关键词： carbon allotrope   mechanical properties   nanotechnology   nanotube   popgraphene   reactive molecular dynamics  

摘要： Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities (on;0THORN and o0;nTHORN) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs (o0;nTHORN) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones (on;0THORN). Moreover, it was obtained that Young's modulus (Y-Mod) (750-900 GPa) and ultimate strength (sUS) (120150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the sUS values for the o0;nTHORN showed a quasi-linear dependence with the temperature, the on;0THORN exhibited no clear trends.

关键词： Wave functions  

摘要： Starting from a model study of the collinear (H, H-2) exchange reaction in 1959, the time-dependent quantum mechanical wave packet (TDQMWP) method has come a long way in dealing with systems as large as Cl + CH4. The fast Fourier transform method for evaluating the second order spatial derivative of the wave function and split-operator method or Chebyshev polynomial expansion for determining the time evolution of the wave function for the system have made the approach highly accurate from a practical point of view. The TDQMWP methodology has been able to predict state-to-state differential and integral reaction cross sections accurately, in agreement with available experimental results for three dimensional (H, H-2) collisions, and identify reactive scattering resonances too. It has become a practical computational tool in predicting the observables for many A + BC exchange reactions in three dimensions and a number of larger systems. It is equally amenable to determining the bound and quasi-bound states for a variety of molecular systems. Just as it is able to deal with dissociative processes (without involving basis set expansion), it is able to deal with multi-mode nonadiabatic dynamics in multiple electronic states with equal ease. We present an overview of the method and its strength and limitations, citing examples largely from our own research groups.

关键词： bending stiffness   chiral phosphorene   tension and compression   buckling  

摘要： Black phosphorus (BP) is a novel two-dimensional nanostructure with wide potential applications in such areas as nanoresonators and nanosensors. In this study, we concentrate on the role of the bending stiffness of the BP monolayer in its mechanical performances, including tension, compression, buckling and bending. Firstly, the stress-strain curve and Young's modulus of the single layer black phosphorus (SLBP) nanoribbon with different chiral structures are obtained in the tension process via the molecular dynamics (MD) simulation. Next, the loading behavior of the SLBP nanoribbon during compression is simulated via MD. It was found that the bending stiffness of the nanoribbon has an essential effect on its postbuckling behaviors, and an empirical formula is proposed which can accurately depict the postbuckling process. Eventually, the bending properties of chiral SLBP nanoribbons are explored via the MD simulation, and the modified expression of the bending stiffness can better predict its large deflection. These findings are beneficial for us to fully understand mechanical responses of BP, which hold implications in engineering new materials and devices at nanoscale.

关键词： 发动机   直线发电机   动力学模型   Maxwell   输出功率  

摘要： 基于传统的活塞式内燃发电机组,设计一种新型动力装置——永磁活塞机械-电力发动机,对其动子组件建立发动机系统动力学模型和电动力学模型,通过编程和有限元建模,对额定工况(曲轴转速为3600 r/min)下的静磁场特性、空载特性和负载特性进行仿真分析,得到空载感应电动势、负载电流电压、电磁推力、额定输出功率和损耗等。结果显示,额定工况下机械输出功率为3660.224 W,输出转矩为9.71 N·m,由于电磁损耗,比原发动机的机械输出功率(3700 W)和输出转矩(9.82 N·m)略有减少,但不影响正常工作。该新型动力装置不仅输出机械动力,还增加了电动力输出,电输出功率为20.33 W,达到双元动力输出,验证了该新型动力装置结构的可行性。

关键词： 机械密封   转子动力学   半分环   失效  

摘要： 根据转子动力学及机械密封动态特性基本原理,考虑机械密封摩擦副的支撑刚度和阻尼,可以把摩擦副等效为柔性轴承,并将轴套和半分环看作一个整体;将主轴—半分环—轴套—机械密封简化为单盘转子系统。通过Ansys Workbench软件计算系统的临界转速及不平衡响应,并通过机械密封试验台进行验证。验证结果表明,半分环—轴套结构在共振频率下会产生较大的轴向位移,导致密封失效。试验结果对机械密封设计及工况实践具有指导作用。

关键词： 肺疾病,慢性阻塞性   通气机,机械   布托啡诺   右美托咪啶  

摘要： 目的探讨右美托咪定联合布托啡诺对慢性阻塞性肺疾病急性加重期(AECOPD)机械通气患者镇静效果、血流动力学指标和氧化应激状态的影响。方法选取2017年10月至2019年9月在广州市增城区人民医院接受治疗的82例AECOPD患者,采用随机数字表法分为对照组和研究组,每组41例。对照组使用右美托咪定,研究组在对照组基础上联合应用布托啡诺。观察两组治疗前和治疗12 h后Ramsay评分、血流动力学指标[平均动脉压(MAP)、中心静脉压(CVP)]、氧化应激指标[8-羟基脱氧鸟苷(8-OHdG)、氧化物歧化酶(SOD)]。结果①研究组治疗12 h后Ramsay评分高于对照组(P<0.05)。②研究组MAP高于对照组,而CVP低于对照组(P<0.05)。③研究组8-OHdG和SOD水平低于对照组(P<0.05)。结论右美托咪定联合布托啡诺用于AECOPD机械通气镇静效果良好,对患者血流动力学指标影响较小,且能够显著改善氧化应激状态。

关键词： 修剪机   Matlab Simulink   运动学   动力学   轨迹规划  

摘要： 针对园林修剪设备自动化、一体化程度低、效率差的问题,提出一种多功能园林机械手复杂曲面的造型修剪方法。采用改进D-H方法创建机械手运动学模型,设计末端执行器运行轨迹为半球螺旋线的造型修剪方案,并分析刀盘约束条件进行逆运动学求解,同时基于Simulink建立修剪机的动力学模型;结合Simulink模型和修剪机三维模型进行联合仿真验证。仿真结果显示半球造型轨迹平滑,表明运动学模型求解正确,同时动力学模型仿真为各关节电机选型提供依据;修剪机样机实验效果与预期相符,修剪机各关节动作平稳流畅,半球造型效果良好,大大提升了园林养护效率,证实本研究的可行性与有效性,为园林修剪机械智能化发展提供参考。

关键词： 机械设计   非线性动力学   动态优化设计  

摘要： 机械设计容易受到非线性因素影响,造成系统动态性能不佳。基于此,通过探究机械设计中的系统振动分析、机构运动弹塑性分析等非线性动力学分析方法,并结合机械设计案例对动力学分析方法应用内容进行探究。通过有限元建模实现机械结构动态优化设计,为机械设计方法改进提供参考,推动机械加工制造业向着高质量方向转变。

关键词： 膀胱,逼尿过度   苓芍枣仁方   尿动力学   大鼠  

摘要： 目的观察苓芍枣仁方对膀胱过度活动症(overactive bladder,OAB)模型大鼠尿动力学及机械敏感离子通道Piezo1表达的影响。方法将30只SPF级雌性SD大鼠按随机数字表法分为空白组、模型组、托特罗定组及苓芍枣仁方低、高剂量组,每组6只。采用环磷酰胺腹腔注射法建立OAB大鼠模型。造模成功后,托特罗定组灌胃酒石酸托特罗定混悬液0.36 mg/kg,苓芍枣仁方低、高剂量组灌胃1.59、3.18 g/kg苓芍枣仁免煎颗粒,空白组与模型组灌胃等体积的蒸馏水,1次/d,连续灌胃14 d。末次给药后检测各组大鼠尿失禁时膀胱容量、尿失禁时最大膀胱压力,采用HE染色观察各组大鼠膀胱组织病理形态学改变,采用免疫组化法及Western blot法检测膀胱组织Piezo1蛋白表达,采用qPCR法检测膀胱组织Piezo1 mRNA表达。结果与空白组比较,模型组大鼠体重明显减轻,膀胱容量、最大膀胱压均明显降低(P<0.01);HE染色显示,模型组尿路上皮增生,上皮细胞变性、坏死、脱落,间质大量炎性细胞浸润,血管增生,血管壁增厚,黏膜平滑肌增生,排列紊乱;膀胱组织Piezo1 mRNA及蛋白表达上调(P<0.05或P<0.01)。与模型组比较,托特罗定组及苓芍枣仁方高剂量组大鼠体重[(244.83±6.05)g、(233.33±11.76)g比(219.00±9.70)g]显著增加(P<0.01),托特罗定组及苓芍枣仁方低、高剂量组大鼠膀胱容量[(0.93±0.31)ml、(1.17±0.17)ml、(1.21±0.23)ml比(0.50±0.16)ml]、最大膀胱压力[(42.00±3.03)cmH_(2)O、(45.83±7.19)cmH_(2)O、(46.83±8.23)cmH_(2)O比(30.50±5.47)cmH_(2)O,1 cmH_(2)O=0.098 kPa]明显升高(P<0.01);膀胱组织上皮增生及变性程度、间质炎性细胞浸润程度、血管增生及黏膜平滑肌增生程度均明显减轻,托特罗定组及苓芍枣仁方低、高剂量组Piezo1 mRNA[(1.50±0.04)、(2.05±0.08)、(1.44±0.10)比(2.56±0.11)]及蛋白表达降低(P<0.01)。结论苓芍枣仁方可增加膀胱过度活动症大鼠逼尿肌活动过度引起的尿失禁的膀胱容量和尿失禁时最大膀胱压,其缓解尿频尿急症状可能与降低机械敏感离子通道Piezo1表达有关。

关键词： 机械臂   ADAMS仿真   运动空间   动力学分析  

摘要： 以架管机的三自由度机械臂为研究对象,建立了架管机三维模型以及D-H坐标系,求解得到了机械臂末端位置的运动空间;用ADAMS软件分析了架管机机械臂不同负载下的运动,得到相关曲线。结果表明:机械臂Z轴运动空间的最大值为2.6 m,可以满足淮南地区的实际架管需求;架管机小臂Z轴的最大质心速度为2 m/s,在周期内会产生不稳定速度波动;速度、加速度曲线变化趋势相吻合,θ_(2)、θ_(3)的最大值分别是120°和58°,其仿真结果为架管机实际模型的搭建奠定了基础。