Influence Of Coupling Strength Research Articles

Chaos synchronization based on cluster fusion in asymmetric coupling semiconductor lasers networks.

A novel cluster fusion method is proposed, based on which chaos synchronization in asymmetric coupling semiconductor lasers (ACSLs) networks is systematically demonstrated. Take the cluster fusion of a mutually-coupled network composed of 7 semiconductor lasers (SLs) for instance, the characteristics of chaos synchronization as well as the influences of coupling strength, bias current, and mismatches of intrinsic parameters and injection strength on the quality of chaos synchronization in hybrid clusters composed of ACSLs are thoroughly investigated. The results show that by using cluster fusion, the ACSLs which originally belong to different clusters can form three types of new hybrid clusters, namely, trivial-hybrid cluster, trivial-nontrivial-hybrid cluster, and nontrivial-hybrid cluster. Compared with the low-correlation inter-cluster ACSLs of original SLs network, high-quality chaos synchronization is achieved in three types of newly generated hybrid clusters over a wide parameter range. Moreover, the cluster fusion and synchronization of side-SLs clusters of star-type SLs networks are also verified, which indicate the universality of the proposed method. This work provides a new way to realize the chaos synchronization among ACSLs of different clusters.

Flexible multipoint-to-multipoint communication in semiconductor laser networks using one-way isolation.

We propose a type of semiconductor laser (SL) network that supports flexible chaos synchronization and multipoint-to-multipoint communications by using one-way isolation (OWI). The properties of chaos synchronization, influences of coupling strength and time delay mismatches on the quality of chaos synchronization, and the performance as well as the security of the SL network-based chaotic communications are systematically discussed. The numerical results demonstrate that, with the introduction of OWI, flexible chaos synchronization can be easily achieved in arbitrary-size SL clusters over wide parameter spaces of coupling strength and current factor. Based on the high-quality flexible chaos synchronization, satisfactory performance for Gb/s chaotic communications can be achieved in arbitrary-size clusters in the SL networks. Moreover, it is also indicated that in the SL networks, the security of intra-cluster communications can be guaranteed in three aspects. Firstly, the eavesdroppers cannot intercept any useful information by using a typical illegal attack. Secondly, due to the OWI, the chaotic carriers are only transmitted in the corresponding clusters, not transmitted among clusters, as such the security can be further improved. Thirdly, the high sensitivity of cross-correlation coefficient to the injection delay mismatches indicates that the injection delays of idle SLs to communicating SLs can be regarded as the keys of the communication clusters. The proposed scheme offers an alternative solution to flexible secure network-type communications.

Dynamic behaviors of nanoscale binary water droplets simultaneously impacting on flat surface

Dynamic wetting of nanoscale binary water droplets simultaneously impacting on flat copper surface is explored using molecular dynamics simulations (MDS). The spreading performance is described through the images of shape evolution and the temporal variations of radial spreading factor and dynamic contact angle. The corresponding spreading characteristic is separately assessed by the following five key aspects: impact velocity, impact direction, the potential depth between oxygen and surface atoms, the center distance of binary nanodroplets and nanodroplet diameter, respectively. Here, the simulated results show that the binary nanodroplets with a low impact velocity exhibit the advancing, receding and coalescing motion states and the fluid with the high impact speed spreading on the solid surface may develop into jet flow along the radial direction. For impact direction, the radial momentum will cause larger axial wetting length with the increase of impact angle. In addition, a wide motion regions of binary water droplets impingement from partial wetting to non-wetting are observed, which helps us better understand the feature of nanodroplet equilibrium. Besides, the influence of coupling strength on dynamics behavior is also considered. We find that the center distance of binary droplets is relatively small, which will be conducive to the jetting occurrence. The enhancement of momentum and mass transport of the colliding two equal-sized nanodroplets also boosts the jetting as the droplet diameter increases.

Synchronous patterns and intermittency in a network induced by the rewiring of connections and coupling.

The connection architecture plays an important role in the synchronization of networks, where the presence of local and nonlocal connection structures are found in many systems, such as the neural ones. Here, we consider a network composed of chaotic bursting oscillators coupled through a Watts-Strogatz-small-world topology. The influence of coupling strength and rewiring of connections is studied when the network topology is varied from regular to small-world to random. In this scenario, we show two distinct nonstationary transitions to phase synchronization: one induced by the increase in coupling strength and another resulting from the change from local connections to nonlocal ones. Besides this, there are regions in the parameter space where the network depicts a coexistence of different bursting frequencies where nonstationary zig-zag fronts are observed. Regarding the analyses, we consider two distinct methodological approaches: one based on the phase association to the bursting activity where the Kuramoto order parameter is used and another based on recurrence quantification analysis where just a time series of the network mean field is required.

Cascading failure analysis and robustness optimization of metro networks based on coupled map lattices: a case study of Nanjing, China

Cascading failure in metro networks is a dynamic chain process induced by the interaction of passenger flow and network topology. In this paper, a bi-directional coupled map lattice model is proposed to study the cascading failure of metro networks. The model considers the two-way traffic problem, and the results are closer to those of actual metro networks than the previous one-way coupling models. A $$\eta$$ -based flow redistribution method is proposed, and different passenger flow redistribution strategies after station failure can be achieved by changing the flow redistribution coefficient $$\eta$$ from 0 to 1. Moreover, the robustness of metro networks can be optimized by searching for the optimal $$\eta$$ that can maximize the critical perturbation leading to global network failure. We study the actual case of Nanjing metro. The analysis results show that the network is more vulnerable to intentional attacks than to random failures, and global network failure is triggered more easily on the largest strength station than on the stations with the largest betweenness and largest degree. The influence of coupling strengths on the critical perturbation is also investigated. The results show that larger coupling strengths correspond to smaller critical perturbations, but a change in the coupling strengths has a small impact on the optimal $$\eta$$ . Under the given traffic data, the optimal $$\eta$$ for Nanjing metro is approximately in the range (0.3, 0.4). This study provides a reference for developing strategies for dynamic safety evaluation and emergency management of passenger flow in metro networks.

Chaotic regimes and synchronization in Tm3+-doped fiber laser with pump modulation

The dynamical behavior of a thulium-doped fiber laser (Tm-DFL) with pump modulation is investigated numerically. A rate equation model is used. Different routes to chaos are identified via intermittent-like or period-doubling regimes. Pulse width and pulse energy are extracted. In the second part, the dynamics of two parallel cavities with mutual injection-locking is studied. The lag synchronization between mutually coupled Tm-DFLs can be achieved. Under some conditions, the butterfly effect is demonstrated with this system, and the influence of coupling strength on time lag synchronization is detailed.

On the Robustness of No-Feedback Interdependent Networks

The continuous operation of modern society is dominated by interdependent networks, such as energy networks, communication networks, and traffic networks. As a result, the robustness of interdependent networks has become increasingly important in recent years. On the basis of past research, a no-feedback interdependent networks model is introduced. Compared with previous work, this model is more consistent with the characteristics of real interdependent systems. In addition, two types of failure modes, unilateral failure and bilateral failure, are defined. For each failure mode, the influence of coupling strength and dependency strength on the robustness of no-feedback interdependent networks was analyzed and discussed in relation to various giant component sizes. The simulation results indicated that the robustness of the no-feedback interdependent networks was inversely proportional to coupling strength and dependency strength, and the effect of coupling strength and dependency strength on the robustness was equivalent. These conclusions are beneficial for helping researchers and engineers to build more robust interdependent systems.

Multi-channel physical random number generation based on two orthogonally mutually coupled 1550 nm vertical-cavity surface-emitting lasers

Physical random number, which is non-reproducible and non-periodical, has attracted much attention due to its potential applications in various fields such as secure communication, statistical analysis, and numerical simulation. Recently, fast physical random number generators based on optical chaotic entropy sources have been demonstrated to reach a rate of up to several hundreds of Gbit/s. Although many efforts have been made to optimize the schemeis of chaotic-based random number generation, most of them are based on distributed feedback semiconductor lasers and can only generate single-channel physical random number. After taking into account the costs and technological applications, the multi-channel physical random number generation technique needs developing. On the other hand, vertical-cavity surface-emitting lasers (VCSELs) can simultaneously emit two orthogonally polarized components under appropriate parameter conditions, and then each polarized component can be used as an entropy source for generating random number. As a result, VCSEL-based chaotic entropy sources may be suitable for multi-channel random number generation. In this work, a scheme for achieving multi-channel physical random number is proposed. Also the influence of the coupling parameters on the performance of the randomness of final bit sequences is investigated. For such a scheme, two orthogonally mutually coupled VCSELs are used to supply four-channel chaotic signals with a comparable output power and weak time-delay signature (TDS). The four-channel chaotic signals, which serve as chaotic entropy, are quantized by 8-bit analog-to-digital converters (ADCs) with 20 GHz sampling rate, and then the m least significant bit (m-LSB) post-processing method is adopted for generating final four-channel random bit sequences. Firstly, based on the spin-flip mode of VCSELs, the influences of coupling strength and frequency detuning on the dynamics of two orthogonally mutually coupled 1550 nm VCSELs are analyzed. Next, the optimized parameter regions for generating four-channel chaotic signals with comparable output power and weak TDS are preliminarily determined. For a given optimized value of coupling strength and different frequency detunings within the optimized parameter regions, the generated four-channel chaotic signals are taken as the entropy sources for obtaining final bit sequence by quantizing the 8-bit ADC and m-LSB post-processing. Finally, the randomness of the four final bit sequences is tested by NIST SP 800-22 statistical test suite, and the regions of preferred coupling parameters for simultaneously generating four-channel random numbers are determined.

Characterizing stochastic resonance in coupled bistable system with Poisson white noises via statistical complexity measures

This paper mainly analyzes the role of Poisson white noise on stochastic resonance in two coupled bistable systems. Statistical complexity and normalized Shannon entropy are used to quantify stochastic resonance behavior induced by modulating the parameters of Poisson white noise and given system. Maximum of statistical complexity and minimum of normalized Shannon entropy for an optimal noise level are considered as a symbol of the occurrence of stochastic resonance. The numerical results demonstrate that stochastic resonance behavior becomes more pronounced when increasing the mean arrival rate of Poisson white noise with fixed noise intensity. Furthermore, one can also find that the dynamical complexity of given system excited by Poisson white noise approaches the one with Gaussian white noise in the condition of same noise intensity when the mean arrival rate of Poisson white noise tends to infinity. Besides, the influences of coupling strength and damping parameter on stochastic resonance are investigated by means of statistical complexity and normalized Shannon entropy.

Investigation of Temperature Sensitivity Under the Influence of Coupling Strength Between a Silica Core and a Satellite Waveguide in a Photonic Crystal Fiber with Selective Infiltration of Glycerin

In this report, we carry out simulation and experimental investigations of directional coupler structures with different separations between the glycerin selectively infiltrated channel and silica core of a large mode area Photonic Crystal Fiber (PCF). We assess their coupling characteristics and the corresponding temperature sensing capabilities. The temperature sensitivities of the glycerin selectively infiltrated channel adjacent to the silica core and two periods away from the silica core are −3.115nm/°C and −2.332nm/°C respectively. The glycerin selectively infiltrated channel three periods away from the silica core displays −107.8 pm/°C, an order of magnitude less temperature sensitive. The simulation results agree with the experimental results that there is a strong correlation between the coupling strength of the glycerin selectively infiltrated channel and the silica core, affecting its temperature response.

Time-delay signatures hidden in the phase of chaotic output of mutually delay-coupled vertical-cavity surface-emitting lasers

Time-delay signature (TDS) extracted from the phase time series (named as P-TDS) generated by a mutually delay-coupled vertical-cavity surface-emitting lasers (MDC-VCSELs) chaotic system is investigated systematically. By adopting self-correlation function (SF) and permutation entropy (PE) methods, the influences of coupling strength and frequency detuning on P-TDS are analyzed, and also compared with the case that TDS is extracted from the intensity of field (named as I-TDS). Through mapping the evolutions of P-TDS and I-TDS in the parameter space of coupling strength and frequency detuning, an optimal range can be determined for simultaneously generating four-channel chaotic signals with both weak P-TDS and I-TDS.

Hyperchaos behaviors and chaos synchronization of two unidirectional coupled simplified Lorenz systems

To design a hyperchaotic generator and apply chaos into secure communication, a linear unidirectional coupling control is applied to two identical simplified Lorenz systems. The dynamical evolution process of the coupled system is investigated with variations of the system parameter and coupling coefficients. Particularly, the influence of coupling strength on dynamics of the coupled system is analyzed in detail. The range of the coupling strength in which the coupled system can generate hyperchaos or realize synchronization is determined, including phase portraits, Lyapunov exponents, and Poincare section. And the critical value of the system parameter between hyperchaos and synchronization is also found with fixed coupled strength. In addition, abundant dynamical behaviors such as four-wing hyperchaotic, two-wing chaotic, single-wing coexisting attractors and periodic orbits are observed and chaos synchronization error curves are also drawn by varying system parameter c. Numerical simulations are implemented to verify the results of these investigations.

Synergetic role of inhibition and excitation in bursting synchronization

We study the influence of coupling strength and network topology on synchronization in strongly coupled networks of square-wave bursters with fast excitatory and inhibitory connections. Fast excitation is known to promote synchrony, which appears in purely excitatory networks of bursting neurons as long as the excitatory coupling exceeds a threshold value. On the contrary, fast strong inhibition leads to anti-phase or asynchronous bursting in purely inhibitory networks. In this work, we report a surprising find that the addition of strong fast inhibitory connections to excitatory networks of square-wave bursters can promote synchrony. More precisely, the inhibitory connections, introduced to an excitatory network, can lower the synchronization threshold much more significantly than strengthening the present excitatory connections. We use the stability methods, developed in [1,2], to explain this synergetic role of otherwise destabilizing inhibition in promoting stable synchronization of bursting neurons in excitatory networks. We demonstrate that there is a balance between the excitatory and inhibitory couplings providing the maximum stability of synchronization. These results are applicable to synchronization in a pair of mutually connected neurons as well as to large networks with mixed excitatory-inhibitory couplings. We also study the interplay between burst synchronization and the excitatory and inhibitory networks’ structures and show that the number of excitatory and inhibitory inputs each neuron receives is often the crucial quantity.

THE EXCITATION DISCHARGE RHYTHM OF SMALL-WORLD BIOLOGICAL NEURAL NETWORKS WITH LATERAL INHIBITION MECHANISM

Research is conducted on the discharge rhythm properties of an artificial biological neural network with lateral inhibition mechanism, which is modeled by Hodgkin–Huxley (HH) equations and coupled by small-world (SW) network. The results show that the excitation frequency increases almost linearly along with increasing stimulation intensity, conversely, the average excitation intensity decreases near linearly with the increase of stimulation intensity, when the current stimulation intensity exceeds threshold value. In addition, the influence of coupling strength on excitation properties is noticeable under relatively weak stimulation. The stronger is the coupling strength, the lower is the excitation frequency, whereas the stronger is the coupling strength the greater is the excitation intensity. However, the influence of coupling strength on excitation properties is unnoticeable under relatively strong stimulation. For comparison, discharge rhythm properties of the neural networks under random connection and full connection are also investigated.

Two-site Hubbard-holstein model polaron of quantum entanglement properties

We obtain the exact solution of energy spectrum and dynamics for the two-site Hubbard-Holstein model by the coherent states orthogonal expansion method. The influences of coupling strength g, the average number of phonons n and the initial electronic state on the evolution of system entanglement and von Neumann entropy are discussed. Numerical results are as follows. (a) Entanglement evolution with time shows a good periodicity. When the other parameters are fixed, the evolution period decreases as the coupling strength g goes up but it is independent of the average number of phonons n. (b) The von Neumann entropy of the system demonstrates strict synchronia with the electronic state occupancy probability. (c) Under the weak coupling strength and low average number of phonons, the initial electronic state c2+ c2+|Oe or c1+ c1+|Oe shows larger maximum von Neumann entropy during its evolution than that of c1+c2+c1+c2++ but they gradually approach to each other with the increase of coupling strength or average number of phonons.

Study of coupling effect on the performance of a spin-current diode: Nonequilibrium Green’s function based model

In this paper, spin-dependent transport through a spin diode composed of a quantum dot coupled to a normal metal and a ferromagnetic lead is studied. The current polarization and the spin accumulation are analyzed using the equations of motion method within the nonequilibrium Green’s function formalism. We present a suitable method for computing Green’s function without carrying out any self-consistent calculation. The influence of coupling strength and magnetic field on the spin current is studied and observed that this device cannot work as a spin diode under certain conditions.

Transition of Firing Patterns in a Complex Neural Network

We study the effects of random long-range connections (shortcuts) on the firing patterns in a network composed of Hindmarsh-Rose neurons. It is found that the system can achieve the transition of neural firing patterns from the lower period state to the higher one, when the number of shortcuts in the neural network is greater than a threshold, indicating that the nervous system may make the optimal response to the change of stimulation by a corresponding adjustment of the shortcuts. Then we discuss the transition degree of firing patterns of neural network and its critical characteristics for different external stimulation current. Furthermore, the influences of coupling strength on such transition behavior of neural firing patterns are also considered. Our results may be useful in comprehending the real mechanism in neural coding and information transmission in neurobiological systems.

Analysis of the fast-slow hyperchaotic Lorenz system

The stability of the origin of the hyperchaotic Lorenz system with two time scales is investigated. The characteristics of Hopf bifurcation from the origin, including the existence condition, the direction as well as the stability of bifurcating periodic solutions are discussed in detail, which can be demonstrated by the numerical simulations. With certain parameter, the fast-slow system can exhibit symmetric bursting and further lead to hyperchaotic movement. Based on the method of slow-fast analysis, different bifurcation forms between quiescent state and spiking has been revealed and the influence of coupling strength on slow passage effect is disscussed.

Diversity-induced coherence resonance in spatially extended chaotic systems

The effect of parameter diversity on coupled Chua systems is investigated. In the absence of diversity, the systems jump back and forth between two variable domains of a chaotic attractor, and the residence times within a single domain are uncertain. By introducing parameter diversity, a combined numerical and analytical approach indicates that the systems can jump regularly from one domain to another at an intermediate range of diversity, a signature of coherence resonance. Furthermore, the influences of coupling strength and the number of units are also considered. Our results provide a possibility for the control of chaos in spatially extended chaotic systems by the manipulation of parameter diversity.

Solute–solvent interaction dynamics studied by photon echo spectroscopies in polymer glasses

The influence of coupling strength and temperature on the solute–solvent interaction of two chromophores in polymer glass is reported. The three-pulse photon echo peak shift method was used to study the dye IR144 in polyvinylformal (PVF) and the dye DTTCI (3,3′-diethylthiatricarbocyanine iodide) in polymethylmethacrylate (PMMA). IR144 is more strongly coupled (larger reorganization energy) to both its intramolecular modes and to the solvent than is DTTCI. Our results can be well described by the linearly coupled harmonic bath model over the range 300 to 30 K. In particular, the strikingly different temperature sensitivities of the long-time (asymptotic) peak shift are well described by the theory. Temperature-independent spectral densities and inhomogeneous widths suffice to quantitatively describe the peak shift data over this temperature range and a number of numerical predictions based on the theoretical model are experimentally confirmed. An ultrafast component corresponding to a decay of ∼100 fs time scale in the transition frequency correlation function is found in all cases, though the amplitude is small for the DTTCI solutions. This ultrafast response is assigned to the inertial response of the solvent. The inertial response measured for DTTCI in PMMA is very similar to our previous measurements of the inertial response for IR144 in PMMA, suggesting that a general characteristic of the solvent is being probed. The weaker coupling of DTTCI produces a drastic increase in the width of the photon echo signal as predicted by theory and strong vibrational quantum beats at 30 K. By contrast, such beats are not observed in the echo signal for IR144.