Accelerated evolution of snake venom phospholipase A2 isozymes for acquisition of diverse physiological functions

The nucleotide sequences of two cDNAs and four genes encoding Trimeresurus gramineus venom gland phospholipase A2 (PLA2) isozymes were determined and compared internally and externally with those encoding Trimeresurus flavoviridis venom gland PLA2 isozymes. It was revealed that the protein-coding regions are much more diversified than the 5' and 3' untranslated regions (UTRs) and the introns except for the signal peptide domain. The numbers of nucleotide substitutions per site (KN) for the UTRs and the introns were approximately one-quarter of the numbers of nucleotide substitutions per synonymous site (KS) for the protein-coding regions and were at the same level as the KN value of T. gramineus and T. flavoviridis TATA box-binding protein (TBP) genes, indicating that the protein-coding regions of PLA2 isozyme genes are unusually variable and that the UTRs including the introns of venom gland PLA2 isozyme genes have evolved at similar rate to those of non-venomous genes. The numbers of nucleotide substitutions per non-synonymous site (KA) values were close to or larger than the KS values for the protein-coding regions in venom gland PLA2 isozyme genes, indicating that the protein-coding regions of snake venom gland PLA2 isozyme genes have evolved via accelerated evolution. Furthermore, the evolutionary trees derived from the combined sequences of the 5' and 3' UTRs and the signal peptide domain of cDNAs were in accord with the consequences from taxonomy. In contrast, the evolutionary trees from the mature protein-coding region sequences of cDNAs and from the amino acid sequences showed random patterns. Estimations of nucleotide divergence of genes and the phylogenetic analysis reveal that snake venom group IJ PLA2 isozyme genes have been evolving under adaptive pressure to acquire new physiological activities.     

钨含量对12％Cr耐热钢力学性能的影响SCIEI

本文报道了钨的含量对12％Cr-W-V-Nb耐热钢高温及室温力学性能的影响。试验结果表明:当钨的含量在2.2—3.0wt-％之间变化时,室温抗拉性能没有明显变化,但冲击韧性却随着钨量的增加而下降。另一方面,钨量的增加提高了短时间的持久强度,但对长时间的持久强度却没有改善作用。钨量的增加对析出行为有两方面的作用:促进Fe_2W型Laves相的形成并增加析出相总量;加速了回火后在高温加热过程中析出相的粗化。钨对高温力学性能的影响与析出特性有密切关系。在持久寿命较短时,析出相来不及粗化,析出量的增加造成了析出强化效果的加强,即钨量的增加提高了高温强度;而当长时间加热后,析出相发生了明显的粗化,降低了析出强化效果。     

Studies on the toxicity of pulp and paper mill effluents—II. Mutagenicity of the extracts of the liver from spotted sea trout (Nibea mitsukurii)

Sediment samples collected at three different coastal points (Shinguu, Ooigawa and Tagonoura) were extracted with diethylether and then methanol. Each extract was separated into five fractions by high-speed liquid chromatography and they were submitted to mutagenic assay using B. subtilis and S. typhimurium and to GC-MS analysis.The ether fraction of sediment sample from Shinguu showed DNA damaging potency on B. subtilis and exhibited mutagenic effect on S. typhimurium TA 98, TA 100 and TA 1537. 2,4,6-Trichlorophenol, 3,4,5,6-tetrachloroguaiacol, dehydroabietic acid, pyrene and fluoranthene were mutagenic substances among 28 substances identified and tested.     

High-voltage planar junction with a field-limiting ring

A twodimensional Poisson equation is solved as part of a program to improve breakdown characteristics of a planar p-n junction by using a field limiting ring. The influences of n^? concentration and n^? layer width of p⁺-n^?-n⁺ diode are investigated. Higher n^? concentration and smaller n^? width make optimum distance between anode and field limiting ring smaller. Breakdown voltages predicted by optimising method reported agree well with the experimental results.     

Fractionation of polypropylene by the rising temperature method

Polypropylene having high isotacticity was fractionated by the rising temperature method. This method was then compared with the solvent gradient method through the characterization of fractions. It was found that the elution behavior in the rising temperature method was explainable by the equation of equilibrium between the polymer in dilute solution and the solid state polymer on the support, assuming that the heat of fusion and transition points for the deposited polymer were variable with polymer species.     

The Discrete Weibull Distribution

The discrete Weibull distribution is defined to correspond with the Weibull distribution in continuous time. A few properties of the discrete Weibull distribution are discussed.     

Vacuum lithography using plasma polymerization and plasma development

A completely dry lithography has been proposed which involves plasma polymerization of methyl methacrylate (MMA) and plasma development with CCl₄. It was called vacuum lithography because all processes were performed in a vacuum. However, the developed pattern had a lower resolution than patterns produced by conventional lithography with a wet process. After several technical refinements, the quality of the resist and the developed pattern was markedly improved. In this paper, recent results will be reported.A gas-flow-type reactor was used instead of a bell-jar-type reactor because the morphology of plasma-polymerized MMA (PPMMA) varied with each experimental run which was performed with the same gas and discharge parameters. The monomer vapour was introduced downstream of the argon discharge, and the polymerized film was formed on the substrate placed further downstream in the mixed gas.The development of pattern was performed by etching with an Ar-O₂ mixture and with hydrogen gas instead of CCl₄ gas, because the etching rate of the resist was too high in a CCl₄ plasma and a clear pattern was not obtained. The evaluated sensitivity and γ value of PPMMA were 1000 μC cm^?2 and 1 respectively. MMA containing 5% tetramethyltin was also used as a monomer gas for plasma polymerization downstream of the argon discharge. In this case the sensitivity and γ value were 10 μC cm^?2 and 2 respectively.     

Factors affecting the photo-induced graft copolymerization of methyl methacrylate onto fibrous polymer

The effects of sample swelling, photosensitizer, and solvent on the photo-induced graft copolymerization of methyl methacrylate onto fibrous polymers such as Vinylon, nylon 6, and polyester were examined. Each separate factor, sample swelling, or solvent, or their combination, increased activity of polymerization. Only some sensitizer were effective. Studying the ESR spectra of photo-irradiated polymers also showed that either the sample swelling, the photosensitizer, or the organic solvent is very effective for the formation of polymer radicals under irradiation.