1,720,958 research outputs found
Effect of sinus size and position on hemodynamics during pulsatile flow in a carotid artery bifurcation
No full textBackground and objectives: Hemodynamics plays a crucial role in the progression of atherosclerosis and the treatment of arterial diseases. Stroke is one of the arterial diseases and a leading cause of death worldwide. Hemodynamics in the carotid artery plays a vital role in the stroke. The common carotid artery bifurcates into the internal carotid artery and the external carotid artery. Carotid sinus, a slightly dilated area, exists in the internal carotid artery just after the bifurcation and acts as a pressure receptor and regulator. The location and size of the sinus can vary in different people; the change in sinus size and location may affect the hemodynamics. It is necessary to study the shift in hemodynamics due to changes in sinus size and position on atherosclerosis. The change in flow behavior may suggest the probable sites of backflow and low wall shear stress, and therefore the sites prone to atherosclerosis. Methods: The model of the carotid artery has been constructed using patient data. Transient computational fluid dynamics simulations have been performed using a finite volume method for the numerical solution in a three-dimensional computational domain using ANSYS Fluent 19.2. Pulsatile flow is specified at the inlet boundary. The coupled scheme is used for the pressure-velocity coupling. The second-order discretization scheme is used for pressure interpolation and second-order upwind scheme is used for the discretisation of momentum equation. The temporal term is discretized using the first-order implicit scheme. Results: The effect of sinus size and location on the overall flow behavior, wall shear stress, and secondary flow are presented. Results show that the outer wall of bifurcation has low wall shear stress and bigger recirculation as compared with that on the inner wall of bifurcation. Numerical results obtained for varying sinus size and position are shown in graphs and contours, including wall shear stress, secondary flow, and velocity streamlines. Conclusion: Numerical results reveal that sinus away from bifurcation, and larger diameter sinus has more recirculation and low wall shear stress. Therefore, the person having sinus away from bifurcation and larger sinus diameter are more susceptible to plaque formation
Experimental investigations on the bubble dynamics in a symmetric bifurcating channel
No full textThe flow of bubbles in a continuous liquid phase in a bifurcating microchannel is a commonly occurring phenomenon in micro-structured devices and physiological flows. Depending on the fluid properties, flow rates, and bifurcation geometry, different bubble dynamics can be observed at the bifurcation. In this work, the flow of bubbles in a continuous liquid stream is investigated experimentally in a Y-shaped bifurcating channel. Experiments are performed for three Newtonian liquids of different viscosities. For short bubbles and at low values of capillary numbers, bubbles remain unsplit and move to one of the daughter tubes. On a Ca-Re plane, long bubbles (lb > dm) are observed to split when Reynolds number (Re) is less than 20, whereas bubble splitting does not occur for higher value of Reynolds numbers. When the bubble splitting occurs, the mother bubble squeezes against the carina of the bifurcation, and a neck forms. The thinning of the neck with time is investigated for the three liquids
Pulsatile flow dynamics in symmetric and asymmetric bifurcating vessels
No full textBifurcating vessel is a characteristic feature of biological systems such as arteries in the cardiovascular system and pulmonary airways. In cardiovascular system, the bifurcations are often asymmetric, flow is pulsatile, and the fluid, blood, shows a complex rheology. In this work, we study computationally pulsatile flow in planar symmetric and asymmetric, three-dimensional bifurcating vessels. The fluid is considered to be Newtonian as well as non-Newtonian following Carreau's model, and the results are compared. While the flow divides in the two daughter tubes equally in symmetric bifurcations, the flow distribution is time-dependent during a cardiac cycle in asymmetric bifurcations. The flow pattern changes significantly during a cardiac cycle. The secondary flow caused by a turning streamline is analyzed in terms of secondary velocity, vorticity, and helicity. Significant variation is observed in the secondary flow in a cardiac cycle. The secondary flow is observed to be stronger at the start of the diastole despite reduced flow rate. The separated flow on the outer wall causes a significant reduction in time-averaged wall shear stress, a biomarker to assess the possibility of atherosclerotic plaque development. While no significant difference is observed in the results obtained for Newtonian and non-Newtonian fluids at high shear rates, for example, during systole, significant differences are observed when the shear rate is low, during diastole or in the separation region. The velocity profile for the non-Newtonian fluid is observed to be flatter than that for Newtonian fluid. Further oscillatory shearing index, relative residence time, the parameters used as biomarkers are presented
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
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