坩埚下降法生长白宝石晶体的研究

本文报道了了坩埚下降法生长大尺寸白宝石单晶。我们使用大尺寸异型钼坩埚，高屯氧化铝原料，在中性气氛下，结晶区温度梯为２５－３０℃／ｃｍ，生长速度为０．８－１．８ｍｍ／ｈ，生长方向选Ｃ面「０００１」取向，成功生长出直径８０ｍｍ，高度９００ｍｍ的完整透明的白宝宝石单晶，在３００－５５００ｎｍ范围内，其光学透过率均在８０％以上。     

Finite superconducting square wire-network based on two-dimensional crystalline Mo2C

Superconducting wire-networks are paradigms to study Cooper pairing issues, vortex dynamics and arrangements. Recently, emergent low-dimensional crystalline superconductors were reported in the minimal-disorder limit, providing novel platforms to reveal vortices-related physics. Study on superconducting loops with high-crystallinity is thus currently demanded. Here, we report fabrication and transport measurement of finite square-network based on two-dimensional crystalline superconductor Mo₂C. We observe oscillations in the resistance as a function of the magnetic flux through the loops. Resistance dips at both matching field and fractional fillings are revealed. Temperature and current evolutions are carried out in magnetoresistance to study vortex dynamics. The amplitude of oscillation is enhanced due to the interaction between thermally activated vortices and the currents induced in the loops. The driving current reduces the effective activation energy for vortex, giving rise to stronger vortex interaction. Moreover, by the thermally activated vortex creep model, we derive the effective potential barrier for vortex dissipation, which shows well-defined correspondence with structures in magnetoresistance. Our work shows that low-dimensional crystalline superconducting network based on Mo₂C possesses pronounced potential in studying the modulation of vortex arrangements and dynamics, paving the way for further investigations on crystalline superconducting network with various configurations.     

北京大学1.7 MV串列静电加速器的离子注入/辐照实验系统

北京大学1.7 MV串列静电加速器运行至今已有三十多年。该加速器配备有高频电荷交换负离子源和铯溅射负离子源,能够引出从H到 Au之间 的大部分元素的离子。离子能量可被加速至几百keV到若干MeV,主要开展离子注入/辐照实验和卢瑟福背散射(RBS)和沟道分析等离子束分析工作。基于辐照实验需求,建立了高温辐照系统,温度最高可达950 ℃。为了实现更加精确的离子注入,设计了直接式与间接式两种法拉第杯结构,使束流扫描面积精确控制,并且在测量束流强度时除了抑制次级电子,还考虑到了次级正离子的影响。利用不同能量的Au离子在单晶Si片上进行了注入实验,通过RBS分析显示测量剂量与期望剂量误差在4%以内,此外,注入均匀性的测试表明注入剂量的相对标准偏差为2%。     

对一道习题解法的探究

(一)题目:通过点(8,6)引四条直线与ox轴的夹角之比为1:2:3:4,已知第二条直线的方程为3x-4y=0,求其余三条直线的方程。 (华东师大数学系编《解析几何习题集》(以下简称甲书)P_71。18题;翟连林等主编《中学数学习题集第三册》(以下简称乙书)P230第7题。) (二)上述两书的解答乙书给出的解答如下: 设四条直线为l_1、l_2、k_3、l_4,倾斜角顺次为α、2α、3α、4α。由l_2的方程3x-4y=0(?)tg2α=3/4即2tgα/(1-tg~2α)=3/4(?)tgα=1/3,tga=-3(舍)(?)tg3α=13/9,tg4α=24/7∴l_1:y-6=(x-8)/3即x-3y+10=0     

高三复习代数训练题(二)

选择题 :本大题共 1 2小题 ;每小题 5分 ,共 6 0分 .在每小题给出的四个选项中 ,只有一项是符合题目要求的 .1　已知θ为锐角 ,则复数ｃｏｓθ -ｉｓｉｎθ的辐角主值为 (　　 )(Ａ)θ .　　　　　　 (Ｂ)π θ .(Ｃ) 2π -θ.(Ｄ) -θ.2　ｌｏｇ(ａ -1) (2ｘ - 1 ) >ｌｏｇ(ａ -1) (ｘ - 1 )成立的充要条件是 (　　 )(Ａ)ｘ >0 .(Ｂ)ｘ >0 ,ａ >2 .(Ｃ)ｘ >1 ,ａ >1 .(Ｄ)ｘ >1 ,ａ >2 .3　若Ｓｎ 是公差为ｄ的等差数列 {ａｎ}的前ｎ项和 ,且Ｓ10 =4Ｓ5 ,则ａ1ｄ的值为 (　　 )(Ａ) 12 . (Ｂ) 2 .(Ｃ) 14. (Ｄ) 4.4　等比数列 {ａｎ}的前…     

New band structures in ~（107）Ag

High spin states in ¹⁰⁷Ag are studied via the ¹⁰⁰Mo(¹¹B, 4n)¹⁰⁷Ag reaction at an incident beam energy of 60 MeV. Prompt γ-γ coincidence and DCO ratios are measured by the detector arrays in CIAE. The level scheme has been updated and a new negative band belonging to ¹⁰⁷Ag is identified. The new negative side band has been constructed and its configuration is tentatively assigned to πg_9/2 νh_11/2(g_7/2/d_5/2).     

对一道2010年高考题的探究

2010年高考数学江苏卷第18题： 在平面直角坐标系XOy中,如图1,已知椭圆x^2/9＋y^2/5=1的左右顶点为A,B,右焦点为F,设过点T（t,m）的直线TA,     

Bridgman法生长Cr∶LiCAF晶体及其闪光灯泵浦性能

本文报道了用Bridgman法生长的优质大尺寸Cr∶LiCAF晶体及其闪光灯泵浦性能研究.晶体尺寸达φ10×120mm和φ20×100mm,光学质量优良.用氙灯泵浦φ4×70mm的Cr∶LiCAF激光棒,在注入能量为137J时,获得了1.84J的能量输出,测得晶体的斜效率为2.38%,无损耗效率为4.31%.     

Microstructure and hardening effect of pure tungsten and ZrO2 strengthened tungsten under carbon ion irradiation at 700℃

Microstructure evolution and hardening effect of pure tungsten and W-1.5%ZrO₂ alloy under carbon ion irradiation are investigated by using transmission electron microscopy and nano-indentation. Carbon ion irradiation is performed at 700 ℃ with irradiation damages ranging from 0.25 dpa to 2.0 dpa. The results show that the irradiation defect clusters are mainly in the form of dislocation loop. The size and density of dislocation loops increase with irradiation damages intensifying. The W-1.5%ZrO₂ alloy has a smaller dislocation loop size than that of pure tungsten. It is proposed that the phase boundaries have the ability to absorb and annihilate defects and the addition of ZrO₂ phase improves the sink strength for irradiation defects. It is confirmed that the W-1.5%ZrO₂ alloy shows a smaller change in hardness than the pure tungsten after being irradiated. From the above results, we conclude that the addition of ZrO₂ into tungsten can significantly reduce the accumulation of irradiated defects and improve the irradiation resistance behaviors of the tungsten materials.     

高考试题新特点 备考复习新策略

高考内容和形式的改革正加大步伐 ,1999年高考数学试卷比较好地体现了高考内容改革的基本思路 ,怎样把握理解 1999年高考数学试卷的基本特点 ,根据高考改革的形势采取新的备考策略 .是我们进行 2 0 0 0年备考应研究的课题 .下面就两个问题谈谈本人的看法 ,以求指正 .1　 1999年高考数学试卷的基本特点1999年高考数学试题的最大特点是“新” .把数学问题纳入新情景之中 ,既体现公平竞争的原则 ,又使具有创新能力的学生发挥最大的潜能 .学生反映题目较难 ,其实难就难在新上 .除了题量减少、把基本公式置于卷首形式创新外 ,还表现在如下方面 :1…