低阈值单谐振周期极化掺镁铌酸锂光参量振荡器

对基于周期极化掺镬铌酸锂晶体的信号光单谐振光学参量振荡器的输出特性进行了实验研究.讨论了光学参量振荡器谐振腔的腔长、周期极化铌酸锂晶体的通光长度、输出镜的透过率以及抽运光的脉冲宽度对光学参量振荡器谐振阈值的影响.光学参量振荡器的抽运源采用输出波长为1 064 nm的声光调Q Nd:YVO_4激光器,在重复频率为2 kHz、周期极化掺镁铌酸锂晶体的温度为30℃的条件下,光学参量振荡器的振荡阈值仅为48 mW.当抽运功率为94 mW时获得了25 mW的信号光输出,其光-光转换效率为26.6%.     

An optimal adaptive quantization index modulation watermarking algorithm

A novel adaptive watermarking algorithm in discrete wavelet transform （DWT） based on quantization index modulation （QIM） technique is presented. The host image is decomposed into wavelet subbands, and then the approximation subband is divided into non-overlapping small embedding blocks. The secret watermark bit is embedded into singular value vector of each embedding block by applying QIM. To improve the invisibility and robustness of watermarking system, the quantization step for each embedding block is set by combining statistical model with particle swarm optimization （PSO） algorithm. The experimental results show that the proposed algorithm not only preserves the high perceptual quality, but also effectively stands against joint photographic experts group （JPEG） compression, low-pass filtering, noise addition, scaling, and cropping attacks, etc. The comparison analysis demonstrates that our scheme has better performance than the previously reported watermarking algorithms.     

角锥棱镜的误差引起的反射光束相位误差分析

提出一种计算角锥棱镜反射光束相位误差的方法.光束通过非理想角锥棱镜时会引入一个附加光程差,从而改变光束的相位特性和反射光束的传播方向.在小误差近似条件下,采用光线追迹法建立了一个有效的数学模型,计算角锥棱镜的二面角误差和反射面面型误差引起的传输光束的附加相位,并分析了该模型的理论误差.在二面角误差为1",反射面面形光圈数小于0.5的条件下,该模型的数值仿真结果显示角锥附加相位具有高度的中心对称性,附加相位对入射光束引入的相位平均斜率为零,这一特性与误差的种类和大小无关.角锥棱镜的附加相位模型为分析其在应用中给系统带来的误差提供了一个新的方法,有助于指导不同应用场景中所使用角锥棱镜的加工指标要求.     

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HL-2M装置低杂波天线被设计为多栅阵列天线,天线由4行波导组成,每行32个子波导。子波导宽度为0.99cm,壁厚0.3cm,相邻子波导相差取90°。计算得到的反射系数R=0.0261,N||峰值中心为2.375。边缘等离子体电子密度梯度对波谱峰值中心位置没有影响,波峰相对宽度则随之增大而减小。在边缘等离子体电子密度梯度 的情况下,相邻子波导相差为81°时,天线方向性系数最好,为0.2010;反射最小,为0.0223,此时波谱峰值中心为2.125。     

Structural and Thermodynamic Properties of M3W3N （M=Fe,Co, Ni）

Ternary transition metal nitrides, Fe3 W3N, Coa W3N, and Nia WaN~ are studied by the use of interatomic potentials acquired from lattice inversion. The study indicates that Fe3 WaN would be more stable than the other compounds in the family of intermetallic tungsten nitrides. The investigation of phonon density of states indi- cates that the lower frequency modes are mostly excited by the metal atoms, and the higher frequency modes are mostly excited by the nitrogen atoms. A qualitative analysis is carried out with the relevant potentials for the phase stability and vibrational modes.     

Probing the Dissipation Mechanism in Ternary Reactions of ^197Au＋^197Au by Mean Free Path of Nucleons

the collision of very heavy nuclei ^197Au＋^197Au at 15AMeV has been studied within the improved quantum molecular dynamics model. A class of ternary events satisfying nearly complete balance of mass numbers is selected. The experimental mass distributions for the system ^197Au＋^197Au ternary fission fragments, the heaviest（A1）, the intermediate （A2） and the lightest （A3）, are reproduced well. The mean free path of nucleons in the reaction system is studied and the shorter mean free path is responsible for the ternary fission with three mass comparable fragments, in which the two-body dissipation mechanism plays a dominant role.     

2阶精度时间后差隐式格式TVD充分条件

非定常流动问题计算中常用到含三个时间层的二阶精度时间后差隐式格式,并且希望构成TVD格式,然而理论上的问题多年一直没有解决。本文找到了解决办法,构造了这种类型的隐式TVD格式,证明了其为TVD的充分条件。理论结果为计算所验证,并表明通常未采取本文对时间差分处理方法的格式尚不具备TVD性质。     

CsI/MCP X射线阴极及其在低强度X射线影像仪中的应用

报道了X射线阴极的光电发射原理,给出CsI／MCPX射线阴极的制作方法。分析了反射式和透射式X射线阴极的量子效率和噪声特点,提出了改进工艺,给出CsI／MCP的输出特性和扫描电镜正面和剖面照片,且指出Lixiscope的发展以及在生物医学中的应用前景。     

超疏水膜表面构造及构造控制研究进展

本文就表面构造对膜表面亲、疏水性的最新研究成果进行了概括,表面化学成分及化学结构聚集态是获得超疏水膜的基础,表面的形貌和微构造是维持超疏水性质的保障。利用含氟材料极低的表面能,将表面化学结构的聚集态,表面形貌微观构造及排列方式进行有机结合,将会获得理想的超疏水材料。     

地方高校物理实验示范中心的建设实践

介绍了以物理实验教学基地为出发点的多方位探索与实践.针对地方院校生源多层次、经费不充裕、青年教师多等特点,采取“优化整合、资源共享、过程管理、注重交流”等改革措施,明显提高了教学质量.