关键词： Graphene  

摘要： Phagraphene is a novel 2D carbon allotrope with interesting electronic properties which has been recently theoretically proposed. Phagraphene is similar to a defective graphene structure with an arrangement of pentagonal, heptagonal and hexagonal rings. In this study we investigate the thermal conductivity and mechanical properties of phagraphene using molecular dynamics simulations. Using the non-equilibrium molecular dynamics method, we found the thermal conductivity of phagraphene to be anisotropic, with room temperature values of 218 +/- 20 W m(-1) K-1 along the armchair direction and 285 +/- 29 W m(-1) K-1 along the zigzag direction. Both values are one order of magnitude smaller than for pristine graphene. The analysis of the phonon group velocities also shows a significant reduction in this quantity for phagraphene in comparison to graphene. By performing uniaxial tensile simulations, we studied the deformation process and mechanical response of phagraphene. We found that phagraphene exhibits a remarkable high tensile strength around 85 +/- 2 GPa, whereas its elastic modulus is also anisotropic along the in-plane directions, with values of 870 +/- 15 GPa and 800 +/- 14 GPa for the armchair and zigzag directions, respectively. The lower thermal conductivity of phagraphene along with its predicted electronic properties suggests that it could be a better candidate than graphene in future carbon-based thermoelectric devices.

关键词： 工厂化育苗   移栽运动机构   试验研究   仿真   动力学分析  

摘要： 目前国内工厂化育苗移栽机械的研究大多开展单个末端执行器移栽作业,作业形式单一,移栽效率不高;在实验过程中暴露出:移栽运动机构在移苗时,钵苗受到额外的运动冲击,导致基质破损,钵苗脱落的问题,直接影响了移栽成功率。针对以上问题,本文设计一种满足多个末端执行器联合作业的移栽运动机构,将从提高移栽运行平稳性和快速性出发,对运动机构设计、移栽性能以及机构动力学分析展开研究。主要研究内容包括以下几个方面:(1)设计一种满足多个末端执行器联合作业的移栽运动机构,控制末端执行器实现“上升、平移、下降”三段直线运行以及多个末端执行器分散运动。利用展合板上斜滑槽实现末端执行器分散,利用同步带传动机构驱动末端执行器横向送苗、竖直取苗,提出增加平衡气缸辅助竖直方向同步带的运动的方法。确定运动控制方法,采用PLC控制伺服电机系统驱动多个末端执行器移栽作业,对控制系统硬件进行合理选型和规划。(2)试制样机,进行定位精度试验、自动移栽以及振动试验的研究,对所设计的自动移栽系统进行取苗移栽检测,试验结果表明,移动128穴盘、4孔花盆对应间隔距离平均值分别为32.2911mm、206.3246mm,标准差分别为0.4405、0.1646,通过单样本t检验发现,在0.05显著性水平下,实测取苗移位间隔与设计的穴孔间隔无显著性差异。开展自动移栽性能、振动试验,当作业效率为360、720、900次/h时,移栽成功率可达94.2%、91.0%、86.7%,试验发现随着工作效率的提高,移栽成功率大大降低。通过对不同测点振动试验发现,随着作业效率的提高,动平台往复运动是引起系统振动主要原因,为开展动力学性能研究提供重要依据。(3)建立了移栽运动机构的动力学数学模型,对动平台在移动过程中振动情况进行分析,得到机构动力学特性,通过试验验证了动力学模型的正确性;利用已建正确动力学模型,探究不同载荷参数(40kg、80kg、120kg)、不同运动频率(1/16Hz、1/8Hz、1/4Hz)对移栽运动机构动力学特性的影响,分析不同工况下位移、速度、加速度变化情况。高速运行作业下移栽运动机构动力学性能,优先选取轻载工况,运动频率的提高会增强机构振动冲击现象。(4)采用改进动平台关键部件结构的方法优化机构动力学性能。对动平台关键部件结构进行拓扑优化设计,通过对结构改进前后的机构动力学特性仿真结果进行比较分析,优化后动平台质量减小了8.83kg,质量减少9%,其振动加速度明显降低20%,机构工作平稳性得到提高。

关键词： Aeroelasticity   finite element method   higher-order theories   thin-walled box   composite material   flutter  

摘要： The coupled bending-torsion flutter is here investigated through Carrera Unified Formulation (CUF). The hierarchical capabilities of CUF offer a procedure to obtain refined one-dimensional models that, by going beyond the assumptions of classical theories, accurately describe the kinematics of structures. Aerodynamic loadings have been determined according to Theodorsen theory, from which the steady formulation can be easily obtained. The displacement variables over the cross section (x-z plane) are approximated by x, z polynomials of any order, N. The finite element method is used to solve the governing equations, which are derived in a weak form through the principle of virtual displacements. The equations are written in terms of "fundamental nuclei," which do not vary with the theory order, N. Several wing configurations have been studied, giving great attention to thin-walled box beams made of orthotropic material. The effects of sweep angle and lamination scheme on flutter conditions have been investigated, and the results have been compared with solutions obtained from two-dimensional theories, experimental tests, and aeroelastic analyses carried out with the doublet lattice method (DLM). The unsteady theory, combined with advanced beam theories, represents a computationally cheap tool for preliminary aeroelastic studies of complex wing structures.

关键词： 高速并联机械手   简化刚体动力学模型   轨迹规划   力矩前馈控制  

摘要： 在国家自然科学基金“基于电机性能参数的高速并联机构集成优化设计”支持下,本文以三自由度的Delta并联机械手为例,从机械手刚体动力学建模、轨迹规划方法、和运动控制方法三个角度入手,系统地研究了在考虑机械手动力学模型的基础上提高机械手运行速度和抓放动作精度的控制方法。并进一步在实时控制系统实验样机上进行了验证。全文取得成果如下:首先,在刚体动力学模型方面,基于虚功原理建立了完备的机械手刚体动力学模型,得到矩阵形式表达的动力学方程。针对动力学模型的简化方法进行了深入的研究,从机械手结构参数与运动轨迹参数两方面出发,分析了各因素对简化模型准确性的影响,以简化动力学模型与完备模型逼近程度作为优化指标,提出了一种新的基于组合质量分配系数的刚体动力学简化方法,为实时动力学控制方法的实现奠定了基础。其次,在轨迹规划方面,为保证机器人高速作业的柔顺性,提出一种新的关节空间内轨迹规划方法。该方法首先通过运动学逆解模型将运动学参数映射至关节空间,随后基于五次非均匀有理B样条曲线构造关节轨迹,进行运动插补,与原有的操作空间内多项式轨迹规划方法进行对比,表明该方法有效地提升了机械手高速运行下的末端定位精度与平顺性。随后,在运动控制方面,首先分析了电机驱动单支链模型,基于MATLAB建立PID控制模型,提出了基于遗传算法的自整定方法并对伺服参数进行了整定。随后基于简化的刚体动力学模型设计了一种动力学前馈控制器,通过在Simulink/SimMechanics中构建控制系统和机械手模型,对机械手单条支链进行动态仿真,表明了该控制方法与运动学闭环控制相比具有良好的动态响应特性,同时该方法可以有效地减少高速作业下机械手动态特性造成的轨迹跟踪误差,提高作业精度。最后,在样机实验方面,采用纯软件实时控制系统TwinCAT搭建实验软件平台,完成了相关控制算法的设计与控制软件的编写。通过实验,一方面验证了上文简化刚体动力学模型和轨迹规划的有效性,另一方面验证了单支链力矩前馈可以显著的改善并联机械手在实际高速运动中的轨迹跟踪精度与动态特性。

关键词： Impact strength  

摘要： In this article, the influence of relatively long hygrothermal ageing on long glass fibre reinforced polyamide 6 (LGF/PA6) composites filled with sepiolite (Sep) are analyzed. The composites with different weight fractions of Sep are exposed in a hygrothermal environment of 80 degrees C and RH 95% for 0-20 days. The mechanical properties with different ageing time show a decrease in tensile strength and an increase in impact strength. The scanning electronic microscopy (SEM) photos of the impact fracture indicate better adhesion of the interface between the glass fibre and polymer matrix in the composites filled with Sep after the ageing process. Then the thermal stability and degradation kinetics of the composites with different filler fractions and ageing times are studied by thermal gravimetric analysis (TGA) with the methods of Kissinger, Friedman and Flynn-Wall-Ozawa in dynamic measurements. Calculated apparent activation energy (E) by the three methods shows that the composites without Sep have an obvious decrease in the value of E after ageing, however, the E values of the composites filled with Sep have a slight increase.

关键词： Congenital   hemodynamic   mechanical ventilation   ultrafiltration  

摘要： Background: Cardiopulmonary bypass is associated with increased fluid accumulation around the heart which influences pulmonary and cardiac diastolic function. he aim of this study was to compare the effects of modified ultrafiltration (MUF) versus conventional ultrafiltration (CUF) on duration of mechanical ventilation and hemodynamic status in children undergoing congenital heart surgery. Materials and Methods: A randomized clinical trial was conducted on 46 pediatric patients undergoing cardiopulmonary bypass throughout their congenital heart surgery. Arteriovenous MUF plus CUF was performed in 23 patients (intervention group) and sole CUF was performed for other 23 patients (control group). In MUF group, arterial cannula was linked to the filter inlet through the arterial line, and for 10 min, 10 ml/kg/min of blood was filtered and returned via cardioplegia line to the right atrium. Different parameters including hemodynamic variables, length of mechanical ventilation, Intensive Care Unit (ICU) stay, and inotrope requirement were compared between the two groups. Results: At immediate post-MUF phase, there was a statistically significant increase in the mean arterial pressure, systolic blood pressure, and diastolic blood pressure (P < 0.05) only in the study group. Furthermore, there was a significant difference in time of mechanical ventilation (P = 0.004) and ICU stay (P = 0.007) between the two groups. Inotropes including milrinone (P = 0.04), epinephrine (P = 0.001), and dobutamine (P = 0.002) were used significantly less frequently for patients in the intervention than the control group. Conclusion: Administration of MUF following surgery improves hemodynamic status of patients and also significantly decreases the duration of mechanical ventilation and inotrope requirement within 48 h after surgery.

关键词： 动力机械   信息化   情报学   原理  

摘要： 信息是情报学研究的对象,信息服务是动力机械信息化发展的核心。随着情报学和动力机械信息化的发展,两者之间的关系越来越密切,但当前对两者之间关系研究的并不多。文章研究情报学对动力机械信息化的影响,探讨情报学基本原理中的离散分布原理、有序性原理、相关性原理、易用性原理、小世界原理和对数透视原理在动力机械信息化中的应用,并从情报学的角度,研究动力机械情报信息,以便对其进行系统化、理论化地整理,来满足动力机械信息化过程中日益增长的情报信息需求。

关键词： 驱动力分析   中国   工程机械行业   固定资产投资   投资拉动   驱动因素   发展趋势   调整阶段   高基数   爆发性   增长   梳理   历史   经历   进程   基建   基调   基础   国内  

摘要： 工程机械行业与固定资产投资息息相关，伴随着国内以兴基建为主基调的发展进程，我国工程机械行业经历10年的高速发展，尤其是在08年的四万亿投资拉动下，行业在高基数的基础上又爆发性的增长了2年，2011年行业创下了历史新高，而后开始步入持续调整阶段。本文重点梳理工程机械驱动因素，探析中国工程机械行业未来的发展趋势。

关键词： Organic pollutants   Photocatalysis   Photoreactors   Synthetic dyes   Water treatment  

摘要： In recent years, heterogeneous photocatalysis has emerged as a new effective, powerful, clean, and safe decontamination technology for the treatment of organic pollutants and the transformation of hazardous chemicals into different forms. This review focuses on the recent development of various conventional technologies of reactors designated for the photodegradation of hazardous organic pollutants with their limitations. This phenomenon is strongly influenced by reaction conditions such as temperature of reaction, pH, light intensity and wavelength, pollutant concentration, photocatalyst quantity, relative humidity (RH), and other parameters. The catalyst photoactivity depends on the structural characteristics of the semiconductor, its morphology, and its particles size. This paper presents the progression of photocatalytic reactors for synthetic dyes degradation with special consideration to the use of supported photocatalyst and nanostructured titanium supported over volcanic ashes, owing to the major advantage of an easy separation of the catalyst when compared to homogenous system, namely suspended catalyst. In addition, special attention was paid to the literature dealing with the promotion of light efficiency by testing various light sources.

关键词： 多功能工程车   多自由度机械臂   工作特性   运动学分析   动力学分析  

摘要： 本文所涉及城市道路多功能工程车旨在完成城市道路两侧的一些不经常需要、但每年偶尔要从事的一些工作,比如修剪绿篱、喷洒农药、修剪树枝、路边挖坑等。多功能工程车尾部安装有多自由度机械臂,能实现升降、回转、俯仰、伸缩的功能,在多自由度机械臂的末端,设计有统一的快换平台,可以快速更换各种工作装置,完成各种相应的工作,实现一车多用,大大减少了仅具有单一功能的工程车的数量、节约了设备和管理成本,提高了工作效率。多功能工程车工作任务差别较大,尾部的多自由度机械臂因工作状况不一而导致姿态要求各异,例如需要屈臂、水平伸缩、垂直升高、频繁回转等,造成运动状况复杂、某些状态处于容易倾覆的危险工况,因尾端的工作装置本身重量较大,工作时还会产生较大和较复杂工作负荷,导致整车和局部机构处于较大交变载荷状态,受力状况复杂而且严峻。本文针对多功能车整车介绍及尾部安装的多自由度机械臂进行运动学及动力学特性分析,主要进行了以下几个方面的分析与研究工作:(1)总体结构及工作情况剖析分析机械臂实现伸缩、俯仰、升降、回转的原理和主体结构,研究如何在满足刚度与强度要求前提下具有较小体积和较好稳定性、可靠性;机械臂末端安装的水平保持装置以及快换装置是工程车实现多种功能的关键,也作了较深入的剖析。(2)三维建模与仿真及抗倾覆性分析利用三维软件UG对机械臂进行建模,并使用仿真软件ADAMS进行动力学仿真,得出了执行装置的位移、速度、加速度曲线,以及相应的角速度、角加速度曲线。并对工程车进行抗倾覆性分析,以验证其在恶劣工况下的稳定性。(3)运动学分析运动学分析包括正、逆向运动学分析,通过建立运动学方程,对机械臂的位移、速度、加速度进行分析,使机械臂的运动轨迹达到合理的要求。(4)动力学分析动力学研究是机械臂的运动和受力的关系,对机械臂的仿真研究、动态性能和最优指标起着重要作用;利用有限元分析软件ANSYS研究机械臂的强度和刚度问题,得出危险部位的最大应变、应力值,并进行模态分析,使机械臂的稳定性和安全性符合要求。