A vertical line passing through the point $(h, 0)$ intersects the ellipse $\frac{x^2}{4}+\frac{y^2}{3}=1$ at the points $P$ and $Q$. Let the tangents to the ellipse at $P$ and $Q$ meet at the point $R$. If $\Delta(h)=$ area of the triangle $P Q R, \Delta_1=\max _{1 / 2 \leq h \leq 1} \Delta(h)$ and $$ \Delta_2=\min _{1 / 2 \leq \mathrm{h} \leq 1} \Delta(\mathrm{~h}), \text { then } \frac{8}{\sqrt{5}} \Delta_1-8 \Delta_2= $$