Positive Potential Difference Research Articles

Urea-Self Powered Biosensors: A Predictive Evolutionary Model for Human Energy Harvesting.

The objective of this study is to create a reliable predictive model for the electrochemical performance of self-powered biosensors that rely on urea-based biological energy sources. Specifically, this model focuses on the development of a human energy harvesting model based on the utilization of urea found in sweat, which will enable the development of self-powered biosensors. In the process, the potential of urea hydrolysis in the presence of a urease enzyme is employed as a bioreaction for self-powered biosensors. The enzymatic reaction yields a positive potential difference that can be harnessed to power biofuel cells (BFCs) and act as an energy source for biosensors. This process provides the energy required for self-powered biosensors as biofuel cells (BFCs). To this end, initially, the platinum electrodes are modified by multi-walled carbon nanotubes to increase their conductivity. After stabilizing the urease enzyme on the surface of the platinum electrode, the amount of electrical current produced in the process is measured. The optimal design of the experiments is performed based on the Taguchi method to investigate the effect of urea concentration, buffer concentration, and pH on the generated electrical current. A general equation is employed as a prediction model and its coefficients calculated using an evolutionary strategy. Also, the evaluation of effective parameters is performed based on error rates. The obtained results show that the established model predicts the electrical current in terms of urea concentration, buffer concentration, and pH with high accuracy.

The cortisol awakening response and the late positive potentials evoked by unpleasant emotional pictures in healthy adults

The cortisol awakening response (CAR) refers to a sharp rise in cortisol concentrations within the 45 min following morning awakening. Alterations in CAR have been associated with various internalizing symptoms and brain function. The current study aimed to investigate the association between CAR and neural activity in response to unpleasant emotional pictures. A total of 46 healthy adults (22.55 years ± 1.69) collected saliva samples at 0, 30, and 45 min post-awakening on two days to assess the CAR. In the afternoon after CAR measurement on the first day, electroencephalograms were recorded when the participants completed a passive viewing task. The results showed that a greater CAR was associated with a decreased late positive potential difference score between unpleasant and neutral stimuli. This finding indicates that a larger CAR may be associated with decreased attentional engagement to unpleasant emotional information in healthy adults.

Effect of CO Molecule Orientation on the Reduction of Cu-Based Nanoparticles.

The adsorption of CO on the surface of Cu-based nanoparticles was studied in the presence of an external electric field by means of scanning tunneling microscopy (STM) and spectroscopy (STS). Nanoparticles were synthesized on the surface of a graphite support by the impregnation–precipitation method. The chemical composition of the surface of the nanoparticles was determined as a mixture of Cu2O, Cu4O3 and CuO oxides. CO was adsorbed from the gas phase onto the surface of the nanoparticles. During the adsorption process, the potential differences ΔV = +1 or −1 V were applied to the vacuum gap between the sample and the grounded tip. Thus, the system of the STM tip and sample surface formed an asymmetric capacitor, inside which an inhomogeneous electric field existed. The CO adsorption process is accompanied by the partial reduction of nanoparticles. Due to the orientation of the CO molecule in the electric field, the reduction was weak in the case of a positive potential difference, while in the case of a negative potential difference, the reduction rate increased significantly. The ability to control the adsorption process of CO by means of an external electric field was demonstrated. The size of the nanoparticle was shown to be the key factor affecting the adsorption process, and particularly, the strength of the local electric field close to the nanoparticle surface.

Bis-(sodium sulfoethyl)-disulfide: A Promising Accelerator for Super-conformal Copper Electrodeposition with Wide Operating Concentration Ranges

Accelerators are indispensable additives for super-conformal copper electrodeposition, which has been widely applied in the fabrication of integrated circuits (ICs), printed circuit boards (PCBs), and advanced semiconductor packaging substrates. Currently, bis-(sodium sulfopropyl)-disulfide (SPS) and sodium 3-mercapto-1-propanesulfonate (MPS) are the most widely used accelerators for super-conformal electroplating. However, owing to the limited operating concentration range, frequent measurements of the SPS (or MPS) concentration during the electroplating process are needed to manage the accelerator concentration in a suitable range, which makes the application of SPS (or MPS) tedious and unreliable. In our previous study, bis-(sodium sulfoethyl)-disulfide (SES), which has a molecular structure that is similar to that of SPS but with shorter alkyl chains, was determined to be a weaker depolarizer than SPS. The weaker antagonistic effect against suppressor and leveler imply that the higher concentration of SES maybe applicable to achieve the super-conformal electroplating. In this study, SES was investigated in detail, and it was found that in combination with Cl−, PEG, and JGB, the SES-containing electrolytes can provide the positive potential difference Δη, excellent microvia filling performance, and good copper deposition physical properties in a wide operating concentration range. SES is a promising accelerator for the super-conformal copper electroplating.

Electric field–prevented adsorption of hydrogen on supported gold nanoparticles

The adsorption of hydrogen on the surface of gold nanoparticles deposited on a graphite support was studied in the presence of an external electric field by means of scanning tunneling microscopy (STM) and spectroscopy (STS). Hydrogen was adsorbed from the gas phase onto the surface of gold nanoparticles synthesized by impregnation-precipitation method. During the adsorption process, the STM tip was removed from the surface of the sample so that the measurable tunneling current could not flow, and potential differences of various polarities were applied to the vacuum gap between the sample and the grounded tip. Thus, the system of the STM tip and sample surface formed an asymmetric capacitor inside which an inhomogeneous electric field existed. No hydrogen adsorption was observed in the case of a positive potential difference, while dissociative adsorption of hydrogen took place in the cases of zero and negative potential differences. The ability to control the adsorption process of hydrogen by means of a weak electric field was demonstrated.

Depression symptomatology correlates with event-related potentials in Parkinson's disease: An affective priming study

BackgroundDepression is a predominant non-motor symptom of Parkinson's disease (PD), which is often under recognised and undertreated. To improve identification of depression in PD it is imperative to examine objective brain-related markers. The present study addresses this gap by using electroencephalography (EEG) to evaluate the processing of emotionally valanced words in PD. MethodsFifty non-demented PD patients, unmedicated for depression or anxiety, completed an affective priming task while EEG was simultaneously recorded. Prime and target word pairs of negative or neutral valence were presented at a short 250 ms stimulus onset asynchrony. Participants were asked to evaluate the valence of the target word by button press. Depression was measured using an established rating scale. Repeated measures analysis of covariance and correlational analyses were performed to examine whether event-related potentials (ERP) varied as a function of depression scores. ResultsKey ERP findings reveal reduced responses in parietal midline P300, N400 and Late Positive Potential (LPP) difference waves between congruent and incongruent neutral targets in patients with higher depression scores. LimitationsComparisons of ERPs were limited by insufficient classification of participants with and without clinical depression. A majority of PD patients who had high depression scores were excluded from the analysis as they were receiving antidepressant and/or anxiolytic medications which could interfere with ERP sensitivity. ConclusionsThe present study suggests that the Pz-P300, N400 and LPP are ERP markers relates to emotional dysfunction in PD. These findings thus advance current knowledge regarding the neurophysiological markers of a common neuropsychiatric deficit in PD.

Retracted: Effect of the potential difference applied on the removal of chromium by adsorption on activated carbon prepared from biomass waste material

The objective of this study is the removal of chromium from aqueous solution by electrosorption on carbon prepared from lignocellulosic natural residue “date stones” thermally treated at 900 °C by imposing potential differences from -0.1 to -0.5V/SCE. The results make it possible to observe that the adsorption kinetics increased at more negative potentials (-0,5V). Chromium desorption tests were performed by applying positive potential differences. The effect of pH and cycles number on the elestosorption process was studied. The experimental results concluded that the better adsorption efficiency was obtained when pH equal to 10, which is about 98%. Furthermore, it was confirmed that the recycling process of adsorption/desorption could be conducted for several cycles.

Polarization modulation of nanotrenches in GaN (0001)/ by surface hydrogenation

Using first-principles total-energy calculations within the framework of the density functional theory, we show that nanometer-scale trenches excavated in GaN with (0001) and surfaces cause a variable electrostatic potential difference, which is tunable by controlling the hydrogen coverage of the surfaces. A positive potential difference of 3.53 V is induced between clean (0001) and surfaces in nanotrenches, while a negative potential difference of −5.93 V is induced in nanotrenches with fully hydrogenated surfaces. The value of the potential difference strongly depends on the H coverage of the surfaces. Nanotrenches excavated in GaN with polar surfaces can supply electricity for various nanoscale devices consisting of molecules, clusters, and atoms inserted into the trenches.

Competition for attentional resources between low spatial frequency content of emotional images and a foreground task in early visual cortex.

Low spatial frequency (LSF) image content has been proposed to play a superior functional role in emotional content extraction via the magnocellular pathway biasing attentional resources toward emotional content in visual cortex. We investigated whether emotionally unpleasant complex images that were presented either unfiltered or with LSF content only in the background while subjects performed a foreground task will withdraw more attentional resources from the task compared to unemotional, neutral images (distraction paradigm). We measured steady-state visual evoked potentials (SSVEPs) driven by flickering stimuli of a foreground task. Unfiltered unpleasant images resulted in a significant reduction of SSVEP amplitude compared to neutral images. No statistically significant differences were found with LSF background images. In a behavioral control experiment, we found no significant differences for complexity ratings between unfiltered and LSF pictures. Content identification was possible for unfiltered and LSF picture (correct responses > 74%). An additional EEG study examined typical emotion-related components for complex images presented either as unfiltered, LSF, or high spatial frequency (HSF, as an additional control) filtered, unpleasant, and neutral images. We found a significant main effect of emotional valence in the early posterior negativity. Late positive potential differences were only found for unfiltered and HSF images. Results suggest that, while LSF content is sufficient to allow for content and emotional cue extraction when images were presented alone, LSF content is not salient enough to serve as emotional distractor that withdraws attentional resources from a foreground task in early visual cortex.

Reduction of stray currents in counter-rotating electrochemical machining by using a flexible auxiliary electrode mechanism

Counter-rotating electrochemical machining (CRECM) is a new ECM technique which can be used to fabricate convex structures on thin-walled revolving parts. During the CRECM process, the non-machined top surface of the convex structure inevitably suffers from stray current attack, resulting in poor machining quality. To reduce the stray currents in CRECM, a flexible auxiliary electrode mechanism has been developed. A positive potential difference is applied between the auxiliary electrode and the anode workpiece. The electric field distribution and the simulated convex profiles show that the stray current density can be reduced effectively by using an auxiliary electrode. The magnitudes of the stray current densities on the non-machined area decrease with increasing potential difference. A suitable positive potential difference of 10V is able to completely eliminate the stray currents from the entire non-machined surface of the convex structure. Experiments have also been conducted to verify the proposed method. It was confirmed that the stray corrosion on the convex surface is significantly reduced and the machining quality is remarkably improved by using a flexible auxiliary electrode mechanism.

Investigation of suppressor polyethylene glycol dodecyl ether on electroplated Cu filling by electrochemical method

In this paper, the use of polyethylene glycol dodecyl ether (POE) with a molecular weight of 1200 (POE-1200) as a suppressor for bottom-up electroplated copper filling of microvias was investigated. Galvanostatic measurement indicated that POE-1200 had much stronger suppression for Cu electrodeposition than PEG-8000 (polyethylene glycol with a molecular weight of 8000) and EPE-8000 (triblock copolymers of ethylene oxide–propylene oxide–ethylene oxide with a molecular weight of 8000). The strong synergistic suppression between POE-1200 and Cl− led to a very thin surface thickness and excellent filling performance of microvias. The cross-sectional observations of the microvias after electroplated confirmed that changing the POE-1200 concentration from 20 to 700 ppm had little effect on the filling performance because of an unchanged positive potential difference. The adsorption strength of POE-1200 on the cathode surface was enhanced greatly only in the presence of Cl− , attributing to a formation of Cl− –Cu+–POE-1200 complex. The critical adsorption concentration of Cl− and POE-1200 to form a saturated barrier film on the electrode surface was studied by Cu stripping peaks of cyclic voltammetry curves. In addition, the relationship between the saturated barrier of Cl− –Cu+–POE-1200 complex and the filling performance has been proposed.

Electrostatic focal spot correction for x-ray tubes operating in strong magnetic fields.

A close proximity hybrid x-ray/magnetic resonance (XMR) imaging system offers several critical advantages over current XMR system installations that have large separation distances (∼5 m) between the imaging fields of view. The two imaging systems can be placed in close proximity to each other if an x-ray tube can be designed to be immune to the magnetic fringe fields outside of the MR bore. One of the major obstacles to robust x-ray tube design is correcting for the effects of the MR fringe field on the x-ray tube focal spot. Any fringe field component orthogonal to the x-ray tube electric field leads to electron drift altering the path of the electron trajectories. The method proposed in this study to correct for the electron drift utilizes an external electric field in the direction of the drift. The electric field is created using two electrodes that are positioned adjacent to the cathode. These electrodes are biased with positive and negative potential differences relative to the cathode. The design of the focusing cup assembly is constrained primarily by the strength of the MR fringe field and high voltage standoff distances between the anode, cathode, and the bias electrodes. From these constraints, a focusing cup design suitable for the close proximity XMR system geometry is derived, and a finite element model of this focusing cup geometry is simulated to demonstrate efficacy. A Monte Carlo simulation is performed to determine any effects of the modified focusing cup design on the output x-ray energy spectrum. An orthogonal fringe field magnitude of 65 mT can be compensated for using bias voltages of +15 and -20 kV. These bias voltages are not sufficient to completely correct for larger orthogonal field magnitudes. Using active shielding coils in combination with the bias electrodes provides complete correction at an orthogonal field magnitude of 88.1 mT. Introducing small fields (<10 mT) parallel to the x-ray tube electric field in addition to the orthogonal field does not affect the electrostatic correction technique. However, rotation of the x-ray tube by 30° toward the MR bore increases the parallel magnetic field magnitude (∼72 mT). The presence of this larger parallel field along with the orthogonal field leads to incomplete correction. Monte Carlo simulations demonstrate that the mean energy of the x-ray spectrum is not noticeably affected by the electrostatic correction, but the output flux is reduced by 7.5%. The maximum orthogonal magnetic field magnitude that can be compensated for using the proposed design is 65 mT. Larger orthogonal field magnitudes cannot be completely compensated for because a pure electrostatic approach is limited by the dielectric strength of the vacuum inside the x-ray tube insert. The electrostatic approach also suffers from limitations when there are strong magnetic fields in both the orthogonal and parallel directions because the electrons prefer to stay aligned with the parallel magnetic field. These challenging field conditions can be addressed by using a hybrid correction approach that utilizes both active shielding coils and biasing electrodes.

Electrochemical Characterization of Guanine and Guanosine Based Biosensors Over Multi-Walled Carbon Nanotube Modified Graphite Electrode

Electroactive purine nucleobase, guanine and purine nucleoside, guanosine were immobilized over multi-walled carbon nanotubes (MWCNT) modified graphite electrode. The electrooxidation properties of purines were evaluated using differential pulse voltammetry. Mixtures of purine nucleobase and nucleoside in various concentrations were prepared and electrochemically immobilized over the working electrodes using positive potential difference. The anodic current at around 0.7 V was used as analytical signal for guanine. The influence of immobilization time, MWCNT concentration and purine concentration were evaluated and electrochemical mechanisms have been discussed. Special emphasis was given to study the stable recognition layer in a redox couple (0.1M NaCl containing 10/10 mM K3Fe(CN)6/K4Fe(CN)6) using electrochemical impedance spectroscopy and cyclic voltammetry. Further, electrochemical interaction of immobilized purine structures over benzene substituted organic compounds were studied using DPV in 0.1M phosphate buffer, and CV and EIS in 0.1 M NaCl containing 10/10 mM K3Fe(CN)6/K4Fe(CN)6. The standardized and calibrated purine immobilized electrode could be potentially used as purine based biosensor for the electrochemical detection of benzene substituted organic compounds.

Role of secondary phase particles of 2519A aluminium alloy in localised corrosion

The localised corrosion due to the galvanic couples between the precipitated particles and matrix in a new aluminium alloy 2519A was investigated by scanning electronic microscopy, transmission electronic microscopy and scanning Kelvin probe force microscopy. Topography and Volta potential differences relative to the matrix in 3·5%NaCl solution were examined for two kinds of Al2Cu and Al7Cu2Fe particles. Almost the particles showed positive Volta potential difference relative to the matrix. A series of particles nobility was detected with Al7Cu2Fe being less noble than Al2Cu. The potential difference of Al2Cu particles from the matrix was 702 mV in average, while Al7Cu2Fe particles 526 mV. Both of the particles act as cathode and localised corrosion originated mainly from the periphery of coarse ones. The more obvious the particles, the more severe the corrosion pits are.

Use of Scanning Kelvin Probe Force Microscopy to Investigate the Effects of Surface Preparation on Intermetallic Particles in AA7xxx Aluminum Alloys

Scanning Kelvin probe force microscopy (SKPFM) was used to quantitatively measure the surface potentials (also referred to as Volta potential) on different intermetallic particles relative to the matrix in AA7xxx aluminum alloys, in combination with scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). Both Cu and Fe-rich intermetallics showed rather high, positive Volta potential differences (~ +400 mV), while Mg/Si-rich one exhibited a negative potential (~ -250 mV) relative to the matrix for the Al alloys investigated. Large variations in the measured Volta potential, which appeared to be independent of particle size, were observed for these Cu and Fe-rich (Al7Cu2Fe) and Mg/Zn rich (Mg2Zn) particles in the custom Al-Zn-Mg-Cu alloy. The effects of different surface preparation on the Volta potentials of Cu/Fe-rich and Mg/Si-rich intermetallic particles were investigated. The results indicate that the influence of surface preparation is complex, but largely depends on the type of intermetallic particles, and whether there is any particle dissolution during the surface preparation.

Fabrication of enhanced anodic aluminum oxide performance at room temperatures using hybrid pulse anodization with effective cooling

Conventional anodic aluminum oxide (AAO) template was performed using potentiostatic method of direct-current anodization (DCA) on costly high-purity (99.997%) aluminum foils at low temperatures of 0–10°C to avoid dissolution effects which occurred frequently at room temperatures (RT) of 20–30°C. In this paper, we show the hybrid pulse anodization (HPA) method with pulsing normal-positive and small-negative potential differences at RT for enhancing performance of AAO structure for both the cheap low-purity (99%) and costly high-purity (99.997%) aluminum foils. The HPA mainly takes advantages of effective cooling that arise from the nearly zero cathodic current and high-thermal-conductivity liquid electrolyte on the foils. The HPA is different from the traditional pulse anodization with alternating both high and low positive potential differences (/currents) or both one-positive and one-zero potential differences. The HPA not only merits manufacturing convenience and cost reduction but also promotes pore distribution uniformity of AAO at severe conditions of cheap low-purity Al foils and relatively high room temperature. The pore distribution uniformity can be improved by HPA in a suitable duration compared with the DCA. Very good AAO distribution uniformity (91%) was achieved in high-purity aluminum foil by HPA because it can suppress the Joule's heat to diminish the dissolution reaction. The evolution of AAO distribution uniformity for both the HPA and DCA on Al foil purities and process durations were comparatively investigated.

Effect of 16-mercaptohexadecanoic acid modification on liquid transport in a nanoporous carbon

The inner surfaces of a nanoporous carbon are modified by 16-mercaptohexadecanioic acid. The degree of wettability is electrically controllable: by applying a negative potential difference across the solid-liquid interface, the ion transport pressure in the nanopores can be considerably lowered; while the effect of applying a positive potential difference is negligible. These phenomena can be attributed to the unique surface chain configuration in the confining nanoenvironment.

Transport Systems of Ventricaria ventricosa: Asymmetry of the Hyper- and Hypotonic Regulation Mechanisms

Hyper- and hypotonic stresses elicit apparently symmetrical responses in the alga Ventricaria. With hypertonic stress, membrane potential difference (PD) between the vacuole and the external medium becomes more positive, conductance at positive PDs (Gmpos) increases and KCl is actively taken up to increase turgor. With hypotonic stress, the membrane PD becomes more negative, conductance at negative PDs (Gmneg) increases and KCl is lost to decrease turgor. We used inhibitors that affect active transport to determine whether agents that inhibit the K(+) pump and hypertonic regulation also inhibit hypotonic regulatory responses. Cells whose turgor pressure was held low by the pressure probe (turgor-clamped) exhibited the same response as cells challenged by hyperosmotic medium, although the response was maintained longer than in osmotically challenged cells, which regulate turgor. The role of active K(+) transport was confirmed by the effects of decreased light, dichlorophenyldimethyl urea and diethylstilbestrol, which induced a uniformly low conductance (quiet state). Cells clamped to high turgor exhibited the same response as cells challenged by hypo-osmotic medium, but the response was similarly transient, making effects of inhibitors hard to determine. Unlike clamped cells, cells challenged by hypo-osmotic medium responded to inhibitors with rapid, transient, negative-going PDs, with decreased Gmneg and increased Gmpos (linearized I-V), achieving the quiet state as PD recovered. These changes are different from those exerted on the pump state, indicating that different transport systems are responsible for turgor regulation in the two cases.

Studies on human insulin adsorption kinetics at an organic–aqueous interface determined using a label-free electroanalytical approach

Protein adsorption represents a considerable challenge in the development and production of macromolecular drugs. From an analytical point of view the adsorption process is difficult to study in an efficient way using currently available techniques. In this work potential and time dependent adsorption and adsorption kinetics of human insulin at an 1,2-dichloroethane-aqueous interface were studied using a novel electroanalytical approach based on measurements of interfacial capacitance. Two different types of measurements were performed; potential scans and time scans. In the potential scans, the capacitance was measured over a range of applied potential differences across the interface. The interfacial potential difference is linked to the charge at the interface. Adsorption of human insulin was detectable at a bulk phase insulin concentration as low as 0.1 μM as a negative shift in the potential of zero charge (pzc). Adsorption kinetics were further studied using time scans in which the interfacial capacitance was measured at a fixed applied interfacial potential difference. Using this approach it was possible to study how the adsorption kinetics and the shape of the time scan curves were related to the bulk concentration of insulin and the interfacial potential difference. The changes in capacitance could be described phenomenologically by pseudo-first-order kinetics at low concentrations of insulin except at positive interfacial potential differences and high insulin concentrations (≥0.25 μM) where a more complex shape of the time scans curves was observed.

Microgalvanic activity of an Mg–Al–Ca-based alloy studied by scanning Kelvin probe force microscopy

An Mg–Al–Ca based alloy was investigated by scanning electron microscopy, energy dispersive spectroscopy and scanning Kelvin probe force microscopy following extrusion. The investigations revealed two main intermetallics, i.e. Al–Ca(Sn,Sr) and Al–Mn–Fe, both distributed along the extrusion direction and having distinctive morphology. The microgalvanic couples, i.e. Al–Ca(Sn,Sr)/α-Mg and Al–Mn–Fe/α-Mg showed positive Volta potential differences with the Al–Mn–Fe intermetallic being the noblest (i.e. 262 ± 18 mV vs 62 ± 7 mV).