电化教学手段在物理教学中的作用

随着科学技术的发展和人民生活水平的不断提高,电脑在人们的日常生活、工作、学习中已经成为一种不可缺少的常用工具.对学校而言,建立先进的电化教学网络和要求教师运用电化教学手段进行授课已经成为学校教学改革的中心任务.这是时代进步的标志,使传统的教学方法找到了更为有效的辅助手段,大大地提高教学质量,为实现对     

DESIGN OF A NOVEL 2-D UNIPLANAR CRLH-TL STRUCTURE

A novel uniplanar 2-D composite right/left-handed transmission line (CRLH-TL) structure is proposed based on a general transmission line theory and the way to increase the relative operating bandwidth in the left-handed (LH) region and lower the LH operating frequency is illustrated. In addition, a new method to extract parameters and calculate the Bloch impedance of the structure is presented. Numerical results of the dispersion as well as the extracted parameters are given, which are calculated based on full-wave simulation. The present 2-D uniplanar CRLH-TL structure is applicable to 2-D left-handed materials in lower and wider LH frequency range. Supported by the National Natural Science Foundation of China (No. 60371010) (No. 60471037) (No. 63531020)     

求解非对称线性方程组的QMRGCGS方法

1 引言 求解非对称线性方程组Ax=b的双共轭梯度方法(BCG)[3]和它的变形共轭梯度平方方法(CGS)[6]都有典型的不规则收敛行为,后来Freund和Nachtigal提出一种BCG类方法,即拟极小剩余方法(QMR)[7],用来补救BCG方法的收敛性并且产生了光滑的收敛曲线。然而,象BCG方法一样,QMR方法要用到系数矩阵A及其转置A~T与向量的乘积,为了解决这一问题,Freund提出TFQMR方法,此方法具有拟极小剩余性,同时不需用到A~T与向量的乘积。     

哌仑西平的单扫描示波极谱法测定

本报道一种测定哌仑西平的单扫描示波极谱法，在０．１ｍｏｌ／ＬＮＨ４Ｃｌ－ＮＨ３．Ｈ２Ｏ（ｐＨ８．０±０．１）缓冲液中，哌仑西平有一极谱还原波，其峰电位为－１．５１Ｖ（ｖｓ．ＳＣＥ），其一阶导数峰高与哌仑西闰浓度在６．６×１０＾－７－４．６×１０＾－６ｍｏｌ／Ｌ（ｒ＝０．９９８１）和６．６×１０＾－６－１．６×１０＾－５ｍｏｌ／Ｌ（ｒ＝０．９９９１）范围内有线性关系，检测限为３．４×１０－７ｍｏｌ     

A convenient catalytic approach to synthesize straight boron nitride nanotubes using synergic nitrogen source

Straight boron nitride nanotubes (BNNTs) with pure hexagonal phase were conveniently prepared by heating the mixture of Mg(BO₂)₂ · H₂O, NH₄Cl, NaN₃ and Mg powder in an autoclave at 600 °C for 20–60 h. These BNNTs had diameters mainly ranging 30–300 nm and lengths up to 5 μm, and a majority of them had at least one closed end. Besides the traditional end tips, additional cone-like tips were frequently found to be attached on the BNNTs. The effects of temperature, reactants and the possible mechanism of the catalytic formation of the BNNTs are discussed.     

光固化阻燃单体、树脂合成及其阻燃机理研究

本文综述了过去十余年间中国科技大学施文芳教授研究组在光固化阻燃技术领域的工作成果，主要包括活性单体、稀释剂、光固化树脂配方等体系，品类有磷酸酯类单体、含磷丙烯酸酯、超支化丙烯酸酯树脂、膦酸酯类单体和树脂、丙烯酸化环状磷腈、甲基丙烯酸化三聚氰胺、含磷环氧单体等十余种。同时介绍了这些配方体系的合成、性能和应用方法，以及对其热降解、阻燃性能评价和阻燃机理的研究。     

Kinetics study of thermal decomposition of epoxy resins containing flame retardant components

Hyperbranched polyphosphate ester (HPPE) and phenolic melamine (PM) were blended in different ratios with a commercial epoxy resin to obtain a series of flame retardant resins. The thermal decomposition mechanism of their cured products in air was studied by thermogravimetric analysis and in situ Fourier-transform infrared spectroscopy. The degradation behaviours of epoxy resins containing various flame retardant components were found to be greatly changed. The incorporation of phosphorus and nitrogen compounds improved the thermal stability at elevated temperature. The kinetics of thermal decomposition was evaluated by Kissinger method, Flynn-Wall-Ozawa method and Horowitz-Metzger method. The results showed that the activation energy at lower degree of the degradation decreased by the incorporation of flame retardant components, while increased at higher degree of the degradation.     

DNA Degradation of Genetically Modified Cottonseed Meal During Feed Processing

The effects of dry heating, wet heating, and extrusion on the degradation of DNA in cottonseed meal (CSM) were studied using polymerase chain reaction (PCR) and real-time PCR approach. Both the sad1 DNA, ranging between 128 and 883 bp in size, and the cry1Ab/c gene, ranging between 183 and 652 bp in size, were detectable in all dry-heated CSM and cottonseed. During wet heating, the sad1 gene (≥883 bp) and the cry1Ab/c (≥952 bp) gene were thoroughly degraded at 105 and 120 °C, respectively. Sizes from 128 to 530 bp for the sad1 gene and sizes from 183 to 652 bp for the cry1Ab/c gene were detected during extrusion at temperatures ranging from 75 to 135 °C. Fragments ≤883 bp for the sad1 gene and ≤952 bp for the cry1Ab/c gene were detected in all of the extruded samples with water content varying between 26 and 34 %. The copy number ratio of cry1Ab/c to sad1 in samples of Bt cottonseed meal decreased rapidly when the temperature increased during the heating process. In conclusion, feed processing markedly degrades the larger DNA fragments of sad1 and cry1Ab/c, with high temperature and water content being the main factors for that degradation.     

Diastereoselective synthesis of oxazolo[3,4-b]tetrahydroisoquinolin-3-ones via Lewis acid TMSOTf-mediated Pictet–Spengler reaction

An alternative and efficient method to stereoselectively synthesize oxazolo[3,4-b]tetrahydroisoquinolin-3-ones via a Pictet–Spengler reaction promoted by Lewis acid TMSOTf from readily available (S)-4-benzyl-2-oxazolidinone with various aromatic, aliphatic, and cyclic aldehydes under room temperature is described.