2007-06-20 21:15:18 +08:00
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\documentstyle[12pt]{article}
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\begin{document}
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\begin{eqnarray}
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2007-10-23 06:21:44 +08:00
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U &=& \frac{2 ~ a^3 ~ \sigma^3 ~ A_{cs}}{9 \left( a^2 - r^2 \right)^3}
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2007-06-20 21:15:18 +08:00
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\left[ 1 - \frac{\left(5 ~ a^6+45~a^4~r^2+63~a^2~r^4+15~r^6\right) \sigma^6}
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{15 \left(a-r\right)^6 \left( a+r \right)^6} \right], ~~ r < r_c \nonumber
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\end{eqnarray}
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\end{document}
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