略谈磁性指向器的形制

司南是最早的磁性指向器.北宋时期,磁化技术的突破,导致磁性指向器的形制有了新的演变,其中,用针指向是磁性指向器形制最重要的改进.指南针的出现,极大提高了磁性指向器的指向精度,加快了磁偏现象的发现.之后,指南针的形制仍不断被改进,指南鱼发展成水罗盘,用以指向的木刻鱼被穿上小木条的磁针取代,"指南鱼"的形制消失;指南龟发展成枢轴支承式,成了旱罗盘.本文对磁性指向器的发明和演进过程稍作梳理,希望对帮助广大读者了解这一问题能够有所裨益.     

走出我国公共部门人力资源绩效考核的困境

文章从我国公共部门人力资源绩效考核面临的现实问题入手，针对现有的考核体系作了比较系统的思考，并给出了相应的建议和措施。     

Optimal multi-asset investment with no-shorting constraint under mean-variance criterion for an insurer

This paper considers the optimal investment strategy for an insurer under the criterion of mean-variance. The risk process is a compound Poisson process and the insurer can invest in a risk-free asset and multiple risky assets. This paper obtains the optimal investment policy using the stochastic linear quadratic (LQ) control theory with no-shorting constraint. Then the efficient strategy (optimal investment strategy) and efficient frontier are derived explicitly by a verification theorem with the viscosity solution of Hamilton-Jacobi-Bellman (HJB) equation.     

Atomic layer deposition on Pd nanocrystals for forming Pd-TiO2 interface toward enhanced CO oxidation

Pd typically exhibits relatively low catalytic activity in CO oxidation, as CO is apt to be adsorbed on Pd to poison the surface for O2 activation. In this Letter, we report that this limitation can be overcome by integrating Pd with TiO2. The TiO2 was coated on Pd nanocubes with a controllable thickness using atomic layer deposition (ALD) method. Given the different work functions of TiO2 and Pd, the electrons in TiO2 semiconductor will flow toward Pd. With the electron density increased on Pd, the adsorption of CO to Pd will be weakened while the oxygen activation can be facilitated. Meanwhile, the interface-confined sites at Pd-TiO2 may further enhance the oxygen activation. As the species adsorption and activation are strongly correlated with electron density, the performance of Pd-TiO2 in CO oxidation turns out to depend on the TiO2 thickness, which determines the number of transferred electrons, within a certain range (<1.8 nm). This work provides a new strategy for enhancing catalytic performance through tailoring charge densities in hybrid catalysts.     

Influence of B,Al and Nb addition on the glass forming ability and stability of mechanically alloyed Zr-Ni amorphous alloys

We investigated the influence of minor additions of B,Al and Nb that have representative atomic sizes on the glass forming ability (GFA) and stability of Zr-Ni amorphous alloys during mechanical alloying. The results show that the minor addition of B,Al or Nb does not shorten the initial time of the full amorphization reaction or improve the glass forming ability of the Zr-Ni alloys at a low rotation speed. However,B addition can effectively improve the mechanical stability of the amorphous phase against me...     

一种改进的高效粒子水平集法及其应用

针对传统粒子水平集法效率较低,难以应用于复杂工程问题的不足,基于积分平均法及局部粒子初始化方法提出一种改进的高效粒子水平集法.将虚拟粒子引入水平集法不仅可以抑制数值扩散,而且可以降低传统方法对高精度离散格式的依赖性,从而使得引入低阶、高效的积分平均法后界面捕捉精度仍保持二阶.通过将粒子布置于界面局部曲率较大的区域,有效地提高了粒子对界面的修正效率,增加了界面光顺性.改进的高效粒子水平集法能保持良好的鲁棒性,在保证界面捕捉精度的同时显著提高计算效率,计算效率约提高90%.     

浅谈雷暴天气变化特征与注意事项

雷暴是一种重要的天气现象,也是一种灾害性天气。文章分别阐述了热雷暴、锋雷暴、地形雷暴的形成条件;雷暴来临时气象要素气温、气压、湿度、风、降水、的变化特征;雷暴观测和记录注意事项,以及其他注意事项。     

仿真软件在数控实训中的应用

太原理工大学工程训练中心选定了一种能在计算机上进行三维仿真,相当于真正的CNC机床的操作功能,并能进行手工编程或CAD/CAM自动编程,与国内数控机床有良好的兼容性的基于PC机上操作的英福花数控仿真软件.     

基于多源信息空间的遥感影像自动解译研究

通过分析遥感影像自动解译的研究现状和存在的问题,提出了基于多源信息空间的遥感影像自动解译的研究方法,将遥感影像分为光谱信息空间、形状信息空间、区域地学信息空间、干扰信息空间等四个信息空间,通过对多源信息空间的数学描述和计算机处理实现了遥感影像的自动解译.     

复合活化沸石粉对水泥胶砂性能影响研究

沸石粉活性较低,在混凝土中掺量较多时,难以成型,使材料强度下降,再加上其比表面积大、吸水率高,导致材料流动度显著降低,不利于实际工程中的应用。为了提升天然沸石粉的活性,使用Ca(OH)₂活化和水热活化复合的方法对沸石粉进行活化处理,等质量取代30%水泥制作胶砂试件,测定其3个龄期的力学强度和流动度,并采用比表面积测定、扫描电子显微镜、X射线衍射、热重试验进行微观机理分析。结果表明：Ca(OH)₂掺量为8%时,胶砂力学强度最高,28 d抗压强度达到35.0 MPa,比掺天然沸石粉的水泥胶砂的抗压强度增加了20.7%;天然沸石粉经复合活化后活性明显提升,最佳Ca(OH)₂掺量为8%,28 d强度活性指数增加16%;复合活化改变了沸石粉表面结构,其表面从粗糙不平变得光滑,有利于流动性增加,且随着Ca(OH)₂掺量的增加,水泥胶砂流动度呈现增长趋势。