50 kV半绝缘GaAs光导开关

 设计了横向结构的半绝缘GaAs光导开关,开关由600 μm厚的半绝缘GaAs晶片制成,电极间隙为20 mm。在不同的直流偏置电压下,使用波长为1 064 nm、能量为9.9 mJ的激光脉冲触发使开关导通,开关置于0.2 MPa的SF6气体环境中。在施加直流50 kV电压的情况下,使用Rogowski线圈测得开关的最大导通电流为1.1 kA。对实验结果进行分析表明：随着初始偏置电压的升高,回路流过的电荷与电容初始储存的电荷的比值不断提高,但都没有达到100%,即非线性模式下光导开关的关断原因并不是由于外电路的能量已经耗尽。对非本征光电导的情况,计算出开关的通态电阻为2.71 Ω。     

Combretastatin A-4 全合成中的光化学Wittig反应

在天然产物Combretastatin A-4全合成的关键步骤——Wittig反应中,引入紫外(254nm)辐射,结果使得Wittig反应的产率从原有的65％提高到83．6％。特别是其产物的Z-式立体异构体选择性大大提高,从原来的Z／E之比为3．6提高到11．5,笔者推测这种光化学反应是按双自由基机理进行。     

Efficient and direct synthesis of poly-substituted indeno[1,2-b]quinolines assisted by p-toluene sulfonic acid using high-temperature water and microwave heating via one-pot, three-component reaction

Reactions of aldehydes, 1,3-indanedione and enaminones were successfully carried out using p-toluene sulfonic acid (p-TsOH) as a catalyst and high-temperature water as a solvent under microwave irradiation. This method provided several advantages such as rapid reaction times, high yields, and a simple workup procedure. In addition, a possible mechanism to account for the reaction was proposed.     

K(a)hler-Einstein度量和Bergman度量的等价问题

华罗庚域的特殊类型Cartan-Hartogs域YⅡ(N,p;K)当K=p/2+1/p+1时,求解了该域上的复Monge-Ampère方程的边值问题,从而得到该域的完备K(a)hler-Einstein度量的显表达式,并且得到此度量下的全纯截曲率的负的上下确界,最后证明了此K(a)hler-Einstein度量与Bergman度量等价.     

The determination of silicon in airborne particulate matter by XRF and LA-ICP-MS

This study reports the analysis of Si in airborne particulate matter by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) as well as X-ray fluorescence (XRF). It was found that Si concentration in airborne particulates collected on PTFE-membrane filters could be accurately determined with a laser beam operated at 160 mJ free running mode, 6.5 mm defocusing distance and 0.8 l/min carrier gas flow rate during the LA-ICP-MS measurement. Standard filters prepared by NIST SRM 1648 urban particulates were used for both XRF and LA-ICP-MS not only to establish the calibration curves of Si, but also to examine the proposed method's effectiveness. The capability of applying both methods for natural sample analysis was also examined. Particulate loaded filter samples collected from a heavily polluted metropolitan area of Kaoshiung, Taiwan were initially measured by XRF, then by LA-ICP-MS. An intercomparison between them was thus performed. As a result, both XRF and LA-ICP-MS proved to be the valid analytical methods for directly determining Si concentrations in airborne particulates on PTFE membrane filters.     

The morphology of pulsed laser-induced damage on the surface of a copper film mirror

A copper film mirror was irradiated using a pulsed Nd:YAG laser (1.06 μm,10 ns) through an aperture. After laser irradiation, the damaged spot was analyzed using an optical microscope and periodic damage rings were found at the laser irradiation spot, the average spacing of these rings being about 40–50 μm. The damage ring could be observed in the periphery of the laser spot under lower laser energy densities. As the laser fluence increased, the periodic damage rings grew to cover the whole laser spot. Under higher laser energy density, the whole film was damaged and the rings disappeared. A Fresnel diffraction model is used to explain the appearance of these rings. The laser beam is diffracted by the aperture in the optic path, the laser intensity distribution at the copper film mirror becomes periodic rings and damage ripple pattern forms instantly with the laser ablation. The laser intensity distribution at the mirror surface is calculated using Collins formula, with which the period of the damage rings and other phenomena can be explained.     

Ab initio molecular dynamics study of the reactions of allene cation induced by intense 7 micron laser pulses

ABSTRACT

The isomerisation and fragmentation of allene cation (H₂C=C=CH₂⁺) by short, intense laser pulses were simulated by Born-Oppenheimer molecular dynamics (BOMD) on the ground state potential energy surface using the B3LYP/6-31?+?G(d,p) level of theory and a 10 cycle 7?µm cosine squared pulse with a maximum field strength of 0.07?au. Laser fields polarised along the C=C=C axis deposits an average of 150?kcal/mol in the molecule, compared to only 25 and 51?kcal/mol for perpendicular polarisations. Approximately 90% of the trajectories with the field aligned with the C=C=C axis underwent one or more structural rearrangement steps to form H₂C=CH–CH⁺ (15%), H₃CCCH⁺ (4%), cyclopropene cation (6%), and allene cation with rearranged hydrogens and carbons (47%). In addition, a variety of fragments including H₂CCCH⁺?+?H (10%), c-C₃H₃⁺?+?H (7%), and HCCCH⁺?+?H₂ (2%) trajectories were produced after isomerisation. With the same amount of thermal energy, field-free BOMD shows good agreements with the BOMD with the field. However, RRKM calculations favour isomerisation to propyne cation and dissociation to HCCCH⁺?+?H₂. This suggests that for molecules in intense laser fields the energy in the intermediate isomers is not distributed statistically.     

500 kV全固态Marx发生器

500 kV全固态Marx发生器采用Z型电路结构,以28个最大工作电压达22 kV、满载最高连续重复运行频率达200 Hz的绝缘栅双极型晶体管组件作为脉冲控制开关,采用以金属化膜电容器和线绕电感构成的梯形脉冲形成网络作为储能和脉冲形成器件。目前已实现500 kV脉冲输出,在50 Hz的重复频率下实现数十个脉冲的猝发输出。该发生器的输出脉冲电压峰值与已有文献报道的最高功率固态Marx发生器技术指标相近,输出脉冲电流峰值提高1倍,达到1000 A,发生器输出脉冲功率峰值达到500 MW。在采用电容器作为储能元件时,此Marx发生器输出脉冲宽度可在3～10 s范围内连续调整。