1,720,984 research outputs found
Slow dynamics of a confined supercooled binary mixture. II. Q space analysis
No full textWe report the analysis in the wave vector space of the density correlator of a Lennard-Jones binary mixture confined in a disordered matrix of soft spheres upon supercooling. In spite of the strong confining medium the behavior of the mixture is consistent with the mode-coupling theory predictions for bulk supercooled liquids. The relaxation times extracted from the fit of the density correlator to the stretched exponential function follow a unique power law behavior as a function of wave vector and temperature. The von Schweidler scaling properties are valid for an extended wave vector range around the peak of the structure factor. The parameters extracted in the present work are compared with the bulk values obtained in literature
Single particle dynamics of a confined Lennard-Jones mixture in the supercooled regime
No full textDynamical properties of a supercooled Lennard-Jones binary mixture in a disordered array of soft spheres are studied by computer simulation close to the Mode Coupling Theory crossover temperature T-c Predictions of the MCT are satisfied by the confined liquid. The b exponent of the von Schweidler law, the gamma exponent and T-c are evaluated for both species. The range of validity of the theory shrinks and a substantial enhancement of hopping processes are observed above T-c with respect to the bulk. (C) 2002 Elsevier Science B.V. All rights reserved
9,10-Anthraquinone hinders beta-aggregation: how does a small molecule interfere with Abeta-peptide amyloid fibrillation?
No full textAmyloid aggregation is linked to a number of neurodegenerative syndromes, the most prevalent one being Alzheimer's disease. In this pathology, the beta-amyloid peptides (Abeta) aggregate into oligomers, protofibrils, and fibrils and eventually into plaques, which constitute the characteristic hallmark of Alzheimer's disease. Several low-molecular-weight compounds able to impair the Abeta aggregation process have been recently discovered; yet, a detailed description of their interactions with oligomers and fibrils is hitherto missing. Here, molecular dynamics simulations are used to investigate the influence of two relatively similar tricyclic, planar compounds, that is, 9, 10-anthraquinone (AQ) and anthracene (AC), on the early phase of the aggregation of the Abeta heptapeptide segment H(14)QKLVFF(20), the hydrophobic stretch that promotes the Abeta self-assembly. The simulations show that AQ interferes with beta-sheet formation more than AC. In particular, AQ intercalates into the beta-sheet because polar interactions between the compound and the peptide backbone destabilize the interstrand hydrogen bonds, thereby favoring disorder. The thioflavin T-binding assay indicates that AQ, but not AC, sensibly reduces the amount of aggregated Abeta(1-40) peptide. Taken together, the in silico and in vitro results provide evidence that structural perturbations by AQ can remarkably affect ordered oligomerization. Moreover, the simulations shed light at the atomic level on the interactions between AQ and Abeta oligomers, providing useful insights for the design of small-molecule inhibitors of aggregation with therapeutic potential in Alzheimer's disease
Organism complexity anti-correlates with proteomic β-aggregation propensity
Full text linkWe introduce a novel approach to estimate differences in the β-aggregation potential of eukaryotic proteomes. The approach is based on a statistical analysis of the β-aggregation propensity of polypeptide segments, which is calculated by an equation derived from first principles using the physicochemical properties of the natural amino acids. Our analysis reveals a significant decreasing trend of the overall β-aggregation tendency with increasing organism complexity and longevity. A comparison with randomized proteomes shows that natural proteomes have a higher degree of polarization in both low and high β-aggregation prone sequences. The former originates from the requirement of intrinsically disordered proteins, whereas the latter originates from the necessity of proteins with a stable folded structure. Published by Cold Spring Harbor Laboratory Press. Copyright © 2005 The Protein Society
The role of aromaticity, exposed surface, and dipole moment in determining protein aggregation rates
Full text linkThe mechanisms by which peptides and proteins form ordered aggregates are not well understood. Here we focus on the physicochemical properties of amino acids that favor ordered aggregation and suggest a parameter-free model that is able to predict the change of aggregation rates over a large set of natural sequences. Furthermore, the results of the parameter-free model correlate well with the aggregation propensities of a set of peptides designed by computer simulations
Mode coupling relaxation scenario in a confined glass former
No full textMolecular-dynamics simulations of a Lennard-Jones binary mixture confined in a disordered array of soft spheres are presented. The single-part isle dynamical behavior of the glass former is examined upon supercooling. Predictions of mode coupling theory are satisfied by the confined liquid. Estimates of the crossover temperature are obtained by power law fit to the diffusion coefficients and relaxation times of the late alpha region. The b exponent of the von Schweidler law is also evaluated. Similarly to the bulls, different values of the exponent gamma are extracted from the power law fit to the diffusion coefficients and relaxation times
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
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