关键词： Rubber blends   Graphene   Vulcanization kinetics  

摘要： Rubber blends are widely used for combining the advantages of individual rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process are still a challenge. Herein, high resolution pyrolysis gas chromatography-mass spectrometry (PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene-butadiene rubber (SBR) in their blends filled with graphene. It is shown that the crosslinking rate of NR chains (k(NR)) was much lower than that of SBR chains (k(SBR)) in the unfilled blends and blends with untreated graphene. Interestingly, the gap between k(SBR) and k(NR) was narrowed effectively in the blends with vulcanization accelerator grafted graphene, showing a better co-vulcanization of NR and SBR. In addition, the vulcanization accelerator grafted graphene was uniformly dispersed in rubber matrix and endowed rubber blends with higher mechanical strength and thermal conductivity did the untreated graphene.

关键词： Molecular dynamics (MD) simulation   Neutral polymeric bonding agent (NPBA)   NEPE propellant   Mechanism   Mechanical property  

摘要： To search a more efficient method for neutral polymeric bonding agents (NPBA) structure screening and nitrate ester plasticized polyether (NEPE) propellant formulation design, the effects of NPBA on interface interaction and mechanical properties of NEPE propellants were investigated by using molecular dynamics (MD) simulations. The simulation results show that the NPBA can significantly improve the interface bonding energy of NEPE propellant, and the pair correlation function g(r) analysis indicates that strong hydrogen bonds exist between NPBA and cyclotrimethylene trinitramine (RDX). Furthermore, the results demonstrate that the mechanical properties of NEPE propellants can be significantly improved by adding small amounts of NPBA. Moreover, it is found that the performance of NPBA(1) is better than NPBA(2), and these simulation results coincide with the experiment results. Our researches afford a microscopic insight into the mechanism of NPBA, and might be helpful to the NPBA molecular structure and NEPE formulation design.

关键词： Acute dacryocystitis   Lacrimal abscess   Endoscopic dacryocystorhinostomy   Lacrimal   Outcomes  

摘要： Purpose: To provide a brief review of the literature on the utility and outcomes of endoscopic dacryocystorhinostomy (DCR) in patients with acute dacryocystitis (ADC) and lacrimal abscess. Methods: The authors performed a PubMed search of all articles published in English on endoscopic powered or mechanical DCR performed during the stage of acute dacryocystitis. Data captured include demographics, clinical presentations, time interval to surgery, intraoperative challenges, post-operative course, complications and outcomes. Specific emphasis was laid on addressing the intra-operative challenges and post-operative outcomes. Results: Increased intra-operative bleeding is a common finding. The use of mitomycin C and silicone intubation are not uncommon and are not reported to have negative influence on the outcomes of surgery. The general consensus is to initiate antibiotics immediately or a day before surgery and continue them in the post-operative period. Symptomatic pain relief was achieved very early (immediate to <3 days) and complete resolution was usually achieved in a week's time. The overall anatomical success rates varied from 81.8 to 96.2% and functional success from 72.7 to 96.2%. Cicatricial closure of the ostium was a common cause of failure. Conclusion: Primary endoscopic DCR appears to be an effective modality in the management of ADC and lacrimal abscess, and results in a rapid resolution of inflammation while achieving comparable surgical success with a traditional approach of conservative management with or without drainage and 2nd stage external DCR. (C) 2019 Elsevier GmbH. All rights reserved.

关键词： Aortic valve replacement   Cardiac surgery   Minimal invasive   Rapid deployment valves   Sutureless valves  

摘要： Objective Rapid deployment surgical aortic valve replacement has emerged as an alternative to the contemporary sutured valve technique. A difference in transvalvular pressure has been observed clinically between RD-SAVR and contemporary SAVR. A mechanistic inquiry into the impact of the rapid deployment valve inflow frame design on the left ventricular outflow tract and valve hemodynamics is needed. Methods A 23 mm EDWARDS INTUITY Elite rapid deployment valve and a control contemporary, sutured valve, a 23 mm Magna Ease valve, were implanted in an explanted human heart by an experienced cardiac surgeon. Per convention, the rapid deployment valve was implanted with three non-pledgeted, simple guiding sutures, while fifteen pledgeted, mattress sutures were used to implant the contemporary surgical valve. In vitro flow models were created from micro-computed tomography scans of the implanted valves and surrounding cardiac anatomy. Particle image velocimetry and hydrodynamic characterization experiments were conducted in the vicinity of the valves in a validated pulsatile flow loop system. Results The rapid deployment and control valves were found to have mean transvalvular pressure gradients of 7.92 +/- 0.37 and 10.13 +/- 0.48 mmHg, respectively. The inflow frame of the rapid deployment valve formed a larger, more circular, left ventricular outflow tract compared to the control valve. Furthermore, it was found that the presence of the control valve's sub-annular pledgets compromised its velocity distribution and consequently its pressure gradient. Conclusions The rapid deployment valve's intra-annular inflow frame provides for a larger, left ventricular outflow tract, thus reducing the transvalvular pressure gradient and improving overall hemodynamic performance.

关键词： Ceramics   Sintering   Kinetics   Scanning electron microscopy   Phase transition  

摘要： The influence of mechanical activation on the formation, sintering kinetics and morphology was investigated in sintered barium strontium titanate (BST) ceramics with different Ba-to-Sr ratios. Initial powders were mechanically activated for 20 and 120 min, leading to mechano-chemical reaction and formation of BaxSr1-xTiO3 phases. Agglomeration was found to represent an important factor in the process of formation of BaxSr1-xTiO3 phases around 800 degrees C and during sintering. It reduces the effectiveness of mechanical activation on formation of BaxSr1-xTiO3 phases beyond the short period (20 min), while in the process of sintering, prolonged mechanical activation (120 min) leads to a significant reduction in sintering temperature and the corresponding value of activation energy. In addition, all three systems show a phase transformation around 1100 degrees C, attributed to the hexagonal-to-cubic phase transition. Morphology of the final sintered ceramics can be correlated primarily with the state of the pre-sintered powder, where mechanically activated powders with smaller particle size produced more compact and less porous final product.

关键词： β3整合素   Talin F3结构域   分子动力学模拟   机械稳定性   双相力依赖性  

摘要： 作为血小板质膜上重要的力敏感蛋白,β3整合素双向传递跨膜信号,在血小板止血功能的发挥中扮演着重要的角色。通常在双向信号通路中,Talin与β3整合素结合,并桥接Actin以力-化学耦连的调控机制传导胞内细胞骨架收缩拉力和胞外血流剪应力,促进整合素活化并介导血小板铺展和聚集。因此,整合素与Talin的连接复合物作为连接胞外配体和胞内细胞骨架的桥梁必须有良好的机械稳定性,才能承受胞内外机械力并传导力学信号,介导血小板的聚集和铺展。整合素尾部与Talin结合的结构简单、亲和性低,其如何能够承受并传递来自胞内外所有作用力仍然是一个谜。以往的研究主要集中在Talin ROD结构域力依赖性的随机展开和重新折叠使得Talin作为一个有效的力缓冲器。但整合素与Talin的连接部分即整合素胞质尾部与Talin头部F3结构域复合体的力学稳定性尚不清楚。由于传统的生物实验方法不能反映出蛋白分子在原子层面的动态构象变化和结构基础,这里我们采用分子动力学模拟（Molecular dynamics,MD）方法研究β3整合素胞质远膜端与Talin头部F3结构域复合物（β3/F3）在不同机械微环境下的构象变化和机械稳定性,以揭示β3整合素和Talin相互作用的力依赖的机械稳定性机制和结构基础,以深入了解Talin和β3整合素介导的血小板黏附聚集过程。我们基于β3/F3的晶体结构（PDB ID:1MK7）搭建模拟体系后,采用MD模拟技术对β3/F3体系施行热平衡和恒速度拉伸MD模拟;同时当恒速度拉伸至预设外力值时转为恒力拉伸模式进行恒力拉伸分子动力学模拟,以模拟复合物生理环境中的受力状况;通过分析模拟过程中复合物构象变化和氢键相互作用网络的演化,以揭示β3/F3在不同程度外力作用下的机械稳定性和结构基础。我们发现Talin F3结构域疏水口袋的形变能有效缓冲约100 p N的拉力,力依赖的F3形变协同β3/F3结合面间氢键相互作用(特别是ASP740与TRP359氢键对)能抵抗约250 p N的拉力（模拟得到的拉力不同于实验所得的绝对值）。适当力的施加能促进β3整合素与Talin F3相互作用。在拉力小于20-60 p N的条件下,复合物呈逆锁键,解离概率随力的增大而减小,结合面面积和氢键数目随力的增大逐渐增大。相反,力大于20-60 p N时,表现为滑移键。残基ALA742、ASN744、TYR747和GLU749在双相力依赖的机械稳定性中起关键作用。双相力依赖的β3整合素与Talin F3相互作用和力依赖的β3/F3构象变化是β3/F3维持稳定的相互作用并传导胞内细胞骨架拉力和胞外血流剪切应力、调节血小板铺展与聚集的基础。研究加深了我们对整合素-Talin介导的血小板黏附、聚集过程的结构基础的认识,为以整合素/Talin相互作用为靶标的新型抗血栓药物设计提供新的思路和可供参考的结构信息。

关键词： PUMA560   ANFIS   旋量   运动学   动力学  

摘要： 当今数字化与智能制造是制造业发展的必然趋势,工业机械臂作为智能工厂的关键,迎来了新一轮的发展机遇。作为现代工业发展的重要基础,工业机械臂的运动精度已经成为衡量一个国家科技和制造水平的重要标志。本文以工业机械臂的一种PUMA560为主要研究对象,分别讨论了6R机械臂的正运动学、逆运动学、动力学、控制方法,主要内容有:首先,基于角轴表示法与DH方法对6R工业机械臂进行了运动学建模,推导出PUMA560正运动学的解,讨论了两种表示方法的区别与联系,利用解析法求出了PUMA560的逆运动学解。以旋量定理为基础得到了空间坐标系中与物体坐标系中末端执行器的速度转换,推导出了用来转换末端执行器速度与关节速度的雅可比矩阵,并利用雅可比矩阵解释了造成奇异位姿的原因,以几个雅可比矩阵推出的量引出了可操作性的概念。其次,提出了一种新逆运动学模型。机械臂腰、肩、肘关节转角由自适应模糊神经系统(ANFIS)求解,腕俯仰、腕摆动、腕旋转关节转角由解析法求解。用此模型得到的解没有姿态误差,但有由ANFIS结构影响的位置误差。以PUMA560为研究对象由实验结果得出,选取SΦ1000mm半球作为训练空间,训练点数为20000个,隶属度函数(MF)的个数为6时,所得的逆解模型效果最好。结果显示平均位置误差为0.158mm,选取合适的工作空间后可将其空间内99.9%的点的位置误差控制在0.5mm内。1000点逆解计算时间为0.082s,而传统的解析法需要3s左右,极大的缩短了计算时间。根据以上特性可以将此模型运用于分拣系统这类实时规划系统中,提高速度、节省计算资源、且误差控制在可接受的范围内。再次,分别讨论了关节空间与笛卡尔空间的轨迹规划问题。在关节空间中主要有五次多项式、梯形速度等方法,还讨论了多段多维的轨迹生成方法,在笛卡尔空间中,利用姿态四元数球形的线性插值解决了旋转的规划问题。最后,以牛顿欧拉方程和拉格朗日方程推导了机械臂的动力学方程。讨论了前馈控制与计算力矩控制的不同,前馈控制方法得到的实际偏差振动幅度大,计算力矩控制方法的误差会随着时间逐渐增大。

关键词： 液压机械无级传动   压力估计   神经网络   逆模型   排量控制  

摘要： 液压机械无级传动是一种双功率流复合传动系统,兼具了机械传动效率高、传递功率大和液压传动无级调速的特性,适用于工程车辆和大功率车辆。本文以等差两段式液压机械无级传动为研究对象,提出液压机械闭式液压回路压力估计方法和液压机械排量控制方法,有助于完善液压机械全功率动力换段控制技术,改善换段品质。主要研究内容包括:(1)分析闭式液压回路工作原理,结合油液动力粘度模型和液压元件泄漏模型,根据液压元件容积效率和液压回路总容积效率之间的关系,建立液压段和液压机械段的闭式液压回路压力估计模型。(2)设计开展不同转速、压力、排量工况下的闭式液压回路压力估计试验,探究漏损系数对液压回路压力的影响,提出基于查表的液压回路压力间接估计方法、基于神经网络的液压回路压力间接和直接估计方法,比较三种方法的准确性和相对误差。(3)分析液压机械排量控制系统的结构和工作原理,建立排量控制系统数学模型,验证排量控制系统的可逆性,运用神经网络建立排量上升过程和排量下降过程的排量控制系统逆模型,提出基于直接逆控制的液压机械排量控制方法,进行在不同需求排量比下液压段和液压机械段之间排量控制系统的仿真,验证排量逆控制方法的准确性。本文提出的排量逆控制方法能够实现排量比的精准调节。

关键词： 冗余机械臂   重复性运动   关节漂移   动力学神经网络   四自由度   设计参数  

摘要： 中国智造2025的提出使得机器人在工业中的应用得到进一步的推广,机械臂是一种在工业生产中广泛应用的机器人,在装配、焊接中均有使用;冗余机械臂是一种特殊的机械臂,相较于普通机械臂其拥有更多的自由度,这也使得其拥有更高的灵活度与适应性;但是也正因为这种灵活性,使得冗余机械臂在执行重复性运动的过程中会产生关节漂移的现象,这会导致机械臂在关节空间中不闭合,最明显的问题就是末端执行器脱离规划轨迹,甚至引发设备损坏。所以,针对冗余机械臂的重复性运动及关节角漂移问题的研究有利于冗余机械臂的进一步发展与使用,针对这一问题,以平面四自由度冗余机械臂为主要对象,本文介绍了冗余机械臂重复性运动的规划方法。首先,本文分析机械臂的正逆运动学方程及各种逆运动学求法。冗余机械臂重复性运动的实现是以逆运动学为基础的,根据规划的末端执行器轨迹求解出各个关节的角速度曲线与角度曲线。机械臂的逆运动学是机械臂运动学研究的重点与难点,而冗余机械臂的逆运动学问题更加复杂。普通机械臂的逆运动学求解方法在解决冗余机械臂的逆运动学问题时存在诸多限制,本文举例介绍了传统逆运动学方法并说明了其求解冗余机械臂的重复性运动的困难。之后,为了突破传统方法求解冗余机械臂逆运动学与重复性运动问题的困难,提出了将冗余机械臂的重复性运动问题转换为二次规划问题,并应用动力学神经网络求解器求解该二次规划问题的方法。该方法将整个重复性运动问题划为一个整体,而不是分为单独的逆运动的集合,具有更好的性能。然后,为了进一步对比各种方法的效果,使用传统方法与动力学神经网络,以平面四自由度冗余机械臂为对象,在Matlab上进行仿真实验,探索动力学神经网络求解冗余机械臂重复性运动的可行性,并与传统方式进行对比。本文使用三种方法来求解平面四自由度冗余机械臂的重复性运动问题并进行仿真。再然后,介绍了冗余机械臂的重复性问题转化为的二次规划问题的重要组成部分——目标函数,本文对比两种目标函数在求解重复性运动上的性能表现;再区别于传统的认知,讨论由目标函数引入的设计参数?对动力学神经网络解决冗余机械臂的重复性运动的性能的影响,提出了由于设计参数?改变导致的动力学神经网络无法求解的问题,并指出问题产生的原因,且提出了设计参数?选取所需要考虑的因素。最后,以步进电机为基础,设计了一个平面四自由度冗余机械臂,使用安装在计算机上的运动控制卡控制该机械臂,按照动力学神经网络求解器求解出来的运动规划进行运动,使用Visual Studio编写MFC程序作为控制程序和人机交互界面,实现平面四自由度冗余机械臂的运动与控制,以便于以后进一步检验动力学神经网络解决冗余机械臂重复性运动问题中的实际效果。

关键词： 发电厂   机械动力设备   检修管理  

摘要： 电能是现代生活与工作中不可或缺的能源,发电厂作为电能生产组织,必须不断进行生产.但发电厂的生产活动离不开机械动力设备的支撑,若此类设备出现异常或无法运作,则电能生产必然中断,导致人们的生活与工作受到负面影响.这一条件下,发电厂必须定期做好机械动力设备的检修工作,尽可能保障此类设备不会出现异常,对此本文为了保障检修工作质量将展开分析,重点阐述该项工作的管理策略.