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1.
Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents. 相似文献
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Ezio Caroli Natalia Auricchio Lorenzo Amati Yuriy Bezsmolnyy Carl Budtz-JøRgensen Rui M. Curado da Silva Filippo Frontera Alessandro Pisa Stefano Del Sordo John B. Stephen Giulio Ventura 《Experimental Astronomy》2005,20(1-3):341-351
The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1mm, an energy resolution of a few keV at 500keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy.
Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies. 相似文献
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S. Maaløe 《Mineralogy and Petrology》2003,77(1-2):1-24
Summary ?Partial melting of the mantle is polybaric which implies that the phase relations change during partial melting. In addition
to the pressure the composition of the melt depends on the melting mode. Various melting models have been suggested. Here
the basic phase relations of polybaric batch, percolative, and critical melting are considered, using a simple ternary system.
The percolative melts are in equilibrium with their residua, but differ somewhat in composition from those of batch melting.
Critical melting is a fractional type of melting where the residuum contain interstitial melt. The critical melts differ in
composition from batch melts. The linear trends of peridotites from ophiolites show that the extracted melts had nearly constant
compositions, and therefore were extracted within a small pressure interval. A comparison between the trends of mantle peridotite
and experimental batch melts suggests strongly that the melt extracted from the peridotites are in equilibrium with their
residua. This could suggest that either batch or percolative melting are relevant melting modes for the mantle. However, isotopic
disequilibria favor instead a critical mode of melting. This inconsistency can be avoided if the ascending melts are accumulated
within a source region and equilibrate with the residuum before the melt is extracted from the source region. The evidence
for equilibrium suggests that multisaturation of tholeiitic compositions in PT-diagrams is relevant for estimating pressure
and temperature of generation of primary tholeiitic magmas.
Received September 2, 2001; revised version accepted March 20, 2002 相似文献
6.
Bjrn Grieger 《Global and Planetary Change》2002,34(3-4)
To drive an atmospheric general circulation model (AGCM), land surface boundary conditions like albedo and morphological roughness, which depend on the vegetation type present, have to be prescribed. For the late Quaternary there are some data available, but they are still sparse. Here an artificial neural network approach to assimilate these paleovegetation data is investigated. In contrast to a biome model the relation between climatological parameters and vegetation type is not based on biological knowledge but estimated from the available vegetation data and the AGCM climatology at the corresponding locations. For a test application, a data set for the modern vegetation reduced to the amount of data available for the Holocene climate optimum (about 6000 years B.P.) is used. From this, the neural network is able to reconstruct the complete global vegetation with a kappa value of 0.56. The most pronounced errors occur in Australia and South America in areas corresponding to large data gaps. 相似文献
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The molecular fingerprints of the chemosynthesis based microbial communities at methane seeps tend to be extremely well preserved in authigenic carbonates. The key process at seeps is the anaerobic oxidation of methane (AOM), which is performed by consortia of methanotrophic archaea and sulphate reducing bacteria. Besides the occurrence of 13C depleted isoprenoids and n-alkyl chains derived from methanotrophic archaea and sulphate reducing bacteria, respectively, 13C depleted triterpenoids have been reported from a number of seep deposits. In order to evaluate the significance of these apparently non-AOM related molecular fossils, the biomarker inventories of one Campanian and two Miocene methane seep limestones are compared. These examples provide strong evidence that methane was not solely oxidized by an anaerobic process. Structural and carbon isotope data reveal that aerobic methanotrophy was common at some ancient methane seeps as well. The Miocene Marmorito limestone contains abundant 3β-methylated hopanoids (δ13C: −100‰). Most likely, 3β-methylated hopanepolyols, prevailing in aerobic methanotrophs, were the precursor lipids of these compounds. A series of isotopically depleted 4-methylated steranes (lanostanes; δ13C: −80‰ to −70‰) and similarly isotopically depleted 17β(H),21β(H)-32-hopanoic acid in the Miocene Pietralunga seep limestone also are derived probably from aerobic methanotrophs. Lanosterol, which is known to be produced by aerobic methanotrophs, is the most likely precursor of 4-methylated steranes. Less obvious is the origin of 8,14-secohexahydrobenzohopanes (δ13C: −110‰ to −107‰) in Late Cretaceous seep limestones. These hopanoids probably reflect early degradational products of precursor lipids locally produced by seep endemic aerobic methanotrophs. 相似文献
9.
Stephan Lowitzer Dan J. Wilson Björn Winkler Victor Milman Julian D. Gale 《Physics and Chemistry of Minerals》2008,35(3):129-135
Knowledge of the defect properties of Lunar and Mercurian minerals has recently become important, with the advent of models
which attempt to explain the formation of the thin exosphere of these celestial bodies. Here, we have calculated the formation
energies of sodium and oxygen vacancies in the mineral albite (NaAlSi3O8), as well as the Schottky defect energy for the removal of a Na2O unit. We have employed both the supercell and Mott–Littleton approaches, using Kohn–Sham density functional theory and classical
interatomic potential methods. As well as reporting the defect energies and structures, we comment upon the relative merits
of the methods used. 相似文献
10.
Erling K. Stenevik Webjrn Melle Eilif Gaard Astthor Gislason Cecilie T.. Broms Irina Prokopchuk Bjrnar Ellertsen 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2672
Egg production of Calanus finmarchicus was studied during joint basin-scale surveys in April–June 2003 in the Norwegian Sea. Surveys covered the whole Norwegian Sea and were conducted from Norwegian, Icelandic and Faroese research vessels. Stations were classified as being in pre-bloom, bloom or post-bloom phase according to levels of chlorophyll a and nitrate. Individual egg production rates and population egg production rates were calculated and compared between areas. Both individual egg production rates (eggs female−1 day−1) and population egg production rates (eggs m−2 day−1) were significantly higher in bloom areas compared with pre-bloom and post-bloom areas. However, when integrated over an estimated duration of the three phases, the time-integrated egg production (eggs m−2) in most years was highest in the pre-bloom phase, and this was explained by the longer duration of this phase compared with the two other phases. 相似文献