1,721,119 research outputs found
Tri-Rotor Propeller Design Concept, Optimization and Analysis of the Lift Efficiency During Hovering
Full text linkThis study introduces the simulation of a tri-rotor contra-rotating propeller for thrust force and hover lift efficiency during vertical take-off. Vertical take-off or landing is a method used by many aircraft and makes the vehicle more convenient and easier to use. The second rotor revolved in the opposite direction of the first and third rotors. The proposed multi-rotor system has NACA 0012 untwisted and symmetric airfoil and includes three rotors with two blades for each. The airflow analysis was optimized with computational fluid dynamics simulation by using different pitch combinations to achieve the highest hover lift efficiency with sufficient overall thrust value. The critical angle of attack for the chosen airfoil gave the boundary conditions for the pitch of rotors. The results showed us that the most efficient combinations for three rotors work better with an increase of pitch angle from top to bottom so that there is a difference of at least two degrees between propellers. Experiments with angles of attack within the boundary conditions showed that the blade combinations starting from three degrees and increasing values gave positive and adequate results in many cases. In addition, the results showed that a regular increase in the angle of attack does not relate to a regular increment in thrust force
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
Mycobacterium tuberculosis virulence: insights and impact on vaccine development
No full textThe existing TB vaccine, the attenuated Mycobacterium bovis strain BCG, is effective in protecting infants from severe forms of the disease, while its efficacy in protecting adults from pulmonary TB is poor. In the last two decades, a renewed interest in TB resulted in the development of several candidate vaccines that are now entering clinical trials. However, most of these vaccines are based on a common rationale and aim to induce a strong T-cell response against Mycobacterium tuberculosis. Recent advancements in the understanding of M. tuberculosis virulence determinants and associated pathogenic strategies are opening a new and broader view of the complex interaction between this remarkable pathogen and the human host, providing insights at molecular level that could lead to a new rationale for the design of novel antitubercular vaccines. A vaccination strategy that simultaneously targets different steps in TB pathogenesis may result in improved protection and reduced TB transmission
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
Basic Considerations and Conceptual Design of a VSTOL Vehicle for Urban Transportation
Full text linkOn-demand air transport is an air-taxi service concept that should ideally use small, autonomous, Vertical Short Takeoff and Landing (VSTOL), “green”, battery-powered electric aircraft (eVSTOL). In addition, these aircraft should be competitive with modern helicopters, which are exceptionally reliable machines capable of the same task. For certification and economic purposes, mobile tilting parts should be avoided. The concept introduced in this paper simplifies the aircraft and makes it economical to build, certify and maintain. Four contrarotating propellers with eight electric motors are installed. During cruise, only two of the eight rotors available are not feathered and active. In the first step, a commercial, certified, jet-fueled APU and an available back-up battery are used. A second solution uses a CNG APU and the same back-up battery. Finally, the third solution has a high-density dual battery that is currently not available. A conceptual design is shown in this paper
Design Issues of Heavy Fuel APUs Derived from Automotive Turbochargers Part III: Combustor Design Improvement
Full text linkHeavy fuel combustion problems with startup and operation may significantly reduce the microturbine efficiency in small APUs (Auxiliary Power Units). The use of commercial automotive-derived turbochargers solves the design problems of compressors and turbines but introduces large issues with combustors. The radial combustor proved to be the best design. Unfortunately, high-pressure injection is not practical for small units. For this reason, primary air and low-pressure fuel spray are heated and mixed. In any case, a high air swirl must achieve a satisfactory combustion efficiency. This swirl should be almost eliminated at the turbine intake. CFD analysis of the combustor design was, therefore, performed with several different geometries and design solutions. In the end, a large offset of the fresh pipe from the compressor proved to be the best solution for a high swirl in the combustion region. The combustion tends to eliminate the swirl, but an undesired tumble motion at the turbine intake takes place. To eliminate the tumble, two small fins were added to straighten the flow to the turbine
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