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31.
Alexandros A. Skordos Ivana K. Partridge 《Journal of Polymer Science.Polymer Physics》2004,42(1):146-154
This article presents a new methodology for the quantitative determination of the progress of the curing reaction of a thermosetting resin, using the results of electrical impedance spectroscopy. The method is an extension of the use of the imaginary impedance maximum as a reaction progress indicator and is based on the demonstration of a close correlation between the reaction rate, as measured by conventional differential scanning calorimetry, and the rate of change of the value of the imaginary impedance spectrum maximum. Tests on a commercial aerospace epoxy resin under both isothermal and dynamic heating conditions with calorimetry and impedance spectroscopy have demonstrated the validity of the method and set the accuracy limits involved. This technique can be used as a real-time online control tool for thermoset composite manufacturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 146–154, 2004 相似文献
32.
Taek‐Joong Kim Baoan Li May‐Britt Hgg 《Journal of Polymer Science.Polymer Physics》2004,42(23):4326-4336
Fixed‐site–carrier membranes were prepared for the facilitated transport of CO2 by casting polyvinylamine (PVAm) on various supports, such as poly(ether sulfone) (PES), polyacrylonitrile (PAN), cellulose acetate (CA), and polysulfone (PSO). The cast PVAm on the support was crosslinked by various methods with glutaraldehyde, hydrochloric acid, sulfuric acid, and ammonium fluoride. Among the membranes tested, the PVAm cast on polysulfone and crosslinked by ammonium fluoride showed the highest selectivity of CO2 over CH4 (>1000). The permeance of CO2 was then measured to be 0.014 m3 (STP)/(m2 bar h) for a 20 μm thick membrane. The effect of the molecular weight of PVAm and feed pressure on the permeance was also investigated. The selectivity increased remarkably with increasing molecular weight and decreased slightly with increased pressure in the range of 1 to 4 bar. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4326–4336, 2004 相似文献
33.
L. A. Utracki 《Journal of Polymer Science.Polymer Physics》2004,42(15):2909-2915
The Simha and Somcynsky (S–S) statistical thermodynamics theory was used to compute the solubility parameters as a function of temperature and pressure [δ = δ(T, P)], for a series of polymer melts. The characteristic scaling parameters required for this task, P*, T*, and V*, were extracted from the pressure–temperature–volume (PVT) data. To determine the potential polymer–polymer miscibility, the dependence of δ versus T (at ambient pressure) was computed for 17 polymers. Close proximity of the δ versus T curves for four miscible polymer pairs: PPE/PS, PS/PVME, and PC/PMMA signaled the usefulness of this approach. It is noteworthy, that the tabulated solubility parameters (derived from the solution data under ambient conditions) propounded the immiscibility of the PVC/PVAc pair. The computed values of δ also suggested miscibility for polymer pairs of unknown miscibility, namely PPE/PVC, PPE/PVAc, and PET/PSF. In recognizing the limitations of the solubility parameter approach (the omission of several thermodynamic contributions), these preliminary results are auspicious because they indicate a new route for estimating the miscibility of any polymeric material at a given temperature and pressure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2909–2915, 2004 相似文献
34.
将爆磁压缩等效为电流源的方法,对爆磁压缩发生器通过脉冲变压器对脉冲形成线充电进行了理论分析,得出爆磁压缩发生器在负载上产生电流波形(简称负载电流)为直线情况和任意电流波形情况下充电电流和充电电压的表达式。分析表明变压器耦合互感与负载电流随时间变化增长率是脉冲形成线充电的两个重要参数,脉冲形成线第一个充电电压峰值与变压器的耦合互感和负载电流波形斜率成正比,负载电流波形斜率的变化可以改变充电电压峰值的时间,斜率不断增加可以延长第一个充电电压峰值时间,从而可能增加充电电压的幅值,提高爆磁压缩发生器能量的利用效率。 相似文献
35.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
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德国夏洛滕堡物理技术研究所(The Physikallisch-Technische Reichanstalt,简称PTR)是世界上第一个国家级的物理技术研究所,它开创了科学研究和技术研究相结合,服务于工业和国家经济之先河。文章从PTR建立的历史背景、早期研究工作和所产生的影响等方面作较为全面的讨论。 相似文献
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本文是[1,12]的继续,研究描述架中概念的结构;本文讨论后半部分,内容涉及概念内涵与外延的转换,清晰关系的内投影与内变换,概念的结构*以及有关问题的注记。 相似文献