1,720,959 research outputs found
AN AMPEROMETRIC NADH BIOSENSOR BASED ON NADH OXIDASE FROM THERMUS-AQUATICUS
No full textA biosensor for the determination of the reduced cofactor nicotinammide adenine dinucleotide (NADH) has been developed using the enzyme NADH oxidase from Thermus aquaticus immobilized on an Immobilon AV membrane. A hydrogen peroxide electrode,was used as the detection system. The NADH electrode showed a monotonous response with near linearity in the 5.10(-7) to 2.10(-5) M range, with a detection limit of 2.10(-7) M. Analytical parameters such as pH, response time and lifetime,vere characterized. The probe showed no change in sensitivity between pH 4.5 and 9.5 and retained 70% of its initial activity after 50 days of storage in buffer. A method for the measurement of lactic dehydrogenase (LDH) activity was developed using the biosensor. The response was linear in the 10-1000 U l(-1) range. The addition of NADH and LDH to serum gave recovery values between 94 and 107%. The determination of LDH in two control sera and in three serum samples was performed with a standard spectrophotometric procedure and the biosensor. The results correlated well.[...
POTENTIOMETRIC DETERMINATION OF GLUTATHIONE AND GLUTATHIONE TRANSFERASE-ACTIVITY
No full textA new method of determination of Glutathione Transferase activity (GST) and Glutathione (GSH) in solution has been developed. The determination was performed by detection of ions (H+, Cl-, F-) produced during the GST catalyzed reaction using ion-selective electrodes. The Michaelis constants of GST pi from human placenta toward GSH, 1-Chloro-2,4-dinitrobenzene (CDNB) and 1-Fluoro-2,4-dinitrobenzene (FDNB) obtained potentiometrically were similar to those calculated with the classical spectrophotometric method. The use of pH electrode gave the best results for GST activity (1 pH unit slope per 0.1 unit of enzyme in 1 ml of solution; detection limit of 0.001 unit/ml). Different purification steps of GST pi from human placenta followed by this method gave results comparable to the spectrophotometric one. The best calibration curve for GSH (2 x 10(-5) M detection limit) was obtained following the production of F- ions with a fixed amount of enzyme at a concentration of 0.2 U/ml. A calibration obtained performing the measurements in filtrated human serum showed the same behaviour.[...
GLUTATHIONE S-TRANSFERASE DOES NOT COMPLEMENT TYROSINASE IN THE SYNTHESIS OF GLUTATHIONYL-DOPA
No full textGoing 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
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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