Electrical Potential Oscillations Research Articles

Characterizing Oscillatory and Excitability Regimes in a Protein-Free Lipid Membrane

Observations of electric potential oscillations in artificial lipid bilayers near the order-disorder transition indicate the existence of a stable limit cycle and, therefore, the possibility of producing excitable signals close to the bifurcation. We present a theoretical investigation of membrane oscillatory and excitability regimes induced by an increase in ion permeability at the order-disorder transition. The model accounts for the coupled effects of state-dependent permeability, membrane charge density, and hydrogen ion adsorption. A bifurcation diagram shows a transition between fixed-point and limit cycle solutions, enabling both oscillatory and excitability responses at different values of the acid association parameter. Oscillations are identified in terms of the membrane state, electric potential difference, and ion concentration near the membrane. The emerging voltage and time scales agree with measurements. Excitability is demonstrated by applying an external electric current stimulus, and the emerging signals display a threshold response and the appearance of repetitive signals upon using a long-lasting stimulus. The approach highlights the important role of the order-disorder transition, enabling membrane excitability in the absence of specialized proteins.

Comparison of in vitro corrosion products on CoCrMo generated via oscillatory electric fields before and after removal of proteinaceous layer

Although surgical success and patient mobility have greatly benefited from the increased modularity found in modern hip prosthetics, significant corrosion complications remain. Whereas the majority of biometallic corrosion research focuses on fretting and/or crevice corrosion, this manuscript investigates a largely unexplored biometallic corrosion phenomenon, induced via low magnitude, high frequency electric potential oscillations without mechanical wear.A detailed comparative study is provided for each test condition before and after the removal of the organic deposition film. Samples shielded from electrical oscillation showed no corrosion activity, whereas samples subjected to electrical activity showed significant corrosion activity. Consistent with in vivo corrosion analysis, the protruding growths contained: Cr2O3, CoO, CoOH, and compounds containing Ca, P, and Cr (VI). In addition to protruding growths, select electrical activity is identified as initiating significant pitting between the organic layer and the metallic surface.This manuscript highlights the following key findings: 1. The presence of low magnitude, high frequency electrical oscillation is sufficient to generate corrosion products, chemically consistent with those recovered in vivo. 2. Variation in electrical signal form significantly alters the initial organic deposition and predominate corrosion mode. 3. The formation of surface pitting, under electrical excitation, was preceded by substantial accumulation of P and Ca in the organic deposition layer.

Moisture-induced autonomous surface potential oscillations for energy harvesting

A variety of autonomous oscillations in nature such as heartbeats and some biochemical reactions have been widely studied and utilized for applications in the fields of bioscience and engineering. Here, we report a unique phenomenon of moisture-induced electrical potential oscillations on polymers, poly([2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide-co-acrylic acid), during the diffusion of water molecules. Chemical reactions are modeled by kinetic simulations while system dynamic equations and the stability matrix are analyzed to show the chaotic nature of the system which oscillates with hidden attractors to induce the autonomous surface potential oscillation. Using moisture in the ambient environment as the activation source, this self-excited chemoelectrical reaction could have broad influences and usages in surface-reaction based devices and systems. As a proof-of-concept demonstration, an energy harvester is constructed and achieved the continuous energy production for more than 15,000 seconds with an energy density of 16.8 mJ/cm2. A 2-Volts output voltage has been produced to power a liquid crystal display toward practical applications with five energy harvesters connected in series.

Investigation of the effects of electrochemical reactions on complex metal tribocorrosion within the human body

Although total hip arthroplasty (THA) is considered to be the most successful orthopedic operation in restoring mobility and relieving pain, common Metal-on-Metal (MoM) implants developed in the past decade suffer from severe inflammatory reactions of the surrounding tissue caused by the premature corrosion and degradation of the implant. A substantial amount of research has been dedicated to the investigation of mechanically driven fretting and crevice corrosion as the primary mechanism of implant failure. However, the exact mechanism by which hip implant breakdown occurs remains unknown, as current in vitro fretting and crevice corrosion studies have failed to completely replicate the corrosion characteristics of recovered implants. Here, we show that minor electric potential oscillations on a model hip implant replicate the corrosion of failed implants without the introduction of mechanical wear. We found in a controlled lab setting that small electrical oscillations, of similar frequency and magnitude as those resulting from ambient electromagnetic waves interacting with the metal of the implant, can force electrochemical reactions within a simulated synovial fluid environment that have not been previously predicted. In lab testing we have shown the replication of titanium, phosphorous, and oxygen deposition onto the surface of ASTM astm:F75 CoCrMo metal alloy test specimens, matching the chemical composition of previously retrieved wear particles from failed patient prosthetics. Our results demonstrate that the electrical activity and ensuing electrochemical activity excites two corrosion failure modes: direct dissolution of the medically implantable alloy, leaching metal ions into the body, and surface deposition growth, forming the precursor of secondary wear particles. We anticipate our findings to be the foundation for the future development and testing of electrochemically resistant implantable material.

Non-stationary thermoelectric effect in He II and how it is affected by the thermal vibrations’ transition from laminar to the turbulent regime

The observation of the thermoelectric effect, which is the spontaneous electric polarization of a cell with liquid He II during the thermal excitation of standing second-sound waves, has been confirmed [Low Temperature Physics 30, 1321 (2004)]. The relationship of this effect with the thermal and hydrodynamic properties of He II is studied in detail in the temperature range of 1.4 K < T < 2 K. It is established that the dependence of the amplitude of electric potential oscillations on the excitation intensity changes significantly during the thermal vibrations’ transition from the laminar to the turbulent regime. The threshold value of the excitation power w = w0 (T) is recorded: in the region w < w0, the potential oscillations are regular and their amplitude increases in proportion to the power; at w > w0, the electric response becomes random in nature as the fluctuations increase and the amplitude decreases to zero, with a peculiar electromagnetic “noise” being observed. The experimental results are compared with the conclusions drawn from the theory of flexoelectric polarization of liquid helium. The polarization of liquid helium upon excitation of the first-sound waves, as well as pressure and temperature shock waves, has also been discussed.

Thermal switch of oscillation frequency in Belousov-Zhabotinsky liquid marbles.

External control of oscillation dynamics in the Belousov–Zhabotinsky (BZ) reaction is important for many applications including encoding computing schemes. When considering the BZ reaction, there are limited studies dealing with thermal cycling, particularly cooling, for external control. Recently, liquid marbles (LMs) have been demonstrated as a means of confining the BZ reaction in a system containing a solid–liquid interface. BZ LMs were prepared by rolling 50 μl droplets in polyethylene (PE) powder. Oscillations of electrical potential differences within the marble were recorded by inserting a pair of electrodes through the LM powder coating into the BZ solution core. Electrical potential differences of up to 100 mV were observed with an average period of oscillation ca 44 s. BZ LMs were subsequently frozen to −1°C to observe changes in the frequency of electrical potential oscillations. The frequency of oscillations reduced upon freezing to 11 mHz cf. 23 mHz at ambient temperature. The oscillation frequency of the frozen BZ LM returned to 23 mHz upon warming to ambient temperature. Several cycles of frequency fluctuations were able to be achieved.

Detection and investigation of chirping Alfvén eigenmodes with heavy ion beam probe in the TJ-II stellarator

Alfvén eigenmodes were studied in the low magnetic shear flexible heliac TJ-II NBI-heated plasmas by heavy ion beam probe (HIBP), which is capable to measure simultaneously the oscillations of the plasma electric potential, density and poloidal magnetic field in the bulk plasmas. The L-mode hydrogen plasma was investigated at various magnetic configurations with rotational transform ι(a)/2π ~ 1.5–1.6. Co-, counter- and balanced beam injection were explored. The present study was focused on the high-frequency chirping modes with 250 kHz < fAE < 350 kHz at the low-density = (0.5–0.7) × 1019 m−3 NBI-heated plasmas without auxiliary ECRH. Here we report the observation of the various types of chirping modes, differing by frequency, radial location, amplitude and shape of the frequency dependence on time (burst pattern). Remarkably, the same mode may evolve, changing its burst pattern in the same frequency range in the single discharge. The radial scan of the HIBP sample volume indicates the radial evolution of the potential and density perturbation during the single frequency burst of the chirping mode. The individual burst of the chirping-up mode can propagate outward with volume-averaged radial velocity ≈70 m s−1. The frequency raise during the burst is in line with Alfvén frequency dependence on density, which decreases over the propagation area.

Spontaneous electrical oscillation in horizontal three-phase liquid membrane systems: Effect of Marangoni effect induced by buoyant convection

We consider spontaneous oscillation phenomena in three–phase liquid membrane systems in a horizontally-placed glass tube with different solutes in the aqueous phase and different oil phase solvents. The relationship between the induction period of electrical potential oscillation and the initial concentration of solute in the source aqueous phase highlights the importance of the density difference owing to differential concentrations of solute. Numerical calculations confirmed the effects of the density difference and revealed the occurrence of buoyant convection in the oil liquid membrane phase. The convection flow (buoyant convection roll) transported solute, which induced Marangoni convection at the interface between the oil phase and the receiving aqueous phase. Our new experimental and numerical approaches taking into account the density difference provide an explanation for the spontaneous non-linear oscillation phenomena at the oil/water interface in horizontal three-phase liquid membrane systems.

Measurement of geodesic acoustic modes and the turbulent particle flux in the T-10 tokamak plasmas

Geodesic acoustic modes (GAMs) and the turbulent particle flux were studied in the T-10 tokamak in discharges with Ohmic (OH) and electron cyclotron heating (ECRH). The broadband oscillations of electric potential and density with frequencies up to 250 kHz were measured using a heavy ion beam probe (HIBP) in the plasma core. At the plasma edge, at a relative radius ρ > 0.8, the dominant GAM peak with a frequency of approximately 20 kHz and the noticeable peak of quasicoherent oscillations in the 40–100 kHz range were observed. Using a multislit energy analyzer, we estimate the poloidal electric field Epol and the radial electrostatic turbulent particle flux, which is driven by drift in crossed E × B fields. The GAM peak was observed in the spectrum of potential oscillations, but it was practically absent in the spectrum of Epol oscillations and in the frequency-resolved particle flux. However, the flux was observed in the broadband range. These results agree with the theoretical concept of GAM and our earlier measurements of symmetric poloidal structure of GAM potential perturbations.

Study of NBI-driven chirping mode properties and radial location by the heavy ion beam probe in the TJ-II stellarator

Alfvén eigenmodes (AEs) were studied in low magnetic shear flexible heliac TJ-II (B0 = 0.95 T, R0 = 1.5 m, = 0.22 m) neutral beam injection (NBI) heated plasmas (PNBI ⩽ 1.1 MW, ENBI = 32 keV) using the heavy ion beam probe (HIBP). L-mode hydrogen plasmas heated with co-, counter- and balanced-NBI and electron cyclotron resonance heating (ECRH) were investigated in various magnetic configurations with rotational transform ι(a)/2π = 1/q ~ 1.5–1.6. The HIBP diagnostic is capable of simultaneously measuring the oscillations of the plasma electric potential, density and poloidal magnetic field. In earlier studies chirping modes have been observed with 250 kHz < fAE < 380 kHz in combined ECR and NBI heated plasmas at low density = (0.3–1.5) × 1019 m−3. In this paper we report the observation of chirping modes obtained with NBI only in plasmas with densities similar to those of earlier studies and obtained after lithium evaporation in the vacuum vessel. The absence of ECRH in the discharges studied here shows that ECRH is not a necessary ingredient to obtain chirping modes in TJ-II but rather a tool for obtaining low-density discharges. Using the HIBP we deduce that the location of the AE chirping mode is −0.8 < ρ < 0.8. Chirping modes have a specific spatial structure: electric potential perturbations have a ballooning character, while the density and Bpol perturbations are nearly symmetric for both ECRH + NBI and NBI-only plasmas. On TJ-II, the dominant effect on the nonlinear evolution of the AE from the chirping state to the steady-frequency state is the magnetic configuration, determined by the vacuum ι and plasma current Ipl.

Information transfer by local field potentials in the hippocampal formation

Extracellular electrical potential oscillations recorded as local field potentials (LFPs) in the hippocampal formation are thought to be involved in cognitive processes such as working memory retention, memory consolidation and spatial navigation. Recent studies have shown that combining spikes with LFP phase can increase the information content of spikes [1,2] and thus suggest LFP oscillations have the capacity to convey information. LFP oscillations within specific frequency bands can interact, for example by phase-phase and phase-amplitude coupling. We hypothesise that these LFP interactions can transfer information between neural networks. To test this hypothesis, we analyse multi-channel recordings of simultaneous LFPs from hippocampal area CA1 and the subiculum of urethane-anaesthetised rodents. Anatomical connections between these two regions in the hippocampal formation predict information in this system flows in 'nested loops' along separate projections [3]. We use advanced neurocomputational methods to determine how information flows within the CA1-subicular circuit by interactions of LFP rhythms. The results of correlation and coherence analyses of LFPs recorded from multiple sites suggest that LFP rhythms can transmit information within and between area CA1 and the subiculum. However, these methods alone are not enough to determine the oscillatory activity in which region drives activity in other regions, that is in which direction information flows. We use transfer entropy [4], which is an information theoretic method that can capture directionality, to quantify information transfer between area CA1 and subiculum. We show that information flow within the CA1-subicular circuit is bi-directional and follows a pattern of feedforward and feedback loops. Our results suggest that LFP interactions can route information at millisecond timescales along the anatomical connections in the hippocampal formation to achieve cognitive processing.

Radial homogeneity of geodesic acoustic modes in ohmic discharges with low B in the T-10 tokamak

The electric potential oscillations in the hot plasma zone have been measured directly using a heavy ion beam probe at the frequencies of geodesic acoustic modes in the T-10 tokamak (the major and minor radii are R = 1.5 m and a = 0.3 m, respectively, and the toroidal magnetic field is B = 1.5–2.5 T). In discharges with the lowered magnetic field B = 1.55 T, the diagnostic beam can probe a rather wide radial plasma region (0.06 < r < 0.28 m). This made it possible to study the radial structure of geodesic acoustic modes. It has been shown that the frequency and amplitude of geodesic acoustic modes in the region under study are constant over the radius in the whole region of observation. Thus, it has been shown experimentally that the observed frequency of geodesic acoustic modes may not correspond to the predictions of the local theory (f∼ √Te) in a wide radial range comparable with the plasma minor radius. The numerical simulation of the turbulence dynamics using the solution of Braginskii magnetohydrodynamic equations for a peripheral plasma has showed the formation of geodesic acoustic modes in the observed frequency range owing to the nonlinear interaction between broadband turbulence modes.

A would-be nervous system made from a slime mold.

The slime mold Physarum polycephalum is a huge single cell that has proved to be a fruitful material for designing novel computing architectures. The slime mold is capable of sensing tactile, chemical, and optical stimuli and converting them to characteristic patterns of its electrical potential oscillations. The electrical responses to stimuli may propagate along protoplasmic tubes for distances exceeding tens of centimeters, as impulses in neural pathways do. A slime mold makes decisions about its propagation direction based on information fusion from thousands of spatially extended protoplasmic loci, similarly to a neuron collecting information from its dendritic tree. The analogy is distant yet inspiring. We speculate on whether alternative-would-be-nervous systems can be developed and practically implemented from the slime mold. We uncover analogies between the slime mold and neurons, and demonstrate that the slime mold can play the roles of primitive mechanoreceptors, photoreceptors, and chemoreceptors; we also show how the Physarum neural pathways develop. The results constituted the first step towards experimental laboratory studies of nervous system implementation in slime molds.

Electrical potential oscillations--movement relations in circumnutating sunflower stem and effect of ion channel and proton pump inhibitors on circumnutation.

The physiological control and molecular mechanism of circumnutation (CN) has not yet been fully understood. To gain information on the CN mechanism, the relationship between the changes of electrical potential and movement in the circumnutating sunflower stem and effect of ion channels and proton pump inhibitors on CN parameters were evaluated. Long-term electrophysiological measurements and injection of solutions of ion channel inhibitors (ICI) into sunflower stem with the simultaneous time-lapse recording of the movement were made. The oscillations of electrical potential (OEP) - movement relations - consist of cells depolarization on the deflected side of the stem and, at this same time, cells hyperpolarization on the opposite side of the stem. The delay of organ movement in relation to electrical changes of approximately 28 min (22% of the period) may indicate that the ionic fluxes causing the OEP are the primary phenomenon. The biggest decrease of CN period was observed after injection of proton pump (approximately 26%) and cation channel (approximately 25%) inhibitors, while length and amplitude were reduced mainly by calcium channel inhibitors (approximately 67%). Existence of OEP only in circumnutating part of sunflower stem and reduction of CN parameters and OEP amplitude after application of ICI prove that the CN cellular mechanism is associated with transmembrane ion transport.

Slime mould logic gates based on frequency changes of electrical potential oscillation

Physarum polycephalum is a large single amoeba cell, which in its plasmodial phase, forages and connects nearby food sources with protoplasmic tubes. The organism forages for food by growing these tubes towards detected foodstuff, this foraging behaviour is governed by simple rules of photoavoidance and chemotaxis. The electrical activity of the tubes oscillates, creating a peristaltic like action within the tubes, forcing cytoplasm along the lumen; the frequency of this oscillation controls the speed and direction of growth. External stimuli such as light and food cause changes in the oscillation frequency. We demonstrate that using these stimuli as logical inputs we can approximate logic gates using these tubes and derive combinational logic circuits by cascading the gates, with software analysis providing the output of each gate and determining the input of the following gate. Basic gates OR, AND and NOT were correct 90%, 77.8% and 91.7% of the time respectively. Derived logic circuits XOR, half adder and full adder were 70.8%, 65% and 58.8% accurate respectively. Accuracy of the combinational logic decreases as the number of gates is increased, however they are at least as accurate as previous logic approximations using spatial growth of P. polycephalum and up to 30 times as fast at computing the logical output. The results shown here demonstrate a significant advancement in organism-based computing, providing a solid basis for hybrid computers of the future.

Technical note: Evaluation of a new system for measuring feeding behavior of dairy cows

Feed intake, feeding and rumination time are important parameters in the identification of suboptimal feeding conditions and possible health disorders. The automatic recording of individual feeding behavior constitutes a reasonable tool for early detection of deviations in feeding behavior and feeding deficiencies. For this reason, a new system for measuring feeding behavior of dairy cows has been developed. The sensor-based system DairyCheck consists of a halter with two incorporated electrodes, a data logger, an accelerometer, power supply, and evaluation software. Measurement of feeding behavior ensues through surface electromyography (EMG), whereby electrical potential oscillations during jaw movements are recorded. Data are transmitted directly via radio transmission to a computer with automatic evaluation software. Automatic analysis software is based on an algorithm to identify single jaw movements and differentiate between active feeding phases and non-active dormant phases. For validation, feeding behavior of 14 cows as determined by both the EMG system and visual observation was analyzed. Results showed adequate agreement of the results of both assessments. However, further progress and research are necessary for automatic data interpretation with a self-learning algorithm, to develop this EMG-based system into an appropriate management tool in the field of precision dairy farming.

Influence of extracellular oscillations on neural communication: a computational perspective

Neural communication generates oscillations of electric potential in the extracellular medium. In feedback, these oscillations affect the electrochemical processes within the neurons, influencing the timing and the number of action potentials. It is unclear whether this influence should be considered only as noise or it has some functional role in neural communication. Through computer simulations we investigated the effect of various sinusoidal extracellular oscillations on the timing and number of action potentials. Each simulation is based on a multicompartment model of a single neuron, which is stimulated through spatially distributed synaptic activations. A thorough analysis is conducted on a large number of simulations with different models of CA3 and CA1 pyramidal neurons which are modeled using realistic morphologies and active ion conductances. We demonstrated that the influence of the weak extracellular oscillations, which are commonly present in the brain, is rather stochastic and modest. We found that the stronger fields, which are spontaneously present in the brain only in some particular cases (e.g., during seizures) or that can be induced externally, could significantly modulate spike timings.

Towards slime mould colour sensor: Recognition of colours by Physarum polycephalum

Acellular slime mould Physarum polycephalum is a popular now user-friendly living substrate for designing of future and emergent sensing and computing devices. P. polycephalum exhibits regular patterns of oscillations of its surface electrical potential. The oscillation patterns are changed when the slime mould is subjected to mechanical, chemical, electrical or optical stimuli. We evaluate feasibility of slime-mould based colour sensors by illuminating Physarum with red, green, blue and white colours and analysing patterns of the slime mould’s electrical potential oscillations. We define that the slime mould recognises a colour if it reacts to illumination with the colour by a unique changes in amplitude and periods of oscillatory activity. In laboratory experiments we found that the slime mould recognises red and blue colour. The slime mould does not differentiate between green and white colours. The slime mould also recognises when red colour is switched off. We also map colours to diversity of the oscillations: illumination with a white colour increases diversity of amplitudes and periods of oscillations, other colours studied increase diversity either of amplitude or period.

Towards slime mould chemical sensor: Mapping chemical inputs onto electrical potential dynamics of Physarum Polycephalum

Plasmodium of slime mould Physarum polycephalum is a large single celled organism visible unaided by the eye. This slime mould is capable of optimising the shape of its protoplasmic networks in spatial configurations of attractants and repellents. Such adaptive behaviour can interpreted as computation. When exposed to attractants and repellents, Physarum changes patterns of its electrical activity. We experimentally derived a unique one-to-one mapping between a range of selected bioactive chemicals and patterns of oscillations of the slime mould's extracellular electrical potential. This direct and rapid change demonstrates detection of these chemicals in a similar manner to a biological contactless chemical sensor. We believe results could be used in future designs of slime mould based chemical sensors and computers.

Slime mould tactile sensor

Slime mould Physarum polycephalum is a single cells visible by unaided eye. The cells shows a wide spectrum of intelligent behaviour. By interpreting the behaviour in terms of computation one can make a slime mould based computing device. The Physarum computers are capable to solve a range of tasks of computational geometry, optimisation and logic. Physarum computers designed so far lack of localised inputs. Commonly used inputs — illumination and chemo-attractants and -repellents — usually act on extended domains of the slime mould's body. Aiming to design massive-parallel tactile inputs for slime mould computers we analyse a temporal dynamic of P. polycephalum's electrical response to tactile stimulation. In experimental laboratory studies we discover how the Physarum responds to application and removal of a local mechanical pressure with electrical potential impulses and changes in its electrical potential oscillation patterns.