The Experts below are selected from a list of 7947 Experts worldwide ranked by ideXlab platform
Stephanie Monty - One of the best experts on this subject based on the ideXlab platform.
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chemo dynamics of outer halo dwarf stars including gaia sausage and gaia Sequoia candidates
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: Stephanie Monty, Kim A Venn, James M M Lane, Deborah Lokhorst, David YongAbstract:The low-metallicity, kinematically interesting dwarf stars studied by Stephens \& Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with [Fe/H]$>-2$; however, large disagreements are found for stars with [Fe/H]$\le-2$, with offsets as large as $\Delta$T$_{\rm eff}\sim+500$ K and $\Delta$log\,$g\sim+1.0$. A subset of six stars (test cases) are analysed ab initio using high resolution spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to include two $\alpha$-challenged dwarf stars, suggestive of origins in a low mass, accreted dwarf galaxy. The orbital parameters for the entire SB02 sample are re-determined using \textit{Gaia} DR2 data. We find 11 stars that are dynamically coincident with the \textit{Gaia}-Sausage accretion event and another 17 with the \textit{Gaia}-Sequoia event in action space. Both associations include low-mass, metal-poor stars with isochrone ages older than 10 Gyr. Two dynamical subsets are identified within \textit{Gaia}-Sequoia. When these subsets are examined separately, a common knee in [$\alpha$/Fe] is found for the \textit{Gaia}-Sausage and high energy \textit{Gaia}-Sequoia stars. A lower metallicity knee is tentatively identified in the \textit{Gaia}-Sequoia low energy stars. If the metal-poor dwarf stars in these samples are true members of the \textit{Gaia}-Sausage and \textit{Gaia}-Sequoia events, then they present a unique opportunity to probe the earlier, more pristine, star formation histories of these systems.
Teresa E. Pawlowska - One of the best experts on this subject based on the ideXlab platform.
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arbuscular mycorrhizal colonization of giant Sequoia Sequoiadendron giganteum in response to restoration practices
Mycologia, 2012Co-Authors: Catherine Fahey, Robert A. York, Teresa E. PawlowskaAbstract:Interactions with soil microbiota determine the success of restoring plants to their native habitats. The goal of our study was to understand the effects of restoration practices on interactions of giant Sequoia Sequoiadendron giganteum with arbuscular mycorrhizal (AM) fungi (Glomeromycota). Natural regeneration of Sequoiadendron is threatened by the absence of severe fires that create forest canopy gaps. Generating artificial canopy gaps offers an alternative tool for giant Sequoia restoration. We investigated the effect of regeneration practices, including (i) sapling location within gaps, (ii) gap size and (iii) soil substrate, on AM fungal colonization of giant Sequoia sapling roots in a native giant Sequoia grove of the Sierra Nevada, California. We found that the extent of AM fungal root colonization was positively correlated with sapling height and light availability, which were related to the location of the sapling within the gap and the gap size. While colonization frequency by arbuscules in saplings on ash substrate was higher relative to saplings in mineral soil, the total AM fungal root colonization was similar between the substrates. A negative correlation between root colonization by Glomeromycota and non-AM fungal species indicated antagonistic interactions between different classes of root-associated fungi. Using DNA genotyping, we identified six AM fungal taxa representing genera Glomus and Ambispora present in Sequoiadendron roots. Overall, we found that AM fungal colonization of giant Sequoia roots was associated with availability of plant-assimilated carbon to the fungus rather than with the AM fungal supply of mineral nutrients to the roots. We conclude that restoration practices affecting light availability and carbon assimilation alter feedbacks between sapling growth and activity of AM fungi in the roots.
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Arbuscular mycorrhizal colonization of giant Sequoia (Sequoiadendron giganteum) in response to restoration practices
Mycologia, 2012Co-Authors: Catherine Fahey, Robert A. York, Teresa E. PawlowskaAbstract:Interactions with soil microbiota determine the success of restoring plants to their native habitats. The goal of our study was to understand the effects of restoration practices on interactions of giant Sequoia Sequoiadendron giganteum with arbuscular mycorrhizal (AM) fungi (Glomeromycota). Natural regeneration of Sequoiadendron is threatened by the absence of severe fires that create forest canopy gaps. Generating artificial canopy gaps offers an alternative tool for giant Sequoia restoration. We investigated the effect of regeneration practices, including (i) sapling location within gaps, (ii) gap size and (iii) soil substrate, on AM fungal colonization of giant Sequoia sapling roots in a native giant Sequoia grove of the Sierra Nevada, California. We found that the extent of AM fungal root colonization was positively correlated with sapling height and light availability, which were related to the location of the sapling within the gap and the gap size. While colonization frequency by arbuscules in sap...
Silvana Nisgoski - One of the best experts on this subject based on the ideXlab platform.
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avaliacao colorimetrica de aglomerados produzidos com particulas de madeira de Sequoia sempervirens e pinus taeda submetidos ao intemperismo natural
Floresta e Ambiente, 2014Co-Authors: Vinicius Gomes De Castro, Rafael Leite Braz, Karine Ramos Da Rosa Bellon, Felipe Gustavo Sanches, Silvana NisgoskiAbstract:The aim of this work was to establish the effect of using different amounts of Sequoia sempervirens and Pinus taeda wood particles on the colorimetric properties of particleboard and to evaluate the color change after outdoor weathering for six months. The colorimetric properties were measure according to the CIE-L*a*b* 1976 system. The results indicated a direct relation between the proportion of Sequoia sempervirens wood particles used in the blend and the red pigment values (a*) and an indirect relation with the yellow pigment (b*). Thus the final color of a particleboard can be predicted by controlling the amount of particles from the different species used in particleboard production. However, natural weathering for 4 months is sufficient to decrease a* and b* values and eliminate the color difference between the particleboards.
David Yong - One of the best experts on this subject based on the ideXlab platform.
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chemo dynamics of outer halo dwarf stars including gaia sausage and gaia Sequoia candidates
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: Stephanie Monty, Kim A Venn, James M M Lane, Deborah Lokhorst, David YongAbstract:The low-metallicity, kinematically interesting dwarf stars studied by Stephens \& Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with [Fe/H]$>-2$; however, large disagreements are found for stars with [Fe/H]$\le-2$, with offsets as large as $\Delta$T$_{\rm eff}\sim+500$ K and $\Delta$log\,$g\sim+1.0$. A subset of six stars (test cases) are analysed ab initio using high resolution spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to include two $\alpha$-challenged dwarf stars, suggestive of origins in a low mass, accreted dwarf galaxy. The orbital parameters for the entire SB02 sample are re-determined using \textit{Gaia} DR2 data. We find 11 stars that are dynamically coincident with the \textit{Gaia}-Sausage accretion event and another 17 with the \textit{Gaia}-Sequoia event in action space. Both associations include low-mass, metal-poor stars with isochrone ages older than 10 Gyr. Two dynamical subsets are identified within \textit{Gaia}-Sequoia. When these subsets are examined separately, a common knee in [$\alpha$/Fe] is found for the \textit{Gaia}-Sausage and high energy \textit{Gaia}-Sequoia stars. A lower metallicity knee is tentatively identified in the \textit{Gaia}-Sequoia low energy stars. If the metal-poor dwarf stars in these samples are true members of the \textit{Gaia}-Sausage and \textit{Gaia}-Sequoia events, then they present a unique opportunity to probe the earlier, more pristine, star formation histories of these systems.
Rainbow Desilva - One of the best experts on this subject based on the ideXlab platform.
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long term demographic decline and late glacial divergence in a californian paleoendemic Sequoiadendron giganteum giant Sequoia
Ecology and Evolution, 2016Co-Authors: Richard S. Dodd, Rainbow DesilvaAbstract:Mediterranean ecosystems comprise a high proportion of endemic taxa whose response to climate change will depend on their evolutionary origins. In the California flora, relatively little attention has been given to the evolutionary history of paleoendemics from a molecular perspective, yet they number among some of the world's most iconic plant species. Here, we address questions of demographic change in Sequoiadendron giganteum (giant Sequoia) that is restricted to a narrow belt of groves in the Sierra Nevada Mountains. We ask whether the current distribution is a result of northward colonization since the last glacial maximum (LGM), restriction of a broader range in the recent past (LGM) or independent colonizations in the deeper past. Genetic diversity at eleven microsatellite loci decreased with increasing latitude, but partial regressions suggested this was a function of smaller population sizes in the north. Disjunct populations north of the Kings River were divergent from those south of the Kings River that formed a single cluster in Bayesian assignment tests. Demographic inferences supported a demographic contraction just prior to the LGM as the most likely scenario for the current disjunct range of the species. This contraction appeared to be superimposed upon a long-term decline in giant Sequoia over the last 2 million years, associated with increasing aridity due to the Mediterranean climate. Overall, low genetic diversity, together with competition in an environment to which giant Sequoia is likely already poorly adapted, will pose major constraints on its success in the face of increasing aridity.
