环自发磁化的几个物理问题的研究

本文总结了我们对π环自发磁化的几个相关物理问题的研究结果.首先分析计算了有一个结是π结的三结π环的自发磁化,发现与单结π环明显不同,当β=2πLIc/φ0趋于零时,环中仍有自发磁化.详细计算表明随温度下降,β增大,自发磁化磁矩很快上升并趋于φ0/2,能和实验很好的符合.继而运用Runge-Kutta四步积分法分析了一个双结π环电路在输入脉冲电流触发下自发磁化电流的翻转过程.并在此基础上计算了电感系数,输入脉冲电流的峰值和峰宽等因素对翻转过程的影响,获得了自发磁化电流在电触发下翻转的一般规律.最后分析和计算了耦合双π环的自由能,结果表明当两个π环自发磁化方向相反时系统的能量较低,还证明了互感为0时的反向自发磁化是来自量子效应.     

氧化钪/氧化硅反射薄膜的355 nm激光损伤特性

采用电子束蒸发法制备了Sc2O3单层薄膜和Sc2O3/SiO2多层反射膜.利用原子力显微镜、X射线衍射仪等方法对薄膜的表面和结构进行,研究.采用355 nm激光研究了Sc2O3/SiO2多层薄膜的损伤特性和预处理效应,并对Sc2O3的损伤原因进行了分析.实验发现,Sc2O3具有较宽的带隙,薄膜结构为立方相,影响Sc2O3/SiO2 多层反射膜抗损伤能力的主要因素足材料的纯度.     

不同沉积参量下ZrO2薄膜的微结构和激光损伤阈值

ZrO2采用X射线衍射(XRD)技术分析了不同充氧条件和沉积温度对ZrO2溥膜组成结构的影响,并对不同工艺下制备的薄膜的表面粗糙度和激光损伤阈值进行了测量。结果发现随着氧压的升高,ZrO2溥膜将由单斜相多晶态逐渐转变为非晶态结构,而随着基片温度的增加,溥膜将由非晶态逐渐转变为单斜相多晶态。同时发现随着氧压升高晶粒尺寸减小,而随着沉积温度增加,晶粒尺寸增大。氧压增加时工艺对表面粗糙度有一定程度的改善,而沉积温度升高,工艺对表面粗糙度的改善不明显。晶粒尺寸大小变化与表面粗糙度变化存在对应关系。激光损伤测量表明,氧压条件和沉积温度对ZrO2薄膜的抗激光损伤能力有着较大影响。     

355 nm紫外激光损伤阈值自动测量装置及实验

介绍了一套355nm紫外激光损伤阈值自动测量装置。该测量装置由一台Nd：YAG激光器产生紫外355nm激光,经过紫外激光传输系统,紫外激光聚焦形成测试激光。脉冲激光能量由激光能量计监测,Normaski显微镜判断样片的激光损伤。另外,整个测量装置和测量过程由计算机集成控制,具有良好的操作性和运行参数控制能力,可实现1—on-1,n-on-1,s—on—1,R-on-1等多种激光损伤测试。     

Inverse computation for cardiac sources using single current dipole and current multipole models

Two cardiac functional models are constructed in this paper. One is a single current model and the other is a current multipole model. Parameters denoting the properties of these two models are calculated by a least-square fit to the measurements using a simulated annealing algorithm. The measured signals are detected at 36 observation nodes by a superconducting quantum interference device (SQUID). By studying the trends of position, orientation and magnitude of the single current dipole model and the current multipole model in the QRS complex during one time span and comparing the reconstructed magnetocardiography (MCG) of these two cardiac models, we find that the current multipole model is a more appropriate model to represent cardiac electrophysiological activity.     

Simulation study of a magnetocardiogram based on a virtual heart model: effect of a cardiac equivalent source and a volume conductor

In this paper,we present a magnetocardiogram(MCG) simulation study using the boundary element method(BEM) and based on the virtual heart model and the realistic human volume conductor model.The different contributions of cardiac equivalent source models and volume conductor models to the MCG are deeply and comprehensively investigated.The single dipole source model,the multiple dipoles source model and the equivalent double layer(EDL) source model are analysed and compared with the cardiac equivalent source models.Meanwhile,the effect of the volume conductor model on the MCG combined with these cardiac equivalent sources is investigated.The simulation results demonstrate that the cardiac electrophysiological information will be partly missed when only the single dipole source is taken,while the EDL source is a good option for MCG simulation and the effect of the volume conductor is smallest for the EDL source.Therefore,the EDL source is suitable for the study of MCG forward and inverse problems,and more attention should be paid to it in future MCG studies.     

The reliability of AlGaN/GaN high electron mobility transistors under step-electrical stresses

In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors (HEMTs) still lack solid reliability. Devices under accelerated DC stress tests (off-state, V_DS =0 state, and on-state step-stress) are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] (Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415). However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.     

高斯-谢尔模光束通过光栅的远场特性

针对现代激光系统中使用的衍射光学元件,以高斯-谢尔模光束为研究对象,分析了部分相干光通过光栅后的远场特性。利用部分相干光的标量传播公式,对不同束腰宽度、相关长度和相干长度的高斯-谢尔模光束经光栅后的传输特性进行了数值计算,得到了多种情况下光束的远场强度分布。     

经典守恒定律的量子力学推导

从量子力学出发,推出了经典动量守恒定律和能量守恒定律,并讨论了在微观领域经典守恒定律适用的条件.     

离子辅助沉积大口径传输反射镜面形控制研究

 针对大型激光系统中光束质量低和波前畸变等特点,采用离子辅助电子束蒸发技术成功实现对多层膜残余应力的精确控制。通过分析氧化铪、氧化硅单层膜残余应力变化规律,研究了离子源束压、束流参量对膜层折射率、残余应力性质及大小的影响。540 mm×340 mm×60 mm规格大口径传输反射镜面形PV值达到0.5λ(λ=632 nm),小光束损伤测试情况下,样品元件的损伤阈值大于30 J/cm2(N-on-1,1 064 nm,5 ns),利用该技术制备的大口径传输反射镜已获得成功应用。