1,721,101 research outputs found
Active control of low frequency ‘buzz-saw’ tones radiated from an aircraft engine on take off
No full textThis thesis details a feasibility study into the use of active control for the attentuation of the low frequency components of the ‘buzz-saw’ sound field radiated from an aircraft engine on take off. Passive liner sections are currently used to attenuate the sound field, however, they have insufficient thickness to attenuate sufficiently the very low frequency components of the sound field. An active control system positioned after the liner section could be used to further attenuate the sound field. This thesis shows that due to the simple modal structure of the buzz-saw noise, effective control of the sound field can be achieved by minimising the sum of the square pressures at a single ring of error sensors using a single ring of control actuators. In the absence of noise and extraneous modes, the level of control performance is fundamentally limited by the level of the evanescent modes at the error sensor array. An analytic model is developed which predicts the sound power reduction. Reflections are shown to be important in the control mechanism with standing wave regions identified between the secondary source array and the exhaust termination and between the inlet termination and the error sensor array. The thesis concludes with the results from an experimental rig. A real-time FXLMS algorithm is used to control a synthesised low order spinning mode by minimising the sum of the squared pressures measured at a single ring of 7 sensors using a simple ring of 7 control actuators. The relationship between sound pressure reduction at the error sensors and the transmitted sound power is investigated. Sound power reductions of up to 14.5dB are achieved. The control mechanism is identified from computer simulation.</p
Active control of buzz-saw tones: experiment and theory
No full textThis paper discusses some theoretical and experimental issues related to the active control of buzz-saw tones radiated from an aircraft engine inlet at takeoff. Buzz-saw tones occur when the rotor tip speed becomes supersonic. It arises due to the formation of shocks at the blade tips, which then propagate non-linearly along the engine duct. Buzz-saw noise comprises a series of tones harmonically related to the shaft rotation frequency (Engine Orders). Moreover, it has been shown that the noise at each Engine Order comprises just one single spinning mode. Whilst there has been considerable work aimed at assessing the feasibility of active control for reducing the tones due to rotor - stator interaction, buzz-saw noise has been overlooked. This is surprising given the low frequencies at which Buzz-Saw noise occurs, and its simple modal content, which both suggest that buzz-saw noise is particularly suited to active control. This paper describes various control strategies for reducing buzz-saw noise. The paper concludes with the results of a laboratory experiment aimed at demonstrated experimentally the effectiveness with which a single spinning mode, characteristic of an EO = 3 buzz-saw tone, can be controlled. Reductions in excess of 14dB are reported at some frequencies
Figure 23 in Three-dimensional geometry of a pterosaur wing skeleton, and its implications for aerial and terrestrial locomotion
No full textFigure 23. Methods of changing the angle of attack of the inner wing. A, left lateral view of Anhanguera configured as in Fig. 18. The broken line indicates the chord line. The angle of attack of the section is zero. B, as in (A), but with the left leg depressed at the hip by 30°. The geometric angle of attack a is indicated. C, as in (A), but with the leg supinated at the hip by 30°. The leg movements shown in (B) and (C) increase both the angle of attack and the camber of the inner wing.Published as part of Wilkinson, Matthew T., 2008, Three-dimensional geometry of a pterosaur wing skeleton, and its implications for aerial and terrestrial locomotion, pp. 27-69 in Zoological Journal of the Linnean Society 154 (1) on page 56, DOI: 10.1111/j.1096-3642.2008.00409.x, http://zenodo.org/record/544643
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
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
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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