基于可信基站和HASH函数的WSN密钥管理方案

针对现有的基于二元多项式或q-composite的密钥管理方案存在的被捕获率高和网络连通率低的缺点,提出了一种基于可信基站产生三元多项式密钥和HASH函数的WSN密钥管理方案;首先,采用层次型分簇路由协议将整个WSN监测区域划分为簇,然后,由可信基站产生三元多项式密钥,并将其分配给簇头,当任意两簇头之间共享的多项式密钥超过q时可以进行通信,并通过HASH函数来生成对应的通信密钥,有效地隐藏了节点的部分密钥信息;理论研究和仿真试验结果表明:文中方法能有效地实现网络的密钥管理,较其他方法相比,具有网络连通率高和抗捕获能力强的优点,具有一定的优越性。     

激光器非线性失真对SCM光波系统的影响

对于宽带副载波复用(SCM)的光波系统,研究并设法减小光源的非线性所引起的谐波失真和交调失真,是一个重要的理论课题。本文分析激光器的P—I曲线的非线性以及谐振腔里光子和电子相互耦合所引起的固有非线性及其对复用信道的影响。     

Observation of macroscopic quantum tunneling in a single Bi2Sr2CaCu2O8+delta surface intrinsic Josephson junction

We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi(2)Sr(2)CaCu(2)O(8+delta) surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinphi current-phase relationship.     

薄膜法布里-珀罗滤光片中的超棱镜效应

基于薄膜法布里珀罗滤光片在其峰值波长处具有较大群延迟的特性,设计并从实验上验证了光束倾斜入射时这种结构中存在的超棱镜效应。根据光学薄膜理论中的特征矩阵法,数值模拟计算了器件的群延迟和空间色散曲线,镀制并对器件进行了测试。测试结果表明器件在透射峰值波长处因超棱镜效应引起的空间色散最大位移值达到65μm,与理论计算结果非常吻合;相对于传统的光栅和棱镜器件而言器件具有更高的空间角度色散,实际测试在784.5 nm至786.5 nm波长范围内器件的角色散达到30°/nm。     

用液晶空间光调制器产生光阱阵列

液晶空间光调制器能够方便地用于制作各种衍射型光学元件, 但液晶空间光调制器存在分辨率有限的缺点, 本文提出了用液晶空间光调制器制作相位型光栅, 产生一维和二维光阱阵列的新方案, 用迭代傅里叶级数算法优化设计光栅的相位分布, 在不改变空间光调制器硬件参数设置的情况下, 充分利用和发掘了空间光调制器的优点, 同时又能较好地回避其所存在的缺陷. 根据现有的空间光调制器的技术参数, 模拟仿真设计光栅, 计算光强分布, 结果表明: 用大失谐、小功率激光照明, 能够产生具有很高峰值光强和光强梯度的光阱阵列, 囚禁冷原子的光学偶极势达到mK量级, 对原子的作用力远大于原子的重力.     

Fabrication and surface enhanced Raman spectroscopy of single Au@SiO2 dimers linked by benzenedithiol

Metal nanoparticle dimers with controllable gap distance have attracted considerable attention because of their promising application in plasmonics. Generally, gaps with nanometer or subnanometer dimensions generate localized surface plasmon resonance (LSPR) coupling effect, thus contributing to a strong electromagnetic field for improving surface enhanced Raman scattering (SERS) effect. Here, we developed a facile approach to fabricate Au@SiO₂ dimers through the steric hindrance effect, in which the SiO₂ shell functioned as a block and a rigid dithiol molecule was employed as linker. The thickness of the SiO₂ shell played a critical role in improving the yield of dimers. The dimerization efficiency increased significantly as the shell thickness decreased to ~1 nm. When 1,4‐benzenedithiol was used as linker molecule, the yield of dimers was ~30%. Few dimers were obtained when mecaptobenzonic acid was used as linker. A thicker shell is associated with a low yield of dimer, whereas a thinner shell resulted in the formation of multimers and linear structures. The low number of linker molecules on the exposed area of monodisperse single nanoparticles and the lack of LSPR coupling effect (‘hot spots’) resulted in the disappearance of SERS signals of the linkers. The estimated SERS enhancement factor was about eight fold because of the strong coupling effect in the gap of the dimer with the distance of the dithiol molecular length. From the above results, SERS combined with SEM could be developed into powerful tools for monitoring the formation of dimers and positioning of single dimers. It may aid the control of assembly of Au nanoparticles and in probing key issues about SERS enhancements. Copyright © 2015 John Wiley & Sons, Ltd.     

Scaling properties of phase-change line memory

Phase-change line memory cells with different line widths are fabricated using focused-ion-beam deposited C-Pt as a hard mask. The electrical performance of these memory devices was characterized. The current-voltage (I-V ) and resistance-voltage (R-V ) characteristics demonstrate that the power consumption decreases with the width of the phase-change line. A three-dimensional simulation is carried out to further study the scaling properties of the phase-change line memory. The results show that the resistive amorphous (RESET) power consumption is proportional to the cross-sectional area of the phase-change line, but increases as the line length decreases.     

Effect of Cu doping on the magnetic and electrical properties of n=2 Ruddlesden-Popper manganates

A series of polycrystalline Cu-doped n=2 Ruddlesden-Popper manganates La1.2Sr1.8CuzMn（2-x）O7 （x=0, 0.04, 0.13） were synthesized by the solid state reaction method. The effect of Cu doping on the magnetic and transport properties has been studied. It is found that Cu substitution for Mn greatly affects the magnetic and electrical properties of the parent phase La1.2Sr1.8Mn2O7. With the increase of Cu content, the system undergoes a transition from longrange ferromagnetic order to the spin glass state and further to an antiferromagnetic order. A little of Cu dopant can lead to the samples showing semiconductor or insulator behaviour in the whole observed temperature range while the parent phase has a metal-insulator transition. These samples show colossal magnetoresistance at low temperatures and the value of it decreases with increasing Cu content.     

拱形激光二极管侧抽运Nd:YAG固体激光器的实验研究

详细阐述了同心抽运、同心冷却的激光二极管紧包侧抽运Nd：YAG激光器的实验研究工作。这种抽运结构使晶体内的增益场与谐振腔基模实现了良好的匹配,易于得到良好的光束质量和大能量输出,基模提取效率高。模拟分析了晶体内的增益场以及横截面内的温度分布,从不同角度探讨了激光二极管的温度特性对器件工作的影响。研究了晶体的热致退偏效应对器件调Q工作的影响．并且初步探讨了不同腔长、不同腔型下器件的工作情况,这些实验结果对进一步优化使用这种抽运结构有指导意义。所设计的激光器在工作频率6Hz时．得到了斜效率为44．3％的多模调Q输出。在抽运能量735mJ时,得到最大输出能量135mJ,脉宽7．6ns的调Q脉冲,光光效率为18．4％,插头效率为11．0％,光束发散角小于1．5mrad。     

低温液体流动沸腾数值计算中的相间传热模型

采用双流体模型预测了液氮在垂直管内的流动沸腾过程,着重考察和评价了五个常用的相间传热模型对数值计算结果的影响,找出了最优的相间传热模型;同时,研究还发现相间传热模型对流动压降的预测并无明显影响.