Computations in Science Seminars
May 2019
22
Wed 12:15
Joshua Shaevitz, Princeton University
e-mail:
Host: Arvind Murugan ()
Organizer: Steven Strong ()
Self-driven phase transitions in living matter

The soil dwelling bacterium Myxococcus xanthus is an amazing organism that uses collective motility to hunt in giant packs when near prey and to form beautiful and protective macroscopic structures comprising millions of cells when food is scarce. I will present an overview of how these cells move and how they regulate that motion to produce different phases of collective behavior. Inspired by recent work on active matter and the physics liquid crystals, I will discuss experiments that reveal how these cells generate nematic order, how defect structure can dictate global behavior, and how Myxo actively tune the Péclet number of the population to drive a phase transition from a gas-like flocking state to an aggregated liquid-droplet state during starvation.

May 2019
29
Wed 12:15
Xiaoming Mao, University of Michigan
e-mail:
Host: William Irvine () and Vincenzo Vitelli () *
Organizer: Elizabeth Lee () and Zhiyue Lu () *
Topological floppy modes in aperiodic networks and a mechanical duality theorem

Topological states of matter have been intensively studied in crystals, leading to fascinating phenomena such as scattering-free edge current in topological insulators. However, the power of topological protection goes well beyond ordered crystal lattices. In this talk we explore how topology protects mechanical edge modes in messy, noncrystalline, systems. We will use disordered fiber networks and quasicrystals as our examples, to demonstrate how topological edge floppy modes can be induced in these structures by controlling their geometry. Fiber networks are ubiquitous in nature and especially important in bio-related materials. Establishing topological mechanics in fiber networks may shed light on understanding robust processes in mechanobiology. Quasicrystals show unusual orientational order with quasiperiodic translational order. We found that a bulk topological polarization can be defined for mechanics of quasicrystals that is unique to their non-crystallographic orientational symmetry. References: (1) Di Zhou, Leyou Zhang, Xiaoming Mao, “Topological Edge Floppy Modes in Disordered Fiber Networks”, Phys. Rev. Lett. 120, 068003 (2018); (2) Di Zhou, Leyou Zhang, Xiaoming Mao, “Topological Boundary Floppy Modes in Quasicrystals”, arXiv:1809.09188 (2018).

Nov 2019
13
Wed 12:15
Orit Peleg, University of Colorado
e-mail:
Host: Arvind Murugan ()
Nov 2019
20
Wed 12:15
W. Benjamin Rogers, Brandeis University
e-mail:
Host: Arvind Murugan ()
Jan 2020
8
Wed 12:15
Bob Rosner, University of Chicago
e-mail:
Host: William Irvine ()