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Tump AN, Deffner D, Pleskac TJ, Romanczuk P, M. Kurvers RHJ. A Cognitive Computational Approach to Social and Collective Decision-Making. Perspect Psychol Sci 2024; 19:538-551. [PMID: 37671891 PMCID: PMC10913326 DOI: 10.1177/17456916231186964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
Collective dynamics play a key role in everyday decision-making. Whether social influence promotes the spread of accurate information and ultimately results in adaptive behavior or leads to false information cascades and maladaptive social contagion strongly depends on the cognitive mechanisms underlying social interactions. Here we argue that cognitive modeling, in tandem with experiments that allow collective dynamics to emerge, can mechanistically link cognitive processes at the individual and collective levels. We illustrate the strength of this cognitive computational approach with two highly successful cognitive models that have been applied to interactive group experiments: evidence-accumulation and reinforcement-learning models. We show how these approaches make it possible to simultaneously study (a) how individual cognition drives social systems, (b) how social systems drive individual cognition, and (c) the dynamic feedback processes between the two layers.
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Affiliation(s)
- Alan N. Tump
- Center for Adaptive Rationality, Max Planck Institute for Human Development
- Science of Intelligence, Technische Universität Berlin
| | - Dominik Deffner
- Center for Adaptive Rationality, Max Planck Institute for Human Development
- Science of Intelligence, Technische Universität Berlin
| | | | - Pawel Romanczuk
- Science of Intelligence, Technische Universität Berlin
- Institute for Theoretical Biology, Department of Biology, Humboldt Universität zu Berlin
- Bernstein Center for Computational Neuroscience Berlin
| | - Ralf H. J. M. Kurvers
- Center for Adaptive Rationality, Max Planck Institute for Human Development
- Science of Intelligence, Technische Universität Berlin
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2
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Giusti A, Maffettone GC, Fiore D, Coraggio M, di Bernardo M. Distributed control for geometric pattern formation of large-scale multirobot systems. Front Robot AI 2023; 10:1219931. [PMID: 37840852 PMCID: PMC10568129 DOI: 10.3389/frobt.2023.1219931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Accepted: 09/05/2023] [Indexed: 10/17/2023] Open
Abstract
Introduction: Geometric pattern formation is crucial in many tasks involving large-scale multi-agent systems. Examples include mobile agents performing surveillance, swarms of drones or robots, and smart transportation systems. Currently, most control strategies proposed to achieve pattern formation in network systems either show good performance but require expensive sensors and communication devices, or have lesser sensor requirements but behave more poorly. Methods and result: In this paper, we provide a distributed displacement-based control law that allows large groups of agents to achieve triangular and square lattices, with low sensor requirements and without needing communication between the agents. Also, a simple, yet powerful, adaptation law is proposed to automatically tune the control gains in order to reduce the design effort, while improving robustness and flexibility. Results: We show the validity and robustness of our approach via numerical simulations and experiments, comparing it, where possible, with other approaches from the existing literature.
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Affiliation(s)
- Andrea Giusti
- Department of Electrical Engineering and Information Technology, University of Naples Federico II, Naples, Italy
| | | | - Davide Fiore
- Department of Mathematics and Applications “R. Caccioppoli”, University of Naples Federico II, Naples, Italy
| | | | - Mario di Bernardo
- Department of Electrical Engineering and Information Technology, University of Naples Federico II, Naples, Italy
- Scuola Superiore Meridionale, Naples, Italy
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3
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James N, Menzies M. Collective Dynamics, Diversification and Optimal Portfolio Construction for Cryptocurrencies. Entropy (Basel) 2023; 25:931. [PMID: 37372275 DOI: 10.3390/e25060931] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 06/07/2023] [Accepted: 06/12/2023] [Indexed: 06/29/2023]
Abstract
Since its conception, the cryptocurrency market has been frequently described as an immature market, characterized by significant swings in volatility and occasionally described as lacking rhyme or reason. There has been great speculation as to what role it plays in a diversified portfolio. For instance, is cryptocurrency exposure an inflationary hedge or a speculative investment that follows broad market sentiment with amplified beta? We have recently explored similar questions with a clear focus on the equity market. There, our research revealed several noteworthy dynamics such as an increase in the market's collective strength and uniformity during crises, greater diversification benefits across equity sectors (rather than within them), and the existence of a "best value" portfolio of equities. In essence, we can now contrast any potential signatures of maturity we identify in the cryptocurrency market and contrast these with the substantially larger, older and better-established equity market. This paper aims to investigate whether the cryptocurrency market has recently exhibited similar mathematical properties as the equity market. Instead of relying on traditional portfolio theory, which is grounded in the financial dynamics of equity securities, we adjust our experimental focus to capture the presumed behavioral purchasing patterns of retail cryptocurrency investors. Our focus is on collective dynamics and portfolio diversification in the cryptocurrency market, and examining whether previously established results in the equity market hold in the cryptocurrency market and to what extent. The results reveal nuanced signatures of maturity related to the equity market, including the fact that correlations collectively spike around exchange collapses, and identify an ideal portfolio size and spread across different groups of cryptocurrencies.
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Affiliation(s)
- Nick James
- School of Mathematics and Statistics, University of Melbourne, Victoria 3010, Australia
| | - Max Menzies
- Beijing Institute of Mathematical Sciences and Applications, Tsinghua University, Beijing 101408, China
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4
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Kaynak BT, Dahmani ZL, Doruker P, Banerjee A, Yang SH, Gordon R, Itzhaki LS, Bahar I. Cooperative mechanics of PR65 scaffold underlies the allosteric regulation of the phosphatase PP2A. Structure 2023; 31:607-618.e3. [PMID: 36948205 PMCID: PMC10164121 DOI: 10.1016/j.str.2023.02.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 01/25/2023] [Accepted: 02/23/2023] [Indexed: 03/24/2023]
Abstract
PR65, a horseshoe-shaped scaffold composed of 15 HEAT (observed in Huntingtin, elongation factor 3, protein phosphatase 2A, and the yeast kinase TOR1) repeats, forms, together with catalytic and regulatory subunits, the heterotrimeric protein phosphatase PP2A. We examined the role of PR65 in enabling PP2A enzymatic activity with computations at various levels of complexity, including hybrid approaches that combine full-atomic and elastic network models. Our study points to the high flexibility of this scaffold allowing for end-to-end distance fluctuations of 40-50 Å between compact and extended conformations. Notably, the intrinsic dynamics of PR65 facilitates complexation with the catalytic subunit and is retained in the PP2A complex enabling PR65 to engage the two domains of the catalytic subunit and provide the mechanical framework for enzymatic activity, with support from the regulatory subunit. In particular, the intra-repeat coils at the C-terminal arm play an important role in allosterically mediating the collective dynamics of PP2A, pointing to target sites for modulating PR65 function.
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Affiliation(s)
- Burak T Kaynak
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA; Computational Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA
| | - Zakaria L Dahmani
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Pemra Doruker
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Anupam Banerjee
- Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA; Laufer Center for Physical and Quantitative Biology, and Department of Biochemistry and Cell Biology, School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Shang-Hua Yang
- Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Reuven Gordon
- Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC V8P 5C2, Canada
| | - Laura S Itzhaki
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
| | - Ivet Bahar
- Laufer Center for Physical and Quantitative Biology, and Department of Biochemistry and Cell Biology, School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
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5
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Galvis D, Hodson DJ, Wedgwood KC. Spatial distribution of heterogeneity as a modulator of collective dynamics in pancreatic beta-cell networks and beyond. Front Netw Physiol 2023; 3:fnetp.2023.1170930. [PMID: 36987428 PMCID: PMC7614376 DOI: 10.3389/fnetp.2023.1170930] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
We study the impact of spatial distribution of heterogeneity on collective dynamics in gap-junction coupled beta-cell networks comprised on cells from two populations that differ in their intrinsic excitability. Initially, these populations are uniformly and randomly distributed throughout the networks. We develop and apply an iterative algorithm for perturbing the arrangement of the network such that cells from the same population are increasingly likely to be adjacent to one another. We find that the global input strength, or network drive, necessary to transition the network from a state of quiescence to a state of synchronised and oscillatory activity decreases as network sortedness increases. Moreover, for weak coupling, we find that regimes of partial synchronisation and wave propagation arise, which depend both on network drive and network sortedness. We then demonstrate the utility of this algorithm for studying the distribution of heterogeneity in general networks, for which we use Watts-Strogatz networks as a case study. This work highlights the importance of heterogeneity in node dynamics in establishing collective rhythms in complex, excitable networks and has implications for a wide range of real-world systems that exhibit such heterogeneity.
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Affiliation(s)
- Daniel Galvis
- Centre for Systems Modelling and Quantitative Biomedicine, University of Birmingham, Birmingham, UK
- Institute of Metabolism and Systems Research (IMSR), University of Birmingham, Birmingham, UK
- Correspondence: Daniel Galvis,
| | - David J. Hodson
- Institute of Metabolism and Systems Research (IMSR), University of Birmingham, Birmingham, UK
- Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK
- Oxford Centre for Diabetes, Endocrinology, and Metabolism (OCDEM), Churchill Hospital, Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- NIHR Oxford Biomedical Research Centre, Churchill Hospital, Radcliffe Department of Medicine, University of Oxford, Oxford, UK
| | - Kyle C.A. Wedgwood
- Living Systems Institute, University of Exeter, Exeter, UK
- EPSRC Hub for Quantitative Modelling in Healthcare, University of Exeter, Exeter, UK
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
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6
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Degond P, Manhart A, Merino-Aceituno S, Peurichard D, Sala L. How environment affects active particle swarms: a case study. R Soc Open Sci 2022; 9:220791. [PMID: 36533200 PMCID: PMC9748504 DOI: 10.1098/rsos.220791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Accepted: 11/11/2022] [Indexed: 06/17/2023]
Abstract
We investigate the collective motion of self-propelled agents in an environment filled with obstacles that are tethered to fixed positions via springs. The active particles are able to modify the environment by moving the obstacles through repulsion forces. This creates feedback interactions between the particles and the obstacles from which a breadth of patterns emerges (trails, band, clusters, honey-comb structures, etc.). We will focus on a discrete model first introduced in Aceves-Sanchez P et al. (2020, Bull. Math. Biol. 82, 125 (doi:10.1007/s11538-020-00805-z)), and derived into a continuum PDE model. As a first major novelty, we perform an in-depth investigation of pattern formation of the discrete and continuum models in two dimensions: we provide phase-diagrams and determine the key mechanisms for bifurcations to happen using linear stability analysis. As a result, we discover that the agent-agent repulsion, the agent-obstacle repulsion and the obstacle's spring stiffness are the key forces in the appearance of patterns, while alignment forces between the particles play a secondary role. The second major novelty lies in the development of an innovative methodology to compare discrete and continuum models that we apply here to perform an in-depth analysis of the agreement between the discrete and continuum models.
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Affiliation(s)
- Pierre Degond
- Institut de Mathématiques de Toulouse, UMR5219, Université de Toulouse, CNRS, UPS, Toulouse Cedex 9 31062, France
| | - Angelika Manhart
- Mathematics Department, University College London, 25 Gordon Street, London, UK
| | - Sara Merino-Aceituno
- Faculty of Mathematics, University of Vienna, Oskar-Morgenstern-Platz 1, Vienna 1090, Austria
| | - Diane Peurichard
- Inria, Laboratoire Jacques-Louis Lions, Sorbonne Université, CNRS, Université de Paris, 4, Place Jussieu, Paris Cedex 05 75252, France
| | - Lorenzo Sala
- INRIA Saclay Ile-de-France, 1 rue Honoré d’Estienne d’Orves, Palaiseau 91120, France
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7
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Phuyal S, Suarez SS, Tung CK. Biological benefits of collective swimming of sperm in a viscoelastic fluid. Front Cell Dev Biol 2022; 10:961623. [PMID: 36211471 PMCID: PMC9535079 DOI: 10.3389/fcell.2022.961623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2022] [Accepted: 08/26/2022] [Indexed: 11/25/2022] Open
Abstract
Collective swimming is evident in the sperm of several mammalian species. In bull (Bos taurus) sperm, high viscoelasticity of the surrounding fluid induces the sperm to form dynamic clusters. Sperm within the clusters swim closely together and align in the same direction, yet the clusters are dynamic because individual sperm swim into and out of them over time. As the fluid in part of the mammalian female reproductive tract contains mucus and, consequently, is highly viscoelastic, this mechanistic clustering likely happens in vivo. Nevertheless, it has been unclear whether clustering could provide any biological benefit. Here, using a microfluidic in vitro model with viscoelastic fluid, we found that the collective swimming of bull sperm in dynamic clusters provides specific biological benefits. In static viscoelastic fluid, clustering allowed sperm to swim in a more progressive manner. When the fluid was made to flow in the range of 2.43-4.05 1/sec shear rate, clustering enhanced the ability of sperm to swim upstream. We also found that the swimming characteristics of sperm in our viscoelastic fluid could not be fully explained by the hydrodynamic model that has been developed for sperm swimming in a low-viscosity, Newtonian fluid. Overall, we found that clustered sperm swam more oriented with each other in the absence of flow, were able to swim upstream under intermediate flows, and better withstood a strong flow than individual sperm. Our results indicate that the clustering of sperm can be beneficial to sperm migrating against an opposing flow of viscoelastic fluid within the female reproductive tract.
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Affiliation(s)
- Shiva Phuyal
- Department of Physics, North Carolina A&T State University, Greensboro, NC, United States
- Applied Science and Technology PhD Program, North Carolina A&T State University, Greensboro, NC, United States
| | - Susan S. Suarez
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, United States
| | - Chih-Kuan Tung
- Department of Physics, North Carolina A&T State University, Greensboro, NC, United States
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8
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Abstract
The collective motion of animal groups often exhibits velocity-velocity correlations between nearest neighbours, with the strongest velocity correlations observed at the shortest inter-animal spacings. This may have been a motivational factor in the development of models based primarily on short-ranged interactions. Here we ask whether such observations necessarily mean that the interactions are short-ranged. We develop a minimal model of collective motion capable of supporting interactions of arbitrary range and show that it represents a counterexample: the strongest velocity correlations emerge at the shortest distances, even when the interactions are explicitly non-local.
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Affiliation(s)
- Arthur E. B. T. King
- Department of Mathematics, University of Warwick, Coventry CV4 7AL, UK
- Centre for Complexity Science, University of Warwick, Coventry CV4 7AL, UK
| | - Matthew S. Turner
- Centre for Complexity Science, University of Warwick, Coventry CV4 7AL, UK
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK
- Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan
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9
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Abstract
While only a single sperm may fertilize the egg, getting to the egg can be facilitated, and possibly enhanced, by sperm group dynamics. Examples range from the trains formed by wood mouse sperm to the bundles exhibited by echidna sperm. In addition, observations of wave-like patterns exhibited by ram semen are used to score prospective sample fertility for artificial insemination in agriculture. In this review, we discuss these experimental observations of collective dynamics, as well as describe recent mechanistic models that link the motion of individual sperm cells and their flagella to observed collective dynamics. Establishing this link in models involves negotiating the disparate time- and length scales involved, typically separated by a factor of 1000, to capture the dynamics at the greatest length scales affected by mechanisms at the shortest time scales. Finally, we provide some outlook on the subject, in particular, the open questions regarding how collective dynamics impacts fertility. This article is part of the theme issue 'Multi-scale analysis and modelling of collective migration in biological systems'.
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Affiliation(s)
- Simon F Schoeller
- Department of Mathematics, Imperial College London, London SW7 2AZ, UK
| | - William V Holt
- Zoological Society of London, Regent's Park, London NW14RY, UK
| | - Eric E Keaveny
- Department of Mathematics, Imperial College London, London SW7 2AZ, UK
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10
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Baravalle R, Montani F. Higher-Order Cumulants Drive Neuronal Activity Patterns, Inducing UP-DOWN States in Neural Populations. Entropy (Basel) 2020; 22:e22040477. [PMID: 33286251 PMCID: PMC7516951 DOI: 10.3390/e22040477] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 04/14/2020] [Accepted: 04/16/2020] [Indexed: 11/16/2022]
Abstract
A major challenge in neuroscience is to understand the role of the higher-order correlations structure of neuronal populations. The dichotomized Gaussian model (DG) generates spike trains by means of thresholding a multivariate Gaussian random variable. The DG inputs are Gaussian distributed, and thus have no interactions beyond the second order in their inputs; however, they can induce higher-order correlations in the outputs. We propose a combination of analytical and numerical techniques to estimate higher-order, above the second, cumulants of the firing probability distributions. Our findings show that a large amount of pairwise interactions in the inputs can induce the system into two possible regimes, one with low activity (“DOWN state”) and another one with high activity (“UP state”), and the appearance of these states is due to a combination between the third- and fourth-order cumulant. This could be part of a mechanism that would help the neural code to upgrade specific information about the stimuli, motivating us to examine the behavior of the critical fluctuations through the Binder cumulant close to the critical point. We show, using the Binder cumulant, that higher-order correlations in the outputs generate a critical neural system that portrays a second-order phase transition.
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Affiliation(s)
- Roman Baravalle
- Instituto de Física de La Plata (IFLP), Universidad Nacional de La Plata, CONICET CCT-La Plata, Diagonal 113 entre 63 y 64, La Plata, Buenos Aires 1900, Argentina;
- Departamento de Física, Facultad de Ciencias Exactas, UNLP Calle 49 y 115. C.C. 67, La Plata, Buenos Aires 1900, Argentina
| | - Fernando Montani
- Instituto de Física de La Plata (IFLP), Universidad Nacional de La Plata, CONICET CCT-La Plata, Diagonal 113 entre 63 y 64, La Plata, Buenos Aires 1900, Argentina;
- Departamento de Física, Facultad de Ciencias Exactas, UNLP Calle 49 y 115. C.C. 67, La Plata, Buenos Aires 1900, Argentina
- Correspondence:
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11
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Abstract
Human learners acquire complex interconnected networks of relational knowledge. The capacity for such learning naturally depends on two factors: the architecture (or informational structure) of the knowledge network itself and the architecture of the computational unit-the brain-that encodes and processes the information. That is, learning is reliant on integrated network architectures at two levels: the epistemic and the computational, or the conceptual and the neural. Motivated by a wish to understand conventional human knowledge, here, we discuss emerging work assessing network constraints on the learnability of relational knowledge, and theories from statistical physics that instantiate the principles of thermodynamics and information theory to offer an explanatory model for such constraints. We then highlight similarities between those constraints on the learnability of relational networks, at one level, and the physical constraints on the development of interconnected patterns in neural systems, at another level, both leading to hierarchically modular networks. To support our discussion of these similarities, we employ an operational distinction between the modeller (e.g. the human brain), the model (e.g. a single human's knowledge) and the modelled (e.g. the information present in our experiences). We then turn to a philosophical discussion of whether and how we can extend our observations to a claim regarding explanation and mechanism for knowledge acquisition. What relation between hierarchical networks, at the conceptual and neural levels, best facilitate learning? Are the architectures of optimally learnable networks a topological reflection of the architectures of comparably developed neural networks? Finally, we contribute to a unified approach to hierarchies and levels in biological networks by proposing several epistemological norms for analysing the computational brain and social epistemes, and for developing pedagogical principles conducive to curious thought. This article is part of the theme issue 'Unifying the essential concepts of biological networks: biological insights and philosophical foundations'.
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Affiliation(s)
- Perry Zurn
- Department of Philosophy, American University, Washington, DC 20016, USA
| | - Danielle S. Bassett
- Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Physics and Astronomy, College of Arts and Sciences, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Electrical and Systems Engineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
- Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
- Santa Fe Institute, Santa Fe, NM 87501, USA
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12
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Abstract
The black soldier fly is a non-pest insect of interest to the sustainability community due to the high eating rates of its edible larvae. When found on carcases or piles of rotting fruit, this larva often outcompetes other species of scavengers for food. In this combined experimental and theoretical study, we elucidate the mechanism by which groups of black soldier fly larvae can eat so quickly. We use time-lapse videography and particle image velocimetry to investigate feeding by black soldier fly larvae. Individually, larvae eat in 5 min bursts, for 44% of the time, they are near food. This results in their forming roadblocks around the food, reducing the rate that food is consumed. To overcome these limitations, larvae push each other away from the food source, resulting in the formation of a fountain of larvae. Larvae crawl towards the food from below, feed and then are expelled on the top layer. This self-propagating flow pushes away potential roadblocks, thereby increasing eating rate. We present mathematical models for the rate of eating, incorporating flow rates measured from our experiments.
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Affiliation(s)
- Olga Shishkov
- 1 School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, GA 30332 , USA
| | - Michael Hu
- 1 School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, GA 30332 , USA
| | - Christopher Johnson
- 1 School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, GA 30332 , USA
| | - David L Hu
- 1 School of Mechanical Engineering, Georgia Institute of Technology , Atlanta, GA 30332 , USA.,2 School of Biology, Georgia Institute of Technology , Atlanta, GA 30332 , USA
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13
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Tuci E, Trianni V, King A, Garnier S. Editorial: Novel Technological and Methodological Tools for the Understanding of Collective Behaviors. Front Robot AI 2019; 6:139. [PMID: 33501154 PMCID: PMC7805949 DOI: 10.3389/frobt.2019.00139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Accepted: 11/26/2019] [Indexed: 11/13/2022] Open
Affiliation(s)
- Elio Tuci
- Faculty of Informatics, University of Namur, Namur, Belgium
| | - Vito Trianni
- Institute of Cognitive Sciences and Technologies, Italian National Research Council (CNR), Rome, Italy
| | - Andrew King
- Department of Biosciences, Swansea University, Swansea, United Kingdom.,Department of Biological Sciences, Institute for Communities and Wildlife in Africa, Cape Town, South Africa
| | - Simon Garnier
- Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ, United States.,Department of Biological Sciences, Rutgers University, Newark, NJ, United States
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14
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Schoeller SF, Keaveny EE. From flagellar undulations to collective motion: predicting the dynamics of sperm suspensions. J R Soc Interface 2019; 15:rsif.2017.0834. [PMID: 29563245 PMCID: PMC5908526 DOI: 10.1098/rsif.2017.0834] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 02/26/2018] [Indexed: 11/12/2022] Open
Abstract
Swimming cells and microorganisms are as diverse in their collective dynamics as they are in their individual shapes and propulsion mechanisms. Even for sperm cells, which have a stereotyped shape consisting of a cell body connected to a flexible flagellum, a wide range of collective dynamics is observed spanning from the formation of tightly packed groups to the display of larger-scale, turbulence-like motion. Using a detailed mathematical model that resolves flagellum dynamics, we perform simulations of sperm suspensions containing up to 1000 cells and explore the connection between individual and collective dynamics. We find that depending on the level of variation in individual dynamics from one swimmer to another, the sperm exhibit either a strong tendency to aggregate, or the suspension exhibits large-scale swirling. Hydrodynamic interactions govern the formation and evolution of both states. In addition, a quantitative analysis of the states reveals that the flows generated at the time scale of flagellum undulations contribute significantly to the overall energy in the surrounding fluid, highlighting the importance of resolving these flows.
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Affiliation(s)
- Simon F Schoeller
- Department of Mathematics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Eric E Keaveny
- Department of Mathematics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
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15
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Aslibeiki B, Kameli P, Salamati H, Concas G, Salvador Fernandez M, Talone A, Muscas G, Peddis D. Co-doped MnFe 2O 4 nanoparticles: magnetic anisotropy and interparticle interactions. Beilstein J Nanotechnol 2019; 10:856-865. [PMID: 31019873 PMCID: PMC6466680 DOI: 10.3762/bjnano.10.86] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 03/16/2019] [Indexed: 05/29/2023]
Abstract
The effect of cobalt doping on the magnetic properties of Mn1- x Co x Fe2O4 nanoparticles was investigated. All samples consist of ensembles of nanoparticles with a spherical shape and average diameter of about 10 nm, showing small structural changes due to the substitution. Besides having the same morpho-structural properties, the effect of the chemical composition, i.e., the amount of Co doping, produces marked differences on the magnetic properties, especially on the magnetic anisotropy, with evident large changes in the coercive field. Moreover, Co substitution has a profound effect on the interparticle interactions, too. A dipolar-based interaction regime is detected for all samples; in addition, the intensity of the interactions shows a possible relation with the single particle anisotropy. Finally, the sample with the strongest interaction regime shows a superspin glass state confirmed by memory effect dynamics.
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Affiliation(s)
- Bagher Aslibeiki
- Department of Physics, University of Tabriz, Tabriz 51666-16471, Iran
| | - Parviz Kameli
- Department of Physics, Isfahan University of Technology, Isfahan, 84156-83111, Iran
| | - Hadi Salamati
- Department of Physics, Isfahan University of Technology, Isfahan, 84156-83111, Iran
| | - Giorgio Concas
- Dipartimento di Fisica, Università di Cagliari, S.P. Monserrato-Sestu km 0,700, 09042 Monserrato (CA), Italy
| | - Maria Salvador Fernandez
- Dipartimento di Scienze, Università degli Studi Roma Tre, via della vasca navale, 84 - 00146 Roma, Italy
- Department of Physics, University of Oviedo, Campus de Viesques, 33204 Gijón, Spain
| | - Alessandro Talone
- Dipartimento di Scienze, Università degli Studi Roma Tre, via della vasca navale, 84 - 00146 Roma, Italy
- Istituto di Struttura della Materia-CNR, 00015 Monterotondo Scalo (RM), Italy
| | - Giuseppe Muscas
- Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
| | - Davide Peddis
- Istituto di Struttura della Materia-CNR, 00015 Monterotondo Scalo (RM), Italy
- Department of Chemistry and Industrial Chemistry (DCIC), University of Genova, Genova, Italy
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16
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Deneke VE, Puliafito A, Krueger D, Narla AV, De Simone A, Primo L, Vergassola M, De Renzis S, Di Talia S. Self-Organized Nuclear Positioning Synchronizes the Cell Cycle in Drosophila Embryos. Cell 2019; 177:925-941.e17. [PMID: 30982601 DOI: 10.1016/j.cell.2019.03.007] [Citation(s) in RCA: 77] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Revised: 12/16/2018] [Accepted: 03/04/2019] [Indexed: 11/22/2022]
Abstract
The synchronous cleavage divisions of early embryogenesis require coordination of the cell-cycle oscillator, the dynamics of the cytoskeleton, and the cytoplasm. Yet, it remains unclear how spatially restricted biochemical signals are integrated with physical properties of the embryo to generate collective dynamics. Here, we show that synchronization of the cell cycle in Drosophila embryos requires accurate nuclear positioning, which is regulated by the cell-cycle oscillator through cortical contractility and cytoplasmic flows. We demonstrate that biochemical oscillations are initiated by local Cdk1 inactivation and spread through the activity of phosphatase PP1 to generate cortical myosin II gradients. These gradients cause cortical and cytoplasmic flows that control proper nuclear positioning. Perturbations of PP1 activity and optogenetic manipulations of cortical actomyosin disrupt nuclear spreading, resulting in loss of cell-cycle synchrony. We conclude that mitotic synchrony is established by a self-organized mechanism that integrates the cell-cycle oscillator and embryo mechanics.
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17
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Beppu K, Izri Z, Maeda YT, Sakamoto R. Geometric Effect for Biological Reactors and Biological Fluids. Bioengineering (Basel) 2018; 5:E110. [PMID: 30551608 PMCID: PMC6316181 DOI: 10.3390/bioengineering5040110] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 12/07/2018] [Accepted: 12/10/2018] [Indexed: 01/21/2023] Open
Abstract
As expressed "God made the bulk; the surface was invented by the devil" by W. Pauli, the surface has remarkable properties because broken symmetry in surface alters the material properties. In biological systems, the smallest functional and structural unit, which has a functional bulk space enclosed by a thin interface, is a cell. Cells contain inner cytosolic soup in which genetic information stored in DNA can be expressed through transcription (TX) and translation (TL). The exploration of cell-sized confinement has been recently investigated by using micron-scale droplets and microfluidic devices. In the first part of this review article, we describe recent developments of cell-free bioreactors where bacterial TX-TL machinery and DNA are encapsulated in these cell-sized compartments. Since synthetic biology and microfluidics meet toward the bottom-up assembly of cell-free bioreactors, the interplay between cellular geometry and TX-TL advances better control of biological structure and dynamics in vitro system. Furthermore, biological systems that show self-organization in confined space are not limited to a single cell, but are also involved in the collective behavior of motile cells, named active matter. In the second part, we describe recent studies where collectively ordered patterns of active matter, from bacterial suspensions to active cytoskeleton, are self-organized. Since geometry and topology are vital concepts to understand the ordered phase of active matter, a microfluidic device with designed compartments allows one to explore geometric principles behind self-organization across the molecular scale to cellular scale. Finally, we discuss the future perspectives of a microfluidic approach to explore the further understanding of biological systems from geometric and topological aspects.
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Affiliation(s)
- Kazusa Beppu
- Department of Physics, Kyushu University, Fukuoka 819-0395, Japan.
| | - Ziane Izri
- Department of Physics, Kyushu University, Fukuoka 819-0395, Japan.
| | - Yusuke T Maeda
- Department of Physics, Kyushu University, Fukuoka 819-0395, Japan.
| | - Ryota Sakamoto
- Department of Physics, Kyushu University, Fukuoka 819-0395, Japan.
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18
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Wilting J, Dehning J, Pinheiro Neto J, Rudelt L, Wibral M, Zierenberg J, Priesemann V. Operating in a Reverberating Regime Enables Rapid Tuning of Network States to Task Requirements. Front Syst Neurosci 2018; 12:55. [PMID: 30459567 PMCID: PMC6232511 DOI: 10.3389/fnsys.2018.00055] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 10/09/2018] [Indexed: 01/02/2023] Open
Abstract
Neural circuits are able to perform computations under very diverse conditions and requirements. The required computations impose clear constraints on their fine-tuning: a rapid and maximally informative response to stimuli in general requires decorrelated baseline neural activity. Such network dynamics is known as asynchronous-irregular. In contrast, spatio-temporal integration of information requires maintenance and transfer of stimulus information over extended time periods. This can be realized at criticality, a phase transition where correlations, sensitivity and integration time diverge. Being able to flexibly switch, or even combine the above properties in a task-dependent manner would present a clear functional advantage. We propose that cortex operates in a “reverberating regime” because it is particularly favorable for ready adaptation of computational properties to context and task. This reverberating regime enables cortical networks to interpolate between the asynchronous-irregular and the critical state by small changes in effective synaptic strength or excitation-inhibition ratio. These changes directly adapt computational properties, including sensitivity, amplification, integration time and correlation length within the local network. We review recent converging evidence that cortex in vivo operates in the reverberating regime, and that various cortical areas have adapted their integration times to processing requirements. In addition, we propose that neuromodulation enables a fine-tuning of the network, so that local circuits can either decorrelate or integrate, and quench or maintain their input depending on task. We argue that this task-dependent tuning, which we call “dynamic adaptive computation,” presents a central organization principle of cortical networks and discuss first experimental evidence.
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Affiliation(s)
- Jens Wilting
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany
| | - Jonas Dehning
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany
| | - Joao Pinheiro Neto
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany
| | - Lucas Rudelt
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany
| | - Michael Wibral
- Magnetoencephalography Unit, Brain Imaging Center, Johann-Wolfgang-Goethe University, Frankfurt, Germany
| | - Johannes Zierenberg
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany.,Bernstein-Center for Computational Neuroscience, Göttingen, Germany
| | - Viola Priesemann
- Max-Planck-Institute for Dynamics and Self-Organization, Göttingen, Germany.,Bernstein-Center for Computational Neuroscience, Göttingen, Germany
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19
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Yang Y, Xiong D, Pipathsouk A, Weiner OD, Wu M. Clathrin Assembly Defines the Onset and Geometry of Cortical Patterning. Dev Cell 2017; 43:507-521.e4. [PMID: 29161594 PMCID: PMC5826602 DOI: 10.1016/j.devcel.2017.10.028] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 09/16/2017] [Accepted: 10/25/2017] [Indexed: 01/20/2023]
Abstract
Assembly of the endocytic machinery is a constitutively active process that is important for the organization of the plasma membrane, signal transduction, and membrane trafficking. Existing research has focused on the stochastic nature of endocytosis. Here, we report the emergence of the collective dynamics of endocytic proteins as periodic traveling waves on the cell surface. Coordinated clathrin assembly provides the earliest spatial cue for cortical waves and sets the direction of propagation. Surprisingly, the onset of clathrin waves, but not individual endocytic events, requires feedback from downstream factors, including FBP17, Cdc42, and N-WASP. In addition to the localized endocytic assembly at the plasma membrane, intracellular clathrin and phosphatidylinositol-3,4-bisphosphate predict the excitability of the plasma membrane and modulate the geometry of traveling waves. Collectively, our data demonstrate the multiplicity of clathrin functions in cortical pattern formation and provide important insights regarding the nucleation and propagation of single-cell patterns.
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Affiliation(s)
- Yang Yang
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore; Centre for Bioimaging Sciences, National University of Singapore, Singapore 117557, Singapore
| | - Ding Xiong
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore; Centre for Bioimaging Sciences, National University of Singapore, Singapore 117557, Singapore
| | - Anne Pipathsouk
- Cardiovascular Research Institute and Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158-9001, USA
| | - Orion D Weiner
- Cardiovascular Research Institute and Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158-9001, USA
| | - Min Wu
- Mechanobiology Institute, National University of Singapore, Singapore 117411, Singapore; Centre for Bioimaging Sciences, National University of Singapore, Singapore 117557, Singapore; Department of Biological Sciences, National University of Singapore, Singapore 117543, Singapore.
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20
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Secchi E, Rusconi R, Buzzaccaro S, Salek MM, Smriga S, Piazza R, Stocker R. Intermittent turbulence in flowing bacterial suspensions. J R Soc Interface 2017; 13:rsif.2016.0175. [PMID: 27307513 DOI: 10.1098/rsif.2016.0175] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Accepted: 05/25/2016] [Indexed: 02/06/2023] Open
Abstract
Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome.
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Affiliation(s)
- Eleonora Secchi
- Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA
| | - Roberto Rusconi
- Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland
| | - Stefano Buzzaccaro
- Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy
| | - M Mehdi Salek
- Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland
| | - Steven Smriga
- Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland
| | - Roberto Piazza
- Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy
| | - Roman Stocker
- Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 02139 Cambridge, MA, USA Department of Civil, Environmental and Geomatic Engineering, Institute for Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland
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21
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Ashraf I, Bradshaw H, Ha TT, Halloy J, Godoy-Diana R, Thiria B. Simple phalanx pattern leads to energy saving in cohesive fish schooling. Proc Natl Acad Sci U S A 2017; 114:9599-9604. [PMID: 28839092 PMCID: PMC5594674 DOI: 10.1073/pnas.1706503114] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The question of how individuals in a population organize when living in groups arises for systems as different as a swarm of microorganisms or a flock of seagulls. The different patterns for moving collectively involve a wide spectrum of reasons, such as evading predators or optimizing food prospection. Also, the schooling pattern has often been associated with an advantage in terms of energy consumption. In this study, we use a popular aquarium fish, the red nose tetra fish, Hemigrammus bleheri, which is known to swim in highly cohesive groups, to analyze the schooling dynamics. In our experiments, fish swim in a shallow-water tunnel with controlled velocity, and stereoscopic video recordings are used to track the 3D positions of each individual in a school, as well as their tail-beating kinematics. Challenging the widespread idea of fish favoring a diamond pattern to swim more efficiently [Weihs D (1973) Nature 241:290-291], we observe that when fish are forced to swim fast-well above their free-swimming typical velocity, and hence in a situation where efficient swimming would be favored-the most frequent configuration is the "phalanx" or "soldier" formation, with all individuals swimming side by side. We explain this observation by considering the advantages of tail-beating synchronization between neighbors, which we have also characterized. Most importantly, we show that schooling is advantageous as compared with swimming alone from an energy-efficiency perspective.
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Affiliation(s)
- Intesaaf Ashraf
- Laboratoire de Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et de Chimie Industrielles Paris-Paris Sciences et Lettres Research University, Sorbonne Universités-Université Pierre et Marie Curie-Paris 6, Sorbonne Paris Cité-Université Paris Diderot-Paris 7, CNRS UMR 7636, 75005 Paris, France
| | - Hanaé Bradshaw
- Laboratoire de Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et de Chimie Industrielles Paris-Paris Sciences et Lettres Research University, Sorbonne Universités-Université Pierre et Marie Curie-Paris 6, Sorbonne Paris Cité-Université Paris Diderot-Paris 7, CNRS UMR 7636, 75005 Paris, France
| | - Thanh-Tung Ha
- Laboratoire de Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et de Chimie Industrielles Paris-Paris Sciences et Lettres Research University, Sorbonne Universités-Université Pierre et Marie Curie-Paris 6, Sorbonne Paris Cité-Université Paris Diderot-Paris 7, CNRS UMR 7636, 75005 Paris, France
| | - José Halloy
- Laboratoire Interdisciplinaire des Energies de Demain, Sorbonne Paris Cité-Université Paris Diderot-Paris 7, Bâtiment Condorcet, UMR CNRS 8236, 75013 Paris, France
| | - Ramiro Godoy-Diana
- Laboratoire de Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et de Chimie Industrielles Paris-Paris Sciences et Lettres Research University, Sorbonne Universités-Université Pierre et Marie Curie-Paris 6, Sorbonne Paris Cité-Université Paris Diderot-Paris 7, CNRS UMR 7636, 75005 Paris, France;
| | - Benjamin Thiria
- Laboratoire de Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et de Chimie Industrielles Paris-Paris Sciences et Lettres Research University, Sorbonne Universités-Université Pierre et Marie Curie-Paris 6, Sorbonne Paris Cité-Université Paris Diderot-Paris 7, CNRS UMR 7636, 75005 Paris, France;
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22
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Rule ME, Vargas-Irwin CE, Donoghue JP, Truccolo W. Dissociation between sustained single-neuron spiking and transient β-LFP oscillations in primate motor cortex. J Neurophysiol 2017; 117:1524-1543. [PMID: 28100654 DOI: 10.1152/jn.00651.2016] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 01/09/2017] [Accepted: 01/17/2017] [Indexed: 01/06/2023] Open
Abstract
Determining the relationship between single-neuron spiking and transient (20 Hz) β-local field potential (β-LFP) oscillations is an important step for understanding the role of these oscillations in motor cortex. We show that whereas motor cortex firing rates and beta spiking rhythmicity remain sustained during steady-state movement preparation periods, β-LFP oscillations emerge, in contrast, as short transient events. Single-neuron mean firing rates within and outside transient β-LFP events showed no differences, and no consistent correlation was found between the beta oscillation amplitude and firing rates, as was the case for movement- and visual cue-related β-LFP suppression. Importantly, well-isolated single units featuring beta-rhythmic spiking (43%, 125/292) showed no apparent or only weak phase coupling with the transient β-LFP oscillations. Similar results were obtained for the population spiking. These findings were common in triple microelectrode array recordings from primary motor (M1), ventral (PMv), and dorsal premotor (PMd) cortices in nonhuman primates during movement preparation. Although beta spiking rhythmicity indicates strong membrane potential fluctuations in the beta band, it does not imply strong phase coupling with β-LFP oscillations. The observed dissociation points to two different sources of variation in motor cortex β-LFPs: one that impacts single-neuron spiking dynamics and another related to the generation of mesoscopic β-LFP signals. Furthermore, our findings indicate that rhythmic spiking and diverse neuronal firing rates, which encode planned actions during movement preparation, may naturally limit the ability of different neuronal populations to strongly phase-couple to a single dominant oscillation frequency, leading to the observed spiking and β-LFP dissociation.NEW & NOTEWORTHY We show that whereas motor cortex spiking rates and beta (~20 Hz) spiking rhythmicity remain sustained during steady-state movement preparation periods, β-local field potential (β-LFP) oscillations emerge, in contrast, as transient events. Furthermore, the β-LFP phase at which neurons spike drifts: phase coupling is typically weak or absent. This dissociation points to two sources of variation in the level of motor cortex beta: one that impacts single-neuron spiking and another related to the generation of measured mesoscopic β-LFPs.
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Affiliation(s)
- Michael E Rule
- Department of Neuroscience, Brown University, Providence, Rhode Island
| | | | - John P Donoghue
- Department of Neuroscience, Brown University, Providence, Rhode Island.,Institute for Brain Science, Brown University, Providence, Rhode Island; and.,Center for Neurorestoration and Neurotechnology, U.S. Department of Veterans Affairs, Providence, Rhode Island
| | - Wilson Truccolo
- Department of Neuroscience, Brown University, Providence, Rhode Island; .,Institute for Brain Science, Brown University, Providence, Rhode Island; and.,Center for Neurorestoration and Neurotechnology, U.S. Department of Veterans Affairs, Providence, Rhode Island
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23
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Abstract
Complex problems often require coordinated group effort and can consume significant resources, yet our understanding of how teams form and succeed has been limited by a lack of large-scale, quantitative data. We analyse activity traces and success levels for approximately 150 000 self-organized, online team projects. While larger teams tend to be more successful, workload is highly focused across the team, with only a few members performing most work. We find that highly successful teams are significantly more focused than average teams of the same size, that their members have worked on more diverse sets of projects, and the members of highly successful teams are more likely to be core members or 'leads' of other teams. The relations between team success and size, focus and especially team experience cannot be explained by confounding factors such as team age, external contributions from non-team members, nor by group mechanisms such as social loafing. Taken together, these features point to organizational principles that may maximize the success of collaborative endeavours.
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Affiliation(s)
- Michael Klug
- Department of Mathematics and Statistics, The University of Vermont, Burlington, VT, USA
| | - James P. Bagrow
- Department of Mathematics and Statistics, The University of Vermont, Burlington, VT, USA
- Vermont Complex Systems Center, The University of Vermont, Burlington, VT, USA
- Vermont Advanced Computing Core, The University of Vermont, Burlington, VT, USA
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24
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Petroff AP, Pasulka AL, Soplop N, Wu XL, Libchaber A. Biophysical basis for convergent evolution of two veil-forming microbes. R Soc Open Sci 2015; 2:150437. [PMID: 26716000 PMCID: PMC4680615 DOI: 10.1098/rsos.150437] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 10/16/2015] [Indexed: 06/05/2023]
Abstract
Microbes living in stagnant water typically rely on chemical diffusion to draw nutrients from their environment. The sulfur-oxidizing bacterium Thiovulum majus and the ciliate Uronemella have independently evolved the ability to form a 'veil', a centimetre-scale mucous sheet on which cells organize to produce a macroscopic flow. This flow pulls nutrients through the community an order of magnitude faster than diffusion. To understand how natural selection led these microbes to evolve this collective behaviour, we connect the physical limitations acting on individual cells to the cell traits. We show how diffusion limitation and viscous dissipation have led individual T. majus and Uronemella cells to display two similar characteristics. Both of these cells exert a force of approximately 40 pN on the water and attach to boundaries by means of a mucous stalk. We show how the diffusion coefficient of oxygen in water and the viscosity of water define the force the cells must exert. We then show how the hydrodynamics of filter-feeding orient a microbe normal to the surface to which it attaches. Finally, we combine these results with new observations of veil formation and a review of veil dynamics to compare the collective dynamics of these microbes. We conclude that this convergent evolution is a reflection of similar physical limitations imposed by diffusion and viscosity acting on individual cells.
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Affiliation(s)
- Alexander P. Petroff
- Laboratory of Experimental Condensed Matter Physics, The Rockefeller University, New York City, NY 10065, USA
| | - Alexis L. Pasulka
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
| | - Nadine Soplop
- Electron Microscopy Resource Center, The Rockefeller University, New York City, NY 10065, USA
| | - Xiao-Lun Wu
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Albert Libchaber
- Laboratory of Experimental Condensed Matter Physics, The Rockefeller University, New York City, NY 10065, USA
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25
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Lu Y, Truccolo W, Wagner FB, Vargas-Irwin CE, Ozden I, Zimmermann JB, May T, Agha NS, Wang J, Nurmikko AV. Optogenetically induced spatiotemporal gamma oscillations and neuronal spiking activity in primate motor cortex. J Neurophysiol 2015; 113:3574-87. [PMID: 25761956 DOI: 10.1152/jn.00792.2014] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Accepted: 03/09/2015] [Indexed: 02/01/2023] Open
Abstract
Transient gamma-band (40-80 Hz) spatiotemporal patterns are hypothesized to play important roles in cortical function. Here we report the direct observation of gamma oscillations as spatiotemporal waves induced by targeted optogenetic stimulation, recorded by intracortical multichannel extracellular techniques in macaque monkeys during their awake resting states. Microelectrode arrays integrating an optical fiber at their center were chronically implanted in primary motor (M1) and ventral premotor (PMv) cortices of two subjects. Targeted brain tissue was transduced with the red-shifted opsin C1V1(T/T). Constant (1-s square pulses) and ramp stimulation induced narrowband gamma oscillations during awake resting states. Recordings across 95 microelectrodes (4 × 4-mm array) enabled us to track the transient gamma spatiotemporal patterns manifested, e.g., as concentric expanding and spiral waves. Gamma oscillations were induced well beyond the light stimulation volume, via network interactions at distal electrode sites, depending on optical power. Despite stimulation-related modulation in spiking rates, neuronal spiking remained highly asynchronous during induced gamma oscillations. In one subject we examined stimulation effects during preparation and execution of a motor task and observed that movement execution largely attenuated optically induced gamma oscillations. Our findings demonstrate that, beyond previously reported induced gamma activity under periodic drive, a prolonged constant stimulus above a certain threshold may carry primate motor cortex network dynamics into gamma oscillations, likely via a Hopf bifurcation. More broadly, the experimental capability in combining microelectrode array recordings and optogenetic stimulation provides an important approach for probing spatiotemporal dynamics in primate cortical networks during various physiological and behavioral conditions.
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Affiliation(s)
- Yao Lu
- School of Engineering, Brown University, Providence, Rhode Island; Department of Chemistry, Brown University, Providence, Rhode Island
| | - Wilson Truccolo
- Department of Neuroscience, Brown University, Providence, Rhode Island; Institute for Brain Science, Brown University, Providence, Rhode Island; Center for Neurorestoration and Neurotechnology, Department of Veterans Affairs Medical Center, Providence, Rhode Island; and
| | - Fabien B Wagner
- Department of Neuroscience, Brown University, Providence, Rhode Island
| | - Carlos E Vargas-Irwin
- Department of Neuroscience, Brown University, Providence, Rhode Island; Institute for Brain Science, Brown University, Providence, Rhode Island
| | - Ilker Ozden
- School of Engineering, Brown University, Providence, Rhode Island
| | - Jonas B Zimmermann
- Department of Neuroscience, Brown University, Providence, Rhode Island; Institute for Brain Science, Brown University, Providence, Rhode Island
| | - Travis May
- School of Engineering, Brown University, Providence, Rhode Island
| | - Naubahar S Agha
- School of Engineering, Brown University, Providence, Rhode Island
| | - Jing Wang
- McGovern Institute for Brain Research, MIT, Cambridge, Massachusetts
| | - Arto V Nurmikko
- School of Engineering, Brown University, Providence, Rhode Island; Institute for Brain Science, Brown University, Providence, Rhode Island;
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26
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Planas-Sitjà I, Deneubourg JL, Gibon C, Sempo G. Group personality during collective decision-making: a multi-level approach. Proc Biol Sci 2015; 282:20142515. [PMID: 25652834 PMCID: PMC4344149 DOI: 10.1098/rspb.2014.2515] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Accepted: 01/07/2015] [Indexed: 12/27/2022] Open
Abstract
Collective decision-making processes emerge from social feedback networks within a group. Many studies on collective behaviour underestimate the role of individual personality and, as a result, personality is rarely analysed in the context of collective dynamics. Here, we show evidence of sheltering behaviour personality in a gregarious insect (Periplaneta americana), which is characterized by a collective personality at the group level. We also highlight that the individuals within groups exhibited consistent personality traits in their probability of sheltering and total time sheltered during the three trials over one week. Moreover, the group personality, which arises from the synergy between the distribution of behaviour profiles in the group and social amplifications, affected the sheltering dynamics. However, owing to its robustness, personality did not affect the group probability of reaching a consensus. Finally, to prove social interactions, we developed a new statistical method that will be helpful for future research on personality traits and group behaviour. This approach will help to identify the circumstances under which particular group compositions may improve the fitness of individuals in gregarious species.
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Affiliation(s)
- Isaac Planas-Sitjà
- Unit of Social Ecology-CP 231, Université libre de Bruxelles (ULB), Campus Plaine, Boulevard du Triomphe, Building NO-level 5, 1050 Bruxelles, Belgium
| | - Jean-Louis Deneubourg
- Unit of Social Ecology-CP 231, Université libre de Bruxelles (ULB), Campus Plaine, Boulevard du Triomphe, Building NO-level 5, 1050 Bruxelles, Belgium
| | - Céline Gibon
- Unit of Social Ecology-CP 231, Université libre de Bruxelles (ULB), Campus Plaine, Boulevard du Triomphe, Building NO-level 5, 1050 Bruxelles, Belgium
| | - Grégory Sempo
- Unit of Social Ecology-CP 231, Université libre de Bruxelles (ULB), Campus Plaine, Boulevard du Triomphe, Building NO-level 5, 1050 Bruxelles, Belgium
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van der Meer B, Qi W, Fokkink RG, van der Gucht J, Dijkstra M, Sprakel J. Highly cooperative stress relaxation in two-dimensional soft colloidal crystals. Proc Natl Acad Sci U S A 2014; 111:15356-61. [PMID: 25319262 DOI: 10.1073/pnas.1411215111] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it is well established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal stresses. We investigate, both experimentally and in simulations, how highly localized stresses relax in 2D soft colloidal crystals. When a single particle is actively excited, by means of optical tweezing, a rich variety of highly collective stress relaxation mechanisms results. These relaxation processes manifest in the form of open strings of cooperatively moving particles through the motion of dissociated vacancy-interstitial pairs, and closed loops of mobile particles, which either result from cooperative rotations in transiently generated circular grain boundaries or through the closure of an open string by annihilation of a vacancy-interstitial pair. Surprisingly, we find that the same collective events occur in crystals that are excited by thermal fluctuations alone; a large thermal agitation inside the crystal lattice can trigger the irreversible displacements of hundreds of particles. Our results illustrate how local stresses can induce large-scale cooperative dynamics in 2D soft colloidal crystals and shed light on the stabilization mechanisms in ultrasoft crystals.
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Truccolo W, Ahmed OJ, Harrison MT, Eskandar EN, Cosgrove GR, Madsen JR, Blum AS, Potter NS, Hochberg LR, Cash SS. Neuronal ensemble synchrony during human focal seizures. J Neurosci 2014; 34:9927-44. [PMID: 25057195 DOI: 10.1523/JNEUROSCI.4567-13.2014] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Seizures are classically characterized as the expression of hypersynchronous neural activity, yet the true degree of synchrony in neuronal spiking (action potentials) during human seizures remains a fundamental question. We quantified the temporal precision of spike synchrony in ensembles of neocortical neurons during seizures in people with pharmacologically intractable epilepsy. Two seizure types were analyzed: those characterized by sustained gamma (∼40-60 Hz) local field potential (LFP) oscillations or by spike-wave complexes (SWCs; ∼3 Hz). Fine (<10 ms) temporal synchrony was rarely present during gamma-band seizures, where neuronal spiking remained highly irregular and asynchronous. In SWC seizures, phase locking of neuronal spiking to the SWC spike phase induced synchrony at a coarse 50-100 ms level. In addition, transient fine synchrony occurred primarily during the initial ∼20 ms period of the SWC spike phase and varied across subjects and seizures. Sporadic coherence events between neuronal population spike counts and LFPs were observed during SWC seizures in high (∼80 Hz) gamma-band and during high-frequency oscillations (∼130 Hz). Maximum entropy models of the joint neuronal spiking probability, constrained only on single neurons' nonstationary coarse spiking rates and local network activation, explained most of the fine synchrony in both seizure types. Our findings indicate that fine neuronal ensemble synchrony occurs mostly during SWC, not gamma-band, seizures, and primarily during the initial phase of SWC spikes. Furthermore, these fine synchrony events result mostly from transient increases in overall neuronal network spiking rates, rather than changes in precise spiking correlations between specific pairs of neurons.
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Longo M, Marconi M, Orecchini A, Petrillo C, Monaco G, Calvitti M, Pirisinu I, Romani R, Sacchetti F, Sebastiani F, Zanatta M, Paciaroni A. Terahertz Dynamics in Human Cells and Their Chromatin. J Phys Chem Lett 2014; 5:2177-2181. [PMID: 26279530 DOI: 10.1021/jz500918w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The terahertz dynamics of human cells of the U937 line and their chromatin has been investigated by high-resolution inelastic X-ray scattering. To highlight its dynamical features in situ, nuclear DNA has been stained by uranyl-acetate salt. The general behavior of the collective dynamics of the whole cell is quite similar to that of bulk water, with a nearly wavevector-independent branch located at about 5 meV and a propagating mode with a linear trend corresponding to a speed of sound of 2900 ± 100 m/s. We provide the first experimental evidence for the existence of two branches also in the dispersion curves of chromatin. The high-energy mode displays an acoustic-like behavior with a sound velocity similar to unstained cells, but in this case the branch likely originates from the superposition of intramolecular DNA optic modes. A low-energy optic-like branch, distinctive of the chromatin moiety, is found at about 2.5 meV.
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Affiliation(s)
- M Longo
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
- ‡Elettra-Sincrotrone Trieste, I-34149 Basovizza, Trieste, Italy
| | - M Marconi
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
| | - A Orecchini
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
| | - C Petrillo
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
| | - G Monaco
- §Dipartimento di Fisica, Università degli Studi di Trento, Via Sommarive 14, I-38123 Povo, Trento, Italy
| | - M Calvitti
- ∥Dipartimento di Medicina Sperimentale, Università degli Studi di Perugia, Sant'Andrea delle Fratte, I-06132 Perugia, Italy
| | - I Pirisinu
- ∥Dipartimento di Medicina Sperimentale, Università degli Studi di Perugia, Sant'Andrea delle Fratte, I-06132 Perugia, Italy
| | - R Romani
- ∥Dipartimento di Medicina Sperimentale, Università degli Studi di Perugia, Sant'Andrea delle Fratte, I-06132 Perugia, Italy
| | - F Sacchetti
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
- ⊥CNR, Istituto Officina dei Materiali, Unità di Perugia, c/o Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia, Italy
| | - F Sebastiani
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
- ⊥CNR, Istituto Officina dei Materiali, Unità di Perugia, c/o Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia, Italy
| | - M Zanatta
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
| | - A Paciaroni
- †Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via A. Pascoli I-06123 Perugia, Italy
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Zanatta M, Fontana A, Orecchini A, Petrillo C, Sacchetti F. Inelastic Neutron Scattering Investigation in Glassy SiSe2: Complex Dynamics at the Atomic Scale. J Phys Chem Lett 2013; 4:1143-1147. [PMID: 26282034 DOI: 10.1021/jz400232c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A detailed investigation of the THz dynamics in glassy SiSe2 by means of neutron inelastic scattering is presented. To carefully map the translational dynamics and the region of the boson peak, we carried out two different experiments with sharp and broad resolutions coupled with a narrow and a wide kinematic range, respectively. Data show a complex pattern of excitations made up of three components. The most intense one is the prolongation of the longitudinal acoustic mode while two other modes appear in the boson peak region below 3 meV. We propose an interaction model that allows for a consistent identification of the nature of these modes.
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Affiliation(s)
| | - A Fontana
- ‡Dipartimento di Fisica, Università di Trento, I-38050 Povo, Trento, Italy
- ¶IPCF CNR, UOS di Roma, c/o Università di Roma ″La Sapienza″, I-00185 Roma, Italy
| | - A Orecchini
- ∥Institut Laue Langevin, F-38042 Grenoble, France
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Romanczuk P, Schimansky-Geier L. Swarming and pattern formation due to selective attraction and repulsion. Interface Focus 2012; 2:746-56. [PMID: 24312728 DOI: 10.1098/rsfs.2012.0030] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Accepted: 08/30/2012] [Indexed: 11/12/2022] Open
Abstract
We discuss the collective dynamics of self-propelled particles with selective attraction and repulsion interactions. Each particle, or individual, may respond differently to its neighbours depending on the sign of their relative velocity. Thus, it is able to distinguish approaching (coming closer) and retreating (moving away) individuals. This differentiation of the social response is motivated by the response to looming visual stimuli and may be seen as a generalization of the previously proposed escape and pursuit interactions motivated by empirical evidence for cannibalism as a driving force of collective migration in locusts and Mormon crickets. The model can account for different types of behaviour such as pure attraction, pure repulsion or escape and pursuit, depending on the values (signs) of the different response strengths. It provides, in the light of recent experimental results, an interesting alternative to previously proposed models of collective motion with an explicit velocity-alignment interaction. We discuss the derivation of a coarse-grained description of the system dynamics, which allows us to derive analytically the necessary condition for emergence of collective motion. Furthermore, we analyse systematically the onset of collective motion and clustering in numerical simulations of the model for varying interaction strengths. We show that collective motion arises only in a subregion of the parameter space, which is consistent with the analytical prediction and corresponds to an effective escape and/or pursuit response.
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Affiliation(s)
- Pawel Romanczuk
- Max Planck Institute for the Physics of Complex Systems, Nöthnitzerstrasse 38, 01187 Dresden, Germany
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Abstract
A new paradigm of mitochondrial function in networks is emerging which includes, without undermining, the glorious and still useful paradigm of the isolated mitochondrion. The mitochondrial network paradigm introduces new concepts, tools, and analytical techniques. Among them is that mitochondrial function in networks exhibits interdependence and multiplicative effects based on synchronization mechanisms, which involve communication between mitochondrial neighbors. The collective dynamics of these networks become advantageous for coordinating function spanning from the cell, to the tissue, and the organ. However, under severely stressful conditions the network behavior of mitochondria may become life threatening.
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Affiliation(s)
- Miguel A Aon
- Johns Hopkins University, School of Medicine, Institute of Molecular Cardiobiology Baltimore, MD, USA.
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Yuan J, Mills K. Exploring Collective Dynamics in Communication Networks. J Res Natl Inst Stand Technol 2002; 107:179-191. [PMID: 27446726 PMCID: PMC4859260 DOI: 10.6028/jres.107.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 01/28/2002] [Indexed: 06/06/2023]
Abstract
A communication network, such as the Internet, comprises a complex system where cooperative phenomena may emerge from interactions among various traffic flows generated and forwarded by individual nodes. To identify and understand such phenomena, we model a network as a two-dimensional cellular automaton. We suspect such models can promote better understanding of the spatial-temporal evolution of network congestion, and other emergent phenomena in communication networks. To search the behavior space of the model, we study dynamic patterns arising from interactions among traffic flows routed across shared network nodes, as we employ various configurations of parameters and two different congestion-control algorithms. In this paper, we characterize correlation in congestion behavior within the model at different system sizes and time granularities. As expected, we find that long-range dependence (LRD) appears at some time granularities, and that for a given network size LRD decays as time granularity increases. As network size increases, we find that long-range dependence exists at larger time scales. To distinguish effects due to network size from effects due to collective phenomena, we compare congestion behavior within networks of selected sizes to congestion behavior within comparably sized sub-areas in a larger network. We find stronger long-range dependence for sub-areas within the larger network. This suggests the importance of modeling networks of sufficiently large size when studying the effects of collective dynamics.
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