= Anisotropic slender-filament drag from Stokeslet integration
{title2=$\xi_\perp/\xi_\parallel\to2$}
Integrating a <Stokeslet> distribution along a straight slender filament explains the leading drag anisotropy. Axial motion samples the tensor component $2/(8\pi\mu|z|)$, while transverse motion samples $1/(8\pi\mu|z|)$. Integrating on both sides from radius $a$ to cutoff $\ell$ gives $\xi_\parallel\sim2\pi\mu/\ln(\ell/a)$ and $\xi_\perp\sim4\pi\mu/\ln(\ell/a)$. End effects and nonlocal hydrodynamic interactions supply the corrections retained by <slender-body theory>.
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