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301.
三峡蓄水成库五年多来,长江海事部门面对库区通航环境不断变化的新挑战,心系库区百姓,凭着坚韧,永不满足,追求卓越的精神,开拓创新,大胆实践,多措并举,为库区通航撑起“安全伞”,便捷百姓出行,展出了良好的海事风貌。日前,本刊记者赴三峡库区对库区当前的通航状况进行了采访。 相似文献
302.
行政处罚是海事监管的重要的手段之一,它在有效震慑海事违法行为,维护水上安全秩序和防止船舶污染方面起着不可替代的重要作用。行政处罚案件的数量变化和违法行为种类的变化能够从一个侧面反映出某辖区、某时期的水上安全形势的基本态势,了解这个基本态势,可以有的放矢,科学地使用监管力量,对我们提高海事监管水平有着很大的促进作用。文中通过用数学方法、逻辑方法,对东港海事处辖区2008年上半年的行政处罚案例进行全面、系统、综合的定量、定性分析,以找出规律性和存在的问题,并采取科学合理的措施解决问题,找出管理重点和难点,提出管理建议,来达到提高海事管理水平和保障水上安全秩序的目的。 相似文献
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306.
The relevance of international transport costs on food prices: Endogenous and exogenous effects 总被引:1,自引:0,他引:1
The paper addresses the problem of transport costs and their influence on food prices for South American imports. While transport does not seem to be in the focus of existing analyses, its impact on food prices might be underestimated and even closely linked to the development of commonly mentioned drivers of food prices. Since transport price formation is a function of demand and supply, drivers of food prices are also expected to impact on transport prices. The authors argue that a number of relevant factors that drive transport costs - and in consequence food prices - can be influenced by policy makers. Based on empirical analysis, the authors explain the functioning of the determinants of transport costs in the segment of international shipping, trying to describe their exogenous and endogenous components. These results are discussed in reference to policy development in the region. 相似文献
307.
John H. Simpson J.A. Mattias Green Tom P. Rippeth Thomas R. Osborn W. Alex M. Nimmo-Smith 《Journal of Marine Systems》2009,77(4):428
We report on an intensive campaign in the summer of 2006 to observe turbulent energy dissipation in the vicinity of a tidal mixing front which separates well mixed and seasonally stratified regimes in the western Irish Sea. The rate of turbulent dissipation ε was observed on a section across the front by a combination of vertical profiles with the FLY dissipation profiler and horizontal profiles by shear sensors mounted on an AUV (Autosub). Mean flow conditions and stratification were obtained from a bed mounted ADCP and a vertical chain of thermistors on a mooring. During an Autosub mission of 60 h, the vehicle, moving at a speed of ~ 1.2 m s− 1, completed 10 useable frontal crossings between end points which were allowed to move with the mean flow. The results were combined with parallel measurements of the vertical profile of ε which were made using FLY for periods of up to 13 h at positions along the Autosub track. The two data sets, which show a satisfactory degree of consistency, were combined to elucidate the space–time variation of dissipation in the frontal zone. Using harmonic analysis, the spatial structure of dissipation was separated from the strong time dependent signal at the M4 tidal frequency to yield a picture of the cross-frontal distribution of energy dissipation. A complementary picture of the frontal velocity field was obtained from a moored ADCP and estimates of the mean velocity derived from the thermal wind using the observed density distribution. which indicated the presence of a strong (0.2 m s− 1) jet-like flow in the high gradient region of the front. Under neap tidal conditions, mean dissipation varied across the section by 3 orders of magnitude exceeding 10− 2 W m− 3 near the seabed in the mixed regime and decreasing to 10− 5 W m− 3. in the strongly stratified interior regime. The spatial pattern of dissipation is consistent in general form with the predictions of models of tidal mixing and does not reflect any strong influence by the frontal jet. 相似文献
308.
Geophysical turbulence is strongly affected by the variation of the Coriolis parameter with latitude. This variation results in the so-called β-effect, which forces energy from small-scales to be transferred preferentially into zonal motions. This effect results in the formation of narrow jet-like zonal flows that dominate the dynamics and act as transport barriers. Here, laboratory experiments are used to reproduce this effect in decaying turbulent flows. An electromagnetic cell is used to generate an initial field of vorticity in a rotating tank. Under conditions of quasi-geostrophic flow, the β-effect is produced by depth variation of the flow instead of variation of the Coriolis parameter. The effects of changing the container geometry and the overall fluid depth on the production of jets are investigated. The results suggest that this laboratory configuration can be used to model jet formation in the oceans and that increasing fluid depth is a practical way to decrease viscous effects. 相似文献
309.
A new higher order closure model for the stable boundary layer is presented and compared with Large Eddy Simulation data. The model includes numerical solutions for the mean values, second and third order moments equations. A satisfactory agreement is found between the calculated vertical profiles of the turbulent quantities with those provided by the LES. Furthermore the new model results are compared with profiles obtained with a lower order closure model in order to verify the effective importance of including third order dynamical equations in the model. 相似文献
310.
Franois G. Schmitt Yongxiang Huang Zhiming Lu Yulu Liu Nicolas Fernandez 《Journal of Marine Systems》2009,77(4):473
We consider here surf zone turbulence measurements, recorded in the Eastern English Channel using a sonic anemometer. In order to characterize the intermittent properties of their fluctuations at many time scales, we analyze the experimental time series using the Empirical Mode Decomposition (EMD) method. The series is decomposed into a sum of modes, each one narrow-banded, and we show that some modes are associated with the energy containing wave breaking scales, and other modes are associated with small-scale intermittent fluctuations. We use the EMD approach in association with a newly developed method based on Hilbert spectral analysis, representing the probability density function in an amplitude–frequency space. We then characterize the fluctuations in a stochastic framework using a cumulant generating function for all scales, and compare the results obtained from direct and classical structure function analysis, to EMD–Hilbert spectral analysis results, showing that the former method saturates at large scales, whereas the latter method is more precise in its scale approach. These results show the strength of the new EMD–Hilbert spectral analysis method for data presenting a strong forcing such as found in shallow water, wave dominated situations. 相似文献