1,721,418 research outputs found
A Study in Semenogelin I Hydrogel Aggregation Kinetics
No full textIn earlier investigations, we have shown that a peptide sequence, Sg I 38-48, derived from the protein human semenogelin I forms a hydrogel. In this work, we describe approaches to examine the kinetics of aggregation of both Sg I 38-48 and an extended sequence, Sg I 37-49. The kinetics experiments are based on using the chromophore Thioflavin T. When bound to extended β-sheet fibrils the intensity of Thioflavin T fluorescence increases dramatically and this can be used to monitor fibril formation. The fibrils have been shown previously by CD and IR spectroscopy to consist of extended β-sheets. In the kinetics experiments, the peptide is first isolated as a monomer employing gel filtration under acidic conditions when it does not aggregate. The pH is then adjusted to pH 8 to trigger fibril formation and the kinetics of aggregation is monitored using a plate reader, with an excitation and an emission wavelength of 440 nm and 480 nm, respectively. We have studied the effect of concentration, pH, and salt on the kinetics of aggregation. We have also carried out disc centrifugation studies in order to determine the size and homogeneity of the aggregates formed. The next step will be to fit our data to a mechanism. For this purpose we are using Global Fitter, and our preliminary data suggest an initial nucleation step from which the fibril extends. We have also carried out rheology experiments in order to characterize the behavior of the Sg I 38-48 sequence, which have confirmed that this peptide forms a hydrogel. These have also shown that the gel is able to recover its original strength after a strain sweep has broken the gel
Charge regulation in peptide self-assembly and hydrogelation
Full text linkThe peptide Ac-KGSFSIQYTYHVD-CONH2 (KD), derived from residues 37–49 of human semenogelin I, forms a pH-responsive hydrogel in an aqueous environment with tunable mechanical properties that evolve over time. We hypothesize that KD self-assembles into a hydrogel through a pH-dependent mechanism involving predominantly a change in histidine protonation state, leading to structural transformations that modulate its mechanical properties.
Time-resolved nuclear magnetic resonance (NMR) spectroscopy and cryo-transmission electron microscopy (cryo-TEM) were employed to elucidate the gelation process and structural evolution of KD. pH measurements were conducted to monitor changes in peptide interactions during self-assembly. Rheological studies, including oscillatory and stationary rheology, were performed to assess the mechanical properties of the hydrogel under varying pH conditions.
A gradual pH drift was observed, associated with a modulation of the ionizable histidine side chain pKa as KD assembled into β-sheet fibrils, integrating into the hydrogel network. Cryo-TEM analysis revealed two distinct nanostructural morphologies: fibrils and twisted curly nanostructures with uniform dimensions, demonstrating micro- and nanoscale transformations over time. Rheological measurements indicated a substantial increase in the elastic modulus as the pH shifted, confirming the dynamic tunability of the hydrogel. Under buffered conditions, KD rapidly formed hydrogels within the experimental dead time, indicating its quick responsiveness to environmental changes. These results provide mechanistic insights into the time-dependent self-assembly of KD and highlight its potential as a pH-tunable hydrogel for therapeutic applications, paving the way for the rational design of next-generation peptide-based biomaterials
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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