Theoretical and experimental study of a bi-stable piezoelectric energy harvester under hybrid galloping and band-limited random excitations

In the practical environment,it is very common for the simultaneous occurrence of base excitation and crosswind.Scavenging the combined energy of vibration and wind with a single energy harvesting structure is fascinating.For this purpose,the effects of the wind speed and random excitation level are investigated with the stochastic averaging method(SAM)based on the energy envelope.The results of the analytical prediction are verified with the Monte-Carlo method(MCM).The numerical simulation shows that the introduction of wind can reduce the critical excitation level for triggering an inter-well jump and make a bi-stable energy harvester(BEH)realize the performance enhancement for a weak base excitation.However,as the strength of the wind increases to a particular level,the influence of the random base excitation on the dynamic responses is weakened,and the system exhibits a periodic galloping response.A comparison between a BEH and a linear energy harvester(LEH)indicates that the BEH demonstrates inferior performance for high-speed wind.Relevant experiments are conducted to investigate the validity of the theoretical prediction and numerical simulation.The experimental findings also show that strong random excitation is favorable for the BEH in the range of low wind speeds.However,as the speed of the incoming wind is up to a particular level,the disadvantage of the BEH becomes clear and evident.

Bi-stable states of initially stressed elastic cylindrical shell structures with two piezoelectric surface layers

A theoretical model is proposed in this paper to predict the bi-stable states of initially stressed cylindrical shell structures attached by surface anisotropic piezoelectric layers.The condition for existence of bi-stability of the shell structural system is presented and analytical expressions for corresponding rolled-up radii of the stable shell are given based on the principle of minimum strain energy.The resulting solution indicates that the shell system may have two stable configurations besides its initial state under a combined action of the actuating electric field and initial stresses characterized by the bending moment.If the piezoelectric layer materials act as only sensor materials without the actuating electric field,initial stresses may produce the bi-stable states,but one corresponding to its initial state.For the shell without initial stresses,the magnitude in the actuating electric field determines the number of the stable states,one or two stable configurations besides the initial state.The theoretical prediction for the bi-stable states is verified by finite element method（FEM） simulation by using the ABAQUS code.

Transient transition behaviors of fractional-order simplest chaotic circuit with bi-stable locally-active memristor and its ARM-based implementation

This paper proposes a fractional-order simplest chaotic system using a bi-stable locally-active memristor.The characteristics of the memristor and transient transition behaviors of the proposed system are analyzed,and this circuit is implemented digitally using ARM-based MCU.Firstly,the mathematical model of the memristor is designed,which is nonvolatile,locally-active and bi-stable.Secondly,the asymptotical stability of the fractional-order memristive chaotic system is investigated and some sufficient conditions of the stability are obtained.Thirdly,complex dynamics of the novel system are analyzed using phase diagram,Lyapunov exponential spectrum,bifurcation diagram,basin of attractor,and coexisting bifurcation,coexisting attractors are observed.All of these results indicate that this simple system contains the abundant dynamic characteristics.Moreover,transient transition behaviors of the system are analyzed,and it is found that the behaviors of transient chaotic and transient period transition alternately occur.Finally,the hardware implementation of the fractional-order bi-stable locally-active memristive chaotic system using ARM-based STM32F750 is carried out to verify the numerical simulation results.

On the evolution of terrestrial planets:Bi-stability,stochastic effects,and the non-uniqueness of tectonic states

The Earth is the only body in the solar system for which significant observational constraints are accessible to such a degree that they can be used to discriminate between competing models of Earth's tectonic evolution.It is a natural tendency to use observations of the Earth to inform more general models of planetary evolution.However,our understating of Earth's evolution is far from complete.In recent years,there has been growing geodynamic and geochemical evidence that suggests that plate tectonics may not have operated on the early Earth,with both the timing of its onset and the length of its activity far from certain.Recently,the potential of tectonic bi-stability(multiple stable,energetically allowed solutions)has been shown to be dynamically viable,both from analytical analysis and through numeric experiments in two and three dimensions.This indicates that multiple tectonic modes may operate on a single planetary body at different times within its temporal evolution.It also allows for the potential that feedback mechanisms between the internal dynamics and surface processes(e.g.,surface temperature changes driven by long term climate evolution),acting at different thermal evolution times,can cause terrestrial worlds to alternate between multiple tectonic states over giga-year timescales.The implication within this framework is that terrestrial planets have the potential to migrate through tectonic regimes at similar‘thermal evolution times'(e.g.,points were they have a similar bulk mantle temperature and energies),but at very different'temporal times'(time since planetary formation).It can be further shown that identical planets at similar stages of their evolution may exhibit different tectonic regimes due to random variations.Here,we will discuss constraints on the tectonic evolution of the Earth and present a novel framework of planetary evolution that moves toward probabilistic arguments based on general physical principals,as opposed to particular rheologies,and incorporates the potential of tectonic regime transitions and multiple tectonics states being viable at equivalent physical and chemical conditions.

Harvesting base vibration energy by a piezoelectric inverted beam with pendulum

We proposed a two-degrees-of-freedom inverted piezoelectric beam with pendulum to promote the performance of vibration energy harvesting. This configuration is composed of an inverted elastic beam and a pendulum attached to its free end. The electromechanical equations governing the nonlinear system were derived. The harmonic balance method(HBM)is applied to solve the equation and the results prove that there exists a 1:3 super-harmonic resonance. The simulation results show that owing to the particular nonlinearity, there appears a special bending effect in the amplitude-frequency response, i.e., bending right for the first natural frequency and left for the second natural frequency, which is beneficial for harvesting vibration energy. The HBM results are verified by the entity simulations. Furthermore, over a relatively wide range of power spectral density, it could reach a dense jumping and give a dense high pulse voltage.

A three dimensional implicit immersed boundary method with application

Most algorithms of the immersed boundary method originated by Peskin are explicit when it comes to the computation of the elastic forces exerted by the immersed boundary to the fluid. A drawback of such an explicit approach is a severe restriction on the time step size for maintaining numerical stability. An implicit immersed boundary method in two dimensions using the lattice Boltzmann approach has been proposed. This paper reports an extension of the method to three dimensions and its application to simulation of a massive flexible sheet interacting with an incompressible viscous flow.

Atom-loss-induced quantum optical bi-stability switch

We investigate the nonlinear dynamics of a system composed of a cigar-shaped Bose-Einstein condensate and an optical cavity with the two sides coupled dispersively.By adopting discrete-mode approximation for the condensate,taking atom loss as a necessary part of the model to analyze the evolution of the system,while using trial and error method to find out steady states of the system as a reference,numerical simulation demonstrates that with a constant pump,atom loss will trigger a quantum optical bi-stability switch,which predicts a new interesting phenomenon for experiments to verify.

Fear and delay effects on a food chain system with two kinds of different functional responses

For food chain system with three populations,direct predation is the basic interaction between species.Different species often have different predation functional responses,so a food chain system with Holling-II response for middle predator and Beddinton-DeAngelis response for top predator is proposed.Apart from direct predation,predator population can significantly impact the survival of prey population by inducing the prey's fear,but the impact often possesses a time delay.This paper is concentrated to explore how the fear and time delay affect the system stability and the species persistence.By use of Lyapunov functional method and bifurcation theory,the positiveness and boundedness of solutions,local and global behavior of species,the system stability around the equilibrium states and various kinds of bifurcation are investigated.Numerically,some simulations are carried out to validate the main findings and the critical values of the bifurcation parameters of fear and conversion rate are obtained.It is observed that fear and delay can not only stabilize,but also destabilize the system,which depends on the magnitude of the fear and delay.The system varies from unstable to stable due to the continuous increase of the prey's fear by middle predator.Small fear induced by top predator or small delay of the prey's fear can stabilize the system,while they are sufficiently large,the system stability is to be destroyed.Simultaneously,the conversion rate can also change the stability and even make the species to be extinct.Some rich dynamics like multiple stabilities and various types of bistability behaviors are also exhibited,which results in the convergence of the species from one stable equilibrium to another.

A soft gripper of fast speed and low energy consumption

Grasping of complicated objects is an active research area which is developing fast throughout the years. Soft grippers can be an effective solution, since they are capable of holding workpieces of various shapes and interacting with unstructured environments effectively. Soft grippers generally consist of soft, flexible and compliant materials, which are able to conform to the shape of the object so that the gripper will not deform or bruise the soft object. Fast grasping of objects with various sizes and shapes remains a challenging task for soft grippers. In the present article, a soft gripper based on bi-stable dielectric elastomer actuator(DEA) inspired by the insect-catching ability of the Venus flytrap, is designed. This soft gripper can achieve good performances in grasping various objects by a simple actuation system. The gripper can switch from one stable state to another when subject to an impulse voltage of 0.04 s. The time duration for each grasping action is 0.17 s, and no continuous voltage is required for holding the gripped object. Thus, energy consumption can be achieved as low as 0.1386 J per grasping action. The mechanism of achieving bi-stable states is related to the duration of impulse voltage applied and the resonant frequency of the structure. The present study demonstrates that bi-stable dielectric elastomer actuators are capable of achieving fast speed for grasping with very low energy consumption, which is significant in the applications to soft grippers and biomimetic robots.

Unraveling the dose-response puzzle of L.monocytogenes:A mechanistic approach

Food-borne disease outbreaks caused by Listeria monocytogenes continue to impose heavy burdens on public health in North America and globally.To explore the threat L.monocytogenes presents to the elderly,pregnant woman and immuno-compromised individuals,many studies have focused on in-host infection mechanisms and risk evaluation in terms of dose-response outcomes.However,the connection of these two foci has received little attention,leaving risk prediction with an insufficient mechanistic basis.Consequently,there is a critical need to quantifiably link in-host infection pathways with the doseresponse paradigm.To better understand these relationships,we propose a new mathematical model to describe the gastro-intestinal pathway of L.monocytogenes within the host.The model dynamics are shown to be sensitive to inoculation doses and exhibit bistability phenomena.Applying the model to guinea pigs,we show how it provides useful tools to identify key parameters and to inform critical values of these parameters that are pivotal in risk evaluation.Our preliminary analysis shows that the effect of gastroenvironmental stress,the role of commensal microbiota and immune cells are critical for successful infection of L.monocytogenes and for dictating the shape of the doseresponse curves.

Chaos control in a discrete-time predator-prey model with weak Allee effect

The stability of the predator-prey model subject to the Allee effect is an interesting topic in recent times.In this paper,we investigate the impact of weak Allee effect on the stability of a discrete-time predator-prey model with Holling type-IV functional response.The mathematical features of the proposed model are analyzed with the help of equilibrium analysis,stability analysis,and bifurcation theory.We provide sufficient conditions for the flip bifurcation by considering Allee parameter as the bifurcation parameter.We observe that the model becomes stable from chaotic dynamics as the Allee parameter increases.Further,we observe bi-stability behavior of the model between only prey existence equilibrium and the coexistence equilibrium.Our analytical findings are illustrated through numerical simulations.

PYRAMIDAL TRAVELING FRONTS OF BISTABLE REACTION-DIFFUSION EQUATIONS WITH DELAY

This paper is concerned with nonplanar traveling fronts for delayed reaction- diffusion equation with bistable nonlinearity in RTM （m〉 3）. By the comparison principle and super- and subsolutions technique, we establish the existence of pyra- midal traveling fronts.

A simple and effective method to achieve the successful start-up of a current reference

Start-up design is a critical issue in current reference as it is very closely related to production yield. However, its function is difficult to predict using normal transaction simulations before the device is put into diffusion. In this paper, we discuss a simple and effective simulation approach which ensures a successful start-up process in a self-biased temperature independent current reference. The circuit is implemented in a class-D power amplifier with a 0.35 #m BiCMOS process and the experimental result validates that, by using this method, the start-up success rate can be greatly improved to 100%.

Tuning of Multi-stability Profile and Transition Sequence of Stacked Miura-Origami Metamaterials

Multi-stable origami structures and metamaterials possess unique advantages and could exhibit multiple stable three-dimensional configurations,which have attracted widespread research interest and held promise for applications in many fields.Although a great deal of attention has been paid to the design and application of multi-stable origami structures,less knowledge is available about the transition sequence among different stable configurations,especially in terms of the fundamental mechanism and the tuning method.To fill this gap,with the multi-stable dual-cell stacked Miura-ori chain as a platform,this paper explores the rules that govern the configuration transition and proposes effective methods for tuning the transition sequence.Specifically,by correlating the energy evolution,the transition paths,and the associated force-displace-ment profiles,we find that the critical extension/compression forces of the component cells play a critical role in governing the transition sequence.Accordingly,we summarize the rules for predicting the transition sequence:the component cell that first reaches the critical force during quasi-static extension or compression will be the first to undergo a configuration switch.Based on these findings,two methods,i.e.,a design method based on crease-stiffness assignment and an online method based on internal pressure regulation,are proposed to tune the stability profile and the transition sequence of the multi-stable origami structure.The crease-stiffness design approach,although effective,cannot be employed for online tuning once the prototype has been fabricated.The pressure-based approach,on the other hand,has been shown experimentally to be effective in adjusting the constitutive force-displacement profiles of the component cells and,in turn,tuning the transition sequence according to the summarized rules.The results of this study will advance the state of the art of origami mechanics and promote the engineering applications of multi-stable origami metamaterials.