有机改性SiO2无支撑膜的溶胶凝胶法制备

采用溶胶凝胶法,以二甲基二乙氧基硅烷／正硅酸乙酯的复合醇盐为前驱体,制备了一种厚度达到３０μｍ￣５００μｍ的大尺寸无载体膜,膜体显示了良好的可弯曲性和成膜性能,原子力显微镜表征得到的表面平均粗糙度为０．３ｎｍ,色质连用谱的分析表明在醇盐水解聚合过程中形成了大量［（ＣＨ３）２Ｓｉ－Ｏ］,环状分子,填充凝胶孔隙,降低毛细管应力,增加结构柔韧性。     

Echo-Planar Imaging of Porous Media with Spatial Resolution below 100 μm

A modified version of the echo-planar imaging technique incorporating a Carr–Purcell train of 180° rf pulses (PEPI) has been implemented on a standard spectrometer. It is demonstrated that artifacts in the image due to cumulative errors in the rf field can be reduced by replacing each 180° pulse by a composite sequence of three rf pulses. Artifact-free 3D images at 94 μm voxel resolution are obtained within 15 min. This technique has been applied to study the drying process in an initially water-saturated model porous medium with characteristicT^*₂of order 700 μs.     

Decay Time of 2.09 eV Luminescence of S2--Vacancy Centers and Their Optical and Thermal Stability in NaCl:S2 Crystals

An investigation was carried out on decay time of the 2.09 eV emission of S²–vacancy pair centers in NaCl crystals. When the crystal was excited by a pulsed 337 nm light from an N₂ laser, the 2.09 eV yellow luminescence principally decayed with the lifetime of 14.2 μs at low temperatures, and exhibited a weak thermal quenching with an activation energy of 51.3 meV above about 150 K. Such S^2--vacancy pair centers responsible for the 2.09 eV luminescence were thermally stable at room temperature, and not bleached even when exposed to ultraviolet lights below about 5 eV. Thus, the 2.09 eV emission center possibly can be used as a solid-state laser active center working at room temperature.     

Spin susceptibility of interacting electrons in one dimension: Luttinger liquid and lattice effects

The temperature-dependent uniform magnetic susceptibility of interacting electrons in one dimension is calculated using several methods. At low temperature, the renormalization group reveals that the Luttinger liquid spin susceptibility approaches zero temperature with an infinite slope in striking contrast with the Fermi liquid result and with the behavior of the compressibility in the absence of umklapp scattering. This effect comes from the leading marginally irrelevant operator, in analogy with the Heisenberg spin 1/2 antiferromagnetic chain. Comparisons with Monte Carlo simulations at higher temperature reveal that non-logarithmic terms are important in that regime. These contributions are evaluated from an effective interaction that includes the same set of diagrams as those that give the leading logarithmic terms in the renormalization group approach. Comments on the third law of thermodynamics as well as reasons for the failure of approaches that work in higher dimensions are given. Received 2 March 1999     

含螺旋单元频率选择表面的宽频带强吸收复合吸波体

设计和制备了含螺旋单元频率选择表面吸波片的三层复合吸波体,上层和下层均为磁性吸波片,中间层为带缺口的螺旋单元频率选择表面.复合吸波体在总厚度分别为1.4,1.7和2.0 mm时,其反射率在-10d B以下的频带宽度分别达到了9.29,6.69和7.11 GHz,与不含有频率选择表面的吸波体相比较(其他参数相同),-10d B以下反射率带宽分别提高了159.5%,69.3%和129.4%,复合吸波体在总厚度低于吸波体时,也取得了更好的反射效果.带缺口圆螺旋单元的频率选择表面嵌入吸波体中,引入了额外的吸收频带,拓宽了吸波体的反射率频带宽度.仿真分析表明嵌入频率选择表面能够改善吸波体的阻抗匹配性,进而影响其反射率.     

碳纳米管/聚二甲基硅氧烷复合薄膜的制备及力敏特性研究

针对传感器的敏感单元发展需求,提出了一种碳纳米管复合材料.该材料是以碳纳米管作为填充粒子,结合聚二甲基硅氧烷(PDMS)有机基体,采用超声共混方法制备的一种新型传感器敏感元件.详细分析研究了复合材料的制备工艺参数,以及在不同工艺参数下该复合材料的力敏特性.扫描电镜测试表明碳纳米管在PDMS中分散均匀且镶嵌良好.通过对不同体积分数的碳纳米管与PDMS复合材料进行电学性能测试,研究薄膜的"力-电阻"和"力-电容"耦合性能,测试了薄膜结构的力敏效应.计算得到复合薄膜材料的压阻灵敏度因子达到40,压电容灵敏度因子达到70.实验研究表明,通过改变碳纳米管与PDMS的比例,可以很好地调节其电子输运特性以及电阻和电容的应力敏感特性,可以为该类型的力敏材料在不同的力敏传感技术领域提供新的研究思路.     

二氧化钛纳米晶/石墨烯复合物的制备及其光催化性能 (cited: 1)

以氧化石墨和TiO₂溶胶为前驱物,结合絮凝与水热技术制备了TiO₂纳米晶/石墨烯复合物,表征了产物的结构、形貌、孔隙率、光谱吸收性质. 结果表明：TiO₂纳米晶的存在一定程度上阻止了石墨烯片层的重组,TiO₂纳米晶/石墨烯复合物较单纯TiO₂材料具有更强的吸光性能、对亚甲基蓝分子更强的吸附性能以及更高的电荷分离效率. 在紫外光和太阳光下,TiO₂纳米晶/石墨烯复合物对亚甲基蓝的光催化降解效率均高于P25和纯TiO₂.     

氢化物发生辅助溶液阴极辉光放电光谱技术检测水体中痕量汞和锡

溶液阴极辉光放电技术作为一种新型的光谱检测技术,被广泛应用于环境污染物的分析和检测等方面.虽然该技术具有结构简单以及成本低等优势,但是在重金属检测方面,其灵敏度还有待提高.针对上述问题,搭建了氢化物发生-溶液阴极辉光放电光谱测量系统,实现了对水体中痕量汞(Hg)和锡(Sn)的简单高效检测.为了得到更优的检测效果,实验选...     

柔性复合薄膜成形极限曲线的视觉测定方法

针对柔性复合薄膜成形试验中极限应变难以测量的问题,提出一种基于双目立体视觉结合数字图像相关法的测量方法。首先对于薄膜材料成形过程中产生大变形或裂纹时图像难以匹配的问题,根据系列图像相邻状态变形的连续性,提出了一种图像匹配基准自适应更新的弱相关分步匹配方法;然后根据薄膜材料表面应变分布不同于钢制件的特性,提出了一种构建应变场截线来拟合薄膜材料的极限应变曲线的方法。专门组建视觉测定的软、硬件系统,通过Q235钢试件进行极限应变曲线测量并与坐标网格方法进行对比,材料极限应变精度能够提高0.02%,证明了本文方法的可行性和精确性。用7组PET/Nylon/Al foil/PP材料制备成的柔性复合薄膜试件进行实测,此方法及系统成功地完成了柔性复合薄膜材料的成形极限曲线测定。对比实验和实际测试证明,本文方法能够快速、准确地测量柔性复合薄膜材料在整个成形过程中的表面应变分布,与传统的坐标网格方法相比具有明显的优势,为测定薄膜材料的成形极限应变曲线提供了一种高可靠性、高精度的手段。     

基于遗传算法的传声器阵列位置有源校正研究

传声器阵列的位置误差会导致高精度定位应用场景中算法性能下降,为解决这一问题,该文提出了一种二维平面传声器阵列位置参数的有源校正方法.在校正声源位置已知的情况下,利用各阵元间的到达时间差均方误差之和最小化作为优化目标设计代价函数,根据遗传算法搜索阵列真实位置的全局最优解,从而估计得到传声器阵列的准确位置信息.仿真与半消声...