1,720,956 research outputs found
Review of perspective space debris mitigation solutions
No full textSpace debris poses an increasing threat to functioning spacecraft every year. In order to solve problems created by space debris and make administrative decisions, it is necessary to assess impact of various measures taken to mitigation and remediation on space debris environment. The article presents an overview of promising methods for limiting of space debris and methods developed by author that allow for a detailed assessment of various space debris sources and measures contribution to space debris environment
Promising method for improving the accuracy of estimates in space debris tasks - Optimal filtering of measurements
No full textSpace debris poses an increasing threat to functioning spacecraft, as well as people and property on Earth. Every
year, dozens of large spacecraft re-entry into atmosphere and reach Earth’s surface, while there is always a risk of
damage to people or property. To date, several collisions have occurred in near-Earth space, which can be
avoided in future if appropriate characteristics of warning systems of such events are provided.
The main method of parrying threats associated with space debris is warn about dangerous situations – time and
place of large objects re-entry, a possible collision between spacecraft and space debris or another spacecraft. To
implement this method and solve corresponding problems, it is necessary to have updated data on parameters of
space objects orbits by measurements. Improving accuracy of estimating spacecraft orbits parameters and their
subsequent prediction is necessary to ensure safety of space activities in conditions of a large number of space debris.
The article presents main mathematical relations of optimal filtering of measurements method, it is shown that
use of this method can significantly improve results accuracy of time of re-entry and space object as collision
probability estimates, in comparison with the traditionally used least squares method. The results of using
optimal filtering of measurements method are shown when predicting re-entry time and place of Tiangong-1
orbital station using available open data. A posteriori evaluation of accuracy prediction results showed that
use of optimal filtering of measurements allows increasing accuracy of estimates up to several times, while not
increasing computational complexity.
One of ways to mitigate new space debris is active removal. Currently, work on space debris active removal
has moved from research to being implemented in daily practice of space activities. In coming years, a number of
projects will be implemented to remove spent upper stages, rocket bodies and spacecraft from orbits. The article
present results of comparing areas for space debris active removal obtained by a method that takes into account
optimal filtering of measurements method with a specific list of objects obtained by a group of international
experts. As can be seen from the comparison - out of 50 objects, 48 fall into calculated areas, which indicate a
good correspondence of results obtained earlier with estimates of international specialists group. In this regard, it
can be assumed that in order to prevent collisions that can lead to a large formation of new objects in near future,
both the ranges of orbits in altitudes and inclinations, and specific objects have been determined.
The use of optimal filtering of measurements method in monitoring and warning systems for hazardous events
related to space debris will increase efficiency of their functioning with existing measuring instruments
Space debris in low earth orbits region: Formation and reduction process analysis in past decade
No full textThe paper considers main features of spacecraft launch traffic, break-up events in orbit, re-entry of space objects from low Earth orbits region (altitude up to 2000 km above the Earth's surface) for the period from 2010 to mid-2021. Conclusions are drawn regarding to main regularities of processes of increasing and decreasing the number of space objects in orbit. Statistical models for predicting space debris based on analyzed data have been developed. © 2021 IA
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
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
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
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