Consider the ODE $x^2 y''+x y' + (x^2-\alpha^2)y = 0$, where $\alpha$ is an arbitrary positive irrational number that is less than $ 2 \pi$. Let $J_{\alpha}(x)$ be a solution to the equation and define
$Z_{\alpha}(l) = \{ x \in [0, l] : J_{\alpha}(x) = 0 \}$.
Is there a reference for an upper bound on the quantity $Z_{\alpha}(l)/l$ in terms of $l$ for large $l$?
