Tuning effect of silicon substitution on magnetic and high frequency electromagnetic properties of R2Fe17 and their composites

In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R₂Fe₁₇ compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R₂Fe₁₇ compounds, making the R₂Fe_17–xSi_x-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (f_RL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm_1.5Y_0.5Fe₁₅Si₂-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd₂Fe₁₅Si₂-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.     

机械合金化Fe-Ni粉末的相结构

使用XRD和Moessbauer等方法，研究了在Ar气氛下机械合金化Fe—Ni粉末相结构的变化．结果表明，在机械合金化Fe64-Ni36粉末过程中，fcc相的数量随着球磨时间的增加先增加然后减少，与加乙醇球磨Fe64-Ni36的情形相同．当Ni的含量(原子分数)大于50％时，有fcc相、顺磁相和FeNi3形成，当Ni的含量低于50％时，bcc相的数量随着Ni含量减少而增加．Moessbauer谱的结果表明，因球磨时间或Fe、Ni比例的不同，Fe—Ni球磨粉末固溶体具有不同结构的原子配比。     

屏蔽人体模型对电磁波吸收的数值模拟研究

本文用时域有限差分法计算了三类电磁特性不同的材料屏蔽下三层无限长椭圆柱人体模型对电磁波的吸收。结果表明 ,功率密度相同 ,频率在 0 .2～ 6GHz之间的平面电磁波照射下 ,模型吸收的能量、能量在体内的分布及两者对入射电磁波频率的敏感程度严重地受到外加屏蔽的影响。考察了屏蔽材料的电磁特性与其屏蔽效能之间的关系。三类材料的比较显示 ,对人体电磁辐射防护 ,耗散材料优于非耗散材料 ,导电材料优于非导电材料。     

纳米二氧化钛的表面修饰与应用的研究进展

介绍了纳米二氧化钛表面修饰的两种主要方法:无机和有机表面包覆,以及进行修饰后的纳米二氧化钛的应用.     

几种火焰喷焊自熔性合金层的耐磨性能

研究了不同自熔性合金粉末火焰喷焊层的显微组织与抗磨粒磨损性能，并对其磨面形貌进行了ＳＥＭ观察分析。结果表明，在Ｎｉ６０自熔性合金中加入适量的镍包ＷＣ粉末可明显提高其喷焊层的抗磨粒磨损性能。当ＷＣ的加入量为３５％（ｗｔ）左右时，该喷焊层与６０Ｓｉ２Ｍｎ调质钢相比，相对的耐磨性可提高６倍以上。     

Perspective:Societally connected multimedia across cultures

The advance of the Internet in the past decade has radically changed the way people communicate and col- laborate with each other. Physical distance is no more a barrier in online social networks, but cultural differences (at the individual, community, as well as societal levels) still govern human-human interactions and must be con- sidered and leveraged in the online world. The rapid de-ployment of high-speed Internet allows humans to interact using a rich set of multimedia data such as texts, pictures, and videos. This position paper proposes to define a new research area called ’connected multimedia’, which is the study of a collection of research issues of the super-area social media that receive little attention in the literature. By connected multimedia, we mean the study of the social and technical interactions among users, multimedia data, and devices across cultures and explicitly exploiting the cultural differences. We justify why it is necessary to bring attention to this new research area and what benefits of this new research area may bring to the broader scientific research community and the humanity.     

地方应用型高校双语课程教学模式探讨 ——以常州工学院"土力学"双语教学为例

"土力学"是普通高等学校土木工程专业本科生的专业基础课.文章提出一种以解决问题为导向的基于CDIO的分阶段双语教学模式,该模式根据课程内容及学生状态对教学手段采取动态调整,既能够保障学生专业知识的学习效果,又能够提高学生的英语思维能力和跨文化交际能力.该教学模式充分考虑了学生的个体差异和双语教学的课程目标,极大提高了学生对双语课程的吸收效果,对双语教学的持续发展与完善具有参考意义.     

GRAIN COARSENING BEHAVIOUR TOWARDS AUSTENITIC HOT WORK TOOL STEELS AND EFFECT OF ALLOYING ELEMENTS

本文用定量金相法分析和讨论了奥氏体热作工具钢的晶粒粗化行为.结果表明,在钢中加入Nb可提高MC的稳定性,增加MC的体积分数.Nj/Mn比对晶粒粗化也有较大的影响,随Ni/Mn比的增加,钢中M_(23)C_6和MC质点的体积分数增加。两者均提高晶粒粗化温度。 比较了已有的晶粒粗化模型,在晶界面为凸凹不平的曲面前提下,对Gladman模型做了修正,提出了如下的修正Gladman公式: R_0=πr/3f_v(3/2-2/Z) 该公式能较好地预测晶粒的实际尺寸。     

EFFECT OF ALLOY ELEMENTS ON QUASIEQUILIBRIUM MICROSTRUCTURE IN Fe-Mn-Ni-Cr STEELS

The microstructures of Fe-Mn-Ni-Cr steels with medium carbon and the effect of alloy ele-ments on them have been investigated by means of X-ray diffraction quantitative phase ana-lyses,metallography and hardness tests.The volume fraction of martensite in steels quenchedat 1100℃ can be expressed as:f_M~(1100)=162.643-15.482Mn-7.36Ni-4.286(Cr+Mo+V)Based on this expression,the quasi-equilibrium microstructure diagram has been obtained.Itis shown that the effect of Mn on the austenite stability is greater than that of Ni.The equiva-lent [Ni]=2.104Mn+Ni and equivalent [Cr]=Cr+Mo+V.The driving force for martensite transformation at M_s point has been calculated to hedrastically decreased by element Mn.