3 research outputs found
An XMM-Newton EPIC X-Ray View of the Symbiotic Star R Aquarii
No full textThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We present the analysis of archival XMM-Newton European Photon Imaging Camera (EPIC) X-ray observations of the symbiotic star R Aquarii. We used the Extended Source Analysis Software package to disclose diffuse soft X-ray emission extending up to 2farcm2 (≈0.27 pc) from this binary system. The depth of these XMM-Newton EPIC observations reveals in unprecedented detail the spatial distribution of this diffuse emission, with a bipolar morphology spatially correlated with the optical nebula. The extended X-ray emission shares the same dominant soft X-ray-emitting temperature as the clumps in the jet-like feature resolved by Chandra in the vicinity of the binary system. The harder component in the jet might suggest that the gas cools down; however, the possible presence of nonthermal emission produced by the presence of a magnetic field collimating the mass ejection cannot be discarded. We propose that the ongoing precessing jet creates bipolar cavities filled with X-ray-emitting hot gas that feeds the more extended X-ray bubble as they get disrupted. These EPIC observations demonstrate that the jet feedback mechanism produced by an accreting disk around an evolved, low-mass star can blow hot bubbles, similar to those produced by jets arising from the nuclei of active galaxies. © 2022. The Author(s). Published by the American Astronomical Society.J.A.T. acknowledges support by the Fundación Marcos Moshinsky (Mexico) and UNAM PAPIIT project IA101622 (Mexico). L.S. acknowledges support by UNAM PAPIIT project IN110122 (Mexico). M.A.G. acknowledges the support of grant PGC 2018-102184-B-I00 of the Ministerio de Educación, Innovación y Universidades cofunded with FEDER funds. G.R.-L. acknowledges support from CONACyT grant 263373. Y.H.C. acknowledges the grant MOST 110-2112-M-001-020 from the Ministry of Science and Technology (Taiwan). Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This research has made use of data obtained from the Chandra Data Archive and software provided by the Chandra X-ray Center (CXC) in the application package CIAO. This work has made extensive use of NASA's Astrophysics Data System.With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.Peer reviewe
Investigation of the use of navigation tools in web-based learning: A data mining approach
No full textWeb-based learning is widespread in educational settings. The popularity of Web-based learning is in great measure because of its flexibility. Multiple navigation tools provided some of this flexibility. Different navigation tools offer different functions. Therefore, it is important to understand how the navigation tools are used by learners with different backgrounds, knowledge, and skills. This article presents two empirical studies in which data-mining approaches were used to analyze learners' navigation behavior. The results indicate that prior knowledge and subject content are two potential factors influencing the use of navigation tools. In addition, the lack of appropriate use of navigation tools may adversely influence learning performance. The results have been integrated into a model that can help designers develop Web-based learning programs and other Web-based applications that can be tailored to learners' needs
Positive Biodiversity–Productivity Relationship Predominant in Global Forests
No full textThe biodiversity–productivity relationship (BPR) is foundational to our understanding of the global extinction crisis and its impacts on ecosystem functioning. Understanding BPR is critical for the accurate valuation and effective conservation of biodiversity. Using ground-sourced data from 777,126 permanent plots, spanning 44 countries and most terrestrial biomes, we reveal a globally consistent positive concave-down BPR, whereby a continued biodiversity loss would result in an accelerating decline in forest productivity worldwide. The value of biodiversity in
maintaining forest productivity—US$396–579 billion per year according to our estimation—is by itself over five times greater than the total cost of effective global conservation. This highlights the need for a worldwide re-assessment of biodiversity values, forest management strategies, and conservation priorities
