经济政策不确定性对中国粮食安全的影响

为探究经济政策不确定性对中国粮食安全的影响,基于2000—2018年中国31个省(市、自治区,统计数据未含港澳台地区)的面板数据,采用PVAR模型,研究经济政策不确定性对中国粮食供给安全、获取安全、稳定性安全和资源安全的影响及区域差异。结果表明:1)总体上,经济政策不确定性对中国粮食安全具有负向影响。2)分区域看,粮食主产区的供给安全受经济政策不确定性负向影响最大,粮食主销区的获取安全受经济政策不确定性冲击最为明显,经济政策不确定性对粮食产销平衡区的冲击最小。3)从粮食安全衡量维度看,经济政策不确定性对供给安全、获取安全和资源安全具有抑制影响,对稳定性安全呈现正向冲击作用。为确保粮食安全,中国应继续加强对粮食生产政策支持、稳定国内粮食价格和健全保障粮食安全的制度机制。     

Prevalence and risk factors of Coxiella burnetii seropositivity in Danish beef and dairy cattle at slaughter adjusted for test uncertainty

Antibodies to Coxiella burnetii have been found in the Danish dairy cattle population with high levels of herd and within herd seroprevalences. However, the prevalence of antibodies to C. burnetii in Danish beef cattle remains unknown. The objectives of this study were to (1) estimate the prevalence and (2) identify risk factors associated with C. burnetii seropositivity in Danish beef and dairy cattle based on sampling at slaughter.     

紫外分光光度法测定阿苯达唑片含量的不确定度评定

对紫外-可见分光光度法测定阿苯达唑片含量的不确定度进行评定以及测量过程中各种不确定度来源进行分析与评估,含量测定结果可表示为（95．7±2．0）％（k=2）。结果表明,仪器的吸光度、重量差异、称样量和移液管的体积引入的不确定度为测量结果不确定度的主要影响因素。     

把不确定性引入生物学参考点F0.1和Fmax的估计以评估东海带鱼渔业资源

东海带鱼(Trichiurus haumela)是东海区重要经济鱼类之一,目前还没有研究在生物学参考点F0.1和Fmax的估计中引入不确定性并在此情况下对东海区带鱼渔业资源进行量化评估。文章应用蒙特卡罗模拟方法研究了渔业数据中不同水平的不确定性和不同初次捕捞年龄对F0.1和Fmax估计的影响,用其与现在的捕捞死亡系数Fcur做比较,初步评估了东海带鱼渔业资源。计算结果表明,高水平的不确定性将会增加在F0.1和Fmax估计中的差异,从而使其被定义为过度捕捞的可能性减小。经过比较表明,F0.1比Fmax是一更好的参考点,且东海区带鱼渔业明显处于过度捕捞状态。不同初次捕捞年龄下单位补充量渔获量的变化情况的研究表明,增大初次捕捞年龄可以减小现在的捕捞死亡率大于参考点死亡率的概率,从而增大初次捕捞年龄可以改善现在捕捞过度的资源状况。     

Introduction of genetic engineering in aquaculture: Ecological and ethical implications for science and governance

Within aquaculture, genetic engineering (GE) is emerging as a powerful method for breeding of fish and shellfish, and for developing alternative sources of feed and vaccines to combat diseases. On the other hand, the use of GE in aquaculture raises ecological, ethical and economic concerns. For instance, genetically modified (GM) feed could be spread to the aquatic environment and consumed by other marine organisms, and horizontal gene transfer may conceivably occur from DNA in feed or vaccines to a recipient genome or by faeces to the environment. Numerous reports have described beneficial effects such as viral disease resistance following DNA vaccination. However, side effects, such as activation of other genes than those which are central in immune defence mechanisms, may occur and warrant further investigations. In order to achieve sustainable introduction of GE, it is crucial that appropriate scientific investigations and ethical considerations are done prior to large-scale introduction of GE products such as DNA/GE vaccines and GM feed in commercial fish farming. This may result in a solid basis for the avoidance of potentially undesirable health and environmental effects. If GE can help make aquaculture a sustainable industry, this opens the possibility of positive market and consumer responses. This can best be achieved by involving the stakeholders from the conceptual stage to the commercial stage by facilitating a transparent process whose purpose is to inform research, to identify decision stakes, and to influence design, adoption and implementation of pro-active policy.     

土壤压实度测量系统研究进展

随着农业机械功率的不断增加和机具下地次数的增多,土壤压实的问题愈加明显.为了定量获得土壤压实特性,研究人员开发了各种各样的土壤压实度测量系统.分析了土壤压实产生原因、危害,重点对国内外压实度测量系统的研究现状进行了综述,指出通过测试土壤阻力获得其三维的分布特性是土壤压实测量的发展趋势.     

微波消解-原子荧光光谱法测定豆粉中总汞的不确定度评定

为了得到准确而完善的检测结果,对微波消解-原子荧光光谱法测定豆粉中总汞结果的不确定度进行了评定,结合各不确定度分量对测定方法中不确定度的主要来源进行了分析。结果表明:样品的前处理方法以及试样的重复性对获得准确测定结果尤为重要,标准曲线的配制也是重要的不确定度来源,同时需要确保仪器的稳定性,而试样定容和样品称样引入的不确定度极低,可以忽略。通过不确定度的评定,明确了测定过程中主要误差的来源,为降低检测过程中的误差提供了依据。     

单腔单振子压电泵流量自测量方法研究

为满足压电泵系统流体精确控制及小型化的需要,提出利用压电自感知及神经网络技术的单腔单振子压电泵流量自测量方法。压电泵结构上采用双压电晶片振子同时作为执行元件与传感元件使用。首先分析了流量影响因素,并分析了传感压电片输出信号与振子变形关系。得出:压电泵流量与振子振动状态存在函数关系,振子的振动状态可由传感压电信号实时反映,因此在信号中隐含着压电泵流量信息。据此制作了传感压电信号参数测量电路样机,将参数测量结果作为神经网络输入,建立了用于压电泵流量预测的BP神经网络模型。实验结果表明:利用该方法得到的预测值与实验测量值之间相关系数在0.999 3以上,最大相对误差率小于3.46%,预测结果与测量值接近。该流量自测量方法具有较好的准确性。     

超重车辆过桥措施的探讨

本文论述了桥梁实际承载能力方法确定及超重车辆过桥的一般要求;同时阐述了桥梁加固措施.