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101.
1 IntroductionSince a quadratic system has no limit cycle around a 3rd-order weak focu,[1]and has at most one limit cycle surrounding a 2nd-order weak fOcus['], study-ing the number of limit cycles of a p1anar quadratic system with a 3rd-order(or 2nd-order) weak focus we only need to study the number of limit cyclessurrounding the strong focus for the system. Without loss of generality thequadratic system with a 3rd--order (or 2nd--order) weak foclls and a strong focuscan be written in the fo.… 相似文献
102.
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104.
采用紫外-可见吸收光谱法现场监测了苯胺电化学聚合时的动力学降解过程,简单、直观地显示了阳极电位、酸度和苯胺浓度对降解过程的影响,结果表明,阳极电位越正、酸度越强、苯胺浓度越大,聚苯胺的降解速度越快。该方法得到的结果与聚苯胺膜在空白溶液中采用循环伏安法研究其降解动力学时得到的结果类似。 相似文献
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106.
用落体法测重力加速度的实验方案选择 总被引:1,自引:0,他引:1
重力加速度是物理学中一个重要的参量.地球上各地区的重力加速度的数值随地理纬度、海拔高度和地质结构的不同而不同.重力加速度的测量不仅在物理中具有重要意义,而且对于研究地层结构和探查地下资源都有实用价值,因此,细致地测量和准确地计算重力加速度是十分必要的.测量重力加速度的方法多种多样,本文利用自由落体原理,借助光电门测重力加速度.为减小误差对具体实验操作及数据处理方法的选择进行深入探讨. 相似文献
107.
本文揭示了单洞 Cata 型六角系统的共振多项式与广义冠的匹配多项式的关系、将1977年 Gutman 提出的方法推广应用到有洞的六角系统,并得到一些共振多项式的比较定理. 相似文献
108.
针对智能电网中存在的缺乏对硬件设备的认证、无法验证初始双方的计算环境安全的问题,提出了一种基于国密算法的、面向智能电网场景的移动终端可信网络通信方案。该方案基于FPGA(field programmable gate array)实现了国密算法以满足智能电网防护自主可控的安全需求,从物理层面增强了智能电网下移动终端的安全性;将可信网络连接技术应用到智能电网移动终端中,设计出适用于智能电网系统中终端的数据安全传输方案,在保证通信链路安全的同时,保证接入智能电网系统中终端的合法性。本文设计并实现了所提方案的原型系统,并基于原型系统完成了仿真实验。实验结果表明,本文提出的可信通信方案可有效提升移动设备网络接入安全性,在智能电网中具有良好的应用前景。 相似文献
109.
Nine aminoglycoside antibiotics were analyzed in two quadrupole ion trap mass spectrometers using electrospray ionization. Structural information was obtained via collision-activated dissociation (CAD) and infrared multi-photon dissociation (IRMPD) of the protonated species. Several of the compounds, having multiple basic sites, preferred the doubly protonated form while some existed in the singly charged state or were distributed between single and doubly protonated species, allowing comparison of the fragmentation patterns of the two charge states. In general, IRMPD is as efficient as CAD, produces more low-mass fragment ions, and is more universally applied owing to its low dependence on trapping, pressure and tuning conditions. Alkali metal complexation using Li(+) and Na(+) was probed as a means of producing different fragmentation patterns, but in most cases the resulting fragmentation patterns were simplified versions of those obtained for the protonated analogs. 相似文献
110.
Porphyrins bearing specific patterns of substituents are crucial building blocks in biomimetic and materials chemistry. We have developed methodology that avoids statistical reactions, employs minimal chromatography, and affords up to gram quantities of regioisomerically pure porphyrins bearing predesignated patterns of up to four different meso substituents. The methodology is based upon the availability of multigram quantities of dipyrromethanes. A procedure for the diacylation of dipyrromethanes using EtMgBr and an acid chloride has been refined. A new procedure for the preparation of unsymmetrical diacyl dipyrromethanes has been developed that involves (1) monoacylation with EtMgBr and a pyridyl benzothioate followed by (2) introduction of the second acyl unit upon reaction with EtMgBr and an acid chloride. The scope of these acylation methods has been examined by preparing multigram quantities of diacyl dipyrromethanes bearing a variety of substituents. Reduction of the diacyl dipyrromethane to the corresponding dipyrromethane-dicarbinol is achieved with NaBH(4) in methanolic THF. Porphyrin formation involves the acid-catalyzed condensation of a dipyrromethane-dicarbinol and a dipyrromethane followed by oxidation with DDQ. Optimal conditions for the condensation were identified after examining various reaction parameters (solvent, temperature, acid, concentration, time). The conditions identified (2.5 mM reactants in acetonitrile containing 30 mM TFA at room temperature for <7 min) provided reaction without detectable scrambling (LD-MS) for aryl-substituted dipyrromethanes, and trace scrambling for alkyl-substituted dipyrromethanes. The desired porphyrins were obtained in 14-40% yield. The synthesis is compatible with diverse functionalities: amide, aldehyde, carboxylic acid, ester, nitrile, ether, bromo, iodo, ethyne, TMS-ethyne, TIPS-ethyne, perfluoroarene. In total 30 porphyrins of the types A(3)B, trans-A(2)B(2), trans-AB(2)C, cis-A(2)B(2), cis-A(2)BC, and ABCD were prepared, including >1-g quantities of three porphyrins. 相似文献