Highly Robust Palladium(II) α‐Diimine Catalysts for Slow‐Chain‐Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate

A series of sterically demanding α‐diimine ligands bearing electron‐donating and electron‐withdrawing substituents were synthesized by an improved synthetic procedure in high yield. Subsequently, the corresponding Pd complexes were prepared and isolated by column chromatography. These Pd complexes demonstrated unique properties in ethylene polymerization, including high thermal stability and high activity, thus generating polyethylene with a high molecular weight and very low branching density. Similar properties were observed for ethylene/methyl acrylate copolymerization. Because of the high molecular weight and low branching density, the generated polyethylene and ethylene/methyl acrylate copolymer were semicrystalline solids. The (co)polymers had unique microstructures originating from the unique slow‐chain‐walking activity of these Pd complexes.     

小学生穿暴走鞋的步行行为研究

通过小学生群体穿运动鞋与暴走鞋的步态,研究运动鞋、无轮暴走鞋、有轮暴走鞋在步行过程中的步行行为特点.用高速摄像机从侧面拍摄小学生穿运动鞋与暴走鞋时的步态过程,分析正常步行时的步长、步频、步速与落地角的步行行为指标特征,检验鞋跟高度差异对步行的影响.结果表明:小学生步行时的最长步长是运动鞋,有轮暴走鞋最短;运动鞋、无轮暴走鞋、有轮暴走鞋的步频、步速与落地角呈现递减趋势;运动鞋与有轮暴走鞋、无轮暴走鞋与有轮暴走鞋的步长、步速与落地角的平均值差异非常显著(P0.01),运动鞋与有轮暴走鞋、无轮暴走鞋与有轮暴走鞋的步频平均值差异显著(P0.05).     

八脚机器爬虫运动仿真分析

采用叠层IPMC为片状脚,设计左右非对称分布的八脚机器爬虫模型,通过输入电压波形实现动力驱动。运用刚-柔混合技术,确定柔性体片状脚与刚性体地面接触模式,设计合理的行走步态,获得向前不间断的动力驱动。整个分析过程借助于ANSYS和ADAMS有限元分析软件完成,在ANSYS中建模,并获取32阶模态,通过ADAMS分析完成八脚机器爬虫的运动分析。经参数研究发现,较小的动力驱动和较高的驱动频率既能让机器爬虫保持一定速度,又能使其载重得到一定程度增加,且整体稳定性良好。     

Effects of Early Physical Therapist-supervised Walking on Clinical Outcomes after Liver Resection: Propensity Score Matching Analysis

Objective: The study aimed to demonstrate the significance of early postoperative physical therapy interventions on clinical outcomes by determining the influence of the distance walked under the supervision of a physical therapist in the early postoperative period after liver cancer. Methods: All consecutive patients who underwent surgery for liver cancer between April 2018 and March 2020 were eligible for enrollment in the study. The total walking distance during physical therapy till the third postoperative day was examined. The clinical outcomes comprised duration of postoperative hospital stay, time to independent walking, and occurrence of postoperative complications. For data analysis, the patients were divided into two groups: those who walked more than the median total distance (the long-distance group) and those who walked less than the median distance (the short-distance group). We used propensity score matching to match the background characteristics between the groups. Results: Of the 65 patients who were eligible, 14 patients were included in the two groups each, after matching. The long-distance walking group had a significantly shorter hospital stay (9.0 days vs. 11.0 days, p=0.008) and a shorter time to independent walking (3.5 days vs. 7.5 days, p=0.019) than the short-distance walking group. There were no significant differences in postoperative complications between the two groups (7.1% vs. 42.8%, p=0.08). Conclusion: In the early postoperative period after liver cancer surgery, increasing the walking distance under the supervision of a physical therapist is important for improving clinical outcomes. Further prospective studies are needed to confirm the findings of this study.     

Revisiting the stability of 2D passive biped walking: Local behavior

Models of biped walking have demonstrated that stable walking motions are possible without active control. Stability of these motions has typically been quantified by studying the stability of an associated Poincaré map (orbital stability). However, additional insight may be obtained by examining how perturbations evolve over the short-term (local stability). For example, there may be regions where small perturbations actually diverge from the unperturbed trajectory, even if over the entire cycle small (but perhaps not large) perturbations are dissipated. We present techniques to calculate local stability, and demonstrate the utility of these techniques by examining the local stability of the 2D compass biped. These techniques are relevant to the design of controllers to maintain stability in robots, and in understanding how the neuromuscular system maintains stability in humans.     

Control of polymer topology through late-transition-metal catalysis

An Erratum has been published for this article in J Polym Sci Part A: Polym Chem (2004) 42 213 In this article, recent examples are reviewed of late-transition-metal catalysis applied to polymer topology control. By the judicious selection or design of late-transition-metal catalysts, polymers with a broad range of topologies, including linear, short-chain-branched, hyperbranched, dendritic, and cyclic topologies, have been successfully synthesized. A distinctive advantage of the catalyst approach is that polymers with complex topologies can be prepared in one pot from simple commercial monomers. A fundamental difference of the catalyst approach with respect to other approaches is that the polymer topology is controlled by the catalysts instead of the monomer structure. In our own laboratory, we have successfully used two strategies to control the polymer topology with late-transition-metal catalysts. In the first strategy, hyperbranched polymers are prepared by the direct free-radical polymerization of divinyl monomers through control of the competition between propagation and chain transfer with a cobalt chain-transfer catalyst. In the second strategy, polyethylene topology is successfully controlled by the regulation of the competition between propagation and chain walking with the Brookhart Pd^II-α-bisimine catalyst. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3680–3692, 2003     

半被动双足机器人控制系统设计

为有针对性地根据不同干扰类型选择正确的抗干扰措施,有必要对无人机数据链所处环境的干扰信号进行分析和分类识别。本文以变换域通信系统(Transform Domain Communication System,TDCS)为载体,对无人机数据链常面临的干扰类型的自动识别进行研究,采用时域、频域、时频联合分析的方法,提出了一组对干信比变化不敏感的特征参数,并利用这组参数提出一种基于决策树理论的干扰分类识别方法,仿真结果表明,该方法能够快速准确地识别出干扰类型,具有很好的鲁棒性,并且在干信比和干噪比在0dB以上时,正确识别率均在90%以上。     

A Self‐Supporting Strategy for Gas‐Phase and Slurry‐Phase Ethylene Polymerization using Late‐Transition‐Metal Catalysts

The polyolefin industry is dominated by gas‐phase and slurry‐phase polymerization using heterogeneous catalysts. In contrast, academic research is focused on homogeneous systems, especially for late‐transition‐metal catalysts. The heterogenization of homogeneous catalysts is a general strategy to provide catalyst solutions for existing industrial polyolefin synthesis. Herein, we report an alternative, potentially general strategy for using homogeneous late‐transition‐metal catalysts in gas‐phase and slurry‐phase polymerization. In this self‐supporting strategy, catalysts with moderate chain‐walking capabilities produced porous polymer supports during gas‐phase ethylene polymerization. Chain walking, in which the metal center can move up and down the polymer chain during polymerization, ensures that the metal center can travel along the polymer chain to find suitable sites for ethylene enchainment. This strategy enables simple heterogenization of catalysts on solid supports for slurry‐phase polymerization. Most importantly, various branched ultra‐high‐molecular‐weight polyethylenes can be prepared under various polymerization conditions with proper catalyst selection.     

人群行走激励的数值模拟及动力耦合作用研究

大跨轻柔结构需要考虑人群行走激励下的结构振动响应以及人体的舒适度.根据单步落足曲线,结合影响人群行走效应的因素如人群分布、行走频率及个体生理特征等,采用随机方法模拟人群行走激励.对不同的人群倍增因子计算方法进行了比较并提出改进建议.将人群等效为具有主体部分和耦合均布质量的时变动力模型,建立了梁板结构与移动人体相耦合的动...