A novel DNA duplex. A parallel-stranded DNA helix with Hoogsteen base pairing

We show here for the first time that a stable parallel double helix with Hoogsteen pairing can exist independently of the triple helix of which it is a component part. The experiments employ DNA oligonucleotides with mixed sequences of normal bases. These duplexes are distinct from previously reported ribopolynucleotide helices containing bulky substituents which prevent Watson-Crick pairing as well as from parallel duplexes with Donohue, or reversed Watson-Crick, pairing. Stoichiometry is established by mixing curves and gel electrophoresis. Tm depends linearly upon pH, increasing with acidity because of the need to protonate N3 of C. The Tm of the 20-mer studied here is 52 degrees C at pH 5.2 and 0.1 M NaCl. At pH above 6, the molecule rearranges to form an antiparallel duplex with imperfect Watson-Crick pairing and loops, and the Tm is then independent of pH. The CD spectrum of the parallel duplex is very similar to that of the corresponding triple helix but quite different from that of the Watson-Crick helix. The infrared spectrum in the double bond region closely resembles that of the triple helix but, as with the CD, is quite different from that of the Watson-Crick duplex. The infrared spectra of the duplex and triple helix are also nearly identical in the region form 800 to 1000 cm-1, which is sensitive to backbone conformation. The only symmetry element present is a pseudorotational axis coincident with the helix axis of the parallel duplex as well as with the axis of the corresponding triple helix.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of substrate and effector binding sites in the ArsA ATPase

The ars operon of plasmid R773 confers resistance to antimonials and arsenicals in Escherichia coli by encoding an ATP-dependent extrusion system for the oxyanions. The catalytic subunit, the ArsA protein, is an ATPase with two nucleotide binding consensus sequences, one in the N-terminal half and one in the C-terminal half of the protein. The ArsA ATPase is allosterically activated by tricoordinate binding of As(3+) or Sb(3+) to three cysteine thiolates. Previous measurements suggested that the intrinsic fluorescence of tryptophans might be useful for examining binding of Mg2+ ATP and antimonite. In the present study an increase in intrinsic tryptophan fluorescence was observed upon addition of Mg2+ ATP. This enhancement was reversed by addition of antimonite. The ArsA protein contains four tryptophan residues: Trp159, Trp253, Trp522, and Trp524. The first two were altered to tyrosine residues by site-directed mutagenesis. Cells expressing both the arsAW159Y and arsAW253Y mutations retained resistance to arsenite, and the purified W159Y and W253Y proteins retained ATPase activity. While the intrinsic tryptophan fluorescence of the W253Y protein responded to addition of Mg2+ ATP, intrinsic tryptophan fluorescence in the purified W159Y protein was no longer enhanced by substrate. These results suggest that Trp159 is conformationally coupled to one or both of the nucleotide binding sites and provides a useful probe for the interaction of effector and substrate binding sites.     

镧系钙钛矿型氧化物（LaBO3）的催化氧化性能及其净化效果的研究

本文在气相色谱仪联用微反应器装置上,研究了LaBO_3型催化剂中的B位元素对催化氧化活性的影响规律,并进行了程序升温脱附实验。另外,还对LaBO_3型载体催化剂进行了活性筛选,并在柴油机台架上与贵金属Pt/Al_2O_3进行了有害气体净化效果的对比实验。实验结果表明,LaBO_3氧化物中LaMnO_3对CO、CH_4的催化氧化活性最高,且CO、CH_4活性中心并不一致。LaMnO_3/γ-Al_2O_3浸渍微量助化剂后,能使CO在130℃完全氧化,CH_4的氧化温度在300～500℃范围内,LaMnO_3载体催化剂对柴油机有害排放物的净化率很低,浸渍微量助化剂后,净化率提高一倍以上,特别是LaMnO_3/堇青石蜂窝陶瓷,浸渍后的净化效果同贵金属Pt/Al_2O_3接近。     

A maximum torque control with a controlled capacitor for asingle-phase induction motor

This paper presents a new method to achieve a maximum torque for a single-phase induction motor. An AC adjustable capacitor using an electronic switch in parallel with a capacitor is proposed. The capacitor is short-circuited in a different period by an electronic switch during each cycle to vary the effective value of the AC capacitor. Two new optimization algorithms, which obtain a maximum starting torque by adjusting the effective capacitor, are proposed. No starting capacitor or centrifugal switch is used here. A theoretical analysis, and simulated and experimental results are presented in this paper     

内燃机节油率计算的探讨

讨论比较了现有内燃机节油率计算方法的优缺点、产生误差的原因，提出了采用曲线拟合的方法求取率的新方法。文中给出了计算公式和计算步骤，通过编制计算机程序，计算了几种典型发动机的节油率指标，并传统的按度试验数据逐点计算方法进行了对比，证明此方法是一种比较客观、科学的节油率指标计算方法。     

化工工艺计算机辅助设计

本文根据化工工艺设计的特点，阐述了化工工艺设计与ＣＡＤ的关系和开发研制计算机辅助化工工艺设计软件的思想，即将工艺设计、工艺图绘制与相关数据处理融为一体，并遵循这一构思，提出了软件开发研制的方法。     

矢量图的参数化重建系统——VACAD

本文重点探讨了如何将矢量图形进行参数化重建，即从只具备纯几何信息的矢量图中抽取元素间的拓扑信息，从而保证尺寸变动时保持拓扑关系不变，并能对多视图进行同步处理。这一方法的最大优点是用户作图时不受约束，因为系统只处理最终图形。另外，该思想并不局限于Ａｕｔｏ ＣＡＤ环境上，可方便地推广到其它二维绘图系统中。     

变速箱结构设计专家系统技术的研究

结构设计是机械产品设计过程中的重要环节，解决结构设计的智能化不但可以缩短产品的设计周期，而且还可以降低成本，提高设计质量。专家系统是解决智能化设计的技术之一。本文讨论有关结构专家系统的几个关键技术，主要包括系统的控制策略，面积对象的知识表达方式及结构设计的并行设计     

Role of RE and Mg on Graphitization of Spheroidal Graphite Malleable Cast Iron

ＲｏｌｅｏｆＲＥａｎｄＭｇｏｎＧｒａｐｈｉｔｉｚａｔｉｏｎｏｆＳｐｈｅｒｏｉｄａｌＧｒａｐｈｉｔｅＭａｌｌｅａｂｌｅＣａｓｔＩｒｏｎ￥ＬｉｕＪｉｎ－Ｈａｉ（ＨｅｂｅｉＩｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏｔｏｇｙ，Ｍｉａｎｊｉｎ３００１３０，Ｃｈｉｎａ）...     

岩石声学参数测量分析系统

刘祝萍等．岩石声学参数测量分析系统．测井技术，１９９４，１８（４）：２８８～２９８岩石声学参数测量是声波测井资料解释的基础性工作。本文介绍一种岩样声学参数测量分析系统，该系统能对岩样的纵（Ｐ）、横（Ｓ）波速度进行测量记录，并可将实测波形进入计算机，对所记录的波形进行频谱分析后，通过与标准试件的比较，可估算岩样的声衰减。