914 research outputs found

    Molecular and fossil evidence place the origin of cichlid fishes long after Gondwanan rifting.

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    Cichlid fishes are a key model system in the study of adaptive radiation, speciation and evolutionary developmental biology. More than 1600 cichlid species inhabit freshwater and marginal marine environments across several southern landmasses. This distributional pattern, combined with parallels between cichlid phylogeny and sequences of Mesozoic continental rifting, has led to the widely accepted hypothesis that cichlids are an ancient group whose major biogeographic patterns arose from Gondwanan vicariance. Although the Early Cretaceous (ca 135 Ma) divergence of living cichlids demanded by the vicariance model now represents a key calibration for teleost molecular clocks, this putative split pre-dates the oldest cichlid fossils by nearly 90 Myr. Here, we provide independent palaeontological and relaxed-molecular-clock estimates for the time of cichlid origin that collectively reject the antiquity of the group required by the Gondwanan vicariance scenario. The distribution of cichlid fossil horizons, the age of stratigraphically consistent outgroup lineages to cichlids and relaxed-clock analysis of a DNA sequence dataset consisting of 10 nuclear genes all deliver overlapping estimates for crown cichlid origin centred on the Palaeocene (ca 65-57 Ma), substantially post-dating the tectonic fragmentation of Gondwana. Our results provide a revised macroevolutionary time scale for cichlids, imply a role for dispersal in generating the observed geographical distribution of this important model clade and add to a growing debate that questions the dominance of the vicariance paradigm of historical biogeography

    Induction-accelerator heavy-ion fusion: Status and beam physics issues

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    Overview of Theory and Simulations in the Heavy Ion Fusion Science Virtual National Laboratory

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    Abstract Abstract The Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL) is a collaboration of Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, and Princeton Plasma Physics Laboratory. These laboratories, in cooperation with researchers at other institutions, are carrying out a coordinated effort to apply intense ion beams as drivers for studies of the physics of matter at extreme conditions, and ultimately for inertial fusion energy. Progress on this endeavor depends upon coordinated application of experiments, theory, and simulations. This paper describes the state of the art, with an emphasis on the coordination of modeling and experiment; developments in the simulation tools, and in the methods that underly them, are also treated

    A systematic evaluation of Silicon-rich Nitride Electro-optic Modulator design and tradeoffs

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    We present a study of linearized \c{hi}^((3)) based electro-optic modulation beginning with an analysis of the nonlinear polarizability, and how to linearize a modulator based on the quadratic third order DC-Kerr effect. Then we perform a numerical study, designing a linearized \c{hi}^((3)) phase modulator utilizing Silicon-rich Nitride where we show that a phase modulator with a V_{\pi} L_{\pi} metric of 1 Vcm or a V_{\pi} L_{\pi} {\alpha} metric of 37VdB is achievable and a V_{\pi} L_{\pi} as low as 0.5Vcm in a push-pull Mach Zehnder Interferometer. This numerical study argues that linearized modulation exploiting the \c{hi}^((3)), and \c{hi}^((2)) as applicable, is possible and can allow for high-speed modulation using a CMOS compatible material platform

    Boston Hospitality Review: Winter 2017

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    Table of contents: Family, Team or Something Else? by John Murtha -- Kitchen Organization in Full-Service Restaurants: Reducing Heat and Stress by Peter Szende and Justin Cipriano -- Rules of Engagement: Building Brand Relationships by Alex Friedman -- Corporate Social Responsibility in the Hospitality Sector by Manisha Singal and Yinyoung Rhou -- “Hold on, I have to post this on Instagram”: Trends, Talk, and Transactions of the Experiential Consumer by Steve Kent -- C-corporation Hotels vs. Hotel-REITs: A Theoretical and Practical Comparison by Tarik Dogru -- Sisters in Restaurant Success: A History of The Maramor by Jan WhitakerFamily, Team or Something Else? by John Murtha -- Kitchen Organization in Full-Service Restaurants: Reducing Heat and Stress by Peter Szende and Justin Cipriano -- Rules of Engagement: Building Brand Relationships by Alex Friedman -- Corporate Social Responsibility in the Hospitality Sector by Manisha Singal and Yinyoung Rhou -- “Hold on, I have to post this on Instagram”: Trends, Talk, and Transactions of the Experiential Consumer by Steve Kent -- C-corporation Hotels vs. Hotel-REITs: A Theoretical and Practical Comparison by Tarik Dogru -- Sisters in Restaurant Success: A History of The Maramor by Jan Whitake

    Vitamin A Status of Women and Children in Yaoundé and Douala, Cameroon, is Unchanged One Year after Initiation of a National Vitamin A Oil Fortification Program.

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    Vitamin A (VA) fortification of cooking oil is considered a cost-effective strategy for increasing VA status, but few large-scale programs have been evaluated. We conducted representative surveys in Yaoundé and Douala, Cameroon, 2 years before and 1 year after the introduction of a mandatory national program to fortify cooking oil with VA. In each survey, 10 different households were selected within each of the same 30 clusters (n = ~300). Malaria infection and plasma indicators of inflammation and VA (retinol-binding protein, pRBP) status were assessed among women aged 15-49 years and children aged 12-59 months, and casual breast milk samples were collected for VA and fat measurements. Refined oil intake was measured by a food frequency questionnaire, and VA was measured in household oil samples post-fortification. Pre-fortification, low inflammation-adjusted pRBP was common among children (33% <0.83 µmol/L), but not women (2% <0.78 µmol/L). Refined cooking oil was consumed by >80% of participants in the past week. Post-fortification, only 44% of oil samples were fortified, but fortified samples contained VA concentrations close to the target values. Controlling for age, inflammation, and other covariates, there was no difference in the mean pRBP, mean breast milk VA, prevalence of low pRBP, or prevalence of low milk VA between the pre- and post-fortification surveys. The frequency of refined oil intake was not associated with VA status indicators post-fortification. In sum, after a year of cooking oil fortification with VA, we did not detect evidence of increased plasma RBP or milk VA among urban women and preschool children, possibly because less than half of the refined oil was fortified. The enforcement of norms should be strengthened, and the program should be evaluated in other regions where the prevalence of VA deficiency was greater pre-fortification

    Phylogenetic informativeness reconciles ray-finned fish molecular divergence times

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    BACKGROUND: Discordance among individual molecular age estimates, or between molecular age estimates and the fossil record, is observed in many clades across the Tree of Life. This discordance is attributed to a variety of variables including calibration age uncertainty, calibration placement, nucleotide substitution rate heterogeneity, or the specified molecular clock model. However, the impact of changes in phylogenetic informativeness of individual genes over time on phylogenetic inferences is rarely analyzed. Using nuclear and mitochondrial sequence data for ray-finned fishes (Actinopterygii) as an example, we extend the utility of phylogenetic informativeness profiles to predict the time intervals when nucleotide substitution saturation results in discordance among molecular ages estimated. RESULTS: We demonstrate that even with identical calibration regimes and molecular clock methods, mitochondrial based molecular age estimates are systematically older than those estimated from nuclear sequences. This discordance is most severe for highly nested nodes corresponding to more recent (i.e., Jurassic-Recent) divergences. By removing data deemed saturated, we reconcile the competing age estimates and highlight that the older mtDNA based ages were driven by nucleotide saturation. CONCLUSIONS: Homoplasious site patterns in a DNA sequence alignment can systematically bias molecular divergence time estimates. Our study demonstrates that PI profiles can provide a non-arbitrary criterion for data exclusion to mitigate the influence of homoplasy on time calibrated branch length estimates. Analyses of actinopterygian molecular clocks demonstrate that scrutiny of the time scale on which sequence data is informative is a fundamental, but generally overlooked, step in molecular divergence time estimation
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