2,013 research outputs found
Properties of Carbon-Oxygen White Dwarfs From Monte Carlo Stellar Models
We investigate properties of carbon-oxygen white dwarfs with respect to the
composite uncertainties in the reaction rates using the stellar evolution
toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the
probability density functions in the reaction rate library STARLIB. These are
the first Monte Carlo stellar evolution studies that use complete stellar
models. Focusing on 3 M models evolved from the pre main-sequence to
the first thermal pulse, we survey the remnant core mass, composition, and
structure properties as a function of 26 STARLIB reaction rates covering
hydrogen and helium burning using a Principal Component Analysis and Spearman
Rank-Order Correlation. Relative to the arithmetic mean value, we find the
width of the 95\% confidence interval to be
0.019 M for the core mass at the first thermal pulse,
12.50 Myr for the age, 0.013 for the central temperature, 0.060 for the central density,
2.610 for the central electron
fraction, 5.810,
0.392, and 0.392. Uncertainties in the experimental
C(, triple-, and
N( reaction rates dominate these variations. We
also consider a grid of 1 to 6 M models evolved from the pre
main-sequence to the final white dwarf to probe the sensitivity of the
initial-final mass relation to experimental uncertainties in the hydrogen and
helium reaction rates.Comment: Accepted for publication in The Astrophysical Journal; 19 Pages, 23
Figures, 5 Table
Intraspecific plant-soil feedback and intraspecific overyielding in Arabidopsis thaliana
1\. Understanding the mechanisms of community coexistence and ecosystem
functioning may help to counteract the current biodiversity loss and its
potentially harmful consequences. In recent years, plant-soil feedback that
can, for example, be caused by below-ground microorganisms, has been suggested
to play a role in maintaining plant coexistence and to be a potential driver
of the positive relationship between plant diversity and ecosystem
functioning. Most of the studies addressing these topics have focused on the
species level. However, in addition to interspecific interactions,
intraspecific interactions might be important for the structure of natural
communities. 2\. Here we examine intraspecific coexistence and intraspecific
diversity effects using 10 natural accessions of the model species Arabidopsis
thaliana (L.) Heynh. We assessed morphological intraspecific diversity by
measuring several above- and below-ground traits. We performed a plant-soil
feedback experiment that was based on these trait differences between the
accessions in order to determine whether A. thaliana experiences feedback at
intraspecific level as a result of trait differences. We also experimentally
tested the diversity-productivity relationship at intraspecific level. 3\. We
found strong differences in above- and below-ground traits between the A.
thaliana accessions. Overall, plant-soil feedback occurred at intraspecific
level. However, accessions differed in the direction and strength of this
feedback: some accessions grew better on their own soils, some on soils from
other accessions. Furthermore, we found positive diversity effects within A.
thaliana: accession mixtures produced a higher total above-ground biomass than
accession monocultures. 4\. Differences between accessions in their feedback
response could not be explained by morphological traits. Therefore, we suggest
that they might have been caused by accession-specific accumulated soil
communities, root exudates or by accession-specific resource use based on
genetic differences that are not expressed in morphological traits. 5\.
Synthesis. Our results provide some of the first evidence for intraspecific
plant-soil feedback and intraspecific overyielding. These findings may have
wider implications for the maintenance of variation within species and the
importance of this variation for ecosystem functioning. Our results highlight
the need for an increased focus on intraspecific processes in plant diversity
research to fully understand the mechanisms of coexistence and ecosystem
functioning.Ecology and Evolution, 4 (12), 2533-254
Energy estimation of cosmic rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30–80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy—corrected for geometrical effects—is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal
Energy estimation of cosmic rays with the Engineering Radio Array of the Pierre Auger Observatory
The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30–80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy—corrected for geometrical effects—is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal
Sum Rules for Magnetic Moments and Polarizabilities in QED and Chiral Effective-Field Theory
We elaborate on a recently proposed extension of the Gerasimov-Drell-Hearn
(GDH) sum rule which is achieved by taking derivatives with respect to the
anomalous magnetic moment. The new sum rule features a {\it linear} relation
between the anomalous magnetic moment and the dispersion integral over a
cross-section quantity. We find some analogy of the linearized form of the GDH
sum rule with the `sideways dispersion relations'. As an example, we apply the
linear sum rule to reproduce the famous Schwinger's correction to the magnetic
moment in QED from a tree-level cross-section calculation and outline the
procedure for computing the two-loop correction from a one-loop cross-section
calculation. The polarizabilities of the electron in QED are considered as well
by using the other forward-Compton-scattering sum rules. We also employ the sum
rules to study the magnetic moment and polarizabilities of the nucleon in a
relativistic chiral EFT framework. In particular we investigate the chiral
extrapolation of these quantities.Comment: 24 pages, 7 figures; several additions, published versio
R-process nucleosynthesis calculations with complete nuclear physics input
The r-process constitutes one of the major challenges in nuclear
astrophysics. Its astrophysical site has not yet been identified but there is
observational evidence suggesting that at least two possible sites should
contribute to the solar system abundance of r-process elements and that the
r-process responsible for the production of elements heavier than Z=56 operates
quite robustly producing always the same relative abundances. From the
nuclear-physics point of view the r-process requires the knowledge of a large
number of reaction rates involving exotic nuclei. These include neutron capture
rates, beta-decays and fission rates, the latter for the heavier nuclei
produced in the r-process. We have developed for the first time a complete
database of reaction rates that in addition to neutron-capture rates and
beta-decay half-lives includes all possible reactions that can induce fission
(neutron-capture, beta-decay and spontaneous fission) and the corresponding
fission yields. In addition, we have implemented these reaction rates in a
fully implicit reaction network. We have performed r-process calculations for
the neutrino-driven wind scenario to explore whether or not fission can
contribute to provide a robust r-process pattern
Molecular and comparative analysis of Salmonella enterica Senftenberg from humans and animals using PFGE, MLST and NARMS
<p>Abstract</p> <p>Background</p> <p><it>Salmonella </it>species are recognized worldwide as a significant cause of human and animal disease. In this study the molecular profiles and characteristics of <it>Salmonella enterica </it>Senftenberg isolated from human cases of illness and those recovered from healthy or diagnostic cases in animals were assessed. Included in the study was a comparison with our own sequenced strain of <it>S. </it>Senfteberg recovered from production turkeys in North Dakota. Isolates examined in this study were subjected to antimicrobial susceptibility profiling using the National Antimicrobial Resistance Monitoring System (NARMS) panel which tested susceptibility to 15 different antimicrobial agents. The molecular profiles of all isolates were determined using Pulsed Field Gel Electrophoresis (PFGE) and the sequence types of the strains were obtained using Multi-Locus Sequence Type (MLST) analysis based on amplification and sequence interrogation of seven housekeeping genes (<it>aroC</it>, <it>dnaN</it>, <it>hemD</it>, <it>hisD</it>, <it>purE</it>, <it>sucA</it>, and <it>thrA</it>). PFGE data was input into BioNumerics analysis software to generate a dendrogram of relatedness among the strains.</p> <p>Results</p> <p>The study found 93 profiles among 98 <it>S</it>. Senftenberg isolates tested and there were primarily two sequence types associated with humans and animals (ST185 and ST14) with overlap observed in all host types suggesting that the distribution of <it>S. </it>Senftenberg sequence types is not host dependent. Antimicrobial resistance was observed among the animal strains, however no resistance was detected in human isolates suggesting that animal husbandry has a significant influence on the selection and promotion of antimicrobial resistance.</p> <p>Conclusion</p> <p>The data demonstrates the circulation of at least two strain types in both animal and human health suggesting that <it>S. </it>Senftenberg is relatively homogeneous in its distribution. The data generated in this study could be used towards defining a pathotype for this serovar.</p
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