八苯基笼型倍半硅氧烷的官能化及其在高分子纳米复合材料中的应用

笼型倍半硅氧烷（POSS）是具有独特分子结构的有机硅化合物,无机硅氧骨架核心为其提供良好的硬度和热稳定性,外围有机基团可增强与聚合物基体间的相容性,以它为前驱体可以制备分子级分散的有机／无机纳米高分子杂化材料。近年来,全芳香结构的八苯基笼型倍半硅氧烷因其高的耐热性和官能化方法的多样性尤其得到关注。本文重点综述了八苯基笼...     

Plate vibration under irregular internal supports

This paper studies the problem of plate vibration under complex and irregular internal support conditions. Such a problem has its widely spread industrial applications and has not been addressed in the literature yet, partially due to the numerical difficulties. A novel computational method, discrete singular convolution (DSC), is introduced for solving this problem. The DSC algorithm exhibits controllable accuracy for approximations and shows excellent flexibility in handling complex geometries, boundary conditions and internal support conditions. Convergence and comparison studies are carried out to check the validity and accuracy of the DSC method. Case studies are considered to the combination of a few different boundary conditions and irregular internal supports. The latter are generated by using an image processing algorithm. Completely independent verifications are conducted by using the established pb-2 Ritz method, which is available for two relatively simpler support patterns. The morphology of the first few eigenmodes is found to be localized to largest support-free spatial regions.     

Effect of 120 keV proton irradiation on mass loss and chemical structure of AG-80 epoxy resin

The AG-80 resin is a new type of thermosetting matrix for advanced carbon/epoxy composites. Mass loss effect and the related outgassing are major concerns for its application in space. The changes in mass loss, outgassing and chemical structure under 120 keV proton exposure were investigated for the AG-80 epoxy resin. The variation in chemistry was characterised by X-ray photoelectron spectroscopy. Experimental results show that by increasing the proton fluence, the surface colour of specimens becomes darker. Mass loss ratios ascend remarkably until the fluence of approximately 6.3×10¹⁵ cm^?2 and then tend to level off. The surface roughness of specimens exhibits an increasing trend followed by a decreasing trend as a function of proton fluence. Under the exposure, the C?C, C?H, C?N and C?O bonds are broken, a variety of molecule ions with smaller molecular weight are formed and carbon is enriched in the surface layer of the specimens. The changes in mass loss and surface roughness of the AG-80 epoxy resin could be attributed to the formation of the molecule ions and the enrichment of carbon content in the surface layer due to proton radiation.     

一种含酚酞结构聚酰亚胺的合成及性能表征

通过酚酞的硝化和还原,得到了一种新型的含酞结构和酚羟基的二胺单体,通过二胺和4,4'-六氟亚异丙基二(邻苯二甲酸酐)(6FDA)缩聚并高温亚胺化,得到了相应的含酚羟基聚酰亚胺PI-HP.利用1H-NMR、FTIR、GPC及热分析表征了PI-HP的结构和热性能,利用紫外-可见光谱表征了其透明性.结果表明,PI-HP在部分极性有机溶剂中如DMF、THF、丙酮中具有良好的溶解性,具有较高的热稳定性并在可见光区域具有较好的透明性,其含羟基可进一步修饰用于制备各种功能材料.     

电感耦合等离子体原子发射光谱法测定低碳高硫钢中铋的含量

采用电感耦合等离子体原子发射光谱法测定某低碳高硫钢中的铋含量。通过实验探讨了钢中基体元素及共存元素对铋元素分析谱线的光谱干扰情况,确定了合适的分析谱线和背景校正方法,铋元素的分析谱线为223．061nm。根据某低碳高硫钢中铋元素含量范围,合成系列标准溶液,建立工作曲线,工作曲线的线性范围为0．01％～0．50％,线性相关系数r=0．9998,方法检出限为0．00279％,测量结果的相对标准偏差小于2．7％,加标回收率为98．2％～101．2％。     

Preparation of SiC nanowires with fins by chemical vapor deposition

SiC nanowires with fins have been prepared by chemical vapor deposition in a vertical vacuum furnace by using a powder mixture of milled Si and SiO₂ and gaseous CH₄ as the raw materials. The products were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These investigations confirm that the nanowires with fins are cubic β-SiC. The diameter of the fins is about 100–120 nm and the diameter of the inner core stems is about 60–70 nm. The formation process of the β-SiC nanowires with fins is analyzed and discussed briefly.     

Occurrence of Taylor vortices in the flow between two rotating conical cylinders

The behavior of the flow between two coaxial conical cylinders with the inner one rotating and the outer one stationary is studied numerically. Special attention is paid to the occurrence of Taylor vortices in basic flow and unsteady helical vortices. It is found that, in basic flow, the vortices occur in the direction toward smaller radius, while toward bigger radius in unsteady helical vortices; moreover, the unsteady helical vortices can coexist with unstable steady Taylor vortices. The results suggest that the behavior of conical flow is dominated by a competition between the meridional flow and radial flow. The effect of meridional flow is most significant at small apex angle or in basic flow and helical vortices, while the radial flow dominates the structure at larger apex angle or in steady vortical flow. In order to get better understanding the competition and the transition of Taylor–Couette flow to conical flow, a velocity angle related to velocity components is defined, and the pattern evolution of velocity, streamlines and the velocity angle are examined with respect to apex angle, as well as Reynolds number. Finally, the statistical properties of turbulent conical flow are investigated.     

Synthesis of Fe3O4 hollow microsphere chains and their magnetic properties

Fe₃O₄ hollow microsphere chains with lengths of 8–11 μm have been solvothermally synthesized in the mixed solution of glycerol and water with 1 M NaOH. The hollow microspheres have diameters in the range 0.7–1 μm, and the thickness of the shells is 150–300 nm. The shell of the hollow microspheres is constructed by octahedrons of 100–170 nm. However, when the concentration of NaOH is adjusted to 3 M, the octahedron chains with lengths of 30–50 μm can be obtained. The magnetic saturation values of hollow microsphere chains and octahedron chains are 88.1 and 102.4 emu/g at room temperature, respectively.     

First principles study of structural, electronic and vibrational properties of heavily boron-doped diamond

The structural, electronic and vibrational properties of a series of heavily B-doped diamond models have been investigated using the density functional theory within a local density approximation. The doped models C_64 − nB_n (n=1-3) were constructed using supercell techniques. The structural and electronic calculations confirmed that the B dimers are always energetically stable and electrical inactive. The superconducting transition temperature TC is not only decided by the B concentration, but also by the lattice configurations of boron atoms. The vibrational frequencies and eigenmodes were determined using the linear response approach, while Raman intensities were obtained by the second response method. The Raman analysis in terms of atomic vibrations found that the “500 cm⁻¹” and “1230 cm⁻¹” bands are both superposed bands including not only C vibrations but also B-B vibrations and B-C vibrations, respectively. The calculated Raman spectra with isotopic substitutions are in excellent agreement with corresponding experimental results. The reasonable explanation was provided for no obvious Raman shift of main bands from ¹⁰B¹²C to ¹¹B¹²C model.     

Numerical simulations of terahertz double-negative metamaterial with isotropic-like fishnet structure

The isotropic-like fishnet metamaterial with an array of cross-shaped holes penetrating through the multiple layers has been numerically studied in the terahertz regime. Its left-handed properties are described by the retrieved effect media parameters and validated by the simulation of a wedge-shaped model. The influences of the various geometrical parameters on the electromagnetic response and the left-handed performance are investigated. This isotropic-like fishnet metamaterial has the advantage of lower losses and higher transmission and holds potential for further applications at higher frequencies.