A study to explain the emission of nitric oxide from a marsh soil   总被引：1，自引：0，他引：1  

Armin Remde  Jörg Ludwig  Franz X. Meixner  Ralf Conrad 《Journal of Atmospheric Chemistry》1993,17(3):249-275

In the period 18–21 September 1989, soil NO emission was studied at Halvergate Marshes, Norfolk (U.K.) within the framework of the BIATEX-LOVENOX joint field experiment. Using a dynamic chamber technique, 186 measurements at four plots were performed showing a net NO flux of 7.2–14.6×10^–12 kgN m^–2 s^–1. Soil samples from a soil profile (1.0 m) at a representative site and from the uppermost layer (0.1 m) of each of the four plots were sent to the laboratory for (a) detailed physical and chemical soil analysis, (b) determination of NO production rates, NO uptake rate constants, and NO compensation mixing ratios, and (c) characterization of the microbial processes involved. A diffusive model (Galbally and Johansson, 1989) was applied to the laboratory results to infer NO fluxes of the individual soil samples. When we compared these fluxes with those measured in the field, we found agreement within a factor 2–4. Furthermore, laboratory studies showed, that NO was produced and consumed only in the upper soil layer (0–0.1 m depth) and that the NO production and consumption activities observed in the Halvergate marsh soil were most probably due to the anaerobic metabolism of denitrifying bacteria operating in anaerobic microniches within the generally aerobic soil.  相似文献   

Lead-isotope inhomogeneity in Precambrian igneous K-feldspars     

Kenneth R. Ludwig  Leon T. Silver 《Geochimica et cosmochimica acta》1977,41(10):1457-1471

Stepwise Pb-removal experiments, using both vacuum volatilization and HF-leaching techniques, on acid-washed K-feldspar concentrates from Precambrian igneous rocks show that all contain some unsupported radiogenic Pb. Two types of radiogenic Pb were recognized. One has a “normal” isotopic composition, with relative abundances of ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb consistent with the age and U-Th contents of the rocks. The other type of unsupported radiogenic lead in the feldspars is apparently pure ²⁰⁶Pb, derived from long-term migration and accumulation of radioactive daughter(s) of ²³⁸U. This “pure ²⁰⁶pb” lead occupies different sites from the “normal” radiogenic lead, and tends to show a release maximum during vacuum volatilization at about 1150°C.The usefulness of stepwise vacuum volatilization may be limited by the tendency of a small amount of radiogenic lead to concentrate in the least volatile fraction. Stepwise partial HF attacks appear to give at least as good separation of radiogenic from original feldspar lead, and are recommended as a routine procedure for isotopic analyses of Precambrian feldspars. The fact that most of the five K-feldspars examined contained unsupported radiogenic lead implies that caution must be used in applying total-sample lead analyses of Precambrian feldspars to problems of lead-isotope evolution in crustal rocks.  相似文献   

Foreword     

Ludwig Schätzl 《Geoforum》1982,13(2):69

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Uranium-lead isotope systematics and apparent ages of zircons and other minerals in precambrian granitic rocks,Granite Mountains,Wyoming     

K. R. Ludwig  J. S. Stuckless 《Contributions to Mineralogy and Petrology》1978,65(3):243-254

Zircon suites from the two main types of granite in the Granite Mountains, Wyoming, yielded concordia-intercept ages of 2,640±20 m.y. for a red, foliated granite (granite of Long Creek Mountain) and 2,595±40 m.y. for the much larger mass of the granite of Lankin Dome. These ages are statistically distinct (40±20 m.y. difference) and are consistent with observed chemical and textural differences. The lower intercepts of the zircon chords of 50±40 and 100+ 75 m.y. for the granite of Long Creek Mountain and granite of Lankin Dome, respectively, are not consistent with reasonable continuous diffusion lead-loss curves but do correspond well with the known (Laramide) time of uplift of the rocks. Epidote, zircon, and apatite from silicified and epidotized zones in the granites all record at least one postcrystallization disturbance in addition to the Laramide event and do not define a unique age of silicification and epidotization. The lower limit of 2,500 m.y. provided by the least disturbed epidote, however, suggests that these rocks were probably formed by deuteric processes shortly after emplacement of the granite of the Lankin Dome. The earlier of the two disturbances that affected the minerals of the silicified-epidotized rock can be bracketed between 1,350 and 2,240 m.y. ago and is probably the same event that lowered mineral K-Ar and ages in the region.Zircon suites from both types of granite show well-defined linear correlations among U content, common-Pb content, and degree of discordance. One of the zircon suites has an extremely high common-Pb content (up to 180 ppm) and exhibits a component of radiogenic-Pb loss that is apparently unrelated to radiation damage.  相似文献   

Zur Funkortung bei weit von einander entfernten Sendern     

Ludwig Hänert 《Ocean Dynamics》1955,8(2):72-76

Zusammenfassung Es wird in dem vorliegenden Aufsatz gezeigt, wie man auf Grund der Funkpeilungen dreier weit voneinander entfernter Sender ohne Benutzung von Karten und Tafeln die geographischen Koordinaten seines Standortes geometrisch exakt konstruieren kann.

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Radio direction finding with the aid of three widely spaced wireless transmitters

Summary The present paper shows how to plot the geographical coordinates of a certain position in a geometrically exact manner with the aid of radio bearings of three widely-spaced transmitters without using charts or tables.

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Relèvement radiogoniométrique à l'aide de trois émetteurs à grande distance l'un de l'autre

Résumé L'article suivant décrit de quelle manière on peut dessiner exactement au sens de la géométrie les coordonnées géographiques d'une certaine position en se servant du relèvement radiogoniométrique de trois émetteurs installés à grande distance l'un de l'autre sans y employer des cartes marines ou des tables.

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Schallausbreitung im Schlick     

Dipl.-Phys. Florian Schirmer 《Ocean Dynamics》1970,23(1):24-30

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Assessment of Cyto‐ and Genotoxic Effects of a Variety of Chemicals Using Saccharomyces cerevisiae     

Marcel Schmitt  Georg Gellert  Jost Ludwig  Hella Lichtenberg‐Frat 《洁净——土壤、空气、水》2005,33(1):56-63

Saccharomyces cerevisiae as the most simple eukaryotic organism is broadly accepted as a laboratory model organism. For the detection of potential toxic effects of pure compounds and complex composed samples like wastewater a miniaturised short‐term in vitro cyto‐ and genotoxicity screening assay was developed. The assay based on genetically modified S. cerevisiae cells deleted in the prominent drug efflux transporters Pdr5, Snq2, and Yor1 that facilitate pleiotropic drug resistance. The yeast strain devoid of these proteins that mediate the efflux of structurally diverse hydrophobic compounds exhibited an increased sensitivity to a variety of organic compounds. The DNA damage inducible RAD54 promoter fused to a yeast optimized derivative of the GFP (green fluorescent protein) gene from the jelly fish Aequorea victoria served as an indicator of DNA damage in this strain. Various pure compounds including the direct‐acting genotoxins methyl‐N‐nitro‐N‐nitrosoguanidine (MNNG), 4‐nitroquinoline‐N‐oxide (4‐NQO), methyl methanesulfonate (MMS) and hydroxyurea as well as the heavy metals cadmium and chromium(VI), the insecticide lindane and the central nervous system stimulant caffeine were tested exhibiting dose dependent induction of green fluorescence. All compounds were in parallel examined for chronic toxicity. A bioassay detecting simultaneously geno‐ and cytotoxic effects of potential toxicants in a single assay can be an important tool with a variety of applications in environmental monitoring and aquatic ecotoxicology. By partial automation and miniaturisation to microtitration scale this bioassay enables sensitive and fast biomonitoring for a multitude of samples.  相似文献   

Calcium isotope fractionation in calcite and aragonite   总被引：1，自引：0，他引：1  

Nikolaus Gussone  Florian Böhm  Martin Dietzel  Barbara M.A. Teichert  Gert Wörheide 《Geochimica et cosmochimica acta》2005,69(18):4485-4494

Calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite. Precipitation temperatures ranged from 0 to 28°C. Calcium isotope fractionation shows a temperature dependence in accordance with previous observations: 1000 · ln(α_cc) = −1.4 + 0.021 · T (°C) for calcite and 1000 · ln(α_ar) = −1.9 + 0.017 · T (°C) for aragonite. Within uncertainty the temperature slopes are identical for the two polymorphs. However, at all temperatures calcium isotopes are more fractionated in aragonite than in calcite. The offset in δ^44/40Ca is about 0.6‰. The underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals, or to different Ca reaction behavior at the solid-liquid interface. Recently, the observed temperature dependence of the Ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting (Lemarchand et al., 2004). We show that this mechanism can in principle also be applied to CaCO₃ precipitation in natural environments in normal marine settings. Following this model, Ca isotope fractionation in marine Ca carbonates is primarily controlled by precipitation rates. On the other hand the larger Ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates. The rate control model of Ca isotope fractionation predicts a strong dependence of the Ca isotopic composition of carbonates on ambient CO₃²⁻ concentration. While this model is in general accordance with our observations in marine carbonates, cultured specimens of the planktic foraminifer Orbulina universa show no dependence of Ca-isotope fractionation on the ambient CO₃²⁻ concentration. The latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water.  相似文献   

Wide-angle observations of ALP 2002 shots on the TRANSALP profile: Linking the two DSS projects     

Florian Bleibinhaus  Ewald Brückl  ALP Working Group 《Tectonophysics》2006,414(1-4):71

Dynamite shots of the crustal-scale refraction seismic project ALP 2002 were recorded by an array of 40 seismological three-component stations on the TRANSALP profile. These observations provide a direct link between the two deep seismic projects. We report preliminary results obtained from these data. In a first approach, we verified the TRANSALP refraction seismic velocity model computing travel times for several shots and comparing them to the new observations. The results generally confirm this model. Significant first-break travel time differences in and near the Tauern Window are explained by anisotropy. Large-scale features of the model, particularly the Moho structure, seem to be continuous towards the east. Travel time residuals of wide-angle reflections indicate a slight eastward dip component of the Adriatic Moho.  相似文献   

The “Mediterraneanization” of the climate in Mediterranean countries —a cause of the unstable ecobudget     

Ludwig Hempel Dr. rer. nat. 《GeoJournal》1987,14(2):163-173

Changes of accumulation, pedogenesis and vertical erosion for the last nearly 20 000 years in connexion with periods of warm and cold climates can be proved for Mediterranean areas. The climate of Mediterranean areas became more arid for the last nearly 5 000 years. Geomorphological processes in Mediterranean areas concur with geomorphological processes in N Africa. Substantial sediments formerly marked as “historical fills” are of natural origin. Pollen analytical observations about forest formations confirm the distinction of holocene sediments: older strata of natural origin and younger layers of anthropogenic origin. Maccia and phrygana in Mediterranean areas stand for a degradation of forest caused by man. They provide eminently efficient protection of the soil cover. This poses an important question: Is afforestation, esp. in mountain areas, ecologically and economically advisable?  相似文献