1 \documentstyle[12pt
]{article
}
6 E &=&
\epsilon \left[ \frac{\sigma^
{6}}{7560}
7 \left(
\frac{6R-D
}{D^
{7}} +
\frac{D+
8R
}{(D+
2R)^
{7}} \right) -
8 \frac{}{} \right.
\nonumber \\
9 &&
\qquad \left.
\frac{1}{6} \left(
\frac{2R(D+R) + D(D+
2R)
10 \left[ \ln D -
\ln (D+
2R)
\right]}{D(D+
2R)
} \right)
\right]
11 \qquad r < r_c
\nonumber