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A theoretical and experimental investigation of nonlinear ultrasound propagation through tissue mimicking fluids
No full textA numerical model [l] is used to investigate finite amplitude ultrasound propagation through multiple layers of tissue-like media. This model uses a finite difference method to solve the nonlinear parabolic KZK wave equation [2]. The code ‘is modified to include an arbitrary frequency dependence of absorption and transmission effects for wave propagation across a plane interface at normal incidence. Measurements are taken of the axial nonlinear pressure field generated from a circular focused, 2.25 MHz source, through single- and multiple-layered tissue mimicking fluids. Two tissue mimicking fluids
are developed to show acoustic properties similar to amniotic fluid and a typical soft tissue. The measured values of the nonlinearity parameter sound velocity and frequency dependence of absorption for both fluids are presented. These acoustic parameters in
addition to the measurement of the source conditions are input to the numerical model allowing the experimental conditions to be simulated. Comparisons are made between the model’s predictions and the axial pressure field measurements. Results are presented in the frequency domain showing the fundamental and three subsequent harmonic amplitudes on axis, as a function of axial distance. The results show that significant onlinear distortion can occur through media with characteristics typical of tissue. Excellent agreement is found between theory and experiment indicating that the model can be used to predict nonlinear ultrasound propagation through multiple layers of tissue-like media
A numerical comparison of nonlinear indicators for diagnostic ultrasound fields
No full textNine measures of nonlinear propagation have been evaluated according to how they describe the transfer of energy from a diagnostic ultrasound beam's fundamental frequency to higher harmonics.
Fields produced by 30 transducer configurations and four scanner models were simulated in water using a finite difference model. Nine parameters proposed in the literature to indicate the degree of nonlinear distortion were calculated from measurements on the modelled fields.
The most robust indicators were the nonlinear propagation parameter sigma m, the spectral index, and two simple local distortion parameters incorporating the measured
pressure, the distance from the source, and the local transducer gain
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
Numerical indicators of nonlinear propagation in acoustic fields
No full textMeasurements of acoustic exposure made in water and then derated to account for the attenuation of tissue can be distorted by nonlinear effects. We have evaluated numerical indicators of such distortion in diagnostic ultrasound fields.We evaluate the indicators of the degree of nonlinearity in diagnostic ultrasound fields that could be used to guarantee 'quasi-linearity' or to correct measurements made under nonlinear conditions. A new indicator, σi, is introduced which can be calculated using measurements currently being made in ultrasound test labs
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
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