Modal interactions in an autoparametric vibration absorber to narrow band random excitation

The main objectives of this study are to examine the random responses of a vibration absorber system with autoparametric coupling in the neighborhood of internal resonance subjected to narrow band random excitation by Gaussian closure scheme and to compare the results with those obtained by Monte Carlo simulation. The Monte Carlo simulation is found to support the main features of the nonlinear modal interaction in the neighborhood of internal resonance conditions. The jump phenomenon of the cantilever mode and saturation phenomenon of the main system are shown to occur if the excitation bandwidth is sufficiently small.     

基于AT89C52的励磁调节器的设计与实现

介绍了一种基于单片机AT89C52的同步发电机微机励磁调节器的设计与研究。在描述自并励励磁系统的接线方式及其系统控制模型和调节器原理的基础上,详细分析了微机励磁调节器的硬件组成和软件构成,它具有硬件电路简单、可靠、配置灵活等优点。     

网络安全性分析

本文针对企业网络系统存在的潜在威胁,分析其网络安全脆弱性的主要原因,结合实际讲述了目前常见的安全性威胁类型以及防范威胁安全机制。     

Stability analysis of the simplest Takagi-Sugeno fuzzy control system using circle criterion

In this paper, we present two sufficient conditions in the frequency domain for the global stability analysis of the simplest Takagi-Sugeno (T-S) fuzzy control system, based on the circle criterion and its graphical interpretation. These conditions are significant in graphically designing the simplest T-S fuzzy controller in the frequency domain. Four numerical examples are provided to demonstrate the efficiency of our two frequency domain-based conditions. Furthermore, this T-S fuzzy controller and the linear proportional controllers are also compared. It is concluded that the simplest T-S fuzzy controller can outperform the linear proportional controllers in a noisy environment with external disturbances.     

Electron microscopy of satellite tobacco mosaic virus crystals: metal-coated, negatively stained and stereo pairs

Highly purified virions of satellite tobacco mosaic virus (STMV) were found to crystallize at relatively low concentrations (300-500 microg ml(-1)) in pure water. Small crystals of these preparations were examined in the transmission electron microscope after either being rotary shadowcast with metal or negatively stained with 4% uranyl acetate. Stereo views were also obtained of both types of preparations. Stereo pairs of metal-coated crystals provided good three-dimensional images. When stereo pairs of negatively stained crystals were printed from second negatives, they provided striking images although the three-dimensional aspect was not so pronounced. Images of both types of preparations were compared with a computer-generated model of the virus. This model was based on data obtained in earlier X-ray diffraction crystallographic studies. Measurements of crystal axes on the EM images were somewhat lower than those of the computer model. It is assumed the reason for this is the dehydration of crystals during preparation for electron microscopy. The EM images did verify the type of crystal lattice determined in the X-ray diffraction studies. Conversely, knowing the exact unit cell parameters and the distribution of virions in the crystal from X-ray diffraction data aids in the further interpretation of electron micrographs of virus crystals.     

压力下极化子效应对有限深量子阱中施主结合能的影响

考虑压力及屏蔽效应,同时计入量子阱结构中三类光学声子模(局域类体光学声子、半空间类体光学声子和界面光学声子)的作用,利用改进的LLP中间耦合方法处理电子-声子相互作用,讨论有限深量子阱中极化子效应对杂质态结合能的影响.结果表明,极化子效应使杂质态结合能明显降低,但压力使极化子效应减弱,屏蔽对极化子效应的影响不明显.     

川西北地区小城镇空间演变特征分析 ——以道孚鲜水镇为例

西部大开发及新型城镇化政策为 川西北少数民族小城镇带来发展机遇,同时 城镇空间的地域特色面临现代化冲击,研究 小城镇的空间演变规律,对城镇空间的文脉 传承有重要意义。以川西北少数民族地区典 型的小城镇鲜水镇为研究对象,综合利用田 野调查、定量分析、空间分析等方法,重建 了城镇10 0年的演变进程。研究表明：鲜水 镇在时间上可分为茶马互市（1662年之前）、 宗教带动（1662—1910年）、立县更名时期 （1911—1949年）、和平解放（1950—1980 年）、震后重建（1981至今）五个时期;空间 上,呈现出城镇功能结构沿过境公路扩展、 街巷自然生长、城镇风貌汉藏融合的特征。 影响鲜水镇城镇聚落演变的主要因素中,“茶 马互市”和宗教传播、过境交通、地震、多民 族融合是城镇空间特征形成的内在机制。     

Analysis of inclusions and precipitates in tough weld metal of X80 steel

Submerged arc welding(SAW)and gas metal arc welding(GMAW)experiments of Nb-bearing X80 steel were conducted with high-toughness wires.The inclusions in weld metals were analyzed in terms of their types and sizes.In GMAW,the inclusions are primarily Ti,Ca,Si,Al,and Mg compounds with no Nb and are generally less than 0.8 pm in size,whereas,in SAW weld,the inclusions are larger,mostly approximately 2-5 μm in size,and are cored with Ca and Ti,exhibiting obvious oxidation metallurgical features.The SAW joint was hot-deformed,and Nb-bearing nano precipitates were newly found in the weld metal through transmission electron microscopy,and Nb-free core-shell inclusion was found through scanning electron microscopy.The inclusions and precipitates were dispersed in or on the boundaries of acicular ferrite,contributing to acicular ferrite nucleation and grain refinement.     

深冷处理对7A99铝合金峰值时效析出相的影响

对7A99超高强铝合金反向挤压材采用T6峰值时效处理与冷热循环峰值时效热处理(简称T6-DCT),通过TEM、HRTEM与3DAP研究深冷处理对峰值时效析出相的种类、分布、尺寸以及析出密度的影响。结果表明,冷热循环峰值时效处理后晶粒内部析出相种类增多,由η'相变成η'相与η相共存;冷热循环峰值时效处理可以将析出相的平均等效半径由1.201nm减小为1.001 nm,将析出相的密度由4.53×10~(24)/m~3提升至7.55×10~(24)/m~3,实现弥散强化;深冷处理可以降低Zn、Mg元素的微观偏聚,提高析出相的分布均匀性。     

两种钙离子络合显色剂在指纹显现中的应用初探

偶氮氯膦Ⅲ和乙二醛缩双(邻氨基酚)与钙离子的显色反应快速、灵敏,是无机及分析化学中常用的检测微量钙离子含量的方法。考虑到汗潜指纹中含有一定的钙离子,文章尝试利用它们与钙离子的显色反应,快速显现或者"定位"指纹。通过实验得到了适用于显现指纹的偶氮氯膦Ⅲ和乙二醛缩双(邻氨基酚)体系,并且将这些体系试用于指纹显现,已在镀锌板、陶瓷、滤纸等材质上取得了良好效果。