论如何提高学校的市场竞争力

论述了中国加入WTO后,教育系统应完善制度,建立相应激励机制,提高学校的市场竞争力-校长要有市场竞争意识,教师队伍应有竞争实力,学校以质量求生存,求发展,走教研兴校,特色兴校之路.     

A New Ferroelectric Phase of YMnO3 Induced by Oxygen‐Vacancy Ordering

Manganese oxides are good candidates of strongly correlated electron materials due to the uniqueness of electronic structure of manganese and the mobility of oxygen among lattice sites under external impacts. Here, we used electron beam as the excitation source to explore the structural evolution of YMnO₃ and identified a new phase under the radiation of electron beam in the transmission electron microscope. Analyses of the electron energy‐loss spectra reveal that this phase originates from ordered oxygen vacancy. We applied the first principles calculation to pick out the optimized stable structure with a lower polarization, and verified its correctness by electron diffraction and image simulations. Analyses of density of states indicate that weak Y–O covalence is favorable for the existence of ferroelectricity, supporting the electrostatic nature of ferroelectricity in the YMnO₃.     

Sintering Behavior and Dielectric Properties of Ultra‐Low Temperature Fired Silver Molybdate Ceramics

Ag₂MoO₄ ceramic was prepared by using the solid‐state reaction method, which could be sintered at 450°C for 2 h, having a relative permittivity of 8.08, a Qf value of 17 000 GHz, and a temperature coefficient of resonance frequency about ?133 ppm/°C. Ag₂MoO₄ ceramic was chemically compatible with silver but reacted seriously with aluminum to form (Ag_0.5Al_0.5)MoO₄ during the sintering. The fitting of infrared spectra and the Shannon's additive rule were employed to study intrinsic dielectric behaviors of the ceramics at microwave region. Ionic displacive polarization and the electronic polarization contributed almost equally to the dielectric permittivity of the ceramic at microwave region. The Ag₂MoO₄ ceramics could be a good candidate for ultra‐low temperature co‐fired microwave devices.     

Synthesis of Heterocycle‐fused Pyridine N‐Oxides from Oximes and Diazo Compounds via RhIII‐Catalyzed C?H Activation and Annulation

A Rh^III‐catalyzed tandem C H activation and C N bond formation reaction between oximes and diazo compounds for the synthesis of heterocycle‐fused pyridine N‐oxides has been developed. The reaction exhibits good functional group tolerance and regioselectivity. After simple transformation, the 1‐substituted, 1,3‐disubstituted, 1,4‐disubstituted and 1,3,4‐trisubstituted heterocycle‐fused pyridines were all obtained in high efficiency. Moreover, this strategy has also been expanded to the synthesis of a key intermediate for the construction of one potential anti‐HIV agent.

     

Surface crystalline characteristics of polyurethane investigated by atomic force microscopy

A polyester—urethane was synthesized by the reaction of 2,4-toluylene diisocyanate (TDI) with poly(butylene glycol adipate) (PBGAD) using 1,4-butanediol (BDO) as a chain extender. Atomic force microscopy was employed to examine the surface morphologies of polyurethane (PU) films formed by heat treatment as well as at room temperature. At both conditions the surface of the PU film appeared as a spherulitic structure with a varied diameter and vertical height. Furthermore, the crystalline structure of heat-treated film was denser than that of the film formed at ambient. © 1996 John Wiley & Sons, Inc.     

相电压时钟法在晶闸管整流装置定相中的应用

介绍晶闸管装置定相的问题及同步变压器的正确连接方式,重点介绍了一种行之有效的相电压时钟法.     

应用"模糊概率加权移动预测"研究电接触性能

以模糊理论和时间序列分析理论为基础,建立了参数的模糊概率加权移动预测模型.用该模型预测得到的预测值时间序列中的每个数据都能从一定程度上反映一段时间内参数的平均水平,而且消除了奇点对预测值的影响,部分消除了样本数据中不确定成分对预测值的影响.对继电器触点闭合过程的静态接触电阻和弹跳时间进行了统计分析,结果表明继电器的接触失效与触点闭合过程的静态接触电阻和弹跳时间的模糊概率分布密切相关.静态接触电阻和弹跳时间的模糊概率加权移动预测值时间序列能够明显反映触点的静态和动态接触性能的变化.     

The visualization of knots and braids

We describe a new method for modelling braids and certain classes of knots and links, and how they may be visualized. The method uses generalized cylinders built around a bicubic spline centre line. We also show how multi-stranded, recursive, hawser laid ropes can be modelled using related techniques.