In nature as well as in many technical applications, one encounters the sometimes problematic phenomenon of intermittent dynamics, e.g. in form of stick-slip motion, associated to strongly correlated dynamics of complex geometrical objects over scales that can span many orders of magnitude. Examples range from the atomic to the tectonic scale, including avalanches in magnetic materials [Laurson2014], superconductors [Verma2016], glasses [Antonaglia2014], cascades of irreversible rearrangements in soft matter systems [Bonn2015], critical dynamics of imbibition [Clotet2016] and crack growth [Kokkoniemi2017]; mechanical response of granular and porous media [Main2017], wood [Mäkinen2015], and geological flows, such as snow avalanches [Van Herwijnen2016] and earthquakes [De Arcangelis2016].
Understanding the complex, nonlinear spatiotemporal response of these systems, and the connections between different scales is crucial for physical predictions, and for the development of reliable models for engineers. Recent theoretical and experimental progress makes this a timely forum for an interdisciplinary effort to advance this important emerging research area.
The most important questions in the field are on the one side to understand the emergence of universality [Denisov2016] and the possibility of defining different universality classes [Ferrero2016, Lin2014, Liu2016], which gave rise to many debates in recent years [Ispánovity2014]. However, we think it is time to investigate in more detail the question of the non-universal features in avalanche dynamics, e.g. due to inertial effects [Salerno2013, Karimi2017] or transient dynamics [Leishangthem2017], and to attack the question considered the Holy Grail in the field of avalanche dynamics, namely the possibility of predicting catastrophic events [Van Herwijnen2016, De Arcangelis2016, Main2017, Amon2017].
Probing these out-of-equilibrium critical phenomena experimentally remains a challenge due to the involved diverging time scales and strong finite size effects, which is why this field can only advance significantly with combined efforts between experiments and modern methods of numerical investigations. Especially when thinking about the possible definition of precursor dynamics, the ability of probing microscopic dynamics through simulations remains one of the crucial techniques to guide the experimental understanding. Recent experimental advances, allowing for measurements on mesoscopic scales using dynamic light scattering [Pons2016] or local velocimetry techniques [Saint-Michel2016] provide additional keys to validate microscopic scenarios and the development of numerical coarse grain approaches. A workshop that aims at linking the efforts in the different communities and the descriptions at the different scales will thus be very timely and needed to boost the understanding in the various fields.
This workshop will not only help to crosslink the theoretical understanding between the different research fields but also and even more importantly to exchange intelligent numerical schemes, coarse graining procedures for the multiscale problems considered and advanced numerical parallelisation techniques for the acceleration of the codes used in the various communities. We strongly believe that the workshop program will promote interactions between participants from statistical physics, mathematics, soft matter, condensed matter physics, and researchers at the boundary of physics and other disciplines such as materials science, solid mechanics, and instabilities in solid earth systems.
The idea of this conference is to bring together international experts in the field of avalanche dynamics, to discuss recent progress and insight from computational, theoretical and experimental approaches. This field is very challenging especially concerning modeling aspects, due to the computational difficulties related to critical slowing down of the dynamics and strong finite size effects. In the recent years, however, the computer power and new parallel coding techniques like GPGPU or large scale MPI programming techniques have allowed for significant progress in accessing reasonable time and length scales to address questions that were difficult to tackle before.
Also on the experimental side, new approaches combining different techniques (e.g. various types of spectroscopy and rheology) allow for an investigation on a more mesoscopic scale of the complex dynamics, being able to probe scales that can be modeled within, for example, MD simulations. In addition, recent theoretical developments now address specifically the non-linear response of soft materials, providing new concepts and ideas to be tested in experiments and simulations. There seems to be a unique opportunity, at this point, in combining such efforts to develop a new understanding of avalanche dynamics, closely related to their technological applications. This is why we think it is extremely timely and important to bring together the different relevant communities with the help of CECAM. The specific topics and questions that we would like to focus on are the following:
1. Non-universal features in avalanche dynamics
This session will focus on introducing the main reasons for non-universal features in avalanche dynamics, such as the presence of inertia, transient phenomena and other non-critical situations where avalanches still play a dominant role for the overall dynamics. This first session also aims at setting the general theme of the conference to set the focus within the different research areas on "Non-universal features and precursors of catastrophic events in avalanche dynamics".
2. Conditions for universality in avalanche dynamics
Much effort has been invested to classify different systems exhibiting avalanche dynamics into universality classes regarding the underlying nature of disorder and the specifies in the interaction kernel (short or long ranged, strictly positive or with altering signs). This session aims at clarifying the conditions under which one can expect universality and what should be the good classification criteria.
3. Precursors of catastrophic events
One of the most urging questions to solve, also with respect to technical application, such as failure prediction and the forecast of extreme events in natural phenomena, is to find possible definitions of precursors of large events in the time series of avalanches. This third session will be completely dedicated to this topic and introduce this general theme also for the discussions within the follow-up sessions.
4. Avalanches in transient dynamics
Some first works are now concentrating on avalanches in transient dynamics instead of being interested in the stationary state dynamics. In many cases this dynamics appear not to be critical, but they are nevertheless still governed by avalanche type events. This session will concentrate on the specific role of initial conditions and parameter dependence on the avalanches in the transient dynamical regimes, a topic very important for applications were transient dynamics are ubiquitous.
5. Depinning transition
The depinning transition is probably the best understood dynamical transitions exhibiting avalanche dynamics. We hope that the knowledge and concept transfer of this research field will promote as well the understanding in other fields. On the other hand the study of transient dynamics and situations with non-universal dynamics have also not been strongly addressed in this context and thus the focus will lie on these new questions in the field of the depinning transition.
5. Yielding transition
The yielding transition has been quite controversial with respect to its belonging in a specific universality class, especially the belonging to the depinning universality class has been shown to be questionable. Depending on the observables considered and the dynamical regime of interest the reasoning can be very different. This session is suppose to sort out the necessary numerical (and experimental) tests needed to converge the understanding of this strongly debated subject.
7. Instability in solid earth systems
Geophysical systems with avalanche dynamics, such as snow avalanches and earthquakes are related to very similar questions compared to the depinning and the yielding transition and this workshop aims at isolating common questions that can be tackled in a common framework.
8. Coarse grained models for avalanche dynamics
The development of mesoscopic models, such as spring block models, mesoscopic elasto-plastic models, birth-death processes and various other coarse grained descriptions can help in understanding better the basic mechanisms for non-universal features in avalanche dynamics. This session will focus on some recent advances in these modeling techniques and its application ranges.
9. Other systems exhibiting avalanche dynamics
Beyond the above examples for systems exhibiting avalanche dynamics there is a myriad of systems dealing with strongly correlated intermittent dynamics, as is the case for example in martinsites, in neural network systems, in social sciences, in vulcanic eruptions and solar flare dynamics. Thus we give in this last session the possibility to develop the understanding of avalanches in a very broad framework to promote the knowledge transfer between a vast number of different fields.