1,721,028 research outputs found
Water-polymer coupling induces a dynamical transition in microgels
Full text linkThe long debated protein dynamical transition was recently found also in nonbiological macromolecules, such as poly- N-isopropylacrylamide (PNIPAM) microgels. Here, by using atomistic molecular dynamics simulations, we report a description of the molecular origin of the dynamical transition in these systems. We show that PNIPAM and water dynamics below the dynamical transition temperature T d are dominated by methyl group rotations and hydrogen bonding, respectively. By comparing with bulk water, we unambiguously identify PNIPAM-water hydrogen bonding as mainly responsible for the occurrence of the transition. The observed phenomenology thus crucially depends on the water-macromolecule coupling, being relevant to a wide class of hydrated systems, independently from the biological function
Neutron and x-ray scattering study of fully deuterated poly(3-n.decylpyrrole)
No full textThe structure of a fully deuterated sample of the conducting polymer poly(3-n.decylpyrrole) was investigated by neutron and x-ray diffraction. The different sensitivity of the two probes to deuterium atoms allowed us to obtain novel insights about the intermolecular organization of the polymer, with special focus on the alkyl substituent. The polymer turns out to be arranged in parallel layers. Within each layer, neighboring pyrrole rings maintain a coplanar disposition, whereas the alkyl decane tails are kinked out of the pyrrole plane. Monomers belonging to different adjacent layers display a high degree of superposition, due to a considerable overlap of both pyrrole rings and decane tails. Thus, despite its folded conformation, the alkyl substituent does not affect the short-range order of the compound, but rather contributes to determine its layered structure. (C) 2003 American Institute of Physic
Direct experimental evidence of free fermion antibunching
No full textFermion antibunching was observed on a beam of free noninteracting neutrons. A monochromatic beam of thermal neutrons was first split by a graphite single crystal, then fed to two detectors, displaying a reduced coincidence rate. The result is a fermionic complement to the Hanbury Brown and Twiss effect for photons
Disclosing the nature of the collective THz dynamics in hydrogen bonded liquids
No full textThe behavior of liquids has always been a subject of strong interest and still presents many challenging issues. A paradigmatic example is the understanding of their atomic-scale collective dynamics. Experimentally accessible to inelastic neutron and X-ray scattering, this regime has recently disclosed an unexpectedly rich scenario made up of more than one collective excitation. However, experiments lack a fundamental piece of information since they cannot distinguish the longitudinal or transverse nature of the detected modes. Here we present an inelastic neutron scattering study of the atomic dynamics of water and sulfuric acid, two prototypes of hydrogen bonded liquids. We propose a novel method that allows the experimental determination of the nature of the observed modes, without resorting to any indirect information. The dynamic structure factors show a complex collective dynamics, with two propagating excitations that we describe in the framework of an interacting-modes model. The first high-energy excitation is usually assumed to be the prolongation of the longitudinal acoustic mode and is characterized by a strong fast sound, which in turn we ascribe to the interaction with the second low-energy mode. Our approach confirms the main longitudinal nature of the first mode and unambiguously identifies the transverse nature of the second one. Finally, the lifetime of the modes suggests a common origin for the second mode, possibly related to the presence of the hydrogen bond network
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
Search for the elusive magnetic state of hexagonal iron: The antiferromagnetic Fe71Ru29hcp alloy
No full textDispelling 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
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