Prof. Ehud Meron, Ben-Gurion University of the Negev, Israel.
Multi-level ecosystem response to drying climate trends
September 30, 2024; 7:30 pm (Indian Standard Time)
Abstract -Climate change and the development of drier climates threaten health of ecosystems and the services they provide to humans. Understanding the response to drier climates of ecosystems in general and plant communities, in particular, may provide clues on how to improve their functioning and resilience. This response is likely to involve mechanisms operating at different levels of ecological organization. At the single-plant level, phenotypic changes can occur; at the population level of many plants of a given species, spatial patterns can form; and at the community level of populations of different species, community reassembly can occur. In this talk, Prof. Meron will focus on the interplay between phenotypic changes and spatial patterning and between spatial patterning and community reassembly. Using mathematical models of water-limited plant communities, he will show that incorporating phenotypic plasticity into vegetation pattern-formation theory can resolve two outstanding puzzles associated with the fascinating Namibian fairy circle phenomenon and describe a predicted buffering effect of spatial patterning on community composition along rainfall gradients.
Bio - Prof. Ehud Meron received his Ph.D. in nonlinear physics from the Weizmann Institute of Science. Prof. Ehud is an expert in the mathematical theory of pattern formation and front dynamics. He has contributed to understanding front dynamics in reaction-diffusion systems, highlighting the roles front instabilities play in initiating growth patterns and nurturing complex spatiotemporal behaviors. He has made pioneering contributions to understanding the mechanisms that drive vegetation pattern formation and the implications of vegetation patterning for biodiversity, ecosystem functioning, and desertification. Prof. Ehud is a Phyllis and Kurt Kilstock Chair Professor in Environmental Physics of Arid Zones and the author of the monograph Nonlinear Physics of Ecosystems (CRC 2015). In 2023, Ehud and his colleagues won an ERC-Synergy grant to study pathways of resilience and evasion of tipping in drylands, savannas, and tundra.
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Prof. Gabriel Mindli, University of Buenos Aires.
Listening to bird's dreams
May 27, 2024; 7:30 pm (Indian Standard Time)
Abstract - During sleep, sporadically, it is possible to find neural patterns of activity in areas of the avian brain that are activated during the generation of the song. It has recently been found that in the vocal muscles of a sleeping bird, it is possible to detect activity patterns during these silent replays. In this talk, Prof. Mindlin will describe a research program in which, by means of a dynamical systems model for birdsong production, the vocal muscles activity during sleep can be converted into synthetic songs. Besides allowing us to translate muscle activity into behaviour, He will show that this approach poses the biomechanics as a unique window into the avian brain, with biophysical, nonlinear models as its probe.
Bio - Prof. Gabriel Mindlin is Professor at the University of Buenos Aires (Department of Physics, Faculty of Exact and Natural Sciences) and a researcher at CONICET. He completed his Ph.D. in Physics at Drexel University (Philadelphia, USA). His area of expertise is nonlinear dynamics. From this perspective, he began investigating problems in behavioral neuroscience, focusing on the study of bird song. This serves as an ideal model for understanding how the nervous system, biophysics, and the environment interact during a learning process. Currently, he is focused on applying artificial intelligence techniques to the study of biodiversity. He is author of 140 publications in journals within his field and 4 books. He has received national and international awards, including the Stimulus Award from the Bunge and Born Foundation, the Arthur Winfree Award from the ICTP in Trieste.
Prof. Kira Rehfeld, University of Tübingen.
Climate variability from the local to the global scale
April 29, 2024
Time: 7:30 PM to 9:00 PM Indian Standard Time
Abstract: From the last Glacial Maximum to today, the Earth has warmed by 3-8 degrees over ~7000 years. This temperature change is in the order of magnitude of that expected in the next centuries in mid-to-high emission scenarios. In this talk, Prof. Rehfeld will first discuss what her group has learned about changes in local to regional and global temperature variability under warming and the role of natural vs. anthropogenic drivers on different timescales. Subsequently, Prof. Rehfeld will show that current climate models succeed in capturing some, but not all, of this variability – and what this implies for the interpretation of projections.
Bio: Prof. Kira Rehfeld is a professor at the University of Tübingen. She works on climate model experiments and studies ice cores, speleothems and pollen as environmental recorders, combining this with complex systems science to study Earth system dynamics. Her group focuses on climate model abilities for simulating climate variability, the role of forcing processes for the continuous spectrum of climate, and carbon dioxide removal.
István Z. Kiss, Department of Chemistry, Saint Louis University, St Louis.
Synchronization Engineering: How to Improve Synchronization with Control and Heterogeneities
March 25, 2024
Time: 7:30 PM to 9:00 PM Indian Standard Time
Abstract: Synchronization of oscillatory (bio)chemical reactions plays an important role in the functioning of biological processes. Physiological condition is often achieved by an optimal level and structure of synchrony. When the synchronization breaks down, engineering techniques are needed to re-establish the structure. Closed- and open-loop techniques for synchronization engineering can be used with linear and nonlinear delayed feedbacks and phase-selective entrainments. A framework for the methodological design of the control allows for adjusting the phase difference between the oscillator and the generation of stable and itinerant clustering, desynchronization, and chimera states. Prof. Kiss will talk about recent advances in synchronization engineering that address the optimality of the control signals, leveraging heterogeneities to enhance synchronization characteristics and design of emergent hypernetworks. Phase model machinery for the collective behaviour of oscillatory processes in discrete units proves to be an important tool for the design of engineering techniques.
Bio: Prof. István Z. Kiss studied Chemistry and received his PhD degree at the University of Debrecen, Hungary. He worked with Jack Hudson at the University of Virginia as a postdoctoral fellow. The research of Prof. Kiss focuses on the nonlinear dynamics of electrochemical systems with emphasis on coupled oscillators and applications to sensors, batteries, and corrosion mitigations. He was a recipient of the Fulbright Fellowship, the National Science Foundation CAREER Award, and the American Chemical Society St Louis Award. Prof. Kiss has published over 130 scientific publications in journals that include Science, Nature, Proceedings of the National Academy of Sciences, Nature Communications, and Physical Review Letters.
Dr. Krishnan Raghavan, Indian Institute of Tropical Meteorology
Fingerprint of volcanic forcing on the ENSO-Indian monsoon coupling
February 26, 2024
Time: 8:30 PM to 10:00 PM Indian Standard Time
Abstract:
There is unequivocal evidence that human-induced climate change has been the main driver of the observed intensification of heavy precipitation over the land regions across the globe and has also contributed to increases in agricultural droughts in some regions, which are further projected to enhance with additional warming during the 21st century (Douville et al., 2021). In this context, it must be highlighted that uncertainties due to unpredictable natural forces, such as large volcanic eruptions, can lower the degree of confidence in projecting near-term monsoonal changes. This talk aims to provide some insights into the role of large volcanic eruptions (LVEs) in influencing the nonlinear behaviour of the El Nino / Southern Oscillation (ENSO) and the Indian Monsoon (IM) dynamical system. The findings by Dr. Krishnan, based on a detailed analysis of historical data, paleoclimate reconstructions, last millennium climate simulations, large-ensemble targeted climate simulations, and advanced analysis techniques, show that LVEs promote a significantly enhanced phase-synchronization of the ENSO and IM oscillations due to an increase in the angular frequency of ENSO. The results also shed innovative insights into the physical mechanism underlying the LVE-induced enhancement of ENSO-IM coupling and strengthen the prospects for improved seasonal monsoon predictions.
Dr. Krishnan Raghavan specializes in climate modelling studies on scientific issues relating to “Climate Change, Asian Monsoon and Water Cycle”. Currently, he heads the Centre for Climate Change Research (CCCR) at IITM, Pune and is the Director of IITM, Pune. Under his leadership, the CCCR developed the IITM Earth System Model (ESM) – India's first global climate model that contributed to the CMIP6 and IPCC Sixth Assessment Report. He is a coordinating lead author in the IPCC AR6 WG1 report (Chapter 8: Water Cycle Changes) and a drafting author in the Summary for Policymakers. He and his team from CCCR-IITM published the First National Climate Change Assessment Report of the Ministry of Earth Sciences. He has an M.Sc degree in Applied Mathematics from MIT, Chennai. He pursued Ph.D. research in Atmospheric Sciences at the Physical Research Laboratory, Ahmedabad. He was awarded Ph.D. degree from the Univ. of Pune. He published 140 scientific articles/papers and supervised 12 Ph.D degrees & 7 Master (M.Sc/M.Tech) dissertations.
Prof. Raissa D'Souza, University of California Davis
Complex networks with complex nodes - emergent behaviors and control
January 29, 2024
Abstract: Real world networks -- from brain networks to social networks to critical infrastructure networks -- are composed of nodes with nonlinear behaviors coupled together via highly non-trivial network structures. Approaches from statistical physics reveal the fundamental implications that complex network structure has on network function and resilience. In contrast, approaches from dynamical systems and control theory reveal the impact that nonlinear nodal dynamics have on emergent behaviors when connected together in simple networks. This talk presents recent work bridging the fields. We show that the interaction between the nodal dynamics and network structure can give rise to novel emergent synchronization behaviors and extend the analysis of cluster synchronization to hypergraphs, capturing higher-order interactions in networks. With respect to cascading failures, we show that adding in oscillatory nodal dynamics to classic models of self-organized-criticality leads to an emergent timescale and the occurrence of self-amplifying dragon king failures that wipe out the system. Finally, we discuss the frontiers of control of complex networks with non-linear nodes, identifying the key challenges and opportunities for bridging control theory, dynamical systems and statistical physics.
Prof. Raissa D'Souza is the Associate Dean of Research for the College of Engineering at UC Davis as well as Professor of Computer Science and of Mechanical and Aerospace Engineering. She is a member of the Board of Reviewing Editors at Science and was a Founding Lead Editor at Physical Review Research of the American Physical Society. She received a PhD in Statistical Physics from MIT in 1999, then was a postdoctoral fellow, first in Fundamental Mathematics and Theoretical Physics at Bell Laboratories, and then in the Theory Group at Microsoft Research. Her interdisciplinary work on network theory and complex systems spans the fields of statistical physics, theoretical computer science and applied math, and has appeared in journals such as Science, PNAS, Physical Review Letters, and Nature Physics. She is a Fellow of the American Physical Society (class of 2016), a Fellow of the Network Science Society (class of 2019), and has received numerous honors such as the inaugural Euler Award of the Network Science Society in 2019, the 2018 ACM Test-of-Time award, and the 2017 UC Davis College of Engineering Outstanding Mid-Career Faculty Research Award. She has served on the editorial board of numerous international mathematics and physics journals and has organized key scientific meetings like NetSci 2014. She was a member of the World Economic Forum's Global Agenda Council on Complex Systems, and served as President of the Network Science Society, 2015-18.
Prof. Henk Dijkstra, Utrecht University
Tipping of the Atlantic Ocean Circulation
October 30, 2023
Abstract: The Atlantic Ocean Circulation, in particular its zonally averaged component called the Atlantic Meridional Overturning Circulation (AMOC), is one of the tipping elements in the climate system. The AMOC is sensitive to freshwater perturbations and may undergo a transition to a climate disrupting state within a few decades under continuing greenhouse gas emissions. In this Webinar, Prof. Dijkstra will focus on the complex systems aspects of the problem of assessing the probability of a collapse of the AMOC under future climate change. .
Prof. Henk A. Dijkstra is professor of Dynamical Oceanography at Utrecht University. His main research interests are on climate variability, in particular climate transitions, with a focus on the role of the oceans. In 2005, he received the Lewis Fry Richardson medal from the European Geosciences Union and in 2021 he was awarded an Advanced Grant from the European Research Council.
Dr. Norbert Marwan, Potsdam Institute for Climate Impact Research and University of Potsdam, Germany
Recurrence quantification analysis for understanding complex systems
September 25, 2023
Abstract: Recurrence is a ubiquitous and fundamental feature in many real world processes. It is present at many scales in time and space, such as in celestial mechanics, alternating sediment layers, thermoacoustic oscillation, cardiac variability, and numerous other contexts. The study of recurrence properties (such as frequency analysis) can provide deeper insights into the underlying dynamical processes in general. A rather novel approach for the study of recurrences is the recurrence plot and its quantification, rooted in the theory of dynamical systems. In this lecture, the basic concepts and the major extensions applicable to various research questions will be introduced and demonstrated. The examples to be discussed will include the temporal change of recurrence properties for identification of regime shifts, for classification, and bivariate extensions for synchronization/coupling analysis.
Norbert Marwan is the Deputy Chair of the Complex Systems Department at the Potsdam Institute of Climate Impact Research (PIK) in Potsdam, Germany. His research focuses on analysing complex systems, with a special interest in further developing and using methods like recurrence plots and complex networks for nonlinear data analysis. He applies these techniques to various interdisciplinary areas, with a particular focus on Earth science and palaeoclimatology.
Dr. Michael Small, The University of Western Australia
Choosing embedding lag and why it matters
May 29, 2023
Abstract: Takens’ theorem guarantees a faithful embedding of a deterministic nonlinear dynamical system from time series data under fairly generic conditions. Embedding, in this way, is the foundation of nonlinear time series analysis and modelling. Since the 1980s many methods have been proposed to estimate the time between observations to provide an embedding – the embedding lag. The basic premise is that time interval should ensure independence but not irrelevance. Almost all methods to choose this lag are based on the application of some heuristic to this premise. Dr. Small reviews some of the more interesting ones and introduces a new topologically well-founded way of doing the same. The method Dr. Small describes is based on using concepts from persistent homology and topological data analysis to ensure that one achieves the “best” attractor for the given data.
Michael Small is the CSIRO-UWA Chair of Complex Systems and holds academic positions at The University of Western Australia and with CSIRO (the Australian government research agency). He is Deputy Editor with Chaos and Main Editor at Physica A. Michael’s research is in nonlinear dynamics, nonlinear time series analysis, complex systems and networks. His work spans a range of application areas and focuses on data-driven methods for understanding complexity and chaos. Applications that he is currently working on include traffic modelling, mineral exploration, mental health, and disease modelling.
Dr. Holger Kantz, Max Planck Institute for the Physics of Complex Systems
Power law error growth rates – A dynamical mechanism for a strictly finite prediction horizon
April 24, 2023
Abstract: While conventional chaotic systems have a finite positive Lyapunov exponent, one can argue that larger the maximal Lyapunov exponent of the model equations of the atmosphere, the smaller are the resolved spatial scales. Specifically, a power law divergence of the scale dependent error growth rate would translate into a strictly finite prediction horizon, since, due to the divergence, additional accuracy of initial conditions is not translated into longer prediction times. Dr. Kantz will present conceptual toy models with such behaviour, and will show its presence in a more realistic spatially extended system with advective transport, and will present numerical results from turbulence simulations where the largest Lyapunov exponent scales as an inverse power of spatial resolution. The idea of a power law scale dependence of error growth rates and of a finite prediction horizon is also supported by re-analysis of numerical error growth experiments performed with an operational weather model. Altogether, this suggests that the prediction horizon of numerical weather prediction is strictly finite.
Holger Kantz studied physics at the University of Wuppertal, Germany, where he obtained his Diplom in 1986 and his Ph.D. in 1989 under the supervision of Peter Grassberger. At that time, he worked on the interface of Hamiltonian chaos and statistical physics, studying the ergodicity of such systems in the thermodynamic limit. After several postdoctoral employments, among them one in Florence (Italy, collaboration with Roberto Livi, Antonio Politi, Stefano Ruffo), he obtained a group leader position at the newly founded Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, in 1995, where he has stayed since then. His scientific interests today cover dynamical systems, stochastic processes, long range temporal correlations, atmospheric dynamics, extreme events. Through his affiliation with the Technical University of Dresden as Adjunct Professor for Statistical Physics, he has till now supervised more than 25 Ph.D. students.
Dr. Henrik Jeldtoft Jensen, Imperial College London
Information theoretic characterisation of emergent behaviour
March 27, 2023
Abstract: Prof. Jensen will discuss emergence for two different cases.
(1) The total number of possible states of N interacting particles are contained in the Cartesian products of individual particle states, i.e., we have that the total number of states W is exponential in N: W ~ k^N, where k is the number of single particle states.
(2) W increases with N sub-exponentially because interactions are sufficiently strong to freeze out states. Or W increases super-exponentially when the interactions allow entirely new states beyond the Cartesian product to form. Think of the formation of hydrogen molecules from hydrogen atoms.
In case (1), one can use information theory based on Shannon’s entropy to derive measures of emergence and analyse the balance between redundancy and synergy. In case (2), new generalised entropies based on formal group theory is useful to define a measure of complexity for stat mech systems and a well behaved measure for the complexity content in time series, i.e., a convergent perturbation entropy rate.
Henrik Jensen is a Professor of mathematical physics, leader of the Centre for Complexity Science at Imperial College London, and Specially-Appointed Professor at Toyo Institute of Technology. He works on the statistical mechanics of complex systems. He has worked on the dynamical properties of condensed matter systems and developed the Tangled Nature model of co-evolutionary dynamics. At present, this framework is being applied in several fields including modelling of socio-economical sustainability, finance, cultural evolution, innovation, cell diversity in cancer tumour growth and more.
His work together with Paolo Sibani on record dynamics and its relevance to a surprisingly broad range of complex system, including macroevolution and the dynamics of ant colonies, have attracted interest from researchers from biology to materials science.
He is also involved in an exciting project together with the Guildhall School of Music and Drama concerning quantitative analysis of audience and performers during improvised or non-improvised classical music.
Generalized synchrony as constrained dynamics
February 27, 2023
Abstract: A defining characteristic of synchronization in coupled systems is that the resulting dynamics occurs on a lower dimensional invariant submanifold S of the phase space P. The confinement of the collective dynamics to S can be viewed as a constraint, with the coupling playing the role of forces of constraint. The process can also be inverted: for many cases, coupling functions can be designed in order to lead the dynamics in coupled systems to a specific target submanifold. The resulting dynamical state is one of generalized synchrony.
For a system of globally coupled chaotic oscillators, when the submanifold S is attracting in all transverse directions this state of generalized synchrony is stable. Several distinct coupling functions can achieve the same state of generalised synchrony, although with different stability properties. Illustrations of generalised projective synchronization schemes for systems of chaotic Lorenz oscillators will be discussed. Extensions of the technique to the case of spatiotemporal synchronization will be described, with applications to swarms of autonomous objects.
Ram Ramaswamy retired from the Jawaharlal Nehru University where he taught from 1986 till October 2018, in the School of Physical Sciences, and the School of Computational and Integrative Sciences. From 1983 to 1986, he was at the Tata Institute of Fundamental Research, Mumbai. Between 2011 and 2015 he served as Vice Chancellor of the University of Hyderabad.
Educated at Madras University, IIT Kanpur, and Princeton University, Prof. Ramaswamy’s research interests have, over the years, been in aspects of theoretical chemistry, statistical physics, molecular dynamics, and computational and systems biology. He is the author of over 200 peer reviewed publications and has edited about 30 books and conference proceedings. He has mentored 35 Ph. D. students at TIFR, JNU, University of Hyderabad, and IIT Delhi.
An elected Fellow of TWAS, The World Academy of Sciences, the Indian National Science Academy, New Delhi, and the Indian Academy of Sciences, Bangalore, he served as President of the Indian Academy of Sciences from 2016 to 2018. Currently, he is Visiting Professor in the Department of Chemistry at IIT Delhi.
Prof. Ulrike Feudel, Carl von Ossietzky University of Oldenburg
Tipping phenomena and resilience in complex systems
January 30, 2023
Abstract: Many systems in nature are characterized by the coexistence of different stable states for a given set of environmental parameters and external forcing. Examples of such behavior can be found in different fields of science ranging from mechanical or chemical systems to ecosystem and climate dynamics. As a consequence of the coexistence of a multitude of stable states, the final state of the system depends strongly on the initial condition. Perturbations, applied to those natural systems can lead to a critical transition from one stable state to another. Such critical transitions are called tipping phenomena in climate science, regime shifts in ecology, or phase transitions in physics. Such critical transitions can happen in various ways: (1) due to bifurcations, i.e. changes in the dynamics when external forcing or parameters are varied extremely slow (2) due to fluctuations that are always inevitable in natural systems, (3) due to rate-induced transitions, i.e. when external forcing changes on a characteristic time scale comparable to the time scale of the considered dynamical system and (4) due to shocks or extreme events. We discuss these critical transitions and their characteristics and illustrate them with examples from mechanical and natural systems. Moreover, we discuss the concept of resilience, which has been originally introduced by C.S. Holling in ecology, and reformulate it in terms of dynamical systems
theory.
Ulrike Feudel studied Physics and got her Ph.D. at Humboldt University Berlin, Germany. She got her habilitation at Potsdam University, Germany. Now she is a professor of Theoretical Physics/Complex Systems at the University of Oldenburg, Germany. Her research covers different topics in nonlinear dynamics and complex systems like multistability, tipping phenomena, extreme events, and pattern formation with applications to environmental science like population dynamics, climate science, and biological activity and particles in fluid flows. She was a long-term visitor at the University of Maryland at College Park (USA), University of California at Santa Barbara (USA), and the Eötvös University Budapest (Hungary). She was awarded the Lewis Fry Richardson medal by the European Geosciences Union in 2021, a fellowship for Distinguished Scientists by the Hungarian Academy of Sciences in 2015, and was the Burgers Professor for Hydrodynamics at the University of Maryland at College Park in 2013.
Prof. Rajarshi Roy, University of Maryland
Complex Photonics Dynamics: counting single photons, birthing chaotic attractors, and generating random numbers
November 28, 2022
Abstract: Light conveys energy and information and is a primary means of communication today. Dr. Rajarshi Roy will describe concepts and experiments that have revealed new aspects of light and its interaction with matter, including synchronization of light sources and the communication of information. Detecting single photons can reveal how a system with complex photonic dynamics can transition from a Poisson process to a chaotic attractor. The application of time-delayed feedback to produce chaotic dynamics at extreme speeds and generate random numbers will illustrate an unexpected benefit of chaotic dynamics. Quantum fluctuations are random seeds amplified to macroscopic levels in a deterministic system.
Rajarshi Roy studied Physics at St. Stephen’s College in Delhi, India, and received a Ph.D. in Physics from the University of Rochester in 1981. He has advised about forty doctoral students at Georgia Tech (1982 – 1999) and the University of Maryland (1999 – present). He has served as chair of the School of Physics at Georgia Tech (1996 – 1999) and Director of the Institute for Physical Science and Technology (2003 – 2014) at the University of Maryland. He is a professor in the Department of Physics and the Institute for Physical Science and Technology. He was a visitor at Bell Labs in Murray Hill in the spring of 1987, a visitor at NIH in 2009 and 2014, and Benedict Distinguished Visiting Professor at Carleton College in 2020 for the fall semester. He is a fellow of the Optical Society of America (now Optica) and the American Physical Society.
Prof. Ginestra Bianconi, Queen Mary University of London
The dynamics of higher-order networks: the effect of topology and triadic interactions
November 7, 2022
Abstract: Higher-order networks capture the interactions among two or more nodes in complex systems ranging from the brain to chemical reaction networks. In this talk, Prof. Bianconi will show that higher-order interactions are responsible for new dynamical processes that cannot be observed in pairwise networks. She will cover how topology is key to defining the synchronization of topological signals, i.e. dynamical signals defined not only on nodes but also on links, triangles, and higher-dimensional simplices in simplicial complexes. Interesting topological synchronization dictated by the Dirac operator can lead to the spontaneous emergence of a rhythmic phase where the synchronization order parameter displays low frequency oscillations which might shed light on possible topological mechanisms for the emergence of brain rhythms. She will also reveal how triadic interactions can turn percolation into a fully-fledged dynamical process in which nodes can turn on and off intermittently in a periodic fashion or even chaotically leading to period doubling and a route to chaos of the percolation order parameter.
Ginestra Bianconi is a Professor of Applied Mathematics in the School of Mathematical Sciences of the Queen Mary University of London, and she is Alan Turing Fellow at the Alan Turing Institute. Currently, she is Chief Editor of JPhys Complexity, Editor of PloSOne, and Scientific Reports, and she is Associate Editor of Chaos, Solitons, and Fractals. Award: Network Science Fellowships by the NetSci Society. Her research activity on Statistical Mechanics and Network Science includes Network Theory and its interdisciplinary applications. She has formulated the Bianconi-Barabasi model that displays the Bose-Einstein condensation in complex networks. She has formulated the statistical mechanics of network ensembles and she has proven their non-equivalence. She has made important contributions on the study of critical phenomena on networks. In the last years, she has been focusing on multilayer networks, simplicial complexes, network geometry and topology, percolation, synchronization, and network control. She is the author of the books Multilayer Networks: Structure and Function (Oxford University Press, 2018), Higher-order Networks: An introduction to simplicial complexes (Cambridge University Press, 2021), and editor of Networks of Networks in Biology (Cambridge University Press, 2021).
Prof. Tomasz Kapitaniak, Lodz University of Technology
Chimera states for coupled pendula
September 26, 2023
Abstract: Chimera states are one of the most intriguing phenomena in complex dynamical systems. Typically, they are identified by the co-existence of two types of patterns within one network scheme: (i) a regular behavior, which corresponds to partial synchronization of system’s units, and (ii) an irregular one, when the motion of a group of oscillators is related to the chaotic dynamics. Both domains can co-exist, even though the topology of coupling is usually symmetrical. This surprising fact shows, that by combining both coherence and incoherence, chimeras become one of the most fundamental structures in the area of modern, nonlinear problems. Chimera states can be found in a variety of dynamical systems, beginning from such fundamental ones as the Kuramoto model, for which they have been originally described, or coupled pendula. The studies on chimeras in chemical oscillators, neuron networks, or delayed systems, as well as the experimental proofs of their existence have shown, that this type of behavior is interdisciplinary and appears universally in different areas of science.
In this study, we consider the dynamics of different networks of pendula: (i) a star network of N+1 nonlinear oscillators (in such networks, there is one central hub node (labeled by site index i=N+1) and N environmentally identical peripheral end–nodes connected to the central one (labeled by indices i=1,…, N)), (ii) a network of locally coupled pendula (each pendulum is connected with the nearest neighbor by the spring and damper elements), (iii) a network of globally coupled pendula (each pendulum is connected with all other pendula by the spring and damper elements). For each network, the route from complete incoherence to coherence is described. A particular attention is paid to the occurrence of the chimera states. Numerical results are partially confirmed experimentally.
Tomasz Kapitaniak is a professor of theoretical and applied mechanics and head of the Division of Dynamics at Lodz University of Technology since 1992. His research is concentrated on nonlinear dynamics. The development of non-feedback methods for chaos control, identification and description of new types of bifurcations, identification of the synchronization mechanism in coupled mechanical oscillators, and the explanation of the origin of randomness in mechanical systems are among his most important scientific discoveries. In 2013 he was elected a member of the Polish Academy of Sciences. He got Doctor Honoris Causa degrees at the Saratov State University (Russia) and Lublin University of Technology (Poland) respectively in 2001 and 2014.
Dr. Viola Priesemann, MPIDS Göttingen
Spreading dynamics: from neural information flow to COVID-19
May 30, 2022
Abstract: Spreading dynamics is ubiquitous: activity spreads in neural networks, news and fake news in social networks, and just recently the spread of a novel virus has disrupted the daily lives of people around the globe. Interestingly, in all these networks, the connections are not static but change over time, e.g., to implement learning in neural networks or when mitigating the spread of SARS-CoV-2. Dr. Priesemann and her group derive the principles of self-organization in these diverse networks, show under which conditions phase transitions and critical phenomena occur, and how these can optimize information flow. Her team then puts these theoretical results to the test in living real-world networks. Overall, their work contributes to our understanding of the self-organization of living systems, from information flow in neural networks to the infodemics-pandemics interaction in social networks.
Viola Priesemann is a physicist and neuroscientist at the Max Planck Institute for Dynamics and Self-Organization, Göttingen. After research projects at the Ecole Normale Superieure Paris (France) and the Caltech (USA), she obtained her Ph.D. at the MPI for Brain Research and the University of Frankfurt. As a postdoc and Fellow at the Bernstein Center Göttingen, she applied for an independent Max Planck Research Group, which started in 2017 at the MPI in Göttingen. She studies self-organization and learning in living and artificial networks, illuminating the basic mechanisms that shape collective information processing. Since the start of the COVID-19 pandemic, she investigated the spread of SARS-CoV-2, quantified the effectiveness of interventions, and derived containment strategies. She has coordinated several position and overview papers on the COVID-19 pandemic and is a member of the advisory board of the German government. Her work has been recognized by several awards, including the Communitas Award of the Max-Planck-Society, the “Niedersächsische Wissenschaftspreis”, the “Medaille für naturwissenschaftliche Publizistik” of the German Physical Society (DPG), and the Dannie-Heineman-Award. She is a board member of the Campus Institute for Data Science, a member of the Cluster of Excellence “Multiscale Bioimaging”, of the Max Planck – University of Toronto Centre for Neural Science and Technology, and of “Die Junge Akademie” of the National Academy.
Prof. M. Lakshmanan, Bharathidasan University
Integrability and Chaos in Simple and Complex Systems
April 25, 2022
Abstract: In my talk, I will present a broad overview of some of the fascinating collective dynamical states which arise in the study of integrable and nonintegrable, including chaotic, nonlinear systems of simple and complex types, and illustrate them with specific examples. These include degenerate and nondegenerate solitons, breathers, rogue waves, bullets, and vortices in nonlinear dispersive systems, and desynchronized states, synchronized states, clusters, chimeras, traveling and solitary waves, chimera death states, and so on in complex nonlinear dissipative dynamical systems. Suitable characterizing measures such as strength of inhomogeneity, discontinuity measure, strength of mixed synchronization symmetry, etc. will be introduced to describe the latter states. Some applications in nonlinear optical systems, magnetic spin systems/spintronics, nonlinear electronic circuits, and mechanical systems including Mathews- Lakshmanan oscillator, Liénard type nonlinear oscillator, and Murali-Lakshmanan-Chua circuit will be touched upon.
Prof. Muthusamy Lakshmanan specializes in the areas of Nonlinear Dynamics/Theoretical Physics with special reference to solitons, nonlinear evolution equations, and chaos. He has made varied and in-depth contributions to the general theory of solitons, integrable systems, magnetic and optical solitons, and classical chaos including bifurcations, control, synchronization, and secure communications, as well as quantum chaos and spatiotemporal patterns. Known for his research on nonlinear dynamics and for the development of Murali-Lakshmanan-Chua (MLC) Circuit, Professor Lakshmanan is a Fellow of all the three Academies of Science of India and is an elected Foreign Member of the Royal Academy of Sciences, Uppsala, Sweden. He is also an elected Fellow of the Academy of Sciences of the Developing Countries (FTWAS 2009).
Prof. Katharina Krischer, TU Munich
Between Synchrony and Turbulence: The Rich Dynamics of Globally Coupled Stuart-Landau Oscillators
March 28, 2022
Abstract: Ensembles of coupled oscillators are a class of seemingly simple dynamical systems that can take on a rich variety of emergent behaviors and have provided insights in virtually every discipline, from the natural sciences to sociology. In many studies, weak coupling between the oscillators has been assumed. In this case, the dynamics of an individual oscillator can be approximated by the evolution of its phase only, and emergent behavior is studied in the framework of coupled phase oscillators, such as the famous Kuramoto model. In this talk, Prof. Krischer will consider situations where the phase approximation breaks down, and the dynamics of the ensemble is instead captured by coupled Stuart-Landau oscillators. First, Prof. Krischer will focus on 2-cluster states and discuss that all possible 2-cluster states emerge from a codimension-2 bifurcation, the so-called cluster singularity, which acts as organizing center for the saddle-node bifurcations creating the 2-cluster states as well as for transverse bifurcations alternating their stability. When coupled nonlinearly, two-cluster states can further differentiate in cluster-splitting cascades, leading to multi-cluster states of widely different sizes. These states may then collide with mirror images in phase space, destroying some of the clusters and rendering the dynamics chaotic. A cascade of such symmetry-increasing bifurcations eventually produces a completely incoherent state in which each oscillator has its own asynchronous dynamics. The penultimate state of this cascade consists of one large synchronized cluster and otherwise only individual oscillators, i.e., a so-called chimera state. Chimera states have received much attention during the last decade. In our example, it is thus just one state of two cascades of other coexistence states that link the synchronous state to a state of complete incoherence.
Prof. Katharina Krischer investigates fundamental aspects of self-organization and pattern formation under non-equilibrium conditions. Her work includes experiments, which mainly focus on nonlinear phenomena at the solid/liquid interface, and theory. In the theoretical work she bridges the gap between system specific models and normal form type approaches. Since 2002 she is a professor of physics at the Technical University of Munich, Germany, and has
coauthored about 130 publications in peer reviewed journals as well as a text book on ‘Physics of Energy Conversion’. She was elected a fellow of the International Society of Electrochemistry and is a member of the German Physical Society (DPG) and the Society of German Chemists (GDCh).
Dr. Louis Pecora, NRL Washington (with Dr. Thomas L. Carroll)
Statistics of Attractor Embeddings in Reservoir Computing
February 28, 2022
Abstract: The question why a reservoir computer (RC), driven by only one time series from a drive system, can be trained to recreate all dynamical time series signals from the drive leads to the idea that the RC must be recreating the attractor from the drive signal, i.e. creating an embedding of the drive attractor in the RC dynamics. There have been some mathematical advances that move that argument closer to a general theorem. However, for RCs constructed from actual physical systems like interacting lasers or analog circuits, the RC dynamics may not be known well or known at all. And many of the existing embedding theorems have restrictive assumptions on the dynamics. We first show that the best way to analyze RC behavior is to first treat it properly like a dynamical system, which it is. This will lead to some conflict with existing ideas about RCs, but also a clarification of those ideas. Secondly, in the absence of complete theories on RCs and attractor embeddings, we show several ways to analyze the RC behavior to help understand what underlying processes are in place, especially regarding good embeddings of the drive system in the RC. We show that a statistic we developed for other uses can help test for homeomorphisms between a drive system and the RC by using the time series from both systems. This statistic is called the continuity statistic and it is modeled on the mathematical definition of a continuous
function. We show the interplay of dynamical quantities (e.g. Lyapunov exponents, Kaplan- Yorke dimensions, generalized synchronization, etc.) and embeddings as exposed by the continuity statistic and other statistics based on ideas from nonlinear dynamical systems theory.
Dr. Lou Pecora is currently a research physicist at the Naval Research Laboratory, Washington, DC, where he heads the section for Magnetic Materials and Nonlinear Dynamics in the Materials and Sensors branch. He received his B.S. degree in physics from Wilkes College and he then received a PhD from Syracuse University in Solid State Science in 1977. In the same year, he was awarded an NRC postdoctoral fellowship at the Naval Research Laboratory where he worked on applications of positron annihilation techniques in determining electronic states in copper alloys. This led to a permanent position at NRL. In the mid-1980’s Dr. Pecora moved into the field of nonlinear dynamics in solid-state systems. Subsequent work has focused on the applications of chaotic behavior, especially the effects of driving systems with chaotic signals and coupling nonlinear dynamical systems in complex networks. This has resulted in the discovery of synchronization of chaotic systems, control and tracking, and dynamics of many coupled, nonlinear systems. His research interests turned to quantum chaos briefly and then to the collective behavior of oscillators in large complex networks which led to the development of the master stability function and, more recently, the use of techniques of computational group theory to study cluster synchronization. Recently, he has expanded his collective behavior research to driven networks of oscillators called reservoir computers. Dr. Pecora has published over 160 scientific papers and has 5 US patents for the applications of chaos. His original paper on the synchronization of chaotic systems has over 14000 (ISI) citations and is the 11th most cited paper ever in Physical Review Letters. In 1995 he received the Sigma Xi award for Pure Science for the study of synchronization in chaotic systems. He is also a Fellow of the American Physical Society (APS) and of the American Association for the Advancement of Science (AAAS). Recently, he and his colleague, Tom Carroll won a Clarivate Citation Award as Clarivate Laureates “Researchers of Nobel Class” by Clarivate (citation index provider) in 2020.
Prof. Steven Brunton, Univeristy of Washington
Machine Learning for Scientific Discovery, with Examples in Fluid Mechanics
January 31, 2022
Abstract: This work describes how machine learning may be used to develop accurate and efficient nonlinear dynamical systems models for complex natural and engineered systems. Prof. Brunton will explore the sparse identification of nonlinear dynamics (SINDy) algorithm, which identifies a minimal dynamical system model that balances model complexity with accuracy, avoiding overfitting. This approach tends to promote models that are interpretable and generalizable, capturing the essential “physics” of the system. He will also discuss the importance of learning effective coordinate systems in which the dynamics may be expected to be sparse. This sparse modeling approach will be demonstrated on a range of challenging modeling problems in fluid dynamics, and Prof. Brunton will discuss how to incorporate these models into existing model-based control efforts. Because fluid dynamics is central to transportation, health, and defense systems, he will emphasize the importance of machine learning solutions that are interpretable, explainable, generalizable, and that respect known physics.
Dr. Steven L. Brunton is a Professor of Mechanical Engineering at the University of Washington. He is also an Adjunct Professor of Applied Mathematics and Computer Science, and a Data Science Fellow at the eScience Institute. Steve received B.S. in Mathematics from Caltech in 2006 and Ph.D. in Mechanical and Aerospace Engineering from Princeton in 2012. His research combines machine learning with dynamical systems to model and control systems in fluid dynamics, biolocomotion, optics, energy systems, and manufacturing. He is a co-author of three textbooks, received the University of Washington College of Engineering junior faculty and teaching awards, the Army and Air Force Young Investigator Program (YIP) awards, and the Presidential Early Career Award for Scientists and Engineers (PECASE).
Prof. Edward Ott, University of Maryland
Prediction of Chaotic Dynamical Systems using Machine Learning
November 29, 2021
Prof. Edward Ott will discuss the use of machine learning for predicting the future evolution of dynamical systems, including systems that are very large, complex, and chaotic. He will explain reservoir computing, the basic machine learning method used in this talk. Following that, he will illustrate prediction on simple systems, hybrid prediction combining machine learning with physical knowledge, and a parallel configuration for treating large spatiotemporally chaotic systems. Illustrations and recent progress on applications to terrestrial weather and climate prediction will be presented.
Professor Ott’s current research is on the basic theory and applications of nonlinear dynamics. Some of his current research projects are in wave chaos, dynamics on large interconnected networks, chaotic dynamics of fluids, and weather prediction. Professor Ott is a fellow of the American Physical Society, the Institute of Electrical and Electronics Engineers, and the Society for Industrial and Applied Mathematics (SIAM). He is the recipient of the APS Julius Edgar Lilienfield Prize for 2014.
Prof. Kazuyuki Aihara, University of Tokyo
Data Analysis on Critical Transitions in Complex Systems and its Application to Early Precision Medicine
Octiber 25, 2021
Prof. Kazuyuki Aihara reviewed his group’s recent studies on DNB (Dynamical Network Biomarkers) that provide early warning signals of imminent bifurcation from a healthy state to a disease state through a pre-disease state. He also explained the possible application of DNB for early precision medicine.
Kazuyuki Aihara received a B.E. degree in electrical engineering and Ph.D. degree in electronic engineering from the University of Tokyo (UTokyo), Tokyo, Japan, in 1977 and 1982, respectively. He led the ERATO (Exploratory Research for Advanced Technology) Aihara Complexity Modelling project by JST (Japan Science and Technology Agency) from 2003 to 2008 and the FIRST Innovative Mathematical Modelling project by JSPS (Japan Society for the Promotion of Science) through the FIRST (Funding Program for World-Leading Innovative R&D Science and Technology) program from 2010 to 2014 designed by CSTP (Council for Science and Technology Policy). Currently, he is University Professor and Professor Emeritus of UTokyo, Deputy Director at the International Research Center for Neurointelligence (IRCN) at UTokyo, and Project Manager of the Moonshot project by the cabinet office of the Japanese government on “Comprehensive Mathematical Understanding of the Complex Control System between Organs and Challenge for Ultra-Early Precision Medicine.”
Prof. Jürgen Kurths, PIK Germany
Exploring Predictability of Extreme Climate Events via a Complex Network Approach
September 27, 2021
Earth is a complex system whose dynamics involve innumerous interactions and multiple feedbacks. This makes predictions and risk analysis of very strong, and sometimes extreme events such as floods, landslides, heatwaves, earthquakes, etc., a challenging task. Here, I will introduce a recently developed approach via complex networks to analyze strong climate events. This leads to an inverse problem: Is there a backbone-like structure underlying the climate system? Towards this, we propose a method to reconstruct and analyze a complex network from observational and reanalysis data. This approach enables us to uncover relations to global and regional circulation patterns in oceans and atmosphere, which leads to substantially better predictions of high-impact phenomena, in particular of the Indian Summer Monsoon, El Nino events, droughts in the central Amazon, extreme rainfall in the Eastern Central Andes, and the Pacific decadal oscillation. I argue that network-based approaches can significantly complement numerical modeling for better predictions of the extreme weather events and lead to a better understanding of meteorological data.
Prof. Jürgen Kurths is Senior Advisor at Research Department for “Complexity Science” at Potsdam Institute for Climate Impact Research (PIK) as well as Professor and Senior Advisor at Humboldt University Berlin.