非水平海底情况下海底地震波时域有限差分数值模拟

研究复杂海洋环境中海底地震波激发及其传播特性,对海底物理力学特性研究、资源勘探等具有重要的意义.目前针对时域海底地震波的研究大都局限于水平分层的情况,而实际的海底地质条件比较复杂,基于理想环境假设得出的数值解与实际差别较大.本文在考虑倾斜、隆起等非水平海底模型的情形下,采用时间2阶精度、空间10阶精度的交错网格有限差分方法,同时结合多轴完全匹配层边界条件,对复杂海洋环境下的海底地震波进行时域数值模拟与分析.利用计算得到的声场时域波形,分析了复杂海洋环境下海底地震波的传播特性.结果表明,采用空间高阶精度的交错网格有限差分方法,可改善数值计算中的频散问题;同时采用多轴完全匹配层替代传统的完全匹配层,解决了液-固介质中远距离声场数值模拟不稳定的问题.在含倾斜与隆起构造的复杂海底模型中,海底基岩隆起改变了 Scholte波的传播方向,更有利于在较浅深度处接收到Scholte 波.     

Organocatalytic copolymerization of mixed type monomers

Triggered by environmental concerns and the rising demands for metal-free polymers in e.g.bio-related and microelectronic applications,studies on organocatalytic polymerization have been launched and developed unprecedentedly during the last 15 years.A wide range of organic molecules are now available in polymer chemists' toolbox to choose from as catalysts for polymerization of (hetero)cyclic and polar vinyl monomers.Apart from the intrinsic merits such as lower toxicity and better solubility compared with (transition) metal catalysts/initiators,organocatalysts have also shown,in many cases,excellence to achieve high polymerization rates and/or good control (selectivity).In addition,particular natures and catalytic/activating mechanisms of organocatalysts have led to new opportunities for rational design and efficient synthesis of macromolecular architectures,i.e.chain structures,topological structures and functionalities.This mini-review is specially themed on pathways to construct copolymer chain structures by organocatalytic copolymerization of mixed type monomers (comonomers bearing different polymerizing moieties) and will be sectioned by different comonomer combinations,including cyclic monoesters of different sizes,cyclic monoesters and lactides,cyclic esters and cyclic carbonates or epoxides,heterocycles and vinyl monomers.     

不同时变延迟下的多AUV编队协调控制

针对无领航者AUV编队协调控制问题,提出了一种不同时变通信延迟下的一致性协调控制方法。首先考虑到AUV之间水下通信存在时间延迟和数据丢失的问题,利用状态反馈线性化理论处理AUV数学模型中的非线性耦合项,从而将复杂的AUV模型转换为双积分器动态模型。其次,针对不同延迟通信情况,设计了位置和速度双独立的拓扑结构以减少编队成员之间发送每个数据包中的数据量。最后,提出了无领航者的多AUV稳定条件,进而将多AUV编队控制问题看作是一致性问题,基于Laypunov-Razumikhin定理证明时延多AUV编队系统的稳定性。该控制方法不仅能够克服不同时变延迟和数据丢失对编队的影响,使所有以随机位置和速度出发的AUV的三维轨迹均能达到一致状态,同时能抑制外界干扰。仿真结果与所提控制方法理论结果一致。