马克思与新制度经济学学者企业边界观点比较研究——以企业边界扩张约束问题为视角的分析     

崔彩周 《湖南农业大学学报(自然科学版)》2008,(1):2-6

马克思与西方新制度经济学学者都对企业的规模边界约束因素进行了分析.但马克思主要从现实的生产环节出发,从生产力与生产关系历史发展之具体角度进行分析;而新制度经济学学者主要从交易费用这一相对抽象角度进行分析.两种理论主张对现实都有一定的启示意义.  相似文献   

A conceptual framework for guiding the participatory development of agricultural decision support systems     

E. Jakku 《Agricultural Systems》2010,103(9):675-682

Scientists develop decision support systems (DSSs) to make agricultural science more accessible for farmers and extension officers. Despite the growing use of participatory approaches in agricultural DSS development, reflection on this endeavour has largely focused on the ‘doing’ of participation or the ‘problem of implementation’ when DSSs have not been adopted by stakeholders. There has been little reference to relevant theoretical approaches to the social processes involved in ‘participation’ or ‘implementation’. However, if DSS use is to reach its full potential, a more conceptually informed understanding of how stakeholders collaborate in the participatory development of DSSs is required. To contribute to this conceptualisation, we developed a framework based on three concepts drawn from the field of science and technology studies: technological frames, interpretative flexibility and boundary objects. The framework highlights the importance and value of social learning for participatory DSS development, which relies upon exploring the participating parties’ different perspectives on the agricultural system represented in the DSS. Our framework provides a broad definition of success for participatory DSS development, placing greater weight on learning during the participatory process compared with subsequent use of the DSS by farmers and/or advisors. Two case studies of stakeholder collaboration to develop an irrigation scheduling DSS for sugarcane production were used to explore the relevance of the framework. The concepts in the framework were clearly displayed during the case studies. At the conclusion of the studies there were contrasting outcomes for the DSS. One group of farmers was keen to apply it in their ongoing irrigation management, while another saw little relative advantage in use of the DSS. In both instances co-learning occurred amongst case study participants, so the participatory process was clearly a success.  相似文献   

滨水景观的规划设计模式探索   总被引：2，自引：0，他引：2  

汤晓敏  王云 《上海交通大学学报(农业科学版)》1999,(3)

本文在分析滨水景观的特性及其在城市生态环境中的重要价值的基础上,结合实例提出了滨水景观的规划设计应遵循的基本原则和基本模式,以期对目前滨水绿地的建设起到一定的参考与借鉴作用。  相似文献   

离心泵轴向力的迭代计算方法   总被引：1，自引：0，他引：1  

丛小青  袁丹青 《排灌机械》1998,16(3):9-12

本文通过对边界层内流动分析,简化泵腔中液体流动的Ｎ－Ｓ方程推导出泵腔内压力分布与泄漏量之间的关系,从而在理论上推导出进一步精确计算轴向力的编程迭代求解公式。  相似文献   

热岛效应造成的城市边界层热力稳定度变化及其对降水的影响     

王建鹏  孙继松  王式功  张弘  曲静  孟小绒  金丽娜 《安徽农业科学》2012,40(4):2280-2283,2372

[目的]研究热岛效应造成的城市边界层热力稳定度变化特征及其对降水的影响。[方法]从热流量方程出发,探讨了因城市加热扰动、热岛效应平均态所引起的城市边界层热力稳定度的变化特征,分析了城市边界层热力稳定度变化对降水的影响,并结合西安地区降水个例进行了验证。[结果]在扰动温度与扰动气流相互作用下,边界层热力扰动稳定度(θ′/z)有利于城区及城市上下游边界层的层结趋于稳定,但中心城区的稳定性弱于郊区,有利于短历时对流降水天气的发生与发展。平均气流(盛行风)、平均水平扰动温度相互作用对热力不稳定分布的影响:当边界层环境气流为上升运动时,边界层平均热力扰动稳定度(θ′/z)表现为上游不稳定、下游稳定的特征,强降水易发生在上游或城市上风方;当边界层环境气流为弱下沉运动时,下游不稳定趋于发展、上游趋于稳定,局地强降水易发生在下游或城市下风方。[结论]该研究在制作城市精细化预报中有一定的参考价值。  相似文献   

Patch and species specific responses of savanna woody vegetation to browser exclusion     

Shaun Levick  Kevin Rogers 《Biological conservation》2008,141(2):489-498

The impact of browsers on the structure of woody vegetation has been well documented in savanna landscapes but the spatial distribution of these impacts is poorly understood. Savannas are structurally heterogeneous and the effects of browsers are unlikely to be evenly distributed across them. A mammalian exclosure in northern Kruger Park, South Africa, was used to explore the impacts of 15 years of browser exclusion on woody vegetation across a wetland/upland boundary. Woody patches inside the exclosure were taller than those outside of the exclosure and differential patch and species specific responses were observed within and without the exclosure. A boundary between upland and wetland patch types showed the greatest response to browser exclusion in terms of woody species composition, height and stem diameter. Browser impacts are not distributed evenly across the landscape, but are focused on certain patch and species types. Browsers have the potential to markedly alter system heterogeneity. Landscape heterogeneity is an integral component of biodiversity, but is often not explicitly dealt with in protected area management. Typically monitoring of vegetation change in conservation areas occurs at broad scales and would not detect the change in either the patch type or species specific responses identified in this study. We recommend that protected area managers adopt a multi-scaled, spatially explicit approach to monitoring change in the landscape. Boundaries between patch types provide valuable indicators of browser mediated changes.  相似文献   

贵州人工草地-农田景观土壤水分界面研究   总被引：1，自引：0，他引：1  

王建立  刘洪来  杨丰  唐文汉  程巍 《草地学报》2015,23(4):697-702

采用野外测定、室内统计和移动窗口法相结合,对贵州人工草地-农田界面土壤水分的时空分布和影响宽度动态进行了研究,以期为西南山区的退耕还草和草田轮作/间作提供参考。结果表明:在空间上,研究区人工草地土壤表层(0～20 cm)的含水量高于农田;在时间上,研究区一年四季土壤表层水分的表现为“高-低-高”的变化规律,表明春季、夏季和秋季、冬季分别为土壤水分的贮存期、消耗期、恢复期。通过移动窗口法判定得出,研究区土壤水分界面位置与景观界面位置重合,春季界面总宽度为41 m,一年四季表现为“宽-窄-宽”的变化规律,土壤水分界面在农田系统的影响域变化与总界面宽度保持一致,而在人工草地系统则表现为随着季节的推移界面影响域越来越窄;由此可将研究区划分为人工草地功能区系统、人工草地-农田复合功能区系统和农田功能区系统。该研究对南方草地畜牧业的可持续发展和界面理论的丰富具有参考价值。  相似文献   

Larval fish distribution and retention in the Canary Current system during the weak upwelling season     

M. Moyano  J.M. Rodríguez  V.M. Benítez‐Barrios  S. Hernández‐León 《Fisheries Oceanography》2014,23(3):191-209

The spatial distribution of fish larvae was studied in the Canaries‐African Coastal Transition Zone, outside the strong upwelling season. An onshore–offshore transition in the larval fish community structure was observed, from a coastal assemblage dominated by small pelagics (sardine, anchovy, mackerel), bounded by the upwelling front, to an offshore assemblage dominated by mesopelagic species (mainly Myctophidae, Phosichthydae, Gonostomatidae). Distribution of the neritic larvae was deeply influenced by the intense mesoscale activity found in the area, both horizontally (larvae were advected offshore but were always retained within the upwelling area) and vertically (larvae were deepened in the vicinity of two anticyclonic eddies). A combined effect of the upwelling front and a cyclonic–anticyclonic eddy dipole is likely the successful retention mechanism for these larvae. These results support the current belief that retention may be higher than previously thought in upwelling areas. Oceanic larvae were also collected in higher abundances near the front and an anticyclonic eddy. Neritic and oceanic larvae frequently showed a differentiated position in the water column, although they sometimes coexisted. Finally, larval connectivity between Islands within the Canary archipelago is suggested. The present study thus contributes to the understanding of the complex dispersal and retention processes in the Canaries‐African Coastal Transition Zone. However, results also highlight the poor knowledge of this region compared with the other three main Eastern Boundary Upwelling Systems in terms of ichthyoplankton dynamics. The importance of routine monitoring programs of commercial and non‐commercial species in the area is emphasized.  相似文献   

基于分形理论的滨海新区土地利用空间格局变化研究     

白新萍 《安徽农业科学》2011,39(24):14728-14730,14808

[目的]探讨基于分形理论的滨海新区土地利用空间格局变化。[方法]利用遥感和地理信息系统技术获取滨海新区1993-2008年城市土地利用现状数据,运用分形理论分别计算了各类用地的边界维数、半径维数、信息维数这3种分维,并对它们所揭示的土地利用空间格局变化特征予以分析。[结果]滨海新区各土地利用类型的空间分布具有明显的分形特征,而各地类3种分维值的大小和变化有效揭示出了研究区土地利用空间格局的复杂性、向心聚集性和均衡性的变化。未利用地、盐田的边界维数不断上升,表明其边界日趋复杂。港口码头、滩涂的边界日趋简单。耕地的半径维数大于2,表明其面积从中心到四周逐步增长;盐田、水域则在距城市中心的不同半径空间中较为均匀的分布;其余地类则从中心向四周分布逐步衰减。林园地、未利用地、滩涂信息维数值较小,呈现较为明显的集中分布;耕地、盐田的空间分布逐渐向外围集中;港口码头则在原有基础上建设面积不断向四方扩展;水域和居民点与工矿用地的空间分布较均匀。[结论]将分形理论运用于城市土地利用空间格局变化研究中能很好地弥补以往城市空间格局研究中定量论证的不足,具有较高的实践价值。  相似文献   

河南省驻马店市地表水出境断面考核体系的研究     

郑立庆  刘群  曹振阳 《安徽农业科学》2008,36(22)

以驻马店市水环境功能区划为基础,通过对污染物总量的核定,采用相应的水质模型确定实际水环境容量,建立驻马店市地表水出境断面考核体系。该体系已在驻马店市责任目标考核中使用,成功地解决了在环境保护目标任务计划执行年度中责任不清造成的问题,把环保目标以数字的形式纳入各县政府的年度GDP考核,取得了良好效果。  相似文献