Application of improved genetic algorithm to locating and sizing of distributed generation

A Prüfer-coded genetic algorithm based on the decimal number of nodes is proposed and it is used to solve collaborative optimization planning of access solution of distributed generation(DG)and structure of distribution network.Using graph theory to generate theoretically feasible topology structureand the access nodes and the installed capacity of distributed generation are coded by the Prüfer number.The coding method makes the distribution network operation structure and the access solution of DG combine into the evolution problem of the same chromosomal gene.The length of the chromosome coding of this method is shorter than binary encoding.This solution takes full advantage of the Prüfer-coded to improve computational efficiency and convergence rateand makes some restrictions and improvements in some key parts of the algorithm to solve the problem illegal solution.Finallyfeasibility and superiority of the algorithm is validated by a case study.     

Utility Analysis of Reclosing in the Distributed Generation System

According to the type of the DG,the working situations of the reclosing are studied.The actual parameters of DG's rated capacity and transient reactance are adopted.According to the location and capacity of the DG, the possibility of auto-reclosing is analyzed,and the parallel feed inverter used in this system and its control method is presented.The system model and calculation results are given in MATLAB.It shows that the auto-reclosing technique is feasible in the distributed generation system and for some DGs connected to the net by inverters,the current instantaneous feedback control can realize the switching condition.     

Theoretical analysis on the protection properties against electric shock of low voltage DC distribution system with different grounding types

The low voltage direct current(LVDC)distribution system has great potential and advantage to be applied to conventional areas, such as residential house, due to its characteristics of energy conservation and being eco-friendly, but there is no existing standard specifications to guide its application in practice to ensure the electrical safety of this system. The protection against electric shock is a key indicator of electric safety, but the effect of electric shocks on AC and DC are different. Refer to the international standard IEC60479-1 and analytical method in AC system, the protection against electric shock between DC 750, 400, 300, 220 V and AC 220 V systems are compared and analyzed based on ideal DC source model. It demonstrates that the negative grounded TT & TN DC distribution system has significant advantages over the traditional AC system, and the safety voltages are given, which could be a reference to develop the normative guidance for the application of LVDC in practical application.     

雷电灾害风险评估中P_B因子选取方法的分析及改进

在分析雷电直接击中建筑物导致物理损害的概率PB的影响因素的基础上,本文基于IEC62305推荐的不同防护等级的保护能力以及雷电流概率分布规律,推导出确定规范中LPL对应的PB因子优选值的一般过程。并针对推导过程完全依赖于规范推荐的防护等级及雷电活动特性,针对性差的特点,提出了根据建筑物直击雷防护实际情况以及项目所在位置雷电环境的统计特征确定PB因子的方法,该方法在一定程度上提高了PB因子选取的科学、准确性。同时,也对由于雷击物理过程复杂性、电气-几何模型的科学性、防护装置性能变化等使得PB因子取值中存在的问题进行了分析。     

Principle and Analysis of Rapid Feeder Protection System for Distribution Network

The scheme of rapid protection will be possibly implemented by using the channel of communication, as the communication network of distribution power system being increasingly perfect and particular foundation of optical cable. The feeder protection based on communication can quickly and selectively isolate fault section and restructure the distribution network. This method is the direction of distribution automation. The action principles of feeder protection using blocking and allowing signals of directional over-current are analyzed. The directional over-current protection utilizing blocking signals is suitablefor distribution automation. The scheme can locate the fault section and instantly separate it. When feeder terminal unit (FTU) fails to act or communicate is interrupted, the feeder protection in the substation can backup.     

中国农村耕地保护的新制度经济学研究

耕地是支撑经济社会发展的重要资源,也是农业、农村经济保持可持续发展的关键。首先阐述了中国农村耕地保护的现状及政策变迁,之后运用新制度经济学的产权理论、制度均衡理论以及制度供求博弈理论探讨了耕地保护问题,得出了建立有效的产权制度是保护耕地的关键,耕地保护制度均衡的重点在于责任的归属和利益分配,同时地方政府与用地企业在促进经济发展而占用耕地追求自身利益的同时要兼顾村集体以及农户利益的结论。并在此基础上,提出了完善土地产权制度,建立有效的制度需求反馈制度,中央政府在保证制度均衡的前提下加大监督力度,从根本上杜绝各级政府的寻租行为以及切实保障农户的利益等对策措施。另外,本研究方法和视角也在应对农村耕地日趋严重的“非农化”问题方面拓展并丰富相关领域的研究。     

Refined Probabilistic Model of Resistance of RC Eccentric Compression Members

The probabilistic model of resistance in the current unified standard for reliability design is imprecise for RC members subjected to eccentric compression. The reason is that it lacks full considerations of influences of varying eccentricities. An improved probabilistic model of resistance with different eccentricities and reinforcement ratios is obtained by using the Monte Carlo sampling method and the current probabilistic models of all resistant factors. The results indicate that it is accurate to fit the probabilistic distribution of resistance with normal distribution. Given that, the applicability of the improved model is analyzed for reliability analysis of RC members subjected to eccentric compression with random eccentricities. It shows that when the design value of eccentricity is close to or larger than the eccentricity producing balanced failure, there would be large errors in reliability analysis if the probabilistic model of resistance given in the current reliability unified standard is used. However, it is accurate when using the proposed probabilistic model. The results also show that the design of RC members subjected to large eccentric compression is unsafe based on the current reliability unified standard because it lacks full considerations of effects that the resistance decreases as eccentricity increases.     

农户植保机械补贴参与意愿的影响因素分析——基于福建省的数据

为了解福建省植保机械购置补贴政策总体实施情况,结合福建省的问卷调查数据,利用Logit模型对农户参与植保机械购置补贴政策意愿的影响因素进行实证分析。研究表明：有69.4%的农户表示愿意参与植保机械购置补贴政策,农户的种植面积对植保机械购置补贴政策的意愿有显著影响并呈负相关,文化程度、种植经验、家庭农业纯收入都对参与补贴政策的意愿具有显著的正向影响。     

多元化农业技术推广体系研究进展

研究旨在梳理当前中国多元化农业技术推广体系发展进程,为今后的多元化农业技术推广体系的建立奠定基础。应用文献计量法,以中国知网数据库为原始文献来源,高级检索“主题”=“多元化农业技术推广体系”、时间为2005—2014年,分析所获得50篇文献的发表年份、期刊分布。结果表明,当前多元化农业技术推广体系发展进程相对缓慢,体系构建不完善。归纳中国多元化农业技术推广体系出现的问题,总结不足并提出展望。当前相关理论性研究较多,但是仍需加强基于农民与农企等多个主体的视角不断扩大研究,从而得出更有针对性与实际价值的结论。     

An EOQ Model at Random when Average Demand Is a Linear Increasing Function

For certain types of inventory, the ordering cycle and demand may be random variants, which satisfy certain types distribution. The classical EOQ model usually neglects the fact. Based on the constant demand, under the hypothesis that the ordering cycle is a random variant which satisfies exponent distribution, average demand is a linear increasing function, this paper considers the effects of the time-value of capital and inflation on replenishment strategy of inventory system. Loosening the condition of basic economic order quantity model under deterministic state, the total cost function of the model is provided. The optimum order quantity and cycle are obtained. The application range of EOQ model under the constant demand is widened. The theoretical evidence is provided for the inventory system to make management decision.     

甘肃民勤生态状况调查与分析

通过对石羊河流域生态状况的科学考察,特别是民勤绿洲荒漠化历史过程及其生态环境恶化成因的调查研究,客观分析了民勤生态环境治理中存在的水资源、生态植被、风沙危害、经济发展与生态保护的矛盾、生态移民、资金投入等方面存在的主要问题,并对民勤生态环境综合治理提出了对策和建议。     

植物根系固土力学机制模型

由于在边坡加固、生态环境保护等方面具有很多优越性,植物固土护坡技术近年来广泛应用于固土护坡工程中。植物固土护坡的力学效应主要体现在植物的根系上,包括植物浅根将岩土体变成加筋复合材料的加筋作用,以及深根将浅层岩土体风化带锚固到深层稳定岩土上的锚固作用。为了揭示并评价植物固土护坡的力学效应,需要具有实际应用价值的根系固土力学机制模型。本研究在分析植物根系固土力学机理的基础上,探讨了3个植物根系固土力学机制模型：Wu氏模型、能量法模型和纤维束模型的应用条件、模型的优缺点、适用范围及其环境适应性等,并展望了植物根系固土力学模型发展的趋势和方向,从模型角度深化植物根系固土力学机制理论研究,为全面揭示植物护坡的力学机理提供理论基础,为水土保持工程植物措施提供科学依据和理论指导。     

The Analysis of the Transformers Saturation Model

Based on some theories,and to analyze transformers and many different models to compare, a new kind of transient mathematical model on transformers is presented. In the model, the saturation of magnetic circuit and core losses are considered and the effects of nonlinearity of main magnetic circuit for voltage and current of transformers are analyzed. Then the applications range and the direction to improve of the model are referred to through comparing the model with other models. And the feasibility and accuracy of the model are verified through comparing the results of simulation with the results of experiments.     

Protection of Historic Villages and Towns in View of Tourism Destination Study

The traditional ways of protecting heritage are often passive when facing the influence of tourism development, which makes the protection measures lag behind relatively. To solve such a problem, this paper analyzes the influence of tourism destination lifecycle and of spatial structure creatively with the theories of Tourism Geography, pointing out that the influences are different in different lifecycle phases with different distinct characteristics, that the special spatial structure always makes tourism destinations facing more complex conditions and take more heavy environment pressure. Therefore, this paper advocates taking active protection, dynamic protection, building protection system to protect the historic villages and towns.     

MecaNiCAL, a supply–demand model of carbon and nitrogen partitioning applied to defoliated grass: 1. Model description and analysis

A model for the dynamic simulation of dry matter distribution between shoots and roots of a grass forage plant is presented. The objective of this work was to develop a relatively simple mechanistic model of grass growth to simulate the response of assimilate partitioning to variations in light and nitrogen supply based on an original theoretical scheme [Gillet, M., Lemaire, G., Gosse, G., 1984. Essai d'élaboration d'un schéma global de la croissance des gramineés forragères. Agronomie 4 (1), 75–82]. In the model, called MecaNiCAL, C and N assimilates are partitioned between shoots and roots according to the availability of carbohydrate substrate, organ demands and a fixed priority between each demand. Demand related to organ synthesis is described as a function of the plant concentration in the organic nitrogen substrate and temperature. To stay within an acceptable range of complexity, the model is applied only in one vegetative regrowth performed on a hydroponic system with different light and nitrogen nutrition. Carbon and nitrogen acquisition per day are computed by independent submodels, which makes it possible to connect simple and robust functions of carbon assimilation and nitrogen uptake to the partitioning model. Carbon assimilation is simulated for a plant in a canopy, and nitrogen uptake is simulated by a function which depends on nitrogen plant requirements directly related to plant net photosynthesis and the amount of nitrogen available in the nutritive solution. All the assumptions used to describe assimilate partitioning are discussed in relation to knowledge of physiological processes in order to examine closely the limits of the model.     

Dropwise Condensation Heat Transfer Coefficient on the Horizontal Circular Surface with Radial Gradient Surface Energy

A theoretical model is developed for the dropwise condensation heat transfer on the horizontal circular surface with radial gradient surface energy based on the heat transfer model of individual condensate drop and the size distribution model of condensate drop on homogeneous condensation surface.The effect of variation of contact angle on the gradient surface on condensation heat transfer and condensate drop size distribution is taken account of in this model.The theoretical calculation method was obtained to predict the dropwise condensation heat transfer coefficient on the horizontal circular surface with radial gradient surface energy under various wall subcooled temperature,contact angle profile on wall surface,and working fluid.The effects of surface energy gradient,wall subcooled temperature,and thermophysical properties of condensate on the condensation heat transfer are discussed respectively.The calculation results show that the condensation heat transfer coefficient increases slightly with the increase of wall subcooled temperature.As latent heat and surface tension increasing,the condensation heat transfer coefficient increases.A larger surface energy gradient induces a larger condensation heat transfer coefficient.     

DEM模拟解析二元混合颗粒粒径偏析分布规律

颗粒粒径偏析分布是高炉炉顶布料过程中不可避免的现象,易造成炉喉处局部料层的空隙度降低和压差升高,影响煤气流的均匀分布,继而间接影响炉况的顺行。通过DEM离散单元法模拟研究二元混合颗粒的偏析分布规律,同时,提出一个偏析指数T,用以表征粒径偏析分布的相对程度。研究结果表明：同一T值图中,相邻区域颗粒的T值相差越大,则该区域颗粒的粒径偏析程度越大;不同T值图中,所有相邻T值之差的平均绝对值越大,则颗粒堆积整体粒径偏析程度越为严重。     

Employment Growth by Firm Size During the Recent Crisis in Italy: A Multifactor Partitioning Analysis

The effects on employment growth in firms, grouped by size class, of the economic crisis that began in 2008 are analysed using multifactor partitioning (MFP). Italy's employment growth is decomposed into four explanatory factors: the stage in the business cycle; the effect of firm size; industry composition; and regional distribution; together with the interactions among these four effects. The interpretation of these effects is facilitated by the introduction within the MFP framework of a new decomposition of several key elements. The results show that the adopted approach and the suggested decompositions are useful to study the effect of size on employment change. This effect is found to be negative only for micro units (with less than 10 employees). For the other classes, it is positive. The observed negative changes in these classes are mainly due to the business cycle and an unfavourable industrial composition.     

覆盖生态木屑对‘染井吉野’樱花根系分布特征的影响

树木的根系分布是影响灌溉效果的重要因素,为实现园林树木的科学灌溉,对‘染井吉野’樱花的根系分布特征和覆盖生态木屑对根系分布特征的影响开展研究。采用根钻法对玉渊潭公园内大面积种植的‘染井吉野’樱花根系进行定点逐层取样,利用Win-RHIZO Pro根系分析系统分析根的总长度、直径小于1 mm的根的总长度、根的投影面积、根的表面积和根尖计数等指标。结果表明：‘染井吉野’樱花的吸收根水平方向可以伸展长达6 m,垂直方向上则主要集中在0~20 cm的土层内;铺设生态木屑对土壤表层樱花根系具有明显的促进作用,铺设不同厚度生态木屑对樱花根系分布特征影响不同,覆盖5~10 cm厚生态木屑后樱花根系总长度达到(782.98±401.29) cm,是不铺生态木屑的樱花根系总长度的10倍,是其他试验组的2倍以上。樱花属于浅根系树种,城市公园环境使‘染井吉野’樱花根系主要分布于土壤表层,但分布范围甚广,能够达到树干投影面积的2倍;铺设生态木屑促使樱花根系向土壤表层集中,铺设5~10 cm厚的生态木屑可以有效促进土壤表层樱花根系生长,但对土壤深度20 cm以下的樱花根系影响较小。     

贺兰山紫蘑菇开发利用现状与发展前景

从贺兰山紫蘑菇分布、分类、形态特征及生理学特性等方面进行了介绍,并结合国内开发利用现状与出现的问题对贺兰山紫蘑菇的发展前景进行展望。