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Complex-valued Hopfield networks which possess the energy function are analyzed. The dynamics of the network with certain forms of an activation function is de-composable into the dynamics of the amplitude and phase of each neuron. Then the phase dynamics is described as a coupled system of phase oscillators with a pair-wise sinusoidal interaction. Therefore its phase synchronization mechanism is useful for the area-wide offset control of the traffic signals. The computer simulations show the effectiveness under the various traffic conditions.

Nonphotic entrainment of an overt sleep-wake rhythm and a circadian pacemaker-driving temperature/melatonin rhythm suggests existence of feedback mechanisms in the human circadian system. In this study, the authors constructed a phase dynamics model that consisted of two oscillators driving temperature/melatonin and sleep-wake rhythms, and an additional oscillator generating an overt sleep-wake rhythm. The feedback mechanism was implemented by modifying couplings between the constituent oscillators according to the history of correlations between them. The model successfully simulated the behavior of human circadian rhythms in response to forced rest-activity schedules under free-run situations: the sleep-wake rhythm is reentrained with the circadian pacemaker after release from the schedule, there is a critical period for the schedule to fully entrain the sleep-wake rhythm, and the forced rest-activity schedule can entrain the circadian pacemaker with the aid of exercise. The behavior of human circadian rhythms was reproduced with variations in only a few model parameters. Because conventional models are unable to reproduce the experimental results concerned here, it was suggested that the feedback mechanisms included in this model underlie nonphotic entrainment of human circadian rhythms.

Various stability features of bimanual rhythmic coordination, including phase transitions, have been modeled successfully by means of a one-dimensional equation of motion for relative phase obeying a gradient dynamics, the Haken-Kelso-Bunz model. The present study aimed at assessing pattern stability for stationary performance and estimating the model parameters (a, b, and Q) for the stochastic extension of this model. Estimates of a and b allowed for reconstruction of the potential defining the gradient dynamics. Two coordination patterns between the forearms (in-phase, antiphase) were performed at seven different frequencies. Model parameters were estimated on the basis of an exponential decay parameter describing the relaxation behavior of continuous relative phase following a mechanical perturbation. Variability of relative phase and relaxation time provided measures of pattern stability. Although the predicted inverse relation between pattern stability and movement frequency was observed for the lower tempo conditions, it was absent for the higher tempos, reflecting the influence of task constraints. No statistically significant differences in stability were observed between the two coordination modes, indicating the influence of intention. The reconstructed potential reflected the observed stability features, underscoring the adequacy of the parameter estimations. The relaxation process could not be captured adequately by means of a simple exponential decay function but required an additional oscillatory term. In accordance with previous assumptions, noise strength Q did not vary as a function of movement frequency. However, systematic differences in Q were observed between the two coordination modes. The advantages and (potential) pitfalls of using stationary performance of single patterns to examine the stability features of a bistable potential were discussed.

Abstract: We formulate a theory for the collective phase description of globally coupled noisy limit-cycle oscillators exhibiting macroscopic rhythms. Collective phase equations describing such macroscopic rhythms are derived by means of a two-step phase reduction. The collective phase sensitivity and collective phase coupling functions, which quantitatively characterize the macroscopic rhythms, are illustrated using three representative models of limit-cycle oscillators. As an important result of the theory, we demonstrate noise-induced anti-phase synchronization between macroscopic rhythms by direct numerical simulations of the three models. [Copyright &y& Elsevier]

Current hardware approaches to biomimetic or neuromorphic artificial intelligence rely on elaborate transistor circuits to simulate biological functions. However, these can instead be more faithfully emulated by higher-order circuit elements that naturally express neuromorphic nonlinear dynamics 1-4 . Generating neuromorphic action potentials in a circuit element theoretically requires a minimum of third-order complexity (for example, three dynamical electrophysical processes) 5 , but there have been few examples of second-order neuromorphic elements, and no previous demonstration of any isolated third-order element 6-8 . Using both experiments and modelling, here we show how multiple electrophysical processes-including Mott transition dynamics-form a nanoscale third-order circuit element. We demonstrate simple transistorless networks of third-order elements that perform Boolean operations and find analogue solutions to a computationally hard graph-partitioning problem. This work paves a way towards very compact and densely functional neuromorphic computing primitives, and energy-efficient validation of neuroscientific models.

A relativistic magnetically isolated vircator with a magnetic mirror on a prelimit electron beam is proposed. Its computer simulation has been carried out. The phase dynamics of an electron beam in a vircator has been studied. It is shown that a number of virtual cathodes appear in the beam after the beam is reflected from the magnetic mirror. The output microwave characteristics are calculated: the average power and the spectral composition of generation, containing a set of narrow spectral lines and their harmonics. The effect of the mirror ratio on the average output power and on the frequencies of the spectral lines is studied. It is found that the power increases with the growth of the mirror ratio. The frequencies of some spectral lines increase with the mirror ratio, while the frequencies of other lines do not depend on this ratio. [ABSTRACT FROM AUTHOR]

The rate of conversion during gasification of char particles depends on the type of reagents, the concentration of reactants, and reactor temperature, among many other parameters; however, the overall conversion depends on the residence time distribution (RTD) of the particles in the reactor. The objective of the present work is to investigate the influence of gasifying agents, their concentration, and reactor wall temperature on the RTD of the char particles. The aim also includes studying the effect of mean residence time on the overall char conversion during gasification of Victorian brown coal in an entrained flow reactor. Two gasifying reagents, namely, CO2 and H2O, are selected in the present study. A discrete particle model (DPM) is coupled with computational fluid dynamics (CFD) to simulate the solid phase dynamics. Gasification is modelled using a lumped approach. The mean residence time of the solid char particles, determined using three different methods, is observed to increase with the CO2 concentration and wall temperature but decrease in the H2O environment. The longer residence time leads to higher overall char conversion in a CO2 environment despite the higher reactivity of H2O compared to CO2 as a gasifying reagent. [ABSTRACT FROM AUTHOR]

Multivalent polymers are a key structural component of many biocondensates. When interacting with their cognate binding proteins, multivalent polymers such as RNA and modular proteins have been shown to influence the liquid-liquid phase separation (LLPS) boundary to both control condensate formation and to influence condensate dynamics after phase separation. Much is still unknown about the function and formation of these condensed droplets, but changes in their dynamics or phase separation are associated with neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and Alzheimer's Disease. Therefore, investigation into how the structure of multivalent polymers relates to changes in biocondensate formation and maturation is essential to understanding and treating these diseases. Here, we use a coarse-grain, Brownian Dynamics simulation with reactive binding that mimics specific interactions in order to investigate the difference between non-specific and specific multivalent binding polymers. We show that non-specific binding interactions can lead to much larger changes in droplet formation at lower protein-polymer interaction energies than their specific, valence-limited counterparts. We also demonstrate the effects of solvent conditions and polymer length on phase separation, and we present how modulating binding energy to the polymer can change the organization of a droplet in a three component system of polymer, binding protein, and solvent. Finally, we compare the effects of surface tension and polymer binding on the condensed phase dynamics, and show that both lower protein solubilities and higher attraction/affinity of the protein to the polymer result in slower droplet dynamics. This research will help to better understand experimental systems and provides additional insight into how multivalent polymers can control LLPS., Competing Interests: The authors have declared that no competing interests exist.

This paper presents a control structure integrating guidance and control loops for tail-controlled missile systems. Motivated by the fact that common tail-controlled missiles involve non-minimum phase dynamics, the proposed controller is designed to prevent the internal dynamics from diverging, as well as achieving homing against the intended target. To minimize the miss distance at the end of homing, we derive a formulation of a zero-effort-miss using engagement kinematics that contain the rotating dynamics of the missile, which is different from existing approaches. Subsequently, to nullify the zero-effort-miss, a nonlinear controller is designed based on the Lyapunov stability theory. Since the derived controller has a similar structure to the conventional three-loop topology that has been utilized for various tail-controlled flight systems, it is expected that the proposed method can be applied to the actual system from a practical point of view. Numerical simulation results also show that the proposed method achieves target interception while possessing stable internal dynamics. [ABSTRACT FROM AUTHOR]

The Hasegawa–Wakatani system, commonly used as a toy model of dissipative drift waves in fusion devices, is revisited with considerations of phase and amplitude dynamics of its triadic interactions. It is observed that a single resonant triad can saturate via three way phase locking, where the phase differences between dominant modes converge to constant values as individual phases increase in time. This allows the system to have approximately constant amplitude solutions. Non-resonant triads show similar behavior only when one of its legs is a zonal wave number. However, when an additional triad, which is a reflection of the original one with respect to the y axis is included, the behavior of the resulting triad pair is shown to be more complex. In particular, it is found that triads involving small radial wave numbers (large scale zonal flows) end up transferring their energy to the subdominant mode which keeps growing exponentially, while those involving larger radial wave numbers (small scale zonal flows) tend to find steady chaotic or limit cycle states (or decay to zero). In order to study the dynamics in a connected network of triads, a network formulation is considered, including a pump mode, and a number of zonal and non-zonal subdominant modes as a dynamical system. It was observed that the zonal modes become clearly dominant only when a large number of triads are connected. When the zonal flow becomes dominant as a "collective mean field," individual interactions between modes become less important, which is consistent with the inhomogeneous wave-kinetic picture. Finally, the results of direct numerical simulation are discussed for the same parameters, and various forms of the order parameter are computed. It is observed that nonlinear phase dynamics results in a flattening of the large scale phase velocity as a function of scale in direct numerical simulations. [ABSTRACT FROM AUTHOR]

We apply phase-reduction analysis to examine synchronization properties of periodic fluid flows. The dynamics of unsteady flows is described in terms of the phase dynamics, reducing the high-dimensional fluid flow to its single scalar phase variable. We characterize the phase response to impulse perturbations, which can in turn quantify the influence of periodic perturbations on the unsteady flow. These insights from phase-based analysis uncover the condition for synchronization. In the present work, we study as an example the influence of periodic external forcing on an unsteady cylinder wake. The condition for synchronization is identified and agrees closely with results from direct numerical simulations. Moreover, the analysis reveals the optimal forcing direction for synchronization. Phase-response analysis holds potential to uncover lock-on characteristics for a range of periodic flows. [ABSTRACT FROM AUTHOR]

Frequency encoded reconfigurable logic gates OR and AND are designed using interferometric switch based on quantum dot semiconductor optical amplifier (QDSOA) and simulated using MATLAB for the first time as far as our knowledge goes. The amplitude modulation (AM) and quality factor ( Q fe ) are calculated using numerical simulations confirming practical feasibility of the logic gates. This paper also investigates the effect of amplified spontaneous emission (ASE) noise on AM, Q fe and signal-to-noise ratio (SNR) values. AM below 0.005 dB and Q fe more than 30 dB ensure error free operation of the logic gates. [ABSTRACT FROM AUTHOR]

The measurement of mixing time in a water model of soft-stirring steelmaking ladles is practically facing a problem of bad repeatability. This uncertainty severely affects both the understandings of transport phenomenon in ladles and the measurement accuracy. Scaled down by a ratio of 1:4, a water model based on an industrial 260-ton ladle is used. This paper studies the transport process paths and mixing time of salt solution tracers in the water model of eccentric gas-stirred ladles with a low gas flow rate. After a large number of repeated experiments, the different transport paths of the tracer and the error of the mixing time in each transport path are discussed and compared with the numerical simulation results. The results of a large number of repeated experiments on the water model show that there are five transport paths for the tracer in the ladle. The tracer of the first path is mainly transported by the left-side main circulation flow, which is identical to the numerical simulation results. The tracer of the second and third paths are also mainly transported by the left-side circulation flow, but bifurcations occur when the tracer in the middle area is transported downward. In the third path, the portion and intensity of the tracer transferring to the right side from the central region is higher than in the second path. The fourth path is that the tracer is transported downward from the left, middle, and right sides with a similar intensity at the same time. While the tracer in the fifth path is mainly transported on the right side, and the tracer forms a clockwise circulation flow on the right side. The mixing times from the first transport path to the fifth transport path are 158.3 s, 149.7 s, 171.7 s, 134 s and 95.7 s, respectively, among which the third transport path and the fifth transport path are the maximum and minimum values among all transport paths. The error between the mixing time and the averaged mixing time at each monitoring point in the five transport paths of the tracer is between −34.7% and 40.9%. Furthermore, the error of the averaged mixing time of each path and the path-based average value is between 5.5% and 32.6%. [ABSTRACT FROM AUTHOR]

Active cell balancing improves the performance of a battery pack by transferring charge from one cell to another. Associated design questions require multiple simulations with 100 cells over several hours. Since the most efficient transfer methods switch between phases in the kilohertz range, these simulations require high computational effort or reduced accuracy. To enable detailed analysis on a large scale, this paper includes state-of-the-art electrical battery models in active balancing simulation while keeping the computation effort for one transfer in the low millisecond range. This is achieved in three steps. First, we model the dynamics of each transfer phase using standard equivalent circuit abstraction. Next, we find closed form equations for the so-defined phase dynamics, yielding an iterative approach that saves computation time by replacing the numerical solver. Finally, we employ error control techniques to aggregate phases in that iteration, systematically reducing the millions of phase evaluations that would be necessary otherwise. Our experiments show that the speedup from equivalent circuit dynamics to error-controlled aggregation almost reaches five orders of magnitude while introducing virtually no additional error. This enables simulations of realistic balancing scenarios in less than a second and is hence suitable for design space exploration. [ABSTRACT FROM PUBLISHER]

We present a unified model to describe the dynamics of optical frequency combs in quantum cascade lasers (QCLs), incorporating both ring and Fabry–Pérot (FP) cavity configurations. The model derives a modified complex Ginzburg–Landau equation (CGLE), leveraging an order parameter approach, and is capable of capturing the dynamics of both configurations, thus enabling a comparative analysis. This result demonstrates that FP QCLs, in addition to ring QCLs, belong to the same universality class of physical systems described by the CGLE, which includes, among others, systems in the fields of superconductivity and hydrodynamics. In the modified CGLE, a nonlinear integral term appears that is associated with the coupling between counterpropagating fields in the FP cavity and whose suppression yields the ring model, which is known to be properly described by a conventional CGLE. We show that this crucial term holds a key role in inhibiting the formation of harmonic frequency combs (HFCs), associated with multi-peaked localized structures, due to its anti-patterning effect. We provide support for a comprehensive campaign of numerical simulations in which we observe a higher occurrence of HFCs in the ring configuration compared to the FP case. Furthermore, the simulations demonstrate the model's capability to reproduce experimental observations, including the coexistence of amplitude and frequency modulation, linear chirp, and typical dynamic scenarios observed in QCLs. Finally, we perform a linear stability analysis of the single-mode solution for the ring case, confirming its consistency with numerical simulations and highlighting its predictive power regarding the formation of harmonic combs. [ABSTRACT FROM AUTHOR]

Partial resetting, whereby a state variable x (t) is reset at random times to a value a x (t) , 0 ⩽ a ⩽ 1 , generalizes conventional resetting by introducing the resetting strength a as a parameter. Partial resetting generates a broad family of non-equilibrium steady states (NESS) that interpolates between the conventional NESS at strong resetting (a = 0) and a Gaussian distribution at weak resetting (a → 1). Here such resetting processes are studied from a thermodynamic perspective, and the mean cost associated with maintaining such NESS are derived. The resetting phase of the dynamics is implemented by a resetting potential Φ (x) that mediates the resets in finite time. By working in an ensemble of trajectories with a fixed number of resets, we study both the steady-state properties of the propagator and its moments. The thermodynamic work needed to sustain the resulting NESS is then investigated. We find that different resetting traps can give rise to rates of work with widely different dependencies on the resetting strength a. Surprisingly, in the case of resets mediated by a harmonic trap with otherwise free diffusive motion, the asymptotic rate of work is insensitive to the value of a. For general anharmonic traps, the asymptotic rate of work can be either increasing or decreasing as a function of the strength a, depending on the degree of anharmonicity. Counter to intuition, the rate of work can therefore in some cases increase as the resetting becomes weaker (a → 1) although the work vanishes at a = 1. Work in the presence of a background potential is also considered. Numerical simulations confirm our findings. [ABSTRACT FROM AUTHOR]

In this paper, a fractional‐order unified system with complex variables is proposed. Firstly, the basic properties of the system including the equilibrium points and symmetry are analyzed. Bifurcations of the system in commensurate‐order and incommensurate‐order cases are studied. Tangent and period‐doubling bifurcations can be observed when a derivative order or a parameter is varied. The stabilization the system is investigated via the predict feedback method. Based on the stability theory of fractional‐order systems, a projective synchronization for the fractional‐order unified complex system is proposed by designing an appropriate controller. Numerical simulations are applied to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

The gas-liquid flow and oxygen content in a pressurized leaching stirred tank significantly influence the chemical reaction rates, while the specific dynamics of gas-liquid flow in the sulfuric acid system remain largely unexplored. In this study, a mathematical model of gas-liquid flow within a stirred tank is developed using the Euler-Euler approach, with the turbulence and drag force models being validated against experimental data. Utilizing this validated and reliable model, this study investigates the impacts of the sulfuric acid concentration, baffles, air inlet velocity, and bubble diameter on the flow field and gas holdup in a two-phase system consisting of a sulfuric acid solution and oxygen. The findings indicate that introducing a specific concentration of sulfuric acid decreases the solution velocity and increases the gas holdup within the tank. However, once the sulfuric acid concentration reaches a certain threshold, further increases have a diminished effect on the gas-liquid phases. The installation of baffles enhances the turbulent kinetic energy and increases the gas holdup while only resulting in a minimal 1.2% increase in power consumption. Additionally, the inlet velocity and bubble diameter have a relatively minor impact on the tank's flow field. However, increasing the inlet velocity significantly boosts the gas holdup, whereas an increase in the bubble diameter marginally reduces it. Furthermore, introducing a sulfuric acid solution into the tank can enhance the gas holdup when the gas inlet velocity is low. Conversely, when the gas inlet velocity is high, the addition of sulfuric acid results in a decrease in the gas holdup. The conclusions from this study contribute to enhancing the mixing effectiveness and oxygen content within the tank, providing a substantial theoretical basis for optimizing the design and operating conditions of pressurized leaching stirred tanks. [ABSTRACT FROM AUTHOR]

Inertial micro-particles, dispersed in turbulent flows, are affected by the local dynamics of the carrier flow field. The presence of a relative dilute loading of particles entails some relevant changes in the mean velocity field. Moreover, the roughness of the solid boundary affects both the carrier and the carried phase dynamics and their mutual interaction. The underlying physics has been exhaustively tackled in the so-called one-way coupling regime, i.e., negligible action of particles onto the fluid, whereas many aspects of the particle back-reaction have been much less investigated and are still poorly understood. Thus the research in this area remains very active. In order to understand the mutual interaction between carrier and carried phases, direct numerical simulations are particularly suitable, even at low Reynolds number. Here, particle laden flow over a complex domain is investigated at friction Reynolds number Reτ = 180. The numerical analysis is based on the Euler-Lagrange approach, taking into account the fluid-particle interaction (two-way coupling). Point forces are used to represent the back-effect of particles on the turbulence and the effect of the wall's roughness is taken into account modeling the elastic rebound of particles onto it, instead of using a virtual rebound model. The interest is focused on the effect of micro-particles of different inertia on fluid and particle statistics in the near-wall region. In particular, turbulent and solid phase statistics are compared with those obtained for a one-way coupled flow, for the same Reynolds number in smooth and rough channel flow configurations. [ABSTRACT FROM AUTHOR]

Much research in metapopulation dynamics has concentrated on identifying factors that affect coherence in spatially structured systems. In this regard, conditions for the attainment of out-of-phase dynamics have received considerable attention, due to the stabilizing effect of asynchrony on global dynamics. At low to moderate rates of dispersal, two coupled subpopulations with intrinsically chaotic dynamics tend to go out-of-phase with one another and also become periodic in their dynamics. The onset of out-of-phase dynamics and periodicity typically coincide. Here, we propose a possible mechanism for the onset of out-of-phase dynamics, and also the stabilization of chaos to periodicity, in two coupled subpopulations with intrinsically chaotic dynamics. We suggest that the onset of out-of-phase dynamics is due to the propensity of chaotic subpopulations governed by a steep, single-humped one-dimensional population growth model to repeatedly reach low subpopulation sizes that are close to a value N t = A ( A ≠equilibrium population size, K ) for which N t +1 = K . Subpopulations with very similar low sizes, but on opposite sides of A , will become out-of-phase in the next generation, as they will end up at sizes on opposite sides of K , resulting in positive growth for one subpopulation and negative growth for the other. The key to the stabilization of out-of-phase periodic dynamics in this mechanism is the net effect of dispersal placing upper and lower bounds to subpopulation size in the two coupled subpopulations, once they have become out-of-phase. We tested various components of this proposed mechanism by simulations using the Ricker model, and the results of the simulations are consistent with predictions from the hypothesized mechanism. Similar results were also obtained using the logistic and Hassell models, and with the Ricker model incorporating the possibility of extinction, suggesting that the proposed mechanism could be key to the attainment and maintenance of out-of-phase periodicity in two-patch metapopulations where each patch has local dynamics governed by a single-humped population growth model. [ABSTRACT FROM AUTHOR]

This paper addresses the robust control problem of Twin Rotor Multi input multi output System (TRMS) via H 2 and H ∞ control techniques. An output error optimization technique is proposed to develop H 2 and H ∞ controllers for the well posed plant. Computer simulation results are presented for closed loop TRMS in hovering positions which show marked improvements over previous works. The simulated plant exhibits stable responses in hovering position at the desired pitch and yaw angles. Corrections are incorporated in model formulation to compensate control and sensor singularities. The output error optimization technique proposed in the present paper can be essentially adopted in controlling of 2 by 2 plants exhibiting non-minimum phase dynamics. [ABSTRACT FROM AUTHOR]

The phase dynamics of Josephson junctions (JJs) under external electromagnetic radiation is studied through numerical simulations. Current-voltage characteristics, Lyapunov exponents, and Poincare sections are analyzed in detail. It is found that the subharmonic Shapiro steps at certain parameters are separated by structured chaotic windows. By performing a linear regression on the linear part of the data, a fractal dimension of D = 0.868 is obtained, with an uncertainty of ±0.012. The chaotic regions exhibit scaling similarity, and it is shown that the devil's staircase of the system can form a backbone that unifies and explains the highly correlated and structured chaotic behavior. These features suggest a system possessing multiple complete devil's staircases. The onset of chaos for subharmonic steps occurs through the Feigenbaum period doubling scenario. Universality in the sequence of periodic windows is also demonstrated. Finally, the influence of the radiation and JJ parameters on the structured chaos is investigated, and it is concluded that the structured chaos is a stable formation over a wide range of parameter values. [ABSTRACT FROM AUTHOR]

A quantitative summary of computer models in diving applications is presented, underscoring dual phase dynamics and quantifying metrics in tissue and blood. Algorithms covered include the multitissue, diffusion, split phase gradient, linear-exponential, asymmetric tissue, thermodynamic, varying permeability, reduced gradient bubble, tissue bubble diffusion, and linear-exponential phase models. Defining relationships are listed, and diver staging regimens are underscored. Implementations, diving sectors, and correlations are indicated for models with a history of widespread acceptance, utilization, and safe application across recreational, scientific, military, research, and technical communities. Presently, all models are incomplete, but many (included above) are useful, having resulted in diving tables, underwater meters, and dive planning software. Those herein employ varying degrees of calibration and data tuning. We discuss bubble metrics in tissue and blood as a backdrop against computer models. The past 15 years, or so, have witnessed changes and additions to diving protocols and table procedures, such as shorter nonstop time limits, slower ascent rates, shallow safety stops, ascending repetitive profiles, deep decompression stops, helium based breathing mixtures, permissible reverse profiles, multilevel techniques, both faster and slower controlling repetitive tissue halftimes, smaller critical tensions, longer flying-after-diving surface intervals, and others. Stimulated by Doppler and imaging technology, table and decompression meter development, theory, statistics, chamber and animal testing, or safer diving consensus, these modifications affect a gamut of activity, spanning bounce to decompression, single to multiday, and air to mixed gas diving. As it turns out, there is growing support for many protocols on operational, experimental, and theoretical grounds, with bubble models addressing many concerns on plausible bases, but with further testing or profile data analyses requisite.

A detailed numerical study was conducted to understand the transient flame propagation process in coal-dust clouds. The model includes detailed chemistry for the gas-phase combustion; devolatilisation kinetics; full coupling between the gas and solid phases; and radiative heat transfer. Furthermore, it solves the gas- and particle-phase momentum equations for the two-phase dynamics. The results show that the flame-speed oscillation phenomenon, which in a previous study was observed for carbon-dust clouds, was not observed for high-volatile coal dust. This is because for high-volatile dusts, such as coal, surface reactions have little impact on flame propagation, which is in fact dominated by volatile combustion. The flame speed largely depends on the devolatilisation rate. For the same reason, neither radiative emission nor absorption is important in high-volatile dust flames because of the much shorter timescale of volatile combustion. The flame structure can be divided into five zones: unburned, preheat, devolatilisation, reaction (gas phase), and post-reaction. Lastly, flame speeds increase when particle size decreases, mainly because the heat released from volatile combustion can be more effectively transported to smaller particles through conduction and convection. This will raise their temperatures more quickly and more profoundly and result in a faster devolatilisation rate and thus faster flame speed. [ABSTRACT FROM PUBLISHER]

The problem of controlled phase adjustment (resetting) for models of biological oscillators is considered. The proposed approach is based on oscillators excitation by a pulse, that results in the phase advancement or delay. Design procedure is presented for a series of pulses generation ensuring the required phase resetting. The solution is based on the direct phase response curve (PRC) approach. The notion of direct PRC is developed and non-local PRC model is proposed for oscillators. This model is more suitable for phase dynamics description under inputs excitation with sufficiently high amplitudes. The proposed model is used for controls design. Two control strategies are tested, the open-loop control (that generates a predefined table of instants of the pulses activation ensuring the resetting) and the feedback control (that utilizes information about the current phase value measured once per pulse application). The open-loop control is easier for implementation, the feedback control needs the estimation of the actual phase in the oscillating system. The algorithm of phase estimation is also presented. The conditions of the model and the controls validity and accuracy are determined. Performance of the obtained solution is demonstrated via computer simulation for two models of circadian oscillations and a model of heart muscle contraction. It is shown that in the absence of disturbances the open-loop and the feedback controls have similar performance. Additionally, the feedback control is insensitive to external disturbances influence. In these examples the presented scheme for phase values estimation demonstrates better accuracy than the conventional one. [ABSTRACT FROM AUTHOR]

Based on neurophysiological evidence, theoretical studies have shown that locomotion is generated by mutual entrainment between the oscillatory activities of central pattern generators (CPGs) and body motion. However, it has also been shown that the time delay in the sensorimotor loop can destabilize mutual entrainment and result in the failure to walk. In this study, a new mechanism called flexible-phase locking is proposed to overcome the time delay. It is realized by employing the Bonhoeffer--Van der Pol formalism -- well known as a physiologically faithful neuronal model for neurons in the CPG. The formalism states that neurons modulate their phase according to the delay so that mutual entrainment is stabilized. Flexible-phase locking derives from the phase dynamics related to an asymptotically stable limit cycle of the neuron. The effectiveness of the mechanism is verified by computer simulations of a bipedal locomotion model. [ABSTRACT FROM AUTHOR]

Biomass straw fuel has the advantage of low-carbon sustainability, and therefore, it has been widely used in recent years in coupled blending combustion with coal-fired utility boilers for power generation. At present, the drag force FD, the lift force FL, and the torque T evaluation model are very limited. In this study, within a wide range of Reynolds numbers (10 ≤ Re ≤ 2000) and incident angles (0° ≤ θ ≤ 90°), the computational fluid dynamics open source code OpenFOAM-body-fitted mesh method is used to carry out the direct numerical simulation of the flow characteristics of large cylindrical biomass particles with a high aspect ratio of L/D = 9:1. The results show that (1) the projected area of the cylinder begins to decrease after reaching the maximum at θ = 15°, while the change in the incident angle causes the formation of a smaller recirculation zone on the leeward side of the structure, and the effect of the pressure difference on the drag coefficient (CD) is reduced. (2) The lift coefficient (CL) displays a parabolic symmetric distribution when θ = 45°, and then the distribution becomes asymmetrical when Re > 100. The torque coefficient (CT) exhibits a similar trend. (3) Based on the simulation data and the literature data, new models for CD, CL, and CT for cylinders with L/D = 9:1, 10 ≤ Re ≤ 2000 and 0° ≤ θ ≤ 90° are obtained, and the mean square errors are 2.4 × 10−2, 1.4 × 10−2, and 6.4 × 10−2, respectively. This new model can improve the accuracy and adaptability of the universal model of gas–solid dynamics for biomass particles. [ABSTRACT FROM AUTHOR]

Single droplet impacts onto thin wall-films are a common phenomenon in many applications. For sufficiently high impact velocities, the droplet impact process consists of three phases, i.e., initial contact stage, droplet deformation with radial momentum transfer inducing an upward rising lamella, and crown propagation. Here, we present the results of a combined numerical and experimental study focusing on the early dynamics of the impact process. Specifically, the effects of the initial droplet shape, wall-film thickness, and contact line motion are analyzed. Prior to impact, an oblate spheroidal droplet shape was observed. Using direct numerical simulation, we show that the droplet shape affects the impact dynamics only during the first two phases, as it is one of the key parameter influencing the correct prediction of the impact zone. The contact line propagation is described by a square-root-time dependence R ¯ CL = α τ for both, dry and wetted surfaces. On dry surfaces, the advancement of the contact line is determined by the rolling motion of the truncated droplet. On wetted surfaces, the value of the α-parameter is controlled by two concurrent effects, namely, rolling motion and wall-film inertia. For impact onto thin films, the rolling motion prevails. With increasing wall-film height, the droplet penetrates into the soft substrates and wall-film inertia becomes the controlling factor. These insights into the early impact dynamics on wetted surface are important for the formulation of a unified modeling approach. [ABSTRACT FROM AUTHOR]

Understanding formation and evolution of oxidation in the thermal spray process is of significance since it affects greatly the corrosion resistance of coatings. In this work, the growth of oxide layers on in-flight Fe-based amorphous powders in high velocity air fuel (HVAF) thermal spray process was studied in detail by means of numerical and experimental methods. An oxidation model, based on the Lagrangian manner, was used to track the Fe-based amorphous particles. The simulation results showed that the increment of oxide layer thickness was codetermined by oxygen partial pressure of in-flight particles and particle temperature. It occurred primarily in the combustion chamber and barrel rather than the outflow field stage after flame flow. Furthermore, the relationship between in-flight particle oxidation and spray parameters was predicted by simulation. The optimal combustion chamber pressure is 90 psi and the optimal oxygen fuel ratio is 2.95. These were verified by the microstructural feature of in-flight collected particles, and low-oxidation Fe-based amorphous coating was obtained by HVAF utilizing the predicted spray parameters. This work offers us beneficial guidance of fabricating low-defect amorphous metallic coating. [ABSTRACT FROM AUTHOR]

We present a phase-amplitude reduction framework for analyzing collective oscillations in networked dynamical systems. The framework, which builds on the phase reduction method, takes into account not only the collective dynamics on the limit cycle but also deviations from it by introducing amplitude variables and using them with the phase variable. The framework allows us to study how networks react to applied inputs or coupling, including their synchronization and phase locking, while capturing the deviations of the network states from the unperturbed dynamics. Numerical simulations are used to demonstrate the effectiveness of the framework for networks composed of FitzHugh–Nagumo elements. The resulting phase-amplitude equations can be used in deriving optimal periodic waveforms or introducing feedback control for achieving fast phase locking while stabilizing the collective oscillations. [ABSTRACT FROM AUTHOR]

Ultrahigh-temperature ceramics (UHTC) have a wide range of applications, particularly in supersonic aircraft vehicles. However, the production of UHTCs with predetermined mechanical parameters is relevant. The paper analyzes the structurization trends and their influence on the properties of film coatings from transition metal nitrides and borides synthesized by ion-plasma and magnetron sputtering methods. Under optimal deposition energy conditions, the films show general regularities in their formation, such as the presence of a columnar (fibrous) structure and growth texture. The average grain size varies from 18–20 nm to 60–80 nm, depending on the deposition parameters and method. The films demonstrate excellent mechanical properties, including hardness, elastic modulus, recoverable elastic indicators under load, etc. Growth directions <111> and <100> are observed for transition metal carbide and nitride coatings, while growth in direction <0001> is typical of transition metal diborides. The identified trends will allow realistic computer modeling of the film formation process, using predetermined film properties and optimal sputtering parameters to promote excellent mechanical characteristics of the surface. A thermodynamic model describing the formation of nuclei for a typical film in the environment of atoms randomly deposited onto the substrate is proposed. The critical radius for nucleus growth and, accordingly, for film crystallization is analytically estimated. The influence of Gibbs energy changes on the crystallization process is discussed within the model. [ABSTRACT FROM AUTHOR]

The process of graphene growth by CVD involves a series of complex gas-phase surface chemical reactions, which generally go through three processes, including gas phase decomposition, surface chemical reaction, and gas phase diffusion. The complexity of the CVD process for growing graphene is that it involves not only chemical reactions but also mass, momentum, and energy transfer. To solve these problems, the method of numerical simulation combined with the reactor structure optimization model provides a good tool for industrial production and theoretical research to explore the influencing factors of the CVD growth of graphene. The objective of this study was to establish a simplified reaction model for the growth of graphene by chemical vapor deposition(CVD) in a vertical rotating disk reactor (VRD). From a macroscopic modeling perspective, computational fluid dynamics (CFD) was used to investigate the conditions for the growth of graphene by chemical vapor deposition in a high-speed rotating vertical disk reactor on a copper substrate surface at atmospheric pressure (101,325 Pa). The effects of gas temperature, air inlet velocity, base rotation speed, and material ratio on the surface deposition rate of graphene in a VRD reactor were studied, and the technological conditions for the preparation of graphene via the CVD method in a VRD reactor based on a special structure were explored. Compared with existing models, the numerical results showed the following: the ideal growth conditions of graphene prepared using a CVD method in a VRD reactor involve a growth temperature of 1310 K, an intake speed of 470 mL/min, a base speed of 300 rpm, and an H2 flow rate of 75 sccm; thus, more uniform graphene with a better surface density and higher quality can be obtained. The effect of the carbon surface deposition rate on the growth behavior of graphene was studied using molecular dynamics (MD) from a microscopic perspective. The simulation showed that the graphene surface deposition rate could control the nucleation density of graphene. The combination of macro- and microsimulation methods was used to provide a theoretical reference for the production of graphene. [ABSTRACT FROM AUTHOR]

A multiple-relaxation-time color gradient lattice Boltzmann model is established for simulating the flow mechanism of viscous fluids or fluids with high viscosity ratios in the microchannel. The regularized method is incorporated in this MRT framework to deal with the high viscosity ratio problems involving practical inlet–outlet boundaries. By taking several static and dynamic cases, we prove that this model could accurately describe interfacial tension, wettability, and flow problems in two-phase flows with a low spurious velocity at the range of viscosity ratio up to O(103). Using this model, we successfully simulate the droplet formation process of fluids with a high viscosity ratio in the common T-junction channel. The results are in good agreement with the experiments in the literature. We further investigate the effect of high viscosity ratios on the dispersion process, revealing that the substantial increase in terms of the viscosity ratio of fluids leads to the enhancement of continuous phase viscous shear and dispersed phase inertia effect, which would bring the deviation of the operating range from mostly reported flow systems. [ABSTRACT FROM AUTHOR]

The Winfree model is a phase-coupled synchronization model which simplifies pulse-coupled models such as the Peskin model on pacemaker cells. It is well-known that the Winfree ensemble with the first-order coupling exhibits discrete asymptotic patterns such as incoherence, locking and death depending on the coupling strength and variance of natural frequencies. In this paper, we further study higher-order couplings which makes the dynamics more close to the behaviors of the Peskin model. For this, we propose several sufficient frameworks for asymptotic patterns compared to the first-order coupling model. Our proposed conditions on the coupling strength, natural frequencies and initial data are independent of the number of oscillators so that they can be applied to the corresponding mean-field model. We also provide several numerical simulations and compare them with analytical results. [ABSTRACT FROM AUTHOR]

The workhorse simulating the dissipative dynamics is mainly based on the harmonic bath potentials together with linear system-bath couplings, but a realistic bath always assumes anharmonicity. In this work, we extend the linear dissipation model to include quadratic couplings and suggest a stochastic simulation scheme for the anharmonic dissipation. We show that the non-Gaussian noises induced by the anharmonic bath can be rigorously constructed, and the resulting stochastic Liouville equation has the same form as that for the linear dissipation model. As a preliminary application, we use this stochastic method to investigate the vibration-induced symmetry breaking in two-level electronic systems and find that the characteristic function of the non-Gaussian noises determines the absorption and fluorescence spectra. [ABSTRACT FROM AUTHOR]

Ising Machines (IMs) have the potential to outperform conventional Von-Neuman architectures in notoriously difficult optimization problems. Various IM implementations have been proposed based on quantum, optical, digital and analog CMOS, as well as emerging technologies. Networks of coupled electronic oscillators have recently been shown to exhibit characteristics required for implementing IMs. However, for this approach to successfully solve complex optimization problems, a highly reconfigurable implementation is needed. In this work, the possibility of implementing highly reconfigurable oscillator-based IMs is explored. An implementation based on quasiperiodically modulated coupling strength through a common medium is proposed and its potential is demonstrated through numerical simulations. Moreover, a proof-of-concept implementation based on CMOS coupled ring oscillators is proposed and its functionality is demonstrated. Simulation results show that our proposed architecture can consistently find the Max-Cut solution and demonstrate the potential to greatly simplify the physical implementation of highly reconfigurable oscillator-based IMs. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition (CVD) has become an important method for growing graphene on copper substrates in order to obtain graphene samples of high quality and density. This paper mainly focuses on the fluid flow and transmission phenomenon in the reactor under different process operating conditions and reactor structures. Two macroscopic physical parameters that are established as important for CVD growth are temperature and pressure. Based on the special structure of a miniature T45-R Tesla valve acting as a CVD reactor structure, this study uses numerical simulation to determine the effect of the pressure field inside a Tesla valve on graphene synthesis and temperature variation on the graphene surface deposition rate. This macroscopic numerical modeling was compared to the existing straight tube model and found to improve the graphene surface deposition rate by two orders of magnitude when the 1290–1310 K reaction temperature range inside the Tesla valve was maintained and verified through the experiment. This study provides a reference basis for optimizing the reactor geometry design and the effects of changing the operating parameters on carbon deposition rates during a CVD reaction, and will furthermore benefit future research on the preparation of high-quality, large-area, and high-density graphene by CVD. [ABSTRACT FROM AUTHOR]

A nonlinear initial boundary value problem for the lithium ion concentration, the electric potential and the electrode-electrolyte interface currents is introduced on the microscale. The model enables the resolution of porous electrode microstructures. Different exchange current densities for Butler–Volmer interface conditions are evaluated. The Cahn–Hilliard equation is used to describe the phase transition from solid-solution diffusion to two-phase dynamics. The resulting phase-field model is then discretized on a regular mesh. A first-order finite-volume scheme with an adaptive time integration method is applied. The parameters and their effects in the non-convex Helmholtz energy are investigated and explained. Furthermore, the numerical convergence of the scheme is examined. In order to illustrate the method, the charging process of several single-particles and a complex structure is numerically simulated. [ABSTRACT FROM AUTHOR]

Controlling and adjusting the size and shape of compound droplets is of increasing interest in manufacturing applications using microfluidic channels of complicated geometry. Using numerical simulation in the evolution of computer science with the ability to expand the scope of research and optimize costs is a current research trend. We here provide a numerical simulation analysis of the dynamics of a compound droplet travelling in a circular and sinusoidal-wave tube. The simulations were performed with variations of the Reynolds number, capillary number, droplet size, and channel geometry. It follows that the capillary number strongly impacts the dynamics of the droplet, and the alternation of breakup and finite deformation modes. The deformation increases and the droplet is stretched along the centerline of the channel as the Reynolds number increases. Increasing the length of the wavy region makes the droplet more deformed and enhance its breakup. Regime diagrams based on some of these parameters are also plotted. [ABSTRACT FROM AUTHOR]

Simulation of the acoustics and biomechanics of sound production in humans and animals began half a century ago. The three major components are the mechanics of tissue under self-sustained oscillation, the transport of air from the lungs to the lips, and the propagation of sound in the airways. Both low-dimensional and high-dimensional computer models have successfully predicted control of pitch, loudness, spectral content, vowel production, and many other features of speaking and singing. However, the problems of computational efficiency, validity, and accuracy have not been adequately addressed. Low-dimensional models are often more revealing of nonlinear phenomena in coupled oscillators, but the simplifying assumptions are not always validated. High-dimensional models can provide more accuracy, but interpretations of results are sometimes clouded by computational redundancy and uncertainty of parameters. The next generation will likely combine pre-calculations and machine learning with abbreviated critical calculations. [ABSTRACT FROM AUTHOR]

Grid spacing dependence in three-dimensional numerical simulations of non-normal drop impact onto thin liquid films is assessed for different impingement angles and grid refinement levels. To describe the liquid phase dynamics, the Navier–Stokes equations are coupled to a Volume-Of-Fluid (VOF) model. Numerical simulations are performed with a modified version software OpenFOAM over a structured grid of hexaedra. Grid adaptation is carried out using an edge subdivision technique which results in non-conformal meshes. Grid convergence is assessed by monitoring integral parameters describing the dynamics of the post-impact free-surface waves. Starting from an initial grid spacing between D / 8 and D / 5 , with D drop diameter, a refinement level of three is found to be sufficient to describe the diverse flow feature and to identify the splashing regime. [ABSTRACT FROM AUTHOR]

Virtual oscillator control (VOC) is a time-domain strategy that leverages the dynamics of nonlinear oscillator circuits for synchronizing and regulating grid-forming inverters. In this article, we examine a class of second-order circuits composed of a harmonic oscillator and nonlinear state-dependent damping that has found extensive interest in the context of VOC. We center our analysis on the Van der Pol, Dead-zone, and Andronov-Hopf oscillators; these are characterized by several distinguishing attributes but they all share the common structure noted above. Analytical methods based on averaging and perturbation theory are outlined to derive several performance metrics related to harmonic and dynamic properties of these oscillators under a unified framework. Our results reveal that the Andronov-Hopf oscillator is well suited for grid-forming inverter applications since it can yield harmonics-free waveforms without compromising dynamic performance. Analytical results are validated with numerical simulations and experiments, and a multiinverter hardware setup is used to illustrate a practical use case. [ABSTRACT FROM AUTHOR]

We theoretically investigate the time dependence of the first-order coherence function for a one-dimensional driven dissipative nonequilibrium condensate. Simulations on the generalized Gross-Pitaevskii equation show that the characteristic time scale of exponential decay agrees with the linearized Bogoliubov theory in the regime of large interaction energy. For very weak interactions, the temporal correlation deviates from the linear theory, and instead respects the dynamic scaling of the Kardar-Parisi-Zhang universality class. This nonlinear dynamics is found to be quantitatively captured by a noisy Kuramoto-Sivashinsky equation for the phase dynamics. [ABSTRACT FROM AUTHOR]

Hydrodynamic and viscoelastic interactions between the turbulent fluid within a channel at R e τ = 180 and a polymeric phase are investigated numerically using a multiscale hybrid approach. Direct numerical simulations are performed to predict the continuous phase and Brownian dynamics simulations using the finitely extensible nonlinear elastic dumbbell approach are carried out to model the trajectories of polymer extension vectors within the flow, using parallel computations to achieve reasonable computation timeframes on large-scale flows. Upon validating the polymeric configuration solver against theoretical predictions in equilibrium conditions, with excellent agreement observed, the distributions of velocity gradient tensor components are analyzed throughout the channel flow wall-normal regions. Impact on polymer stretching is discussed, with streamwise extension dominant close to the wall, and wall-normal extension driven by high streamwise gradients of wall-normal velocity. In this case, it is shown that chains already possessing high wall-normal extensions may attempt to orientate more in the streamwise direction, causing a curling effect. These effects are observed in instantaneous snapshots of polymer extension, and the effects of the bulk Weissenberg number show that increased W e B leads to more stretched configurations and more streamwise orientated conformities close to the wall, whereas, in the bulk flow and log-law regions, the polymers tend to trace fluid turbulence structures. Chain orientation angles are also considered, with W e B demonstrating little influence on the isotropic distributions in the log-law and bulk flow regions. Polymer–fluid coupling is implemented through a polymer contribution to the viscoelastic stress tensor. The effect of the polymer relaxation time on the turbulent drag reduction is discussed, with greater Weissenberg numbers leading to more impactful reduction. Finally, the velocity gradient tensor invariants are calculated for the drag-reduced flows, with polymers having a significant impact on the Q–R phase diagrams, with the presence of polymers narrowing the range of R values in the wall regions and causing flow structures to become more two-dimensional. [ABSTRACT FROM AUTHOR]

Rotating waves are a common occurrence in large scale recordings of brain oscillations. We examine the existence, stability, and form of rigid rotating waves in a nonlocally coupled phase model on the annulus. For odd interaction functions, it is possible to write down an explicit solution. When interactions are more general, we prove existence of the waves and use perturbation theory to estimate the shape, frequency, and stability of the waves. For large holes, we show that the phase satisfies a Burgers-type equation. We show that as the hole in the annulus decreases, the waves lose stability. Through numerical simulations, we suggest that the bifurcation that occurs with the shrinking hole is a saddle-node infinite cycle and gives rise to so-called spiral chimeras. [ABSTRACT FROM AUTHOR]

We introduce a model to mimic the dynamics of oscillators that are coupled by mean-field nonlinear memductance. Notably, nonlinear memductance produces dynamic nonlinearity, which causes the direction of coupling to change over time. Depending on the parameters, such a dynamic coupling drives the trajectory of oscillators to a synchronization or anti-synchronization manifold. Specifically, depending on the forcing frequency and coupling strength, we find anti-phase and intermittent synchronization. With the increase in coupling magnitude, one can observe a transition from intermittent synchronization to complete synchronization through anti-phase synchronization. The results are validated through numerical simulations. The hypothesis has a huge impact on the study of neuronal networks. [ABSTRACT FROM AUTHOR]

Catalytic reactions on flexible sheets generate fluid flows that transform the shape of the sheet, which in turn modifies the flow. These complex interactions make computer models vital for designing and harnessing these feedback loops to create soft active matter that autonomously performs self-sustained mechanical work. [ABSTRACT FROM AUTHOR]