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Geophysics: Lightning-Fast Tremors research highlights RANDOM NUMBERS difference introduces less noise than other than having one winner monopolizing A quantum coin toss detection schemes. DA the resources? One approach to resolving Phys. Rev. X 7, 041050 (2017) this sort of paradox is the ‘kill the winner’ BIOMIMETICS hypothesis: the most successful species is Fold-up skeleton selectively decimated (by, say, a predator) and Proc. Natl Acad. Sci. USA different prey species take turns at winning. http://doi.org/cgwk (2017) That model has proved insightful, but Chi Xue and Nigel Goldenfeld argue that in Fluids are popular design components for its original form it misses important aspects artificial muscles, but usually operate under that actually prevent a stable coexistence high pressures that compromise safety and state. Luckily, they also show how diversity robustness. Now, Shuguang Li and co-workers can be restored. have come up with an architecture driven The original model assumes continuous by fluids at negative pressures — exploiting population densities, which is not ZOONAR GMBH / ALAMY STOCK PHOTO STOCK GMBH / ALAMY ZOONAR ideas from origami metamaterials to build warranted for finite populations. Xue and biocompatible muscles capable of complex Goldenfeld took into account ‘demographic The ability to generate genuinely random multiaxial motions. stochasticity’ — think shot noise for numbers is crucial for digital security, The design proposed and tested by populations — and found that coexistence and typically relies on hardware design to Li et al. involves a flexible skin filled with broke down as species became extinct. But introduce randomness. The emergence of fluid and wrapped around a skeletal structure when predators and prey were allowed to light-based circuits for data processing means comprising structural voids — like those coevolve, continuously adapting to one that an all-optical method for generating found in the complex folds of origami. A another, then the appearance of fit mutants random sequences would be very useful. mechanical model explains the interaction of counteracted the elimination of species. And Tobias Steinle and collaborators have the three components: pressure differences for sufficiently large mutation rates, winner- accomplished this, using a technique with between the internal and external fluids alternating and coexisting phases emerged several practical advantages. cause the skin to deform inward towards the from the interplay between ecological and An optical parametric oscillator produces voids, which in turn are driven to contract evolutionary processes. AHT single photons by down-converting a under tension. pumped state into one of two possible states The team investigated different skeletal GEOPHYSICS that are either in phase or out of phase with structures, finding that linear zigzag Lightning-fast tremors a reference signal. Which state emerges actuators with nylon skins were able to Science 358, 1164–1168 (2017) is determined by, among other effects, generate actuation stresses of up to 600 kPa, the randomness of the quantum vacuum six times larger than that of mammalian In this era of gravitational-wave detection, fluctuations in the optical cavity. The skeletal muscle. AK our imagination is routinely captured generated state can be interpreted as a binary by astronomical events of colossal bit, or the head and tail of a coin toss. BIODIVERSITY magnitude. But one need not travel far to Analysis of the output shows that the Winning ways encounter phenomena capable of shaking generated bit stream is random with perfect Phys. Rev. Lett. (in the press); preprint at the gravitational field — it’s enough to entropy for up to 105 samples. Importantly, https://arxiv.org/abs/1706.02666 consider what happened in Japan seven the non-degeneracy of the two output years ago. Using data from the 2011 Tohoku states means that the generation scheme Biodiversity is stunning yet puzzling. How earthquake, Martin Vallée and co-workers is robust against fluctuations in the pump can several species compete for the same have demonstrated that perturbations power, and the state detection via phase nutrient sources and still coexist, rather to the gravitational field generated by elastogravity waves leave a detectable signal EVOLUTIONARY GAME THEORY in distant seismometers. Acting as additional sources of elastic Metric of cooperation Nat. Commun. 8, 1888 (2017) deformation, these gravitational disturbances are difficult to isolate, as seismographs are The theoretical machinery used to study complex networks has found extensive use in attached to the ground, and thus detect evolutionary game theory, particularly when it comes to understanding the dynamics of both gravity’s pull and the acceleration of cooperation and the emergence of complex societies. the ground. A careful computation allowed Most contact networks have a heterogeneous structure: they are made up of many the authors to derive the difference between connected clusters of varying size, as opposed to the homogeneous lattice structure these two quantities, obtaining the actual commonly seen in models describing (say) magnetic systems. Provided the distribution detected signal, and revealing that it contains of the connected clusters in a contact network is scale free — so that the degree of their information about both the earthquake and connectivity follows a power law distribution — it has been shown theoretically that its magnitude. Travelling at the speed of light, cooperation is favoured. Unfortunately, this prediction has not been confirmed in recent the gravitational perturbation might allow experiments, suggesting something deeper must be at play. a much earlier detection of the strength of By mapping the nodes of real complex networks onto a metric space, Kaj-Kolja Kleineberg larger seismic events, which is notoriously was able to make a more useful representation, in which the popularity of a node and its difficult to establish near the epicentre. FL degree of similarity to other nodes was made explicit. Using this representation, he confirmed that heterogeneity does not always favour cooperation. It can, in fact, even hinder it. AT Written by David Abergel, Abigail Klopper, Federico Levi, Andrea Taroni and Andreas H. Trabesinger. NATURE PHYSICS | VOL 14 | JANUARY 2018 | www.nature.com/naturephysics 7 ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved. .
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