1,720,958 research outputs found
BREAK-UP OF A NEWTONIAN DROP IN A VISCOELASTIC MATRIX UNDER SIMPLE SHEAR FLOW
No full textThe effect of matrix elasticity on the break-up of an isolated Newtonian drop under step shear flow is herein presented. Constantviscosity, elastic polymer solutions (Boger fluids) were used as matrix phase. Newtonian silicon oils were used as drop phase. Three viscosity ratios were explored (drop/matrix), i.e. 2, 0.6 and 0.04. Following the theoretical analysis of Greco [Greco F (2002) J Non-Newtonian Fluid Mech 107:111–131], the role of elasticity on drop fluid dynamics was quantified according to the value of the parameter p=s/sem, where s is a constitutive relaxation time of the matrix fluid and sem is the emulsion time. Different fluids were prepared in order to have p ranging from 0.1 to 10. At all the viscosity ratios explored, break-up was hindered by matrix elasticity. The start-up transient of drop deformation, at high, but sub-critical capillary numbers, showed an overshoot, during which the drop enhanced its orientation toward the flow direction. Both phenomena increase if the p parameter increases. Finally, the nondimensional pinch-off length and break-up time were also found to increase with p
Shear-induced clustering of gelling droplets in aqueous biphasic mixtures of gelatin and dextran
No full textThe flow-induced morphology of aqueous mixtures of gelatin and dextran was investigated during gelation of the dispersed phase. Mixtures with 5% volume fraction of gelatin-rich phase dispersed in the dextran-rich phase were sheared in a parallel plate apparatus coupled with an optical microscope. Gelation of the dispersed phase was brought about by decreasing mixture temperature under flow. As a consequence of gelation, the dispersed phase aggregated, forming clusters of gelled, partially coalesced, spherical drops. When the temperature was increased again above the gelation temperature, the gelled drops melted and the clusters rapidly coalesced, leading to complete phase separation. Cluster size was found to depend on the shear rate applied during gelation and on the temperature profile. Indeed, smaller clusters were formed: a) under faster flows, b) if the temperature was decreased to lower levels and c) if gelation was induced under quiescent conditions and the flow started only afterwards. By acting on these parameters, it is possible to suppress or enhance cluster formation and to tune cluster size
Shear-induced clustering of gelling droplets in aqueous biphasic mixtures of gelatin and dextran
No full textThe flow-induced morphology of aqueous mixtures of gelatin and dextran was investigated during gelation of the dispersed phase. Mixtures with 5% volume fraction of gelatin-rich phase dispersed in the dextran-rich phase were sheared in a parallel plate apparatus coupled with an optical microscope. Gelation of the dispersed phase was brought about by decreasing mixture temperature under flow. As a consequence of gelation, the dispersed phase aggregated, forming clusters of gelled, partially coalesced, spherical drops. When the temperature was increased again above the gelation temperature, the gelled drops melted and the clusters rapidly coalesced, leading to complete phase separation. Cluster size was found to depend on the shear rate applied during gelation and on the temperature profile. Indeed, smaller clusters were formed: a) under faster flows, b) if the temperature was decreased to lower levels and c) if gelation was induced under quiescent conditions and the flow started only afterwards. By acting on these parameters, it is possible to suppress or enhance cluster formation and to tune cluster size
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Time-lapse imaging and 3D cell tracking by computer-controlled video microscopy. Applications to chemotaxis
No full textIn this work, we investigate cell migration in 3D reconstituted collagen gel substrata under anisotropic conditions, such as chemotaxis and contact guidance. Collagen solutions seeded with cells are loaded in especially designed two-well chambers and incubated at 37°C to allow gel formation. The samples are then transferred to a video microscopy workstation equipped with an incubating system and motor units for remote operation of focus drive and x-y stage. Time-lapse imaging is carried out by computer-controlled, iterative focusing of selected regions of the samples followed by image acquisition and storage. A dedicated software is used to control system operation, including sample scanning, optical sectioning and temperature control. Image analysis techniques are used to extract cell contours from the archived images and reconstruct cell trajectories. The motility parameters of the cell populations under investigations, which include Jurkat cells and lymphocytes, are presented both for the isotropic case and in presence of a concentration gradient (chemotaxis). The data are discussed and compared to previous studies [1], including contact guidance experiments [2]. [1] P. V. Moghe; R. D. Nelson, and R. T. Tranquillo, “Cytokine-stimulated chemotaxis of human neutrophils in a 3-D conjoined fibrin gel assay,” J. Immunol. Methods, 180, 193–211 (1995).[2] S. Guido, and R. T. Tranquillo, "A methodology for the systematic and quantitative study of cell contact guidance in oriented collagen gels. Correlation of fibroblast orientation and gel birefringence," J. Cell Sci., 105, 317-331 (1993)
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