TY - JOUR A1 - Ocampo-Espindola, Jorge Luis A1 - Omel'chenko, Oleh A1 - Kiss, Istvan Z. T1 - Non-monotonic transients to synchrony in Kuramoto networks and electrochemical oscillators JF - Journal of physics. Complexity N2 - We performed numerical simulations with the Kuramoto model and experiments with oscillatory nickel electrodissolution to explore the dynamical features of the transients from random initial conditions to a fully synchronized (one-cluster) state. The numerical simulations revealed that certain networks (e.g., globally coupled or dense Erdos-Renyi random networks) showed relatively simple behavior with monotonic increase of the Kuramoto order parameter from the random initial condition to the fully synchronized state and that the transient times exhibited a unimodal distribution. However, some modular networks with bridge elements were identified which exhibited non-monotonic variation of the order parameter with local maximum and/or minimum. In these networks, the histogram of the transients times became bimodal and the mean transient time scaled well with inverse of the magnitude of the second largest eigenvalue of the network Laplacian matrix. The non-monotonic transients increase the relative standard deviations from about 0.3 to 0.5, i.e., the transient times became more diverse. The non-monotonic transients are related to generation of phase patterns where the modules are synchronized but approximately anti-phase to each other. The predictions of the numerical simulations were demonstrated in a population of coupled oscillatory electrochemical reactions in global, modular, and irregular tree networks. The findings clarify the role of network structure in generation of complex transients that can, for example, play a role in intermittent desynchronization of the circadian clock due to external cues or in deep brain stimulations where long transients are required after a desynchronization stimulus. KW - synchronization KW - networks KW - Kuramoto model KW - electrochemistry KW - chemical KW - oscillations Y1 - 2021 U6 - https://doi.org/10.1088/2632-072X/abe109 SN - 2632-072X VL - 2 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Hsu, H. F. A1 - Krekhov, Andrey A1 - Tarantola, Marco A1 - Beta, Carsten A1 - Bodenschatz, Eberhardt T1 - Interplay between myosin II and actin dynamics in chemotactic amoeba JF - New journal of physics : the open-access journal for physics N2 - The actin cytoskeleton and its response to external chemical stimuli is fundamental to the mechano-biology of eukaryotic cells and their functions. One of the key players that governs the dynamics of the actin network is the motor protein myosin II. Based on a phase space embedding we have identified from experiments three phases in the cytoskeletal dynamics of starved Dictyostelium discoideum in response to a precisely controlled chemotactic stimulation. In the first two phases the dynamics of actin and myosin II in the cortex is uncoupled, while in the third phase the time scale for the recovery of cortical actin is determined by the myosin II dynamics. We report a theoretical model that captures the experimental observations quantitatively. The model predicts an increase in the optimal response time of actin with decreasing myosin II-actin coupling strength highlighting the role of myosin II in the robust control of cell contraction. KW - actin KW - myosin II KW - chemotaxis KW - oscillations KW - coupling KW - delay differential equation KW - contraction Y1 - 2019 U6 - https://doi.org/10.1088/1367-2630/ab5822 SN - 1367-2630 VL - 21 IS - 11 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Charpinet, Stéphane A1 - Brassard, P. A1 - Fontaine, G. A1 - Van Grootel, Valerie A1 - Zong, Weika A1 - Giammichele, N. A1 - Heber, Ulrich A1 - Bognár, Zsófia A1 - Geier, Stephan A1 - Green, Elizabeth M. A1 - Hermes, J. J. A1 - Kilkenny, D. A1 - Ostensen, R. H. A1 - Pelisoli, Ingrid Domingos A1 - Silvotti, R. A1 - Telting, J. H. A1 - Vuckovic, Maja A1 - Worters, H. L. A1 - Baran, Andrzej S. A1 - Bell, Keaton J. A1 - Bradley, Paul A. A1 - Debes, J. H. A1 - Kawaler, S. D. A1 - Kolaczek-Szymanski, P. A1 - Murphy, S. J. A1 - Pigulski, A. A1 - Sodor, A. A1 - Uzundag, Murat A1 - Handberg, R. A1 - Kjeldsen, H. A1 - Ricker, G. R. A1 - Vanderspek, R. K. T1 - TESS first look at evolved compact pulsators Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009x2006;M-circle dot) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (greater than or similar to 2;M-circle dot) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010;M-circle dot), radius (0.1694 +/- 0.0081;R-circle dot), and luminosity (8.2 +/- 1.1;L-circle dot). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt similar to 43% (in mass) of its central helium and possesses a relatively large mixed core (M-core;=;0.198 +/- 0.010;M-circle dot), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)(core) = 0.16(-0.05)(+0.13)X(O)core=0.16-0.05+0.13$ X(mathrm{O})_{mathrm{core}}=0.16_{-0.05}<^>{+0.13} $) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C-12(alpha,;gamma)O-16 nuclear reaction rate. KW - asteroseismology KW - stars KW - interiors KW - oscillations KW - horizontal-branch KW - individual KW - TIC 278659026 KW - subdwarfs Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201935395 SN - 0004-6361 SN - 1432-0746 VL - 632 PB - EDP Sciences CY - Les Ulis ER -