Description:

Sumitabha Brahmachari
Title: Free energy model for double-helix DNA braids

Abstract: I will talk about free energy modeling of intertwined double-helix DNAs or DNA 'braid', which is a biologically relevant DNA structure. I will discuss the single-molecule experiments that motivated the model, then the analytical model, and finally, compare numerical predictions with the experiments. I will very briefly introduce the worm-like chain model for double-helix DNA, which has been widely studied, and is central to my free energy model. The goal with this model is to quantitatively understand the mechanical properties of DNA braids under tensile and torsional stress.
 

Sam Hadden
Title: Kepler Planet Masses and Eccentricities from Transit Timing Variations

Abstract:

The Kepler mission has discovered thousands of extrasolar planets and readily provides measurements of their sizes and orbital periods.

Learning more about the origin and evolution of these extrasolar planetary systems requires measurements of their masses and orbits, which are often difficult to obtain. In multi-planet systems gravitational interactions result in transit timing variations (TTVs) that can provide exquisitely sensitive probes of planet masses of and eccentricities. However, inverting TTV measurements in order to infer planet properties can be challenging: it involves fitting a nonlinear model with a large number of parameters to noisy data, often with significant degeneracies between parameters. I present results from two complementary approaches to TTV inversion: Markov chain Monte Carlo simulations that use N-body integrations to compute transit times and a simplified analytic model for computing the TTVs of planets near mean motion resonances.

Pizza will be available.