两步合金法制作p-GaN高反电极

利用两步合金法获得了能与p-GaN形成良好欧姆接触的高反射电极.电极的构成采用透明电极 高反射金属方案,厚的Ag层或Al层覆盖在合金后的Ni/Au上以提高电极的反射率,以Pt和Au作为覆盖层,可有效地防止Ag的氧化和团聚,短时间的热处理有助于Ag基电极反射率的提高.可靠性测试表明Ag基电极的稳定性较好,对于Al基电极,热处理后反射镜上出现暗斑,导致其反射率的下降.最终获得了波长在460nm处反射率为74%的Ag基高反射电极.     

加速器核物理大科学平台现状及展望

文章首先回顾了加速器核物理大科学平台的发展历史,随后总结了核物理研究前沿对加速器平台的需求,介绍了不稳定核束的产生和加速方法,综述了现有的加速器装置情况,最后给出了在建的和计划中的加速器装置展望。     

化学激光器燃烧室两步反应法的实验研究

在环柱型增益发生器实验系统燃烧室的设计中,将主稀释剂He从两个不同的区域注入燃烧室,其中一部分与D2预混以后通过D2喷注孔注入,另一部分通过主喷管叶片后端的后向喷注孔注入。讨论了不同区域的主稀释剂流量的变化对激光器特性的影响。实验结果表明：后He流量改变时,激光器的功率变化及点火稳定性等明显优于前He流量改变的情况。若要增加主稀释剂比例,应优先考虑调整后He。     

自支撑聚酰亚胺/锆膜的制备及性能改善

采用直流磁控溅射法制备自支撑锆(Zr)膜,采用二步法制备聚酰亚胺(PI)膜,在Zr膜表面沉积PI膜得到自支撑PI/Zr复合膜。均苯四甲酸酐(PMDA)和二甲基二苯醚(ODA)在二甲基乙酰胺(DMAC)中反应得到聚酰胺酸(PAA),然后PAA高温亚胺化得到PI;PI成膜时采用提拉法成膜。经国家同步辐射实验室计量线站测定,实际测量结果与理论分析一致,PI膜的引入虽然会导致自支撑薄膜透过率有所下降,但在类镍-银软X射线13.9 nm波段PI(200 nm)/Zr(300 nm)和PI(200 nm)/Zr(400 nm)自支撑薄膜的透过率仍然分别达到14.9%和7.5%。     

北京市中心商区射频电磁环境测试与分析

城市电磁环境强度的逐渐升高对人体健康和电子系统正常工作构成潜在威胁,为实现对电磁环境状况的快速判别,提出一种电磁环境与人口热力及建筑密度的关联规则挖掘方法. 首先通过两步聚类分别将电磁环境、人口热力、建筑密度数据离散为三种等级,再基于动态阈值FP增长（Frequent Pattern Growth）算法进行规则挖掘,最后筛选出有效的关联规则. 将所提出方法应用于北京城区道路采样的28 424组数据,实验结果表明：人口热力为中、低等级的区域或建筑密度低的区域,电磁环境强度通常低于1.52 V/m;建筑密度高的区域,电磁环境强度通常在1.52～3.50 V/m;而电磁环境强度高于3.50 V/m的情况主要出现在人口热力高的区域. 本文的研究工作为城市电磁环境的快速估计与监测预警提供了新思路和参考.

     

Y~(3+)掺杂ZnO压敏陶瓷的微结构和电性能研究

采用两步烧结法制备了Y3+掺杂的(以Y(NO3)3·6H2O形式加入)ZnO压敏陶瓷,通过XRD、SEM和EDX系统研究了Y3+掺杂量对ZnO压敏陶瓷微结构和电性能的影响。结果表明:随着Y3+掺杂量的增加,电位梯度VT和非线性系数α提高,晶粒尺寸减小,施主浓度Nd和晶界态密度Ns降低,势垒宽度ω增大。当掺杂的x[Y(NO3)3·6H2O]为1.2%、烧结温度为1100℃时,ZnO压敏陶瓷电性能最好,其VT为675V/mm,α为63.9,漏电流IL为2.40μA。     

非定常的热传导-对流问题的非线性Galerkin混合元法(Ⅲ):时间二阶精度的全离散格式

In this paper, a fully discrete format of nonlinear Galerkin mixed element method with two-step discretization of time for the non stationary conduction-convection problems is presented. The existence and the convergence of the fully discrete mixed element solution are shown. On the basis of [9] and [10], we have proved that the schemes have second-order convergence accuracy for the time discretization.     

Geodesic orbit and naturally reductive nilmanifolds associated with graphs

We study Riemannian nilmanifolds associated with graphs. We prove that such a nilmanifold is geodesic orbit if and only if it is naturally reductive if and only if its defining graph is the disjoint union of complete graphs and the left-invariant metric is generated by a certain naturally defined inner product.     

由锂分子高位三重态跃迁产生的435.0～445.0nm扩散带受激辐射

本文报道了以590.0～625.0nm宽波段范围内任何波长的脉冲激光双光子激发锂分子,均可产生435.0～445.0nm扩散带受激辐射的实验结果,对激发和发射机制进行了讨论。     

Numerical solution of a nonlinear parabolic control problem by a reduced SQP method

We consider a control problem for a nonlinear diffusion equation with boundary input that occurs when heating ceramic products in a kiln. We interpret this control problem as a constrained optimization problem, and we develop a reduced SQP method that presents for this problem a new and efficient approach of its numerical solution. As opposed to Newton's method for the unconstrained problem, where at each iteration the state must be computed from a set of nonlinear equations,in the proposed algorithm only the linearized state equations need to be solved. Furthermore, by use of a secant update formula, the calculation of exact second derivatives is avoided. In this way the algorithm achieves a substantial decrease in the total cost compared to the implementation of Newton's method in [2]. Our method is practicable with regard to storage requirements, and by choosing an appropriate representation for the null space of the Jacobian of the constraints we are able to exploit the sparsity pattern of the Jacobian in the course of the iteration. We conclude with a presentation of numerical examples that demonstrate the fast two-step superlinear convergence behavior of the method.