The mixed-type integral equations for transient elastodynamic plane crack problems

In the present paper, by use of the boundary integral equation method and the techniques of Green fundamental solution and singularity analysis, the dynamic infinite plane crack problem is investigated. For the first time, the problem is reduced to solving a system of mixed-typed integral equations in Laplace transform domain. The equations consist of ordinary boundary integral equations along the outer boundary and Cauchy singular integral equations along the crack line. The equations obtained are strictly proved to be equivalent with the dual integral equations obtained by Sih in the special case of dynamic Griffith crack problem. The mixed-type integral equations can be solved by combining the numerical method of singular integral equation with the ordinary boundary element method. Further use the numerical method for Laplace transform, several typical examples are calculated and their dynamic stress intensity factors are obtained. The results show that the method proposed is successful and can be used to solve more complicated problems.     

超微粒乳剂的制备及量子尺寸效应的研究

本文制备了四种不同粒度的超微粒AgBr照相乳剂,用X射线衍射技术对其粒子的大小进行了测定;观察到乳剂的紫外吸收峰随晶体颗粒的减小表现出逐渐蓝移;本文提出晶体表面的悬键的存在使得纳米晶体的平均键能升高,并对纳米AgBr乳剂的量子尺寸效应进行了解释。     

TiO_2载体表面酸性的研究

利用NH_3吸附和吡啶吸附红外技术研究TiO_2的制备条件对其表面酸性的影响。结果表明,用NH_3水中和TiCl_4溶液方法制备的TiO_2(A)表面有较强的L酸中心,中和条件对表面酸性中心数目和强度有显著影响。由TiOSO_4水解方法制备的TiO_2(B)表面具有较强的L酸中心和较弱的B酸中心,引入不同添加剂可有效地调变TiO_2载体表面的酸性。     

Effect of pentobarbital on normal brain protection and on the response of 9L rat brain tumor to radiation therapy

The authors attempted to confirm published reports that pentobarbital protects against radiation-induced damage to normal rat brain, as well as enhances radiotherapeutic efficacy in a rat brain tumor model. They evaluated animal survival in 9L gliosarcoma-burdened rats that received whole-brain radiation therapy (16, 24, 32, or 40 Gy) while under intraperitoneal pentobarbital (60 mg/kg) or intramuscular ketamine (60 mg/kg) sedation. The animals were examined at autopsy to attribute death to either intracranial tumor growth or normal brain toxicity in the absence of discernible tumor. There was no difference between the two anesthesia groups regarding the survival of unirradiated animals. Radiation therapy produced a significant dose-dependent prolongation in animal survival, which was limited by the development of normal tissue toxicity at the higher doses. When compared to ketamine anesthesia, pentobarbital anesthesia appeared to offer some protection (not statistically significant) against early (but not late) toxicity at selected radiation doses. A reduction in the number of deaths from tissue toxicity suggested an increased antitumor effect, but again this was not statistically significant. Only in one case was there even a marginal significant difference (p = 0.045) between overall therapeutic efficacy in rats sedated with pentobarbital versus ketamine. While there may be a radioprotective effect of pentobarbital in rat brains without intracranial tumor, there is no conclusive evidence for either radioprotection or significant improvement of radiotherapeutic efficacy in this 9L rat brain tumor model.     

含淀粉聚乙烯膜的时控光降解研究

使用复合光降解剂，得到了可光降解的生物降解膜。对膜的光降解进行了考察，并对影响光降解的因素进行了讨论，结果表明，我们所制得的膜是一种较好的时控光降解膜。     

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