1,721,015 research outputs found
Shear-Induced Particle Diffusion in Dilute Suspensions: Some Recent Theoretical Results
No full textMobile particulate systems involve the mechanics, flow and transport properties of mixtures of fluids and solids. These systems are intrinsic to the rheology of emulsions and suspensions, flocculation and aggregation, sedimentation and fluidization, flow of granular media, nucleation and growth of small particles, segregation, attrition and solidification processes. Its diversity means that the area has been studied by a number of different disciplines (e.g. chemical or civil engineering, mechanics, hydrodynamics, geophysics, condensed matter and statistical physics, etc.).
Mobile Particulate Systems features general, orientational lectures and advanced topics, covering state of the art approaches to the study of suspensions, fluidized beds, sedimentation and granular flows
On the Measurement of the Relative Viscosity of Suspensions
No full textThe relative viscosity of a suspension of rigid, noncolloidal particles immersed in a Newtonian fluid was measured in a Couette device and was found to be shear thinning even for values of the solids fraction as low as 20%. Although such behavior was reported previously, no satisfactory explanation appears to have been given thus far. It shall be shown presently, however, that, at least for our systems, this shear-thinning effect was due to a slight mismatch in the densities of the two phases. Moreover, the apparent relative viscosities measured in our apparatus were found to be in excellent agreement with those predicted theoretically using a model, originally proposed by Leighton and Acrivos [Chem. Eng. Sci. 41, 1377–1384 (1986)], to describe viscous resuspension, according to which the measured relative viscosity should depend on the bulk particle concentration and on the dimensionless Shields number A, and should attain its correct value for a well-mixed suspension only as A. The predictions of this model are also in excellent agreement with the measured transient response of the apparent relative viscosity due to a sudden change in the shear rate
Shear-Induced Resuspension in a Couette Device
No full textThe viscous resuspension of an initially settled bed of particles resulting from the application of a laminar shear flow was studied experimentally in a narrow-gas Couette device. The measured height of the resuspended layer was found to be in excellent agreement with that predicted theoretically using a model developed by Leighton & Acrivos, in which the downward gravitational particle flux is balanced by a correspong upward flux due to shear-induced particle diffusion
Thermocapillary Migration of a Bidisperse Suspension of Bubbles
No full textWe consider the thermocapillary motion of a well-mixed suspension of non-conducting spherical bubbles of negligible viscosity in a viscous conducting liquid under conditions of vanishingly small Reynolds and Marangoni numbers. Recently, Acrivos, Jeffrey & Saville (1990) showed that when all the bubbles are of identical size, the ensemble-averaged migration velocity U1 of a test bubble of radius a1 within the suspension equals U10 [1 - (3/2)c1 + O(c1^2)], where c1 is the volume fraction of the bubbles and U10 is the thermocapillary velocity of a single bubble given by Young, Goldstein & Block (1959). Here we extend this result to a bi-disperse suspension containing bubbles of radii a1 and a2 = k a1, in which case U1 = U10 [1 - (3/2 )c1 - S(k) c2 + ...], where c1 and c2 are the corresponding volume fractions of the two sets of bubbles. Values for S(k) are presented for some typical size ratio, and asymptotic expressions for S(k) are derived for k tending to zero and infinity
Transverse Shear-Induced Gradient Diffusion in a Dilute Suspension of Spheres
No full textWe study the shear-induced gradient diffusion of particles in a inhomogeneous dilute suspension of neutrally buoyant spherical particles undergoing a simple shearing motion, with all inertia and Brownian motion effects assumed negligible. An expansion is derived for the flux of particles due to a concentration gradient along the directions perpendicular to the ambient flow. This expression involves the average velocity of the particles, which in turn is expressed as an integral over contributions from all possible configurations. The integral is divergent when expressed in terms of three-particle interactions and must be renormalized. For the monolayer case, such a renormalization is achieved by imposing the condition of zero total macroscopic flux in the transverse direction whereas, for the three-dimensional case, the additional constraint of zero total macroscopic pressure gradient is required. Following the scheme of Wang, Mauri & Acrivos (1996), the renormalized integral is evaluated numerically for the case of a monolayer of particles, giving for the gradient diffusion coefficient 0.077 gamma a^2 c^2, where gamma is the applied shear rate, a the radius of the spheres asnd c their areal fraction
The Transverse Shear-Induced Liquid and Particle Tracer Diffusivities of a Dilute Suspension of Spheres Undergoing a Simple Shear Flow
No full textWe study the shear-induced self-diffusion of both liquid tracer and a tagged spherical particle along the directions perpendicular to the ambient flow in a dilute suspension of neutrally buoyant spheres undergoing a simple shearing motion in the absence of inertia and Brownian motion effects. The calculation of the liquid diffusivity requires the velocity of a fluid point under the influence of two spheres, which was determined via Lamb's series expansion; conversely, the calculation of the particle diffusivity involves the trajectoruees of three spheres, which was determined using far-field and near-field asymptotic expressions. The displacements of the liquid tracer and of the tagged sphere were then computed analytically when the spheres and the tracer are all far apart, and numerically for close encounters. After summing over all possible encounters, the leading terms of the lateral lipuid diffusion coefficients, both within and normal to the plane of shear, were thereby found to be 0.12 gamma a^2 c^2 and 0.004 gamma a^2 c^2, respectively, where gamma is the applied shear rate, a the radius of the spheres and c their volume fraction. The analogous coefficients of the lateral particle diffusivity were found to be 0.11 gamma a^2 c^2 and 0.005 gamma a^2 c^2, respectively. Also, liquid and particle diffusivities in a monolayer, with the liquid tracer and all the particle centres lying on the same plane of shear, were found to be 0.067 gamma a^2 c^2 and 0.032 gamma a^2 c^2, respectively, with c denoting the areal fraction occupied by the spheres on the plane
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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