不同年份老香黄定量分析及其化学模式识别研究

建立了一种联合化学标志物定量分析和化学模式识别技术快速判别不同年份老香黄的方法,并筛选其差异性化学标志物。采用超高效液相色谱-串联质谱(UPLC-MS/MS)建立了对21种与老香黄相关的化学标志物及其内标物山柰酚-3-O-芸香糖苷的检测方法,该方法的线性关系良好,灵敏度高,专属性强,可用于对不同年份老香黄的区别分析。根据检出的不同年份老香黄的15个化学标志物含量,结合主成分分析(PCA)、聚类分析(HCA)、正交偏最小二乘法判别分析(OPLS-DA)法进行分析,可快速判别不同年份的老香黄,并筛选出6个差异性化学标志物。结果表明,贡献最大的差异化学标志物为5,7-二甲氧基香豆素,其中0年含量为(47.465±1.987)μg/g,3年含量为(17.069±0.542)μg/g,5年含量为(11.073±1.862)μg/g,8年含量为(41.905±2.240)μg/g,10年含量为(21.079±2.270)μg/g,15年含量为(43.267±2.432)μg/g,20年含量为(51.711±1.439)μg/g,该标志物的含量在一定程度上体现了不同年份的老香黄,可用于区分老香黄的贮藏年份。为了验证方法的可靠性,进行盲样适用性能力测试,测定结果所得年份和厂家提供的保持一致。该研究给市面上老香黄的质量控制及其品质鉴定提供了快速可靠的方法。     

铁路围岩分类专家系统中的不确定性推理问题

本文将专家的经验分类标准与需要评判的围岩用模糊数学中择近原则的方法进行模糊模式识别,对专家评判中有关因素采用因素关系图描述,将被评定的围岩视为论域上的一个模糊子集,把推理过程抽象为多维论域上确定隶属度的过程,进而提出用连续隶属函数进行围岩类别的模糊推理。最后,以隶属度的形式,给出评判的分类结果。     

基于神经网络的口腔非线性动力学系统建模

神经网络方法是用于非线性动力学系统建模的有效方法，本文针对多层神经网络结构，运用递推预报误差（ＲＰＥ）算法对离散非线性动力学系统进行了辨识研究，并对口腔非线性动力学系统进行了神经网络动态建模，为了解语音和实用化的语音识别提供了良好的基础。     

从珠心算起步 走上多彩多姿的人生路——记珠心算选手吴宇恩清华园生活剪影

吴宇恩,小时是广西少数民族珠心算选手,现清华大学在读博士研究生。他是广西龙胜各族自治县侗族人家的子弟,今年26岁,在清华园里他已住了长长的八个年头。回顾曾经走过的路,他感慨万千,常常会回想,自己是怎样走进清华园这个科学知识殿堂的。在一次历届同学的座谈会上,同学们很想分享吴宇恩的成长体会,向他提出:你为什么会选择学习珠     

课外练习

初一年级1.已知:x=2000/2001,y=2001/2002,试比较x与y的大小.     

Dependence of Structure and Haemocompatibility of Amorphous Carbon Films on Substrate Bias Voltage

Tetrahedral amorphous hydrogenated carbon (ta-C:H) films on Si(lO0) substrates were prepared by using a magnetic-field-filter plasma stream deposition system. Samples with different ratios of sp^3-bond to sp^2-bond were obtained by changing the bias voltage applied to the substrates. The ellipsometric spectra of various carbon films in the photon energy range of 1.9-5.4eV were measured. The refractive index n and the relative sp^3 C ratio of these films were obtained by simulating their ellipsometric spectra using the Forouhi-Bloomer model and by using the Bruggeman effective medium approximation, respectively. The haemocompatibility of these ta-C:H films was analysed by observation of platelet adhesion and measurement of kinetic clotting time. The results show that the sp^3 C fraction is dependent on the substrate bias voltage, and the haemocompatibility is dependent on the ratio of sp^3-bond to sp^2-bond. A good haemocompatibility material of ta-C:H films with a suitable sp^3 C fraction can be prepared by changing the substrate bias voltage.     

Si衬底GaN基LED的结温特性

结温是发光二极管的重要参数之一,它对器件的内量子效率、输出功率、可靠性及LED的其他一些性能有很大的影响。首次报道Si衬底GaN基LED的结温特性。利用正向压降法测量Si衬底上GaN基LED的结温,通过与蓝宝石衬底上GaNLED的结温比较,发现Si衬底GaNLED有更低的结温,原因归结为Si有更好的导热性。同时也表明:用Si作GaNLED的衬底在大功率LED方面具有更大的应用潜力。     

巧用特殊法 妙解课本题

根据题目条件的信息,选用恰当的化简技巧,是解决课本二次根式题的关键.一、变换所求,以简驭繁例1已知x=1/2(7~(1/2)+5~(1/2)),y=1/2(7~(1/2)-5~(1/2)),求x2-xy+y2的值.解当x=1/2(7~(1/2)+5~(1/2)),y=1/2(7~(1/2)-5~(1/2))时,有x-y=5~(1/2),xy=1/2.∴原式=(x-y)2+xy=(5~(1/2))2+1/2=11/2.二、化简变形,化难为易例2已知x=(3~(1/2)+2)/(3~(1/2)-2),y=(3~(1/2)-2)/(3~(1/2)+2),求     

Growth Mechanism of Vertically Aligned Ag（TCNQ） Nanowires

Highly oriented Ag(TCNQ) nanowires have been prepared on Si(111) wafer at 1O0℃ by the vapour-transport reaction between silver and TCNQ without any other catalyst. X-ray diffraction analysis shows that the composition and crystal structure of the obtained nanostructure were Ag(TCNQ) crystalline. Most Ag(TCNQ) nanowires were grown uniformly and vertically on the substrate with diameters ranging from 50 to 30Onto and the lengths measuring from 2 to 50μm by scanning electron microscopy. Ag particles were observed on the substrate from pure thin Ag film heated under the same conditions as used in synthesizing the nanowires. Nucleation and short Ag(TCNQ) nanowires were prepared by controlling the reaction time, providing direct evidence of the growth mechanism in a nanometre scale. The growth process was explained according to the vapour-liquid-solid model. The gradient of temperature and the densely distributed Ag particles may contribute to the vertically aligned growth. These results will be helpful for the controllable synthesis of Ag(TCNQ) nanowires.     

数字竞赛题的几个新知识

在近几年的数学竞赛试题中,出现了一些新亮点——以新知识为背景的题目.它通过介绍一种课本以外的知识,现学现解,以体现同学们分析、解决问题的能力.下面以2004年“创新杯”数学竞赛题为例,供大家参考.