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  • 1
    Electronic Resource
    Electronic Resource
    Sulfur isotopic evidence for the supergene origin of alunite deposits, Tolfa district, Italy (1972)
    Springer
    Mineralium deposita 7 (1972), S. 113-125 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Die Schwefel-Isotopen-Häufigkeiten von Mineralen der historisch wichtigen Alunit-Vorkommen des Gebietes um Tolfa zeigen (1) eine große Ähnlichkeit der Isotopen-Zusammensetzungen zwischen Sulfaten und Sulfiden (Mittelwerte für δS34 von +5,54 bzw. +6,34‰), (2) höchstens sehr geringe Fraktionierungs-Faktoren (0,995 bis 1,004) für Mineralpaare von Sulfat und Sulfid, (3) zwei verschiedene Gruppen von Isotopenverhältnissen bei den Sulfiden, und zwar für Pyrit (+8,34‰) und Markasit (−1,05‰), wobei der jeweils begleitende Alunit ähnliche Unterschiede aufweist, und (4) eine mögliche Beeinflussung des hydrothermalen Systems durch Sulfat aus Salzlagerstätten (+25,1‰), weil hypogener Pyrit, Galenit und Zinnober eine Anreicherung von S34 zeigen (+6,1 bis +10,3‰). Wir nehmen an, daß Alunit, Baryt und möglicherweise auch Markasit supergen gebildet wurden, und daß der Sulfat-Schwefel durch die Oxydation von Sulfiden an der Erdoberfläche entstand. Unsere Schlußfolgerung ist mit den geologischen Befunden vereinbar und bestätigt die supergene Hypothese für die Bildung der Alunitvorkommen von Tolfa, wie sie von Fuchs und De Launay (1893) und De Launay (1906; 1913) vertreten wurde.
    Notes: Abstract Sulfur isotope abundance data for minerals of the historically important alunite deposits of the Tolfa district indicate (1) compositional similarity between sulfates and sulfides (mean δS34 values of +5.54 and +6.34 permil respectively), (2) negligible fractionation factors (0.995 to 1.004) for sulfate-sulfide mineral pairs, (3) two distinct sulfide isotopic populations characterized by pyrite (+8.34 permil) and marcasite (−1.05 permil) and with associated alunite displaying a covariant isotopic shift, and (4) possible contamination of the hydrothermal system by evaporite sulfate (+25.1 permil) because hypogene pyrite, galena, and cinnabar are enriched in S34 (+6.1 to +10.3 permil). We suggest that alunite, barite, and possibly marcasite are of supergene origin and that the sulfate-sulfur was derived from the surficial oxidation of sulfides. Our conclusion is compatible with the geologic evidence and confirms the supergene hypothesis for the genesis of Tolfa alunites proposed by Fuchs and De Launay (1893) and De Launay (1906; 1913).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00207149
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  • 2
    Electronic Resource
    Electronic Resource
    Electrical properties ofValonia ventricosa (1976)
    Springer
    The journal of membrane biology 29 (1976), S. 81-94 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The cytoplasmic electrical potential and membrane resistance of mature cells ofValonia ventricosa have been measured by inserting a microelectrode concentric with another electrode into the vacuole of the cell. The cytoplasmic region was investigated by advancing the microelectrode into the cell wall from the vacuolar side. The results revealed a unique region where the vacuolar electric potential and membrane resistance changed in a simultaneous single step to values close to zero. The measured potential always remained positive immediately after the step. At no time was a highly negative potential region encountered. Further penetration of the microelectrode revealed a low resistance negative potential region of −12.6±1.1 mV associated with the cell wall. Experiments were also carried out on aplanospores ofV. ventricosa to compare mature and immature cells. The chemical composition of the vacuolar and protoplasmic phases of mature cells was determined. The results agreed with previous results except that the Cl− ion content of the protoplasm was significantly higher at 381±20 mmoles/liter (H2O). It was concluded that mature cells ofValonia are significantly different from immature cells in that no highly negative potential cytoplasmic region was found in mature cells. It was considered that the measured step change in electric potential and membrane resistance occurred at the plasmalemma and that the tonoplast was a region of very low resistance. The implications of these findings in terms of models of ion transport intoValonia are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868953
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  • 3
    Electronic Resource
    Electronic Resource
    Dietary Lipids Influence Insulin Action (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 683 (1993), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1993.tb35701.x
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  • 4
    Electronic Resource
    Electronic Resource
    Arresting of vortex motion in YBaCuO crystals with splay in columnar defects
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 235-240 (1994), S. 2969-2970 
    Details
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0921-4534(94)91011-1
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrogen limitation of microbial decomposition in a grassland under elevated CO 2 (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 409 (2001), S. 188-191 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Carbon accumulation in the terrestrial biosphere could partially offset the effects of anthropogenic CO2 emissions on atmospheric CO 2 (refs 1, 2). The net impact of increased CO2 on the carbon balance of terrestrial ecosystems is ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35051576
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  • 6
    Electronic Resource
    Electronic Resource
    Responses of Terrestrial Ecosystems to the Changing Atmosphere: A Resource-Based Approach (1992)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 23 (1992), S. 201-235 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.23.110192.001221
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  • 7
    Electronic Resource
    Electronic Resource
    Satellite estimates of productivity and light use efficiency in United States agriculture, 1982–98 (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Remote sensing of net primary production (NPP) is a critical tool for assessing spatial and temporal patterns of carbon exchange between the atmosphere and biosphere. However, satellite estimates suffer from a lack of large-scale field data needed for validation, as well as the need to parameterize plant light-use efficiencies (LUEs). In this study, we estimated cropland NPP with the Carnegie-Ames-Stanford-Approach (CASA), a biogeochemical model driven by satellite observations, and then compared these results with field estimates based on harvest data from United States Department of Agriculture National Agriculture Statistics Service (NASS) county statistics. Observed interannual variations in NPP over a 17-year period were well modelled by CASA, with exceptions mainly due to occasional difficulties in estimating NPP from harvest yields. The role of environmental stressors in agriculture was investigated by running CASA with and without temperature and moisture down-regulators, which are used in the model to simulate climate impacts on plant LUE. In most cases, correlations with NASS data were highest with modelled stresses, while the opposite was true for irrigated and temperature resistant crops. Analysis of the spatial variability in computed LUE revealed significantly higher values for corn than for other crops, suggesting a simple parameterization of LUE for future studies based on the fraction of area with corn. Absolute values of LUE were much lower than those reported in field trials, due to uncommonly high yields in most field trials, as well as overestimates of absorbed radiation in CASA attributed to bias from temporal compositing of satellite data. Total NPP for US croplands, excluding Alaska and Hawaii, was estimated as 0.62 Pg C year−1, representing ∼20% of total US NPP, and exhibited a positive trend of 3.7 Tg C year−2. These results have several implications for large-scale carbon cycle research that are discussed, and are especially relevant for studies of the role of agriculture in the global carbon balance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00503.x
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  • 8
    Electronic Resource
    Electronic Resource
    The effects of chamber pressurization on soil-surface CO2 flux and the implications for NEE measurements under elevated CO2 (1999)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Soil and ecosystem trace gas fluxes are commonly measured using the dynamic chamber technique. Although the chamber pressure anomalies associated with this method are known to be a source of error, their effects have not been fully characterized. In this study, we use results from soil gas-exchange experiments and a soil CO2 transport model to characterize the effects of chamber pressure on soil CO2 efflux in an annual California grassland. For greater than ambient chamber pressures, experimental data show that soil-surface CO2 flux decreases as a nonlinear function of increasing chamber pressure; this decrease is larger for drier soils. In dry soil, a gauge pressure of 0.5 Pa reduced the measured soil CO2 efflux by roughly 70% relative to the control measurement at ambient pressure. Results from the soil CO2 transport model show that pressurizing the flux chamber above ambient pressure effectively flushes CO2 from the soil by generating a downward flow of air through the soil air-filled pore space. This advective flow of air reduces the CO2 concentration gradient across the soil–atmosphere interface, resulting in a smaller diffusive flux into the chamber head space. Simulations also show that the reduction in diffusive flux is a function of chamber pressure, soil moisture, soil texture, the depth distribution of soil CO2 generation, and chamber diameter. These results highlight the need for caution in the interpretation of dynamic chamber trace gas flux measurements. A portion of the frequently observed increase in net ecosystem carbon uptake under elevated CO2 may be an artifact resulting from the impact of chamber pressurization on soil CO2 efflux.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00218.x
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  • 9
    Electronic Resource
    Electronic Resource
    Comparing global models of terrestrial net primary productivity (NPP): introduction (1999)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00001.x
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  • 10
    Electronic Resource
    Electronic Resource
    Toward an allocation scheme for global terrestrial carbon models (1999)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The distribution of assimilated carbon among the plant parts has a profound effect on plant growth, and at a larger scale, on terrestrial biogeochemistry. Although important progress has been made in modelling photosynthesis, less effort has been spent on understanding the carbon allocation, especially at large spatial scales. Whereas several individual-level models of plant growth include an allocation scheme, most global terrestrial models still assume constant allocation of net primary production (NPP) among plant parts, without any environmental coupling. Here, we use the CASA biosphere model as a platform for exploring a new global allocation scheme that estimates allocation of photosynthesis products among leaves, stems, and roots depending on resource availability. The philosophy underlying the model is that allocation patterns result from evolved responses that adjust carbon investments to facilitate capture of the most limiting resources, i.e. light, water, and mineral nitrogen. In addition, we allow allocation of NPP to vary in response to changes in atmospheric CO2. The relative magnitudes of changes in NPP and resource-use efficiency control the response of root:shoot allocation. For ambient CO2, the model produces realistic changes in above-ground allocation along productivity gradients. In comparison to the CASA standard estimate using fixed allocation ratios, the new allocation scheme tends to favour root allocation, leading to a 10% lower global biomass. Elevated CO2, which alters the balance between growth and available resources, generally leads to reduced water stress and consequently, decreased root:shoot ratio. The major exception is forest ecosystems, where increased nitrogen stress induces a larger root allocation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00269.x
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