Computations in Science Seminars
Jan 2019
23
Wed 12:15
Shmuel Rubinstein, Harvard
e-mail:
Host: William Irvine ()
Organizer: Grayson Jackson ()
The physics of crushing and smashing: Cascades and cataclysmic change

Many of the big problems we are facing involve far from equilibrium systems that entail a cataclysmic change. Climate, turbulence and earthquakes, developmental biology, evolution and even aging and death. These phenomena are rare (sometimes occurring only once) and are entirely irreversible. While understanding the physics of such irreversible processes is of both fundamental and practical importance, these problems also pose unique challenges. These challenges, as they manifest in turbulence, were beautifully portrayed by Richardson:

“Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity” Lewis Fry Richardson (1922)

In his short verse, Richardson captures the essence of the turbulent cascade—the conveyance of kinetic energy across scales that underlies the universal dynamics of turbulent flows. Indeed, such conveyance of important physical quantities (energy, stress, frustration and even information) down and up a vast range of scales underlines the dynamics of many systems. The same applies to how a multi-contact frictional interface will form and break or how correlated defect structures determine the strength of a space-rocket, how an intricate network of creases will form when we crumple a thin sheet or when soda can is smashed. The challenge in understanding these systems is in capturing the events as they occur, keeping up with the dynamics on all scales and at all times. Here, I will review our work on several key irreversible system and introduce the new tools we developed to address their unique evolution and discuss the interesting physics we learned.

Jan 2019
30
Wed 12:15
Xiang Cheng, University of Minnesota
e-mail:
Host: Tom Witten ()
Organizer: Zhiyue Lu ()
From Flocking Birds to Swarming Bacteria: A Study of the Dynamics of Active Fluids

Active fluids are a novel class of non-equilibrium complex fluids with examples across a wide range of biological and physical systems such as flocking animals, swarming microorganisms, vibrated granular rods, and suspensions of synthetic colloidal swimmers. Different from familiar non-equilibrium systems where free energy is injected from boundaries, an active fluid is a dispersion of large numbers of self-propelled units, which convert the ambient/internal free energy and maintain non-equilibrium steady states at microscopic scales. Due to this distinct feature, active fluids exhibit fascinating and unusual behaviors unseen in conventional complex fluids. Here, combining high-speed confocal microscopy, holographic imaging, rheological measurements and biochemical engineering, we experimentally investigate the dynamics of active fluids. In particular, we use E. coli suspensions as our model system and illustrate three unique properties of active fluids, i.e., (i) abnormal rheology, (ii) enhanced diffusion of passive tracers and (iii) emergence of collective swarming. Using theoretical tools of fluid mechanics and statistical mechanics, we develop a quantitative understanding of these interesting behaviors. Our study illustrates the general organizing principles of active fluids that can be exploited for designing “smart” fluids with controllable fluid properties. Our results also shed new light on fundamental transport processes in microbiological systems.

Feb 2019
6
Wed 12:15
Andrej Košmrlj, Princeton University
e-mail:
Host: Arvind Murugan ()
Organizer: Elizabeth Lee ()
Feb 2019
13
Wed 12:15
Jörn Dunkel, MIT
e-mail:
Host: William Irvine ()
Organizer: Peter Chung ()
Feb 2019
20
Wed 12:15
Greg Voth, Wesleyan University
e-mail:
Host: William Irvine ()
Organizer: Steven Strong ()
Feb 2019
27
Wed 12:15
OPEN
Mar 2019
13
Wed 12:15
OPEN
Mar 2019
20
Wed 12:15
Hana El-Samad, University of California, San Francisco
e-mail:
Host: Arvind Murugan ()
Mar 2019
27
Wed 12:15
Arvind Murugan, University of Chicago
e-mail:
Host: William Irvine ()
Apr 2019
3
Wed 12:15
Greg Bewley, Cornell University
e-mail:
Host: William Irvine ()
Apr 2019
10
Wed 12:15
Oskar Hallatschek, UC Berkeley
e-mail:
Host: Arvind Murugan ()
Apr 2019
17
Wed 12:15
Nikta Fakhri, MIT
e-mail:
Apr 2019
24
Wed 12:15
Detlef Lohse, University of Twente
e-mail:
Host: William Irvine ()
May 2019
1
Wed 12:15
Pankaj Mehta, Boston University
e-mail:
Host: Stefano Allesina ()
May 2019
8
Wed 12:15
Thierry Emonet, Yale University
e-mail:
Host: Stephanie Palmer ()
May 2019
15
Wed 12:15
David Lentik, Stanford
e-mail:
Host: William Irvine ()
May 2019
22
Wed 12:15
Joshua Shaevitz, Princeton University
e-mail:
Host: Arvind Murugan ()
May 2019
29
Wed 12:15
Xiaoming Mao, University of Michigan
e-mail:
Host: William Irvine () and Vincenzo Vitelli ()