Lower bounds for self-adjoint Sturm-Liouville operators

In this note we provide estimates for the lower bound of the self-adjoint operator associated with the three-coefficient Sturm-Liouville differential expression $$\frac{1}{r} \left(-\frac{\mathrm d}{\mathrm dx} p \frac{\mathrm d}{\mathrm dx} + q\right)$$ in the weighted $L^2$-Hilbert space $L^2(\mathbb R; rdx)$.