1,720,979 research outputs found
Numerical Modelling of Blood Flow for Coarctation of the Aorta: Pre- and Post-treatment Simulations
No full textCoarctation of the Aorta (CoA) is a disease that is present in newborns and is
commonly described as a short section of narrowing in the aorta. This thesis uses
mathematical and numerical modelling to investigate both pre- and post-treatment
issues experienced by CoA patients, by examining the effect of the coarctation, some
associated cardiovascular abnormalities, as well as treatments for CoA, on blood flow
properties.
CoA is a serious congenital heart disease, and the mean age of mortality has
been estimated to be 34 years. Treatments generally focus on resolving the physical
restriction in the aorta, which is the coarctation, although CoA is associated with
many cardiovascular abnormalities. Despite the availability of several treatments,
treated CoA patients experience late hypertension and have a decreased life expectancy
compared to normal people. Two examples of treatments are resection
and end-to-end anastomosis (REA) and stents. REA is a surgical treatment that
involves excising the coarctation and suturing the remaining aorta together. Stents
are a catheter-based intervention where a catheter is inserted into the artery and
used to expand a metal stent into the coarctation. It is unclear whether a particular
treatment is superior, as there is insufficient long-term data for some treatments.
Several reviews of treatments for CoA have concluded that additional data are
required to understand whether these recently utilised treatments result in superior
long-term outcomes.
Numerical simulation of mathematical models of blood flow in arteries can be used
to investigate and compare treatments where clinical data are lacking, and difficult or
expensive to obtain. This thesis uses existing one-dimensional mathematical models
of blood flow in arteries, which have been shown to reproduce the main features of
hemodynamics. Equations are developed to implement altered arterial properties,
such as artery wall stiffness and cross-sectional luminal area, in the models. These are
used in simulations to investigate the effect of various conditions that are observed
in CoA patients, pre- and post-treatment, on blood flow properties that are related
to negative outcomes.
Treatments for coarctation necessarily affect the compliance and wall properties
of the aorta, in the region where they are implemented. REA involves excising the
coarctation and suturing the remaining aorta together, and is studied as a short
section of increased stiffness in the aorta wall in this thesis. Stents are studied as a
longer region of increased stiffness.
First a single tube model of the aorta is used to investigate the local effects
of the REA and stent treatments. It is found that the increased stiffness in the
aorta wall from REA and stent treatments, compared to normal people, results in
increased blood pressure and increased radial expansion of the artery walls, which may
contribute to the incidence of hypertension and aneurysms in treated CoA patients.
This increased blood pressure and radial expansion is found in both untapered and
tapered aortas. Flow in a tapered stent, which narrows with the aorta in a tapered
aorta model, is also simulated and compared to flow in a straight stent in a tapered
aorta. Unexpectedly, the straight stent produces some superior (closer to normal)
blood flow properties, compared to the tapered stent.
To identify possible causes of isolated systolic hypertension, which is common in
CoA patients, parameters in the model are modified and simulations are performed
to identify the effect of altered parameters on blood flow properties. Of the parameters
tested, artery wall stiffness is identified as a suitable parameter for further
investigation, based on the results of this thesis, as well as other studies that have
shown increased stiffness in the upper body arteries of CoA patients.
Next a network model of the major arteries is adapted to incorporate a range of
coarctation severities, various increases to the stiffness in the arteries in the upper
body, the REA and stent treatments used in the previous aorta model, and eccentric
left ventricular hypertrophy, which are all present in some CoA patients pre- or
post-treatment. CoA is known to be difficult to diagnose and is underdiagnosed
in early life, and simulation results suggest CoA with mild or moderate severity
coarctations may not produce the symptoms that are typically associated with CoA.
The artery stiffness associated with CoA is known to increase with age in untreated
patients, and simulations show that increased stiffness may increase the severity
of CoA symptoms, which may explain why some CoA patients are not diagnosed
until later in life. This increased stiffness is known to persist post-treatment, and it
results in increased systolic blood pressure when simulated, which may explain why
hypertension persists in treated patients.
Two blood velocity indices, Gosling’s pulsatility index and Pourcelot’s resistivity
index, are calculated from results in the models, in an attempt to find measurements
that could be tested in patients to aid in diagnosis. Gosling’s pulsatility index, which
is a calculation involving systolic, diastolic and average blood velocity, is found to
differentiate between mild, moderate and severe coarctations, which may improve
diagnosis rates in infants.
The stent and REA treatments are also compared in the network artery model.
REA is found to produce the most normal blood flow properties, which suggests that
the REA treatment is likely to produce better long-term outcomes for patients than
the stent treatment.
Eccentric left ventricular hypertrophy is an increase in the mass of the left
ventricle of the heart, without a relative increase in wall thickness, and is detected
in a significant number of CoA patients, including post-treatment. In all presented
simulations, the inflow from the heart into the aorta is specified as a flow waveform,
and eccentric left ventricular hypertrophy is modelled as a scaling of the waveform.
The results in this thesis suggest that this type of hypertrophy could be associated
with the hypertension and aneurysms observed in CoA patients. Other results that
are found suggest that the diagnosis and treatment of CoA patients may be affected
by eccentric left ventricular hypertrophy.
Although CoA increasingly appears to have life-long negative outcomes despite
treatment, it is hoped that the findings in this thesis may help to explain and improve
these outcomes for patients.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)School of Environment and ScScience, Environment, Engineering and TechnologyFull Tex
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
