Northwestern Events Calendar

Apr
4
2018

Brown Bag Lunch Series with Riley Hanus and Sumitabha Brahmachari

When: Wednesday, April 4, 2018
12:00 PM - 1:00 PM CT

Where: Technological Institute, F160, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Post Docs/Docs - Graduate Students

Contact: Bud Robinson   (847) 491-3644

Group: Physics and Astronomy PAECRS

Category: Academic

Description:

“Phonon diffraction and dimensionality crossover in phonon-interface scattering”
Riley Hanus, Northwestern University

This theoretical work provides several mechanistic understandings of phonon-interface scat- tering. The treatment provided here defines the interface as an array of linear defects, as opposed to a structureless planar defect which is inherent in current models. This is the basis on which prevailing models for the structure and energy of interfaces are grounded, and we extend this definition to phonon-interface scattering. We apply the analytical expression derived here to phonon-GB strain field scattering from a symmetric tilt grain boundary. It is shown that pho- non diffraction conditions arise from the periodic nature of these defect arrays as can be expected from the wave-like nature of phonons. Furthermore, for diffuse heat conduction, a dimensiona- lity crossover is observed in the frequency (ω) dependence of the scattering rate which arises from phase space considerations. This crossover in defect dimensionality provides a mechanis- tic understanding for ω-dependence in phonon-interface scattering, transmissivity, specularity, and the T2 behavior in the low temperature lattice thermal conductivity of polycrystalline and nanocrystalline materials.

“Mechanics and Segregation of Topology-Constrained Double-Helix DNA”
Sumitabha Brahmachari, Northwestern University

Cellular DNA is constantly being mechanically manipulated by various DNA-binding proteins, which has motivated the study of the mechanical properties of DNA. I will talk about a semiflexible-polymer model for DNA, with a focus on how to treat inhomogeneities or ''defects'', that explains experiments studying DNA mechanics and points at possible physical mechanisms that may be biologically relevant. A remarkable feature of the cellular DNA -- a topologically-constrained, confined polymer -- is its macroscopic organization driven by proteins working at the molecular length scales, and the principles governing the organization of our genome are only beginning to be uncovered. I will also talk about our ongoing efforts in modeling compaction and segregation of the genome via active extrusion of loops.

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