Variation in crystallization conditions allows the isolation of trimeric as well as dimeric and monomeric forms of [(alkyl isocyanide)4RhI]+

Trimeric green [(i-PrNC)12Rh(I)3]Cl3.4.5H2O, monomeric [(C6H11NC)4Rh(I)](BPh4) and [(i-PrNC)4Rh(I)](BPh4) (both yellow), and red, dimeric [(C6H11NC)8Rh(I)2]Cl2.0.5C6H6.2H2O have been crystallized.     

Kinetic pathways of phase ordering in lipid raft model systems

We studied kinetic pathways of order-order transitions in bilayer lipid mixtures using a time-dependent Ginzburg-Landau (TDGL) approach. During the stripe-to-hexagonal phase transition in an incompressible two-component system, the stripe phase first develops a pearl-like instability along the phase boundaries, which grows and drives the stripes to break up into droplets that arrange into a hexagonal pattern. These dynamic features are consistent with recent experimental observations. During the disorder-to-hexagonal phase transition in an incompressible three-component system, the disordered state first passes through a transient stripelike structure, which eventually breaks up into a hexagonal droplet phase. Our results suggest experiments with synthetic vesicles where the stripelike patterns could be observed.     

Specialized Runge-Kutta methods for index differential-algebraic equations

We consider the numerical solution of systems of semi-explicit index differential-algebraic equations (DAEs) by methods based on Runge-Kutta (RK) coefficients. For nonstiffly accurate RK coefficients, such as Gauss and Radau IA coefficients, the standard application of implicit RK methods is generally not superconvergent. To reestablish superconvergence projected RK methods and partitioned RK methods have been proposed. In this paper we propose a simple alternative which does not require any extra projection step and does not use any additional internal stage. Moreover, symmetry of Gauss methods is preserved. The main idea is to replace the satisfaction of the constraints at the internal stages in the standard definition by enforcing specific linear combinations of the constraints at the numerical solution and at the internal stages to vanish. We call these methods specialized Runge-Kutta methods for index DAEs (SRK-DAE).

     

Responses of enantioselective characteristics of imidazolinone herbicides and Chiralcel OJ column to temperature variations

Temperature affects not only the chromatographic characteristics of solute but may also alter the conformation of the stationary phase. However, temperature influences on enantioseparation of solute and conformation of chiral stationary phase (CSP) are seldom considered simultaneously. In this study, three temperature programs, a conventional heating procedure, a cyclic van't Hoff program, and a step-temperature program, were employed to evaluate temperature effects on enantioseparation of five imidazolinone herbicides on Chiralcel OJ column and the conformational state of the stationary phase. The van't Hoff plots of retention factor (k'), distribution constant (K) and separation factor (alpha) for imazapyr (1), imazapic (2), imazethapyr (3), and imazamox (4) were linear within 15-50 degrees C. Nonlinear van't Hoff plots of alpha were observed for imazaquin (5) with mobile phase of n-hexane (0.1% TFA)-2-propanol at 70/30 or 60/40 (v/v). The large molecular size of imazaquin (5) and van't Hoff plots of alpha were therefore more sensitive at detecting conformational changes of the stationary phase. Small but irreversible conformational changes occurred at 5-10 degrees C with the solvent ratio of 60/40. During the cyclic van't Hoff program, reversible conformational changes were observed at >or=15 degrees C. A switch was even visible at about 25 degrees C with the solvent ratio of 60/40 during the re-cooling cycle. The cyclic van't Hoff temperature program showed that using OJ column may yield satisfactory results at 15-50 degrees C but not at 相似文献   

Local structure and local conduction paths in amorphous (In,Ga,Hf)–ZnO semiconductor thin films

The local structure and local conduction paths of Ga–In–Zn–O (GIZO) and Hf–In–Zn–O (HIZO) amorphous thin films were investigated by the extended X-ray absorption fine structure (EXAFS). We found that the local hindrance paths of In–Ga and In–Hf exist in the conduction paths of amorphous GIZO and HIZO semiconductor thin films, respectively.     

2-Halo-subsituted tetracenes: their generation and single crystal OFET characteristics

2-Chlorotetracene and 2-bromotetracene were generated in high purity from their monoketone precursors either by heating or upon irradiation of light. Crystals of two compounds were prepared by physical vapor transport method. Organic field effect transistors made with the single crystals of these two compounds were fabricated effectively. Their p-type transistor characteristics are described.     

Anisotropic thermal transport in a crosslinked polyisoprene rubber subjected to uniaxial elongation

Anisotropic thermal transport in a crosslinked polyisoprene (natural rubber) subjected to uniaxial elongation is investigated experimentally. Using a novel optical technique based on forced Rayleigh scattering, two components of the thermal diffusivity tensor are measured as a function of stretch ratio. The thermal diffusivity is found to increase in the direction parallel, and decrease in the direction perpendicular, to the stretch direction. The level of anisotropy for the natural rubber is substantially lower than that reported by Tautz 50 years ago but comparable to that found in our previous studies on molten polymers, quenched thermoplastics, and other crosslinked elastomers. Thermal diffusivity data along with measurements of the tensile stress were used to evaluate the stress‐thermal rule, which was found to be valid over the entire range of stretch ratios. In contrast, failure of the stress‐optic rule was observed at stretch ratios well below the largest value at which the stress‐thermal rule was valid. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and stretch of polymer chain segments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Sustainability performance of polyethylene terephthalate,clarifying challenges and opportunities

Publications on polyethylene terephthalate (PET) continue to increase including the number of publications on recycling. PET is a versatile material with the ability to be remade from its polymer state through mechanical recycling and even back to its original monomer through advanced recycling. The scale of PET's use affords continued research and applications in improved recycling. Publications on new uses of discarded PET and the ability to clean and convert it into many forms including alternative materials are expanding with an attempt to complete circular use or improve the end of life. As indicated in life cycle assessment studies, increases in recycling lower the energy required to manufacture products. The future for PET will reduce energy demands further with the largest breakthroughs in recycling technologies and bio-sourced resins trending toward zero energy and carbon negative solutions. Opportunities remain for improvement in the use of PET with light weighting. The testing of new resins, development of bio-feedstocks, improvements in engineering, processing, recycling, and design continue to provide benefits. This review provides context for these developments.