Al-26-Mg-26 ages of iron meteorites

An exposure age for an iron meteorite can be calculated from measurements of a radioactive nuclide and a stable nuclide that are produced by similar sets of nuclear reactions, provided that the stable nuclide is present with low initial abundance. The standard methods rely on either K-40 (t(sub 1/2) = 1.26 Gy), K-39, and K-41 or on a shorter-lived radionuclide and a stable, noble gas isotope. Widely used pairs of this type include Cl-36/Ar-36 and Al-26/Ne-21. Other pairs that may serve the purpose for iron meteorites contain many stable isotopes besides those of K and the noble gases that are produced partly by cosmic rays. We consider here the calculation of exposure ages, t(sub 26), from measurements of Al-26 (t(sub 1/2) = 0.7 My) and (stable) Mg-26. Ages based on Al-26/Mg-26 ratios, like those based on Cl-36/Ar-36 ratios, are 'buffered' against changes in relative production rates due to shielding because decay of the radioactive nuclide accounts for a good part of the inventory of the stable nuclide

Introduction to Linked Data and Its Lifecycle on the Web

With linked data, a very pragmatic approach towards achieving the vision of the semantic web has gained some traction in the last years. The term linked data refers to a set of best practices for publishing and interlinking structured data on the web. While many standards, methods and technologies developed within by the semantic web community are applicable for linked data, there are also a number of specific characteristics of linked data, which have to be considered. In this article we introduce the main concepts of linked data. We present an overview of the linked data lifecycle and discuss individual approaches as well as the state-of-the-art with regard to extraction, authoring, linking, enrichment as well as quality of linked data. We conclude the chapter with a discussion of issues, limitations and further research and development challenges of linked data. This article is an updated version of a similar lecture given at reasoning web summer school 2011

Introduction to Linked Data and Its Lifecycle on the Web

With linked data, a very pragmatic approach towards achieving the vision of the semantic web has gained some traction in the last years. The term linked data refers to a set of best practices for publishing and interlinking structured data on the web. While many standards, methods and technologies developed within by the semantic web community are applicable for linked data, there are also a number of specific characteristics of linked data, which have to be considered. In this article we introduce the main concepts of linked data. We present an overview of the linked data lifecycle and discuss individual approaches as well as the state-of-the-art with regard to extraction, authoring, linking, enrichment as well as quality of linked data. We conclude the chapter with a discussion of issues, limitations and further research and development challenges of linked data. This article is an updated version of a similar lecture given at reasoning web summer school 2011