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正交各向异性层合板弯曲问题的X样条有限条方法
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作者 汪伟 《河北水利专科学校学报》 1991年第2期1-12,共12页
本文以Whitney不均匀层合板理论为基础,运用X样条有限条方法,研究了正交对称铺设纤维加强层合板弯曲问题。适用于规则形状板、不规则形状板、各种边界条件下弯曲问题的计算。具有比现有有限元方法明显为高的计算效率。
关键词 复合材料 层合板 正交异性 x样条
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Effect of Crystallization Conditions on Polymorphic Diversity of Malic Acid RS-Racemate
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作者 Isakov A I Kotelnikova E N +1 位作者 Kryuchkova L Yu Lorenz H 《Transactions of Tianjin University》 EI CAS 2013年第2期86-91,共6页
Enantiomers (R (+) and S(-)), RS-racemate mixture of enantiomers) of malic acid C4H605 have been (double compound) and (R + S) -conglomerate (mechanical investigated by means of X-ray diffractometry and ... Enantiomers (R (+) and S(-)), RS-racemate mixture of enantiomers) of malic acid C4H605 have been (double compound) and (R + S) -conglomerate (mechanical investigated by means of X-ray diffractometry and high tern- perature X-ray diffraction method. The RS-racemate was found to be able to form three polymorphic modifications, which we denominated as M1 (monoclinic, space group P21/c), M2 (monoclinic, space group Cc), and Tc (triclinic, space group P-l ), the latter modification having been unknown before. Modification Tc was also described, and its X- ray diffraction characteristics, including interplanar spacings d, hkl indices, unit cell parameters, were defined. In addi- tion, X-ray diffraction characteristics for both reported earlier M1 and M2 monoclinic polymorphic modifications were measured with higher accuracy. The ability of RS-racemate to form one of the above three modifications (MI, M2, and Tc) or their mixtures containing various proportions and combinations of the components (M1 + M2, M1 + Tc, or M2 + Tc) was found to depend on the type of crystallization medium (a melt, aqueous medium, ethanol or acetone solu- tion), crystallization rate (from 2--3 minutes to 4 months), and crystallization temperature. Heating S-enantiomer and M1 RS-racemate up to their respective melting points (100 ℃ and 124 ℃, correspondingly) only made them undergo thermal deformations, while heating (R + S) -conglomerate in the temperature range of 96--110 ℃ resulted in its homogenization to form M2 RS-racemate, which, near the melting point (118 ℃), namely, in the range of 112-116 ℃, was transformed into MI RS-racemate. Keywords: polvmorDhism; racemic, chiral 展开更多
关键词 POLYMORPHISM RACEMIC CHIRAL
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