Bistable Response Research Articles

Subwavelength plasmonic kinks in arrays of metallic nanoparticles

We analyze nonlinear effects in optically driven arrays of nonlinear metallic nanoparticles. We demonstrate that such plasmonic systems are characterized by a bistable response, and they can support the propagation of dissipative switching waves (or plasmonic kinks) connecting the states with different polarization. We study numerically the properties of such plasmonic kinks which are characterized by a subwavelength extent and a tunable velocity.

Reading and writing operations of memory device in micro-electromechanical resonator

Micro-electromechanical resonators substantially exhibit bistable and hysteretic response when nonlinear characteristics appear. Badzey et al. reported that the nonlinear micro-electromechanical resonators can be used as a mechanical 1 bit memory. Based on their results, the authors propose reading and writing operations of the memory device. The reading and writing operations imply a displacement measurement and a switching of two stable periodic vibrations, respectively. In this paper, we realize a displacement measurement along an approach avoiding supplemented sensors. In addition, we achieve the switching operation between two coexisting periodic states by a displacement feedback control.

Bi-stability, hysteresis, and memory of voltage-gated lysenin channels

Lysenin, a 297 amino acid pore-forming protein extracted from the coelomic fluid of the earthworm E. foetida, inserts constitutively open large conductance channels in natural and artificial lipid membranes containing sphingomyelin. The inserted channels show voltage regulation and slowly close at positive applied voltages. We report on the consequences of slow voltage-induced gating of lysenin channels inserted into a planar Bilayer Lipid Membrane (BLM), and demonstrate that these pore-forming proteins constitute memory elements that manifest gating bi-stability in response to variable external voltages. The hysteresis in macroscopic currents dynamically changes when the time scale of the voltage variation is smaller or comparable to the characteristic conformational equilibration time, and unexpectedly persists for extremely slow-changing external voltage stimuli. The assay performed on a single lysenin channel reveals that hysteresis is a fundamental feature of the individual channel unit and an intrinsic component of the gating mechanism. The investigation conducted at different temperatures reveals a thermally stable reopening process, suggesting that major changes in the energy landscape and kinetics diagram accompany the conformational transitions of the channels. Our work offers new insights on the dynamics of pore-forming proteins and provides an understanding of how channel proteins may form an immediate record of the molecular history which then determines their future response to various stimuli. Such new functionalities may uncover a link between molecular events and macroscopic processing and transmission of information in cells, and may lead to applications such as high density biologically-compatible memories and learning networks.

Robust Network Topologies for Generating Switch-Like Cellular Responses

Signaling networks that convert graded stimuli into binary, all-or-none cellular responses are critical in processes ranging from cell-cycle control to lineage commitment. To exhaustively enumerate topologies that exhibit this switch-like behavior, we simulated all possible two- and three-component networks on random parameter sets, and assessed the resulting response profiles for both steepness (ultrasensitivity) and extent of memory (bistability). Simulations were used to study purely enzymatic networks, purely transcriptional networks, and hybrid enzymatic/transcriptional networks, and the topologies in each class were rank ordered by parametric robustness (i.e., the percentage of applied parameter sets exhibiting ultrasensitivity or bistability). Results reveal that the distribution of network robustness is highly skewed, with the most robust topologies clustering into a small number of motifs. Hybrid networks are the most robust in generating ultrasensitivity (up to 28%) and bistability (up to 18%); strikingly, a purely transcriptional framework is the most fragile in generating either ultrasensitive (up to 3%) or bistable (up to 1%) responses. The disparity in robustness among the network classes is due in part to zero-order ultrasensitivity, an enzyme-specific phenomenon, which repeatedly emerges as a particularly robust mechanism for generating nonlinearity and can act as a building block for switch-like responses. We also highlight experimentally studied examples of topologies enabling switching behavior, in both native and synthetic systems, that rank highly in our simulations. This unbiased approach for identifying topologies capable of a given response may be useful in discovering new natural motifs and in designing robust synthetic gene networks.

System-level feedbacks make the anaphase switch irreversible

The mitotic checkpoint prevents a eukaryotic cell from commencing to separate its replicated genome into two daughter cells (anaphase) until all of its chromosomes are properly aligned on the metaphase plate, with the two copies of each chromosome attached to opposite poles of the mitotic spindle. The mitotic checkpoint is exquisitely sensitive in that a single unaligned chromosome, 1 of a total of ~50, is sufficient to delay progression into anaphase; however, when the last chromosome comes into alignment on the metaphase plate, the mitotic checkpoint is quickly satisfied, and the replicated chromosomes are rapidly partitioned to opposite poles of the dividing cell. The mitotic checkpoint is also curious in the sense that, before metaphase alignment, chromosomes that are not being pulled in opposite directions by the mitotic spindle activate the checkpoint, but during anaphase, these same tensionless chromosomes can no longer activate the checkpoint. These and other puzzles associated with the mitotic checkpoint are addressed by a proposed molecular mechanism, which involves two positive feedback loops that create a bistable response of the checkpoint to chromosomal tension.

Planform effects upon the bistable response of cross-ply composite shells

This research aims at investigating the bistable characteristics of unsymmetric cross-ply laminates resulting from thermally induced stresses while curing. The bistable characteristics are examined with a focus on the change in geometry for a subset of configurations, namely, rectangular, trapezoidal and triangular. To this end, these geometries are systematically investigated leading to a set of non-dimensional parameters establishing the values required for bistable behavior. A new apparatus is designed to measure the magnitude of the force required for snap-through and snap-back. The influence of friction at the supports of the tested panels is minimized by utilizing air cushion for frictionless motion. Predictions from a nonlinear finite element based methodology using the ABAQUS™ code are validated through comparisons with test data.

Nonlinear dynamics of double-cavity optical bistability of a three-level ladder system

We present non-linear dynamical features of two-photon double-cavity optical bistability exhibited by a three level ladder system in the mean field limit. The system exhibits a hump like feature in the lower branch of the bistable response, wherein a new region of instability develops. The system displays a range of dynamical features varying from normal stable switching, periodic self-pulsing to a period-doubling route to chaos. The inclusion of two competing cooperative atom-field couplings leads to such rich nonlinear dynamical behavior. We provide a domain map that clearly delineates the various regions of stability that will aid the realization of any desired dynamics. We also present bifurcation diagram and the associated supporting evidence that clearly identifies the period-doubling route to chaos, which occurs at low input light levels.

Bistable and Self-Tunable Negative-Index Metamaterial at Optical Frequencies

We introduce a metamaterial design composed of square plasmonic loops loaded by Kerr nonlinearities that combines enhanced nonlinear response with strong artificial magnetism, ensuring a negative refractive index with bistable and self-tunable response. We verify with full-wave simulations that positive-to-negative switching of refractive index may be obtained with moderate loss. The design of a finite-size metamaterial prism is also presented, supporting at the same frequency, and for the same light intensity, positive or inverted Snell refraction as a function of its previous excitation history.

Bistable responses in bacterial genetic networks: Designs and dynamical consequences

A key property of living cells is their ability to react to stimuli with specific biochemical responses. These responses can be understood through the dynamics of underlying biochemical and genetic networks. Evolutionary design principles have been well studied in networks that display graded responses, with a continuous relationship between input signal and system output. Alternatively, biochemical networks can exhibit bistable responses so that over a range of signals the network possesses two stable steady states. In this review, we discuss several conceptual examples illustrating network designs that can result in a bistable response of the biochemical network. Next, we examine manifestations of these designs in bacterial master-regulatory genetic circuits. In particular, we discuss mechanisms and dynamic consequences of bistability in three circuits: two-component systems, sigma-factor networks, and a multistep phosphorelay. Analyzing these examples allows us to expand our knowledge of evolutionary design principles networks with bistable responses.

Analysis on Bistable Response of a Disk-Rod-Fastening Rotor

In the view of the fault of bistable response appeared in the disk-rod-fastening rotor, the peculiar structure of this kind rotor was taken into account in this paper. By considering the influence of contact effect of discontinuous interfaces on the rotor stiffness, the tie-rod and the contact surface between the wheel disks were equated to a bending resistance spring with nonlinear stiffness. Then the equation of motion of the disk-rod-fastening rotor was put forward according to this simplification. The vibration characteristics of rotor was calculated by the harmonic balance method that combined with the predict-correct and homotopy arithmetic. The bistable response behaviors recurred in this simplified model was much closer to the measured results in flying. The study showed that the nonlinear factor of stiffness, resulted from the contact effect of discontinuous interfaces, was the main reason which led to the appearance of bistable response in the disk-rod-fastening rotor.

Design and Construction of a Versatile Synthetic Network for Bistable Gene Expression in Mammalian Systems

We constructed and modeled a novel synthetic network which may be able to exhibit bistable expression of a reporter gene in mammalian cells. This network is based on an aptamer-fused short-hairpin RNA (shRNA) directed against a single mRNA encoding both a EGFP reporter gene and the repressor tTR-KRAB, which, in turn, represses transcription of the shRNA. The activity of the shRNA can be controlled by an inducer molecule (theophylline) which prevents the aptamer-fused shRNA to be properly processed. Repression of the tTR-KRAB can be relieved by treatment with doxycyline. This reciprocal negative feed-back loop can exhibit a bistable response, as shown through the mathematical analysis performed here. Specifically, the network can be controlled to induce sustained expression of a shRNA, or the reporter gene, with a transient input of two different inducer molecules.

Identifying New Variables During Infection: Proximity to the Host Epithelium and Epigenetic Programs Alter the Expression of Virulence Factors in Vibrio Cholerae

Identifying New Variables During Infection: Proximity to the Host Epithelium and Epigenetic Programs Alter the Expression of Virulence Factors in Vibrio Cholerae

Synthetic conversion of a graded receptor signal into a tunable, reversible switch

The ability to engineer an all-or-none cellular response to a given signaling ligand is important in applications ranging from biosensing to tissue engineering. However, synthetic gene network 'switches' have been limited in their applicability and tunability due to their reliance on specific components to function. Here, we present a strategy for reversible switch design that instead relies only on a robust, easily constructed network topology with two positive feedback loops and we apply the method to create highly ultrasensitive (n(H)>20), bistable cellular responses to a synthetic ligand/receptor complex. Independent modulation of the two feedback strengths enables rational tuning and some decoupling of steady-state (ultrasensitivity, signal amplitude, switching threshold, and bistability) and kinetic (rates of system activation and deactivation) response properties. Our integrated computational and synthetic biology approach elucidates design rules for building cellular switches with desired properties, which may be of utility in engineering signal-transduction pathways.

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

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

Optical nanoantenna arrays loaded with nonlinear materials

Optical nanoantennas loaded by nanoparticles are used to provide large and controllable field enhancement at the nanoscale. Here we show how the introduction of nonlinearities at the nanoload may realize a whole set of all-optical nanoscale functionalities, such as memories, switches and transistors, as a function of whether the nanoantenna is excited ``below'' or ``above'' its resonance frequency. After discussing the main features of this nonlinear nanoantenna operation, we employ its bistable and self-tunable response in a planar array design, which may constitute different nonlinear devices and functionalities of significant interest for optical computing applications.

Digital and Analog Modes of Stat5 Signaling Regulate Basal and Stress Erythropoiesis

AbstractAbstract 4766Erythropoietin concentration in serum spans three orders of magnitude as it regulates erythropoietic rates in basal and stress erythropoiesis. It is not clear how Epo concentration is encoded intracellularly to generate the required erythropoietic rate. Stat5 activation by the Epo receptor (EpoR) is required for both basal and stress erythropoiesis. We asked whether dynamic properties of Stat5 signaling, namely the manner in which the Stat5 signal intensity varies with time or with Epo concentration, might somehow encode downstream responses. To this end, we studied the Stat5 signaling response quantitatively in freshly-isolated single cells in mouse erythropoietic tissue, by flow cytometry. Using wild type mice, as well as mutant EpoR-HM mice expressing a truncated EpoR that lacks cytoplasmic domain tyrosines, we identified two modes of Stat5 signaling, digital and analog, which are specifically required for basal and stress erythropoiesis, respectively.We found that expression levels of the Stat5 protein are key in shaping the Stat5 signal. Early erythroblasts, 'S1' (Subset 1) cells, express high levels of of Stat5, and are able to respond to high Epo with a high intensity graded, or analog, signal. By contrast, mature erythroblasts, labeled 'S3' (Subset 3), express lower Stat5 levels, and their response to Epo is limited to a low intensity signal. We found that this low –intensity response is nevertheless decisive, responding to an Epo stimulus with a binary (or digital) 'on' or ‘off’ signal. The digital character of this low-intensity signal can be measured quantitatively: we found that its reposnse to increasing levels of Epo may be fitted by a Hill curve with a high Hill coefficient, similar in magnitude to that found for the cooperative binding of oxygen to hemoglobin.Mechanistically, the digital, low-intensity Stat5 signal is due to bistable Stat5 activation, in turn a result of a positive feedback interaction whereby phosphorylated Stat5 promotes further Stat5 phosphorylation. Following bistable activation, however, and in the presence of high Stat5 expression, Stat5 activation can increase further in a graded fashion, in response to increasing Epo levels. In mature S3 erythroblasts, however, in the absence of high Stat5 levels, no further increase in the signal occurs, giving rise to a digital behavior. Stat5 activation is therefore analogous to that of a dimmer light switch: a toggle-mechanism controls an initial bistable activation, giving rise to a low-level light signal; further graded rotation of a dial lower the circuit's resistance and gives rise to a graded increase in light intensity (Figure 1).We found that the EpoR-HM erythroblasts lost the ability to signal via the analog Stat5 signaling mode, but retained digital signaling. By comparing genetic models that either completely lack Stat5 function (the Stat5-/- mouse), or that specifically lack the graded, high intensity signal (the EpoR-HM mouse), we found that the digital, low-intensity signal was both necessary and sufficient for erythroblast survival and for maintenance of basal erythropoiesis. By contrast, the high intensity analog p-Stat5 signal was required for the response to erythropoietic stress, as seen from the inability of EpoR-HM mice to respond to stress. Further, we identified a specific gene target of analog Stat5 signaling during stress. We found that the stress-dependent upregulation of CD71 in early erythroblasts was absent in EpoR-HM. By exogenously expressing high levels of Stat5 in EpoR-HM erythroblasts in vitro, we were able to rescue both the analog high-intensity Stat5 signal in these cells, as well as their ability to express high CD71 in response to stress levels of Epo.We propose that the combined bistable and graded Stat5 signaling responses in early erythroblasts has evolved in order to generate a high fidelity response to Epo over its broad concentration range in basal and stress erythropoiesis. Digital low-intensity signaling transduces a clear signal in response to low-levels of Epo; whereas the ability to respond to higher levels of Epo with a graded, high intensity signal, is retained.This work was funded by NIH/NHLBI RO1 HL084168 and by American Cancer Society [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Nonlinear light propagation in the defect band of one-dimensional defective structures

In this paper we numerically investigate the nonlinear propagation of defect state in one-dimensional structures with defects. We investigate the nonlinear transmission spectra and the bistable response for defective structures with different index gradients. The results show that positive Kerr nonlinearity can suppress the Wannier–Stark localization. And the nonlinear response of defect states band exhibits an optical switch behavior, which may be applied to all-optical devices. And the gap solitons from these defect states are presented.

Switching and defect dynamics in multistable liquid crystal devices

We investigate the switching dynamics of multistable nematic liquid crystal devices. In particular, we identify a remarkably simple two-dimensional device which exploits hybrid alignment at the surfaces to yield a bistable response. We also consider a three-dimensional tristable nematic device with patterned anchoring, recently implemented in practice, and discuss how the director and disclination patterns change during switching.

Hysteresis in the Cell Response to Time-Dependent Substrate Stiffness

Mechanical cues like the rigidity of the substrate are main determinants for the decision-making of adherent cells. Here we use a mechano-chemical model to predict the cellular response to varying substrate stiffnesses. The model equations combine the mechanics of contractile actin filament bundles with a model for the Rho-signaling pathway triggered by forces at cell-matrix contacts. A bifurcation analysis of cellular contractility as a function of substrate stiffness reveals a bistable response, thus defining a lower threshold of stiffness, below which cells are not able to build up contractile forces, and an upper threshold of stiffness, above which cells are always in a strongly contracted state. Using the full dynamical model, we predict that rate-dependent hysteresis will occur in the cellular traction forces when cells are exposed to substrates of time-dependent stiffness.

Low-power optical bistability in a free-standing silicon ring resonator

We demonstrate low-power thermo-optic-based optical bistability in a free-standing silicon ring resonator. A bistable optical response is achieved at reduced pump powers by thermally isolating the ring resonator from its supporting substrate with an air gap. The conversion efficiency from optical power to temperature change in the silicon core is enhanced. The optical transfer function of the resulting free-standing resonator exhibits a hysteresis loop for 80 microW input optical power. Similar nonthermally isolated resonators at the same detuning do not exhibit a bistable mode for input powers less than 2 mW.