2,507 research outputs found
Selenium Hyperaccumulators Facilitate Selenium-Tolerant Neighbors via Phytoenrichment and Reduced Herbivory
SummaryBackgroundSoil surrounding selenium (Se) hyperaccumulator plants was shown earlier to be enriched in Se, impairing the growth of Se-sensitive plant species. Because Se levels in neighbors of hyperaccumulators were higher and Se has been shown to protect plants from herbivory, we investigate here the potential facilitating effect of Se hyperaccumulators on Se-tolerant neighboring species in the field.ResultsWe measured growth and herbivory of Artemisia ludoviciana and Symphyotrichum ericoides as a function of their Se concentration and proximity to hyperaccumulators Astragalus bisulcatus and Stanleya pinnata. When growing next to hyperaccumulators, A. ludoviciana and S. ericoides contained 10- to 20-fold higher Se levels (800â2,000 mg kgâ1 DW) than when growing next to nonaccumulators. The roots of both species were predominantly (70%â90%) directed toward hyperaccumulator neighbors, not toward other neighbors. Moreover, neighbors of hyperaccumulators were 2-fold bigger, showed 2-fold less herbivory damage, and harbored 3- to 4-fold fewer arthropods. When used in laboratory choice and nonchoice grasshopper herbivory experiments, Se-rich neighbors of hyperaccumulators experienced less herbivory and caused higher grasshopper Se accumulation (10-fold) and mortality (4-fold).ConclusionsEnhanced soil Se levels around hyperaccumulators can facilitate growth of Se-tolerant plant species through reduced herbivory and enhanced growth. This study is the first to show facilitation via enrichment with a nonessential element. It is interesting that Se enrichment of hyperaccumulator neighbors may affect competition in two ways, by reducing growth of Se-sensitive neighbors while facilitating Se-tolerant neighbors. Via these competitive and facilitating effects, Se hyperaccumulators may affect plant community composition and, consequently, higher trophic levels
A Statistical View of Learning in the Centipede Game
In this article we evaluate the statistical evidence that a population of
students learn about the sub-game perfect Nash equilibrium of the centipede
game via repeated play of the game. This is done by formulating a model in
which a player's error in assessing the utility of decisions changes as they
gain experience with the game. We first estimate parameters in a statistical
model where the probabilities of choices of the players are given by a Quantal
Response Equilibrium (QRE) (McKelvey and Palfrey, 1995, 1996, 1998), but are
allowed to change with repeated play. This model gives a better fit to the data
than similar models previously considered. However, substantial correlation of
outcomes of games having a common player suggests that a statistical model that
captures within-subject correlation is more appropriate. Thus we then estimate
parameters in a model which allows for within-player correlation of decisions
and rates of learning. Through out the paper we also consider and compare the
use of randomization tests and posterior predictive tests in the context of
exploratory and confirmatory data analyses
Density Profile Asymptotes at the Centre of Dark Matter Halos
For the spherical symmetric case, all quantities describing the relaxed dark
matter halo can be expressed as functions of the gravitational potential
. Decomposing the radial velocity dispersion with respect to
at very large and very small radial distances the possible asymptotic
behavior for the density and velocity profiles can be obtained. If reasonable
boundary conditions are posed such as a finite halo mass and force-free halo
centre the asymptotic density profiles at the centre should be much less steep
than the profiles obtained within numerical simulations. In particular cases
profiles like Plummer's model are obtained. The reasons of that seeming
discrepancy with respect to the results of N-body simulations are discussed.Comment: Accepted for publication in Astronomy & Astrophysics, LaTeX, 7 pages,
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Low pressure sand casting of ultrasonically degassed AlSi7Mg0.3 alloy: Modelling and experimental validation of mould filling
The effect of combining smooth mould cavity filling and ultrasonic degassing by using a low pressure sand casting process with US melt treatment on the microstructure and mechanical properties of AlSi7Mg0.3 alloy was investigated. Computational fluid dynamics (CFD) modelling and experimental validation was used to study the liquid metal flow behaviour and oxide film defect distribution for different filling rates, using two pressurization curves (p-t). The effect of ultrasonic degassing on the resultant microstructure (morphology and presence of porosities and inclusions) was studied for 650 and 700 degrees C melt degassing temperatures. Results show that ultrasonic degassing and mould filling velocities below 0.5 m/s improve the alloy microstructure and lead to high mechanical properties.This research was supported by FEDER/COMPETE funds and by national funds through FCT - Portuguese Foundation for Science and Technology and was developed on the aim of the research project PTDC/EME-TME/119658/2010 and the Post-Doctoral grant SFRH/BPD/76680/2011. Also, this work has been supported by the FCT in the scope of the project: UID/EEA/04436/2013.info:eu-repo/semantics/publishedVersio
Polymerase chain reaction detection of genes responsible for multiple antibiotic resistance Staphylococcus aureus isolated from food of animal origin in Egypt
Lost but Not ForgottenâThe Economics of Improving Patient Retention in AIDS Treatment Programs
Gregory Bisson and Jeffrey Stringer discuss the implications of a new study showing how loss to follow-up affects the effectiveness of a public sector HIV program in CĂŽte d'Ivoire
Testicular caspase-3 and ÎČ-catenin regulators predicted via comparative metabolomics and docking studies
Evaluation of antibacterial effect of some Sinai medicinal plant extracts on bacteria isolated from bovine mastitis
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