1,720,960 research outputs found
Probing membrane permeabilization by the antibiotic lipopeptaibol trichogin GA IV in a tethered bilayer lipid membrane
No full textAbstractThe lipopeptaibol trichogin GA IV (TCG) can be incorporated in the lipid bilayer moiety of a mercury-supported tethered bilayer lipid membrane (tBLM) at a non-physiological transmembrane potential of about −240mV, negative on the trans side of the bilayer. Once incorporated in the tBLM, TCG is stable over the range of physiological transmembrane potentials and permeabilizes the membrane at transmembrane potentials negative of −80÷−90mV. The chronocoulometric behavior is consistent with a kinetics of nucleation and growth of bundles of TCG building blocks with ion-channel properties. The TCG building blocks also permeabilize the lipid bilayer, albeit at more negative transmembrane potentials, and can be tentatively regarded as dimers of aligned TCG helical monomers. The cyclic voltammograms of tBLMs incorporating TCG point to a voltage-gated behavior of the TCG channel, similar to that exhibited by the peptaibol alamethicin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
A Peptide-tethered Lipid Bilayer on Mercury as a Biomimetic System
No full textA novel spacer consisting of a hexapeptide molecule with a high tendency to form a 310-helical structure, which terminates with a sulfydryl group for anchoring to a metal, was tailored for use as a tethered hydrophilic spacer to be interposed between a metal support and a lipid bilayer. The thiol peptide has two triethylenoxy side chains that impart it a satisfactory hydrophilicity and are intended to keep the anchored thiol peptide chains sufficiently apart so as to accommodate water molecules and inorganic ions and to create a suitable environment for the incorporation of integral proteins. This thiol peptide was anchored to a hanging mercury drop electrode. The formation of a phospholipid bilayer on top of the self-assembled thiol peptide was carried out by a novel procedure which exploits the spontaneous tendency of a lipid film to form a bilayer when interposed between two hydrophilic phases. The resulting mercury-supported thiol peptide/lipid bilayer system was characterized by ac voltammetry with phase resolution, chronocoulometry, and impedance spectroscopy. The suitability of this tethered film as a biomembrane model was tested by incorporating ubiquinone-10 and valinomycin
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
A metal-supported biomimetic micromembrane allowing the recording of single- channel activity and of impedance spectra of membrane proteins
No full textA novel tethered bilayer lipid micromembrane (tBLμM) was prepared and characterized. It consists of a mercury cap electrodeposited on a platinum microelectrode, about 20 μm in diameter. The micromembrane was prepared by tethering to the mercury cap a thiolipid monolayer and by then self-assembling a lipid monolayer on top of it. The thiolipid consisted of a disulfidated tetraoxyethylene hydrophilic spacer covalently linked to two phytanyl chains. Upon incorporating OmpF porin in the tBLμM, its single-channel activity was recorded by the patch-clamp technique, and its particular features described. An electrochemical impedance spectrum of the tBLμM incorporating OmpF porin is also reported. To the best of our knowledge, this tBLμM is the first metal-supported biomimetic micromembrane capable of incorporating non-engineered channel proteins in a functionally active state from their detergent solutions, and of allowing the recording of single-channel activity and of impedance spectra of these proteins via ion translocation into the hydrophilic spacer. The limited spaciousness of the spacer prevents a statistical analysis based on current–amplitude or blockage–time histograms. Nonetheless, the robustness, stability, ease of preparation and disposability of the present tBLμM may open the way to the realization of a channel-protein microarray platform allowing a high throughput drug screening
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