Discussion Meeting: Soft matter & Statistical Physics

G-Lectures: Discussion on Soft matter and Statistical Physics

Dates: June 26, 2023 through June 30, 2023.

Location: Lab 4, Level E, Room 48 (L4E48), OIST Graduate University

Seminar format: There is no set format for the talks, in that they do not follow the standard 45 - 60 minute format. Each speaker is free to discuss a topic of their choice and for as long a duration as they would like (with sufficient breaks) owing to a single stipulation imposed on all speakers -- they should take time to provide a broad (historical) introduction of the topic for the interested novice, explain why the particular question is interesting (to them), delve into every attack that failed and why, before finally explaining the trick that helped solve the problem. Alternatively, one can also discuss a bunch of open problems in the topic of their choice rather than explain a solved one, after providing sufficient in depth background.

Speakers:

• Prof. Robert Ecke, Los Alamos National Laboratory and University of Washington
• Prof. Sriram Ramswamy, Dept. of Physics, Indian Institute of Science
• Prof. Sidney Nagel, Dept. of Physics, University of Chicago
• Prof. Hisao Hayakawa, Yukawa Institute of Theoretical Physics, Kyoto University
• Prof. Masaki Sano, Shanghai Jiao Tong University and The University of Tokyo
• Prof. Paul Chaikin, Dept. of Physics and the Center for Soft Matter Research, New York University
• Prof. Takahiro Hatano, Dept. of Earth and Space Science, Osaka University
• Prof. Dov Levine, Physics Dept., Israel Institute of Technology (Technion)
• Prof. Anton Zilman, Dept. of Physics, University of Toronto

Daily Meeting Schedule Format:

• 0900 - 1030: Session 1
• 1030 - 1045: Coffee/Tea Break
• 1045 - 1130: Session 2
• 1130 - 1230: Lunch
• 1230 - 1430: Session 3
• 1430 - 1500: Coffee/Tea Break
• 1500 - 1700: Session 4 or Break, lab visits, meet with OIST colleagues etc.
• 1730 - 2000: Dinner

Monday, June 26, 2023:

• Session 1 & 2, Prof. Hayakawa. Title: Theory of Mpemba effect: an anomalous relaxation process.
• Session 3: Prof. Sano. Title: Modeling the Dynamics of Cell Monolayers by Analyzing Integer Topological Defects.

Tuesday, June 27, 2023:

• Session 1 & 2, Prof. Nagel. Title: Memories in Matter
• Session 3, Prof. Hatano. Title: Models for creep and earthquake nucleation

Wednesday, June 28, 2023:

• Session 1 & 2 Prof. Levine. Title: A Brief Introduction to Information & Entropy

Thursday, June 29, 2023:

• Session 1 & 2 Prof. Chaikin. Title: Order and Information with applications to packing problems
• Session 3: Prof. Ramaswamy. Title: Non-reciprocity and other stories in active matter.
• 1500 - 1630: Prof. Nagel's Presidential Lecture (B250).

Friday, June 30, 2023:

• Session 1 & 2, Prof. Zilman. Title: Physics of the Nuclear Pore Complex
• Session 3, Prof. Ecke. Title: The physics of thermal convection with and without rotation.

Talk Abstracts

Prof. Hayakawa. Title: Theory of Mpemba effect: an anomalous relaxation process

The Mpemba effect (MPE) is a fascinating counter intuitive phenomenon that corresponds to the fact that hot liquid can freeze faster than cold liquid, discovered by Mpemba and Osborne [1]. Since the observation of MPE in liquids, there have been various proposed mechanisms to explain it, still surprisingly lacking any unified theory. Although there exist some debates on the validity of MPE [2], most researchers believe the existence of MPE-like processes as an anomalous relaxation process by a recent experimental support for colloidal suspensions [3].

In this talk, I would like to review the history of studies of MPE and some typical theoretical approaches on MPE such as Ref. [4,5]. Then, I will explain some my recent theoretical trials to reveal the mechanism of MPE through the analysis of an inertial suspension [6], a quantum dot [7] with clarifying the role of exceptional points [8] and a double well potential [9] corresponding to the experiment [3].

[1] E. B. Mpemba and D. G. Osborne, Phys. Educ. 4, 172 (1969).
[2] H. C. Burridge and P. F. Linden, Sci. Rep. 6, 37665 (2016).
[3] A. Kumar and J. Bechhoefer, Nature 584, 64 (2020).
[4] A. Lasanta, F. V. Reyes, A. Prados, and A. Santos, Phys. Rev. Lett. 119, 148001 (2017).
[5] Z. Lu and O. Raz, Proc. Natl. Acad. Sci. U.S.A. 114, 5083 (2017)
[6] S. Takada, H. Hayakawa and A. Santos, Phys. Rev. E 103, 032901 (2021) .
[7] A. K. Chatterjee, S. Takada and H. Hayakawa, arXiv:2304.02411.
[8] A. K. Chatterjee, S. Takada and H. Hayakawa, in preparation.
[9] R. . Chétrite, H. Hayakawa and F. van Wijland, in prepatation.

Prof. Sano. Title: Modeling the Dynamics of Cell Monolayers by Analyzing Integer Topological Defects

Recently, collective motions and morphogenesis of cell monolayers around topological defects have attracted much attention in statistical physics, soft matter, and biophysics. However, validity and universality of the governing equations for those systems are still in debate. Neural Progenitor Cells (NPC) have an elongated shape and reciprocate along their elongated axes, creating nematic orientational order. We induced integer topological defects with different director angles by using microfabrication on the substrate. Integer topological defects are usually difficult to appear spontaneously except for rosetta structures consisting of polarized cells. We found that all types of integer topological defects, including aster (radial), spiral, and circular patterns, attract cells toward the center of the defect. This cannot be explained by the minimum model of dry active nematics. The analysis of the flow and orientation fields consistently deviates from the minimum model. The background and basic concepts of the study will be explained, followed by a discussion of possible extensions of the governing equations.

Prof. Nagel. Title: Memories in Matter

Preamble: The recollection of events from childhood is part of what makes each of us unique. Manipulation of memories allows us to think and reason. Repetition allows precision performance in music and sports. When our faculties fail and no reason is left, we may still recall the names of our closest relatives – a memory that lasts when our brains can no longer retrieve newer information. Our muscular aches and pains remind us of recent activities. Yes! Our experience of memory is an indelible imprint of being alive. Non-biological materials can mimic the biological memories mentioned above: There are materials that perform functions only because of how they were initially manipulated – a form of rote memory. There are others that, akin to muscle memory, learn pathways between initial and final states. Some physical systems store many memories initially and then forget all but one – losing the ability to learn anything new. Many materials accumulate the dings and scratches caused by everyday use. Memory connotes the ability to encode, access, and erase signatures of past history. Once a system has reached thermal equilibrium, it can no longer recall aspects of its evolution. Thus, memory is tied intrinsically to far-from-equilibrium behavior and to transient response to a perturbation. There is currently no common description of memory formation in condensed-matter systems.

Memories in sheared jammed packings: An example of a system with a physical memory is a cyclically sheared jammed packing that can fall into a periodic orbit where each particle returns to its identical position in subsequent cycles. The packing encodes a memory of the shear amplitude at which it was trained. Simple models, based on collections of bistable objects (called hysterons), treat clusters of rearranging particles as isolated two-state systems. Such models offer insight but fail to account for other behavior. Adding interactions between hysterons overcomes some of these deficiencies, and of particular interest, allow simultaneous encoding of a second, novel form of memory. Hysterons are typically treated quasistatically but can be generalized to include dynamics to study how the system chooses a minimum. Changing the timescale of forcing allows a transition between a situation where the fate is determined by the local energy minimum to one determined by the path taken through configuration space.

Prof. Levine. Title: A Brief Introduction to Information and Entropy

Shannon entropy, which may be thought of as a generalization of thermodynamic entropy, quantifies our knowledge of a random variable. While the thermodynamic entropy is inextricably tied to the idea of equilibrium, the Shannon entropy has no such restrictions. It is defined as

 \(H \equiv - \Sigma~p (x)~\text{log}~p(X)\)

where the sum is over all values x that the random variable can take, with p(x) being the respective probabilities. As such, one might reasonably ask whether H might be a quantity of interest for systems far from equilibrium, where x would denote a microstate of the system

There are two main obstacles to pursuing this program: First, we do not generally know what the microstates are, and second, unlike the case of equilibrium statistical mechanics, we do not know the a priori probabilities of these microstates. Thus, it would appear that there is no way to calculate H.

I will introduce and discuss some relevant concepts in Information Theory which allows us to circumvent these obstacles. The discussion will be aimed at physicists with basic knowledge of Statistical Mechanics. In lectures which will follow mine, Paul Chaikin will discuss the relevance to these ideas to some far-from-equilibrium systems.

Prof. Chaikin. Tentative Title: Order and Information with applications to packing problems.

Abstract: A classic example of an order - disorder transition is the crystallization of hard spheres as density is increased. We study this and similar transitions experimentally. Then we use lossless data compression, a Shannon entropy approximate, to study several equilibrium and out-of-equilibrium systems, and show that they identify ordering, phase transitions, critical behavior, and critical exponents in thermodynamic and dynamic transitions. Guided by these results we performed experiments to test predictions on the nature of dynamical and equilibrium phase transitions and the ensembles they produce. Using both experiments and simulations we gain insight into the ancient problems of ordered and random sphere packings in different dimensions.

Prof. Zilman. Title: Physics of the Nuclear Pore Complex.

Nuclear Pore Complex (NPC) is a very large molecular “biomachine” that controls macromolecular transport between the cell nucleus and the cytoplasm. Unlike many cellular transporters, it does not possess a molecular “gate” and the translocation of cargoes is not directly coupled to the non-equilibrium input of energy. Yet, it is capable of transporting cargoes against their concentration gradients with very high specificity and speed. The key part of the transport mechanism of the NPC is the assembly of intrinsically disordered proteins that fills its transport channel and serves as a milieu for the translocation of the cargo-carrying transport proteins. I will review the current understanding of the transport mechanism of the NPC, which has been partially recapitulated in biomimetic nanochannels, and will report on the recent computational/theoretical and experimental works providing explanation for a number of puzzling abilities of the NPC to conduct rapid and selective transport in a very crowded environment. I will conclude by the implications of these results for viral transport through the NPC and design of biomimetic channels for protein sorting.

Prof. Ecke. Title: The Physics of Thermal Convection with and without Rotation

The fundamental forces of the electromagnetic, weak, and strong interactions are much more powerful than gravity but they are confined to small spatial and temporal scales and largely cancel out on the scales we observe and feel every day. On macroscopic length scales, gravity dominates as evidenced, for exaple, by the motions of planets or the very existence of the Sun itself. With gravity comes the phenomena of buoyancy in which density differences can give rise to highly complex motions from the interior of the Earth and the atmosphere on its surface to the life cycle of stars including their spectacular demise in a supernova. Thus, the motion of fluids owing to buoyancy in the presence of gravity is arguably the most important macroscopic physical process in the universe. Rotation is also ubiquitous in nature and is fundamental in understanding the motions of atmospheres and oceans on rotating planets and stars. I will describe the physics of convection, i.e. buoyancy-induced fluid flow deriving from thermal gradients. Starting from its history and foundations, I will describe experiments, numerical simulations, and theory applied to the laboratory realization of convection known as Rayleigh-Bénard convection (after Lord Rayleigh for the theory and Henri Bénard for related experiments). The talk will conclude with recent exciting discoveries in rotating thermal convection.

Prof. Ramaswamy. Title: Non-reciprocity and other stories in active matter

Abstract: I will begin with a introduction aimed at de-mystifying active dynamics. I will then discuss non-reciprocality and its intimate connection to active matter. I will then explore various topics, time and interruptions (which are welcome) permitting, including new directions in "wet" and chiral active matter. At each stage I will discuss points that worry me.