Synthesis and Conformation of 3,6‐Connected Cyclohexadiene Chains

3,6‐Connected cyclohexadienes as precursors for polyphenylenes are synthesized and characterized by mass spectrometry and NMR spectroscopy. Pure fractions of trimers, hexamers, and nonamers are collected after separation of the product mixture by recycling GPC. The anticipated formation of rigid linear structures, due to the trans‐configuration of the monomeric units, is supported by density functional theory and experimentally confirmed by dynamic light scattering from dilute solution at low scattering angles. The obtained translational diffusion coefficients are represented by rigid rod‐like or prolate ellipsoid‐like molecular shapes. The measurements of diffusion coefficients reveal a length‐dependent ratio of 1:2:3 between the three oligomers, which directly correlates to the expected length extension from trimer to nonamer.

     

三线摆实验中摆角偏大产生的误差及修正方法

研究了三线摆实验中摆角偏大(5°θ20°)时对测量转动惯量产生的误差和修正办法。实验发现随着摆角的增大,测得的圆盘转动惯量也会相应偏大,从而导致测量误差增大。文章通过进一步的理论分析解释了这一现象,并对测量结果进行了系统误差修正。     

Natural Soft/Rigid Superlattices as Anodes for High-Performance Lithium-Ion Batteries

Volume expansion and poor conductivity are two major obstacles that hinder the pursuit of the lithium-ion batteries with long cycling life and high power density. Herein, we highlight a misfit compound PbNbS₃ with a soft/rigid superlattice structure, confirmed by scanning tunneling microscopy and electrochemical characterization, as a promising anode material for high performance lithium-ion batteries with optimized capacity, stability, and conductivity. The soft PbS sublayers primarily react with lithium, endowing capacity and preventing decomposition of the superlattice structure, while the rigid NbS₂ sublayers support the skeleton and enhance the migration of electrons and lithium ions, as a result leading to a specific capacity of 710 mAh g⁻¹ at 100 mA g⁻¹, which is 1.6 times of NbS₂ and 3.9 times of PbS. Our finding reveals the competitive strategy of soft/rigid structure in lithium-ion batteries and broadens the horizons of single-phase anode material design.     

A novel three‐dimensional tetranuclear CoII coordination polymer with water hexamers based on the V‐shaped tetracarboxylate ligand 4‐(2,4‐dicarboxylatophenoxy)phthalate

A new coordination polymer (CP), namely, poly[[diaquatris[μ₂‐1,4‐bis(1H‐imidazol‐1‐yl)benzene]bis[μ₆‐4‐(2,4‐dicarboxylatophenoxy)phthalato]tetracobalt(II)] hexahydrate], {[Co₄(C₁₆H₆O₉)₂(C₁₂H₁₀N₄)₃(H₂O)₂]·6H₂O}_n, has been synthesized by solvothermal reaction. The CP was fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single‐crystal X‐ray diffraction. It presents a three‐dimensional (3D) structure based on tetranuclear Co^II secondary building units (SBUs) with a tfz‐d net and point symbol (4³)₂(4⁶·6¹⁸·8⁴). The 4‐(2,4‐dicarboxyphenoxy)phthalic acid (H₄dcppa) ligands are completely deprotonated and link {Co₄(COO)₄}^4? SBUs into two‐dimensional (2D) layers. Furthermore, adjacent layers are connected by 1,4‐bis(1H‐imidazol‐1‐yl)benzene (bib) ligands, giving rise to a 3D supramolecular architecture. Interestingly, there are numerous elliptical cavities in the CP where isolated unique discrete hexameric water clusters have been observed. The results of thermogravimetric and magnetic analyses are described in detail.     

Kirchhoff动力学比拟对弹性薄壳的推广

将弹性细杆的"Kirchhoff动力学比拟"方法推广到弹性薄壳,使弹性薄壳的变形在物理概念上和刚体的运动对应,在数学表述上等同,从而可以用刚体动力学的理论和方法研究弹性薄壳的变形,为连续的弹性薄壳提供新的离散化方法.在直法线假设下,在弹性中面上构筑空间正交轴系,此轴系沿坐标线"运动"的角速度构成两自变量的弯扭度.沿两个...     

非均匀多孔介质有效热导率分析

本文采用控制容积法,界面调和平均导热系数值以及图形处理方法对典型非均匀多孔介质硬质聚氨酯泡沫材料的导热过程进行了分析与模拟计算。结果表明:多孔介质的内部结构是影响温度分布和热量传递的主要的因素,其影响程度与骨架和孔隙的导热系数,孔隙的大小和分布有关;计算得到的有效热导率值与文献中实验测量结果吻合较好。本文的研究结果可以推广到更为复杂的非均匀多孔介质的场合,从而可以进一步认识非均匀多孔介质中的导热规律,为工程计算提供更精确的计算方法。     

MSC折纸结构设计及其双稳态解析与实验

折纸是一门古老艺术,其本质是将平面材料沿着事先设计好的折痕进行折叠,进而形成一个复杂的三维结构．柔性折纸结构是实现三维结构轻量化的重要途径．因此,解析折纸结构几何特性和力学性质十分必要．本文以MSC(Magic Spiral Cube)为研究对象,通过实际折痕和虚拟折痕的方法,建立了该结构的几何模型,确定了实现完全展开和完全折叠对刚性面和可变形面的设计条件,在虚拟折痕上引入了扭转刚度,证明了该扭转刚度与柔性面变形的等效性,从而得到了MSC 折纸结构的弹性势能,得到了使结构变形的力与位移本构．通过力学特性分析,发现了MSC折纸结构具有双稳态特性,这种特性是由面内变形诱发的,与虚拟折痕刚度与弹性折痕刚度的比值有直接的关系．最后,我们对MSC折纸结构进行设计和制备,通过实验,验证了理论 模型的准确性．本文的研究结果不仅进一步加深了我们对于MSC折纸结构力学特性的认识,同时也为其工程应用提供理论基础．     

苯二甲酸衍生物及含氮配体构筑的两个镍配位聚合物的合成、晶体结构与热稳定性研究

使用硝酸镍分别与2个含取代基的苯基二羧酸3-硝基邻苯二甲酸（3-NPAH₂）和5-溴间苯二甲酸（H₂BIPA）以及2个刚性含氮配体4,4’-联吡啶（4,4’-bipy）、1,4’-二咪唑基二苯（L=1,4’-bis（imidazol-yl）benzene）在水热条件下合成了2个镍配位聚合物,即,[Ni（3-NPA）（4,4’-bipy）（H₂O）]_n（1）和[Ni（BIPA）（L）]_n（2）。表征了2个化合物的红外光谱、元素分析、热重、X-射线单晶衍射以及X-射线粉末衍射。化合物1是三斜晶系,P1空间群,含有[Ni（OCO）₄Ni]双核单元,该双核单元再通过4,4’-联吡啶连接而成一个二维单层结构。层与层之间通过羧酸氧原子与配位水分子之间产生氢键作用。化合物2是单斜晶系,P2₁/c空间群,含有[Ni₂（COO）₂]双核单元,该双核单元进一步通过BIPA^2-构成了一个双链结构,该双链再通过1,4’-二咪唑基二苯桥联配体连接形成了一个三维框架结构。此外,热重分析结果显示化合物2具有较高的热稳定性。     

刃型位错和圆弧形刚性线夹杂的干涉效应

位错和夹杂的干涉效应对于理解材料的强化和韧化机理具有十分重要的意义。文中研究了晶体材料中刃型位错和多条共圆弧刚性线夹杂的干涉作用。利用Riemann—Schwarz反照原理和复势函数的奇性主部分析技术，得到了问题的一般解答；对于只含一条刚性线夹杂的情况，给出了复势函数的封闭形式解。由Peach-Koehler公式求出了作用在刃型位错上的位错力，并讨论了圆弧形刚性线夹杂对位错力的影响规律，发现弧形刚性线对刃型位错有很强的排斥作用。本文解答不但可作为格林函数获得任意分布位错的相应解答，而且可以用于研究刚性线夹杂和任意形状裂纹的干涉效应问题。     

Chaotic motions of a rigid rotor in short journal bearings

In the present paper the conditions that give rise to chaotic motions in a rigid rotor on short journal bearings are investigated and determined. A suitable symmetry was given to the rotor, to the supporting system, to the acting system of forces and to the system of initial conditions, in order to restrict the motions of the rotor to translatory whirl. For an assigned distance between the supports, the ratio between the transverse and the polar mass moments of the rotor was selected conveniently small, with the aim of avoiding conical instability. Since the theoretical analysis of a system's chaotic motions can only be carried out by means of numerical investigation, the procedure here adopted by the authors consists of numerical integration of the rotor's equations of motion, with trial and error regarding the three parameters that characterise the theoretical model of the system: m, the half non-dimensional mass of the rotor, , the modified Sommerfeld number relating to the lubricated bearings, and , the dimensionless value of rotor unbalance. In the rotor's equations of motion, the forces due to the lubricating film are written under the assumption of isothermal and laminar flow in short bearings. The number of numerical trials needed to find the system's chaotic responses has been greatly reduced by recognition of the fact that chaotic motions become possible when the value of the dimensionless static eccentricity % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbnL2yY9% 2CVzgDGmvyUnhitvMCPzgarmWu51MyVXgaruWqVvNCPvMCG4uz3bqe% fqvATv2CG4uz3bIuV1wyUbqee0evGueE0jxyaibaieYlf9irVeeu0d% Xdh9vqqj-hEeeu0xXdbba9frFf0-OqFfea0dXdd9vqaq-JfrVkFHe9% pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaaca% qabeaadaabauaaaOqaaiabew7aLnaaBaaaleaacaWGZbaabeaaaaa!4046!\[\varepsilon _s \] is greater than 0.4. In these conditions, non-periodic motions can be obtained even when rotor unbalance values are not particularly high (=0.05), whereas higher values (>0.4) make the rotor motion periodic and synchronous with the driving rotation. The present investigation has also identified the route that leads an assigned rotor to chaos when its angular speed is varied with prefixed values of the dimensionless unbalance . The theoretical results obtained have then been compared with experimental data. Both the theoretical and the experimental data have pointed out that in the circumstances investigated chaotic motions deserve more attention, from a technical point of view, than is normally ascribed to behaviours of this sort. This is mainly because such behaviours are usually considered of scarce practical significance owing to the typically bounded nature of chaotic evolution. The present analysis has shown that when the rotor exhibits chaotic motions, the centres of the journals describe orbits that alternate between small and large in an unpredictable and disordered manner. In these conditions the thickness of the lubricating film can assume values that are extremely low and such as to compromise the efficiency of the bearings, whereas the rotor is affected by inertia forces that are so high as to determine severe vibrations of the supports.Nomenclature C radial clearance of bearing (m) - D diameter of bearing (m) - e dimensional eccentricity of journal (m) - e _s value of e corresponding to the static position of the journal - E dimensional static unbalance of rotor (m) - f _x, f _y =F _x/(P), F _y/(P): non-dimensional components of fluid film force - F _x, F _y dimensional components of fluid film force (N) - g acceleration of gravity (m/s²) - L axial length of bearing (m) - m % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbnL2yY9% 2CVzgDGmvyUnhitvMCPzgarmWu51MyVXgaruWqVvNCPvMCG4uz3bqe% fqvATv2CG4uz3bIuV1wyUbqee0evGueE0jxyaibaieYlf9irVeeu0d% Xdh9vqqj-hEeeu0xXdbba9frFf0-OqFfea0dXdd9vqaq-JfrVkFHe9% pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaaca% qabeaadaabauaaaOqaaiabg2da9maalaaabaGaeqyYdC3aaWbaaSqa% beaacaaIYaaaaaGcbaGaeqyYdC3aa0baaSqaaGabciaa-bdaaeaaca% WFYaaaaaaakiabg2da9maalaaabaGaeqyYdC3aaWbaaSqabeaacaaI% YaaaaOGaam4qaaqaaiabeo8aZjaadEgaaaaaaa!4C14!\[ = \frac{{\omega ^2 }}{{\omega _0^2 }} = \frac{{\omega ^2 C}}{{\sigma g}}\]: half non-dimensional mass of rotor - M half mass of rotor (kg) - n angular speed of rotor (in r.p.m.=60/2) - t time