微型轴流风扇噪声特性分析及试验研究

本文对微型轴流风扇噪声的产生机理进行了系统分析及教育处，并进行了实验测试。得出的分析计算结果与实验数据作了比较验证，在声压随观测角度和距离的变化关系上，两者显示出基本一致的趋势。文中以等流量为前提，对降低微型风扇噪声的一种途径作了计算，结果表明采用转轴很细的风扇，可使噪声明显降低（大于3dB）。     

Flash器件中氧化硅/氮化硅/氧化硅的特性

对普遍采用的氧化硅/氮化硅/氧化硅( ONO)三层复合结构介质层的制备工艺及特性进行了研究分析,研究了ONO的漏电特性以及顶氧( top oxide)和底氧( bottom oxide)的厚度对ONO层漏电的影响.结果表明,采用较薄的底氧和较厚的顶氧,既能保证较高的临界电场强度,又能获得较薄的等效氧化层厚度,提高耦合率,降低编程电压.     

Magnetic Properties of Fe-Doped Rutile

Ball-milling method was applied to dissolve Fe into titanium dioxide (TiO₂). X-ray diffraction indicated the starting anatase changed to a rutile-type structure with oxygen deficiency after ball milling. Transmission electron microscopy and X-ray absorption experiments were conducted to examine the possible existence of magnetic impurities in the ball-milled powders after they were leached in HCl solutions. Temperature dependence of the resistivity shows semiconducting behavior and the magnetic hysteresis loops at 5 and 300 K exhibit ferromagnetic characteristics. Fe-doped TiO₂ films were also prepared by pulsed laser deposition. The magnetic properties of the films are discussed.     

Characterization of Austempered Ductile Iron Through Barkhausen Noise Measurements

The outstanding mechanical properties of austempered ductile irons (ADI) are linked to the microstructure of the matrix obtained by subjecting a ductile iron with an appropriate composition to a heat treatment called austempering. Then the microstructure of the matrix consists of bainitic ferrite with different volume fractions of retained austenite. The aim of this work is to use the magnetic Barkhausen noise (MBN) as a nondestructive method for characterizing the microstructure of ADI. First, it is shown that the amplitude and position of the peak-shaped MBN response is quite sensitive to the microstructure of the matrix of ductile irons. Thus each type of constituent (equiaxial ferrite, pearlite, martensite or bainite) exhibits a typical response and, in turn, it can be identified from the MBN response. Furthermore, a good correlation is found between MBN signal parameters and ADI heat treatment parameters, indicating that MBN is also quite sensitive to fine evolutions of the microstructure of ADI. MBN peak position is especially sensitive to the type of bainite, whereas peak amplitude is linked to the progress of the bainite reaction. Hence MBN measurements appear to be a powerful tool to assess some important microstructural features of ADI castings.     

Electronic properties of magnetically doped nanotubes

Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered in this paper. In the case of semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic (except for Cr).     

Science in High Magnetic Fields: What Could Be Learned?

High magnetic fields are one of the most powerful tools available to scientists for the study, modification and control of matter. This includes the knowledge on correlations effects, interaction mechanisms, structural information and understanding of mesoscopic effects. In this context, a review of recent scientific achievements at the Grenoble High Magnetic Laboratory is given to illustrate, on specific examples, the power of the Magnetic Field probe.     

堆石料与基岩面直剪试验

介绍了堆石料与基岩面的现场直剪试验方法，6个组次的直剪试验结果表明，堆石料与基岩面的抗剪强度指标随基岩面坚硬度的增大而增加，并随基岩面粗糙度的加大而加大。     

水力脉动冲击钻井工具初步研究与试验

掘力脉动冲击钻井是将水力脉冲、机械冲击振动结合为一体提高钻井速度的一种方法，介绍了辽河油田研制的脉动冲击钻井工具的结构、工作原理及现场试验情况。在潜山混合花岗岩、砂岩，硬脆性泥岩等不同地层的现场试验表明：水力脉动工具工作平稳，未出现蹩跳钻现象，也没有出现脱、落、断、掉等问题，主体安全性、可靠性较好；在潜山混舍花岗岩、砂岩、硬脆性泥岩地层机械钻速提高幅度较大，但在部分泥岩地层效果不佳。试验中发现密封圈耐温性差、脉冲腔易磨损等问题，并据此提出了水力脉动冲击工具的下一步研究方向。     

现场总线系统控制网络的检查和调试

现场总线控制系统是计算机、网络与自动控制三项技术相互结合的一门新技术。文章介绍了现场总线控制系统仪表网络的典型结构,对现场总线控制系统与集散控制系统进行了比较,论述了现场总线控制系统检查和调试的程序、内容与操作方法。     

Curie Temperatures of III–V Diluted Magnetic Semiconductors Calculated from First-Principles in Mean Field Approximation

Electronic structure and ferromagnetism in III–V compound-based diluted magnetic semiconductors (DMS) are investigated based on first-principles calculations by using the Korringa-Kohn-Rostoker method combined with the coherent-potential-approximation. The stability of the ferromagnetic phase in GaN-, GaAs-, GaP-, GaSb-based DMS is investigated systematically. The calculations show that 3d-impurities from the first-half of the transition metal series favor the ferromagnetic state, while impurities from the latter-half of the series exhibit spin-glass behavior. This chemical trend in the magnetism is explained by the double exchange mechanism taking the local symmetry at the impurity gap states into account. Curie temperatures of GaAs- and GaN-based DMS are estimated by using the Heisenberg model in a mean field approximation with the parameters calculated from first-principles. It is suggested that room-temperature ferromagnetism can be realized in these systems.