1,721,019 research outputs found
Status of the Space Environment: Current Level of Adherence to the Space Debris Mitigation Policy
Full text linkTo counter an ever increasing number of man-made objects orbiting Earth which are endangering current and future space missions, the Space Debris Mitigation (SDM) guidelines, issued by the Inter-Agency Space Debris Coordination Committee (IADC), were first published in 2002. These guidelines were a model for various international and national standardisation and regulation activities on SDM. One part of the research conducted at the Space Debris Office at the European Space Operations Centre (ESOC) is to study and monitor the level of implementation of these guidelines. This report summarises the status of the near Earth space environment by illustrating the number of objects orbiting Earth. The current and historical environment is assessed, with a focus on the interference of the IADC protected regions, the Low Earth Orbit (LEO) and the Geostationary Orbit (GEO). It includes an estimate of the evolution of the collision risk of payloads and rocket bodies with space debris, computed with ESA's Meteoroid and Space Debris Terrestrial Environment Reference (MASTER) tool. And it illustrates the current level of adherence to the SDM guidelines in terms of end-of-life operations and the release of mission related objects
Transformation of Satellite Breakup Distribution for Probabilistic Orbital Collision Hazard Analysis
Full text linkFragmentation clouds from explosions or collision of payloads and rocket bodies in space pose a threat to objects in Earth orbit. Most of the fragments are too small to be tracked and can only be accounted for statistically. Here, a framework for the fully statistical treatment of a fragmentation cloud, its evolution and ramifications, without the need of simplifying assumptions, is presented. The cloud is modeled as an uncertainty around a single fragment, which can be propagated using any of the existing, nondeterministic, nonlinear orbital uncertainty propagation methods. This work is focused on providing the initial distribution and the estimation of the statistical collision probability. The NASA standard breakup model is revisited to derive a probability distribution of the initial fragment cloud. Two density transformation methods are discussed to obtain the distribution in a subset of orbital elements, suitable for mid-to long-term evolution. The fragment spatial density and the impact rates on targets in any orbit are obtained. The method is applied to show the fragment cloud distribution of a payload collision in low Earth orbit (LEO). Its collision probability with a satellite in LEO and a rocket body in the geostationary transfer orbit are estimated. The result is compared against, and shows the limitations of, sampling and methods based on finite differences
Jörg Frey, Stefan Krauer, Hermann Lichtenberger (éd.), Heil und Geschichte. Die Geschichtsbezogenheit des Heils und das Problem der Heilsgeschichte in der biblischen Tradition und in der theologischen Deutung, (Wissenschaftliche Untersuchungen zum Neuen Testament, 248) Tübingen, Mohr Siebeck, 2009
No full textGrappe Christian. Jörg Frey, Stefan Krauer, Hermann Lichtenberger (éd.), Heil und Geschichte. Die Geschichtsbezogenheit des Heils und das Problem der Heilsgeschichte in der biblischen Tradition und in der theologischen Deutung, (Wissenschaftliche Untersuchungen zum Neuen Testament, 248) Tübingen, Mohr Siebeck, 2009. In: Revue d'histoire et de philosophie religieuses, 90e année n°2, Avril-Juin 2010. pp. 295-296
Evolution of Fragmentation Cloud in Highly Eccentric Orbit Using Representative Objects
No full textMany historical on-orbit satellite fragmentations occurred in Highly Eccentric Orbits (HEOs) such as the Geostationary Transfer Orbit (GTO). Such fragmentations produce fragment clouds that interfere with the Low Earth Orbit (LEO) environment and pose a threat to operational satellites. Objects in HEO undergo complex dynamics due to the influence of perturbations varying as a function mainly of their altitude and area-to-mass ratio. The evolution of such a cloud, including small objects down to 1 mm, is not well understood. This paper describes a method to model the evolution of a fragmentation cloud in HEO under the influence of atmospheric drag and Earth's oblateness. Semi-analytical techniques are applied to propagate represen- tative objects constituting the cloud; rather than following the evolution of many distinct fragments. The proposed method is applied on a GTO upper stage using the standard NASA break-up model to nd the distribution right after the fragmentation. The evolution of the fragment cloud is analysed statistically and time of closures are calculated for the formation of the torus along the parent orbit and the band around Earth. Assumptions on the evolution of the cloud that are valid in LEO are shown to be invalid for clouds in HEO
Deletion of Smgpi1 encoding a GPI-anchored protein suppresses sterility of the STRIPAK mutant Smmob3 in the filamentous ascomycete Sordaria macrospora
No full textThe striatin interacting phosphatase and kinase (STRIPAK) complex, which is composed of striatin, protein phosphatase PP2A and kinases, is required for fruiting-body development and cell fusion in the filamentous ascomycete Sordaria macrospora. Here, we report on the interplay of the glycosylphosphatidylinositol (GPI)-anchored protein SmGPI1 with the kinase activator SmMOB3, a core component of human and fungal STRIPAK complexes. SmGPI1 is conserved among filamentous ascomycetes and was first identified in a yeast two-hybrid screen using SmMOB3 as bait. The physical interaction of SmMOB3 and SmGPI1 was verified by co-immunoprecipitation. In vivo localization and differential centrifugation revealed that SmGPI1 is predominantly secreted and attached to the cell wall but is also associated with mitochondria and appears to be a dual-targeted protein. Deletion of Smgpi1 led to an increased number of fruiting bodies that were normally shaped but reduced in size. In addition, Smmob3 and Smgpi1 genetically interact. In the sterile Delta Smmob3 background deletion of Smgpi1 restores fertility, vegetative growth as well as hyphal-fusion defects. The suppression effect was specific for the Delta Smmob3 mutant as deletion of Smgpi1 in other STRIPAK mutants does not restore fertility
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
- …
