火试金预浓集结合中子活化和电感耦合等离子体质谱法测定铂族元素

建立了两种以火试金预浓集为基础的、可用于准确测定铂族元素的方法;中子活化法和电感耦合等离子体质谱法。讨论了它们的分析检出限、准确度及其适应性。并用这两种方法测定了5种候选地质参考物质中铂族元素的含量。     

高压下BeP2N4结构相变和电子结构的第一性原理计算

 基于密度泛函理论的第一性原理方法,计算了硅铍石型和尖晶石型结构BeP₂N₄的总能量随体积的变化关系。利用Brich-Murnaghan状态方程,通过能量和体积拟合,得到了2种结构的体变模量及其对压强的一阶导数。在压力作用下,BeP₂N₄的相变是从硅铍石型结构（空间群R-3,No.148）转变到尖晶石型结构（空间群Fd-3m,No.227）,计算出的相变点与其它理论值符合得非常好。同时计算了BeP₂N₄的相对晶格常数a/a₀和相对体积V/V₀的压缩率,在低压下发现,尖晶石结构BeP₂N₄的压缩率接近金刚石,进一步计算了不同压力下的体弹模量B_H、剪切模量G_H、B_H/G_H和杨氏模量E。此外,对两种结构的BeP₂N₄的电子态密度和带隙随压强的变化关系进行了计算和分析。结果表明：在压力作用下,上价带顶向费米能级移动,并有一定的展宽。Be—N、P—N键缩短,电子转移增加,导致电荷发生重新分布。     

Dynamic process of self-started self-mode-locked Ti:sapphire laser with a semiconductor saturable absorber mirror

Dynamic process of self-started self-mode-locked Ti : sapphire laser with a semiconductor saturable absorber mirror (SESAM) was investigated and two mode-locking starting processes were found in which one is fast and the other is slow. In the fast starting process, a mode-locking build-up time of about 400 μs was needed during which pure passive mode-locking process was caused by the SESAM and Kerr-lens mode-locking process arose from the nonlinearity of the Ti : sapphire gain medium. In the slow starting process, a build-up time of about several minutes was found in which temperature effect of the SESAM dominates the dynamic process.     

半导体可饱和吸收镜启动的高功率飞秒掺钛蓝宝石激光器

半导体可饱和吸收镜（SESAM）启动的高功率飞秒掺钛蓝宝石激光器,在Ar^ 激光器10W全线抽运下,其平均输出功率达到1.7W,脉冲宽度小于16fs,斜率效率为22％。文中对半导体可饱和吸收镜自启动的动力学过程进行了实验研究。这种自启动、高功率、窄脉宽的飞秒激光器将具广泛的应用前景。     

Theoretical Analyses of 4f11 →4f105d Excitation Spectra of Er3+ Doped in LiYF4

Spectral terms and J-spectral multiplet of low-spin 4f^105d configuration of Er^3 were obtained with the method of ligand field theory. According to the selection rules for dipole transitions, the excitation spectra of Er^3 doped in LiYF4 in vacuum ultraviolet region (120～160nm) of the spectrum were theoretically interpreted by applying the crystal field model, and the six bands were assigned to the spin-allowed transitions from the ground state (^4I15/2) to J-spectral multiplet of low-spin 4f^105d configuration of Er^3 ion.     

Effect and optimization of the diminution of the sensitizing intensity in two-center recording

The effect of the diminution of the sensitizing intensity from initially high value on two-center recording is experimentally and theoretically investigated. A linear diminution of the sensitizing intensity is designed,and three different diminution rates are employed for the experimental investigation. The results show that the dynamic range can be improved by reducing the diminution rate of the sensitizing intensity. Compared with that of traditional two-center recording, the recording sensitivity obtained in the experiment is more improved when the maximum dynamic range is achieved. The effect of the diminution of the sensitizing intensity on grating uniformity and the effect of the initial sensitizing intensity on the recording sensitivity are theoretically investigated.     

Catalytic pyrolysis of waste wood chip over mesoporous materials using Py-GC/MS

Research on Chemical Intermediates - Pyrolysis Gas Chromatography/Mass Spectroscopy (Py-GC/MS) was used to investigate the catalytic pyrolysis of waste wood chip. Two different mesoporous...     

Narrow disperse polymers using amine functionalized dithiobenzoate RAFT agent and easy removal of thiocarbonyl end group from the resultant polymers

A novel amine functionalized RAFT agent, 2‐cyanoprop‐2‐yl(4‐N,N‐dimethylaminophenyl) dithiobenzoate has been synthesized and used to control the polymerization of vinyl monomers. This dithiobenzoate RAFT agent, although air sensitive, controlled the polymerization of MMA and St very well in an inert atmosphere and the polymerization results obtained were marginally better than using the most popular 2‐cyanoprop‐2‐yl dithiobenzoate RAFT agent. The living nature of these polymerizations was confirmed by kinetics study and chain extension reactions to yield narrow disperse di‐block copolymers. Most importantly, use of this novel RAFT agent simplified the removal procedure of the color causing end thiocarbonyl group from the RAFT derived polymers and thereby leading to polymers with improved appearance. The removal of end group from the polymer was confirmed by ¹H NMR and UV‐vis spectroscopic techniques. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Multi-pass,multi-bunch beam breakup for 9-cell Tesla cavities in the ERL

Generally, the Energy Recovery Linac (ERL) needs specially designed high current superconducting RF cavities. In this paper, the threshold current of beam breakup for compact ERL facilities with 9-cell Tesla type cavities are investigated. The results show that it is feasible to adopt the 9-cell Tesla cavity for compact ERL test facilities with just a few cavities and beam current around 10 mA.