The importance of solvent reorganisation in the effect of an ionic liquid on a unimolecular substitution process

Temperature dependent rate studies demonstrate an enthalpic benefit and an entropic cost associated with the change in the rate of a unimolecular substitution process on addition of a high proportion of an ionic liquid, the latter effect being supported by molecular dynamics simulations.     

Derivations, isomorphisms, and second cohomology of generalized Witt algebras

Generalized Witt algebras, over a field of characteristic , were defined by Kawamoto about 12 years ago. Using different notations from Kawamoto's, we give an essentially equivalent definition of generalized Witt algebras over , where the ingredients are an abelian group , a vector space over , and a map which is linear in the first variable and additive in the second one. In this paper, the derivations of any generalized Witt algebra
, with the right kernel of being , are explicitly described; the isomorphisms between any two simple generalized Witt algebras are completely determined; and the second cohomology group for any simple generalized Witt algebra is computed. The derivations, the automorphisms and the second cohomology groups of some special generalized Witt algebras have been studied by several other authors as indicated in the references.

     

Recent development of polyimides: Synthesis,processing, and application in gas separation

High-performance polymers have been concomitant with advanced technology for half a century. With the advancement of synthetic chemistry, the recent development of high-performance polymers has provided superior properties and enabled wide applications. This article reviews recent research progress in aromatic high-performance polymers. Particularly, we focus on the synthesis and processing of polyimides, as well as the application in gas separation membranes. We begin with a brief introduction to highlight important history and physiochemical characteristics of polyimides. Then, we review the various synthesis methods, followed by recent advances for improving processability. Finally, we evaluate the use of high-performance polymers in gas separation membranes with focus given to the key issues of plasticization and aging. Overall, the information presented herein provides an up-to-date overview of high-performance polymers, polyimides particularly, and serves as a guide for further research involving the applications in membrane technologies.     

FLUOROALKYLTHIO SUBSTITUTED BENZOYL DERIVATIVES

Abstract

Electrophilic substitution with fluoroalkanesulfenyl chlorides on appropriately activated acetophenones, benzophenones, benzaldehydes, and benzoates is described.     

Measurement error models and variance estimation in the presence of rounding error effects

An approach to estimating measurement error variances for any instrument having round-off effects that might also have instrument bias is presented. Recently finite instrument resolution effects on error variances have been studied, but negligible instrument bias was assumed and the contexts were different than considered here. Our intent is to use repeated measurements on several standards to estimate the instrument’s random and systematic error variances. Recognizing that rounding impacts item bias and variance in a manner that depends on the true value, an approach is presented to estimate random error variance and instrument systematic error variance. The key finding is that item-specific bias can interfere with the estimation of overall instrument bias unless appropriate error modeling and associated inference steps are taken.     

Impact of the detector energy resolution on the performance of MGA and MGAU isotopic codes

Nondestructive measurements of γ-ray and X-ray emissions are often made to characterize special nuclear materials. Various computer codes are available to determine the relative isotopic composition of uranium or plutonium (along with certain other associated nuclides) from analysis of the spectra resulting from such measurements. MGA (Gunnink, Proceedings of the 9th ESARDA symposium on safeguards and nuclear management 167, 1987) and MGAU (Gunnink et al., Proceedings of the IAEA symposium on international safeguards 541, 1994) are among the major isotopic codes. The purpose of this study was to investigate MGA and MGAU performance versus energy resolution of the counting system.