气相色谱/三重四极杆串联质谱法测定牛奶及奶粉中213种农药多残留

在系统优化固相萃取吸附剂填料类型、洗脱溶剂种类及体积的基础上,建立了牛奶和奶粉中213种农药残留的气相色谱-三重四极杆串联质谱(GC-MS/MS)方法。试样用乙腈均质提取,采用石墨化炭黑/氨基柱(ENVI-Carb/NH₂)净化后,用GC-MS/MS多反应离子监测(MRM)模式进行检测,外标法定量。结果表明,197种农药在10~1000 μ g/L,16种农药在50~1000 μ g/L范围内线性关系良好,相关系数均大于0.99,方法的检出限(S/N=3)为0.03~7.59 μ g/kg,定量限(S/N=10)为0.10~21.94 μ g/kg,平均添加回收率为66.9%~120.1%,相对标准偏差(RSD)为1.23%~17.6%。该方法样品处理简单快速,相比其他多残留分析方法净化效果好,灵敏度和选择性高,适用于日常检测工作。     

模拟电子技术教学改革探讨

模拟电子技术是工科类学生的一门专业基础课程,与实践联系紧密,由于课程本身物理概念抽象,学习起来比较枯燥,使得学生普遍反映该门课程入门难、学习难.鉴于此本文在介绍如何提高课堂教学质量的同时着重提出小课题实验教学,通过简单的实验项目,帮助学生从直观上认识半导体器件,将各知识点串联起来,引导学生入门,激发学生学习兴趣.     

超临界CO2技术制备超细SiO2的研究

本文以水玻璃为硅源,利用超临界CO2(sc CO2)技术制备出超细SiO2粉体,研究了压力、温度对超细SiO2粒子粒径和Zeta电位的影响,采用Zeta电位及激光粒度分析仪、X射线衍射(XRD)、自动吸附仪等测试方法对粉体的结构和性能进行了分析表征.结果表明:当压力为8 MPa,温度为50℃时,所得超细SiO2粒子粒径分布较窄且平均粒径最小,为472.9 nm,且Zeta电位取得较小值,为-55.68 mV;所得超细SiO2粒子属于非晶态,且与市售的T36-5 SiO2粒子相比,其孔结构更加致密.     

Structural,electronic, and optical properties of phenol‐pyridyl boron complexes for light‐emitting diodes

The coordination chemistry of polydentate chelating ligands that contain mixed pyridinephenol donor sets has been a sought‐after target of study and is a possible extension to the chemistry of polypyridines. In this article, seven compounds, which are the four‐coordinate boron complexes containing the mixed phenol‐pyridyl group, have been studied by theoretical calculation. They can function as charge transport materials and emitters, with high efficiency and stability. To reveal the relationship between the structures and properties of these bifunctional or multifunctional electroluminescent materials, the ground and excited state geometries were optimized at the B3LYP/6‐31G(d), HF/6‐31G(d), and CIS/6‐31G(d) levels, respectively. The ionization potentials (IPs) and electron affinities (EAs) were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The lowest excitation energies, and the maximum absorption and emission wavelengths of these compounds were calculated by time‐dependent density functional theory method. As a result of these calculations, the values of HOMO, LUMO, energy gaps, IPs, EAs, and the balance between the hole‐ and electron‐transfer are greatly improved with the substitution of carbazole in compound 6 . The calculated emission spectra of the seven studied molecules can almost cover the full UV‐vis range (from 447.4 to 649.3 nm). Also, the Stokes shifts are unexpectedly large, ranging from 139.4 to 335.1 nm. This will result in the relatively long fluorescence lifetimes. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Isothermal Titration Calorimetry and Theoretical Studies on Host-guest Interaction of Ibuprofen with <Emphasis Type="Bold">α</Emphasis>-, <Emphasis Type="Bold">β</Emphasis>- and <Emphasis Type="Bold">γ</Emphasis>-Cyclodextrin

Thermodynamic parameters for formation of the inclusion complexes of α-, β- and γ-cyclodextrin (α-, β- and γ-CD) with ibuprofen (BF) in Tris-HCl buffer solutions (pH=7.0) have been determined by isothermal titration calorimetry (ITC) with nanowatt sensitivity, and the inclusion structures have been investigated by using ¹H-NMR spectra at 298.15 K. A theoretical study on the inclusion processes between BF and CDs has been performed with the B3LYP/6-31G*//PM3 method in order to investigate the formation mechanism of the inclusion complexes. An analysis of the thermodynamic data indicates that the stoichiometries of α-, β- and γ-CD with BF are all 1:1 and formation of the inclusion complexes α-CD⋅BF and β-CD⋅BF are driven by enthalpy and entropy, whereas formation of γ-CD⋅BF is an entropy driven process. The ¹H-NMR spectra provide clear evidence for the inclusion phenomenon, and show that the isobutyl group and aromatic ring of the guest molecule are trapped inside the cavity of the CDs. Theoretical calculations suggest that the complex formed by the BF molecule entering into the cavity of the CD molecule from the wide side is more stable than that from the narrow side.     

基于PAMAM/聚2,6-吡啶二甲酸膜DNA电化学生物传感器的制备及对禽病毒基因检测的研究

以铂电极上聚合的2,6-吡啶二甲酸(PDC)膜组装G5.0树状高分子(PAMAM)固定ssDNA探针, 制备了一种新型的DNA电化学生物传感器. 用[Fe(CN)6]3－/4－作氧化还原指示剂, 以电化学交流阻抗和循环伏安技术对探针ssDNA的固定和杂交进行了表征. 实验表明, 当ssDNA在复合膜上固定及与其互补序列杂交后, 电极表面的传递电阻(Ret)依次增大. 因此, 可以利用Ret的明显差异, 以此固定探针的修饰电极, 对互补序列DNA进行无标记交流阻抗检测. 基于该生物传感器结合交流阻抗技术对禽病毒基因进行检测, 在优化实验条件下, 靶基因ssDNA-2在2.0×10－11～1.0×10－8 mol•L－1线性范围内, 其浓度与电极表面的电子传递电阻(Ret)之间呈良好的线性关系, 检测限为3.6×10－12 mol•L－1. 表明该方法为病毒灵敏地检测提供了一个有益的传感平台.     

Bounded Tiles in ℚp are Compact Open Sets

Any bounded tile of the field Qp of p-adic numbers is a compact open set up to a set of zero Haar measure.In this note,we present two simple and direct proofs of this fact.     

基于企业网络舆情的客户满意度分析及管理方法

社交网络平台的迅速发展,促使网络舆情成为企业获取商业情报、扩大竞争优势的重要信息来源。本文针对网络舆情环境下的企业客户关系管理问题展开研究。通过构建企业客户推动式信息反馈模型,描述了企业客户、网络用户与企业网络舆情间的联系,并依据信息反馈模型,提出变尺度聚类算法。该算法将传统聚类方法的求解过程由单一尺度分析扩展到多尺度分析,克服了实际数据聚类应用过程中的聚类结果特征不显著问题。本文选取新浪微博作为数据源,利用企业网络舆情数据集和企业客户数据集进行数据分析实验。实验结果表明,企业可以通过获取与其主营业务相关的网络舆情信息,实现客户满意度预测;同时,变尺度聚类算法结果能够为企业进一步制定销售战略和销售战术提供决策支持。     

过阻尼布朗棘轮的斯托克斯效率研究

根据随机能量理论解析得到阻尼环境中布朗粒子的概率流和斯托克斯效率,并进一步研究布朗粒子的输运性能.详细讨论了空间的不对称性、外偏置力及外势结构等对棘轮定向输运的影响.研究发现,合适的外偏置力能使棘轮的定向输运达到最强.通过调节外势的不对称性可使棘轮中粒子的运动反向,当选择合适的空间不对称性时布朗粒子的反向输运可获得最强.此外,一定条件下合适的外势高度也能增强棘轮输运,且能使粒子克服黏滞阻力的斯托克斯效率达到最大.所得结论能够启发实验上设计合适的外势及外偏置来优化布朗棘轮的定向输运性能,并为生物纳米器件的研制提供一定的理论参考.