在中国环境条件下油菜花粉介导的除草剂抗性基因飘逸

依据转基因安全评估的个案原则, 研究了抗除草剂转基因油菜花粉向中国传统油菜品种的飘逸概率及其影响因素. 通过检测受体植株后代的除草剂抗性检测转基因油菜花粉的飘逸率. 结果表明, 花粉飘逸的距离达2000 m, 且飘逸率随着与花粉源区距离的增加而急剧减少. 但在距花粉源区33.5~2000 m的范围内, 花粉飘逸率均低于0.015%, 且并不随距离增加而逐渐下降, 表现了花粉长距离飘逸和授粉的随机性. 绝大多数花粉散布在花粉源区周围4.5 m范围内, 其中最大飘逸率为1.19%, 出现在距源区1.4 m的取样点. 风向显著影响花粉飘逸的方向和距离. 但是, 授粉昆虫蜜蜂的数量与花粉飘逸方向和距离没有相关性, 表明花粉飘逸的方向性差异并不是由于蜜蜂的数量及分布引起的. 本研究在中国自然环境条件下开展大面积田间试验, 为转基因油菜的商品化生产和安全管理提供科学依据. 花粉空间分布模型为油菜杂交种生产的隔离距离与杂种纯度估计等研究提供了重要的依据.     

基于微丝的PDMS微流动通道制作技术

微流动通道是微流控芯片的重要组成部分, 其加工技术的每一步进化或简化一直为国际学术界与工业界所重视. 提出了一种基于微丝的PDMS微流动通道制作技术. 该技术利用一些简单的模具辅助固定和布置微丝, 然后将PDMS预聚物浇注于模具中浸没微丝并固化, 固化后抽出微丝形成PDMS微通道或通道阵列, 在与通道垂直的方向上打孔并封装, 形成与通道外部物质交换的接口. 实际制作通道时可采用商用化的金属微丝(如不锈钢微丝), 直径从100~20 μm不等. 较为详细地介绍了利用这种技术来构建多种拓扑结构的二维或三维通道或通道阵列, 例如直通道、交叉通道、弯曲通道等的能力. 进一步, 基于金属微丝的电磁特性, 这样的微通道制作工艺还被应用来构建出适于电磁控制和温度控制的微流动通道装置. 最后, 通过圆截面微通道的光路分析、微通道内粒子流动的图像测速(Micro-PIV)与微液滴形成实验及分析进一步印证了这种微流动通道制作技术的可行性和适用性.     

全方位移动避障实时轨迹控制算法的研究

针对机器人避障轨迹控制过程中存在的路径优化以及如何躲避大障碍物或者是多障碍物的情况,本文提出一种基于狄克斯特拉算法与贝塞尔曲线的机器人移动避障实时控制改进算法,该算法引入机器人与目标终点路径的速度分量,采用狄克斯特拉算法进行移动轨迹路径优化,进而采用贝赛尔曲线修订优化路径,以此满足动态约束条件.仿真结果表明:相对于改进人工势场算法,本文构建的改进算法使得机器人移动时间缩短,机器人避障运动规划明显改善,具有较强的鲁棒性.     

广域差分系统中的卫星钟差改正方法

在深入分析星钟和星历分离的广域差分原理的基础上, 利用简易的广域差分仿真平台, 分析了这种原理在差分站时间同步时采用的绝对分离, 以及在主差分站同步、副差分站时间不同步时采用相对分离这两种方法的异同, 分两步给出了副差分站不同步时卫星钟差一站式改正方法, 提出并重点讨论了星钟二次改正的逆向推理算法. 仿真分析得出当差分站采用码相位的伪距测量时, 采用这种钟差改正方法可以实现5~7 ns的授时精度, 当差分站采用载波相位平滑伪距时, 这种钟差改正方法可以实现1~3 ns的授时精度.     

Design and Analysis of Prioritized Medium Access Control Protocol for Backbone Routers in Wireless Mesh Networks

A Prioritized Medium Access Control (P-MAC) protocol is proposed for wireless routers of mesh networks with quality-of-service provisioning. The simple yet effective design of P-MAC offers strict service differentiation for prioritized packets. A Markov model is developed to yield important performance matrices including the packet blocking probability due to queue overflow and the packet reneging probability due to delay bound. It is further proved that the service time of P-MAC approximates exponential distribution, and can be effectively estimated. The analytic models with preemptive and non-preemptive schemes, validated via simulations, show that P-MAC can effectively support traffic differentiation and achieve very low packet dropping (both reneging and blocking) probabilities when the traffic load is below the channel capacity. When the network is overloaded, P-MAC can still maintain extremely stable and high channel throughput. Moreover, it is demonstrated that P-MAC performs superior in multihop networks, further proving the advantages of the proposed protocol.     

Modeling Car-Following Dynamics During the Starting and Stopping Process Based on a Spring System Model

Car-following models describe how one vehicle follows the preceding vehicles.ln order to better model and explain car-following dynamics,this paper categorizes the state of a traveling vehicle into three sub-processes:the starting(acceleration)process,the car-folloing process,and the stopping(deceleration)process.The stating process primarily involves vehicle acceleration behavior.The stopping process involves not only car-following behavior but also deceleration behavior.This paper regards both the stopping process and the starting process as spring systems.The car-following dynamics during the starting process and the stopping process is modeled in this paper.The parameters of the proposed models,which are represented in the form of trigonometric functions,possess explicit hysical meaning and definitive ranges.We have calibrated the model of the starting process using data form the Traffic Engineering Handbook and ob-tained reasonable results.Compared with traditional stimulus-response car-following mo     

Toward interoperable bioscience data

To make full use of research data, the bioscience community needs to adopt technologies and reward mechanisms that support interoperability and promote the growth of an open 'data commoning' culture. Here we describe the prerequisites for data commoning and present an established and growing ecosystem of solutions using the shared 'Investigation-Study-Assay' framework to support that vision.     

ANLL中转录因子GATA—2基因点突变

了解转录因子ＧＡＴＡ－２基因在ＡＮＬＬ中的表达和突变情况,方法：采用ＲＴ－ＰＣＲ检测８５例ＡＮＬＬ病人外周血单个核细胞中ＧＡＴＡ－２基因的表达情况,ＰＣＲ产物进一步经单链构象多态性（ＳＳＣＰ）分析以了解基因突变情况。结果：绝大多数ＡＮＬＬ都表达了ＧＡＴＡ－２基因（８９．４％）,ＳＳＣＰ分析发现一例Ｍ２型的ＰＣＲ产物出现异常迁移带,核苷序列分析显示在ＧＡＴＡ－２基因第８９２位的核苷酸出现点突变,即第     

Reciprocal crossover asymmetry and meiotic drive in a human recombination hot spot

Human DNA diversity arises ultimately from germline mutation that creates new haplotypes that can be reshuffled by meiotic recombination. Reciprocal crossover generates recombinant haplotypes but should not influence the frequencies of alleles in a population. We demonstrate crossover asymmetry at a recombination hot spot in the major histocompatibility complex, whereby reciprocal exchanges in sperm map to different locations in the hot spot. We identify a single-nucleotide polymorphism at the center of the hot spot and show that, when heterozygous, it seems sufficient to cause this asymmetry, apparently by influencing the efficiency of highly localized crossover initiation. As a consequence, crossovers in heterozygotes are accompanied by biased gene conversion, most likely occurring by gap repair, that can also affect nearby polymorphisms through repair of an extended gap. The result is substantial over-transmission of the recombination-suppressing allele and neighboring markers to crossover products. Computer simulations show that this meiotic drive, although weak at the population level, is sufficient to favor eventual fixation of the recombination-suppressing variant. These findings provide an explanation for the relatively uniform widths of human crossover hot spots and suggest that hot spots may be generally prone to extinction by meiotic drive.