Bistability Phenomenon Research Articles

CFD Simulation of Gas–Liquid–Liquid Three-Phase Flow in an Annular Centrifugal Contactor

A computational fluid dynamics (CFD) simulation of gas–liquid–liquid three-phase flow was carried out on an annular centrifugal contactor. An Euler–Euler, volume-of-fluid, multiphase-flow model was used for the three-phase flow simulation. The three-phase flow behaviors in the open and sealed inlet operation modes were investigated under various operating conditions. The location and morphology of the aqueous/organic interface were discussed in detail in light of the simulated pressure distribution. An interesting bistability phenomenon was observed in the simulation. The throughput of the annular centrifugal contactor was obtained from the simulation under various phase ratios and compared with experimental results. Excellent agreement was obtained, supporting the validity of the simulation method.

Bistability signatures in nonequilibrium charge transport through molecular quantum dots

We investigate the transient nonequilibrium dynamics of a molecular junction biased by a finite voltage and strongly coupled to internal vibrational degrees of freedom. Using two different, numerically exact techniques, diagrammatic Monte Carlo and the multilayer multiconfiguration time-dependent Hartree method, we show that the steady-state current through the junction may depend sensitively on the initial preparation of the system, thus revealing signatures of bistability. The influence of the bias voltage and the transient dynamics on the phenomenon of bistability is analyzed. Furthermore, a possible relation to the phenomenon of stochastic switching in nanoelectromecanical devices is discussed.

Flexible ring flapping in a uniform flow

AbstractAn improved version of the immersed boundary (IB) method for simulating an initially circular or elliptic flexible ring pinned at one point in a uniform flow has been developed. The boundary of the ring consists of a flexible filament with tension and bending stiffness. A penalty method derived from fluid compressibility was used to ensure the conservation of the internal volume of the flexible ring. At$\mathit{Re}= 100$, two different flapping modes were identified by varying the tension coefficient for a fixed bending stiffness, or by changing the bending coefficient for a fixed tension coefficient. The optimal tension and bending coefficients that minimize the drag force of the flexible ring were found. Visualization of the vorticity field showed that the two flapping modes correspond to different vortex shedding patterns. We observed the hysteresis property of the flexible ring, which exhibits bistable states over a range of flow velocities depending on the initial inclination angle, i.e. one is a stationary stable state and the other a self-sustained periodically flapping state. The Reynolds number range of the bistability region and the flapping amplitude were determined for various aspect ratios$a/ b$. For$a/ b= 0. 5$, the hysteresis region arises at the highest Reynolds number and the flapping amplitude in the self-sustained flapping state is minimized. A new bistability phenomenon was observed: for certain aspect ratios, two periodically flapping states coexist with different amplitudes in a particular Reynolds number range, instead of the presence of a stationary stable state and a periodically flapping state.

Controlling double-cavity optical switching in a K-type multilevel system including spontaneously generated coherence

A composite system consisting of a K-type atomic medium and a double optical cavity configuration is considered to study the phenomenon of atomic optical bistability (AOB) in the mean field approximation. The controllability of this phenomenon achieved by additional electromagnetic fields not circulating in the cavities is studied. Also, the effect of spontaneously generated coherence due to the quantum interference in decaying nearby levels on the multi-branched AOB is discussed. The system displays a new class of bifurcations.

Nonlinear dynamics of silk and Mylar flags flapping in axial flow

In this study, experiments were conducted on the flapping dynamics of flags immersed in fairly noisy axial flow. The experimental set-up was first validated by comparing the critical conditions for flapping onset with relevant results from other experimental investigations, numerical simulations and theoretical models found in the literature. Short and long flags, as well as flags with aspect ratio equal to unity, were considered. Nonlinear dynamic analyses including power spectra, phase-space portraits, Poincaré sections and circle maps obtained from the flag transverse displacement time-series indicate that the observed non-periodic flapping mainly arises through a quasi-periodic scenario. This paper also reports for the first time a "switching" oscillation phenomenon, which is closely related to hysteresis and bistability phenomena.

Bistability and self-pulsation phenomena in silicon microring resonators based on nonlinear optical effects

Bistability (BS) and self-pulsation (SP) phenomena in silicon microring resonators (MRR) with intense CW light injection are studied. Several nonlinear optical effects including Kerr effect, two-photon absorption, free carrier absorption and free carrier dispersion are taken into account. The threshold optical intensity of BS and SP is derived from the coupled mode theory and a linear stability analysis method. The influences of MRR's parameters (carrier lifetime, linear loss and radius) and light injection conditions (input power, wavelength detuning) on the characteristics of SP (modulation depth and oscillating frequency) are analyzed and discussed. It is shown that, SP occurs only if the carrier lifetime ranges from several ps to several-hundred ps and the input light intensity is higher than 10⁶W/cm². The modulation depth of SP can be as large as 8dB and the associated oscillating frequency is in the range from several GHz to beyond 10 GHz.

밴딩 전파 구동을 이용한 파리지옥 로봇의 소프트 모핑 동작

This paper presents a bending propagating actuation using SMA (Shape Memory Alloy) spring for an effective shape transition of a flytrap-inspired soft morphing structure. The flytrap-inspired soft morphing structure is made from unsymmetric CFRP (Carbon Fiber Reinforced Prepreg) structure which shows bi-stability and snap-through phenomenon. For a thin and large curved bistable CFRP structure, SMA spring is more acceptable than SMA wire and piezoelectric actuator which used in previous investigations. A bending propagating actuation is proposed which can induce snap-through of the bi-stable CFRP structure effectively. From this research, effective shape transition of soft morphing structure is possible.

Optical Bistability in an Acousto-Optic Tunable Filter (AOTF) Operating with Short Optical Pulses

In this paper we report for the first time the presence of bistability in an acoustic-optic tunable filter (AOTF) operating with ultrashort (2 ps) optical light pulses. The results for the study of bistability has shown the dependence of the hysteresis curve with the product of the coupling constant (κ) by the length of the device (ξL) and the conversion power-coupling constant factor (G). The range of bistability varies significantly with both G and with κξL parameters. The variation of κξL directly increases the size of the range of bistability hysteresis while the increase in G causes the bistability to occur at low powers. The phenomenon of optical bistability (OB) is the object of increasing interest due to its possibilities for important device applications. A bistable device is a device with a capability to generate two different outputs for a given input and the physical requirements for this are an intensity-dependence refractive index and an optical feedback mechanism.

Flapping dynamics of a flexible filament

This paper investigates the dynamics of the flapping regime of a filament placed in a two-dimensional soap-film flow for different filament lengths and flow speeds. It was found that the onset of flapping is quasiperiodic, with the main flapping amplitude and frequency modulated by low-amplitude, low-frequency oscillation. At higher flow velocities, the oscillation becomes chaotic. The transition to chaos occurs via the quasiperiodic route to chaos. A new bistability phenomenon was discovered in which the system alternates between the stretched-straight and oscillatory states, which is here referred to as "switching oscillation." Unlike some previously reported forms of bistability, in this case the system alternates between the two states continuously, without any external perturbation.

Bistability phenomena in one-dimensional polariton wires

We investigate the phenomena of bistability and domain wall propagation in polaritonic systems with dissipation provided by the interaction with incoherent phonon bath. The results on the temperature dependence of the polariton bistability behavior and polariton neuron switching are presented.

Analytical theory of optical bistability in plasmonic nanoresonators

We present approximate analytical expressions describing the optical bistability phenomenon in a plasmonic-gap-waveguide-based nonlinear device. The device is formed by a metal–dielectric–metal (MDM) waveguide perpendicularly coupled to a stub structure that is filled with an optically nonlinear medium. Among the recently reported studies on nonlinearity-induced bistability in plasmonic nanostructures, our work stands out because of its pure analytic approach and the considered device geometry. The scattered-field technique that we employ here is hinged on the concepts of circuit theory and the characteristic-impedance model for single-mode MDM waveguides. By properly accounting for surface-plasmon damping, multiple reflections, and the Kerr effect, we obtain a fairly accurate parametric relation connecting the input and output intensities of the device. The impact of changing the operating wavelength and geometrical parameters of the stub on the bistable switching thresholds and the hysteresis loop width is demonstrated using a number of numerical examples. The derived relation is useful for rapid design optimization of plasmonic switches and memories.

Multistablity, bistability and bubbles phenomena in a periodically forced ethanol fermentor

The numerical investigation results of the dynamic behavior of an ethanol fermentor excited by external sinusoidal periodic perturbations are reported. The characteristics of the discriminant of the cubic polynomial of the steady state autonomous model of the unforced fermentor were used to divide the parameter space into regions with different number of steady state solutions. The bioethanol fermentor exhibits interesting complicated dynamic behavior when the center of forcing is close to a static limit point (SLP) i.e. the discriminant=0. Numerical simulations have presented evidence for the existence of multistability, bistability and bubbles phenomena in the forced bioethanol fermentor. This is – to the best of our knowledge – the first study that shows these phenomena in the forced bioethanol fermentor. Multistablity is characterized by the coexistence of several attractors. It has been shown that, the multistability exhibits the coexistence of three attractors, two of them are chaotic and one quasi-periodic, and the bistability exhibits the coexistence of two attractors, one of them is periodic and the other is either periodic, quasi-periodic or chaotic attractor. In the multistabiliy region, we have observed that changing the forcing amplitude with the sequence of events there is an appearance of the bistability and then a transition to multistabilty. It has been shown that, the bubble region acts as a period doubling killer, which has a lethal effect in killing the universal period doubling scenario to chaos by reversing the sequence to period halving. It is also shown that, the unforced (14.55% increase in ethanol average concentration relative to the steady state operation) or forced (8.87% increase in ethanol average concentration relative to the steady state operation) unsteady state operations give better fermentor performance than the steady state operations with respect to the average ethanol concentration and yield. The investigation shows that the nature and the position of the center of forcing have significant effect on the dynamic response of the periodically forced fermentors. It has been found that, the forcing could be beneficial or harmful to the fermentor performance depending on the position of center of forcing. The system shows interesting phase planes at certain forcing amplitudes.

ANALYTICAL MODEL FOR OPTICAL BISTABILITY IN LASER WITH SATURABLE ABSORBER

In this paper, we develop a theoretical model that accurately describes the nonlinear phenomenon of optical bistability in Fabry-Perot laser containing a saturable absorber "LSA". We present an analytical model for optical bistability in a LSA. The physics of optical bistability in a classical optical resonant system such as Fabry-Perot etalon has been well-established, and can be described by simple analytical models. The photon intensities were determined as a function of the pumping rate of the active medium, and we analyzed the linear stability of the stationary solutions obtained.

Reactive Oxygen Species Production by Forward and Reverse Electron Fluxes in the Mitochondrial Respiratory Chain

Reactive oxygen species (ROS) produced in the mitochondrial respiratory chain (RC) are primary signals that modulate cellular adaptation to environment, and are also destructive factors that damage cells under the conditions of hypoxia/reoxygenation relevant for various systemic diseases or transplantation. The important role of ROS in cell survival requires detailed investigation of mechanism and determinants of ROS production. To perform such an investigation we extended our rule-based model of complex III in order to account for electron transport in the whole RC coupled to proton translocation, transmembrane electrochemical potential generation, TCA cycle reactions, and substrate transport to mitochondria. It fits respiratory electron fluxes measured in rat brain mitochondria fueled by succinate or pyruvate and malate, and the dynamics of NAD+ reduction by reverse electron transport from succinate through complex I. The fitting of measured characteristics gave an insight into the mechanism of underlying processes governing the formation of free radicals that can transfer an unpaired electron to oxygen-producing superoxide and thus can initiate the generation of ROS. Our analysis revealed an association of ROS production with levels of specific radicals of individual electron transporters and their combinations in species of complexes I and III. It was found that the phenomenon of bistability, revealed previously as a property of complex III, remains valid for the whole RC. The conditions for switching to a state with a high content of free radicals in complex III were predicted based on theoretical analysis and were confirmed experimentally. These findings provide a new insight into the mechanisms of ROS production in RC.

Genes contribute to the switching dynamics of bistable perception

Ordinarily, the visual system provides an unambiguous representation of the world. However, at times alternative plausible interpretations of a given stimulus arise, resulting in a dynamic perceptual alternation of the differing interpretations, commonly referred to as bistable or rivalrous perception. Recent research suggests that common neural mechanisms may be involved in the dynamics of very different types of bistable phenomena. Further, evidence has emerged that genetic factors may be involved in determining the rate of switch for at least one form of bistable perception, known as binocular rivalry. The current study evaluated whether genetic factors contribute to the switching dynamics for distinctly different variants of bistable perception in the same participant sample. Switching rates were recorded for MZ and DZ twin participants in two different bistable perception tasks, binocular rivalry and the Necker Cube. Strong concordance in switching rates across both tasks was evident for MZ but not DZ twins, indicating that genetic factors indeed contribute to the dynamics of multiple forms of bistable perception.

An epidemic spreading model in adaptive networks based on cellular automata

An adaptive network is a kind of co-evolutionary network in which the behaviors of nodes and the dynamics of the network affect each other. A susceptible-infected-susceptible epidemics spreading model in the adaptive network is proposed using cellular automata. Under different rewriting rules for avoiding the epidemic spreading, the changes in epidemic dynamics and the properties of the network statistic are investigated. The simulation results show that the introduction of rewiring can slow down the spreading speed of epidemic and suppress the infected scale of epidemic. The random rewiring rules make the properties of an original network with any topology tend to those of a random network. Furthermore, the proposed cellular automata model can clearly exhibit the phenomenon of bi-stability in epidemic dynamics.

Influence of an absorbing dielectric background on bistable response of a dense collection of two-level atoms

The stationary problem of light interaction with a dense collection of two-level atoms embedded in a dielectric is treated semiclassically. The effect of dielectric absorption on the phenomenon of intrinsic optical bistability is discussed in terms of the complex local-field enhancement factor. The calculations accounting for propagation effects (nonlocal regime) show that even low dielectric absorption results in the elimination of response instabilities.

Disrupting Parietal Function Prolongs Dominance Durations in Binocular Rivalry

Human brain imaging studies of bistable perceptual phenomena revealed that frontal and parietal areas are activated during perceptual switches between the two conflicting percepts. However, these studies do not provide information about causality, i.e., whether activity reports a consequence or a cause of the perceptual change. Here we used functional magnetic resonance imaging to individually localize four parietal regions involved in perceptual switches during binocular rivalry in 15 subjects and subsequently disturbed their neural processing and that of a control site using 2 Hz repetitive transcranial magnetic stimulation (TMS) during binocular rivalry. We found that TMS over one of the sites, the right intraparietal sulcus (IPS), prolonged the periods of stable percepts. Additionally, the more lateralized the blood oxygen level-dependent signal was in IPS, the more lateralized the TMS effects were. Lateralization varied considerably across subjects, with a right-hemispheric bias. Control replay experiments rule out nonspecific effects of TMS on task performance, reaction times, or eye blinks. Our results thus demonstrate a causal, destabilizing, and individually lateralized effect of normal IPS function on perceptual continuity in rivalry. This is in accord with a role of IPS in perceptual selection, relating its role in rivalrous perception to that in attention.

Current-driven state-bistability and power-bistability in a DFB semiconductor laser subject to optical injection

In this paper, current-driven state-bistability and power-bistability in a distributed feedback (DFB) semiconductor laser (LD) subject to external optical injection have been investigated experimentally. The results show that, by sweeping the bias current of slave LD along different routes nearby the threshold, both the power-bistability and the state-bistability between locking and bimodal regime can be observed under the suitable injection power, but these bistable phenomena will disappear under much large injection power. Additionally, the dependence of the width of the state-bistablility loop on the injection power has been discussed.

Analysis of an idealized heat-recirculating microcombustor

The structure and stability of two-dimensional premixed flames in an idealized microcombustor are investigated numerically within the context of a diffusive-thermal model with an imposed flow field satisfying the Navier–Stokes equations. The combustible mixture flows in a straight channel with a bend at its end that forces the flow to turn back and reverts its direction. Heat exchange occurs near the bend along a segment of the wall separating the two opposing streams; the remaining walls are assumed adiabatic. Response curves identifying the dependence of the combustion characteristics on the mass flow rate illustrate the existence of multiple steady states for a certain range of the parameters with hysteresis and bi-stability phenomena. Stable solutions correspond to flames attached to the dividing wall, where intense heat exchange occurs, or stabilized by the flow near the front wall. Depending on the conditions, one or both solutions are physically possible. At high flow rates the flame is quenched by the flow.