机械合金化工艺对Fe-Ni合金显微结构的影响

对机械合金化制备的Fe-Ni粉体利用X射线衍射(XRD)进行分析，得到了不同Ni含量和不同球磨时间Fe-Ni纳米晶的XRD谱．实验表明，w(Ni)=10％和20％时，Ni溶入Fe晶格，分别在球磨20h和50h后形成单一的a(bcc)相；w(Ni)=50％时，其先后经历了γ(fcc)→←a(bcc)正逆转变，在球磨120h后最终形成单一γ(fcc)相．无论是a(bcc)相还是γ(fcc)相．它们的固溶度均比块体Fe-Ni合金显著提高．w(Ni)=35％时，则始终是两相共存．对试样的XRD谱采用3种不同的方法测定了Fe-Ni粉体的晶粒尺寸和显微畸变，发现经球磨20h后，不同Ni含量的粉体均呈纳米结构，并随球磨时间延长，Fe-Ni纳米晶的晶粒尺寸下降而显微畸变上升．     

N-P基本引理的严密化、标准化研究——兼评国内某些教材对此定理的引述与证明

我国目前所引述的Neyman-Pearson基本引理(下简称N-P引理),可谓是五花八门、应有尽有.就其证明的严密性而言,要么只给出了一致最大功效检验(下简记UMPT)函数的非随机化检验形式,要么仅局限于其充分性的证明.文章从N-P引理的本质特征出发,把φ的随机化检验形式,和引理的充要条件的证明统一在一起,因而形式更为完美,证明更加严谨,并且还给出了它直观的图像表示和扩大了检验函数的集类φ.     

多元Jensen不等式及其应用

简明扼要地给出了多元凸函数的最一般概念,简化了Jensen加权不等式及Jensen积分不等式的证明,定理的证明方法采取了由特殊到一般的归纳证法,导出了某些特殊不等式作为其应用.     

欧拉应用分析于数论研究综述

扼要而又系统地综述了欧拉应用分析于数论研究的早期工作.其中有许多激动人心的数论公式与定理.例如,关于自然数方幂倒数的无穷和公式、关于Zeta函数的欧拉乘积公式、欧拉对4平方数定理的思考与证明,及其欧拉在解决这些问题的同时所创造的有关数论函数、分拆函数和理想数的概念等等.这些概念、定理或公式都是欧拉首先发现并加以精确论证的.与众不同的是,他善于把一个纯数论问题变换为一个分析问题,事实上欧拉的想法更具一般性.它足以展示欧拉的数学工作的深刻与广博.最后我们引述了欧拉发现的数论中几个著名的级数公式和二次互反性定律,它们都是欧拉在数论文库中留给我们的宝贵遗产.     

From Pingcheng to Luoyang-Substantiation of the climatic cause for capital relocation of the Beiwei Dynasty

Emperor Tuoba Hong1) of Beiwei relocated the capital from Pingcheng to Luoyang approximately 1500 years ago. Most historians speculate that his motivation was based on considerations of politics, economics, military, history, and Chinese culture. However, Sima Guang, a famous historian during the Song Dynasty, claimed 1000 years ago that cold climate was the cause of this historical event. In order to assess the credibility of Sima Guang's claim, this research examines related ancient documents and the recent frost data for a comparative study. It is found that the mean minimum temperature in Pingcheng during 479AD～509AD is estimated to be lower than present minimum temperature by 2.48 ℃.     

From Pingcheng to Luoyang—Substantiation of the climatic cause for capital relocation of the Beiwei Dynasty

1　ProblemsarousedChinesehistoriansoftenassertedthatEmperorTuobaHong’sdecisiontomovehiscapitalfromPingchengtoLuoyangin 4 94ADwasmotivatedbyhispersonalbiastowardsChineseidealsandvalues ,alongwithotherconsiderationssuchaspolitics ,mili tarydefense ,historyandculture .ThefactthattheEmperorwantedtochangethetriballifestylefromnomadictoagricultural[1] wasconsideredaveryprob ablemotivationfortherelocation .However,SimaGuang (10 19～ 10 86AD)wroteinhisbookZizhi tongjianthat“theEmperorofWeimove…     

方孔炤“《崇祯历书》约”来源新证

在《周易时论合编图象几表》中,方孔炤(1591—1655年)记载他对《崇祯历书》"故约其概",使后人误认为"《崇祯历书》约"是《崇祯历书》的约略或概要。研究发现它大量引用或改写王英明《重刻历体略》内容,与《崇祯历书》无关。王英明于万历四十年(1612年)撰《历体略》,两年后病逝。崇祯十二年(1639年)次子王□初刊《历体略》。顺治三年(1646年)汲古阁重刻时,增订的补注中提到《崇祯历书》,因而误导方孔炤,误认他采用的《重刻历体略》内容来自《崇祯历书》的概要,而名为"《崇祯历书》约"。基于此一发现,我们得重新评估方孔炤对西学的认识。     

Isothermal section of ternary Sn-Zn-Ni phase equilibria at 250℃

Ternary Sn-Zn-Ni alloys were prepared and equilibrated at 250℃for 4-15 weeks.The phases formed in these equilibrated alloys were determined experimentally.The isothermal section of Sn-Zn-Ni system was constructed,based on the phase diagrams of the three constituent binary systems and the ternary phase equilibria data,determined in this study and referenced in literatures.12 single-phase regions were identified in the Sn-Zn-Ni ternary system at 250℃,including the three ternary compounds,δ,τ_1 andτ_2.There...     

Improved performance of GaN-based light-emitting diodes by using short-period superlattice structures

An InGaN/GaN multiple-quantum-well (MQW) light-emitting diode (LED) with a ten-period i (undoped) -InGaN/p (Mg doped) -GaN (2.5 nm/5.0 nm) superlattice (SL) structure, was fabricated. This SL structure that can be regarded as a confinemen t layer of holes to enhance the hole injection efficiency is inse rted between MQW and p-GaN layers. The studied LED device exhibits better current spreading performance and an improved quality, compared with a conventional one without SL structure. Due to the reduced contact resistance as well as more uniformity of carrier s injection, the operation voltage at 20 mA is decreased from 3.32 to 3.14 V. A remarkably reduced reverse-biased leakage current (10^-7?10^-9 A) and higher endurance of the reverse current pulse are found. The measured output power and external quantum efficiency (EQE) of the studied LED are 13.6 mW and 24.8%, respectively. In addition, significant enhancement of 25.4% in output power as well as increment of 5% in EQE for the studied devices is observed, as the studied devices show s uperior current spreading ability and reduction in dislocations offered by the SL structure.