1,721,091 research outputs found
Unveiling the role of histidine and tyrosine residues on the conformation of the avian prion hexarepeat domain
No full textThe prion protein (PrPC) is a glycoprotein that in mammals, differently from avians, can lead to prion diseases,
by misfolding into a â-sheet-rich pathogenic isoform (PrPSc). Mammal and avian proteins show different
N-terminal tandem repeats: PHGGGWGQ and PHNPGY, both containing histidine, whereas tyrosine is
included only in the primary sequence of the avian protein. Here, by means of potentiometric, circular dichroism
(CD), and molecular dynamics (MD) studies at different pH values, we have investigated the conformation
of the avian tetrahexarepeat (PHNPGY)4 (TetraHexaPY) with both N- and C-termini blocked by acetylation
and amidation, respectively. We have found, also with the help of a recently proposed protein chirality indicator
(Pietropaolo, A.; Muccioli, L.; Berardi, R.; Zannoni, C. Proteins 2008, 70, 667-677), a conformational
dependence on the protonation states of histidine and tyrosine residues: the turn formation is pH driven, and
at physiological pH a pivotal role is played by the tyrosine OH groups which give rise to a very compact bent
structure of backbone upon forming a hydrogen-bond network
A deformable Gay-Berne model for the simulation of liquid crystals and soft materials
No full textWe present a deformable Gay-Berne (DGB) pair potential for ellipsoidal particles that allows for dynamic fluctuations in their shape and interaction anisotropy. We investigate the effect that various intrinsic distributions of shape and interaction parameters have on the liquid crystal phases formed by a system of DGB particles. We show that deformability can stabilise smectic formation and that all mesomorphic phase transitions are accompanied by a change of molecular shape. (c) 2006 Elsevier B.V. All rights reserved
Simulation of vapor-phase deposition and growth of a pentacene thin film on C 60 (001)
No full textThe formation of the heterojunction between two organic semiconductors, pentacene on top of Buckminster fullerene, is simulated using a virtual vapor deposition experiment. The thin-film growth is characterized by a lying-to-standing collective reorientation of pentacene molecules, corresponding to the onset of crystalline order. The mechanism is coverage dependent and reorientation occurs earlier for the second monolayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Charge separation energetics at organic heterojunctions: On the role of structural and electrostatic disorder
No full textImproving the performance of organic photovoltaic cells requires the individuation of the specific factors limiting their efficiency, by rationalizing the relationship between the chemical nature of the materials, their morphology, and the electronic processes taking place at their interface. In this contribution, we present recent theoretical advances regarding the determination of the energetics and dynamics of charge carriers at organic-organic interfaces, highlighting the role of structural and electrostatic disorder in the separation of electron-hole pairs. The influence of interfacial electrostatic interactions on charge carrier energetics is first illustrated in model aggregates. Then, we review some of our recent theoretical studies in which we combined molecular dynamics, quantum-chemical and classical micro-electrostatic methods to evaluate the energy landscape explored by the mobile charges in the vicinity of donor-acceptor interfaces with realistic morphologies. Finally, we describe the theoretical challenges that still need to be overcome in order to gain a complete overview of the charge separation processes at the molecular level. © the Partner Organisations 2014
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
- …
