Presolar nanodiamonds: faster, cleaner, and limits on platinum-HL     

Silke Merchel  Ulrich Ott  Siegfried Herrmann  Thomas Faestermann  Gunther Korschinek  Anton Wallner 《Geochimica et cosmochimica acta》2003,67(24):4949-4960

We have developed a procedure that allows extraction of clean nanodiamond samples from primitive meteorites for isotopic analyses of trace elements on a timescale of just a week. This procedure includes microwave digestion and optimization of existing isolation techniques for further purification. Abundances of trace elements that are difficult to dissolve using standard procedures (e.g., Ir) are lower in the diamond residues prepared using the new technique. Accelerator mass spectrometry (AMS) was explored as a means for isotopic measurements. Results obtained on diamond fractions from Allende and Murchison show the need for suitable matrix-adjusted standards to correct for fractionation effects; nevertheless they allow putting an upper limit on the abundance of ¹⁹⁸Pt-H in nanodiamonds of ∼1 × 10¹⁴ atoms/g. This limit is on the order of what can be expected from predictions of competing nucleosynthesis models and extrapolation of the apparently mass dependent abundance trend of the associated noble gases.Unfortunately, and unexpectedly, presolar silicon carbide is almost quantitatively dissolved during microwave digestion with HCl/HF/HNO₃. Re-evaluation of the standard extraction technique, however, shows that it also may lead to severe loss of fine-grained SiC, a fact not commonly appreciated. A lower limit to SiC abundance in Murchison is 20 ppm, and previous conclusions that Murchison SiC is unusually coarse-grained compared to SiC in other primitive meteorites seem not to be warranted. Graphite and silicon nitride may survive and possibly can be separated after this step as suggested by a simulation experiment using terrestrial analog material, but the detailed behavior of meteoritic graphite requires further study.  相似文献   

Magnetic record associated with tree ring density: Possible climate proxy     

Gunther Kletetschka  Petr Pruner  Daniela Venhodova  Jaroslav Kadlec 《Geochemical transactions》2007,8(1):2

A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition.  相似文献   

Cross sections from 5 to 35 MeV for the reactions natMg(3He,x)26Al, 27Al(3He,x)26Al,natCa(3He,x)41Ca,and natCa(3He,x)36Cl: Implications for early irradiation in the solar system     

Gregory F. HERZOG  Marc W. CAFFEE  Thomas FAESTERMANN  R. HERTENBERGER  Gunther KORSCHINEK  Ingo LEYA  Robert C. REEDY  J. M. SISTERSON 《Meteoritics & planetary science》2011,46(10):1427-1446

Abstract– Cross sections were measured for the nuclear reactions ^natMg(³He,x)²⁶Al, ²⁷Al(³He,x)²⁶Al, ^natCa(³He,x)⁴¹Ca, and ^natCa(³He,x)³⁶Cl in the energy region from approximately 5–35 MeV. The rates of these reactions are important for studies of early solar system irradiation scenarios. The ²⁶Al, ³⁶Cl, and ⁴¹Ca were separated chemically, and the numbers of atoms produced in each reaction channel were measured using accelerator mass spectrometry (AMS). From these results, 26 cross sections were determined and compared with predictions of the TALYS code. Agreement is within 40% for most cross sections. Our measurements were used to model the production of ⁷Be, ¹⁰Be, ²⁶Al, and ⁴¹Ca in the early solar system. For projectiles ¹H, ³He, and ⁴He, we assumed energy spectra of the general form E^?α. For a wide range of parameterizations, the modeled ratios of ⁷Be/Be and ¹⁰Be/Be on the one hand and of ²⁶Al/²⁷Al and ⁴¹Ca/Ca on the other are coupled because the excitation functions for the relevant nuclear reactions have similar shapes. Modeling of a closed system with the constraint that ¹⁰Be/⁹Be = 0.001 fails to reproduce simultaneously the range of ⁷Be/⁹Be, ²⁶Al/²⁷Al, and ⁴¹Ca/Ca ratios inferred for the early solar system from studies of meteorites.  相似文献   

Critical tissue copper residues for marine bivalve (Mytilus galloprovincialis) and echinoderm (Strongylocentrotus purpuratus) embryonic development: conceptual, regulatory and environmental implications     

Rosen G  Rivera-Duarte I  Chadwick DB  Ryan A  Santore RC  Paquin PR 《Marine environmental research》2008,66(3):327-336

Critical tissue copper (Cu) residues associated with adverse effects on embryo-larval development were determined for the Mediterranean mussel (Mytilus galloprovincialis) and purple sea urchin (Strongylocentrotus purpuratus) following laboratory exposure to Cu-spiked seawater collected from San Diego Bay, California, USA. Whole body no-observed-effect-residues (NOER) were similar, with means of 21 and 23mugg(-1)dw, for M. galloprovincialis and S. purpuratus, respectively. Mean whole body median effect residues (ER50) were 49 and 142mugg(-1)dw for M. galloprovincialis and S. purpuratus, respectively. The difference in ER50s between species was reduced to a factor of <2 when expressed as soft tissue residues. Coefficients of variation among whole body-ER50s were 3-fold lower than median waterborne effect concentrations (EC50) for both species exposed to samples varying in water quality characteristics. This suggests that tissue concentrations were a better predictor of toxicity than water concentrations. The CBRs described herein do not differentiate between the internal Cu concentrations that are metabolically available and those that are accumulated and then detoxified. They do appear, however, to be well enough related to the level of accumulation at the site of action of toxicity that they serve as useful surrogates for the copper concentration that affects embryonic development of the species tested. Results presented have potentially important implications for a variety of monitoring and assessment strategies. These include regulatory approaches for deriving saltwater ambient water quality criteria for Cu, contributions towards the development of a saltwater biotic ligand model, the conceptual approach of using CBRs, and ecological risk assessment.  相似文献   

Acoustic backscatter and sediment textural properties of inner shelf sands,northeastern Gulf of Mexico     

Kenneth S. Davis  Niall C. Slowey  Ingo H. Stender  Hannelore Fiedler  William R. Bryant  Gunther Fechner 《Geo-Marine Letters》1996,16(3):273-278

The relationship between spatial variations of the properties of sea-floor sediments and acoustic backscatter from the surface of the sea floor on the continental shelf off of Panama City, Florida, USA, is investigated using surficial sediment grab samples and digital side-scan sonar data. Acoustic backscatter strength has a high, direct correlation with the mean grain size of the sediments. Acoustic backscatter strength also correlates directly with the carbonate content of the sediments, particularly in medium-and coarse-sand facies, because large, irregularly shaped, carbonate particles affect both the mean grain size of the sediments and the roughness of the surface of the sea floor.  相似文献   

Sensitivity study of pulsed neutron-gamma saturation monitoring at the Altmark site in the context of CO2 storage     

Gunther Baumann  Jan Henninges 《Environmental Earth Sciences》2012,67(2):463-471

The injection of CO₂ into depleted natural gas reservoirs has been proposed as a promising new technology for combining enhanced gas recovery and geological storage of CO₂. During the injection, application of suitable techniques for monitoring of the induced changes in the subsurface is required. Observing the movement and the changes in saturation of the fluids contained in the reservoir and the confining strata is among the primary aims here. It is shown that under conditions similar to the Altmark site, Germany, pulsed neutron-gamma logging can be applied with limitations. The pulsed neutron-gamma method can be applied for detection and quantification of changes in brine saturation and water content, whereas changes in the gas composition are below the detection limit. A method to account for the effects of salt precipitation resulting from evaporation of residual brine is presented.  相似文献   

Copper bioavailability and toxicity to Mytilus galloprovincialis in Shelter Island Yacht Basin,San Diego,CA     

Casey Bosse  Gunther Rosen  Marienne Colvin  Patrick Earley  Robert Santore  Ignacio Rivera-Duarte 《Marine pollution bulletin》2014

The bioavailability and toxicity of copper (Cu) in Shelter Island Yacht Basin (SIYB), San Diego, CA, USA, was assessed with simultaneous toxicological, chemical, and modeling approaches. Toxicological measurements included laboratory toxicity testing with Mytilus galloprovincialis (Mediterranean mussel) embryos added to both site water (ambient) and site water spiked with multiple Cu concentrations. Chemical assessment of ambient samples included total and dissolved Cu concentrations, and Cu complexation capacity measurements. Modeling was based on chemical speciation and predictions of bioavailability and toxicity using a marine Biotic Ligand Model (BLM). Cumulatively, these methods assessed the natural buffering capacity of Cu in SIYB during singular wet and dry season sampling events. Overall, the three approaches suggested negligible bioavailability, and isolated observed or predicted toxicity, despite an observed gradient of increasing Cu concentration, both horizontally and vertically within the water body, exceeding current water quality criteria for saltwater.  相似文献   

Reconstruction of historical pressure patterns over Japan using two-point pressure–temperature datasets since the nineteenth century     

Masumi Zaiki  Gunther P. Können  Keiji Kimura  Takehiko Mikami  Togo Tsukahara 《Climatic change》2009,95(1-2):231-248

The temperature and pressure differences between Tokyo and Nagasaki were used to reconstruct past climate conditions. January and July in each available year since the 1820s were classified into several types with characteristic sea level atmospheric pressure patterns. This results in 18 years of pre-1881 data and a continuous series thereafter. The series indicate that the warming after 1900 (after the end of the so-called Little Ice Age) and again after 1960 can at least partly be attributed to an increase in the frequency of warm circulation pattern types at the expense of cold types. The difference in nature of the shifts in circulation types that occurred in the late nineteenth century compared with that in the late twentieth centuries suggests that the mechanism behind the warming in the late nineteenth century differs from that in the late twentieth century.  相似文献   

Quantitative assessment of future development of copper/silver resources in the Kootenai National Forest,Idaho/Montana: Part II—Economic and policy analysis     

Thomas M. Gunther 《Natural Resources Research》1992,1(4):267-280

Quantitative assessments and analyses of mineral resources can provide important input to decisions affecting public lands. This article, a companion article to Spanski, 1992, presents an application of resource assessment and analysis tools developed by the U.S. Bureau of Mines and the U.S. Geological Survey to U.S. Forest Service lands in northwest Montana. The analytical system described here integrates mineral deposit models, mine and mill cost-estimation models, and relevant economic and policy assumptions to estimate potential mineral production and the associated direct and indirect mineral-related economic impacts that could follow development of minerals. Finally, the impacts of land-use policies are estimated using the model.  相似文献   

Genese und Charakteristik der Rauhwacken im Pittental (Niederösterreich)     

Riedmüller  Gunther 《International Journal of Earth Sciences》1976,65(1):290-332

International Journal of Earth Sciences - Rauhwacken aus dem Pittental wurden mit feldgeologischen, lichtoptischen, raster-elektronenmikroskopischen, chemischen und röntgenographischen...  相似文献