1,720,960 research outputs found
Peroxidase Based Amperometric Biosensors for the Determination of GABA.
No full textThis work presents the realization of enzymatic bioelectrodes, suitable for the determination of g-aminobutyric acid (GABA). The biosensors are based on the catalytic activity of the enzymes g-aminobutyric glutamic transaminase (GABA-T), succinic semialdehyde dehydrogenase (SSDH) and horseradish peroxidase (HPO). The first two enzymes are usually indicated by the general term "GABASE". All the biosensors presented in this work are realized by immobilizing the enzyme HPO on the tip of an amperometric oxygen selective electrode: the resulting NADPH-sensitive biosensor is used in combination with GABASE to determine the concentration of GABA in aqueous samples. Since SSDH depends on the NADP+/NADPH equilibrium, it follows that, in the presence of HPO, the NADPH formed is oxidized to NADP+, and the decrease in the concentration of dissolved oxygen is proportional to the concentration of NADPH and, in turn, to that of GABA. The experiments were performed either with GABASE free in solution or co-immobilized with HPO on the surface of the oxygen electrode. In the latter case, the immobilization of the three enzymes has been performed either on a single membrane or on two separated membranes. In both cases there is an almost perfect linearity between the electrode signal and GABA concentration in the range 5.0x10-5 - 1.210-3 M, with a lower detection limit of 2.010-5 M; but the single-membrane biosensor showed a better overall performance, especially in terms of repeatability of measurements and lifetime of operation
Interactions between calcium entry blocking drugs and carbonic anhydrase.
No full textThe interactions between some of the most common calcium entry blocker drugs (CEB) and the enzyme carbonic anhydrase (CA) are studied in the present work by an electroanalytical approach. The study comprises drugs belonging to the classes of phenylalkylamines, dihydropyridines, benzothiazepines and piperazines. The evaluation of the potential inhibitory power towards CA was performed either by measuring the speed of CO2 diffusion taking place from a buffered solution of NaHCO3, or by monitoring the metabolic activity of yeast cells. The results obtained according to both of these procedures have shown that verapamil and gallopamil are endowed with a relevant inhibitory power on CA catalytic activity, whereas all the other compounds, tested in the same experimental conditions, did not show any effect on CA activity
Data-Driven Constraint Handling in Multi-Objective Inductor Design
Get PDFThis paper analyses the multi-objective design of an inductor for a DC-DC buck converter. The core volume and total losses are the two competing objectives, which should be minimised while satisfying the design constraints on the required differential inductance profile and the maximum overheating. The multi-objective optimisation problem is solved by means of a population-based metaheuristic algorithm based on Artificial Immune Systems (AIS). Despite its effectiveness in finding the Pareto front, the algorithm requires the evaluation of many candidate solutions before converging. In the case of the inductor design problem, the evaluation of a configuration is time-consuming. In fact, a non-linear iterative technique (fixed point) is needed to obtain the differential inductance profile of the configuration, as it may operate in conditions of partial saturation. However, many configurations evaluated during an optimisation do not comply with the design constraint, resulting in expensive and unnecessary calculations. Therefore, this paper proposes the adoption of a data-driven surrogate model in a pre-selection phase of the optimisation. The adopted model should classify newly generated configurations as compliant or not with the design constraint. Configurations classified as unfeasible are disregarded, thus avoiding the computational burden of their complete evaluation. Interesting results have been obtained, both in terms of avoided configuration evaluations and the quality of the Pareto front found by the optimisation procedure
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Plant tissue biosensors for the determination of biogenic diamines and of their amino acid precursors: effect of carbonic anhydrase
No full textA new class of plant tissue biosensors has been set up and applied to the determination of biogenic diamines. All the biosensors presented in this work are based on the amperometric determination of H2O2 produced by the enzymatic oxidation of diamines (putrescine and cadaverine) by the diamine oxidase (DAO) contained in the cotyledon of legumes (pea and lentil). Putrescine and cadaverine were quantitatively determined by means of these plant tissue electrodes in a range of concentrations between 0.5 and 320 μM and between 0.5 and 200 μM, respectively. The same lentil tissue-based sensor was then used, in combination with a lysine decarboxylase (LDC) membrane, for the realization of a hybrid enzyme electrode for the determination of lysine. The performances of the sensor here proposed, tested in lysine standard solutions, were comparable to those of traditional lysine bienzyme electrodes. A similar enzyme electrode was assembled for the determination of ornithine: in this case the lentil tissue diamine oxidase sensor was used in combination with an adequate amount of ornithine decarboxylase (ODC), added directly into the measuring cell. The effect of carbonic anhydrase (CA) on the speed of the LDC- and ODC-catalysed reactions was also evaluated. The synergistic interaction observed between the decarboxylation reaction, operated by either LDC or ODC, and the faciliated transport of CO2, operated by CA, is discussed both in terms of its analytical relevance and of its broader physiopathologic implications
Determination of glutamic acid decarboxylase activity and inhibition by an H2O2-sensing glutamic acid oxidase biosensor.
No full textThe catalytic activity of the enzyme L-glutamic acid decarboxylase (GAD) is determined by an amperometric method based on a recently developed glutamate-selective biosensor. The biosensor is composed of an amperometric H2O2 electrode and a biocatalytic membrane containing the enzyme glutamic acid oxidase (GAO). The biosensor allows the direct and continuous measurement of GA levels by monitoring the H2O2 produced at the electrode interface as a coproduct of the GAO-catalyzed GA oxidation to alpha-ketoglutaric acid. Since GA is transformed to gamma-aminobutyric acid and CO2 under the catalytic activity of GAD, the rate of GA consumption in solution, monitored by the GAO biosensor, represents a reliable measure of GAD catalytic activity. Additional experiments performed in the presence of different concentrations of the GAD inhibitor valproic acid have shown the suitability of the proposed approach for the study of GAD inhibitors also. Discussion of the main experimental characteristics of this new analytical method is given in terms of sensitivity, reproducibility, and reliability of the experimental results and ease, time, and cost of operation
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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