999 resultados para G. A. Cohen


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The glass transition behaviour, microphase separation morphology and crystallization of poly(vinyl alcohol)-g-poly(methyl methacrylate) graft copolymers (PVA-g-PMMA) were studied. A lamellar microphase separation morphology was formed, even for a copolyme

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A new graft copolymer (PP-MA)-g-PEO was synthesized by means of the chemical reaction between maleated polypropylene (PP-MA) and mono hydroxyl poly(ethylene oxide) (PEO-OH). The effect of reaction conditions on the degree of grafting of PEO-OH was studied

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最近,关于用接枝或嵌段共聚物作为增容剂来提高不相容聚合物共混体系相容性的研究越来越受到人们的重视因为这是开发新型高性能聚合物材料最简单最有效的方法之一.通常,适当选择接枝或嵌段共聚物,其链段可能同相应相区的链段相同,或者同某一相相容,因而可起到界面剂的作用:减小不相容组分的界

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合成了端丙烯酰胺基聚(β-胺基两酸)大分子单体,用端基滴定法和1H—NMR法测定了大分子单体的分子量,用13C—NMR和氢氧化钠水解法测定了支化度.在水溶液中用硫酸亚铁/异丙苯过氧化氢氧化还原引发体系引发丙烯酸胺、丙烯酸钠与聚(β-胺基丙酸)大分子单体的共聚反应,合成了聚(丙烯酰胺-co-丙烯酸钠)-g-聚(β-胺基丙酸)接枝共聚物.用1H—NMR和滴定法测定了接枝共聚物的组成.溶液性质的数据表明,与部分水解聚丙烯酰胶相比,聚(β-胺基丙酸)含量较高的接枝共聚物具有较好的耐盐性和优异的贮存稳定性.

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本文给出了原子和离子能量表达式中的库仑积分与交换积分系数fk、gk的计算方法,同时给出了计算中所涉及的Racah系数、U(k)、V(lk)和C(k)‘矩阵等光谱参量的计算方法,用FORTRANw语言编写了关于fk和gk的计算机程序,只要输入与光谱项有关的量子数,即可迅速得到相应的kf、gk值,避免了烦琐的人工推算。

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通过粘度的测量,考察了壳聚糖在不同条件下经不同剂量γ射线辐照所引起的分子量的变化,并分别计算了真空和空气中壳聚糖辐射裂解的G(S)值。

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合成了聚乙烯醇-g-聚丙烯酸接枝聚合物(PVA-g-PAA),分别用KOH、NaOH、LiCl的乙醇-水溶液处理PVA-g-PAA膜。发现离子膜用于乙醇-水的渗透气化分离可以大幅度提高分离系数,特别是用KOH处理,分离系数可达400。

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本文给出了原子和离子能量表达式中的库仑积分与交换积分系数f~k与g~k的计算方法,同时给出了计算中所涉及的Racah系数、U~(k)、V~(lk)和C~(k)矩阵等光谱参量的计算方法,我们用FORTRAN语言编写了关于f~k与g~k的计算机程序,只要输入与光谱项有关的量子数,即可迅速得到相应的f~k与g~k值,避免了烦琐的人工推算。

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利用~(60)Co辐照合成了HDPE与丁二烯的接枝共聚物,PE-g-PB。动态力学试验表明,它与PB较PE与PB有更好的相容性。PB含量相同时PB/PE-g-PB共混物比PB/PE共混物有较高的抗张强度和断裂伸长率。前者中两相分布较均匀,相区尺寸较小。

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Financial support from the Ministry of Science and Technology of China (2010CB833802 and 2007AA09Z446) and from the National Science Foundation of China (30910103914) is gratefully acknowledged.

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Sectional velocity distribution of the East China Sea Kuroshio is one of the basic points in the study of the Kuroshio. Hydrographic temperature and salinity data at G-PN section in the East China Sea from June 1955 to November 2001 are collected and properly processed to calculate the geostrophic current using dynamic height method at the transect of the Kuroshio. After analysis of calculation results, the basic current structure of the Kuroshio in its main part is examined together with scalar estimate and characters of multi- core structure, and spacial-temporal variations of current cores' position. Main result shows that (1) single-core structure, double-core structure and multi-core structure are basic forms in axial part of the Kuroshio; (2) abvious temporal variations exist in current structure of the Kuroshio; (3) the current of structure of the Kuroshio has distinctly seasonal association. The number of current cores is on the high side of core numbers in average and multi-core stucture appears in fall mostly.

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扇贝养殖是我国传统的海水养殖产业,但自1997 年以来,养殖扇贝陆续爆发的大规模死亡,不但造成了巨大的经济损失,而且严重影响了该产业的健康发展。扇贝病害的不断爆发以及病因的多样性迫切要求制定新的疾病防治措施和开发新型的抗菌物质。 从扇贝自身的免疫防御因子入手,筛选和克隆参与免疫防御的功能基因,一方面可以研究抗病功能基因在病原感染或环境胁迫条件下的表达规律,深入探讨扇贝的免疫防御机制,并可作为抗病良种选育的分子标记,指导扇贝的遗传改良和抗病品系的培育;另一方面,可对抗菌效应物实现重组表达,开发新型的病害预防治疗制剂,取代目前普遍使用的抗生素和化学药物。抗菌效应物是机体在免疫应答过程中产生的多肽类物质,对侵入生物体内的细菌、病毒具有很强的免疫杀灭作用,对抗菌效应物的研究有助于深入了解机体先天性免疫防御的机制。 本研究采用大规模EST测序方法,结合cDNA端快速扩增(RACE)技术,从海湾扇贝血淋巴中克隆到了大防御素基因(big defensin, AiBD)的全长cDNA列,该cDNA长为531 bp,其中5' 非编码区(UTR)为24 bp,开放阅读框(Open Reading Frame, ORF)含有369 bp,编码122 个氨基酸残基;随后为138-bp 的3' UTR,包括一个多聚腺苷酸信号序列(AATAAA和ploy A巴。分析表明,海湾扇贝大防御素是以前体的形式合成,前体分子包括信号肽、前域和成熟肽三部分。采用Northern blot方法,以DIG记的DNA针检测了 AiBD mRNA不同组织中的表达。结果发现,AiBD 基因的转录本主要在血淋巴中表达,在鳃中也有微量的表达,而在外套膜、闭壳肌、性腺及肝胰腺中检测不到杂交信号。采用QRT-PCR(quantitative real time PCR)对鳗弧菌感染后海湾扇贝血淋巴中AiBD mRNA 的表达量进行了检测,结果发现在感染后8 h 内, AiBD mRNA 的相对表达量平缓升高;随着刺激时间的增长,AiBD基因的mRNA达量急剧增加,在刺激后16 h 和32 h 分别达到了空白组的72.3 倍和131.1 倍。为了研究海湾扇贝大防御素的抗菌活性,将其成熟肽编码区克隆到毕赤酵母表达载体pPIC9K并实现了重组表达。抑菌实验表明,重组AiBD具有广谱的抗菌活性,其对供试的三株革兰氏阳性菌(藤黄微球菌、溶壁微球菌、金黄色葡萄球菌)都表现出显著的抗菌活性,而对革兰氏阴性菌(鳗弧菌、亮弧菌)的抑菌活性则相对较弱;此外,重组AiBD对表达宿主也表现出杀菌活性,证明其具有抗真菌活性。 根据栉孔扇贝G 型溶菌酶基因的cDNA列,利用构建的Genome Walking 文库获得了栉孔扇贝G 型溶菌酶基因的全长序列,该基因序列全长为8131 bp,由六个外显子和五个内含子组成。六个外显子长度分别为55 bp,60 bp,90 bp,113 bp,145 bp 和140 bp;五个内含子的长度分别为1126 bp,2161 bp,2744 bp,750 bp和592 bp;内含子的两侧都具有RNA确剪接所必需的识别位点(GT/AG)。利用TRANSFAC 软件对栉孔扇贝G 型溶菌酶基因的5' 侧翼序列分析发现,该基因的5' 侧翼具有 TATA box 和 CAAT box 的共有序列;此外,在该基因的5' 侧翼发现了C/EBP、NF-κB、OCT-1 和 NF-IL6 等参与免疫基因激活的转录因子潜在结合位点。采用Northern blot方法,以生物素标记的RNA 探针检测了栉孔扇贝G 型溶菌酶基因在不同组织中的表达。结果发现,该基因的转录本主要在鳃、性腺及肝胰腺中表达,在血细胞和外套膜中也有微量的的表达,而在闭壳肌中检测不到杂交信号,这表明栉孔扇贝G 型溶菌酶可能兼备参与机体免疫防御和消化的功能。为了研究栉孔扇贝G 型溶菌酶的抗菌活性,将其成熟肽编码区克隆到毕赤酵母表达载体pPIC9K并实现了重组表达。抑菌实验表明,重组产物具有显著的抗阳性菌活性,其对供试的藤黄微球菌、溶壁微球菌表现出明显的抑制作用,对金黄色葡萄球菌未检测到抑制活性;而对革兰氏阴性菌仅表现出微弱的抑菌活性(亮弧菌和鳗弧菌),对大肠杆菌则基本无抑制活性。

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Azadirachtin (Az), as a botanical insecticide, is relatively safe and biodegradable. It affects a wide vaariety of biological processes, including the reduction of feeding, suspension of molting, death of larvae and pupae, and sterility of emerged adults in a dose-dependent manner. However, the mode of action of this toxin remains obscure. By using ion chromatography, we analyzed changes in six inorganic cation (Li+, Na+, NH4+, K+, Mg2+, and Ca2+) distributions of the whole body and hemolymph in Ostrinia furnacalis (G.) after exposure to sublethal doses of Az. The results showed that Az dramatically interfered with Na+, NH4+, K+, Mg2+, and Ca2+ distributions in hemolymph of O. furnacalis (G.) and concentrations of these five cations dramatically increased. However, in the whole body, the levels of K+, Mg2+, and Ca2+ significantly, decreased after exposure to Az, except that Na+ and NH4+ remained constant. Li+ was undetected in both the control and treated groups in the whole body and hemolymph. It is suggested that Az exerts its insecticidal effects on O. furnacalis (G.) by interfering with the inorganic cation distributions related to ion channels.