,=U心+U=U0+r)号0) 4支小号-小品 n-小rtr 重 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 2 2 * 1 1 8 Re 2 1 1 2 1 1 1 2 1 v v g s L L L V g s v g g L V s L V P R U P U I R U R U U U R I U U U U U = = - G = - G = - = - G = - G = + = + G = + G + + + - + - +