45,218 research outputs found
Photo-ionization of planetary winds: case study HD209458b
Close-in hot Jupiters are exposed to a tremendous photon flux that ionizes
the neutral escaping material from the planet leaving an observable imprint
that makes them an interesting laboratory for testing theoretical models. In
this work we present 3D hydrodynamic simulations with radiation transfer
calculations of a close-in exoplanet in a blow-off state. We calculate the
Ly- absorption and compare it with observations of HD 209458b an
previous simplified model results.Our results show that the hydrodynamic
interaction together with a proper calculation of the photoionization proccess
are able to reproduce the main features of the observed Ly- absorption,
in particular at the blue-shifted wings of the line. We found that the ionizing
stellar flux produce an almost linear effect on the amount of absorption in the
wake. Varying the planetary mass loss rate and the radiation flux, we were able
to reproduce the absorption observed at .Comment: 9 pages, 6 figure
A Robust Filter for the BeppoSAX Gamma Ray Burst Monitor Triggers
The BeppoSAX Gamma Ray Burst Monitor (GRBM) is triggered any time a
statistically significant counting excess is simultaneously revealed by at
least two of its four independent detectors. Several spurious effects,
including highly ionizing particles crossing two detectors, are recorded as
onboard triggers. In fact, a large number of false triggers is detected, in the
order of 10/day. A software code, based on an heuristic algorithm, was written
to discriminate between real and false triggers. We present the results of the
analysis on an homogeneous sample of GRBM triggers, thus providing an estimate
of the efficiency of the GRB detection system consisting of the GRBM and the
software.Comment: Proc. 5th Huntsville GRB Symposiu
Indefinite Causal Order in a Quantum Switch
In quantum mechanics events can happen in no definite causal order: in
practice this can be verified by measuring a causal witness, in the same way
that an entanglement witness verifies entanglement. Indefinite causal order can
be observed in a quantum switch, where two operations act in a quantum
superposition of the two possible orders. Here we realise a photonic quantum
switch, where polarisation coherently controls the order of two operations,
and , on the transverse spatial mode of the photons. Our
setup avoids the limitations of earlier implementations: the operations cannot
be distinguished by spatial or temporal position. We show that our quantum
switch has no definite causal order, by constructing a causal witness and
measuring its value to be 18 standard deviations beyond the definite-order
bound
Effective restoration of the U_A(1) symmetry with temperature and density
We investigate the full U(3)U(3) chiral symmetry restoration, at
finite temperature and density, on the basis of a quark model which
incorporates the most relevant properties of QCD in this context: explicit and
spontaneous breaking of chiral symmetry and axial U(1) symmetry breaking. A
specific lattice-inspired behavior of the topological susceptibility, combined
with the convergence of chiral partners, signals the onset of an effective
chiral symmetry restoration. The results suggest that the axial part of the
symmetry is restored before the possible restoration of the full
U(3)U(3) chiral symmetry can occur. This conclusion is valid in the
context of both finite temperature and density.Comment: 5 pages, 2 figures; PRD versio
Efeito da restrição hídrica no solo sobre o crescimento e desenvolvimento de cultivares de girassol.
K X-Ray Energies and Transition Probabilities for He-, Li- and Be-like Praseodymium ions
Theoretical transition energies and probabilities for He-, Li- and Be-like
Praseodymium ions are calculated in the framework of the multi-configuration
Dirac-Fock method (MCDF), including QED corrections. These calculated values
are compared to recent experimental data obtained in the Livermore SuperEBIT
electron beam ion trap facility
Low-energy electron scattering from methanol and ethanol
Measured and calculated differential cross sections for elastic (rotationally unresolved) electron scattering from two primary alcohols, methanol (CH3OH) and ethanol (C2H5OH), are reported. The measurements are obtained using the relative flow method with helium as the standard gas and a thin aperture as the collimating target gas source. The relative flow method is applied without the restriction imposed by the relative flow pressure conditions on helium and the unknown gas. The experimental data were taken at incident electron energies of 1, 2, 5, 10, 15, 20, 30, 50, and 100 eV and for scattering angles of 5°–130°. There are no previous reports of experimental electron scattering differential cross sections for CH3OH and C2H5OH in the literature. The calculated differential cross sections are obtained using two different implementations of the Schwinger multichannel method, one that takes all electrons into account and is adapted for parallel computers, and another that uses pseudopotentials and considers only the valence electrons. Comparison between theory and experiment shows that theory is able to describe low-energy electron scattering from these polyatomic targets quite well
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