Origins of green band emission in high-temperature annealed N-doped ZnO

Nitrogen-doped ZnO sample has been annealed in O₂ ambient at high temperature (1000 °C) to improve its photoluminescence property. Low-temperature photoluminescence spectra of the sample are dominated by three near-band-edge emissions at 3.377, 3.362, and 3.332 eV, which are ascribed to free exciton emission (FX_A), and neutral donor-bound exciton (D⁰X), and its two-electron satellite (TES), respectively. With increasing temperature in low temperature region, the intensity of FX_A increases and the green band (GB) shows a negative thermal quenching effect resulting from thermal dissociation of D⁰X with more free excitons and neutral donors formed. The doublet structure with energy space ∼30 meV and repeated separation of longitudinal-optical phonon energy of 72 meV are observed in GB at low temperatures. The temperature independent energy position of GB indicates a typical recombination characteristic within strongly localized complexes. The doublet structures are considered to originate from the ground and exited states of shallow donors recombining with deep acceptors such as zinc vacancies.     

Aerobic Oxidation of Benzylic Halides to Carbonyl Compounds with Molecular Oxygen Catalyzed by TEMPO/KNO2 in Aqueous Media

Benzylic halides were successfully oxidized to the corresponding aldehydes and ketones in good to excellent yields in aqueous media with molecular oxygen as oxidant in the presence of catalytic amounts of TEMPO (2,2,6,6-tetramethylpiperidyl-1-oxy) and potassium nitrite (KNO₂).     

强流多注电子束高效率引入的模拟研究

强流相对论多注速调管相对于单注速调管具有导流系数低,输出功率高和效率高的优点,并且可以明显降低引导磁场强度,因此得到快速发展。但是其多注电子束引入漂移管效率低的问题,影响了多注速调管的整管效率,限制了其稳定高效运行和应用推广。论文采用粒子仿真软件CHIPIC对多注速调管二极管爆炸发射过程进行仿真研究,寻找影响多注速调管引入效率的主要因素,并对阴极结构进行了优化,设计出三种两段式新型多注阴极结构并进行冷阴极爆炸发射模拟研究。研究结果表明：给定参数下,常规结构由于底座边缘的不必要的环形电子束发射,只能达到82%的引入效率,而三种新型阴极结构通过抑制不必要电子发射,引入效率都可以提高至95%以上,最高达到99%。     

X波段长脉冲多注相对论速调管放大器杂模振荡抑制

为进一步提高相对论速调管放大器(RKA)的工作频率和输出功率,开展了X波段GW级长脉冲多注RKA实验研究,对实验中出现的杂模振荡现象进行了模拟和实验分析。结果表明,电子回流是导致实验中出现杂模振荡的主要因素,采取了相应措施减少电子回流从而抑制杂模振荡,实现多注RKA输出微波功率约为0.98 GW,脉宽为95 ns,频率为9.405 GHz。     

碳碳复合阴极在相对论速调管放大器中的应用

研制了一种碳纤维分布具有高取向性的碳碳复合材料, 并采用该材料制作的阴极开展了相对论速调管放大器的实验研究。实验结果表明：碳碳复合阴极爆炸发射的点火机制以尖端场增强为主, 运行1000发后碳纤维结构稳定, 重复频率25 Hz运行时输出微波功率大于1 GW, 脉冲宽度大于100 ns, 阴极发射电流密度约3.82 kA/cm2。碳碳复合阴极在启动速度、电流延迟时间及阻抗特性等方面性能还有待进一步的研究。     

An endochronic constitutive model for rate-dependent and nonproportional cyclic plasticity

The total stress response of material is decomposed into a sum of an equilibrium stress response and a non-equilibrium overstress response. Correspondingly, the rate-independent intrinsic time and the rate-dependent intrinsic time are defined respectively. Additional hardening functions for describing the isotropic and anisotropic nonproportional effects are assumed to be related to the accumulation of plastic strain component along the normal of equilibrium stress trajectory, in which the effects of geometry of the loading path are included. An endochronic constitutive model for rate-dependent, nonproportional cyclic plasticity is formulated and applied to simulate the stress responses of stainless steel XCrNi18.9 for some typical loading programs at different loading rates. A comparison between predicted results and experimental ones by Haupt and Lion shows that the former are in agrreement with the latter.     

正常与钙化变厚度生物心瓣应力分布的数值模拟

采用八结点超参数板壳元，对猪主动脉瓣在闭合承载状态下的应力分布进行了非线性有限元数值模拟．分析了变厚度瓣膜和等厚度瓣膜应力分布的差别，发现厚度对应力分布具有较大影响．进一步分析了正常及具有几个散布钙化点的瓣膜的应力分布，发现钙化区域应力显著增大．本文结果与临床病变瓣膜的观察结果较为符合     

焊接接头材质和力学非均匀体低周疲劳特性研究

焊接接头是由母材区、热影响区和焊缝组成的材质和力学性质非均匀体,与均匀材料相比,有关非均匀体低周疲劳特性的研究还相当少,许多问题尚未完全搞清.本文通过16MnR压力容器用钢焊接接头的应变控制低周疲劳试验,采用宏观试验与微观分析相结合的方法,考虑了焊接接头材质和力学非均匀性的影响,对其疲劳特性进行了较为深入的研究,得出一些新的十分有意义的结论.     

Synthesis and growth mechanism: A novel comb-like ZnO nanostructure

A novel multilayer comb-like Zinc oxide nanostructure has been successfully synthesized via pure Zn chemical vapor deposition on anodic aluminum oxide substrate at 950 °C. X-ray diffraction and selected area electron diffraction indicate that the nanocombs are of wurtzite structure and single crystalline. The morphology and the microstructure of the nanocombs are investigated by the scanning electron microscopy. Transmission electron microscopy shows the growth direction, and energy-dispersive X-ray spectroscopy reveals the atomic composition ratio of Zn/O. The growth mechanism of such interesting and unique morphologies is briefly discussed.     

微型装置与测试技术

本文提出并尝试用微电子技术制作的微型越置来更新现有的测试装置,这对推动教学、科研和生产的发展无疑是一种最有效的方法。