Current bottleneck in an inhomogeneous condensate
= Current bottleneck in an inhomogeneous condensate
{title2=$\rho_Lv_L=\rho_Rv_R$}
Stationary one-dimensional flow has constant particle current $j=\rho v$. A lower-density segment must flow faster at the same current and also has smaller local <speed of sound> $\sqrt{g\rho/m}$. It can therefore lose local <phonon> energetic stability before a denser segment.