Hysteresis-like Behavior Research Articles

Hysteresis and bistability in synaptic transmission modeled as a chain of biochemical reactions with a positive feedback

In this paper, we employ computational analysis to investigate the long-term potentiation (LTP) and memory formation in synapses between neurons. We use a mathematical model describing the synaptic transmission as a signal transduction pathway with a positive feedback loop formed by diffusion of nitric oxide (NO) to the presynaptic site. We found that the model of synaptic transmission exhibits a hysteresis-like behavior, where the strength of synaptic transmission depends not just on instantaneous interstimulus intervals, but also on the history of activity. The switching between resting and memory states can be induced by physiologically relevant and moderate (less than 50%) changes in the duration of interstimulus intervals.

Delayed Hopf bifurcation and control of a ferrofluid interface via a time-dependent magnetic field.

A ferrofluid droplet confined in a Hele-Shaw cell can be deformed into a stably spinning "gear," using crossed magnetic fields. Previously, fully nonlinear simulation revealed that the spinning gear emerges as a stable traveling wave along the droplet's interface bifurcates from the trivial (equilibrium) shape. In this work, a center manifold reduction is applied to show the geometrical equivalence between a two-harmonic-mode coupled system of ordinary differential equationsarising from a weakly nonlinear analysis of the interface shape and a Hopf bifurcation. The rotating complex amplitude of the fundamental mode saturates to a limit cycle as the periodic traveling wave solution is obtained. An amplitude equationis derived from a multiple-time-scale expansion as a reduced model of the dynamics. Then, inspired by the well-known delay behavior of time-dependent Hopf bifurcations, we design a slowly time-varying magnetic field such that the timing and emergence of the interfacial traveling wave can be controlled. The proposed theory allows us to determine the time-dependent saturated state resulting from the dynamic bifurcation and delayed onset of instability. The amplitude equationalso reveals hysteresislike behavior upon time reversal of the magnetic field. The state obtained upon time reversal differs from the state obtained during the initial (forward-time) period, yet it can still be predicted by the proposed reduced-order theory.

Optically tunable guide-mode resonance grating based on VO2 phase transition material

In this paper, highly efficient tunable guide-mode resonance (GMR) grating patterned on top of a film of the phase transition material, vanadium dioxide (VO2), is demonstrated. The optimal optical transmission and tuning can be achieved by optimizing the device structure. Based on the large insulator-to-metal transition (IMT) characteristic tuned by thermally driven of VO2 in the near-infrared range, we show that the full width at half maximum (FWHM) of about 100 nm of the transmittance resonance spectra of the dielectric GMR in VO2 grating offers remarkable extinction modulation depths (68%) at 1535 nm for tunability. The tunability is accompanied by a hysteresis-like behavior that can be exploited for versatile memory effects. In addition, we experimentally demonstrate tuning of the reflection phase over 20°. This work further improves the research topic of GMR and expands the design of novel reconfigurable devices for photonics.

Spatial and temporal variation in δ13C values of methane emitted from a hemiboreal mire: methanogenesis, methanotrophy, and hysteresis

Abstract. The reasons for spatial and temporal variation in methane emission from mire ecosystems are not fully understood. Stable isotope signatures of the emitted methane can offer clues to the causes of these variations. We measured the methane emission (FCH4) and 13C signature (δ13C) of emitted methane by automated chambers at a hemiboreal mire for two growing seasons. In addition, we used ambient methane mixing ratios and δ13C to calculate a mire-scale 13C signature using a nocturnal boundary-layer accumulation approach. Microbial methanogenic and methanotrophic communities were determined by a captured metagenomics analysis. The chamber measurements showed large and systematic spatial variations in δ13C-CH4 of up to 15 ‰ but smaller and less systematic temporal variation. According to the spatial δ13C–FCH4 relations, methanotrophy was unlikely to be the dominating cause for the spatial variation. Instead, these were an indication of the substrate availability of methanogenesis being a major factor in explaining the spatial variation. Genetic analysis indicated that methanogenic communities at all sample locations were able to utilize both hydrogenotrophic and acetoclastic pathways and could thus adapt to changes in the available substrate. The temporal variation in FCH4 and δ13C over the growing seasons showed hysteresis-like behavior at high-emission locations, indicative of time-lagged responses to temperature and substrate availability. The upscaled chamber measurements and nocturnal boundary-layer accumulation measurements showed similar average δ13C values of −81.3 ‰ and −79.3 ‰, respectively, indicative of hydrogenotrophic methanogenesis at the mire. The close correspondence of the δ13C values obtained by the two methods lends confidence to the obtained mire-scale isotopic signature. This and other recently published data on δ13C values of CH4 emitted from northern mires are considerably lower than the values used in atmospheric inversion studies on methane sources, suggesting a need for revision of the model input.

Thermal Conductivity Evolution of Carbon-Fiber Ablators Submitted to High Temperatures

Carbon-phenolic ablators are widely used as thermal protection materials for atmospheric entry capsules. The knowledge of their thermophysical properties is therefore of primary importance to correctly simulate their thermal response, eventually reducing design safety margins without the risk of compromising the integrity of the underlying vehicle structure and payload. In this work, we present the results of an experimental work that aimed to evaluate the effective thermal conductivity of the carbon-phenolic ablator ZURAM® in its charred state. The material thermal conductivity was obtained, up to 2790°C, using the available heat-capacity law for this material, ad hoc laser flash analysis thermal diffusivity measurements, and material density estimates. The results suggest a strong impact of the material heating history on the thermal conductivity. As a consequence of this hysteresis-like behavior, measurements taken during the heating or the cooling phases differ sensibly, with discrepancies far beyond the quantified experimental uncertainties. Heating-phase measurements follow a specific trend and could be reduced to a fitting polynomial law with associated error bounds. Measurements performed during the cooling phase seem to be affected by a modification process of the material intrinsic properties that is speculated to be related to the graphitization of the carbon fibers composing the material.

The influence of aspect ratio on flow states in the buoyancy-driven turbulence with free slip boundaries

Buoyancy driven turbulence with free-slip top and bottom plates in a confined box is studied via direct numerical simulations (DNS). The Rayleigh number is fixed to Ra=108 and the Prandtl number is Pr=10. The length/height aspect ratio Γy is fixed to 2, while the depth/height aspect ratio Γx varies from 0.125 to 0.3. With the variation of Γx, the hysteresis-like behavior of the heat and momentum transfer is found due to the emergence of two stable states of flow organization. For small Γx, the sheared flow occurs with disordered plumes occupying the entire bulk region, while it is replaced by convection rolls with increasing Γx. The striking feature is that the heat and momentum transport is greatly suppressed in the shear flow (SF) state, compared with that in the convection roll (CR) state. The turbulent kinetic energy budget is performed to delineate the relative contributions of physical processes that govern energy transport. It is found that the kinetic energy in the SF state is mainly produced by the buoyancy force, while it is dominated by the shear production near the plates in the CR state. During energy transport, it seems that the buoyancy force plays a more important role in the SF state than in the CR state, particularly in the bulk. Furthermore, through the analysis of dynamic mode decomposition of temperature fields, we illustrate that the flow in the SF state is dominated by the cloud-like spatially coherent structures with low frequencies, while the low-frequency roll structures play a leading role in the CR state. The flow state transition from SF to CR corresponds to the process that the cloud-like coherent structures form roll structures.

Adaptive network approach for emergence of societal bubbles

Far beyond its relevance for commercial and political marketings, opinion formation and decision making processes are central for representative democracy, government functioning, and state organization. In the present report, a stochastic agent-based model is investigated. The model assumes that bounded confidence and homophily mechanisms drive both opinion dynamics and social network evolution through either rewiring or breakage of social contacts. In addition to the classical transition from global consensus to opinion polarization, our main findings are (i) a cascade of fragmentation of the social network into echo chambers (modules) holding distinct opinions and rupture of the bridges interconnecting these modules as the tolerance for opinion differences increases. There are multiple surviving opinions associated to these modules within which consensus is formed; and (ii) the adaptive social network exhibits a hysteresis-like behavior characterized by irreversible changes in its topology as the opinion tolerance cycles from radicalization towards consensus and backward to radicalization.

Two-phase tension of a carbon nanotube

Heterostructures consisting of new two-dimensional nanomaterials may possess non-trivial physical and mechanical properties, promising for many applications. It is interesting that in some cases it is possible to create heterostructures simultaneously consisting of weakly and strongly stretched domains having the same chemical composition, as have been witnessed earlier for some polymer chains, DNA, and intermetallic nanofibres that demonstrate the effect of two-phase stretching. These materials with relatively large tensile forces tend to split into domains with less and greater tensile deformation. Within the two-phase region of deformation, the average deformation of the sample increases with a constant tensile force, with the growth of a domain with a higher strain due to a domain with a lower strain. In this paper, the two-phase stretching of carbon nanotubes has been studied by means of molecular dynamics simulation. It has been established that the load-deflection curves during axial tension exhibit hysteresis-like behavior due to energy dissipation during nucleation and motion of domain walls. It is shown that in the two-phase tension regime, a carbon nanotube is a special case of a heterostructure, the properties of which can be controlled by changing the size of the domains of each phase by applying elastic deformation.

Voltage-driven strain-induced coexistence of both volatile and non-volatile interfacial magnetoelectric behaviors in LSMO/PMN-PT (0 0 1)

We report on the inhomogeneous electric field response of the magnetization in a La1−xSrxMnO3 (LSMO) film on a ferroelectric [Pb(Mg1/2Nb2/3)O3]1−x-[PbTiO3]x (PMN-PT) substrate. X-ray diffraction patterns of the LSMO film confirm successful epitaxial growth of LSMO along the [0 0 1] orientation of PMN-PT, where a sudden lattice relaxation in the LSMO film occurs due to a large lattice mismatch. The LSMO film exhibits magnetic anisotropy that lies in-plane and isotropic in all directions of the plane with a Curie temperature of 345 K. The polarization versus electric field (P–E) loop shows that a sharp switching of electric dipoles occurs and the switching field decreases with decreasing maximum applied electric field. The coexistence of hysteresis-like (non-volatile) and butterfly-like (volatile) behavior of the voltage induced Kerr signal is observed. We consider that 109° switching of the ferroelectric domains is responsible for the rotation of magnetic easy axis that results in the hysteresis like behavior while 71° and 180° switching of the ferroelectric polarization has no effect on the magnetic anisotropy, leading to the butterfly-like behavior.

Effect of Background Magnetic Field on Type-II Superconductor under Oscillating Magnetic Field Simulated Using Ginzburg-Landau Model

Cubic superconducting sample was simulated using time-dependent Ginzburg-Landau model under oscillating magnetic field with and without additional background static magnetic field. Vortex dynamics including entrance and exit from the sample was simulated. Magnetization and carrier concentration densities of the sample were studied as a function of external magnetic field variations. Anomalies in carrier concentration density were observed at certain values of the magnetic field which were correlated with the entrance and exit processes of vortices. Area swept by superconductor magnetization with magnetic field was observed to have a hysteresis-like behavior where area representing energy dissipated per cycle. This energy accumulation was suggested to cause instability in superconductor over the number of cycles and may result in thermal quenching. Temporal distribution of energy components showed consistency with the pattern observed for carrier concentration and magnetization under oscillating magnetic field. Rapid phase changes with magnetic oscillations resulted in oscillations in energy components, and irregular peaks and ripples in superconducting energy represent the situation of exit and entry of vortices. While the rise in interaction energy with cycles is referred to vortex relaxation time in a cycle, this energy is expected to accumulate and take other forms (e.g., heat) and is predicted to cause thermal quenching. In the presence of background static magnetic field, this energy dissipation was calculated to increase significantly while superconductor is subjected to oscillating magnetic field.

Graphene nanoribbon as an elastic damper

Heterostructures composed of dissimilar two-dimensional nanomaterials can have nontrivial physical and mechanical properties which are potentially useful in many applications. Interestingly, in some cases, it is possible to create heterostructures composed of weakly and strongly stretched domains with the same chemical composition, as has been demonstrated for some polymer chains, DNA, and intermetallic nanowires supporting this effect of two-phase stretching. These materials, at relatively strong tension forces, split into domains with smaller and larger tensile strains. Within this region, average strain increases at constant tensile force due to the growth of the domain with the larger strain, at the expense of the domain with smaller strain. Here, the two-phase stretching phenomenon is described for graphene nanoribbons with the help of molecular dynamics simulations. This unprecedented feature of graphene that is revealed in our study is related to the peculiarities of nucleation and the motion of the domain walls separating the domains of different elastic strain. It turns out that the loading–unloading curves exhibit a hysteresis-like behavior due to the energy dissipation during the domain wall nucleation and motion. Here, we put forward the idea of implementing graphene nanoribbons as elastic dampers, efficiently converting mechanical strain energy into heat during cyclic loading–unloading through elastic extension where domains with larger and smaller strains coexist. Furthermore, in the regime of two-phase stretching, graphene nanoribbon is a heterostructure for which the fraction of domains with larger and smaller strain, and consequently its physical and mechanical properties, can be tuned in a controllable manner by applying elastic strain and/or heat.

Electrical conduction in a transformer oil-based magnetic nanofluid under a DC electric field

In this paper, we report on the experimental study of the direct current electrical conduction in a magnetic nanofluid based on transformer oil and iron oxide nanoparticles stabilized with oleic acid. We present the current–voltage characteristics of the pure transformer oil and the magnetic nanofluid with various particle volume fractions. From the Ohmic region, we calculate the electrical conductivity values and confirm the effect of increasing conductivity with increasing particle volume fraction. A few sources of space charge have been taken into account, among which the ion impurities play the key role. It was found that the current–voltage characteristics exhibit the inverse hysteresis-like behavior. Then, we focus on the magnetic field influence on the hysteresis behavior of a selected sample. The external magnetic field was applied in both, parallel and perpendicular configuration in regard to the electric field direction. It is shown that the magnetic field acting on the magnetic nanofluid in the perpendicular configuration results in the remarkable thinning of the current–voltage inverse hysteresis loop.

Simultaneous measurement of unfrozen water content and hydraulic conductivity of partially frozen soil near 0 °C

It is important to know the unfrozen water content and hydraulic conductivity of frozen soils when assessing water, heat, and solute transport in freezing and thawing soils for frozen soil engineering. To study these effects, an Andisol was packed into an acrylic column with an inner diameter of 70mm and a height of 30mm. First, the soil was frozen and thawed at different rates, and the soil freezing and thawing curves were measured. Second, water was added to flow through the thawing soil, and change in hydraulic conductivity with temperature was measured simultaneously with the thawing curve. The frozen soil contained more unfrozen water under a faster freezing rate and less unfrozen water under a faster thawing rate, resulting in a hysteresis-like behavior in the soil freezing and thawing curves. This is considered to be related to the pore ice growth lagging behind the change in the bulk soil temperature. Frozen soil below −0.5°C was practically impermeable. When water flows through a frozen soil, the soil has a higher unfrozen water content than without water flow. For a temperature increase from −0.5 to −0.2°C, the hydraulic conductivity increased by more than four orders of magnitude with increasing unfrozen water content. No significant difference was observed in the hydraulic conductivity of soils with different bulk densities or water flow rates. The hydraulic conductivity of the frozen soil was higher than that estimated from the unsaturated hydraulic conductivity of unfrozen soil through the Clausius–Clapeyron equation. This is likely related to the frozen soil having more unfrozen water than the amount estimated from the water retention curve of the unfrozen soil. At temperatures warmer than −0.2°C, the hydraulic conductivity approached a constant value, while the unfrozen water content continuously increased. Near 0°C, pore ice, which does not contribute to the water flow path, would remain frozen such as in inner-aggregate pores.

Effect of thermal annealing on the spin Seebeck effect in Pt/Ni81Fe19 at room temperature

The spin Seebeck effect was observed in Pt/Ni81Fe19. Hysteresis-like behavior was discovered, and the saturated voltage was proportional to the temperature gradient. The measured voltage increased as the Pt thickness was decreased, because the injected spin current intensity drastically decreased. Thermal annealing temperature also strongly affected the observed voltage, which was lower at higher thermal annealing temperatures. The anomalous Nernst effect was also observed in Ni81Fe19 films of various thicknesses. The voltage was nearly constant when the Ni81Fe19 film was thicker than 30nm but drastically decreased for lesser thicknesses.

Solar irradiance in the heterogeneous albedo environment of the Arctic coast: measurements and a 3-D model study

Abstract. We present a unique case study of the solar global irradiance in a highly heterogeneous albedo environment at the Arctic coast. Diodearray spectroradiometers were deployed at three sites around Ny Ålesund, Svalbard, and spectral irradiances were simultaneously measured under clear-sky conditions during a 24 h period. The 3-D radiative transfer model MYSTIC is applied to simulate the measurements in various model scenarios. First, we model the effective albedos of ocean and snow and consequently around each measurement site. The effective albedos at 340 nm increase from 0.57 to 0.75, from the coastal site in the west towards the site 20 km east, away from the coast. The observed ratios of the global irradiance indicate a 15% higher average irradiance, at 340 nm east relative to west, due to the higher albedo. The comparison of our model scenarios suggest a snow albedo of > 0.9 and confirm the observation that drift ice has moved into the Fjord during the day. The local time shift between the locations causes a hysteresis-like behavior of these east–west ratios with solar zenith angle (SZA). The observed hysteresis, however, is larger and, at 340 nm, can be explained by the drift ice. At 500 nm, a plausible explanation is a detector tilt of about 1°. The ratios between afternoon and morning irradiances at the same SZA are investigated, which confirm the above conclusions. At the coastal site, the measured irradiance is significantly higher in the afternoon than in the morning. Besides the effect of changing drift ice and detector tilt, the small variations of the aerosol optical depth have to be considered also at the other stations to reduce the discrepancies between model and observations. Remaining discrepancies are possibly due to distant high clouds.

Magnetization plateaus in generalized Shastry-Sutherland models

We study an anisotropic Heisenberg antiferromagnet with ferromagnetic transverse spin exchange using exact quantum Monte Carlo methods. Such a model is relevant to a class of rare earth tetraboride materials that display a range of magnetization plateaus under applied magnetic field. The layered arrangement of magnetic ions in these materials is topologically equivalent to the Shastry-Sutherland lattice. In this frustrated geometry, we study the interplay of next-nearest neighbor interactions in stabilizing a plateau at half the saturation magnetization (or 1/2 plateau). We also show hysteresis-like behavior at the onset of the 1/3 plateau.

Modulating the Charge‐Transfer Enhancement in GERS using an Electrical Field under Vacuum and an n/p‐Doping Atmosphere

The modulation of charger-transfer (CT) enhancement in graphene-enhanced Raman scattering (GERS) by an electric field under different atmospheres is reported. The GERS spectra of cobalt phthalocyanine (CoPc) molecules were collected by in situ Raman measurements under ambient air, vacuum, NH(3) atmosphere, and O(2) atmosphere, in which the Fermi level of graphene was modulated by an electrical field effect (EFE). The Raman scattering intensities of adsorbed molecules can be tuned to be stronger or weaker as the graphene Fermi level down-shifts or up-shifts under electrical field modulation. However, the Raman intensity modulation in GERS is seriously influenced by the hysteresis effect in graphene EFE, which makes the modulation ability small and shows strong gate voltage sweep rate dependence in ambient air. Fortunately, the hysteresis effect in graphene EFE can be decreased by performing the measurement under vacuum conditions, and thus the Raman modulation ability in GERS can be increased. Furthermore, compared with the vacuum condition, the Raman modulation ability shows an increase under an NH(3) atmosphere, while it shows a decrease under an O(2) atmosphere, which is due to the different Fermi level modulation region in different atmospheres. More interestingly, this Raman intensity modulation in GERS shows a hysteresis-like behavior that is the same as the graphene Fermi level modulation under the EFE in a different atmosphere. All these observations suggest that the Raman enhancement in GERS occurs through a charge-transfer (CT) enhancement mechanism and the CT process can be modulated by the graphene EFE. This technique will benefit the study of the basic properties of both graphene and chemical enhancement mechanism in surface-enhanced Raman spectroscopy (SERS).

Multiple stable states and relationship between thresholds in processes and states

The concept of thresholds is applied broadly in ecology to both processes and states that exhibit step-like behavior. Thresholds are observed in parameters, equilibrium states, and in states over time, but presence or absence of thresholds at any of these levels does not provide information about the occurrence of thresholds at the other levels. Here we explore the relationship between thresholds and theory of multiple stable states. We present a 2-species Lotka-Volterra model of competition to illustrate that thresholds and hysteresis-like behavior are possible in linear systems. A grazing model is presented to show that multiple stable states are possible without thresholds in the underlying processes. The concept of thresholds within the context of multiple stable states is reviewed in an attempt to resolve some of the confusion that stems from the different meanings of thresholds.

In Situ Studies on the Switching Behavior of Ultrathin Poly(acrylic acid) Polyelectrolyte Brushes in Different Aqueous Environments

The pH-dependent switching of a poly(acrylic acid) (PAA) polyelectrolyte brush was investigated in situ using infrared spectroscopic ellipsometry (IRSE). The brush was synthesized by a "grafting to" procedure on silicon substrate with a native oxide layer. The overall thickness of the PAA brush in the dry state was approximately 5 nm. Reversible switching of the polymer brush was studied at titration from pH 2 to 10 and back in steps of 1 pH unit. The switching process was observed by monitoring the characteristic vibrational bands of the carboxylic groups of the PAA molecules. Decreasing of the C=O vibrational band amplitude and arising of a COO(-) vibrational band proved the chemical changes in the molecular structure of the brushes due to changes of the pH value in the aqueous solution. Due to the strong absorption of these bands in the IR region, the switching process could be monitored clearly. Switching the brush in several cycles with increasing and decreasing pH value showed a hysteresis-like behavior. For the first time, such hysteresis is observed in titration experiments of polyelectrolyte brushes. This behavior is attributed to the complex mechanisms of the ion's mobility in the brush layer which is explained with a suggested simplifying model describing the influence of ions inside the brush layer. In addition to the IRSE measurements, X-ray standing waves (XSW), in situ visible ellipsometry, and contact angle measurements have been performed and were in good agreement with the results from IRSE. Repetition of the in situ measurement cycles proved the good reversibility of the switching process which is highly important for practical applications of polymer brushes.

Magnetic behavior of one- and two-dimensional nanostructures stabilized by surface-state electrons: a kinetic Monte Carlo study

Recent experiments have demonstrated that it is possible to create macroscopic-ordered one- and two-dimensional nanostructures on (111) noble metal surfaces exploiting long-range substrate-mediated interaction. Here, we report on the systematic theoretical studies of magnetic properties of these atomic structures in the externally applied magnetic field. The spin dynamics is investigated by means of the kinetic Monte Carlo method based on transition-state theory. For the characteristic values of (i) magnetic anisotropy energy of adatoms and (ii) exchange coupling between adatoms in the considered class of nanostructures, we reveal the hysteresis-like behavior at low temperatures (typically at 1–3 K).