1,720,988 research outputs found
Amperometric mediated carbon nanotube paste biosensor for fructose determination
No full textA new mediated carbon nanotube paste (CNTP) amperometric biosensor for fructose is described. The biosensor is formed by a CNTP electrode modified with an electropolymerized film of 3,4-dihydroxybenzaldehyde (3,4-DHB) and is based on the activity of a commercial available D-fructose dehydrogenase (FDH) immobilized on an immobilon membrane placed on the top of the electrode surface. Analytical parameters such as enzyme immobilization, pH, temperature, and probe lifetime were studied and optimized. The biosensor response current was directly proportional to D-fructose concentration from 5 x 10(-6) to 2 x 10(-3) mol/L with a detection limit of 1 x 10(-6) mol/L and a good reproducibility (RSD = 1.8%, n = 5). The biosensor was used for the determination of fructose content in three honey samples and validated with a commercial spectrophotometric enzymatic kit
An extended method for the practical evaluation of the standard rate constant from cyclic voltammetric data
No full textThe Nicholson's treatment for the evaluation of the heterogeneous standard rate constant k(0) of electron transfer from cyclic voltammetric (CV) data is combined with the Klingler and Kochi method suitable to totally irreversible systems in order to use very large DeltaE(P) x n values, where n is the number of electrons involved in a simple electron-transfer process O + n e(-) reversible arrow R. An empirical relationship between the dimensionless parameter Psi = k(0) [piDnvF/(RT)](-1/2) and DeltaE(P) x n which practically replaces the Nicholson's working curve up to about 200 mV is reported
Single-wall carbon nanotube paste electrodes: a comparison with carbon paste, platinum and glassy carbon electrodes via cyclic voltammetric data
No full textA new carbon electrode material, obtained by mixing single wall carbon nanotubes (SWNTs) with a mineral oil binder is studied. Carbon nanotube pastes show the special properties of carbon nanotubes combined with the various advantages of composite electrodes such as a very low capacitance (background current) and the possibility of an easy preparation, modification and renewal. A better knowledge of the characteristics of electrode reactions at carbon nanotube paste (CNTP) electrodes was obtained studying the electron transfer rates of various redox couples under different pretreatment conditions. A critical comparison with carbon paste (CP), platinum (Pt) and glassy carbon (GC) electrodes was also carried out. Capacitance and resistance values were also calculated for all electrodes investigated. Both untreated and treated CNTP electrodes showed a low resistance while the capacitance was markedly reduced with CNTP electrodes previously treated with concentrated nitric acid. An electrochemical pretreatment on CNTP electrodes was developed which showed an excellent result towards two-electron quinonic structure species. After this treatment the heterogeneous standard rate constants for p-methylaminophenol sulfate (MAP) and dopamine resulted to be significantly higher (2.1 x 10(-2) cm/s and 2.0 x 10(-2) cm/s, respectively) than those obtained with the other electrodes studied. Reproducibility, stability and storage characteristics of CNTP electrodes were also reported
Electroanalytical investigation on the stability of tetracoordinate nickel(I) complexes
No full textThe stability of tetracoordinate nickel(I) complexes, of the type [Ni(CN)2P2]− (P=substituted phosphine), generated by cathodic reduction of the parent nickel(II) complexes, has been studied by cyclic voltammetry and double potential step techniques. Evidence has been obtained that nickel(I) complexes decay to the dimeric species Ni2(CN)2P4 via a first order chemical reaction the rate determining step being the release of a cyanide ion leading to the radical species [Ni(CN)P2]. The experimental trend obtained for the first order kinetic constants has been explained on the basis of the different “trans-effect” induced by a cyanide ligand in comparison with that induced by a phosphine group and taking into account the different basic character of the phosphine ligands
A comparison between the use of a redox mediator in solution and of surface modified electrodes in the electrocatalytic oxidation of nicotinamide adenine dinucleotide
No full textCyclic voltammetry was successfully applied to study the oxidation of nicotinamide adenine dinucleotide (NADH) both in homogeneous and heterogeneous phase. The first case was realized with a solution containing p-methylamino-phenolsulphate (MAP) as redox mediator and the diaphorase (DI) from Clostridium kluveri as enzyme while the second one by using both a glassy carbon (GC) and a carbon nanotube paste (CNTP) electrode modified with electrodeposited films derived from 3,4-dihydroxybenzaldehyde (3,4-DHB). Such systems were successively coupled with glucose dehydrogenase (GDH) reaction to realize the redox chain present in glucose biosensors. A critical comparison of the two systems was also reported. (C) 2004 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Theil-Sen nonparametric regression technique on univariate calibration, inverse regression and detection limits
No full textThis paper reports the combined use of the nonparametric Theil–Sen (TS) regression technique and of the
statistics of Lancaster–Quade (LQ) concerning the linear regression parameters to solve typical analytical
problems, like method comparison, calculation of the uncertainty in the inverse regression, determination
of the detection limit. The results of this new approach are compared to those obtained with
appropriate reference methods, using simulated and real data sets. The nonparametric Theil–Sen regression
technique appears a new robust tool for the problems considered because it is free from restrictive
statistical constraints, avoids searching for the error nature on x and y, which may require long analysis
times, and it is easy to use. The only drawback is that the intrinsic nature of the method may lead to a
possible enlargement of the uncertainty interval of the discriminated concentration and to the determination
of larger detection limits than those obtainable with the commonly used, less robust, regression
techniques
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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