Ooplasmic streaming
Many processes in biology are so complex and hard to model using physics laws. The problem of how a Drosophila egg manages to mix its contents would naively appear to be in this category. However as it turns out, it can be understood very well with a physical model that only has a few ingredients: a fluid, semiflexible fibers, and motors that walk on them. Using hydrodynamics, and nonlinear equations, many intriguing aspects of this system can be predicted and found to be in excellent agreement with observation. The long range nature of hydrodynamic flows allows a relatively small number of motors to drive bulk mixing of the cell. The mixing is aided by chaotic motion of microtubules, and this motion can be well understood by modeling the motion of semiflexible chains with kinesin motors walking up them.
Entanglement entropy
Entropy for isolated systems
How do the laws of statistical mechanics emerge from quantum mechanics? Although there is a pretty good explanation classically of this question, the quantum case is certainly not as clear. Earlier work by the author and others proposed the Eigenstate Thermalization Hypothesis. More recent work by the author has examined a more subtle problem, to understand the thermodynamic entropy for an isolated quantum system.
  • Using simulations techniques borrowed from quantum and statistical physics, masses of data from microarrays can be analyzed to determine the most important genes in diagnosing similar cancers. For example, less than 15 genes can be used to perfectly predict which of four related childhood cancers a patient has.
  • By understanding the underlying physics of these devices, their reliability can be greatly increased.
time autocorrelation function
Polymers in a vacuum
The 2002 Nobel prize in Chemistry was awarded in large part for the discovery of how to put single protein molecules into a vacuum. This is then used to do mass spectrometry on these large molecules such as proteins. Despite this technology`s great importance, very little had been done to understand the behavior of polymers in this situation. Conservation of angular momentum alters the statistical properties, and in many circumstances, chains can show oscillatory behavior very different from what is found in solution.
Dynamics of magnets
Nonequilibrium dynamics of magnetic systems have a wide variety of applications including to hard drives. New phenomena explored are:
  • Often avalanches should be viewed more like combustion than previously understood, where the flipping of magnetic spins was thought to be more like the the falling of dominoes.
  • Hysteresis loop "multicycles"
  • Domain patterns seen going from positive to negative applied field are not simply related to what happens when the field is inverted.
One dimensional heat conduction
The dynamics of one dimensional system, such as nanotubes, show anomalous dynamics because of conservation laws. One of the most striking consequences of this is that the heat transfered across such a system does not scale with the inverse of the system length, but instead a power of it. Determining the exact relationship is challenging and requires the use of highly nonlinear models. By devising a new model incorporating random collisions but still obeying conservation of energy and momentum, a clearer understanding emerged of the large scale dynamical description.