1,720,975 research outputs found
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
Electrical impedance imaging of the modiolus using the cochlear implant electrode array
No full textDissertaion (MEng (BioEngineering))--University of Pretoria, 2022.Imaging the cochlea in vivo is a challenging task. Regardless of the quality of images obtained from modern clinical imaging techniques, the internal structures of the cochlea remain mainly obscured. Electrical impedance tomography (EIT) is a safe, low-cost alternative medical imaging technique, with applications in a variety of clinical scenarios. In this study, EIT is investigated as an alternative method to image and extract the centre of gravity of the modiolus (CoG) in vivo. This information can be used to augment present postoperative medical imaging techniques to investigate the cochlea.
The cochlear implant (CI) electrode array was used in conjunction with the EIT software Electrical Impedance Tomography and Diffuse Optical Reconstruction Software (EIDORS) to develop a CI-EIT system. A methodology was successfully developed to import models of varying complexity, along with the electrode contacts and domains of arbitrary conductivity, from COMSOL to EIDORS. An adapted stimulation protocol compliant with CI specifications was also developed and employed, in conjunction with the imported models, for EIT image reconstruction using CI electrode arrays.
The CI-EIT system was simulated by modelling user-specific electrode array trajectories within a simple conductive medium containing an inhomogeneity representing the modiolus. The method included an adapted adjacent stimulation protocol for data collection. For the image reconstruction, NOSER and Tikhonov priors were considered. A parameter analysis was conducted to find the most robust combination of image priors and hyperparameters for this application. The CI-EIT system methodology was validated at different noise levels for four electrode array trajectories. Comparing the NOSER and Tikhonov priors, it was observed that the NOSER prior exhibits superior centre of gravity localisation performance in cochlear implant EIT image reconstruction for different noise levels and user-dependent variability in electrode array trajectories. Image reconstruction, using a NOSER prior at a hyperparameter value of approximately 0.001, resulted in an average centre of gravity localisation error of less than 4 % for all electrode array trajectories using difference imaging, and less than 5.5 % using absolute imaging. Using the same optimal image reconstruction parameters, an average conductivity estimation error ranging between 10 % to 50 % for all electrode array trajectories was observed.
After the establishment of the most robust image reconstruction parameters, four new anatomically realistic mesh geometries with unique electrode trajectories were implemented. Additionally, a simple mesh containing only the four electrode trajectories in a volume, and a duplicate of the latter with mesh refinement in the region of interest was implemented. The effect of the complexity of the mesh on the CoG localisation was investigated. The CoG localisation using the anatomically realistic mesh geometry provided marginally more accurate results than the simple mesh implementations, with a maximum of only 4 % improvement. However, the simpler mesh geometries decreased the computational time for reconstruction to less than 30 % of the time required for solving the anatomically realistic mesh for difference image, and to less than 25 % of the time required for solving the absolute image using the anatomically realistic mesh. The ability of the proposed CI-EIT system to reconstruct typically obscured internal structures of the cochlea, such as the modiolar wall trajecory, was investigated. A discrete Frechet distance analysis revealed that the trajectory of the automatically extracted modiolar wall from the EIT reconstruction is similar to the theoretical trajectory. A Procrustes analysis also revealed that the Bezier curves representing the modiolar wall are similar in shape among the three mesh complexities.
It was concluded that the proposed CI-EIT system to image and extract geometric properties of the modiolus is a viable proposition. However, more research and a multidisciplinary approach are required for the proposed CI-EIT system to become a clinical reality.Electrical, Electronic and Computer EngineeringMEng (BioEngineering)Unrestricte
Modelling of the electrode-auditory nerve fibre interface in cochlear prostheses
Full text linkDissertation (PhD(Electronic Engineering))--University of Pretoria, 2001.The objective of this thesis is to provide additional insight into the electrode array-nerve fibre interface that exists in the implanted cochlea and to facilitate investigation of new electrode arrays in interaction with the cochlea and auditory nerve fibres. The focus is on potential distributions and excitation profiles generated by different electrode array types and factors that could have an influence on these distributions and profiles. Research contributions made by the thesis are the creation of a detailed 3-D model of the implanted cochlea that accurately predicts measurable effects in cochlear implant wearers and facilitates effortless simulation of existing and new electrode array variations; the establishment of the important anatomical structures required in a 3-D representation of the implanted cochlea; establishment of evidence that array location is the primary parameter that controls spread of excitation; definition of the critical focussing intensity of intracochlear electrode pairs; confirmation thatmonopolar stimulation could deliver focussed stimulation to approximately the same degree than that delivered by widely spaced electrode configurations and that the use of monopolar configurations over bipolar configurations are therefore advantageous under certain conditions; explanation of the effect that encapsulation tissue around cochlear implant electrodes could have on neural excitation profiles; extension of the information available on the focussing ability of multipolar intracochlear electrode configurations; and establishment of evidence that a higher lateral electrode density could facilitate better focussing of excitation, continuous shaping of excitation profiles and postoperative customization of electrode arrays for individual implant wearers.Electrical, Electronic and Computer EngineeringUnrestricte
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
Deriving the internal bony structure of the cochlea from high-resolution µCT images for translation to low resolution image-based construction of person-specific computational models of cochlear implants
No full textThesis (PhD (Biosystems))--University of Pretoria, 2019.To investigate cochlear implant (CI) performance, geometric computational models of the cochlea have been used to assess and optimise electrode insertion strategies and to investigate current flow through the cochlear volume as a result of intra-cochlear stimulation. Most of these models are derived low-resolution computed tomography (CT) and radiographic scans of humans or high-resolution histological sections of cochleae that are not viable for in vivo studies. Often these models lack a significant set of detail, still use a generic shape of the inner structures of the cochlea or obscured structures and are not clinically translatable. A method for the predication of obscured landmarks from reference landmarks is needed to generate user-specific computational models of the cochlea if the data source is of low quality. A standard set of prediction polynomial functions derived from high-resolution μCT scans needs to be developed and applied to clinically available CT images of the cochlea. Although histological sections of the human cochlea provide the best
resolution of the cochlear structures, midmodialar sequential sectioning of the cochlea is not possible. μCT scans provide a solution, as the images are still of high quality and allow for detailed measurement of cochlear parameters on midmodiolar sections. Secondly, the more recent construction of a knowledge-based automated landmark computational model needs to be refined. The search fields that the automated models template uses to place a landmark need to be standardised and should have the ability to morph the cochlear shape together with the inner bony structures. Such models are of great clinical importance, as they can be generated much more quickly to inform CI surgeons on the individual cochlear anatomy of a CI patient and maintenance of CI.
Lastly, the effect that taxonomic class has on the functional implications of an implanted electrode array has yet to be determined. The cochlear geometry that best predicts the location of the electrode array is important, as it has a significant implication for hearing outcomes.
This thesis assesses the anatomical geometric factors that affect inter-person variations at the peripheral-electrode interface by developing a pre-operative approach to person-specific model design for implant candidates. This approach aims to increase the accuracy and details of geometric parameters that are available for model construction and integrate the image data into three-dimensional (3D) computational volume conduction models. The study used a landmark-based approach to measure the cochlear parameters that contribute to cochlear variation, as well as the development of algorithms to derive obscured landmarks from consistently available cochlear landmarks. A workflow in the form of a custom script UPCochlea.m that describes the technical aspects of landmark analysis was created to describe each cochlea algorithmically and to extract spiral trajectories that describe cochlear anatomy. Polynomial algorithms for the description of each spiral were created for use as standard for determining each cochlear class and the prediction of obscured spirals on clinically available data. This is the first study of its kind to describe all eight spirals that constitute the cochlea and spiral lamina.
Automatic generation of user-specific landmark-based 3D computational models is a rapid process that can easily be translated into a clinical tool that may inform surgeons, manufacturers of CI’s and bio-engineers on the maintenance of such models. By refining the search fields for the template that landmark-based automated cochlear computational models
search for a landmark to be placed, more accurate automated computational models could be generated.
Psychometric data from CI users are correlated with the anatomical dimensions, their taxonomic classification and electrode locations derived from postoperative patient scans to determine the factors, if any, that may affect electrode array locations and thus the functional outcomes of CI users. The factors that contribute to speech and hearing outcomes may be used to optimise the parameter settings for CI user device programmingElectrical, Electronic and Computer EngineeringPhD (Biosystems)Restricte
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
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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