Anodic Current Pulses Research Articles

A 14-Bit, 12 V-to-100 V Voltage Compliance Electrical Stimulator with Redundant Digital Calibration.

Electrical stimulation is an important technique for modulating the functions of the nervous system through electrical stimulus. To implement a more competitive prototype that can tackle the domain-specific difficulties of existing electrical stimulators, three key techniques are proposed in this work. Firstly, a load-adaptive power saving technique called over-voltage detection is implemented to automatically adjust the supply voltage. Secondly, redundant digital calibration (RDC) is proposed to improve current accuracy and ensure safety during long-term electrical stimulation without costing too much circuit area and power. Thirdly, a flexible waveform generator is designed to provide arbitrary stimulus waveforms for particular applications. Measurement results show the stimulator can adjust the supply voltage from 12 V to 100 V automatically, and the measured effective resolution of the stimulation current reaches 14 bits in a full range of 6.5 mA. Without applying charge balancing techniques, the average mismatch between the cathodic and anodic current pulses in biphasic stimulus is 0.0427%. The proposed electrical stimulator can generate arbitrary stimulus waveforms, including sine, triangle, rectangle, etc., and it is supposed to be competitive for implantable and wearable devices.

Effect of microarc oxidation on the properties of aluminum alloy samples

Currently, modern manufacturing industries impose special requirements on structural materials such as aluminum, titanium, and their alloys. Various methods are used to improve the physicomechanical and corrosion properties of these materials. One of the promising ways to modify the surface in order to give it multifunctional properties is the treatment of micro-arc oxidation. A distinctive feature of the process is the formation of the oxide coatings on valve metals because of exposure to micro-arc discharges. At the same time, coatings with unique properties are formed. However, the effect of the micro-arc oxidation process on the properties of the base material has been little studied. The purpose of this work is to study the effect of the micro-arc process, implemented in pulsed mode, on the properties of oxide layers, and the base material. Modification of the alloy surface was carried out in the anode mode, with small values of the duration of the anode current pulse. An alkaline electrolyte solution was used as the electrolyte. Studies of the microhardness of the oxide layer, as well as the metal layer from the interface – oxide layer /metal deep into the metal, have shown that micro-arc discharges affect not only the properties of the oxide layer but also structural changes in the thickness of the metal. It is shown that the formed oxide coating is characterized by high microhardness. The oxide coatings obtained at the duration of the anode current pulse of 100 µs – 200 µs are wear-resistant, the coatings do not collapse, and do not wear to the ground under the accepted test conditions.

Investigation of the properties of oxide coatings on titanium alloys obtained by plasma electrolytic oxidation

The use of structures made of titanium and its alloys, which have improved corrosion, physical and mechanical properties, are in demand in many industries. In this regard, the processes of modifying the surface of metals are of interest. One of the modern and promising methods of metal surface treatment is plasma electrolytic oxidation. Currently, there is a problem of widespread use of this process when DC modes are used in the implementation of the process. This is due to the large consumption of electricity. The purpose of this work is to study the morphological and corrosion properties of oxide coatings obtained in the pulsed anodecathode mode on titanium alloys VT1-0 and VT5 in various electrolyte solutions. Modification of the surface of titanium alloys was carried out at the duration of the anode current pulse of 250 ± 25 microseconds, the duration of the cathode current pulse of 5 ± 0.5 ms, the repetition frequency of the anode and cathode pulses of 50 ± 0.5 Hz. Alkaline solutions served as electrolytes. Oxide coatings obtained in various electrolytes are characterized by different porosity and coating thickness. Coatings with a finely porous structure, with an average pore diameter from 0.09 microns to 0.4 microns, and larger pore sizes of 0.6 – 0.7 microns were obtained. The porosity of the coatings ranges from 6.12% to 12.2%. According to the data of energy dispersion analysis, it was found that the structure of oxide coatings includes both components of the processed metal and components of the electrolyte solution. The main components, in this case, are oxygen and processed metal, as well as other elements such as boron, phosphorus, aluminium, fluorine, sodium, silicon and others. Corrosion tests according to GOST 9.308-85 under the influence of neutral salt mist at a temperature of (35 ± 2) °C with 1500 hours in the Ascott CC 450 chamber, it was shown that there was no corrosion damage to the coatings.

Исследование защитных свойств покрытий, полученных методом микродугового оксидирования в щелочных растворах электролитов

The article presents the results of a study of the corrosion properties of oxide coatings compacted with polymers and without compaction. Oxide coatings were obtained on VT1-0 and VT5 titanium alloys under the influence of fast pulsed actions of the micro-arc oxidation (MAO) process. To form MAO coatings, a pulsed mode of the process was used with an anodic current pulse duration of 250 ± 25 μs; the cathodic current pulse duration of 5 ± 0.5 ms; pause between anodic and cathodic current pulses 250 ± 25 μs; repetition rate of anodic and cathodic pulses 50 ± 0.5 Hz. Alkaline solutions were used as electrolytes. Fluoroplastic and epoxy resin solutions were used to seal the oxide coatings. The obtained MAO coatings have 4.4 – 7.5 % porosity on the VT1-0 alloy and 5.4 – 12.1 % on the VT5 alloy. The average diameter of oxide coating pores varies from 0.1 to 0,5 µm. X-ray phase analysis showed titanium dioxide in anatase and rutile modification in the oxide coatings composition. Tests performed in a 24 % solution of sulfuric acid at 40 and 75°C showed that the coatings on the VT1-0 alloy, both oxide and oxide-polymer, are more corrosion resistant than similar coatings on the VT5 alloy. All types of coatings produced on VT1-0 alloy are corrosion-resistant at a test temperature of 40 °C. Consolidation of MAO coatings with polymeric materials improves corrosion properties.

Plasma electrolytic oxidation of magnesium by sawtooth pulse current

Mg 2 SiO 4 coatings were formed on cp-Mg by Plasma Electrolytic Oxidation (PEO) using electrical regimes based on sawtooth anodic current pulses with extended ascending or descending segments (ramps). Voltage, current and light emission signals were simultaneously acquired to derive and analyse the evolution of system current and discharge population density during PEO process, while optical emission spectroscopy was employed for identification of plasma species. Coating morphological characterisation was carried out using Scanning Electron Microscopy. Phase composition was identified by X-ray diffraction. The corrosion performance was evaluated with Electrochemical Impedance Spectroscopy at various periods of exposure to corrosive media (0.5 wt% NaCl). It was shown that the application of sawtooth pulses allowed the controlling of microdischarge characteristics and coating morphology in both pulsed unipolar and reversed current regimes. Results further demonstrate that the application of anodic sawtooth pulses with the negative ramp facilitated defect healing during coating formation leading to production of more uniform PEO coatings with lower porosity and a slower degradation rate of magnesium substrate. A steady decay in the coating resistance with immersion time provides a possibility for controlling magnesium degradation and thereby for optimisation of component lifetime in applications where predictable Mg dissolution rate is required, such as sacrificial anodic protection of metallic structures and resorbable biomedical implants. • The quality of PEO coatings is modified by sawtooth pulse current regimes with controlled positive or negative anodic ramp. • Applying sawtooth waveforms with positive ramps refined the coating morphology. • Negative ramps introduced a defect healing effect reducing coating porosity and roughness. • Corrosion resistance of refined coating was proved to be better by EIS measurement.

An Implantable Neural Stimulator IC With Anodic Current Pulse Modulation Based Active Charge Balancing

Implantable electrical stimulators can be used to treat a variety of neurological disorders and restore paralyzed body functions. In electrical neural stimulation, the stimulator circuit with safe charge balancing is essential to minimize damage to electrodes and biological tissue. In this paper, an implantable current-mode neural stimulator for long-term safe electrical stimulation is presented. Anodic current pulse modulation active charge balancing technique is proposed to keep the residual voltage on the electrode within the safe window, which enables long-term safe stimulation. To ensure more complete charge balancing, the proposed active charge balancing technique can also be used with passive electrode shorting. Transistor stacking and dynamic gate biasing techniques can prevent the breakdown of standard MOSFET devices from high supply voltages, which enable the implementation of output current driver and charge balancing circuits without using HV process. The stimulator IC designed with 0.18- $\mu \text{m}$ standard CMOS process can generate up to 1 mA of stimulation current and only consumes an area of 0.11 mm2. Since all functions are implemented on-chip without using external components, the proposed stimulator IC is suitable for high-density implantable stimulation applications.

Preventing the Deactivation of Gold Cathodes During Electrocatalytic CO2 Reduction While Avoiding Gold Dissolution

The electrochemical reduction of CO2 on gold cathodes was investigated, and the major products were found to be CO, H2 and formate, which is consistent with existing literature. The Faradaic efficiency for CO production decreased from around 60 to 10% over the course of 4 h when the electrolysis was performed at – 5 mA cm–2 in 0.2 M KHCO3 saturated with CO2. This deactivation was accompanied by an increase in the selectivity of the cathode towards H2 and formate production, which is normally attributed to the deposition of metals from trace impurities in the electrolyte or surface-bound species formed during the reaction. In this case, the deactivation was found to be due to the deposition of Cu, Zn and possibly Fe from the electrolyte, with the presence of Fe strongly enhancing H2 production, the Cu deposition increasing the formate production rate and Zn enhancing both H2 and formate production. While the accumulation of these poisons can be prevented with periodic anodic treatments (using methods previously described in the literature), these treatments lead to significant gold dissolution, with up to 450 ppb of gold found in the electrolyte after 4 h of electrolysis, and thus is unsuitable for use in long-term CO2 reduction systems. This dissolution is expected to alter the surface structure and thus selectivity of the cathode. Therefore, alternative electrochemical cleaning protocols (periodic cyclic voltammetry, open-circuit and low anodic current treatments) were investigated as methods to remove these poisons without significant gold corrosion occurring. The best approach to prevent the deactivation of gold cathodes during CO2 reduction is to cycle the potential between − 0.5 and 0.5 V vs Ag|AgCl every 15 min during long-term electrolysis. It is also shown that simply interrupting the CO2 reduction process every 15 min with 4 min at open circuit can also partially prevent the deactivation of the CO2 reduction reaction as will short anodic current pulses.

A 0.034% Charge-Imbalanced Neural Stimulation Front-End (SFE) IC With on-Chip Voltage Compliance Monitoring Circuit and Analysis on Resting Potential by Utilizing the SFE IC

The proposed SFE IC adopts an eight-channel H-bridge structure with an integrated voltage compliance monitoring circuit. It has stimulation current ranged from 0.78mA to 6.2mA selected by 3b control and the stimulation current level can be controlled with 7b resolution within a selected current range. The current range can be expanded by using a high current option ranged from 2.71mA to 21.7mA under 3b control. The worst DNL and INL of the stimulation current source are 0.32 LSB and 0.3 LSB, respectively, from all the current ranges. The average mismatch between the cathodic and anodic current pulses in a biphasic stimulus is measured as 0.034% without using charge balancing techniques. The voltage compliance monitoring circuit is based on triode detection of a sensing MOSFET and it shows the detection accuracy of 45mV from its measurement results. The maximum steady-state voltage across the electrodes/ solution interface (resting potential) is also rigorously analyzed and verified through bench-top and saline experiments by utilizing the proposed stimulator. The SFE IC was fabricated in $0.18~\mu \text{m}$ 24 V CMOS process.

Effect of frequency on black coating formation on AZ31 magnesium alloy by plasma electrolytic oxidation in aluminate-tungstate electrolyte

Plasma electrolytic oxidation (PEO) has been carried out under unipolar and bipolar pulsed current regimes to investigate the formation of black ceramic coatings on AZ31 magnesium alloy in an aluminate-tungstate electrolyte at frequencies of 100, 1000 and 2000 Hz. The coatings were characterized by scanning electron microscopy (SEM) assisted by energy dispersive X-ray spectroscopy (EDS), and micro-discharges were investigated by real-time imaging and photomultiplier methods. Coating color was quantified by the CIELAB method. Blackness of coatings increased with frequency and tungsten incorporation, with blackest coatings obtained under unipolar conditions. Blacker coatings also revealed increased roughness and large internal pores, which were attributed to stronger plasma discharges and greater gas evolution. Continuing light emission after termination of each anodic current pulse suggested that sites of high coating temperature may facilitate discharge initiation in the subsequent anodic pulse when the cycle time is short. Large porosity and increased voltage indicated cathodic discharges also occur at high frequency when the coating is sufficiently thick. However, it seems that the cathodic discharges have no effect on the blackness of the coating.

Redox fusion of metal particles using deep eutectic solvents.

Alternating anodic and cathodic current pulses have been applied to a metal powder on an electrode surface to fuse the particles together. It is shown that homogeneous films can be electroformed with different morphologies depending on the size of the powder and the experimental conditions.

Flexible Supercapacitor Stackable with Solar Cells Based on PEDOT-Carbon Nanotube Nanocomposite Electrodes Using Ionic Liquid Gel Electrolytes for Solar Electricity Storage

Electrically conducting polymers (ECP) showing pseudo-capacitive property are actively researched as supercapacitor electrodes for energy storage. Nanocomposites with structured carbons contribute additional charge storage through electric double layer component enhancing the charge storage ability. The nanocomposites with CNTs hold additional promise to compensate for weak mechanical property of ECPs useful for flexible supercapacitor devices and enhance its electronic conductivity. Conventionally, the supercapacitor performance is evaluated using anion dopants in aqueous medium having voltage limitation and in organic electrolytes which are toxic. Ionic liquid gel electrolytes are promising but not widely studied for supercapacitor applications. Besides enabling stable high voltage operation, ionic liquid gel electrolyte makes supercapacitor assembly simple which can be configured as flat stackable layered device. These attributes are exploited in integration with the solar cells for the storage of solar electricity. We have investigated electrochemical and energy storage performance of poly(3,4-ethylenedioxy-thiophene) (PEDOT) and CNT nanocomposite electrodes based supercapacitors in the flexible solid-state format with ionic liquid gel electrolyte. In this work nanocomposite electrode was formed by co-deposition of PEDOT and CNT over the flexible graphite substrates using the galvanic pulsed electro-polymerization. The method involves ultrasonic dispersion of 1 wt% anionic CNT for 2 h in acetonitrile to which 0.1 M EDOT monomer and 0.2 M LiClO4 dopant was added. The PEDOT-CNT composite deposition is initiated as unipolar anodic current pulses of 4 mA.cm-2 amplitude with 10 ms ON time interspaced with 100 ms OFF time were sequentially applied for 20k cycles providing a unique way to control the electrode morphology. The symmetrical supercapacitor device was fabricated using ionic liquid 1-butyl-3-methylimidazolium tetrafluoro-borate ([BMIm]BF4) immobilized in poly(vinylidenefluoride -co-hexafluoropropylene (PVdF-HFP) forming a gel which was applied uniformly as ~50-70 μ layer sandwiched between the two PEDOT-CNT composite electrodes. With such stackable flat plate- supercapacitor device design, enhanced energy density is obtained and direct charge storage performance was realized when connected to solar cell module while mounted at the rear without affecting the form factor. The electrode morphology show randomly dispersed CNT of average diameter of 20-30 nm embedded within and encased by copolymerized PEDOT forming a 3-D network structure. The CNT is observed to enhance the PEDOT polymerization by facilitating charge transport at the substrate and also increase the electrode conductivity. Raman shifts in the 1425 cm−1 band assigned to symmetric Cα=Cβ (−O) stretching show in the formation of nanocomposite, the CNTs interact with the ethylenedioxy group of PEDOT resulting in high degree of conjugation and enhancrd charge transfer between CNTs and PEDOT molecular chains. Conjugated interaction is further confirmed by shift in disordered A1g mode of CNT. The cyclic voltammetry curves recorded over -1 to +1 V range showed fast and near vertical current switching at end potentials over wide 10-100 mV s-1 scan rates signifying highly capacitive property. Supercapacitor showed areal capacitance density of 357 mF.cm-2 yielding high single electrode specific capacitance of 297 F.g-1. The high areal specific capacitance in the PEDOT-CNT composite is due to dopant anion aggregation along the CNTs and enhanced conduction of dopant ions in ionic liquid through embedded CNT nanopores providing rapid pathways to delocalize the electrons from along the PEDOT molecular chain. Impedance data as Nyquist plots feature near vertical trend in the low frequency region and lower real impedance cutoff suggestive of highly capacitive property and low electrode-electrolyte resistance. Occurrence of high knee frequency of > 10 Hz suggests compared to PEDOT, the CNT nanocomposite has minimal diffusion limitation. Charge-discharge (CD) data at various currents cycled between 0.05-1.0V are triangular with low ESR of 20 Ohm.cm2 and Coulomb efficiency > 90%. Long-term CD cycling for 2000 cycles showed overall degradation of 21% with a nominal aggravation of merely 7% occurring in initial 400 cycles. These data show comparatively higher stability of CNT nanocomposite compared to PEDOT. The supercapacitor device functional properties were evaluated in terms of energy and power density parameters and presented as Ragone plots. Energy density of 18.3 Wh.kg-1 and corresponding power density of 5.1kW.kg-1 was recorded from CD data at 0.5 mA.cm-2 for 1V operation which is reasonably high for a gel electrolyte supercapacitor device. This paper would present detailed analysis of the pulse polymerization synthesis mechanism, microstructure and electrochemical properties of PEDOT-CNT nanocomposite. The supercapacitor device data on CV, CD, impedance and Ragone plots will be presented along with its efficacy in storing the solar electricity in combination with the solar cells.

Reversible Electrochemical Sensor for Detection of High-Charge Density Polyanion Contaminants in Heparin.

We present a simple, rapid, and inexpensive electrochemical sensor based on a reversible pulsed chronopotentiometric polyanion-selective membrane electrode for the detection and quantification of oversulfated chondroitin sulfate (OSCS) and other high charge-density polyanions that could potentially be used to adulterate heparin. The membrane is free of ion exchanger and is formulated with plasticized poly(vinyl chloride) (PVC) and an inert lipophilic salt, tridodecylmethylammonium-dinonylnaphthaline sulfonate (TDMA-DNNS). The neutral salt is used to reduce membrane resistance and to ensure reversibility of the sensor. More importantly, TDMA(+) is used as the recognition element for the polyanions. Here an anodic galvanostatic current pulse is applied across the membrane to cause the extraction of the polyanions from the sample into the membrane and potential is measured at the sample-membrane interface. The measured electromotive force (emf) is proportional to the concentration and the charge density of the polyanions. High charge-density polyanion contaminants and impurities in heparin can be detected using this method since the overall equilibrium potential response of polyions increases with increasing charge density of the polyions. Here, first the potential response of pure heparin is measured at a saturation concentration, the concentration beyond which further addition of heparin does not produce a change in potential response. Then the potential response of heparin tainted with different quantities of the high charge-density contaminant is measured at a fixed total polyion concentration (heparin concentration + contaminant concentration). The latter gives a greater negative potential response due to the presence of the high charge-density contaminant. The increase in the negative potential response can be used for detection and quantification of high charge-density contaminants in heparin. We demonstrate here that 0.3% (w/w) OSCS as well as 0.1% (w/w) dextran sulfate can be detected in heparin at 20-mg/mL total polyion concentration. It has also been shown that 1% (w/w) of dextran sulfate can readily be detected in heparin at only 2-mg/mL total polyanion concentration with a linear response (R(2) = 0.994).

Хронопотенциометрия на платине в расплаве KF-NaF-AlF3-Al2O3

Some features of the mechanism of the anode process on platinum in KF–NaF–AlF3–Al2O3 melt at 750-780 °C depending on the of anodic current density (0.5 mA/cm2 to 2.0 A/cm2) and anodic pulse duration have been studied using chronopotentiometry method. In curves of change in the platinum anode potential a small peak at current densities of 10-30 mA/cm2 and a clear peak at current densities of 0.5-2.0 A/cm2 are recorded when the current is cut on. Analysis of dependencies of the transition time on the current density indicates that the first peak in curve is associated with the formation of an oxide compound on the platinum surface, and the second one is related to hindering the diffusion for delivery of electroactive particles to its surface.

No more conventional reference electrode: Transition time for determining chloride ion concentration

Ion selective electrodes (ISE) are used extensively for the potentiometric determination of ion concentrations in electrolytes. However, the inherent drift in these measurements and the requirement of a stable reference electrode restrict the feasibility of this method for long-term in-situ applications. This work presents a chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode for measuring chloride ion concentration. An anodic current pulse is applied to a Ag/AgCl working electrode which initiates a faradaic reaction that depletes the chloride ions near the electrode surface. The rate of change in potential at the Ag/AgCl electrode, due to chloride ion depletion, reaches an inflection point once the chloride ions deplete completely near the electrode surface. The moment of the inflection point, also known as the transition time, is a function of the chloride ion concentration and is described by the Sand equation. It is shown that the square root of the transition time is linearly proportional to the chloride ion concentration. Drift in the response over two weeks is negligible: 59μM/day when measuring 1mM of Cl− ions using a 10Am−2 current pulse. The transition time at a specific ion concentration can be tuned by the applied current pulse, e.g., in a solution containing 5mM chloride ions, the transition times with current pulses of 10 and 20Am−2 are 1.56 and 0.25s, respectively. The moment of inflection determines the response, and thus is independent of the absolute potential of reference electrode. Therefore, any metal wire can act as a pseudo-reference electrode, enabling this approach for long-term and integrated-sensor applications such as measurement inside concrete structures.

Processing-Microstructure Relationships in the Plasma Electrolytic Oxidation (PEO) Coating of a Magnesium Alloy

In the plasma electrolytic oxidation (PEO) coating of light metal alloys, changing the electrical parameters and electrolytic composition can change the discharge behaviour and, ultimately, the thickness, surface morphology and porosity of the coating. In the present study a combination of cathodic and anodic current pulses with suitable Ton and Toff periods were used to control the porosity and other structural defects of PEO coatings of an AM60B magnesium alloy. In order to investigate the effect of a current mode on the plasma discharge behaviour and coating microstructure during the PEO treatment of magnesium alloy, the emission intensities of six different spectral lines from the plasma species were recorded simultaneously as a function of both time and current mode using optical emission spectroscopy (OES) system. The fluctuations in signal intensities and temperature during the coating process reflect differences in location of both the discharge initiation, and discharge type. The coating surface morphology and microstructure that are obtained can be linked to the plasma discharge behavior. These results are discussed in relation to the discharge behaviour, and how such changes in discharge behaviour relate to the coating mechanisms.

Effects of electrical parameters on plasma electrolytic oxidation of aluminium

The plasma electrolytic oxidation (PEO) of aluminium alloys is investigated for different electrical working conditions using a pulsed bipolar current supply. A particular attention is paid to the effect of the anodic current density (from 10 to 90Adm−2) and current pulse frequency (from 100 to 900Hz) on the resulting oxide layer. Micro-discharges are characterized during the process by means of fast video imaging with a time and a space resolution of 8μs and 0.017mm2, respectively. Correlations are established between the micro-discharge characteristics (surface density, lifetime and size) and the elaborated oxide layers (morphology, growth rate and surface roughness). The highest coating growth rate measured (2.1μmmin−1) is achieved with the combination of the highest current density (75.7Adm−2) and the highest current pulse frequency (900Hz). Within these specific current conditions it is concluded that the detrimental effects of numerous micro-discharges are minimized. The results also show that the surface roughness may be largely affected by the presence of long-lived and large micro-discharges which develop over the processed surface. The strongest micro-discharges (live duration up to 0.3ms and cross-sectional area up to 1mm2) are mainly observed with the combination of the highest current density (75.7Adm−2) and the lowest current pulse frequency (100Hz).

Electrical stimulation of retinal neurons in epiretinal and subretinal configuration using a multicapacitor array

Electrical stimulation of retinal neurons offers the possibility of partial restoration of visual function. Challenges in neuroprosthetic applications are the long-term stability of the metal-based devices and the physiological activation of retinal circuitry. In this study, we demonstrate electrical stimulation of different classes of retinal neurons with a multicapacitor array. The array--insulated by an inert oxide--allows for safe stimulation with monophasic anodal or cathodal current pulses of low amplitude. Ex vivo rabbit retinas were interfaced in either epiretinal or subretinal configuration to the multicapacitor array. The evoked activity was recorded from ganglion cells that respond to light increments by an extracellular tungsten electrode. First, a monophasic epiretinal cathodal or a subretinal anodal current pulse evokes a complex burst of action potentials in ganglion cells. The first action potential occurs within 1 ms and is attributed to direct stimulation. Within the next milliseconds additional spikes are evoked through bipolar cell or photoreceptor depolarization, as confirmed by pharmacological blockers. Second, monophasic epiretinal anodal or subretinal cathodal currents elicit spikes in ganglion cells by hyperpolarization of photoreceptor terminals. These stimuli mimic the photoreceptor response to light increments. Third, the stimulation symmetry between current polarities (anodal/cathodal) and retina-array configuration (epi/sub) is confirmed in an experiment in which stimuli presented at different positions reveal the center-surround organization of the ganglion cell. A simple biophysical model that relies on voltage changes of cell terminals in the transretinal electric field above the stimulation capacitor explains our results. This study provides a comprehensive guide for efficient stimulation of different retinal neuronal classes with low-amplitude capacitive currents.

Selectivity Enhancement for Chloride Ion by In(III)‐Porphyrin‐Based Polymeric Membrane Electrode Operated in Pulsed Chronopotentiometric Mode

A robust selectivity enhancement of an In(III)-porphyrin ionophore-based chloride-selective electrode under pulsed chronopotentiometric measurement mode that enables the detection of chloride ions in the presence of a normally interfering concentration of salicylate ions is described. This enhancement is achieved by the rapid depletion of the surface concentration of the more dilute lipophilic anion during an initial anodic current pulse period due to extraction of this preferred anion into the membrane phase. Measurement of chloride with a detection limit of 8 mM and near Nernstian response slope in the presence of 1 mM salicylate is possible using the pulstrode method.

Frequency dependent effect of selective biphasic left vagus nerve stimulation on heart rate and arterial pressure

Activation of the parasympathetic pathway leads to negative chronotropic, dromotropic, and inotropic changes of heart function. The ability to selectively stimulate certain superficial compartments of peripheral nerves has been demonstrated previously. The aim of the present study was to find a clinically acceptable selective biphasic vagus nerve stimulation technique, which could allow gradual regulation of heart rate and systemic arterial pressure. In two patients, the left vagus nerve was stimulated with a combination of quasi-trapezoidal cathodic and rectangular anodic current pulses with different stimulation frequencies (10Hz, 20Hz, 30Hz) and increasing current. The heart rate and systemic arterial pressure decreased with increasing current at all different stimulation frequencies (p<0.05). The heart rate and arterial pressure response was more gradual with 10Hz compared to 20Hz/30Hz vagus nerve stimulation (p<0.05). In conclusion, selective vagus nerve stimulation, with a combination of quasi-trapezoidal cathodic and rectangular anodic current pulses at 10Hz, offers gradual heart rate and systolic arterial pressure control.

Pulsed-reverse current electrodeposition of Zn and Zn-TiO2 nanocomposite films

Abstract Zn and Zn-TiO 2 nanocomposite films were prepared by pulsed-reverse current electrolysis, from acidic zinc sulphate solutions, on a Ti support. The influence of the anodic pulse current, on the electrodeposit structural and morphological characteristics, has been investigated. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The amount of TiO 2 incorporated into the film was determined by induced coupled plasma spectroscopy (ICPS). It was found that the anodic pulse current density ( i a ) plays a remarkable influence on the coatings morphology and zinc crystallite size. When no anodic pulse is applied, both the zinc average crystallite size and TiO 2 content present the minimum values. By contrast, the nanocomposites prepared with the highest i a value (19 mA cm − 2 ), exhibit the highest values for the zinc average crystallite size and TiO 2 content. SEM results confirm that the pulse-plating parameters and the presence of boric acid have a strong influence on the deposit surface morphology. Moreover, an increase of the anodic current pulse leads to smoother coating surfaces. XRD, SEM and ICPS data indicate that the increase on the anodic current pulse promotes the incorporation of the nanoparticles into the nanocomposite deposits.