Solar Twins and Possible Solutions of the Solar and Jupiter Abundance Problems

Implications of the recently discovered systematic abundance difference between the Sun and two collections of `solar twins' are discussed. The differences can be understood as an imprint on the abundances of the solar convection zone caused by the lock-up of heavy elements in the planets. Such a scenario also leads naturally to possible solutions of two other abundance peculiarities; 1) the discrepancy between photospheric abundances derived from accurate 3-D models of the solar photosphere and the abundance of heavy elements in the solar interior deduced from helioseismology, and 2) the abundance pattern of Jupiter, which can either--with great difficulty--be interpreted as a general and similar overabundance of both common elements such as carbon, nitrogen and sulphur and rare inert gases such as argon, krypton and xenon, or--much more simply--as an under-abundance of hydrogen.Comment: 4 pages, submitted to ApJL, v2 has improved formatting of reference lis

Information Literacy Instruction for Upper-Year Undergraduate Students: A Stratified Course-Integrated Approach

Undergraduate students face many potential barriers to learning about the process of conducting research. Information literacy instruction provided through faculty-librarian collaboration in an effort to expand the abilities of the “novice researcher” can ease the experience of undergraduate students. In addition, information literacy instruction may invoke increased student participation in the scholarly discourse of their chosen discipline. The implementation of a stratified course-integrated approach may be particularly valuable to upper-level undergraduates in preparation for completing a thesis or other culminating project in their final year of study. This claim is examined within the context of an instruction session observed as a component of a third-year undergraduate Materials Science and Engineering course

Perceived Constraints and Opportunities for Brazilian Smallholders Going Organic: a case of coffee in the state of Minas Gerais

This paper presents the findings of an analysis of the perceived rationales of smallholders for declining or entering organically certified coffee production, in the case Poço Fundo region, Minas Gerais. Based on group interviews and questionnaires, the rationale for farmers who declined organic production were found to be avoidance of perceived risk of harvest failure associated with the process of convertion from conventional to organic coffee production. Rationales for farmers who entered organic production included non-market benefits such as environmental quality and life quality enhancement

Dis-embedded Openness: Inequalities in European Economic Integration at the Sectoral Level

The process of European integration resulted in a marked increase in transnational economic flows, yet regional inequalities along many developmental indicators remain. We analyze the unevenness of European economies with respect to the embedding of export sectors in upstream domestic flows, and their dependency on dominant export partners. We use the WIOD data set of sectoral flows for the period of 1995-2011 for 24 European countries. We found that East European economies were significantly more likely to experience increasing unevenness and dependency with increasing openness, while core countries of Europe managed to decrease their unevenness while increasing their openness. Nevertheless, by analyzing the trajectories of changes for each country, we see that East European countries are also experiencing a turning point, either switching to a path similar to the core, or to a retrograde path with decreasing openness. We analyze our data using pooled time series models and case studies of country trajectories

The observable prestellar phase of the IMF

The observed similarities between the mass function of prestellar cores (CMF) and the stellar initial mass function (IMF) have led to the suggestion that the IMF is already largely determined in the gas phase. However, theoretical arguments show that the CMF may differ significantly from the IMF. In this Letter, we study the relation between the CMF and the IMF, as predicted by the IMF model of Padoan and Nordlund. We show that 1) the observed mass of prestellar cores is on average a few times smaller than that of the stellar systems they generate; 2) the CMF rises monotonically with decreasing mass, with a noticeable change in slope at approximately 3-5 solar masses, depending on mean density; 3) the selection of cores with masses larger than half their Bonnor-Ebert mass yields a CMF approximately consistent with the system IMF, rescaled in mass by the same factor as our model IMF, and therefore suitable to estimate the local efficiency of star formation, and to study the dependence of the IMF peak on cloud properties; 4) only one in five pre-brown-dwarf core candidates is a true progenitor to a brown dwarf.Comment: ApJ Letters, accepte

3D non-LTE line formation in the solar photosphere and the solar oxygen abundance

We study the formation of O I and OH spectral lines in three-dimensional hydrodynamic models of the solar photosphere. The line source function of the O I 777 nm triplet is allowed to depart from local thermodynamic equilibrium (LTE), within the two-level-atom approximation. Comparison with results from 1D models show that the 3D models alleviate, but do not remove, the discrepancy between the oxygen abundances reported from non-LTE work on the 777 nm triplet and from the [O I] 630 nm and OH lines. Results for the latter two could imply that the solar oxygen abundance is below 8.8 (lg(H) = 12). If this is confirmed, the discrepancy between theory and observation for the 777 nm triplet lines might fall within the range of errors in equivalent width measurements and f-values. The line source function of the 777 nm triplet in the 1.5D approximation is shown to differ insignificantly from the full 3D non-LTE result.Comment: 10 pages, uuencoded compressed PostScript file including figures, to appear in Astronomy & Astrophysics. Also available at ftp://www.astro.su.se/pub/da