Use of graphene for forming Al-based p-type reflectors for near ultraviolet InGaN/AlGaN-based light-emitting diode

We demonstrated the improved performance of near UV (365 nm) InGaN/AlGaN-based LEDs using highly reflective Al-based p-type reflectors with graphene sheets as a diffusion barrier. The use of graphene sheets did not degrade the reflectance of ITO/Al contacts, viz. ∼81% at 365 nm. The ITO/graphene/Al contacts annealed at 300 °C exhibited better ohmic behavior with a specific contact resistance of 1.5 × 10⁻³ Ωcm² than the ITO/Al contact (with 9.5 × 10⁻³ Ωcm²). Near UV LEDs fabricated with the ITO/graphene/Al contact annealed at 300 °C showed a 7.2% higher light output (at 0.1 W) than LEDs with the ITO/Al reflector annealed at 300 °C. The SIMS results exhibited that, unlike the ITO/graphene/Al, the ITO/Al contacts undergo a significant indiffusion of Al atoms toward the GaN after annealing. Furthermore, both Ga and Mg atoms were also more extensively outdiffused in the ITO/Al contacts after annealing. On the basis of the SIMS and electrical results, the possible explanations for the annealing-induced degradation of the ITO/Al contacts are described and discussed.     

The criteria for selecting a method for unfolding neutron spectra based on the information entropy theory

To further expand the application of an artificial neural network in the field of neutron spectrometry, the criteria for choosing between an artificial neural network and the maximum entropy method for the purpose of unfolding neutron spectra was presented. The counts of the Bonner spheres for IAEA neutron spectra were used as a database, and the artificial neural network and the maximum entropy method were used to unfold neutron spectra; the mean squares of the spectra were defined as the differences between the desired and unfolded spectra. After the information entropy of each spectrum was calculated using information entropy theory, the relationship between the mean squares of the spectra and the information entropy was acquired. Useful information from the information entropy guided the selection of unfolding methods. Due to the importance of the information entropy, the method for predicting the information entropy using the Bonner spheres' counts was established. The criteria based on the information entropy theory can be used to choose between the artificial neural network and the maximum entropy method unfolding methods. The application of an artificial neural network to unfold neutron spectra was expanded.     

基于CdSe/ZnS量子点薄膜结构的高双折射光子晶体光纤的色散与损耗控制

基于有限元法,设计了一种六边形排列含CdSe/ZnS量子点薄膜结构的高双折射光子晶体光纤,分析了具有不同厚度CdSe/ZnS量子点薄膜光子晶体光纤的色散及损耗特性.结果表明,含CdSe/ZnS量子点薄膜结构的光子晶体光纤在x和y方向均存在基模.当泵浦光波长逐渐增加时,具有相同厚度CdSe/ZnS量子点薄膜光子晶体光纤的双折射值逐渐增大,x和y方向总色散先增大后减小且存在两个零色散点,损耗逐渐增大并在可见光波段趋近于零;具有不同厚度CdSe/ZnS量子点薄膜光子晶体光纤随CdSe/ZnS量子点薄膜厚度的增加,在相同泵浦光波长处,双折射值逐渐减小,x和y方向总色散逐渐减小且两个零色散点逐渐靠近,损耗逐渐增大.通过沉积不同厚度CdSe/ZnS量子点薄膜和选择合适泵浦光波长,可有效控制光子晶体光纤的色散和损耗.     

量子点CdSe／ZnS的浓度对其荧光的影响研究

影响量子点荧光特性除了量子点尺寸因素外,其溶液浓度也会对其荧光特性起很重要的作用。但到目前,还未见到有关量子点 CdSe／ZnS 在溶液中浓度对其荧光影响的详细报道。为了掌握影响量子点CdSe／ZnS荧光特性的因素及其物理机制,利用紫外-可见吸收光谱仪和荧光光谱仪测量了尺寸为4 nm的量子点CdSe／ZnS在氯仿中不同浓度下的吸收光谱和荧光光谱,并侧重研究了量子点CdSe／ZnS的浓度对其发光特性的影响并分析了其物理机制。结果表明量子点对光谱的吸收随其浓度的增加而增大,但其发光却具有一个最佳浓度2μmol·L－1。当量子点的浓度＞2μmol·L－1时,量子点的荧光强度随着量子点浓度的增加而降低,而当量子点的浓度＜2μmol·L－1时,量子点的发光强度则随其浓度的降低而降低。其原因主要有两个：（1）荧光猝灭效应;（2）荧光发射与光吸收的竞争效应。当量子点的浓度＞2μmol·L－1时,由于量子点之间相距太近（仅为94 nm）而引起了荧光猝灭效应,且其荧光猝灭效应随量子点间距的减小而增大,且因为吸收过大,导致受激的量子点并未增加,因此,其荧光随浓度的增加而降低。而当量子点的浓度＜2μmol·L－1时,因为量子点之间的距离足够大,不再引起荧光猝灭效应,其荧光强度取决于单位体积内的量子点的个数,单位体积内量子点的个数越多,其发光强度越强。因此其发光强度随量子点溶液的浓度降低而降低。     

基于改进巴氏指标和模型更新的视觉跟踪算法

传统的Mean Shift算法采用巴氏系数度量模型与候选模型之间的统计特征相似性,但是由于背景特征的影响,有时应用巴氏指标进行匹配得到最优解的位置并不一定是目标的实际位置,在跟踪过程中可能导致目标定位出现偏差。该文提出一种改进的巴氏系数相似度指标,指标由于引入了前景/背景置信值,能够有效抑制待匹配区域中背景特征的影响,突出目标特征的权重,与原始的巴氏指标相比,明显提高了目标匹配的准确性。基于改进的巴氏指标,对目标与背景区域双模型相似度系数进行综合分析,合理地判断干扰目标匹配的原因,从而采取相应的模型更新策略。采用4段具有挑战性的视频序列对5种跟踪算法进行了测试,通过定量实验分析可知,文中算法处理1帧视频所需的平均时间为75.76 ms,实时性仅次于原始的Mean Shift跟踪算法,同时跟踪误差在5种跟踪算法中取得了最优结果。实验结果表明,该算法能够有效抑制背景干扰和避免模型漂移,在不同的复杂场景下都具有一定的鲁棒性。     

舰载导弹振动环境状态实时监测系统设计

为了全面监测舰上导弹贮存的振动环境,设计了对舰艇横摇、纵摇和升沉条件下的加速度信号实时监测系统;该系统采用一体化、模块化设计的思想,应用堆栈式结构总线PC104,提高了系统的便携性、可靠性;采用两种供电方式提高了系统适应性;文章详细阐述了硬件系统和软件系统的设计,并重点对数据采集存储和数据显示功能实现进行了论述;在1 000 Hz采样频率的实验条件下,采集数据准确可靠,精确度为99.75%,达到了系统设计的要求。     

ε-CL-20/F_(2311) PBXs力学性能和结合能的分子动力学模拟

本文应用分子动力学(MD)模拟方法,研究高能量密度化合物六硝基六氮杂异伍兹烷(ε-CL-20)与常用高聚物粘结剂F2311所构成的CL-20/F2311高聚物粘结炸药(PBXs)的力学性能和结合能随温度和高聚物浓度而变化的规律.结果表明,添加高聚物于主体炸药中,使其弹性模量减小,表明刚性减小,弹性增大,机械力学性能大为改善;在一定范围内,随高聚物F2311在PBXs中浓度的增加,体系结合能从正值变为负值,而随温度升高,体系的结合能变化不是很明显.     

A combined analytical singularity subtraction method and compact implicit differencing scheme for aerodynamic mixing

In spite of the rapid advances in both scalar and parallel computational tools, the large number and breadth of variables involved in both design and inverse problems make the use of sophisticated fluid flow models impractical. With this restriction, it may be concluded that an important family of methods for mathematical/computational development are reduced or approximate models. In this study, a combined perturbation/numerical modeling methodology is developed. The numerical portion of the model uses a compact finite difference scheme, while analytical solutions are used to resolve singular behavior that is inherent to this flow. Solutions are presented to illustrate the efficiency of this methodology.     

Cd_(0.96)Zn_(0.04)S/Cd_(0.97)Mn_(0.03)S/Cd_(0.96)Zn_(0.04)S多层纳米线中s-d交换作用的研究

以氧化铝纳米孔为模板,采用直流电化学沉积的方法制备了Cd_(0.96)Zn_(0.04)S/Cd_(0.97)Mn_(0.03)S/Cd_(0.96)Zn_(0.04)S量子阱纳米线阵列,并系统研究了该纳米线阵列在不同温度和不同磁场下的电学输运特性.随着外磁场的变化,样品表现出共振传输特性.通过量子阱理论对实验现象进行了分析,直接得到了稀磁层Cd_(0.97)Mn_(0.03)S中s-d交换作用常数N_0α的定量结果.研究发现该交换作用常数随温度具有e~(-1/T)的变化趋势.