Presenter:          Akash Vardhan

Title:                    Self organizations via collisions in dry shape changing active matter

Date:                   Tuesday, May 16, 2023

Time:                   11:00 a.m.

Place:                  Howey N201/202

Committee:       Dr. Daniel Goldman, School of Physics, Georgia Institute of Technology (advisor)

Dr. Zeb Rocklin, School of Physics, Georgia Institute of Technology

Dr. Kurt Wiesenfeld, School of Physics, Georgia Institute of Technology

Dr. Dana Randall, School of Mathematics, Georgia Institute of Technology

Abstract:

Dry active matter, [1, 2] which is the study of collective behavior arising from
local interactions between agents driven out of equilibrium on a frictional sub- strate, has 
exhibited an assortment of rich and varied emergent phenomena. Most of these studies have by 
default focused on convex shaped particles that self-propel under the drive. There is another class 
of active matter that uses it’s drive to change shape and can either self propel or remain 
immotile, depending on the reaction forces exerted by the environment. These extended rigid bodies 
can take concave shapes during their self-deformation cycles which offers the emergent benefit of 
entanglement via geometry due to interpenetration, as in the case of a pile of passive staples [4] 
or active worm blobs and staple like robots [10].
The diffraction patterns observed when snakes [11] and a snake like robot [8] are allowed to pass 
through a pegged lattice. The mechanical intelligence shown by nematodes and a worm inspired robot 
[13] by modulating it’s compliance upon collision with a lattice element. The contact mediated 
synchronization of swimming nematodes [7, 6], which motivated a study on synchronization in 3 link 
robotic swimmers [14] are some examples of novel phenomena exhibited by this class of active 
matter.
In this dissertation, I will focus on describing the gait dependent emergent self-organization, 
mediated via collisions in a robo-physical dry active matter system called Smarticles [9]. Rattling 
theory [3] selects the configurations of a complex multi body system which experience the least 
amount of fluctuations. I will describe in detail the elemental low rattling excitation called the 
Gliders
[12] which spontaneously emerge during the relaxation of densely packed col- lectives of 
smarticles. These excitations dynamically phase lock to a constant phase difference in their gaits, 
and can remain bound and locomoting for several cycles without any external source of attraction. I 
will give an explanation for the binding mechanism and the transport of these gliders. These 
mechanical counter-parts to the simulated gliders observed in several elementary cellular automata 
like ECA-54 and 110 in 1D and the famous Game of life in 2D, also cycle through the same set of 
configurations as they propagate like their digital
cousins. Finally, I will shift to large ensembles of these robots and describe the
self organization exhibited in the bulk from the propensity of gliders to link with other 
smarticles, thus forming polymer chain like structures. I will end with the on-going endeavors on 
trying to harness the observed self-organization via feedback and control towards something 
functional and task oriented [5].