水泵水轮机反水泵工况的特性研究

可逆试水泵水轮机同时具备了发电和储能的双重特点,它既满足了人们对电功率的控制与平衡,也满足了环保的需求。为了深入的分析水泵水轮机发水泵工况的性能,笔者以某中型抽蓄水电站为模板,试图构建一个水力性能测评的模型,并运用SSTκ-ω模型和Presto差分格式模拟反水泵工况的内流场和外特性,以此来对试验所得数据进行论证,从而为有效解决水泵水轮机的＂S＂特性问题提供依据。     

大连引碧北段水源泵站变频调速设计

水源泵站的流量相对恒定，但是河流、湖泊、水库的水位是随季节变化的，且变化幅度很大，所以泵站的几何扬程也是变化的。随着水库水位的升高，水泵几何扬程减少，管路特性曲线平行下移。为了适应水泵的特性曲线，大多数情况下采取调节控制出口闸门、水泵运行台数等方法来调整管路的特性曲线，造成水泵能量的浪费。如果能同时改变水泵转速，使水泵的特性曲线适应管路特性曲线的变化。不但可以充分地利用水库的位能，同时也大量地减少电耗。     

热水供暖系统中循环水泵的选择

本文对循环水泵的选择原则、参数确定和选择中的几个问题进行分析，指出泵的特性与热网特性不相匹配的原因和解决的方法，对并联泵的效果和管路联接方式进行了分析计算后，提出一些建设性意见和建议，同时讲述正确选择缉环水泵的容量和热网调节方式是供暖系统循环水泵节电的重要措施。     

离心泵联合运行特性曲线的拟合方法研究

针对两台离心泵联合运行方式下特性曲线及管路特性曲线难以确定的现状，通过采用基于最小二乘法的多项式、三次样条函数和神经网络法分别对联合运行的特性参数进行拟合和分析。     

浅析泵站水泵机组的安全运行

水泵机组是水泵站工作的重要设备,水泵机组的安全运行关系到水泵站的正常工作,本文结合工作实践,首先分析水泵机组运行的方式,提出对水泵机组管理与维护的具体对策,然后针对水泵机组运行中存在的问题提出具体的对策。     

实现水泵变流量调节发展水泵变转速技术

调节阀门开度来改变水泵运行参数,是以消耗水泵运行能耗为代价,浪费能源;若采用水泵的变转速技术同样可以实现对系统的变流量调节,发展水泵的变转速技术是实现循环水泵的变流量调节和节能的有效途径,其中最理想的方法就是变频调速.     

浅谈建筑物消防水泵的应用

立足于消防水泵在建筑灭火设施中的重要性，谈谈消防水泵在灭火设施中一些基本认识。     

水泵的安装与故障排除

一、安装要点1.合理选址。水泵的安装位置应满足允许吸上真空高度的要求,基础必须水平、稳固,保证动力机械的旋转方向与水泵的旋转方向一致。此外,水泵基础上的预留孔,应根据水泵的尺寸浇注。2.正确连接。水泵和动力机采用     

晶体三极管输出特性曲线教学研究

模拟电子技术中常采用的图解法依据是三极管的特性曲线,只有充分掌握了特性曲线,才能正确理解放大电路的三个区:饱和区、放大区、截止区。而特性曲线中的输出特性曲线对初学者来说更为难理解。如何使学生正确轻松地理解特性曲线,这就需要教师用形象直观的教学手法去诠释曲线的含义,化难为易,使学生轻松入门,为后续学习打下扎实的基础。     

水泵变频节能技术浅析

在全球倡导节能经济发展的背景下,搞好水泵的节能工作,对国民经济的发展具有重要意义。本文介绍了变频水泵控制系统的节能原理、适用场合及影响变频调速范围的因素,并指出了实际应用中应注意的问题。     

基于接收机特性曲线的非相干积分平方损耗计算方法

通过对非相干积分下接收机工作特性曲线进行分析,提出一种平 方损耗计算方法,该方法在信号检测有效范围内具有计算简洁和准确度高的优点,且可以大 大降低运算复杂度,可用于雷达信号检测、电力线通信、卫星通信等领域弱信号检测中预检 测积分时间计算     

PID调节在恒压供水中的应用

随着变频器的应用普及,变频器越来越多地应用到了恒压供水系统中来,由于采用闭环控制方式,使供水（油）压力自动保持恒定。在控制方式中PID调节有着比较广泛的应用,而且有专用的水泵PID恒压控制器在市场供应,使控制设备和调试趋于简单化,便于恒压控制的推广。     

Conditions for linearity of the wage curve

For a given technique, the wage-rate of profit curve is linear in one-sector models. In multisector models, Wicksell effects appear and some paradoxes in capital theory are linked to the complex shape of the wage curve. We study the conditions ensuring the linearity of the curve for a bisector model and for models satisfying a specific rank condition.     

Regime switching in the yield curve

The article investigates the effect of interest‐rate variance on the shape of the yield curve with the use of a bivariate two‐state Markov switching model for the short‐rate changes and the yield curve slope. The two states are characterized by the variance of the short‐rate changes: low and high variance. In the high‐variance regime the yield curve becomes steeper with the interest‐rate variance; in the low‐variance regime the slope is independent hereof. A nonswitching specification amounts to averaging across the two states. The economy is in the high‐variance state during unusual economic periods. © 2004 Wiley Periodicals, Inc. Jrl Fut Mark 24:315–336, 2004     

Yield curve risks in currency carry forwards

We provide empirical evidence that cross-country yield curve gaps (parallel gap, twist gap, and butterfly gap) are predictive to the expected currency carry premiums using currency forward contracts. We find that the expected currency gains are more notable as these yield curve risk factors at time t indicate short-term bond prices of investment currencies to go up (positive parallel movement, negative twist, and positive butterfly). We also find carry gains are more sensitively affected by cross-country monetary shocks than currency-country inflation pressures and business cycles. Our findings support that cross-country yield curve risk premiums still exist even after considering transaction costs.     

关于市场均衡论的反论与反思

研究发现,古典主义经济学乃至新古典主义经济学所奉行的市场均衡模型（包括一般均衡和局部均衡）并非白璧无瑕,关于这一模型的经典著述中隐含着许多反论,而右下斜(斜率为负)的供给曲线以及右上斜(斜率为正)的需求曲线是这些反论的核心。这些反论促成了如下反思：供给价格不等于边际成本;供给表并非来自实践,而是来自传统供给法则的主观拟断;边际收益递减并不决定供给曲线的右上扬,相反倒决定了供给曲线的右下斜趋势,而边际收益递增则决定了供给曲线右上斜的趋势。以上反思得出一个基本结论：市场均衡模型并非马歇尔的那个交叉,真实的模型中至少应当包含着右下斜的供给曲线和右上斜的需求曲线。     

论垄断性市场中厂商产品供给曲线的存在性

西方微观经济学一直认为,只有完全竞争市场上的厂商才有产品的供给曲线,而在其它任何具有垄断性的产品市场上的厂商则没有此曲线的存在。然而,这一结论是错误的。原因在于西方微观经济学对需求变化的错误理解,并由此进一步导致了西方经济学需求理论前后逻辑上的自相矛盾。按西方微观经济学需求理论的逻辑推导,垄断性的产品市场上的厂商也同样存在可以描述和定义的产品供给曲线。这一结论的存在为宏观总产品供给曲线的推导提供了微观基础。     

Putting the learning curve in context

In implementation of change, people learn new ways of doing things, develop new skills, and adopt new organizational routines. This paper applies learning curve theory to implementation by developing a system dynamics model that includes two extensions to classic learning curve theory. First, the model includes a required output level for the individual. Second, the model includes a budget constraint on time that forces a choice between an old and a new way to achieve the output. Doing work the new way builds experience, increasing productivity and thus favoring continued use of the new skill, but model analysis demonstrates that this reinforcing process works to favor the new skill only at relatively high levels of productivity. Otherwise, the same process is a vicious cycle, driving out the new skill. The model exhibits a mode of behavior in which learning begins and then stalls and another mode in which the new skill becomes the preferred one. The paper identifies the tipping point between these two modes and characterizes the transition problem: Learning by doing is a dynamic process, a transition from use of an old way to a new way that requires accumulating experience beyond a threshold.     

A COMPLETE CHARACTERIZATION OF THE INVERTED S‐SHAPED LABOR SUPPLY CURVE

Empirical evidence suggests that labor supply curves are downward sloping at low wage levels, i.e. ‘forward‐falling labor supply’. In contrast, the supply curve is only downward sloping at high wage levels in the canonical labor supply model, i.e. ‘backward‐bending’. This paper derives a labor supply curve with both forward‐falling and backward‐bending segments, or an ‘inverted S‐shape’ by incorporating two elements into a standard utility function: a subsistence level of consumption and a decreasing elasticity of substitution. It is also shown that the subsistence level of consumption plays a key role in determining the shape of the labor supply curve.     

An experience curve explanation of export expansion

Various explanatory variables have been identified in past research as determinants of the export behavior of firms. This article proposes that while many factors contribute to export behavior, experience curve effects are a major variable explaining the international activities of firms. The research reported here finds that younger firms are much more faborably disposed toward and active in international marketing than older firms. This is attributed to the competitive domestic situation younger firms encounter. Since older firms are often well entrenched in the domestic market, exporting may be the only alternative available to younger firms to obtain the production expertise and efficiency necessary to become a successful domestic competitor.