1,720,986 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
EFFECT OF PYRIDOXAL 5'-PHOSPHATE AND VALPROICACID ON PHOSPHOLIPID SYNTHESIS INNEUROBLASTOMA NA
No full textPhospholipid metabolism in neuroblastoma cells in monolayer culture after acute exposure to pyridoxal phosphate (PLP) has been studied. (a) A strong depression of the rate of biosynthesis of cellular phospholipids from labeled choline and ethanolamine, is demonstrated in neuroblastoma cells grown in culture media containing PLP. (b) Valproic acid reverses the effect of PLP on ethanolamine and choline incorporation into cell lipid. Other anticonvulsants (clonazepam, diazepam, carbamazepine,
diphenylhydantoin and ethosuximide) have Iittle or no effect on reversing the inhibition of lipid synthesis produced by PLP. (c) PLP decreases the cellular uptake of choline. This effect might be responsible for the decreased lipid synthesis and is partially reversed by valproic acido. (d) The energy charge of the cell
is not affected by either PLP or valproic acid, but it is diminished by the two compounds together. (e) The degradation of choline lipids is decreased by PLP and valproic acid. The hydrolysis of phosphocholine and the outflow of choline from cultured cells is also affected by the drugs. Variations of ethanolamine and choline transport should not be due to any effects of PLP or valproic acid on the lipid phase of the membranes since these molecules have no effect on the permeability of liposomes. (f) It is concluded
that ethanolamine and choline lipid metabolism in cultured neuroblastoma cells is influenced by PLP and/or valproic acid, probably through a mechanism involving the transport of precursors across the membrane, although other mechanisms cannot be ruled out
Ethanolamine Base-Exchange Reaction in Rat BrainMicrosomal Subfractions
No full textCrude microsomal fractions have been subfractionated
by differential ultracentrifugation into subfractions
A, B, and C, corresponding to light smooth. heavy
smooth, and rough microsomal membranes, respectively.
The purity and the vesiculation of the membranes were
checked biochemically. Subfraction C showed the highest
ethanolamine base-exchange activity, both on phospholipid
and protein bases. The other two subfractions had
roughly similar activities. The kinetic behavior of the
enzyme activity, although anomalous, was similar in the
three subfractions. Treatment of the vesicles with
Pronase or with mercury-dextran produced inactivation
of the ethanolamine base-exchange reaction in the three
subfractions. These findings suggest that the active site
of base-exchange activity would be localized on the external
leaflet of the vesicles. Treatment of the membranes
with trinitrobenzenesulfonic acid (TNBS) has shown that
the newly synthesized phosphatidylethanolamine (PE)
belongs to a pool easily reacting with the probe, independent
of the subfraction investigated. On the other
hand, the distribution of the bulk membrane PE reacting
with TNBS differs in the three subfractions examined. It
is concluded that the newly synthesized PE and probably
the active site of the enzyme are on the external leaflet
of the membrane in all subfractions and that the ethanolamine
base-exchange reaction has similar properties
in all subfractions. Key Words: Phosphatidylethanolamine-
Base exchange-Brain microsomal subfractions-
Trinitrobenzenesulfonic acid-Trinitrophenylphosphatidylethanolamine-
Mercury-dextran-Proteases.
Corazzi L. et al. Ethanolamine base-exchange
reaction in rat brain microsomal subfractions
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
Compartmentation of Newly Synthesized Phosphatidylethanolamine in Rat Brain Microsomes
No full textThe compartmentation of the phosphatidylethanolamine
newly synthesized in brain microsomes in vitro either by
base exchange or net synthesis has been studied, using difluorodinitrobenzene as a chemical probe. The experimental results demonstrate that in rat brain microsomes the phosphatidylethanolamine molecules synthesized by base exchange and the bulk membrane lipid belong to different pools. Ca2+ bound to microsomes seems to be involved in the maintenance of the compartmentation of phosphatidylethanolamine. In the presence of Ca2+ the newly synthesized phosphatidylethanolamine molecules react with difìuorodinitrobenzene as though they are organized
in clusters. After biosynthesis in vivo or in vitro through
the cytidine pathway, the compartmentation of the newly formed
phosphatidylethanolamine appears less marked than after the
synthesis through base exchange
Compartmentation of membrane phosphatidylethanolamine formed by base-exchange reaction in rat brain microsomes
No full textThe compartmentation of membrane phosphatidylethanolamine (PE) formed by base-exchange reaction in rat brain microsomal vesicIes has been investigated. After labelling membrane PE by base-exchange in vitro, microsomal vesicIes were treated with trinitrobenzenesulfonic acid (TNBS). The amount of membrane PE
reacting with TNBS depends on the duration and the temperature of the reaction as well as on the TNBS concentration. It was found that almost all of the labelled PE molecules, but only about 24% of membrane PE, were accessible to TNBS, under very mild reaction conditions. It is concIuded that PE labelled by
base-exchange is completely localized in the cytoplasmic leaflet of microsomal vesicIes
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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