冲击压缩下甲烷-空气混合气体状态参数实验研究

 为研究强冲击状态下混入少量空气的甲烷气体的冲击状态参数,利用二级轻气炮加载技术,使加速到5 km/s的钨合金飞片撞击封装有常态下空气混入量依次为零（纯甲烷气体）、1%、5%、10%的甲烷-空气混合气体铝靶。采用六通道瞬态光学高温计记录冲击压缩气体的光辐射历程曲线,得到了相同初始条件下4种不同比例混合气体的冲击状态参数。结果表明,在强冲击压缩下,混合气体的冲击温度随着空气混入比例的增大而增高,冲击波后混合气体存在非平衡辐射过程。采用Saha电离平衡方程,对空气混入量为10%的混合气体的电离度进行了估算。结果表明,常态下空气含量C_air≤10%的甲烷 空气混合气体具有电探针保护能力。     

CdSe:Nd纳米晶及CdSe:Nd@SiO2核壳结构的合成及发光性能

利用有机相法合成Nd³⁺掺杂CdSe纳米晶（CdSe∶Nd）,通过X射线粉末衍射（XRD）、透射电镜（TEM）、紫外吸收光光谱及荧光光谱表征,证明Nd³⁺已经成功掺入到CdSe的晶格中。与纯CdSe纳米晶相比,CdSe∶Nd纳米晶的结构仍为立方晶型,且形貌近似球形,均匀分散,粒径约为2~4 nm。紫外吸收峰和荧光发射峰都发生红移,而且掺杂后的CdSe∶Nd纳米晶量子产率也提高,这可能是由于掺杂Nd³⁺引入了新的杂质能级,带隙减小。为了实现CdSe∶Nd纳米晶的可加工性和功能性,通过微乳法合成SiO₂壳包覆的CdSe∶Nd纳米球（CdSe∶Nd@SiO₂纳米球）,CdSe∶Nd@SiO₂纳米球呈均匀球形,直径约为100~115 nm,并且包壳后的CdSe∶Nd@SiO₂纳米球发射峰（581 nm）与CdSe∶Nd纳米晶（598 nm）相比,发光强度提高且发射峰蓝移,蓝移约为17 nm,可能是因为SiO₂壳可以减少纳米晶表面的非辐射跃迁以及改善表面缺陷导致的。     

Co-Ni合金纳米线有序阵列的制备与磁性研究

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Ion-implanted Nd:YVO(4) planar waveguide: refractive-index characterization and propagation mode reduction

We report for what is believed to be the first time planar waveguide formation and propagation mode reduction in Nd:YVO(4) crystal, which were achieved by 3.0-MeV silicon-ion implantation followed by annealing under specific conditions. After the implantation, an enhanced refractive-index region was formed with a width of ~2microm beneath the sample surface to act as a waveguide structure. We found that there were four propagation modes for the as-implanted Nd:YVO(4) waveguide, whereas after annealing at 240-360 degrees C for several hours the number of modes could be reduced to three, two, and one. After annealing at 400 degrees C for 1 h the monomode waveguide was destroyed completely, and no mode was observed in the sample.     

分位点函数的光滑非参数估计的BAHADUR表示

文中对分位函数给出了具有更广泛应用的光滑分位估计,证明了该光滑分位估计的逐点和一致的Bahadur强表示定理;并由此结果推导了估计的重对数律,强逼近等深刻结果。     

STOCHASTIC LINEAR QUADRATIC OPTIMAL CONTROL PROBLEMS WITH RANDOM COEFFICIENTS

61. IntroductionLet (fi, F, P, {R}tZo) be a complete filtered probability space on which a standard onedimensional Brownian motion w(') is defined such that {R}tZo is the natural filtrationgenerated by w(.), augmented by all the p-null sets in i. We consider the following stateequationwhere T E T[0, TI, the set of all {R}tZo-stopping times taking values in [0, T], (E sigLlt (fi;IR"); A, B, C, D are matrix-valued {R}tZo-adapted bounded processes. In the above, u(.) EU[T, T]gLI(T, T…     

Piezoelectric resonators with mechanical damping and resistance in current conduction

A novel design method for high Q piezoelectric resonators was presented and proposed using the 3-D equations of linear piezoelectricity with quasi-electrostatic approximation which include losses attributed to mechanical damping in solid and resistance in current conduction. There is currently no finite element sofware for estimating the Q of a resonator without apriori assumptions of the resonator impedance or damping. There is a necessity for better and more realistic modeling of resonators and filters due to miniaturization and the rapid advances in frequency ranges in telecommunication. We presented new three-dimensional finite element models of quartz and barium titanate resonators with mechanical damping and resistance in current conduction. Lee, Liu and Ballato’s 3-D equations of linear piezoelectricity with quasi-electrostatic approximation which include losses attributed to mechanical damping in solid and resistance in current conduction were formulated in a weak form and implemented in COMSOL. The resulting finite element model could predict the Q and other electrical parameters for any piezoelectric resonator without apriori assumptions of damping or resistance. Forced and free vibration analyses were performed and the results for the Q and other electrical parameters were obtained. Comparisons of the Q and other electrical parameters obtained from the free vibration analysis with their corresponding values from the forced vibration analysis were found to be in excellent agreement. Hence, the frequency spectra obtained from the free vibration analysis could be used for designing high Q resonators. Results for quartz thickness shear AT-cut and SC-cut resonators and thickness stretch poled barium titanate resonators were presented. An unexpected benefit of the model was the prediction of resonator Q with energy losses via the mounting supports.     

YbxY1-xBa2Cu3O7-y的超导载流特性

本文系统地研究了Yb_xY_1-xBa₂Cu₃O_7-y系统的微结构、超导临界温度以及超导载流特性。发现:随着Yb含量的增大,样品的超导临界温度没有很大变化,但晶粒度逐渐减小,超导临界电流密度系统地下降。作者认为:在这种弱连接颗粒超导体中,细化晶粒无助于提高其临界电流密度。 关键词：     

地下水位变化中的地震信息

为挖掘地下水位中蕴含的地震信息, 我们通过对地下水位与地震事件序列关系的分析提出了一个新统计量, 进而得到一种寻找地震前兆的方法. 数据分析表明这种探索地震前兆方法有应用价值.     

从对Cu的取代看YBa2Cu3O7-y中Cu-O平面和Cu—O链的作用

通过测量YBa₂Cu_3-xM_xO_7-y(M=Zn,Ni,x=0,0.025,0.05,0.075,0.1,0.15,0.2,0.3)系列样品的晶体结构、正常态电子输运性质、超导电性以及O含量,给出了Zn择优取代Cu(2)的更直接证据;同时,观察到掺Zn系统中的由正交相Ⅰ到正交相Ⅱ的结构相变以及Ni取代Cu带来的电子局域化效应。研究结果表明,具有正二价态的Zn对Cu(2)具有择优取代性,而具有正二价和正三价的Ni并不具有明显的择优取代。对Cu(2)的取代引起超导临界温度的显著变化,但对正常态电子输运性质的影响不明显;对Cu(1)的取代更显著地影响了晶体结构和正常态电子输运性质,同时对T_c产生抑制,我们认为,YBa₂Cu₃0₇中的高温超导电性以及正常态输运性质是由CU-O平面和Cu-0链共同承担,而Cu-O平面和Cu-0链之间的耦合强度决定着该系统的超导电性的强弱。 关键词：