1,720,953 research outputs found
Mechanical Design and Arrangement of nanosatellite Delfi-n3Xt
No full textDesign of the different elements in the Structural Subsystem of Delfi-n3Xt. This is done by implementation of the lessons learned and solutions to problems encountered with Delfi-C3. First different options for CubeSats are considered and traded. Afterwards the detailed design is treated. Also the arrangement of the different subsystems and payload is discussed, since Delfi-n3Xt has a limited volume.Space Systems EngineeringAerospace Engineerin
Design, Integration and Verification of the Delfi-n3Xt Reaction Wheel System
No full textTo improve the pointing capabilities of nanosatellites a fast response attitude control system is required. Reaction wheels are an effective solution and rely on the simple principle of conservation of angular momentum. Also they can be developed within the stringent budgets of nanosatellites with current technologies. The Delfi-n3Xt satellite of the Delft University of Technology also includes reaction wheels and this thesis covers the design, integration and verification of the Delfi-n3Xt reaction wheel system, which will be among the first three-axis reaction wheel systems for nanosatellites in space.Space Systems EngineeringSpace EngineeringAerospace Engineerin
Design and analysis of parachute triggering algorithms for re-entry vehicles
No full textMost re-entry vehicles utilize a Descent and Landing System (DLS) for a safe descent through the lowest part of the atmosphere. It usually requires deployment in a certain suitable range of flight conditions, which has to be estimated by limited means of navigation. The investigation performed is a comparison of currently used trigger methods and triggering algorithms which are based on correlation between in-flight measurements and the DLS triggering conditions for a ballistic re-entry vehicle, where the correlations have been extracted by multiple Monte Carlo campaigns. This approach gives an improvement of the estimation of the deployment conditions of a factor of two over direct measurements of the Mach number. The Mach number is determined to be the most critical parameter for the parachute deployment, because its opening range is the smallest compared to the dynamic pressure and the altitude. Furthermore a sensor sensitivity analysis is performed for a lifting entry trajectory in order to support an upcoming ESA re-entry mission. The velocity drift appears to be the dominant dispersion by a factor ten for the Mach estimation, if the Mach estimation is performed by estimating the drag using axial deceleration measurements. Such a method is the preferred method for the estimation of the deployment conditions, because it has an expected error of less than Mach 0.1. For the lifting-re-entry mission, a strategy was developed to have redundant parachute deployment triggering if a certain system on the vehicle fails. This strategy involves the use of an Inertial Measurement Unit, Global Positioning System measurements and as last resort, a static pressure probe. Furthermore it appeared that the vehicle can estimate its state using no inputs from the guidance navigation and control system for four minutes. Finally a case study has been performed to investigate the possibility to reduce the footprint by a dynamic parachute opening window. This has found to be ineffective on Earth, but could be effective for Mars re-entry using a parachute able to deploy beyond Mach 2.5, which would reduce the footprint 15 to 25 kilometers if the NASA MER missions are used as a reference; this would be a reduction of 30 to 50 % of the footprints of current missions. A higher opening velocity is already desired in order to be able to land on the Martian highlands. Modified parachute designs can be developed to incorporate both benefits.Space Systems EngineeringAerospace Engineerin
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
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
Detailed design and verification of a structure and mechanisms for Delfi-n3Xt
No full textThe objective of this thesis is to perform systems engineering, detailed (re-)design and testing of the structural and mechanisms subsystems and facilitate the production of components.Space Systems EngineeringEarth Observation and Space SystemsAerospace Engineerin
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