1,720,968 research outputs found
Voltammetric determination of the geometrical parametres of inlaid microdisks with shields of thickness comparable to the electrode radius
No full textThe cyclic voltammetric behavior of disk microelectrodes surrounded by thin insulating shields (TSM) was investigated from both theoretical and experimental points of view. In particular, microdisks with shields of thickness (b - a), a few electrode radii (a) were considered. A finite difference simulation procedure with a nonuniform, expanding spatial grid, already available in the literature, was employed for predicting shape and height of the voltammograms. The parameters of this numerical simulation were optimized again, and the steady-state limiting currents found in this work for a range of TSMs compared well with previous publications. The steady-state limiting current at TSMs was enhanced with respect to microelectrodes surrounded by thick insulating sheaths (i.e., b ≫ a), and steady-state conditions were achieved faster. Under these conditions, the difference in potential observed on the forward and backward waves, when the current is half of its maximum value (ΔE1/2), was almost equal to zero. Nonsteady-state cyclic voltammograms were also simulated using the optimized parameters, and the effect of scan rate on ΔE1/2 was examined in detail. Based on this dependence, a voltammetric procedure for the simultaneous determination of microdisk radius and its insulator thickness was proposed. Experimental measurements were performed by using platinum wires, 10-12.5-μm radius, and carbon fibers, 4-μm radius, coated with 4-6-μm-thick electrophoretic paint. The shield thickness produced around the wires was such that b/a < 3. The experimental results obtained were in general congruent with the theory and demonstrated the validity of the method proposed here for the simultaneous determination of radius and shield thickness of a TSM
L’attività ß-glucanasica è coinvolta nell’azione antimicrobica della tossina killer di Kluyveromyces phaffii.
No full textEFFECT OF THE INSULATING SHIELD THICKNESS ON THE STEADY-STATE DIFFUSION-LIMITING CURRENT OF SPHERE CAP MICROELECTRODES
No full textThe effect of the insulating shield thickness on the steady-state diffusion-limiting current of sphere caps microelectrodes is investigated. Theoretical steady-state limiting currents are obtained by using a simulation procedure, which relies on the explicit finite difference method with a fixed time grid and an exponentially spatial grid. The results obtained indicate that the current increases by decreasing the thickness of the insulating sheath or by increasing the aspect ratio of the sphere cap (h/a, where h is the height of the sphere cap and a is the electrode basal radius), similarly to other types of microelectrodes with different electrode geometry, such as disks and finite cones. The simulated data are fitted to approximate analytical expressions to describe the dependence of the limiting current on both h/a and RG (RG = b/a, where b is the overall tip radius) parameters. Theoretical currents are also compared with experimental data, which are obtained with a range of mercury coated platinum microelectrodes having different RG and h/a values. The measurements are performed by using cyclic voltammetry at 1 mVs-1, in aqueous solutions containing Ru(NH3)6Cl3 as electroactive species. A good agreement (within 3%) between theoretical and experimental steady-state currents is found. Finally, SECM operating in the feedback mode is used to asses the validity of the shape parameters found by voltammetry for sphere cap microelectrodes, whose insulating shields are of thickness comparable to the electrode radius
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
Effects of surface pressare on oxygen transfer across monolayers at the air/water interface: Scanning electrochemical microscopy investigations using a mercury hemispherical microelectrode probe
No full textInvestigations of the kinetics of molecular transfer across the liquid/gas interface and the effect of a molecular monolayer are of considerable interest as a model for certain biological and environmental processes. In this work, a combined scanning electrochemical microscopy (SECM)-Langmuir trough technique has been used to investigate the effect of the chemical character and mechanical compression of molecular monolayers on the rate of oxygen transfer across the air/water (A/W) interface. Specifically, monolayers comprising the fatty alcohol 1-octadecanol and the phospholipid L-α-dipalmitoyl phosphatidic acid were considered. A mercury hemispherical microelectrode probe has been used to measure interfacial kinetics in SECM, and a numerical model has been developed for mass transport in this configuration to allow quantitative analysis of experimental data. The results obtained suggest that, for both monolayers, the oxygen-transfer rate across the interface decreased compared to that across the clean interface, with the blocking effect becoming more pronounced as the surface pressure of the monolayer increased. A simple energy-barrier model was used successfully to interpret the dependence of the rate constant of oxygen transfer on the surface pressure. The experimental data also provide evidence for the effect of the SECM probe on the deformation of the water surface at very close distances to the A/W interface
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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