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31.
A regularized version of the direct interaction approximation closure (RDIA) is compared with ensemble averaged direct numerical simulations (DNS) for decaying two-dimensional turbulence at large-scale Reynolds numbers ranging between low (≈?50) and high (≈?4000). The regularization localizes transfer by removing the interaction between large-scale and small-scale eddies depending on a specified cut-off ratio α. It thus eliminates spurious convection effects of small-scale eddies by large-scale eddies in the Eulerian direct interaction approximation (DIA) that causes the underestimation of small-scale kinetic energy by the DIA. Cumulant update versions of the RDIA closure that have comparable performance but are much more efficient computationally have also been analyzed. Both the closures and DNS use discrete wavenumber representations relevant to flows on a doubly periodic domain. This means that any differences between them are intrinsic and not partly due to using continuous wavenumber formulation for the closures. Comparisons between the regularized closures and DNS have focused on evolved kinetic energy and palinstrophy spectra and as well on enstrophy flux spectra and on the evolution of skewness which depends sensitively on small-scale differences. All of these diagnostics compare quite well when α = 6. And this is the case for runs started from each of three initial spectra, for the range of evolved large-scale Reynolds numbers ranging from ≈?50 to ≈?4000 and for regularized DIA closures with, and particularly without, cumulant update restarts. The performance of the RDIA compared with quasi-Lagrangian closure models is discussed. 相似文献
32.
Jorgen Klein 《GeoJournal》2002,56(3):191-199
The Madagascar central highlands with their red soils and erosion gullies are often held up as a frightening example of the
consequences of deforestation. They are also used as a model of how the entire island will look if so-called `forest unfriendly
activities' of local people continue. This insight is based on a narrative that describes the highlands as totally forested
by the time of human arrival and gradually deforested as a response to human activities. This paper questions the deforestation
narrative of Madagascar and points at alternative explanations for present day land cover. By the use of alternative sources
of information the paper presents a counter-narrative that sees the treeless rolling planes of Madagascar as a result of several
abiotic and biotic changes and not as the work of one single agent. The paper points at the political nature of the deforestation
narrative as an explanation for its hegemonic position. On a theoretical level the paper makes an attempt to investigate the
epistemological implication of a social constructivist approach to environmental discourses in Third World settings.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
33.
魏印心 《中国海洋湖沼学报》1998,16(3):256-266
rmDUCTIONEXtensiveinvestigaionsonthemphicaldistributionofsilica-scaledchrysoPhytesinChinahaVebeeninprogresssincel988.Kristiansen(l989,199o),Kristiansen&TOng(l988,l989a,l989bandl99l)andWei&Kristiansen(1994)rePOrtedtheirre-sultsofstUdiesonsilica-scaledchrysoPhyteshantheeastem,northeasern,western,southwsternandcentndPaItsofChina(includingllprovinces).kltogether6ltaxawererecoIded,mostofthembelongingtothegenusMallomonas.Al993tol994simultaneousstirveyofthephytoplankonandstUdyofthesilica-sc… 相似文献
34.
The paper presents a method for generating a new and efficient time-domain formulation of the equations of motion for a vessel with frequency-dependent hydrodynamic coefficients. Previous work on this topic has relied on the use of convolution terms, whereas in this work state-space models are used. This leads to a model formulation that is well suited for controller design and simulation. 相似文献
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37.
Jan Mangerud Sven Erik Lie Harald Furnes Inger Lise Kristiansen Leif Lømo 《Quaternary Research》1984,21(1):85-104
A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic. 相似文献
38.
Jorgen Lauridsen Mariluz Maté Sánchez Mickael Bech 《Journal of Geographical Systems》2010,12(2):175-188
The aim of the present study is to analyse the spatio-temporal dynamics underlying Spanish pharmaceutical expenditure increases.
We suggest alternative ways to resolve the problem of identifying exogenous and endogenous spatial spillover in a seemingly
unrelated regression framework, while parametric instability is captured using linear time trends in the coefficients. The
results highlight the need of considering these dynamic aspects in the pharmaceutical expenditure analysis. 相似文献
39.
The option of storing CO2 in subsea rock formations to mitigate future increases in atmospheric CO2 may induce problems for animals in the deep sea. In the present study the deep-sea bivalve Acesta excavata was subjected to environmental hypercapnia (pHSW 6.35, PCO2 = 33,000 μatm) corresponding to conditions reported from natural CO2 seeps. Effects on acid–base status and metabolic rate were related to time of exposure and subsequent recovery. During exposure there was an uncompensated drop in both hemolymph and intracellular pH. Intracellular pH returned to control values, while extracellular pH remained significantly lower during recovery. Intracellular non-bicarbonate buffering capacity of the posterior adductor muscle of hypercapnic animals was significantly lower than control values, but this was not the case for the remaining tissues analyzed. Oxygen consumption initially dropped by 60%, but then increased during the final stages of exposure, which may suggest a higher tolerance to hypercapnia than expected for a deep-living species. 相似文献
40.