1,720,956 research outputs found
A mathematical and computational model of blood flow regulation in microvessels : application to the eye retina circulation
No full textThis paper presents a mathematical model and a computational framework for the resolution of large networks of distensible blood microvessels characterized by a hierarchy of different diameters. We analyze the contribution of different distensibility relations, representing both active and passive responses in the case of the microvascular network in the eye retina. Model predictions indicate that, depending on the geometrical (hierarchical) location in the network, distensibility effects may be significantly different and lead, over long times, to possible geometrically-driven remodeling processes
Mathematical and numerical methods for modeling drug delivery to the posterior segment of the eye
Get PDFThe high incidence of diseases that affect the posterior segment of the eye (PSE) - here intended as composed
by sclera, choroid and retina-prompts for establishing effective and well tolerated therapies. Topical application
(instillation of drops) and systemic assumption remain the most widespread drug administration routes. However,
the drug achieved levels are not therapeutically sufficient therapeutic, since in the first case the drug is mainly washed
away by different pathways (aqueous humor, systemic adsorption, tears) and in the second reaches the PSE target in
a minimal fraction. Intravitreal injections and biodegradable episcleral implants have emerged in the last decades as
alternative, more effective, administration routes. Whilst these techniques already offer significant improvements,
much space is still open to research. The difficulty in delivering drugs to the PSE via the intravitreal (IV) or episcleral
(EP) route resides in the several physical and dynamical barriers-including blood retinal barrier, clearance from
choriocapillaries and lymphatics-which hinder the passage of the drug molecules. In combination, and in support of
clinical experiments, mathematical and computational methods can be used to simulate drug concentration levels in
the tissues upon IV or EP administration. In this respect, this short review gives an update of the most recent (from
year 2000 to present time) developments on mathematical models for drug delivery to the PSE. We specifically focus
our attention on physiological modeling works that include spatial dependency. Our review work is organized in short
sections accompanied by detailed tables. We discuss descriptions of the PSE morphology, considering “anatomically
accurate” as well as reduced models and we analyze the biophysical phenomena included in the examined models.
We present the numerical techniques adopted to solve the resulting systems of partial differential equations and
we deal with the delicate issue of parameter choice and validation of the results. Eventually, we examine the main
results and scientific achievements of the considered models. Our conclusions point out the absence of a “standard
mathematical model” and highlight a significant scattering of the results obtained from the different authors
Mathematical modeling of local perfusion in large distensible microvascular networks
Get PDFMicrovessels – blood vessels with diameter less than 200μm – form large intricate networks, functionally organized into arterioles, capillaries and venules. In these networks, the distribution of flow and pressure drop stems in a complex manner from single vessel behavior and mutual vessel interactions. In this paper, we propose a mathematical and computational model to study the behavior of large networks of compliant microvessels. The network geometry is simplified for computational purposes. The arteriolar and venular trees are represented by graphs of straight cylinders, each one corresponding to a vessel. The two trees are connected through a capillary bed. The blood flow and pressure drop across each vessel are related via a simplified fluid–structure interaction (FSI) model, represented by a generalized Ohm's law featuring a conductivity parameter. The conductivity is a function of the vessel cross section area (shape and area), which, in turn, undergoes deformations due to luminal and external pressure loads. The membrane theory is used for the description of the deformation of vessel lumina, adapted to consider thick-walled arterioles and thin-walled venules. An original point of the present work is represented by the inclusion of a buckling model in the FSI problem for venules. As a matter of fact, venules can experience negative values of transmural pressure (difference between luminal and interstitial pressure) and may assume a deformed and even collapsed configuration due to their minimal cross-sectional bending stiffness. The complete model including flow in distensible arterioles, capillaries and venules represents a nonlinear coupled system of PDEs, which is approached numerically by finite element discretization and linearization techniques. As an example of application, we use the model to simulate flow in the microcirculation of the human eye retina, a terminal system with a single inlet and outlet. After a phase of validation against experimental measurements of the correctness of the blood flow and pressure fields in the network, we compute the network response to different conditions. Significant redistributions of the blood flow in the network are observed, highlighting the importance of considering the single vessel behavior along with its position and connectivity in the network
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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