以非线性理论阐述反馈振荡器的频率与幅度的稳定性

本文首先对线性的频率稳定理论用于近似正弦反馈振荡器的线性频率稳定理论,进行了评论性的回顾。在这方面,解释所谓的线性振荡器是清楚的。其后,是应用描述函数法和判决方程法所得到新的表达式,去阐述反馈振荡器考虑成一个非线性网络时的振荡频率和振荡幅度的稳定性。     

Status of development,regulation and adoption of GM agriculture in Africa: Views and positions of stakeholder groups

The use of genetically modified (GM) crop technology in tackling food security problems and poverty reduction in Africa continues to generate debates over its benefits and safety. Only four countries, South Africa, Sudan, Burkina Faso and Egypt have commercialized GM crops in Africa but controversy surrounds current cultivation of GM maize in Egypt. Our study provides new perspectives on the status, development and regulation of GM crops through examining the views of 305 stakeholders in six African countries across four regions: South Africa, Kenya (East Africa), Egypt and Tunisia (North Africa), Ghana and Nigeria (West Africa), supplemented by interviews with relevant international organizations. The study revealed the challenges leading to the development of biosafety regulatory frameworks and the role of individual stakeholders in the facilitation of GM crops across African countries. This study also revealed that some countries may go through a Fiber–Feed–Food (F3) approach to adopt GM crops where Bt cotton will be adopted first followed by GM crops for livestock feed while undergoing all the necessary assessments before producing GM foods for human consumption. An overwhelming majority of stakeholders placed emphasis on risk analysis (risk assessment and management) in view of limited capacity, lack of scientific expertise and public concern, and encouraged a centralized approach to risk assessment similar to the European Union model of the European Food Safety Authority (EFSA).     

国外饲料安全的研究进展

通过查阅国外近20年发表的关于饲料安全方面研究的文献,调查国外饲料安全研究的进展情况。结果显示近几年国外对饲料安全越来越关注,主要包括：对欧盟饲料安全法律法规及监管体系的介绍和评价;快速识别原料来源的检测技术研究;转基因产品作为饲料的安全性研究;饲料中二英/多氯联苯的报道;饲料中微生物污染调查和控制及益生菌的研究;对饲料添加剂的研究报道;对植物毒素和真菌毒素的研究。     

金融风暴之后的中国产品内贸易问题研究

本文首先综述了产品内贸易理论问题,其次,分析国际金融风暴之后,以来料加工装配贸易和进料加工贸易为主的中国产品内贸易问题,最后,从产品结构、贸易方式、区域发展、服务外包等方面对中国产品内贸易给出相关政策建议。     

双反馈晶振和石英谐振器低噪声性能的进一步研究

本文进一步探讨了有关双反馈晶振低噪声性能的问题,着重分析了石英谐振器静电容C_0对双反馈晶振电路Q倍增固子、石英谐振器Q值及净噪特性的影响。为验证上述C_0的影响,也对不同C_0的石英谱振器的相噪特性进行了测量并得到了与分析一致的结果。     

基于Feed4JUnit架构的单元测试技术研究与应用

软件测试技术在软件质量控制过程中一直起着非常重要的作用。JUnit是被广泛应用的Java单元测试框架,主要测试基于java语言编写的程序代码,用于编写和运行可重复的测试。Feed4JUnit是开源的基于JUnit的扩展,通过使用Feed4JUnit提供的注释,用户可以很方便地把测试数据存放在文件或其他数据源。本文分析了应用Feed4JUnit进行单元测试的方法,并通过实际开发示例实现数据与代码分离的测试。     

出口玻璃食品接触材料风险分析

根据世界各国对玻璃食品接触材料卫生要求和2000-2010年欧盟食品与饲料快速预警系统对我国出口的玻璃类食品接触材料的通报情况,分析我国出口玻璃类食品接触材料的风险和通报原因,提出相关的应对措施和检验监管建议。     

Decompositions of corn price effects: implications for feed grain demand and livestock supply

This article examines how corn prices affect the demand for feed grains and the supply of livestock outputs. The differential approach to the theory of the multiproduct firm is employed to examine ex ante decisions about feed grain demand and livestock supply. The estimation results suggest that livestock producers have little flexibility in adjusting the demand for corn in response to an increase in corn prices. The substitutable relationship between corn and distillers’ grains contributes to alleviating pressures on feed costs in response to high corn prices. In addition, the estimation results highlight that the composition of livestock supply can be altered by changes in livestock prices. On the basis of the estimated elasticities, the decompositions of profit‐maximizing input demand are conducted to examine the effects of changes in corn prices on feed grain demand and livestock supply. The decomposition results reveal that an increase in corn prices reduces corn demand but raises the demand for distillers’ grains mainly due to the substitution effects of corn price changes. The decomposition results also show that an increase in the price of corn reduces cattle supply but raises the supply of chicken and pork due to the output relationships in supply.     

Demand for improved fish feed in the presence of a subsidy: a double hurdle application in Kenya

Fish farming households’ demand for improved fish feed from the private market in Kenya is potentially influenced by the government's feed subsidy program. This article applies the double‐hurdle model to a cross‐section of fish farms to analyze demand for improved fish feed from private markets, and whether the government feed subsidy program has an effect on private demand for improved feed. The results indicate that households’ decisions to participate in the improved feed market are affected by the quantity of improved feed received from the government. Once the participation decision has been made, we find evidence of crowding‐in of the private improved feed sector; that is, the government's allocations of subsidized feed appear to increase private sector demand. In addition, the price of improved feed negatively affects the quantity purchased as expected. Education, extension contacts, and ease of marketing matured fish increase household propensity to purchase improved feed commercially. Policies that help reduce the price of improved feed such as reduction in tariffs on imported feeds and feed ingredients will foster demand for the feed, as will policies that facilitate marketing of fish at reasonable prices by households.     

饲粮中高铜高锌在组织中残留及排泄规律的研究

研究了在20～100kg生长猪饲粮中添加不同水平的铜和锌对猪组织中铜和锌残留量及排泄规律的影响。54头（长白×约克二元杂交）猪随机分成6个组,各组在基础日粮中添加铜和锌（硫酸铜/硫酸锌,mg/kg）水平为：0/0、170/130、250/430、300/630、350/830、400/1030,试验期为90d。结果表明,与对照组比较,使用高铜高锌饲粮会显著增加肝中铜和锌的残留量（P〈0.05）,铜的残留量随用量的增加呈线性上升,锌的残留量在添加（铜/锌）量250/430mg/kg时,最高;肉中铜和锌在添加量（铜/锌）分别达到350/830mg/kg、300/630mg/kg时,达到最高（P〈0.05）;粪中排出的铜和锌量与饲粮中添加量有密切关系,添加量越多,排泄量越多,呈线性上升。使用高铜高锌饲粮会增加肝脏、肌肉中铜和锌的残留量,增加粪中的排泄量。