1,720,962 research outputs found
Reti di fibre colloidali sotto sforzo : deformazione di taglio e carico gravitazionale
No full textWe describe our investigation of the yield behavior of a network of hydrophobic fibers in an aqueous surfactant solution, when submitted either to a macroscopic shear stress or to the gravitational load of density-mismatched particles. In both cases, the gel undergoes an initial, slow deformation followed by delayed yielding or respectively collapse. However, the time scales for the yielding process strongly differ from each other both on an absolute scale and in their dependence on the effective stress applied. We discuss the analogies, the differences and the interplay between these destabilization modes
Colloidal fiber networks under stress : shear versus gravitational load
No full textColloidal gels are widely used in applications to modify the mechanical properties of fluids; in particular, they can provide yield stress, i.e. the ability to display solid-like properties at rest, while flowing upon application of a mechanical load. In this contribution we describe the yield behavior of a colloidal fiber network when it is subjected either to a macroscopic shear stress, or to a gravitational load obtained by inserting density-mismatched particles into the network. Delayed yielding is observed in both experiments. However, the time scales for the yielding process strongly differ from each other both on an absolute scale and in their dependence on the effective stress applied. We discuss how delayed yielding depends on background viscosity, intrinsic network relaxations, and on network porosity and elasticity
Isotropic to Nematic Transition of Aerosil-Disordered Liquid Crystals
No full textWe present a high-resolution study of the isotropic to nematic phase transition of a low birefringence liquid-crystal compound incorporating an aerosil gel. Calorimetry, light scattering, and microscopy data coherently combine to allow for an accurate determination of the temperature dependence of the onset of the nematic state. The nematic order develops on cooling through two distinct processes while the nematic correlation length mildly decreases.We understand the doubling of the phase transition as due to a crossover from a random-dilution regime, where the silica gel couples to the scalar part of the nematic order parameter, to a low-T random-field regime, where the coupling induces distortions in the director field
Coil-to-globule transition of poly(N-isopropylacrylamide) doped with chiral amino acidic comonomers
No full textBy combined light scattering and circular dichroism measurements (CD), we have investigated the coil-to-globule transition of the thermosensitive polymer poly(N-isopropylacrylamide) (pNIPAAm) copolymerized with a 1/10 fraction of valine- or leucine-derived groups randomly positioned along the chains. The comonomers provide the pNIPAAm chains with chirality, electric charge, and increased hydrophobicity. For valine-derived copolymers, the coil-globule transition is basically unmodified with respect to pNIPAAm, whereas doping with leucine-derived groups significantly lowers the transition temperature and makes the transition discontinuous. We find the CD signal of the chiral comonomers to cleanly depend on the local chain density. We interpret this behavior as an effect of the whole chain conformation on the conformations accessible to the chiral groups
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
Pretransitional behavior in water-DDAB-5CB microemulsion close to the demixing transition. Evidence for intermicellar attraction mediated by paranematic fluctuations
No full textWe present a study of a water-in-oil microemulsion in which
surfactant coated water nanodroplets are dispersed in the
isotropic phase of the thermotropic liquid crystal 5CB. As the
temperature is lowered below the isotropic to nematic phase
transition of pure 5CB, the system displays a demixing transition
leading to a coexistence of a droplet rich isotropic phase with a
droplet poor nematic. The transition is anticipated, in the high T
side, by increasing pretransitional fluctuations in 5CB molecular
orientation and in the nanodroplet concentration. The observed
phase behavior supports the notion that the nanosized droplets,
while large enough for their statistical behavior to be probed via
light scattering, are also small enough to act as impurities,
disturbing the local orientational ordering of the liquid crystal
and thus experiencing pretransitional attractive interaction
mediated by paranematic fluctuations. The pretransitional
behavior, together with the topology of the phase diagram, can be
understood on the basis of a diluted Lebwohl-Lasher model which
describes the nanodroplets simply as holes in the liquid crystal
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
- …
