1,720,982 research outputs found
Fragmentation model and strewn field estimation for meteoroids entry
Get PDFEveryday thousands of meteoroids enter the Earth's atmosphere. The vast majority burn up harmlessly during the descent, but the larger objects survive, occasionally experiencing intense fragmentation events, and reach the ground. These events can pose a non-negligible threat for a village or a small city; therefore, models of asteroid fragmentation, together with accurate post breakup trajectory and strewn field estimation, are needed to enable a reliable risk assessment of these hazards. In this work, a comprehensive methodology to describe meteoroids entry, fragmentation, descent, and strewn field is presented by means of a continuum approach. At breakup, a modified version of the NASA Standard Breakup Model is used to generate the fragments distribution in terms of their area-to-mass ratio and ejection velocity. This distribution, combined with the meteoroid state, is directly propagated using the continuity equation coupled with the non-linear entry dynamics. At each time step, the fragments probability density time-evolution is reconstructed using Gaussian Mixture Model interpolation. Using this information is then possible to estimate the meteoroid's ground impact probability. This approach departs from the current state-of-the-art models: it has the flexibility to include large fragmentation events while maintaining a continuum formulation for a better physical representation of the phenomenon. The methodology is also characterised by a modular structure, so that updated asteroids fragmentation models can be readily integrated into the framework, allowing a continuously improving prediction of re-entry and fragmentation events. The propagation of the fragments' density and its reconstruction, at the moment considering only one fragmentation point, is first compared against Monte Carlo simulations, and then against real observations. Both deceleration due to atmospheric drag and ablation due to aerothermodynamics effects have been considered
Modelling the Break-Up and Re-Entry Propagation of Meteorites Through a Continuum Approach
Get PDFThe study of the fragmentation of meteorites entering the Earth's atmosphere allow to predict the consequences such events can have on the ground. Existing models for meteoroid fragmentation follow either a pancake approach, where the cloud of fragments resulting from the meteorite explosion expands together in the shape of a disk, or a discrete fragmentation approach, where successive fragmentation events split the bolide into several pieces. In this work, a comprehensive approach in which the fragments resulting from the breakup of a meteorite are modelled using a continuum distribution it is proposed. A modified version of the NASA Standard Breakup Model is used to generate the fragments distribution in terms of their area-to-mass ratio and ejection velocity. This distribution is then combined with the nominal entry state of the meteorite to generate the initial conditions for the entire ensemble of fragments resulting from the breakup. The fragments distribution is then directly propagated using the continuity equation combined with the non-linear entry dynamics, considering both deceleration and ablation. The result is the evolution of the fragments cloud in time, which is then reconstructed at each time step using a Gaussian mixture model. This model moves away from the simplified pancake method and has the flexibility to include large fragmentation events for a better physical representation of the entry of meteorites, given the fragments distribution as an initial condition only. This means that improved meteorites fragmentation models can be easily integrated into this framework for better propagation of the trajectory of the fragments. The propagation of the fragments density and its reconstruction is first compared against Monte Carlo simulations, and then against real observations
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
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
- …
