chance rate
6.Abstract: The influence of electron screening on electroncaptu re for the most abundant nuclei in massive stars at the presupernova stage is discussed by using the shell model.It is shown that the total rate of chance of el ectronfraction should be multiplied by a factor of about 0.8~0.9 with the elec tron screeningtaken into account.
7.Results Average positive rate among 10 year was 1.59%,it ignificantly declined to conpare to 90*ss before,but it ascended again in the middle of 90*ss. The results showed that brucellosis epidemic was seriously taken place in the Liangshan state and young adults and veterinarians were mainly risk object which were infected by brucellosis in equal chance in gender.

