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排序方式: 共有73条查询结果,搜索用时 15 毫秒
41.
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将存在亏格为1的Heegaard分解T’1∪F T’2的三维流形记为M=L(p,q),其中p和q是互素整数,q/p为T’2的纬线在T’1上的斜率.若环面F上的简单闭曲线γ在M中非平凡,则称γ是M中的环面纽结.本文对在M中沿环面纽结作m/n-Dehn手术所得流形进行了分类,并给出了两个实心环体沿边界上平环作融合所得流形是L(p,q)中环面纽结补的特征描述. 相似文献
43.
动态弹塑性断裂韧性测试方法的比较研究 总被引:7,自引:0,他引:7
利用示波冲击试验,对动态弹塑性断裂韧性测试的不同方法(单试样法和多试样法)进行了研究.结果表明,单试样法(柔度变化率)测定材料的动态断裂韧性是一种简单、准确、适合于工程应用的好方法 相似文献
44.
Characterizations and thermal stability of soluble polyimide derived from novel unsymmetrical diamine monomers 总被引:1,自引:0,他引:1
Fengchun Yang Qianqian Bu Shujiang Zhang Tao Ma Jiujiang Zhao 《Polymer Degradation and Stability》2010,95(9):1950-1958
Two kinds of novel aromatic, unsymmetrical diamines with ether-ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 3-amino-4′-(4-aminophenoxy)-benzophenone, was successfully synthesized by two different synthetical routes and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride, via a conventional two-step thermal or chemical imidization method to produce a series of fluorinated polyimides. The polyimides were characterized with solubility tests, viscosity measurements, mechanical properties tests, IR-FT, and thermogravimetric analysis. The polyimides had inherent viscosities of 0.54-0.77 dL/g and were easily dissolved in both polar, aprotic solvents and common, low-boiling-point solvents. The resulting strong and flexible polyimide films exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 573 °C and glass-transition temperatures in the range of 222-251 °C. Moreover, the polymer films showed outstanding mechanical properties, with tensile strengths of 86.5-121.6 MPa, elongations at break of 9-16%, and initial moduli of 1.26-1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications. 相似文献
45.
Two kinds of aromatic, unsymmetrical diamines with ether-ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 4-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone, were successfully synthesized with two different synthetic routes. Then, they were polymerized with 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride to form a series of fluorinated polyimides via a conventional two-step thermal or chemical imidization method. The resulting polyimides were characterized by measuring their solubility, viscosity, mechanical properties, IR-FT, and thermal analysis. The results showed that the polyimides had inherent viscosities of 0.48-0.68 dl/g and were easily dissolved in bipolarity solvents and common, low-boiling point solvents. Meanwhile, the resulting strong and flexible polyimide films exhibited excellent thermal stability, e.g., decomposition temperatures (at 10% weight loss) are above 575 °C and glass-transition temperatures in the range of 218-242 °C. The polymer films also showed outstanding mechanical properties, such as tensile strengths of 86.5-132.8 MPa, elongations at break of 8-14%, and initial moduli of 1.32-1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications. 相似文献
46.
Lei Fengchun Zhang Ying 《东北数学》1998,(4)
§1.BackgroundandMainResultsSincetheconceptofthinpositionforknotsinthe3-spherewasdevelopedbyGabai[1],manyitsapplicationstodeal... 相似文献
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48.
Lei Fengchun 《东北数学》1995,(2)
An Extension of The Handle Addition TheoremLeiFengchun(雷逢春)(DepartmentofMathematics,JilinUniversity,Changchun130023)Abstract:... 相似文献
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Lei Fengchun 《东北数学》1994,(3)
SomePropertiesofanAnnulusSumof3-manifoldsLeiFengchun(雷逢春)(DepartmentofMathematicsJilinUniversity,Changchun130023)Abstract:Let... 相似文献