Regiochemistry in radical cyclization of allenes

The cyclization of allenic radicals was systematically studied for the first time by computational methods. It was found that the theoretical results at the ONIOM(QCISD(T)/6-311+G(2df,2p):UB3LYP/6-311+G(2df,2p)) level were in good agreement with all the available experimental data. For the cyclization of penta-3,4-dien-1-yl radicals the major product was penta-1,2-diene from direct reduction whereas a small amount of vinylcyclopropane may also be produced. For the cyclization of hexa-4,5-dien-1-yl radicals the major product is 1-methyl-cyclopentene. Furthermore, for the cyclization of hepta-5,6-dien-1-yl radicals both vinylcyclopentane and 1-methyl-cyclohexene are produced. Marcus theory analysis indicated that the formation of an olefinic radical product always had a lower intrinsic energy barrier than the formation of an allylic radical product. On the other hand, the formation of an olefinic radical product was always much less favorable than the formation of an allylic radical product in the thermodynamic term. For the cyclization of substituted hexa-4,5-dien-1-yl radicals, substitution at the allene moiety does not affect the regioselectivity where the allylic radical product is always favored. For the cyclization of hepta-5,6-dien-1-yl radicals, substitution at the allene moiety dramatically affects the regioselectivity, where some radical-stabilizing groups such as -CN and -COMe may even completely reserve the regioselectivity.     

水泥聚苯模壳格构式混凝土墙体的抗侧性能试验及分析

论文介绍6片不同高宽比的水泥聚苯模壳格构式混凝土墙体在轴压力和水平往复侧推力作用下的试验,分析这种墙体的抗侧强度、刚度和延性等力学性能.试验表明,高宽比大于1的墙体破坏时表现为墙体跟部的单一水平裂缝,其他部位完好;高宽比3∶4的墙体破坏时存在多条通过格构梁柱的斜向裂缝,墙体裂缝分布密集,变形能力好.     

高超声速飞行器气动热关联换算方法研究

气动热风洞实验是地面研究和预测飞行器气动热环境的重要手段之一, 但由于风洞实验模拟能力的限制, 风洞实验的流场参数和模型的几何尺度都会与实际飞行情况存在一定的差别, 导致地面风洞实验中得到的模型表面气动加热率数据无法直接用于飞行条件下的热环境预测和热防护设计. 以往通过针对具体飞行器的试验结果进行数据拟合后外插的气动热关联换算方法指向性较强, 没有考虑到气动热的具体影响参数, 存在一定局限性, 难以外推应用于其他外形的飞行器. 为解决通过气动热风洞实验数据外推预测飞行条件下气动热的技术难题, 基于无量纲NS方程和边界层理论分析研究了影响气动热的主要参数, 并通过推导化简边界层近似解热流公式, 针对层流流态建立了气动热关联换算方法, 可以考虑当地边界层外缘参数的影响, 具有一定通用性. 在此基础上, 利用建立的方法将Reentry-F飞行器缩比模型的风洞实验数据换算到该飞行器飞行条件下的典型工况, 并与飞行测量结果进行了比较, 外推预测结果与飞行测量结果符合较好, 表明建立的关联方法可以用于气动热风洞实验数据的外推换算.      

Cr12MoV钢表面磁控溅射Ti/TiN涂层的摩擦磨损性能研究

采用非平衡磁控溅射方法在Cr12MoV钢表面制备了厚度约为3 μm的Ti/TiN涂层,测定了涂层的显微硬度,并通过划痕试验和摩擦磨损试验考察了涂层同基体的结合强度及其摩擦磨损性能.结果表明:Ti/TiN涂层能够显著提高Cr12MoV钢的表面硬度和承载能力;涂层同Cr12MoV钢基体的结合强度较高,划痕临界载荷高于60 N;与此同时,磁控溅射Ti/TiN涂层可以显著改善Cr12MoV钢的耐磨性能.这是由于磁控溅射Ti/TiN涂层硬度高且与Cr12MoV钢基体的结合强度较高所致.     

Minimum-time optimal control of robotic manipulators based on Hamel’s integrators

Meccanica - In this paper, we develop a framework of time optimization path planning for robotic manipulators surrounded by static obstacles. Our approach is based on the recursive dynamics method...     

两空间耦合下齿轮传动系统多稳态特性研究

通过将系统参数定义为参数变量, 构成参数空间,研究齿轮传动系统在参数空间和状态空间耦合下的非线性全局动力学特性,以及多参数、多初值和多稳态行为之间的关联特性.首先设计了一个两空间耦合下非线性系统多稳态行为的计算和辨识方法.其次,基于该方法并结合相图、Poincaré映射图、分岔图、最大Lyapunov指数、吸引域等,研究齿轮传动系统在不同参数平面上多稳态行为的存在区域和分布特性,以及多稳态行为在状态平面上的分布特性,揭示了参数平面和状态平面上系统可能隐藏的多稳态行为和分岔,并分析了多稳态行为的形成机理. 结果发现,两空间耦合下系统在参数平面上存在大量多稳态行为并呈"带状"分布, 状态平面上多稳态行为出现两种不同的侵蚀现象, 即内部侵蚀和边界侵蚀.分岔点或分岔曲线对初值的敏感性导致多稳态行为的出现.当齿侧间隙和误差波动在较小的范围内变化时,系统全局动力学特性受间隙和误差扰动的影响较小,受啮合频率的影响较大.两空间耦合下系统全局动力学特性变得丰富和复杂.      

基于非线性梁理论的有限质点法

有限质点法是以向量式力学为基础,用有限数量的质点来模拟结构的变形行为,质点的运动由牛顿运动定律来计算。在有限质点法中,质点通过构件相连,构件约束着质点的运动,并且其内力由质点的运动变量来描述。基于向量式力学的基本思想和非线性梁理论,提出了一种新的有限质点法,该方法在共旋单元坐标系中描述梁的非线性变形。以空间梁系结构为例,推导了计算构件内力的非线性公式,并考虑了弯扭耦合变形。通过两个连续欧拉角的变换公式得到共旋坐标系的旋转矩阵。与传统的有限质点法相比,本文提出的方法避免了刚体虚转动分析。通过四个结构的数值求解,验证了本文方法在计算结构大变形响应时具有较高的精度。     

Heat capacity and thermodynamic properties of 1-hexadecanol

Three different nitrocellulose (NC) samples produced from linters were investigated. DSC studies on the NC+sym-diethyldiphenylurea (C1) mixtures were carried out. The influence of storage time on their pore structures was examined using thermoporometry. The results led to conclusion that large pores are multiples of small ones. The parameter n was used to characterize the number of C1 molecules equivalent to NC ring. Its value for short storage time was about 9 but for longer time reached the value of 3. The influence of thermal history on the phase transition and porosity of the different nitrocellulose samples was different.     

Vapor-phase synthesis of V-butylaniline from aniline and 1-butanol over Cu/SiO2 catalyst

The Cu/SiO2 catalyst prepared by incipient wetness method exhibited very high activity and selectivity for the vapor-phase synthesis of JV-butylaniline from aniline and 1-butanol. When Cu loading was 0.70 mmol/g-SiO2 and the catalyst precursor was calcined at 500 ℃, 1-butanol conversion reached 99%, and the selectivity of JV-butylaniline exceeded 97%.     

共轭二烯烃定向加成研究进展

以1,3-丁二烯为代表的共轭二烯烃是重要的有机合成原料,在有机合成领域有重要的应用价值.综述了以1,3-丁二烯等为代表的共轭二烯烃定向加成的研究进展,并展望了其发展和应用前景.