187 research outputs found
Asymptotic Safety of Gravity Coupled to Matter
Nonperturbative treatments of the UV limit of pure gravity suggest that it
admits a stable fixed point with positive Newton's constant and cosmological
constant. We prove that this result is stable under the addition of a scalar
field with a generic potential and nonminimal couplings to the scalar
curvature. There is a fixed point where the mass and all nonminimal scalar
interactions vanish while the gravitational couplings have values which are
almost identical to the pure gravity case. We discuss the linearized flow
around this fixed point and find that the critical surface is four-dimensional.
In the presence of other, arbitrary, massless minimally coupled matter fields,
the existence of the fixed point, the sign of the cosmological constant and the
dimension of the critical surface depend on the type and number of fields. In
particular, for some matter content, there exist polynomial asymptotically free
scalar potentials, thus providing a solution to the well-known problem of
triviality.Comment: 18 pages,typeset with revtex
Duality Theorems in Ergodic Transport
We analyze several problems of Optimal Transport Theory in the setting of
Ergodic Theory. In a certain class of problems we consider questions in Ergodic
Transport which are generalizations of the ones in Ergodic Optimization.
Another class of problems is the following: suppose is the shift
acting on Bernoulli space , and, consider a fixed
continuous cost function . Denote by the set
of all Borel probabilities on , such that, both its and
marginal are -invariant probabilities. We are interested in the
optimal plan which minimizes among the probabilities on
.
We show, among other things, the analogous Kantorovich Duality Theorem. We
also analyze uniqueness of the optimal plan under generic assumptions on .
We investigate the existence of a dual pair of Lipschitz functions which
realizes the present dual Kantorovich problem under the assumption that the
cost is Lipschitz continuous. For continuous costs the corresponding
results in the Classical Transport Theory and in Ergodic Transport Theory can
be, eventually, different.
We also consider the problem of approximating the optimal plan by
convex combinations of plans such that the support projects in periodic orbits
Cryptic Eimeria genotypes are common across the southern but not northern hemisphere
The phylum Apicomplexa includes parasites of medical, zoonotic and veterinary significance. Understanding the global distribution and genetic diversity of these protozoa is of fundamental importance for efficient, robust and long-lasting methods of control. Eimeria spp. cause intestinal coccidiosis in all major livestock animals and are the most important parasites of domestic chickens in terms of both economic impact and animal welfare. Despite having significant negative impacts on the efficiency of food production, many fundamental questions relating to the global distribution and genetic variation of Eimeria spp. remain largely unanswered. Here, we provide the broadest map yet of Eimeria occurrence for domestic chickens, confirming that all the known species (Eimeria acervulina, Eimeria brunetti, Eimeria maxima, Eimeria mitis, Eimeria necatrix, Eimeria praecox, Eimeria tenella) are present in all six continents where chickens are found (including 21 countries). Analysis of 248 internal transcribed spacer sequences derived from 17 countries provided evidence of possible allopatric diversity for species such as E. tenella (FST values ⩜0.34) but not E. acervulina and E. mitis, and highlighted a trend towards widespread genetic variance. We found that three genetic variants described previously only in Australia and southern Africa (operational taxonomic units x, y and z) have a wide distribution across the southern, but not the northern hemisphere. While the drivers for such a polarised distribution of these operational taxonomic unit genotypes remains unclear, the occurrence of genetically variant Eimeria may pose a risk to food security and animal welfare in Europe and North America should these parasites spread to the northern hemisphere
Accurate fundamental parameters and detailed abundance patterns from spectroscopy of 93 solar-type Kepler targets
We present a detailed spectroscopic study of 93 solar-type stars that are
targets of the NASA/Kepler mission and provide detailed chemical composition of
each target. We find that the overall metallicity is well-represented by Fe
lines. Relative abundances of light elements (CNO) and alpha-elements are
generally higher for low-metallicity stars. Our spectroscopic analysis benefits
from the accurately measured surface gravity from the asteroseismic analysis of
the Kepler light curves. The log g parameter is known to better than 0.03 dex
and is held fixed in the analysis. We compare our Teff determination with a
recent colour calibration of V-K (TYCHO V magnitude minus 2MASS Ks magnitude)
and find very good agreement and a scatter of only 80 K, showing that for other
nearby Kepler targets this index can be used. The asteroseismic log g values
agree very well with the classical determination using Fe1-Fe2 balance,
although we find a small systematic offset of 0.08 dex (asteroseismic log g
values are lower). The abundance patterns of metals, alpha elements, and the
light elements (CNO) show that a simple scaling by [Fe/H] is adequate to
represent the metallicity of the stars, except for the stars with metallicity
below -0.3, where alpha-enhancement becomes important. However, this is only
important for a very small fraction of the Kepler sample. We therefore
recommend that a simple scaling with [Fe/H] be employed in the asteroseismic
analyses of large ensembles of solar-type stars.Comment: MNRAS, in press, 12 page
Unbound states in quantum heterostructures
We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron â hole states. The part played by Auger scattering in Quantum Dots is also discussed
Origin of the hot gas in low-mass protostars, Herschel-PACS spectroscopy of HH 46
Aims. âWater In Star-forming regions with Herschelâ (WISH) is a Herschel key programme aimed at understanding the physical and chemical
structure of young stellar objects (YSOs) with a focus on water and related species.
Methods. The low-mass protostar HH 46 was observed with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space
Observatory to measure emission in H2O, CO, OH, [O i], and [C ii] lines located between 63 and 186 ÎŒm. The excitation and spatial distribution
of emission can disentangle the different heating mechanisms of YSOs, with better spatial resolution and sensitivity than previously possible.
Results. Far-IR line emission is detected at the position of the protostar and along the outflow axis. The OH emission is concentrated at the
central position, CO emission is bright at the central position and along the outflow, and H2O emission is concentrated in the outflow. In addition,
[O i] emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km sâ1 in both the red- and
blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical
envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels
at >2500 K above the ground state. Instead, warm CO and H2O emission is probably produced in the walls of an outflow-carved cavity in the
envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and [Oi] emission is attributed to J-type shocks in
dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to
be 2 Ă 10â2 L, with 60â80% attributed to J- and C-type shocks produced by interactions between the jet and the envelope
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