Permeation of gases through modified polymer films III. Gas permeability and separation characteristics of gamma-irradiated teflon FEP copolymer films

A study has been made of the diffusion, solubility, and separation of nitrogen and methane gases at temperatures ranging from 15° to 50°C in a series of Teflon FEP copolymer films which were irradiated by γ rays in air and under vacuum. The irradiated films were subjected to postirradiation treatment temperatures above and below the glass I transition temperature of the copolymer. The effect of radiation on crystallinity and cross-linking was examined by density, thermal, and tensile strength measurements. Diffusion and permeability coefficients of both gases decreased with irradiation dose but solubility coefficients were not greatly affected. Nitrogen-methane separation factors for vacuum-irradiated films increased with irradiation dose, but little change was observed for the air-irradiated films. Chain scission appeared to be the predominant reaction in air-irradiated films whereas both cross-linking and chain scission occurred in vacuum-irradiated films depending on post-irradiation heat-treatment conditions. The permselectivity of the Teflon FEP films was increased by γ irradiation but this was achieved at the expense of the permeation rate.     

Influence of tensile deformation on the crystalline organization of ethylene copolymers

The influence of tensile deformation on the crystalline properties of ethylene copolymers (ethylene-vinyl acetate [EVA] copolymers) was investigated by differential scanning calorimetry (DSC). The consequence of drawing on the mobility of the amorphous phase also was investigated through the study of the glass transition temperature. The results indicate that more disorganized crystals, melting at a lower temperature, are present after the tensile deformation, reducing the mobility of the amorphous chains, as shown by an increase of the glass transition temperature. For the lowest molecular weight copolymer. less crystalline changes are observed after the tensile test, probably due to the fact that no stiffening appears during the drawing.     

A Review of Online Real-Time Process Analyses of Melt-State Polymer Using the Near-Infrared Spectroscopy and Chemometrics

Abstract

This review describes the online process monitoring of the melt-state polymer by near-infrared (NIR) spectroscopy and chemometrics. The spectra of linear low-density polyethylene (LLDPE), random polypropylene (RPP), block polypropylene (BPP), and ethylene-vinylacetate (EVA) copolymer in melt states measured by an online monitoring system with a Fourier transform near-infrared spectrometer are discussed. The calibration models for the density of LLDPE, the content of ethylene copolymers in RPP and BPP, and vinylacetate concentration (VA) in EVA copolymers using partial least squares regression are reported. The continuous monitoring of the LLDPE density at the real plant is described as an example of online monitoring using NIR spectroscopy and chemometrics. For the precise prediction of VA in EVA, a combination method using regression and discrimination was inducted. Three compensation methods for the effect of the temperature change in the RPP and BPP samples are shown. Conventional calibration transfer methods are introduced, and a practical calibration transfer method using two samples and its performance are reported using BPP and RPP spectra. Moreover, the possibility of a calibration correction method using one sample for the realization of long-term traceability is indicated by the example of the relocation.     

The Projective Cover of the Trivial Module Over a Group Algebra of a Finite Group

We determine all finite groups G such that the Loewy length (socle length) of the projective cover P(k _G ) of the trivial kG-module k _G is four, where k is a field of characteristic p > 0 and kG is the group algebra of G over k, by using previous results and also the classification of finite simple groups. As a by-product we prove also that if p = 2 then all finite groups G such that the Loewy lengths of the principal block algebras of kG are four, are determined.     

Optimal Pair Matching With Two Control Groups

In an effort to detect hidden biases due to failure to control for an unobserved covariate, some observational or nonrandomized studies include two control groups selected to systematically vary the unobserved covariate. Comparisons of the treated group and two control groups must, of course, control for imbalances in observed covariates. Using the three groups, we form pairs optimally matched for observed covariates—that is, we optimally construct from observational data an incomplete block design. The incomplete block design may use all available data, or it may use data selectively to produce a balanced incomplete block design, or it may be the basis for constructing a matched sample when expensive outcome information is to be collected only for sampled individuals. The problem of optimal pair matching with two control groups is shown by a series of transformations to be equivalent to a particular form of optimal nonbipartite matching, a problem for which polynomial time algorithms exist. In our examples, we implement the procedure using a nonbipartite matching algorithm due to Derigs. We illustrate the method with data from an observational study of the employment effects of the minimum wage.     

Cycle Extensions in BIBD Block‐Intersection Graphs

A cycle C in a graph G is extendable if there is some other cycle in G that contains each vertex of C plus one additional vertex. A graph is cycle extendable if every non‐Hamilton cycle in the graph is extendable. A balanced incomplete block design, BIBD, consists of a set V of v elements and a block set of k‐subsets of V such that each 2‐subset of V occurs in exactly λ of the blocks of . The block‐intersection graph of a design is the graph having as its vertex set and such that two vertices of are adjacent if and only if their corresponding blocks have nonempty intersection. In this paper, we prove that the block‐intersection graph of any BIBD is cycle extendable. Furthermore, we present a polynomial time algorithm for constructing cycles of all possible lengths in a block‐intersection graph.     

Stability analysis of block boundary value methods for neutral pantograph equation

This paper deals with the convergence and stability properties of block boundary value methods (BBVMs) for the neutral pantograph equation. Due to its unbounded time lags and limited computer memory, a change in the independent variable is used to transform a pantograph equation into a non-autonomous differential equation with a constant delay but variable coefficients. It is shown under the classical Lipschitz condition that a BBVM is convergent of order p if the underlying boundary value method is consistent with order p. Furthermore, it is proved under a certain condition that BBVMs can preserve the asymptotic stability of exact solutions for the neutral pantograph equation. Meanwhile, some numerical experiments are given to confirm the main conclusions.     

正交平衡区组设计统计模型中的方差分析

正交平衡区组设计(或广义正交表)的数据分析类似于正交拉丁方(或正交表)的数据分析.利用类似于正交表数据分析中的投影矩阵的正交分解技术,研究正交平衡区组设计的统计分析模型,给出了方差分析中的二次型以及各因子的二次型的分布性质,从而给出正交平衡区组设计统计模型中的方差分析方法.     

Asymptotic theory for delay differene equations

Using the new notion of block dichotomy we investigate the asymptotic behavior of nonlinear delay difference equations. Our results produce a discrete analogue of Levinson-type theorems.