1,720,986 research outputs found
A general approch for multiple sensor hot wire probes
Full text linkA method of calibration of multiple-sensor probes and for interpretation
of measurement signals is presented in a systematic way in this paper. The
method is based on an extension of Jorgensen’s directional response relationship.
The measurements are not affected by deviations of the sensors from nominal
construction angles or by interference and positioning imperfections. These errors
are automatically balanced during the calibration phase. The use of a statistical
approach reduces the random errors when the calibration data set presents a
sufficient degree of overdetermination. The technique allows the determination of
the influence cone as a function of the accepted uncertainty, by means of a
post-processing procedure. The method allows an ad hoc angular calibration
resulting in an error reduction when a very small variation in velocity direction is
expected. The calibration and measurement procedures are very easy to perform.
Finally the accuracy of the method for a three-sensor probes has been evaluated
by comparison with acquired data and available nominal values
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
Mixing enhancement in hybrid rocket motor using vortex generators
No full textA hybrid rocket is a compromise between a solid and a liquid rocket motor: uses a solid fuel and a liquid oxidizer. This configuration has several well known advantages, such as less security problems, smaller costs, etc. On the other hand, main problem of this type of motors, is the poor mixing, inside the combustion chamber, between the solid propellant and the oxidizer injected. As consequence, combustion chamber usually results to be quite long in order to respect mixing time between propellant and oxidizer. Several different solutions have been proposed in the past to overcome this problem, going from complex design of the internal propellant grain to different grain composition. In a previous work the authors have studied the presence of protrusions of thermal protections in a large solid rocket motor (i.e. ARIANE V - P230) because they are the reason for the production of large coherent vortex structures that are responsible of undesirable pressure oscillations. During that study by chance, it has been observed that these structures are also responsible for increased internal mixing with extraction of fluid from the boundary layer near the propellant grain. Therefore the possibility of improving internal mixing by means of obstacles placed in the combustion chamber has been discussed. Aim of the present work is to study the effects of vortex structures in the combustion chamber on propellant- oxidizer mixing in hybrid rocket motors. The proposed way for the production of these vorticity structures is the introduction in the combustion chamber of ad-hoc obstacles and localized oxidizer injection. For this reason a parametric study, by varying: The length of the combustion chamber, the height of an obstacle place in the combustion chamber and the possibility of side injection of oxidizer, has been conducted. Results, obtained by means of CFD simulations, have shown that the values of mixing intensity are several times larger than the case of the motor without obstacle and injection. Therefore starting from these results, an improved solution with the proposed devices and a reduced length has been finally tested.©2012 by the International Astronautical Federation
Development of a Payload Dispersion and Contamination Analysis Tool for the Vega Maiden Flight
No full textThe ESA VEGA program started back in the 90’s, motivated by the rising market of micro/mini-satellites, mainly driven by institutional programs, which motivated the development of a dedicated launch vehicle. The VEGA Qualification Flight is currently scheduled to take place by the end of 2010 and several payloads (PLs) will be released in orbit including: LARES satellite, ALMASat-1 and nine Cubsat provided by the ESA Education Office. The Italian Space Agency (ASI) and the VEGA Integrated Project Team (IPT) decided to carry out a payloads separation analysis and to take advantage of the support from the University of Bologna ALMASat-1 team. At the University of Bologna, a MATLAB/Simulink-based payload dispersion and contamination simulator was then implemented in order to study possible payload collisions and pollution-contaminations
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