HIRFL改造中的加速器物理问题

从加速器运行的角度对兰州重离子加速器 HIRFL建成以来所存在的问题进行了总结 ,结合放射束物理和冷却储存环 CSR对 HIRFL的新要求 ,从加速器的物理设计方面提出了一些改进方案 .主要问题有 :超低能束流传输的空间电荷效应的影响 ,扇聚焦回旋加速器 SFC高频加速电压不对称对束流轨道的影响 ,用半频聚束的方式补偿两台回旋加速器的纵向不匹配 ,前束线上聚束器的工作模式的选取 ,强杂散磁场对超低能和低能束流传输的影响 ,分离扇回旋加速器 SSC注入区过垫补磁场对注入束流轨道的影响 ,SFC和 SSC的单圈引出 ,重离子通过剥离膜后的束流损失和束流品质的变坏

Evolutionary and functional diversity of green fluorescent proteins in cephalochordates

Green fluorescent protein (GFP) has been widely used as a molecular marker in modern biological research. Before the recent report of one GFP gene in Branchiostoma floridae, GFP family members were cloned only from other two groups of species: Cnidaria and Copepoda. Here we describe the complete GFP gene repertoire of B. floridae which includes 13 functional genes and 2 pseudogenes, representing the largest GFP family found so far. Coupling with nine other GFP sequences from another two species of genus Branchiostoma and the sequences from Cnidaria and Copepoda, we made a deep-level phylogenetic analysis for GFP genes in cephalochordates and found: 1) GFP genes have experienced a divergent evolution in cephalochordates; 2) all amphioxus GFP genes form four main clades on the tree which had diverged before the radiation of the last common ancestor of all extant cephalochordates; 3) GFP genes in amphioxus shared a common ancestor with that in Copepoda rather than being derived from horizontal gene transfer, which indicates that our ancestor was derived from a fluorescent organism and lost this ability after its separation from Cephalochordata, and also makes GFP a rare gene which has a rather unusual evolutionary path. In addition, we also provided evidence indicating that GFP genes have evolved divergent functions by specializing their expression profile, and different fluorescent spectra by changing their emission peaks. These findings spark two interesting issues: what are GFP in vivo functions in cephalochordates and why they are lost in other examined deuterostomes? (C) 2009 Elsevier B.V. All rights reserved.National Natural Science Foundation of China [30830023]; National High Technology Research and Development Program of China (863 Program) [2008AA092602