1,720,978 research outputs found
Analytical model and numerical simulations for solid propellant using a Random Loose Packing approach
No full textDue to the powder nature of a solid rocket propellant, a better understanding of the packing structure is needed. In this study, a constructive algorithm in order to simulate the Random Loose packing process, is developed, and it is an improvement of the classical, so called, dropping and roll method. In particular, the final position of each sphere is determined solving an analytical model, and it leads to better accuracy in the final results. Moreover, this algorithm can be applied not just to a mono-sized sphere packing, but each sphere can have a different radius. Furthermore, a 2D map is created in order to find the volume fraction for bi-modal propellant function of the radius ratio and different percentage of each components. Also the contact number behavior (related with the inner structure) is analyzed
Prediction of Tail-Off Pressure Peak Anomaly on Small-Scale Rocket Motors
Full text linkNumerical studies intended to predict solid rocket motors anomalies are the major contributors when developing strategies to both limit expensive fire tests and to investigate and understand the physical phenomena from which anomalies can arise. This paper aims to present a mathematical–physical method to evaluate the pressure peak, namely Friedman Curl, occurring at the tail-off phase of small-scale rocket motors. Such phenomenon is linked to the grain solid particles arrangement (i.e., packing effect); indeed, those particles show a tendency to accumulate at a certain distance from the metallic case, implying a local burn rate increment and a combustion chamber pressure rise close to the tail-off phase. Comparisons between experimental and simulated combustion chamber pressure profiles are outlined to prove the effectiveness of the mathematical–physical approach. Simulations were carried out with an internal ballistic simulation tool developed by the authors of this work
The HERMES Mission: A CubeSat Constellation For Multi-Messenger Astrophysics
No full textThe High Energy Rapid Modular Ensemble of Satellites (HERMES) is a project that plays a key role in the Multi-Messenger Astrophysics of the next decade. The implementation of a distributed space asset to continuously monitor the random electromagnetic emissions of bright high-energy transients in the Universe is proposed. Specifically, the technological and scientific pathfinder constellation, up to six 3U CubeSat, embarks a new generation of miniaturised detectors for science. Having just closed the PDR, the project goes into phase C&D: Politecnico di Milano, together with INAF, oversees the space segments and payload implementation, respectively. The challenging mission feasibility was assessed from both technological and scientific points of view. The possibility to correctly keep the spacecraft triplets geometry and to ensure the correct overlapping of instrument field-of-view for a successful triangulation of highenergy transient has been achieved with no orbital control on board. The paper, starting from an introduction on scientific mission constraints, focuses on the description of platform subsystems design. The constellation complexity is highlighted in terms of pointing accuracy, power demand, and scientific data packages transmission. The program is co-funded by the National Ministry for Research (MIUR), the Italian Space Agency, (HERMES-TP), and the EC-H2020 framework (HERMES-SP)
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
HERMES Constellation for Astrophysics: the Thermal Modeling and Testing Strategy for Qualification
Full text linkVariations 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
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