Polycyclic aromatic hydrocarbons in recent sediments from a subtropical estuary in Brazil     

Raphael Pietzsch  Sambasiva R. Patchineelam  João P.M. Torres 《Marine Chemistry》2010,118(1-2):56-66

The scope of this work was to evaluate the levels of polycyclic aromatic hydrocarbons (PAHs) and their possible sources in two shallow sediment cores from an estuarine area located in the south region of Brazil, the Guaratuba Bay. The estuary is encompassed by an Environmental Protection Area (EPA) of 1306 km², which is still considered to be pristine, despite recent urban growth. To assess levels of 14 selected PAHs in the sediments, among those listed as “priority pollutants” by the US Environmental Protection Agency, the cores were divided in several sections, followed by extraction, clean-up, fractionation and subsequent analysis using HPLC coupled to a fluorescence detector. Among the PAHs detected, phenanthrene and fluoranthene showed the highest concentrations. PAHs with more than four rings were usually present in low concentrations or were undetectable. To assist in the identification of possible sources, the ratios An/(An + Phe) and Flt/(Flt + Py) (anthracene to anthracene plus phenanthrene and fluoranthene to fluoranthene plus pyrene) and a PCA model were also used. Total concentrations of PAHs ranged between 1.5 and 3130 ng/g (mean 495) dry weight for the core collected in the inner part of the estuary, and between 78.5 and 3270 ng/g (mean 899) dry weight for the other core, collected in the outer part. Compared to values found in other studies in coastal zones along South American eastern margin, this area can be considered to range from low polluted to moderately polluted. From the data, it was also possible to conclude that there is predominance of petroleum sources, and essentially close to the more urbanised areas. Combustion sources have only minor contribution and are episodic, when compared to the latter.  相似文献   

Non‐synchronous deposition of North Atlantic Ash Zone II in Greenland ice cores,and North Atlantic and Norwegian Sea sediments: an example of complex glacial‐stage tephra transport     

Jo Brendryen  Haflidi Haflidason  Hans Petter Sejrup 《第四纪科学杂志》2011,26(7):739-745

Tephra provides regional chronostratigraphical marker horizons that can link different climate archives with highly needed accuracy and precision. The results presented in this work exemplify, however, that the intermittent storage of tephra in ice sheets and during its subsequent iceberg transport, especially during glacial stages, constitutes a potential source of serious error for the application of tephrochronology to Nordic Seas and North Atlantic sediment archives. The peak shard concentration of the rhyolitic component of the North Atlantic Ash Zone II (NAAZ‐II) tephra complex, often used to correlate marine and ice core records in Marine Isotope Stage (MIS) 3, is shown to lag the eruption event by ca. 100–400 years in some North Atlantic and Norwegian Sea cores. While still allowing for a correlation of archives on millennial timescales, this time delay in deposition is a major obstacle when addressing the lead–lag relationship on short timescales (years to centuries). A precise and accurate determination of lead–lag relationships between archives recording different parts of the climate system is crucial in order to test hypotheses about the processes leading to abrupt climate change and to evaluate results from climate models. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Sensitivity Analysis of Time Dependent Settlements in Hydraulic Fills     

João Flávio Vieira de Vasconcellos  Shailesh Singh  Nagaratnam Sivakugan 《Geotechnical and Geological Engineering》2010,28(4):351-360

This paper reports some numerical investigation carried out on hydraulic fills. A methodology based on the numerical solution of the governing equation via the finite volume method is introduced and tested, and proven to be very efficient. Typical dimensional performance curves are obtained and the influence of governing parameters is discussed. A sensitivity analysis is carried out in order to characterize the influence of the numerous parameters used to simulate the time dependent settlement in hydraulic fills on the outputs of the model.  相似文献   

Origin and evolution of a salty gypsum/anhydrite karst spring: the case of Poiano (Northern Apennines, Italy)     

Mauro Chiesi  Jo De Waele  Paolo Forti 《Hydrogeology Journal》2010,18(5):1111-1124

Poiano is the largest karst spring of the Emilia Romagna region (northern Italy). It drains an aquifer of unique properties composed of anhydrite with halite lenses at depth and gypsum at the surface (both with high NaCl content). Hydrogeological research has been undertaken using automatically recorded hourly data on temperature, electrical conductivity, and water level. Water feeding the Poiano spring is restricted within the gypsum/anhydrite outcrop between the Lucola, Sologno and Secchia rivers. Karstification in the Upper Secchia Valley only concerns the gypsum rocks mainly present along the border and in the shallower parts of the sulfate outcrop and does not appear to occur at depth. Data strongly support the hypothesis that the salt content in the spring water derives from active halokinetic movements. For the first time, the fundamental hydrogeological importance of the anhydrite part inside the sulfate rocks is demonstrated. If gypsum prevails over anhydrite the karst drainage network can extend deep into the rocks following a network of fractures and fissures. Instead, if in the deep parts of the aquifer anhydrite prevails over gypsum, the karst evolution cannot take place at depth and the structure of the underground drainage paths only follows near-surface paths in gypsum.  相似文献   

Formulation of a tropical town energy budget (t-TEB) scheme     

Hugo Abi Karam  Augusto José Pereira Filho  Valery Masson  Joël Noilhan  Edson Pereira Marques Filho 《Theoretical and Applied Climatology》2010,101(1-2):109-120

This work describes the tropical town energy budget (t-TEB) scheme addressed to simulate the diurnal occurrence of the urban heat island (UHI) as observed in the Metropolitan Area of Rio de Janeiro (MARJ; ?22° S; ?44° W) in Brazil. Reasoning about the tropical urban climate have guided the scheme implementation, starting from the original equations from Masson (Bound-Lay Meteorol 94:357–397, 2000). The modifications include (a) local scaling approaches for obtaining flux–gradient relationships in the roughness sub-layer, (b) the Monin-Obukhov similarity framework in the inertial sub-layer, (c) increasing aerodynamic conductance toward more unstable conditions, and (d) a modified urban subsurface drainage system to transfer the intercepted rainwater by roofs to the roads. Simulations along 2007 for the MARJ are obtained and compared with the climatology. The t-TEB simulation is consistent with the observations, suggesting that the timing and dynamics of the UHI in tropical cities could vary significantly from the familiar patterns observed in mid-latitude cities—with the peak heat island intensity occurring in the morning than at night. The simulations are suggesting that the thermal phase shift of this tropical diurnal UHI is a response of the surface energy budget to the large amount of solar radiation, intense evapotranspiration, and thermal response of the vegetated surfaces over a very humid soil layer.  相似文献   

Application of Fuzzy Sets to the Determination of Sunspot Areas     

Cidália C. Fonte  João Fernandes 《Solar physics》2009,260(1):21-41

The computation of sunspot areas is important for many applications in solar physics. Some uncertainty is, however, inherent to this determination, since there is uncertainty in defining the limits of sunspots, as well as their umbrae and penumbrae, particularly in high-resolution images where large variations in intensity are observed, mainly in the penumbrae and photosphere regions. In this paper a methodology based on the classical histogram method is presented that enables the generation of fuzzy sets that correspond to the umbrae and penumbrae of sunspots, as well as to the complete sunspots, which enable the representation of the uncertainty in their locations. The areas of the sunspots and of their umbrae and penumbrae are then obtained by computing the areas of the fuzzy sets used to represent them. Two operators are used: the Rosenfeld Area operator, which generates a real number for the area, and the Fuzzy Area operator, which generates a fuzzy number, providing more information about the uncertainty of the area. A comparison of the obtained results with the area values given by the classical cumulative histogram method is made and the differences analyzed.  相似文献   

Comparative study of Langmuir probe characteristics in different ionospheric conditions     

Joëlle Margot-Chaker  A.G. McNamara 《Planetary and Space Science》1984,32(11):1427-1437

This paper examines the role played by the high energy tail of the electron distribution function on Langmuir probe characteristics. A model is developed to derive the mean energy and the density of the hyperthermal electrons from probe characteristics for two ionospheric rocket flights involving different plasma conditions. The hyperthermal electrons are shown to influence the electron temperature measurement even if they constitute only a small fraction of the total electron concentration. The influence of the geomagnetic field, the collisions and the velocity of the vehicle on the probe data are also examined.  相似文献   

Distribution of mercury and methylmercury in deep-sea surficial sediments of the Mediterranean Sea     

Nives Ogrinc  Mathilde Monperrus  Jože Kotnik  Vesna Fajon  Klara Vidimova  David Amouroux  David Kocman  Emmanuel Tessier  Suzana Žižek  Milena Horvat 《Marine Chemistry》2007

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Finite-element computation of wave impact load due to a violent sloshing     

Jo Hyun Kyoung  Sa Young Hong  Jang Whan Kim  Kwang June Bai   《Ocean Engineering》2005,32(17-18):2020-2039

A nonlinear sloshing problem is numerically simulated. During excessive sloshing, the sloshing-induced impact load can cause a critical damage on the tank structure. Recently the problem becomes an important research topic in LNG (Liquefied Natural Gas) Tanker and FPSO (Floating Production Storage Offloading) design. In this study, the wave impact load on the structure is obtained numerically by imposing the exact nonlinear free surface conditions and compared with that predicted by Morison's formula. As a theoretical model, a three-dimensional free surface flow in a tank is formulated in the scope of potential flow theory with the exact nonlinear free-surface conditions. A finite-element method based on Hamilton's principle is employed as a numerical method. The problem is treated as an initial-value problem. The nonlinear problem is numerically solved through an iterative scheme at each time step.  相似文献   

Detailed Study of Three Contiguous Segments of the Mid-Atlantic Ridge,South of the Azores (37° N to 38°30′ N), Using Acoustic Imaging Coupled with Submersible Observations     

Ondréas  Hélène  Fouquet  Yves  Voisset  Michel  Radford-Knoery  Joël 《Marine Geophysical Researches》1997,19(3):231-255

Using a new tool of seafloor characterisation (sonar images from FARA-SIGMA cruise; Needham et al., 1992), coupled with submersible observations (DIVA1 cruise) we compare, at different scales of observation, three contiguous segments of the Mid-Atlantic Ridge, South of the Azores Triple Junction, between 37° N and 38°30 N.The two northernmost segments (38°20 N and Menez-Gwen) show unusual morphological features for the MAR; the rift valley is absent and the present-day magmatism is focused on shallow axial volcanoes. On the third segment (Lucky Strike), the morphology is the one usually found on the MAR. On the Menez-Gwen and 38°20 N segments, volcanic constructional activity can obliterate, during periods of high magmatic supply, the morphology inherited from tectonic activity. The dive results constrain the recent evolution of each segment and show that a temporal variability in volcanic dynamics exists. On the three segments, outcrops of eruptive lavas alternate with large areas of explosive volcanic ejecta. This cycle in volcanic activity is influenced by changes in water depth, both spatially (i.e. between segments) and temporally (i.e. for the same segment through time).Each segment has known a specific history in its accretionary processes with a succession of tectonic and volcanic predominance and changes in its volcanic phases between volcanic ejecta and effusive dynamics.The hydrothermal activity is focused at the central part of each segment and is controlled by the presence of fresh lava and major tectonic features.  相似文献