  Within Takahashi's spin-wave theory we study finite size and temperature
effects near the quantum critical point in the $J_{1}-J_{2}$ Heisenberg
antiferromagnet defined on a strip ($L\times\infty$). In the continuum limit,
the theory predicts universal finite size and temperature corrections and
describes the dimensional crossover in magnetic properties from 2+1 to 1+1
space-time dimensions.
