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排序方式: 共有843条查询结果,搜索用时 15 毫秒
71.
Harald Geiger Ian Barnes Karl H. Becker Birger Bohn Theo Brauers Birgit Donner Hans-Peter Dorn Manfred Elend Carlos M. Freitas Dinis Dirk Grossmann Heinz Hass Holger Hein Axel Hoffmann Lars Hoppe Frank Hülsemann Dieter Kley Björn Klotz Hans G. Libuda Tobias Maurer Djuro Mihelcic Geert K. Moortgat Romeo Olariu Peter Neeb Dirk Poppe Lars Ruppert Claudia G. Sauer Oleg Shestakov Holger Somnitz William R. Stockwell Lars P. Thüner Andreas Wahner Peter Wiesen Friedhelm Zabel Reinhard Zellner Cornelius Zetzsch 《Journal of Atmospheric Chemistry》2002,42(1):323-357
Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere. 相似文献
72.
Stefan Becker Marco Gemmer Tong Jiang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(6):435-444
Precipitation trends in the Yangtze River catchment (PR China) have been analyzed for the past 50 years by applying the Mann-Kendall trend test and geospatial analyses. Monthly precipitation trends of 36 stations have been calculated. Significant positive trends at many stations can be observed for the summer months, which naturally show precipitation maxima. They were preceded and/or followed by negative trends. This observation points towards a concentration of summer precipitation within a shorter period of time. The analysis of a second data set on a gridded basis with 0.5° resolution reveals trends with distinct spatial patterns. The combination of classic trend tests and spatially interpolated precipitation data sets allows the spatiotemporal visualization of detected trends. Months with positive trends emphasize the aggravation of severe situation in a region, which is particularly prone to flood disasters during summer. Reasons for the observed trends were found in variations in the meridional wind pattern at the 850 hPa level, which account for an increased transport of warm moist air to the Yangtze River catchment during the summer months. 相似文献
73.
Stress Sensitivity of Seismic and Electric Rock Properties of the Upper Continental Crust at the KTB
We test the hypothesis that the general trend of P-wave and S-wave sonic log velocities and resistivity with depth in the pilot hole of the KTB site Germany, can be explained by the progressive
closure of the compliant porosity with increasingly effective pressure. We introduce a quantity θc characterizing the stress sensitivity of the mentioned properties. An analysis of the downhole measurements showed that estimates
of the quantitiy θc for seismic velocities and electrical formation factor of the in situ formation coincide. Moreover, this quantity is 3.5 to 4.5 times larger than the averaged stress sensitivity obtained from
core samples. We conclude that the hypothesis mentioned above is consistent with both data sets. Moreover, since θc corresponds approximately to the inverse of the effective crack aspect ratio, larger in situ estimates of θc might reflect the influence of fractures and faults on the stress sensitivity of the crystalline formation in contrast to
the stress sensitivity of the nearly intact core samples. Finally, because the stress sensitivity is directly related to the
elastic nonlinearity we conclude that the elastic nonlinearity (i.e., deviation from linear stress-strain relationship i.e.,
Hooke's law) of the KTB rocks is significantly larger in situ than in the laboratory. 相似文献
74.
Using paleoclimate proxy-data to select optimal realisations in an ensemble of simulations of the climate of the past millennium 总被引:1,自引:0,他引:1
Hugues Goosse Hans Renssen Axel Timmermann Raymond S. Bradley Michael E. Mann 《Climate Dynamics》2006,27(2-3):165-184
We present and describe in detail the advantages and limitations of a technique that combines in an optimal way model results and proxy-data time series in order to obtain states of the climate system consistent with model physics, reconstruction of past radiative forcing and proxy records. To achieve this goal, we select among an ensemble of simulations covering the last millennium performed with a low-resolution 3-D climate model the ones that minimise a cost function. This cost function measures the misfit between model results and proxy records. In the framework of the tests performed here, an ensemble of 30 to 40 simulations appears sufficient to reach reasonable correlations between model results and reconstructions, in configurations for which a small amount of data is available as well as in data-rich areas. Preliminary applications of the technique show that it can be used to provide reconstructions of past large-scale temperature changes, complementary to the ones obtained by statistical methods. Furthermore, as model results include a representation of atmospheric and oceanic circulations, it can be used to provide insights into some amplification mechanisms responsible for past temperature changes. On the other hand, if the number of proxy records is too low, it could not be used to provide reconstructions of past changes at a regional scale. 相似文献
75.
Axel Kleidon 《Climatic change》2007,85(3-4):259-266
In his critique of Kleidon (Clim Change 66:271–319, 2004), Volk (Clim Change 85:3–4, 2007) concludes that maximum entropy production (MEP) has no great relevance for biological evolution and the time history of
life on Earth. I think that most of his points are not justified but rather reflect (a) a lack of appreciation of the central
importance of entropy production as the “universal currency” that measures what keeps systems working, including the biosphere,
(b) a misunderstanding of how biotic activity is embedded in the global entropy budget, and (c) a lack of distinction between
optimal environmental conditions that maximize productivity and result from environmental tradeoffs versus optimal function
of organisms to some internal tradeoffs. The examples that he uses to support his conclusions show flaws in that these mostly
discuss single environmental effects and immediate system responses. Optimal environmental conditions, however, requires at
least two effects that result in a trade-off, so it is not surprising that his examples seem to contradict optimality and
MEP. And the immediate response of a system to change can be very different than the response in steady state, for which MEP
applies. This is specifically important to be considered in the context of the “cheater” problem. In summary, I do not think
that Volk makes convincing arguments that contradict MEP, although I certainly agree that there is a lot more work to be done
to fully recognize the great importance that thermodynamics and MEP play in shaping the Earth’s biosphere and its evolutionary
history. 相似文献
76.
Economic transition in central and eastern Europe (CEE) has had a particularly strong impact on industrial cities and regions. Following their economic collapse, most of them are now confronted with serious problems such as high unemployment and vast ecological damage. The paper presents findings from a pan European research project that investigated the problems of these cities and regions as well as the strategies being adopted to cope with structural change. It examines the differences in approaches and addresses the question whether existing EU policy is suitable for supporting the redevelopment of old industrial cities and regions in CEE countries. The paper concludes with recommendations for future directions in policy making. 相似文献
77.
Axel Müller 《Geology Today》2007,23(3):114-120
Rapakivi granites, especially the famous rapakivis from southern Finland, are some of the most attractive building and decorative stones, used world-wide because of their striking textures and beautiful colours. But rapakivi granites are more than just building material, they have also been studied scientifically for over 100 years to try to explain the formation of their plagioclase-mantled alkali feldspar ovoids, the rapakivi feldspars which are responsible for the unique texture of the rock. Despite all the work which has been done on them, the formation of this distinctive texture is still not fully understood. Rapakivi granite complexes are not just a 'pretty face', they are also associated with important tin deposits in Rondônia and Amazonas in Brazil. 相似文献
78.
Timur Ustaomer Petek Ayda Ustaömer Alastair H. F. Robertson Axel Gerdes 《International Geology Review》2020,62(9):1159-1186
ABSTRACT Zircons from Carboniferous sandstones (three samples) and Mid-Late Triassic sandstones (four samples) from the Tauride and Anatolide continental units were analysed for U-Pb-Hf isotopes. For comparison, zircons were also analysed from Carboniferous granites of the Afyon Zone, Anatolides (three samples). A NE African/Arabian source is inferred for both the Carboniferous sandstones of the Taurides (Alada?) and the Anatolides (Konya Complex). In contrast, the Carboniferous Karaburun Melange is characterised by a NW African provenance. A prominent Devonian population occurs in the Carboniferous Karaburun Melange, characterised by mainly positive εHf(t) values that differ significantly from those of the Devonian granites of the Sakarya continental crustal unit (Pontides). Middle-Late Triassic Tauride sandstones include minor Palaeozoic and Early Mesozoic zircons. In contrast, Devonian and Carboniferous zircons are relatively abundant in Late Triassic sandstones of the Karaburun Peninsula. The Hf isotopic compositions of 25 Carboniferous-aged zircons from three samples of Mid-Late Triassic sandstone and one of Late Carboniferous age (one sample) overlap with the εHf(t) values of Carboniferous arc-type granites in the Anatolides. Taking account of the available U-Pb and Lu-Hf isotopic data from comparative crustal units, the Devonian zircon populations from the melanges in the Karaburun Peninsula and the Konya Complex are inferred to have a westerly source (e.g. granitic rocks of Aegean region or central Europe). A tectonic model is proposed in which Palaeozoic Tethys sutured during the late Carboniferous in the west (Aegean region westwards), leaving an eastward-widening oceanic gulf in which sandstone turbidites accumulated, including Devonian zircons. 相似文献
79.
A Discussion of IGS Solutions and Their Impact on Geodetic and Geophysical Applications 总被引:1,自引:0,他引:1
The International Association of Geodesy officially established the International GPS Service (IGS) on Janaury 1, 1994. Its
prime objective is to provide support and a rerefence system for a wide variety of scientific and practical applications involving
GPS. To fulfill its role the IGS also generates, in addition to its fundamental products (orbital/staion positions and consistent
Earth orientation parameters), additional reference-system products providing the necessary infrastructure, standards, and
means of calibrations for timing and various atmospheric applications of GPS. The generation and efficient application of
IGS products and their impact on a number of positioning and atmospheric applications, including low earth orbit satellites,
is reviewed and discussed. @ 1998 John Wiley & Sons, Inc. 相似文献
80.