Influence of secondary void damage in the matrix material around voids

The mechanism of ductile damage caused by secondary void damage in the matrix around primary voids is studied by large strain, finite element analysis. A cylinder embedding an initially spherical void, a plane stress cell with a circular void and plane strain cell with a cylindrical or a flat void are analysed under different loading conditions. Secondary voids of smaller scale size nucleate in the strain hardening matrix, according to the requirements of some stress/strain criteria. Their growth and coalescence, handled by the empty element technique, demonstrate distinct mechanisms of damage as circumstances change. The macroscopic stress-strain curves are decomposed and illustrated in the form of the deviatoric and the volumetric parts. Concerning the stress response and the void growth prediction, comparisons are made between the present numerical results and those of previous authors. It is shown that loading condition, void growth history and void shape effect incorporated with the interaction between two generations of voids should be accounted for besides the void volume fraction.

Sequence of genome segments 1, 2, and 3 of the grass carp reovirus (Genus Aquareovirus, family Reoviridae)

The genome segments 1, 2, and 3 of the grass carp reovirus (GCRV), a tentative species assigned to genus Aquareouirus, family Reouiridae, were sequenced. The respective segments 1, 2, and 3 were 3949, 3877, and 3702 nucleotides long. Conserved moths 5' (GUUAUUU) and 3' (UUCAUC) were found at the ends of each segment. Each segment contains a single ORF and the negative strand does not permit identification of consistent ORFs. Sequence analysis revealed that VP2 is the viral polymerase, while VPI might represent the viral guanyly/methyl transferase (involved in the capping process of RNA transcripts) and VP3 the NTPase/helicase (involved in the transcription and capping of viral RNAs), The highest amino acid identities (26-41%) were found with orthoreovirus proteins. Further genomic characterization should provide insight about the genetic relationships between GCRV, aquareoviruses, and orthoreoviruses, It should also permit to precise the taxonomic status of these different viruses. (C) 2000 Academic Press.

Surface pigments,algal biomass profiles,and potential production of the euphotic layer:Relationships reinvestigated in view of remote-sensing applications

Maps of surface chlorophyllous pigment (Chl a + Pheo a) are currently produced from ocean color sensors. Transforming such maps into maps of primary production can be reliably done only by using light-production models in conjuction with additional information about the column-integrated pigment content and its vertical distribution. As a preliminary effort in this direction. $\ticksim 4,000$ vertical profiles pigment (Chl a + Pheo a) determined only in oceanic Case 1 waters have been statistically analyzed. They were scaled according to dimensionless depths (actual depth divided by the depth of the euphotic layer, $Z_e$) and expressed as dimensionless concentrations (actual concentration divided by the mean concentration within the euphotic layer). The depth $Z_e$ generally unknown, was computed with a previously develop bio-optical model. Highly sifnificant relationships were found allowing $\langle C \rangle_tot$, the pigment content of the euphotic layer, to be inferred from the surface concentration, $\bar C_pd$, observed within the layer of one penetration depth. According to their $\bar C_pd$ values (ranging from $0.01 to > 10 mg m^-3$), we categorized the profiles into seven trophic situations and computed a mean vertical profile for each. Between a quasi-uniform profile in eutrophic waters and a profile with a strong deep maximum in oligotrophic waters, the shape evolves rather regularly. The wellmixed cold waters, essentially in the Antarctic zone, have been separately examined. On average, their profiles are featureless, without deep maxima, whatever their trophic state. Averaged values their profiles are featureless, without deep maxima, whatever their trophic state. Averaged values their profiles are featureless, without deep maxima, whatever their trophic state. Averaged values of $ρ$, the ratio of Chl a tp (Chl a + Pheo a), have also been obtained for each trophic category. The energy stored by photosynthesizing algae, once normalized with respect to the integrated chlorophyll biomass $\langle C \rangle _tot $ is proportional to the available photosythetic energy at the surface via a parameter $ψ∗$ which is the cross-section for photosynthesis per unit of areal chlorophyll. By tanking advantage of the relative stability of $ψ∗.$ we can compute primary production from ocean color data acquired from space. For such a computation, inputs are the irradiance field at the ocean surface, the "surface" pigment from which $\langle C \rangle _tot$ can be derived, the mean $ρ value pertinent to the trophic situation as depicted by the $\bar C_pd or $\langle C \rangle _tot$ values, and the cross-section $ψ∗$. Instead of a contant $ψ∗.$ value, the mean profiles can be used; they allow the climatological field of the $ψ∗.$ parameter to be adjusted through the parallel use of a spectral light-production model.

迟缓爱德华氏菌铁调控蛋白与溶血素调控蛋白的分子生物学研究

爱德华氏菌病是海水养殖鱼类牙鲆（Japanese flounder）的一种常见细菌病。迟缓爱德华氏菌的致病相关因子有凝血素、溶血素、铁载体、粘附素及侵袭素等，其中调控铁载体的蛋白即是铁调控蛋白（Ferric uptake regulator）Fur。 本论文首先用简并PCR及染色体步移的方法获得了迟缓爱德华氏菌fur基因(etfur)(GenBank 号EF197912)，发现其氨基酸序列与大肠杆菌的fur基因(ecfur)的氨基酸序列有大约90％的相似性。功能分析表明迟缓爱德华氏菌Fur（Etfur）能与大肠杆菌的Fur(Ecfur)功能互补；功能域分析发现Etfur的C92和C95为功能所必需，而E112K突变则增强FurEt的抑制功能；启动子活性分析发现Etfur具有自我调控功能，随之通过定点突变及引物延伸的方法确定了etfur的启动子。为了研究Etfur的调控干扰作用，我们构建了Etfur过量表达菌株TX1/pJRTF,发现该菌株的生长速度明显比野生型菌株慢，而且其外膜蛋白的表达与野生型相比有明显差异；随后我们提取了差异蛋白，用反免疫方法筛选差异表达基因。进一步的毒力研究表明Etfur过量表达能使细菌毒力显著下降。分析迟缓爱德华氏菌溶血素基因(ethB)启动子活性发现Etfur能够调控ethB的表达。最后，我们构建了一个调控抑制子筛选系统，并由此筛选到另一个ethB调控因子EthR,该调控因子属于GntR调控蛋白家族；实验分析表明EthR是一个比Fur效应更强的调控因子。