Bistable States Research Articles

The dynamics of synchronization of two-stage van der Pol generator

Results of numerical simulation of self-oscillations synchronization process in two-cascade ring generator van der Pol by harmonic signal are presented. Studies were carried out within the framework of the DT- model of the dynamic system. The model was developed on the basis of the principle of compliance within the framework of the method of slowly changing amplitudes of characteristics of a discrete system with characteristics of an analog prototype. Shortened equations for complex oscillation amplitudes in generator stages are obtained. It was found that in an autonomous system there is an effect of bistability of amplitudes. In the synchronization mode with an external harmonic signal, solutions of shortened equations made it possible to calculate amplitude-frequency and phase-frequency characteristics of synchronous oscillations. It is shown that transitions between bistable states are observed in the synchronous oscillation holding band. Differences of frequency characteristics of synchronization of classical and two-stage oscillators van der Pol were analyzed.

Electrically and Optically Controllable p-n Junction Memtransistor Based on an Al2 O3 Encapsulated 2D Te/ReS2 van der Waals Heterostructure.

The exploration of memtransistors as a combination of a memristor and a transistor has recently attracted intensive attention because it offers a promising candidate for next-generation multilevel nonvolatile memories and synaptic devices. However, the present state-of-the-art memtransistors, which are based on a single material, such as MoS2 or perovskite, exhibit a relatively low switching ratio, require extremely high electric fields to modulate bistable resistance states and do not perform multifunctional operations. Here, the realization of an electrically and optically controllable p-n junction memtransistor using an Al2 O3 encapsulated 2D Te/ReS2 van der Waals heterostructure is reported. The hybrid memtransistor shows a reversible bipolar resistance switching behavior between a low resistance state and a high resistance state with a high switching ratio up to 106 at a low operating voltage (<10V), high cycling endurance, and long retention time. Moreover, multiple resistance states are achieved by applying different bias voltages, gate voltages, or light powers. In addition, logical operations, including the inverter and AND/OR gates, and synaptic activities are performed by controlling the optical and electrical inputs. The work offers a novel strategy for the reliable fabrication of p-n junction memtransistors for multifunctional devices and neuromorphic applications.

Influence of the rounded rear edge on wake bi-stability of a notchback bluff body

The wake bi-stability behind notchback Ahmed bodies is investigated by performing wind tunnel experiments and large eddy simulations (LESs). The focus of this study is on the suppression of bi-stable wakes achieved by rounding the roof's trailing edge of the body. The suppression effect is found to depend on the Reynolds number (Re). The wake behind a sharp edge remains bi-stable for all tested Re. However, for a rounded edge with small radius, wake bi-stability at Re=0.5×105 and wake symmetrization with 0.75×105≤Re≤1.5×105 are observed. Increasing Re with Re≥1.75×105, the wake returns to the bi-stable state. Particularly, with Re≥2×105, a stable asymmetric wake state with no switches is observed for long periods. Performing LES confirms the expected wake asymmetry at Re=0.5×105 and symmetry at Re=1×105 for the case of rounded edge with a small radius. Besides, another wake symmetry is observed for the rounded edge with a large radius at Re=0.5×105. For the two wake symmetries shown in the LES results, the symmetrization is attributed to wake suppression in the notchback region, forcing the flow separation from the rear roof to attach to the slant on both sides of the body.

Quantifying the Landscape of Decision Making From Spiking Neural Networks.

The decision making function is governed by the complex coupled neural circuit in the brain. The underlying energy landscape provides a global picture for the dynamics of the neural decision making system and has been described extensively in the literature, but often as illustrations. In this work, we explicitly quantified the landscape for perceptual decision making based on biophysically-realistic cortical network with spiking neurons to mimic a two-alternative visual motion discrimination task. Under certain parameter regions, the underlying landscape displays bistable or tristable attractor states, which quantify the transition dynamics between different decision states. We identified two intermediate states: the spontaneous state which increases the plasticity and robustness of changes of minds and the “double-up” state which facilitates the state transitions. The irreversibility of the bistable and tristable switches due to the probabilistic curl flux demonstrates the inherent non-equilibrium characteristics of the neural decision system. The results of global stability of decision-making quantified by barrier height inferred from landscape topography and mean first passage time are in line with experimental observations. These results advance our understanding of the stochastic and dynamical transition mechanism of decision-making function, and the landscape and kinetic path approach can be applied to other cognitive function related problems (such as working memory) in brain networks.

The influence of background turbulence on Ahmed-body wake bistability

The discovery of wake bistability has generated an upsurge in experimental investigations into the wakes of simplified vehicle geometries. Particular focus has centred on the probabilistic switching between two asymmetrical bistable wake states of a square-back Ahmed body; however, the majority of this research has been undertaken in wind tunnels with turbulence intensities of less than$1\,\%$, considerably lower than typical atmospheric levels. To better simulate bistability under on-road conditions, in which turbulence intensities can easily reach levels of$10\,\%$or more, this experimental study investigates the effects of free-stream turbulence on the bistability characteristics of the square-back Ahmed body. Through passive generation and quantification of the free-stream turbulent conditions, a monotonic correlation was found between the switching rate and free-stream turbulence intensity.

Dune bistability identified by remote sensing in a semi-arid dune field of northern China

Sand dunes could have bistable states based on the observation that bare dunes and vegetation-stabilized dunes can coexist in the same area under the same environmental conditions. So far, more quantitative evidence on such an interesting phenomenon has remained elusive. In this study, the vegetation coverage and spatial distribution of dunes in the semi-arid Mu Us dune field, north-central China, were investigated by different remote sensing indices derived from the Landsat images using the Google Earth Engine platform, and the results were verified using the aerial images. Frequency distribution of vegetation coverage in many sub-regions (5 km × 5 km) across the dune field clearly shows two dominant peaks, one around 5% and the other around 40%, representing active and stabilized dune states, respectively. The boundaries between the patches of these two states are sharp, and have hardly shifted during the last twenty years. Such coexistence of bistable states is mostly distributed across a precipitation gradient from 200 to 400 mm in the study area. The relative portion of active dunes in total is reduced with increasing precipitation, while the dominant peaks of vegetation coverage for two dune states remain largely unchanged. All these lines of evidence are in accordance with the theory of alternative stable states and model predictions. Because the reversal would be difficult once the dunes shifted into an undesired state from the standpoint of environmental management, detecting and monitoring these transitions, which are often abrupt, is important for better process-based understanding of the mechanisms involved and anticipating future transitions.

Optical Bistability of 1-D Photonic Crystals Containing of Nonlinear Plasma

In this article, a novel nonlinear model is proposed to describe the permittivity of the plasma, and the nonlinear optical bistable phenomenon of the 1-D photonic crystals, which is composed of a nonlinear plasma defect layer, is theoretically investigated by the conventional transfer matrix method (TMM) under TM wave. It is figured out that the permittivity of nonlinear plasma exists in bistable state. Then, the tuning effects of the number of the photonic crystals’ (PCs) periodic layers, the incident frequency, the thicknesses of the nonlinear plasma layer, and the incident angle on the optical bistability (OB) have been emphatically studied. Additionally, the transmission and the reflectance under the influences of this bistable tuning are further proposed. The calculated results show that the adjustment of the OB can be achieved without changing the multi-layer material geometry. This multi-composite nonlinear plasma defect structure with the tunable bistable phenomenon can be applied to numerous valuable optical devices, such as novel optical power threshold devices, logic gates, and optical information memory.

Dynamical system model predicts when social learners impair collective performance

A key question concerning collective decisions is whether a social system can settle on the best available option when some members learn from others instead of evaluating the options on their own. This question is challenging to study, and previous research has reached mixed conclusions, because collective decision outcomes depend on the insufficiently understood complex system of cognitive strategies, task properties, and social influence processes. This study integrates these complex interactions together in one general yet partially analytically tractable mathematical framework using a dynamical system model. In particular, it investigates how the interplay of the proportion of social learners, the relative merit of options, and the type of conformity response affect collective decision outcomes in a binary choice. The model predicts that, when the proportion of social learners exceeds a critical threshold, a bistable state appears in which the majority can end up favoring either the higher- or lower-merit option, depending on fluctuations and initial conditions. Below this threshold, the high-merit option is chosen by the majority. The critical threshold is determined by the conformity response function and the relative merits of the two options. The study helps reconcile disagreements about the effect of social learners on collective performance and proposes a mathematical framework that can be readily adapted to extensions investigating a wider variety of dynamics.

Solution‐Processed Dual Gate Ferroelectric–Ferroelectric Organic Polymer Field‐Effect Transistor for the Multibit Nonvolatile Memory

AbstractThe stable multibit storage operation of solution‐processed organic nonvolatile memories (ONVMs) based on ferroelectric field‐effect transistors (FeFETs) for high density data storage devices are demonstrated. The proposed multibit ONVM structure consists of a p‐type polymer semiconductor sandwiched between poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)] layers serving as ferroelectric gate insulators to form a dual gate ferroelectric–ferroelectric memory transistor (DG Fe‐FeMT). With the extra memory space created by the spatially separated ferroelectrics, a 2‐bit memory representation (“11”, “10”, “01” and “00”) with clear memory margins is achieved due to the bistability of each P(VDF‐TrFE) and the high performance of the polymer semiconductor. The distinct four‐level reading of memory output currents (IM,OUTs) results from the independent programming voltages of the dual gates. An excellent distinct six‐levelIM,OUTsare also achieved in DG Fe‐FeMT using the intermediate programming voltages. Finally, the possibility of 3−bit, or 8 memory states, are demonstrated by optimizing the bistability and intermediate polarization states of the ferroelectrics without increasing the device area horizontally. The DG Fe‐FeMT has a great potential for cost−effective flexible nonvolatile multibit data storage devices due to its solution‐process and low annealing temperatures.

Presynaptic Gαo (GOA-1) signals to depress command neuron excitability and allow stretch-dependent modulation of egg laying in Caenorhabditis elegans.

Egg laying in the nematode worm Caenorhabditis elegans is a two-state behavior modulated by internal and external sensory input. We have previously shown that homeostatic feedback of embryo accumulation in the uterus regulates bursting activity of the serotonergic HSN command neurons that sustains the egg-laying active state. How sensory feedback of egg release signals to terminate the egg-laying active state is less understood. We find that Gαo, a conserved Pertussis Toxin-sensitive G protein, signals within HSN to inhibit egg-laying circuit activity and prevent entry into the active state. Gαo signaling hyperpolarizes HSN, reducing HSN Ca2+ activity and input onto the postsynaptic vulval muscles. Loss of inhibitory Gαo signaling uncouples presynaptic HSN activity from a postsynaptic, stretch-dependent homeostat, causing precocious entry into the egg-laying active state when only a few eggs are present in the uterus. Feedback of vulval opening and egg release activates the uv1 neuroendocrine cells which release NLP-7 neuropeptides which signal to inhibit egg laying through Gαo-independent mechanisms in the HSNs and Gαo-dependent mechanisms in cells other than the HSNs. Thus, neuropeptide and inhibitory Gαo signaling maintain a bi-stable state of electrical excitability that dynamically controls circuit activity in response to both external and internal sensory input to drive a two-state behavior output.

Generation of hidden bistable images in a cholesteric liquid crystal device

ABSTRACT Generation of hidden images in a cholesteric liquid crystal device is presented. The device operation is based on the dependence of the threshold voltage for unwinding the helical molecular order in cholesteric liquid crystal (being initially ether in Grandjean or Focal conic texture) on the surface anchoring conditions of the supporting substrates. This threshold voltage, however, is different for planar and homeotropic anchoring. By patterning the substrates’ surface anchoring condition, permanently or temporarily, so-called pre-determined hidden bistable images, can be visualised and memorised by a proper electronic driving. These images are constituting of areas being either in Grandjean, Focal conic or Uniform Lying Helix (ULH) textures, that is, appearing as light reflecting, light scattering or transparent, respectively. Due to bistability of these textures (states), the visualised hidden images are bistable too. So far, the lifetime of the visualised hidden images was proven to be a decade long and being switchable to any of the other bistable states.

Bistability of squeezing and entanglement in cavity magnonics

We demonstrate how magnon Kerr nonlinearity creates bistability of quantum states when the magnon mode is strongly driven by a microwave field in a nonlinear cavity magnonic system. Numerical simulation results with experimentally feasible parameters show that the method where the system is driven far from equilibrium is a reliable way to achieve squeezed states for magnons and photons and to carry out magnon-photon entanglement, revealing mysterious phenomena of bistability. In addition, the Kittel mode can jump from one state to another one near two switching points, thus achieving the hysteresis loop phenomenon. Our results indicate that bistable quantum states could provide a way to study macroscopic quantum bistable phenomena in nonlinear systems and also can be found in broad applications in magnetic spintronics.Received 30 October 2020Accepted 19 April 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.023126Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum opticsAtomic, Molecular & Optical

Triboelectric-optical responsive cholesteric liquid crystals for self-powered smart window, E-paper display and optical switch

Intelligent responsive devices are crucial for a variety of applications ranging from smart electronics to robotics. Electro-responsive cholesteric liquid crystals (CLC) have been widely applied in display panels, smart windows, and so on. In this work, we realize the mechanical stimuli-triggered optical responses of the CLC by integrating it with a triboelectric nanogenerator (TENG), which converts the mechanical motion into alternating current electricity and then tunes the different optical responses of the CLC. When the voltage applied on the CLC is relatively low (15–40 V), the TENG drives the switching between the bistable planar state and focal conic state of the CLC, which shows potential applications in self-powered smart windows or E-paper displays. When the voltage supplied by the TENG is larger than 60 V, a self-powered optical switch is demonstrated by utilizing the transformation between focal conic state and instantons homeotropic state of the CLC. This triboelectric-optical responsive device consumes no extra electric power and suggests a great potential for future smart electronics.

Bio-Inspired Origami Metamaterials With Metastable Phases Through Mechanical Phase Transitions

Abstract Structural instability, once a catastrophic phenomenon to be avoided in engineering applications, is being harnessed to improve functionality of structures and materials, and has been a catalyst of substantial research in the field. One important application is to create functional metamaterials that deform their internal structure to adjust performance, resembling phase transformations in natural materials. In this paper, we propose a novel origami pattern, named the Shrimp pattern, with application to multi-phase architected metamaterials whose phase transition is achieved mechanically by snap-through. The Shrimp pattern consists of units that can be easily tessellated in two dimensions, either periodically with homogeneous local geometry or non-periodically with heterogeneous local geometries. We can use a few design parameters to program the unit cell to become either monostable or tune the energy barrier between the bistable states. By tessellating these unit cells into an architected metamaterial, we can create complex yet navigable energy landscapes, leading to multiple metastable phases of the material. As each phase has different geometries, the metamaterial can switch between different mechanical properties and shapes. The geometric origin of the multi-stable behavior implies that, conceptually, our designs are scale-independent, making them candidates for a variety of innovative applications, including reprogramable materials, reconfigurable acoustic waveguides, and microelectronic mechanical systems and energy storage systems.

Performance of a novel dual-magnet tri-stable piezoelectric energy harvester subjected to random excitation

Usually conventional nonlinear tri-stable piezoelectric energy harvesters (TPEHs) contain two external magnets, which make both the system structure and dynamic analysis more complex. Herein, a novel dual-magnet TPEH with only one external magnet is proposed. This TPEH consists of a rectangular magnet, a piezoelectric cantilever beam, a ring magnet and a base. Next, the lumped-parameter model of the TPEH is established to obtain the dynamic equation, circuit equation, magnetic force expression and potential function. The analysis of the magnetic force expression and potential function finds that the system degenerates from a tri-stable state to a bi-stable state, and then to a mono-stable state with the increase of magnet distance due to the changes of magnetic force. Subsequently, Runge-Kutta method is used to simulate the nonlinear dynamics and energy harvesting performance of the energy harvester under the filtered Gaussian white noise over the frequency range of 0–120 Hz. Simulation results shows that the harvester changes from intra-well movement to inter-well movement with a few transitions, and then to inter-well movement with many transitions as excitation level increases. Additionally, the output performance in the bi-stable state is better than that in the tri-stable state when the excitation is small, and the output performance in the tri-stable state is better than that in the bi-stable state when the excitation is large enough. The reason is that the depth and width of the outer potential wells in the tri-stable state are deeper and narrower, while the distance between the two outer wells in the tri-stable state is larger, when compared to the bi-stable state. Finally, designed experiments are carried out to determine the parameters in the dynamic equation and measure the energy harvesting performance of the TPEH. Experimental results are consistent with simulation results. This study suggests that it is practicable to use the dual-magnet structure for constructing a multi-stable piezoelectric energy harvester.

Irreversible Resistive State Switching in Devices with a Homoleptic Cobalt(II) Complex Active Layer.

Molecules with bi-stable electronic transport behaviour have been in upfront research topics of the molecular semiconductor devices in the past few decades due to the use of such materials in resistive data storage devices. Transition metal complexes (TMC) are expected to be potential candidates in regard to the tunable and manifold redox behaviour expecting multiple bulk transport states. Finding alternate mechanisms in such devices with TMC as the active layer materials would revoke the multifaceted approach to the functional gain. We have succeeded in demonstrating write once-read many (WORM) type of resistive memory device using a homoleptic Cobalt(II) (Co(II)) complex with large on/off current ratio ensuring the easy readout process at lower voltage. The advantage of this device was the turn on voltage was found to be the low (<2.7 V) operational voltage and the success ratio of the devices were more than 83%. The durability of the stored data was found to be more than 35,000 seconds which ensures the stability of the bistable state in the fabricated devices. Such ambient stable, solution processable devices are important for the large-scale printable devices. The manuscript describes the preparation, optical and electrochemical characterisation of the metal complex used along with a detailed mechanistic investigations and electrical characterisation of memory device obtained from a stable cobalt complex.

Topological Boundary Constraints in Artificial Colloidal Ice.

The effect of boundaries and how these can be used to influence the bulk behavior in geometrically frustrated systems are both long-standing puzzles, often relegated to a secondary role. Here, we use numerical simulations and "proof of concept" experiments to demonstrate that boundaries can be engineered to control the bulk behavior in a colloidal artificial ice. We show that an antiferromagnetic frontier forces the system to rapidly reach the ground state (GS), as opposed to the commonly implemented open or periodic boundary conditions. We also show that strategically placing defects at the corners generates novel bistable states, or topological strings, which result from competing GS regions in the bulk. Our results could be generalized to other frustrated micro- and nanostructures where boundary conditions may be engineered with lithographic techniques.

Simplicial SIRS epidemic models with nonlinear incidence rates.

Mathematical epidemiology that describes the complex dynamics on social networks has become increasingly popular. However, a few methods have tackled the problem of coupling network topology with complex incidence mechanisms. Here, we propose a simplicial susceptible-infected-recovered-susceptible (SIRS) model to investigate the epidemic spreading via combining the network higher-order structure with a nonlinear incidence rate. A network-based social system is reshaped to a simplicial complex, in which the spreading or infection occurs with nonlinear reinforcement characterized by the simplex dimensions. Compared with the previous simplicial susceptible-infected-susceptible (SIS) models, the proposed SIRS model can not only capture the discontinuous transition and the bistability of a complex system but also capture the periodic phenomenon of epidemic outbreaks. More significantly, the two thresholds associated with the bistable region and the critical value of the reinforcement factor are derived. We further analyze the stability of equilibrium points of the proposed model and obtain the condition of existence of the bistable states and limit cycles. This work expands the simplicial SIS models to SIRS models and sheds light on a novel perspective of combining the higher-order structure of complex systems with nonlinear incidence rates.

Self-Powered Rewritable Electrochromic Display based on WO3-x Film with Mechanochemically Synthesized MoO3-y Nanosheets.

Electrochromic displays with bistable color states provide a promising means toward transparent human-machine interfaces. However, the need for external power and the weak optical modulation in the visible light region of most electrochromic devices hinder their practical applications in displays. Here we prepare the MoO3-y/WO3-x films based on MoO3-y nanosheets, which show a dark blue color that matches the response of the eye and meets visual comfort standards compared to pure WO3-x film. By introducing the highly transparent Al3+ ion hydrogel layer, a convenient electrochromic device driven by the internal chemical potential has been designed. The device based on the MoO3-y /WO3-x film exhibits a high optical modulation in the whole visible light range and can operate at self-powered mode with fast response speed and excellent cycle stability. Moreover, we develop an ionic writing board based on the MoO3-y/WO3-x film to surmount the fixed display information issue in conventional electrochromic displays. The ionic writing board exhibits excellent visual display quality and realizes arbitrary writing with a self-powered characteristic. This work provides a simple mechanochemical synthesis procedure of MoO3-y nanosheets and an ingenious design of self-powered electrochromic devices, which will enable the development of next-generation high-performance electrochromic displays.

Investigation on the energy trapping and conversion performances of a multi-stable vibration absorber

Multi-stable energy harvesters have emerged as the most attractive candidates for vibration-based energy harvesting recently. Energy trapping and energy conversion are the main characteristics of a vibration-based energy harvester, similarly, energy absorption and damping dissipation are the main features of a conventional dynamic vibration absorber (DVA). Therefore, combination of vibration absorption and energy conversion is a potential strategy for vibration control and self-powered wireless sensors. This paper presents the principle design of tri-stable systems and mathematical modeling of a 2-dof tri-stable DVA and energy harvester. The energy harvesting performances of multi-stable energy harvesters in terms of tri-stable electromagnetic energy harvester (TEEH) and bi-stable electromagnetic energy harvester (BEEH) are evaluated under impulsive excitations and harmonic vibrations, respectively. The energy trapping capacity of TEEH is calculated under single impulsive excitation and compared with its counterpart of BEEH. Furthermore, the dynamic characteristics of the multi-stable DVA (tri-stable and bi-stable) are studied. Simulation results show that TEEH induces a more rapid attenuation in the residual kinetic energy of the primary system excited by a weak impulse than its counterpart of BEEH, and the trapped energy in TEEH increases remarkably with the application of a weak impulse. Compared with BEEH, the energy dissipation and harvesting performances of TEEH are more satisfactory under low-amplitude impulse and low mass ratio conditions. Additionally, the snap-through motion can be more easily triggered in TEEH under broadband and low-amplitude vibrations. With the increase in vibration amplitude, the multi-stable mechanism of TEEH can be readily understood through observing phase portrait and Poincaré mapping, from which tri-stable state, chaotic attractors and bi-stable state are presented successively. Moreover, the energy harvesting efficiency of TEEH is more advanced under broadband ambient vibrations in comparison with BEEH. Finally, a prototype of tunable tri-stable system composed of a linear spring and magnetic spring is proposed.