research

I study how crystals start to form, which is as a microscopic crystallite (to the left is a microscopic crystallite) that then goes on to grow into a large crystal like a snow flake, or a salt crystal. The most recent thing I have worked on is looking at how the rate at which crystals form (nucleate) can vary by orders of magnitude due to hidden differences between one crystallising droplet or air sample, and another. See my LabTalk article on a recent paper of mine. I am also interested in how defects in the crystal lattice affect how crystals start to form - it is well known that defects affect growth but apart from some work by my now-ex PhD student Amanda Page, there is very little work on the effect of defects on how crystallisation starts. However, as we can see above, quite complex patterns of defects can appear even in microscopic crystallites.

In the snapshot above colours denote different local ordering of each (Lennard-Jones model) atom. Yellow denotes that the atom is a local face-centered crystalline (fcc) environment, and blue is hexagonal close-packed. Thus if the crystal was, for example, a defect free pure fcc it would be completely yellow. It is not. Although it has yellow fcc domains they are split by what are called stacking faults - which show up as planes of locally blue (hcp) atoms.

There are also atoms with local five-fold symmetry (grey) - a symmetry that is forbidden in large crystals. See here for a 3D interactive view of the snapshot. I also have interests in heterogeneous nucleation, and the nucleation of competing polymorphs. I recently got an EPSRC grant, to see the research I proposed doing with the postdoc, see the Case for Support that was funded.

My biological physics research both tries to answer fundamental questions about how cells function and tries to understand specific systems, in collaboration with experimentalists. In practice there is no sharp divide between the two, recent work with experimentalists has found that a protein of medical interest diffuses surprisingly rapidly given its large size. This finding raises the question of how our cells have evolved to allow proteins to move rapidly around inside them -- many proteins need to move from A to B inside our cells to perform their function.

The images just above are from an experiment by Berni Schmierer (then working at the Cancer Research labs in London) on a protein called Smad2. The protein Smad2 acts to control specific genes and to do that it has to basically move around the nucleus until it finds them. The bright ovals are the nuclei of cells and they are bright as they contain high concentrations of a fusion protein of Smad2 and GFP - GFP fluoresces which is why the cells are bright. The 3 images are of the same nucleus at 3 different times; earliest on the left. Berni bleached a strip (middle image) and then watched diffusion of Smad2-GFP within the nucleus restore the fluorescence unifomity in the nucleus (right-hand image). The rate at which the fluorescence in the bleached strip returns allows us to estimate how fast Smad2 moves in the nucleus. The scale bar is 10 micrometres.