Estuarine management strategies and the predictability of ecosystem changes

The Dutch Delta Region (S-W Netherlands) originally consisted of interconnected estuaries, interfacing the rivers Rhine, Meuse and Schelde with the North Sea. The ecosystems were immature, with physical rather than biological control of population dynamics. Main functions were shipping and shellfisheries. An emergent function of the interconnected estuaries was the buffering and upgrading of river-borne substances before they entered the sea. Execution of the Delta Project in the period 1960–1986 resulted in isolation of several water systems disconnected from rivers and sea, and loss of gradients within these systems. Population dynamics were now controlled by chemical and biological rather than physical factors. Vulnerability to external perturbation increased. These changes also affected the buffering capacity, i.e. reduced the utility of the area as stabiliser of the geosystem. Recreational use and appreciation of natural values increased, potentially conflicting with shipping and shellfisheries. Retrospective analysis of the environmental policy and management revealed three consecutive strategies in the Delta Project. 1. Reactive one-issue management, focusing on safety against flooding only. This strategy aimed at complete closure of the estuaries thus transforming them into fresh water lakes. It has destroyed feed-backs and buffering between coastal and inland waters. This strategy has not promoted sustainable development and has increased the vulnerability of the area to future catastrophes. 2. Protective bio-ecological management focused on the preservation of existing values of landscape and environment, and resulted in the maintenance of saline conditions and preservation of marshes by shore protection measures. The drawback of this passive orientation to existing values ?where they are now? is the necessity of continuous intensive care because the natural adaptive ability is not being restored. 3. Constructive geo-ecological management is based on understanding functional properties within and between ecosystems as integrated elements of the landscape structure. This strategy aims at environmental protection, restoration and development of values ?where they must be?. Re-establishment of gradients by e.g. re-introducing tidal influence and by restoring salt marshes should contribute to sustainable development.     

长江流域城市发展的个性与共性问题

建国 50年来 ,长江流域各大、中、小城市发生了巨大的变化 ,特别是城市经济实力、城市性质与功能结构 ,城市生态环境以及区域成绩体系等产生了质的飞跃 ,向着更高层次的城市战略目标发展。从本流域各个城市发展过程与现状特征分析 ,具有五个比较鲜明的个性与共性问题 ,共同构成了长江流域城市化的特征与趋势。本文着重阐述了五个特征 :①城市化的速度 ,比例各省具有自己的鲜明的特征 ;②流域内各省城市空间结构有自己的特点 ;③城市发展条件与形态有自己的个性 ;④城市用地的结构性特点 ;⑤流域内各大中城市的合理发展模式     

用期货市场思路建立南水北调水市场设想

南水北调是缓解北方水资源危机而实施的大规模调水工程 ,适应社会主义市场经济的要求 ,该工程中水资源配置将采用市场机制运作 ,但由于水价波动决定了价格风险的存在 ,而水价过高将给企业带来成本的提高或利润的下降。为此 ,针对南水北调中的水市场建设 ,尤其是对于城市工业用水 ,本文提出利用期货市场的基本功能来规避水价波动给企业带来的风险 ,有利于增强企业的国际竞争力     

基于径向基函数(RBF)网在线建模的民航安全风险监测仿真系统设计与实现

通过分析国内外民航安全风险监测的研究现状,指出当前我国民航安全风险监测方面的不足,进而提出了基于径向基函数(RBF)网在线建模的民航安全风险监测仿真系统。在仿真系统设计中,详细讨论了实现系统的网络拓扑结构、体系结构,并将仿真系统分为三大功能模块,提出以安全隐患指标和安全性能指标分别作为仿真模块的输入段和输出段。在该基础上,利用C#语言和SQL SEVER数据库共同开发出该模拟仿真系统,并以空管仿真系统华东管理局年度仿真实例作了验证。     

IDENTIFICATION OF AN OPTIMAL GROUNDWATER MANAGEMENT STRATEGY IN A CONTAMINATED AQUIFER1

A groundwater hydraulic management model is used to identify the optimal strategy for allocating limited fresh-water supplies and containing wastes in a hypothetical aquifer affected by brine contamination from surface disposal ponds. The present cost of pumping from a network of potential supply and interception wells is minimized over a five-year planning period, subject to a set of hydraulic, institutional, and legal constraints. Hydraulic constraints are formulated using linear systems theory to describe drawdown and velocity variables as linear functions of supply and interception well discharge decision variables. Successful validation of the optimal management strategy suggests that the model formulation can feasibly be applied to define management options for locally contaminated aquifer systems which are used to fulfill fresh-water demands.     

四辊轧机横向刚度的理论计算

运用影响函数法,对不同工艺制度及轧机参数条件下的轧机横向刚度进行了理论计算及分析讨论.     

基于罚函数法和Backofen模型的刚粘塑性有限元列式推导

讨论了刚粘塑性有限元法，对其基于罚函数法和Backofen模型的求解列式进行了详细的推导。     

Using selection functions to describe changes in environmental variables

The selection function (which shows how the frequency of sampling units with the value X = x at one point in time must change in order to produce the distribution that occurs at a later point in time) is proposed for describing the changes over time in an environmentally important variable X. It is shown that the theory of selection functions as used in the study of natural selection and resource selection by animals requires some modifications in this new application and that a selection function is a useful tool in long-term monitoring studies because all changes in a distribution can be examined (rather than just changes in single parameters such as the mean), and because graphical presentations of the selection function are easy for non-statisticians to understand. Estimation of the selection function is discussed using a method appropriate for normal distributions and bootstrapping is suggested as a method for assessing the precision of estimates and for testing for significant differences between samples taken at different times. Methods are illustrated using data on water chemical variables from a study of the effects of acid precipitation in Norway.     

A NOTE ON AREAL RAINFALL DEFINITION

A discussion is presented of the likely sources of error in defining areal rainfall on a storm basis. These include the instrumental error, sampling fluctuations over the area, and network density. The analysis of dense raingage data provides some perspective of the magnitude of the errors that might be encountered from the natural variability of rainfall. Except for one watershed in Arizona, the coefficient of variation, based on a sample of storm totals from the individual gages in various size areas, remains relatively constant with increasing area for a particular storm. The error due to rainfall variability over the area is probably the most important and must be considered in experiments which attempt to resolve small-area hydrologic problems.     

电除尘器末端微细粉尘收集装置研究

电除尘器末端是针对二次扬尘超细粉尘颗粒的收集的最后一道屏障。通过分析前人在此方面开展研究的技术成果基础上,集成多项技术,探索一条经济性较高的电除尘器增容提效改造的途径。