The September, 2008 issue of Journal of Fluid Mechanics features on the cover research done in Physics Division. "An Experimental Investigation of Mixing Mechanisms in Shock-Accelerated Flow," by C. Tomkins et al., [J. Fluid Mechanics 611, 131 (2008)] describes an experimental investigation of mixing mechanisms in a shock-induced instability flow. For the case of a shock accelerated cylinder of heavy gas in air, quantitative two-dimensional maps of the heavy-gas (SF6) concentration using planar laser-induced fluorescence is obtained. The instantaneous scalar dissipation rate, or mixing rate, is estimated experimentally for the first time in this type of flow, and used to identify the regions of most intense post-shock mixing and to examine the underlying mechanisms. Instability growth is observed in certain regions of the flow beginning at intermediate times. The mixing rate results show that while these unstable regions play a significant role in the mixing process, a large amount of mixing also occurs by mechanisms directly associated with the primary instability, including gradient intensification via the large-scale strain field in a particular non-turbulent region of the flow. Such understanding of the true physical mechanisms is critical for accurate, predictive simulations and proper design of models of turbulent flow.