The Solar Twin Planet Search Maia, M Tucci; Ramirez, I; Melendez, J ...
Astronomy and astrophysics (Berlin),
6/2016, Letnik:
590
Journal Article
Recenzirano
Context. Solar twins are stars with similar stellar (surface) parameters to the Sun that can have a wide range of ages. This provides an opportunity to analyze the variation of their chemical ...abundances with age. Nissen (2015, A&A, 579, A52) recently suggested that the abundances of the s-process element Y and the alpha-element Mg could be used to estimate stellar ages. Aims. This paper aims to determine with high precision the Y, Mg, and Fe abundances for a sample of 88 solar twins that span a broad age range (0.3-10.0 Gyr) and investigate their use for estimating ages. Methods. We obtained high-quality Magellan Inamori Kyocera Echelle (MIKE) spectra and determined Y and Mg abundances using equivalent widths and a line-by-line differential method within a 1D LTE framework. Stellar parameters and iron abundances were measured in Paper I of this series for all stars, but a few (three) required a small revision. Results. The Y/Mg ratio shows a strong correlation with age. It has a slope of ?0.041 + or - 0.001 dex/Gyr and a significance of 41sigma. This is in excellent agreement with the relation first proposed by Nissen (2015). We found some outliers that turned out to be binaries where mass transfer may have enhanced the yttrium abundance. Given a precise measurement of Y/Mg with typical error of 0.02 dex in solar twins, our formula can be used to determine a stellar age with ~0.8 Gyr precision in the 0 to 10 Gyr range.
The Solar Twin Planet Search Ramirez, I; Melendez, J; Bean, J ...
Astronomy and astrophysics (Berlin),
12/2014, Letnik:
572
Journal Article
Recenzirano
We are carrying out a search for planets around a sample of solar twin stars using the HARPS spectrograph. The goal of this project is to exploit the advantage offered by solar twins to obtain ...chemical abundances of unmatched precision. This survey will enable new studies of the stellar composition -- planet connection. We determine the fundamental parameters of the 88 solar twin stars that have been chosen as targets for our experiment. We present the largest sample of solar twins analyzed homogeneously using high quality spectra. The fundamental parameters derived from this work will be employed in subsequent work that aims to explore the connections between planet formation and stellar chemical composition.
ABSTRACT
This work aims to examine in detail the depletion of lithium in solar twins to better constrain stellar evolution models and investigate its possible connection with exoplanets. We employ ...spectral synthesis in the region of the asymmetric 6707.75 Å Li I line for a sample of 77 stars plus the Sun. As in previous works based on a smaller sample of solar twins, we find a strong correlation between Li depletion and stellar age. In addition, for the first time we show that the Sun has the lowest Li abundance in comparison with solar twins at similar age (4.6 ± 0.5 Gyr). We compare the lithium content with the condensation temperature slope for a subsample of the best solar twins and determine that the most lithium-depleted stars also have fewer refractory elements. We speculate whether the low lithium content in the Sun might be related to the particular configuration of our Solar system.
Morpholino oligonucleotides (MOs) are an effective, gene-specific antisense knockdown technology used in many model systems. Here we describe the application of MOs in zebrafish (Danio rerio) for in ...vivo functional characterization of gene activity. We summarize our screening experience beginning with gene target selection. We then discuss screening parameter considerations and data and database management. Finally, we emphasize the importance of off-target effect management and thorough downstream phenotypic validation. We discuss current morpholino limitations, including reduced stability when stored in aqueous solution. Advances in MO technology now provide a measure of spatiotemporal control over MO activity, presenting the opportunity for incorporating more finely tuned analyses into MO-based screening. Therefore, with careful management, MOs remain a valuable tool for discovery screening as well as individual gene knockdown analysis.
We describe a conditional in vivo protein-trap mutagenesis system that reveals spatiotemporal protein expression dynamics and can be used to assess gene function in the vertebrate Danio rerio. ...Integration of pGBT-RP2.1 (RP2), a gene-breaking transposon containing a protein trap, efficiently disrupts gene expression with >97% knockdown of normal transcript amounts and simultaneously reports protein expression for each locus. The mutant alleles are revertible in somatic tissues via Cre recombinase or splice-site-blocking morpholinos and are thus to our knowledge the first systematic conditional mutant alleles outside the mouse model. We report a collection of 350 zebrafish lines that include diverse molecular loci. RP2 integrations reveal the complexity of genomic architecture and gene function in a living organism and can provide information on protein subcellular localization. The RP2 mutagenesis system is a step toward a unified 'codex' of protein expression and direct functional annotation of the vertebrate genome.
Over the last few years, the technology to create targeted knockout and knockin zebrafish animals has exploded. We have gained the ability to create targeted knockouts through the use of zinc finger ...nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats/CRISPR associated system (CRISPR/Cas). Furthermore, using the high-efficiency TALEN system, we were able to create knockin zebrafish using a single-stranded DNA (ssDNA) protocol described here. Through the use of these technologies, the zebrafish has become a valuable vertebrate model and an excellent bridge between the invertebrate and mammalian model systems for the study of human disease.
Traditionally, drug dosing is based on a concentration-response relationship estimated in a population. Yet, in specific individuals, decisions based on the population-level effects frequently result ...in over or under-dosing. Here, we interrogate the relationship between population-based and individual-based responses to anesthetics in mice and zebrafish. The anesthetic state was assessed by quantifying responses to simple stimuli. Individual responses dynamically fluctuated at a fixed drug concentration. These fluctuations exhibited resistance to state transitions. Drug sensitivity varied dramatically across individuals in both species. The amount of noise driving transitions between states, in contrast, was highly conserved in vertebrates separated by 400 million years of evolution. Individual differences in anesthetic sensitivity and stochastic fluctuations in responsiveness complicate the ability to appropriately dose anesthetics to each individual. Identifying the biological substrate of noise, however, may spur novel therapies, assure consistent drug responses, and encourage the shift from population-based to personalized medicine.
Abstract Bedell GM, Khetani MA, Cousins MA, Coster WJ, Law MC. Parent perspectives to inform development of measures of children's participation and environment. Objective To obtain parents' ...perspectives on children's participation and environment to inform the development of new measures. Design Descriptive design using qualitative methods with focus groups and semistructured interviews. Setting Focus groups and interviews with parents of children with disabilities were held on campus, in the home, and at community agencies; interviews with parents of children without disabilities were conducted in their homes. Participants Parents (N=42): parents of children with disabilities (n=25) from the United States (n=14) and Canada (n=11) and parents of children without disabilities (n=17) from the United States. Most children (93%) were aged 5 to 16 years. Children with disabilities had diagnoses characterized by psychosocial, learning, attention, and sensory-processing difficulties. Interventions Not applicable. Main Outcome Measure Not applicable. Results Parents described common life activities and environmental factors that were similar to and expanded on categories currently reported in the literature. Differences identified among parents mainly focused on impairments and challenges of children with disabilities and concerns related to activities and programs designed for them. Parents spontaneously talked about participation and environmental factors together. Their descriptions consistently included information about features of the physical and social environment and other factors that influenced their child's participation, such as demands of the activity, parent strategies, and the child's age, preferences, and abilities. Parents' standards and expectations for their child's participation often varied depending on the specific setting, activity, and situation. Conclusions Findings have informed the development of a parent-report measure that explicitly links participation and environmental factors specific to home, school, and community settings. Having 1 measure to assess participation and environment rather than using distinct tools to assess each construct separately should situate the child's participation in real-life contexts.
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