Langevin dynamics encapsulate the microscopic and emergent macroscopic properties of midge swarms

In contrast with bird flocks, fish schools and animal herds, midge swarms maintain cohesion but do not process global order. High-speed imaging techniques are now revealing that these swarms have surprisingly properties. Here I show that simple models found on the Langevin equation are consistent with this wealth of recent observations. The models predict correctly that large accelerations, exceeding 10 g, will be common and they predict correctly the co-existence of core condensed phases surrounded by dilute vapour phases. The models also provide new insights into the influence of environmental conditions on swarm dynamics. They predict that correlations between midges increase the strength of the effective force binding the swarm together. This may explain why such correlations are absent in laboratory swarms but present in natural swarms which contend with the wind and other disturbances. Finally, the models predict that swarms have fluid-like macroscopic mechanical properties and will slosh rather than slide back-and-forth after being abruptly displaced. This prediction offers a promising avenue for future experimentation that goes beyond current quasi-static testing which has revealed solid-like responses

Numerical test of the Edwards conjecture shows that all packings are equally probable at jamming

In the late 1980s, Sam Edwards proposed a possible statistical-mechanical framework to describe the properties of disordered granular materials1. A key assumption underlying the theory was that all jammed packings are equally likely. In the intervening years it has never been possible to test this bold hypothesis directly. Here we present simulations that provide direct evidence that at the unjamming point, all packings of soft repulsive particles are equally likely, even though generically, jammed packings are not. Typically, jammed granular systems are observed precisely at the unjamming point since grains are not very compressible. Our results therefore support Edwards’ original conjecture. We also present evidence that at unjamming the configurational entropy of the system is maximal.S.M. acknowledges financial support by the Gates Cambridge Scholarship. K.J.S. acknowledges support by the Swiss National Science Foundation under Grant No. P2EZP2-152188 and No. P300P2-161078. D.F. acknowledges support by EPSRC Programme Grant EP/I001352/1 and EPSRC grant EP/I000844/1. K.R. and B.C. acknowledge the support of NSF-DMR 1409093 and the W. M. Keck Foundation

Collective Gradient Perception in a Flocking Robot Swarm

© 2020, Springer Nature Switzerland AG.Animals can carry their environmental sensing abilities beyond their own limits by using the advantage of being in a group. Some animal groups use this collective ability to migrate or to react to an environmental cue. The environmental cue sometimes consists of a gradient in space, for example represented by food concentration or predators’ odors. In this study, we propose a method for collective gradient perception in a swarm of flocking agents where single individuals are not capable of perceiving the gradient but only sample information locally. The proposed method is tested with multi-agent simulations and compared to standard collective motion methods. It is also evaluated using realistic dynamical models of autonomous aerial robots within the Gazebo simulator. The results suggest that the swarm can move collectively towards specific regions of the environment by following a gradient while solitary agents are incapable of doing it

Ultrafast in cellulo photoinduced dynamics processes of the paradigm molecular light switch [Ru(bpy)2dppz]2+

An in cellulo study of the ultrafast excited state processes in the paradigm molecular light switch [Ru(bpy)(2)dppz](2+) by localized pump-probe spectroscopy is reported for the first time. The localization of [Ru(bpy)(2)dppz](2+) in HepG2 cells is verified by emission microscopy and the characteristic photoinduced picosecond dynamics of the molecular light switch is observed in cellulo. The observation of the typical phosphorescence stemming from a (3)MLCT state suggests that the [Ru(bpy)(2)dppz](2+) complex intercalates with the DNA in the nucleus. The results presented for this benchmark coordination compound reveal the necessity to study the photoinduced processes in coordination compounds for intracellular use, e.g. as sensors or as photodrugs, in the actual biological target environment in order to derive a detailed molecular mechanistic understanding of the excited-state properties of the systems in the actual biological target environment

Dynamic scaling in natural swarms

Collective behaviour in biological systems presents theoretical challenges beyond the borders of classical statistical physics. The lack of concepts such as scaling and renormalization is particularly problematic, as it forces us to negotiate details whose relevance is often hard to assess. In an attempt to improve this situation, we present here experimental evidence of the emergence of dynamic scaling laws in natural swarms of midges. We find that spatio-temporal correlation functions in different swarms can be rescaled by using a single characteristic time, which grows with the correlation length with a dynamical critical exponent z ≈ 1, a value not found in any other standard statistical model. To check whether out-of-equilibrium effects may be responsible for this anomalous exponent, we run simulations of the simplest model of self-propelled particles and find z ≈ 2, suggesting that natural swarms belong to a novel dynamic universality class. This conclusion is strengthened by experimental evidence of the presence of non-dissipative modes in the relaxation, indicating that previously overlooked inertial effects are needed to describe swarm dynamics. The absence of a purely dissipative regime suggests that natural swarms undergo a near-critical censorship of hydrodynamics.Fil: Cavagna, Andrea. Consiglio Nazionale delle Ricerche; ItaliaFil: Conti, Daniele. Università degli studi di Roma "La Sapienza"; ItaliaFil: Creato, Chiara. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; ItaliaFil: Del Castello, Lorenzo. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; ItaliaFil: Giardina, Irene. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; Italia. INFN; ItaliaFil: Grigera, Tomas Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Melillo, Stefania. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; ItaliaFil: Parisi, Leonardo. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; ItaliaFil: Viale, Massimiliano. Consiglio Nazionale delle Ricerche; Italia. Università degli studi di Roma "La Sapienza"; Itali