E1 少 2 2 pe/ od EU E 0 2 &a& 0r2 r 2 2 FeEl 0r1 0 0r1 2E2= 0 r r 2 0r2 0 0r2 D1=D2 1515 0 1 0 1 r E    = 0 1 2 2 1 1 0 r r r d d U            + = 1 2 2 1 1 r r r d d U          + = 0 2 0 2 r E    = 0 2 2 2 1 1 0 r r r d d U            + = 2 2 2 1 1 r r r d d U          + = D1 0 r1E1 =   0 1 0 0 1 r r    =   =  0 2 2 1 1 0 r r d d U    + = D2 0 r2E2 =   0 2 0 0 2 r r    =   =  0 D1 = D2 =  0