Radio-frequency compressed electron pulse-width characterization by cross-correlation between electron bunches and laser-induced plasma

A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.     

Shear-induced long-range uniaxial assembly of polyaromatic monolayers at molecular resolution

The control of spatial arrangements of molecular building blocks on surfaces opens the foundational step of the bottom-up approach toward future nanotechnologies. Contemporarily, the domain size of monolayers exhibiting crystallinity falls in the submicrometer scale. Developed herein is a method that allows the alignment of polyaromatics with one-single domain for as long as 7 mm. Even more exciting is the fact that the method is applicable to every laboratory and costs practically nothing. The monolayers are prepared simply by placing a piece of folded lens paper against the substrate and the deposition solution containing the compound of interest. The preparation scheme is similar to the Couette flow where the laminar flow takes place between two concentric walls, one of which rotates and creates viscous drag proven useful to align macromolecules. The method can induce an edge-on orientation for 3,6,11,14-tetradodecyloxydibenzo[g,p]chrysene (DBC-OC12), 3,6,12,15-tetrakis(dodecyloxy)tetrabenz[a,c,h,j]anthracene (TBA-OC12), and hexakis(4-dodecyl)-peri-hexabenzocoronene (HBC-C12) and unsubstituted coronene which would otherwise adopt the face-on arrangement on graphite. This finding will be useful to the research and industry that demands high quality alignment of polyaromatics such as OTFTs, optical polarizers, and nanodevices associated with molecular self-assembly.     

Encapsulation of quinine by beta-cyclodextrin: excellent model for mimicking enzyme-substrate interactions

An inclusion complex formed by beta-cyclodextrin and quinine has been investigated in solution and in the solid state, in which the quinoline ring and the aliphatic ring locate in different hydrophobic cavities, respectively. The study on the inclusion geometry and weak interactions shows that the difference in conformation for this complex is a result of three main packing arrangement considerations, which can provide an ideal model mimicking enzyme-substrate interactions.     

具有星形结点的平面五次系统的全局结构分析

该文对具有星形结点的平面五次系统的全局结构的拓扑分类应用Ⅰ Ⅳ型区域(见［2］),讨 论了平面五次系统（1）的全局结构的拓扑分类，并得到93种全局结构及其右边多项式系统的判定方法。      

Phase Transition-Promoted Rapid Photomechanical Motions of Single Crystals of a Triene Coordination Polymer

Molecular crystals with the ability to transform light energy into macroscopic mechanical motions are a promising class of materials with potential applications in actuating and photonic devices. In regard to such materials, coordination polymers that exhibit dynamic photomechanical motion, associated with a phase transition, are unknown. Herein, we report an intriguing photoactive, one-dimensional Zn^II coordination polymer, 1 , derived from 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene and 3,5-difluorobenzoate. Single crystals of 1 under UV light irradiation exhibit rapid shrinking and bending, violent bursting-jumping, splitting, and cracking behavior. Single-crystal X-ray diffraction analysis and ¹H NMR spectroscopy reveal an unusual photoinduced phase transition involving a single-crystal-to-single-crystal [2+2] cycloaddition reaction that results in photomechanical responses. Interestingly, crystals of 1 , which are triclinic with space group , are transformed into a higher symmetry, monoclinic cell with space group C2/c. This process represents a rare example of symmetry enhancement upon photoirradiation. The photomechanical activity is likely due to the sudden release of stress associated with strained molecular geometries and significant solid-state molecular movement arising from cleavage and formation of chemical bonds. A composite membrane fabricated from 1 and polyvinyl alcohol (PVA) also displays interesting photomechanical behavior under UV light illumination, indicating the material's potential as a photoactuator.