关键词： Poly(ester-ether-imide)   thermal degradation   kinetics   thermal stability   mechanical properties  

摘要： A novel poly(ester-ether-imide) (PEEI) based on N,N-bis(2-hydroxyethyl)-pyromellitimide unit was synthesized via a conventional two-stage procedure with 1,4-butanediol (BD), dimethyl terephthalate (DMT) and poly(tetramethylene glycol) (PTMG1000). The structures of imide dihydric alcohol and PEEI were confirmed by FT-IR and H-1-NMR spectra, respectively. The thermal properties and mechanical properties were investigated. The results show PEEI possesses good mechanical properties and excellent thermal stability with the 5% weight loss temperature of the PEEI at 367.3 degrees C, and melting temperature of hard segments (T-mh) at 209.7 degrees C. In addition, the kinetic parameters of thermal degradation of the PEEI were studied by thermogravimetric analysis (TGA) at different heating rates. The activation energy of the solid-state process was determined to be 174.83 and 175.83 kJ/mol using Kissinger and FlynnWallOzawa methods, respectively. The degradation mechanism model of PEEI was determined bythe Coats-Redfern method. Compared with the values obtained from the Kissinger and FlynnWallOzawa methods, the actual reaction mechanism of the novel PEEI is a F-1 type (Random nucleation with one nucleus on the individual particle nucleation) and growth model with integral g(a)=ln(1a)).

关键词： 弹簧刚度   曳引电梯   动力学分析   曳引钢丝绳   机械   曳引轮绳槽   隔振装置   电梯运行  

摘要： 电梯的绳头弹簧是一个安装在曳引钢丝绳与轿厢之间的隔振装置，其主要作用是：消耗曳引机、钢丝绳振动产生的能量；当曳引轮绳槽磨损造成节径差较大或各根钢丝绳长度伸长有差异时，仍能保持各根钢丝绳能承受一定的力，有力的均衡作用。因此配置合适刚度的绳头弹簧对电梯运行的安全性和舒适性非常重要。

关键词： mechanical properties   high carbon steel   wires   conventional and hydrodynamic dies   redundant strain  

摘要： In the paper the influence of the hydrodynamic die on mechanical properties has been assessed. The drawing process of phi 5,5 mm wires to the final wire of phi 2,5 mm was conducted in 7 passes, in industrial conditions, by means of a modern Koch multi-die drawing machine. The drawing speed in the last passes was 8,2 m/s. On the basis of numerical analyses wire drawing process, the redundant strain of wires has been determined. In the case of the wires drawn with hydrodynamic dies the increase of plasticity properties have been noted. It has been shown that the increase of strength properties in wires drawn with conventional die is related to the occurrence in their bigger redundant strain.

关键词： Axially moving beams   Post-buckling analysis   Divergence   Nonlinear dynamics   Stability  

摘要： The thermo-mechanical nonlinear dynamics of a buckled axially moving beam is numerically investigated, with special consideration to the case with a three-to-one internal resonance between the first two modes. The equation of motion of the system traveling at a constant axial speed is obtained using Hamilton's principle. A closed form solution is developed for the post-buckling configuration for the system with an axial speed beyond the first instability. The equation of motion over the buckled state is obtained for the forced system. The equation is reduced into a set of nonlinear ordinary differential equations via the Galerkin method. This set is solved using the pseudo-arclength continuation technique to examine the frequency response curves and direct-time integration to construct bifurcation diagrams of Poincar, maps. The vibration characteristics of the system at points of interest in the parameter space are presented in the form of time histories, phase-plane portraits, and Poincar, sections.

关键词： metals   nanocontacts   nanowires   surface   electronic structure   electronic density functional theory   first-principle molecular dynamics   computer simulation  

摘要： The atomic and electronic structures of AgAuAg, AuAgAg, and AuCoCo mixed nanocontacts are investigated by the method of first-principle molecular dynamics. The characteristic interatomic distances in contacts depending on their component composition are determined. The interrelationship between the structural and electronic properties of mixed nanocontacts is shown. The formation of stable bonds between the atoms of various elements in the contact chain, which makes it possible to explain the cause of stabilization and an increase in the contact strength at large interatomic distances is found. It is shown that the addition of Co atoms into pure-gold nanocontacts increases their strength (increases the breaking force of the contact), while the addition of Ag atoms leads to an increase in the range of interatomic distances at which the existence of the nanocontact is possible.

关键词： BEDSORES   ANTIPSYCHOTIC drugs   ANALYSIS of variance   CORRELATION (Statistics)   FALLS (Accidents)   FRACTURES   LIFTING & carrying (Human mechanics)   MEDICAL care -- Evaluation   MULTIVARIATE analysis   NURSE administrators   NURSING care facilities   QUESTIONNAIRES   FINANCING of research   RESTRAINT of patients   STATISTICS   DATA analysis   SECONDARY analysis   TRANSPORTATION of patients   DATA analysis software   DESCRIPTIVE statistics   RISK factors   THERAPEUTIC use  

摘要： Objective: To determine associations between long-term care powered mechanical lift (PML) availability and mobility-related resident outcomes. Methods: Long-term care directors of nursing (N = 271) nationwide gave facility information on the PML availability and the lifting policy to which we linked data on mobility-related resident outcomes from the Centers for Medicare & Medicaid Services Minimum Data Set Quality Indicators. Results: Four of six Centers for Medicare & Medicaid Services derived resident indicators improved with the PML number but were maximal for the sit stand lift use. In facilities with the fewest lifts, 16% of residents had pressure ulcers and 4% were bedfast. In facilities with the maximum number of lifts, only 10% had pressure ulcers (P = 0.000) and 2% were bedfast (P = 0.002). Although falls were more frequent with more lift use, this risk was blunted by a comprehensive safe lift program. Conclusion: The PML availability is associated with benefits to resident outcomes, and accompanying risks are mitigated by safe lift policies.

关键词： Underactuated nonlinear mechanical systems   Sliding mode control   Trajectory tracking   Stabilization   Actuators dynamics  

摘要： The paper deals with a novel control algorithm for simultaneous stabilization and trajectory tracking of underactuated nonlinear mechanical systems (UNMS) with included actuators dynamics. Simultaneous stabilization and trajectory tracking refer to arbitrary chosen actuated and unactuated degrees of freedom (DOF) of the system. The proposed control approach can be applied both to the second-order nonholonomic systems and the systems with input coupling, while a general model of actuators dynamics includes electrical, pneumatic, and hydraulic drives. Control law is based on linear combination of two control signals, where the first signal is designed to separately control only actuated DOF, and second to separately control only unactuated DOF. Simulation example of rotational inverted pendulum driven by electrical DC motor is presented, showing the effectiveness of the proposed approach.

关键词： Newton's Laws   active and reaction torques   d'Alembert's principle of dynamics  

摘要： In most discussions, the Principles of Dynamics are expressed using the force as a measure of mechanical interaction between the bodies. The intention of the paper is to extend the usual discussion on basic theorems, laws and principles in Dynamics of rigid bodies including the torque as another independent measure of mechanical interaction between the bodies. In D'Alambert's principle of Dynamics, beside the forces, the active and reaction torques are also included. The torque is introduced in the Euler-Newton equations for general motion of the rigid body. The General Equation of Dynamics is reformulated by including the virtual work of the torques on the virtual rotation. An additional view to Newton's Laws is also given.

关键词： 内部控制   有效性   缺陷   改进建议  

摘要： 内部控制是当代企业管理的重要手段,是目前企业应对激烈的市场竞争、规避风险、实现战略目标而普遍采用的管理方法和手段。中国航天行业蓬勃发展、竞争加剧。内蒙航天动力机械测试所作为军工集团中的一家企业,在这样复杂和残酷的环境中要做强,构建内部控制体系是企业强烈的内在需求。虽然内蒙航天动力机械测试所正在逐步构建起自己的内部控制体系,但还是存在许多问题,需不断改善,以适应新形势的要求。 论文阐述了内部控制相关基础理论,结合相关理论,对内蒙航天动力机械测试所内部控制进行了较为全面的评价。在对内蒙航天动力机械测试所基本情况和内部控制制度运行背景详细介绍的基础上,从内部环境、风险评估、控制活动、信息与沟通、监督这五个方面描述了内蒙航天动力机械测试所内部控制运行情况,并针对现状进行了分析,对内蒙航天动力机械测试所内部控制状况进行了评价。最后,根据评价结果,分析内蒙航天动力机械测试所内部控制中存在的不足点,从内部控制构成要素角度提出了相应的改进措施。

关键词： 变截面辊弯成形   运动分析   动力学建模   机电系统动力学   矩形公式  

摘要： 本论文以国家科技支撑项目(高强钢先进成形技术及其应用)的子课题“三维辊弯成形装备研制”选题,开展高强钢三维辊弯成形生产线样机机械系统动力学分析的研究。所开展的工作为：建立样机机械系统动力学方程,通过工程算例,结合有限元仿真数据及实际成形试验数据对动力学方程进行求解,并对求解结果进行分析。 首先,本文对变截面辊弯成形工艺进行了研究,重点对变截面辊弯成形的道次数目、成形角度、轧辊的设计方法以及成形缺陷与解决方法进行了研究。 其次,本文在完成样机机械系统关键结构“双齿条单齿轮结构”的运动分析之后建立了样机机械系统的运动学方程。并根据变截面辊弯成形的工艺的特点,确定了成形机架的运动控制方式,为系统动力学方程的建立奠定了基础。 之后本文在完成机构转动惯量计算的基础上,利用机电系统动力学方法建立了系统的动力学模型：形成了以伺服电机的转矩为输入,以TRIP590变截面辊弯成形过程的成形力和成形力矩为载荷,以辊组伺服运动和转动为广义坐标的系统动力学方程。通过工程算例,在MATLAB软件中,利用ABAQUS有限元仿真分析得到的数据,绘制了负载力以及负载力矩与时间的关系曲线。通过成形试验,采集了伺服电机的输出转矩、齿条位置、轧辊伺服电机的角速度等数据。将有限元仿真数据及成形试验数据代入系统动力学方程当中,使用矩形公式对系统的动力学方程进行了求解,得到了伺服电机“角加速度-时间”以及“角速度-时间”的关系曲线,并依据系统的运动学方程求得了成形机架的位置-时间曲线以及转角时间曲线,验证了系统动力学方程的正确性。通过对求解结果的分析,本文得到了符合样机动态特性的结论,为后续三维辊弯成形生产线的研制提供了理论参考依据。