8,182 research outputs found
Phases dynamics in VCSELs with delayed optical feedback and cross re-injection
We study theoretically the non linear polarization dynamics of
Vertical-Cavity Surface-Emitting Lasers in the presence of an external cavity
providing delayed optical feedback and cross polarization re-injection. We show
that far from the laser threshold, the dynamics remains confined close to the
equatorial plane of a Stokes sphere of a given radius and we reduce the
dynamics to a dynamical system composed of two phases: the orientation phase of
the quasi-linear polarization and the optical phase of the field. We explore
the complex modal structure given by the double feedback configuration and
recovers as particular cases the Lang-Kobayashi modes and the modes founds by
Giudici et al. [1]. We also re-interpret the square waves switching dynamics as
phase kinks.Comment: 10 pages, 7 figures, pre-submission to Phys. Rev.
The Relation between Black Hole Mass, Bulge Mass, and Near-Infrared Luminosity
We present new accurate near-infrared (NIR) spheroid (bulge) structural
parameters obtained by two-dimensional image analysis for all galaxies with a
direct black hole (BH) mass determination. As expected, NIR bulge luminosities
Lbul and BH masses are tightly correlated, and if we consider only those
galaxies with secure BH mass measurement and accurate Lbul (27 objects), the
spread of MBH-Lbul is similar to MBH-sigma, where sigma is the effective
stellar velocity dispersion. We find an intrinsic rms scatter of ~0.3 dex in
log MBH. By combining the bulge effective radii R_e measured in our analysis
with sigma, we find a tight linear correlation (rms ~ 0.25 dex) between MBH and
the virial bulge mass (propto R_e sigma^2), with ~ 0.002. A partial
correlation analysis shows that MBH depends on both sigma and R_e, and that
both variables are necessary to drive the correlations between MBH and other
bulge properties.Comment: Astrophysical Journal Letters, in pres
The RD53 Collaboration's SystemVerilog-UVM Simulation Framework and its General Applicability to Design of Advanced Pixel Readout Chips
The foreseen Phase 2 pixel upgrades at the LHC have very challenging
requirements for the design of hybrid pixel readout chips. A versatile pixel
simulation platform is as an essential development tool for the design,
verification and optimization of both the system architecture and the pixel
chip building blocks (Intellectual Properties, IPs). This work is focused on
the implemented simulation and verification environment named VEPIX53, built
using the SystemVerilog language and the Universal Verification Methodology
(UVM) class library in the framework of the RD53 Collaboration. The environment
supports pixel chips at different levels of description: its reusable
components feature the generation of different classes of parameterized input
hits to the pixel matrix, monitoring of pixel chip inputs and outputs,
conformity checks between predicted and actual outputs and collection of
statistics on system performance. The environment has been tested performing a
study of shared architectures of the trigger latency buffering section of pixel
chips. A fully shared architecture and a distributed one have been described at
behavioral level and simulated; the resulting memory occupancy statistics and
hit loss rates have subsequently been compared.Comment: 15 pages, 10 figures (11 figure files), submitted to Journal of
Instrumentatio
Spectroastrometry of rotating gas disks for the detection of supermassive black holes in galactic nuclei. I. Method and simulations
This is the first in a series of papers in which we study the application of
spectroastrometry in the context of gas kinematical studies aimed at measuring
the mass of supermassive black holes. The spectroastrometrical method consists
in measuring the photocenter of light emission in different wavelength or
velocity channels. In particular we explore the potential of spectroastrometry
of gas emission lines in galaxy nuclei to constrain the kinematics of rotating
gas disks and to measure the mass of putative supermassive black holes. By
means of detailed simulations and test cases, we show that the fundamental
advantage of spectroastrometry is that it can provide information on the
gravitational potential of a galaxy on scales significantly smaller (~ 1/10)
than the limit imposed by the spatial resolution of the observations. We then
describe a simple method to infer detailed kinematical informations from
spectroastrometry in longslit spectra and to measure the mass of nuclear mass
concentrations. Such method can be applied straightforwardly to integral field
spectra, which do not have the complexities due to a partial spatial covering
of the source in the case of longslit spectra.Comment: Accepted for publication in A&
Theoretical insights into the RR Lyrae K-band Period-Luminosity relation
Based on updated nonlinear, convective pulsation models computed for several
values of stellar mass, luminosity and metallicity, theoretical constraints on
the K-band Period-Luminosity (PLK) relation of RR Lyrae stars are presented. We
show that for each given metal content the predicted PLK is marginally
dependent on uncertainties of the stellar mass and/or luminosity. Then, by
considering the RR Lyrae masses suggested by evolutionary computations for the
various metallicities, we obtain that the predicted infrared magnitude M_K over
the range 0.0001< Z <0.02 is given by the relation
MK=0.568-2.071logP+0.087logZ-0.778logL/Lo, with a rms scatter of 0.032 mag.
Therefore, by allowing the luminosities of RR Lyrae stars to vary within the
range covered by current evolutionary predictions for metal-deficient (0.0001<
Z <0.006) horizontal branch models, we eventually find that the infrared
Period-Luminosity- Metallicity (PLZK) relation is
MK=0.139-2.071(logP+0.30)+0.167logZ, with a total intrinsic dispersion of 0.037
mag. As a consequence, the use of such a PLZK relation should constrain within
+-0.04 mag the infrared distance modulus of field and cluster RR Lyrae
variables, provided that accurate observations and reliable estimates of the
metal content are available. Moreover, we show that the combination of K and V
measurements can supply independent information on the average luminosity of RR
Lyrae stars, thus yielding tight constraints on the input physics of stellar
evolution computations. Finally, for globular clusters with a sizable sample of
first overtone variables, the reddening can be estimated by using the PLZK
relation together with the predicted MV-logP relation at the blue edge of the
instability strip (Caputo et al. 2000).Comment: 8 pages, including 5 postscript figures, accepted for publication on
MNRA
A theoretical approach for the interpretation of pulsating PMS intermediate-mass stars
The investigation of the pulsation properties of pre-main-sequence
intermediate-mass stars is a promising tool to evaluate the intrinsic
properties of these stars and to constrain current evolutionary models. Many
new candidates of this class have been discovered during the last decade and
very accurate data are expected from space observations obtained for example
with the CoRoT satellite. In this context we aim at developing a theoretical
approach for the interpretation of observed frequencies, both from the already
available ground-based observations and from the future more accurate and
extensive CoRoT results. To this purpose we have started a project devoted to
the computations of fine and extensive grids of asteroseismic models of
intermediate mass pre-main-sequence stars. The obtained frequencies are used to
derive an analytical relation between the large frequency separation and the
stellar luminosity and effective temperature and to develop a tool to compare
theory and observations in the echelle diagram. The predictive capabilities of
the proposed method are verified through the application to two test stars. As
a second step, we apply the procedure to two true observations from multisite
campaigns and we are able to constrain their stellar parameters, in particular
the mass, in spite of the small number of frequencies. We expect that with a
significantly higher number of frequencies both the stellar mass and age could
be constrained and, at the same time, the physics of the models could be
tested.Comment: Accepted for publication on A&
Reversible Vortex Ratchet Effects and Ordering in Superconductors with Simple Asymmetric Potential Arrays
We demonstrate using computer simulations that the simplest vortex ratchet
system for type-II superconductors with artificial pinning arrays, an
asymmetric one-dimensional (1D) potential array, exhibits the same features as
more complicated two-dimensional vortex ratchets that have been studied in
recent experiments. We show that the 1D geometry, originally proposed by Lee et
al. [Nature 400, 337 (1999)], undergoes multiple reversals in the sign of the
ratchet effect as a function of vortex density, substrate strength, and ac
drive amplitude, and that the sign of the ratchet effect is related to the type
of vortex lattice structure present. When the vortex lattice is highly ordered,
an ordinary vortex ratchet effect occurs which is similar to the response of an
isolated particle in the same ratchet geometry. In regimes where the vortices
form a smectic or disordered phase, the vortex-vortex interactions are relevant
and we show with force balance arguments that the ratchet effect can reverse in
sign. The dc response of this system features a reversible diode effect and a
variety of vortex states including triangular, smectic, disordered and square.Comment: 10 pages, 12 postscript figures. Version to appear in Phys. Rev.
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