Properties of copolyimides prepared from different tetracarboxylic dianhydrides and diamines

Various copolymides were prepared from two acid dianhydrides (BPDA, 3,3′,4,4′-biphenyl tetracarboxylic dianhydride; PMDA, pyromelitic dianhydride) and two diamines (PPD, p-phenylene diamine; ODA, 4,4′-oxydianiline). The thermal and mechanical properties of these polyimides were examined in detail. By appropriately selecting the ratios of the acid dianhydride component and the diamine component, polyimide films having desirable mechanical and thermal characteristics can be obtained. Further, it was proved that there is a correlation between the properties and the compositions of the copolyimides and that the properties could be estimated from the compositions by the use of multiple regression analysis. © 1996 John Wiley & Sons, Inc.     

Preparation of high-modulus poly(ethylene terephthalate) fibers by vibrating hot drawing

A novel drawing method, vibrating hot drawing, was successfully applied to poly(ethylene terephthalate) fiber, which has a normal molecular weight (IV = 0.7 dL/g) and was prepared by melt spinning. The process was divided into three steps, with differing conditions in drawing temperature, applied tension, vibrating frequency, and amplitude. The drawing temperature and vibration frequency were decided by considering the α_a dispersion of the polymer. In spite of a low draw ratio (7.7) and a low crystallinity (0.55), the birefringence and dynamic storage modulus at room temperature of the 3rd-step fiber reached 0.260 and 36 GPa, respectively. The modulus remains at a high level at elevated temperatures, for example, 29 GPa at 100°C and 17 GPa at 200°C. Further, it was found from temperature and intensity of the α_a dispersion peak that the movements of amorphous chains are strongly inhibited. © 1996 John Wiley & Sons, Inc.     

Size- and shape-controlled synthesis of colloidal gold through autoreduction of the auric cation by poly(ethylene oxide)-poly(propylene oxide) block copolymers in aqueous solutions at ambient conditions

Gold nanoparticles with an average diameter in the range 5-20?nm have been synthesized from hydrogen tetrachloroaureate (III) hydrate (HAuCl(4)·3H(2)O) in air-saturated aqueous PEO-PPO-PEO block copolymer solutions at ambient temperature in the absence of any other reducing agent (PEO: poly(ethylene oxide), PPO: poly(propylene oxide)). The particle size was controlled by the block copolymer concentration and PEO and PPO block lengths. Our findings indicate that longer PEO blocks lead to an increase in particle size because of an increase in reaction activity. Adsorption of PO segments on gold nanoparticles seems to prevent particle growth from aggregation, and results in small particle size and high colloidal stability. An increase of the HAuCl(4) concentration causes a change in the particle shape from spherical to triangular or hexagonal nanoplates.     

SiC－TiC陶瓷韧化机制探讨

采用ＣＶＤ法合成ＳｉＣ－ＴｉＣ陶资,探讨了ＴｉＣ含量与断裂韧性之间的关系。结果表明,当ＴｉＣ体积含量为４０％时,断裂韧性高达７．０ＭＰａ·ｍ１／２韧化效应归功于闭合效应以及弯曲效应。断裂韧性与体积含量之间存在ＫＩＣ＝［（ＫＩＣ０）＋Ｂｖｉ］　ＫＩＣ０＝（１＋Ａ）ＫＩＣｍ关系。建立的韧化模型与实验结果相一致。     

一种新的使用两种比特分辨率图象的块匹配运动估计算法及其低功耗VLSI结构

本文给出了一种新的块匹配运动估计算法,它根据视频图像内容的复杂程度自适应地选择常规的或者低比特分辨率的图像来进行块匹配,并且采用了一种混合使用两种比特分辨率图像的新望远镜搜索算法.模拟结果表明,新算法具有较低的计算复杂性,并且能够保证较好的视频质量.基于该算法,我们设计了一种新的脉动阵列结构的搜索引擎.该引擎具有可分割的数据通道,从而在使用低比特分辨率图像进行块匹配时能够通过加强处理的并行性来提高吞吐率.新的运动估计器可工作在较低的时钟频率和电源电压之下,具有低的功耗消耗.     

Nucleotide sequences of alcohol acetyltransferase genes from lager brewing yeast,Saccharomyces carlsbergensis

The nucleotide sequences of alcohol acetyltransferase genes isolated from lager brewing yeast, Saccharomyces carlsbergensis have been determined. S. carlsbergensis has one ATF1 gene and another homologous gene, the Lg-ATF1 gene. There was a high degree of homology between the amino acid sequences deduced for the ATF1 protein and the Lg-ATF1 protein (75·7%), but the N-terminal region has a relatively low degree of homology. Southern analysis and contour-clamped homogeneous electric field analysis of Saccharomyces strains suggest that the ATF1 gene is located on chromosome XV in S. cerevisiae and that the Lg-ATF1 gene might originate from the ‘non-S. cerevisiae’ genome of S. carlsbergensis, which is similar to that of S. bayanus and S. pastorianus. The nucleotide sequence data reported in this paper will appear in the DDBJ, EMBL and GenBank data banks with the Accession Numbers D63449 (ATF1) and D63450 (Lg-ATF1).