Especially on july 21st , 2005 , after more than a decade of strictly pegging the renminbi to the u . s . dollar at an exchange rate of 8 . 28 , the people ’ s bank of china ( pboc 2005a ) announced a revaluation of the currency and a reform of the exchange rate regime , more scientists and economists have put their emphasis on this new exchange rate regime . up till now , this new arrangement has worked in our country for more than ten months 选择不适当的汇率制度将直接危及到一国经济金融的安全和稳定,这点从20世纪90年代以来,前苏联、东欧国家从计划经济向市场经济转型过程中出现的宏观经济震荡、墨西哥金融危机、东南亚金融危机,以及之后发生的阿根廷金融危机等可以得到直接证明。
In our laboratory , a unique mutation detection system using a shuttle vector plasmid has been established to demonstrate that a low concentration of mnng ( 0 . 2 m ) can induce nontargeted mutation in mammalian cells : the mammalian cells were exposed to 0 . 2m mnng for 2 . 5h , then a shuttle plasmid pz189 carrying supf trna gene was transfected into cells after 24h culture . we found a 5 - fold higher mutation frequency of the plasmid replicated in pretreated cells than the spontaneous mutation frequency of the plasmid replicated in control cells . this kind of mutation did not occur immediately after mnng exposure 我们实验室曾用一特殊的突变检测系统，直接证明dna损伤剂可在哺乳动物细胞诱发非定标性突变：首先用低浓度( 0 . 2 m )的短寿烷化剂mnng (半寿期为1 . 1hr )处理细胞2 . 5h后，继续培养24h ，将重组有用作突变检测的靶基因supftrna基因的穿梭质粒pz189转入细胞复制，发现在未受致癌物直接攻击的穿梭质粒中有较自发突变率高5倍以上的靶基因突变。
