1,720,962 research outputs found
Photoinduced electroreduction of chlorophyllide on alkanethiol-coated mercury
No full textMonolayers of n-alkanethiols of chain length from C-12 to C-18 were self-assembled on a hanging mercury drop electrode, and a film of chlorophyllide (Chlide) was adsorbed on top of them. The reduction photocurrents following illumination of the Chlide film were measured over the potential range in which the Chlide is electroinactive in the dark, and their action spectra were determined. Plotting the derivative of the photocurrents with respect to the applied potential against potential yields bell-shaped curves that can be fitted to a Gaussian. The potential of the Gaussian maximum was used to determine the reorganization energy for the Chlide electroreduction process. An increase in the thiol chain length causes A to decrease regularly and the photocurrent to decay exponentially with the monolayer thickness, with a decay constant beta of about 0. 17 Angstrom(-1)
Incorporation of channel-forming peptides in a Hg-supported lipid bilayer
No full textThe channel-forming peptides gramicidin and alamethicin were incorporated in a mercury-supported lipid bilayer composed of a tethered thiolipid monolayer with a self-assembled dioleoylphosphatidylcholine monolayer on top of it. The thiolipid consists of a hexapeptide chain with a high tendency to form a 310-helical structure, which terminates at the N-terminus end with a sulfydryl group for anchoring to the metal while the C-terminus end is covalently linked to the polar head of dimyristolylphosphatidylethanolamine. The hexapeptide moiety has two triethyleneoxy side chains that impart a satisfactory hydrophilicity and are intended to keep the anchored thiolpeptide chains sufficiently apart, so as to accommodate water molecules and inorganic ions and to create a suitable environment for the incorporation of integral proteins. Changes in the conductance of this biomimetic membrane following the incorporation of gramicidin and alamethicin were detected by impedance spectroscopy. The surface dipole potential of the hexapeptide chain and the transmembrane potential of the lipid bilayer were estimated by using a simple electrostatic model of the mercury|solution interphase
Electrogenic Ion Pumps Investigated on a Solid Supported Membrane: Comparison of Current and Voltage Measurements
No full textCurrent and voltage measurements were performed on Na,K-ATPase and sarcoplasmic reticulum (SR) Ca-ATPase. Measurements of current transients under short-circuit conditions and of voltage transients under open-circuit conditions were carried out by employing a solid supported membrane (SSM). Purified membrane fragments containing Na,K-ATPase or native SR vesicles were adsorbed on a SSM and were activated by performing substrate concentration jumps. Current and voltage transients were recorded in the external circuit, that are related to pump activity, and can be attributed to electrogenic events in the reaction cycles of the two enzymes. While current transients of very small amplitude are difficult to detect, the corresponding voltage transients can be measured with higher accuracy thanks to a much more favourable signal to noise ratio. Therefore, voltage measurements are preferable for the investigation of slow processes generating low current signals, e.g. for the analysis of low turnover transporters
Translocation of Platinum Anticancer Drugs by Human Copper ATPases ATP7A and ATP7B
No full textCisplatin, carboplatin, and oxaliplatin are widely used anticancer drugs. Their efficacy is strongly reduced by development of cell resistance. Down-regulation of CTR1 and up-regulation of the Cu-ATPases, ATP7A and ATP7B, have been associated to augmented drug resistance. To gain information on translocation of Pt drugs by human Cu-ATPases, we performed electrical measurements on the COS-1 cell microsomal fraction, enriched with recombinant ATP7A, ATP7B, and selected mutants, and adsorbed on a solid supported membrane. The experimental results indicate that Pt drugs activate Cu-ATPases and undergo ATP-dependent translocation in a fashion similar to that of Cu. We then used NMR spectroscopy and ESI-MS to determine the binding mode of these drugs to the first N-terminal metal-binding domain of ATP7A (Mnk1)
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
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
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