二维TiC层表面H2的化学吸附与物理吸附

第一性原理计算研究发现由于二维TiC单原子层具有高的比表面积与大量的暴露在表面的Ti原子,其是一种非常有潜力的储氢材料.计算结果显示H2可以在二维TiC单原子层表面进行物理吸附与化学吸附.其中化学吸附能为每个氢分子0.36 eV,物理吸附能是每个氢分子0.09 eV.覆盖度为1和1/4层(ML)时,H2分子在二维TiC单原子层表面的离解势垒分别为1.12和0.33 eV.因此,除了物理吸附与化学吸附,TiC表面还存在H单原子吸附.最大的H2储存率可以达到7.69％(质量分数).其中,离解的H原子、化学吸附的H2、物理吸附的H2的储存率分别为1.54％、3.07％、3.07％.符合Kubas吸附特征的储存率为3.07％.化学吸附能随覆盖度的变化非常小,这有利于H2分子的吸附与释放.     

High Power THz Undulator Radiation from Linear Accelerator

A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the power, frequency spectrum. First experiments show the averaged power at THz to be about 20mW.     

Electronic structure,mechanical and optical properties of ternary semiconductors Si1-xGexC (X = 0, 0.25, 0.50, 0.75, 1)

The electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si_1-xGe_xC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243?eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si _0.75 Ge _0.25 C, Si _0.50 Ge _0.50 C, Si _0.25 Ge _0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657?eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si_1-x Ge_xC (X?=?0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results.     

The structural and electronic properties of silicon nanoribbons on Ag(110): A first principles study

We have investigated the structures of silicon nanoribbons on Ag(110) using first principles calculations. The armchair silicon nanoribbons (ASiNRs) and zigzag silicon nanoribbons (ZSiNRs) with different widths are analyzed. The formation energy study shows that the ASiNRs with the width of 16 Å are the most stable structures. These ASiNRs have the structural parameters same as experimental ones. The simulated scanning tunneling microscope (STM) images of these ASiNRs also agree well with the experimental results. Thus, these ASiNRs are supposed to be the nanoribbons grown in experiment. The electronic structures shows that the ASiNRs are metallic, which is in agreement with the experiments.     

La单掺4H-SiC电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及La掺杂4H-SiC的电子结构和光学性质进行理论计算。计算结果表明,未掺杂4C-SiC其禁带宽度为2.257 eV。La掺杂后带隙宽度下降为1.1143eV,导带最低点为G点,价带最高点为F点,是P型间接半导体。掺杂La原子在价带的低能区间贡献比较大,而对价带的高能区和导带的贡献比较小。未掺杂4H-SiC在光子能量为6.25 eV时,出现一个介电峰,这是由于价带电子向导带电子跃迁产生。而La掺杂后,出现3个介电峰,分别对应的光子能量为0.47eV、2.67eV、6.21eV,前两个介电峰是由于价带电子向杂质能级跃迁产生,第三个介电峰是由于价带电子向导带电子跃迁产生。La掺杂后4H-SiC变成负介电半导体材料。未掺杂4h-SiC的静态介电常数为2.01,La掺杂的静态常数为12.01。     

导数阴极溶出方波伏安法测定卡那霉素注射液含量

研究了汞 卡那霉素络合物的电化学行为 ,并建立了导数阴极溶出方波伏安法测定卡那霉素注射液含量的方法。在 pH 4 .7的HOAc NaOAc缓冲溶液中 ,在约 0 .12 6V (vs.SCE)处出现一个汞 卡那霉素络合物的还原峰 ,卡那霉素的浓度在 0 .0 2～ 1.5mg·ml- 1之间与导数方波伏安图的峰高存在良好的线性关系 ,回归方程ip(10 - 4A) =3.6C(mg·ml- 1) + 0 .4 6 ,相关系数为 0 .992 0。方法简便、灵敏、准确 ,可用于卡那霉素注射液含量测定     

Generalized Solution of a Kind of Nonparametric Curvature Evolution with Boundary Condition

The existence and uniqueness of the generalized solution for a kind of nonparametric curvature flow problem are obtained. This kind of curvature flow problem describes the evolution of graphs with speed depending on the reciprocal of the Gauss curvature.     

高压下BaHfO3电子结构与光学性质的第一性原理研究

从第一性原理出发,在局域密度近似下,采用基于密度泛函理论的平面波超软赝势计算方法系统地研究了高压对BaHfO₃电子结构与光学性质的影响.能带结构分析表明;无压强和施加正压强作用时,BaHfO₃为直接带隙绝缘体,而施加负压强时,BaHfO₃则转变为间接带隙半导体;BaHfO₃的带隙随压强增加而减小,且具有明显的非线性关系.对光学性质的分析发现:施加正压强后,光学吸收带边产生蓝移;负压强作用时介电函数虚部尖峰减少,光学吸收带边产生红移;施加压强后BaHfO₃的静态介电常数和静态折射率均增大.上述研究表明施加高压有效调制了BaHfO₃的电子结构和光学性质,计算结果为BaHfO₃光电材料的设计与应用提供了理论依据.     

Existence and uniqueness of periodic solutions for a kind of first order neutral functional differential equations

In this paper, we use the coincidence degree theory to establish new results on the existence and uniqueness of T-periodic solutions for the first order neutral functional differential equation of the form

(x(t)+Bx(t−δ)^)′=g₁(t,x(t))+g₂(t,x(t−τ))+p(t).     

测地极坐标下空间形式的度量特征

将R3中Gauss曲率为常数k0的常曲率曲面S的度量特征推广到了一般的空间形式,主要工作是利用活动标架法和测地极坐标的理论,通过对结构方程的微分,找到了关于度量的一个内在方程,由此给出了定理的一个证明。