Daily Variation of Heavy Carbon Dioxide in Mars Atmosphere

NASA Astrophysics Data System (ADS)

Livengood, T. A.; Kostiuk, Th; Kolasinski, J.; Hewagama, T.; Henning, W. G.; Sornig, M.; Stangier, T.; Krause, P.; Sonnabend, G.

2015-10-01

The atmosphere of Mars is significantly enriched in C and O heavy isotopes, detected by ground based high-resolution infrared spectroscopy as well as in situ measurements by the Phoenix lander and Mars Science Laboratory Curiosity rover. Heavy isotope enrichment is consistent with the preferential loss of light isotopes in eroding Mars' primordial atmosphere. Infrared spectroscopy of Mars collected in May 2012 as well as in March and May of 2014 from the NASA IRTF resolves rovibrational transitions of normal-isotope carbon dioxide as well as singly-substituted minor isotopologues, enabling remote measurements of carbon and oxygen isotope ratios as a function of latitude and local time of day. Earlier measurements obtained in October 2007 demonstrated that the relative abundance of O-18 increased linearly with increasing surface temperature over a relatively warm early-afternoon temperature range, but did not extend far enough to inspect the effect of late-afternoon cooling. These results imply that isotopically enriched gas is sequestered overnight when surface temperature is minimum and desorbs through the course of the day as temperature increases. Current spectroscopic constants indicate that the peak isotopic enrichment could be significantly greater than what has been measured in situ, apparently due to sampling the atmosphere at different time of day and surface temperature. The observing runs in 2012 and 2014 measured O-18 enrichment at several local times in both morning and afternoon sectors as well as at the subsolar, equatorial, and anti-subsolar latitudes. The two runs in 2014 have additionally observed O-17 and C-13 transitions in the morning sector, from local dawn to noon. These observations include a limited sampling of measurements over Gale Crater, which can be compared with contemporary in situ measurements by the Curiosity rover to investigate the degree of agreement between in situ and remote methods and potentially to calibrate the spectroscopic constants required to accurately evaluate isotope ratios all over Mars.

Target materials for exotic ISOL beams

NASA Astrophysics Data System (ADS)

Gottberg, A.

2016-06-01

The demand for intensity, purity, reliability and availability of short-lived isotopes far from stability is steadily high, and considerably exceeding the supply. In many cases the ISOL (Isotope Separation On-Line) method can provide beams of high intensity and purity. Limitations in terms of accessible chemical species and minimum half-life are driven mainly by chemical reactions and physical processes inside of the thick target. A wide range of materials are in use, ranging from thin metallic foils and liquids to refractory ceramics, while poly-phasic mixed uranium carbides have become the reference target material for most ISOL facilities world-wide. Target material research and development is often complex and especially important post-irradiation analyses are hindered by the high intrinsic radiotoxicity of these materials. However, recent achievements have proven that these investigations are possible if the effort of different facilities is combined, leading to the development of new material matrices that can supply new beams of unprecedented intensity and beam current stability.

Seasonality of bottom water temperature in the northern North Sea reconstructed from the oxygen isotope composition of the bivalve Arctica islandica

NASA Astrophysics Data System (ADS)

Trofimova, Tamara; Andersson, Carin; Bonitz, Fabian

2017-04-01

The seasonality of temperature changes is an important characteristic of climate. However, observational data for the ocean are only available for the last 150 year from a limited number of locations. Prior to 18th century information is only available from proxy reconstructions. The vast majority of such reconstructions depend on land-based archives, primarily from dendrochronology. Established marine proxy records for the ocean, especially at high latitudes, are both sparsely distributed and poorly resolved in time. Therefore, the identification and development of proxies for studying key ocean processes at sub-annual resolution that can extend the marine instrumental record is a clear priority in marine climate science. In this study, we have developed a record of early Holocene seasonal variability of bottom water temperature from the Viking Bank in the northern most North Sea. This area is of a particular interest since the hydrography is controlled by the inflow of Atlantic water. The reconstruction is based on the oxygen isotope composition of the growth increments in two sub-fossil shells of Arctica islandica (Bivalvia), dated to 9600-9335 cal. yr BP. By combining radiocarbon dating and sclerochronological techniques a floating chronology spanning over 200 years was constructed. Using the chronology as an age model, oxygen isotope measurements from 2 shells were combined into a 22-years long record. The results from this oxygen isotope record are compared with stable oxygen isotope profiles from modern shells to estimate changes in the mean state and seasonality between present and early Holocene. Shell-derived oxygen isotope values together with ice-volume corrected oxygen isotope values for the seawater were used to calculate bottom-water temperatures on a sub-annual time-scale. Preliminary results of the reconstructed early Holocene bottom water temperature indicate higher seasonality and lower minimum temperature compared to the present.

Daily Variation of Isotope Ratios in Mars Atmospheric Carbon Dioxide

NASA Astrophysics Data System (ADS)

Livengood, Timothy A.; Kostiuk, Theodor; Kolasinski, John R.; Hewagama, Tilak; Henning, Wade G.; Sornig, Manuela; Stangier, Tobias; Krause, Pia; Sonnabend, Guido; Mahaffy, Paul R.

2014-11-01

The atmosphere of Mars has been shown by ground based high-resolution infrared spectroscopy and in situ measurements with the Phoenix lander and Mars Science Laboratory Curiosity rover to be enriched in C and O heavy isotopes, consistent with preferential loss of light isotopes in eroding Mars’ primordial atmosphere. The relative abundance of heavy isotopes, combined with contemporary measurements of loss rates to be obtained with MAVEN, will enable estimating the primordial atmospheric inventory on Mars. IR spectroscopy of Mars collected in May 2012 as well as in March and May of 2014 from the NASA IRTF has resolved transitions of all three singly-substituted minor isotopologues of carbon dioxide in addition to the normal isotope, enabling remote measurements of all the carbon and oxygen isotope ratios as a function of latitude, longitude, and time of day. Earlier measurements obtained in October 2007 demonstrated that the relative abundance of O-18 increased linearly with increasing surface temperature over a relatively warm early-afternoon temperature range, but did not extend far enough to inspect the effect of late-afternoon cooling. These results imply that isotopically enriched gas is sequestered overnight when surface temperature is minimum and desorbs through the course of the day as temperature increases. Current spectroscopic constants indicate that the peak isotopic enrichment could be significantly greater than what has been measured in situ, apparently due to sampling the atmosphere at different time of day and surface temperature. The observing runs in 2012 and 2014 measured O-18 enrichment at several local times in both morning and afternoon sectors as well as at the subsolar, equatorial, and anti-subsolar latitudes. The two runs in 2014 have additionally observed O-17 and C-13 transitions in the morning sector, from local dawn to noon. These observations include a limited sampling of measurements over Gale Crater, which can be compared with contemporary in situ measurements by the Curiosity rover to investigate the degree of agreement between in situ and remote methods and potentially to calibrate the spectroscopic constants required to accurately evaluate isotope ratios all over Mars.

Antimatter and Dark Matter Search in Space: BESS-Polar Results

NASA Technical Reports Server (NTRS)

Mitchell, John W.; Yamamoto, Akira

2009-01-01

The apex of the Balloon-borne Experiment with a Superconducting Spectrometer program was reached with the Antarctic flight of BESS-Polar II, during the 2007-2008 Austral Summer, that obtained 24.5 days of data on over 4.7 billion cosmic-ray events. The US-Japan BESS Collaboration uses elementary particle measurements to study the early Universe and provides fundamental data on the spectra of light cosmic-ray elements and isotopes. BESS measures the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic sources, such as dark-matter candidates, and searches for heavier anti-nuclei that might reach Earth from antimatter domains formed during symmetry breaking processes in the early Universe. Since 1993, BESS has carried out eleven high-latitude balloon flights, two of long duration, that together have defined the study of antiprotons below about 4 GeV, provided standard references for light element and isotope spectra, and set the most sensitive limits on the existence of anti-deuterons and anti-helium, The BESS-Polar II flight took place at Solar Minimum, when the sensitivity of the low-energy antiproton measurements to a primary source is greatest. The rich BESS-Polar II dataset more than doubles the combined data from all earlier BESS flights and has 10-20 times the statistics of BESS data from the previous Solar Minimum. Here, we summarize the scientific results of BESS program, focusing on the results obtained using data from the long-duration flights of BESS-Polar I (2004) and BESS-Polar II.

The BESS Search for Cosmic-Ray Antiproton Origins and for Cosmological Antimatter

NASA Technical Reports Server (NTRS)

Mitchell, John; Yamamoto, Akira

2009-01-01

The apex of the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) program was reached with the Antarctic flight of BESS-Polar II, during the 2007-2008 Austral Summer, that obtained 24.5 days of data on over 4.7 billion cosmic-ray events. The US-Japan BESS Collaboration uses elementary particle measurements to study the early Universe and provides fundamental data on the spectra of light cosmic-ray elements and isotopes. BESS measures the energy spectra of cosmic-ray antiprotons to investigate signatures of possible exotic sources, such as dark-matter candidates, and searches for heavier antinuclei that might reach Earth from antimatter domains formed during symmetry breaking processes in the early Universe. Since 1993, BESS has carried out eleven high-latitude balloon flights, two of long duration, that together have defined the study of antiprotons below about 4 GeV, provided standard references for light element and isotope spectra, and set the most sensitive limits on the existence of antideuterons and antihelium. The BESS-Polar II flight took place at Solar Minimum, when the sensitivity of the low-energy antiproton measurements to a primary source is greatest. The rich BESS-Polar II dataset more than doubles the combined data from all earlier BESS flights and has 10-20 times the statistics of BESS data from the previous Solar Minimum. Here, we summarize the scientific results of BESS program, focusing on the results obtained using data from the long-duration flights of BESS-Polar I (2004) and BESS-Polar II.

Charge radii of neutron-deficient Ca isotopes

NASA Astrophysics Data System (ADS)

Miller, A. J.; Minamisono, K.; Klose, A.; Everett, N.; Kalman, C.; Powel, R. C.; Watkins, J.; Garand, D.; Sumithrarachchi, C.; Krämer, J.; Maa, B.; Nörtershäuser, W.; Rossi, D. M.; Kujawa, C.; Pineda, S.; Lantis, J.; Liu, Y.; Mantica, P. F.; Pearson, M. R.

2017-09-01

Nucleon shell closures are generally associated with a local minimum in mean-square charge radii, 〈r2 〉 , along an isotopic chain. The 〈r2 〉 of 18Ar and 19K isotopes, however, do not show this signature at the N = 20 neutron shell closure. To gain a microscopic understanding of this abnormal behavior, measurements of 〈r2 〉 of neutron-deficient Ca isotopes below N = 20 have been proposed at the BEam COoling and LAser spectroscopy (BECOLA) facility at NSCL/MSU. Preliminary results will be presented and the deduced charge radii will be compared to theoretical calculations and the trends in the nearby isotopic chains. Work supported in part by NSF Grant PHY-15-65546, U.S. DOE Grant DE-NA0002924 and by the Deutsche Forschungsgemeinschaft through Grant SFB 1245.

Implications for chloro- and pheopigment synthesis and preservation from combined compound-specific δ13C, δ15N, and Δ14C analysis

NASA Astrophysics Data System (ADS)

Kusch, S.; Kashiyama, Y.; Ogawa, N. O.; Altabet, M.; Butzin, M.; Friedrich, J.; Ohkouchi, N.; Mollenhauer, G.

2010-12-01

Chloropigments and their derivative pheopigments preserved in sediments can directly be linked to photosynthesis. Their carbon and nitrogen stable isotopic compositions have been shown to be a good recorder of recent and past surface ocean environmental conditions tracing the carbon and nitrogen sources and dominant assimilation processes of the phytoplanktonic community. In this study we report results from combined compound-specific radiocarbon and stable carbon and nitrogen isotope analysis to examine the time-scales of synthesis and fate of chlorophyll-a and its degradation products pheophytin-a, pyropheophytin-a, and 132,173-cyclopheophorbide-a-enol until burial in Black Sea core-top sediments. The pigments are mainly of marine phytoplanktonic origin as implied by their stable isotopic compositions. Pigment δ15N values indicate nitrate as the major uptake substrate but 15N-depletion towards the open marine setting indicates either contribution from N2-fixation or direct uptake of ammonium from deeper waters. Radiocarbon concentrations translate into minimum and maximum pigment ages of approximately 40 to 1200 years. This implies that protective mechanisms against decomposition such as association with minerals, storage in deltaic anoxic environments, or eutrophication-induced hypoxia and light limitation are much more efficient than previously thought. Moreover, seasonal variations of nutrient source, growth period, and habitat and their associated isotopic variability are likely at least as strong as long-term trends. Combined triple isotope analysis of sedimentary chlorophyll and its primary derivatives is a powerful tool to delineate biogeochemical and diagenetic processes in the surface water and sediments, and to assess their precise time-scales.

Multi-element compound specific stable isotope analysis of volatile organic compounds at trace levels in groundwater samples

NASA Astrophysics Data System (ADS)

Herrero-Martín, Sara; Nijenhuis, Ivonne; Schmidt, Marie; Wolfram, Diana; Richnow, Hans. H.; Gehre, Matthias

2013-04-01

Groundwater pollution remains one of the major environmental and health concerns. A thorough understanding of sources, sinks and transformation processes of groundwater contaminants is needed to improve risk management evaluation, and to design efficient remediation and water treatment strategies. Isotopic tools provide unique information for an in-depth understanding of the fate of organic chemicals in the environment. During the last decades compound specific isotope analysis (CSIA) of complex mixtures, using gas chromatography-isotope ratio mass spectrometry (GC-IRMS), has gained popularity for the characterization and risk assessment of hazardous waste sites and for isotope forensics of organic contaminants. Multi-element isotope fingerprinting of organic substances provides a more robust framework for interpretation than the isotope analysis of only one element. One major challenge for application of CSIA is the analysis of trace levels of organic compounds in environmental matrices. It is necessary to inject 1 nmol carbon or 8 nmol hydrogen on column, to obtain an accurate and precise measurement of the isotope ratios, which is between two and three orders of magnitude larger than the amount of compound needed for conventional analysis of compound concentrations. Therefore, efficient extraction and pre-concentration techniques have to be integrated with GC-IRMS. Further research is urgently needed in this field, to evaluate the potential of novel and environmental-friendly sample pre-treatment techniques for CSIA to lower the detection limits and extending environmental applications. In this study, the novel coupling of a headspace autosampler (HS) with a programmed temperature vaporizer (PTV), allowing large volume injection of headspace samples, is proposed to improve the sensitivity of CSIA. This automatic, fast and solvent free strategy provides a significant increase on the sensitivity of GC-based methods maintaining the simple headspace instrumentation. The method was developed for the multi-element isotope analysis (carbon and hydrogen) of priority volatile organic groundwater pollutants (methyl tert-butyl ether (MTBE), benzene, toluene, ethylbenzene and o-xylene (BTEX)), and for carbon isotope analysis of chlorinated benzenes and ethenes. The extraction and injection conditions were optimized in terms of maximum sensitivity and minimum isotope effects. During the injection of the headspace sample, the liner is maintained at a low temperature, such that the compounds are retained in a hydrophobic insert packing while the water vapor is eliminated through the split line. With the optimized conditions, it was possible to inject up to 5mL headspace sample with no significant carbon or hydrogen isotopic effects except for the most hydrophobic substance (MTBE), which was subject to a small and reproducible isotope fractionation for hydrogen. The increment on method sensitivity was at least 20 fold in comparison with conventional static headspace analysis. The environmental applicability of the HS-PTV-GC-IRMS method was evaluated by the analysis of groundwater samples from different contaminated field sites, containing BTEX and chlorinated volatile organic contaminants in the low µg/L range. The results obtained demonstrate that this pre-concentration technique is highly promising to enhance the limits of detection of current CSIA methods and broaden its possibilities.

Diffusive Fractionation of Lithium Isotopes in Olivine Grain Boundaries

NASA Astrophysics Data System (ADS)

Homolova, V.; Watson, E. B.

2012-12-01

Diffusive fractionation of isotopes has been documented in silicate melts, aqueous fluids, and single crystals. In polycrystalline rocks, the meeting place of two grains, or grain boundaries, may also be a site of diffusive fractionation of isotopes. We have undertaken an experimental and modeling approach to investigate diffusive fractionation of lithium (Li) isotopes by grain boundary diffusion. The experimental procedure consists of packing a Ni metal capsule with predominantly ground San Carlos olivine and subjecting the capsule to 1100C and 1GPa for two days in a piston cylinder apparatus to create a nominally dry, 'dunite rock'. After this synthesis step, the capsule is sectioned and polished. One of the polished faces of the 'dunite rock' is then juxtaposed to a source material of spodumene and this diffusion couple is subject to the same experimental conditions as the synthesis step. Li abundances and isotopic profiles (ratios of count rates) were analyzed using LA-ICP-MS. Li concentrations linearly decrease away from the source from 550ppm to the average concentration of the starting olivine (2.5ppm). As a function of distance from the source, the 7Li/6Li ratio decreases to a minimum before increasing to the background ratio of the 'dunite rock'. The 7Li/6Li ratio minimum coincides with the lowest Li concentrations above average 'dunite rock' abundances. The initial decrease in the 7Li/6Li ratio is similar to that seen in other studies of diffusive fractionation of isotopes and is thought to be caused by the higher diffusivity (D) of the lighter isotope relative to the heavier isotope. The relationship between D and mass (m) is given by (D1/D2) =(m2/m1)^β, where β is an empirical fractionation factor; 1 and 2 denote the lighter and heavier isotope, respectively. A fit to the Li isotopic data reveals an effective DLi of ~1.2x10^-12 m/s^2 and a β of 0.1. Numerical modelling was utilized to elucidate the relationship between diffusive fractionation produced in the grain boundaries versus the lattices of the individual grains of the 'dunite rock'. The model assumes a linear grain boundary juxtaposed to the long side of a rectangular crystal lattice. During a simulation, the diffusant may directly enter the lattice or the grain boundary. Once in the grain boundary, the diffusant may then continue to diffuse away from the source until the end of the simulation or, alternatively, it may be incorporated into the lattice at some point during its travels down the grain boundary. The model system is similar to that considered by Whipple-LeClaire (1963) and our model results agree well with their analytical solution. Preliminary modeling results show that the distinctive minimum in the isotopic ratio is only produced when diffusive fractionation occurs in the grain boundary and not when the fractionation occurs only in the lattice. This suggests that the isotopic profile observed in the experiments may be a product of diffusive fractionation in grain boundaries. Implications of these results extend to the longevity of Li isotopic heterogeneities in the mantle, and suggest that the isotopes of other elements, which have a large relative mass difference, may also be diffusively fractionated by grain boundary diffusion.

Atmospheric studies of C2 white dwarfs

NASA Astrophysics Data System (ADS)

Swanson, Steven Roger

Model atmosphere and line formation calculations for the delta nu = + 1 Swan bands of the C2 molecule are presented for seven white dwarfs and are compared to high resolution optical spectra. Limits on the C-12 to C-13 ratio are computed for highly pressure broadened lines and are used to analyze the observed spectra for any sign of absorption by the (C-12)(C-13) molecule. The metal abundances in cool white dwarf atmospheres and the usefulness of the determination of the C-12 to C-13 ratio are discussed. The line center shift and the pressure broadening are used to determine a value for the van der Waals interaction constant, C6. This is done using a detailed line modelling program which explicitly includes approximately 2000 rotational transition lines within the vibrational bands, in conjunction with atmospheric models calculated by the LUCIFER atmosphere modelling program. The isotopic shift of the vibrational and rotational lines is also included in the model to compare the detectability of various C-12 to C-13 ratios. The line models fit the observed spectra with varying degrees of accuracy. One star, WD0548-001, shows an unusually small pressure shift and broadening for the high pressures that the atmospheric model predicts. The results show that only in the hottest stars with the least pressure broadened lines in this study can the isotopic effect be seen. With the data available, the best limit on the C-12 to C-13 ratio is a minimum of 40 for WD0856 + 331. The models show that even for very high signal to noise data, the isotopic shift in the Swan bands in very cool white dwarfs would be difficult to separate from the pressure broadening effects. It is shown that the isotopic ratio is high enough to rule out the possibility that the carbon is a relic from previous CNO burning.

Determination of tin isotope ratios in cassiterite by femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry

NASA Astrophysics Data System (ADS)

Schulze, Marie; Ziegerick, Marco; Horn, Ingo; Weyer, Stefan; Vogt, Carla

2017-04-01

In comparison to isotope analysis of dissolved samples femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS) enables precise isotope ratio analyses consuming much less sample material and with a minimum effort in sample preparation. This is especially important for the investigation of valuable historical objects for which visual traces of sampling are unwanted. The present study provides a basis for tin isotope ratio measurements using LA-MC-ICP-MS technique. For this, in house isotope standards had to be defined. Investigations on interferences and matrix effects illustrate that beside Sb only high Te contents (with values above those to be expected in cassiterite) result in a significant shift of the measured tin isotope ratios. This effect can partly be corrected for using natural isotope abundances. However, a natural isotope fractionation of Te cannot be excluded. Tin beads reduced from cassiterite were analysed by laser ablation and after dissolution. It was shown that tin isotope ratios can be determined accurately by using fs-LA-MC-ICP-MS. Furthermore the homogeneity of tin isotope ratios in cassiterite was proven.

Selenium isotope ratios as indicators of selenium sources and oxyanion reduction

USGS Publications Warehouse

Johnson, T.M.; Herbel, M.J.; Bullen, T.D.; Zawislanski, P.T.

1999-01-01

Selenium stable isotope ratio measurements should serve as indicators of sources and biogeochemical transformations of Se. We report measurements of Se isotope fractionation during selenate reduction, selenite sorption, oxidation of reduced Se in soils, and Se volatilization by algae and soil samples. These results, combined with previous work with Se isotopes, indicate that reduction of soluble oxyanions is the dominant cause of Se isotope fractionation. Accordingly, Se isotope ratios should be useful as indicators of oxyanion reduction, which can transform mobile species to forms that are less mobile and less bioavailable. Additional investigations of Se isotope fractionation are needed to confirm this preliminary assessment. We have developed a new method for measurement of natural Se isotope ratio variation which requires less than 500 ng Se per analysis and yields ??0.2??? precision on 80Se/76Se. A double isotope spike technique corrects for isotopic fractionation during sample preparation and mass spectrometry. The small minimum sample size is important, as Se concentrations are often below 1 ppm in solids and 1 ??g/L in fluids. The Se purification process is rapid and compatible with various sample matrices, including acidic rock or sediment digests.

Selenium isotope ratios as indicators of selenium sources and oxyanion reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, T.M.; Herbel, M.J.; Bullen, T.D.

1999-09-01

Selenium stable isotope ratio measurements should serve as indicators of sources and biogeochemical transformations of Se. The authors report measurements of Se isotope fractionation during selenate reduction, selenite sorption, oxidation of reduced Se in soils, and Se volatilization by algae and soil samples. These results, combined with previous work with Se isotopes, indicate that reduction of soluble oxyanions is the dominant cause of Se isotope fractionation. Accordingly, Se isotope ratios should be useful as indicators of oxyanion reduction, which can transform mobile species to forms that are less mobile and less bioavailable. Additional investigations of Se isotope fractionation are neededmore » to confirm this preliminary assessment. The authors have developed a new method for measurement of natural Se isotope ratio variation which requires less than 500 ng Se per analysis and yields {+-}0.2% precision on {sup 80}Se/{sup 76}Se. A double isotope spike technique corrects for isotopic fractionation during sample preparation and mass spectrometry. The small minimum sample size is important, as Se concentrations are often below 1 ppm in solids and 1 {micro}g/L in fluids. The Se purification process is rapid and compatible with various sample matrices, including acidic rock or sediment digests.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Douglas, Matthew; Bernacki, Bruce E.; Erchinger, Jennifer L.

Liquid scintillation counting (LSC) is a versatile and commonplace method for radiometric measurement of charged particle emitting radionuclides. The LSC method provides utility in a range of environmental science applications including hydrological studies of water transport, anthropogenic releases of radionuclides into the environment, and vertical mixing rates within oceans. Instrumental measurement background is one limiting factor of radiometric measurement sensitivity. As part of the development of a custom low background LSC system located in a shallow underground laboratory at Pacific Northwest National Laboratory, a number of measurement applications of LSC have been considered and are summarized here. The focus ismore » on determining which aspects of such measurements would gain the greatest benefit from the reduction of LSC backgrounds by a factor of 10-100 relative to values reported in the literature. Examples of benefits include lowering the minimum detectable activity, reducing the sample size required, and shortening the elapsed timeline of the processing and analysis sequence. In particular tritium, strontium, and actinium isotopes are examined as these isotopes cover a range of requirements related to the LSC measurement method (e.g., 3H: low energy; Sr: spectral deconvolution; Ac: alpha/beta discrimination).« less

Detection and structural characterization of nitrosamide H2NNO: A central intermediate in deNOx processes.

PubMed

McCarthy, Michael C; Lee, Kin Long Kelvin; Stanton, John F

2017-10-07

The structure and bonding of H 2 NNO, the simplest N-nitrosamine, and a key intermediate in deNO x processes, have been precisely characterized using a combination of rotational spectroscopy of its more abundant isotopic species and high-level quantum chemical calculations. Isotopic spectroscopy provides compelling evidence that this species is formed promptly in our discharge expansion via the NH 2 + NO reaction and is collisionally cooled prior to subsequent unimolecular rearrangement. H 2 NNO is found to possess an essentially planar geometry, an NNO angle of 113.67(5)°, and a N-N bond length of 1.342(3) Å; in combination with the derived nitrogen quadrupole coupling constants, its bonding is best described as an admixture of uncharged dipolar (H 2 N-N=O, single bond) and zwitterion (H 2 N + =N-O - , double bond) structures. At the CCSD(T) level, and extrapolating to the complete basis set limit, the planar geometry appears to represent the minimum of the potential surface, although the torsional potential of this molecule is extremely flat.

Detection and structural characterization of nitrosamide H2NNO: A central intermediate in deNOx processes

NASA Astrophysics Data System (ADS)

McCarthy, Michael C.; Lee, Kin Long Kelvin; Stanton, John F.

2017-10-01

The structure and bonding of H2NNO, the simplest N-nitrosamine, and a key intermediate in deNOx processes, have been precisely characterized using a combination of rotational spectroscopy of its more abundant isotopic species and high-level quantum chemical calculations. Isotopic spectroscopy provides compelling evidence that this species is formed promptly in our discharge expansion via the NH2 + NO reaction and is collisionally cooled prior to subsequent unimolecular rearrangement. H2NNO is found to possess an essentially planar geometry, an NNO angle of 113.67(5)°, and a N-N bond length of 1.342(3) Å; in combination with the derived nitrogen quadrupole coupling constants, its bonding is best described as an admixture of uncharged dipolar (H2N-N=O, single bond) and zwitterion (H2N+=N-O-, double bond) structures. At the CCSD(T) level, and extrapolating to the complete basis set limit, the planar geometry appears to represent the minimum of the potential surface, although the torsional potential of this molecule is extremely flat.

Repeated occurrences of methanogenic zones, diagenetic dolomite formation and linked silicate alteration in southern Bering Sea sediments (Bowers Ridge, IODP Exp. 323 Site U1341)

NASA Astrophysics Data System (ADS)

Wehrmann, L. M.; Ockert, C.; Mix, A. C.; Gussone, N.; Teichert, B. M. A.; Meister, P.

2016-03-01

Diagenetic precipitates, such as dolomite, and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments. A 600 m thick sedimentary section, recently drilled at Integrated Ocean Drilling Program (IODP) Site U1341 on Bowers Ridge (southern Bering Sea), provides insight into such a 4.3 Ma old paleo-diagenetic archive. Hard-lithified calcite-dolomite layers, and laminae of disseminated carbonate, were recovered in diatom-rich sediments over a depth range of 400 m. Carbon isotope values of the diagenetic carbonates between -16.6 and -14.4‰ (VPDB) and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon (DIC) during elevated rates of organic carbon mineralization, primarily via sulfate reduction, at shallow sediment depth below the paleo-seafloor. Diagenetic carbonates at 280-440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane (AOM) at sulfate-methane transition zones (SMTZ). These microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2.58-2.51 Ma. A minimum in sulfate concentrations in modern porewaters and low sedimentary Ba/Al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone. The minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations, less radiogenic strontium and isotopically light calcium in the porewater. It is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater. The isotopic composition of porewater calcium was also influenced by ammonium-calcium exchange on clay minerals and carbonate recrystallization. Our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites (>2000 m water depth) over prolonged timescales. It shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization.

Trophic ecology and vertical patterns of carbon and nitrogen stable isotopes in zooplankton from oxygen minimum zone regions

NASA Astrophysics Data System (ADS)

Williams, Rebecca L.; Wakeham, Stuart; McKinney, Rick; Wishner, Karen F.

2014-08-01

The unique physical and biogeochemical characteristics of oxygen minimum zones (OMZs) influence plankton ecology, including zooplankton trophic webs. Using carbon and nitrogen stable isotopes, this study examined zooplankton trophic webs in the Eastern Tropical North Pacific (ETNP) OMZ. δ13C values were used to indicate zooplankton food sources, and δ15N values were used to indicate zooplankton trophic position and nitrogen cycle pathways. Vertically stratified MOCNESS net tows collected zooplankton from 0 to 1000 m at two stations along a north-south transect in the ETNP during 2007 and 2008, the Tehuantepec Bowl and the Costa Rica Dome. Zooplankton samples were separated into four size fractions for stable isotope analyses. Particulate organic matter (POM), assumed to represent a primary food source for zooplankton, was collected with McLane large volume in situ pumps. The isotopic composition and trophic ecology of the ETNP zooplankton community had distinct spatial and vertical patterns influenced by OMZ structure. The most pronounced vertical isotope gradients occurred near the upper and lower OMZ oxyclines. Material with lower δ13C values was apparently produced in the upper oxycline, possibly by chemoautotrophic microbes, and was subsequently consumed by zooplankton. Between-station differences in δ15N values suggested that different nitrogen cycle processes were dominant at the two locations, which influenced the isotopic characteristics of the zooplankton community. A strong depth gradient in zooplankton δ15N values in the lower oxycline suggested an increase in trophic cycling just below the core of the OMZ. Shallow POM (0-110 m) was likely the most important food source for mixed layer, upper oxycline, and OMZ core zooplankton, while deep POM was an important food source for most lower oxycline zooplankton (except for samples dominated by the seasonally migrating copepod Eucalanus inermis). There was no consistent isotopic progression among the four zooplankton size classes for these bulk mixed assemblage samples, implying overlapping trophic webs within the total size range considered.

Quantitative determination of four nitrofuran metabolites in meat by isotope dilution liquid chromatography-electrospray ionisation-tandem mass spectrometry.

PubMed

Mottier, Pascal; Khong, Seu-Ping; Gremaud, Eric; Richoz, Janique; Delatour, Thierry; Goldmann, Till; Guy, Philippe A

2005-03-04

A confirmatory method based on isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the low-level determination of residues of four nitrofuran veterinary drugs in meat, e.g., furazolidone, furaltadone, nitrofurantoin, and nitrofurazone. The procedure entails an acid-catalysed release of protein-bound metabolites, followed by their in situ conversion into the 2-nitrobenzaldehyde (NBA) imine-type derivatives. Liquid-liquid extraction and clean-up on a polymeric solid phase extraction cartridge are then performed before LC-MS/MS analysis by positive electrospray ionisation (ESI) applying multiple reaction monitoring of three transition reactions for each compound. Reliable quantitation is obtained by using one deuterated analogue per analyte (d4-NBA derivative) as internal standard (IS). Validation of the method in chicken meat was conducted following the European Union (EU) criteria for the analysis of veterinary drug residues in foods. The decision limits (CCalpha) were 0.11-0.21 microg/kg, and the detection capabilities (CCbeta) 0.19-0.36 microg/kg, thus below the minimum required performance limit (MRPL) set at 1 microg/kg by the EU. The method is robust and suitable for routine quality control operations, and more than 200 sample injections were performed without excessive pollution of the mass spectrometer or loss of LC column performance.

High-resolution U-series dates from the Sima de los Huesos hominids yields 600 +∞-66: implications for the evolution of the early Neanderthal lineage

USGS Publications Warehouse

Bischoff, James L.; Williams, Ross W.; Rosenbauer, Robert J.; Aramburu, Arantza; Arsuaga, Juan Luis; Garcia, Nuria; Cuenca-Bescos, Gloria

2007-01-01

The Sima de los Huesos site of the Atapuerca complex near Burgos, Spain contains the skeletal remains of at least 28 individuals in a mud-breccia underlying an accumulation of the Middle Pleistocene cave bear (Ursus deningeri). We report here on new high-precision dates on the recently discovered speleothem SRA-3 overlaying human bones within the Sima de los Huesos. Earlier analyses of this speleothem by TIMS (thermal-ionization mass-spectrometry) showed the lower part to be indistinguishable from internal isotopic equilibrium at the precision of the TIMS instrumentation used, yielding minimum age of 350 kyr (kyr = 103 yr before present). Reanalysis of six samples of SRA-3 by inductively-coupled plasma-multicollector mass-spectrometry (ICP-MS) produced high-precision analytical results allowing calculation of finite dates. The new dates cluster around 600 kyr. A conservative conclusion takes the lower error limit ages as the minimum age of the speleothem, or 530 kyr. This places the SH hominids at the very beginnings of the Neandertal evolutionary lineage.

Seasonal temperature and precipitation recorded in the intra-annual oxygen isotope pattern of meteoric water and tree-ring cellulose

NASA Astrophysics Data System (ADS)

Schubert, Brian A.; Jahren, A. Hope

2015-10-01

Modern and ancient wood is a valuable terrestrial record of carbon ultimately derived from the atmosphere and oxygen inherited from local meteoric water. Many modern and fossil wood specimens display rings sufficiently thick for intra-annual sampling, and analytical techniques are rapidly improving to allow for precise carbon and oxygen isotope measurements on very small samples, yielding unprecedented resolution of seasonal isotope records. However, the interpretation of these records across diverse environments has been problematic because a unifying model for the quantitative interpretation of seasonal climate parameters from oxygen isotopes in wood is lacking. Towards such a model, we compiled a dataset of intra-ring oxygen isotope measurements on modern wood cellulose (δ18Ocell) from 33 globally distributed sites. Five of these sites represent original data produced for this study, while the data for the other 28 sites were taken from the literature. We defined the intra-annual change in oxygen isotope value of wood cellulose [Δ(δ18Ocell)] as the difference between the maximum and minimum δ18Ocell values determined within the ring. Then, using the monthly-resolved dataset of the oxygen isotope composition of meteoric water (δ18OMW) provided by the Global Network of Isotopes in Precipitation database, we quantified the empirical relationship between the intra-annual change in meteoric water [Δ(δ18OMW)] and Δ(δ18Ocell). We then used monthly-resolved datasets of temperature and precipitation to develop a global relationship between Δ(δ18OMW) and maximum/minimum monthly temperatures and winter/summer precipitation amounts. By combining these relationships we produced a single equation that explains much of the variability in the intra-ring δ18Ocell signal through only changes in seasonal temperature and precipitation amount (R2 = 0.82). We show how our recent model that quantifies seasonal precipitation from intra-ring carbon isotope profiles can be incorporated into the oxygen model above in order to separately quantify both seasonal temperature and seasonal precipitation. Determination of seasonal climate variation using high-resolution isotopes in tree-ring records makes possible a new understanding of the seasonal fluctuations that control the environmental conditions to which organisms are subject, both during recent history and in the geologic past.

Weathering During Glacial-Interglacial Cycles Based on Pb Isotopes at Orphan Knoll, NW Atlantic

NASA Astrophysics Data System (ADS)

Flynn, S. N.; Martin, E. E.

2017-12-01

Seawater Pb isotopes extracted from FeMn oxyhydroxide coatings on deep sea sediments preserve a record of regional variations in continental weathering intensity. Crocket et al. (2012) documented a distinct increase in seawater Pb isotopes across Termination I (TI) at IODP Sites U1302/03 on Orphan Knoll in the NW Atlantic which they attributed to an increase in weathering intensity associated with ice sheet retreat. Deglaciation during Termination II (TII) was more rapid than TI due to higher insolation forcing and elevated CO2 levels. This rapid warming followed Heinrich Stadial 11 (HS11) cooling and circulation changes, but was not interrupted by a Younger Dryas-type reversal in warming. In this study, Pb isotopic data from leachates of the <63 µm fraction of bulk sediment from TII at Sites U1302/03 are used to test whether changes in weathering are a feature of terminations and whether differences in the character of the termination translate to differences in the weathering response. We analyzed the clay/silt fraction to minimize preformed FeMn oxyhydroxides associated with IRD. All three Pb isotopic systems display similar patterns. Seawater 206Pb/204Pb values are 19.5 during MIS 6, reach a minimum of 18.7 during HS11, increase in < 1 ky to 20.6 in MIS 5e, and then vary between 19.9 - 20.5 across MIS 5e-d. In comparison to the TI study (Crocket et al., 2009), the TII HS is defined by a minimum in Pb isotopes that suggests suppressed chemical weathering during cooling and ice sheet advance. The increase in 206Pb/204Pb during TII indicates a rapid increase in weathering at high latitudes following glacial retreat. This result is consistent with a negative shift in ɛNd values during TII observed farther south on Bermuda Rise and interpreted as increased weathering of old continental material (Deaney et al. 2017). Future research on TII at Orphan Knoll includes analyses of detrital Pb isotopes to isolate the impact of changes in source material versus weathering intensity on seawater Pb isotopes, and analyses of seawater Nd isotopes to better understand how changes in circulation might impact delivery of silt/clay fractions to Orphan Knoll. Overall, trends in seawater Pb isotopes at TII illustrate that variations in weathering intensity are sensitive to the rate and magnitude of climate change.

Quantitative Determination of Isotope Ratios from Experimental Isotopic Distributions

PubMed Central

Kaur, Parminder; O’Connor, Peter B.

2008-01-01

Isotope variability due to natural processes provides important information for studying a variety of complex natural phenomena from the origins of a particular sample to the traces of biochemical reaction mechanisms. These measurements require high-precision determination of isotope ratios of a particular element involved. Isotope Ratio Mass Spectrometers (IRMS) are widely employed tools for such a high-precision analysis, which have some limitations. This work aims at overcoming the limitations inherent to IRMS by estimating the elemental isotopic abundance from the experimental isotopic distribution. In particular, a computational method has been derived which allows the calculation of 13C/12C ratios from the whole isotopic distributions, given certain caveats, and these calculations are applied to several cases to demonstrate their utility. The limitations of the method in terms of the required number of ions and S/N ratio are discussed. For high-precision estimates of the isotope ratios, this method requires very precise measurement of the experimental isotopic distribution abundances, free from any artifacts introduced by noise, sample heterogeneity, or other experimental sources. PMID:17263354

Cosmic-ray isotopic composition of C, N, O, Ne, Mg, Si nuclei in the energy range 50-200 MeV per nucleon measured by the Voyager spacecraft during the solar minimum period

NASA Technical Reports Server (NTRS)

Lukasiak, A.; Ferrando, P.; Mcdonald, F. B.; Webber, W. R.

1994-01-01

The isotopic composition of C, N, O, Ne, Mg, Si cosmic ray nuclei has been measured in the energy range 50-200 MeV per nucleon using data collected by the High-Energy Telescope of the cosmic-ray subsystem experiment on the Voyager 1 and 2 spacecraft. These data were collected during the period of minimum solar activity in 1986-1988 at an average distance of 27 AU with an effective solar modulation that was much less than at the Earth. The isotope analysis, based on the energy loss - total energy method, has a mass resolution of 0.2 amu for carbon and 0.4 amu at silicon. We find a (C-13)/(C-12) ratio slightly lower and a (O-18)/(O-16) ratio slightly enhanced over their solar system value. We also observe the previously reported enhancement of the (Ne-22)/(Ne-20) ratio relative to solar at the cosmic-ray source but only a weak, if any, enhancement of the (Mg-25)/(Mg-24), (Mg-26)/(Mg 24), and (Si-30)/(Si-28) ratios.

EasyDelta: A spreadsheet for kinetic modeling of the stable carbon isotope composition of natural gases

NASA Astrophysics Data System (ADS)

Zou, Yan-Rong; Wang, Lianyuan; Shuai, Yanhua; Peng, Ping'an

2005-08-01

A new kinetic model and an Excel © spreadsheet program for modeling the stable carbon isotope composition of natural gases is provided in this paper. The model and spreadsheet could be used to describe and predict the variances in stable carbon isotope of natural gases under both experimental and geological conditions with heating temperature or geological time. It is a user-friendly convenient tool for the modeling of isotope variation with time under experimental and geological conditions. The spreadsheet, based on experimental data, requires the input of the kinetic parameters of gaseous hydrocarbons generation. Some assumptions are made in this model: the conventional (non-isotope species) kinetic parameters represent the light isotope species; the initial isotopic value is the same for all parallel chemical reaction of gaseous hydrocarbons generation for simplicity, the re-exponential factor ratio, 13A/ 12A, is a constant, and both heavy and light isotope species have similar activation energy distribution. These assumptions are common in modeling of isotope ratios. The spreadsheet is used for searching the best kinetic parameters of the heavy isotope species to reach the minimum errors compared with experimental data, and then extrapolating isotopic changes to the thermal history of sedimentary basins. A short calculation example on the variation in δ13C values of methane is provided in this paper to show application to geological conditions.

Application of stable isotope (δ13C and δ18O) composition of mollusc shells in palaeolimnological studies - possibilities and limitations

NASA Astrophysics Data System (ADS)

Apolinarska, Karina; Pełechaty, Mariusz; Kossler, Annette; Pronin, Eugeniusz; Noskowiak, Daria

2017-04-01

Carbon (δ13C) and oxygen (δ18O) stable isotope analyses are among the standard methods applied in the studies of past environment, including climate. In lacustrine sediments, δ13C and δ18O values can be measured in fine carbonate fraction (carbonate mud), in charophyte encrustations, ostracod carapaces and mollusc shells. Application of the stable isotope record of each of the above-mentioned components of the lake sediment requires knowledge about possibilities and limitations of the method. The present research discusses the most important results of the studies carried out between 2011 and 2013, concentrated on the stable isotope composition of snail shells, primarily, the species commonly preserved in central European Quaternary lacustrine sediments. The stable isotope studies involved also, the zebra mussel (Dreissena polymorpha), one of the most invasive freshwater species in the world. The research involved shell isotope studies of both recent (Apolinarska, 2013; Apolinarska et al., 2016; Apolinarska and Pełechaty, in press) and fossil molluscs derived from the Holocene sediments (Apolinarska et al., 2015a, b). Shell δ13C values were species-specific and among the gastropods studied the same order of species from the most to the least 13C-depleted was observed at all sites sampled. Shell δ18O values were more uniform. The wide range of δ13C and δ18O values were observed in population and subpopulation, i.e. when live snails were sampled live from restricted area within the lake littoral zone. Carbon and oxygen stable isotope values of the mono-specific shells sampled from 1 cm thick sediment samples were highly variable. Those intra-specific differences (n=20) were as large as several permill. Such significant variability in δ13C and δ18O values indicates that stable isotope composition of single shells is unlikely to be representative of the sediment sample. In conclusion, samples of freshwater molluscs for stable isotope analyses should be monospecific and composed of at least several shells. The number of shells being dependent on the difference between the minimum and maximum values within the sediment layer. The research was funded by the Polish Ministry of Science and Higher Education, Iuventus Plus Program, grant No. IP2010 000670. Apolinarska, K., 2013. Stable isotope compositions of recent Dreissena polymorpha (Pallas) shells: paleoenvironmental implications. Journal of Paleolimnology 50, 353-364. Apolinarska, K., Pełechaty, M. & Kossler, A., 2015a. Within-sample variability of δ13C and δ18O values of freshwater gastropod shells and the optimum number of shells to measure per sediment layer in the Paddenluch palaeolacustrine sequence, Germany. Journal of Paleolimnology 54, 305-323. Apolinarska, K., Pełechaty, M. & Noskowiak, D., 2015b. Differences in stable isotope compositions of freshwater snails from surface sediments of two Polish shallow lakes. Limnologica 53, 95-105. Apolinarska, K., Pełechaty, M. & Pronin, E., 2016. Discrepancies between the stable isotope compositions of water, macrophyte carbonates and organics, and mollusc shells in the littoral zone of a charophyte-dominated lake (Lake Lednica, Poland). Hydrobiologia 768, 1-17. Apolinarska, K. & Pełechaty, M., Inter- and intra-specific variability in δ13C and δ18O values of freshwater gastropod shells from Lake Lednica, western Poland. DOI: 10.1515/agp-2016-0028

Synchronized Northern Hemisphere climate change and solar magnetic cycles during the Maunder Minimum.

PubMed

Yamaguchi, Yasuhiko T; Yokoyama, Yusuke; Miyahara, Hiroko; Sho, Kenjiro; Nakatsuka, Takeshi

2010-11-30

The Maunder Minimum (A.D. 1645-1715) is a useful period to investigate possible sun-climate linkages as sunspots became exceedingly rare and the characteristics of solar cycles were different from those of today. Here, we report annual variations in the oxygen isotopic composition (δ(18)O) of tree-ring cellulose in central Japan during the Maunder Minimum. We were able to explore possible sun-climate connections through high-temporal resolution solar activity (radiocarbon contents; Δ(14)C) and climate (δ(18)O) isotope records derived from annual tree rings. The tree-ring δ(18)O record in Japan shows distinct negative δ(18)O spikes (wetter rainy seasons) coinciding with rapid cooling in Greenland and with decreases in Northern Hemisphere mean temperature at around minima of decadal solar cycles. We have determined that the climate signals in all three records strongly correlate with changes in the polarity of solar dipole magnetic field, suggesting a causal link to galactic cosmic rays (GCRs). These findings are further supported by a comparison between the interannual patterns of tree-ring δ(18)O record and the GCR flux reconstructed by an ice-core (10)Be record. Therefore, the variation of GCR flux associated with the multidecadal cycles of solar magnetic field seem to be causally related to the significant and widespread climate changes at least during the Maunder Minimum.

Synchronized Northern Hemisphere climate change and solar magnetic cycles during the Maunder Minimum

PubMed Central

Yamaguchi, Yasuhiko T.; Yokoyama, Yusuke; Miyahara, Hiroko; Sho, Kenjiro; Nakatsuka, Takeshi

2010-01-01

The Maunder Minimum (A.D. 1645–1715) is a useful period to investigate possible sun–climate linkages as sunspots became exceedingly rare and the characteristics of solar cycles were different from those of today. Here, we report annual variations in the oxygen isotopic composition (δ18O) of tree-ring cellulose in central Japan during the Maunder Minimum. We were able to explore possible sun–climate connections through high-temporal resolution solar activity (radiocarbon contents; Δ14C) and climate (δ18O) isotope records derived from annual tree rings. The tree-ring δ18O record in Japan shows distinct negative δ18O spikes (wetter rainy seasons) coinciding with rapid cooling in Greenland and with decreases in Northern Hemisphere mean temperature at around minima of decadal solar cycles. We have determined that the climate signals in all three records strongly correlate with changes in the polarity of solar dipole magnetic field, suggesting a causal link to galactic cosmic rays (GCRs). These findings are further supported by a comparison between the interannual patterns of tree-ring δ18O record and the GCR flux reconstructed by an ice-core 10Be record. Therefore, the variation of GCR flux associated with the multidecadal cycles of solar magnetic field seem to be causally related to the significant and widespread climate changes at least during the Maunder Minimum. PMID:21076031

Hydrogen Isotopic Systematics of Nominally Anhydrous Phases in Martian Meteorites

NASA Astrophysics Data System (ADS)

Tucker, Kera

Hydrogen isotope compositions of the martian atmosphere and crustal materials can provide unique insights into the hydrological and geological evolution of Mars. While the present-day deuterium-to-hydrogen ratio (D/H) of the Mars atmosphere is well constrained (~6 times that of terrestrial ocean water), that of its deep silicate interior (specifically, the mantle) is less so. In fact, the hydrogen isotope composition of the primordial martian mantle is of great interest since it has implications for the origin and abundance of water on that planet. Martian meteorites could provide key constraints in this regard, since they crystallized from melts originating from the martian mantle and contain phases that potentially record the evolution of the H 2O content and isotopic composition of the interior of the planet over time. Examined here are the hydrogen isotopic compositions of Nominally Anhydrous Phases (NAPs) in eight martian meteorites (five shergottites and three nakhlites) using Secondary Ion Mass Spectrometry (SIMS). This study presents a total of 113 individual analyses of H2O contents and hydrogen isotopic compositions of NAPs in the shergottites Zagami, Los Angeles, QUE 94201, SaU 005, and Tissint, and the nakhlites Nakhla, Lafayette, and Yamato 000593. The hydrogen isotopic variation between and within meteorites may be due to one or more processes including: interaction with the martian atmosphere, magmatic degassing, subsolidus alteration (including shock), and/or terrestrial contamination. Taking into consideration the effects of these processes, the hydrogen isotope composition of the martian mantle may be similar to that of the Earth. Additionally, this study calculated upper limits on the H2O contents of the shergottite and nakhlite parent melts based on the measured minimum H2O abundances in their maskelynites and pyroxenes, respectively. These calculations, along with some petrogenetic assumptions based on previous studies, were subsequently used to infer the H2O contents of the mantle source reservoirs of the depleted shergottites (200-700 ppm) and the nakhlites (10-100 ppm). This suggests that mantle source of the nakhlites is systematically drier than that of the depleted shergottites, and the upper mantle of Mars may have preserved significant heterogeneity in its H2O content. Additionally, this range of H2O contents is not dissimilar to the range observed for the Earth's upper mantle.

Localization of groundwater infiltration in the combined sewers of Brussels by stable isotopes measurements (δ18O, δD) by Cavity Ring Down Spectroscopy.

NASA Astrophysics Data System (ADS)

De Bondt, Kevin; Claeys, Philippe

2014-05-01

In the last 20 years research has been conducted to quantify the infiltration of groundwater into the sewers. This groundwater, called parasitic water, increases the volume of waste-water to be treated and consequently the cost of this treatment. Moreover, in the case of combined sewer systems, the parasitic water also limits the sewer capacity and indirectly increases the risks of combined sewer overflows and floods. The infiltration of groundwater occurs trough cracks, sewer collapses and from direct connections with old springs. Different methods quantify the intrusion of parasitic water. Among these, the use of the stable isotopes of water (δ18O & δD) shows good result in catchments or cities close to Mountainous regions (example from Lyon, Zurich), where isotopic signals vary significantly because of continental and altitude effects. However many cities, such as Brussels, are located in more oceanic settings and theoretically offer less potential for the application of the stable isotopes method. In the case of Brussels, river-water from the Meuse is used to produce domestic-water. The catchment of this river extends into the Ardennes, which are affected by slightly different climatic conditions. δ18O & δD analyzes of groundwater from the main aquifer (Ledo-Paniselian-Brusselian) and domestic-water from the Callois reservoir fed by the Meuse River show sufficient isotopic differences in the south of Brussels, but only during the summer. The discrimination potential is better with δD than with δ18O. The improvement of δD measurements (precision, costs,...) brought by Cavity Ring Down Spectroscopy largely contributes to the potential of using stable isotopes method to trace water in Brussels. The first campaigns in the sewers also show a little enrichment (in heavy isotopes) of the waste-water in comparison with the reservoir waters and tap waters. This increases the potential of the method but constrains the sampling to pure waste-water in sewer segments without infiltration generally localized upstream. Anyway, it is in the localization of parasitic water entrance from upstream to downstream that the stable isotopes method is the most powerful. Other methods (e.g. minimum night flow,...) are available at the treatment plants or at flow measurement stations downstream but will not be able to localize parasitic water intrusion towards old springs.

Discrimination Factors and Incorporation Rates for Organic Matrix in Shark Teeth Based on a Captive Feeding Study.

PubMed

Zeichner, S S; Colman, A S; Koch, P L; Polo-Silva, C; Galván-Magaña, F; Kim, S L

Sharks migrate annually over large distances and occupy a wide variety of habitats, complicating analysis of lifestyle and diet. A biogeochemical technique often used to reconstruct shark diet and environment preferences is stable isotope analysis, which is minimally invasive and integrates through time and space. There are previous studies that focus on isotopic analysis of shark soft tissues, but there are limited applications to shark teeth. However, shark teeth offer an advantage of multiple ecological snapshots and minimum invasiveness during removal because of their distinct conveyor belt tooth replacement system. In this study, we analyze δ 13 C and δ 15 N values of the organic matrix in leopard shark teeth (Triakis semifasciata) from a captive experiment and report discrimination factors as well as incorporation rates. We found differences in tooth discrimination factors for individuals fed different prey sources (mean ± SD; Δ 13 C squid = 4.7‰ ± 0.5‰, Δ 13 C tilapia = 3.1‰ ± 1.0‰, Δ 15 N squid = 2.0‰ ± 0.7‰, Δ 15 N tilapia = 2.8‰ ± 0.6‰). In addition, these values differed from previously published discrimination factors for plasma, red blood cells, and muscle of the same leopard sharks. Incorporation rates of shark teeth were similar for carbon and nitrogen (mean ± SE; λ C = 0.021 ± 0.009, λ N = 0.024 ± 0.007) and comparable to those of plasma. We emphasize the difference in biological parameters on the basis of tissue substrate and diet items to interpret stable isotope data and apply our results to stable isotope values from blue shark (Prionace glauca) teeth to illustrate the importance of biological parameters to interpret the complex ecology of a migratory shark.

A tracer study of ventilation in the Japan/East Sea

NASA Astrophysics Data System (ADS)

Postlethwaite, C. F.; Rohling, E. J.; Jenkins, W. J.; Walker, C. F.

2005-06-01

During the Circulation Research in East Asian Marginal Seas (CREAMS) summer cruises in 1999, a suite of samples was collected for tracer analysis. Oxygen isotopes combined with tritium-helium ventilation timescales and noble gas measurements give unique insights into the ventilation of water masses in the Japan/East Sea (JES). In particular, noble gases and oxygen isotopes are indicators of brine rejection, which may assist in explaining the recent changes observed in the ventilation of the JES. Oxygen isotope data presented here indicate that both thermally driven convection and brine rejection have played significant roles in deep-water formation but that brine rejection is unlikely to be a significant contributor at the moment. A 6-box ventilation model of the JES, calibrated with tritium and helium-3 measurements, performed better when a significant decrease of dense-water formation rates in the mid-1960s was incorporated. However, the model calculations suggest that Japan Sea Intermediate Water formation is still occurring. Subduction of sea-ice melt water may be a significant ventilation mechanism for this water mass, based on an argon saturation minimum at the recently ventilated salinity minimum in the northwestern sector of the JES. The salinity and oxygen isotope budgets imply a potential bottom-water formation rate of 3.97±0.89×10 12 m 3 yr -1 due to brine rejection, which could account for a time averaged fraction of between 25% and 35% of the ventilation of subsurface water formation in the JES.

Preparative chromatography for specific δ13C isotopic analysis of individual carbohydrates in environmental samples

NASA Astrophysics Data System (ADS)

Nouara, Amel; Panagiotopoulos, Christos; Balesdent, Jérôme; Sempéré, Richard

2017-04-01

Carbohydrates are among the most abundant organic molecules on the Earth and are present in all geochemical systems. Despite their high abundance in the environment, very few studies assessed their origin using molecular carbohydrate isotopic analyses. In contrast with bulk stable isotope analysis (BSIA), which gives the isotopic signature of the entire sample without any specification about its chemical composition, compound specific 13C isotopic analysis of individual sugars (CSIA) offers valuable information about the origin of single molecules. Previous investigations used gas or liquid chromatography coupled with isotope ratio mass spectroscopy (GC-IRMS; HPLC-IRMS) for CSIA of sugars however the former requires δ13C corrections due to the carbon added to the sugar (derivatization) while the later does not provide always adequate separations among monosaccharides. Here we used cation preparative chromatography (Ca2+, Pb2+ and Na+) with refractive index detection in order to produce pure monosaccharide targets for subsequent EA-IRMS analyses. Milli-Q water was used as eluant at a flow rate 0.6 ml min-1. In general, three successive purifications (Ca2+, Pb2+, Ca2+) were sufficient to produce pure compounds. Pure monosaccharides were compared with authentic monosaccharide standards using 1H NMR and/or mass spectroscopy. The detection limit of our technique was about 1µM/sugar with a precision of 10% (n=6). Blanks run with Milli-Q water after three successive purifications resulted in carbon content of 0.13 to 2.77 µgC per collected sugar. These values are much lower than the minimum required amount (5 µgC) of the EA-IRSMS system with a precision of ± 0.35 ‰. Application of our method to environmental samples resulted in δ13C values of glucose, fructose, and levoglucosan in the range of -24 to -26 ‰ (PM10 atmospheric particles), and -15‰ to -22 ‰ for arabinose, glucose, and xylose (marine high molecular dissolved organic matter). These results fall in the range of previous reported values for terrestrial and aquatic ecosystems.

Absolute vibrational numbering from isotope shifts in fragmentary spectroscopic data

NASA Astrophysics Data System (ADS)

Pashov, A.; Kowalczyk, P.; Jastrzebski, W.

2018-05-01

We discuss application of the isotope effect to establish the absolute vibrational numbering in electronic states of diatomic molecules. This is illustrated by examples of states with potential energy curves of both regular and irregular shape, with one or two potential minima. The minimum number of spectroscopic data (either term values or spectral line positions) necessary to provide a unique numbering is considered. We show that at favourable conditions just four term energies (or spectral lines) in one isotopologue and one term energy in the other suffice.

Isotope effects on desorption kinetics of hydrogen isotopes implanted into stainless steel by glow discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsuyama, M.; Kondo, M.; Noda, N.

2015-03-15

In a fusion device the control of fuel particles implies to know the desorption rate of hydrogen isotopes by the plasma-facing materials. In this paper desorption kinetics of hydrogen isotopes implanted into type 316L stainless steel by glow discharge have been studied by experiment and numerical calculation. The temperature of a maximum desorption rate depends on glow discharge time and heating rate. Desorption spectra observed under various experimental conditions have been successfully reproduced by numerical simulations that are based on a diffusion-limited process. It is suggested, therefore, that desorption rate of a hydrogen isotope implanted into the stainless steel ismore » limited by a diffusion process of hydrogen isotope atoms in bulk. Furthermore, small isotope effects were observed for the diffusion process of hydrogen isotope atoms. (authors)« less

Verification of Egg Farming Systems from The Netherlands and New Zealand Using Stable Isotopes.

PubMed

Rogers, Karyne M; van Ruth, Saskia; Alewijn, Martin; Philips, Andy; Rogers, Pam

2015-09-30

Stable isotopes were used to develop authentication criteria of eggs laid under cage, barn, free range, and organic farming regimens from The Netherlands and New Zealand. A training set of commercial poultry feeds and egg albumen from 49 poultry farms across The Netherlands was used to determine the isotopic variability of organic and conventional feeds and to assess trophic effects of these corresponding feeds and barn, free range, and organic farming regimens on corresponding egg albumen. A further 52 brands of New Zealand eggs were sampled from supermarket shelves in 2008 (18), 2010 (30), and 2014 (4) to characterize and monitor changes in caged, barn, free range, and organic egg farming regimens. Stable carbon (δ(13)C) and nitrogen (δ(15)N) isotopes of 49 commercial poultry feeds and their corresponding egg albumens reveals that Dutch poultry are fed exclusively on a plant-based feed and that it is possible to discriminate between conventional and organic egg farming regimens in The Netherlands. Similarly, it is possible to discriminate between New Zealand organic and conventional egg farming regimens, although in the initial screening in 2008, results showed that some organic eggs had isotope values similar to those of conventional eggs, suggesting hens were not exclusively receiving an organic diet. Dutch and New Zealand egg regimens were shown to have a low isotopic correlation between both countries, because of different poultry feed compositions. In New Zealand, both conventional and organic egg whites have higher δ(15)N values than corresponding Dutch egg whites, due to the use of fishmeal or meat and bone meal (MBM), which is banned in European countries. This study suggests that stable isotopes (specifically nitrogen) show particular promise as a screening and authentication tool for organically farmed eggs. Criteria to assess truthfulness in labeling of organic eggs were developed, and we propose that Dutch organic egg whites should have a minimum δ(15)N value of 4.8‰ to account for an organic plant derived diet. Monitoring of New Zealand egg isotopes over the past 7 years suggests that organic eggs should have a minimum δ(15)N value of 6.0‰, and eggs falling below this value should be investigated further by certification authorities.

U and Th isotope constraints on the duration of Heinrich events H0-H4 in the southeastern Labrador Sea

NASA Astrophysics Data System (ADS)

Veiga-Pires, C. C.; Hillaire-Marcel, C.

1999-04-01

The duration and sequence of events recorded in Heinrich layers at sites near the Hudson Strait source area for ice-rafted material are still poorly constrained, notably because of the limit and uncertainties of the 14C chronology. Here we use high-resolution 230Th-excess measurements, in a 6 m sequence raised from Orphan Knoll (southern Labrador Sea), to constrain the duration of the deposition of the five most recent Heinrich (H) layers. On the basis of maximum/minimum estimates for the mean glacial 230Th-excess flux at the studied site a minimum/maximum duration of 1.0/0.6, 1.4/0.8, 1.3/0.8, 1.5/0.9, and 2.1/1.3 kyr is obtained for H0 (˜Younger Dryas), Hl, H2, H3, and H4, respectively. Thorium-230-excess inventories and other sedimentological features indicate a reduced but still significant lateral sedimentary supply by the Western Boundary Undercurrent during the glacial interval. U and Th series systematics also provide insights into source rocks of H layer sediments (i.e., into distal Irminger Basin/local Labrador Sea supplies).

Determination of compound-specific Hg isotope ratios from transient signals using gas chromatography coupled to multicollector inductively coupled plasma mass spectrometry (MC-ICP/MS).

PubMed

Dzurko, Mark; Foucher, Delphine; Hintelmann, Holger

2009-01-01

MeHg and inorganic Hg compounds were measured in aqueous media for isotope ratio analysis using aqueous phase derivatization, followed by purge-and-trap preconcentration. Compound-specific isotope ratio measurements were performed by gas chromatography interfaced to MC-ICP/MS. Several methods of calculating isotope ratios were evaluated for their precision and accuracy and compared with conventional continuous flow cold vapor measurements. An apparent fractionation of Hg isotopes was observed during the GC elution process for all isotope pairs, which necessitated integration of signals prior to the isotope ratio calculation. A newly developed average peak ratio method yielded the most accurate isotope ratio in relation to values obtained by a continuous flow technique and the best reproducibility. Compound-specific isotope ratios obtained after GC separation were statistically not different from ratios measured by continuous flow cold vapor measurements. Typical external uncertainties were 0.16 per thousand RSD (n = 8) for the (202)Hg(/198)Hg ratio of MeHg and 0.18 per thousand RSD for the same ratio in inorganic Hg using the optimized operating conditions. Using a newly developed reference standard addition method, the isotopic composition of inorganic Hg and MeHg synthesized from this inorganic Hg was measured in the same run, obtaining a value of delta (202)Hg = -1.49 +/- 0.47 (2SD; n = 10). For optimum performance a minimum mass of 2 ng per Hg species should be introduced onto the column.

Trees, History, and Isotopes - the Late Maunder Minimum (1675-1715) in the Pannonian Basin, Hungary

NASA Astrophysics Data System (ADS)

Kazmer, M.; Demeny, A.; Grynaeus, A.; Racz, L.; Varkonyi, A.

2002-05-01

First results of a comprehensive study on climate change in the Pannonian Basin during the Late Maunder Minimum (1675-1715) are presented. The Pannonian Basin has continental climate, distinctly warm and dry in summer, cold in winter, unlike the Atlantic-type climate of Western Europe. Surrounded by the arc of the Carpathians, exposed to Atlantic, Mediterranean, and Siberian influences, the regional climate displays steep gradients. More than one tree-ring chronology for oak is being built, independent of the south German series. Rethly's rich database of historical sources has been assembled, and completed with recently published letters. Ring-width series are measured on oak, and skeleton plots are logged. Study of hydrogen isotope composition of tree rings is in progress. Tree-ring width faithfully reflects historical indices on spring (i.e. earlywood growth season) precipitation. Generally, precipitation - as shown both by indices and tree-ring width - was high and temperature low during the growth season in the first half of the LMM. The second half has seen a retardation in oak growth and an increase in spring temperature. The decades of the Late Maunder Minimum was a politically turbulent era: it saw the decline and fall of the Ottoman domination in Hungary, followed by a rebellion against Austrian rule, associated with disruption of national economy.

A novel method for rapid in vitro radiobioassay

NASA Astrophysics Data System (ADS)

Crawford, Evan Bogert

Rapid and accurate analysis of internal human exposure to radionuclides is essential to the effective triage and treatment of citizens who have possibly been exposed to radioactive materials in the environment. The two most likely scenarios in which a large number of citizens would be exposed are the detonation of a radiation dispersal device (RDD, "dirty bomb") or the accidental release of an isotope from an industrial source such as a radioisotopic thermal generator (RTG). In the event of the release and dispersion of radioactive materials into the environment in a large city, the entire population of the city -- including all commuting workers and tourists -- would have to be rapidly tested, both to satisfy the psychological needs of the citizens who were exposed to the mental trauma of a possible radiation dose, and to satisfy the immediate medical needs of those who received the highest doses and greatest levels of internal contamination -- those who would best benefit from rapid, intensive medical care. In this research a prototype rapid screening method to screen urine samples for the presence of up to five isotopes, both individually and in a mixture, has been developed. The isotopes used to develop this method are Co-60, Sr-90, Cs-137, Pu-238, and Am-241. This method avoids time-intensive chemical separations via the preparation and counting of a single sample on multiple detectors, and analyzing the spectra for isotope-specific markers. A rapid liquid-liquid separation using an organic extractive scintillator can be used to help quantify the activity of the alpha-emitting isotopes. The method provides quantifiable results in less than five minutes for the activity of beta/gamma-emitting isotopes when present in the sample at the intervention level as defined by the Centers for Disease Control and Prevention (CDC), and quantifiable results for the activity levels of alpha-emitting isotopes present at their respective intervention levels in approximately 30 minutes of sample preparation and counting time. Radiation detector spectra -- e.g. those from high-purity germanium (HPGe) gamma detectors and liquid scintillation detectors -- which contain decay signals from multiple isotopes often have overlapping signals: the counts from one isotope's decay can appear in energy channels associated with another isotope's decay, complicating the calculation of each isotope's activity. The uncertainties associated with analyzing these spectra have been traced in order to determine the effects of one isotope's count rate on the sensitivity and uncertainty associated with each other isotope. The method that was developed takes advantage of activated carbon filtration to eliminate quenching effects and to make the liquid scintillation spectra from different urine samples comparable. The method uses pulse-shape analysis to reduce the interference from beta emitters in the liquid scintillation spectrum and improve the minimum detectable activity (MDA) and minimum quantifiable activity (MQA) for alpha emitters. The method uses an HPGe detector to quantify the activity of gamma emitters, and subtract their isotopes' contributions to the liquid scintillation spectra via a calibration factor, such that the pure beta and pure alpha emitters can be identified and quantified from the resulting liquid scintillation spectra. Finally, the method optionally uses extractive scintillators to rapidly separate the alpha emitters from the beta emitters when the activity from the beta emitters is too great to detect or quantify the activity from the alpha emitters without such a separation. The method is able to detect and quantify all five isotopes, with uncertainties and biases usually in the 10-40% range, depending upon the isotopic mixtures and the activity ratios between each of the isotopes.

Fractionation of lithium isotopes in magmatic systems as a natural consequence of cooling

NASA Astrophysics Data System (ADS)

Gallagher, Kerry; Elliott, Tim

2009-02-01

High-temperature, diffusive fractionation has been invoked to account for striking Li isotopic variability recently observed within individual phenocrysts and xenolith minerals. It has been argued that chemical potential gradients required to drive such diffusion arise from changes in Li partitioning between coexisting phases during cooling. If so, Li isotopic zoning should be a common occurrence but the role of temperature-dependent partition coefficients in generating Li isotopic variability remains to be tested in a quantitative manner. Here we consider a basic scenario of a phenocryst in a cooling lava, using simple parameterisations of the temperature dependence of Li partitioning and diffusivity in clinopyroxene. Our model initially produces an asymmetric isotope profile across the crystal with a δ7Li minimum that remains close to the edge of a crystal. Such a distinctive shape mimics Li isotopic profiles documented in some olivine and clinopyroxene phenocrysts, which have isotopically normal cores but anomalously light rims. The temperature dependence of both the diffusivity and the partition coefficient of Li are key factors in generating this form of diffusion profile. Continued diffusion leads to an inversion in the sense of isotopic change between core and rim and results in the whole phenocryst attaining markedly light isotopic values. Our calculations show that significant Li isotopic zoning can occur as a natural consequence of cooling magmatic systems. Crystals that have experienced more complex thermal histories (e.g. re-entrained cumulates versus true phenocrysts) will therefore exhibit contrasting isotopic profiles and, as such, these data may be useful for tracing sub-volcanic processes.

Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sediment

NASA Astrophysics Data System (ADS)

Zhu, R.; Lin, Y.-S.; Lipp, J. S.; Meador, T. B.; Hinrichs, K.-U.

2014-01-01

Amino sugars are quantitatively significant constituents of soil and marine sediment, but their sources and turnover in environmental samples remain poorly understood. The stable carbon isotopic composition of amino sugars can provide information on the lifestyles of their source organisms and can be monitored during incubations with labeled substrates to estimate the turnover rates of microbial populations. However, until now, such investigation has been carried out only with soil samples, partly because of the much lower abundance of amino sugars in marine environments. We therefore optimized a procedure for compound-specific isotopic analysis of amino sugars in marine sediment employing gas chromatography-isotope ratio mass spectrometry. The whole procedure consisted of hydrolysis, neutralization, enrichment, and derivatization of amino sugars. Except for the derivatization step, the protocol introduced negligible isotopic fractionation, and the minimum requirement of amino sugar for isotopic analysis was 20 ng, i.e. equivalent to ~ 8 ng of amino sugar carbon. Our results obtained from δ13C analysis of amino sugars in selected marine sediment samples showed that muramic acid had isotopic imprints from indigenous bacterial activities, whereas glucosamine and galactosamine were mainly derived from organic detritus. The analysis of stable carbon isotopic compositions of amino sugars opens a promising window for the investigation of microbial metabolisms in marine sediments and the deep marine biosphere.

Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sediment

NASA Astrophysics Data System (ADS)

Zhu, R.; Lin, Y.-S.; Lipp, J. S.; Meador, T. B.; Hinrichs, K.-U.

2014-09-01

Amino sugars are quantitatively significant constituents of soil and marine sediment, but their sources and turnover in environmental samples remain poorly understood. The stable carbon isotopic composition of amino sugars can provide information on the lifestyles of their source organisms and can be monitored during incubations with labeled substrates to estimate the turnover rates of microbial populations. However, until now, such investigation has been carried out only with soil samples, partly because of the much lower abundance of amino sugars in marine environments. We therefore optimized a procedure for compound-specific isotopic analysis of amino sugars in marine sediment, employing gas chromatography-isotope ratio mass spectrometry. The whole procedure consisted of hydrolysis, neutralization, enrichment, and derivatization of amino sugars. Except for the derivatization step, the protocol introduced negligible isotopic fractionation, and the minimum requirement of amino sugar for isotopic analysis was 20 ng, i.e., equivalent to ~8 ng of amino sugar carbon. Compound-specific stable carbon isotopic analysis of amino sugars obtained from marine sediment extracts indicated that glucosamine and galactosamine were mainly derived from organic detritus, whereas muramic acid showed isotopic imprints from indigenous bacterial activities. The δ13C analysis of amino sugars provides a valuable addition to the biomarker-based characterization of microbial metabolism in the deep marine biosphere, which so far has been lipid oriented and biased towards the detection of archaeal signals.

Impact of isotopic disorders on thermal transport properties of nanotubes and nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Tao; Kang, Wei; Wang, Jianxiang, E-mail: jxwang@pku.edu.cn

2015-01-21

We present a one-dimensional lattice model to describe thermal transport in isotopically doped nanotubes and nanowires. The thermal conductivities thus predicted, as a function of isotopic concentration, agree well with recent experiments and other simulations. Our results display that for any given concentration of isotopic atoms in a lattice without sharp atomic interfaces, the maximum thermal conductivity is attained when isotopic atoms are placed regularly with an equal space, whereas the minimum is achieved when they are randomly inserted with a uniform distribution. Non-uniformity of disorder can further tune the thermal conductivity between the two values. Moreover, the dependence ofmore » the thermal conductivity on the nanoscale feature size becomes weak at low temperature when disorder exists. In addition, when self-consistent thermal reservoirs are included to describe diffusive nanomaterials, the thermal conductivities predicted by our model are in line with the results of macroscopic theories with an interfacial effect. Our results suggest that the disorder provides an additional freedom to tune the thermal properties of nanomaterials in many technological applications including nanoelectronics, solid-state lighting, energy conservation, and conversion.« less

Preliminary design of a mobile lunar power supply

NASA Technical Reports Server (NTRS)

Schmitz, Paul C.; Kenny, Barbara H.; Fulmer, Christopher R.

1991-01-01

A preliminary design for a Stirling isotope power system for use as a mobile lunar power supply is presented. Performance and mass of the components required for the system are estimated. These estimates are based on power requirements and the operating environment. Optimizations routines are used to determine minimum mass operational points. Shielding for the isotope system are given as a function of the allowed dose, distance from the source, and the time spent near the source. The technologies used in the power conversion and radiator systems are taken from ongoing research in the Civil Space Technology Initiative (CSTI) program.

Multiple stable isotope fronts during non-isothermal fluid flow

NASA Astrophysics Data System (ADS)

Fekete, Szandra; Weis, Philipp; Scott, Samuel; Driesner, Thomas

2018-02-01

Stable isotope signatures of oxygen, hydrogen and other elements in minerals from hydrothermal veins and metasomatized host rocks are widely used to investigate fluid sources and paths. Previous theoretical studies mostly focused on analyzing stable isotope fronts developing during single-phase, isothermal fluid flow. In this study, numerical simulations were performed to assess how temperature changes, transport phenomena, kinetic vs. equilibrium isotope exchange, and isotopic source signals determine mineral oxygen isotopic compositions during fluid-rock interaction. The simulations focus on one-dimensional scenarios, with non-isothermal single- and two-phase fluid flow, and include the effects of quartz precipitation and dissolution. If isotope exchange between fluid and mineral is fast, a previously unrecognized, significant enrichment in heavy oxygen isotopes of fluids and minerals occurs at the thermal front. The maximum enrichment depends on the initial isotopic composition of fluid and mineral, the fluid-rock ratio and the maximum change in temperature, but is independent of the isotopic composition of the incoming fluid. This thermally induced isotope front propagates faster than the signal related to the initial isotopic composition of the incoming fluid, which forms a trailing front behind the zone of transient heavy oxygen isotope enrichment. Temperature-dependent kinetic rates of isotope exchange between fluid and rock strongly influence the degree of enrichment at the thermal front. In systems where initial isotope values of fluids and rocks are far from equilibrium and isotope fractionation is controlled by kinetics, the temperature increase accelerates the approach of the fluid to equilibrium conditions with the host rock. Consequently, the increase at the thermal front can be less dominant and can even generate fluid values below the initial isotopic composition of the input fluid. As kinetics limit the degree of isotope exchange, a third front may develop in kinetically limited systems, which propagates with the advection speed of the incoming fluid and is, therefore, traveling fastest. The results show that oxygen isotope signatures at thermal fronts recorded in rocks and veins that experienced isotope exchange with fluids can easily be misinterpreted, namely if bulk analytical techniques are applied. However, stable isotope microanalysis on precipitated minerals may - if later isotope exchange is kinetically limited - provide a valuable archive of the transient thermal and hydrological evolution of a system.

Forensic analysis of explosives using isotope ratio mass spectrometry (IRMS)--discrimination of ammonium nitrate sources.

PubMed

Benson, Sarah J; Lennard, Christopher J; Maynard, Philip; Hill, David M; Andrew, Anita S; Roux, Claude

2009-06-01

An evaluation was undertaken to determine if isotope ratio mass spectrometry (IRMS) could assist in the investigation of complex forensic cases by providing a level of discrimination not achievable utilising traditional forensic techniques. The focus of the research was on ammonium nitrate (AN), a common oxidiser used in improvised explosive mixtures. The potential value of IRMS to attribute Australian AN samples to the manufacturing source was demonstrated through the development of a preliminary AN classification scheme based on nitrogen isotopes. Although the discrimination utilising nitrogen isotopes alone was limited and only relevant to samples from the three Australian manufacturers during the evaluated time period, the classification scheme has potential as an investigative aid. Combining oxygen and hydrogen stable isotope values permitted the differentiation of AN prills from three different Australian manufacturers. Samples from five different overseas sources could be differentiated utilising a combination of the nitrogen, oxygen and hydrogen isotope values. Limited differentiation between Australian and overseas prills was achieved for the samples analysed. The comparison of nitrogen isotope values from intact AN prill samples with those from post-blast AN prill residues highlighted that the nitrogen isotopic composition of the prills was not maintained post-blast; hence, limiting the technique to analysis of un-reacted explosive material.

An Isotopic Dilution Experiment Using Liquid Scintillation: A Simple Two-System, Two-Phase Analysis.

ERIC Educational Resources Information Center

Moehs, Peter J.; Levine, Samuel

1982-01-01

A simple isotonic, dilution analysis whose principles apply to methods of more complex radioanalyses is described. Suitable for clinical and instrumental analysis chemistry students, experimental manipulations are kept to a minimum involving only aqueous extraction before counting. Background information, procedures, and results are discussed.…

Improvements in Cd stable isotope analysis achieved through use of liquid-liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography.

PubMed

Murphy, Katy; Rehkämper, Mark; Kreissig, Katharina; Coles, Barry; van de Flierdt, Tina

2016-01-23

Organic compounds released from resins that are commonly employed for trace element separations are known to have a detrimental impact on the quality of isotopic analyses by MC-ICP-MS. A recent study highlighted that such effects can be particularly problematic for Cd stable isotope measurements (M. Gault-Ringold and C. H. Stirling, J. Anal. At. Spectrom. , 2012, 27 , 449-459). In this case, the final stage of sample purification commonly applies extraction chromatography with Eichrom TRU resin, which employs particles coated with octylphenyl- N , N -di-isobutyl carbamoylphosphine oxide (CMPO) dissolved in tri- n -butyl phosphate (TBP). During chromatography, it appears that some of these compounds are eluted alongside Cd and cannot be removed by evaporation due to their high boiling points. When aliquots of the zero-ε reference material were processed through the purification procedure, refluxed in concentrated HNO 3 and analyzed at minimum dilution (in 1 ml 0.1 M HNO 3 ), they yielded Cd isotopic compositions (ε 114/110 Cd = 4.6 ± 3.4, 2SD, n = 4) that differed significantly from the expected value, despite the use of a double spike technique to correct for instrumental mass fractionation. This result was accompanied by a 35% reduction in instrumental sensitivity for Cd. With increasing dilution of the organic resin residue, both of these effects are reduced and they are insignificant when the eluted Cd is dissolved in ≥3 ml 0.1 M HNO 3 . Our results, furthermore, indicate that the isotopic artefacts are most likely related to anomalous mass bias behavior. Previous studies have shown that perchloric acid can be effective at avoiding such effects (Gault-Ringold and Stirling, 2012; K. C. Crocket, M. Lambelet, T. van de Flierdt, M. Rehkämper and L. F. Robinson, Chem. Geol. , 2014, 374-375 , 128-140), presumably by oxidizing the resin-derived organics, but there are numerous disadvantages to its use. Here we show that liquid-liquid extraction with n -heptane removes the organic compounds, dramatically improving quality of the Cd isotope data for samples that are analyzed at or close to minimum dilution factors. This technique is quick, simple and may be of use prior to analysis of other isotope systems where similar resins are employed.

Stable isotope-labelled feed nutrients to assess nutrient-specific feed passage kinetics in ruminants.

PubMed

Warner, Daniel; Dijkstra, Jan; Hendriks, Wouter H; Pellikaan, Wilbert F

2014-03-30

Knowledge of digesta passage kinetics in ruminants is essential to predict nutrient supply to the animal in relation to optimal animal performance, environmental pollution and animal health. Fractional passage rates (FPR) of feed are widely used in modern feed evaluation systems and mechanistic rumen models, but data on nutrient-specific FPR are scarce. Such models generally rely on conventional external marker techniques, which do not always describe digesta passage kinetics in a satisfactory manner. Here the use of stable isotope-labelled dietary nutrients as a promising novel tool to assess nutrient-specific passage kinetics is discussed. Some major limitations of this technique include a potential marker migration, a poor isotope distribution in the labelled feed and a differential disappearance rate of isotopes upon microbial fermentation in non-steady state conditions. Such limitations can often be circumvented by using intrinsically stable isotope-labelled plant material. Data are limited but indicate that external particulate markers overestimate rumen FPR of plant fibre compared with the internal stable isotope markers. Stable isotopes undergo the same digestive mechanism as the labelled feed components and are thus of particular interest to specifically measure passage kinetics of digestible dietary nutrients. © 2013 Society of Chemical Industry.

Nitric oxide isotopic analyzer based on a compact dual-modulation Faraday rotation spectrometer.

PubMed

Zhang, Eric; Huang, Stacey; Ji, Qixing; Silvernagel, Michael; Wang, Yin; Ward, Bess; Sigman, Daniel; Wysocki, Gerard

2015-10-14

We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope ((15)NO) detection sensitivity of 0.36 ppbv·Hz(-1/2), corresponding to noise-equivalent Faraday rotation angle (NEA) of 1.31 × 10(-8) rad·Hz(-1/2) and noise-equivalent absorbance (αL)min of 6.27 × 10(-8) Hz(-1/2). White-noise limited performance at 2.8× the shot-noise limit is observed up to ~1000 s, allowing reliable calibration and sample measurement within the drift-free interval of the spectrometer. Integration with wet-chemistry based on acidic vanadium(III) enables conversion of aqueous nitrate/nitrite samples to gaseous NO for total nitrogen isotope analysis. Isotopic ratiometry is accomplished via time-multiplexed measurements of two NO isotope transitions. For 5 μmol potassium nitrate samples, the instrument consistently yields ratiometric precision below 0.3‰, thus demonstrating potential as an in situ diagnostic tool for environmental nitrogen cycle studies.

Calcium Isotope Analysis by Mass Spectrometry

NASA Astrophysics Data System (ADS)

Boulyga, S.; Richter, S.

2010-12-01

The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. This presentation discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. Additionally, the availability of Ca isotope reference materials will be discussed.

Inverse methods for estimating primary input signals from time-averaged isotope profiles

NASA Astrophysics Data System (ADS)

Passey, Benjamin H.; Cerling, Thure E.; Schuster, Gerard T.; Robinson, Todd F.; Roeder, Beverly L.; Krueger, Stephen K.

2005-08-01

Mammalian teeth are invaluable archives of ancient seasonality because they record along their growth axes an isotopic record of temporal change in environment, plant diet, and animal behavior. A major problem with the intra-tooth method is that intra-tooth isotope profiles can be extremely time-averaged compared to the actual pattern of isotopic variation experienced by the animal during tooth formation. This time-averaging is a result of the temporal and spatial characteristics of amelogenesis (tooth enamel formation), and also results from laboratory sampling. This paper develops and evaluates an inverse method for reconstructing original input signals from time-averaged intra-tooth isotope profiles. The method requires that the temporal and spatial patterns of amelogenesis are known for the specific tooth and uses a minimum length solution of the linear system Am = d, where d is the measured isotopic profile, A is a matrix describing temporal and spatial averaging during amelogenesis and sampling, and m is the input vector that is sought. Accuracy is dependent on several factors, including the total measurement error and the isotopic structure of the measured profile. The method is shown to accurately reconstruct known input signals for synthetic tooth enamel profiles and the known input signal for a rabbit that underwent controlled dietary changes. Application to carbon isotope profiles of modern hippopotamus canines reveals detailed dietary histories that are not apparent from the measured data alone. Inverse methods show promise as an effective means of dealing with the time-averaging problem in studies of intra-tooth isotopic variation.

Effect of bolus fluid intake on energy expenditure values as determined by the doubly labeled water method

NASA Technical Reports Server (NTRS)

Drews, D.; Stein, T. P.

1992-01-01

The doubly labeled water (DLW, 2H(2)18O) method is a highly accurate method for measuring energy expenditure (EE). A possible source of error is bolus fluid intake before body water sampling. If there is bolus fluid intake immediately before body water sampling, the saliva may reflect the ingested water disproportionately, because the ingested water may not have had time to mix fully with the body water pool. To ascertain the magnitude of this problem, EE was measured over a 5-day period by the DLW method. Six subjects were dosed with 2H2(18)O. After the reference salivas for the two-point determination were obtained, subjects drank water (700-1,000 ml), and serial saliva samples were collected for the next 3 h. Expressing the postbolus saliva enrichments as a percentage of the prebolus value, we found 1) a minimum in the saliva isotopic enrichments were reached at approximately 30 min with the minimum for 2H (95.48 +/- 0.43%) being significantly lower than the minimum for 18O (97.55 +/- 0.44, P less than 0.05) and 2) EE values calculated using the postbolus isotopic enrichments are appreciably higher (19.9 +/- 7.5%) than the prebolus reference values. In conclusion, it is not advisable to collect saliva samples for DLW measurements within approximately 1 h of bolus fluid intake.

Benthic iron cycling in a high-oxygen environment: Implications for interpreting the Archean sedimentary iron isotope record.

PubMed

McCoy, V E; Asael, D; Planavsky, N

2017-09-01

The most notable trend in the sedimentary iron isotope record is a shift at the end of the Archean from highly variable δ 56 Fe values with large negative excursions to less variable δ 56 Fe values with more limited negative values. The mechanistic explanation behind this trend has been extensively debated, with two main competing hypotheses: (i) a shift in marine redox conditions and the transition to quantitative iron oxidation; and (ii) a decrease in the signature of microbial iron reduction in the sedimentary record because of increased bacterial sulfate reduction (BSR). Here, we provide new insights into this debate and attempt to assess these two hypotheses by analyzing the iron isotope composition of siderite concretions from the Carboniferous Mazon Creek fossil site. These concretions precipitated in an environment with water column oxygenation, extensive sediment pile dissimilatory iron reduction (DIR) but limited bacterial sulfate reduction (BSR). Most of the concretions have slightly positive iron isotope values, with a mean of 0.15‰ and limited iron isotope variability compared to the Archean sedimentary record. This limited variability in an environment with high DIR and low BSR suggests that these conditions alone are insufficient to explain Archean iron isotope compositions. Therefore, these results support the idea that the unusually variable and negative iron isotope values in the Archean are due to dissimilatory iron reduction (DIR) coupled with extensive water column iron cycling. © 2017 John Wiley & Sons Ltd.

Insights into Mechanistic Models for Evaporation of Organic Liquids in the Environment Obtained by Position-Specific Carbon Isotope Analysis.

PubMed

Julien, Maxime; Nun, Pierrick; Robins, Richard J; Remaud, Gérald S; Parinet, Julien; Höhener, Patrick

2015-11-03

Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring (13)C nuclear magnetic resonance spectrometry during the evaporation of 10 liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation, distillation). The observed effects are used to assess the validity of the Craig-Gordon isotope model for organic liquids. For seven liquids the overall isotope effect (IE) includes a vapor-liquid contribution that is strongly position-specific in polar compounds but less so in apolar compounds and a diffusive IE that is not position-specific, except in the alcohols, ethanol and propan-1-ol. The diffusive IE is diminished under forced evaporation. The position-specific isotope pattern created by liquid-vapor IEs is manifest in five liquids, which have an air-side limitation for volatilization. For the alcohols, undefined processes in the liquid phase create additional PSIEs. Three other liquids with limitations on the liquid side have a lower, highly position-specific, bulk diffusive IE. It is concluded that evaporation of organic pollutants creates unique position-specific isotope patterns that may be used to assess the progress of remediation or natural attenuation of pollution and that the Craig-Gordon isotope model is valid for the volatilization of nonpolar organic liquids with air-side limitation of the volatilization rate.

Quantification of cefazolin in serum and adipose tissue by ultra high performance liquid chromatography-Tandem mass spectrometry (UHPLC-MS/MS): application to a pilot study of obese women undergoing cesarean delivery.

PubMed

Lillico, Ryan; Sayre, Casey L; Sitar, Daniel S; Davies, Neal M; Baron, Cynthia M; Lakowski, Ted M

2016-09-15

Higher doses of cefazolin are required in obese patients for preoperative antibiotic prophylaxis, owing to its low lipophilicity. An ultra high performance liquid chromatography-tandem mass spectrometry method was developed to quantify cefazolin in serum and adipose tissue from 6 obese patients undergoing cesarean delivery, and using stable-isotope labeled cefazolin as an internal standard. The method has a 2μg/g lower limit of quantitation. The concentration in adipose tissue was 3.4±1.6μg/mL, which is less than half of the reported minimum inhibitory concentration of 8μg/mL for cefazolin. Serum cefazolin concentrations were more than 30-fold higher than in adipose tissue. Copyright © 2016 Elsevier B.V. All rights reserved.

Implications of 187Os isotopic heterogeneities in a mantle plume: evidence from Gorgona Island and Curaçao

NASA Astrophysics Data System (ADS)

Walker, Richard J.; Storey, Michael; Kerr, Andrew C.; Tarney, John; Arndt, Nicholas T.

1999-03-01

Recent work has suggested that the mafic-ultramafic volcanism in evidence throughout portions of the Caribbean, Central America, and northern South America, including the islands of Gorgona and Curaçao, was generated as part of a middle-Cretaceous, large igneous province. New Re-Os isochron results for tholeiitic basalts from Gorgona and Curaçao indicate crystallization ages of 89.2 ± 5.2 and 85.6 ± 8.1 Ma, respectively, consistent with reported Ar ages. The Gorgona ultramafic suite shows a large range in initial Os isotopic composition, with γ Os values ranging from -0.5 to +12.4. This large range reflects isotopic heterogeneities in the mantle source similar to those observed for modern ocean island basalts. In contrast to ocean island basalts, however, Os isotopic compositions do not correlate with variations in Nd, Sr, or Pb isotopic compositions, which are within the range of depleted mid-ocean ridge basalts. The processes that produced these rocks evidently resulted in the decoupling of Os isotopes from the Nd, Sr, and Pb isotopic systems. Picrites from Curaçao have very uniform, chondritic initial Os isotopic compositions, with initial γ Os values ranging only from -0.4 to ±1.4. Basalts from Curaçao, however, define an isochron with a 187Os-enriched initial isotopic composition (γ Os = +9.5). In contrast to the 187Os-enriched ultramafic rocks from Gorgona, the enrichment in these basalts could have resulted from lithospheric contamination. If the Gorgona and Curaçao rocks were derived from the same plume, Os results, combined with Sr, Nd, and Pb data indicate a heterogeneous plume, with multiple compositionally and isotopically distinct domains. The Os isotopic results require derivation of Os from a minimum of two distinct reservoirs, one with a composition very similar to the chondritic average and one with long-term enriched Re/Os. Oceanic crustal recycling has been invoked to explain most of the 187Os enrichments that have been observed in ocean island basalt sources and could potentially apply to the Gorgona suite. Crustal recycling, however, requires large proportions of very ancient recycled basaltic crust in the sources of the 187Os-enriched ultramafic rocks to explain the magnitude of 187Os enrichments observed. For example, addition of 20% oceanic crust to fertile mantle, and nearly 3 billion years are necessary to generate a reservoir with the Os isotopic composition of the most radiogenic komatiites. If the recycled oceanic crust was added to basalt-depleted mantle, as may be indicated by ɛ Nd values for the komatiites averaging about +10, even larger proportions of older crust are required. Large proportions of oceanic mafic crust in the sources of the 187Os-enriched komatiites, although petrologically conceivable under certain melting conditions, is unlikely here given the limited trace element and lithophile isotope system variations. These results raise questions about the efficacy of using Os isotopes to constrain the proportion of recycled oceanic crust in other plumes. Other possible mechanisms for generating 187Os-enriched mantle include invoking the existence of a 187Os-enriched lower mantle, and minor outer core-lower mantle interactions.

Computer program calculates gamma ray source strengths of materials exposed to neutron fluxes

NASA Technical Reports Server (NTRS)

Heiser, P. C.; Ricks, L. O.

1968-01-01

Computer program contains an input library of nuclear data for 44 elements and their isotopes to determine the induced radioactivity for gamma emitters. Minimum input requires the irradiation history of the element, a four-energy-group neutron flux, specification of an alloy composition by elements, and selection of the output.

Kinetic control on Zn isotope signatures recorded in marine diatoms

NASA Astrophysics Data System (ADS)

Köbberich, Michael; Vance, Derek

2017-08-01

Marine diatoms dominate the oceanic cycle of the essential micronutrient zinc (Zn). The stable isotopes of zinc and other metals are increasingly used to understand trace metal micronutrient cycling in the oceans. One clear feature of the early isotope data is the heavy Zn isotope signature of the average oceanic dissolved pool relative to the inputs, potentially driven by uptake of light isotopes into phytoplankton cells and export to sediments. However, despite the fact that diatoms strip Zn from surface waters across the Antarctic polar front in the Southern Ocean, the local upper ocean is not isotopically heavy. Here we use culturing experiments to quantify the extent of Zn isotope fractionation by diatoms and to elucidate the mechanisms driving it. We have cultured two different open-ocean diatom species (T. oceanica and Chaetoceros sp.) in a series of experiments at constant medium Zn concentration but at bioavailable medium Fe ranging from limiting to replete. We find that T. oceanica can maintain high growth rates and Zn uptake rates over the full range of bioavailable iron (Fe) investigated, and that the Zn taken up has a δ66Zn that is unfractionated relative to that of the bioavailable free Zn in the medium. The studied representative of the genus Chaetoceros, on the other hand, shows more significantly reduced Zn uptake rates at low Fe and records more variable biomass δ66Zn signatures, of up to 0.85‰ heavier than the medium. We interpret the preferential uptake of heavy isotopes at extremely low Zn uptake rates as potentially due to either of the following two mechanisms. First, the release of extracellular polymeric substances (EPS), at low Fe levels, may preferentially scavenge heavy Zn isotopes. Second, the Zn uptake rate may be slow enough to establish pseudo-equilibrium conditions at the transporter site, with heavy Zn isotopes forming more stable surface complexes. Thus we find that, in our experiments, Fe-limitation exerts a key control that not only limits diatom growth, but also affects the Zn uptake physiology of diatoms. Uptake of heavy isotopes occurs under Fe-limiting conditions that drive extremely low Zn uptake rates. On the other hand, more rapid Zn uptake rates result in biomass that is indistinguishable from the external bioavailable free Zn pool. These experimental results can, in principle, explain the range of Zn isotopic compositions found in the real surface ocean, given the geographically variable interplay between Fe-limitation, Zn uptake rates, and the degree of organic complexation of oceanic Zn.

22 CFR 151.4 - Minimum limits for motor vehicle insurance.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 22 Foreign Relations 1 2011-04-01 2011-04-01 false Minimum limits for motor vehicle insurance. 151.4 Section 151.4 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.4 Minimum limits for motor vehicle...

22 CFR 151.4 - Minimum limits for motor vehicle insurance.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 22 Foreign Relations 1 2012-04-01 2012-04-01 false Minimum limits for motor vehicle insurance. 151.4 Section 151.4 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.4 Minimum limits for motor vehicle...

22 CFR 151.4 - Minimum limits for motor vehicle insurance.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 22 Foreign Relations 1 2010-04-01 2010-04-01 false Minimum limits for motor vehicle insurance. 151.4 Section 151.4 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.4 Minimum limits for motor vehicle...

22 CFR 151.4 - Minimum limits for motor vehicle insurance.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 22 Foreign Relations 1 2013-04-01 2013-04-01 false Minimum limits for motor vehicle insurance. 151.4 Section 151.4 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.4 Minimum limits for motor vehicle...

22 CFR 151.4 - Minimum limits for motor vehicle insurance.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 22 Foreign Relations 1 2014-04-01 2014-04-01 false Minimum limits for motor vehicle insurance. 151.4 Section 151.4 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.4 Minimum limits for motor vehicle...

The cycling of iron, zinc and cadmium in the North East Pacific Ocean - Insights from stable isotopes

NASA Astrophysics Data System (ADS)

Conway, Tim M.; John, Seth G.

2015-09-01

Dissolved stable isotope ratios of the transition metals provide useful information, both for understanding the cycling of these bioactive trace elements through the oceans, and tracing their marine sources and sinks. Here, we present seawater dissolved Fe, Zn and Cd concentration and stable isotope ratio (δ56Fe, δ66Zn, and δ114Cd) profiles from two stations in the Pacific Ocean, the SAFe Station (30°N 140°W) in the subtropical North East Pacific from the GEOTRACES IC2 cruise, and the marginal San Pedro Basin (33.8°N 118.4°W) within the South California Bight. These data represent, to our knowledge, the first full-water column profiles for δ66Zn and δ56Fe from the open-ocean North Pacific, and the first observations of dissolved δ66Zn and δ114Cd in a low-oxygen marginal basin. At the SAFe station, δ56Fe is isotopically lighter throughout the water column (-0.6 to +0.1‰, relative to IRRM-014) compared to the North Atlantic, suggesting significant differences in Fe sources or Fe cycling between these two ocean basins. A broad minimum in δ56Fe associated with the North Pacific oxygen minimum zone (OMZ; <75 μmol kg-1 dissolved oxygen; ∼550-2000 m depth) is consistent with reductive sediments along the California margin being an important source of dissolved Fe to the North Pacific. Other processes which may influence δ56Fe at SAFe include biological cycling in the upper ocean, and input of Fe from hydrothermal vents and oxic sediments below the OMZ. Zn and Cd concentration profiles at both stations broadly match the distribution of the macronutrients silicate and phosphate, respectively. At SAFe, δ114Cd increases towards the surface, reflecting the biological preference for assimilation of lighter Cd isotopes, while negative Cd∗ (-0.12) associated with low oxygen waters supports the recently proposed hypothesis of water-column CdS precipitation. In contrast to δ114Cd, δ66Zn at SAFe decreases towards the surface ocean, perhaps due to scavenging of isotopically heavy Zn, while at intermediate depths δ66Zn provides further evidence of a mid-depth dissolved δ66Zn maximum. We suggest this may be a global feature of Zn biogeochemistry related to either regeneration of heavy adsorbed Zn, or to ZnS formation and removal within the water column. Data from San Pedro shows that anoxic sediments can be a source of isotopically light Zn to the water column (δ66Zn of ∼-0.3‰ relative to JMC Lyon), though evidence of this signal is not observed being transported to SAFe. Within North Pacific Intermediate Water at SAFe (NPIW; ∼500 m) elevated Cd∗ and Zn∗ and a focused minimum in δ56Fe suggest possible transport of Fe, Zn, and Cd over thousands of km from subpolar waters, meaning that NPIW may have a strong influence on the subsurface distribution of trace metals throughout the North Pacific.

Local Prediction Models on Mid-Atlantic Ridge MORB by Principal Component Regression

NASA Astrophysics Data System (ADS)

Ling, X.; Snow, J. E.; Chin, W.

2017-12-01

The isotopic compositions of the daughter isotopes of long-lived radioactive systems (Sr, Nd, Hf and Pb ) can be used to map the scale and history of mantle heterogeneities beneath mid-ocean ridges. Our goal is to relate the multidimensional structure in the existing isotopic dataset with an underlying physical reality of mantle sources. The numerical technique of Principal Component Analysis is useful to reduce the linear dependence of the data to a minimum set of orthogonal eigenvectors encapsulating the information contained (cf Agranier et al 2005). The dataset used for this study covers almost all the MORBs along mid-Atlantic Ridge (MAR), from 54oS to 77oN and 8.8oW to -46.7oW, including replicating the dataset of Agranier et al., 2005 published plus 53 basalt samples dredged and analyzed since then (data from PetDB). The principal components PC1 and PC2 account for 61.56% and 29.21%, respectively, of the total isotope ratios variability. The samples with similar compositions to HIMU and EM and DM are identified to better understand the PCs. PC1 and PC2 are accountable for HIMU and EM whereas PC2 has limited control over the DM source. PC3 is more strongly controlled by the depleted mantle source than PC2. What this means is that all three principal components have a high degree of significance relevant to the established mantle sources. We also tested the relationship between mantle heterogeneity and sample locality. K-means clustering algorithm is a type of unsupervised learning to find groups in the data based on feature similarity. The PC factor scores of each sample are clustered into three groups. Cluster one and three are alternating on the north and south MAR. Cluster two exhibits on 45.18oN to 0.79oN and -27.9oW to -30.40oW alternating with cluster one. The ridge has been preliminarily divided into 16 sections considering both the clusters and ridge segments. The principal component regression models the section based on 6 isotope ratios and PCs. The prediction residual is about 1-2km. It means that the combined 5 isotopes are a strong predictor of geographic location along the ridge, a slightly surprising result. PCR is a robust and powerful method for both visualizing and manipulating the multidimensional representation of isotope data.

Integrated carbon and chlorine isotope modeling: applications to chlorinated aliphatic hydrocarbons dechlorination.

PubMed

Jin, Biao; Haderlein, Stefan B; Rolle, Massimo

2013-02-05

We propose a self-consistent method to predict the evolution of carbon and chlorine isotope ratios during degradation of chlorinated hydrocarbons. The method treats explicitly the cleavage of isotopically different C-Cl bonds and thus considers, simultaneously, combined carbon-chlorine isotopologues. To illustrate the proposed modeling approach we focus on the reductive dehalogenation of chlorinated ethenes. We compare our method with the currently available approach, in which carbon and chlorine isotopologues are treated separately. The new approach provides an accurate description of dual-isotope effects regardless of the extent of the isotope fractionation and physical characteristics of the experimental system. We successfully applied the new approach to published experimental results on dehalogenation of chlorinated ethenes both in well-mixed systems and in situations where mass-transfer limitations control the overall rate of biodegradation. The advantages of our self-consistent dual isotope modeling approach proved to be most evident when isotope fractionation factors of carbon and chlorine differed significantly and for systems with mass-transfer limitations, where both physical and (bio)chemical transformation processes affect the observed isotopic values.

Closing in on the limits of life through open-access instrumentation.

NASA Astrophysics Data System (ADS)

Girguis, P. R.; Hoer, D.

2016-12-01

Put simply, metabolic activity by living organisms can discriminate against elemental isotopes, resulting in an isotopic fractionation that is manifest in their biomolecules, substrates and endproducts. For decades, investigators have used these isotope ratios to make inferences about organismal activity and physiological capacity in modern day and paleo-environments. However, a long standing challenge in the life sciences is identifying and characterizing the limits of life. Whereas the limits of metazoan (animal) life are known to some degree, the extent of microbial life remains unconstrained. For example, we do not know the upper temperature limits of life, nor the lower energy limits of life. Discrete samples and the subsequent geochemical and biological measurements provide a means of bounding these questions, but there are major challenges associated with collecting such samples from the deep sea and other "extreme" habitats. A complementary approach is in situ geo-referenced isotope mapping. To date, we have developed instruments capable of measuring methane-carbon isotope ratios in situ and used the to "map" the activity and influence of anaerobic methanotrophs around natural hydrocarbon seeps (Wankel et al., 2012). While these instruments provide isotopic data in realtime, their greatest value is in producing geo-referenced "maps" of these isotope ratios, enabling investigators to better understand where microbial activity is highest, and the extent to which methane-derived carbon is found in the neighboring sediments and overlying water column. Now, our efforts are aimed at developing a 2nd generation instrument that will be substantially smaller and far more energy efficient, enabling deployment in more challenging environments such as boreholes and beneath ice. Most importantly, we are designing it to be capable of quantifying differences in the isotopes of multiple volatile compounds, e.g. carbon and sulfur, enabling a greater degree of fidelity in detecting biological activity in the subsurface and in other challenging locales. Here we will present our designs and data, and discuss how this and other instruments -such as integrated autonomous sensor and sampling packages- can advance our understanding of the limits of life here on Earth and -potentially- on other bodies.

Annual INTEC Groundwater Monitoring Report for Group 5 - Snake River Plain Aquifer (2001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roddy, Michael Scott

2002-02-01

This report describes the monitoring activities conducted and presents the results of groundwater sampling and water-level measurements from October 2000 to September 2001. Groundwater samples were initially collected from 41 wells from the Idaho Nuclear Technology and Engineering Center and the Central Facilities Area and analyzed for iodine-129, strontium-90, tritium, gross alpha, gross beta, technetium-99, uranium isotopes, plutonium isotopes, neptunium-237, americium-241, gamma spectrometry, and mercury. Samples from 41 wells were collected in April and May 2001. Additional sampling was conducted in August 2001 and included the two CFA production wells, the CFA point of compliance for the production wells, onemore » well that was previously sampled and five additional monitoring wells. Iodine-129 and strontium-90 were the only analytes above their respective maximum contaminant levels. Iodine-129 was detected just above its maximum contaminant level of 1 pCi/L at two of the Central Facilities Area landfill wells. Iodine-129 was detected in the CFA production wells at 0.35±0.083 pCi/L in CFA-1, but was below detectable activity in CFA-2. Strontium-90 was above its maximum contaminant level of 8 pCi/L in several wells near the Idaho Nuclear Technology and Engineering Center but was below its maximum contaminant level in the downgradient wells at the Central Facilities Area landfills. Sr-90 was not detected in the CFA production wells. Gross beta results generally mirrored the results for strontium-90 and technetium-99. Plutonium isotopes and neptunium-237 were not detected. Uranium-233/234 and uranium-238 isotopes were detected in all samples. Concentrations of background and site wells were similar and are within background limits for total uranium determined by the USGS, suggesting that the concentrations are background. Uranium-235/236 was detected in 11 samples, but all the detected concentrations were similar and near the minimum detectable activity. Americium-241 was detected at three locations near the minimum detectable activity of approximately 0.07 pCi/L. The gamma spectrometry results detected cesium-137 in three samples, potassium-40 at eight locations, and radium-226 at one location. Mercury was below its maximum contaminant level of 2 µg/L in all samples. Gamma spectrometry results for the CFA production wells did not detect any analytes. Water-level measurements were taken from wells in the Idaho Nuclear Technology and Engineering Center, Central Facilities Area, and the area south of Central Facilities Area to evaluate groundwater flow directions. Water-level measurements indicated groundwater flow to the south-southwest from the Idaho Nuclear Technology and Engineering Center.« less

22 CFR 151.10 - Minimum limits of insurance for aircraft and/or vessels.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 22 Foreign Relations 1 2012-04-01 2012-04-01 false Minimum limits of insurance for aircraft and/or vessels. 151.10 Section 151.10 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.10 Minimum limits of insurance for...

22 CFR 151.10 - Minimum limits of insurance for aircraft and/or vessels.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 22 Foreign Relations 1 2011-04-01 2011-04-01 false Minimum limits of insurance for aircraft and/or vessels. 151.10 Section 151.10 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.10 Minimum limits of insurance for...

22 CFR 151.10 - Minimum limits of insurance for aircraft and/or vessels.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 22 Foreign Relations 1 2013-04-01 2013-04-01 false Minimum limits of insurance for aircraft and/or vessels. 151.10 Section 151.10 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.10 Minimum limits of insurance for...

22 CFR 151.10 - Minimum limits of insurance for aircraft and/or vessels.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 22 Foreign Relations 1 2010-04-01 2010-04-01 false Minimum limits of insurance for aircraft and/or vessels. 151.10 Section 151.10 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.10 Minimum limits of insurance for...

22 CFR 151.10 - Minimum limits of insurance for aircraft and/or vessels.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 22 Foreign Relations 1 2014-04-01 2014-04-01 false Minimum limits of insurance for aircraft and/or vessels. 151.10 Section 151.10 Foreign Relations DEPARTMENT OF STATE DIPLOMATIC PRIVILEGES AND IMMUNITIES COMPULSORY LIABILITY INSURANCE FOR DIPLOMATIC MISSIONS AND PERSONNEL § 151.10 Minimum limits of insurance for...

Bryophytes as Climate Indicators: moss and liverwort photosynthetic limitations and carbon isotope signals in organic material and peat deposits

NASA Astrophysics Data System (ADS)

Griffiths, H.; Royles, J.; Horwath, A.; Hodell, D. A.; Convey, P.; Hodgson, D.; Wingate, L.; Ogeé, J.

2011-12-01

Bryophytes make a significant contribution to carbon sequestration and storage in polar, boreal, temperate and tropical biomes, and yet there is limited understanding of the determinants of carbon isotope composition. Bryophytes are poikilohydric and lack stomata in the vegetative (gametophyte) stage, and lack of roots and reliance on liquid water to maintain hydration status also imposes diffusional limitations on CO2 uptake and extent of carbon isotope discrimination. Real-time gas exchange and instantaneous discrimination studies can be used to quantify responses to liquid phase limitation. Thus, wetted tissues show less negative δ13C signals due to liquid phase conductance and, as the thallus surface dries, maximum CO2 assimilation and discrimination are attained when the limitation is primarily the internal (mesophyll) conductance. Continued desiccation then leads to additional biochemical limitation in drought tolerant species, and low discrimination, although the carbon gain is low at this time. In this paper we explore the extent of carbon isotope discrimination in bulk organic material and cellulose as a function of climatic and environmental conditions, in temperate, tropical and Antarctic bryophytes. Field studies have been used to investigate seasonal variations in precipitation and water vapour inputs for cloud forest formations as a function of bryophyte biomass, diversity and isotope composition in epiphytes (particularly leafy liverworts) along an altitudinal gradient in Peru. In the Antarctic, moss banks sampled on Signy Island consisted of only two species, primarily Chorisodontium aciphyllum and some Polytrichum strictum, allowing the collection of shallow and deep cores representative of growth over the past 200 to 2000 years. The well-preserved peat has provided data on growth (14C) and stable isotopic proxies (13C, 18O) for material contemporary with recent anthropogenic climate forcing (over the past 200 years), for comparison with longer-term trends. Once corrected for source CO2 inputs, the carbon isotope signals are consistent with recent increases in growing season length. Laboratory studies on real-time CO2 uptake and isotope discrimination as a function of water content, for the desiccation-tolerant moss Syntrichia ruralis, reveal the interactions between surface water, liquid phase and mesophyll diffusion limitation. These data have been used to develop a model for isotope discrimination in mosses as a function of water status and we will discuss the extent that such a model can be used predictively to determine moss-peat water status, and infer current and past climatic conditions.

50 CFR 622.492 - Minimum size limit.

Code of Federal Regulations, 2013 CFR

2013-10-01

... ADMINISTRATION, DEPARTMENT OF COMMERCE FISHERIES OF THE CARIBBEAN, GULF OF MEXICO, AND SOUTH ATLANTIC Queen Conch Resources of Puerto Rico and the U.S. Virgin Islands § 622.492 Minimum size limit. (a) The minimum size...

50 CFR 622.492 - Minimum size limit.

Code of Federal Regulations, 2014 CFR

2014-10-01

... ADMINISTRATION, DEPARTMENT OF COMMERCE FISHERIES OF THE CARIBBEAN, GULF OF MEXICO, AND SOUTH ATLANTIC Queen Conch Resources of Puerto Rico and the U.S. Virgin Islands § 622.492 Minimum size limit. (a) The minimum size...

50 CFR 622.454 - Minimum size limit.

Code of Federal Regulations, 2013 CFR

2013-10-01

... ADMINISTRATION, DEPARTMENT OF COMMERCE FISHERIES OF THE CARIBBEAN, GULF OF MEXICO, AND SOUTH ATLANTIC Spiny Lobster Fishery of Puerto Rico and the U.S. Virgin Islands § 622.454 Minimum size limit. (a) The minimum...

50 CFR 622.454 - Minimum size limit.

Code of Federal Regulations, 2014 CFR

2014-10-01

... ADMINISTRATION, DEPARTMENT OF COMMERCE FISHERIES OF THE CARIBBEAN, GULF OF MEXICO, AND SOUTH ATLANTIC Spiny Lobster Fishery of Puerto Rico and the U.S. Virgin Islands § 622.454 Minimum size limit. (a) The minimum...

Nitric Oxide Isotopic Analyzer Based on a Compact Dual-Modulation Faraday Rotation Spectrometer

PubMed Central

Zhang, Eric; Huang, Stacey; Ji, Qixing; Silvernagel, Michael; Wang, Yin; Ward, Bess; Sigman, Daniel; Wysocki, Gerard

2015-01-01

We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope (15NO) detection sensitivity of 0.36 ppbv·Hz−1/2, corresponding to noise-equivalent Faraday rotation angle (NEA) of 1.31 × 10−8 rad·Hz−1/2 and noise-equivalent absorbance (αL)min of 6.27 × 10−8 Hz−1/2. White-noise limited performance at 2.8× the shot-noise limit is observed up to ~1000 s, allowing reliable calibration and sample measurement within the drift-free interval of the spectrometer. Integration with wet-chemistry based on acidic vanadium(III) enables conversion of aqueous nitrate/nitrite samples to gaseous NO for total nitrogen isotope analysis. Isotopic ratiometry is accomplished via time-multiplexed measurements of two NO isotope transitions. For 5 μmol potassium nitrate samples, the instrument consistently yields ratiometric precision below 0.3‰, thus demonstrating potential as an in situ diagnostic tool for environmental nitrogen cycle studies. PMID:26473876

Elemental GCR Observations during the 2009-2010 Solar Minimum Period

NASA Technical Reports Server (NTRS)

Lave, K. A.; Israel, M. H.; Binns, W. R.; Christian, E. R.; Cummings, A. C.; Davis, A. J.; deNolfo, G. A.; Leske, R. A.; Mewaldt, R. A.; Stone, E. C.;

Muskellunge growth potential in northern Wisconsin: implications for trophy management

USGS Publications Warehouse

Faust, Matthew D.; Isermann, Daniel A.; Luehring, Mark A.; Hansen, Michael J.

2015-01-01

The growth potential of Muskellunge Esox masquinongy was evaluated by back-calculating growth histories from cleithra removed from 305 fish collected during 1995–2011 to determine whether it was consistent with trophy management goals in northern Wisconsin. Female Muskellunge had a larger mean asymptotic length (49.8 in) than did males (43.4 in). Minimum ultimate size of female Muskellunge (45.0 in) equaled the 45.0-in minimum length limit, but was less than the 50.0-in minimum length limit used on Wisconsin's trophy waters, while the minimum ultimate size of male Muskellunge (34.0 in) was less than the statewide minimum length limit. Minimum reproductive sizes for both sexes were less than Wisconsin's trophy minimum length limits. Mean growth potential of female Muskellunge in northern Wisconsin appears to be sufficient for meeting trophy management objectives and angler expectations. Muskellunge in northern Wisconsin had similar growth potential to those in Ontario populations, but lower growth potential than Minnesota's populations, perhaps because of genetic and environmental differences.

Floodplain ecohydrology: Climatic, anthropogenic, and local physical controls on partitioning of water sources to riparian trees.

PubMed

Singer, Michael Bliss; Sargeant, Christopher I; Piégay, Hervé; Riquier, Jérémie; Wilson, Rob J S; Evans, Cristina M

2014-05-01

Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co-occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years. Water shifts due to climatic fluctuations between floodplain storage reservoirsAnthropogenic changes to hydrology directly impact water available to treesEcohydrologic approaches to integration of hydrology afford new possibilities.

Floodplain ecohydrology: Climatic, anthropogenic, and local physical controls on partitioning of water sources to riparian trees

PubMed Central

Singer, Michael Bliss; Sargeant, Christopher I; Piégay, Hervé; Riquier, Jérémie; Wilson, Rob J S; Evans, Cristina M

2014-01-01

Seasonal and annual partitioning of water within river floodplains has important implications for ecohydrologic links between the water cycle and tree growth. Climatic and hydrologic shifts alter water distribution between floodplain storage reservoirs (e.g., vadose, phreatic), affecting water availability to tree roots. Water partitioning is also dependent on the physical conditions that control tree rooting depth (e.g., gravel layers that impede root growth), the sources of contributing water, the rate of water drainage, and water residence times within particular storage reservoirs. We employ instrumental climate records alongside oxygen isotopes within tree rings and regional source waters, as well as topographic data and soil depth measurements, to infer the water sources used over several decades by two co-occurring tree species within a riparian floodplain along the Rhône River in France. We find that water partitioning to riparian trees is influenced by annual (wet versus dry years) and seasonal (spring snowmelt versus spring rainfall) fluctuations in climate. This influence depends strongly on local (tree level) conditions including floodplain surface elevation and subsurface gravel layer elevation. The latter represents the upper limit of the phreatic zone and therefore controls access to shallow groundwater. The difference between them, the thickness of the vadose zone, controls total soil moisture retention capacity. These factors thus modulate the climatic influence on tree ring isotopes. Additionally, we identified growth signatures and tree ring isotope changes associated with recent restoration of minimum streamflows in the Rhône, which made new phreatic water sources available to some trees in otherwise dry years. Key Points Water shifts due to climatic fluctuations between floodplain storage reservoirs Anthropogenic changes to hydrology directly impact water available to trees Ecohydrologic approaches to integration of hydrology afford new possibilities PMID:25506099

Calcium isotope analysis by mass spectrometry.

PubMed

Boulyga, Sergei F

2010-01-01

The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. The present article discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. In Sections 2 and 3, mass spectrometric methods applied to precise stable isotope analysis and to the determination of (41)Ca are described. Section 4 contains a short summary of selected applications, and includes tracer experiments and the potential use of biological isotope fractionation in medical studies, paleoclimatic and paleoceanographic, and other terrestrial as well as extraterrestrial investigations. 2009 Wiley Periodicals, Inc.

Mechanistic investigations of the hydrolysis of amides, oxoesters and thioesters via kinetic isotope effects and positional isotope exchange.

PubMed

Robins, Lori I; Fogle, Emily J; Marlier, John F

2015-11-01

The hydrolysis of amides, oxoesters and thioesters is an important reaction in both organic chemistry and biochemistry. Kinetic isotope effects (KIEs) are one of the most important physical organic methods for determining the most likely transition state structure and rate-determining step of these reaction mechanisms. This method induces a very small change in reaction rates, which, in turn, results in a minimum disturbance of the natural mechanism. KIE studies were carried out on both the non-enzymatic and the enzyme-catalyzed reactions in an effort to compare both types of mechanisms. In these studies the amides and esters of formic acid were chosen because this molecular structure allowed development of methodology to determine heavy-atom solvent (nucleophile) KIEs. This type of isotope effect is difficult to measure, but is rich in mechanistic information. Results of these investigations point to transition states with varying degrees of tetrahedral character that fit a classical stepwise mechanism. This article is part of a special issue entitled: Enzyme Transition States from Theory and Experiment. Copyright © 2014 Elsevier B.V. All rights reserved.

D/H ratios and hydrogen exchangeability of type-II kerogens with increasing thermal maturity

USGS Publications Warehouse

Lis, G.P.; Schimmelmann, A.; Mastalerz, Maria

2006-01-01

Stable isotope ratios of non-exchangeable hydrogen (??Dn) and of carbon were measured in type-II kerogens from two suites of Late Devonian to Early Mississippian black shale, one from the New Albany Shale (Illinois Basin) and the other from the Exshaw Formation (Alberta Basin). The largely marine-derived organic matter had similar original stable isotope ratios, but today the suites of kerogens express gradients in thermal maturity that have altered their chemical and isotopic compositions. In both suites, ??D n values increase with maturation up to a vitrinite reflectance of Ro 1.5%, then level out. Increasing ??Dn values suggest isotopic exchange of organic hydrogen with water-derived deuterium and/or preferential loss of 1H-enriched chemical moieties from kerogen during maturation. The resulting changes in ??Dn values are altering the original hydrogen isotopic paleoenvironmental signal in kerogen, albeit in a systematic fashion. The specific D/H response of each kerogen suite through maturation correlates with H/C elemental ratio and can therefore be corrected to yield paleoenvironmentally relevant information for a calibrated system. With increasing thermal maturity, the abundance of hydrogen in the kerogen that is isotopically exchangeable with water hydrogen (expressed as Hex, in % of total hydrogen) first decreases to reach a minimum at Ro ??? 0.8-1.1%, followed by a substantial increase at higher thermal maturity. ?? 2005 Elsevier Ltd. All rights reserved.

Improvements in Cd stable isotope analysis achieved through use of liquid–liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5ja00115c Click here for additional data file.

PubMed Central

Rehkämper, Mark; Kreissig, Katharina; Coles, Barry; van de Flierdt, Tina

2016-01-01

Organic compounds released from resins that are commonly employed for trace element separations are known to have a detrimental impact on the quality of isotopic analyses by MC-ICP-MS. A recent study highlighted that such effects can be particularly problematic for Cd stable isotope measurements (M. Gault-Ringold and C. H. Stirling, J. Anal. At. Spectrom., 2012, 27, 449–459). In this case, the final stage of sample purification commonly applies extraction chromatography with Eichrom TRU resin, which employs particles coated with octylphenyl-N,N-di-isobutyl carbamoylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). During chromatography, it appears that some of these compounds are eluted alongside Cd and cannot be removed by evaporation due to their high boiling points. When aliquots of the zero-ε reference material were processed through the purification procedure, refluxed in concentrated HNO3 and analyzed at minimum dilution (in 1 ml 0.1 M HNO3), they yielded Cd isotopic compositions (ε114/110Cd = 4.6 ± 3.4, 2SD, n = 4) that differed significantly from the expected value, despite the use of a double spike technique to correct for instrumental mass fractionation. This result was accompanied by a 35% reduction in instrumental sensitivity for Cd. With increasing dilution of the organic resin residue, both of these effects are reduced and they are insignificant when the eluted Cd is dissolved in ≥3 ml 0.1 M HNO3. Our results, furthermore, indicate that the isotopic artefacts are most likely related to anomalous mass bias behavior. Previous studies have shown that perchloric acid can be effective at avoiding such effects (Gault-Ringold and Stirling, 2012; K. C. Crocket, M. Lambelet, T. van de Flierdt, M. Rehkämper and L. F. Robinson, Chem. Geol., 2014, 374–375, 128–140), presumably by oxidizing the resin-derived organics, but there are numerous disadvantages to its use. Here we show that liquid–liquid extraction with n-heptane removes the organic compounds, dramatically improving quality of the Cd isotope data for samples that are analyzed at or close to minimum dilution factors. This technique is quick, simple and may be of use prior to analysis of other isotope systems where similar resins are employed. PMID:27284213

N-loss isotope effects in the Peru oxygen minimum zone studied using a mesoscale eddy as a natural tracer experiment

NASA Astrophysics Data System (ADS)

Bourbonnais, Annie; Altabet, Mark A.; Charoenpong, Chawalit N.; Larkum, Jennifer; Hu, Haibei; Bange, Hermann W.; Stramma, Lothar

2015-06-01

Mesoscale eddies in Oxygen Minimum Zones (OMZs) have been identified as important fixed nitrogen (N) loss hotspots that may significantly impact both the global rate of N-loss as well as the ocean's N isotope budget. They also represent "natural tracer experiments" with intensified biogeochemical signals that can be exploited to understand the large-scale processes that control N-loss and associated isotope effects (ɛ; the ‰ deviation from 1 in the ratio of reaction rate constants for the light versus heavy isotopologues). We observed large ranges in the concentrations and N and O isotopic compositions of nitrate (NO3-), nitrite (NO2-), and biogenic N2 associated with an anticyclonic mode-water eddy in the Peru OMZ during two cruises in November and December 2012. In the eddy's center where NO3- was nearly exhausted, we measured the highest δ15N values for both NO3- and NO2- (up to ~70‰ and 50‰) ever reported for an OMZ. Correspondingly, N deficit and biogenic N2-N concentrations were also the highest near the eddy's center (up to ~40 µmol L-1). δ15N-N2 also varied with biogenic N2 production, following kinetic isotopic fractionation during NO2- reduction to N2 and, for the first time, provided an independent assessment of N isotope fractionation during OMZ N-loss. We found apparent variable ɛ for NO3- reduction (up to ~30‰ in the presence of NO2-). However, the overall ɛ for N-loss was calculated to be only ~13-14‰ (as compared to canonical values of ~20-30‰) assuming a closed system and only slightly higher assuming an open system (16-19‰). Our results were similar whether calculated from the disappearance of DIN (NO3- + NO2-) or from the appearance of N2 and changes in isotopic composition. Further, we calculated the separate ɛ values for NO3- reduction to NO2- and NO2- reduction to N2 of ~16-21‰ and ~12‰, respectively, when the effect of NO2- oxidation could be removed. These results, together with the relationship between N and O of NO3- isotopes and the difference in δ15N between NO3- and NO2-, confirm a role for NO2- oxidation in increasing the apparent ɛ associated with NO3- reduction. The lower ɛ for N-loss calculated in this study could help reconcile the current imbalance in the global N budget if representative of global OMZ N-loss.

Do deposit-feeders compete? Isotopic niche analysis of an invasion in a species-poor system

PubMed Central

Karlson, Agnes M. L.; Gorokhova, Elena; Elmgren, Ragnar

2015-01-01

Successful establishment of invasive species is often related to the existence of vacant niches. Competition occurs when invaders use the same limiting resources as members of the recipient community, which will be reflected in some overlap of their trophic niches. The concept of isotopic niche has been used to study trophic niche partitioning among species. Here, we present a two-year field study comparing isotopic niches of the deposit-feeding community in a naturally species-poor system. The isotopic niche analyses showed no overlap between a recent polychaete invader and any of the native species suggesting that it has occupied a vacant niche. Its narrow isotopic niche suggests specialized feeding, however, the high δ15N values compared to natives are most likely due to isotope fractionation effects related to nitrogen recycling and a mismatch between biological stoichiometry of the polychaete and the sediment nitrogen content. Notably, highly overlapping isotopic niches were inferred for the native species, which is surprising in a food-limited system. Therefore, our results demonstrate that invaders may broaden the community trophic diversity and enhance resource utilization, but also raise questions about the congruence between trophic and isotopic niche concepts and call for careful examination of assumptions underlying isotopic niche interpretation. PMID:25988260

Development and validation of an universal interface for compound-specific stable isotope analysis of chlorine (37Cl/35Cl) by GC-high-temperature conversion (HTC)-MS/IRMS.

PubMed

Renpenning, Julian; Hitzfeld, Kristina L; Gilevska, Tetyana; Nijenhuis, Ivonne; Gehre, Matthias; Richnow, Hans-Hermann

2015-03-03

A universal application of compound-specific isotope analysis of chlorine was thus far limited by the availability of suitable analysis techniques. In this study, gas chromatography in combination with a high-temperature conversion interface (GC-HTC), converting organic chlorine in the presence of H2 to gaseous HCl, was coupled to a dual-detection system, combining an ion trap mass spectrometer (MS) and isotope-ratio mass spectrometer (IRMS). The combination of the MS/IRMS detection enabled a detailed characterization, optimization, and online monitoring of the high-temperature conversion process via ion trap MS as well as a simultaneous chlorine isotope analysis by the IRMS. Using GC-HTC-MS/IRMS, chlorine isotope analysis at optimized conversion conditions resulted in very accurate isotope values (δ(37)Cl(SMOC)) for measured reference material with known isotope composition, including chlorinated ethylene, chloromethane, hexachlorocyclohexane, and trichloroacetic acids methyl ester. Respective detection limits were determined to be <15 nmol Cl on column with achieved precision of <0.3‰.

Rate dependent fractionation of sulfur isotopes in through-flowing systems

NASA Astrophysics Data System (ADS)

Giannetta, M.; Sanford, R. A.; Druhan, J. L.

2017-12-01

The fidelity of reactive transport models in quantifying microbial activity in the subsurface is often improved through the use stable isotopes. However, the accuracy of current predictions for microbially mediated isotope fractionations within open through-flowing systems typically depends on nutrient availability. This disparity arises from the common application of a single `effective' fractionation factor assigned to a given system, despite extensive evidence for variability in the fractionation factor between eutrophic environments and many naturally occurring, nutrient-limited environments. Here, we demonstrate a reactive transport model with the capacity to simulate a variable fractionation factor over a range of microbially mediated reduction rates and constrain the model with experimental data for nutrient limited conditions. Two coupled isotope-specific Monod rate laws for 32S and 34S, constructed to quantify microbial sulfate reduction and predict associated S isotope partitioning, were parameterized using a series of batch reactor experiments designed to minimize microbial growth. In the current study, we implement these parameterized isotope-specific rate laws within an open, through-flowing system to predict variable fractionation with distance as a function of sulfate reduction rate. These predictions are tested through a supporting laboratory experiment consisting of a flow-through column packed with homogenous porous media inoculated with the same species of sulfate reducing bacteria used in the previous batch reactors, Desulfovibrio vulgaris. The collective results of batch reactor and flow-through column experiments support a significant improvement for S isotope predictions in isotope-sensitive multi-component reactive transport models through treatment of rate-dependent fractionation. Such an update to the model will better equip reactive transport software for isotope informed characterization of microbial activity within energy and nutrient limited environments.

On the influence of anharmonicity on the isotope effect

NASA Astrophysics Data System (ADS)

Galbaatar, T.; Drechsler, S. L.; Plakida, N. M.; Vujicic, G. M.

1991-12-01

The effect of double-well type lattice anharmonicity on the superconducting temperature and its isotope effect is investigated beyond the two-level approximation (TLA) within the Eliashberg theory. It is shown that anharmonicity can greatly modify the isotope effect; In particular anomalously large as well as negative values of the isotope effect exponent α are obtained in the strong and weak coupling limits, respectively.

Detecting isotopic ratio outliers

NASA Astrophysics Data System (ADS)

Bayne, C. K.; Smith, D. H.

An alternative method is proposed for improving isotopic ratio estimates. This method mathematically models pulse-count data and uses iterative reweighted Poisson regression to estimate model parameters to calculate the isotopic ratios. This computer-oriented approach provides theoretically better methods than conventional techniques to establish error limits and to identify outliers.

Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds

NASA Astrophysics Data System (ADS)

Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.

2006-12-01

The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number: Da = kh/D, where h is the width of the 2D calculation domain. Varying the nondimensional Da in the model is equivalent to varying the scale (h) in the model. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, the isotopic fractionations are dominated by kinetic effects, and similar to those predicted by the spherical diffusion model. Dendritic crystals are constrained to be relatively large, with dimension much greater than D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. A different approach, using a larger scale simulation to derive boundary conditions for a nested smaller scale calculation is in progress. The results to date clarify the controls on dendritic crystal growth, the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation, and provide limits on the value of the accommodation coefficient.

Coupling meteorology, metal concentrations, and Pb isotopes for source attribution in archived precipitation samples.

PubMed

Graney, Joseph R; Landis, Matthew S

2013-03-15

A technique that couples lead (Pb) isotopes and multi-element concentrations with meteorological analysis was used to assess source contributions to precipitation samples at the Bondville, Illinois USA National Trends Network (NTN) site. Precipitation samples collected over a 16month period (July 1994-October 1995) at Bondville were parsed into six unique meteorological flow regimes using a minimum variance clustering technique on back trajectory endpoints. Pb isotope ratios and multi-element concentrations were measured using high resolution inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) on the archived precipitation samples. Bondville is located in central Illinois, ~250km downwind from smelters in southeast Missouri. The Mississippi Valley Type ore deposits in Missouri provided a unique multi-element and Pb isotope fingerprint for smelter emissions which could be contrasted to industrial emissions from the Chicago and Indianapolis urban areas (~125km north and east, of Bondville respectively) and regional emissions from electric utility facilities. Differences in Pb isotopes and element concentrations in precipitation corresponded to flow regime. Industrial sources from urban areas, and thorogenic Pb from coal use, could be differentiated from smelter emissions from Missouri by coupling Pb isotopes with variations in element ratios and relative mass factors. Using a three endmember mixing model based on Pb isotope ratio differences, industrial processes in urban airsheds contributed 56±19%, smelters in southeast Missouri 26±13%, and coal combustion 18±7%, of the Pb in precipitation collected in Bondville in the mid-1990s. Copyright © 2012 Elsevier B.V. All rights reserved.

Evaluating the influence of chemical weathering on the composition of the continental crust using lithium and its isotopes

NASA Astrophysics Data System (ADS)

Rudnick, R. L.; Liu, X.

2011-12-01

The continental crust has an "intermediate" bulk composition that is distinct from primary melts of peridotitic mantle (basalt or picrite). This mismatch between the "building blocks" and the "edifice" of the continental crust points to the operation of processes that preferentially remove mafic to ultramafic material from the continents. Such processes include lower crustal recycling (via density foundering or lower crustal subduction - e.g., relamination, Hacker et al., 2011, EPSL), generation of evolved melts via slab melting, and/or chemical weathering. Stable isotope systems document the influence of chemical weathering on the bulk crust composition: the oxygen isotope composition of the bulk crust is distinctly heavier than that of primary, mantle-derived melts (Simon and Lecuyer, 2005, G-cubed) and the Li isotopic composition of the bulk crust is distinctly lighter than that of mantle-derive melts (Teng et al., 2004, GCA; 2008, Chem. Geol.). Both signatures mark the imprint of chemical weathering on the bulk crust composition. Here, we use a simple mass balance model for lithium inputs and outputs from the continental crust to quantify the mass lost due to chemical weathering. We find that a minimum of 15%, a maximum of 60%, and a best estimate of ~40% of the original juvenile rock mass may have been lost via chemical weathering. The accumulated percentage of mass loss due to chemical weathering leads to an average global chemical weathering rate (CWR) of ~ 8×10^9 to 2×10^10 t/yr since 3.5 Ga, which is about an order of magnitude higher than the minimum estimates based on modern rivers (Gaillardet et al., 1999, Chem. Geol.). While we cannot constrain the exact portion of crustal mass loss via chemical weathering, given the uncertainties of the calculation, we can demonstrate that the weathering flux is non-zero. Therefore, chemical weathering must play a role in the evolution of the composition and mass of the continental crust.

Constraints on continental crustal mass loss via chemical weathering using lithium and its isotopes

NASA Astrophysics Data System (ADS)

Rudnick, R. L.; Liu, X. M.

2012-04-01

The continental crust has an "intermediate" bulk composition that is distinct from primary melts of peridotitic mantle (basalt or picrite). This mismatch between the "building blocks" and the "edifice" that is the continental crust points to the operation of processes that preferentially remove mafic to ultramafic material from the continents. Such processes include lower crustal recycling (via density foundering or lower crustal subduction - e.g., relamination, Hacker et al., 2011, EPSL), generation of evolved melts via slab melting, and/or chemical weathering. Stable isotope systems point to the influence of chemical weathering on the bulk crust composition: the oxygen isotope composition of the bulk crust is distinctly heavier than that of primary, mantle-derived melts (Simon and Lecuyer, 2005, G-cubed) and the Li isotopic composition of the bulk crust is distinctly lighter than that of mantle-derive melts (Teng et al., 2004, GCA; 2008, Chem. Geol.). Both signatures mark the imprint of chemical weathering on the bulk crust composition. Here, we use a simple mass balance model for lithium inputs and outputs from the continental crust to quantify the mass lost due to chemical weathering. We find that a minimum of 15%, a maximum of 60%, and a best estimate of ~40% of the original juvenile rock mass may have been lost via chemical weathering. The accumulated percentage of mass loss due to chemical weathering leads to an average global chemical weathering rate (CWR) of ~ 1×10^10 to 2×10^10 t/yr since 3.5 Ga, which is about an order of magnitude higher than the minimum estimates based on modern rivers (Gaillardet et al., 1999, Chem. Geol.). While we cannot constrain the exact portion of crustal mass loss via chemical weathering, given the uncertainties of the calculation, we can demonstrate that the weathering flux is non-zero. Therefore, chemical weathering must play a role in the evolution of the composition and mass of the continental crust.

Chromium Isotope Anomaly Scaling with Past Warming Episodes

NASA Astrophysics Data System (ADS)

Remmelzwaal, S.; O'Connor, L.; Preston, W.; Parkinson, I. J.; Schmidt, D. N.

2017-12-01

The recent expansion of oxygen minimum zones caused by anthropogenic global warming raises questions about the scale of this expansion with different emission scenarios. Ocean deoxygenation will impact marine ecosystems and fisheries demanding an assessment of the possible extent and intensity of deoxygenation. Here, we used past climate warming events to quantify a potential link between warming and the spread of oxygen minimum zones: including Ocean Anoxic Event (OAE) 1a, OAE 2 in the Cretaceous, the Palaeocene-Eocene Thermal Maximum (PETM), the Eocene Thermal Maximum 2 (ETM2), and Pleistocene glacial-interglacial cycles. We applied the emerging proxy of chromium isotopes in planktic foraminifera to assess redox changes during the PETM, ETM2, and Pleistocene and bulk carbonate for the OAEs. Both δ53Cr and chromium concentrations respond markedly during the PETM indicative of a reduction in dissolved oxygen concentrations caused by changes in ocean ventilation and associated warming [1]. A strong correlation between Δδ53Cr and benthic Δδ18O, a measure of the excursion size in both oxygen and chromium isotopes, suggest temperatures to be one of the main drivers of ocean deoxygenation in the past [1]. Chromium concentrations decrease during ETM2 and OAE1a, and, increase by 4.5 ppm over the Plenus Cold Event during OAE2, which suggests enhanced seafloor ventilation. [1] Remmelzwaal, S.R.C., Dixon, S., Parkinson, I.J., Schmidt, D.N., Monteiro, F.M., Sexton, P., Fehr, M., Peacock, C., Donnadieu, Y., James, R.H., in review. Ocean deoxygenation during the Palaeocene-Eocene Thermal Maximum. EPSL.

The role of stable isotopes in understanding rainfall ...

EPA Pesticide Factsheets

The isotopic composition of water transmitted by the canopy as throughfall or stemflow reflects important hydrologic processes occurring in the canopy. A synthesis of the literature shows that complex spatiotemporal variations of isotopic composition are created by canopy interception. As a whole, the studies suggest a set of controlling factors including fractionation, exchange among liquid and vapor phase water, and spatiotemporal redistribution along varying canopy flowpaths. However, our limited understanding of physical processes and water routing in the canopy limits the ability to discern all details for predicting interception isotope effects. We suggest that the isotopic composition of throughfall and stemflow may be the key to improve our understanding of water storage and transport in the canopy, similar to how isotopic analysis contributed to progress in our understanding of watershed runoff processes. While interception isotope effects have largely been studied under the premise that they are a source of error, previous works also indicate a wide range of possible interactions that intercepted water may have with the canopy and airspace. We identify new research questions that may be answered by stable isotopes as a path forward in examining and generalizing small-scale interception processes that could facilitate integration of interception into watershed ecohydrological concepts. Evaporation from forest canopies (interception loss) is a prominent

Advances and limitations on interpreting the erosional record from isotopic analysis of single detrital mineral grains

NASA Astrophysics Data System (ADS)

Parrish, Randall

2010-05-01

The analysis of provenance of clastic sediments is useful for reconstructing the characteristics and rates of exhumation of source areas, and sometimes placing minimum age constraints on depositional age. Due largely to increased availability and ease of access to LA-ICP-MS instrumentation, the analysis of provenance using single detrital accessory minerals has grown very rapidly over recent years. With this however is a culture of casual users who may not fully appreciate subtleties of measurement and isotope interpretation. The isotopic provenance literature is dominated by zircon-centric studies that use U-Pb dating and Hf isotope measurements of single zircons, but unfortunately an increasing number of these studies appear to lack sufficient understanding of U-Pb and Hf systematics; misleading interpretations are increasingly common. The inherent information contained in detrital accessory minerals is potentially immense, scientifically, but comprehensive interpretations attempting to reconstruct the geological make-up and evolution of sources require dating of multiple types of accessory minerals (i.e. zircon, titanite, monazite, garnet inclusions, micas, allanite, rutile, apatite) by various methods (U-Pb, fission track, Ar-Ar…) at times accompanied by isotope geochemical data (Lu-Hf, Sm-Nd, Rb-Sr) of phases where Sr, Hf, or REE comprise a major element (≥0.5%). Many approaches have been demonstrated but the mix of methodologies needs to be tailored to the problem, in view of the variable effort and expense needed to acquire good datasets. To date there are few comprehensive multi-mineral, multi-isotope system applications, and too many studies that follow a prescriptive cookbook that lacks innovation and fails to address a problem. The field needs to focus effort on the approaches that can solve a problem well rather than doing either just the easy methods or too many methods only moderately well. Zircon studies require strategies that reduce or eliminate discordance, collect sufficient data on each grain to make a robust age interpretation, improve accuracy of data by more attention to standards and uncertainties, can analyze thin overgrowths that reveal the magmatic or metamorphic age, and minimize sample consumption, not an easy task for the vast majority of laboratories doing provenance applications. Detrital monazite, monazite-in garnet, titanite and rutile can reveal much of the higher temperature metamorphic time-temperature path, and coupled U-Pb and fission track studies of single zircon and apatite grains can be useful for determining lower temperature exhumation rates. Isotope geochemistry (Hf-Nd-Sr-O) is more time consuming but can be pivotal to distinguish subtle differences in sources and to test specific hypotheses. Examples of improved methods and applications will be presented to illustrate the presentation.

Isotope fractionation during the anaerobic consumption of acetate by methanogenic and sulfate-reducing microorganisms

NASA Astrophysics Data System (ADS)

Gövert, D.; Conrad, R.

2009-04-01

During the anaerobic degradation of organic matter in anoxic sediments and soils acetate is the most important substrate for the final step in production of CO2 and/or CH4. Sulfate-reducing bacteria (SRB) and methane-producing archaea both compete for the available acetate. Knowledge about the fractionation of 13C/12C of acetate carbon by these microbial groups is still limited. Therefore, we determined carbon isotope fractionation in different cultures of acetate-utilizing SRB (Desulfobacter postgatei, D. hydrogenophilus, Desulfobacca acetoxidans) and methanogens (Methanosarcina barkeri, M. acetivorans). Including literature values (e.g., Methanosaeta concilii), isotopic enrichment factors (epsilon) ranged between -35 and +2 permil, possibly involving equilibrium isotope effects besides kinetic isotope effects. The values of epsilon were dependent on the acetate-catabolic pathway of the particular microorganism, the methyl or carboxyl position of acetate, and the relative availability or limitation of the substrate acetate. Patterns of isotope fractionation in anoxic lake sediments and rice field soil seem to reflect the characteristics of the microorganisms actively involved in acetate catabolism. Hence, it might be possible using environmental isotopic information to determine the type of microbial metabolism converting acetate to CO2 and/or CH4.

Validation of GC-IRMS techniques for δ13C and δ2H CSIA of organophosphorus compounds and their potential for studying the mode of hydrolysis in the environment.

PubMed

Wu, Langping; Kümmel, Steffen; Richnow, Hans H

2017-04-01

Compound-specific stable isotope analysis (CSIA) is among the most promising tools for studying the fate of organic pollutants in the environment. However, the feasibility of multidimensional CSIA was limited by the availability of a robust method for precise isotope analysis of heteroatom-bearing organic compounds. We developed a method for δ 13 C and δ 2 H analysis of eight organophosphorus compounds (OPs) with different chemical properties. In particular, we aimed to compare high-temperature conversion (HTC) and chromium-based HTC (Cr/HTC) units to explore the limitations of hydrogen isotope analysis of heteroatom-bearing compounds. Analysis of the amount dependency of the isotope values (linearity analysis) of OPs indicated that the formation of HCl was a significant isotope fractionation process leading to inaccurate δ 2 H analysis in HTC. In the case of nonchlorinated OPs, by-product formation of HCN, H 2 S, or PH 3 in HTC was observed but did not affect the dynamic range of reproducible isotope values above the limit of detection. No hydrogen-containing by-products were found in the Cr/HTC process by use of ion trap mass spectrometry analysis. The accuracy of gas chromatography - isotope ratio mass spectrometry was validated in comparison with elemental analyzer - isotope ratio mass spectrometry. Dual-isotope fractionation yielded Λ values of 0 ± 0 at pH 7, 7 ± 1 at pH 9, and 30 ± 6 at pH 12, indicating the potential of 2D CSIA to characterize the hydrolysis mechanisms of OPs. This is the first report on the combination of δ 2 H and δ 13 C isotope analysis of OPs, and this is the first study providing a systematic evaluation of HTC and Cr/HTC for hydrogen isotope analysis using OPs as target compounds. Graphical Abstract Comparison of δ 2 H measurement of non-chlorinated and chlorinated OPs via GC-Cr/HTC-IRMS and GC-HTC-IRMS system.

On the conversion of tritium units to mass fractions for hydrologic applications

USGS Publications Warehouse

Stonestrom, David A.; Andraski, Brian J.; Cooper, Clay A.; Mayers, Charles J.; Michel, Robert L.

2013-01-01

We develop a general equation for converting laboratory-reported tritium levels, expressed either as concentrations (tritium isotope number fractions) or mass-based specific activities, to mass fractions in aqueous systems. Assuming that all tritium is in the form of monotritiated water simplifies the derivation and is shown to be reasonable for most environmental settings encountered in practice. The general equation is nonlinear. For tritium concentrations c less than 4.5×1012 tritium units (TU) - i.e. specific tritium activities11 Bq kg-1 - the mass fraction w of tritiated water is approximated to within 1 part per million by w ≈ c×2.22293×10-18, i.e. the conversion is linear for all practical purposes. Terrestrial abundances serve as a proxy for non-tritium isotopes in the absence of sample-specific data. Variation in the relative abundances of non-tritium isotopes in the terrestrial hydrosphere produces a minimum range for the mantissa of the conversion factor of [2.22287; 2.22300].

Organic Rankine Kilowatt Isotope Power System. Final phase I report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1978-07-15

On 1 August 1975 under Department of Energy Contract EN-77-C-02-4299, Sundstrand Energy Systems commenced development of a Kilowatt Isotope Power System (KIPS) directed toward satisfying the higher power requirements of satellites of the 1980s and beyond. The KIPS is a /sup 238/PuO/sub 2/ fueled organic Rankine cycle turbine power system which will provide design output power in the range of 500 to 2000 W/sub (e)/ with a minimum of system changes. The principal objectives of the Phase 1 development effort were to: conceptually design a flight system; design a Ground Demonstration System (GDS) that is prototypic of the flight systemmore » in order to prove the feasibility of the flight system design; fabricate and assemble the GDS; and performance and endurance test the GDS using electric heaters in lieu of the isotope heat source. Results of the work performed under the Phase 1 contract to 1 July 1978 are presented.« less

Stable Isotope Applications for Understanding Shark Ecology in the Northeast Pacific Ocean.

PubMed

Reum, Jonathan C P; Williams, Gregory D; Harvey, Chris J

Stable isotopes are used to address a wide range of ecological questions and can help researchers and managers better understand the movement and trophic ecology of sharks. Here, we review how shark studies from the Northeast Pacific Ocean (NEP) have employed stable isotopes to estimate trophic level and diet composition and infer movement and habitat-use patterns. To date, the number of NEP shark studies that have used stable isotopes is limited, suggesting that the approach is underutilized. To aid shark researchers in understanding the strengths and limitations of the approach, we provide a brief overview of carbon and nitrogen stable isotope trophic discrimination properties (e.g., change in δ 15 N between predator and prey), tissue sample preparation methods specific to elasmobranchs, and methodological considerations for the estimation of trophic level and diet composition. We suggest that stable isotopes are a potentially powerful tool for addressing basic questions about shark ecology and are perhaps most valuable when combined and analysed with other data types (e.g., stomach contents, tagging data, or other intrinsic biogeochemical markers). © 2017 Elsevier Ltd. All rights reserved.

Hybrid fusion reactor for production of nuclear fuel with minimum radioactive contamination of the fuel cycle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Velikhov, E. P.; Kovalchuk, M. V.; Azizov, E. A., E-mail: Azizov-EA@nrcki.ru

2015-12-15

The paper presents the results of the system research on the coordinated development of nuclear and fusion power engineering in the current century. Considering the increasing problems of resource procurement, including limited natural uranium resources, it seems reasonable to use fusion reactors as high-power neutron sources for production of nuclear fuel in a blanket. It is shown that the share of fusion sources in this structural configuration of the energy system can be relatively small. A fundamentally important aspect of this solution to the problem of closure of the fuel cycle is that recycling of highly active spent fuel canmore » be abandoned. Radioactivity released during the recycling of the spent fuel from the hybrid reactor blanket is at least two orders of magnitude lower than during the production of the same number of fissile isotopes after the recycling of the spent fuel from a fast reactor.« less

A heat-pipe mechanism for volcanism and tectonics on Venus

NASA Technical Reports Server (NTRS)

Turcotte, D. L.

1989-01-01

A heat-pipe mechanism is proposed for the transport of heat through the lithosphere of Venus. This mechanism allows the crust and lithosphere on Venus to be greater than 150 km. thick. A thick basaltic crust on Venus is expected to transform eclogite at a depth of 60 to 80 km; the dense eclogite would contribute to lithospheric delamination that returns the crust to the interior of the planet completing the heat-pipe cycle. Topography and the associated gravity anomalies can be explained by Airy compensation of the thick crust. The principal observation that is contrary to this hypothesis is the mean age of the surface that is inferred from crater statistics; the minimum mean age is about 130 Myr and this implies an upper limit of 2 cubic kilometers per year for the surface volcanic flux. If the heat-pipe mechanism was applicable on the Earth in the Archean it would provide the thick lithosphere implied by isotopic data from diamonds.

WDR-PK-AK-018

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hollister, R

2009-08-26

Method - CES SOP-HW-P556 'Field and Bulk Gamma Analysis'. Detector - High-purity germanium, 40% relative efficiency. Calibration - The detector was calibrated on February 8, 2006 using a NIST-traceable sealed source, and the calibration was verified using an independent sealed source. Count Time and Geometry - The sample was counted for 20 minutes at 72 inches from the detector. A lead collimator was used to limit the field-of-view to the region of the sample. The drum was rotated 180 degrees halfway through the count time. Date and Location of Scans - June 1,2006 in Building 235 Room 1136. Spectral Analysismore » Spectra were analyzed with ORTEC GammaVision software. Matrix and geometry corrections were calculated using OR TEC Isotopic software. A background spectrum was measured at the counting location. No man-made radioactivity was observed in the background. Results were determined from the sample spectra without background subtraction. Minimum detectable activities were calculated by the Nureg 4.16 method. Results - Detected Pu-238, Pu-239, Am-241 and Am-243.« less

Properties of the surface snow in Princess Elizabeth Land, East Antarctica - climate and non-climate dependent variability of the surface mass balance and stable water isotopic composition

NASA Astrophysics Data System (ADS)

Vladimirova, D.; Ekaykin, A.; Lipenkov, V.; Popov, S. V.; Petit, J. R.; Masson-Delmotte, V.

2017-12-01

Glaciological and meteorological observations conducted during the past four decades in Princess Elizabeth Land, East Antarctica, are compiled. The database is used to investigate spatial patterns of surface snow isotopic composition and surface mass balance, including detailed information near subglacial lake Vostok. We show diverse relationships between snow isotopic composition and surface temperature. In the most inland part (elevation 3200-3400 m a.s.l.), surface snow isotopic composition varies independently from surface temperature, and is closely related to the distance to the open water source (with a slope of 0.98±0.17 ‰ per 100 km). Surface mass balance values are higher along the ice sheet slope, and relatively evenly distributed inland. The minimum values of snow isotopic composition and surface mass balance are identified in an area XX km southwestward from Vostok station. The spatial distribution of deuterium excess delineates regions influenced by the Indian Ocean and Pacific Ocean air masses, with Vostok area being situated close to their boundary. Anomalously high deuterium excess values are observed near Dome A, suggesting high kinetic fractionation for its moisture source, or specifically high post-deposition artifacts. The dataset is available for further studies such as the assessment of skills of general circulation or regional atmospheric models, and the search for the oldest ice.

Stable isotopes in water vapor and rainwater over Indian sector of Southern Ocean and estimation of fraction of recycled moisture.

PubMed

Rahul, P; Prasanna, K; Ghosh, Prosenjit; Anilkumar, N; Yoshimura, Kei

2018-05-15

Stable Hydrogen and Oxygen isotopic composition of water vapor, rainwater and surface seawater show a distinct trend across the latitude over the Southern Indian Ocean. Our observations on isotopic composition of surface seawater, water vapor and rainwater across a transect covering the tropical Indian Ocean to the regions of the Southern Ocean showed a strong latitudinal dependency; characterized by the zonal process of evaporation and precipitation. The sampling points were spread across diverse zones of SST, wind speed and rainfall regimes. The observed physical parameters such as sea surface temperature, wind speed and relative humidity over the oceanic regions were used in a box model calculation across the latitudes to predict the isotopic composition of water vapor under equilibrium and kinetic conditions, and compared with results from isotope enabled global spectral model. Further, we obtained the average fraction of recycled moisture across the oceanic transect latitudes as 13.4 ± 7.7%. The values of recycled fraction were maximum at the vicinity of the Inter Tropical Convergence Zone (ITCZ), while the minimum values were recorded over the region of subsidence and evaporation, at the Northern and Southern latitudes of the ITCZ. These estimates are consistent with the earlier reported recyling values.

Determination of plutonium-239, thorium-232, and natural uranium isotopic concentrations in biological samples using photofission track analysis

NASA Astrophysics Data System (ADS)

Parry, James Roswell

Fission track analysis (FTA) has many uses in the scientific community including but not limited to geological dating, neutron flux mapping, and dose reconstruction. The common method of fission for FTA is through neutrons from a nuclear reactor. This dissertation investigates the use of bremsstrahlung radiation produced from an electron linear accelerator to induce fission in FTA samples. This provides a means of simultaneously measuring the amount of Pu-239, U-nat, and Th-232 in a single sample. The benefit of measuring the three isotopes simultaneously is the possible elimination of costly and time consuming chemical processing for dose reconstruction samples. Samples containing the three isotopes were irradiated in two different bremsstrahlung spectra and a neutron spectrum to determine the amount of Pu-239, U-nat, and Th-232 in the samples. The reaction rate from the calibration samples and the counted fission tracks on the samples were used in determining the concentration of each isotope in the samples. The results were accurate to within a factor of two or three, showing that the method can work to predict the concentrations of multiple isotopes in a sample. The limitations of current accelerators and detectors limits the application of this specific procedure to higher concentrations of isotopes. The method detection limits for Pu-239, U-nat, and Th-232 are 20 pCi, 1 fCi, and 0.4 flCI respectively. Analysis of extremely low concentrations of isotopes would require the use of different detectors such as quartz due to the embrittlement encountered in the Lexan at high exposures. Cracking of the Texan detectors started to appear at a fluence of about 2 x 1018 electrons from the accelerator. This may be partly due to the beam stop not being an adequate thickness. The procedure is likely limited to specialty applications for the near term. However, with the world concerns of exposure to depleted uranium, this procedure may find applications in this area since it would be simple to adapt the procedure to depleted uranium detection.

Continental fragmentation and the strontium isotopic evolution of seawater.

NASA Astrophysics Data System (ADS)

Eric, H.; Jean Pascal, C.

2008-12-01

The time evolution of the strontium isotopic composition of seawater over the last 600 million years has the form of an asymmetric trough. The values are highest in the Cambrian and recent and lowest in the Jurassic. Superimposed on this trend are a number of smaller oscillations. The mechanisms responsible for these global isotopic fluctuations are subject to much debates. In order to get a quantitative picture of the changing paleogeography, we have characterized land-ocean distributions over Late Proterozoic to Phanerozoic times from measurement of perimeters and areas of continental fragments, based on paleomagnetic reconstructions. These measurements served to calculate geophysically constrainted breakup and scatter indexes of continental land masses from 0 to 1100 Ma (Cogne and Humler, 2008). Both parameters (strontium isotopic ratios of seawater and continental fragmentation indexes) are obviously highly correlated during the last 600 Ma. Low continental dispersion (that is large continental land masses) are associated with low seawater strontium isotopic ratios (that is when the continental inputs to oceans are minimum) and high continental dispersion (that is relatively small and widely distributed continents) with high seawater strontium isotopic ratios (that is when the continental input to ocean is maximum). Importantly, this first order evolution appears to conflict with the common idea of mountains erosion as a source for radiogenic strontium to oceans because high strontium isotopic ratios in seawater correspond to period of maximum dispersion of continents and not with period of general collisions. At first glance, it would seem that continental erosion increases with the degree of continental dispersion. Models showing that continental precipitation increases when continental masses are smaller and more widely dispersed and/or the length of continental margins available for rivers to carry continental material to oceans are thus favoured in order to resolve the paradox.

Insights into Wilson's Warbler migration from analyses of hydrogen stable-isotope ratios

Treesearch

Jeffrey F. Kelly; Viorel Atudorei; Zachary D. Sharp; Deborah M. Finch

2002-01-01

Our ability to link the breeding locations of individual passerines to migration stopover sites and wintering locations is limited. Stable isotopes of hydrogen contained in bird feathers have recently shown potential in this regard. We measured hydrogen stable-isotope ratios (deltaD) of feathers from breeding, migrating, and wintering Wilson's Warblers. Analyses...

Limitations of the isotopic composition of nitrates as a tracer of their origin

NASA Astrophysics Data System (ADS)

Kloppmann, Wolfram; Mayer, Bernhard; Otero, Neus; Sebilo, Mathieu; Gooddy, Daren; Lapworth, Dan; Surridge, Ben; Petelet Giraud, Emmanuelle; Flehoc, Christine; Baran, Nicole

2017-04-01

Nitrogen and oxygen isotopes are traditionally considered and frequently used as tracers of nitrate sources in watersheds used for drinking water production. The enrichment of synthetic nitrate-containing fertilizers in 18O due to the contribution of atmospheric oxygen in the production process confers a specific isotopic fingerprint to mineral fertilizers. In spite of the still widespread use on nitrate-containing synthetic fertilizers, their characteristic N and O isotope signatures are rarely unambiguously observed in nitrate-contaminated groundwater. We postulate, in line with Mengis et al. (2001), that fertilizer-derived nitrate is not directly and rapidly transferred to groundwater but rather retained in the soil-plant system as organic N and then mineralized and re-oxidized (termed the mineralization-immobilization turnover, MIT) thereby re-setting the oxygen isotope composition of nitrate and also changing its N isotope ratios. We show examples from watersheds on diverse alluvial/clastic and carbonate aquifers in eastern and northern France where, in spite of the use of mineral fertilizers, evidenced also through other isotopic tracers (boron isotopes), both N and O-isotope ratios are very homogeneous and compatible with nitrification of ammonium where 2/3 of oxygen is derived from soil water and 1/3 from atmospheric O2. These field data are corroborated by lysimeter data from Canada. Even if in areas where ammonium is derived from chemical fertilizers, N values still tend to be lower than in areas where ammonium is derived from manure/sewage, this is clearly a limitation to the dual isotope method (N, O) for nitrate source identification, but has important implications for the nitrogen mobility and residence time in soils amended with synthetic fertilizers (Sebilo et al., 2013). Mengis M., Walther U., Bernasconi S. M., Wehrli B. (2001) Limitations of Using δ18O for the Source Identification of Nitrate in Agricultural Soils. Environmental Science & Technology, 35, 1840-1844. Sebilo M., Mayer B., Nicolardot B., Pinay G., Mariotti A. (2013) Long-term fate of nitrate fertilizer in agricultural soils. Proceedings of the National Academy of Sciences of the United States of America, 110, 18185-18189.

Iron isotope fractionation during pyrite formation in a sulfidic Precambrian ocean analogue

DOE PAGES

Rolison, John M.; Stirling, Claudine H.; Middag, Rob; ...

2018-02-19

We present that the chemical response of the Precambrian oceans to rising atmospheric O 2 levels remains controversial. The iron isotope signature of sedimentary pyrite is widely used to trace the microbial and redox states of the ocean, yet the iron isotope fractionation accompanying pyrite formation in nature is difficult to constrain due to the complexity of the pyrite formation process, difficulties in translating the iron isotope systematics of experimental studies to natural settings, and insufficient iron isotope datasets for natural euxinic (i.e. anoxic and sulfidic) marine basins where pyrite formation occurs. Herein we demonstrate, that a large, permil-level shiftmore » in the isotope composition of dissolved iron occurs in the Black Sea euxinic water column during syngenetic pyrite formation. Specifically, iron removal to syngenetic pyrite gives rise to an iron isotope fractionation factor between Fe(II) and FeS 2 of 2.75 permil (‰), the largest yet reported for reactions under natural conditions that do not involve iron redox chemistry. These iron isotope systematics offer the potential to generate permil-level shifts in the sedimentary pyrite iron isotope record due to partial drawdown of the oceanic iron inventory. The implication is that the iron stable isotope signatures of sedimentary pyrites may record fundamental regime shifts between pyrite formation under sulfur-limited conditions and pyrite formation under iron-limited conditions. To this end, the iron isotope signatures of sedimentary pyrite may best represent the extent of euxinia in the past global ocean, rather than its oxygenation state. On this basis, the reinterpreted sedimentary pyrite Fe isotope record suggests a fundamental shift towards more sulfidic oceanic conditions coincident with the ‘Great Oxidation Event’ around 2.3 billion years ago. Importantly, this does not require the chemical state of the ocean to shift from mainly de-oxygenated to predominantly oxygenated in parallel with the permanent rise in atmospheric oxygen, contrary to other interpretations based on iron isotope systematics.« less

Iron isotope fractionation during pyrite formation in a sulfidic Precambrian ocean analogue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rolison, John M.; Stirling, Claudine H.; Middag, Rob

We present that the chemical response of the Precambrian oceans to rising atmospheric O 2 levels remains controversial. The iron isotope signature of sedimentary pyrite is widely used to trace the microbial and redox states of the ocean, yet the iron isotope fractionation accompanying pyrite formation in nature is difficult to constrain due to the complexity of the pyrite formation process, difficulties in translating the iron isotope systematics of experimental studies to natural settings, and insufficient iron isotope datasets for natural euxinic (i.e. anoxic and sulfidic) marine basins where pyrite formation occurs. Herein we demonstrate, that a large, permil-level shiftmore » in the isotope composition of dissolved iron occurs in the Black Sea euxinic water column during syngenetic pyrite formation. Specifically, iron removal to syngenetic pyrite gives rise to an iron isotope fractionation factor between Fe(II) and FeS 2 of 2.75 permil (‰), the largest yet reported for reactions under natural conditions that do not involve iron redox chemistry. These iron isotope systematics offer the potential to generate permil-level shifts in the sedimentary pyrite iron isotope record due to partial drawdown of the oceanic iron inventory. The implication is that the iron stable isotope signatures of sedimentary pyrites may record fundamental regime shifts between pyrite formation under sulfur-limited conditions and pyrite formation under iron-limited conditions. To this end, the iron isotope signatures of sedimentary pyrite may best represent the extent of euxinia in the past global ocean, rather than its oxygenation state. On this basis, the reinterpreted sedimentary pyrite Fe isotope record suggests a fundamental shift towards more sulfidic oceanic conditions coincident with the ‘Great Oxidation Event’ around 2.3 billion years ago. Importantly, this does not require the chemical state of the ocean to shift from mainly de-oxygenated to predominantly oxygenated in parallel with the permanent rise in atmospheric oxygen, contrary to other interpretations based on iron isotope systematics.« less

Iron isotope fractionation during pyrite formation in a sulfidic Precambrian ocean analogue

NASA Astrophysics Data System (ADS)

Rolison, John M.; Stirling, Claudine H.; Middag, Rob; Gault-Ringold, Melanie; George, Ejin; Rijkenberg, Micha J. A.

2018-04-01

The chemical response of the Precambrian oceans to rising atmospheric O2 levels remains controversial. The iron isotope signature of sedimentary pyrite is widely used to trace the microbial and redox states of the ocean, yet the iron isotope fractionation accompanying pyrite formation in nature is difficult to constrain due to the complexity of the pyrite formation process, difficulties in translating the iron isotope systematics of experimental studies to natural settings, and insufficient iron isotope datasets for natural euxinic (i.e. anoxic and sulfidic) marine basins where pyrite formation occurs. Herein we demonstrate, that a large, permil-level shift in the isotope composition of dissolved iron occurs in the Black Sea euxinic water column during syngenetic pyrite formation. Specifically, iron removal to syngenetic pyrite gives rise to an iron isotope fractionation factor between Fe(II) and FeS2 of 2.75 permil (‰), the largest yet reported for reactions under natural conditions that do not involve iron redox chemistry. These iron isotope systematics offer the potential to generate permil-level shifts in the sedimentary pyrite iron isotope record due to partial drawdown of the oceanic iron inventory. The implication is that the iron stable isotope signatures of sedimentary pyrites may record fundamental regime shifts between pyrite formation under sulfur-limited conditions and pyrite formation under iron-limited conditions. To this end, the iron isotope signatures of sedimentary pyrite may best represent the extent of euxinia in the past global ocean, rather than its oxygenation state. On this basis, the reinterpreted sedimentary pyrite Fe isotope record suggests a fundamental shift towards more sulfidic oceanic conditions coincident with the 'Great Oxidation Event' around 2.3 billion years ago. Importantly, this does not require the chemical state of the ocean to shift from mainly de-oxygenated to predominantly oxygenated in parallel with the permanent rise in atmospheric oxygen, contrary to other interpretations based on iron isotope systematics.

Calcium and Titanium Isotope Fractionation in CAIS: Tracers of Condensation and Inheritance in the Early Solar Protoplanetary Disk

NASA Technical Reports Server (NTRS)

Simon, J. I.; Jordan, M. K.; Tappa, M. J.; Kohl, I. E.; Young, E. D.

2016-01-01

The chemical and isotopic compositions of calcium-aluminum-rich inclusions (CAIs) can be used to understand the conditions present in the protoplantary disk where they formed. The isotopic compositions of these early-formed nebular materials are largely controlled by chemical volatility. The isotopic effects of evaporation/sublimation, which are well explained by both theory and experimental work, lead to enrichments of the heavy isotopes that are often exhibited by the moderately refractory elements Mg and Si. Less well understood are the isotopic effects of condensation, which limits our ability to determine whether a CAI is a primary condensate and/or retains any evidence of its primordial formation history.

Partial Least Squares Calibration Modeling Towards the Multivariate Limit of Detection for Enriched Isotopic Mixtures via Laser Ablation Molecular Isotopic Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harris, Candace; Profeta, Luisa; Akpovo, Codjo

The psuedo univariate limit of detection was calculated to compare to the multivariate interval. ompared with results from the psuedounivariate LOD, the multivariate LOD includes other factors (i.e. signal uncertainties) and the reveals the significance in creating models that not only use the analyte’s emission line but also its entire molecular spectra.

Geology and geochemistry of the Mammoth breccia pipe, Copper Creek mining district, southeastern Arizona: Evidence for a magmatic-hydrothermal origin

USGS Publications Warehouse

Anderson, E.D.; Atkinson, William W.; Marsh, T.; Iriondo, A.

2009-01-01

The Copper Creek mining district, southeastern Arizona, contains more than 500 mineralized breccia pipes, buried porphyry-style, copper-bearing stockworks, and distal lead-silver veins. The breccia pipes are hosted by the Copper Creek Granodiorite and the Glory Hole volcanic rocks. The unexposed Mammoth breccia pipe, solely recognized by drilling, has a vertical extent of 800 m and a maximum width of 180 m. The pipe consists of angular clasts of granodiorite cemented by quartz, chalcopyrite, bornite, anhydrite, and calcite. Biotite 40Ar/ 39Ar dates suggest a minimum age of 61.5??0.7 Ma for the host Copper Creek Granodiorite and 40Ar/39Ar dates on hydrothermal sericite indicate an age of 61.0??0.5 Ma for copper mineralization. Fluid inclusion studies suggest that a supercritical fluid with a salinity of approximately 10 wt.% NaCl equiv. condensed to a dilute aqueous vapor (1-2.8 wt.% NaCl equiv.) and a hypersaline brine (33.4-35.1 wt.% NaCl equiv.). Minimum trapping temperatures are 375??C and trapping depths are estimated at 2 km. Sulfur isotope fractionation of cogenetic anhydrite and chalcopyrite yields a temperature of mineralization of 469??25??C. Calculated oxygen and hydrogen isotope values for fluids in equilibrium with quartz and sericite range from 10.2??? to 13.4??? and -60??? to -39???, respectively, suggesting that the mineralizing fluid was dominantly magmatic. Evidence from the stable isotope and fluid inclusion analyses suggests that the fluids responsible for Cu mineralization within the Mammoth breccia pipe exsolved from a gray porphyry phase found at the base of the breccia pipe. ?? Springer-Verlag 2008.

Seasonal-Scale Dating of a Shallow Ice Core From Greenland Using Oxygen Isotope Matching Between Data and Simulation

NASA Astrophysics Data System (ADS)

Furukawa, Ryoto; Uemura, Ryu; Fujita, Koji; Sjolte, Jesper; Yoshimura, Kei; Matoba, Sumito; Iizuka, Yoshinori

2017-10-01

A precise age scale based on annual layer counting is essential for investigating past environmental changes from ice core records. However, subannual scale dating is hampered by the irregular intraannual variabilities of oxygen isotope (δ18O) records. Here we propose a dating method based on matching the δ18O variations between ice core records and records simulated by isotope-enabled climate models. We applied this method to a new δ18O record from an ice core obtained from a dome site in southeast Greenland. The close similarity between the δ18O records from the ice core and models enables correlation and the production of a precise age scale, with an accuracy of a few months. A missing δ18O minimum in the 1995/1996 winter is an example of an indistinct δ18O seasonal cycle. Our analysis suggests that the missing δ18O minimum is likely caused by a combination of warm air temperature, weak moisture transport, and cool ocean temperature. Based on the age scale, the average accumulation rate from 1960 to 2014 is reconstructed as 1.02 m yr-1 in water equivalent. The annual accumulation rate shows an increasing trend with a slope of 3.6 mm yr-1, which is mainly caused by the increase in the autumn accumulation rate of 2.6 mm yr-1. This increase is likely linked to the enhanced hydrological cycle caused by the decrease in Arctic sea ice area. Unlike the strong seasonality of precipitation amount in the ERA reanalysis data in the southeast dome region, our reconstructed accumulation rate suggests a weak seasonality.

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

NASA Astrophysics Data System (ADS)

Altabet, M. A.; Ryabenko, E.; Stramma, L.; Wallace, D. W. R.; Frank, M.; Grasse, P.; Lavik, G.

2012-07-01

Fixed nitrogen (N) loss to biogenic N2 in intense oceanic O2 minimum zones (OMZ) accounts for a large fraction of the global N sink and is an essential control on the ocean's N budget. However, major uncertainties exist regarding microbial pathways as well as net impact on the magnitude of N-loss and the ocean's overall N budget. Here we report the discovery of a N-loss hotspot in the Peru OMZ associated with a coastally trapped mesoscale eddy that is marked by an extreme N deficit matched by biogenic N2 production, high NO2- levels, and the highest isotope enrichments observed so far in OMZ's for the residual NO3-. High sea surface chlorophyll (SSC) in seaward flowing streamers provides evidence for offshore eddy transport of highly productive, inshore water. Resulting pulses in the downward flux of particles likely stimulated heterotrophic dissimilatory NO3- reduction and subsequent production of biogenic N2. The associated temporal/spatial heterogeneity of N-loss, mediated by a local succession of microbial processes, may explain inconsistencies observed among prior studies. Similar transient enhancements of N-loss likely occur within all other major OMZ's exerting a major influence on global ocean N and N isotope budgets.

Assessing compartmentalized flux in lipid metabolism with isotopes

DOE PAGES

Allen, Doug K.

2016-03-18

Metabolism in plants takes place across multiple cell types and within distinct organelles. The distributions equate to spatial heterogeneity; though the limited means to experimentally assess metabolism frequently involve homogenizing tissues and mixing metabolites from different locations.Most current isotope investigations of metabolism therefore lack the ability to resolve spatially distinct events. Recognition of this limitation has resulted in inspired efforts to advance metabolic flux analysis and isotopic labeling techniques. Though a number of these efforts have been applied to studies in central metabolism; recent advances in instrumentation and techniques present an untapped opportunity to make similar progress in lipid metabolismmore » where the use of stable isotopes has been more limited. These efforts will benefit from sophisticated radiolabeling reports that continue to enrich our knowledge on lipid biosynthetic pathways and provide some direction for stable isotope experimental design and extension of MFA. Evidence for this assertion is presented through the review of several elegant stable isotope studies and by taking stock of what has been learned from radioisotope investigations when spatial aspects of metabolism were considered. The studies emphasize that glycerolipid production occurs across several locations with assembly of lipids in the ER or plastid, fatty acid biosynthesis occurring in the plastid, and the generation of acetyl-CoA and glycerol-3-phosphate taking place at multiple sites. Considering metabolism in this context underscores the cellular and subcellular organization that is important to enhanced production of glycerolipids in plants. An attempt is made to unify salient features from a number of reports into a diagrammatic model of lipid metabolism and propose where stable isotope labeling experiments and further flux analysis may help address questions in the field.« less

Assessing compartmentalized flux in lipid metabolism with isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Doug K.

Metabolism in plants takes place across multiple cell types and within distinct organelles. The distributions equate to spatial heterogeneity; though the limited means to experimentally assess metabolism frequently involve homogenizing tissues and mixing metabolites from different locations.Most current isotope investigations of metabolism therefore lack the ability to resolve spatially distinct events. Recognition of this limitation has resulted in inspired efforts to advance metabolic flux analysis and isotopic labeling techniques. Though a number of these efforts have been applied to studies in central metabolism; recent advances in instrumentation and techniques present an untapped opportunity to make similar progress in lipid metabolismmore » where the use of stable isotopes has been more limited. These efforts will benefit from sophisticated radiolabeling reports that continue to enrich our knowledge on lipid biosynthetic pathways and provide some direction for stable isotope experimental design and extension of MFA. Evidence for this assertion is presented through the review of several elegant stable isotope studies and by taking stock of what has been learned from radioisotope investigations when spatial aspects of metabolism were considered. The studies emphasize that glycerolipid production occurs across several locations with assembly of lipids in the ER or plastid, fatty acid biosynthesis occurring in the plastid, and the generation of acetyl-CoA and glycerol-3-phosphate taking place at multiple sites. Considering metabolism in this context underscores the cellular and subcellular organization that is important to enhanced production of glycerolipids in plants. An attempt is made to unify salient features from a number of reports into a diagrammatic model of lipid metabolism and propose where stable isotope labeling experiments and further flux analysis may help address questions in the field.« less

Stable isotope tracers and exercise physiology: past, present and future.

PubMed

Wilkinson, Daniel J; Brook, Matthew S; Smith, Kenneth; Atherton, Philip J

2017-05-01

Stable isotope tracers have been invaluable assets in physiological research for over 80 years. The application of substrate-specific stable isotope tracers has permitted exquisite insight into amino acid, fatty-acid and carbohydrate metabolic regulation (i.e. incorporation, flux, and oxidation, in a tissue-specific and whole-body fashion) in health, disease and response to acute and chronic exercise. Yet, despite many breakthroughs, there are limitations to 'substrate-specific' stable isotope tracers, which limit physiological insight, e.g. the need for intravenous infusions and restriction to short-term studies (hours) in controlled laboratory settings. In recent years significant interest has developed in alternative stable isotope tracer techniques that overcome these limitations, in particular deuterium oxide (D 2 O or heavy water). The unique properties of this tracer mean that through oral administration, the turnover and flux through a number of different substrates (muscle proteins, lipids, glucose, DNA (satellite cells)) can be monitored simultaneously and flexibly (hours/weeks/months) without the need for restrictive experimental control. This makes it uniquely suited for the study of 'real world' human exercise physiology (amongst many other applications). Moreover, using D 2 O permits evaluation of turnover of plasma and muscle proteins (e.g. dynamic proteomics) in addition to metabolomics (e.g. fluxomics) to seek molecular underpinnings, e.g. of exercise adaptation. Here, we provide insight into the role of stable isotope tracers, from substrate-specific to novel D 2 O approaches, in facilitating our understanding of metabolism. Further novel potential applications of stable isotope tracers are also discussed in the context of integration with the snowballing field of 'omic' technologies. © 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.

The application of carbon isotope discrimination of charred wheat grains to reconstruct Late Holocene climate change and identify water management strategy in northwest China

NASA Astrophysics Data System (ADS)

Wang, W.; An, C.; Duan, F.; Zhao, Y.; Cao, Z.

2017-12-01

The AMS 14C dating and corresponding carbon stable isotope datum of charred wheat grains from archaeological sites in northwest China especially Hexi Corridor and Xinjiang have been collected widely to study its potential roles in reconstructing past climate change and identifying water management strategies through comparison with integrated regional humidity index, carbon isotope data of wheat grown under modern irrigation environment from study area and Mediterranean charred wheat carbon isotope data. The results suggest (1) carbon isotope discrimination values of charred wheat both in Hexi corridor and Xinjiang could respond well to regional moisture change, and there are also good positive correlation relationship between them (2) in contrast to consistent relationship between decreased carbon isotope discrimination values of charred wheat and dry climate condition, increased carbon isotope discrimination values does not represent wetter regional climate completely and may also reveal effects of human irrigation activities. The higher carbon isotope discrimination value of charred wheat which occurred in the Hexi Corridor from 4000 to 3850 a BP, 2100 a BP and 550 a BP and in Tianshan area of Xinjiang from 3730 a BP could be likely to be related with human activities (3) the carbon isotope discrimination value of charred wheat may have a certain limit which is generally not beyond 19‰. And this upper limit could influence its availability in reflecting abrupt change of precipitation/humidity especially rapid wetter trend. We conclude that carbon isotope analysis of charred wheat grains could be a good tool for reconstructing past climate change and identifying ancient irrigation practices.

Controls on the barium isotope compositions of marine sediments

NASA Astrophysics Data System (ADS)

Bridgestock, Luke; Hsieh, Yu-Te; Porcelli, Donald; Homoky, William B.; Bryan, Allison; Henderson, Gideon M.

2018-01-01

The accumulation of barium (Ba) in marine sediments is considered to be a robust proxy for export production, although this application can be limited by uncertainty in BaSO4 preservation and sediment mass accumulation rates. The Ba isotope compositions of marine sediments could potentially record insights into past changes in the marine Ba cycle, which should be insensitive to these limitations, enabling more robust interpretation of sedimentary Ba as a proxy. To investigate the controls on the Ba isotope compositions of marine sediments and their potential for paleo-oceanographic applications, we present the first Ba isotope compositions results for sediments, as well as overlying seawater depth profiles collected in the South Atlantic. Variations in Ba isotope compositions of the sediments predominantly reflect changes in the relative contributions of detrital and authigenic Ba sources, with open-ocean sediments constraining the isotope composition of authigenic Ba to be δ 138/134Ba ≈ + 0.1 ‰. This value is consistent with the average isotope composition inferred for sinking particulate Ba using simple mass balance models of Ba in the overlying water column and is hypothesized to reflect the removal of Ba from the upper water column with an associated isotopic fractionation of Δ diss-part 138/134Ba ≈ + 0.4 to +0.5. Perturbations to upper ocean Ba cycling, due to changes in export production and the supply of Ba via upwelling, should therefore be recorded by the isotope compositions of sedimentary authigenic Ba. Such insights will help to improve the reliable application of Ba accumulation rates in marine sediments as a proxy for past changes in export production.

Non-linear dynamics of stable carbon and hydrogen isotope signatures based on a biological kinetic model of aerobic enzymatic methane oxidation.

PubMed

Vavilin, Vasily A; Rytov, Sergey V; Shim, Natalia; Vogt, Carsten

2016-06-01

The non-linear dynamics of stable carbon and hydrogen isotope signatures during methane oxidation by the methanotrophic bacteria Methylosinus sporium strain 5 (NCIMB 11126) and Methylocaldum gracile strain 14 L (NCIMB 11912) under copper-rich (8.9 µM Cu(2+)), copper-limited (0.3 µM Cu(2+)) or copper-regular (1.1 µM Cu(2+)) conditions has been described mathematically. The model was calibrated by experimental data of methane quantities and carbon and hydrogen isotope signatures of methane measured previously in laboratory microcosms reported by Feisthauer et al. [ 1 ] M. gracile initially oxidizes methane by a particulate methane monooxygenase and assimilates formaldehyde via the ribulose monophosphate pathway, whereas M. sporium expresses a soluble methane monooxygenase under copper-limited conditions and uses the serine pathway for carbon assimilation. The model shows that during methane solubilization dominant carbon and hydrogen isotope fractionation occurs. An increase of biomass due to growth of methanotrophs causes an increase of particulate or soluble monooxygenase that, in turn, decreases soluble methane concentration intensifying methane solubilization. The specific maximum rate of methane oxidation υm was proved to be equal to 4.0 and 1.3 mM mM(-1) h(-1) for M. sporium under copper-rich and copper-limited conditions, respectively, and 0.5 mM mM(-1) h(-1) for M. gracile. The model shows that methane oxidation cannot be described by traditional first-order kinetics. The kinetic isotope fractionation ceases when methane concentrations decrease close to the threshold value. Applicability of the non-linear model was confirmed by dynamics of carbon isotope signature for carbon dioxide that was depleted and later enriched in (13)C. Contrasting to the common Rayleigh linear graph, the dynamic curves allow identifying inappropriate isotope data due to inaccurate substrate concentration analyses. The non-linear model pretty adequately described experimental data presented in the two-dimensional plot of hydrogen versus carbon stable isotope signatures.

Paleoclimate Reconstruction at Lamanai, Belize Using Oxygen-Isotope Tropical Dendrochronology

NASA Astrophysics Data System (ADS)

Prentice, A.; Webb, E. A.; White, C. D.; Graham, E.

2009-05-01

Tropical dendrochronology can be complicated because many trees growing in these areas lack distinct visible annual rings. However, the oxygen-isotope composition of wood growing in tropical regions can provide a record of seasonal fluctuations in the amount of precipitation even when visible rings are absent. Variations in the oxygen-isotope compositions of cellulose as the trees grow can be related to the relative timing of wet and dry seasons and used to identify periods of drought. In this study, the oxygen-isotope composition was determined for cellulose extracted from living trees at the site of Lamanai, Belize to assess the variation in oxygen-isotope values that result from heterogeneity within individual tree rings and seasonal fluctuations in amount of precipitation. In temperate regions, the latewood rings that form during periods of reduced growth are traditionally selected for oxygen-isotope analysis of cellulose because their oxygen-isotope compositions are more directly influenced by climate and precipitation during the growing season. However, in tropical isotope dendrochronology, when visible rings are present, detailed sampling of both the light coloured earlywood and the denser latewood is required. At Lamanai, a seasonal signal was evident in the oxygen- isotope composition of the cellulose when tree rings were sectioned in very small increments (approximately every mm), sub-sampling both earlywood and latewood. However, the visible rings did not always correspond with minimum or maximum oxygen-isotope values. As a result, the amplitude of the oxygen-isotope signal obtained by considering only latewood samples is smaller than that obtained from fine-increment sampling. Hence, the oxygen-isotope values of latewood samples alone did not provide accurate data for climate reconstruction. Multiple series of latewood samples extracted from different cross-sections of the same tree did not consistently show the same trends in oxygen isotope values, which can differ by up to 2 permil around the circumference of the same ring. This indicates that even when visible rings are present in tropical trees, the rings may not be annual or continuous. However, the amplitude of variation in the oxygen-isotope values of cellulose from both early and latewood can be related to seasonal signals across the modern tree rings. These signals will be compared to the oxygen-isotope composition of tree ring cellulose extracted from a wood sample excavated from an ancient tomb at the site of Lamanai to assess the preservation of the cellulose- isotope signal in this artefact. If similar oxygen-isotope patterns are preserved in ancient cellulose they can be used as a proxy to determine past climate conditions, such as those experienced by the ancient Maya populations in Belize.

Balancing the (carbon) budget: Using linear inverse models to estimate carbon flows and mass-balance 13C:15N labelling experiments in low oxygen sediments.

NASA Astrophysics Data System (ADS)

Hunter, William Ross; Van Oevelen, Dick; Witte, Ursula

2013-04-01

Over 1 million km2 of seafloor experience permanent low-oxygen conditions within oxygen minimum zones (OMZs). OMZs are predicted to grow as a consequence of climate change, potentially affecting oceanic biogeochemical cycles. The Arabian Sea OMZ impinges upon the western Indian continental margin at bathyal depths (150 - 1500m) producing a strong depth dependent oxygen gradient at the sea floor. The influence of the OMZ upon the short term processing of organic matter by sediment ecosystems was investigated using in situ stable isotope pulse chase experiments. These deployed doses of 13C:15N labeled organic matter onto the sediment surface at four stations from across the OMZ (water depth 540 - 1100 m; [O2] = 0.35 - 15 μM). In order to prevent experimentally anoxia, the mesocosms were not sealed. 13C and 15N labels were traced into sediment, bacteria, fauna and 13C into sediment porewater DIC and DOC. However, the DIC and DOC flux to the water column could not be measured, limiting our capacity to obtain mass-balance for C in each experimental mesocosm. Linear Inverse Modeling (LIM) provides a method to obtain a mass-balanced model of carbon flow that integrates stable-isotope tracer data with community biomass and biogeochemical flux data from a range of sources. Here we present an adaptation of the LIM methodology used to investigate how ecosystem structure influenced carbon flow across the Indian margin OMZ. We demonstrate how oxygen conditions affect food-web complexity, affecting the linkages between the bacteria, foraminifera and metazoan fauna, and their contributions to benthic respiration. The food-web models demonstrate how changes in ecosystem complexity are associated with oxygen availability across the OMZ and allow us to obtain a complete carbon budget for the stationa where stable-isotope labelling experiments were conducted.

Minimum length from quantum mechanics and classical general relativity.

PubMed

Calmet, Xavier; Graesser, Michael; Hsu, Stephen D H

2004-11-19

We derive fundamental limits on measurements of position, arising from quantum mechanics and classical general relativity. First, we show that any primitive probe or target used in an experiment must be larger than the Planck length lP. This suggests a Planck-size minimum ball of uncertainty in any measurement. Next, we study interferometers (such as LIGO) whose precision is much finer than the size of any individual components and hence are not obviously limited by the minimum ball. Nevertheless, we deduce a fundamental limit on their accuracy of order lP. Our results imply a device independent limit on possible position measurements.

Stable isotopic investigations of early development in extant and fossil chambered cephalopods I. Oxygen isotopic composition of eggwater and carbon isotopic composition of siphuncle organic matter in Nautilus

NASA Astrophysics Data System (ADS)

Crocker, Kimberley C.; DeNiro, Michael J.; Ward, Peter D.

1985-12-01

Eggwaters from the chambered cephalopod Nautilus are depleted in both 18O and deuterium relative to ambient seawater. Eggwaters from six other species, including the related chambered cephalopod Sepia, do not show such depletion. These observations indicate that the previously observed step towards more positive δ 18O values in calcium carbonate laid down after Nautilus hatches, relative to carbonate precipitated prior to hatching, can be explained by equilibration of the carbonate with water in the egg before hatching and with seawater after hatching. The presence of an oxygen isotope difference between eggwater and seawater for Nautilus and its absence for Sepia suggest that hatching will be recorded in the δ 18O values of shell carbonates for some but not all extinct and extant chambered cephalopods. The δ 13C values of the organic fraction of the siphuncle in Nautilus do not show any consistent pattern with regard to the time of formation before or after hatching. This observation suggests that the minimum in δ 13C values previously observed for calcium carbonate precipitated after Nautilus hatches is not caused by a change in food sources once the animal becomes free-swimming, as has been suggested.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cantone, M.C.

The interest in biokinetic studies is driven by problems related to the physiopathology of oligoelements, chemical elemental pollution and radioactive release in case of nuclear accidents. The application of stable isotopes as tracers in studies of trace elements in the area of nutritional and food science is particularly attractive and specifically if considering the investigations on the most radiosensitive age groups of the population and the repeated studies on healthy people for the assessment of the bioavailability of different compounds. A tracer method based on stable isotope administration, which combines the simultaneous use of two tracers and proton activation analysismore » is presented. A study aimed to obtain molybdenum biokinetic data in humans was performed. One tracer ({sup 96}Mo) was orally administered and another ({sup 95}Mo) was intravenously injected to two fasting volunteer subjects. Venous blood samples were withdrawn at different postinjection times. The concentration in plasma for both the isotopes was determined by measuring the intensities of the gamma-lines from the technetium radioisotopes produced via (p,n) reactions. In the adopted experimental conditions a minimum detectable concentration of 2 ng isotope/ml plasma was attained. The parameters describing molybdenum kinetics were obtained for the two individuals. Moreover, the investigation was repeated with different tracer amounts for one of the two subjects, in both fasting and non-fasting condition.« less

Rb-Sr and Sm-Nd Ages of Zagami DML and SR Isotopic Heterogeneity in Zagami

NASA Technical Reports Server (NTRS)

Nyquist, L.aurenceE.; Shih, C.-Y.; Reese, Y. D.

2010-01-01

Zagami contains lithologic heterogeneity suggesting that it did not form in a homogeneous, thick lava flow [1]. We have previously investigated the Sr and Nd isotopic systematics of Coarse-Grained (CG) and Fine-Grained (FG) lithologies described by [2]. Both appear to belong to Normal Zagami (NZ) [1,3], but their initial Sr-isotopic compositions differ [4,5]. Here we report new analyses of the Dark Mottled Lithology (DML, [3]) that show its age and initial Sr and Nd isotopic compositions to be identical within error limits with those of CG, but Sr initial isotopic compositions differ from those of FG.

Effects of Iron and Nitrogen Limitation on Sulfur Isotope Fractionation during Microbial Sulfate Reduction

PubMed Central

Ono, Shuhei; Bosak, Tanja

2012-01-01

Sulfate-reducing microbes utilize sulfate as an electron acceptor and produce sulfide that is depleted in heavy isotopes of sulfur relative to sulfate. Thus, the distribution of sulfur isotopes in sediments can trace microbial sulfate reduction (MSR), and it also has the potential to reflect the physiology of sulfate-reducing microbes. This study investigates the relationship between the availability of iron and reduced nitrogen and the magnitude of S-isotope fractionation during MSR by a marine sulfate-reducing bacterium, DMSS-1, a Desulfovibrio species, isolated from salt marsh in Cape Cod, MA. Submicromolar levels of iron increase sulfur isotope fractionation by about 50% relative to iron-replete cultures of DMSS-1. Iron-limited cultures also exhibit decreased cytochrome c-to-total protein ratios and cell-specific sulfate reduction rates (csSRR), implying changes in the electron transport chain that couples carbon and sulfur metabolisms. When DMSS-1 fixes nitrogen in ammonium-deficient medium, it also produces larger fractionation, but it occurs at faster csSRRs than in the ammonium-replete control cultures. The energy and reducing power required for nitrogen fixation may be responsible for the reverse trend between S-isotope fractionation and csSRR in this case. Iron deficiency and nitrogen fixation by sulfate-reducing microbes may lead to the large observed S-isotope effects in some euxinic basins and various anoxic sediments. PMID:23001667

Regional pattern of snow characteristics around Antarctic Lake Vostok

NASA Astrophysics Data System (ADS)

Vladimirova, Diana; Ekaykin, Alexey; Popov, Sergey; Shibaev, Yuriy; Kozachek, Anna; Lipenkov, Vladimir

2015-04-01

Since 1998 Russian Antarctic Expedition has organized several scientific traverses in the region of subglacial Lake Vostok mainly devoted to the radar echo and seismic sounding of the glacier and water (the results have been published elsewhere). Along with the geophysical studies, a number of glaciological investigations have been carried out: snow pit digging, installation of accumulation stakes, snow sampling to study the stable water isotope content. Here we for the first time present a synthesis of these works and demonstrate a series of maps that characterize the snow density, isotope content and accumulation rate the studied region. A general tendency of the snow accumulation rate and isotope content is a significant increase from south (south-west) to north (north-east) from 35 to 23 mm w.e. per year and from -53,3 ‰ to -57,3 ‰ for delta oxygen-18 respectively, which likely reflects the continental-scale pattern, i.e., increase from inland to the coast. Deuterium excess varies from 11,7 ‰ to 16,3 ‰ is negatively correlated with the isotope content, which is typical for central Antarctica. The snow density demonstrate different pattern: higher values offshore the lake (up to 0,356 g/cm^3), and lower values within the lake's shoreline (lower limit is 0,328 g/cm^3). We suggest that this is related to the katabatic wind activity: very flat nearly horizontal surface of the glacier above the lake is not favorable for the strong winds, which leads to lower surface snow density. Superimposed on the main trend is the regional pattern, namely, curved contour lines in the middle part of the lake. We suggest that it may be related to the local anomalies of the snow drift by wind. Indeed, on the satellite images of the lake one can easily see a snowdrift stretching from the lake's western shore downwind in the middle part of the lake. The isolines of delta oxygen-18 and deuterium excess become perpendicular to each other in the north part of the lake which also could be related to wind activity and different time of exposition snow on the surface which potentially leads to changing in d-excess and water isotopes ratio relation. Another interesting feature is the minimum values of snow accumulation rate and isotope content to the south-east from Vostok station. Before present, the Vostok's close vicinity was the record-holder, but now it is obvious that the pole of the lowest values of these parameters is somewhere else. This finding may be important in terms of the search of the oldest ice in frames of the IPICS "1.5Ma" project.

Using MASHA+TIMEPIX Setup for Registration Beta Decay Isotopes Produced in Heavy Ion Induced Reactions

NASA Astrophysics Data System (ADS)

Rodin, A. M.; Belozerov, A. V.; Chernysheva, E. V.; Dmitriev, S. N.; Gulyaev, A. V.; Gulyaeva, A. V.; Itkis, M. G.; Novoselov, A. S.; Oganessian, Yu. Ts.; Salamatin, V. S.; Stepantsov, S. V.; Vedeneev, V. Yu.; Yukhimchuk, S. A.; Krupa, L.; Granja, C.; Pospisil, S.; Kliman, J.; Motycak, S.; Sivacek, I.

2015-06-01

Radon and mercury isotopes were produced in multi nucleon transfer (48Ca + 232Th) and complete fusion (48Ca + naturalNd) reactions, respectively. The isotopes with given masses were detected using two detectors: a multi-strip detector of the well-type (made in CANBERRA) and a position-sensitive quantum counting hybrid pixel detector of the TIMEPIX type. The isotopes implanted into the detectors then emit alpha- and betaparticles until reaching the long lived isotopes. The position of the isotopes, the tracks, the time and energy of beta-particles were measured and analyzed. A new software for the particle recognition and data analysis of experimental results was developed and used. It was shown that MASHA+ TIMEPIX setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

O and C stable isotopes in cryogenic cave calcite (CCC) - possible proxy for past climate changes

NASA Astrophysics Data System (ADS)

-Andreea, Badaluta Carmen; Ersek, Vasile; Piotrowska, Natalia; Persoiu, Aurel

2017-04-01

Perennial ice deposits in caves host various proxies of past climate variability, most notable, the isotopic composition of ice, which has been shown to reflect, generally, the temperature outside the cave during the formation of ice (usually, autumn though spring). This ice forms by the freezing of water, water that contains large amounts of dissolved calcium carbonate. The freezing is accompanied by degassing of CO2, and precipitation of cryogenic cave calcite (CCC) under strong kinetic conditions. These kinetic processes could lead to the alteration of the original putative climatic signal carried by the isotopic composition of CCC. Here, we present a possibly climatic explanation of the isotopic composition of CCC from a 1000 years old cave ice deposit from Scărișoara Ice Cave (SIC) in Romania, Eastern Europe. In a 7 m core from the Great Hall of SIC we have analyzed the isotopic composition of the water (oxygen and hydrogen) and CCC (oxygen and carbon) from individual ice layers in the core, as well as that of precipitation , outside the cave. The isotopic composition of precipitation from the cave area varies between -3.6 ‰ for δˡ⁸O and -22 ‰ for δ2H in summer, and -17.8 ‰ for δˡ⁸O and -22 ‰ for δ2H in winter, with mean values of -9.1 ‰ for δˡ⁸O and -62 ‰ for δ2H. A positive correlation between air temperature and the isotopic composition of precipitation, as well as drip water in the cave has been found. The mean values in the ice core during the past 1000 years are -10.3‰ for δ18O and -71 ‰ for δ2H. The water isotopic values in the ice core show low values up to 900 AD, higher values between 900 and 1300 AD (Medieval Warm Period, MWP), and again lower values after 1300 AD (Little Ice Age, LIA), reaching their minimum after 1800 AD. The isotopic composition of CCC shows slightly higher values in the MWP and lower in LIA, possibly suggesting a climatic influence. Modern observations are too short to be able to calibrate this putative signal. Further, clumped isotope thermometry has shown that the kinetic fractionation that dominates during the freezing of water leads to unusual reconstructed formative temperature: +20°C. However, δˡ3C and δˡ⁸O values in CCC have higher values for samples from the MWP than those from the LIA. CCC results from the deposition of CaCO3 from Ca(CO3)2. The main source of CO2 to form carbonic acid is soil CO2, produced by root respiration. Previous studies have shown that δˡ⁸O of this CO2 is in equilibrium with the δˡ⁸O of water, so that the higher (lower) δˡ⁸O values of CCC could reflect warmer (colder) conditions during the MPW (LIA). The interpretation of δˡ3C values of CCC is less straightforward. Higher δˡ3C values in soil CO2 are determined by moisture limitation on plants, either due to low moisture or higher evaporative conditions. While the MWP was warmer in the study area, conflicting data exists on precipitation, with studies suggesting both drier and wetter conditions, so that is difficult to interpret our carbon isotope data. Apart from the direct climatic influence, the depth of soil could have also played a part, as deeper soils, as expected under birch forests that dominated during the MWP, would have had more enrichment in the heavy isotopes with depth, than the thiner soils of the LIA (formed under mostly spruce forests). Further, drought/higher temperatures could also influence the kinetics of the reaction, which can be large enough to overprint any soil signal in δˡ3C.

Planetary Accretion, Oxygen Isotopes and the Central Limit Theorem

NASA Technical Reports Server (NTRS)

Nuth, Joseph A., III; Hill, Hugh G. M.; Vondrak, Richard R. (Technical Monitor)

2001-01-01

The accumulation of presolar dust into increasingly larger aggregates (CAIs and Chondrules, Asteroids, Planets) should result in a very drastic reduction in the numerical spread in oxygen isotopic composition between bodies of similar size, in accord with the Central Limit Theorem. Observed variations in oxygen isotopic composition are many orders of magnitude larger than would be predicted by a simple, random accumulation model that begins in a well-mixed nebula - no matter which size-scale objects are used as the beginning or end points of the calculation. This discrepancy implies either that some as yet unspecified process acted on the solids in the Solar Nebula to increase the spread in oxygen isotopic composition during each and every stage of accumulation or that the nebula was heterogeneous and maintained this heterogeneity throughout most of nebular history. Large-scale nebular heterogeneity would have significant consequences for many areas of cosmochemistry, including the application of some well-known isotopic systems to the dating of nebular events or the prediction of bulk compositions of planetary bodies on the basis of a uniform cosmic abundance.

Maximum reasonable radioxenon releases from medical isotope production facilities and their effect on monitoring nuclear explosions.

PubMed

Bowyer, Theodore W; Kephart, Rosara; Eslinger, Paul W; Friese, Judah I; Miley, Harry S; Saey, Paul R J

2013-01-01

Fission gases such as (133)Xe are used extensively for monitoring the world for signs of nuclear testing in systems such as the International Monitoring System (IMS). These gases are also produced by nuclear reactors and by fission production of (99)Mo for medical use. Recently, medical isotope production facilities have been identified as the major contributor to the background of radioactive xenon isotopes (radioxenon) in the atmosphere (Stocki et al., 2005; Saey, 2009). These releases pose a potential future problem for monitoring nuclear explosions if not addressed. As a starting point, a maximum acceptable daily xenon emission rate was calculated, that is both scientifically defendable as not adversely affecting the IMS, but also consistent with what is possible to achieve in an operational environment. This study concludes that an emission of 5 × 10(9) Bq/day from a medical isotope production facility would be both an acceptable upper limit from the perspective of minimal impact to monitoring stations, but also appears to be an achievable limit for large isotope producers. Copyright © 2012 Elsevier Ltd. All rights reserved.

On the trophic ecology of Gammaridea (Crustacea: Amphipoda) in coastal waters: A European-scale analysis of stable isotopes data

NASA Astrophysics Data System (ADS)

Mancinelli, Giorgio

2012-12-01

Gammaridean amphipods are found throughout a diverse range of coastal and brackish environments and are generally considered macrophagous herbivores/detritivores. While predation and cannibalism have been shown to be common in freshwater species, motivating a revision of the group functional role, only qualitative information is available on marine Gammaridea. In this study, a survey was conducted of the available literature on stable C and N isotopic signatures of macrophagous, fully aquatic Gammaridea and their potential basal resources in European brackish and coastal environments. The contribution of intra- and inter-specific predation to the signatures of gammarideans was verified by a mixing model procedure where the diet-tissue enrichment constant was not set a priori. Specifically, for each study included in the survey the minimum and maximum diet-tissue nitrogen enrichment factors (Δ15Nmin and Δ15Nmax) providing a non-zero solution were calculated for a range of carbon enrichment factors, assuming that both metrics would increasingly differ from the values expected for a single trophic level as predation and/or cannibalism increased in the diet of the consumer. The minimum enrichment factors Δ15Nmin estimated for a Δ13C of -2.6‰ and +0.5‰ were found to be independent from resource-related artefacts and provided the highest number of successful model runs. Δ15Nmin values were consistent with a diet based on living or decaying primary producers and not compatible with cannibalism or intra-guild predation. However, they showed a bimodal distribution and were on average far below the range found in the literature, matching the enrichment factors of gammarideans measured under laboratory conditions. These results are discussed considering the interaction of the distinctive isotopic features of basal resources in coastal habitats and the biology and ecology of gammaridean amphipods. Particular emphasis is placed on the high variability of nitrogen enrichment factors, and on their crucial role in attaining reliable results from isotopic models used for food web studies.

Solar wind noble gases and nitrogen in metal from lunar soil 68501

NASA Technical Reports Server (NTRS)

Becker, Richard H.; Pepin, Robert O.

1994-01-01

Noble gases and N were analyzed in handpicked metal separates from lunar soil 68501 by a combination of step-wise combustions and pyrolyses. Helium and Ne were found to be unfractionated with respect to one another when normalized to solar abundances, for both the bulk sample and for all but the highest temperature steps. However, they are depleted relative to Ar, Kr and Xe by at least a factor of 5. The heavier gases exhibit mass-dependent fractionation relative to solar system abundance ratios but appear unfractionated, both in the bulk metal and in early temperature steps, when compared to relative abundances derived from lunar ilmenite 71501 by chemical etching, recently put forward as representing the abundance ratios in solar wind. Estimates of the contribution of solar energetic particles (SEP) to the originally implanted solar gases, derived from a basic interpretation of He and Ne isotopes, yield values of about 10%. Analysis of the Ar isotopes requires a minimum of 20% SEP, and Kr isotopes, using our preferred composition for solar wind Kr, yield a result that overlaps both these values. It is possible to reconcile the data from these gases if significant loss of solar wind Ar, Kr and presumably Xe has occurred relative to the SEP component, most likely by erosive processes that are mass independent, although mass-dependent losses (Ar greater than Kr greater than Xe) cannot be excluded. If such losses did occur, the SEP contribution to the solar implanted gases must have been no more than a few percent. Nitrogen is a mixture of indigenous meteoritic N, whose isotopic composition is inferred to be relatively light, and implanted solar N, which has probably undergone diffusive redistribution and fractionation. If the heavy noble gases have not undergone diffusive loss, then N/Ar in the solar wind can be inferred to be at least several times the accepted solar ratio. The solar wind N appears, even after correction for fractionation effects, to have a minimum delta N-15 value equal to or greater than +150% and a more probable value equal to or greater than +200%.

Sulfur isotope variability of oceanic DMSP generation and its contributions to marine biogenic sulfur emissions

NASA Astrophysics Data System (ADS)

Oduro, Harry; Van Alstyne, Kathryn L.; Farquhar, James

2012-06-01

Oceanic dimethylsulfoniopropionate (DMSP) is the precursor to dimethylsulfide (DMS), which plays a role in climate regulation through transformation to methanesulfonic acid (MSA) and non-seasalt sulfate (NSS-SO42-) aerosols. Here, we report measurements of the abundance and sulfur isotope compositions of DMSP from one phytoplankton species (Prorocentrum minimum) and five intertidal macroalgal species (Ulva lactuca, Ulva linza, Ulvaria obscura, Ulva prolifera, and Polysiphonia hendryi) in marine waters. We show that the sulfur isotope compositions (δ34S) of DMSP are depleted in 34S relative to the source seawater sulfate by ∼1-3‰ and are correlated with the observed intracellular content of methionine, suggesting a link to metabolic pathways of methionine production. We suggest that this variability of δ34S is transferred to atmospheric geochemical products of DMSP degradation (DMS, MSA, and NSS-SO42-), carrying implications for the interpretation of variability in δ34S of MSA and NSS-SO42- that links them to changes in growth conditions and populations of DMSP producers rather than to the contributions of DMS and non-DMS sources.

Sub-micron Hard X-ray Fluorescence Imaging of Synthetic Elements

PubMed Central

Jensen, Mark P.; Aryal, Baikuntha P.; Gorman-Lewis, Drew; Paunesku, Tatjana; Lai, Barry; Vogt, Stefan; Woloschak, Gayle E.

2013-01-01

Synchrotron-based X-ray fluorescence microscopy (SXFM) using hard X-rays focused into sub-micron spots is a powerful technique for elemental quantification and mapping, as well as microspectroscopic measurement such as μ-XANES (X-ray absorption near edge structure). We have used SXFM to image and simultaneously quantify the transuranic element plutonium at the L3 or L2 edge as well as lighter biologically essential elements in individual rat pheochromocytoma (PC12) cells after exposure to the long-lived plutonium isotope 242Pu. Elemental maps reveal that plutonium localizes principally in the cytoplasm of the cells and avoids the cell nucleus, which is marked by the highest concentrations of phosphorus and zinc, under the conditions of our experiments. The minimum detection limit under typical acquisition conditions for an average 202 μm2 cell is 1.4 fg Pu/cell or 2.9 × 10−20 moles Pu/μm2, which is similar to the detection limit of K-edge SXFM of transition metals at 10 keV. Copper electron microscopy grids were used to avoid interference from gold X-ray emissions, but traces of strontium present in naturally occurring calcium can still interfere with plutonium detection using its Lα X-ray emission. PMID:22444530

Empirical calibration of the clinopyroxene-garnet magnesium isotope geothermometer and implications

NASA Astrophysics Data System (ADS)

Li, Wang-Ye; Teng, Fang-Zhen; Xiao, Yilin; Gu, Hai-Ou; Zha, Xiang-Ping; Huang, Jian

2016-07-01

The large equilibrium Mg isotope fractionation between clinopyroxene and garnet observed in eclogites makes it a potential high-precision geothermometer, but calibration of this thermometer by natural samples is still limited. Here, we report Mg isotopic compositions of eclogite whole rocks as well as Mg and O isotopic compositions of clinopyroxene and garnet separates from 16 eclogites that formed at different temperatures from the Dabie orogen, China. The whole-rock δ26Mg values vary from -1.20 to +0.10 ‰. Among them, 11 samples display limited δ26Mg variations from -0.36 to -0.17 ‰, similar to those of their protoliths. The mineral separates exhibit very different δ26Mg values, from -0.39 to +0.39 ‰ for clinopyroxenes and from -1.94 to -0.81 ‰ for garnets. The clinopyroxene-garnet Mg isotope fractionation (Δ26Mgclinopyroxene-garnet = δ26Mgclinopyroxene-δ26Mggarnet) varies from 1.05 to 2.15 ‰. The clinopyroxene-garnet O isotope fractionation (Δ18Oclinopyroxene-garnet = δ18Oclinopyroxene-δ18Ogarnet) varies from -1.01 to +0.98 ‰. Equilibrium Mg isotope fractionation between clinopyroxene and garnet in the investigated samples is selected based on both the δ26Mgclinopyroxene versus δ26Mggarnet plot and the state of O isotope equilibrium between clinopyroxene and garnet. The equilibrium Δ26Mgclinopyroxene-garnet and corresponding temperature data obtained in this study, together with those available so far in literatures for natural eclogites, are used to calibrate the clinopyroxene-garnet Mg isotope thermometer. This yields a function of Δ26Mgclinopyroxene-garnet = (0.99 ± 0.06) × 106/ T 2, where T is temperature in Kelvin. The refined function not only provides the best empirically calibrated clinopyroxene-garnet Mg isotope thermometer for precise constraints of temperatures of clinopyroxene- and garnet-bearing rocks, but also has potential applications in high-temperature Mg isotope geochemistry.

Use of alpha spectroscopy for conducting rapid surveys of transuranic activity on air sample filters and smears.

PubMed

Hayes, Robert B; Peña, Adan M; Goff, Thomas E

2005-08-01

This paper demonstrates the utility of a portable alpha Continuous Air Monitor (CAM) as a bench top scalar counter for multiple sample types. These include using the CAM to count fixed air sample filters and radiological smears. In counting radiological smears, the CAM is used very much like a gas flow proportional counter (GFPC), albeit with a lower efficiency. Due to the typically low background in this configuration, the minimum detectable activity for a 5-min count should be in the range of about 10 dpm which is acceptably below the 20 dpm limit for transuranic isotopes. When counting fixed air sample filters, the CAM algorithm along with other measurable characteristics can be used to identify and quantify the presence of transuranic isotopes in the samples. When the radiological control technician wants to take some credit from naturally occurring radioactive material contributions due to radon progeny producing higher energy peaks (as in the case with a fixed air sample filter), then more elaborate techniques are required. The techniques presented here will generate a decision level of about 43 dpm for such applications. The calibration for this application should alternatively be done using the default values of channels 92-126 for region of interest 1. This can be done within 10 to 15 min resulting in a method to rapidly evaluate air filters for transuranic activity. When compared to the 1-h count technique described by , the technique presented in the present work demonstrates a technique whereby more than two thirds of samples can be rapidly shown (within 10 to 15 min) to be within regulatory compliant limits. In both cases, however, spectral quality checks are required to insure sample self attenuation is not a significant bias in the activity estimates. This will allow the same level of confidence when using these techniques for activity quantification as is presently available for air monitoring activity quantification using CAMs.

Collectivity of light Ge and As isotopes

NASA Astrophysics Data System (ADS)

Corsi, A.; Delaroche, J.-P.; Obertelli, A.; Baugher, T.; Bazin, D.; Boissinot, S.; Flavigny, F.; Gade, A.; Girod, M.; Glasmacher, T.; Grinyer, G. F.; Korten, W.; Libert, J.; Ljungvall, J.; McDaniel, S.; Ratkiewicz, A.; Signoracci, A.; Stroberg, R.; Sulignano, B.; Weisshaar, D.

2013-10-01

Background: The self-conjugate nuclei of the A˜70 mass region display rapid shape evolution over isotopic or isotonic chains. Shape coexistence has been observed in Se and Kr isotopes reflecting the existence of deformed subshell gaps corresponding to different shell configurations. As and Ge isotopes are located halfway between such deformed nuclei and the Z=28 shell closure.Purpose: The present work aims at clarifying the low-lying spectroscopy of 66Ge and 67As, and providing a better insight into the evolution of collectivity in light even-even Ge and even-odd As isotopes.Methods: We investigate the low-lying levels and collectivity of the neutron deficient 67As and 66Ge through intermediate-energy Coulomb excitation, inelastic scattering, and proton knockout measurements. The experiment was performed using a cocktail beam of 68Se, 67As, and 66Ge nuclei at an energy of 70-80 MeV/nucleon. Spectroscopic properties of the low-lying states are compared to those calculated via shell model with the JUN45 interaction and beyond-mean-field calculations with the five-dimensional collective Hamiltonian method implemented using the Gogny D1S interaction. The structure evolution of the lower-mass Ge and As isotopes is discussed.Results: Reduced electric quadrupole transition probabilities B(E2) have been extracted from the Coulomb-excitation cross sections measured in 66Ge and 67As. The value obtained for the B(E2;01+→21+) in 66Ge is in agreement with a recent measurement, ruling out the existence of a minimum at N=34 in the B(E2) systematics as previously observed. New transitions have been found in 67As and were assigned to the decay of low-lying negative-parity states.

14 CFR 25.1523 - Minimum flight crew.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Minimum flight crew. 25.1523 Section 25.1523 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... Limitations § 25.1523 Minimum flight crew. The minimum flight crew must be established so that it is...

14 CFR 29.1523 - Minimum flight crew.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Minimum flight crew. 29.1523 Section 29.1523 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... Limitations § 29.1523 Minimum flight crew. The minimum flight crew must be established so that it is...

A Future Moon Mission: Curatorial Statistics on Regolith Fragments Applicable to Sample Collection by Raking

NASA Technical Reports Server (NTRS)

Allton, J. H.; Bevill, T. J.

2003-01-01

The strategy of raking rock fragments from the lunar regolith as a means of acquiring representative samples has wide support due to science return, spacecraft simplicity (reliability) and economy [3, 4, 5]. While there exists widespread agreement that raking or sieving the bulk regolith is good strategy, there is lively discussion about the minimum sample size. Advocates of consor-tium studies desire fragments large enough to support petrologic and isotopic studies. Fragments from 5 to 10 mm are thought adequate [4, 5]. Yet, Jolliff et al. [6] demonstrated use of 2-4 mm fragments as repre-sentative of larger rocks. Here we make use of cura-torial records and sample catalogs to give a different perspective on minimum sample size for a robotic sample collector.

Rate-dependent carbon and nitrogen kinetic isotope fractionation in hydrolysis of isoproturon.

PubMed

Penning, Holger; Cramer, Christopher J; Elsner, Martin

2008-11-01

Stable isotope fractionation permits quantifying contaminant degradation in the field when the transformation reaction is associated with a consistent isotope enrichment factor epsilon. When interpreted in conjunction with dual isotope plots, isotope fractionation is also particularly useful for elucidating reaction mechanisms. To assess the consistency of epsilon and dual isotope slopes in a two-step reaction, we investigated the abiotic hydrolysis of the herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) using a fragmentation method that allows measuring isotope ratios in different parts of the molecule. Carbon and nitrogen position-specific isotope fractionation, as well as slopes in dual isotope plots, varied linearly with rate constants k(obs) depending on the presence of buffers that mediate the initial zwitterion formation. The correlation can be explained by two consecutive reaction steps (zwitterion formation followed by dimethylamine elimination) each of which has a different kinetic isotope effect and may be rate-limiting. Intrinsic isotope effects for both steps, extracted from our kinetic data using a novel theoretical treatment, agree well with values computed from density functional calculations. Our study therefore demonstrates that more variable isotope fractionation may be observed in simple chemical reactions than commonly thought, but that consistent epsilon or dual isotope slopes may nonetheless be encountered in certain molecular fragments.

Measurements of galactic hydrogen and helium isotopes from 1978 through 1983

NASA Technical Reports Server (NTRS)

Evenson, P.; Kroeger, R.; Meyer, P.; Miller, D.

1985-01-01

The differential flux of the hydrogen and helium isotopes was measured using an instrument on the ISEE-3 spacecraft during solar quiet time periods from August 1978 through December 1983. These measurements cover the energy range from 26 MeV/nucleon through 138 MeV/nucleon for both H-1 and He-4, from 24 to 89 MeV/nucleon for H-2, and from 43 to 146 solar activity varied from near minimum to maximum conditions causing the observed flux of galactic cosmic rays to modulate by an order of magnitude. To describe the propagation in the galaxy, it was found that the standard leaky box approximation with an escape path length of 6.7 g/sq cms forms a self consistent model for the light cosmic ray nuclei at the observed energies.

Electrochemically controlled iron isotope fractionation

NASA Astrophysics Data System (ADS)

Black, Jay R.; Young, Edward D.; Kavner, Abby

2010-02-01

Variations in the stable isotope abundances of transition metals have been observed in the geologic record and trying to understand and reconstruct the physical/environmental conditions that produced these signatures is an area of active research. It is clear that changes in oxidation state lead to large fractionations of the stable isotopes of many transition metals such as iron, suggesting that transition metal stable isotope signatures could be used as a paleo-redox proxy. However, the factors contributing to these observed stable isotope variations are poorly understood. Here we investigate how the kinetics of iron redox electrochemistry generates isotope fractionation. Through a combination of electrodeposition experiments and modeling of electrochemical processes including mass-transport, we show that electron transfer reactions are the cause of a large isotope separation, while mass transport-limited supply of reactant to the electrode attenuates the observed isotopic fractionation. Furthermore, the stable isotope composition of electroplated transition metals can be tuned in the laboratory by controlling parameters such as solution chemistry, reaction overpotential, and solution convection. These methods are potentially useful for generating isotopically-marked metal surfaces for tracking and forensic purposes. In addition, our studies will help interpret stable isotope data in terms of identifying underlying electron transfer processes in laboratory and natural samples.

14 CFR 25.1513 - Minimum control speed.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Minimum control speed. 25.1513 Section 25.1513 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... Limitations § 25.1513 Minimum control speed. The minimum control speed V MC determined under § 25.149 must be...

14 CFR 25.1513 - Minimum control speed.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Minimum control speed. 25.1513 Section 25.1513 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT... Limitations § 25.1513 Minimum control speed. The minimum control speed V MC determined under § 25.149 must be...

Clinical value of dual-isotope fat absorption test system (FATS) using glycerol (/sup 125/I)trioleate and glycerol (/sup 75/Se)triether

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lembcke, B.; Loesler, A.C.; Caspary, W.F.

1986-08-01

In order to delineate the clinical value of a dual-isotope fat absorption test system (FATS) using glycerol (/sup 75/Se)triether as lipid-phase marker and glycerol (/sup 125/I)trioleate as the test lipid, fecal isotope ratios from single stools (and a 72-hr stool homogenate) were compared to quantitative fecal fat excretion. The study included 11 patients without and 24 patients with steatorrhea. With a figure of 0.8% as the upper limit of normal, the test was a reliable indicator of steatorrhea with 87.5% sensitivity and 81.8% specificity; efficiency was 85.7%. Related to a prevalence of steatorrhea of 45.9% as the mean value ofmore » 1269 consecutive 72-hr specimens investigated for steatorrhea during 1978-1982, the positive (negative) predictive value of the FATS is 80.3% (87.2%). With 2% as the upper limit of normal, no false positive results ensued. It is concluded that a two-step interpretation of the FATS (0.8% limit and 2% limit) may be regarded a valid qualitative index for steatorrhea. The FATS isotope ratio using single stools correlated well with FATS ratios in the 72-hr stool homogenates (r = 0.97). FATS therefore allows a convenient estimate of steatorrhea from measuring single stools. As a quantitative measure of fecal fat excretion, the FATS is unreliable.« less

Controls of Isotopic Patterns in Saprotrophic and Ectomycorrhizal Fungi

EPA Science Inventory

Isotopes of nitrogen (δ15N) and carbon (δ13C) in ectomycorrhizal and saprotrophic fungi contain important information about ecological functioning, but the complexity of physiological and ecosystem processes contributing to fungal carbon and nitrogen dynamics has limited our abil...

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

NASA Astrophysics Data System (ADS)

Altabet, M. A.; Ryabenko, E.; Stramma, L.; Wallace, D. W. R.; Frank, M.; Grasse, P.; Lavik, G.

2012-12-01

Fixed nitrogen (N) loss to biogenic N2 in intense oceanic O2 minimum zones (OMZ) accounts for a large fraction of the global N sink and is an essential control on the ocean's N-budget. However, major uncertainties exist regarding microbial pathways as well as net impact on the magnitude of N-loss and the ocean's overall N-budget. Here we report the discovery of a N-loss hotspot in the Peru OMZ associated with a coastally trapped mesoscale eddy that is marked by an extreme N-deficit matched by biogenic N2 production, high NO2- levels, and the highest isotope enrichments observed so far in OMZ's for the residual NO3-. High sea surface chlorophyll in seaward flowing streamers provides evidence for offshore eddy transport of highly productive, inshore water. Resulting pulses in the downward flux of particles likely stimulated heterotrophic dissimilatory NO3- reduction and subsequent production of biogenic N2 within the OMZ. A shallower biogenic N2 maximum within the oxycline is likely a feature advected by the eddy streamer from the shelf. Eddy-associated temporal-spatial heterogeneity of N-loss, mediated by a local succession of microbial processes, may explain inconsistencies observed among prior studies. Similar transient enhancements of N-loss likely occur within all other major OMZ's exerting a major influence on global ocean N and N isotope budgets.

Oxygen isotope geochemistry of mafic magmas at Mt. Vesuvius

NASA Astrophysics Data System (ADS)

Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano

2010-05-01

Pumice and scoria from different eruptive layers of Mt. Vesuvius volcanic products contain mafic minerals consisting of High-Fo olivine and Diopsidic Pyroxene. These phases were crystallized in unerupted trachibasaltic to tephritic magmas, and were brought to surface by large phonolitic/tephri-phonolitic (e.g. Avellino and Pompei) and/or of tephritic and phono-tephritic (Pollena) eruptions. A large set of these mm-sized crystals was accurately separated from selected juvenile material and measured for their chemical compositions (EPMA, Laser Ablation ICP-MS) and 18O/16O ratios (conventional laser fluorination) to constrain the nature and evolution of the primary magmas at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary melts during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). At Mt. Vesuvius, measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas. Trace element composition constrains the near primary nature of the phases. Published data on volatile content of melt inclusions hosted in these crystals reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth occurred in a reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali magmas from trachybasaltic melts. Accordingly, the δ18O variability and the trace element content of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. Low, nearly primitive δ18O values are observed for olivine from Pompeii eruption, although still above the range of typical mantle minerals. The δ18Oolivine and δ18Ocpxof the minerals from all the studied eruptions define variable degrees of carbonate interaction and magma crystallization for the different eruptions, and possibly within the same eruption, and show evidence of oxygen isotope equilibrium at high temperature. However, energy-constrained AFC model suggest that carbonate assimilation was limited. On the basis of our data, we suggest that interaction between magma and a fluxing, decarbonation-derived CO2 fluid may be partly accounted for the measured O-isotope compositions.

Hydraulic constraints modify optimal photosynthetic profiles in giant sequoia trees.

PubMed

Ambrose, Anthony R; Baxter, Wendy L; Wong, Christopher S; Burgess, Stephen S O; Williams, Cameron B; Næsborg, Rikke R; Koch, George W; Dawson, Todd E

2016-11-01

Optimality theory states that whole-tree carbon gain is maximized when leaf N and photosynthetic capacity profiles are distributed along vertical light gradients such that the marginal gain of nitrogen investment is identical among leaves. However, observed photosynthetic N gradients in trees do not follow this prediction, and the causes for this apparent discrepancy remain uncertain. Our objective was to evaluate how hydraulic limitations potentially modify crown-level optimization in Sequoiadendron giganteum (giant sequoia) trees up to 90 m tall. Leaf water potential (Ψ l ) and branch sap flow closely followed diurnal patterns of solar radiation throughout each tree crown. Minimum leaf water potential correlated negatively with height above ground, while leaf mass per area (LMA), shoot mass per area (SMA), leaf nitrogen content (%N), and bulk leaf stable carbon isotope ratios (δ(13)C) correlated positively with height. We found no significant vertical trends in maximum leaf photosynthesis (A), stomatal conductance (g s), and intrinsic water-use efficiency (A/g s), nor in branch-averaged transpiration (E L), stomatal conductance (G S), and hydraulic conductance (K L). Adjustments in hydraulic architecture appear to partially compensate for increasing hydraulic limitations with height in giant sequoia, allowing them to sustain global maximum summer water use rates exceeding 2000 kg day(-1). However, we found that leaf N and photosynthetic capacity do not follow the vertical light gradient, supporting the hypothesis that increasing limitations on water transport capacity with height modify photosynthetic optimization in tall trees.

Increasing the Accuracy in the Measurement of the Minor Isotopes of Uranium: Care in Selection of Reference Materials, Baselines and Detector Calibration

NASA Astrophysics Data System (ADS)

Poths, J.; Koepf, A.; Boulyga, S. F.

2008-12-01

The minor isotopes of uranium (U-233, U-234, U-236) are increasingly useful for tracing a variety of processes: movement of anthropogenic nuclides in the environment (ref 1), sources of uranium ores (ref 2), and nuclear material attribution (ref 3). We report on improved accuracy for U-234/238 and U-236/238 by supplementing total evaporation protocol TIMS measurement on Faraday detectors (ref 4)with multiplier measurement for the minor isotopes. Measurement of small signals on Faraday detectors alone is limited by noise floors of the amplifiers and accurate measurement of the baseline offsets. The combined detector approach improves the reproducibility to better than ±1% (relative) for the U-234/238 at natural abundance, and yields a detection limit for U-236/U-238 of <0.2 ppm. We have quantified contribution of different factors to the uncertainties associated with these peak jumping measurement on a single detector, with an aim of further improvement. The uncertainties in the certified values for U-234 and U-236 in the uranium standard NBS U005, if used for mass bias correction, dominates the uncertainty in their isotopic ratio measurements. Software limitations in baseline measurement drives the detection limit for the U-236/U-238 ratio. This is a topic for discussion with the instrument manufacturers. Finally, deviation from linearity of the response of the electron multiplier with count rate limits the accuracy and reproducibility of these minor isotope measurements. References: (1) P. Steier et al(2008) Nuc Inst Meth(B), 266, 2246-2250. (2) E. Keegan et al (2008) Appl Geochem 23, 765-777. (3) K. Mayer et al (1998) IAEA-CN-98/11, in Advances in Destructive and Non-destructive Analysis for Environmental Monitoring and Nuclear Forensics. (4) S. Richter and S. Goldberg(2003) Int J Mass Spectrom, 229, 181-197.

Expanding lipid proxies to the next dimension: Developing methods for determination of oxygen isotope ratios in plant waxes

NASA Astrophysics Data System (ADS)

Mason, P. R. D.; Roerdink, D. L.; Galic, A.; Martin, W.

2014-12-01

The Archean oceans are thought to have been depleted in sulfate, reflecting widespread anoxic conditions and limited input of oxidized sulfur species from atmospheric photolysis. This is supported by the paucity of sulfate-bearing minerals and the relatively limited mass-dependent sulfur isotope fractionation in the majority of the Archean geological record. An exception to this is the occurrence of barite deposits in the Palaeoarchean (3.5-3.2 Ga) which indicate spatial or temporal increases in sulfate concentration. The origin and extent of these enrichments remains controversial and has been difficult to assess due to limited and highly variable data. Here we compile an extensive new database of SIMS multiple sulfur isotope data for pyrite and barite from across the Barberton Greenstone Belt in South Africa in order to further investigate the extent and origin of any sulfate enrichment. Individual pyrites were measured with good stratigraphic and petrographic control. Pyrite δ56Fe was used to further delineate pyrite populations and pathways of pyrite formation. Our new sulfur isotope data support conventional models where a positive Δ33S was derived from heterogeneous photolytic elemental S, with negative Δ33S capturing a homogenized marine sulfate reservoir. Pyrite multiple S isotope data closely track the abundance of barite, suggesting that marine sulfate levels were generally low and that sulfate increases were sporadic and localized. We speculate that the subsequent Neoarchean scarcity was controlled by biological evolution.

In-situ Isotopic Analysis at Nanoscale using Parallel Ion Electron Spectrometry: A Powerful New Paradigm for Correlative Microscopy

NASA Astrophysics Data System (ADS)

Yedra, Lluís; Eswara, Santhana; Dowsett, David; Wirtz, Tom

2016-06-01

Isotopic analysis is of paramount importance across the entire gamut of scientific research. To advance the frontiers of knowledge, a technique for nanoscale isotopic analysis is indispensable. Secondary Ion Mass Spectrometry (SIMS) is a well-established technique for analyzing isotopes, but its spatial-resolution is fundamentally limited. Transmission Electron Microscopy (TEM) is a well-known method for high-resolution imaging down to the atomic scale. However, isotopic analysis in TEM is not possible. Here, we introduce a powerful new paradigm for in-situ correlative microscopy called the Parallel Ion Electron Spectrometry by synergizing SIMS with TEM. We demonstrate this technique by distinguishing lithium carbonate nanoparticles according to the isotopic label of lithium, viz. 6Li and 7Li and imaging them at high-resolution by TEM, adding a new dimension to correlative microscopy.

The natural radioactivity in some Nigerian foodstuffs

NASA Astrophysics Data System (ADS)

Olomo, James B.

1990-12-01

The average activity concentrations of seven locally produced food commodities that form the total diets of a baby, a teenager or an adult male in Nigeria were measured by means of a well-calibrated high-resolution lithium-drifted germanium (Ge(Li)) spectrometer system. The food commodities were collected at several centers such as a nuclear research center as well as metropolitan and industrial areas. The emission lines identified with reliable regularity belonged to the 238U and 232Th decay series. The other isotope is a non-related naturally occurring radionuclide, 40K. Average total specific-activity values of 7.29 ± 1.08, 6.27 ± 1.01 and 11.23 ± 1.64 Bq/kg for 238U, 232Th and 40K, respectively, were obtained for the seven food commodities studied. The food samples were also checked for fission-product residues ( 137Cs and 90Sr) from atmospheric weapons tests which are slowly being purged from the food chain. Their estimation revealed that they were below the minimum detectable limit determined at a two-standard deviation analytical error.

Role of (n,2n) reactions in transmutation of long-lived fission products

DOE Office of Scientific and Technical Information (OSTI.GOV)

Apse, V. A.; Kulikov, G. G., E-mail: ggkulikov@mephi.ru; Kulikov, E. G.

2016-12-15

The conditions under which (n,γ) and (n,2n) reactions can help or hinder each other in neutron transmutation of long-lived fission products (LLFPs) are considered. Isotopic and elemental transmutation for the main long-lived fission products, {sup 79}Se, {sup 93}Zr, {sup 99}Tc, {sup 107}Pd, {sup 126}Sn, {sup 129}I, and {sup 135}Cs, are considered. The effect of (n,2n) reactions on the equilibrium amount of nuclei of the transmuted isotope and the neutron consumption required for the isotope processing is estimated. The aim of the study is to estimate the influence of (n,2n) reactions on efficiency of neutron LLFP transmutation. The code TIME26 andmore » the libraries of evaluated nuclear data ABBN-93, JEF-PC, and JANIS system are applied. The following results are obtained: (1) The effect of (n,2n) reactions on the minimum number of neutrons required for transmutation and the equilibrium amount of LLFP nuclei is estimated. (2) It is demonstrated that, for three LLFP isotopes ({sup 126}Sn, {sup 129}I, and {sup 135}Cs), (n,γ) and (n,2n) reactions are partners facilitating neutron transmutation. The strongest effect of (n,2n) reaction is found for {sup 126}Sn transmutation (reduction of the neutron consumption by 49% and the equilibrium amount of nuclei by 19%).« less

Residence times and age distributions of spring waters at the Semmering catchment area, Eastern Austria, as inferred from tritium, CFCs and stable isotopes.

PubMed

Han, Liangfeng; Hacker, Peter; Gröning, Manfred

2007-03-01

The groundwater system in the mountainous area of Semmering, Austria, was studied by environmental tracers in several karst springs. The tracers used included stable isotopes ((18)O, (2)H), tritium ((3)H) and chlorofluorocarbons (CFCs). The tracers provided valuable information in regard to (1) the mean altitude of the spring catchment areas; (2) the residence time and age distribution of the spring waters; and (3) the interconnection of the springs to a sinkhole. The combination of the stable isotopic data and the topography/geology provided the estimates of the mean altitudes of the catchment areas. Based on the stable isotopic data the recharge temperature of the spring waters was estimated. The smoothing of precipitation's isotopic signal in spring discharge provided information on the minimum transit time of the spring waters. Due to short observation time, (3)H data alone cannot be used for describing the mean residence time of the karst waters. CFCs, though useful in recognizing the co-existence of young (post-1993) water with old (CFC-free) water, could not be used to resolve age distribution models. It is shown in this article, however, that the combined use of tritium and CFCs can provide a better assessment of models to account for different groundwater age distributions. In Appendix A, a simplified method for collecting groundwater samples for the analysis of CFCs is described. The method provides a real facilitation for fieldwork. Test data are given for this sampling method in regard to potential contamination by atmospheric CFCs.

Global climatic changes during the Devonian-Mississippian: Stable isotope biogeochemistry of brachiopods

NASA Astrophysics Data System (ADS)

Brand, Uwe

1989-12-01

A progressive trend towards heavier δ 13C values of Devonian-Mississippian brachiopods from North America, Europe, Afghanistan and Algeria probably reflects expansion of the terrestrestrial and/or marine biomass and/or burial of carbon in soils/sediments. Oceanic Productivity crises, based on perturbations in the overall δ 13C trend, are recognized for the Mid Givetian, Early Famennian, Late Kinderhookian, Late Osagean and Early and Late Meramecian. The Givetian productivity crisis was probably accompanied by massive overturn of biologically toxic deep-ocean water. Temperature data, adjusted for the possible secular variation of seawater, support the hypothesis of global greenhouse conditions for the Devonian (mean of 30°C, mean of 26°C if extrinsic data are deleted) and icehouse conditions for the Mississippian (mean of 17°C). During the Mid Givetian, Frasnian and Early Famennian calculated water temperatures for tropical epeiric seas were generally above the thermal threshold limit (˜ 38°C) of most marine invertebrates or epeiric seawater was characterized by unusually low salinities (˜ pp ppt) or a combination of the two. These elevated water temperatures and/or low salinities, in conjunction with the postulated productivity crises and overturning of toxic deep waters are considered prime causes for the biotic crisis of the Late Devonian. In addition, a presumed expanding oxygen-minimum zone and general anoxia in the oceans prevented shallow-water organisms from escaping these inhospitable conditions. Re-population of the tropical seas occurred, after either water temperatures had dropped below the thermal threshold limit and/or salinities were back to normal, and oceanic productivity had increased due to more vigorous oceanic circulation, sometime during the Mid-Late Famennian. Migration of eurythermal, shallow- and deeper-water organisms into the vacant niches of the shallow seas was possible because of, generally, slightly lower sea levels, but, more importantly of more restricted oxygen-minimum zone and generally reduced oceanic anoxia.

Static, Mixed-Array Total Evaporation for Improved Quantitation of Plutonium Minor Isotopes in Small Samples

NASA Astrophysics Data System (ADS)

Stanley, F. E.; Byerly, Benjamin L.; Thomas, Mariam R.; Spencer, Khalil J.

2016-06-01

Actinide isotope measurements are a critical signature capability in the modern nuclear forensics "toolbox", especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10-6) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Results are presented for small sample (~20 ng) applications involving a well-known plutonium isotope reference material, CRM-126a, and compared with traditional total evaporation methods.

Fuel preparation for use in the production of medical isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Policke, Timothy A.; Aase, Scott B.; Stagg, William R.

The present invention relates generally to the field of medical isotope production by fission of uranium-235 and the fuel utilized therein (e.g., the production of suitable Low Enriched Uranium (LEU is uranium having 20 weight percent or less uranium-235) fuel for medical isotope production) and, in particular to a method for producing LEU fuel and a LEU fuel product that is suitable for use in the production of medical isotopes. In one embodiment, the LEU fuel of the present invention is designed to be utilized in an Aqueous Homogeneous Reactor (AHR) for the production of various medical isotopes including, butmore » not limited to, molybdenum-99, cesium-137, iodine-131, strontium-89, xenon-133 and yttrium-90.« less

Seawater sulfate reduction and sulfur isotope fractionation in basaltic systems: interaction of seawater with fayalite and magnetite at 200–350°C

USGS Publications Warehouse

Shanks, Wayne C.; Bischoff, James L.; Rosenbauer, Robert J.

1981-01-01

Systematics of sulfur isotopes in the 250 and 350°C experiments indicate that isotopic equilibrium is reached, and can be modeled as a Rayleigh distillation process. Isotopic composition of hydrothermally produced H2S in natural systems is strongly dependent upon the seawater/basalt ratio in the geothermal system, which controls the relative sulfide contributions from the two important sulfur sources, seawater sulfate and sulfide phases in basalt. Anhydrite precipitation during geothermal heating severely limits sulfate ingress into high temperature interaction zones. Quantitative sulfate reduction can thus be accomplished without producing strongly oxidized rocks and resultant sulfide sulfur isotope values represent a mixture of seawater and basaltic sulfur.

Static, Mixed-Array Total Evaporation for Improved Quantitation of Plutonium Minor Isotopes in Small Samples.

PubMed

Stanley, F E; Byerly, Benjamin L; Thomas, Mariam R; Spencer, Khalil J

2016-06-01

Actinide isotope measurements are a critical signature capability in the modern nuclear forensics "toolbox", especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10(-6)) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Results are presented for small sample (~20 ng) applications involving a well-known plutonium isotope reference material, CRM-126a, and compared with traditional total evaporation methods. Graphical Abstract ᅟ.

The Bess Investigation of the Origin of Cosmic-ray Antiprotons and Search for Cosmological Antimatter

NASA Technical Reports Server (NTRS)

Mitchell, John; Yamamoto, Akira; Yoshimura, Koji; Makida, Yasuhiro; Matsuda, Shinya; Hasegawa, Masaya; Horikoshi, Atsushi; Tanaka,Ken-ichi; Suzuki, Junichi; Nishimura, Jun;

A Noninvasive Isotopic Approach to Estimate the Bone Lead Contribution to Blood in Children: Implications for Assessing the Efficacy of Lead Abatement

PubMed Central

Gwiazda, Roberto; Campbell, Carla; Smith, Donald

2005-01-01

Lead hazard control measures to reduce children’s exposure to household lead sources often result in only limited reductions in blood lead levels. This may be due to incomplete remediation of lead sources and/or to the remobilization of lead stores from bone, which may act as an endogenous lead source that buffers reductions in blood lead levels. Here we present a noninvasive isotopic approach to estimate the magnitude of the bone lead contribution to blood in children following household lead remediation. In this approach, lead isotopic ratios of a child’s blood and 5-day fecal samples are determined before and after a household intervention aimed at reducing the child’s lead intake. The bone lead contribution to blood is estimated from a system of mass balance equations of lead concentrations and isotopic compositions in blood at the different times of sample collection. The utility of this method is illustrated with three cases of children with blood lead levels in the range of 18–29 μg/dL. In all three cases, the release of lead from bone supported a substantial fraction of the measured blood lead level postintervention, up to 96% in one case. In general, the lead isotopic compositions of feces matched or were within the range of the lead isotopic compositions of the household dusts with lead loadings exceeding U.S. Environmental Protection Agency action levels. This isotopic agreement underscores the utility of lead isotopic measurements of feces to identify household sources of lead exposure. Results from this limited number of cases support the hypothesis that the release of bone lead into blood may substantially buffer the decrease in blood lead levels expected from the reduction in lead intake. PMID:15626656

Correcting speleothem oxygen isotopic variations for growth-rate controlled kinetic fractionation effects

NASA Astrophysics Data System (ADS)

Stoll, Heather; Moreno, Ana; Cacho, Isabel; Mendez Vicence, Ana; Gonzalez Lemos, Saul; Pirla Casasayas, Gemma; Cheng, Hai; Wang, Xianfeng; Edwards, R. Lawrence

2015-04-01

The oxygen isotopic signature may be the most widely used climate indicator in stalagmites, but recent experimental and theoretical studies indicate the potential for kinetic fractionation effects which may be significant, especially in situations where the primary signal from rainfall isotopic composition and cave temperature is limited to a few permil. Here we use a natural set of stalagmites to illustrate the magnitude of such effects and the potential for deconvolving kinetic signals from the primary temperature and rainfall signals. We compare isotopic records from 6 coeval stalagmites covering the interval 140 to 70 ka, from two proximal caves in NW Spain which experienced the same primary variations in temperature and rainfall d18O, but exhibit a large range in growth rates and temporal trends in growth rate. Stalagmites growing at faster rates near 50 microns/year have oxygen isotopic ratios more than 1 permil more negative than coeval stalagmites with very slow (5 micron/year) growth rates. Because growth rate variations also occur over time within any given stalagmite, the measured oxygen isotopic time series for a given stalagmite includes both climatic and kinetic components. Removal of the kinetic component of variation in each stalagmite, based on the dependence of the kinetic component on growth rate, is effective at distilling a common temporal evolution among the oxygen isotopic records of the multiple stalagmites. However, this approach is limited by the quality of the age model. For time periods characterized by very slow growth and long durations between dates, the presence of crypto-hiatus may result in average growth rates which underestimate the instantaneous speleothem deposition rates and which therefore underestimate the magnitude of kinetic effects. We compare the composite corrected oxygen isotopic record with other records of the timing of glacial inception in the North Atlantic realm.

49 CFR Appendix A to Part 172 - Office of Hazardous Materials Transportation Color Tolerance Charts and Tables

Code of Federal Regulations, 2010 CFR

2010-10-01

... .3308 .2328 Dark 10.0P 4.0/10 12.00 .3306 .2162 1 Maximum chroma is not limited. 2 For the colors green and purple, the minimum saturation (chroma) limits for porcelain enamel on metal are lower than for most other surface coatings. Therefore, the minimum chroma limits of these two colors as displayed on...

40 CFR Table 11 to Subpart Xxxx of... - Minimum Data for Continuous Compliance With the Emission Limits for Tire Cord Production Affected...

Code of Federal Regulations, 2010 CFR

2010-07-01

... With the Emission Limits for Tire Cord Production Affected Sources 11 Table 11 to Subpart XXXX of Part... for Hazardous Air Pollutants: Rubber Tire Manufacturing Pt. 63, Subpt. XXXX, Table 11 Table 11 to Subpart XXXX of Part 63—Minimum Data for Continuous Compliance With the Emission Limits for Tire Cord...

Determination of the Minimum Use Level of Fuel System Icing Inhibitor (FSII) in JP-8 That Will Provide Adquate Icing Inhibition and Biostatic Protection for Air Force Aircraft

DTIC Science & Technology

2013-12-01

experimental studies and analyses performed and the resulting recommendations. Results from the present effort indicated that a minimum use limit of... experimental studies performed and the resulting recommendations regarding the minimum on-board use limit of FSII while maintaining safe operability...sumping. A detailed summary of the experimental efforts and results are provided in a separate report (Balster et al., 2010). For the ATCC

The Effect of Temperature and Hydrogen Limited Growth on the Fractionation of Sulfur Isotopes by Thermodesulfatator indicus, a Deep-sea Hydrothermal Vent Sulfate-Reducing Bacterium

NASA Astrophysics Data System (ADS)

Hoek, J.; Reysenbach, A.; Habicht, K.; Canfield, D. E.

2004-12-01

Sulfate-reducing bacteria fractionate sulfur isotopes during dissimilatory sulfate reduction, producing sulfide depleted in 34S. Although isotope fractionation during sulfate reduction of pure cultures has been extensively studied, most of the research to date has focused on mesophilic sulfate reducers, particularly for the species Desulfovibrio desulfuricans. Results from these studies show that: 1) fractionations range from 3-46‰ with an average around 18‰ , 2) when organic electron donors are utilized, the extent of fractionation is dependent on the rate of sulfate reduction, with decreasing fractionations observed with higher specific rates, 3) fractionations are suppressed with low sulfate concentrations, and when hydrogen is used as the electron donor. High specific sulfate-reduction rates are encountered when sulfate-reducing bacteria metabolize at their optimal temperature and under non-limiting substrate conditions. Changes in both temperature and substrate availability could shift fractionations from those expressed under optimal growth conditions. Sulfate reducers may frequently experience substrate limitation and sub-optimal growth temperatures in the environment. Therefore it is important to understand how sulfate-reducing bacteria fractionate sulfur isotopes under conditions that more closely resemble the restrictions imposed by the environment. In this study the fractionation of sulfur isotopes by Thermodesulfatator indicus was explored during sulfate reduction under a wide range of temperatures and with both hydrogen-saturating and hydrogen-limited conditions. T. indicus is a thermophilic (temperature optimum = 70° C) chemolithotrophic sulfate-reducing bacterium, which was recently isolated from a deep-sea hydrothermal vent on the Central Indian Ridge. This bacterium represents the type species of a new genus and to date is the most deeply branching sulfate-reducing bacterium known. T. indicus was grown in carbonate-buffered salt-water medium with H2 as the sole electron donor, and CO2 as primary carbon source. The fractionation of sulfur isotopes was measured in batch cultures and in a thermal gradient block over the full temperature range of growth (40-80° C). For experiments in the gradient block, cell-specific rates of sulfate reduction increased with increasing temperatures to 70° C after which sulfate-reduction rates rapidly decreased. The range of fractionations (1.5-10‰ ) was typical for growth with hydrogen as the electron donor. Fractionations decreased with increasing temperature from 40--60° C, and increased with increasing temperatures from 60-80° C. Growth under H2-limited conditions in a fed-batch culture revealed high fractionations of 24-37‰ . This is the first report of sulfur isotope fractionation under H2 limited growth and indicates that large fractionations are produced when H2 is supplied as a limiting substrate. Our results suggest that fractionation is controlled by the competition of forward and reverse enzymatic reaction rates during sulfate reduction and by sulfate transport into the cell.

The utility of arginine-citrulline stable isotope tracer infusion technique in the assessment of nitric oxide production in MELAS syndrome

USDA-ARS?s Scientific Manuscript database

The correspondence titled “Analytical challenges in the assessment of NO synthesis from L-arginine in the MELAS syndrome” suggested challenges that can limit the utility of stable isotope infusion methodology in assessing NO production....

50 CFR 622.50 - Caribbean spiny lobster import prohibitions.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 50 Wildlife and Fisheries 8 2010-10-01 2010-10-01 false Caribbean spiny lobster import... ATLANTIC Management Measures § 622.50 Caribbean spiny lobster import prohibitions. (a) Minimum size limits for imported spiny lobster. There are two minimum size limits that apply to importation of spiny...

50 CFR 622.50 - Caribbean spiny lobster import prohibitions.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 50 Wildlife and Fisheries 10 2011-10-01 2011-10-01 false Caribbean spiny lobster import... ATLANTIC Management Measures § 622.50 Caribbean spiny lobster import prohibitions. (a) Minimum size limits for imported spiny lobster. There are two minimum size limits that apply to importation of spiny...

20 CFR 229.48 - Family maximum.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 20 Employees' Benefits 1 2010-04-01 2010-04-01 false Family maximum. 229.48 Section 229.48... OVERALL MINIMUM GUARANTEE Computation of the Overall Minimum Rate § 229.48 Family maximum. (a) Family... month on one person's earnings record is limited. This limited amount is called the family maximum. The...

If We Can't Predict Solar Cycle 24, What About Solar Cycle 34?

NASA Technical Reports Server (NTRS)

Pesnell. William Dean

2008-01-01

Predictions of solar activity in Solar Cycle 24 range from 50% larger than SC 23 to the onset of a Grand Minimum. Because low levels of solar activity are associated with global cooling in paleoclimate and isotopic records, anticipating these extremes is required in any longterm extrapolation of climate variability. Climate models often look forward 100 or more years, which would mean 10 solar cycles into the future. Predictions of solar activity are derived from a number of methods, most of which, such as climatology and physics-based models, will be familiar to atmospheric scientists. More than 50 predictions of the maximum amplitude of SC 24 published before solar minimum will be discussed. Descriptions of several methods that result in the extreme predictions and some anticipation of even longer term predictions will be presented.

Mini-Brayton heat source assembly design study. Volume 2: Titan 3C mission. [minimum weight modifications

NASA Technical Reports Server (NTRS)

1973-01-01

Major conclusions of the space shuttle heat source assembly study are reported that project a minimum weight design for a Titan 3 C synchronous orbit mission; requirements to recover the heat source in orbit are eliminated. This concept permits location of the heat source end enclosure supports and heat source assembly support housing in a low temperature region external to the insulation enclosure and considers titanium and beryllium alloys for these support elements. A high melting insulation blanket consisting of nickel foil coated with zirconia, or of gold foil separated with glass fiber layers, is selected to provide emergency cooling in the range 2000 to 2700 F to prevent the isotope heat source from reaching unsafe temperatures. A graphic view of the baseline heat source assembly is included.

Is it really organic?--multi-isotopic analysis as a tool to discriminate between organic and conventional plants.

PubMed

Laursen, K H; Mihailova, A; Kelly, S D; Epov, V N; Bérail, S; Schjoerring, J K; Donard, O F X; Larsen, E H; Pedentchouk, N; Marca-Bell, A D; Halekoh, U; Olesen, J E; Husted, S

2013-12-01

Novel procedures for analytical authentication of organic plant products are urgently needed. Here we present the first study encompassing stable isotopes of hydrogen, carbon, nitrogen, oxygen, magnesium and sulphur as well as compound-specific nitrogen and oxygen isotope analysis of nitrate for discrimination of organically and conventionally grown plants. The study was based on wheat, barley, faba bean and potato produced in rigorously controlled long-term field trials comprising 144 experimental plots. Nitrogen isotope analysis revealed the use of animal manure, but was unable to discriminate between plants that were fertilised with synthetic nitrogen fertilisers or green manures from atmospheric nitrogen fixing legumes. This limitation was bypassed using oxygen isotope analysis of nitrate in potato tubers, while hydrogen isotope analysis allowed complete discrimination of organic and conventional wheat and barley grains. It is concluded, that multi-isotopic analysis has the potential to disclose fraudulent substitutions of organic with conventionally cultivated plants. Copyright © 2013 Elsevier Ltd. All rights reserved.

[Research progress on food sources and food web structure of wetlands based on stable isotopes].

PubMed

Chen, Zhan Yan; Wu, Hai Tao; Wang, Yun Biao; Lyu, Xian Guo

2017-07-18

The trophic dynamics of wetland organisms is the basis of assessing wetland structure and function. Stable isotopes of carbon and nitrogen have been widely applied to identify trophic relationships in food source, food composition and food web transport in wetland ecosystem studies. This paper provided an overall review about the current methodology of isotope mixing model and trophic level in wetland ecosystems, and discussed the standards of trophic fractionation and baseline. Moreover, we characterized the typical food sources and isotopic compositions of wetland ecosystems, summarized the food sources in different trophic levels of herbivores, omnivores and carnivores based on stable isotopic analyses. We also discussed the limitations of stable isotopes in tra-cing food sources and in constructing food webs. Based on the current results, development trends and upcoming requirements, future studies should focus on sample treatment, conservation and trophic enrichment measurement in the wetland food web, as well as on combing a variety of methodologies including traditional stomach stuffing, molecular markers, and multiple isotopes.

Natural trophic variability in a large, oligotrophic, near-pristine lake

USGS Publications Warehouse

Young, Talia; Jensen, Olaf P.; Weidel, Brian C.; Chandra, Sudeep

2015-01-01

Conclusions drawn from stable isotope data can be limited by an incomplete understanding of natural isotopic variability over time and space. We quantified spatial and temporal variability in fish carbon and nitrogen stable isotopes in Lake Hövsgöl, Mongolia, a large, remote, oligotrophic lake with an unusually species-poor fish community. The fish community demonstrated a high degree of trophic level overlap. Variability in δ13C was inversely related to littoral-benthic dependence, with pelagic species demonstrating more δ13C variability than littoral-benthic species. A mixed effects model suggested that space (sampling location) had a greater impact than time (collection year) on both δ13C and δ15N variability. The observed variability in Lake Hövsgöl was generally greater than isotopic variability documented in other large, oligotrophic lakes, similar to isotopic shifts attributed to introduced species, and less than isotopic shifts attributed to anthropogenic chemical changes such as eutrophication. This work complements studies on isotopic variability and changes in other lakes around the world.

PRODUCTION OF HELIUM IN IRON METEORITES BY THE ACTION OF COSMIC RAYS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, J.H.; Nier, A.O.

1958-12-15

The helium distribution in a slice from the iron meteorite, Grant, was measured aud plotted in the form of contour maps. The contours of constant helium show a minimum helium content and isotopic ratio, He/sup 3//He/sup 4/, near the center of the slice, tbe isotopic ratio varying from 0.26 near the center to 0.30 at the surface. A cosmogenic helium production rate equation was fitted to the data giving a He/sup 3//He/sup 4/ production ratio by primary cosmic rays of 0.50 and by secondary particles of 0.14. Primary and secondary particle interaction cross sections were found to be 540 mbmore » and 720 mb, respectively. The ratio of the average post-atmospheric radius to the pre- atmospheric radius of Grant was calculated to be 0.65. (auth)« less

Rhenium-osmium-isotope constraints on the age of iron meteorites

NASA Technical Reports Server (NTRS)

Horan, M. F.; Morgan, J. W.; Walker, R. J.; Grossman, J. N.

1992-01-01

Rhenium and osmium concentrations and the osmium isotopic compositions of iron meteorites were determined by negative thermal ionization mass spectrometry. Data for the IIA iron meteorites define an isochron with an uncertainty of approximately +/-31 million years for meteorites about 4500 million years old. Although an absolute rhenium-osmium closure age for this iron group cannot be as precisely constrained because of uncertainty in the decay constant of Re-187, an age of 4460 million years ago is the minimum permitted by combined uncertainties. These age constraints imply that the parent body of the IIAB magmatic irons melted and subsequently cooled within 100 million years after the formation of the oldest portions of chondrites. Other iron meteorites plot above the IIA isochron, indicating that the planetary bodies represented by these iron groups may have cooled significantly later than the parent body of the IIA irons.

Rhenium-osmium isotope constraints on the age of iron meteorites

USGS Publications Warehouse

Horan, M.F.; Morgan, J.W.; Walker, R.J.; Grossman, J.N.

1992-01-01

Rhenium and osmium concentrations and the osmium isotopic compositions of iron meteorites were determined by negative thermal ionization mass spectrometry. Data for the IIA iron meteorites define an isochron with an uncertainty of approximately ??31 million years for meteorites ???4500 million years old. Although an absolute rhenium-osmium closure age for this iron group cannot be as precisely constrained because of uncertainty in the decay constant of 187Re, an age of 4460 million years ago is the minimum permitted by combined uncertainties. These age constraints imply that the parent body of the IIAB magmatic irons melted and subsequently cooled within 100 million years after the formation of the oldest portions of chondrites. Other iron meteorites plot above the IIA isochron, indicating that the planetary bodies represented by these iron groups may have cooled significantly later than the parent body of the IIA irons.

Contribution of bulk mass spectrometry isotopic analysis to characterization of materials in the framework of CMX-4

DOE PAGES

Kuchkin, A.; Stebelkov, V.; Zhizhin, K.; ...

2018-01-30

Seven laboratories used the results of bulk uranium isotopic analysis by either inductively coupled plasma mass spectrometry (ICP-MS) or thermal ionization mass spectrometry (TIMS) for characterization of the samples in the Nuclear Forensic International Technical Working Group fourth international collaborative material exercise, CMX-4. Comparison of the measured isotopic compositions of uranium in three exercise samples is implemented for identifying any differences or similarities between the samples. The role of isotopic analyses in the context of a real nuclear forensic investigation is discussed. Several limitations in carrying out ICP-MS or TIMS analysis in CMX-4 are noted.

Contribution of bulk mass spectrometry isotopic analysis to characterization of materials in the framework of CMX-4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuchkin, A.; Stebelkov, V.; Zhizhin, K.

Seven laboratories used the results of bulk uranium isotopic analysis by either inductively coupled plasma mass spectrometry (ICP-MS) or thermal ionization mass spectrometry (TIMS) for characterization of the samples in the Nuclear Forensic International Technical Working Group fourth international collaborative material exercise, CMX-4. Comparison of the measured isotopic compositions of uranium in three exercise samples is implemented for identifying any differences or similarities between the samples. The role of isotopic analyses in the context of a real nuclear forensic investigation is discussed. Several limitations in carrying out ICP-MS or TIMS analysis in CMX-4 are noted.

On-line nuclear orientation of the deformed neutron-deficient Eu, Sm and Pm isotopes

NASA Astrophysics Data System (ADS)

Singleton, B. D. D.; Walker, P. M.; Bhagwat, A.; Al-Ghamdi, S. S.; Barham, C. G.; Grant, I. S.; Griffiths, A. G.; Rikovska, J.; Stone, N. J.

1992-11-01

Low-temperature nuclear orientation measurements made on-line at the SERC Daresbury Laboratory on142 m Eu,141 m Sm, and141Pm, with known magnetic dipole moments, have yielded the magnitude of the hyperfine fields of these isotopes in an iron host lattice. Thus measurements for the isotopes139, 138Eu,139 m Sm, and138Pm yielded values for the respective magnetic moments. Limits on the thermal relaxation times of Eu and Sm isotopes in Fe were also deduced. The results for138Eu appear to contradict the earlier πh11/2⊗νh11/2 ground-state configuration assignment.

On feasibility of a closed nuclear power fuel cycle with minimum radioactivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrianova, E. A.; Davidenko, V. D.; Tsibulskiy, V. F., E-mail: Tsibulskiy-VF@nrcki.ru

2015-12-15

Practical implementation of a closed nuclear fuel cycle implies solution of two main tasks. The first task is creation of environmentally acceptable operating conditions of the nuclear fuel cycle considering, first of all, high radioactivity of the involved materials. The second task is creation of effective and economically appropriate conditions of involving fertile isotopes in the fuel cycle. Creation of technologies for management of the high-level radioactivity of spent fuel reliable in terms of radiological protection seems to be the hardest problem.

Bifurcations on Potential Energy Surfaces of Organic Reactions

PubMed Central

Ess, Daniel H.; Wheeler, Steven E.; Iafe, Robert G.; Xu, Lai; Çelebi-Ölçüm, Nihan; Houk, K. N.

2009-01-01

A single transition state may lead to multiple intermediates or products if there is a post-transition state reaction path bifurcation. These bifurcations arise when there are sequential transition states with no intervening energy minimum. For such systems, the shape of the potential energy surface and dynamic effects control selectivity rather than transition state energetics. This minireview covers recent investigations of organic reactions exhibiting reaction pathway bifurcations. Such phenomena are surprisingly general and affect experimental observables such as kinetic isotope effects and product distributions. PMID:18767086

Commercial-Off-The-Shelf (COTS) Indirect Energy Conversion Isotope (IDEC) Design Structure and Power Management

DTIC Science & Technology

2014-12-01

RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) December 2014 2. REPORT TYPE Final 3. DATES COVERED (From - To) 4. TITLE AND...must last the lifetime of the sensor. Unlike chemical batteries, the higher energy densities of radioisotopes allow the sensors to operate for...because they are self-contained energy sources using radioisotope decay. The minimum power needed to fully accomplish a wide range of duties would be

New U-series dates at the Caune de l'Arago, France

USGS Publications Warehouse

Falgueres, Christophe; Yokoyama, Y.; Shen, G.; Bischoff, J.L.; Ku, T.-L.; de Lumley, Henry

2004-01-01

In the beginning of the 1980s, the Caune de l'Arago was the focus of an interdisciplinary effort to establish the chronology of the Homo heidelbergensis (Preneandertals) fossils using a variety of techniques on bones and on speleothems. The result was a very large spread of dates particularly on bone samples. Amid the large spread of results, some radiometric data on speleothems showed a convergence in agreement with inferences from faunal studies. We present new U-series results on the stalagmitic formation located at the bottom of Unit IV (at the base of the Upper Stratigraphic Complex). Samples and splits were collaboratively analyzed in the four different laboratories with excellent interlaboratory agreement. Results show the complex sequence of this stalagmitic formation. The most ancient part is systematically at internal isotopic equilibrium (>350 ka) suggesting growth during or before isotopic stage 9, representing a minimum age for the human remains found in Unit III of the Middle Stratigraphical Complex which is stratigraphically under the basis of the studied stalagmitic formation. Overlaying parts of the speleothem date to the beginning of marine isotope stages 7 and 5. ?? 2003 Elsevier Science Ltd. All rights reserved.

Pre-Whaling Genetic Diversity and Population Ecology in Eastern Pacific Gray Whales: Insights from Ancient DNA and Stable Isotopes

PubMed Central

Alter, S. Elizabeth; Newsome, Seth D.; Palumbi, Stephen R.

2012-01-01

Commercial whaling decimated many whale populations, including the eastern Pacific gray whale, but little is known about how population dynamics or ecology differed prior to these removals. Of particular interest is the possibility of a large population decline prior to whaling, as such a decline could explain the ∼5-fold difference between genetic estimates of prior abundance and estimates based on historical records. We analyzed genetic (mitochondrial control region) and isotopic information from modern and prehistoric gray whales using serial coalescent simulations and Bayesian skyline analyses to test for a pre-whaling decline and to examine prehistoric genetic diversity, population dynamics and ecology. Simulations demonstrate that significant genetic differences observed between ancient and modern samples could be caused by a large, recent population bottleneck, roughly concurrent with commercial whaling. Stable isotopes show minimal differences between modern and ancient gray whale foraging ecology. Using rejection-based Approximate Bayesian Computation, we estimate the size of the population bottleneck at its minimum abundance and the pre-bottleneck abundance. Our results agree with previous genetic studies suggesting the historical size of the eastern gray whale population was roughly three to five times its current size. PMID:22590499

New U-series dates at the Caune de l'Arago, France

USGS Publications Warehouse

Falgueres, Christophe; Yokoyama, Y.; Shen, G.; Bischoff, J.L.; Ku, T.-L.; de Lumley, Henry

2004-01-01

In the beginning of the 1980s, the Caune de l'Arago was the focus of an interdisciplinary effort to establish the chronology of the Homo heidelbergensis (Preneandertals) fossils using a variety of techniques on bones and on speleothems. The result was a very large spread of dates particularly on bone samples. Amid the large spread of results, some radiometric data on speleothems showed a convergence in agreement with inferences from faunal studies. We present new U-series results on the stalagmitic formation located at the bottom of Unit IV (at the base of the Upper Stratigraphic Complex). Samples and splits were collaboratively analyzed in the four different laboratories with excellent interlaboratory agreement. Results show the complex sequence of this stalagmitic formation. The most ancient part is systematically at internal isotopic equilibrium (>350 ka) suggesting growth during or before isotopic stage 9, representing a minimum age for the human remains found in Unit III of the Middle Stratigraphical Complex which is stratigraphically under the basis of the studied stalagmitic formation. Overlaying parts of the speleothem date to the beginning of marine isotope stages 7 and 5. ?? 2003 Elsevier Ltd. All rights reserved.

Charge Radii of Neutron Deficient Fe,5352 Produced by Projectile Fragmentation

NASA Astrophysics Data System (ADS)

Minamisono, K.; Rossi, D. M.; Beerwerth, R.; Fritzsche, S.; Garand, D.; Klose, A.; Liu, Y.; Maaß, B.; Mantica, P. F.; Miller, A. J.; Müller, P.; Nazarewicz, W.; Nörtershäuser, W.; Olsen, E.; Pearson, M. R.; Reinhard, P.-G.; Saperstein, E. E.; Sumithrarachchi, C.; Tolokonnikov, S. V.

2016-12-01

Bunched-beam collinear laser spectroscopy is performed on neutron deficient Fe,5352 prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δ ⟨r2⟩ of Fe,5352 are determined relative to stable 56Fe as δ ⟨r2⟩56 ,52=-0.034 (13 ) fm2 and δ ⟨r2⟩56 ,53=-0.218 (13 ) fm2 , respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ ⟨r2⟩. The values of δ ⟨r2⟩ exhibit a minimum at the N =28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. The trend of δ ⟨r2⟩ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ ⟨r2⟩ of closed-shell Ca isotopes.

Skiing in the Eocene Uinta Mountains? Isotopic evidence in the Green River Formation for snow melt and large mountains

NASA Astrophysics Data System (ADS)

Norris, Richard D.; Jones, Lawrence S.; Corfield, Richard M.; Cartlidge, Julie E.

1996-05-01

Isotopic analysis of lacustrine carbonates from the Eocene Green River Formation suggests that lake waters were derived partly from snow melt. This evidence for cool climates is in marked contrast to paleontological and model evidence for mild temperatures in the continental interior. Oxygen isotope ratios of carbonates frequently reach -12‰ to nearly -16‰ (Peedee belemnite), which suggests that lake waters probably had δ18O of <-13‰ (standard mean ocean water). Consideration of the evaporative 18O enrichment that typically occurs in modern large saline lakes suggests that the source waters to the Green River basin had a δ18O of <-18‰. These ratios are consistent with snow melt and are too negative to be easily accounted for by distillation in the atmosphere during heavy rainfall. The Green River lakes formed in a closed basin encircled by large mountains; this suggests that the snow melt was locally produced. The mountains surrounding the lake must have been high enough to occasionally supply significant melt water to the much lower lake. Lapse rate calculations suggest minimum altitudes of >3000 m for the mountains encircling the Green River basin.

Implementation of a solid target production facility

NASA Astrophysics Data System (ADS)

Tochon-Danguy, H. J.; Poniger, S. S.; Sachinidis, J. I.; Panopoulos, H. P.; Scott, A. M.

2012-12-01

The desire to utilize long-lived PET isotopes in Australia has significantly increased over the years and several research projects for labelling of peptides, proteins and biomolecules, including labelling of recombinant antibodies has been restricted due to the limited availability of suitable isotopes. This need has led to the recent installation and commissioning of a new facility dedicated to fully automated solid target isotope production, including 24I, 64Cu, 89Zr and 86Y at the Austin Health Centre for PET.

Seasonal variations and cycling of nitrous oxide using nitrogen isotopes and concentrations from an unsaturated zone of a floodplain

NASA Astrophysics Data System (ADS)

Bill, M.; Conrad, M. E.; Kolding, S.; Williams, K. H.; Tokunaga, T. K.

2014-12-01

Nitrous oxide (N2O) concentrations and isotope ratios of 15N to 14N of N2O in the vadose zone mainly depend on atmospheric deposition, symbiotic or non-symbiotic N2 fixation, and nitrification/denitrification processes in underlying groundwater. In an effort to quantify N2O seasonal variations, cycling and N budgets in an alluvial aquifer in western Colorado (Rifle, CO), the concentrations and nitrogen stable isotopes of N2O within the pore space of partially saturated sediments have been monitored over the 2013-2014 years. Vertically resolved profiles spanning from 0m to 3m depth were sampled at 0.5m increments at a periodicity of one month. At each of the profile locations, N2O concentrations decreased from 3m depth to the surface. The maximum concentrations were observed at the interface between the unsaturated zone and groundwater, with minimum values observed in the near surface samples. The d15N values tend to increase from the unsaturated zone/groundwater interface to the surface. Both variation of N2O concentrations and d15N values suggest that denitrification is the main contribution to N2O production and both parameters exhibited a strong seasonal variation. The maximum concentrations (~10ppmv) were observed at the beginning of summer, during the annual maximum in water table elevation. The minimum N2O concentrations were observed in the period from January to May and coincided with low water table elevations. Additionally, nitrogen concentrations and d15N values of the shallowest sediments within the vertical profiles do not show variation, suggesting that the main source of N2O is associated with groundwater denitrification, with the shallower, partially saturated sediments acting as a sink for N2O.

Methane production and consumption monitored by stable H and C isotope ratios at a crude oil spill site, Bemidji, Minnesota

USGS Publications Warehouse

Revesz, Kinga; Coplen, Tyler B.; Baedecker, Mary J.; Glynn, Pierre D.

1995-01-01

Stable isotopic ratios of C and H in dissolved CH4 and C in dissolved inorganic C in the ground water of a crude-oil spill near Bemidji, Minnesota, support the concept of CH4production by acetate fermentation with a contemporaneous increase in HCO3−concentration. Methane concentrations in the saturated zone decrease from 20.6 mg L−1 to less than 0.001 mg L−1 along the investigated flow path. Dissolved N2 and Ar concentrations in the ground water below the oil plume are 25 times lower than background; this suggests that gas exsolution is removing dissolved CH4 (along with other dissolved gases) from the ground water. Oxidation of dissolved CH4 along the flow path seems to be minimal because no measurable change in isotopic composition of CH4 occurs with distance from the oil body. However, CH4 is partly oxidized to CO2 as it diffuses upward from the ground water through a 5- to 7-m thick unsaturated zone; theδ13C of the remaining CH4 increases, theδ13C of the CO2 decreases, and the partial pressure of CO2 increases.Calculations of C fluxes in the saturated and unsaturated zones originating from the degradation of the oil plume lead to a minimum estimated life expectancy of 110 years. This is a minimum estimate because the degradation of the oil body should slow down with time as its more volatile and reactive components are leached out and preferentially oxidized. The calculated life expectancy is an order of magnitude estimate because of the uncertainty in the average linear ground-water velocities and because of the factor of 2 uncertainty in the calculation of the effective CO2 diffusion coefficient.

Redefining the utility of the three-isotope method

NASA Astrophysics Data System (ADS)

Cao, Xiaobin; Bao, Huiming

2017-09-01

The equilibrium isotope fractionation factor αeq is a fundamental parameter in the study of stable isotope effects. Experimentally, it has been difficult to establish that a system has attained equilibrium. The three-isotope method, using the initial trajectory of changing isotope ratios (e.g. 16O, 17O, and 18O) to deduce the final equilibrium point of isotope exchange, has long been hailed as the most rigorous experimental approach. However, over the years some researchers have cautioned on the limitations of this method, but the foundation of three-isotope method has not been properly examined and the method is still widely used in calibrating αeq for both traditional and increasingly non-traditional isotope systems today. Here, using water-water and dissolved CO2-water oxygen exchange as model systems, we conduct an isotopologues-specific kinetic analysis of the exchange processes and explore the underlying assumptions and validity of the three-isotope method. We demonstrate that without knowing the detailed exchange kinetics a priori the three-isotope method cannot lead to a reliable αeq. For a two-reservoir exchanging system, α determined by this method may be αeq, kinetic isotope effect, or apparent kinetic isotope effect, which can all bear different values. When multiple reservoirs exist during exchange, the evolving trajectory can be complex and hard to predict. Instead of being a tool for αeq determination, three-isotope method should be used as a tool for studying kinetic isotope effect, apparent kinetic isotope effect, and detailed exchange kinetics in diverse systems.

Natural Isotope Abundance in Metabolites: Techniques and Kinetic Isotope Effect Measurement in Plant, Animal, and Human Tissues.

PubMed

Tea, Illa; Tcherkez, Guillaume

2017-01-01

The natural isotope abundance in bulk organic matter or tissues is not a sufficient base to investigate physiological properties, biosynthetic mechanisms, and nutrition sources of biological systems. In fact, isotope effects in metabolism lead to a heterogeneous distribution of 2 H, 18 O, 13 C, and 15 N isotopes in metabolites. Therefore, compound-specific isotopic analysis (CSIA) is crucial to biological and medical applications of stable isotopes. Here, we review methods to implement CSIA for 15 N and 13 C from plant, animal, and human samples and discuss technical solutions that have been used for the conversion to CO 2 and N 2 for IRMS analysis, derivatization and isotope effect measurements. It appears that despite the flexibility of instruments used for CSIA, there is no universal method simply because the chemical nature of metabolites of interest varies considerably. Also, CSIA methods are often limited by isotope effects in sample preparation or the addition of atoms from the derivatizing reagents, and this implies that corrections must be made to calculate a proper δ-value. Therefore, CSIA has an enormous potential for biomedical applications, but its utilization requires precautions for its successful application. © 2017 Elsevier Inc. All rights reserved.

Oxygen isotope composition of mafic magmas at Vesuvius

NASA Astrophysics Data System (ADS)

Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.

2009-12-01

The oxygen isotope composition of olivine and clinopyroxene from four plinian (AD 79 Pompeii, 3960 BP Avellino), subplinian (AD 472 Pollena) and violent strombolian (Middle Age activity) eruptions were measured to constrain the nature and evolution of the primary magmas of the last 4000 years of Mt. Vesuvius activity. A large set of mm-sized crystals was accurately separated from selected juvenile material of the four eruptions. Crystals were analyzed for their major and trace element compositions (EPMA, Laser Ablation ICP-MS), and for 18O/16O ratios. As oxygen isotope composition of uncontaminated mantle rocks on world-wide scale is well constrained (δ18Oolivine = 5.2 ± 0.3; δ18Ocpx = 5.6 ± 0.3 ‰), the measured values can be conveniently used to monitor the effects of assimilation/contamination of crustal rocks in the evolution of the primary magmas. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary magmas during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). Low δ18O values have been measured in olivine from Pompeii eruption (δ18Oolivine = 5.54 ± 0.03‰), whereas higher O-compositions are recorded in mafic minerals from pumices or scoria of the other three eruptions. Measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas, as also constrained by their trace element compositions. Data on melt inclusions hosted in crystals of these compositions have been largely collected in the past demonstrating that they crystallized from mafic melt, basaltic to tephritic in composition. Published data on volatile content of these melt inclusions reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth possibly occurred during magma ascent from the source region or in a shallow reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali magmas from trachybasaltic melts. Accordingly, the δ18O variability and the trace element contents of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. The δ18Oolivine and δ18Ocpx of the studied minerals define variable degrees of carbonate assimilation and magma crystallization for the different eruptions, and possibly within the same eruption, and show evidence of oxygen isotope equilibrium at high temperature. However, energy-constrained AFC model suggest that carbonate contamination was limited. On the basis of our data, we suggest that interaction between magma and a fluxing, decarbonation-derived CO2 fluid may be partly accounted for the measured O-isotope compositions.

Static, mixed-array total evaporation for improved quantitation of plutonium minor isotopes in small samples

DOE PAGES

Stanley, F. E.; Byerly, Benjamin L.; Thomas, Mariam R.; ...

2016-03-31

Actinide isotope measurements are a critical signature capability in the modern nuclear forensics “toolbox”, especially when interrogating anthropogenic constituents in real-world scenarios. Unfortunately, established methodologies, such as traditional total evaporation via thermal ionization mass spectrometry, struggle to confidently measure low abundance isotope ratios (<10 -6) within already limited quantities of sample. Herein, we investigate the application of static, mixed array total evaporation techniques as a straightforward means of improving plutonium minor isotope measurements, which have been resistant to enhancement in recent years because of elevated radiologic concerns. Furthermore, results are presented for small sample (~20 ng) applications involving a well-knownmore » plutonium isotope reference material, CRM-126a, and compared with traditional total evaporation methods.« less

Physiological minimum temperatures for root growth in seven common European broad-leaved tree species.

PubMed

Schenker, Gabriela; Lenz, Armando; Körner, Christian; Hoch, Günter

2014-03-01

Temperature is the most important factor driving the cold edge distribution limit of temperate trees. Here, we identified the minimum temperatures for root growth in seven broad-leaved tree species, compared them with the species' natural elevational limits and identified morphological changes in roots produced near their physiological cold limit. Seedlings were exposed to a vertical soil-temperature gradient from 20 to 2 °C along the rooting zone for 18 weeks. In all species, the bulk of roots was produced at temperatures above 5 °C. However, the absolute minimum temperatures for root growth differed among species between 2.3 and 4.2 °C, with those species that reach their natural distribution limits at higher elevations also tending to have lower thermal limits for root tissue formation. In all investigated species, the roots produced at temperatures close to the thermal limit were pale, thick, unbranched and of reduced mechanical strength. Across species, the specific root length (m g(-1) root) was reduced by, on average, 60% at temperatures below 7 °C. A significant correlation of minimum temperatures for root growth with the natural high elevation limits of the investigated species indicates species-specific thermal requirements for basic physiological processes. Although these limits are not necessarily directly causative for the upper distribution limit of a species, they seem to belong to a syndrome of adaptive processes for life at low temperatures. The anatomical changes at the cold limit likely hint at the mechanisms impeding meristematic activity at low temperatures.

Isotope fractionation by multicomponent diffusion (Invited)

NASA Astrophysics Data System (ADS)

Watkins, J. M.; Liang, Y.; Richter, F. M.; Ryerson, F. J.; DePaolo, D. J.

2013-12-01

Isotope fractionation by multicomponent diffusion The isotopic composition of mineral phases can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The ability to interpret stable isotope variations is limited by our knowledge of three key parameters and their relative importance in determining the composition of a mineral grain and its surroundings: (1) thermodynamic (equilibrium) partitioning, (2) mass-dependent diffusivities, and (3) mass-dependent reaction rate coefficients. Understanding the mechanisms of diffusion and reaction in geological liquids, and how these mass transport processes discriminate between isotopes, represents an important problem that is receiving considerable attention in the geosciences. Our focus in this presentation will be isotope fractionation by chemical diffusion. Previous studies have documented that diffusive isotope effects vary depending on the cation as well as the liquid composition, but the ability to predict diffusive isotope effects from theory is limited; for example, it is unclear whether the magnitude of diffusive isotopic fractionations might also vary with the direction of diffusion in composition space. To test this hypothesis and to further guide the theoretical treatment of isotope diffusion, two chemical diffusion experiments and one self diffusion experiment were conducted at 1250°C and 0.7 GPa. In one experiment (A-B), CaO and Na2O counter-diffuse rapidly in the presence of a small SiO2 gradient. In the other experiment (D-E), CaO and SiO2 counter-diffuse more slowly in a small Na2O gradient. In both chemical diffusion experiments, Ca isotopes become fractionated by chemical diffusion but by different amounts, documenting for the first time that the magnitude of isotope fractionation by diffusion depends on the direction of diffusion in composition space. The magnitude of Ca isotope fractionation that develops is positively correlated with the rate of CaO diffusion; in A-B, the total variation is 2.5‰ whereas in D-E it is only 1.3‰. The diffusion of isotopes in a multicomponent system is modeled using a new expression for the isotope-specific diffusive flux that includes self diffusion terms in addition to the multicomponent chemical diffusion matrix. Kinetic theory predicts a mass dependence on isotopic mobility, i.e., self diffusivity, but it is unknown whether or how the mass dependence on self diffusivity translates into a mass dependence on chemical diffusion coefficients. The new experimental results allow us to assess several empirical expressions relating the self diffusivity and its mass dependence to the elements of the diffusion matrix and their mass dependence. Several plausible theoretical treatments can fit the data equally well. We are currently at the stage where experiments are guiding the theoretical treatment of the isotope fractionation by diffusion problem, underscoring the importance of experiments for aiding interpretations of isotopic variations in nature.

PCP METHODOLOGY FOR DETERMINING DOSE RATES FOR SMALL GRAM QUANTITIES IN SHIPPING PACKAGINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nathan, S.

The Small Gram Quantity (SGQ) concept is based on the understanding that small amounts of hazardous materials, in this case radioactive materials, are significantly less hazardous than large amounts of the same materials. This study describes a methodology designed to estimate an SGQ for several neutron and gamma emitting isotopes that can be shipped in a package compliant with 10 CFR Part 71 external radiation level limits regulations. These regulations require packaging for the shipment of radioactive materials perform, under both normal and accident conditions, the essential functions of material containment, subcriticality, and maintain external radiation levels within regulatory limits.more » 10 CFR 71.33(b)(1)(2)&(3) state radioactive and fissile materials must be identified and their maximum quantity, chemical and physical forms be included in an application. Furthermore, the U.S. Federal Regulations require application contain an evaluation demonstrating the package (i.e., the packaging and its contents) satisfies the external radiation standards for all packages (10 CFR 71.31(2), 71.35(a), & 71.47). By placing the contents in a He leak-tight containment vessel, and limiting the mass to ensure subcriticality, the first two essential functions are readily met. Some isotopes emit sufficiently strong photon radiation that small amounts of material can yield a large external dose rate. Quantifying of the dose rate for a proposed content is a challenging issue for the SGQ approach. It is essential to quantify external radiation levels from several common gamma and neutron sources that can be safely placed in a specific packaging, to ensure compliance with federal regulations. The Packaging Certification Program (PCP) Methodology for Determining Dose Rate for Small Gram Quantities in Shipping Packagings described in this report provides bounding mass limits for a set of proposed SGQ isotopes. Methodology calculations were performed to estimate external radiation levels for the 9977 shipping package using the MCNP radiation transport code to develop a set of response multipliers (Green's functions) for 'dose per particle' for each neutron and photon spectral group. The source spectrum for each isotope generated using the ORIGEN-S and RASTA computer codes was folded with the response multipliers to generate the dose rate per gram of each isotope in the 9977 shipping package and its associated shielded containers. The maximum amount of a single isotope that could be shipped within the regulatory limits contained in 10 CFR 71.47 for dose rate at the surface of the package is determined. If a package contains a mixture of isotopes, the acceptability for shipment can be determined by a sum of fractions approach. Furthermore, the results of this analysis can be easily extended to additional radioisotopes by simply evaluating the neutron and/or photon spectra of those isotopes and folding the spectral data with the Green's functions provided.« less

14 CFR 135.203 - VFR: Minimum altitudes.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false VFR: Minimum altitudes. 135.203 Section 135.203 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED... Operating Limitations and Weather Requirements § 135.203 VFR: Minimum altitudes. Except when necessary for...

14 CFR 135.203 - VFR: Minimum altitudes.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false VFR: Minimum altitudes. 135.203 Section 135.203 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED... Operating Limitations and Weather Requirements § 135.203 VFR: Minimum altitudes. Except when necessary for...

14 CFR 135.203 - VFR: Minimum altitudes.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false VFR: Minimum altitudes. 135.203 Section 135.203 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED... Operating Limitations and Weather Requirements § 135.203 VFR: Minimum altitudes. Except when necessary for...

26 CFR 1.514(c)-2 - Permitted allocations under section 514(c)(9)(E).

Code of Federal Regulations, 2013 CFR

2013-04-01

.... (ii) Limitation on chargebacks of partial allocations. (3) Minimum gain chargebacks attributable to nonrecourse deductions. (4) Minimum gain chargebacks attributable to distribution of nonrecourse debt proceeds. (i) Chargebacks disregarded until allocations made. (ii) Certain minimum gain chargebacks related to...

26 CFR 1.514(c)-2 - Permitted allocations under section 514(c)(9)(E).

Code of Federal Regulations, 2011 CFR

2011-04-01

.... (ii) Limitation on chargebacks of partial allocations. (3) Minimum gain chargebacks attributable to nonrecourse deductions. (4) Minimum gain chargebacks attributable to distribution of nonrecourse debt proceeds. (i) Chargebacks disregarded until allocations made. (ii) Certain minimum gain chargebacks related to...

26 CFR 1.514(c)-2 - Permitted allocations under section 514(c)(9)(E).

Code of Federal Regulations, 2014 CFR

2014-04-01

.... (ii) Limitation on chargebacks of partial allocations. (3) Minimum gain chargebacks attributable to nonrecourse deductions. (4) Minimum gain chargebacks attributable to distribution of nonrecourse debt proceeds. (i) Chargebacks disregarded until allocations made. (ii) Certain minimum gain chargebacks related to...

26 CFR 1.514(c)-2 - Permitted allocations under section 514(c)(9)(E).

Code of Federal Regulations, 2012 CFR

2012-04-01

.... (ii) Limitation on chargebacks of partial allocations. (3) Minimum gain chargebacks attributable to nonrecourse deductions. (4) Minimum gain chargebacks attributable to distribution of nonrecourse debt proceeds. (i) Chargebacks disregarded until allocations made. (ii) Certain minimum gain chargebacks related to...

Submicron hard X-ray fluorescence imaging of synthetic elements.

PubMed

Jensen, Mark P; Aryal, Baikuntha P; Gorman-Lewis, Drew; Paunesku, Tatjana; Lai, Barry; Vogt, Stefan; Woloschak, Gayle E

2012-04-13

Synchrotron-based X-ray fluorescence microscopy (XFM) using hard X-rays focused into sub-micron spots is a powerful technique for elemental quantification and mapping, as well as microspectroscopic measurements such as μ-XANES (X-ray absorption near edge structure). We have used XFM to image and simultaneously quantify the transuranic element plutonium at the L(3) or L(2)-edge as well as Th and lighter biologically essential elements in individual rat pheochromocytoma (PC12) cells after exposure to the long-lived plutonium isotope (242)Pu. Elemental maps demonstrate that plutonium localizes principally in the cytoplasm of the cells and avoids the cell nucleus, which is marked by the highest concentrations of phosphorus and zinc, under the conditions of our experiments. The minimum detection limit under typical acquisition conditions with an incident X-ray energy of 18 keV for an average 202 μm(2) cell is 1.4 fg Pu or 2.9×10(-20) moles Pu μm(-2), which is similar to the detection limit of K-edge XFM of transition metals at 10 keV. Copper electron microscopy grids were used to avoid interference from gold X-ray emissions, but traces of strontium present in naturally occurring calcium can still interfere with plutonium detection using its L(α) X-ray emission. Copyright © 2012 Elsevier B.V. All rights reserved.

Mechanism of Nitrogenase H 2 Formation by Metal-Hydride Protonation Probed by Mediated Electrocatalysis and H/D Isotope Effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khadka, Nimesh; Milton, Ross D.; Shaw, Sudipta

Nitrogenase catalyzes the reduction of dinitrogen (N2) to ammonia (NH3) with obligatory reduction of protons (H+) to dihydrogen (H2) through a mechanism involving reductive elimination of two [Fe-H-Fe] bridging hydrides at its active site FeMo-cofactor. The overall rate-limiting step is associated with ATP-driven electron delivery from Fe protein, precluding isotope effect measurements on substrate reduction steps. Here, we use mediated bioelectrocatalysis to drive electron delivery to MoFe protein without Fe protein and ATP hydrolysis, thereby eliminating the normal rate-limiting step. The ratio of catalytic current in mixtures of H2O and D2O, the proton inventory, changes linearly with the D2O/H2O ratio,more » revealing that a single H/D is involved in the rate limiting step. Kinetic models, along with measurements that vary the electron/proton delivery rate and use different substrates, reveal that the rate-limiting step under these conditions is the H2 formation reaction. Altering the chemical environment around the active site FeMo-cofactor in the MoFe protein either by substituting nearby amino acids or transferring the isolated FeMo-cofactor into a different peptide matrix, changes the net isotope effect, but the proton inventory plot remains linear, consistent with an unchanging rate-limiting step. Density functional theory predicts a transition state for H2 formation where the proton from S-H+ moves to the hydride in Fe-H-, predicting the number and magnitude of the observed H/D isotope effect. This study not only reveals the mechanism of H2 formation, but also illustrates a strategy for mechanistic study that can be applied to other enzymes and to biomimetic complexes.« less

Past leaded gasoline emissions as a nonpoint source tracer in riparian systems: A study of river inputs to San Francisco Bay

USGS Publications Warehouse

Dunlap, C.E.; Bouse, R.; Flegal, A.R.

2000-01-01

Variations in the isotopic composition of lead in 1995-1998 river waters flowing into San Francisco Bay trace the washout of lead deposited in the drainage basin from leaded gasoline combustion. At the confluence of the Sacramento and San Joaquin rivers where they enter the Bay, the isotopic compositions of lead in the waters define a linear trend away from the measured historical compositions of leaded gas in California. The river waters are shifted away from leaded gasoline values and toward an isotopic composition similar to Sierra Nevadan inputs which became the predominant source of sedimentation in San Francisco Bay following the onset of hydraulic gold mining in 1853. Using lead isotopic compositions of hydraulic mine sediments and average leaded gasoline as mixing end members, we calculate that more than 50% of the lead in the present river water originated from leaded gasoline combustion. The strong adsorption of lead (log K(d) > 7.4) to particulates appears to limit the flushing of gasoline lead from the drainage basin, and the removal of that lead from the system may have reached an asymptotic limit. Consequently, gasoline lead isotopes should prove to be a useful nonpoint source tracer of the environmental distribution of particle- reactive anthropogenic metals in freshwater systems.

Status of stable isotope enrichment, products, and services at the Oak Ridge National Laboratory

NASA Astrophysics Data System (ADS)

Scott Aaron, W.; Tracy, Joe G.; Collins, Emory D.

1997-02-01

The Oak Ridge National Laboratory (ORNL) has been supplying enriched stable and radioactive isotopes to the research, medical, and industrial communities for over 50 y. Very significant changes have occurred in this effort over the past several years, and, while many of these changes have had a negative impact on the availability of enriched isotopes, more recent developments are actually improving the situation for both the users and the producers of enriched isotopes. ORNL is still a major producer and distributor of radioisotopes, but future isotope enrichment operations to be conducted at the Isotope Enrichment Facility (IEF) will be limited to stable isotopes. Among the positive changes in the enriched stable isotope area are a well-functioning, long-term contract program, which offers stability and pricing advantages; the resumption of calutron operations; the adoption of prorated conversion charges, which greatly improves the pricing of isotopes to small users; ISO 9002 registration of the IEF's quality management system; and a much more customer-oriented business philosophy. Efforts are also being made to restore and improve upon the extensive chemical and physical form processing capablities that once existed in the enriched stable isotope program. Innovative ideas are being pursued in both technical and administrative areas to encourage the beneficial use of enriched stable isotopes and the development of related technologies.

Application of Twin Beams in Mach-Zehnder Interferometer

NASA Technical Reports Server (NTRS)

Zhang, J. X.; Xie, C. D.; Peng, K. C.

1996-01-01

Using the twin beams generated from parametric amplifier to drive the two port of a Mach-Zehnder interferometer, it is shown that the minimum detectable optical phase shift can be largly reduced to the Heisenberg limit(1/n) which is far below the Shot Noise Limit(1/square root of n) the large gain limit. The dependence of the minimum detectable phase shift on parametric gain and the inefficient photodetectors has been discussed.

New constraints on the sources and behavior of neodymium and hafnium in seawater from Pacific Ocean ferromanganese crusts

USGS Publications Warehouse

van de Flierdt, T.; Frank, M.; Lee, D.-C.; Halliday, A.N.; Reynolds, B.C.; Hein, J.R.

2004-01-01

The behavior of dissolved Hf in the marine environment is not well understood due to the lack of direct seawater measurements of Hf isotopes and the limited number of Hf isotope time-series obtained from ferromanganese crusts. In order to place better constraints on input sources and develop further applications, a combined Nd-Hf isotope time-series study of five Pacific ferromanganese crusts was carried out. The samples cover the past 38 Myr and their locations range from sites at the margin of the ocean to remote areas, sites from previously unstudied North and South Pacific areas, and water depths corresponding to deep and bottom waters. For most of the samples a broad coupling of Nd and Hf isotopes is observed. In the Equatorial Pacific ENd and EHf both decrease with water depth. Similarly, ENd and EHf both increase from the South to the North Pacific. These data indicate that the Hf isotopic composition is, in general terms, a suitable tracer for ocean circulation, since inflow and progressive admixture of bottom water is clearly identifiable. The time-series data indicate that inputs and outputs have been balanced throughout much of the late Cenozoic. A simple box model can constrain the relative importance of potential input sources to the North Pacific. Assuming steady state, the model implies significant contributions of radiogenic Nd and Hf from young circum-Pacific arcs and a subordinate role of dust inputs from the Asian continent for the dissolved Nd and Hf budget of the North Pacific. Some changes in ocean circulation that are clearly recognizable in Nd isotopes do not appear to be reflected by Hf isotopic compositions. At two locations within the Pacific Ocean a decoupling of Nd and Hf isotopes is found, indicating limited potential for Hf isotopes as a stand-alone oceanographic tracer and providing evidence of additional local processes that govern the Hf isotopic composition of deep water masses. In the case of the Southwest Pacific there is evidence that decoupling may have been the result of changes in weathering style related to the buildup of Antarctic glaciation. Copyright ?? 2004 Elsevier Ltd.

Separation of copper, iron, and zinc from complex aqueous solutions for isotopic measurement

USGS Publications Warehouse

Borrok, D.M.; Wanty, R.B.; Ridley, W.I.; Wolf, R.; Lamothe, P.J.; Adams, M.

2007-01-01

The measurement of Cu, Fe, and Zn isotopes in natural samples may provide valuable information about biogeochemical processes in the environment. However, the widespread application of stable Cu, Fe, and Zn isotope chemistry to natural water systems remains limited by our ability to efficiently separate these trace elements from the greater concentrations of matrix elements. In this study, we present a new method for the isolation of Cu, Fe, and Zn from complex aqueous solutions using a single anion-exchange column with hydrochloric acid media. Using this method we are able to quantitatively separate Cu, Fe, and Zn from each other and from matrix elements in a single column elution. Elution of the elements of interest, as well as all other elements, through the anion-exchange column is a function of the speciation of each element in the various concentrations of HCl. We highlight the column chemistry by comparing our observations with published studies that have investigated the speciation of Cu, Fe, and Zn in chloride solutions. The functionality of the column procedure was tested by measuring Cu, Fe, and Zn isotopes in a variety of stream water samples impacted by acid mine drainage. The accuracy and precision of Zn isotopic measurements was tested by doping Zn-free stream water with the Zn isotopic standard. The reproducibility of the entire column separation process and the overall precision of the isotopic measurements were also evaluated. The isotopic results demonstrate that the Cu, Fe, and Zn column separates from the tested stream waters are of sufficient purity to be analyzed directly using a multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS), and that the measurements are fully-reproducible, accurate, and precise. Although limited in scope, these isotopic measurements reveal significant variations in ??65Cu (- 1.41 to + 0.30???), ??56Fe (- 0.56 to + 0.34???), and ??66Zn (0.31 to 0.49???) among samples collected from different abandoned mines within a single watershed. Hence, Cu, Fe, and Zn isotopic measurements may be a powerful tool for fingerprinting specific metal sources and/or examining biogeochemical reactions within fresh water systems.

Quantification of spatial and seasonal variations in the proportional contribution of nitrate sources using a multi-isotope approach and Bayesian isotope mixing model.

PubMed

Meghdadi, Aminreza; Javar, Narmin

2018-04-01

Spatial and seasonal variations in nitrate contamination are a globally concern. While numerous studies have used δ 15 N-NO 3 and δ 18 O-NO 3 to elucidate the dominant sources of nitrate in groundwater, this approach has significant limitations due to the overlap of nitrate isotopic ranges and the occurrence of nitrate isotopic fractionation. This study quantitatively assessed the spatial and seasonal variations in the proportional contributions of nitrate sources from different land uses in the Tarom watershed in North-West Iran. To achieve this aim, orthogonal projection of the hydrochemical and isotopic dataset of the principal component analysis (PCA) as well as correlation coefficient matrix (Corr-PCA) were evaluated to reduce the dimensionality of the inter-correlated dataset. Next, a nitrate isotopic biplot accompanied with a Bayesian isotope mixing model (SIAR) were applied to specify the spatial and seasonal trends in the proportional contribution of three dominant sources of nitrate (fertilizers, animal manure and residential waste) in the watershed. Finally, in order to provide a sensitive framework for nitrate source appointment and overcome the associated limitations of dual nitrate isotope application, the integration of boron isotope (δ 11 B) and strontium isotopic ratio ( 87 Sr/ 86 Sr) was introduced. The results revealed that the mean contribution of residential sewage increased (17%-27.5%), while the mean contribution of fertilizers decreased (28.3%-19%), from late spring to early autumn. Also, fertilizer was the highest contributor (42.1% ± 3.2) during late spring, especially in regions with more than 75% agricultural land. Meanwhile, the mean contribution of sewage was highest in early autumn (32.1% ± 2.8) in the areas with more than 20% residential land. These results were confirmed by coupled application of δ 11 B and 87 Sr/ 86 Sr. This study provides a useful insight for environmental managers to verify groundwater pollution contributors and to better apply remedial solutions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Genome-wide association mapping of carbon isotope and oxygen isotope ratios in diverse soybean genotypes

USDA-ARS?s Scientific Manuscript database

Water deficit stress is a major factor limiting soybean [Glycine max (L.) Merr.] yield. High water use efficiency (WUE) offers a means to potentially ameliorate drought impact, but increased WUE is often associated with a reduction in transpiration (T) and an accompanied reduction in photosynthesis....

A reliable compound-specific nitrogen isotope analysis of amino acids by GC-C-IRMS following derivatisation into N-pivaloyl-iso-propyl (NPIP)esters for high-resolution food webs estimation.

PubMed

Zhang, Zhongyi; Tian, Jing; Xiao, Hongwei; Zheng, Nengjian; Gao, Xiaofei; Zhu, Renguo; Xiao, Huayun

2016-10-15

The signatures of natural stable nitrogen isotopic composition (δ(15)N) of individual amino acid (AA) have been confirmed to be a potentially effective tool for elucidating nitrogen cycling and trophic position of various organisms in food webs. In the present study, a two-stage derivatisation approach of esterification followed by acylation was evaluated. The biological samples underwent acid hydrolysis and the released individual AA was derivatived into corresponding N-pivaloyl-isopropyl (NPIP) esters for nitrogen isotopic analysis in gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Usually, 13 individual AA derivatives were separated with fine baseline resolution based on a nonpolar gas chromatography column (DB-5ms). The minimum sample amount required under the presented conditions is larger than 20ngN on column in order to accurately determine the δ(15)N values. The δ(15)N values determined by GC-C-IRMS with a precision of better than 1‰, were within 1‰ after empirical correction compared to the corresponding measured by element analysis (EA)-IRMS. Bland-Altman plot showed highly consistency of the δ(15)N values determined by the two measurement techniques. Cation-exchange chromatography was applied to remove interfering fraction from the extracts of plant and animal samples and without nitrogen isotope fractionation during the treatment procedure. Moreover, this approach was carried out to estimate the trophic level of various natural organisms in a natural lake environment. Results highly proved that the trophic level estimated via the presented AA method well reflected the actual food web structure in natural environments. Copyright © 2016 Elsevier B.V. All rights reserved.

Importance of carbon isotopic data of the Permian-Triassic boundary layers in the Verkhoyansk region for the global correlation of the basal Triassic layer

NASA Astrophysics Data System (ADS)

Zakharov, Yu. D.; Biakov, A. S.; Richoz, S.; Horacek, M.

2015-01-01

This paper is dedicated to a global correlation of marine Permian-Triassic boundary layers on the basis of partially published and original data on the δ13Corg and δ13Ccarb values of the Suol section (Setorym River, South Verkhoyansk region). The section consists of six carbon isotopic intervals, which are easily distinguishable in the carbon isotopic curves for a series of Permian-Triassic reference sections of Eurasia and Northern America, including paleontologically described sections of Central Iran, Kashmir, and Southern China. This suggests that the Permian-Triassic boundary in the Suol section is close to the carbon isotopic minimum of interval IV. In light of new data, we suggest considering the upper part of the Late Permian Changhsingian Stage and the lower substage of the Early Triassic Induan Stage of Siberia in the volumes of the rank Otoceras concavum zone and the Tompophiceras pascoei and Wordieoceras decipiens zones, respectively. The O. concavum zone of the Verkhoyansk region probably corresponds to the Late Changhsingian Hypophiceras triviale zone of Greenland. The carbon isotopic intervals II, III, IV, and V in the Permian-Triassic boundary layers of the Verkhoyansk region traced in a series of the reference sections of Eurasia correspond, most likely, to intensification of volcanic activity at the end of the Late Changhsingian and to the first massive eruptions of Siberian traps at the end of the Changhsingian and the beginning of the Induan Stages. New data indicate the possible survival of ammonoids of the Otoceratoidea superfamily at the species level after mass extinction of organisms at the end of the Permian.

Growth patterns of an intertidal gastropod as revealed by oxygen isotope analysis

NASA Astrophysics Data System (ADS)

Bean, J. R.; Hill, T. M.; Guerra, C.

2007-12-01

The size and morphology of mollusk shells are affected by environmental conditions. As a result, it is difficult to assess growth rate, population age structure, shell morphologies associated with ontogenetic stages, and to compare life history patterns across various environments. Oxygen isotope analysis is a useful tool for estimating minimum ages and growth rates of calcium carbonate secreting organisms. Calcite shell material from members of two northern California populations of the intertidal muricid gastropod Acanthinucella spirata was sampled for isotopic analysis. Individual shells were sampled from apex to margin, thus providing a sequential record of juvenile and adult growth. A. spirata were collected from a sheltered habitat in Tomales Bay and from an exposed reef in Bolinas. Abiotic factors, such as temperature, wave exposure, and substrate consistency, and biotic composition differ significantly between these sites, possibly resulting in local adaptations and variation in life history and growth patterns. Shell morphology of A. spirata changes with age as internal shell margin thickenings of denticle rows associated with external growth bands are irregularly accreted. It is not known when, either seasonally and/or ontogentically, these thickenings and bands form or whether inter or intra-populational variation exists. Preliminary results demonstrate the seasonal oxygen isotopic variability present at the two coastal sites, indicating 5-6 degC changes from winter to summertime temperatures; these data are consistent with local intertidal temperature records. Analysis of the seasonal patterns indicate that: 1) differences in growth rate and seasonal growth patterns at different ontogenetic stages within populations, and 2) differences in growth patterns and possibly age structure between the two A. spirata populations. These findings indicate that isotopic analyses, in addition to field observations and morphological measurements, are necessary to assess life history strategies and compare population dynamics under varying environmental conditions.

High Tensile Strength Amalgams for In-Space Fabrication and Repair

NASA Technical Reports Server (NTRS)

Grugel, Richard N.

2006-01-01

Amalgams are well known for their use in dental practice as a tooth filling material. They have a number of useful attributes that include room temperature fabrication, corrosion resistance, dimensional stability, and very good compressive strength. These properties well serve dental needs but, unfortunately, amalgams have extremely poor tensile strength, a feature that severely limits other potential applications. Improved material properties (strength and temperature) of amalgams may have application to the freeform fabrication of repairs or parts that might be necessary during an extended space mission. Advantages would include, but are not limited to: the ability to produce complex parts, a minimum number of processing steps, minimum crew interaction, high yield - minimum wasted material, reduced gravity compatibility, minimum final finishing, safety, and minimum power consumption. The work presented here shows how the properties of amalgams can be improved by changing particle geometries in conjunction with novel engineering metals.

Diode laser based resonance ionization mass spectrometric measurement of strontium-90

NASA Astrophysics Data System (ADS)

Bushaw, B. A.; Cannon, B. D.

1997-10-01

A diode laser based scheme for the isotopically selective excitation and ionization of strontium is presented. The double-resonance excitation 5s 21S 0→5s5p 3P 1→5s6s 3S 1 is followed by photoionization at 488 nm. The isotope shifts and hyperfine structure in the resonance transitions have been accurately measured for the stable isotopes and 90Sr, with the measurement of the 90Sr shifts using sub-pg samples. Analytical tests, using graphite crucible atomization, demonstrated 90Sr detection limits of 0.8 fg and overall (optical+mass spectrometer) isotopic selectivity of >10 10 against stable strontium.

Contrasting Physiological and Proteomic Adaptations to Iron and/or Copper Limitation in Two Strains of the Same Open Ocean Diatom Thalassiosira oceanica

NASA Astrophysics Data System (ADS)

Schuback, N.; Hippmann, A.; Maldonado, M. T.; Allen, A. E.; McCrow, J.; Foster, L. J.; Green, B. R.; Alami, M.

2016-02-01

Iron plays a significant role in controlling marine primary productivity. Despite that extremely low dissolved iron (Fe) concentrations are found in Fe-limited regions, some phytoplankton are able to survive and thrive. Two strains of the model oceanic diatom Thalassiosira oceanica, TO 1003 and TO 1005, have both been used in previous studies to characterize adaptations to iron limitation. These studies have shown that T. oceanica has lowered its Fe requirements and increased its Fe acquisition efficiency compared to coastal counterparts. Both strategies may impose a higher cellular copper (Cu) demand. However, the underlying biochemical adaptations in these oceanic diatoms remain unknown. Recently, the genome, as well as the first proteomic and transcriptomic analyses of T. oceanica 1005 grown under different Fe levels, were published. To further our understanding of the interplay between Fe- and Cu- physiology in open ocean diatoms, we examined an array of physiological responses to varying degrees of Fe-, Cu- and Fe/Cu co-limitation in both strains. We also determined the differential expression of proteins using stable isotope labeling and LC-MS/MS proteomic analysis. The two strains, TO 1003 and TO 1005, need markedly different metal concentrations in the media. TO1003 requires 30% less Cu to sustain its optimal growth and less than 1/10th of the minimum Cu that is needed by TO 1005 to survive. In contrast, TO 1005 is able to grow with less Fe available in the media. The physiological and proteomic responses of these two strains when acclimated to low Fe and/or Cu concentrations will be presented. The evolutionary implications will be discussed.

Changes in the structure of nuclei between the magic neutron numbers 50 and 82 as indicated by a rotating-cluster analysis of the energy values of the first 2+ excited states of isotopes of cadmium, tin, and tellurium

PubMed Central

Pauling, Linus

1981-01-01

Values of R, the radius of rotation of the rotating cluster, are calculated from the observed values of the energy of the lowest 2+ states of the even isotopes of 48Cd, 50Sn, and 52Te with the assumption that the cluster is α, p2, and α, respectively. R shows a maximum at ≈N = 58, a minimum at ≈N = 62, and a second maximum at ≈N = 70. The increase to the first maximum is interpreted as resulting from the overcrowding of spherons (alphas and tritons) in the mantle (outer layer) of the nuclei, causing the cluster to change from rotating in the mantle to skimming over its surface; the decrease to the minimum results from the addition of three dineutrons to the core, expanding the mantle and permitting the rotating cluster to begin to drop back into it; and the increase to the second maximum results from the overcrowding of the larger mantle surrounding the core containing the semi-magic number 14 of neutrons rather than the magic number 8 for N = 50. The decrease after the second maximum results from the further increase in the number of core neutrons to 20, corresponding to the magic number 82. Some additional evidence for the change to an intermediate structure between N = 50 and N = 82 is also discussed. PMID:16593084

Dual element ((15)N/(14)N, (13)C/(12)C) isotope analysis of glyphosate and AMPA by derivatization-gas chromatography isotope ratio mass spectrometry (GC/IRMS) combined with LC/IRMS.

PubMed

Mogusu, Emmanuel O; Wolbert, J Benjamin; Kujawinski, Dorothea M; Jochmann, Maik A; Elsner, Martin

2015-07-01

To assess sources and degradation of the herbicide glyphosate [N-(phosphonomethyl) glycine] and its metabolite AMPA (aminomethylphosphonic acid), concentration measurements are often inconclusive and even (13)C/(12)C analysis alone may give limited information. To advance isotope ratio analysis of an additional element, we present compound-specific (15)N/(14)N analysis of glyphosate and AMPA by a two step derivatization in combination with gas chromatography/isotope ratio mass spectrometry (GC/IRMS). The N-H group was derivatized with isopropyl chloroformate (iso-PCF), and remaining acidic groups were subsequently methylated with trimethylsilyldiazomethane (TMSD). Iso-PCF treatment at pH <10 gave too low (15)N/(14)N ratios indicating an incomplete derivatization; in contrast, too high (15)N/(14)N ratios at pH >10 indicated decomposition of the derivative. At pH 10, and with an excess of iso-PCF by 10-24, greatest yields and accurate (15)N/(14)N ratios were obtained (deviation from elemental analyzer-IRMS: -0.2 ± 0.9% for glyphosate; -0.4 ± 0.7% for AMPA). Limits for accurate δ(15)N analysis of glyphosate and AMPA were 150 and 250 ng injected, respectively. A combination of δ(15)N and δ(13)C analysis by liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) (1) enabled an improved distinction of commercial glyphosate products and (2) showed that glyphosate isotope values during degradation by MnO2 clearly fell outside the commercial product range. This highlights the potential of combined carbon and nitrogen isotopes analysis to trace sources and degradation of glyphosate.

The origin of Neoproterozoic Cap Carbonates: a view from Mg and Sr Isotopes

NASA Astrophysics Data System (ADS)

Liu, C.; Raub, T. D.; Evans, D. A.; Wang, Z.

2010-12-01

Neoproterozoic cap carbonates are suggested to document Earth’s transition from a ‘snowball earth’ to an ‘extreme greenhouse’ environment. Geochemistry of these rocks is essential for its paleo-environment reconstruction, and Mg and Sr isotopes can help to understand its origin and constrain geochemical evolution of the contemporary ocean. In this study, we studied Mg and Sr isotope composition of 18 cap dolostone samples from Nuccaleena formation carbonate and one from the the mixed siliciclastic transition at its base at Elatina Creek in Adelaide Geosyncline of South Australia. We established a step-leaching procedure using ammonium acetate, various concentrations of acetic acid, and HCl on four of these cap carbonate samples to untangle the isotopic signatures of its various constituent phases. 87Sr/86Sr values of the leachates in each sample decrease continuously as leaching process proceeds and sometimes rebound as silicates are dissolved. The lowest leachate 87Sr/86Sr values, down to 0.7084, are lower than the reported dolostone(~0.7096) but still higher than those of limestones overlying the dolostone in other basins(~0.7079), indicating an input of increasing level of weathering to the ocean over the course of cap-carbonate precipitation. In contrast, δ26MgDSM3 variation with progressing leaching steps exhibits a wave pattern (variation up to 0.4~0.5‰) during the leaching processes, due to different chemical affinity of Mg in various mineral phases. More importantly, Mg isotope composition of the portion that is associated with stratigraphically low, minimum Sr isotope composition is similar to those of contemporary corals (or inorganic aragonite precipitation), but up to ca. 0.6 per mil lower than stratigraphically-higher values, suggesting a warmer weather and/or more significant silicate weathering than contemporary Earth’s climate, and a transition from physical weathering to chemical weather during deglaciation.

Paleoclimatic and paleoceanographic records through Marine Isotope Stage 19 at the Chiba composite section, central Japan: A key reference for the Early-Middle Pleistocene Subseries boundary

NASA Astrophysics Data System (ADS)

Suganuma, Yusuke; Haneda, Yuki; Kameo, Koji; Kubota, Yoshimi; Hayashi, Hiroki; Itaki, Takuya; Okuda, Masaaki; Head, Martin, J.; Sugaya, Manami; Nakazato, Hiroomi; Igarashi, Atsuo; Shikoku, Kizuku; Hongo, Misao; Watanabe, Masami; Satoguchi, Yasufumi; Takeshita, Yoshihiro; Nishida, Naohisa; Izumi, Kentaro; Kawamura, Kenji; Kawamata, Moto; Okuno, Jun'ichi; Yoshida, Takeshi; Ogitsu, Itaru; Yabusaki, Hisashi; Okada, Makoto

2018-07-01

Marine Isotope Stage (MIS) 19 is an important analogue for the present interglacial because of its similar orbital configuration, especially the phasing of the obliquity maximum to precession minimum. However, sedimentary records suitable for capturing both terrestrial and marine environmental changes are limited, and thus the climatic forcing mechanisms for MIS 19 are still largely unknown. The Chiba composite section, east-central Japanese archipelago, is a continuous and expanded marine sedimentary succession well suited to capture terrestrial and marine environmental changes through MIS 19. In this study, a detailed oxygen isotope chronology is established from late MIS 20 to early MIS 18, supported by a U-Pb zircon age and the presence of the Matuyama-Brunhes boundary. New pollen, marine microfossil, and planktonic foraminiferal δ18O and Mg/Ca paleotemperature records reveal the complex interplay of climatic influences. Our pollen data suggest that the duration of full interglacial conditions during MIS 19 extends from 785.0 to 775.1 ka (9.9 kyr), which offers an important natural baseline in predicting the duration of the present interglacial. A Younger Dryas-type cooling event is present during Termination IX, suggesting that such events are linked to this orbital configuration. Millennial- to multi-millennial-scale variations in our δ18O and Mg/Ca records imply that the Subarctic Front fluctuated in the northwestern Pacific Ocean during late MIS 19, probably in response to East Asian winter monsoon variability. The climatic setting at this time appears to be related to less severe summer insolation minima at 65˚N and/or high winter insolation at 50˚N. Our records do not support a recently hypothesized direct coupling between variations in the geomagnetic field intensity and global/regional climate change. Our highly resolved paleoclimatic and paleoceanographic records, coupled with a well-defined Matuyama-Brunhes boundary (772.9 ka; duration 1.9 kyr), establish the Chiba composite section as an exceptional climatic and chronological reference section for the Early-Middle Pleistocene boundary.

26 CFR 1.383-2 - Limitations on certain capital losses and excess credits in computing alternative minimum tax...

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 4 2010-04-01 2010-04-01 false Limitations on certain capital losses and excess credits in computing alternative minimum tax. [Reserved] 1.383-2 Section 1.383-2 Internal Revenue INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) INCOME TAX (CONTINUED) INCOME TAXES Insolvency...

40 CFR Table 3 to Subpart Jjjjjj... - Operating Limits for Boilers With Emission Limits

Code of Federal Regulations, 2013 CFR

2013-07-01

... as defined in § 63.11237. 4. Dry sorbent or activated carbon injection control Maintain the 30-day rolling average sorbent or activated carbon injection rate at or above the minimum sorbent injection rate or minimum activated carbon injection rate as defined in § 63.11237. When your boiler operates at...

Evaporation loss and evaporation/transpiration partitioning from isotope-based monitoring of Canada's provincial and national river networks

NASA Astrophysics Data System (ADS)

Gibson, J. J.; Birks, S. J.; Stadnyk, T.; Delavau, C. J.

2017-12-01

Stable isotopes of water have been measured since the 1990's as part of hydrometric monitoring programs within Canada's Water Survey of Canada gauging network and Alberta's Long-Term River Network. These datasets are being applied for hydrograph separation of streamflow sources, including rain, snow, groundwater, and surface water, as well as for estimation of watershed evaporation losses and evaporation/transpiration partitioning. Here we describe an innovative isotope mass balance approach, discuss benefits and limitations of the method, and present selected results that illustrate important regional trends in the contemporary hydrology of Canada. Overall, isotopes are shown to be useful for constraining water balance variations across regions with low monitoring density. Recommendations for future activities are identified, including regional comparisons with outputs from isotope-capable distributed hydrologic models.

Voyager measurements of the isotopic composition of cosmic-ray aluminum and implications for the propagation of cosmic rays

NASA Technical Reports Server (NTRS)

Lukasiak, A.; Mcdonald, F. B.; Webber, W. R.

1994-01-01

We report a new measurement of the cosmic-ray isotopic composition of aluminum in the low-energy range form 75 to 206 MeV per nucleon.This measurement was made using the high-energy telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1993 with an average solar modulation level about 497 MV, roughly the same as at Earth near sunspot minimum. We obtain approximately 430 Al events of which approximately 35 are Al-26 and 395 are Al-27. The Al isotopes were separated with an average mass resolution sigma of 0.35 amu. Our interpretation of the isotopic composition of cosmic-ray aluminum is based on a standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the latest cross sections of the New Mexico-Saclay collaboration as well as a disk-halo diffusion model. From our observed ratio Al-26/Al-27 of 8.3 +/- 2.4 % we deduce an average interstellar density of about 0.52 (+0.26, -0.2) atoms per cu cm. This density is larger than the value of 0.28 (+0.14, -0.11) atoms per cu cm we found from an analysis of the observed abundance of the longer lived Be-10 made using data from the Voyager detectors over almost the same time interval and using essentially the same propagation program.

Oxygen Isotope Ratios of Magnetite in CI-Like Clasts from a Polymict Ureilite

NASA Technical Reports Server (NTRS)

Kita, N. T.; Defouilloy, C.; Goodrich, C. A.; Zolensky, M. E.

2017-01-01

Polymict ureilites contain a variety of Less than or equal to mm to cm sized non-ureilitic clasts, many of which can be identifed as chondritic and achondritic meteorite types. Among them, dark clasts have been observed in polymict ureilites that are similar to CI chondrites in mineralogy, containing phyllosilicates, magnetite, sulfide and carbonates. Bulk oxygen isotope analyses of a dark clast in Nilpena plot along the CCAM line and above the terrestrial fractionation line, on the O-poor extension of the main group ureilite trend and clearly different from bulk CI chondrites. One possible origins of such dark clast is that they represent aqueously altered precursors of ureilite parent body (UPB) that were preserved on the cold surface of the UPB. Oxygen isotope analyses of dark clasts are key to better understanding their origins. Oxygen isotope ratios of magnetite are of special interest because they reflect the compositions of the fluids in asteroidal bodies. In primitive chondrites, Delta O (= Delta O - 0.52× Delta O) values of magnetites are always higher than those of the bulk meteorites and represent minimum Delta O values of the initial O-poor aqueous fluids in the parent body. Previous SIMS analyses on magnetite and fayalite in dark clasts from the DaG 319 polymict ureilite were analytically difficult due to small grain sizes, though data indicated positive Delta O values of 3-4 per mille, higher than that of the dark clast in Nilpena (1.49per mille).

Submarine Alkalic Lavas Around the Hawaiian Hotspot; Plume and Non-Plume Signatures Determined by Noble Gases

NASA Astrophysics Data System (ADS)

Hanyu, T.; Clague, D. A.; Kaneoka, I.; Dunai, T. J.; Davies, G. R.

2004-12-01

Noble gas isotopic ratios were determined for submarine alkalic volcanic rocks distributed around the Hawaiian islands to constrain the origin of such alkalic volcanism. Samples were collected by dredging or using submersibles from the Kauai Channel between Oahu and Kauai, north of Molokai, northwest of Niihau, Southwest Oahu, South Arch and North Arch volcanic fields. Sites located downstream from the center of the hotspot have 3He/4He ratios close to MORB at about 8 Ra, demonstrating that the magmas erupted at these sites had minimum contribution of volatiles from a mantle plume. In contrast, the South Arch, located upstream of the hotspot on the Hawaiian Arch, has 3He/4He ratios between 17 and 21 Ra, indicating a strong plume influence. Differences in noble gas isotopic characteristics between alkalic volcanism downstream and upstream of the hotspot imply that upstream volcanism contains incipient melts from an upwelling mantle plume, having primitive 3He/4He. In combination with lithophile element isotopic data, we conclude that the most likely source of the upstream magmatism is depleted asthenospheric mantle that has been metasomatised by incipient melt from a mantle plume. After major melt extraction from the mantle plume during production of magmas for the shield stage, the plume material is highly depleted in noble gases and moderately depleted in lithophile elements. Partial melting of the depleted mantle impregnated by melts derived from this volatile depleted plume source may explain the isotopic characteristics of the downstream alkalic magmatism.

New determinations of 40Ar/39Ar isotopic ages and flow volumes for Cenozoic volcanism in the Terror Rift, Ross Sea, Antarctica

NASA Astrophysics Data System (ADS)

Rilling, S.; Mukasa, S.; Wilson, T.; Lawver, L.; Hall, C.

2009-12-01

This study provides new determinations of 40Ar/39Ar isotopic ages and flow volumes for submarine and subaerial Neogene volcanism developed within the Terror Rift, Ross Sea, Antarctica, the youngest segment of the West Antarctic Rift System. The study is based on the first dredged samples from seven seamounts north of Ross Island, as well as new data from Franklin and Beaufort Islands. The sampled foidite and basanitic lavas range in age from Quaternary (90 ± 66 ka) on a small seamount ˜10 km north of Franklin Island to 6.80 ± 0.05 Ma on Beaufort Island. These ages are consistent with ages of volcanism in both the Melbourne and Erebus Volcanic Provinces and significantly expand the documented area of Neogene magmatism in Victoria Land. There is no geographic progression of volcanism through time, but volcanism was voluminous in the Pliocene and particularly widespread during the Pleistocene. Two of the dredges sampled edifices comprised of less than 0.2 km3 of volcanic materials. The largest seamount in the study area has 58.8 km3 of volcanic material and represents growth over a period of several thousand years. Estimated minimum eruption rates range from 2 × 10-4 km3 y-1 to 2 × 10-3 km3 y-1, consistent with rates proposed for other rift systems and nearby Mt. Erebus. Recent estimates of extension magnitude for the Terror Rift correspond to minimal decompression of only 0.10 to 0.22 GPa and therefore limited melt output of a typical peridotite source.

Gasdynamic Inlet Isolation in Rotating Detonation Engine

DTIC Science & Technology

2010-12-01

2D Total Variation Diminishing (TVD): Continuous Riemann Solver Minimum Dissipation: LHS & RHS Activate pressure switch : Supersonic Activate...Total Variation Diminishing (TVD) limiter: Continuous Riemann Solver Minimum Dissipation: LHS & RHS Activate pressure switch : Supersonic Activate...Continuous 94 Riemann Solver Minimum Dissipation: LHS & RHS Activate pressure switch : Supersonic Activate pressure gradient switch: Normal

14 CFR 135.221 - IFR: Alternate airport weather minimums.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false IFR: Alternate airport weather minimums... VFR/IFR Operating Limitations and Weather Requirements § 135.221 IFR: Alternate airport weather minimums. No person may designate an alternate airport unless the weather reports or forecasts, or any...

14 CFR 135.221 - IFR: Alternate airport weather minimums.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 3 2013-01-01 2013-01-01 false IFR: Alternate airport weather minimums... VFR/IFR Operating Limitations and Weather Requirements § 135.221 IFR: Alternate airport weather minimums. No person may designate an alternate airport unless the weather reports or forecasts, or any...

14 CFR 135.221 - IFR: Alternate airport weather minimums.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 3 2011-01-01 2011-01-01 false IFR: Alternate airport weather minimums... VFR/IFR Operating Limitations and Weather Requirements § 135.221 IFR: Alternate airport weather minimums. No person may designate an alternate airport unless the weather reports or forecasts, or any...

14 CFR 135.221 - IFR: Alternate airport weather minimums.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false IFR: Alternate airport weather minimums... VFR/IFR Operating Limitations and Weather Requirements § 135.221 IFR: Alternate airport weather minimums. No person may designate an alternate airport unless the weather reports or forecasts, or any...

14 CFR 135.221 - IFR: Alternate airport weather minimums.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 3 2012-01-01 2012-01-01 false IFR: Alternate airport weather minimums... VFR/IFR Operating Limitations and Weather Requirements § 135.221 IFR: Alternate airport weather minimums. No person may designate an alternate airport unless the weather reports or forecasts, or any...

Definition of Small Gram Quantity Contents for Type B Radioactive Material Transportation Packages: Activity-Based Content Limitations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sitaraman, S; Kim, S; Biswas, D

2010-10-27

Since the 1960's, the Department of Transportation Specification (DOT Spec) 6M packages have been used extensively for transportation of Type B quantities of radioactive materials between Department of Energy (DOE) facilities, laboratories, and productions sites. However, due to the advancement of packaging technology, the aging of the 6M packages, and variability in the quality of the packages, the DOT implemented a phased elimination of the 6M specification packages (and other DOT Spec packages) in favor of packages certified to meet federal performance requirements. DOT issued the final rule in the Federal Register on October 1, 2004 requiring that use ofmore » the DOT Specification 6M be discontinued as of October 1, 2008. A main driver for the change was the fact that the 6M specification packagings were not supported by a Safety Analysis Report for Packaging (SARP) that was compliant with Title 10 of the Code of Federal Regulations part 71 (10 CFR 71). Therefore, materials that would have historically been shipped in 6M packages are being identified as contents in Type B (and sometimes Type A fissile) package applications and addenda that are to be certified under the requirements of 10 CFR 71. The requirements in 10 CFR 71 include that the Safety Analysis Report for Packaging (SARP) must identify the maximum radioactivity of radioactive constituents and maximum quantities of fissile constituents (10 CFR 71.33(b)(1) and 10 CFR 71.33(b)(2)), and that the application (i.e., SARP submittal or SARP addendum) demonstrates that the external dose rate (due to the maximum radioactivity of radioactive constituents and maximum quantities of fissile constituents) on the surface of the packaging (i.e., package and contents) not exceed 200 mrem/hr (10 CFR 71.35(a), 10 CFR 71.47(a)). It has been proposed that a 'Small Gram Quantity' of radioactive material be defined, such that, when loaded in a transportation package, the dose rates at external points of an unshielded packaging not exceed the regulatory limits prescribed by 10 CFR 71 for non-exclusive shipments. The mass of each radioisotope presented in this paper is limited by the radiation dose rate on the external surface of the package, which per the regulatory limit should not exceed 200 mrem/hr. The results presented are a compendium of allowable masses of a variety of different isotopes (with varying impurity levels of beryllium in some of the actinide isotopes) that, when loaded in an unshielded packaging, do not result in an external dose rate on the surface of the package that exceeds 190 mrem/hr (190 mrem/hr was chosen to provide 5% conservatism relative to the regulatory limit). These mass limits define the term 'Small Gram Quantity' (SGQ) contents in the context of radioactive material transportation packages. The term SGQ is isotope-specific and pertains to contents in radioactive material transportation packages that do not require shielding and still satisfy the external dose rate requirements. Since these calculated mass limits are for contents without shielding, they are conservative for packaging materials that provide some limited shielding or if the contents are placed into a shielded package. The isotopes presented in this paper were chosen as the isotopes that Department of Energy (DOE) sites most likely need to ship. Other more rarely shipped isotopes, along with industrial and medical isotopes, are planned to be included in subsequent extensions of this work.« less

[Interest and limits of inductively coupled plasma mass spectrometry (ICP-MS) for urinary diagnosis of radionuclide internal contamination].

PubMed

Lecompte, Yannick; Bohand, Sandra; Laroche, Pierre; Cazoulat, Alain

2013-01-01

After a review of radiometric reference methods used in radiotoxicology, analytical performance of inductively coupled plasma mass spectrometry (ICP-MS) for the workplace urinary diagnosis of internal contamination by radionuclides are evaluated. A literature review (covering the period from 2000 to 2012) is performed to identify the different applications of ICP-MS in radiotoxicology for urine analysis. The limits of detection are compared to the recommendations of the International commission on radiological protection (ICRP 78: "Individual monitoring for internal exposure of workers"). Except one publication describing the determination of strontium-90 (β emitter), all methods using ICP-MS reported in the literature concern actinides (α emitters). For radionuclides with a radioactive period higher than 10(4) years, limits of detection are most often in compliance with ICRP publication 78 and frequently lower than radiometric methods. ICP-MS allows the specific determination of plutonium-239 + 240 isotopes which cannot be discriminated by α spectrometry. High resolution ICP-MS can also measure uranium isotopic ratios in urine for total uranium concentrations lower than 20 ng/L. The interest of ICP-MS in radiotoxicology concerns essentially the urinary measurement of long radioactive period actinides, particularly for uranium isotope ratio determination and 239 and 240 plutonium isotopes discrimination. Radiometric methods remain the most efficient for the majority of other radionuclides.

Reduction of chemical formulas from the isotopic peak distributions of high-resolution mass spectra.

PubMed

Roussis, Stilianos G; Proulx, Richard

2003-03-15

A method has been developed for the reduction of the chemical formulas of compounds in complex mixtures from the isotopic peak distributions of high-resolution mass spectra. The method is based on the principle that the observed isotopic peak distribution of a mixture of compounds is a linear combination of the isotopic peak distributions of the individual compounds in the mixture. All possible chemical formulas that meet specific criteria (e.g., type and number of atoms in structure, limits of unsaturation, etc.) are enumerated, and theoretical isotopic peak distributions are generated for each formula. The relative amount of each formula is obtained from the accurately measured isotopic peak distribution and the calculated isotopic peak distributions of all candidate formulas. The formulas of compounds in simple spectra, where peak components are fully resolved, are rapidly determined by direct comparison of the calculated and experimental isotopic peak distributions. The singular value decomposition linear algebra method is used to determine the contributions of compounds in complex spectra containing unresolved peak components. The principles of the approach and typical application examples are presented. The method is most useful for the characterization of complex spectra containing partially resolved peaks and structures with multiisotopic elements.

Isotopic determination of uranium in soil by laser induced breakdown spectroscopy

DOE PAGES

Chan, George C. -Y.; Choi, Inhee; Mao, Xianglei; ...

2016-03-26

Laser-induced breakdown spectroscopy (LIBS) operated under ambient pressure has been evaluated for isotopic analysis of uranium in real-world samples such as soil, with U concentrations in the single digit percentage levels. The study addresses the requirements for spectral decomposition of 235U and 238U atomic emission peaks that are only partially resolved. Although non-linear least-square fitting algorithms are typically able to locate the optimal combination of fitting parameters that best describes the experimental spectrum even when all fitting parameters are treated as free independent variables, the analytical results of such an unconstrained free-parameter approach are ambiguous. In this work, five spectralmore » decomposition algorithms were examined, with different known physical properties (e.g., isotopic splitting, hyperfine structure) of the spectral lines sequentially incorporated into the candidate algorithms as constraints. It was found that incorporation of such spectral-line constraints into the decomposition algorithm is essential for the best isotopic analysis. The isotopic abundance of 235U was determined from a simple two-component Lorentzian fit on the U II 424.437 nm spectral profile. For six replicate measurements, each with only fifteen laser shots, on a soil sample with U concentration at 1.1% w/w, the determined 235U isotopic abundance was (64.6 ± 4.8)%, and agreed well with the certified value of 64.4%. Another studied U line - U I 682.691 nm possesses hyperfine structure that is comparatively broad and at a significant fraction as the isotopic shift. Thus, 235U isotopic analysis with this U I line was performed with spectral decomposition involving individual hyperfine components. For the soil sample with 1.1% w/w U, the determined 235U isotopic abundance was (60.9 ± 2.0)%, which exhibited a relative bias about 6% from the certified value. The bias was attributed to the spectral resolution of our measurement system - the measured line width for this U I line was larger than its isotopic splitting. In conclusion, although not the best emission line for isotopic analysis, this U I emission line is sensitive for element analysis with a detection limit of 500 ppm U in the soil matrix; the detection limit for the U II 424.437 nm line was 2000 ppm.« less

Quantifying inter-laboratory variability in stable isotope analysis of ancient skeletal remains.

PubMed

Pestle, William J; Crowley, Brooke E; Weirauch, Matthew T

2014-01-01

Over the past forty years, stable isotope analysis of bone (and tooth) collagen and hydroxyapatite has become a mainstay of archaeological and paleoanthropological reconstructions of paleodiet and paleoenvironment. Despite this method's frequent use across anthropological subdisciplines (and beyond), the present work represents the first attempt at gauging the effects of inter-laboratory variability engendered by differences in a) sample preparation, and b) analysis (instrumentation, working standards, and data calibration). Replicate analyses of a 14C-dated ancient human bone by twenty-one archaeological and paleoecological stable isotope laboratories revealed significant inter-laboratory isotopic variation for both collagen and carbonate. For bone collagen, we found a sizeable range of 1.8‰ for δ13Ccol and 1.9‰ for δ15Ncol among laboratories, but an interpretatively insignificant average pairwise difference of 0.2‰ and 0.4‰ for δ13Ccol and δ15Ncol respectively. For bone hydroxyapatite the observed range increased to a troublingly large 3.5‰ for δ13Cap and 6.7‰ for δ18Oap, with average pairwise differences of 0.6‰ for δ13Cap and a disquieting 2.0‰ for δ18Oap. In order to assess the effects of preparation versus analysis on isotopic variability among laboratories, a subset of the samples prepared by the participating laboratories were analyzed a second time on the same instrument. Based on this duplicate analysis, it was determined that roughly half of the isotopic variability among laboratories could be attributed to differences in sample preparation, with the other half resulting from differences in analysis (instrumentation, working standards, and data calibration). These findings have serious implications for choices made in the preparation and extraction of target biomolecules, the comparison of results obtained from different laboratories, and the interpretation of small differences in bone collagen and hydroxyapatite isotope values. To address the issues arising from inter-laboratory comparisons, we devise a novel measure we term the Minimum Meaningful Difference (MMD), and demonstrate its application.

Quantifying Inter-Laboratory Variability in Stable Isotope Analysis of Ancient Skeletal Remains

PubMed Central

Pestle, William J.; Crowley, Brooke E.; Weirauch, Matthew T.

2014-01-01

Over the past forty years, stable isotope analysis of bone (and tooth) collagen and hydroxyapatite has become a mainstay of archaeological and paleoanthropological reconstructions of paleodiet and paleoenvironment. Despite this method's frequent use across anthropological subdisciplines (and beyond), the present work represents the first attempt at gauging the effects of inter-laboratory variability engendered by differences in a) sample preparation, and b) analysis (instrumentation, working standards, and data calibration). Replicate analyses of a 14C-dated ancient human bone by twenty-one archaeological and paleoecological stable isotope laboratories revealed significant inter-laboratory isotopic variation for both collagen and carbonate. For bone collagen, we found a sizeable range of 1.8‰ for δ13Ccol and 1.9‰ for δ15Ncol among laboratories, but an interpretatively insignificant average pairwise difference of 0.2‰ and 0.4‰ for δ13Ccol and δ15Ncol respectively. For bone hydroxyapatite the observed range increased to a troublingly large 3.5‰ for δ13Cap and 6.7‰ for δ18Oap, with average pairwise differences of 0.6‰ for δ13Cap and a disquieting 2.0‰ for δ18Oap. In order to assess the effects of preparation versus analysis on isotopic variability among laboratories, a subset of the samples prepared by the participating laboratories were analyzed a second time on the same instrument. Based on this duplicate analysis, it was determined that roughly half of the isotopic variability among laboratories could be attributed to differences in sample preparation, with the other half resulting from differences in analysis (instrumentation, working standards, and data calibration). These findings have serious implications for choices made in the preparation and extraction of target biomolecules, the comparison of results obtained from different laboratories, and the interpretation of small differences in bone collagen and hydroxyapatite isotope values. To address the issues arising from inter-laboratory comparisons, we devise a novel measure we term the Minimum Meaningful Difference (MMD), and demonstrate its application. PMID:25061843

Sulfur isotope change across the Early Mississippian K-O (Kinderhookian-Osagean) δ13C excursion

NASA Astrophysics Data System (ADS)

Maharjan, Dev; Jiang, Ganqing; Peng, Yongbo; Nicholl, Michael J.

2018-07-01

Paired carbonate associate sulfate (CAS) sulfur isotopes (δ34SCAS), pyrite sulfur isotopes (δ34SPY) and CAS oxygen isotopes (δ18OCAS) across the Early Mississippian K-O δ13C excursion are documented from two sections of a west-dipping carbonate ramp in the southern Great Basin, western U.S.A. A 4-6‰ positive δ34SCAS anomaly, accompanied by negative shifts in δ34SPY and δ18OCAS, is found within the K-O δ13C excursion. In the section with a broader δ13C excursion, Δ34S (Δ34 S =δ34SCAS-δ34SPY) increases from 15‰ to 45‰ and δ13Ccarb drops from 7‰ to 4‰ at the same stratigraphic interval. If this δ34SCAS anomaly represents a global phenomenon, the large magnitude (4-6‰) and short duration (shorter than that of δ13C) suggest an unusual pyrite burial event that expanded from sediments to the ocean water column. In this scenario, the areal and volumetric expansion of sulfate reduction and pyrite burial was likely triggered by abundantly available organic matter near the peak of the K-O δ13C excursion, during which organic carbon production and burial may have reached a maximum, thus substantially expanding the oxygen minimum zone (OMZ). Numerical simulations suggest that pyrite burial rates 2.5-5 times higher than that of the modern ocean followed by sulfide oxidation are required to produce the observed δ34SCAS anomaly in a sulfate-rich ([SO4] ≥28 mM) Early Mississippian ocean. Alternatively, the sulfur and CAS oxygen isotope anomalies may record local sulfur cycling in a foreland basin where changes in weathering input and bottom-water redox conditions in response to sea-level fall and cooling resulted in isotope changes. In both scenarios (either local or global), the integrated carbon, sulfur, and CAS-oxygen isotope data suggest a much more dynamic sulfur cycle across the K-O δ13C excursion than has been previously suggested.

Nuclear tracks, Sm isotopes and neutron capture effects in the Elephant Morraine shergottite

NASA Technical Reports Server (NTRS)

Rajan, R. S.; Lugmair, G.; Tamhane, A. S.; Poupeau, G.

1986-01-01

Nuclear track studies, uranium concentration measurements and Sm-isotope studies have been performed on both lithologies A and B of the Elephant Morraine shergottite, EETA 79001. Track studies show that EETA 79001 was a rather small object in space with a preatmospheric radius of 12 + or - 2 cm, corresponding to a preatmospheric mass of 28 + or - 13 kg. Phosphates have U concentrations ranging from 0.3 to 1.3 ppm. There are occasional phosphates with excess fission tracks, possibly produced from neutron-induced fission of U and Th, during the regolith exposure in the shergottite parent body (SPB). Sm-isotope studies, while not showing any clear-cut excess in Sm-150, make it possible to derive meaningful upper limits to thermal neutron fluences of 2 to 3 x 10 to the 15th n/sq cm, during a possible regolith irradiation. These limits are consistent with the track data and also make it possible to derive an upper limit to the neutron exposure age of EETA 79001 of 55 Myr in the SPB regolith.

Magnesium Isotopic Composition of Kamchatka Sub-Arc Mantle Peridotites

NASA Astrophysics Data System (ADS)

Hu, Y.; Teng, F. Z.; Ionov, D. A.

2016-12-01

Subduction of the oceanic slab may add a crustal isotopic signal to the mantle wedge. The highly variable Mg isotopic compositions (δ26Mg) of the subducted oceanic crust input[1] and arc lava output[2] imply a distinctive Mg isotopic signature of the mantle wedge. Magnesium isotopic data on samples from the sub-arc mantle are still limited, however. To characterize the Mg isotopic composition of typical sub-arc mantle, 17 large and fresh spinel harzburgite xenoliths from Avacha volcano were analyzed. The harzburgites were formed by 30% melt extraction at ≤ 1 2 GPa and fluid fluxing condition, and underwent possible fluid metasomatism as suggested by distinctively high orthopyroxene mode in some samples, the presence of accessory amphibole and highly variable Ba/La ratios[3]. However, their δ26Mg values display limited variation from -0.32 to -0.21, which are comparable to the mantle average at -0.25 ± 0.07[4]. The overall mantle-like and homogenous δ26Mg of Avacha sub-arc peridotites are consistent with their similar chemical compositions and high MgO contents (> 44 wt%) relative to likely crustal fluids. Furthermore, clinopyroxene (-0.24 ± 0.10, 2SD, n = 5), a late-stage mineral exsolved from high-temperature, Ca-rich residual orthopyroxene, is in broad Mg isotopic equilibrium with olivine (-0.27 ± 0.04, 2SD, n = 17) and orthopyroxene (-0.22 ± 0.06, 2SD, n = 17). Collectively, this study finds that the Kamchatka mantle wedge, as represented by the Avacha peridotites, has a mantle-like δ26Mg, and low-degree fluid-mantle interaction does not cause significant Mg isotope fractionation in sub-arc mantle peridotites. [1] Wang et al., EPSL, 2012 [2] Teng et al., PNAS, 2016 [3] Ionov, J. Petrol., 2010, [4] Teng et al., GCA, 2010.

Evaporative fractionation of marine water isotopes in the Arctic Ocean help understand a changing Arctic water cycle

NASA Astrophysics Data System (ADS)

Klein, E. S.; Welker, J. M.

2017-12-01

Most of the global hydrologic cycle occurs in oceanic waters. This oceanic derived moisture is critical to the precipitation and evapotranspiration regimes that influence terrestrial Earth systems. Thus understanding oceanic water processes has important global implications for our knowledge of modern and past hydrologic cycles. As they are influenced by environmental variables such as sea surface temperature and atmospheric humidity, water isotope ratios (e.g., δ18O, δ2H) can help understand the patterns driving the water cycle. However, our knowledge of marine isotopes is relatively limited. In particular, the fractionation of water isotopes during evaporation of oceanic water, essentially the start of the hydrologic cycle, is largely based on theoretical relationships derived from spatially and temporally limited data sets. This constrained understanding of oceanic evaporation fractionation patterns is especially pronounced in the rapidly changing Arctic Ocean. These changes are associated with reduced sea ice coverage, which is increasing the amount of local Artic Ocean sourced moisture in atmospheric and terrestrial systems and amplifying the Arctic hydrologic cycle. Here we present new data revealing the nuances of evaporative fractionation of Arctic Ocean water isotopes with the first collection of continuous, contemporaneous sea water and vapor isotopes. These data, collected in situ aboard the icebreaker Healy, show that the difference between actual ocean vapor isotope values and vapor values estimated by the closure equation increases progressively with latitude (especially beyond 70°) and varies between δ18O and δ2H. These differences are likely due to more isotopic mixing in the troposphere and/or closure equation assumptions inapplicable to Arctic regions. Moreover, we find: 1) a positive relationship between fractionation magnitude and latitude; and 2) the influence of evaporative fractionation from environmental variables such as wind and relative humidity reverses with the presence of sea ice. These new data increase our understanding of the patterns and processes governing past, present, and future changes to the Arctic hydrologic cycle.

Combined 34S, 33S and 18O isotope fractionations record different intracellular steps of microbial sulfate reduction

NASA Astrophysics Data System (ADS)

Antler, Gilad; Turchyn, Alexandra V.; Ono, Shuhei; Sivan, Orit; Bosak, Tanja

2017-04-01

Several enzymatic steps in microbial sulfate reduction (MSR) fractionate the isotope ratios of 33S/32S, 34S/32S and 18O/16O in extracellular sulfate, but the effects of different intracellular processes on the isotopic composition of residual sulfate are still not well quantified. We measured combined multiple sulfur (33S/32S, 34S/32S) and oxygen (18O/16O) isotope ratios of sulfate in pure cultures of a marine sulfate reducing bacterium Desulfovibrio sp. DMSS-1 grown on different organic substrates. These measurements are consistent with the previously reported correlations of oxygen and sulfur isotope fractionations with the cell-specific rate of MSR: faster reduction rates produced smaller isotopic fractionations for all isotopes. Combined isotope fractionation of oxygen and multiple sulfur isotopes are also consistent with the relationship between the rate limiting step during microbial sulfate reduction and the availability of the DsrC subunit. These experiments help reconstruct and interpret processes that operate in natural pore waters characterized by high 18O/16O and moderate 34S/32S ratios and suggest that some multiple isotope signals in the environment cannot be explained by microbial sulfate reduction alone. Instead, these signals support the presence of active, but slow sulfate reduction as well as the reoxidation of sulfide.

Methods for the preparation and analysis of solids and suspended solids for methylmercury

USGS Publications Warehouse

DeWild, John F.; Olund, Shane D.; Olson, Mark L.; Tate, Michael T.

2004-01-01

This report presents the methods and method performance data for the determination of methylmercury concentrations in solids and suspended solids. Using the methods outlined here, the U.S. Geological Survey's Wisconsin District Mercury Laboratory can consistently detect methylmercury in solids and suspended solids at environmentally relevant concentrations. Solids can be analyzed wet or freeze dried with a minimum detection limit of 0.08 ng/g (as-processed). Suspended solids must first be isolated from aqueous matrices by filtration. The minimum detection limit for suspended solids is 0.01 ng per filter resulting in a minimum reporting limit ranging from 0.2 ng/L for a 0.05 L filtered volume to 0.01 ng/L for a 1.0 L filtered volume. Maximum concentrations for both matrices can be extended to cover nearly any amount of methylmercury by limiting sample size.

A Procedure to Simultaneously Determine the Calcium, Chromium, and Titanium Isotopic Compositions of Astromaterials

NASA Technical Reports Server (NTRS)

Tappa, M. J.; Simon, J. I; Jordan, M. K.; Young, E. D.

2015-01-01

Many elements display both linear (mass-dependent) and non-linear (mass-independent) isotope anomalies (relative to a common reservoir). In early Solar System objects, with the exception of oxygen, mass-dependent isotope anomalies are most commonly thought to result from phase separation processes such as evaporation and condensation, whereas many mass-independent isotope anomalies likely reflect radiogenic ingrowth or incomplete mixing of presolar components in the proto-planetary disk. Coupling the isotopic characterization of multiple elements with differing volatilities in single objects may provide information regarding the location, source material, and/or processes involved in the formation of early Solar System solids. Here, we follow up on the work presented in, and detail new procedures developed to make high-precision multi-isotope measurements of Calcium, Chromium, and Titanium with small or limited amounts of sample using thermal ionization mass spectrometry and multi-collector ICP-MS, and characterize a suite of chondritic and terrestrial standards.

Quantifying nitrous oxide production pathways in wastewater treatment systems using isotope technology - A critical review.

PubMed

Duan, Haoran; Ye, Liu; Erler, Dirk; Ni, Bing-Jie; Yuan, Zhiguo

2017-10-01

Nitrous oxide (N 2 O) is an important greenhouse gas and an ozone-depleting substance which can be emitted from wastewater treatment systems (WWTS) causing significant environmental impacts. Understanding the N 2 O production pathways and their contribution to total emissions is the key to effective mitigation. Isotope technology is a promising method that has been applied to WWTS for quantifying the N 2 O production pathways. Within the scope of WWTS, this article reviews the current status of different isotope approaches, including both natural abundance and labelled isotope approaches, to N 2 O production pathways quantification. It identifies the limitations and potential problems with these approaches, as well as improvement opportunities. We conclude that, while the capabilities of isotope technology have been largely recognized, the quantification of N 2 O production pathways with isotope technology in WWTS require further improvement, particularly in relation to its accuracy and reliability. Copyright © 2017 Elsevier Ltd. All rights reserved.

Iranian speleothems: Investigating Quaternary climate variability in semi-arid Western Asia

NASA Astrophysics Data System (ADS)

Carolin, Stacy; Morgan, Jacob; Peckover, Emily; Walker, Richard; Henderson, Gideon; Rowe, Peter; Andrews, Julian; Ersek, Vasile; Sloan, Alastair; Talebian, Morteza; Fattahi, Morteza; Nezamdoust, Javad

2016-04-01

Rapid population growth and limited water supply has highlighted the need for vigorous water resource management practices in the semi-arid regions of Western Asia. One significant unknown in this discussion is the future change in rainfall amount due to the consequential effects of today's greenhouse gas forcing on the regional climate system. Currently, there is little paleoclimate proxy data in Western Asia to extend climate records beyond the limits of the instrumental period, leaving scant evidence to investigate the system's response to various climate forcings on different timescales. Here we present a synthesis of speleothem climate records across northern Iran, from the wetter climate of the Alborz and Zagros mountain ranges to the dry northeast, in order to investigate the magnitude of past climate variability and the forcings responsible. The stalagmites collected from the west and north-central mountain ranges, areas with ~200-400mm mean annual precipitation mostly falling within the fall-winter-spring months, all demonstrate growth limited to the interglacial periods of the Quaternary. We present overlapping Holocene stable isotope records with a complementary trace element record to assist in interpreting the isotopic variability. One of the records is sampled at <4yr resolution and spans 3.7-5.3 kyBP, a contested period of catastrophic droughts that allegedly eradicated civilizations in areas of the near East. Imposed upon decadal-scale variability, the record reveals a 1,000-yr gradual trend toward enriched stable oxygen isotope values, interpreted as a trend toward drier conditions, which ends with an abrupt 300-yr cessation in growth beginning at 4.3 kyBP, coincident with the so-called 4.2 kyBP drought event. From the northeast Iranian plateau, we present a new stalagmite record that spans the penultimate deglaciation and Stages 5e-5a. This region presently receives limited rain annually (~100-300mm/yr, regularly falling between November and May), and the record presented is one of the first speleothem climate records to span a deglaciation in West Asia. To improve our interpretation of the speleothem climate proxy timeseries, we use multiple decades of Tehran GNIP data, meteorological data, and isotope-equipped climate model outputs to investigate the large-scale mechanisms forcing isotopic variations in rainwater across northern Iran. We also examine possible transformation of water isotopes during the transition through the karst aquifer based on site properties, measured dripwater isotopes, and simple model experiments.

Use of radiation sources with mercury isotopes for real-time highly sensitive and selective benzene determination in air and natural gas by differential absorption spectrometry with the direct Zeeman effect.

PubMed

Revalde, Gita; Sholupov, Sergey; Ganeev, Alexander; Pogarev, Sergey; Ryzhov, Vladimir; Skudra, Atis

2015-08-05

A new analytical portable system is proposed for the direct determination of benzene vapor in the ambient air and natural gas, using differential absorption spectrometry with the direct Zeeman effect and innovative radiation sources: capillary mercury lamps with different isotopic compositions ((196)Hg, (198)Hg, (202)Hg, (204)Hg, and natural isotopic mixture). Resonance emission of mercury at a wavelength of 254 nm is used as probing radiation. The differential cross section of benzene absorption in dependence on wavelength is determined by scanning of magnetic field. It is found that the sensitivity of benzene detection is enhanced three times using lamp with the mercury isotope (204)Hg in comparison with lamp, filled with the natural isotopic mixture. It is experimentally demonstrated that, when benzene content is measured at the Occupational Exposure Limit (3.2 mg/m(3) for benzene) level, the interference from SO2, NO2, O3, H2S and toluene can be neglected if concentration of these gases does not exceed corresponding Occupational Exposure Limits. To exclude the mercury effect, filters that absorb mercury and let benzene pass in the gas duct are proposed. Basing on the results of our study, a portable spectrometer is designed with a multipath cell of 960 cm total path length and detection limit 0.5 mg/m(3) at 1 s averaging and 0.1 mg/m(3) at 30 s averaging. The applications of the designed spectrometer to measuring the benzene concentration in the atmospheric air from a moving vehicle and in natural gas are exemplified. Copyright © 2015 Elsevier B.V. All rights reserved.

Nitrogen isotope patterns in Alaskan black spruce reflect organic nitrogen sources and the activity of ectomycorrihizal fungi

Treesearch

Jordan R. Mayor; Edward A.G. Schuur; Michelle C. Mack; Teresa N. Hollingsworth; Erland Bääth

2012-01-01

Global patterns in soil, plant, and fungal stable isotopes of N (15N) show promise as integrated metrics of N cycling, particularly the activity of ectomycorrhizal (ECM) fungi. At small spatial scales, however, it remains difficult to differentiate the underlying causes of plant 15N variability and this limits the...

Operational Range Assessment Program (ORAP) Phase II Overview for Active Installations

DTIC Science & Technology

2011-05-01

Dissolved Metals by EPA 1638M • Isotopic Uranium by EML A-01-R Mod  Sediment Analysis • None  Benthic Macroinvertebrates • Diversity Indices...Metals by EPA 200.8 • Dissolved Metals by EPA 200.8 (if turbid) • Isotopic Uranium by EML A-01- R Mod (if total U is > action limit) Groundwater

System for high throughput water extraction from soil material for stable isotope analysis of water

USDA-ARS?s Scientific Manuscript database

A major limitation in the use of stable isotope of water in ecological studies is the time that is required to extract water from soil and plant samples. Using vacuum distillation the extraction time can be less than one hour per sample. Therefore, assembling a distillation system that can process m...

Stable isotope deltas: Tiny, yet robust signatures in nature

USGS Publications Warehouse

Brand, Willi A.; Coplen, Tyler B.

2012-01-01

Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including 14C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. 13C, 2H, and 18O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as−25 per mil can be written as−25 mUr (or−2.5 cUr or−0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg ‘units’ are easily included (e.g. either+0.015 ‰ or+15 per meg can be written as+15 μUr.

High Precision Low-blank Lithium Isotope Ratios in Forams.

NASA Astrophysics Data System (ADS)

Misra, S.; Froelich, P. N.

2007-12-01

We present a high precision (±1‰, 2σ) low blank (<500 fg/ml) method for Li isotope measurements of forams using <2 ng of Li by single collector Quad ICP-MS (Agilent 7500cs). The Li isotope ratio of seawater (δ7Li) recorded in planktonic forams has the potential to constrain the evolution of seawater chemistry and elucidate the factors driving variations of oceanic mass balances linked to the continental and sea floor/hydrothermal silica cycles. In addition a δ7Li record of seawater will complement other long-term recorders of seawater chemistry such as Sr, Os and S isotopes. Li isotope measurements of forams are limited by several factors: low Li concentrations in forams (1-2 ppm), instrument-induced fractionation and mass bias effects, matrix effects, high Li blanks and incomplete recovery of Li during column separation. Modest concentrations of alkali and alkaline earth elements in the matrix result in variable mass bias in measured Li isotope ratios. Even worse, Li strongly fractionates during chromatographic clean-up to remove Na+, Ca2+ and Mg2+, from +100‰ in the leading edge to - 100‰ in the trailing edge of elution peaks (Urey 1938). Consequently, miniscule incomplete recoveries of Li during chromatographic separations can result in large unrecognized isotope fractionation of eluents. Large mass-dependent fractionation caused by a difference of 17% in mass between 6Li and 7Li, makes Li a powerful tracer of geochemical processes, but also promotes large and difficult-to-fix isotope fractionations during laboratory chemical processing. Matrix effects of Na & Ca and of column chromatography on Li isotope ratios were investigated using artificial Li solutions representative of foram compositions (matrix matching). Li/Ca and Li/Na ratios in cleaned forams are 10 μmol/mol and 3 mmol/mol respectively. An ICP-MS tolerance limit of 20 ppb for Na and 20 μM for Ca was established, much higher tolerances than by TIMS. A single step chromatographic method to quantitatively separate Li from matrix elements using both small volume resin (3.4 meq/2ml AG50W-X8) and acid (6 ml of 0.5N HCl) was developed. Our low blank (<0.5 pg/ml) and high yield (>99.99%) column method minimizes errors in measured Li isotope ratios associated with incomplete column recovery and presence of matrix elements. High sensitivity and precision achieved with a 7500cs using cold plasma (600W), soft extraction and peak jumping coupled with very low sample to blank ratios enables high precision (±1‰, 2σ) statistically significant Li isotope measurements using very small mass of Li (0.8 ng). The development of this technique makes possible good quality Li isotope measurements from samples that are mass limited for Li, i.e., reasonable number of picked forams. This will enable us to test interferences regarding chemical cleaning and species effects in planktonic forams along the road toward creating a δ7Li record of seawater for the Cenozoic.

ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes.

PubMed

Ghorbani, Ramin; Schmidt, Florian M

2017-05-29

We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a low-volume circular multipass cell and wavelength modulation absorption spectroscopy. A fringe-limited (1σ) sensitivity of 6.5 × 10 -8 cm -1 Hz -1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy. Integration over 10 s increases the precision to 0.6 ppbv. The setup also allows measuring the stable isotope 13 CO in breath. We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking. Isotope ratio analysis indicates depletion of 13 CO in breath compared to natural abundance.

The Effect of Minimum Wage Rates on High School Completion

ERIC Educational Resources Information Center

Warren, John Robert; Hamrock, Caitlin

2010-01-01

Does increasing the minimum wage reduce the high school completion rate? Previous research has suffered from (1. narrow time horizons, (2. potentially inadequate measures of states' high school completion rates, and (3. potentially inadequate measures of minimum wage rates. Overcoming each of these limitations, we analyze the impact of changes in…

Magnesium isotopic evidence for chemical disequilibrium among cumulus minerals in layered mafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Lie-Meng; Teng, Fang-Zhen; Song, Xie-Yan; Hu, Rui-Zhong; Yu, Song-Yue; Zhu, Dan; Kang, Jian

2018-04-01

Magnesium isotopic compositions of olivine, clinopyroxene, and ilmenite from the Baima intrusion, SW China, for the first time, are investigated to constrain the magnitude and mechanisms of Mg isotope fractionation among cumulus minerals in layered mafic intrusions and to evaluate their geological implications. Olivine and clinopyroxene have limited Mg isotope variations, with δ26Mg ranging from -0.33 to +0.05‰ and from -0.29 to -0.13‰, respectively, similar to those of mantle xenolithic peridotites. By contrast, ilmenites display extremely large Mg isotopic variation, with δ26Mg ranging from -0.50 to +1.90‰. The large inter-mineral fractionations of Mg isotopes between ilmenite and silicates may reflect both equilibrium and kinetic processes. A few ilmenites have lighter Mg isotopic compositions than coexisting silicates and contain high MgO contents without compositional zoning, indicating equilibrium fractionation. The implication is that the light Mg isotopic compositions of lunar high-Ti basalts may result from an isotopically light source enriched in cumulate ilmenites. On the other hand, most ilmenites have heavy Mg isotopic compositions, coupled with high MgO concentration and chemical zoning, which can be quantitatively modeled by kinetic Mg isotope fractionations induced by subsolidus Mg-Fe exchange between ilmenite and ferromagnesian silicates during the cooling of the Baima intrusion. The extensive occurrence of kinetic Mg isotope fractionation in ilmenites implies the possibility of widespread compositional disequilibrium among igneous minerals in magma chambers. Consequently, disequilibrium effects need to be considered in studies of basaltic magma evolution, magma chamber processes, and magmatic Fe-Ti oxide ore genesis.

Application of non-traditional stable isotopes in analytical ecogeochemistry assessed by MC ICP-MS--A critical review.

PubMed

Irrgeher, Johanna; Prohaska, Thomas

2016-01-01

Analytical ecogeochemistry is an evolving scientific field dedicated to the development of analytical methods and tools and their application to ecological questions. Traditional stable isotopic systems have been widely explored and have undergone continuous development during the last century. The variations of the isotopic composition of light elements (H, O, N, C, and S) have provided the foundation of stable isotope analysis followed by the analysis of traditional geochemical isotope tracers (e.g., Pb, Sr, Nd, Hf). Questions in a considerable diversity of scientific fields have been addressed, many of which can be assigned to the field of ecogeochemistry. Over the past 15 years, other stable isotopes (e.g., Li, Zn, Cu, Cl) have emerged gradually as novel tools for the investigation of scientific topics that arise in ecosystem research and have enabled novel discoveries and explorations. These systems are often referred to as non-traditional isotopes. The small isotopic differences of interest that are increasingly being addressed for a growing number of isotopic systems represent a challenge to the analytical scientist and push the limits of today's instruments constantly. This underlines the importance of a metrologically sound concept of analytical protocols and procedures and a solid foundation of data processing strategies and uncertainty considerations before these small isotopic variations can be interpreted in the context of applied ecosystem research. This review focuses on the development of isotope research in ecogeochemistry, the requirements for successful detection of small isotopic shifts, and highlights the most recent and innovative applications in the field.

The minimum control authority of a system of actuators with applications to Gravity Probe-B

NASA Technical Reports Server (NTRS)

Wiktor, Peter; Debra, Dan

1991-01-01

The forcing capabilities of systems composed of many actuators are analyzed in this paper. Multiactuator systems can generate higher forces in some directions than in others. Techniques are developed to find the force in the weakest direction. This corresponds to the worst-case output and is defined as the 'minimum control authority'. The minimum control authority is a function of three things: the actuator configuration, the actuator controller and the way in which the output of the system is limited. Three output limits are studied: (1) fuel-flow rate, (2) power, and (3) actuator output. The three corresponding actuator controllers are derived. These controllers generate the desired force while minimizing either fuel flow rate, power or actuator output. It is shown that using the optimal controller can substantially increase the minimum control authority. The techniques for calculating the minimum control authority are applied to the Gravity Probe-B spacecraft thruster system. This example shows that the minimum control authority can be used to design the individual actuators, choose actuator configuration, actuator controller, and study redundancy.

Experimental determination of iron isotope fractionations among Fe aq 2 + -FeSaq-Mackinawite at low temperatures: Implications for the rock record

NASA Astrophysics Data System (ADS)

Wu, Lingling; Druschel, Greg; Findlay, Alyssa; Beard, Brian L.; Johnson, Clark M.

2012-07-01

The Fe isotope fractionation factors among aqueous ferrous iron (Fe aq 2 +), aqueous FeS clusters (FeSaq), and nanoparticulate mackinawite under neutral and mildly acidic and alkaline pH conditions have been determined using the three-isotope method. Combined voltammetric analysis and geochemical modeling were used to determine the Fe speciation in the experimental systems. The equilibrium 56Fe/54Fe fractionation factor at 20 °C and pH 7 has been determined to be -0.32 ± 0.29 (2σ)‰ between Fe aq 2 + (minor FeSaq also present in the experiment) and mackinawite. This fractionation factor was essentially constant when pH was changed to 6 or 8. When equal molarity of HS- and Fe aq 2 + were added to the system, however, the isotopic fractionation at pH 7 changed to -0.64 ± 0.36 (2σ)‰, correlating with a significant increase in the proportion of FeHS+ and FeSaq. These results highlight a more important role of aqueous Fe-S speciation in the equilibrium Fe isotope fractionation factor than recognized in previous studies. The isotopic fractionation remained constant when temperature was increased from 20 °C to 35 °C for fractionation factors between Fe aq 2 + , and mackinawite and between dominantly FeHS+ and mackinawite. Synthesis experiments similar to those of Butler et al. (2005) and Guilbaud et al. (2010) at pH 4 show consistent results: over time, the aqueous Fe-mackinawite fractionation decreases but even after 38 days of aging the fractionation factor is far from the equilibrium value inferred using the three-isotope method. In contrast, at near-neutral pH the fractionation factor for the synthesis experiment reached the equilibrium value in 38 days. These differences are best explained by noting that at low pH the FeS mackinawite particles coarsen more rapidly via particle aggregation, which limits isotopic exchange, whereas at higher pH mackinawite aggregation is limited, and Fe isotope exchange occurs more rapidly, converging on the equilibrium value. These results suggest that mackinawite formed in natural environments at near-neutral or alkaline pH are unlikely to retain kinetic isotope fractionations, but are more likely to reflect equilibrium isotope compositions. This in turn has important implications for interpreting iron isotope compositions of Fe sulfides in natural systems.

Combinatorial effects on clumped isotopes and their significance in biogeochemistry

NASA Astrophysics Data System (ADS)

Yeung, Laurence Y.

2016-01-01

The arrangement of isotopes within a collection of molecules records their physical and chemical histories. Clumped-isotope analysis interrogates these arrangements, i.e., how often rare isotopes are bound together, which in many cases can be explained by equilibrium and/or kinetic isotope fractionation. However, purely combinatorial effects, rooted in the statistics of pairing atoms in a closed system, are also relevant, and not well understood. Here, I show that combinatorial isotope effects are most important when two identical atoms are neighbors on the same molecule (e.g., O2, N2, and D-D clumping in CH4). When the two halves of an atom pair are either assembled with different isotopic preferences or drawn from different reservoirs, combinatorial effects cause depletions in clumped-isotope abundance that are most likely between zero and -1‰, although they could potentially be -10‰ or larger for D-D pairs. These depletions are of similar magnitude, but of opposite sign, to low-temperature equilibrium clumped-isotope effects for many small molecules. Enzymatic isotope-pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect, although it is not limited to biological reactions. Chemical-kinetic isotope effects, which are related to a bond-forming transition state, arise independently and express second-order combinatorial effects related to the abundance of the rare isotope. Heteronuclear moeties (e.g., Csbnd O and Csbnd H), are insensitive to direct combinatorial influences, but secondary combinatorial influences are evident. In general, both combinatorial and chemical-kinetic factors are important for calculating and interpreting clumped-isotope signatures of kinetically controlled reactions. I apply this analytical framework to isotope-pairing reactions relevant to geochemical oxygen, carbon, and nitrogen cycling that may be influenced by combinatorial clumped-isotope effects. These isotopic signatures, manifest as either directly bound isotope ;clumps; or as features of a molecule's isotopic anatomy, are linked to molecular mechanisms and may eventually provide additional information about biogeochemical cycling on environmentally relevant spatial scales.

A high-resolution paleosecular variation record from Black Sea sediments indicating fast directional changes associated with low field intensities during marine isotope stage (MIS) 4

NASA Astrophysics Data System (ADS)

Nowaczyk, Norbert R.; Jiabo, Liu; Frank, Ute; Arz, Helge W.

2018-02-01

A total of nine sediment cores recovered from the Archangelsky Ridge in the SE Black Sea were systematically subjected to intense paleo- and mineral magnetic analyses. Besides 16 accelerator mass spectrometry (AMS) 14C ages available for another core from this area, dating was accomplished by correlation of short-term warming events during the last glacial monitored by high-resolution X-ray fluorescence (XRF) scanning as maxima in both Ca/Ti and K/Ti ratios in Black Sea sediments to the so-called 'Dansgaard-Oeschger events' recognized from Greenland ice cores. Thus, several hiatuses could be identified in the various cores during the last glacial/interglacial cycle. Finally, core sections documenting marine isotope stage (MIS) 4 at high resolution back to 69 ka were selected for detailed analyses. At 64.5 ka, according to obtained results from Black Sea sediments, the second deepest minimum in relative paleointensity during the past 69 ka occurred, with the Laschamp geomagnetic excursion at 41 ka being associated with the lowest field intensities. The field minimum during MIS 4 is associated with large declination swings beginning about 3 ka before the minimum. While a swing to 50°E is associated with steep inclinations (50-60°) according to the coring site at 42°N, the subsequent declination swing to 30°W is associated with shallow inclinations of down to 40°. Nevertheless, these large deviations from the direction of a geocentric axial dipole field (I = 61 °, D = 0 °) still can not yet be termed as 'excursional', since latitudes of corresponding virtual geomagnetic poles (VGP) only reach down to 51.5°N (120°E) and 61.5°N (75°W), respectively. However, these VGP positions at opposite sides of the globe are linked with VGP drift rates of up to 0.2° per year in between. These extreme secular variations might be the mid-latitude expression of a geomagnetic excursion with partly reversed inclinations found at several sites much further North in Arctic marine sediments between 69°N and 81°N. Thus, the pronounced intensity minimum at 64.5 ka and described directional variations might be the effect of a weak geomagnetic field with a multi-polar geometry in the middle of MIS 4.

Correlated helium, neon, and melt production on the super-fast spreading East Pacific Rise near 17°S

NASA Astrophysics Data System (ADS)

Kurz, Mark D.; Moreira, Manuel; Curtice, Joshua; Lott, Dempsey E.; Mahoney, John J.; Sinton, John M.

2005-03-01

We report new helium and neon isotopic compositions in dredged basalt glasses from the superfast spreading East Pacific Rise (EPR) between 13° and 23°S. The 3He/ 4He ratios vary from 8.0 to 11.0 times the atmospheric value (Ra) [ 4He/ 3He between 65,700 and 90,300], with the least radiogenic values in samples from near 16.75°S. Atmospheric contamination corrections on neon isotopes are made using step heating and extrapolated 21Ne/ 22Ne ratios (to a solar 20Ne/ 22Ne value of 13.8). The lowest corrected 21Ne/ 22Ne ratios are found near 16.75°S, and are consistent with the helium isotopes in suggesting a less degassed mantle source. The EPR at 17°S is unusual in displaying such isotopic anomalies in the absence of any known hotspot. The minima in 4He/ 3He and 21Ne/ 22Ne correspond to extremes in Sr, Nd and Pb isotope ratios, but the length scale of the helium and neon anomalies are shorter along-axis than the peaks for the other isotopic ratios. The minimum in 4He/ 3He is observed from 16° to 18°S (a distance of ˜220 km), whereas the elevated Sr and Pb values, and lower 143Nd/ 144Nd, are observed between 16° and 20.7°S (a distance of ˜500 km); neon isotope anomalies are observed on an intermediate length scale along-axis. Unradiogenic helium and neon values correlate with low mantle Bouguer anomalies, and maxima in the axial cross-sectional area, all of which are attributed to higher melt production near 17°S. A conceptual model that fits the observations includes melting of an entrained heterogeneity beneath the EPR at 17 °S. The relationship between helium and neon isotopes and along-axis geophysical characteristics (and by inference melt distribution) is probably related to the extreme incompatibility of helium and neon. High concentrations of 3He and 21Ne (extrap) are found in the glasses near 17°S, which is consistent with higher noble gas concentrations in the anomalous mantle.

Distribution of oxygen isotopes in the water masses of Drake Passage and the South Atlantic

NASA Astrophysics Data System (ADS)

Meredith, Michael P.; Grose, Katie E.; McDonagh, Elaine L.; Heywood, Karen J.; Frew, Russell D.; Dennis, Paul F.

1999-09-01

Measurements of the ratio of stable isotopes of oxygen (18O and 16O) from samples collected on World Ocean Circulation Experiment sections SR1b (eastern Drake Passage) and A11 (Punta Arenas to Cape Town) are used, together with hydrographic data, to deduce information about the formation and variability of South Atlantic and Southern Ocean water masses. The Drake Passage surface waters south of the Polar Front (PF) are isotopically light (δ18O around -0.4‰) owing to the influence of meteoric waters. The salinity and δ18O of the A11 surface waters yield an apparent freshwater end-member which is much isotopically lighter than the local precipitation, thus advection of these waters from farther south dominates over local effects in determining the surface water properties. The Drake Passage section shows unusual proximity of the two main fronts of the Antarctic Circumpolar Current (the PF and Subantarctic Front (SAF)), and we observe cold, fresh, and isotopically light water derived from the temperature-minimum Winter Water at the SAF. This water is of the correct density to freshen the intermediate water north of the SAF and thus play a role in the formation of the comparatively fresh Antarctic Intermediate Water (AAIW) of the South Atlantic. This confirms the role of Antarctic water in forming the South Atlantic variety of AAIW. Across the A11 section the oxygen isotope and salinity data at the AAIW core show very similar traces, with waters in the Malvinas Current loop showing lowest values of both. At the eastern boundary of the South Atlantic, the input of Red Sea Water from east of South Africa is observed via the presence of anomalously isotopically heavy AAIW. We deduce potentially significant temporal variability in the isotopic composition of Weddell Sea Deep Water (WSDW) by comparing the Drake Passage data to earlier data covering the outflow of the Weddell Sea. The A11 data show WSDW consistent with such variability, indicating that its effects could persist in the waters as they flow north into the western South Atlantic. We speculate that such variability could be due to small changes in the amount of glacial ice melt in WSDW.

Isospin degree of freedom in even-even 68-76Ge and 62-70Zn isotopes

NASA Astrophysics Data System (ADS)

Jalili Majarshin, A.

2018-01-01

The introduction of isotopic spin is significant in light nuclei as Ge and Zn isotopes in order to take into account isospin effects on energy spectra. Dynamical symmetries in spherical, γ-soft limits and transition in the interacting boson model IBM-3 are analyzed. Analytic expressions and exact eigenenergies, electromagnetic transitions probabilities are obtained for the transition between spherical and γ-soft shapes by using the Bethe ansatz within an infinite-dimensional Lie algebra in light mass nuclei. The corresponding algebraic structure and reduction chain are studied in IBM-3. For examples, the nuclear structure of the 68-76Ge and 62-70Zn isotopes is calculated in IBM-3 and compared with experimental results.

NSCL and FRIB at Michigan State University: Nuclear science at the limits of stability

NASA Astrophysics Data System (ADS)

Gade, A.; Sherrill, B. M.

2016-05-01

The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) is a scientific user facility that offers beams of rare isotopes at a wide range of energies. This article describes the facility, its capabilities, and some of the experimental devices used to conduct research with rare isotopes. The versatile nuclear science program carried out by researchers at NSCL continues to address the broad challenges of the field, employing sensitive experimental techniques that have been developed and optimized for measurements with rare isotopes produced by in-flight separation. Selected examples showcase the broad program, capabilities, and the relevance for forefront science questions in nuclear physics, addressing, for example, the limits of nuclear existence; the nature of the nuclear force; the origin of the elements in the cosmos; the processes that fuel explosive scenarios in the Universe; and tests for physics beyond the standard model of particle physics. NSCL will cease operations in approximately 2021. The future program will be carried out at the Facility for Rare Isotope Beams, FRIB, presently under construction on the MSU campus adjacent to NSCL. FRIB will provide fast, stopped, and reaccelerated beams of rare isotopes at intensities exceeding NSCL’s capabilities by three orders of magnitude. An outlook will be provided on the enormous opportunities that will arise upon completion of FRIB in the early 2020s.

Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater-brine interface

NASA Astrophysics Data System (ADS)

Shah, S. R.; Joye, S. B.; Brandes, J. A.; McNichol, A. P.

2013-05-01

Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawater-brine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater-brine interface region as the likely source region for DOC to the brine as well as DIC.

Actinides in deer tissues at the rocky flats environmental technology site.

PubMed

Todd, Andrew S; Sattelberg, R Mark

2005-11-01

Limited hunting of deer at the future Rocky Flats National Wildlife Refuge has been proposed in U.S. Fish and Wildlife planning documents as a compatible wildlife-dependent public use. Historically, Rocky Flats site activities resulted in the contamination of surface environmental media with actinides, including isotopes of americium, plutonium, and uranium. In this study, measurements of actinides [Americium-241 (241Am); Plutonium-238 (238Pu); Plutonium-239,240 (239,240Pu); uranium-233,244 (233,234U); uranium-235,236 (235,236U); and uranium-238 (238U)] were completed on select liver, muscle, lung, bone, and kidney tissue samples harvested from resident Rocky Flats deer (N = 26) and control deer (N = 1). In total, only 17 of the more than 450 individual isotopic analyses conducted on Rocky Flats deer tissue samples measured actinide concentrations above method detection limits. Of these 17 detects, only 2 analyses, with analytical uncertainty values added, exceeded threshold values calculated around a 1 x 10(-6) risk level (isotopic americium, 0.01 pCi/g; isotopic plutonium, 0.02 pCi/g; isotopic uranium, 0.2 pCi/g). Subsequent, conservative risk calculations suggest minimal human risk associated with ingestion of these edible deer tissues. The maximum calculated risk level in this study (4.73 x 10(-6)) is at the low end of the U.S. Environmental Protection Agency's acceptable risk range.

Analysis of Ni-HYDRIDE Thin Film after Surface Plasmon Generation by Laser Technique

NASA Astrophysics Data System (ADS)

Violante, V.; Castagna, E.; Sibilia, C.; Paoloni, S.; Sarto, F.

2005-12-01

A nickel hydride thin film was studied by the attenuated total reflection method. The differences in behavior between a "black" film, and a pure nickel film "blank," are shown. The black nickel hydride film has been obtained by a short electrolysis with 1 M Li2SO4 electrolyte in light water, A shift in the minimum of the observed reflected light occurs, together with a change in the minimum shape (i.e. its half-height width increases). These two phenomenon are due to the change in the electronic band structure of the metal induced by electrons added to the lattice by hydrogen. The change of the electronic structure, revealed by the laser coupling conditions, leads us to consider that a hydride phase was created. Both the blank (not hydrogenated) and black (hydrogenated) specimens were taken under He-Ne laser beam at the reflectance minimum angle for about three hours. A SIMS analysis was also implemented to reveal differences in the isotopic composition of Cu, as marker element between the blank and black films, in order to study the coupled effect of electrolysis and plasmon-polariton excitation on LENR processes in condensed matter.

Using combinations of metal isotopes as tracers of tailings pond discharges to subsurface aquifers in the Athabasca Oil Sands area, Canada.

NASA Astrophysics Data System (ADS)

Gammon, P. R.; Savard, M. M.; Ahad, J. M.; Girard, I.

2016-12-01

The Athabasca Oil Sands (AOS) industry in Alberta, Canada deposits voluminous waste streams in Earth's largest tailings ponds (TPs). Detecting and tracing contaminant discharge from TPs to subsurface aquifers has proven difficult because tailings have the same composition as the surrounding environment of unmined oil sand. To trace pond discharge to the subsurface therefore relies on the waste stream hosting additions or alterations induced by mining or industrial processes. Inorganic element or contaminant concentration data have proven ineffective at tracing because there is insufficient alteration of the chemical constituents or their ratios. Metal isotopes have not generally been applied to tracing emissions even though isotopic fractionation is likely induced via the high temperature and pH industrial process. We have generated Mg, Li, Pb and Zn isotopic data for a range of groundwater wells and TPs. Mg isotopes are excellent for distinguishing deep saline brines that are pumped into the waste stream during mine dewatering. Li isotopes appear to be heavily fractionated during processing, which produces a heavy isotopic signature that is an excellent tracer of production water. Pb isotopes discriminate Pb derived from oil-sand versus bedrock carbonate. Juxtapositions of TPs, carbonates and near-surface aquifers are common and of significant regulatory concern, making Pb isotopes particularly useful. Zn isotopic data indicates similarities to Pb isotopes, but are difficult to obtain due to low concentrations. Combining the isotopic data with concentration data and hydrologic models will assist in determining the fluxes of discharges from the TPs to near-surface aquifers. The range of environmental contexts of AOS TPs is limited and thus monitoring discharges to nearby aquifers from TPs could feasibly be accomplished using tailored suites of metal isotopes.

Movement patterns and dispersal potential of Pecos bluntnose shiner (Notropis simus pecosensis) revealed using otolith microchemistry

USGS Publications Warehouse

Chase, Nathan M.; Caldwell, Colleen A.; Carleton, Scott A.; Gould, William R.; Hobbs, James A.

2015-01-01

Natal origin and dispersal potential of the federally threatened Pecos bluntnose shiner (Notropis simus pecosensis) were successfully characterized using otolith microchemistry and swimming performance trials. Strontium isotope ratios (87Sr:86Sr) of otoliths within the resident plains killifish (Fundulus zebrinus) were successfully used as a surrogate for strontium isotope ratios in water and revealed three isotopically distinct reaches throughout 297 km of the Pecos River, New Mexico, USA. Two different life history movement patterns were revealed in Pecos bluntnose shiner. Eggs and fry were either retained in upper river reaches or passively dispersed downriver followed by upriver movement during the first year of life, with some fish achieving a minimum movement of 56 km. Swimming ability of Pecos bluntnose shiner confirmed upper critical swimming speeds (Ucrit) as high as 43.8 cm·s−1 and 20.6 body lengths·s−1 in 30 days posthatch fish. Strong swimming ability early in life supports our observations of upriver movement using otolith microchemistry and confirms movement patterns that were previously unknown for the species. Understanding patterns of dispersal of this and other small-bodied fishes using otolith microchemistry may help redirect conservation and management efforts for Great Plains fishes.

Charge radii of neutron deficient Fe 52 , 53 produced by projectile fragmentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minamisono, K.; Rossi, D. M.; Beerwerth, R.

Bunched-beam collinear laser spectroscopy is performed on neutron deficient 52,53Fe prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δmore » $$\\langle$$r 2$$\\rangle$$ of 52,53Fe are determined relative to stable 56Fe as δ$$\\langle$$r2$$\\rangle$$ 56,52=$-$0.034(13) fm 2 and δ$$\\langle$$r 2$$\\rangle$$56,53=$-$0.218(13) fm 2, respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ$$\\langle$$r 2$$\\rangle$$. The values of δ$$\\langle$$r 2$$\\rangle$$ exhibit a minimum at the N=28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. As a result, the trend of δ$$\\langle$$r 2$$\\rangle$$ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ$$\\langle$$r 2$$\\rangle$$ of closed-shell Ca isotopes« less

Charge radii of neutron deficient Fe 52 , 53 produced by projectile fragmentation

DOE PAGES

Minamisono, K.; Rossi, D. M.; Beerwerth, R.; ...

2016-12-15

Bunched-beam collinear laser spectroscopy is performed on neutron deficient 52,53Fe prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δmore » $$\\langle$$r 2$$\\rangle$$ of 52,53Fe are determined relative to stable 56Fe as δ$$\\langle$$r2$$\\rangle$$ 56,52=$-$0.034(13) fm 2 and δ$$\\langle$$r 2$$\\rangle$$56,53=$-$0.218(13) fm 2, respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ$$\\langle$$r 2$$\\rangle$$. The values of δ$$\\langle$$r 2$$\\rangle$$ exhibit a minimum at the N=28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. As a result, the trend of δ$$\\langle$$r 2$$\\rangle$$ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ$$\\langle$$r 2$$\\rangle$$ of closed-shell Ca isotopes« less

How Low Can You Go? The Importance of Quantifying Minimum Generation Levels for Renewable Integration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denholm, Paul L; Brinkman, Gregory L; Mai, Trieu T

One of the significant limitations of solar and wind deployment is declining value caused by the limited correlation of renewable energy supply and electricity demand as well as limited flexibility of the power system. Limited flexibility can result from thermal and hydro plants that cannot turn off or reduce output due to technical or economic limits. These limits include the operating range of conventional thermal power plants, the need for process heat from combined heat and power plants, and restrictions on hydro unit operation. To appropriately analyze regional and national energy policies related to renewable deployment, these limits must bemore » accurately captured in grid planning models. In this work, we summarize data sources and methods for U.S. power plants that can be used to capture minimum generation levels in grid planning tools, such as production cost models. We also provide case studies for two locations in the U.S. (California and Texas) that demonstrate the sensitivity of variable generation (VG) curtailment to grid flexibility assumptions which shows the importance of analyzing (and documenting) minimum generation levels in studies of increased VG penetration.« less

Variation in catchment areas of Indiana bat (Myotis sodalis) hibernacula inferred from stable hydrogen (δ2H) isotope analysis.

Treesearch

E.R. Britzke; S.C. Loeb; C.S. Romanek; K.A. Hobson; M.J. Vonhof

2013-01-01

Understanding seasonal movements of bats is important for effective conservation efforts. Although female Indiana bats (Myotis sodalis Miller and Allen, 1928) have been documented to migrate >500 km, knowledge of their migratory patterns is still extremely limited. We used the relationship between latitude and stable hydrogen isotope ratio in bat hair (δ...

Current capabilities and limitations of the stable isotope technologies and applied mathematical equations in determining whole body vitamin A status

USDA-ARS?s Scientific Manuscript database

Vitamin A (VA) stable isotope dilution methodology provides a quantitative estimate of total body VA stores and is the best method currently available for assessing VA status in adults and children. The methodology has also been used to test the efficacy of VA interventions in a number of low-incom...

Calcium inputs and transport in a base-poor forest ecosystem as interpreted by Sr isotopes

Treesearch

Scott W. Bailey; James W. Hornbeck; Charles T. Driscoll; Henri E. Gaudette

1996-01-01

Depletion of Ca in forests and its effects on forest health are poorly quantified. Depletion has been difficult to document due to limitations in determining rates at which Ca becomes available for ecosystem processes through weathering, and difficulty in determining changes in ecosystem storage. We coupled a detailed analysis of Sr isotopic composition with a mass...

Shot-noise Limited Faraday Rotation Spectroscopy for Detection of Nitric Oxide Isotopes in Breath, Urine, and Blood

PubMed Central

Wang, Yin; Nikodem, Michal; Zhang, Eric; Cikach, Frank; Barnes, Jarrod; Comhair, Suzy; Dweik, Raed A.; Kao, Christina; Wysocki, Gerard

2015-01-01

Measurement of NO and/or its metabolites in the various body compartments has transformed our understanding of biology. The inability of the current NO measurement methods to account for naturally occurring and experimental NO isotopes, however, has prevented the scientific community from fully understating NO metabolism in vivo. Here we present a mid-IR Faraday rotation spectrometer (FRS) for detection of NO isotopes. The instrument utilizes a novel dual modulation/demodulation (DM) FRS method which exhibits noise performance at only 2 times the fundamental quantum shot-noise level and provides the record sensitivity in its class. This is achieved with a system that is fully autonomous, robust, transportable, and does not require cryogenic cooling. The DM-FRS enables continuous monitoring of nitric oxide isotopes with the detection limits of 3.72 ppbv/Hz1/2 to14NO and 0.53 ppbv/Hz1/2 to15NO using only 45 cm active optical path. This DM-FRS measurement method can be used to improve the performance of conventional FRS sensors targeting other radical species. The feasibility of the instrument to perform measurements relevant to studies of NO metabolism in humans is demonstrated. PMID:25767064

Discerning autotrophy, mixotrophy and heterotrophy in marine TACK archaea from the North Atlantic.

PubMed

Seyler, Lauren M; McGuinness, Lora R; Gilbert, Jack A; Biddle, Jennifer F; Gong, Donglai; Kerkhof, Lee J

2018-03-01

DNA stable isotope probing (SIP) was used to track the uptake of organic and inorganic carbon sources for TACK archaea (Thaumarchaeota/Aigarchaeota/Crenarchaeota/Korarchaeota) on a cruise of opportunity in the North Atlantic. Due to water limitations, duplicate samples from the deep photic (60-115 m), the mesopelagic zones (local oxygen minimum; 215-835 m) and the bathypelagic zone (2085-2835 m) were amended with various combinations of 12C- or 13C-acetate/urea/bicarbonate to assess cellular carbon acquisition. The SIP results indicated the majority of TACK archaeal operational taxonomic units (OTUs) incorporated 13C from acetate and/or urea into newly synthesized DNA within 48 h. A small fraction (16%) of the OTUs, often representing the most dominant members of the archaeal community, were able to incorporate bicarbonate in addition to organic substrates. Only two TACK archaeal OTUs were found to incorporate bicarbonate but not urea or acetate. These results further demonstrate the utility of SIP to elucidate the metabolic capability of mesothermal archaea in distinct oceanic settings and suggest that TACK archaea play a role in organic carbon recycling in the mid-depth to deep ocean.

Physical requirements and milestones for the HIT-PoP Experiment

NASA Astrophysics Data System (ADS)

Jarboe, Thomas

2011-10-01

Recent success with HIT-SI demonstrates the viability of steady inductive helicity injection (SIHI) as a spheromak formation and sustainment method. Results include the sustainment of toroidal current of over 50 kA, up to 40 kA of plasma current that is separate from the injectors, toroidal flux up to 6 times the peak injected flux, and j/n > 1014Am. All were achieved with 10MW or less applied power. This paper explores the requirements for a confinement test of the concept using a larger proof of principle experiment. The confinement experiment must not exceed the beta limit, the drift parameter limit, or the wall loading limit, where the drift parameter is (drift of electrons relative to ions to produce current)/(ion thermal speed). It must also exceed a minimum j/n, a minimum n a, and a minimum electron temperature, where a is the minor radius. The drift parameter limit and beta limit appear to play defining roles in spheromak performance leading to a very favorable scaling of wall loading with size. The milestones sequence suggested is the following: 1. Startup at drift parameter and beta limit minimum density. 2. Raise current until j/n exceeds 10-14Am. 3. Raise the current and temperature until T ~ 50 eV for good ionization. 4. Raise the current and density until n a > 2x1019 m-2 for neutral screening. 5. Raise current and temperature until T > 200eV so magnetic confinement can be studied.

Seasonal cycles of atmospheric methane and its carbon and hydrogen isotopic ratios in the lower and upper troposphere of the western Pacific region

NASA Astrophysics Data System (ADS)

Umezawa, T.; Aoki, S.; Nakazawa, T.; Machida, T.; Matsueda, H.; Sawa, Y.; Ishijima, K.; Patra, P. K.

2009-12-01

Although carbon and hydrogen isotopic ratios (δ13C and δD) of CH4 provide useful information about its sources and sinks, systematic measurements were quite limited. Tohoku University group and NIES group have conducted air-sampling programs by using commercial container ships sailing between Japan and New Zealand and by using commercial airliners flying between Australia and Japan, respectively. Using air samples collected by the programs, systematic measurements of δ13C and δD of atmospheric CH4 as well as CH4 concentration ([CH4]) have been made since 2006. Here, we report their spatial and temporal variations in the lower and upper troposphere (LT and UT). In the LT of the northern hemisphere (NH), the seasonal cycle of [CH4] showed the maximum in winter and the minimum in summer. δ13C varied seasonally almost negatively correlating with the [CH4], and the seasonality of δD showed much more significant negative correlation with the [CH4]. It was also found that CH4 sources with seasonally varying strength, such as wetlands with high emissions in late summer, play an important role in the atmospheric CH4 variations. In the tropics, a seasonally-dependent air exchange between the NH and the southern hemisphere (SH) was found to characterize the seasonal CH4 cycle. When the NH and SH air arrived, high and low [CH4] were observed, accompanied by low and high δ13C and δD values, respectively. In the LT of the SH, the seasonal maximum and minimum of the [CH4] appeared in austral winter and summer, respectively. The seasonal CH4 cycle was mainly ascribed to the seasonality in the CH4+OH reaction, but δ13C and δD showed rather complicated seasonality with larger amplitudes than expected from the CH4+OH reaction alone, suggesting additional contribution of a CH4+Cl reaction in the marine boundary layer. In the UT of the NH, the seasonal maximum and minimum of the [CH4] appeared in summer and winter-spring, respectively, with low and high values of δ13C and δD in corresponding seasons. The summertime high [CH4] was observed when the [CH4] showed the seasonal minimum in the LT. By examining the relationship between δ13C (or δD) and the [CH4], as well as the results of tagged tracer experiments using the CCSR/NIES/FRCGC AGCM-based chemical transport model, we found that biogenic CH4 emissions from India, Southeast Asia and China are responsible for such summertime high [CH4] in the UT. By comparing the latitudinal distributions of the annual average [CH4], δ13C and δD in the UT and LT, we found that [CH4] and δD in the NH were higher and lower in the LT than in the UT, respectively, while the situation was opposite in the SH, due to NH air intrusion through the UT. On the other hand, δ13C showed no different distributions in the LT and UT of the NH, while δ13C in the SH was higher in the LT than in the UT, probably due to the contribution of the CH4+Cl reaction in the marine boundary layer.

40 CFR Table 3 to Subpart Ddddd of... - Operating Limits for Boilers and Process Heaters With Mercury Emission Limits and Boilers and...

Code of Federal Regulations, 2010 CFR

2010-07-01

... minimum pressure drop and liquid flow-rate at or above the operating levels established during the... leak detection system alarm does not sound more than 5 percent of the operating time during a 6-month... control Maintain the minimum sorbent or carbon injection rate at or above the operating levels established...

40 CFR Table 3 to Subpart Ddddd of... - Operating Limits for Boilers and Process Heaters With Mercury Emission Limits and Boilers and...

Code of Federal Regulations, 2011 CFR

2011-07-01

... minimum pressure drop and liquid flow-rate at or above the operating levels established during the... leak detection system alarm does not sound more than 5 percent of the operating time during a 6-month... control Maintain the minimum sorbent or carbon injection rate at or above the operating levels established...

Metal Stable Isotope Tagging: Renaissance of Radioimmunoassay for Multiplex and Absolute Quantification of Biomolecules.

PubMed

Liu, Rui; Zhang, Shixi; Wei, Chao; Xing, Zhi; Zhang, Sichun; Zhang, Xinrong

2016-05-17

The unambiguous quantification of biomolecules is of great significance in fundamental biological research as well as practical clinical diagnosis. Due to the lack of a detectable moiety, the direct and highly sensitive quantification of biomolecules is often a "mission impossible". Consequently, tagging strategies to introduce detectable moieties for labeling target biomolecules were invented, which had a long and significant impact on studies of biomolecules in the past decades. For instance, immunoassays have been developed with radioisotope tagging by Yalow and Berson in the late 1950s. The later languishment of this technology can be almost exclusively ascribed to the use of radioactive isotopes, which led to the development of nonradioactive tagging strategy-based assays such as enzyme-linked immunosorbent assay, fluorescent immunoassay, and chemiluminescent and electrochemiluminescent immunoassay. Despite great success, these strategies suffered from drawbacks such as limited spectral window capacity for multiplex detection and inability to provide absolute quantification of biomolecules. After recalling the sequences of tagging strategies, an apparent question is why not use stable isotopes from the start? A reasonable explanation is the lack of reliable means for accurate and precise quantification of stable isotopes at that time. The situation has changed greatly at present, since several atomic mass spectrometric measures for metal stable isotopes have been developed. Among the newly developed techniques, inductively coupled plasma mass spectrometry is an ideal technique to determine metal stable isotope-tagged biomolecules, for its high sensitivity, wide dynamic linear range, and more importantly multiplex and absolute quantification ability. Since the first published report by our group, metal stable isotope tagging has become a revolutionary technique and gained great success in biomolecule quantification. An exciting research highlight in this area is the development and application of the mass cytometer, which fully exploited the multiplexing potential of metal stable isotope tagging. It realized the simultaneous detection of dozens of parameters in single cells, accurate immunophenotyping in cell populations, through modeling of intracellular signaling network and undoubted discrimination of function and connection of cell subsets. Metal stable isotope tagging has great potential applications in hematopoiesis, immunology, stem cells, cancer, and drug screening related research and opened a post-fluorescence era of cytometry. Herein, we review the development of biomolecule quantification using metal stable isotope tagging. Particularly, the power of multiplex and absolute quantification is demonstrated. We address the advantages, applicable situations, and limitations of metal stable isotope tagging strategies and propose suggestions for future developments. The transfer of enzymatic or fluorescent tagging to metal stable isotope tagging may occur in many aspects of biological and clinical practices in the near future, just as the revolution from radioactive isotope tagging to fluorescent tagging happened in the past.

Fractionation of Sulfur Isotopes by Desulfovibrio vulgaris Mutants Lacking Periplasmic Hydrogenases or the Type I Tetraheme Cytochrome c3

NASA Astrophysics Data System (ADS)

Sim, M.; Ono, S.; Bosak, T.

2012-12-01

A large fraction of anaerobic mineralization of organic compounds relies on microbial sulfate reduction. Sulfur isotope fractionation by these microbes has been widely used to trace the biogeochemical cycling of sulfur and carbon, but intracellular mechanisms behind the wide range of fractionations observed in nature and cultures are not fully understood. In this study, we investigated the influence of electron transport chain components on the fractionation of sulfur isotopes by culturing Desulfovibrio vulgaris Hildenborough mutants lacking hydrogenases or type I tetraheme cytochrome c3 (Tp1-c3). The mutants were grown both in batch and continuous cultures. All tested mutants grew on lactate or pyruvate as the sole carbon and energy sources, generating sulfide. Mutants lacking cytoplasmic and periplasmic hydrogenases exhibited similar growth physiologies and sulfur isotope fractionations to their parent strains. On the other hand, a mutant lacking Tp1-c3 (ΔcycA) fractionated the 34S/32S ratio more than the wild type, evolving H2 in the headspace and exhibiting a lower specific respiration rate. In the presence of high concentrations of pyruvate, the growth of ΔcycA relied largely on fermentation rather than sulfate reduction, even when sulfate was abundant, producing the largest sulfur isotope effect observed in this study. Differences between sulfur isotope fractionation by ΔcycA and the wild type highlight the effect of electron transfer chains on the magnitude of sulfur isotope fractionation. Because Tp1-c3 is known to exclusively shuttle electrons from periplasmic hydrogenases to transmembrane complexes, electron transfers in the absence of Tp1-c3 should bypass the periplasmic hydrogen cycling, and the loss of reducing equivalents in the form of H2 can impair the flow of electrons from organic acids to sulfur, increasing isotope fractionation. Larger fractionation by ΔcycA can inform interpretations of sulfur isotope data at an environmental scale as well, because intracellular concentrations of electron transport components can be altered by environmental factors such as iron availability. Simultaneous sulfate reduction and fermentation, and their corresponding sulfur isotope effects, also generate a hypothesis that links sulfur isotope fractionation to the cellular energy budget. Theoretically, the largest fractionation during microbial sulfate reduction occurs when the backward fluxes equal the forward fluxes in sulfate reduction pathway. However, when the generation of ATP depends exclusively on sulfate respiration, a minimum respiration rate is required to fulfill the maintenance energy requirement. In contrast, when sulfate reduction occurs simultaneously with fermentation, the latter process may contribute toward maintenance energy, enabling slower and more reversible sulfate reduction, and leading to larger fractionation. Given that many sulfate-reducing microbes are also facultative fermenters, fermentation by sulfate reducing microbes in natural habitats and sulfur isotope signatures produced by such communities deserve further exploration.

Studies on the optogalvanic effect and isotope-selective excitation of ytterbium in a hollow cathode discharge lamp using a pulsed dye laser.

PubMed

Kumar, Pankaj; Kumar, Jitendra; Prakash, Om; Saini, Vinod K; Dixit, Sudhir K; Nakhe, Shankar V

2013-09-01

This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed.

25 CFR 542.42 - What are the minimum internal control standards for internal audit for Tier C gaming operations?

Code of Federal Regulations, 2010 CFR

2010-04-01

... reconciliation process; (ii) Pull tabs, including but not limited to, statistical records, winner verification... 25 Indians 2 2010-04-01 2010-04-01 false What are the minimum internal control standards for... COMMISSION, DEPARTMENT OF THE INTERIOR HUMAN SERVICES MINIMUM INTERNAL CONTROL STANDARDS § 542.42 What are...

Sulfur- and oxygen-isotopes in sediment-hosted stratiform barite deposits

USGS Publications Warehouse

Johnson, C.A.; Emsbo, P.; Poole, F.G.; Rye, R.O.

2009-01-01

Sulfur- and oxygen-isotope analyses have been obtained for sediment-hosted stratiform barite deposits in Alaska, Nevada, Mexico, and China to examine the environment of formation of this deposit type. The barite is contained in sedimentary sequences as old as Late Neoproterozoic and as young as Mississippian. If previously published data for other localities are considered, sulfur- and oxygen-isotope data are now available for deposits spanning a host-rock age range of Late Neoproterozoic to Triassic. On a ??34S versus ??18O diagram, many deposits show linear or concave-upward trends that project down toward the isotopic composition of seawater sulfate. The trends suggest that barite formed from seawater sulfate that had been isotopically modified to varying degrees. The ??34S versus ??18O patterns resemble patterns that have been observed in the modern oceans in pore water sulfate and water column sulfate in some anoxic basins. However, the closest isotopic analog is barite mineralization that occurs at fluid seeps on modern continental margins. Thus the data favor genetic models for the deposits in which barium was delivered by seafloor seeps over models in which barium was delivered by sedimentation of pelagic organisms. The isotopic variations within the deposits appear to reflect bacterial sulfate reduction operating at different rates and possibly with different electron donors, oxygen isotope exchange between reduction intermediates and H2O, and sulfate availability. Because they are isotopically heterogeneous, sediment-hosted stratiform barite deposits are of limited value in reconstructing the isotopic composition of ancient seawater sulfate.

Carbon Monoxide Stable Isotopes: Extraction Technique Development and Urban Atmospheric Analysis

NASA Astrophysics Data System (ADS)

Vimont, Isaac Josef

We have developed an extraction system to analyze isotopes of carbon monoxide (CO). We then analyzed CO isotopes for two years at Indianapolis, IN, USA. These measurements were done at three towers, one of which measured incoming, background air into the city. We quantitatively removed the background signal and determined the urban CO mole fraction and isotopic enhancements. During the winter months, we constrained the isotopic signature and concluded that the majority of CO produced during the winter was produced by fossil fuel combustion. We found that the Indianapolis fossil fuel signature differed from that of studies done in Europe. Further, we performed a limited traffic study to look at CO isotopes from traffic. While this was not conclusive, it did support our hypothesis that a larger fraction of the Indianapolis vehicle fleet may have malfunctioning catalytic systems, which biases the isotopic results, particularly for delta18O. We used the wintertime fossil fuel isotopic signature to help constrain the summertime budget. It was hypothesized that a second source of CO was significant during the summer months. Oxidation of biogenically produced volatile organic compounds (BVOC's) was one possible source. Oxidized BVOC's were consistent with the changes between our winter and summer isotopic source signatures. We then used the isotopic signatures to determine that between zero and sixty percent of the summertime CO budget was produced from oxidized VOC's. This provided the first direct evidence of a larger percentage of urban CO being produced by oxidized VOC's.

Frost damage in citric and olive production as the result of climate degradation

NASA Astrophysics Data System (ADS)

Saa Requejo, A.; Díaz Alvarez, M. C.; Tarquis, A. M.; Burgaz Moreno, F.; Garcia Moreno, R.

2009-04-01

Low temperature is one of the chief limiting factors in plant distribution. Freezing temperature shortens the growing season and may lower the yield and quality of any number of fruit crops. Minimum temperatures records for the Spanish region of Murcia were studied as limiting factor in fruit production. An analysis of temperature series since 1935 showed that the range of the absolute minimum temperatures (Tmin) on frost days in the target year, namely -0.5 °C to -4.0°C, was statistically similar to the range recorded in 1993, while the mean minimum temperatures (tmin) were found to have risen. The historical series also showed the mean minimum temperatures (tmin) to have increased, however. Through 1985, tmin ranged from 4.0 to -2.0 °C, depending on the area, while these limits shifted in more recent years to 7.0 - 0.5 °C. This increase in mean temperature produced that the frost episodes in March 2004 was considered by lemon, mandarin and olive producers as the worst in many years for frost damage since the minimum temperature was reached in a more sensitive phenological stage, despite the statistical evidence that similar freezing temperatures had been reached on similar dates in other years.

FE and MG Isotopic Analyses of Isotopically Unusual Presolar Silicate Grains

NASA Technical Reports Server (NTRS)

Nguyen, A. N.; Messenger, S.; Ito, M.; Rahman, Z.

2011-01-01

Interstellar and circumstellar silicate grains are thought to be Mg-rich and Fe-poor, based on astronomical observations and equilibrium condensation models of silicate dust formation in stellar outflows. On the other hand, presolar silicates isolated from meteorites have surprisingly high Fe contents and few Mg-rich grains are observed. The high Fe contents in meteoritic presolar silicates may indicate they formed by a non-equilibrium condensation process. Alternatively, the Fe in the stardust grains could have been acquired during parent body alteration. The origin of Fe in presolar silicates may be deduced from its isotopic composition. Thus far, Fe isotopic measurements of presolar silicates are limited to the Fe-54/Fe-56 ratios of 14 grains. Only two slight anomalies (albeit solar within error) were observed. However, these measurements suffered from contamination of Fe from the adjacent meteorite matrix, which diluted any isotopic anomalies. We have isolated four presolar silicates having unusual O isotopic compositions by focused ion beam (FIB) milling and obtained their undiluted Mg and Fe isotopic compositions. These compositions help to identify the grains stellar sources and to determine the source of Fe in the grains.

A numerical model for the movement of H 2O, H 218O, and 2HHO in the unsaturated zone

NASA Astrophysics Data System (ADS)

Shurbaji, Abdel-Rahman M.; Phillips, Fred M.

1995-09-01

Vertical profiles of H 218O and 2HHO concentrations have yielded useful information on evaporation and infiltration processes in soils. However, in the field, quantitative interpretation of such profiles has been limited by the restrictions inherent in the quasi-steady-state and transient analytical models available to describe the physical processes. This study presents a flexible numerical model that simulates transient fluxes of heat, liquid water, water vapor, and isotopic species. The model can simulate both infiltration and evaporation under fluctuating meteorological conditions and thus should be useful in reproducing changes in field isotope profiles. A transition factor is introduced in the isotope transport equation. This factor combines hydrologic and isotopic parameters and changes slowly with depth in the soil profile but strongly in the evaporation zone, owing to the rapid change in the dominant phase of water from liquid to vapor. Using the transition factor in the isotope transport equation facilitates obtaining the typical shape of the isotope profile (bulge at the evaporation zone). This factor also facilitates producing broad isotope enrichment peaks that may be seen in very dry soils.

Isotopic and noble gas geochemistry in geothermal research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kennedy, B.M.; DePaolo, D.J.

1997-12-31

The objective of this program is to provide, through isotopic analyses of fluids, fluid inclusions, and rocks and minerals coupled with improved methods for geochemical data analysis, needed information regarding sources of geothermal heat and fluids, the spatial distribution of fluid types, subsurface flow, water-rock reaction paths and rates, and the temporal evolution of geothermal systems. Isotopic studies of geothermal fluids have previously been limited to the light stable isotopes of H, C, and O. However, other isotopic systems such as the noble gases (He, Ne, Ar, Kr and Xe) and reactive elements (e.g. B, N, S, Sr and Pb)more » are complementary and may even be more important in some geothermal systems. The chemistry and isotopic composition of a fluid moving through the crust will change in space and time in response to varying chemical and physical parameters or by mixing with additional fluids. The chemically inert noble gases often see through these variations, making them excellent tracers for heat and fluid sources. Whereas, the isotopic compositions of reactive elements are useful tools in characterizing water-rock interaction and modeling the movement of fluids through a geothermal reservoir.« less

Variation in the terrestrial isotopic composition and atomic weight of argon

USGS Publications Warehouse

Böhlke, John Karl

2014-01-01

The isotopic composition and atomic weight of argon (Ar) are variable in terrestrial materials. Those variations are a source of uncertainty in the assignment of standard properties for Ar, but they provide useful information in many areas of science. Variations in the stable isotopic composition and atomic weight of Ar are caused by several different processes, including (1) isotope production from other elements by radioactive decay (radiogenic isotopes) or other nuclear transformations (e.g., nucleogenic isotopes), and (2) isotopic fractionation by physical-chemical processes such as diffusion or phase equilibria. Physical-chemical processes cause correlated mass-dependent variations in the Ar isotope-amount ratios (40Ar/36Ar, 38Ar/36Ar), whereas nuclear transformation processes cause non-mass-dependent variations. While atmospheric Ar can serve as an abundant and homogeneous isotopic reference, deviations from the atmospheric isotopic ratios in other Ar occurrences limit the precision with which a standard atomic weight can be given for Ar. Published data indicate variation of Ar atomic weights in normal terrestrial materials between about 39.7931 and 39.9624. The upper bound of this interval is given by the atomic mass of 40Ar, as some samples contain almost pure radiogenic 40Ar. The lower bound is derived from analyses of pitchblende (uranium mineral) containing large amounts of nucleogenic 36Ar and 38Ar. Within this interval, measurements of different isotope ratios (40Ar/36Ar or 38Ar/36Ar) at various levels of precision are widely used for studies in geochronology, water–rock interaction, atmospheric evolution, and other fields.

pH-dependent equilibrium isotope fractionation associated with the compound specific nitrogen and carbon isotope analysis of substituted anilines by SPME-GC/IRMS.

PubMed

Skarpeli-Liati, Marita; Turgeon, Aurora; Garr, Ashley N; Arnold, William A; Cramer, Christopher J; Hofstetter, Thomas B

2011-03-01

Solid-phase microextraction (SPME) coupled to gas chromatography/isotope ratio mass spectrometry (GC/IRMS) was used to elucidate the effects of N-atom protonation on the analysis of N and C isotope signatures of selected aromatic amines. Precise and accurate isotope ratios were measured using polydimethylsiloxane/divinylbenzene (PDMS/DVB) as the SPME fiber material at solution pH-values that exceeded the pK(a) of the substituted aniline's conjugate acid by two pH-units. Deviations of δ(15)N and δ(13)C-values from reference measurements by elemental analyzer IRMS were small (<0.9‰) and within the typical uncertainties of isotope ratio measurements by SPME-GC/IRMS. Under these conditions, the detection limits for accurate isotope ratio measurements were between 0.64 and 2.1 mg L(-1) for δ(15)N and between 0.13 and 0.54 mg L(-1) for δ(13)C, respectively. Substantial inverse N isotope fractionation was observed by SPME-GC/IRMS as the fraction of protonated species increased with decreasing pH leading to deviations of -20‰ while the corresponding δ(13)C-values were largely invariant. From isotope ratio analysis at different solution pHs and theoretical calculations by density functional theory, we derived equilibrium isotope effects, EIEs, pertinent to aromatic amine protonation of 0.980 and 1.001 for N and C, respectively, which were very similar for all compounds investigated. Our work shows that N-atom protonation can compromise accurate compound-specific N isotope analysis of aromatic amines.

Archival processes of the water stable isotope signal in East Antarctic ice cores

NASA Astrophysics Data System (ADS)

Casado, Mathieu; Landais, Amaelle; Picard, Ghislain; Münch, Thomas; Laepple, Thomas; Stenni, Barbara; Dreossi, Giuliano; Ekaykin, Alexey; Arnaud, Laurent; Genthon, Christophe; Touzeau, Alexandra; Masson-Delmotte, Valerie; Jouzel, Jean

2018-05-01

The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition. By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation-condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas.

Development of ion beam sputtering techniques for actinide target preparation

NASA Astrophysics Data System (ADS)

Aaron, W. S.; Zevenbergen, L. A.; Adair, H. L.

1985-06-01

Ion beam sputtering is a routine method for the preparation of thin films used as targets because it allows the use of a minimum quantity of starting material, and losses are much lower than most other vacuum deposition techniques. Work is underway in the Isotope Research Materials Laboratory (IRML) at ORNL to develop the techniques that will make the preparation of actinide targets up to 100 μg/cm 2 by ion beam sputtering a routinely available service from IRML. The preparation of the actinide material in a form suitable for sputtering is a key to this technique, as is designing a sputtering system that allows the flexibility required for custom-ordered target production. At present, development work is being conducted on low-activity actinides in a bench-top system. The system will then be installed in a hood or glove box approved for radioactive materials handling where processing of radium, actinium, and plutonium isotopes among others will be performed.

Authentication and dating of biomass components of industrial materials; links to sustainable technology

NASA Astrophysics Data System (ADS)

Currie, L. A.; Klinedinst, D. B.; Burch, R.; Feltham, N.; Dorsch, R.

2000-10-01

There are twin pressures mounting in US industry for increased utilization of biomass feedstocks and biotechnology in production. The more demanding pressure relates to economic sustainability, that is, because of increased competition globally, businesses will fail unless a minimum margin of profit is maintained while meeting the demands of consumers for less expensive products. The second pressure relates to "Green Technology" where environmental sustainability, linked for example to concerns about climate change and the preservation of natural resources, represents a worldwide driving force to reduce the consumption of fossil hydrocarbons. The resulting transition of biomass production in the industrial plant, as opposed to the agricultural plant, has resulted in an increasing need for isotopic methods of authenticating and dating feedstocks, intermediates and industrial products. The research described represents a prototypical case study leading to the definition of a unique dual isotopic ( 13C, 14C) signature or "fingerprint" for a new biomass-based commercial polymer, polypropylene terephthalate (3GT).

Method and apparatus for detecting dilute concentrations of radioactive xenon in samples of xenon extracted from the atmosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warburton, William K.; Hennig, Wolfgang G.

A method and apparatus for measuring the concentrations of radioxenon isotopes in a gaseous sample wherein the sample cell is surrounded by N sub-detectors that are sensitive to both electrons and to photons from radioxenon decays. Signal processing electronics are provided that can detect events within the sub-detectors, measure their energies, determine whether they arise from electrons or photons, and detect coincidences between events within the same or different sub-detectors. The energies of detected two or three event coincidences are recorded as points in associated two or three-dimensional histograms. Counts within regions of interest in the histograms are then usedmore » to compute estimates of the radioxenon isotope concentrations. The method achieves lower backgrounds and lower minimum detectable concentrations by using smaller detector crystals, eliminating interference between double and triple coincidence decay branches, and segregating double coincidences within the same sub-detector from those occurring between different sub-detectors.« less

Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition

NASA Astrophysics Data System (ADS)

Nielson, Kristine E.; Bowen, Gabriel J.

2010-03-01

Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ 2H values in the early spring to autochthonous particulate matter with significantly lower δ 2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

Coupled extremely light Ca and Fe isotopes in peridotites

NASA Astrophysics Data System (ADS)

Zhao, Xinmiao; Zhang, Zhaofeng; Huang, Shichun; Liu, Yufei; Li, Xin; Zhang, Hongfu

2017-07-01

Large metal stable isotopic variations have been observed in both extraterrestrial and terrestrial samples. For example, Ca exhibits large mass-dependent isotopic variation in terrestrial igneous rocks and mantle minerals (on the order of ∼2‰ variation in 44Ca/40Ca). A thorough assessment and understanding of such isotopic variations in peridotites provides important constraints on the evolution and compositon of the Earth's mantle. In order to better understand the Ca and Fe isotopic variations in terrestrial silicate rocks, we report Ca isotopic compositions in a set of peridotitic xenoliths from North China Craton (NCC), which have been studied for Fe isotopes. These NCC peridotites have large Ca and Fe isotopic variations, with δ44/40Ca ranging from -0.08 to 0.92 (delta value relative to SRM915a) and δ57/54Fe (delta value relative to IRMM-014) ranging from -0.61 to 0.16, and these isotopic variations are correlated with large Mg# (100 × Mg/(Mg + Fe) molar ratio) variation, ranging from 80 to 90. Importantly, NCC Fe-rich peridotites have the lowest 44Ca/40Ca and 57Fe/54Fe ratios in all terrestrial silicate rocks. In contrast, although ureilites, mantle rocks from a now broken differentiated asteroid(s), have large Mg# variation, from 70 to 92, they have very limited δ57Fe/54Fe variation (0.03-0.21, delta value relative to IRMM-014). Our model calculations show that the coupled extremely light Ca-Fe isotopic signatures in NCC Fe-rich peridotites most likely reflect kinetic isotopic fractionation during melt-peridotite reaction on a timescale of several to 104 years. In addition, our new data and compiled literature data show a possible compositional effect on the inter-mineral Ca isotopic fractionation between co-existing clinopyroxene and orthopyroxene pairs.

Finite mixture models for the computation of isotope ratios in mixed isotopic samples

NASA Astrophysics Data System (ADS)

Koffler, Daniel; Laaha, Gregor; Leisch, Friedrich; Kappel, Stefanie; Prohaska, Thomas

2013-04-01

Finite mixture models have been used for more than 100 years, but have seen a real boost in popularity over the last two decades due to the tremendous increase in available computing power. The areas of application of mixture models range from biology and medicine to physics, economics and marketing. These models can be applied to data where observations originate from various groups and where group affiliations are not known, as is the case for multiple isotope ratios present in mixed isotopic samples. Recently, the potential of finite mixture models for the computation of 235U/238U isotope ratios from transient signals measured in individual (sub-)µm-sized particles by laser ablation - multi-collector - inductively coupled plasma mass spectrometry (LA-MC-ICPMS) was demonstrated by Kappel et al. [1]. The particles, which were deposited on the same substrate, were certified with respect to their isotopic compositions. Here, we focus on the statistical model and its application to isotope data in ecogeochemistry. Commonly applied evaluation approaches for mixed isotopic samples are time-consuming and are dependent on the judgement of the analyst. Thus, isotopic compositions may be overlooked due to the presence of more dominant constituents. Evaluation using finite mixture models can be accomplished unsupervised and automatically. The models try to fit several linear models (regression lines) to subgroups of data taking the respective slope as estimation for the isotope ratio. The finite mixture models are parameterised by: • The number of different ratios. • Number of points belonging to each ratio-group. • The ratios (i.e. slopes) of each group. Fitting of the parameters is done by maximising the log-likelihood function using an iterative expectation-maximisation (EM) algorithm. In each iteration step, groups of size smaller than a control parameter are dropped; thereby the number of different ratios is determined. The analyst only influences some control parameters of the algorithm, i.e. the maximum count of ratios, the minimum relative group-size of data points belonging to each ratio has to be defined. Computation of the models can be done with statistical software. In this study Leisch and Grün's flexmix package [2] for the statistical open-source software R was applied. A code example is available in the electronic supplementary material of Kappel et al. [1]. In order to demonstrate the usefulness of finite mixture models in fields dealing with the computation of multiple isotope ratios in mixed samples, a transparent example based on simulated data is presented and problems regarding small group-sizes are illustrated. In addition, the application of finite mixture models to isotope ratio data measured in uranium oxide particles is shown. The results indicate that finite mixture models perform well in computing isotope ratios relative to traditional estimation procedures and can be recommended for more objective and straightforward calculation of isotope ratios in geochemistry than it is current practice. [1] S. Kappel, S. Boulyga, L. Dorta, D. Günther, B. Hattendorf, D. Koffler, G. Laaha, F. Leisch and T. Prohaska: Evaluation Strategies for Isotope Ratio Measurements of Single Particles by LA-MC-ICPMS, Analytical and Bioanalytical Chemistry, 2013, accepted for publication on 2012-12-18 (doi: 10.1007/s00216-012-6674-3) [2] B. Grün and F. Leisch: Fitting finite mixtures of generalized linear regressions in R. Computational Statistics & Data Analysis, 51(11), 5247-5252, 2007. (doi:10.1016/j.csda.2006.08.014)

Investigation of sulphur isotope variation due to different processes applied during uranium ore concentrate production.

PubMed

Krajkó, Judit; Varga, Zsolt; Wallenius, Maria; Mayer, Klaus; Konings, Rudy

The applicability and limitations of sulphur isotope ratio as a nuclear forensic signature have been studied. The typically applied leaching methods in uranium mining processes were simulated for five uranium ore samples and the n ( 34 S)/ n ( 32 S) ratios were measured. The sulphur isotope ratio variation during uranium ore concentrate (UOC) production was also followed using two real-life sample sets obtained from industrial UOC production facilities. Once the major source of sulphur is revealed, its appropriate application for origin assessment can be established. Our results confirm the previous assumption that process reagents have a significant effect on the n ( 34 S)/ n ( 32 S) ratio, thus the sulphur isotope ratio is in most cases a process-related signature.

Asymptotic Analysis of Time-Dependent Neutron Transport Coupled with Isotopic Depletion and Radioactive Decay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brantley, P S

2006-09-27

We describe an asymptotic analysis of the coupled nonlinear system of equations describing time-dependent three-dimensional monoenergetic neutron transport and isotopic depletion and radioactive decay. The classic asymptotic diffusion scaling of Larsen and Keller [1], along with a consistent small scaling of the terms describing the radioactive decay of isotopes, is applied to this coupled nonlinear system of equations in a medium of specified initial isotopic composition. The analysis demonstrates that to leading order the neutron transport equation limits to the standard time-dependent neutron diffusion equation with macroscopic cross sections whose number densities are determined by the standard system of ordinarymore » differential equations, the so-called Bateman equations, describing the temporal evolution of the nuclide number densities.« less

The Potential of Isotope Ratio Mass Spectrometry (IRMS) and Gas Chromatography-IRMS Analysis of Triacetone Triperoxide in Forensic Explosives Investigations.

PubMed

Bezemer, Karlijn D B; Koeberg, Mattijs; van der Heijden, Antoine E D M; van Driel, Chris A; Blaga, Cornelia; Bruinsma, Jildert; van Asten, Arian C

2016-09-01

Studying links between triacetone triperoxide (TATP) samples from crime scenes and suspects can assist in criminal investigations. Isotope ratio mass spectrometry (IRMS) and gas chromatography (GC)-IRMS were used to measure the isotopic compositions of TATP and its precursors acetone and hydrogen peroxide. In total, 31 TATP samples were synthesized with different raw material combinations and reaction conditions. For carbon, a good differentiation and a linear relationship were observed for acetone-TATP combinations. The extent of negative (δ(13) C) fractionation depended on the reaction yield. Limited enrichment was observed for the hydrogen isotope (δ(2) H) values of the TATP samples probably due to a constant exchange of hydrogen atoms in aqueous solution. For oxygen (δ(18) O), the small isotopic range and excess of water in hydrogen peroxide resulted in poor differentiation. GC-IRMS and IRMS data were comparable except for one TATP sample prepared with high acid concentration demonstrating the potential of compound-specific isotope analysis. Carbon IRMS has practical use in forensic TATP investigations. © 2016 American Academy of Forensic Sciences.

Development of a compound-specific isotope analysis method for acetone via 2,4-dinitrophenylhydrazine derivatization.

PubMed

Wen, Sheng; Feng, Yanli; Wang, Xinming; Sheng, Guoying; Fu, Jiamo; Bi, Xinhui

2004-01-01

A novel method has been developed for compound-specific isotope analysis for acetone via DNPH (2,4-dinitrophenylhydrazine) derivatization together with combined gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Acetone reagents were used to assess delta13C fractionation during the DNPH derivatization process. Reduplicate delta13C analyses were designed to evaluate the reproducibility of the derivatization, with an average error (1 standard deviation) of 0.17 +/- 0.05 per thousand, and average analytical error of 0.28 +/- 0.09 per thousand. The derivatization process introduces no isotopic fractionation for acetone (the average difference between the predicted and analytical delta13C values was 0.09 +/- 0.20 per thousand, within the precision limits of the GC/C/IRMS measurements), which permits computation of the delta13C values for the original underivatized acetone through a mass balance equation. Together with further studies of the carbon isotopic effect during the atmospheric acetone-sampling procedure, it will be possible to use DNPH derivatization for carbon isotope analysis of atmospheric acetone. Copyright (c) 2004 John Wiley & Sons, Ltd.

Determination of phenylalanine isotope ratio enrichment by liquid chromatography/time- of-flight mass spectrometry.

PubMed

Wu, Zhanpin; Zhang, Xiao-Jun; Cody, Robert B; Wolfe, Robert R

2004-01-01

The application of time-of-flight mass spectrometry to isotope ratio measurements has been limited by the relatively low dynamic range of the time-to-digital converter detectors available on commercial LC/ToF-MS systems. Here we report the measurement of phenylalanine isotope ratio enrichment by using a new LC/ToF-MS system with wide dynamic range. Underivatized phenylalanine was injected onto a C18 column directly with 0.1% formic acid/acetonitrile as the mobile phase. The optimal instrument parameters for the time-of-flight mass spectrometer were determined by tuning the instrument with a phenylalanine standard. The accuracy of the isotope enrichment measurement was determined by the injection of standard solutions with known isotope ratios ranging from 0.02% to 9.2%. A plot of the results against the theoretical values gave a linear curve with R2 of 0.9999. The coefficient of variation for the isotope ratio measurement was below 2%. The method is simple, rapid, and accurate and presents an attractive alternative to traditional GC/MS applications.

Isotope composition and volume of Earth's early oceans.

PubMed

Pope, Emily C; Bird, Dennis K; Rosing, Minik T

2012-03-20

Oxygen and hydrogen isotope compositions of Earth's seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen's was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth's oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH(4) and CO(2) concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth.

Isotope composition and volume of Earth’s early oceans

PubMed Central

Pope, Emily C.; Bird, Dennis K.; Rosing, Minik T.

2012-01-01

Oxygen and hydrogen isotope compositions of Earth’s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen’s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth’s oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH4 and CO2 concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth. PMID:22392985

EVALUATION OF A NON-LETHAL SAMPLING TECHNIQUE FOR THE MEASUREMENT OF MERCURY (HG) CONCENTRATIONS AND STABLE-NITROGEN (15N/14N) ISOTOPE RATIOS IN LARGE MOUTH BASS (MICROPTERUS SALMOIDES)

EPA Science Inventory

Contaminant bioaccumulation studies often rely on fish muscle filets as the tissue of choice for the measurement of nitrogen stable isotope ratios ( 15N) and mercury (Hg). Lethal sampling techniques may not be suitable for studies on limited populations from smaller sized aquati...

Monitoring Lead (Pb) Pollution and Identifying Pb Pollution Sources in Japan Using Stable Pb Isotope Analysis with Kidneys of Wild Rats.

PubMed

Nakata, Hokuto; Nakayama, Shouta M M; Oroszlany, Balazs; Ikenaka, Yoshinori; Mizukawa, Hazuki; Tanaka, Kazuyuki; Harunari, Tsunehito; Tanikawa, Tsutomu; Darwish, Wageh Sobhy; Yohannes, Yared B; Saengtienchai, Aksorn; Ishizuka, Mayumi

2017-01-10

Although Japan has been considered to have little lead (Pb) pollution in modern times, the actual pollution situation is unclear. The present study aims to investigate the extent of Pb pollution and to identify the pollution sources in Japan using stable Pb isotope analysis with kidneys of wild rats. Wild brown ( Rattus norvegicus , n = 43) and black ( R. rattus , n = 98) rats were trapped from various sites in Japan. Mean Pb concentrations in the kidneys of rats from Okinawa (15.58 mg/kg, dry weight), Aichi (10.83), Niigata (10.62), Fukuoka (8.09), Ibaraki (5.06), Kyoto (4.58), Osaka (4.57), Kanagawa (3.42), and Tokyo (3.40) were above the threshold (2.50) for histological kidney changes. Similarly, compared with the previous report, it was regarded that even structural and functional kidney damage as well as neurotoxicity have spread among rats in Japan. Additionally, the possibility of human exposure to a high level of Pb was assumed. In regard to stable Pb isotope analysis, distinctive values of stable Pb isotope ratios (Pb-IRs) were detected in some kidney samples with Pb levels above 5.0 mg/kg. This result indicated that composite factors are involved in Pb pollution. However, the identification of a concrete pollution source has not been accomplished due to limited differences among previously reported values of Pb isotope composition in circulating Pb products. Namely, the current study established the limit of Pb isotope analysis for source identification. Further detailed research about monitoring Pb pollution in Japan and the demonstration of a novel method to identify Pb sources are needed.

Non-linear mixing effects on mass-47 CO2 clumped isotope thermometry: Patterns and implications.

PubMed

Defliese, William F; Lohmann, Kyger C

2015-05-15

Mass-47 CO(2) clumped isotope thermometry requires relatively large (~20 mg) samples of carbonate minerals due to detection limits and shot noise in gas source isotope ratio mass spectrometry (IRMS). However, it is unreasonable to assume that natural geologic materials are homogenous on the scale required for sampling. We show that sample heterogeneities can cause offsets from equilibrium Δ(47) values that are controlled solely by end member mixing and are independent of equilibrium temperatures. A numerical model was built to simulate and quantify the effects of end member mixing on Δ(47). The model was run in multiple possible configurations to produce a dataset of mixing effects. We verified that the model accurately simulated real phenomena by comparing two artificial laboratory mixtures measured using IRMS to model output. Mixing effects were found to be dependent on end member isotopic composition in δ(13)C and δ(18)O values, and independent of end member Δ(47) values. Both positive and negative offsets from equilibrium Δ(47) can occur, and the sign is dependent on the interaction between end member isotopic compositions. The overall magnitude of mixing offsets is controlled by the amount of variability within a sample; the larger the disparity between end member compositions, the larger the mixing offset. Samples varying by less than 2 ‰ in both δ(13)C and δ(18)O values have mixing offsets below current IRMS detection limits. We recommend the use of isotopic subsampling for δ(13)C and δ(18)O values to determine sample heterogeneity, and to evaluate any potential mixing effects in samples suspected of being heterogonous. Copyright © 2015 John Wiley & Sons, Ltd.

Geochemical and isotopic study of soils and waters from an Italian contaminated site: Agro Aversano (Campania)

USGS Publications Warehouse

Bove, M.A.; Ayuso, R.A.; de Vivo, B.; Lima, A.; Albanese, S.

2011-01-01

Lead isotope applications have been widely used in recent years in environmental studies conducted on different kinds of sampled media. In the present paper, Pb isotope ratios have been used to determine the sources of metal pollution in soils and waters in the Agro Aversano area. During three different sampling phases, a total of 113 surface soils (5-20. cm), 20 samples from 2 soil profiles (0-1. m), 11 stream waters and 4 groundwaters were collected. Major element concentrations in sampled media have been analyzed by the ICP-MS technique. Surface soils (20 samples), all soil profiles and all waters have been also analyzed for Pb isotope compositions by thermal ionization (TIMS). The geochemical data were assessed using statistic methods and cartographically elaborated in order to have a clear picture of the level of disturbance of the area. Pb isotopic data were studied to discriminate between anthropogenic and geologic sources. Our results show that As (5.6-25.6. mg/kg), Cu (9-677. mg/kg), Pb (22-193. mg/kg), Tl (0.53-3.62. mg/kg), V (26-142. mg/kg) and Zn (34-215. mg//kg) contents in analyzed soils, exceed the intervention limits fixed by the Italian Environmental Law for residential areas in some of the sampled sites, while intervention limit for industrial areas is exceeded only for Cu concentrations. Lead isotopic data, show that there is a high similarity between the ratios measured in the leached soil samples and those deriving from anthropic activities. This similarity with anthropogenic Pb is also evident in the ratios measured in both groundwater and stream water samples. ?? 2010 Elsevier B.V.

Advances in Multicollector ICPMS for precise and accurate isotope ratio measurements of Uranium isotopes

NASA Astrophysics Data System (ADS)

Bouman, C.; Lloyd, N. S.; Schwieters, J.

2011-12-01

The accurate and precise determination of uranium isotopes is challenging, because of the large dynamic range posed by the U isotope abundances and the limited available sample material. Various mass spectrometric techniques are used for the measurement of U isotopes, where TIMS is the most accepted and accurate one. Multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) can offer higher productivity compared to TIMS, but is traditionally limited by low efficiency of sample utilisation. This contribution will discuss progress in MC-ICPMS for detecting 234U, 235U, 236U and 238U in various uranium reference materials from IRMM and NBL. The Thermo Scientific NEPTUNE Plus with Jet Interface offers a modified dry plasma ICP interface using a large interface pump combined with a special set of sample and skimmer cones giving ultimate sensitivity for all elements across the mass range. For uranium, an ion yield of > 3 % was reported previously [1]. The NEPTUNE Plus also offers Multi Ion Counting using discrete dynode electron multipliers as well as two high abundance-sensitivity filters to discriminate against peak tailing effects on 234U and 236U originating from the major uranium beams. These improvements in sensitivity and dynamic range allow accurate measurements of 234U, 235U and 236U abundances on very small samples and at low concentration. In our approach, minor U isotopes 234U and 236U were detected on ion counters with high abundance sensitivity filters, whereas 235U and 238U were detected on Faraday Cups using a high gain current amplifier (10e12 Ohm) for 235U. Precisions and accuracies for 234U and 236U were down to ~1%. For 235U, subpermil levels were reached.

Monitoring Lead (Pb) Pollution and Identifying Pb Pollution Sources in Japan Using Stable Pb Isotope Analysis with Kidneys of Wild Rats

PubMed Central

Nakata, Hokuto; Nakayama, Shouta M. M.; Oroszlany, Balazs; Ikenaka, Yoshinori; Mizukawa, Hazuki; Tanaka, Kazuyuki; Harunari, Tsunehito; Tanikawa, Tsutomu; Darwish, Wageh Sobhy; Yohannes, Yared B.; Saengtienchai, Aksorn; Ishizuka, Mayumi

2017-01-01

Although Japan has been considered to have little lead (Pb) pollution in modern times, the actual pollution situation is unclear. The present study aims to investigate the extent of Pb pollution and to identify the pollution sources in Japan using stable Pb isotope analysis with kidneys of wild rats. Wild brown (Rattus norvegicus, n = 43) and black (R. rattus, n = 98) rats were trapped from various sites in Japan. Mean Pb concentrations in the kidneys of rats from Okinawa (15.58 mg/kg, dry weight), Aichi (10.83), Niigata (10.62), Fukuoka (8.09), Ibaraki (5.06), Kyoto (4.58), Osaka (4.57), Kanagawa (3.42), and Tokyo (3.40) were above the threshold (2.50) for histological kidney changes. Similarly, compared with the previous report, it was regarded that even structural and functional kidney damage as well as neurotoxicity have spread among rats in Japan. Additionally, the possibility of human exposure to a high level of Pb was assumed. In regard to stable Pb isotope analysis, distinctive values of stable Pb isotope ratios (Pb-IRs) were detected in some kidney samples with Pb levels above 5.0 mg/kg. This result indicated that composite factors are involved in Pb pollution. However, the identification of a concrete pollution source has not been accomplished due to limited differences among previously reported values of Pb isotope composition in circulating Pb products. Namely, the current study established the limit of Pb isotope analysis for source identification. Further detailed research about monitoring Pb pollution in Japan and the demonstration of a novel method to identify Pb sources are needed. PMID:28075384

Light Isotopes and Trace Organics Analysis of Mars Samples with Mass Spectrometry

NASA Technical Reports Server (NTRS)

Mahaffy, P.; Niemann, Hasso (Technical Monitor)

2001-01-01

Precision measurement of light isotopes in Mars surface minerals and comparison of this isotopic composition with atmospheric gas and other, well-mixed reservoirs such as surface dust are necessary to understand the history of atmospheric evolution from a possibly warmer and wetter Martian surface to the present state. Atmospheric sources and sinks that set these ratios are volcanism, solar wind sputtering, photochemical processes, and weathering. Measurement of a range of trace organic species with a particular focus on species such as amino acids that are the building blocks of terrestrial life are likewise important to address the questions of prebiotic and present or past biological activity on Mars. The workshop topics "isotopic mineralogy" and "biology and pre-biotic chemistry" will be addressed from the point of view of the capabilities and limitations of insitu mass spectrometry (MS) techniques such as thermally evolved gas analysis (TEGA) and gas chromatography (GC) surface experiments using MS, in both cases, as a final chemical and isotopic composition detector. Insitu experiments using straightforward adaptations of existing space proven hardware can provide a substantial improvement in the precision and accuracy of our present knowledge of isotopic composition both in molecular and atomic species in the atmosphere and those chemically bound in rocks and soils. Likewise, detection of trace organic species with greatly improved sensitivity from the Viking GCMS experiment is possible using gas enrichment techniques. The limits to precision and accuracy of presently feasible insitu techniques compared to laboratory analysis of returned samples will be explored. The insitu techniques are sufficiently powerful that they can provide a high fidelity method of screening samples obtained from a diverse set of surface locations such as the subsurface or the interior of rocks for selection of those that are the most interesting for return to Earth.

Characterization Of Nuclear Materials Using Time-Of-Flight ICP-MS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buerger, Stefan; Riciputi, Lee R; Bostick, Debra A

2006-01-01

The investigation of illicit trafficking of nuclear materials, nuclear safeguards analysis, and non-proliferation control requires sensitive and isotope-selective detection methods to gain crucial nuclear forensic information like isotope 'fingerprints' and multi-element signatures. The advantage of time-of-flight (TOF) mass spectrometry - quasi-simultaneous multi-mass analysis - combined with an inductively coupled plasma (ICP) ion source provides an analytical instrument with multi-element and multi-isotope capability and good detection limits. A TOF-ICP-MS system thus appears to be an advantageous choice for the investigation and characterization of nuclear materials. We present here results using a GBC OptiMass 8000 time-of-flight ICP-MS for the isotope screening ofmore » solid samples by laser ablation and the multi-element determination of impurities in uranium ore concentrates using matrix matched standards. A laser ablation system (New Wave Research, UP 213) coupled to the TOF-ICP-MS instrument has been used to optimize the system for analysis of non-radioactive metal samples of natural isotopic composition for a variety of elements including Cu, Sr, Zr, Mo, Cd, In, Ba, Ta, W, Re, Pt, and Pb in pure metals, alloys, and glasses to explore precision, accuracy, and detection limits. Similar methods were then applied to measure uranium. When the laser system is optimized, no mass bias correction is required. Precision and accuracy for the determination of the isotopic composition is typically 1 - 3% for elemental concentrations of as little as 50 ppm in the matrix, with no requirement for sample preparation. The laser ablation precision and accuracy are within ~10x of the instrumental limits for liquid analysis (0.1%). We have investigated the capabilities of the TOF-ICP-MS for the analysis of impurities in uranium matrices. Matrix matching has been used to develop calibration curves for a range of impurities (alkaline, earth-alkaline, transition metals, and rare earth elements). These calibration curves have been used to measure impurities in a number of uranium samples. The results from the TOF-ICP-MS will be compared with other mass spectrometric methods.« less

25 CFR 542.22 - What are the minimum internal control standards for internal audit for Tier A gaming operations?

Code of Federal Regulations, 2010 CFR

2010-04-01

... but not limited to, bingo card control, payout procedures, and cash reconciliation process; (ii) Pull... 25 Indians 2 2010-04-01 2010-04-01 false What are the minimum internal control standards for... COMMISSION, DEPARTMENT OF THE INTERIOR HUMAN SERVICES MINIMUM INTERNAL CONTROL STANDARDS § 542.22 What are...

25 CFR 542.32 - What are the minimum internal control standards for internal audit for Tier B gaming operations?

Code of Federal Regulations, 2010 CFR

2010-04-01

... but not limited to, bingo card control, payout procedures, and cash reconciliation process; (ii) Pull... 25 Indians 2 2010-04-01 2010-04-01 false What are the minimum internal control standards for... COMMISSION, DEPARTMENT OF THE INTERIOR HUMAN SERVICES MINIMUM INTERNAL CONTROL STANDARDS § 542.32 What are...

The Age 21 Minimum Legal Drinking Age Law. Prevention Update

ERIC Educational Resources Information Center

Higher Education Center for Alcohol, Drug Abuse, and Violence Prevention, 2011

2011-01-01

Currently, all 50 states limit alcohol purchases to people aged 21 and over. But that hasn't always been the case. In fact, it was July 17, 1984, when President Ronald Reagan signed the national 21 minimum legal drinking age (MLDA) legislation into law. At that time, only 23 states had minimum alcohol purchasing ages of 21 years old. The…

PACKAGING CERTIFICATION PROGRAM METHODOLOGY FOR DETERMINING DOSE RATES FOR SMALL GRAM QUANTITIES IN SHIPPING PACKAGINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nathan, S.; Loftin, B.; Abramczyk, G.

The Small Gram Quantity (SGQ) concept is based on the understanding that small amounts of hazardous materials, in this case radioactive materials (RAM), are significantly less hazardous than large amounts of the same materials. This paper describes a methodology designed to estimate an SGQ for several neutron and gamma emitting isotopes that can be shipped in a package compliant with 10 CFR Part 71 external radiation level limits regulations. These regulations require packaging for the shipment of radioactive materials, under both normal and accident conditions, to perform the essential functions of material containment, subcriticality, and maintain external radiation levels withinmore » the specified limits. By placing the contents in a helium leak-tight containment vessel, and limiting the mass to ensure subcriticality, the first two essential functions are readily met. Some isotopes emit sufficiently strong photon radiation that small amounts of material can yield a large dose rate outside the package. Quantifying the dose rate for a proposed content is a challenging issue for the SGQ approach. It is essential to quantify external radiation levels from several common gamma and neutron sources that can be safely placed in a specific packaging, to ensure compliance with federal regulations. The Packaging Certification Program (PCP) Methodology for Determining Dose Rate for Small Gram Quantities in Shipping Packagings provides bounding shielding calculations that define mass limits compliant with 10 CFR 71.47 for a set of proposed SGQ isotopes. The approach is based on energy superposition with dose response calculated for a set of spectral groups for a baseline physical packaging configuration. The methodology includes using the MCNP radiation transport code to evaluate a family of neutron and photon spectral groups using the 9977 shipping package and its associated shielded containers as the base case. This results in a set of multipliers for 'dose per particle' for each spectral group. For a given isotope, the source spectrum is folded with the response for each group. The summed contribution from all isotopes determines the total dose from the RAM in the container.« less

Chemical data and lead isotopic compositions of geochemical baseline samples from streambed sediments and smelter slag, lead isotopic compositions in fluvial tailings, and dendrochronology results from the Boulder River watershed, Jefferson County, Montana

USGS Publications Warehouse

Unruh, Daniel M.; Fey, David L.; Church, Stan E.

2000-01-01

IntroductionAs a part of the U.S. Geological Survey Abandoned Mine Lands Initiative, metal-mining related wastes in the Boulder River study area in northern Jefferson County, Montana, have been evaluated for their environmental effects. The study area includes a 24-km segment of the Boulder River in and around Basin, Montana and three principal tributaries to the Boulder River: Basin Creek, Cataract Creek, and High Ore Creek. Mine and prospect waste dumps and mill wastes are located throughout the drainage basins of these tributaries and in the Boulder River. Mine-waste material has been transported into and down streams, where it has mixed with and become incorporated into the streambed sediments. In some localities, mine waste material was placed directly in stream channels and was transported downstream forming fluvial tailings deposits along the stream banks. Water quality and aquatic habitat have been affected by trace-element-contaminated sediment that moves from mine wastes into and down streams during snowmelt and storm runoff events within the Boulder River watershed.Present-day trace element concentrations in the streambed sediments and fluvial tailings have been extensively studied. However, in order to accurately evaluate the impact of mining on the stream environments, it is also necessary to evaluate the pre-mining trace-element concentrations in the streambed sediments. Three types of samples have been collected for estimation of pre-mining concentrations: 1) streambed sediment samples from the Boulder River and its tributaries located upstream from historical mining activity, 2) stream terrace deposits located both upstream and downstream of the major tributaries along the Boulder River, and 3) cores through sediment in overbank deposits, in abandoned stream channels, or beneath fluvial tailings deposits. In this report, we present geochemical data for six stream-terrace samples and twelve sediment-core samples and lead isotopic data for six terrace and thirteen core samples. Sample localities are in table 1 and figures 1 and 2, and site and sample descriptions are in table 2.Geochemical data have been presented for cores through fluvial tailings on High Ore Creek, on upper Basin Creek, and on Jack Creek and Uncle Sam Gulch. Geochemical and lead isotopic data for modern streambed-sediment samples have been presented by Fey and others.Lead isotopic determinations in bed sediments have been shown to be an effective tool for evaluating the contributions from various sources to the metals in bed sediments. However, in order to make these calculations, the lead isotopic compositions of the contaminant sources must also be known. Consequently, we have determined the lead isotopic compositions of five streambed-sediment samples heavily contaminated with fluvial mine waste immediately downstream from large mines in the Boulder River watershed in order to determine the lead isotopic signatures of the contaminants. Summary geochemical data for the contaminants are presented here and geochemical data for the streambed-sediment samples are given by Fey and others.Downstream from the Katie mill site and Jib tailings, fluvial deposits of mill tailings are present on a 10-m by 50-m bar in the Boulder River below the confluence with Basin Creek. The source of these tailings is not known, but fluvial tailings are also present immediately downstream from the Katie mill site, which is immediately upstream from the confluence with Basin Creek. Nine cores of fluvial tailings from this bar were analyzed.Dendrochronology samples were taken at several stream terrace localities to provide age control on the stream terrace deposits. Trees growing on the surfaces of stream terraces provide a minimum age for the terrace deposits, although floods subsequent to the trees' growth could have deposited post-mining overbank deposits around the trees. Historical data were also used to provide estimates of minimum ages of cultural features and to bracket the age of events.

High-precision Pb Isotopes Reveal Two Small Magma Bodies Beneath the Summit of Kilauea Volcano

NASA Astrophysics Data System (ADS)

Pietruszka, A. J.; Heaton, D. E.; Marske, J. P.; Garcia, M. O.

2013-12-01

The summit magma storage reservoir of Kilauea Volcano is one of the most important components of the volcano's magmatic plumbing system, but its geometry is poorly known. High-precision Pb isotopic analyses of Kilauea summit lavas (1959-1982) define the minimum number of magma bodies within the summit reservoir and their volumes. The 206Pb/204Pb ratios of these lavas display a temporal decrease due to changes in the composition of the parental magma delivered to the volcano. Analyses of multiple lavas from some individual eruptions reveal small but significant differences in 206Pb/204Pb. The extra-caldera lavas from Aug. 1971 and Jul. 1974 display lower Pb isotope ratios and higher MgO contents (10 wt. %) than the intra-caldera lavas (MgO ~7-8 wt. %) from each eruption. From 1971 to 1982, the 206Pb/204Pb ratios of the lavas define two separate decreasing temporal trends. The intra-caldera lavas from 1971, 1974, 1975, Apr. 1982 and the lower MgO lavas from Sep. 1982 have higher 206Pb/204Pb ratios at a given time (compared to the extra-caldera lavas and the higher MgO lavas from Sep. 1982). These trends require that the intra- and extra-caldera lavas (and the Sep. 1982 lavas) were supplied from two separate, partially isolated magma bodies. Numerous studies (Fiske and Kinoshita, 1969; Klein et al., 1987) have long identified the locus of Kilauea's summit reservoir ~2 km southeast of Halemaumau (HMM) at a depth of ~2-7 km, but more recent investigations have discovered a second magma body located <1 km below the east rim of HMM (Battaglia et al., 2003; Johnson et al., 2010). The association between the vent locations of the extra-caldera lavas near the southeast rim of the caldera and their higher MgO contents suggests that these lavas tapped the deeper magma body. In contrast, the lower MgO intra-caldera lavas were likely derived from the shallow magma body beneath HMM. Residence time modeling based on the Pb isotope ratios of the lavas suggests that the magma volume of the deeper body is ~0.2 km3, whereas the shallow body holds a minimum of ~0.04 km3 of magma. These estimates are smaller than a previous calculation of ~2-3 km3 for Kilauea's summit reservoir based on trace element ratios (Pietruszka and Garcia, 1999), but are similar to the volume of the magma body that underlies Piton de la Fournaise Volcano on Réunion Island (Albarède, 1993).

Constraints on the Miocene landscape evolution of the Eastern Alps from the Kalkspitze region, Niedere Tauern (Austria)

NASA Astrophysics Data System (ADS)

Dertnig, Florian; Stüwe, Kurt; Woodhead, Jon; Stuart, Finlay M.; Spötl, Christoph

2017-12-01

In order to unravel aspects of the Miocene landscape evolution of the eastern European Alps, we present geomorphic and isotopic data from the western Niedere Tauern region (Austria). The region is critical for such interpretations, because it is one of the few regions along the topographic axis of the Eastern Alps where the highest peaks (up to 2500 m a.s.l.) are dominated by limestone. As such, the region contains a record of Miocene landscape-forming events that survived the Pleistocene glaciations, not preserved elsewhere in the central Eastern Alps. This record includes karst caves, karstified planation surfaces and crystalline fluvial pebbles (Augenstein Formation) preserved on planation surfaces and in karst caves. Caves in the region occur in three distinct levels that correlate with well-known cave levels in the Northern Calcareous Alps, although they are somewhat higher in the Niedere Tauern. In part, these cave elevations also correlate with three planation surfaces and knickpoints of major streams draining the region, testifying their pre-glacial origin. We report details of a karst cave (Durchgangshöhle) from the highest cave level located at 2340 m a.s.l. In this cave, allochthonous fluvial gravels are present, overgrown by speleothems. One speleothem yielded an early middle Pleistocene U-Pb age (682 ± 17 ka). We regard this as a minimum age for the erosion of the fluvial cave deposits during Marine Isotope Stages 17 or 16. Carbon and oxygen isotope data of these speleothems imply a climate that is consistent with this interpretation. Cosmogenic 21Ne data of fluvial quartz clasts collected from the surface on plateaus of the Northern Calcareous Alps suggest minimum exposure durations of 115 and 262 ka. They probably reflect successive exposure since removal of the sediment cover of the Oligocene Augenstein Formation during the Pleistocene. While our geochronological data fail to record aspects of the earlier Miocene uplift history, they are consistent with the overall geomorphic history inferred from the geomorphic markers. This suggests that the Niedere Tauern share a common uplift history with the Northern Calcareous Aps and implies a moderate south-north topographic gradient that has been maintained since the Miocene.

Quasi ?non-destructive? laser ablation-inductively coupled plasma-mass spectrometry fingerprinting of sapphires

NASA Astrophysics Data System (ADS)

Guillong, M.; Günther, D.

2001-07-01

A homogenized 193 nm excimer laser with a flat-top beam profile was used to study the capabilities of LA-ICP-MS for 'quasi' non-destructive fingerprinting and sourcing of sapphires from different locations. Sapphires contain 97-99% of Al 2O 3 (corundum), with the remainder composed of several trace elements, which can be used to distinguish the origin of these gemstones. The ablation behavior of sapphires, as well as the minimum quantity of sample removal that is required to determine these trace elements, was investigated. The optimum ablation conditions were a fluency of 6 J cm -2, a crater diameter of 120 μm, and a laser repetition rate of 10 Hz. The optimum time for the ablation was determined to be 2 s, equivalent to 20 laser pulses. The mean sample removal was 60 nm per pulse (approx. 3 ng per pulse). This allowed satisfactory trace element determination, and was found to cause the minimum amount of damage, while allowing for the fingerprinting of sapphires. More than 40 isotopes were measured using different spatial resolutions (20-120 μm) and eight elements were reproducibly detected in 25 sapphire samples from five different locations. The reproducibility of the trace element distribution is limited by the heterogeneity of the sample. The mean of five or more replicate analyses per sample was used. Calibration was carried out using NIST 612 glass reference material as external standard. The linear dynamic range of the ICP-MS (nine orders of magnitude) allowed the use of Al, the major element in sapphire, as an internal standard. The limits of detection for most of the light elements were in the μg g -1 range and were better for heavier elements (mass >85), being in the 0.1 μg g -1 range. The accuracy of the determinations was demonstrated by comparison with XRF analyses of the same set of samples. Using the quantitative analyses obtained using LA-ICP-MS, natural sapphires from five different origins were statistically classified using ternary plots and principal multi-component analysis.

Recent Developments in MC-ICP-MS for Uranium Isotopic Determination from Small Samples.

NASA Astrophysics Data System (ADS)

Field, P.; Lloyd, N. S.

2016-12-01

V002: Advances in approaches and instruments for isotope studies Session ID#: 12653 Recent Developments in MC-ICP-MS for Uranium Isotopic Determination from small samples.M. Paul Field 1 & Nicholas S. Lloyd. 1 Elemental Scientific Inc., Omaha, Nebraska, USA. field@icpms.com 2 Thermo Fisher Scientific, Hanna-Kunath-Str. 11, 28199 Bremen, Germany. nicholas.lloyd@thermofisher.com Uranium isotope ratio determination for nuclear, nuclear safeguards and for environmental applications can be challenging due to, 1) the large isotopic differences between samples and 2) low abundance of 234U and 236U. For some applications the total uranium quantities can be limited, or it is desirable to run at lower concentrations for radiological protection. Recent developments in inlet systems and detector technologies allow small samples to be analyzed at higher precisions using MC-ICP-MS. Here we evaluate the combination of Elemental Scientific apex omega desolvation system and microFAST-MC dual loop-loading flow-injection system with the Thermo Scientific NEPTUNE Plus MC-ICP-MS. The inlet systems allow for the automated syringe loading and injecting handling of small sample volumes with efficient desolvation to minimize the hydride interference on 236U. The highest ICP ion sampling efficiency is realized using the Thermo Scientific Jet Interface. Thermo Scientific 1013 ohm amplifier technology allows small ion beams to be measured at higher precision, offering the highest signal/noise ratio with a linear and stable response that covers a wide dynamic range (ca. 1 kcps - 30 Mcps). For nanogram quantities of low enriched and depleted uranium standards the 235U was measured with 1013 ohm amplifier technology. The minor isotopes (234U and 236U) were measured by SEM ion counters with RPQ lens filters, which offer the lowest detection limits. For sample amounts ca. 20 ng the minor isotopes can be moved onto 1013 ohm amplifiers and the 235U onto standard 1011 ohm amplifier. To illustrate the application a set of solutions from environmental particles [1] were analyzed, the use of precise three isotope ratio plots allows for source attribution with increased confidence. [1] Lloyd et al. 2009, J. Anal. At. Spectrom., 24(6), 752-758.

Effects of Low-Molecular-Weight Organic Acids on the Dissolution of Hydroxyapatite Nanoparticles in Batch and Column Experiments: A Perspective from Phosphate Oxygen Isotope Fractionation

NASA Astrophysics Data System (ADS)

Wang, D.; Jaisi, D. P.; Jin, Y.

2015-12-01

Hydroxyapatite nanoparticles (HANPs) are increasingly being advocated as an efficient and environment-friendly "green" phosphorus nanofertilizer attributed to their nanoscale dimension, large reactive surface area, and low leaching potential. However, knowledge of how naturally occurring low-molecular-weight organic acids (LMWOAs) that are secreted by plant roots mediate the dissolution of HANPs (releasing PO43- ion for plant growth) is nonexistent. Here three most commonly encountered LMWOAs (acetic acid, oxalic acid, and citric acid) at environmentally relevant concentration (1 mM) were evaluated for their effects on HANPs' dissolution in static batch and dynamic column systems. Particularly, phosphate oxygen isotope fractionation of HANPs during dissolution was examined to disentangle mechanisms controlling the evolution of O-isotopic composition of dissolved PO43- ion. Our results reveal that in batch experiments the dissolution of HANPs was fast but the overall dissolution efficiency of HANPs was limited (≤30%). In contrast, ~100% HANPs were dissolved in columns where LMWOAs were continuously injected. The limited dissolution of HANPs in static batch systems was due primarily to pH buffer effect (pH increased sharply when LMWOA was added in HANPs suspension), whereas in dynamic column systems the HANPs were continuously dissolved by low pH LMWOAs and leached away. Regardless of LMWOA type and experimental system, the isotopically light phosphate (P16O4) was preferentially released during dissolution and the O-isotopic composition of dissolved PO43- ion increased gradually with increasing dissolution due to equilibrium isotope effect between dissolved PO43- ion and HANPs. However, the overall magnitude of O-isotopic fractionation of dissolved PO43- ion was less in batch than in column systems, due to less mass transfer between dissolved PO43- ions and HANPs in batch relative to column experiments. Our findings provide new insights into bioavailability, transformation, and evolution of O-isotopic signatures of phosphate-based nanoparticles in agricultural soils particularly in the rhizosphere where such LMWOAs are ubiquitous.

Iron and silicon isotope behaviour accompanying weathering in Icelandic soils, and the implications for iron export from peatlands

NASA Astrophysics Data System (ADS)

Opfergelt, S.; Williams, H. M.; Cornelis, J. T.; Guicharnaud, R. A.; Georg, R. B.; Siebert, C.; Gislason, S. R.; Halliday, A. N.; Burton, K. W.

2017-11-01

Incipient warming of peatlands at high latitudes is expected to modify soil drainage and hence the redox conditions, which has implications for Fe export from soils. This study uses Fe isotopes to assess the processes controlling Fe export in a range of Icelandic soils including peat soils derived from the same parent basalt, where Fe isotope variations principally reflect differences in weathering and drainage. In poorly weathered, well-drained soils (non-peat soils), the limited Fe isotope fractionation in soil solutions relative to the bulk soil (Δ57Fesolution-soil = -0.11 ± 0.12‰) is attributed to proton-promoted mineral dissolution. In the more weathered poorly drained soils (peat soils), the soil solutions are usually lighter than the bulk soil (Δ57Fesolution-soil = -0.41 ± 0.32‰), which indicates that Fe has been mobilised by reductive mineral dissolution and/or ligand-controlled dissolution. The results highlight the presence of Fe-organic complexes in solution in anoxic conditions. An additional constraint on soil weathering is provided by Si isotopes. The Si isotope composition of the soil solutions relative to the soil (Δ30Sisolution-soil = 0.92 ± 0.26‰) generally reflects the incorporation of light Si isotopes in secondary aluminosilicates. Under anoxic conditions in peat soils, the largest Si isotope fractionation in soil solutions relative to the bulk soil is observed (Δ30Sisolution-soil = 1.63 ± 0.40‰) and attributed to the cumulative contribution of secondary clay minerals and amorphous silica precipitation. Si supersaturation in solution with respect to amorphous silica is reached upon freezing when Al availability to form aluminosilicates is limited by the affinity of Al for metal-organic complexes. Therefore, the precipitation of amorphous silica in peat soils indirectly supports the formation of metal-organic complexes in poorly drained soils. These observations highlight that in a scenario of decreasing soil drainage with warming high latitude peatlands, Fe export from soils as Fe-organic complexes will increase, which in turn has implications for Fe transport in rivers, and ultimately the delivery of Fe to the oceans.

SrNdPb isotopic and trace element evidence for crustal contamination of plume-derived flood basalts: Oligocene flood volcanism in western Yemen

NASA Astrophysics Data System (ADS)

Baker, J. A.; Thirlwall, M. F.; Menzies, M. A.

1996-07-01

Oligocene flood basalts from western Yemen have a relatively limited range in initial isotopic composition compared with other continental flood basalts: 87Sr/86Sr = 0.70365-0.70555 ; 143Nd/144Nd = 0.5129-0.51248 ( ɛNd = +6.0 to -2.4) ; 206pb/204Pb = 17.9-19.3 . Most compositions lie outside the isotopic ranges of temporally and spatially appropriate mantle source compositions observed in this area, i.e., Red Sea/Gulf of Aden MORB mantle, the Afar plume, and Pan-African lithospheric mantle Correlations between indices of fractionation, silica, and isotope ratios suggest that crustal contamination has substantially modified the primary isotopic and incompatible trace element characteristics of the flood basalts. However, significant scatter in these correlations was produced by: (a) the heterogeneous isotopic composition of Pan-African crust; (b) the difference in susceptibility of magmas to contamination as a result of variable incompatible trace element contents in primary melts produced by differing degrees of partial melting; (c) the presence or absence of plagioclase as a fractionating phase generating complex contamination trajectories for Sr; (d) sampling over a wide area not representing a single coherent magmatic system; and (e) variation in contamination mechanisms from assimilation associated with fractionation (AFC) to assimilation by hot mafic magmas with little concomitant fractionation. The presence of plagioclase as a fractionating phase in some suites that were undergoing AFC requires assimilation to have taken place within the crust and, coupled with the limited LREE-enrichment accompanying isotopic variations, excludes the possibility that an AFC-type process took place during magma transfer through the lithospheric mantle. Isotopic compositions of some of the inferred crustal assimilants are similar to those postulated by other workers for an enriched lithospheric mantle source of many flood basalts in southwestern Yemen, Ethiopia, and Djibouti. The western Yemen flood basalts contain 0-30% crust which largely swamps their primary lead isotopic signature, but the primary SrNd isotopic signature is close to that of the least contaminated and isotopically most depleted flood basalts. LREE/HFSE and LILE/HFSE ratios also correlate with isotopic data as a result of crustal contamination. However, Nb/La and K/Nb ratios of >1.1 and <150, respectively, in least contaminated samples require an OIB-like source. The pre-contamination isotopic signature is estimated to be: 87Sr/86Sr ˜ 0.7036; 143Nd/144Nd ˜ 0.51292 ; 206Pb/204Pb ˜ 18.4-19.0 . This, coupled with low LILE/HFSE ratios, suggest the source has characteristics akin to the Afar plume. A mantle source isotopically more depleted than Bulk Earth, but not as depleted as MORB, coupled with LILE depletion, also characterises other examples of plume-derived flood volcanism. This mantle reservoir is responsible for the second largest outbursts of volcanism on Earth and has radiogenic isotopic characteristics akin to PREMA mantle, but the incompatible trace element signature of HIMU mantle.

Osmium isotopic homogeneity in the CK carbonaceous chondrites

NASA Astrophysics Data System (ADS)

Goderis, Steven; Brandon, Alan D.; Mayer, Bernhard; Humayun, Munir

2017-11-01

Variable proportions of isotopically diverse presolar components are known to account for nucleosynthetic isotopic anomalies for a variety of elements (e.g., Ca, Ti, Cr, Ni, Sr, Zr, Mo, Ru, Pd, Ba, Nd, and Sm) in both bulk chondrites and achondrites. However, although large Os isotopic anomalies have been measured in acid leachates and residues of unequilibrated chondrites, bulk chondrites of various groups, iron meteorites, and pallasites exhibit Os isotopic compositions that are indistinguishable from terrestrial or bulk solar isotopic abundances. Since the magnitude of nucleosynthetic anomalies is typically largest in the carbonaceous chondrites, this study reports high-precision Os isotopic compositions and highly siderophile element (HSE) concentrations for ten CK chondrites. The isotope dilution concentration data for HSE and high-precision Os isotope ratios were determined on the same digestion aliquots, to precisely correct for radiogenic contributions to 186Os and 187Os. While acid leached bulk unequilibrated carbonaceous chondrites show deficits of s-process Os components to the same extent as revealed by unequilibrated enstatite, ordinary, and Rumuruti chondrites, equilibrated bulk CK chondrites exhibit no resolvable Os isotopic anomalies. These observations support the idea that acid-resistant, carbon-rich presolar grains, such as silicon carbide (SiC) or graphite, are major carriers for nucleosynthetic isotopic anomalies of Os. The destruction of these presolar grains, which are omnipresent in unequilibrated meteorites, must have occurred during aqueous alteration and thermal metamorphism, early in the CK chondrite parent body history. The dispersal of CK chondrites along the IIIAB iron meteorite isochron on a 187Os/188Os versus 187Re/188Os diagram, with Re/Os ratios from 0.032 to 0.083, in combination with the observed redistribution of other HSE (e.g., Pt, Pd), highlights the influence of parent body processes, overprinted by effects of recent terrestrial alteration. Under the oxidizing conditions prevalent on the CK parent body, evident from high abundances of magnetite and limited Fe-Ni metal in CK chondrites, these parent body processes made all isotopically anomalous Os, originally hosted in reduced presolar grains, accessible. The absence of Os isotopic anomalies in ordinary, enstatite, and now also carbonaceous chondrites, implies that the carriers of s- and r-process Os must have been effectively homogenized across the region of chondrite formation, and possibly even the entire solar protoplanetary nebula, as suggested by the Os isotopic compositions of iron meteorites and non-anomalous ureilites. Except for a limited number of ureilites, the relative proportions of presolar s- and r-process carriers of Os (and other elements such as W) in chondrites, and most other planetary bodies, must have remained constant during all subsequent nebular and planetary processes, which appears not to have been the case for other siderophile elements, including Mo, Ru, and Pd. The existence of Mo, Ru, Pd and other siderophile element isotopic anomalies thus appears to be in part controlled by the chemical properties of these elements (e.g., volatility), their host phase(s) (e.g., SiC, graphite, metal, sulfides), and the nature of the nebular or planetary processes experienced in the early solar system.

37 CFR 385.13 - Minimum royalty rates and subscriber-based royalty floors for specific types of services.

Code of Federal Regulations, 2014 CFR

2014-07-01

..., and Copyrights COPYRIGHT ROYALTY BOARD, LIBRARY OF CONGRESS RATES AND TERMS FOR STATUTORY LICENSES... PHYSICAL AND DIGITAL PHONORECORDS Interactive Streaming and Limited Downloads § 385.13 Minimum royalty...

Processes affecting the stable isotope composition of calcite during precipitation on the surface of stalagmites: Laboratory experiments investigating the isotope exchange between DIC in the solution layer on top of a speleothem and the CO2 of the cave atmosphere

NASA Astrophysics Data System (ADS)

Dreybrodt, Wolfgang; Hansen, Maximilian; Scholz, Denis

2016-02-01

We present a theoretical derivation of the exchange time, τex, needed to establish isotopic equilibrium between atmospheric CO2 in a cave and HCO3- dissolved in a thin water film covering the surface of a speleothem. The result is τex = τredex · [HCO3-]/ (KH · pCO2cave) , where τredex depends on the depth, a, of the water film and on temperature. [HCO3-] is the concentration of bicarbonate, pCO2cave the partial pressure of CO2, and KH is Henry's constant. To test the theory we prepared stagnant or flowing thin films of a NaHCO3 solution and exposed them at 20 °C to an CO2 containing atmosphere of pCO2 500, 12,500, or 25,000 ppmV and defined isotope composition. The δ13C and δ18O values of the DIC in the solution were measured as a function of the exposure time. For stagnant films with depths between 0.06 and 0.2 cm the δ13C values exhibit an exponential approach towards isotope equilibrium with the atmospheric CO2 with exchange time, τex. The δ18O values first evolve towards isotopic equilibrium with atmospheric CO2, reach a minimum value and then drift away from the isotopic equilibrium with atmospheric CO2 approaching a steady state caused by isotopic exchange of oxygen with water. The experimental findings are in satisfactory agreement with the theoretical predictions. To further investigate isotope evolution in cave analogue conditions, a water film containing 5 mmol/L of NaHCO3 with a depth of 0.013 cm flowing down an inclined borosilicate glass plate was exposed to an atmosphere with pCO2 = 500 ppmV at a temperature of 20 °C. The δ13C and δ18O values were measured as a function of flow (exposure) time, t. The isotope compositions in the DIC of the water film decrease linear in time by δDIC (t) =δDIC (0) - (δDIC (0) -δDIC (∞)) · t /τex where δDIC (0) is the initial isotope composition of dissolved inorganic carbon (DIC) in the water film and δDIC (∞) its final value. From these data an exchange time τex of ca. 7000 s was obtained, in satisfactory agreement with the theoretical predictions. The exchange times can be calculated by τex = τredex · [HCO3-]/ (KH · pCO2cave), where τredex is given by the theory as function of temperature and the depth, a, of the water film. This way it is possible to obtain exchange times for various conditions of stalagmite growth as they occur in caves.

The human, primate and rabbit ultraviolet action spectra

NASA Technical Reports Server (NTRS)

Pitts, D. G.; Gibbons, W. D.

1972-01-01

A 5000 watt xenon-mercury high pressure lamp was used to produce a continuous ultraviolet spectrum. Human and animal exposures were made to establish the photokeratitis threshold and abiotic action spectrum. The lower limit of the abiotic action spectrum was 220 nm while the upper limit was 310 nm. The radiant exposure threshold at 270 nm was 0.005 watts/sq cm for the rabbit, 0.004 watts/sq cm for the primate, and 0.004 watts/ sq cm for the human. The rabbit curve was bi-peaked with minimums at 220 nm, 240 nm and 270 nm. The primate curve was tri-peaked with minimums at 220 nm, 240 nm and 270 nm. The human data showed a rather shallow curve with a minimum at 270 nm. Formulas and calculations are given to predict minimum exposure times for ocular damage to man in outer space, to establish valid safety criteria, and to establish protective design criteria.

Isotopic coherence of refractory inclusions from CV and CK meteorites: Evidence from multiple isotope systems

NASA Astrophysics Data System (ADS)

Shollenberger, Quinn R.; Borg, Lars E.; Render, Jan; Ebert, Samuel; Bischoff, Addi; Russell, Sara S.; Brennecka, Gregory A.

2018-05-01

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials in the Solar System and numerous previous studies have revealed nucleosynthetic anomalies relative to terrestrial rock standards in many isotopic systems. However, most of the isotopic data from CAIs has been limited to the Allende meteorite and a handful of other CV3 chondrites. To better constrain the isotopic composition of the CAI-forming region, we report the first Sr, Mo, Ba, Nd, and Sm isotopic compositions of two CAIs hosted in the CK3 desert meteorites NWA 4964 and NWA 6254 along with two CAIs from the CV3 desert meteorites NWA 6619 and NWA 6991. After consideration of neutron capture processes and the effects of hot-desert weathering, the Sr, Mo, Ba, Nd, and Sm stable isotopic compositions of the samples show clearly resolvable nucleosynthetic anomalies that are in agreement with previous results from Allende and other CV meteorites. The extent of neutron capture, as manifested by shifts in the observed 149Sm-150Sm isotopic composition of the CAIs is used to estimate the neutron fluence experienced by some of these samples and ranges from 8.40 × 1013 to 2.11 × 1015 n/cm2. Overall, regardless of CAI type or host meteorite, CAIs from CV and CK chondrites have similar nucleosynthetic anomalies within analytical uncertainty. We suggest the region that CV and CK CAIs formed was largely uniform with respect to Sr, Mo, Ba, Nd, and Sm isotopes when CAIs condensed and that CAIs hosted in CV and CK meteorites are derived from the same isotopic reservoir.

'Trophic' and 'source' amino acids in trophic estimation: a likely metabolic explanation.

PubMed

O'Connell, T C

2017-06-01

Amino acid nitrogen isotopic analysis is a relatively new method for estimating trophic position. It uses the isotopic difference between an individual's 'trophic' and 'source' amino acids to determine its trophic position. So far, there is no accepted explanation for the mechanism by which the isotopic signals in 'trophic' and 'source' amino acids arise. Yet without a metabolic understanding, the utility of nitrogen isotopic analyses as a method for probing trophic relations, at either bulk tissue or amino acid level, is limited. I draw on isotopic tracer studies of protein metabolism, together with a consideration of amino acid metabolic pathways, to suggest that the 'trophic'/'source' groupings have a fundamental metabolic origin, to do with the cycling of amino-nitrogen between amino acids. 'Trophic' amino acids are those whose amino-nitrogens are interchangeable, part of a metabolic amino-nitrogen pool, and 'source' amino acids are those whose amino-nitrogens are not interchangeable with the metabolic pool. Nitrogen isotopic values of 'trophic' amino acids will reflect an averaged isotopic signal of all such dietary amino acids, offset by the integrated effect of isotopic fractionation from nitrogen cycling, and modulated by metabolic and physiological effects. Isotopic values of 'source' amino acids will be more closely linked to those of equivalent dietary amino acids, but also modulated by metabolism and physiology. The complexity of nitrogen cycling suggests that a single identifiable value for 'trophic discrimination factors' is unlikely to exist. Greater consideration of physiology and metabolism should help in better understanding observed patterns in nitrogen isotopic values.

Sulfur- and oxygen-isotopes in sediment-hosted stratiform barite deposits

NASA Astrophysics Data System (ADS)

Johnson, Craig A.; Emsbo, Poul; Poole, Forrest G.; Rye, Robert O.

2009-01-01

Sulfur- and oxygen-isotope analyses have been obtained for sediment-hosted stratiform barite deposits in Alaska, Nevada, Mexico, and China to examine the environment of formation of this deposit type. The barite is contained in sedimentary sequences as old as Late Neoproterozoic and as young as Mississippian. If previously published data for other localities are considered, sulfur- and oxygen-isotope data are now available for deposits spanning a host-rock age range of Late Neoproterozoic to Triassic. On a δ 34S versus δ 18O diagram, many deposits show linear or concave-upward trends that project down toward the isotopic composition of seawater sulfate. The trends suggest that barite formed from seawater sulfate that had been isotopically modified to varying degrees. The δ 34S versus δ 18O patterns resemble patterns that have been observed in the modern oceans in pore water sulfate and water column sulfate in some anoxic basins. However, the closest isotopic analog is barite mineralization that occurs at fluid seeps on modern continental margins. Thus the data favor genetic models for the deposits in which barium was delivered by seafloor seeps over models in which barium was delivered by sedimentation of pelagic organisms. The isotopic variations within the deposits appear to reflect bacterial sulfate reduction operating at different rates and possibly with different electron donors, oxygen isotope exchange between reduction intermediates and H 2O, and sulfate availability. Because they are isotopically heterogeneous, sediment-hosted stratiform barite deposits are of limited value in reconstructing the isotopic composition of ancient seawater sulfate.

Vanadium isotope heterogeneity of the early solar system

NASA Astrophysics Data System (ADS)

Nielsen, S.; Auro, M. E. E.; Magna, T.; Davis, D. M.; Mezger, K.; Sarafian, A. R.

2017-12-01

Vanadium (V) has two isotopes with masses 50 and 51 that have 51V/50V ratio of 410. This ratio can be modified by production of 50V through cosmic irradiation, heterogeneous distribution of anomalous nucleosynthetic material and stable isotope fractionation. Due to the existence of only two V isotopes in nature, these latter processes cannot directly be distinguished from irradiation processes. Previous data has suggested that Earth is characterized by 51V/50V that is significantly different to that of meteorites. These data are difficult to reconcile with a singular process that caused the V isotope variation in the early Solar System. Here we present new V isotope data for a large range of meteorites in order to investigate the ultimate origin of V isotope variation in the early Solar System. We find limited and non-systematic 51V/50V variation of 0.3‰ for 25 martian meteorites (depleted/intermediate/enriched shergottites, nakhlites, and chassignite and orthopyroxenite ALH 84001), which suggests that igneous processes on Mars did not induce significant V isotope shifts. Our best estimate for V isotope composition of the bulk silicate Mars can thus be approximated by the mean value of the entire Martian meteorite suite. This value is significantly lighter ( 0.4‰) than that measured for pristine terrestrial rocks. In contrast, meteorites from the HED parent body reveal significant 51V/50V variation that may be linked to magmatic processes such as fractional crystallization of Vestan magma ocean. The two data sets illustrate that several processes are likely to explain the V isotope variation found in meteorites. We will also present new V isotope data for carbonaceous and ordinary chondrites and put them in the context of the values found for Earth, Mars and the HED parent body.

Fractionation of Cu and Zn isotopes during adsorption onto amorphous Fe(III) oxyhydroxide: Experimental mixing of acid rock drainage and ambient river water

USGS Publications Warehouse

Balistrieri, L.S.; Borrok, D.M.; Wanty, R.B.; Ridley, W.I.

2008-01-01

Fractionation of Cu and Zn isotopes during adsorption onto amorphous ferric oxyhydroxide is examined in experimental mixtures of metal-rich acid rock drainage and relatively pure river water and during batch adsorption experiments using synthetic ferrihydrite. A diverse set of Cu- and Zn-bearing solutions was examined, including natural waters, complex synthetic acid rock drainage, and simple NaNO3 electrolyte. Metal adsorption data are combined with isotopic measurements of dissolved Cu (65Cu/63Cu) and Zn (66Zn/64Zn) in each of the experiments. Fractionation of Cu and Zn isotopes occurs during adsorption of the metal onto amorphous ferric oxyhydroxide. The adsorption data are modeled successfully using the diffuse double layer model in PHREEQC. The isotopic data are best described by a closed system, equilibrium exchange model. The fractionation factors (??soln-solid) are 0.99927 ?? 0.00008 for Cu and 0.99948 ?? 0.00004 for Zn or, alternately, the separation factors (??soln-solid) are -0.73 ?? 0.08??? for Cu and -0.52 ?? 0.04??? for Zn. These factors indicate that the heavier isotope preferentially adsorbs onto the oxyhydroxide surface, which is consistent with shorter metal-oxygen bonds and lower coordination number for the metal at the surface relative to the aqueous ion. Fractionation of Cu isotopes also is greater than that for Zn isotopes. Limited isotopic data for adsorption of Cu, Fe(II), and Zn onto amorphous ferric oxyhydroxide suggest that isotopic fractionation is related to the intrinsic equilibrium constants that define aqueous metal interactions with oxyhydroxide surface sites. Greater isotopic fractionation occurs with stronger metal binding by the oxyhydroxide with Cu > Zn > Fe(II).

Determining the N and O isotope effects of microbial nitrite reduction: the global N cycle implications of an enzyme-dependent isotope effect

NASA Astrophysics Data System (ADS)

Martin, T. S.; Casciotti, K. L.

2014-12-01

The marine nitrogen (N) cycle is a dynamic system of critical importance, since nitrogen is the limiting nutrient in over half of the world's oceans. Denitrification and anammox, the main N loss processes from the ocean, have different effects on carbon cycling and greenhouse gas emission. Understanding the balance between the two processes is vital to understanding the role of the N cycle in global climate change. One approach for investigating these processes is by using stable isotope analysis to estimate the relative magnitudes of N fluxes, particularly for biologically mediated processes. In order to make the most of the currently available isotope analysis techniques, it is necessary to know the isotope effects for each processes occurring in the environment. Nitrite reduction is an important step in denitrification. Previous work had begun to explore the N isotope effects for nitrite reduction, but no oxygen (O) isotope effect has been measured. Additionally, no consideration has been given to the type of nitrite reductase carrying out the reaction. There are two main types of respiratory nitrite reductase, one that is Cu-based and another that is Fe-based. We performed batch culture experiments with denitrifier strains possessing either a Cu-type or Fe-type nitrite reductase. Both N and O isotope effects for nitrite reduction were determined for each of these experiments by measuring the NO2- concentration, as well as the N and O isotopes of nitrite and applying a Rayleigh fractionation model. Both the N and O isotope effects were found to be significantly different between the two types of enzymes. This enzyme-linked difference in isotope effects emphasizes the importance of microbial community composition within the global N cycle.

Isotopic evidence for enhanced fossil fuel sources of aerosol ammonium in the urban atmosphere.

PubMed

Pan, Yuepeng; Tian, Shili; Liu, Dongwei; Fang, Yunting; Zhu, Xiaying; Gao, Meng; Gao, Jian; Michalski, Greg; Wang, Yuesi

2018-07-01

The sources of aerosol ammonium (NH 4 + ) are of interest because of the potential of NH 4 + to impact the Earth's radiative balance, as well as human health and biological diversity. Isotopic source apportionment of aerosol NH 4 + is challenging in the urban atmosphere, which has excess ammonia (NH 3 ) and where nitrogen isotopic fractionation commonly occurs. Based on year-round isotopic measurements in urban Beijing, we show the source dependence of the isotopic abundance of aerosol NH 4 + , with isotopically light (-33.8‰) and heavy (0 to +12.0‰) NH 4 + associated with strong northerly winds and sustained southerly winds, respectively. On an annual basis, 37-52% of the initial NH 3 concentrations in urban Beijing arises from fossil fuel emissions, which are episodically enhanced by air mass stagnation preceding the passage of cold fronts. These results provide strong evidence for the contribution of non-agricultural sources to NH 3 in urban regions and suggest that priority should be given to controlling these emissions for haze regulation. This study presents a carefully executed application of existing stable nitrogen isotope measurement and mass-balance techniques to a very important problem: understanding source contributions to atmospheric NH 3 in Beijing. This question is crucial to informing environmental policy on reducing particulate matter concentrations, which are some of the highest in the world. However, the isotopic source attribution results presented here still involve a number of uncertain assumptions and they are limited by the incomplete set of chemical and isotopic measurements of gas NH 3 and aerosol NH 4 + . Further field work and lab experiments are required to adequately characterize endmember isotopic signatures and the subsequent isotopic fractionation process under different air pollution and meteorological conditions. Copyright © 2018 Elsevier Ltd. All rights reserved.

Quantification of in Situ Biodegradation Rate Constants Using a Novel Combined Isotope Approach

NASA Astrophysics Data System (ADS)

Blum, P.; Sültenfuß, J.; Martus, P.

2014-12-01

Numerous studies have shown the enormous potential of the compound-specific isotope analysis (CSIA) for studying the biodegradation of organic compounds such as monoaromatic hydrocarbons (BTEX), polyaromatic hydrocarbons (PAH), chlorinated solvents and other organic contaminants and environmental transformation mechanisms in groundwater. In addition, two-dimensional isotope analysis such as carbon and hydrogen have been successfully studied indicating the potential to also investigate site-specific reaction mechanisms. The main objective of the current study however is to quantify real effective in situ biodegradation rate constants in a coal-tar contaminated aquifer by combining compound-specific isotope analysis (CSIA) and tracer-based (3H-3He) ground-water dating (TGD). Hence, groundwater samples are used to determine groundwater residence times, and carbon and hydrogen stable isotopes are analyzed for selected BTEX and PAH. The results of the hydrogen stable isotopes surprisingly indicate no isotope fractionation and therefore no biodegradation. In contrast, for stable carbon isotopes of selected BTEX such as o-xylene and toluene, isotope shifts are detected indicating active biodegradation under sulfate-reducing conditions. These and previous results of stable carbon isotopes show that only for o-xylene a clear evidence for biodegradation is possible for the studied site. Nevertheless, in combining these results with the groundwater residence times, which range between 1 year for the shallow wells (20 m below surface) and 41 years for the deeper wells (40 m below surface), it is feasible to effectively determine in situ biodegradation rate constants for o-xylene. Conversely, the outcome also evidently demonstrate the major limitations of the novel combined isotope approach for a successful implementation of monitored natural attenuation (MNA) at such field sites.

Laser ablation inductively coupled plasma mass spectrometry for direct isotope ratio measurements on solid samples

NASA Astrophysics Data System (ADS)

Pickhardt, Carola; Dietze, Hans-Joachim; Becker, J. Sabine

2005-04-01

Isotope ratio measurements have been increasingly used in quite different application fields, e.g., for the investigation of isotope variation in nature, in geoscience (geochemistry and geochronology), in cosmochemistry and planetary science, in environmental science, e.g., in environmental monitoring, or by the application of the isotope dilution technique for quantification purposes using stable or radioactive high-enriched isotope tracers. Due to its high sensitivity, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is today a challenging mass spectrometric technique for the direct determination of precise and accurate isotope ratios in solid samples. In comparison to laser ablation quadrupole ICP-MS (LA-ICP-QMS), laser ablation coupled to a double-focusing sector field ICP-MS (LA-ICP-SFMS) with single ion detection offers a significant improvement of sensitivity at low mass resolution, whereby isotope ratios can be measured with a precision to 0.1% relative standard deviation (R.S.D.). In LA-ICP-SFMS, many disturbing isobaric interferences of analyte and molecular ions can be separated at the required mass resolution (e.g., 40Ar16O+ and 56Fe+ for iron isotope ratio measurements). The precision on isotope ratio measurements was improved by one order of magnitude via the simultaneous detection of mass-separated ion currents of isotopes using multiple ion collectors in LA-ICP-MS (LA-MC-ICP-MS). The paper discusses the state of the art, the challenges and limits in isotope ratio measurements by LA-ICP-MS using different instrumentations at the trace and ultratrace level in different fields of application as in environmental and biological research, geochemistry and geochronology with respect to their precision and accuracy.

Galactic Cosmic-Ray Energy Spectra and Composition during the 2009-2010 Solar Minimum Period

NASA Technical Reports Server (NTRS)

Lave, K. A.; Wiedenbeck, Mark E.; Binns, W. R.; Christian, E. R.; Cummings, A. C.; Davis, A. J.; deNolfo, G. A.; Israel, M. H..; Leske, R. A.; Mewaldt, R. A.;

The plasma separation process as a pre-cursor for large scale radioisotope production

NASA Astrophysics Data System (ADS)

Stevenson, Nigel R.

2001-07-01

Radioisotope production generally employs either accelerators or reactors to convert stable (usually enriched) isotopes into the desired product species. Radioisotopes have applications in industry, environmental sciences, and most significantly in medicine. The production of many potentially useful radioisotopes is significantly hindered by the lack of availability or by the high cost of key enriched stable isotopes. To try and meet this demand, certain niche enrichment processes have been developed and commercialized. Calutrons, centrifuges, and laser separation processes are some of the devices and techniques being employed to produce large quantities of selective enriched stable isotopes. Nevertheless, the list of enriched stable isotopes in sufficient quantities remains rather limited and this continues to restrict the availability of many radioisotopes that otherwise could have a significant impact on society. The Plasma Separation Process is a newly available commercial technique for producing large quantities of a wide range of enriched isotopes and thereby holds promise of being able to open the door to producing new and exciting applications of radioisotopes in the future.

U-Pb systematics in iron meteorites - Uniformity of primordial lead

NASA Astrophysics Data System (ADS)

Gopel, C.; Manhes, G.; Allegre, C. J.

1985-08-01

Pb isotopic compositions and U-Pb abundances were determined in the metal phase of six iron meteorites: Canyon Diablo IA, Toluca IA, Odessa IA, Youndegin IA, Deport IA, and Mundrabilla An. Prior to complete dissolution, samples were subjected to a series of leachings and partial dissolutions. Isotopic compositions and abundances of the etched Pb indicate a contamination by terrestrial Pb which is attributable to previous cutting of the meteorite. Pb isotopic compositions measured in the decontaminated samples are identical within 0.2 percent and essentially confirm the primordial Pb value defined by Tatsumoto et al. (1973). These data invalidate more radiogenic Pb isotopic compositions published for iron meteorites, which are the result of terrestrial Pb contamination introduced mainly by analytical procedure. The results of this study support the idea of a solar nebula which was isotopically homogeneous for Pb 4.55 Ga ago. The new upper limit for U-abundance in iron meteorites, 0.001 ppb, is in agreement with its expected thermodynamic solubility in the metal phase.

Lead (Pb) isotopic fingerprinting and its applications in lead pollution studies in China: a review.

PubMed

Cheng, Hefa; Hu, Yuanan

2010-05-01

As the most widely scattered toxic metal in the world, the sources of lead (Pb) observed in contamination investigation are often difficult to identify. This review presents an overview of the principles, analysis, and applications of Pb isotopic fingerprinting in tracing the origins and transport pathways of Pb in the environment. It also summarizes the history and current status of lead pollution in China, and illustrates the power of Pb isotopic fingerprinting with examples of its recent applications in investigating the effectiveness of leaded gasoline phase-out on atmospheric lead pollution, and the sources of Pb found in various environmental media (plants, sediments, and aquatic organisms) in China. The limitations of Pb isotopic fingerprinting technique are discussed and a perspective on its development is also presented. Further methodological developments and more widespread instrument availability are expected to make isotopic fingerprinting one of the key tools in lead pollution investigation. Copyright 2009 Elsevier Ltd. All rights reserved.

Dendritic network models: Improving isoscapes and quantifying influence of landscape and in-stream processes on strontium isotopes in rivers

USGS Publications Warehouse

Brennan, Sean R.; Torgersen, Christian E.; Hollenbeck, Jeff P.; Fernandez, Diego P.; Jensen, Carrie K; Schindler, Daniel E.

2016-01-01

A critical challenge for the Earth sciences is to trace the transport and flux of matter within and among aquatic, terrestrial, and atmospheric systems. Robust descriptions of isotopic patterns across space and time, called “isoscapes,” form the basis of a rapidly growing and wide-ranging body of research aimed at quantifying connectivity within and among Earth's systems. However, isoscapes of rivers have been limited by conventional Euclidean approaches in geostatistics and the lack of a quantitative framework to apportion the influence of processes driven by landscape features versus in-stream phenomena. Here we demonstrate how dendritic network models substantially improve the accuracy of isoscapes of strontium isotopes and partition the influence of hydrologic transport versus local geologic features on strontium isotope ratios in a large Alaska river. This work illustrates the analytical power of dendritic network models for the field of isotope biogeochemistry, particularly for provenance studies of modern and ancient animals.

A new design approach to achieve a minimum impulse limit cycle in the presence of significant measurement uncertainties

NASA Technical Reports Server (NTRS)

Martin, M. W.; Kubiak, E. T.

1982-01-01

A new design was developed for the Space Shuttle Transition Phase Digital Autopilot to reduce the impact of large measurement uncertainties in the rate signal during attitude control. The signal source, which was dictated by early computer constraints, is characterized by large quantization, noise, bias, and transport lag which produce a measurement uncertainty larger than the minimum impulse rate change. To ensure convergence to a minimum impulse limit cycle, the design employed bias and transport lag compensation and a switching logic with hysteresis, rate deadzone, and 'walking' switching line. The design background, the rate measurement uncertainties, and the design solution are documented.

Constraining late stage melt-peridotite interaction in the lithospheric mantle of southern Ethiopia: evidence from lithium elemental and isotopic compositions

NASA Astrophysics Data System (ADS)

Alemayehu, Melesse; Zhang, Hong-Fu; Seitz, Hans-Michael

2017-10-01

Lithium (Li) elemental and isotopic compositions for mineral separates of coexisting olivine, orthopyroxene and clinopyroxene of mantle xenoliths from the Quaternary volcanic rocks of southern Ethiopian rift (Dillo and Megado) reveal the influence of late stage melt-peridotite interaction on the early depleted and variably metasomatized lithospheric mantle. Two types of lherzolites are reported (LREE-depleted La/Sm(N) = 0.11-0.37 × Cl and LREE-enriched, La/Sm(N) = 1.88-15.72 × Cl). The depleted lherzolites have variable range in Li concentration (olivine: 2.1-5.4 ppm; opx: 1.1-2.3 ppm; cpx: 1.0-1.8 ppm) and in Li isotopic composition (δ7Li in olivine: -9.4 to 1.5‰; in opx: -4.5 to 3.6‰; in cpx: -17.0 to 4.8‰), indicating strong disequilibrium in Li partitioning and Li isotope fractionation between samples. The enriched lherzolites have limited range in both Li abundances (olivine: 2.7-3.0 ppm; opx: 1.1-3.1 ppm; cpx: 1.1-2.3 ppm) and Li isotopic compositions (δ7Li in olivine: -1.3 to +1.3‰; in opx: -2.0 to +5.0‰; in cpx: -7.5 to +4.8‰), suggest that the earlier metasomatic event which lead to LREE enrichment could also homogenize the Li contents and its isotopes. The enriched harzburgite and clinopyroxenite minerals show limited variation in Li abundances and variable Li isotopic compositions. The Li enrichments of olivine and clinopyroxene correlate neither with the incompatible trace element enrichment nor with the Sr-Nd isotopic compositions of clinopyroxene. These observations indicate that the metasomatic events which are responsible for the LREE enrichment and for the Li addition are distinct, whereby the LREE-enrichment pre-dates the influx of Li. The presence of large Li isotopic disequilibria within and between minerals of depleted and enriched peridotites suggest that the lithospheric mantle beneath the southern Ethiopian rift has experienced recent melt-peridotite interaction. Thus, the Li data set reported in this study offer new additional evidence for the existence of late stage metasomatism, which probably occurred at shallow depth briefly before and/or during entrainment and ascent of mantle xenoliths to the surface.

Performance and limits of liquid chromatography isotope ratio mass spectrometry system for halogenated compounds

NASA Astrophysics Data System (ADS)

Gilevska, Tetyana; Gehre, Matthias; Richnow, Hans

2014-05-01

Compound Specific Isotope Analysis (CSIA) has been an important step for the assessment of the origin and fate of compounds in environmental science.[1] Biologically or pharmaceutically important compounds often are not amenable for gas chromatographic separation because of high polarity and lacking volatility, thermostability. In 2004 liquid chromatography isotope ratio mass spectrometry (LC-IRMS) became commercially available. LC-IRMS system intent a quantitative conversion of analytes separation into CO2 via wet oxidation with sodium persulfate in the presence of phosphoric acid while analytes are still dissolved in the aqueous liquid phase.[2] The aim of this study is to analyze the oxidation capacity of the interface of the LC-IRMS system and determine which parameters could improve oxidation of compounds which are resistant to persulfate oxidation. Oxidation capacity of the liquid chromatography isotope ratio mass spectrometry system was tested with halogenated acetic acid and a set of aromatic compounds with different substitutes. Acetic acid (AA) was taken as a model compound for complete oxidation and compared to the oxidation of other analytes on a molar basis. Correct values were obtained for di- and mono chlorinated and fluorinated and also for tribrominated acetic acid and for all studied aromatic compounds. Incomplete oxidation for trichloroacetic (TCAA) and trifluoroacetic (TFAA) acid was revealed with lower recovery compared to acetic acid and isotope fractionation leading to depleted carbon isotope composition compared to values obtained with an elementary analyzer connected to an isotope mass spectrometer Several optimization steps were tried in order to improve the oxidation of TCAA and TFAA: (i) increasing the concentration of the oxidizing agent, (ii) variation of flow rate of the oxidizing and acid solution, (iii) variation of flow rate of liquid chromatography pump (iv) addition of a catalyzer. These modifications lead to longer reaction time in the coil and increase in the concentration of radical but complete combustion of highly chlorinated or fluorinated compounds was not achieved. Due to these findings the limit for a LC-IRMS system for similar structure compounds can be predicted. 1. Elsner, M., et al., Current challenges in compound-specific stable isotope analysis of environmental organic contaminants. Analytical and Bioanalytical Chemistry, 2012. 403(9): p. 2471-2491. 2. Krummen, M., et al., A new concept for isotope ratio monitoring liquid chromatography/mass spectrometry. Rapid Communications in Mass Spectrometry, 2004. 18(19): p. 2260-2266.

Automated production of 124I and 64Cu using IBA Terimo and Pinctada metal electroplating and processing modules

NASA Astrophysics Data System (ADS)

Poniger, S. S.; Tochon-Danguy, H. J.; Panopoulos, H. P.; O'Keefe, G. J.; Peake, D.; Rasool, R.; Scott, A. M.

2012-12-01

There is worldwide growing interest for the production of long-lived positron emitters for molecular imaging and the development of novel immuno-PET techniques for drugs discovery. The desire to produce solid target isotopes in Australia has significantly increased over the years and several research projects for labelling of peptides, proteins and biomolecules, including labelling of recombinant antibodies has been limited due to the availability of suitable isotopes. This has led to the recent installation and commissioning of a new lab dedicated to fully automated solid target isotope production, including 124I, 64Cu, 89Zr and 86Y.

Ultra low-level measurements of actinides by sector field ICP-MS.

PubMed

Pointurier, F; Baglan, N; Hémet, P

2004-01-01

In the present work, a double-focusing sector field inductively coupled plasma-mass spectrometer was optimised for ultra trace and isotopic analyses of actinide long-lived isotopes in low concentration solutions of the fgml(-1) to the ngml(-1) range. Sensitivities of about 3GHz/(microgml(-1)), with as low a background as 0.1cps, were obtained for U using a conventional concentric pneumatic nebuliser. Detection limits are below the fg range for 239Pu and 240Pu. With natural U, a precision lower than 0.5% RSD is currently obtained for 235U/238U isotopic ratio at the 200pgml(-1) level.

Accounting for cyanide and its degradation products at three Nevada gold mines; constraints from stable C- and N-isotopes

USGS Publications Warehouse

Johnson, C.A.; Grimes, D.J.; Rye, R.O.

1998-01-01

An understanding of the fate of cyanide (CN-) in mine process waters is important for addressing environmental concerns and for taking steps to minimize reagent costs. The utility of stable isotope methods in identifying cyanide loss pathways has been investigated in case studies at three Nevada gold mines. Freshly prepared barren solutions at the mines have cyanide d15N and d13C values averaging -4 ? and -36 ?, respectively, reflecting the nitrogen and carbon sources used by commercial manufacturers, air and natural gas methane. Pregnant solutions returning from ore heaps display small isotopic shifts to lower d15N and d13C values. The shifts are similar to those observed in laboratory experiments where cyanide was progressively precipitated as a cyanometallic compound, and are opposite in sign and much smaller in magnitude than the shifts observed in experiments where HCN was offgassed. Offgassing is inferred to be a minor cyanide loss mechanism in the heap leach operations at the three mines, and precipitation as cyanometallic compounds, and possibly coprecipitation with ferric oxides, is inferred to be an important loss mechanism. Isotopic analysis of dissolved inorganic carbon (DIC) shows that uptake of high d13C air CO2 has been important in many barren and pregnant solutions. However, DIC in reclaim pond waters at all three mines has low d13C values of -28 to -34 ? indicating cyanide breakdown either by hydrolysis or by other chemical pathways that break the C-N bond. Isotope mass balance calculations indicate that about 40 % of the DIC load in the ponds, at a minimum, was derived from cyanide breakdown. This level of cyanide hydrolysis accounts for 14-100 % of the dissolved inorganic nitrogen species present in the ponds. Overall, isotope data provide quantitative evidence that only minor amounts of cyanide are lost via offgassing and that significant amounts are destroyed via hydrolysis and related pathways. The data also highlight the possibility that significant cyanide may be either retained in the ore heaps or destroyed via other chemical pathways.

Stable sulfur isotope ratios and chemical compositions of fine aerosols (PM2.5) in Beijing, China.

PubMed

Wei, Lianfang; Yue, Siyao; Zhao, Wanyu; Yang, Wenyi; Zhang, Yingjie; Ren, Lujie; Han, Xiaokun; Guo, Qingjun; Sun, Yele; Wang, Zifa; Fu, Pingqing

2018-08-15

Pervasive particulate pollution has been observed over large areas of the North China Plain. The high level of sulfate, a major component in fine particles, is pronounced during heavy pollution periods. Being different from source apportionments by atmospheric chemistry-transport model and receptor modeling methods, here we utilize sulfur isotopes to discern the potential emission sources. Sixty-five daily PM 2.5 samples were collected at an urban site in Beijing between September 2013 and July 2014. Inorganic ions, organic/elemental carbon and stable sulfur isotopes of sulfate were analyzed. The "fingerprint" characteristics of stable sulfur isotopic composition, together with trajectory clustering modeled by HYSPLIT-4 (HYbrid Single-Particle Lagrangian Integrated Trajectory) and FLEXPART ("FLEXible PARTicle dispersion model"), was employed to identify potential aerosol sources in Beijing. Results exhibited a distinctive seasonality with sulfate, nitrate, ammonium, organic matter, and element carbon being the dominant species of PM 2.5 . Elevated concentrations of chloride with high organic matter were found in autumn and winter as a result of enhanced fossil fuel (mainly coal) combustion. The δ 34 S values of the Beijing aerosols ranged from 2.8‰ to 9.9‰ with an average of 6.0 ± 1.8‰, further indicating that the major sulfur source was direct coal burning emission. Owing to the changing patterns between oxidation pathways of S(IV) in different seasons, δ 34 S values varied with a winter maximum (8.2 ± 1.1‰) and a summer minimum (4.9 ± 1.9‰). The results of trajectory clustering and FLEXPART demonstrated that higher concentrations of sulfate with lower sulfur isotope ratios (4.6 ± 0.8‰) were associated with air masses from the south or east, whereas lower sulfate concentrations with heavier sulfur isotope ratios (6.7 ± 1.6‰) were observed when the air masses were mainly from the north or northwest. These results suggested that the fine aerosol pollution in Beijing, especially sulfate pollution, was mainly due to coal combustion sources from regional and local regions. Copyright © 2018 Elsevier B.V. All rights reserved.

Limits to Open Class Performance?

NASA Technical Reports Server (NTRS)

Bowers, Albion H.

2008-01-01

This presentation discusses open or unlimited class aircraft performance limitations and design solutions. Limitations in this class of aircraft include slow climbing flight which requires low wing loading, high cruise speed which requires high wing loading, gains in induced or viscous drag alone which result in only half the gain overall and other structural problems (yaw inertia and spins, flutter and static loads integrity). Design solutions include introducing minimum induced drag for a given span (elliptical span load or winglets) and introducing minimum induced drag for a bell shaped span load. It is concluded that open class performance limits (under current rules and technologies) is very close to absolute limits, though some gains remain to be made from unexplored areas and new technologies.

Dual Si and O Isotope Measurement of Lunar Samples Using IRMS

NASA Astrophysics Data System (ADS)

Banerjee, N.; Hill, P. J. A.; Osinski, G. R.

2016-12-01

The use of isotopic systems and their associated theoretical models have become an increasingly sophisticated tool for investigating the origin of planetary bodies in the solar system. It was originally hypothesized that evidence for the impact origin of Moon would manifest itself as an isotopic heterogeneity between lunar and terrestrial samples; however, most isotope systems show no difference between the bulk Earth and Moon. The stable isotopes of both silicon (Si) and oxygen (O) have been essential in further understanding planetary processes including core formation. Historically the analysis of the Si and O isotope ratios in terrestrial and extraterrestrial material has primarily been measured independent of each other through three main techniques: isotope ratio mass spectrometry (IRMS), secondary ion mass spectrometry (SIMS), and multi-collector inductively coupled plasma mass-spectrometry (MC-ICPMS). Each technique has its own strength and weakness in regards to resolution and precision; however, one of the main limiting factors in all three of these techniques rests on the requirement of multiple aliquots. As most literature focuses on the measurement of oxygen or silicon isotopes, this unique line allows for the precise analysis of Si and O isotopes from the same aliquot of bulk sample, which cannot be done with SIMS or ICP-MS analysis. To deal with this problem a unique laser line system has been developed in the Laboratory for Stable Isotope Science at Western University, Canada, that simultaneously extracts SiF4 and O2 from the same 1-2 mg aliquot. We present the application of analyzing both isotopic systems from the sample aliquot to Apollo, meteoritic, and terrestrial samples and its implication for the formation of the Moon. Preliminary results from this line suggest that although the O isotopes ratios are consistent with a homogenous Moon-Earth system, a difference is observed in Si isotopes between Apollo and terrestrial samples compared to previous studies.

Ca and Mg isotope constraints on the origin of Earth's deepest δ13 C excursion

NASA Astrophysics Data System (ADS)

Husson, Jon M.; Higgins, John A.; Maloof, Adam C.; Schoene, Blair

2015-07-01

Understanding the extreme carbon isotope excursions found in carbonate rocks of the Ediacaran Period (635-541 Ma), where δ13 C of marine carbonates (δ13 Ccarb) reach their minimum (- 12 ‰) for Earth history, is one of the most vexing problems in Precambrian geology. Known colloquially as the 'Shuram' excursion, the event has been interpreted by many as a product of a profoundly different Ediacaran carbon cycle. More recently, diagenetic processes have been invoked, with the very negative δ13 C values of Ediacaran carbonates explained via meteoric alteration, late-stage burial diagenesis or growth of authigenic carbonates in the sediment column, thus challenging models which rely upon a dramatically changing redox state of the Ediacaran oceans. Here we present 257 δ 44 / 40 Ca and 131 δ26 Mg measurements, along with [Mg], [Mn] and [Sr] data, from carbonates of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia to bring new isotope systems to bear on understanding the 'Shuram' excursion. Data from four measured sections spanning the basin reveal stratigraphically coherent trends, with variability of ∼1.5‰ in δ26 Mg and ∼1.2‰ in δ 44 / 40 Ca. This Ca isotope variability dwarfs the 0.2-0.3 ‰ change seen coeval with the Permian-Triassic mass extinction, the largest recorded in the rock record, and is on par with putative changes in the δ 44 / 40 Ca value of seawater seen over the Phanerozoic Eon. Changes in both isotopic systems are too large to explain with changes in the isotopic composition of Ca and Mg in global seawater given modern budgets and residence times, and thus must be products of alternative processes. Relationships between δ 44 / 40 Ca and [Sr] and δ26 Mg and [Mg] are consistent with mineralogical control (e.g., aragonite vs. calcite, limestone vs. dolostone) on calcium and magnesium isotope variability. The most pristine samples in the Wonoka dataset, preserving Sr concentrations (in the 1000s of ppm range) and δ 44 / 40 Ca values inherited from an originally aragonitic polymorph, have δ13 Ccarb of - 8 ‰ to - 7 ‰ , thereby providing strong geochemical evidence that extremely negative δ13 Ccarb values are primary products of the Ediacaran surface environment.

Carbonate clumped-isotope constraints on the burial and exhumation history of the Colorado Plateau

NASA Astrophysics Data System (ADS)

Ryb, U.; Lloyd, M. K.; Eiler, J. M.

2016-12-01

Reconstruction of the thermal history of rocks is key to study the geodynamic evolution of sedimentary basins. Carbonate clumped-isotope measurements of minerals formed or re-equilibrated at elevated temperatures can constrain thermal histories of rocks. Experimental constraints on solid state isotopic reordering in carbonates let us translate clumped-isotope measurements into quantitative statements about the thermal history, and thus burial and exhumation. We use this approach to constrain peak burial temperatures of Paleozoic rocks across the Colorado Plateau, sampled carbonate rocks from the southwestern Plateau margin and from borehole cores in the Plateau interior. We sub-sampled specific fabrics (fossils, cements, etc.), determined their calcite and dolomite proportions using XRD, and analyzed clumped-isotope compositions (reported as apparent temperatures using Stolper and Eiler's (2015) calibration) for pure calcite or dolomite samples (>97 wt.%). At the Plateau margin, calcite and dolomite apparent temperatures are 49-79°C and 67-97°C, respectively. The maximum apparent temperature constrains the minimum peak burial temperature. The distribution of calcite apparent temperatures independently constrains the maximum burial temperature as follows: If the "coldest" sample had an initial apparent temperature of 20°C, then its observed value can be explained by isotopic reordering to a peak temperature of 105-120°C. We therefore hypothesize peak temperature at the base of the Paleozoic was 97-120°C. At the Plateau interior, apparent temperatures of Mississippian calcite samples are depth-dependent: Samples cored from <2km depth have apparent temperatures of 54-68°C; similar samples from 3km depth have apparent temperatures of 105-165°C and a smaller variability between sub-samples, interpreted to result from isotopic reordering at >150°C. Assuming a surface temperature of 20°C and a thermal gradient of 25°C km-1, we calculate total overburden (above the Mississippian) and exhumation of 2.7-3.7 km and 1.8-2.8 km, respectively, at the Plateau margin; and total overburden and exhumation of 5.8-6.6 km, and 3-3.8 km, respectively, at the Plateau interior. Our findings are consistent with peak burial estimates based on thermochronometry and other proxies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watrous, Matthew George; Adamic, Mary Louise; Olson, John Eric

The goal of the project, New Paradigms for Isotope Ratio Mass Spectrometry: Raising the Scientific Profile and Improved Performance for Accelerator Mass Spectrometry (AMS) and Thermal Ionization Mass Spectrometry (TIMS), is to ensure that the ongoing isotope ratio determination capability within the U.S. Department of Energy complex is the world’s best for application to nonproliferation. This report spells out the progress of Task 4, Transition of TIMS to AMS for Iodine Analysis, of the larger project. The subtasks under Task 4 and the accomplishments throughout the three year project life cycle are presented in this report. Progress was made inmore » optimization of chemical extraction, determination of a detection limit for 127Iodine, production of standard materials for AMS analysis quality assurance, facilitation of knowledge exchange with respect to analyzing iodine on an AMS, cross comparison with a world-leading AMS laboratory, supercritical fluid extraction of iodine for AMS analysis and electrodeposition of seawater as a direct method of preparation for iodine analysis by AMS--all with the goal of minimizing the time required to stand up an AMS capability for iodine analysis of exposed air filters at INL. An effective extraction method has been developed and demonstrated for iodine analysis of exposed air filters. Innovative techniques to accomplish the cathode preparation for AMS analysis were developed and demonstrated and published. The known gap of a lack of available materials for reference standards in the analysis of iodine by AMS was filled by the preparation of homogenous materials that were calibrated against NIST materials. A minimum limit on the amount of abundant isotope in a sample was determined for AMS analysis. The knowledge exchange occurred with fantastic success. Scientists engaged the international AMS community at conferences, as well as in their laboratories for collaborative work. The supercritical fluid extraction work has positive data, but is not a replacement for leaching yet. The added seawater work has led to a good method and a possible publication. The focus of this project was to minimize the time to stand up the AMS capability, by having all the preparation and supporting functions worked out ahead of the instrument arrival. Due to all the preparatory work and its success, the instrument was delivered and turned over to the INL in February 2015. Since then, INL scientists have been successfully vetting the capabilities and accomplishing their own measurements that agree well with the leading laboratories of the world for iodine analysis by AMS. Initially, all AMS data was gathered on other laboratories instruments, but during the last six months data for this project has come from INL’s AMS.« less

Density of Gadolinium Nitrate Solutions for the High Flux Isotope Reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, Paul Allen; Lee, Denise L

2009-05-01

In late 1992, the High Flux Isotope Reactor (HFIR) was planning to switch the solution contained in the poison injection tank from cadmium nitrate to gadolinium nitrate. The poison injection system is an emergency system used to shut down the reactor by adding a neutron poison to the cooling water. This system must be able to supply a minimum of 69 pounds of gadolinium to the reactor coolant system in order to guarantee that the reactor would become subcritical. A graph of the density of gadolinium nitrate solutions over a concentration range of 5 to 30 wt% and a temperaturemore » range of 15 to 40{sup o}C was prepared. Routine density measurements of the solution in the poison injection tank are made by HFIR personnel, and an adaptation of the original graph is used to determine the gadolinium nitrate concentration. In late 2008, HFIR personnel decided that the heat tracing that was present on the piping for the poison injection system could be removed without any danger of freezing the solution; however, the gadolinium nitrate solution might get as cold as 5{sup o}C. This was outside the range of the current density-concentration correlation, so the range needed to be expanded. This report supplies a new density-concentration correlation that covers the extended temperature range. The correlation is given in new units, which greatly simplifies the calculation that is required to determine the pounds of gadolinium in the tank solution. The procedure for calculating the amount of gadolinium in the HFIR poison injection system is as follows: (1) Calculate the usable volume in the system; (2) Measure the density of the solution; (3) Calculate the gadolinium concentration using the following equation: Gd(lb/ft{sup 3}) = measured density (g/mL) x 34.681 - 34.785; (4) Calculate the amount of gadolinium in the system using the following equation: Amount of Gd(lb) = Gd concentration (lb/ft{sup 3}) x usable volume (ft{sup 3}). The equation in step 3 is exact for a temperature of 5{sup o}C, and overestimates the gadolinium concentration at all higher temperatures. This guarantees that the calculation is conservative, in that the actual concentration will be at least as high as that calculated. If an additional safety factor is desired, it is recommended that an administrative control limit be set that is higher than the required minimum amount of gadolinium.« less

Crystallization Age and Source Signature of Chassigny

NASA Technical Reports Server (NTRS)

Misawa, K.; Shih, C.-Y.; Reese, Y.; Nyquist, L. E.

2005-01-01

Chassigny is the Martian dunite composed of cumulate olivine (92%), chromite (1.4%), pyroxene (5%) and interstitial feldspar (1.7%). Although nakhlites (clinopyroxenite) are less intensely affected by shock metamorphism, Chassigny has been subjected to a peak shock pressure of about 35 GPa. The cosmic-ray exposure age of Chassigny (11.3 +/- 0.6 Ma) is comparable to those of nakhlites, suggesting launch pairing of these meteorites. Prior chemical and isotopic studies of Chassigny suggest that the meteorite crystallized approx. 1.3 Ga ago and is closely related to nakhlites. Nevertheless, compared to other Martian meteorites there are limited isotopic data for Chassigny. To examine the relationship of Chassigny to nakhlites, we have undertaken new Rb-Sr and Sm-Nd isotopic studies. Here we present the new Sm-Nd isotopic data for Chassigny and discuss the nature of its source materials.

Pollutant Source Tracking (PST) Technical Guidance

DTIC Science & Technology

2011-12-01

in the context of heavy metals (lead, copper), is considered to be a minor process contribution to the source fingerprint. 3.7 RAPID SCREENING...limits (summarized in Table 2) support the use of ICP-AES (ICP-OES) for heavy metal determination in soils , sediments, wastewater and other matrices...are included here. Isotopic ratios of stable isotopes of the metal of interest can be used for source identification and apportionment in complex

Identifying sources of nitrogen to Hanalei Bay, Kauai, utilizing the nitrogen isotope signature of macroalgae

USGS Publications Warehouse

Derse, E.; Knee, K.L.; Wankel, Scott D.; Kendall, C.; Berg, C.J.; Paytan, A.

2007-01-01

Sewage effluent, storm runoff, discharge from polluted rivers, and inputs of groundwater have all been suggested as potential sources of land derived nutrients into Hanalei Bay, Kauai. We determined the nitrogen isotopic signatures (??15N) of different nitrate sources to Hanalei Bay along with the isotopic signature recorded by 11 species of macroalgal collected in the Bay. The macroalgae integrate the isotopic signatures of the nitrate sources over time, thus these data along with the nitrate to dissolved inorganic phosphate molar ratios (N:P) of the macroalgae were used to determine the major nitrate source to the bay ecosystem and which of the macro-nutrients is limiting algae growth, respectively. Relatively low ??15N values (average -0.5???) were observed in all algae collected throughout the Bay; implicating fertilizer, rather than domestic sewage, as an important external source of nitrogen to the coastal water around Hanalei. The N:P ratio in the algae compared to the ratio in the Bay waters imply that the Hanalei Bay coastal ecosystem is nitrogen limited and thus, increased nitrogen input may potentially impactthis coastal ecosystem and specifically the coral reefs in the Bay. Identifying the major source of nutrient loading to the Bay is important for risk assessment and potential remediation plans. ?? 2007 American Chemical Society.

Selective recharge and isotopic composition of shallow groundwater within temperate, epigenic carbonate aquifers

NASA Astrophysics Data System (ADS)

Florea, Lee J.

2013-05-01

This paper considers the variation of δ18O and δ2H (VSMOW) in precipitation and shallow groundwater from carbonate aquifers that lend insight into the source and timing of recharge within temperate, epigenic karst. The shallow groundwater collected during 2010 and 2011 at Stream Cave (SC) and Natural Bridge Caverns (NBC) represent one input to and the primary output from the Redmond Creek karst aquifer in the Cumberland Plateau of southeast Kentucky, respectively. These data are compared with the isotopic composition of concurrent samples of precipitation from the same watershed that covers some 1900 ha. Values of δ18O and δ2H at SC and NBC are statistically similar and cluster at the midpoint of the local meteoric water line. These values remain surprisingly constant despite seasonal changes in temperature regimens and discharge. Samples in 2012 from regional springs that include Redmond Creek are more depleted in the heavier isotope and similarly stable despite coming from aquifers of a range of sizes and physical characteristics. Applying a Priestly-Taylor model for daily values of potential evapotranspiration, only 43% of the 1.10 m of precipitation in the 2010-2011 dataset remains as potential recharge, primarily during cooler months with lower solar insolation. Weighting δ18O and δ2H values of precipitation by potential recharge creates a better match with the isotopic composition of shallow groundwater than by weighting by precipitation amount. The isotopic composition and deuterium excess of precipitation samples are directly and inversely proportional to temperature, respectively. Deuterium excess in this study and displays intra- and inter-annual variation that ranges from a minimum of +11.1‰ to a maximum of +29.5‰ that demonstrate the higher-than-average deuterium excess in greater Appalachia and the shifting latitude of moisture sources, including a significant winter component of re-evaporated, continental moisture.

An annually-resolved stalagmite tropical cyclone reconstruction from Belize reveals a northward shift in North Atlantic storm track position since 1550 C.E.

NASA Astrophysics Data System (ADS)

Baldini, Lisa; Baldini, James; McElwaine, Jim; Frappier, Amy; Asmerom, Yemane; Liu, Kam-biu; Prufer, Keith; Ridley, Harriet; Polyak, Victor; Kennett, Douglas; Macpherson, Colin; Aquino, Valorie; Awe, Jaime; Breitenbach, Sebastian

2017-04-01

Hurricanes are large-scale atmospheric phenomena that typically produce high volume, high intensity, and isotopically depleted rainfall. Such storms have the ability to alter the isotopic composition of the groundwater reservoir, imparting a uniquely negative isotopic fingerprint to actively growing stalagmites. In regions influenced by the Intertropical Convergence Zone (ITCZ), large volumes of rainfall delivered during the wet season can obscure the tropical cyclone (TC) rainfall proxy signal. Coupled annually resolved carbon and oxygen isotope ratios were used to isolate the low δ18O TC signal from the isotopically more enriched background rainfall associated with seasonal ITCZ migration. The new composite stalagmite proxy record yielded a 99.7% significant correlation with the western Caribbean-filtered HURDAT2 database over the instrumental record based on a non-parametric bootstrap approach. The new annually-resolved TC reconstruction for the western Caribbean spans the last 450 years and reveals a peak in western Caribbean TCs at 1650 C.E. and a gradual decline until a marked decrease is observed at the start of the Industrial Era. Comparison with documentary records of TC occurrence along the US eastern seaboard reveals a clear pattern of north-eastward TC track migration since peak Little Ice Age cooling. This pattern is consistent with natural warming since the Little Ice Age temperature minimum and with anthropogenic influences after industrialisation. Satellite observations reveal Hadley cell expansion has occurred over the last three decades and modelling studies implicate rising atmospheric greenhouse gas concentrations as the driver. Our results suggest that Hadley cell position and width is a major control on hurricane track position and that future emissions scenarios (continued rising greenhouse gases coupled with decreasing Northern Hemisphere aerosol emissions) are likely to increase storm risk to the north-eastern USA.

Interpretation of 3He variations in the solar wind

NASA Technical Reports Server (NTRS)

Coplan, M. A.; Ogilvie, K. W.; Geiss, J.; Bochsler, P.

1983-01-01

The ion composition instrument (ICI) on ISEE-3 observed the isotopes of helium of mass 3 and 4 in the solar wind almost continuously between August 1978 and July 1982. This period included the increase towards the maximum of solar activity cycle 21, the maximum period, and the beginning of the descent towards solar minimum. Observations were made when the solar wind speed was between 300 and 620 km/s. For part of the period evidence for regular interplanetary magnetic sector structure was clear and a number of 3He flares occurred during this time.

Interpretation of He-3 abundance variations in the solar wind

NASA Technical Reports Server (NTRS)

Coplan, M. A.; Ogilvie, K. W.; Bochsler, P.; Geiss, J.

1984-01-01

The ion composition instrument (ICI) on ISEE-3 observed the isotopes of helium of mass 3 and 4 in the solar wind almost continuously between August 1978 and July 1982. This period included the increase towards the maximum of solar activity cycle 21, the maximum period, and the beginning of the descent towards solar minimum. Observations were made when the solar wind speed was between 300 and 620 km/s. For part of the period evidence for regular interplanetary magnetic sector structure was clear and a number of He-3 flares occurred during this time.

A microcomputer-based whole-body counter for personnel routine monitoring.

PubMed

Chou, H P; Tsai, T M; Lan, C Y

1993-05-01

The paper describes a cost-effective NaI(Tl) whole-body counter developed for routine examinations of worker intakes at an isotope production facility. Signal processing, data analysis and system operation are microcomputer-controlled for minimum human interactions. The pulse height analyzer is developed as an microcomputer add-on card for easy manipulation. The scheme for radionuclide analysis is aimed for fast running according to a knowledge base established from background samples and phantom experiments in conjunction with a multivariate regression analysis. Long-term stability and calibration with standards and in vivo measurements are reported.

[A review of water and carbon flux partitioning and coupling in SPAC using stable isotope techniques].

PubMed

Xu, Xiao Wu; Yu, Xin Xiao; Jia, Guo Dong; Li, Han Zhi; Lu, Wei Wei; Liu, Zi Qiang

2017-07-18

Soil-vegetation-atmosphere continuum (SPAC) is one of the important research objects in the field of terrestrial hydrology, ecology and global change. The process of water and carbon cycling, and their coupling mechanism are frontier issues. With characteristics of tracing, integration and indication, stable isotope techniques contribute to the estimation of the relationship between carbon sequestration and water consumption in ecosystems. In this review, based on a brief introduction of stable isotope principles and techniques, the applications of stable isotope techniques to water and carbon exchange in SPAC using optical stable isotope techniques were mainly explained, including: partitioning of net carbon exchange into photosynthesis and respiration; partitioning of evapotranspiration into transpiration and evaporation; coupling of water and carbon cycle at the ecosystem scale. Advanced techniques and methods provided long-term and high frequency measurements for isotope signals at the ecosystem scale, but the issues about the precision and accuracy for measurements, partitioning of ecosystem respiration, adaptability for models under non-steady state, scaling up, coupling mechanism of water and carbon cycles, were challenging. The main existing research findings, limitations and future research prospects were discussed, which might help new research and technology development in the field of stable isotope ecology.

Atmospheric controls on the precipitation isotopes over the Andaman Islands, Bay of Bengal

PubMed Central

Chakraborty, S.; Sinha, N.; Chattopadhyay, R.; Sengupta, S.; Mohan, P. M.; Datye, A.

2016-01-01

Isotopic analysis of precipitation over the Andaman Island, Bay of Bengal was carried out for the year 2012 and 2013 in order to study the atmospheric controls on rainwater isotopic variations. The oxygen and hydrogen isotopic compositions are typical of the tropical marine sites but show significant variations depending on the ocean-atmosphere conditions; maximum depletion was observed during the tropical cyclones. The isotopic composition of rainwater seems to be controlled by the dynamical nature of the moisture rather than the individual rain events. Precipitation isotopes undergo systematic depletions in response to the organized convection occurring over a large area and are modulated by the integrated effect of convective activities. Precipitation isotopes appear to be linked with the monsoon intraseasonal variability in addition to synoptic scale fluctuations. During the early to mid monsoon the amount effect arose primarily due to rain re-evaporation but in the later phase it was driven by moisture convergence rather than evaporation. Amount effect had distinct characteristics in these two years, which appeared to be modulated by the intraseasonal variability of monsoon. It is shown that the variable nature of amount effect limits our ability to reconstruct the past-monsoon rainfall variability on annual to sub-annual time scale. PMID:26806683

Measurement of plutonium isotope ratios in nuclear fuel samples by HPLC-MC-ICP-MS

NASA Astrophysics Data System (ADS)

Günther-Leopold, I.; Waldis, J. Kobler; Wernli, B.; Kopajtic, Z.

2005-04-01

Radioactive isotopes are traditionally quantified by means of radioactivity counting techniques ([alpha], [beta], [gamma]). However, these methods often require extensive matrix separation and sample purification before the identification of specific isotopes and their relative abundance is possible as it is necessary in the frame of post-irradiation examinations on nuclear fuel samples. The technique of multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) is attracting much attention because it permits the precise measurement of the isotope compositions for a wide range of elements combined with excellent limits of detection due to high ionization efficiencies. The present paper describes one of the first applications of an online high-performance liquid chromatographic separation system coupled to a MC-ICP-MS in order to overcome isobaric interferences for the determination of the plutonium isotope composition and concentrations in irradiated nuclear fuels. The described chromatographic separation is sufficient to prevent any isobaric interference between 238Pu present at trace concentrations and 238U present as the main component of the fuel samples. The external reproducibility of the uncorrected plutonium isotope ratios was determined to be between 0.04 and 0.2% (2 s) resulting in a precision in the [per mille sign] range for the isotopic vectors of the irradiated fuel samples.

Measurement of isotope ratios on transient signals by MC-ICP-MS.

PubMed

Günther-Leopold, Ines; Wernli, Beat; Kopajtic, Zlatko; Günther, Detlef

2004-01-01

Precise and accurate isotope ratio measurements are an important task in many applications such as isotope-dilution mass spectrometry, bioavailability studies, or the determination of isotope variations in geological or nuclear samples. The technique of MC-ICP-MS has attracted much attention because it permits the precise measurement of isotope compositions for a wide range of elements combined with excellent detection limits due to high ionisation efficiencies. However, the results are based mainly on measurements using continuous sample introduction. In the present study the determination of isotope ratios on various transient signals with a time duration of 30 to 60 s has been achieved by coupling high-performance liquid chromatography to a multicollector inductively coupled plasma mass spectrometer. In order to investigate the origin of ratio drifts across the transient signals for this hyphenated technique, measurements with the same standard solutions were also carried out using a flow-injection device for sample introduction. As a result of this application it could be concluded that the main source of the bias in the measured isotope ratios is within the ICP-MS instead of fractionation effects on the chromatographic column material. Preliminary studies on short transient signals of gaseous samples (dry plasma) showed a reverse fractionation effect compared with wet plasma conditions (flow injection and HPLC).

Lunar mass spectrometer test program

NASA Technical Reports Server (NTRS)

Torney, F. L.; Dobrott, J. R.

1972-01-01

The procedures are described along with results obtained in a test program conducted to demonstrate the performance of a candidate lunar mass spectrometer. The instrument was designed to sample and measure gases believed to exist in the lunar atmosphere at the surface. The subject instrument consists of a cold cathode ion source, a small quadrupole mass analyzer and an off axis electron multiplier ion counting detector. The major program emphasis was placed on demonstrating instrument resolution, sensitivity and S/N ratio over the mass range 0-150 amu and over a partial pressure range from 10 to the minus 9th power to 10 to the minus 13th power torr. Ultrahigh vacuum tests were conducted and the minimum detectable partial pressure for neon, argon, krypton and xenon was successfully determined for the spectrometer using isotopes of these gases. With the exception of neon, the minimum detectable partial pressure is approximately 4 x 10 to the minus 14th power torr for the above gases.

Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone

NASA Astrophysics Data System (ADS)

Pozzato, L.; Van Oevelen, D.; Moodley, L.; Soetaert, K.; Middelburg, J. J.

2013-11-01

The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for phytodetritus.

Sink or link? The bacterial role in benthic carbon cycling in the Arabian sea oxygen minimum zone

NASA Astrophysics Data System (ADS)

Pozzato, L.; Van Oevelen, D.; Moodley, L.; Soetaert, K.; Middelburg, J. J.

2013-06-01

The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic aquatic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea Oxygen Minimum Zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient in these sediments. Moreover, metazoans directly consume labile particulate organic matter resources and thus compete with bacteria for phytodetritus.

Variation in the carbon and oxygen isotope composition of plant biomass and its relationship to water-use efficiency at the leaf- and ecosystem-scales in a northern Great Plains grassland.

PubMed

Flanagan, Lawrence B; Farquhar, Graham D

2014-02-01

Measurements of the carbon (δ(13) Cm ) and oxygen (δ(18) Om ) isotope composition of C3 plant tissue provide important insights into controls on water-use efficiency. We investigated the causes of seasonal and inter-annual variability in water-use efficiency in a grassland near Lethbridge, Canada using stable isotope (leaf-scale) and eddy covariance measurements (ecosystem-scale). The positive relationship between δ(13) Cm and δ(18) Om values for samples collected during 1998-2001 indicated that variation in stomatal conductance and water stress-induced changes in the degree of stomatal limitation of net photosynthesis were the major controls on variation in δ(13) Cm and biomass production during this time. By comparison, the lack of a significant relationship between δ(13) Cm and δ(18) Om values during 2002, 2003 and 2006 demonstrated that water stress was not a significant limitation on photosynthesis and biomass production in these years. Water-use efficiency was higher in 2000 than 1999, consistent with expectations because of greater stomatal limitation of photosynthesis and lower leaf ci /ca during the drier conditions of 2000. Calculated values of leaf-scale water-use efficiency were 2-3 times higher than ecosystem-scale water-use efficiency, a difference that was likely due to carbon lost in root respiration and water lost during soil evaporation that was not accounted for by the stable isotope measurements. © 2013 John Wiley & Sons Ltd.

ATTA-3: a State-of-the-Art Instrument for Radio-Krypton Dating

NASA Astrophysics Data System (ADS)

Jiang, W.; Zappala, J. C.; Bailey, K.; Lu, Z.; Müller, P.; O'Connor, T. P.

2013-12-01

The ATTA-3 instrument at Argonne has recently enabled routine Kr-81 dating. The instrument is based on Atom Trap Trace Analysis (ATTA), a novel laser based atom counting technique that allows detection of long lived noble gas radioisotopes (Kr-81, Kr-85 and Ar-39) with extremely low abundance (1E-16 to 1E-10). At the center of the instrument is a magneto-optical trap (MOT), which traps and counts only the atoms of the desired isotope. This unique feature makes ATTA free of interference from any other isotopes or molecular species. For Kr-81 dating in the age range of 150 - 1,500 kyr, the required sample size is 5 - 10 micro-L STP of krypton gas, which can be extracted from approximately 100 - 200 kg of water or 40 - 80 kg of ice. Several recent developments in our lab may lead to further improvements to the current ATTA-3 apparatus: 1) The isotopic abundance ratio between the unknown, rare isotope (either Kr-81 or Kr-85) and the stable, abundant isotope (Kr-83) is measured. Here the stable isotope serves as a control isotope. A new method has been developed that allows more accurate measurements of the control isotope Kr-83. Combined with the ability to measure the rare Kr-81 and Kr-85 isotopes, this scheme allows ATTA-3 to directly determine 81Kr/Kr and 85Kr/Kr ratios without other supplemental measurements, to reduce the overall uncertainties of the measured isotope ratios, and also to improve the long term stability of the system. 2) The current capacity of the ATTA-3 instrument is about 120 samples per year. The throughput is mainly limited by the so called 'memory effect', which is caused by the residual samples trapped in the system after each measurement. These residual samples are gradually released in subsequent measurements, causing cross-sample contaminations. In order to mitigate this problem, we wash the system with a xenon discharge for about 36 hours between measurements. This practice limits the overall sample processing speed. Preliminary investigations of the memory effect indicate that it can be reduced and the wash time between measurements shortened. This will increase the number of samples that the ATTA-3 instrument can handle annually in the future. This work is supported by DOE, Office of Nuclear Physics, under contract DE-AC02-06CH11357.

Stable isotope analysis of Dacryoconarid carbonate microfossils: a new tool for Devonian oxygen and carbon isotope stratigraphy.

PubMed

Frappier, Amy Benoit; Lindemann, Richard H; Frappier, Brian R

2015-04-30

Dacryoconarids are extinct marine zooplankton known from abundant, globally distributed calcite microfossils in the Devonian, but their shell stable isotope composition has not been previously explored. Devonian stable isotope stratigraphy is currently limited to less common invertebrates or bulk rock analyses of uncertain provenance. As with Cenozoic planktonic foraminifera, isotopic analysis of dacryoconarid shells could facilitate higher-resolution, geographically widespread stable isotope records of paleoenvironmental change, including marine hypoxia events, climate changes, and biocrises. We explored the use of Dacryoconarid isotope stratigraphy as a viable method in interpreting paleoenvironments. We applied an established method for determining stable isotope ratios (δ(13) C, δ(18) O values) of small carbonate microfossils to very well-preserved dacryoconarid shells. We analyzed individual calcite shells representing five common genera using a Kiel carbonate device coupled to a MAT 253 isotope ratio mass spectrometer. Calcite shell δ(13) C and δ(18) O values were compared by taxonomic group, rock unit, and locality. Single dacryoconarid calcite shells are suitable for stable isotope analysis using a Kiel-IRMS setup. The dacryoconarid shell δ(13) C values (-4.7 to 2.3‰) and δ(18) O values (-10.3 to -4.8‰) were consistent across taxa, independent of shell size or part, but varied systematically through time. Lower fossil δ(18) O values were associated with warmer water temperature and more variable δ(13) C values were associated with major bioevents. Dacryoconarid δ(13) C and δ(18) O values differed from bulk rock carbonate values. Dacryoconarid individual microfossil δ(13) C and δ(18) O values are highly sensitive to paleoenvironmental changes, thus providing a promising avenue for stable isotope chemostratigraphy to better resolve regional to global paleoceanographic changes throughout the upper Silurian to the upper Devonian. Our results warrant further exploration of dacryoconarid stable isotope proxy sensitivity, the isotopic contrast among dacryoconarids, other taxa, and bulk rock, as well as other potential dacryoconarid proxies (Mg/Ca, Sr/Ca, (87) Sr/(86) Sr, microlaser and ion microprobe isotope techniques, and clumped isotopes) for stratigraphic research. Copyright © 2015 John Wiley & Sons, Ltd.

Paleogene Seawater Osmium Isotope Records

NASA Astrophysics Data System (ADS)

Rolewicz, Z.; Thomas, D. J.; Marcantonio, F.

2012-12-01

Paleoceanographic reconstructions of the Late Cretaceous and early Cenozoic require enhanced geographic coverage, particularly in the Pacific, in order to better constrain meridional variations in environmental conditions. The challenge with the existing inventory of Pacific deep-sea cores is that they consist almost exclusively of pelagic clay with little existing age control. Pelagic clay sequences are useful for reconstructions of dust accumulation and water mass composition, but accurate correlation of these records to other sites requires improved age control. Recent work indicates that seawater Os isotope analyses provide useful age control for red clay sequences. The residence time of Os in seawater is relatively long compared to oceanic mixing, therefore the global seawater 187Os/188Os composition is practically homogeneous. A growing body of Late Cretaceous and Cenozoic data has constrained the evolution of the seawater Os isotopic composition and this curve is now a viable stratigraphic tool, employed in dating layers of Fe-Mn crusts (e.g., Klemm et al., 2005). Ravizza (2007) also demonstrated that the seawater Os isotopic composition can be extracted reliably from pelagic red clay sediments by analyzing the leached oxide minerals. The drawback to using seawater Os isotope stratigraphy to date Paleogene age sediments is that the compilation of existing data has some significant temporal gaps, notably between ~38 and 55 Ma. To improve the temporal resolution of the seawater Os isotope curve, we present new data from Ocean Drilling Program (ODP) Site 865 in the equatorial Pacific. Site 865 has excellent biostratigraphic age control over the interval ~38-55Ma. Preliminary data indicate an increase in the seawater composition from 0.427 at 53.4 Ma to 0.499 by 43 Ma, consistent with the apparent trend in the few existing data points. We also analyzed the Os isotopic composition recorded by oxide minerals at Integrated Ocean Drilling Program (IODP) Site U1370 to construct an age model for this predominantly pelagic clay section. The 187Os/188Os values generally increase from 0.312 at 64.46 mbsf to 0.531 at 28.26 mbsf. The low value recorded at 64.46 likely reflects the Os isotope minimum recorded across the K/Pg boundary, while the uppermost value likely correlates to the E/O interval. Comparison of the Os-derived ages with a crude linearly interpolated sedimentation rate age model reveals variations in sediment accumulation rate between 0.86 and 1.5 m/Myr.

A New Method of Obtaining High-Resolution Paleoclimate Records from Speleothem Fluid Inclusions

NASA Astrophysics Data System (ADS)

Logan, A. J.; Horton, T. W.

2010-12-01

We present a new method for stable hydrogen and oxygen isotope analysis of ancient drip water trapped within cave speleothems. Our method improves on existing fluid inclusion isotopic analytical techniques in that it decreases the sample size by a factor of ten or more, dramatically improving the spatial and temporal precision of fluid inclusion-based paleoclimatology. Published thermal extraction methods require large samples (c. 150 mg) and temperatures high enough (c. 500-900°C) to cause calcite decomposition, which is also associated with isotopic fractionation of the trapped fluids. Extraction by crushing faces similar challenges, where the failure to extract all the trapped fluid can result in isotopic fractionation, and samples in excess of 500 mg are required. Our new method combines the strengths of these published thermal and crushing methods using continuous-flow isotope ratio analytical techniques. Our method combines relatively low-temperature (~250°C) thermal decrepitation with cryogenic trapping across a switching valve sample loop. In brief, ~20 mg carbonate samples are dried (75°C for >1 hour) and heated (250°C for >1 hour) in a quartz sample chamber under a continuously flowing stream of ultra-high purity helium. Heating of the sample chamber is achieved by use of a tube furnace. Fluids released during the heating step are trapped in a coiled stainless steel cold trap (~ -98°C) serving as the sample loop in a 6-way switching valve. Trapped fluids are subsequently injected into a high-temperature conversion elemental analyzer by switching the valve and rapidly thawing the trap. This approach yielded accurate and precise measurements of injected liquid water IAEA reference materials (GISP; SMOW2; SLAP2) for both hydrogen and oxygen isotopic compositions. Blanking tests performed on the extraction line demonstrate extremely low line-blank peak heights (<50mv). Our tests also demonstrate that complete recovery of liquid water is possible and that a minimum quantity of ~100nL water was required. In contrast to liquid water analyses, carbonate inclusion waters gave highly variable results. As plenty of signal was produced from relatively small sample sizes (~20 mg), the observed isotopic variation most likely reflects fractionation during fluid extraction, or natural isotopic variability. Additional tests and modifications to the extraction procedure are in progress, using a recently collected New Zealand stalagmite from a West Coast cave (DOC collection permit WC-27462-GEO). U-Th age data will accompany a paleoclimate record from this stalagmite obtained using standard carbonate analytical techniques, and compared to the results from our new fluid inclusion analyses.

Quantifying environmental limiting factors on tree cover using geospatial data.

PubMed

Greenberg, Jonathan A; Santos, Maria J; Dobrowski, Solomon Z; Vanderbilt, Vern C; Ustin, Susan L

2015-01-01

Environmental limiting factors (ELFs) are the thresholds that determine the maximum or minimum biological response for a given suite of environmental conditions. We asked the following questions: 1) Can we detect ELFs on percent tree cover across the eastern slopes of the Lake Tahoe Basin, NV? 2) How are the ELFs distributed spatially? 3) To what extent are unmeasured environmental factors limiting tree cover? ELFs are difficult to quantify as they require significant sample sizes. We addressed this by using geospatial data over a relatively large spatial extent, where the wall-to-wall sampling ensures the inclusion of rare data points which define the minimum or maximum response to environmental factors. We tested mean temperature, minimum temperature, potential evapotranspiration (PET) and PET minus precipitation (PET-P) as potential limiting factors on percent tree cover. We found that the study area showed system-wide limitations on tree cover, and each of the factors showed evidence of being limiting on tree cover. However, only 1.2% of the total area appeared to be limited by the four (4) environmental factors, suggesting other unmeasured factors are limiting much of the tree cover in the study area. Where sites were near their theoretical maximum, non-forest sites (tree cover < 25%) were primarily limited by cold mean temperatures, open-canopy forest sites (tree cover between 25% and 60%) were primarily limited by evaporative demand, and closed-canopy forests were not limited by any particular environmental factor. The detection of ELFs is necessary in order to fully understand the width of limitations that species experience within their geographic range.

Textural and Rb-Sr isotopic evidence for late Paleozoic mylonitization within the Honey Hill fault zone southeastern Connecticut

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Hara, K.D.; Gromet, L.P.

A petrographic and Rb-Sr isotopic study of rocks within and near the Honey Hill fault zone places important constraints on its history of movement. Rb-Sr apparent ages for micas and plagioclase from these rocks have been reset and range from Permian to Triassic, considerably younger than the minimum stratigraphic age (Ordovician) of the rocks studied or of Acadian (Devonian) regional metamorphism. Permian Rb-Sr ages of dynamically recrystallized muscovite date the development of mylonite fabric. An older age is precluded by the excellent preservation of unrecovered quartz, which indicates that these rocks did not experience temperatures high enough to anneal quartzmore » or thermally reset Rb-Sr isotopic systems in muscovite since the time of mylonitization. Metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist-lower amphibolite grade conditions during Permian to Triassic time. Collectively these results indicate that the Honey Hill fault zone was active during the Late Paleozoic and that ductile deformation and metamorphism associated with the Alleghanian orogeny extend well into southern Connecticut. An Alleghanian age for mylonitization within the Honey Hill fault zone suggests it should be considered as a possible site for the major Late Paleozoic strike-slip displacements inferred from paleomagnetic studies for parts of coastal New England and maritime Canada.« less

Isotopic and elemental analysis of fish tissues for provenance determination

NASA Astrophysics Data System (ADS)

Zannella, Carmela; Adamo, Paola; Opper, Christine; Schwendinger, Susanne; Knezevic, Sara; Van den Oever, Sabrina; Tchaikovsky, Anastassiya; Zitek, Andreas; Prohaska, Thomas

2017-04-01

The reliable tracing of the productions flows of food products through the entire supply chain is an essential requirement for all types of food commodities qualified by origin, composition and quality. This is a minimum requirement to implement safety for the consumer, enhance consumer confidence and countervail fraudulent practices. One important food commodity is fish and fish products. Reliable methods to trace the origin of fish have become of high importance. The investigation focused on the identification of adequate geochemical marker in fish meat and the corresponding linkage to the ambient water. The Sr/Ca ratio along with the 87Sr/86Sr isotope ratio analyzed by (multi collector) inductively coupled plasma mass spectrometry (MC ICP-MS) proved to be the most potential tools in this respect. For the first time, a direct link of fish meat to water could be accomplished.In addition, fish hard parts (otoliths, fin rays, fish bones) were under investigation to reconstruct the habitat changes during the lifespan of a fishes life. Fish hard parts have the potential to serve as "life time recorder". Thus the spatial investigation of the elemental and isotopic composition can be used to monitor habitat changes with time. The spatially resolved data of hard tissues was collected by means of Laser Ablation Split Stream ICP-MS/MC ICP-MS. This work is accomplished within the scope of the project "CSI: TRACE YOUR FOOD".

Integration of metagenomic and stable carbon isotope evidence reveals the extent and mechanisms of carbon dioxide fixation in high-temperature microbial communities

DOE PAGES

Jennings, Ryan de Montmollin; Moran, James J.; Jay, Zackary J.; ...

2017-02-03

Biological fixation of CO 2 is the primary mechanism of C reduction in natural systems, and provides a diverse suite of organic compounds utilized by chemoorganoheterotrophs. The extent and mechanisms of CO 2 fixation were evaluated across a comprehensive set of high-temperature, chemotrophic microbial communities in Yellowstone National Park by combining metagenomic and stable 13C isotope analyses. Fifteen geothermal sites representing three distinct habitat types (iron-oxide mats, anoxic sulfur sediments, and filamentous ‘streamer’ communities) were investigated. Genes of the 3-hydroxypropionate/4-hydroxybutyrate, dicarboxylate/4-hydroxybutyrate, and reverse tricarboxylic acid CO 2 fixation pathways were identified in assembled genome sequence corresponding to the predominant Crenarchaeotamore » and Aquificales observed across this habitat range. Stable 13C analyses of dissolved inorganic and organic C (DIC, DOC), and possible landscape C sources were used to interpret the 13C content of microbial community samples. Isotope mixing models showed that the minimum amounts of autotrophic C in microbial biomass were > 50 % in the majority of communities analyzed, but were also dependent on the amounts of heterotrophy and/or accumulation of landscape C. Furthermore, the significance of CO 2 as a C source in these communities provides a foundation for understanding metabolic linkages among autotrophs and heterotrophs, community assembly and succession, and the likely coevolution of deeply-branching thermophiles.« less

Minimum information about a single amplified genome (MISAG) and a metagenome-assembled genome (MIMAG) of bacteria and archaea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowers, Robert M.; Kyrpides, Nikos C.; Stepanauskas, Ramunas

We present two standards developed by the Genomic Standards Consortium (GSC) for reporting bacterial and archaeal genome sequences. Both are extensions of the Minimum Information about Any (x) Sequence (MIxS). The standards are the Minimum Information about a Single Amplified Genome (MISAG) and the Minimum Information about a Metagenome-Assembled Genome (MIMAG), including, but not limited to, assembly quality, and estimates of genome completeness and contamination. These standards can be used in combination with other GSC checklists, including the Minimum Information about a Genome Sequence (MIGS), Minimum Information about a Metagenomic Sequence (MIMS), and Minimum Information about a Marker Gene Sequencemore » (MIMARKS). Community-wide adoption of MISAG and MIMAG will facilitate more robust comparative genomic analyses of bacterial and archaeal diversity.« less

Minimum information about a single amplified genome (MISAG) and a metagenome-assembled genome (MIMAG) of bacteria and archaea

DOE PAGES

Bowers, Robert M.; Kyrpides, Nikos C.; Stepanauskas, Ramunas; ...

2017-08-08

Here, we present two standards developed by the Genomic Standards Consortium (GSC) for reporting bacterial and archaeal genome sequences. Both are extensions of the Minimum Information about Any (x) Sequence (MIxS). The standards are the Minimum Information about a Single Amplified Genome (MISAG) and the Minimum Information about a MetagenomeAssembled Genome (MIMAG), including, but not limited to, assembly quality, and estimates of genome completeness and contamination. These standards can be used in combination with other GSC checklists, including the Minimum Information about a Genome Sequence (MIGS), Minimum Information about a Metagenomic Sequence (MIMS), and Minimum Information about a Marker Genemore » Sequence (MIMARKS). Community-wide adoption of MISAG and MIMAG will facilitate more robust comparative genomic analyses of bacterial and archaeal diversity.« less

Minimum information about a single amplified genome (MISAG) and a metagenome-assembled genome (MIMAG) of bacteria and archaea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowers, Robert M.; Kyrpides, Nikos C.; Stepanauskas, Ramunas

Here, we present two standards developed by the Genomic Standards Consortium (GSC) for reporting bacterial and archaeal genome sequences. Both are extensions of the Minimum Information about Any (x) Sequence (MIxS). The standards are the Minimum Information about a Single Amplified Genome (MISAG) and the Minimum Information about a MetagenomeAssembled Genome (MIMAG), including, but not limited to, assembly quality, and estimates of genome completeness and contamination. These standards can be used in combination with other GSC checklists, including the Minimum Information about a Genome Sequence (MIGS), Minimum Information about a Metagenomic Sequence (MIMS), and Minimum Information about a Marker Genemore » Sequence (MIMARKS). Community-wide adoption of MISAG and MIMAG will facilitate more robust comparative genomic analyses of bacterial and archaeal diversity.« less

Nitrogen and Oxygen Isotope Effects of Ammonia Oxidation by Thermophilic Thaumarchaeota from a Geothermal Water Stream

PubMed Central

Sakai, Sanae; Konno, Uta; Nakahara, Nozomi; Takaki, Yoshihiro; Saito, Yumi; Imachi, Hiroyuki; Tasumi, Eiji; Makabe, Akiko; Koba, Keisuke; Takai, Ken

2016-01-01

ABSTRACT Ammonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in the in situ quantification of ammonia oxidation activity. Nitrogen and oxygen isotope ratios of nitrite (δ15NNO2− and δ18ONO2−, respectively) are geochemical tracers for evaluating the sources and the in situ rate of nitrite turnover determined from the activities of nitrification and denitrification; however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. We first report the isotope effects of ammonia oxidation at 70°C by thermophilic Thaumarchaeota populations composed almost entirely of “Candidatus Nitrosocaldus.” The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. The δ18O value of nitrite produced from ammonia oxidation varied with the δ18O value of water in the medium but was lower than the isotopic equilibrium value in water. Because experiments have shown that the half-life of abiotic oxygen isotope exchange between nitrite and water is longer than 33 h at 70°C and pH ≥6.6, the rate of ammonia oxidation by thermophilic Thaumarchaeota could be estimated using δ18ONO2− in geothermal environments, where the biological nitrite turnover is likely faster than 33 h. This study extended the range of application of nitrite isotopes as a geochemical clock of the ammonia oxidation activity to high-temperature environments. IMPORTANCE Because ammonia oxidation is generally the rate-limiting step in nitrification that regulates the balance of reduced and oxidized nitrogen pools in nature, it is important to understand the biological and environmental factors underlying the regulation of the rate of ammonia oxidation. The discovery of ammonia-oxidizing archaea (AOA) in marine and terrestrial environments has transformed the concept that ammonia oxidation is operated only by bacterial species, suggesting that AOA play a significant role in the global nitrogen cycle. However, the archaeal contribution to ammonia oxidation in the global biosphere is not yet completely understood. This study successfully identified key factors controlling nitrogen and oxygen isotopic ratios of nitrite produced from thermophilic Thaumarchaeota and elucidated the applicability and its limit of nitrite isotopes as a geochemical clock of ammonia oxidation rate in nature. Oxygen isotope analysis in this study also provided new biochemical information on archaeal ammonia oxidation. PMID:27208107

Nitrogen and Oxygen Isotope Effects of Ammonia Oxidation by Thermophilic Thaumarchaeota from a Geothermal Water Stream.

PubMed

Nishizawa, Manabu; Sakai, Sanae; Konno, Uta; Nakahara, Nozomi; Takaki, Yoshihiro; Saito, Yumi; Imachi, Hiroyuki; Tasumi, Eiji; Makabe, Akiko; Koba, Keisuke; Takai, Ken

2016-08-01

Ammonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in the in situ quantification of ammonia oxidation activity. Nitrogen and oxygen isotope ratios of nitrite (δ(15)NNO2- and δ(18)ONO2-, respectively) are geochemical tracers for evaluating the sources and the in situ rate of nitrite turnover determined from the activities of nitrification and denitrification; however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. We first report the isotope effects of ammonia oxidation at 70°C by thermophilic Thaumarchaeota populations composed almost entirely of "Candidatus Nitrosocaldus." The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. The δ(18)O value of nitrite produced from ammonia oxidation varied with the δ(18)O value of water in the medium but was lower than the isotopic equilibrium value in water. Because experiments have shown that the half-life of abiotic oxygen isotope exchange between nitrite and water is longer than 33 h at 70°C and pH ≥6.6, the rate of ammonia oxidation by thermophilic Thaumarchaeota could be estimated using δ(18)ONO2- in geothermal environments, where the biological nitrite turnover is likely faster than 33 h. This study extended the range of application of nitrite isotopes as a geochemical clock of the ammonia oxidation activity to high-temperature environments. Because ammonia oxidation is generally the rate-limiting step in nitrification that regulates the balance of reduced and oxidized nitrogen pools in nature, it is important to understand the biological and environmental factors underlying the regulation of the rate of ammonia oxidation. The discovery of ammonia-oxidizing archaea (AOA) in marine and terrestrial environments has transformed the concept that ammonia oxidation is operated only by bacterial species, suggesting that AOA play a significant role in the global nitrogen cycle. However, the archaeal contribution to ammonia oxidation in the global biosphere is not yet completely understood. This study successfully identified key factors controlling nitrogen and oxygen isotopic ratios of nitrite produced from thermophilic Thaumarchaeota and elucidated the applicability and its limit of nitrite isotopes as a geochemical clock of ammonia oxidation rate in nature. Oxygen isotope analysis in this study also provided new biochemical information on archaeal ammonia oxidation. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Improved Discrimination for Brassica Vegetables Treated with Agricultural Fertilizers Using a Combined Chemometric Approach.

PubMed

Yuan, Yuwei; Hu, Guixian; Chen, Tianjin; Zhao, Ming; Zhang, Yongzhi; Li, Yong; Xu, Xiahong; Shao, Shengzhi; Zhu, Jiahong; Wang, Qiang; Rogers, Karyne M

2016-07-20

Multielement and stable isotope (δ(13)C, δ(15)N, δ(2)H, δ(18)O, (207)Pb/(206)Pb, and (208)Pb/(206)Pb) analyses were combined to provide a new chemometric approach to improve the discrimination between organic and conventional Brassica vegetable production. Different combinations of organic and conventional fertilizer treatments were used to demonstrate this authentication approach using Brassica chinensis planted in experimental test pots. Stable isotope analyses (δ(15)N and δ(13)C) of B. chinensis using elemental analyzer-isotope ratio mass spectrometry easily distinguished organic and chemical fertilizer treatments. However, for low-level application fertilizer treatments, this dual isotope approach became indistinguishable over time. Using a chemometric approach (combined isotope and elemental approach), organic and chemical fertilizer mixes and low-level applications of synthetic and organic fertilizers were detectable in B. chinensis and their associated soils, improving the detection limit beyond the capacity of individual isotopes or elemental characterization. LDA shows strong promise as an improved method to discriminate genuine organic Brassica vegetables from produce treated with chemical fertilizers and could be used as a robust test for organic produce authentication.

Review: Current applications and challenges for liquid chromatography coupled to isotope ratio mass spectrometry (LC/IRMS).

PubMed

Godin, Jean-Philippe; McCullagh, James S O

2011-10-30

High-precision isotope analysis is recognized as an essential research tool in many fields of study. Until recently, continuous flow isotope ratio mass spectrometry (CF-IRMS) was available via an elemental analyzer or a gas chromatography inlet system for compound-specific analysis of light stable isotopes. In 2004, however, an interface that coupled liquid chromatography with IRMS (LC/IRMS) became commercially available for the first time. This brought the capability for new areas of application, in particular enabling compound-specific δ(13)C analysis of non-volatile, aqueous soluble, compounds from complex mixtures. The interface design brought with it several analytical constraints, however, in particular a lack of compatibility with certain types of chromatography as well as limited flow rates and mobile phase compositions. Routine LC/IRMS methods have, however, been established for measuring the δ(13)C isotopic ratios of underivatized individual compounds for application in archeology, nutrition and physiology, geochemistry, hydrology, soil science and food authenticity. Seven years after its introduction, we review the technical advances and constraints, methodological developments and new applications of liquid chromatography coupled to isotope ratio mass spectrometry. Copyright © 2011 John Wiley & Sons, Ltd.

The isotropic condition of energetic particles emitted from a large solar flare. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Spalding, J.

1983-01-01

Isotope abundance ratios for 5 to 50 MeV/nuc nuclei from a large solar flare were measured. The measurements were made by the heavy isotope spectrometer telescope (HIST) on the ISEE-3 satellite orbiting the Sun near an Earth-Sun liberation point approximately one million miles sunward of the Earth. Finite values for the isotope abundance ratios C-13/C-12, N-15/N-14, O-18/O-16, Ne-22/Ne-20, Mg-25/Mg-24, and Mg-26/Mg-24, and upper limits for the isotope abundance ratios He-3/He-4, C-14/C-12, O-17/O-16 and Ne-21/Ne-20 were reported. Element abundances and spectra were measured to compare the flare with other reported flares. The flare is a typical large flare with low Fe/O abundance or = to 0.1). For C-13/C-12, N-15/N-14, O-18/O-16, Mg-25/Mg-24 and Mg-26/Mg-24 isotope abundance ratios agree with the solar system abundance ratios. Measurement for Ne-22/Ne-20 agree with the isotopic composition of the meteoritic component neon-A.

Estimating the Diets of Animals Using Stable Isotopes and a Comprehensive Bayesian Mixing Model

PubMed Central

Hopkins, John B.; Ferguson, Jake M.

2012-01-01

Using stable isotope mixing models (SIMMs) as a tool to investigate the foraging ecology of animals is gaining popularity among researchers. As a result, statistical methods are rapidly evolving and numerous models have been produced to estimate the diets of animals—each with their benefits and their limitations. Deciding which SIMM to use is contingent on factors such as the consumer of interest, its food sources, sample size, the familiarity a user has with a particular framework for statistical analysis, or the level of inference the researcher desires to make (e.g., population- or individual-level). In this paper, we provide a review of commonly used SIMM models and describe a comprehensive SIMM that includes all features commonly used in SIMM analysis and two new features. We used data collected in Yosemite National Park to demonstrate IsotopeR's ability to estimate dietary parameters. We then examined the importance of each feature in the model and compared our results to inferences from commonly used SIMMs. IsotopeR's user interface (in R) will provide researchers a user-friendly tool for SIMM analysis. The model is also applicable for use in paleontology, archaeology, and forensic studies as well as estimating pollution inputs. PMID:22235246

Pb, Sr, and Nd isotopes in seamount basalts from the Juan de Fuca Ridge and Kodiak-Bowie seamount chain, northeast Pacific

USGS Publications Warehouse

Hegner, E.; Tatsumoto, M.

1989-01-01

Pb, Sr, and Nd isotopic ratios and their parent/daughter element concentrations for 28 basalts from 10 hotspot and nonhotspot seamounts are reported. Nd and Sr isotopic compositions (143Nd/144Nd = 0.51325-0.51304; 87Sr/86Sr = 0.70237-0.70275) plot in the envelope for Juan de Fuca-Gorda ridge basalts with tholeiitic basalts showing more depleted sources and a better negative correlation than transitional to alkalic basalts. Pb isotopic ratios in tholeiitic and alkalic basalts overlap (206Pb/204Pb = 18.29-19.44) and display a trend toward more radiogenic Pb in alkalic basalts. The isotopic data for hotspot and nonhotspot basalts are indistinguishable and correlate broadly with rock composition, implying that they are controlled by partial melting. The isotopic variation in the seamount basalts is about 60% (Nd-Sr) to 100% (Pb) of that in East Pacific Rise basalts and is interpreted as a lower limit for the magnitude of mantle heterogeneity in the northeast Pacific. The data indicate absence of a chemically distinct plume component in the linear seamount chains and strongly suggest an origin from mid-ocean ridge basalt-like east Pacific mantle. -Authors

Variations in some environmental characteristics including C and N stable isotopic composition of suspended organic matter in the Mandovi estuary.

PubMed

Maya, M V; Soares, Melena A; Agnihotri, Rajesh; Pratihary, A K; Karapurkar, Supriya; Naik, Hema; Naqvi, S W A

2011-04-01

Chemical and isotopic (δ13C and δ15N) investigation of the Mandovi estuary along the Indian west coast affected strongly by the seasonal monsoon cycle was carried out. The Mandovi estuary is a major waterway for Goa and extensively used for transportation of iron and manganese ore. In addition, with large population centers as well as agricultural fields located on its shores, the estuary is assumed to have been influenced by human activities. Measurements of chemical and isotopic parameters made in the lower part of the estuary during the southwest (SW) monsoon and post-monsoon seasons reveal distinct changes, and it is observed that despite considerable enrichment of macronutrients during the SW monsoon, productivity of the estuary (phytoplankton biomass), as inferred from the chlorophyll-a content, is not as high as expected. This is due to occurrences of high turbidity and cloud cover that limits photosynthetic productivity. The isotopic characterization (C and N isotopes) of suspended organic matter produced/transported during the monsoon and post-monsoon seasons of year 2007 provides a baseline dataset for future isotopic studies in such type of tropical estuaries.

Fingerprints of carbon, nitrogen, and silicon isotopes in small interstellar SiC grains from the Murchison meteorite

NASA Technical Reports Server (NTRS)

Hoppe, Peter; Geiss, Johannes; Buehler, Fritz; Neuenschwander, Juerg; Amari, Sachiko; Lewis, Roy S.

1993-01-01

We report ion microprobe determinations of the carbon, nitrogen, and silicon isotopic compositions of small SiC grains from the Murchison CM2 chondrite. Analyses were made on samples containing variable numbers of grains and on 14 individual grains. In some cases the multiple-grain sample compositions were probably dominated by only one or two grains. Total ranges observed are given. Only a few grains show values near the range limits. Both the total ranges of carbon and nitrogen isotopic compositions, and even the narrower ranges typical for the majority of the grains, are similar to those observed for larger SiC grains. Two rare components appear to be present in the smaller-size fraction, one characterized by C-12/C-13 about 12-16 and the other by very heavy nitrogen. The carbon and nitrogen isotopic compositions qualitatively may reflect hydrostatic H-burning via the CNO cycle and He-burning in red giants, as well as explosive H-burning in novae. The silicon isotopic compositions of most grains qualitatively show what is the signature of He-burning. The silicon isotopic composition of one grain, however, suggests a different process.

Column Experiments for Radionuclide Adsorption Studies of the Culebra Dolomite: Retardation Parameter Estimation for Non-Eluted Actinide Species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, G.O.; Lucero, D.A.; Perkins, W.G.

The U.S. Department of Energy (DOE) has been developing a nuclear waste disposal facility, the Waste Isolation Pilot Plant (WIPP), located approximately 42 km east of Carlsbad, New Mexico. The WIPP is designed to demonstrate the safe disposal of transuranic wastes produced by the defense nuclear-weapons program. Performance assessment analyses (U.S. DOE, 1996) indicate that human intrusion by inadvertent and intermittent drilling for resources provide the only credible mechanisms for significant releases of radionuclides horn the disposal system. These releases may occur by five mechanisms: (1) cuttings, (2) cavings, (3) spallings, (4) direct brine releases, and (5) long-term brine releases.more » The first four mechanisms could result in immediate release of contaminant to the accessible environment. For the last mechanism, migration pathways through the permeable layers of rock above the Salado are important, and major emphasis is placed on the Culebra Member of the Rustler Formation because this is the most transmissive geologic layer in the disposal system. For reasons of initial quantity, half-life, and specific radioactivity, certain isotopes of Th, U, Am, and Pu would dominate calculated releases from the WIPP. In order to help quanti~ parameters for the calculated releases, radionuclide transport experiments have been carried out using five intact-core columns obtained from the Culebra dolomite member of the Rustler Formation within the Waste Isolation Pilot Plant (WIPP) site in southeastern New Mexico. This report deals primarily with results of mathematical analyses related to the retardation of %J%, 24%, and 24'Am in two of these cores (B-Core - VPX26-11A and C-Core - VPX28-6C). All B-Core transport experiments were done using Culebra-simukmt brine relevant to the core recovery location (the WIPP air-intake shaft - AIS). Most experiments with C-Core were done with AIS brine with some admixture of a brine composition (ERDA-6) that simulated deeper formation brines. No significant changes in transport behavior were observed for changes in brine. Hydraulic characteristics (i.e., apparent porosity and apparent dispersion coefficient) for the cores were obtained via experiments using conservative tracer `Na. Elution experiments carried out over periods of a few days with tracers `*U and %Np indicated that these tracers were weakly retarded as indicated by delayed elution of these species. Elution experiments with tracers `%, 24'Pu, and 24'Ani were performed, but no elution of any of these species was observed in any flow experiment to date, including experiments of up to two years duration. However, B-Core was subjected to tomographic analysis from which a retardation factor can be inferred for%. Moreover, the fact of non- elution for 24*Pu and 24'Am after more than two years brine flow through C-Core can be coupled with the minimum detectable activity for each of these species to compute minimum retardation factors in C-Core. The retardation factors for all three species can then be coupled with the apparent hydraulic characteristics to estimate an apparent minimum solutionhock distribution coefficient, &, for each actinide. The specific radionuclide isotopes used in these experiments were chosen to facilitate analysis. Even though these isotopes are not necessarily the same as those that are most important to WIPP performance, they are isotopes of the same elements, and . their chemical and transport properties are therefore identical to those of isotopes in the WIPP inventory. The retardation factors and & values deduced from experimental results strongly support the contention that sorption in the Culebra provides an effective barrier to release of Th, Pu, and Am during the regulatory period.« less

The effect of the isotope on the H-mode density limit

NASA Astrophysics Data System (ADS)

Huber, A.; Wiesen, S.; Bernert, M.; Brezinsek, S.; Chankin, A. V.; Sergienko, G.; Huber, V.; Abreu, P.; Boboc, A.; Brix, M.; Carralero, D.; Delabie, E.; Eich, T.; Esser, H. G.; Guillemaut, C.; Jachmich, S.; Joffrin, E.; Kallenbach, A.; Kruezi, U.; Lang, P.; Linsmeier, Ch.; Lowry, C. G.; Maggi, C. F.; Matthews, G. F.; Meigs, A. G.; Mertens, Ph.; Reimold, F.; Schweinzer, J.; Sips, G.; Stamp, M.; Viezzer, E.; Wischmeier, M.; Zohm, H.; contributors, JET; ASDEX Upgrade Team

2017-08-01

In order to understand the mechanisms for the H-mode density limit in machines with fully metallic walls, systematic investigations of H-mode density limit plasmas in experiments with deuterium and hydrogen external gas fuelling have been performed on JET-ILW. The observed H-mode density limit on JET in D- as well as in H-plasmas demonstrates similar operation phases: the stable H-mode phase, degrading H-mode, breakdown of the H-mode with energy confinement deterioration accompanied by a dithering cycling phase, followed by the L-mode phase. The density limit is not related to an inward collapse of the hot core plasma due to an overcooling of the plasma periphery by radiation. Indeed, independently of the isotopic effect, the total radiated power stay almost constant during the H-mode phase until the H-L back transition. It was observed in D- and H-plasmas that neither detachment, nor the X-point MARFE itself do trigger the H-L transition and that they thus do not present a limit on the plasma density. It is the plasma confinement, most likely determined by edge parameters, which is ultimately responsible for the H-mode DL. By comparing similar discharges but fuelled with either deuterium or hydrogen, we have found that the H-mode density limit exhibits a dependence on the isotope mass: the density limit is up to 35% lower in hydrogen compared to similar deuterium plasma conditions (the obtained density limit is in agreement with the Greenwald limit for D-plasma). In addition, the density limit is nearly independent of the applied power both in deuterium or hydrogen fuelling conditions. The measured Greenwald fractions are consistent with the predictions from a theoretical model based on an MHD instability theory in the near-SOL. The JET operational domains are significantly broadened when increasing the plasma effective mass (e.g. tritium or deuterium-tritium operation), i.e. the L to H power threshold is reduced whereas the density limit for the L-mode back transition is increased.

Stable isotope phenotyping via cluster analysis of NanoSIMS data as a method for characterizing distinct microbial ecophysiologies and sulfur-cycling in the environment

NASA Astrophysics Data System (ADS)

Dawson, K.; Scheller, S.; Dillon, J. G.; Orphan, V. J.

2016-12-01

Stable isotope probing (SIP) is a valuable tool for gaining insights into ecophysiology and biogeochemical cycling of environmental microbial communities by tracking isotopically labeled compounds into cellular macromolecules as well as into byproducts of respiration. SIP, in conjunction with nanoscale secondary ion mass spectrometry (NanoSIMS), allows for the visualization of isotope incorporation at the single cell level. In this manner, both active cells within a diverse population as well as heterogeneity in metabolism within a homogeneous population can be observed. The ecophysiological implications of these single cell stable isotope measurements are often limited to the taxonomic resolution of paired fluorescence in situ hybridization (FISH) microscopy. Here we introduce a taxonomy-independent method using multi-isotope SIP and NanoSIMS for identifying and grouping phenotypically similar microbial cells by their chemical and isotopic fingerprint. This method was applied to SIP experiments in a sulfur-cycling biofilm collected from sulfidic intertidal vents amended with 13C-acetate, 15N-ammonium, and 33S-sulfate. Using a cluster analysis technique based on fuzzy c-means to group cells according to their isotope (13C/12C, 15N/14N, and 33S/32S) and elemental ratio (C/CN and S/CN) profiles, our analysis partitioned 2200 cellular regions of interest (ROIs) into 5 distinct groups. These isotope phenotype groupings are reflective of the variation in labeled substrate uptake by cells in a multispecies metabolic network dominated by Gamma- and Deltaproteobacteria. Populations independently grouped by isotope phenotype were subsequently compared with paired FISH data, demonstrating a single coherent deltaproteobacterial cluster and multiple gammaproteobacterial groups, highlighting the distinct ecophysiologies of spatially-associated microbes within the sulfur-cycling biofilm from White Point Beach, CA.

Forest Fires as a Possible Source of Isotopically Light Marine Fe Aerosols

NASA Astrophysics Data System (ADS)

Tegler, L. A.; Sherry, A. M.; Romaniello, S. J.; Anbar, A. D.

2016-12-01

Iron (Fe) is an important limiting micronutrient for primary productivity in many high-nutrient, low-chlorophyll (HNLC) regions of the ocean. These marine systems receive a significant fraction of their Fe from atmospheric deposition, which is thought to be dominated by mineral dust with an Fe isotopic composition at or above 0‰. However, Mead et al. (2013) observed isotopically light Fe in marine aerosols smaller than 2.5 μm, which is difficult to reconcile with known sources of marine aerosols. Based on previous experimental work, we hypothesize that biomass burning is the source of isotopically light Fe in atmospheric particles and suggest that biomass burning might represent an underappreciated source of Fe to marine ecosystems. While Guelke et al (2007) demonstrated that Fe in agricultural plants is isotopically light, few studies have examined the Fe isotope composition of naturally occurring forests likely to be a significant source of Fe during forest fires. To address this question, we measured the isotopic composition of Ponderosa pine growing in northern Arizona. Ponderosa pine is one the most common forest types in the western US and thus representative of an important North American fire region. Pine needles were chosen because they are susceptible to complete combustion during biomass burning events. To determine the Fe isotopic composition of pine trees, pine needles were sampled at various tree heights. We found that these samples had δ56Fe values between -1.5 and 0‰, indicating that pine needles can be isotopically light compared to local grasses and soil. These results support the hypothesis that biomass burning may contribute isotopically light Fe to marine aerosols.

Investigating human geographic origins using dual-isotope (87Sr/86Sr, δ18O) assignment approaches.

PubMed

Laffoon, Jason E; Sonnemann, Till F; Shafie, Termeh; Hofman, Corinne L; Brandes, Ulrik; Davies, Gareth R

2017-01-01

Substantial progress in the application of multiple isotope analyses has greatly improved the ability to identify nonlocal individuals amongst archaeological populations over the past decades. More recently the development of large scale models of spatial isotopic variation (isoscapes) has contributed to improved geographic assignments of human and animal origins. Persistent challenges remain, however, in the accurate identification of individual geographic origins from skeletal isotope data in studies of human (and animal) migration and provenance. In an attempt to develop and test more standardized and quantitative approaches to geographic assignment of individual origins using isotopic data two methods, combining 87Sr/86Sr and δ18O isoscapes, are examined for the Circum-Caribbean region: 1) an Interval approach using a defined range of fixed isotopic variation per location; and 2) a Likelihood assignment approach using univariate and bivariate probability density functions. These two methods are tested with enamel isotope data from a modern sample of known origin from Caracas, Venezuela and further explored with two archaeological samples of unknown origin recovered from Cuba and Trinidad. The results emphasize both the potential and limitation of the different approaches. Validation tests on the known origin sample exclude most areas of the Circum-Caribbean region and correctly highlight Caracas as a possible place of origin with both approaches. The positive validation results clearly demonstrate the overall efficacy of a dual-isotope approach to geoprovenance. The accuracy and precision of geographic assignments may be further improved by better understanding of the relationships between environmental and biological isotope variation; continued development and refinement of relevant isoscapes; and the eventual incorporation of a broader array of isotope proxy data.

Stable Isotope Phenotyping via Cluster Analysis of NanoSIMS Data As a Method for Characterizing Distinct Microbial Ecophysiologies and Sulfur-Cycling in the Environment

PubMed Central

Dawson, Katherine S.; Scheller, Silvan; Dillon, Jesse G.; Orphan, Victoria J.

2016-01-01

Stable isotope probing (SIP) is a valuable tool for gaining insights into ecophysiology and biogeochemical cycling of environmental microbial communities by tracking isotopically labeled compounds into cellular macromolecules as well as into byproducts of respiration. SIP, in conjunction with nanoscale secondary ion mass spectrometry (NanoSIMS), allows for the visualization of isotope incorporation at the single cell level. In this manner, both active cells within a diverse population as well as heterogeneity in metabolism within a homogeneous population can be observed. The ecophysiological implications of these single cell stable isotope measurements are often limited to the taxonomic resolution of paired fluorescence in situ hybridization (FISH) microscopy. Here we introduce a taxonomy-independent method using multi-isotope SIP and NanoSIMS for identifying and grouping phenotypically similar microbial cells by their chemical and isotopic fingerprint. This method was applied to SIP experiments in a sulfur-cycling biofilm collected from sulfidic intertidal vents amended with 13C-acetate, 15N-ammonium, and 33S-sulfate. Using a cluster analysis technique based on fuzzy c-means to group cells according to their isotope (13C/12C, 15N/14N, and 33S/32S) and elemental ratio (C/CN and S/CN) profiles, our analysis partitioned ~2200 cellular regions of interest (ROIs) into five distinct groups. These isotope phenotype groupings are reflective of the variation in labeled substrate uptake by cells in a multispecies metabolic network dominated by Gamma- and Deltaproteobacteria. Populations independently grouped by isotope phenotype were subsequently compared with paired FISH data, demonstrating a single coherent deltaproteobacterial cluster and multiple gammaproteobacterial groups, highlighting the distinct ecophysiologies of spatially-associated microbes within the sulfur-cycling biofilm from White Point Beach, CA. PMID:27303371

MG Isotopic Measurement of FIB-Isolated Presolar Silicate Grains

NASA Technical Reports Server (NTRS)

Messenger, Scott R.; Nguyen, A.; Ito, M.; Rahman, Z.

2010-01-01

The majority of presolar oxide and silicate grains are ascribed to origins in low-mass red giant and asymptotic giant branch (AGB) stars based on their O isotopic ratios. However, a minor population of these grains (< 10%) has O isotopic ratios incompatible with these sources. Two principle alternative sources are higher-than-solar metallicity (Z) stars or, more likely, supernovae (SN) [1-3]. These rare (Group 4) grains [3] are characterized by enrichments in O-18, and typically also enrichments in O-17. An even rarer subset of grains with extremely large enrichments in O-17 and smaller depletions in O-18 were suggested to come from binary star systems [2]. To establish the origins of these isotopically unusual grains, it is necessary to examine isotopic systems in addition to O. Presolar silicates offer several elements diagnostic of their stellar sources and nuclear processes, including O, Si, Mg, Fe and Ca. However, the database for minor element isotopic compositions in silicates is seriously lacking. To date only two silicate grains have been analyzed for Mg [4] or Fe [5]. One major complicating factor is their small size (average 230 nm), which greatly limits the number of measurements that can be performed on any one grain and makes it more difficult to obtain statistically relevant data. This problem is compounded because the grains are identified among isotopically solar silicates, which contribute a diluting signal in isotopic measurements [1]. Thus, relatively small isotopic anomalies are missed due to this dilution effect. By applying focused ion beam (FIB) milling, we obtain undiluted Mg isotopic ratios of isolated rare presolar silicate grains to investigate their sources.

High-precision measurement of (186)Os/(188)Os and (187)Os/(188)Os: isobaric oxide corrections with in-run measured oxygen isotope ratios.

PubMed

Chu, Zhu-Yin; Li, Chao-Feng; Chen, Zhi; Xu, Jun-Jie; Di, Yan-Kun; Guo, Jing-Hui

2015-09-01

We present a novel method for high precision measurement of (186)Os/(188)Os and (187)Os/(188)Os ratios, applying isobaric oxide interference correction based on in-run measurements of oxygen isotopic ratios. For this purpose, we set up a static data collection routine to measure the main Os(16)O3(-) ion beams with Faraday cups connected to conventional 10(11) amplifiers, and (192)Os(16)O2(17)O(-) and (192)Os(16)O2(18)O(-) ion beams with Faraday cups connected to 10(12) amplifiers. Because of the limited number of Faraday cups, we did not measure (184)Os(16)O3(-) and (189)Os(16)O3(-) simultaneously in-run, but the analytical setup had no significant influence on final (186)Os/(188)Os and (187)Os/(188)Os data. By analyzing UMd, DROsS, an in-house Os solution standard, and several rock reference materials, including WPR-1, WMS-1a, and Gpt-5, the in-run measured oxygen isotopic ratios were proven to present accurate Os isotopic data. However, (186)Os/(188)Os and (187)Os/(188)Os data obtained with in-run O isotopic compositions for the solution standards and rock reference materials show minimal improvement in internal and external precision, compared to the conventional oxygen correction method. We concluded that, the small variations of oxygen isotopes during OsO3(-) analytical sessions are probably not the main source of error for high precision Os isotopic analysis. Nevertheless, use of run-specific O isotopic compositions is still a better choice for Os isotopic data reduction and eliminates the requirement of extra measurements of the oxygen isotopic ratios.

Kinetic isotopic fractionation during diffusion of ionic species in water

NASA Astrophysics Data System (ADS)

Richter, Frank M.; Mendybaev, Ruslan A.; Christensen, John N.; Hutcheon, Ian D.; Williams, Ross W.; Sturchio, Neil C.; Beloso, Abelardo D.

2006-01-01

Experiments specifically designed to measure the ratio of the diffusivities of ions dissolved in water were used to determine DLi/DK,D/D,D/D,D/D,andD/D. The measured ratio of the diffusion coefficients for Li and K in water (D Li/D K = 0.6) is in good agreement with published data, providing evidence that the experimental design being used resolves the relative mobility of ions with adequate precision to also be used for determining the fractionation of isotopes by diffusion in water. In the case of Li, we found measurable isotopic fractionation associated with the diffusion of dissolved LiCl (D/D=0.99772±0.00026). This difference in the diffusion coefficient of 7Li compared to 6Li is significantly less than that reported in an earlier study, a difference we attribute to the fact that in the earlier study Li diffused through a membrane separating the water reservoirs. Our experiments involving Mg diffusing in water found no measurable isotopic fractionation (D/D=1.00003±0.00006). Cl isotopes were fractionated during diffusion in water (D/D=0.99857±0.00080) whether or not the co-diffuser (Li or Mg) was isotopically fractionated. The isotopic fractionation associated with the diffusion of ions in water is much smaller than values we found previously for the isotopic fractionation of Li and Ca isotopes by diffusion in molten silicate liquids. A major distinction between water and silicate liquids is that water surrounds dissolved ions with hydration shells, which very likely play an important but still poorly understood role in limiting the isotopic fractionation associated with diffusion.

50 CFR 622.275 - Size limits.

Code of Federal Regulations, 2013 CFR

2013-10-01

..., DEPARTMENT OF COMMERCE FISHERIES OF THE CARIBBEAN, GULF OF MEXICO, AND SOUTH ATLANTIC Dolphin and Wahoo Fishery Off the Atlantic States § 622.275 Size limits. All size limits in this section are minimum size...

50 CFR 622.275 - Size limits.

Code of Federal Regulations, 2014 CFR

2014-10-01

..., DEPARTMENT OF COMMERCE FISHERIES OF THE CARIBBEAN, GULF OF MEXICO, AND SOUTH ATLANTIC Dolphin and Wahoo Fishery Off the Atlantic States § 622.275 Size limits. All size limits in this section are minimum size...

Latitudinal change in precipitation and water vapor isotopes over Southern ocean

NASA Astrophysics Data System (ADS)

Rahul, P.

2015-12-01

The evaporation process over ocean is primary source of water vapor in the hydrological cycle. The Global Network of Isotopes in Precipitation (GNIP) dataset of rainwater and water vapor isotopes are predominantly based on continental observations, with very limited observation available from the oceanic area. Stable isotope ratios in precipitation provide valuable means to understand the process of evaporation and transport of water vapor. This is further extended in the study of past changes in climate from the isotopic composition of ice core. In this study we present latitudinal variability of water vapor and rainwater isotopic composition and compared it with factors like physical condition of sea surface water from near equator (1°S) to the polar front (56°S) during the summer time expedition of the year 2013. The water vapor and rainwater isotopes showed a sharp depletion in isotopes while progressively move southward from the tropical regions (i.e. >30°S), which follows the pattern recorded in the surface ocean water isotopic composition. From the tropics to the southern latitudes, the water vapor d18O varied between -11.8‰ to -14.7‰ while dD variation ranges between -77.7‰ to -122.2‰. Using the data we estimated the expected water vapor isotopic composition under kinetic as well as equilibrium process. Our observation suggests that the water vapor isotopic compositions are in equilibrium with the sea water in majority of cases. At one point of observation, where trajectory of air parcel originated from the continental region, we observed a large deviation from the existing trend of latitudinal variability. The deduced rainwater composition adopting equilibrium model showed a consistent pattern with observed values at the tropical region, while role of kinetic process become dominant on progressive shift towards the southern latitudes. We will draw comparison of our observation with other data available in the literature together with isotope model data during the presentation.

Application of ultrafiltration and stable isotopic amendments to field studies of mercury partitioning to filterable carbon in lake water and overland runoff.

PubMed

Babiarz, Christopher L; Hurley, James P; Krabbenhoft, David P; Gilmour, Cynthia; Branfireun, Brian A

2003-03-20

Results from pilot studies on colloidal phase transport of newly deposited mercury in lake water and overland runoff demonstrate that the combination of ultrafiltration, and stable isotope amendment techniques is a viable tool for the study of mercury partitioning to filterable carbon. Ultrafiltration mass balance calculations were generally excellent, averaging 97.3, 96.1 and 99.8% for dissolved organic carbon (DOC), total mercury (Hg(T)), and methylmercury (MeHg), respectively. Sub nanogram per liter quantities of isotope were measurable, and the observed phase distribution from replicate ultrafiltration separations on lake water agreed within 20%. We believe the data presented here are the first published colloidal phase mercury data on lake water and overland runoff from uncontaminated sites. Initial results from pilot-scale lake amendment experiments indicate that the choice of matrix used to dissolve the isotope did not affect the initial phase distribution of the added mercury in the lake. In addition there was anecdotal evidence that native MeHg was either recently produced in the system, or at a minimum, that this 'old' MeHg partitions to the same subset of DOC that binds the amended mercury. Initial results from pilot-scale overland runoff experiments indicate that less than 20% of newly deposited mercury was transported in the filterable fraction (<0.7 microm). There is some indication of colloidal phase enrichment of mercury in runoff compared to the phase distribution of organic carbon, but the mechanism of this enrichment is unclear. The phase distribution of newly deposited mercury can differ from that of organic carbon and native mercury, suggesting that the quality of the carbon (available ligands), not the quantity of carbon, regulates partitioning. Further characterization of DOC is needed to clarify the underlying mechanisms.

Stable Cl isotope composition of the Changjiang River water

NASA Astrophysics Data System (ADS)

Lang, Y.; Liu, C. Q.; LI, S. L.; Aravena, R.; Ding, H.; WANG, B.; Benjamin, C.

2017-12-01

To understand chemical wreathing, nutrient cycling, and the impact of human activities on eco-environments of the Changjiang River (Yangtze River) Basin, we carried out a geochemical study on water chemistry and multiple isotopes (C, N, S, Sr…...) of Changjiang River water in the summer season. Some of the research results about the water chemistry, boron isotope geochemistry and suspended matter have been published (Chetelat et al., 2008; Li et al., 2010). Ten samples were selected for the measurement of δ37Cl values, among which 7 samples were collected from main stream and 3 samples from tributaries. The range of δ37Cl values varies between 0.02‰ and 0.33‰ in the main stream and between 0.16‰ and 0.71‰ in the tributary waters. The δ37Cl values in general are negatively correlated with Cl- concentrations for both main stream and tributary waters. δ37Cl value of Wujiang, which is one of the large tributaries in the upper reach of Changjiang and dominated by carbonate rocks in lithology of the watershed, has the maximum value but minimum value of Cl- concentration in this study. The lowest δ37Cl value was measured for the water collected from the estuary of Changjiang River. The variation of δ37Cl values in the waters would be attributed to mixing of different sources of chlorine, which most likely include rain water, ground water, seawater, and pollutants. Systematic characterization of different Cl sources in terms of their chlorine isotope composition is imperative for better understanding of sources and processes of chlorine cycling. Acknowledgements: This work was financially supported by NSFC through project 41073099. (Omit references)

Implications of Liebig’s law of the minimum for tree-ring reconstructions of climate

NASA Astrophysics Data System (ADS)

Stine, A. R.; Huybers, P.

2017-11-01

A basic principle of ecology, known as Liebig’s Law of the Minimum, is that plant growth reflects the strongest limiting environmental factor. This principle implies that a limiting environmental factor can be inferred from historical growth and, in dendrochronology, such reconstruction is generally achieved by averaging collections of standardized tree-ring records. Averaging is optimal if growth reflects a single limiting factor and noise but not if growth also reflects locally variable stresses that intermittently limit growth. In this study a collection of Arctic tree ring records is shown to follow scaling relationships that are inconsistent with the signal-plus-noise model of tree growth but consistent with Liebig’s Law acting at the local level. Also consistent with law-of-the-minimum behavior is that reconstructions based on the least-stressed trees in a given year better-follow variations in temperature than typical approaches where all tree-ring records are averaged. Improvements in reconstruction skill occur across all frequencies, with the greatest increase at the lowest frequencies. More comprehensive statistical-ecological models of tree growth may offer further improvement in reconstruction skill.

Relation between Streamflow of Swiftcurrent Creek, Montana, and the Geometry of Passage for Bull Trout (Salvelinus confluentus)

USGS Publications Warehouse

Auble, Gregor T.; Holmquist-Johnson, Christopher L.; Mogen, Jim T.; Kaeding, Lynn R.; Bowen, Zachary H.

2009-01-01

Operation of Sherburne Dam in northcentral Montana has typically reduced winter streamflow in Swiftcurrent Creek downstream of the dam and resulted in passage limitations for bull trout (Salvelinus confluentus). We defined an empirical relation between discharge in Swiftcurrent Creek between Sherburne Dam and the downstream confluence with Boulder Creek and fish passage geometry by considering how the cross-sectional area of water changed as a function of discharge at a set of cross sections likely to limit fish passage. With a minimum passage window of 15 x 45 cm, passage at the cross sections increased strongly with discharge over the range of 1.2 to 24 cfs. Most cross sections did not satisfy the minimum criteria at 1.2 cfs, 25 percent had no passage at 12.7 cfs, whereas at 24 cfs all but one of 26 cross sections had some passage and 90 percent had more than 3 m of width satisfying the minimum criteria. Sensitivity analysis suggests that the overall results are not highly dependent on exact dimensions of the minimum passage window. Combining these results with estimates of natural streamflow in the study reach further suggests that natural streamflow provided adequate passage at some times in most months and locations in the study reach, although not for all individual days and locations. Limitations of our analysis include assumptions about minimum passage geometry, measurement error, limitations of the cross-sectional model we used to characterize passage, the relation of Sherburne Dam releases to streamflow in the downstream study reach in the presence of ephemeral accretions, and the relation of passage geometry as we have measured it to fish responses of movement, stranding, and mortality, especially in the presence of ice cover.

Analysis of the site-specific carbon isotope composition of propane by gas source isotope ratio mass spectrometer

NASA Astrophysics Data System (ADS)

Piasecki, Alison; Sessions, Alex; Lawson, Michael; Ferreira, A. A.; Neto, E. V. Santos; Eiler, John M.

2016-09-01

Site-specific isotope ratio measurements potentially provide valuable information about the formation and degradation of complex molecules-information that is lost in conventional bulk isotopic measurements. Here we discuss the background and possible applications of such measurements, and present a technique for studying the site-specific carbon isotope composition of propane at natural abundance based on mass spectrometric analysis of the intact propane molecule and its fragment ions. We demonstrate the feasibility of this approach through measurements of mixtures of natural propane and propane synthesized with site-specific 13C enrichment, and we document the limits of precision of our technique. We show that mass balance calculations of the bulk δ13C of propane based on our site-specific measurements is generally consistent with independent constraints on bulk δ13C. We further demonstrate the accuracy of the technique, and illustrate one of its simpler applications by documenting the site-specific carbon isotope signature associated with gas phase diffusion of propane, confirming that our measurements conform to the predictions of the kinetic theory of gases. This method can be applied to propane samples of moderate size (tens of micromoles) isolated from natural gases. Thus, it provides a means of studying the site-specific stable isotope systematics of propane at natural isotope abundances on sample sizes that are readily recovered from many natural environments. This method may also serve as a model for future techniques that apply high-resolution mass spectrometry to study the site-specific isotopic distributions of larger organic molecules, with potential applications to biosynthesis, forensics and other geochemical subjects.

Tracing metal-silicate segregation and late veneer in the Earth and the ureilite parent body with palladium stable isotopes

NASA Astrophysics Data System (ADS)

Creech, J. B.; Moynier, F.; Bizzarro, M.

2017-11-01

Stable isotope studies of highly siderophile elements (HSE) have the potential to yield valuable insights into a range of geological processes. In particular, the strong partitioning of these elements into metal over silicates may lead to stable isotope fractionation during metal-silicate segregation, making them sensitive tracers of planetary differentiation processes. We present the first techniques for the precise determination of palladium stable isotopes by MC-ICPMS using a 106Pd-110Pd double-spike to correct for instrumental mass fractionation. Results are expressed as the per mil (‰) difference in the 106Pd/105Pd ratio (δ106Pd) relative to an in-house solution standard (Pd_IPGP) in the absence of a certified Pd isotopic standard. Repeated analyses of the Pd isotopic composition of the chondrite Allende demonstrate the external reproducibility of the technique of ±0.032‰ on δ106Pd. Using these techniques, we have analysed Pd stable isotopes from a range of terrestrial and extraterrestrial samples. We find that chondrites define a mean δ106Pdchondrite = -0.19 ± 0.05‰. Ureilites reveal a weak trend towards heavier δ106Pd with decreasing Pd content, similar to recent findings based on Pt stable isotopes (Creech et al., 2017), although fractionation of Pd isotopes is significantly less than for Pt, possibly related to its weaker metal-silicate partitioning behaviour and the limited field shift effect. Terrestrial mantle samples have a mean δ106Pdmantle = -0.182 ± 0.130‰, which is consistent with a late-veneer of chondritic material after core formation.

Production of exotic nuclei in projectile fragmentation at relativistic and Fermi energies

NASA Astrophysics Data System (ADS)

Ogul, R.; Ergun, A.; Buyukcizmeci, N.

2017-02-01

Isotopic distributions of projectile fragmentation in peripheral heavy ion collisions of 86Kr on 112Sn are calculated within the statistical multifragmentation model. Obtained data are compared to the experimental cross section measurements. We show the enhancement in the production of neutron-rich isotopes close to the projectile, observed in the experiments. Our results show the universality of the limitation of the excitation energy induced in the projectile residues.

Nicotine, acetanilide and urea multi-level2H-,13C- and15N-abundance reference materials for continuous-flow isotope ratio mass spectrometry

USGS Publications Warehouse

Schimmelmann, A.; Albertino, A.; Sauer, P.E.; Qi, H.; Molinie, R.; Mesnard, F.

2009-01-01

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the S values of these reference materials should bracket the isotopic range of samples with unknown S values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for ??13C and ??13N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: ??2Hnicotine -162 to -45%o, ??13Cnicotine -30.05 to +7.72%, ?? 15Nnicotine -6.03 to +33.62%; ??15N acetanilide +1-18 to +40.57%; ??13Curea -34.13 to +11.71%, ??15Nurea +0.26 to +40.61% (recommended ?? values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different ??13N values. Comparative ??13C and ??15N on-line EA-IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA-IRMS reference materials.

Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

NASA Astrophysics Data System (ADS)

Okumura, Tomoyo; Kawagucci, Shinsuke; Saito, Yayoi; Matsui, Yohei; Takai, Ken; Imachi, Hiroyuki

2016-12-01

Hydrogen and carbon isotope systematics of H2O-H2-CO2-CH4 in hydrogenotrophic methanogenesis and their relation to H2 availability were investigated. Two H2-syntrophic cocultures of fermentatively hydrogenogenic bacteria and hydrogenotrophic methanogens under conditions of <102 Pa-H2 and two pure cultures of hydrogenotrophic methanogens under conditions of 105 Pa-H2 were tested. Carbon isotope fractionation between CH4 and CO2 during hydrogenotrophic methanogenesis was correlated with pH2, as indicated in previous studies. The hydrogen isotope ratio of CH4 produced during rapid growth of the thermophilic methanogen Methanothermococcus okinawensis under high pH2 conditions ( 105 Pa) was affected by the isotopic composition of H2, as concluded in a previous study of Methanothermobacter thermautotrophicus. This " {δ D}_{{H}_2} effect" is a possible cause of the diversity of previously reported values for hydrogen isotope fractionation between CH4 and H2O examined in H2-enriched culture experiments. Hydrogen isotope fractionation between CH4 and H2O, defined by (1000 + {δ D}_{{CH}_4} )/(1000 + {δ D}_{{H}_2O} ), during hydrogenotrophic methanogenesis of the H2-syntrophic cocultures was in the range 0.67-0.69. The hydrogen isotope fractionation of our H2-syntrophic dataset overlaps with those obtained not only from low- pH2 experiments reported so far but also from natural samples of "young" methane reservoirs (0.66-0.74). Conversely, such hydrogen isotope fractionation is not consistent with that of "aged" methane in geological samples (≥0.79), which has been regarded as methane produced via hydrogenotrophic methanogenesis from the carbon isotope fractionation. As a possible process inducing the inconsistency in hydrogen isotope signatures between experiments and geological samples, we hypothesize that the hydrogen isotope signature of CH4 imprinted at the time of methanogenesis, as in the experiments and natural young methane, may be altered by diagenetic hydrogen isotope exchange between extracellular CH4 and H2O through reversible reactions of the microbial methanogenic pathway in methanogenic region and/or geological methane reservoirs.

Site-Specific Carbon Isotopes in Organics

NASA Astrophysics Data System (ADS)

Piasecki, A.; Eiler, J. M.

2012-12-01

Natural organic molecules exhibit a wide range of internal site-specific isotope variation (i.e., molecules with same isotopic substitution type but different site). Such variations are generally unconstrained by bulk isotopic measurements. If known, site-specific variations might constrain temperatures of equilibrium, mechanisms of formation or consumption reactions, and possibly other details. For example, lipids can exhibit carbon isotope differences of up to 30‰ between adjacent carbon sites as a result of fractionations arising during decarboxylation of pyruvate and other steps in lipid biosynthesis(1). We present a method for site-specific carbon isotope analysis of propane, based on high-resolution, multi-collector gas source mass spectrometry, using a novel prototype instrument - the Thermo MAT 253 Ultra. This machine has an inlet system and electron bombardment ion source resembling those in conventional stable isotope gas source mass spectrometers, and the energy filter, magnet, and detector array resembling those in multi-collector ICPMS and TIMS. The detector array has 7 detector positions, 6 of which are movable, and each of which can collect ions with either a faraday cup (read through amplifiers ranging from 107-1012 ohms) or an SEM. High mass resolving power (up to 27,000, MRP = M/dM definition) is achieved through a narrow entrance slit, adjustable from 250 to 5 μm. Such resolution can cleanly separate isobaric interferences between isotopologues of organic molecules having the same cardinal mass (e.g., 13CH3 and 12CH2D). We use this technology to analyze the isotopologues and fragments of propane, and use such data to solve for the site-specific carbon isotope fractionation. By measuring isotopologues of both the one-carbon (13CH3) and the two-carbon (13C12CH4) fragment ion, we can solve for both bulk δ13C and the difference in δ13C between the terminal and central carbon position. We tested this method by analyzing mixtures between natural propane and labeled propane (13CH3-12CH2-12CH3). Results are consistent with the expected relative fractionations between the two fragments, indicating limited 'scrambling' of carbon positions of less than 2% in the source. The limits of precision of this method are currently ~0.5 ‰, sufficient to resolve known or suspected position-specific isotope effects in propane. We have explored the expected temperature-dependent equilibrium isotopic distributions of propane using density functional theory and quantum mechanical models of vibrational isotope effects. These models predict the homogeneous isotope exchange equilibria among the various isotopologues of propane, which include several of a wide range of effects that should be measurable by our methods. At 300 K we predict that the central carbon site is 15‰ higher in δ13C and 95 ‰ higher in δD than the terminal carbon site; similarly the molecule containing both a 13C and D in the central site is enriched by ~120 ‰ relative to a random isotopic distribution at 300 K. These predictions present targets for future experimental and empirical studies of the temperature dependence of isotopic ordering in propane. More generally, the methods we are developing for the study of intramolecular isotopic distributions in propane will serve as a model for future study of similar effects in other organic compounds. [1]DeNiro, Epstein (1977) Science Volume 197, 261-263.

Middle Pleistocene Climate Change Recorded in Fossil Mammal Teeth from Tarija, Bolivia, and Upper Limit of the Ensenadan Land-Mammal Age

NASA Astrophysics Data System (ADS)

MacFadden, Bruce J.

2000-07-01

Fossiliferous middle Pleistocene sediments of the Tarija basin of southern Bolivia contain a classic Ensenadan land-mammal fauna. New carbon isotopic data reported here for 50 specimens of the grazing mammals Equus (horse) and Cuvieronius (mastodon), documented from eight stratigraphic levels at Tarija, vary significantly in the δ13C values of their teeth. The pattern of variation appears to reflect the proportion of C3 and C4 grasses eaten during colder (more C3) and warmer (more C4) times. Within age limits set by associated magnetostratigraphy, the cold periods can be correlated with particular even-numbered stages in the marine oxygen-isotope record, and the warm periods can be correlated with odd-numbered stages. The oldest fossil teeth analyzed from the Tarija section can thereby be assigned to stage 29, and the youngest to stages 17 or 15, that is; the teeth range in age from about 1.1 myr to as young as 0.7 myr. Based on correlation of the upper part of the Tarija beds to the isotopic stages, the upper limit of the Ensenadan land-mammal age is between 0.7 and 0.6 myr, which is younger than stated in most previous studies.

USING SUSTAINABILITY CRITERIA TO GUIDE LAND-USE DECISIONS

EPA Science Inventory

Human society and our economic systems are limited by the capacities of natural systems, and the sustainability of natural systems will be dependent upon the attainment of undetermined but minimum conditions of social and economic systems. These minimum conditions of intact econo...

41 CFR 101-25.301 - General.

Code of Federal Regulations, 2010 CFR

2010-07-01

... which shall be applied by all executive agencies. Additional criteria above these minimum standards shall be established by each executive agency, limiting its property to the minimum requirements necessary for the efficient functioning of the particular office concerned. This subpart does not apply to...

Survey of Occupational Noise Exposure in CF Personnel in Selected High-Risk Trades

DTIC Science & Technology

2003-11-01

peak, maximum level , minimum level , average sound level , time weighted average, dose, projected 8-hour dose, and upper limit time were measured for...10 4.4.2 Maximum Sound Level ...11 4.4.3 Minimum Sound Level

The O and H stable isotope composition of freshwaters in the British Isles. 2. Surface waters and groundwater

NASA Astrophysics Data System (ADS)

Darling, W. G.; Bath, A. H.; Talbot, J. C.

The utility of stable isotopes as tracers of the water molecule has a long pedigree. The study reported here is part of an attempt to establish a comprehensive isotopic "baseline" for the British Isles as background data for a range of applications. Part 1 of this study (Darling and Talbot, 2003) considered the isotopic composition of rainfall in Britain and Ireland. The present paper is concerned with the composition of surface waters and groundwater. In isotopic terms, surface waters (other than some upland streams) are poorly characterised in the British Isles; their potential variability has yet to be widely used as an aid in hydrological research. In what may be the first study of a major British river, a monthly isotopic record of the upper River Thames during 1998 was obtained. This shows high damping of the isotopic variation compared to that in rainfall over most of the year, though significant fluctuations were seen for the autumn months. Smaller rivers such as the Stour and Darent show a more subdued response to the balance between runoff and baseflow. The relationship between the isotopic composition of rainfall and groundwater is also considered. From a limited database, it appears that whereas Chalk groundwater is a representative mixture of weighted average annual rainfall, for Triassic sandstone groundwater there is a seasonal selection of rainfall biased towards isotopically-depleted winter recharge. This may be primarily the result of physical differences between the infiltration characteristics of rock types, though other factors (vegetation, glacial history) could be involved. In the main, however, groundwaters appear to be representative of bulk rainfall within an error band of 0.5‰ δ18O. Contour maps of the δ18O and δ2H content of recent groundwaters in the British Isles show a fundamental SW-NE depletion effect modified by topography. The range of measured values, while much smaller than those for rainfall, still covers some ‰ for δ18O and 30‰ for δ2H. Over lowland areas the "altitude effect" is of little significance, but in upland areas is consistent with a range of -0.2 to -0.3‰ per 100 m increase in altitude. Groundwaters dating from the late Pleistocene are usually modified in δ18O and δ2H owing to the effects of climate change on the isotopic composition of rainfall and thus of recharge. Contour maps of isotopic variability prior to 10 ka BP, based on the relatively limited information available from the British Isles, allow a first comparison between groundwaters now and at the end of the last Ice Age. The position of the British Isles in the context of the stable isotope systematics of NW Europe is reviewed briefly.

Computation of distribution of minimum resolution for log-normal distribution of chromatographic peak heights.

PubMed

Davis, Joe M

2011-10-28

General equations are derived for the distribution of minimum resolution between two chromatographic peaks, when peak heights in a multi-component chromatogram follow a continuous statistical distribution. The derivation draws on published theory by relating the area under the distribution of minimum resolution to the area under the distribution of the ratio of peak heights, which in turn is derived from the peak-height distribution. Two procedures are proposed for the equations' numerical solution. The procedures are applied to the log-normal distribution, which recently was reported to describe the distribution of component concentrations in three complex natural mixtures. For published statistical parameters of these mixtures, the distribution of minimum resolution is similar to that for the commonly assumed exponential distribution of peak heights used in statistical-overlap theory. However, these two distributions of minimum resolution can differ markedly, depending on the scale parameter of the log-normal distribution. Theory for the computation of the distribution of minimum resolution is extended to other cases of interest. With the log-normal distribution of peak heights as an example, the distribution of minimum resolution is computed when small peaks are lost due to noise or detection limits, and when the height of at least one peak is less than an upper limit. The distribution of minimum resolution shifts slightly to lower resolution values in the first case and to markedly larger resolution values in the second one. The theory and numerical procedure are confirmed by Monte Carlo simulation. Copyright © 2011 Elsevier B.V. All rights reserved.

Potential of Sr isotopic analysis in ceramic provenance studies: Characterisation of Chinese stonewares

NASA Astrophysics Data System (ADS)

Li, Bao-Ping; Zhao, Jian-Xin; Greig, Alan; Collerson, Kenneth D.; Zhuo, Zhen-Xi; Feng, Yue-Xin

2005-11-01

We compare the trace element and Sr isotopic compositions of stoneware bodies made in Yaozhou and Jizhou to characterise these Chinese archaeological ceramics and examine the potential of Sr isotopes in provenance studies. Element concentrations determined by ICP-MS achieve distinct characterisation for Jizhou samples due to their restricted variation, yet had limited success with Yaozhou wares because of their large variability. In contrast, 87Sr/86Sr ratios in Yaozhou samples have a very small variation and are all significantly lower than those of Jizhou samples, which show a large variation and cannot be well characterised with Sr isotopes. Geochemical interpretation reveals that 87Sr/86Sr ratios will have greater potential to characterise ceramics made of low Rb/Sr materials such as kaolin clay, yet will show larger variations in ceramics made of high Rb/Sr materials such as porcelain stone.

Stable isotope and chemical compositions of European and Australasian ciders as a guide to authenticity.

PubMed

Carter, James F; Yates, Hans S A; Tinggi, Ujang

2015-01-28

This paper presents a data set derived from the analysis of bottled and canned ciders that may be used for comparison with suspected counterfeit or substitute products. Isotopic analysis of the solid residues from ciders (predominantly sugar) provided a means to determine the addition of C4 plant sugars. The added sugars were found to comprise cane sugar, high-fructose corn syrup, glucose, or combinations. The majority of ciders from Australia and New Zealand were found to contain significant amounts of added sugar, which provided a limited means to distinguish these ciders from European ciders. The hydrogen and oxygen isotopic compositions of the whole ciders (predominantly water) were shown to be controlled by two factors, the water available to the parent plant and evaporation. Analysis of data derived from both isotopic and chemical analysis of ciders provided a means to discriminate between regions and countries of manufacture.

Sulphur isotopic ratios in mosses indicating atmospheric sulphur sources in southern Chinese mountainous areas

NASA Astrophysics Data System (ADS)

Xiao, Hua-Yun; Tang, Cong-Guo; Liu, Xue-Yan; Xiao, Hong-Wei; Liu, Cong-Qiang

2008-10-01

Many mountainous regions in South China have been confronted with the consequences of acidic deposition, but studies on atmospheric S sources are still very limited. In this study, isotopic ratios in mosses were used to discriminate atmospheric S sources. A continuous increase in S isotopic ratios was observed from the south to the north in mountainous mosses and in accord with the previously reported changing trends in urban mosses, indicating a contribution of local anthropogenic S from urban cities. Based on comparisons of S isotopic ratios in mountainous mosses with those in nearby urban mosses, we found that mountainous mosses had significantly higher 34S contents than urban mosses, especially in West China, reflecting an introduction of 34S-enriched sulphur. In conjunction with cloud water data in the literature, we concluded that 34S-enriched sulphur in northerly air masses contributed much to atmospheric S in southern Chinese mountainous areas.

Pb and Sr isotope measurements by inductively coupled plasma mass spectrometer: efficient time management for precision improvement

NASA Astrophysics Data System (ADS)

Monna, F.; Loizeau, J.-L.; Thomas, B. A.; Guéguen, C.; Favarger, P.-Y.

1998-08-01

One of the factors limiting the precision of inductively coupled plasma mass spectrometry is the counting statistics, which depend upon acquisition time and ion fluxes. In the present study, the precision of the isotopic measurements of Pb and Sr is examined. The time of measurement is optimally shared for each isotope, using a mathematical simulation, to provide the lowest theoretical analytical error. Different algorithms of mass bias correction are also taken into account and evaluated in term of improvement of overall precision. Several experiments allow a comparison of real conditions with theory. The present method significantly improves the precision, regardless of the instrument used. However, this benefit is more important for equipment which originally yields a precision close to that predicted by counting statistics. Additionally, the procedure is flexible enough to be easily adapted to other problems, such as isotopic dilution.

High-Resolution Triple Resonance Autoionization of Uranium Isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schumann, Philipp G.; Wendt, K; Bushaw, Bruce A.

2005-11-01

The near-threshold autoionization (AI) spectrum of uranium has been investigated by triple-resonance excitation with single-mode continuous lasers. Spectra were recorded over the first {approx}30 cm-1 above the first ionization limit at a resolution of 3x10-4 cm 1 using intermediate states with different J values (6, 7, 8) to assign AI level total angular momentum JAI = 5 to 9. Resonances with widths ranging from 8 MHz to 30 GHz were observed; the strongest ones have JAI = 9 and widths of {approx} 60 MHz. Hyperfine structures for 235U and isotope shifts for 234,235U have been measured in the two intermediatemore » levels and in the final AI level for the most favorable excitation path. These measurements were performed using aqueous samples containing sub-milligram quantities of uranium at natural isotopic abundances, indicating the potential of this approach for trace isotope ratio determinations.« less

Astrophysics of CAI formation as revealed by silicon isotope LA-MC-ICPMS of an igneous CAI

NASA Astrophysics Data System (ADS)

Shahar, Anat; Young, Edward D.

2007-05-01

Silicon isotope ratios of a typical CAI from the Leoville carbonaceous chondrite, obtained in situ by laser ablation MC-ICPMS, together with existing 25Mg/ 24Mg data, reveal a detailed picture of the astrophysical setting of CAI melting and subsequent heating. Models for the chemical and isotopic effects of evaporation of the molten CAI are used to produce a univariant relationship between PH 2 and time during melting. The result shows that this CAI was molten for a cumulative time of no more than 70 days and probably less than 15 days depending on temperature. The object could have been molten for an integrated time of just a few hours if isotope ratio zoning was eliminated after melting by high subsolidus temperatures (e.g., > 1300 K) for ˜ 500 yr. In all cases subsolidus heating sufficient to produce diffusion-limited isotope fractionation at the margin of the solidified CAI is required. These stable isotope data point to a two-stage history for this igneous CAI involving melting for a cumulative timescale of hours to months followed by subsolidus heating for years to hundreds of years. The thermobarometric history deduced from combining Si and Mg isotope ratio data implicates thermal processing in the disk, perhaps by passage through shockwaves, following melting. This study underscores the direct link between the meaning of stable isotope ratio zoning, or lack thereof, and the inferred astrophysical setting of melting and subsequent processing of CAIs.

Isotopic studies of metabolic systems by mass spectrometry: using Pascal's triangle to produce biological standards with fully controlled labeling patterns.

PubMed

Millard, Pierre; Massou, Stéphane; Portais, Jean-Charles; Létisse, Fabien

2014-10-21

Mass spectrometry (MS) is widely used for isotopic studies of metabolism in which detailed information about biochemical processes is obtained from the analysis of isotope incorporation into metabolites. The biological value of such experiments is dependent on the accuracy of the isotopic measurements. Using MS, isotopologue distributions are measured from the quantitative analysis of isotopic clusters. These measurements are prone to various biases, which can occur during the experimental workflow and/or MS analysis. The lack of relevant standards limits investigations of the quality of the measured isotopologue distributions. To meet that need, we developed a complete theoretical and experimental framework for the biological production of metabolites with fully controlled and predictable labeling patterns. This strategy is valid for different isotopes and different types of metabolisms and organisms, and was applied to two model microorganisms, Pichia augusta and Escherichia coli, cultivated on (13)C-labeled methanol and acetate as sole carbon source, respectively. The isotopic composition of the substrates was designed to obtain samples in which the isotopologue distribution of all the metabolites should give the binomial coefficients found in Pascal's triangle. The strategy was validated on a liquid chromatography-tandem mass spectrometry (LC-MS/MS) platform by quantifying the complete isotopologue distributions of different intracellular metabolites, which were in close agreement with predictions. This strategy can be used to evaluate entire experimental workflows (from sampling to data processing) or different analytical platforms in the context of isotope labeling experiments.

Stable isotope labeling by essential nutrients in cell culture for preparation of labeled coenzyme A and its thioesters.

PubMed

Basu, Sankha S; Mesaros, Clementina; Gelhaus, Stacy L; Blair, Ian A

2011-02-15

Stable isotope dilution mass spectrometry (MS) represents the gold standard for quantification of endogenously formed cellular metabolites. Although coenzyme A (CoA) and acyl-CoA thioester derivatives are central players in numerous metabolic pathways, the lack of a commercially available isotopically labeled CoA limits the development of rigorous MS-based methods. In this study, we adapted stable isotope labeling by amino acids in cell culture (SILAC) methodology to biosynthetically generate stable isotope labeled CoA and thioester analogues for use as internal standards in liquid chromatography/multiple reaction monitoring mass spectrometry (LC/MRM-MS) assays. This was accomplished by incubating murine hepatocytes (Hepa 1c1c7) in media in which pantothenate (a precursor of CoA) was replaced with [(13)C(3)(15)N(1)]-pantothenate. Efficient incorporation into various CoA species was optimized to >99% [(13)C(3)(15)N(1)]-pantothenate after three passages of the murine cells in culture. Charcoal-dextran-stripped fetal bovine serum (FBS) was found to be more efficient for serum supplementation than dialyzed or undialyzed FBS, due to lower contaminating unlabeled pantothenate content. Stable isotope labeled CoA species were extracted and utilized as internal standards for CoA thioester analysis in cell culture models. This methodology of stable isotope labeling by essential nutrients in cell culture (SILEC) can serve as a paradigm for using vitamins and other essential nutrients to generate stable isotope standards that cannot be readily synthesized.

Testing Urey's carbonate-silicate cycle using the calcium isotopic composition of sedimentary carbonates

NASA Astrophysics Data System (ADS)

Blättler, Clara L.; Higgins, John A.

2017-12-01

Carbonate minerals constitute a major component of the sedimentary geological record and an archive of a fraction of the carbon and calcium cycled through the Earth's surface reservoirs for over three billion years. For calcium, carbonate minerals constitute the ultimate sink for almost all calcium liberated during continental and submarine weathering of silicate minerals. This study presents >500 stable isotope ratios of calcium in Precambrian carbonate sediments, both limestones and dolomites, in an attempt to characterize the isotope mass balance of the sedimentary carbonate reservoir through time. The mean of the dataset is indistinguishable from estimates of the calcium isotope ratio of bulk silicate Earth, consistent with the Urey cycle being the dominant mechanism exchanging calcium among surface reservoirs. The variability in bulk sediment calcium isotope ratios within each geological unit does not reflect changes in the global calcium cycle, but rather highlights the importance of local mineralogical and/or diagenetic effects in the carbonate record. This dataset demonstrates the potential for calcium isotope ratios to help assess these local effects, such as the former presence of aragonite, even in rocks with a history of neomorphism and recrystallization. Additionally, 29 calcium isotope measurements are presented from ODP (Ocean Drilling Program) Site 801 that contribute to the characterization of altered oceanic crust as an additional sink for calcium, and whose distinct isotopic signature places a limit on the importance of this subduction flux over Earth history.

Water balance model for mean annual hydrogen and oxygen isotope distributions in surface waters of the contiguous United States

NASA Astrophysics Data System (ADS)

Bowen, Gabriel J.; Kennedy, Casey D.; Liu, Zhongfang; Stalker, Jeremy

2011-12-01

The stable H and O isotope composition of river and stream water records information on runoff sources and land-atmosphere water fluxes within the catchment and is a potentially powerful tool for network-based monitoring of ecohydrological systems. Process-based hydrological models, however, have thus far shown limited power to replicate observed large-scale variation in U.S. surface water isotope ratios. Here we develop a geographic information system-based model to predict long-term annual average surface water isotope ratios across the contiguous United States. We use elevation-explicit, gridded precipitation isotope maps as model input and data from a U.S. Geological Survey monitoring program for validation. We find that models incorporating monthly variation in precipitation-evapotranspiration (P-E) amounts account for the majority (>89%) of isotopic variation and have reduced regional bias relative to models that do not consider intra-annual P-E effects on catchment water balance. Residuals from the water balance model exhibit strong spatial patterning and correlations that suggest model residuals isolate additional hydrological signal. We use interpolated model residuals to generate optimized prediction maps for U.S. surface water δ2H and δ18O values. We show that the modeled surface water values represent a relatively accurate and unbiased proxy for drinking water isotope ratios across the United States, making these data products useful in ecological and criminal forensics applications that require estimates of the local environmental water isotope variation across large geographic regions.

The first Lu-Hf zircon isotope data for gabbro-diorite-tonalite associations of the Urals

NASA Astrophysics Data System (ADS)

Ronkin, Yu. L.; Smirnov, V. N.; Ivanov, K. S.; Gerdes, A.

2017-01-01

The Lu-Hf isotope systematics of zircon from the gabbro-plagiogranite association (gabbro, diorite, tonalite, and plagiogranite), which is one of the most typical associations of igneous rocks in the Urals, was studied for the first time. The isotope study yielded a unified age limit of 433 Ma, which corresponds to the time of formation of this rock association. The younger "rejuvenated" ages characterize superimposed thermal impact events, induced by the volcanic arc activity, as well as collisional and postcollisional processes. Here, the initial 176Hf/177Hf( t) ratio in the studied zircon from gabbro and plagiogranite corresponds in fact to a highly LILE-depleted (DM) mantle.

Fabrication of 12% {sup 240}Pu calorimetry standards

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, S.M.; Hildner, S.; Gutierrez, D.

1995-08-01

Throughout the DOE complex, laboratories are performing calorimetric assays on items containing high burnup plutonium. These materials contain higher isotopic range and higher wattages than materials previously encountered in vault holdings. Currently, measurement control standards have been limited to utilizing 6% {sup 240}Pu standards. The lower isotopic and wattage value standards do not complement the measurement of the higher burnup material. Participants of the Calorimetry Exchange (CALEX) Program have identified the need for new calorimetric assay standards with a higher wattage and isotopic range. This paper describes the fabrication and verification measurements of the new CALEX standard containing 12% {supmore » 240}Pu oxide with a wattage of about 6 to 8 watts.« less

Determination of uranium and thorium in materials associated with real time electronic solar neutrino detectors

NASA Astrophysics Data System (ADS)

Fassett, J. D.; Kelly, W. R.

1992-07-01

The application of isotope dilution thermal ionization mass spectrometry to the determination of both uranium and thorium in four different target materials used or proposed for electronic neutrino detectors is described. Isotope dilution analysis is done using highly enriched 233U and 230Th separated isotopes. Sensitivity of the technique is such that sub-picogram amounts of material are readily measured. The overall limit to measurement is caused by contamination of these elements during the measurement process. Uranium is more easily measured than thorium because both the instrumental sensitivity is higher and contamination is better controlled. The materials analyzed were light and heavy water, pseudocumene, and mineral oil.

Pleistocene Thermocline Reconstruction and Oxygen Minimum Zone Evolution in the Maldives

NASA Astrophysics Data System (ADS)

Yu, S. M.; Wright, J.

2017-12-01

Drift deposits of the southern flank the Kardiva Channel in the eastern Inner Sea of the Maldives provide a complete record of Pleistocene water column changes in conjunction with monsoon cyclicity and fluctuations in the current system. We sampled IODP Site 359-U1467 to reconstruct water column using foraminiferal stable isotope records. This unlithified lithostratigraphic unit is rich in well-preserved microfossils and has an average sedimentation rate of 3.4 cm/yr. Marine Isotope Stages 1-6 were identified and show higher sedimentation rates during the interglacial sections approaching 6 cm/kyr. We present the δ13C and δ18O record of planktonic and benthic foraminiferal species taken at intervals of 3 cm. Globigerinoides ruber was used to constrain surface conditions. The thermocline dwelling species, Globorotalia menardii, was chosen to monitor fluctuations in the thermocline compared to the mixed layer. Lastly, the δ13C of the benthic species, Cibicidoides subhaidingerii and Planulina renzi, reveal changes to the bottom water ventilation and expansion of oxygen minimum zones over time. All three taxa recorded similar changes in δ18O over the glacial/interglacial cycles which is remarkable given the large sea level change ( 120 m) and the relatively shallow water depth ( 450 m). There is a small increase in the δ13C gradient during the glacial intervals which might reflect less ventilated bottom waters in the Inner Sea. This multispecies approach allows us to better constrain the thermocline hydrography and suggests that changes in the OMZ thickness are driven by the intensification of the monsoon cycles while painting a more cohesive picture to the changes in the water column structure.

Pleistocene to Holocene contrasts in organic matter production and preservation on the California continental margin

USGS Publications Warehouse

Dean, W.E.; Gardner, J.V.

1998-01-01

Organic matter in sediments from cores collected from the upper continental slope (200-2700 m) off California and southern Oregon shows marked differences in concentration and marine character between the last glacial interval (ca. 24-10 ka) and either Holocene time or last interstadial (oxygen isotope stage 3, ca. 60-24 ka). In general, sediments deposited during Holocene time and stage 3 contain higher amounts of marine organic matter than those deposited during the last glacial interval, and this contrast is greatest in cores collected off southern California. The most profound differences in stage 3 sediments are between predominantly bioturbated sediments and occasional interbeds of laminated sediments. The sediments are from cores collected within the present oxygen minimum zone on the upper continental slope from as far north as the Oregon-California border to as far south as Point Conception. These upper Pleistocene laminated sediments contain more abundant hydrogen-rich (type II) marine algal organic matter than even surface sediments that have large amounts of nonrefractory organic matter. The stable carbon-isotopic composition of the organic matter does not change with time between bioturbated and laminated sediments, indicating that the greater abundance of type II organic matter in the laminated sediments is not due to a change in source but rather represents a greater degree of production and preservation of marine organic matter. The presence of abundant, well-preserved organic matter supports the theory that the oxygen minimum zone in the northeastern Pacific Ocean was more intense, and possibly anoxic, during late Pleistocene time as a result of increased coastal upwelling that enhanced algal productivity.

Molecules and elements for quantitative bioanalysis: The allure of using electrospray, MALDI, and ICP mass spectrometry side-by-side.

PubMed

Linscheid, Michael W

2018-03-30

To understand biological processes, not only reliable identification, but quantification of constituents in biological processes play a pivotal role. This is especially true for the proteome: protein quantification must follow protein identification, since sometimes minute changes in abundance tell the real tale. To obtain quantitative data, many sophisticated strategies using electrospray and MALDI mass spectrometry (MS) have been developed in recent years. All of them have advantages and limitations. Several years ago, we started to work on strategies, which are principally capable to overcome some of these limits. The fundamental idea is to use elemental signals as a measure for quantities. We began by replacing the radioactive 32 P with the "cold" natural 31 P to quantify modified nucleotides and phosphorylated peptides and proteins and later used tagging strategies for quantification of proteins more generally. To do this, we introduced Inductively Coupled Plasma Mass Spectrometry (ICP-MS) into the bioanalytical workflows, allowing not only reliable and sensitive detection but also quantification based on isotope dilution absolute measurements using poly-isotopic elements. The detection capability of ICP-MS becomes particularly attractive with heavy metals. The covalently bound proteins tags developed in our group are based on the well-known DOTA chelate complex (1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid) carrying ions of lanthanoides as metal core. In this review, I will outline the development of this mutual assistance between molecular and elemental mass spectrometry and discuss the scope and limitations particularly of peptide and protein quantification. The lanthanoide tags provide low detection limits, but offer multiplexing capabilities due to the number of very similar lanthanoides and their isotopes. With isotope dilution comes previously unknown accuracy. Separation techniques such as electrophoresis and HPLC were used and just slightly adapted workflows, already in use for quantification in bioanalysis. Imaging mass spectrometry (MSI) with MALDI and laser ablation ICP-MS complemented the range of application in recent years. © 2018 Wiley Periodicals, Inc.

40 CFR Figure C-4 to Subpart C of... - Illustration of the Minimum Limits for Correlation Coefficient for PM 2.5 and PM 10-2,5 Class II...

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 6 2013-07-01 2013-07-01 false Illustration of the Minimum Limits for Correlation Coefficient for PM 2.5 and PM 10-2,5 Class II and III Methods C Figure C-4 to Subpart C of Part 53... Methods and Reference Methods Pt. 53, Subpt. C, Fig. C-4 Figure C-4 to Subpart C of Part 53—Illustration...

40 CFR Figure C-4 to Subpart C of... - Illustration of the Minimum Limits for Correlation Coefficient for PM 2.5 and PM 10-2.5 Class II...

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 6 2014-07-01 2014-07-01 false Illustration of the Minimum Limits for Correlation Coefficient for PM 2.5 and PM 10-2.5 Class II and III Methods C Figure C-4 to Subpart C of Part 53... Methods and Reference Methods Pt. 53, Subpt. C, Fig. C-4 Figure C-4 to Subpart C of Part 53—Illustration...

40 CFR Table 6 to Subpart Dddd of... - Model Rule-Emission Limitations That Apply to Incinerators on and After [Date to be specified in...

Code of Federal Regulations, 2012 CFR

2012-07-01

... per million dry volume 3-run average (1 hour minimum sample time per run) Performance test (Method 10... (Reapproved 2008) c. Oxides of nitrogen 53 parts per million dry volume 3-run average (1 hour minimum sample... average (1 hour minimum sample time per run) Performance test (Method 6 or 6c at 40 CFR part 60, appendix...

40 CFR Table 6 to Subpart Dddd of... - Model Rule-Emission Limitations That Apply to Incinerators on and After [Date to be specified in...

Code of Federal Regulations, 2011 CFR

2011-07-01

... per million dry volume 3-run average (1 hour minimum sample time per run) Performance test (Method 10... (Reapproved 2008) c. Oxides of nitrogen 53 parts per million dry volume 3-run average (1 hour minimum sample... average (1 hour minimum sample time per run) Performance test (Method 6 or 6c at 40 CFR part 60, appendix...

40 CFR Table 2 to Subpart Dddd of... - Model Rule-Emission Limitations That Apply to Incinerators Before [Date to be specified in state...

Code of Federal Regulations, 2014 CFR

2014-07-01

... parts per million by dry volume 3-run average (1 hour minimum sample time per run) Performance test..., appendix A-4). Oxides of nitrogen 388 parts per million by dry volume 3-run average (1 hour minimum sample... (1 hour minimum sample time per run) Performance test (Method 6 or 6c of appendix A of this part) a...

40 CFR Table 2 to Subpart Dddd of... - Model Rule-Emission Limitations That Apply to Incinerators Before [Date to be specified in state...

Code of Federal Regulations, 2013 CFR

2013-07-01

... parts per million by dry volume 3-run average (1 hour minimum sample time per run) Performance test..., appendix A-4). Oxides of nitrogen 388 parts per million by dry volume 3-run average (1 hour minimum sample... (1 hour minimum sample time per run) Performance test (Method 6 or 6c of appendix A of this part) a...

Brief Report: Investigating Uncertainty in the Minimum Mortality Temperature: Methods and Application to 52 Spanish Cities.

PubMed

Tobías, Aurelio; Armstrong, Ben; Gasparrini, Antonio

2017-01-01

The minimum mortality temperature from J- or U-shaped curves varies across cities with different climates. This variation conveys information on adaptation, but ability to characterize is limited by the absence of a method to describe uncertainty in estimated minimum mortality temperatures. We propose an approximate parametric bootstrap estimator of confidence interval (CI) and standard error (SE) for the minimum mortality temperature from a temperature-mortality shape estimated by splines. The coverage of the estimated CIs was close to nominal value (95%) in the datasets simulated, although SEs were slightly high. Applying the method to 52 Spanish provincial capital cities showed larger minimum mortality temperatures in hotter cities, rising almost exactly at the same rate as annual mean temperature. The method proposed for computing CIs and SEs for minimums from spline curves allows comparing minimum mortality temperatures in different cities and investigating their associations with climate properly, allowing for estimation uncertainty.

Pre-main Sequence Evolution and the Hydrogen-Burning Minimum Mass

NASA Astrophysics Data System (ADS)

Nakano, Takenori

There is a lower limit to the mass of the main-sequence stars (the hydrogen-burning minimum mass) below which the stars cannot replenish the energy lost from their surfaces with the energy released by the hydrogen burning in their cores. This is caused by the electron degeneracy in the stars which suppresses the increase of the central temperature with contraction. To find out the lower limit we need the accurate knowledge of the pre-main sequence evolution of very low-mass stars in which the effect of electron degeneracy is important. We review how Hayashi and Nakano (1963) carried out the first determination of this limit.

Following Carbon Isotopes from Methane to Molecules

NASA Astrophysics Data System (ADS)

Freeman, K. H.

2017-12-01

Continuous-flow methods introduced by Hayes (Matthews and Hayes, 1978; Freeman et al., 1990; Hayes et al., 1990) for compound-specific isotope analyses (CSIA) transformed how we study the origins and fates of organic compounds. This analytical revolution launched several decades of research in which researchers connect individual molecular structures to diverse environmental and climate processes affecting their isotopic profiles. Among the first applications, and one of the more dramatic isotopically, was tracing the flow of natural methane into cellular carbon and cellular biochemical constituents. Microbial oxidation of methane can be tracked by strongly 13C-depleted organic carbon in early Earth sedimentary environments, in marine and lake-derived biomarkers in oils, and in modern organisms and their environments. These signatures constrain microbial carbon cycling and inform our understanding of ocean redox. The measurement of molecular isotopes has jumped forward once again, and it is now possible to determine isotope abundances at specific positions within increasingly complex organic structures. In addition, recent analytical developments have lowered sample sensitivity limits of CSIA to picomole levels. These new tools have opened new ways to measure methane carbon in the natural environment and within biochemical pathways. This talk will highlight how molecular isotope methods enable us to follow the fate of methane carbon in complex environments and along diverse metabolic pathways, from trace fluids to specific carbon positions within microbial biomarkers.

Uranium Isotope Ratios in Modern and Precambrian Soils

NASA Astrophysics Data System (ADS)

DeCorte, B.; Planavsky, N.; Wang, X.; Auerbach, D. J.; Knudsen, A. C.

2015-12-01

Uranium isotopes (δ238U values) are an emerging paleoredox proxy that can help to better understand the redox evolution of Earth's surface environment. Recently, uranium isotopes have been used to reconstruct ocean and atmospheric redox conditions (Montoya-Pino et al., 2010; Brennecka et al., 2011; Kendall et al., 2013; Dahl et al., 2014). However, to date, there have not been studies on paleosols, despite that paleosols are, arguably better suited to directly tracking the redox conditions of the atmosphere. Sedimentary δ238U variability requires the formation of the soluble, oxidized form of U, U(VI). The formation of U(VI) is generally thought to require oxygen levels orders of magnitude higher than prebiotic levels. Without significant U mobility, it would have been impossible to develop isotopically distinct pools of uranium in ancient Earth environments. Conversely, an active U redox cycle leads to significant variability in δ238U values. Here we present a temporally and geographically expansive uranium isotope record from paleosols and modern soils to better constrain atmospheric oxygen levels during the Precambrian. Preliminary U isotope measurements of paleosols are unfractionated (relative to igneous rocks), possibly because of limited fractionation during oxidation (e.g., {Wang, 2015 #478}) or insufficient atmospheric oxygen levels to oxidize U(IV)-bearing minerals in the bedrock. Further U isotope measurements of paleosols with comparison to modern soils will resolve this issue.

A novel methodology to investigate isotopic biosignatures

NASA Astrophysics Data System (ADS)

Horner, T. J.; Lee, R. B. Y.; Henderson, G. M.; Rickaby, R. E. M.

2012-04-01

An enduring goal of trace metal isotopic studies of Earth History is to find isotopic 'fingerprints' of life or of life's individual physiochemical processes. Generally, such signatures are sought by relating an isotopic effect observed in controlled laboratory conditions or a well-characterized environment to a more complex system or the geological record. However, such an approach is ultimately limited because life exerts numerous isotopic fractionations on any one element so it is hard to dissect the resultant net fractionation into its individual components. Further, different organisms, often with the same apparent cellular function, can express different isotopic fractionation factors. We have used a novel method to investigate the isotopic fractionation associated with a single physiological process-enzyme specific isotopic fractionation. We selected Cd isotopes since only one biological use of Cd is known, CdCA (a Cd/Zn carbonic anhydrase from the coastal diatom T. Weissflogii). Thus, our investigation can also inform the long standing mystery as to why this generally toxic element appears to have a nutrient-like dissolved isotopic and concentration profile in the oceans. We used the pET-15b plasmid to insert the CdCA gene into the E. coli genome. There is no known biochemical function for Cd in E. coli, making it an ideal vector for studying distinct physiological processes within a single organism. The uptake of Cd and associated isotopic fractionation was determined for both normal cells and those expressing CdCA. It was found that whole cells always exhibited a preference for the light isotopes of Cd, regardless of the expression of CdCA; adsorption of Cd to cell surfaces was not seen to cause isotopic fractionation. However, the cleaning procedure employed exerted a strong control on the observed isotopic composition of cells. Using existing protein purification techniques, we measured the Cd isotopic composition of different subcellular fractions of E. coli (e.g. membranes, cytosol, etc.), including the catalytic metal atoms within CdCA. These experiments allow isotopic exchange reactions to be observed in biological systems at an unparalleled resolution, demonstrating that isotopic fractionation can occur, in vivo, on length scales as small as a few Å. We will explore future applications of this technique using the marine geochemistry of Cd as a case study. This experimental approach has great promise for studying the individual isotopic biosignatures of other biochemical reactions, in particular those which may have been active during early Earth History.

A GREEN'S FUNCTION APPROACH FOR DETERMINING DOSE RATES FOR SMALL GRAM QUANTITIES IN SHIPPING PACKAGINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nathan, S.

The Small Gram Quantity (SGQ) concept is based on the understanding that small amounts of hazardous materials, in this case radioactive materials (RAM), are significantly less hazardous than large amounts of the same materials. This paper describes a methodology designed to estimate an SGQ for several neutron and gamma emitting isotopes that can be shipped in a package in compliance with 10 CFR Part 71 external radiation level limits regulations. The neutron and photon sources were calculated using both ORIGEN-S and RASTA. The response from a unit source in each neutron and photon group was calculated using MCNP5 with eachmore » unshielded and shielded container configuration. Effects of self-shielding on both neutron and photon response were evaluated by including either plutonium oxide or iron in the source region for the case with no shielded container. For the cases of actinides mixed with light elements, beryllium is the bounding light element. The added beryllium (10 to 90 percent of the actinide mass) in the cases studied represents between 9 and 47 percent concentration of the total mixture mass. For beryllium concentrations larger than 50 percent, the increase in the neutron source term and dose rate tend to increase at a much lower rate than at concentrations lower than 50%. The intimately mixed actinide-beryllium form used in these models is very conservative and thus the limits presented in this report are practical bounds on the mass that can be safely shipped. The calculated dose rate from one gram of each isotope was then used to determin the maximum amount of a single isotope that could be shipped in the Model 9977 Package (or packagings having the same or larger external dimensions as well as similar structural materials) and have the external radiation level within the regulatory dose limits at the surface of the package. The estimates of the mass limits presented would also serve as conservative limits for both the Models 9975 and 9978 packages. If a package contains a mixture of isotopes, the acceptability for shipment can be determined by a sum of fractions approach. It should be noted that the SGQ masses presented in this report represent limits that would comply with the external radiation limits under 10CFR Part 71. They do not necessarily bound lower limits that may be required to comply with other factors such as heat load of the package.« less

Coordinated In Situ Nanosims Analyses of H-C-O Isotopes in ALH 84001 Carbonates

NASA Technical Reports Server (NTRS)

Usui, T.; Alexander, C. M. O'D.; Wang, J.; Simon, J. I.; Jones, J. H.

2016-01-01

The surface geology and geomorphology of Mars indicate that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. This study reports the hydrogen, carbon, and oxygen isotope compositions of the ancient atmosphere/hydrosphere of Mars based on in situ ion microprobe analyses of approximately 4 Ga-old carbonates in Allan Hills (ALH) 84001. The ALH 84001 carbonates are the most promising targets because they are thought to have formed from fluid that was closely associated with the Noachian atmosphere. While there are a number of carbon and oxygen isotope studies of the ALH 84001 carbonates, in situ hydrogen isotope analyses of these carbonates are limited and were reported more than a decade ago. Well-documented coordinated in situ analyses of carbon, oxygen and hydrogen isotopes provide an internally consistent dataset that can be used to constrain the nature of the Noachian atmosphere/hydrosphere and may eventually shed light on the hypothesis of ancient watery Mars.

Calculation of airborne radioactivity in a Technegas lung ventilation unit.

PubMed

López Medina, A; Miñano, J A; Terrón, J A; Bullejos, J A; Guerrero, R; Arroyo, T; Ramírez, A; Llamas, J M

1999-12-01

Airborne contamination by 99Tcm has been monitored in the Nuclear Medicine Department in our hospital to assess the risk of internal contamination to occupational workers exposed to Technegas studies. An air sampler fitted with a membrane filter was used. The optimum time for air absorption for obtaining the maximum activity in the filter was calculated. Maximum activity in the membrane filter ensures minimum uncertainty, which is especially important when low-level activities are being measured. The optimum time depends on air absorption velocity, room volume and filter efficiency for isotope collection. It tends to 1/lambda (lambda = disintegration constant for 99Tcm) for large volume and low velocity. Room activity with the air pump switched on was related to filter activity, and its variation with time was studied. Free activity in air for each study was approximately 7 x 10(-4) the activity used, and the effective half-life of the isotope in the room was 13.9 min (decay and diffusion). For a typical study (630 MBq), the effective dose to staff was 0.01 microSv when in the room for 10 min.

Nitrogen isotopic composition of nitrate in the South China Sea: A clue to the origin of nitrogen

NASA Astrophysics Data System (ADS)

Yang, Z.; Chen, J.; Chen, M.; Ran, L.; Li, H.; Zhu, Y.; Wang, C.; Ji, Z.; Zhang, J.; Zhang, D.

2016-02-01

Nitrogen isotopic composition of water column nitrate was measured in the South China Sea to clarify the sources of nitrogen. The δ15NNO3 value in deep water (5.4±0.2‰) was higher than the average deep oceanic δ15NNO3 ( 5‰), and a weak δ15NNO3 maximum (5.9±0.2‰) was observed at 500 m depth, matching the salinity minimum. These indicated the intrusion of the North Pacific Water which carried nitrate with a high δ15NNO3 and showed a similar δ15NNO3 distribution profile with the South China Sea. The high N* (1.74±0.23 μmol/L) combined with the low δ15NNO3 (4.7±0.2‰) at 100 m depth indicated that N2 fixation (and possibly Atmospheric Deposition) introduces new N to the surface ocean. The distribution of δ15N values of nitrate, sinking particles and surface sediment suggest that laterally-advected sediments may be a source of nitrogen to the deep ocean.

Radionuclides, stable isotopes, inorganic constituents, and organic compounds in water from selected wells and springs from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman Area, Idaho, 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bartholomay, R.C.; Williams, L.M.; Campbell, L.J.

1995-10-01

The US Geological Survey and the Idaho Department of Water Resources, in response to a request from the US Department of Energy, samples 18 sites as part of a long-term project to monitor water quality of the Snake River Plain aquifer from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman area. Water samples were collected and analyzed for selected radionuclides, stable isotopes, inorganic constituents, and organic compounds. The samples were collected from seven irrigation wells, seven domestic wells, two springs, one stock well, and one observation well. Two quality assurance samples also were collected and analyzed.more » None of the radionuclide, inorganic constituent, or organic compound concentrations exceeded the established maximum contaminant levels for drinking water. Many of the radionuclide and inorganic constituent concentrations exceeded their respective reporting levels. All samples analyzed for dissolved organic carbon had concentrations that exceeded their minimum reporting levels.« less

Radionuclides, stable isotopes, inorganic constituents, and organic compounds in water from selected wells and springs from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman Area, Idaho, 1995

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bartholomay, R.C.; Williams, L.M.; Campbell, L.J.

1996-09-01

The US Geological Survey and the Idaho Department of Water Resources, in cooperation with the US Department of Energy, sampled 17 sites as part of a long-term project to monitor water quality of the Snake River Plain aquifer from the southern boundary of the Idaho National Engineering Laboratory to the Hagerman area. Water samples were collected and analyzed for selected radionuclides, stable isotopes, inorganic constituents, and organic compounds. The samples were collected from 11 irrigation wells, 2 domestic wells, 2 stock wells, 1 spring, and 1 public-supply well. Two quality assurance samples also were collected and analyzed. None of themore » radionuclide, inorganic constituents, or organic compound concentrations exceeded the established maximum contaminant levels for drinking water. Many of the radionuclide and inorganic constituent concentrations were greater than their respective reporting levels. All samples analyzed for dissolved organic carbon had concentrations that were greater than the minimum reporting level.« less

Application of the isotope-dilution principle to the analysis of factors affecting the incorporation of [3H]uridine and [3H]cytidine into cultured lymphocytes. Evaluation of pools in serum and culture media

PubMed Central

Forsdyke, D. R.

1971-01-01

1. Rat lymph-node cells were incubated in serum and medium 199 with [5-3H]uridine or [5-3H]cytidine and acid-precipitable radioactivity was measured. Results were interpreted in terms of an isotope-dilution model. 2. Both serum and medium 199 contained pools that inhibited radioactive labelling in a competitive manner. The serum activity was diffusible and inhibited labelling with [3H]cytidine more than with [3H]uridine; in these respects the activity resembled cytidine (14μm). 3. The pools in serum and plasma were the same size; however, the rate of labelling was greater in plasma, owing to a diffusible factor. 4. Paradoxically, relatively simple media (Earle's salts and Eagle's minimum essential) appeared to have a larger pool than the more complex pyrimidine-containing medium 199; this suggests a contribution to the pool by cells in the simple media. 5. In the absence of pools the average cell was capable of incorporating 2000 radioactive nucleoside molecules/s. PMID:4947658

Enzymatic hydrolysis of p-nitroacetanilide: mechanistic studies of the aryl acylamidase from Pseudomonas fluorescens.

PubMed

Stein, Ross L

2002-01-22

Aryl acylamidase (EC 3.1.5.13; AAA) catalyzes the hydrolysis of p-nitroacetanilide (PNAA) via the standard three-step mechanism of serine hydrolases: binding of substrate (K(s)), acylation of active-site serine (k(acyl)), and hydrolytic deacylation (k(deacyl)). Key mechanistic findings that emerged from this study include that (1) AAA requires a deprotonated base with a pK(a) of 8.3 for expression of full activity toward PNAA. Limiting values of kinetic parameters at high pH are k(c) = 7 s(-1), K(m) = 20 microM, and k(c)/K(m) = 340 000 M(-1) s(-1). (2) At pH 10, where all the isotope effects were conducted, k(c) is equally rate-limited by k(acyl) and k(deacyl). (3) The following isotope effects were determined: (D)()2(O)(k(c)/K(m)) = 1.7 +/- 0.2, (D)()2(O)k(c) = 3.5 +/- 0.3, and (beta)(D)(k(c)/K(m)) = 0.83 +/- 0.04, (beta)(D)k(c) = 0.96 +/- 0.01. These values, together with proton inventories for k(c)/K(m) and k(c), suggest the following mechanism: (i) The initial binding of substrate to enzyme to form the Michaelis complex is accompanied by solvation changes that generate solvent deuterium isotope effects originating from hydrogen ion fractionation at multiple sites on the enzyme surface. (ii) From within the Michaelis complex, the active site serine attacks the carbonyl carbon of PNAA with general-base catalysis to form a substantially tetrahedral transition state enroute to the acyl-enzyme. (iii) Finally, deacylation occurs through a process involving a rate-limiting solvent isotope effect, generating conformational change of the acyl-enzyme that positions the carbonyl bond in a polarizing environment that is optimal for attack by water.

Limited fluid in carbonate-shale hosted thrust faults of the Rocky Mountain Fold-and-Thrust Belt (Sun River Canyon, Montana)

NASA Astrophysics Data System (ADS)

OBrien, V. J.; Kirschner, D. L.

2001-12-01

It is widely accepted that fluids play a fundamental role in the movement of thrust faults in foreland fold-and-thrust belts. We have begun a combined structure-geochemistry study of faults in the Rocky Mountain fold-and-thrust belt in order to provide more insight into the occurrence and role(s) of fluid in the deformation of thrust faults. We focus on faults exposed in the Sun River Canyon of Montana, an area that contains some of the best exposures of the Rocky Mountain fold-and-thrust belt in the U.S. Samples were collected from two well exposed thrusts in the Canyon -- the Diversion and French thrusts. Both faults have thrust Mississippian dolostones over Cretaceous shales. Displacement exceeds several kilometers. Numerous small-displacement, subsidiary faults characterize the deformation in the hanging wall carbonates. The footwall shales accommodated more penetrative deformation, resulting in well developed foliation and small-scale folds. Stable isotope data have been obtained from host rock samples and veins from these faults. The data delimit an arcuate trend in oxygen-carbon isotope space. Approximately 50 host rock carbonate samples from the hanging walls have carbon and oxygen isotope values ranging from +3 to 0 and 28 to 19 per mil, respectively. There is no apparent correlation between isotopic values and distance from thrust fault at either locality. Fifteen samples of fibrous slickensides on small-displacement faults in the hanging walls have similar carbon and lower oxygen isotope values (down to 16 per mil). And 15 veins that either post-date thrusting or are of indeterminate origin have carbon and oxygen isotope values down to -3 and12 per mil, respectively. The isotopic data collected during the initial stages of this project are similar to some results obtained several hundred kilometers north in the Front Ranges of the Canadian Rockies (Kirschner and Kennedy, JGR 2000) and in carbonate fold-thrust belts of the Swiss Helvetic Alps and Italian Apennines. These data are consistent with limited infiltration of fluid through fractures and minor faults into hanging walls of large-displacement thrust faults.