Dust grain growth and the formation of the extremely primitive star SDSS J102915+172927

Dust grains in low-metallicity star-forming regions may be responsible for the formation of the first low-mass stars. The minimal conditions to activate dust-induced fragmentation require the gas to be pre-enriched above a critical dust-to-gas mass ratio Dcr=[2.6--6.3]x10^-9 with the spread reflecting the dependence on the grain properties. The recently discovered Galactic halo star SDSS J102915+172927 has a stellar mass of 0.8 Msun and a metallicity of Z=4.5x10^-5 Zsun and represents an optimal candidate for the dust-induced low-mass star formation. Indeed, for the two most plausible Population III supernova progenitors, with 20 Msun and 35 Msun, the critical dust-to-gas mass ratio can be overcome provided that at least 0.4 Msun of dust condenses in the ejecta, allowing for moderate destruction by the reverse shock. Here we show that even if dust formation in the first supernovae is less efficient or strong dust destruction does occur, grain growth during the collapse of the parent gas cloud is sufficiently rapid to activate dust cooling and likely fragmentation into low-mass and long-lived stars. Silicates and magnetite grains can experience significant grain growth in the density range 10^9 /cc < nH<10^12 /cc by accreting gas-phase species (SiO, SiO2, and Fe) until their gas-phase abundance drops to zero, reaching condensation efficiencies =1. The corresponding increase in the dust-to-gas mass ratio allows dust-induced cooling and fragmentation to be activated at 10^12 /cc < nH < 10^14 /cc, before the collapsing cloud becomes optically thick to continuum radiation. We show that for all the initial conditions that apply to the parent cloud of SDSS J102915+172927, dust-driven fragmentation is able to account for the formation of the star.Comment: 8 pages, 4 figures, submitted to MNRA

The origin of the most iron-poor star

We investigate the origin of carbon-enhanced metal-poor (CEMP) stars starting from the recently discovered $\rm [Fe/H]<-7.1$ star SMSS J031300 (Keller et al. 2014). We show that the elemental abundances observed on the surface of SMSS J031300 can be well fit by the yields of faint, metal free, supernovae. Using properly calibrated faint supernova explosion models, we study, for the first time, the formation of dust grains in such carbon-rich, iron-poor supernova ejecta. Calculations are performed assuming both unmixed and uniformly mixed ejecta and taking into account the partial destruction by the supernova reverse shock. We find that, due to the paucity of refractory elements beside carbon, amorphous carbon is the only grain species to form, with carbon condensation efficiencies that range between (0.15-0.84), resulting in dust yields in the range (0.025-2.25)M$_{\odot}$. We follow the collapse and fragmentation of a star forming cloud enriched by the products of these faint supernova explosions and we explore the role played by fine structure line cooling and dust cooling. We show that even if grain growth during the collapse has a minor effect of the dust-to-gas ratio, due to C depletion into CO molecules at an early stage of the collapse, the formation of CEMP low-mass stars, such as SMSS J031300, could be triggered by dust cooling and fragmentation. A comparison between model predictions and observations of a sample of C-normal and C-rich metal-poor stars supports the idea that a single common pathway may be responsible for the formation of the first low-mass stars.Comment: 14 pages, 8 figures, accepted for publication in ApJ. Rephrased sentence in section 5 to avoid text overlap with arXiv:1307.2239 in their model descriptio

Creep-Fatigue Evaluation Methodologies and Related Issues for Japan Sodium Cooled Fast Reactor (JSFR)

AbstractThis paper describes the main topics on creep-fatigue evaluation methodologies for the Japan Sodium Cooled Fast Reactor (JSFR). JSFR's operating temperature is 550C and design life is 60 years with key technologies in terms of creep-fatigue being the adoption of new materials, 316FR and Mod.9Cr-1Mo steel, and the development of evaluation methodologies for those materials: 316FR is low-carbon nitrogen-added 316 steel which has superior creep properties and will be used for the reactor vessel and internal structures. Mod.9Cr-1Mo steel will be applied to most of the coolant systems including primary piping, intermediate heat exchangers, secondary piping and steam generators. Creep-fatigue evaluation methodologies for those materials are being developed concentrating on capturing long-term materials behavior and strength so that the evaluation of 60-year design is justified, and simplified evaluation methods for strain ranges and stress relaxation behaviors applicable to JSFR structures which have various configurations and loading conditions are also being developed. The results of R&D will be incorporated in a JSME (Japan Society of Mechanical Engineers) code for the design and construction of fast reactors

日本語母音のサロゲート解析

Nonlinear deterministic dynamical structure of the normal phonation of Japanese vowels is studied by the method of surrogate. The surrogate analysis exploits Wayland translation error and nonlinear deterministic predictability as the discriminating statistics. The results imply that the vowel signals have strong nonlinear dynamical characteristics that can not be detected by conventional linear dynamical systems analyses of speech.特集 : 「産業におけるソフトコンピューティングに関する国際会議\u2799」発表論文選

教員志望学生の数学的アイデンティティに関する調査研究―教育法を学修する前の大学2 年生を対象として―

　本稿の目的は，教員志望学生の数学的アイデンティティの質問紙を作成し調査を行い，指導者としての数学的アイデンティティを高めることとA私立大学の算数教育カリキュラムの改善に関する示唆を得ることである。　教員志望で算数（または数学）科教育法を履修する前の4大学の2年生計204名を対象に，数学的アイデンティティに関する質問紙調査を行った結果，指導者としての数学的アイデンティティを認識レベルで高めるためには算数・数学学習の陶冶性・文化性・実用性の重要性をそれぞれ認識させる必要があることが示唆された。一方，指導者としての数学的アイデンティティを行動レベルで高めるには，未修の教育法や実習での学びの経験が必要となる可能性が示唆された。今後，縦断的な調査を通じて，この推測を検証していく必要がある。　また，A大学における算数関連カリキュラムにおいて，「算数・数学学習に関する態度」の向上よりも「算数・数学を学ぶ陶冶性・文化性・実用性に関する認識や陶冶性に関する意欲・習慣」を高める指導に重心をおいた指導を行うことが有効である可能性が示唆された