed binding to large structures such as microtubules would increase the local concentration of Aurora-B. Here we show that microtubules accelerate the kinase activity of Aurora-B by a “reduction in dimensionality.” We find that microtubules increase the kinase activity of Aurora-B toward microtubule-associated substrates while reducing the phosphorylation levels of substrates not associated to microtubules. Using the single molecule assay for microtubule-associated proteins, we show that a minimal CPC construct binds to microtubules and diffuses in a one-dimensional (1D) random walk. The binding of Aurora-B to microtubules is salt-dependent and requires the C-terminal tails of tubulin, indicating that the interaction is electrostatic. We show that the rate of Aurora-B auto-activation is faster with increasing concentrations of microtubules. Finally, we demonstrate that microtubules lose their ability to stimulate Aurora-B when their C-terminal tails are removed by proteolysis. We propose a model in which microtubules act as scaffolds for the enzymatic activity of Aurora-B. The scaffolding activity of microtubules enables rapid Aurora-B activation and efficient phosphorylation of microtubule-associated substrates. PMID:24498282

  7. Charge transfer efficiency in HST WFC3/UVIS: monitoring and mitigation

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia M.; Anderson, Jay; Sosey, Megan L.; Bourque, Matthew; Martlin, Catherine; Kurtz, Heather; Shanahan, Clare; Kozhurina-Platais, Vera; Sabbi, Elena; WFC3 Team

    2017-01-01

    The UVIS channel of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) contains a 4096x4096 pixel e2v CCD array. The detectors have been performing well on-orbit but as expected, are exhibiting the cumulative effects of radiation damage. The result is a growing hot pixel population and declining charge transfer efficiency. We summarize the progression of the CTE losses, their effects on science data, and discuss two of the primary mitigation options: post-flash and a pixel-based CTE correction. The latter is now part of the automated WFC3 calibration pipeline in the Mikulski Archive for Space Telescopes (MAST), providing observers with both standard and CTE-corrected data products.

  8. ESTIMATION OF MICROBIAL REDUCTIVE TRANSFORMATION RATES FOR CHLORINATED BENZENES AND PHENOLS USING A QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIP APPROACH

    EPA Science Inventory

    A set of literature data was used to derive several quantitative structure-activity relationships (QSARs) to predict the rate constants for the microbial reductive dehalogenation of chlorinated aromatics. Dechlorination rate constants for 25 chloroaromatics were corrected for th...

  9. Cassini UVIS Observations of the Io Plasma Torus. 3; Observations of Temporal and Azimuthal Variability

    NASA Technical Reports Server (NTRS)

    Steffl, A. J.; Delamere, P. A.; Bagenal, F.

    2006-01-01

    In this third paper in a series presenting observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS) of the Io plasma torus, we show remarkable, though subtle, spatio-temporal variations in torus properties. The Io torus is found to exhibit significant, near sinusoidal variations in ion composition as a functions of azimuthal position. The azimuthal variation in composition is such that the mixing ratio of S II us strongly correlated with the mixing ratio of S III and the equatorial electron density and strongly anti-correlated with the mixing ratios of both S IV and O II and the equatorial electron temperature. Surprisingly, the azimuthal variation in ion composition is observed to have a period of 10.07 h -- 1.5% longer than the System III rotation period of Jupiter, yet 1.3% shorter than the System UV period defined by [Brown, M. E., 1995. J. Geophys. Res. 100, 21683-21696]. Although the amplitude of the azimuthal variation of S III and O II remained in the range of 2-5%, the amplitude of the S II and S IV compositional variation ranged between 5 and 25% during the UVIS observations. Furthermore, the amplitude of the azimuthal variations of S II and S IV appears to be modulated by its location in System III longitude, such that when the region of maximum S II mixing ration (minimum S IV mixing ratio) is aligned with a System III longitude of 200 deg +/-, the amplitude is a factor of 4 greater than when the variation is anti-aligned. This behavior can explain numerous, often apparently contradictory, observations of variations in the properties of the Io plasma torus with the System III and System IV coordinate systems.

  10. WFC3/UVIS External CTE Monitor: Single-Chip CTE Measurements

    NASA Astrophysics Data System (ADS)

    Gosmeyer, C. M.; Baggett, S.

    2016-12-01

    We present the first results of single-chip measurements of charge transfer efficiency (CTE) in the UVIS channel of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3). This test was performed in Cycle 20 in two visits. In the first visit a field in the star cluster NGC 6583 was observed. In a second visit, the telescope returned to the field, but rotated by 180 degrees and with a shift in pointing that allowed the same stars to be imaged, near and far from the amplifiers, on the same chip of the two-chip UVIS field of-view. This dataset enables a measurement of CTE loss on each separate chip. The current CTE monitor measures CTE loss as an average of the two chips because it dithers by a chip-height to obtain observations of the same sources near and far from the amplifiers, instead of the more difficult to-schedule 180-degree rotation. We find that CTE loss is worse on Chip 1 than on Chip 2 across all cases for which we had data: short and long exposures and w! ith and without the pixel-based CTE correction. In the best case, for long exposures with the CTE correction applied, the max difference between the two chip's flux losses is 3%/2048 pixels. This case should apply for most science observations where the background is 12 e-/pixel. In the worst case of low-background short exposures, e.g. those without post-flash, the max difference between the two chips is 17% flux loss/2048 pixels. Uncertainties are <0.01% flux loss/2048 pixels. Because of the two chips' different CTE loss rates, we will consider adding this test as part of the routine yearly monitor and creating a chip-specific CTE correction software.

  11. Ionospheric Convection in the Postnoon Auroral Oval: SuperDARN and Polar UVI Observations

    NASA Technical Reports Server (NTRS)

    Kozlovsky, A.; Koustov, A.; Lyatsky, W.; Kangas, J.; Parks, G.; Chua, D.

    2002-01-01

    Super Dual Auroral Radar Network (SuperDARN) observations, ultraviolet imaging from the Polar satellite (UVI), and particle precipitation data from DMSP satellites have been used to investigate the electrodynamics of the postnoon auroral oval in the Northern hemisphere. We show that: (1) For negative IMF By, the convection reversal (CR) was co-located with the maximum of auroral luminosity, but during positive IMF By the convection reversal was poleward of the auroral oval up to several degrees in latitude; (2) Postnoon auroral oval was associated with a large-scale upward field-aligned current (FAC) of the order of 6x10(exp -7). A m(exp -2) in magnitude (the FAC was inferred from the SuperDARN and UVI data). For negative IMF By, maximum of the auroral intensity coincides in latitude with the maximum of the upward field-aligned current. However, for positive IMF By. the maximum of the upward FAC was shifted to the poleward edge of the auroral oval; (3) In response to the IMF By turning from positive to negative, the maximum of the auroral luminosity did not change its position noticeably, but the position of the convection reversal changed considerably from 80-81 degs to about 76 degs MLAT, and the maximum of FAC moved from 77-78 degs to about 76 degs MLAT. Thus, after IMF By turns negative, both the FAC maximum and CR tend to coincide with the auroral maximum; (4) The IMF Bz positive deflection was followed by a decrease in both field-aligned current intensity and auroral luminosity. However, the decrease in the auroral luminosity lags behind the FAC decrease by about 12 min. Firstly, these observations allow us to suggest that the IMF By-related electric field can penetrate into the closed magnetosphere and produce convection and FAC changes in the region of the postnoon auroral oval. Secondly, we suggest that the interchange instability is a promising mechanism for the postnoon auroras.

  12. Similarity of the Surface Reactivity of Hydrous Ferric Oxide and Hematite: Sorption and Redox of U(VI) and Fe(II)

    SciTech Connect

    Je-Hun Jang; Dempsey, Brian A.; Burgos, William D.; Yeh, George; Roden, Eric

    2004-03-17

    Hydrous Ferric Oxide (HFO) vs. Hematite--Thermodynamically distinctive bulk phases, but the surfaces could be similar due to hydration of the interface. Hypothesis--The surface of HFO is energetically similar to the surface of hematite. Objective--Compare the reactions of HFO and hematite with U(VI) and Fe(II). Experimental--The reactions of interests were (1) preparation of sub-micron hematite, (2) sorption of U(VI), and (3) redox of U(VI) and Fe(II) with HFO or hematite.

  13. Reduction of adsorption capacity of coconut shell activated carbon for organic vapors due to moisture contents.

    PubMed

    Abiko, Hironobu; Furuse, Mitsuya; Takano, Tsuguo

    2010-01-01

    In occupational hygiene, activated carbon produced from coconut shell is a common adsorbent material for harmful substances including organic vapors due to its outstanding adsorption capacity and cost advantage. However, moisture adsorption of the carbon generally decreases the adsorption capacity for organic vapors. In a previous report, we prepared several coconut shell activated carbons which had been preconditioned by equilibration with moisture at different relative humidities and measured the breakthrough times for 6 kinds of organic vapor, in order to clarify the effect of preliminary moisture content in activated carbon on the adsorption capacity in detail. We found that the relative percent weight increase due to moisture adsorption of the carbon specimen had a quantitative effect, reducing the breakthrough time. In this report, we carried out further measurements of the effect of moisture content on the adsorption of 13 kinds of organic vapor, and investigated the relationship between moisture adsorption and the reduction of the breakthrough time of activated carbon specimens. We also applied the data to the Wood's breakthrough time estimation model which is an extension of the Wheeler-Jonas equation.

  14. Steps in reductive activation of the disulfide-generating enzyme Ero1p

    PubMed Central

    Heldman, Nimrod; Vonshak, Ohad; Sevier, Carolyn S; Vitu, Elvira; Mehlman, Tevie; Fass, Deborah

    2010-01-01

    Ero1p is the primary catalyst of disulfide bond formation in the yeast endoplasmic reticulum (ER). Ero1p contains a pair of essential disulfide bonds that participate directly in the electron transfer pathway from substrate thiol groups to oxygen. Remarkably, elimination of certain other Ero1p disulfides by mutation enhances enzyme activity. In particular, the C150A/C295A Ero1p mutant exhibits increased thiol oxidation in vitro and in vivo and interferes with redox homeostasis in yeast cells by hyperoxidizing the ER. Inhibitory disulfides of Ero1p are thus important for enzyme regulation. To visualize the differences between de-regulated and wild-type Ero1p, we determined the crystal structure of Ero1p C150A/C295A. The structure revealed local changes compared to the wild-type enzyme around the sites of mutation, but no conformational transitions within 25 Å of the active site were observed. To determine how the C150—C295 disulfide nonetheless participates in redox regulation of Ero1p, we analyzed using mass spectrometry the changes in Ero1p disulfide connectivity as a function of time after encounter with reducing substrates. We found that the C150—C295 disulfide sets a physiologically appropriate threshold for enzyme activation by guarding a key neighboring disulfide from reduction. This study illustrates the diverse and interconnected roles that disulfides can play in redox regulation of protein activity. PMID:20669236

  15. Experimental Study of Active Techniques for Blade/Vortex Interaction Noise Reduction

    NASA Astrophysics Data System (ADS)

    Kobiki, Noboru; Murashige, Atsushi; Tsuchihashi, Akihiko; Yamakawa, Eiichi

    This paper presents the experimental results of the effect of Higher Harmonic Control (HHC) and Active Flap on the Blade/Vortex Interaction (BVI) noise. Wind tunnel tests were performed with a 1-bladed rotor system to evaluate the simplified BVI phenomenon avoiding the complicated aerodynamic interference which is characteristically and inevitably caused by a multi-bladed rotor. Another merit to use this 1-bladed rotor system is that the several objective active techniques can be evaluated under the same condition installed in the same rotor system. The effects of the active techniques on the BVI noise reduction were evaluated comprehensively by the sound pressure, the blade/vortex miss distance obtained by Laser light Sheet (LLS), the blade surface pressure distribution and the tip vortex structure by Particle Image Velocimetry (PIV). The correlation among these quantities to describe the effect of the active techniques on the BVI conditions is well obtained. The experiments show that the blade/vortex miss distance is more dominant for BVI noise than the other two BVI governing factors, such as blade lift and vortex strength at the moment of BVI.

  16. Reduction of protein translation and activation of autophagy protect against PINK1 pathogenesis in Drosophila melanogaster.

    PubMed

    Liu, Song; Lu, Bingwei

    2010-12-09

    Mutations in PINK1 and Parkin cause familial, early onset Parkinson's disease. In Drosophila melanogaster, PINK1 and Parkin mutants show similar phenotypes, such as swollen and dysfunctional mitochondria, muscle degeneration, energy depletion, and dopaminergic (DA) neuron loss. We previously showed that PINK1 and Parkin genetically interact with the mitochondrial fusion/fission pathway, and PINK1 and Parkin were recently proposed to form a mitochondrial quality control system that involves mitophagy. However, the in vivo relationships among PINK1/Parkin function, mitochondrial fission/fusion, and autophagy remain unclear; and other cellular events critical for PINK1 pathogenesis remain to be identified. Here we show that PINK1 genetically interacted with the protein translation pathway. Enhanced translation through S6K activation significantly exacerbated PINK1 mutant phenotypes, whereas reduction of translation showed suppression. Induction of autophagy by Atg1 overexpression also rescued PINK1 mutant phenotypes, even in the presence of activated S6K. Downregulation of translation and activation of autophagy were already manifested in PINK1 mutant, suggesting that they represent compensatory cellular responses to mitochondrial dysfunction caused by PINK1 inactivation, presumably serving to conserve energy. Interestingly, the enhanced PINK1 mutant phenotype in the presence of activated S6K could be fully rescued by Parkin, apparently in an autophagy-independent manner. Our results reveal complex cellular responses to PINK1 inactivation and suggest novel therapeutic strategies through manipulation of the compensatory responses.

  17. MURMoT. Design and Application of Microbial Uranium Reduction Monitoring Tools

    SciTech Connect

    Loeffler, Frank E.

    2014-12-31

    Uranium (U) contamination in the subsurface is a major remediation challenge at many DOE sites. Traditional site remedies present enormous costs to DOE; hence, enhanced bioremediation technologies (i.e., biostimulation and bioaugmentation) combined with monitoring efforts are being considered as cost-effective corrective actions to address subsurface contamination. This research effort improved understanding of the microbial U reduction process and developed new tools for monitoring microbial activities. Application of these tools will promote science-based site management decisions that achieve contaminant detoxification, plume control, and long-term stewardship in the most efficient manner. The overarching hypothesis was that the design, validation and application of a suite of new molecular and biogeochemical tools advance process understanding, and improve environmental monitoring regimes to assess and predict in situ U immobilization. Accomplishments: This project (i) advanced nucleic acid-based approaches to elucidate the presence, abundance, dynamics, spatial distribution, and activity of metal- and radionuclide-detoxifying bacteria; (ii) developed proteomics workflows for detection of metal reduction biomarker proteins in laboratory cultures and contaminated site groundwater; (iii) developed and demonstrated the utility of U isotopic fractionation using high precision mass spectrometry to quantify U(VI) reduction for a range of reduction mechanisms and environmental conditions; and (iv) validated the new tools using field samples from U-contaminated IFRC sites, and demonstrated their prognostic and diagnostic capabilities in guiding decision making for environmental remediation and long-term site stewardship.

  18. MURMoT. Design and Application of Microbial Uranium Reduction Monitoring Tools

    SciTech Connect

    Loffler, Frank E.; Ritalahti, Kirsti; Sanford, Robert A.; Lundstrom, Craig C.; Johnson, Thomas M.; Kemner, Kenneth; Boyanov, Maxim

    2009-07-01

    Uranium (U) contamination in the subsurface is a major remediation challenge at many DOE sites. Traditional site remedies present enormous costs to DOE; hence, enhanced bioremediation technologies (i.e., biostimulation and bioaugmentation) combined with monitoring efforts are being considered as cost-effective corrective actions to address subsurface contamination. This research effort improved understanding of the microbial U reduction process and developed new tools for monitoring microbial activities. Application of these tools will promote science-based site management decisions that achieve contaminant detoxification, plume control, and long-term stewardship in the most efficient manner. The overarching hypothesis was that the design, validation and application of a suite of new molecular and biogeochemical tools advance process understanding, and improve environmental monitoring regimes to assess and predict in situ U immobilization. Accomplishments: This project (i) advanced nucleic acid-based approaches to elucidate the presence, abundance, dynamics, spatial distribution, and activity of metal- and radionuclide-detoxifying bacteria; (ii) developed proteomics workflows for detection of metal reduction biomarker proteins in laboratory cultures and contaminated site groundwater; (iii) developed and demonstrated the utility of U isotopic fractionation using high precision mass spectrometry to quantify U(VI) reduction for a range of reduction mechanisms and environmental conditions; and (iv) validated the new tools using field samples from U-contaminated IFRC sites, and demonstrated their prognostic and diagnostic capabilities in guiding decision making for environmental remediation and long-term site stewardship.

  19. Model-based Analysis of Mixed Uranium(VI) Reduction by Biotic and Abiotic Pathways During in Situ Bioremediation

    SciTech Connect

    Zhao, Jiao; Scheibe, Timothy D.; Mahadevan, Radhakrishnan

    2013-10-24

    Uranium bioremediation has emerged as a potential strategy of cleanup of radionuclear contamination worldwide. An integrated geochemical & microbial community model is a promising approach to predict and provide insights into the bioremediation of a complicated natural subsurface. In this study, an integrated column-scale model of uranium bioremediation was developed, taking into account long-term interactions between biotic and abiotic processes. It is also combined with a comprehensive thermodynamic analysis to track the fate and cycling of biogenic species. As compared with other bioremediation models, the model increases the resolution of the connection of microbial community to geochemistry and establishes direct quantitative correlation between overall community evolution and geochemical variation, thereby accurately predicting the community dynamics under different sedimentary conditions. The thermodynamic analysis examined a recently identified homogeneous reduction of U(VI) by Fe(II) under dynamic sedimentary conditions across time and space. It shows that the biogenic Fe(II) from Geobacter metabolism can be removed rapidly by the biogenic sulphide from sulfate reducer metabolism, hence constituting one of the reasons that make the abiotic U(VI) reduction thermodynamically infeasible in the subsurface. Further analysis indicates that much higher influent concentrations of both Fe(II) and U(VI) than normal are required to for abiotic U(VI) reduction to be thermodynamically feasible, suggesting that the abiotic reduction cannot be an alternative to the biotic reduction in the remediation of uranium contaminated groundwater.

  20. Glycine cleavage system in ketotic hyperglycinemia: a reduction of H-protein activity.

    PubMed

    Hayasaka, K; Narisawa, K; Satoh, T; Tateda, H; Metoki, K; Tada, K; Hiraga, K; Aoki, T; Kawakami, T; Akamatsu, H; Matsuo, N

    1982-01-01

    Glycine cleavage activity was compared in the livers from three cases of ketotic hyperglycinemia (two cases of propionic acidemia and one case of methylmalonic acidemia) and three controls. In one case of propionic acidemia, glycine cleavage activity (5.2 nmole/mg protein/hr) was normal in the liver obtained at biopsy when the patient was well controlled by the treatment with low protein diet (0.8 g/kg/day) and the level of serum glycine was lowered to normal. In the two other cases of ketotic hyperglycinemia, glycine cleavage activity was significantly reduced in the liver obtained at autopsy when the patients died in the state of metabolic acidosis. Its activity in the liver of one case of propionic acidemia (0.7 nmole/mg protein/hr) was 6-26% of that in controls (2.7-10.8 nmole/mg protein/hr), and 2-7% in the case of methylmalonic acidemia (0.2 nmole/mg protein/hr). Analysing of the individual components of the glycine cleavage system, a marked decrease in the activity of H-protein was revealed in the livers of the both patients; it (0.2 nmole/mg protein/hr) was only 3-4% of that in controls (4.9-6.3 nmole/mg Protein/hr). These findings suggest that the reduction of the glycine cleavage system in the liver of ketotic hyperglycinemia occurs secondarily as speculated previously and is caused mainly by a decrease of H-protein activity.

  1. Optimization of actuator and sensor positions for an active noise reduction system

    NASA Astrophysics Data System (ADS)

    Böhme, Sten; Sachau, Delf; Breitbach, Harald

    2006-03-01

    Different systems and strategies have been invented in order to reduce the noise level inside the fuselage of aircrafts. First of all passive methods like adding materials with high damping or vibration absorbing qualities were used. Due to mass reduction as a major aspect in aircraft design a lot of research is focused on active noise reduction (ANR). The level of attenuation gained by an ANR - system is depending on several attributes of the system like hardware and software in use. Another important parameter, which has a great impact on the performance, is the positioning of the actuators and sensors. Because of the high number of possible arrangements of actuators and sensors in three dimensional spaces, it is almost impossible to determine the optimal positions by experimental work. Therefore numerical optimization is applied. In this paper a hybrid evolutionary algorithm is introduced for the calculation of appropriate configurations for a fixed number of actuator and sensors out of a high number of possible positions for an ANR - system within a military aircraft. The presented COSA - algorithm (cooperative simulated annealing) connects qualities of two well known optimization algorithms, the simulated annealing (SA) and genetic algorithm (GA). A general description of the algorithm and the acoustical basics will be provided together with an overview of the results.

  2. Reductive dehalogenation activity of indigenous microorganism in sediments of the Hackensack River, New Jersey.

    PubMed

    Sohn, Seo Yean; Häggblom, Max M

    2016-07-01

    Organohalogen pollutants are of concern in many river and estuarine environments, such as the New York-New Jersey Harbor estuary and its tributaries. The Hackensack River is contaminated with various metals, hydrocarbons and halogenated organics, including polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins. In order to examine the potential for microbial reductive dechlorination by indigenous microorganisms, sediment samples were collected from five different estuarine locations along the Hackensack River. Hexachlorobenzene (HCB), hexabromobenzene (HBB), and pentachloroaniline (PCA) were selected as model organohalogen pollutants to assess anaerobic dehalogenating potential. Dechlorinating activity of HCB and PCA was observed in sediment microcosms for all sampling sites. HCB was dechlorinated via pentachlorobenzene (PeCB) and trichlorobenzene (TriCB) to dichlorobenzene (DCB). PCA was dechlorinated via tetrachloroaniline (TeCA), trichloroanilines (TriCA), and dichloroanilines (DCA) to monochloroaniline (MCA). No HBB debromination was observed over 12 months of incubation. However, with HCB as a co-substrate slow HBB debromination was observed with production of tetrabromobenzene (TeBB) and tribromobenzene (TriBB). Chloroflexi specific 16S rRNA gene PCR-DGGE followed by sequence analysis detected Dehalococcoides species in sediments of the freshwater location, but not in the estuarine site. Analysis targeting 12 putative reductive dehalogenase (rdh) genes showed that these were enriched concomitant with HCB or PCA dechlorination in freshwater sediment microcosms.

  3. Electrocatalytic activities of alkyne-functionalized copper nanoparticles in oxygen reduction in alkaline media

    NASA Astrophysics Data System (ADS)

    Liu, Ke; Song, Yang; Chen, Shaowei

    2014-12-01

    Stable alkyne-capped copper nanoparticles were prepared by chemical reduction of copper acetate with sodium borohydride in the presence of alkyne ligands. Transmission electron microscopic measurements showed that nanoparticles were well dispersed with a diameter in the range of 4-6 nm. FTIR and photoluminescence spectroscopic measurements confirmed the successful attachment of the alkyne ligands onto the nanoparticle surface most likely forming Cu-Ctbnd interfacial bonds. XPS measurements indicated the formation of a small amount of CuO in the nanoparticles with a satellite peak where the binding energy red-shifted with increasing Cu(II) concentration. Cu2O was also detected in the nanoparticles. Similar results were observed with commercial CuO nanoparticles. Electrochemical studies showed that the as-prepared alkyne-capped copper nanoparticles exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, a performance that was markedly better than those reported earlier with poly- or single-crystalline copper electrodes; and the fraction of peroxides in the final products decreased with decreasing concentration of oxide components in the nanoparticles.

  4. Active Aerodynamic Load Reduction on a Rotorcraft Fuselage With Rotor Effects: A CFD Validation Effort

    NASA Technical Reports Server (NTRS)

    Allan, Brian G.; Schaeffler, Norman W.; Jenkins, Luther N.; Yao, Chung-Sheng; Wong, Oliver D.; Tanner, Philip E.

    2015-01-01

    A rotorcraft fuselage is typically designed with an emphasis on operational functionality with aerodynamic efficiency being of secondary importance. This results in a significant amount of drag during high-speed forward flight that can be a limiting factor for future high-speed rotorcraft designs. To enable higher speed flight, while maintaining a functional fuselage design (i.e., a large rear cargo ramp door), the NASA Rotary Wing Project has conducted both experimental and computational investigations to assess active flow control as an enabling technology for fuselage drag reduction. This paper will evaluate numerical simulations of a flow control system on a generic rotorcraft fuselage with a rotor in forward flight using OVERFLOW, a structured mesh Reynolds-averaged Navier-Stokes flow solver developed at NASA. The results are compared to fuselage forces, surface pressures, and PN flow field data obtained in a wind tunnel experiment conducted at the NASA Langley 14-by 22-Foot Subsonic Tunnel where significant drag and download reductions were demonstrated using flow control. This comparison showed that the Reynolds-averaged Navier-Stokes flow solver was unable to predict the fuselage forces and pressure measurements on the ramp for the baseline and flow control cases. While the CFD was able to capture the flow features, it was unable to accurately predict the performance of the flow control.

  5. Heterogeneous Au-Pt nanostructures with enhanced catalytic activity toward oxygen reduction.

    PubMed

    Ye, Feng; Liu, Hui; Hu, Weiwei; Zhong, Junyu; Chen, Yingying; Cao, Hongbin; Yang, Jun

    2012-03-14

    Heterogeneous Au-Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core-shell Au-Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H(2)PtCl(6) solution, whose chemical reaction can be described as 4Ag + PtCl(6)(2-)→ Pt + 4AgCl + 2Cl(-), is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag-Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core-shell Au-Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au-Pt nanostructures. The heterogeneous Au-Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.

  6. Particle size reduction effectively enhances the cholesterol-lowering activities of carrot insoluble fiber and cellulose.

    PubMed

    Chou, Sze-Yuan; Chien, Po-Jung; Chau, Chi-Fai

    2008-11-26

    This study investigated and compared the effects of particle size reduction on the cholesterol-lowering activities of carrot insoluble fiber-rich fraction (IFF) and plant cellulose. Our results demonstrated that micronization treatment effectively pulverized the particle sizes of these insoluble fibers to different microsizes. Feeding the micronized insoluble fibers, particularly the micronized carrot IFF, significantly (p < 0.05) improved their abilities in lowering the concentrations of serum triglyceride (18.6-20.0%), serum total cholesterol (15.5-19.5%), and liver lipids (16.7-20.3%) to different extents by means of enhancing (p < 0.05) the excretion of lipids (124-131%), cholesterol (120-135%), and bile acids (130-141%) in feces. These results suggested that particle size was one of the crucial factors in affecting the characteristics and physiological functions of insoluble fibers. Therefore, particle size reduction by micronization might offer the industry an opportunity to improve the physiological functions of insoluble fibers, particularly the carrot IFF, in health food applications.

  7. Size effect of silver nanoclusters on their catalytic activity for oxygen electro-reduction

    NASA Astrophysics Data System (ADS)

    Lu, Yizhong; Chen, Wei

    2012-01-01

    Two different sized silver nanoclusters are prepared by two different synthetic routs. First, a small nanocluster (NC) which is 0.7 nm in diameter was synthesized by using meso-2, 3-dimercapto-succinic acid (DMSA) as a capping ligand, and second a larger nanoparticle (NP) which is 3.3 nm in diameter was prepared by chemical reduction and coated with DMSA. The as-prepared silver nanoclusters or nanoparticles are then loaded onto a glassy carbon electrode and the size effect on their electrocatalytic activity toward oxygen reduction reaction (ORR) is investigated with electrochemical techniques in alkaline electrolyte. The cyclic voltammetric (CV) studies show that the onset potential of ORR on 0.7 nm silver nanoclusters is 150 mV more positive than that from 3.3 nm silver nanoparticles. And compared to the larger nanoparticles, five times higher current density of ORR at -0.80 V is obtained from the 0.7 nm silver nanoclusters. These CV results indicate that the smaller Ag nanoclusters exhibit higher catalytic performance for ORR. Rotating disk voltammetric studies show ORR on both DMSA monolayer-protected silver clusters is dominated first by a two-electron transfer pathway to produce H2O2 and then peroxide is reduced by 2 more electrons to produce water.

  8. Reaction-based Transport Modeling of Iron Reduction and Uranium Immobilization at Area 2 of the NABIR Field Research Center

    SciTech Connect

    Tsyh Yeh, Gour

    2007-12-21

    This research sought to examine biogeochemical processes likely to take place in the less conductive materials above and below the gravel during the in situ ethanol biostimulation experiment conducted at Area 2 during 2005-2006. The in situ experiment in turn examined the hypothesis that injection of electron donor into this layer would induce formation of a redox barrier in the less conductive materials, resulting in decreased mass transfer of uranium out these materials and attendant declines in groundwater U(VI) concentration. Our project focuses on the development of a mechanistic understanding and quantitative models of coupled Fe(III)/U(VI) reduction in FRC Area 2 sediments. This report summarizes research activities conducted at The University of Central Florida (2004-2007), the development of biogeochemical and reactive transport models and the conduction of numerical simulations at laboratory, column, and field scales.

  9. N2O reduction by the mu4-sulfide-bridged tetranuclear CuZ cluster active site.

    PubMed

    Chen, Peng; Gorelsky, Serge I; Ghosh, Somdatta; Solomon, Edward I

    2004-08-13

    Nitrous oxide (N2O) reduction is a chemical challenge both in the selective oxidation of organic substrates by N2O and in the removal of N2O as a green-house gas. The reduction of N2O is thermodynamically favorable but kinetically inert, and requires activating transition-metal centers. In biological systems, N2O reduction is the last step in the denitrification process of the bacterial nitrogen cycle and is accomplished by the enzyme nitrous oxide reductase, whose active site consists of a micro4-sulfide-bridged tetranuclear CuZ cluster which has many unusual spectroscopic features. Recent studies have developed a detailed electronic-structure description of the resting CuZ cluster, determined its catalytically relevant state, and provided insight into the role of this tetranuclear copper cluster in N2O activation and reduction.

  10. Concentration Effects of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Activity for Three Platinum Catalysts

    DOE PAGES

    Christ, J. M.; Neyerlin, K. C.; Richards, R.; ...

    2014-10-04

    A rotating disk electrode (RDE) along with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were used to investigate the impact of two model compounds representing degradation products of Nafion and 3M perfluorinated sulfonic acid membranes on the electrochemical surface area (ECA) and oxygen reduction reaction (ORR) activity of polycrystalline Pt, nano-structured thin film (NSTF) Pt (3M), and Pt/Vulcan carbon (Pt/Vu) (TKK) electrodes. ORR kinetic currents (measured at 0.9 V and transport corrected) were found to decrease linearly with the log of concentration for both model compounds on all Pt surfaces studied. Ultimately, model compound adsorption effects on ECA weremore » more abstruse due to competitive organic anion adsorption on Pt surfaces superimposing with the hydrogen underpotential deposition (HUPD) region.« less

  11. Reduction of Free Edge Peeling Stress of Laminated Composites Using Active Piezoelectric Layers

    PubMed Central

    Huang, Bin; Kim, Heung Soo

    2014-01-01

    An analytical approach is proposed in the reduction of free edge peeling stresses of laminated composites using active piezoelectric layers. The approach is the extended Kantorovich method which is an iterative method. Multiterms of trial function are employed and governing equations are derived by taking the principle of complementary virtual work. The solutions are obtained by solving a generalized eigenvalue problem. By this approach, the stresses automatically satisfy not only the traction-free boundary conditions, but also the free edge boundary conditions. Through the iteration processes, the free edge stresses converge very quickly. It is found that the peeling stresses generated by mechanical loadings are significantly reduced by applying a proper electric field to the piezoelectric actuators. PMID:25025088

  12. Concentration Effects of Polymer Electrolyte Membrane Degradation Products on Oxygen Reduction Activity for Three Platinum Catalysts

    SciTech Connect

    Christ, J. M.; Neyerlin, K. C.; Richards, R.; Dinh, H. N.

    2014-10-04

    A rotating disk electrode (RDE) along with cyclic voltammetry (CV) and linear sweep voltammetry (LSV), were used to investigate the impact of two model compounds representing degradation products of Nafion and 3M perfluorinated sulfonic acid membranes on the electrochemical surface area (ECA) and oxygen reduction reaction (ORR) activity of polycrystalline Pt, nano-structured thin film (NSTF) Pt (3M), and Pt/Vulcan carbon (Pt/Vu) (TKK) electrodes. ORR kinetic currents (measured at 0.9 V and transport corrected) were found to decrease linearly with the log of concentration for both model compounds on all Pt surfaces studied. Ultimately, model compound adsorption effects on ECA were more abstruse due to competitive organic anion adsorption on Pt surfaces superimposing with the hydrogen underpotential deposition (HUPD) region.

  13. Repetition-Related Reductions in Neural Activity during Emotional Simulations of Future Events

    PubMed Central

    2015-01-01

    Simulations of future experiences are often emotionally arousing, and the tendency to repeatedly simulate negative future outcomes has been identified as a predictor of the onset of symptoms of anxiety. Nonetheless, next to nothing is known about how the healthy human brain processes repeated simulations of emotional future events. In this study, we present a paradigm that can be used to study repeated simulations of the emotional future in a manner that overcomes phenomenological confounds between positive and negative events. The results show that pulvinar nucleus and orbitofrontal cortex respectively demonstrate selective reductions in neural activity in response to frequently as compared to infrequently repeated simulations of negative and positive future events. Implications for research on repeated simulations of the emotional future in both non-clinical and clinical populations are discussed. PMID:26390294

  14. NASA Propulsion Concept Studies and Risk Reduction Activities for Resource Prospector Lander

    NASA Technical Reports Server (NTRS)

    Trinh, Huu P.; Williams, Hunter; Burnside, Chris

    2015-01-01

    The Resource Prospector mission is to investigate the Moon's polar regions in search of volatiles. The government-version lander concept for the mission is composed of a braking stage and a liquid-propulsion lander stage. A propulsion trade study concluded with a solid rocket motor for the braking stage while using the 4th-stage Peacekeeper (PK) propulsion components for the lander stage. The mechanical design of the liquid propulsion system was conducted in concert with the lander structure design. A propulsion cold-flow test article was fabricated and integrated into a lander development structure, and a series of cold flow tests were conducted to characterize the fluid transient behavior and to collect data for validating analytical models. In parallel, RS-34 PK thrusters to be used on the lander stage were hot-fire tested in vacuum conditions as part of risk reduction activities.

  15. Phoretic drag reduction of chemically active homogeneous spheres under force fields and shear flows

    NASA Astrophysics Data System (ADS)

    Yariv, Ehud; Kaynan, Uri

    2017-01-01

    Surrounded by a spherically symmetric solute cloud, chemically active homogeneous spheres do not undergo conventional autophoresis when suspended in an unbounded liquid domain. When exposed to external flows, solute advection deforms that cloud, resulting in a generally asymmetric distribution of diffusio-osmotic slip which, in turn, modifies particle motion. Inspired by classical forced-convection analyses [Acrivos and Taylor, Phys. Fluids 5, 387 (1962), 10.1063/1.1706630; Frankel and Acrivos, Phys. Fluids 11, 1913 (1968), 10.1063/1.1692218] we illustrate this phoretic phenomenon using two prototypic configurations, one where the particle sediments under a uniform force field and one where it is subject to a simple shear flow. In addition to the Péclet number Pe associated with the imposed flow, the governing nonlinear problem also depends upon α , the intrinsic Péclet number associated with the chemical activity of the particle. As in the forced-convection problems, the small-Péclet-number limit is nonuniform, breaking down at large distances away from the particle. Calculation of the leading-order autophoretic effects thus requires use of matched asymptotic expansions, the outer region being at distances that scale inversely with Pe and Pe1 /2 in the respective sedimentation and shear problems. In the sedimentation problem we find an effective drag reduction of fractional amount α /8 ; in the shear problem we find that the magnitude of the stresslet is decreased by a fractional amount α /4 . For a dilute particle suspension the latter result is manifested by a reduction of the effective viscosity.

  16. In situ probing of the active site geometry of ultrathin nanowires for the oxygen reduction reaction

    SciTech Connect

    Liu, Haiqing; Wong, Stanislaus S.; An, Wei; Li, Yuanyuan; Frenkel, Anatoly I.; Sasaki, Kotaro; Koenigsmann, Christopher; Su, Dong; Anderson, Rachel M.; Crooks, Richard M.; Adzic, Radoslav R.; Liu, Ping

    2015-09-24

    To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (~2 nm) core–shell Pt~Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu~Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Thus, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.

  17. Early reduction in toe flexor strength is associated with physical activity in elderly men

    PubMed Central

    Suwa, Masataka; Imoto, Takayuki; Kida, Akira; Yokochi, Takashi

    2016-01-01

    [Purpose] To compare the toe flexor, hand grip and knee extensor strengths of young and elderly men, and to examine the association between toe flexor strength and physical activity or inactivity levels. [Subjects and Methods] Young (n=155, 18–23 years) and elderly (n=60, 65–88 years) men participated in this study. Toe flexor, hand grip, and knee extensor strength were measured. Physical activity (time spent standing/walking per day) and inactivity (time spent sitting per day) were assessed using a self-administered questionnaire. [Results] Toe flexor, hand grip, and knee extensor strength of the elderly men were significantly lower than those of the young men. Standing/walking and sitting times of the elderly men were lower than those of the young men. Toe flexor strength correlated with hand grip and knee extensor strength in both groups. In elderly men, toe flexor strength correlated with standing/walking time. In comparison to the young men’s mean values, toe flexor strength was significantly lower than knee extensor and hand grip strength in the elderly group. [Conclusion] The results suggest that age-related reduction in toe flexor strength is greater than those of hand grip and knee extensor strengths. An early loss of toe flexor strength is likely associated with reduced physical activity in elderly men. PMID:27313353

  18. Meso-structured platinum thin films: active and stable electrocatalysts for the oxygen reduction reaction.

    PubMed

    Kibsgaard, Jakob; Gorlin, Yelena; Chen, Zhebo; Jaramillo, Thomas F

    2012-05-09

    Improving both the activity and the stability of the cathode catalyst in platinum-based polymer electrolyte fuel cells is a key technical challenge. Here, we synthesize a high surface area meso-structured Pt thin film that exhibits higher specific activity for the oxygen reduction reaction (ORR) than commercial carbon-supported Pt nanoparticles (Pt/C). An accelerated stability test demonstrates that the meso-structured Pt thin film also displays significantly enhanced stability as compared to the commercial Pt/C catalyst. Our study reveals the origin of the high turnover frequency (TOF), and excellent durability is attributed to the meso-structure, which yields a morphology with fewer undercoordinated Pt sites than Pt/C nanoparticles, a key difference with substantial impact to the surface chemistry. The improved catalyst activity and stability could enable the development of a high-performance gas diffusion electrode that is resistant to corrosion even under the harsh conditions of start-up, shut-down, and/or hydrogen starvation.

  19. Shell-anchor-core structures for enhanced stability and catalytic oxygen reduction activity

    NASA Astrophysics Data System (ADS)

    Ramirez-Caballero, Gustavo E.; Hirunsit, Pussana; Balbuena, Perla B.

    2010-10-01

    Density functional theory is used to evaluate activity and stability properties of shell-anchor-core structures. The structures consist of a Pt surface monolayer and a composite core having an anchor bilayer where C atoms in the interstitial sites lock 3d metals in their locations, thus avoiding their surface segregation and posterior dissolution. The modified subsurface geometry induces less strain on the top surface, thus exerting a favorable effect on the surface catalytic activity where the adsorption strength of the oxygenated species becomes more moderate: weaker than on pure Pt(111) but stronger than on a Pt monolayer having a 3d metal subsurface. Here we analyze the effect of changing the nature of the 3d metal in the subsurface anchor bilayer, and we also test the use of a Pd monolayer instead of Pt on the surface. It is found that a subsurface constituted by two layers with an approximate composition of M2C (M=Fe, Ni, and Co) provides a barrier for the migration of subsurface core metal atoms to the surface. Consequently, an enhanced resistance against dissolution in parallel to improved oxygen reduction activity is expected, as given by the values of adsorption energies of reaction intermediates, delayed onset of water oxidation, and/or low coverage of oxygenated species at surface oxidation potentials.

  20. In Situ Probing of the Active Site Geometry of Ultrathin Nanowires for the Oxygen Reduction Reaction.

    PubMed

    Liu, Haiqing; An, Wei; Li, Yuanyuan; Frenkel, Anatoly I; Sasaki, Kotaro; Koenigsmann, Christopher; Su, Dong; Anderson, Rachel M; Crooks, Richard M; Adzic, Radoslav R; Liu, Ping; Wong, Stanislaus S

    2015-10-07

    To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (∼2 nm) core-shell Pt∼Pd9Au nanowires, which have been previously shown to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu∼Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Hence, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.

  1. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    DOE PAGES

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; ...

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can bemore » attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.« less

  2. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    PubMed Central

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; Mavrikakis, Manos; Xia, Younan

    2015-01-01

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. These results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability. PMID:26133469

  3. Cerebral Activity Associated with Transient Sleep-Facilitated Reduction in Motor Memory Vulnerability to Interference

    PubMed Central

    Albouy, Geneviève; King, Bradley R.; Schmidt, Christina; Desseilles, Martin; Dang-Vu, Thien Thanh; Balteau, Evelyne; Phillips, Christophe; Degueldre, Christian; Orban, Pierre; Benali, Habib; Peigneux, Philippe; Luxen, André; Karni, Avi; Doyon, Julien; Maquet, Pierre; Korman, Maria

    2016-01-01

    Motor memory consolidation is characterized, in part, by a sleep-facilitated decrease in susceptibility to subsequent interfering experiences. Surprisingly, the cerebral substrates supporting this phenomenon have never been examined. We used fMRI to investigate the neural correlates of the influence of sleep on interference to motor memory consolidation. Healthy young adults were trained on a sequential motor task, and subsequently practiced a second competing sequence after an interval including diurnal sleep or wakefulness. Participants were then retested on the initial sequence 8 h and 24 h (including nocturnal sleep) after training. Results demonstrated that a post-training nap significantly protected memory against interference at 8 h and modulated the link between cerebral activity and behavior, such that a smaller post-interference decrease in cortico-striatal activity was associated with better performance. Interestingly, the protective effect of a nap was only transitory, as both groups performed similarly at 24 h. Activity in cortico-striatal areas that was disrupted during the day, presumably due to interference and accentuated in the absence of a nap, was restored overnight. Altogether, our findings offer the first evidence that cortico-striatal areas play a critical role in the transient sleep-facilitated reduction in motor memory vulnerability and in the overnight restoration of previously degraded memories. PMID:27725727

  4. In situ probing of the active site geometry of ultrathin nanowires for the oxygen reduction reaction

    DOE PAGES

    Liu, Haiqing; Wong, Stanislaus S.; An, Wei; ...

    2015-09-24

    To create truly effective electrocatalysts for the cathodic reaction governing proton exchange membrane fuel cells (PEMFC), namely the oxygen reduction reaction (ORR), necessitates an accurate and detailed structural understanding of these electrocatalysts, especially at the nanoscale, and to precisely correlate that structure with demonstrable performance enhancement. To address this key issue, we have combined and interwoven theoretical calculations with experimental, spectroscopic observations in order to acquire useful structural insights into the active site geometry with implications for designing optimized nanoscale electrocatalysts with rationally predicted properties. Specifically, we have probed ultrathin (~2 nm) core–shell Pt~Pd9Au nanowires, which have been previously shownmore » to be excellent candidates for ORR in terms of both activity and long-term stability, from the complementary perspectives of both DFT calculations and X-ray absorption spectroscopy (XAS). The combination and correlation of data from both experimental and theoretical studies has revealed for the first time that the catalytically active structure of our ternary nanowires can actually be ascribed to a PtAu~Pd configuration, comprising a PtAu binary shell and a pure inner Pd core. Moreover, we have plausibly attributed the resulting structure to a specific synthesis step, namely the Cu underpotential deposition (UPD) followed by galvanic replacement with Pt. Thus, the fundamental insights gained into the performance of our ultrathin nanowires from our demonstrated approach will likely guide future directed efforts aimed at broadly improving upon the durability and stability of nanoscale electrocatalysts in general.« less

  5. Synthesis of highly active and dual-functional electrocatalysts for methanol oxidation and oxygen reduction reactions

    NASA Astrophysics Data System (ADS)

    Zhao, Qi; Zhang, Geng; Xu, Guangran; Li, Yingjun; Liu, Baocang; Gong, Xia; Zheng, Dafang; Zhang, Jun; Wang, Qin

    2016-12-01

    The promising Pt-based ternary catalyst is crucial for polymer electrolyte membrane fuel cells (PEMFCs) due to improving catalytic activity and durability for both methanol oxidation reaction and oxygen reduction reaction. In this work, a facile strategy is used for the synthesis ternary RuMPt (M = Fe, Co, Ni, and Cu) nanodendrities catalysts. The ternary RuMPt alloys exhibit enhanced specific and mass activity, positive half-wave potential, and long-term stability, compared with binary Pt-based alloy and the commercial Pt/C catalyst, which is attributed to the high electron density and upshifting of the d-band center for Pt atoms, and synergistic catalytic effects among Pt, M, and Ru atoms by introducing a transition metal. Impressively, the ternary RuCoPt catalyst exhibits superior mass activity (801.59 mA mg-1) and positive half-wave potential (0.857 V vs. RHE) towards MOR and ORR, respectively. Thus, the RuMPt nanocomposite is a very promising material to be used as dual electrocatalyst in the application of PEMFCs.

  6. Cerebral Activity Associated with Transient Sleep-Facilitated Reduction in Motor Memory Vulnerability to Interference.

    PubMed

    Albouy, Geneviève; King, Bradley R; Schmidt, Christina; Desseilles, Martin; Dang-Vu, Thien Thanh; Balteau, Evelyne; Phillips, Christophe; Degueldre, Christian; Orban, Pierre; Benali, Habib; Peigneux, Philippe; Luxen, André; Karni, Avi; Doyon, Julien; Maquet, Pierre; Korman, Maria

    2016-10-11

    Motor memory consolidation is characterized, in part, by a sleep-facilitated decrease in susceptibility to subsequent interfering experiences. Surprisingly, the cerebral substrates supporting this phenomenon have never been examined. We used fMRI to investigate the neural correlates of the influence of sleep on interference to motor memory consolidation. Healthy young adults were trained on a sequential motor task, and subsequently practiced a second competing sequence after an interval including diurnal sleep or wakefulness. Participants were then retested on the initial sequence 8 h and 24 h (including nocturnal sleep) after training. Results demonstrated that a post-training nap significantly protected memory against interference at 8 h and modulated the link between cerebral activity and behavior, such that a smaller post-interference decrease in cortico-striatal activity was associated with better performance. Interestingly, the protective effect of a nap was only transitory, as both groups performed similarly at 24 h. Activity in cortico-striatal areas that was disrupted during the day, presumably due to interference and accentuated in the absence of a nap, was restored overnight. Altogether, our findings offer the first evidence that cortico-striatal areas play a critical role in the transient sleep-facilitated reduction in motor memory vulnerability and in the overnight restoration of previously degraded memories.

  7. Update on Risk Reduction Activities for a Liquid Advanced Booster for NASA's Space Launch System

    NASA Technical Reports Server (NTRS)

    Crocker, Andrew M.; Doering, Kimberly B; Meadows, Robert G.; Lariviere, Brian W.; Graham, Jerry B.

    2015-01-01

    The stated goals of NASA's Research Announcement for the Space Launch System (SLS) Advanced Booster Engineering Demonstration and/or Risk Reduction (ABEDRR) are to reduce risks leading to an affordable Advanced Booster that meets the evolved capabilities of SLS; and enable competition by mitigating targeted Advanced Booster risks to enhance SLS affordability. Dynetics, Inc. and Aerojet Rocketdyne (AR) formed a team to offer a wide-ranging set of risk reduction activities and full-scale, system-level demonstrations that support NASA's ABEDRR goals. For NASA's SLS ABEDRR procurement, Dynetics and AR formed a team to offer a series of full-scale risk mitigation hardware demonstrations for an affordable booster approach that meets the evolved capabilities of the SLS. To establish a basis for the risk reduction activities, the Dynetics Team developed a booster design that takes advantage of the flight-proven Apollo-Saturn F-1. Using NASA's vehicle assumptions for the SLS Block 2, a two-engine, F-1-based booster design delivers 150 mT (331 klbm) payload to LEO, 20 mT (44 klbm) above NASA's requirements. This enables a low-cost, robust approach to structural design. During the ABEDRR effort, the Dynetics Team has modified proven Apollo-Saturn components and subsystems to improve affordability and reliability (e.g., reduce parts counts, touch labor, or use lower cost manufacturing processes and materials). The team has built hardware to validate production costs and completed tests to demonstrate it can meet performance requirements. State-of-the-art manufacturing and processing techniques have been applied to the heritage F-1, resulting in a low recurring cost engine while retaining the benefits of Apollo-era experience. NASA test facilities have been used to perform low-cost risk-reduction engine testing. In early 2014, NASA and the Dynetics Team agreed to move additional large liquid oxygen/kerosene engine work under Dynetics' ABEDRR contract. Also led by AR, the

  8. Density Functional Theory Study of Oxygen Reduction Activity on Ultrathin Platinum Nanotubes

    SciTech Connect

    Matanovic, Ivana; Kent, Paul; Garzon, Fernando; Henson, Neil J.

    2012-07-13

    The structure, stability, and catalytic activity of a number of single- and double-wall platinum (n,m) nanotubes ranging in diameter from 0.3 to 2.0 nm were studied using plane-wave based density functional theory in the gas phase and water environment. The change in the catalytic activity toward the oxygen reduction reaction (ORR) with the size and chirality of the nanotube was studied by calculating equilibrium adsorption potentials for ORR intermediates and by constructing free energy diagrams in the ORR dissociative mechanism network. In addition, the stability of the platinum nanotubes is investigated in terms of electrochemical dissolution potentials and by determining the most stable state of the material as a function of pH and potential, as represented in Pourbaix diagrams. Our results show that the catalytic activity and the stability toward electrochemical dissolution depend greatly on the diameter and chirality of the nanotube. On the basis of the estimated overpotentials for ORR, we conclude that smaller, approximately 0.5 nm in diameter single-wall platinum nanotubes consistently show a huge, up to 400 mV larger overpotential than platinum, indicating very poor catalytic activity toward ORR. This is the result of substantial structural changes induced by the adsorption of any chemical species on these tubes. Single-wall n = m platinum nanotubes with a diameter larger than 1 nm have smaller ORR overpotentials than bulk platinum for up to 180 mV and thus show improved catalytic activity relative to bulk. We also predict that these nanotubes can endure the highest cell potentials but dissolution potentials are still for 110 mV lower than for the bulk, indicating a possible corrosion problem.

  9. Early active motion protocol following open reduction internal fixation of the scaphoid: A pilot study.

    PubMed

    Dunn, J-C; Kusnezov, N; Fares, A; Buccino, Z; Esquivel, D; Mitchell, J

    2017-02-01

    Scaphoid fractures are common injuries which traditionally have been treated with long periods of immobilization even after open reduction and internal fixation (ORIF). The purpose of this pilot investigation was two-fold: 1) describe a precise postoperative Early Active Motion (EAM) rehabilitation protocol following ORIF of scaphoid fractures and 2) record the outcomes of the EAM protocol. Eight consecutive patients having undergone ORIF of the scaphoid were enrolled in the EAM and followed for a minimum of 1 year. At 12 weeks, Disabilities of the Arm Shoulder and Hand (DASH) score, Mayo Wrist score, and range of motion values were obtained. At 1 year, a telephone survey was conducted and several data points were obtained including DASH and Mayo Wrist score, number of push-ups, satisfaction with surgery and ability to remain on active duty. All 8 patients were male, on active duty, with an average age of 26 years. Two patients used tobacco products and none had major health problems. All patients completed the EAM protocol and obtained CT; all CT exams demonstrated healing at 8 weeks. At 12 weeks postoperatively, the average DASH score was 8.8±16 (range: 0-47.5), Mayo wrist score was 88±10 (range: 75-100) and range of motion nearly symmetrical. At a mean final follow-up of 15.4 months postoperatively, the average DASH score was 1.1±1.7 (Range: 0-4.5), Mayo wrist score was 97.5±4 (range 90-100), average number of push-ups was 57 (40-70) at the prior Army Physical Fitness Test. All patients were satisfied with surgery and all remained on active duty at 1 year. There were no reported complications. The EAM protocol following scaphoid fracture ORIF is safe and effective. The EAM can reliably return patients back to high demand activity earlier than a traditional protocol.

  10. Effect of radiation-induced reduction of nitroimidazoles on biologically active DNA

    SciTech Connect

    Lafleur, M.V.; Pluijmackers-Westmijze, E.J.; Loman, H.

    1986-07-01

    Radiation-chemical reductions have been carried out with several nitroimidazoles. Reduction of these drugs in the presence of single-stranded phi chi 174 DNA causes extensive lethal damage. However, relatively stable (end) products, do not contribute to the damage, although glyoxal is potentially toxic. This demonstrates that a short-lived intermediate in the reduction process is responsible. Further, the quantity of damage in the DNA depends on both dose (reduction)-rate and also the nature of the drug.

  11. Interactions between Silicon Oxide Nanoparticles (SONPs) and U(VI) Contaminations: Effects of pH, Temperature and Natural Organic Matters

    PubMed Central

    Wu, Hanyu; Li, Ping; Pan, Duoqiang; Yin, Zhuoxin; Fan, Qiaohui; Wu, Wangsuo

    2016-01-01

    The interactions between contaminations of U(VI) and silicon oxide nanoparticles (SONPs), both of which have been widely used in modern industry and induced serious environmental challenge due to their high mobility, bioavailability, and toxicity, were studied under different environmental conditions such as pH, temperature, and natural organic matters (NOMs) by using both batch and spectroscopic approaches. The results showed that the accumulation process, i.e., sorption, of U(VI) on SONPs was strongly dependent on pH and ionic strength, demonstrating that possible outer- and/or inner-sphere complexes were controlling the sorption process of U(VI) on SONPs in the observed pH range. Humic acid (HA), one dominated component of NOMs, bounded SONPs can enhance U(VI) sorption below pH~4.5, whereas restrain at high pH range. The reversible sorption of U(VI) on SONPs possibly indicated that the outer-sphere complexes were prevalent at pH 5. However, an irreversible interaction of U(VI) was observed in the presence of HA (Fig 1). It was mainly due to the ternary SONPs-HA-U(VI) complexes (Type A Complexes). After SONPs adsorbed U(VI), the particle size in suspension was apparently increased from ~240 nm to ~350 nm. These results showed that toxicity of both SONPs and U(VI) will decrease to some extent after the interaction in the environment. These findings are key for providing useful information on the possible mutual interactions among different contaminants in the environment. PMID:26930197

  12. Interactions between Silicon Oxide Nanoparticles (SONPs) and U(VI) Contaminations: Effects of pH, Temperature and Natural Organic Matters.

    PubMed

    Wu, Hanyu; Li, Ping; Pan, Duoqiang; Yin, Zhuoxin; Fan, Qiaohui; Wu, Wangsuo

    2016-01-01

    The interactions between contaminations of U(VI) and silicon oxide nanoparticles (SONPs), both of which have been widely used in modern industry and induced serious environmental challenge due to their high mobility, bioavailability, and toxicity, were studied under different environmental conditions such as pH, temperature, and natural organic matters (NOMs) by using both batch and spectroscopic approaches. The results showed that the accumulation process, i.e., sorption, of U(VI) on SONPs was strongly dependent on pH and ionic strength, demonstrating that possible outer- and/or inner-sphere complexes were controlling the sorption process of U(VI) on SONPs in the observed pH range. Humic acid (HA), one dominated component of NOMs, bounded SONPs can enhance U(VI) sorption below pH~4.5, whereas restrain at high pH range. The reversible sorption of U(VI) on SONPs possibly indicated that the outer-sphere complexes were prevalent at pH 5. However, an irreversible interaction of U(VI) was observed in the presence of HA (Fig 1). It was mainly due to the ternary SONPs-HA-U(VI) complexes (Type A Complexes). After SONPs adsorbed U(VI), the particle size in suspension was apparently increased from ~240 nm to ~350 nm. These results showed that toxicity of both SONPs and U(VI) will decrease to some extent after the interaction in the environment. These findings are key for providing useful information on the possible mutual interactions among different contaminants in the environment.

  13. Skeletal muscle regeneration is delayed by reduction in Xin expression: consequence of impaired satellite cell activation?

    PubMed

    Nissar, Aliyah A; Zemanek, Bart; Labatia, Rita; Atkinson, Daniel J; van der Ven, Peter F M; Fürst, Dieter O; Hawke, Thomas J

    2012-01-01

    Xin is a striated muscle-specific actin-binding protein whose mRNA expression has been observed in damaged skeletal muscle. Here we demonstrate increased Xin protein expression early postinjury (≤ 12 h) and localization primarily to the periphery of damaged myofibers. At 1 day postinjury, Xin is colocalized with MyoD, confirming expression in activated satellite cells (SCs). By 5 days postinjury, Xin is evident in newly regenerated myofibers, with a return to preinjury levels by 14 days of regeneration. To determine whether the increased Xin expression is functionally relevant, tibialis anterior muscles of wild-type mice were infected with Xin-short hairpin RNA (shRNA) adenovirus, whereas the contralateral tibialis anterior received control adenovirus (Control). Four days postinfection, muscles were harvested or injured with cardiotoxin and collected at 3, 5, or 14 days thereafter. When compared with Control, Xin-shRNA infection attenuated muscle regeneration as demonstrated by Myh3 expression and fiber areas. Given the colocalization of Xin and MyoD, we isolated single myofibers from infected muscles to investigate the effect of silencing Xin on SC function. Relative to Control, SC activation, but not proliferation, was significantly impaired in Xin-shRNA-infected muscles. To determine whether Xin affects the G0-G1 transition, cell cycle reentry was assessed on infected C2C12 myoblasts using a methylcellulose assay. No difference in reentry was noted between groups, suggesting that Xin contributes to SC activation by means other than affecting G0-G1 transition. Together these data demonstrate a critical role for Xin in SC activation and reduction in Xin expression results in attenuated skeletal muscle repair.

  14. Activation of oxygen evolving perovskites for oxygen reduction by functionalization with Fe-N(x)/C groups.

    PubMed

    Rincón, Rosalba A; Masa, Justus; Mehrpour, Sara; Tietz, Frank; Schuhmann, Wolfgang

    2014-12-07

    The incorporation of Fe-Nx/C moieties into perovskites remarkably activates them for the oxygen reduction reaction (ORR) and also leads to notable improvement of their activity towards the oxygen evolution reaction (OER) thus presenting a new route for realizing high performance, low cost bifunctional catalysts for reversible oxygen electrodes.

  15. Reduction of COD in refinery wastewater through adsorption on date-pit activated carbon.

    PubMed

    El-Naas, Muftah H; Al-Zuhair, Sulaiman; Abu Alhaija, Manal

    2010-01-15

    Experiments were carried out to evaluate the batch adsorption of COD from petroleum refinery wastewater on a locally prepared date-pit activated carbon (DP-AC), and its adsorption effectiveness was compared to that of commercially available BDH activated carbon (BDH-AC). Adsorption equilibrium and kinetic data were determined for both adsorbents and fitted to several adsorption isotherm and kinetics models, respectively. The Langmuir monolayer isotherm fitted well the equilibrium data of COD on both adsorbents; whereas, the kinetics data were best fitted by the pseudo-second order model. Modeling of the controlling mechanisms indicated that both intrinsic kinetics and mass transfer contributed to controlling the adsorption process. Mass transfer seemed to be the dominant mechanism at low COD content, while intrinsic kinetics dominates at high concentrations. In general, the adsorption effectiveness of locally prepared DP-AC was proven to be comparable to that of BDH-AC. Therefore, DP-AC can be utilized as an effective and less expensive adsorbent for the reduction of COD in refinery wastewater.

  16. Reduction of computational complexity in the image/video understanding systems with active vision

    NASA Astrophysics Data System (ADS)

    Kuvich, Gary

    2003-10-01

    The vision system evolved not only as a recognition system, but also as a sensory system for reaching, grasping and other motion activities. In advanced creatures, it became a component of prediction function, allowing creation of environmental models and activity planning. Fast information processing and decision making is vital for any living creature, and requires reduction of informational and computational complexities. The brain achieves this goal using symbolic coding, hierarchical compression, and selective processing of visual information. Network-Symbolic representation, where both systematic structural / logical methods and neural / statistical methods are the parts of a single mechanism, is the most feasible for such models. It converts visual information into the relational Network-Symbolic structures, instead of precise computations of a 3-dimensional models. Narrow foveal vision provides separation of figure from ground, object identification, semantic analysis, and precise control of actions. Rough wide peripheral vision identifies and tracks salient motion, guiding foveal system to salient objects. It also provides scene context. Objects with rigid bodies and other stable systems have coherent relational structures. Hierarchical compression and Network-Symbolic transformations derive more abstract structures that allow invariably recognize a particular structure as an exemplar of class. Robotic systems equipped with such smart vision will be able effectively navigate in any environment, understand situation, and act accordingly.

  17. Subjective evaluation of an active crosstalk reduction system for mobile autostereoscopic displays

    NASA Astrophysics Data System (ADS)

    Chappuis, Alexandre; Rerabek, Martin; Hanhart, Philippe; Ebrahimi, Touradj

    2014-03-01

    The Quality of Experience (QoE) provided by autostereoscopic 3D displays strongly depends on the user position. For an optimal image quality, the observer should be located at one of the relevant positions, called sweet spots, where artifacts reducing the QoE, such as crosstalk, are minimum. In this paper, we propose and evaluate a complete active crosstalk reduction system running on an HTC EVO 3D smartphone. To determine the crosstalk level at each position, a full display characterization was performed. Based on the user position and crosstalk profile, the system first helps the user to find the sweet spot using visual feedback. If the user moves away from the sweet spot, then the active crosstalk compensation is performed and reverse stereo phenomenon is corrected. The user preference between standard 2D and 3D modes, and the proposed system was evaluated through a subjective quality assessment. Results show that in terms of depth perception, the proposed system clearly outperforms the 3D and 2D modes. In terms of image quality, 2D mode was found to be best, but the proposed system outperforms 3D mode.

  18. Proteolytic activity of Enterococcus faecalis VB63F for reduction of allergenicity of bovine milk proteins.

    PubMed

    Biscola, V; Tulini, F L; Choiset, Y; Rabesona, H; Ivanova, I; Chobert, J-M; Todorov, S D; Haertlé, T; Franco, B D G M

    2016-07-01

    With the aim of screening proteolytic strains of lactic acid bacteria to evaluate their potential for the reduction of allergenicity of the major bovine milk proteins, we isolated a new proteolytic strain of Enterococcus faecalis (Ent. faecalis VB63F) from raw bovine milk. The proteases produced by this strain had strong activity against caseins (αS1-, αS2-, and β-casein), in both skim milk and sodium caseinate. However, only partial hydrolysis of whey proteins was observed. Proteolysis of Na-caseinate and whey proteins, observed after sodium dodecyl sulfate-PAGE, was confirmed by analysis of peptide profiles by reversed-phase HPLC. Inhibition of proteolysis with EDTA indicated that the proteases produced by Ent. faecalis VB63F belonged to the group of metalloproteases. The optimal conditions for their activity were 42°C and pH 6.5. The majority of assessed virulence genes were absent in Ent. faecalis VB63F. The obtained results suggest that Ent. faecalis VB63F could be efficient in reducing the immunoreactivity of bovine milk proteins.

  19. Reduction of transition metals by human (THP-1) monocytes is enhanced by activators of protein kinase C.

    PubMed

    Wood, J L; Graham, A

    1999-11-01

    Macrophages oxidize low density lipoprotein (LDL) by enzymatic and non-enzymatic mechanisms; however, it is evident that macrophage reduction of transition metals can accelerate LDL oxidation in vitro, and possibly in vivo. Distinct cellular pathways contribute to this process, including trans-plasma membrane electron transport (TPMET), and production of free thiols or superoxide. Here, we explore the role of protein kinase C (PKC) in regulating transition metal reduction by each of these redox-active pathways, in human (THP-1) monocytes. We demonstrate that PKC agonists and/or inhibitors modulate reduction of transition metals by monocytes: both thiol-independent (direct) and thiol-dependent (indirect) pathways for transition metal reduction are enhanced by PKC activation, suggesting a potential strategy for therapeutic intervention.

  20. Incorporation of Np(V) and U(VI) in Carbonate and Sulfate Minerals Crystallized from Aqueous Solution

    SciTech Connect

    Balboni, Enrica; Morrison, Jessica M.; Wang, Zheming; Engelhard, Mark H.; Burns, Peter C.

    2015-02-15

    The neptunyl Np(V)O2 + and uranyl U(VI)O2 2+ ions are soluble in groundwater, although their interaction with minerals in the subsurface may impact their mobility. One mechanism for the immobilization of actinyl ions in the subsurface is coprecipitation in low-temperature minerals that form naturally, or that are induced to form as part of a remediation strategy. Important differences in the crystal-chemical behavior of the Np(V) neptunyl and U(VI) uranyl ions suggest their behavior towards incorporation into growing crystals may differ significantly. Using a selection of low temperature minerals synthesized in aqueous systems under ambient conditions, this study examines the factors that impact the structural incorporation of the Np(V) neptunyl and U(VI) uranyl ions in carbonate and sulfate minerals.

  1. Studies of Cobalt-Mediated Electrocatalytic CO2 Reduction Using a Redox-Active Ligand

    PubMed Central

    2015-01-01

    The cobalt complex [CoIIIN4H(Br)2]+ (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7),2,11,13,15-pentaene) was used for electrocatalytic CO2 reduction in wet MeCN with a glassy carbon working electrode. When water was employed as the proton source (10 M in MeCN), CO was produced (fCO= 45% ± 6.4) near the CoI/0 redox couple for [CoIIIN4H(Br)2]+ (E1/2 = −1.88 V FeCp2+/0) with simultaneous H2 evolution (fH2= 30% ± 7.8). Moreover, we successfully demonstrated that the catalytically active species is homogeneous through the use of control experiments and XPS studies of the working glassy-carbon electrodes. As determined by cyclic voltammetry, CO2 catalysis occurred near the formal CoI/0redox couple, and attempts were made to isolate the triply reduced compound (“[Co0N4H]”). Instead, the doubly reduced (“CoI”) compounds [CoN4] and [CoN4H(MeCN)]+ were isolated and characterized by X-ray crystallography. Their molecular structures prompted DFT studies to illuminate details regarding their electronic structure. The results indicate that reducing equivalents are stored on the ligand, implicating redox noninnocence in the ligands for H2 evolution and CO2 reduction electrocatalysis. PMID:24773584

  2. Chromate Reduction by a Pseudomonad Isolated from a Site Contaminated with Chromated Copper Arsenate

    PubMed Central

    McLean, Jeff; Beveridge, Terry J.

    2001-01-01

    A pseudomonad (CRB5) isolated from a decommissioned wood preservation site reduced toxic chromate [Cr(VI)] to an insoluble Cr(III) precipitate under aerobic and anaerobic conditions. CRB5 tolerated up to 520 mg of Cr(VI) liter−1 and reduced chromate in the presence of copper and arsenate. Under anaerobic conditions it also reduced Co(III) and U(VI), partially internalizing each metal. Metal precipitates were also found on the surface of the outer membrane and (sometimes) on a capsule. The results showed that chromate reduction by CRB5 was mediated by a soluble enzyme that was largely contained in the cytoplasm but also found outside of the cells. The crude reductase activity in the soluble fraction showed a Km of 23 mg liter−1 (437 μM) and a Vmax of 0.98 mg of Cr h−1 mg of protein−1 (317 nmol min−1 mg of protein−1). Minor membrane-associated Cr(VI) reduction under anaerobiosis may account for anaerobic reduction of chromate under nongrowth conditions with an organic electron donor present. Chromate reduction under both aerobic and anaerobic conditions may be a detoxification strategy for the bacterium which could be exploited to bioremediate chromate-contaminated or other toxic heavy metal-contaminated environments. PMID:11229894

  3. Reduction of Hexavalent Uranium from Organic Complexes by Sulfate- and Iron-Reducing Bacteria

    PubMed Central

    Ganesh, R.; Robinson, K. G.; Reed, G. D.; Sayler, G. S.

    1997-01-01

    The influence of organic-hexavalent-uranium [U(VI)] complexation on U(VI) reduction by a sulfate-reducing bacterium (Desulfovibrio desulfuricans) and an iron-reducing bacterium (Shewanella alga) was evaluated. Four aliphatic ligands (acetate, malonate, oxalate, and citrate) and an aromatic ligand (tiron [4,5-dihydroxy-1,3-benzene disulfonic acid]) were used to study complexed-uranium bioavailability. The trends in uranium reduction varied with the nature and the amount of U(VI)-organic complex formed and the type of bacteria present. D. desulfuricans rapidly reduced uranium from a monodentate aliphatic (acetate) complex. However, reduction from multidentate aliphatic complexes (malonate, oxalate, and citrate) was slower. A decrease in the amount of organic-U(VI) complex in solution significantly increased the rate of reduction. S. alga reduced uranium more rapidly from multidentate aliphatic complexes than from monodentate aliphatic complexes. The rate of reduction decreased with a decrease in the amount of multidentate complexes present. Uranium from an aromatic (tiron) complex was readily available for reduction by D. desulfuricans, while an insignificant level of U(VI) from the tiron complex was reduced by S. alga. These results indicate that selection of bacteria for rapid uranium reduction will depend on the organic composition of waste streams. PMID:16535729

  4. Mechanism of enhanced nitrate reduction via micro-electrolysis at the powdered zero-valent iron/activated carbon interface.

    PubMed

    Luo, Jinghuan; Song, Guangyu; Liu, Jianyong; Qian, Guangren; Xu, Zhi Ping

    2014-12-01

    Nitrate reduction by zero-valent iron (Fe(0)) powder always works well only at controlled pH lower than 4 due to the formation of iron (hydr)oxides on its surface. Fe(0) powder combined with activated carbon (AC), i.e., Fe(0)/AC micro-electrolysis system, was first introduced to enhance nitrate reduction in aqueous solution. Comparative study was carried out to investigate nitrate reduction by Fe(0)/AC system and Fe(0) under near-neutral conditions, showing that the Fe(0)/AC system successfully reduced nitrate even at initial pH 6 with the reduction efficiency of up to 73%, whereas for Fe(0) only ∼10%. The effect of Fe(0) to AC mass ratio on nitrate reduction efficiency was examined. Easier nitrate reduction was achieved with more contact between Fe(0) and AC as the result of decreasing Fe(0) to AC mass ratio. Ferrous ion and oxidation-reduction potential were measured to understand the mechanism of enhanced nitrate reduction by Fe(0)/AC micro-electrolysis. The results suggest that a relative potential difference drives much more electrons from Fe(0) to AC, thus generating adsorbed atomic hydrogen which makes it possible for nitrate to be reduced at near-neural pH. Fe(0)/AC micro-electrolysis thus presents a great potential for practical application in nitrate wastewater treatment without excessive pH adjustment.

  5. Coupled Biogeochemical Processes Governing the Stability of Bacteriogenic Uraninite and Release of U(VI) in Heterogeneous Media: Molecular to Meter Scales

    SciTech Connect

    Bargar, John R.

    2006-11-15

    In-situ reductive biotransformation of subsurface U(VI) to U(IV) (as ?UO2?) has been proposed as a bioremediation method to immobilize uranium at contaminated DOE sites. The chemical stability of bacteriogenic ?UO2? is the seminal issue governing its success as an in-situ waste form in the subsurface. The structure and properties of chemically synthesized UO2+x have been investigated in great detail. It has been found to exhibit complex structural disorder, with nonstoichiometry being common, hence the designation ?UO2+x?, where 0 < x < 0.25. Little is known about the structures and properties of the important bacteriogenic analogs, which are believed to occur as nanoparticles in the environment. Chemically synthesized UO2+x exhibits an open fluorite structure and is known to accommodate significant doping of divalent cations. The extent to which bacteriogenic UO2+x incorporates common ground water cations (e.g., Ca2+) has not been investigated, and little is known about nonstoichiometry and structure defects in the bacteriogenic material. Particle size, nonstoichiometry, and doping may significantly alter the reactivity, and hence stability, of bacteriogenic UO2+x in the subsurface. The presence of associated sulfide minerals, and solid phase oxidants such as bacteriogenic Mn oxides may also affect the longevity of bacteriogenic UO2 in the subsurface.

  6. In vivo chelation of Am(III), Pu(IV), Np(V), and U(VI) in mice by TREN-(Me-3,2-HOPO)

    SciTech Connect

    Durbin, P.W.; Kullgren, B.; Xu, J.; Raymond, K.N.

    1993-08-01

    Octadentate 3,4,3-LI(1,2-HOPO), composed of the acidic hydroxypyridine isomer, 1,2-HOPO, is the most effective ligand yet prepared for in vivo chelation of Pu(IV) and Am(III), but it is difficult to prepare and acutely toxic. Hexadentate TREN-(Me-3,2-HOPO), composed of the less acidic Me-3,2-HOPO isomer, can be produced in relatively large quantities. TREN-(Me-3,2-HOPO) (30 {mu}mol.kg{sup {minus}1} injected intraperitoneally in mice 3 min to 1 h after intravenous injection of an actinide) removed significant body Pu(IV), Am(III), Np(V), or U(VI) (compared with controls), and those actinide reductions were significantly greater than were obtained with CaNa{sub 3}-DTPA. TREN-(Me-3,2-HOPO) was almost as effective for reducing body PU(IV) as 3,4,3-LI(1,2-HOPO). TREN-(Me-3,2-HOPO) is of low acute toxicity in mice and its clinical potential, as a practical compromise between the effectiveness of 3,4,3-LI(1,2-HOPO) and the safety of CaNa{sub 3}-DTPA, merits further investigation.

  7. Radiative transfer modelling for the NOMAD-UVIS instrument on the ExoMars Trace Gas Orbiter mission

    NASA Astrophysics Data System (ADS)

    Dawson, D. G.; Patel, M. R.; Lewis, S. R.; Mason, J. P.; Irwin, P. G. J.

    2013-09-01

    The NOMAD (Nadir and Occultation for MArs Discovery) instrument is a 3-channel (2 IR, 1 UV/Vis) spectrometer due to fly on the 2016 ExoMars Trace Gas Orbiter mission. A radiative transfer model for Mars has been developed providing synthetic spectra to simulate observations of the UVIS channel in both solar occultation and nadir viewing geometries. This will allow for the characterization and mitigation of the influence of dust on retrievals of ozone abundance.

  8. Titanium cobalt nitride supported platinum catalyst with high activity and stability for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Xiao, Yonghao; Zhan, Guohe; Fu, Zhenggao; Pan, Zhanchang; Xiao, Chumin; Wu, Shoukun; Chen, Chun; Hu, Guanghui; Wei, Zhigang

    2015-06-01

    We describe a facile route to the development of novel robust non-carbon titanium cobalt nitride (Ti0.9Co0.1N) used as a support for Pt, and the catalyst exhibits high activity and stability for the oxygen reduction reaction (ORR). XRD and TEM results show that the synthesized Ti0.9Co0.1N is formed as a single-phase solid solution with high purity. The XPS measurements verified the strong metal/support interaction between Pt nanoparticles (NPs) and the Ti0.9Co0.1N support. Most importantly, Ti0.9Co0.1N supported Pt catalyst (Pt/Ti0.9Co0.1N) exhibits a much higher mass activity and durability than that of the commercial JM Pt/C electrocatalyst for ORR. The accelerated durability test (ADT) reveals that the novel Ti0.9Co0.1N support can dramatically enhance the durability of the catalyst and maintain the electrochemical surface area (ECSA) of Pt. Pt/Ti0.9Co0.1N shows great improvement in ECSA preservation, with only 35% of the initial ECSA drop even after 10 000 ADT cycles. The experimental data indicate that the electronic structure of Pt can be modified by Co doping, and there exists a strong interaction between Pt and the Ti0.9Co0.1N support, both of them are playing an important role in improving the activity and durability of the Pt/Ti0.9Co0.1N catalyst.

  9. Reduction of training costs using active classification in fused hyperspectral and LiDAR data

    NASA Astrophysics Data System (ADS)

    Wuttke, Sebastian; Schilling, Hendrik; Middelmann, Wolfgang

    2012-11-01

    This paper presents a novel approach for the reduction of training costs in classification with co-registered hyperspectral (HS) and Light Detection and Ranging (LiDAR) data using an active classification framework. Fully automatic classification can be achieved by unsupervised learning, which is not suited for adjustment to specific classes. On the other hand, supervised classification with predefined classes needs a lot of training examples, which need to be labeled with the ground truth, usually at a significant cost. The concept of active classification alleviates these problems by the use of a selection strategy: only selected samples are ground truth labeled and used as training data. One common selection strategy is to incorporate in a first step the current state of the classification algorithm and choose only the examples for which the expected information gain is maximized. In the second step a conventional classification algorithm is trained using this data. By alternating between these two steps the algorithm reaches high classification accuracy results with less training samples and therefore lower training costs. The approach presented in this paper involves the user in the active selection strategy and the k-NN algorithm is chosen for classification. The results further benefit from fusing the heterogeneous information of HS and LiDAR data within the classification algorithm. For this purpose, several HS features, such as vegetation indices, and LiDAR features, such as relative height and roughness, are extracted. This increases the separability between different classes and reduces the dimensionality of the HS data. The practicability and performance of this framework is shown for the detection and separation of different kinds of vegetation, e.g. trees and grass in an urban area of Berlin. The HS data was obtained by the SPECIM AISA Eagle 2 sensor, LiDAR data by Riegl LMS Q560.

  10. Trichloramine Removal with Activated Carbon Is Governed by Two Reductive Reactions: A Theoretical Approach with Diffusion-Reaction Models.

    PubMed

    Matsushita, Taku; Matsui, Yoshihiko; Ikekame, Shohei; Sakuma, Miki; Shirasaki, Nobutaka

    2017-04-06

    Mechanisms underlying trichloramine removal with activated carbon treatment were proven by batch experiments and theoretical analysis with diffusion-reaction models. The observed values of trichloramine and free chlorine were explained only by the model in which (1) both trichloramine and free chlorine were involved as reactants, (2) the removals of reactants were affected both by the intraparticle diffusion and by the reaction with activated carbon, and (3) trichloramine decomposition was governed by two distinct reductive reactions. One reductive reaction was expressed as a first-order reaction: the reductive reaction of trichloramine with the basal plane of PAC, which consists of graphene sheets. The other reaction was expressed as a second-order reaction: the reductive reaction of trichloramine with active functional groups located on the edge of the basal plane. Free chlorine competitively reacted with both the basal plane and the active functional groups. The fact that the model prediction succeeded even in experiments with different activated carbon doses, with different initial trichloramine concentrations, and with different sizes of activated carbon particles clearly proved that the mechanisms described in the model were reasonable for explaining trichloramine removal with activated carbon treatment.

  11. The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains.

    PubMed

    Pan, Xiaohong; Chen, Zhi; Chen, Fanbing; Cheng, Yangjian; Lin, Zhang; Guan, Xiong

    2015-10-30

    The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains was investigated in the present work. Our data showed that the bacteria isolated from uranium mine possessed highly accumulation ability to U(VI), and the maximum accumulation capacity was around 400 mg U/g biomass (dry weight). X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) analyzes indicated that the U(VI) was adsorbed on the bacterial surface firstly through coordinating with phosphate, CH2 and amide groups, and then needle-like amorphous uranium compounds were formed. With the extension of time, the extracellular crystalline substances were disappeared, but some particles were appeared in the intracellular region, and these particles were characterized as tetragonal-uramphite. Moreover, the disrupted experiment indicated that the cell-free extracts had better uranium-immobilization ability than cell debris. Our findings provided the understanding of the uranium transformation process from amorphous uranium to crystalline uramphite, which would be useful in the regulation of uranium immobilization process.

  12. Complexation of U(VI) with 1-Hydroxyethane-1,1-diphosphonicAcid (HEDPA) in Acidic to Basic Solutions

    SciTech Connect

    Reed, W A; Rao, L; Zanonato, P; Garnov, A; Powell, B A; Nash, K L

    2007-01-24

    Complexation of U(VI) with 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) in acidic to basic solutions has been studied with multiple techniques. A number of 1:1 (UO{sub 2}H{sub 3}L), 1:2 (UO{sub 2}H{sub j}L{sub 2} where j = 4, 3, 2, 1, 0 and -1) and 2:2 ((UO{sub 2}){sub 2}H{sub j}L{sub 2} where j = 1, 0 and -1) complexes form, but the 1:2 complexes are the major species in a wide pH range. Thermodynamic parameters (formation constants, enthalpy and entropy of complexation) were determined by potentiometry and calorimetry. Data indicate that the complexation of U(VI) with HEDPA is exothermic, favored by the enthalpy of complexation. This is in contrast to the complexation of U(VI) with dicarboxylic acids in which the enthalpy term usually is unfavorable. Results from electrospray ionization mass spectrometry (ESI-MS) and {sup 31}P NMR have confirmed the presence of 1:1, 1:2 and 2:2 U(VI)-HEDPA complexes.

  13. Protonation of the binuclear active site in cytochrome c oxidase decreases the reduction potential of CuB.

    PubMed

    Blomberg, Margareta R A; Siegbahn, Per E M

    2015-10-01

    One of the remaining mysteries regarding the respiratory enzyme cytochrome c oxidase is how proton pumping can occur in all reduction steps in spite of the low reduction potentials observed in equilibrium titration experiments for two of the active site cofactors, CuB(II) and Fea3(III). It has been speculated that, at least the copper cofactor can acquire two different states, one metastable activated state occurring during enzyme turnover, and one relaxed state with lower energy, reached only when the supply of electrons stops. The activated state should have a transiently increased CuB(II) reduction potential, allowing proton pumping. The relaxed state should have a lower reduction potential, as measured in the titration experiments. However, the structures of these two states are not known. Quantum mechanical calculations show that the proton coupled reduction potential for CuB is inherently high in the active site as it appears after reac