Steady-state Current Response Research Articles

Nonlinear transport and kinetics in electrocatalytic thin film of arbitrary shape for non-Michaelis-Menten reaction kinetics

The mathematical model for non-Michael-Menten kinetics, which describes a substrate that produces a complex with the immobilised catalyst, is discussed. This paper analytically solves the nonlinear reaction–diffusion equation in an electrocatalytic thin film of arbitrary shape. We provide a mathematical process that enables a comprehensive analytical solution to the nonlinear boundary value problem. Closed and simple forms of the approximate expression for substrate concentration profiles for general geometry (planar, cylindrical, and spherical) and corresponding steady-state amperometric current response are presented. The results obtained by three analytical methods are then compared with numerical solutions. The comparison has been represented graphically, and the Tabler form shows the effectiveness and advantages of the featured techniques. The effect of the parameters on concentration is also discussed.

Transient theory for scanning electrochemical microscopy of biological membrane transport: uncovering membrane-permeant interactions.

Scanning electrochemical microscopy (SECM) has emerged as a powerful method to quantitatively investigate the transport of molecules and ions across various biological membranes as represented by living cells. Advantageously, SECM allows for the in situ and non-destructive imaging and measurement of high membrane permeability under simple steady-state conditions, thereby facilitating quantitative data analysis. The SECM method, however, has not provided any information about the interactions of a transported species, i.e., a permeant, with a membrane through its components, e.g., lipids, channels, and carriers. Herein, we propose theoretically that SECM enables the quantitative investigation of membrane-permeant interactions by employing transient conditions. Specifically, we model the membrane-permeant interactions based on a Langmuir-type isotherm to define the strength and kinetics of the interactions as well as the concentration of interaction sites. Finite element simulation predicts that each of the three parameters uniquely affects the chronoamperometric current response of an SECM tip to a permeant. Significantly, this prediction implies that all three parameters are determinable from an experimental chronoamperometric response of the SECM tip. Complimentarily, the steady-state current response of the SECM tip yields the overall membrane permeability based on the combination of the three parameters. Interestingly, our simulation also reveals the optimum strength of membrane-permeant interactions to maximize the transient flux of the permeant from the membrane to the tip.

Discrete-Time Active Disturbance Rejection Current Control of PM Motor at Low Speed Using Resonant Sliding Mode

A discrete-time active disturbance rejection control (ADRC) method using resonant sliding mode is proposed to solve the disturbance characteristics of the current loop of permanent magnet (PM) motor at low speed. The extended state observer (ESO) is used to estimate the disturbance, but there is a contradiction between disturbance rejection and noise rejection in parameter design of ESO, which will affect the accuracy of the estimation, especially at low speed. In order to solve the problem, sliding mode control is combined with ADRC, while traditional integral sliding mode control still has poor rejection effect on the specific frequency harmonics. The resonant sliding mode is proposed to add resonance term to the integral sliding mode surface, which mitigates the impact of the disturbance that ESO fails to estimate on the tracking accuracy. Therefore, resonant sliding mode in the feedback control law of ADRC (RSM-ADRC) is employed to current loop to reduce the steady-state error. Meanwhile, the stability of the proposed algorithm is verified by discretization method. The steady and dynamic performances of the four control methods are compared through experiments to verify the feasibility and effectiveness of the proposed method. For example, when the reference current of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis is 0A and 1A respectively at 50rpm, the total harmonic distortion of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current decreases from 1.68% to 0.64% and the 6th harmonic of current also drops to 0.135%. Despite the sudden change of inductance parameters, the steady-state current response is largely unaffected.

The self-powered photodetector of n-Si/n-ZnO heterojunction with enhanced temperature adaptability via transient current response

Self-powered photodetectors (PDs) have great application potential in distributed sensor networks, imaging systems and Internet of Things (IoT) due to their simple structure and long-term mobile detection without external power supply. However, the steady-state current response of PD decreases sharply with the increase of temperature, which restricts its application in high temperature environment. Here, a self-powered PD of n-Si/n-ZnO heterojunction with transient current response has been prepared, and the current generation mechanism and response characteristics under various temperature have been studied as being excited by periodic light pulses. The results show that the transient current response can not only improve the photocurrent responsivity and specific detectivity of PD, but also improve the performance of PD at high temperature. When the temperature rises to 340 K, the transient current holding factor η t (η t′) of device excited by 127 μW cm−2, 365 nm light are increased by 115% (315%) compared with steady state current holding factor η s. The corresponding transient current enhancement factor α tt′ (α t′) of PD increase monotonically with the temperature, and the maximum values α tt′ (α t′) of PD excited by 365 nm light are 12.5 (5.0). As the temperature increases, the t r and t f of PD excited by 365 nm (287 μW cm−2) light decrease from 0.16 and 0.15 ms to 0.11 and 0.11 ms, respectively. The transient current response is caused by the transport of excess photo-generated carriers in the PD at the moment of light on and off. The transient current increases significantly with decrease resistance and is less affected by decreasing built-in electric field that make PD has high holding factor under high temperature conditions. This work provides a new avenue for designing high-performance self-powered PDs capable of operating in higher temperature environments, and promotes the wide application of transient-response self-powered PDs in the fields of IoT, fast detecting, and imaging.

Robust Stabilization of Inverter-Based Resources Using Virtual Resistance-Based Control

This paper proposes a virtual resistance-based nonlinear control to stabilize and robustify the current layer of inverter-based resources, subject to the grid voltage disturbances, and the grid parameter uncertainties. A class of virtual resistances is proposed and analyzed using concepts from dissipative systems theory. Moreover, specific nonlinear virtual resistance-based controllers are derived, with their corresponding performance analytically bounded. The theoretical and simulation results show that the proposed nonlinear virtual resistance-based controllers significantly reduce the L2 gain of the closed-loop error system to grid voltage variation and parametric uncertainties. Significant improvements of the transient and steady-state current responses are also demonstrated over linear virtual resistance counterparts.

Generalized Formulation of Steady-State Equivalent Circuit Models of Grid-Forming Inverters

Abstract: This work proposes positive- and negative-sequence equivalent circuits of grid-forming inverters for steady-state analysis. The proposed models are especially attractive for performing long-duration voltage regulation analysis and short-circuit studies involving grid-forming inverters. Our proposed equivalent circuit models are based on the inverter’s voltage and current control loops in the αβ and dq frames. For this reason, they operate according to prescribed control functions and specified impedances (i.e., filter impedance, current limiter block, virtual admittance block, and PI/PR controller block). The equivalent circuit model accuracy is validated by comparing system steady-state voltage and current responses obtained by detailed time-domain models in PSCAD/EMTDC to those by the equivalent circuit models implemented in steady-state load flow program (e.g., OpenDSS). Two distinct control structures implemented in the αβ and dq frames are used for the validation. Single line-to-ground and line-to-lineto-ground faults are simulated in a small islanded microgrid as well as the IEEE 34-node test feeder. Fault impedances varying from 0 to 5 ohms are simulated. We show that the equivalent models precisely replicate the steady-state response of the detailed time-domain models.

Single Potential Step Chronoamperometry for EC’ Reaction at Rough Electrodes: Theory and Experiment

The theory is developed for the chronoamperometry of first order homogeneous catalytic chemical reaction coupled with electron transfer ($\rm{EC^{\prime}}$) on a rough electrode. We obtained a solution for the diffusion problem on an arbitrary and random topography of the electrode to generalize Danckwerts' equation. Derived equation of random electrode roughness is used for developing theory of (statistically isotropic) self-affine fractal on limited length scales. The characteristics fractal morphological parameters, viz. $D_{H}$, $\ell$ and $\ell_{\tau}$, are varied for detailed analysis of current transient. The current transient shows anomalously enhanced response for a rough electrode. Our theoretical results explain both transient and steady-state behavior of the current response under the influence of roughness. Steady-state current response depends on the rate constant, the diffusion coefficient of electroactive species and width of roughness. Finally, the theory is compared and validated with experimental data of ferrocyanide and ascorbic acid coupled system on rough Pt electrodes.

Fabrication of a Novel, Cost-Effective Double-Sided Indium Tin Oxide-Based Nanoribbon Electrode and Its Application of Acute Toxicity Detection in Water.

Microelectrode plays a crucial role in developing a rapid biosensor for detecting toxicity in water. In this study, a nanoribbon electrode (NRE) with amplified microelectrode signal was successfully prepared by electrodepositing 2-allylphenol on a double-sided indium tin oxide glass. The NRE provided a simple mean for obtaining large steady-state current response. Its advantages were discussed by contrasting the toxicity detection of 3,5-dichlorophenol (DCP) with single microelectrode, microelectrode array, and millimeter electrode as working electrodes in which potassium ferricyanide (K3[Fe(CN)6]) was adopted as a mediator, and Escherichia coli was selected as bioreceptor. At a constant potential of 450 mV, the current reached a steady state within 10 s. The biosensor was constructed using the NRE as working electrode, and its feasibility was verified by determining the toxicity of DCP. A 50% inhibitory concentration (IC50) of 3.01 mg/L was obtained by analyzing the current responses of different concentrations of DCP within 1 h. These results exhibited that the proposed method based on the as-prepared NRE was a rapid, sensitive, and cost-effective way for toxicity detection in water.

Design criterion and guidelines for three‐phase asymmetric coupled inductors in interleaving DC/DC converter for VRM in data centres and POL

Multiphase interleaving buck DC/DC converters (BCs) with magnetically coupled inductors (CIs) have been researched to improve the performance of voltage regulator module (VRM) and point-of-load (POL). Commercial three or more phase CIs are asymmetric CIs (ACIs) offering unequal phase self-inductance and unequal coupling between phases. By analysing the steady-state current ripple and transient current response speed of three-phase interleaving BCs with three-phase ACIs, the design criterion and design guidelines for three-phase ACIs are presented to simultaneously improve the steady-state performance and transient performance of three-phase interleaving BC with three-phase ACIs. A three-phase interleaving BC prototype with three-phase ACIs is constructed. The experimental results show that three-phase interleaving BC's steady-state phase current ripple can reduce 45%, and its transient output current response speed can increase 63.9% simultaneously by using three-phase ACIs instead of three-phase discrete inductors, and with a smaller total core volume and higher efficiency. The results of this study can be used to design VRM in data centres and POL with smaller steady-state phase current ripple, faster transient output current response speed, and higher efficiency.

Transport and kinetics in electrocatalytic thin film biosensors: bounded diffusion with non-Michaelis-Menten reaction kinetics

In this paper, we describe the problem of describing the transport and catalytic kinetics at immobilized enzymes in an electronically conductive polymer thin film where substrate inhibition is important. Here, the enzyme kinetics are not well described by the Michaelis-Menten equation. We describe a mathematical procedure based on the recently developed Akbari-Ganji method (AGM) which facilitates a full analytical solution of the boundary value problem which is valid for all values of substrate concentration. Closed form expressions for both the substrate concentration in the film and the steady-state amperometric current response are presented. Limiting kinetic cases are identified and are expressed pictorially in parameter space using a kinetic case diagram.

Analysis of the steady-state behavior of pseudo-first-order EC-catalytic mechanism at a rotating disk electrode

An efficient analytical method is applied to solve a system of convection-diffusion equations in the pseudo-first-order EC-catalytic mechanism at a rotating disk electrode. A simple closed form analytical expression for the concentration of oxidized and reduced catalyst species in the electrochemical reaction is obtained and analyzed for various values of parameters. Also, closed form analytical expressions are derived for the steady-state current response and the current ratio at potential steps for various values of diffusion coefficients, rate constant, and rotation rate. The derived approximate analytical results are shown to be in satisfactory agreement with numerical simulation results.

Simple digital algorithm for improved performance in a boost PFC converter operating in CCM

In power factor correction (PFC) converters, achieving both good steady-state input current waveform and fast output dynamic response is a challenge. This is due to the effect of the double-line frequency ripple present in the sensed output voltage signal which tends to distort the reference current applied to the current controller, thus leading to a distorted input current waveform. Low bandwidth (BW) voltage loop designs to reduce this input current distortion make the output dynamic response very sluggish. A digital control algorithm for the estimation of the average value of the sensed output voltage is proposed in this study to achieve low total harmonic distortion input current and fast dynamic response with a higher BW voltage loop. The proposed algorithm is computationally less intensive and requires no additional sensors or circuitry. The effectiveness of the proposed control algorithm is validated through simulation and experimental tests on a 300 W boost PFC converter prototype operating in continuous conduction mode.

Enzymatic sensor for phenols based on titanium dioxide generating surface confined ROS after treatment with H2O2

Titanium dioxide (TiO2) is a popular material as host matrix for enzymes. We now evidence that TiO2 can accumulate and retain reactive oxygen species after treatment by hydrogen peroxide (H2O2) and support redox cycling of a phenolic analyte between horseradish peroxidase (HRP) and an electrode. The proposed detection scheme is identical to that of second generation biosensors, but the measuring solution requires no dissolved H2O2. This significantly simplifies the analysis and overcomes issues related to H2O2 being present (or generated) in the solution. The modified electrodes showed rapid stabilization of the baseline, a low noise level, fast realization of a steady-state current response, and, in addition, improved sensitivity and limit of detection compared to the conventional approach, i.e. in the presence of H2O2 in the measuring solution. Hydroquinone, 4-aminophenol, and other phenolic compounds were successfully detected at sub-μM concentrations. Particularly, a linear response in the concentration range between 0.025 and 2 μM and LOD of 24 nM was demonstrated for 4-aminophenol. The proposed sensor design goes beyond the traditional concept with three sensors’ generations offering a new possibility for the development of enzymatic sensors based on peroxidases and the formation of ROS on titania after treatment with H2O2.

Analysis of Electrical Analogue of a Biological Cell and Its Response to External Electric Field

Abstract: The use of electric field stimulation to elicit a desired cell/tissue response has become a versatile strategy in regenerative medicine. Using an array of cell types and biomaterial substrates, our group has experimentally investigated the influence of external electric field parameters on the modulation of cellular functionality in vitro. However, the mechanism of action of electric field is not clearly understood, especially in cases where cell fate processes such as differentiation and proliferation are significantly enhanced due to electric field stimulation. In order to understand these important phenomena, it is necessary to first examine the response on a single cell. In this direction, we analyze the response of an electrical analogue of a single biological cell, wherein an electrical equivalent resistor-capacitor (R-C) network has been constructed by considering membranes as capacitive and surrounding biological media (cytoplasm and nucleoplasm) as resistive components. The response of this electrical analogue of a biological cell to external electric field (E-field) is determined using analytical techniques and SPICE-based simulations. The solutions for the network provide a time constant of â�� 30 I¼s, which is higher compared to the case when membranes were considered to be purely capacitive. The above model formulation has been further extended to determine the steady-state current response under various input signals, like sinusoidal, square, and triangular pulses using SPICE simulation package. In the context of regenerative engineering, the results of the present work are perceived to be important to design electric field-based stimulation strategies to obtain desired responses of electroactive tissues. Lay Summary: The importance of the effect of electric field on cells and tissues has become evident over the last two decades. Prior studies indicate that based on the electric field parameters, it is possible to get various cellular responses. The current study is an attempt to investigate why this is the case by approximating a single cell into an equivalent electrical network with resistors and capacitors. The network response is studied using simulation tools to get current waveforms and analytical techniques to obtain time constants, which provide vital insights into the observed cell behaviors reported in the literature. © 2018, The Regenerative Engineering Society.

Gold foil-based biosensor for the determination of hydrogen peroxide.

Hydrogen peroxide ($\text{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$) plays a critical role in the regulation of multifarious physiological processes. We developed a sensor containing a mercaptopropionic acid (MPA) monolayer covalently immobilized with Horseradish peroxidase (HRP) enzyme for the electrochemical detection of hydrogen peroxide ($\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$). A gold foil substrate was chemically treated with nitric acid and were used as working electrode. Platinum wire and Ag-Ag/Cl were used as counter and reference electrodes, respectively. The acid treated gold electrode with the immobilized enzyme shown to have improved catalytic activity in the reduction of $\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$. The steady-state current response increases linearly with $\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$ concentration from 10 $\mu \textbf{M}$ to 9 mM with a low detection limit of 60 $\mu \textbf{M}$ and showed a sensitivity of 0.4 mA/ mM cm$^{\mathbf {2}}$. This electrochemical sensor is demonstrated to be highly selective and sensitive in the presence of interfering analytes. The improved activity and simple preparation method of the electrode makes the MPAHRP modified gold electrode promising for being developed as an attractive robust material for electrochemical $\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$ sensing.

In-vitro model for assessing glucose diffusion through skin

Pig ear skin membrane-covered glucose biosensor based on oxygen electrode has been assessed as a tool to evaluate glucose penetration through skin in-vitro. For this, glucose oxidase (GOx) was immobilised on oxygen electrode and covered with the skin membrane. Exposing this electrode to the solution of glucose resulted in glucose penetration though skin membrane, its oxidation catalysed by GOx, consumption of O2 and decrease of the current of the oxygen electrode. By processing the biosensor responses to glucose, we found that glucose penetration through 250 µm thick skin membrane is slow; 90% of steady-state current response was reached in 32( ± 22) min. Apparent diffusion coefficient for glucose in skin was found to be equal to 0.15( ± 0.07)* 10−6 cm2 s−1. This value is 45 times lower than glucose diffusion coefficient in water. Tape-stripping of stratum corneum (SC) allows considerably faster glucose penetration. The electrodes covered with tape-stripped skin reached 90% of steady-state current response in 5.0(± 2.7) min. The theoretical estimate of glucose flux through SC was considered exploiting four-pathway theory of transdermal penetration. Theoretical flux values were more that three orders lower than measured experimentally. This high discrepancy might indicate that glucose penetration through healthy human skin could be even slower, allowing much lower flux, than it was found in our study for skin membranes from pig ears.

Generator–collector electrochemical sensor configurations based on track-Etch membrane separated platinum leaves

Abstract We report a novel, simple and cheap generator–collector electrode system, employing platinum leaves, with micron-sized pores and typically 100–300 nm thickness, sandwiched with a porous track etch membrane spacer with typically 30 nm diameter pores. The electrode assembly is sealed into a polymer lamination pouch with one side 2 mm diameter exposed to electrolyte solution. The generator electrode with sweeping potential (top or bottom electrode) shows transient current with high capacitive current component. The collector electrode with fixed potential shows well-defined steady state current response at low potential sweep rates. The fabricated device shows good performance in monitoring both 1,1′-ferrocenedimethanol oxidation and proton reduction redox processes. Oxygen sensor signals are assigned to a lowering of the steady state proton reduction current.

A facile synthesis of a 3D high-index Au NCs@CuO supported on reduced graphene oxide for glucose sensing

A novel electrochemical sensor based on 3D reduced graphene oxide supported high-index Au NCs@CuO (RGO-Au NCs@CuO) for detection of glucose was reported in this work. A facile one-pot hydrothermal synthetic method was employed at room temperature with electrostatic self-assembly technology for the synthesis of reduced graphene oxide supported high-index Au nanocrystals. Morphology, structure and composition of RGO-Au NCs@CuO were characterized by various technologies including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Significantly, with the combination of large active surface area and high conductivity, electrocatalytic activity toward the oxidation of glucose was markedly enhanced. Under the best experimental conditions, the steady-state current response was linearly proportional to glucose concentration in the range from 0.1μM to 3mM with a low detection limit (30nM). Meanwhile, the sensor was of excellent selectivity and stability and successfully applied to the detection of glucose in human serum.

CoA-dependent coordination polymer as a novel electrochemical sensing platform for sensitive detection of hydrogen peroxide in biological environments

A growing body of evidences suggests that hydrogen peroxide (H2O2) plays an effective role in the regulation of multifarious physiological processes. Development of sensitive probes for H2O2 is an urgent hotspot. In this work, we recommended a coenzyme A (CoA)-mediated gold coordination polymer (CoA-Au(I) CP) for sensitive electrochemical detection of H2O2. The biosensing mechanism is based on the following highlights: the formation of an unordinary structure with -thiol-Au(I)- repeated units derived from thiol in CoA; an extraordinary interaction between graphene (GO) and CoA-Au(I) CP due to massive adenines. A potential application of the resultant CoA-Au(I) CP as a novel sensing platform to monitor H2O2 is investigated. Such CoA-Au(I) CP-based sensor exhibited an excellent electro-catalytic property for H2O2 reduction. The steady-state current response increases linearly with H2O2 concentration from 0.1 to 300μM with a low detection limit of 0.02μM. Importantly, the proposed electrochemical biosensor has shown a new perspective for detection of H2O2 levels in human real samples and that released from human cervical cancer cells with satisfactory results. This novel CoA-Au(I) CP nanomaterial may provide a cost-efficient, robust and high-sensitive platform for detecting various species involving H2O2-generation reactions for biomedical applications.

Graphene oxide directed in-situ synthesis of Prussian blue for non-enzymatic sensing of hydrogen peroxide released from macrophages

A novel electrochemical non-enzymatic hydrogen peroxide (H2O2) sensor has been developed based on Prussian blue (PB) and electrochemically reduced graphene oxide (ERGO). The GO was covalently modified on glassy carbon electrode (GCE), and utilized as a directing platform for in-situ synthesis of electroactive PB. Then the GO was electrochemically treated to reduction form to improve the effective surface area and electroactivity of the sensing interface. The fabrication process was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The results showed that the rich oxygen containing groups play a crucial role for the successful synthesis of PB, and the obtained PB layer on the covalently immobilized GO has good stability. Electrochemical sensing assay showed that the modified electrode had tremendous electrocatalytic property for the reduction of H2O2. The steady-state current response increased linearly with H2O2 concentrations from 5μM to 1mM with a fast response time (less than 3s). The detection limit was estimated to be 0.8μM. When the sensor was applied for determination of H2O2 released from living cells of macrophages, satisfactory results were achieved.