We have studied shrinkage-crack patterns which form when a thin layer of an alumina/water slurry dries. Both isotropic and directional drying were studied. The dynamics of the pattern formation process and the geometric properties of the isotropic crack patterns are similar to what is expected from recent models, assuming weak disorder. There is some evidence of a gradual increase in disorder as the drying layer become thinner, but no sudden transition, in contrast to what has been seen in previous experiments. The morphology of the crack patterns is influenced by drying gradients and front propagation effects, with sharp gradients having a strong orienting and ordering effect.

We present the results of experiments on impact craters formed by dropping a steel ball vertically into a container of small glass beads. As the energy of impact increases, we observe a progression of crater morphologies analogous to that seen in craters on the moon. We find that both the diameter and the depth of the craters are proportional to the 1/4 power of the energy. The ratio of crater diameter to rim-to-floor depth is constant for low-energy impacts, but increases at higher energy, similar to what is observed for lunar craters.

We review the history of experimental work on Rayleigh-Bénard convection in gases, and then describe a modern apparatus which has been used in our experiments on gas convection. This system allows the study of patterns in a cell with an aspect ratio (cell radius/fluid layer depth) as large as 100, with the cell thickness uniform to a fraction of a µm, and with the pressure controlled at the level of one part in 10 5. This level of control can yield a stability of the critical temperature difference for the convective onset of better than one part in 10 4. The convection patterns are visualized and the temperature field can be inferred using the shadowgraph technique. We describe the flow visualization and image processing necessary for this. Some interesting results obtained with the system are briefly summarized.

We study the penetration of steel spheres dropped vertically into a container of loosely packed, small glass beads. We find that the penetration depth of the spheres increases linearly with the incident momentum of the projectile, but with a zero-momentum intercept that can be either positive or negative. This behavior can be understood by modelling the granular medium as a non-Newtonian fluid with a yield stress and an effective viscosity. We derive the scaling behavior of the viscosity and find agreement with our experimental results. PACS Nos.: 45.70.–n, 83.80.Fg, 47.50.+d

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