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Zhengtong Xie Peter R. Voke Paul Hayden Alan G. Robins 《Boundary-Layer Meteorology》2004,111(3):417-440
A family of wall models is proposed that exhibits moresatisfactory performance than previousmodels for the large-eddy simulation (LES) of the turbulentboundary layer over a rough surface.The time and horizontally averaged statistics such asmean vertical profiles of windvelocity, Reynolds stress, turbulent intensities, turbulentkinetic energy and alsospectra are compared with wind-tunnel experimental data.The purpose of the present study is to obtain simulatedturbulent flows that are comparable with wind-tunnelmeasurements for use as the wind environment for thenumerical prediction by LES of source dispersion in theneutral atmospheric boundary layer. 相似文献
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Jaye E. Cable Jonathan B. Martin Peter W. Swarzenski Mary K. Lindenberg Joel Steward 《Ground water》2004,42(7):1011-1020
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The changing nature of, and approaches to, UK coastal management at the start of the twenty-first century 总被引:2,自引:0,他引:2
Peter W French 《The Geographical journal》2004,170(2):116-125
As we enter the twenty-first century, effective coastal management will become more of a central issue for coastal users and governors alike. The new century sees the review of many of the UK's existing management plans, and the subsequent publication of revised versions. Some of these new editions will have to show changes from their predecessors because of natural processes of erosion and accretion, yet other changes will be because of human interference. In this, we mean the continued ignoring of previous management plan recommendations regarding new development and coastal usage. Coastal management needs to adapt and develop, yet along with this, increased education and awareness is also necessary to allow users to understand and appreciate what is being recommended in management plans. 相似文献
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Using microprobe laser-desorption, laser-ionization mass spectrometry (μL2MS), we measured the distributions of alkylated and unalkylated polycyclic aromatic hydrocarbons (PAHs) in the free organic material of 20 carbonaceous chondrites. These meteorites represent a variety of meteorite classes and alteration histories, including CI, CK, CM, CO, CR, CV, and Tagish Lake. This work provides information on free organic compounds that is complementary to studies of the structure and composition of meteoritic macromolecular content.For the nine CM2 meteorites analyzed, we observe that higher relative abundances of alkylated PAHs correlate with more intense aqueous activity. We attribute this correlation to the differences in solubility and volatility between unalkylated and alkylated PAHs. Naphthalene and its alkylation series are more susceptible to the effects of aqueous exposure than the less-soluble PAH phenanthrene and its alkylated derivatives. These observations are consistent with the possibility of chromatographic separations on the meteorite parent bodies. We identify six CM2 meteorites with similar PAH distributions that may represent the original, unaltered organic composition of the parent body.Increased metamorphic intensity reduces the abundance of all PAHs. The thermally metamorphosed CK chondrites had no detectable levels of typical meteoritic PAHs. This observation might be explained either by a loss of PAHs caused by volatilization or by a significantly different organic content of the CK parent body. 相似文献
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Friedrich Lucassen Peter Dulski Rainer Abart Gerhard Franz Dieter Rhede Rolf L. Romer 《Contributions to Mineralogy and Petrology》2010,160(2):279-295
Titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon. We investigated an amphibolite sample from the Tromsø eclogite facies terrain in Northern Norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite. Patchy compositional zoning of Al, Ti, and F in titanite relates to the presence of a fluid with variable Ti/Al and/or F during its growth. Laser ablation ICP–MS and electron microprobe data for high field strength elements (HFSE: Nb, Zr, Ta, and Hf) of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal (~8 mm) and a systematic decrease towards uniform HFSE contents in the large core. HFSE contents of smaller rutile grains (~0.5 mm) and rutile inclusions (<100 μm) in the titanite overgrowth are similar or higher than in the rims of large rutile crystals. Element profiles from the rim inward demonstrate that HFSE enrichment in rutile is controlled by diffusion. HFSE ratios in diffusion-altered rutile show systematic variations compared with the uniform core composition of the large rutile. Modelling of Zr and Nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid-dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems. Variations of HFSE contents in the newly formed titanite show no systematic spatial distribution. HFSE ratios in titanite and the rims of rutile are different, indicating different solid/fluid distribution coefficients in these minerals. Element fractionation by diffusion into the relict rutile and during fluid-mediated growth of new titanite could substantially change the HFSE budget of these minerals and could affect their use for geochemical tracing and other applications, such as Zr-based geothermobarometry. 相似文献
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Bradley D. Eyre Søren Rysgaard Tage Dalsgaard Peter Bondo Christensen 《Estuaries and Coasts》2002,25(6):1077-1087
Denitrification has been measured during the last few years using two different methods in particular: isotope pairing measured on a triple-collector isotopic ratio mass spectrometer and N2:Ar ratios measured on a membrane inlet mass spectrometer (MIMS). This study compares these two techniques in short-term batch experiments. Rates obtained using the original N2∶Ar method were up to 3 to 4 times higher than rates obtained using the isotope pairing technique due to O2 reacting with the N2 during MIMS analysis. Oxygen combines with N2 within the mass spectrometer ion source forming NO+ which reduces the N2 concentration. The decrease in N2 is least at lower O2 concentrations and since oxygen is typically consumed during incubations of sediment cores, the result is often a pseudo-increase in N2 concentration being interpreted as denitrification activity. The magnitude of this ocygen effect may be instrument specific. The reaction of O2 with N2 and the subsequent decrease in N2 was only partly correctly using an O2 correction curve for the relationship between N2 and O2 concentrations. The O2 corrected N2∶Ar denitrification rates were lower, but still did not match the isotope pairing rates and the variability between replicates was much higher. Using a copper reduction column heated to 600°C to remove all of the O2 from the sample before MIMS analysis resulted in comparable rates (slightly lower), and comparable variability between replicates, to the isotope pairing technique. The N2:Ar technique determines the net N2 production as the difference between N2 production by denitrification and N2 consumption by N-fixation, while N-fixation has little effect on the isotope pairing technique which determines a rate very close to the gross N2 production. When the two different techniques were applied on the same sediment, the small difference in rates obtained by the two methods seemed to reflect N-fixation as also supported from measurements of ethylene production in acetylene enriched sediment cores. The N2:Ar and isotope pairing techniques may be combined to provide simultaneous measurements of denitrification and N-fixation. Both techniques have several assumptions that must be met to achieve accurate rates; a number of tests are outlined that can be applied to demonstrate that these assumptions are being meet. 相似文献
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