Asteroseismology

Asteroseismology is the determination of the interior structures of stars by using their oscillations as seismic waves. Simple explanations of the astrophysical background and some basic theoretical considerations needed in this rapidly evolving field are followed by introductions to the most important concepts and methods on the basis of example. Previous and potential applications of asteroseismology are reviewed and future trends are attempted to be foreseen.Comment: 38 pages, 13 figures, to appear in: "Planets, Stars and Stellar Systems", eds. T. D. Oswalt et al., Springer Verla

Evolutionary and pulsational properties of white dwarf stars

Abridged. White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. The study of white dwarfs has potential applications to different fields of astrophysics. In particular, they can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow to use these stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. They can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants. In this work, we review the essentials of the physics of white dwarf stars. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.Comment: 85 pages, 28 figures. To be published in The Astronomy and Astrophysics Revie

Revealing the nature of magnetic phases in the semi-Heusler alloy Cu0.85Ni015MnSb

We report the magnetic, magnelocaloric, and magnelolransporl properties of the semi-Heusler alloy Cu(0.85)Ni(015)MnSla, which exhibits coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) phases. A broad magnetic phase transition is evident from the temperature variations of magnetization, heat capacity, and isothermal magnetic entropy change. This is due to the presence of both AFM and FM phases at low temperatures. The variation or electrical resistivity with temperature shows three distinct regions of magnetic phases. The magnetoresistance (MR) results also show the presence of AFM and FM phases at temperatures below 45 K, and a FM phase at temperature above 45 K. Though there is no signature of a spin-glass state at low temperatures, various results point towards the presence of shortrange magnetic correlations at low temperatures. (C) 2014 Elsevier B.V. All rights reserved

Risk factors for dementia in Brazil: Differences by region and race

Introduction: Twelve risk factors (RFs) account for 40% of dementia cases worldwide. However, most data for population attributable fractions (PAFs) are from high-income countries (HIC). We estimated how much these RFs account for dementia cases in Brazil, stratifying estimates by race and socioeconomic level. / Methods: We calculated the prevalence and communalities of 12 RFs using 9412 Brazilian Longitudinal Study of Aging participants, then stratified according to self-reported race and country macro-regions. / Results: The overall weighted PAF was 48.2%. Less education had the largest PAF (7.7%), followed by hypertension (7.6%), and hearing loss (6.8%). PAF was 49.0% and 54.0% in the richest and poorest regions, respectively. PAFs were similar among White and Black individuals (47.8% and 47.2%, respectively) but the importance of the main RF varied by race. / Discussion: Brazil's potential for dementia prevention is higher than in HIC. Education, hypertension, and hearing loss should be priority targets

Mycophenolate therapy in interstitial pneumonia with autoimmune features: a cohort study

Sara S McCoy,1 Zubin Mukadam,2 Keith C Meyer,2 Jeffrey P Kanne,3 Cristopher A Meyer,3 Maria D Martin,3 Emmanuel Sampene,4 Scott W Aesif,5 Laurie N Rice,6 Christie M Bartels1 1Division of Rheumatology, Department of Internal Medicine, School of Medicine and Public Health, University of Wisconsin, Madison, WI 53705, USA; 2Division of Pulmonary and Critical Care, Department of Internal Medicine, School of Medicine and Public Health, University of Wisconsin, Madison, WI 53705, USA; 3Department of Radiology, University of Wisconsin, Madison, WI 53792-3252, USA; 4Department of Biostatistics, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA; 5Department of Pathology, University of Wisconsin, Madison, WI 53792-3252, USA; 6Department of Pulmonology, SSM Health Dean Medical Group, Madison, WI 53715, USA Objectives: International experts recently characterized interstitial pneumonia with autoimmune features (IPAF) as a provisional diagnosis for patients with interstitial lung disease who have characteristics of autoimmune disease but do not meet criteria for a specific autoimmune disease. We describe clinical characteristics of IPAF patients and examine responses to mycophenolate as a therapy for IPAF.Methods: This retrospective cohort included adult patients meeting European Respiratory Society/American Thoracic Society classification criteria for IPAF. Sociodemographic, clinical, and pulmonary function test data were abstracted for patients with and without mycophenolate treatment and followed longitudinally from interstitial lung disease diagnosis for change in pulmonary function test results.Results: We identified 52 patients who met criteria for IPAF. Of 52 IPAF patients, 24 did not receive mycophenolate and 28 did, with median time to mycophenolate treatment 22 months. Changes in FVC% and percentage predicted lung diffusion capacity for carbon monoxide (DLCO%) between the mycophenolate-treated and untreated groups were not significantly different (FVC% change P=0.08, DLCO% change P=0.17). However, there was a trend toward more rapid baseline decline of both FVC% and DLCO% in the mycophenolate-treated cohort before vs after mycophenolate therapy. The slope of both FVC% and DLCO% values improved after onset of mycophenolate exposure for the treated group, although this finding was not statistically significant.Conclusion: Patients with IPAF might benefit from mycophenolate therapy. Larger prospective clinical trials are needed to evaluate the efficacy of mycophenolate for patients who meet criteria for IPAF. Keywords: interstitial lung disease, autoimmune disease, connective tissue disease, myco­phenolat

Structural and magnetic properties of cobalt iron disulfide (CoxFe1−xS2) nanocrystals

Abstract We report on synthesis and investigation of nanocrystalline cobalt-iron-pyrites with an emphasis on nanocrystal structure, morphology and magnetic behavior. The nanocrystals (NCs) were 5–25 nm in diameter as characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). With an increase in Fe fraction, X-ray diffraction and small-angle-X-ray scattering (SAXS) showed a systematic decrease in lattice constant, primary grain/NC size (15 to 7 nm), and nanoparticle (NP) size (70 to 20 nm), respectively. The temperature dependence of the DC magnetization and AC susceptibility versus frequency revealed a number of magnetic phases in Co x Fe1−x S2. Samples with x = 1 and x = 0.875–0.625 showed evidence of superspin glass (SSG) behavior with embedded ferromagnetic (FM) clusters of NPs. For x = 0.5, samples retained their mixed phases, but showed superparamagnetic (SPM) behavior with antiferromagnetic clusters suppressing magnetic dipolar interactions. Below x = 0.5, the pyrites show increasing paramagnetic character. We construct a phase diagram, which can be understood in terms of competition between the various dipolar, exchange, inter- and intracluster interactions. Our results suggest that NC size and shape can be tuned to engineer spin-polarized ferromagnetism of n-doped iron pyrite