1,720,955 research outputs found
Multiscale relaxation in aging colloidal gels: From localized plastic events to system-spanning quakes
No full textRelaxation of internal stresses through a cascade of microscopic restructuring events is the hallmark of many materials, ranging from amorphous solids like glasses and gels to geological structures subjected to a persistent external load. By means of photon correlation imaging, a recently developed technique that blends the powers of scattering and imaging, we provide a spatially and temporally resolved survey of the restructuring and aging processes that spontaneously occur in physical gels originating from an arrested phase separation. We show that the temporal dynamics is characterized by an intermittent sequence of spatially localized "microquakes" that eventually lead to global rearrangements occurring at a rate that scales with the gel age. Notably, these dramatic upheavals of the gel structure are heralded by a progressive acceleration of the microscopic gel dynamics that originates from recognizable active spots and then spreads at a large but finite speed through the gel. Within the "slack" phase between two of these "macroquakes," the fluctuations of the degree of temporal correlation obey a non-Gaussian statistics described by a generalized logistic distribution. The evidence we obtained bear consistent analogies with the stress relaxation processes taking place in earthquake sequences and with the intermittent restructuring of plastic crystals at the microscale
Temperature-driven flows in nanochannels: Theory and simulations
No full textThe motion of a fluid induced by thermal gradients in the absence of external forces is known as thermo-osmosis. The physical explanation of this phenomenon stems from the emergence of gradients in the tangential pressure due to the presence of a confining surface. The microscopic origin of the effect has recently been elucidated in the framework of linear response theory. Here, by use of conservation laws, we provide an explicit solution of the equations governing the fluid flow at stationarity in slab geometry, expressing the thermo-osmotic coefficient as the integrated mass current-heat current correlation function (which vanishes in the bulk). A very simple expression for the pressure gradient in terms of equilibrium properties is also derived. To test the theoretical predictions in a controlled setting, we performed extensive nonequilibrium molecular dynamics simulations in two dimensions. Few simple models of wall-particle interactions are examined, and the resulting pressure drop and velocity profile are compared with the theoretical predictions both in the liquid regime and in the gas regime
Fluid flow at interfaces driven by thermal gradients
No full textThermal forces drive several nonequilibrium phenomena able to set a fluid in motion without pressure gradi-ents. Although the most celebrated effect is thermophoresis, also known as Ludwig-Soret effect, probably the simplest example where thermal forces are at play is thermo-osmosis: The motion of a confined fluid exclusively due to the presence of a temperature gradient. We present a concise but complete derivation of the microscopic theory of thermo-osmosis based on linear response theory. This approach is applied to a simple fluid confined in a slab geometry, mimicking the flow through a pore in a membrane separating two fluid reservoirs at different temperatures. We consider both the case of an open channel, where the fluid can flow freely, and that of a closed channel, where mass transport is inhibited and a pressure drop sets in at the boundaries. Quantitative results require the evaluation of generalized transport coefficients, but a preliminary check on a specific prediction of the theory has been successfully performed via nonequilibrium molecular dynamics simulations
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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