Let<math>\mathcal{J}(r')=\int_0^a rdr\int_0^2\pi d\phi \frac{e^{ik|\mathbf{r}-\mathbf{r}'|}}{|\mathbf{r}-\mathbf{r}'|}</math><br><br> | Let<math>\mathcal{J}(r')=\int_0^a rdr\int_0^2\pi d\phi \frac{e^{ik|\mathbf{r}-\mathbf{r}'|}}{|\mathbf{r}-\mathbf{r}'|}</math><br><br> |