  We have studied the thickness-induced superconductor-to-insulator transition
in the presence of a magnetic field for a-NbSi thin films. Analyzing the
critical behavior of this system within the "dirty boson model", we have found
a critical exponents product of $\nu_d z$ > 0.4. The corresponding phase
diagram in the (H,d) plane is inferred. This small exponent product as well as
the non-universal value of the critical resistance found at the transition call
for further investigations in order to thoroughly understand these transitions.
