Synchronization Regime Research Articles

Flow patterns of a low mass-damping cylinder undergoing vortex-induced vibration: Transition from initial branch and upper branch

This paper presents an experimental study of the structural dynamics and the wake vortex modes of a lightly damped, elastically mounted cylinder undergoing vortex-induced vibration (VIV) in the transverse direction. The cylinder is neutrally buoyant with the mass ratio m*=1.0, and has a low damping coefficient ζ=0.0173. The influence of variation in the free-stream velocity (corresponding to the reduced velocity range 1.53≤U*≤6.62, or the Reynolds number range 3000≤Re≤13,000) on the structural dynamics of the cylinder is examined, in conjunction with detailed flow measurements around the cylinder using digital Particle Image Velocimetry (PIV). The cylinder is stationary at U*≤2.55, and begins to vibrate at U*≥3.05 (or in synchronization regime). The vibrating cylinder exhibits the so-called “soft” synchronization phenomenon that the vortex shedding frequency is synchronous with the structural vibration frequency (or response frequency) of the cylinder, rather than with the natural frequency of the system. The measured data for the cylinder undergoing VIV fall within the initial branch and the upper branches, and agree well with published data on free vibrating cylinders at similar low mass and damping. The transition from initial- to upper-branch is characterized by a switch of vortex formation mode from the classical 2S mode to the newly-discovered 2PO mode by Morse and Williamson (2009, Journal of Fluid Mechanics, Vol. 634, pp. 5–39) based on a forced vibrating cylinder. The distinction between the 2S and 2PO modes is vivid in terms of length- and velocity-scales of the shed vortices, and is also reflected by quantitative characterization of near-wake flow statistics, including the mean and turbulence properties.

High-order synchronization of hair cell bundles.

Auditory and vestibular hair cell bundles exhibit active mechanical oscillations at natural frequencies that are typically lower than the detection range of the corresponding end organs. We explore how these noisy nonlinear oscillators mode-lock to frequencies higher than their internal clocks. A nanomagnetic technique is used to stimulate the bundles without an imposed mechanical load. The evoked response shows regimes of high-order mode-locking. Exploring a broad range of stimulus frequencies and intensities, we observe regions of high-order synchronization, analogous to Arnold Tongues in dynamical systems literature. Significant areas of overlap occur between synchronization regimes, with the bundle intermittently flickering between different winding numbers. We demonstrate how an ensemble of these noisy spontaneous oscillators could be entrained to efficiently detect signals significantly above the characteristic frequencies of the individual cells.

Emergent dynamics of spiking neurons with fluctuating threshold

Role of fluctuating threshold on neuronal dynamics is investigated. The threshold function is assumed to follow a normal probability distribution. Standard deviation of inter-spike interval of the response is computed as an indicator of irregularity in spike emission. It has been observed that, the irregularity in spiking is more if the threshold variation is more. A significant change in modal characteristics of Inter Spike Intervals (ISI) is seen to occur as a function of fluctuation parameter. Investigation is further carried out for coupled system of neurons. Cooperative dynamics of coupled neurons are discussed in view of synchronization. Total and partial synchronization regimes are depicted with the help of contour plots of synchrony measure under various conditions. Results of this investigation may provide a basis for exploring the complexities of neural communication and brain functioning.

Dynamics of liquid-crystalline magnetic suspensions in a rotating magnetic field.

We theoretically study the dynamics of the orientational structure of a ferronematic liquid crystal with soft planar coupling between the director and the magnetization in a rotating magnetic field. We determine critical parameters characterizing the boundary between synchronous and asynchronous rotation regimes. We show that the magnetic impurity increases the stability threshold of an asynchronous rotation regime. The critical angular velocity, the angles of the director and the magnetization rotation in each regime of orientational structure rotation are found for rigid planar coupling. We obtain that in weak magnetic fields when the main mechanism of the field influence on a ferronematic liquid crystal is associated with the effect on the magnetic particles, the critical angular velocity is linearly dependent on the field strength, while in strong magnetic fields, when the influence of a field is determined by a diamagnetic mechanism, the critical velocity is quadratically dependent on the field strength.

EFFECT OF ESTRUS SYNCHRONIZATION PROTOCOLS ON THE REPRODUCTIVE PERFORMANCE OF BARKI SHEEP

The study aimed to determine the influence of estrus synchronization regimes on reproductive performance in Barki ewes. Forty Barki ewes were randomly allocated into 2 equal groups (A & B). Group A were treated with vaginal sponges impregnated with 25 mg medroxy-progesterone acetate (MAP). On the day of sponge's withdrawal the ewes were reassigned according to eCG dose into three subgroups (A1, A2 and A3). Group A1, served as control, without eCG injection, while groups A2 and A3 were injected IM with 300 and 500 IU/eCG, respectively. The ewes of group B have received vaginal sponge containing 50 mg of MAP. At the day of sponge removal, the ewes were subdivided into 3 subgroups B1, B2 and B3 and treated with eCG as subgroups A1, A2 and A3, respectively. Three fertile rams were subjected to run with ewes for heat detection and natural mating. Blood samples were taken from mated ewes on day 17 post mating, for determination the level of progesterone for pregnancy determination. Results revealed that the incidence of estrus response were 74.60±9.71 and 79.37±9.71 for groups A (25 mg MAP) and B (50 mg MAP), respectively. Irrespective to MAP sponge concentrations, the estrus response in ewes injected with 500 IU/eCG (A3B3) was higher (92.86±11.58%) than group A2B2 (71.43±11.58%) which treated with 300 IU/eCG and control group A1B1 without eCG (66.67±12.51%) with no significant differences. The onset of estrus in ewes of group A was significantly shorter (P<0.05) than group B (36.23±3.18 h vs 46.10±3.41 h). Regardless of MAP, the onset of estrus in control ewes (without eCG) was significantly longer (56.02±4.70 h; P<0.01) than ewes treated with 300 IU/eCG, (36.20±3.82 h) and 500 IU/eCG (31.27±3.49 h). The means of estrus duration were similar with no significant effects of MAP and eCG doses. No significant differences in the pregnancy rates between group A and B, whereas, the pregnancy rate was significantly higher in group A3B3 (92.86±11.21%) than groups A1B1 and A2B2 (50.00±14.24 and 80.00±12.74%, respectively). Neither MAP nor eCG has been a significant effects on the lambing and fecundity rates. In conclusion, Sponges containing 25mg MAP co-treated with 300-500 IU/eCG is suitable protocol for estrus synchronization and improve pregnancy rate in Barki ewes.

Synchronization of polarization chaos from a free-running VCSEL

We theoretically demonstrate the possibility to synchronize polarization chaos generated by a free-running vertical-cavity surface-emitting laser (VCSEL). We highlight two distinct synchronization regimes: 1) a high-quality synchronization regime where all polarization modes and total intensity are synchronized, which shows good robustness against parameter mismatch, and 2) a "slow time-scale" synchronization where the slower part of the dynamics-that is, the random-like hopping between the two scrolls of the chaotic attractor-synchronizes while the faster oscillations remain unsynchronized.

Synchronization Regime of Star-Type Laser Network With Heterogeneous Coupling Delays

The synchronization properties and the sensitivity of generalized lag synchronization (GLS) in all-optical star network with mutually coupled semiconductor laser in the presence of heterogeneous delays are investigated numerically. The hub node and the side nodes are optically coupled with asymmetrical injection strength. The dependence of GLS on the effects of lasers’ pump current, injection strength, asymmetrical injection factor, and frequency detuning distribution is examined. It is found that, except for the injection strength and frequency detuning, the pump current of hub laser and the asymmetrical injection factor are also key factors that determine the quality of GLS in star network with heterogeneous delays. Extremely asymmetrical injection as well as large pump current of hub laser is suggested to obtain high-quality GLS in wide parameter regions. Such GLS can also be obtained in a large-scale laser network with heterogeneous coupling delays, and is hardly affected by the time delay distribution, which opens possibilities for multi-user chaotic communication and synchronization-based secure key distribution network among the side nodes.

Noise-induced binary synchronization in nonlinear systems

The phenomenon of noise-induced binary synchronization has been discovered in two independent dynamical systems generating aperiodic binary signals under the action of a common noise source. The presence of a synchronous regime was confirmed by the calculation of Lyapunov exponents for the two systems. The mechanism of development of the noise-induced binary synchronization regime has been found. A relation of the observed regime to binary generalized synchronization is established.

Frequency-locked chaotic opto-RF oscillator.

A driven opto-RF oscillator, consisting of a dual-frequency laser (DFL) submitted to frequency-shifted feedback, is experimentally and numerically studied in a chaotic regime. Precise control of the reinjection strength and detuning permits isolation of a parameter region of bounded-phase chaos, where the opto-RF oscillator is frequency-locked to the master oscillator, in spite of chaotic phase and intensity oscillations. Robust experimental evidence of this synchronization regime is found, and phase noise spectra allow us to compare phase-locking and bounded-phase chaos regimes. In particular, it is found that the long-term phase stability of the master oscillator is well transferred to the opto-RF oscillator, even in the chaotic regime.

Low Starting Electron Beam Current in Degenerate Band Edge Oscillators

We propose a new principle of operation in vacuum electron-beam-based oscillators that leads to a low beam current for starting oscillations. The principle is based on super synchronous operation of an electron beam interacting with four degenerate electromagnetic modes in a slow-wave structure (SWS). The four mode super synchronous regime is associated with a very special degeneracy condition in the dispersion diagram of a cold periodic SWS called degenerate band edge (DBE). This regime features a giant group delay in the finitelength SWS and low starting-oscillation beam current. The starting beam current is at least an order of magnitude smaller compared to a conventional backward wave oscillator (BWO) of the same length. As a representative example we consider a SWS conceived by a periodically-loaded metallic waveguide supporting a DBE, and investigate starting-oscillation conditions using Pierce theory generalized to coupled transmission lines (CTL). The proposed super synchronism regime can be straightforwardly adapted to waveguide geometries others than the periodically-loaded waveguide considered here since DBE is a general property that can be realized in a variety of structures.

Estimate of the degree of synchronization in the intermittent phase synchronization regime from a time series (model systems and neurophysiological data)

A method for determining the degree of synchronization of intermittent phase synchronization regime from a time series has been proposed on the basis of estimating the zero conditional Lyapunov exponent. The efficiency of the method has been tested on model systems near the boundary of the appearance of the synchronous regime. The method has been used to determine the degree of synchronization between various regions of the brain of rats of the WAG/Rij line having a genetic predisposition to epilepsy.

Microsaccades enable efficient synchrony-based coding in the retina: a simulation study.

It is now reasonably well established that microsaccades (MS) enhance visual perception, although the underlying neuronal mechanisms are unclear. Here, using numerical simulations, we show that MSs enable efficient synchrony-based coding among the primate retinal ganglion cells (RGC). First, using a jerking contrast edge as stimulus, we demonstrate a qualitative change in the RGC responses: synchronous firing, with a precision in the 10 ms range, only occurs at high speed and high contrast. MSs appear to be sufficiently fast to be able reach the synchronous regime. Conversely, the other kinds of fixational eye movements known as tremor and drift both hardly synchronize RGCs because of a too weak amplitude and a too slow speed respectively. Then, under natural image stimulation, we find that each MS causes certain RGCs to fire synchronously, namely those whose receptive fields contain contrast edges after the MS. The emitted synchronous spike volley thus rapidly transmits the most salient edges of the stimulus, which often constitute the most crucial information. We demonstrate that the readout could be done rapidly by simple coincidence-detector neurons without knowledge of the MS landing time, and that the required connectivity could emerge spontaneously with spike timing-dependent plasticity.

Wake instability modes for forced transverse oscillation of a sphere

The present numerical study aims to identify the instability modes in the wake behind a transversely oscillating sphere with amplitude A=0.5 at Reynolds number Re=300. The governing equations are solved in the non-inertial frame using the immersed boundary method. The longitudinal thread-like structure is accompanied by asymmetric shedding before the onset of a “lock-in” regime. The wake is found to exhibit symmetric vortex shedding and organized chain like structures in the synchronized regime. Lesser flow inertia at a relatively low Re is dominated by the externally applied motion of the sphere resulting in negative energy transfer by the fluid to the sphere. In the synchronous regime different timing of vortex shedding and phases of coefficient of vortex with sphere motion demarcate two wake modes which have close resemblance with the modes found in induced vibration of a sphere.

Magnetic Nanoparticle Stimulation for Detection of High-Order Mode-Locking in Hair Cells of the Inner Ear

Hair cells of the inner ear exhibit a highly nonlinear response to applied signals, and this nonlinearity has been shown to be crucial for achieving the extreme sensitivity of mechanical detection. Under in vitro conditions, hair cell bundles can exhibit active motility that can be readily entrained even by very weak stimuli. We explore experimentally the response of oscillatory hair bundles to signals significantly higher than that of the innate oscillations. To enable access to higher frequencies of stimulation without mechanically loading the hair bundles, we apply a recently developed technique that uses superparamagnetic particles to actuate the cells. Magnetic nanoparticles are conjugated to bind to the stereovilli of the hair cell and are controlled with an electromagnet to deflect the bundles. This allows for sensitive mechanical control of the position of the stereovilli, without imposing a mechanical load. We apply the technique to study the dynamics of synchronization between spontaneously oscillating hair bundles and an imposed stimulus at increasing frequencies. The evoked response consistently shows regimes of high-order mode-locking, which take the form of Arnold Tongues. Significant areas of overlap occur between synchronization regimes, with the bundle intermittently flickering between different winding numbers. We demonstrate how an ensemble of these noisy nonlinear oscillators could be entrained to detect signals significantly above the characteristic frequencies of the individual cells.

Establishing generalized synchronization in Rössler oscillator networks

The processes of establishing of generalized chaotic synchronization in a network of mutually coupled continuous-time systems are investigated. The nature of interaction between the network elements in transitioning from synchronous to asynchronous behavior while increasing the communication parameter is studied. A synchronization regime, the nearest neighbors method, and calculations of the spectrum of Lyapunov exponents are used to clarify features of the interaction between network elements and the occurrence of a generalized chaotic.

Phase switching in Hindmarsh-Rose relay neurons

A system of Hindmarsh-Rose relay neurons with time delay coupling is considered in which the relay (central) neuron has an additional feedback term that represents the interaction activity with a local environment. The strength of environmental coupling with the central neuron plays an important role in inducing synchronization and de-synchronization between the outer neurons. The strength of feedback developed from the environmental coupling has created a gradual quenching in the oscillations of the central neuron. At a higher feedback coupling strength, oscillation of the central neuron is suppressed drastically and a transition from a regime of synchronization to out-of-phase synchronization take place between the oscillations of the two outer neurons.

Quantifying Neural Oscillatory Synchronization: A Comparison between Spectral Coherence and Phase-Locking Value Approaches

Synchronization or phase-locking between oscillating neuronal groups is considered to be important for coordination of information among cortical networks. Spectral coherence is a commonly used approach to quantify phase locking between neural signals. We systematically explored the validity of spectral coherence measures for quantifying synchronization among neural oscillators. To that aim, we simulated coupled oscillatory signals that exhibited synchronization dynamics using an abstract phase-oscillator model as well as interacting gamma-generating spiking neural networks. We found that, within a large parameter range, the spectral coherence measure deviated substantially from the expected phase-locking. Moreover, spectral coherence did not converge to the expected value with increasing signal-to-noise ratio. We found that spectral coherence particularly failed when oscillators were in the partially (intermittent) synchronized state, which we expect to be the most likely state for neural synchronization. The failure was due to the fast frequency and amplitude changes induced by synchronization forces. We then investigated whether spectral coherence reflected the information flow among networks measured by transfer entropy (TE) of spike trains. We found that spectral coherence failed to robustly reflect changes in synchrony-mediated information flow between neural networks in many instances. As an alternative approach we explored a phase-locking value (PLV) method based on the reconstruction of the instantaneous phase. As one approach for reconstructing instantaneous phase, we used the Hilbert Transform (HT) preceded by Singular Spectrum Decomposition (SSD) of the signal. PLV estimates have broad applicability as they do not rely on stationarity, and, unlike spectral coherence, they enable more accurate estimations of oscillatory synchronization across a wide range of different synchronization regimes, and better tracking of synchronization-mediated information flow among networks.

Noise-induced transitions in optomechanical synchronization

We study how quantum and thermal noise affects synchronization of two optomechanical limit-cycle oscillators. Classically, in the absence of noise, optomechanical systems tend to synchronize either in-phase or anti-phase. Taking into account the fundamental quantum noise, we find a regime where fluctuations drive transitions between these classical synchronization states. We investigate how this ‘mixed’ synchronization regime emerges from the noiseless system by studying the classical-to-quantum crossover and we show how the time scales of the transitions vary with the effective noise strength. In addition, we compare the effects of thermal noise to the effects of quantum noise.

Binary generalized synchronization

In this paper we report for the first time on the binary generalized synchronization, when for the certain values of the coupling strength two unidirectionally coupled dynamical systems generating the aperiodic binary sequences are in the generalized synchronization regime. The presence of the binary generalized synchronization has been revealed with the help of both the auxiliary system approach and the largest conditional Lyapunov exponent calculation. The mechanism resulting in the binary generalized synchronization has been explained. The finding discussed in this paper gives a strong potential for new applications under many relevant circumstances.

Kuramoto Phase Model with Inertia: Bifurcations Leading to the Loss of Synchrony and to the Emergence of Chaos

We consider a finite-dimensional model of phase oscillators with inertia in the case of star configuration of coupling. The system of equations is reduced to a nonlinearly coupled system of pendulum equations. We prove that the transition from synchronous to asynchronous oscillations occurs via bifurcation of saddle-node equilibrium. In this connection the asynchronous regime can be partially synchronous rotations. We find that the reverse transition from asynchronous to synchronous regime occurs via bifurcation of homoclinic orbit both of the saddle equilibrium point and of the saddle periodic orbit. In the case of homoclinic loop of the saddle point the synchrony appears only from asynchronous mode without partially synchronized rotations. In the case of the homoclinic curve of the saddle periodic orbit the system undergoes a chaotic rotation regime which results in a random return to synchrony. We establish that return transitions are hysteretic in the case of large inertia.