1,720,959 research outputs found
Ultrasonic wave propagation in colloid suspensions and emulsions: Recent experimental results
No full textEarly theories of acoustic propagation such as those by Urick, and Urick and Ament, are attractive because of their computational simplicity, but limited in application. The more complex models of Allegra and Hawley, and Harker and Temple, have since gained application. A wideband ultrasonic attenuation and phase velocity spectrometer have been used to determine the validity of these models for a range of colloidal materials. Measurements taken validate the Allegra and Hawley model for colloids with spherical base particles. The Harker and Temple model is used to infer changes in the flocculation state of kaolin slurries which result from chemical intervention
The effects of flocculation on the propagation of ultrasound in dilute kaolin slurries
No full textA broadband ultrasonic spectrometer has been used to measure ultrasonic attenuation and phase velocity dispersion as functions of frequency in kaolin suspensions over a range of solid volume fractions from φ = 0.01 to φ = 0.08 and over a pH range from 3 to 9. The Harker and Temple theory was used to simulate ultrasound propagation in the suspension, using measured slope viscosity, particle size, and size distribution. Simulated results for ultrasonic attenuation and phase velocity agree well with measured values. Both sets of results agree well and show that for volume fractions above φ ∼ 0.05 attenuation and velocity dispersion increase for increasing floc size, whereas for volume fractions below φ ∼ 0.05 attenuation and velocity dispersion both decrease. It is proposed that the mechanism for this change in behavior around φ ∼ 0.05 involves changes in floc density and floc size distribution with φ and pH
The detection of structural transformations in kaolin suspensions by ultrasound
No full textThefractal dimension of kaolin flocs suspended in water was increased by the addition of potassium chloride and indirectly monitored by low-power ultrasonic pulses in a test cell with a “pitch-catch” configuration. The results from these measurements were compared with fractal dimensions obtained from quasi-elastic light-scattering measurements in a kaolin suspension of a much lower solid volume fraction. Further comparison with a coupled phase theory of ultrasound propagation, utilizing measured slope viscosity and particle size distribution, revealed that the observed changes in the ultrasound signature were commensurate with changes in the fractal dimension observed by light scattering over a potassium chloride concentration range of approximately 0–1 mM
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
Ultrasonic propagation through aqueous kaolin suspensions during degassing
No full textA degassing procedure is necessary prior to taking ultrasonic measurements in aqueous kaolin suspensions as well as many other liquid based colloids. In this work we compare two degassing methods and show that subjecting a sample to a power ultrasound field is easier and less time consuming than exposing it to a vacuum. We also combine degassing and deflocculation procedures to show that air bubbles are trapped in cage-like kaolin flocs and are released when such flocs break up
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
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