Towers of Function Fields over Non-prime Finite Fields
  Over all non-prime finite fields, we construct some recursive towers of function fields with many rational places. Thus we obtain a substantial improvement on all known lower bounds for Ihara's quantity $A(\ell)$, for $\ell = p^n$ with $p$ prime and $n>3$ odd. We relate the explicit equations to Drinfeld modular varieties. 
Alp Bassa, Peter Beelen, Arnaldo Garcia, Henning Stichtenoth
math.AG math.NT