基于三维表面增强拉曼基底的水中多环芳烃检测

为了快速检测水中痕量多环芳烃(PAHs),制备了一种高灵敏度的三维表面增强拉曼散射(SERS)基底。将GMA-EDMA多孔材料与参数优化的金纳米颗粒相结合,形成了高灵敏度三维SERS活性基底。相比仅用参数优化的金溶胶SERS基底,该三维SERS基底的信号强度有近一个数量级的增强,相比未调pH值的金溶胶基底,增强效果有2~3个数量级的提高,且具有良好的重复性,该基底内探测相对标准偏差(RSD)为4.78%~9.27%,基底间RSD为2.05%。利用该基底对三种较有代表性的多环芳烃菲、芘、苯并(k)荧蒽进行了SERS光谱探测,得到检测限分别为9.0×10~(-10),2.3×10~(-10),5.9×10~(-10) mol·L~(-1)。结果表明,这种检测方法操作简便、重复性好、灵敏度高,可以实现水中多环芳烃的痕量检测。     

A super junction SiGe low-loss fast switching power diode

This paper proposes a novel super junction (SJ) SiGe switching power diode which has a columnar structure of alternating p^- and n^- doped pillar substituting conventional n^- base region and has far thinner strained SiGe p⁺ layer to overcome the drawbacks of existing Si switching power diode. The SJ SiGe diode can achieve low specific on-resistance, high breakdown voltages and fast switching speed. The results indicate that the forward voltage drop of SJ SiGe diode is much lower than that of conventional Si power diode when the operating current densities do not exceed 1000 A/cm², which is very good for getting lower operating loss. The forward voltage drop of the Si diode is 0.66V whereas that of the SJ SiGe diode is only 0.52 V at operating current density of 10 A/cm². The breakdown voltages are 203 V for the former and 235 V for the latter. Compared with the conventional Si power diode, the reverse recovery time of SJ SiGe diode with 20 per cent Ge content is shortened by above a half and the peak reverse current is reduced by over 15%. The SJ SiGe diode can remarkably improve the characteristics of power diode by combining the merits of both SJ structure and SiGe material.     

Dissociation of H_2 on Mg-coated B_(12)C_6N_6

The dissociation of H_2 molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to determine the kinetics of the regeneration of the storage material. In this paper, we investigate the hydrogen adsorption and dissociation on Mg-coated B_(12)C_6N_6. The B_(12)C_6N_6 is an electron deficient fullerene, and Mg atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The preferred binding sites for Mg atoms are the B_2C_2 tetragonal rings. The positive charge quantity on the Mg atom is 1.50 when a single Mg atom is coated on a B_2C_2 ring. The stable dissociation products are determined and the dissociation processes are traced. Strong orbital interaction between the hydrogen and the cluster occurs in the process of dissociation, and H_2 molecule can be easily dissociated. We present four dissociation paths, and the lowest energy barrier is only 0.11 eV, which means that the dissociation can take place at ambient temperature.     

基于在线购买历史聚合的B2C电子商务差异化折扣模型

众多B2C网站已建立起会员等级制度,并据此向买家提供价格折扣。但会员等级制模型仅考虑买家交易金额,无法全面反映买家在线购买历史(online purchase history),故不能准确提供差异化折扣。针对上述问题,提出了一种面向B2C电子商务的差异化折扣模型,该模型包含能体现买家在线购买历史的交易、退单、推荐购买、晒单等四个指标,将买家在线购买历史聚合为一个综合值,进而通过min-max标准化方法进行线性转换,将转换后的聚合值与会员等级基准折扣结合得到最终的差异化折扣,从而使得B2C网站可向同级别会员实施更精准的一对一营销和价格歧视策略。以京东商城为背景的仿真实验结果证明了本文新模型的有效性。     

火焰原子吸收法测定粗锡中的铜含量

本文讨论了用火焰原子吸收法测定粗锡中的铜含量的方法。试料用盐酸、硝酸、酒石酸溶解。在5%盐酸介质中,使用空气-乙炔火焰,波长选用324.7 nm,用原子吸收光谱法测量铜的吸光度。以工作曲线法计算铜含量。研究了仪器的最佳测量条件,元素测定的质量数以及酸度的影响等实验。方法测定结果准确、可靠,样品加标回收率在97.20%~102.00%。能满足日常检测应用。     

脉动冷却流对冷却孔出口附近流动结构的影响

为了探索新型高效能的气膜冷却技术,本文提出了一种脉冲射流冷却方法,并以平板上垂直方形冷却孔为几何模型,以正弦曲线分布的射流速度为冷却气流模型,采用非定常CFD数值模拟技术,在给定横向流速和非定常射流速度的条件下,对孔附近局部三维流场的非定常特性和流场结构进行了数值模拟研究.     

Chemisorption of Fe on Au-passivated Si（001） surface

The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au－Fe mixed layer at the Fe/Au－Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au－Si(001) interface effectively, which is in agreement with the experimental results.     

带粗糙核的多重Marcinkiewicz积分算子的L~p有界性

主要利用Littlewood-Paley理论和Fourier变换估计研究在一些相当弱的尺寸条件下,建立多重Marcinkiewicz积分算子的Lp有界性,从而改进和推广前人的结论.     

石英片基表面联吡啶钌配合物的合成与表征

将6-溴-2,2'∶6',2"-三联吡啶转化为6-甲酰基-2,2'∶6',2"-三联吡啶, 再将其与表面组装有氨基硅氧烷的石英片基反应, 使甲酰基与片基表面的氨基反应生成Schiff碱型化合物, 在氨基化片基表面成功地固定6-甲酰基-2,2'∶6',2"-三联吡啶及相应的钌配合物, 并用紫外-可见吸收光谱及光电子能谱(XPS)检测联吡啶及相应钌配合物的组装过程.     

显微标本无损分析仪的研究

将传统光学显微镜和CCD、计算机相结合,实现对标本的无损显微观察.在介绍系统硬件组成的同时,着重说明了图像清晰度评价与图片重建的核心算法,并用VC++加以验证和实现.清晰度评价函数采用自行设计的类灰度方差算法,即采用图像的灰度值方差作为图像的清晰度.无损显微分析仪通过精密位置控制机械结构上下移动载物台,采集样本和显微物镜在不同距离时的多幅局部清晰的图像,通过清晰度评价算法找到满足清晰度要求的局部图像,再对多个清晰的局部图像进行合成,得到清晰的整体图像.