1,720,987 research outputs found
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
TRP channels expression in Chronic Low Back Pain
No full textChronic Low Back Pain (CLBP) is an inflammatory condition that may originate from an injury, disease or stress on tendons, ligaments and discus of the spinal structure. It is known that neuroinflammatory processes are pathologichallmarks of CLBP that lead to the release of proinflammatory molecules that increase nociceptors sensitization, pain hypersensitivity or hyperalgesia. Transient Receptor Potential (TRP) channels are known to act as receptors of various stimuli in peripheral sensory neurons and in other somatic structure. Numerous studies highlighted the activation and/or sensitization of these channels during inflammation as the major mechanism underlying neuropathic and inflammatory pain. In order to investigate the roleplayed and to classify TRPs channels in samples from 6 patients affected by CLBP, the TRPs expression was measured and morphological, ultrastructural and immunohistochemical alterations were analyzed. Immunofluorescence and expression analyses showed a significant increase in the levels of TRPs (A1, V1, V2, V4 and M8) in the pathological capsule compared to control tissues. Interesting, in each patient analyzed, we found an over-expression of TRPV4, independently by the location and number of affected sites. Moreover, using silver impregnation, it was shown that in CLBP patients the capsular connective tissue appeared degraded and infiltrated by sensitive unmyelinated nervous fibers. The findings confirm the involvement of TRP channels, in particularly of the TRPV4 and TRPM8 in CLBP pathological condition suggesting that these channels could represent a target for new therapeutic approaches
A comparative electrophysiological characterization of Slc15a1 transporters, PepT1a and PepT1b, of two teleost fishes
No full textThe Solute Carrier 15 (SLC15) family includes H+-coupled membrane transporters known for their role in the cellular uptake/reuptake of di/tripeptides and peptidomimetic molecules. Among its members, SLC15A1 (PepT1) mediates intestinal absorption by transporting luminal di/tripeptides with an electrogenic process that follows Michaelis Menten kinetics. Due to the teleost specific whole-genome duplication event, two pept1 paralogues pept1b and pept1a, are found in the genome of teleost species. The function of PepT1b transporters is known in several teleosts, including zebrafish (Danio rerio) and Atlantic salmon (Salmo salar). In this study, we functionally characterized zebrafish PepT1a (zfPepT1a) and salmon PepT1a (asPepT1a) to gain insights into their role in animal nutrition. Their function, measured as the current elicited in the presence of substrates, were recorded using Two-Electrode Voltage-Clamp technique after heterologous expression in Xenopus laevis oocytes. For both PepT1a transporters, the Gly-Gln transport followed Michaelis Menten type saturation kinetics with apparent affinity (1/K0.5) and maximal relative current (Imax) values differently affected by membrane potential and external pH. Regarding Imax, the asPepT1a was only slightly affected by pH, whereas zfPepT1a showed a larger increase at pH 7.6 than pH 6.5 similarly to zfPepT1b. For all transporters (PepT1a and b of zebrafish and salmon), the K0.5 was in the hundreds of micromolar range and only slightly voltage-dependent at pH 6.5. At pH 7.6, all transporters K0.5 values increased to millimolar range, but only PepT1a was strongly voltage-dependent. A clear different substrate preference between PepT1a and b was highlighted when testing charged substrates (Gly-Lys, Lys-Gly, Met-Lys, Lys-Met, Gly-Asp and Asp-Gly). Our data supports the hypothesis that PepT1a and PepT1b have distinct roles in intestinal peptide recognition and transport
Functional analysis, properties and kinetics of a PepT2-type di/tripeptide transporter of the Atlantic salmon (Salmo salar) highly expressed in midgut and hindgut
No full textThe SoLute Carrier 15 (Slc15) family includes H+-dependent transporters that play a key role in the cellular uptake/reuptake of di/tripeptides and peptidomimetics. In mammals, in the epithelial cells of intestine and renal tubules two di/tripeptide transport systems have been characterized: the low-affinity/high-capacity system Slc15a1 (PepT1) and the highaffinity/low-capacity system Slc15a2 (PepT2). While PepT1 transporters have been studied in many teleost species, data on PepT2 is still lacking, except for zebrafish (Danio rerio). Here, we performed basic functional and expression analyses of a newly cloned Atlantic salmon (Salmo salar) PepT2. In Xenopus laevis oocytes, transient currents analysis showed that both total amount of charges moved (Q) and decay time (τ) vs membrane voltage shifted to more positive potential values when extracellular pH decreased, highlighting the role of H+ in the first step of transport cycle. Transport current vs voltage relations, as from Gly-L-Gln dose-response experiments, allowed kinetic parameters to be determined as a function of potential (from 140 to +20 mV) and external pH (5.5, 6.5, 7.6). Salmon PepT2 showed the higher apparent Gly-L-Gln affinity (K0.5) at pH 5.5 and 6.5 at the physiological membrane potential and an increase of maximal relative current (Imax) for more negative potentials and more acidic conditions. Notably, mRNA tissue expression analysis revealed that it is highly expressed in midgut and hindgut. Similar to zebrafish, this salmon PepT2 is a high-affinity/low-capacity transporter (K0.5 for Gly-Gln 4,4 μM, Imax -10 nA at -40 mV at pH 6.5), but its specific expression in the mid-to-distal portions of the gut opens to distinct and not yet known roles for a PepT2-type protein in fish physiology
Slc15a1 transporters in teleosts fish: PepT1a and PepT1b, comparative functional studies
No full textDi/tripeptides are key nutrients in animal diets, and fundamental for growth. They are transported across the membrane of enterocytes via the Slc15a1/PepT1 peptide transporter, that uses an inwardly-directed proton electrochemical gradient to drive the uptake. Due to a genome duplication event, PepT1a and PepT1b paralogues are found in teleost fish. Two PepT1a transporters, respectively cloned from the Atlantic salmon (Salmo salar) and zebrafish (Danio rerio), namely asPepT1a and zfPepT1a, have been characterized. For both orthologs, function was verified by heterologous expression in Xenopus laevis oocytes, highlighting electrogenic, Na+-independent and pH-dependent transport similarly to the well-known PepT1b. The transient currents and the transport currents recorded from asPept1a and zfPepT1a indicate significant functional differences with respect to PepT1b. PepT1a can be described as a low‐affinity/high‐capacity system, but its substrates preference profile is peculiar in the species, particularly for charged dipeptides. Moreover, the pre-steady state (PSS) currents, that reflect the first steps of transport cycle display in the charge/voltage relationship differences with respect to Pept1b in the voltage dependence. Considering that the PSS are consequence of the rearrangement of the protein in the membrane electric field, PepT1a transporters interact with the substrate at physiological pH, differently from PepT1b. In addition, PepT1a and PepT1b have similar expression profile but different expression levels. These data together with a significant dissimilar substrate specificity, support the idea of distinct roles for these proteins in peptide recognition and transport
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