1,720,968 research outputs found
Radiofrequency dielectric spectroscopy of ribosome suspensions
No full textDielectric measurements on different ribosome suspensions were carried out in the frequency range from 10 kHz to 1 GHz. In intact ribosomes two dispersions were detected: one around 100 kHz and the other one in the MHz region. In separated ribosomal subunits and in ribosomes resuspended in a buffer with no magnesium ions (relaxed ribosomes) only the MHz dispersion was observed. Electrical conductivities of the samples at 1 kHz were also measured. The temperature dependence of the two dispersions was investigated and a tentative attribution was proposed
La capsula del cristallino e la prevenzione della cataratta secondaria
No full textSono state studiate le modificazioni della proliferazione e della sopravvivenza di cellule in coltura, al fine di individuare gli eventuali effetti tossici di due farmaci per anestesia locale, normalmente utilizzati negli interventi chirurgici oculari. I risultati ottenuti hanno dimostrato che la lidocaina possiede un’elevata azione citotossica e citostatica a concentrazioni dell’ordinedi 10mM, concentrazioni paragonabili a quelle normalmente utilizzate in sala operatoria per uso anestetico. Viceversa, la ropivacaina presenta una tossicità nettamente inferiore e sostanzialmente trascurabile alle concentrazioni da noi saggiate e paragonabili a quelle utilizzate in anestesia. E’ lecito ipotizzare che l’azione citotossica e citostatica della lidocaina può essere impiegata nella prevenzione della opacizzazione della capsula del cristallino (cataratta secondaria)
Effects of magnesium ions on ribosomes: A fluorescence study
No full textFluorescence intensity measurements of ethidium bromide (EB) bound to ribosomal RNA (rRNA) in suspensions of 30S and 50S subunits, of 70S ribosomal particles and of protein-free extracted rRNA are presented. Changes in the intercalation of EB reflect changes in conformation and degree of exposure of rRNA. The effect of removal of magnesium ions on the binding of EB is compared in protein-free rRNA and in ribosomal particles by a Scatchard plot analysis. In free ribosomal RNA the number of bound EBs do not depend on magnesium content, only the association constant is affected. In intact 70S particles and both in the separated 50S and 30S subunits the presence of magnesium greatly reduces binding of EB and no saturation of the fluorescence intensity with rRNA concentration is observed, preventing a Scatchard plot analysis. Removal of magnesium restores a strong EB intercalation. Then magnesium ions induce a conformational change in the 70S particles as well as in the separated subunits. The different behavior of the free-rRNA and of the ribosomal particles indicates that ribosomal proteins are relevant to the structural changes induced by magnesium ions. The comparison of the number of excluded sites and of the association constant in the 30S, 50S subunits and in the 70S particles indicates that even without Mg2+ ions the two subunits still interact, at variance with the commonly shared opinion that subunits dissociation takes place at low magnesium concentration
Electrical conductivity and dielectric dispersion of E. coli 70S ribosomes and of 30S and 50S subunits: effects of magnesium ions
No full textElectrical conductivity and dielectric dispersions have been measured on suspensions of 30S, 50S subunits and 70S ribosomal particles from E. coli, in the presence and absence of magnesium ions. Conductivity measurements show a net contribution due to the disperzed phase. Ribosomal particles act in general as obstructants to the ionic motions in the solution, but besides this effect, there is an intrinsic contribution to the overall conductivity which is more pronounced in the absence than in the presence of magnesium ions. This effect suggests the existence of an interfacial conductivity, modulated by bound magnesium ions. The intrinsic conductivity is higher in the 30S subunit than in the 50S. Dielectric dispersions show a consistent difference between 30S and 50S, indicating that the exposure of ribosomal RNA should be greater in the 30S than in the 50S. Structural information is derived from the conductivity measurement, via the Looyenga equation
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
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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