87 research outputs found
Neon Lights Up a Controversy: the Solar Ne/O Abundance
The standard solar model was so reliable that it could predict the existence
of the massive neutrino. Helioseismology measurements were so precise that they
could determine the depth of the convection zone. This agreement between theory
and observation was the envy of all astrophysics -- until recently when
sophisticated three-dimensional hydrodynamic calculations of the solar
atmosphere reduced the metal content by a factor of almost two. Antia & Basu
(2005) suggested that a higher value of the solar neon abundance, Ne/O = 0.52,
would resolve this controversy. Drake & Testa (2005) presented strong evidence
in favor of this idea from a sample of 21 Chandra stars with enhanced values of
the neon abundance, Ne/O = 0.41. In this paper, we have analyzed solar active
region spectra from the archive of the Flat Crystal Spectrometer on Solar
Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra
from the pioneering days of X-ray astronomy in the 1960s. These data seem
consistent with the standard neon-to-oxygen abundance value, Ne/O = 0.15
(Grevesse & Sauval 1998). If these results prove to be correct, than the
enhanced-neon hypothesis will not resolve the current controversy.Comment: submitted to ApJ Letter
An experimental method of measuring the quasi-static and dynamic confined behaviour of PMMA
A testing device is presented for the experimental study of the confined
behaviour of PMMA in compression under quasi-static loading or at high
strain-rates. The constitutive relation of the material ring (allowing to
confine the PMMA) being known, transverse gauges glued on its lateral surface
allow for the measurement of the lateral confining pressure. The hydrostatic
pressure and the Mises stress may be computed. Quasi-static and dynamic tests
performed in a strain-rate range of 1e-3/s 1e3/s are processed with the method
and compared to results of unconfined compression tests. It is found that the
compressive behaviour of PMMA is weakly influenced by the level of pressure and
much more sensitive to strain-rate: an elastic brittle behaviour is observed at
high strain-rates in unconfined or confined conditions whereas elastoplastic
behaviour is noted under quasi-static loading
Web Mining for Web Personalization
Web personalization is the process of customizing a Web site to the needs of specific users, taking advantage of the knowledge acquired from the analysis of the user\u27s navigational behavior (usage data) in correlation with other information collected in the Web context, namely, structure, content, and user profile data. Due to the explosive growth of the Web, the domain of Web personalization has gained great momentum both in the research and commercial areas. In this article we present a survey of the use of Web mining for Web personalization. More specifically, we introduce the modules that comprise a Web personalization system, emphasizing the Web usage mining module. A review of the most common methods that are used as well as technical issues that occur is given, along with a brief overview of the most popular tools and applications available from software vendors. Moreover, the most important research initiatives in the Web usage mining and personalization areas are presented
Contribution of grazing areas to small ruminant production systems in the Mediterranean countries
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Webometrics benefitting from web mining? An investigation of methods and applications of two research fields
Webometrics and web mining are two fields where research is focused on quantitative analyses of the web. This literature review outlines definitions of the fields, and then focuses on their methods and applications. It also discusses the potential of closer contact and collaboration between them. A key difference between the fields is that webometrics has focused on exploratory studies, whereas web mining has been dominated by studies focusing on development of methods and algorithms. Differences in type of data can also be seen, with webometrics more focused on analyses of the structure of the web and web mining more focused on web content and usage, even though both fields have been embracing the possibilities of user generated content. It is concluded that research problems where big data is needed can benefit from collaboration between webometricians, with their tradition of exploratory studies, and web miners, with their tradition of developing methods and algorithms
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