??????? ????????????? (Boston Universtity) ????????????? ???? ??????????? ??????????? ????????? ????????? ?????????? ??? ??????? ????????? ?????????????.????? 4000???? ???????? ????????????? 31000???? ???????? ??????????? ???????.????????????? ??? ????? ?????????????????? ??????? ??????????????? ?????.6 ?????? ????? ???????????????, 22 ????????? ????? ??????????????? ??????? ???????????? ???????????????.