Chimera states in hybrid coupled neuron populations

Here we study the emergence of chimera states, a recently reported phenomenon referring to the coexistence of synchronized and unsynchronized dynamical units, in a population of Morris-Lecar neurons which are coupled by both electrical and chemical synapses, constituting a hybrid synaptic architecture, as in actual brain connectivity. This scheme consists of a nonlocal network where the nearest neighbor neurons are coupled by electrical synapses, while the synapses from more distant neurons are of the chemical type. We demonstrate that peculiar dynamical behaviors, including chimera state and traveling wave, exist in such a hybrid coupled neural system, and analyze how the relative abundance of chemical and electrical synapses affects the features of chimera and different synchrony states (i.e. incoherent, traveling wave and coherent) and the regions in the space of relevant parameters for their emergence. Additionally, we show that, when the relative population of chemical synapses increases further, a new intriguing chaotic dynamical behavior appears above the region for chimera states. This is characterized by the coexistence of two distinct synchronized states with different amplitude, and an unsynchronized state, that we denote as a chaotic amplitude chimera. We also discuss about the computational implications of such state. (c) 2020 Elsevier Ltd. All rights reserved.MU acknowledges Bulent Ecevit University Research Foundation, Turkey under Project No. BAP2018-39971044-01. JJT acknowledges the Spanish Ministry for Science and Technology and the "Agencia Espanola de Investigacion, Spain'' (AEI) for financial support under grant FIS2017-84256-P (FEDER funds). AC acknowledges financial support from the Scientific and Technological Research Council of Turkey (TUBITAK) BIDEB-2214/A International Research Fellowship Program, and the hospitality of the Institute Carlos I for Theoretical and Computational Physics at University of Granada

Anomalous Wave Dispersion in the Cyclohexanedione-Bromate Chemical Oscillator

A modified six-variable Oregonator model presented here successfully reproduces a significant portion of the behavior observed in the Ferroin-catalyzed cyclohexanedione variant of the Belousov-Zhabotinsky (CHD-BZ) reaction. The phenomena of anomalous velocity dispersion (in which following waves may catch up to, rather than fall behind an initial excitation wave), wave-stacking, and backfiring have been successfully reproduced numerically as resulting from non-monotonic [Br-] decay to the steady state in the wake of an excitation pulse. The non-monotonic decay is seen as a dip in [Br-] following the passage of a chemical wave. This dip in [Br-] decay curve allows a following wave to accelerate and catch up to the initial wave. The origin of anomalous dispersion as the result of such a non-monotonic decay curve in [Br-] has been suggested previously by Steinbock et al. and Szalai et al. However, the work presented here is the first successful representation of anomalous wave-velocity dispersion using a chemical model. This model is based on the well-understood chemistry of the Oregonator model of the Belousov-Zhabotinsky reaction, coupled to a second pathway (based on chemistry related to uncatalyzed bromate oscillators) for the oxidation of organic substrate to provide the new dynamics

Advances in Global and Local Helioseismology: an Introductory Review

Helioseismology studies the structure and dynamics of the Sun's interior by observing oscillations on the surface. These studies provide information about the physical processes that control the evolution and magnetic activity of the Sun. In recent years, helioseismology has made substantial progress towards the understanding of the physics of solar oscillations and the physical processes inside the Sun, thanks to observational, theoretical and modeling efforts. In addition to the global seismology of the Sun based on measurements of global oscillation modes, a new field of local helioseismology, which studies oscillation travel times and local frequency shifts, has been developed. It is capable of providing 3D images of the subsurface structures and flows. The basic principles, recent advances and perspectives of global and local helioseismology are reviewed in this article.Comment: 86 pages, 46 figures; "Pulsation of the Sun and Stars", Lecture Notes in Physics, Vol. 832, Rozelot, Jean-Pierre; Neiner, Coralie (Eds.), 201

Dynamical processes in the middle atmosphere as observed from Upper Atmosphere Research Satellite limb-sounding data

This study uses data from the Upper Atmosphere Research Satellite (UARS) to investigate two topics in middle atmosphere dynamics: the 4-day wave and transport processes deduced from atmospheric carbon monoxide. The 4-day wave is an eastward moving quasi-nondispersive feature with 4 day period occurring near the winter polar stratopause. Evidence of the 4-day feature is presented in UARS Microwave Limb Sounder (MLS) temperature, geopotential height, quasigeostrophic potential vorticity (PV), and ozone from the late southern winters of 1992 and 1993. Space-time spectral analyses reveal a double-peaked vertical temperature structure with an out-of-phase relationship between the two peaks. The height variation of the 4-day ozone signal compares well with a linear advective-photochemical tracer model. Regions of negative PV gradient and positive Eliassen-Palm flux divergence are shown to occur, consistent with instability dynamics playing a role in wave forcing. The three-dimensional wave structure resembles the PV charge concept, wherein a PV anomaly in the atmosphere (analogous to an electrical charge in a dielectric material) induces a geopotential field, a vertically oriented temperature dipole, and circulation about the vertical axis;Observations of carbon monoxide in the upper stratosphere and lower mesosphere from the UARS Improved Stratospheric and Mesospheric Sounder (ISAMS) are presented during the early northern winter 1991/1992. High CO mixing ratios are found to saturate the polar vortex. 2D analyses in the meridional plane indicate: (1) Increasing mixing ratio with altitude. (2) Large mixing ratios near the Arctic winter pole due to downward advection from the diabatic circulation. (3) A tropical upper stratosphere maximum likely due largely to methane oxidation. ISAMS CO data are compared with CO output from a 3D chemistry and transport model (CTM), initialized with ISAMS CO. ISAMS and CTM horizontal distributions compare favorably near the stratopause, while disagreement in the vertical zonal mean CO distributions occurs several weeks into the model run, with CTM mixing ratios biased high in the upper stratosphere outside the polar vortex and low in the stratospheric vortex and lower mesosphere. Novel modified Lagrangian mean diagnostics applied to ISAMS and CTM data provide insight into horizontal mixing processes during a rapid merger of two anticyclones

Neural Cartography: Computer Assisted Poincare Return Mappings for Biological Oscillations

This dissertation creates practical methods for Poincaré return mappings of individual and networked neuron models. Elliptic bursting models are found in numerous biological systems, including the external Globus Pallidus (GPe) section of the brain; the focus for studies of epileptic seizures and Parkinson\u27s disease. However, the bifurcation structure for changes in dynamics remains incomplete. This dissertation develops computer-assisted Poincaré ́maps for mathematical and biologically relevant elliptic bursting neuron models and central pattern generators (CPGs). The first method, used for individual neurons, offers the advantage of an entire family of computationally smooth and complete mappings, which can explain all of the systems dynamical transitions. A complete bifurcation analysis was performed detailing the mechanisms for the transitions from tonic spiking to quiescence in elliptic bursters. A previously unknown, unstable torus bifurcation was found to give rise to small amplitude oscillations. The focus of the dissertation shifts from individual neuron models to small networks of neuron models, particularly 3-cell CPGs. A CPG is a small network which is able to produce specific phasic relationships between the cells. The output rhythms represent a number of biologically observable actions, i.e. walking or running gates. A 2-dimensional map is derived from the CPGs phase-lags. The cells are endogenously bursting neuron models mutually coupled with reciprocal inhibitory connections using the fast threshold synaptic paradigm. The mappings generate clear explanations for rhythmic outcomes, as well as basins of attraction for specific rhythms and possible mechanisms for switching between rhythms