标准物质新老定义的理解与比较

近年来,国际标准化组织/标准物质委员会(ISO/REMCO)对标准物质进行了重新定义,国际计量学词汇第3版(VIM3)对标准物质赋予新的定义,两组定义存在着一定的差异。对标准物质的新老定义进行了比较。     

蓄热调温石蜡相变微胶囊的制备及性能

采用界面聚合法,以甲苯2,4-二异氰酸酯和哌嗪为反应单体、30号相变石蜡为芯材,制得了一种智能纺织品用蓄热调温相变微胶囊。通过红外光谱、扫描电镜、差示扫描量热仪对微胶囊的化学组成、形貌和蓄热性能进行了表征,测试了其耐热和耐溶剂性。结果表明:所得微胶囊主要为球形,表面光滑,平均粒径为10.6μm,对w=0.40的NaOH溶液、w=0.60的H2SO4溶液、无水乙醇、丙酮稳定,能被甲苯、二甲基甲酰胺、乙醚破坏。相变潜热为118 J/g,石蜡在微胶囊中的质量分数为84%。     

两个基本计数原理的教学设计及教后反思

一、教材分析本节课是高中数学选修2—3第一章计数原理中1.1分类加法计数原理与分步乘法计数原理,本小节共需4课时,这节课是第一课时.分类加法计数原理、分步乘法计数原理这两个计数原理是人们在大量实践的基础上归纳出来的基本规律.它们不仅是推导本章1.2排列与组合中排列数、组合数计算公式的依据,也是求解排列、组合问题的基本思想,且教材将排列、组合及二项式定理的研究都作为两个计数原理的典型应用而设置的.可见,其基本思想方法贯穿本章内容的始终,因而,它们是学好本章内容的关键.     

金属线膨胀系数、德拜温度和杨氏模量之间关联特性

利用解析势能函数研究了FCC,HCP及BCC共19种金属的线膨胀系数、德拜温度和杨氏模量等之间的关联性,给出了金属的德拜温度和杨氏模量的解析计算式,其理论计算值与实验值符合较好.     

Quasibound states in graphene quantum-dot nanostructures generated by concentric potential barrier rings

We study the quasibound states in a graphene quantum-dot structure generated by the single-, double-, and triple-barrier electrostatic potentials. It is shown that the strongest quasibound states are mainly determined by the innermost barrier. Specifically, the positions of the quasibound states are determined by the barrier height, the number of the quasibound states is determined by the quantum-dot radius and the angular momentum, and the localization degree of the quasibound states is influenced by the width of the innermost barrier, as well as the outside barriers. Furthermore, according to the study on the double- and triple-barrier quantum dots, we find that an effective way to generate more quasibound states with even larger energy level spacings is to design a quantum dot defined by many concentric barriers with larger barrier-height differences. Last, we extend our results into the quantum dot of many barriers, which gives a complete picture about the formation of the quasibound states in the kind of graphene quantum dot created by many concentric potential barrier rings.     

Determination of the series resistance under the Schottky contacts of AlGaN/AlN/GaN Schottky barrier diodes

Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) were fabricated,and the gate and the source of the HFETs consisted of AlGaN/AlN/GaN Schottky barrier diodes (SBDs).Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs,the series resistance under the Schottky contacts (RS) was calculated using the method of power consumption,which has been proved to be valid.Finally,the method of power consumption for calculating R S was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs.It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AlGaN/AlN/GaN SBDs and the AlGaN/AlN/GaN HFETs.     

一节高中数学课堂提问的实证研究

一、研究的目的和意义 高中数学教学的目的是进一步培养和发展学生的数学品质,养成良好的思维习惯,从而提高分析问题、解决问题的能力．在大力倡导素质教育的今天,这种观点显得尤为重要,它直接影响了高中数学课堂的教学模式．因此,如何在课堂教学中既教给学生知识又培养学生的能力是每个教师都关心的问题．笔者认为在课堂教学中,课堂提问是一种行之有效的手段,也是所有教师普遍采用的一种课堂组织形式．设置有效的问题能充分调动学生学习的积极性,让学生积极参与到教与学的互动过程中来,让学生变成课堂的主体,在这过程中实现知识和能力的双丰收,因此数学课堂教学中必须预设有效问题．     

＂五严＂背景下高中数学作业布置的思考

作业是巩固知识的一种手段,是课堂教学的一个延伸,它既具有复习巩固、内化知识的作用,又具有拓展延伸、深化知识的功能,还具有评价、反馈的效应,因此它是师生交流互动的一个重要环节和有效方式．而长期以来,教师往往把作业的功能仅仅定位于“巩固所学知识”与“强化方法技能”上,使得学生陷入了机械重复的“数学题海”中,苦不堪言,严重禁锢了学生潜能的发展．     

A Spectral Coupled-Mode Formulation for Sound Propagation around Axisymmetric Seamounts

A spectral coupled-mode solution of the three-dimensional （319） acoustic field generated by a point source in the presence o[ an axisymmetric seamount is developed. Based on the same theoretical foundation as the for- mulation presented by Taroudakis [3. Comput. Acoust. 4 （1996） 101], the present approach combines a spectral decomposition in azimuth with a coupled-mode theory for two-way range-dependent propagation. However, the earlier formulations are severely limited in terms of frequency, size and geometry o[ the seamount, the seabed composition, and the distance between the source and the seamount, and are there/ore severely limited in regard to realistic seamount problems. Without changing the fundamental theoretical foundation, the present approach applies a number of modifications to the formulation, leading to orders of magnitude improvement in numerical efficiency for realistic problems. Therefore, realistic propagation and scattering scenarios can be modeled, including effects of seamount roughness and realistic sedimentary structure.     

腔QED技术实现最优非对称经济型1到3的相位协变克隆方案

本文提出一个在腔QED中实现最优非对称经济型1到3相位协变克隆的可行性方案,这种克隆不需要辅助粒子.在这个方案中,三个原子中的两个同时与腔场发生作用,并且受经典场的作用.此方案不受腔场的态和腔衰变的影响,因此,在实验上是可能实现的.