Potential Drop Research Articles

Influence of non-linear slip dependent zeta potential on the bi-layered electrohydrodynamic flow in an electrically actuated microsystem

In this paper, the electro-osmotic flow (EOF) of two immiscible fluids through an electrically actuated micro-slit with a non-linear slip-dependent zeta potential is considered. The main objective of this work is to enhance the EOF velocity of non-polar fluid with an intensive flow variation in micro-confinements. We present the comparison between the Poisson–Nernst–Planck (P–N–P) and the Poisson–Boltzmann model and illustrate the impact of different parameters, such as Debye–Hückel parameter, slip coefficient, and interfacial potential drop, on the ionic concentration and the induced potential in detail. In this study, the interface between two immiscible fluids is considered to be planar, and a potential drop is observed close to the interface due to the development of back-to-back diffuse layers. At the interface between two layers, the continuity of the velocity and total stresses (Maxwell stress and shear stress) are taken into account to investigate the flow field in the system of immiscible electrolytes. The P–N–P model, linked with the ion transport equation and the Poisson equation, is employed to describe the motion of electrolyte solutions. The non-linear governing equations are numerically computed using a pressure-correction-based finite volume technique based on a staggered grid algorithm. Closed-form analytical solutions are derived for both steady and unsteady EOF field of two immiscible fluids for the low wall zeta potential and non-overlapping electrical double layer. The analytical solutions are well validated with our numerical results under suitable assumptions. It is also observed that the slip-dependent zeta potential successfully provides a considerable enhancement in EOF velocity over a broad range of parameters such as zeta potential, Debye–Hückel parameter, as well as boundary slip parameter. The results for both layers are highly affected by unequal wall potential, and the ion concentrations are highly actuated by the external electric field.

Effect of electron-electron collisions on entrance potential drop in high-mobility 2DEG channels

Usually, the evidence of viscous hydrodynamic transport of frequently colliding conduction electrons is considered to be the “Gurzhi effect,” which requires the scattering of electrons on the channel walls with momentum loss. However, we demonstrate that expansion of Sharvin’s potential drop directly related to frequent electron-electron collisions can be detected even in channels with ideally smooth walls in a two-dimensional degenerate electron gas (2DEG). In theory, this effect could be experimental evidence of the predicted earlier difference between the relaxation times of the antisymmetric and symmetric momentum distributions attributed to the Pauli principle and topological limitations in 2DEG.

Potential-tuned magnetic switches and half-metallicity transition in zigzag graphene nanoribbons

Realizing controllable room-temperature ferromagnetism in carbon-based materials is one of recent prospects. The magnetism in graphene nanostructures reported previously is mostly localized by breaking the local sublattice imbalance. Here, we predict a robustly potential-tuned ferromagnetic domain lying between the inter-chain carbon atoms inside the zigzag graphene nanoribbons. We show that the effective zigzag edges provide the strong correlation background through narrowing the band width, while the internal Van Hove filling (VHF) provides the strong ferromagnetic background inherited from the bulk. The induced ferromagnetism exhibit interesting switching effect when the nominal VHF crosses the intra- and inter-chain region by tuning the potential drops. We further observe a robust half-metallicity transition from one spin channel to another within the same magnetic phase. These novel properties provide promising ways to manipulate the spin degree of freedom in graphene nanostructures.

Fretting crack detection of a railway axle with a mounted wheel using an induced current potential drop and electromagnetic-field distribution

Fretting crack detection of a railway axle with a mounted wheel using an induced current potential drop and electromagnetic-field distribution

Linking Topographical Ring Features to Geochemical and Geophysical Anomalies

Circular features in forests seen from air have been studied for several decades at different locations around the world. Forest rings, as they are called in Canada’s boreal forests, express several geochemical (pH, carbonate content) and geophysical (surface potential) anomalies on their 20–30 m wide ring edges. Although it has been proposed that microbial processes may cause these anomalies, the exact mechanisms of ring formation are still unknown. We focused on the Thorn North forest ring in Ontario, Canada to correlate the surface potential anomaly to soil gas concentrations. Field measurements showed that the surface potential drop at the ring edge center is framed by peaks in CO2 production, which is linked to O2 depletion and methane generation. Carbon isotope signatures were found to drop to lighter values (down to −20‰), suggesting increased respiration. Higher concentrations of uronic acids bound to extracellular polymeric substances were found, indicating that the surface potential anomaly is linked to respiration. 16S rRNA gene sequencing of shallow soil did not indicate a dominant microbial group on the edges; instead, principal component analysis showed that the microbial composition was controlled by the substrate (clayey vs. sandy soil), therefore future studies should focus on deeper ground layers.

Electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged non-uniform microfluidic device

BackgroundMicro-scale systems depict a different flow behavior from the macro-scale systems due to more vital surface forces such as surface tension, electrical charges, magnetic field, etc., which significantly affect the micro-scale flow. Further, among others, electrokinetic phenomena play a significant role at the micro-scale for controlling practical microfluidic applications. Therefore, it is essential to understand the fluid dynamics in micron-sized channels to develop efficient and reliable microfluidic devices. MethodsThe electroviscous effects in pressure-driven flow of electrolyte liquid through an asymmetrically charged contraction-expansion (4:1:4) slit microfluidic device have been investigated numerically. The mathematical model (i.e., Poisson's, Navier-Stokes, and Nernst-Planck equations) is solved using the finite element method to obtain the electrical potential, velocity, pressure, ion concentration fields, excess charge, an induced electric field strength for the following ranges of parameters: Reynolds number (Re=0.01), Schmidt number (Sc=1000), inverse Debye length (2≤K≤20), top wall surface charge density (4≤St≤16), surface charge density ratio (0≤Sr≤2) and contraction ratio (dc=0.25). Significant FindingsResults show that the charge asymmetry (Sr) at the different walls of the microfluidic device plays a significant role on the induced electric field development and microfluidic hydrodynamics. The total potential (|ΔU|) and pressure drop (|ΔP|) maximally increase by 197.45% and 25.46%, respectively with asymmetry of the charge. The electroviscous correction factor (ratio of apparent to physical viscosity) maximally changes by 20.85% (at K=2, St=16 for 0≤Sr≤2), 34.16% (at St=16, Sr=2 for 2≤K≤20), and 39.13% (at K=2, Sr=2 for 0≤St≤16). Thus, charge asymmetry (0≤Sr≤2) remarkably influences the fluid flow in the microfluidic devices, which is used for controlling the microfluidic processes, such as, mixing efficiency, heat, and mass transfer rates. Further, a simpler analytical model is developed to predict the pressure drop in electroviscous flow considering asymmetrically charged surface, based on the Poiseuille flow in the individual uniform sections and pressure losses due to orifice, estimates the pressure drop 1–2% within the numerical results. The robustness of this model enables the use of present numerical results for design aspects in the microfluidic applications.

Impedance of porous electrodes in the presence of electroactive species and solution resistance

In a recent paper, we have presented behavior of the porous electrodes in the presence of electroactive species and the absence of the dc and ac potential gradients. This paper presents a model without dc potential gradient but including ac potential drop due to the solution resistance in pores. In this case, a high-frequency straight line at 45° characteristic of porous electrodes appears at high frequencies on the complex plane plots followed by two semicircles. This high-frequency line increases with the increase of the electrode porosity, i.e. Thiele modulus, and solution resistivity. Fitting these impedances to the classical de Levie’s model does not reproduce well the parameters of the second semicircle although the overall fit is good for moderate porosities.

Changes in Activity of Antioxidant Systems of <i>Escherichia coli</i> under Phosphate Starvation

Changes in the activity of antioxidant systems in Escherichia coli during phosphate starvation were studied. It was shown that starvation was accompanied by a decrease in the intensity of respiration, an increase in the rate of superoxide production, and a decrease in the level of ATP. Simultaneously, there was a decrease in H2O2 in the medium and a significant increase in the expression of the katG and katE genes encoding the HPI and HPII catalases, respectively. At the same time, there was no drop in the membrane potential, which may indicate the retention of normal membrane activity in starving cells. It has been shown for the first time that the transition of E. coli to phosphate starvation is accompanied by significant changes in the status of glutathione. The most important of them are associated with a decrease in the level of glutathione reductive form (GSH) in the medium (GSHout) and with a simultaneous increase in its content in the cytoplasm (GSHin), as well as a shift in the GSHin to oxidized glutathione form (GSSGin) ratio towards reductive values, and GSHout/GSSGout towards oxidative values. Among the mutants used in the work, the double mutant gor trxB, deficient in the synthesis of glutathione reductase and thioredoxin reductase, showed the most pronounced distinctive features. Compared to the parental strain, this mutant showed a multiple higher expression of katG::lacZ, the highest level of oxidized intra- and extracellular glutathione, and, accordingly, the lowest GSH/GSSG ratio in both compartments. In general, the data obtained indicate that during phosphate starvation the interaction of the glutathione redox-system and regulons that control protection against reactive oxygen species creates conditions that allow maintaining the concentration of ROS below the toxic level. As a result, phosphate-starved E. coli cells can maintain a high viability for a long time that allows them quickly to resume growth after the addition of phosphate.

NiCo-layered double hydroxide modified TiO2 nanotube arrays and its application in photoelectrochemical cathodic protection of 304 stainless steel

NiCo-layered double hydroxide (NiCo-LDH) modified TiO2 (NiCo/TiO2) were prepared by a simple electrochemical deposition method. The morphology, chemical composition, light adsorption and photoelectrochemical (PEC) properties of these composites were fully characterized. The performance of NiCo/TiO2 in PEC cathodic protection of 304 stainless steel (304 SS) was investigated in NaCl solution. The results showed that NiCo(−0.8)/TiO2 had the best PEC cathodic protection performance, as indicated by the largest photo-induced potential drop (−440 mV) of 304 SS. It was proposed that a type II heterojunction was built between NiCo-LDH and TiO2, leading to a more efficient separation of photo-generated charge carriers.

Educational problems in electrochemical thermodynamics

This article reviews educational problems of electrochemical thermodynamics required as introduction to any electrochemistry-related course. Specifically, the most important, electromotive force (EMF) equation, – is generally derived from Guggenheim’s formulation of electrochemical potential. For this aim the more general equation for equilibrium between phases is introduced. Special attention is given to the measurement of electrode potential. Potential drop across metal|metal contacts, usually displayed in potential profiles of electrochemical cells, can be excluded from them. The conclusion is based on Lord Kelvin’s formulation of the case, when metals are in contact, as “metallic zero”. Concerning absolute potentials, for the cases when the electrode material does not participate in electrochemical reaction, it can be calculated from the Gibbs free energy of the corresponding chemical reaction occurring in solution. Accordingly, the absolute hydrogen electrode potential is determined by thermodynamics of H+/H2 reaction.

Analysis of potential flow networks: Variations in transport time with discrete, continuous, and selfish operation

In potential flow networks, the equilibrium flow rates are usually not proportional to the demands and flow control elements are required to regulate the flow. The control elements can broadly be classified into two types—discrete and continuous. Discrete control elements can have only two operational states: fully open or fully closed. On the other hand, continuous control elements may be operated in any intermediate position in addition to the fully open and fully closed states. Naturally, with their increased flexibility, continuous control elements can provide better network performance, but to what extent?We consider a class of branched networks with a single source and multiple sinks. The potential drop across edges (ΔH) is assumed to be proportional to the nth power of flow rate (Q), i.e., ΔH=kQn , (n≥1). We define R as the ratio of minimal operational times required to transport a given quantum of material with either type of control element and show that 1≤R≤m1−1/n, where m is the maximum depth of the network. The results point to the role of network topology in the variations in operational time. Further analysis reveals that the selfish operation of a network with continuous control valves has the same bounds on the price of anarchy.

Ginger exosome-like nanoparticles (GELNs) induced apoptosis, cell cycle arrest, and anti-metastatic effects in triple-negative breast cancer MDA-MB-231 cells

Ginger exosome-like nanoparticles (GELNs) have been extensively implicated in alleviating inflammation, maintaining intestinal microbiome and are considered competent drug delivery vehicles. Despite this, the current knowledge of the GELN interaction with cancer cells is limited. Triple-negative breast cancer (TNBC), an aggressive variant lacking efficient therapeutics, necessitates novel natural counterparts with minimal side effects. This study investigates the action of GELNs isolated from ginger rhizomes against TNBC cells. GELNs were isolated by ultracentrifugation and characterized physicochemically. The interaction of GELNs with TNBC cells (MDA-MB-231) was studied in detail. The GELNs induced a concentration-dependent decrease in cell viability in MDA-MB-231 cells without affecting the normal cell lines tested. GELNs induced apoptosis as indicated by morphological changes, nuclear fragmentation, membrane damage, phosphatidyl serine translocation, ROS generation, drop in mitochondrial membrane potential, expression of apoptotic specific proteins, and increased caspase activity. GELNs also instigated cell cycle arrest, retarded cell migration and colony formation in TNBC cells. These findings report a novel action of GELNs against TNBC cells and a closer look at the underlying molecular mechanism of this interspecies communication. This opens newer prospects for using dietary ELNs to target therapeutically challenging cancers.

CaIn2S4 nanosheets and SnO2 nanoflowers co-sensitized TiO2 nanotubes photoanode for continuous and efficient photocathodic protection of Q235 carbon steel

To solve the problem of poor photocathodic protection (PCP) effect of pure TiO2 nanotubes (NTs) on Q235 carbon steel (CS), CaIn2S4 nanosheets (NSs) and SnO2 nanoflowers (NFs) co-sensitized TiO2 NTs were prepared by anodization, hydrothermal and solvothermal method. Results showed that the absorption edge of CaIn2S4/SnO2/TiO2 NTs extended to 540 nm, indicating the utilization efficiency of visible light was greatly improved. Under light, the CaIn2S4/SnO2/TiO2 NTs exhibited an open circuit potential drop of 530 mV vs. SCE and a photocurrent density of 624 μA cm−2, which was 23 and 48 times that of TiO2 NTs, respectively. The PCP properties of CaIn2S4/SnO2/TiO2 NTs were better than that of TiO2 NTs because the separation and transfer efficiency of electrons and holes were promoted due to the heterojunction structure formed between TiO2, SnO2 and CaIn2S4. Furthermore, the CaIn2S4/SnO2/TiO2 NTs could also provide time-delay protection up to 10 h in the dark state. Obviously, CaIn2S4/SnO2/TiO2 NTs have excellent electron storage capacity and could provide efficient and continuous protection, which may be due to the presence of SnO2 NFs. This work provides an effective strategy of designing more efficient photoanodes for PCP of metals.

Design and modeling of the electrostatically controlled nanowire FET for ppt-level hydrogen sensing

We present the design of a H2 gas sensor based on palladium (Pd) decorated silicon-on-insulator (SOI) nanowire field effect transistor (FET) with a standard SOI complementary metal-oxide-semiconductor fabrication process, where a top Pd layer plays a dual role of a catalyst and a surrounding metal gate. A numerical study was conducted based on a simplified steady-state model to describe the sensing mechanism of H2 in dry air at 300 K. The simulation is based on the model of dissociative H2 adsorption on the Pd surface and the formation of a dipole layer at the Pd/SiO2 interface. The H atoms induced dipoles lead to a potential drop which exponentially increases the FET drain current and consequently, the sensor response. The FET drain current is controlled by its back-gate bias and by varying the H2 concentrations; it is shown that the drain current response reaches 1.8 × 108% for 0.8% H2 in air and a superior sensitivity of 4.58 × 104%/ppm in the sub-threshold operation regime. The sensor exhibits an outstanding theoretical detection limit of 50 ppt (response of 1%) and an upper dynamic range limit of 7000 ppm which allow for timely and accurate detection of H2 gas presence. The power consumption ranges between ∼10 fW (dry air) to ∼20 nW (0.8% H2 in dry air) and therefore paves the way for a very large-scale integration commercial sensing platform.

Anode region of a low-pressure gas discharge

This paper considers the processes that occur in the anode region of a low-pressure gas discharge. Two modes of the longitudinal transport of charged particles in the anode region have been revealed: the free flight mode and the diffusion-drift mode. It has been shown that the anode potential drop in the free flight mode should be negative at any discharge current. For the diffusion-drift mode, the distributions of the electric field strength and potential, as well as the velocities of directed motion of electrons and ions in the anode region have been calculated. Analysis of the results obtained has made it possible to determine the conditions for a positive and a negative anode potential drop to occur. The calculated values of the anode potential drop are in satisfactory agreement with experimental data. A similarity criterion has been formulated to determine the sign of the anode potential drop.

SYNTHESIS AND STUDY OF NANO-SIZED COMPLEX OF Fe(III) WITH ETHYLENEDIAMINEDISUCCINIC ACID

In this work, the FeEDDSNP nanocomplex was synthesized by dissolution peptization of a freshly precipitated sol of iron hydroxide Fe(OH)3 in an aqueous solution of the racemic form of Н4EDDS. The complex was characterized by electron absorption spectroscopy and IR spect­roscopy. It was shown that the structure of the nanocomplex is identical to the structure of the FeEDDS complex obtained using a two-stage technology. The position of the absorption maxima of iron nanoparticles practically does not change depending on the sto­rage time at room temperature, which indicates the stability of the synthesized nanocomplex. The nano­dispersed FeEDDSNP complex is more soluble in water (275 g/l) compared to the FeEDDS complex obtained by the classical method (150 g/l), which greatly facilitates its use as a biologically active compound. To determine the stability of the system depending on the pH, the electrokinetic potential was measured to select the optimal pH of the medium and concentrations to obtain stable dispersed systems. It is shown that at low pH (1.5–4.0) there is a drop in the electrokinetic potential, and when the pH increases, the

Highly sensitive detection of malaria biomarker through matching channel and gate capacitance of integrated organic electrochemical transistors

Organic electrochemical transistors (OECTs) possess versatile advantages for biochemical and electrophysiological applications due to electrochemical gating and ion-to-electron conversion capability. Although OECTs have been successfully applied for biochemical sensing, the effect of relative capacitance for specific sensing events is still unclear. In the present work, we design integrated interdigitated OECTs (iOECTs) with on-plane gold gate and different channel geometries for point-of-care diagnosis of malaria using aptamer as receptor. The transconductance of the iOECTs gated with micro-size gold electrodes decreased with increasing the channel thicknesses, especially for devices with large channel areas, which is inconsistent with devices gated by typical Ag/AgCl electrodes, attributing to the limited gating efficiency of the micro-size gate electrode. The capacitance of gate electrode was heavily suppressed by receptors but increased with the incubation of targets. In addition, the integrated iOECTs with thin channels exhibited superior sensitivity for malaria detection with the detection limit as low as 3.2 aM, much lower than their thick channel counterpart and other state-of-the-art biosensors. These deviations could be caused by the high relative capacitances, with respect to the gate and channel capacitance (Cg/Cch), resulting in a high gate potential drop over the organic channel and thus entirely gating on the thin channel device. These findings provide guidance to optimize the geometry of OECT devices with on-chip integrated gates and the fabrication of miniaturized OECTs for biosensing applications.

Enhanced visible-light-driven photocatalytic activity in SiPGaS/arsenene-based van der Waals heterostructures

Van der Waals heterostructures (vdWHs) showcase robust and tunable light-matter interactions, establishing an intriguing realm for investigating atomic-scale photocatalytic properties. Here, we employ ab initio methods to study the photocatalytic and optical properties of semiconducting SiPGaS/arsenene-based vdWHs with a type-II band alignment. Across the heterointerfaces, there exists significant built-in electric fields and large potential drop, in turn facilitating the spatial separation of photo-generated electron-hole pairs. These vdWHs further possess high carrier mobility in the order of 102 cm2V⁻1S⁻1, which combining with appropriate band edge positions, endow the vdWHs an absorption coefficient of ∼10⁵ cm⁻1 to harvest a maximal portion of the solar spectrum for visible-light-driven photocatalytic applications. Our findings also reveal transition of the type-II band alignment in a type-III configuration via compressive strain for tunneling field-effect transistor application. Furthermore, both types of vdWHs exhibit enhanced suitability for photocatalysis under conditions with a pH of 2.

Strip-saturation model for arbitrary polarized electro-elastic material weakened by an eccentrically situated anti-plane semi-permeable crack

A strip-saturation model is studied to observe the effect of changing polarization axis on an electro-elastic strip, weakened by an eccentrically situated anti-plane semipermeable crack. The model is modified by considering that the saturated limit of electric displacement over rims of the saturation zone is quadratic interpolating polynomial times. The proposed model is formulated and then solved by using the Fourier integral transform technique and integral equations method. Closed-form analytic expressions are derived for developed saturation zone and fracture parameters viz. electric crack condition parameter, crack-sliding displacement, crack-opening potential drop, field intensity factors, energy release rate, etc. The influence of poling angle, prescribed electro-mechanical loadings, crack length, and material constants on fracture parameters are presented and analyzed graphically.

Electrodes as the protagonists in composite barrier Ferroelectric Tunnel Junctions

The role of electrodes in composite barrier Ferroelectric Tunnel Junctions (FTJs) is investigated for the systems (//Pt/STO/BTO/SRO, //Pt/STO/BTO/Pt, //SRO/STO/BTO/SRO and //SRO/STO/BTO/Pt). The tunneling current is controlled by the potential drop in the accumulation and depletion region in the electrodes which depends on the ratio of their screening length to permittivity (δ/). The Tunneling electro resistance ratio (TER) becomes significant for bias potential wherein the screening charge density remains negative causing the pull-down of the barrier towards the Fermi level and an increase in the tunneling current. Among the studied systems //Pt/20Å STO/24Ǻ BTO/SRO system with an active device length of 7.6 nm is found to have a current density of 3.38 × 104 A cm−2 and 0.22 A cm−2 in the ON and OFF state and an absolute TER of around 1.52 × 105% at the bias of 0.77 V conform to the necessary conditions of efficient application in memory devices.