WorldWideScience

Sample records for voltammetric current response

  1. Cyclic Voltammetric Responses of Nitrate Reductase on Chemical Modified Electrodes

    Institute of Scientific and Technical Information of China (English)

    YaRuSONG; HuiBoSHAO; 等

    2002-01-01

    Electrochemistry of nitrate reductases (NR) incorporated into 2-aminoethanethiol self-assembled on the gold electrode and polyacrylamide cast on the pyrolytic graphite electrode was examined. NR on chemical modified electrode showed electrochemical cyclic voltammetric responses in phosphate buffers.

  2. The voltammetric responses of nanometer-sized electrodes in weakly supported electrolyte: A theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Liu Yuwen; Zhang Qianfan [Hubei Electrochemical Power Sources Key Laboratory, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University, Wuhan 430072 (China); Chen Shengli, E-mail: slchen@whu.edu.c [Hubei Electrochemical Power Sources Key Laboratory, Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education), Department of Chemistry, Wuhan University, Wuhan 430072 (China)

    2010-11-30

    The effect of the supporting electrolyte concentration on the interfacial profiles and voltammetric responses of nanometer-sized disk electrodes have been investigated theoretically by combining the Poisson-Nernst-Planck (PNP) theory and Butler-Volmer (BV) equation. The PNP-theory is used to treat the nonlinear couplings of electric field, concentration field and dielectric field at electrochemical interface without the electroneutrality assumption that has been long adopted in various voltammetric theories for macro/microelectrodes. The BV equation is modified by using the Frumkin correction to account for the effect of the diffuse double layer potential on interfacial electron-transfer (ET) rate and by including a distance-dependent ET probability in the expression of rate constant to describe the radial heterogeneity of the ET rate constant at nanometer-sized disk electrodes. The computed voltammetric responses for disk electrodes larger than 200 nm in radii in the absence of the excess of the supporting electrolyte using the present theoretical scheme show reasonable agreements with the predications of the conventional microelectrode voltammetric theory which uses the combined Nernst-Planck equation and electroneutrality equation to describe the mixed electromigration-diffusion mass transport without including the possible effects of the diffuse double layer (Amatore et al. ). For electrodes smaller than 200 nm, however, the voltammetric responses predicated by the present theory exhibit significant deviation from the microelectrode theory. It is shown that the deviations are mainly resulted from the overlap between the diffuse double layer and the concentration depletion layer (CDL) at nanoscale electrochemical interfaces in weakly supported media, which will result in the invalidation of the electroneutrality condition in CDL, and from the radial inhomogeneity of ET probability at nanometer-sized disk electrodes.

  3. Voltammetric current oscillations due to general and pitting corrosion of tantalum: Implications for electrochemical-mechanical planarization

    Energy Technology Data Exchange (ETDEWEB)

    Sulyma, Christopher M. [Department of Physics, Clarkson University, Potsdam, NY 13699-5820 (United States); Roy, Dipankar, E-mail: samoy@clarkson.ed [Department of Physics, Clarkson University, Potsdam, NY 13699-5820 (United States)

    2010-09-15

    Anodic corrosion of Ta is examined for potential applications in electrochemical-mechanical planarization (ECMP) of diffusion barriers. This strategy involves electro-oxidation of Ta in the presence of NO{sub 3}{sup -} (or Br{sup -}) to form mechanically weak surface-oxide films, followed by mechanical removal of the latter. The voltammetric currents exhibit oscillatory behaviour with frequencies that are signature attributes of localised pitting by Br{sup -} or general surface corrosion by NO{sub 3}{sup -}. SEM, voltammetry, and impedance spectroscopy are used to probe these corrosion mechanisms. Apart from their relevance for ECMP, the results also address certain fundamental aspects of pitting and general corrosion of valve metals.

  4. Sensitive voltammetric and amperometric responses of respiratory toxins at hemin-adsorbed carbon-felt

    Institute of Scientific and Technical Information of China (English)

    Yasushi Hasebe; Yue Wang

    2013-01-01

    A hemin [iron-Fe(Ⅲ) protoporphyrin Ⅸ chloride] was adsorbed onto a carbon-felt (CF),which is a microelectrode ensemble of micro carbon fiber (ca.7 μm diameter).The resulting hemin-adsorbed-CF (hemin-CF) showed a well-defined redox wave based on the hemin-Fe(2)/Fe(Ⅱ) redox process with the formal potential of-0.225 Ⅴ vs.Ag/AgCI in deoxygenated phosphate/citrate buffer solution (0.1mol/L,pH 5.0).The apparent heterogenous electron transfer rate constant was estimated to be 8.6 sec-1.In air-saturated electrolyte solution,the hemin-CF exhibited an excellent electrocatalytic activity for the reduction of dioxygen (O2).This activity was reversibly inhibited by respiratory toxins such as cyanide and azide,which bind sixth coordination position of iron active center of hemin.The electrocatalytic O2 reduction current at the hemin-CF was modulated by the toxins in a concentration-depending manner.Based on the relationship between the %inhibition and the toxin concentration,apparent inhibition constants of cyanide and azide were evaluated to be 4.52 and 1.98 μmol/L,respectively.When the hemin-CF was used as a working electrode unit of the CF-based electrochemical flow-through detector with air-saturated carrier,the injection of the azide induced peak-shape current responses,which allowed rapid and continuous flow-amperometric determination of azide with high sensitivity.

  5. Voltammetric response of ferroceneboronic acid to diol and phenolic compounds as possible pollutants

    Institute of Scientific and Technical Information of China (English)

    Shigehiro Takahashi; Naoyuki Abiko; Nobuhiro Haraguchi; Hiroyuki Fujita; Eriko Seki; Tetsuya Ono; Kentaro Yoshida; Jun-ichi Anzai

    2011-01-01

    A voltametric determination of possible organic pollutants such as diol and phenolic compounds in water was studied using ferroceneboronic acid (FBA) as a redox-active marker.A cyclic voltammogram of FBA exhibited a pair of oxidation and reduction peaks at 230 and 170 mV at pH 7.0, respectively, while another pair of redox peaks was observed in the presence of diol or phenolic compounds tested.The results were rationalized based on the formation of boronate esters of FBA with the added compounds.The changes in the redox peak currents were dependent on the concentration of the additives, suggesting a usefulness of FBA in the electrochemical determination of these compounds in water.

  6. Voltammetric Response of Epinephrine at Carbon Nanotube Modified Glassy Carbon Electrode and Activated Glassy Carbon Electrode

    Institute of Scientific and Technical Information of China (English)

    WANG Juan; TANG Ping; ZHAO Fa-qiong; ZENG Bai-zhao

    2005-01-01

    The electrochemical behavior of epinephrine at activated glassy carbon electrode and carbon nanotube-coated glassy carbon electrode was studied. Epinephrine could exhibit an anodic peak at about 0.2 V (vs. SCE) at bare glassy carbon electrode, but it was very small.However, when the electrode was activated at certain potential (i. e. 1.9V) or modified with carbon nanotube, the peak became more sensitive,resulting from the increase in electrode area in addition to the electrostatic attraction. Under the selected conditions, the anodic peak current was linear to epinephrine concentration in the range of 3.3 × 10-7-1.1 × 10-5mol/L at activated glassy carbon electrode and in the range of 1.0 × 10-6-5.0 × 10-5 mol/L at carbon nanotube-coated electrode. The correlation coefficients were 0. 998 and 0. 997, respectively. The determination limit was 1.0 × 10-7 mol/L. The two electrodes have been successfully applied for the determination of epinephrine in adrenaline hydrochloride injection with recovery of 95%-104%.

  7. Theoretical voltammetric response of electrodes coated by solid polymer electrolyte membranes.

    Science.gov (United States)

    Gómez-Marín, Ana M; Hernández-Ortíz, Juan P

    2014-09-24

    A model for the differential capacitance of metal electrodes coated by solid polymer electrolyte membranes, with acid/base groups attached to the membrane backbone, and in contact with an electrolyte solution is developed. With proper model parameters, the model is able to predict a limit response, given by Mott-Schottky or Gouy-Chapman-Stern theories depending on the dissociation degree and the density of ionizable acid/base groups. The model is also valid for other ionic membranes with proton donor/acceptor molecules as membrane counterions. Results are discussed in light of the electron transfer rate at membrane-coated electrodes for electrochemical reactions that strongly depend on the double layer structure. In this sense, the model provides a tool towards the understanding of the electro-catalytic activity on modified electrodes. It is shown that local maxima and minima in the differential capacitance as a function of the electrode potential may occur as consequence of the dissociation of acid/base molecular species, in absence of specific adsorption of immobile polymer anions on the electrode surface. Although the model extends the conceptual framework for the interpretation of cyclic voltammograms for these systems and the general theory about electrified interfaces, structural features of real systems are more complex and so, presented results only are qualitatively compared with experiments.

  8. Effect of concentration of lithium ions on the voltammetric responses of nitro-substituted aromatic sulfides in dimethylformamide on glassy carbon electrodes

    Science.gov (United States)

    Chellammal, S.; Noel, M.; Anantharaman, P. N.

    Lithium salts are used as supporting electrolytes and ion-pair forming reagents during voltammetric investigations in aprotic solvents. In the present work, these ions are found to have a significant influence on the voltammetric responses of aromatic sulfides in dimethylformamide given their concentration and the cathodic potential limits applied. At very low concentrations (reduction of nitro groups on the electrode surface. This is the conventional lithium ion-pair formation effect reported in the literature. With increasing lithium ion concentration and increasing cathodic limit, the ion-pairs tend to form an insoluble salt film on the electrode surface. This leads to inhibition of further electron transfer. The inhibiting effect does not seem to correlate with the size of the reactant organic molecule involved. At cathodic potential limits exceeding - 2 V, lithium ions appear to undergo direct reduction and subsequent reaction with trace levels of water in the solvent to produce a passive LiOH layer. This inhibits all further electron transfer.

  9. Resistance to oxidation of white wines assessed by voltammetric means.

    Science.gov (United States)

    Rodrigues, Astride; Silva Ferreira, A C; Guedes de Pinho, Paula; Bento, Fátima; Geraldo, Dulce

    2007-12-26

    This work concerns the development of a methodology suited to measure the resistance to oxidation of white wines by cyclic voltammetry. The voltammetric responses of several white wines of different origin and age were analyzed in the oxidation potential range (0.2-1.2 V vs SCE). Currents measured at fixed potentials were correlated to the concentration of ascorbic acid, SO2, and total phenolics. A forced degradation study was monitored by cyclic voltammetry; from plots of current versus time, the consumption rates of oxidizable species in wine were estimated.

  10. Square-Wave Voltammetric Determination of Sulpiride

    OpenAIRE

    1999-01-01

    The basic redox properties of sulpiride are investigated by means of cyclic voltammetry and square-wave voltammetryat a hanging mercury drop electrode. Sulpiride undergoes electrochemical reaction in basic media. The voltammetric response of sulpiride strongly depends on pH of the medium. A square-wave method for quantitative determination of sukpiride was developed.

  11. Cyclic voltammetric current functions determined with a prescribed accuracy by the adaptive Huber method for Abel integral equations.

    Science.gov (United States)

    Bieniasz, Lesław K

    2008-12-15

    Modern electroanalytical applications of cyclic voltammetry require that theoretical current functions be obtainable automatically, efficiently, and with a prescribed accuracy, by computer simulation algorithms. One of the classical simulation approaches relies on formulating and solving relevant integral equations. Numerical solution methods, used for this purpose so far, are nonautomatic and do not provide information about accuracy of the results. The adaptive variant of the Huber method, developed by the present author, can generate theoretical cyclic voltammograms automatically, with a given target accuracy, and more efficiently than the formerly studied patch-adaptive direct simulation method. This is demonstrated using examples of cyclic voltammograms described by the first-kind Abel integral equations. The method is therefore a candidate for automatic integral equation solvers, needed for building a new generation of problem solving environments for electroanalytical chemistry and for widely understood automation of electroanalytical investigations.

  12. Voltammetric behaviour of oligonucleotide lipoplexes adsorbed onto glassy carbon electrodes

    OpenAIRE

    Piedade, J. A. P.; M. Mano; Lima, M. C. Pedroso de; Oretskaya, T S; Oliveira-Brett, A. M.

    2004-01-01

    The voltammetric behaviour of oligonucleotide lipoplexes (ODN-lipoplexes) prepared from short oligodeoxynucleotides (ODN), with different base compositions, and liposomes of the cationic lipid DOTAP, was studied by differential pulse voltammetry with a glassy carbon mini-electrode. It was found that the ODN base composition influences the ODN-lipoplex voltammetric response. Differential pulse voltammograms for ODN-lipoplexes of the ODN adenosine nucleotides present two different features when...

  13. Voltammetric detection of biological molecules using chopped carbon fiber.

    Science.gov (United States)

    Sugawara, Kazuharu; Yugami, Asako; Kojima, Akira

    2010-01-01

    Voltammetric detection of biological molecules was carried out using chopped carbon fibers produced from carbon fiber reinforced plastics that are biocompatible and inexpensive. Because chopped carbon fibers normally are covered with a sizing agent, they are difficult to use as an electrode. However, when the surface of a chopped carbon fiber was treated with ethanol and hydrochloric acid, it became conductive. To evaluate the functioning of chopped carbon fibers, voltammetric measurements of [Fe(CN)(6)](3-) were carried out. Redoxes of FAD, ascorbic acid and NADH as biomolecules were recorded using cyclic voltammetry. The sizing agents used to bundle the fibers were epoxy, polyamide and polyurethane resins. The peak currents were the greatest when using the chopped carbon fibers that were created with epoxy resins. When the electrode response of the chopped carbon fibers was compared with that of a glassy carbon electrode, the peak currents and the reversibility of the electrode reaction were sufficient. Therefore, the chopped carbon fibers will be useful as disposable electrodes for the sensing of biomolecules.

  14. Anodic voltammetric behavior and determination of rosiglitazone in pharmaceutical dosage forms and biological fluids on solid electrode.

    Science.gov (United States)

    Dogan-Topal, Burcu; Tuncel, Secil; Ozkan, Sibel A

    2010-09-01

    The anodic voltammetric behavior and electroanalytical determination of rosiglitazone was studied using cyclic, linear sweep, differential pulse and square wave voltammetric techniques on glassy carbon electrode. The oxidation of rosiglitazone was irreversible and exhibited diffusion controlled process depending on pH. Different parameters were tested to optimize the conditions for the determination of the oxidation mechanism of rosiglitazone. The dependence of current intensities and potentials on pH, concentration, scan rate, nature of the buffer was also investigated. According to the linear relationship between the peak current and the concentration, differential pulse and square wave voltammetric methods for rosiglitazone assay in pharmaceutical dosage forms and biological fluids were developed. A linear response was obtained within the range of 1x10-6M - 6x10-5M in 0.1 M H2SO4 and acetate buffer at pH 5.70 for both voltammetric methods in human serum samples. The practical analytical value of the method is demonstrated by quantitative determination of rosiglitazon in pharmaceutical formulation and human serum, without the need for separation or complex sample preparation, since there was no interference from the excipients and endogenous substances. The methods were fully validated and successfully applied to the high throughput determination of the drug in tablets and human serum with good recoveries.

  15. A zeolite modified carbon paste electrode as useful sensor for voltammetric determination of acetaminophen

    Energy Technology Data Exchange (ETDEWEB)

    Ahmadpour-Mobarakeh, Leila; Nezamzadeh-Ejhieh, Alireza, E-mail: arnezamzadeh@iaush.ac.ir

    2015-04-01

    The voltammetric behavior of a carbon paste electrode modified with Co(II)-exchanged zeolite A (Co(II)-A/ZMCPE) for determination of acetaminophen was studied. The proposed electrode showed a diffusion controlled reaction with the electron transfer rate constant (K{sub s}) of 0.44 s{sup −1} and charge transfer coefficient of 0.73 in the absence of acetaminophen. A linear voltammetric response was obtained in the range of 0.1 to 190 μmol L{sup −1} of acetaminophen [r{sup 2} = 0.9979, r = 0.9989 (n = 10)] with a detection limit of 0.04 μmol L{sup −1}. The method was successfully applied to the analysis of acetaminophen in some drugs. - Highlights: • Modified carbon paste electrode with Co(II)-zeolite A improved the voltammetric current in determination of acetaminophen. • Modified electrode is applicable for acetaminophen in real samples. • The proposed method has good reproducibility and repeatability.

  16. Microscopic and voltammetric properties of lustrous bismuth deposits

    OpenAIRE

    Krolicka, Agnieszka; Bobrowski, Andrzej; Pamuła, Elżbieta

    2010-01-01

    A comparison of lustrous bismuth films, plated at glassy carbon, platinum and gold supports, is presented. The voltammetric performance of preplated bismuth film electrodes was tested using 50 μg/L In(III) and 50 μg/L Pb(II) solutions in 0.1 M acetic buffer in square wave and differential pulse modes. The influence of support material, plating solution concentration and storing conditions on the voltammetric response of BiFEs is discussed. The results of microscopic examination...

  17. VOLTAMMETRIC DETERMINATION OF CHLORAMPHENICOL AT ...

    African Journals Online (AJOL)

    a

    A sensitive square wave voltammetric method for the determination of ... involve UV-spectroscopy and HPLC, but have limited selectivity and ore often subjected to ..... The effect of the preservative associated with CAP in its pure form and its ...

  18. Voltammetric determination of imidacloprid and thiamethoxam

    Directory of Open Access Journals (Sweden)

    SZILVIA N. ÖKRÉSZ

    2005-05-01

    Full Text Available A simple voltammetric method using a glassy carbon working electrode was developed for the determination of two members from the neonicotinoid group of insecticides: imidacloprid and thiamethoxam. The experiments showed that the voltammetric response depends on the mode of electrode surface pretreatment and the polarization mode. The response appeared to be linear in the range from 0.028 to 0.50 mg/cm3 for both analytes. The limit of detection was 0.0077 mg/cm3 for imidacloprid and 0.0085 mg/cm3 for thiamethoxam, the limit of quantitation was 0.026 mg/cm3 and 0.028 mg/cm3, respectively. The developed method was applied for the determination of these insecticides in potato samples sprayed with Confidor 200-SL or Actara 25-WG as well as commercial formulations of imidacloprid and thiamethoxam. Arecovery trial was performed to assess the accuracy of the results, the recovery values being between 95–102 % for both of neonicotinoids.

  19. Voltammetric scanning electrochemical cell microscopy: dynamic imaging of hydrazine electro-oxidation on platinum electrodes

    NARCIS (Netherlands)

    Chen, C.-H.; Jacobse, L.; McKelvey, K.; Lai, S.C.S.; Koper, M.T.M.; Unwin, P.R.

    2015-01-01

    Voltammetric scanning electrochemical cell microscopy (SECCM) incorporates cyclic voltammetry measurements in the SECCM imaging protocol, by recording electrochemical currents in a wide potential window at each pixel in a map. This provides much more information compared to traditional fixed potenti

  20. Evaluation of levels of defect sites present in highly ordered pyrolytic graphite electrodes using capacitive and faradaic current components derived simultaneously from large-amplitude Fourier transformed ac voltammetric experiments.

    Science.gov (United States)

    Lee, Chong-Yong; Bond, Alan M

    2009-01-15

    The level of edge plane defect sites present in highly ordered pyrolytic graphite (HOPG) electrodes has been evaluated via analysis of dc, ac fundamental, and higher-order ac harmonics available from a single large-amplitude Fourier transformed (FT) ac voltammetric experiment. Deliberate introduction of a low level of edge plane defect was achieved by polishing, with a higher level being introduced via electrochemical pretreatment. Kinetics regimes associated with fast electron transfer on the edge plane defect sites and slow electron transfer on the basal plane surface are resolved under ac conditions when using the surface-sensitive [Fe(CN)(6)](3-/4-) redox probe. However, because of their insensitivity to slow electron transfer, higher-order ac faradaic harmonics almost exclusively detect only the much faster processes that emanate from edge plane defect sites. Thus, detection of fourth- and higher-order ac Faradaic harmonic components that are devoid of background capacitive current is possible at freshly cleaved HOPG in the region near the reversible potential for the [Fe(CN)(6)](3-/4-) process. Under these circumstances, dc cyclic voltammograms exhibit only reduction and oxidation peaks separated by more than 1 V. The fundamental ac harmonic provides detailed information on the capacitive current, which increases with the level of edge plane defect sites. Apparent charge transfer rate constants also can be derived from peak-to-peak separations obtained from the dc aperiodic component. Estimates of the percentage of edge plane defect sites based on ac higher harmonics, capacitance, and dc aperiodic component that are available from a single experiment have been compared. The edge plane defect levels deduced from capacitance (fundamental harmonic ac component) and higher harmonic Faradaic currents are considered to be more reliable than estimations based on apparent rate constants derived from the dc aperiodic component or conventional dc cyclic voltammogram.

  1. Utility of Activated Glassy Carbon and Pencil Graphite Electrodes for Voltammetric Determination of Nalbuphine Hydrochloride in Pharmaceutical and Biological Fluids

    Directory of Open Access Journals (Sweden)

    Hoda M. Elqudaby

    2016-01-01

    Full Text Available This work compares voltammetric response of nalbuphine hydrochloride (NP·HCl at both activated glassy carbon and pencil graphite electrodes. The electrochemical oxidation of the drug was studied using cyclic voltammetry (CV, differential pulse voltammetry (DPV, and square wave voltammetry (SWV techniques. For analytical purpose a well-resolved irreversible diffusion controlled voltammetric peak was established in Britton-Robinson (B-R buffer solution of pH 6.00 using pencil graphite electrode (PGE. Using activated glassy carbon electrode (GCE a well-resolved irreversible diffusion controlled voltammetric peak was obtained at pH 7.00 using the same buffer solution. According to the linear relationship between the peak current and NP·HCl concentration, DPV and SWV methods were developed for their quantitative determination in pharmaceutical and human biological fluids. The linear response was obtained in the range from 1.6×10-5 to 1.5×10-4 mol L−1 using PGE and from 12.5×10-6 to 13.75×10-5 mol L−1 using a GC electrode, respectively. Precision and accuracy of the developed method were checked by recovery studies.

  2. Stripping voltammetric detection of nephrotoxic drug cefitizoxime in wastewater

    Directory of Open Access Journals (Sweden)

    Jahangir Ahmad Rather

    2015-06-01

    Full Text Available The objective of the present work is to develop the stripping voltammetric method for determination of nephrotoxic drug cefitizoxime in pharmaceutical formulation and its application to wastewater analysis. Solubilized system of different surfactants viz. cationic, anionic and non-ionic influences the electrochemical response of cefitizoxime. Solubilized system of CTAB containing cefitizoxime enhanced the peak current while anionic and non-ionic showed an opposite effect. The current signal due to the reduction process is a function of concentration of the cefitizoxime, pH of medium, type of surfactant and accumulation time at electrode surface. The proposed SWCAdSV (Squarewave Cathodic Adsorptive Voltammtery and DPCAdSV (Differential Pulse Cathodic Adsorptive Voltammetry are linear over concentration range 1.732–6.901 μg/mL and 4.792–30.672 μg/mL with detection limit of 0.76 ng/mL and 2.63 ng/mL, respectively. The method is successfully applied for determination of cefitizoxime in pharmaceutical formulation and wastewater with mean percentage recovery of 99.73% and 98.51%, respectively.

  3. Voltammetric method for the determination of sildenafil citrate (Viagra) in pure form and in pharmaceutical formulations.

    Science.gov (United States)

    Tyszczuk, Katarzyna; Korolczuk, Mieczyslaw

    2010-06-01

    A highly sensitive and simple voltammetric method for the determination of sildenafil citrate (SC) was developed. The method is based on the accumulation by adsorption of SC on a lead film modified glassy carbon electrode (LF/GCE) and then the reduction of SC throughout the stripping step. During the determinations of SC at the lead film electrode three adsorptive stripping voltammetric peaks at -1.2, -1.33 and -1.45V were observed. The respective response selected for identification and quantification has been evaluated with respect to the composition and pH of the supporting electrolyte, the potential and the time of the lead film formation, the potential and the time of the SC accumulation and other variables. Experimental results indicate an excellent linear correlation between the peak current and concentration in the range of 2x10(-9)-1.5x10(-7)mol/L (for peaks 1 and 2) and 1x10(-8)-1.5x10(-7)mol/L (for the peak 3). The detection limits (LOD) for SC following 30s of accumulation time were equal to 9x10(-10)mol/L (for peaks 1 and 2) and 4.5x10(-9)mol/L (for the peak 3). The method was successfully applied to the determination of SC in the tablets (Viagra 25 and Viagra 50) and average the contents were in close agreement with those quoted by the manufacturer and with those obtained by the reported spectrophotometric method and voltammetric method using a hanging mercury drop electrode.

  4. Voltammetric sensor for vanillylmandelic acid based on molecularly imprinted polymer-modified electrodes.

    Science.gov (United States)

    Blanco-López, M C; Lobo-Castañón, M J; Miranda-Ordieres, A J; Tuñón-Blanco, P

    2003-04-01

    Despite the increasing number of applications of molecularly imprinted polymers (MIPs) in analytical chemistry, the construction of a biomimetic voltammetric sensor remains still challenging. This work investigates the development of a voltammetric sensor for vanillylmandelic acid (VMA) based on acrylic MIP-modified electrodes. Thin layers of MIPs for VMA have been prepared by spin coating the surface of a glassy carbon electrode with the monomers mixture (template, methacrylic acid, a cross-linking agent and solvent), followed by in situ photopolymerisation. After extraction of the template molecule, the peak current recorded with the imprinted sensor after rebinding was linear with VMA concentration in the range 19-350 microg ml(-1), whereas the response of the control electrode is independent of incubation concentration, and was about one-tenth of the value recorded with the imprinted sensor at the maximum concentration tested. Under the conditions used, the sensor is able to differentiate between VMA and other closely structural-related compounds, such as 3-methoxy-4-hydroxyphenylethylene glycol (not detected), or 3,4- and 2,5-dihydroxyphenilacetic acids, which are adsorbed on the bare electrode surface but not at the polymer layer. Homovanillic acid was detected with the imprinted sensors after incubation, indicating that the presence of both methoxy and carboxylic groups in the same position as in VMA is necessary for effective binding in the imprinted sites. Nevertheless, both species can be differentiated by the oxidation potential. It can be concluded that MIP-based voltammetric electrodes are very promising analytical tool for the development of highly selective analytical sensors.

  5. Differential pulse voltammetric determination of acyclovir in pharmaceutical preparations using a pencil graphite electrode.

    Science.gov (United States)

    Dilgin, Didem Giray; Karakaya, Serkan

    2016-06-01

    In this study, a new selective and sensitive voltammetric procedure for determination of acyclovir (ACV) was proposed using a disposable electrode, pencil graphite electrode (PGE). Cyclic and differential pulse voltammograms of ACV were recorded in Britton-Robinson buffer solution containing 0.10 M KCl with pH of 4.0 at PGE. The PGE displayed a very good electrochemical behavior with significant enhancement of the peak current compared to a glassy carbon electrode (GCE). Under experimental conditions, the PGE had a linear response range from 1.0 μM to 100.0 μM ACV with a detection limit of 0.3 μM (based on 3 Sb). Relative standard deviations of 4.8 and 3.6% were obtained for five successive determinations of 10.0 and 50.0 μM ACV, respectively, which indicate acceptable repeatability. This voltammetric method was successfully applied to the direct determination of ACV in real pharmaceutical samples. The effect of various interfering compounds on the ACV peak current was studied.

  6. Implementation of a statistically supported heuristic approach to alternating current voltammetric harmonic component analysis: re-evaluation of the macrodisk glassy carbon electrode kinetics for oxidation of ferrocene in acetonitrile.

    Science.gov (United States)

    Mashkina, Elena; Bond, Alan M

    2011-03-01

    Sinusoidal large amplitude ac voltammetric techniques gene-rate very large data sets. When analyzed in the frequency domain, using a Fourier transform (FT)-band filtering- inverse FT sequence, the data may be resolved into the aperiodic dc, fundamental, second, and higher order ac harmonics. Each of these components exhibit a different level of sensitivity to electrode kinetics, uncompensated resistance and capacitance. Detailed simulations illustrate how the heuristic approach for evaluation of each data subset may be implemented and exploited in the assessment of the electrode kinetics for the fast Fc [symbol:see text] Fc(+) + e (Fc = ferrocene) oxidation process at a glassy carbon macrodisk electrode. The simulations presented in this study are based on the Butler-Volmer model and incorporate consideration of the uncompensated resistance (R(u)), double-layer capacitance (C(dl)), rate constant (k(0)), and charge transfer coefficient (α). Error analysis of the heuristically evaluated simulation-experiment comparison is used to assist in establishing the best fit of data for each harmonic. The result of the heuristic pattern recognition type approach for analysis of the oxidation of ferrocene (0.499, 0.999, and 5.00 mM) at a glassy carbon macrodisk electrode in acetonitrile (0.1 M Bu(4)NPF(6)) implies that k(0) ≥ 0.25 cm s(-1) on the basis of analysis of the first 4 harmonics and plausibly lies in the range of 0.25-0.5 cm s(-1) with α = 0.25-0.75 when analysis of the next four harmonics is undertaken. The k(0) value is significantly faster then indicated in most literature reports based on use of dc cyclic voltammetry under transient conditions at glassy carbon macrodisk electrode. The data analysis with a sinusoidal amplitude of 80 mV is conducted at very low frequency experiments of 9 Hz to minimize contribution from electrode heterogeneity, frequency dispersion, and adsorption, all of which can complicate the response for the oxidation of Fc in acetonitrile

  7. Active voltammetric microsensors with neural signal processing.

    Energy Technology Data Exchange (ETDEWEB)

    Vogt, M. C.

    1998-12-11

    Many industrial and environmental processes, including bioremediation, would benefit from the feedback and control information provided by a local multi-analyte chemical sensor. For most processes, such a sensor would need to be rugged enough to be placed in situ for long-term remote monitoring, and inexpensive enough to be fielded in useful numbers. The multi-analyte capability is difficult to obtain from common passive sensors, but can be provided by an active device that produces a spectrum-type response. Such new active gas microsensor technology has been developed at Argonne National Laboratory. The technology couples an electrocatalytic ceramic-metallic (cermet) microsensor with a voltammetric measurement technique and advanced neural signal processing. It has been demonstrated to be flexible, rugged, and very economical to produce and deploy. Both narrow interest detectors and wide spectrum instruments have been developed around this technology. Much of this technology's strength lies in the active measurement technique employed. The technique involves applying voltammetry to a miniature electrocatalytic cell to produce unique chemical ''signatures'' from the analytes. These signatures are processed with neural pattern recognition algorithms to identify and quantify the components in the analyte. The neural signal processing allows for innovative sampling and analysis strategies to be employed with the microsensor. In most situations, the whole response signature from the voltammogram can be used to identify, classify, and quantify an analyte, without dissecting it into component parts. This allows an instrument to be calibrated once for a specific gas or mixture of gases by simple exposure to a multi-component standard rather than by a series of individual gases. The sampled unknown analytes can vary in composition or in concentration, the calibration, sensing, and processing methods of these active voltammetric microsensors can

  8. Differential Pulse Voltammetric Determination of Fulvestrant in Pharmaceutical Dosage Forms and Serum Samples

    Directory of Open Access Journals (Sweden)

    Dilek Kul

    2011-01-01

    Full Text Available The electrooxidation behavior and determination of fulvestrant at a glassy carbon electrode were investigated. The voltammetric study of the model compounds allowed elucidating the possible oxidation mechanism of fulvestrant. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate was determined. The oxidation of fulvestrant showed a single and irreversible peak at glassy carbon electrode, and the process was found diffusion controlled. Linear responses were obtained for the concentrations between 4×10−6 M and 6×10−5 M in standard samples and between 2×10−5 M and 1×10−4 M in serum samples. The repeatability of the method was found 0.93 RSD%. The repeatability, reproducibility, precision, and accuracy of proposed method were investigated.

  9. Voltammetric behavior of ketoconazole and its determination in cosmetic preparation using a β-cyclodextrin modified glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    M.A. El Ries

    2013-06-01

    Full Text Available A voltammetric determination of ketoconazole (KCZ at a beta-cyclo-dextrin modified glassy carbon (CDMGC is described. A large increase in the peak currents was observed in cyclic voltammetry (CV and differential pulse voltammetry (DPV of KCZ. This increase in the big current were attributed to the complex formation of the KCZ with β-cyclodextrin. CV studies indicate that the process is irreversible and adsorption-controlled. The effect of pH, scan rate, cyclodextrin concentration and stability of electrodes on the current responses of KCZ was studied. The linearity was obeyed over the concentration range (1–8 × 10−5 mole/l with a common correlation coefficient and limit of detection of 0.9996 and 10.54 × 10−8, respectively, in pH 9 Britton–Robinson (BR buffer. The modified electrode exhibited good sensitivity, and stability. The voltammetric method was successfully applied for the determination of KCZ in pure solution and in cosmetic preparation under batch condition.

  10. Metrological characteristics of the flat voltammetric electrode in time domain with a reversible electrochemical reaction running on the surface

    Science.gov (United States)

    Suchocki, Krzysztof

    2016-11-01

    The study deals with metrological characteristics of the flat voltammetric electrode used for determination of ions concentration by the DC voltammetric method, where a reversible reaction of electrochemical oxidation/reduction takes place on the surface. The analysis shows that such voltammetric electrode acts as a transducer of the first order, where the input signal is a concentration of marked ions in tested solution and the output signal is the current associated with a reversible reaction of oxidation / reduction. Metrological characteristics of such electrode in the time domain are determined by its sensitivity and time constant. The values of these parameters are defined by measurements of characteristics of the voltammetric electrode, polarization voltage and marked ions. To determine the effect of a particular volume of each of these parameters several numerical simulations are presented.

  11. Response Current from Spin-Vortex-Induced Loop Current System to Feeding Current

    Science.gov (United States)

    Morisaki, Tsubasa; Wakaura, Hikaru; Abou Ghantous, Michel; Koizumi, Hiroyasu

    2017-07-01

    The spin-vortex-induced loop current (SVILC) is a loop current generated around a spin-vortex formed by itinerant electrons. It is generated by a U(1) instanton created by the single-valued requirement of wave functions with respect to the coordinate, and protected by the topological number, "winding number". In a system with SVILCs, a macroscopic persistent current is generated as a collection of SVILCs. In the present work, we consider the situation where external currents are fed in the SVILC system and response currents are measured as spontaneous currents that flow through leads attached to the SVILC system. The response currents from SVILC systems are markedly different from the feeding currents in their directions and magnitude, and depend on the original current pattern of the SVILC system; thus, they may be used in the readout process in the recently proposed SVILC quantum computer, a quantum computer that utilizes SVILCs as qubits. We also consider the use of the response current to detect SVILCs.

  12. Voltammetric Behaviour of Sulfamethoxazole on Electropolymerized-Molecularly Imprinted Overoxidized Polypyrrole

    Directory of Open Access Journals (Sweden)

    Yücel Sahin

    2008-12-01

    Full Text Available In this work, preparation of a molecularly imprinted polymer (MIP film and its recognition properties for sulfamethoxazolewere investigated. The overoxidized polypyrrole (OPPy film was prepared by the cyclic voltammetric deposition of pyrrole (Py in the presence of supporting electrolyte (tetrabutylammonium perchlorate-TBAP with and without a template molecule (sulfamethoxazole on a pencil graphite electrode (PGE. The voltammetric behaviour of sulfamethoxazole on imprinted and non-imprinted (NIP films was investigated by differential pulse voltammetry (DPV in Britton-Robinson (BR buffer solutions prepared in different ratio of acetonitrile-water binary mixture, between the pH 1.5 and 7.0. The effect of the acetonitrile-water ratio and pH, monomer and template concentrations, electropolymerization cycles on the performance of the MIP electrode was investigated and optimized. The MIP electrode exhibited the best reproducibility and highest sensitivity. The results showed that changing acetonitrile-water ratio and pH of BR buffer solution changes the oxidation peak current values. The highest anodic signal of sulfamethoxazole was obtained in BR buffer solution prepared in 50% (v/v acetonitrile-water at pH 2.5. The calibration curve for sulfamethoxazole at MIP electrode has linear region for a concentration range of 25.10-3 to 0.75 mM (R2=0.9993. The detection limit of sulfamethoxazole was found as 3.59.10-4 mM (S/N=3. The same method was also applied to determination of sulfamethoxazole in commercial pharmaceutical samples. Method precision (RSD87% were satisfactory. The proposed method is simple and quick. The polypyrrole (PPy electrodes have low response time, good mechanical stability and are disposable simple to construct.

  13. A novel voltammetric sensor for citalopram based on multiwall carbon nanotube/(poly(p-aminobenzene sulfonic acid)/β-cyclodextrin)

    Energy Technology Data Exchange (ETDEWEB)

    Gholivand, Mohammad-Bagher, E-mail: mbgholivand2013@gmail.com; Akbari, Arezoo

    2016-05-01

    Multi-walled carbon nanotube (MWCNTS) coated with poly p-aminobenzene sulfonic acid/β-cyclodextrin (p-ABSA/β-CD) film was used as an effective strategy for modification of the surface of glassy carbon electrode (GCE). Electrochemical study and determination of citalopram (CT) were investigated at the p (p-ABSA)/β-CD/MWCNT/GC using cyclic and differential pulse anodic stripping voltammetric techniques. The results indicate that the p (p-ABSA)/β-CD/MWCNT/GC significantly enhanced the oxidation peak current of CT. The modified electrode was characterized by electrochemical impedance spectroscopy (EIS), scanning electron microscopy(SEM) and cyclic voltammetry (CV).The fabricated electrochemical sensor exhibits a fast and reversible linear response toward CT within the concentration ranges of 90 nM–1 μM, 1–11 μM and 11–100 μM with correlation coefficients greater than 0.99 and detection limit of 44 nM. The resulting functionalized polymer film features interesting electrochemical properties such good recovery, reproducibility and selectivity toward CT. The applicability of the proposed sensor was tested by determination of CT in pharmaceutical combinations and human body fluids. - Highlights: • A novel voltammetric sensor for CT based on p (p-ABSA)/β-CD/MWCNT/GC • Electrochemical study of CT was investigated using CV and DPASV techniques. • This sensor is made easy with good sensitivity and reproducibility. • The method was developed in real sample in the presence of matrix effect.

  14. Electroanalytical characteristics of piribedil and its differential pulse and square wave voltammetric determination in pharmaceuticals and human serum.

    Science.gov (United States)

    Uslu, Bengi; Ozkan, Sibel A

    2003-03-10

    The electrochemical oxidative behavior of piribedil (PR) was described. It was investigated by cyclic, linear sweep, differential pulse (DPV) and square wave (SWV) voltammetric techniques. The redox behavior of PR was found irreversible. Different parameters were tested to optimize the conditions for the determination of PR. The dependence of intensities of currents and potential on pH, concentration, scan rate, nature of the buffer was investigated. Two sensitive methods for the measurement of PR were described. For analytical purposes, a very well resolved diffusion controlled voltammetric peak was obtained in 0.1 M H(2)SO(4) and pH 5.7 acetate buffer. The determination peaks are obtained at 1.27 and 0.95 V for differential pulse and 1.29 and 0.97 V for SWV in 0.1 M H(2)SO(4) and pH 5.7 acetate buffer, respectively. The linear response was obtained in the ranges of 2 x 10(-6)-1 x 10(-3) M in 0.1 M H(2)SO(4) and 2 x 10(-6)-8 x 10(-4) M in pH 5.7 acetate buffer for both techniques. The proposed techniques were successfully applied to the determination of PR in tablet dosage forms and human serum. Excipients did not interfere in the determination. The necessary statistical validation reveals that the proposed methods are free from significant systematic errors.

  15. Sensitive voltammetric determination of lead released from ceramic dishes by using of bismuth nanostructures anchored on biochar.

    Science.gov (United States)

    Agustini, Deonir; Mangrich, Antonio Salvio; Bergamini, Márcio F; Marcolino-Junior, Luiz Humberto

    2015-09-01

    A simple and sensitive electroanalytical method was developed for determination of nanomolar levels of Pb(II) based on the voltammetric stripping response at a carbon paste electrode modified with biochar (a special charcoal) and bismuth nanostructures (nBi-BchCPE). The proposed methodology was based on spontaneous interactions between the highly functionalized biochar surface and Pb(II) ions followed by reduction of these ions into bismuth nanodots which promote an improvement on the stripping anodic current. The experimental procedure could be summarized in three steps: including an open circuit pre-concentration, reduction of accumulated lead ions at the electrode surface and stripping step under differential pulse voltammetric conditions (DPAdSV). SEM images revealed dimensions of bismuth nanodots ranging from 20 nm to 70 nm. The effects of main parameters related to biochar, bismuth and operational parameters were examined in detail. Under the optimal conditions, the proposed sensor has exhibited linear range from 5.0 to 1000 nmol L(-1) and detection limit of 1.41 nmol L(-1) for Pb(II). The optimized method was successfully applied for determination of Pb(II) released from overglaze-decorated ceramic dishes. Results obtained were compared with those given by inductively coupled plasma optical emission spectroscopy (ICP-OES) and they are in agreement at 99% of confidence level. Copyright © 2015. Published by Elsevier B.V.

  16. Spectroscopic Determination of the AC Voltammetric Response.

    Science.gov (United States)

    1984-01-06

    By A. Scott Hinman Jerome F. McAleer Stanley Pons* .~ Prepared for Publication in Journal of Electroanalytical Chemistry University of Utah...REFERENCES 1. M.D. Ryan and G.S. Wilson# Anal. Chem. 54, 2OR (1982). 2. T. ICuvana and N. Winograd# in " Electroanalytical Chemistry " vol. 7p A.J...New York, 1980 and references therein. 11. D.E. Smith# in " Electroanalytical Chemistry ", Vol. 1, A.J. Bard, Ed., Marcel Dekker, New York (1966), pp

  17. Development of a rapid and simple voltammetric method to determine total antioxidative capacity of edible oils.

    Science.gov (United States)

    Gulaboski, Rubin; Mirčeski, Valentin; Mitrev, Saša

    2013-05-01

    In this work we report on a new, rapid and simple voltammetric method to determine the total antioxidant capacity (TAC) of the edible oils. The method explores the ABTS radical (2,2'-azinobis(3-ethylbenzothiazoline-6-sulphonic acid)) assay as a redox probe and it relays on measuring catalytic voltammetric currents. The electrocatalysis comprises redox regeneration of the electrochemically created ABTS(+) radical either by Trolox (6-hydroxy-2,5,7,8-tetramethychroman-2-carboxylic acid) or by antioxidants present in studied oils. The detection limit of the method is determined to be 0.5 mg/L of Trolox equivalent, being a slightly lower than the corresponding UV-VIS spectrophotometric method. Applying the proposed voltammetric method the total antioxidant capacity of three types of commercially available cold-pressed edible oils are determined, and the results are found to be in a very good agreement with those obtained by UV-VIS spectrophotometry. The reported voltammetric method is cheap, rapid and simple, and it can be used as a sustainable alternative to the UV-VIS methods for the determination of total antioxidant capacitance of oils and other liquid lipophilic nutrients. Potent antioxidant capacity of studied oils was also confirmed by electron paramagnetic resonance spectroscopy of superoxide anion produced by macrophages.

  18. Immune cellular response to HPV: current concepts

    Directory of Open Access Journals (Sweden)

    Maria Alice Guimarães Gonçalves

    Full Text Available Although cellular immunity is essential for the elimination of human papillomavirus (HPV, the mechanisms involved are still poorly understood. We summarize the main mechanisms involved in cellular immune response to infections caused by HPV. Immunotherapies for HPV-related cancers require the disruption of T-cell response control mechanisms, associated with the stimulation of the Th1 cytokine response.

  19. Maize tassel-modified carbon paste electrode for voltammetric determination of Cu(II).

    Science.gov (United States)

    Moyo, Mambo; Okonkwo, Jonathan O; Agyei, Nana M

    2014-08-01

    The preparation and application of a practical electrochemical sensor for environmental monitoring and assessment of heavy metal ions in samples is a subject of considerable interest. In this paper, a carbon paste electrode modified with maize tassel for the determination of Cu(II) has been proposed. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to study morphology and identify the functional groups on the modified electrode, respectively. First, Cu(II) was adsorbed on the carbon paste electrode surface at open circuit and voltammetric techniques were used to investigate the electrochemical performances of the sensor. The electrochemical sensor showed an excellent electrocatalytic activity towards Cu(II) at pH 5.0 and by increasing the amount of maize tassel biomass, a maximum response at 1:2.5 (maize tassel:carbon paste; w/w) was obtained. The electrocatalytic redox current of Cu(II) showed a linear response in the range (1.23 μM to 0.4 mM) with the correlation coefficient of 0.9980. The limit of detection and current-concentration sensitivity were calculated to be 0.13 (±0.01) μM and 0.012 (±0.001) μA/μM, respectively. The sensor gave good recovery of Cu(II) in the range from 96.0 to 98.0 % when applied to water samples.

  20. Fusion of Potentiometric & Voltammetric Electronic Tongue for Classification of Black Tea Taste based on Theaflavins (TF) Content

    Science.gov (United States)

    Bhattacharyya, Nabarun; Legin, Andrey; Papieva, Irina; Sarkar, Subrata; Kirsanov, Dmitry; Kartsova, Anna; Ghosh, Arunangshu; Bandyopadhyay, Rajib

    2011-09-01

    Black tea is an extensively consumed beverage worldwide with an expanding market. The final quality of black tea depends upon number of chemical compounds present in the tea. Out of these compounds, theaflavins (TF), which is responsible for astringency in black tea, plays an important role in determining the final taste of the finished black tea. The present paper reports our effort to correlate the theaflavins contents with the voltammetric and potentiometric electronic tongue (e-tongue) data. Noble metal-based electrode array has been used for collecting data though voltammetric electronic tongue where as liquid filled membrane based electrodes have been used for potentiometric electronic tongue. Black tea samples with tea taster score and biochemical results have been collected from Tea Research Association, Tocklai, India for the analysis purpose. In this paper, voltammetric and potentiometric e-tongue responses are combined to demonstrate improvement of cluster formation among tea samples with different ranges of TF values.

  1. Gold nanoparticles modified carbon paste electrode for differential pulse voltammetric determination of eugenol.

    Science.gov (United States)

    Afzali, Daryoush; Zarei, Somaye; Fathirad, Fariba; Mostafavi, Ali

    2014-10-01

    In the present study, a carbon paste electrode chemically modified with gold nanoparticles was used as a sensitive electrochemical sensor for determination of eugenol. The differential pulse voltammetric method was employed to study the behavior of eugenol on this modified electrode. The effect of variables such as percent of gold nanoparticles, pH of solution, accumulation potential and time on voltammogram peak current were optimized. The proposed electrode showed good oxidation response for eugenol in 0.1 mol L(-1) phosphate buffer solution (pH8) and the peak potential was about +285 mV (vs. Ag/AgCl). The peak current increased linearly with the eugenol concentration in the range of 5-250 μmol L(-1). The detection limit was found to be 2.0 μmol L(-1) and the relative standard deviation was 1.2% (n=7). The effect of interferences on the eugenol peak current was studied. The method has been applied to the determination of eugenol in different real samples, spiked recoveries were in the range of 96%-99%.

  2. Investigation on Voltammetric Behavior of Camptothecin and Its Analytical Application

    Institute of Scientific and Technical Information of China (English)

    ZHENG, Jian-Bin; MENG, Zu-Chao; LIU, Bo; ZHANG, Hong-Fang

    2006-01-01

    The voltammetric behavior of camptothecin (CPT) in Britton-Robinson (B-R) buffer solutions (pH 2.09-9.07)was studied by the means of linear sweep voltammetry (LSV), cyclic voltammetry (CV) and normal pulse voltammetry (NPV) at a hanging mercury drop electrode. In different pH range of B-R buffer solutions, CPT could cause three reduction waves. In B-R buffer solutions (pH 2.09-5.46), wave P1 yielded by CPT was a two-electron wave.Between pH 6.01 and 9.07, CPT could yield two reduction waves P2 and P3. In addition, the pure CPT obtained from camptotheca acumina grown only in China was determined by NPV, and a linear response was observed in the tion limit for CPT.

  3. Impulse-response functions of several detectors used in flow-injection analysis

    NARCIS (Netherlands)

    Nugteren-Osinga, van I.C.; Hoogendam, E.; Bos, M.; Linden, van der W.E.

    1990-01-01

    A procedure for the determination of the impulse-response function of a detector is given. Its application to photometers, ion-sensitive field effect transistors, a potentiometric detector at constant current and a voltammetric detector shows that the impulse-response function can be used to obtain

  4. Voltammetric characteristics of miconazole and its cathodic stripping voltammetric determination

    Directory of Open Access Journals (Sweden)

    FRANCISCO C. PEREIRA

    2002-09-01

    Full Text Available Miconazole is reduced at mercury electrode above pH 6 involving organometallic compound formation, responsible for an anomalous polarographic behavior. The electrodic process presents a large contribution of the adsorption effects. The drug can be determined by cathodic stripping voltammetry from 8.0 x 10-8 to 1, 5 x 10-6 molL-1 in Britton-Robinson buffer pH 8.0, when pre-accumulated for 30s at an accumulation potential of 0V. A relative standard deviation of 3.8% was obtained for ten measurements of 1.0 x 10-7 molL-1 miconazole in B-R buffer pH 8.0 and a limit detection of 1, 7 x 10-8 molL-1 was determined using 60s of deposition time and scan rate of 100 mVs-1. The proposed method is simple, precise and it was applied successfully for the determination of the miconazole in pure form and in commercial formulations, showing mean recoveries of 99.7-98.4%.Miconazol é reduzido no eletrodo de mercúrio em valor de pH acima de 6,0 envolvendo formação de composto organometálico, responsável por um comportamento polarográfico anômalo. O processo eletródico apresenta uma larga contribuição de efeitos de adsorção. A droga pode ser determinada por voltametria de redissolução catódica de 8, 0 x 10-8 a 1, 5 x 10-6 mol L-1 em tampão Britton-Robinson pH 8,0 quando pré-acumulada por 30s em potencial de acúmulo de 0V. Um desvio padrão relativo de 3,8% foi obtido de 10 medidas de 1, 0 x 10-7 mol L-1 de miconazol em tampão B-R pH 8,0 e um limite de detecção de 1, 7 x 10-8 mol L-1 foi determinado usando 60s de tempo de deposição e velocidade de varredura de 100 mV s-1. O método proposto é simples, preciso e foi aplicado com sucesso para a determinação de miconazol na forma pura e em formulações comerciais, mostrando médias de recuperação de 99, 7 - 98, 4%.

  5. Differential pulse voltammetric determination of eugenol at a pencil graphite electrode.

    Science.gov (United States)

    Sağlam, Özlem; Dilgin, Didem Giray; Ertek, Bensu; Dilgin, Yusuf

    2016-03-01

    In this study, the electrochemical behavior of eugenol, a widely used herbal drug, was investigated at a pencil graphite electrode (PGE). A low-cost, disposable, sensitive and selective electrochemical sensor is proposed for the determination of eugenol by recording its differential pulse voltammograms in Britton-Robinson buffer solution containing 0.1 M KCl with pH of 2.0 at the PGE. The PGE displayed a very good electrochemical behavior with significant enhancement of the peak current compared to a glassy carbon electrode. Under experimental conditions, the PGE had a linear response range from 0.3 μM to 50.0 μM eugenol with a detection limit of 0.085 μM (based on 3S(b)). Relative standard deviations of 2.4 and 4.8% were obtained for five successive determinations of 30.0 and 5.0 μM eugenol, respectively, which indicate acceptable repeatability. This voltammetric method was successfully applied for the direct determination of eugenol in real samples. The effect of various interfering compounds on the eugenol peak current was also studied.

  6. [The notion of medical responsibility. Current evolution].

    Science.gov (United States)

    Michaud, J

    1998-01-01

    Medical responsibility can be evaluated from a penal or a civil standpoint. In the first case it is referable to common law or other specific provisions, notably those included in the laws voted on July 29 1994. In the second case it is viewed within the contractual relationship, since the physician's obligation is theoretically one of means and not of results. The circumstances under which medical responsibility is questioned have evolved under the influence of three factors affecting the medical art: it is now characterized by techniques that have often become scientific; team practice; an increase in patients' demands. Nonetheless it is most important to maintain a genuine relationship of trust between physician and patient.

  7. A zeolite modified carbon paste electrode as useful sensor for voltammetric determination of acetaminophen.

    Science.gov (United States)

    Ahmadpour-Mobarakeh, Leila; Nezamzadeh-Ejhieh, Alireza

    2015-04-01

    The voltammetric behavior of a carbon paste electrode modified with Co(II)-exchanged zeolite A (Co(II)-A/ZMCPE) for determination of acetaminophen was studied. The proposed electrode showed a diffusion controlled reaction with the electron transfer rate constant (Ks) of 0.44s(-1) and charge transfer coefficient of 0.73 in the absence of acetaminophen. A linear voltammetric response was obtained in the range of 0.1 to 190μmolL(-1) of acetaminophen [r(2)=0.9979, r=0.9989 (n=10)] with a detection limit of 0.04μmolL(-1). The method was successfully applied to the analysis of acetaminophen in some drugs.

  8. Differential pulse voltammetric determination of tin in the presence of noble metals

    Energy Technology Data Exchange (ETDEWEB)

    Monticelli, Damiano; Pozzi, Andrea; Dossi, Carlo; Recchia, Sandro [Universita degli Studi dell' Insubria, Dipartimento di Scienze Chimiche e Ambientali, Como (Italy); Psaro, Rinaldo [CNR Institute ' ' ISTM' ' , Milano (Italy)

    2005-09-01

    A voltammetric method for the determination of tin is proposed to minimise interferences from noble metals that are commonly encountered with other analytical techniques. Strong distortions of voltammetric peaks are observed in the presence of platinum. On the basis of a full investigation, the formation of an intermediate Sn(II)-Pt mixed chloro-complex at the electrode surface is identified as being responsible for the platinum interference, as it competes with the normal Sn(IV){yields}Sn(0){sub Hg} reduction. The use of a higher scan rate prevents the relatively low reaction kinetics and thus gets rid of this interference. No problems are encountered with other noble metals such as Pd, Ir, Re, Rh and Ru when using the modified method, although a baseline subtraction is necessary for the latter one. The proposed method is validated with real Pt-Sn catalysts. (orig.)

  9. Voltammetric determination of antioxidant character in Berberis lycium Royel, Zanthoxylum armatum and Morus nigra Linn plants.

    Science.gov (United States)

    Ahmed, Safeer; Shakeel, Faria

    2012-07-01

    The antioxidant activity potential of three different plant extracts was investigated against superoxide anion radical while employing cyclic voltammetry technique. The plants Berberis lyceum Royle, Morus nigra Linn and Zanthoxylum armatum were selected because of their potential use in the traditional medicine. The voltammetric response of the electrochemically generated superoxide anion radial in DMSO was monitored in the absence and presence of the plat extracts. The decrease in the current was interpreted in terms of antiradical activity of the added extract. The thermodynamic feasibility of the radical scavenging by extracts was accounted in terms of antioxidant activity coefficient (K(ao)) and standard Gibbs free energy (ΔG(o)). The values of K(ao) and ΔG(o) ranged from 1.0 x 102 to 57 x 102 L(-1) and -18 to -27 kJmol(-1), respectively. The possible mechanism of the antioxidant reaction was regarded as E(r)C(i) mechanism i.e. reversible electron transfer followed by hydrogen atom transfer- an irreversible chemical reaction.

  10. Adsorptive stripping voltammetric determination of netilmicin in the presence of formaldehyde.

    Science.gov (United States)

    Sun, Nan; Mo, Weimin; Hu, Baoxiang; Shen, Zhenlu

    2006-05-01

    A linear sweep adsorptive stripping voltammetric method for the determination of netilmicin in the presence of formaldehyde has been proposed for the first time. In the presence of 3.0 x 10(-3) g ml(-1) formaldehyde, netilmicin exhibits a sensitive cathodic peak at -1.30 V (vs. the saturated calomel electrode, SCE) in a medium of Britton-Robinson buffer (pH 8.7) with a scan rate of 100 mV s(-1) after a preconcentration period of 120 s at -1.10 V (vs. SCE). The peak current showed a linear dependence on the netilmicin concentration over the range 4.2 x 10(-9)-1.0 x 10(-7) g ml(-1). The achieved limits of detection and quantitation were 1.0 x 10(-10) and 3.3 x 10(-10) g ml(-1) netilmicin, respectively. It was deduced from the experiments that the amine-aldehyde condensation product formed between netilmicin and formaldehyde is mainly responsible for the appearance of the peak. The electrochemical behavior of netilmicin in the presence of formaldehyde has been studied. The method was applied to the direct determination of netilmicin in injectable formulations and spiked human urine and serum samples.

  11. Adsorptive Stripping Voltammetric Determination of Hydroquinone using an Electrochemically Pretreated Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Abdul Niaz1,

    2008-12-01

    Full Text Available A simple and efficient adsorptive stripping voltammetric (AdSV method was developed for the determination of hydroquinone at an electrochemically pretreated glassy carbon (GC electrode in waste water. Various parameters such as solvent system, accumulation potential, accumulation time and scan rate were optimized. The electrochemically pretreated GC electrode showed good response towards hydroquinone determination by using AdSV. Under the optimized conditions the peak current showed good linear relationship with the hydroquinone concentration in the range of 0.5-4.0mg L-1 and 5-30mg L-1. The 60/40 methanol/water composition was found to be the best solvent system and 0.05mol L-1 H2SO4 was found as useful supporting electrolyte concentration. The accumulation time was 60 s and the detection limit was 50µg L-1. The developed method was successfully applied for the determination of hydroquinone in polymeric industrial discharge samples waste photographic developer solution and cream sample without any significant effect of surface fouling.

  12. Electrochemical Investigation of Catechol at Poly(niacinamide Modified Carbon Paste Electrode: A Voltammetric Study

    Directory of Open Access Journals (Sweden)

    A. B. Teradale

    2016-01-01

    Full Text Available A polymeric thin film modified electrode, that is, poly(niacinamide modified carbon paste electrode (MCPE, was developed for the electrochemical determination of catechol (CC by using cyclic voltammetric technique. Compared to bare carbon paste electrode (BCPE, the poly(niacinamide MCPE shows good electrocatalytic activity towards the oxidation of catechol in phosphate buffer solution (PBS of physiological pH 7.4. All experimental parameters were optimized. Poly(niacinamide modified carbon paste electrode gave a linear response between concentration of CC and its anodic peak current in the range within 20.6–229.0 μM. The limit of detection (3S/M and limit of quantification (10S/M were 1.497 μM and 4.99 μM, respectively. From the study of scan rate variation, the electrode process was found to be adsorption-controlled. The involvement of protons and electrons in the oxidation of CC was found to be equal. The probable electropolymerisation mechanism of niacinamide was proposed. Finally, this method can be used in development of a sensor for sensitive determination of CC.

  13. Novel electrochemical sensor based on N-doped carbon nanotubes and Fe3O4 nanoparticles: simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid.

    Science.gov (United States)

    Fernandes, Diana M; Costa, Marta; Pereira, Clara; Bachiller-Baeza, Belén; Rodríguez-Ramos, Inmaculada; Guerrero-Ruiz, Antonio; Freire, Cristina

    2014-10-15

    A new modified electrode based on N-doped carbon nanotubes functionalized with Fe3O4 nanoparticles (Fe3O4@CNT-N) has been prepared and applied on the simultaneous electrochemical determination of small biomolecules such as dopamine (DA), uric acid (UA) and ascorbic acid (AA) using voltammetric methods. The unique properties of CNT-N and Fe3O4 nanoparticles individually and the synergetic effect between them led to an improved electrocatalytic activity toward the oxidation of AA, DA and UA. The overlapping anodic peaks of these three biomolecules could be resolved from each other due to their lower oxidation potentials and enhanced oxidation currents when using the Fe3O4@CNT-N modified electrode. The linear response ranges for the square wave voltammetric determination of AA, DA and UA were 5-235, 2.5-65 and 2.5-85μmoldm(-3) with detection limit (S/N=3) of 0.24, 0.050 and 0.047μmoldm(-3), respectively. These results show that Fe3O4@CNT-N nanocomposite is a promising candidate of cutting-edge electrode materials for electrocatalytic applications.

  14. Voltammetric determination of Δ9-THC in glassy carbon electrode: An important contribution to forensic electroanalysis.

    Science.gov (United States)

    Balbino, Marco Antonio; de Menezes, Matheus Manoel Teles; Eleotério, Izabel Cristina; Saczk, Adelir Aparecida; Okumura, Leonardo Luiz; Tristão, Heloísa Maria; de Oliveira, Marcelo Firmino

    2012-09-10

    A new voltammetric method for the determination of Δ(9)-tetrahydrocannabinol (Δ(9)-THC) is described. The voltammetric experiments were accomplished in N-N dimethylformamide/water (9:1, v/v), using tetrabutylammonium tetrafluoroborate (TBATFB) 0.1mol/L as supporting electrolyte and a glassy carbon disk electrode as the working electrode. The anodic peak current was observed at 0.0V (vs. Ag/AgCl) after a 30s pre-concentration step under an applied potential of -1.2V (vs. Ag/AgCl). A linear dependence of Δ(9)-THC detection was obtained in the concentration range 2.4-11.3ng/mL, with a linear correlation coefficient of 0.999 and a detection limit of 0.34ng/mL. The voltammetric method was used to measure the content of Δ(9)-THC in samples (hemp and hashish) confiscated by the police. The elimination of chemical interferences from the samples was promptly achieved through prior purification using the TLC technique, by employing methanol/water (4:1, v/v) as the mobile phase. The results showed excellent correlation with results attained by HPLC.

  15. Ion-transfer voltammetric determination of folic acid at meso-liquid-liquid interface arrays.

    Science.gov (United States)

    Jiang, Xuheng; Gao, Kui; Hu, Daopan; Wang, Huanhuan; Bian, Shujuan; Chen, Yong

    2015-04-21

    Voltammetric studies on the simple ion transfer (IT) behaviors of an important water-soluble B-vitamin, folic acid (FA), at the liquid-liquid (L-L) interface were firstly performed and then applied as a novel detection method for FA under physiological conditions. Meso-water-1,6-dichlorohexane (W-DCH) and meso-water-organogel interface arrays were built by using a hybrid mesoporous silica membrane (HMSM) with a unique structure of pores-in-pores and employed as the new platforms for the IT voltammetric study. In view of the unique structure of the HMSM, the impact of the ionic surfactant cetyltrimethylammonium bromide (CTAB), self-assembled within the silica nanochannels of the HMSM, was investigated. In particular, its effect on the IT voltammetric behavior and detection of FA at meso-L-L interface arrays was systematically examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and differential pulse stripping voltammetry (DPSV). It was found that all the voltammetric responses of CV, DPV, and DPSV and the corresponding detection limit of FA at such meso-L-L interface arrays are closely related to the CTAB in the HMSM. Significantly, the calculated detection limit of FA could be improved to 80 nM after the combination of the DPSV technique with the additional preconcentration of FA in the silica-CTAB nanochannels, achieved through an anion-exchange process between FA(-) and the bromide of CTAB in HMSM. This provides a new and attractive strategy for the detection of those biological anions.

  16. Electropolymerized supramolecular tetraruthenated porphyrins applied as a voltammetric sensor

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Monize M. da; Ribeiro, Gabriel H.; Faria, Anizio M. de; Bogado, Andre L.; Dinelli, Luis R., E-mail: dinelli@pontal.ufu.br [Universidade Federal de Uberlandia (UFU), Ituiutaba, MG (Brazil). Faculdade de Ciencias Integradas do Pontal; Batista, Alzir A. [Universidade Federal de Sao Carlos (UFSCar), SP (Brazil). Departamento de Quimica

    2013-11-15

    Porphyrin 5,10,15,20-Tetra(4-pyridyl)manganese(III), [Mn-TPyP(H{sub 2}O){sub 2}]PF{sub 6}, and electropolymerized supramolecular porphyrins (ESP), {l_brace}Mn-TPyP(H{sub 2}O){sub 2}[RuCl{sub 3}(dppb)]{sub 4}{r_brace}PF{sub 6} (dppb = 1,4-bis(diphenylphosphine)butane), were synthesized and characterized. A thin solid film of ESP was obtained on a glass carbon electrode surface by a cyclic voltammetry method. The peak current increased with the number of voltammetric cycles, which shows a typical behavior of the species being adsorbed on the surface of the electrode. Cyclic voltammetry was also employed for acetaminophen quantification using an ESP modified electrode. The modified electrode shows a linear relationship between the anodic peak current and the concentration of acetaminophen (in the rage 0.05 to 0.7 mmol L{sup -1}. The performance of the modified electrode was verified by the determination of acetaminophen in a commercial pharmaceutical product and the results were in good agreement with those obtained by a control HPLC method. (author)

  17. Lower-Dark-Current, Higher-Blue-Response CMOS Imagers

    Science.gov (United States)

    Pain, Bedabrata; Cunningham, Thomas; Hancock, Bruce

    2008-01-01

    Several improved designs for complementary metal oxide/semiconductor (CMOS) integrated-circuit image detectors have been developed, primarily to reduce dark currents (leakage currents) and secondarily to increase responses to blue light and increase signal-handling capacities, relative to those of prior CMOS imagers. The main conclusion that can be drawn from a study of the causes of dark currents in prior CMOS imagers is that dark currents could be reduced by relocating p/n junctions away from Si/SiO2 interfaces. In addition to reflecting this conclusion, the improved designs include several other features to counteract dark-current mechanisms and enhance performance.

  18. Differential pulse voltammetric assay of lercanidipine in tablets.

    Science.gov (United States)

    Alvarez-Lueje, Alejandro; Pujol, Sara; Núñez-Vergara, Luis J; Squella, Juan A

    2002-01-01

    Lercanidipine in ethanol-0.04M Britton-Robinson buffer (20 + 80) gives an irreversible anodic response on a glassy carbon electrode in a broad pH range (2-12) that depends on pH. This signal can be attributed to oxidation of the 1,4-dihydropyridine ring to give the corresponding pyridine derivative. For analytical purposes, differential pulse voltammetry at pH 4 was selected. Under these conditions, good values of both within- and interday reproducibility were obtained, with coefficient of variation (CV) values of 1.56 and 1.70%, respectively, for 10 successive runs. For quantitation, the calibration curve method was used for lercanidipine concentrations ranging from 1 x 10(-5) to 1 x 10(-4) M. The detection and quantitation limits were 1.39 x 10(-5) and 1.49 x 10(-5), respectively. A liquid chromatographic method with electrochemical detection was used for comparison. The voltammetric method showed good selectivity with respect to both excipients and degradation products. The recovery study exhibited a CV of 0.94% and an average recovery of 98.3%, and it was not necessary to treat the sample before the analysis. The method was successfully applied to the individual tablet assay of lercanidipine in commercial tablets.

  19. Simultaneous voltammetric determination of tramadol and acetaminophen using carbon nanoparticles modified glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Ghorbani-Bidkorbeh, Fatemeh [Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of); Department of Pharmaceutics, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Shahrokhian, Saeed, E-mail: shahrokhian@sharif.ed [Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of); Institute for Nanoscience and Technology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Mohammadi, Ali [Department of Drug and Food Control, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Dinarvand, Rassoul [Department of Pharmaceutics, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran (Iran, Islamic Republic of); Nanotechnology Research Centre, Faculty of Pharmacy, Tehran University of Medical Sciences, P.O. Box 14155-6451, Tehran (Iran, Islamic Republic of)

    2010-03-01

    A sensitive and selective electrochemical sensor was fabricated via the drop-casting of carbon nanoparticles (CNPs) suspension onto a glassy carbon electrode (GCE). The application of this sensor was investigated in simultaneous determination of acetaminophen (ACE) and tramadol (TRA) drugs in pharmaceutical dosage form and ACE determination in human plasma. In order to study the electrochemical behaviors of the drugs, cyclic and differential pulse voltammetric studies of ACE and TRA were carried out at the surfaces of the modified GCE (MGCE) and the bare GCE. The dependence of peak currents and potentials on pH, concentration and the potential scan rate were investigated for these compounds at the surface of MGCE. Atomic force microscopy (AFM) was used for the characterization of the film modifier and its morphology on the surface of GCE. The results of the electrochemical investigations showed that CNPs, via a thin layer model based on the diffusion within a porous layer, enhanced the electroactive surface area and caused a remarkable increase in the peak currents. The thin layer of the modifier showed a catalytic effect and accelerated the rate of the electron transfer process. Application of the MGCE resulted in a sensitivity enhancement and a considerable decrease in the anodic overpotential, leading to negative shifts in peak potentials. An optimum electrochemical response was obtained for the sensor in the buffered solution of pH 7.0 and using 2 muL CNPs suspension cast on the surface of GCE. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity for the determination of ACE and TRA in wide linear ranges of 0.1-100 and 10-1000 muM, respectively. The resulted detection limits for ACE and TRA was 0.05 and 1 muM, respectively. The CNPs modified GCE was successfully applied for ACE and TRA determinations in pharmaceutical dosage forms and also for the determination of ACE in human plasma.

  20. Glyphosate Detection by Means of a Voltammetric Electronic Tongue and Discrimination of Potential Interferents

    Science.gov (United States)

    Bataller, Román; Campos, Inmaculada; Laguarda-Miro, Nicolas; Alcañiz, Miguel; Soto, Juan; Martínez-Máñez, Ramón; Gil, Luís; García-Breijo, Eduardo; Ibáñez-Civera, Javier

    2012-01-01

    A new electronic tongue to monitor the presence of glyphosate (a non-selective systemic herbicide) has been developed. It is based on pulse voltammetry and consists in an array of three working electrodes (Pt, Co and Cu) encapsulated on a methacrylate cylinder. The electrochemical response of the sensing array was characteristic of the presence of glyphosate in buffered water (phosphate buffer 0.1 mol·dm−3, pH 6.7). Rotating disc electrode (RDE) studies were carried out with Pt, Co and Cu electrodes in water at room temperature and at pH 6.7 using 0.1 mol·dm−3 of phosphate as a buffer. In the presence of glyphosate, the corrosion current of the Cu and Co electrodes increased significantly, probably due to the formation of Cu2+ or Co2+ complexes. The pulse array waveform for the voltammetric tongue was designed by taking into account some of the redox processes observed in the electrochemical studies. The PCA statistical analysis required four dimensions to explain 95% of variance. Moreover, a two-dimensional representation of the two principal components differentiated the water mixtures containing glyphosate. Furthermore, the PLS statistical analyses allowed the creation of a model to correlate the electrochemical response of the electrodes with glyphosate concentrations, even in the presence of potential interferents such as humic acids and Ca2+. The system offers a PLS prediction model for glyphosate detection with values of 098, −2.3 × 10−5 and 0.94 for the slope, the intercept and the regression coefficient, respectively, which is in agreement with the good fit between the predicted and measured concentrations. The results suggest the feasibility of this system to help develop electronic tongues for glyphosate detection. PMID:23250277

  1. Current responsivity of semiconductor superlattice THz-photon detectors

    DEFF Research Database (Denmark)

    Ignatov, Anatoly A.; Jauho, Antti-Pekka

    1999-01-01

    The current responsivity of a semiconductor superlattice THz-photon detector is calculated using an equivalent circuit model which takes into account the finite matching efficiency between a detector antenna and the superlattice in the presence of parasitic losses. Calculations performed for curr......The current responsivity of a semiconductor superlattice THz-photon detector is calculated using an equivalent circuit model which takes into account the finite matching efficiency between a detector antenna and the superlattice in the presence of parasitic losses. Calculations performed...... for currently available superlattice diodes show that both the magnitudes and the roll-off frequencies of the responsivity are strongly influenced by an excitation of hybrid plasma-Bloch oscillations which are found to be eigenmodes of the system in the THz-frequency band. The expected room temperature values...

  2. Using silver nanoparticle to enhance current response of biosensor.

    Science.gov (United States)

    Ren, Xiangling; Meng, Xianwei; Chen, Dong; Tang, Fangqiong; Jiao, Jun

    2005-09-15

    In this paper, we present a simple procedure to increase the sensitivity of a glucose biosensor. The feasibility of an amperometric glucose biosensor based on immobilization of glucose oxidase (GOx) in silver (Ag) sol was investigated for the first time. GOx was simply mixed with Ag nanoparticles and cross-linked with a polyvinyl butyral (PVB) medium by glutaraldehyde. Then a platinum electrode was coated with the mixed solution. The effects of the amount of the Ag particles used, with respect to the current response for enzyme electrodes, were studied. A set of experimental results indicate that the current response for the enzyme electrode containing hydrophobic Ag sol increased from 0.531 to 31.17 microA in the solution of 10 mmol/L beta-D glucose. The time reaching the steady-state current response reduced from 60 to 20s, three times less than those without Ag particles involved.

  3. STUDY OF ELECTROPOLIMERIZATION PROCESSES OF PYRROLE BY CYCLIC VOLTAMMETRIC TECHNIQUE

    Directory of Open Access Journals (Sweden)

    Adhitasari Suratman

    2010-06-01

    Full Text Available Electropolymerization processes and electrochemical properties of polypyrrole as electroactive polymer have been studied by cyclic voltammetric technique. Pyrrole was electropolymerized to form polypyrrole in water-based solvent containing sodium perchlorate as supporting electrolyte in several pH values. The pH of the solutions were varied by using Britton Robinson buffer. The results showed that oxidation potential limit of electropolymerization processes of pyrrole was 1220 mV vs Ag/AgCl reference electrode. It can be seen that cyclic voltammetric respon of polypyrrole membrane that was prepared by electropolymerization processes of pyrrole at the scanning rate of 100 mV/s was stable. While the processes of pyrrole electropolymerization carried out at the variation of pH showed that the best condition was at the pH range of 2 - 6.   Keywords: polypyrolle, electropolymer, voltammetric technique

  4. Selective Voltammetric Determination of Uric Acid in the Presence of Ascorbic Acid at Ordered Mesoporous Carbon Modified Electrodes

    Institute of Scientific and Technical Information of China (English)

    WEN,Yan-Li; JIA,Neng-Qin; WANG,Zhi-Yong; SHEN,He-Bai

    2008-01-01

    A novel chemically modified electrode was fabricated by immobilizing ordered mesoporous carbon (OMC)onto a glassy carbon (GC) electrode.The electrocatalytic behavior of the OMC modified electrode towards the oxidation of uric acid (UA) and ascorbic acid (AA) was studied.Compared to a glassy carbon electrode,the OMC modified electrode showed a faster electron transfer rate and reduced the overpotentials greatly.Furthermore,the OMC modified electrode resolved the overlapping voltammetric responses of UA and AA into two well-defined voltammetric peaks with peak separation of ca.0.38 V.All results show that the OMC modified electrode has a good electrocatalytic ability to UA and AA,and has an excellent response towards UA even in the presence of high concentration AA.

  5. Single Nanoparticle Voltammetry: Contact Modulation of the Mediated Current.

    Science.gov (United States)

    Li, Xiuting; Batchelor-McAuley, Christopher; Whitby, Samuel A I; Tschulik, Kristina; Shao, Lidong; Compton, Richard G

    2016-03-18

    The cyclic voltammetric responses of individual palladium-coated carbon nanotubes are reported. Upon impact-from the solution phase-with the electrified interface, the nanoparticles act as individual nanoelectrodes catalyzing the hydrogen-oxidation reaction. At high overpotentials the current is shown to reach a quasi-steady-state diffusion limit, allowing determination of the tube length. The electrochemical response of the individual nanotubes also reveals the system to be modulated by the electrical contact between the electrode and carbon nanotube. This modulation presents itself as fluctuations in the recorded Faradaic current.

  6. Microconcentric ring electrode/injector assembly for sensitive voltammetric analysis in single droplets of ultrasmall volumes.

    Science.gov (United States)

    Kai, Tianhan; Chen, Shu; Monterroso, Estuardo; Hailu, Amanuel; Zhou, Feimeng

    2014-08-19

    This paper describes the construction of a microring electrode concentric to an inner injection capillary for voltammetric determination of trace analytes in nanoliter- to picoliter-sized droplets. The gold microring is sandwiched between a pulled fused-silica capillary and borosilicate glass tubing. Compared to polymer-coated microring electrodes, the glass-encapsulated electrode is more robust and does not swell in organic solvents. Consequently, the microring electrode is suitable for voltammetric studies of redox-active species and their accompanying ion transfers between two immiscible solvents. Droplets of variable sizes can be conveniently dispensed from front-loaded sample plugs into an immiscible liquid, greatly simplifying the experimental procedure and facilitating analysis of samples of limited availability. The size of the microring and the volume of the droplet deduced from well-defined voltammograms correlate well with those estimated from their geometric dimensions. The thin-layer cell behavior can be attained with well-defined voltammetric peaks and small capacitive current. Exhaustive electrolysis in single droplets can be accomplished in short times (e.g., ∼85 s in a droplet of 1.42 nL at a microring of 11.4 μm in radius). Anodic stripping voltammetry of Ag deposited onto the microring electrode resulted in a detection limit of 0.13 fmol (14 fg) of Ag(+). The microring electrode/injector assembly can be polished repeatedly and is versatile for various applications (e.g., sample plugs can also be back-loaded via a rotary injection valve and an HPLC pump for flow injection analysis).

  7. Cathodic adsorptive stripping voltammetric determination of Ribavirin in pharmaceutical dosage form, urine and serum

    Directory of Open Access Journals (Sweden)

    Ahmed A. Abdel Gaber

    2017-05-01

    Full Text Available A sensitive, simple and rapid square-wave adsorptive stripping voltammetric method was developed and validated for the determination of Ribavirin in pharmaceutical formulations. The proposed method was based on the electrochemical reduction of Ribavirin at a hanging mercury drop electrode in Britton Robinson buffer at pH 10. A well-defined peak was observed at 880 mV with 30 s of accumulation time and 50 mV of accumulation potential. Under these optimized conditions, the square-wave adsorptive stripping voltammetric peak current showed a linear correlation on drug concentration over the range of 1 × 10−10–2 × 10−7 mol L−1 with a correlation coefficient of 0.9995 for the proposed method. The detection and quantitation limits for this method were 2.02 × 10−10 and 6.80 × 10−10 mol L−1, respectively. The results obtained for intra-day and inter-day precision (as RSD % were between 0.447% and 1.024%. This method was applied successfully for the determination of Ribavirin in its pharmaceutical dosage forms with mean recoveries of 99.68 ± 0.13 with RSD % of 0.81% and 99.20 ± 0.24 with RSD % of 0.49% for two concentrations 5 × 10−9 and 5 × 10−8 mol L−1, respectively for 200 mg capsules. The results obtained from the developed square-wave adsorptive stripping voltammetric method were compared with those obtained by the analytical method reported in the literature.

  8. application of ascorbic acid 2-phosphate as a new voltammetric ...

    African Journals Online (AJOL)

    a

    acid 2-phosphate (AAP) as a new voltammetric substrate has been ... further applied to determine the ALP content in healthy human serum and the results were in ... substrates to produce phenol or p-aminophenol, which is electroactive and can be ... bovine serum, human serum and untreated human blood with the linear ...

  9. Determination of total polyphenol index in wines employing a voltammetric electronic tongue

    Energy Technology Data Exchange (ETDEWEB)

    Ceto, Xavier [Sensors and Biosensors Group, Department of Chemistry, Universitat Autonoma de Barcelona, Edifici Cn, 08193 Bellaterra (Spain); Gutierrez, Juan Manuel [Bioelectronics Section, Department of Electrical Engineering, CINVESTAV, 07360 Mexico D.F. (Mexico); Gutierrez, Manuel [Instituto de Microelectronica de Barcelona (IMB-CNM), CSIC, 08193 Bellaterra (Spain); Cespedes, Francisco [Sensors and Biosensors Group, Department of Chemistry, Universitat Autonoma de Barcelona, Edifici Cn, 08193 Bellaterra (Spain); Capdevila, Josefina; Minguez, Santiago [Estacio de Viticultura i Enologia, INCAVI, Vilafranca del Penedes (Spain); Jimenez-Jorquera, Cecilia [Instituto de Microelectronica de Barcelona (IMB-CNM), CSIC, 08193 Bellaterra (Spain); Valle, Manel del, E-mail: manel.delvalle@uab.cat [Sensors and Biosensors Group, Department of Chemistry, Universitat Autonoma de Barcelona, Edifici Cn, 08193 Bellaterra (Spain)

    2012-06-30

    Highlights: Black-Right-Pointing-Pointer Array of voltammetric sensors modified with nanoparticles or conducting polymers. Black-Right-Pointing-Pointer It has been applied in wine analysis to predict polyphenol content index. Black-Right-Pointing-Pointer Uses data processing tools such as discrete wavelet transform and artificial neural network. Black-Right-Pointing-Pointer Identification of phenolics like gallic acid, catechin, caffeic acid, catechol. Black-Right-Pointing-Pointer Predicted polyphenol index agrees with Folin-Ciocalteau method and I{sub 280} index. - Abstract: This work reports the application of a voltammetric electronic tongue system (ET) made from an array of modified graphite-epoxy composites plus a gold microelectrode in the qualitative and quantitative analysis of polyphenols found in wine. Wine samples were analyzed using cyclic voltammetry without any sample pretreatment. The obtained responses were preprocessed employing discrete wavelet transform (DWT) in order to compress and extract significant features from the voltammetric signals, and the obtained approximation coefficients fed a multivariate calibration method (artificial neural network-ANN-or partial least squares-PLS-) which accomplished the quantification of total polyphenol content. External test subset samples results were compared with the ones obtained with the Folin-Ciocalteu (FC) method and UV absorbance polyphenol index (I{sub 280}) as reference values, with highly significant correlation coefficients of 0.979 and 0.963 in the range from 50 to 2400 mg L{sup -1} gallic acid equivalents, respectively. In a separate experiment, qualitative discrimination of different polyphenols found in wine was also assessed by principal component analysis (PCA).

  10. Voltammetric Detection of Diquat at the Carbon Paste Electrode Containing a Ca10(PO46(OH2

    Directory of Open Access Journals (Sweden)

    Moulay Abderrahim EL MHAMMEDI

    2007-01-01

    Full Text Available We report a sensitive electrochemical voltammetric method for analyzing diquat (DQ ions using a carbon paste electrochemical (CPE modified by porous material, such as hydroxyapatite (HAP. Diquat strongly adsorbed on a HAP-CPE surface and provides facile electrochemical quantitative methods for electroactive DQ ions. Operational parameters have been optimized, and the stripping voltammetric performance has been studied using square wave voltammetry. The peaks current intensity are highly linear over the 7×10-7–3×10-4 mol L-1 diquat range examined (10-min accumulation time, with a good sensitivity. These findings can lead to a widespread use of electrochemical sensors to detect DQ contaminates.Scanning electron microscopy was used for morphology observation and in particular the X-ray diffraction analysis (XRD and Fourier transformed infrared spectroscopy (FTIR analysis for characterization of synthesis powder.

  11. Voltammetric Study and Determination of Phenylephrine Hydrochloride at INP-Nafion-Modified CPE Sensor Employing Differential Pulse Voltammetry

    Directory of Open Access Journals (Sweden)

    Zeinab Pourghobadi

    2014-03-01

    Full Text Available In this study, describes the voltammetric oxidation and determination of phenylephrine (PHE hydrochloride at a new chemically modified electrode. Iron nanoparticle (INPs was dispersed in Nafion solution to obtain a INP-Nafion-modified CPE for the voltammetric analysis of PHE .The electrochemical behaviour of PHE on INP-Nafion-modified CPE was studied, using cyclic voltammetry as a diagnostic technique. The effects of amount of INPs-Nafion dispersion, pH, and scan rate on the response of modified electrode for the oxidation of PHE were investigated. Using differential pulse voltammetry (DPV, the modified electrode indicated a dynamic linear range for quantitative determination of PHE in the range of 5 μM−130 μM, and the detection limit was estimated to be 0.76 μM. The method was developed for the determination of PHE in pharmaceutical samples with satisfactory results.

  12. Sensitive voltammetric detection of yeast RNA based on its interaction with Victoria Blue B

    Directory of Open Access Journals (Sweden)

    WEI SUN

    2009-12-01

    Full Text Available Voltammetric studies of the interaction of yeast RNA (y-RNA with Victoria Blue B (VBB are described in this paper. Furthermore, a linear sweep voltammetric method for the detection of y-RNA was established. The reaction conditions, such as acidity and amount of buffer solution, the concentration of VBB, the reaction time and temperature, etc., were carefully investigated by second order derivative linear sweep voltammetry. Under the optimal conditions, the reduction peak current of VBB at –0.75 V decreased greatly after the addition of y-RNA to the solution without any shift of the reduction peak potential. Based on the decrease of the peak current, a new quantitative method for the determination of y-RNA was developed. The effects of co-existing substances on the determination were carefully investigated and three synthetic samples were determined with satisfactory results. The stoichiometry of the VBB–y-RNA complex was calculated by linear sweep voltammetry and the interaction mechanism is discussed.

  13. Voltammetric behaviour of drotaverine hydrochloride in surfactant media and its enhancement determination in Tween-20.

    Science.gov (United States)

    Jain, Rajeev; Vikas; Rather, Jahangir Ahmad

    2011-02-01

    Simple, sensitive and rapid adsorptive voltammetric behaviour of drotaverine hydrochloride onto the HMDE has been explored and validated in surfactant media by using cyclic, differential pulse and square-wave voltammetry. Addition of Tween-20 to the drotaverine hydrochloride containing electrolyte enhances the reduction current signal. The voltammograms of the drug with Tween-20 in phosphate buffers of pH 2.5-11.0 exhibit a single well defined reduction peak which may be due to the reduction of -CC- group. The cyclic voltammetric studies indicated the reduction of drotaverine hydrochloride at the electrode surface through two electron irreversible step and diffusion-controlled. The peak current showed a linear dependence with the drug concentration over the range 0.8-7.2μgmL(-1). The calculated LOD and LOQ are 1.8 and 6.0ngmL(-1) by SWCAdSV and 8.1 and 27.2ngmL(-1) by DPCAdSV, respectively. The procedure was applied to the assay of the drug in tablet form with mean percentage recoveries of 100.2% with SWCAdSV and 99.7% with DPCAdSV. The validity of the proposed methods was further assessed by applying a standard addition technique.

  14. Vapor permeation-stepwise injection simultaneous determination of methanol and ethanol in biodiesel with voltammetric detection.

    Science.gov (United States)

    Shishov, Andrey; Penkova, Anastasia; Zabrodin, Andrey; Nikolaev, Konstantin; Dmitrenko, Maria; Ermakov, Sergey; Bulatov, Andrey

    2016-02-01

    A novel vapor permeation-stepwise injection (VP-SWI) method for the determination of methanol and ethanol in biodiesel samples is discussed. In the current study, stepwise injection analysis was successfully combined with voltammetric detection and vapor permeation. This method is based on the separation of methanol and ethanol from a sample using a vapor permeation module (VPM) with a selective polymer membrane based on poly(phenylene isophtalamide) (PA) containing high amounts of a residual solvent. After the evaporation into the headspace of the VPM, methanol and ethanol were transported, by gas bubbling, through a PA membrane to a mixing chamber equipped with a voltammetric detector. Ethanol was selectively detected at +0.19 V, and both compounds were detected at +1.20 V. Current subtractions (using a correction factor) were used for the selective determination of methanol. A linear range between 0.05 and 0.5% (m/m) was established for each analyte. The limits of detection were estimated at 0.02% (m/m) for ethanol and methanol. The sample throughput was 5 samples h(-1). The method was successfully applied to the analysis of biodiesel samples.

  15. Voltammetric studies of Azathioprine on the surface of graphite electrode modified with graphene nanosheets decorated with Ag nanoparticles.

    Science.gov (United States)

    Asadian, Elham; Iraji Zad, Azam; Shahrokhian, Saeed

    2016-01-01

    By using graphene nanosheets decorated with Ag nanoparticles (AgNPs-G) as an effective approach for the surface modification of pyrolytic graphite electrode (PGE), a sensing platform was fabricated for the sensitive voltammetric determination of Azathioprine (Aza). The prepared AgNPs-G nanosheets were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis and Raman spectroscopy techniques. The electrochemical behavior of Aza was investigated by means of cyclic voltammetry. Comparing to the bare PGE, a remarkable enhancement was observed in the response characteristics of Aza on the surface of the modified electrode (AgNPs-G/PGE) as well as a noticeable decrease in its reduction overpotential. These results can be attributed to the incredible enlargement in the microscopic surface area of the electrode due to the presence of graphene nanosheets together with strong adsorption of Aza on its surface. The effect of experimental parameters such as accumulation time, the amount of modifier suspension and pH of the supporting electrolyte were also optimized toward obtaining the maximum sensitivity. Under the optimum conditions, the calibration curve studies demonstrated that the peak current increased linearly with Aza concentrations in the range of 7 × 10(-7) to 1 × 10(-4)mol L(-1) with the detection limit of 68 nM. Further experiments revealed that the modified electrode can be successfully applied for the accurate determination of Aza in pharmaceutical preparations.

  16. Voltammetric behaviour of levodopa and its quantification in pharmaceuticals using a -cyclodextrine doped poly (2,5-diaminobenzenesulfonic acid) modified electrode

    Indian Academy of Sciences (India)

    Mehmet Aslanoglu; Aysegul Kutluay; Sultan Goktas; Serpil Karabulut

    2009-03-01

    A cyclic voltammetric method based on a -cyclodextrine doped poly(2,5-diaminobenzenesulfonic acid) modified glassy carbon electrode (GCE) was developed for the determination of levodopa. Compared with bare GCE and poly(2,5-diaminobenzenesulfonic acid)/GCE, the poly(2,5-diaminobenzenesulfonic acid)--cyclodextrine/GCE exhibits a remarkable shift of the oxidation potentials of levodopa in the cathodic direction and a drastic enhancement of the anodic current response. The incorporation of -cyclodextrine into the polymer film exhibited that the electrode provides more stable and sensitive current responses for levodopa. Levodopa exhibited a single broad peak at about 0.6 V at bare GCE. However, at the -cyclodextrine doped poly(2,5-diaminobenzenesulfonic acid)/GCE, a well-defined redox wave of levodopa was obtained, with the oxidation and the reduction peak potential at 0.193 and 0.164 V, respectively. The separation of peak potentials was 29 mV. The linear current response was obtained in the range of 1.0 × 10-6 ∼ 2.0 ∼ 10-4 M with a detection limit of 4.18 ∼ 10-7 M for levodopa, The poly(2,5-diaminobenzenesulfonic acid)--cyclodextrine/GCE was also effective to simultaneously detect levodopa and ascorbic acid. The modified electrode has been successfully applied for the determination of levodopa in pharmaceuticals. The poly(2,5-diaminobenzenesulfonic acid)--cyclodextrine/GCE showed excellent stability and reproducibility.

  17. Voltammetric Determination of Estrogens Based on the Enhancement Effect of Surfactant at Carbon Paste Electrode

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Highly sensitive voltammetric method for the determination of estrogens, based on the enhancement effect of cetyltrimethylammonium bromide (CTAB) has been described. In the presence of CTAB, the oxidation peak currents of estrogens (estradiol, estrone, estriol, estradiol valerate and diethylstilbestrol) at the carbon paste electrode (CPE) increased significantly after open-circuit accumulation. The peak current was proportional to the concentration of estradiol over the range from 5×10-9 to 2.5×10-6 mol\\5L-1. The detection limit was 8×10-10 mol\\5L-1 at 6 min of accumulation. The total amounts of estrogens in the blood serums were determined and the average recovery was 104.92%. Under the conditions used, the electrode process of estradiol was examined and the mechanism for peak current enhancement was also discussed.

  18. Voltammetric studies on the electrochemical determination of methylmercury in chloride medium at carbon microelectrodes

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, F. [Centro de Electroquimica e Cinetica da Universidade de Lisboa, Departamento de Quimica e Bioquimica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisbon (Portugal); Neto, M.M.M. [Centro de Electroquimica e Cinetica da Universidade de Lisboa, Departamento de Quimica e Bioquimica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisbon (Portugal) and Departamento de Quimica Agricola e Ambiental, Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisbon (Portugal)]. E-mail: mm.neto@netcabo.pt; Rocha, M.M. [Centro de Electroquimica e Cinetica da Universidade de Lisboa, Departamento de Quimica e Bioquimica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisbon (Portugal); Fonseca, I.T.E. [Centro de Electroquimica e Cinetica da Universidade de Lisboa, Departamento de Quimica e Bioquimica, Faculdade de Ciencias, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisbon (Portugal)

    2006-10-10

    Electroanalytical techniques have been used to determine methylmercury at low levels in environmental matrices. The electrochemical behaviour of methylmercury at carbon microelectrodes in a hydrochloric acid medium using cyclic, square wave and fast-scan linear-sweep voltammetric techniques has been investigated. The analytical utility of the methylmercury reoxidation peak has been explored, but the recorded peak currents were found to be poorly reproducible. This is ascribed to two factors: the adsorption of insoluble chloromercury compounds on the electrode surface, which appears to be an important contribution to hinder the voltammetric signal of methylmercury; and the competition between the reoxidation of the methylmercury radical and its dimerization reaction, which limits the reproducibility of the methylmercury peak. These problems were successfully overcome by adopting the appropriate experimental conditions. Fast-scan rates were employed and an efficient electrochemical regeneration procedure of the electrode surface was achieved, under potentiostatic conditions in a mercury-free solution containing potassium thiocyanate-a strong complexing agent. The influence of chloride ion concentration was analysed. Interference by metals, such as lead and cadmium, was considered. Calibration plots were obtained in the micromolar and submicromolar concentration ranges, allowing the electrochemical determination of methylmercury in trace amounts. An estuarine water sample was analysed using the new method with a glassy carbon microelectrode.

  19. Voltammetric behavior of nitrofurazone and its hydroxymethyl prodrug with potential anti-Chagas activity

    Energy Technology Data Exchange (ETDEWEB)

    La-Scalea, Mauro Aquiles [Sao Paulo Univ., SP (Brazil). Faculdade de Ciencias Farmaceuticas; Sao Paulo Univ., SP (Brazil). Inst. de Quimica]. E-mail: scalea@usp.br; Menezes, Carla Maria de Souza; Ferreira, Elizabeth Igne [Sao Paulo Univ., SP (Brazil). Faculdade de Ciencias Farmaceuticas; Juliao, Murilo Sergio da Silva [Sao Paulo Univ., SP (Brazil). Inst. de Quimica; Universidade Estadual Vale do Acaraju, Fortaleza, CE (Brazil). Centro de Ciencias Exatas e Tecnologicas; Man Chin Chung [UNESP, Araraquara, SP (Brazil). Faculdade de Ciencias Farmaceuticas; Serrano, Silvia Helena Pires [Sao Paulo Univ., SP (Brazil). Inst. de Quimica

    2005-07-15

    Chagas' disease is a serious health problem for Latin America. The situation is worsened by the lack of efficient chemotherapy. The two available commercial drugs, benznidazole and nifurtimox, are more effective in the acute phase of the disease. Nitrofurazone is active against Trypanosoma cruzi, however its high toxicity precludes its current use in parasitosis. Hydroxymethyl nitrofurazone is a prodrug of nitrofurazone. It is more active against Trypanosoma cruzi than nitrofurazone, besides being less toxic. This work shows the voltammetric behavior of nitrofurazone and a comparison with those of metronidazole and chloramphenicol using cyclic, linear sweep and differential pulse voltammetries. For these drugs also the prediction of the diffusion coefficients using Wilke-Chang equation was performed. The reduction of nitrofurazone is pH-dependent and in acidic medium the hydroxylamine derivative, involving four electrons, is the principal product formed. In aqueous-alkaline medium and with a glassy carbon electrode pre-treatment the reduction of nitrofurazone occurs in two steps, the first involving one electron to form the nitro-radical anion and the second corresponding to the hydroxylamine derivative formation. Hydroxymethyl nitrofurazone presented the same voltammetric behavior and electroactivity, indicating that the molecular modification performed in nitrofurazone did not change its capacity to be reduced. A brief discussion regarding the differences in biological activity between the two compounds is also presented. (author)

  20. Manganese dioxide-graphene nanocomposite film modified electrode as a sensitive voltammetric sensor of indomethacin detection

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yuxia; Zhang, Zhenfa; Zhang, Cuizong; Huang, Wei; Liang, Caiyun; Peng, Jinyun [Guangxi Normal University for Nationalities, Chongzuo (China)

    2016-08-15

    Excess amount of analgesic and anti-inflammatory drug, such as indomethacin, often leads to serious gastrointestinal complications; therefore, amount of such active compound should be regulated in commercial drugs. This study proposes an efficient analytical technique to detect indomethacin selectively. We prepared and investigated electrochemical properties of a manganese dioxide-graphene nanocomposite film modified glassy carbon electrode (MnO{sub 2}-Gr/GCE). The behavior of the modified electrode as electrocatalyst towards indomethacin oxidation was also examined. The cyclic voltammetric results reveal that the electrocatalytic activity for the oxidation of indomethacin can significantly be enhanced on the MnO{sub 2}-Gr/GCE. Indomethacin exhibited a sensitive anodic peak at about 0.90 V at MnO{sub 2}-Gr/GCE. The data obtained from differential pulse voltammetry showed that the anodic peak currents were linearly dependent on the indomethacin concentrations in the range of 1.0 X 10{sup -7} to 2.5 X 10{sup -5} mol/L with a detection limit of 3.2 X 10{sup -8} mol/L (S/N = 3). Most importantly, the proposed method shows efficient and selective sensing of indomethacin in commercial harmaceutical formulations. This is the first report of a voltammetric sensor for indomethacin using MnO{sub 2}-Gr/GCE. We believe that this new method can be commercialized for routine applications in laboratories.

  1. A Rapid and Sensitive Diagnosis of Typhoid Fever Based On Nested PCR-Voltammetric DNA Biosensor Using Flagellin Gene Fragment

    Directory of Open Access Journals (Sweden)

    Yeni Wahyuni Hartati

    2016-03-01

    Full Text Available Typhoid fever caused by Salmonella typhi is an important issue for public health in the world. Laboratory methods for rapid and sensitive diagnosis are very important for disease management. The purpose of this study was to determine the performance of nested PCR–voltammetric DNA biosensor using flagellin gene (fla of S. typhi as a marker. The differential pulse voltammetry using pencil graphite electrode was applied to measure the guanine oxidation signal of probes vs synthetic target stDNA and probes vs fla PCR product hybridizations. The probe DNA selectivity was examined by hybridized probes vs non-complementary sequence. The result showed that the first round nested PCR product can not be visualized by agarose electrophoresis, whereas using the voltammetric biosensor methods can be detected both for the first or second round nested PCR product. The average peak current of hybridized probe vs first and second round of PCR product was 2.32 and 1.47 μA respectively, at 0.9 V. Detection of the DNA sequences of the infectious diseases from PCR amplified real sample was also carried out using this voltammetric DNA biosensor methods.

  2. Determination of total polyphenol index in wines employing a voltammetric electronic tongue.

    Science.gov (United States)

    Cetó, Xavier; Gutiérrez, Juan Manuel; Gutiérrez, Manuel; Céspedes, Francisco; Capdevila, Josefina; Mínguez, Santiago; Jiménez-Jorquera, Cecilia; del Valle, Manel

    2012-06-30

    This work reports the application of a voltammetric electronic tongue system (ET) made from an array of modified graphite-epoxy composites plus a gold microelectrode in the qualitative and quantitative analysis of polyphenols found in wine. Wine samples were analyzed using cyclic voltammetry without any sample pretreatment. The obtained responses were preprocessed employing discrete wavelet transform (DWT) in order to compress and extract significant features from the voltammetric signals, and the obtained approximation coefficients fed a multivariate calibration method (artificial neural network-ANN-or partial least squares-PLS-) which accomplished the quantification of total polyphenol content. External test subset samples results were compared with the ones obtained with the Folin-Ciocalteu (FC) method and UV absorbance polyphenol index (I(280)) as reference values, with highly significant correlation coefficients of 0.979 and 0.963 in the range from 50 to 2400 mg L(-1) gallic acid equivalents, respectively. In a separate experiment, qualitative discrimination of different polyphenols found in wine was also assessed by principal component analysis (PCA).

  3. Evaluation of antimony microparticles supported on biochar for application in the voltammetric determination of paraquat.

    Science.gov (United States)

    Gevaerd, Ava; de Oliveira, Paulo R; Mangrich, Antonio S; Bergamini, Márcio F; Marcolino-Junior, Luiz H

    2016-05-01

    This work describes the construction and application of carbon paste electrodes modified with biochar and antimony microparticles (SbBCPE) for voltammetric determination of paraquat using a simple and sensitive procedure based on voltammetric stripping analysis. Some parameters such as amount of biochar and antimony used in the composition of the carbon paste and instrumental parameters were examined in detail. Under optimized conditions, an analytical curve was obtained for paraquat determination employing SbBCPE, which showed a linear response ranging from 0.2 to 2.9 μmol L(-1), with limit of detection and quantification of 34 nmol L(-1) and 113 nmol L(-1), respectively, after paraquat pre-concentration of 120 s. The repeatability study presented a RSD=2.0% for 10 consecutive measurements using the same electrode surface and the reproducibility study showed a RSD=2.7% for measurements with 10 different electrode surfaces. The proposed sensor was successfully applied for paraquat determination in tap water and citric fruit juice spiked samples and good recoveries were obtained without any sample pre-treatment, showing its promising analytical performance.

  4. Microgravimetric and voltammetric study of Zn underpotential deposition on platinum in alkaline medium

    Science.gov (United States)

    Calegaro, M. L.; Santos, M. C.; Miwa, D. W.; Machado, S. A. S.

    2005-03-01

    The microgravimetric and voltammetric responses of a polycrystalline Pt electrode in 0.1 mol L -1 NaOH solution in the presence and the absence of 1.6 × 10 -4 Zn 2+, at 0.1 V s -1 were analyzed. During the positive potential sweep, the water molecules are progressively substituted by OH - ions, prior to PtO formation. The voltammetric charges obtained under the Zn ads dissolution peaks suggest that 0.7 monolayers are deposited, with each Zn ad-atom occupying one active site and transferring two electrons. The total loss of mass due to the dissolution of the Zn ad-layer was 136.6 ng cm -2 and the mass increase due to PtO formation was found to be only 12 ng cm -2 less than the theoretical ones, 157.5 and 37.4 ng cm -2, respectively, indicating that both processes are overlapped. In this way it is proposed that an adsorbed by-layer of Zn and OH - ions is formed.

  5. Voltammetric estimation of the content of antibiotics in veterinary preparations

    Directory of Open Access Journals (Sweden)

    Slepchenko Galina

    2016-01-01

    Full Text Available The voltammetric method for determination of tylosin tartrate, gentamicin sulfate, and cefalexin in veterinary preparations was for the first time developed. Electrochemical behavior of these antibiotics on the mercury film electrode was studied, and the working conditions (background electrolyte, deposition potential were defined for getting analytical signals using the voltammetry. The methods of real objects preparation for determination of tylosin tartrate, gentamicin sulfate, and cefalexin were offered. The techniques for the voltammetric determination of antibiotics in the veterinary preparations may be used in cefalexin ranging from 0.1 to 2.0 g/dm3, tylosin tartrate in the range from 0.1 to 1.7 g/dm3, and gentamicin sulfate from 0.1 to 1.5 g/dm3 (Sr is not more than 25 %

  6. Voltammetric estimation of the content of antibiotics in veterinary preparations

    OpenAIRE

    2016-01-01

    The voltammetric method for determination of tylosin tartrate, gentamicin sulfate, and cefalexin in veterinary preparations was for the first time developed. Electrochemical behavior of these antibiotics on the mercury film electrode was studied, and the working conditions (background electrolyte, deposition potential) were defined for getting analytical signals using the voltammetry. The methods of real objects preparation for determination of tylosin tartrate, gentamicin sulfate, and cefale...

  7. New molecular imprinted voltammetric sensor for determination of ochratoxin A

    Energy Technology Data Exchange (ETDEWEB)

    Yola, Mehmet Lütfi, E-mail: mehmetyola@gmail.com [Department of Metallurgical and Materials Engineering, Faculty of Engineering, Sinop University, Sinop (Turkey); Gupta, Vinod Kumar, E-mail: vinodfcy@iitr.ac.in [Indian Institute of Technology, Department of Chemistry, Roorkee, Roorkee 247667 (India); Department of Applied Chemistry, University of Johannesburg, Johannesburg (South Africa); Atar, Necip [Department of Chemical Engineering, Faculty of Engineering, Pamukkale University, Denizli (Turkey)

    2016-04-01

    In this report, a novel molecular imprinted voltammetric sensor based on silver nanoparticles (AgNPs) involved in a polyoxometalate (H{sub 3}PW{sub 12}O{sub 40}, POM) functionalized reduced graphene oxide (rGO) modified glassy carbon electrode (GCE) was presented for determination of ochrattoxin A (OCH). The developed surfaces were characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) method. OCH imprinted GCE was prepared via electropolymerization process of 100 mM phenol as monomer in the presence of phosphate buffer solution (pH 6.0) containing 25 mM OCH. The linearity range and the detection limit of the method were calculated as 5.0 × 10{sup −11} − 1.5 × 10{sup −9} M and 1.6 × 10{sup −11} M, respectively. The voltammetric sensor was applied to grape juice and wine samples with good selectivity and recovery. The stability of the voltammetric sensor was also reported. - Highlights: • Ochratoxin A-imprinted electrochemical sensor is developed for the sensitive detection of ochratoxin A • The nanomaterial and ochratoxin A-imprinted surfaces were characterized by several methods • Ochratoxin A-imprinted electrochemical sensor is sensitive and selective in analysis of food • Ochratoxin A-imprinted electrochemical sensor is preferred to the other methods.

  8. Spectrophotometric and Voltammetric Studies on the Interaction of Heparin with Phenosafranine

    Institute of Scientific and Technical Information of China (English)

    Wei SUN; Ya Qin DING; Kui JIAO

    2005-01-01

    The interaction of phenosafranine (PSF) with a glycosaminoglycans of heparin (Hep) in aqueous solution has been characterized by UV-Vis absorption spectrophotometry and cyclic voltammetry in pH 1.5 Britton-Robinson (B-R) buffer solution. The addition of Hep caused decrease of the absorbance of PSF at 532 nm and the redox peak current of PSF. The study showed that an supramolecular complex of PSF-Hep was formed because of the electrostatic attraction of negatively charged Hep with the positively charged PSF, which resulted in the decrease of the equilibrium concentration of PSF in solutions, and the decrease of the absorbance or the Peak current of PSF. The stoichiometry of the Hep/PSF complex was further calculated by voltammetric data with the result of 1:1 complex.

  9. Current Debates in Corporate Social Responsibility: An Agenda for Research

    Directory of Open Access Journals (Sweden)

    David Crowther

    2007-06-01

    Full Text Available Corporate Social Responsibility (CSR has a particular prominence at this point in time, featuring heavily in the discourses of both academe and business. The understanding of what is meant by CSR continues to evolve as a consensus is reached. Nevertheless some important debates continue – or are commencing – which need to be resolved. It is the purpose of this paper to highlight these as some of the current debates within the CSR community – and hence form a significant part of an agenda for research in the area. Specifically we focus upon three key areas for the management of business, namely setting standards for reporting, identifying and implementing sustainable practice, and the management of risk.

  10. Current trends in gamma radiation detection for radiological emergency response

    Science.gov (United States)

    Mukhopadhyay, Sanjoy; Guss, Paul; Maurer, Richard

    2011-09-01

    Passive and active detection of gamma rays from shielded radioactive materials, including special nuclear materials, is an important task for any radiological emergency response organization. This article reports on the current trends and status of gamma radiation detection objectives and measurement techniques as applied to nonproliferation and radiological emergencies. In recent years, since the establishment of the Domestic Nuclear Detection Office by the Department of Homeland Security, a tremendous amount of progress has been made in detection materials (scintillators, semiconductors), imaging techniques (Compton imaging, use of active masking and hybrid imaging), data acquisition systems with digital signal processing, field programmable gate arrays and embedded isotopic analysis software (viz. gamma detector response and analysis software [GADRAS]1), fast template matching, and data fusion (merging radiological data with geo-referenced maps, digital imagery to provide better situational awareness). In this stride to progress, a significant amount of inter-disciplinary research and development has taken place-techniques and spin-offs from medical science (such as x-ray radiography and tomography), materials engineering (systematic planned studies on scintillators to optimize several qualities of a good scintillator, nanoparticle applications, quantum dots, and photonic crystals, just to name a few). No trend analysis of radiation detection systems would be complete without mentioning the unprecedented strategic position taken by the National Nuclear Security Administration (NNSA) to deter, detect, and interdict illicit trafficking in nuclear and other radioactive materials across international borders and through the global maritime transportation-the so-called second line of defense.

  11. Label-free voltammetric aptasensor for the sensitive detection of microcystin-LR using graphene-modified electrodes.

    Science.gov (United States)

    Eissa, Shimaa; Ng, Andy; Siaj, Mohamed; Zourob, Mohammed

    2014-08-05

    The development of successful biosensing platforms is highly dependent upon the biorecognition properties of the recognition receptor and the sensitivity of the transducer of the binding signal. The integration of the high affinity and specificity of DNA aptamers with the unique properties of the carbon nanomaterial graphene offers an excellent avenue for sensitive and selective biosensing architectures. In this work, a highly sensitive and selective aptasensor which utilizes an unlabeled DNA aptamer assembled on a graphene electrode for microcystin-LR detection was developed. A facile strategy was used for the aptasensor fabrication on the basis of the noncovalent assembly of DNA aptamer on graphene-modified screen printed carbon electrodes. Assembly of the DNA aptamer on the graphene-modified electrodes caused a marked drop in the square wave voltammetric reduction signal of the [Fe(CN)6](4-/3-) redox couple. The presence of microcystin-LR, on the other hand, caused a dose-responsive increase in peak current, allowing the quantification of microcystin-LR through the measurement of peak current change. Under optimal conditions, the detection limit of the developed aptasensor was 1.9 pM in buffer, a concentration much lower than those offered by previously reported biosensors for microcystin-LR. The developed aptasensor also exhibited excellent selectivity for microcystin-LR with no detectable cross-reactivity to okadaic acid, microcystin-LA, and microcystin-YR. Moreover, the proposed aptasensor has been applied for the analysis of spiked tap water and fish samples showing good recovery percentages. This novel, simple, high-performance, and low-cost detection platform would facilitate the routine monitoring of microcystin-LR in real samples.

  12. Voltammetric Behavior of Sodium 7-Methoxyl-4'-hydroxylisoflavone-3'-sulfonate and Its Application

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zun-Ting张尊听; DONG She-Ying董社英; ZHENG Jian-Bin郑建斌; ZHANG Hong-Fang张宏芳; GAO Hong高鸿

    2004-01-01

    Voltammetric behavior of sodium 7-methoxyl-4'-hydroxylisoflavone-3'-sulfonate (SMHS) in the aqueous solution from pH 1 to 5 was studied by linear sweep voltammetry, cyclic voltammetry and normal pulse voltammetry.SMHS caused only one reduction wave at -1.34 V (vs. saturated calomel electrode, SCE), which was an irreversible adsorptive wave of SMHS protonized involving one electron and one proton. The peak current of SMHS on synthetic samples. In addition, its scavenging effect on superoxide anion radical was studied by the auto-oxidation of pyrogallol in HCl-tris buffer solution (pH=8.2) in order to explain its peculiar biological effects. The experimental results proved that SMHS has antioxidant quality, and it is an efficient free radical scavenger of superoxide anion radical.

  13. Rapid screening and guided extraction of antioxidants from microalgae using voltammetric methods.

    Science.gov (United States)

    Goiris, Koen; De Vreese, Peter; De Cooman, Luc; Muylaert, Koenraad

    2012-08-01

    Currently, microalgae draw much attention as a promising source of natural antioxidants to replace synthetic antioxidants for food applications. In this paper, the use of voltammetric techniques as a fast alternative for chemical assays to determine the antioxidant power of microalgal biomass is discussed. It was found that antioxidant activities determined by square wave voltammetry correlate well with the results from other established antioxidant assays, such as Trolox equivalent antioxidant capacity (R(2) = 0.737), ferric reducing antioxidant potential (R(2) = 0.729), and AAPH-induced oxidation of linoleic acid (R(2) = 0.566). Besides yielding quantitative data on the antioxidant activity, square wave voltammetry provides additional information on the antioxidant profile of microalgal biomass as the peak potentials of antioxidant components are determined. Consequently, square wave voltammetry can be used as a tool for optimizing the extraction processes to recover antioxidant components from microalgae.

  14. Electrochemical Quartz Crystal Microbalance Monitoring of the Cyclic Voltammetric Deposition of Polyaniline

    Science.gov (United States)

    Xie, Qingji; Li, Zhili; Deng, Chunyan; Liu, Meiling; Zhang, Youyu; Ma, Ming; Xia, Shaoxi; Xiao, Xiaoming; Yin, Dulin; Yao, Shouzhuo

    2007-01-01

    A real-time, labeled-free and nanogram-sensitive mass sensor, electrochemical quartz crystal microbalance (EQCM) is used to monitor a cyclic voltammetric deposition of polyaniline (PANI). The results determined that the efficiency for PANI deposition and the anion-doping ratio is calculated in one single cyclic voltammetric.

  15. Epidemics: Lessons from the past and current patterns of response

    Science.gov (United States)

    Martin, Paul

    2008-09-01

    Hippocrates gave the term 'epidemic' its medical meaning. From antiquity to modern times, the meaning of the word epidemic has continued to evolve. Over the centuries, researchers have reached an understanding of the varying aspects of epidemics and have tried to combat them. The role played by travel, trade, and human exchanges in the propagation of epidemic infectious diseases has been understood. In 1948, the World Health Organization was created and given the task of advancing ways of combating epidemics. An early warning system to combat epidemics has been implemented by the WHO. The Global Outbreak Alert and Response Network (GOARN) is collaboration between existing institutions and networks that pool their human and technical resources to fight outbreaks. Avian influenza constitutes currently the most deadly epidemic threat, with fears that it could rapidly reach pandemic proportions and put several thousands of lives in jeopardy. Thanks to the WHO's support, most of the world's countries have mobilised and implemented an 'Action Plan for Pandemic Influenza'. As a result, most outbreaks of the H5N1 avian flu virus have so far been speedily contained. Cases of dengue virus introduction in countries possessing every circumstance required for its epidemic spread provide another example pertinent to the prevention of epidemics caused by vector-borne pathogens.

  16. Pivotal response treatment for autism spectrum disorder: current perspectives

    Directory of Open Access Journals (Sweden)

    Lei J

    2017-06-01

    Full Text Available Jiedi Lei, Pamela Ventola Yale Child Study Center, Yale University School of Medicine, New Haven, CT, USA Abstract: Pivotal response treatment (PRT is an evidence-based behavioral intervention based on applied behavior analysis principles aimed to improve social communication skills in individuals with autism spectrum disorder (ASD. PRT adopts a more naturalistic approach and focuses on using a number of strategies to help increase children’s motivation during intervention. Since its conceptualization, PRT has received much empirical support for eliciting therapeutic gains in greater use of functional social communication skills in individuals with ASD. Building upon the empirical evidence supporting PRT, recent advancements have increasingly turned to using interdisciplinary research integrating neuroimaging techniques and behavioral measures to help identify objective biomarkers of treatment, which have two primary purposes. First, neuroimaging results can help characterize how PRT may elicit change, and facilitate partitioning of the heterogeneous profiles of neural mechanisms underlying similar profile of behavioral changes observed over PRT. Second, neuroimaging provides an objective means to both map and track how biomarkers may serve as reliable and sensitive predictors of responder profiles to PRT, assisting clinicians to identify who will most likely benefit from PRT. Together, a better understanding of both mechanisms of change and predictors of responder profile will help PRT to serve as a more precise and targeted intervention for individuals with ASD, thus moving towards the goal of precision medicine and improving quality of care. This review focuses on the recent emerging neuroimaging evidences supporting PRT, offering current perspectives on the importance of interdisciplinary research to help clinicians better understand how PRT works and predict who will respond to PRT. Keywords: PRT, ASD, biomarkers, neuroimaging

  17. Current human immunodeficiency virus epidemic and its response in China

    Institute of Scientific and Technical Information of China (English)

    KANG Lai-Yi

    2012-01-01

    The first patient with acquired immunodeficiency syndrome (AIDS) was identified in 1985; since then, as of October 31, 2010, a total accumulative number of 370 000 patients with human immunodeficiency virus (HIV)/AIDS have been reported. The estimated number of patients living with HIV (PLHIV) in China was 740 000 in 2009. Although China is still a low-HIV prevalence region (rate of 0.057%), the epidemic has spread more widely from the high-risk groups to the general population. This paper covers five topics of importance, i.e., current trends of the HIV epidemic; HIV-1 subtype diversity; emergence of HIV drug resistance (HIVDR); the country's response to the disease; and future challenges and additional actions needed. This paper emphasizes sexual transmission as the predominant route of transmission and it being spread more frequently among men who have sex with men; the epidemic being concentrated over particular areas in China. We also discuss the fact that diverse HIV-1 subtypes have been found throughout the entire country and that recombinant subtypes became predominant. We also explore other topics such as the possibility of HIVDR, including primary and secondary resistance, with the use of free highly active anti-retroviral therapy (HAART); the integrated strategy of HIVDR surveillance and individual clinical HIVDR testing as a new attempt in China. For many years both policy-makers and professionals (including non-governmental organizations) have expressed strong commitment to prevention, control, and care of HIV/sexual transmission infection (STI), promoted the research and conducted different actions to slow the rising trend of the HIV epidemics. Although China is facing many challenges, its citizens need to be persistent on continuing the campaign of the State Council titled "Information of Strengthening Work on Prevention and Control of AIDS".

  18. Acetylene black paste electrode modified with graphene as the voltammetric sensor for selective determination of tryptophan in the presence of high concentrations of tyrosine.

    Science.gov (United States)

    Deng, Peihong; Xu, Zhifeng; Feng, Yonglan

    2014-02-01

    A reliable sensor was fabricated by modifying an acetylene black paste electrode with graphene (denoted as GR/ABPE) for sensitive and selective determination of tryptophan (Trp). Due to the high sorption ability, large surface area and numerous active sites, the GR/ABPE showed a strong enhancement effect on the oxidation of Trp, and greatly increased the peak current. The parameters affecting the Trp determination were investigated. In 1.0 M H2SO4 the voltammetric responses of Trp and tyrosine (Tyr) were well separated into two distinct peaks with peak potential difference (ΔE(pa)) of 115 mV. Under the optimized conditions, in the presence of 0.1 mM Tyr, the oxidation peak current of Trp was proportional to its concentration in the range between 0.1 μM and 0.1 mM, with the limit of detection of 60 nM (S/N=3). The GR/ABPE was applied to the direct detection of Trp in pharmaceutical and biological samples with satisfactory results. This work provides a simple and easy approach to selective detection of Trp in the presence of Tyr.

  19. Anodic behavior of sertindole and its voltammetric determination in pharmaceuticals and human serum using glassy carbon and boron-doped diamond electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Altun, Yuksel [Gazi University, Faculty of Education, Department of Chemistry, 06500 Teknikokullar, Ankara (Turkey); Dogan-Topal, Burcu; Uslu, Bengi [Ankara University, Faculty of Pharmacy, Department of Analytical Chemistry, 06100 Tandogan, Ankara (Turkey); Ozkan, Sibel A. [Ankara University, Faculty of Pharmacy, Department of Analytical Chemistry, 06100 Tandogan, Ankara (Turkey)], E-mail: ozkan@pharmacy.ankara.edu.tr

    2009-02-15

    The electrochemical oxidation of sertindole was investigated using cyclic, linear sweep voltammetry at a glassy carbon and boron-doped diamond electrodes. The aim of this study was to determine sertindole levels in serum and pharmaceutical formulations, by means of electrochemical methods. In cyclic voltammetry, depending on pH values, sertindole showed one or two irreversible oxidation responses. These two responses were found related to the different electroactive part of the molecule. Using second and sharp oxidation peak, two voltammetric methods were described for the determination of sertindole by differential pulse and square wave voltammetry at the glassy carbon and boron-doped diamond electrodes. Under optimized conditions, the current showed a linear dependence with concentration in the range between 1 x 10{sup -6} and 1 x 10{sup -4} M in acetate buffer at pH 3.5 and between 4 x 10{sup -6} and 1 x 10{sup -4} M in spiked human serum samples for both methods. The repeatability, reproducibility, selectivity, precision and accuracy of all the methods in all media were investigated and calculated. These methods were successfully applied for the analysis of sertindole pharmaceutical dosage forms and human serum samples. No electroactive interferences from the tablet excipients and endogenous substances from biological material were found.

  20. A novel voltammetric sensor based on carbon nanotubes and nanoparticles of antimony tin oxide for the determination of ractopamine

    Energy Technology Data Exchange (ETDEWEB)

    Baytak, Aysegul Kutluay; Teker, Tugce; Duzmen, Sehriban; Aslanoglu, Mehmet, E-mail: maslanoglu@harran.edu.tr

    2016-02-01

    An electrochemical sensor was prepared by the modification of a glassy carbon electrode (GCE) with carbon nanotubes (CNTs) and nanoparticles of antimony tin oxide (ATO). The surface layer was characterized by scanning electron microscopy (SEM), energy dispersive X-ray diffraction method (EDX) and ATR FT-IR spectroscopy. The proposed electrode was assessed in respect to the electro-oxidation of ractopamine. Compared with a bare GCE and a GCE electrode modified with CNTs, the ATONPs/CNTs/GCE exhibited a great catalytic activity towards the oxidation of ractopamine with a well-defined anodic peak at 600 mV. The current response was linear with the concentration of ractopamine over the range from 10 to 240 nM with a detection limit of 3.3 nM. The proposed electrode enabled the selective determination of ractopamine in the presence of high concentrations of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The proposed electrode was successfully applied for the determination of ractopamine in feed and urine samples. The sensitive and selective determination of ractopamine makes the developed method of great interest for monitoring its therapeutic use and doping control purposes. - Highlights: • A novel voltammetric sensor was prepared using nanoparticles of ATO and CNTs. • The ATONPs/CNTs/GCE has greatly improved the voltammetry of ractopamine. • The proposed electrode enabled a detection limit of 3.3 nM. • AA, DA and UA did not interfere with the selective detection of ractopamine. • Measurements were precise and accurate.

  1. Voltammetric studies of Azathioprine on the surface of graphite electrode modified with graphene nanosheets decorated with Ag nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Asadian, Elham [Institute for Nanoscience and Nanotechnology (INST), Sharif University of Technology, Tehran (Iran, Islamic Republic of); Iraji zad, Azam [Institute for Nanoscience and Nanotechnology (INST), Sharif University of Technology, Tehran (Iran, Islamic Republic of); Department of Physics, Sharif University of Technology, Tehran 14588-89694 (Iran, Islamic Republic of); Shahrokhian, Saeed, E-mail: shahrokhian@sharif.edu [Institute for Nanoscience and Nanotechnology (INST), Sharif University of Technology, Tehran (Iran, Islamic Republic of); Department of Chemistry, Sharif University of Technology, Tehran 11155-9516 (Iran, Islamic Republic of)

    2016-01-01

    By using graphene nanosheets decorated with Ag nanoparticles (AgNPs-G) as an effective approach for the surface modification of pyrolytic graphite electrode (PGE), a sensing platform was fabricated for the sensitive voltammetric determination of Azathioprine (Aza). The prepared AgNPs-G nanosheets were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–vis and Raman spectroscopy techniques. The electrochemical behavior of Aza was investigated by means of cyclic voltammetry. Comparing to the bare PGE, a remarkable enhancement was observed in the response characteristics of Aza on the surface of the modified electrode (AgNPs-G/PGE) as well as a noticeable decrease in its reduction overpotential. These results can be attributed to the incredible enlargement in the microscopic surface area of the electrode due to the presence of graphene nanosheets together with strong adsorption of Aza on its surface. The effect of experimental parameters such as accumulation time, the amount of modifier suspension and pH of the supporting electrolyte were also optimized toward obtaining the maximum sensitivity. Under the optimum conditions, the calibration curve studies demonstrated that the peak current increased linearly with Aza concentrations in the range of 7 × 10{sup −7} to 1 × 10{sup −4} mol L{sup −1} with the detection limit of 68 nM. Further experiments revealed that the modified electrode can be successfully applied for the accurate determination of Aza in pharmaceutical preparations. - Highlights: • A novel electrochemical sensing platform based on graphene nanosheets decorated with Ag nanoparticles was constructed for determination of Azathioprine. • The prepared modified electrode showed an efficient catalytic role toward the electro-reduction of Azathioprine. • The prepared modified electrode shows a wide linear dynamic range and a nanomolar detection limit for Azathioprine. • The modification procedure provides a

  2. Electrochemistry of moexipril: experimental and computational approach and voltammetric determination.

    Science.gov (United States)

    Taşdemir, Hüdai I; Kiliç, E

    2014-09-01

    The electrochemistry of moexipril (MOE) was studied by electrochemical methods with theoretical calculations performed at B3LYP/6-31 + G (d)//AM1. Cyclic voltammetric studies were carried out based on a reversible and adsorption-controlled reduction peak at -1.35 V on a hanging mercury drop electrode (HMDE). Concurrently irreversible diffusion-controlled oxidation peak at 1.15 V on glassy carbon electrode (GCE) was also employed. Potential values are according to Ag/AgCI, (3.0 M KCI) and measurements were performed in Britton-Robinson buffer of pH 5.5. Tentative electrode mechanisms were proposed according to experimental results and ab-initio calculations. Square-wave adsorptive stripping voltammetric methods have been developed and validated for quantification of MOE in pharmaceutical preparations. Linear working range was established as 0.03-1.35 microM for HMDE and 0.2-20.0 microM for GCE. Limit of quantification (LOQ) was calculated to be 0.032 and 0.47 microM for HMDE and GCE, respectively. Methods were successfully applied to assay the drug in tablets by calibration and standard addition methods with good recoveries between 97.1% and 106.2% having relative standard deviation less than 10%.

  3. Linear sweep voltammetric studies on the supramolecular complex of alizarin red S with lysozyme and determination of lysozyme

    Indian Academy of Sciences (India)

    Wei Sun; Na Zhao; Xueliang Niu; Yan Wang; Kui Jiao

    2009-03-01

    An electrochemical method for the determination of lysozyme (LYS) based on its interaction with alizarin red S (ARS) was established by linear sweep voltammetry in this paper. The electrochemical behaviour of ARS with LYS was investigated on a dropping mercury working electrode in 0.2 mol/L pH 4.8 Britton-Robinson (B-R) buffer solution. ARS showed a sensitive second order derivative linear sweep voltammetric reductive peak at -0.42 V (vs SCE). After the addition of LYS, the reductive peak current of ARS decreased without the shift of the reductive peak potential and no new waves appeared, which was due to the formation of a supramolecular complex of ARS with LYS in the solution. The stoichiometry of the ARS-LYS complex was further calculated by the electrochemical data with the results of the binding ratio as 3 : 1 and the binding constant as 2.82 × 1014. Under the selected conditions, the decrease of the second order derivative linear sweep voltammetric reductive peak current of ARS was in proportion to the LYS concentration in the range from 0.8 to 35.0 mg/L and the detection limit of LYS was calculated as 0.52 mg/L (3). Different kinds of LYS samples were detected satisfactorily with this method.

  4. Large amplitude Fourier transformed AC voltammetric investigation of the active state electrochemistry of a copper/aqueous base interface and implications for electrocatalysis.

    Science.gov (United States)

    Shiddiky, Muhammad J A; O'Mullane, Anthony P; Zhang, Jie; Burke, L Declan; Bond, Alan M

    2011-08-16

    The higher harmonic components available from large-amplitude Fourier-transformed alternating current (FT-ac) voltammetry enable the surface active state of a copper electrode in basic media to be probed in much more detail than possible with previously used dc methods. In particular, the absence of capacitance background current allows low-level Faradaic current contributions of fast electron-transfer processes to be detected; these are usually completely undetectable under conditions of dc cyclic voltammetry. Under high harmonic FT-ac voltammetric conditions, copper electrodes exhibit well-defined and reversible premonolayer oxidation responses at potentials within the double layer region in basic 1.0 M NaOH media. This process is attributed to oxidation of copper adatoms (Cu*) of low bulk metal lattice coordination numbers to surface-bonded, reactive hydrated oxide species. Of further interest is the observation that cathodic polarization in 1.0 M NaOH significantly enhances the current detected in each of the fundamental to sixth FT-ac harmonic components in the Cu*/Cu hydrous oxide electron-transfer process which enables the underlying electron transfer processes in the higher harmonics to be studied under conditions where the dc capacitance response is suppressed; the results support the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis. The underlying quasi-reversible interfacial Cu*/Cu hydrous oxide process present under these conditions is shown to mediate the reduction of nitrate at a copper electrode, while the mediator for the hydrazine oxidation reaction appears to involve a different mediator or active state redox couple. Use of FT-ac voltammetry offers prospects for new insights into the nature of active sites and electrocatalysis at the electrode/solution interface of Group 11 metals in aqueous media.

  5. Nonlinear response of superconductors to alternating fields and currents

    Energy Technology Data Exchange (ETDEWEB)

    McDonald, Jason [Iowa State Univ., Ames, IA (United States)

    1997-10-08

    This report discusses the following topics on superconductivity: nonlinearities in hard superconductors such as surface impedance of a type II superconductimg half space and harmonic generation and intermodulation due to alternating transport currents; and nonlinearities in superconducting weak links such as harmonic generation by a long Josephson Junction in a superconducting slab.

  6. Ion-transfer voltammetric determination of the beta-blocker propranolol in a physiological matrix at silicon membrane-based liquid|liquid microinterface arrays.

    Science.gov (United States)

    Collins, Courtney J; Arrigan, Damien W M

    2009-03-15

    In this work, the ion-transfer voltammetric detection of the protonated beta-blocker propranolol in artificial saliva is presented. Cyclic voltammetry, differential pulse voltammetry, and differential pulse stripping voltammetry (DPSV) were employed in the detection of the cationic drug based on ion-transfer voltammetry across arrays of microinterfaces between artificial saliva and an organogel phase. It was found that the artificial saliva matrix decreased the available potential window for ion-transfer voltammetry at this liquid|liquid interface but transfer of protonated propranolol was still achieved. The DPSV method employed a preconditioning step as well as a preconcentration step followed by analytical signal generation based on the back-transfer of the drug across the array of microinterfaces. The DPSV peak current response was linear with drug concentration in the artificial saliva matrix over the concentration range of 0.05-1 microM (i(p) = -8.13 (nA microM(-1))(concentration) + 0.07 (nA), R = 0.9929, n = 7), and the calculated detection limit (3s(b)) was 0.02 microM. These results demonstrate that DPSV at arrays of liquid|liquid microinterfaces is a viable analytical approach for pharmaceutical determinations in biomimetic matrixes.

  7. An electrochemical sensor based on poly (solochrome dark blue) film coated electrode for the determination of dopamine and simultaneous separation in the presence of uric acid and ascorbic acid: a voltammetric method.

    Science.gov (United States)

    Reddaiah, Kasetty; Reddy, Matti Mohan; Raghu, Pamula; Reddy, Tukiakula Madhusudana

    2013-06-01

    In this paper, the carbon paste electrode (CPE) was modified with poly- Solochrome dark blue (poly-SDB), through polymerization process, and it was used for the sensitive and selective determination of dopamine (DA). The simultaneous determination of Dopamine (DA) Ascorbic acid (AA) and Uric acid (UA) in 0.1 M Phosphate buffer solution (PBS) of pH 6.0 was carried out by employing differential pulse voltammetric technique (DPV). The effect of pH, concentration, scan rate, accumulation time, repetability and reproducibility of DA was studied at poly-SDB film modified electrode. The poly-SDBCPE exhibited a strong electrocatalytic action toward the oxidation of DA, AA and UA. The overlapping voltammetric response of biomolecules separated in to three well defined peaks with lower oxidation potential and significant increase in the anodic peak currents in the presence of poly-SDBCPE was achieved. The results showed a good sensitivity, selectivity and high reproducibility of electro synthesized polymer electrode. The limit of detection, limit of quantification and correlation coefficient of DA at poly-SDBCPE was 0.8 μM, 2.8 μM and 0.99765 respectively. The effect of interference was studied by DPV technique. The developed modified electrode was used for the analysis of DA in pharmaceutical formulations with satisfactory results. The interfacial electron transfer behavior of DA was studied by electrochemical impedance spectroscopy (EIS) and results showed that the charge transfer rate was enhanced at poly- SDBCPE, when compared with bare CPE, glassy carbon electrode (GCE) and platinum electrode (Pt).

  8. Host response to nontuberculous mycobacterial infections of current clinical importance.

    Science.gov (United States)

    Orme, Ian M; Ordway, Diane J

    2014-09-01

    The nontuberculous mycobacteria are a large group of acid-fast bacteria that are very widely distributed in the environment. While Mycobacterium avium was once regarded as innocuous, its high frequency as a cause of disseminated disease in HIV-positive individuals illustrated its potential as a pathogen. Much more recently, there is growing evidence that the incidence of M. avium and related nontuberculous species is increasing in immunocompetent individuals. The same has been observed for M. abscessus infections, which are very difficult to treat; accordingly, this review focuses primarily on these two important pathogens. Like the host response to M. tuberculosis infections, the host response to these infections is of the TH1 type but there are some subtle and as-yet-unexplained differences.

  9. Social Responsability, Depolitisation and the Current Civil Service in Yugoslavia

    Directory of Open Access Journals (Sweden)

    Zelijko SEVIC

    1999-01-01

    Full Text Available This paper looks at the broad theoretical issues of social responsibility vis-a-vis depolitisation in Contemporary Civil Service Systems. A clear distinction has been established between the existing models of Public Administration from a politicoadministrative perspective. The paper argues for larger involvement of non-governmental organisations (NGOs in the national policy-making process, and for the promotion of civil education amongst citizens. It also argues for more appropriate and socially responsible Public Administration, capable of meeting the increasing demand from citizens and a modern society. Finally, different theoretical ideas developed in the first part of the paper are applied to the Federal Republic of Yugoslavia's Civil Service(s in a case study.

  10. XCII. A Low-Cost Voltammetric Signal Generator for the Electroanalytical Chemistry Laboratory

    Science.gov (United States)

    Ewing, Galen W., Ed

    1977-01-01

    Describes the construction of a versatile signal generator suitable for use in cyclic voltammetric experiments, which can also be adapted to a conventional dc polarograph by replacing its ramp source. (MLH)

  11. Discrimination of Rice with Different Pretreatment Methods by Using a Voltammetric Electronic Tongue

    OpenAIRE

    2015-01-01

    In this study, an application of a voltammetric electronic tongue for discrimination and prediction of different varieties of rice was investigated. Different pretreatment methods were selected, which were subsequently used for the discrimination of different varieties of rice and prediction of unknown rice samples. To this aim, a voltammetric array of sensors based on metallic electrodes was used as the sensing part. The different samples were analyzed by cyclic voltammetry with two sample-p...

  12. Electrooxidative decarboxylation of vanillylmandelic acid: voltammetric differentiation between the structurally related compounds homovanillic acid and vanillylmandelic acid.

    Science.gov (United States)

    Li, Qian; Batchelor-McAuley, Christopher; Compton, Richard G

    2010-07-29

    Vanillylmandelic acid (VMA) and homovanillic acid (HVA) are the major end products of catecholamine metabolism. Abnoramally high levels in both plasma and urine may be indicative of a number of diseases including neuroblastoma and phaeochromocytoma. Commonly the VMA:HVA ratio is used as a disease marker, so that any measurement techniques need to be able to differentiate between these two structurally similar compounds. Electrochemistry is often limited in selectivity due to many organic molecules being oxidized or reduced at similar potentials. This work investigates the electrochemical oxidation mechanism of VMA at an edge-plane pyrolytic graphite electrode and highlights how, although structurally similar to HVA, their voltammetric responses may be differentiated through appropriate selection of the electrode material. The oxidation of VMA exhibits two clear peaks and the mechanism is shown to proceed through the decarboxylation of VMA to form vanillin, which is further oxidized resulting in the second peak. Modification of the electrode with a porous layer of multiwalled carbon nanotubes so as to change the mass transport to that of a thin layer system causes the voltammetric resolution between the two species to be enhanced. Differential pulse voltammetry is used to measure the limits of detection for VMA on an edge-plane pyrolytic graphite electrode and on commercially available multiwalled carbon nanotube screen printed electrode, with limits of detection of 1.7 and 1.0 microM, respectively. These limits of detection are well within the range of sensitivity required for clinical sample measurement.

  13. Response of Mycorrhizal Diversity to Current Climatic Changes

    Directory of Open Access Journals (Sweden)

    Stephen E. Williams

    2011-01-01

    Full Text Available Form and function of mycorrhizas as well as tracing the presence of the mycorrhizal fungi through the geological time scale are herein first addressed. Then mycorrhizas and plant fitness, succession, mycorrhizas and ecosystem function, and mycorrhizal resiliency are introduced. From this, four hypotheses are drawn: (1 mycorrhizal diversity evolved in response to changes in Global Climate Change (GCC environmental drivers, (2 mycorrhizal diversity will be modified by present changes in GCC environmental drivers, (3 mycorrhizal changes in response to ecological drivers of GCC will in turn modify plant, community, and ecosystem responses to the same, and (4 Mycorrhizas will continue to evolve in response to present and future changes in GCC factors. The drivers of climate change examined here are: CO2 enrichment, temperature rise, altered precipitation, increased N-deposition, habitat fragmentation, and biotic invasion increase. These impact the soil-rhizosphere, plant and fungal physiology and/or ecosystem(s directly and indirectly. Direct effects include changes in resource availability and change in distribution of mycorrhizas. Indirect effects include changes in below ground allocation of C to roots and changes in plant species distribution. GCC ecological drivers have been partitioned into four putative time frames: (1 Immediate (1–2 years impacts, associated with ecosystem fragmentation and habitat loss realized through loss of plant-hosts and disturbance of the soil; (2 Short-term (3–10 year impacts, resultant of biotic invasions of exotic mycorrhizal fungi, plants and pests, diseases and other abiotic perturbations; (3 Intermediate-term (11–20 year impacts, of cumulative and additive effects of increased N (and S deposition, soil acidification and other pollutants; and (4 Long-term (21–50+ year impacts, where increased temperatures and CO2 will destabilize global rainfall patterns, soil properties and plant ecosystem resilience. Due

  14. Study of toroidal current penetration during current ramp in JIPP T-IIU with fast response Zeeman polarimeter

    Energy Technology Data Exchange (ETDEWEB)

    Kuramoto, H.; Hiraki, N. [Kyushu Inst. of Tech., Kitakyushu, Fukuoka (Japan); Toi, K. [and others

    1997-01-01

    The toroidal current penetration is studied in current ramp experiments of the JIPP T-IIU tokamak. The poloidal magnetic field profile in the peripheral region of a plasma (0.5 {<=} {rho} {<=} 1.0) has been measured directly with a newly developed fast response Zeeman polarimeter. The experimental results indicate that an obvious skin effect of toroidal current density is clearly observed during both the current ramp-up and ramp-down experiments. The experimentally obtained toroidal current density profiles are well described by the profiles calculated on the assumption of the neoclassical electrical conductivity. Quasi-linear {Delta}`-analysis of tearing modes for the measured current density profile is consistent with time behaviour of coherent MHD modes such as m=4/n=1 or m=3/n=1 (m: poloidal mode number, n: toroidal mode number) often observed during the current ramp-up phase. The effect of these MHD modes on current penetration during the current ramp-up discharges is studied. (author)

  15. Review of current neutron detection systems for emergency response

    Science.gov (United States)

    Mukhopadhyay, Sanjoy; Maurer, Richard; Guss, Paul; Kruschwitz, Craig

    2014-09-01

    Neutron detectors are used in a myriad of applications—from safeguarding special nuclear materials (SNM) to determining lattice spacing in soft materials. The transformational changes taking place in neutron detection and imaging techniques in the last few years are largely being driven by the global shortage of helium-3 (3He). This article reviews the status of neutron sensors used specifically for SNM detection in radiological emergency response. These neutron detectors must be highly efficient, be rugged, have fast electronics to measure neutron multiplicity, and be capable of measuring direction of the neutron sources and possibly image them with high spatial resolution. Neutron detection is an indirect physical process: neutrons react with nuclei in materials to initiate the release of one or more charged particles that produce electric signals that can be processed by the detection system. Therefore, neutron detection requires conversion materials as active elements of the detection system; these materials may include boron-10 (10B), lithium-6 (6Li), and gadollinium-157 (157Gd), to name a few, but the number of materials available for neutron detection is limited. However, in recent years, pulse-shape-discriminating plastic scintillators, scintillators made of helium-4 (4He) under high pressure, pillar and trench semiconductor diodes, and exotic semiconductor neutron detectors made from uranium oxide and other materials have widely expanded the parameter space in neutron detection methodology. In this article we will pay special attention to semiconductor-based neutron sensors. Modern microfabricated nanotubes covered inside with neutron converter materials and with very high aspect ratios for better charge transport will be discussed.

  16. Voltammetric and mathematical evidence for dual transport mediation of serotonin clearance in vivo.

    Science.gov (United States)

    Wood, Kevin M; Zeqja, Anisa; Nijhout, H Frederik; Reed, Michael C; Best, Janet; Hashemi, Parastoo

    2014-08-01

    The neurotransmitter serotonin underlies many of the brain's functions. Understanding serotonin neurochemistry is important for improving treatments for neuropsychiatric disorders such as depression. Antidepressants commonly target serotonin clearance via serotonin transporters and have variable clinical effects. Adjunctive therapies, targeting other systems including serotonin autoreceptors, also vary clinically and carry adverse consequences. Fast scan cyclic voltammetry is particularly well suited for studying antidepressant effects on serotonin clearance and autoreceptors by providing real-time chemical information on serotonin kinetics in vivo. However, the complex nature of in vivo serotonin responses makes it difficult to interpret experimental data with established kinetic models. Here, we electrically stimulated the mouse medial forebrain bundle to provoke and detect terminal serotonin in the substantia nigra reticulata. In response to medial forebrain bundle stimulation we found three dynamically distinct serotonin signals. To interpret these signals we developed a computational model that supports two independent serotonin reuptake mechanisms (high affinity, low efficiency reuptake mechanism, and low affinity, high efficiency reuptake system) and bolsters an important inhibitory role for the serotonin autoreceptors. Our data and analysis, afforded by the powerful combination of voltammetric and theoretical methods, gives new understanding of the chemical heterogeneity of serotonin dynamics in the brain. This diverse serotonergic matrix likely contributes to clinical variability of antidepressants. © 2014 International Society for Neurochemistry.

  17. Voltammetric Electronic Tongue for Discrimination of Milk Adulterated with Urea, Formaldehyde and Melamine

    Directory of Open Access Journals (Sweden)

    Lígia Bueno

    2014-11-01

    Full Text Available We report the fabrication of a voltammetric electronic tongue for the detection and discrimination of harmful substances intentionally added to milk to increase its shelf life or imitate protein content. The electronic tongue consisted of three working electrodes composed of platinum, gold, and copper. The measurement principles involved the extraction of information from cyclic voltammograms recorded in unadulterated and adulterated milk. The extracted data were analysed using principal component analysis and the contaminants were successfully differentiated from one another in a score plot. Electrochemical quartz crystal microbalance analysis was used to investigate the electrode response in order to understand the mechanism by which the tongue could discriminate between the samples. It was found that the electrochemical formation and dissolution of platinum and gold oxides, and the reduction of a copper-melamine ionic pair formed at the surface of the copper electrode were the main factors responsible for discrimination. In addition, the electronic tongue was capable of identifying adulterations in different types of milk (whole, skimmed, and semi-skimmed and milk from different brands. The lowest concentration of adulterant that resulted in a good discrimination was 10.0, 4.16, and 0.95 mmol·L−1 for formaldehyde, urea, and melamine, respectively.

  18. Electrochemical studies of 1,5-dihydroxynaphthalene as substrate for voltammetric enzyme immunoassay

    Institute of Scientific and Technical Information of China (English)

    JIAO Kui; YAO Hong; XU Jin; ZHANG Shusheng

    2004-01-01

    A sensitive voltammetric enzyme immunoanalytical method is described for assay of horseradish peroxidase (HRP), labelled-HRP and antigen:antibody:labelled-HRP conjugate (Ag︰AB︰IgG-HRP) using 1,5-dihydroxynaphthalene (1,5-DHN) as substrate. 1,5-DHN is an electrochemical inactive substance, but it may be oxidized by O2 in air to 5-hydroxy-1,4-naphtho- quinone in basic solution, which produces a well-defined voltammetric reduction peak. After adding H2O2 and HRP, HRP catalyzes H2O2 oxidizing 5-hydroxy-1,4-naphthoquinone to 3-hydroxyphthalic acid, leading to the decrease of the voltammetric reduction peak, with which the activity of HRP and the labelled-HRP, further the antigen and antibody may be determined. The mechanism of this voltammetric enzyme-linked immunoassay system is different from the previous reports, in which there are no voltammetric reduction peaks before the addition of H2O2 and HRP, and the reduction peaks appear after the addition of H2O2 and HRP. The height of the voltammetric peak is directly proportional to the concentration of HRP in the previous systems, while the decrease of the voltammetric peak is linear with the concentration of HRP in this system. This new electrochemical method is combined with an indirect enzyme immunoassay using direct antigen-coating format for the detection of the purified tobacco mosaic virus (TMV) with a linear range from 25.0 to 340.0 ng/mL, and a detection limit 25.0 ng/mL.

  19. Relative reactivity of dihydropyridine derivatives to electrogenerated superoxide ion in DMSO solutions: a voltammetric approach.

    Science.gov (United States)

    Oriz, María Eugenia; Núñez-Vergara, Luis Joaquin; Squella, Juan Arturo

    2003-02-01

    To evaluate the reaction of a large series of pharmacologically significant 1,4-dihydropyridine (1,4-DHP) compounds with superoxide (O2.-) in dimethylsulfoxide using differential pulse voltammetry and controlled potential electrolysis. Differential pulse voltammetry was used to track the consumption of O2.-, and controlled potential electrolysis was used to electrogenerate O2.-. With the addition of 1,4-DHP, the oxidation peak current of O2.- decreased concentration dependently, suggesting that 1,4-DHP reacts with O2.-, that is, 1,4-DHP scavenges O2.- in dimethylsulfoxide. very easy and direct voltammetric procedure to study the relative reactivity of different 1,4-DHP with O2.- is proposed. Using the proposed method we have found that all commercial 1,4-DHP reacts with O2.-. The following order of rates was obtained: felodipine > or = vitamin E > isradipine > nimodipine > furnidipine > nitrendipine > nisoldipine > nifedipine. Furthermore, it was demonstrated that the hydrogen at the N-position of 1,4-DHP compounds could be released as a proton in the presence of O2.-, thus the electrogenerated O2.- worked as a proton acceptor to 1,4-DHP.

  20. Synthesis, characterization and cyclic voltammetric study of copper(II) and nickel(II) polymer chelates.

    Science.gov (United States)

    Azmeera, Venkanna; Rastogi, Pankaj Kumar; Adhikary, Pubali; Ganesan, Vellaichamy; Krishnamoorthi, S

    2014-09-22

    Graft copolymers based on dextran (Dx) and 2-acrylamido-2-methyl-1-propane sulphonic acid (AMPS) were synthesized by free radical initiated solution polymerization technique using ceric ammonium nitrate as initiator. These graft copolymers were used to prepare Cu(II) and Ni(II) chelates by reactions with Cu(II) and Ni(II) metal ions respectively. Graft copolymer and metal chelates were characterized by elemental analysis, intrinsic viscosity, FT-IR, scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). Elemental analysis, intrinsic viscosity and FT-IR studies revealed the incorporation of metal ions to form metal chelates. SEM studies showed the change in morphology due to metal incorporation. From AFM studies it was observed that there was increase in Root mean square (RMS) roughness values in case of metal complexes. Metal chelates were observed to be thermally more stable than graft copolymer from TGA. UV-vis spectroscopy study revealed increase in absorbance values and cyclic voltammetric (CV) studies showed more than tenfold increase in redox current due to formation of Cu(II) and Ni(II) metal chelates. The binding constants of each complex determined by using UV-visible spectroscopy revealed that Cu(II) has more binding ability than Ni(II).

  1. Stripping Voltammetric Determination of Analgesics in Their Pharmaceuticals Using Nano-Riboflavin-Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Gopalakrishnan Gopu

    2011-01-01

    Full Text Available Cyclic voltammetric behaviors of three analgesics, acetaminophen (AAP, acetylsalicylic acid (ASA, and dipyrone (DP, were studied using nano-riboflavin-modified glassy carbon electrode. One well-defined oxidation peak each for AAP and ASA and three oxidation peaks for DP were observed. The influence of pH, scan rate, and concentration reveals irreversible diffusion controlled reaction. The SEM analysis confirmed good accumulation of the drugs on the electrode surface. Calibration was made under the maximum peak current conditions. The concentration range studied for the determination of drugs was 0.02 to 0.4 μg mL−1 for AAP and ASA and 0.025 to 0.4 μg mL−1 for DP. The lower limit of detection observed for AAP, ASA, and DP was 0.016, 0.007 μg mL−1, and 0.013 μg mL−1, respectively. The suitability of the method for the determination of these analgesics in pharmaceutical preparations and urine samples was also ascertained.

  2. Thrombin-Binding Aptamer Quadruplex Formation: AFM and Voltammetric Characterization

    Directory of Open Access Journals (Sweden)

    Victor Constantin Diculescu

    2010-01-01

    Full Text Available The adsorption and the redox behaviour of thrombin-binding aptamer (TBA and extended TBA (eTBA were studied using atomic force microscopy and voltammetry at highly oriented pyrolytic graphite and glassy carbon. The different adsorption patterns and degree of surface coverage were correlated with the sequence base composition, presence/absence of K+, and voltammetric behaviour of TBA and eTBA. In the presence of K+, only a few single-stranded sequences present adsorption, while the majority of the molecules forms stable and rigid quadruplexes with no adsorption. Both TBA and eTBA are oxidized and the only anodic peak corresponds to guanine oxidation. Upon addition of K+ ions, TBA and eTBA fold into a quadruplex, causing the decrease of guanine oxidation peak and occurrence of a new peak at a higher potential due to the oxidation of G-quartets. The higher oxidation potential of G-quartets is due to the greater difficulty of electron transfer from the inside of the quadruplex to the electrode surface than electron transfer from the more flexible single strands.

  3. Voltammetric Determination of Ni and Co in Water Samples

    Science.gov (United States)

    Herrera-Melian, Jose Alberto; Dona-Rodriguez, Jose Miguel; Hernandez-Brito, Joaquin; Perez Pena, Jesus

    1997-12-01

    Stripping voltammetry has attracted considerable attention for the determination of trace and ultratrace metals. This is mainly due to its high sensitivity and low cost of instrumentation. In adsorptive stripping voltammetry an organometallic complex is formed by the addition of a suitable ligand to the sample. The complex is adsorbed onto the Hg-drop by the application of the proper adsorption potential (more positive than E1/2) and solution stirring. After an adsorption period a cathodic (negative going) potential scan is applied and the metal concentration is calculated by the standard addition method. Nickel is found in natural waters at nM levels and is closely related with phosphates and silicates. Cobalt is a component of vitamin B12 and occurs in natural waters at concentration about 0.1 nM. We propose the voltammetric analysis of these elements by adsorptive stripping voltammetry as an introductory laboratory experiment for advanced chemistry or for chemical or environmental engineering students. The experiment has been proven to be very suitable for the laboratory part of the instrumental analysis course at the University of Las Palmas de Gran Canaria (Spain). In general, about 70% of the students have obtained good agreement (less than 10% of difference) between their results and the expected ones. Two hours is enough for the overall instrumental performance and the preparation of Ni and Co standards.

  4. Voltammetric Determination of Paraquat Using Graphite Pencil Electrode Modified with Doped Polypyrrole

    CERN Document Server

    Sayyahmanesh, Maryam; Meibodi, Azam S Emami; Ahooyi, Taha Mohseni

    2016-01-01

    Recognition and determination of paraquat (PQ) using graphite pencil electrode (GPE) modified with polypyrrole (Ppy) doped with Eriochrome blue-black B (EBB) is reported. To that end, a thin film of Ppy was deposited onto the electrode surface by electropolymerization in the presence of a functional doping ion, EBB. The Ppy/EBB-coated electrode was templated by PQ ion and then the performance of the molecularly imprinted EBB/Ppy/GPE was evaluated by voltammetric technique. The prepared electrode exhibited considerable increase in electroactivity of the sensor toward this herbicide compared to the non-imprinted electrode. To enhance the detection capability of the prepared system, the factors controlling its response were investigated and optimized using differential pulse voltammetry. The proposed analytical procedure was proved to be applicable in the concentration range of 5 to 50 {\\mu}M (R^2 = 0.9939) and detection limit of (3{\\sigma}) 0.22 {\\mu}M. Ultimately, the proposed analytical methodology was applie...

  5. Application of graphene for preconcentration and highly sensitive stripping voltammetric analysis of organophosphate pesticide

    Energy Technology Data Exchange (ETDEWEB)

    Wu Shuo, E-mail: wushuo@dlut.edu.cn [School of Chemistry, Dalian University of Technology, Dalian 116023 (China); Lan Xiaoqin; Cui Lijun; Zhang Lihui; Tao Shengyang; Wang Hainan; Han Mei; Liu Zhiguang; Meng Changgong [School of Chemistry, Dalian University of Technology, Dalian 116023 (China)

    2011-08-12

    Highlights: {yields} An electrochemical sensor is fabricated based on {beta}-CD dispersed graphene. {yields} The sensor could selectively detect organophosphate pesticide with high sensitivity. {yields} The {beta}-CD dispersed graphene owns large adsorption capacity for MP and superconductivity. {yields} The {beta}-CD dispersed graphene is superior to most of the porous sorbents ever known. - Abstract: Electrochemical reduced {beta}-cyclodextrin dispersed graphene ({beta}-CD-graphene) was developed as a sorbent for the preconcentration and electrochemical sensing of methyl parathion (MP), a representative nitroaromatic organophosphate pesticide with good redox activity. Benefited from the ultra-large surface area, large delocalized {pi}-electron system and the superconductivity of {beta}-CD-graphene, large amount of MP could be extracted on {beta}-CD-graphene modified electrode via strong {pi}-{pi} interaction and exhibited fast accumulation and electron transfer rate. Combined with differential pulse voltammetric analysis, the sensor shows ultra-high sensitivity, good selectivity and fast response. The limit of detection of 0.05 ppb is more than 10 times lower than those obtained from other sorbent based sensors. The method may open up a new possibility for the widespread use of electrochemical sensors for monitoring of ultra-trace OPs.

  6. Dual-nanomaterial based electrode for voltammetric stripping of trace Fe(II) in coastal waters.

    Science.gov (United States)

    Lin, Mingyue; Pan, Dawei; Zhu, Yun; Hu, Xueping; Han, Haitao; Wang, ChenChen

    2016-07-01

    In this work, a dual-nanomaterial based electrode was established for selective and sensitive detection of trace Fe(II) in the presence of complexing agent (2,2'-bipyridyl). Titanium carbide nanoparticles (TiCNPs) were used as the growth-template for the formation of three-dimensional platinum nanoflowers (PtNFs) due to their unique cubic structures. Nafion was employed as the conducting matrix to help TiCNPs better attached onto the surface of the electrode and slow down the crystal rate of PtNFs during electrodeposition, which resulted in flower structure and more active surface of PtNFs. Taking advantage of synergistic effects of TiCNPs and Nafion as well as the catalytic amplifying effect of PtNFs, the excellent anodic signal responses for the voltammetric stripping determination of Fe(II) were obtained. The linear range of Fe(II) on this dual-nanomaterial based electrode was from 1nmolL(-1) to 6μmolL(-1) with the lowest detectable concentration of 0.1nmolL(-1) and a detection limit of 0.03nmolL(-1). Additionally, the effect of several experimental parameters, such as concentration and pH value of buffer solution, concentration of modifier and ligand, deposition potential and time of electrochemical determination, and scan rate were studied for analytical applications. The fabricated sensor had been successfully applied for the sensitive determination of trace Fe(II) in coastal waters.

  7. Voltammetric Detection of Urea on an Ag-Modified Zeolite-Expanded Graphite-Epoxy Composite Electrode

    Directory of Open Access Journals (Sweden)

    Joop Schoonman

    2008-09-01

    Full Text Available In this paper, a modified expanded graphite composite electrode based on natural zeolitic volcanic tuff modified with silver (EG-Ag-Z-Epoxy was developed. Cyclic voltammetry measurements revealed a reasonably fast electron transfer and a good stability of the electrode in 0.1 M NaOH supporting electrolyte. This modified electrode exhibited moderate electrocatalytic effect towards urea oxidation, allowing its determination in aqueous solution. The linear dependence of the current versus urea concentration was reached using square-wave voltammetry in the concentrations range of urea between 0.2 to 1.4 mM, with a relatively low limit of detection of 0.05 mM. A moderate enhancement of electroanalytical sensitivity for the determination of urea at EG-Ag-Z-Epoxy electrode was reached by applying a chemical preconcentration step prior to voltammetric/amperometric quantification.

  8. Principal component analysis of Birkeland currents determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment

    Science.gov (United States)

    Milan, S. E.; Carter, J. A.; Korth, H.; Anderson, B. J.

    2015-12-01

    Principal component analysis is performed on Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. Principal component analysis (PCA) identifies the patterns in the FACs that respond coherently to different aspects of geomagnetic activity. The regions 1 and 2 current system is shown to be the most reproducible feature of the currents, followed by cusp currents associated with magnetic tension forces on newly reconnected field lines. The cusp currents are strongly modulated by season, indicating that their strength is regulated by the ionospheric conductance at the foot of the field lines. PCA does not identify a pattern that is clearly characteristic of a substorm current wedge. Rather, a superposed epoch analysis of the currents associated with substorms demonstrates that there is not a single mode of response, but a complicated and subtle mixture of different patterns.

  9. Principle Component Analysis of Birkeland Currents Determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment

    Science.gov (United States)

    Milan, S. E.; Carter, J. A.; Korth, H.; Anderson, B. J.

    2015-12-01

    Principle Component Analysis is performed on northern and southern hemisphere Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). PCA identifies the patterns in the FACs that respond coherently to different aspects of geomagnetic activity. The region 1 and 2 current system is shown to be the most reproducible feature of the currents, followed by cusp currents associated with magnetic tension forces on newly-reconnected field lines. The cusp currents are strongly modulated by season, indicating that their strength is regulated by the ionospheric conductance at the foot of the field lines. PCA does not identify a pattern that is clearly characteristic of a substorm current wedge. Rather, a superposed epoch analysis of the currents associated with substorms demonstrates that there is not a single mode of response, but a complicated and subtle mixture of different patterns. Other interhemispheric differences are discussed.

  10. Principal component analysis of Birkeland currents determined by the Active Magnetosphere and Planetary Electrodynamics Response Experiment

    CERN Document Server

    Milan, S E; Korth, H; Anderson, B J

    2016-01-01

    Principal component analysis is performed on Birkeland or field-aligned current (FAC) measurements from the Active Magnetosphere and Planetary Electrodynamics Response Experiment. Principal component analysis (PCA) identifies the patterns in the FACs that respond coherently to different aspects of geomagnetic activity. The regions 1 and 2 current system is shown to be the most reproducible feature of the currents, followed by cusp currents associated with magnetic tension forces on newly reconnected field lines. The cusp currents are strongly modulated by season, indicating that their strength is regulated by the ionospheric conductance at the foot of the field lines. PCA does not identify a pattern that is clearly characteristic of a substorm current wedge. Rather, a superposed epoch analysis of the currents associated with substorms demonstrates that there is not a single mode of response, but a complicated and subtle mixture of different patterns.

  11. NONLINEAR DYNAMICS RESPONSE OF CASING PIPE UNDER COMBINED WAVE-CURRENT

    Institute of Scientific and Technical Information of China (English)

    TANG You-gang; GU Jia-yang; ZUO Jian-li; MIN Jian-qin

    2005-01-01

    The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison's nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin's method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160 m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.

  12. Thick-film voltammetric pH-sensors with internal indicator and reference species

    DEFF Research Database (Denmark)

    Musa, Arnaud Emmanuel; Alonso-Lomillo, María Asunción; del Campo, Francisco Javier

    2012-01-01

    The following paper describes the development of a screen-printed voltammetric pH-sensor based on graphite electrodes incorporating both internal indicator (i.e., phenanthraquinone) and reference species (i.e., dimethylferrocene). The key advantages of this type of system stem from its simplicity......, low cost and ease of fabrication. More importantly, as opposed to conventional voltammetric systems where the height of the voltammetric peaks is taken into account to quantify the amount of a species of interest, here, the difference between the peak potential of the indicator species and the peak...... potential of the reference species is used. Thus, this measurement principle makes the electrochemical system presented here less dependent on the potential of the reference electrode (RE), as is often the case in other electrochemical systems. The developed system displays very promising performances...

  13. Researching corporate social responsibility in the Middle East - the current state and future directions

    OpenAIRE

    Taposh, Roy; Ahmed, Al-Abdin; Nicholson, John

    2017-01-01

    Corporate social responsibility (CSR) has the potential to yield economic and social value in the Middle East (ME), especially given the current high environmental flux in the region. Although much scholarly has been paid to CSR issues, a key question remains about how to operate responsibly in the ME, particularly since institutional environments and stakeholders’ needs vary across ME states. The purpose of this paper is to provide a systematic review of the current state of CSR in the ME. W...

  14. Is transcranial direct current stimulation a potential method for improving response inhibition?

    Science.gov (United States)

    Kwon, Yong Hyun; Kwon, Jung Won

    2013-04-15

    Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments. This study used a stop-signal task to determine whether transcranial direct-current stimulation over the pre-supplementary motor area alters the reaction time in motor inhibition. Forty healthy subjects were recruited for this study and were randomly assigned to either the transcranial direct-current stimulation condition or a sham-transcranial direct-current stimulation condition. All subjects consecutively performed the stop-signal task before, during, and after the delivery of anodal transcranial direct-current stimulation over the pre-supplementary motor area (pre-transcranial direct-current stimulation phase, transcranial direct-current stimulation phase, and post-transcranial direct-current stimulation phase). Compared to the sham condition, there were significant reductions in the stop-signal processing times during and after transcranial direct-current stimulation, and change times were significantly greater in the transcranial direct-current stimulation condition. There was no significant change in go processing-times during or after transcranial direct-current stimulation in either condition. Anodal transcranial direct-current stimulation was feasibly coupled to an interactive improvement in inhibitory control. This coupling led to a decrease in the stop-signal process time required for the appropriate responses between motor execution and inhibition. However, there was no transcranial direct-current stimulation effect on the no-signal reaction time during the stop-signal task. Transcranial direct-current stimulation can adjust certain behaviors, and it could be a useful clinical intervention for patients who have difficulties with response inhibition.

  15. Is transcranial direct current stimulation a potential method for improving response inhibition?

    Institute of Scientific and Technical Information of China (English)

    Yong Hyun Kwon; Jung Won Kwon

    2013-01-01

    Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments. This study used a stop-signal task to determine whether transcranial direct-current stimulation over the pre-supplementary motor area alters the reaction time in motor inhibition. Forty healthy subjects were recruited for this study and were randomly assigned to either the transcranial direct-current stimulation condition or a sham-transcranial direct-current stimulation condition. All subjects consecutively performed the stop-signal task before, during, and after the delivery of anodal transcranial direct-current stimulation over the pre-supplementary motor area (pre-transcranial direct-current stimulation phase, transcranial direct-current stimulation phase, and post-transcranial direct-current stimulation phase). Compared to the sham condition, there were significant reductions in the stop-signal processing times during and after transcranial direct-current stimulation, and change times were significantly greater in the transcranial direct-current stimulation condition. There was no significant change in go processing-times during or after transcranial direct-current stimulation in either condition. Anodal transcranial direct-current stimulation was feasibly coupled to an interactive improvement in inhibitory control. This coupling led to a decrease in the stop-signal process time required for the appropriate responses between motor execution and inhibition. However, there was no transcranial direct-current stimulation effect on the no-signal reaction time during the stop-signal task. Transcranial direct-current stimulation can adjust certain behaviors, and it could be a useful clinical intervention for patients who have difficulties with response inhibition.

  16. Time-dependent current-density-functional theory for the metallic response of solids

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    2005-01-01

    We extend the formulation of time-dependent current-density-functional theory for the linear response properties of dielectric and semi-metallic solids [Kootstra , J. Chem. Phys. 112, 6517 (2000)] to treat metals as well. To achieve this, the Kohn-Sham response functions have to include both interba

  17. Time-dependent current-density-functional theory for the metallic response of solids

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    We extend the formulation of time-dependent current-density-functional theory for the linear response properties of dielectric and semi-metallic solids [Kootstra , J. Chem. Phys. 112, 6517 (2000)] to treat metals as well. To achieve this, the Kohn-Sham response functions have to include both

  18. Adsorptive stripping voltammetric determination of trace amounts of lead in environmental water samples with complicated matrix

    Directory of Open Access Journals (Sweden)

    Grabarczyk M.

    2013-04-01

    Full Text Available A sensitive, simple and fast adsorptive stripping voltammetric procedure for trace determination of lead in environmental water samples has been developed. The method is based on adsorptive accumulation of the Pb(II-cupferron complex onto a hanging mercury drop electrode, followed by the reduction of the adsorbed species by a voltammetric scan using differential pulse modulation. The interference from surface active substances was eliminated by adsorption of interferents onto an Amberlite XAD-16 resin. Optimumconditions for removing the surfactants by mixing the analysed sample with resin were evaluated. The accuracy of the method was tested by analyzing certified reference material (SPS-WW1 Waste Water.

  19. Indirect differential pulse voltammetric determination of aluminum by a pyrocatechol violet-modified electrode

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G.; Bi, S.; Dai, L.; Cao, M.; Chen, Y. Wang, X. [Nanjing Univ. (China)

    1999-03-01

    Aluminum is one of the abundant elements in the earth`s crust. It has been considered to be a causative agent for various neurological disorders such as Alzheimer Senile, presenile dementia and amyotrophic lateral sclerosis. It is also very harmful to plants and aquatic organisms. Therefore, the determination of Al is very important. A Pyrocatechol Violet (PCV) modified electrode for the voltammetric determination of aluminum is reported. The modified electrode is simply prepared by dip-coating a pyrolytic graphite electrode in a NaAc-HAc buffer solution of PCV. Optimum experimental conditions for aluminum determination include a 0.2 mol/L NaAc-HAc buffer solution of pH 4.8, a PCV concentration of 0.02 mol/L used to modify the electrode and the use of differential-pulse mode for measurement. The peak currents of differential pulse voltammograms (DPV) decrease with the addition of Al into the buffer solution while the peak potentials remain the same. The decreasing value of peak current {Delta}i{sub p} is linear with Al concentration in the range of 1{times}10{sup {minus}8} to 1{times}10{sup {minus}7} mol/L and 1{times}10{sup {minus}7} to 1{times}10{sup {minus}6} mol/L. The detection limit is 5{times}10{sup {minus}9} mol/L and the relative standard deviation for 4{times}10{sup {minus}8} mol/L Al is 2.9% (n=8). The stability of this electrode is satisfactory. No serious interference is found. This method has been applied to determine Al in drinking water samples.

  20. Optimization of Stripping Voltammetric Sensor by a Back Propagation Artificial Neural Network for the Accurate Determination of Pb(II) in the Presence of Cd(II).

    Science.gov (United States)

    Zhao, Guo; Wang, Hui; Liu, Gang; Wang, Zhiqiang

    2016-09-21

    An easy, but effective, method has been proposed to detect and quantify the Pb(II) in the presence of Cd(II) based on a Bi/glassy carbon electrode (Bi/GCE) with the combination of a back propagation artificial neural network (BP-ANN) and square wave anodic stripping voltammetry (SWASV) without further electrode modification. The effects of Cd(II) in different concentrations on stripping responses of Pb(II) was studied. The results indicate that the presence of Cd(II) will reduce the prediction precision of a direct calibration model. Therefore, a two-input and one-output BP-ANN was built for the optimization of a stripping voltammetric sensor, which considering the combined effects of Cd(II) and Pb(II) on the SWASV detection of Pb(II) and establishing the nonlinear relationship between the stripping peak currents of Pb(II) and Cd(II) and the concentration of Pb(II). The key parameters of the BP-ANN and the factors affecting the SWASV detection of Pb(II) were optimized. The prediction performance of direct calibration model and BP-ANN model were tested with regard to the mean absolute error (MAE), root mean square error (RMSE), average relative error (ARE), and correlation coefficient. The results proved that the BP-ANN model exhibited higher prediction accuracy than the direct calibration model. Finally, a real samples analysis was performed to determine trace Pb(II) in some soil specimens with satisfactory results.

  1. Discrimination of Rice with Different Pretreatment Methods by Using a Voltammetric Electronic Tongue

    Directory of Open Access Journals (Sweden)

    Li Wang

    2015-07-01

    Full Text Available In this study, an application of a voltammetric electronic tongue for discrimination and prediction of different varieties of rice was investigated. Different pretreatment methods were selected, which were subsequently used for the discrimination of different varieties of rice and prediction of unknown rice samples. To this aim, a voltammetric array of sensors based on metallic electrodes was used as the sensing part. The different samples were analyzed by cyclic voltammetry with two sample-pretreatment methods. Discriminant Factorial Analysis was used to visualize the different categories of rice samples; however, radial basis function (RBF artificial neural network with leave-one-out cross-validation method was employed for prediction modeling. The collected signal data were first compressed employing fast Fourier transform (FFT and then significant features were extracted from the voltammetric signals. The experimental results indicated that the sample solutions obtained by the non-crushed pretreatment method could efficiently meet the effect of discrimination and recognition. The satisfactory prediction results of voltammetric electronic tongue based on RBF artificial neural network were obtained with less than five-fold dilution of the sample solution. The main objective of this study was to develop primary research on the application of an electronic tongue system for the discrimination and prediction of solid foods and provide an objective assessment tool for the food industry.

  2. Discrimination of Rice with Different Pretreatment Methods by Using a Voltammetric Electronic Tongue.

    Science.gov (United States)

    Wang, Li; Niu, Qunfeng; Hui, Yanbo; Jin, Huali

    2015-07-22

    In this study, an application of a voltammetric electronic tongue for discrimination and prediction of different varieties of rice was investigated. Different pretreatment methods were selected, which were subsequently used for the discrimination of different varieties of rice and prediction of unknown rice samples. To this aim, a voltammetric array of sensors based on metallic electrodes was used as the sensing part. The different samples were analyzed by cyclic voltammetry with two sample-pretreatment methods. Discriminant Factorial Analysis was used to visualize the different categories of rice samples; however, radial basis function (RBF) artificial neural network with leave-one-out cross-validation method was employed for prediction modeling. The collected signal data were first compressed employing fast Fourier transform (FFT) and then significant features were extracted from the voltammetric signals. The experimental results indicated that the sample solutions obtained by the non-crushed pretreatment method could efficiently meet the effect of discrimination and recognition. The satisfactory prediction results of voltammetric electronic tongue based on RBF artificial neural network were obtained with less than five-fold dilution of the sample solution. The main objective of this study was to develop primary research on the application of an electronic tongue system for the discrimination and prediction of solid foods and provide an objective assessment tool for the food industry.

  3. VOLTAMMETRIC BEHAVIOR OF SOME STEELS IN AQUEOUS SOLUTIONS OF HNO3

    Directory of Open Access Journals (Sweden)

    Gheorghe Nemtoi

    2011-06-01

    Full Text Available The corrosion process of some steels immersed in HNO3 solutions of different concentrations by means of voltammetric measurements was investigated. For different values of the corrosion potential, or of the contact time: solid steel-aggressive medium, several equations of the type: I = f (E were proposed, only for linear domains of the voltammograms.

  4. Voltammetric Determination of Prochlorperazine and Ethopropazine Using a Gold Electrode Modified with Decanethiol SAM

    Directory of Open Access Journals (Sweden)

    Baizhao Zeng

    2003-12-01

    Full Text Available The voltammetric behavior of prochlorperazine and ethopropazine at a decanethiol (DEC self-assembled monolayer (SAM modified gold electrode (DEC/Au has been studied. It was observed that prochlorperazine exhibited an anodic peak at about 0.60 V (vs SCE, while ethopropazine exhibited two anodic peaks at about 0.49 V and 0.58 V on DEC/Au in pH 10 sodium carbonate buffer. This was due to their different electrochemical oxidation mechanisms. In this case, the oxidation of prochlorperazine and ethopropazine included one 2e step and two 1e steps, respectively. In the presence of some reductants such as ascorbic acid, the oxidation products of them can catalyze the oxidation of the reductants and thus make the peaks grow. In addition, it was found that the SAM structure became not so compact when prochlorperazine and ethopropazine were present, resulting from their permeating in the SAM. Various conditions were optimized for their determination. Under the selected conditions (i.e. 0.080 M pH 10 sodium carbonate buffer; scan rate: 100 mV/s; accumulation potential: –0.4 V or 0 V; accumulation time: 60 s, the peak currents were linear to prochlorperazine concentration in the ranges of 0.1~2.0 μM and 5.0~50 μM, and linear with ethopropazine in the ranges of 10 nM~0.1 μM and 0.5~20 μM. The RSD was 4.28% for 8 successive measurements of 1.0 μM prochlorperazine. The influence of some coexistents was examined.

  5. Linear Response of Field-Aligned Currents to the Interplanetary Electric Field

    DEFF Research Database (Denmark)

    Weimer, D. R.; R. Edwards, T.; Olsen, Nils

    2017-01-01

    Many studies that have shown that the ionospheric, polar cap electric potentials (PCEP) exhibit a “saturation” behavior in response to the level of the driving by the solar wind. As the magnitude of the interplanetary magnetic field (IMF) and electric field (IEF) increase, the PCEP response...... of the field-aligned currents (FAC) with the solar wind/magnetosphere/ionosphere system has a role. As the FAC are more difficult to measure, their behavior in response to the level of the IEF has not been investigated as thoroughly. In order to resolve the question of whether or not the FAC also exhibit...... saturation, we have processed the magnetic field measurements from the Ørsted, CHAMP, and Swarm missions, spanning more than a decade. As the amount of current in each region needs to be known, a new technique is used to separate and sum the current by region, widely known as R0, R1, and R2. These totals...

  6. Study of the voltammetric behaviour of metam and its application to an amperometric flow system.

    Science.gov (United States)

    Barroso, M Fátima; Paíga, Paula; Vaz, M Carmo V F; Delerue-Matos, Cristina

    2005-11-01

    The electrochemical behaviour of the pesticide metam (MT) at a glassy carbon working electrode (GCE) and at a hanging mercury drop electrode (HMDE) was investigated. Different voltammetric techniques, including cyclic voltammetry (CV) and square wave voltammetry (SWV), were used. An anodic peak (independent of pH) at +1.46 V vs AgCl/Ag was observed in MT aqueous solution using the GCE. SWV calibration curves were plotted under optimized conditions (pH 2.5 and frequency 50 Hz), which showed a linear response for 17-29 mg L(-1). Electrochemical reduction was also explored, using the HMDE. A well defined cathodic peak was recorded at -0.72 V vs AgCl/Ag, dependent on pH. After optimizing the operating conditions (pH 10.1, frequency 150 Hz, potential deposition -0.20 V for 10 s), calibration curves was measured in the concentration range 2.5 x 10(-1) to 1.0 mg L(-1) using SWV. The electrochemical behaviour of this compound facilitated the development of a flow injection analysis (FIA) system with amperometric detection for the quantification of MT in commercial formulations and spiked water samples. An assessment of the optimal FIA conditions indicated that the best analytical results were obtained at a potential of +1.30 V, an injection volume of 207 muL and an overall flow rate of 2.4 ml min(-1). Real samples were analysed via calibration curves over the concentration range 1.3 x 10(-2) to 1.3 mg L(-1). Recoveries from the real samples (spiked waters and commercial formulations) were between 97.4 and 105.5%. The precision of the proposed method was evaluated by assessing the relative standard deviation (RSD %) of ten consecutive determinations of one sample (1.0 mg L(-1)), and the value obtained was 1.5%.

  7. Dynamic response of jetting and cementing bucket platform to wave and current loading

    Institute of Scientific and Technical Information of China (English)

    Wang Hu; Wang Deyu

    2006-01-01

    The jetting and cementing bucket platform (JCBP) is a new type offshore oil-drilling platform. This paper aims to establish an analysis method for calculating the dynamic response of this platform. Based on the theory of elastic half space, the dynamic stiffness and damping of the platform's foundation were obtained and attached to the end of the platform's main jackets as a boundary condition. Then using finite element method (FEM), the dynamic response of the platform due to wave and current loading was calculated. Furthermore, the whole platform's finite element model was established and the dynamic response of the platform was calculated. The numerical results demonstrate that the present method by the usage of elastic half space theory and FEM is simple and it is reliable and efficient to calculate dynamic behavior of the platform in response to wave and current loading.

  8. Tilt-shift eddy current probe impact on information value of response signal

    OpenAIRE

    Chudacik Vladimir; Smetana Milan

    2016-01-01

    This article deals with the possibility for increasing of the informational value of a response signal using tilt-shift eddy current probe. Numerical simulations based on the FEM method using the OPERA 3D software as well as gained experimental results are presented. The simulated cracks are evaluated at the selected eddy current probe tilts and shifts with respect to conductive plate to obtain additional data needed for its evaluation and localization. Obtained simulation results are compare...

  9. Effect of cocaine, nomifensine, GBR 12909 and WIN 35428 on carbon fiber microelectrode sensitivity for voltammetric recording of dopamine.

    Science.gov (United States)

    Davidson, C; Ellinwood, E H; Douglas, S B; Lee, T H

    2000-08-15

    Electrochemical measurements using voltammetry or amperometry at carbon-fiber microelectrodes have been used in vitro and in vivo to examine regulatory mechanisms for the central dopamine system. In many of these experiments, dopamine efflux concentrations under control conditions are determined followed by their alterations in response to a drug treatment. The present study demonstrates that some drugs can affect dopamine measurements, not only by their expected pharmacological action but also by directly altering the microelectrode responsivity. The commonly used reuptake inhibitors GBR 12909 (10 microM) and nomifensine (5 microM) drastically reduce electrode sensitivity and, in the case of nomifensine, increase the time to reach a plateau in response to dopamine boluses (i.e. reduced 'frequency response'). Cocaine (10 microM) and WIN 35428 (2 microM) have negligible effect on these indices. This decrease in sensitivity was found in both nafion and non-nafion coated electrodes. Further, the reduction in sensitivity seen in non-nafion coated electrodes was not prevented by increasing the reversal potential (from +1.0 to +1.3 V) and voltage scan rate (from 350 to 450 V/s). These data suggest that care must be taken when interpreting data from voltammetric or amporometric experiments using carbon electrodes where GBR 12909 or nomifensine are used, especially at high concentrations. Furthermore, wherever possible, direct effects of a drug on electrode sensitivity and frequency response should be determined.

  10. Is transcranial direct current stimulation a potential method for improving response inhibition?☆

    OpenAIRE

    Kwon, Yong Hyun; Kwon, Jung Won

    2013-01-01

    Inhibitory control of movement in motor learning requires the ability to suppress an inappropriate action, a skill needed to stop a planned or ongoing motor response in response to changes in a variety of environments. This study used a stop-signal task to determine whether transcranial direct-current stimulation over the pre-supplementary motor area alters the reaction time in motor inhibition. Forty healthy subjects were recruited for this study and were randomly assigned to either the tran...

  11. Development of a selective and sensitive voltammetric sensor for propylparaben based on a nanosized molecularly imprinted polymer-carbon paste electrode.

    Science.gov (United States)

    Gholivand, Mohammad Bagher; Shamsipur, Mojtaba; Dehdashtian, Sara; Rajabi, Hamid Reza

    2014-03-01

    The design and construction of a selective voltammetric sensor for propylparaben (PP) in cosmetics by using a molecularly imprinted polymer (MIP) as recognition element was introduced. The MIP was synthesized by using PP as template and methacrylic acid as functional monomer and then incorporated in the carbon paste electrode as PP sensor. The molecularly imprinted polymer-carbon paste electrode (MIP-CPE) showed very high recognition ability in comparison to non-imprinted polymer-carbon paste electrode (NIP-CPE). It was shown that electrode washing after PP extraction, led to enhanced selectivity, without noticeably decreasing the sensitivity. Some parameters affecting sensor response were optimized, and a calibration curve was then plotted using differential pulse voltammetric (DPV) technique. A dynamic linear range of 1 nM to 100 nM was obtained. The detection limit of the sensor was calculated to be equal to 0.32 nM. The imprinted electrode also displayed good selectivity for PP and selectivity coefficients were 2.29 and 1.66 for methylparaben (MP) and ethylparaben (EP) respectively. Structural analogs, such as phenol and p-hydroxybenzoic acid had almost no response. This sensor was used successfully for propylparaben determination in cosmetic sample.

  12. Forget the Desk Job: Current Roles and Responsibilities in Entry-Level Reference Job Advertisements

    Science.gov (United States)

    Detmering, Robert; Sproles, Claudene

    2012-01-01

    This study examines the evolving roles and responsibilities of entry-level academic reference positions, as stated in recent job advertisements posted on the American Library Association's JobLIST Web site and other sources. Findings from a content analysis of these advertisements indicate that current entry-level reference positions in academic…

  13. Forget the Desk Job: Current Roles and Responsibilities in Entry-Level Reference Job Advertisements

    Science.gov (United States)

    Detmering, Robert; Sproles, Claudene

    2012-01-01

    This study examines the evolving roles and responsibilities of entry-level academic reference positions, as stated in recent job advertisements posted on the American Library Association's JobLIST Web site and other sources. Findings from a content analysis of these advertisements indicate that current entry-level reference positions in academic…

  14. Responses of atmospheric electric field and air-earth current to variations of conductivity profiles

    Science.gov (United States)

    Makino, M.; Ogawa, T.

    1984-05-01

    A global circuit model is constructed to study responses of air-earth current and electric field to a variation of atmospheric electrical conductivity profile. The model includes the orography and the global distribution of thunderstorm generators. The conductivity varies with latitude and exponentially with altitude. The thunderstorm cloud is assumed to be a current generator with a positive source at the top and a negative one at the bottom. The UT diurnal variations of the global current and the ionospheric potential are evaluated considering the local-time dependence of thunderstorm activity. The global distribution of the electric field and the air-earth current are affected by the orography and latitudinal effects. Assuming a variation of conductivity profile, responses of atmospheric electrical parameters are investigated. The nonuniform decrement of the conductivity with altitude increases both the electric field and the air-earth current. The result suggests a possibility that the increment of the electric field and the air-earth current after a solar flare may be caused by this scheme, due to Forbush decrease.

  15. Comparison of Ring Current and Radiation Belt Responses during Transient Solar Wind Structures

    Science.gov (United States)

    Mulligan, T. L.; Roeder, J. L.; Lemon, C.; Fennell, J. F.

    2013-12-01

    The analysis of radiation belt dynamics provides insight into the physical mechanisms of trapping, energization, and loss of energetic particles in the magnetosphere. It is well known that the storm-time ring current response to solar wind drivers changes the magnetic field in the inner magnetosphere, which modifies radiation belt particle trajectories as well as the magnetopause and geomagnetic cutoff locations. What is not well known is the detailed space-time structure of solar wind transient features that drive the dynamics of the ring-current and radiation belt response. We compare observed responses of the ring current and radiation belts during two geomagnetic storms of similar intensity on 15 November 2012 and 29 June 2013. Using the self-consistent ring current model RCM-Equilibrium (RCM-E), which ensures a force-balanced ring-current response at each time step, we generate a simulated ring current in response to the changing conditions as the storm evolves on a timescale of hours. Observations of the plasma sheet particles, fields, and solar wind parameters are used to specify the dynamic boundary conditions as the storm evolves. This allows more realistic magnetospheric field and plasma dynamics during solar wind transients than can be obtained from existing empirical models. Using a spatial mapping algorithm developed by Mulligan et al., (2012) we create two-dimensional contour maps of the solar wind bulk plasma parameters using ACE, Wind, Geotail, and THEMIS data to quantitatively follow upstream spatial variations in the radial and azimuthal dimensions driving the storm. We perform a comparison of how the structure and impact angle of the solar wind transients affect the intensity and duration of energization of the ring current and radiation belt at various energies. We also investigate how the varying geomagnetic conditions determined by the solar wind affect dominant loss mechanisms such as magnetopause shadowing. Comparison of energetic particle

  16. Transient response of microbial communities in a water well field to application of an impressed current.

    Science.gov (United States)

    Medihala, P G; Lawrence, J R; Swerhone, G D W; Korber, D R

    2013-02-01

    Deterioration of water wells due to clogging and corrosion over time is a common problem where solutions may be costly and ineffective. Pilot studies have suggested that impressed current or cathodic protection may be used to reduce microbially-induced declines in water well performance. Two water wells in an alluvial aquifer close to the North Saskatchewan River were selected to study the response of subsurface microbial communities to the application of an impressed current as an anti-fouling technology. The treated well was exposed to an impressed current while the untreated well was used as a reference site. Biofilms grown on in situ coupons under the influence of the impressed current were significantly (p anti-fouling technology but actually promoted both microbial growth and physical clogging in this aquifer.

  17. Transient Eddy Current Response Due to a Subsurface Crack in a Conductive Plate

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Fangwei [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    Eddy current nondestructive evaluation (NDE) is usually carried out by exciting a time harmonic field using an inductive probe. However, a viable alternative is to use transient eddy current NDE in which a current pulse in a driver coil produces a transient .eld in a conductor that decays at a rate dependent on the conductivity and the permeability of the material and the coil configuration. By using transient eddy current, it is possible to estimate the properties of the conductive medium and to locate and size potential .aws from the measured probe response. The fundamental study described in this dissertation seeks to establish a theoretical understanding of the transient eddy current NDE. Compared with the Fourier transform method, the derived analytical formulations are more convenient when the transient eddy current response within a narrow time range is evaluated. The theoretical analysis provides a valuable tool to study the effect of layer thickness, location of defect, crack opening as well as the optimization of probe design. Analytical expressions have been developed to evaluate the transient response due to eddy currents in a conductive plate based on two asymptotic series. One series converges rapidly for a short time regime and the other for a long time regime and both of them agree with the results calculated by fast Fourier transform over all the times considered. The idea of asymptotic expansion is further applied to determine the induced electromotive force (EMF) in a pick-up coil due to eddy currents in a cylindrical rod. Starting from frequency domain representation, a quasi-static time domain dyadic Green's function for an electric source in a conductive plate has been derived. The resulting expression has three parts; a free space term, multiple image terms and partial reflection terms. The dyadic Green's function serves as the kernel of an electric field integral equation which defines the interaction of an ideal crack with the

  18. Differential pulse voltammetric determination of P(V) following adsorptive accumulation of alpha-[PMo(12)O(40)](3-) on a polypyrrole-modified glassy carbon electrode.

    Science.gov (United States)

    Takamoto, Masayo; Himeno, Sadayuki

    2003-03-01

    On the basis of the formation and pre-concentration of an alpha-Keggin-type [PMo(12)O(40)](3-) complex, a novel voltammetric method was developed for the determination of trace levels of P(V). The alpha-[PMo(12)O(40)](3-) complex was formed by heating a 5x10(-4) M Mo(VI)-0.2 M HCl-40% (v/v) CH(3)CN system containing a trace amount of P(V) at 70 degrees C for 30 min. During the electrochemical polymerization of pyrrole in the alpha-[PMo(12)O(40)](3-) solution, the alpha-[PMo(12)O(40)](3-) complex was accumulated into the polypyrrole film on a glassy carbon electrode. The differential pulse voltammetric peak current due to the alpha-[PMo(12)O(40)](3-) complex incorporated in the polypyrrole film was linearly dependent on the P(V) concentration in the range of 5x10(-9)-5x10(-7) M; a detection limit of 2x10(-9) M was achieved.

  19. Responsivity Dependent Anodization Current Density of Nanoporous Silicon Based MSM Photodetector

    Directory of Open Access Journals (Sweden)

    Batool Eneaze B. Al-Jumaili

    2016-01-01

    Full Text Available Achieving a cheap and ultrafast metal-semiconductor-metal (MSM photodetector (PD for very high-speed communications is ever-demanding. We report the influence of anodization current density variation on the response of nanoporous silicon (NPSi based MSM PD with platinum (Pt contact electrodes. Such NPSi samples are grown from n-type Si (100 wafer using photoelectrochemical etching with three different anodization current densities. FESEM images of as-prepared samples revealed the existence of discrete pores with spherical and square-like shapes. XRD pattern displayed the growth of nanocrystals with (311 lattice orientation. The nanocrystallite sizes obtained using Scherrer formula are found to be between 20.8 nm and 28.6 nm. The observed rectifying behavior in the I-V characteristics is ascribed to the Pt/PSi/n-Si Schottky barrier formation, where the barrier height at the Pt/PSi interface is estimated to be 0.69 eV. Furthermore, this Pt/PSi/Pt MSM PD achieved maximum responsivity of 0.17 A/W and quantum efficiency as much as 39.3%. The photoresponse of this NPSi based MSM PD demonstrated excellent repeatability, fast response, and enhanced saturation current with increasing anodization current density.

  20. Evaluation of lung tumor response to therapy: Current and emerging techniques.

    Science.gov (United States)

    Coche, E

    2016-10-01

    Lung tumor response to therapy may be evaluated in most instances by morphological criteria such as RECIST 1.1 on computed tomography (CT) or magnetic resonance imaging (MRI). However, those criteria are limited because they are based on tumoral dimensional changes and do not take into account other morphologic criteria such as density evaluation, functional or metabolic changes that may occur following conventional or targeted chemotherapy. New techniques such as dual-energy CT, PET-CT, MRI including diffusion-weighted MRI has to be considered into the new technical armamentarium for tumor response evaluation. Integration of all informations provided by the different imaging modalities has to be integrated and represents probably the future goal of tumor response evaluation. The aim of the present paper is to review the current and emerging imaging criteria used to evaluate the response of therapy in the field of lung cancer.

  1. Tilt-shift eddy current probe impact on information value of response signal

    Directory of Open Access Journals (Sweden)

    Chudacik Vladimir

    2016-03-01

    Full Text Available This article deals with the possibility for increasing of the informational value of a response signal using tilt-shift eddy current probe. Numerical simulations based on the FEM method using the OPERA 3D software as well as gained experimental results are presented. The simulated cracks are evaluated at the selected eddy current probe tilts and shifts with respect to conductive plate to obtain additional data needed for its evaluation and localization. Obtained simulation results are compared and discussed with the experimental results.

  2. Magnetic response and critical current properties of mesoscopic-size YBCO superconducting samples

    Energy Technology Data Exchange (ETDEWEB)

    Lisboa-Filho, P N [UNESP - Universidade Estadual Paulista, Grupo de Materiais Avancados, Departamento de Fisica, Bauru (Brazil); Deimling, C V; Ortiz, W A, E-mail: plisboa@fc.unesp.b [Grupo de Supercondutividade e Magnetismo, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos (Brazil)

    2010-01-15

    In this contribution superconducting specimens of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} were synthesized by a modified polymeric precursor method, yielding a ceramic powder with particles of mesoscopic-size. Samples of this powder were then pressed into pellets and sintered under different conditions. The critical current density was analyzed by isothermal AC-susceptibility measurements as a function of the excitation field, as well as with isothermal DC-magnetization runs at different values of the applied field. Relevant features of the magnetic response could be associated to the microstructure of the specimens and, in particular, to the superconducting intra- and intergranular critical current properties.

  3. A rapid cyclic voltammetric method for studying cement factors affecting the corrosion of reinforced concrete

    Energy Technology Data Exchange (ETDEWEB)

    Foulkes, F.R.; McGrath, P. (Univ. of Toronto, Ontario (Canada))

    1999-06-01

    A rapid cyclic voltammetric method for studying the influence of cement factors on the corrosion of embedded iron and steel in hardened cement paste is described. The technique employs a cement electrode'' consisting of an iron or steel wire embedded in a miniature cylinder of hardened cement paste. The rapid cyclic voltammetric method is fast, reproducible, and provides information on the corrosiveness of the pore solution environment surrounding the embedded metal. The usefulness of the method is demonstrated by showing how it can be used to evaluate the threshold chloride content of hardened ordinary portland cement paste at which corrosion begins and by using it to evaluate the relative efficacy of several admixed corrosion inhibitors.

  4. Adsorptive Cathodic Stripping Voltammetric Determination of Cefoperazone in Bulk Powder, Pharmaceutical Dosage Forms, and Human Urine

    Science.gov (United States)

    Hoang, Vu Dang; Huyen, Dao Thi; Phuc, Phan Hong

    2013-01-01

    The electroreduction behaviour and determination of cefoperazone using a hanging mercury drop electrode were investigated. Cyclic voltammograms of cefoperazone recorded in universal Britton-Robinson buffers pH 3–6 exhibited a single irreversible cathodic peak. The process was adsorption-controlled. Britton-Robinson buffer 0.04 M pH 4.0 was selected as a supporting electrolyte for quantitative purposes by differential pulse and square wave adsorptive cathodic stripping voltammetry. The experimental voltammetric conditions were optimized using Central Composite Face design. A reduction wave was seen in the range from −0.7 to −0.8 V. These voltammetric techniques were successfully validated as per ICH guidelines and applied for the determination of cefoperazone in its single and sulbactam containing powders for injection and statistically comparable to USP-HPLC. They were further extended to determine cefoperazone in spiked human urine with no matrix effect. PMID:24109542

  5. Adsorptive Cathodic Stripping Voltammetric Determination of Cefoperazone in Bulk Powder, Pharmaceutical Dosage Forms, and Human Urine

    Directory of Open Access Journals (Sweden)

    Vu Dang Hoang

    2013-01-01

    Full Text Available The electroreduction behaviour and determination of cefoperazone using a hanging mercury drop electrode were investigated. Cyclic voltammograms of cefoperazone recorded in universal Britton-Robinson buffers pH 3–6 exhibited a single irreversible cathodic peak. The process was adsorption-controlled. Britton-Robinson buffer 0.04 M pH 4.0 was selected as a supporting electrolyte for quantitative purposes by differential pulse and square wave adsorptive cathodic stripping voltammetry. The experimental voltammetric conditions were optimized using Central Composite Face design. A reduction wave was seen in the range from −0.7 to −0.8 V. These voltammetric techniques were successfully validated as per ICH guidelines and applied for the determination of cefoperazone in its single and sulbactam containing powders for injection and statistically comparable to USP-HPLC. They were further extended to determine cefoperazone in spiked human urine with no matrix effect.

  6. Adsorptive cathodic stripping voltammetric determination of cefoperazone in bulk powder, pharmaceutical dosage forms, and human urine.

    Science.gov (United States)

    Hoang, Vu Dang; Huyen, Dao Thi; Phuc, Phan Hong

    2013-01-01

    The electroreduction behaviour and determination of cefoperazone using a hanging mercury drop electrode were investigated. Cyclic voltammograms of cefoperazone recorded in universal Britton-Robinson buffers pH 3-6 exhibited a single irreversible cathodic peak. The process was adsorption-controlled. Britton-Robinson buffer 0.04 M pH 4.0 was selected as a supporting electrolyte for quantitative purposes by differential pulse and square wave adsorptive cathodic stripping voltammetry. The experimental voltammetric conditions were optimized using Central Composite Face design. A reduction wave was seen in the range from -0.7 to -0.8 V. These voltammetric techniques were successfully validated as per ICH guidelines and applied for the determination of cefoperazone in its single and sulbactam containing powders for injection and statistically comparable to USP-HPLC. They were further extended to determine cefoperazone in spiked human urine with no matrix effect.

  7. The Development of Forms of Corporate Social Responsibility in Russia in the Current Economic Conditions

    Directory of Open Access Journals (Sweden)

    Natalya Arzumanova

    2015-02-01

    Full Text Available The article reveals the characteristic features of modern trends in the formation and implementation of corporate social responsibility in Russia in the current economic conditions, which is based on the fact that reasonable economic interests oriented business not only on maximizing profits, but also to improve their own macro - socio-economic, natural, political, through voluntary investment profits in the respective areas.

  8. Plagiarism: A Shared Responsibility of All, Current Situation, and Future Actions in Yemen.

    Science.gov (United States)

    Muthanna, Abdulghani

    2016-01-01

    As combating plagiarism is a shared responsibility of all, this article focuses on presenting the current situation of higher education in Yemen. The critical review of four implementable policy documents and interviews revealed the absence of research ethics code, research misconduct policy, and institutional policies in the country. This led to the presence of several acts of research dishonesty. The article concludes with an initiative for necessary future actions in the nation.

  9. Novel voltammetric and impedimetric sensor for femtomolar determination of lysozyme based on metal-chelate affinity immobilized onto gold nanoparticles.

    Science.gov (United States)

    Arabzadeh, Abbas; Salimi, Abdollah

    2015-12-15

    In this study, we reported iminodiacetic acid-copper ion complex (IDA-Cu) immobilized onto gold nanoparticles (GNPs)-modified glassy carbon electrode as a novel electrochemical platform for selective and sensitive determination of lysozyme (Lys). IDA-Cu complex acted as an efficient recognition element capable of capturing Lys molecules. GNPs acts as a substrate to immobilize IDA-Cu coordinative complex and its interaction with Lys leds to a great signal amplification through measuring changes in differential pulse voltammetric (DPV) peak current of [Fe(CN)6](3-/4-) redox probe. Upon the recognition of the Lys to the IDA-Cu, the peak current decreased due to the hindered electron transfer reaction on the electrode surface. Under optimum condition, it was found that the proposed method could detect Lys at wide linear concentration range (0.1 pM to 0.10 mM) with detection limit of 60 fM. Furthermore, electrochemical impedance spectroscopy (EIS) detection of Lys was demonstrated as a simple and rapid alternative analytical technique with detection limit of 80 fM at concentration range up to 0.1mM. In addition, the proposed sensor was satisfactorily applied to the determination of Lys in real samples such as hen egg white. The proposed modified electrode showing the high selectivity, good sensitivity and stability toward Lys detection may hold a great promise in developing other electrochemical sensors based on metal-chelate affinity complexes.

  10. Sensitive voltammetric determination of tryptophan using an acetylene black paste electrode modified with a Schiff's base derivative of chitosan.

    Science.gov (United States)

    Deng, Peihong; Fei, Junjie; Feng, Yonglan

    2011-12-21

    Chitosan was modified by salicylaldehyde via Schiff's base reaction and the resulting product was modified on the surface of an acetylene black paste electrode (ABPE) by the drop-coating method. In 0.5 mol L(-1) acetate buffer (pH 4.2), a substantial increase in the anodic stripping peak current of tryptophan (Trp) (compared to conventional bare carbon paste electrode (CPE) and bare ABPE) is observed at the Schiff's base chitosan-modified electrode. The parameters influencing voltammetric determination of Trp have been optimized. Under the selected conditions, the linearity between the anodic peak currents and concentrations of Trp demonstrated a wide range of 6.0 × 10(-8) mol L(-1) to 2.0 × 10(-6) mol L(-1), 2.0 × 10(-6) mol L(-1) to 4.0 × 10(-5) mol L(-1) and 4.0 × 10(-5) mol L(-1) to 1.0 × 10(-4) mol L(-1), a low detection limit of 2.0 × 10(-9) mol L(-1) was obtained after a 60 s accumulation. In addition, the developed electrochemical sensor has been successfully applied for the determination of Trp in pharmaceutical and biological samples with satisfactory assay results.

  11. Ionic currents underlying difference in light response between type A and type B photoreceptors.

    Science.gov (United States)

    Blackwell, K T

    2006-05-01

    In Hermissenda crassicornis, the memory of light associated with turbulence is stored as changes in intrinsic and synaptic currents in both type A and type B photoreceptors. These photoreceptor types exhibit qualitatively different responses to light and current injection, and these differences shape the spatiotemporal firing patterns that control behavior. Thus the objective of the study was to identify the mechanisms underlying these differences. The approach was to develop a type B model that reproduced characteristics of type B photoreceptors recorded in vitro, and then to create a type A model by modifying a select number of ionic currents. Comparison of type A models with characteristics of type A photoreceptors recorded in vitro revealed that type A and type B photoreceptors have five main differences, three that have been characterized experimentally and two that constitute hypotheses to be tested with experiments in the future. The three differences between type A and type B photoreceptors previously characterized include the inward rectifier current, the fast sodium current, and conductance of calcium-dependent and transient potassium channels. Two additional changes were required to produce a type A photoreceptor model. The very fast firing frequency observed during the first second after light onset required a faster time constant of activation of the delayed rectifier. The fast spike adaptation required a fast, noninactivating calcium-dependent potassium current. Because these differences between type A and type B photoreceptors have not been confirmed in comparative experiments, they constitute hypotheses to be tested with future experiments.

  12. Voltammetric behaviour of bromhexine and its determination in pharmaceuticals.

    Science.gov (United States)

    Turchán, M; Jara-Ulloa, P; Bollo, S; Nuñez-Vergara, L J; Squella, J A; Alvarez-Lueje, A

    2007-10-31

    A complete electrochemical study and a novel electroanalytical procedure for bromhexine quantitation are described. Bromhexine in methanol/0.1molL(-1) Britton-Robinson buffer solution (2.5/97.5) shows an anodic response on glassy carbon electrode between pH 2 and 7.5. By DPV and CV, both peak potential and current peak values were pH-dependent in all the pH range studied. A break at pH 5.5 in E(P) versus pH plot revealing a protonation-deprotonation (pK(a)) equilibrium of bromhexine was observed. Spectrophotometrically, an apparent pK(a) value of 4.3 was also determined. An electrodic mechanism involving the oxidation of bromhexine via two-electrons and two-protons was proposed. Controlled potential electrolysis followed by HPLC-UV and GC-MS permitted the identification of three oxidation products: N-methylcyclohexanamine, 2-amino-3,5-dibromobenzaldehyde and 2,4,8,10-tetrabromo dibenzo[b,f][1,5] diazocine. DPV at pH 2 was selected as optimal pH for analytical purposes. Repeatability, reproducibility and selectivity parameters were adequate to quantify bromhexine in pharmaceutical forms. The recovery was 94.50+/-2.03% and the detection and quantitation limits were 1.4x10(-5) and 1.6x10(-5)molL(-1), respectively. Furthermore, the DPV method was applied successfully to individual tablet assay in order to verify the uniformity content of bromhexine. No special treatment of sample were required due to excipients do not interfered with the analytical signal. Finally the method was not time-consuming and less expensive than the HPLC one.

  13. Voltammetric Studies of the Interaction of Tris (1, 10-phenanthroline) Cobalt (Ⅲ) with Bovine Serum Albumin

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The voltammetric methods were used to prove the interaction of metal complex Co(phen)33+ with bovine serum albumin (BSA). The interaction of BSA with Co(phen)33+ molecules using BSA-modified electrode is described. Information of the binding ratio and interaction mode can be obtained from their electrochemical behavior and electrochemical data. Furthermore, attenuated total reflection infrared experiment was performed to prove the interaction between complexes and BSA.

  14. Mesoporous carbon-containing voltammetric biosensor for determination of tyramine in food products

    OpenAIRE

    Kochana, Jolanta; Wapiennik, Karolina; Knihnicki, Paweł; Pollap, Aleksandra; Janus, Paula; Oszajca, Marcin; Kuśtrowski, Piotr

    2016-01-01

    A voltammetric biosensor based on tyrosinase (TYR) was developed for determination of tyramine. Carbon material (multi-walled carbon nanotubes or mesoporous carbon CMK-3-type), polycationic polymer—i.e., poly(diallyldimethylammonium chloride) (PDDA), and Nafion were incorporated into titania dioxide sol (TiO2) to create an immobilization matrix. The features of the formed matrix were studied by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The analytical performance of the d...

  15. Atmospheric Wind Relaxations and the Oceanic Response in the California Current Large Marine Ecosystem

    Science.gov (United States)

    Fewings, M. R.; Dorman, C. E.; Washburn, L.; Liu, W.

    2010-12-01

    On the West Coast of North America in summer, episodic relaxation of the upwelling-favorable winds causes warm water to propagate northward from southern to central California, against the prevailing currents [Harms and Winant 1998, Winant et al. 2003, Melton et al. 2009]. Similar wind relaxations are an important characteristic of coastal upwelling ecosystems worldwide. Although these wind relaxations have an important influence on coastal ocean dynamics, no description exists of the regional atmospheric patterns that lead to wind relaxations in southern California, or of the regional ocean response. We use QuikSCAT wind stress, North American Regional Reanalysis atmospheric pressure products, water temperature and velocity from coastal ocean moorings, surface ocean currents from high-frequency radars, and MODIS satellite sea-surface temperature and ocean color images to analyze wind relaxation events and the ocean response. We identify the events based on an empirical index calculated from NDBC buoy winds [Melton et al. 2009]. We describe the regional evolution of the atmosphere from the Gulf of Alaska to Baja California over the few days leading up to wind relaxations, and the coastal ocean temperature, color, and current response off southern and central California. We analyze ~100 wind relaxation events in June-September during the QuikSCAT mission, 1999-2009. Our results indicate south-central California wind relaxations in summer are tied to mid-level atmospheric low-pressure systems that form in the Gulf of Alaska and propagate southeastward over 3-5 days. As the low-pressure systems reach southern California, the atmospheric pressure gradient along the coast weakens, causing the surface wind stress to relax to near zero. The weak wind signal appears first at San Diego and propagates northward. QuikSCAT data indicate the relaxed winds extend over the entire Southern California Bight and up to 200 km offshore of central California. Atmospheric dynamics in

  16. Simultaneous determination of cefotaxime and desacetylcefotaxime in real urine sample using voltammetric and high-performance liquid chromatographic methods.

    Science.gov (United States)

    Aleksić, Mara M; Kapetanović, Vera; Atanacković, Jasmina; Jocić, Biljana; Zecević, Mira

    2008-10-19

    Two rapid, accurate and sensitive methods are developed and validated for the quantitative simultaneous determination of cefotaxime (CFX) and its active metabolite desacetylcefotaxime (DCFX) in urine. Based on the previous results which showed the four electron reduction of CFX at approximately -0.5 V, and the new findings that DCFX reduction occurred at more positive potential (-0.23 V), the new adsorptive stripping differential pulse voltammetric (AdSDPV) method was developed for determination of CFX in the presence of DCFX. Linear responses were observed over a wide concentration range (0.07-0.52 microg/ml for CFX and 0.22-1.3 microg/ml for DCFX) in urine. The second assay involves subsequent separation on a reversed-phase HPLC column, with ultraviolet detection at 262 nm. Retention times were 4.057 and 1.960 min for CFX and DCFX, respectively. Linear responses were observed over a wide range, 0.55-6.60 microg/ml for CFX and 1.10-11.00 microg/ml for DCFX, in urine. The statistical evaluation for both methods was examined by means of within-day repeatability (n=5) and day-to-day precision (n=3) and was found to be satisfactory with high accuracy and precision.

  17. A voltammetric and mathematical analysis of histaminergic modulation of serotonin in the mouse hypothalamus.

    Science.gov (United States)

    Samaranayake, Srimal; Abdalla, Aya; Robke, Rhiannon; Nijhout, H Frederik; Reed, Michael C; Best, Janet; Hashemi, Parastoo

    2016-08-01

    Histamine and serotonin are neuromodulators which facilitate numerous, diverse neurological functions. Being co-localized in many brain regions, these two neurotransmitters are thought to modulate one another's chemistry and are often implicated in the etiology of disease. Thus, it is desirable to interpret the in vivo chemistry underlying neurotransmission of these two molecules to better define their roles in health and disease. In this work, we describe a voltammetric approach to monitoring serotonin and histamine simultaneously in real time. Via electrical stimulation of the axonal bundles in the medial forebrain bundle, histamine release was evoked in the mouse premammillary nucleus. We found that histamine release was accompanied by a rapid, potent inhibition of serotonin in a concentration-dependent manner. We developed mathematical models to capture the experimental time courses of histamine and serotonin, which necessitated incorporation of an inhibitory receptor on serotonin neurons. We employed pharmacological experiments to verify that this serotonin inhibition was mediated by H3 receptors. Our novel approach provides fundamental mechanistic insights that can be used to examine the full extent of interconnectivity between histamine and serotonin in the brain. Histamine and serotonin are co-implicated in many of the brain's functions. In this paper, we develop a novel voltammetric method for simultaneous real-time monitoring of histamine and serotonin in the mouse premammillary nucleus. Electrical stimulation of the medial forebrain bundle evokes histamine and inhibits serotonin release. We show voltammetrically, mathematically, and pharmacologically that this serotonin inhibition is H3 receptor mediated.

  18. Electrochemical behavior and voltammetric determination of vanillin based on an acetylene black paste electrode modified with graphene-polyvinylpyrrolidone composite film.

    Science.gov (United States)

    Deng, Peihong; Xu, Zhifeng; Zeng, Rongying; Ding, Chunxia

    2015-08-01

    The graphene-polyvinylpyrrolidone composite film modified acetylene black paste electrode (GR-PVP/ABPE) was fabricated and used to determine vanillin. In 0.1M H3PO4 solution, the oxidation peak current of vanillin increased significantly at GR-PVP/ABPE compared with bare ABPE, PVP/ABPE and GR/ABPE. The oxidation mechanism was discussed. The experimental conditions that exert influence on the voltammetric determination of vanillin, such as supporting electrolytes, pH values, accumulation potential and accumulation time, were optimized. Besides, the interference, repeatability, reproducibility and stability measurements were also evaluated. Under the optimal experimental conditions, the oxidation peak current was proportional to vanillin concentration in the range of 0.02-2.0 μM, 2.0-40 μM and 40-100 μM. The detection limit was 10nM. This sensor was used successfully for vanillin determination in various food samples.

  19. Individualized model predicts brain current flow during transcranial direct-current stimulation treatment in responsive stroke patient.

    Science.gov (United States)

    Datta, Abhishek; Baker, Julie M; Bikson, Marom; Fridriksson, Julius

    2011-07-01

    Although numerous published reports have demonstrated the beneficial effects of transcranial direct-current stimulation (tDCS) on task performance, fundamental questions remain regarding the optimal electrode configuration on the scalp. Moreover, it is expected that lesioned brain tissue will influence current flow and should therefore be considered (and perhaps leveraged) in the design of individualized tDCS therapies for stroke. The current report demonstrates how different electrode configurations influence the flow of electrical current through brain tissue in a patient who responded positively to a tDCS treatment targeting aphasia. The patient, a 60-year-old man, sustained a left hemisphere ischemic stroke (lesion size = 87.42 mL) 64 months before his participation. In this study, we present results from the first high-resolution (1 mm(3)) model of tDCS in a brain with considerable stroke-related damage; the model was individualized for the patient who received anodal tDCS to his left frontal cortex with the reference cathode electrode placed on his right shoulder. We modeled the resulting brain current flow and also considered three additional reference electrode positions: right mastoid, right orbitofrontal cortex, and a "mirror" configuration with the anode over the undamaged right cortex. Our results demonstrate the profound effect of lesioned tissue on resulting current flow and the ability to modulate current pattern through the brain, including perilesional regions, through electrode montage design. The complexity of brain current flow modulation by detailed normal and pathologic anatomy suggest: (1) That computational models are critical for the rational interpretation and design of individualized tDCS stroke-therapy; and (2) These models must accurately reproduce head anatomy as shown here.

  20. Frequency dependence of CA3 spike phase response arising from h-current properties

    Directory of Open Access Journals (Sweden)

    Melodie eBorel

    2013-12-01

    Full Text Available The phase of firing of hippocampal neurons during theta oscillations encodes spatial information. Moreover, the spike phase response to synaptic inputs in individual cells depends on the expression of the hyperpolarisation-activated mixed cation current (Ih, which differs between CA3 and CA1 pyramidal neurons. Here, we compared the phase response of these two cell types, as well as their intrinsic membrane properties. We found that both CA3 and CA1 pyramidal neurons show a voltage sag in response to negative current steps but that this voltage sag is significantly smaller in CA3 cells. Moreover, CA3 pyramidal neurons have less prominent resonance properties compared to CA1 pyramidal neurons. This is consistent with differential expression of Ih by the two cell types. Despite their distinct intrinsic membrane properties, both CA3 and CA1 pyramidal neurons displayed bidirectional spike phase control by excitatory conductance inputs during theta oscillations. In particular, excitatory inputs delivered at the descending phase of a dynamic clamp-induced membrane potential oscillation delayed the subsequent spike by nearly 50 mrad. The effect was shown to be mediated by Ih and was counteracted by increasing inhibitory conductance driving the membrane potential oscillation. Using our experimental data to feed a computational model, we showed that differences in Ih between CA3 and CA1 pyramidal neurons could predict frequency-dependent differences in phase response properties between these cell types. We confirmed experimentally such frequency-dependent spike phase control in CA3 neurons. Therefore, a decrease in theta frequency, which is observed in intact animals during novelty, might switch the CA3 spike phase response from unidirectional to bidirectional and thereby promote encoding of the new context.

  1. Voltammetric determination of dopamine and norepinphrine on a glassy carbon electrode modified with poly (L-aspartic acid)

    Indian Academy of Sciences (India)

    Zhangyu Yu; Xiaochun Li; Xueliang Wang; Xinying Ma; Xia Li; Kewei Cao

    2012-03-01

    A convenient and useful method for the voltammetric determination of dopamine (DA) and norepinphrine (NE) based on poly(L-aspartic acid) modified glassy carbon electrode (GCE) is reported in this paper. The modified electrode exhibits excellent electro-catalytic activities for the oxidation-reduction of DA and NE, as well as eliminating the interference of ascorbic acid (AA) and uric acid (UA). Factors influencing the detection processes are optimized and the kinetic parameters are calculated. Under the optimal conditions, the anodic peak currents of DA and NE are linear with their concentration and the detection limits (S/N = 3) are 1.0 × 10−9 mol L-1 for DA and 4.31 10−9 mol L-1 for NE, respectively. The practical application of this method is demonstrated by determining the concentration of NE and DA in injection which is commercially available with satisfactory results. Compared with other electrochemical methods, this method is simple, highly selective and sensitive.

  2. Adsorptive stripping voltammetric determination of nitroimidazole derivative on multiwalled carbon nanotube modified electrodes: influence of size and functionalization of nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Jara-Ulloa, Paola; Canete-Rosales, Paulina; Nunez-Vergara, Luis J; Squella, Juan A., E-mail: asquella@ciq.uchile.c [University of Chile, Santiago (Chile). Chemical and Pharmaceutical Sciences Faculty. Bioelectrochemistry Lab.

    2011-07-01

    1-Methyl-4-nitro-2-bromine methylimidazole (4-NimMeBr), was electrochemically reduced on mercury, glassy carbon and multiwalled carbon nanotubes (MWCNT) modified electrodes. 4-NimMeBr was adsorbed on the MWCNT modified electrode thus permitting the implementation of an adsorptive stripping voltammetric (ASV) method. We have used 4-NimMeBr as a prototype electroactive nitro compound to study the effect of both the size of the nanotubes and its functionalization by oxidation. The oxidized MWCNT forms better dispersions than the non-oxidized, producing electrode surface with higher density of MWCNT as was determined by electrochemical mapping using scanning electrochemical microscopy (SECM). Under the optimized conditions, the peak current was proportional to the concentration of 4-NimMeBr in the range of 10{sup -6} mol L{sup -1} to 10{sup -4} mol L{sup -1} with detection and quantification limits of 4.41 x 10{sup -6} mol L{sup -1} and 6.21 x 10{sup -6} mol L{sup -1}, respectively. The sensibility of bare electrode was 0.01 {mu}A per mmol L{sup -1}, which was lower than the value of 5.34 and 6.97 mA per mmol L{sup -1} obtained using short and large oxidized MWCNT, respectively. (author)

  3. A novel poly(cyanocobalamin) modified glassy carbon electrode as electrochemical sensor for voltammetric determination of peroxynitrite.

    Science.gov (United States)

    Wang, Yan; Chen, Zhen-zhen

    2010-07-15

    This report described the direct voltammetric detection of peroxynitrite (ONOO(-)) at a novel cyanocobalamin modified glassy carbon electrode prepared by electropolymeriation method. The electrochemical behaviors of peroxynitrite at the modified electrode were studied by cyclic voltammetry. The results showed that this new electrochemical sensor exhibited an excellent electrocatalytic activity to oxidation of peroxynitrite. The mechanism of catalysis was discussed. Based on electrocatalytic oxidation of peroxynitrite at the poly(cyanocobalamin) modified electrode, peroxynitrite was sensitively detected by differential pulse voltammetry. Under optimum conditions, the anodic peak current was linear to concentration of peroxynitrite in the range of 2.0x10(-6) to 3.0x10(-4) mol L(-1) with a detection limit of 1.0x10(-7) mol L(-1) (S/N of 3). The proposed method has been applied to determination of peroxynitrite in human serum with satisfactory results. This poly(cyanocobalamin) modified electrode showed high selectivity and sensitivity to peroxynitrite determination, which could be used in quantitative detection of peroxynitrite in vivo and in vitro. Copyright 2010 Elsevier B.V. All rights reserved.

  4. Application of renewable silver amalgam annular band electrode to voltammetric determination of vitamins C, B1 and B2.

    Science.gov (United States)

    Baś, Bogusław; Jakubowska, Małgorzata; Górski, Łukasz

    2011-05-30

    In this work, the design and results of applying silver liquid amalgam film-modified silver solid amalgam annular band electrode (AgLAF-AgSAE), refreshed before each measurement, to voltammetric determination of vitamins C (VC), B(1) (VB1) and B(2) (VB2) are presented. The method is based on adsorptive accumulation of analytes at the AgLAF-AgSAE in a phosphate buffer (VB1), phosphate buffer with Triton X-100 (VB2) and an alkaline borate buffer with Triton X-100 (VC). The analytical parameters and procedure of electrode activation were optimized. The calibration graphs obtained for vitamins C, B(1) and B(2) are linear, respectively, for concentration range 0.05-12, 0.01-0.1 and 0.05-3 mg L(-1). The detection limits were calculated and equaled 0.02, 0.003 and 0.009 mg L(-1), while repeatability of the peak current was 2%, 1% and 3%, respectively. These results are comparable with results obtained for polarographic determination of the same vitamins using mercury electrodes. Finally, the AgLAF-AgSAE was applied to the determination of vitamins in pharmaceutical samples and fruit juices with satisfactory results.

  5. Voltammetric and spectroscopic studies on binding of antitumor Morin, Morin-Cu complex and Morin-β-cyclodextrin with DNA

    Science.gov (United States)

    Temerk, Y. M.; Ibrahim, M. S.; Kotb, M.

    2009-01-01

    A systematic comparative study of the binding of antitumor Morin and its complexes with DNA has been investigated in the Britton-Robison (BR) buffer solutions using voltammetric and spectroscopic methods. The results show that Morin molecule, acting as an intercalator, is inserted into the cavity of the β-cyclodextrin (β-CD) as well as into the base stacking domain of the DNA double helix. The interaction of Morin-Cu complex or the inclusion complex of Morin-β-CD with ds-DNA causes hypochromism in the absorption spectra, along with pronounced changes in the electrochemical behavior of the Morin complexes. An isobestic point and a new spectrum band appeared indicating the formation of the new system of Morin-Cu-DNA at λm = 391 nm and Morin-β-CD-DNA at λm = 375 nm. The intercalation of Morin-Cu and Morin-β-CD complexes with DNA produces an electrochemically inactive supramolecular complex. The binding constants were calculated from the increase of the solubility, the strong hypochromism, and the decrease in peak current of Morin and its complexes upon the addition of the host molecules. Calculation of the thermodynamic parameters of the interaction of the inclusion complex of Morin-β-CD with DNA, including Gibbs free energy change, Helmholz free energy and entropy change shows that the complexation is a spontaneous process of association.

  6. Simultaneous voltammetric determination of morphine and noscapine by adsorptive differential pulse stripping method and least-squares support vector machines.

    Science.gov (United States)

    Niazi, Ali; Ghasemi, Jahanbakhsh; Zendehdel, Mojgan

    2007-11-30

    An adsorptive differential pulse stripping method for the simultaneous determination of morphine and noscapine is proposed. The procedure involves an adsorptive accumulation of morphine and noscapine on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed morphine and noscapine by voltammetric scan using differential pulse modulation. The optimum experimental conditions are: pH 10.0, accumulation potential of -100 mV versus Ag/AgCl, accumulation time of 150 s, scan rate of 40 mV s(-1) and pulse height of 100 mV. Morphine and noscapine peak currents were observed in same potential region at about +0.25 V. The simultaneous determination of morphine and noscapine by using voltammetry is a difficult problem in analytical chemistry, due to voltammogram interferences. The resolution of mixture of morphine and noscapine by the application of least-squares support vector machines (LS-SVM) was performed. The linear dynamic ranges were 0.01-3.10 and 0.015-2.75 microg mL(-1) and detection limits were 3 and 7 ng mL(-1) for morphine and noscapine, respectively. The capability of the method for the analysis of real samples was evaluated by the determination of morphine and noscapine in addict's human plasma with satisfactory results.

  7. Global, Energy-Dependent Ring Current Response During Two Large Storms

    Science.gov (United States)

    Goldstein, J.; Angelopoulos, V.; Burch, J. L.; De Pascuale, S.; Fuselier, S. A.; Genestreti, K. J.; Kurth, W. S.; LLera, K.; McComas, D. J.; Reeves, G. D.; Spence, H. E.; Valek, P. W.

    2015-12-01

    Two recent large (~200 nT) geomagnetic storms occurred during 17--18 March 2015 and 22--23 June 2015. The global, energy-dependent ring current response to these two extreme events is investigated using both global imaging and multi-point in situ observations. Energetic neutral atom (ENA) imaging by the Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission provides a global view of ring current ions. Local measurements are provided by two multi-spacecraft missions. The two Van Allen Probes measure in situ plasma (including ion composition) and fields at ring current and plasmaspheric L values. The recently launched Magnetospheric Multiscale (MMS) comprises four spacecraft that have just begun to measure particles (including ion composition) and fields at outer magnetospheric L-values. We analyze the timing and energetics of the stormtime evolution of ring current ions, both trapped and precipitating, using TWINS ENA images and in situ data by the Van Allen Probes and MMS.

  8. Voltammetric behavior, biocidal effect and synthesis of some new nanomeric fused cyclic thiosemicarbazones and their mercuric(II salts

    Directory of Open Access Journals (Sweden)

    M.S.T. Makki

    2014-11-01

    Full Text Available New nanomeric 3-thioxo-5-methoxy-4,5-dihydro-6-methyl-9-unsubstituted/substituted-1,2,4-triazino[5,6-b]indoles (2a–c and 3-thioxo-5-methoxy-4,5-dihydro-6,7-dihydroxy-1,2,4-triaino[5,6]-cyclobut-6-ene (3 were prepared via reaction of thiosemicarbazide with 5-unsubstitutedand/substituted-indol-2,3-diones and/or 3,4-dihydroxycyclobutane-1,2-dione in methanol–concentrated HCl at room temperature. A series of mercury(II–ligand salts e.g. compound 4b and Hg(II complexes 5a,b and 6 of cyclic Schiff base were prepared. Structures of these compounds were established by elemental analysis and spectral measurements. The redox characteristics of selected compounds were studied for use as chelating agents for stripping voltammetric determination of mercuric(II ions in aqueous media. The compounds were also screened for their use as molluscicidal agents against Biomophalaria Alexandrina Snails responsible for Bilhariziasis.

  9. Breast fibromatosis response to tamoxifen: dynamic MRI findings and review of the current treatment options.

    Science.gov (United States)

    Plaza, Michael J; Yepes, Monica

    2012-03-01

    Breast fibromatosis is a rare entity responsible for 0.2% of all solid breast tumors. It has been associated with scars, pregnancy, implants, and familial adenomatous polyposis. We present an interesting case of breast fibromatosis in a 29 year old woman which encroached upon her saline implant and subsequently filled its cavity once the implant was removed. The patient was put on tamoxifen therapy and at 14 month follow-up there was a significant decrease in the size of the mass. Dynamic MRI images are offered for review and current treatment options are discussed.

  10. Modification of carbon paste electrode with Fe(III)-clinoptilolite nano-particles for simultaneous voltammetric determination of acetaminophen and ascorbic acid

    Energy Technology Data Exchange (ETDEWEB)

    Sharifian, Samira [Department of Chemistry, Shahreza Branch, Islamic Azad University, P.O. Box 311-86145, Shahreza, Isfahan (Iran, Islamic Republic of); Young Researchers and Elite Club, Shahreza Branch, Islamic Azad University, Shahreza (Iran, Islamic Republic of); Nezamzadeh-Ejhieh, Alireza, E-mail: arnezamzadeh@iaush.ac.ir [Department of Chemistry, Shahreza Branch, Islamic Azad University, P.O. Box 311-86145, Shahreza, Isfahan (Iran, Islamic Republic of); Young Researchers and Elite Club, Shahreza Branch, Islamic Azad University, Shahreza (Iran, Islamic Republic of); Razi Chemistry Research Center (RCRC), Shahreza Branch, Islamic Azad University, Isfahan (Iran, Islamic Republic of)

    2016-01-01

    A novel carbon paste electrode (CPE) modified with Fe(III)-exchanged clinoptilolite nano-particles (Fe(III)-NClino/CPE) was constructed and used for simultaneous voltammetric (CV, SqW and chronoamperometry) determination of ascorbic acid and acetaminophen. Raw and modified zeolites were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). The square wave peak current was linearly increased in the concentration ranges of 1.0 × 10{sup −9}–1.0 × 10{sup −2} mol L{sup −1} for ascorbic acid and 1.0 × 10{sup –10–}1.0 × 10{sup −2} mol L{sup −1} for acetaminophen with detection limits of 1.8 × 10{sup −9} mol L{sup −1} and 9.9 × 10{sup −10} mol L{sup −1}, respectively. The detection limits of 2.4 × 10{sup −10} mol L{sup −1} and 2.5 × 10{sup −11} mol L{sup −1} were also obtained for AA and AC in chronoamperometric measurements, respectively. The diffusion coefficients of 7.5 × 10{sup −5} cm{sup 2} s{sup −1} and 2.4 × 10{sup −5} cm{sup 2} s{sup −1} were respectively calculated for the oxidation of AC and AA by chronoamperometry. The proposed electrode exhibited high sensitivity and good stability, and would be valuable for the clinical assay of ascorbic acid and acetaminophen. - Graphical abstract: Comparison of CV voltammograms of the raw CPE (‘a’ and ‘b’) and the modified Fe(III)-NClino-CPE (‘c’ and ‘d’) confirmed good electrocatalytic activity of the modified electrode for voltammetric determination of AC and AA, so the peak currents significantly increased in presence of AA or AC species in solution (‘c’ and ‘d’). - Highlights: • Usefulness of Fe(III)-Nclino for simultaneous voltammetric determination of AA + AC • Electrocatalytic behavior of the electrode for AA determination • Complexation behavior of the electrode for AC determination • Considerable increase in sensitivity of the process • More efficient of nanonized clinoptilolite than the micronized one.

  11. Transcription Factors and Plants Response to Drought Stress: Current Understanding and Future Directions

    Science.gov (United States)

    Joshi, Rohit; Wani, Shabir H.; Singh, Balwant; Bohra, Abhishek; Dar, Zahoor A.; Lone, Ajaz A.; Pareek, Ashwani; Singla-Pareek, Sneh L.

    2016-01-01

    Increasing vulnerability of plants to a variety of stresses such as drought, salt and extreme temperatures poses a global threat to sustained growth and productivity of major crops. Of these stresses, drought represents a considerable threat to plant growth and development. In view of this, developing staple food cultivars with improved drought tolerance emerges as the most sustainable solution toward improving crop productivity in a scenario of climate change. In parallel, unraveling the genetic architecture and the targeted identification of molecular networks using modern “OMICS” analyses, that can underpin drought tolerance mechanisms, is urgently required. Importantly, integrated studies intending to elucidate complex mechanisms can bridge the gap existing in our current knowledge about drought stress tolerance in plants. It is now well established that drought tolerance is regulated by several genes, including transcription factors (TFs) that enable plants to withstand unfavorable conditions, and these remain potential genomic candidates for their wide application in crop breeding. These TFs represent the key molecular switches orchestrating the regulation of plant developmental processes in response to a variety of stresses. The current review aims to offer a deeper understanding of TFs engaged in regulating plant’s response under drought stress and to devise potential strategies to improve plant tolerance against drought. PMID:27471513

  12. Fractional Modeling of the AC Large-Signal Frequency Response in Magnetoresistive Current Sensors

    Directory of Open Access Journals (Sweden)

    Sergio Iván Ravelo Arias

    2013-12-01

    Full Text Available Fractional calculus is considered when derivatives and integrals of non-integer order are applied over a specific function. In the electrical and electronic domain, the transfer function dependence of a fractional filter not only by the filter order n, but additionally, of the fractional order α is an example of a great number of systems where its input-output behavior could be more exactly modeled by a fractional behavior. Following this aim, the present work shows the experimental ac large-signal frequency response of a family of electrical current sensors based in different spintronic conduction mechanisms. Using an ac characterization set-up the sensor transimpedance function  is obtained considering it as the relationship between sensor output voltage and input sensing current,[PLEASE CHECK FORMULA IN THE PDF]. The study has been extended to various magnetoresistance sensors based in different technologies like anisotropic magnetoresistance (AMR, giant magnetoresistance (GMR, spin-valve (GMR-SV and tunnel magnetoresistance (TMR. The resulting modeling shows two predominant behaviors, the low-pass and the inverse low-pass with fractional index different from the classical integer response. The TMR technology with internal magnetization offers the best dynamic and sensitivity properties opening the way to develop actual industrial applications.

  13. Transcription factors and plant response to drought stress: Current understanding and future directions

    Directory of Open Access Journals (Sweden)

    Rohit Joshi

    2016-07-01

    Full Text Available Increasing vulnerability of plants to a variety of stresses such as drought, salt and extreme temperatures poses a global threat to sustained growth and productivity of major crops. Of these stresses, drought represents a considerable threat to plant growth and development. In view of this, developing staple food cultivars with improved drought tolerance emerges as the most sustainable solution towards improving crop productivity in a scenario of climate change. In parallel, unraveling the genetic architecture and the targeted identification of molecular networks using modern OMICS analyses, that can underpin drought tolerance mechanisms, is urgently required. Importantly, integrated studies intending to elucidate complex mechanisms can bridge the gap existing in our current knowledge about drought stress tolerance in plants. It is now well established that drought tolerance is regulated by several genes, including transcription factors (TFs that enable plants to withstand unfavorable conditions, and these remain potential genomic candidates for their wide application in crop breeding. These TFs represent the key molecular switches orchestrating the regulation of plant developmental processes in response to a variety of stresses. The current review aims to offer a deeper understanding of TFs engaged in regulating plant’s response under drought stress and to devise potential strategies to improve plant tolerance against drought.

  14. Waveguide-integrated black phosphorus photodetector with high responsivity and low dark current

    CERN Document Server

    Youngblood, Nathan; Koester, Steven J; Li, Mo

    2014-01-01

    Layered two-dimensional materials have shown novel optoelectronic properties and are well suited to be integrated in planar photonic circuits. For example, graphene has been utilized as a wideband photodetector. However, because it lacks a band gap, graphene photodetectors suffer from extremely high dark current8. In contrast, few-layer black phosphorous, the latest addition to the family of 2D materials, is well-suited for photodetector applications due to its narrow but finite energy gap. Here, we demonstrate a gated multilayer black phosphorus photodetector integrated in a silicon photonic waveguide operating in the near-infrared telecom band. In a significant advantage over graphene devices, black phosphorus photodetectors can operate under a bias with very low dark current and attain intrinsic responsivity up to 125 mA/W and 657 mA/W in 11.5nm and 100 nm thick devices, respectively. The photocurrent is dominated by the photovoltaic effect with a high response bandwidth exceeding 3 GHz.

  15. Waveguide-integrated black phosphorus photodetector with high responsivity and low dark current

    Science.gov (United States)

    Youngblood, Nathan; Chen, Che; Koester, Steven J.; Li, Mo

    2015-04-01

    Layered two-dimensional materials have demonstrated novel optoelectronic properties and are well suited for integration in planar photonic circuits. Graphene, for example, has been utilized for wideband photodetection. However, because graphene lacks a bandgap, graphene photodetectors suffer from very high dark current. In contrast, layered black phosphorous, the latest addition to the family of two-dimensional materials, is ideal for photodetector applications due to its narrow but finite bandgap. Here, we demonstrate a gated multilayer black phosphorus photodetector integrated on a silicon photonic waveguide operating in the near-infrared telecom band. In a significant advantage over graphene devices, black phosphorus photodetectors can operate under bias with very low dark current and attain an intrinsic responsivity up to 135 mA W-1 and 657 mA W-1 in 11.5-nm- and 100-nm-thick devices, respectively, at room temperature. The photocurrent is dominated by the photovoltaic effect with a high response bandwidth exceeding 3 GHz.

  16. Cyclic voltammetric technique for the determination of the critical micelle concentration of surfactants, self-diffusion coefficient of micelles, and partition coefficient of an electrochemical probe

    Energy Technology Data Exchange (ETDEWEB)

    Mandal, A.B.; Nair, B.U. (Central Leather Research Inst., Madras (India))

    1991-10-31

    Critical micelle concentrations (cmc) of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) surfactants in aqueous solution have been determined by using the cyclic voltammetric technique. (Co(en){sub 3})(ClO{sub 4}){sub 3} has been used as the redox-active electrochemical probe. The cmc values so obtained for the surfactants were found to be in good agreement with the literature values. The partition coefficient, K, of the electrochemical probe between water and surfactants in nonmicellar and micellar states was estimated using the peak current, i{sub p} and half-wave potential, E{sub 1/2} values. The self-diffusion coefficient, D{sub m}, interaction parameter, k{sub f}, and hydrodynamic radius of the micelles were also estimated. The results suggest that the probe is sensitive to the nature of surfactant as well as surfactant concentration.

  17. A voltammetric sensor with a multiwall carbon nanotube paste electrode and naphthol green as a mediator for the determination of N-actylcysteine in the presence of tryptophan

    Institute of Scientific and Technical Information of China (English)

    Mohsen Keyvanfard; Maryam Tahmasbi; Hassan Karimi-Maleh; Khadijeh Alizad

    2014-01-01

    A multiwall carbon nanotube modified electrode prepared by incorporating multiwall carbon nanotubes in the electrode of a sensor and naphthol green as a homogeneous mediator was used as a voltammetric sensor for the determination of N-actylcysteine (N-AC) in the presence of tryptophan (Trp). The voltammograms of differential pulse voltammetry of N-AC in a mixture with Trp were separated from each other by a potential difference of 200 mV, which allowed the determination of both N-AC and Trp simultaneously. Under the optimum conditions, the electrocatalytic currents increased linearly with N-AC concentration in the range of 0.25-400 μmol/L (two linear segments with different slopes). The detection limit for N-AC was 0.08 μmol/L. The kinetic parameters of the system were determined using electrochemical methods. The method was applied for the determination of N-AC in drug and urine samples.

  18. A miniaturized Rogowski current transducer with wide bandwidth and fast response

    Science.gov (United States)

    Bian, Hao; Shan, Chao; Liu, Keyin; Chen, Feng; Yang, Qing; Yong, Jiale; Hou, Xun

    2016-11-01

    The miniaturization of the 3D Rogowski current transducer down to the micro-scale is essential for device integration and expansion of its application scope, particularly for ‘lab-on-a-chip’ systems. However, fabrication of 3D miniaturized Rogowski coils remains challenging as most relative methods still rely on the 2D micromachining process. In this paper, a miniaturized Rogowski coil current transducer was fabricated using an improved femtosecond laser wet etching technology and a metal microsolidification process, in which a metal alloy with a relatively high melting point was used and a robust but simple packaging structure based on a conical electrode was developed. The results show that the miniaturized Rogowski coil current transducer reveals a response time of less than 1 ns, high sensitivity and good detection capability for high-frequency electrical signals. The miniaturized Rogowski coil can easily be integrated into functional microsystems and will be widely applicable for high-frequency electric signal detection and circuit protection.

  19. Voltammetric and impedimetric properties of nano-scaled -Fe2O3 catalysts supported on multi-walled carbon nanotubes: catalytic detection of dopamine

    CSIR Research Space (South Africa)

    Adekunle, AS

    2010-12-01

    Full Text Available to their different surface electroactive materials. 3.6. Interference study Figure 10 shows the square wave voltammetric responses of AA in the absence (i) 1 mM AA alone, and mixture of (ii) 4.76 ?M DA and 0.95 mM AA, (iii) 9.09 ?M DA and 0.91 mM AA, (iv) 13....04 ?M DA and 0.87 mM AA, (v) 20.0 ?M DA and 0.8 mM AA, (vi) 25.93 ?M DA and 0.74 mM AA and (vii) 28.57 ?M DA and 0.71 mM AA in PBS pH 7.0 at the EPPGE-MWCNT-Fe2O3 electrode. In the presence of DA, AA signal was seen at about 0.18 V and DA at around 0...

  20. Malignant gliomas: current perspectives in diagnosis, treatment, and early response assessment using advanced quantitative imaging methods

    Directory of Open Access Journals (Sweden)

    Ahmed R

    2014-03-01

    Full Text Available Rafay Ahmed,1 Matthew J Oborski,2 Misun Hwang,1 Frank S Lieberman,3 James M Mountz11Department of Radiology, 2Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA; 3Department of Neurology and Department of Medicine, Division of Hematology/Oncology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USAAbstract: Malignant gliomas consist of glioblastomas, anaplastic astrocytomas, anaplastic oligodendrogliomas and anaplastic oligoastrocytomas, and some less common tumors such as anaplastic ependymomas and anaplastic gangliogliomas. Malignant gliomas have high morbidity and mortality. Even with optimal treatment, median survival is only 12–15 months for glioblastomas and 2–5 years for anaplastic gliomas. However, recent advances in imaging and quantitative analysis of image data have led to earlier diagnosis of tumors and tumor response to therapy, providing oncologists with a greater time window for therapy management. In addition, improved understanding of tumor biology, genetics, and resistance mechanisms has enhanced surgical techniques, chemotherapy methods, and radiotherapy administration. After proper diagnosis and institution of appropriate therapy, there is now a vital need for quantitative methods that can sensitively detect malignant glioma response to therapy at early follow-up times, when changes in management of nonresponders can have its greatest effect. Currently, response is largely evaluated by measuring magnetic resonance contrast and size change, but this approach does not take into account the key biologic steps that precede tumor size reduction. Molecular imaging is ideally suited to measuring early response by quantifying cellular metabolism, proliferation, and apoptosis, activities altered early in treatment. We expect that successful integration of quantitative imaging biomarker assessment into the early phase of clinical trials could provide a novel approach for testing new therapies

  1. pH-Responsive carriers for oral drug delivery: challenges and opportunities of current platforms.

    Science.gov (United States)

    Liu, Lin; Yao, WenDong; Rao, YueFeng; Lu, XiaoYang; Gao, JianQing

    2017-11-01

    Oral administration is a desirable alternative of parenteral administration due to the convenience and increased compliance to patients, especially for chronic diseases that require frequent administration. The oral drug delivery is a dynamic research field despite the numerous challenges limiting their effective delivery, such as enzyme degradation, hydrolysis and low permeability of intestinal epithelium in the gastrointestinal (GI) tract. pH-Responsive carriers offer excellent potential as oral therapeutic systems due to enhancing the stability of drug delivery in stomach and achieving controlled release in intestines. This review provides a wide perspective on current status of pH-responsive oral drug delivery systems prepared mainly with organic polymers or inorganic materials, including the strategies used to overcome GI barriers, the challenges in their development and future prospects, with focus on technology trends to improve the bioavailability of orally delivered drugs, the mechanisms of drug release from pH-responsive oral formulations, and their application for drug delivery, such as protein and peptide therapeutics, vaccination, inflammatory bowel disease (IBD) and bacterial infections.

  2. Tropical forest responses to increasing [CO2]: current knowledge and opportunities for future research

    Energy Technology Data Exchange (ETDEWEB)

    Cernusak, Lucas [Australian National University, Canberra, Australia; Winter, Klaus [Smithsonian Tropical Research Institute; Dalling, James [University of Illinois, Urbana-Champaign; Holtum, Joseph [James Cook University; Jaramillo, Carlos [Smithsonian Tropical Research Institute; Korner, Christian [University of Basel; Leakey, Andrew D.B. [University of Illinois; Norby, Richard J [ORNL; Poulter, Benjamin [Laboratoire des Sciences du Climat et de l' Environement, France; Turner, Benjamin [Smithsonian Tropical Research Institute; Wright, S. Joseph [Smithsonian Tropical Research Institute

    2013-01-01

    Elevated atmospheric [CO2] (ca) will undoubtedly affect the metabolism of tropical forests worldwide; however, critical aspects of how tropical forests will respond remain largely unknown. Here we review the current state of knowledge about physiological and ecological responses, with the aim of providing a framework that can help to guide future experimental research. Modelling studies have indicated that elevated ca can potentially stimulate photosynthesis more in the tropics than at higher latitudes, because suppression of photorespiration by elevated ca increases with temperature. However, canopy leaves in tropical forests could also potentially reach a high temperature threshold under elevated ca that will moderate the rise in photosynthesis. Belowground responses, including fine root production, nutrient foraging, and soil organic matter processing, will be especially important to the integrated ecosystem response to elevated CO2. Water-use efficiency will increase as ca rises, potentially impacting upon soil moisture status and nutrient availability. Recruitment may be differentially altered for some functional groups, potentially decreasing ecosystem carbon storage. Whole-forest CO2 enrichment experiments are urgently needed to test predictions of tropical forest functioning under elevated ca. Smaller scale experiments in the understory and in gaps would also be informative, and could provide stepping stones toward stand-scale manipulations.

  3. A direct in situ fingerprinting method for acid rock drainage using voltammetric techniques with a single renewable gold microelectrode.

    Science.gov (United States)

    Nuzzio, Donald B; Zettler, Erik R; Aguilera, Angeles; Amaral-Zettler, Linda A

    2011-04-15

    Electrochemistry allows for rapid identification of multiple metals and other chemical complexes common in acid rock drainage (ARD) systems. Voltammetric scans using a single gold microelectrode of water samples from geochemically distinct areas of the Río Tinto (RT) in southwestern Spain were clearly recognizable in the field and in samples stored at room temperature for over 6 months. Major voltammetric peaks of iron(III) and copper(II) were identified on a single constantly renewable gold microelectrode. Confirmation of these peaks was performed by spiking with standard metal solutions in the laboratory. This voltammetric technique is a rapid, direct and inexpensive in situ method for identification of water sources and their chemical characteristics, as well as an economical way to monitor environmental changes and remediation efforts.

  4. Anodic stripping voltammetric determination of Zn, Pb and Cu traces in whisky samples

    Energy Technology Data Exchange (ETDEWEB)

    Barbeira, P.J.S. [Departamento de Quimica - ICEx - UFMG, Belo Horizonte, MG (Brazil); Stradiotto, N.R. [Departamento de Quimica - FFCLRP - USP, Ribeirao Preto, SP (Brazil)

    1998-07-01

    The simultaneous ``in natura`` determination of trace Zn, Pb and Cu in whisky samples by anodic stripping voltammetry (ASV), using a hanging mercury drop electrode, without previous treatment or addition of supporting electrolyte is described. The choice of an appropriate stripping voltammetric method and deposition potential minimizes the influence of the organic content and ensures a good reproducibility of the measurements. The reliability of the method was tested comparing the results with those of atomic absorption spectroscopy (AAS), with differences of about 10%. The method allows the determination of heavy metal ions in the {mu}g L{sup -1} range. (orig.) With 3 figs., 1 tab., 18 refs.

  5. A New Voltammetric Enzyme Immunoassay System for the Detection of Alkaline Phosphatase

    Institute of Scientific and Technical Information of China (English)

    KuiJIAO; WeiSUN; 等

    2002-01-01

    A new voltammetric enzyme immunoassay system was invesigated based on p-nitrophenyl phosphate (PNPP) as the subsrate for alkaline phosphatase (ALP). PNPP is enzymatically hydrolyzed and the product p-nitrophenol (PNP) is detected by differential pulse voltammetry (DPV), which can be oxidized at +1.02 V(vs.Ag/AgCl) on bare glass carbon electrode (GCE). The conditions for enzymatic reaction and electrochemical detection were studied. According to this method,ALP can be detected with a detection limit of 2.8×102 mU/L and a linear range of 4.0×102-1.0×106mU/L.

  6. A New Voltammetric Enzyme Immunoassay System for the Detection of Alkaline Phosphatase

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A new voltammetric enzyme immunoassay system was investigated based on p-nitrophenyl phosphate (PNPP) as the substrate for alkaline phosphatase (ALP). PNPP is enzymatically hydrolyzed and the product p-nitrophenol (PNP) is detected by differential pulse voltammetry (DPV), which can be oxidized at +1.02 V (vs. Ag/AgCl) on bare glass carbon electrode (GCE). The conditions for enzymatic reaction and electrochemical detection were studied. According to this method, ALP can be detected with a detection limit of 2.8′102 mU/L and a linear range of 4.0′102 ~ 1.0′106 mU/L.

  7. Stripping voltammetric determination of mercury(II) at antimony-coated carbon paste electrode.

    Science.gov (United States)

    Ashrafi, Amir M; Vytřas, Karel

    2011-10-15

    A new procedure was elaborated to determine mercury(II) using an anodic stripping square-wave voltammetry at the antimony film carbon paste electrode (SbF-CPE). In highly acidic medium of 1M hydrochloric acid, voltammetric measurements can be realized in a wide potential window. Presence of cadmium(II) allows to separate peaks of Hg(II) and Sb(III) and apparently catalyses reoxidation of electrolytically accumulated mercury, thus allowing its determination at ppb levels. Calibration dependence was linear up to 100 ppb Hg with a detection limit of 1.3 ppb. Applicability of the method was tested on the real river water sample.

  8. Biological responses to current UV-B radiation in Arctic regions

    DEFF Research Database (Denmark)

    Albert, Kristian; N. Mikkelsen, Teis; Ro-Poulsen, Helge

    Depletion of the ozone layer and the consequent increase in solar ultraviolet-B radiation (UV-B) may impact living conditions for arctic plants significantly. In order to evaluate how the prevailing UV-B fluxes affect the heath ecosystem at Zackenberg (74°30'N, 20°30'W) and other high......-arctic regions, manipulation experiments with various set-ups have been performed. Activation of plant defence mechanisms by production of UV-B absorbing compounds was significant in ambient UV-B in comparison to a filter treatment reducing the UV-B radiation. Despite the UV-B screening response, ambient UV...... (mycorrhiza) or in the biomass of microbes in the soil of the root zone. However, the composition of the soil microbial community was different in the soils under ambient and reduced UV radiation after three treatment years. These results provide new insight into the negative impact of current UV-B fluxes...

  9. High-grade glioma management and response assessment—recent advances and current challenges

    Science.gov (United States)

    Khan, M.N.; Sharma, A.M.; Pitz, M.; Loewen, S.K.; Quon, H.; Poulin, A.; Essig, M.

    2016-01-01

    The management of high-grade gliomas (hggs) is complex and ever-evolving. The standard of care for the treatment of hggs consists of surgery, chemotherapy, and radiotherapy. However, treatment options are influenced by multiple factors such as patient age and performance status, extent of tumour resection, biomarker profile, and tumour histology and grade. Follow-up cranial magnetic resonance imaging (mri) to differentiate treatment response from treatment effect can be challenging and affects clinical decision-making. An assortment of advanced radiologic techniques—including perfusion imaging with dynamic susceptibility contrast mri, dynamic contrast-enhanced mri, diffusion-weighted imaging, proton spectroscopy, mri subtraction imaging, and amino acid radiotracer imaging—can now incorporate novel physiologic data, providing new methods to help characterize tumour progression, pseudoprogression, and pseudoresponse. In the present review, we provide an overview of current treatment options for hgg and summarize recent advances and challenges in imaging technology. PMID:27536188

  10. The decrease in hypothalamic dopamine secretion induced by suckling: comparison of voltammetric and radioisotopic methods of measurement. [Rats

    Energy Technology Data Exchange (ETDEWEB)

    Plotsky, P.M.; Neill, J.D.

    1982-03-01

    Previous in situ voltammetric microelectrode measurements of median eminence dopamine release during mammary nerve stimulation of anesthetized lactating rats revealed a transient (1-3 min) 70% decline of dopamine concentrations. This dopamine was believed to be destined for secretion into the hypophysial portal circulation, but direct experimental support for this supposition was lacking. Thus, in the present study, (3H)dopamine release into brief sequential samples of hypophysial portal blood was compared with dopamine release in the median eminence measured by voltammetry. Lactating female rats were urethane anesthetized, and the median eminence pituitary region was exposed. (3H)Tyrosine was injected into a jugular cannula (100 microCi) followed by continuous infusion (5 microCi/min). In a preliminary experiment, this regimen produced a steady state level of (3H)dopamine in the portal blood within 45 min. In subsequent experiments, portal blood was collected as sequential 3-min samples, and electrochemical sampling from a microelectrode placed in the median eminence occurred at 1-min intervals. Electrochemical current resulting from the oxidation of dopamine in the medial median eminence was unvarying throughout the 75-min experiment in control rats (n . 4) and during the 30-min control period preceding mammary nerve stimulation in the other group (n . 4). These results were paralled by (3H) dopamine levels in portal blood during the same periods of time. All animals showed simultaneous decreases in oxidation current and (3H)dopamine levels within 1-4 min after initiation of mammary nerve stimulation. These and earlier results demonstrate that mammary nerve stimulation (and by extension, suckling) induces a momentary, but profound, decrease in hypothalamic dopamine secretion which precedes or accompanies the rise in PRL secretion evoked by the same stimulus.

  11. Thermal stimulated current response in cupric oxide single crystal thin films over a wide temperature range

    Science.gov (United States)

    Yang, Kungan; Wu, Shuxiang; Yu, Fengmei; Zhou, Wenqi; Wang, Yunjia; Meng, Meng; Wang, Gaili; Zhang, Yueli; Li, Shuwei

    2017-01-01

    Cupric oxide single crystal thin films (~26 nm) were grown by plasma-assisted molecular beam epitaxy. X-ray diffraction, Raman spectra and in situ reflection high-energy electron diffraction show that the thin films are 2  ×  2 reconstructed with an in-plane compression and out-of-plane stretching. A thermal stimulated current measurement indicates that the electric polarization response is shown in the special 2D cupric oxide single crystal thin film over a wide temperature range from 130 K to near-room temperature. We infer that the abnormal electric response involves the changing of phase transition temperature induced by structure distortion, the spin frustration and the magnetic fluctuation effect of a short-range magnetic order, or the combined action of both of the two factors mentioned above. This work suggests a promising clue for finding new room temperature single phase multiferroics or tuning phase transition temperatures.

  12. Reducing aggressive responses to social exclusion using transcranial direct current stimulation.

    Science.gov (United States)

    Riva, Paolo; Romero Lauro, Leonor J; DeWall, C Nathan; Chester, David S; Bushman, Brad J

    2015-03-01

    A vast body of research showed that social exclusion can trigger aggression. However, the neural mechanisms involved in regulating aggressive responses to social exclusion are still largely unknown. Transcranial direct current stimulation (tDCS) modulates the excitability of a target region. Building on studies suggesting that activity in the right ventrolateral pre-frontal cortex (rVLPFC) might aid the regulation or inhibition of social exclusion-related distress, we hypothesized that non-invasive brain polarization through tDCS over the rVLPFC would reduce behavioral aggression following social exclusion. Participants were socially excluded or included while they received tDCS or sham stimulation to the rVLPFC. Next, they received an opportunity to aggress. Excluded participants demonstrated cognitive awareness of their inclusionary status, yet tDCS (but not sham stimulation) reduced their behavioral aggression. Excluded participants who received tDCS stimulation were no more aggressive than included participants. tDCS stimulation did not influence socially included participants' aggression. Our findings provide the first causal test for the role of rVLPFC in modulating aggressive responses to social exclusion. Our findings suggest that modulating activity in a brain area (i.e. the rVLPFC) implicated in self-control and emotion regulation can break the link between social exclusion and aggression.

  13. Observation of ocean current response to 1998 Hurricane Georges in the Gulf of Mexico

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The ocean current response to a hurricane on the shelf-break is examined. The study area is the DeSoto Canyon in the northeast Gulf of Mexico, and the event is the passage of 1998 Hurricane Georges with a maximum wind speed of 49 m/s. The data sets used for analysis consist of the mooring data taken by the Field Program of the DeSoto Canyon Eddy Intrusion Study, and simultaneous winds observed by NOAA (National Oceanic and Atmospheric Administration) Moored Buoy 42040. Time-depth ocean current energy density images derived from the observed data show that the ocean currents respond almost immediately to the hurricane with important differences on and offthe shelf. On the shelf, in the shallow water of 100 m, the disturbance penetrates rapidly downward to the bottom and forms two energy peaks, the major peak is located in the mixed layer and the secondary one in the lower layer. The response dissipates quickly after external forcing disappears. Off the shelf, in the deep water, the major disturbance energy seems to be trapped in the mixed layer with a trailing oscillation; although the disturbance signals may still be observed at the depths of 500 and 1 290 m. Vertical dispersion analysis reveals that the near-initial wave packet generated off the shelf consists of two modes. One is a barotropic wave mode characterized by a fast decay rate of velocity amplitude of 0.020 s-1, and the other is baroclinic wave mode characterized by a slow decay rate of 0.006 9 s-1. The band-pass-filtering and empirical function techniques are employed to the frequency analysis. The results indicate that all frequencies shift above the local inertial frequency. On the shelf, the average frequency is 1.04fin the mixed layer, close to the diagnosed frequency of the first baroclinic mode, and the average frequency increases to 1.07fin the thermocline.Off the shelf, all frequencies are a little smaller than the diagnosed frequency of the first mode. The average frequency decreases from 1

  14. Individual Differences and State-Dependent Responses in Transcranial Direct Current Stimulation.

    Science.gov (United States)

    Hsu, Tzu-Yu; Juan, Chi-Hung; Tseng, Philip

    2016-01-01

    Transcranial direct current stimulation (tDCS) has been extensively used to examine whether neural activities can be selectively increased or decreased with manipulations of current polarity. Recently, the field has reevaluated the traditional anodal-increase and cathodal-decrease assumption due to the growing number of mixed findings that report the effects of the opposite directions. Therefore, the directionality of tDCS polarities and how it affects each individual still remain unclear. In this study, we used a visual working memory (VWM) paradigm and systematically manipulated tDCS polarities, types of different independent baseline measures, and task difficulty to investigate how these factors interact to determine the outcome effect of tDCS. We observed that only low-performers, as defined by their no-tDCS corsi block tapping (CBT) performance, persistently showed a decrement in VWM performance after anodal stimulation, whereas no tDCS effect was found when participants were divided by their performance in digit span. In addition, only the optimal level of task difficulty revealed any significant tDCS effect. All these findings were consistent across different blocks, suggesting that the tDCS effect was stable across a short period of time. Lastly, there was a high degree of intra-individual consistency in one's responsiveness to tDCS, namely that participants who showed positive or negative effect to anodal stimulation are also more likely to show the same direction of effects for cathodal stimulation. Together, these findings imply that tDCS effect is interactive and state dependent: task difficulty and consistent individual differences modulate one's responsiveness to tDCS, while researchers' choices of independent behavioral baseline measures can also critically affect how the effect of tDCS is evaluated. These factors together are likely the key contributors to the wide range of "noises" in tDCS effects between individuals, between stimulation protocols

  15. Modified electrode voltammetric sensors for trace metals in environmental samples

    Directory of Open Access Journals (Sweden)

    Brett Christopher M.A.

    2000-01-01

    Full Text Available Nafion-modified mercury thin film electrodes have been investigated for the analysis of trace metals in environmental samples of waters and effluent by batch injection analysis with square wave anodic stripping voltammetry. The method, involving injection over the detector electrode of untreated samples of volume of the order of 50 microlitres has fast response, blocking and fouling of the electrode is minimum as shown by studies with surface-active components. Comparison is made between glassy carbon substrate electrodes and carbon fibre microelectrode array substrates, the latter leading to a small sensitivity enhancement. Application to analysis of river water and industrial effluent for labile zinc, cadmium, lead and copper ions is demonstrated in collected samples and after acid digestion.

  16. Voltammetric Determination of Captopril Using Chlorpromazine as a Homogeneous Mediator

    Directory of Open Access Journals (Sweden)

    Hossein Bahramipur

    2011-01-01

    Full Text Available Chlorpromazine was used as a homogeneous electrocatalyst in the oxidation of captopril. The anodic peak current of chlorpromazine was increased substantially in the presence of low concentrations of captopril (pH 4. Cyclic voltammetry and chronoamperometry were used to study the kinetics of the catalytic electron transfer reaction. The values of electron transfer coefficient ( and catalytic rate constant (cat were estimated to be 0.34 and 8.48×102M−1sec−1, respectively. Linear sweep voltammetry was used for the determination of captopril in the presence of chlorpromazine. A linear calibration curve was obtained in the concentration range of captopril of 10.0–300.0 μM, with a limit of detection of 3.65 μM. The relative standard deviation (RSD% for 5 replicate measurements of captopril (100 μM was 1.96%. The method was applied to the determination of captopril in pharmaceutical formulations and blood serum samples with satisfactory results.

  17. Voltammetric studies on free radicals of lower fatty alco- hols

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In this work, both generation and reduction processes of the a-radicals of lower fatty alcohols were studied by voltammetry in lower fatty alcohols/peroxydisul- fate/phosphate buffer system. Experimental results showed that such three reactions were successively completed at negative potential on mercury electrode surface: (ⅰ) sulfate radical anion was generated electrochemically from one-electron reduction of peroxydisulfate ion , (ⅱ) the oxidized lower fatty alcohols to the corresponding a-radicals and (ⅲ) the a-radicals were reduced in one-electron and one-proton addition to produce their own re-duction waves. The apparent free energy ΔrGm of the a-radicals of lower straight-chain fatty alcohols such as metha-nol, ethanol, propanol, butanol and pentanol obtained were 107.09, 116.74, 122.53, 126.39 and 129.28 kJ·mol/L, respec-tively. The proposed method is more simple and convenient than the current approaches based on the radical-chain reac-tion for studying alcohol oxidation.

  18. Electrochemistry and determination of cefdinir by voltammetric and computational approaches

    Directory of Open Access Journals (Sweden)

    İbrahim Hüdai Taşdemir

    2014-12-01

    Full Text Available The oxidation and reduction behavior of cefdinir (CEF was studied by experimental methods and computational calculations at B3LYP/6-31+G (d//AM1. Voltammetric studies were carried out based on two irreversible reduction peaks at approximately −0.5 and −1.2 V on a hanging mercury drop electrode (HMDE and on one irreversible oxidation peak at approximately 1.0 V on a glassy carbon electrode (GCE versus Ag/AgCl, KCl (3.0M in Britton–Robinson (BR buffer at pH 4.2 and 5.0, respectively. Differential pulse adsorptive stripping voltammetric methods have been developed and validated for determination of CEF in different samples. The linear range was established as 0.25–40.0 μM for HMDE and 0.40–10.0 μM for GCE. Limit of quantification was calculated to be 0.20 and 0.26 μM for HMDE and GCE, respectively. These methods were successfully applied to assay the drug in tablets and human serum with good recoveries between 92.7% and 107.3% having relative standard deviation less than 10%.

  19. TRACE LEVEL VOLTAMMETRIC DETERMINATION OF HEAVY METALS AND TOTAL MERCURY IN TEA MATRICES (Camellia sinensis).

    Science.gov (United States)

    Melucci, Dora; Locatelli, Marcello; Locatelli, Clinio

    2013-10-24

    An analytical procedure regarding the voltammetric determination of mercury(II), copper(II), lead(II), cadmium(II) and zinc(II) by square wave anodic stripping voltammetry (SWASV) in matrices involved in food chain is proposed. In particular, tea leaves were analysed as real samples. The digestion of each matrix was carried out using a concentrated HCl-HNO3-H2SO4 acidic attack mixture; 0.01 mol L(-1) EDTA-Na2 + 0.15 mol L(-1) NaCl + 0.5 mol L(-1) HCl was employed as the supporting electrolyte. The voltammetric measurements were carried out using a conventional three electrode cell, employing, as working electrodes, a gold electrode (GE) and a stationary hanging mercury drop electrode (HMDE). The analytical procedure has been verified on the standard reference materials Spinach Leaves NIST-SRM 1570a, Tomato Leaves NIST-SRM 1573a and Apple Leaves NIST-SRM 1515. For all the elements, the precision as repeatability, expressed as relative standard deviation (sr) was of the order of 3-5 %, while the trueness, expressed as relative error (e) was of the order of 3-7 %. Once set up on the standard reference materials, the analytical procedure was applied to commercial tea leaves samples. A critical comparison with spectroscopic measurements is also discussed.

  20. Copper(II) complexes of prion protein PEG11-tetraoctarepeat fragment: spectroscopic and voltammetric studies.

    Science.gov (United States)

    Bonomo, Raffaele P; Di Natale, Giuseppe; Rizzarelli, Enrico; Tabbì, Giovanni; Vagliasindi, Laura I

    2009-04-14

    Spectroscopic (UV-Vis and EPR) and voltammetric studies have been carried out on the copper(II) complexes with the Ac-PEG11-(PHGGGWGQ)4-NH2 (L) polypeptide. In the ratios Cu : L 3 : 1 and 4 : 1, the two [Cu3(L)H(-6)] and [Cu4(L)H(-8)] complex species have been characterized at neutral pH values. All the copper atoms occupy similar coordination sites formed by imidazole, peptidic nitrogen atoms and carbonyl oxygen atoms in a square base pyramidal geometry. Voltammetric measurements on these systems point out the cooperativity in the electron transfer processes among the copper(II) sites during their reduction. NO interaction with these polynuclear copper species is characterized by the reduction of the copper sites through the formation of two different intermediate complex species. When an excess of the Ac-PEG11-(PHGGGWGQ)4-NH2 ligand is considered, frozen solution EPR parameters and UV-Vis spectroscopic data identify the [Cu(N(im))4]2+ chromophore, which does not interact with NO.

  1. Top-Down Effect of Direct Current Stimulation on the Nociceptive Response of Rats

    Science.gov (United States)

    Dimov, Luiz Fabio; Franciosi, Adriano Cardozo; Campos, Ana Carolina Pinheiro; Brunoni, André Russowsky

    2016-01-01

    Transcranial direct current stimulation (tDCS) is an emerging, noninvasive technique of neurostimulation for treating pain. However, the mechanisms and pathways involved in its analgesic effects are poorly understood. Therefore, we investigated the effects of direct current stimulation (DCS) on thermal and mechanical nociceptive thresholds and on the activation of the midbrain periaqueductal gray (PAG) and the dorsal horn of the spinal cord (DHSC) in rats; these central nervous system areas are associated with pain processing. Male Wistar rats underwent cathodal DCS of the motor cortex and, while still under stimulation, were evaluated using tail-flick and paw pressure nociceptive tests. Sham stimulation and naive rats were used as controls. We used a randomized design; the assays were not blinded to the experimenter. Immunoreactivity of the early growth response gene 1 (Egr-1), which is a marker of neuronal activation, was evaluated in the PAG and DHSC, and enkephalin immunoreactivity was evaluated in the DHSC. DCS did not change the thermal nociceptive threshold; however, it increased the mechanical nociceptive threshold of both hind paws compared with that of controls, characterizing a topographical effect. DCS decreased the Egr-1 labeling in the PAG and DHSC as well as the immunoreactivity of spinal enkephalin. Altogether, the data suggest that DCS disinhibits the midbrain descending analgesic pathway, consequently inhibiting spinal nociceptive neurons and causing an increase in the nociceptive threshold. This study reinforces the idea that the motor cortex participates in the neurocircuitry that is involved in analgesia and further clarifies the mechanisms of action of tDCS in pain treatment. PMID:27071073

  2. Cathodic Voltammetric Behavior of Pillar[5]quinone in Nonaqueous Media. Symmetry Effects on the Electron Uptake Sequence.

    Science.gov (United States)

    Cheng, Beijun; Kaifer, Angel E

    2015-08-12

    The cathodic voltammetric behavior of pillar[5]quinone was investigated in dichloromethane solution. Our data show that the symmetry of the macrocycle has a pronounced effect on the electron uptake sequence. The uptake of the first five electrons follows a 2-1-2 pattern, and only a total of eight electrons could be injected into the macrocycle under our experimental conditions.

  3. A square-wave adsorptive stripping voltammetric method for the determination of Amaranth, a food additive dye.

    Science.gov (United States)

    Alghamdi, Ahmad H

    2005-01-01

    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.

  4. The contribution of interindividual factors to variability of response in transcranial direct current stimulation studies

    Directory of Open Access Journals (Sweden)

    Lucia M Li

    2015-05-01

    Full Text Available There has been an explosion of research using transcranial direct current stimulation (tDCS for investigating and modulating human cognitive and motor function in healthy populations. It has also been used in many studies seeking to improve deficits in disease populations. With the slew of studies reporting ‘promising results’ for everything from motor recovery after stroke to boosting memory function, one could be easily seduced by the idea of tDCS being the next panacea for all neurological ills. However, huge variability exists in the reported effects of tDCS, with great variability in the effect sizes and even contradictory results reported. In this review, we consider the interindividual factors that may contribute to this variability. In particular, we discuss the importance of baseline neuronal state and features, anatomy, age and the inherent variability in the injured brain. We additionally consider how interindividual variability affects the results of motor evoked potential (MEP testing with transcranial magnetic stimulation (TMS, which, in turn, can lead to apparent variability in response to tDCS in motor studies.

  5. Defining Clinical Response Criteria and Early Response Criteria for Precision Oncology: Current State-of-the-Art and Future Perspectives

    Directory of Open Access Journals (Sweden)

    Vivek Subbiah

    2017-02-01

    Full Text Available In this era of precision oncology, there has been an exponential growth in the armamentarium of genomically targeted therapies and immunotherapies. Evaluating early responses to precision therapy is essential for “go” versus “no go” decisions for these molecularly targeted drugs and agents that arm the immune system. Many different response assessment criteria exist for use in solid tumors and lymphomas. We reviewed the literature using the Medline/PubMed database for keywords “response assessment” and various known response assessment criteria published up to 2016. In this article we review the commonly used response assessment criteria. We present a decision tree to facilitate selection of appropriate criteria. We also suggest methods for standardization of various response assessment criteria. The relevant response assessment criteria were further studied for rational of development, key features, proposed use and acceptance by various entities. We also discuss early response evaluation and provide specific case studies of early response to targeted therapy. With high-throughput, advanced computing programs and digital data-mining it is now possible to acquire vast amount of high quality imaging data opening up a new field of “omics in radiology”—radiomics that complements genomics for personalized medicine. Radiomics is rapidly evolving and is still in the research arena. This cutting-edge technology is poised to move soon to the mainstream clinical arena. Novel agents with new mechanisms of action require advanced molecular imaging as imaging biomarkers. There is an urgent need for development of standardized early response assessment criteria for evaluation of response to precision therapy.

  6. Current impulse response of thin InP p+-i-n+ diodes using full band structure Monte Carlo method

    Science.gov (United States)

    You, A. H.; Cheang, P. L.

    2007-02-01

    A random response time model to compute the statistics of the avalanche buildup time of double-carrier multiplication in avalanche photodiodes (APDs) using full band structure Monte Carlo (FBMC) method is discussed. The effect of feedback impact ionization process and the dead-space effect on random response time are included in order to simulate the speed of APD. The time response of InP p+-i-n+ diodes with the multiplication region of 0.2μm is presented. Finally, the FBMC model is used to calculate the current impulse response of the thin InP p+-i-n+ diodes with multiplication lengths of 0.05 and 0.2μm using Ramo's theorem [Proc. IRE 27, 584 (1939)]. The simulated current impulse response of the FBMC model is compared to the results simulated from a simple Monte Carlo model.

  7. The placebo response in clinical trials-the current state of play.

    Science.gov (United States)

    Enck, Paul; Klosterhalfen, Sibylle

    2013-04-01

    While randomized, placebo-controlled double-blinded trials have become the pharmacological standard over the last 60 years, the gain in knowledge of the mechanisms behind the placebo response in recent years has raised substantial concerns about the appropriateness of some of its underlying assumptions. The following questions will be addressed: Is the assumed model of drug and placebo being additive (still) valid? Does the likelihood of receiving active treatment affect the placebo response? What is the size of the placebo response in "active comparator studies"? Minimizing the placebo response/maximizing the drug-placebo difference? How to maximize the placebo response in daily medicine? What is the placebo response with personalized medicines in the future? This and other questions require answers that can only be generated with more experimental studies on the placebo response and with thorough meta- and re-analyses of placebo responses in clinical trials.

  8. Voltammetric Behaviour of Doxycycline in the Presence of Surfactant and Its Determination%表面活性效应下强力霉素伏安行为及其检测

    Institute of Scientific and Technical Information of China (English)

    张旭志; 刘文文; 丁东生; 郭萌萌; 赵俊; 曲克明

    2015-01-01

    The effects of surfactant on the voltammetric behavior of doxycycline (DOC) were investigated using conductive carbon black paste electrode (CCBPE) as working electrode. A new electrochemical method for determining DOC in aqueous solution was developed with the help of surfactant. The electrostatic interaction between the DOC molecules and the sodium dodecyl benzene sulfonate (SDBS) by self-assembled on the surface of CCBPE promoted the accumulation of the analyte. In B-R buffer solution of pH 2.0, the presence of 2.0×10–4 mol/L SDBS significantly improved the sensitivity of detection of DOC. In the presence of SDBS, the voltammetric behavior of DOC was investigated by cyclic voltammetry. An irreversible and adsorption-controlled electrode reaction occurs with 1 proton and 2 electrons participation. Under the optimum conditions, the anodic peak current of DOC is proportional to its concentration in the range of 1.0×10–7−2.3×10–5 mol/L with a detection limit of 4.5×10–8 mol/L (S/N=3). Inorganic ions do not have negative effects on the determination, while organic molecules have positive effects probably due to the competitive adsorption function. The average recoveries in the range of 97.44%−105.28% were obtained. Thus, the developed method for the determination of DOC possesses advantages such as simple operation, fast response, low detection limitation, good recovery, and repeatability.%研究了表面活性效应对强力霉素(DOC)伏安行为的影响及表面活性剂存在下该分子的伏安检测方法。以B-R缓冲溶液(pH=2.0)为支持电解质,2.0×10−4 mol/L十二烷基苯磺酸钠(SDBS)的存在将明显有助于DOC的富集。在该实验条件下,DOC在导电碳黑糊电极上发生1质子、2电子转移的不可逆氧化,过程受扩散控制。对表面活性剂种类及其浓度、缓冲液种类及pH值、富集电位及时间等影响伏安分析的因素进行了研究。优化条件下, DOC 的

  9. A self-polishing platinum ring voltammetric sensor and its application to complex media.

    Science.gov (United States)

    Cavanillas, Santiago; Winquist, Fredrik; Eriksson, Mats

    2015-02-15

    A self-polishing voltammetric sensor was recently developed and has been applied to samples of urea, milk and sewage water. The polishing device continuously grinds a platinum ring electrode, offering a reproducible and clean electrode surface. Principal component analysis (PCA) and partial least squares (PLS) techniques were applied to interpret the data and to build prediction models. In an evaluation of samples with different urea concentrations, the grinding step allows for repeatable measurements, similar to those after electrochemical cleaning. Furthermore, for the determination of sewage water concentrations in drinking water and for the evaluation of different fat contents in milk samples, the polishing eliminates sensor drift produced by electrode fouling. The results show that the application of a self-polishing unit offers a promising tool for electrochemical studies of difficult analytes and complex media. Copyright © 2014 Elsevier B.V. All rights reserved.

  10. Anodic stripping tin titration: a method for the voltammetric determination of platinum at trace levels.

    Science.gov (United States)

    Giussani, Barbara; Roncoroni, Simone; Nemenyi, Anna; Dal Santo, Vladimiro; Monticelli, Damiano; Recchia, Sandro

    2014-07-01

    We propose here a novel voltammetric method for the determination of platinum at trace levels. The method is based on the interference that platinum generates on the anodic stripping signal of tin acidic solutions: in appropriate conditions platinum uses the intermediate formation of tin(II) ions, taking place during the tin cathodic reduction, to reduce itself and to form mixed Pt(II)-Sn(II) chloro-complexes. From the analysis of the anodic stripping plots obtained after subsequent additions of tin in a Pt-containing solution, it is possible to quantify accurately and precisely the Pt concentration from 3 ppb to more than 10 ppm. This novel method is validated for the analysis of Pt in heterogeneous catalysts, but in principle could be extended to other matrixes.

  11. Detection of Adulteration in Argan Oil by Using an Electronic Nose and a Voltammetric Electronic Tongue

    Directory of Open Access Journals (Sweden)

    Madiha Bougrini

    2014-01-01

    Full Text Available Adulteration detection of argan oil is one of the main aspects of its quality control. Following recent fraud scandals, it is mandatory to ensure product quality and customer protection. The aim of this study is to detect the percentages of adulteration of argan oil with sunflower oil by using the combination of a voltammetric e-tongue and an e-nose based on metal oxide semiconductor sensors and pattern recognition techniques. Data analysis is performed by three pattern recognition methods: principal component analysis (PCA, discriminant factor analysis (DFA, and support vector machines (SVMs. Excellent results were obtained in the differentiation between unadulterated and adulterated argan oil with sunflower one. To the best of our knowledge, this is the first attempt to demonstrate whether the combined e-nose and e-tongue technologies could be successfully applied to the detection of adulteration of argan oil.

  12. Voltammetric copper(II) determination with a montmorillonite-modified carbon paste electrode

    Energy Technology Data Exchange (ETDEWEB)

    Kula, P. [Institute of Geonics, Academy of Sciences of Czech Republic, Studertska 1768, 708 00 Ostrava (Czech Republic); Navratilova, Z. [Institute of Geonics, Academy of Sciences of Czech Republic, Studertska 1768, 708 00 Ostrava (Czech Republic)

    1996-03-01

    The clay mineral montmorillonite has been tested as modifier for the carbon paste electrode with a novel electrode modification technique. The differential pulse voltammetric determination of copper(II) by means of this modified carbon paste electrode has been studied. A detection limit of 4 x 10{sup -8} mol/l has been achieved after 10 min preconcentration under open circuit conditions with subsequent anodic stripping voltammetry. The calibration curve for Cu(II) is linear in the range of 4 x 10{sup -8}-8 x 10{sup -7} mol/l. Pb interferes in a 10-fold molar and Cd and Hg in a 100-fold molar excess. The interference by humic ligands is significant. (orig.). With 5 figs., 1 tab.

  13. Optimization and validation of an automated voltammetric stripping technique for ultratrace metal analysis

    Energy Technology Data Exchange (ETDEWEB)

    Monticelli, D. [Dipartimento di Scienze Chimiche e Ambientali, Universita degli Studi dell' Insubria, Via Valleggio 11, 22100 Como (Italy)]. E-mail: damiano.monticelli@uninsubria.it; Ciceri, E. [Dipartimento di Scienze Chimiche e Ambientali, Universita degli Studi dell' Insubria, Via Valleggio 11, 22100 Como (Italy); Dossi, C. [Dipartimento di Scienze Chimiche e Ambientali, Universita degli Studi dell' Insubria, Via Valleggio 11, 22100 Como (Italy)

    2007-07-02

    A new automated batch method for the determination of ultratrace metals (nanogram per liter level) was developed and validated. Instrumental and chemical parameters affecting the performance of the method were carefully assessed and optimized. A wide range of voltammetric methods under different chemical conditions were tested. Cadmium, lead and copper were determined by anodic stripping voltammetry (ASV), while nickel, cobalt, rhodium and uranium by adsorptive cathodic stripping voltammetry (AdCSV). The figures of merit of all of these methods were determined: very good precision and accuracy were achieved, e.g. relative percentage standard deviation in the 4-13% for ASV and 2-5% for AdCSV. The stripping methods were applied to the determination of cadmium, lead, copper, nickel, cobalt, rhodium and uranium in lake water samples and the results were found to be comparable with ICP-MS data.

  14. Transient Response of Organo-Metal-Halide Solar Cells Analyzed by Time-Resolved Current-Voltage Measurements

    Directory of Open Access Journals (Sweden)

    M. Greyson Christoforo

    2015-11-01

    Full Text Available The determination of the power conversion efficiency of solar cells based on organo-metal-halides is subject to an ongoing debate. As solar cell devices may exhibit very slow transient response, current-voltage scans in different directions may not be congruent, which is an effect often referred to as hysteresis. We here discuss time-resolved current-voltage measurements as a means to evaluate appropriate delay times (voltage settling times to be used in current-voltage measurements of solar cells. Furthermore, this method allows the analysis of transient current response to extract time constants that can be used to compare characteristic differences between devices of varying architecture types, selective contacts and changes in devices due to storage or degradation conditions.

  15. Discrimination of Apple Liqueurs (Nalewka Using a Voltammetric Electronic Tongue, UV-Vis and Raman Spectroscopy

    Directory of Open Access Journals (Sweden)

    Magdalena Śliwińska

    2016-10-01

    Full Text Available The capability of a phthalocyanine-based voltammetric electronic tongue to analyze strong alcoholic beverages has been evaluated and compared with the performance of spectroscopic techniques coupled to chemometrics. Nalewka Polish liqueurs prepared from five apple varieties have been used as a model of strong liqueurs. Principal Component Analysis has demonstrated that the best discrimination between liqueurs prepared from different apple varieties is achieved using the e-tongue and UV-Vis spectroscopy. Raman spectra coupled to chemometrics have not been efficient in discriminating liqueurs. The calculated Euclidean distances and the k-Nearest Neighbors algorithm (kNN confirmed these results. The main advantage of the e-tongue is that, using PLS-1, good correlations have been found simultaneously with the phenolic content measured by the Folin–Ciocalteu method (R2 of 0.97 in calibration and R2 of 0.93 in validation and also with the density, a marker of the alcoholic content method (R2 of 0.93 in calibration and R2 of 0.88 in validation. UV-Vis coupled with chemometrics has shown good correlations only with the phenolic content (R2 of 0.99 in calibration and R2 of 0.99 in validation but correlations with the alcoholic content were low. Raman coupled with chemometrics has shown good correlations only with density (R2 of 0.96 in calibration and R2 of 0.85 in validation. In summary, from the three holistic methods evaluated to analyze strong alcoholic liqueurs, the voltammetric electronic tongue using phthalocyanines as sensing elements is superior to Raman or UV-Vis techniques because it shows an excellent discrimination capability and remarkable correlations with both antioxidant capacity and alcoholic content—the most important parameters to be measured in this type of liqueurs.

  16. Discrimination of Apple Liqueurs (Nalewka) Using a Voltammetric Electronic Tongue, UV-Vis and Raman Spectroscopy.

    Science.gov (United States)

    Śliwińska, Magdalena; Garcia-Hernandez, Celia; Kościński, Mikołaj; Dymerski, Tomasz; Wardencki, Waldemar; Namieśnik, Jacek; Śliwińska-Bartkowiak, Małgorzata; Jurga, Stefan; Garcia-Cabezon, Cristina; Rodriguez-Mendez, Maria Luz

    2016-10-09

    The capability of a phthalocyanine-based voltammetric electronic tongue to analyze strong alcoholic beverages has been evaluated and compared with the performance of spectroscopic techniques coupled to chemometrics. Nalewka Polish liqueurs prepared from five apple varieties have been used as a model of strong liqueurs. Principal Component Analysis has demonstrated that the best discrimination between liqueurs prepared from different apple varieties is achieved using the e-tongue and UV-Vis spectroscopy. Raman spectra coupled to chemometrics have not been efficient in discriminating liqueurs. The calculated Euclidean distances and the k-Nearest Neighbors algorithm (kNN) confirmed these results. The main advantage of the e-tongue is that, using PLS-1, good correlations have been found simultaneously with the phenolic content measured by the Folin-Ciocalteu method (R² of 0.97 in calibration and R² of 0.93 in validation) and also with the density, a marker of the alcoholic content method (R² of 0.93 in calibration and R² of 0.88 in validation). UV-Vis coupled with chemometrics has shown good correlations only with the phenolic content (R² of 0.99 in calibration and R² of 0.99 in validation) but correlations with the alcoholic content were low. Raman coupled with chemometrics has shown good correlations only with density (R² of 0.96 in calibration and R² of 0.85 in validation). In summary, from the three holistic methods evaluated to analyze strong alcoholic liqueurs, the voltammetric electronic tongue using phthalocyanines as sensing elements is superior to Raman or UV-Vis techniques because it shows an excellent discrimination capability and remarkable correlations with both antioxidant capacity and alcoholic content-the most important parameters to be measured in this type of liqueurs.

  17. Downfall of the current antibody correlates of influenza vaccine response in yearly vaccinated subjects: Toward qualitative rather than quantitative assays.

    Science.gov (United States)

    Cagigi, Alberto; Cotugno, Nicola; Rinaldi, Stefano; Santilli, Veronica; Rossi, Paolo; Palma, Paolo

    2016-02-01

    Response to seasonal influenza vaccination is currently evaluated by antibody correlates that estimate vaccine seroconversion as well as immune protection. These correlates rely on the general dogmas surrounding seasonal influenza vaccination; that is, that vaccine-induced antibodies would exclusively generate immunity to influenza vaccine strains and that protective immunity would wane before the next season. Here, we summarize recently reported data on immunity to seasonal influenza in healthy individuals and rediscuss results on yearly vaccinated pediatric immunocompromised patients that together highlight the need for revision of the current correlates of vaccine response to shift from quantitative to qualitative measurements.

  18. Construction and evaluation of a carbon paste electrode modified with polyaniline-co-poly(dithiodianiline) for enhanced stripping voltammetric determination of metal ions

    CSIR Research Space (South Africa)

    Somerset, V

    2014-05-01

    Full Text Available copolymer of polyaniline-co-poly(2,2'- dithiodianiline) (PANI-co-PDTDA) was used as a modified substrate transducer to achieve enhanced selectivity in stripping voltammetric analysis. The experimental conditions optimised included the supporting electrolyte...

  19. Study of the underlying electrochemistry of polycrystalline gold electrodes in aqueous solution and electrocatalysis by large amplitude fourier transformed alternating current voltammetry.

    Science.gov (United States)

    Lertanantawong, Benchaporn; O'Mullane, Anthony P; Surareungchai, Werasak; Somasundrum, Mithran; Declan Burke, L; Bond, Alan M

    2008-03-18

    Polycrystalline gold electrodes of the kind that are routinely used in analysis and catalysis in aqueous media are often regarded as exhibiting relatively simple double-layer charging/discharging and monolayer oxide formation/removal in the positive potential region. Application of the large amplitude Fourier transformed alternating current (FT-ac) voltammetric technique that allows the faradaic current contribution of fast electron-transfer processes to be emphasized in the higher harmonic components has revealed the presence of well-defined faradaic (premonolayer oxidation) processes at positive potentials in the double-layer region in acidic and basic media which are enhanced by electrochemical activation. These underlying quasi-reversible interfacial electron-transfer processes may mediate the course of electrocatalytic oxidation reactions of hydrazine, ethylene glycol, and glucose on gold electrodes in aqueous media. The observed responses support key assumptions associated with the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis.

  20. Response of the waterlouse Asellus aquaticus to multiple stressors : effects of current velocity and mineral substratum

    NARCIS (Netherlands)

    Peeters, E.T.H.M.; Camu, J.M.; Beijer, J.A.J.; Scheffer, M.; Gardeniers, J.J.P.

    2002-01-01

    Experiments were performed to study the individual and combined effects of current velocity and substratum composition on the waterlouse Asellus aquaticus (L.). Both factors affected growth, mortality, behavior, and food consumption of A. aquaticus. Short-term effects of increasing current velocity

  1. Fabrication of the DNA/poly(3-methylthiophene)composite film modified electrode and its application for the study on the voltammetric behavior and determination of 8-hydroxy-2'-deoxyguanosine

    Institute of Scientific and Technical Information of China (English)

    WANG YanHuai; LI Jing; LIU Yan; MA RongNa; JIA WenLi; CUI Hui; WANG HuaiSheng

    2009-01-01

    A composite film of DNA/poly(3-methylthiophene) (P3MT) modified glassy carbon electrode (GCE) has been fabricated by electro-deposition method.P3MT film was first electropolymerized at the GCE and the DNA layer was then immobilized on the P3MT layer by electrochemical method.The voltammetric behavior of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) at the composite film modified electrode was studied.The effects of scan rates,pH and the interference of uric acid (UA) on the voltammetric behavior and detection of 8-OH-dG were also discussed.The experimental results suggest that the electrochemical behavior of 8-OH-dG at the composite film modified electrode was greatly improved due to the combination of the advantages of P3MT and DNA.In 0.1 M pH 7.0 phosphate buffer solution (PBS),the anodic peak currents of 8-OH-dG were linear with the 8-OH-dG concentration in two intervals,viz.0.28-4.2 μM and 4.2-19.6 μM.The detection limit of 56 nM 8-OH-dG could be estimated (S/N=3).This proposed composite film modified electrode shows excellent reproducibility and stability.It may have the potential application for the detection of 8-OH-dG in human urine.

  2. Extended producer responsibility for packaging waste in South Africa: Current approaches and lessons learned

    CSIR Research Space (South Africa)

    Nahman, Anton

    2010-01-01

    Full Text Available Extended producer responsibility (EPR) is a policy concept aimed at extending producers’ responsibility for their products to the post-consumer stage of their products’ life cycle. One of the outcomes of an effective EPR programme is to move waste...

  3. Transient Response of Arc Temperature and Iron Vapor Concentration Affected by Current Frequency with Iron Vapor in Pulsed Arc

    Science.gov (United States)

    Tanaka, Tatsuro; Maeda, Yoshifumi; Yamamoto, Shinji; Iwao, Toru

    2016-10-01

    TIG arc welding is chemically a joining technology with melting the metallic material and it can be high quality. However, this welding should not be used in high current to prevent cathode melting. Thus, the heat transfer is poor. Therefore, the deep penetration cannot be obtained and the weld defect sometimes occurs. The pulsed arc welding has been used for the improvement of this defect. The pulsed arc welding can control the heat flux to anode. The convention and driving force in the weld pool are caused by the arc. Therefore, it is important to grasp the distribution of arc temperature. The metal vapor generate from the anode in welding. In addition, the pulsed current increased or decreased periodically. Therefore, the arc is affected by such as a current value and current frequency, the current rate of increment and the metal vapor. In this paper, the transient response of arc temperature and the iron vapor concentration affected by the current frequency with iron vapor in pulsed arc was elucidated by the EMTF (ElectroMagnetic Thermal Fluid) simulation. As a result, the arc temperature and the iron vapor were transient response as the current frequency increase. Thus, the temperature and the electrical conductivity decreased. Therefore, the electrical field increased in order to maintain the current continuity. The current density and electromagnetic force increased at the axial center. In addition, the electronic flow component of the heat flux increased at the axial center because the current density increased. However, the heat conduction component of the heat flux decreased.

  4. Response of the Kuroshio Current to Eddies in the Luzon Strait

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jie; LUO De-Hai

    2010-01-01

    The impact of eddies on the Kuroshio Current in the Luzon Strait(LS)area is investigated by using the sea surface height anomaly(SSHA)satellite observation data and the sea surface height(SSH)assimilation data.The influence of the eddies on the mean current depends upon the type of eddies and their relative position.The mean current is enhanced(weakened)as the cyclonic(anticyclonic)eddy becomes slightly far from it,whereas it is weakened(enhanced)as the cyclonic(anticyclonic)eddy moves near or within the position of the mean current;this is explained as the eddy-induced meridional velocity and geostrophic flow relationship.The anticyclonic(cyclonic)eddy can increase(decrease)the mean meridional flow due to superimposition of the eddy-induced meridional flow when the eddy is within the region of the mean current.However,when the eddy is slightly far from the mean current region,the anticyclonic(cyclonic)eddy tends to decrease(increase)the zonal gradient of the SSH,which thus results in weakening(strengthening)of the mean current in the LS region.

  5. Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments

    DEFF Research Database (Denmark)

    Vicca, S.; Bahn, M.; Estiarte, M.

    2014-01-01

    As a key component of the carbon cycle, soil CO2 efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes ...

  6. Membrane voltage differently affects mIPSCs and current responses recorded from somatic excised patches in rat hippocampal cultures.

    Science.gov (United States)

    Pytel, Maria; Mozrzymas, Jerzy W

    2006-01-30

    Recent analysis of current responses to exogenous GABA applications recorded from excised patches indicated that membrane voltage affected the GABAA receptor gating mainly by altering desensitization and binding [M. Pytel, K. Mercik, J.W. Mozrzymas, Membrane voltage modulates the GABAA receptor gating in cultured rat hippocampal neurons, Neuropharmacology, in press]. In order investigate the impact of such voltage effect on GABAA receptors in conditions of synaptic transmission, mIPSCs and current responses to rapid GABA applications were recorded from the same culture of rat hippocampal neurons. We found that I-V relationship for mIPSCs amplitudes showed a clear outward rectification while for current responses an inward rectification was seen, except for very low GABA concentrations. A clear shift in amplitude cumulative distributions indicated that outward rectification resulted from the voltage effect on the majority of mIPSCs. Moreover, the decaying phase of mIPSCs was clearly slowed down at positive voltages and this effect was represented by a shift in cumulative distributions of weighted decaying time constants. In contrast, deactivation of current responses was only slightly affected by membrane depolarization. These data indicate that the mechanisms whereby the membrane voltage modulates synaptic and extrasynaptic receptors are qualitatively different but the mechanism underlying this difference is not clear.

  7. Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments

    DEFF Research Database (Denmark)

    Vicca, S.; Bahn, M.; Estiarte, M.;

    2014-01-01

    As a key component of the carbon cycle, soil CO2 efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes ...

  8. Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments

    NARCIS (Netherlands)

    Vicca, S.; Bahn, M.; Estiarte, M.; van Loon, E.E.; Vargas, R.; Alberti, G.; Ambus, P.; Arlain, M.A.; Beier, C.; Bentley, L.P.; Borken, W.; Buchmann, N.; Collins, S.L.; De Dato, G.; Dukes, J.S.; Escolar, C.; Fay, P.; Guidolotti, G.; Hanson, P.J.; Kahmen, A.; Kröel-Dulay, G.; Ladreiter-Knauss, T.; Larsen, K.S.; Lellei-Kovacs, E.; Lebrija-Trejos, E.; Maestre, F.T.; Marhan, S.; Marshall, M.; Meir, P.; Miao, Y.; Muhr, J.; Niklaus, P.A.; Ogaya, R.; Peñuelas, J.; Poll, C.; Rustad, L.E.; Savage, K.; Schindlbacher, A.; Schmidt, I.K.; Smith, A.R.; Scotta, E.D.; Suseela, V.; Tietema, A.; Van Gestel, N.; Van Straaten, O.; Wan, S.; Weber, U.; Janssens, I.A.

    2014-01-01

    As a key component of the carbon cycle, soil CO2 efflux (SCE) is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes and

  9. Application of voltammetric techniques at microelectrodes to the study of the chemical stability of highly reactive species.

    Science.gov (United States)

    Laborda, Eduardo; Olmos, José-Manuel; Torralba, Encarnación; Molina, Angela

    2015-02-03

    The application of voltammetric techniques to the study of chemical speciation and stability is addressed both theoretically and experimentally in this work. In such systems, electrode reactions are coupled to homogeneous chemical equilibria (complexations, protonations, ion associations, ...) that can be studied in a simple, economical, and accurate way by means of electrochemical methods. These are of particular interest when some of the participating species are unstable given that the generation and characterization of the species are performed in situ and on a short time scale. With the above aim, simple explicit solutions are presented in this article for quantitative characterization with any voltammetric technique and with the most common electrode geometries. From the theoretical results obtained, it is pointed out that the use of square-wave voltammetry in combination with microelectrodes is very suitable. Finally, the theory is applied to the investigation of the ion association between the anthraquinone radical monoanion and the tetrabutylammonium cation in acetonitrile medium.

  10. Influence of melatonin or its antagonism on alcohol consumption in ethanol drinking rats: a behavioral and in vivo voltammetric study.

    Science.gov (United States)

    Crespi, Francesco

    2012-05-03

    Melatonin, an indoleamine hormone synthesized in the pinealocytes, has been implicated as influencing the intake of alcohol in rats. It has been shown that this hormone is voltammetrically electroactive at the surface of pretreated carbon fiber microelectrodes in vitro and in vivo, in rat cerebral melatonergic regions such the pineal gland. The aim of this work consisted in the study of the influence of melatonin on spontaneously ethanol drinking or ethanol avoiding rats selected throughout a free choice two bottle test. It appeared that only the water preferring rats were affected by treatment with the hormone and that in vivo voltammetric related levels of melatonin were higher in the pineal gland of ethanol drinking rats versus water preferring rats. In addition, when treated with the melatonin antagonist GR128107 ethanol drinking rats significantly reduced the spontaneous consumption of alcohol.

  11. Investigation of voltammetric enzyme-linked immunoassay based on new system of ODA-H2O2-HRP

    Institute of Scientific and Technical Information of China (English)

    焦奎; 张书圣; 韦璐

    1996-01-01

    A voltammetric enzyme-linked immunoassay based on a new system of ODA-H2O2-HRP has first been developed and used in the detection of HRP and labelled HRP. By this method, the enzyme-catalyzing reaction of H2O2 oxidizing odianisidine (ODA) couples the electrode-reduction reaction of the oxidizing product of odianisidine, which produces a sensitive polarographic wave at potential of -0.56V (SCE) in Britton-Robinson buffer solution. In using this polarographic wave, a detection limit to HRP is 3.7×10-12g/mL and a linear range 1.0×10-11-2.0×10-9g/mL. And the mechanisms of the coupling reaction and the process of electro-reduction in the ODA-H2O2-HRP voltammetric enzyme-linked immunoassay system have also been carefully studied.

  12. Modification of glassy carbon electrode with a bilayer of multiwalled carbon nanotube/tiron-doped polypyrrole: Application to sensitive voltammetric determination of acyclovir.

    Science.gov (United States)

    Shahrokhian, Saeed; Azimzadeh, Mahnaz; Amini, Mohammad K

    2015-08-01

    A novel voltammetric sensor based on glassy carbon electrode (GCE) modified with a thin film of multi-walled carbon nanotubes (MWCNTs) coated with an electropolymerized layer of tiron-doped polypyrrole was developed and the resulting electrode was applied for the determination of acyclovir (ACV). The surface morphology and property of the modified electrode were characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy techniques. The electrochemical performance of the modified electrode was investigated by means of linear sweep voltammetry (LSV). The effect of several experimental variables, such as pH of the supporting electrolyte, drop size of the cast MWCNTssuspension, number of electropolymerization cycles and accumulation time was optimized by monitoring the LSV response of the modified electrode toward ACV. The best response was observed at pH7.0 after accumulation at open circuit for 160 s. Under the optimized conditions, a significant electrochemical improvement was observed toward the electrooxidation of ACV on the modified electrode surface relative to the bare GCE, resulting in a wide linear dynamic range (0.03-10.0μ M) and a low detection limit (10.0 nM) for ACV. Besides high sensitivity, the sensor represented high stability and good reproducibility for ACV analysis, and provided satisfactory results for the determination of this compound in pharmaceutical and clinical preparations. Copyright © 2015 Elsevier B.V. All rights reserved.

  13. Surficial Sedimentary Diatoms in Okinawa Trough and Its Response to Kuroshio Current

    Institute of Scientific and Technical Information of China (English)

    Lan Dongzhao; Fang Qi; Liao Lianzhao

    2002-01-01

    This paper describes the relative contents of dominant diatom species and the distributive characteristics of tropical pelagic species and diatom assemblages, and also discusses the relations between the relative content of tropical pelagic species and Kuroshio Current and between the distribution of diatom assemblages and material sources. The results show that the limit of>20% relative content of tropical pelagic species is basically consistent with the demarcation of Kuroshio Current, and that the distributions of dominant diatom species and diatom assemblages reserve the records of their closer relations to material sources.

  14. Responses of action potential and K+ currents to temperature acclimation in fish hearts: phylogeny or thermal preferences?

    Science.gov (United States)

    Haverinen, Jaakko; Vornanen, Matti

    2009-01-01

    Electrical activity of the heart is assumed to be one of the key factors that set thermal tolerance limits for ectothermic vertebrates. Therefore, we hypothesized that in thermal acclimation--the duration of cardiac action potential and the repolarizing K+ currents that regulate action potential duration (APD)--the rapid component of the delayed rectifier K+ current (I(Kr)) and the inward rectifier K+ current (I(K1)) are more plastic in eurythermal than in stenothermal fish species. The hypothesis was tested in six freshwater teleosts representing four different fish orders (Cadiformes, Cypriniformes, Perciformes, Salmoniformes) acclimated at +4 degrees C (cold acclimation) or +18 degrees C (warm acclimation). In cold acclimation, a compensatory shortening of APD occurred in all species regardless of thermal tolerances, life styles, or phylogenies of the fish, suggesting that this response is a common characteristic of the teleost heart. The strength of the response did not, however, obey simple eurythermy-stenothermy gradation but differed among the phylogenetic groups. Salmoniformes fish showed the greatest acclimation capacity of cardiac electrical activity, whereas the weakest response appeared in the perch (Perciformes) heart. The underlying ionic mechanisms were also partly phylogeny dependent. Modification of the I(Kr) current was al- most ubiquitously involved in acclimation response of fish cardiac myocytes to temperature, while the ability to change the I(K1) current under chronic thermal stress was absent or showed inverse compensation in Salmoniformes species. Thus, in Salmoniformes fish, the thermal plasticity of APD is strongly based on I(Kr), while other fish groups rely on both I(Kr) and I(K1).

  15. Biological responses to current UV-B radiation in Arctic regions

    DEFF Research Database (Denmark)

    Albert, Kristian; N. Mikkelsen, Teis; Ro-Poulsen, Helge

    -B was demonstrated to decrease photosynthesis and shift carbon allocation from shoots to roots. Moreover, ambient UV-B increased plant stress with detrimental effects on electron processing in the photosynthetic apparatus. Plant responses did not lead to clear changes in the amount of fungal root symbionts...... on high-arctic vegetation. They supplement previous investigations from the Arctic focussing on other variables like growth etc., which have reported no or minor plant responses to UV-B, and clearly indicates that UV-B radiation is an important factor affecting plant life at high-arctic Zackenberg...

  16. Extreme precipitation and temperature responses to circulation patterns in current climate: statistical approaches

    NARCIS (Netherlands)

    Photiadou, C.

    2015-01-01

    Climate change is likely to influence the frequency of extreme extremes - temperature, precipitation and hydrological extremes, which implies increasing risks for flood and drought events in Europe. In current climate, European countries were often not sufficiently prepared to deal with the great so

  17. Higher Education in Kenya: An Assessment of Current Responses to the Imperative of Widening Access

    Science.gov (United States)

    Odhiambo, George

    2016-01-01

    Higher education is a key factor in a nation's effort to develop a highly skilled workforce for competing in the global economy. In this paper, current trends in accessibility, equity, participation and financing of higher education in Kenya are examined. The paper explores the challenges which need to be confronted and discusses the way forward…

  18. Biological responses to current UV-B radiation in Arctic regions

    DEFF Research Database (Denmark)

    Albert, Kristian; N. Mikkelsen, Teis; Ro-Poulsen, Helge

    (mycorrhiza) or in the biomass of microbes in the soil of the root zone. However, the composition of the soil microbial community was different in the soils under ambient and reduced UV radiation after three treatment years. These results provide new insight into the negative impact of current UV-B fluxes...

  19. Frequency Response Analysis of Current Controllers for Selective Harmonic Compensation in Active Power Filters

    DEFF Research Database (Denmark)

    Lascu, C.; Asiminoaei, L.; Boldea, I.;

    2009-01-01

    This paper compares four current control structures for selective harmonic compensation in active power filters. All controllers under scrutiny perform the harmonic compensation by using arrays of resonant controllers, one for the fundamental and one for each harmonic of interest, in order to ach...

  20. [Current distribution of Schisandra chinensis in China and its predicted responses to climate change].

    Science.gov (United States)

    Hu, Li-Le; Zhang, Hai-Ying; Qin, Ling; Yan, Bo-Qian

    2012-09-01

    With integration of literature data, specimens records, and field surveys, the current distribution map of Schisandra chinensis in China was drawn, and, based on this map and considering 21 environmental factors, the future distribution of S. chinensis in China in the 2050s and 2080s under the IPCC A2 and A1B climate change scenarios was predicted by using Maxent software. Currently, the S. chinensis in China occurred in 15 provinces, involving 151 counties, and its distribution area decreased with decreasing latitude and longitude. The main distribution area included Heilongjiang, Liaoning, Inner Mongolia, and Jilin. The potential distribution area of S. chinensis in China was 145.12 x 10(4) km2, 48.6% of which were the favorable habitat area, mainly distributed in Changbai Mountains, Xiaoxing'anling Mountains, Daxing'anling Mountains, and the regions between Hebei and Liaoning provinces. The most favorable habitat area only accounted for 0.3%, and was mainly in the Kuandian Manchu Autonomous County, Benxi Manchu Autonomous County, and Huanren Manchu Autonomous County of Liaoning Province, the Antu County and Helong County of Jilin Province, and the Yakeshi City of Inner Mongolia. Under the two climate change scenarios, the potential future distribution area of S. chinensis in China would have a gradual decrease, and the decrement would be larger under A2 than under A1B scenario. By 2050, the distribution area of the S. chinensis under A1B and A2 scenarios would be moderately decreased to 84.0% and 81.5% of the current distribution area, respectively; by 2080, the distribution of S. chinensis under A2 scenario would be dramatically decreased to only 0.5% of the current range, and that under A1B scenario would be decreased to 1/2 of the current range.

  1. Synthesis, characterization of amide substituted dexibuprofen derivatives and their spectral, voltammetric and docking investigations for DNA binding interactions.

    Science.gov (United States)

    Arshad, Nasima; Zafran, Muhammad; Ashraf, Zaman; Perveen, Fouzia

    2017-04-01

    Three amide derivatives - methyl-2-[2-(4-isobutylphenyl)propanamido]propanoate (Dex-2), methyl 2-[2-(4-isobutylphenyl) propanamido]-3-phenylpropanoate (Dex-3) and methyl 2-[2-(4-isobutylphenyl)-propanamido]-4-methylpentanoate (Dex-4) of dexibuprofen (Dex-1) 2-(4-isobutylphenyl)propanoic acid were synthesized and conformed for structures by physical data and spectral analysis. Further, all the compounds were studied for their binding with ds.DNA through experimental (UV-visible/and fluorescence spectroscopy, cyclic voltammetry) and theoretical (molecular docking) techniques. Spectral and voltammetric responses as well as kinetic and thermodynamic data interpretations at stomach (4.7) and blood (7.4) pH and at human body temperature (37°C) indicated spontaneous interaction of all the compounds with DNA via intercalation and external bindings. The binding constants (Kb) and Gibbs free energy changes (-ΔG) were evaluated greater at pH7.4 attributing comparatively more significant binding of all the compounds with DNA at blood pH. Among all compounds, Dex-4 showed greater binding with DNA at both pH with greater Kb values i.e., {UV-visible: pH 4.7 (2.36×10(4)M(-1)); pH7.4 (2.42×10(4)M(-1)), fluorescence: pH4.7 (2.24×10(4)M(-1)); pH7.4 (2.56×10(4)M(-1)) and CV: pH4.7 (4.06×10(4)M(-1)); pH7.4 (4.89×10(4)M(-1))}. Binding site size (n) at both pH values was evaluated n≥1 for Dex-2 and Dex-4 which assured intercalation as a major mode of interaction between compounds and DNA. For Dex-1 and Dex-3 (n) was evaluated n≤1 at both pH values and the values n<1 indicated the possibility of binding via groove or electrostatic interactions. Electrochemical processes were found diffusion controlled and diffusion coefficients (Do) for all the compounds - DNA adducts were evaluated lesser than unbound compounds. Docking studies further supported DNA binding evidences obtained from spectral and electrochemical investigations. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Early response to sibutramine in patients not meeting current label criteria: preliminary analysis of SCOUT lead-in period

    DEFF Research Database (Denmark)

    Caterson, Ian; Coutinho, Walmir; Finer, Nick;

    2010-01-01

    The Sibutramine Cardiovascular Outcomes (SCOUT) trial protocol defines a patient population predominantly outside current European Union label criteria. This article explores responses to sibutramine during the 6-week, single-blind, lead-in period between patients who conformed to the label......-in period. Initial responses were assessed post hoc in label conformers and nonconformers. Of that 8.1% patients met label criteria; 91.9%, the majority with cardiovascular disease and/or blood pressure >145/90 mm Hg, were nonconformers. Conformers and nonconformers had similar reductions in body weight...

  3. Dosimetric response for crystalline and nanostructured aluminium oxide to a high-current pulse electron beam.

    Science.gov (United States)

    Nikiforov, S V; Kortov, V S

    2014-11-01

    The main thermoluminescent (TL) and dosimetric properties of the detectors based on anion-defective crystalline and nanostructured aluminium oxide after exposure to a high-current pulse electron beam are studied. TL peaks associated with deep-trapping centres are registered. It is shown that the use of deep-trap TL at 200-600°С allows registering absorbed doses up to 750 kGy for single-crystalline detectors and those up to 6 kGy for nanostructured ones. A wide range of the doses registered, high reproducibility of the TL signal and low fading contribute to a possibility of using single-crystalline and nanostructured aluminium oxide for the dosimetry of high-current pulse electron beams.

  4. Gyrotropic elastic response of skyrmion crystals to current-induced tensions

    Science.gov (United States)

    Ochoa, Hector; Kim, Se Kwon; Tchernyshyov, Oleg; Tserkovnyak, Yaroslav

    2017-07-01

    We theoretically study the dynamics of skyrmion crystals in electrically insulating chiral magnets subjected to current-induced spin torques by adjacent metallic layers. We develop an elasticity theory that accounts for the gyrotropic force engendered by the nontrivial topology of the spin texture, tensions at the boundaries due to the exchange of linear and spin angular momentum with the metallic reservoirs, and dissipation in the bulk of the film. A steady translation of the skyrmion crystal is triggered by the current-induced tensions and subsequently sustained by dissipative forces, generating an electromotive force on itinerant spins in the metals. This phenomenon should be revealed as a negative drag in an open two-terminal geometry, or equivalently, as a positive magnetoresistance when the terminals are connected in parallel. We propose nonlocal transport measurements with these salient features as a tool to characterize the phase diagram of insulating chiral magnets.

  5. Transcranial direct current stimulation in patients with Alzheimer’s disease: Challenges and responses

    OpenAIRE

    Yuan, Hong; Tabarak, Serik; Yu, Jing; Lei, Xu

    2015-01-01

    The use of transcranial direct current stimulation (tDCS) as a noninvasive therapeutic approach for Alzheimer’s disease (AD) has gained increasing attention. Research regarding the utility of tDCS in AD is inconsistent. In this study, we reviewed the importance of individual diversity among AD patients, starting from the uninformative mean results. We also demonstrated variation among AD patients. Highly educated patients seem to benefit more; education also seems to modulate baseline measure...

  6. Investigations on the electrical current-voltage response in protein light receptors

    CERN Document Server

    Alfinito, E; Reggiani, L

    2014-01-01

    We report a theoretical/computational approach for modeling the current-voltage characteristics of sensing proteins. The modeling is applied to a couple of transmembrane proteins, bacteriorhodopsin and proteorhodopsin, sensitive to visible light and promising biomaterials for the development of a new generation of photo-transducers. The agreement between theory and experiments sheds new light on the microscopic interpretation of charge transfer in proteins and biological materials in general.

  7. A fast transient response low dropout regulator with current control methodology

    Institute of Scientific and Technical Information of China (English)

    Ma Zhuo; Guo Yang; Duan Zhikui; Xie Lunguo; Chen Jihua; Yu Jinshan

    2011-01-01

    A transient performance optimized CCL-LDO regulator is proposed.In the CCL-LDO,the control method of the charge pump phase-locked loop is adopted.A current control loop has the feedback signal and reference current to be compared,and then a loop filter generates the gate voltage of the power MOSFET by integrating the error current.The CCL-LDO has the optimized damping coefficient and natural resonant frequency,while its output voltage can be sub-1-V and is not restricted by the reference voltage.With a 1μF decoupling capacitor,the experimental results based on a 0.13 μm CMOS process show that the output voltage is 1.0 V; when the workload changes from 100 μA to 100 mA transiently,the stable dropout is 4.25 mV,the settling time is 8.2 μs and the undershoot is 5.11 mV; when the workload changes from 1 00 mA to 100 μA transiently,the stable dropout is 4.25 mV,the settling time is 23.3 μs and the overshoot is 6.21 mV.The PSRR value is more than -95 dB.Most of the attributes of the CCL-LDO are improved rapidly with a FOM value of 0.0097.

  8. Genetic and physiological bases for phenological responses to current and predicted climates

    OpenAIRE

    Wilczek, A. M.; Burghardt, L. T.; Cobb, A. R.; Cooper, M D; Welch, S. M.; Schmitt, J

    2010-01-01

    We are now reaching the stage at which specific genetic factors with known physiological effects can be tied directly and quantitatively to variation in phenology. With such a mechanistic understanding, scientists can better predict phenological responses to novel seasonal climates. Using the widespread model species Arabidopsis thaliana, we explore how variation in different genetic pathways can be linked to phenology and life-history variation across geographical regions and seasons. We sho...

  9. Osteoblastic differentiation and stress response of human mesenchymal stem cells exposed to alternating current electric fields

    Directory of Open Access Journals (Sweden)

    Kaplan David L

    2011-01-01

    Full Text Available Abstract Background Electric fields are integral to many biological events, from maintaining cellular homeostasis to embryonic development to healing. The application of electric fields offers substantial therapeutic potential, while optimal dosing regimens and the underlying mechanisms responsible for the positive clinical impact are poorly understood. Methods The purpose of this study was to track the differentiation profile and stress response of human bone marrow derived mesenchymal stem cells (hMSCs undergoing osteogenic differentiation during exposure to a 20 mV/cm, 60 kHz electric field. Morphological and biochemical changes were imaged using endogenous two-photon excited fluorescence (TPEF and quantitatively assessed through eccentricity calculations and extraction of the redox ratio from NADH, FAD and lipofuscin contributions. Real time reverse transcriptase-polymerase chain reactions (RT-PCR were used to track osteogenic differentiation markers, namely alkaline phosphatase (ALP and collagen type 1 (col1, and stress response markers, such as heat shock protein 27 (hsp27 and heat shock protein 70 (hsp70. Comparisons of collagen deposition between the stimulated hMSCs and controls were examined through second harmonic generation (SHG imaging. Results Quantitative differences in cell morphology, as described through an eccentricity ratio, were found on days 2 and days 5 (p Conclusions Electrical stimulation is a useful tool to improve hMSC osteogenic differentiation, while heat shock proteins may reveal underlying mechanisms, and optical non-invasive imaging may be used to monitor the induced morphological and biochemical changes.

  10. The Acute Inflammatory Response in Trauma / Hemorrhage and Traumatic Brain Injury: Current State and Emerging Prospects

    Directory of Open Access Journals (Sweden)

    Y Vodovotz

    2009-01-01

    Full Text Available Traumatic injury/hemorrhagic shock (T/HS elicits an acute inflammatory response that may result in death. Inflammation describes a coordinated series of molecular, cellular, tissue, organ, and systemic responses that drive the pathology of various diseases including T/HS and traumatic brain injury (TBI. Inflammation is a finely tuned, dynamic, highly-regulated process that is not inherentlydetrimental, but rather required for immune surveillance, optimal post-injury tissue repair, and regeneration. The inflammatory response is driven by cytokines and chemokines and is partiallypropagated by damaged tissue-derived products (Damage-associated Molecular Patterns; DAMP’s.DAMPs perpetuate inflammation through the release of pro-inflammatory cytokines, but may also inhibit anti-inflammatory cytokines. Various animal models of T/HS in mice, rats, pigs, dogs, and nonhumanprimates have been utilized in an attempt to move from bench to bedside. Novel approaches, including those from the field of systems biology, may yield therapeutic breakthroughs in T/HS andTBI in the near future.

  11. Human immune system mice: current potential and limitations for translational research on human antibody responses.

    Science.gov (United States)

    Vuyyuru, Raja; Patton, John; Manser, Tim

    2011-12-01

    It has recently become possible to generate chimeric mice durably engrafted with many components of the human immune system (HIS mice). We have characterized the maturation and function of the B cell compartment of HIS mice. The antibody response of HIS mice to T cell-dependent B cell antigens is limited, and contributing factors may be the general immaturity of the B cell compartment, infrequent helper T cells selected on human MHC class II antigens, and incomplete reconstitution of secondary lymphoid organs and their microenvironments. In contrast, HIS mice generate protective antibody responses to the bacterium Borrelia hermsii, which acts as a T cell-independent antigen in mice, but do not respond to purified polysaccharide antigens (PPS). We speculate that the anti-B. hermsii response of HIS mice is derived from an abundant B cell subset that may be analogous to B1 B cells in mice. We suggest that failure of HIS mice to respond to PPS is due to the lack of a B cell subset that may originate from adult bone marrow and is highly dependent on human interleukin-7 for development.

  12. Behavioral Responses Of Fish To A Current-Based Hydrokinetic Turbine Under Mutlipe Operational Conditions: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Grippo, Mark A. [Argonne National Lab. (ANL), Argonne, IL (United States); Shen, Haixue [Univ. of Maine, Orono, ME (United States); Zydlewski, Gayle [Univ. of Maine, Orono, ME (United States); Rao, Shivanesh [Univ. of Maine, Orono, ME (United States); Goodwin, Andy [United States Army Engineer R & D Center, Vicksburg, MI (United States)

    2017-02-01

    There is significant interest in the interaction of aquatic organisms with current-based marine and hydrokinetic (MHK) technologies. Determining the potential impacts of MHK devices on fish behavior is critical to addressing the environmental concerns that could act as barriers to the permitting and deployment of MHK devices. To address these concerns, we use field monitoring and fish behavior models to characterize the behavioral responses of fish to MHK turbines and infer potential stimuli that may have elicited the observed behavioral changes.

  13. Effects of an NMDA antagonist on the auditory mismatch negativity response to transcranial direct current stimulation.

    Science.gov (United States)

    Impey, Danielle; de la Salle, Sara; Baddeley, Ashley; Knott, Verner

    2016-09-13

    Transcranial direct current stimulation (tDCS) is a non-invasive form of brain stimulation which uses a weak constant current to alter cortical excitability and activity temporarily. tDCS-induced increases in neuronal excitability and performance improvements have been observed following anodal stimulation of brain regions associated with visual and motor functions, but relatively little research has been conducted with respect to auditory processing. Recently, pilot study results indicate that anodal tDCS can increase auditory deviance detection, whereas cathodal tDCS decreases auditory processing, as measured by a brain-based event-related potential (ERP), mismatch negativity (MMN). As evidence has shown that tDCS lasting effects may be dependent on N-methyl-D-aspartate (NMDA) receptor activity, the current study investigated the use of dextromethorphan (DMO), an NMDA antagonist, to assess possible modulation of tDCS's effects on both MMN and working memory performance. The study, conducted in 12 healthy volunteers, involved four laboratory test sessions within a randomised, placebo and sham-controlled crossover design that compared pre- and post-anodal tDCS over the auditory cortex (2 mA for 20 minutes to excite cortical activity temporarily and locally) and sham stimulation (i.e. device is turned off) during both DMO (50 mL) and placebo administration. Anodal tDCS increased MMN amplitudes with placebo administration. Significant increases were not seen with sham stimulation or with anodal stimulation during DMO administration. With sham stimulation (i.e. no stimulation), DMO decreased MMN amplitudes. Findings from this study contribute to the understanding of underlying neurobiological mechanisms mediating tDCS sensory and memory improvements.

  14. Modification of carbon paste electrode with Fe(III)-clinoptilolite nano-particles for simultaneous voltammetric determination of acetaminophen and ascorbic acid.

    Science.gov (United States)

    Sharifian, Samira; Nezamzadeh-Ejhieh, Alireza

    2016-01-01

    A novel carbon paste electrode (CPE) modified with Fe(III)-exchanged clinoptilolite nano-particles (Fe(III)-NClino/CPE) was constructed and used for simultaneous voltammetric (CV, SqW and chronoamperometry) determination of ascorbic acid and acetaminophen. Raw and modified zeolites were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). The square wave peak current was linearly increased in the concentration ranges of 1.0 × 10(-9)-1.0 × 10(-2) mol L(-1) for ascorbic acid and 1.0 × 10(-10-)1.0 × 10(-2) mol L(-1) for acetaminophen with detection limits of 1.8 × 10(-9) mol L(-1) and 9.9 × 10(-10) mol L(-1), respectively. The detection limits of 2.4 × 10(-10) mol L(-1) and 2.5 × 10(-11) mol L(-1) were also obtained for AA and AC in chronoamperometric measurements, respectively. The diffusion coefficients of 7.5 × 10(-5) cm(2) s(-1) and 2.4 × 10(-5) cm(2) s(-1) were respectively calculated for the oxidation of AC and AA by chronoamperometry. The proposed electrode exhibited high sensitivity and good stability, and would be valuable for the clinical assay of ascorbic acid and acetaminophen.

  15. Amplified voltammetric detection of miRNA from serum samples of glioma patients via combination of conducting magnetic microbeads and ferrocene-capped gold nanoparticle/streptavidin conjugates.

    Science.gov (United States)

    Lu, Zhixuan; Tang, Hailin; Wu, Daohong; Xia, Yonghong; Wu, Minghua; Yi, Xinyao; Li, Hengfeng; Wang, Jianxiu

    2016-12-15

    MicroRNA (miRNA) plays a key regulatory role in many biological processes, emerging as an important biomarker for a large variety of cancer diseases. Employing gold nanoparticle (AuNP)-coated magnetic microbeads (AuNP-MMBs) as an immobilization matrix for higher loading density of hairpin-structured DNA probes and then ferrocene (Fc)-capped gold nanoparticle/streptavidin conjugates, amplified electrochemical assay of miRNA has been performed. In the presence of target miRNA, a novel assembly was formed via linking biotinylated hairpin DNA probe-covered AuNP-MMBs with Fc-capped gold nanoparticle/streptavidin conjugates and then collected by magnetic electrodes for voltammetric detection. The enlarged surface area, good conductivity of AuNP-MMBs and the multiple Fc tags on the electrode surface ensure high sensitivity of the method. The oxidation peak current of Fc tags is proportional to the concentrations of miRNA ranging from 5 fM to 100 fM, and a detection limit of 0.14 fM was achieved. The proposed assay is highly selective and reproducible, serving as a viable alternative for the detection of miRNA-182 from serum samples of glioma patients. Copyright © 2016 Elsevier B.V. All rights reserved.

  16. A Fast Strategy for Determination of Vitamin B₉ in Food and Pharmaceutical Samples Using an Ionic Liquid-Modified Nanostructure Voltammetric Sensor.

    Science.gov (United States)

    Khaleghi, Fatemeh; Irai, Abolfazl Elyasi; Sadeghi, Roya; Gupta, Vinod Kumar; Wen, Yangping

    2016-05-24

    Vitamin B₉ or folic acid is an important food supplement with wide clinical applications. Due to its importance and its side effects in pregnant women, fast determination of this vitamin is very important. In this study we present a new fast and sensitive voltammetric sensor for the analysis of trace levels of vitamin B₉ using a carbon paste electrode (CPE) modified with 1,3-dipropylimidazolium bromide (1,3-DIBr) as a binder and ZnO/CNTs nanocomposite as a mediator. The electro-oxidation signal of vitamin B₉ at the surface of the 1,3-DIBr/ZnO/CNTs/CPE electrode appeared at 800 mV, which was about 95 mV less positive compared to the corresponding unmodified CPE. The oxidation current of vitamin B₉ by square wave voltammetry (SWV) increased linearly with its concentration in the range of 0.08-650 μM. The detection limit for vitamin B₉ was 0.05 μM. Finally, the utility of the new 1,3-DIBr/ZnO/CNTs/CPE electrode was tested in the determination of vitamin B₉ in food and pharmaceutical samples.

  17. A Fast Strategy for Determination of Vitamin B9 in Food and Pharmaceutical Samples Using an Ionic Liquid-Modified Nanostructure Voltammetric Sensor

    Directory of Open Access Journals (Sweden)

    Fatemeh Khaleghi

    2016-05-01

    Full Text Available Vitamin B9 or folic acid is an important food supplement with wide clinical applications. Due to its importance and its side effects in pregnant women, fast determination of this vitamin is very important. In this study we present a new fast and sensitive voltammetric sensor for the analysis of trace levels of vitamin B9 using a carbon paste electrode (CPE modified with 1,3-dipropylimidazolium bromide (1,3-DIBr as a binder and ZnO/CNTs nanocomposite as a mediator. The electro-oxidation signal of vitamin B9 at the surface of the 1,3-DIBr/ZnO/CNTs/CPE electrode appeared at 800 mV, which was about 95 mV less positive compared to the corresponding unmodified CPE. The oxidation current of vitamin B9 by square wave voltammetry (SWV increased linearly with its concentration in the range of 0.08–650 μM. The detection limit for vitamin B9 was 0.05 μM. Finally, the utility of the new 1,3-DIBr/ZnO/CNTs/CPE electrode was tested in the determination of vitamin B9 in food and pharmaceutical samples.

  18. Voltammetric behavior of dopamine at a glassy carbon electrode modified with NiFe(2)O(4) magnetic nanoparticles decorated with multiwall carbon nanotubes.

    Science.gov (United States)

    Ensafi, Ali A; Arashpour, B; Rezaei, B; Allafchian, Ali R

    2014-06-01

    Voltammetric behavior of dopamine was studied on a glassy carbon electrode (GCE) modified-NiFe(2)O(4) magnetic nanoparticles decorated with multiwall carbon nanotubes. Impedance spectroscopy and cyclic voltammetry were used to characterize the behavior of dopamine at the surface of modified-GCE. The modified electrode showed a synergic effect toward the oxidation of dopamine. The oxidation peak current is increased linearly with the dopamine concentration (at pH7.0) in wide dynamic ranges of 0.05-6.0 and 6.0-100μmolL(-1) with a detection limit of 0.02μmolL(-1), using differential pulse voltammetry. The selectivity of the method was studied and the results showed that the modified electrode is free from interference of organic compounds especially ascorbic acid, uric acid, cysteine and urea. Its applicability in the determination of dopamine in pharmaceutical, urine samples and human blood serum was also evaluated. The proposed electrochemical sensor has appropriate properties such as high selectivity, low detection limit and wide linear dynamic range when compared with that of the previous reported papers for dopamine detection.

  19. Biochar prepared from castor oil cake at different temperatures: A voltammetric study applied for Pb(2+), Cd(2+) and Cu(2+) ions preconcentration.

    Science.gov (United States)

    Kalinke, Cristiane; Mangrich, Antonio Sálvio; Marcolino-Junior, Luiz H; Bergamini, Márcio F

    2016-11-15

    Biochar is a carbonaceous material similar produced by pyrolysis of biomass under oxygen-limited conditions. Pyrolysis temperature is an important parameter that can alters biochar characteristics (e.g. surface area, pore size distribution and surface functional groups) and affects it efficacy for adsorption of several probes. In this work, biochar samples have been prepared from castor oil cake using different temperatures of pyrolysis (200-600°C). For the first time, a voltammetric procedure based on carbon paste modified electrode (CPME) was used to investigate the effect of temperature of pyrolysis on the adsorptive characteristics of biochar for Pb(II), Cd(II) and Cu(II) ions. Besides the electrochemical techniques, several characterizations have been performed to evaluate the physicochemical properties of biochar in function of the increase of the pyrolysis temperature. Results suggest that biochar pyrolized at 400°C (BC400) showed a better potential for ions adsorption. The CPME modified with BC400 showed better relative current signal with adsorption affinity: Pb(II)>Cd(II)>Cu(II). Kinetic studies revealed that the pseudo-second order model describes more accurately the adsorption process suggesting that the surface reactions control the adsorption rate. Values found for amount adsorbed were 15.94±0.09; 4.29±0.13 and 2.38±0.39μgg(-1) for Pb(II), Cd(II) and Cu(II) ions, respectively.

  20. Voltammetric sensor based on carbon paste electrode modified with molecular imprinted polymer for determination of sulfadiazine in milk and human serum.

    Science.gov (United States)

    Sadeghi, Susan; Motaharian, Ali

    2013-12-01

    A new sensitive voltammetric sensor for determination of sulfadiazine is described. The developed sensor is based on carbon paste electrode modified with sulfadiazine imprinted polymer (MIP) as a recognition element. For comparison, a non-imprinted polymer (NIP) modified carbon paste electrode was prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were performed to study the binding event and electrochemical behavior of sulfadiazine at the modified carbon paste electrodes. The determination of sulfadiazine after its extraction onto the electrode surface was carried out by DPV at 0.92 V vs. Ag/AgCl owing to oxidation of sulfadiazine. Under the optimized operational conditions, the peak current obtained at the MIP modified carbon paste electrode was proportional to the sulfadiazine concentration within the range of 2.0×10(-7)-1.0×10(-4) mol L(-1) with a detection limit and sensitivity of 1.4×10(-7) mol L(-1) and 4.2×10(5) μA L mol(-1), respectively. The reproducibility of the developed sensor in terms of relative standard deviation was 2.6%. The sensor was successfully applied for determination of sulfadiazine in spiked cow milk and human serum samples with recovery values in the range of 96.7-100.9%.

  1. Integration of PET/CT in Current Diagnostic and Response Evaluation Methods in Patients with Tuberculosis

    Energy Technology Data Exchange (ETDEWEB)

    Oezmen, Oelem; Goekcek, Atila; Tatci, Ebru; Biner, Inci; Akkalyoncu, Behiye [Atatuerk Chest Diseases and Thoracic Surgery Training and Research Hospital, Ankara (Turkmenistan)

    2014-03-15

    Tuberculosis is a systemic disease that still affects many people. While pleural involvement is frequently observed in extrapulmonary tuberculosis, multiple skeletal system and articular involvements are quite rare. FDG PET imaging could be a promising diagnostic and treatment monitoring method, especially in complicated cases and if the other methods are inadequate. In this case study, we report a patient who was admitted with suspected malignancy and then diagnosed with tuberculosis pleuritis, lymphadenitis, spondylodiscitis, and sacroiliitis with specific symptoms; the response to anti-tuberculosis therapy was shown using FDG PET/CT.

  2. New insights into the chemistry of Coenzyme Q-0: A voltammetric and spectroscopic study.

    Science.gov (United States)

    Gulaboski, Rubin; Bogeski, Ivan; Kokoskarova, Pavlinka; Haeri, Haleh H; Mitrev, Sasa; Stefova, Marina; Stanoeva, Jasmina Petreska; Markovski, Velo; Mirčeski, Valentin; Hoth, Markus; Kappl, Reinhard

    2016-10-01

    Coenzyme Q-0 (CoQ-0) is the only Coenzyme Q lacking an isoprenoid group on the quinoid ring, a feature important for its physico-chemical properties. Here, the redox behavior of CoQ-0 in buffered and non-buffered aqueous media was examined. In buffered aqueous media CoQ-0 redox chemistry can be described by a 2-electron-2-proton redox scheme, characteristic for all benzoquinones. In non-buffered media the number of electrons involved in the electrode reaction of CoQ-0 is still 2; however, the number of protons involved varies between 0 and 2. This results in two additional voltammetric signals, attributed to 2-electrons-1H(+) and 2-electrons-0H(+) redox processes, in which mono- and di-anionic compounds of CoQ-0 are formed. In addition, CoQ-0 exhibits a complex chemistry in strong alkaline environment. The reaction of CoQ-0 and OH(-) anions generates several hydroxyl derivatives as products. Their structures were identified with HPLC/MS. The prevailing radical reaction mechanism was analyzed by electron paramagnetic resonance spectroscopy. The hydroxyl derivatives of CoQ-0 have a strong antioxidative potential and form stable complexes with Ca(2+) ions. In summary, our results allow mechanistic insights into the redox properties of CoQ-0 and its hydroxylated derivatives and provide hints on possible applications. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. Enzyme-catalyzed reaction of voltammetric enzyme-linked immunoassay system based on OAP as substrate

    Institute of Scientific and Technical Information of China (English)

    张书圣; 陈洪渊; 焦奎

    1999-01-01

    The o-aminophenol (OAP)-H2O2-horseradish peroxidase (HRP) voltammetric enzyme-linked immunoassay new system has extremely high sensitivity. HRP can be measured with a detection limit of 6.0×10-(10) g/L and a linear range of 1.0×10-9—4.0×10-6 g/L. The pure product of H2O2 oxidizing OAP catalyzed by HRP was prepared with chemical method. The enzyme-catalyzed reaction has been investigated with electroanalytical chemistry, UV/Vis spectrum, IR spectrum, 13C NMR, 1H NMR, mass spectrum, elemental analysis, etc. Under the selected enzyme-catalyzed reaction conditions, the oxidation product of OAP with H2O2 catalyzed by HRP is 2-aminophe-noxazine-3-one. The processes of the enzyme-catalyzed reaction and the electroreduction of the product of the enzymecatalyzed reaction have been described.

  4. Solar UV Photooxidation as Pretreatment for Stripping Voltammetric Trace Metal Analysis in River Water

    Directory of Open Access Journals (Sweden)

    Gelaneh Woldemichael

    2011-01-01

    Full Text Available The application of solar ultraviolet radiation as sample pretreatment or preparation step in stripping voltammetric analysis of trace metals in presence of low levels of dissolved organic carbon (DOC natural water samples (river water was studied. River water samples were collected from downstream of Warnow river (Germany and acidified to pH of 2±0.2 (by addition of 1 mL of ultrapure 65% HNO3 per liter sample. Furthermore, 100 μL/L of hydrogen peroxide solution (ultrapure, 30% H2O2 was added to the samples as photochemical reaction initiator. The samples were transferred to polyethylene terephthalate (PET bottles and irradiated with solar radiation of UV-A intensity of 3.6 mW/m2 for six hours, and the concentrations of Zn, Cd, Pb, and Cu were determined by differential pulse anodic stripping voltammetry (DPASV. The comparison of the values with the results obtained for the original untreated sample and artificial UV-treated one proved that solar UV radiation can be applied to the digestion of dissolved organic carbon in trace metal analysis in natural waters like river water, lake waters, well waters, and so forth.

  5. Classification and prediction of rice wines with different marked ages by using a voltammetric electronic tongue.

    Science.gov (United States)

    Wei, Zhenbo; Wang, Jun; Ye, Linshuang

    2011-08-15

    A voltammetric electronic tongue (VE-tongue) was developed to discriminate the difference between Chinese rice wines in this research. Three types of Chinese rice wine with different marked ages (1, 3, and 5 years) were classified by the VE-tongue by principal component analysis (PCA) and cluster analysis (CA). The VE-tongue consisted of six working electrodes (gold, silver, platinum, palladium, tungsten, and titanium) in a standard three-electrode configuration. The multi-frequency large amplitude pulse voltammetry (MLAPV), which consisted of four segments of 1 Hz, 10 Hz, 100 Hz, and 1000 Hz, was applied as the potential waveform. The three types of Chinese rice wine could be classified accurately by PCA and CA, and some interesting regularity is shown in the score plots with the help of PCA. Two regression models, partial least squares (PLS) and back-error propagation-artificial neural network (BP-ANN), were used for wine age prediction. The regression results showed that the marked ages of the three types of Chinese rice wine were successfully predicted using PLS and BP-ANN.

  6. Detection of antibiotic residues in bovine milk by a voltammetric electronic tongue system.

    Science.gov (United States)

    Wei, Zhenbo; Wang, Jun

    2011-05-23

    A voltammetric electronic tongue (VE-tongue) was developed to detect antibiotic residues in bovine milk. Six antibiotics (Chloramphenicol, Erythromycin, Kanamycin sulfate, Neomycin sulfate, Streptomycin sulfate and Tetracycline HCl) spiked at four different concentration levels (0.5, 1, 1.5 and 2 maximum residue limits (MRLs)) were classified based on VE-tongue by two pattern recognition methods: principal component analysis (PCA) and discriminant function analysis (DFA). The VE-tongue was composed of five working electrodes (gold, silver, platinum, palladium, and titanium) positioned in a standard three-electrode configuration. The Multi-frequency large amplitude pulse voltammetry (MLAPV) which consisted of four segments (1 Hz, 10 Hz, 100 Hz and 1000 Hz) was applied as potential waveform. The six antibiotics at the MRLs could not be separated from bovine milk completely by PCA, but all the samples were demarcated clearly by DFA. Three regression models: Principal Component Regression Analysis (PCR), Partial Least Squares Regression (PLSR), and Least Squares-Support Vector Machines (LS-SVM) were used for concentrations of antibiotics prediction. All the regression models performed well, and PCR had the most stable results.

  7. Detection of antibiotic residues in bovine milk by a voltammetric electronic tongue system

    Energy Technology Data Exchange (ETDEWEB)

    Wei Zhenbo [Zhejiang University, Department of Bio-Systems Engineering, 268 Kaixuan Road, Hangzhou, Zhejiang 310029 (China); Wang Jun, E-mail: jwang@zju.edu.cn [Zhejiang University, Department of Bio-Systems Engineering, 268 Kaixuan Road, Hangzhou, Zhejiang 310029 (China)

    2011-05-23

    A voltammetric electronic tongue (VE-tongue) was developed to detect antibiotic residues in bovine milk. Six antibiotics (Chloramphenicol, Erythromycin, Kanamycin sulfate, Neomycin sulfate, Streptomycin sulfate and Tetracycline HCl) spiked at four different concentration levels (0.5, 1, 1.5 and 2 maximum residue limits (MRLs)) were classified based on VE-tongue by two pattern recognition methods: principal component analysis (PCA) and discriminant function analysis (DFA). The VE-tongue was composed of five working electrodes (gold, silver, platinum, palladium, and titanium) positioned in a standard three-electrode configuration. The Multi-frequency large amplitude pulse voltammetry (MLAPV) which consisted of four segments (1 Hz, 10 Hz, 100 Hz and 1000 Hz) was applied as potential waveform. The six antibiotics at the MRLs could not be separated from bovine milk completely by PCA, but all the samples were demarcated clearly by DFA. Three regression models: Principal Component Regression Analysis (PCR), Partial Least Squares Regression (PLSR), and Least Squares-Support Vector Machines (LS-SVM) were used for concentrations of antibiotics prediction. All the regression models performed well, and PCR had the most stable results.

  8. Electrodeposited apatite coating for solid-phase microextraction and sensitive indirect voltammetric determination of fluoride ions.

    Science.gov (United States)

    Mao, Yuehong; Chen, Yufei; Chu, Lin; Zhang, Xiaoli

    2013-10-15

    Electrodeposition was used to prepare a new solid phase microextraction (SPME) coatings. Two apatite SPME coatings, dicalcium phosphate dihydrate (DCPD or brushite) and hydroxyapatite (HAP) were validly and homogeneously one-step electrodeposited on glassy carbon electrode (GCE) under different conditions. The coatings were characterized by XRD, FTIR, SEM, CV and EIS. The apatite SPME coatings showed excellent and selective adsorbability to fluoride ions. A novel indirect voltammetric strategy for sensitive detection of fluoride was proposed using K3Fe(CN)6 as indicating probe. The detection principle of fluoride ions was based on the increment of steric hindrance after fluoride adsorption, which resulting in the decrease of the amperometric signal to Fe(CN)6(3-). The liner ranges were 0.5-20.0 μmol/L for n-DCPD/GCE with the limit of detection of 0.14 μmol/L and 0.1-50.0 μmol/L for n-HAP/GCE with the limit of detection of 0.069 μmol/L, respectively. The developed method was applied to the analysis of water samples (lake, spring and tap water) and the recovery values were found to be in the range of 90-106%.

  9. Mesoporous carbon-containing voltammetric biosensor for determination of tyramine in food products.

    Science.gov (United States)

    Kochana, Jolanta; Wapiennik, Karolina; Knihnicki, Paweł; Pollap, Aleksandra; Janus, Paula; Oszajca, Marcin; Kuśtrowski, Piotr

    2016-07-01

    A voltammetric biosensor based on tyrosinase (TYR) was developed for determination of tyramine. Carbon material (multi-walled carbon nanotubes or mesoporous carbon CMK-3-type), polycationic polymer-i.e., poly(diallyldimethylammonium chloride) (PDDA), and Nafion were incorporated into titania dioxide sol (TiO2) to create an immobilization matrix. The features of the formed matrix were studied by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The analytical performance of the developed biosensor was evaluated with respect to linear range, sensitivity, limit of detection, long-term stability, repeatability, and reproducibility. The biosensor exhibited electrocatalytic activity toward tyramine oxidation within a linear range from 6 to 130 μM, high sensitivity of 486 μA mM(-1) cm(-2), and limit of detection of 1.5 μM. The apparent Michaelis-Menten constant was calculated to be 66.0 μM indicating a high biological affinity of the developed biosensor for tyramine. Furthermore, its usefulness in determination of tyramine in food product samples was also verified. Graphical abstract Different food samples were analyzed to determine tyramine using biosensor based on tyrosinase.

  10. On the Nature of Voltammetric Signals Originating from Hydrogen Electrosorption into Palladium-Noble Metal Alloys

    Science.gov (United States)

    Łukaszewski, Mariusz; Hubkowska, Katarzyna; Koss, Urszula; Czerwiński, Andrzej

    2013-01-01

    Hydrogen sorption/desorption signals observed on cyclic voltammograms in experiments on hydrogen electrosorption into Pd-noble metal alloys (Pd-Au, Pd-Pt, Pd-Rh, Pd-Ru, Pd-Pt-Rh, Pd-Pt-Au) were characterized. The influence of electrosorption potential, scan rate and alloy bulk composition on the features of the hydrogen peaks was investigated. The experimental results were compared with those obtained on the basis of a model taken from the literature. It was confirmed that the rate of the α-β phase transition controls the overall rate of the process of hydrogen absorption/desorption into/from thin Pd-based electrodes. It was demonstrated that from the analysis of the changes of the hydrogen oxidation peak potential with the hydrogen electrosorption potential in cyclic voltammetric experiments it is possible to determine the limiting Pd bulk content, below which the β-phase in the alloy-hydrogen system is not formed. PMID:28788362

  11. Simultaneous Voltammetric/Amperometric Determination of Sulfide and Nitrite in Water at BDD Electrode

    Directory of Open Access Journals (Sweden)

    Anamaria Baciu

    2015-06-01

    Full Text Available This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., −0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix.

  12. Simultaneous Voltammetric/Amperometric Determination of Sulfide and Nitrite in Water at BDD Electrode

    Science.gov (United States)

    Baciu, Anamaria; Ardelean, Magdalena; Pop, Aniela; Pode, Rodica; Manea, Florica

    2015-01-01

    This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD) electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., −0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix. PMID:26102487

  13. Adsorptive cathodic stripping voltammetric determination of dexamethasone in formulations and biological fluids.

    Science.gov (United States)

    Ghoneim, Enass M; El-Attar, Mona A; Ghoneim, Mohamed M

    2009-01-01

    The electrochemical behavior of dexamethasone at a hanging mercury drop electrode (HMDE) in a universal buffer series of pH 2-10 was studied using cyclic voltammetry. Based on the interfacial adsorptive character of dexamethasone onto the HMDE (electrode surface coverage = 1.4 x 10(-10) mol/cm2), a fully validated simple square-wave adsorptive cathodic stripping voltammetric method is described for its determination in bulk form with a limit of detection (LOD) of 3.1 x 10(-9) M. The described method was successfully applied to analysis of dexamethasone in its pharmaceutical formulations (deltasone tablets and fortecortin ampule) and in spiked samples of human urine, bovine urine, and protein-free bovine milk. The achieved LODs of dexamethasone in human urine, bovine urine, and protein-free bovine milk were 1.5 x 10(-8), 2 x 10(-8), and 9 x 10(-9) M, respectively. The mean percentage recoveries of 4 x 10(-7) M dexamethasone in bulk form, spiked human urine, bovine urine, and bovine milk, based on the average of 3 replicate measurements, were 99.8 +/- 0.25, 100.4 +/- 0.96, 99.6 +/- 0.79, and 100.1 +/- 0.26, respectively.

  14. Voltammetric methods for determination and speciation of inorganic arsenic in the environment-A review

    Energy Technology Data Exchange (ETDEWEB)

    Mays, Douglas E. [Centre for Clean Water and Sustainable Technologies, Department of Chemistry and Biochemistry, George Mason University, Fairfax, VA 20120 (United States); Hussam, Abul, E-mail: ahussam@gmu.edu [Centre for Clean Water and Sustainable Technologies, Department of Chemistry and Biochemistry, George Mason University, Fairfax, VA 20120 (United States)

    2009-07-30

    The measurement of inorganic arsenic in the environment has received considerable attention over the past 40+ years due to its toxicity and prevalence in drinking water. This paper provides an overview of voltammetric techniques used since 2001. More than fifty papers from refereed analytical chemistry journals on the speciation and measurement of inorganic arsenic (As(III) and As(V)) in practical and environmental samples are included. The present review shows that stripping voltammetry is a sensitive and inexpensive technique. The new approaches include development of novel measurement protocols through media variation, development and use of new boron doped diamond electrodes modified with metals, nano Au-modified electrodes on carbon or carbon nano-tubes, novel rotating disc and vibrating electrodes to enhance mass transfer, and modified Hg(l) and thin film Bi on carbon for cathodic stripping voltammetry are discussed. Although, majority of the papers were of exploratory in nature, the trend towards developing a commercial standalone instrument for field use is still in progress.

  15. Simultaneous Voltammetric/Amperometric Determination of Sulfide and Nitrite in Water at BDD Electrode.

    Science.gov (United States)

    Baciu, Anamaria; Ardelean, Magdalena; Pop, Aniela; Pode, Rodica; Manea, Florica

    2015-06-19

    This work reported new voltammetric/amperometric-based protocols using a commercial boron-doped diamond (BDD) electrode for simple and fast simultaneous detection of sulfide and nitrite from water. Square-wave voltammetry operated under the optimized working conditions of 0.01 V step potential, 0.5 V modulation amplitude and 10 Hz frequency allowed achieving the best electroanalytical parameters for the simultaneous detection of nitrite and sulfide. For practical in-field detection applications, the multiple-pulsed amperometry technique was operated under optimized conditions, i.e., -0.5 V/SCE for a duration of 0.3 s as conditioning step, +0.85 V/SCE for a duration of 3 s that assure the sulfide oxidation and +1.25 V/SCE for a duration of 0.3 s, where the nitrite oxidation occurred, which allowed the simultaneously detection of sulfide and nitrite without interference between them. Good accuracy was found for this protocol in comparison with standardized methods for each anion. Also, no interference effect was found for the cation and anion species, which are common in the water matrix.

  16. Improvement of the ultra-trace voltammetric determination of Rh in environmental samples using signal transformation.

    Science.gov (United States)

    Almécija, C; Cobelo-García, A; Santos-Echeandía, J

    2016-01-01

    Rhodium (Rh) is present at the Earth's surface at ultra-trace concentrations (0.06 ng g(-1)); however, its use in catalytic converters has increased its deposition nearby traffic pressure and therefore the interest in analytical techniques for Rh determination has raised in the recent years. In this study we propose an improvement of Rh measurement by adsorptive voltammetry applying second-derivative signal transformation. The optimization of experimental parameters affecting the voltammetric analysis were carried out using sediment samples; these include the amount of sample digest used, the hydrochloric acid and formaldehyde concentrations, deposition potential and equilibration time. The use of the second derivative transformation provided well-defined peaks due to the minimization of background interferences, leading to a significant decrease in the detection limits. Accordingly, a detection limit of 200 fM Rh in the cell was obtained, which corresponds to 14 pg g(-1) of Rh for 200mg of sediments. The optimized methodology was applied to the analysis of Rh in a sediment core collected close to a motorway bridge from Tagus Estuary (Lisbon, Portugal). Here, Rh concentrations ranged from 0.06 to 0.47 ng g(-1), showing a surface Rh-enrichment linked to traffic, which was consistent with a Pt superficial peak. Reference materials were also analyzed, including road dust (BCR-723) and river sediment (JSD-2), and values obtained were in agreement with certified concentrations and previously values reported in the literature. Copyright © 2015 Elsevier B.V. All rights reserved.

  17. Centri-voltammetric study with amberlite XAD-7 resin as a carrier system.

    Science.gov (United States)

    Anik Kirgöz, Ulkü; Tural, Hüseyin; Nil Ertaş, F

    2005-01-15

    Centri-voltammetry is a novel method, which allows combining the advantages of centrifugation and voltammetry. The method offers a practical way for application of coprecipitation in trace analysis allowing direct voltammetric scan hence prevents the loss of the analyte, which usually is the case for other preconcentration techniques. The performance of the method was successfully tested using trace amounts of Pb(2+) ions in aqueous solution in a vessel specially designed to be compatible to both centrifugation and voltammetry. XAD-7 resin was used as the carrier material and the parameters related to the carrier material and medium characteristics as well as the centrifugation settings were investigated. The sensitivity of the method was found comparable to that of stripping techniques and the detection limit for lead ions was calculated as 5.2 x 10(-9)M with mercury coated gold sphere electrode. The precision of the method depends on the configuration of the working electrode and better reproducibility was obtained with mercury coated plate electrodes (R.S.D. 3.3%, n = 6).

  18. Frequency-dependent reduction of voltage-gated sodium current modulates retinal ganglion cell response rate to electrical stimulation

    Science.gov (United States)

    Tsai, David; Morley, John W.; Suaning, Gregg J.; Lovell, Nigel H.

    2011-10-01

    The ability to elicit visual percepts through electrical stimulation of the retina has prompted numerous investigations examining the feasibility of restoring sight to the blind with retinal implants. The therapeutic efficacy of these devices will be strongly influenced by their ability to elicit neural responses that approximate those of normal vision. Retinal ganglion cells (RGCs) can fire spikes at frequencies greater than 200 Hz when driven by light. However, several studies using isolated retinas have found a decline in RGC spiking response rate when these cells were stimulated at greater than 50 Hz. It is possible that the mechanism responsible for this decline also contributes to the frequency-dependent 'fading' of electrically evoked percepts recently reported in human patients. Using whole-cell patch clamp recordings of rabbit RGCs, we investigated the causes for the spiking response depression during direct subretinal stimulation of these cells at 50-200 Hz. The response depression was not caused by inhibition arising from the retinal network but, instead, by a stimulus-frequency-dependent decline of RGC voltage-gated sodium current. Under identical experimental conditions, however, RGCs were able to spike at high frequency when driven by light stimuli and intracellular depolarization. Based on these observations, we demonstrated a technique to prevent the spiking response depression.

  19. Differential pulse anodic stripping voltammetric determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone modified carbon paste electrode.

    Science.gov (United States)

    Mousavi, M F; Rahmani, A; Golabi, S M; Shamsipur, M; Sharghi, H

    2001-08-30

    A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters.

  20. Simultaneous voltammetric determination of paracetamol and ascorbic acid using a boron-doped diamond electrode modified with Nafion and lead films.

    Science.gov (United States)

    Tyszczuk-Rotko, Katarzyna; Bęczkowska, Ilona; Wójciak-Kosior, Magdalena; Sowa, Ireneusz

    2014-11-01

    The paper describes the fabrication and application of a novel sensor (a boron-doped diamond electrode modified with Nafion and lead films) for the simultaneous determination of paracetamol and ascorbic acid by differential pulse voltammetry. The main advantage of the lead film and polymer covered boron-doped diamond electrode is that the sensitivity of the stripping responses is increased and the separation of paracetamol and ascorbic acid signals is improved due to the modification of the boron-doped diamond surface by the lead layer. Additionally, the repeatability of paracetamol and ascorbic acid signals is improved by the application of the Nafion film coating. In the presence of oxygen, linear calibration curves were obtained in a wide concentration range from 5×10(-7) to 2×10(-4) mol L(-1) for paracetamol and from 1×10(-6) to 5×10(-4) mol L(-1) for ascorbic acid. The analytical utility of the differential pulse voltammetric method elaborated was tested in the assay of paracetamol and ascorbic acid in commercially available pharmaceutical formulations and the method was validated by high performance liquid chromatography coupled with diode array detector.

  1. Glassy carbon electrode modified with horse radish peroxidase/organic nucleophilic-functionalized carbon nanotube composite for enhanced electrocatalytic oxidation and efficient voltammetric sensing of levodopa.

    Science.gov (United States)

    Shoja, Yalda; Rafati, Amir Abbas; Ghodsi, Javad

    2016-01-01

    A novel and selective enzymatic biosensor was designed and constructed for voltammetric determination of levodopa (L-Dopa) in aqueous media (phosphate buffer solution, pH=7). Biosensor development was on the basis of to physically immobilizing of horse radish peroxidase (HRP) as electrochemical catalyst by sol-gel on glassy carbon electrode modified with organic nucleophilic carbon nanotube composite which in this composite p-phenylenediamine (pPDA) as organic nucleophile chemically bonded with functionalized MWCNT (MWCNT-COOH). The results of this study suggest that prepared bioorganic nucleophilic carbon nanotube composite (HRP/MWCNT-pPDA) shows fast electron transfer rate for electro oxidation of L-Dopa because of its high electrochemical catalytic activity toward the oxidation of L-Dopa, more--NH2 reactive sites and large effective surface area. Also in this work we measured L-Dopa in the presence of folic acid and uric acid as interferences. The proposed biosensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), FT-IR spectroscopy and cyclic voltammetry (CV). The differential pulse voltammetry (DPV) was used for determination of L-Dopa from 0.1 μM to 1.9 μM with a low detection limit of 40 nM (for S/N=3) and sensitivity was about 35.5 μA/μM. Also this biosensor has several advantages such as rapid response, high stability and reproducibility.

  2. From Ethics, Integrity and Moral Probity to Responsible Research and Innovation in Current Educational Practices

    Directory of Open Access Journals (Sweden)

    Laura Monica GORGHIU

    2016-12-01

    Full Text Available As other social domains, the area of education is in a strong interdependence with environmental contexts, being in accordance with the economic conditions, political decisions, technological development and, not in the end, the demographic dynamics. Changes in all the above-mentioned aspects lead to modification of several educational variables. However, the actual educational settings and practices must take into consideration the future, projecting and addressing in this respect, the major challenges that will occur in the society in the following decades. In education, there were recorded a series of changes in theoretical frameworks or paradigms over the past decades. We have to admit that not all of them proved to be good or welcome, mostly in the cases when some of them were introduced considering the temporary social changes, limiting their evolution to a specific era or developmental goal or educational cult (Lindgren, 2013. But, it is obvious that paradigms or concepts which answer to the actual societal developments, which help the students in the process of becoming future responsible citizens, are more than welcome and beneficial. In this respect, this number of the Romanian Journal of Multidimensional Education tries to offer some answers to possible educational values of equity, integrity or relevance principles, together with the possibilities of exploiting the dimensions of Responsible Research and Innovation in the actual education.

  3. Large-amplitude Fourier transformed high-harmonic alternating current cyclic voltammetry: kinetic discrimination of interfering Faradaic processes at glassy carbon and at boron-doped diamond electrodes.

    Science.gov (United States)

    Zhang, Jie; Guo, Si-Xuan; Bond, Alan M; Marken, Frank

    2004-07-01

    Significant advantages of Fourier transformed large-amplitude ac higher (second to eighth) harmonics relative to responses obtained with conventional small-amplitude ac or dc cyclic voltammetric methods have been demonstrated with respect to (i) the suppression of capacitive background currents, (ii) the separation of the reversible reduction of [Ru(NH(3))(6)](3+) from the overlapping irreversible oxygen reduction process under conditions where aerobic oxygen remains present in the electrochemical cell, and (iii) the kinetic resolution of the reversible [Ru(NH(3))(6)](3+/2+) process in mixtures of [Fe(CN)(6)](3-) and [Ru(NH(3))(6)](3+) at appropriately treated boron-doped diamond electrodes, even when highly unfavorable [Fe(CN)(6)](3-) to [Ru(NH(3))(6)](3+) concentration ratios are employed. Theoretical support for the basis of kinetic discrimination in large-amplitude higher harmonic ac cyclic voltammetry is provided.

  4. Delayed baroclinic response of the Antarctic circumpolar current to surface wind stress

    Institute of Scientific and Technical Information of China (English)

    YANG XiaoYi; HUANG RuiXin; WANG Jia; WANG DongXiao

    2008-01-01

    The Antarctic Circumpolar Current (ACC) responds to the surface windstress via two processes,i.e.,the instant barotropic process and the delayed baroclinic process. This study focuses on the baroclinic instability mechanism in ACC,which was less reported in the literatures. Results show that the strengthening of surface zonal windstress causes the enhanced tilting of the isopycnal surface,leading to more intense baroclinic instability. Simultaneously,the mesoscale eddies resulting from the baroclinic instability facilitate the transformation of mean potential energy to eddy energy,which causes the remarkable decrease of the ACC volume transport with the 2-year lag time. This delayed negative correlation between the ACC transport and the zonal windstress may account for the steadiness of the ACC transport during last two decades.

  5. Blood Stage Plasmodium falciparum Exhibits Biological Responses to Direct Current Electric Fields

    Science.gov (United States)

    Coronado, Lorena M.; Montealegre, Stephania; Chaverra, Zumara; Mojica, Luis; Espinosa, Carlos; Almanza, Alejandro; Correa, Ricardo; Stoute, José A.; Gittens, Rolando A.

    2016-01-01

    The development of resistance to insecticides by the vector of malaria and the increasingly faster appearance of resistance to antimalarial drugs by the parasite can dangerously hamper efforts to control and eradicate the disease. Alternative ways to treat this disease are urgently needed. Here we evaluate the in vitro effect of direct current (DC) capacitive coupling electrical stimulation on the biology and viability of Plasmodium falciparum. We designed a system that exposes infected erythrocytes to different capacitively coupled electric fields in order to evaluate their effect on P. falciparum. The effect on growth of the parasite, replication of DNA, mitochondrial membrane potential and level of reactive oxygen species after exposure to electric fields demonstrate that the parasite is biologically able to respond to stimuli from DC electric fields involving calcium signaling pathways. PMID:27537497

  6. Delayed baroclinic response of the Antarctic circum-polar current to surface wind stress

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The Antarctic Circumpolar Current (ACC) responds to the surface windstress via two processes, i.e., the instant barotropic process and the delayed baroclinic process. This study focuses on the baroclinic instability mechanism in ACC, which was less reported in the literatures. Results show that the strengthening of surface zonal windstress causes the enhanced tilting of the isopycnal surface, leading to more intense baroclinic instability. Simultaneously, the mesoscale eddies resulting from the baro- clinic instability facilitate the transformation of mean potential energy to eddy energy, which causes the remarkable decrease of the ACC volume transport with the 2-year lag time. This delayed negative cor- relation between the ACC transport and the zonal windstress may account for the steadiness of the ACC transport during last two decades.

  7. Central Banks’ Response to the Current Financial Crisis – Between Costs and Benefits

    Directory of Open Access Journals (Sweden)

    Teodora Cristina Barbu

    2012-01-01

    Full Text Available Our study is inserted in the thematic area dedicated, during recent years, to the research on central banks’ response to financial crisis. The global financial crisis has outlined a series of weaknesses located at regulatory and supervisory activities’ level, causing major central banks to face a new operating environment, in which traditional monetary policy tools are ineffective (key interest rate close to zero in restoring the financial markets’ proper functioning. The unconventional monetary policy measures, the dramatic fall of the key interest rate, the balance sheet structure modification and extension of collateral accepted by central banks are the main issues on which we focused our attention, to highlight the costs and benefits recorded by these institutions. All major central banks have implemented highly innovative, flexible facilities and the main beneficiaries have been the banking systems in their entirety.

  8. Western Interventions in Current Wars: Political Justification and Civil Society´s Response

    Directory of Open Access Journals (Sweden)

    Noelia Bueno Gómez

    2017-01-01

    Full Text Available On the one hand, it seems to be an agreement in Western countries in favor of values included in the Universal Declaration of Human Rights. On the other hand, Western countries initiate or intervene in armed conflicts outside their territories, which implies actions contrary to such values. This article examines this apparent contradiction: it describes briefly the international context of contemporary conflicts and it refers to the just-war tradition in order to analyze both the position of the Charter of the United Nations and the justifications given by Western countries. Moreover, the arguments used by the US and the Spanish Governments to justify their interventions in the Afghanistan (2001 and Iraq (2008 wars, and the responses of civil society are considered.

  9. Enhanced Brain Responses to Pain-Related Words in Chronic Back Pain Patients and Their Modulation by Current Pain

    Science.gov (United States)

    Ritter, Alexander; Franz, Marcel; Puta, Christian; Dietrich, Caroline; Miltner, Wolfgang H. R.; Weiss, Thomas

    2016-01-01

    Previous functional magnetic resonance imaging (fMRI) studies in healthy controls (HC) and pain-free migraine patients found activations to pain-related words in brain regions known to be activated while subjects experience pain. The aim of the present study was to identify neural activations induced by pain-related words in a sample of chronic back pain (CBP) patients experiencing current chronic pain compared to HC. In particular, we were interested in how current pain influences brain activations induced by pain-related adjectives. Subjects viewed pain-related, negative, positive, and neutral words; subjects were asked to generate mental images related to these words during fMRI scanning. Brain activation was compared between CBP patients and HC in response to the different word categories and examined in relation to current pain in CBP patients. Pain-related words vs. neutral words activated a network of brain regions including cingulate cortex and insula in subjects and patients. There was stronger activation in medial and dorsolateral prefrontal cortex (DLPFC) and anterior midcingulate cortex in CPB patients than in HC. The magnitude of activation for pain-related vs. negative words showed a negative linear relationship to CBP patients’ current pain. Our findings confirm earlier observations showing that pain-related words activate brain networks similar to noxious stimulation. Importantly, CBP patients show even stronger activation of these structures while merely processing pain-related words. Current pain directly influences on this activation. PMID:27517967

  10. Comparison of anamnestic responses to rabies vaccination in dogs and cats with current and out-of-date vaccination status.

    Science.gov (United States)

    Moore, Michael C; Davis, Rolan D; Kang, Qing; Vahl, Christopher I; Wallace, Ryan M; Hanlon, Cathleen A; Mosier, Derek A

    2015-01-15

    To compare anamnestic antibody responses of dogs and cats with current versus out-of-date vaccination status. Cross-sectional study. 74 dogs and 33 cats. Serum samples were obtained from dogs and cats that had been exposed to rabies and brought to a veterinarian for proactive serologic monitoring or that had been brought to a veterinarian for booster rabies vaccination. Blood samples were collected on the day of initial evaluation (day 0) and then again 5 to 15 days later. On day 0, a rabies vaccine was administered according to label recommendations. Paired serum samples were analyzed for antirabies antibodies by means of a rapid fluorescent focus inhibition test. All animals had an antirabies antibody titer ≥ 0.5 IU/mL 5 to 15 days after booster vaccination. Dogs with an out-of-date vaccination status had a higher median increase in titer, higher median fold increase in titer, and higher median titer following booster vaccination, compared with dogs with current vaccination status. Most (26/33) cats, regardless of rabies vaccination status, had a titer ≥ 12 IU/mL 5 to 15 days after booster vaccination. Results indicated that dogs with out-of-date vaccination status were not inferior in their antibody response following booster rabies vaccination, compared with dogs with current vaccination status. Findings supported immediate booster vaccination followed by observation for 45 days of dogs and cats with an out-of-date vaccination status that are exposed to rabies, as is the current practice for dogs and cats with current vaccination status.

  11. Response of stream benthic macroinvertebrates to current water management in Alpine catchments massively developed for hydropower.

    Science.gov (United States)

    Quadroni, Silvia; Crosa, Giuseppe; Gentili, Gaetano; Espa, Paolo

    2017-12-31

    The present work focuses on evaluating the ecological effects of hydropower-induced streamflow alteration within four catchments in the central Italian Alps. Downstream from the water diversions, minimum flows are released as an environmental protection measure, ranging approximately from 5 to 10% of the mean annual natural flow estimated at the intake section. Benthic macroinvertebrates as well as daily averaged streamflow were monitored for five years at twenty regulated stream reaches, and possible relationships between benthos-based stream quality metrics and environmental variables were investigated. Despite the non-negligible inter-site differences in basic streamflow metrics, benthic macroinvertebrate communities were generally dominated by few highly resilient taxa. The highest level of diversity was detected at sites where upstream minimum flow exceedance is higher and further anthropogenic pressures (other than hydropower) are lower. However, according to the current Italian normative index, the ecological quality was good/high on average at all of the investigated reaches, thus complying the Water Framework Directive standards. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. Comparison of Twitch Responses During Current- or Voltage-Controlled Transcutaneous Neuromuscular Electrical Stimulation.

    Science.gov (United States)

    Vargas Luna, José Luis; Krenn, Matthias; Löfler, Stefan; Kern, Helmut; Cortés R, Jorge A; Mayr, Winfried

    2015-10-01

    Neuromuscular electrical stimulation (NMES) is an established method for functional restoration of muscle function, rehabilitation, and diagnostics. In this work, NMES was applied with surface electrodes placed on the anterior thigh to identify the main differences between current-controlled (CC) and voltage-controlled (VC) modes. Measurements of the evoked knee extension force and the myoelectric signal of quadriceps and hamstrings were taken during stimulation with different amplitudes, pulse widths, and stimulation techniques. The stimulation pulses were rectangular and symmetric biphasic for both stimulation modes. The electrode-tissue impedance influences the differences between CC and VC stimulation. The main difference is that for CC stimulation, variation of pulse width and amplitude influences the amount of nerve depolarization, whereas VC stimulation is only dependent on amplitude variations for pulse widths longer than 150 μs. An important remark is that these findings are strongly dependent on the characteristics of the electrode-skin interface. In our case, we used large stimulation electrodes placed on the anterior thigh, which cause higher capacitive effects. The controllability, voltage compliance, and charge characteristics of each stimulation technique should be considered during the stimulators design. For applications that require the activation of a large amount of nerve fibers, VC is a more suitable option. In contrast, if the application requires a high controllability, then CC should be chosen prior to VC.

  13. Can current moisture responses predict soil CO2 efflux under altered precipitation regimes? A synthesis of manipulation experiments

    Directory of Open Access Journals (Sweden)

    S. Vicca

    2014-01-01

    Full Text Available As a key component of the carbon cycle, soil CO2 efflux (SCE is being increasingly studied to improve our mechanistic understanding of this important carbon flux. Predicting ecosystem responses to climate change often depends on extrapolation of current relationships between ecosystem processes and their climatic drivers to conditions not yet experienced by the ecosystem. This raises the question to what extent these relationships remain unaltered beyond the current climatic window for which observations are available to constrain the relationships. Here, we evaluate whether current responses of SCE to fluctuations in soil temperature and soil water content can be used to predict SCE under altered rainfall patterns. Of the 58 experiments for which we gathered SCE data, 20 were discarded because either too few data were available, or inconsistencies precluded their incorporation in the analyses. The 38 remaining experiments were used to test the hypothesis that a model parameterized with data from the control plots (using soil temperature and water content as predictor variables could adequately predict SCE measured in the manipulated treatment. Only for seven of these 38 experiments, this hypothesis was rejected. Importantly, these were the experiments with the most reliable datasets, i.e., those providing high-frequency measurements of SCE. Accordingly, regression tree analysis demonstrated that measurement frequency was crucial; our hypothesis could be rejected only for experiments with measurement intervals of less than 11 days, and was not rejected for any of the 24 experiments with larger measurement intervals. This highlights the importance of high-frequency measurements when studying effects of altered precipitation on SCE, probably because infrequent measurement schemes have insufficient capacity to detect shifts in the climate-dependencies of SCE. We strongly recommend that future experiments focus more strongly on establishing response

  14. Assessment and monitoring of treatment response in adult ADHD patients: current perspectives

    Science.gov (United States)

    Ramsay, J Russell

    2017-01-01

    Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental syndrome that emerges in childhood or early adolescence and persists into adulthood for a majority of individuals. There are many other adults with ADHD who may not seek out evaluation and treatment until adulthood, having been able to “get by” before struggling with inattention, hyperactivity, and/or impulsivity in adulthood, in addition to facing the associated features of disorganization, poor time management, and procrastination among many others. A lifetime diagnosis of ADHD is associated with a wide range of life impairments, which makes a comprehensive and accurate diagnostic assessment essential in order to obtain appropriate treatment. Moreover, while there are effective medical and psychosocial treatments for ADHD, it is important to be able to track treatment response in order to evaluate whether adjustments in specific interventions are needed or referrals for adjunctive treatments and supports are indicated to facilitate optimal therapeutic outcomes. The goal of this article is to provide a clinically useful review of the various measures that practicing clinicians can use to aid in the diagnostic assessment and monitoring of psychosocial and medical treatment of ADHD in adult patients. This review includes various structured interviews, screening scales, adult ADHD symptom inventories, measures of associated features of ADHD, as well as ratings of impairment and functioning which can be adapted to clinicians’ practice needs in order to track treatment progress and optimize treatments for adults with ADHD. PMID:28184164

  15. Surface Modified Multifunctional and Stimuli Responsive Nanoparticles for Drug Targeting: Current Status and Uses

    Science.gov (United States)

    Siafaka, Panoraia I.; Üstündağ Okur, Neslihan; Karavas, Evangelos; Bikiaris, Dimitrios N.

    2016-01-01

    Nanocarriers, due to their unique features, are of increased interest among researchers working with pharmaceutical formulations. Polymeric nanoparticles and nanocapsules, involving non-toxic biodegradable polymers, liposomes, solid lipid nanoparticles, and inorganic–organic nanomaterials, are among the most used carriers for drugs for a broad spectrum of targeted diseases. In fact, oral, injectable, transdermal-dermal and ocular formulations mainly consist of the aforementioned nanomaterials demonstrating promising characteristics such as long circulation, specific targeting, high drug loading capacity, enhanced intracellular penetration, and so on. Over the last decade, huge advances in the development of novel, safer and less toxic nanocarriers with amended properties have been made. In addition, multifunctional nanocarriers combining chemical substances, vitamins and peptides via coupling chemistry, inorganic particles coated by biocompatible materials seem to play a key role considering that functionalization can enhance characteristics such as biocompatibility, targetability, environmental friendliness, and intracellular penetration while also have limited side effects. This review aims to summarize the “state of the art” of drug delivery carriers in nanosize, paying attention to their surface functionalization with ligands and other small or polymeric compounds so as to upgrade active and passive targeting, different release patterns as well as cell targeting and stimuli responsibility. Lastly, future aspects and potential uses of nanoparticulated drug systems are outlined. PMID:27589733

  16. Three-dimensional surface current loops in broadband responsive negative refractive metamaterial with isotropy

    Institute of Scientific and Technical Information of China (English)

    He Xun-Jun; Wang Yue; Mei Jin-Shuo; Gui Tai-Long; Yin Jing-Hua

    2012-01-01

    We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses.The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs,which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI.The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity.The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave,but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%.In addition,the NRI band is insensitive to the polarization and the incident angle of the incident EM wave.Therefore,the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.

  17. Current dependence of the hot-spot response spectrum of superconducting single-photon detectors with different layouts

    Science.gov (United States)

    Charaev, I.; Semenov, A.; Doerner, S.; Gomard, G.; Ilin, K.; Siegel, M.

    2017-02-01

    We show that avoiding bends in a current-carrying superconducting nanowire enhances the probability for low energy photons to be detected and that this enhancement is entirely due to the increase in the experimentally achievable critical current. We studied nanowires shaped as either meander or spiral. The spirals had different layouts, a double-spiral layout with an S-turn in the middle and a single-spiral layout without such a turn. Nanowires were prepared from films of niobium nitride with a thickness of 5 nm. For specimens with each layout we measured the spectra of the single-photon response in the wavelength range from 400 nm to 1600 nm and defined the cut-off wavelength (λ c) beyond which the response rolls off. The largest and the smallest λ c were found for the single-spiral layout and for the meander, respectively. For all three layouts the relationship between λ c and the relative bias current falls onto a universal curve which has been predicted earlier in the framework of the modified hot-spot model. For the single-spiral layout, the efficiency of photon detection at wavelengths smaller than λ c reaches the expected absorbance of the spiral structure and the timing jitter per unit length of the nanowire has the smallest value.

  18. Impairments of motor-cortex responses to unilateral and bilateral direct current stimulation in schizophrenia

    Directory of Open Access Journals (Sweden)

    Alkomiet eHasan

    2013-10-01

    Full Text Available Transcranial direct current stimulation (tDCS is a non-invasive stimulation technique that can be applied to modulate cortical activity through induction of cortical plasticity. Since various neuropsychiatric disorders are characterised by fluctuations in cortical activity levels (e.g. schizophrenia, tDCS is increasingly investigated as a treatment tool. Several studies have shown that the induction of cortical plasticity following classical, unilateral tDCS is reduced or impaired in the stimulated and non-stimulated primary motor cortices (M1 of schizophrenia patients. Moreover, an alternative, bilateral tDCS setup has recently been shown to modulate cortical plasticity in both hemispheres in healthy subjects, highlighting another potential treatment approach. Here we present the first study comparing the efficacy of unilateral tDCS (cathode left M1, anode right supraorbital with simultaneous bilateral tDCS (cathode left M1, anode right M1 in schizophrenia patients. tDCS-induced cortical plasticity was monitored by investigating motor-evoked potentials induced by single-pulse transcranial magnetic stimulation applied to both hemispheres. Healthy subjects showed a reduction of left M1 excitability following unilateral tDCS on the stimulated left hemisphere and an increase in right M1 excitability following bilateral tDCS. In schizophrenia, no plasticity was induced following both stimulation paradigms. The pattern of these results indicates a complex interplay between plasticity and connectivity that is impaired in schizophrenia patients. Further studies are needed to clarify the biological underpinnings and clinical impact of these findings.

  19. Impairments of motor-cortex responses to unilateral and bilateral direct current stimulation in schizophrenia.

    Science.gov (United States)

    Hasan, Alkomiet; Bergener, Theresa; Nitsche, Michael A; Strube, Wolfgang; Bunse, Tilmann; Falkai, Peter; Wobrock, Thomas

    2013-01-01

    Transcranial direct current stimulation (tDCS) is a non-invasive stimulation technique that can be applied to modulate cortical activity through induction of cortical plasticity. Since various neuropsychiatric disorders are characterized by fluctuations in cortical activity levels (e.g., schizophrenia), tDCS is increasingly investigated as a treatment tool. Several studies have shown that the induction of cortical plasticity following classical, unilateral tDCS is reduced or impaired in the stimulated and non-stimulated primary motor cortices (M1) of patients with schizophrenia. Moreover, an alternative, bilateral tDCS setup has recently been shown to modulate cortical plasticity in both hemispheres in healthy subjects, highlighting another potential treatment approach. Here we present the first study comparing the efficacy of unilateral tDCS (cathode left M1, anode right supraorbital) with simultaneous bilateral tDCS (cathode left M1, anode right M1) in patients with schizophrenia. tDCS-induced cortical plasticity was monitored by investigating motor-evoked potentials induced by single-pulse transcranial magnetic stimulation applied to both hemispheres. Healthy subjects showed a reduction of left M1 excitability following unilateral tDCS on the stimulated left hemisphere and an increase in right M1 excitability following bilateral tDCS. In schizophrenia, no plasticity was induced following both stimulation paradigms. The pattern of these results indicates a complex interplay between plasticity and connectivity that is impaired in patients with schizophrenia. Further studies are needed to clarify the biological underpinnings and clinical impact of these findings.

  20. Late radiation responses in man: Current evaluation from results from Hiroshima and Nagasaki

    Science.gov (United States)

    Schull, William J.

    Among the late effects of exposure to the atomic bombings of Hiroshima and Nagasaki, none looms larger than radiation related malignancies. Indeed, the late effects of A-bomb radiation on mortality appear to be limited to an increase in malignant tumors. At present, it can be shown that cancers of the breast, colon, esophagus, lungs, stomach, thyroid, and urinary tract as well as leukemia and multiple myeloma increase in frequency with an increase in exposure. No significant relationship to radiation can as yet be established for malignant lymphoma, nor cancers of the rectum, pancreas or uterus. Radiation induced malignancies other than leukemia seem to develop proportionally to the natural cancer rate for the attained age. For specific age-at-death intervals, both relative and absolute risks tend to be higher for those of younger age at the time of bombing. Other late effects include radiation-related lenticular opacities, disturbances of growth among those survivors still growing at the time of exposure, and mental retardation and small head sizes among the in utero exposed. Chromosomal abnormalities too are more frequently encountered in the peripheral leucocytes of survivors, and this increase is functionally related to their exposure. Some uncertainty continues to surround both the quantity and quality of the radiation released by these two nuclear devices, particularly the Hiroshima bomb. A recent reassessment suggests that the gamma radiation estimates which have been used in the past may be too low at some distances and the neutron radiation estimates too high at all distances; moreover, the energies of the neutrons released now appear ``softer'' than previously conjectured. These uncertainties not sufficiently large, however, to compromise the reality of the increased frequency of malignancy, but make estimates of the dose response, particularly in terms of gamma and neutron exposures, tentative.

  1. Assessment and monitoring of treatment response in adult ADHD patients: current perspectives

    Directory of Open Access Journals (Sweden)

    Ramsay JR

    2017-01-01

    Full Text Available J Russell Ramsay Adult ADHD Treatment & Research Program, Perelman School of Medicine, University of Pennsylvania Philadelphia, PA, USA Abstract: Attention-deficit/hyperactivity disorder (ADHD is a neurodevelopmental syndrome that emerges in childhood or early adolescence and persists into adulthood for a majority of individuals. There are many other adults with ADHD who may not seek out evaluation and treatment until adulthood, having been able to “get by” before struggling with inattention, hyperactivity, and/or impulsivity in adulthood, in addition to facing the associated features of disorganization, poor time management, and procrastination among many others. A lifetime diagnosis of ADHD is associated with a wide range of life impairments, which makes a comprehensive and accurate diagnostic assessment essential in order to obtain appropriate treatment. Moreover, while there are effective medical and psychosocial treatments for ADHD, it is important to be able to track treatment response in order to evaluate whether adjustments in specific interventions are needed or referrals for adjunctive treatments and supports are indicated to facilitate optimal therapeutic outcomes. The goal of this article is to provide a clinically useful review of the various measures that practicing clinicians can use to aid in the diagnostic assessment and monitoring of psychosocial and medical treatment of ADHD in adult patients. This review includes various structured interviews, screening scales, adult ADHD symptom inventories, measures of associated features of ADHD, as well as ratings of impairment and functioning which can be adapted to clinicians’ practice needs in order to track treatment progress and optimize treatments for adults with ADHD. Keywords: adult attention-deficit/hyperactivity disorder, adult ADHD, pharmacotherapy, psychosocial treatment, symptoms, functional impairments, executive functions

  2. Current treatment options and response rates in children with chronic hepatitis C

    Institute of Scientific and Technical Information of China (English)

    Stefan Wirth

    2012-01-01

    Vertical transmission has become the most common mode of transmission of hepatitis C virus (HCV) in children. The rate of perinatal transmission from an HCVinfected mother to her child ranges from 2% to 5% and the prevalence of HCV in children in developed countries ranges between 0.1% and 0.4%. Spontaneous viral clearance seems to be dependent on the genotype and has been reported between 2.4%-25%. For chronically infected patients, treatment with recombinant polyethylene glycol (PEG)-interferon α-2b and daily ribavirin has now been approved as standard treatment for children 2-17 years of age. In five large prospective studies, a total of 318 children and adolescents aged 3-17 years were treated either with subcutaneous PEG-interferon α-2b at a dose of 1-1.5 μg/kg or 60 μg/m2 once a week in combination with oral ribavirin (15 mg/kg per day) or PEG-interferon α-2a with ribavirin. Subjects with genotype 1 and 4 received the medication for 48 wk and individuals with genotype 2 and 3 mainly for 24 wk. Overall sustained viral response (SVR) was achieved in 193/318 (60.7%) of treated patients. Stratified for genotype; 120/234 (51%) with genotype 1, 68/73 (93%) with genotype 2/3, and 6/11 (55%) with genotype 4 showed SVR. Relapse rate was between 7.7% and 17%. Overall, treatment was well tolerated; however,notable side effects were present in approximately 20%. According to recent experiences in the treatment of chronic hepatitis C in children and adolescents, a combination of PEG-interferon α with ribavirin has been found to be well tolerated and highly efficacious, particularly in individuals with genotype 2/3. Thus, this treatment can be recommended as standard of care until more effective treatment options will become available for genotype 1 patients.

  3. Focal Hemodynamic Responses in the Stimulated Hemisphere During High-Definition Transcranial Direct Current Stimulation.

    Science.gov (United States)

    Muthalib, Makii; Besson, Pierre; Rothwell, John; Perrey, Stéphane

    2017-07-17

    High-definition transcranial direct current stimulation (HD-tDCS) using a 4 × 1 electrode montage has been previously shown using modeling and physiological studies to constrain the electric field within the spatial extent of the electrodes. The aim of this proof-of-concept study was to determine if functional near-infrared spectroscopy (fNIRS) neuroimaging can be used to determine a hemodynamic correlate of this 4 × 1 HD-tDCS electric field on the brain. In a three session cross-over study design, 13 healthy males received one sham (2 mA, 30 sec) and two real (HD-tDCS-1 and HD-tDCS-2, 2 mA, 10 min) anodal HD-tDCS targeting the left M1 via a 4 × 1 electrode montage (anode on C3 and 4 return electrodes 3.5 cm from anode). The two real HD-tDCS sessions afforded a within-subject replication of the findings. fNIRS was used to measure changes in brain hemodynamics (oxygenated hemoglobin integral-O2 Hbint ) during each 10 min session from two regions of interest (ROIs) in the stimulated left hemisphere that corresponded to "within" (Lin ) and "outside" (Lout ) the spatial extent of the 4 × 1 electrode montage, and two corresponding ROIs (Rin and Rout ) in the right hemisphere. The ANOVA showed that both real anodal HD-tDCS compared to sham induced a significantly greater O2 Hbint in the Lin than Lout ROIs of the stimulated left hemisphere; while there were no significant differences between the real and sham sessions for the right hemisphere ROIs. Intra-class correlation coefficients showed "fair-to-good" reproducibility for the left stimulated hemisphere ROIs. The greater O2 Hbint "within" than "outside" the spatial extent of the 4 × 1 electrode montage represents a hemodynamic correlate of the electrical field distribution, and thus provides a prospective reliable method to determine the dose of stimulation that is necessary to optimize HD-tDCS parameters in various applications. © 2017 International Neuromodulation Society.

  4. A 3 A sink/source current fast transient response low-dropout Gm driven linear regulator*

    Institute of Scientific and Technical Information of China (English)

    Chu Xiuqin; Li Qingwei; Lai Xinquan; Yuan Bing; LiYanming; Zhao Yongrui

    2011-01-01

    A 3 A sink/source Gm-driven CMOS low-dropout regulator (LDO), specially designed for low input voltage and low cost, is presented by utilizing the structure of a current mirror Gm (transconductance) driving technique, which provides high stability as well as a fast load transient response. The proposed LDO was fabricated by a 0.5μm standard CMOS process, and the die size is as small as 1.0 mm2. The proposed LDO dissipates 220 μA of quiescent current in no-load conditions and is able to deliver up to 3 A of load current. The measured results show that the output voltage can be resumed within 2 μs with a less than l mV overshoot and undershoot in the output current step from -1.8 to 1.8 A with a 0.1μs rising and falling time at three 10μF ceramic capacitors.

  5. Overlapping voltammetric peaks - an analytical procedure for simultaneous determination of trace metals. Application to food and environmental matrices

    Energy Technology Data Exchange (ETDEWEB)

    Locatelli, Clinio [University of Bologna, Department of Chemistry, G. Ciamician, Bologna (Italy); University of Bologna, CIRSA (Centro Interdipartimentale di Ricerca per le Scienze Ambientali - Interdepartment Centre for Research in Environmental Sciences), Laboratory of Environmental Analytical Chemistry, Ravenna (Italy)

    2005-03-01

    Voltammetric methods are very suitable, versatile and rapid techniques for simultaneous determination of metals in complex matrices. The present work, determination of Cu(II), Sn(II), Sb(III), Tl(I), and Pb(II) by square-wave anodic-stripping voltammetry and Cr(VI) by square-wave adsorptive-stripping voltammetry, is an interesting example of the possibility of simultaneous determination of each single element in food and environmental samples, even in the presence of reciprocal interference. Dibasic ammonium citrate, pH 6.3 or 8.2, was employed as supporting electrolyte. The voltammetric measurements were carried out using a stationary hanging mercury drop electrode as working electrode and a platinum electrode and an AgAgClKCl{sub sat} electrode as auxiliary and reference electrodes, respectively. The analytical procedure was verified by analysis of standard reference materials - wholemeal BCR-CRM 189, wheat flour NIST-SRM 1567a, rice flour NIST-SRM 1568a, estuarine sediment BCR-CRM 277, river sediment BCR-CRM 320, and Montana soil with moderately elevated traces NIST-SRM 2711. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were generally below 6% whereas limits of detection for each element were below 0.069 {mu}g g{sup -1}. In the presence of reciprocal interference the standard addition method considerably improved the resolution of the voltammetric technique, even for very high element concentration ratios. After being set up on the standard reference materials the analytical procedure was transferred and applied to commercial samples of meal and soil samples taken from sites devoted to agricultural practice. A critical comparison with graphite furnace atomic-absorption spectroscopy is also discussed. (orig.)

  6. Controlled functionalisation of single-walled carbon nanotube network electrodes for the enhanced voltammetric detection of dopamine.

    Science.gov (United States)

    E, Sharel P; Miller, Thomas S; Macpherson, Julie V; Unwin, Patrick R

    2015-10-21

    Voltammetric studies of dopamine (DA) oxidation on pristine and acid-treated single-walled carbon nanotube (SWNT) network electrodes were undertaken in order to investigate both the effect of network density and acid treatment times on the voltammetric characteristics for DA oxidation and the susceptibility of the electrodes to fouling. Through careful control of catalysed chemical vapour deposition growth parameters, multiply interconnected and randomly oriented SWNT networks of two significantly different densities were grown (high density, HD, coverage ≫10 μm length of SWNT per μm(-2) and low density, LD, coverage = 5 (±1) μmSWNTμm(-2)). Acid treatment was performed to provide materials with different electrochemical properties and SWNT coverage, as determined by field emission-scanning electron microscopy, atomic force microscopy and micro-Raman spectroscopy. A high concentration of DA (100 μM) was deliberately employed to accelerate the fouling phenomenon associated with DA oxidation in order to evaluate the lifetime of the electrodes. HD pristine SWNT networks were found to promote more facile electron transfer (ET) and were less susceptible to blocking, compared to LD pristine SWNT networks. Acid treatment resulted in both a further enhancement of the ET rate and a reduction in susceptibility towards electrode fouling. However, lengthy acid treatment detrimentally affected ET, due to a decrease in network density and significant damage to the SWNT network structure. These studies highlight the subtle interplay between SWNT coverage and degree of acid functionalisation when seeking to achieve the optimal SWNT electrode for the voltammetric detection of DA.

  7. Striatal dopamine terminals release serotonin after 5-HTP pretreatment: in vivo voltammetric data.

    Science.gov (United States)

    Stamford, J A; Kruk, Z L; Millar, J

    1990-05-07

    Peripheral administration of 5-hydroxytryptophan (5-HTP) to rats causes 'wet dog' shakes and a parallel elevation of brain serotonin (5-HT) levels. The increase in 5-HT concentration does not, however, correlate with the endogenous 5-HT innervation raising the possibility that some 5-HTP is decarboxylated in non-serotonergic cells. In the present study we used in vivo voltammetry to establish whether 5-HTP treatment led to formation of 5-HT as a 'false transmitter' in striatal dopamine (DA) neurons. Fast cyclic voltammetry at carbon fibre microelectrodes (CFMs) was used to monitor striatal monoamine release following electrical stimulation of the median forebrain bundle (MFB). In the absence of any pretreatment DA was the sole compound released by stimulation. However, when DA release was abolished with alpha-methyl-p-tyrosine (AMPT), 5-HTP administration (after peripheral decarboxylase inhibition) caused a dose-dependent release of 5-HT, confirmed by the voltammetric characteristics. Central decarboxylase inhibition prevented release indicating that 5-HTP itself was not released. By monitoring reduction peaks it was possible to record DA and 5-HT release simultaneously at a single CFM. While DA and 5-HT oxidised at the same potential their reduction peaks were separated by approximately 450 mV. It was shown, using this means, that 5-HT was still detectable even when DA release was not abolished by AMPT. DA and 5-HT release showed a significant positive correlation suggesting that they were released from the same nerves. We conclude that, after 5-HTP treatment, 5-HT can be released as a false transmitter from striatal DA neurones.

  8. Voltammetric detection of As(III) with Porphyridium cruentum based modified carbon paste electrode biosensor.

    Science.gov (United States)

    Zaib, M; Saeed, A; Hussain, I; Athar, M M; Iqbal, M

    2014-12-15

    A novel biosensor based on carbon paste electrode modified with Porphyridium cruentum biomass was developed for the determination of As(III) in contaminated water. As(III) was first biosorbed-accumulated on the electrode surface at open circuit potential and then stripped off by applying anodic scan range of -0.8 to +0.8 V using differential pulse anodic stripping voltammetric technique. The best result was obtained at pH 6.0 with 0.1M HNO3 solution as stripping medium, allowing biosorption-accumulation time of 8 min using 5% P. cruentum biomass in graphite-mineral oil paste. Linear range for As(III) detection with the modified electrode-biosensor was observed between 2.5 and 20 µg L(-1). The FTIR spectrum of P. cruentum biomass confirmed the presence of active functional groups that participate in the binding of As(III). Scanning Electron Microscopy (SEM) indulged the surface morphology of modified electrode-biosensor before and after As(III) adsorption. Similarly, Atomic Force Microscopy (AFM) showed that the average roughness of the modified electrode decreased indicating the successful incorporation of P. cruentum biomass. Efficiency of the biosensor in the presence of different interfering metal (Na(+), K(+), Ca(2+), and Mg(2+)) ions were also evaluated. The application of P. cruentum modified biosensor was successfully used for the detection of As(III) in the binary metal (Fe(3+), Mn(2+), Cd(2+), Cu(2+), Ni(2+), Hg(2+), and Pb(2+)) contaminated system. The accuracy of application of biosorption based biosensor for the detection of As(III) is as low as 2.5 µg L(-1).

  9. Penicillamine-modified sensor for the voltammetric determination of Cd(II) and Pb(II) ions in natural samples.

    Science.gov (United States)

    Pérez-Ràfols, Clara; Serrano, Núria; Díaz-Cruz, José Manuel; Ariño, Cristina; Esteban, Miquel

    2015-11-01

    A new penicillamine-GCE was developed based on the immobilization of d-penicillamine on aryl diazonium salt monolayers anchored to the glassy carbon electrode (GCE) surface and it was applied for the first time to the simultaneous determination of Cd(II) and Pb(II) ions by stripping voltammetric techniques. The detection and quantification limits at levels of µg L(-1) suggest that the penicillamine-GCE could be fully suitable for the determination of the considered ions in natural samples.

  10. Bleaching Susceptibility and Recovery of Colombian Caribbean Corals in Response to Water Current Exposure and Seasonal Upwelling

    Science.gov (United States)

    Bayraktarov, Elisa; Pizarro, Valeria; Eidens, Corvin; Wilke, Thomas; Wild, Christian

    2013-01-01

    Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP) in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34%) compared to the exposed site (8%). Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs. PMID:24282551

  11. Bleaching susceptibility and recovery of Colombian Caribbean corals in response to water current exposure and seasonal upwelling.

    Science.gov (United States)

    Bayraktarov, Elisa; Pizarro, Valeria; Eidens, Corvin; Wilke, Thomas; Wild, Christian

    2013-01-01

    Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP) in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34%) compared to the exposed site (8%). Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs.

  12. Bleaching susceptibility and recovery of Colombian Caribbean corals in response to water current exposure and seasonal upwelling.

    Directory of Open Access Journals (Sweden)

    Elisa Bayraktarov

    Full Text Available Coral bleaching events are globally occurring more frequently and with higher intensity, mainly caused by increases in seawater temperature. In Tayrona National Natural Park (TNNP in the Colombian Caribbean, local coral communities are subjected to seasonal wind-triggered upwelling events coinciding with stronger water currents depending on location. This natural phenomenon offers the unique opportunity to study potential water current-induced mitigation mechanisms of coral bleaching in an upwelling influenced region. Therefore, coral bleaching susceptibility and recovery patterns were compared during a moderate and a mild bleaching event in December 2010 and 2011, and at the end of the subsequent upwelling periods at a water current-exposed and -sheltered site of an exemplary bay using permanent transect and labeling tools. This was accompanied by parallel monitoring of key environmental variables. Findings revealed that in 2010 overall coral bleaching before upwelling was significantly higher at the sheltered (34% compared to the exposed site (8%. Whereas 97% of all previously bleached corals at the water current-exposed site had recovered from bleaching by April 2011, only 77% recovered at the sheltered site, but 12% had died there. In December 2011, only mild bleaching (<10% at both sites was observed, but corals recovered significantly at both sites in the course of upwelling. No differences in water temperatures between sites occurred, but water current exposure and turbidity were significantly higher at the exposed site, suggesting that these variables may be responsible for the observed site-specific mitigation of coral bleaching. This indicates the existence of local resilience patterns against coral bleaching in Caribbean reefs.

  13. Thermodynamics, electrostatics, and ionic current in nanochannels grafted with pH-responsive end-charged polyelectrolyte brushes.

    Science.gov (United States)

    Chen, Guang; Das, Siddhartha

    2017-03-01

    In this paper, we study the thermodynamics, electrostatics, and an external electric field driven ionic current in a pH-responsive, end-charged polyelectrolyte (PE) brush grafted nanochannel. By employing a mean field theory, we unravel a highly nonintuitive interplay of pH and electrolyte salt concentration in dictating the height of the end-charged PE brush. Larger pH or weak hydrogen ion concentration leads to maximum ionization of the charge-producing group-as a consequence, the resulting the electric double layer (EDL) energy get maximized causing a maximum deviation of the brush height from the value (d0 ) of the uncharged brush. This deviation may result in enhancement or lowering of the brush height as compared to d0 depending on whether the PE end locates lower or higher than h/2 (h is the nanochannel half height) and the salt concentration. Subsequently, we use this combined PE-brush-configuration-EDL-electrostatics framework to compute the ionic current in the nanochannel. We witness that the ionic current for smaller pH is much larger despite the corresponding magnitude of the EDL electrostatic potential being much smaller-this stems from the presence of a much larger concentration of H+ ions at small pH and the fact that H+ ions have very large mobilities. In fact, this ionic current shows a steep variation with pH that can be useful in exploring new designs for applications involving quantification and characterization of ionic current in PE-brush-grafted nanochannels. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. The role of relativity in the optical response of gold within the time-dependent current-density-functional theory.

    Science.gov (United States)

    Romaniello, P; de Boeij, P L

    2005-04-22

    We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the zeroth-order regular approximation in the ground-state density-functional theory calculations, as well as in the time-dependent response calculations. The results for the dielectric function of gold calculated in the spectral range of 0-10 eV are compared with experimental data reported in literature and recent ellipsometric measurements. As well known, relativistic effects strongly influence the color of gold. We find that the onset of interband transitions is shifted from around 3.5 eV, obtained in a nonrelativistic calculation, to around 1.9 eV when relativity is included. With the inclusion of the scalar-relativistic effects there is an overall improvement of both real and imaginary parts of the dielectric function over the nonrelativistic ones. Nevertheless some important features in the absorption spectrum are not well reproduced, but can be explained in terms of spin-orbit coupling effects. The remaining deviations are attributed to the underestimation of the interband gap (5d-6sp band gap) in the local-density approximation and to the use of the adiabatic local-density approximation in the response calculation.

  15. Modification of glassy carbon electrode with a bilayer of multiwalled carbon nanotube/tiron-doped polypyrrole: Application to sensitive voltammetric determination of acyclovir

    Energy Technology Data Exchange (ETDEWEB)

    Shahrokhian, Saeed, E-mail: shahrokhian@sharif.edu [Department of Chemistry, Sharif University of Technology, Tehran 11155-3516 (Iran, Islamic Republic of); Institute for Nanoscience and Technology, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Azimzadeh, Mahnaz [Department of Chemistry, Sharif University of Technology, Tehran 11155-3516 (Iran, Islamic Republic of); Amini, Mohammad K. [Department of Chemistry, Isfahan University, Isfahan (Iran, Islamic Republic of)

    2015-08-01

    A novel voltammetric sensor based on glassy carbon electrode (GCE) modified with a thin film of multi-walled carbon nanotubes (MWCNTs) coated with an electropolymerized layer of tiron-doped polypyrrole was developed and the resulting electrode was applied for the determination of acyclovir (ACV). The surface morphology and property of the modified electrode were characterized by field emission scanning electron microscopy and electrochemical impedance spectroscopy techniques. The electrochemical performance of the modified electrode was investigated by means of linear sweep voltammetry (LSV). The effect of several experimental variables, such as pH of the supporting electrolyte, drop size of the cast MWCNTssuspension, number of electropolymerization cycles and accumulation time was optimized by monitoring the LSV response of the modified electrode toward ACV. The best response was observed at pH 7.0 after accumulation at open circuit for 160 s. Under the optimized conditions, a significant electrochemical improvement was observed toward the electrooxidation of ACV on the modified electrode surface relative to the bare GCE, resulting in a wide linear dynamic range (0.03–10.0 μM) and a low detection limit (10.0 nM) for ACV. Besides high sensitivity, the sensor represented high stability and good reproducibility for ACV analysis, and provided satisfactory results for the determination of this compound in pharmaceutical and clinical preparations. - Highlights: • A simple method was employed to construct a thin film modified electrode. • Tiron-doped polypyrrole was electropolymerized on MWCNT precast glassy carbon electrode. • Electrode surface characterization was performed by microscopic and spectroscopic techniques. • The modified electrode showed nano-molar detection limit for acyclovir. • The modified electrode was applied for the detection of ACV in pharmaceutical and clinical preparations.

  16. Aging Reduces L-Type Calcium Channel Current and the Vasodilatory Response of Small Mesenteric Arteries to Calcium Channel Blockers

    Science.gov (United States)

    Albarwani, Sulayma A.; Mansour, Fathi; Khan, Abdul Aleem; Al-Lawati, Intisar; Al-Kaabi, Abdulla; Al-Busaidi, Al-Manar; Al-Hadhrami, Safa; Al-Husseini, Isehaq; Al-Siyabi, Sultan; Tanira, Musbah O.

    2016-01-01

    Calcium channel blockers (CCBs) are widely used to treat cardiovascular disease (CVD) including hypertension. As aging is an independent risk factor for CVD, the use of CCBs increases with increasing age. Hence, this study was designed to evaluate the effect of aging on the sensitivity of small mesenteric arteries to L-type voltage-gated calcium channel (LTCC) blockers and also to investigate whether there was a concomitant change in calcium current density. Third order mesenteric arteries from male F344 rats, aged 2.5–3 months (young) and 22–26 months (old) were mounted on wire myograph to measure the tension during isometric contraction. Arteries were contracted with 100 mM KCl and were then relaxed in a cumulative concentration-response dependent manner with nifedipine (0.1 nM–1 μM), verapamil (0.1 nM–10 μM), or diltiazem (0.1 nM–10 μM). Relaxation-concentration response curves produced by cumulative concentrations of three different CCBs in arteries of old rats were shifted to the right with statistically significant IC50s. pIC50 ± s.e.m: (8.37 ± 0.06 vs. 8.04 ± 0.05, 7.40 ± 0.07 vs. 6.81 ± 0.04, and 6.58 ± 0.07 vs. 6.34 ± 0.06) in young vs. old. It was observed that the maximal contractions induced by phenylephrine and reversed by sodium nitroprusside were not different between young and old groups. However, Bay K 8644 (1 μM) increased resting tension by 23 ± 4.8% in young arteries and 4.7 ± 1.6% in old arteries. LTCC current density were also significantly lower in old arteries (−2.77 ± 0.45 pA/pF) compared to young arteries (−4.5 ± 0.40 pA/pF); with similar steady-state activation and inactivation curves. Parallel to this reduction, the expression of Cav1.2 protein was reduced by 57 ± 5% in arteries from old rats compared to those from young rats. In conclusion, our results suggest that aging reduces the response of small mesenteric arteries to the vasodilatory effect of the CCBs and this may be due to, at least in part, reduced

  17. Aging Reduces L-type Calcium Channel Current and the Vasodilatory Response of Small Mesenteric Arteries to Calcium Channel Blockers

    Directory of Open Access Journals (Sweden)

    Sulayma A Albarwani

    2016-05-01

    Full Text Available Calcium channel blockers are widely used to treat cardiovascular disease (CVD including hypertension. As aging is an independent risk factor for CVD, the use of calcium channel blockers increases with increasing age. Hence, this study was designed to evaluate the effect of aging on the sensitivity of small mesenteric arteries to L-type voltage-gated calcium channel (LTCC blockers and also to investigate whether there was a concomitant change in calcium current density. Third order mesenteric arteries from male F344 rats, aged 2.5 - 3 months (young and 22 - 26 months (old were mounted on wire myograph to measure the tension during isometric contraction. Arteries were contracted with 100 mM KCl and were then relaxed in a cumulative concentration-response dependent manner with nifedipine (0.1nM - 10 µM, verapamil (0.1nM-10 µM or diltiazem (0.1nM - 10µM. Relaxation-concentration response curves produced by cumulative concentrations of three different calcium channel blockers (CCBs in arteries of old rats were shifted to the right with statistically significant IC50s. pEC50 ± s.e.m: (8.37 ± 0.06 vs 8.04 ± 0.05 , 7.40 ± 0.07 vs 6.81 ± 0.04 and 6.58 ± 0.07 vs 6.34 ± 0.06 in young vs old. It was observed that the maximal contractions induced by 100 mM KCl, phenylephrine and reversed by sodium nitroprusside were not different between young and old groups. However, Bay K 8644 increased resting tension by 23±4.8% in young arteries and 4.7±1.6% in old arteries. LTCC current density were also significantly lower in old arteries (-2.77 ± 0.45 pA/pF compared to young arteries (-4.5 ± 0.40 pA/pF; with similar steady-state activation and inactivation curves. Parallel to this reduction, the expression of Cav1.2 protein was reduced by 57 ± 5% in arteries from old rats compared to those from young rats. In conclusion, our results suggest that aging reduces the response of small mesenteric arteries to the vasodilatory effect of the CCBs and this may

  18. Voltammetric reduction of 4-nitroimidazole derivatives: Influence of the N-1 substitution in protic and aprotic media

    Energy Technology Data Exchange (ETDEWEB)

    Bollo, S.; Jara-Ulloa, P.; Zapata-Torres, G.; Cutino, E.; Sturm, J.C.; Nunez-Vergara, L.J. [Bioelectrochemistry Laboratory, Chemical and Pharmaceutical Sciences Faculty, University of Chile, Postal Code 838492 Santiago (Chile); Squella, J.A., E-mail: asquella@ciq.uchile.c [Bioelectrochemistry Laboratory, Chemical and Pharmaceutical Sciences Faculty, University of Chile, Postal Code 838492 Santiago (Chile)

    2010-06-01

    The voltammetric reduction of 1-methyl- and 1-H- 4-nitroimidazole derivatives was studied in different protic and aprotic media to investigate the influence of the N-1 substitution in the mechanism of reduction, the susceptibility of the nitro group to reduction, and the stability of the nitro radical anion. The elucidation of their voltammetric behavior was carried out using differential pulse polarography and cyclic voltammetry with two different mixed media (Britton-Robinson/ethanol: 70/30 and DMF/citrate: 60/40) and an aprotic media (DMF) at the mercury electrode. In addition, we used UV-vis spectroscopy for the study of their chemistry in solution and quantum-chemical calculations to evaluate LUMO energies, HOMO and LUMO energy gaps, dipole moments and electron affinity, using water and DMF as solvents. The mechanism of reduction was strongly dependent on both the substitution at the N-1 position and the nature of the media. In all media, the methyl-substituted derivative (M-4-NImOH) was always more easily reduced than the demethylated species (H-4-NImOH). On the other hand, the nitro radical anion from M-4-NImOH was more stable than the nitro radical anion from H-4-NImOH.

  19. Taxonomic and functional composition of the algal benthos exhibits similar successional trends in response to nutrient supply and current velocity.

    Science.gov (United States)

    Larson, Chad A; Passy, Sophia I; Laanbroek, Riks

    2012-05-01

    In an effort to identify the causes and patterns of temporal change in periphytic communities, we examined biomass accumulation, taxonomic and functional composition, rate of species turnover, and pairwise species correlations in response to variability in current velocity and nutrient supply in artificial stream flumes. Divergent patterns in community growth and succession were observed between nutrient treatments and, to a lesser extent, between flow treatments best described by shifts in taxonomic and functional composition. Specifically, understory low profile species, tolerant to low resource supply, became dominant under low nutrients, while overstory high profile and motile species with higher nutrient demands dominated the high nutrient treatments. Increased resource supply or current velocity did not influence the species turnover rate, measured by a time-lag analysis. Interspecific interactions, especially competition, did not appear to be driving community dynamics, as the number of positive and negative pairwise species correlations ranged between low and extremely low, respectively. The overwhelming majority of correlations were not significant, indicating that species within the biofilm matrix were not perceptibly influencing one another. Thus, temporal trends in taxonomic and functional composition were largely environmentally driven, signifying that coexistence in biofilms is defined by the same mechanism along the hierarchy from species to functional groups.

  20. Optimal Environmental Conditions and Anomalous Ecosystem Responses: Constraining Bottom-up Controls of Phytoplankton Biomass in the California Current System

    Science.gov (United States)

    Jacox, Michael G.; Hazen, Elliott L.; Bograd, Steven J.

    2016-06-01

    In Eastern Boundary Current systems, wind-driven upwelling drives nutrient-rich water to the ocean surface, making these regions among the most productive on Earth. Regulation of productivity by changing wind and/or nutrient conditions can dramatically impact ecosystem functioning, though the mechanisms are not well understood beyond broad-scale relationships. Here, we explore bottom-up controls during the California Current System (CCS) upwelling season by quantifying the dependence of phytoplankton biomass (as indicated by satellite chlorophyll estimates) on two key environmental parameters: subsurface nitrate concentration and surface wind stress. In general, moderate winds and high nitrate concentrations yield maximal biomass near shore, while offshore biomass is positively correlated with subsurface nitrate concentration. However, due to nonlinear interactions between the influences of wind and nitrate, bottom-up control of phytoplankton cannot be described by either one alone, nor by a combined metric such as nitrate flux. We quantify optimal environmental conditions for phytoplankton, defined as the wind/nitrate space that maximizes chlorophyll concentration, and present a framework for evaluating ecosystem change relative to environmental drivers. The utility of this framework is demonstrated by (i) elucidating anomalous CCS responses in 1998-1999, 2002, and 2005, and (ii) providing a basis for assessing potential biological impacts of projected climate change.

  1. Optimal Environmental Conditions and Anomalous Ecosystem Responses: Constraining Bottom-up Controls of Phytoplankton Biomass in the California Current System.

    Science.gov (United States)

    Jacox, Michael G; Hazen, Elliott L; Bograd, Steven J

    2016-06-09

    In Eastern Boundary Current systems, wind-driven upwelling drives nutrient-rich water to the ocean surface, making these regions among the most productive on Earth. Regulation of productivity by changing wind and/or nutrient conditions can dramatically impact ecosystem functioning, though the mechanisms are not well understood beyond broad-scale relationships. Here, we explore bottom-up controls during the California Current System (CCS) upwelling season by quantifying the dependence of phytoplankton biomass (as indicated by satellite chlorophyll estimates) on two key environmental parameters: subsurface nitrate concentration and surface wind stress. In general, moderate winds and high nitrate concentrations yield maximal biomass near shore, while offshore biomass is positively correlated with subsurface nitrate concentration. However, due to nonlinear interactions between the influences of wind and nitrate, bottom-up control of phytoplankton cannot be described by either one alone, nor by a combined metric such as nitrate flux. We quantify optimal environmental conditions for phytoplankton, defined as the wind/nitrate space that maximizes chlorophyll concentration, and present a framework for evaluating ecosystem change relative to environmental drivers. The utility of this framework is demonstrated by (i) elucidating anomalous CCS responses in 1998-1999, 2002, and 2005, and (ii) providing a basis for assessing potential biological impacts of projected climate change.

  2. Application of direct torque control to electric screw presses for speeding up torque response and reducing starting current

    Institute of Scientific and Technical Information of China (English)

    FENG Yi; HUANG Shu-huai; LI Jun-chao; XIONG Xiao-hong

    2009-01-01

    Fast response and stable torque output are crucial to the performance of electric screw presses. This paper describes the design of a direct torque control (DTC) system for speeding up torque response and reducing the starting current of electric screw presses and its application to the J58K series of numerical control electric screw presses with a dual-motor drive. The DTC drive system encompasses speed control, torque reference control, and switching frequency control. Comparison of the DTC duaI-AC induction motor drive with corresponding AC servo motor drive showed that for the J58K-315 electric screw press, the DTC drive system attains a higher maximum speed (786 r/min) within a shorter time (1.13 s) during a 250 mm stroke and undergoes smaller rise in temperature (42.0 ℃) in the motor after running for 2 h at a 12 min strike fi'equency than the AC servo motor drive does (751 r/min within 1.19 s, and 50.6 ℃ rise). Moreover, the DTC AC induction motor drive, with no need for a tachometer or position encoder to feed back the speed or position of the motor shaft, enjoys increased reliability in a strong-shock work environment.

  3. The Use of Silver Solid Amalgam Electrodes for Voltammetric and Amperometric Determination of Nitrated Polyaromatic Compounds Used as Markers of Incomplete Combustion

    Directory of Open Access Journals (Sweden)

    Oksana Yosypchuk

    2012-01-01

    Full Text Available Genotoxic nitrated polycyclic aromatic hydrocarbons (NPAHs are formed during incomplete combustion processes by reaction of polycyclic aromatic hydrocarbons (PAHs with atmospheric nitrogen oxides. 1-Nitropyrene, 2-nitrofluorene, and 3-nitrofluoranthene as the dominating substances are used as markers of NPAHs formation by these processes. In the presented study, voltammetric properties and quantification of these compounds and of 5-nitroquinoline (as a representative of environmentally important genotoxic heterocyclic compounds have been investigated using a mercury meniscus modified silver solid amalgam electrode (m-AgSAE, which represent a nontoxic alternative to traditional mercury electrodes. Linear calibration curves over three orders of magnitude and limits of determination mostly in the 10−7 mol L−1 concentration range were obtained using direct current and differential pulse voltammetry. Further, satisfactory HPLC separation of studied analytes in fifteen minutes was achieved using 0.01 mol L−1 phosphate buffer, pH 7.0 : methanol (15 : 85, v/v mobile phase, and C18 reversed stationary phase. Limits of detection of around 1 · 10−5 mol L−1 were achieved using amperometric detection at m-AgSAE in wall-jet arrangement for all studied analytes. Practical applicability of this technique was demonstrated on the determination of 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, and 5-nitroquinoline in drinking water after their preliminary separation and preconcentration using solid phase extraction with the limits of detection around 1 · 10−6 mol L−1.

  4. A novel voltammetric sensor for sensitive detection of mercury(II) ions using glassy carbon electrode modified with graphene-based ion imprinted polymer

    Energy Technology Data Exchange (ETDEWEB)

    Ghanei-Motlagh, Masoud, E-mail: m.ghaneimotlagh@yahoo.com [Young Researchers and Elite Club, Kerman Branch, Islamic Azad University, Kerman (Iran, Islamic Republic of); Taher, Mohammad Ali; Heydari, Abolfazl [Department of Chemistry, Faculty of Sciences, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Ghanei-Motlagh, Reza [Department of Pathobiology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of); Gupta, Vinod K. [Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Department of Applied Chemistry, University of Johannesburg, Johannesburg (South Africa)

    2016-06-01

    In this paper, a novel strategy was proposed to prepare ion-imprinted polymer (IIP) on the surface of reduced graphene oxide (RGO). Polymerization was performed using methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, 2,2′–((9E,10E)–1,4–dihydroxyanthracene–9,10–diylidene) bis(hydrazine–1–carbothioamide) (DDBHCT) as the chelating agent and ammonium persulfate (APS) as initiator, via surface imprinted technique. The RGO–IIP was characterized by means of Fourier transform infrared spectroscopy (FT–IR), field emission scanning electron microscopy (FE–SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The electrochemical procedure was based on the accumulation of Hg(II) ions at the surface of a modified glassy carbon electrode (GCE) with RGO–IIP. The prepared RGO–IIP sensor has higher voltammetric response compared to the non-imprinted polymer (NIP), traditional IIP and RGO. The RGO–IIP modified electrode exhibited a linear relationship toward Hg(II) concentrations ranging from 0.07 to 80 μg L{sup −1}. The limit of detection (LOD) was found to be 0.02 μg L{sup −1} (S/N = 3), below the guideline value from the World Health Organization (WHO). The applicability of the proposed electrochemical sensor to determination of mercury(II) ions in different water samples was reported. - Highlights: • The novel Hg(II)-imprinted polymer was synthesized and characterized. • The resulting RGO–IIP was applied for electrochemical monitoring of Hg(II) ions. • The proposed sensor was successfully applied for determination of Hg(II) in real water samples.

  5. Glassy carbon electrode modified with horse radish peroxidase/organic nucleophilic-functionalized carbon nanotube composite for enhanced electrocatalytic oxidation and efficient voltammetric sensing of levodopa

    Energy Technology Data Exchange (ETDEWEB)

    Shoja, Yalda; Rafati, Amir Abbas, E-mail: aa_rafati@basu.ac.ir; Ghodsi, Javad

    2016-01-01

    A novel and selective enzymatic biosensor was designed and constructed for voltammetric determination of levodopa (L-Dopa) in aqueous media (phosphate buffer solution, pH = 7). Biosensor development was on the basis of to physically immobilizing of horse radish peroxidase (HRP) as electrochemical catalyst by sol–gel on glassy carbon electrode modified with organic nucleophilic carbon nanotube composite which in this composite p-phenylenediamine (pPDA) as organic nucleophile chemically bonded with functionalized MWCNT (MWCNT-COOH). The results of this study suggest that prepared bioorganic nucleophilic carbon nanotube composite (HRP/MWCNT-pPDA) shows fast electron transfer rate for electro oxidation of L-Dopa because of its high electrochemical catalytic activity toward the oxidation of L-Dopa, more −NH{sub 2} reactive sites and large effective surface area. Also in this work we measured L-Dopa in the presence of folic acid and uric acid as interferences. The proposed biosensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), FT-IR spectroscopy and cyclic voltammetry (CV). The differential pulse voltammetry (DPV) was used for determination of L-Dopa from 0.1 μM to 1.9 μM with a low detection limit of 40 nM (for S/N = 3) and sensitivity was about 35.5 μA/μM. Also this biosensor has several advantages such as rapid response, high stability and reproducibility. - Highlights: • Glassy carbon electrode modified by a novel composite in which pPDA as nucleophile is chemically attached to MWCNTs. • The developed biosensor exhibited excellent electrocatalytic activity in electrochemically determination of L-Dopa. • The biosensor showed acceptable sensitivity, reproducibility, detection limit, selectivity and stability. • MWCNT-pPDA provides a good electrical conductivity and large effective surface area for enzyme immobilization.

  6. Trace level determination of titanium in real samples by alternating current voltammetry

    Energy Technology Data Exchange (ETDEWEB)

    Locatelli, C.; Fagioli, F.; Garai, T.; Bighi, C.

    1988-11-01

    The fundamental and second harmonic alternating current voltammetric determination of titanium(IV) in the presence of a large excess of iron(III) is reported. The measurements were carried out with a semistationary mercury electrode (long-lasting sessile-drop mercury electrode) as the working electrode. The analytical procedure was controlled by the analysis of standard reference materials: Portland cement BCS 372, stainless steel (AISI 321) SRM 121 d, and highly alloyed steel (Eurostandard 281-1). The confidence interval of the experimental data was in agreement with the certified values for the titanium(IV) content of the samples. The precision, expressed by the relative standard deviation, and the accuracy, expressed by the relative error, were on the order of 3-5%. The standard addition technique was found to improve the resolution of alternating current voltammetric methods, even in the case of very high c/sub Fe:c/sub Tl/ concentration ratios.

  7. Voltammetric determination of wedelolactone, an anti-HIV herbal drug, at boron-doped diamond electrode

    Indian Academy of Sciences (India)

    Sachin Saxena; Ratnanjali Shrivastava; Soami P Satsangee

    2015-05-01

    Boron-doped diamond electrode has been utilized for the study of electrochemical behaviour of an anti-HIV herbal drug wedelolactone in Britton-Robinson buffer (pH-2.5) by square-wave and cyclic voltammetry techniques. The response characteristics of cyclic voltammetry and square wave voltammetry showed a remarkable increase in the anodic peak current and electrochemical impedance spectroscopy revealed a lowering in charge transfer resistance at the boron-doped diamond electrode as compared to the glassy carbon electrode that can be attributed to the higher sensitivity of boron-doped diamond sensor. Cyclic voltammetry at the boron-doped diamond surface revealed the oxidation of wedelolactone with two oxidation peaks (P1 and P2) with Ep1 = 0.4V and Ep2 =1.00 V with scan rate varying from 10 - 220 mV/s and exhibits diffusion-controlled process. Based on the electrochemical measurements, a probable oxidation mechanism has been deduced and the electrode dynamics parameters have been evaluated. The effect of concentration on the peak currents of wedelolactone was found to have a linear relationship within the concentration range of 50–700 ng/mL. The LOD and LOQ were found to be 43.87 and 132.93 ng/mL respectively. The applicability of the proposed method was further scrutinized by the successful determination of wedelolactone in real plant samples.

  8. The VEMAP integrated dataset for simulation of ecological responses to global change: Current climate and climate change scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Kittel, T.G.F. [NCAR/UCAR, Boulder, CO (United States)]|[Colorado State Univ., Ft. Collins, CO (United States)

    1995-06-01

    The Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) dataset consists of inputs for biogeochemical and biogeographical models, including current climate, climate scenarios, soils, and vegetation for the conterminous United States on a 0.5 deg lat./lon. grid. The set has daily and monthly representations of climate. Monthly temperature (T) and precipitation (PPT) were derived from station records or statistically-generated from nearby stations. These values were interpolated to the grid accounting for orographic effects in an effort to make the grid-scale climate representative of actual bioclimates within grid cells; this was crucial because ecosystem responses are nonlinearly related to climate. Daily T and PPT were stochastically simulated with WGEN, and daily solar radiation and humidity empirically estimated with CLIMSIM. Equilibrium climate change scenarios were selected to capture a range of potential change from GCM experiments. Transient scenario rates of change were based on atmosphere-ocean GCM results. Mean climate, equilibrium scenarios, vegetation, and soil data are available on CD-ROM.

  9. Morphological and compositional engineering of Ni/carbon nanotube composite film via a novel cyclic voltammetric route

    Indian Academy of Sciences (India)

    Yu Jun Yang

    2012-08-01

    Ni/multi-walled carbon nanotubes (MWCNTs) composite films were deposited on the glassy carbon electrode (GCE) by a Ni plating bath containing homogeneously dispersed MWCNTs using polyvinylpyrrolidone (PVP) as dispersion additive. Incorporation of MWCNTs into Ni matrix was greatly enhanced by the application of cyclic voltammetric (CV) deposition technique. The structure and nature of the Ni/MWCNT were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The results show that the content of MWCNT and the morphology of the deposited Ni/MWCNT composite film can be controlled by selecting the appropriate electroplating conditions. Further study indicates that the obtained Ni/MWCNT showed excellent electro-catalytic activity for the oxidation of ethanol in alkaline solution.

  10. Solar UV-treatment of water samples for stripping-voltammetric determination of trace heavy metals in Awash river, Ethiopia

    Directory of Open Access Journals (Sweden)

    Gelaneh Woldemichael

    2016-03-01

    Full Text Available We report about testing a new mobile and sustainable water sample digestion method in a preliminary field trial in Ethiopia. In order to determine heavy metals at the ultra-trace level by stripping voltammetric techniques in water samples from Awash River, we applied our new method of solar UV-assisted sample pretreatment to destroy the relevant interfering dissolved organic matter. The field tests revealed that 24 h of solar UV irradiation were sufficient to achieve the same sample pretreatment results as with classic digestion method based on intense and hard UV. Analytical results of this study suggest that both a hydroelectric power station and agrichemical applications at Koka Lake have increased the levels of the investigated metals zinc, cadmium, lead, copper, cobalt, nickel, and uranium.

  11. Stripping voltammetric determination of Cd(Ⅱ) based on multiwalled carbon nanotube functionalized with 1-(2-pyridylazo)-2-naphthol

    Institute of Scientific and Technical Information of China (English)

    Alireza Mohadesi; Hadi Beitollahi; Mohammad Ali Karimi

    2011-01-01

    The present work has focused on the modification of multiwalled carbon nanotube with a ligand, l-(2-pyridylazo)-2-naphthol, and its potential application for the development of a new, simple and selective modified glassy carbon electrode for stripping voltammetric determination of Cd(Ⅱ). The analytical curve for Cd(Ⅱ) ions covered the linear range varying from 0.8 up to 220.4 μg L-1. The limit of detection was found to be 0.1 μg L-1, while the relative standard deviation (RSD) at 50.0 μg L-1 was 1.8% (n = 5). This modified electrode was successfully applied for determination of Cd(Ⅱ) in some water samples.

  12. Cadmium binding in mixtures of phytochelatins and their fragments: a voltammetric study assisted by multivariate curve resolution and mass spectrometry.

    Science.gov (United States)

    Gusmão, Rui; Ariño, Cristina; Díaz-Cruz, José Manuel; Esteban, Miquel

    2010-01-01

    Phytochelatins (PC(n), (gamma-Glu-Cys)(n)Gly) are cysteine-rich peptides synthesized by plants which are involved in metal bioregulation and phytoremediation. Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) is applied to voltammetric data obtained from the analysis of the competitive binding of Cys or Cys-Gly with PC(2) or PC(3) by Cd(2+). The displacements between ligands, the chain length dependence on the competitive binding to PC(n) and the possible existence of mixed ligand metal-complexes are investigated. The shape analysis of the resulting pure voltammograms and concentration profiles of the components resolved by MCR-ALS suggests that ligands containing more thiol groups are able to displace the shorter chain ligands from their metal complexes, whereas the opposite does not happen. Electrochemical results are compared with ESI-MS measurements.

  13. Elimination of interferences from surface active substances in voltammetric determination of trace amounts of titanium in environmental water samples

    Directory of Open Access Journals (Sweden)

    Grabarczyk M.

    2013-04-01

    Full Text Available A cathodic stripping voltammetric method for determination of Ti(IV in water samples containing high concentrations of surfactants is described. The linear calibration plot for Ti(IV was achieved in the simultaneous presence of 5 mg L-1 anionic, 1 mg L-1 cationic and 2 mg L-1 nonionic surfactants for an accumulation time of 30 s in the range 2.5 × 10-8 to 5 × 10-7 mol L-1, the detection limit for accumulation time of 30 s was about 8.4 × 10-9 mol L-1. The developed method was successfully applied to Ti(IV determination in environmental waters, such as river water (Bystrzyca, Czerniejówka, stagnant water (Lake Zemborzyce and rain water (collected from eastern areas of Poland with satisfactory results.

  14. The Application of Nafion Metal Catalyst Free Carbon Nanotube Modified Gold Electrode: Voltammetric Zinc Detection in Serum

    Science.gov (United States)

    Yue, Wei; Bange, Adam; Riehl, Bill L.; Johnson, Jay M.; Papautsky, Ian; Heineman, William R.

    2013-01-01

    Metal catalyst free carbon nanotube (MCFCNT) whiskers were first used as an electrode modification material on a gold electrode surface for zinc voltammetric measurements. A composite film of Nafion and MCFCNT whiskers was applied to a gold electrode surface to form a mechanically stable sensor. The sensor was then used for zinc detection in both acetate buffer solution and extracted bovine serum solution. A limit of detection of 53 nM was achieved for a 120 s deposition time. The zinc in bovine serum was extracted via a double extraction procedure using dithizone in chloroform as a zinc chelating ligand. The modified electrode was found to be both reliable and sensitive for zinc measurements in both matrices. PMID:24436574

  15. Amplified voltammetric characterization of cleavage of the biotinylated peptide by BACE1 and screening of BACE1 inhibitors.

    Science.gov (United States)

    Yi, Xinyao; Han, Hongxing; Zhang, Yu; Wang, Jianxiu; Zhang, Yi; Zhou, Feimeng

    2013-12-15

    Cleavage of amyloid precursor protein (APP) by the β-site APP cleaving enzyme 1 (BACE1) is a key step in the formation of amyloid beta (Aβ) peptide, the main component of amyloid plaques in Alzheimer's disease (AD). Suppression of BACE1 activity has thus become an efficient way for the treatment of AD. In this study, BACE1 in the absence or presence of BACE1 inhibitors was exposed to the biotinylated peptide substrate-modified electrode. This step was followed by the attachment of ferrocene (Fc)-capped gold nanoparticle/streptavidin conjugates. Due to the blockage of the BACE1 activity by select inhibitors, well-defined voltammetric peaks of high signal intensity were obtained. However, featureless voltammogram was obtained upon initiating the cleavage reaction. The proposed method is simple, sensitive, and suitable for monitoring of BACE1 activity and screening of BACE1 inhibitors.

  16. Electrochemistry of metoclopramide at multi-walled carbon nanotube modified electrode and its voltammetric detection.

    Science.gov (United States)

    Guo, Wei; Geng, Mingjiang; Zhou, Lingyun

    2012-01-01

    A simple, sensitive and inexpensive electrochemical method was developed for the determination of metoclopramide (MCP) with a multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE). MWNT was dispersed into polyacrylic acid (PAA); the aqueous suspension was then cast on GCE electrodes, forming MWNT-PAA films after evaporation of the solvent. The electrochemical behavior of MCP at the MWNT-modified electrode was investigated in detail. Compared with the bare GCE, the MWNT-modified electrode exhibits electrocatalytic activity to the oxidation of MCP because of the significant oxidation peak-current enhancement. Furthermore, various experimental parameters, such as the solution pH value, the amount of MWNT-PAA suspension and accumulation conditions were optimized for the determination of MCP. Based on the electrocatalytic effect of the MWNT-modified electrode, linear sweep voltammetry (LSV) was developed for the determination of MCP with the linear response in the range from 1.0 × 10(-7) to 1.0 × 10(-5) mol L(-1) and a detection limit of 5.0 × 10(-8) mol L(-1). The method has been successfully applied to the determination of MCP in commercial MCP tablets.

  17. A Validated Adsorptive Stripping Voltammetric Determination of Antidiabetic Agent Pioglitazone HCl in Tablets and Biological Fluids

    Science.gov (United States)

    Al-Arfaj, Nawal Ahmad; Al-Abdulkareem, Eman Abdullah; Aly, Fatma Ahmad

    2008-01-01

    Square-wave adsorptive cathodic stripping voltammetry was used to determine pioglitazone HCl in Britton Robinson buffer of pH5. The adsorptive cathodic peak was observed at -1.5 V vs. Ag/AgCl. The peak response was characterized with respect to pH, supporting electrolyte, frequency, scan increment, pulse-amplitude, accumulation potential and pre-concentration time. Under optimal conditions, the peak current is proportional to the concentration of pioglitazone HCl, and a linear calibration graphs were obtained within the concentration levels of 10-8 and 10-4 M following different accumulation time periods (0-300 s). The obtained results were analyzed and the statistical parameters were calculated. The detection limit is 8.08 × 10-9 M (3.17 ng ml-1) using 300 s pre-concentration time, whereas the quantitative limit is 2.45 × 10-8 M (9.63 ng ml-1). The proposed method was applied to assay the drug in pharmaceutical formulations and biological fluids. The pharmacokinetic parameters of drug in human plasma were estimated as: Cmax=785.8 ng ml-1, tmax=1.5 h, Ke=0.125 h-1 and t1/2=8 h which are favorably compared with those reported in literature. PMID:23675103

  18. Public response to alerts and warnings using social media: report of a workshop on current knowledge and research gaps

    National Research Council Canada - National Science Library

    Computer Science and Telecommunications Board; Division on Engineering and Physical Sciences; National Research Council

    "Following an earlier NRC workshop on public response to alerts and warnings delivered to mobile devices, a related workshop was held on February 28 and 29, 2012 to look at the role of social media in disaster response...

  19. Preparation of Graphene-modified Electrode and Voltammetric Determination of Acetaminophen%石墨烯修饰电极的制备及其对对乙酰氨基酚的伏安测定

    Institute of Scientific and Technical Information of China (English)

    马心英; 吴义芳; 李霞

    2012-01-01

    利用滴涂的方法制备了石墨烯修饰电极;石墨烯修饰电极对对乙酰氨基酚(ACOP)的电化学氧化具有明显的催化作用.研究了ACOP在石墨烯修饰电极上的电化学行为,建立了测定ACOP的电化学分析新方法.考察了磷酸盐缓冲溶液的pH值对ACOP电化学行为的影响.结果表明,氧化还原峰电位随pH值升高发生负移;在pH =6.0磷酸盐缓冲溶液中,对乙酰氨基酚在修饰电极上呈现一对灵敏的氧化还原峰.对乙酰氨基酚在石墨烯修饰电极上的氧化峰峰电流与其浓度在6.00×10-7 ~4.00×10-5 mol/L范围内呈良好的线性关系,相关系数为0.9940;检出限为5.00×10-8 mol/L.其回归方程为:i(βa)(A)=3.00c +1.21 ×10-5.该修饰电极具有良好的灵敏度、选择性和稳定性,可用于对乙酰氨基酚药片分析.%A glassy carbon electrode was modified with graphene by casting. The modified electrode showed an excellent electrocatalytical effect on the oxidation of acetaminophen (ACOP). The voltammetric behavior and electrochemical analysis method of ACOP were studied on the modified electrode. The effect of pH value on the response of ACOP was studied in phosphate buffer solution (PBS). The results showed that the redox peak potential of ACOP shifted negatively with increasing pH value, and a pair of well-defined redox waves were obtained in PBS of pH = 6.0. The oxidation peak currents of ACOP increased linearly with the concentration, in the range of 6.00 × 10-7 -4.00 × 10-5 mol/L, the linear regression equation was ips(A) =3.00c+ 1.21 × 10-5 with correlation coefficient 0.9940. The detection limit (S/N = 3) was 5. 00 × 10-8 mol/L. The graphene modified electrode showed a good sensitivity, selectivity and stability. It was applied to the ACOP tablets analysis.

  20. Resolution of galactose, glucose, xylose and mannose in sugarcane bagasse employing a voltammetric electronic tongue formed by metals oxy-hydroxide/MWCNT modified electrodes

    OpenAIRE

    2016-01-01

    Second generation ethanol is produced from the carbohydrates released from the cell wall of bagasse and straw of sugarcane. The objective of this work is the characterization and application of a voltammetric electronic tongue using an array of glassy carbon electrodes modified with multi-walled carbon nanotubes containing metal (Paladium, Gold, Copper, Nickel and Cobalt) oxy-hydroxide nanoparticles (GCE/MWCNT/MetalsOOH) towards a simpler analysis of carbohydrates (glucose, xylose, galactose ...

  1. Construction and evaluation of a carbon paste electrode modified with polyaniline-co-poly(dithiodianiline) for enhanced stripping voltammetric determination of metal ions

    OpenAIRE

    Somerset, Vernon; Silwana, Bongiwe; Horst, Charlton van der; Iwuoha, Emmanuel

    2014-01-01

    A modified carbon paste electrodes (MCPE) have been prepared in this study as an alternative “mercury-free” electrochemical sensor for the determination of Pb2+ and Cd2+ metal ions in aqueous solutions. CPE containing a conducting copolymer of polyaniline-co-poly(2,2'- dithiodianiline) (PANI-co-PDTDA) was used as a modified substrate transducer to achieve enhanced selectivity in stripping voltammetric analysis. The experimental conditions optimised included the supporting electrolyte pH, d...

  2. Poly-Alizarin red S/multiwalled carbon nanotube modified glassy carbon electrode for the boost up of electrocatalytic activity towards the investigation of dopamine and simultaneous resolution in the presence of 5-HT: A voltammetric study.

    Science.gov (United States)

    Reddaiah, K; Madhusudana Reddy, T; Venkata Ramana, D K; Subba Rao, Y

    2016-05-01

    Poly-Alizarin red S/multiwalled carbon nanotube film on the surface of glassy carbon electrode (poly-AzrS/MWCNT/GCE) was synthesized by electrochemical process and was used for the sensitive and selective determination of dopamine (DA) by employing voltammetric techniques. The electrocatalytic response of the modified electrode was found to exhibit admirable activity. The simultaneous determination of dopamine in the presence of serotonin (5-HT) was found to exhibit very good response at poly-AzrS/MWCNTs/GCE. The effect of pH, scan rate, accumulation time and concentration of dopamine was studied at the developed poly-AzrS/MWCNTs/GCE. The poly-AzrS/MWCNTs/GCE exhibited an efficient electron mediating behavior together with well resolved peaks for dopamine, in 0.1 mol/dm(3) phosphate buffer (PBS) solution of pH 7.0. The limit of detection (LOD) and limit of quantification (LOQ) were found to be as 1.89 × 10(-7) mol/dm(3) and 6.312 × 10(-7) mol/dm(3) respectively with a dynamic range from 1 × 10(-6) to 1.8 × 10(-5) mol/dm(3). The interfacial electron transfer behavior of DA was studied by electrochemical impedance spectroscopy (EIS); the studies showed that the charge transfer rate was enhanced at poly-AzrS/MWCNTs/GCE when compared with bare GCE and poly-AzrS/GCE.

  3. The Acute Inflammatory Response in Trauma/Hemorrhage and Traumatic Brain Injury : Current State and Emerging Prospects

    NARCIS (Netherlands)

    Namas, R.; Ghuma, A.; Hermus, L.; Zamora, R.; Okonkwo, D. O.; Billiar, T. R.; Vodovotz, Y.

    2009-01-01

    Traumatic injury/hemorrhagic shock (T/HS) elicits an acute inflammatory response that may result in death. Inflammation describes a coordinated series of molecular, cellular, tissue, organ, and systemic responses that drive the pathology of various diseases including T/HS and traumatic brain injury

  4. Improved heat-responsive electrode for the measurement of electrochemical Peltier heat. The Peltier heat for electrosorption and electrodesorption of oxygen on a platinum electrode in sulfuric acid solution

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Shigeo; Sumino, M.P.; Yamada, Akifumi

    1985-01-01

    A new plate type electrode with high sensitivity and response to temperature change was made using a thick film thermistor. The electrochemical Peltier heat for the oxygen surface process at a platinized platinum electrode in 0.5 M H/sub 2/SO/sub 4/ solution was measured with this electrode by potentiodynamic and galvanostatic transient techniques. It was demonstrated that the most of Peltier heat is caused by the overpotential due to the irreversible oxygen electrode reaction. That is, a Tafel-type relation between the Peltier heat and the current was confirmed. A step-wise heat change corresponding to consecutive stages of platinum lattice occupation by OH was observed. The amount of heat evolved on PtO formation was apparently larger than that on PtOH formation. The results were compared with those obtained by the voltammetric measurement. (orig.).

  5. Alignment and Elongation of Human Adipose-Derived Stem Cells in Response to Direct-Current Electrical Stimulation

    OpenAIRE

    Tandon, Nina; Goh, Brian; Marsano, Anna; Chao, Pen-Hsiu Grace; Montouri-Sorrentino, Chrystina; Gimble, Jeffrey; Vunjak-Novakovic, Gordana

    2009-01-01

    In vivo, direct current electric fields are present during embryonic development and wound healing. In vitro, direct current (DC) electric fields induce directional cell migration and elongation. For the first time, we demonstrate that cultured human adipose tissue-derived stem cells (hASCs) respond to the presence of direct-current electric fields. Cells were stimulated for 2–4 hours with DC electric fields of 6 V/cm that were similar to those encountered in vivo post-injury. Upon stimulatio...

  6. Polarographic and Voltammetric Behavior of Cadmium(Ⅱ)-meso-tetrakis (p-sulfophenyl)porphyrin Complex%镉(Ⅱ)-meso(4-磺基苯)卟啉络合物的极谱伏安行为

    Institute of Scientific and Technical Information of China (English)

    王小萍; 张勇; 潘景浩

    2001-01-01

    The Polarographic and voltammetric behavior of Cd (Ⅱ)-meso-tetrakis(p-sulfophenyl)prophyrin (TPPS4) complex was defined and the cyclic voltammetric peak was obtained at 1.200 V (vs. SCE) in 0.3 mol/L NaoH solution. The characteristics of the peak have been examined in detail and the experimental results prove that the peak has adsorption properties. In addition to the number of electrons transferred in the reaction and the complex ratio, the stability const ant (β=1.19×107) was calculated. The peak current was proportional to the concentration of Cd (Ⅱ) over the rang 3×10-7~1×10-5 mol/L and the limit of detection was 6×10-8 mol/L. Furthermore a possible mechanism was proposed for the reduction of the complex.%用紫外分光光度法和循环伏安法考察了镉与meso(4-磺基苯)卟啉在强碱性溶液中形成的络合物的特性。结果表明,加入Cd(Ⅱ)后该卟啉的索瑞特(Soret)吸收带发生发红移,循环伏安图上出现了新的还原峰,峰电位为-1.20V(vs.SCE),络合物的络合比为1∶1,稳定常数β=1.19×107。本文还用多种电化学技术证明了络合物的还原峰电流具有吸附特征;用示波极谱法二阶导数波测试了峰电流与镉离子浓度的关系,结果表明镉离子在3×10-7~1×10-5mol/L的浓度范围内与络合物峰电流有良好的线性关系;并求得了电极反应的电子转移数为2。此外本文还对络合物的电极反应机理进行了探讨

  7. Whole-cell recording from honeybee olfactory receptor neurons: ionic currents, membrane excitability and odourant response in developing workerbee and drone.

    Science.gov (United States)

    Laurent, Stéphanie; Masson, Claudine; Jakob, Ingrid

    2002-04-01

    Whole-cell recording techniques were used to characterize ionic membrane currents and odourant responses in honeybee olfactory receptor neurons (ORNs) in primary cell culture. ORNs of workerbee (female) and drone (male) were isolated at an early stage of development before sensory axons connect to their target in the antennal lobe. The results collectively indicate that honeybee ORNs have electrical properties similar, but not necessarily identical to, those currently envisaged for ORNs of other species. Under voltage clamp at least four ionic currents could be distinguished. Inward currents were made of a fast transient, tetrodotoxin-sensitive sodium current. In some ORNs a cadmium-sensitive calcium current was detected. ORNs showed heterogeneity in their outward currents: either outward currents were made of a delayed rectifier type potassium current, which was partially blocked by tetraethyl ammonium or quinidine, or were composed of a delayed rectifier type and a transient calcium-dependent potassium current, which was cadmium-sensitive and abolished by removal of external calcium. The proportion of each of the two outward currents, however, was different within the ORNs of the two sexes suggesting a gender-specific functional heterogeneity. ORNs showed heterogeneity in action potential firing properties: depolarizing current steps elicited either one action potential or, as in most of the cells, it led to repetitive spiking. Action potentials were tetrodotoxin-sensitive suggesting they are carried by sodium. Odourant stimulation with different mixtures and pure substances evoked depolarizing receptor potentials with superimposed action potentials when spike threshold was reached. In summary, honeybee ORNs are remarkably mature at early stages in their development.

  8. Femtosecond optical response of Y-Ba-Cu-O thin films: The dependence on optical frequency, excitation intensity, and electric current

    Energy Technology Data Exchange (ETDEWEB)

    Gong, T.; Zheng, L.X.; Xiong, W.; Kula, W.; Kostoulas, Y.; Sobolewski, R.; Fauchet, P.M. (Laboratory for Laser Energetics and Department of Electrical Engineering, University of Rochester, Rochester, New York 14627 (United States))

    1993-06-01

    We have performed a series of femtosecond reflectivity experiments on various Y-Ba-Cu-O thin films at temperatures ranging from 12 to 300 K. In particular, the dependence of the optical response on probing laser frequency, pumping laser intensity, and bias electric current has been measured. Results obtained at room temperature provide quantitative information on the position of the Fermi level in films with different oxygen content. Systematic analysis of the measurements performed in the superconducting state indicates that the optical response associated with nonequilibrium properties of Y-Ba-Cu-O depends strongly on excitation intensity, sample thickness, and bias current. The results cannot be satisfactorily interpreted as the relaxation dynamics of quasiparticles, and a simple two-fluid model is shown to fail to explain data obtained under low laser excitation. Several tentative explanations are proposed, which provide a more comprehensive understanding of the transient optical response of Y-Ba-Cu-O.

  9. Coupled atmosphere-mixed layer ocean response to ocean heat flux convergence along the Kuroshio current extension

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Young-Oh [Woods Hole Oceanographic Institution, Physical Oceanography Department, Woods Hole, MA (United States); Deser, Clara [National Center for Atmospheric Research, Boulder, CO (United States); Cassou, Christophe [CNRS-CERFACS, Toulouse (France)

    2011-06-15

    The winter response of the coupled atmosphere-ocean mixed layer system to anomalous geostrophic ocean heat flux convergence in the Kuroshio Extension is investigated by means of experiments with an atmospheric general circulation model coupled to an entraining ocean mixed layer model in the extra-tropics. The direct response consists of positive SST anomalies along the Kuroshio Extension and a baroclinic (low-level trough and upper-level ridge) circulation anomaly over the North Pacific. The low-level component of this atmospheric circulation response is weaker in the case without coupling to an extratropical ocean mixed layer, especially in late winter. The inclusion of an interactive mixed layer in the tropics modifies the direct coupled atmospheric response due to a northward displacement of the Pacific Inter-Tropical Convergence Zone which drives an equivalent barotropic anomalous ridge over the North Pacific. Although the tropically driven component of the North Pacific atmospheric circulation response is comparable to the direct response in terms of sea level pressure amplitude, it is less important in terms of wind stress curl amplitude due to the mitigating effect of the relatively broad spatial scale of the tropically forced atmospheric teleconnection. (orig.)

  10. MWCNTs/Cu(OH){sub 2} nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

    Energy Technology Data Exchange (ETDEWEB)

    Arvand, Majid, E-mail: arvand@guilan.ac.ir; Gholizadeh, Tahereh M.; Zanjanchi, Mohammad Ali

    2012-08-01

    This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH){sub 2} nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF{sub 6}) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 {mu}M, with a detection limit of 0.04 {mu}M. Electrochemical studies suggested that the MWCNTs/Cu(OH){sub 2} nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current. Highlights: Black-Right-Pointing-Pointer This work examines oxidation of diclofenac at a nanocomposite modified electrode. Black-Right-Pointing-Pointer The salient feature of this electrode is large diffusion coefficient. Black-Right-Pointing-Pointer The proposed electrode decreased overpotential of diclofenac electrooxidation. Black-Right-Pointing-Pointer The modified electrode has good stability and reproducibility.

  11. Current Situation of Modern College Students'Sense of Responsibility%当代大学生责任感现状分析

    Institute of Scientific and Technical Information of China (English)

    陈秀珍; 吉家文

    2015-01-01

    目的:了解当代大学生责任感现状。方法:编制大学生责任感问卷,以海南省4所高校的849名大学生作为研究对象,实施了问卷调查。结果:通过因素分析抽取出5个因素,即国家责任感、社会责任感、家庭责任感、集体责任感、他人责任感。专科院校学生的国家责任感、集体责任感分值显著高于本科院校( t=-3.332,-3.471;P<0.01),而本科院校学生的社会责任感分值则显著高于专科院校(t=2.026,P<0.05)。男生的家庭责任感、集体责任感分值均显著高于女生( t=2.264,3.475;P<0.01)。结论:大学生的责任感由国家、社会、家庭、集体、他人5个方面组成,并有人口学因素影响。%Objective:To understand current situation and basic trend of modern college students 'sense of responsibility .Methods:849 students completed a questionnaire survey at the four colleges and universities in Hainan Province .Results:The five factors:national responsibility , social responsibility , family responsibility ,group responsibility and the responsibility towards other people , were obtained with factor analysis .Through the survey ,it was found that junior college students got significantly lower values on national responsibility and social responsibility (t=-3.332,-3.471;P<0.01),but significantly higher value on social responsibility than undergraduates (t=2.026,P<0.05);male students got significantly higher values on family responsibility and group responsibility than female students (t=2.264,3.475;P<0.05,P<0.01).Conclusion:The responsibility sense of modern college students is affected by five factors:National responsibility ,social responsibility ,family responsibility ,group responsibility and the re-sponsibility towards other people ,and can be influenced by demographic factors .

  12. Electrochemical quartz crystal microbalance study on the two-electrode-system cyclic voltammetric behavior of Prussian blue films

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A two-channel electrochemical quartz crystal microbalance (EQCM) was used to investigate the cyclic voltammetric behavior of two Prussian blue (PB) film-modified Au electrodes in a two-electrode con-figuration in aqueous solution. The redox peaks observed in the two-electrode cyclic voltammogram (CV) are assigned to the intrinsic redox transitions among the Everitt’s salt, PB, and Prussian yellow for the film itself, the redox process of the Au substrate and the redox process of small-quantity ferri-/ferrocyanide impurities entrapped in the PB film, as also supported by ultraviolet-visible (UV-Vis) spectroelectrochemical data. The profile of the two-electrode solid-state CV for the PB powder sand-wiched between two gold-coated indium-tin oxide (ITO) electrodes is similar to that for two PB-modified Au electrodes in aqueous solution, implying similar origins for the corresponding redox peaks. The two-channel EQCM method is expected to become a highly effective technique for the studies of the two-electrode electrochemical behaviors of many other species/materials.

  13. Voltammetric Determination of Homocysteine Using Multiwall Carbon Nanotube Paste Electrode in the Presence of Chlorpromazine as a Mediator

    Directory of Open Access Journals (Sweden)

    Fathali Gholami-Orimi

    2012-01-01

    Full Text Available We propose chlorpromazine (CHP as a new mediator for the rapid, sensitive, and highly selective voltammetric determination of homocysteine (Hcy using multiwall carbon nanotube paste electrode (MWCNTPE. The experimental results showed that the carbon nanotube paste electrode has a highly electrocatalytic activity for the oxidation of Hcy in the presence of CHP as a mediator. Cyclic voltammetry, double potential step chronoamperometry, and square wave voltammetry (SWV are used to investigate the suitability of CHP at the surface of MWCNTPE as a mediator for the electrocatalytic oxidation of Hcy in aqueous solutions. The kinetic parameters of the system, including electron transfer coefficient, and catalytic rate constant were also determined using the electrochemical approaches. In addition, SWV was used for quantitative analysis. SWV showed wide linear dynamic range (0.1–210.0 μM Hcy with a detection limit of 0.08 μM Hcy. Finally, this method was also examined as a selective, simple, and precise electrochemical sensor for the determination of Hcy in real samples.

  14. Sensitive Voltammetric Determination of Captopril Using a Carbon Paste Electrode Modified with Nano-TiO2/Ferrocene Carboxylic Acid

    Institute of Scientific and Technical Information of China (English)

    Jahan Bakhsh RAOOF; Reza OJANI; Mehdi BAGHAYERI

    2011-01-01

    A carbon paste electrode (CPE) modified with ferrocene carboxylic acid (FcCA) and TiO2 nanoparticles was constructed by incorporating TiO2 nanoparticles and ferrocene carboxylic acid into the carbon paste matrix.The electrochemical behavior of captopril (CAP) at the surface of the modified electrode was investigated using electroanalytical methods.The modified electrode showed excellent electrocatalytic activity for the oxidation of CAP in aqueous solutions at physiological pH values.Cyclic voltammetric curves showed that the oxidation of CAP at the surface of the modified electrode reduced its overpotential by more than 290 mV.The modified electrode was used for detecting captopril using cyclic voltammetry and square wave voltammetry techniques.A calibration curve in the range of 0.03 to 2400μmol/L was obtained that had a detection limit of 0.0096 μmol/L (3σ) under the optimized conditions.The modified electrode was successfully used for the determination of captopril in pharmaceutical and biological samples.

  15. Simultaneous square-wave voltammetric determination of aspartame and cyclamate using a boron-doped diamond electrode.

    Science.gov (United States)

    Medeiros, Roberta Antigo; de Carvalho, Adriana Evaristo; Rocha-Filho, Romeu C; Fatibello-Filho, Orlando

    2008-07-30

    A simple and highly selective electrochemical method was developed for the simultaneous determination of aspartame and cyclamate in dietary products at a boron-doped diamond (BDD) electrode. In square-wave voltammetric (SWV) measurements, the BDD electrode was able to separate the oxidation peak potentials of aspartame and cyclamate present in binary mixtures by about 400 mV. The detection limit for aspartame in the presence of 3.0x10(-4) mol L(-1) cyclamate was 4.7x10(-7) mol L(-1), and the detection limit for cyclamate in the presence of 1.0x10(-4) mol L(-1) aspartame was 4.2x10(-6) mol L(-1). When simultaneously changing the concentration of both aspartame and cyclamate in a 0.5 mol L(-1) sulfuric acid solution, the corresponding detection limits were 3.5x10(-7) and 4.5x10(-6) mol L(-1), respectively. The relative standard deviation (R.S.D.) obtained was 1.3% for the 1.0x10(-4) mol L(-1) aspartame solution (n=5) and 1.1% for the 3.0x10(-3) mol L(-1) cyclamate solution. The proposed method was successfully applied in the determination of aspartame in several dietary products with results similar to those obtained using an HPLC method at 95% confidence level.

  16. Adsorptive Cathodic Stripping Voltammetric Method with Alizarin for the Simultaneous Determination of Cadmium, and Zinc in Water Samples

    Directory of Open Access Journals (Sweden)

    Deswati

    2016-12-01

    Full Text Available This paper reports on the development of adsorptive cathodic stripping voltammetric (AdCSV method with 1,2-dihydroxyanthraquinone or Alizarin (AZ as a complexing agent used in the simultaneous determination of ultra trace of Cd and Zn because it has a good sensitivity, and selectivity. The influence of several parameters was studied: the effects of 1,2-dihydroxyanthraquinone or Alizarin (AZ concentration, pH, accumulation potential, and accumulation time. The relative standard deviation (RSD, and recovery is determined to get the accuracy and precision method. It also determined the limit of detection (LOD of the method to get the sensitivity. In this case, the optimum conditions were AZ concentration of 0.5 mM, pH 5, step deposition (70 s, -0.5 V. This method has been applied in water samples successfully, was obtained (Cd 23, and Zn 124 µg/L, LOD (Cd 0.006, and Zn 0.004 µg/L, RSD (Cd 0.4, and Zn 1.4 % (n = 10, recovery (Cd 99.36, and Zn 99.28%. The Atomic absorption spectrometric (AAS method is used as a comparison AdCSV optimum, was obtained (Cd 16, and Zn 115 µg/L.

  17. Preparation of NiO-graphene oxide nanosensor for adsorptive stripping voltammetric determination of dinoterbon in food samples

    Directory of Open Access Journals (Sweden)

    Kasaram Roja

    2016-09-01

    Full Text Available Graphene oxide (GO modified NiO electrochemical nanosensor was developed for the determination of the dinoterbon in food samples using adsorptive stripping voltammetry. The modified nanosensor characterized by TEM, XRD, cyclic and adsorptive stripping voltammetry. Dinoterbon pesticide exhibited a single well-defined cathodic peak at pH 4.0 at Britton–Robinson buffer (-810.0 mV. The voltammetric characterization of the pesti­cide residues is evaluated and the parameter such as the effect of pH, scan rate, pulse amplitude, deposition potential and deposition time were optimized. The current–concen­tration plot obtained using this peak was straight-lined over the range from 0.05 to 50.00 µg mL-1 with limit of detection (LOD 0.028 µg mL-1. The proposed method was efficiently applied to the determination of dinoterbon in food samples. The mean recoveries of the pesticide 97.40 to 99.88 % with a relative standard deviation of 0.114 % in food samples respectively.

  18. A Simple Autonomous Current-Sharing Control Strategy for Fast Dynamic Response of Parallel Inverters in Islanded Microgrids

    DEFF Research Database (Denmark)

    Guan, Yajuan; Vasquez, Juan Carlos; Guerrero, Josep M.

    2014-01-01

    This paper proposed a novel control strategy based on a virtual resistance and a phase locked loop for parallel three-phase inverters. The proposed controller can overcome the drawbacks of the conventional droop control such as slow transient response, complex design, and limited stability margin...

  19. Current and emerging quantitative magnetic resonance imaging methods for assessing and predicting the response of breast cancer to neoadjuvant therapy

    Directory of Open Access Journals (Sweden)

    Abramson RG

    2012-10-01

    Full Text Available Richard G Abramson,1,2,9 Lori R Arlinghaus,1,2 Jared A Weis,1,2 Xia Li,1,2 Adrienne N Dula,1,2 Eduard Y Chekmenev,1–4,9 Seth A Smith,1–3,5 Michael I Miga,1–3,6 Vandana G Abramson,7,9 Thomas E Yankeelov1–3,5,8,91Institute of Imaging Science, 2Department of Radiology and Radiological Sciences, 3Department of Biomedical Engineering, 4Department of Biochemistry, 5Department of Physics, 6Department of Neurosurgery, 7Department of Medical Oncology, 8Department of Cancer Biology, 9Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville,TN, USAAbstract: Reliable early assessment of breast cancer response to neoadjuvant therapy (NAT would provide considerable benefit to patient care and ongoing research efforts, and demand for accurate and noninvasive early-response biomarkers is likely to increase. Response assessment techniques derived from quantitative magnetic resonance imaging (MRI hold great potential for integration into treatment algorithms and clinical trials. Quantitative MRI techniques already available for assessing breast cancer response to neoadjuvant therapy include lesion size measurement, dynamic contrast-enhanced MRI, diffusion-weighted MRI, and proton magnetic resonance spectroscopy. Emerging yet promising techniques include magnetization transfer MRI, chemical exchange saturation transfer MRI, magnetic resonance elastography, and hyperpolarized MR. Translating and incorporating these techniques into the clinical setting will require close attention to statistical validation methods, standardization and reproducibility of technique, and scanning protocol design.Keywords: treatment response, presurgical treatment, neoadjuvant chemotherapy

  20. Adsorptive stripping voltammetric study of vitamin B1 at multi-walled carbon nanotube paste electrode

    Directory of Open Access Journals (Sweden)

    Pradeep Kumar Brahman

    2016-11-01

    The reduction peak current varies linearly with the concentration of vitamin B1 over the range of 1.0 × 10−7–1.0 × 10−6 M. The limits of detection and quantification of the pure drug are 1.1 × 10−10 M and 2.0 × 10−9 M, with the correlation coefficient, r = 0.997 and the relative standard deviation, RSD = 1.2% (n = 5. Experimental results reveal that the MWCNTPE has advantages of small background current, high signal to background current ratio and good reproducibility.

  1. Calcium window currents, periodic forcing, and chaos: Understanding single neuron response with a discontinuous one-dimensional map

    Science.gov (United States)

    Laudanski, J.; Sumner, C.; Coombes, S.

    2010-07-01

    Thalamocortical (TC) neurones are known to express the low-voltage activated, inactivating Ca2+ current IT . The triggering of this current underlies the generation of low threshold Ca2+ potentials that may evoke single or bursts of action potentials. Moreover, this current can contribute to an intrinsic slow (dynamics for the gating variables in the model of IT . This model can be analyzed in closed form and is shown to support an unstable set of periodic orbits. Trajectories are repelled from these organizing centers until they reach the threshold for firing. By determining the condition for a grazing bifurcation (at the border between a spiking and nonspiking event) we show how knowledge of the unstable periodic orbits (existence and stability) can be combined with the grazing condition to determine an effective one-dimensional map that captures the essentials of the chaotic behavior. This map is discontinuous and has strong similarities with the universal limit mapping in grazing bifurcations derived in the context of impacting mechanical systems [A. B. Nordmark, Phys. Rev. E 55, 266 (1997)10.1103/PhysRevE.55.266].

  2. 有限厚铁磁性试件脉冲涡流响应研究%Pulsed eddy current response to a ferromagnetic specimen with finite thickness

    Institute of Scientific and Technical Information of China (English)

    徐志远; 武新军; 黄琛; 康宜华

    2011-01-01

    Method for the pulsed eddy current (PEC) response to a specimen based on direct analysis of transient eddy currents and induced magnetic fields was presented. Based on the experimental verification, the PEC response to a ferromagnetic specimen of finite thickness was computed with numerical simulation method. The law of eddy current diffusion in specimen was studied, and thus the PEC response was divided into two stages. The relation between the response and resistivity or permeability of the specimen was obtained by fitting the response curves of different resistivity or permeability models at the same time points, and the relation between the response and time was obtained by fitting the response curves with time. The results show that early PEC response decays with 0. 5 powers to the resistivity, 0. 5 powers to the permeability, and 1. 5 powers to the time. The latter response decays with negative exponent to time, and the exponential decay coefficient is proportional to the resistivity but inversely proportional to the permeability.%提出了通过直接分析瞬变涡流和感应磁场来研究被测试件脉冲涡流响应的方法.在实验验证的基础上,采用数值模拟的方法计算得到了有限厚铁磁性试件的脉冲涡流响应.研究了试件中涡流扩散规律并将脉冲涡流响应分为前后2个阶段,将相同时间点不同电阻率、磁导率模型的响应曲线及感应电压随时间变化的曲线进行拟合,得到了感应电压与电阻率、磁导率及时间的关系.结果表明:脉冲涡流前期感应电压按试件电阻率的0.5次幂、磁导率的0.5次幂进行衰减,按时间的1.5次幂进行衰减;后期感应电压随时间按照负指数规律衰减,指数衰减系数与试件电阻率成正比,与磁导率成反比.

  3. Differences in the effects of turns and constrictions on the resistive response in current-biased superconducting wire after single photon absorption

    OpenAIRE

    Zotova, A. N.; Vodolazov, D. Y.

    2013-01-01

    We study how turns and constrictions affect the resistive response of the superconducting wire after instant in time and local in space heating, which models the absorption of the single photon by the wire. We find that the presence of constriction favors detection of photons of various energies but the presence of turn increases only ability to detect relatively "low" energy photons. The main reason is that in case of constriction the current density is increased over whole length and width ...

  4. Slow-rise and fast-drop current feature of ultraviolet response spectra for ZnO-nanowire film modulated by water molecules

    Institute of Scientific and Technical Information of China (English)

    Ren Shou-Tian; Wang Qiang; Zhao Feng; Qu Shi-Liang

    2012-01-01

    This study describes the fabrication of ZnO-nanowire films by electro-chemical anodization of Zn foil.The ZnO films are characterized by field emission scanning electron microscopy,X-ray diffraction patterns,and transmission electron microscopy,respectively.The ultraviolet (UV) photo-response properties of the surface-contacted ZnO film are studied through the current evolution processes under different relative humidities.Unlike the usually observed current spectra of the ZnO films,the drop time is shorter than the rise time.The photo-conductivity gain G and the response time γ are both increased with the increase of the applied bias.The photo-conductivity gain G is lowered with the increase of the environmental humidity,while the response time γ is increased.These results can be explained by considering three different surface processes:1) the electron-hole (e-p) pair generation by the UV light illumination,2)the following surface (O-2) species desorption,and 3) the photo-catalytic hydrolysis of water molecules adsorbed on the ZnO surface.The slow-rise and fast-drop current feature is suggested to originate from the sponge-like structure of the ZnO nanowires.

  5. Current analogues of future climate indicate the likely response of a sensitive montane tropical avifauna to a warming world.

    Directory of Open Access Journals (Sweden)

    Alexander S Anderson

    Full Text Available Among birds, tropical montane species are likely to be among the most vulnerable to climate change, yet little is known about how climate drives their distributions, nor how to predict their likely responses to temperature increases. Correlative models of species' environmental niches have been widely used to predict changes in distribution, but direct tests of the relationship between key variables, such as temperature, and species' actual distributions are few. In the absence of historical data with which to compare observations and detect shifts, space-for-time substitutions, where warmer locations are used as analogues of future conditions, offer an opportunity to test for species' responses to climate. We collected density data for rainforest birds across elevational gradients in northern and southern subregions within the Australian Wet Tropics (AWT. Using environmental optima calculated from elevational density profiles, we detected a significant elevational difference between the two regions in ten of 26 species. More species showed a positive (19 spp. than negative (7 spp. displacement, with a median difference of ∼80.6 m across the species analysed that is concordant with that expected due to latitudinal temperature differences (∼75.5 m. Models of temperature gradients derived from broad-scale climate surfaces showed comparable performance to those based on in-situ measurements, suggesting the former is sufficient for modeling impacts. These findings not only confirm temperature as an important factor driving elevational distributions of these species, but also suggest species will shift upslope to track their preferred environmental conditions. Our approach uses optima calculated from elevational density profiles, offering a data-efficient alternative to distribution limits for gauging climate constraints, and is sensitive enough to detect distribution shifts in this avifauna in response to temperature changes of as little as 0

  6. Mechanism of the Pyroelectric Response under Direct-Current Bias in La-Modified Lead Zirconate Titanate Stannate Ceramics

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hong-Ling; WANG Gen-Shui; CHEN Xue-Feng; CAO Fei; DONG Xian-Lin; GU Yan; HE Hong-Liang; LIU Yu-Sheng

    2011-01-01

    Dielectric and pyroelectric properties ofPbo.97Lao.o2(Zro.42Sno.4oTio.i8)03 ceramics are investigated as functions of temperature and dc bias field. Induced and intrinsic pyroelectric coefficients pind and p0 are calculated and analyzed. It is found that the sign, value and variation of the net pyroelectric coefficient p with increasing dc bias all are dominated by p0 under applied biases. Polarization and depolarization processes under dc biases are analyzed. Besides the contribution of pind, the diffuse and decreased pyroelectric response under dc bias compared with that of an identical Geld poled sample without dc bias is mainly attributed to the depolarization process under dc bias.%@@ Dielectric and pyroelectric properties of Pbo.s7Lao.o2(Zro.42Sno.4OTio.is)O3 ceramics are investigated as functions of temperature and do bias field.Induced and intrinsic pyroelectric coefficients pind and p0 are calculated and analyzed.It is found that the sign,value and variation of the net pyroelectric coefficient p with increasing dc bias all are dominated by p0 under applied biases.Polarization and depolarization processes under do biases are analyzed.Besides the contribution of pind,the diffuse and decreased pyroelectric response under do bias compared with that of an identical field poled sample without do bias is mainly attributed to the depolarization process under do bias.

  7. A current view of the diagnosis, clinical variants, response to treatment and prognosis of chronic inflammatory demyelinating polyradiculoneuropathy.

    Science.gov (United States)

    Viala, Karine; Maisonobe, Thierry; Stojkovic, Tanya; Koutlidis, Régine; Ayrignac, Xavier; Musset, Lucile; Fournier, Emmanuel; Léger, Jean-Marc; Bouche, Pierre

    2010-03-01

    We retrospectively analyzed 146 patients fulfilling the European Federation of Neurological Societies and the Peripheral Nerve Society (EFNS/PNS) criteria for definite chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) to (1) evaluate the relevance of these criteria, (2) assess the frequency of CIDP variants, and (3) determine the response to treatment and the prognosis. We found that 75% of these patients fulfilled the main EFNS/PNS clinical and electrophysiological criteria (type I). The remaining patients were diagnosed using laboratory tools as supportive criteria. The common form of CIDP represented 51% of patients. We observed a high frequency of the sensory variant (35% of patients) and the rapid onset form (18%). A positive response to treatment was observed in 87% of patients, with a similar efficacy of prednisone and IVIg. However, in the long term, 40% of treated patients remained dependent on treatment. The IVIg dependency rate was higher than the prednisone or plasma exchange dependency rate (55%, 18%, and 23%, respectively; p = 0.0054). Severe handicap was observed in 24% of patients.

  8. Differential pulse voltammetric studies on the effects of Al(Ⅲ) on the lactate dehydrogenase activity

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this paper, differential pulse voltammetry (DPV) was applied to study the effects of aluminum Al(Ⅲ) on the lactate dehydrogenase (LDH) activity. Michaelis-Menten constant (KNADHm) and maximum velocity (vmax) in the enzyme promoting catalytic reaction of "pyruvate(Pyr) + NADH + H+ LDH(=) lactate + NAD+" under different conditions by monitoring DPV reduction current of NAD+ were reported.(C) 2007 Shu Ping Bi. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

  9. The Pedersen current carried by electrons: a non-linear response of the ionosphere to magnetospheric forcing

    Directory of Open Access Journals (Sweden)

    S. C. Buchert

    2008-09-01

    Full Text Available Observations by the EISCAT Svalbard radar show that electron temperatures Te in the cusp electrojet reach up to about 4000 K. The heat is tapped and converted from plasma convection in the near Earth space by a Pedersen current that is carried by electrons due to the presence of irregularities and their demagnetising effect. The heat is transfered to the neutral gas by collisions. In order to enhance Te to such high temperatures the maximally possible dissipation at 50% demagnetisation must nearly be reached. The effective Pedersen conductances are found to be enhanced by up to 60% compared to classical values. Conductivities and conductances respond significantly to variations of the electric field strength E, and "Ohm's law" for the ionosphere becomes non-linear for large E.

  10. Mesoporous film of WO3-the "sunlight" assisted decomposition of surfactant in wastewater for voltammetric determination of Pb

    Science.gov (United States)

    Krasnodębska-Ostręga, Beata; Bielecka, Agnieszka; Biaduń, Ewa; Miecznikowski, Krzysztof

    2016-12-01

    In this paper we present the application of "sunlight" assisted digestion in the presence of WO3 to the decomposition of dissolved organic matter, using the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant (1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton™X-114) in natural water samples, prior to the determination of traces residues of lead by stripping voltammetry methods. The results of the study showed firstly that the preparation of reproducible WO3 layers characterized by high mechanical and chemical resistance was possible, and secondly that it was also possible to obtain a high efficiency of decomposition, equal in efficiency to that of the reference method, which was the hydrogen peroxide oxidation assisted by UV, with evaporation nearly to dryness. The developed procedure is suggested to be a no-reagents method for the decomposition of added SDS, leading to 100% recovery of added Pb (II). The anodic stripping voltammetric curves recorded in solution after 4 h irradiation with UV assisted by WO3 were repeatable and increased linearly with standard additions, but the data finally obtained were incorrect. The curves recorded in solution after "sunlight" assisted digestion in the presence of WO3 were repeatable, and increased linearly with an increasing of concentration of standard additions (100% recovery of Pb). In the case of a nonionic surfactant, the decomposition time is at least 6 h. The advantage of the proposed method is the fact that the digestion process does not need the addition of any chemicals for the complete decomposition of organic matter.

  11. Response of current phosphorus mitigation measures across the nutrient transfer continuum in two hydrological contrasting agricultural catchments

    Science.gov (United States)

    McDonald, Noeleen; Shore, Mairead; Mellander, Per-Erik; Shortle, Ger; Jordan, Phil

    2015-04-01

    Effective assessment of National Action Programme (NAP) measures introduced under the EU Nitrates Directive (ND), to manage nutrient use and risk of loss to waters from agriculture, is best achieved when examined across the nutrient transfer continuum at catchment scale. The Irish NAP measures are implemented on a whole-territory basis for both nitrogen (N) and phosphorus (P), with P being the key trophic pressure. The aim of this research was to observe the efficacy of P regulation measures and P source management across the transfer continuum and resultant water quality status (i.e. source to impact), in two contrasting agricultural catchments over a four year period. The catchments are ca. 11 km2 and are located in the south-east of Ireland. One is well-drained and arable dominated, while the other is mostly poorly-drained and grassland dominated. In 2009 and 2013 soil surveys for plant-available P were carried out (sustained level of P inputs in both catchments. Indications of responses to soil P change in the surface waters of these catchments appeared to be highly influenced by their hydrological differences and the impact that annual and inter-annual climate and hydrological processes have on nutrient delivery. In the arable catchment total reactive P (TRP) concentrations in interpreted pathways declined across the quickflow, interflow and shallow groundwater of the slowflow, while TRP concentrations in the deeper groundwater, mostly contributing to baseflow, remained the same. However, the complexity of the flow pathways in the grassland catchment made it difficult to determine any trends in P concentrations as a result of changes in P source pressures. Additionally, although there were some inter annual trends, there was no clear indication of improvement in the ecological quality status in either catchment. Overall, a positive response to NAP measures (high soil P declines) was more clearly observable in the source component of the P transfer continuum

  12. Spatial analysis of plague in California: niche modeling predictions of the current distribution and potential response to climate change

    Directory of Open Access Journals (Sweden)

    Tucker James R

    2009-06-01

    Full Text Available Abstract Background Plague, caused by the bacterium Yersinia pestis, is a public and wildlife health concern in California and the western United States. This study explores the spatial characteristics of positive plague samples in California and tests Maxent, a machine-learning method that can be used to develop niche-based models from presence-only data, for mapping the potential distribution of plague foci. Maxent models were constructed using geocoded seroprevalence data from surveillance of California ground squirrels (Spermophilus beecheyi as case points and Worldclim bioclimatic data as predictor variables, and compared and validated using area under the receiver operating curve (AUC statistics. Additionally, model results were compared to locations of positive and negative coyote (Canis latrans samples, in order to determine the correlation between Maxent model predictions and areas of plague risk as determined via wild carnivore surveillance. Results Models of plague activity in California ground squirrels, based on recent climate conditions, accurately identified case locations (AUC of 0.913 to 0.948 and were significantly correlated with coyote samples. The final models were used to identify potential plague risk areas based on an ensemble of six future climate scenarios. These models suggest that by 2050, climate conditions may reduce plague risk in the southern parts of California and increase risk along the northern coast and Sierras. Conclusion Because different modeling approaches can yield substantially different results, care should be taken when interpreting future model predictions. Nonetheless, niche modeling can be a useful tool for exploring and mapping the potential response of plague activity to climate change. The final models in this study were used to identify potential plague risk areas based on an ensemble of six future climate scenarios, which can help public managers decide where to allocate surveillance resources

  13. Spatial analysis of plague in California: niche modeling predictions of the current distribution and potential response to climate change.

    Science.gov (United States)

    Holt, Ashley C; Salkeld, Daniel J; Fritz, Curtis L; Tucker, James R; Gong, Peng

    2009-06-28

    Plague, caused by the bacterium Yersinia pestis, is a public and wildlife health concern in California and the western United States. This study explores the spatial characteristics of positive plague samples in California and tests Maxent, a machine-learning method that can be used to develop niche-based models from presence-only data, for mapping the potential distribution of plague foci. Maxent models were constructed using geocoded seroprevalence data from surveillance of California ground squirrels (Spermophilus beecheyi) as case points and Worldclim bioclimatic data as predictor variables, and compared and validated using area under the receiver operating curve (AUC) statistics. Additionally, model results were compared to locations of positive and negative coyote (Canis latrans) samples, in order to determine the correlation between Maxent model predictions and areas of plague risk as determined via wild carnivore surveillance. Models of plague activity in California ground squirrels, based on recent climate conditions, accurately identified case locations (AUC of 0.913 to 0.948) and were significantly correlated with coyote samples. The final models were used to identify potential plague risk areas based on an ensemble of six future climate scenarios. These models suggest that by 2050, climate conditions may reduce plague risk in the southern parts of California and increase risk along the northern coast and Sierras. Because different modeling approaches can yield substantially different results, care should be taken when interpreting future model predictions. Nonetheless, niche modeling can be a useful tool for exploring and mapping the potential response of plague activity to climate change. The final models in this study were used to identify potential plague risk areas based on an ensemble of six future climate scenarios, which can help public managers decide where to allocate surveillance resources. In addition, Maxent model results were significantly

  14. Platinum(II), palladium(II), rhodium(III) and lead(II) voltammetric determination in sites differently influenced by vehicle traffic.

    Science.gov (United States)

    Melucci, Dora; Locatelli, Clinio

    2007-01-01

    The present work reports analytical results relevant to voltammetric determination of Pt(II), Pd(II), Rh(III) [Platinum Group Metals (PGMs)] and Pb(II) in superficial water sampled in sites differently influenced by vehicle traffic, especially considering their temporal behaviour. For all the elements, in addition to detection limits, precision, expressed as relative standard deviation (s(r) %) and accuracy, expressed as percentage recovery (R %) are also reported. In all cases they show to be good, being the former lower than 6% and the latter in the range 94-105%. A critical comparison with spectroscopic measurements is also discussed.

  15. Variation in response dynamics of regular and irregular vestibular-nerve afferents during sinusoidal head rotations and currents in the chinchilla.

    Science.gov (United States)

    Kim, Kyu-Sung; Minor, Lloyd B; Della Santina, Charles C; Lasker, David M

    2011-05-01

    In mammals, vestibular-nerve afferents that innervate only type I hair cells (calyx-only afferents) respond nearly in phase with head acceleration for high-frequency motion, whereas afferents that innervate both type I and type II (dimorphic) or only type II (bouton-only) hair cells respond more in phase with head velocity. Afferents that exhibit irregular background discharge rates have a larger phase lead re-head velocity than those that fire more regularly. The goal of this study was to investigate the cause of the variation in phase lead between regular and irregular afferents at high-frequency head rotations. Under the assumption that externally applied galvanic currents act directly on the nerve, we derived a transfer function describing the dynamics of a semicircular canal and its hair cells through comparison of responses to sinusoidally modulated head velocity and currents. Responses of all afferents were fit well with a transfer function with one zero (lead term). Best-fit lead terms describing responses to current for each group of afferents were similar to the lead term describing responses to head velocity for regular afferents (0.006 s + 1). This finding indicated that the pre-synaptic and synaptic inputs to regular afferents were likely to be pure velocity transducers. However, the variation in phase lead between regular and irregular afferents could not be explained solely by the ratio of type I to II hair cells (Baird et al 1988), suggesting that the variation was caused by a combination of pre- (type of hair cell) and post-synaptic properties.

  16. Voltammetric interaction of vitamin B1 with DNA at multiwalled carbon nanotube paste electrode

    Directory of Open Access Journals (Sweden)

    Pradeep Kumar Brahman

    2016-09-01

    Full Text Available The interaction between vitamin B1 and DNA was studied with differential pulse voltammetry (DPV at the bare and DNA modified MWCNTPE. The differential pulse voltammograms of vitamin B1 showed that peak potentials shifted to a more negative value and peak currents decreased with the addition of DNA, indicating the dominance of electrostatic interactions. The combining constant (β and combining number (m of DNA–mVB1 were determined too. The work has been supplemented by an UV spectral study.

  17. VOLTAMMETRIC CHARACTERIZATION OF THE BEHAVIOR OF BIOLOGICALLY ACTIVE COMPOUND ENOXIL IN VARIOUS MEDIA

    Directory of Open Access Journals (Sweden)

    Gheorghe Nemţoi

    2011-06-01

    Full Text Available This paper presents the results of scientific research related to the electrochemical behavior of the complex preparation Enoxil. It was established that the oxidation-reduction process of Enoxil is quasireversible. The reactivity of Enoxil obtained from alcohol soluble enotannins is more pronounced, compared to that obtained from standard enotannins. The dependence of cathodic current intensity on Enoxil concentration is linear. This can be used to establish Enoxil concentration in solution. Cyclic voltamograms were used to establish reduction and oxidation potential and the formal redox potential on platinum electrode in sodium perchlorate aqueous environment. These features can be used for identification and determination of Enoxil in pharmaceuticals.

  18. No effect of anodal transcranial direct current stimulation over the motor cortex on response-related ERPs during a conflict task.

    Directory of Open Access Journals (Sweden)

    Alexander Christian Conley

    2016-08-01

    Full Text Available Anodal transcranial direct current stimulation (tDCS over the motor cortex is considered a potential treatment for motor rehabilitation following stroke and other neurological pathologies. However, both the context under which this stimulation is effective and the underlying mechanisms remain to be determined. In this study, we examined the mechanisms by which anodal tDCS may affect motor performance by recording event-related potentials (ERPs during a cued go/nogo task after anodal tDCS over dominant M1 in young adults (Experiment 1 and both dominant and non-dominant M1 in old adults (Experiment 2. In both experiments, anodal tDCS had no effect on either response time or response-related ERPs, including the cue-locked contingent negative variation (CNV and both target-locked and response-locked lateralised readiness potentials (LRP. Bayesian model selection analyses showed that, for all measures, the null effects model was stronger than a model including anodal tDCS vs. sham. We conclude that anodal tDCS has no effect on response time or response-related ERPs during a cued go/nogo task in either young or old adults.

  19. Electrochemical studies of quinine in surfactant media using hanging mercury drop electrode: a cyclic voltammetric study.

    Science.gov (United States)

    Dar, Riyaz Ahmad; Brahman, Pradeep Kumar; Tiwari, Sweety; Pitre, Krishna Sadashiv

    2012-10-01

    The electrochemical behavior of quinine was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) using surfactant. The reduction peak current of quinine increases remarkably in presence of 1% CTAB. Its electrochemical behavior is quasi-reversible in the Britton-Robinson buffers of pH 10.38 by exhibiting the well-defined single cathodic and anodic waves and the ratio of I(p)(a)/I(p)(c) approaching one at the scan rate of 500 mVs(-1). On the basis of CV, SWV and Coulometry, electrochemical reduction mechanism of quinine has been proposed which has shown that protonation occurs on the nitrogen of the quinoline moiety. Linearity was obtained when the peak currents (I(p)) were plotted against concentrations of quinine in the range of 30.0-230.0 ng mL(-1) with a detection limit of 0.132 ng mL(-1) in SWV and 90.0-630.0 ng mL(-1) with a detection limit of 0.238 ng mL(-1) in DPV. Fast and sensitive SWV has been applied for the quantitative analysis of quinine in bark of Cinchona sp. and in soft drinks and a good recovery was obtained. The accuracy and precision of the method are determined and validated statistically. No interferences from other food additives were observed. The relative standard deviation for intraday and interday assay was 0.89 and 0.73% (n=3) respectively.

  20. Association of heart rate variability and inflammatory response in patients with cardiovascular diseases: current strengths and limitations.

    Science.gov (United States)

    Papaioannou, Vasilios; Pneumatikos, Ioannis; Maglaveras, Nikos

    2013-01-01

    Many experimental and clinical studies have confirmed a continuous cross-talk between both sympathetic and parasympathetic branches of autonomic nervous system and inflammatory response, in different clinical scenarios. In cardiovascular diseases, inflammation has been proven to play a pivotal role in disease progression, pathogenesis and resolution. A few clinical studies have assessed the possible inter-relation between neuro-autonomic output, estimated with heart rate variability analysis, which is the variability of R-R in the electrocardiogram, and different inflammatory biomarkers, in patients suffering from stable or unstable coronary artery disease (CAD) and heart failure. Moreover, different indices derived from heart rate signals' processing, have been proven to correlate strongly with severity of heart disease and predict final outcome. In this review article we will summarize major findings from different investigators, evaluating neuro-immunological interactions through heart rate variability analysis, in different groups of cardiovascular patients. We suggest that markers originating from variability analysis of heart rate signals seem to be related to inflammatory biomarkers. However, a lot of open questions remain to be addressed, regarding the existence of a true association between heart rate variability and autonomic nervous system output or its adoption for risk stratification and therapeutic monitoring at the bedside. Finally, potential therapeutic implications will be discussed, leading to autonomic balance restoration in relation with inflammatory control.

  1. Current and calcium responses to local activation of axonal NMDA receptors in developing cerebellar molecular layer interneurons.

    Directory of Open Access Journals (Sweden)

    Bénédicte Rossi

    Full Text Available In developing cerebellar molecular layer interneurons (MLIs, NMDA increases spontaneous GABA release. This effect had been attributed to either direct activation of presynaptic NMDA receptors (preNMDARs or an indirect pathway involving activation of somato-dendritic NMDARs followed by passive spread of somatic depolarization along the axon and activation of axonal voltage dependent Ca(2+ channels (VDCCs. Using Ca(2+ imaging and electrophysiology, we searched for preNMDARs by uncaging NMDAR agonists either broadly throughout the whole field or locally at specific axonal locations. Releasing either NMDA or glutamate in the presence of NBQX using short laser pulses elicited current transients that were highly sensitive to the location of the spot and restricted to a small number of varicosities. The signal was abolished in the presence of high Mg(2+ or by the addition of APV. Similar paradigms yielded restricted Ca(2+ transients in interneurons loaded with a Ca(2+ indicator. We found that the synaptic effects of NMDA were not inhibited by blocking VDCCs but were impaired in the presence of the ryanodine receptor antagonist dantrolene. Furthermore, in voltage clamped cells, bath applied NMDA triggers Ca(2+ elevations and induces neurotransmitter release in the axonal compartment. Our results suggest the existence of preNMDARs in developing MLIs and propose their involvement in the NMDA-evoked increase in GABA release by triggering a Ca(2+-induced Ca(2+ release process mediated by presynaptic Ca(2+ stores. Such a mechanism is likely to exert a crucial role in various forms of Ca(2+-mediated synaptic plasticity.

  2. Probing genetic control of swine responses to PRRSV infection: current progress of the PRRS host genetics consortium

    Directory of Open Access Journals (Sweden)

    Lunney Joan K

    2011-06-01

    Full Text Available Abstract Background Understanding the role of host genetics in resistance to porcine reproductive and respiratory syndrome virus (PRRSV infection, and the effects of PRRS on pig health and related growth, are goals of the PRRS Host Genetics Consortium (PHGC. Methods The project uses a nursery pig model to assess pig resistance/susceptibility to primary PRRSV infection. To date, 6 groups of 200 crossbred pigs from high health farms were donated by commercial sources. After acclimation, the pigs were infected with PRRSV in a biosecure facility and followed for 42 days post infection (dpi. Blood samples were collected at 0, 4, 7, 10, 14, 21, 28, 35 and 42 dpi for serum and whole blood RNA gene expression analyses; weekly weights were recorded for growth traits. All data have been entered into the PHGC relational database. Genomic DNAs from all PHGC1-6 pigs were prepared and genotyped with the Porcine SNP60 SNPchip. Results Results have affirmed that all challenged pigs become PRRSV infected with peak viremia being observed between 4-21 dpi. Multivariate statistical analyses of viral load and weight data have identified PHGC pigs in different virus/weight categories. Sera are now being compared for factors involved in recovery from infection, including speed of response and levels of immune cytokines. Genome-wide association studies (GWAS are underway to identify genes and chromosomal locations that identify PRRS resistant/susceptible pigs and pigs able to maintain growth while infected with PRRSV. Conclusions Overall, the PHGC project will enable researchers to discover and verify important genotypes and phenotypes that predict resistance/susceptibility to PRRSV infection. The availability of PHGC samples provides a unique opportunity to continue to develop deeper phenotypes on every PRRSV infected pig.

  3. The response of O3 and PM2.5 to temperature under current and future conditions

    Science.gov (United States)

    Harkey, M.; Holloway, T.; Bickford, E.; Janssen, M.

    2012-12-01

    Although both observational and model studies have shown clear links between climate and air quality, rarely are observed climate-chemistry relationships used to evaluate model skill. Here we present an analysis of the correlation between temperature (and other meteorological variables) and ambient concentrations of ozone, fine particulate matter (PM2.5) and individual PM2.5 constituents. We employ the EPA Community Multiscale Air Quality (CMAQ) v. 4.7.1, with meteorology from the Weather Research and Forecasting (WRF) model. The study domain covers the eastern United States at a 12 km x 12 km resolution. For both historic and future simulations we use an emissions inventory reflecting 2007 technology and activity, developed by the Lake Michigan Air Directors Consortium (LADCO). In previous studies, our group used the same inventory as input to CMAQ over the Upper Midwestern U.S. and found strong performance against ground-based measurements. Simulated chemistry-climate correlations from the summers of 2006 and 2007 are evaluated against those of ground-based observations from the EPA Air Quality System (AQS) database, the Ozone Monitoring Instrument (OMI) retrievals of nitrogen dioxide (NO2), and the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol product. For comparison with CMAQ results, OMI and MODIS data have been re-gridded using the Wisconsin Horizontal Interpolation Program for Satellites (WHIPS). The observed climate-chemistry response is compared to CMAQ simulations to assess model skill in capturing key climate dependencies. These climate-chemistry relationships are also considered under future climate scenarios, which take as input the WRF-Community Climate System Model (CCSM) climate projection from the North American Regional Climate Change Program (NARCCAP), further downscaled with WRF.

  4. Osteryoung square wave voltammetric determination of lactose in food samples by a derivative procedure

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A method for determination of lactose in food samples by Osteryoung square wave voltammetry (OSWV) was developed. It was based on the nucleophilic addition reaction between lactose and aqua ammonia. The carbonyl group of lactose can be changed into imido group, and this increases the electrochemical activity in reduction and the sensitivity. The optimal condition for the nucleophilic addition reaction was investigated and it was found that in NH4Cl-NH3 buffer of pH 10.1, the linear range between the peak current and the concentration of lactose was 0.6-8.4 mg L-1, and the detection limits was 0.44 mg L-1. The proposed method was applied to the "determination of lactose in food samples and satisfactory results were obtained.

  5. Amorphous palladium-silicon alloys for the oxidation of formic acid and formaldehyde. A voltammetric investigation

    Directory of Open Access Journals (Sweden)

    Correia A.N.

    1999-01-01

    Full Text Available The electrocatalytic oxidation of formic acid and formaldehyde on Pd and on amorphous Pd(Si was studied by cyclic voltammetry and the results compared with the literature for similar systems. The oxidation of HCOOH on Pd occurs through direct catalytic dehydrogenation via (:C(OH2ads while on Pd(Si this intermediate does not appear to be formed. This is a consequence of the presence of inert Si on the surface that diminishes the probability of adjacent free sites. At high HCOOH concentrations, that intermediate undergoes dehydration on the Pd surface and COads oxidation peak is observed. For HCHO, the oxidation mechanism on both electrode materials appears similar to that previously proposed for Pt. However, the oxides formed on the amorphous Pd(Si alloy are more reactive than those on Pd thus affecting the overall kinetics of the process for both organic molecules, a fact revealed by the increase in anodic currents observed in the voltammograms.

  6. Sensitive voltammetric determination of vanillin with an AuPd nanoparticles-graphene composite modified electrode.

    Science.gov (United States)

    Shang, Lei; Zhao, Faqiong; Zeng, Baizhao

    2014-05-15

    In this work, graphene oxide was reduced to graphene with an endogenous reducing agent from dimethylformamide, and then AuPd alloy nanoparticles were electrodeposited on the graphene film. The obtained AuPd-graphene hybrid film was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and voltammetry. The electrochemical behavior of vanillin was studied using the AuPd-graphene hybrid based electrode. It presented high electrocatalytic activity and vanillin could produce a sensitive oxidation peak at it. Under the optimal conditions, the peak current was linear to the concentration of vanillin in the ranges of 0.1-7 and 10-40 μM. The sensitivities were 1.60 and 0.170 mA mM(-1) cm(-2), respectively; the detection limit was 20 nM. The electrode was successfully applied to the detection of vanillin in vanilla bean, vanilla tea and biscuit samples.

  7. Effective solubilization of chalcones in micellar phase: Conductivity and voltammetric study

    Science.gov (United States)

    Ahmed, Safeer; Khan, Gul Tiaz; Shah, Syed Sakhawat

    2013-12-01

    The solubilization of four chalcones, between aqueous and micellar phases of ionic surfactants (SDS and CTAB), was investigated by conductivity and cyclic voltammetry (CV) techniques. From conductivity data, a decrease in the critical micellar concentration (CMC) of the surfactants, in presence of the chalcones was ascribed to the decreased charge density over the surfactants. The results were seconded by thermodynamic parameters including degree of ionization (α), counter ion binding (β), and standard Gibbs free energy of micellization (Δ G {m/○}). The added surfactant decreased the peak current of the oxidized chalcone and shifted the peak potential either positively (in presence of SDS) or negatively (in presence of CTAB). The effect is rationalized as chalcone-surfactant interaction and quantitated as binding constant ( K b) assorting values from 8.78 to 552.97 M-1. The preferred solubilization of the chalcones in the micellar phase has been inferred.

  8. Voltammetric Determination of Flunixin on Molecularly Imprinted Polypyrrole Modified Glassy Carbon Electrode

    Directory of Open Access Journals (Sweden)

    Abd-Elgawad Radi

    2016-01-01

    Full Text Available A novel electrochemical sensing approach, based on electropolymerization of a molecularly imprinted polypyrrole (MIPpy film onto a glassy carbon electrode (GCE surface, was developed for the detection of flunixin (FXN. The sensing conditions and the performance of the constructed sensor were assessed by cyclic, differential pulse and (DPV square wave voltammetry (SWV. The sensor exhibited high sensitivity, with linear responses in the range of 5.0 to 50.0 µM with detection limits of 1.5 and 1.0 µM for DPV and SWV, respectively. In addition, the sensor showed high selectivity towards FXN in comparison to other interferents. The sensor was successfully utilized for the direct determination of FXN in buffalo raw milk samples.

  9. Voltammetric Determination of Flunixin on Molecularly Imprinted Polypyrrole Modified Glassy Carbon Electrode.

    Science.gov (United States)

    Radi, Abd-Elgawad; Abd El-Ghany, Nadia; Wahdan, Tarek

    2016-01-01

    A novel electrochemical sensing approach, based on electropolymerization of a molecularly imprinted polypyrrole (MIPpy) film onto a glassy carbon electrode (GCE) surface, was developed for the detection of flunixin (FXN). The sensing conditions and the performance of the constructed sensor were assessed by cyclic, differential pulse and (DPV) square wave voltammetry (SWV). The sensor exhibited high sensitivity, with linear responses in the range of 5.0 to 50.0 µM with detection limits of 1.5 and 1.0 µM for DPV and SWV, respectively. In addition, the sensor showed high selectivity towards FXN in comparison to other interferents. The sensor was successfully utilized for the direct determination of FXN in buffalo raw milk samples.

  10. Poly-Alizarin red S/multiwalled carbon nanotube modified glassy carbon electrode for the boost up of electrocatalytic activity towards the investigation of dopamine and simultaneous resolution in the presence of 5-HT: A voltammetric study

    Energy Technology Data Exchange (ETDEWEB)

    Reddaiah, K. [Electrochemical Research Laboratory, Department of Chemistry, S.V.U. College of Sciences, Sri Venkateswara University, Tirupati 517 502, Andhra Pradesh (India); Madhusudana Reddy, T., E-mail: tmsreddysvu@gmail.com [Electrochemical Research Laboratory, Department of Chemistry, S.V.U. College of Sciences, Sri Venkateswara University, Tirupati 517 502, Andhra Pradesh (India); Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, MN 55455 (United States); Venkata Ramana, D.K. [Department of Safety Engineering, Dongguk University, 123 Dongdae-ro, Gyeongju, Gyeongbuk 780 714 (Korea, Republic of); Subba Rao, Y. [DST-PURSE Centre, Sri Venkateswara University, Tirupati 517502, Andhra Pradesh (India)

    2016-05-01

    Poly-Alizarin red S/multiwalled carbon nanotube film on the surface of glassy carbon electrode (poly-AzrS/MWCNT/GCE) was synthesized by electrochemical process and was used for the sensitive and selective determination of dopamine (DA) by employing voltammetric techniques. The electrocatalytic response of the modified electrode was found to exhibit admirable activity. The simultaneous determination of dopamine in the presence of serotonin (5-HT) was found to exhibit very good response at poly-AzrS/MWCNTs/GCE. The effect of pH, scan rate, accumulation time and concentration of dopamine was studied at the developed poly-AzrS/MWCNTs/GCE. The poly-AzrS/MWCNTs/GCE exhibited an efficient electron mediating behavior together with well resolved peaks for dopamine, in 0.1 mol/dm{sup 3} phosphate buffer (PBS) solution of pH 7.0. The limit of detection (LOD) and limit of quantification (LOQ) were found to be as 1.89 × 10{sup −7} mol/dm{sup 3} and 6.312 × 10{sup −7} mol/dm{sup 3} respectively with a dynamic range from 1 × 10{sup −6} to 1.8 × 10{sup −5} mol/dm{sup 3}. The interfacial electron transfer behavior of DA was studied by electrochemical impedance spectroscopy (EIS); the studies showed that the charge transfer rate was enhanced at poly-AzrS/MWCNTs/GCE when compared with bare GCE and poly-AzrS/GCE. - Highlights: • The poly-AzrS/MWCNTs/GCE showed good sensitivity towards DA sensing. • The sensor reduced the overoxidation potentials for DA. • This electrode was successfully used for simultaneous sensing of DA and 5-HT. • The electrode was effectively used for the determination of DA in pharmaceutical formulations.

  11. A biophysical model examining the role of low-voltage-activated potassium currents in shaping the responses of vestibular ganglion neurons.

    Science.gov (United States)

    Hight, Ariel E; Kalluri, Radha

    2016-08-01

    The vestibular nerve is characterized by two broad groups of neurons that differ in the timing of their interspike intervals; some fire at highly regular intervals, whereas others fire at highly irregular intervals. Heterogeneity in ion channel properties has been proposed as shaping these firing patterns (Highstein SM, Politoff AL. Brain Res 150: 182-187, 1978; Smith CE, Goldberg JM. Biol Cybern 54: 41-51, 1986). Kalluri et al. (J Neurophysiol 104: 2034-2051, 2010) proposed that regularity is controlled by the density of low-voltage-activated potassium currents (IKL). To examine the impact of IKL on spike timing regularity, we implemented a single-compartment model with three conductances known to be present in the vestibular ganglion: transient sodium (gNa), low-voltage-activated potassium (gKL), and high-voltage-activated potassium (gKH). Consistent with in vitro observations, removing gKL depolarized resting potential, increased input resistance and membrane time constant, and converted current step-evoked firing patterns from transient (1 spike at current onset) to sustained (many spikes). Modeled neurons were driven with a time-varying synaptic conductance that captured the random arrival times and amplitudes of glutamate-driven synaptic events. In the presence of gKL, spiking occurred only in response to large events with fast onsets. Models without gKL exhibited greater integration by responding to the superposition of rapidly arriving events. Three synaptic conductance were modeled, each with different kinetics to represent a variety of different synaptic processes. In response to all three types of synaptic conductance, models containing gKL produced spike trains with irregular interspike intervals. Only models lacking gKL when driven by rapidly arriving small excitatory postsynaptic currents were capable of generating regular spiking.

  12. Square Wave Voltammetric Label-free Determination of the Natural Protein Material Silk Fibroin

    Institute of Scientific and Technical Information of China (English)

    MA Ming-Ming; SONG Jun-Feng

    2008-01-01

    The electrochemical behavior of silk fibroin(SF)was investigated by cyclic voltammetry and square wave voltammetry in 0.01 mol/L HCI for the first time.Within the potential scan range of 0.0 to1.2 V(vs.SCE),two oxi-dative peaks at 0.91 V(Pa,1)and 0.43 V(Pa,2)as well as one reductive peak at 0.24 V(Pc)were observed on cyclic voltammogram at scan rate of 0.2 V/s.The peak current of the peak Pa,1 was linear with SF concentration in the range of 5.8×10-8 to 1.1×10-6 mol/L,with the limit of detection 3.0×10-8 mol/L(SIN=3).The proposed method was of high selectivity without the interferences from the coexisting substances such as another natural protein material sericin and other small molecular substances.It was applied to the determination of SF in raw silk liquid samples without any pre-separation and pre-purification.

  13. Porous silicon membrane-modified electrodes for label-free voltammetric detection of MS2 bacteriophage.

    Science.gov (United States)

    Reta, Nekane; Michelmore, Andrew; Saint, Christopher; Prieto-Simón, Beatriz; Voelcker, Nicolas H

    2016-06-15

    A proof of concept for the label-free detection of bacteriophage MS2, a model indicator of microbiological contamination, is validated in this work as a porous silicon (pSi) membrane-based electrochemical biosensor. PSi membranes were used to afford nanochannel architectures. The sensing mechanism was based on the nanochannel blockage caused by MS2 binding to immobilized capture antibodies. This blockage was quantified by measuring the oxidation current of the electroactive species reaching the electrode surface, by means of differential pulse voltammetry (DPV). The immunosensor showed a limit of detection of 6 pfu/mL in buffer, allowing the detection of MS2 to levels commonly found in real-world applications, and proved to be unaffected by matrix effects when analyzing MS2 in reservoir water. This platform enables the straightforward, direct and sensitive detection of a broad range of target analytes and constitutes a promising approach towards the development of portable electronic point of sample analysis devices.

  14. Differential Pulse Anodic Stripping Voltammetric Determination of Lead with Heparin Modified Electrode

    Institute of Scientific and Technical Information of China (English)

    LI,Nian-Bing(李念兵); DUAN,Jian-Ping(段建平); CHEN,Guo-Nan(陈国南)

    2004-01-01

    A novel differential pulse anodic stripping voltammetry for the determination of trace amounts of lead, using a biomacromolecule heparin drop-coated modified glassy carbon electrode, has been described. Pb2+ was deposited on the surface of a heparin-modified electrode at - 1.0 V (vs. SCE) via forming Pb2+-heparin and subsequent reduction at the electrode. In the following step, Pb-heparin was oxidized, and voltammograms were recorded by scanning the potential in a positive direction. Conditions were optimized with respect to the pH of the medium, the mass of drop-coated heparin, accumulation potential and accumulation time. The peak current was proportional to the Pb2+ concentration in the range of 2.0× 10-9 to 7.0× 10-7 mol/L, The detection limit was 3.0× 10-10 mol/L.The relative standard deviation was 4.83% for 1.0× 10-8mol/L Pb2- (n= 10). The developed method has been applied to the determination of Pb2- in water samples with satisfactory results.

  15. In vivo voltammetric detection of rat brain lactate with carbon fiber microelectrodes coated with lactate oxidase.

    Science.gov (United States)

    Shram, N F; Netchiporouk, L I; Martelet, C; Jaffrezic-Renault, N; Bonnet, C; Cespuglio, R

    1998-07-01

    To allow rat brain lactate measurement in vivo, a specific sensor based on a carbon fiber (phi = 30 microns) microelectrode coated with lactate oxidase was prepared. Combined with the differential normal pulse voltammetry measurement method, such a sensor, with a sensitivity of 9.15 +/- 0.91 mA.M-1.cm-2, provided a lactate linear response in concentrations ranging from 0.1 to 2.0 mM. The measurements performed appeared to be essentially insensitive to usual interference caused by the electroactive compounds present in the brain (ascorbic acid and peptides). In vivo detection performed in the cortex of the anesthetized rat led to the determination of a lactate concentration of 0.41 +/- 0.02 mM. Moreover, to validate the results obtained in vivo, an ex vivo determination of the lactate level was also performed in samples of brain tissue, plasma, and cerebrospinal fluid, using both voltammetry and a clinical analyzer with colorimetric-based detection. A good correlation was observed between the sets of data established by both methods.

  16. Voltammetric behavior of zaleplon and its differential pulse polarographic determination in capsules.

    Science.gov (United States)

    Larenas, Gipsy; Bollo, Soledad; Rodriguez, Marcelo; Lemus, Igor; Nuñez-Vergara, Luis J; Squella, Juan A; Alvarez-Lueje, Alejandro

    2005-01-01

    In this work both the electrochemical behavior and the analysis of the hypnotic pyrazolopyrimidine derivative zaleplon were studied. Zaleplon in ethanol-0.1M Britton Robinson buffer solution (30-70) showed 2 irreversible, well-defined cathodic responses in the pH range of 2-12 using differential pulse polarography (DPP), tast polarography, and cyclic voltammetry. From chronocoulometric studies, it was possible to conclude that one electron was transferred in each reduction peak or wave. For analytical purposes, the DPP technique working at pH 4.5 for peak I was selected, which exhibited adequate repeatability, reproducibility, and selectivity. The recovery was 99.97 +/- 1.52%, and the detection and quantitation limits were 5.13 x 10(-7)M and 1.11 x 10(-6)M, respectively. The DPP method was applied successfully to the individual assay of capsules in order to verify the content uniformity of zaleplon. Treatment of the sample is not required because the excipients do not interfere, the method is not time consuming, and it is less expensive than column liquid chromatography.

  17. Voltammetric reduction of finasteride at mercury electrode and its determination in tablets.

    Science.gov (United States)

    Alvarez-Lueje, A; Brain-Isasi, S; Núñez-Vergara, L J; Squella, J A

    2008-05-15

    Finasteride in hydroalcoholic solutions (ethanol/Britton-Robinson buffer, 30/70) exhibits cathodic response in a wide range of pH (-0.5 to 12) using differential pulse (DPP) and test polarography (TP). The reduction peak of finasteride at acidic pH, is a catalytic proton peak resulting from a mechanism involving a first protonation of finasteride followed by the reduction of the protons combined with finasteride in order to regenerate finasteride and liberate hydrogen. Based on the catalytic hydrogen wave, a novel method for the determination of finasteride can be proposed. For analytical purposes we selected DPP technique in an ethanol/0.0625 mol L(-1) H(2)SO(4) (30/70) solution medium. In this condition the I(p) varied linearly with finasteride concentration between 5 x 10(-5) and 5 x 10(-4) mol L(-1). Within-day and inter-day reproducibility's were adequate with R.S.D. values lower than 2%. The selectivity of the method was checked with both accelerated degradation trials and typical excipients formulations. The developed method was applied to the assay and the uniformity content of finasteride tablets and compared with the standard HPLC method. The DPP-developed method was adequate for the finasteride determination in pharmaceutical forms as that exhibited an adequate accuracy, reproducibility and selectivity. Furthermore, treatment of the sample was not required as in HPLC; the method is not time-consuming and less expensive than the HPLC ones.

  18. Ultratrace Detection of Histamine Using a Molecularly-Imprinted Polymer-Based Voltammetric Sensor.

    Science.gov (United States)

    Akhoundian, Maedeh; Rüter, Axel; Shinde, Sudhirkumar

    2017-03-21

    Rapid and cost-effective analysis of histamine, in food, environmental, and diagnostics research has been of interest recently. However, for certain applications, the already-existing biological receptor-based sensing methods have usage limits in terms of stability and costs. As a result, robust and cost-effective imprinted polymeric receptors can be the best alternative. In the present work, molecularly-imprinted polymers (MIPs) for histamine were synthesized using methacrylic acid in chloroform and acetonitrile as two different porogens. The binding affinity of the MIPs with histamine was evaluated in aqueous media. MIPs synthesized in chloroform displayed better imprinting properties for histamine. We demonstrate here histamine MIPs incorporated into a carbon paste (CP) electrode as a MIP-CP electrode sensor platforms for detection of histamine. This simple sensor format allows accurate determination of histamine in the sub-nanomolar range using an electrochemical method. The sensor exhibited two distinct linear response ranges of 1 × 10(-10)-7 × 10(-9) M and 7 × 10(-9)-4 × 10(-7) M. The detection limit of the sensor was calculated equal to 7.4 × 10(-11) M. The specificity of the proposed electrode for histamine is demonstrated by using the analogous molecules and other neurotransmitters such as serotonin, dopamine, etc. The MIP sensor was investigated with success on spiked serum samples. The easy preparation, simple procedure, and low production cost make the MIP sensor attractive for selective and sensitive detection of analytes, even in less-equipped laboratories with minimal training.

  19. Dynamic movement of N100m current sources in auditory evoked fields: comparison of ipsilateral versus contralateral responses in human auditory cortex.

    Science.gov (United States)

    Jin, Chun Yu; Ozaki, Isamu; Suzuki, Yasumi; Baba, Masayuki; Hashimoto, Isao

    2008-04-01

    We recorded auditory evoked magnetic fields (AEFs) to monaural 400Hz tone bursts and investigated spatio-temporal features of the N100m current sources in the both hemispheres during the time before the N100m reaches at the peak strength and 5ms after the peak. A hemispheric asymmetry was evaluated as the asymmetry index based on the ratio of N100m peak dipole strength between right and left hemispheres for either ear stimulation. The results of asymmetry indices showed right-hemispheric dominance for left ear stimulation but no hemispheric dominance for right ear stimulation. The current sources for N100m in both hemispheres in response to monaural 400Hz stimulation moved toward anterolateral direction along the long axis of the Heschl gyri during the time before it reaches the peak strength; the ipsilateral N100m sources were located slightly posterior to the contralateral N100m ones. The onset and peak latencies of the right hemispheric N100m in response to right ear stimulation are shorter than those of the left hemispheric N100m to left ear stimulation. The traveling distance of the right hemispheric N100m sources following right ear stimulation was longer than that for the left hemispheric ones following left ear stimulation. These results suggest the right-dominant hemispheric asymmetry in pure tone processing.

  20. Age or ischemia uncouples the blood flow response, tissue acidosis, and direct current potential signature of spreading depolarization in the rat brain.

    Science.gov (United States)

    Menyhárt, Ákos; Zölei-Szénási, Dániel; Puskás, Tamás; Makra, Péter; Bari, Ferenc; Farkas, Eszter

    2017-08-01

    Spreading depolarization (SD) events contribute to lesion maturation in the acutely injured human brain. Neurodegeneration related to SD is thought to be caused by the insufficiency of the cerebral blood flow (CBF) response; yet the mediators of the CBF response, or their deficiency in the aged or ischemic cerebral cortex, remain the target of intensive research. Here, we postulated that tissue pH effectively modulates the magnitude of hyperemia in response to SD, the coupling of which is prone to be dysfunctional in the aged or ischemic cerebral cortex. To test this hypothesis, we conducted systematic correlation analysis between the direct current (DC) potential signature of SD, SD-associated tissue acidosis, and hyperemic element of the CBF response in the isoflurane-anesthetized, young or old, and intact or ischemic rat cerebral cortex. The data demonstrate that the amplitude of the SD-related DC potential shift, tissue acidosis, and hyperemia are tightly coupled in the young intact cortex; ischemia and old age uncouples the amplitude of hyperemia from the amplitude of the DC potential shift and acidosis; the duration of the DC potential shift, hyperemia and acidosis positively correlate under ischemia alone; and old age disproportionally elongates the duration of acidosis with respect to the DC potential shift and hyperemia under ischemia. The coincidence of the variables supports the view that local CBF regulation with SD must have an effective metabolic component, which becomes dysfunctional with age or under ischemia. Finally, the known age-related acceleration of ischemic neurodegeneration may be promoted by exaggerated tissue acidosis.NEW & NOTEWORTHY The hyperemic element of the cerebral blood flow response to spreading depolarization is effectively modulated by tissue pH in the young intact rat cerebral cortex. This coupling becomes dysfunctional with age or under ischemia, and tissue acidosis lasts disproportionally longer in the aged cortex, making

  1. 接地线缆HEMP电流响应规律研究%Study on Current Response of Grounding Cable in HEMP Environment

    Institute of Scientific and Technical Information of China (English)

    柴焱杰; 张春光; 许凯; 赵煜

    2014-01-01

    The cable connecting the information systems may be coupled by the electromagnetic pulse energy to the internal cir-cuit,resulting in system performance degradation,damage and even burned,and bringing great harm. Therefore,the work to research cables’ effects under electromagnetic pulse is the precondition to take electromagnetic protective measures. The finite-difference time-domain ( FDTD) method and Noda thin models are used to establish the space and computational model with high-altitude nuclear elec-tromagnetic pulse (HEMP) as the incident source,the grounding cable HEMP current response in the different states is analyzed and calculated. The results show that the response current of grounding cable attenuates rapidly in the oscillation process with a large peak at a position higher;the incident direction changes of the wave source can produce different results in response,and the response current mainly appears from the cable laid in the same direction with the electric field excitation component. The conclusions can provide useful guidance for the cable electromagnetic protection.%连接电子系统的线缆能够将电磁脉冲能量耦合至系统的内部电路,造成系统性能降级、损伤甚至烧毁,带来极大的危害,因此开展线缆的电磁脉冲效应研究工作是采取针对性电磁防护措施的必要前提。以高空核爆电磁脉冲(HEMP)为入射源,基于时域有限差分(FDTD)方法和Noda细线模型建立仿真空间和计算模型,分析计算了不同状态下接地线缆的HEMP电流响应。结果表明,接地线缆的响应电流在振荡过程中迅速衰减,且在较高位置处峰值较大;波源入射方向的改变会产生不同的响应结果,线缆响应电流主要来自与其布设方向一致的电场分量的激励。所得结论能够为线缆的电磁防护提供有益指导。

  2. Amyloid–β peptides time-dependent structural modifications: AFM and voltammetric characterization

    Energy Technology Data Exchange (ETDEWEB)

    Enache, Teodor Adrian; Chiorcea-Paquim, Ana-Maria; Oliveira-Brett, Ana Maria, E-mail: brett@ci.uc.pt

    2016-07-05

    The human amyloid beta (Aβ) peptides, Aβ{sub 1-40} and Aβ{sub 1-42}, structural modifications, from soluble monomers to fully formed fibrils through intermediate structures, were investigated, and the results were compared with those obtained for the inverse Aβ{sub 40-1} and Aβ{sub 42-1}, mutant Aβ{sub 1-40}Phe{sup 10} and Aβ{sub 1-40}Nle{sup 35}, and rat Aβ{sub 1-40}Rat peptide sequences. The aggregation was followed at a slow rate, in chloride free media and room temperature, and revealed to be a sequence-structure process, dependent on the physicochemical properties of each Aβ peptide isoforms, and occurring at different rates and by different pathways. The fibrilization process was investigated by atomic force microscopy (AFM), via changes in the adsorption morphology from: (i) initially random coiled structures of ∼0.6 nm height, corresponding to the Aβ peptide monomers in random coil or in α-helix conformations, to (ii) aggregates and protofibrils of 1.5–6.0 nm height and (iii) two types of fibrils, corresponding to the Aβ peptide in a β-sheet configuration. The reactivity of the carbon electrode surface was considered. The hydrophobic surface induced rapid changes of the Aβ peptide conformations, and differences between the adsorbed fibrils, formed at the carbon surface (beaded, thin, <2.0 nm height) or in solution (long, smooth, thick, >2.0 nm height), were detected. Differential pulse voltammetry showed that, according to their primary structure, the Aβ peptides undergo oxidation in one or two steps, the first step corresponding to the tyrosine amino acids oxidation, and the second one to the histidine and methionine amino acids oxidation. The fibrilization process was electrochemically detected via the decrease of the Aβ peptide oxidation peak currents that occurred in a time dependent manner. - Highlights: • The Aβ peptide fibrilization process was followed by AFM and DP voltammetry. • The human Aβ{sub 1-40} and Aβ{sub 1

  3. Differences in the effects of turns and constrictions on the resistive response in current-biased superconducting wire after single photon absorption

    Science.gov (United States)

    Zotova, A. N.; Y Vodolazov, D.

    2013-07-01

    We study how turns and constrictions affect the resistive response of superconducting wire after instantaneous, localized heating, by modeling the absorption of a single photon by the wire. We find that the presence of constrictions favors the detection of photons with a range of energies whereas the presence of turns increases the ability to detect only relatively ‘low’ energy photons. The main reason is that in the case of a constriction the current density is increased over the whole length and width of the constriction while in the case of a turn the current density is enhanced only near the inner corner of the turn. This results in inhomogeneous Joule heating near the turn and worsens the conditions for the appearance of the normal domain at relatively small currents, where the ‘high’ energy photons could already create a normal domain in the straight part of the wire. We also find that the amplitude of the voltage pulse depends on the location at which the photon is absorbed, being smallest when the photon is absorbed near the turn and largest when the photon is absorbed near the constriction. This effect is due to the difference in the resistance of constrictions and turns in the normal state from the resistance of the rest of the wire.

  4. Current Situation and Education Exploration of Vocational Students' Sense of Responsibility%高职生责任意识现状及其教育探讨

    Institute of Scientific and Technical Information of China (English)

    梁晓军; 朱琦

    2012-01-01

    高等职业院校培养的是高素质技能型专门人才,他们的责任意识直接关系到自身职业能力的获取以及经济社会的发展。当前,高职生责任意识的缺失已成为现阶段我国高职教育中一个不可忽视的问题。本文在分析高职生责任意识现状及其缺失原因的基础上,提出了相应的对策建议。%The vocational institutions cultivate high-quality skilled expertise, their sense of responsibility is directly related to their own professional ability as well as the economic and social development. Currently, the lack of the sense of responsibility of the vocational high school students has become a problem can not be ignored at this stage of higher vocational education in China. In this paper, based on the analysis of vocational high school students a sense of responsibility to the status quo and its deletion causes, put forward corresponding suggestions.

  5. Changes in gas exchange characteristics during the life span of giant sequoia: Implications for response to current and future concentrations of atmospheric ozone

    Energy Technology Data Exchange (ETDEWEB)

    Grulke, N.E.; Miller, P.R. (USDA Forest Service, Riverside, CA (United States))

    Native stands of giant sequoia are being exposed to relatively high concentrations of atmospheric ozone produced in urban and agricultural areas upwind. The expected change in environmental conditions over the next 100 y is likely to be unprecendented in the life span (ca 2,500 y) of giant sequoia. Changes in the physiological responses of three age classes of giant sequoia (current year, 12 y and 25 y) to different concentrations of ozone were determined, and age-related differences in sensitivity to pollutants were assessed by examining physiological changes (gas exchange, water use efficiency) across the life span of giant sequoia. The CO[sub 2] exchange rate (CER) was greater in current year (12.1 [mu]mol CO[sub 2]/m[sup 2]s) and 2 year old seedlings (4.8 [mu]mol CO[sub 2]/m[sup 2]s) than in all older trees (average of 3.0 [mu]mol CO[sub 2]/m[sup 2]s). Dark respiration was highest for current year seedlings and was increased twofold in symptotic individuals exposed to elevated ozone concentrations. Stomatal conductance was greater in current-year and 2 year old seedlings (335 and 200 mmol H[sub 2]O/m[sup 2]s), respectively, than in all older trees (50 mmol H[sub 2]O/m[sup 2]s), indicating that the ozone concentration in substomatol cavities is higher in young seedlings than in older trees. Significant changes in water use efficiency occurred in trees between ages 5 and 20 years. It is concluded that giant sequoia seedlings are sensitive to atmospheric ozone until they are ca 5 y old. Low conductance, high water use efficiency, and compact mesophyll all contribute to a natural ozone tolerance, or defense, or both, in foliage of older trees. 11 refs., 1 fig., 1 tab.

  6. Sensitive Adsorptive Voltammetric Method for Determination of Bisphenol A by Gold Nanoparticle/Polyvinylpyrrolidone-Modified Pencil Graphite Electrode.

    Science.gov (United States)

    Yaman, Yesim Tugce; Abaci, Serdar

    2016-05-25

    A novel electrochemical sensor gold nanoparticle (AuNP)/polyvinylpyrrolidone (PVP) modified pencil graphite electrode (PGE) was developed for the ultrasensitive determination of Bisphenol A (BPA). The gold nanoparticles were electrodeposited by constant potential electrolysis and PVP was attached by passive adsorption onto the electrode surface. The electrode surfaces were characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The parameters that affected the experimental conditions were researched and optimized. The AuNP/PVP/PGE sensor provided high sensitivity and selectivity for BPA recognition by using square wave adsorptive stripping voltammetry (SWAdSV). Under optimized conditions, the detection limit was found to be 1.0 nM. This new sensor system offered the advantages of simple fabrication which aided the expeditious replication, low cost, fast response, high sensitivity and low background current for BPA. This new sensor system was successfully tested for the detection of the amount of BPA in bottled drinking water with high reliability.

  7. Modeling mid-ocean ridge hydrothermal response to earthquakes, tides, and ocean currents: a case study at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

    Science.gov (United States)

    Xu, G.; Bemis, K. G.

    2014-12-01

    Seafloor hydrothermal systems feature intricate interconnections among oceanic, geological, hydrothermal, and biological processes. The advent of the NEPTUNE observatory operated by Ocean Networks Canada at the Endeavour Segment, Juan de Fuca Ridge enables scientists to study these interconnections through multidisciplinary, continuous, real-time observations. The multidisciplinary observatory instruments deployed at the Grotto Mound, a major study site of the NEPTUNE observatory, makes it a perfect place to study the response of a seafloor hydrothermal system to geological and oceanic processes. In this study, we use the multidisciplinary datasets recorded by the NEPTUNE Observatory instruments as observational tools to demonstrate two different aspects of the response of hydrothermal activity at the Grotto Mound to geological and oceanic processes. First, we investigate a recent increase in venting temperature and heat flux at Grotto observed by the Benthic and Resistivity Sensors (BARS) and the Cabled Observatory Vent Imaging Sonar (COVIS) respectively. This event started in Mar 2014 and is still evolving by the time of writing this abstract. An initial interpretation in light of the seismic data recorded by a neighboring ocean bottom seismometer on the NEPTUNE observatory suggests the temperature and heat flux increase is probably triggered by local seismic activities. Comparison of the observations with the results of a 1-D mathematical model simulation of hydrothermal sub-seafloor circulation elucidates the potential mechanisms underlying hydrothermal response to local earthquakes. Second, we observe significant tidal oscillations in the venting temperature time series recorded by BARS and the acoustic imaging of hydrothermal plumes by COVIS, which is evidence for hydrothermal response to ocean tides and currents. We interpret the tidal oscillations of venting temperature as a result of tidal loading on a poroelastic medium. We then invoke poroelastic

  8. Changes in gas exchange characteristics during the life span of giant sequoia: implications for response to current and future concentrations of atmospheric ozone.

    Science.gov (United States)

    Grulke, N. E.; Miller, P. R.

    1994-01-01

    Native stands of giant sequoia (Sequoiadendron giganteum Bucholz) are being exposed to relatively high concentrations of atmospheric ozone produced in urban and agricultural areas upwind. The expected change in environmental conditions over the next 100 years is likely to be unprecedented in the life span (about 2,500 years) of giant sequoia. We determined changes in physiological responses of three age classes of giant sequoia (current-year, 12-, and 125-year-old) to differing concentrations of ozone, and assessed age-related differences in sensitivity to pollutants by examining physiological changes (gas exchange, water use efficiency) across the life span of giant sequoia (current-year, 2-, 5-, 20-, 125-, and > 2,000-year-old trees). The CO(2) exchange rate (CER) was greater in current-year (12.1 micro mol CO(2) m(-2) s(-1)) and 2-year-old seedlings (4.8 micro mol CO(2) m(-2) s(-1)) than in all older trees (3.0 micro mol CO(2) m(-2) s(-1), averaged across the four older age classes). Dark respiration was highest for current-year seedlings (-6.5 +/- 0.7 micro mol CO(2) m(-2) s(-1)) and was increased twofold in symptomatic individuals exposed to elevated ozone concentrations. Stomatal conductance (g(s)) was greater in current-year (355 mmol H(2)O m(-2) s(-1)) and 2-year-old seedlings (200 mmol H(2)O m(-2) s(-1)) than in all older trees (50 mmol H(2)O m(-2) s(-1)), indicating that the ozone concentration in substomatal cavities is higher in young seedlings than in trees. Significant changes in water use efficiency, as indicated by C(i)/C(a), occurred in trees between ages 5 and 20 years. We conclude that giant sequoias seedlings are sensitive to atmospheric ozone until they are about 5 years old. Low conductance, high water use efficiency, and compact mesophyll all contribute to a natural ozone tolerance, or defense, or both, in foliage of older trees.

  9. Current induced magnetic flux response in frustrated three-band superconductors as a bulk probe of broken time reversal symmetry (BTRS) ground states

    Energy Technology Data Exchange (ETDEWEB)

    Yerin, Yuriy; Omelyanchouk, Alexander [Verkin Inst. for Low Temperature Physics and Engineering. 61103 Kharkiv (Ukraine); Drechsler, Stefan-Ludwig; Brink, Jeroen van den; Efremov, Dmitriy [Inst. for Theorretical Solid State Physics at the Leibniz Inst. for Solid State an Materials Research, IFW-Dresden, D-01171 Dresden (Germany)

    2016-07-01

    Within the Ginzburg-Landau formalism we provide a classification of all possible ground states (GS) of a three-band superconductor (3BSC) where either frustrated states with BTRS or a single non-BTRS GS with unconventional/conventional s-wave symmetry, respectively, exist. The necessary condition for a BTRS GS in general cannot be reduced to a ''-''sign of the product of all interband couplings (IBC) valid in the case of 3 equivalent bands with repulsive equal IBC, only. It corresponds to a maximal IBC frustration. We show that with increasing diversity of the parameter space this frustration is reduced and the regions of possible BTRS GS start to shrink. We track possible evolutions of a BTRS GS of a 3BSC based doubly-connected system in an external magnetic field. Depending on its parameters, a magnetic flux can induce various current density leaps, connected with adiabatic or non-adiabatic transitions from BTRS to non-BTRS states and vice versa. The current induced magnetic flux response of samples with a doubly-connected geometry e.g. as a thin tube provides a suitable experimental tool for the detection of BTRS GS.

  10. 2,3-Butanedione monoxime attenuates the β-adrenergic response of the L-type Ca2+ current in rat ventricular cardiomyocytes

    Directory of Open Access Journals (Sweden)

    Julio Alvarez-Collazo

    2016-12-01

    Full Text Available Context: 2,3-Butanedione monoxime (BDM, an uncoupler of cardiac contraction, is commonly used in enzymatic dissociations to prevent hypercontraction of cardiomyocytes and in cardioplegic solutions to decrease oxygen demand during surgery. However, BDM affects multiple cellular systems including the L-type Ca2+ current (ICaL. If its phosphatase activity is the mechanism underlying the decrease ICaL in cardiomyocytes is a still unresolved question. Aims: To study the effects of BDM on ICaL of rat ventricular cardiomyocytes focusing our attention on the response of ICaL to β-adrenergic stimulation. Methods: The whole-cell patch-clamp method was used to study ICaL in enzymatically dissociated rat ventricular cardiomyocytes. Results: Extracellular BDM (5 mM decreased peak ICaL by ≈45%, slowed its fast inactivation but accelerated its slow inactivation. Cardiomyocytes incubated in BDM (≥ 30 min; 5 mM perfused with normal extracellular solution, showed normal ICaL properties. However, extracellular BDM (in cardiomyocytes incubated in BDM or not markedly reduced the response of ICaL to isoproterenol (1 µM. BDM also strongly attenuated the increase of ICaL in cardiomyocytes intracellularly perfused with cyclic AMP (50 µM. Conclusions: The decrease of basal ICaL by BDM is not related to its dephosphorylation action. Its effect on the Ca2+ channel occurs most probably in a site in the extracellular side or within the sarcolemmal membrane. Due to its phosphatase action, BDM strongly attenuates the response of ICaL to β-adrenergic stimulation. These actions of BDM must be taken into account both for its use in the dissociation of cardiomyocytes and in cardioplegic solutions and myocardial preservation.

  11. Determination of platinum-group metals and lead in vegetable environmental bio-monitors by voltammetric and spectroscopic techniques: critical comparison.

    Science.gov (United States)

    Locatelli, Clinio; Melucci, Dora; Torsi, Giancarlo

    2005-08-01

    This paper reports voltammetric sequential determination of Pt(II), Pd(II), and Rh(III), by square-wave adsorption stripping voltammetry (SWAdSV), and Pb(II), by square-wave anodic stripping voltammetry (SWASV), in vegetable environmental matrices. Analytical procedures were verified by the analysis of the standard reference materials: Olive Leaves BCR-CRM 062 and Tomato Leaves NIST-SRM 1573a. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were always less than 6% and the limits of detection (LOD) for each element were below 0.096 mug g(-1). Once set up on the standard reference materials, the analytical procedure was transferred and applied to laurel leaves sampled in proximity to a superhighway and in the Po river mouth area. A critical comparison with spectroscopic measurements is discussed.

  12. Inappropriate Use of the Quasi-Reversible Electrode Kinetic Model in Simulation-Experiment Comparisons of Voltammetric Processes That Approach the Reversible Limit

    KAUST Repository

    Simonov, Alexandr N.

    2014-08-19

    Many electrode processes that approach the "reversible" (infinitely fast) limit under voltammetric conditions have been inappropriately analyzed by comparison of experimental data and theory derived from the "quasi-reversible" model. Simulations based on "reversible" and "quasi-reversible" models have been fitted to an extensive series of a.c. voltammetric experiments undertaken at macrodisk glassy carbon (GC) electrodes for oxidation of ferrocene (Fc0/+) in CH3CN (0.10 M (n-Bu)4NPF6) and reduction of [Ru(NH 3)6]3+ and [Fe(CN)6]3- in 1 M KCl aqueous electrolyte. The confidence with which parameters such as standard formal potential (E0), heterogeneous electron transfer rate constant at E0 (k0), charge transfer coefficient (α), uncompensated resistance (Ru), and double layer capacitance (CDL) can be reported using the "quasi- reversible" model has been assessed using bootstrapping and parameter sweep (contour plot) techniques. Underparameterization, such as that which occurs when modeling CDL with a potential independent value, results in a less than optimal level of experiment-theory agreement. Overparameterization may improve the agreement but easily results in generation of physically meaningful but incorrect values of the recovered parameters, as is the case with the very fast Fc0/+ and [Ru(NH3)6]3+/2+ processes. In summary, for fast electrode kinetics approaching the "reversible" limit, it is recommended that the "reversible" model be used for theory-experiment comparisons with only E0, R u, and CDL being quantified and a lower limit of k 0 being reported; e.g., k0 ≥ 9 cm s-1 for the Fc0/+ process. © 2014 American Chemical Society.

  13. Response ofPinus koraiensisseedling growth to different light condi-tions based on the assessment of photosynthesis in current and one-year-old needles

    Institute of Scientific and Technical Information of China (English)

    Jiaojun Zhu; Kai Wang; Yirong Sun; Qiaoling Yan

    2014-01-01

    As one of the three major five-leaved pines in the northern hemisphere,Pinus koraiensis is the most important dominant tree species in the natural mixed-broadleaved Korean pine forests. However, the regeneration ofP. koraiensisunder the canopy of secondary forest stands is poor because of the light limitation. This study was conducted to understand howP. koraiensisseedlings adapt to different light intensities and what would be the optimum light level for their establishment and growth. Three repetition plots with four light intensities (15%, 30%, 60% and 100% of the natural incident irradiances, achieved by suspending layers of black nylon net above and surrounding the plots) were set up under natural climate conditions in a montane region in eastern Liaoning Province, Northeast China. A total of 80P. koraiensis seedlings with similar height and root collar diameter were transplanted into four plots. After one year of acclimation to the specific light conditions, the seasonal variations of the photosynthetic variables and needle traits of the current and one-year-old needles, and the growth parameters were observed under four light intensities. The results indicated that: (1) The seedling at 60% treatment exhibited the greatest growth, which agreed with the response of the light-saturated photosynthetic rates (Amax) and the dark respiration rate (Rd) in the current and one-year-old needles, i.e.,Rd at 60% treatment was significantly lower than that at 100% treatment, but Amax did not differ between the seedlings at 100% and 60% treatments. (2) TheP. koraiensis seedlings have a certain photosynthetic plasticity to adapt the light conditions by adjusting their needle traits and regulating the physiological processes, becauseAmax,Rd, light saturation point and compensation point, the needle mass area, needle nitrogen and chlorophyll contents were significantly (p<0.05) correlated with the light intensities. Especially,Amax at 100% and 60% treatments was

  14. Ocean current data measured by the Acoustic Doppler Current Profiler (ADCP) aboard the Development Driller III from 2010-05-31 to 2010-07-04 in the Gulf of Mexico in response to the Deepwater Horizon oil spill (NODC Accession 0083634)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Ocean current data were collected by ADCP aboard the Discoverer Enterprise in the Gulf of Mexico in response to the Deepwater Horizon oil spill event on April 20,...

  15. Ocean current data measured by the Acoustic Doppler Current Profiler (ADCP) aboard the Discoverer Enterprise oil platform from May 23, 2010 to July 04, 2010 in the Gulf of Mexico in response to the Deepwater Horizon oil spill (NODC Accession 0083684)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Ocean current data were collected by ADCP aboard the Discoverer Enterprise in the Gulf of Mexico in response to the Deepwater Horizon oil spill event on April 20,...

  16. Sensitive Adsorptive Voltammetric Method for Determination of Bisphenol A by Gold Nanoparticle/Polyvinylpyrrolidone-Modified Pencil Graphite Electrode

    Directory of Open Access Journals (Sweden)

    Yesim Tugce Yaman

    2016-05-01

    Full Text Available A novel electrochemical sensor gold nanoparticle (AuNP/polyvinylpyrrolidone (PVP modified pencil graphite electrode (PGE was developed for the ultrasensitive determination of Bisphenol A (BPA. The gold nanoparticles were electrodeposited by constant potential electrolysis and PVP was attached by passive adsorption onto the electrode surface. The electrode surfaces were characterized by electrochemical impedance spectroscopy (EIS and scanning electron microscopy (SEM. The parameters that affected the experimental conditions were researched and optimized. The AuNP/PVP/PGE sensor provided high sensitivity and selectivity for BPA recognition by using square wave adsorptive stripping voltammetry (SWAdSV. Under optimized conditions, the detection limit was found to be 1.0 nM. This new sensor system offered the advantages of simple fabrication which aided the expeditious replication, low cost, fast response, high sensitivity and low background current for BPA. This new sensor system was successfully tested for the detection of the amount of BPA in bottled drinking water with high reliability.

  17. A novel voltammetric sensor based on carbon nanotubes and nanoparticles of antimony tin oxide for the determination of ractopamine.

    Science.gov (United States)

    Baytak, Aysegul Kutluay; Teker, Tugce; Duzmen, Sehriban; Aslanoglu, Mehmet

    2016-02-01

    An electrochemical sensor was prepared by the modification of a glassy carbon electrode (GCE) with carbon nanotubes (CNTs) and nanoparticles of antimony tin oxide (ATO). The surface layer was characterized by scanning electronmicroscopy (SEM), energy dispersive X-ray diffraction method (EDX) and ATR FT-IR spectroscopy. The proposed electrode was assessed in respect to the electro-oxidation of ractopamine. Compared with a bare GCE and a GCE electrode modified with CNTs, the ATONPs/CNTs/GCE exhibited a great catalytic activity towards the oxidation of ractopamine with a well-defined anodic peak at 600 mV. The current response was linear with the concentration of ractopamine over the range from 10 to 240 nM with a detection limit of 3.3 nM. The proposed electrode enabled the selective determination of ractopamine in the presence of high concentrations of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The proposed electrode was successfully applied for the determination of ractopamine in feed and urine samples. The sensitive and selective determination of ractopamine makes the developed method of great interest for monitoring its therapeutic use and doping control purposes.

  18. Cyclic voltammetric acetylcholinesterase biosensor for the detection of captan in apple samples with the aid of chemometrics.

    Science.gov (United States)

    Nesakumar, Noel; Sethuraman, Swaminathan; Krishnan, Uma Maheswari; Rayappan, John Bosco Balaguru

    2015-06-01

    The presence of captan residues in apples shows high toxicity, which often causes eye and skin irritation, dermatitis, conjunctivitis, and vomiting in humans. In this context, an electrochemical biosensor based on acetylcholinesterase (AChE) immobilized on a ZnO nanorod interface has been proposed. In this work, Hill, dose-response, and first-, second-, and third-order polynomial regression models were successfully applied and the prediction ability of these models was tested with the use of current density obtained from the cyclic voltammograms of appropriate captan solutions. The Pt/ZnO/AChE bioelectrode showed a high sensitivity of 0.538 μA cm(-2) μM(-1) in the linear range from 0.05 to 25.0 μM with a limit of detection of 107 nM. The recovery results were observed between 98.4 and 102.4 % from the apple sample. This work provides a new promising tool for the detection of captan in apple samples.

  19. Transcranial direct current stimulation combined with aerobic exercise to optimize analgesic responses in fibromyalgia: A randomized placebo-controlled clinical trial

    Directory of Open Access Journals (Sweden)

    Mariana Emerenciano Mendonça

    2016-03-01

    Full Text Available Fibromyalgia is a chronic pain syndrome that is associated with maladaptive plasticity in neural central circuits. One of the neural circuits that are involved in pain in fibromyalgia is the primary motor cortex. We tested a combination intervention that aimed to modulate the motor system: transcranial direct current stimulation (tDCS of the primary motor cortex (M1 and aerobic exercise (AE. In this phase II, sham-controlled randomized clinical trial, 45 subjects were assigned to 1 of 3 groups: tDCS + AE, AE only, and tDCS only. The following outcomes were assessed: intensity of pain, level of anxiety, quality of life, mood, pressure pain threshold, and cortical plasticity, as indexed by transcranial magnetic stimulation. There was a significant effect for the group-time interaction for intensity of pain, demonstrating that tDCS/AE was superior to AE (F(13,364=2.25, p=0.007 and tDCS (F(13.364=2.33, p=0.0056 alone. Post hoc adjusted analysis showed a difference between tDCS/AE and tDCS group after the first week of stimulation and after one month intervention period (p=0.02 and p=0.03, respectively. Further, after treatment there was a significant difference between groups in anxiety and mood levels. The combination treatment effected the greatest response. The three groups had no differences regarding responses in motor cortex plasticity, as assessed by TMS. The combination of tDCS with aerobic exercise is superior compared with each individual intervention (cohen’s d effect sizes > 0.55. The combination intervention had a significant effect on pain, anxiety and mood. Based on the similar effects on cortical plasticity outcomes, the combination intervention might have affected other neural circuits, such as those that control the affective-emotional aspects of pain.

  20. Impaired beta-adrenergic response and decreased L-type calcium current of hypertrophied left ventricular myocytes in postinfarction heart failure

    Directory of Open Access Journals (Sweden)

    R.M. Saraiva

    2003-05-01

    Full Text Available Infarct-induced heart failure is usually associated with cardiac hypertrophy and decreased ß-adrenergic responsiveness. However, conflicting results have been reported concerning the density of L-type calcium current (I Ca(L, and the mechanisms underlying the decreased ß-adrenergic inotropic response. We determined I Ca(L density, cytoplasmic calcium ([Ca2+]i transients, and the effects of ß-adrenergic stimulation (isoproterenol in a model of postinfarction heart failure in rats. Left ventricular myocytes were obtained by enzymatic digestion 8-10 weeks after infarction. Electrophysiological recordings were obtained using the patch-clamp technique. [Ca2+]i transients were investigated via fura-2 fluorescence. ß-Adrenergic receptor density was determined by [³H]-dihydroalprenolol binding to left ventricle homogenates. Postinfarction myocytes showed a significant 25% reduction in mean I Ca(L density (5.7 ± 0.28 vs 7.6 ± 0.32 pA/pF and a 19% reduction in mean peak [Ca2+]i transients (0.13 ± 0.007 vs 0.16 ± 0.009 compared to sham myocytes. The isoproterenol-stimulated increase in I Ca(L was significantly smaller in postinfarction myocytes (Emax: 63.6 ± 4.3 vs 123.3 ± 0.9% in sham myocytes, but EC50 was not altered. The isoproterenol-stimulated peak amplitude of [Ca2+]i transients was also blunted in postinfarction myocytes. Adenylate cyclase activation through forskolin produced similar I Ca(L increases in both groups. ß-Adrenergic receptor density was significantly reduced in homogenates from infarcted hearts (Bmax: 93.89 ± 20.22 vs 271.5 ± 31.43 fmol/mg protein in sham myocytes, while Kd values were similar. We conclude that postinfarction myocytes from large infarcts display reduced I Ca(L density and peak [Ca2+]i transients. The response to ß-adrenergic stimulation was also reduced and was probably related to ß-adrenergic receptor down-regulation and not to changes in adenylate cyclase activity.

  1. A FRAME response to the Draft Report on Alternative (Non-animal) Methods for Cosmetics Testing: Current Status and Future Prospects--2010.

    Science.gov (United States)

    Balls, Michael; Clothier, Richard

    2010-10-01

    This response on behalf of FRAME to the European Commission's consultation on the five chapters of the Draft Report on Alternative (Non-animal) Methods for Cosmetics Testing: Current Status and Future Prospects--2010, is via a Comment in ATLA, rather than via the template supplied by the Commission. This is principally so that a number of general points about cosmetic ingredient testing can be made. It is concluded that the five draft chapters do not provide a credible basis for the Commission's forthcoming report to the European Parliament and the European Council on the five cosmetic ingredient safety issues for which the 7th Amendment to the Cosmetic Directive's ban on animal testing was postponed until 2013. This is mainly because there is insufficient focus in the draft chapters on the specific nature of cosmetic ingredients, their uses, their local effects and metabolism at their sites of application, and, in particular, on whether their possible absorption into the body would be likely to lead to their accumulation in target sites at levels approaching Thresholds of Toxicological Concern. Meanwhile, there continues to be uncertainty about how the provisions of the Cosmetics Directive should be applied, given the requirements of the REACH system and directives concerned with the safety of other chemicals and products. © 2010 FRAME.

  2. Seasonal effects in the ionosphere-thermosphere response to the precipitation and field-aligned current variations in the cusp region

    Directory of Open Access Journals (Sweden)

    A. A. Namgaladze

    Full Text Available The seasonal effects in the thermosphere and ionosphere responses to the precipitating electron flux and field-aligned current variations, of the order of an hour in duration, in the summer and winter cusp regions have been investigated using the global numerical model of the Earth's upper atmosphere. Two variants of the calculations have been performed both for the IMF By < 0. In the first variant, the model input data for the summer and winter precipitating fluxes and field-aligned currents have been taken as geomagnetically symmetric and equal to those used earlier in the calculations for the equinoctial conditions. It has been found that both ionospheric and thermospheric disturbances are more intensive in the winter cusp region due to the lower conductivity of the winter polar cap ionosphere and correspondingly larger electric field variations leading to the larger Joule heating effects in the ion and neutral gas temperature, ion drag effects in the thermospheric winds and ion drift effects in the F2-region electron concentration. In the second variant, the calculations have been performed for the events of 28–29 January, 1992 when precipitations were weaker but the magnetospheric convection was stronger than in the first variant. Geomagnetically asymmetric input data for the summer and winter precipitating fluxes and field-aligned currents have been taken from the patterns derived by combining data obtained from the satellite, radar and ground magnetometer observations for these events. Calculated patterns of the ionospheric convection and thermospheric circulation have been compared with observations and it has been established that calculated patterns of the ionospheric convection for both winter and summer hemispheres are in a good agreement with the observations. Calculated patterns of the thermospheric circulation are in a good agreement with the average circulation for the Southern (summer Hemisphere obtained

  3. Determinação voltamétrica do herbicida glifosato em águas naturais utilizando eletrodo de cobre Voltammetric determination of glyphosate in natural waters with a copper electrode

    Directory of Open Access Journals (Sweden)

    Andresa Fabiana Garcia

    2007-01-01

    Full Text Available The aim of this work was to investigate the copper electrode behavior in the voltammetric determination of glyphosate. The best conditions for this determination are phosphate buffer 0.05 mol L-1 and pH 7.3, and the peak potential is observed at 187 mV. LD and LQ values are 59 µg L-1 e 196 µg L-1, respectively. A water sample was analysed for glyphosate and identical results were obtained by using the analytical curve and the standard addition method. The comparison with a voltammetric method with Hg electrode, after a reaction with nitrite, showed quite concordant results for the analysis of the surface water sample. Therefore, the proposed method can be applied to direct determinations of the herbicide in waters, decreasing the time of analysis; besides, the method is in agreement with the "green chemistry" concept.

  4. A novel method for modeling the neutron time of flight (nTOF) detector response in current mode to inertial confinement fusion experiments.

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, Alan J. [University of New Mexico, Albuquerque, NM; Cooper, Gary Wayne [University of New Mexico, Albuquerque, NM; Ruiz, Carlos L.; Chandler, Gordon Andrew; Fehl, David Lee; Hahn, Kelly Denise; Leeper, Ramon Joe; Smelser, Ruth Marie; Torres, Jose A.

    2013-09-01

    There are several machines in this country that produce short bursts of neutrons for various applications. A few examples are the Zmachine, operated by Sandia National Laboratories in Albuquerque, NM; the OMEGA Laser Facility at the University of Rochester in Rochester, NY; and the National Ignition Facility (NIF) operated by the Department of Energy at Lawrence Livermore National Laboratory in Livermore, California. They all incorporate neutron time of flight (nTOF) detectors which measure neutron yield, and the shapes of the waveforms from these detectors contain germane information about the plasma conditions that produce the neutrons. However, the signals can also be %E2%80%9Cclouded%E2%80%9D by a certain fraction of neutrons that scatter off structural components and also arrive at the detectors, thereby making analysis of the plasma conditions more difficult. These detectors operate in current mode - i.e., they have no discrimination, and all the photomultiplier anode charges are integrated rather than counted individually as they are in single event counting. Up to now, there has not been a method for modeling an nTOF detector operating in current mode. MCNPPoliMiwas developed in 2002 to simulate neutron and gammaray detection in a plastic scintillator, which produces a collision data output table about each neutron and photon interaction occurring within the scintillator; however, the postprocessing code which accompanies MCNPPoliMi assumes a detector operating in singleevent counting mode and not current mode. Therefore, the idea for this work had been born: could a new postprocessing code be written to simulate an nTOF detector operating in current mode? And if so, could this process be used to address such issues as the impact of neutron scattering on the primary signal? Also, could it possibly even identify sources of scattering (i.e., structural materials) that

  5. The utility and limitations of current web-available algorithms to predict peptides recognized by CD4 T cells in response to pathogen infection #

    Science.gov (United States)

    Chaves, Francisco A.; Lee, Alvin H.; Nayak, Jennifer; Richards, Katherine A.; Sant, Andrea J.

    2012-01-01

    The ability to track CD4 T cells elicited in response to pathogen infection or vaccination is critical because of the role these cells play in protective immunity. Coupled with advances in genome sequencing of pathogenic organisms, there is considerable appeal for implementation of computer-based algorithms to predict peptides that bind to the class II molecules, forming the complex recognized by CD4 T cells. Despite recent progress in this area, there is a paucity of data regarding their success in identifying actual pathogen-derived epitopes. In this study, we sought to rigorously evaluate the performance of multiple web-available algorithms by comparing their predictions and our results using purely empirical methods for epitope discovery in influenza that utilized overlapping peptides and cytokine Elispots, for three independent class II molecules. We analyzed the data in different ways, trying to anticipate how an investigator might use these computational tools for epitope discovery. We come to the conclusion that currently available algorithms can indeed facilitate epitope discovery, but all shared a high degree of false positive and false negative predictions. Therefore, efficiencies were low. We also found dramatic disparities among algorithms and between predicted IC50 values and true dissociation rates of peptide:MHC class II complexes. We suggest that improved success of predictive algorithms will depend less on changes in computational methods or increased data sets and more on changes in parameters used to “train” the algorithms that factor in elements of T cell repertoire and peptide acquisition by class II molecules. PMID:22467652

  6. Efficient Preparation of Streptochlorin from Marine Streptomyces sp. SYYLWHS-1-4 by Combination of Response Surface Methodology and High-Speed Counter-Current Chromatography

    Directory of Open Access Journals (Sweden)

    Lin Li

    2016-05-01

    Full Text Available Since first isolated from the lipophilic extract of Streptomyces sp. SF2583, streptochlorin, has attracted a lot of attention because of its various pharmacological properties, such as antibiotic, antiallergic, antitumor, and anti-inflammatory activities. For the efficient preparation of streptochlorin from a producing strain Streptomyces sp. SYYLWHS-1-4, we developed a combinative method by using response surface methodology (RSM and high-speed counter-current chromatography (HSCCC. In the fermentation process, we used RSM to optimize the condition for the efficient accumulation of streptochlorin, and the optimal parameters were: yeast extract 1.889 g/L, soluble starch 8.636 g/L, K2HPO4 0.359 g/L, CaCl2 2.5 g/L, MgSO4 0.625 g/L, marine salt 25 g/L, medium volume 50%, initial pH value 7.0, temperature 27.5 °C, which enhanced streptochlorin yield by 17.7-fold. During the purification process, the preparative HSCCC separation was performed using a petroleum ether–ethyl acetate–methanol–water (9:0.8:5:5, v/v/v/v biphasic solvent system, where 300 mg of crude sample yielded 16.5 mg streptochlorin with over 95% purity as determined by UPLC. Consequently, the combination method provided a feasible strategy for highly effective preparation of streptochlorin, which ensured the supply of large amounts of streptochlorin for in vivo pharmacological assessments or other requirements.

  7. 振荡磁场量子点中自旋流的交流响应%Alternating response of spin current in a magnetic-oscillating quantum dot

    Institute of Scientific and Technical Information of China (English)

    宋红岩; 宋小龙; 张爱芳; 吴留坡; 施耀铭

    2007-01-01

    We investigate alternating response of the spin current in a quantum dot system coupled to a normal metal electrode, to which an alternating driving voltage and a pumping rotating magnetic field are applied. The expression of the time-averaged spin current and its differential is obtained based on a non-equilibrium Green's function method. We find that for a given rotating frequency, the spin current increases rapidly and appears to have small steps when the driven frequency increases. As the driven frequency is further increasing, the spin current can be significantly enhanced and approaches a stable value. The photon-assisted processes bring about interesting features of spin current. The influence of the gate voltage and temperature on the spin current is examined in detail.

  8. Spin current

    CERN Document Server

    Valenzuela, Sergio O; Saitoh, Eiji; Kimura, Takashi

    2012-01-01

    In a new branch of physics and technology called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called 'spin current', are manipulated and controlled together. This book provides an introduction and guide to the new physics and application of spin current.

  9. Electrochemical behavior and voltammetric determination of acetaminophen based on glassy carbon electrodes modified with poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite films.

    Science.gov (United States)

    Zhu, Wencai; Huang, Hui; Gao, Xiaochun; Ma, Houyi

    2014-12-01

    Poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite film modified glassy carbon electrodes (4-ABA/ERGO/GCEs) were fabricated by a two-step electrochemical method. The electrochemical behavior of acetaminophen at the modified electrode was investigated by means of cyclic voltammetry. The results indicated that 4-ABA/ERGO composite films possessed excellent electrocatalytic activity towards the oxidation of acetaminophen. The electrochemical reaction of acetaminophen at 4-ABA/ERGO/GCE is proved to be a surface-controlled process involving the same number of protons and electrons. The voltammetric determination of acetaminophen performed with the 4-ABA/ERGO modified electrode presents a good linearity in the range of 0.1-65 μM with a low detection limit of 0.01 μM (S/N=3). In the case of using the 4-ABA/ERGO/GCE, acetaminophen and dopamine can be simultaneously determined without mutual interference. Furthermore, the 4-ABA/ERGO/GCE has good reproducibility and stability, and can be used to determine acetaminophen in tablets.

  10. Development of a Nafion/MWCNT-SPCE-Based Portable Sensor for the Voltammetric Analysis of the Anti-Tuberculosis Drug Ethambutol

    Directory of Open Access Journals (Sweden)

    Rosa A. S. Couto

    2016-06-01

    Full Text Available Herein we describe the development, characterization and application of an electrochemical sensor based on the use of Nafion/MWCNT-modified screen-printed carbon electrodes (SPCEs for the voltammetric detection of the anti-tuberculosis (anti-TB drug ethambutol (ETB. The electrochemical behaviour of the drug at the surface of the developed Nafion/MWCNT-SPCEs was studied through cyclic voltammetry (CV and square wave voltammetry (SWV techniques. Electrochemical impedance spectroscopy (EIS and scanning electron microscopy (SEM were employed to characterize the modified surface of the electrodes. Results showed that, compared to both unmodified and MWCNTs-modified SPCEs, negatively charged Nafion/MWCNT-SPCEs remarkably enhanced the electrochemical sensitivity and selectivity for ETB due to the synergistic effect of the electrostatic interaction between cationic ETB molecules and negatively charged Nafion polymer and the inherent electrocatalytic properties of both MWCNTs and Nafion. Nafion/MWCNT-SPCEs provided excellent biocompatibility, good electrical conductivity, low electrochemical interferences and a high signal-to-noise ratio, providing excellent performance towards ETB quantification in microvolumes of human urine and human blood serum samples. The outcomes of this paper confirm that the Nafion/MWCNT-SPCE-based device could be a potential candidate for the development of a low-cost, yet reliable and efficient electrochemical portable sensor for the low-level detection of this antimycobacterial drug in biological samples.

  11. Development of a voltammetric procedure for assay of the antihistamine drug hydroxyzine at a glassy carbon electrode: Quantification and pharmacokinetic studies.

    Science.gov (United States)

    Beltagi, A M; Abdallah, O M; Ghoneim, M M

    2008-01-15

    An electrochemical study of hydroxyzine at a glassy carbon electrode was carried out in the Britton-Robinson universal buffer of pH 2-11. Hydroxyzine was oxidized in a single two-electron irreversible process controlled mainly by adsorption. A simple, sensitive and time-saving square-wave adsorptive anodic stripping voltammetric procedure has been developed for determination of hydroxyzine in its commercial tablets and human serum without prior extraction. The optimized procedural conditions were: frequency=120Hz, scan increment=10mV, pulse-amplitude=25mV, accumulation potential=-0.3V, accumulation time=90-300s and a Britton-Robinson universal buffer of pH 4 as a supporting electrolyte. Mean recoveries of 100.5+/-0.71 and 98.6+/-1.12% (n=5) were achieved for assay of hydroxyzine in Atarax 10 and 25mg dosage forms, respectively. Limit of detection of 1.5x10(-8)molL(-1) (5.624ngmL(-1)) and limit of quantitation of 5.0x10(-8)molL(-1) (18.746ngmL(-1)) were achieved in human serum with a mean recovery of 98.4+/-1.22%, without prior extraction of the drug. Moreover, the described procedure was applied for evaluating the pharmacokinetic parameters of hydroxyzine in plasma of two healthy volunteers after administration of a single oral dose (Atarax)-25mg).

  12. Sensors properties of an alkylamine-intercalated kaolinite material towards the voltammetric preconcentration of [Ru(CN)6]4- at a clay-modified electrode

    Energy Technology Data Exchange (ETDEWEB)

    Tonle, I.K. [Ottawa Univ., ON (Canada). Dept. of Chemistry, Center for Catalysis Research and Innovation; Yanoude Univ. (Cameroon). Laboratoire de Chimie Analytique, Faculte des Sciences; Dschang Univ. (Cameroon). Dept. de Chimie; Bouwe, B.; Rose, G.; Ngameni, E. [Yanoude Univ. (Cameroon). Laboratoire de Chimie Analytique, Faculte des Sciences; Detellier, C. [Yanoude Univ. (Cameroon). Laboratoire de Chimie Analytique, Faculte des Sciences

    2008-07-01

    This study discussed the sensor properties of a kaolinite material in relation to the voltammetric preconcentration of ruthenium (Ru) anions in a clay-modified electrode. An organoclay was intercalated at room temperature with a layer of hexylamine. Dimethylsulfoxide (DMSO) was intercalated between the clay layers and displaced in wet conditions by the akylamine. The modified clay was then characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The analyses confirmed the incorporation of the hexylamine between the kaolinite platelets. The organokaolinite was then studied for use as a preconcentration agent when coated on the active surface of a glassy carbon electrode for the accumulation of [Ru(CN)6]4- anions in a hydrochloric acid medium. Factors that influenced the conductivity of the film and the diffusion of the electroactive species within the film included the concentration of the electrolyte, and the redox probe. The study showed that kaolinite can be used as a material in electrochemical sensors.

  13. Electrochemical behavior and voltammetric determination of acetaminophen based on glassy carbon electrodes modified with poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite films

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Wencai [Key Laboratory for Colloid and Interface Chemistry of State Education Ministry, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (China); School of Chemistry and Chemical Engineering, Qilu Normal University, Jinan 250013 (China); Huang, Hui; Gao, Xiaochun [Key Laboratory for Colloid and Interface Chemistry of State Education Ministry, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (China); Ma, Houyi, E-mail: hyma@sdu.edu.cn [Key Laboratory for Colloid and Interface Chemistry of State Education Ministry, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100 (China)

    2014-12-01

    Poly(4-aminobenzoic acid)/electrochemically reduced graphene oxide composite film modified glassy carbon electrodes (4-ABA/ERGO/GCEs) were fabricated by a two-step electrochemical method. The electrochemical behavior of acetaminophen at the modified electrode was investigated by means of cyclic voltammetry. The results indicated that 4-ABA/ERGO composite films possessed excellent electrocatalytic activity towards the oxidation of acetaminophen. The electrochemical reaction of acetaminophen at 4-ABA/ERGO/GCE is proved to be a surface-controlled process involving the same number of protons and electrons. The voltammetric determination of acetaminophen performed with the 4-ABA/ERGO modified electrode presents a good linearity in the range of 0.1–65 μM with a low detection limit of 0.01 μM (S/N = 3). In the case of using the 4-ABA/ERGO/GCE, acetaminophen and dopamine can be simultaneously determined without mutual interference. Furthermore, the 4-ABA/ERGO/GCE has good reproducibility and stability, and can be used to determine acetaminophen in tablets. - Highlights: • The 4-ABA/ERGO/GCE was fabricated by a two-step electrochemical method. • Electrochemical behavior of acetaminophen at the 4-ABA/ERGO/GCE was investigated. • The electrochemical sensor exhibited a low detection limit and good selectivity. • This sensor was applied to the detection of acetaminophen in commercial tablets.

  14. Nanogold-penetrated poly(amidoamine) dendrimer for enzyme-free electrochemical immunoassay of cardiac biomarker using cathodic stripping voltammetric method.

    Science.gov (United States)

    Zhang, Bo; Zhang, Yi; Liang, Wenbin; Cui, Bin; Li, Jiabei; Yu, Xuejun; Huang, Lan

    2016-01-21

    Methods based on immunoassays have been developed for cardiac biomarkers, but most involve the low sensitivity and are unsuitable for early disease diagnosis. Herein we design an electrochemical immunoassay for sensitive detection of myoglobin (a cardiac biomarker for acute myocardial infarction) by using nanogold-penetrated poly(amidoamine) dendrimer (AuNP-PAMAM) for signal amplification without the need of natural enzymes. The assay was carried out on the monoclonal mouse anti-myoglobin (capture) antibody-anchored glassy carbon electrode using polyclonal rabbit anti-myoglobin (detection) antibody-labeled AuNP-PAMAM as the signal tag. In the presence of target myoglobin, the sandwiched immunocomplex could be formed between capture antibody and detection antibody. Accompanying AuNP-PAMAM, the carried gold nanoparticles could be directly determined via stripping voltammetric method under acidic conditions. Under optimal conditions, the detectable electrochemical signal increased with the increasing target myoglobin in the sample within a dynamic working range from 0.01 to 500 ng mL(-1) with a detection limit of 3.8 pg mL(-1). The electrochemical immunoassay also exhibited high specificity and good precision toward target myoglobin. Importantly, our strategy could be applied for quantitative monitoring of myoglobin in human serum specimens, giving well matched results with those obtained from commercialized enzyme-linked immunosorbent assay (ELISA) method.

  15. Aging time and brand determination of pasteurized milk using a multisensor e-nose combined with a voltammetric e-tongue.

    Science.gov (United States)

    Bougrini, Madiha; Tahri, Khalid; Haddi, Zouhair; El Bari, Nezha; Llobet, Eduard; Jaffrezic-Renault, Nicole; Bouchikhi, Benachir

    2014-12-01

    A combined approach based on a multisensor system to get additional chemical information from liquid samples through the analysis of the solution and its headspace is illustrated and commented. In the present work, innovative analytical techniques, such as a hybrid e-nose and a voltammetric e-tongue were elaborated to differentiate between different pasteurized milk brands and for the exact recognition of their storage days through the data fusion technique of the combined system. The Principal Component Analysis (PCA) has shown an acceptable discrimination of the pasteurized milk brands on the first day of storage, when the two instruments were used independently. Contrariwise, PCA indicated that no clear storage day's discrimination can be drawn when the two instruments are applied separately. Mid-level of abstraction data fusion approach has demonstrated that results obtained by the data fusion approach outperformed the classification results of the e-nose and e-tongue taken individually. Furthermore, the Support Vector Machine (SVM) supervised method was applied to the new subset and confirmed that all storage days were correctly identified. This study can be generalized to several beverage and food products where their quality is based on the perception of odor and flavor. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro do Carmo, Devaney, E-mail: docarmo@dfq.feis.unesp.br [Faculdade de Engenharia de Ilha Solteira UNESP - Univ Estadual Paulista, Departamento de Fisica e Quimica, Av. Brasil Centro, 56 CEP 15385-000, Ilha Solteira, SP (Brazil); Paim, Leonardo Lataro [Instituto de Quimica de Araraquara UNESP - Univ Estadual Paulista, Rua Francisco Degni s/n, CEP 14801-970, Araraquara, SP (Brazil); Metzker, Gustavo [Instituto de Quimica de Sao Carlos, Universidade de Sao Paulo, Av. Trabalhador Sao-carlense, 400, 13566-590 Sao Carlos, SP (Brazil); Dias Filho, Newton Luiz [Faculdade de Engenharia de Ilha Solteira UNESP - Univ Estadual Paulista, Departamento de Fisica e Quimica, Av. Brasil Centro, 56 CEP 15385-000, Ilha Solteira, SP (Brazil); Stradiotto, Nelson Ramos [Instituto de Quimica de Araraquara UNESP - Univ Estadual Paulista, Rua Francisco Degni s/n, CEP 14801-970, Araraquara, SP (Brazil)

    2010-09-15

    This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E{sub 1/2}{sup ox}) = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v=20mVs{sup -1}). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 x 10{sup -4} to 4.0 x 10{sup -3} mol L{sup -1} for the determination of nitrite, with a detection limit of 2.1 x 10{sup -4} mol L{sup -1} and the amperometric sensitivity of 8.04 mA/mol L{sup -1}.

  17. Voltammetric determination of Se(IV) and Se(VI) in saline samples-Studies with seawater, hydrothermal and hemodialysis fluids

    Energy Technology Data Exchange (ETDEWEB)

    Nascimento, Paulo C. do, E-mail: npaulo@quimica.ufsm.br [Departamento de Quimica, Universidade Federal de Santa Maria, C.P. 5051, 97105-970 Santa Maria, RS (Brazil); Jost, Cristiane L.; Carvalho, Leandro M. de; Bohrer, Denise [Departamento de Quimica, Universidade Federal de Santa Maria, C.P. 5051, 97105-970 Santa Maria, RS (Brazil); Koschinsky, Andrea [School of Engineering and Science, Geosciences and Astrophysics, Jacobs University Bremen GmbH, P.O. Box 750561, D-28725 Bremen (Germany)

    2009-08-26

    Determination of Se(IV) and Se(VI) in high saline media was investigated by cathodic stripping voltammetry (CSV). The voltammetric method was applied to assay selenium in seawater, hydrothermal and hemodialysis fluids. The influence of ionic strength on selenium determination is discussed. The CSV method was based on the co-electrodeposition of Se(IV) with Cu(II) ions and Se(VI) determined by difference after sample UV-irradiation for photolytic selenium reduction. UV-irradiation was also used as sample pre-treatment for organic matter decomposition. Detection limit of 0.030 {mu}g L{sup -1} (240 s deposition time) and relative standard deviation (RSD) of 6.19% (n = 5) for 5.0 {mu}g L{sup -1} of Se(IV) were calculated. Linear calibration range for selenium was observed from 1.0 to 100.0 {mu}g L{sup -1}. Concerning the pre-treatment step, best results were obtained by using 60 min UV-irradiation interval in H{sub 2}O{sub 2}/HCl medium. Se(VI) was reduced to the Se(IV) electroactive species with recoveries between 91.7% and 112.9%. Interferents were also investigated.

  18. Impact of Microdialysis Probes on Vasculature and Dopamine in the Rat Striatum: a Combined Fluorescence and Voltammetric Study

    OpenAIRE

    Mitala, Christina. M.; Wang, Yuexiang; Borland, Laura M.; Jung, Moon; Shand, Stuart; Watkins, Simon; Weber, Stephen G.; Michael, Adrian C.

    2008-01-01

    Measuring extracellular dopamine in the brain of living animals by means of microdialysis and/or voltammetry is a route towards understanding both normal brain function and pathology. Previous reports, however, suggest that the tissue response to implantation of devices may affect the outcome of the measurements. To address the source of the tissue response and its impact on striatal dopamine systems microdialysis probes were placed in the striatum of anesthetized rats. Images obtained by dua...

  19. Responses to atmospheric CO2 concentrations in crop simulation models: a review of current simple and semicomplex representations and options for model development.

    Science.gov (United States)

    Vanuytrecht, Eline; Thorburn, Peter J

    2017-01-30

    Elevated atmospheric CO2 concentrations ([CO2 ]) cause direct changes in crop physiological processes (e.g. photosynthesis and stomatal conductance). To represent these CO2 responses, commonly used crop simulation models have been amended, using simple and semicomplex representations of the processes involved. Yet, there is no standard approach to and often poor documentation of these developments. This study used a bottom-up approach (starting with the APSIM framework as case study) to evaluate modelled responses in a consortium of commonly used crop models and illuminate whether variation in responses reflects true uncertainty in our understanding compared to arbitrary choices of model developers. Diversity in simulated CO2 responses and limited validation were common among models, both within the APSIM framework and more generally. Whereas production responses show some consistency up to moderately high [CO2 ] (around 700 ppm), transpiration and stomatal responses vary more widely in nature and magnitude (e.g. a decrease in stomatal conductance varying between 35% and 90% among models was found for [CO2 ] doubling to 700 ppm). Most notably, nitrogen responses were found to be included in few crop models despite being commonly observed and critical for the simulation of photosynthetic acclimation, crop nutritional quality and carbon allocation. We suggest harmonization and consideration of more mechanistic concepts in particular subroutines, for example, for the simulation of N dynamics, as a way to improve our predictive understanding of CO2 responses and capture secondary processes. Intercomparison studies could assist in this aim, provided that they go beyond simple output comparison and explicitly identify the representations and assumptions that are causal for intermodel differences. Additionally, validation and proper documentation of the representation of CO2 responses within models should be prioritized.

  20. Current surges and seabed erosion near the shelf break in the Canadian Beaufort Sea: A response to wind and ice motion stress

    Science.gov (United States)

    Forest, Alexandre; Osborne, Philip D.; Curtiss, Gregory; Lowings, Malcolm G.

    2016-08-01

    Estimating the erosion potential of seabed sediments and the magnitude of the resulting suspended load in relation to current dynamics near the shelf break is a key issue for better understanding shelf-slope sediment transport. On the outer Mackenzie Shelf (Canadian Beaufort Sea, Arctic Ocean), a thin and discontinuous veneer of recent surficial clays overlie old glaciomarine sediments that further pinch out at the shelf edge. Gas and fluid venting is known to underlie part of sediment instability in the area, but recent mooring-based measurements also indicate that sediments near the shelf break are recurrently remobilized by strong subsurface currents. Here, we relate storms to the development of current surges that resulted in the abrupt resuspension of sediments at two locations along the shelf break. Near-bottom concentrations of suspended sediments were estimated using the acoustic backscatter of high-frequency acoustic Doppler current profilers deployed from September 2011 to September 2013 as part of the Beaufort Regional Environmental Assessment (BREA) program. Near-bottom currents near the shelf edge (140 to 150 m isobaths) were characterized by recurring episodes of elevated velocities (instantaneous speeds up to ~ 40-50 cm s-1) that were extensions of current surges (~ 60-80 cm s-1) occurring in the core of the shelfbreak jet located at ca. 90-120 m. Sudden peaks in suspended sediments (above 100 g m-3) corresponded closely with current surges in the near-bottom boundary layer (fade, such as during the major ice fracturing events of January to March 2013 that were associated with strong and persistent current speeds.

  1. Pulmonary responses in current smokers and ex-smokers following a two hour exposure at rest to clean air and fine ambient air particles.

    Science.gov (United States)

    BACKGROUND: Increased susceptibility of smokers to ambient PM may potentially promote development of COPD and accelerate already present disease. OBJECTIVES: To characterize the acute and subacute lung function response and inflammatory effects of controlled chamber exposure t...

  2. Redução voltamétrica de artemisinina e sua interação com grupo heme (hemina Voltammetric reduction of artemisinin and its interaction with heme (hemin

    Directory of Open Access Journals (Sweden)

    Mauro Aquiles La-Scalea

    2007-09-01

    absence of effective treatment. However, the plasmodium resistance to artemisinin does not show clinical relevance. The drug mechanism of action is associated to the heme group, with free radical formation and endoperoxide moiety breakage. The voltammetric behavior of artemisinin was studied by cyclic and square-wave voltametries. This drug was irreversibly reduced on glassy carbon electrode and the peak potential values are pH independent, however the biggest value of current peak was observed at pH 6.0. The voltammetric behavior of artemisinin was significantly changed in the heme group presence, provoking an anticipation of about 600 mV on cathodic peak. By square-wave voltammetry it was observed that this new peak was sensitive to the hemin concentration, reaching a value around 10 times larger regarding the original cathodic peak of artemisinin, being the concentration of 20 mmol/L for the former and 50 mmol/L for the latter. In addition, results indicated that this electro-catalytic process depends on the Fe(II-hemin formation on the electrode surface, indicating the possible electro-polymerization of hemin on the glassy carbon electrode. This adsorptive effect was evaluated from the superficial concentration (G estimation of the hemin on the working electrode at pH 6.0. The modification of the glassy carbon electrode using hemin showed that the interaction between artemisinin and the heme group predominantly occurs on the electrode surface and not in solution. Therefore, clarifying artemisinin mechanism of action is important in order to contribute for the design and development of new antimalarial agents.

  3. Experimentally-Based Computational Investigation into Beat-To-Beat Variability in Ventricular Repolarization and Its Response to Ionic Current Inhibition.

    Directory of Open Access Journals (Sweden)

    E Pueyo

    Full Text Available Beat-to-beat variability in repolarization (BVR has been proposed as an arrhythmic risk marker for disease and pharmacological action. The mechanisms are unclear but BVR is thought to be a cell level manifestation of ion channel stochasticity, modulated by cell-to-cell differences in ionic conductances. In this study, we describe the construction of an experimentally-calibrated set of stochastic cardiac cell models that captures both BVR and cell-to-cell differences in BVR displayed in isolated canine action potential measurements using pharmacological agents. Simulated and experimental ranges of BVR are compared in control and under pharmacological inhibition, and the key ionic currents determining BVR under physiological and pharmacological conditions are identified. Results show that the 4-aminopyridine-sensitive transient outward potassium current, Ito1, is a fundamental driver of BVR in control and upon complete inhibition of the slow delayed rectifier potassium current, IKs. In contrast, IKs and the L-type calcium current, ICaL, become the major contributors to BVR upon inhibition of the fast delayed rectifier potassium current, IKr. This highlights both IKs and Ito1 as key contributors to repolarization reserve. Partial correlation analysis identifies the distribution of Ito1 channel numbers as an important independent determinant of the magnitude of BVR and drug-induced change in BVR in control and under pharmacological inhibition of ionic currents. Distributions in the number of IKs and ICaL channels only become independent determinants of the magnitude of BVR upon complete inhibition of IKr. These findings provide quantitative insights into the ionic causes of BVR as a marker for repolarization reserve, both under control condition and pharmacological inhibition.

  4. Current limiters

    Energy Technology Data Exchange (ETDEWEB)

    Loescher, D.H. [Sandia National Labs., Albuquerque, NM (United States). Systems Surety Assessment Dept.; Noren, K. [Univ. of Idaho, Moscow, ID (United States). Dept. of Electrical Engineering

    1996-09-01

    The current that flows between the electrical test equipment and the nuclear explosive must be limited to safe levels during electrical tests conducted on nuclear explosives at the DOE Pantex facility. The safest way to limit the current is to use batteries that can provide only acceptably low current into a short circuit; unfortunately this is not always possible. When it is not possible, current limiters, along with other design features, are used to limit the current. Three types of current limiters, the fuse blower, the resistor limiter, and the MOSFET-pass-transistor limiters, are used extensively in Pantex test equipment. Detailed failure mode and effects analyses were conducted on these limiters. Two other types of limiters were also analyzed. It was found that there is no best type of limiter that should be used in all applications. The fuse blower has advantages when many circuits must be monitored, a low insertion voltage drop is important, and size and weight must be kept low. However, this limiter has many failure modes that can lead to the loss of over current protection. The resistor limiter is simple and inexpensive, but is normally usable only on circuits for which the nominal current is less than a few tens of milliamperes. The MOSFET limiter can be used on high current circuits, but it has a number of single point failure modes that can lead to a loss of protective action. Because bad component placement or poor wire routing can defeat any limiter, placement and routing must be designed carefully and documented thoroughly.

  5. Predicting the response of the Amazon rainforest to persistent drought conditions under current and future climates: a major challenge for global land surface models

    Directory of Open Access Journals (Sweden)

    E. Joetzjer

    2014-08-01

    Full Text Available While a majority of Global Climate Models project dryer and longer dry seasons over the Amazon under higher CO2 levels, large uncertainties surround the response of vegetation to persistent droughts in both present-day and future climates. We propose a detailed evaluation of the ability of the ISBACC Land Surface Model to capture drought effects on both water and carbon budgets, comparing fluxes and stocks at two recent ThroughFall Exclusion (TFE experiments performed in the Amazon. We also explore the model sensitivity to different Water Stress Function (WSF and to an idealized increase in CO2 concentration and/or temperature. In spite of a reasonable soil moisture simulation, ISBACC struggles to correctly simulate the vegetation response to TFE whose amplitude and timing is highly sensitive to the WSF. Under higher CO2 concentration, the increased Water Use Efficiency (WUE mitigates the ISBACC's sensitivity to drought. While one of the proposed WSF formulation improves the response of most ISBACC fluxes, except respiration, a parameterization of drought-induced tree mortality is missing for an accurate estimate of the vegetation response. Also, a better mechanistic understanding of the forest responses to drought under a warmer climate and higher CO2 concentration is clearly needed.

  6. Review of current Southern California edison load management programs and proposal for a new market-driven, mass-market, demand-response program

    Energy Technology Data Exchange (ETDEWEB)

    Weller, G.H.

    2002-01-01

    Utility load management programs, including direct load control and interruptible load programs, constitute a large installed base of controllable loads that are employed by utilities as system reliability resources. In response to energy supply shortfalls expected during the summer of 2001, the California Public Utilities Commission in spring 2001 authorized new utility load management programs as well as revisions to existing programs. This report provides an independent review of the designs of these new programs for a large utility (Southern California Edison) and suggests possible improvements to enhance the price responsiveness of the customer actions influenced by these programs. The report also proposes a new program to elicit a mass-market demand response to utility price signals.

  7. Phreatophytic vegetation and groundwater fluctuations: a review of current research and application of ecosystem response modeling with an emphasis on great basin vegetation.

    Science.gov (United States)

    Naumburg, Elke; Mata-Gonzalez, Ricardo; Hunter, Rachael G; McLendon, Terry; Martin, David W

    2005-06-01

    Although changes in depth to groundwater occur naturally, anthropogenic alterations may exacerbate these fluctuations and, thus, affect vegetation reliant on groundwater. These effects include changes in physiology, structure, and community dynamics, particularly in arid regions where groundwater can be an important water source for many plants. To properly manage ecosystems subject to changes in depth to groundwater, plant responses to both rising and falling groundwater tables must be understood. However, most research has focused exclusively on riparian ecosystems, ignoring regions where groundwater is available to a wider range of species. Here, we review responses of riparian and other species to changes in groundwater levels in arid environments. Although decreasing water tables often result in plant water stress and reduced live biomass, the converse is not necessarily true for rising water tables. Initially, rising water tables kill flooded roots because most species cannot tolerate the associated low oxygen levels. Thus, flooded plants can also experience water stress. Ultimately, individual species responses to either scenario depend on drought and flooding tolerance and the change in root system size and water uptake capacity. However, additional environmental and biological factors can play important roles in the severity of vegetation response to altered groundwater tables. Using the reviewed information, we created two conceptual models to highlight vegetation dynamics in areas with groundwater fluctuations. These models use flow charts to identify key vegetation and ecosystem properties and their responses to changes in groundwater tables to predict community responses. We then incorporated key concepts from these models into EDYS, a comprehensive ecosystem model, to highlight the potential complexity of predicting community change under different fluctuating groundwater scenarios. Such models provide a valuable tool for managing vegetation and

  8. Voltammetric studies on mercury behavior in different aqueous solutions for further development of a warning system designed for environmental monitoring

    Directory of Open Access Journals (Sweden)

    Paul-Cristinel Verestiuc

    2014-12-01

    Full Text Available This article presents some results concerning the electrochemical detection of mercury in different aqueous solutions, using the following electrodes: platinum-disk electrode (PDE, carbon paste electrode (CPE and glass carbon electrode (GCE. Using the voltam­metric technique applied on the above mentioned electrodes, the experimental conditi­ons were established in order to obtain the maximum current peaks, in terms of the best analytical characteristics for mercury analyses. The dependence equations of cathodic current intensity on the scan rate were established in the case of mercury ion discharge in each prepared solution of 0.984 mM HgCl2 in different electrolyte background: 0.1 M KCl, 0.1 M H2SO4 and 0.9 % NaCl. Among the three investigated electrodes, the carbon paste electrode presented the highest detection sensitivity toward mercury ions in the aqueous solution. It was observed that, at a low scanning rate, the pH had an in­si­gnificant influence over the current peak intensity; however, the quantification of this in­fluence was achieved using a quadratic polynomial equation, which could prevent the er­rors in mercury detection in case of industrial waste stream pH changes. The calibration curves for mercury in 0.9 % NaCl solution and in the tap water respectively were carried out.

  9. The Effect of Eddy Current in External Magnetic Circuit on Response Time of Ferrite Switch%外磁路涡流对铁氧体开关响应时间的影响

    Institute of Scientific and Technical Information of China (English)

    范兵

    2012-01-01

    The effect of eddy current is studied deeply in terms of switch circuit and response magnetic field. The effect of eddy current effect on response time of switch circuit of external magnetic circuit is derived from the change of equivalent impedance of excitation coil. With regard to response magnetic field, in the type of typical mode, effect of typical model eddy current on response magnetic field is educed through deducing with mathematic formula using Ampere's law, lenz's law, and electromagnetic induction equation. As such, effect factor and order of eddy current on response time of switch of external magnetic circuit are gotten. Furthermore, the conclusion is justified through design and verification of a specific product.%从开关电路和响应磁场2个方面对涡流的影响进行了研究.以激励线圈等效阻抗的变化,得出涡流效应对外磁路开关电路响应时间的影响;在响应磁场方面,以典型模的方式,应用安培定律、楞次定律、电磁感应方程,以数学推导得出典型模涡流对响应磁场的影响,以此得出涡流对外磁路开关响应时间的影响因素及其量级大小.通过具体产品的设计验证,证明了结论的正确.

  10. Aging time and brand determination of pasteurized milk using a multisensor e-nose combined with a voltammetric e-tongue

    Energy Technology Data Exchange (ETDEWEB)

    Bougrini, Madiha [Sensor Electronic and Instrumentation Group, Moulay Ismaïl University, Faculty of Sciences, Physics Department, B.P. 11201, Zitoune, Meknes (Morocco); Université de Lyon, Université Claude Bernard Lyon 1, Institut des Sciences Analytiques, UMR CNRS 5280, 5, rue de la Doua, 69100 Villeurbanne Cedex (France); Tahri, Khalid [Sensor Electronic and Instrumentation Group, Moulay Ismaïl University, Faculty of Sciences, Physics Department, B.P. 11201, Zitoune, Meknes (Morocco); Haddi, Zouhair [Sensor Electronic and Instrumentation Group, Moulay Ismaïl University, Faculty of Sciences, Physics Department, B.P. 11201, Zitoune, Meknes (Morocco); MINOS-EMaS, Electronic Engineering Department, Universitat Rovira i Virgili, Avda. Països Catalans, 26, 43007 Tarragona (Spain); El Bari, Nezha [Biotechnology Agroalimentary and Biomedical Analysis Group, Moulay Ismaïl University, Faculty of Sciences, Biology Department, B.P. 11201, Zitoune, Meknes (Morocco); Llobet, Eduard [MINOS-EMaS, Electronic Engineering Department, Universitat Rovira i Virgili, Avda. Països Catalans, 26, 43007 Tarragona (Spain); Jaffrezic-Renault, Nicole [Université de Lyon, Université Claude Bernard Lyon 1, Institut des Sciences Analytiques, UMR CNRS 5280, 5, rue de la Doua, 69100 Villeurbanne Cedex (France); Bouchikhi, Benachir, E-mail: benachir.bouchikhi@gmail.com [Sensor Electronic and Instrumentation Group, Moulay Ismaïl University, Faculty of Sciences, Physics Department, B.P. 11201, Zitoune, Meknes (Morocco)

    2014-12-01

    A combined approach based on a multisensor system to get additional chemical information from liquid samples through the analysis of the solution and its headspace is illustrated and commented. In the present work, innovative analytical techniques, such as a hybrid e-nose and a voltammetric e-tongue were elaborated to differentiate between different pasteurized milk brands and for the exact recognition of their storage days through the data fusion technique of the combined system. The Principal Component Analysis (PCA) has shown an acceptable discrimination of the pasteurized milk brands on the first day of storage, when the two instruments were used independently. Contrariwise, PCA indicated that no clear storage day's discrimination can be drawn when the two instruments are applied separately. Mid-level of abstraction data fusion approach has demonstrated that results obtained by the data fusion approach outperformed the classification results of the e-nose and e-tongue taken individually. Furthermore, the Support Vector Machine (SVM) supervised method was applied to the new subset and confirmed that all storage days were correctly identified. This study can be generalized to several beverage and food products where their quality is based on the perception of odor and flavor. - Highlights: • Five pasteurized milk brands were differentiated using e-nose and e-tongue. • E-tongue allowed a correct distinction of the milk brands comparing to the e-nose. • The combined system allows determining the storage days of pasteurized milk. • No clear storage day’s discrimination can be drawn when applied e-systems separately. • Data fusion method has been successful in the identification of the storage days.

  11. Analytical procedure for the simultaneous voltammetric determination of trace metals in food and environmental matrices. Critical comparison with atomic absorption spectroscopic measurements.

    Science.gov (United States)

    Melucci, Dora; Torsi, Giancarlo; Locatelli, Clinio

    2007-01-01

    An analytical procedure fit for the simultaneous determination of copper (II), chromium(VI), thallium(I), lead(II), tin(II), antimony(III), and zinc(II) by square wave anodic stripping voltammetry (SWASV) in three interdependent environmental matrices involved in foods and food chain as meals, cereal plants and soils is described. The digestion of each matrix was carried out using a concentrated HCl-HNO3-H2SO4 (meals and cereal plants) and HCl-HNO3 (soils) acidic attack mixtures. 0.1 mol/L dibasic ammonium citrate pH 8.5 was employed as the supporting electrolyte. The voltammetric measurements were carried out using, as working electrode, a stationary hanging mercury drop electrode (HMDE) and a platinum electrode and an Ag/AgCl/KClsat electrode as auxiliary and reference electrodes, respectively. The analytical procedure was verified by the analyses of the standard reference materials: Wholemeal BCR-CRM 189, Tomato Leaves NIST-SRM 1573a and Montana Soil Moderately Elevated Traces NIST-SRM 2711. For all the elements in the certified matrix, the precision as repeatability, expressed as relative standard deviation (Sr %) was lower than 5%. The accuracy, expressed as percentage relative error (e %) was of the order of 3-7%, while the detection limits were in the range 0.015-0.103 microg/g. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meal samples, cereal plants and soils samples drawn in sites devoted to agricultural practice. A critical comparison with spectroscopic measurements is also discussed.

  12. A validated stripping voltammetric procedure for quantification of the anti-hypertensive and benign prostatic hyperplasia drug terazosin in tablets and human serum.

    Science.gov (United States)

    Ghoneim, M M; El Ries, M A; Hammam, E; Beltagi, A M

    2004-10-20

    The electrochemical behavior of terazosin at the hanging mercury drop electrode was studied in Britton-Robinson buffer (pH 2-11), acetate buffer (4.5-5.5), and in 0.1M solution of each of sodium sulfate, sodium nitrate, sodium perchlorate and potassium chloride as supporting electrolytes. The square-wave adsorptive cathodic stripping voltammogram of terazosin exhibited a single well-defined two-electron irreversible cathodic peak which may be attributed to the reduction of CO double bond of the drug molecule. A fully validated, simple, high sensitive, precise and inexpensive square-wave adsorptive cathodic stripping voltammetric procedure was described for determination of terazosin in bulk form, tablets and human serum. A mean recovery for 1x10(-8)M terazosin in bulk form, following preconcentration onto the hanging mercury drop electrode for 60s at a -1.0V (versus Ag/AgCl/KCl(s)), of 99+/-0.7% (n=5) was obtained. Limits of detection (LOD) and quantitation (LOQ) of 1.5x10(-11) and 5x10(-11)M bulk terazosin were achieved, respectively. The proposed procedure was successfully applied to determination of the drug in its Itrin((R)) tablets and human serum samples. The achieved LOD and LOQ of the drug in human serum samples were 5.3x10(-11) and 1.8x10(-10)M THD, respectively. The pharmacokinetic parameters of the drug in human plasma were estimated as: C(max)=77.5ngml(-1), t(max)=1.75h, AUC(0-t)=602.3nghml(-1), K(e)=0.088h(-1) and t(1/2)=11.32h) which are favorably compared with those reported in literature.

  13. Voltammetric and electrochemical impedance spectroscopy characterization of a cathodic and anodic pre-treated boron doped diamond electrode

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, S. Carlos B. [Departamento de Quimica, Faculdade de Ciencias e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra (Portugal); Oliveira-Brett, Ana Maria, E-mail: brett@ci.uc.p [Departamento de Quimica, Faculdade de Ciencias e Tecnologia, Universidade de Coimbra, 3004-535 Coimbra (Portugal)

    2010-06-01

    The effect of boron doped diamond (BDD) surface termination, immediately after cathodic and anodic electrochemical pre-treatments, on the electrochemical response of a BDD electrode in aqueous media and the influence of the different supporting electrolytes utilized in these pre-treatments on the final surface termination was investigated with [Fe(CN){sub 6}]{sup 4-/3-}, as redox probe, by cyclic and differential pulse voltammetry and electrochemical impedance spectroscopy. The cyclic voltammetry results indicate that the electrochemical behavior for the redox couple [Fe(CN){sub 6}]{sup 4-/3-} is very dependent on the state of the BDD surface, and a reversible response was observed after the cathodic electrochemical pre-treatment, whereas a quasi-reversible response occurred after anodic electrochemical pre-treatment. Differential pulse voltammetry in acetate buffer also showed that the potential window is very much influenced by the electrochemical pre-treatment of the BDD surface. Electroactivity of non-diamond carbon surface species (sp{sup 2} inclusions) incorporated into the diamond structure was observed after cathodic and anodic pre-treatments. Electrochemical impedance spectroscopy confirmed the cyclic voltammetry results and indicates that the BDD surface resistance and capacitance vary significantly with the electrolyte and with the electrochemical pre-treatment, caused by different surface terminations of the BDD electrode surface.

  14. Influence of potential pulses amplitude sequence in a voltammetric electronic tongue (VET) applied to assess antioxidant capacity in aliso.

    Science.gov (United States)

    Fuentes, Esteban; Alcañiz, Miguel; Contat, Laura; Baldeón, Edwin O; Barat, José M; Grau, Raúl

    2017-06-01

    Four signals configurations were studied, two of them built by small increases of potential and two with bigger increments. The highest current values were obtained when pulses with bigger change of potential were used although the best results were shown by the pulse sequence which included an intermediate pulse before the relevant pulse. A mathematical model based on trolox pattern was developed to predict antioxidant capacity of aliso, employing information obtained from all the electrodes, although model validation could be done only employing the information from gold electrode. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Mechanisms Responsible for the Trophic Effect of Beta-Adrenoceptors on the Ito Current Density in Type 1 Diabetic Rat Cardiomyocytes

    Directory of Open Access Journals (Sweden)

    Raúl Setién

    2013-01-01

    Full Text Available Background/Aims: In diabetic ventricular myocytes, transient outward potassium current (Ito amplitude is severely reduced because of the impaired catecholamine release that characterizes diabetic autonomic neuropathy. Sympathetic nervous system exhibits a trophic effect on Ito since incubation of myocytes with noradrenaline restores current amplitude via beta-adrenoceptor (βAR stimulation. Here, we investigate the intracellular signalling pathway though which incubation of diabetic cardiomyocytes with the βAR agonist isoproterenol recovers Ito amplitude to normal values. Methods: Experiments were performed in ventricular myocytes isolated from streptozotocin-diabetic rats. Ito current was recorded by using the patch-clamp technique. Kv4 channel expression was determined by immunofluorescence. Protein-protein interaction was determined by coimmunoprecipitation. Results: Stimulation of βAR activates first a Gαs protein, adenylyl cyclase and Protein Kinase A. PKA-phosphorylated receptor then switches to the Gαi protein. This leads to the activation of the βAR-Kinase-1 and further receptor phosphorylation and arrestin dependent internalization. The internalized receptor-arrestin complex recruits and activates cSrc and the MAPK cascade, where Ras, c-Raf1 and finally ERK1/2 mediate the increase in Kv4.2 and Kv4.3 protein abundance in the plasma membrane. Conclusion: β2AR stimulation activates a Gαs and Gαi protein dependent pathway where the ERK1/2 modulates the Ito current amplitude and the density of the Kv4.2 and Kv4.2 channels in the plasma membrane upon sympathetic stimulation in diabetic heart.

  16. Transcranial Direct Current Stimulation Combined with Aerobic Exercise to Optimize Analgesic Responses in Fibromyalgia: A Randomized Placebo-Controlled Clinical Trial

    OpenAIRE

    Mendonca, Mariana E.; Simis, Marcel; Grecco, Luanda C.; Battistella, Linamara R.; Baptista, Abrahão F; Fregni, Felipe

    2016-01-01

    Fibromyalgia is a chronic pain syndrome that is associated with maladaptive plasticity in neural central circuits. One of the neural circuits that are involved in pain in fibromyalgia is the primary motor cortex. We tested a combination intervention that aimed to modulate the motor system: transcranial direct current stimulation (tDCS) of the primary motor cortex (M1) and aerobic exercise (AE). In this phase II, sham-controlled randomized clinical trial, 45 subjects were assigned to 1 of 3 gr...

  17. Estudo voltamétrico do complexo de cobre(II com o ligante vermelho de alizarina S, adsorvido na superfície do eletrodo de grafite pirolítico Voltammetric study of complex of copper (II with alizarin red S ligand, absorbed on surface of pyrolytic graphite electrode

    Directory of Open Access Journals (Sweden)

    Victor E. Mouchrek Filho

    1999-06-01

    Full Text Available The alizarin red S (ARS has been used as a spectrophotometric reagent of several metals for a long time. Now this alizarin has been used as modifier agent of electrodes, for voltammetric analyses. In this work cyclic voltammetry experiments was accomplished on closed circuit, with the objective of studying the voltammetric behavior of alizarin red S adsorbed and of its copper complex, on the surface of the pyrolytic graphite electrode. These studies showed that ARS strongly adsorbs on the surface of this electrode. This adsorption was used to immobilize ions copper(II from the solution.

  18. Voltammetric detection of the α-dicarbonyl compound: methylglyoxal as a flavoring agent in wine and beer.

    Science.gov (United States)

    Chatterjee, Sanghamitra; Chen, Aicheng

    2012-11-02

    A simple, rapid and highly selective method for the determination of the most abundant α-dicarbonyl compound in wine and beer has been developed for the first time by employing square wave voltammetry. A novel electrochemical sensor, based on the electrodeposition of platinum nanoparticles onto single wall carbon nanotubes that were cast on a glassy carbon electrode (GCE) substrate, is presented in this paper. This modified electrode exhibited excellent catalytic activity in the electroreduction of methylglyoxal, showing much higher peak currents than those measured on an unmodified GCE. The effects of different experimental and instrumental parameters, such as solution pH and square wave frequency, were examined. The reduction peak current showed a linear range of from 0.1×10(-6) to 100×10(-6)M with a 0.9979 correlation coefficient; and a low detection limit of 2.8×10(-9)M was also obtained. The proposed methodology was successfully applied to the quantitative analysis of methylglyoxal in wine and beer samples. The developed sensor possesses advantageous properties such as a high active surface area, stability, and rapid electron transfer rate, which cumulatively demonstrate high performance toward the electrocatalytic reduction and detection of methylglyoxal.

  19. Voltammetric determination of theophylline at a Nafion/multi-wall carbon nanotubes composite film-modified glassy carbon electrode

    Indian Academy of Sciences (India)

    Suling Yang; Ran Yang; Gang Li; Jianjun Li; Lingbo Qu

    2010-11-01

    A Nafion/multi-wall carbon nanotubes (MWNTs) composite film-modified electrode was fabricated and applied to the sensitive and convenient determination of theophylline (TP). Multi-wall carbon nanotubes (MWNTs) were easily dispersed homogeneously into 0.1% Nafion methanol solution by sonication. Appropriate amount of Nafion/MWNTs suspension was coated on a glassy carbon electrode. After evaporating methanol, a Nafion/MWNTs composite film-modified electrode was achieved. TP could effectively accumulate at Nafion/MWNTs composite film-modified electrode and cause a sensitive anodic peak at around 1180 mV (vs SCE) in 0.01 mol/L H2SO4 medium (pH 1.8). In contrast with the bare glassy carbon electrode, Nafion film-modified electrode, Nafion/MWNTs film-modified electrode could remarkably increase the anodic peak current and decreased the overpotential of TP oxidation. Under the optimized conditions, the anodic peak current was proportional to TP concentration in the range of 8.0 × 10-8-6.0 × 10-5 mol/L, with a detection limit of 2.0 × 10-8 mol/L. This newly developed method was used to determine TP in drug samples with good percentage of recoveries.

  20. Biosensor based on ds-DNA decorated chitosan modified multiwall carbon nanotubes for voltammetric biodetection of herbicide amitrole.

    Science.gov (United States)

    Ensafi, Ali A; Amini, Maryam; Rezaei, Behzad

    2013-09-01

    The interaction of amitrole and salmon sperm ds-DNA was studied using UV-vis and differential pulse voltammetry (DPV) at both bare and DNA-modified electrodes. Amitrole showed an oxidation peak at 0.445 V at a bare pencil graphite electrode (PGE). When ds-DNA was added into the amitrole solution, the peak current of amitrole decreased and the peak potential underwent a shift. UV-vis spectra showed that the absorption intensity of the ds-DNA at 260 nm decreased with increasing amitrole concentration, proving the interaction between amitrole and the ds-DNA. The results also showed that amitrole could interact with the ds-DNA molecules via the intercalative binding mode. Finally, a pretreated pencil graphite electrode (PGE) modified with multiwall carbon nanotubes (MWCNTs) and chitosan (CHIT) decorated with the ds-DNA were tested in order to determine amitrole content in solution. Electrochemical oxidation of amitrole bonded on DNA/MWCNTs-CHIT/PGE was used to obtain an analytical signal. A linear dependence was observed to exist between the peak current and 0.025-2.4 ng mL(-1) amitrole with a detection limit of 0.017 ng mL(-1). The sensor showed a good selectivity and precision for the determination of amitrole. Finally, applicability of the biosensor was evaluated by measuring the analyte in soil and water samples with good selectivity. Copyright © 2013 Elsevier B.V. All rights reserved.

  1. A novel voltammetric sensor for nevirapine, based on modified graphite electrode by MWCNs/poly(methylene blue)/gold nanoparticle.

    Science.gov (United States)

    Gholivand, Mohammad Bagher; Ahmadi, Elahe; Haseli, Mozhdeh

    2017-06-15

    In the present study, a graphite electrode (GE) modified by conductive film (containing functionalized multi-walled carbon nanotubes (f-MWCNTs), poly methylene blue p(MB) and gold nanoparticles (AuNPs)) was introduced for determination of nevirapine (NVP) as an anti-HIV drug by applying the differential pulse anodic stripping voltammetry (DPASV) technique. Modification of the electrode was investigated by scanning electron microscopy (SEM) and impedance electrochemical spectroscopy (EIS). All electrochemical effective parameters on detection of NVP were optimized and the oxidation peak current of drug was used for its monitoring. The obtained results confirmed that the oxidation peak currents increased linearly by increasing in NVP concentrations in the range of 0.1-50 μM and a detection limit of 53 nM was achieved. The proposed sensor (AuNPs/p(MB)/f-MWCNTs/GE) was successfully applied for the determination of NVP in blood serum and pharmaceutical samples. It revealed the excellent stability, repeatability and reproducibility as well. Copyright © 2017 Elsevier Inc. All rights reserved.

  2. 全身炎症反应综合征的治疗现状%Current treatment of systemic inflammatory response syndrome(Review)

    Institute of Scientific and Technical Information of China (English)

    杨新军; 吴广礼

    2003-01-01

    @@ 全身炎症反应综合征(systemic inflammatory response syndrome,SIRS)是由不同疾病,包括微生物感染、创伤、烧伤等感染性疾病所引起的全身性的非特异性炎症反应,最终导致机体对炎症反应失控.

  3. Sexual and reproductive health needs of young people : a study examining the fit between needs and current programming responses in India

    OpenAIRE

    Kolencherry, Shuby

    2004-01-01

    The study intended to explore the magnitude and characteristics of sexual and reproductive health risks of young people in Gujarat, India. In particular, the study examined the fit between sexual and reproductive health needs and the existing programming responses in terms of policies, programs and access to health care services. The study is based on empirical research and Social Cognitive Theory framework. The investigation was conceived in the context following the International Conference...

  4. Antimicrobial activity of cationic antimicrobial peptides against gram-positives: Current progress made in understanding the mode of action and the response of bacteria

    Directory of Open Access Journals (Sweden)

    Soraya Omardien

    2016-10-01

    Full Text Available Antimicrobial peptides (AMPs have been proposed as a novel class of antimicrobials that could aid the fight against antibiotic resistant bacteria. The mode of action of AMPs as acting on the bacterial cytoplasmic membrane has often been presented as an enigma and there are doubts whether the membrane is the sole target of AMPs. Progress has been made in clarifying the possible targets of these peptides, which is reported in this review with as focus gram-positive vegetative cells and spores. Numerical estimates are discussed to evaluate the possibility that targets, other than the membrane, could play a role in susceptibility to AMPs. Concerns about possible resistance that bacteria might develop to AMPs are addressed. Proteomics, transcriptomics and other molecular techniques are reviewed in the context of explaining the response of bacteria to the presence of AMPs and to predict what resistance strategies might be. Emergent mechanisms are cell envelope stress responses as well as enzymes able to degrade and/or specifically bind (and thus inactivate AMPs. Further studies are needed to address the broadness of the AMP resistance and stress responses observed.

  5. Antimicrobial Activity of Cationic Antimicrobial Peptides against Gram-Positives: Current Progress Made in Understanding the Mode of Action and the Response of Bacteria

    Science.gov (United States)

    Omardien, Soraya; Brul, Stanley; Zaat, Sebastian A. J.

    2016-01-01

    Antimicrobial peptides (AMPs) have been proposed as a novel class of antimicrobials that could aid the fight against antibiotic resistant bacteria. The mode of action of AMPs as acting on the bacterial cytoplasmic membrane has often been presented as an enigma and there are doubts whether the membrane is the sole target of AMPs. Progress has been made in clarifying the possible targets of these peptides, which is reported in this review with as focus gram-positive vegetative cells and spores. Numerical estimates are discussed to evaluate the possibility that targets, other than the membrane, could play a role in susceptibility to AMPs. Concerns about possible resistance that bacteria might develop to AMPs are addressed. Proteomics, transcriptomics, and other molecular techniques are reviewed in the context of explaining the response of bacteria to the presence of AMPs and to predict what resistance strategies might be. Emergent mechanisms are cell envelope stress responses as well as enzymes able to degrade and/or specifically bind (and thus inactivate) AMPs. Further studies are needed to address the broadness of the AMP resistance and stress responses observed.

  6. Impact of microdialysis probes on vasculature and dopamine in the rat striatum: a combined fluorescence and voltammetric study.

    Science.gov (United States)

    Mitala, Christina M; Wang, Yuexiang; Borland, Laura M; Jung, Moon; Shand, Stuart; Watkins, Simon; Weber, Stephen G; Michael, Adrian C

    2008-09-30

    Measuring extracellular dopamine in the brain of living animals by means of microdialysis and/or voltammetry is a route towards understanding both normal brain function and pathology. Previous reports, however, suggest that the tissue response to implantation of devices may affect the outcome of the measurements. To address the source of the tissue response and its impact on striatal dopamine systems microdialysis probes were placed in the striatum of anesthetized rats. Images obtained by dual-label fluorescence microscopy show signs of ischemia and opening of the blood-brain barrier near the probe tracks. Opening of the blood-brain barrier was further examined by determining dialysate concentrations of carbi-DOPA, a drug that normally does not penetrate the brain. Although carbi-DOPA was recovered in brain dialysate, it did not alter dialysate dopamine levels or evoked dopamine release as measured by voltammetry near the probes. Microdialysis probes also significantly diminished the effect of intrastriatal infusion of kynurenate on extracellular dopamine levels as measured by voltammetry near the probes.

  7. Zanamivir immobilized magnetic beads for voltammetric measurement of neuraminidase at gold-modified boron doped diamond electrode

    Energy Technology Data Exchange (ETDEWEB)

    Wahyuni, Wulan Tri, E-mail: wulantriws@gmail.com [Department of Chemistry, Faculty of Mathematics and Natural Sciences, Bogor Agricultural University, Kampus IPB Darmaga, Bogor 16680 (Indonesia); Department of Chemistry, FMIPA, Universitas Indonesia, Kampus UI Depok (Indonesia); Ivandini, Tribidasari A.; Saepudin, Endang [Department of Chemistry, FMIPA, Universitas Indonesia, Kampus UI Depok (Indonesia); Einaga, Yasuaki [Department of Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Yokohama 223-8522 (Japan); CREST, JST, 3-14-1 Hiyoshi, Yokohama 223-8522 (Japan)

    2016-04-19

    Biomolecule modified magnetic beads has been widely used in separation and sensing process. This study used streptavidin modified magnetic beads to immobilize biotin modified zanamivir. Biotin-streptavidin affinity facilitates immobilization of zanamivir on magnetic beads. Then interaction of zanamivir and neuraminidase was adopted as basic for enzyme detection. Detection of neuraminidase was performed at gold modified BDD using cyclic voltammetry technique. The measurement was carried out based on alteration of electrochemical signals of working electrode as neuraminidase response. The result showed that zanamivir was successfully immobilized on magnetic beads. The optimum amount of magnetic beads for zanamivir immobilization was 120 ug. Linear responses of neuraminidase were detected in concentration range of 0-15 mU. Detection limit (LOD) of measurement was 2.32 mU (R2 = 0.959) with precision as % RSD of 1.41%. Measurement of neuraminidase on magnetic beads could be also performed in the presence of mucin matrix. The linearity range was 0-8 mU with LOD of 0.64 mU (R2 = 0.950) and % RSD of 7.25%.

  8. Current concepts in osteolysis.

    Science.gov (United States)

    Ollivere, B; Wimhurst, J A; Clark, I M; Donell, S T

    2012-01-01

    The most frequent cause of failure after total hip replacement in all reported arthroplasty registries is peri-prosthetic osteolysis. Osteolysis is an active biological process initiated in response to wear debris. The eventual response to this process is the activation of macrophages and loss of bone. Activation of macrophages initiates a complex biological cascade resulting in the final common pathway of an increase in osteolytic activity. The biological initiators, mechanisms for and regulation of this process are beginning to be understood. This article explores current concepts in the causes of, and underlying biological mechanism resulting in peri-prosthetic osteolysis, reviewing the current basic science and clinical literature surrounding the topic.

  9. Rapid Voltammetric Measurements at Conducting Polymer Microelectrodes Using Ultralow-Capacitance Poly(3,4-ethylenedioxythiophene):Tosylate

    DEFF Research Database (Denmark)

    Meier, Adam R.; Matteucci, Marco; Vreeland, Richard F.

    2016-01-01

    :tOsylate microelectrodes and were used to perform fast-scan cyclic voltammetry (FSCV) measurements. Using a scan rate of 100 V/s, we measured ferrocene carboxylic acid and dopamine by FSCV. In contrast to carbon-fiber microelectrodes, the reduction peak showed higher sensitivity when compared to the oxidation peak......We use a vapor-phase synthesis to generate conducting polymer films with low apparent capacitance and high conductance enabling rapid electrochemical measurements. Specifically, oxidative chemical vapor deposition was used to create thin films of poly(3,4-ethylenedioxythiophene):tosylate (PEDOT......:tosylate). These films had a conductance of 17.1 ± 1.7 S/cm. Furthermore, they had an apparent capacitance of 197 ± 14 μF/cm2, which is an order of magnitude lower than current commercially available and previously reported PEDOT. Using a multistage photolithography process, these films were patterned into PEDOT...

  10. Estimation of phase signal change in neuronal current MRI for evoke response of tactile detection with realistic somatosensory laminar network model.

    Science.gov (United States)

    BagheriMofidi, Seyed Mehdi; Pouladian, Majid; Jameie, Seyed Behnamedin; Abbaspour Tehrani-Fard, Ali

    2016-09-01

    Magnetic field generated by neuronal activity could alter magnetic resonance imaging (MRI) signals but detection of such signal is under debate. Previous researches proposed that magnitude signal change is below current detectable level, but phase signal change (PSC) may be measurable with current MRI systems. Optimal imaging parameters like echo time, voxel size and external field direction, could increase the probability of detection of this small signal change. We simulate a voxel of cortical column to determine effect of such parameters on PSC signal. We extended a laminar network model for somatosensory cortex to find neuronal current in each segment of pyramidal neurons (PN). 60,000 PNs of simulated network were positioned randomly in a voxel. Biot-savart law applied to calculate neuronal magnetic field and additional phase. The procedure repeated for eleven neuronal arrangements in the voxel. PSC signal variation with the echo time and voxel size was assessed. The simulated results show that PSC signal increases with echo time, especially 100/80 ms after stimulus for gradient echo/spin echo sequence. It can be up to 0.1 mrad for echo time = 175 ms and voxel size = 1.48 × 1.48 × 2.18 mm(3). With echo time less than 25 ms after stimulus, it was just acquired effects of physiological noise on PSC signal. The absolute value of the signal increased with decrease of voxel size, but its components had complex variation. External field orthogonal to local surface of cortex maximizes the signal. Expected PSC signal for tactile detection in the somatosensory cortex increase with echo time and have no oscillation.

  11. Voltammetric detection of the {alpha}-dicarbonyl compound: Methylglyoxal as a flavoring agent in wine and beer

    Energy Technology Data Exchange (ETDEWEB)

    Chatterjee, Sanghamitra [Department of Chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1 (Canada); Chen Aicheng, E-mail: achen@lakeheadu.ca [Department of Chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1 (Canada)

    2012-11-02

    Highlights: Black-Right-Pointing-Pointer Synergistic electrocatalytic effect of Pt nanoparticles and single-wall carbon nanotubes on the reduction of methylglyoxal. Black-Right-Pointing-Pointer Novel electrochemical Pt/SWNT/GCE sensor designed for the determination of methylglyoxal. Black-Right-Pointing-Pointer Excellent analytical performance with low detection limit and high sensitivity. Black-Right-Pointing-Pointer The developed methylglyoxal sensor shows promising process control, clinical and, biomedical applications. - Abstract: A simple, rapid and highly selective method for the determination of the most abundant {alpha}-dicarbonyl compound in wine and beer has been developed for the first time by employing square wave voltammetry. A novel electrochemical sensor, based on the electrodeposition of platinum nanoparticles onto single wall carbon nanotubes that were cast on a glassy carbon electrode (GCE) substrate, is presented in this paper. This modified electrode exhibited excellent catalytic activity in the electroreduction of methylglyoxal, showing much higher peak currents than those measured on an unmodified GCE. The effects of different experimental and instrumental parameters, such as solution pH and square wave frequency, were examined. The reduction peak current showed a linear range of from 0.1 Multiplication-Sign 10{sup -6} to 100 Multiplication-Sign 10{sup -6} M with a 0.9979 correlation coefficient; and a low detection limit of 2.8 Multiplication-Sign 10{sup -9} M was also obtained. The proposed methodology was successfully applied to the quantitative analysis of methylglyoxal in wine and beer samples. The developed sensor possesses advantageous properties such as a high active surface area, stability, and rapid electron transfer rate, which cumulatively demonstrate high performance toward the electrocatalytic reduction and detection of methylglyoxal.

  12. Current Titles

    Energy Technology Data Exchange (ETDEWEB)

    Various

    2006-06-01

    This booklet is published for those interested in current research being conducted at the National Center for Electron Microscopy. The NCEM is a DOE-designated national user facility and is available at no charge to qualified researchers. Access is controlled by an external steering committee. Interested researchers may contact Jane Cavlina, Administrator, at 510/486-6036.

  13. Voltammetric Determination of Acetaminophen Using Carbon Paste Modified Electrode Doped with Selenium%掺杂硒修饰碳糊电极伏安法测定对乙酰氨基酚

    Institute of Scientific and Technical Information of China (English)

    谭君林; 张连明; 胡存杰; 魏小平

    2014-01-01

    Carbon paste modified electrode doped with selenium was prepared by cyclic voltammetry,and the electrochemical behavior of acetaminophen (ACOP)at this electrode was studied by cyclic voltammetry and differential pulse voltammetry.A cyclic voltammetric method for the determination of ACOP with carbon paste modified electrode doped with selenium was established.In 0.1 mol·L-1 HOAc-NaOAc buffer solution of pH 4.6, a sensitive oxidation peak of ACOP at +0.61 V (vs.SCE)was observed.Linear relationship between values of oxidation peak current and concentration of ACOP was kept in the range of 6.0×10-7 -1.5×10-4 mol·L-1 with detection limit (3s/k)of 2.8×10-7 mol·L-1 .The proposed method was applied to the analysis of tablet samples, giving results in consistency with the values obtained by pharmacopoeia method with RSD′s (n=5)in the range of 2.1%-2.5%.%采用循环伏安法制备了掺杂硒修饰碳糊电极,用循环伏安法和差分脉冲伏安法研究了对乙酰氨基酚在掺杂硒修饰碳糊电极上的电化学行为,建立了掺杂硒修饰碳糊电极测定对乙酰氨基酚的电化学方法。在 pH 4.6的0.1 mol ·L-1乙酸-乙酸钠缓冲溶液中,对乙酰氨基酚在+0.61 V呈现一个灵敏的氧化峰。对乙酰氨基酚的浓度在6.0×10-7~1.5×10-4 mol·L-1范围内与其氧化峰电流呈线性关系,检出限(3s/k)为2.8×10-7 mol·L-1。方法用于药品中对乙酰氨基酚的测定,测定结果与药典法测定值相符,测定值的相对标准偏差(n=5)在2.1%~2.5%之间。

  14. Voltammetric and impedance studies of the electropolishing of type 316 stainless steel in a choline chloride based ionic liquid

    Energy Technology Data Exchange (ETDEWEB)

    Abbott, Andrew P. [Chemistry Department, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)]. E-mail: Andrew.abbott@le.ac.uk; Capper, Glen [Chemistry Department, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); McKenzie, Katy J. [Chemistry Department, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Ryder, Karl S. [Chemistry Department, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

    2006-06-01

    We demonstrate the first practical alternative to the use of phosphoric and sulphuric acid mixtures for the electropolishing of stainless steel. In this paper, efficient electropolishing of type 316 stainless steel is demonstrated in an ionic liquid composed of ethylene glycol (HOCH{sub 2}CH{sub 2}OH) and choline chloride (HOC{sub 2}H{sub 4}N(CH{sub 3}){sub 3} {sup +}Cl{sup -}). Linear sweep voltammetry, chronoamperometry, scanning electron microscopy, atomic force microscopy and AC impedance methods were used to investigate the steel dissolution mechanism and the results are compared to polishing done in aqueous acidic solutions. It is shown that the quality of the polish is related to the breakdown of the oxide film and preliminary data suggest that the polishing process may be controlled by the diffusion of chloride ions. The dissolution is different from that found in aqueous acid solutions, and oxide breakdown is shown to be slower, which can lead to pitting at low current densities.

  15. Voltammetric determination of chlorogenic acid in pharmaceutical products using poly(aminosulfonic acid modified glassy carbon electrode

    Directory of Open Access Journals (Sweden)

    Mingyong Chao

    2014-12-01

    Full Text Available In this work, a poly(aminosulfonic acid modified glassy carbon electrode was fabricated and the electrochemical behavior of chlorogenic acid (CGA was studied by cyclic voltammetry. Compared with a bare glassy carbon electrode, the modified electrode exhibits excellent catalytic effect on the electrochemical redox of CGA. Utilizing this catalytic effect, a sensitive and selective electrochemical method for the determination of CGA was developed. The analytical parameters were optimized. Under the optimized conditions, the oxidation peak current is linearly proportional to the concentration of CGA in the range from 4.00 × 10−7 to 1.20 × 10−5 mol/L and the detection limit is 4.00 × 10−8 mol/L. Further, the performance of the proposed method has been validated in terms of linearity (r = 0.9995, recovery (96.3–102.8%, reproducibility (RSD < 4.0%, n = 6 and robustness. The developed method has been successfully applied for the determination of CGA in a variety of pharmaceutical products.

  16. Preparation and electrochemical application of rutin biosensor for differential pulse voltammetric determination of NADH in the presence of acetaminophen

    Directory of Open Access Journals (Sweden)

    HAMID R. ZARE

    2010-10-01

    Full Text Available The electrocatalytic behavior of reduced nicotinamide adenine di-nucleotide (NADH was studied at the surface of a rutin biosensor, using various electrochemical methods. According to the results, the rutin biosensor had a strongly electrocatalytic effect on the oxidation of NADH with the overpotential being decreased by about 450 mV as compared to the process at a bare glassy carbon electrode, GCE. This value is significantly greater than the value of 220 mV that was reported for rutin embedded in a lipid-cast film. The kinetic parameters of the electron transfer coefficient, a, and the heterogeneous charge transfer rate constant, kh, for the electrocatalytic oxidation of NADH at the rutin biosensor were estimated. Furthermore, the linear dynamic range; sensitivity and limit of detection for NADH were evaluated using the differential pulse voltammetry method. The advantages of this biosensor for the determination of NADH are excellent catalytic activity and reproducibility, good detection limit and high exchange current density. The rutin biosensor could separate the oxidation peak potentials of NADH and acetaminophen present in the same solution while at a bare GCE, the peak potentials were indistinguishable.

  17. A current reader's response to the article of 50 years ago by Karpman, B. (1949): "The principles and methods of objective psychotherapy".

    Science.gov (United States)

    Luborsky, L

    2000-07-01

    The first aim is to describe the psychotherapy of 1949 in the light of today's psychotherapies. The old psychotherapy is suited to treating severely ill patients. It does not use free association, but rather is focused on current problems. It uses dreams, yet it also uses homework and bibliotherapy. The second aim is to critique the treatment. Consistent with its era. it does not make use of medications, and there is an absence of references to psychotherapy research, which was then just starting. The treatment relies over-heavily on the authority of the therapist. A third aim is to describe the changes in our field in the past 50 years and examine the predictions for the future. Although the treatment is called objective psychotherapy, it does not make use of the most up-to-date means of measuring accuracy of interpretations, such as the Core Conflictual Relationship Theme (CCRT) method and other methods like it.

  18. Electrochemical Oxidation of l-selenomethionine and Se-methylseleno-l-cysteine at a Thiol-Compound-Modified Gold Electrode: Its Application in a Flow-Through Voltammetric Sensor.

    Science.gov (United States)

    Wang, Lai-Hao; Zhang, Yu-Han

    2017-02-16

    A flow-electrolytic cell that consists of a bare gold wire or of different thiol-compound-modified gold electrodes (such as 2,4-thiazolidinedione, 2-mercapto-5-thiazoline, 2-mercaptothiazoline, l-cysteine, thioglycolic acid) was designed to be used in a voltammetric detector to identify l-selenomethionine and Se-methylseleno-l-cysteine using high-performance liquid chromatography. Both l-selenomethionine and Se-methylseleno-l-cysteine are more efficiently electrochemically oxidized on a thiol/gold than on a bare gold electrode. For the DC mode, and for measurements with suitable experimental parameters, a linear concentration from 10 to 1600 ng·mL(-1) was found. The limits of quantification for l-selenomethionine and Se-methylseleno-l-cysteine were below 10 ng·mL(-1). The method can be applied to the quantitative determination of l-selenomethionine and Se-methylseleno-l-cysteine in commercial selenium-containing supplement products. Findings using high-performance liquid chromatography with a flow-through voltammetric detector and ultraviolet detector are comparable.

  19. Cathodic stripping voltammetric determination of chromium in coastal waters on cubic Nano-titanium carbide loaded gold nanoparticles modified electrode

    Directory of Open Access Journals (Sweden)

    Haitao eHan

    2015-09-01

    Full Text Available The novel cubical nano-titanium carbide loaded gold nanoparticles modified electrode for selective and sensitive detection of trace chromium (Cr in coastal water was established based on a simple approach. Nano-titanium carbide is used as the typical cubical nanomaterial with wonderful catalytic activity towards the reduction of Cr(VI. Gold nanopart