105 research outputs found

    Evaluation of the 13N(α,p)16O thermonuclear reaction rate and its impact on the isotopic composition of supernova grains

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    It has been suggested that hydrogen ingestion into the helium shell of massive stars could lead to high 13^{13}C and 15^{15}N excesses when the shock of a core-collapse supernova passes through its helium shell. This prediction questions the origin of extremely high 13^{13}C and 15^{15}N abundances observed in rare presolar SiC grains which is usually attributed to classical novae. In this context 13^{13}N(α\alpha,p)16^{16}O the reaction plays an important role since it is in competition with 13^{13}N β+\beta^+-decay to 13^{13}C. The 13^{13}N(α\alpha,p)16^{16}O reaction rate used in stellar evolution calculations comes from the CF88 compilation with very scarce information on the origin of this rate. The goal of this work is to provide a recommended 13^{13}N(α\alpha,p)16^{16}O reaction rate, based on available experimental data. Unbound nuclear states in the 17^{17}F compound nucleus were studied using the spectroscopic information of the analog states in 17^{17}O nucleus that were measured at the Alto facility using the 13^{13}C(7^7Li,t)17^{17}O alpha-transfer reaction, and spectroscopic factors were derived using a DWBA analysis. This spectroscopic information was used to calculate a recommended 13^{13}N(α\alpha,p)16^{16}O reaction rate with meaningful uncertainty using a Monte Carlo approach. The present 13^{13}N(α\alpha,p)16^{16}O reaction rate is found to be within a factor of two of the previous evaluation, with a typical uncertainty of a factor 2-3. The source of this uncertainty comes from the three resonances at Erc.m.=221E_r^{c.m.} = 221, 741 and 959 keV. This new error estimation translates to an overall uncertainty in the 13^{13}C production of a factor of 50. The main source of uncertainty on the re-evaluated 13^{13}N(α\alpha,p)16^{16}O reaction rate currently comes from the uncertain alpha-width of relevant 17^{17}F states

    Spatial cognition and science achievement: The contribution of intrinsic and extrinsic spatial skills from 7 to 11 years

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    Background. Prior longitudinal and correlational research with adults and adolescents indicates that spatial ability is a predictor of science learning and achievement. However, there is little research to date with primary-school aged children that addresses this relationship. Understanding this association has the potential to inform curriculum design and support the development of early interventions. Aims. The current study examined the relationship between primary-school children’s spatial skills and their science achievement. Method. Children aged 7-11 years (N=123) completed a battery of five spatial tasks, based on a model of spatial ability in which skills fall along two dimensions: intrinsic-extrinsic; static-dynamic. Participants also completed a curriculum-based science assessment. Results. Controlling for verbal ability and age, mental folding (intrinsic- dynamic spatial ability) and spatial scaling (extrinsic-static spatial ability) each emerged as unique predictors of overall science scores, with mental folding a stronger predictor than spatial scaling. These spatial skills combined accounted for 8% of the variance in science scores. When considered by scientific discipline, mental folding uniquely predicted both physics and biology scores, and spatial scaling accounted for additional variance in biology and variance in chemistry scores. The children’s embedded figures task (intrinsic-static spatial ability) only accounted for variance in chemistry scores. The patterns of association were consistent across the age range. Conclusion. Spatial skills, particularly mental folding, spatial scaling and dis-embedding, are predictive of 7-11 year olds’ science achievement. These skills make a similar contribution to performance for each age group

    New fossil remains of Homo naledi from the Lesedi Chamber, South Africa

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    The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to H. naledi. Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species

    Irish cardiac society - Proceedings of annual general meeting held 20th & 21st November 1992 in Dublin Castle

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    The James Webb Space Telescope Mission

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    Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least 4m4m. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the 6.5m6.5m James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

    Finishing the euchromatic sequence of the human genome

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    The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead
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