Experimental study of polarity dependence in repetitive nanosecond-pulse breakdown

Pulsed breakdown of dry air at ambient pressure has been investigated in the point-plane geometry, using repetitive nanosecond pulses with 10 ns risetime, 20--30 ns duration, and up to 100 kV amplitude. A major concern in this paper is to study the dependence of breakdown strength on the point-electrode polarity. Applied voltage, breakdown current and repetitive stressing time are measured under the experimental conditions of some variables including pulse voltage peak, gap spacing and repetition rate. The results show that increasing the E-field strength can decrease breakdown time lag, repetitive stressing time and the number of applied pulses as expected. However, compared with the traditional polarity dependence it is weakened and not significant in the repetitive nanosecond-pulse breakdown. The ambiguous polarity dependence in the experimental study is involved with an accumulation effect of residual charges and metastable states. Moreover, it is suggested that the reactions associated with the detachment of negative ions and impact deactivation of metastable species could provide a source of primary initiating electrons for breakdown.     

有机磷化合物的研究 XXV.溶剂性质对烯丙基膦酸酯碳阴离子和芳醛反应区域选择性的影响

杂原子稳定的烯丙基碳阴离子反应区域选择性的研究是一个很活跃的领域。取代烯丙基膦酸二乙酯碳阴离子和醛、酮的反应已有记载。本文研究烯丙基膦酸二乙酯碳阴离子(1)和苯甲醛(2a)、对甲基苯甲醛(2b)的反应,考察溶剂对反应区域选择性的影响。 1和2反应,同时生成α-位反应产物3和γ-位反应产物4。     

邻苯二酚在活化玻碳电极上的电化学行为

邻苯二酚( QH2,儿茶酚)等有机化合物是人体内的电活性物质,直接参与人体内的各种生理过程.     

水杨酸在多壁碳纳米管修饰电极上的电化学行为及其测定

用循环伏安法(CV)研究了水杨酸(SA)在多壁碳纳米管修饰玻碳电极上的电化学行为,并初步探讨了反应机理.实验结果表明,水杨酸在该电极上为一个2e/H~+的完全不可逆过程.在pH=5.0的磷酸盐缓冲溶液(PBS)中,用循环伏安法在该电极上测定了水杨酸.方法线性范围为2.0×10~(-5)～1.0×10~(-3)mol/L,检出限为8.93×10~(-6)mol/L.将该电极用于药品分析,结果令人满意.     

阻抑动力学分光光度法测定微量碘

基于在稀磷酸介质中,痕量碘离子对亚硝酸根催化溴酸钾氧化甲基红的的阻抑作用,提出了测定痕量碘离子的阻抑动力学分光光度分析的方法.测定碘离子的线性范围在0.66 mg·L-1以内,检出限(3Sb/K)为7.5×10-6g·L-1.用于海带及食盐中微量碘的测定,测定结果的相对标准偏差(n=6)在1.4%～2.2%之间,测得方法的回收率为99.7%～100.1%.     

CuCl对Et3NHCl/AlCl3离子液体催化性能的影响

 用CuCl对Et3NHCl/AlCl3离子液体进行改性,并考察了其对异丁烷-丁烯烷基化反应的催化性能. 结果表明,烷基化油的收率达到178%,C8组分的含量达到85%,辛烷值(RON)达到94.8. 通过结构组成及电荷分布分析可知,在CuCl改性的Et3NHCl/AlCl3离子液体中形成了新的配位结构AlCl4CuCl-,它作为更好的碳正离子受体,在反应过程中可降低碳正离子的浓度,进而降低烯烃的聚合程度,抑制较长碳链烷烃的生成,改善烷基化油的组成.     

边界元法在辐射换热中的一个应用

运用Stokes公式及边界元理论，导出了辐射换热计算中的辐射角系数与相互辐射面积的计算基本公式。通过四个典型例子的计算，结果与精确解加以对比，表明本方法计算可靠、稳定，具有输入数据少，准确度高等优点。分析了影响计算准确度有关因素，对所遇到的奇异积分给予了有效的处理。     

Low-Threshold Random Laser with One Mirror and Feedbacks in PMMA Nano-Composite Films

A low-threshold random laser with one mirror and feedback is investigated in the PMMA film containing rhodamine 590 and TiO2 nano-particles. Incoherent and coherent laser emission is observed. Effect of particle concentration on light emission is explored, and the optimum particle concentration is obtained. Optical microscopy and scanning probe microscopy are used to investigate the film structure, and the principle of incoherent and coherent laser is analysed.