25,369 research outputs found
Effects of external global noise on the catalytic CO oxidation on Pt(110)
Oxidation reaction of CO on a single platinum crystal is a reaction-diffusion
system that may exhibit bistable, excitable, and oscillatory behavior. We
studied the effect of a stochastic signal artificially introduced into the
system through the partial pressure of CO. First, the external signal is
employed as a turbulence suppression tool, and second, it modifies the
boundaries in the bistable transition between the CO and oxygen covered phases.
Experiments using photoemission electron microscopy (PEEM) together with
numerical simulations performed with the Krischer-Eiswirth-Ertl (KEE) model are
presented.Comment: 15 pages, 7 figures, accepted in J. Chem. Phy
Quicksort with unreliable comparisons: a probabilistic analysis
We provide a probabilistic analysis of the output of Quicksort when
comparisons can err.Comment: 29 pages, 3 figure
Further constraints on the optical transmission spectrum of HAT-P-1b
We report on novel observations of HAT-P-1 aimed at constraining the optical
transmission spectrum of the atmosphere of its transiting Hot-Jupiter
exoplanet. Ground-based differential spectrophotometry was performed over two
transit windows using the DOLORES spectrograph at the Telescopio Nazionale
Galileo (TNG). Our measurements imply an average planet to star radius ratio
equal to =(0.11590.0005). This result is consistent
with the value obtained from recent near infrared measurements of this object
but differs from previously reported optical measurements being lower by around
4.4 exoplanet scale heights. Analyzing the data over 5 different spectral bins
600\AA wide we observed a single peaked spectrum (3.7 level)
with a blue cut-off corresponding to the blue edge of the broad absorption wing
of sodium and an increased absorption in the region in between 6180-7400\AA. We
also infer that the width of the broad absorption wings due to alkali metals is
likely narrower than the one implied by solar abundance clear atmospheric
models. We interpret the result as evidence that HAT-P-1b has a partially clear
atmosphere at optical wavelengths with a more modest contribution from an
optical absorber than previously reported.Comment: Accepted by Ap
NLTE determination of the aluminium abundance in a homogeneous sample of extremely metal-poor stars
Aims: Aluminium is a key element to constrain the models of the chemical
enrichment and the yields of the first supernovae. But obtaining precise Al
abundances in extremely metal-poor (EMP) stars requires that the non-LTE
effects be carefully taken into account.
Methods: The NLTE profiles of the blue resonance aluminium lines have been
computed in a sample of 53 extremely metal-poor stars with a modified version
of the program MULTI applied to an atomic model of the Al atom with 78 levels
of Al I and 13 levels of Al II, and compared to the observations.
Results: With these new determinations, all the stars of the sample show a
ratio Al/Fe close to the solar value: [Al/Fe] =-0.06 +- 0.10 with a very small
scatter. These results are compared to the models of the chemical evolution of
the halo using different models of SN II and are compatible with recent
computations. The sodium-rich giants are not found to be also aluminium-rich
and thus, as expected, the convection in these giants only brings to the
surface the products of the Ne-Na cycle.Comment: To be published on A&
Spectroscopic characterization and detection of Ethyl Mercaptan in Orion
New laboratory data of ethyl mercaptan, CHCHSH, in the millimeter
and submillimeter-wave domains (up to 880 GHz) provided very precise values of
the spectroscopic constants that allowed the detection of
-CHCHSH towards Orion KL. 77 unblended or slightly blended
lines plus no missing transitions in the range 80-280 GHz support this
identification. A detection of methyl mercaptan, CHSH, in the spectral
survey of Orion KL is reported as well. Our column density results indicate
that methyl mercaptan is 5 times more abundant than ethyl mercaptan in
the hot core of Orion KL.Comment: Accepted for publication in ApJL (30 January 2014)/ submitted (8
January 2014
Semiclassical expansions in the Toda hierarchy and the hermitian matrix model
An iterative algorithm for determining a class of solutions of the
dispersionful 2-Toda hierarchy characterized by string equations is developed.
This class includes the solution which underlies the large N-limit of the
Hermitian matrix model in the one-cut case. It is also shown how the double
scaling limit can be naturally formulated in this schemeComment: 22 page
Efficient formalism for large scale ab initio molecular dynamics based on time-dependent density functional theory
A new "on the fly" method to perform Born-Oppenheimer ab initio molecular
dynamics (AIMD) is presented. Inspired by Ehrenfest dynamics in time-dependent
density functional theory, the electronic orbitals are evolved by a
Schroedinger-like equation, where the orbital time derivative is multiplied by
a parameter. This parameter controls the time scale of the fictitious
electronic motion and speeds up the calculations with respect to standard
Ehrenfest dynamics. In contrast to other methods, wave function orthogonality
needs not be imposed as it is automatically preserved, which is of paramount
relevance for large scale AIMD simulations.Comment: 5 pages, 3 color figures, revtex4 packag
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