Evidence for fullerenes in solid bitumen from pillow lavas of Proterozoic age from Mítov (Bohemian Massif, Czech Republic)     

Jan Jehli?ka  Aleš Svatoš  Filip Uhlík 《Geochimica et cosmochimica acta》2003,67(8):1495-1506

Andesitic pillow lavas containing biogenic, solid bitumen (SB) are a constituent of a Neoproterozoic volcanosedimentary sequence (Teplá-Barrandian unit, Bohemian Massif) in the Mítov area of the Czech Republic. A black shale formation that is crosscut by these andesitic basalts is 565 Ma old. Carbon disulfide extracts of two powdered samples of SB contain 0.2 and 0.3 ppm of C₆₀, respectively, as determined by high-pressure liquid chromatography. The peak assignment based on retention time is fully supported by high-resolution electron ionization mass spectrometry (EI-MS). No C₇₀ was detected, nor was C₆₀ found in two other SB samples from this locality. Other investigated carbonaceous samples from Bohemia (coals and anthracites of Upper Paleozoic age and anthraxolite, graphitoids, and graphite of Upper Proterozoic age) did not contain fullerenes at concentrations above the detection limit of 0.01 ppm. The absence of C₆₀ in these samples was confirmed by EI-MS. The proposed mechanism of fullerene formation involves a primary algal phase, generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series, and their high-temperature transformation related to the extrusion of basalt. An important feature for fullerene conservation was the enclosure of fullerenes in SB with a structure similar to glasslike carbon, where the fullerene was protected against oxidation.  相似文献   

Understanding Climatic Impacts, Vulnerabilities, and Adaptation in the United States: Building a Capacity for Assessment     

Edward A. Parson  Robert W. Corell  Eric J. Barron  Virginia Burkett  Anthony Janetos  Linda Joyce  Thomas R. Karl  Michael C. MacCracken  Jerry Melillo  M. Granger Morgan  David S. Schimel  Thomas Wilbanks 《Climatic change》2003,57(1-2):9-42

Based on the experience of the U.S. National Assessment, we propose a program of research and analysis to advance capability for assessment of climate impacts, vulnerabilities, and adaptation options. We identify specific priorities for scientific research on the responses of ecological and socioeconomic systems to climate and other stresses; for improvement in the climatic inputs to impact assessments; and for further development of assessment methods to improve their practical utility to decision-makers. Finally, we propose a new institutional model for assessment, based principally on regional efforts that integrate observations, research, data, applications, and assessment on climate and linked environmental-change issues. The proposed program will require effective collaboration between scientists, resource managers, and other stakeholders, all of whose expertise is needed to define and prioritize key regional issues, characterize relevant uncertainties, and assess potential responses. While both scientifically and organizationally challenging, such an integrated program holds the best promise of advancing our capacity to manage resources and the economy adaptively under a changing climate.  相似文献   

Aquatic chemistry: 3rd ed. by W. Stumm and J. J. Morgan. A Wiley-Interscience Publication, John Wiley & Sons, Inc., 1996, xvi + 1022p., US $29.95 (ISBN 0-471-51184-6)     

Tomas Pa?es 《Geochimica et cosmochimica acta》1996,60(24):5158-5159

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Quantitative methods in the earth sciences     

A. F?rster  D. F. Merriam 《Mathematical Geology》1997,29(2):315

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Simulation of normal distributed smooth fields by Karhunen-Loéve expansion in combination with kriging     

Nils-Otto Kitterr?d  Lars Gottschalk 《Stochastic Hydrology and Hydraulics》1997,11(6):459-482

Simulation of multigaussian stochastic fields can be made after a Karhunen-Loéve expansion of a given covariance function. This method is also called simulation by Empirical Orthogonal Functions. The simulations are made by drawing stochastic coefficients from a random generator. These numbers are multiplied with eigenfunctions and eigenvalues derived from the predefined covariance model. The number of eigenfunctions necessary to reproduce the stochastic process within a predefined variance error, turns out to be a cardinal question. Some ordinary analytical covariance functions are used to evaluate how quickly the series of eigenfunctions can be truncated. This analysis demonstrates extremely quick convergence to 99.5% of total variance for the 2nd order exponential (‘gaussian’) covariance function, while the opposite is true for the 1st order exponential covariance function. Due to these convergence characteristics, the Karhunen-Loéve method is most suitable for simulating smooth fields with ‘gaussian’ shaped covariance functions. Practical applications of Karhunen-Loéve simulations can be improved by spatial interpolation of the eigenfunctions. In this paper, we suggest interpolation by kriging and limits for reproduction of the predefined covariance functions are evaluated.  相似文献   

Structure and tectonics of convergent plate margins     

Aleš Špi?ák  Ond?ej ?adek  E.Robert Engdahl 《Physics of the Earth and Planetary Interiors》2004,141(4):241

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Influence of the zone of weakness on dip angle and shear heating of subducted slabs     

Martin Kuka?ka  Ctirad Matyska 《Physics of the Earth and Planetary Interiors》2004,141(4):243-252

We study the importance of the zones of weakness and the pattern of downgoing flow in steady-state models of subducting lithosphere, which interacts mechanically and thermally with the ambient mantle. The non-linear system of governing equations consists of (i) the momentum equation in stream function formulation and (ii) the steady-state heat transfer equation including conduction and advection of heat and dissipation. A finite element method has been applied to this system. We consider the viscosity to be a non-linear function of both the temperature and the stream function. In steady-state two-dimensional (2D) flow, the stream function isolines follow material trajectories. They are used to follow the top of the subducting slab, which because of its possible increase in water content, is assumed to have a lower viscosity. The zone of weakness has been thus obtained in the self-consistent fashion since the stream function as well as the temperature are the output from our modeling and no a priori assumptions about the shape of the bending lithosphere are taken into account. It was shown that several orders decrease of viscosity in the zone of weakness is required to obtain the dip angle of about 45°. If the decrease of viscosity is not sufficient enough, the subducted slab either sinks almost vertically or does not exhibit a plate-like behavior. We have also demonstrated that shear heating can unrealistically increase at the zone of weakness for fast subductions if decrease of viscosity is underestimated.  相似文献   

A Modeling Study of the Effects of Anomalous Snow Cover over the Tibetan Plateau upon the South Asian Summer Monsoon   总被引：1，自引：0，他引：1  

刘华强  孙照渤王举 闵锦忠 《大气科学进展》2004,21(6):964-975

The effect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SNINIR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo effect, which is compensated by weaker upward sensible heat flux associated with colder surface temperature, whereas the effects of snow melting and evaporation are relatively smaller.The anomalies of surface heat fluxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May.The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this influence is only obvious in early summer and almost disappears in later stages.  相似文献   

Oxygen isotope heterogeneity in chondrules from the Mokoia CV3 carbonaceous chondrite     

Rhian H Jones  Laurie A Leshin  Zachary D Sharp  Alan J Schilk 《Geochimica et cosmochimica acta》2004,68(16):3423-3438

We report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the Mokoia, oxidized CV3 chondrite. Bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination, and oxygen isotope ratios of individual grains, mostly olivine, were obtained in situ on polished mounts using secondary ion mass spectrometry (SIMS). Our results can be compared with data obtained previously for the oxidized CV3 chondrite, Allende. Bulk oxygen isotope ratios of Mokoia chondrules form an array on an oxygen three-isotope plot that is subparallel to, and slightly displaced from, the CCAM (carbonaceous chondrite anhydrous minerals) line. The best-fit line for all CV3 chondrite chondrules has a slope of 0.99, and is displaced significantly (by δ¹⁷O ∼ −2.5‰) from the Young and Russell slope-one line for unaltered calcium-aluminum-rich inclusion (CAI) minerals. Oxygen isotope ratios of many bulk CAIs also lie on the CV-chondrule line, which is the most relevant oxygen isotope array for most CV chondrite components. Bulk oxygen isotope ratios of most chondrules in Mokoia have δ¹⁸O values around 0‰, and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values. In general, it appears that chondrule mesostases have higher δ¹⁸O values than olivines in the same chondrules. Our bulk chondrule data spread to lower δ¹⁸O values than any ferromagnesian chondrules that have been measured previously. Two chondrules with the lowest bulk δ¹⁸O values (−7.5‰ and −11.7‰) contain olivine grains that display an extremely wide range of oxygen isotope ratios, down to δ¹⁷O, δ¹⁸O around -50‰ in one chondrule. In these chondrules, there are no apparent relict grains, and essentially no relationships between olivine compositions, which are homogeneous, and oxygen isotopic compositions of individual grains. Heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates, followed by solid-state chemical diffusion without concomitant oxygen equilibration. Alternatively, oxygen isotope exchange between an ¹⁶O-rich precursor and an ¹⁶O-poor gas may have taken place during chondrule formation, and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains. If this is the case, we can infer that the earliest nebular solids from which chondrules formed had δ¹⁷O and δ¹⁸O values around -50‰, similar to those observed in refractory inclusions.  相似文献   

The neoliberalization of ecosystem services: wetland mitigation banking and problems in environmental governance   总被引：1，自引：0，他引：1  

Morgan M. Robertson 《Geoforum》2004,35(3):361-373

Wetland mitigation banking is an American neoliberal environmental policy that has created a functioning market in `ecosystem services', commodities defined using the holistic measures of ecological science. The development of this market is discussed as a project of environmental governance, defined as the nation-state's regulation of ecological relations within its territory towards stabilizing capitalist relations of power and accumulation. I argue that the wetland banking industry serves as a bellwether that presages problems that other strategies of neoliberal environmental governance will experience. Ethnographic, economic and ecological data from the Chicago-area wetland banking industry inform a discussion of two major obstacles to neoliberal strategy: the problem of relying on ecological science to define the unit of trade, and the problem of aligning the somewhat independent relations of law, politics, markets and ecosystems across an array of spatial scales. Theoretical guidance is sought from recent work on `social natures' and from the Regulationist approach to institutional political economics.  相似文献