南极绕极波的行波与驻波共存系统分析          下载免费PDF全文

李宜振  赵进平 《极地研究》2007,19(1):38-48

南极绕极波(ACW)是近10年来海洋和大气科学领域研究的重要内容之一,其特征表现为一种海气耦合的年际信号在南大洋的明显东向传播。文中依据波动的基本原理,利用非线性拟合方法得到了绕极波行波的平均波速、波数和角频率和印度洋驻波的表达形式,得出行波和驻波具有相同的角频率。针对绕极波纬圈传播的不连续现象,提出了南极绕极波是行波和驻波共存系统的新见解。行波与驻波共存系统由三部分组成:在南大洋的太平洋西侧发生SLP振动,与发生在太平洋中低纬度的过程有关;在太平洋和大西洋存在传播的行波,行波在太平洋最强,到大西洋明显减弱;在印度洋SLP系统表现为局地变化,体现明显的驻波特征。三部分有共同的周期,表明三部分是统一的动力学系统,证实了行波与驻波共存系统可以很好地表达南极绕极波的时空特性和传播特征。  相似文献   

江西南昌-樟树地区农业土壤环境质量评价     

詹天卫  鄢新华  谢勇  李幼华  戴君扬  毛大发 《物探与化探》2007,31(3):261-264

在研究区内,由于各种自然地质作用及人类活动综合影响,使作物营养有益元素及有毒、有害组分在区内表层土壤中的分布存在明显的不均衡性.以土壤中元素的含量分布为主要依据,在分析南昌-樟树地区土壤污染现状、农作物营养有益元素丰缺现状的基础上,对区内农业土壤环境质量进行了评价,并按环境质量的优劣划分了A、B、C、D共4个等级.  相似文献   

基于多时相影像的农业作物非参数与概率分类     

俞军  Bo Ranneby 《遥感学报》2007,11(5):748-755

本文提出了一种新的结合多光谱和变化检测技术的多时相卫星数据集分类方法。该方法以数理统计中的最近邻法为基础,其目标函数是使得正确分类的平均概率得到最优化,即把每个分类类别看成同等重要。该新算法被应用于一个农业作物分类的研究区域,并利用覆盖该区的不同季节的SPOT和LANDSAT TM多时像影像。结果表明,与单时像影像相比,使用五个不同季节的多时像影像可以充分地提高分类精度。为了说明该方法在大尺度范围内的效果,本文选取瑞典道拉河流域作为研究区。由于不同地物的分布高度重叠,不可能得到像元水平上满意的分类精度。这就需要引进一种新的概念：像元概率分类法。基于像元的概率向量可用于判别传统分类法的可靠性并测量单个像元的不确定性（熵）。概率分类法同时提供了不同地物的面积的无偏估计,无论所感兴趣的区域的大小。这已经在不同特性的耕地试验点进行了检验。  相似文献   

不完全立波的二维数值波浪水槽模拟   总被引：4，自引：1，他引：4  

李炎保  黄凌燕  谷汉斌 《海洋学报》2002,24(4):105-110

利用二维数值波浪水槽研究波浪在防波堤前的运动状态.模型选用Navier-Stokes方程作为基本方程,以有限元法对基本方程进行离散.以直立堤前完全立波和越浪条件的不完全立波、斜坡堤前的不完全立波等典型情况的模拟为基础,组合这些典型情况模拟削角堤前不完全立波运动,探讨其堤前波面、波节点及波腹点位置、波压力等特性变化.  相似文献   

立波作用下的底沙运动     

孙青  陈士荫 《海岸工程》1996,15(3):7-14

立波作用下的底沙运动关系到港口的规划和建筑物的安全。本文以实验为基础，综合前人研究成果，得到立波作用下床面形态及冲刷类型。对较粗颗粒底沙在立波作用上进行受力分析，得到了一周期内沙粒累计推移距离，净输沙率及冲刷强度。认为冲刷形态的不同与近底速度和加速度的分布密切相连。  相似文献   

Numerical Modelling of Standing Waves with Three-Dimensional Non-Linear Wave Propagation Model   总被引：1，自引：0，他引：1  

ZHANG Hongsheng HONG Guangwen DING Pingxing 《中国海洋工程》2001,(4):521-530

Based on the theoretical high-order model with a dissipative term for non-linear and dispersive wave in water of varying depth, a 3-D mathematical model of non-linear wave propagation is presented. The model, which can be used to calculate the wave particle velocity and wave pressure, is suitable to the complicated topography whose relative depth ratio of the characteristic water depth to the characteristic wavelength in deep-water) is equal to or smaller than one. The governing equations are discretized with the improved 2-D Crank-Nicolson method in which the first-order derivatives are corrected by Taylor series expansion, .and the general boundary conditions with an arbitrary reflection coefficient and phase shift are adopted in the model. The surface elevation, horizontal and vertical velocity components and wave pressure of standing waves are numerically calculated. The results show that the numerical model can effectively simulate the complicated standing waves, and the general boundary conditions  相似文献   

Explaining the stickiness of supply chain relations in the Brazilian soybean trade     

《Global Environmental Change》2023

The global trade of agricultural commodities has profound social-ecological impacts, from potentially increasing food availability and agricultural efficiency, to displacing local communities, and to incentivizing environmental destruction. Supply chain stickiness, understood as the stability in trading relationships between supply chain actors, moderates the impacts of agricultural commodity production and the possibilities for supply-chain interventions. However, what factors determine stickiness, that is, how and why farmers, traders, food processors, and consumer countries, develop and maintain trading relationships with specific producing regions, remains unclear. Here, we use data on the Brazilian soy supply chain, a mixed methods approach based on extensive actor-based fieldwork, and an explanatory regression model, to identify and explore the factors that influence stickiness between places of production and supply chain actors. We find four groups of factors to be important: economic incentives, institutional enablers and constraints, social and power dimensions, and biophysical and technological conditions. Among the factors we explore, surplus capacity in soy processing infrastructure, (i.e., crushing and storage facilities) is important in increasing stickiness, as is export-oriented production. Conversely, volatility in market demand expressed by farm-gate soy prices and lower land-tenure security are key factors reducing stickiness. Importantly, we uncover heterogeneity and context-specificity in the factors determining stickiness, suggesting tailored supply-chain interventions are beneficial. Understanding supply chain stickiness does not, in itself, provide silver-bullet solutions to stopping deforestation, but it is a crucial prerequisite to understanding the relationships between supply chain actors and producing regions, identifying entry points for supply chain sustainability interventions, assessing the effectiveness of such interventions, forecasting the restructuring of trade flows, and considering sourcing patterns of supply chain actors in territorial planning.  相似文献   

Identifying farmer attitudes towards genetically modified (GM) crops in Scotland: Are they pro- or anti-GM?     

Clare Hall 《Geoforum》2008,39(1):204-212

The GM debate in the European Union has been consistently presented as being conflictual and contentious, characterised as being polarised into those who are pro-GM and those who are anti-GM. This is largely based on the positions adopted by the public (consumers), non-governmental organisations (NGOs), and industry and corporate bodies. One group largely lacking from this debate is farmers, and yet their decisions about whether or not to cultivate GM crops will be crucial to the future of the technology in European agriculture. This paper reports findings from a study investigating farmers’ attitudes to GM crops in Scotland using Q methodology. Results reveal three discourses, one inclined to be positive towards the idea of GM and demonstrating an expectation of benefits, the second representing a more uncertain position, wary of the potential risks of the technology but likely to be reluctant adopters, and the third describing a group who demonstrate a somewhat fatalistic attitude towards the issue of GM technology adoption and impact. These findings contribute to the GM debate by elaborating the views of this important stakeholder group and suggest that they may be less profoundly pro- or anti-GM than other groups involved in the debate. This is significant if they represent the ‘middle ground’ between the biotechnology industry and the public.  相似文献   

Slowing things down: Lessons from the GM controversy     

Nick Bingham 《Geoforum》2008,39(1):111-122

This paper stages an encounter between one strand of the controversy around genetically modified food crops and some conceptual resources from the field of science and technology studies, with the aim of illuminating the relationship between science and politics. Contrary to some suggestions, it is argued that the spatial, temporal and material imagination encapsulated in the figure of Progress remains central to their contemporary articulation. Best described as an ‘anti-political’ strategy, Progress does not leave room for anything else but one story of the world. Through following the attempts of both scientists in the field and protestors on the streets to make public some of the trajectories which this story leaves out, what emerges is the possibility of an alternative to Progress that is not based simply on its rejection. Instead, such efforts offer resources for inventing another way of collectively going forward which chime with some more theoretical attempts to elaborate how things might be productively ‘slowed down’. An example of how government was forced to construct a way of dealing with things that is more adequate and appropriate to life in a full world is compared with Bruno Latour’s model of due process for nonhumans, before some conclusions are drawn about whether we should be depressed or hopeful about our ability to move on in the lights of such attempts.  相似文献   

基于北斗 CORS 系统的海上钻井平台精确站桩导航系统的设计与开发     

于双  董光利  刘壮  潘红章  黄华文 《测绘工程》2016,25(11)

由于海洋环境的复杂性与不可预测性,海上石油平台站桩或拖船是一项相当艰难的作业。海上钻井平台精确站桩导航系统是针对上海外高桥造船有限公司的JU-2000E型石油钻井平台开发设计,利用北斗CORS系统实时获得平台厘米级精度的位置信息,为移动平台精确站桩提供了可靠保障。  相似文献