ICTS

Week 1

1. Chandan Dasgupta

   ICTS & IISc, Bangalore, India

   Statistical mechanics of systems of interacting classical particles: Mayer cluster expansion for non-ideal gas, correlation and response functions (Lecture 1)

   TBA

   Statistical mechanics of systems of interacting classical particles: Elements of liquid-state theory, introduction to classical density functional theory (Lecture 2)

   TBA

 

 

 

2. Sanat Kumar

   Department of Chemical Engineering, Columbia University, New York, NY

   The Role of Chain Conformational Entropy on Self-Assembly of Surfactants, Polymers and Nanoparticles

   “Self-assembly (SA) in the classic sense can be defined as the spontaneous and reversible organization of molecular units into ordered structures by non-covalent interactions. The first property of a self-assembled system that this definition suggests is the spontaneity of the self-assembly process: the interactions responsible for the formation of the self-assembled system act on a strictly local level—in other words, the nanostructure builds itself. “ - WIkipedia

   This lecture will first focus on the basics of self-assembly and will show that this process only occurs for special systems. The ideas of Israelachvili on the critical micelle concentration and the packing parameter will be introduced. This lecture then naturally leads to delineating the conformational entropy of the surfactant tail, which is driven by ideas of entropic elasticity first espoused by Flory and deGennes. The application of these ideas to block copolymer self-assembly, to polymer crystallization and nanoparticle self-assembly will be explored in lecture 3.

   Texts:

   Israelachvili, Intermolecular and Surface Forces, Academic Press, 1992

   Rubinstein, Colby Polymer Physics, Oxford, 2003

   Lecture 1 (Israleachvili, Chapters 16,17)

   1. What is self-assembly. Examples including Crystallization – colloids, polymers; Surfactants – Small molecules, Block copolymers; Nanoparticles – their growth, assembly; Self-assembled monolayers; Templated Synthesis from Surfactant Assemblies – ZSM 5; Lipid Bilayers….

   2. Mass action law- finite clusters vs. phase separation

   3. CMC

   4. Packing parameter idea

   Lecture 2 (Rubinstein & Colby, Chapters 2, 3, 5)

   1. Importance of chain entropy

   2. Flory entropy idea

   3. Entropic springs

   4. Scaling

   5. Chain dimensions under stretching, good solvent etc

   Lecture 3 (Various sources)

   1. Application of these ideas to BCP self-assembly

   2. Application to polymer crystallization

   3. Nanoparticle self assembly

   4. How do you measure this – SANS.

 

 

 

3. Dov Levine

   Technion Israel Institute of Technology, Haifa, Israel

   Order, Entropy, Information, and Compression

   In my lectures, I will begin with an idiosyncratic discussion of the idea of organization, ordering, and order. I will then introduce some relevant ideas from information theory, including Shannon entropy, Kolmogorov complexity, and elementary concepts from coding theory, followed by to a discussion of data compression and its relation to Shannon entropy. This will lead to a resume of results from ongoing research into the identification and quantification of order in systems far from equilibrium.

 

 

 

4. Dapeng Bi(1), Silke Henkes(2), Karen E. Daniels(3), and Bulbul Chakraborty(4)

   1. Department of Physics, Syracuse University, Syracuse, New York 13244
   2. ICSMB, Department of Physics, University of Aberdeen, Aberdeen, AB24 3UE, United Kingdom
   3. Department of Physics, North Carolina State University, Raleigh, North Carolina 27695
   4. Martin Fisher School of Physics, Brandeis University, Waltham, Massachusetts 02454

   Introduction to Edwards’ ideas, Microcanonical and Canonical Ensembles, Concept of Compactivity and Angoricity (Lecture 1)

   At the core of equilibrium statistical mechanics lies the notion of sta- tistical ensembles: a collection of microstates, each occurring with a given a priori probability that depends on only a few macroscopic parameters, such as temperature, pressure, volume, and energy. In this review, we discuss recent advances in establishing statistical ensem- bles for athermal materials. The broad class of granular and particu- late materials is immune to the effects of thermal fluctuations because the constituents are macroscopic. In addition, interactions between grains are frictional and dissipative, which invalidates the fundamen- tal postulates of equilibrium statistical mechanics. However, granular materials exhibit distributions of microscopic quantities that are re- producible and often depend on only a few macroscopic parameters. We explore the history of statistical ensemble ideas in the context of granular materials, clarify the nature of such ensembles and their foundational principles, highlight advances in testing key ideas, and discuss applications of ensembles to analyze the collective behavior of granular materials.

   Reference 1

 

 

 

5. Sriram Ramaswamy

   Department of Physics, Indian Institute of Science, Bengaluru 560 012

   Dynamics, Entropy Production & Defects in Active Matter

   I will begin with a general Langevin framework for ac- tive matter dynamics [1] in which the “active terms” are directly linked to a driving force most naturally in- terpreted as a chemical potential imbalance between fuel and reaction products. I will consider the entropy- production properties of specific instances of such equations of motion for individual active particles as well as for active field theories [2, 3]. I will also discuss the defect-unbinding transition of active nematic sys- tems [4], which has a natural energy-entropy aspect.

   I acknowledge support from the Tata Education and Development Trust and from a J C Bose Fellowship of the Science & Engineering Research Board.

   Corresponding author: sriram@iisc.ac.in

   1. S Ramaswamy, J Stat Mech 2017:054002
   2. L P Dadhichi, A Maitra and S Ramaswamy, in preparation
   3. C Nardini et al., Phys Rev X 7, 021007 (2017).
   4. S Shankar et al., arXiv:1804.06350

 

 

 

6. Kabir Ramola(1) and Bulbul Chakraborty(2)

   1. Department of Physics, Syracuse University, Syracuse, New York 13244
   2. ICSMB, Department of Physics, University of Aberdeen, Aberdeen, AB24 3UE, United Kingdom

   Statistical Mechanics of Athermal Systems: Edwards Ensemble, Entropy and Friction: The dual networks of jammed packings: Contact network and Force Tilings (Lecture 2)

   We analyse properties of contact networks formed in packings of soft frictionless disks near the unjamming transition. We construct polygonal tilings and triangulations of the contact network that partitions space into convex regions which are either covered or uncovered. This allows us to characterize the local spatial structure of the packing near the transition using well-defined geometric objects. We construct bounds on the number of polygons and triangulation vectors that appear in such packings. We study these networks using simulations of bidispersed disks interacting via a one- sided linear spring potential. We find that several underlying geometric distributions are reproducible and display self averaging properties. We find that the total covered area is a reliable real space parameter that can serve as a substitute for the packing fraction. We find that the unjamming transition occurs at a fraction of covered area = ( ) ∗ AG 0.446 1 . We determine scaling exponents of the excess covered area as the energy of the system approaches zero → + EG 0 , and the coordination number ⟨zg⟩ approaches its isostatic value ∆ = ⟨ ⟩ − ⟨ ⟩ → + Z zg gz 0 iso . We find ∆A E ∼ ∆ ( ) G G 0.28 1 and ∆A Z ∼ ∆ ( ) G 1.00 1 , representing new structural critical exponents. We use the distribution functions of local areas to study the underlying geometric disorder in the packings. We find that a finite fraction of order Ψ = ( ) ∗ O 0.369 1 persists as the transition is approached.

   Reference 2

 

 

 

7. Sumantra Sarkar(1), Dapeng Bi(2), Jie Zhang(3), Jie Ren(4), R. P. Behringer(5) and Bulbul Chakraborty(6)

   1. Martin Fisher School of Physics, Brandeis University, Waltham, Massachusetts 02453, USA
   2. Department of Physics, Syracuse University, Syracuse, New York 13224, USA
   3. Center for Studies in Physics and Biology, Rockefeller University, New York, New York 10065, USA
   4. Institute of Natural Sciences and Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China
   5. Department of Physics, Duke University, Durham, North Carolina, USA

   Shear induced rigidity of granular systems (Lecture 3)

   Solids are distinguished from fluids by their ability to resist shear. In equilibrium systems, the resistance to shear is associated with the emergence of broken translational symmetry as exhibited by a nonuniform density pattern that is persistent, which in turn results from minimizing the free energy. In this work, we focus on a class of systems where this paradigm is challenged. We show that shear-driven jamming in dry granular materials is a collective process controlled by the constraints of mechanical equilibrium. We argue that these constraints can lead to a persistent pattern in a dual space that encodes the statistics of contact forces and the topology of the contact network. The shear-jamming transition is marked by the appearance of this persistent pattern. We investigate the structure and behavior of patterns both in real space and the dual space as the system evolves through the rigidity transition for a range of packing fractions and in two different shear protocols. We show that, in the protocol that creates homogeneous jammed states without shear bands, measures of shear jamming do not depend on strain and packing fraction independently but obey a scaling form with a packing-fraction-dependent characteristic strain that goes to zero at the isotropic jamming point φJ . We demonstrate that it is possible to define a protocol-independent order parameter in this dual space, which provides a quantitative measure of the rigidity of shear-jammed states.

   Reference 3

   Reference 4

 

 

 

8. Srikanth Sastry

   JNCASR, Bengaluru

   Phenomenology of glass forming liquids and glasses

   An overview will be presented of the phenomenology of glass forming liquids, glasses, and the glass transition, as a prelude to more extended expositions of specific themes that will be explored in the subsequent lectures in the school. The topics covered will include the nature and characterization of the dynamics, and dynamical slow down in glass forming liquids, the role of configurational entropy in descriptions of such dynamical slow down, heterogeneous dynamics, growing length scales in glass formers, and a mention of related topics concerning yielding of glasses and jamming.

   [1] S Ramaswamy, J Stat Mech 2017:054002
   [2] L P Dadhichi, A Maitra and S Ramaswamy, arxiv:1808.08997
   [3] C Nardini, E Fodor, E Tjhung, F van Wijland, J Tailleur, M E Cates, Phys Rev X 7, 021007 (2017).
   [4] S Shankar, S Ramaswamy, M C Marchetti, M J Bowick, Phys. Rev. Lett. 121, 108002 (2018); arxiv:1804.06350
   

 

 

 

9. Hideyuki Mizuno

   The University of Tokyo

   Vibrational properties in the continuum limit of amorphous solids

   The thermal properties of crystalline solids follow universal laws that are explained in terms of phonons. Amorphous solids are also characterized by universal laws that are, however, anomalous with respect to their crystalline counterparts. These anomalies begin to emerge at very low temperatures, suggesting that the vibrational properties of amorphous solids differ from phonons at very low frequencies, even in the continuum limit. In this talk, I will show that phonons coexist with soft localized modes in the continuum limit. I will also show that the phonons follow the Debye law, whereas the soft localized modes follow another universal non-Debye law. Finally I will discuss about origin of the soft localized modes.

 

 

 

10. Giuseppe Foffi

    University of Paris-Sud, France

    Beyond isotropic models for dynamically arrested colloids, introducing directionality

    In this talk I will briefly review the dynamic phase diagram of colloidal particle interacting with a short-ranged attractive interactions. This realistic model posses a number of exotic properties such as a reentrant melting, two different kid of glass, an arrested phase separation resulting in a gel structure. Most of this unusual phenomenology has been now confirmed in experiments and computer simulations.

    The above scenario, is restricted to isotropic colloid, however in recent years a lot of interest has been devoted to the effect of directional attractive forces due to the progress in particles synthesis. I will present some recent results on the effect of directionality on the dynamics of these systems in connection, in particular, with the idea of locally favoured structure of a glass former.

 

 

 

Week 2

1. Francesco Sciortino

   Sapienza Universita’ di Roma, Piazzale Moro 2, 00185 Rome Italy

   Entropy in Self-Assembly

   I will discuss the role of entropy in some of the most relevant self-assembly processes. The outline of the lectures is the following:

   Introduction

   • Entropy and Translational Order: Hard Sphere Crystallisation [1]
   • Entropy and Orientational Order: Transition [2]
   • Entropy Attracts: Depletion Interactions [3]
   • Entropy Attracts: tions [4]
   • Competition between energy and entropy in self-assembly [5]
   • Entropy and flexibility in networks [6]

   Corresponding author: francesco.sciortino@uniroma1.it

   1. B. Alder and T. Wainwright, The Journal of chemical physics 27, 1208 (1957).
   2. L. Onsager, Annals of the New York Academy of Sci-ences 51, 627 (1949).
   3. H. N. Lekkerkerker and R. Tuinier, Colloids and the depletion interaction, Vol. 833 (Springer, 2011).
   4. A. Zilman, J. Kieffer, F. Molino, G. Porte, and S. Safran, Physical review letters 91, 015901 (2003).
   5. F. Sciortino, Soft Matter Self-Assembly, Varenna School, Italian Physical Society 193, 1 (2016).
   6. F. Smallenburg and F. Sciortino, Nature Physics 9, 554 (2013).

 

 

 

2. Jorge Kurchan

   ENS, Paris, France

   Entropy in the evolution of almost integrable systems

   Almost integrable systems are ubiquitous: weakly nonlinear waves, planetary systems, globular clusters, the Fremi-Pasta-Ulam problem, many well studied Quantm chains... The approach to equilibrium is slow, because it is done precisely through the integrability breaking. On the other hand, they offer us an opportu- nity of understanding the precise role played by Entropy at each stage, because the evolution is, in a sense, reversible.

   1. Integrable systems. Constants of motion. Approximate constants of motion.
   2. Examples: solar system, Fermi-Pasta-Ulam chain, weak turbulence.
   3. Generalized Gibbs Ensemble. Approach to equilibrium.
   4. A Fluctuation Theorem

 

 

 

3. Francesco Zamponi

   1. Laboratoire de Physique Théorique, Département de Physique de l’ENS,
   2. École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France

   Mean field theory of the glass transition

   The development of a mean field theory of glasses started in the 80s, through the work of Kirkpatrick, Thirumalai and Wolynes. They identified a class of mean field spin glass models, whose qualitative behav- ior is very similar to the one of supercooled liquid and glasses measured in the laboratory. They proposed that these spin glass models could serve as represen- tative of a broad universality class, called the Ran- dom First Order Transition (RFOT) class, in which the glass transition would fall, at least at the mean field level. To substantiate this claim, they proposed that a system of d-dimensional interacting particles would fall in this class in the d → ∞ limit [1].

   During the subsequent two decades, a lot of work has been done on RFOT spin glass models, which provided many important predictions on the thermodynamics and dynamics of RFOT systems: glass transition, aging, effective temperatures, complexity, dynamical heterogeneities... However, proving that the original conjecture of [1] is correct took another decade, and the program was completed in the last few years.

   In these lectures I will review the solution of parti- cle systems in d → ∞. I will show that the behavior is precisely the one of the RFOT universality class. I will start by the study of the equilibrium dynamics and show the existence of a dynamical glass transition similar to the one of Mode-Coupling Theory [2]. Next, I will show how the long time limit of the dynamics in the glass phase can be studied via the replica method using the “state following” or Franz-Parisi construc- tion [3]. Finally, I will briefly discuss the Gardner and jamming transitions [4].

   During the lectures, physical concepts such as the dy- namical glass transition, the complexity, the Kauz- mann transition, the out-of-equilibrium glass state, and the criticality of jamming will be discussed. Methodologically, we will introduce dynamical and replica techniques. The lectures are based on a book which is currently being written [5].

   Corresponding author: www.phys.ens.fr/∼zamponi

   1. T.R.Kirkpatrick and P. G. Wolynes, “Connections be-tween some kinetic and equilibrium theories of the glass transition”, Physical Review A 35, 3072 (1987).
   2. T.Maimbourg, J.Kurchan, and F.Zamponi, “Solution of the dynamics of liquids in the large-dimensional limit”, Physical Review Letters 116, 015902 (2016).
   3. C.Rainone, P.Urbani, H.Yoshino, and F.Zamponi, “Following the evolution of hard sphere glasses in in-finite dimensions under external perturbations: com-pression and shear strain”, Physical Review Letters 114, 015701 (2015).
   4. P.Charbonneau, J.Kurchan, G.Parisi, P.Urbani, F.Zamponi, “Fractal free energy landscapes in struc-tural glasses”, Nature Communications 5, 3725 (2014).
   5. G.Parisi, P.Urbani, F.Zamponi, “Theory of simple glasses”, book in preparation (Cambrige University Press).

 

 

 

4. Patrick Charbonneau

   1. Department of Chemistry, Duke University, Durham, North Carolina 27708, USA
   2. Department of Physics, Duke University, Durham, North Carolina 27708, USA

   Bridging between mean-field and real glasses

   Recent years have seen remarkable advances in the mean-field theory of glasses. But do these theoretical predictions actually explain the behavior of real physi- cal systems? In these lectures, we will study this ques- tion using numerical and theoretical tools that allow to systematically interpolate between one limit [1] and the other. By tuning spatial dimension or the inter- action range between particles, we can indeed identify theoretically robust features and physical phenomena that fall beyond the mean-field scenario.

   In these lectures, I will build on the material presented in previous and parallel lectures, especially the basics of liquid state theory and the mean-field theory of glasses. While L. Berthier’s lectures will mostly fo- cus on the properties of glassy states, mine will center on the dynamical slowdown of an (metastable) equi- librium liquid. More specifically, I will explore the following topics.

   1. The mechanics, advantages and challenges of running numerical simulations in higher dimen-sions [2–5].
   2. The theoretical expectations for finite-dimensional systems from RFOT [6].
   3. The theoretical and numerical results for the Mari-Kurchan (MK) model [5, 7–9].
   4. The lessons from the MK model for going be-yond → ∞ mean-field, especially from insights void percolation and random Lorentz gas [10–12].

   I thank warmly all my collaborators in this extended scientific effort. The last couple of years of this re- search program were supported by a grant from the Simons Foundation (No. 454937).

   Corresponding author: https://chem.duke.edu/labs/charbonneau

   1. P. Charbonneau, J. Kurchan, G. Parisi, P. Urbani, and F. Zamponi, Ann. Rev. Condens. Matter Phys. 8, 265 (2017).
   2. P. Charbonneau, A. Ikeda, G. Parisi, and F. Zam-poni, Phys. Rev. Lett. 107, 185702 (2011).
   3. B. Charbonneau, P. Charbonneau, and G. Tarjus, Phys. Rev. Lett. 108, 035701 (2012).
   4. B. Charbonneau, P. Charbonneau, Y. Jin, G. Parisi, and F. Zamponi, J. Chem. Phys. 139, 164502 (2013).
   5. P. Charbonneau, Y. Jin, G. Parisi, and F. Zamponi, Proc. Nat. Acad. Sci. U.S.A. 111, 15025 (2014).
   6. L. Berthier and G. Biroli, Rev. Mod. Phys. 83, 587 (2011).
   7. R. Mari, F. Krzakala, and J. Kurchan, Phys. Rev. Lett. 103, 025701 (2009).
   8. R. Mari and J. Kurchan, J. Chem. Phys. 135, 124504 (2011).
   9. M. Mézard, G. Parisi, M. Tarzia, and F. Zamponi, J. Stat. Mech. 2011, P03002 (2011).
   10. F. Hoefling, T. Franosch, and E. Frey, Phys. Rev. Lett. 96, 165901 (2006).
   11. T. Bauer, F. Hfling, T. Munk, E. Frey, and T. Fra-nosch, Eur. Phys. J. 189, 103 (2010).
   12. Y. Jin and P. Charbonneau, Phys. Rev. E 91, 042313 (2015).

 

 

 

5. Ludovic Berthier

   Laboratoire Charles Coulomb (L2C), University of Montpellier, CNRS, Montpellier, France

   Measuring the configurational entropy in computer simulations of deeply supercooled liquids

   In these lectures, I will employ the material presented in the introductory lectures, in particular the basics of liquid state theory and statistical mechanics to ex- plain how the configurational entropy of supercooled liquids can be measured in computer simulations of supercooled liquids [1].

   I will first explain why we must care about the con- figurational entropy, how it is defined and what are the conceptual problems associated to this important quantity, from the ill-defined concept of thermody- namic metastability to issues related to polydisperse liquid models.

   I will then talk about computer simulations of super- cooled liquids, how they are done, and what can be hoped to be achieved using this important tool. In particular, I will emphasize the new opportunities of- fered by the recent development of the SWAP algo- rithm [2] to explore more ambitiously than before the thermodynamic properties of deeply supercooled liq- uids [3].

   Then I will show how in practice one defines and mea- sures using computer simulations various proxies for the configurational entropy, from the potential energy landscape approach, from the Frenkel-Ladd thermo- dynamic construction, from the Franz-Parisi free en- ergy, and from the point-to-set correlation length mea- surement.

   These lectures have strong connections with the mean- field results presented in the parallel lectures by F. Zamponi and J. Kurchan.

   Corresponding author: ludovic.berthier@umontpellier.fr

   1. L. Berthier and G. Biroli, Theoretical perspective on the glass transition and amorphous materials, Rev. Mod. Phys. 83, 587 (2011).
   2. A. Ninarello, L. Berthier, and D. Coslovich, Models and algorithms for the next generation of glass transition studies, Phys. Rev. X 7, 021039 (2017).
   3. L. Berthier, P. Charbonneau, D. Coslovich, A. Ninarello, M. Ozawa, and S. Yaida, Configurational entropy measurements in extremely supercooled liquids that break the glass ceiling, Proc. Natl. Acad. Sci U. S. A. 114, 11356 (2017).

 

 

 

6. Susan Coppersmith

   University of Wisconsin-Madison, Wisconsin

   From bits to qubits: a quantum leap for computers

   The steady increase in computational power of information processors over the past half-century has led to smart phones and the internet, changing commerce and our social lives. Up to now, the primary way that computational power has increased is that the electronic components have been made smaller and smaller, but within the next decade feature sizes are expected to reach the fundamental limits imposed by the size of atoms. However, it is possible that further huge increases in computational power could be achieved by building quantum computers, which exploit in new ways of the laws of quantum mechanics that govern the physical world. This talk will discuss the challenges involved in building a large-scale quantum computer as well as progress that we have made in developing a quantum computer using silicon quantum dots, some of which is enabled by concepts developed in the context of statistical physics and nonlinear dynamics. Prospects for further development will also be discussed. 

 

 

 

Week 3

1. Remi Monasson

   ENS, Paris, France

   Phase transitions in high-dimensional statistical inference

   Lecture 1: High-Dimensional Inference: Basic techniques

   1. Bayesian inference
   2. Principal Component Analysis (PCA)
   3. Spiked covariance model and retarded learning phase transition
   4. Role of prior information
   Lecture 2: High-Dimensional Inference: Unsupervised Learning with Neural Networks
   1. What is Unsupervised learning?
   2. Autoencoders and connection with PCA
   3. Boltzmann machines and Restricted Boltzmann machines
   Lecture 3: High-Dimension Inference: Application to protein modeling
   1. Biological motivations
   2. Methods
   3. Results
   References:
   1. Information theory, inference, learning algorithms
      David MacKay, Cambridge University Press
   Link
   2. Introduction to the theory of neural computation
      John Hertz, Andreas Hertz, Richard Palmer, Santa Fe Institute series
   3. Statistical physics and representations in real and artificial neural networks
      Simona Cocco, Remi Monasson, Lorenzo Posani, Sophie Rosay, Jerome Tubiana, Physica A (2018)
      Link
   4. Inverse statistical physics of protein sequences: a key issues review
      Simona Cocco, Christoph Feinauer, Matteo Figliuzzi, Remi Monasson, Martin Weigt, Rep. Phys. Prog. (2018)
      Link

 

 

 

2. Magdaleno Medina-Noyola

   Universidad Autonoma de San Luis Potosi

   Non-equilibrium Kinetics of the Transformation of Liquids into Physical Gels

   J. M. Olais-Govea, L. Lopez-Flores, and M. Medina-Noyola

   A major stumbling block for statistical physics and materials science has been the lack of a universal principle that allows us to understand and predict elementary structural, morphological, and dynamical properties of non-equilibrium amorphous states of matter. The recently-developed non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory, however, has been shown to provide a fundamental tool for the understanding of the most essential features of the transformation of liquids into amorphous solids, such as their aging kinetics or their dependence on the protocol of fabrication. In this work we focus on the predicted kinetics of one of the main fingerprints of the formation of gels by arrested spinodal decomposition of suddenly and deeply quenched simple liquids, namely, the arrest of structural parameters associated with the morphological evolution from the initially uniform fluid, to the dynamically arrested sponge-like amorphous material. The comparison o f the theoretical predictions with simulation and experimental data measured on similar but more complex materials, suggests the universality of the predicted scenario.

 

 

 

3. Amit Amal Ghosal

   IISER Kolkata

   Glassy behavior associated with melting of two-dimensional Coulomb clusters

   We present responses of a small number of Coulomb-interacting particles in two-dimensional confinements, across the crossover from their solid- to liquid-like behaviors. Here, irregular confinements emulate the role of disorder.

   Focusing first on the thermal melting, where zero-point motion of the particles are frozen, we explore the signatures of a 'hexatic-glass' like behavior. While static correlations, which investigate the translational and bond orientational order [1,2], indicate a hexatic-like phase at low temperatures, dynamical correlations show considerably slow relaxations. Using density correlations we probe intriguing inhomogeneities arising from the interplay of the irregularity in the confinement and long-range interactions. The relaxation at multiple time scales show stretched-exponential decay of spatial correlations for Coulomb-particles in irregular traps [1,3]. Temperature dependence of characteristic time scales, depicting the structural relaxation of the system, show strong similarities with those observed for the glassy systems. Our results indicate that some of the key features of supercooled liquids emerge in confined systems. more so with irregular confinements. The analysis of normal modes [4] elucidates how long time behavior of the system is encoded in the quasi-localized modes.

   Time permitting, we extend our discussions to include the effects of quantum fluctuations. Our results, using quantum Monte Carlo techniques for Boltzmann particles, seem to indicate complementary mechanism for the quantum and thermal crossovers in Wigner molecules [5]. We will also discuss our recent analyses upon including the effects of quantum statistics.

   1. B. Ash, J. Chakrabarti and A. Ghosal, Phys. Rev. E 96, 042105 (2017).
   2. D. Bhattacharya and A. Ghosal, Eur. Phys. J. B 86, 499 (2013).
   3. B. Ash, J. Chakrabarti and A. Ghosal, Euro. Phys. Lett., 114, 4, (2016).
   4. B. Ash, C. Dasgupta and A. Ghosal, To appear in Phys. Rev. E (2018) (arXiv:1805.11180).
   5. D. Bhattacharya, A. V. Filinov, A. Ghosal and M.Bonitz, Eur. Phys. J. B 89, 60, (2016).

 

 

 

4. Mahesh M Bandi

   Okinawa Institute of Science and Technology

   Applying Higher-order Turbulence Spectra from Energy to UAV

   Kolmogorov’s 1941 theory elucidating the spectrum of turbulent velocity fluctuations forms the cornerstone of contemporary turbulence research. This result requires one to measure the velocity everywhere within the turbulent flow at the same time instant. However, many situations exist where measurements are needed over time at one or few fixed spatial (Eulerian) locations, sometimes involving not velocity but its higher powers. The physical interpretation of such measurements strongly diverges from the Kolmogorov framework. In this talk, I will review the revised theoretical framework and support it with evidence from our experiments in two and three dimensional flows. I will then explain how this revised framework provides a toolkit to address a diverse range of questions in Energy, UAV mechanics, Environmental Sciences, and perhaps even Life Sciences.

 

 

 

5. Stephan Herminghaus

   Max Planck Institute for Dynamics and Self-Organization

   Artificial microswimmers: individual and collective phenomena

   Plankton provides the most important route of injection of solar energy into the biosystem. It is therefore of major importance to attain a deep understanding of swimming motility and swarming of these microorganisms. As their natural habitats include turbulent (oceanic photosphere) and still (lacustrine) waters as well as the benthic (seafloor) areas, a wide variety of geometries and flow conditions are to be studied. We discuss a number of phenomena found recently in both natural single-cell swimmers (Chlamydomonas reinhartii) and artificial liquid microswimmers consisting of self-propelling 'oil' droplets. Some emphasis is given to properties which may be relevant for biofilm formation, such as adhesion and swarm formation, in particular in non-trivial geometries.

 

 

 

6. Vijay Kumar Krishnamurthy

   ICTS, Bangalore

   Interacting active particles: single-file diffusion and fluctuation-induced forces

   Active-Brownian-particles (ABPs) and run-and-tumble particles (RTPs) are minimal realizations of scalar active matter. We will start by discussing exact solutions for non-interacting RTPs in 1D in both unconfined and confined geometries. We will then move on to discuss single-file-diffusion in a system of interacting RTPs in 1D and show that the MSD of a tagged particle displays scaling behavior with the density and activity with an asymptotic $t^{1/2}$ dependence on time. This is true also for ABPs confined in a narrow annular channel. We will then present our preliminary experimental results on interacting ABPs, realized as isotropic self-propelled disks on a vibrated granular shaker, and demonstrate that various statistical quantities compare favourably with simulations. Finally, we will discuss fluctuation-induced interactions between anisotropic inclusions in a nonequilibrium heat-bath composed of interacting ABPs.

 

 

 

1. Yagyik Goswami and Srikanth Sastry

   JNCASR, Bengaluru, India

   Investigation of the free energy barriers to liquid-liquid and liquid-solid transformations in supercooled Silicon

   The existence of a first order liquid-liquid phase transition in liquids that have local tetrahedral ordering, such as water and Silicon, has been the subject of extensive and rigorous study.

   This first-order phase transition is understood to be the cause of the well-known anomalous properties of such liquids (eg., anomalous expansion upon cool- ing). A number of simulations studies of Si show evi- dence both for and against the existence of a first or- der phase transition separating a high density liquid (HDL) phase from a low density liquid (LDL) phase. Notably, Sastry and Angell, 2003, measured an en- thalpy of transformation in the vicinity of T=1055K, P=0GPa for Stillinger-Weber Si. Subsequently, free energy calculations by Limmer and Chandler, 2013, showed that no basin corresponding to the LDL phase existed at the expected state point, pointing to the possibility of finite-time effects.

   Here, we study the choice of order parameters in constructing a Landau free energy surface. In particular, for a polycrystalline sample, the bond orientational order is often liquid-like, meaning that a bias potential applied to constrain the system to liquid configurations will not prevent the formation of postcritical crystalline clusters. We consider alternative order parameters that give a direct handle on the degree of crystallinity in the system. We also study the timescales relevant to the stability of the metastable liquid, the relaxation time τα and the average nucleation time.

   Lastly, We perform a free energy calculation using Umbrella Sampling Monte Carlo simulations with parallel tempering to probe the existence of free energy barriers for supercooled Stillinger-Weber Si.

   YG would like to thank Prof. Sastry, under whose advisement he is pursuing a PhD. He would also like to thank JNCASR, Bengaluru for the opportunity to pursue his studies and the organisers for the opportunity to present this work.

   ∗ Corresponding author: sastry@jncasr.ac.in

   1. Sastry, Srikanth, and C. Austen Angell. ”Liquid-liquid phase transition in supercooled silicon.” Nature Materials 2.11 (2003): 739.
   2. Vasisht, Vishwas V., Shibu Saw, and Srikanth Sastry. ”Liquid-liquid critical point in supercooled silicon.” Nature Physics 7.7 (2011): 549.
   3. Limmer, David T., and David Chandler. ”The putative liquid-liquid transition is a liquid-solid transition in atomistic models of water. II.” The Journal of chemical physics 138.21 (2013): 214504.

 

 

 

2. Vinay Vaibhav(1), Pinaki Chaudhuri(1), and Juergen Horbach(2)

   1. The Institute of Mathematical Sciences, Chennai, India
   2. Institute for Theoretical Physics II, Heinrich-Heine-University Duesseldorf, Germany

   Thermal Response of Glassy Liquids

   The response of a model glass-forming liquid [1] to an externally applied thermal gradient has been studied using extensive non-equilibrium molecular dynamics simulations [2][3].

   In the supercooled liquid regime, we have demon- strated that the mixture responds by the formation of concentration gradients, which are dependent on the local temperature. The interplay between the trans- port processes, related to temperature and concentra- tion, occurring in the system, is characterized via the Soret-coefficient, which is the ratio of the thermal dif- fusion coefficient and inter-diffusion coefficient. The behavior of Soret-coefficient in supercooled regime is found to increase as the temperature is lowered, which we relate to the behaviour of the inter-diffusion coef- ficient near the mode-coupling temperature.

   In the supercooled regime, we also observed that when larger thermal gradients are imposed, the spatial pro- files of the particle concentrations become non-linear. We have characterized in details how the onset of the non-linear regime depends on the mean temperature and the thermal gradient.

   The response near glassy regime has also been ex- plored: local concentration is almost not affected, in the presence of the thermal gradient, wherever local temperature is below mode-coupling temperature.

   We acknowledge the computations performed on clus- ters Annapurna and Nandadevi at IMSc, Chennai, In- dia (https://hpc.imsc.res.in/).

   ∗ Corresponding author: vinayv@imsc.res.in

   1. W. Kob and H. C. Andersen, Physical review letters 73(10), 1376 (1994).
   2. P. J. Bhuyan, R. Mandal, P. Chaudhuri, A. Dhar and C. Dasgupta, arXiv:1703.04494 (2017).
   3. F. Bresme, B. Hafskjold and I. Wold, The Journal of Physical Chemistry, 100.5, 1879 (1996).

 

 

 

3. Susana Marin Aguilar, Giuseppe Foffi, Frank Smallenburg, and Rik Wensink

   Laboratoire de Physique des Solides, Universit ́e Paris Sud, Orsay, France.

   Glass Transition in Patchy Colloidal Systems

   We explored the behavior of systems of patchy colloids in the glassy regime. In this regime the times of relax- ation grow rapidly and the translational dynamics are much more slower, the addition of new dependencies in the system by constraining the way the particles in- teract with their neighbors is clear, such is the case of the rotational dynamics which now they are relevant for the relaxation time. We studied the effect of the variation of the number and size of the patches.

   The particles used are the ones from Kern-Frenkel model [1]. The analysis of translational and rotational relaxation were made by calculating the density cor- relators and the second Legendre polynomia. Our re- sults show that the reentrant behavior of the phase diagram found in systems of short ranged potential in the glassy regime [2] [3] is conserved. At equal second virial coefficient the systems relax in the same man- ner excepting for the system composed of 12 patches located in an icosahedral way. This particular system enhances the formation of icosahedral cages through the glass that slow down the relaxation.

   ∗ Corresponding author: susana.marin-aguilar@u- psud.fr

   1. N. Kern and D. Frenkel, J. Chem. Phys. 118, 21 (2003).
   2. F. Sciortino, Nature materials 1, (2002).
   3. E. Zaccarelli and G. Foffi and K. A. Dawson and S. V. Buldyrev and F. Sciortino and P. Tartaglia, Phys. Rev. E 66, (2002).

 

 

 

4. Shikha Kumari(1), and Syed Rashid Ahmad(2)

   1. Department of Physics, Jamia Millia Islamia, New Delhi, India
   2. School of Physical Sciences, Jawaharlal Nehru University, New Delhi, India

   Velocity autocorrelation function in driven granular gas

   We have studied the aging of velocity autocorre- lation function[1] of a uniformly heated granular gas. Autocorrelation function specifies memory in the particle velocity and it is computed at collision time τ with respect to a reference time τw. For a non-equilibrium system the autocorrelation func- tion depends on both τ and τw. The dependence on τw is called aging or history dependency. A cooling granular gas is a non-equilibrium system and therefore the corresponding velocity autocorre- lation function is expected to exhibit aging properties.

   We use large-scale event-driven molecular dynamics simulations[2] to study aging property of velocity au- tocorrelation function for a uniformly heated granular gas. The system is heated by appropriately adding a Gaussian white noise to the velocity of each particle after a certain time-step which mimics heating of the system. We have simulated granular gas consisting of identical hard spheres in two and three dimensional box under periodic boundary conditions applied in all the directions. The aging property has been studied for a set of coefficient of restitution values.

   From our simulation results, it is observed that after a few collisions per particle, the system attains steady state. During early stages, the velocity auto- correlation function shows aging as there is explicit dependence of the function on waiting time τw but after steady state is reached, the velocity autocorre- lation function become independent of waiting time and does not show any aging. Velocity correlations develop even after steady state is reached. These correlations are less pronounced in three dimensional system[3].

   The computational facility provided by Department of Physics, Jamia Millia Islamia is highly acknowledged.

   ∗ Corresponding author: shikhakumari138048 @st.jmi.ac.in

   1. E. Ben-Naim and P. L. Krapivsky, Phys. Rev. E 66(4), 011309 (2002).
   2. S. Kumari and S. R. Ahmad, Particulate Science and Technology 36(4), 140082 (2018).
   3. S. Kumari and S. R. Ahmad, EPJ Web of Conference 140, 04007 (2017).

 

 

 

5. Sameer Kumar and Shradha Mishra

   Department of Physics, Indian Institute of Technology (BHU), Varanasi, U.P. India - 221005

   Dynamics of Particle moving on one dimensional deterministic Lorentz Lattice Gas

   We study the dynamics of a particle moving on one-dimensional Lorentz lattice-gas. The two types of scatterers, viz reflector and transmitters are randomly placed on the lattice. Reflector are such that it re- verse the particle’s velocity direction and transmitter let it pass through. Scatterers also change their char- acteristic with flipping probability α once particle pass through. The density of scatterers is controlled R ; where by a number r which is defined as r = C L C +C R C R and C L are the initial concentration of reflector and transmitters respectively. Hence there are two control parameter in the system, one is r and other is α, the probability of flipping. For α = 0 and α = 1 dynamics of particle is purely deterministic else it is probabilistic. A cartoon picture of the model is shown in figure 1. In the pure deterministic case dynamics of particle is either propagating in one direction or confined between two near-by reflectors present. Speed of propagation and span of confined trajectory depends on initial density of reflectors which we calculated analytically. For the probabilistic case α 6 = 1 and 6 = 0, dynamics of particles shows anomalous diffusion where dynamics is faster, slower and comparable to normal diffusion on the variation of system parameters (α, r). Hence it shows a transi- tion from one types of motion to others. In general, dynamics shows monotonic variation with varying (α, r) except when α is close to 0, where it shows a non-monotonic change from super-diffusion to sub-diffusion. Our study shows that small change in system parameters can lead to huge difference in the dynamics of particle. Hence our study can give some insight to the dynamics of complex biological systems.

 

 

 

6. Saheli Mitra(1), Giuseppe Foffi(1) and Srikanth Sastry(2)

   1. Laboratoire de Physique des Solides,Universit Paris Sud, Orsay, France
   2. Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India

   Yielding in Glassy Systems

   Yielding transition in glassy system is observed by putting the system under shear deformation. We investigate this phenomenon in a model glass system by computer simulation. The simulation box is tilted back and forth in an oscillatory manner following AQS protocol with shearing amplitude γ = γmax ,i.e., for one cycle of deformation γ varies as, 0 → γmax → 0 → −γmax → 0

   To identify critical shearing amplitude γc above which system will yield, we can take snapshots of the configurations corresponding to γ = 0 for many cycles and their energy and msd can be plotted as a function of time, or γacc = Pdγ. As it was observed earlier [1],below γc, after a transient the Mean Square Displacement (MSD) from undeformed initial configuration becomes a constant, that means that the particles return to their positions after each cycles of deformation, system gets stuck in configuration space. Whereas above γc MSD increases with time, the system becomes diffusive.

   We know for disordered systems across jamming transition ,the systems show hyperuniformity [2] ,i.e. , suppression of fluctuations at large length scales. Now, we seek if there is any similar change in fluctuations across yielding.

   We are grateful to the former students of JNCASR, Bangalore, Anshul D. S. Parmar and Premkumar Leishangthem for their contribution to the project and H. A. Vinutha for useful discussions. We would like to thank CEFIPRA for supporting the project.

   1. Fiocco, Davide, Giuseppe Foffi, and Srikanth Sastry. ”Oscillatory athermal quasistatic deformation of a model glass.” Physical Review E 88.2 (2013): 020301.
   2. Berthier, Ludovic, et al. ”Suppressed compressibility at large scale in jammed packings of sizedisperse spheres.” Physical review letters 106.12 (2011): 120601.

 

 

 

7. Ruma Maity(1), and P. S. Burada(1)(2)

   1. Department of Physics, Indian Institute of Technology, Kharagpur, West Bengal, India, 721302
   2. Center for Theoretical Studies, Indian Institute of Technology, Kharagpur, West Bengal, India, 721302

   Effect of noise on the chemotaxis of a single chiral squirmer

   Several biological phenomenon like wound healing, embryogenesis are possible because of chemotaxis. Ciliated microorganisms like Paramecium changes its trajectory by sensing external chemical gradient. In the process of chemotaxis the chemoattractants bind to the receptors on the body in order to activate the internal signalling network of the body which help the squirmer to respond to the stimulus [1]. This discrete chemoattractant- receptor binding can be described in terms of Poisson process and is the source of external noise in the signalling system of the microorganism. Behaviour of microorganisms has been studied here under the linear and the radial chemical gradients in presence of noise using the chiral squirmer model [2]. At lower concentration gradient noise dominates the system and the squirmer faces a difficulty to reach the target. With increasing concentration gradient the squirmer takes lesser time to reach the target. The steeper gradient hibernates the effect of noise, as a result the deviation of the squirmer from the original trajectory is small

   ∗ Corresponding author: rumamaity@phy.iitkgp.ernet.in

   1. B. M. Friedrich and F. J¨ulicher, Proc. Natl. Acad. Sci.USA, 104, 13256 (2007).
   2. P. S. Burada and F. J¨ulicher, to be communicated
   3. R. Maity and P. S. Burada, arXiv:1804.06100.

 

 

 

8. Pratik M. Gaiki

   1. Department of Physics,RTM Nagpur University,Nagpur-440033
   2. Study of Persistence in Kinetic Ising Model of Glass Transition by Fredrikson and Andersen

   Here we study the persistence in microscope theory of glass transition based on kinetic Ising model with cooperative spin flip rates. We consider spin models that are standard Ising ferromagnetic ones. The state of the jth spin σj can take values +1 (spin up) or -1 (spin down). [1]

   In spin systems, (local) persistence is defined as the fraction of spins which did not change their initial spin state even once till a given time. Thus non-zero persistence implies that the system retains memory of the initial conditions indefinitely.[2]

   In these models, usual dynamics of Ising-model is altered. The spin flip occurs when at least one of the neighbors is in spin up state. This is a 1-spin facilitated model. Another variant is a two-spin facilitated model in which the spin occurs only if both of its neighbors are in spin up state. (An n-spin facilitated model is defined as the one for which the flip rate of jthspin is non − zero only if n or more near neighbors of spin j are in spin up state in spin conf iguration σ. W e take n = 1 or n = 2.)

   The one spin model (n=1) defined at the rate at which j th spin flips down is : [1] Wj,down[σ] = m(σ)α The two spin model (n=2) defined by the down flipping rate is : [1] Wj,down[σ] = 1/2 m(σ)[m(σ) − 1]α α is a constant that determines the time scale of relaxation at high temperature. m is the number of near neighbors of spin j that are in spin up state.

   The equilibrium properties of two spin model correspond to the equilibrium properties of the Ising model; since its thermodynamic singularities have a non-zero field. The glass transition predicted by the Ising model has no underlying thermodynamic singularity. Hence the transition is a purely kinetic effect resulting from dramatically increased cooperativity of relaxation at low temperature

   I would like to express my gratitude towards Prof.Prashant M. Gade for encouraging me in this project.

   ∗ Corresponding author: pmgaiki@yahoo.com

   1. G.Fredricson and H.Andersen,Phys Rev A,53, 1244(1984).
   2. P.Gade and G.Sahasrabudhe,Phys Rev E,87, 052905(2013).

 

 

 

9. Pallabi Das,∗ Vinutha H. A., and Srikanth Sastry

   Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur Campus, Bengaluru 560064, India.

   Reversible-Irreversible, jamming and yielding transition in soft sphere packings under cyclic shear deformation

   Cyclic shear deformation induces the reversibleirreversible transition in both unjammed and jammed soft sphere packings. Above isotropic jamming density(φJ ), reversible-irreversible transition corresponds to the yielding transition [1] which is a solid to liquid-like transformation. For below φJ densities, by looking at the displacement of a single particle in a cycle, in steady state, we identify two different kinds of reversible states namely point reversible and loop reversible [2] whereas above φJ , reversible states are only loop reversible. For densities below and above φJ , mean squared displacement show same characteristics for reversible and irreversible states. For below φJ , the irreversible states have structures that can be jammed in the presence of friction. Interestingly, the region where we start finding these jammed like structures shows to have a close correspondence to irreversible transition. The study in the vicinity of φJ shows an unjammed phase emerges between jammed and yielded phase as we move closer to the isotropic jamming density from above. The emergence of this unjammed phase implies that cyclic shear deformation shifts frictionless jamming density at a higher density recognised as φ cyclic J .

   In this work, we subject frictionless spheres interacting via soft repulsive harmonic potential to cyclic deformation, for packings below and above φj . The advantage of using this model system is that various transitions and phenomena observed in amorphous materials like glasses, emulsions, foams and granular systems, can be studied by varying one control parameter packing fraction. We study reversible-irreversible transition below, close to and above φj and connect it to yielding and jamming behaviour. Our work aims to provide a unified picture of yielding and jamming transition in sphere packings using the microscopic behaviour of particles under cyclic deformation.

   ∗ Corresponding author: Pallabi Das. dashpalllavi@gmail.com

   1. Leishangthem, Premkumar, Anshul DS Parmar, and Srikanth Sastry,Nature communications 8, 14653 (2017)
   2. Schreck, C. F., Hoy, R. S., Shattuck, M. D., OHern, C. S., Physical Review E 88(5), , 052205 (2013).

 

 

 

10. Onofrio Mazzarisi(1), ∗ and Federico Corberi(2)

    1. Dipartimento di Fisica ’E. R. Caianiello’, Universit`a di Salerno, via Giovanni Paolo II 132, 84084 Fisciano (SA), Italy.
    2. Dipartimento di Fisica ’E. R. Caianiello’, and INFN, Gruppo Collegato di Salerno, and CNISM, Unit`a di Salerno, Universit`a di Salerno, via Giovanni Paolo II 132, 84084 Fisciano (SA), Italy

    Condensation of fluctuations and development of a rare event in the Gaussian model

    Condensation is the phenomenon whereby a finite fraction of some quantity concentrates into a small region of phase-space.

    A particular manifestation of condensation is observed when fluctuating observables are considered, in this case fluctuations from the typical value can happen to be associated to a condensed configuration of the system. This phenomenon is referred to as condensation of fluctuations[1].

    In the framework of large deviation theory[2], through an appropriate mapping of rare events in a given system to typical events in a biased one, we discuss how a phase-transition in the latter is the counterpart of the singular behaviour of the former.

    Condensation of fluctuations may occur even in systems which cannot sustain condensation on average, in order to emphasize this point we focus on the Gaussian model.

    We analyze the dynamics leading to the development of a rare fluctuation, characterized by condensation, of an observable prepared in a non-condensed state[3].

    ∗ Corresponding author: omazzarisi@unisa.it

    1. M. Zannetti, F. Corberi, G. Gonnella, Phys. Rev. E 90, 012143 (2014)
    2. H. Touchette, Phys. Rep. 478, 1 (2009)
    3. F. Corberi, Phys. Rev. E 95, 032136 (2017)

 

 

 

11. Monoj Adhikari∗ and Srikanth Sastry

    Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, India.

    Memory formation in cyclically deformed amorphous solids and sphere assemblies

    We study a model amorphous solid that is subjected to repeated athermal cyclic shear deformation [1]. It has previously been demonstrated that the memory of the amplitudes of shear deformation the system is subjected to (or trained at) is encoded, and can be retrieved by subsequent deformation cycles that serve as read operations [2]. Here we consider different read protocols and measurements and show that single and multiple memories can be robustly retrieved through these different protocols. We also show that shear deformation by a larger amplitude always erases the stored memories

    These observations are similar to those in experiments with non-Brownian colloidal suspensions and corresponding models [3], but differ in the possibility of storing multiple memories non-transiently. Such a possibility has been associated with the presence of cycles of transitions that take place in the model amorphous solids, between local energy minima.

    Here, we also study low density sphere assemblies which serve as models for non-Brownian colloidal suspensions, under athermal deformation, and identify a regime where the signatures of memory encoding are similar to the model glass, even when transition between local energy minima are absent. We show that such a regime corresponds to the presence of loop reversibility, rather than point reversibility of configurations under cyclic deformation

    ∗ Corresponding author: monoj@jncasr.ac.in

    1. M. Adhikari and S. Sastry arXiv:1805.09113 [condmat.soft] (2018)
    2. D. Fiocco, G. Foffi and S. Sastry Phys. Rev. Lett. 112, 025702, (2014)
    3. N.C. Keim, J.D. Paulsen, and S.R. Nagel Phys. Rev. Lett. 107, 010603, (2011)

 

 

 

12. Masanari Shimada(1),∗ Hideyuki Mizuno(1), Matthieu Wyart(2) and Atsushi Ikeda(1)

    1. Graduate School of Arts and Sciences, The University of Tokyo, Japan
    2. Institute of Physics, Ecole Polytechnique F´ed´erale de Lausanne, Switzerland

    Spatial structure of low-frequency quasi-localized vibrations in nearly jammed amorphous solids

    Lattice vibrations in crystals are fully described by the Debye theory, in which plane waves, phonons, play a central role. Vibrations in amorphous solids are, on the other hand, noticeably different from those of crystals. One of the most striking differences is the presence of the non-phonon, low frequency vibrational modes in glasses. These modes are spatially (quasi)localized and can never be described by the Debye theory even though their frequency is very low. Intuitively, however, this seems to be mysterious because solils have only phonons as low-frequency excitations. These modes are now believed to play key roles in various anomalies of glassy systems; for examples, they are expected to explain the anomalous temperature dependence of the specific heat C and the thermal conductivity κ of glasses below 10K, which are completely different from those of crystals [1]. For example, the specific heat of crystals obey the famous Debye T 3 law C ∝ T 3 , where T is temperature while that of glasses show completely different behaviour C ∝ T. They are also expected to control the dynamics of supercooled liquids near the glass transitions and yielding of glasses under shear. Therefore, understanding the nature of localized vibrations is one of the main problems in the physics of glasses.

    Recent large-scale numerical simulations have made great progress in quantitative characterization of these localized modes [2–4]. It was revealed that these modes persist even in the low-frequency limit and their vibrational density of states obeys the non-Debye scaling law g(ω) ∝ ω 4 .

    However, the microscopic origin of these localized modes is not understood yet. In this work [5], we used large-scale simulations of the harmonic spheres near the jamming transition to study the spatial structure of the localized modes. We have revealed that the motions of particles in the localized modes are not random but almost perpendicular to interacting bonds. This motion shares the same feature with those of the structural buckling. In other words, particles with large vibrations destabilized the whole system by the buckling-like motions while other particles stabilize the system and prevent the buckling. Furthermore, we analyzed the spatial extension of the localized modes and have found that their characteristic size diverges towards the jamming transition (see Fig. 1 for visualization). By comparing the diverging behavior of this size with other diverging length scales, we discuss the origin of the soft localized modes in light of the physics of the jamming. Especially, we discuss the connection between the localized vibrations and so-called “anomalous modes”, which are considered to be responsible for the boson peak in the jamming systems.

    ∗ Corresponding author: masanari-shimada444@g.ecc.utokyo.ac.jp

    1. W. A. Phillips, Amorphous Solids: Low Temperature Properties, 3rd ed. (Springer, Berlin, 1981).
    2. E. Lerner and G. D¨uring, E. Bouchbinder, Phys. Rev. Lett. 177, 035501 (2016).
    3. H. Mizuno, H. Shiba, and A. Ikeda, Proc. Natl. Acad. Sci. USA 114, E9767 (2017).
    4. M. Shimada, H. Mizuno, and A. Ikeda, Phys. Rev. E 97, 022609 (2018).
    5. M. Shimada, H. Mizuno, M. Wyart, and A. Ikeda, arXiv:1804.08865

 

 

 

13. Manodeep Mondal(1), ∗ Chandan K Mishra(1), A K Sood(2)(3), and Rajesh Ganapathy(3)

    1. Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India
    2. Department of Physics, Indian Institute of Science, Bangalore 560012, India
    3. International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India

    Self-organised colloidal self assembly

    The spectacular colors of the natural world make scientists enthusiastic about its origin. Unlike the colors due to dyes and pigments, most of the colors observed in organisms are due to remarkable self-assembled structures of the individual building blocks. Over a decade it has been a central focus of the scientific community to assemble nano and micro size particles on specific sites either using external field or by means of a chemical route. Owing to its large size and low mobility, without applying external stimuli self-assembly of micro and nano-size particles on the desired site is still challenging. We have made it possible to grow periodic islands of micrometer size colloidal particles without applying any external stimuli and this selfgenerated super periodicity of colloidal islands will have an immense impact in the development of photonic bandgap materials.

    Given that the laws of atomic epitaxy are equally applicable to microscale particles (1), we can probe the insight of atomic heteroepitaxy at single particle level. In this poster, I will show results about the growth mechanism involved in colloidal heteroepitaxy and try to shed light on the much debated controversies in atomic thin film growth. I will discuss how strain relaxation happens in colloidal heteroepitaxy in the presence of short-range attraction, where formation of dislocations is energetically costly(2). I will bring forth the intriguing factors involved in colloidal self-assembly on strained Moir´e templates, where surface topography along with strain play a vital role in forming super-periodic structures.

    ∗ Corresponding author: deep.manodeep10@gmail.com

    1. Ganapathy Rajesh, Mark R. Buckley, Sharon J. Gerbode, and Itai Cohen. “Direct measurements of island growth and step-edge barriers in colloidal epitaxy.” Science 327, no. 5964 (2010): 445-448
    2. Meng, Guangnan, Jayson Paulose, David R. Nelson, and Vinothan N. Manoharan. “Elastic instability of a crystal growing on a curved surface.”, Science 343, no. 6171 (2014): 634-637.

 

 

 

14. Indrajit Tah(1), Saurish Chakrabarty(2), Smarajit Karmakar(1) and Chandan Dasgupta(3)

    1. Tata Institute of Fundamental Research, 36/P, Gopanpally Village, Serilingampally Mandal, Ranga Reddy District, Hyderabad 500107;
    2. International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Shivakote, Hesaraghatta, Hubli, Bangalore, 560089, India;
    3. Centre for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore 560012, India

    Block Analysis for the Calculation of Dynamic and Static Length Scales in Glass-Forming Liquids

    We present block analysis, an efficient method of performing finite-size scaling for obtaining the length scale of dynamic heterogeneity and the point-to-set length scale for generic glass-forming liquids. This method involves considering blocks of varying sizes embedded in a system of a fixed (large) size. The length scale associated with dynamic heterogeneity is obtained from a finite-size scaling analysis of the dependence of the four-point dynamic susceptibility on the block size. The block size dependence of the variance of the α relaxation time yields the static pointto-set length scale. The values of the obtained length scales agree quantitatively with those obtained from other conventional methods. This method provides an efficient experimental tool for studying the growth of length scales in systems such as colloidal glasses for which performing finite-size scaling by carrying out experiments for varying system sizes may not be feasible.

 

 

 

15. Himangsu Bhaumik∗ and Srikanth Sastry

    Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur Campus, Bengaluru 560064, India

    Mechanical properties of silica under cyclic deformation

    Understanding the behavior of amorphous solid under mechanical stress is one of the recent trends in the soft matter physics. Particular focus has been given on the zero temperature behaviour of amorphous solid under shearing conditions in which the system is kept in the minimal energy configuration while the strain is varied cyclically in a quasi-static manner [1–3]. Since such studies mainly focused on the model of atomic glass former (binary Lennard-Jones mixture) in the high density regime, it is interesting to ask how other glass formers, for example, glasses whose behaviour is dominated by attractive interactions, behaves under such protocol.

    In this work we study the modified BKS model [4] of silica as an attractive glass former under cyclic deformation. We performed NVT simulation at temperature T = 2500K of liquid silica taking N = 1728 ions at density ρ = 2.8gm/cm3 . Five different configurations sampled from the equilibrated trajectory are subjected to energy minimization, using the conjugate-gradient algorithm, to obtain sets of inherent structures. Each such inherent structure is then subjected to athermal quasistatic shearing protocol in which two steps are involved: (i) affine transformation by incrementing the strain by small amount dγ in the xz-direction (x 0 → x+dγz, y 0 → y, z 0 → z) and (ii) energy minimization. Choosing dγ = 0.0002, the strain γ is varied cyclically as : 0 → γmax → −γmax → 0. Repeating the deformation cycle for a fixed γmax, systems are shear deformed and driven to the steady state. The steady state characteristic behaviour of the system is studied for different strain amplitudes: γmax = 0.12 to 0.24 in increment of 0.02.

    The averaged stress-strain curve and potential energy for a cycle of deformation in the steady state are shown in Figure 1 (a) and 1 (b), respectively. It can be seen that with the increment of strain amplitude hysteresis loop is developed for the stress-strain curve. It is also notable that for γmax ≤ 0.18 the potential energy display a single minimum close to γ = 0 whereas for γmax > 0.18 we obtain double minima, a signature of plasticity. Such an observation helps us to identify the critical value γy = 0.18 of the yielding transition. Interestingly, the critical value γy for silica is found to be higher than that of the binary Lennard-Jones system where γy = 0.07.

    The mechanical properties of silica is further characterized by studying the distribution of cluster size (s) of the avalanche and distribution of energy drop (∆U) during the avalanche occurring in the steady state. An avalanche is identified when ∆U/N dγ2 > 100. Both the distributions P(s) and P(∆U), as shown in Figure 1 (c) and 1 (d), respectively, exhibit power-law scaling behaviour. However, as observed for the model glass former [3], the power-law exponents are found different for different quantities: P(∆U) ∼ ∆U −1 and P(s) ∼ s −3/2 . It is also notable that the maximum size of the avalanche cluster is of the order of system size for γmax ≥ γy, whereas for γmax < γy it is not. Hence, there could be a percolation transition of the avalanche cluster at the yielding point as reported before [3, 5].

    To summarize, the mechanical behaviour silica as an attractive glass former is studied through oscillatory deformation. Analyzing the energy landscape the critical yielding point has been identified which is consistence with stress-strain curve. The statistics of avalanche cluster size and energy drop during avalanche exhibit similar behaviour as that of the model glass former.

    ∗ Corresponding author: himangsu@jncasr.ac.in

    1. D. J. Lacks and M. J. Osborne, Phys. Rev. Lett. 93, 255501 (2004).
    2. D. Fiocco, G. Foffi, and S. Sastry, Phys. Rev. E 88, 020301 (2013).
    3. P. Leishangthem, A. D. S. Parmar, and S. Sastry, Nature Communications 8, 14653 (2017).
    4. E. Lascaris, M. Hemmati, S. V. Buldyrev, H. E. Stanley, and C. A. Angell, The Journal of Chemical Physics 140, 224502 (2014).
    5. G. P. Shrivastav, P. Chaudhuri, and J. Horbach, Phys. Rev. E 94, 042605 (2016).

 

 

 

16. D. A. M´artin(1), ∗ T. S. Grigera(2) and V.I. Marconi(3)

    1. IFIMAR, CONICET and UNMdP, Funes no. 3350, 7600, Mar del Plata, Argentina
    2. IFLYSIB, CONICET and UNLP, Calle 59 no. 789, B1900BTE La Plata, Argentina
    3. FaMAF and IFEG (UNC-CONICET), Universidad Nacional de C´ordoba, X5000HUA C´ordoba, Argentina

    Speeding up the study of diluted dipolar systems

    We study the regimes of a diluted dipolar system through Monte Carlo numerical simulations in the NV T ensemble, under periodic boundary conditions. The temperature is T and the number density is ρ = N/V . Following [1], we used a shifted and truncated potential.

    In order to accelerate the dynamics, several approximations and speed up algorithms are proposed and tested. In particular, it turns out that “Cluster Move Monte Carlo” (CMMC) algorithm is about 1 decade faster than traditional Monte Carlo.

    To define a cluster, we consider two particles as neighbors if they separated by a distance rN = √ 1.5 or smaller. A cluster is then defined as the smallest set of particles such that of a particle belong to the same cluster. In CMMC, we perform typical movements (single-particle rotation and translation), but also “Cluster Moves”: a cluster is selected and displaced uniformly to a random location in the simulation box, in such whay that detailed balance is fulfilled.

    With the aid of these agoritms, we find gas, stringliquid, ring-liquid, gel and antiparallel crystal regimes as a function of temperature and density. Such regimes are studied and characterised through positional, orientational and thermodynamical observables.

    The transition between gas and liquid can be found counting the numer of particles with no neighbors.

    The transition between liquid and Gel can be determined through percolation parameters.

    The transition between Gel and Crystal can be found meassuring local density, the number of particles with more than two neighbors or local magnetization (The gel has net local magnetization while the crystal has antiferromagnetic-like order).

    We would like to thank Ernesto Loscar. Support from CONICET and Agencia Nacional de Promocin Cientfica is acknowledged.

    ∗ Corresponding author: dmartin@ifimar-conicet.gob.ar

    1. M. Lamichhane, J. D. Gezelter and K. E. Newman, JCP 141, 134109 (2014).
    2. L. Rovigatti, J. Russo, and F. Sciortino, Phys. rev. lett., 107, 237801 (2011).

 

 

 

17. Charuhansini Kulkarni(1), ∗ and Shashi Thutupalli(1), (2)

    1. Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore
    2. International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bangalore

    Cellular adaptations to freeze-thaw

    Any living cell is characterized by various properties like molecular composition, material and energy flux, structure and organization that are important for its functioning. If any of these parameters are perturbed by the environment, the physico-chemical state of the cell can change. Interestingly, the cells that we see today have survived many such perturbations in evolutionary history. We study what mechanisms facilitate cells to survive such perturbations. One such perturbation is temperature extreme cold. Both on ecological and evolutionary timescales, many extant organisms have gone through freezing and thawing events. Here, we study what mechanisms facilitate cells to make these transitions during freeze-thaw so that they survive the perturbation. A controlled method to understand these mechanisms is to distinguish between cells of the same organism that can and cannot survive freeze-thaw and characterize which of these differences serve as a mechanism of tolerance to freeze-thaw. For this, we have allowed yeast populations (S. cerevisiae) that initially had low tolerance to freeze-thaw to adapt to this stress and characterize differences between the two. We also study how duration in between freezethaw cycles and duration at cold temperatures affect survival mechanisms. All these methods put together help us understand the processes occurring in a cell upon freeze-thaw and hence possible mechanisms of freeze-thaw tolerance.

    ∗ Corresponding author: charuhansini@ncbs.res.in

 

 

 

18. CA Brackley(1), J Johnson(1), A Bentivoglio(1), S Corless(1), N Gilbert(2), G Gonnella(3) and D Marenduzzo(1)

    1. SUPA, School of Physics and Astronomy, The University of Edinburgh
    2. MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, The University of Edinburgh
    3. Dipartimento di Fisica, Universit`a di Bari and INFN, Sezione di Bari

    Stochastic Model of Supercoiling-Dependent Transcription

    DNA is involved in a lot of processes among which replication that is production of two identical replicas of DNA starting from one DNA molecule, and transcription in which a specific piece of DNA is copied into a new molecule: RNA. These processes are achieved by specialised enzymes as DNA polymerase (DNApol) for replication and RNA polymerase (RNApol) for transcription [1].

    In order to do their job properly these enzymes need to separate the two complementary strands of DNA molecule and this can lead DNA double helix to a torsional stress that can increase the number of base pairs (bp) per turn of helix (overtwisting) or decrease it (untwisting) and eventually the DNA will tend to coil upon itself forming superhelices (helices of helices) [2]. This phenomenon is commonly known as supercoiling of DNA and it is due to the inherently chiral nature of DNA.

    Several observations suggest that DNA supercoiling is intimately related to transcription and that it can regulate gene expression [3]. For example it is well known that RNA polymerase binding is more likely when the DNA molecule is slightly negatively supercoiled in the region of the promoter of the gene involved [2].

    In the late 80s Liu and Wang developed the “twin supercoiled domain” model [4] in order to explain some experimental results. The model is based on the observation that if rotation of the RNA polymerase and its associated transcription machinery is hindered then gene transcription leads to the creation of positive supercoiling ahead of the tracking polymerase and negative supercoiling in its wake (Fig. 1). Within this framework we propose a model [6] that incorporates the dynamics of supercoiling - where polymerases create supercoiling as they unwind the DNA helix - into a stochastic description of gene regulation [5].

    We show that when the transcriptionally induced flux of supercoiling J¯ created by RNApol increases, there is a sharp crossover from a regime where torsional stresses relax quickly and gene transcription is random, to one where gene expression is highly correlated and tightly regulated by supercoiling. In the latter regime, the model can displays transcriptional bursts and waves of supercoiling

    In the case of a circular DNA molecule with overall positive supercoiling, we find a non-equilibrium phase transition between an absorbing phase, where all genes are switched off due to the supercoiling, and an active phase with a non-zero transcription rate [7].

    1. B. Alberts, Molecular Biology of the Cell (Garland Science, 2014)
    2. A. D. Bates and A. Maxwell, DNA Topology (Oxford University Press, 2005)
    3. J. Ma and M.D. Wang, Biophys. Rev.,8,75-87, 2016
    4. L.F. Liu and J.C. Wang, Proc. Natl. Acad. Sci. U. S. A. 84, 70247027, 1987.
    5. A. Raj and A. van Oudenaarden, Cell 135, 216-226, 2008
    6. C.A. Brackley, J. Johnson, A. Bentivoglio, S. Corless, N. Gilbert, G. Gonnella and D. Marenduzzo, Phys. Rev. Lett.,117, 018101,2016.
    7. A. Bentivoglio, M. Ancona, C.A. Brackley, G. Gonnella and D. Marenduzzo, Soft Matter 14, 3632-3639 (2018).

 

 

 

19. Arjun H^{1, 2}, ∗ and Pinaki Chaudhuri^1,2

    1. The Institute of Mathematical Sciences, IV Cross Road, CIT Campus,Taramani, Chennai
    2. Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai

    Glass Forming Liquid in a Quenched random potential

    Using numerical simulations, we study the dynamical and structural properties of a glass forming liquid, in the presense of an external quenched random potential. Our study is motivated by the recent exper- iments of Stefan U. Egelhaaf et al [1], where in the background of such a potential, a low density liquid exhibited dynamical slowing down.

    In our study, we consider a 50-50 binary mixture of hard-disks with diameter ratio 1.4. For this glass former, the control parameter is the packing fraction φ. The external quenched potential is sampled from a Normal distribution with standard deviation , which therefore acts as another control parameter. Our stud- ies are carried out by varying φ in the range 0.60 to 0.80 and in the range 0.0 to 5.0.

    We characterise the dynamical properties using different time correlation functions, viz. mean-square displacement and overlap functions. At a fixed φ, we find an increasing slowing down in dynamics and as- sociated spatio-temporal heterogeneties, with increasing. From the long-time diffusion coefficients, the MCT and VFT lines in the (φ,ε) plane are mapped, thereby marking the regime where glassy dynamics is observed. We also probe for aging behaviour in the large (φ,ε) regime.

    To characterise the positional ordering in the system, we consider the pair correlation functions, g(r), and we find that the g(r) is not sensitive to the change in at a fixed φ. But the orientational correlation calculated from the hexatic order of the particles are found to be decreasing with increasing , since the spatial randomness of the potential possibly restricts the formation of any particular orientational order.

    We plan to study the role of entropy in determining the above behaviour.

    Corresponding author: arjunh@imsc.res.in

    [1] F. Evers et al, Physical Review E 88, 022125 (2013).

 

 

 

20. Federico Corberi¹, Manoj Kumar², Eugenio Lippiello³ and Sanjay Puri⁴

    1. Dipartimento di Fisica “E. R. Caianiello”, and INFN, Gruppo Collegato di Salerno, and CNISM, Unit`a di Salerno, Universit`a di Salerno, via Giovanni Paolo II 132, 84084 Fisciano (SA), Italy.
    2. International Centre for Theoretical Sciences, Tata Institute of Fundamental Research, Bengaluru 560089, India
    3. Dipartimento di Matematica e Fisica, Seconda Universit`a di Napoli, Viale Lincoln, Caserta, Italy
    4. School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India

    Ordering in a disordered magnet with tunable frustration

    We study numerically the ordering kinetics in a system where the amount of randomness can be gradually tuned. We show that, upon increasing such features, the behavior changes in a radical way. Small randomness does not prevent the system from a complete ordering, but this occurs in an extremely (logarithmically) slow manner. However, large randomness destroys complete ordering, a feature denoted as frustration, and the evolution is comparatively faster (algebraic). Our study shows a precise correspondence between the kind of developing order, complete versus frustrated, and the speed of evolution. Also, we presented an interpretation in terms of the different nature of phase space.

    Corresponding author: corberi@sa.infn.it
    [1] F. Corberi, M. Kumar, S. Puri, and E. Lippiello, Phys. Rev. E 95, 062136 (2017).
    [2] F. Corberi, E. Lippiello, R. Burioni, A. Vezzani, and M. Zannetti, Phys. Rev. E 91, 062122 (2015).
    [3] F. Corberi, E. Lippiello, and M. Zannetti, J. Stat.Mech. P10001 (2015).

 

 

 

21. Navneet Singh¹, A K Sood^{2, 3} and Rajesh Ganapathy³

    1. Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India
    2. Department of Physics, Indian Institute of Science, Bangalore 560012, India
    3. International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India

    Dynamics of supercooled liquids on curved space

    The statics and dynamics of a crystal residing on flat space is fundamentally different from those residing on curved space[1]. Intuition however suggests that spatial curvature should play a less influential role in the dynamics of disordered systems. Recent simulations however find that glass forming liquid on the surface of a 4D hypersphere freezes via a sharp transition into fully icosahedral structure on curving 3D space[2] and a monoatomic liquid on the hyperbolic plane exhibits increase in fragility with increasing curvature[3]. Experimental studies that have investigated the role of spatial curvature on dynamics of supercooled liquid are scarce. We have developed a model binary colloidal system residing on surface of a 3D sphere to understand the role of curvature on the dynamics of supercooled liquid. We used fast confocal microscopy to probe dynamics at the single particle level. In this poster, we will highlight recent findings on role of spa- tial curvature on the behaviour of dynamical heterogeneities on approaching mode coupling glass transition.

    Corresponding author: navneet22may@gmail.com
    [1] William T. M. Irvine, Mark J. Bowick and Paul M.Chaikin, Fractionalization of interstitials in curved colloidal crystals, Nature Materials 11, 948 951, 2012.
    [2] Francesco Turci, Gilles Tarjus and C. Patrick Royall, From Glass Formation to Icosahedral Ordering by Curving Three-Dimensional Space, Physical Review Letters 118, 215501, 2017.
    [3] Franois Sausset, Gilles Tarjus, and Pascal Viot, Tuning the Fragility of a Glass-Forming Liquid by Curving Space, Physical Review Letters 101, 155701, 2008.

 

 

 

22. Narender¹, ∗ and P.S. Burada¹

    Department of Physics, Indian Institute of Technology, Kharagpur- 721302, India

    Entropic particle transport in symmetric channel

    We investigate the transport of Brownian particles in symmetric periodic channel. The problem is analysed in the context of the Fick-Jacobs equation which accounts for the effect of the lateral confinement by introducing an entropic barrier in the equation [1–3]. The entropic transport of Brownian particles through two-dimensional narrow, symmetric and spatially periodic structure that is subjected to a constant external force, in the channel direction is numerically and analytically analysed. The numerically simulated results, produced by impos- ing both the no-flow and elastic reflection boundary con- ditions at the channel walls, are compared. The influence of different channel geometries are discussed for both the non-linear mobility and the effective diffusion coefficient.

    The whole dynamics can be described in terms of a sin- gle dimensionless parameter f which is the ratio of the work done to the particle and the available thermal en- ergy. This mechanism enables the proper design of the channel structure for the transport of ions, molecules, and small particles.

    Acknowledgments
    The first author would like to acknowledge Indian Institute of Technology for the fellowship to pursue the PhD program.

    [1] P.S. Burada, Entropic transport in confined media, PhD dissertation (Augsburg University, Germany, 2008).
    [2] D. Reguera, G. Schmid, P.S. Burada, J.M. Rubi, P. Riemann, and P. H ̈anggi, Entropic transport: kinetics, scaling, and control mechanism, PRL 96 (13), 130603, (2006).
    [3] D. Reguera, and J.M. Rubi, Kinetic equation for diffusion in the presence of entropic barrier, Physical review E 64, 061106, (2001).