Self-assembling structures and thin-film microscopic morphologies of amphiphilic rod-coil block oligomers

This paper examines the influences of solvent evaporation and atmosphere humidity on self-assembling structures and thin-film microscopic morphologies of amphiphilic rod-coil block oligomers (EOnOPV) containing conjugated oligo(phenylene vinylene) dimer (OPV) coupled to poly(ethylene oxide) (PEO; n, the average number of ethylene oxides, is 16, 12, 7, and 3, respectively) on hydrophilic substrates. Atomic force microscopy (AFM), UV-vis absorption, and small angle X-ray diffraction are employed to investigate the thin-film morphology and structure. Solvent evaporation and atmosphere humidity are found to exert a strong influence on thin-film morphology and structure. Under the condition of quick evaporation and dry atmosphere, all EOnOPV oligomers form the monolayer islands. Increasing the solute volume, both EO16OPV and EO12OPV oligomers can form the polar lamellas with a head-to-tail packing arrangement. Under the condition of slow evaporation and humid atmosphere, EO16OPV and EO12OPV may self-assembly into curvy nanoribbons with well-defined width and curvature radii on mica, while EO7OPV and EO3OPV with the shorter PEO coils do not form. A symmetric bilayer structure for the ribbons is proposed. Plausible reasons for the variation in thin-film morphology are discussed, based on the results obtained from investigation of PEO coil length, solvent evaporation, and atmosphere humidity effects.     

Lewis acid-Lewis acid heterobimetallic cooperative catalysis: mechanistic studies and application in enantioselective aza-Michael reaction

The full details of a catalytic asymmetric aza-Michael reaction of methoxylamine promoted by rare earth-alkali metal heterobimetallic complexes are described, demonstrating the effectiveness of Lewis acid-Lewis acid cooperative catalysis. First, enones were used as substrates, and the 1,4-adducts were obtained in good yield (57-98%) and high ee (81-96%). Catalyst loading was successfully reduced to 0.3-3 mol % with enones. To broaden the substrate scope of the reaction to carboxylic acid derivatives, alpha,beta-unsaturated N-acylpyrroles were used as monodentate, carboxylic acid derivatives. With beta-alkyl-substituted N-acylpyrroles, the reaction proceeded smoothly and the products were obtained in high yield and good ee. Transformation of the 1,4-adducts from enones and alpha,beta-unsaturated N-acylpyrroles afforded corresponding chiral aziridines and beta-amino acids. Detailed mechanistic studies, including kinetics, NMR analysis, nonlinear effects, and rare earth metal effects, are also described. The Lewis acid-Lewis acid cooperative mechanism, including the substrate coordination mode, is discussed in detail.     

Evaluation of critical parameters for measurement of pH by flow injection analysis determination of pH in soil extracts

A systematic evaluation of the parameters affecting the measurement of pH in a flow injection system incorporating a tubular PVC-based pH-sensitive membrane electrode is presented. In order to obtain reliable results, it is necessary to have a dispersion coefficient D^max ? 1.008 at peak maximum and to adjust the buffering capacity of the carrier stream to be less than that of the sample solution. A suitable design of system to meet these criteria is discussed. The applicability of this approach is demonstrated for the determination of pH in a series of soil extracts; the results are compared with those obtained by conventional glass electrode measurements.     

HfO_2单层膜的吸收和激光损伤阈值测试

薄膜吸收是降低膜层激光损伤阈值的重要原因,为了研究薄膜吸收对激光损伤阈值的影响,对HfO2单层膜在1 064 nm处的吸收及其在不同波长激光辐照下的损伤阈值进行了测试和分析。研究结果表明:薄膜的激光损伤阈值由薄膜吸收平均值(决定于薄膜中缺陷的种类和数量)和吸收均匀性(决定于薄膜中缺陷的分布)共同决定;根据HfO2单层膜在1064 nm波长处的吸收值,不但可以定性判断薄膜在1 064 nm波长,而且还可以判断在其它波长激光辐照下的抗激光损伤能力。     

紫外Sc_2O_3薄膜的光学和结构性能表征及其激光作用下的损伤机理

利用电子束蒸发方法,在不同沉积温度(50~350℃)下制备了Sc2O3薄膜。分别用分光光度计,小角掠入射X射线衍射仪和轮廓仪测试了薄膜样品的光谱、微结构和表面粗糙度信息,并用薄膜分析软件Essential Macleod计算了Sc2O3薄膜的折射率和消光系数。结果表明:随着沉积温度升高,Sc2O3薄膜结晶程度增强,晶粒尺寸增大,且较高的沉积温度有利于获得较高的折射率。最后用355 nm,8 ns的三倍频Nd:YAG激光器测试了其激光损伤阈值(LIDT),最大值为2.6 J/cm2,且阈值与薄膜的消光系数、表面粗糙度、光学损耗均呈现相反的变化趋势。用光学显微镜和扫描电子显微镜表征了该薄膜的破坏形貌,详细分析了薄膜在不同激光能量作用下破坏的发展过程,以及Sc2O3薄膜在355 nm紫外激光作用下LIDT与制备工艺的关系,重点分析了355 nm激光作用下薄膜的破坏机理。     

Mono- and binuclear complexes of iron(II) and iron(III) with an N4O ligand: synthesis, structures and catalytic properties in alkane oxidation

Three mononuclear iron complexes and one binuclear iron complex, [Fe(tpoen)Cl].0.5(Fe2OCl6) (1), [Fe(tpoen)Cl]PF6 (2), Fe(tpoen)Cl3 (3) and [[Fe(tpoen)]2(mu-O)](ClO4)4 (4) (tpoen = N-(2-pyridylmethoxyethyl)-N,N-bis(2-pyridylmethyl)amine), were synthesized as functional models of non-heme iron oxygenases. Crystallographic studies revealed that the Fe(II) center of 1 is in a pseudooctahedral environment with a pentadentate N4O ligand and a chloride ion trans to the oxygen atom. The Fe(III) center of 3 is ligated by three nitrogen atoms of tpoen and three chloride ions in a facial configuration. Each Fe(III) center of 4 is coordinated with four nitrogen atoms and an oxygen atom of tpoen with the Fe-O-Fe angle of 172.0(3) angstroms. Complexes 2, 3 and 4 catalysed the oxidation of cyclohexane with H2O2 in the total TNs of 24-36 with A/K ratios of 1.9-2.4. Under the same conditions they also catalysed both the oxidation of ethylbenzene to benzylic alcohol and acetobenzene with good activity (30-47 TN) and low selectivity (A/K 0.7), and the oxidation of adamantane with moderate activity (15-18 TN) and low regioselectivity (3 degrees/2 degrees 3.0-3.2). With mCPBA as oxidant the catalytic activities of 2, 3 and 4 increased 1.8 to 2.3-fold for the oxidation of cyclohexane and ethylbenzene and 6.3 to 7.5-fold for the oxidation of adamantane. Drastic enhancement of the regioselectivity was observed in the oxidation of adamantane (3 degrees/2 degrees 18.5-30.3).     

Electron beam evaporated LaF3 thin films prepared by different temperatures and deposition rates

LaF₃ thin films were prepared by electron beam evaporation with different temperatures and deposition rates. Microstructure properties including crystalline structure and surface roughness were investigated by X-ray diffraction (XRD) and optical profilograph. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical composition of the films. Optical properties (transmittance and refractive index) and laser induce damage threshold (LIDT) at 355 nm of the films were also characterized. The effects of deposition rate and substrate temperature on microstructure, optical properties and LIDT of LaF₃ thin films were discussed, respectively.     

The cancellation property of rings

A ring R is said to have the finitely generated cancellation property provided that the module isomorphism R⊕B?R⊕C implies B?C for any finitely generated R-modules B and C. It is proved that R has this property is equivalent to the existence of the cancellation matrices over R. Moreover, the structure of such matrices is investigated and finite weakly stable rings are characterized in terms of their cancellation matrices.     

Liquid–Liquid Transition and Detrapping of Trapped Carriers of P(MMA/BA) Copolymers by Thermally Stimulated Depolarization Current

Poly (methyl methacrylate/butyl acrylate) [P(MMA/BA)] copolymers (M _η～2×10⁵) with different mass percentages of PMMA (100/0, 90/10, 81/19, and 75/25), were synthesized by the method of solution polymerization. In addition to the normal α and ρ peak, a third τ peak is observed in thermally stimulated depolarization current (TSDC) spectra of the copolymers in the high temperature region. The α peak‐corresponds to the glass transition, the ρ peak originates from the detrapping of trapped carriers in the bulk amorphous structure related with flexible side groups, and the τ peak can be attributed to the charge detrapping related to the liquid–liquid transition of the copolymers. The three peaks all move to lower temperature with an increase of the BA component, indicating that the flexible side groups of butyl acrylate not only have an effect of plasticization on the glass transition and liquid–liquid transition, but also make the trap depth shallower and the detrapping process easier for the ρ and τ peaks. The experimental results confirm that TSDC analysis is very sensitive for investigating the liquid–liquid transition of polymers. The liquid–liquid transition temperature (T _LL) of the copolymers follows a type of the Fox equation. Fitting the results gives a T _LL of 102°C for polybutyl acrylate.     

Separating doubly nonnegative and completely positive matrices

The cone of Completely Positive (CP) matrices can be used to exactly formulate a variety of NP-Hard optimization problems. A tractable relaxation for CP matrices is provided by the cone of Doubly Nonnegative (DNN) matrices; that is, matrices that are both positive semidefinite and componentwise nonnegative. A natural problem in the optimization setting is then to separate a given DNN but non-CP matrix from the cone of CP matrices. We describe two different constructions for such a separation that apply to 5 × 5 matrices that are DNN but non-CP. We also describe a generalization that applies to larger DNN but non-CP matrices having block structure. Computational results illustrate the applicability of these separation procedures to generate improved bounds on difficult problems.