1,720,975 research outputs found
Large scale, population-based finite element analysis of cementless tibial tray fixation
No full textJoint replacements are a common treatment of osteoarthritis, rheumatoid arthritis, or fractures of both the hip and knee. The rising number of procedures being performed each year means that there is a need to assess the performance of an implant design in the general population. The majority of computational studies assessing implants do not take into account inter-patient variability and only use a single patient model. More often than not, it is then assumed that the results can be extrapolated to the general population. This thesis describes a method allowing population-based assessment of joint replacements, focussing on the tibial tray component of a total knee replacement. To generate a large population of models for finite element analysis, two statistical models were used. One was of the tibia, capturing both the variability of the morphology and bone quality, and the other was of the internal knee loads during a gait cycle. Assessment of the statistical models showed that they could adequately generate representative tibiae and gait cycle loads. An automated method was then developed to size, position, and implant the tibial tray in the generated population of tibiae in preparation for finite element analysis. The use of a population-based study, a unique approach compared to current studies, was demonstrated using three case studies assessing the performance of the tibial tray. The first case study examined the factors which might increase the risk of failure of the tibial tray and the effect of under sizing the tibial tray on primary stability. Factors such as bone quality and patient weight were seen to increase the risk of failure. It was found that under sizing the tibial tray did not significantly affect the primary stability of the tibial tray. It was also observed that the peak strain occurred during swing phase of the gait cycle, whereas peak micromotion occurred at the beginning of stance phase of the gait. The second case study investigated the effect of tibia resection depth on primary stability of the tibial tray. A more distal resection was found to increase the peak strain and micromotion of the bone-tray interface. The worsening primary stability with a more distal resection, suggest that to obtain optimal primary stability of the tibial tray it is necessary to resect as little bone as possible. The third case study compared three tibial tray designs. It was found that the trays with pegs or flanges surrounding the stem tended to perform better, reducing the strain and the micromotion at the bone-tray interface. It was noted that the performance of the trays predicted by the analysis was similar to that observed clinically. This shows the potential use of population-based studies to help predict the clinical outcome of joint replacements
Development of a statistical model of knee kinetics for applications in pre-clinical testing
No full textPre-clinical computational testing of total knee replacements (TKRs) often only considers a single patient model with simplified applied loads. In studies of multiple patients, most only take into account geometric differences, especially in studies on the knee. Limited availability of kinetic data means that it is difficult to account for inter-patient variability. Principal component analysis (PCA) based statistical models have been used to capture the variation of a set of data and generate new instances of the data. This study presents a method to create a statistical model of kinetic waveform data. A PCA based statistical model was created of the tibiofemoral joint loads for level gait of preoperative TKR patients using data predicted from a musculoskeletal model. A reconstruction test showed that, using principal components (PCs) representing 95% variance, the median root-mean-squared (RMS) error was <0.1 body weight (BW) for the forces and <0.001 BWm for the moments. Leave-one-out tests were also performed and although the median RMS error increased for each load in comparison to the reconstruction error (maximum was 0.2 BW for the axial force and 0.012 BWm for the varus–valgus moment) these were considered within an acceptable limit. The purpose of creating a statistical model is to be able to sample a large set of data representing a population from a small set of clinical data. Such models can potentially be used in population based studies of TKRs incorporating inter-patient variability
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
A large scale finite element study of an osseointegrated cementless tibial tray
No full textA large scale finite element study of an osseointegrated cementless tibial tra
Statistical modelling of the whole human femur incorporating geometric and material properties
No full textWhen analysing the performance of orthopaedic implants the vast majority of computational studies use either a single or limited number of bone models. The results are then extrapolated to the population as a whole, overlooking the inherent and large interpatient variability in bone quality and geometry. This paper describes the creation of a three dimensional, statistical, finite element analysis (FEA) ready model of the femur using principal component analysis. To achieve this a registration scheme based on elastic surface matching and a mesh morphing algorithm has been developed. This method is fully automated enabling registration and generation of high resolution models. The variation in both geometry and material properties was extracted from 46 computer tomography scans and captured by the statistical model. Analysis of mesh quality showed this was maintained throughout the model generation and sampling process. Reconstruction of the training femurs showed 35 eigenmodes were required for accurate reproduction. A set of unique, anatomically realistic femur models were generated using the statistical model, with a variation comparable to that seen in the population. This study illustrates a methodology with the potential to generate femur models incorporating material properties for large scale multi-femur finite element studie
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
An exploration of the state of self-publishing in the academic publishing sector of South Africa
Get PDFDissertation (MIS)--University of Pretoria, 2008.The academic publishing sector in South Africa is facing many changes and challenges in a post- 1994 democracy. Most of these changes were brought about by the Higher Education Act No 101 of 1997. Challenges and new trends include new business and threats from multinational corporations; a limited buying market at higher education level; a need for localised content; new emerging technologies in publishing and knowledge distribution; the merging of 36 higher education institutions into 22; escalating book production costs and book prices; a non-book buying and book reading culture; illegal photocopying and widespread copyright infringement; changing student and lecturer profiles including the language of instruction; increasing pressure on academics to publish research; inefficient student loan schemes; decreasing library acquisition budgets and the transformation of the publishing industry itself in terms of BBBEE. Within the midst of all these challenges, publishers are faced with a new trend, that of selfpublishing of academic textbooks, which lecturers then prescribe to their own group of students. Self-publishing implies that authors undertake all processes related to publishing on their own, including the financial risk of publishing a book. There is a multitude of literature available on self-publishing, but very little focuses on this trend within the academic environment. A literature survey of self-publishing provided various reasons and conditions for the existence of the phenomenon. The researcher made use of two questionnaires that were sent to academic campus bookshops and academic self-publishing authors. From the results of these two surveys it is evident that academic self-publishing is an increasing trend in the higher education environment of South Africa. Reasons for self-publishing collected from the literature survey were supported by the empirical research findings from the two surveys. The main reasons for self-publishing in the academic environment include financial incentives; a volatile author-publisher relationship; issues of copyright and control; possible rejection suffered by authors; technological advances and a sense of community service among academics and lecturing staff. The study was able to prove the existence of academic self-publishing in the higher education environment of South Africa. Academic self-publishing is most apparent in the academic fields of Business, Economics and Management Sciences to the extent that it could have far-reaching financial impact on markets that are traditionally lucrative for commercial publishers. Commercial publishers are encouraged to engage with author associations and seek out possible new alternatives to satisfying author needs in a changing market place.Information Scienceunrestricte
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
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