圆形巷道围岩弹性应力场的复变函数解析

为得出圆形巷道围岩弹性应力分布特征,采用复变函数对圆形巷道围岩弹性应力进行解析,得到了与应力函数解法相同的应力场解析表达式,证明了复变函数解法求解巷道围岩应力场的可行性.对圆形巷道边界应力分布规律及沿水平线的应力分布规律进行了分析,结果表明:1)圆形巷道边界的径向应力和剪应力等于0,环向应力集中系数随侧压系数和位置角度变化而变化,与巷道半径无关;2)沿水平线的圆形巷道围岩剪应力等于0,径向应力和环向应力集中系数随侧压力系数和巷道半径变化而变化;3)沿水平线方向,侧压系数对巷道围岩径向应力的影响大于环向应力影响.还分析了侧压系数对巷道围岩应力的影响规律,讨论了侧压系数等于0、大于0小于1、等于1和大于1等4种情况下的巷道边界环向应力分布情况,得出了巷道边界环向应力的拉压区域及环向应力集中系数最大位置.     

Agricultural landscapes as multi-scale public good and the role of the Common Agricultural Policy

During the last 50 years, the Common Agricultural Policy (CAP) has impacted the evolution of European agricultural landscapes by driving changes in land use and farming practices. We propose a typology characterising the scales relevant for agricultural landscapes management and argue that action is required on three scales: (1) a landscape oriented management at the farm level; (2) the coordination of land managers’ actions at the landscape level; and (3) the conservation of the diversity of agricultural landscapes in the EU. We provide evidence that until now the CAP has mainly focused on the first scale. We also illustrate how agricultural policy could encourage coordinated actions at the landscape- and EU-scales. In particular, we propose policy instruments to coordinate actions of individual land owners (e.g. collective bonus in agro-environmental contracts or support to environmental cooperatives (scale 2)). We also analyse how the recognition and transposition of the European Landscape Convention could promote trans-frontier landscape cooperation in order, not only to conserve high-quality rural landscapes, but also to ensure the conservation of the diversity of EU landscapes (scale 3). This paper provides a knowledge base to support an integrated CAP design in the direction of improved landscape management, as an important component of the EU project towards more sustainable agriculture.     

扰动和加藻共同作用下太湖沉积物中形态磷变化规律

为了阐明反复扰动下,不同初始浓度藻对沉积物中各形态磷释放的影响.以太湖梅梁湾沉积物和上覆水作为研究材料,探讨了扰动和藻类共同作用下沉积物中各形态磷的变化规律.结果表明,无扰动状态下,NH4Cl-P和Res-P均有所降低,而Fe/Al-P和Ca-P则有所增加.其中,Ca-P随藻类初始浓度增加而增加,分别增加48%、66%、74%.但是,扰动状态下,NH4Cl-P和Res-P也明显降低.Fe/Al-P明显增加,其占总磷的百分比为66.2%(3组试验的平均值)高于不扰动状态(53.4%,3组试验的平均值);此外,Ca-P占总磷的百分比为24.1%(3组扰动试验的平均值)明显低于不扰动状态(33.0%,3组试验的平均值).这暗示了扰动和藻类共同作用下促进了Fe/Al-P的形成,而无扰动下藻类却促进了Ca-P的形成.     

一种无奇异参数椭圆柱形电磁隐身斗篷的设计基础理论

目的研究无奇异参数的椭圆柱形超材料电磁隐身斗篷的设计方法。方法应用变换光学原理建立空间变换坐标表达式,推导出该斗篷的电磁参数张量,再采用Matlab软件验证所推导张量的无奇异性,最后采用有限元仿真软件验证该斗篷的电磁隐身性能。结果椭圆柱形斗篷具备良好的电磁隐身性能,并且其电磁参数张量的各个分量均无奇异性。结论设计出的空间坐标变换方式能够从理论上实现无奇异参数的超材料电磁隐身斗篷,这种方法也拓展了变换光学原理在超材料隐身装置设计方面的应用。     

Cadmium in soybeans and the relevance to human exposure

<正>Introduction Cadmium is considered a human carcinogen by the International Agency for Research on Cancer(IARC,1993)and the US National Toxicology Program(NTP,1997).Cadmium contamination of food crops is a persistent issue for both the agricultural industry as well as consumers.This is an issue for agriculture because cadmium can be present in soils naturally or as a result of industrial processes and can contaminate foods that are consumed by humans.Industrial     

浅析原油罐二次密封在线改造过程中的风险与对策

介绍了外浮顶储罐二次密封的机理,剖析了原油储罐二次密封在线改造过程中潜在的风险,并结合某企业改造案例提出了控制措施,对类似油罐二次密封在线改造具有一定的借鉴意义。     

土地利用变化下的生态系统服务敏感性研究——以克里雅绿洲为例

通过剖析传统的敏感性分析法,提出交叉敏感性概念,评价生态服务价值对土地利用类型转换的响应性。以克里雅绿洲为研究区域,以1991、2002 和2011 年三期遥感影像数据为基本信息源,运用交叉敏感性分析,计算生态系统服务价值对土地利用类型转换的敏感性,确定生态系统日趋敏感的土地利用变化过程,为土地管理对策提供参考依据。研究结果表明:20 a来,克里雅绿洲生态服务价值较敏感的土地利用转换类型相对稳定,主要集中在湿地和水体向荒漠和低覆盖度草地的转换;与1991 和2011 年相比,2002 年的交叉敏感性系数普遍上升,这主要是因为湿地、水体面积的减少加剧了研究区的生态脆弱性,从而表现出更大的敏感性;湿地和水体向耕地转换的交叉敏感性一直处于上升趋势,并不断接近于-1,表明生态服务价值对高强度的人为活动变得越来越敏感,从而警示地方管理部门采取必要措施制止此种转换的持续。     

Implementing the Water Framework Directive: Contract Design and the Cost of Measures to Reduce Nitrogen Pollution from Agriculture

The performance of different policy design strategies is a key issue in evaluating programmes for water quality improvement under the Water Framework Directive (60/2000). This issue is emphasised by information asymmetries between regulator and agents. Using an economic model under asymmetric information, the aim of this paper is to compare the cost-effectiveness of selected methods of designing payments to farmers in order to reduce nitrogen pollution in agriculture. A principal-agent model is used, based on profit functions generated through farm-level linear programming. This allows a comparison of flat rate payments and a menu of contracts developed through mechanism design. The model is tested in an area of Emilia Romagna (Italy) in two policy contexts: Agenda 2000 and the 2003 Common Agricultural Policy (CAP) reform. The results show that different policy design options lead to differences in policy costs as great as 200–400%, with clear advantages for the menu of contracts. However, different policy scenarios may strongly affect such differences. Hence, the paper calls for greater attention to the interplay between CAP scenarios and water quality measures.     

Shorter fries? An alternative policy to support a reduction of nitrogen contamination from agricultural crop production

Feeding the growing population of the world poses significant policy challenges for the sustainability of global ecosystems. A prime example is the degradation of water quality due to the growing imbalance in the terrestrial nitrogen (N) cycle linked to increasing production of reactive N (Nr). Environmental impacts such as groundwater quality degradation and eutrophication of coastal estuaries tend to be local in nature but may be closely connected to global economic factors. Environmental accounting of the N fluxes entering, leaving or remaining in Prince Edward Island (PEI), a small agricultural region, demonstrate the importance of a single industry (potato production) in controlling the local N cycle. The resulting burden of Nr has its most profound effect on groundwater, the sole source of drinking water and the primary pathway of N to the Province's economically and ecologically important estuaries. At the same time, agriculture is a vital part of the local economy, and regulators are faced with the challenge of meeting environmental goals and still maintaining an industry that is competitive and responsive to global market trends. New, innovative policy alternatives are needed to foster more effective implementation of sustainable agricultural practices. An approach that focuses on influencing consumer choices toward more environmentally responsible production practices at the point of origin may help remove some of the important, non-technical barriers to sustainable food production practices. In practice, a system that documents the environmental performance throughout the full supply chain from producer to retailer would have to be implemented.     

Towards phosphorus sustainability in North America: A model for transformational change

Global food production and security rely heavily on finite reserves of newly mined phosphate for fertilizers. However, systemic inefficiencies result in the deposition in aquatic ecosystems of much of the phosphorus mined for food production causing costly eutrophication problems that damage aquatic ecosystems and human health. The Sustainable Phosphorus Alliance (SPA, formerly named North American Partnership for Phosphorus Sustainability) was created to implement sustainable phosphorus solutions through active engagement of stakeholders in both the private and public sectors. This paper describes a conceptual model of transformative change to a sustainable phosphorus system for the North American region. The model emerged from discussions at a series of formal and informal meetings held in conjunction with a ‘Future of Phosphorus’ event (National Science Foundation’s Phosphorus Sustainability Research Coordination Network) and an inaugural SPA Board meeting. Model development drew on the multi-level perspective of socio-technical transitions to develop a series of pathways to a transformed phosphorus system. The uses of the model and transition pathways are discussed in terms of their potential to form an important first step towards the development of a regional vision for improved phosphorus sustainability. The process provides an example of how research in sustainability science can contribute to action on environmental improvement.