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71.
A novel phenylacetylene derivative containing urea groups was synthesized and polymerized with a Rh catalyst to give the corresponding polymer, poly(1) with moderate number-average molecular weights. The poly(1) was soluble in toluene, CHCI3, CH2C12, THF, DMF, and DMSO, but insoluble in hexane, diethyl ether and MeOH. The specific rotation and circular dichroism (CD) spectroscopic studies revealed that poly(1) took predominantly one-handed helical structures. The presence of intramolecular hydrogen bonding was confirmed by liquid-state IR spectroscopy. The helicity of poly(1) could be tuned by temperature and anion. The helical conformation of the polymer was stable against Br but susceptible to F. 相似文献
72.
In a recent XUV photoabsorption spectrum of Cs Ⅲ ions by Cummings and O'Sullivan [2001 J. Phys. B 34 199], rather large linewidths were found for the 4d^95s^25p^6 - 4d^105s^25p^5 transition which are quite in disagreement with corresponding quasi-relativistic multiconfiguration Hartree Fock (MCHF) calculation. In the present work, a detailed multiconfiguration Dirac-Fock study has been carried out to explore this discrepancy. Owing to the detailed consideration of electron correlation effects, some ‘forbidden' Auger decay channels, such as 4d^105s^25p^35d and 4d^105s^05p^6, would become ‘open'. As a result, remarkable improvement of the linewidths has been obtained in our calculation. Furthermore, the theoretical Auger spectrum of the 4d^ 95s^25p^6 core-excited states of Cs Ⅲ ions is Riven in the present work. 相似文献
73.
Stabilization of spiral wave and turbulence in the excitable media using parameter perturbation scheme 下载免费PDF全文
This paper proposes a scheme of parameter perturbation to suppress the stable rotating spiral wave, meandering spiral wave and turbulence in the excitable media, which is described by the modified Fitzhug-Nagumo (MFHN) model. The controllable parameter in the MFHN model is perturbed with a weak pulse and the pulse period is decided by the rotating period of the spiral wave approximatively. It is confirmed that the spiral wave and spiral turbulence can be suppressed greatly. Drift and instability of spiral wave can be observed in the numerical simulation tests before the whole media become homogeneous finally. 相似文献
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76.
基于Kirchhoff理论讨论圆截面弹性螺旋杆的动力学问题.以杆中心线的Frenet坐标系为参考系,建立用欧拉角描述的弹性杆动力学方程.讨论其在端部轴向力和扭矩作用下保持的无扭转螺旋线平衡状态.在静力学和动力学领域内讨论其平衡稳定性问题.还讨论了弹性杆平衡的Lyapunov稳定性和欧拉稳定性两种不同稳定性概念之间的区别和联系.在一次近似意义下证明了螺旋杆在空间域内的欧拉稳定性条件是时域内Lyapunov稳定性的必要条件.导出了解析形式螺旋杆三维弯曲振动的固有频率,为螺旋线倾角和受扰挠性线波数的函数.
关键词:
弹性螺旋杆
Kirchhoff动力学比拟
Lyapunov稳定性
欧拉稳定性 相似文献
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78.
作为数字信号处理的一种算法,线性调频Z变换(Chirp-Z)是适用于更为一般情况下沿螺旋曲线计算有限时宽Z变换的快速变换算法,它使得DFT的运算变得相当灵活,为数字信号处理技术应用于各种高速信号的快速处理创造了良好的条件,从而大大推动了数字信号处理技术的发展. 相似文献
79.
Helical Shell Structures of Ni-A1 Alloy Nanowires and Their Electronic Transport Properties 下载免费PDF全文
Six kinds of Ni-A1 alloy nanowires are optimized by means of simulated annealing. The optimized structures show that the Ni-A1 alloy nanowires are helical shell structures that are wound by three atomic strands, which is very similar to the case with pure metallic nanowires. The densities of states (DOS), transmission function T( E), current-voltage (I - V) curves, and the conductance spectra of these alloy nanowires are also investigated. Our results indicate that the conductance spectra depend on the geometric structure properties and the ingredients of the alloy nanowires. We observe and study the nonlinear contribution to the I-V characteristics that are due to the quantum size effect and the impurity effect. The addition of Ni atoms decreases the conductance of the Ni-A1 alloy nanowire because the doping atom Ni change the electronic band structures and the charge density distribution. The interesting statistical results shed light on the physics of quantum transport at the nano-scale. 相似文献
80.
邻苯二甲酸L—(+)—2,3—O—亚异丙基苏力糖酯的两种构象式的 … 总被引:3,自引:0,他引:3
在晶(固)态下,化合物邻苯二甲酸L-(+)-2,3-O-亚异丙苏力糖酯存在两种不同的构象形式,利用螺旋片段判定规则及ω^-值,结合X射线衍线数据及扭转角数据,对这两种构象形式的所有螺旋片段进行了分析,尽管两种构象形式的净值螺旋性相反,但仍然得出总净值螺旋性与旋光方向一致的总论。 相似文献