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491.
The aim of this work was to study seasonal variation of histopathological and histochemical markers in blue mussels (Mytilus edulis L.) exposed to pyrogenic PAH contaminants. Mussels were collected in January, June, September and October from a sampling site in the vicinity of the discharge from an aluminium smelter and from a clean reference site. Histopathological analysis was carried out on the digestive gland (DG) and the gonads, lipofuscin and neutral lipids were analysed in the DG. Clear responses in lipofuscin and neutral lipids were detected in the DG of mussels collected from the polluted site at some sampling times. Moreover, these mussels presented atrophy in digestive tubules and haemocytic aggregates in the gonad and DG. However, in all parameters studied, the magnitude of the response showed clear seasonal variation. 相似文献
492.
Gerasimos K. Politis 《Ocean Engineering》2011,38(4):699-711
We solve the problem of unsteady potential flow around a system of arbitrarily moving rigid or flexible, lifting or non-lifting bodies, in an infinite fluid free of distributed vorticity. For the solution we use a time stepping algorithm and a potential based formulation of the corresponding free BVP. Nonlinear free shear layer dynamics are included in our modeling. This is a major innovation in treating complex unsteady propulsion problems since no simplifying assumptions (like that of a helicoidal wake) are used regarding the wake model. Bilinear quadrilateral elements are used to describe body and shear layer geometry at each time t. Three types of Kutta conditions can be alternatively applied for the determination of the shed vorticity from lifting bodies. The theoretical and numerical aspects of the method are presented followed by a number of applications, elucidating the qualitative and quantitative physical characteristics of a number of complex unsteady propulsion problems. 相似文献
493.
494.
In the long-wave approximation, we perform the numerical analysis of the plane problem of runup of waves of various shapes
on a sloping beach. We study transformations of the shape of waves flooding the beach and in the course of their subsequent
rundown. The dependence of maximum elevations and lowerings of the sea level on the parameters of the waves approaching the
beach, the depth of the shelf, and the slope of the bottom are investigated. It is shown that the shape of waves affects the
amplitude characteristics of oscillations of the coastline. The heights of the vertical runup of waves incident on a sloping
beach can be several times higher than the amplitude of waves entering the shelf zone. 相似文献
495.
Three different barge sizes were tested in uniform current in a tank of limited width. One of the barges was tested with and without bilge keels. Tests were conducted in both deep and shallow water. The barges were placed broadside to the current flow and the lateral forces on the barges were measured. The effect of the tank walls on these forces is clearly shown. 相似文献
496.
Major variations in type and rate of tectonic movement in the southwestern margin of the Ulleung Basin coincide in time with
changes in stratal patterns at succession boundaries, suggesting that the effect of tectonism was dominant for the development
of sequence architecture. During the back-arc opening (16–12 Ma), the rise of relative sea level and the high rate of sediment
supply gave rise to sequences with sigmoid progradational patterns. During the back-arc closing (12–6.5 Ma), fall- and rise-dominated
relative sea-level fluctuations resulted in sequences with varying stratal patterns depending upon changes in deposition rate.
The rise-dominated relative sea level has been prevalent during the later stage (6.5 Ma–Present) with low sedimentation rate.
Received: 16 January 1996 / Revision received: 7 February 1997 相似文献
497.
Geoacoustic and physical properties of carbonate sediments of the Lower Florida Keys 总被引:4,自引:0,他引:4
Near-surface sediment geoacoustic and physical properties were measured from a variety of unconsolidated carbonate sediments
in the Lower Florida Keys. Surficial values of compressional and shear speed correlate with sediment physical properties and
near-surface acoustic reflectivity. Highest speeds (shear 125–150 m s-1; compressional 1670–1725 m s-1) are from sandy sediments near Rebecca Shoal and lowest speeds (shear 40–65 m s-1; compressional 1520–1570 m s-1) are found in soft, silty sediments which collect in sediment ponds in the Southeast Channel of the Dry Tortugas. High compressional
wave attenuation is attributed to scattering of acoustic waves from heterogeneity caused by accumulation of abundant shell
material and other impedance discontinuities rather than high intrinsic attenuation. Compared to siliciclastic sediments,
carbonate sediment shear wave speed is high for comparable values of sediment physical properties. Sediment fabric, rather
than changes due to the effects of biogeochemical processes, is responsible for these differences. 相似文献
498.
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