新型常压离子化技术研究进展

随着社会的不断发展,人们对与日常生活密切相关的食品质量检测以及国家安全的需求越来越迫切。新型大气压离子化技术具有分析速度快、灵敏度高、实时在线等优点,在食品检测、药物分析、爆炸物筛查、化学反应监控、活体成像等领域得到了广泛应用。从传统大气压离子化技术出发,系统阐述离子化的基本原理和方法,并在此基础上介绍了直接电离技术、直接解吸/电离技术、辅助解吸/电离技术,以及不同电离技术的区别和联系。最后,对常压离子化技术未来发展趋势进行了展望。     

Precise timing of lacustrine gypsum in Luobubo, Xinjiang using the thermal ionization mass spectrometry U-series method

Dating techniques including gypsum dissolution in water, iron hydroxide co-precipitation with uranium and thorium and mass spectrometric determination have been investigated in this note. The ages of the gypsum samples in a CK core from Luobubo lacustrine sediments are in the range of (12.85±0.21) kaBP (4 m distance from the top core) to (153.2±7.2) kaBP (49 m distance from the top core) with the relative errors of ±1.6%–±4.7%. It indicates that the sedimental environment of the CK core was situated in the middle-late Pleistocene and Holocene periods, corresponding to 1–6 stages of oxygen isotopes in the abyssal sediments and included much information from last interglacial to Holocene warm periods.     

用电喷雾四极杆飞行时间质谱研究头孢类药物的质谱裂解规律

利用电喷雾四极杆飞行时间质谱研究了3种常用头孢类药物的质谱裂解行为. 二级质 谱数据结果显示： 在正离子模式下, β-内酰胺结构不太稳定, 在C（6）_C（7）和C（8）_N（1）键处易于断裂, 进而形成稳定的共轭结构, 此类药物易失去中性碎片NH₃.     

丙烷/空气低温等离子体点火起爆数值研究

为研究脉冲爆震发动机低温等离子体点火起爆机理, 充分考虑丙烷/空气详细化学反应动力学机理, 将低温等离子体点火器放电区等效为高温高压热核, 利用FLUENT 软件内置的层流有限速率化学反应模型, 对脉冲爆震发动机低温等离子体点火后由缓燃转爆震(DDT)的过程进行模拟, 并对该过程进行详细分析。实验结果表明, 将低温等离子体点火器简化成一定压力和温度的火核进行数值模拟是可行的, 压力接近常压, 壁面温度为常温更合理。数值模拟的爆震波发展时间小于实验结果, 考虑到实验时有点火延迟和测量误差, 可以认为实验值符合数值模拟时火核为常压、壁温为常温的计算结果。     

High-precision thermal ionization mass spectrometry dating of young volcanic rocks by using U-series method

A high precision thermal ionization mass spectrometric (HP-TIMS) technique is used to determine²³⁸U,²³⁴U,²³²Th,²³⁰Th concentrations and their ratios in whole rocks and minerals separated from Quaternary Maanshan, Dayingshan and Heikongshan volcanic rocks of Tengchong volcanic field, Yunnan Province, China. The²³⁸U-²³⁰Th isochrons are given, yielding four age values (227±20) ka (D-1, Dayingshan), (79.6±5.5) ka (D-7, Dayingshan), (21.9±3.0) ka (h-1, Heikongshan), and (7.5±1.0) ka (M-1, Maanshan). The result is not only consistent with but also preciser than those measured by the K-Ar method and the alpha spectrometry U-series method, indicating that the HP-TIMS method is reliable and has high precision. Besides, a procedure of HP-TIMS analysis of young volcanic rocks in China is set up preliminarily.     

正极性雷云作用下避雷针流注形成研究

讨论了在正极性雷云作用下避雷针流注形成过程,对从电子崩出现到流注形成的整个初始放电过程进行了分析。使用含电子、正离子、负离子的连续方程对雷电下气体的放电过程建模,通过耦合泊松方程求解空问电荷对电场的畸变影响。采用变量耦合计算得到了整个过程中电子浓度、正离子浓度、电子热能的空间分布,分析了电子浓度、正离子共同作用下对电场的影响。通过分析还得出在电子浓度高的区域电子热能并不高,两种的分布趋势并不完全一致。     

三能级系统的（1＋1′＋1′）共振电离动力学的理论研究

根据三能级系统三光子共振激发过程，建立了求解各能级布居数和电离效率的速率方程组，通过拉普拉斯变换方法，得到了在多光子激发电离过程中各能级布居率和电离效率的解析表达式，并运用该表达式研究了铯原子在典型实验条件下，基态6s（S1／2）相继吸收2个光子到达共振态6p（P3／2）、7d（D3／2）后再吸收一个光子电离的（1＋1′＋1′）过程中，各激发光强度以及激光脉冲宽度对各共振激发态布居率和电离效率的影响，并得到了各能级分别抽空时激发光强度必须满足的条件．     

Glutamate synthase: a fascinating pathway from L-glutamine to L-glutamate

Glutamate synthase is a multicomponent iron-sulfur flavoprotein belonging to the class of N-terminal nucleophile amidotransferases. It catalyzes the conversion of L-glutamine and 2-oxoglutarate into two molecules of L-glutamate. In recent years the X-ray structures of the ferredoxin-dependent glutamate synthase and of the a subunit of the NADPH-dependent glutamate synthase have become available. Thanks to X-ray crystallography, it is now known that the ammonia reaction intermediate is transferred via an intramolecular tunnel from the amidotransferase domain to the synthase domain over a distance of about 32Å. Although ammonia channeling is a recurrent theme for N-terminal nucleophile and triad-type amidotransferases, the molecular mechanisms of ammonia transfer and its control are different for each known amidotransferase. This review focuses on the intriguing mechanism of action and self-regulation of glutamate synthase with a special focus on the structural data.Received 8 August 2003; received after revision 15 September 2003; accepted 17 September 2003