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Irreversibility and emergent structure in active matter

Complexity Digest - Thu, 10/10/2019 - 09:30

Active matter is rapidly becoming a key paradigm of out-of-equilibrium soft matter exhibiting complex collective phenomena, yet the thermodynamics of such systems remain poorly understood. In this article we study the dynamical irreversibility of large scale active systems capable of motility-induced phase separation and polar alignment. We use a model with momenta in both translational and rotational degrees of freedom, revealing a hidden component not previously reported in the literature. Steady state irreversibility is quantified at each point in the phase diagram which exhibits sharp discontinuities at phase transitions. Identification of the irreversibility in individual particles lays the groundwork for discussion of the thermodynamics of micro-features, such as defects in the emergent structure. The interpretation of the time reversal symmetry in the dynamics of the particles is found to be crucial.


Irreversibility and emergent structure in active matter
Phys. Rev. E
Emanuele Crosato, Mikhail Prokopenko, and Richard E. Spinney

Source: journals.aps.org

Scalar model of flocking dynamics on complex social networks

Complexity Digest - Wed, 10/09/2019 - 17:43

We investigate the effects of long-range social interactions in flocking dynamics by studying the dynamics of a scalar model of collective motion embedded in a complex network representing a pattern of social interactions, as observed in several social species. In this scalar model we find a phenomenology analogous to that observed in the classic Vicsek model: In networks with low heterogeneity, a phase transition separates an ordered from a disordered phase. At high levels of heterogeneity, instead, the transition is suppressed and the system is always ordered. This observation is backed up analytically by the solution of a modified scalar model within an heterogeneous mean-field approximation. Our work extends the understanding of the effects of social interactions in flocking dynamics and opens the path to the analytical study of more complex topologies of social ties.


Scalar model of flocking dynamics on complex social networks
M. Carmen Miguel, Romualdo Pastor-Satorras

Source: arxiv.org

U.S. Social Fragmentation at Multiple Scales

Complexity Digest - Wed, 10/09/2019 - 15:41

Despite global connectivity, societies seem to be increasingly polarized and fragmented. This phenomenon is rooted in the underlying complex structure and dynamics of social systems. Far from homogeneously mixing or adopting conforming views, individuals self-organize into groups at multiple scales, ranging from families up to cities and cultures. In this paper, we study the fragmented structure of the American society using mobility and communication networks obtained from geo-located social media data. We find self-organized patches with clear geographical borders that are consistent between physical and virtual spaces. The patches have multi-scale structure ranging from parts of a city up to the entire nation. Their significance is reflected in distinct patterns of collective interests and conversations. Finally, we explain the patch emergence by a model of network growth that combines mechanisms of geographical distance gravity, preferential attachment, and spatial growth. Our observations are consistent with the emergence of social groups whose separated association and communication reinforce distinct identities. Rather than eliminating borders, the virtual space reproduces them as people mirror their offline lives online. Understanding the mechanisms driving the emergence of fragmentation in hyper-connected social systems is imperative in the age of the Internet and globalization.


Leila Hedayatifar, Rachel A. Rigg, Yaneer Bar-Yam, and Alfredo J. Morales, U.S. social fragmentation at multiple scales, Journal of the Royal Society Interface (October 8, 2019).

Source: necsi.edu

The Nobel Prize in Chemistry 2019

Complexity Digest - Wed, 10/09/2019 - 08:36

The Nobel Prize in Chemistry 2019 rewards the development of the lithium-ion battery. This lightweight, rechargeable and powerful battery is now used in everything from mobile phones to laptops and electric vehicles. It can also store significant amounts of energy from solar and wind power, making possible a fossil fuel-free society.

Source: www.nobelprize.org

Anger while driving in Mexico City

Complexity Digest - Tue, 10/08/2019 - 11:42

This study aims to analyze the level of anger developed by drivers in Mexico City and also understand the behavior that those drivers use to express that anger, using four different survey methods. The first focuses on personal information, the second Driving Anger Expression Inventory (DAX), the third refers to a shorten version of Driving Anger Scale (DAS) and the fourth being the Dula Dangerous Driving Index (DDDI). These have previously been applied and validated in several different countries. The questionnaires were filled out online by 626 drivers. Using the data collected through the online platform, it was possible to identify the kind of reactions volunteers displayed while driving. Also, it was possible to identify that people in Mexico City developed anger depending on their driving area. Our analyses shows that in the Adaptive/Constructive Expression subscale, males and females show a significant difference in their mean score, with women express their anger in a more constructive way than males.


Hernández-Hernández AM, Siqueiros-García JM, Robles-Belmont E, Gershenson C (2019) Anger while driving in Mexico City. PLoS ONE 14(9): e0223048. https://doi.org/10.1371/journal.pone.0223048

Source: journals.plos.org

The Nobel Prize in Physics 2019

Complexity Digest - Tue, 10/08/2019 - 11:25

The Nobel Prize in Physics 2019 was awarded "for contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos" with one half to James Peebles "for theoretical discoveries in physical cosmology", the other half jointly to Michel Mayor and Didier Queloz "for the discovery of an exoplanet orbiting a solar-type star."

Source: www.nobelprize.org

Chaos Scientist Finds Hidden Financial Risks That Regulators Miss

Complexity Digest - Tue, 10/08/2019 - 09:19

Today, in a more bucolic setting—the Institute for New Economic Thinking at the Oxford Martin School—Farmer is drawing on decades of complexity research that began with roulette. After winning acclaim as a pioneer of chaos theory, which helps explain the unpredictability of complex systems such as the weather, he jumped into markets, co-founding one of the early quantitative investment firms in the 1990s. Now, Farmer and a band of central bank researchers are focusing on the tangled web of global finance, using a tool of the natural sciences called agent-based models to find dangers lurking in the system and uncover ways to avoid them.

Source: www.bloomberg.com

Self-domesticated by violence to be peaceful. And violent

Complexity Digest - Mon, 10/07/2019 - 11:14

R Wrangham. The goodness paradox: How evolution made us both more and less violent. London, England: Profile Books, 2019, 400 pp., ISBN: 9781781255834 (hbk), £25.

In comparison to other species, humans are both surprisingly peaceful in their day-to-day interactions with unrelated conspecifics and unprecedently violent toward them when the situation requires it. A goodness paradox, as Wrangham (2019) dubs this strange relationship of humankind to violence, is the theme of his latest book attempting to comprise decades of research into a coherent theory of aggressive behavior focused on humans. Drawing on his expertise in primatology, Wrangham presents an evolutionary theory that not only expands contemporary thinking about human behavior but also challenges and refines several crucial notions of human evolution.


Self-domesticated by violence to be peaceful. And violent
Dan Řezníček

Adaptive Behavior

Source: journals.sagepub.com

The 2019 Nobel Prize in Physiology or Medicine 

Complexity Digest - Mon, 10/07/2019 - 08:59

Animals need oxygen for the conversion of food into useful energy. The fundamental importance of oxygen has been understood for centuries, but how cells adapt to changes in levels of oxygen has long been unknown.

William G. Kaelin Jr., Sir Peter J. Ratcliffe and Gregg L. Semenza discovered how cells can sense and adapt to changing oxygen availability. They identified molecular machinery that regulates the activity of genes in response to varying levels of oxygen.

The seminal discoveries by this year’s Nobel Laureates revealed the mechanism for one of life’s most essential adaptive processes. They established the basis for our understanding of how oxygen levels affect cellular metabolism and physiological function. Their discoveries have also paved the way for promising new strategies to fight anemia, cancer and many other diseases.

Source: www.nobelprize.org

Novelist Cormac McCarthy’s tips on how to write a great science paper

Complexity Digest - Sat, 10/05/2019 - 04:47

The Pulitzer prizewinner shares his advice for pleasing readers, editors and yourself.

Source: www.nature.com

Social Network Analysis for Social Neuroscientists

Complexity Digest - Fri, 10/04/2019 - 04:34

Although social neuroscience is concerned with understanding how the brain interacts with its social environment, prevailing research in the field has primarily considered the human brain in isolation, deprived of its rich social context. Emerging work in social neuroscience that leverages tools from network analysis has begun to pursue this issue, advancing knowledge of how the human brain influences and is influenced by the structures of its social environment. In this paper, we provide an overview of key theory and methods in network analysis (especially for social systems) as an introduction for social neuroscientists who are interested in relating individual cognition to the structures of an individual’s social environments. We also highlight some exciting new work as examples of how to productively use these tools to investigate questions of relevance to social neuroscientists. We include tutorials to help with practical implementation of the concepts that we discuss. We conclude by highlighting the broad range of exciting research opportunities for social neuroscientists who are interested in using network analysis to study social systems.


Baek, Elisa, Mason A. Porter, and Carolyn Parkinson. 2019. “Social Network Analysis for Social Neuroscientists.” PsyArXiv. September 26. doi:10.31234/osf.io/kgc2h.

Source: psyarxiv.com

To find the best parking spot, do the math

Complexity Digest - Thu, 10/03/2019 - 04:19

The next time you’re hunting for a parking spot, mathematics could help you identify the most efficient strategy, according to a recent paper in the Journal of Statistical Mechanics. It’s basically an optimization problem: weighing different variables and crunching the numbers to find the optimal combination of those factors. In the case of where to put your car, the goal is to strike the optimal balance of parking close to the target—a building entrance, for example—without having to waste too much time circling the lot hunting for the closest space.

Source: arstechnica.com

Measuring complexity

Complexity Digest - Wed, 10/02/2019 - 22:37

Complexity is heterogenous, involving nonlinearity, self-organisation, diversity, adaptive behaviour, among other things. It is therefore obviously worth asking whether purported measures of complexity measure aggregate phenomena, or individual aspects of complexity and if so which. This paper uses a recently developed rigorous framework for understanding complexity to answer this question about measurement. The approach is two-fold: find measures of individual aspects of complexity on the one hand, and explain measures of complexity on the other. We illustrate the conceptual framework of complexity science and how it links the foundations to the practised science with examples from different scientific fields and of various aspects of complexity. Furthermore, we analyse a selection of purported measures of complexity that have found wide application and explain why and how they measure aspects of complexity. This work gives the reader a tool to take any existing measure of complexity and analyse it, and to take any feature of complexity and find the right measure for it.


Measuring complexity

Karoline Wiesner, James Ladyman

Source: arxiv.org

Collective Irrationality and Positive Feedback

Complexity Digest - Wed, 10/02/2019 - 16:32

Recent experiments on ants and slime moulds have assessed the degree to which they make rational decisions when presented with a number of alternative food sources or shelter. Ants and slime moulds are just two examples of a wide range of species and biological processes that use positive feedback mechanisms to reach decisions. Here we use a generic, experimentally validated model of positive feedback between group members to show that the probability of taking the best of options depends crucially on the strength of feedback. We show how the probability of choosing the best option can be maximized by applying an optimal feedback strength. Importantly, this optimal value depends on the number of options, so that when we change the number of options the preference of the group changes, producing apparent “irrationalities”. We thus reinterpret the idea that collectives show "rational" or "irrational" preferences as being a necessary consequence of the use of positive feedback. We argue that positive feedback is a heuristic which often produces fast and accurate group decision-making, but is always susceptible to apparent irrationality when studied under particular experimental conditions.


Nicolis SC, Zabzina N, Latty T, Sumpter DJT (2011) Collective Irrationality and Positive Feedback. PLoS ONE 6(4): e18901. https://doi.org/10.1371/journal.pone.0018901

Source: journals.plos.org

From classical to modern opinion dynamics

Complexity Digest - Wed, 10/02/2019 - 04:26

In this age of Facebook, Instagram and Twitter, there is rapidly growing interest in understanding network-enabled opinion dynamics in large groups of autonomous agents. The phenomena of opinion polarization, the spread of propaganda and fake news, and the manipulation of sentiment are of interest to large numbers of organizations and people, some of whom are resource rich. Whether it is the more nefarious players such as foreign governments that are attempting to sway elections or large corporations that are trying to bend sentiment — often quite surreptitiously, or it is more open and above board, like researchers that want to spread the news of some finding or some business interest that wants to make a large group of people aware of genuinely helpful innovations that they are marketing, what is at stake is often significant. In this paper we review many of the classical, and some of the new, social interaction models aimed at understanding opinion dynamics. While the first papers studying opinion dynamics appeared over 60 years ago, there is still a great deal of room for innovation and exploration. We believe that the political climate and the extraordinary (even unprecedented) events in the sphere of politics in the last few years will inspire new interest and new ideas. It is our aim to help those interested researchers understand what has already been explored in a significant portion of the field of opinion dynamics. We believe that in doing this, it will become clear that there is still much to be done.


From classical to modern opinion dynamics

Hossein Noorazar, Kevin R. Vixie, Arghavan Talebanpour, Yunfeng Hu

Source: arxiv.org

Neutral and niche forces as drivers of species selection

Complexity Digest - Tue, 10/01/2019 - 23:22

The evolutionary and ecological processes behind the origin of species are among the most fundamental problems in biology. In fact, many theoretical hypothesis on different type of speciation have been proposed. In particular, models of sympatric speciation leading to the formation of new species without geographical isolation, are based on the niche hypothesis: the diversification of the population is induced by the competition for a limited set of available resources. Interestingly, neutral models of evolution have shown that stochastic forces are sufficient to generate coexistence of different species. In this work, we put forward this dichotomy within the context of species formation, studying how neutral and niche forces contribute to sympatric speciation in a model ecosystem. In particular, we study the evolution of a population of individuals with asexual reproduction whose inherited characters or phenotypes are specified by both niche-based and neutral traits. We analyze the stationary state of the dynamics, and study the distribution of individuals in the whole phenotypic space. We show, both numerically and analytically, that there is a non-trivial coupling between neutral and niche forces induced by stochastic effects in the evolution of the population allowing the formation of clusters, that is, species in the phenotypic space. Remarkably, our framework can be generalized also to sexual reproduction or other type of population dynamics.

Source: www.sciencedirect.com

Advantage of Being Multicomponent and Spatial: Multipartite Viruses Colonize Structured Populations with Lower Thresholds

Complexity Digest - Tue, 10/01/2019 - 16:37

Multipartite viruses have a genome divided into different disconnected viral particles. A majority of multipartite viruses infect plants; very few target animals. To understand why, we use a simple, network-based susceptible-latent-infectious-recovered model. We show both analytically and numerically that, provided that the average degree of the contact network exceeds a critical value, even in the absence of an explicit microscopic advantage, multipartite viruses have a lower threshold to colonizing network-structured populations compared to a well-mixed population. We further corroborate this finding on two-dimensional lattice networks, which better represent the typical contact structures of plants.


Advantage of Being Multicomponent and Spatial: Multipartite Viruses Colonize Structured Populations with Lower Thresholds

Yi-Jiao Zhang, Zhi-Xi Wu, Petter Holme, and Kai-Cheng Yang
Phys. Rev. Lett. 123, 138101

Source: link.aps.org

Topological portraits of multiscale coordination dynamics

Complexity Digest - Mon, 09/30/2019 - 23:27

Living systems exhibit complex yet organized behavior on multiple spatiotemporal scales. To investigate the nature of multiscale coordination in living systems, one needs a meaningful and systematic way to quantify the complex dynamics, a challenge in both theoretical and empirical realms. The present work shows how integrating approaches from computational algebraic topology and dynamical systems may help us meet this challenge. In particular, we focus on the application of multiscale topological analysis to coordinated rhythmic processes. First, theoretical arguments are introduced as to why certain topological features and their scale-dependency are highly relevant to understanding complex collective dynamics. Second, we propose a method to capture such dynamically relevant topological information using persistent homology, which allows us to effectively construct a multiscale topological portrait of rhythmic coordination. Finally, the method is put to test in detecting transitions in real data from an experiment of rhythmic coordination in ensembles of interacting humans. The recurrence plots of topological portraits highlight collective transitions in coordination patterns that were elusive to more traditional methods. This sensitivity to collective transitions would be lost if the behavioral dynamics of individuals were treated as separate degrees of freedom instead of constituents of the topology that they collectively forge. Such multiscale topological portraits highlight collective aspects of coordination patterns that are irreducible to properties of individual parts. The present work demonstrates how the analysis of multiscale coordination dynamics can benefit from topological methods, thereby paving the way for further systematic quantification of complex, high-dimensional dynamics in living systems.


Topological portraits of multiscale coordination dynamics

Mengsen Zhang, William D. Kalies, J. A. Scott Kelso, Emmanuelle Tognoli

Source: arxiv.org

Tenure Track position in Complexity – University of Amsterdam

Complexity Digest - Mon, 09/30/2019 - 23:24
The UvA’s Faculty of Science is launching a major recruitment campaign called ‘Connecting Science’ in the areas of Physics, Chemistry, Mathematics, and Computer Science. Our ambition is to attract top talent from all over the world to a large number of newly created faculty positions in a wide range of exciting scientific directions. We offer a stimulating environment and excellent conditions for research, tightly connected to challenging educational programmes. We are looking for ambitious and motivated scientists to connect different scientific disciplines. Our goal is to have a maximal impact on science and society.

Source: www.uva.nl

MPIDR – W2 Research Faculty Position (equivalent to Associate Professor) in the Lab of Digital and Computational Demography

Complexity Digest - Mon, 09/30/2019 - 21:26

The MPIDR is recruiting a highly qualified Research Faculty (W2 level, equivalent to Associate Professor in the German academic system) to join the Lab of Digital and Computational Demography .

Source: www.demogr.mpg.de


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