中国农产品国际贸易中的虚拟水流动分析   总被引：2，自引：1，他引：2  

马超  许长新  田贵良 《资源科学》2011,33(4):729-735

基于虚拟水战略视角,在综述国内外研究进展的基础上,对2005年-2009年我国农产品国际贸易中的虚拟水流动情况进行了实证分析。研究得出:我国在农产品贸易方面依然存在较大逆差,由此决定了虚拟水净进口量的逐年增加,2005年-2009年间,我国平均每年约有900亿m~3虚拟水净输入,一定程度上缓解了国内水资源短缺问题;金融危机引起了我国农产品贸易中逆差的持续加大,2008年我国农产品虚拟水净进口量首次超过1000亿m~3,意味着对虚拟水进口依赖程度的显著增加;金融危机导致农产品贸易的内部结构发生了一定改变,而从贸易品种来看,目前我国农产品的对外贸易结构依然较为单一。同时研究认为,应将虚拟水贸易理论引入我国农产品贸易体系,按照虚拟水要素的比较优势制定国际农产品贸易的相关政策,为改变目前虚拟水对外依赖程度较高和农产品贸易结构单一的格局,应努力实现我国农产品贸易结构优化及贸易伙伴多元化。  相似文献   

1996年和2011年全球农产品贸易中氮素流向和流量的变化     

李洁静  张卫峰  马林  郭明亮  张福锁 《资源科学》2014,36(8):1755-1764

为了更有效地利用资源同时保护环境,有必要了解新时期全球养分的分布特征。本文通过量化不同农产品中所包含的氮,研究比较了全球肥料氮、植物性食品氮、动物性食品氮和饲料氮等在1996年和2011年的流量和流向变化。结果表明,与1996年相比,全球氮素贸易量增加了1 371.3万t,到2011年达到3 380.1万t。从产品来看,肥料氮、饲料氮、植物性食品氮对增量的贡献分别为59.3%、19.7%和18.7%,说明能源和土地是氮素流量变化的关键因素。从区域来看,北美和南美对肥料氮进口增量的贡献为39.5%和28.5%,其加强了矿产依赖型的氮肥产品进口,而增加了土地依赖型的植物性食品和饲料出口;而亚非发展中国家与地区则相反,其对植物性食品氮和饲料氮进口增量的贡献为44.7%和21.3%。向以矿产换土地模式的转变加剧了亚非发展中国家与地区的食物安全和能源安全问题,而氮素的跨地区运输又加剧了所有地区的环境问题。因此,各国应据此思考本国食物安全、能源安全和环境安全的最优氮管理策略。  相似文献   

基于PSD-BPA的县级电网无功优化分析     

张一新 《大众科技》2014,(7):104-106

文章主要介绍了利用PSD-BPA潮流计算软件进行县级电网潮流计算的方法、步骤及进行县级电网潮流计算结果优化调整的一些具体措施;并以横县电网为例,介绍了县级电网无功优化结果对县级电网规划建设的重要作用。除此之外,文章还简单的介绍了进行县级电网潮流计算的方法、步骤和进行县级电网规划建设的原则、方法和步骤,以期能为有关部门进行县级电网的无功优化和规划建设提供一定的参考。  相似文献   

学报管理信息系统建模与增量式开发研究     

赵剑冬  王志云 《技术与创新管理》2014,(3):218-221,253

为了提高学术论文出版效率,高校学报编辑部需要建设基于Web的学报管理信息系统。充分利用大学教师和学生协作团队的人力资源优势开发一个满足基本需求和具有扩展功能的学报管理信息系统是可行的。研究首先进行系统需求分析并采用数据流图对学报管理信息系统六种用户角色进行建模,描述了增量式开发方法在学报管理信息系统开发中的实际应用流程。  相似文献   

一种模拟液化后的砂土在高孔压比状态下流动特性的试验方法研究     

姜兆起  陈晓冬  万小旗 《科教文汇》2014,(30):112-113

根据流体力学中的绕球定常黏性流动理论,在传统振动台试验的基础上,设计了一套模拟液化砂土高孔压比状态下流动特性的试验装置,在装有与氯化钠溶液混合的塑料砂的模型箱中埋入可以竖直滑动的有机玻璃半球,半球在其中竖直运动时可以模拟出半球在液化砂土中的运动,可以观察半球运动过程中塑料砂颗粒的运动特性。试验结果表明,本方法可以有效地做到模拟砂土液化后的力学状态,并且性质稳定,可以较好地获得砂土液化后的流动特性。  相似文献   

The impacts of science and technology policy interventions on university research: Evidence from the U.S. National Nanotechnology Initiative     

Hyun Ju Jung  Jeongsik “Jay” Lee 《Research Policy》2014

We examine how the National Nanotechnology Initiative (NNI), a recent U.S. government science and technology (S&T) program launched in 2000, affects the nature of university research in nanotechnology. We characterize the NNI as a policy intervention that targets the commercialization of technology and a focused research direction to promote national economic growth. As such, we expect that the NNI has brought about unintended consequences in the direction of university–industry knowledge flows and the characteristics of university research output in nanotechnology. Using a difference-in-differences analysis of U.S. nanotechnology patents filed between 1996 and 2007, we find that, after the NNI, U.S. universities have significantly increased knowledge inflows from the industry, reduced the branching-out to novel technologies, narrowed down the research scope, and become less likely to generate technological breakthroughs, as compared to other U.S. and non-U.S. research institutions. Our findings suggest that, at least in the case of the NNI, targeted government S&T programs may increase the efficiency of university research, but potentially do so at a price.  相似文献   

弹性集群研究评述     

孟祥芳 《科技管理研究》2014,(18)

弹性集群作为一个新概念,为集群的可持续发展研究提供了新的视角。通过对国外弹性集群研究文献进行梳理,以路径依赖理论和复杂自适应系统理论为基础,从知识流动视角、复杂网络视角、生命周期与自适应周期视角对弹性集群的相关研究进行分析,希望为我国的产业集群转型升级以及高新区二次创业提供参考和借鉴。  相似文献   

Versatile on-demand droplet generation for controlled encapsulation     

Minsoung Rhee  Peng Liu  Robert J. Meagher  Yooli K. Light  Anup K. Singh 《Biomicrofluidics》2014,8(3)

We present a droplet-based microfluidic system for performing bioassays requiring controlled analyte encapsulation by employing highly flexible on-demand droplet generation. On-demand droplet generation and encapsulation are achieved pneumatically using a microdispensing pump connected to a constant pressure source. The system generates single droplets to the collection route only when the pump is actuated with a designated pressure level and produces two-phase parallel flow to the waste route during the stand-by state. We analyzed the effect of actuation pressure on the stability and size of droplets and optimized conditions for generation of stable droplets over a wide pressure range. By increasing the duration of pump actuation, we could either trigger a short train of identical size droplets or generate a single larger droplet. We also investigated the methodology to control droplet contents by fine-tuning flow rates or implementing a resistance bridge between the pump and main channels. We demonstrated the integrated chip for on-demand mixing between two aqueous phases in droplets and on-demand encapsulation of Escherichia coli cells. Our unique on-demand feature for selective encapsulation is particularly appropriate for bioassays with extremely dilute samples, such as pathogens in a clinical sample, since it can significantly reduce the number of empty droplets that impede droplet collection and subsequent data analysis.  相似文献   

Experimental study on calculation of hydro-geological parameters for unsteady flow     

熊春宝  陈雯  叶作安 《天津大学学报(英文版)》2013,19(5):351-355

After the linear analytical method of unsteady flow theory is further improved, an innovative and faster algorithm is introduced. The water storage in a confined aquifer is derived from the water transmissivity coefficient and the water-pressure conductivity coefficient. The water transmissivity coefficient is approximated by a Taylorseries expansion of drawdown, and the water-pressure conductivity coefficient is obtained by the average drawdown. In this algorithm, the distance of the observation points from the pumping well must be short. When the distance is as short as the radius of the main pumping well, the data of the drawdown difference between the sidewall and the center of pumping well are difficult to measure, but the same results can be achieved based on the assumption that the drawdown difference approximates to the drawdown of the observation wells at a radial distance from the pumping well according to the algorithm. Without the help of charts, this algorithm is more concise and efficient, which has been verified by the test of water pumping project in Tianjin Binhai International Airport.  相似文献   

从教师交流政策看实施教育公平的政策逻辑     

邓旭 《辽宁教育研究》2013,(8):46-49

为实现义务教育师资的均衡发展,2006年全国各省市相继出台了“中小学教师交流政策”,至2012年此项政策执行的6年时间里并没有很好地实现政策目标。教育公平为教师交流政策研究提供了新视角,从教育公平的起点、过程、结果三个阶段,分析教师交流政策的合法性和合理性问题,有助于教师交流政策的实施和教育公平的实现。  相似文献