Introduction: Many chondrules clearly contain relict grains that result from incomplete melting of precursor material. Most discussions of relict grains have focused on grains that are easy to identify because they have compositions significantly different from their host chondrules, including forsterite in type II chondrules and dusty olivine in type I chondrules [1]. However, in order to full...

the study of nucleation mechanism of new grains during severe plastic deformation of magnesium alloys is of great importance to control the characteristics of final microstructures.  to investigate the role of discontinuous recrystallization, a wrought az31 magnesium alloy was deformed by accumulative back extrusion process at 330 °c.  the obtained microstructures were studied using optical and...

Introduction: After silicon carbide (SiC), graphite is the best studied presolar mineral. A wealth of information exists on the isotopic compositions of C and of many minor/trace elements in micrometer-sized grains [e.g., 1-5]. Presolar graphite grains exhibit large C-isotopic anomalies with C/C ratios between 2 and 7000. Although this range is compatible with what is observed for SiC [6, 7], t...

From millimeter observations of classical T Tauri stars, it is suggested that dust grains in circumstellar disks have grown to millimeter size or larger. However, gas drag on such large grains induces rapid accretion of the dust. We examined the evolution of dust disks composed of millimeter sized grains, and showed that rapid accretion of the dust disk causes attenuation of millimeter continuu...

Presolar SiC grains of the types mainstream, Y, and Z are believed to have formed in thermally pulsing asymptotic giant branch stars with a range of metallicity: mainstream grains in stars of close-to-solar metallicity, Y grains in stars of around half-solar metallicty, and Z grains in stars of around one-third solar metallicity. From their Si and Ti isotopic ratios, it is possible to obtain in...

A 28 g sample of the Qingzhen enstatite (EH3) chondrite was subjected to chemical and physical separation procedures to yield several grain-size residues. Ion mapping of isotopes of Si, O, and C in the ion microprobe of two size fractions (QZR4: 0.4–0.8 lm; QZR5: 0.8–2 lm) identified 55 30Si-depleted candidates out of 37,917 Si-rich grains and six 18O-depleted grains out of 54,410 oxides. Subse...

Neon was measured in 39 individual olivine (or olivine-rich) grains separated from individual chondrules from Dhajala, Bjurböle, Chainpur, Murchison, and Parsa chondrites with spallation-produced Ne the result of interaction of energetic particle irradiation. The apparent Ne cosmic ray exposure (CRE) ages of most grains are similar to those of the matrix with the exception of three grains from ...

background: this study was aimed to investigate the association of consuming white rice and potato, as well as the bread type with anthropometric measures and blood pressure (bp) in a national sample of iranian children and adolescents. methods: this nationwide study was conducted in 2011-2012 among 14,880 students, aged 6-18 years, selected by multistage cluster sampling from 30 provinces of i...

nonea medik. is a genus of the boraginaceae tribe boragineae, with approximately 35 species worldwide. examination of their palynological characters supported the separation of taxa, which is usually based on morphological and micromorphological reproductive features. pollen grains of 10 taxa representing three groups of taxa in iran, the n. caspica group, the n. persica group and the n. lutea ...

Introduction: Among circumstellar grains produced around O-rich evolved stars, silicate grains are the most abundant [1]. Until recently, the identification of presolar silicate grains in extraterrestrial materials proved difficult due in part to their destruction by parent body processes, requiring analysis of very primitive samples, and to the experimental challenge presented by their submicr...