Morphological and molecular phylogenetic analysis of two Saprolegnia sp (Oomycetes) isolated from silver crucian carp and zebra fish

Two Saprolegnia isolates, JY isolated from silver crucian carp (Carassius auratus gibelio Bloch) and BMY isolated from zebra fish (Brachydanio rerio Hamilton) came from infections occurring concurrently in different locations in China. To confirm whether the two isolates were from the same Saprolegnia clone, comparative studies have been carried out based on their morphological, physiological and molecular characteristics. Observations showed that morphologically (both asexual and sexual organs) the two isolates were broadly similar and both isolates under-went repeated zoospore emergence. Comparing 704 base pairs of internal transcribed spacer (ITS) region and the 5.8S rDNA, we found isolates JY and BMY shared an identical ITS sequence with a minor variation (99.6 % similarity). Forty available sequences for representatives Saprolegnia spp. belonged to four phylogenetically separate clades. The two studied isolates fell within clade I that comprised a group of isolates which showed almost an identical ITS sequence but had been identified as a number of different morphological species. our findings suggest that isolates JY and BMY appear to belong to the S. ferax clade and this clade (1) contains a number of closely related phylogenetic species. This is distinct from the more common fish pathogenic isolates, which belong to the S. parasitica clade (III) and are characterized by having cysts decorated by bundles of long hooked hairs and two further clades (II and IV) containing largely saprotrophic or soil born species. (C) 2009 Published by Elsevier Ltd on behalf of The British Mycological Society.

Influences of the Fish-Mouth Project and the Groins on the Flow and Sediment Ratio of the Yangtze River Waterway

A depth-integrated two-dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigati

迎风紧致格式求解Hamilton-Jacobi方程

基于Hamilton-Jaeobi(H-J)方程和双曲型守恒律之间的关系,将三阶和五阶迎风紧致格式推广应用于求解H-J方程,建立了高精度的H-J方程求解方法.给出了一维和二维典型数值算例的计算结果,其中包括一个平面激波作用下的Richtmyer-Meshkov界面不稳定性问题.数值试验表明,在解的光滑区域该方法具有高精度,而在导数不连续的不光滑区域也获得了比较好的分辨效果.相比于同阶精度的WENO格式,本方法具有更小的数值耗散,从而有利于多尺度复杂流动的模拟中H-J方程的求解.

非平整运动海底上n层流动中波浪传播的Hamilton逼近

在海洋水域，界面波对大尺度变化流的作用是一种典型的分层流动现象。考虑一不可压缩、无黏的分层势流运动，建立了一个在非平整运动海底上的n层流体演化系统，并对其进行了Hamilton描述。每层流体具有各自的常密度、均匀流水平速度，其厚度由未扰动和扰动部分构成。相对于顶层流体的自由表面，刚性、运动的海底具有一般地形变化特征。在明确指出n层流体运动的控制方程和各层交界面上的运动学、动力学边界条件（包含各层交界面上张力效应）后，对该分层动力系统进行了Hamilton构造，即给出其正则方程和其下述的正则变量：各交界面位移和各交界面上的动量势密度差。