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991.
Agostino Tomasello Germana Di Maida Sebastiano Calvo Maria Pirrotta Marco Borra & Gabriele Procaccini 《Marine Ecology》2009,30(3):288-300
Atoll‐like structures of the endemic Mediterranean seagrass Posidonia oceanica were encountered in the innermost area of the Stagnone di Marsala, a semi‐enclosed coastal lagoon along the western coasts of Sicily. The area is characterized by limited water exchange with the open sea and by a marked seasonal variation of water salinity and temperature, reaching beyond the theoretical tolerance limits of the species. In the present study we determined the genetic composition of the atoll‐like structures, as well as the growth performance and flowering rate of these stands. We also assessed whether and to what extent the atoll‐like structures are genetically isolated from plants growing in meadows outside the lagoon. For this purpose we utilized 13 microsatellite markers to genotype single shoots sampled inside and outside the lagoon. Lepidochronological analyses were performed on the same shoots to determine the annual rhizome growth rate, the number of leaves and the inflorescences formed as an estimate of growth‐ and reproductive performance over the years. The innermost area of the lagoon showed a lower number of alleles, a lower percentage of polymorphic loci, a lower clonal diversity, but higher heterozygosis excess with respect to the other areas analysed. Spatial autocorrelation was here significant, up to slightly below 300 m. Shoots collected in the atolls exhibited a 25% lower vertical growth rate and 16% lower leaf formation in comparison to those in open‐sea meadows. No flowering events were recorded during 24 years of investigation, whereas inflorescences were observed frequently in meadows outside the lagoon. Results from Fst and factorial correspondence analysis confirmed the expected genetic isolation of the confined atolls with respect to the meadows outside the lagoon and revealed limited gene flow within the lagoon itself. Apparently, the enclosed system of the Stagnone lagoon is genetically isolated, with a possible selection of genotypes adapted to persistent stressful conditions, consistent with reduced growth and lack of flowering events. 相似文献
992.
Friedemann Baur Matias Di Benedetto Thomas Fuchs Carolyn Lampe Simone Sciamanna 《Marine and Petroleum Geology》2009
For the first time, a new approach to petroleum systems analysis is presented which allows full integration of tectonic and palinspastic restoration with three-dimensional (3D), PVT-controlled, multi-component, three-phase petroleum migration analysis through time. A systematic modeling study has been applied to a study area dominated by fold and thrust belts located in the Sub Andean orogeny near Tarija, Bolivia. The project has been performed with a special focus on the simulation technique and on the correct distribution of temperature, source-rock maturity and pressure development through time with reference to its input data. This is the first pilot project presenting a 3D numerical model in a compressional structural regime to which the basin modeling approach has been applied to explain the observed distribution of temperature, pressure, maturity and petroleum accumulations in general. 相似文献
993.
珠江口伶仃洋海域营养盐的历史变化及影响因素研究 总被引:2,自引:0,他引:2
根据2006年丰水期和枯水期对珠江口伶仃洋海域的调查资料,分析了该海域营养盐的现状,发现丰水期NO3-N和SiO3-Si含量呈自口门向外逐渐降低的变化,NO2-N和PO4-P高值区则集中在深圳附近海域,枯水期各项营养盐均呈自口门向外逐渐降低的变化。结合1990年、1998年、2001年3个年份的资料,分析了珠江口邻近海域5项营养盐(SiO3-Si,NO3-N,NO2-N,NH4-N和PO4-P)近20 a来的变化规律,并对其影响因素进行了探讨和分析。结果发现,NO3-N,NO2-N,NH4-N和PO4-P含量呈现显著上升趋势,DIN/DIP呈下降趋势。NO3-N和SiO3-Si含量丰水期显著高于枯水期,NO2-N和PO4-P则相反,径流携带作用是NO3-N和SiO3-Si的主要来源,而径流对NO2-N和PO4-P则起稀释作用。另外农业施肥的影响、围填海造成的海域面积缩小以及网箱养殖业饵料的不合理投放亦是造成珠江口伶仃洋海域DIN,DIP含量上升的因素。 相似文献
994.
V.L. Meccia C.G. Simionato M.E. Fiore E.E. D'Onofrio W.C. Dragani 《Estuarine, Coastal and Shelf Science》2009,85(2):327-343
A long term simulation of the barotropic circulation in the Río de la Plata estuary was performed with the aim of identifying the characteristic patterns of sea surface height (SSH) variability from synoptic to inter-annual time scales and their forcing mechanisms. Hamburg Shelf Ocean Model (HamSOM), forced by tides, monthly mean runoffs and 4-daily 10 m winds and surface atmospheric pressure from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis was run. The solution was analyzed for the period 1965–2004. Inter-annual variability accounts for almost 10% of the variance. The first EOF mode of SSH variability on this time scale is associated with a mean anomaly of approximately 0.25 m at the upper estuary forced by both runoff and winds, which seems to be strongly associated with the ENSO cycles. Other two modes, with periodicities around 2.5 and 10 years were also found. Even though they are linked to weaker SSH anomalies, they are consistent with inter-annual modes of wind variability reported by other authors. Those modes are important, particularly if they act in phase, because they can provide a background for stronger surges. In contrast with the salinity field, SSH variability on seasonal time scales accounts for a very small percentage of variance and it is the combination of an annual and a semi-annual signal forced by winds and runoff, respectively. Approximately 90% of the variance is due to wind driven variability on sub-annual time scales. The most significant SSH anomalies in this band are associated with cyclogenetic events in the atmosphere, occurring either over Uruguay or over the Patagonian Shelf, whereas the strengthening or weakening of the semi-permanent South Atlantic anticyclone displays a relatively smaller influence. In agreement with previous publications, the estuary's spatial patterns in response to short-scale wind variability seem to be determined by wind direction more than by wind speed. 相似文献
995.
996.
997.
通过对上海市全市两万多千米的电缆实施数据整合、处理与入库,建立并完善了不同类别电力管线数据整合、技术处理、作业细则、质量控制等一套数据建库的技术文件和实现方案. 相似文献
998.
Sedimentary characteristics of the Jurassic Zhiluo Formation and uranium deposits in Zhiluo-Diantou area,southern Ordos Basin 下载免费PDF全文
Wang Xiao-Peng Liu Kun-Peng Chen Hong-Bin Gong Bin-Li Yu Hong-Wei Gong Qi-Fu Han Di 《古地理学报》1999,22(2):295-308
Diantou uranium deposits and multiple uranium mineralization sites have been discovered in the sandstones in the lower member of the Jurassic Zhiluo Formation in the southern Ordos Basin. However, the study on the sedimentary facies of the Zhiluo Formation, which restricts the prospecting work of sandstone-type uranium deposits. Based on the outcrop measurements and drilling core cataloging, and combined with the geological drilling data of petroleum, coal, and nuclear industry, we have elaborated the sedimentary characteristics of the Zhiluo Formation in the Fuxian area. We have also combined uranium source, structure, post-alteration and other factors to explore the relationship between sedimentary faces and uranium metallogenic conditions in the study area. The study found that in the lower member of the Jurassic Zhiluo Formation, the thickness of the sand body is 30-65 m and sand ratio is 0.6-0.75. It is gravel and sandy braided river deposit. In the upper member of the Jurassic Zhiluo Formation, the thickness of the sand body is 10-38 m, and the sand ratio is 0.15-0.45 and is a meandering river deposit. The study area is located at the center of the lake basin and sedimentary facies is coastal shallow lacustrine in the upper member of the Jurassic Zhiluo Formation. Sedimentary environment, sedimentary facies, the intersection of braided river channels, sand body thickness, sediment particle size and mudstone interlayer play an important role in controlling uranium mineralization. The exploration of uranium deposits in the northern part of the deposit should focus on the intersection or bifurcation of the braided river channel in the lower part of the Zhiluo Formation. The charcoal- and pyrite-bearing sandstone of channel bar can be used as a prospecting indicator for uranium mineralization. 相似文献
999.
1 IntroductionItisnowwellacceptedthemagneticfieldinfilamentisnearlyhorizontalandthecomponentofthefieldalongthefilamentaxisisdominant (D啨moulin ,1 997) .Whenafilamentispresentinactiveregion ,thephotospherictransversefieldbeneathfilamentmostlyliealongthepolar… 相似文献
1000.
M. Guainazzi G. Matt L. A. Antonelli L. Bassani A. C. Fabian R. Maiolino A. Marconi F. Fiore K. Iwasawa L. Piro 《Monthly notices of the Royal Astronomical Society》1999,310(1):10-20
We present an X-ray spectroscopic study of the bright Compton-thick Seyfert 2 galaxies NGC 1068 and the Circinus Galaxy, performed with BeppoSAX . Matt et al. interpreted the spectrum above 4 keV as the superposition of Compton reflection and warm plasma scattering of the nuclear radiation. When this continuum is extrapolated downwards to 0.1 keV, further components arise. The NGC 1068 spectrum is rich in emission lines, mainly owing to K α transitions of He-like elements from oxygen to iron, plus a K α fluorescent line from neutral iron. If the ionized lines originate in the warm scatterer, its thermal and ionization structure must be complex. From the continuum and line properties, we estimate a column density, N warm , of the warm scatterer less than a few×1021 cm−2 . In the Circinus Galaxy, the absence of highly ionized iron is consistent with a scattering medium with U X ≲5 and N warm ∼ a few×1022 cm−2 . In both cases the neutral iron line is most naturally explained as fluorescence in the medium responsible for the Compton reflection continuum. In NGC 1068 an optically thin plasma emission with kT ≃500 eV and strongly sub-solar metallicity is required, while such a component is only marginal in the Circinus Galaxy. We tentatively identify this component as emission of diffuse hot gas in the nuclear starbursts. Possible causes for the metal depletion are discussed. 相似文献