1,962 research outputs found
Role of the phase in the identification of delay time in semiconductor lasers with optical feedback
We consider a semiconductor laser with external optical feedback operating at a regime for which the delay time signature is extremely difficult to identify from the analysis of the intensity time series, using standard techniques. We show that such delay signature can be successfully retrieved by computing the same quantifiers from the phase, the real or the imaginary part of the field, even in presence of noise. Therefore the choice of the observable is determinant for parameter identification.Financial support from the Ministerio de Ciencia e Innovacion (MICINN), Spain, and the Fondo Europeo de
Desarrollo Regional under projects FIS2007-60327 [FĂsica Interdisciplinar de Sistemas Complejos (FISICOS)]
and TEC2009-14101 [Delay-Coupled Diode Lasers for
Photonic Applications (DeCoDicA)] and by the European
Commission (EC) Project PHOCUS (FP7-ICT-2009-C-
240763) is acknowledged. R. M. Nguimdo also acknowledges fellowship BES-2007-14627 under the FPI program
of MICINN.Peer reviewe
Analytic Reconstruction of heavy-quark two-point functions at O(\alpha_s^3)
Using a method previously developed, based on the Mellin-Barnes transform, we
reconstruct the two-point correlators in the vector, axial, scalar and
pseudoscalar channels from the Taylor expansion at q^2=0, the threshold
expansion at q^2=4m^2 and the OPE at q^2\rightarrow -\infty, where m is the
heavy quark mass. The reconstruction is analytic and systematic and is
controlled by an error function which becomes smaller as more terms in those
expansions are known.Comment: 19 pages, 11 figure
Fission fragment angular distribution measurements of U-235 and U-238 at CERN n_TOF facility
Neutron-induced fission cross sections of U-238 and U-235 are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection efficiency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process.
In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new U-235(n,f) and U-238(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data.Postprint (published version
Approaching the precursor nuclei of the third r-process peak with RIBs
The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the
main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical.
The impact of the uncertainties connected with the eta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to
obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA,
commonly used in r-process model calculations. Further measurements around N 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.Postprint (published version
Non-universal results induced by diversity distribution in coupled excitable systems
We consider a system of globally coupled active rotators near the excitable
regime. The system displays a transition to a state of collective firing
induced by disorder. We show that this transition is found generically for any
diversity distribution with well defined moments. Singularly, for the
Lorentzian distribution (widely used in Kuramoto-like systems) the transition
is not present. This warns about the use of Lorentzian distributions to
understand the generic properties of coupled oscillators
A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations
Stellar activity and, in particular, convection-related surface structures,
potentially cause fluctuations that can affect the transit light curves.
Surface convection simulations can help the interpretation of ToV. We used
realistic three-dimensional radiative hydrodynamical simulation of the Sun from
the Stagger-grid and synthetic images computed with the radiative transfer code
Optim3D to provide predictions for the transit of Venus in 2004 observed by the
satellite ACRIMSAT. We computed intensity maps from RHD simulation of the Sun
and produced synthetic stellar disk image. We computed the light curve and
compared it to the ACRIMSAT observations and also to the light curves obtained
with solar surface representations carried out using radial profiles with
different limb-darkening laws. We also applied the same spherical tile imaging
method to the observations of center-to-limb Sun granulation with HINODE. We
managed to explain ACRIMSAT observations of 2004 ToV and showed that the
granulation pattern causes fluctuations in the transit light curve. We
evaluated the contribution of the granulation to the ToV. We showed that the
granulation pattern can partially explain the observed discrepancies between
models and data. This confirms that the limb-darkening and the granulation
pattern simulated in 3D RHD Sun represent well what is imaged by HINODE. In the
end, we found that the Venus's aureole contribution during ToV is less intense
than the solar photosphere, and thus negligible. Being able to explain
consistently the data of 2004 ToV is a new step forward for 3D RHD simulations
that are becoming essential for the detection and characterization of
exoplanets. They show that the granulation have to be considered as an
intrinsic incertitude, due to the stellar variability, on precise measurements
of exoplanet transits of, most likely, planets with small diameters.Comment: Accepted for publication in Astronomy and Astrophysic
- …