Capacitance Parameters Research Articles

Composite Sorbents Based on Chitosan Polymer Matrix and Derivatives of 4-Amino-N'-hydroxy-1,2,5-oxadiazole-3-carboximidamide for Uranium Removal from Liquid Mineralized Media.

Composite adsorbents based on a natural biopolymer matrix of chitosan, to which 4-amino-N'-hydroxy-1,2,5-oxadiazole-3-carboximidamide and its Se derivative were attached, were synthesized. A complex of physicochemical analysis methods indicates that the direct introduction of a matrix with high ionic permeability into the reaction mixture contributes to the formation of homogeneous particles of composite with developed surface morphology, which enhances the kinetic and capacitive parameters of uranium sorption in liquid media. It has been established that the direct introduction of a matrix with high ionic permeability into the reaction mixture contributes to the formation of homogeneous particles with a developed surface morphology, which enhances the kinetic and capacitive parameters of uranium sorption in liquid media. The synthesized materials had increased sorption-selective properties towards uranium in the pH range from 4 to 9 under static sorption conditions. The formation of the Se derivative of amidoxime during its attachment to the polymer matrix (Se-chit) contributes to the creation of a more chemically stable and highly effective adsorbent, compared to the direct binding of 4-amino-N'-hydroxy-1,2,5-oxadiazole-3-carboximidamide with chitosan (43AF-chit). The optimal parameters for the synthesis of materials were established. It was demonstrated that the ratio of amidoxime to chitosan should be within the range of 2:1 to 1:2. As the mass content of chitosan increases, the material gradually dissolves and transforms into a gel, resulting in the formation of liquid radioactive waste with a complex chemical composition. It was found that the kinetic sorption parameters of composite materials increase 2-10 times compared to those of non-composite materials. The sorption capacity of uranium in solutions with pH 6 and pH 8 can reach approximately 400-450 mg g-1. Under dynamic sorption conditions, the effective filtration cycle values (before uranium slips into the filtrate ≥ 50%) improve significantly when transitioning from a non-composite adsorbent to a composite one: increasing from 50 to 800 b.v. for pH 6 and from 2700 to 4000 b.v. for pH 8. These results indicate that the synthesized sorbents are promising materials for uranium removal from liquid media, suitable for both purification and the recovery of radionuclides as valuable raw materials.

Исследование проницаемости эпителиального слоя клеток TEER методом

The study investigated the electrical characteristics of the Caco-2 cellular layer grown on a cellulose acetate membrane using impedance spectroscopy and cyclic voltammetry methods. The effect of ethanol solutions of varying concentrations on the electrophysical properties of the cellular layer was studied. During measurements of the layer characteristics by the cyclic voltammetry method under direct current, it was found that its resistance before ethanol treatment was 642 kOhm. Treatment with a 25% ethanol solution increased this value to 645 kOhm, while 50% and 95% solutions decreased it to 505 kOhm and 373 kOhm, respectively. During the study of the cellular layer's properties using impedance spectroscopy with alternating current, dependencies of the real and imaginary parts of the resistance on the ethanol concentration in the treatment solution were obtained. The obtained data were used to construct Nyquist diagrams. Their analysis allowed for the proposal of an equivalent circuit describing the process of current flow through the studied system. The equivalent circuit included parameters of paracellular transport, membrane resistance and capacitance, as well as elements accounting for electrode polarization. As a result, values of capacitance and membrane layer resistance were obtained. It was established that the membrane layer capacitance changes under the influence of ethanol. When treated with a 50% ethanol solution, capacitance increases, indicating degradation of the cell membrane and a reduction in its barrier function. Treatment with a 95% solution led to a decrease in capacitance, which can be attributed to the compression of the cell layer, reducing the capacitance contribution to the system's overall conductivity. The results demonstrate the importance of quantitative analysis of cellular electrical parameters for studying their response to chemical stress and confirm the potential of such approaches in biomedicine for creating sensors and «organ-on-a-chip» systems.

DC-DC Buck Converters with Quasi-Online Estimation of Filter Capacitor Equivalent Parameters

The article focuses on devising solutions for monitoring the condition of the filter capacitors of DC-DC converters. The article introduces two novel DC-DC buck converter designs that monitor the equivalent series resistance (ESR) and the capacitance of capacitors using a parameter observer (PO) and simple variable electrical networks (VEN). For the first scheme, the PO processes in real time the voltage at the capacitor terminals during a discharge-charge cycle. For the second scheme, the filtering is performed with two or more capacitors in parallel, and the PO processes the voltage at the terminals of each capacitor during two discharge processes without interrupting the filtering operation of the converter. The paper presents the principles and theoretical support on which the two schemes of DC-DC buck converters are based, design details regarding PO and VEN, as well as experiments performed with each of the schemes. In the experimental schemes, the PO is implemented with a microcontroller, and the parameters of some aluminum electrolytic filter capacitors are calculated in a real-time manner of about . The calculation accuracy of the equivalent capacity is very good. Regarding the calculation accuracy of the ESR, it is shown that it depends on the fulfillment of certain ratios between the VEN resistances, on the one hand, as well as between them and the ESR, on the other hand.

Poly(3,4-ethylenedioxythiophene) and Poly(3-octylthiophene-2,5-diyl) Molecules as Composite Transducers in Potentiometric Sensors-Synthesis and Application.

The aim of this paper is to investigate the influence of the molecules of conducting polymers on the properties of potentiometric sensors. Two conducting polymers, poly(3-octylthiophene-2,5-diyl) and poly(3,4-ethylene-1,4-dioxythiophene), were compared in the context of the design of ion-selective electrodes. This study offers a comparison of the most popular conducting polymers in the context of the design of potentiometric sensors. Firstly, the properties of both materials, such as their microstructure, electrical performance, wettability, and thermic properties, were examined. Subsequently, conducting polymers were applied as transducer layers in potassium-selective sensors. The properties of both groups of sensors were evaluated using the potentiometry method. Research has shown that the presence of poly(3-octylthiophene-2,5-diyl) (POT) in the transducer layer makes it superhydrophobic, leading to a long lifetime of sensors. On the other hand, the addition of poly(3,4-ethylene-1,4-dioxythiophene) polystyrene sulfonate (PEDOT:PSS) allows for the enhancement of electrical capacitance parameter values, which beneficially influence the stability of the potentiometric response of sensors. Both examined conducting polymers turned out to be perfect materials for transducer layers in potentiometric sensors, each being responsible for enhancing different properties of electrodes.

THE EVOLUTION OF A CLAY CRUST IN A BOREHOLE

Based on the previously proposed quasi-stationary model of clay crust formation when drilling wells in depth intervals with permeable rocks, software was created and computational experiments were performed, which made it possible to clarify the contribution of various physical parameters to the process of its growth.Based on the analysis of the results of computational experiments, the contribution of the physical parameters of the formation and clay crust to the dependence of its size on time has been clarified. The model assumes that the filtration pressure fields are described by stationary piezo conductivity equations. This made it possible to construct explicit dependences of pressure, thickness of the clay crust, radius of the zone of pressure disturbances in the reservoir during drilling and other parameters on time. Simple approximate formulas have been found for the dependence of the thickness of the clay crust, the filtration rate and the radius of the pressure disturbance zone in the reservoir on time, which describe their evolution with high accuracy.Based on the analysis of the calculation results, it was found that the thickness of the clay crust significantly depends on the permeability of the reservoir and repression, and these parameters determine the process of its formation. The porosity of the collector makes a smaller contribution, and the filtration and capacitance parameters of the clay crust have little effect on its thickness.New possibilities for estimating the physical parameters of reservoirs based on cavernometry have been identified. The solution of this problem is especially important for horizontal wells, in which the clay crust intervals have a significant length, and its formation occurs under conditions of a wide range of reservoir properties of the formation. The considered problem is of practical importance, since the zone of penetration of drilling mud filtrate into the formation has a screening effect on the use of geophysical methods to determine reservoir saturation. The results obtained can be used both to improve the interpretation of geophysical methods and to develop those.When conducting computational experiments using an exact formula, the stochastic behavior of the calculated curves was found. It was found that the noted effect is associated with rounding error, and in this sense is a manifestation of the features of the processor. An approach is proposed to eliminate the detected stochastic errors.

A theoretical investigation on wavefronts evolution governed by the modified Nagumo equation

A myelinated nerve fiber model with nonlinear membrane capacitance is considered, and the dynamics of the system is shown to be governed by the modified discrete Nagumo equation. Within the discrete limit, we examined saltatory conduction with the possibility of the capacitive feedback parameter influencing propagation failure. The time series solutions and profile of stationary impulses are equally investigated within the continuum limit approximation. This enhances our understanding of wavefronts initiation in the myelinated fiber under uniform and non-uniform excitabilities. We employed the Bilinear Hirota method and obtained wavefront solutions of the modified Nagumo equation. It is observed that an increase in the capacitive feedback parameter favors the narrowing of wavefronts, while its speed is rapidly increased; thereby enhancing excitability and transfer of neuronal information in the whole of the myelinated axon. The influence of capacitive feedback parameter on the stability of the homogeneous states, is equally brought into sharp focus. Results of numerical simulations of the modified discrete Nagumo equation, portrays a clear concordance with the analytical predictions. This is because the speed of the propagating anti-kink increases as the capacitive feedback parameter is gradually stepped up. We hope that future experimental investigations will validate the theoretical predictions highlighted in this study.

Exploration of Factors Affecting Resonance in Photovoltaic Cluster Grid Integration System

Abstract A significant number of distributed photovoltaics being connected to the grid leads to a more complex harmonic content in the photovoltaic cluster grid integration system. When a specific harmonic frequency approaches the system resonance frequency of the system, a resonance phenomenon occurs. This paper conducts an analysis of the complex resonance coupling relationship. Subsequently, it separately examines the impact of grid impedance, filter capacitor parameters, and the number of parallel inverters on the resonant frequency. It is verified through simulation that the aforementioned factors will bring about a change in the resonant frequency.

A high robust control scheme of grid‐side converter for DFIG system

AbstractIn this study, a high robust control—second‐order sliding‐mode control (SOSMC) scheme is proposed to improve the DC‐link voltage dynamic performance of the grid‐side converter (GSC) for the doubly‐fed induction generator (DFIG) system under the wind turbine power disturbance and DC‐link capacitance parameter disturbance. In general, the wind speed is change with the environment and further has an effect on the power generation of the DFIG system. Besides, the capacitance of DC‐link capacitor may change with the working condition. To address this issue, a SOSMC scheme is proposed to replace the conventional proportional integral (PI) control for the DC‐link voltage controller of the GSC for the DFIG system in this study. By using the non‐linear SOSMC controller, the DFIG system is robust to the disturbance of the wind speed and the parameter of DC‐link capacitance. Compared with the conventional PI control scheme, the DFIG system with the proposed SOSMC scheme is much more robust, which has been verified in the MATLAB/Simulink platform.

Method of calculation of a two-stage separation system of a biofuel production installation

Currently, the processing of plant waste is a promising area of development in modern energy. There are many methods for recycling waste, but not all of them are economically feasible and environmentally friendly. One of the most common processing methods is fast ablative pyrolysis, designed for thermal processing of waste without access to oxygen. As a result of such processing, carbon residue and pyrolysis gas are formed. The amount of pyrolysis gases produced is 60 % or more of the mass of processed raw materials. In order for pyrolysis gases to become high-quality fuel, they must be subjected to a separation process that takes place in devices called a vapor condenser. When separating pyrolysis gases, it is better not to use conventional oil and gas condensers since the condensed pyrolysis gases have a high tar content, which causes faster wear of the device. For the installation for the production of pyrolysis fuel, a two-stage separation system is proposed, designed to separate pyrolysis gases into fractional components: pyrolysis distillate, non-condensable combustible gas and water. The article presents the design of a two-stage separation system. The principle of operation of a two-stage separation system is described, and a diagram of its structure is given. A method for calculating a two-stage separation system is presented, which makes it possible to determine the geometric parameters of scrubber and ejector type capacitors.

Optimizing Wireless Power Transfer Systems: A Simulation-Based Approach Using CST Studio Suite

In the rapidly evolving field of wireless power transfer (WPT), achieving systems that combine efficiency with reliability is crucial. This paper presents a simulation-based approach using CST Studio Suite to optimize WPT systems for wireless battery chargers in electric bikes. The study fixes the size of both the transmitter and receiver coils, the spacing between turns, and the number of coil turns, with a set distance of 20mm between the transmitter and receiver coils. CST Studio Suite is employed to determine the parameters of resonance capacitors and the optimal switching frequency to enhance WPT efficiency. This powerful simulation tool allows researchers and engineers to design resonance compensation circuits more effectively, optimizing power transfer efficiency. The simulation conducted with CST Studio Suite confirms its effectiveness in designing a WPT system, achieving an impressive peak efficiency of 99.61% at the resonant frequency. The paper demonstrates CST Studio Suite's capability to accurately predict WPT system performance by developing detailed electromagnetic models and fine-tuning simulation parameters to reflect real operating conditions. Iterative simulations resulted in optimized practices, validated by select results that highlight the method's effectiveness and showcase an optimal balance between system complexity and efficiency. These findings provide a strategic framework for future WPT system development, offering practical guidance for researchers and industry professionals aiming to advance WPT technology.

Pseudocapacitive Na ion storage in binder-less, carbon additive-free Nb2O5-x electrode synthesised via solvothermal-assisted electro-coating with enhanced areal capacitance and lowered impedance parameters

Negatrodes with wide negative operating voltage, high electrochemical storage capacity, and intrinsic metal ion intercalation abilities are vital to the continuous development of storage devices with simultaneous energy and power density improvement. Herein, we report binder-less coating of non-stoichiometric vacancy-implanted Nb2O5-x as carbon additive-free negatrode on FTO substrate for asymmetric supercapacitor and sodium ion capacitor applications. The negatrode was fabricated through vacuum-less and low-temperature solvothermal-assisted electro-coating technique and yielded several orders of enhancement in its areal capacitance and retained ca. 90 % of its capacity after 5000 cycles of charge-discharge in aqueous Na+ electrolyte. The solvothermal treated electro-coated electrode (STT_Nb2O5-x) achieved an areal capacitance of 22.58 mF/cm2, which was far higher than those of hydrothermal-treated electro-coated HTT_Nb2O5 and Nb2O5 electrodes. The solvothermal treatment simultaneously enhanced the electro-coated samples' impedance properties and mass load through oxygen vacancy implantation and re-crystallization of the electro-coated Nb2O5 layer, respectively. This study presented a facile and energy-efficient technique of direct coating of defect-enhanced pseudocapacitive nanomaterials for the fabrication of electrochemical storage devices.

Online condition monitoring for DC-link capacitors of three-level NPC converters using noninvasive signal injection

This paper introduces an online method for monitoring the health condition of the DC-link in three-level NPC converters. This method does not require hardware changes or modifications to the control algorithm. It involves injecting a zero-sequence signal, added to the system reference voltages to generate a neutral-point current injection. A square waveform with an interharmonic cycle frequency is used for the signal injection to minimize estimation errors caused by existing signals. This combined signal allows for the simultaneous estimation of the capacitor equivalent series resistance (ESR) and capacitance (C) at different frequency components using wavelet decomposition. Additionally, a balance between the magnitudes of the system reference voltage and the signal injection is established to prevent power quality issues. Besides, the capacitor parameters are estimated in the time-frequency domain, enabling tracking of capacitor degradation and wear-out failure. A comparison with a Fourier-based approach shows that this method provides highly accurate capacitor parameter estimation with less than 2% errors, instilling confidence in its results. Experimental results from a three-level NPC converter’s laboratory setup demonstrate the proposed method’s effectiveness.

Volterra operator-based fixed-time adaptive parameter estimation for DC-DC buck converters without current sensors

This paper investigates the problem of parameter estimation for DC-DC buck converter without current sensors. For the circuit, all the parameters of capacitance, inductance, resistance, and input voltage are unknown. A novel Volterra operator-based fixed-time adaptive algorithm is proposed by using only the output voltage and control input signals. By selecting proper kernel function for the Volterra integral operator, the influence of the system initial values can be eliminated, and the calculation of the derivative of the system output can also be avoided. Strict analysis shows that the proposed estimation algorithm can ensure the estimation errors converge to zero in a fixed time independent of the initial error values. Finally, simulation results with different initial values verify the advantages of the proposed algorithm.

Detuning analysis and power tracking of dual‐ended resonant circuit based on improved variable‐step perturbation observation for wireless power transfer system

AbstractA power tracking method based on improved variable‐step perturbation observation approach has been proposed in this paper. This method is aimed at addressing the detuning issues caused by capacitor parameter drift in MCR‐WPT systems based on S‐S compensation circuits. Compared with traditional tuning methods, the proposed method has fast response, high accuracy, low complexity, and less prone to over‐tracking. Firstly, a mathematical model of the system based on the detuning factor has been established. Secondly, the impact of different detuning conditions on the system at the initial resonant frequency has been studied. Thirdly, the response characteristics of the system to different frequencies under different detuning conditions have been studied. Fourthly, based on the above researches, an improved variable‐step perturbation observation method based on the single‐step power drop factor has been proposed. Finally, an experimental platform was constructed, and relevant experiments were conducted. Experimental results validate the effectiveness of power tracking under different detuning conditions, with the lowest transmission efficiency being 81.51%.

Ion-Selective Electrode for Nitrates Based on a Black PCV Membrane.

Carbon nanomaterials were introduced into this research as modifiers for polymeric membranes for single-piece electrodes, and their properties were studied for the case of nitrate-selective sensors. The use of graphene, carbon black and carbon nanotubes is shown to significantly improve the potentiometric response, while no redox response was observed. The use of carbon nanomaterials results in a near-Nernstian response (54 mV/pNO3-) towards nitrate ions over a wide linear range (from 10-1 to 10-6 M NO3-). The results obtained by chronopotentiometry and electrochemical impedance spectroscopy reveal little resistance, and the capacitance parameter is as high as 0.9 mF (for graphene-based sensor). The high electrical capacity of electrodes results in the good stability of the potentiometric response and a low potential drift (0.065 mV/h). Introducing carbon nanomaterials into the polymetric membrane, instead of using them as separate layers, allows for the simplification of the sensors' preparation procedure. With single-piece electrodes, one step of the procedure could be omitted, in comparison to the procedure for the preparation of solid-contact electrodes.

Reactivity of Resorcinol on Pt(511) Single-Crystal Surface and Its Effect on the Kinetics of Underpotentially Deposited Hydrogen and Hydrogen Evolution Reaction in 0.1 M NaOH Electrolyte.

This article presents cyclic voltammetry, Tafel polarization, and ac. impedance spectroscopy examinations of resorcinol (RC) ion reactivity on Pt(511) single-crystal plane and the effect of surface-electrosorbed RC ions on the kinetics of UPD H (underpotentially deposited hydrogen) and HER (hydrogen evolution reaction) processes in 0.1 M NaOH solution. Obtained data delivered a proof for the RC ion surface adsorption and its later electroreduction over the potential range characteristic for the UPD H. A favourable role of platinum-adsorbed resorcinol anions on the kinetics of the UPD H and HER processes is also discussed. The above was explained via the recorded capacitance and charge-transfer resistance parameters (the presence of resorcinol at 1.5 × 10-3 M in 0.1 M NaOH caused significant reduction in the resistance parameter values by 3.9 and 2.6 times, correspondingly, for the UPD of H at 50 mV and the HER process, examined at -50 mV vs. RHE) along with the charge transients, produced by injecting small amounts of RC-based 0.1 M NaOH solution to initially RC-free base electrolyte on the Pt(511) electrode plane (a large cathodic charge-transient density of -90 µC cm-2 was recorded at the electrode potential of 50 mV).

Hierarchical Porous Activated Carbon Derived from Pleurotus Eryngii and the Influence of Pore Structural Parameters on Capacitance Performance

Hierarchical porous activated carbon derived from pleurotus eryngii was prepared by a one-step activation method. It was found that the specific surface area of the obtained sample increased with the increase in activation temperature (700–900 °C). The sample activated at 900 °C has a specific surface area of 2002.2 m2 g−1 and the highest specific capacitance (319 F g−1), which is mainly attributed to the high utilization rate of specific surface area brought by the hierarchical porous structure. The assembled PEK-900//PEK-900 capacitor measured a specific capacity of 258 F g−1 at a current density of 0.5 A g−1. After 10,000 cycles of charging and discharging, the specific capacitance increased by 10%. Based on the correlation analysis of experimental data between the specific capacitance and pore structural parameters, Lasso dimensionality reduction and binary linear regression were used to reveal the relationship between the two. The residual sum of squares obtained by this method decreased by 38.4% compared to the univariate linear regression, providing a simple and reliable theoretical method for predicting the capacitance performance of biomass carbon materials.

Research on new method of transformer winding deformation detection

As one of the most important electrical equipment in power system, the stable operation of transformer is the key factor to ensure the safety of power grid system. Winding deformation is the most common fault of transformer, which will seriously affect the reliable operation of the whole power system. Therefore, the detection of transformer winding deformation is of great significance to prevent transformer accidents. In order to further improve the reliability of transformer winding deformation detection, this paper proposes a transformer winding deformation detection method based on oscillation wave method. Firstly, the equivalent circuit model of transformer winding is established, and the transformer winding fault is simulated by changing the inductance and capacitance parameters in the model, and the law between the change of oscillation wave curve and the change of related performance indexes and equivalent parameters is obtained. Finally, the field test verification is carried out on a 10 kV transformer in the laboratory. The results show that the oscillation wave method can diagnose the transformer winding deformation and can be used for the actual transformer winding deformation detection.

Design of main parameter of modular multilevel converter applied in power grid simulator

Abstract In the context of application in a power grid simulator, we investigated the parameter design issues of several crucial components of the Modular Multilevel Converter (MMC) topology applied to the power grid simulator system. These components include the bridge arm inductance and submodule capacitance. Based on the fundamental circuit of the MMC applied to the power grid simulator system, we introduced an equal discharge time constant H. We analyzed the capacitor voltage fluctuation rate and the equivalent capacitance discharge time constant “H”, discovering that they still exhibit an inversely proportional relationship across different engineering scenarios. Consequently, a general method for determining submodule capacitance parameters was proposed, and in conjunction with previous engineering parameters, recommended values for an equal discharge time constant of 40 ms were provided. Furthermore, we introduced the concepts of double-frequency circulating resonant angular frequency and phase resonant angular frequency, outlining the principles for determining the bridge arm reactance values. Through the analysis of corresponding parameters in previous engineering studies, universally applicable recommended values for the bridge arm reactance parameters were proposed, considering the unit resonant angular frequency as the power grid frequency angular frequency 1.0ω.

Analysis of Energy During Spark Discharge in Short Circuit of Capacitive Circuit

ABSTRACT In the explosive environments, the electrical sparks with short circuit of capacitor output will ignite the surrounding explosive medium, and the relationship between effective ignition energy, capacitance energy conversion rate, capacitor capacitance and capacitor terminal voltage is unclear. Based on the three stages of breakdown, discharge and attenuation of the discharge characteristic curve of capacitive circuit, this paper deduces the expressions of spark resistance and discharge current including voltage, capacitance and polar distance parameters. Based on the programmable micro-nano gap discharge experimental platform, experiments under different voltages and different capacitances were carried out. It is found that the theoretical voltage-current curve and spark energy conversion rate are in good agreement with the experimental fitting curve and spark energy conversion rate. And with the increase of capacitance or voltage, the peak current and discharge time increase, which leads to the increase of energy. The conversion rate of spark energy decreases with the increase of capacitance or voltage, and the conversion rate changes between 20% and 30%. The change of spark energy conversion rate is also related to spark resistance, and with the decrease of spark resistance, the spark energy conversion rate also decreases. This study can further understand the energy variation in the discharge gap and is of great significance for the research of intrinsically safe circuits.