A novel microwave method for measuring the complex dielectric constant of polymer thin sheets

A new method of measuring the complex dielectric constant of a thin sheet of polymer samples at microwave frequency is presented. In order to obtain the complex dielectric constant in terms of reflection coefficient, a higher order power series solution has been introduced. Application of lower order power series solution to the greater thickness of the sample requires a frequency of less than 1.5 GHz. To overcome this constraint and to extend the range of working frequency, the higher order power series solution is used to obtain the complex dielectric constant. This method is used to measure the complex dielectric constant of poly(ethylene vinyl acetate), polyurethane, polyvinyl acetate, and polystyrene. The results obtained are in good agreement with literature. Electronic Publication     

Nanoindentation mapping of mechanical properties of cement paste and natural rocks

This paper reports a study to assess nanoindentation mapping of mechanical properties of cement paste and natural rocks. Initial work seems to show that mechanical property mapping by nanoindentation is feasible and can be related to microscopic information. Further work is however required on the effect of indent size and spacing. Such a testing technique can be very useful for materials with different phases to study the intrinsic properties of each component, and also the interaction and properties of the interfacial regions of different phases. The values of Young's modulus and hardness of the individual mineral phases were also determined by statistically analysing a large number of experimental data.     

基于简化LSCMA算法的STBCMC—CDMA系统盲多用户检测

在空时分组编码（STBC）的MC—CDMA系统中，根据STBC正交编码的特点，提出了一种简单可行的基于常模（CM）准则的盲多用户检测算法。该算法基于最小二乘常模算法（LSCMA）的盲多用户检测算法，算法大为简化，抽头系数减少了一半，性能略有下降。     

Effect of Solidification Conditions on Structure and Properties of Rapidly-Solidified Sn-7.5wt%Sb Alloy

The effect of cooling speed on structure and properties of the rapidly-solidified Sn-7.5wt%Sb has been investigated. The samples in this study were prepared using a single roller melt spinning technique with two speeds: 15.7 and 30.7 m/s, respectively. The results showed formation of the intermetallic compound SnSb. This intermetallic compound changes in the amount which precipitated in the two samples. This behavior tends to affect the properties of these two samples. Also higher cooling speed tends to reduce the crystallite size, which in turn reduces the melting point of the resulting alloy compared to that of the lower cooling speed.     

Fe基非晶合金的恒导磁性能研究

研究了Fe基非晶合金在不同热处理工艺条件下的恒导磁性能.结果表明,通过简单的横向磁场热处理工艺,可将具有高饱和磁感应强度的Fe基非晶合金制成无间隙的恒导磁磁芯,并且具有良好的综合磁特性.合金在350℃处理时,恒磁范围达到400A/m,磁导率约为3.14×10-3T·m/A,随保温时间的延长,恒磁场范围提高到600A/m以上,但磁导率降低,约为1.25×10-3T@m/A.在晶化温度以下,提高横向磁场热处理温度有利于提高材料的恒导磁性能.     

POSS基低介电常数多孔薄膜的制备与性能研究

通过4，4’-二（4-烯丙氧基苯甲酸）苯酯与POSS分子的硅氢化反应，合成了POSS交联聚合物。用FTIR、XRD对聚合物结构进行了表征，利用椭偏仪测量了薄膜的折射率和介电常数。通过改变单体与POSS投料摩尔比，可制备出k＜2.5的低介电常数薄膜。     

Low temperature solid-phase synthesis of tetragonal BaTiO3 powders and its characterization

We report an alternative synthesis route for tetragonal and submicron barium titanate particles through a low temperature isothermal heat treatment of a precursor powder obtained from the BaO₂-TiO₂-C mixture utilizing combustion synthesis technique. Effort has been concentrated on the investigation and optimization of the synthesis process including combustion temperature and velocity, heat treatment procedure, and the characteristics of the powder obtained. It was shown that precursor powder prepared by the combustion method easily transformed to the tetragonal BaTiO₃ starting from 700 °C. Characterization of the products was performed by powder X-ray diffraction, scanning electron microscopy (SEM) and BET. From the results, it has been found that the formation of tetragonal BaTiO₃ powder at low temperature is conditioned by high chemical activity and specific characteristics of combustion products. The BaTiO₃ specimens were found to possess high dielectric constant and low dissipation factor at room temperature.     

考虑纤维方向分布的玻纤增强PP复合材料拉伸性能

纤维方向及其分布对玻纤增强PP复合材料的力学特性具有至为关键的影响.提出了一种快速获取纤维数量及每根纤维方向的方法.通过引入方向张量,利用Moldflow软件进行玻纤增强PP树脂注塑成型模拟获得纤维方向的平均分布,结合显微方法观察判断特定点的纤维沿厚度方向的分层情况及定量判断纤维方向的分布.对轿车玻璃纤维增强注塑仪表板的纤维方向相对一致处取与纤维方向呈0°、45°、90°的样条,通过拉伸实验测得拉伸模量,利用所提出的方法研究了仪表板内玻纤方向的分布及其对拉伸模量的影响.研究结果表明:玻纤增强注塑仪表板的力学性能是各向异性的,其沿厚度方向纤维按方向大致可分为三层.     

MgO/Pd底层对CoSiB/Pd多层膜垂直磁各向异性及热稳定性的影响EI北大核心CSCD

采用磁控溅射方法在玻璃基片上制备以MgO/Pd为底层的CoSiB/Pd多层膜样品,研究MgO底层厚度t对CoSiB/Pd多层膜垂直磁各向异性(perpendicular magnetic anisotropy,PMA)的影响,分析具有MgO/Pd底层的多层膜的热稳定性。通过对样品的反常霍尔效应的测试分析发现,底层中引入MgO层能够提高其PMA性能,当t为3.5 nm时,样品的矩形度最好。对最佳样品MgO(3.5 nm)/Pd(3 nm)/[CoSiB(0.5 nm)/Pd(0.8 nm)]2/Ta(2 nm)的磁滞回线进行测试,其有效磁各向异性常数K eff达到2.0×10^5 J/m^3。热稳定性分析发现,当退火温度为200℃时,样品的K eff达到最大值2.6×10^5 J/m^3;当退火温度达到400℃时,样品仍能保持良好的PMA性能。     

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.