11th Nordic Workshop on Statistical Physics: Biological, Complex and Non-Equilibrium Systems

14 Apr 2021, 13:00 → 16 Apr 2021, 17:00 Europe/Stockholm

Nordita

Alberto Imparato (Aarhus University), Ralf Eichhorn (Nordita)

Virtual Meeting

 

Platform: 

Time zone: CEST - Central European Summer Time (Stockholm time)

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Scope

This workshop series provides a “forum” where scientists in the Nordic countries working in the area of Statistical Physics can meet regularly. The meeting brings together experts interested in the broad spectrum of timely problems in (classical) Statistical Physics, ranging from fundamental aspects in the theory of non-equilibrium processes to modern applications in biophysics. Topics covered include diffusion problems, non-equilibrium transport, work relations and fluctuation theorems, microscopic heat engines, soft condensed matter (colloids, liquid crystals etc.), microfluidics, pattern formation, self-assembly, population dynamics, physics of DNA and bio-molecules, single-molecule kinetics, dynamics and structure of networks, statistical inference, neuronal networks, quantum thermodynamics and many more.

The 2021 event is the 11th edition in this Nordic Workshop series. The series has been initiated at Nordita in 2010. Since then a workshop has been held every year, except for the 2020 edition, which had to be cancelled because of the outbreak of the COVID-pandemic.

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Setup

Being aware that it is more difficult and tiresome to sit in front of a screen and focus on online presentation with minimal personal interaction we decided to run this virtual workshop in a reduced format:
We will have three talks per day, starting at 1.30 pm every day and ending around 5 pm. Each talk will be allocated 60 min in total, consisting of 45 min for the presentation itself, 10 min for questions and about 5 min for a short break in between the talks.

We are planning to conclude each day with a "discussion session" of about 30 min, centered around the three talks of the day. The idea is that each speaker of the day will be invited to host a Zoom room, so that the participants of the workshop can freely switch between these rooms, ask questions, contribute to the discussion etc.

In summary, each day will be organized like this (for the detailed time-table click here):

13:30-14:30	talk 1 13:30 - 14:15 presentation 14:15 - 14:25 questions 14:25 - 14:30 break
14:30-15:30	talk 2 14:30 - 15:15 presentation 15:15 - 15:25 questions 15:25 - 15:30 break
15:30-16:30	talk 3 15:30 - 16:15 presentation 16:15 - 16:25 questions 16:25 - 16:30 break
16:30-17:00	discussion session

 

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Invited Speakers

Erik Aurell (KTH) Lorenzo Costigliola (Roskilde University) Supriya Krishnamurthy (SU) Lasse Laurson (Tampere University)

Bernhard Mehlig (Gothenburg University) Yasser Roudi (Norwegian University of Science and Technology) Marc Suñé Simon (Nordita) Giovanni Volpe (Gothenburg University) Astrid de Wijn (Norwegian University of Science and Technology)

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Registration

If you want to participate in the workshop, please fill in the registration form.

Registration deadline: 12 April, 2021

There is no registration fee.

Sponsored by:

Wednesday 14 April

13:00 → 13:30 Virtual Gathering ("Coffee & Cake")

Speakers: Alberto Imparato, Ralf Eichhorn (Stockholm University)

13:30 → 14:25 Understanding the friction of atomically thin layered materials

Friction is a ubiquitous phenomenon that greatly affects our everyday lives and
is responsible for large amounts of energy loss in industrialised societies.
Layered materials such as graphene have interesting frictional properties and
are often used as (additives to) lubricants to reduce friction and protect
against wear. Experimental Atomic Force Microscopy studies and detailed
simulations have shown a number of intriguing effects such as friction
strengthening and dependence of friction on the number of layers covering a
surface. Here, we propose a simple, fundamental, model for friction on thin
sheets. We use our model to explain a variety of seemingly contradictory
experimental as well as numerical results. We also use it to study thermal
effects and aging in these systems.

Speaker: Astrid de Wijn (Norwegian University of Science and Technology)

14:30 → 15:25 Quantitative analysis of non-equilibrium systems from short experiments

We provide a minimal strategy for the quantitative analysis of a large class of non-equilibrium systems in transient or steady state using the short-time Thermodynamic Uncertainty Relation (TUR). From short-time trajectory data obtained from numerics or experiments, we demonstrate how we can simultaneously infer quantitatively, both the thermodynamic force field acting on the system, as well as the exact rate of entropy production. We benchmark the scheme against exactly solvable models, before applying it to cases where neither analytical nor numerical results are available.

Speaker: Supriya Krishnamurthy (Stockholm University)

15:30 → 16:25 The Vernon transform and its use in quantum thermodynamics

Speaker: Erik Aurell (KTH)

16:30 → 17:00 Discussion Sessions

Speakers: Astrid de Wijn (Norwegian University of Science and Technology), Erik Aurell (KTH), Supriya Krishnamurthy (Stockholm University)

Thursday 15 April

13:30 → 14:25 The unbearable lightness of single neuron non-linearities in neural network learning algorithms

Speaker: Yasser Roudi (Norwegian University of Science and Technology)

14:30 → 15:25 Machine Learning for Active Matter: Opportunities and Challenges

Machine-learning methods are starting to shape active-matter research. Which new trends will this start? Which new groundbreaking insight and applications can we expect? More fundamentally, what can this contribute to our understanding of active matter? Can this help us to identify unifying principles and systematise active matter? This presentation addresses some of these questions with some concrete examples, exploring how machine learning is steering active matter towards new directions, offering unprecedented opportunities and posing practical and fundamental challenges. I will illustrate some most successful recent applications of machine learning to active matter with a slight bias towards work done in my research group: enhancing data acquisition and analysis; providing new data-driven models; improving navigation and search strategies; offering insight into the emergent dynamics of active matter in crowded and complex environments. I will discuss the opportunities and challenges that are emerging: implementing feedback control; uncovering underlying principles to systematise active matter; understanding the behaviour, organisation and evolution of biological active matter; realising active matter with embodied intelligence. Finally, I will highlight how active matter and machine learning can work together for mutual benefit.

Speaker: Giovanni Volpe (Gothenburg University)

15:30 → 16:25 Complexity in crystal plasticity: strain burst statistics and machine learning

In this talk I will review our recent results concerning critical-like statistics of dislocation avalanches, i.e., strain bursts observed in plastically deforming crystals, as obtained from two and three-dimensional discrete dislocation dynamics simulations. Specifically, I will discuss the “glassy” dislocation dynamics in pure crystals without any additional defects, as well as the depinning phase transition exhibited by dislocation
assemblies interacting with a quenched pinning field due to other defects in the crystal such as precipitates. Moreover, I will also discuss our recent attempts to employ machine learning to quantify the degree of predictability of the plastic deformation process, which in the case of small crystals exhibits significant sample-to-sample variability.

Speaker: Lasse Laurson (Tampere University)

16:30 → 17:00 Discussion Sessions

Speakers: Giovanni Volpe (Gothenburg University), Lasse Laurson (Tampere University), Yasser Roudi (Nordita)

Friday 16 April

13:30 → 14:25 Capillary control of failure in soft composite materials

Since Euler’s original study, the buckling instability of a column subjected to longitudinal compression forces has been extensively studied in homogeneous, isotropic, linear–elastic solids. In our work we examine the nature of the buckling in inhomogeneous soft composite materials. In particular, we consider a soft host with liquid inclusions both large and small relative to the elastocapillarity length, which lead to softening and stiffening of a homogeneous composite respectively. However, by imposing a gradient of the inclusion volume fraction or by varying the inclusion size we can deliberately manipulate the spatial structure of the composite properties of a column and thereby control the nature of Euler buckling.

Speaker: Marc Suné (Nordita)

14:30 → 15:25 The isomorph filter: identifying when an equation can be universal

In the last few decades the density-scaling approach has widened our knowledge of liquids and glasses. Density scaling allows for a drastic reduction of the amount of information required to describe the structure and dynamics of a system in its phase diagram. One of the possible explanations for why density scaling holds is provided by the isomorph theory. In this theoretical framework a key point is the recognition that the physical properties of a system should be expressed in reduced units, i.e., made dimensionless using inverse density as length scale, thermal energy as energy scale and the ratio of l0 and thermal velocity as time scale. A consequence of the use of reduced units is the so-called isomorph filter which allows one to identify whether a given relation between physical properties can be universal or not. In this talk the isomorph theory and the concept of isomorph filter will be introduced in a general way and then the isomorph filter will be tested on two practical cases: describing the viscosity of simple liquids at high densities [1] and a modified version of the Stokes-Einstein relation [2].

References
[1] L. Costigliola, U.R. Pedersen, D.M. Heyes, T. B. Schroder, and J.C. Dyre Communication: Simple liquids' high-density viscosity. J. Chem. Phys. 148, 081101
(2018).
[2] L. Costigliola, D. M. Heyes, T. B. Schroder, and J. C. Dyre Revisiting the Stokes-Einstein relation without a hydrodynamic diameter. J. Chem. Phys. 150, 021101
(2019).

Speaker: Lorenzo Costigliola (Department of Science and Environment, Roskilde University)

15:30 → 16:25 Angular dynamics of an ice crystal settling in a turbulent cloud

Small non-spherical particles settling in a quiescent fluid tend to orient so that their broad side faces down, because this is a stable fixed point of their angular dynamics at small particle Reynolds number. Turbulence randomises the orientations to some extent, and this affects the reflection patterns of polarised light from turbulent clouds containing ice crystals. An overdamped theory predicts that turbulence-induced fluctuations of the orientation are very small when the settling number Sv (a dimensionless measure of the settling speed) is large. At small Sv, by contrast, the overdamped theory predicts that turbulence randomises the orientations. This overdamped theory neglects the effect of particle inertia. Therefore we consider here how particle inertia affects the orientation of small crystals settling in turbulent air. We find that it can significantly increase the orientation variance, even when the Stokes number St (a dimensionless measure of particle inertia) is quite small. We identify different asymptotic parameter regimes where the tilt-angle variance is proportional to different inverse powers of Sv. We estimate parameter values for ice crystals in turbulent clouds and show that they cover several of the identified regimes. The theory predicts how the degree of alignment depends on particle size, shape and turbulence intensity, and that the strong horizontal alignment of small crystals is only possible when the turbulent energy dissipation is weak, of the order of 1cm^2/s^3 or less.

Speaker: Bernhard Mehlig (University of Gothenburg)

16:30 → 17:00 Discussion Sessions

Speakers: Bernhard Mehlig (University of Gothenburg), Lorenzo Costigliola (Department of Science and Environment, Roskilde University), Marc Suné (Nordita)