Structure and aggregation of a helix-forming polymer

We have studied the competition between helix formation and aggregation for a simple polymer model. We present simulation results for a system of two such polymers, examining the potential of mean force, the balance between intermolecular and intramolecular interactions, and the promotion or disruption of secondary structure brought on by the proximity of the two molecules. In particular, we demonstrate that proximity between two such molecules can stabilize secondary structure. However, for this model, observed secondary structure is not stable enough to prevent collapse of the system into an unstructured globule.     

Chiral Iodine‐Catalyzed Dearomatizative Spirocyclization for the Enantioselective Construction of an All‐Carbon Stereogenic Center

The first enantioselective dearomatizative spirocyclization of 1‐hydroxy‐N‐aryl‐2‐naphthamide derivatives has been accomplished by chiral organoiodine catalysis to stereoselectively create an all‐carbon stereogenic center, providing a straightforward approach to access spirooxindole derivatives in good yields and with high to excellent levels of enantioselectivity. Chiral hypervalent phenyl‐λ³‐iodanes generated in situ from the oxidation of the chiral phenyl iodine actually participate in the asymmetric oxidative dearomatizative spirocyclization reaction.     

Photocontrolled Reversible Conversion of Nanotube and Nanoparticle Mediated by β‐Cyclodextrin Dimers

A photochemically interconvertible supramolecular nanotube–nanoparticle system was constructed through secondary assembling of self‐aggregates of amphiphilic porphyrin derivatives mediated by trans‐ and cis‐azobenzene‐bridged bis(permethyl‐β‐cyclodextrin). Significantly, these nanotubes and nanoparticles were able to interconvert upon irradiation at different wavelengths, and this photocontrolled morphological conversion is reversible and recyclable for tens of times, which will provide a feasible and convenient way to construct the ordered nanostructure with various morphologies that can be smartly controlled by the environmentally benign external stimulus.     

Synthesis,characterization and modeling of ABC triblock terpolymers: the effect of block sequence

Four equimolar terpolymers comprising ten units from each of the monomers methoxy hexa(ethylene glycol) methacrylate (HEGMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) were prepared by group transfer polymerization (GTP), and characterized by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (¹H NMR) spectroscopy to confirm size homogeneity and composition. These terpolymers were the three block sequence isomers, ABC, BAG and ACB, as well as the statistical isomer. Aqueous solutions of the terpolymers were characterized by dynamic light scattering and turbidimetry to determine the hydrodynamic sizes and cloud points. The results indicated micelle formation in the triblocks, and absence of micellization with the statistical terpolymer. In general, a strong dependence of the hydrodynamic size and cloud point on polymer architecture was observed. Monte Carlo simulations on non-aggregating isomeric terpolymers of similar structure also showed a strong dependence of the radius of gyration on polymer architecture.     

Synchronization of chaotic systems with different orders

A controller is designed to realize the synchronization between chaotic systems with different orders. The structure of the controller, the error equations and the Lyapunov functions are determined based on stability theory. Hyperchaotic Chen system and Rossler system are taken for example to demonstrate the method to be effective and feasible. Simulation results show that all the state variables of Rossler system can be synchronized with those of hyperchaotic Chen system by using only one controller, and the error signals approach zero smoothly and quickly.     

应力调控单层MoSe2的光致发光光谱特性

为了探究二维材料在片上可调有源光学器件领域的应用潜力,通过干法转印将由机械剥离法得到的高品质单层二硒化钼转移到正面涂有150nm厚聚甲基丙烯酸甲酯的双轴压电陶瓷上,制作出可应力调控发光性质的单层二硒化钼光源.对双轴压电陶瓷施加驱动电压,使电信号转化为应力信号,观察低温下(～5K)二硒化钼光致发光光谱中本征激子态、带电激子态信号峰随应力变化的规律.结果表明:在应力由拉伸应力转变为压应力并逐渐增大的过程中,本征激子态、带电激子态信号峰分别出现了～3.8meV、～3.7meV的波长蓝移.增大压应力、拉伸应力都会导致本征激子态、带电激子态信号峰光强线性降低.同时,与泵浦光圆极化相关的圆偏振度也随应力变化表现出规律性改变.此项研究证明了应力调控与单层二硒化钼光学性质之间的紧密关系,为开发各类基于二维材料的片上可调有源光学器件提供支持.     

Exact on-event expressions for discrete potential systems

The properties of systems composed of atoms interacting though discrete potentials are dictated by a series of events which occur between pairs of atoms. There are only four basic event types for pairwise discrete potentials and the square-well/shoulder systems studied here exhibit them all. Closed analytical expressions are derived for the on-event kinetic energy distribution functions for an atom, which are distinct from the Maxwell-Boltzmann distribution function. Exact expressions are derived that directly relate the pressure and temperature of equilibrium discrete potential systems to the rates of each type of event. The pressure can be determined from knowledge of only the rate of core and bounce events. The temperature is given by the ratio of the number of bounce events to the number of disassociation/association events. All these expressions are validated with event-driven molecular dynamics simulations and agree with the data within the statistical precision of the simulations.     

Viscous froth model for a bubble staircase structure under rapid applied shear: An analysis of fast flowing foam

The viscous froth model is applied to the rapid shear of ‘2-dimensional’, dry foams for bubbles confined in a monolayer and arranged in an ordered staircase configuration that forms part of a hexagonal honeycomb structure. High system energies are attained as particular films in the staircase become highly elongated under shear. Topological transformations during which bubbles exchange neighbours can relax the staircase energy, but their onset is postponed at high shear rates. Moreover as the imposed shear rate increases, the rate at which topological transformations subsequently occur cannot keep pace with the imposed shear, and secular film stretching onsets. A critical capillary number (a dimensionless measure of shear rate) separates a regime where film lengths are periodic functions of imposed strain from a regime of secular growth.     

On principal Hessian directions for multivariate response regressions

We consider a multivariate response regression analysis with a vector of predictors. In this article, we develop the modification of principal Hessian directions based on principal components for estimating the central mean subspace without requiring a prespecified parametric model. We use a permutation test suggested by Cook and Yin (Aust New Z J Stat 43:147–199, 2001) for inference about the dimension. Simulation results and one real data are reported, and comparisons are made with four methods—most predictable variates, k-means inverse regression, optimal method of Yoo and Cook (Biometrika 94:231–242, 2007) and canonical correlation approach.