Bistable Properties Research Articles

INTENSITY CONTROLLED, NONSPECULAR RESONANT BACK REFLECTION OF LIGHT

Subject and Purpose. Theoretical demonstration of controllable features of a non-conventional resonant back reflection of light, realizable with the aid of a structured silicon-on-metal covering. Methods and Methodology. The investigation has been performed through a full-wave numerical simulation in a finite-element technique. Results. The nonlinear optical properties of a planar structure, involving a set of silicon disks disposed periodically on a silver substrate, have been studied in the Littrow scenario of wave reflection. The structure manifests a bistable resonant reflectivity property. The magnitudes of both specular and back reflection ratios can be controlled by means of varying the incident light intensity. Conclusions. An array of identical silicon disks, placed in a periodic order on a silver substrate, can be employed as an efficiently excitable and tunable nonlinear resonant reflective structure implementing Littrow’s non-specular diffraction scenario. As has been found, the effect of nonlinear response from the silicon disks can be used for implementing a regimen of bistable back reflection, controllable by means of varying the incident wave’s intensity. The nonlinear tunability of the silicon-on-silver structure does promise extensions of the operation area of classical metamaterials of sub-wavelength scale sizes as it offers new

Preparation and property optimization of bistable electrochromic microcapsules

In the improvement of stability and lifetime of bistable electrochromic (EC) materials, the microcapsule technique was used to protect the EC materials in a polymer shell, which was named bistable EC microcapsules (BEC-Ms). However, the particle size and shell thickness of microcapsules will affect their properties, such as response time, coloration efficiency, and bistable property. In this study, BEC-Ms was prepared via solvent evaporation method filled with PMMA as the shell and the mixture of crystal violet lactone (CVL), tetrabutylammonium perchlorate (TBAP), and phase change material (PCM) as the core. The particle size and shell thickness of microcapsules were adjusted and systematically investigated by controlling the emulsification rate and mass ratio of polymer shell to core. The optimized BEC-Ms with 2 μm size and 22.94 nm thickness showed excellent performance including fast response time (about 1 s), far lower than the safety of human body drive voltage (2 V), coloration efficiency (932 cm2 C−1), and good bistability (216 h). This approach provides a viable and alternative to flexible energy-efficient wearable display-related devices and smart textiles.

Bio-inspired soft bistable actuator with dual actuations

Soft bending actuators, as one of the most important components of soft robotics, have attracted significantly increasing attention due to their robustness, compliance, inherent safety, and ease of manufacture. However, the key disadvantages can be the low output force, slow response speed, large deformation and vibration, which can potentially be addressed by introducing a bistable mechanism enabled by a prestressed steel shell. This work proposes a novel soft actuator with bistable property, which can maintain the predefined initial state and enhance bending motion at the corresponding stable state. A novel dual-actuation mechanism, which utilises pneumatic pressure for closing and tendon-driven for opening process, is proposed for autonomous transition between both states, and for a fast response. Mathematical model is proposed and compared with the experimental result for triggering pressure, which serves as a threshold to activate the transition of the stable state. Experimental results also indicate that closing and opening speeds are enhanced by 9.82% and more than ten times, respectively, as compared with the existing pneumatic bistable reinforced actuator design. Mathematical and experimental results suggest that a programmable bending angle at the second stable state can also be achieved by adjusting the preset tendon extension. The tendon arrangement also acts as a passive damping mechanism to reduce the oscillation while closing. The damping ratio is increased by more than four times, indicating that the oscillation decay is significantly accelerated for quick stabilization. Finally, a three-finger soft gripper is developed based on the proposed actuator design, which demonstrates promising performance in grasping objects with various shapes and sizes. The experimental results also show that the proposed bistable gripper can grasp the object with a weight up to 2067 g, which is more than 17 times heavier than that of three actuators.

Regulatory feedback effects on tissue growth dynamics in a two-stage cell lineage model.

Identifying the mechanism of intercellular feedback regulation is critical for the basic understanding of tissue growth control in organisms. In this paper, we analyze a tissue growth model consisting of a single lineage of two cell types regulated by negative feedback signaling molecules that undergo spatial diffusion. By deriving the fixed points for the uniform steady states and carrying out linear stability analysis, phase diagrams are obtained analytically for arbitrary parameters of the model. Two different generic growth modes are found: blow-up growth and final-state controlled growth which are governed by the nontrivial fixed point and the trivial fixed point, respectively, and can be sensitively switched by varying the negative feedback regulation on the proliferation of the stem cells. Analytic expressions for the characteristic timescales for these two growth modes are also derived. Remarkably, the trivial and nontrivial uniform steady states can coexist and a sharp transition occurs in the bistable regime as the relevant parameters are varied. Furthermore, the bistable growth properties allows for the external control to switch between these two growth modes. In addition, the condition for an early accelerated growth followed by a retarded growth can be derived. These analytical results are further verified by numerical simulations and provide insights on the growth behavior of the tissue. Our results are also discussed in the light of possible realistic biological experiments and tissue growth control strategy. Furthermore, by external feedback control of the concentration of regulatory molecules, it is possible to achieve a desired growth mode, as demonstrated with an analysis of boosted growth, catch-up growth and the design for the target of a linear growth dynamic.

Multi-Stability Property of Magneto-Kresling Truss Structures

AbstractThe Kresling truss structure, derived from Kresling origami, has been widely studied for its bi-stability and various other properties that are useful for diverse engineering applications. The stable states of Kresling trusses are governed by their geometry and elastic response, which involves a limited design space that has been well explored in previous studies. In this work, we present a magneto-Kresling truss design that involves embedding nodal magnets in the structure, which results in a more complex energy landscape, and consequently, greater tunability under mechanical deformation. We explore this energy landscape first along the zero-torque folding path and then release the restraint on the path to explore the complete two-degree-of-freedom behavior for various structural geometries and magnet strengths. We show that the magnetic interaction could alter the potential energy landscape by either changing the stable configuration, adjusting the energy well depth, or both. Energy wells with different minima endow this magneto-elastic structure with an outstanding energy storage capacity. More interestingly, proper design of the magneto-Kresling truss system yields a tri-stable structure, which is not possible in the absence of magnets. We also demonstrate various loading paths that can induce desired conformational changes of the structure. The proposed magneto-Kresling truss design sets the stage for fabricating tunable, scalable magneto-elastic multi-stable systems that can be easily utilized for applications in energy harvesting, storage, vibration control, as well as active structures with shape-shifting capability.

A bistable X-structured electromagnetic wave energy converter with a novel mechanical-motion-rectifier: Design, analysis, and experimental tests

Beneficial nonlinearities have been intentionally introduced to improve energy harvesting performance. However, few results are reported on the issues of exploiting bistable and quasi-zero stiffness structures or mechanisms simultaneously to enhance ocean energy conversion in the literature. In this study, a novel bistable electromagnetic wave energy converter is proposed, which includes a bio-inspired X-shaped supporting structure/mechanism and a mechanical-motion-rectifier. This is for the first time that the bistable stiffness and quasi-zero stiffness are employed together (in all working range) to strengthen wave energy conversion, by developing a novel bistable X-structured system as a wave energy converter, which can bear with large vibration stroke simultaneously. Additionally, a novel mechanical-motion-rectifier with a novel energy-storing-releasing mechanism is specially designed as the power take-off system to convert linear motion to rotary motion, which greatly improves the instant voltage and power generated. The novel X-structured system demonstrates very designable nonlinear bistable and quasi-zero stiffness and thus can significantly enhance the wave energy conversion performance. Compared with traditional linear converters, much more power can be generated, especially in the low-frequency range due to the quasi-zero and bistable properties. The experiments show that, with the wave height of 0.15 m as well as the wave period of 4 s, it can generate a voltage peak at around 15 V and a power peak at about 1 W. The present results indicate that, the proposed nonlinear bistable X-structured system holds promising potentials in acting as a floating-point energy converter, which could power seashore environmental monitoring systems and wireless communication devices for smart oceans.

Tristable properties and limit point behaviour in electrostatically actuated initially curved coupled micro beams

A limit point behaviour of a metastructure, composed of two double clamped, initially curved beams, coupled via a rigid truss at their respective centres, is studied when subjected to a distributed electrostatic load. The analysis is based on a reduced order (RO) model, resulting from Galerkin’s decomposition, with symmetric buckling modes used as the base functions. To better understand the behaviour of the structure, the electrostatic analysis is preceded by a study of the model under “mechanical”, displacement-independent, load, allowing validation against a finite elements (FE) model, which served as proving ground for the RO model. In addition, results obtained by the RO model are compared with those extracted via finite differences (FD) solutions, facilitating the usage of the latter as the reference in the electrostatic, displacement-dependent, analysis. To accommodate for winding equilibrium paths, all solutions employed the implicit arc-length “Riks” method. The analysis has produced complicated equilibrium paths, which necessitated a corresponding local stability analysis, conducted using the energy method, allowing for limit point characterisation. The analyses have shown that the double beam metastructure is able to possess bistable and tristable properties, usually found in highly complex structures, which can be cumbersome for design and miniaturisation, provided that it meets certain geometrical parameters. Several variations of tristability are disclosed in the study, hitherto unknown, providing insight to the complexity of the structure. The analysis indicates that a model with at least three degrees-of-freedom (DOF) is needed to predict the various critical thresholds with reasonable errors. In so doing, the model can be used for static characterisation and design of various applications, where a simple structure, possessing tristable properties, is required.

Self-bleaching dual responsive poly(ionic liquid) with optical bistability toward climate-adaptable solar modulation

In the development of smart windows, functional polymer materials play a crucial role, which can provide a more comfortable indoor environment for people to enjoy a better lifestyle. However, many of the implied smart windows that have been studied to date respond to only one stimulus, but studies on dual-responsive smart windows have been increasing. The growing interest in multi-responsive smart windows is due to the many opportunities in terms of utility and activity that they offer. Herein, our group has adopted a strategy to combine the thermo- and electro-chromic as well as electrolyte properties in one single molecule. Dual-responsive poly(ionic liquid) (PIL) 6 based electrolyte was synthesized via radical polymerization of poly(ethylene glycol) diacrylate (PEGDA) with N-isopropylacrylamide (NIPAM) with viologen based electroactive monomer utilizing AIBN as an initiator in DMSO. One single molecule (all-in-one) single-layer device consisting of ITO/smart PIL/ITO was assembled on a glass substrate, that can enhance its optical efficiency and characteristics of phase shift. The proposed electrochromic device exhibits tunable transparency and electrochromic properties due to the thermo-responsive property of PNIPAM and the bistable electrochromic property of a viologen-based electroactive monomer, respectively. Consequently, the acquired dual-responsive properties of smart PIL 6 for the development of bistability smart windows can not only control solar energy input but can also provide a more comfortable color tone to boost people's feelings and emotions in indoor environments.

Dynamical Mechanisms for Gene Regulation Mediated by Two Noncoding RNAs in Long-Term Memory Formation.

Noncoding RNAs such as miRNAs and piRNAs have long-lasting effects on the regulation of gene expression involved in long-term synaptic changes. To characterize gene regulation mediated by small noncoding RNAs associated with long-term memory in Aplysia, we consider two noncoding RNAs stimulated by 5-HT into a gene regulatory network motif model, including miR-124 that binds to and inhibits the mRNA of CREB1 and piR-F that facilitates serotonin-dependent DNA methylation to lead to repression of CREB2. Codimension-1 and -2 bifurcation analyses of 5-HT regulating both miR-124 and piR-F and a negative feedback strength for oscillation reveal rich dynamical properties of bistability and oscillations robust to variations in all other parameters. More importantly, we verify three stimulus protocols of 5-HT in experiments by our model and find that application of five pulses of 5-HT leads to a transient decrease of miR-124 but increase of piR-F concentrations, which matters sustained high level of CREB1 concentration associated with long-term memory. Furthermore, we perform bifurcation analyses for the concentrations of miR-124 and piR-F as two parameters to explore dynamical mechanisms underlying the epigenetic regulation in long-term memory formation. This study provides insights into revealing regulatory roles of epigenetic changes in gene expression involving noncoding RNAs associated with synaptic plasticity.

Analysis and manufacturing of bistable metallic profiles

Bistable metal sheets with a coiled transport geometry and an unfolded profile as second stable state, are of great interest as lightweight components. It is well known that a specific distribution of residual stresses is necessary to enable bistable properties. With the help of numerical FE models, the optimal process parameters for production of such sheets are evaluated. Afterwards, incremental bending and roll forming experiments are conducted in order to analyse possible continuous production methods for bistable metallic profiles. Finally, the influence of bending and rolling radii on bistability and profile geometries in stable states are investigated.

Spin crossover and valence tautomerism conductors

Abstract Multifunctional molecular materials exhibiting both magnetic bistability and electrical conductivity have excellent application potential in microelectronic devices. In the last two decades, research into conductive magnets and switching materials has continuously expanded and provided materials with practical application prospects. In this review, we present the recent progress on spin crossover and valence tautomerism conductors, focusing on syntheses, strategies, crystal structures, magnetic properties, and conductivities of such materials as well as synergistic and cooperative properties of bistability and conductivity.

Active perception during angiogenesis: filopodia speed up Notch selection of tip cells in silico and in vivo.

How do cells make efficient collective decisions during tissue morphogenesis? Humans and other organisms use feedback between movement and sensing known as ‘sensorimotor coordination’ or ‘active perception’ to inform behaviour, but active perception has not before been investigated at a cellular level within organs. Here we provide the first proof of concept in silico/in vivo study demonstrating that filopodia (actin-rich, dynamic, finger-like cell membrane protrusions) play an unexpected role in speeding up collective endothelial decisions during the time-constrained process of ‘tip cell’ selection during blood vessel formation (angiogenesis). We first validate simulation predictions in vivo with live imaging of zebrafish intersegmental vessel growth. Further simulation studies then indicate the effect is due to the coupled positive feedback between movement and sensing on filopodia conferring a bistable switch-like property to Notch lateral inhibition, ensuring tip selection is a rapid and robust process. We then employ measures from computational neuroscience to assess whether filopodia function as a primitive (basal) form of active perception and find evidence in support. By viewing cell behaviour through the ‘basal cognitive lens' we acquire a fresh perspective on the tip cell selection process, revealing a hidden, yet vital time-keeping role for filopodia. Finally, we discuss a myriad of new and exciting research directions stemming from our conceptual approach to interpreting cell behaviour.This article is part of the theme issue ‘Basal cognition: multicellularity, neurons and the cognitive lens’.

BAX and SMAC regulate bistable properties of the apoptotic caspase system

The initiation of apoptosis is a core mechanism in cellular biology by which organisms control the removal of damaged or unnecessary cells. The irreversible activation of caspases is essential for apoptosis, and mathematical models have demonstrated that the process is tightly regulated by positive feedback and a bistable switch. BAX and SMAC are often dysregulated in diseases such as cancer or neurodegeneration and are two key regulators that interact with the caspase system generating the apoptotic switch. Here we present a mathematical model of how BAX and SMAC control the apoptotic switch. Formulated as a system of ordinary differential equations, the model summarises experimental and computational evidence from the literature and incorporates the biochemical mechanisms of how BAX and SMAC interact with the components of the caspase system. Using simulations and bifurcation analysis, we find that both BAX and SMAC regulate the time-delay and activation threshold of the apoptotic switch. Interestingly, the model predicted that BAX (not SMAC) controls the amplitude of the apoptotic switch. Cell culture experiments using siRNA mediated BAX and SMAC knockdowns validated this model prediction. We further validated the model using data of the NCI-60 cell line panel using BAX protein expression as a cell-line specific parameter and show that model simulations correlated with the cellular response to DNA damaging drugs and established a defined threshold for caspase activation that could distinguish between sensitive and resistant melanoma cells. In summary, we present an experimentally validated dynamic model that summarises our current knowledge of how BAX and SMAC regulate the bistable properties of irreversible caspase activation during apoptosis.

Acid-catalysed liquid-to-solid transitioning of arylazoisoxazole photoswitches.

Molecular photoswitches play a vital role in the development of responsive materials. These molecular building blocks are particularly attractive when multiple stimuli can be combined to bring about physical changes, sometimes leading to unexpected properties and functions. The arylazoisoxazole molecular switch was recently shown to be capable of efficient photoreversible solid-to-liquid phase transitions with application in photoswitchable surface adhesion. Here, we show that the arylazoisoxazole forms thermally stable and photoisomerisable protonated Z- and E-isomers in an apolar aprotic solvent when the pKa of the applied acid is sufficiently low. The tuning of isomerisation kinetics from days to seconds by the pKa of the acid not only opens up new reactivity in solution, but also the solid-state photoswitching of azoisoxazoles can be efficiently reversed with selected acid vapours, enabling acid-gated photoswitchable surface adhesion.

One molecule, two states: Single molecular switch on metallic electrodes

AbstractThe state‐of‐the‐art density functional theory (DFT) has become an essential tool for the investigation and development of molecular electronics at the electronic and atomic level. In this review paper, we show several typical examples to demonstrate that the DFT approaches, combined with nonequilibrium Green's function method, are able to design many prominent molecular switches—the most fundamental component in molecular electronics that can be utilized in information storage and logic gates. We mainly review the progress and important features of four remarkable switches with distinct transition mechanisms: (a) azobenzene‐like switches based on the cis–trans isomerization; (b) diarylethene‐like switches based on open‐closed transition; (c) porphyrin‐like switches based on tautomerizations; and (d) benzene‐like switches based on the physisorbed state and chemisorbed state. Special attentions have been paid on the molecular configuration, switching mechanism, and the role of van der Waals forces between the molecules and the metallic electrodes. We also summarize the avenues to effectively tailor the bistability, reversibility, and transport properties of these systems.This article is categorized under: Structure and Mechanism > Computational Materials Science Electronic Structure Theory > Density Functional Theory

DARPP-32 40 years later.

DARPP-32 (dopamine- and cAMP-regulated phosphoprotein with an apparent Mr of 32,000), now also known as phosphoprotein phosphatase 1 regulatory subunit 1B (PPP1R1B), is a potent inhibitor of protein phosphatase 1 (PP1, also known as PPP1) when phosphorylated at Thr34 by cAMP-dependent protein kinase (PKA). DARPP-32 exhibits a remarkable regional distribution in brain, roughly similar to that of dopamine innervation. Its discovery was a culmination of the long-standing effort of Paul Greengard to understand the mechanisms through which neurotransmitters such as dopamine exert their effects on target neurons. DARPP-32 is particularly enriched in striatal projection neurons where it is regulated by numerous signals through which it integrates and amplifies responses to many stimuli. Molecular studies of DARPP-32 have revealed that its regulation and function are more complex than anticipated. It is phosphorylated on multiple sites by several protein kinases that modulate DARPP-32 properties. Primarily, when phosphorylated at Thr34 DARPP-32 is a potent inhibitor of PP1, whereas when phosphorylated at Thr75 by Cdk5 it inhibits PKA. Phosphorylation at serine residues by CK1 and CK2 modulates its intracellular localization and its sensitivity to kinases or phosphatases. Modeling studies provide evidence that the signaling pathways including DARPP-32 are endowed of strong robustness and bistable properties favoring switch-like responses. Thus DARPP-32 combined with a set of other distinct signaling molecules enriched in striatal projection neurons plays a key role in the characteristic properties and physiological function of these neurons.

Geometry-Based Thick Origami Simulation

Abstract Origami is the art of creating a three-dimensional (3D) shape by folding paper. It has drawn much attention from researchers, and the designs that origami has inspired are used in various engineering applications. Most of these designs are based on familiar origami patterns and their known deformations, but origami patterns were originally intended for materials of near-zero thickness, primarily paper. To use the designs in engineering applications, it is necessary to simulate origami in a way that enables designers to explore and understand the designs while taking the thickness of the material to be folded into account. Because origami is primarily a problem in geometric design, this paper develops a geometric simulation for thick origami. The actuation, constraints, and assignment of mountain and valley folds in origami are also incorporated into the geometric formulation. The experimental results show that the proposed method is efficient and accurate. The method can successfully simulate a flat-foldable degree-four vertex, two different action origami, the bistable property of a waterbomb base, and the elasticity of non-rigid origami panels.

Multistable shells with designable configurations based on localized nanocrystallization processes

Highly multistable shells of designable configurations are proposed for morphing surfaces, which are manufactured by using nanocrystallization process, i.e. surface mechanical attrition treatment (SMAT). Through a localized treatment, the nanostructuring process can bring bistable properties for localized regions, whose configurations were determined by their shapes and sizes. With coupled deformations among multiple nanostructured regions, the processed shell can hold different stable configurations with localized bistable regions capping toward different sides. The stable configurations are determined by the shapes and sizes of the localized bistable regions and their in-plane distributions. Furthermore, the stable configurations of the multistable shells can be further mechanically modified by plastic bending. To guide the design and investigation of the multistable behavior, finite element analysis and experimental work have been conducted to correlate the stable configurations to design parameters, including shapes and sizes of the localized nanostructuring regions, their pattern distributions, applied mechanical processes as well as boundary conditions.

Dynamic Behaviors of a Single Species Stage Structure Model with Michaelis–Menten-TypeJuvenile Population Harvesting

A single species stage structure model with Michaelis–Menten-type juvenile population harvesting is proposed and investigated. The existence and local stability of the model equilibria are studied. It shows that for the model, two cases of bistability may exist. Some conditions for the global asymptotic stability of the boundary equilibrium are derived by constructing some suitable Lyapunov functions. After that, based on the Bendixson–Dulac discriminant, we obtain the sufficient conditions for the global asymptotic stability of the internal equilibrium. Our study shows that nonlinear harvesting can make the dynamics of the system more complex than linear harvesting; for example, the system may admit the bistable stability property. Numeric simulations support our theoretical results.

Earwig fan designing: Biomimetic and evolutionary biology applications

Technologies to fold structures into compact shapes are required in multiple engineering applications. Earwigs (Dermaptera) fold their fanlike hind wings in a unique, highly sophisticated manner, granting them the most compact wing storage among all insects. The structural and material composition, in-flight reinforcement mechanisms, and bistable property of earwig wings have been previously studied. However, the geometrical rules required to reproduce their complex crease patterns have remained uncertain. Here we show the method to design an earwig-inspired fan by considering the flat foldability in the origami model, as informed by X-ray microcomputed tomography imaging. As our dedicated designing software shows, the earwig fan can be customized into artificial deployable structures of different sizes and configurations for use in architecture, aerospace, mechanical engineering, and daily use items. Moreover, the proposed method is able to reconstruct the wing-folding mechanism of an ancient earwig relative, the 280-million-year-old Protelytron permianum This allows us to propose evolutionary patterns that explain how extant earwigs acquired their wing-folding mechanism and to project hypothetical, extinct transitional forms. Our findings can be used as the basic design guidelines in biomimetic research for harnessing the excellent engineering properties of earwig wings, and demonstrate how a geometrical designing method can reveal morphofunctional evolutionary constraints and predict plausible biological disparity in deep time.