Cerium contained conversion films were deposited on LC4 aluminum alloy usingsquare wave pulse (SWP) in a CeCl_3 solution with KMnO_4 as the oxidant. Energy dispersivespectroscopy (EDS) and scanning electron microscopy...Cerium contained conversion films were deposited on LC4 aluminum alloy usingsquare wave pulse (SWP) in a CeCl_3 solution with KMnO_4 as the oxidant. Energy dispersivespectroscopy (EDS) and scanning electron microscopy (SEM) were adopted to study the composition andthe morphology of the film. It is found that the film is composed of Al, Zn, Cu, and small amount ofcerium. The polarization curves of the specimens treated with SWP technique measured in 3.5% (massfraction) NaCl solution reveal that the film thus formed inhibits both the anodic and cathodicprocess of the corrosion of the specimen. The immersion tests of treated specimens in 3.5% NaClsolution indicate that the corrosion resistance of the SWP treated specimen is better than that ofthe untreated and is equivalent to or even better than that of the traditionally electro-chemicallytreated specimens.展开更多
This paper reported a compact system of capacitively coupled contactless conductivity detection (C4D) based on the square wave excitation voltage for capillary electrophoresis, and it exhibited excellent sensitivity...This paper reported a compact system of capacitively coupled contactless conductivity detection (C4D) based on the square wave excitation voltage for capillary electrophoresis, and it exhibited excellent sensitivity at the optimal frequency of 198 kHz. The feasibility and sensitivity of this detector was demonstrated by simultaneous detection of thirteen ions including alkali, alkaline earth and heavy metal ions. And the detection limits (S/N 3) were in the range of 0.2-1μmol/L for Mn^2+, K^+, Na^+, Mg^2+, Ca^2+, Li^+, Ba^2+, and 7-25 μmol/L for Ni^2+, Cu^2+, Cd^2+, Pb^2+, Co^2+, Zn^2+.展开更多
In wind power system,the randomness of wind energy increases the probability of components fault.once the switch fault of the PWM rectifier is detected,it will lead to the distortion of the motor voltage and current w...In wind power system,the randomness of wind energy increases the probability of components fault.once the switch fault of the PWM rectifier is detected,it will lead to the distortion of the motor voltage and current waveform,the increase of torque ripple,the fluctuation of filter capacitor voltage,and the increase of harmonic content,which will affect the control performance and operation safety of the system.A common fault in a three-phase PWM rectifier is the open-circuit fault of the switch.This paper analyzes the current waveform distortion of the square wave motor when the rectifier switch fault,and proposes different fault-tolerant control strategies for different situations of switch fault,include single,double and triple switches fault.This method is based on several special driving modes under power generation situation of square wave motor.The strategy is easy to implement and does not need to change the circuit topology.It can realize fault-tolerant control of switch faults in the same side half bridge or the same bridge arm of the three-phase PWM rectifier.The effectiveness of the proposed fault-tolerant strategy is verified by simulation and experiment at the end of the article.展开更多
The moisture content measurement of human skin is a significant way to assess skin conditions and diagnose diseases that influence skin function.The necessity of evaluating the efficacy of a cosmetic product makes it ...The moisture content measurement of human skin is a significant way to assess skin conditions and diagnose diseases that influence skin function.The necessity of evaluating the efficacy of a cosmetic product makes it important to improve the accuracy and reproducibility of the measurement.A pair of interdigitated gold electrodes was fabricated on the printed circuit board (PCB) substrate and utilized directly in contact with the measured skin.A square-wave voltage at a single frequency was applied to the electrodes and the corresponding response current was measured to get the equivalent impedance of human skin.Since it's easy to generate and control a square-wave signal by digital electric circuits,this method is suitable to be used in the portable application.The experimental results indicate that good repeatability and satisfied accuracy can be obtained by this method.展开更多
In this research, copper oxide nanoparticles modified carbon paste electrode was developed for the voltammetric determination of lidocaine. The square wave voltammogram of lidocaine solution showed a well-defined peak...In this research, copper oxide nanoparticles modified carbon paste electrode was developed for the voltammetric determination of lidocaine. The square wave voltammogram of lidocaine solution showed a well-defined peak between +0.5 and +1.5 V. Instrumental and chemical parameters influencing voltammetric response were optimized by both one at a time and Box–Behnken model of response surface methodology. The results revealed that there was no significant difference between two methods of optimization. The linear range was 1–2500 μmol L^-1(Ip= 0.11 C(LH)+ 17.38, R^2= 0.999). The LOD and LOQ based on three and ten times of the signal to noise(S/N) were 0.39 and 1.3 μmol L^-1(n = 10),respectively. The precision of the method was assessed for 10 replicate square wave voltammetry(SWV)determinations each of 0.05, 0.5 and 1 μmol L^-1 of lidocaine showing relative standard deviations 4.1%,3.7% and 2.1%, respectively. The reliability of the proposed method was established by application of the method for the determination of lidocaine in two pharmaceutical preparations, namely injection and gel.展开更多
Electroactive self-assembled monolayers (SAMs) containing viologen group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is N,N'-dialkylbipyridinium ...Electroactive self-assembled monolayers (SAMs) containing viologen group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is N,N'-dialkylbipyridinium (i.e. a viologen group), onto gold electrodes from methanol/water solution and its electrochemical behavior is investigated ty Ac voltammetry and square wave voltammetry, which have the high sensitivity against background charging. The viologen SAM formed is a sub-monolayer and the normal potentials corresponding to the two successive one-electron transfer processes of the active centers (viologen) are -360 mV and -750 mV (vs. Ag/AgCl) in 0.1 mol/L phosphate buffer solutions (pH 6.96) respectively, and the standard electron transfer rate constant is 9.0 s(-1). The electrochemical behavior of this SAM in various solutions has been preliminarily discussed.展开更多
Electrochemical detection of 3-methyl-4-nitrophenol (MNP) in direct phenol oxidation occurs at high potentials and generally leads to progressive passivation of the electrochemical sensor. This study describes the use...Electrochemical detection of 3-methyl-4-nitrophenol (MNP) in direct phenol oxidation occurs at high potentials and generally leads to progressive passivation of the electrochemical sensor. This study describes the use of a carbon fiber microelectrode modified with a tetrasulfonated nickel phthalocyanine complex for the detection of MNP at a lower potential than that of direct phenol oxidation. The MNP voltammogram showed the presence of an anodic peak at -0.11 V vs SCE, corresponding to the oxidation of the hydroxylamine group generated after the reduction of the nitro group. The effect of buffer pH on the peak current and SWV parameters such as frequency, scan increment, and pulse amplitude were studied and optimized to have better electrochemical response of the proposed sensor. With these optimal parameters, the calibration curve shows that the peak current varied linearly as a function of MNP concentration, leading to a limit of detection (LoD) of 1.1 μg/L. These results show an appreciable sensitivity of the sensor for detecting the MNP at relatively low potentials, making it possible to avoid passivation phenomena.展开更多
Significant wave height(SWH) can be computed from the returning waveform of radar altimeter, this parameter is only raw estimates if it does not calibrate. But accurate calibration is important for all applications,...Significant wave height(SWH) can be computed from the returning waveform of radar altimeter, this parameter is only raw estimates if it does not calibrate. But accurate calibration is important for all applications, especially for climate studies. HY-2a altimeter has been operational since April 2012 and its products are available to the scientific community. In this work, SWH data from HY-2A altimeters are calibrated against in situ buoy data from the National Data Buoy Center(NDBC), Distinguished from previous calibration studies which generally regarded buoy data as "truth", the work of calibration for HY-2A altimeter wave data against in situ buoys was applied a more sophisticated statistical technique-the total least squares(TLS) method which can take into account errors in both variables. We present calibration results for HY-2A radar altimeter measurement of wave height against NDBC buoys. In addition, cross-calibration for HY-2A and Jason-2 wave data are talked over and the result is given.展开更多
Heavy metals,notably Pb2+and Cu^(2+),are some of the most persistent contaminants found in groundwater.Frequent monitoring of these metals,which relies on efficient,sensitive,cost-effective,and reliable methods,is a n...Heavy metals,notably Pb2+and Cu^(2+),are some of the most persistent contaminants found in groundwater.Frequent monitoring of these metals,which relies on efficient,sensitive,cost-effective,and reliable methods,is a necessity.We present a nanocomposite-based miniaturized electrode for the concurrent measurement of Pb2+and Cu^(2+)by exploiting the electroanalytical technique of square wave voltammetry.We also propose a facile in situ hydrothermal calcination method to directly grow binder-free mesoporous Ni O on a three-dimensional nickel foam,which is then electrochemically seeded with gold nanoparticles(Au NPs).The meticulous design of a low-barrier Ohmic contact between mesoporous Ni O and Au NPs facilitates target-mediated nanochannel-confined electron transfer within mesoporous Ni O.As a result,the heavy metals Pb2+(0.020 mg.L^(-1)detection limit;2.0–16.0 mg.L^(-1)detection range)and Cu^(2+)(0.013 mg.L^(-1)detection limit;0.4–12.8 mg.L^(-1)detection range)can be detected simultaneously with high precision.Furthermore,other heavy metal ions and common interfering ions found in groundwater showed negligible impacts on the electrode’s performance,and the recovery rate of groundwater samples varied between 96.3%±2.1%and 109.4%±0.6%.The compactness,flexible shape,low power consumption,and ability to remotely operate our electrode pave the way for onsite detection of heavy metals in groundwater,thereby demonstrating the potential to revolutionize the field of environmental monitoring.展开更多
The cathodic process of cerium(III) ions in NaCl-2CsCl melt was studied bycyclic voltammetry and square wave voltammetry with tungsten and gold electrodes at 873 K. The twoelectroanalytical methods yield similar resul...The cathodic process of cerium(III) ions in NaCl-2CsCl melt was studied bycyclic voltammetry and square wave voltammetry with tungsten and gold electrodes at 873 K. The twoelectroanalytical methods yield similar results. The cathodic process of cerium(III) ions consistsof two reversible steps: Ce^(3+)+ e^-= Ce^(2+) and Ce^(2+) + 2e^-= Ce. The half wave potentials ofCe^(3+)/Ce^(2+) and Ce^(2+)/Ce were determined as -2.525 V vs. Cl_2/Cl^- and -2.975 V vs. Cl_2/Cl^-,respectively. The diffusion coefficient of Ce^(3+) was also determined as 5.5 X 10^(-5) cm^2 centredot s^(-1).展开更多
Electroanalytical techniques could be a reliable and promising alternative to classical and sophisticated methods because of their simplicity(small and portable),easy use,the ability to deliver fast response with hi...Electroanalytical techniques could be a reliable and promising alternative to classical and sophisticated methods because of their simplicity(small and portable),easy use,the ability to deliver fast response with high sensitivity and selectivity.A square wave voltammetric method was developed for the assessment of organophosphorus(OPs) compound impact on acetylcholinesterase(AChE) of Pheretima with 2,6-dimethyl-p-benzoquinone(2,6DMBQ) as a redox indicator.The substrate of acetylthiocholine is hydrolyzed by AChE and the produced thiocholine reacts with 2,6-DMBQ to give an obvious shift of electrochemical signal.The reduction peak of 2,6-DMBQ is located at around 0.18 V which is far away from the oxidation potential of possible interference components often present in biosample.The decreased rate of reduction current was related with the activity of AChE.The inhibition of parathion-methyl on AChE was assessed.The inhibiton rate of OPs on AChE activity increased quickly during the first 10 min inhibition,and after that the value of inhibition rate approached to be constant.AChE lost almost 29.3% of activity after 10 min incubation with 1 μg/mL parathion-methyl and 67.5% of activity with 10 μg/mL parathion-methyl,while the activity that corresponds to 40 μg/mL parathion-methyl was nearly completely inhibited(94.9%).Compared to cyclic voltammetry and amperometry,Square wave voltammetry(SWV) method is a high sensitive electroanalysis with fast scan-rate(only several seconds for one signal value) which is useful to prevent the electrodes from possible fouling or passivation.This method can be employed to assess the inhibition of organophosphate on AChE and investigate OPs impact on environmental animals.展开更多
The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts.In this paper,homogene...The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts.In this paper,homogeneous electrocatalytic reaction between hydroxymethylferrocene(HMF)and L-cysteine is intensively investigated by cyclic voltammetry and square wave voltammetry for which,the secondorder rate constant(k_(ec))of the chemical reaction between HMF^(+)and L-cysteine is determined via a 1D homogeneous electrocatalytic reaction model based on finite element simulation.The corresponding k_(ec)(1.1(mol·m^(-3))^(-1)·s^(-1))is further verified by linear sweep voltammograms under the same model.Square wave voltammetry parameters including potential frequency(f),increment(Estep)and amplitude(ESW)have been comprehensively investigated in terms of the voltammetric waveform transition of homogeneous electrocatalytic reaction.Specifically,the effect of potential frequency and increment is in accordance with the potential scan rate in cyclic voltammetry and the increase of pulsed potential amplitude results in a conspicuous split oxidative peaks phenomenon.Moreover,the proposed methodology of k_(ec)prediction is examined by hydroxyethylferrocene(HEF)and L-cysteine.The present work facilitates the understanding of homogeneous electrocatalytic reaction for energy storage purpose,especially in terms of electrochemical kinetics extraction and flow battery design.展开更多
In this work,carbon nanosheet(CNS) based electrode was designed for electrochemical biosensing of glucose.CNS has been obtained by the pyrolysis of barley at 600-750℃ in a muffle furnace:it was then purified and f...In this work,carbon nanosheet(CNS) based electrode was designed for electrochemical biosensing of glucose.CNS has been obtained by the pyrolysis of barley at 600-750℃ in a muffle furnace:it was then purified and functionalized.The CNS has been characterized by scanning electron microscopy(SEM).X-ray diffraction(XRD) and Raman spectroscopic techniques.The electrochemical activity of CNS-based electrode was investigated by linear sweep vollammetry(LSV) and square wave voltammetry(SWV),for the oxidation of glucose in 0.001 M H2SO4(pH 6.0).The linear range of the sensor was found to be 10-4-10-6M(1-100 μM) within the response time of 4 s.Interestingly,its sensitivity reached as high as 26.002±0.01 μA/μM cm2.Electrochemical experiments revealed that the proposed electrode offered an excellent electrochemical activity towards the oxidation of glucose and could be applied for the construction of non-enzymatic glucose biosensors.展开更多
The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was s...The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.展开更多
Electrochemical determination of paracetamol(PCT)was successfully performed using carbon paste electrodes(CPEs)modified with treated coffee husks(CHt)or cellulose powder(Ce).Scanning electron microscopy was used to ch...Electrochemical determination of paracetamol(PCT)was successfully performed using carbon paste electrodes(CPEs)modified with treated coffee husks(CHt)or cellulose powder(Ce).Scanning electron microscopy was used to characterize unmodified or modified CPEs prior to their use.The electrochemical oxidation of PCT was investigated using square wave voltammetry(SWV)and cyclic voltammetry(CV).The oxidation current density of PCT was two-fold higher with the CPE-CHt sensor and 30%higher with CPE-Ce in comparison with the unmodified CPE,and this correlated with the higher hydrophilicity of the modified electrodes.Using SWV for the electrochemical analysis of PCT,carbon paste electrode modified with raw coffee husks(CPE-CHr)showed the presence of impurities at+0.27 V/SCE,showing the interest in using pure cellulose for the present analytical application.Furthermore,CPE-Ce presented a higher real area compared to CPE-CHr,which explains the increase in the limit of saturation from 400 mg/L to 950 mg/L.The better saturation limit exhibited by CPE-Ce justifies its choice for electroanalysis of PCT in commercialized tablets.The proposed method was successfully applied in the determination of PCT in commercialized tablets(DolipraneR 500)with a recovery rate close to 100%,and no interference with the excipients contained in the tablets analyzed was observed.This novel sensor opens the way for sustainable development of electroanalytical control of drugs sold individually in developing countries.展开更多
A simple electrochemical sensor for dopamine detection, is based on molecularly imprinted and electropolymerized over-oxidized polypyrrole (OPPy). The MIP-based electrode is obtained by electrocopolymerization of pyrr...A simple electrochemical sensor for dopamine detection, is based on molecularly imprinted and electropolymerized over-oxidized polypyrrole (OPPy). The MIP-based electrode is obtained by electrocopolymerization of pyrrole (0.1 M) in the presence of the template molecular (dopamine, DA) (10<sup>-3</sup> M). The square wave voltammetry (SWV) is used for the detection of dopamine in buffer solution. The current peak obtained at the MIP electrode was proportional to the logarithm of the DA concentration in the range of 10<sup>-11</sup> to 5 × 10<sup>-8</sup> M with a detection limit of 10<sup>-11</sup> M. The proposed sensor was used for the detection of DA in spiked blood serum, satisfactory results were obtained.展开更多
The electrochemical behavior of duloxetine HCl (DXT.HCl) at a carbon paste electrode (CPE) was achieved by cyclic voltammetry and a mechanism of its oxidation was reported and illustrated. A sensitive linear sweep and...The electrochemical behavior of duloxetine HCl (DXT.HCl) at a carbon paste electrode (CPE) was achieved by cyclic voltammetry and a mechanism of its oxidation was reported and illustrated. A sensitive linear sweep and square-wave adsorptive anodic stripping voltammetry methods were described for trace determination of DXT.HCl. Introduction: DXT.HCl, N-methyl-3-(nap-thalen-1- yloxy)-3-(thiophene-2-yl) propan-1-amine hydrochloride is a selective serotonin-norepinephrine reuptake inhibitor (SNRI) originally developed as an antidepressant and is currently recommended for maintenance treatment of major depressive disorder. Methods: Electrochemical behavior was studied using cyclic voltammetric method, and the analytical application was studied using linear sweep and square wave voltammetric methods. Solution pH has been measured by pH meter. Results: The process on the surface of carbon paste electrode was found to be irreversible and diffusion-controlled. The number of proton and electron transferred were calculated. Possible reaction mechanism taking place on the surface of electrode was proposed. Calibration plot constructed using square wave voltammetric technique was used for quantitative analysis in pharmaceutical and human serum samples. Limit of detection (LOD) and limit of quantification (LOQ) were calculated. Conclusions: In the present work, we described the electrochemical behavior of DXT.HCl drug. Two precise linear sweep and square wave adsorptive anodic stripping voltammetry methods have been described for its trace quantitation in pharmaceutical formulation and human serum. The method shows the development of a sensor for selective and sensitive determination of DXT.HCl.展开更多
Laser shock peening(LSP) is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy...Laser shock peening(LSP) is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot.Nd:glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied.The surface morphology and surface residual stress of the TC17 titanium alloy,treated with varying peening parameters such as laser power density and overlapping ratio,have been studied in detail.The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas,and compressive residual stresses are saturated as laser pulse energy is over 55 J.There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios.A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 %.The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz.The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.展开更多
Voltammetry measurements have been employed to investigate the redox behaviour of curcumin in aqueous media using functionalized carbon nanotube(FCNTs)modified glassy carbon electrode(GCE).The electro-catalytic proper...Voltammetry measurements have been employed to investigate the redox behaviour of curcumin in aqueous media using functionalized carbon nanotube(FCNTs)modified glassy carbon electrode(GCE).The electro-catalytic properties of FCNTs modified electrode are superior in comparison to the conventional electrode in generating the electrochemical response from curcumin.The oxidation process of the curcumin over the modified substrate is found to be p H dependent and shows 2e^(-)and 2H^(+)proton transfer electrochemical process.The oxidation peak is obtained at 0.37 V and the peak current is found to be linear with the varying concentration of curcumin.The limit of detection(LOD)and the limit of quantification(LOQ)for the curcumin are obtained as 60 and 200 nmol/L,respectively using the FCNTs modified GCE.The enhanced electrochemical response from the FCNTs modified GCE has been utilized in the evaluation of the chemical and biochemical behaviour of curcumin in presence of transition metal ions(Cu^(2+))and ds DNA,and the observation has been supported by the spectrochemical characteristics of the interactions.展开更多
Phenylacetic acid(PAA)is a primary raw material for illegal Methamphetamine(MATM)synthesis under the strong precursor chemicals supervisions of safrole and isosafrole.Therefore,trace detection of PAA at ultra-low conc...Phenylacetic acid(PAA)is a primary raw material for illegal Methamphetamine(MATM)synthesis under the strong precursor chemicals supervisions of safrole and isosafrole.Therefore,trace detection of PAA at ultra-low concentration is a strategic technique and an urgent issue in the field of drug control.In this paper,trace determination of PAA at sub-nmol-L-1 concentration level is achieved by hydrogen bond adsorption and electrochemical catalysis through the prepared aminated SiO_(2)nanoparticles(SiO_(2)-NH_(2) NPs)and MoS_(2) nanosheets(NSs)modified glassy carbon electrode(GCE).The prepared MoS_(2) NS s/SiO_(2)-NH_(2) NPs modified electrode represents a detecting limit of 0.0989 nmol·L^(-1)and an obvious increasing linear range before the concentration increasement up to 60 nmol·L^(-1)in square wave voltammetry(SWV)responses of PAA.The SWV response of the modified electrode to PAA in the concentration range within 100 nmol·L^(-1)is higher than phenol,acetic acid(HOAc)and benzoic Acid(BEN).This electrochemical method for trace detection of PAA in aqueous solution with desired performance provides a feasible scheme for the detection of other drugs and aromatic precursor chemicals.展开更多
基金This work was financially supported by the National Natural Science Foundation of China (No. 59771067) and the National Key Laboratory of New Metal Materials.
文摘Cerium contained conversion films were deposited on LC4 aluminum alloy usingsquare wave pulse (SWP) in a CeCl_3 solution with KMnO_4 as the oxidant. Energy dispersivespectroscopy (EDS) and scanning electron microscopy (SEM) were adopted to study the composition andthe morphology of the film. It is found that the film is composed of Al, Zn, Cu, and small amount ofcerium. The polarization curves of the specimens treated with SWP technique measured in 3.5% (massfraction) NaCl solution reveal that the film thus formed inhibits both the anodic and cathodicprocess of the corrosion of the specimen. The immersion tests of treated specimens in 3.5% NaClsolution indicate that the corrosion resistance of the SWP treated specimen is better than that ofthe untreated and is equivalent to or even better than that of the traditionally electro-chemicallytreated specimens.
基金support from the National Natural Science Foundation of China(No.20475018)the Key Program of Guangdong Natural Science Foundation(No.05103552)
文摘This paper reported a compact system of capacitively coupled contactless conductivity detection (C4D) based on the square wave excitation voltage for capillary electrophoresis, and it exhibited excellent sensitivity at the optimal frequency of 198 kHz. The feasibility and sensitivity of this detector was demonstrated by simultaneous detection of thirteen ions including alkali, alkaline earth and heavy metal ions. And the detection limits (S/N 3) were in the range of 0.2-1μmol/L for Mn^2+, K^+, Na^+, Mg^2+, Ca^2+, Li^+, Ba^2+, and 7-25 μmol/L for Ni^2+, Cu^2+, Cd^2+, Pb^2+, Co^2+, Zn^2+.
文摘In wind power system,the randomness of wind energy increases the probability of components fault.once the switch fault of the PWM rectifier is detected,it will lead to the distortion of the motor voltage and current waveform,the increase of torque ripple,the fluctuation of filter capacitor voltage,and the increase of harmonic content,which will affect the control performance and operation safety of the system.A common fault in a three-phase PWM rectifier is the open-circuit fault of the switch.This paper analyzes the current waveform distortion of the square wave motor when the rectifier switch fault,and proposes different fault-tolerant control strategies for different situations of switch fault,include single,double and triple switches fault.This method is based on several special driving modes under power generation situation of square wave motor.The strategy is easy to implement and does not need to change the circuit topology.It can realize fault-tolerant control of switch faults in the same side half bridge or the same bridge arm of the three-phase PWM rectifier.The effectiveness of the proposed fault-tolerant strategy is verified by simulation and experiment at the end of the article.
文摘The moisture content measurement of human skin is a significant way to assess skin conditions and diagnose diseases that influence skin function.The necessity of evaluating the efficacy of a cosmetic product makes it important to improve the accuracy and reproducibility of the measurement.A pair of interdigitated gold electrodes was fabricated on the printed circuit board (PCB) substrate and utilized directly in contact with the measured skin.A square-wave voltage at a single frequency was applied to the electrodes and the corresponding response current was measured to get the equivalent impedance of human skin.Since it's easy to generate and control a square-wave signal by digital electric circuits,this method is suitable to be used in the portable application.The experimental results indicate that good repeatability and satisfied accuracy can be obtained by this method.
基金funding provided by Jundishapur University of Medical Sciences–Nanotechnology Research Center under grant No.N-11
文摘In this research, copper oxide nanoparticles modified carbon paste electrode was developed for the voltammetric determination of lidocaine. The square wave voltammogram of lidocaine solution showed a well-defined peak between +0.5 and +1.5 V. Instrumental and chemical parameters influencing voltammetric response were optimized by both one at a time and Box–Behnken model of response surface methodology. The results revealed that there was no significant difference between two methods of optimization. The linear range was 1–2500 μmol L^-1(Ip= 0.11 C(LH)+ 17.38, R^2= 0.999). The LOD and LOQ based on three and ten times of the signal to noise(S/N) were 0.39 and 1.3 μmol L^-1(n = 10),respectively. The precision of the method was assessed for 10 replicate square wave voltammetry(SWV)determinations each of 0.05, 0.5 and 1 μmol L^-1 of lidocaine showing relative standard deviations 4.1%,3.7% and 2.1%, respectively. The reliability of the proposed method was established by application of the method for the determination of lidocaine in two pharmaceutical preparations, namely injection and gel.
基金Project supported by the National Natural Science Foundation of China.
文摘Electroactive self-assembled monolayers (SAMs) containing viologen group are formed through the adsorption of thiol-functionalized viologen compound CH3(CH2)(9)V2+(CH2)(8)SH, where V2+ is N,N'-dialkylbipyridinium (i.e. a viologen group), onto gold electrodes from methanol/water solution and its electrochemical behavior is investigated ty Ac voltammetry and square wave voltammetry, which have the high sensitivity against background charging. The viologen SAM formed is a sub-monolayer and the normal potentials corresponding to the two successive one-electron transfer processes of the active centers (viologen) are -360 mV and -750 mV (vs. Ag/AgCl) in 0.1 mol/L phosphate buffer solutions (pH 6.96) respectively, and the standard electron transfer rate constant is 9.0 s(-1). The electrochemical behavior of this SAM in various solutions has been preliminarily discussed.
文摘Electrochemical detection of 3-methyl-4-nitrophenol (MNP) in direct phenol oxidation occurs at high potentials and generally leads to progressive passivation of the electrochemical sensor. This study describes the use of a carbon fiber microelectrode modified with a tetrasulfonated nickel phthalocyanine complex for the detection of MNP at a lower potential than that of direct phenol oxidation. The MNP voltammogram showed the presence of an anodic peak at -0.11 V vs SCE, corresponding to the oxidation of the hydroxylamine group generated after the reduction of the nitro group. The effect of buffer pH on the peak current and SWV parameters such as frequency, scan increment, and pulse amplitude were studied and optimized to have better electrochemical response of the proposed sensor. With these optimal parameters, the calibration curve shows that the peak current varied linearly as a function of MNP concentration, leading to a limit of detection (LoD) of 1.1 μg/L. These results show an appreciable sensitivity of the sensor for detecting the MNP at relatively low potentials, making it possible to avoid passivation phenomena.
基金The Marine Public Welfare Project of China under contract No.201305032
文摘Significant wave height(SWH) can be computed from the returning waveform of radar altimeter, this parameter is only raw estimates if it does not calibrate. But accurate calibration is important for all applications, especially for climate studies. HY-2a altimeter has been operational since April 2012 and its products are available to the scientific community. In this work, SWH data from HY-2A altimeters are calibrated against in situ buoy data from the National Data Buoy Center(NDBC), Distinguished from previous calibration studies which generally regarded buoy data as "truth", the work of calibration for HY-2A altimeter wave data against in situ buoys was applied a more sophisticated statistical technique-the total least squares(TLS) method which can take into account errors in both variables. We present calibration results for HY-2A radar altimeter measurement of wave height against NDBC buoys. In addition, cross-calibration for HY-2A and Jason-2 wave data are talked over and the result is given.
基金supported by the National Key Research and Development Project of China(2019YFC1804802)。
文摘Heavy metals,notably Pb2+and Cu^(2+),are some of the most persistent contaminants found in groundwater.Frequent monitoring of these metals,which relies on efficient,sensitive,cost-effective,and reliable methods,is a necessity.We present a nanocomposite-based miniaturized electrode for the concurrent measurement of Pb2+and Cu^(2+)by exploiting the electroanalytical technique of square wave voltammetry.We also propose a facile in situ hydrothermal calcination method to directly grow binder-free mesoporous Ni O on a three-dimensional nickel foam,which is then electrochemically seeded with gold nanoparticles(Au NPs).The meticulous design of a low-barrier Ohmic contact between mesoporous Ni O and Au NPs facilitates target-mediated nanochannel-confined electron transfer within mesoporous Ni O.As a result,the heavy metals Pb2+(0.020 mg.L^(-1)detection limit;2.0–16.0 mg.L^(-1)detection range)and Cu^(2+)(0.013 mg.L^(-1)detection limit;0.4–12.8 mg.L^(-1)detection range)can be detected simultaneously with high precision.Furthermore,other heavy metal ions and common interfering ions found in groundwater showed negligible impacts on the electrode’s performance,and the recovery rate of groundwater samples varied between 96.3%±2.1%and 109.4%±0.6%.The compactness,flexible shape,low power consumption,and ability to remotely operate our electrode pave the way for onsite detection of heavy metals in groundwater,thereby demonstrating the potential to revolutionize the field of environmental monitoring.
文摘The cathodic process of cerium(III) ions in NaCl-2CsCl melt was studied bycyclic voltammetry and square wave voltammetry with tungsten and gold electrodes at 873 K. The twoelectroanalytical methods yield similar results. The cathodic process of cerium(III) ions consistsof two reversible steps: Ce^(3+)+ e^-= Ce^(2+) and Ce^(2+) + 2e^-= Ce. The half wave potentials ofCe^(3+)/Ce^(2+) and Ce^(2+)/Ce were determined as -2.525 V vs. Cl_2/Cl^- and -2.975 V vs. Cl_2/Cl^-,respectively. The diffusion coefficient of Ce^(3+) was also determined as 5.5 X 10^(-5) cm^2 centredot s^(-1).
基金Supported by the Natural Science Foundation of Shanxi Province,China(No.20001057)
文摘Electroanalytical techniques could be a reliable and promising alternative to classical and sophisticated methods because of their simplicity(small and portable),easy use,the ability to deliver fast response with high sensitivity and selectivity.A square wave voltammetric method was developed for the assessment of organophosphorus(OPs) compound impact on acetylcholinesterase(AChE) of Pheretima with 2,6-dimethyl-p-benzoquinone(2,6DMBQ) as a redox indicator.The substrate of acetylthiocholine is hydrolyzed by AChE and the produced thiocholine reacts with 2,6-DMBQ to give an obvious shift of electrochemical signal.The reduction peak of 2,6-DMBQ is located at around 0.18 V which is far away from the oxidation potential of possible interference components often present in biosample.The decreased rate of reduction current was related with the activity of AChE.The inhibition of parathion-methyl on AChE was assessed.The inhibiton rate of OPs on AChE activity increased quickly during the first 10 min inhibition,and after that the value of inhibition rate approached to be constant.AChE lost almost 29.3% of activity after 10 min incubation with 1 μg/mL parathion-methyl and 67.5% of activity with 10 μg/mL parathion-methyl,while the activity that corresponds to 40 μg/mL parathion-methyl was nearly completely inhibited(94.9%).Compared to cyclic voltammetry and amperometry,Square wave voltammetry(SWV) method is a high sensitive electroanalysis with fast scan-rate(only several seconds for one signal value) which is useful to prevent the electrodes from possible fouling or passivation.This method can be employed to assess the inhibition of organophosphate on AChE and investigate OPs impact on environmental animals.
基金the support of National Natural Science Foundation of China, China (Grant No. 22005010)Beijing Municipal Education Commission Research Project (KM202010005012)
文摘The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts.In this paper,homogeneous electrocatalytic reaction between hydroxymethylferrocene(HMF)and L-cysteine is intensively investigated by cyclic voltammetry and square wave voltammetry for which,the secondorder rate constant(k_(ec))of the chemical reaction between HMF^(+)and L-cysteine is determined via a 1D homogeneous electrocatalytic reaction model based on finite element simulation.The corresponding k_(ec)(1.1(mol·m^(-3))^(-1)·s^(-1))is further verified by linear sweep voltammograms under the same model.Square wave voltammetry parameters including potential frequency(f),increment(Estep)and amplitude(ESW)have been comprehensively investigated in terms of the voltammetric waveform transition of homogeneous electrocatalytic reaction.Specifically,the effect of potential frequency and increment is in accordance with the potential scan rate in cyclic voltammetry and the increase of pulsed potential amplitude results in a conspicuous split oxidative peaks phenomenon.Moreover,the proposed methodology of k_(ec)prediction is examined by hydroxyethylferrocene(HEF)and L-cysteine.The present work facilitates the understanding of homogeneous electrocatalytic reaction for energy storage purpose,especially in terms of electrochemical kinetics extraction and flow battery design.
基金AICTE,New Delhi,for the financial support and NEHU,Shillong,for characterizations
文摘In this work,carbon nanosheet(CNS) based electrode was designed for electrochemical biosensing of glucose.CNS has been obtained by the pyrolysis of barley at 600-750℃ in a muffle furnace:it was then purified and functionalized.The CNS has been characterized by scanning electron microscopy(SEM).X-ray diffraction(XRD) and Raman spectroscopic techniques.The electrochemical activity of CNS-based electrode was investigated by linear sweep vollammetry(LSV) and square wave voltammetry(SWV),for the oxidation of glucose in 0.001 M H2SO4(pH 6.0).The linear range of the sensor was found to be 10-4-10-6M(1-100 μM) within the response time of 4 s.Interestingly,its sensitivity reached as high as 26.002±0.01 μA/μM cm2.Electrochemical experiments revealed that the proposed electrode offered an excellent electrochemical activity towards the oxidation of glucose and could be applied for the construction of non-enzymatic glucose biosensors.
文摘The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.
文摘Electrochemical determination of paracetamol(PCT)was successfully performed using carbon paste electrodes(CPEs)modified with treated coffee husks(CHt)or cellulose powder(Ce).Scanning electron microscopy was used to characterize unmodified or modified CPEs prior to their use.The electrochemical oxidation of PCT was investigated using square wave voltammetry(SWV)and cyclic voltammetry(CV).The oxidation current density of PCT was two-fold higher with the CPE-CHt sensor and 30%higher with CPE-Ce in comparison with the unmodified CPE,and this correlated with the higher hydrophilicity of the modified electrodes.Using SWV for the electrochemical analysis of PCT,carbon paste electrode modified with raw coffee husks(CPE-CHr)showed the presence of impurities at+0.27 V/SCE,showing the interest in using pure cellulose for the present analytical application.Furthermore,CPE-Ce presented a higher real area compared to CPE-CHr,which explains the increase in the limit of saturation from 400 mg/L to 950 mg/L.The better saturation limit exhibited by CPE-Ce justifies its choice for electroanalysis of PCT in commercialized tablets.The proposed method was successfully applied in the determination of PCT in commercialized tablets(DolipraneR 500)with a recovery rate close to 100%,and no interference with the excipients contained in the tablets analyzed was observed.This novel sensor opens the way for sustainable development of electroanalytical control of drugs sold individually in developing countries.
文摘A simple electrochemical sensor for dopamine detection, is based on molecularly imprinted and electropolymerized over-oxidized polypyrrole (OPPy). The MIP-based electrode is obtained by electrocopolymerization of pyrrole (0.1 M) in the presence of the template molecular (dopamine, DA) (10<sup>-3</sup> M). The square wave voltammetry (SWV) is used for the detection of dopamine in buffer solution. The current peak obtained at the MIP electrode was proportional to the logarithm of the DA concentration in the range of 10<sup>-11</sup> to 5 × 10<sup>-8</sup> M with a detection limit of 10<sup>-11</sup> M. The proposed sensor was used for the detection of DA in spiked blood serum, satisfactory results were obtained.
文摘The electrochemical behavior of duloxetine HCl (DXT.HCl) at a carbon paste electrode (CPE) was achieved by cyclic voltammetry and a mechanism of its oxidation was reported and illustrated. A sensitive linear sweep and square-wave adsorptive anodic stripping voltammetry methods were described for trace determination of DXT.HCl. Introduction: DXT.HCl, N-methyl-3-(nap-thalen-1- yloxy)-3-(thiophene-2-yl) propan-1-amine hydrochloride is a selective serotonin-norepinephrine reuptake inhibitor (SNRI) originally developed as an antidepressant and is currently recommended for maintenance treatment of major depressive disorder. Methods: Electrochemical behavior was studied using cyclic voltammetric method, and the analytical application was studied using linear sweep and square wave voltammetric methods. Solution pH has been measured by pH meter. Results: The process on the surface of carbon paste electrode was found to be irreversible and diffusion-controlled. The number of proton and electron transferred were calculated. Possible reaction mechanism taking place on the surface of electrode was proposed. Calibration plot constructed using square wave voltammetric technique was used for quantitative analysis in pharmaceutical and human serum samples. Limit of detection (LOD) and limit of quantification (LOQ) were calculated. Conclusions: In the present work, we described the electrochemical behavior of DXT.HCl drug. Two precise linear sweep and square wave adsorptive anodic stripping voltammetry methods have been described for its trace quantitation in pharmaceutical formulation and human serum. The method shows the development of a sensor for selective and sensitive determination of DXT.HCl.
基金Subject in Advance of General Armament Department(813040405-1)
文摘Laser shock peening(LSP) is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot.Nd:glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied.The surface morphology and surface residual stress of the TC17 titanium alloy,treated with varying peening parameters such as laser power density and overlapping ratio,have been studied in detail.The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas,and compressive residual stresses are saturated as laser pulse energy is over 55 J.There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios.A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 %.The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz.The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.
文摘Voltammetry measurements have been employed to investigate the redox behaviour of curcumin in aqueous media using functionalized carbon nanotube(FCNTs)modified glassy carbon electrode(GCE).The electro-catalytic properties of FCNTs modified electrode are superior in comparison to the conventional electrode in generating the electrochemical response from curcumin.The oxidation process of the curcumin over the modified substrate is found to be p H dependent and shows 2e^(-)and 2H^(+)proton transfer electrochemical process.The oxidation peak is obtained at 0.37 V and the peak current is found to be linear with the varying concentration of curcumin.The limit of detection(LOD)and the limit of quantification(LOQ)for the curcumin are obtained as 60 and 200 nmol/L,respectively using the FCNTs modified GCE.The enhanced electrochemical response from the FCNTs modified GCE has been utilized in the evaluation of the chemical and biochemical behaviour of curcumin in presence of transition metal ions(Cu^(2+))and ds DNA,and the observation has been supported by the spectrochemical characteristics of the interactions.
基金financially supported by the National Natural Science Foundation of China (Nos.62033002,62071112 and 61973058)the Program of the Ministry of Education of China for Introducing Talents of Discipline to Universities (No.B16009)+1 种基金the Fundamental Research Funds for the Central Universities in China (No.N2201008)Hebei Natural Science Foundation (No.F2020501040)。
文摘Phenylacetic acid(PAA)is a primary raw material for illegal Methamphetamine(MATM)synthesis under the strong precursor chemicals supervisions of safrole and isosafrole.Therefore,trace detection of PAA at ultra-low concentration is a strategic technique and an urgent issue in the field of drug control.In this paper,trace determination of PAA at sub-nmol-L-1 concentration level is achieved by hydrogen bond adsorption and electrochemical catalysis through the prepared aminated SiO_(2)nanoparticles(SiO_(2)-NH_(2) NPs)and MoS_(2) nanosheets(NSs)modified glassy carbon electrode(GCE).The prepared MoS_(2) NS s/SiO_(2)-NH_(2) NPs modified electrode represents a detecting limit of 0.0989 nmol·L^(-1)and an obvious increasing linear range before the concentration increasement up to 60 nmol·L^(-1)in square wave voltammetry(SWV)responses of PAA.The SWV response of the modified electrode to PAA in the concentration range within 100 nmol·L^(-1)is higher than phenol,acetic acid(HOAc)and benzoic Acid(BEN).This electrochemical method for trace detection of PAA in aqueous solution with desired performance provides a feasible scheme for the detection of other drugs and aromatic precursor chemicals.