Bistable States Research Articles

Experimental Modelling and Amplitude-Frequency Response Analysis of a Piecewise Linear Vibration System

The amplitude-frequency response of a nonlinear vibration system with the coexistence of stiffness and viscous damping piecewise linearities are analysed by means of analytical, numerical and experimental investigations. First, a mechanical model of the piecewise linear system under simple harmonic base excitation is established, and the amplitude-frequency response equation is obtained by the averaging method. Second, an experimental device is built to realize the piecewise linear system. The stiffness and damping coefficients are identified by the least square method. Third, case studies are conducted to illustrate the effect of the clearance and base excitation amplitude on the amplitude-frequency response. The experimental results show that the introduction of the piecewise linear stiffness and damping significantly decreases the response amplitude at the primary resonance. The piecewise linear stiffness, damping coefficients, primary resonance frequency and frequency range of the bi-stable state depend on the clearance and excitation amplitude. The experimental results are consistent with the theoretical predictions and numerical simulation results of the method of backward differentiation formulas. This research provides instructive ideas to the design of the nonlinear isolator in practical engineering.

Nonlinear Analysis of Rod Fastened Rotor under Nonuniform Contact Stiffness

Rod fastened rotor is widely used in gas turbine, aero engine, and other occasions. The bending stiffness of the contact interface directly affects the stable operation of the rotor. Dynamic model of the rod fastened rotor-bearing system has been established considering nonuniform stiffness of interface. The motion equation of this system has been deduced from Lagrange’s equations. The linear dynamic characteristics of this rotor has been investigated, such as Campbell diagram, critical speed, and formation, and the nonlinear characteristics of this system, such as chaos and bifurcation, has been investigated too. The result shows that “bistable state” characteristic appeared on the rod fastened rotor system; that is, there are two critical speeds for each order, and they are all positive precession critical speed, and the amplitude response to the lower critical speed is much larger than that its counterparts to the higher critical speed. In terms of nonlinear characteristics, the rod fastened bearing system has experienced periodic 1 motion, multiple periodic motion, quasi-periodic motion, periodic 1 motion, and chaotic motion successively.

Self-sustained rolling of a thermally responsive rod on a hot surface

Recent experiments have reported an intriguing phenomenon of self-sustained rolling of a polymer rod on a flat and hot surface (Baumann et al., 2018; Ahn et al., 2018; Bazir et al., 2020). Although it has been postulated that the rod rolling is driven by its inhomogeneous thermal expansion, a quantitative thermo-mechanics model of the phenomenon, capable of explaining all the experimental observations, is not yet available. In this article, we have constructed a thermo-mechanics model of a rod rolling on a hot surface. In the model, we calculate the thermally induced deformation and stress field in the rod during its steady rolling, further enabling the prediction of its rolling speed at different conditions. Our model has also successfully predicted bistable state of the rod, which agrees well with the experimental observations.

Spontaneous Activity Induced by Gaussian Noise in the Network-Organized FitzHugh-Nagumo Model.

In this paper, we show some dynamical and biological mechanisms of the short-term memory (the fixed point attractor) through the toggle switch in the FitzHugh-Nagumo model (FN). Firstly, we obtain the bistable conditions, show the effect of Gaussian noise on the toggle switch, and explain the short-term memory's switch mechanism by mean first passage time (MFPT). Then, we obtain a Fokker-Planck equation and illustrate the meaning of the monostable and bistable state in the short-term memory. Furthermore, we study the toggle switch under the interaction of network and noise. Meanwhile, we show that network structure and noise play a vital role in the toggle switch based on network mean first passage time (NMFPT). And we illustrate that the modest clustering coefficient and noise are necessary to maintain memories. Finally, the numerical simulation shows that the analytical results agree with it.

Acidity-Driven Bidirectional Room-Temperature Spin-State Switch and Fluorescence Modulation of a Mononuclear Fe(II) Complex

Room-temperature switchable materials showing multiple responses toward external stimuli are highly desired. Herein, we report bidirectional spin-state switch and fluorescence modulation of an Fe(I...

Reversible Control of Spintronic Properties of Ferromagnetic Metal/Organic Interfaces through Selective Molecular Switching

Controlling spintronic properties of ferromagnetic metal/organic interfaces in a reversible manner provides novel avenues in spin memory and logic operations. Until now, most previous work has been performed by adsorbing magnetic organometallic complexes with bistable magnetic states on metal surfaces. However, the strong coupling between the molecule and metal surface usually destroys the switching ability or even leads to dissociation of the adsorbates, obstructing efficient control of spintronic properties at the interface. Here, we propose a new design to realize the switchable magnetic properties based on bistable chemisorbed and physisorbed states of nonmagnetic molecules on ferromagnetic metal surfaces. The switching between the two states leads to distinct local magnetic moments and yields actively controlled spin polarization of the tunneling current. Based on this strategy, we have predicted a series of switchable spinterfaces from halogenated aromatic hydrocarbons on ferromagnetic metal surfaces, allowing highly tunable interfacial spintronic properties.

Bistable states and separation hysteresis in curved compression ramp flows

The separation hysteresis of the boundary layer induced by the variation of the angle of attack (AOA) is observed and investigated numerically in curved compression ramp (CCR) flows. The occurrence of this new phenomenon is based on the bistable states of CCR flows even for the same free-stream and boundary conditions, indicating that the boundary layer’s state (attachment/separation) depends on its evolutionary history with AOA varying. Specifically, beginning with an attachment state, the boundary layer remains attached as AOA increases slowly and suddenly separates once AOA reaches a marginal angle αs. However, if we decrease AOA back from this angle, the boundary layer will not attach and remain separated until AOA reaches a small enough angle αa. The AOA extent [αa, αs] is called the dual-solution region. Three characteristic adverse pressure gradients (APGs), Isb, Icw, and Ib, are proposed to explain the existence of this dual-solution region, where Icw and Isb (Icw < Isb) are induced by the curved wall and the separation bubble, respectively, and Ib is the maximum APG that the boundary layer can resist. (i) When Ib > Isb, the flow must be attached, (ii) when Ib < Icw, the flow must be separated, and (iii) when Icw < Ib < Isb, both of these two states are theoretically possible. Since AOA-variation can make (i), (ii), and (iii) occur alternately, it could induce the separation hysteresis of CCR flows, which has been observed in this paper.

Effective control and switching of optical multistability in a three-level V-type atomic system

We theoretically analyze the behavior of single optical bistability (OB), double OB, and tristability (OT) in a three-level V-type atomic system confined in a unidirectional optical ring cavity. The physics behind the emergence of various bistable and tristable states, and switching from the absorptive to the dispersive characteristics, are explored. The role of probe- and control-field detunings on the input-output characteristics is probed. Further, it is found that the switching between various bistable phenomena is defined by the ratio between the absolute peak values of the parameters describing dispersion and absorption, respectively. This ratio sets a criterion for obtaining absorptive OB, OT, double OB, and dispersive OB. The role of control-field intensity and detuning as well as the cooperation parameter on the input-output characteristics are explored. Finally, a scheme is discussed to control the width of the middle branch of double OB and OT as well as single OB.

Tunable and asymmetric optical bistability of one-dimensional photonic crystals based on InSb and nonlinear materials.

In this paper, one-dimensional (1D) photonic crystals (PCs) based on InSb and nonlinear materials are studied using the transmission matrix method. It is found that in the terahertz band, due to the magneto-optical characteristics of InSb, when the incident light propagates through such 1D PCs in two different directions (forward and backward propagation), an asymmetric optical bistable state can be obtained. Propagating from the forward direction, the bistable state is achieved. Spreading from the backward direction, the multistable state can be observed. Compared with the bistable threshold value for the case of forward incidence, the similar value that appeared in the multistable curve is significantly reduced. The polarization-sensitive features of the asymmetric optical bistability of the presented 1D PCs are also investigated under TM waves, which focuses on the tuning effects of incident angle, external magnetic field, temperature, and the thicknesses of the InSb and nonlinear dielectric layers on the asymmetric optical bistability. The results show that when the incident light enters from two different directions, the tailoring effects of the incident angle and thickness of the InSb layer on the bistable state are obviously different, but the tuning influences of the magnetic field, temperature, and the thickness of the nonlinear material layer on the bistable state are similar. The asymmetric optical bistability we made in this paper can be applied to multifunctional devices and nonreciprocal optical isolators.

Numerical and experimental analysis of the bi-stable state for frictional continuous system

Unstable friction-induced vibrations are considered an annoying problem in several fields of engineering. Although several theoretical analyses have suggested that friction-excited dynamical systems may experience sub-critical bifurcations, and show multiple coexisting stable solutions, these phenomena need to be proved experimentally and on continuous systems. The present work aims to partially fill this gap. The dynamical response of a continuous system subjected to frictional excitation is investigated. The frictional system is constituted of a 3D printed oscillator, obtained by additive manufacturing that slides against a disc rotating at a prescribed velocity. Both a finite element model and an experimental setup has been developed. It is shown both numerically and experimentally that in a certain range of the imposed sliding velocity the oscillator has two stable states, i.e. steady sliding and stick–slip oscillations. Furthermore, it is possible to jump from one state to the other by introducing an external perturbation. A parametric analysis is also presented, with respect to the main parameters influencing the nonlinear dynamic response, to determine the interval of sliding velocity where the oscillator presents the two stable solutions, i.e. steady sliding and stick–slip limit cycle.

Large converse magnetoelectric effect in Sm doped Pb(Mg1/3Nb2/3)-PbTiO3 and NiFe2O4 laminate composite

The magnetoelectric bilayer composite Sm-doped Pb(Mg1/3Nb2/3)-PbTiO3/NiFe2O4 (Sm:PMN-PT/NFO) developed in this study exhibits a converse magnetoelectric coefficient (αCME) of 0.34 G cm/V at resonance. This value is at least an order of magnitude higher than any previously reported αCME for polycrystalline ferrite-based laminate composites. The large CME coefficients in both dc- and self-biased modes are attributed to the high transverse piezoelectric coefficient (d31 ∼ −421 pC/N) of the piezoelectric phase Sm:PMN-PT. High converse magnetoelectric coefficient and characteristic advantages of ferrite-based magnetoelectric (ME) materials such as low eddy current losses make this composite a potential candidate for the ME devices operating in the converse mode. In particular, its performance characteristics for two applications —voltage to current converter, and as a magnetic switch —have been investigated. The laminate composite exhibits current to voltage conversion performance of 14 mA/V at the resonance frequency. The performance characteristics as a magnetic switch show that the bi-stable states separated by 25 G can be realized through an AC signal of 5V.

Electroforming-free flexible organic resistive random access memory based on a nanocomposite of poly(3-hexylthiophene-2,5-diyl) and orange dye with a low threshold voltage

The charge trapping characteristics of an organic nanocomposite based on two polymers, poly(3-hexylthiophene-2,5-diyl) (P3HT) and orange dye (OD), were investigated by fabricating a sandwiched structure on a flexible polyethylene terephthalate substrate. The fabricated flexible organic device with a configuration of silver (Ag)/P3HT–OD/Ag displayed highly stable results consistent with a bipolar non-volatile resistive random access memory (RRAM) device using simple and controllable fabrication technology. It was observed that by the addition of OD, low threshold voltages (V th) of V set = 1.5 V and V reset = −1.5 V were achieved owing to the values of work function and energy bandgap of the materials used. Electrical rewritable effects of the fabricated memory device were tested for 102 voltage sweeps and 104s without any considerable degradation of its bistable resistive states. The switching mechanism was considered to be space charge limited current and this was verified by plotting the double logarithmic I–V curve. This is the first RRAM device based on P3HT polymer whose mechanical robustness has been tested for its mechanical robustness by bending it for 25 bending cycles at a bending diameter ranging from 15 cm to 5 cm without any considerable change in its properties. This finding offers important guidelines for reproducing next-generation flexible organic nanocomposite-based memory devices that are simple to fabricate and have low operating voltages and highly stable memory behavior.

High-speed simultaneous PLIF/PIV imaging of a lift-off swirling flame under acoustic forcing

The detailed understanding of the flow-flame interaction in a swirling flame is crucial for the study of turbine engine combustion. The phase and amplitude of the heat release rate as a function of the frequency and amplitude of the flow-field oscillations determine the thermo-acoustic instability of the combustion system. The responses of a lift-off swirling flame under acoustic forcing, which operates near its blow-off limit and often shows flame shape bifurcation between attached and lift-off configurations, have not been experimentally investigated. Here, we present simultaneous 20 kHz particle image velocimetry (PIV), fuel tracer and CH2O planar laser-induced fluorescence (PLIF) measurement of a lean-premixed swirling flame enclosed in a model gas turbine burner in order to study the effect of equivalence ratio and forcing on the flame structure and dynamics. We studied the bistable states that have intermittent transitions between the anchored V-shape flame and the detached lift-off flame in which the precessing vortex core is formed. The time-resolved lift-off and re-attachment transitions between the V-flame and lifted flame configuration of the bistable flames are captured by the high repetition rate burst mode imaging. The high-repetition PLIF/PIV results demonstrate that the lifted flame can be re-attached on increasing the equivalence ratio or the forcing frequencies and amplitudes.

Surface effects on temperature-driven spin crossover in Fe(phen)2(NCS)2.

Despite their importance in molecular spintronics, the surface effects on spin crossover (SCO) behaviors are still poorly understood. Here, we report the impact of substrates on thermal SCO in Fe(phen)2(NCS)2 (phen = 1,10-phenanthroline) deposited on metallic surfaces and monolayer two-dimensional materials. By first-principles calculations, we show that temperature-driven SCO is preserved on both hexagonal boron nitride and molybdenum disulfide (MoS2), while low-spin ground states are locked on metal surfaces, including Cu(111), Ag(111), and Au(111). On the contrary, the molecule in contact with graphene exhibits a high-spin ground state. We demonstrate that the spin transition temperature Tc depends critically on surface environments, and we correlate this effect with the modification of electronic structures and molecular vibrations upon adsorption. In particular, a sulfur vacancy in MoS2 considerably increases Tc. These findings open a way to nanoscale applications related to spin state bistability.

Attractor-state itinerancy in neural circuits with synaptic depression

Neural populations with strong excitatory recurrent connections can support bistable states in their mean firing rates. Multiple fixed points in a network of such bistable units can be used to model memory retrieval and pattern separation. The stability of fixed points may change on a slower timescale than that of the dynamics due to short-term synaptic depression, leading to transitions between quasi-stable point attractor states in a sequence that depends on the history of stimuli. To better understand these behaviors, we study a minimal model, which characterizes multiple fixed points and transitions between them in response to stimuli with diverse time- and amplitude-dependencies. The interplay between the fast dynamics of firing rate and synaptic responses and the slower timescale of synaptic depression makes the neural activity sensitive to the amplitude and duration of square-pulse stimuli in a nontrivial, history-dependent manner. Weak cross-couplings further deform the basins of attraction for different fixed points into intricate shapes. We find that while short-term synaptic depression can reduce the total number of stable fixed points in a network, it tends to strongly increase the number of fixed points visited upon repetitions of fixed stimuli. Our analysis provides a natural explanation for the system’s rich responses to stimuli of different durations and amplitudes while demonstrating the encoding capability of bistable neural populations for dynamical features of incoming stimuli.

Behavior of the square-back Ahmed body global modes at low ground clearance

A study of the evolution of the wake flow of a square-back Ahmed body is presented. Various ground clearance configurations around the critical case associated with the onset of the lateral bistability are investigated. The oscillation modes vary between stable and bistable states, the corresponding Strouhal numbers for the horizontal (respectively, vertical) evolve from 0.16 (respectively, 0.27) to 0.13 (respectively, 0.18).

Four-dimensional printed self-deploying circular structures with large folding ratio inspired by origami

Inspired by the origami, a series of smart circular structures with large folding ratio was designed and fabricated by four-dimensional printing in this article. The structure consists of the crease and plate parts by embedding the Miura-ori into a folding fan, and has the characteristics of bi-stable states and self-deployment by introducing soft and hard shape memory polymers. The shape memory polymer material parameters were obtained by the dynamic-mechanical analyzer, and then the constitutive equation can be determined. To demonstrate the folding and deployment performance of the smart structures, the experiment and finite element simulation was carried out. It is shown that the structures can repeatedly be folded and deployed by temperature-controlled shape memory effect of shape memory polymer. This design can be applied to the large-scale and multiple level smart structures such as antennas and deployable solar sails.

High-Performance Nonvolatile Organic Photonic Transistor Memory Devices using Conjugated Rod-Coil Materials as a Floating Gate.

A novel approach for using conjugated rod-coil materials as a floating gate in the fabrication of nonvolatile photonic transistor memory devices, consisting of n-type Sol-PDI and p-type C10-DNTT, is presented. Sol-PDI and C10-DNTT are used as dual functions of charge-trapping (conjugated rod) and tunneling (insulating coil), while n-type BPE-PDI and p-type DNTT are employed as the corresponding transporting layers. By using the same conjugated rod in the memory layer and transporting channel with a self-assembled structure, both n-type and p-type memory devices exhibit a fast response, a high current contrast between "Photo-On" and "Electrical-Off" bistable states over 105 , and an extremely low programing driving force of 0.1 V. The fabricated photon-driven memory devices exhibit a quick response to different wavelengths of light and a broadband light response that highlight their promising potential for light-recorder and synaptic device applications.

Isolas of multi-pulse solutions to lattice dynamical systems

This work investigates the existence and bifurcation structure of multi-pulse steady-state solutions to bistable lattice dynamical systems. Such solutions are characterized by multiple compact disconnected regions where the solution resembles one of the bistable states and resembles another trivial bistable state outside of these compact sets. It is shown that the bifurcation curves of these multi-pulse solutions lie along closed and bounded curves (isolas), even when single-pulse solutions lie along unbounded curves. These results are applied to a discrete Nagumo differential equation and we show that the hypotheses of this work can be confirmed analytically near the anti-continuum limit. Results are demonstrated with a number of numerical investigations.

Observation of Bistable Turbulence in Quasi-Two-Dimensional Superflow.

Turbulent flow restricted to two dimensions can spontaneously develop order on large scales, defying entropy expectations and in sharp contrast with turbulence in three dimensions where nonlinear turbulent processes act to destroy large-scale order. In this work we report the observation of unusual turbulent behavior in steady-state flow of superfluid ^{4}He-a liquid with vanishing viscosity and discrete vorticity-in a nearly two-dimensional channel. Surprisingly, for a range of experimental parameters, turbulence is observed to exist in two bistable states. This bistability can be well explained by the appearance of large-scale regions of flow of opposite vorticity.