1,720,965 research outputs found
Investigation of propeller characteristics at low Reynolds number with an angle of attack: A computational aeroacoustic study
No full textAdvancements in technology have made commercial unmanned aerial vehicles reliable and readily available, leading to an exponential rise in their market demand over the past few years. COVID-19 has further accelerated this growth through an increase in demand for contact-less delivery and crowd monitoring systems. However, despite these favorable conditions, their limited range, perceived threat, and concerns about noise pollution in urban environments have prevented them from being widely accepted by society. A recent study by NASA found that people perceive UAV noise to be more annoying than cars, and trucks at a similar sound pressure level, which highlights the need to understand the acoustic characteristic of these aircraft. These UAVs are generally powered by electric motors, making their propellers the most dominant source of noise. In the past, researchers have conducted several studies to understand and characterize the noise produced by aircraft propellers. However, these studies were limited to high Reynolds (>1,000,000) and Mach number operations for large commercial aircraft, creating a significant gap in the understanding of the aerodynamic and acoustic characteristics of propellers operating at low Reynolds (<200,000) and Mach number. This thesis aims to address the research gap by performing a high-fidelity computational simulation using Dassault Systèmes PowerFLOW®. The tool uses a lattice Boltzmann very large eddy simulation (LBM-VLES) based approach to compute the aerodynamic results and the Ffowcs-Williams and Hawkings (FWH) aeroacoustic analogy to calculate far-field acoustic values. The main objective of the thesis is: “To characterize and quantify the effect of non-axisymmetric inflow conditions on the aerodynamic and acoustic properties of propellers operating at low Reynolds numbers.” To meet the objective, a computational setup consisting of a twin-bladed propeller with a radius of 15 cm is designed in PowerFLOW®. The propeller is analyzed at 0º and 15º AoA, operating at 6000 RPM with a free stream velocity of 12 m/sec and the results validated against experimental data. Aerodynamic measurements and flow analysis revealed that the change in angle of attack (AoA) resulted in a 3.87% increase in the net thrust, and 1.16% increase in the net torque value of the propeller. Operating at an AoA, the propeller blade experiences asymmetric loading around the propeller plane, the loads fluctuate by 35% between the points of maximum and minimum loading. Further analysis of the propeller flow field is carried out by averaging the velocity field and performing a phase-locked analysis to visualize the vortex field. The analysis helps in understanding the effect of AoA on propeller wake and quantifies its a symmetric nature. Far-field acoustic data is acquired by two circular microphone arrays, with a polar angle resolution of 10º. The arrays are placed around the propeller plane and along the axial axis of the propeller. The change in AoA results in a 3 dB higher noise at an azimuthal angle (Ψ) of 90º and reduces by an equal magnitude at Ψ = 270º. The shift is attributed to the change in propeller tip Mach number and local blade AoA as a function of its azimuthal location and propeller AoA. Further analysis of the sound power level (PWL) produced by the propeller is carried out, showing a 1.5 dB increase in the PWL produced by the propeller blade at 15º AoA than 0º.Aerospace Engineerin
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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