关键词： 柔性负载   变形旋量   受限运动   动力学  

摘要： 针对机械臂操作受作业环境约束柔性负载,约束力、负载变形不易控制等问题,基于变形旋量理论,结合拉格朗日方程建立了机械臂操作受限柔性负载系统的动力学模型。首先,将系统分解为刚性机械臂与柔性负载两个子系统,分别建立了其动力学方程。然后,根据柔性负载与环境约束力及机械臂末端执行器的约束关系,推导了系统的运动方程。在给定机械臂的运行状态及环境约束力或给定机械臂各关节驱动力矩及负载末端的期望轨迹的情况下,分别推导了系统的逆动力学模型与正动力学模型。最后,通过三自由度(DOF)机械臂操作受限柔性梁进行了仿真,验证了该方法的有效性,并对系统的动力学特性进行了分析。

关键词： 劳动力转移   农业机械化   耦合协调度   湘乡市  

摘要： 以湖南省湘乡市为例,通过构建劳动力转移和农业机械化评价指标体系,运用耦合协调度模型分析劳动力转移与农业机械化发展水平之间的耦合协调度。结果表明:湘乡市的劳动力转移和农业机械化发展水平在2010~2015年间持续提高,劳动力转移的发展水平优于农业机械化,同时两者之间存在着相互促进的关系。所以,湘乡市要加强农机社会化服务体系建设和劳动力转移与农业机械化的协调程度,以此来提高农业机械化发展水平,推动劳动力转移与农业机械化协同发展。

关键词： 右美托咪定   儿科   PICU   镇静   血流动力学   戒断  

摘要： 目的右美托咪定用于儿童重症监护逐渐增加，其作为单一持续镇静药物时的长期效应尚无明确研究。本研究旨在了解长时间应用右美托咪定为唯一持续镇静药物时，其对血流动力学的影响、撤药策略及戒断反应风险因素。设计回顾性病历分析。场所大型单中心四级儿科医学院。对象共纳入382例患儿；〈18岁且于PICU内无创机械通气（non—invasive ventilation，NIPPV）期间仅静点右美托咪定镇静〉24h。干预措施记录右美托咪定常规用药方法。撤药策略分为：骤停，逐渐减停及改为口服可乐定。

关键词： 农业机械   农业机械收获设备   行走变速箱   动力换挡   不停车换挡  

摘要： 针对大型农业机械收获设备,主要使用的驱动桥箱换挡操作复杂、效率低,驾驶员劳动强度大(需要踩离合器将动力切断后再换挡),离合器在半离合状态工作时,容易导致离合器片易烧结、损坏等问题,设计了一种能不停车换挡,且操纵简单、驾驶员劳动强度低和工作效率高的驱动桥箱。

关键词： 石油钻杆   拾取机械手   运动规划   阵风载荷   动力学分析  

摘要： 目前,国内市场用于钻杆管具抬升的机械手产品较少,据此某公司根据市场需要自行设计了一款用于斜直井管具拾取的机械手。由于该机械手户外工况较复杂,确保其工作时的安全性则极为重要。现以该机械手为对象进行运动规划,并运用理论计算与虚拟建模仿真相结合的方法对其运动进行动力学分析。利用ADAMS模拟该机械手在8~11级风载和基座振动频率为50 Hz情况下结构的动态受力状况,并与无风载无基座振动情况下的结构受力进行对比,分析其结构是否满足户外阵风或基座振动工况下安全工作的要求。结果表明,该机械手结构设计和运动规划设计较为合理,并提出了进一步优化的可能性,同时数值仿真技术也大大降低了新产品的技术开发成本和开发周期。

关键词： 并联机械手   简化刚体动力学模型   组合分配系数  

摘要： 基于虚功原理建立了机械手的完备刚体动力学模型,并对机械手动力学模型的各组成部分(惯性力矩项、惯性力项和重力项)进行了分类;在分析从动臂的运动对机械手力矩各组成部分贡献的基础上,提出了一种基于组合分配系数的刚体动力学模型简化策略;以简化刚体动力学模型与完备刚体动力学模型逼近度为优化目标,提出一种基于运动过程力矩偏差最小的优化指标,从而确定组合分配系数;基于以上刚体动力学简化方法,从机械手尺度参数与运动轨迹参数两方面因素出发,结合机械手典型运动轨迹,采用多因素分析方法,通过仿真分析了各因素对简化刚体动力学模型准确性的影响,结果表明该刚体动力学模型简化方法针对不同机械手尺度参数与运动轨迹参数均具有较高的计算速度和精度。

关键词： Molecular dynamics simulations   Multi-layered graphyne-n   Elastic properties   Fracture properties  

摘要： This paper aims to study the mechanical properties of the multi-layered graphyne and other members of the graphyne family under the uniaxial tensile loading. For this purpose, molecular dynamics simulations are used. The effects of the size and number of layers on the fracture and elastic properties are studied. It is shown that Young's modulus of the zigzag multi-layered graphyne is slightly larger than armchair one. Comparing the stress-strain curves of the multi-layered graphynes with different number of layers, it is observed that the fracture stress and strain of the nanosheets are inversely related to the number of layers. Investigating the influence of the number of acetylene linkage in the structure of the graphyne-n family on their mechanical properties, it is shown increasing the number of triple bonds leads to weakening the fracture stress and Young's modulus of the nanosheet. (C) 2017 Published by Elsevier Inc.

关键词： Forecasting   Real-time modelling   Infectious disease dynamics   Outbreak  

摘要： Real-time forecasts of infectious diseases can help public health planning, especially during outbreaks. If forecasts are generated from mechanistic models, they can be further used to target resources or to compare the impact of possible interventions. However, paremeterising such models is often difficult in real time, when information on behavioural changes, interventions and routes of transmission are not readily available. Here, we present a semi-mechanistic model of infectious disease dynamics that was used in real time during the 2013-2016 West African Ebola epidemic, and show fits to a Ebola Forecasting Challenge conducted in late 2015 with simulated data mimicking the true epidemic. We assess the performance of the model in different situations and identify strengths and shortcomings of our approach. Models such as the one presented here which combine the power of mechanistic models with the flexibility to include uncertainty about the precise outbreak dynamics may be an important tool in combating future outbreaks. (c) 2016 The Author(s). Published by Elsevier B.V.

关键词： Mechanical activation   Carbothermic reduction   Non-isothermal kinetics   Isoconversional models   Model-fitting methods   Coats-Redfern  

摘要： Effect of mechanical activation on carbothermic reduction kinetics and mechanism of ilmenite concentrate containing self-reducing mixture has been investigated using a combination of thermogravimetry and X-ray diffraction. Thermogravimetric comparative study of mechanically activated and non-activated ilmenite concentrate containing self-reducing mixtures with C/O molar ratio of 1.5 was conducted non-isothermally. The samples were heated up to 1573 K at three different heating rates (10, 15, and 20 K min(-1)) under controlled atmosphere. The reduction mechanism of mechanically activated mixture was followed by X-ray diffraction analysis of arrested samples at different reduction extents. In addition, reaction kinetics was further investigated and corresponding kinetic parameters were estimated using isoconversional (model-free) and model-fitting (Coats-Redfern) methods.

关键词： Silica   Silicon carbide   Kinetic   Carbothermic synthesis  

摘要： The effect of mechanical activation on the synthesis temperature decreasing of silicon carbide was investigated and a kinetic model of a carbothermic reduction of silicon carbide was obtained. Silicon carbide was synthesized using silica activated in a planetary mill at different times up to 40 h under an argon atmosphere. Structural changes due to the milling and the reduction of the activated silica were studied by the X-Ray diffraction (XRD) method and non-isothermal TGA with a heating rate of 10(ay)C min(-1) respectively. The kinetic model obtained by the fitting technique for an unmilled sample was found to be chemically controlled of the second order with E = 138.92 ***(-1) and A =3.92x10(15) s(-1). For the sample milled up to 20 h, according to the Avrami-Erofeev3 equation;A = 1465633 s(-1) and E = 66.71 ***(-1).