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101.
Assessing the shear-sheltering theory applied to low-level jets in the nocturnal stable boundary layer 总被引:1,自引:0,他引:1
Henrique F. Duarte Monique Y. Leclerc Gengsheng Zhang 《Theoretical and Applied Climatology》2012,110(3):359-371
This paper investigates the existence of shear sheltering on turbulence data over a quasi-ideal experimental site in Oklahoma, USA. Originally developed for engineering flows, the shear-sheltering theory is predicated upon the idea of low-level jets blocking large eddies aloft, preventing them from propagating to the surface. In this scenario, suppression of low-frequency turbulence energy and reduction of surface fluxes would be expected. Results from the Oklahoma experiment show instead an enhancement of surface turbulence intensity and of the relative contribution of large scales to total (co)variances for low-level jet cases with strong shear, thus suggesting the absence of shear sheltering at the site. The results underline the complexity of surface-atmosphere interactions in nocturnal stable conditions. Atmospheric modeling of exchange using various scenarios of surface characteristics, flow regimes, and low-level jet properties is suggested to further assess the potential applicability of the shear-sheltering theory to atmospheric flows. 相似文献
102.
103.
Blanco-Delgado Nuria Duarte Nunes Fernando Seco-Granados Gonzalo 《GPS Solutions》2017,21(3):1139-1147
GPS Solutions - The geometric dilution of precision (GDOP) is related to the satellite geometry. Thus far, research has focused on minimizing the GDOP by selecting a set of satellites that... 相似文献
104.
西秦岭凤太矿集区丝毛岭金矿床地质地球化学特征 总被引:1,自引:0,他引:1
西秦岭凤太矿集区丝毛岭金矿床位于八卦庙造山型金矿床西侧5km左右,是一个新探明的剪切带型金矿。其成矿作用过程可分为早期石英-绢云母-硫化物阶段、中期多金属-硫化物阶段和晚期碳酸盐阶段。对早、中期的石英流体包裹体测试结果表明,丝毛岭金矿床成矿流体以富CO2、中温、低盐度为特征,总体上属于中温低盐度CO2-H2O体系,流体包裹体类型的多样性是流体不混溶性的产物。从早阶段到主成矿阶段成矿流体的温度、压力和盐度均有降低,硫逸度增高,有利于金的沉淀富集。H、O、S、C同位素研究结果,以及与八卦庙金矿床的对比分析表明,二者的成矿流体具有相似性和同源性,都是以深部来源为主的多源流体。由于丝毛岭金矿床产出的层位高于八卦庙金矿床,其成矿环境相对开放。 相似文献
105.
106.
Ana L.Duarte Kátia DaBoit Marcos L.S.Oliveira Elba C.Teixeira Ismael L.Schneider Luis F.O.Silva 《地学前缘(英文版)》2019,10(3):927-939
In Brazil, intense coal exploitation activities have led to environmental deterioration, including soil mortification, water contamination, loss of ecosystem, and atmospheric contamination. In addition,considerable quantities of sulfur-rich residues are left behind in the mining area; these residues pose grave environmental issues as they undergo sulfide oxidation reactions. When sulfur oxides come in contact with water, extreme acid leachate is produced with great proportions of sulfate, and hazardous elements(HEs), which are identified as coal drainage(CMD). CMD is an environmental pollution challenge, particularly in countries with historic or active coal mines. To prevent CMD formation or its migration, the source must be controlled; however, this may not be feasible at many locations. In such scenarios, the mine water should be collected, treated, and discharged. In this study, data from 2005 to2010 was gathered on the geochemistry of 11 CMD discharges from ten different mines. There are several concerns and questions on the formation of nanominerals in mine acid drainage and on their reactions and interfaces. The detailed mineralogical and geochemical data presented in this paper were derived from previous studies on the coal mine areas in Brazil. Oxyhydroxides, sulfates, and nanoparticles in these areas possibly go through structural transformations depending on their size and formation conditions. The geochemistry of Fe-precipitates(such as jarosite, goethite, and hematite) existent in the CMD-generating coal areas and those that could be considered as a potential source of hazardous elements(HEs)(e.g., Cr) were also studied because these precipitates are relatively stable in extremely low pH conditions. To simplify and improve poorly ordered iron, strontium, and aluminum phase characterization, field emission scanning electron microscopy(FE-SEM), high-resolution transmission electron microscopy(HR-TEM), micro-Raman spectroscopy, and X-ray diffraction(XRD) and sequential extraction(SE) studies were executed on a set CMD samples from the Brazilian mines. This study aimed to investigate the role of both nanomineral and amorphous phase distribution throughout the reactive coal cleaning rejects profile and HEs removal from the water mine to provide holistic insights on the ecological risks posed by HEs, nanominerals, amorphous phases, and to assess sediments in complex environments such as estuaries. 相似文献
107.
Iris E. Hendriks Miguel Cabanellas-Reboredo Tjeerd J. Bouma Salud Deudero Carlos M. Duarte 《Estuaries and Coasts》2011,34(1):60-67
We assess the sheltering effect of Posidonia oceanica meadows on drag forces exerted on shells of the fan mussel Pinna nobilis. We examine a range of shell sizes under four unidirectional flow speeds (0.05–0.34 m s−1) and two oscillating regimes. Three meadow densities are evaluated and a control without vegetation. We found that the attenuating
effect of the meadow on drag forces experienced by bivalves is determined by the form of the hydrodynamic energy, e.g., as
unidirectional flow or wave action. In tidal currents, the meadow protects most sizes of bivalves, with a higher efficiency
for dense meadows, while in wave dominant zones the meadow reduces drag forces for bivalves with shell areas below a threshold
of 0.019 m2, whereas larger animals experience increased drag forces within the meadow independent of meadow density. Reduction of shoot
density in seagrass meadows might therefore not affect the effectiveness of the canopy to reduce drag forces on associated
species like the fan mussel in wave-dominated areas while increased storm frequency could result into losses of larger individuals
during periods of high wave action. 相似文献
108.
HSU Weibiao 《《地质学报》英文版》2004,78(5)
Coupled with a petrographical study, I carried out an ion probe study of rare earth element microdistributions in mineral phases of silicate inclusions from the Colomera ⅡE iron meteorite. Most mineral grains have homogeneous REEs, but show considerable inter-grain variations by a factor of 2 to 100. The whole rock REE abundances for Colomera, estimated by combining REE data with modal abundances, are relatively LREE-enriched with REEs of -10'CI, which suggest that Colomera silicates were highly differentiated and might represent a low degree partial melt (-10%) of a chondritic source. REE geochemistry of Colomera silicate inclusions points to an origin that involves differentiation, dynamic mixing, remelting, reduction, recrystallization, and subsequent rapid cooling near the surface of a planetary body. 相似文献
109.
Eduardo Duarte Marques Emmanoel V. Silva-Filho Giovana V. C. Souza Olga Venimar O. Gomes 《Environmental Earth Sciences》2016,75(24):1498
The São João Drainage Basin is a very important and strategic waterbody located in the Lagos Region, Rio de Janeiro State, one of the most popular tourist regions of Brazil. However, the fast economic and subsequent population growth in that region has created untreated wastes from several anthropogenic activities, which include the trace metals disposal into the surface waterbody. This study aims to relate the major ions and trace metals behavior during a 1-year sampling campaign and to provide information about the sources of chemical constituents and the factors that control their concentrations in the three main fluvial compartments of the drainage basin, including the Juturnaíba Reservoir which has a crucial role for water supply in the Lagos Region. The chemical data reveal that rainfall is the main factor responsible for the physicochemical parameters and the water dissolved constituent’s variations. The geological and anthropogenic factors which are the main sources of water constituents were assessed by the Inorganic Chemical Index. Those data corroborate the great influence of rainfall and reveal the importance of anthropogenic sources of chemical constituents in some parts of the Juturnaíba Reservoir. The geochemical modeling suggests that hydrolysis reactions are primarily responsible for the trace metals availability in the three fluvial compartments in both dry and wet seasons, followed by carbonate and sulfate complexation. 相似文献
110.
B.?OlesenEmail author N.?Marba C.?M.?Duarte R.?S.?Savela M.?D.?Fortes 《Estuaries and Coasts》2004,27(5):770-780
Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold
in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m2 gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate
the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively,
recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured
successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence
of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors
to the overall 450 m2 increase in vegetation cover through fast lateral extension (144±6 cm yr−1) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude
that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization
potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances
within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed
dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows. 相似文献