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991.
Kazuhiro Tanaka Yasuharu Osada Hidetoshi Kita Ken-ichi Okamoto 《Journal of Polymer Science.Polymer Physics》1995,33(13):1907-1915
Polyimides with large aromatic rings were prepared from 3,6-diaminocarbazole (CDA), N-ethyl-3,6-diaminocarbazole (ECDA), 2,7-diaminofluorene (DAF), 2,7-diaminofluorenon (DAFO), and dimethyl-3,7-diaminodibenzothiophene-5,5-dioxide (DDBT) with 2-bis(2,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). Their physical properties, including gas permeability and permselectivity, were investigated in comparison with those of the related polyimides from 1,3-phenylenediamine (mPD). Glass transition temperatures of the polyimides with large aromatic rings were much higher than those of the mPD-based polyimides as a result of increased rigidity of the former polymer chains. With changing diamine from mPD to the large aromatic diamines, charge transfer (CT) interaction between the moieties of acid anhydride and diamine seems to be enhanced, judging from the red shift of absorption edge of the polyimide films and the red shift of CT excitation band of the 6FDA-based polyimides in solution. Fraction of free space (VF) was a little smaller for the polyimides with large aromatic rings except DDBT than for the mPD-based polyimides, probably because of enhancement in polymer chain-chain interactions as a result of the increased CT interaction. The DDBT-based polyimides had large VF than the mPD-based polyimides because of the nonplanar structure of neighboring dibenzothiophene-5,5-dioxide and imide rings. For the 6FDA-based polyimides, permeability coefficients to H2, O2, N2, CO2, and CH4 were in the order, DAFO < mPD ~ DAF < CDA < ECDA < DDBT. As for the membrane performance for H2/CH4, CO2/CH4, and O2/N2 systems, it is significant to change diamine from mPD to DDBT or CDA, but not to DAF or DAFO. The DDBT-based polyimides were excellent for H2/CH4 and CO2/CH4 separations. © 1995 John Wiley & Sons, Inc. 相似文献
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We examine, from a constructive perspective, the relation between the complements of S, T, and S ∩ T in X, where X is either a metric space or a normed linear space. The fundamental question addressed is: If x is distinct from each element of S ∩ T, if s ? S, and if t ? T, is x distinct from s or from t? Although the classical answer to this question is trivially affirmative, constructive answers involve Markov's principle and the completeness of metric spaces. Mathematics Subject Classification: 03F65, 46S30. 相似文献
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Munehisa Matsumoto Toru Sakai Masahiro Sato Hajime Takayama Synge Todo 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):660
Recently many interesting magnetic nanostructures have been fabricated and much attention is arising on the rich magnetic properties that originate in the quantum effects eminent in the nanoscale world. One of the peculiar aspects of the quantum effects is the spin excitation gap. In the spin-1/2 low-dimensional systems, the spin gap often appears when the lattice dimerization or the frustration in the spin–spin interaction are introduced. In the present study, we investigate the ground-state property of the spin-1/2 antiferromagnetic spin chiral nanotubes with the spatial modulation in the spin–spin interaction. The ground-state phase diagrams of them are determined by observing the behavior of the expectation value of the Lieb–Schultz–Mattis slow-twist operator calculated by the quantum Monte Carlo method with the continuous-time loop algorithm. We discuss the relation between the characteristic of the topology of the phase diagram and the chiral vector of the nanotubes. 相似文献
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Four wave mixing (FWM) is of considerable interest in generation of a phase conjugate beam with photorefractive crystals. The common methods of FWM are parallel polarization FWM and cross polarization FWM. In this paper, we analyze the phase matching property of the latter. First, we consider the phase matching condition, and derive equations representing the angler relationship of interacting beams. Then, we consider the phase mismatching which is caused by shift of the probe beam angle from the phase matching condition, and calculate the effect of the shift of this angle on the amount of phase mismatching. We also determine and closely examine the coupling constant. 相似文献
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