Negative Sweep Research Articles

Study of the influence of the polyalcohol mannitol on zinc electrodeposition from an alkaline bath

In this paper, the effects of adding mannitol to an alkaline plating bath on the electrodeposition of zinc onto AISI 1010 steel are described and assessed. From cyclic voltammograms with various lower-limit potentials, it is concluded that an initial zinc bulk deposition (region of wave c0) occurs from −1.45 V in the negative sweep. When the sweep is reversed at −1.60 V, an anodic peak a1 is seen in the positive sweep both in the absence and in presence of mannitol, which was assigned to zinc dissolution. This peak indicates that the primary nucleation and growth of zinc in region c0 is followed by zinc secondary nucleation and growth (region of peak c1). Scanning electron micrographs show that zinc electrodeposits obtained at mannitol concentrations ≥0.10 M were more refined than at lower concentrations. Energy-dispersive X-ray spectroscopy of these electrodeposits show oxygen contents that are generally low or below detection limit.

Conceptual design of a medium-sized joined-wing aircraft

The joined-wing aircraft is a very promising concept to reduce the ever-increasing fuel costs and CO2 emissions. Joined-wing aircraft employ tandem wings having positive and negative sweep and dihedral, arranged to form diamond shapes in both plan and front views. This article evaluates its capabilities by establishing a comparison with respect to a reference conventional wing-plus-horizontal tail aircraft. Both airplanes are designed for the same medium-/long-range transport mission. The topics considered include structural arrangement, weights and aerodynamic characteristics, as well as operational issues, such as performance and direct operating costs. The conclusions drawn at the end of this preliminary study are very positive, but further research is required in order to confirm some hypotheses regarding the structural arrangement.

A Square-Wave Adsorptive Stripping Voltammetric Method for Determination of Fast Green Dye

Square-wave adsorptive stripping voltammetric (SW-AdSV) determinations of trace concentrations of the coloring agent fast green were described. The analytical methodology used was based on the adsorptive preconcentration of the dye on the hanging mercury drop electrode, and then a negative sweep was initiated. In pH 10 carbonate supporting electrolyte, fast green gave a well-defined and sensitive SW-AdSV peak at -1220 mV. The electroanalytical determination of this dye was found to be optimized in carbonate buffer (pH 10) with the following experimental conditions: accumulation time (120 s); accumulation potential (-0.8 V); scan rate (800 mV/s); pulse amplitude (90 mV); frequency (90 Hz); surface area of the working electrode (0.6 mm2); and the convection rate (2000 rpm). Under these optimized conditions, the AdSV peak current was proportional over the concentration range 2 x 10(-8) -6 x 10(-7) M (r = 0.999), with an LOD of 1.63 x 10(-10) M (0.132 ppb). This analytical approach possessed more enhanced sensitivity than conventional chromatography or spectrophotometry, and was simple and quick. The precision of the method in terms of RSD was 0.17%, whereas the accuracy was evaluated via the mean recovery of 99.6%. Possible interferences by several substances usually present as food additive azo dyes (E110, E102, E123, and E129), natural and artificial sweeteners, and antioxidants were also investigated. Applicability of the developed electroanalysis method was illustrated via the determination of fast green in ice cream and soft drink samples.

Electronic transport characteristics of electrolyte-gated conducting polyaniline nanowire field-effect transistors

We investigate the electronic transport characteristics of an electrolyte-gated conducting polyaniline (PANI) nanowire field-effect transistor (FET) assembled between two Au electrodes on SiO2/Si substrate using nanochannel-assisted chemical oxidative polymerization. This is the first demonstration that the current-voltage characteristics for a PANI nanowire FET exhibit significant hysteresis, which is typically greater on the positive sweep of the potential than on the negative sweep. We suggest that this hysteresis is due to changes in the PANI structure and the effects of Coulombic repulsion in PANI nanowires on oxidation process. We also present degradation properties of PANI nanowire FETs with electrochemical gate potential.

Voltammetric and spectroelectrochemical properties of titanylphthalocyanines bearing catecholato and naphthalenediolato moieties

Detailed electrochemical characterization of catecholato-octakis(2-dimethylaminoethylsulfanyl phthalocyaninato) titanium(IV) and (2,3-naphthalenediolato)-octa-(2-dimethylaminoethylsulfanylphthalocyaninato) titanium(IV) derivatives has been carried out by cyclic voltammetry, differential pulse voltammetry, double potential step coulometry, controlled potential coulometry and spectroelectrochemical measurements. Cyclic and differential pulse voltammograms of the complexes are similar with two metal-based and two ligand-based reduction and two ligand-based oxidation couples. Capping of TiO core of octakis(2-dimethylaminoethylsulfanyl)phthalocyaninato oxotitanium(IV) with catecholato and naphthalenediolato changed the redox mechanism of the complexes. (2,3-naphthalenediolato)-octa-(2-dimethylaminoethylsulfanylphthalocyaninato) titanium(IV) derivative is dimetallised during the negative potential sweeps. Spectroelectrochemical measurements confirm the metal- and ligand-based assignments of the redox couples. Distinctive voltammetric and spectroscopic changes during the titration with soft metal ions, Ag+ and Pd2+, shows the metal sensing and coordinating properties of the complexes.

Electrochemical Studies and Square‐Wave Adsorptive Stripping Voltammetry of Spironolactone Drug

A sensitive and reliable stripping voltammetric method was developed to determine Spironolactone drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then a negative sweep was initiated, which yield a well defined cathodic peak at −1000 mV versus Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, frequency, pulse amplitude, convection rate and working electrode area. The monitored adsorptive current was directly proportional to the concentration of Spironolactone and it shows a linear response in the range from 1×10−8 to 2.5×10−7 mol l−1 (correlation coefficient=0.999) and the detection limit (S/N=3) is 1.72×10−10 mol l−1 at an accumulation time of 90 sec. The developed AdSV procedure shows a good reproducibility, the relative standard deviation RSD% (n=8) at a concentration level of 1.5×10−7 mol l−1 was 1.4%, whereas the method accuracy was indicated via the mean recovery of 97.5%±2.04. Possible interferences by several substances usually present in the pharmaceutical formulations have been also evaluated. The applicability of this approach was illustrated by the determination of Spironolactone in pharmaceutical preparation and biological fluids such as serum and urine.

Electrochemically Induced Iron Release of Adsorbed Horse Spleen Ferritin: Quantitation of Iron Using Long Optical Path Length Thin‐Layer Spectroelectrochemistry

AbstractIn this work, long optical path length thin‐layer electrochemical cell was constructed using indium‐tin oxide on glass as the electrode material. Iron release from ferritin adsorbed on the electrode was induced by applying a negative potential sweep in the presence of 1,10‐phenanthroline. The usefulness of spectroelectrochemistry as a means of determining the quantity of iron released from an adsorbed layer of ferritin is demonstrated.

Hysteresis phenomena in nanoscale rectifying diodes: A Monte Carlo interpretation in terms of surface effects

Hysteresis effects taking place in the rectifying current-voltage characteristic of self-switching diodes are studied by means of a semiclassical Monte Carlo simulator. When the applied voltage is higher than a certain threshold, in both negative and positive voltage sweeps, a well-defined hysteresis loop appears which can be exploited for memory applications. An algorithm for the simulation of surface effects has been introduced in the Monte Carlo simulator to explain this behavior in terms of the charging and discharging of the surface states on the etched sidewalls of the structure. Devices with different geometries have been simulated, and a detailed microscopic analysis of the behavior of surface charge and potential profiles has been performed. The reduction of the channel length or the increase of the width improves the discrimination of the memory state (by providing a higher reverse current); however, this induces a decrease of the reverse voltage threshold.

A voltammetric and nanogravimetric study of ZnSe electrodeposition from an acid bath containing Zn(II) and Se(IV)

The negative potential sweep of a polycrystalline Au electrode in a solution containing 5 × 10 − 4 mol L − 1 SeO 2, 0.2 mol L − 1 Zn(ClO 4) 2 and 0.5 mol L − 1 HClO 4 was analyzed at 0.05 V s − 1 . The simultaneously collected voltammetric and nanogravimetric responses allowed to analyze the several electrochemical processes occurring in the studied range of potential, finishing with the formation of a thin film of ZnSe. The association of results obtained using both techniques was applied to identify the species involved in the AuO reduction as (AuO) 2H 2SeO 3, which was desorbed during the oxide reduction with a mass variation much larger than that one observed in the supporting electrolyte. Initially, the Se(IV) reduction results in Se ads coverage, followed by a further reduction to H 2Se, which is a gas and desorbs from the electrode surface. Finally, the Zn(II) reduction inhibits the H 2Se formation and generates a thin film of ZnSe, as the final coating. The strong dependence of the nature of reacting compound and the mass as well as the charge variations allowed to postulate a reaction mechanism.

Half-Integer Flux Quantization in a Superconducting Loop with a Ferromagnetic π-Junction

Superconducting loops containing a π-junction are predicted to show a spontaneous magnetic moment in zero external magnetic field. In order to confirm this longstanding prediction experimentally, we performed magnetization measurements on individual mesoscopic superconducting niobium loops with a ferromagnetic (PdNi) π-junction. The loops are prepared on top of the active area of a micro Hall-sensor based on high mobility GaAs/AlGaAs heterostructures. We observe switching of the loop between different magnetization states at very low-magnetic fields, which is asymmetric for positive and negative sweep direction. This is evidence for a spontaneous current induced by the intrinsic phase shift of the π-junction. In addition, the presence of the spontaneous current at zero applied field is directly revealed by an increase of the magnetic moment with decreasing temperature, which results in a half integer flux quantization in the loop at low temperatures.

The Role of Surface Active States in Copper Electrodeposition in Acid Solution.

Copper metal electrodes in aqueous acid media exhibit two different types of electrochemistries, one related to the redox behaviour of low energy surface metal atoms (Cu/Cu2+) and the other based on the redox behaviour of low coverage, high energy, surface metal atoms (it is assumed that the latter transition involves magic number surface cluster species, Cu2/Cu2 +). The latter transition occurs well within the double layer region and the conversion of Cu2 + to Cu2in the negative sweep triggers the onset of electrocatalysis, e.g. of nitrate reduction, and the loss of inhibition, in the presence of thiourea or PEG+Cl- ions, of the copper plating reaction. The behaviour of the combination of bath additives used in Damascene copper plating is complex and requires further investigation.

Effects of blade sweep on the performance characteristics of axial flow turbomachinery rotors

Experimental studies were carried out in order to survey the performance and efficiency aspects of spanwise constant forward and backward sweep in axial flow rotors of low aspect ratio (AR) blading for incompressible flow, for part-load, near-design, and overload operational ranges. The experiments involved overall performance tests, laser Doppler velocimetry, and stationary total pressure probe measurements. The overall performance data and pitchwise averaged and resolved flow characteristics were evaluated in detail. For moderate and high flow rates, it was pointed out that positive or negative sweep tends to reduce or increase the blade load in the vicinity of the endwalls, respectively. It has been concluded that the loss-modifying effect of sweep can be judged by considering the three-dimensional viscous phenomena, and the influence of sweep on local blade efficiency depends on the balance of changes in blade load and losses. For low flow rates, forward sweep was found beneficial over the entire span from the aspect of improved stall margin and efficiency. The influence of AR on the performance reducing effect of sweep was studied on the basis of literature data.

Cathodic Stripping Voltammetry Determination of Ceftiofur Antibiotic in Formulations and Bovine Serum

A sensitive and reliable stripping voltammetry method was developed to determine the presence of Ceftiofur antibiotic drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then the initiation of a negative sweep that yielded well‐defined cathodic peaks at −0.65 V (1 C) and −1.00 V (2 C) vs. Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, convection rate, and working electrode area. The monitored adsorptive current of peak 1 C was directly proportional to the concentration of Ceftiofur; it shows a linear response in the range from 0.50×10−8 to 8.00×10−8 mol L−1 (correlation coefficient=0.998); and the limit of detection is 6.00×10−10 mol L−1 at an accumulation time of 300 s. The applicability of this approach was illustrated by the determination of Ceftiofur in pharmaceutical preparations and bovine serum.

A WORM-Type Memory Device with Rectifying Effect Based on a Conjugated Copolymer of PF6Eu on Si Substrate

ABSTRACTWe report a non-volatile, write-once-read-many times (WORM) memory device based on a simple organic-inorganic heterojunction. The organic film used is 9, 9-dihexylfluorene and Eu-complexed benzoate (PF6Eu (DBM)), which contains both electron-donor (9, 9-dihexylfluorene) and electron-acceptor (europium complex) groups. The inorganic n-type silicon substrate is used as the bottom electrode, while the Al is used as the top electrode. Under current-voltage testing, the device is able to switch from one initial non-conducting state (OFF) to a conducting state (ON) once a threshold voltage is reached under the first positive sweep. The “OFF” state is not recoverable with subsequent negative sweep after the device is turned “ON”. The ON/OFF current ratio is around 4×104. Diode rectifying characteristics is also observed for the turned-on device with a current ratio of 7×104, which is essential to address one memory cell in large passive matrix circuits. Reliability test is carried out and the device is able to sustain its “ON” state for at least 12 hours without any external bias.

Five Current Peaks in Voltammograms for Oxidations of Formic Acid, Formaldehyde, and Methanol on Platinum

We have found that five current peaks are present in the voltammograms in the positive and negative sweep directions for the oxidations of formic acid, formaldehyde, and methanol on Pt in the potential range of 0.05-1.8 V, although the experimental conditions for the peaks to appear are different. In particular, a current peak at ca. 0.6 V, the negative slope of which on the positive side is closely related to autocatalysis, inducing oscillation, has been observed even for methanol. We have clarified that the three substances produce very similar voltammograms at a very slow sweep rate, such as 0.1 mV/s, and show some of the same behaviors of the peaks in their voltammograms. All these facts support the idea that the electrochemical oxidation mechanisms for the three substances have the same dominating elementary reaction steps, which induce oscillation phenomena, although with different reaction and adsorption rate constants.

A Square-Wave Adsorptive Stripping Voltammetric Method for the Determination of Amaranth, a Food Additive Dye

Square-wave adsorptive stripping voltammetric (AdSV) determinations of trace concentrations of the azo coloring agent Amaranth are described. The analytical methodology used was based on the adsorptive preconcentration of the dye on the hanging mercury drop electrode, followed by initiation of a negative sweep. In a pH 10 carbonate supporting electrolyte, Amaranth gave a well-defined and sensitive AdSV peak at -518 mV. The electroanalytical determination of this azo dye was found to be optimal in carbonate buffer (pH 10) under the following experimental conditions: accumulation time, 120 s; accumulation potential, 0.0 V; scan rate, 600 mV/s; pulse amplitude, 90 mV; and frequency, 50 Hz. Under these optimized conditions the AdSV peak current was proportional over the concentration range 1 x 10(-8)-1.1 x 10(-7) mol/L (r = 0.999) with a detection limit of 1.7 x 10(-9) mol/L (1.03 ppb). This analytical approach possessed enhanced sensitivity, compared with conventional liquid chromatography or spectrophotometry and it was simple and fast. The precision of the method, expressed as the relative standard deviation, was 0.23%, whereas the accuracy, expressed as the mean recovery, was 104%. Possible interferences by several substances usually present as food additive azo dyes (E110, E102), gelatin, natural and artificial sweeteners, preservatives, and antioxidants were also investigated. The developed electroanalyticals method was applied to the determination of Amaranth in soft drink samples, and the results were compared with those obtained by a reference spectrophotometric method. Statistical analysis (paired t-test) of these data showed that the results of the 2 methods compared favorably.

Microwave pulse compression using a helically corrugated waveguide

Summary form only given. There has been a drive in recent years to produce ultra-high power short pulses for a range of applications. These high power pulses can be produced by microwave pulse compression. Sweep-frequency based microwave pulse compression using smooth bore hollow waveguides is one technique of pulse compression, however at very high powers this method has some limitation due to its operation close to cut-off. In optimum cases, the frequency at the beginning of an input pulse should be only 0.5-1% above the cutoff frequency. If a Cherenkov type TWT is used to drive the compressor then it is inevitable that the low-frequency part of the amplification band is below the cutoff which then reflected from the compressor back to the amplifier resulting in its possible parasitic self-oscillation. If a relativistic BWO is used as a source of frequency-modulated pulses for a smooth-waveguide compressor, then the necessary frequency sweep that would be required can only be produced by using a difficult-to-realize voltage modulation on the BWO. The two combined problems of wave reflection from a compressor and optimum frequency modulation can be solved using a waveguide with a special helical corrugation of its inner surface. A special helical corrugation of a circular waveguide ensures an eigenwave having a strongly frequency-dependent group velocity far from cut-off, which makes the helically corrugated waveguide attractive for using as a compressor of pulses from very high power amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a PIC code are presented. In the experiments a 70 ns 1 kW pulse from a conventional TWT was compressed in a 2 metre long helical waveguide. The compressed pulse had a peak power of 10.9 kW and duration of 3 ns. In order to find the optimum pulse compression ratio the waveguide's dispersion characteristics must be well known. The dispersion of the helix was calculated using the PIC code MAGIC and verified using an experimental technique. For a helical compressor the optimum negative frequency sweep can quite naturally be realized at the falling edge of a relativistic BWO pulse. For example, if a BWO generates hundreds of MW during 50 ns over a voltage drop from 700 kV to 400 kV, this frequency modulated radiation can be compressed up to 10-20 times in power with efficiency higher than 50%. Future work detailing plans to produce short, ultra-high power (multi-GW) pulses discussed.

Electrochemical impedance analysis of the redox switching hysteresis of poly(3,4-ethylenedioxythiophene) films

The effect of the redox hysteresis of poly(3,4-ethylenedioxythiophene) films on the electrochemical mechanisms analyzed by impedance has been studied. Impedance spectra were recorded at fixed steady-state potentials under both negative and positive sweeps. The effects of film thickness were also investigated by varying the polymerization charge used. It has been shown that not only do quasi-equilibrium circuit elements (low-frequency capacitance) vary with the potential sweep direction but also kinetics elements (interfacial charge transfer resistance) depend on it, both exhibiting hysteretic effects. The onset of the charge transfer resistance increase is shifted approximately −300 mV during the negative polarization.

Rh electrodeposition on Pt in acidic medium: a study using cyclic voltammetry and an electrochemical quartz crystal microbalance

This paper describes Rh electrodeposition on Pt electrodes in HClO 4 solutions. Using cyclic voltammetry (CV), coupled with electrochemical quartz crystal microbalance (EQCM) studies, we determined the main characteristics related to oxide formation on rhodium deposited on platinum. During the deposition, the results demonstrated that Rh 0 ad-atoms are stable on Pt in the potential range investigated at different saturation coverages. Data obtained using EQCM and CV show that the number of electrons transferred in the oxidation of Rh ads on Pt is 3 and a Rh(OH) 3 species was proposed as the adsorbed product. At potentials higher than 1.0 V, Rh(OH) 3 is oxidized to RhO(OH) 3. This species is reduced to Rh(OH) 3 and then to Rh 0 during the negative potential sweep.

Electrochemical determination of Cephalothin antibiotic by adsorptive stripping voltammetric technique

A sensitive and reliable stripping voltammetric method was developed to determine Cephalothin antibiotic drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then a negative sweep was initiated, which yield a well defined cathodic peak at −625 mV versus Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, convection rate and working electrode area. The monitored adsorptive current was directly proportional to the concentration of Cephalothin and it shows a linear response in the range from 4×10 −7 to 1.2×10 −6 mol l −1 (correlation coefficient=0.9995) and the detection limit (S/N=3) is 3.3×10 −9 mol l −1 at an accumulation time of 3 min. The developed AdSV procedure shows a good reproducibility, the relative standard deviation R.S.D.% ( n=10) at a concentration level of 5×10 −7 mol l −1 was 0.94%. Possible interferences by other pharmaceutical drugs and surfactants have been also evaluated. The applicability of this approach was illustrated by the determination of Cephalothin in pharmaceutical preparation and biological fluids such as serum and urine.