1,721,085 research outputs found
Mechanical Models of the Dynamics of Vitreous Substitutes
No full textIn the present paper we discuss some aspects of the fluid dynamics of vitreous substitutes in the vitreous chamber, focussing on the flow induced by rotations of the eye bulb. We use simple, yet not trivial, theoretical models to highlight mechanical concepts which are of great relevance to understand the behaviour of vitreous substitutes in the vitreous chamber and also to identify ideal properties for vitreous replacement fluids. We first consider the dependency of the maximum shear stress on the retina on the viscosity of the fluid, and also discuss the differences between the motion of purely viscous and viscoelastic fluids. We then investigate how the wall shear stress changes if a thin layer of aqueous is present in the vitreous chamber, separating the retina from the vitreous replacement fluid. In relation to this, we also discuss results from a theoretical model that predicts the stability conditions of the interface between aqueous and a vitreous substitute. We discuss the implications of this model results to understand the mechanisms leading to the formation of an emulsion in the vitreous chamber
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
A model for the linear stability of the interface between aqueous humor and vitreous substitutes after vitreoretinal surgery
No full textWe consider the motion of two immiscible viscous fluids induced by periodic oscilla- tions of a flat solid surface along its plane. The interface between the two fluids is parallel to the solid wall; one fluid occupies the region between the wall and the in- terface and the other extends from the interface to infinity. We study numerically the linear stability of the interface with respect to two-dimensional perturbations using the normal mode analysis and assuming quasi-steady flow conditions. The analysis is motivated by the need of understanding the behavior of vitreous substitutes inserted in the vitreous chamber of the eye after vitrectomy. This is a common surgical pro- cedure adopted to treat retinal detachments, whereby the vitreous humor is removed from the eye and replaced by fluids immiscible with water. Owing to their hydropho- bic nature vitreous substitutes coexist in the vitreous chamber with a certain amount of aqueous humor (the fluid produced in the anterior part of the eye) and, typically, a thin layer of aqueous separates the tamponade fluid from the retina. A common problem with this treatment is that, in some cases, the interface between the two fluids breaks down and this might eventually lead to the generation of an emulsion. It is believed that mechanics plays an important role in this process but the problem remains very poorly understood. We find that instability of the interface is possible in a range of parameters that is relevant for the problem that motivated the present analysis. This suggests that shear instability is likely a possible mechanism triggering the onset of vitreous substitutes–aqueous interface instability
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
Comparison of Smartphone-based Ophthalmoscopy versus Dilated Ophthalmic Examination for Diabetic and Nondiabetic Eye Disease
No full textPurpose: To evaluate the ability of smartphone-based imaging to grade diabetic retinopathy (DR) compared to dilated ophthalmic examination by retinal specialist ophthalmologists. Methods: A subset of 120 diabetic patients underwent dilated examination and smartphone ophthalmoscopy. The smartphone was equipped with a compact add-on that filtered and delivered the smartphone’s LED light coaxially to the camera, allowing a clear and convenient view of the retina. Results: There was exact agreement in 213 eyes (88.8%) and agreement within 1 step in 237 (98.8%). Weighted kappa was 0.80 ± 0.04. Conclusion: Smartphone ophthalmoscopy showed near-perfect agreement with dilated ophthalmic examination in the detection of D
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
25-gauge 2 port minimal vitrectomy in selected rhegmatogenous retinal detachment patients
Full text linkComparison of Smartphone-Based Ophthalmoscopy With Dilated Ophthalmic Examination to Detect Ocular Pathologic Features
No full textPurpose: To evaluate the ability of smartphone-based imaging to detect ocular pathologic features compared to dilated ophthalmic examination by retinal specialist ophthalmologists. Methods: 160 outpatients underwent dilated examination and smartphone ophthalmoscopy. The smartphone was equipped with a compact add-on that filtered and delivered the smartphone’s LED light coaxially to the camera, allowing a clear and convenient view of the retina. Results: K-values for all lesions (k ≥ 0.66) demonstrated substantial agreement between smartphone-based imaging and clinical examination. Conclusion: Smartphone ophthalmoscopy showed considerable agreement with clinical examination in the detection of ocular diseases, suggesting a potential role in screening environments for smartphone-based imagin
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
- …
