1,720,975 research outputs found
Patient-specific Modeling of the Human Brain using Magnetic Resonance Imaging
No full textDementia is a growing concern for the health-care in the world and most treatment strategies are not successful. Dementia is associated with accumulation of metabolic waste in the form of protein fragments. Recent breakthroughs have suggested that the accumulation of waste is caused by malfunction of clearance mechanism, called the glymphatic system, that provides bulk flow through the extracellular matrix. To what extent this system accelerates transport provided by extracellular diffusion, is an open question. Recent research also shows that transport can be accelerated during sleep and by deep breathing.
In this work, I have investigated the enrichment and clearance of a tracer in the brain using magnetic resonance imaging (MRI), developed methods for constructing computational geometries from MRI and evaluated the tracer diffusion using patient-specific computational simulations. The medical data used in this study are novel imaging recently performed at Rikshopspitalet where MRI tracer was administrated into fluid compartment along the spine and transported up and into the brain. Based on these data I have analyzed the tracer movement, and observed that the tracer had a brain-wide distribution. Additionally, this thesis aims to provide methodology and software tools for constructing computational geometries from brain MRI in a patient-specific manner. In particular, I have solved PDE constrained optimization problems with finite elements to assess the efficiency of the transport mechanism in a patient-specific manner.
Compared to controls, in the patients with dementia the tracers demonstrated a slower clearance. Thus suggesting a brain-wide clearance system and an impairment in the waste-removal in dementia. Additionally, these observations may provide the possibility for a new and more effective method for administrating medicine to the brain. Diffusion coefficients were found to be higher than the expected, henceforth diffusion alone does not explain the clearance of waste from the brain
Accumulated Plastic Strain Program
Full text linkIn this thesis we will look at the implementation and results of the APS program. The program computes the accumulated plastic strain in a umbilical tube for the deformations axial tension, bending and internal pressure. The computation is based on solving incremental problems with the finite element method and the return-mapping algorithm. The return-mapping algorithm encountered convergence failure for large strain increments, this was solved by using the strain increment of 1.0e\sp{-4}\%.The implementation of axial tension and bending was consistent with the results provided by Nexans Norway.While the plastic behaviour of the internal pressure proved to be more complex, so the implementation requires improvement
Accumulated Plastic Strain Program
No full textIn this thesis we will look at the implementation and results of the APS program. The program computes the accumulated plastic strain in a umbilical tube for the deformations axial tension, bending and internal pressure. The computation is based on solving incremental problems with the finite element method and the return-mapping algorithm. The return-mapping algorithm encountered convergence failure for large strain increments, this was solved by using the strain increment of 1.0e\sp{-4}\%.The implementation of axial tension and bending was consistent with the results provided by Nexans Norway.While the plastic behaviour of the internal pressure proved to be more complex, so the implementation requires improvement
Mathematical Modelling of the Human Brain II
No full textThis open access book revolves around predictive mathematical modelling and simulation of brain multiphysics with an emphasis on cerebrospinal fluid flow and solute transport in and around the human brain. The book consists of 10 self-contained and relatively short chapters, each offering a rapid introduction to a key problem or topic, supported by open source software. Readers will gain insights into state-of-the-art mathematical tools and techniques for modelling and simulation of brain multiphysics ranging from classical finite element approaches, network-based modelling techniques and deep neural networks. The target audiences are researchers in applied mathematics, scientific computing, biophysics, bioengineering or computational neuroscience interested in a compact introduction to image-based computational modeling of brain multiphysics and cutting-edge available tools
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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