1,721,117 research outputs found
Unliganded human mutant alpha 7 nicotinic receptors are modulated by Ca2+ and trace levels of Zn2+
No full textA large body of evidence indicates that ligand-gated channels may open spontaneously, exhibiting a basal activity in the absence of the neurotransmitter. In the present work. we were interested in studying the Ca2+-induced modulation of the basal channel activity of unliganded human L248alpha7 receptors expressed in Xenopus oocytcs. While the basal channel activity was blocked by either the nicotinic antagonist methyllycaconitine or the superfusion With a Ca2+-free medium, it was enhanced by increasing external Ca2+ concentrations. External Ca2+ significantly influenced the channel properties lengthening the channel duration and reducing the channel conductance, in a dose dependent manner. Furthermore, the basal channel activity in standard medium was blocked by N,N,N',N'-tetrakis-2-pyrdylmethyl-ethylenediamine, the chelator of divalent cations with very high affinity for Zn2+, and was induced by Zn2+ when Ca2+ was present in the external medium. We conclude that basal activity of alpha7 mutant receptor-channels is caused by divalent cation contaminants present in the external medium, namely Zn2+; is positively modulated by the external Ca2+ and is inhibited when Ca2+ is absent front the medium. The patho-physiological consequences of these findings are discussed. (C) 2004 Elsevier Ltd. All rights reserved
Auger-electron emission induced by Ar+ impact on silicides
No full textImpact of ions of several kilo-electron-volts (keV) with solids produces inner-shell excitations. The consequent decay results in the emission of Auger electrons whose spectra differ considerably from electrons or x-ray-excited spectra. Si (L23-derived) Auger emission, induced by Ar+ bombardment in pure Si and silicides of different metals (Cr,Ni,Pt) and stoichiometry (from NiSi2 to Ni3Si), has been studied by varying both the energy of the primary ions (in the 1–5-keV range) and the takeoff angle (from grazing to normal geometry). We separated the background of inelastic scattered electrons from the Auger electrons, and in a further step the contributions to the spectra coming from deexcitation inside and outside the solid. The portion of the Auger emission which originates from sputtered atoms (‘‘atomic spectrum’’) was found to depend on the target composition and takeoff angle, being larger in metal-rich silicides and at grazing geometry. The parents of ‘‘atomic’’ Auger electrons were found to be mainly neutral and excited sputtered atoms in Si and Si-rich silicides, while in metal-rich silicides there is a dominant contribution from sputtered ions. These results have been discussed in terms of the inner-shell ionization mechanism and the in-depth distribution of exciting collisions. The ‘‘atomic’’ spectral shape dependencies on ion energy and takeoff angle have been interpreted in terms of the Doppler shift imparted to the Auger-electron velocity by an anisotropic jet of high-energy parent atoms
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
Reply to comments on 'EPR study of He-implanted Si' by P. Pivac, B. Rakvin, R. Tonini, F. Corni, G. Ottaizani, Published in Mater. Sci. Eng. B73 (2000) 60-63 - Written by M. Kakazey, M. Vlasova, and J.G. Gonzalez-Rodriguez - Reply to discussion
No full textReply to comments on 'EPR study of He-implanted Si' by P. Pivac, B. Rakvin, R. Tonini, F. Corni, G. Ottaizani, Published in Mater. Sci. Eng. B73 (2000) 60-63 - Written by M. Kakazey, M. Vlasova, and J.G. Gonzalez-Rodriguez - Reply to discussio
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
Properties of neuronal alpha7 mutant nicotinic acetylcholine receptors gated by bicuculline.
No full textWe have shown previously that mutating to threonine the leucine residue in the M2 domain of the alpha7 nicotinic acetylcholine receptor (human L248T, L248T; chick L247T, L247T) converts bicuculline (BIC) from an antagonist into an agonist. In this work we studied the functional properties of the BIC-activated channels and report that, in Xenopus oocytes injected with L248T subunit cDNA, BIC activates single-channel currents that have similar conductances, but shorter mean burst duration, than the channels activated by ACh. In contrast, both the conductance and kinetics of the channels activated by either ACh or BIC are substantially the same in oocytes expressing L247T receptors. We have also shown previously that if Cys 189 and 190, which are thought to be at or near the transmitter binding site, are additionally mutated to Ser, the new mutant receptor (L247T-C189S-C190S) has a reduced affinity for ACh. We now find that the EC(50) in the BIC dose-current response relation, as well the characteristics of the channels activated by BIC, are similar in oocytes expressing either L247T or L247T-C189S-C190S receptors. On the other hand, ACh activation of L247T-C189S-C190S receptors gates channels whose mean open time and burst duration are much shorter than those of ACh-gated L247T-channels. Therefore, the gating kinetics of both L248T and L247R-C189S-C190S receptor-channels change when BIC is replaced by ACh; and we conclude that both ACh and BIC activate mutant alpha7 receptors with different patterns of activation
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