Gas permeability and permselectivity of fluorinated polybenzoxazoles

Gas permeability and permselectivity are investigated for polybenzoxazoles from bis(3-amino-4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (BAHHP) and aromatic diacid chlorides. Effects of thermal cyclization on the permeation properties are also investigated. The polybenzoxazole from BAHHP and 4,4′-(1,1,1,3,3,3-hexafluoroisopropylidene)dibenzoyl chloride (HFDB) displays high performance for CO₂/CH₄ separation ( $ {\rm P}_{{\rm CO}_2 } $ = 6.1 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, and $ {{{\rm P}_{{\rm CO}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm CO}_2 } } {{\rm P}_{{\rm CH}_4 } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_4 } }} $ = 38 at 35°C). The polybenzoxazole from BAHHP and 2,6-naphthalene dicarbonyl chloride displays high performance for H₂/CO or H₂/CH₄ separation ( $ {\rm P}_{{\rm H}_2 } $ = 2.4 × 10^?9 cm³ (STP) cm^?1 s^?1 cm-Hg^?1, $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CO}} }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CO}} }} $ = 71, and $ {{{\rm P}_{{\rm H}_2 } } \mathord{\left/ {\vphantom {{{\rm P}_{{\rm H}_2 } } {{\rm P}_{{\rm CH}_{\rm 4} } }}} \right. \kern-\nulldelimiterspace} {{\rm P}_{{\rm CH}_{\rm 4} } }} $ = 250). Permeation properties for the polybenzoxazole from BAHHP and HFDB are close to those for a polyimide of similar chemical structure. The permeation properties are discussed in connection with packing density and local segmental mobility. © 1992 John Wiley & Sons, Inc.     

A tensor product of the Steinberg module and a certain simple kG(pr)-module

Let G be a connected, semisimple, and simply connected algebraic group defined and split over the finite field of order p, and let G(q) be the corresponding finite Chevalley or twisted group, where q = p^r. Recently, Anwar determines the direct sum decomposition of the tensor product of the rth Steinberg module and a simple G-module with a (p,r)-minuscule highest weight λ. In this paper, we determine that of the tensor product regarded as a module for G(q) under some weak assumptions for λ.     

Oscillations of nonlinear hyperbolic equations with functional arguments via Riccati method

This paper is devoted to the study of the oscillatory behavior of solutions of nonlinear hyperbolic equations with functional arguments by using integral averaging method and a generalized Riccati technique. First, we establish oscillation results for nonlinear hyperbolic equations by applying oscillation criteria for Riccati inequality. Secondly, we present interval oscillation results for nonlinear hyperbolic equations. These results improve and extend oscillation results of Cui and Xu [1].     

An approximation analysis for an assembly-like queueing system with time-constraint items

We study an assembly-like queueing system one of whose queues has items with generally distributed time-constraints, where this system has a single server providing services using each item individually. It is well-known that analysis of a queueing system which has items with time-constraint (i.e., impatient items) is difficult since the analytical model must involve all the departure times of these impatient items. We therefore propose to employ the techniques of Whitt’s approximation and show the method for obtaining the stationary distribution of the model. Through some simulation experiments, we discuss the validation of our approximation model, and show that the approximation is accurate in various kinds of situations (e.g., service time distribution and the number of queues).     

On nets of orderq 2 and degreeq+1 admitting GL(2,q)

In this paper we consider finite nets of orderq ² and degreeq + 1 which admit GL(2,q). Our main result says that if a net of orderq ² and degreeq + 1 admits a collineation group with a point-regular normal subgroupT such that /T GL(2,q), then is isomorphic to a regulus net, a twisted regulus net, a Hering net, or . Except in the last one, each of them corresponds to a surface in PG(3,q) obtained from a homogeneous polynomial in two variables.     

Analysis of an SPP/G/1 system with multiple vacations and E-limited service discipline

Many researchers have studied variants of queueing systems with vacations. Most of them have dealt with M/G/1 systems and have explicitly analyzed some of their performance measures, such as queue length, waiting time, and so on. Recently, studies on queueing systems whose arrival processes are not Poissonian have appeared. We consider a single server queueing system with multiple vacations and E-limited service discipline, where messages arrive to the system according to a switched Poisson process. First, we consider the joint probability density functions of the queue length and the elapsed service time or the elapsed vacation time. We derive the equations for these pdf's, which include a finite number of unknown values. Using Rouché's theorem, we determine the values from boundary conditions. Finally, we derive the transform of the stationary queue length distribution explicitly.     

Analysis of NMAR missing data without specifying missing-data mechanisms in a linear latent variate model

It is natural to assume that a missing-data mechanism depends on latent variables in the analysis of incomplete data in latent variate modeling because latent variables are error-free and represent key notions investigated by applied researchers. Unfortunately, the missing-data mechanism is then not missing at random (NMAR). In this article, a new estimation method is proposed, which leads to consistent and asymptotically normal estimators for all parameters in a linear latent variate model, where the missing mechanism depends on the latent variables and no concrete functional form for the missing-data mechanism is used in estimation. The method to be proposed is a type of multi-sample analysis with or without mean structures, and hence, it is easy to implement. Complete-case analysis is shown to produce consistent estimators for some important parameters in the model.     

A family of non class-regular symmetric transversal designs of spread type

Many classes of symmetric transversal designs have been constructed from generalized Hadamard matrices and they are necessarily class regular. In (Hiramine, Des Codes Cryptogr 56:21–33, 2010) we constructed symmetric transversal designs using spreads of \mathbbZ_p²ⁿ{\mathbb{Z}_p^{2n}} with p a prime. In this article we show that most of them admit no class regular automorphism groups. This implies that they are never obtained from generalized Hadamard matrices. As far as we know, this is the first infinite family of non class-regular symmetric transversal designs.     

Construction of additional variables conforming to a common factor model

It is shown that if a random p-vector x conforms to an r-common factor model and an external variable Z is given, then there exists a family of linear combinations X of x and Z such that [x′: X]′ conforms to an r-common factor model     

Enantioselective ester synthesis in the presence of optically active polymers

Enantiomer-differentiating ester syntheses from acid salts, chlorides, and an anhydride were studied in the presence of optically active polyamines. Enantiomer selection occurred in reactions of a racemic salt with an achiral alkyl bromide and vice versa, which is good evidence of the importance of activation of the carboxylate group by complexation of the counterion and activation of alkyl bromide by the formation of a quaternary salt with polyamine under solid–liquid, phase-transfer reaction conditions. Only small optical activity was observed in the products of acid anhydride or chloride with alcohol.