TY - JOUR AB - Collective cell migration offers a rich field of study for non-equilibrium physics and cellular biology, revealing phenomena such as glassy dynamics, pattern formation and active turbulence. However, how mechanical and chemical signalling are integrated at the cellular level to give rise to such collective behaviours remains unclear. We address this by focusing on the highly conserved phenomenon of spatiotemporal waves of density and extracellular signal-regulated kinase (ERK) activation, which appear both in vitro and in vivo during collective cell migration and wound healing. First, we propose a biophysical theory, backed by mechanical and optogenetic perturbation experiments, showing that patterns can be quantitatively explained by a mechanochemical coupling between active cellular tensions and the mechanosensitive ERK pathway. Next, we demonstrate how this biophysical mechanism can robustly induce long-ranged order and migration in a desired orientation, and we determine the theoretically optimal wavelength and period for inducing maximal migration towards free edges, which fits well with experimentally observed dynamics. We thereby provide a bridge between the biophysical origin of spatiotemporal instabilities and the design principles of robust and efficient long-ranged migration. AU - Boocock, Daniel R AU - Hino, Naoya AU - Ruzickova, Natalia AU - Hirashima, Tsuyoshi AU - Hannezo, Edouard B ID - 8602 JF - Nature Physics SN - 17452473 TI - Theory of mechanochemical patterning and optimal migration in cell monolayers VL - 17 ER - TY - JOUR AB - Our ability to trust that a random number is truly random is essential for fields as diverse as cryptography and fundamental tests of quantum mechanics. Existing solutions both come with drawbacks—device-independent quantum random number generators (QRNGs) are highly impractical and standard semi-device-independent QRNGs are limited to a specific physical implementation and level of trust. Here we propose a framework for semi-device-independent randomness certification, using a source of trusted vacuum in the form of a signal shutter. It employs a flexible set of assumptions and levels of trust, allowing it to be applied in a wide range of physical scenarios involving both quantum and classical entropy sources. We experimentally demonstrate our protocol with a photonic setup and generate secure random bits under three different assumptions with varying degrees of security and resulting data rates. AU - Pivoluska, Matej AU - Plesch, Martin AU - Farkas, Máté AU - Ruzickova, Natalia AU - Flegel, Clara AU - Valencia, Natalia Herrera AU - Mccutcheon, Will AU - Malik, Mehul AU - Aguilar, Edgar A. ID - 9255 JF - npj Quantum Information TI - Semi-device-independent random number generation with flexible assumptions VL - 7 ER - TY - JOUR AB - The International Young Physicists' Tournament (IYPT) continued in 2018 in Beijing, China and 2019 in Warsaw, Poland with its 31st and 32nd editions. The IYPT is a modern scientific competition for teams of high school students, also known as the Physics World Cup. It involves long-term theoretical and experimental work focused on solving 17 publicly announced open-ended problems in teams of five. On top of that, teams have to present their solutions in front of other teams and a scientific jury, and get opposed and reviewed by their peers. Here we present a brief information about the competition with a specific focus on one of the IYPT 2018 tasks, the 'Ring Oiler'. This seemingly simple mechanical problem appeared to be of such a complexity that even the dozens of participating teams and jurying scientists were not able to solve all of its subtleties. AU - Plesch, Martin AU - Plesník, Samuel AU - Ruzickova, Natalia ID - 7622 IS - 3 JF - European Journal of Physics SN - 01430807 TI - The IYPT and the 'Ring Oiler' problem VL - 41 ER -