Influence of terminal alkyl chain length on helical twisting property of chiral 1,2-propanediol derivatives

In this study,a novel series of chiral 1,2-propanediol derivatives with different terminal alkyl chain length were synthesized and characterized by FT-IR,~1H NMR and DSC.After doped into a nematic liquid crystal host,all the chiral dopants induced chiral nematic liquid crystals exhibiting a helix inversion with temperature variation.The results indicate that terminal alkyl chain length has a prominent influence on helical twisting property of the chiral dopants.With increasing the terminal alkyl chain le...     

Aerodynamic mechanism of forces generated by twisting model-wing in bat flapping flight

The aerodynamic mechanism of the bat wing membrane Mong the lateral border of its body is studied. The twist-morphing that alters the angle of attack （AOA） along the span-wise direction is observed widely during bat flapping flight. An assumption is made that the linearly distributed AOA is along the span-wise direction. The plate with the aspect ratio of 3 is used to model a bat wing. A three-dimensional （3D） unsteady panel method is used to predict the aerodynamic forces generated by the flapping plate with leading edge separation. It is found that, relative to the rigid wing flapping, twisting motion can increase the averaged lift by as much as 25% and produce thrust instead of drag. Furthermore, the aerodynamic forces （lift/drag） generated by a twisting plate-wing are similar to those of a pitching rigid-wing, meaning that the twisting in bat flight has the same function as the supination/pronation motion in insect flight.     

一类二桥结补中本质曲面的性质

设K是一类只含扭转的二桥结(即纽结投影图不含单一交叉点),通过对这一类纽结补中的本质曲面F与纽结交点对应的bubbles相交的所有可能情况进行分析,得到如果本质曲面F对应的拓扑图T(F)是简单的,便可得到曲面的亏格为零,并且进一步给出了不论本质曲面F对应的拓扑图T(F)是否简单,都可经过讨论曲线的不同穿越形式得到曲面F是穿孔球面.     

Rigidity of Coxeter Groups and Artin Groups

A Coxeter group is rigid if it cannot be defined by two nonisomorphic diagrams. There have been a number of recent results showing that various classes of Coxeter groups are rigid, and a particularly interesting example of a nonrigid Coxeter group has been given by Bernhard Mühlherr. We show that this example belongs to a general operation of diagram twisting. We show that the Coxeter groups defined by twisted diagrams are isomorphic, and, moreover, that the Artin groups they define are also isomorphic, thus answering a question posed by Charney. Finally, we show a number of Coxeter groups are reflection rigid once twisting is taken into account.     

Observation of banded spherulites and lamellar structures by atomic force microscopy

Spherulites are common structures of semi-crystalline polymers. It has been known that semi-crystalline polymers can form spherulites when crystallized from solution or from melt. A dark Maltese cross of a spherulite could be easily observed under the polarized optical microscopy (POM). Moreover, some spherulites show an additional alternating dark and bright concentric ring structure that is attributed to the regular twisting of the radial crystallite ribbons as they grow from the spherulit…     

Why chiral tartaric imide derivatives give large helical twisting powers in nematic liquid crystal phases: substituent-effect approach to investigate intermolecular interactions between dopant and liquid crystalline molecules

Novel C₂-symmetric chiral dopant derivatives, namely, N-substituted (2R, 3R)-2,3-bis(4-(4-octyloxyphenyl)benzoyloxy)succinimides1a-h, were synthesised, and the effects of the N-substituent and imide-carbonyl groups on the helical twisting powers (HTPs) were investigated in two nematic liquid crystalline compounds, 4-n-pentyl-4?-cyanobiphenyl (5CB) and N-(4-ethoxybenzylidene)-4-n-butylaniline (EBBA). As a result, it was clarified that the bulkiness of the N-substituents has a significant correlation with the HTPs, and the imide-carbonyl group interacts strongly with the cyano group of 5CB to give high HTPs in the nematic phases. However, it is assumed that the imide-carbonyl groups of the dopants do not have strong electrostatic attractive interactions with EBBA molecules in the nematic phase to afford the moderate HTPs.     

Unusual Aggregation‐Induced Emission of a Coumarin Derivative as a Result of the Restriction of an Intramolecular Twisting Motion

Aggregation‐induced emission (AIE) is commonly observed for propeller‐like luminogens with aromatic rotors and stators. Herein, we report that a coumarin derivative containing a seven‐membered aliphatic ring (CD‐7) but no rotors showed typical AIE characteristics, whereas its analogue with a five‐membered aliphatic ring (CD‐5) exhibited an opposite aggregation‐caused quenching (ACQ) effect. Experimental and theoretical results revealed that a large aliphatic ring in CD‐7 weakens structural rigidity and promotes out‐of‐plane twisting of the molecular backbone to drastically accelerate nonradiative excited‐state decay, thus resulting in poor emission in solution. The restriction of twisting motion in aggregates blocks the nonradiative decay channels and enables CD‐7 to fluoresce strongly. The results also show that AIE is a general phenomenon and not peculiar to propeller‐like molecules. The AIE and ACQ effects can be switched readily by the modulation of molecular rigidity.     

Spectrum of the Schrödinger Operator in a Perturbed Periodically Twisted Tube

We study Dirichlet Laplacian in a screw-shaped region, i.e. a straight twisted tube of a non-circular cross section. It is shown that a local perturbation which consists of “slowing down” the twisting in the mean gives rise to a non-empty discrete spectrum Mathematical Subject Classifications: 35P05, 81Q10.     

扭摆内耗仪的发明和内耗研究的开拓与发展

本文对笔者关于滞弹性内耗研究的早期工作（１９４５一１９４９年于芝加哥）作了历史回顾。概述用滞弹性测量方法研究了金属中晶粒间界和滑移带的力学性质,并为此目的而创制了扭摆内耗仪和转动线圈的扭转装置,从而可以用同一试样测定内耗、动态模量亏损,在恒应力下的蠕变和在恒应变下的应力弛豫。首次观测到晶粒间界内耗峰（作为温度的函数）,测出了晶界弛豫的激活能,提出了大角晶界的＂无序原子群＂模型;在部分再结晶的冷加工金属试样中观测到与滑移带弛豫有关的内耗峰,在冷加工并经过部分退火的含铜的铝中发现了反常内耗峰（作为温度和应变振幅的函数）。最后指出,近年来在晶界弛豫和位错弛豫的研究中发现了大量非线性滞弹性现象,基本上奠定了非线性滞弹性理论的实验基础,标志着非线性滞弹性这一新学科领域的开端。      

Analysis of Off-Axial Optical Systems (2)

The extended 4×4 Gaussian bracket matrix Gij represents the lowest order quantity of “aberration coefficient tensor quantities” which are defined to as the peculiarity of off-axial optical systems and are independent of azimuths. We newly confirmed this extended 4×4 Gaussian bracket matrix of deflection (refraction or reflection), transmission and “twisting.” The result determined by use of a new representative method of asymmetrical surfaces and a method of paraxial expansion along the folded reference axis shows that the 4×4 Gaussian bracket matrix is the extended form of the 2x2 Gaussian bracket matrix which is used in co-axial rotational symmetric optical systems. Furthermore, we analyze and formalize the crossterm effects, which are the most serious problem in optical systems having multiple off-axial surfaces, using the concept of a chain of “optical systems divided into former and latter” and the vector-tensor analysis method. The result of this analysis reveals the structure of the cross-term effects and proves the usefulness of the vector-tensor analysis method in general image analysis.