On the number of unique expansions in non-integer bases

Let q>1 be a real number and let m=m(q) be the largest integer smaller than q. It is well known that each number can be written as with integer coefficients 0?ci<q. If q is a non-integer, then almost every x∈Jq has continuum many expansions of this form. In this note we consider some properties of the set Uq consisting of numbers x∈Jq having a unique representation of this form. More specifically, we compare the size of the sets Uq and Ur for values q and r satisfying 1<q<r and m(q)=m(r).