1,720,968 research outputs found
Irreversibility and rate dependence in sheared adhesive suspensions
Full text linkRecent experiments report that slowly sheared noncolloidal particle suspensions unexpectedly exhibit rate(omega)-dependent complex viscosities in oscillatory shear, despite a constant relative viscosity in steady shear. Using a minimal hydrodynamic model, we show that van der Waals attraction gives rise to this behavior. At volume fractions phi = 20-50%, the complex viscosities in both experiments and simulations display power-law reductions in shear, with a phi-dependent exponent maximum at phi = 40%, resulting from the interplay between hydrodynamic, collision, and adhesive interactions. Furthermore, this rate dependence is accompanied by diverging particle diffusivities and pronounced cluster formations after repeated oscillations. Previous studies established that suspensions transition from reversible absorbing states to irreversible diffusing states when the oscillation amplitude exceeds a phi-dependent critical value. gamma(c)(0,phi). Here, we show that a second transition to irreversibility occurs below an omega-dependent critical amplitude, gamma(c)(0,omega) <= gamma(c)(0,phi), in the presence of weak attractions
Theory of hydrodynamic interaction of two spheres in wall-bounded shear flow
Full text linkThe seminal Batchelor-Green's (BG) theory on the hydrodynamic interaction of two spherical particles of radii a suspended in a viscous shear flow assumes unbounded fluid. In the present paper we study how a rigid plane wall modifies this interaction. Using an integral equation for the surface traction we derive the expression for the particles' relative velocity as a sum of the BG's velocity and the term due to the presence of a wall at finite distance, z(0). Our calculation is not the perturbation theory of the BG solution, so the contribution due to the wall is not necessarily small. We indeed demonstrate that the presence of the wall is a singular perturbation, i.e., its effect cannot be neglected even at large distances. The distance at which the wall significantly alters the particles interaction scales as z(0)(3/5). The phase portrait of the particles' relative motion is different from the BG theory, where there are two singly connected regions of open and closed trajectories both of infinite volume. For finite z(0), besides the BG's domains of open and closed trajectories, there is a domain of closed (dancing) and open (swapping) trajectories that do not materialize in an unbounded shear flow. The width of this region grows as 1/z(0) at smaller separations from the wall. Along the swapping trajectories, which have been previously observed numerically, the incoming particle is turning back after the encounter with the reference particle, rather than passing it by, as the BG theory anticipates. The region of dancing trajectories has infinite volume and is separated from a BG-type domain of closed trajectories that becomes compact due to presence of the wall. We found a one-parameter family of equilibrium states that were previously overlooked, whereas the pair of spheres flows as a whole without changing its configuration. These states are marginally stable and their perturbation yields a two-parameter family of the dancing trajectories, whereas the test particle is orbiting around a fixed point in a frame comoving with the reference particle. We suggest that the phase portrait obtained at z(0) >> a is topologically stable and can be extended down to rather small z(0) of several particle diameters. We confirm this hypothesis by direct numerical simulations of the Navier-Stokes equations with z(0) = 5a. Qualitatively the distant wall is the third body that changes the global topology of the phase portrait of two-particle interaction
A mass-preserving interface-correction level set/ghost fluid method for modeling of three-dimensional boiling flows
No full textWe present an efficient method for the direct numerical simulation of three-dimensional (3D) boiling flows. The liquid-vapor interface dynamics is captured using an interface-correction level set method, modified to account for the interface heat and mass transfer due to phase change. State-of-the-art com- putational techniques, such as the fast pressure-correction and ghost-fluid methods, are implemented to accurately solve the coupled thermo-fluid problem involving large density contrasts and jump conditions. The solver is thoroughly validated against four benchmark cases with increasing complexity, which show better mass conservation properties than traditional level set methods, thus allowing for coarser grid resolutions and lower computational costs. We further demonstrate our method by simulating two real- istic 3D boiling flows in greater details. In the first case, a saturated film boiling of water vapor at near critical conditions over a horizontal hot flat plate is considered. The results are analyzed by comparing the transient evolution of the interface morphology, temperature distribution, space and time averaged Nusselt numbers obtained from numerical simulations with the semi-empirical correlation of Berenson and existing numerical literature. In the second case, we simulate the condensation and buoyancy-driven motion of a single spherical water vapor bubble at different subcooled liquid temperatures and satura- tion pressures. We find opposite trends of the condensation rate and the bubble rising velocity when the degree of subcooling is increased, and an increase of the condensation rate at lower saturation pressures, due to variation of the thermophysical properties
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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