A new polymer supported BINOL ligand(4) was prepared by means of anchoring binaphthyl molecule(3) to aminoethylated polystyrene through a procedure of solid phase peptide synthesis. The key compound ( R ) 2,2 dihydroxy 1,1 binaphthyl 3 carboxylic acid(3) was prepared from R BINOL by protection of hydroxyl groups and then reaction with n butyllithium followed by carboxylation. By controlling the amount of BuLi, (3) was obtained in 55% overall yield. Ligand (4) was prepared through condensation of (3) with aminoethylated polystyrene in the presence of DCC and HOBt and found to have a loading of 0.40 mmol/g (by mass increase). The linkage between binaphthyl and aminoethylated polystyrene was indicated by a new absorption in IR spectrum of (4) at 1 644 cm -1 in comparing with what of the polystyrene. By mixing (4) with Ti(OiPr) 4 in dry CH 2Cl 2, a complex was easily prepared and this complex was found to be an efficient heterogeneous catalyst in asymmetric addition of diethylzinc to aldehydes. Optical active alcohols with up to 82% ee were obtained from the asymmtric addition with high chemical yields when 20% of (4) was used. And when benzaldehyde was used as substrate, we found that enantioselectivity increased obviously when the amount of (4) used in reaction increased from 5% to 20%;decreased the load of BINOL in ligand (4) reduced the ee of addition product; and R form of products was resulted. [WT5HZ]
近几年,无线传感器网络能够实时监测和传输环境数据信息变得日益重要,尤其在民用和军事领域得到很广泛的应用。无线传感器网络具有传统网络无可比拟的优势,每个传感器节点用来感知周围环境事件和采集数据,并将采集的数据通过一跳或者多跳路由传给簇头节点或者接收器节点,然后发送到基站或数据中心进行处理。假定每个节点对信息的处理看作是一个任务,考虑节点能量限制,节点采用唤醒/休眠机制,在唤醒期间确保节点任务完成,簇头节点能够调度处理多个传感器节点的任务。文中解决的问题:在满足多个传感器节点任务处理的截止期失效前,簇头节点如何合理的调度任务,提出了改进的RM(rate-monotonic)调度算法和动态的抢占式最早截止期优先任务调度算法(Preemptive Earliest Deadline First Algorithm,PEDFA)。通过具体任务实例说明算法的实现过程,结果表明该算法运行简单,能够很好减少节点任务的延迟时间,实现节点任务的合理调度。
