1,721,013 research outputs found
Accurate Simulation of Low-Intensity Transcranial Ultrasound Propagation for Neurostimulation
Get PDFNeural stimulation with low-intensity ultrasound is a potentially transformative technology with applications in therapy and research. To develop, it will require ultrasound to be tightly focused on brain structures with accurate spatial targeting and fine control over the ultrasound amplitude at the target. However, the skull is an impediment to the effective focusing of ultrasound. Simulations of ultrasound propagation through acoustic property maps derived from medical images can be used to derive focusing drive signals for multi-element arrays. Focusing effectiveness is dependent on the fidelity of the numerical simulations. In combination with MRI based treatment verification, model based focusing has been used to focus high-intensity ultrasound onto the brain for ablation. This thesis presents a thorough and systematic study of the simulation parameters required to achieve effective transcranial focusing. The literature on ultrasonic neurostimulation, transcranial ultrasonic focusing, and the derivation of property maps from medical images is reviewed. The sampling criteria required to ensure numerical accuracy for the k-space pseudospectral time domain simulation scheme is established through testing of individual sources of numerical error, and convergence testing of a simulated time-reversal protocol. With numerical accuracy assured, the importance of acoustic property maps is examined through simulations to determine the sensitivity of intracranial fields to the properties of the skull layer. These results are corroborated by matching experimental measurements of ultrasound propagation through skull bone phantoms with spatially registered simulations. Finally, the impact of image related homogenisation and loss of internal bone structure is determined using simulations through co-registered clinical CT and micro-CT data of the skull
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
Accurate Time-Varying Sources in K-Space Pseudospectral Time Domain Acoustic Simulations
Get PDFThe pseudospectral time domain (PSTD) method is
popular as a wave equation solver, one of its advantages being
that it permits the use of coarse grids, as long as the spatial
sampling is greater than two points-per-wavelength. The k-space
PSTD method improves on this by incorporating an additional
factor to remove the numerical dispersion which arises from the
discretisation of the time derivatives. However, the effect of the
temporal discretisation of time-varying sources has not previously
been considered, although it can lead to substantial errors in the
predicted field unless the timestep is sufficiently small to ensure
the highest frequency is sampled at many points-per-period. Here,
a correction factor is derived which eliminates this source of
error, resulting in a k-space PSTD method that retains the spatial
sampling advantage of conventional PSTD schemes but is also
accurate as long as the temporal sampling is greater than two
points-per-period and the CFL number is < 1
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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