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排序方式: 共有435条查询结果,搜索用时 15 毫秒
281.
282.
M. Isinibilir L. Svetlichny E. Hubareva I.N. Yilmaz F. Ustun G. Belmonte B. Toklu-Alicli 《Journal of Marine Systems》2011,84(1-2):18-27
During 2005–2008 species composition, abundance patterns, natural mortality rates and salinity effects on zooplankton were studied in the Bosphorus regions of the Black and Marmara Seas. The tendencies to diminish for abundance and biomass of the Black Sea originated zooplankton species and to increase for the proportion of their carcasses in the direction from the Black Sea toward the Marmara Sea were found. The mortality in the Black Sea species increased with depth in the Marmara Sea. The contribution of organic matter of carcasses of the Black Sea originated organisms to bacterial processes in the deep strata of the Marmara Sea was estimated. Different salinity and temperature regimes restrict mutual penetration of the species in these seas. 相似文献
283.
K. Falk C. Hjort C. Andreasen K. D. Christensen M. Elander M. Ericson K. Kampp R. M. Kristensen N. Mbjerg S. Mller J. M. Weslawski 《Journal of Marine Systems》1997,10(1-4)
A small seabird community depends on the resources of the Northeast Water (NEW) polynya. In spring, at least 1000 King Eiders and 2500 Common Eiders form pre-breeding congregations at Ob Bank before dispersing in mid June to breeding areas. The most abundant species is the Fulmar, which breeds in six colonies with a total of 2550 “apparently occupied sites”, corresponding to approx. 1475 active pairs in 1993. Kittiwakes occupied almost 900 sites at Mallemukfjeld, with an estimated 733 breeding pairs. The entire NEW area probably holds 400–500 pairs of Ivory Gulls, and about 500 individuals were associated with a colony on Henrik Krøyer Holme; this is one of the world's largest known colonies. Sabine's Gulls breed at the same islands and on Kilen (approx. 50 pairs in each place). Small colonies (total less than 1000 birds) of Arctic Terns are distributed along the edge of the polynya, with the largest colony of about 100 pairs on Henrik Krøyer Holme. The Black Guillemot is the only breeding auk species (< 20 pairs) in the area. Small numbers of Red Phalaropes were observed in the polynya in 1992 and 1993, and the species may have bred at Henrik Krøyer Holme in 1993; the polynya area may also serve as a staging area for transpolar migrants. In late summer a few hundreds of Ross's Gull—non-breeding adults and immatures—show up in and around the polynya, and in recent years a few cases of breeding have also been recorded. The relatively small seabird populations are evidence of a generally low carrying capacity of the polynya area.Apart from the benthic foraging eiders and the Black Guillemot, the seabird community of NEW consists of surface feeders—Fulmars and gulls—dependent on small fish and zooplankton. During their stay in the NEW area, the five most abundant surface feeders will annually consume approximately 243,000 kg (wet weight) of food, of which the Fulmars alone take 67%. Food demand in relation to area of open water in the polynya is highest in spring (approx. 0.2 kg/km2), which is 相似文献
284.
The paper presents an outline of the advanced theory of thin-walled girders. The improvement includes shear influence on torsion as an extension of shear influence on bending. The analogy between bending and torsion is recognized and pointed out throughout the paper. Complete differential equations of coupled flexural and torsional vibrations for a prismatic girder are derived. In addition, the 8 d.o.f. beam finite element, utilizing the energy approach, is constituted with stiffness and mass matrices, and load vectors. The paper describes determining of geometrical properties of multi-cell open cross-sections by employing the strip element method. Numerical procedures for vibration analyses are outlined. Furthermore, dry natural vibrations of a VLCS (Very Large Container Ship) are analysed by 1D FEM model as a prerogative for hydroelastic analyses of these relatively flexible vessels. Influence of transverse bulkheads is taken into account by increasing torsional stiffness of the ship hull proportionally to their deformation energies. Validation of 1D FEM model is checked by correlation analysis with the vibration response of the fine 3D FEM model. 相似文献
285.
Swimming for survival: A role of phytoplankton motility in a stratified turbulent environment 总被引:2,自引:0,他引:2
We investigate a role for vertical migration in stratified coastal water, where the swimming speed is generally significantly less than the typical turbulent fluctuations in a tidally-mixed bottom layer. In our modelling approach we use a k- turbulence model to describe the physical forcing, a Lagrangian random walk model to describe the vertical displacement of individual cells in response to turbulence and due to cell motility, and a phytoplankton growth model to direct the swimming behaviour of the phytoplankton according to their light and nutrient requirements. The model results show how the cells form a stable subsurface chlorophyll maximum (SCM) at the base of the thermocline where episodic tidal turbulence causes erosion of part of the SCM biomass into the bottom mixed layer (BML). We then focus on the question of whether an ability to swim (weakly, compared to typical bottom layer turbulent intensities) provides any advantage by allowing return to the SCM. Our results show that tidal turbulence in the BML helps both motile and neutrally-buoyant cells by periodically pushing them into the base of the thermocline. Motile cells then have the advantage that they can swim further into the thermocline towards higher light which also reduces the likelihood of being re-mixed back into the BML. 相似文献
286.
Late-Quaternary changes in productivity of the Southern Ocean 总被引:1,自引:0,他引:1
R.F. Anderson N. Kumar R.A. Mortlock P.N. Froelich P. Kubik B. Dittrich-Hannen M. Suter 《Journal of Marine Systems》1998,17(1-4)
Paleoceanographic records based on new proxies of export production have been constructed for the South Atlantic sector of the Southern Ocean. A radionuclide-ratio proxy of particle flux (10Be/230Th) and the accumulation rate of authigenic uranium, which responds to the flux of organic carbon to the sea bed, both indicate a dramatic increase, compared to the present, in the export production of the Subantarctic zone (approximately the region between the present-day positions of the Subtropical Convergence and the Antarctic Polar Front) during glacial periods. If the South Atlantic is representative of the entire Southern Ocean, then export production in the Southern Ocean during the Last Glacial Maximum was substantially greater than at present. Previous studies, focusing on the burial of biogenic opal, failed to recognize the glacial increase in export production of the Southern Ocean because of a strong non-linearity between accumulation rates of opal and of organic carbon. 相似文献
287.
Dimitrios V. Lyridis Nikolaos P. Ventikos Panayotis G. Zacharioudakis Konstantinos Dilzas Harilaos N. Psaraftis 《WMU Journal of Maritime Affairs》2005,4(1):33-55
This paper proposes a tool to estimate crew composition based on safety/operational and financial requirements. As there is
a tendency of ship owners to implement improved technologies on board their vessels, there is no systematic way to predict
their potential effect on crew size and composition (typically determined by flag state authorities on a case-to-case basis)
nor on the type and complexity of on board duties new technologies might dictate. The main aim of this paper is to develop
a tool to assist in determining crew composition, by taking into account both administration’s and the ship owner’s point
of view. Based on data collected from ship owners, a data mining technique is implemented in order to form a generalized framework
that estimates crew composition as a function of ship type, size, and degree of automation. The agreement of model predictions
with records from specific (vessel) cases is very good in terms of safety (for operations such as watchkeeping, mooring/unmooring,
loading/unloading). The specific intended use of this tool is to help a ship owner decide whether it is cost-beneficial to
retrofit a conventional vessel with advanced technologies that would potentially entail a reduced crew (probably dealing with
different and more complex on board duties). Its main benefits are that it can be used to estimate crew composition before
any vessel construction or upgrade has actually taken place and that it allows crew composition to be easily adapted to the
technological evolution of ship systems even at their current rapid pace. 相似文献
288.
This paper presents an improved, significantly more efficient formulation of an existing model for bulk cargo or semi-bulk cargo ship scheduling problems with a single loading port. The original model, published by Ronen in 1986, was formulated as a non-linear, mixed integer program. In this work, the authors were able to re-formulate it into a linear one, by eliminating all the non-linearities of the original model. In addition, this model has far fewer integer variables than the original one. A numerical example has been given to illustrate the elimination of non-linearities and how 40 integer variables, in the original model, are reduced to just eight. This example also shows that this model is better at finding exact optimal solutions than the original one. It is also worth observing that the resulting model is a generalization of the 'capacitated facility location problem'. 相似文献
289.
290.