Kenneth Desmond
     5th Year Graduate Student
Rheology     Microrheology     Why Study Microrheology     Ellipsoidal Diffusion    

Rheology is the study of how and why materials flow which is typically expressed mathematically using the two quantities; visocsity and elasticity. These two quantities can mathematically be written as one complex term called the bulk modulus. For many materials, simply knowing the bulk modulus is sufficient for predicting the flow and deformation of many materials under certain conditions.

Here is a paper that gives a more advanced explanation of rheology and the tools used.