Experimental evidence for three universality classes for reaction fronts   in disordered flows
  Self-sustained reaction fronts in a disordered medium subject to an external flow display self-affine roughening, pinning and depinning transitions. We measure spatial and temporal fluctuations of the front in $1+1$ dimensions, controlled by a single parameter, the mean flow velocity. Three distinct universality classes are observed, consistent with the Kardar-Parisi-Zhang (KPZ) class for fast advancing or receding fronts, the quenched KPZ class (positive-qKPZ) when the mean flow approximately cancels the reaction rate, and the negative-qKPZ class for slowly receding fronts. Both quenched KPZ classes exhibit distinct depinning transitions, in agreement with the theory. 
S\'everine Atis, Awadhesh Kumar Dubey, Dominique Salin, Laurent Talon,   Pierre Le Doussal and Kay J\"org Wiese
cond-mat.stat-mech