多自由度参激系统稳定性的数值分析

提出多自由度周期参激系统稳定性的数值直接法。通过将扰动方程表示成状态方程形式,再根据Flo-quet理论将扰动解表示成指数特征分量与周期分量之积,并将其周期分量与系统周期系数展成Fourier级数,导出一系列代数方程,建立矩阵特征值问题,从而由数值求解特征值可直接确定参激系统的稳定性。该方法可用于一般周期参激阻尼系统,特征值矩阵不含逆子阵。应用于斜拉索在支座周期运动激励下的参激振动不稳定性分析,数值结果表明该方法的有效性。     

Introduction of functional groups into some chlorofluorocarbon ethers.

The electrochemical fluorination of 2-methyloxane, oxepane, 2-chloromethyloxane and 2-chloromethyloxolane has been carried out. The corresponding perfluoro(2-methyloxane) and perrfluorooxepane were obtained in fair yields from the first two compounds, but from the later two, the corresponding chlorine-containing perfluorocyclic ethers, i.e. perfluoro(2-chloromethyloxane) and perfluoro(2-chloromethyloxolane), were obtained only in small yields, respectively. These new compounds have been characterized by elemental analysis, and infrared, mass and ¹⁹F nmr spectra.     

Synthesis and characterization of the first examples of perfluoroalkyl-substituted trialkyloxonium salts, [(CH3)2OCF3]+[Sb2F11]- and [(CH3)2OCF(CF3)2]+[Sb2F11]-

In the superacidic HF/SbF(5) system, methyl trifluoromethyl ether forms at -78 degrees C the new tertiary oxonium salt [(CH(3))(2)OCF(3)](+)[Sb(2)F(11)](-), which was characterized by Raman and multinuclear NMR spectroscopy and its crystal structure. The same oxonium salt was also obtained by methylation of CH(3)OCF(3) with CH(3)F and SbF(5) in HF solution at -30 to -10 degrees C. Replacement of one methyl group in the trimethyloxonium cation by the bulkier and more electronegative trifluoromethyl group increases the remaining O-CH(3) bond lengths by 0.037(1) A and the sum of the C-O-C bond angles by about 4.5 degrees. Methylation of CH(3)OCF(CF(3))(2) with CH(3)F in HF/SbF(5) solution at -30 degrees C produces [(CH(3))(2)OCF(CF(3))(2)](+)[Sb(2)F(11)](-). The observed structure and vibrational and NMR spectra were confirmed by theoretical studies at the B3LYP/6-311++G(2d,2p) and the MP2/6-311++G(2d,p) levels.     

Syntheses of NF4 salts derived from the lewis acids AlF3 and BeF2

The new salts NF₄Be₂F₅ and NF₄AlF₄ were prepared from concentrated NF₄HF₂ solutions and BeF₂ and AlF₃ respectively.     

The race for the first generation of the pentazolate anion in solution is far from over

The previous claim for the first generation of the pentazolate anion in solution was carefully reexamined; no evidence for the formation of cyclo-(N5-) was found under the reported conditions.