8,818 research outputs found
Synthetic extinction maps around intermediate-mass black holes in Galactic globular clusters
During the last decades, much effort has been devoted to explain the
discrepancy between the amount of intracluster medium (ICM) estimated from
stellar evolution theories and that emerging from observations in globular
clusters (GCs). One possible scenario is the accretion of this medium by an
intermediate-mass black hole (IMBH) at the centre of the cluster. In this work,
we aim at modelling the cluster colour-excess profile as a tracer of the ICM
density, both with and without an IMBH. Comparing the profiles with
observations allows us to test the existence of IMBHs and their possible role
in the cleansing of the ICM. We derive the intracluster density profiles from
hydrodynamical models of accretion onto a central IMBH in a GC and we determine
the corresponding dust density. This model is applied to a list of 25 Galactic
GCs. We find that central IMBHs decrease the ICM by several orders of
magnitude. In a subset of 9 clusters, the absence of the black hole combined
with a low intracluster medium temperature would be at odds with present gas
mass content estimations. As a result, we conclude that IMBHs are an effective
cleansing mechanism of the ICM of GCs. We construct synthetic extinction maps
for M 62 and {\omega} Cen, two clusters in the small subset of 9 with observed
2D extinction maps. We find that under reasonable assumptions regarding the
model parameters, if the gas temperature in M 62 is close to 8000 K, an IMBH
needs to be invoked. Further ICM observations regarding both the gas and dust
in GCs could help to settle this issue.Comment: Accepted for publication in MNRAS.11 pages, 7 figure
Line-profile variations in radial-velocity measurements: Two alternative indicators for planetary searches
Aims. We introduce two methods to identify false-positive planetary signals
in the context of radial-velocity exoplanet searches. The first is the
bi-Gaussian cross-correlation function fitting, and the second is the
measurement of asymmetry in radial-velocity spectral line information content,
Vasy.
Methods. We make a systematic analysis of the most used common line profile
diagnosis, Bisector Inverse Slope and Velocity Span, along with the two
proposed ones. We evaluate all these diagnosis methods following a set of
well-defined common criteria and using both simulated and real data. We apply
them to simulated cross-correlation functions created with the program SOAP and
which are affected by the presence of stellar spots, and to real
cross-correlation functions, calculated from HARPS spectra, for stars with a
signal originating both in activity and created by a planet.
Results. We demonstrate that the bi-Gaussian method allows a more precise
characterization of the deformation of line profiles than the standard bisector
inverse slope. The calculation of the deformation indicator is simpler and its
interpretation more straightforward. More importantly, its amplitude can be up
to 30% larger than that of the bisector span, allowing the detection of
smaller-amplitude correlations with radial-velocity variations. However, a
particular parametrization of the bisector inverse slope is shown to be more
efficient on high-signal-to-noise data than both the standard bisector and the
bi-Gaussian. The results of the Vasy method show that this indicator is more
effective than any of the previous ones, being correlated with the
radial-velocity with more significance for signals resulting from a line
deformation. Moreover, it provides a qualitative advantage over the bisector,
showing significant correlations with RV for active stars for which bisector
analysis is inconclusive. (abridged)Comment: 12 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics, comments welcom
A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons
The study of Earth-mass extrasolar planets via the radial-velocity technique
and the measurement of the potential cosmological variability of fundamental
constants call for very-high-precision spectroscopy at the level of
\updelta\lambda/\lambda<10^{-9}. Wavelength accuracy is obtained by providing
two fundamental ingredients: 1) an absolute and information-rich wavelength
source and 2) the ability of the spectrograph and its data reduction of
transferring the reference scale (wavelengths) to a measurement scale (detector
pixels) in a repeatable manner. The goal of this work is to improve the
wavelength calibration accuracy of the HARPS spectrograph by combining the
absolute spectral reference provided by the emission lines of a thorium-argon
hollow-cathode lamp (HCL) with the spectrally rich and precise spectral
information of a Fabry-P\'erot-based calibration source. On the basis of
calibration frames acquired each night since the Fabry-P\'erot etalon was
installed on HARPS in 2011, we construct a combined wavelength solution which
fits simultaneously the thorium emission lines and the Fabry-P\'erot lines. The
combined fit is anchored to the absolute thorium wavelengths, which provide the
`zero-point' of the spectrograph, while the Fabry-P\'erot lines are used to
improve the (spectrally) local precision. The obtained wavelength solution is
verified for auto-consistency and tested against a solution obtained using the
HARPS Laser-Frequency Comb (LFC). The combined thorium+Fabry-P\'erot wavelength
solution shows significantly better performances compared to the thorium-only
calibration. The presented techniques will therefore be used in the new HARPS
and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.Comment: 15 pages, 8 figure
Feedback local optimality principle applied to rocket vertical landing VTVL
Vertical landing is becoming popular in the last fifteen years, a technology known under the acronym VTVL, Vertical Takeoff and Vertical Landing [1,2]. The interest in such landing technology is dictated by possible cost reductions [3,4], that impose spaceship’s recycling. The rockets are not generally de- signed to perform landing operations, rather their design is aimed at takeoff operations, guaranteeing a very high forward acceleration to gain the velocity needed to escape the gravitational force. In this paper a new control method based on Feedback Local Optimality Principle, named FLOP is applied to the rocket landing problem. The FLOP belongs to a special class of optimal controllers, developed by the mechatronic and vehicle dynamics lab of Sapienza, named Variational Feedback Controllers - VFC, that are part of an ongoing research and are recently applied in different field: nonlinear system [5], marine and terrestrial autonomous vehicles [6,7,8], multi agents interactions and vibration control [9, 10]. The paper is devoted to show the robustness of the nonlinear controlled system, comparing the performances with the LQR, one of the most acknowledged methods in optimal control
NEW YORK COURT OF APPEALS CASE COMPILATIONS: McCoY v. FEINMAN, ET.AL.
McCoY v. FEINMAN, ET.AL. (Decided November 19, 2002
Spiral phases and two-particle bound states from a systematic low-energy effective theory for magnons, electrons, and holes in an antiferromagnet
We have constructed a systematic low-energy effective theory for hole- and
electron-doped antiferromagnets, where holes reside in momentum space pockets
centered at and where electrons live in
pockets centered at or . The effective
theory is used to investigate the magnon-mediated binding between two holes or
two electrons in an otherwise undoped system. We derive the one-magnon exchange
potential from the effective theory and then solve the corresponding
two-quasiparticle Schr\"odinger equation. As a result, we find bound state wave
functions that resemble -like or -like symmetry. We also
study possible ground states of lightly doped antiferromagnets.Comment: 2 Pages; Proc. of SCES'07, Housto
Selection of Lactobacillus strains from fermented sausages for their potential use as probiotics.
A rapid screening method was used to isolate potentially probiotic Lactobacillus strains from fermented sausages after enrichment in MRS broth at pH 2.5 followed by bile salt stressing (1% bile salts w/v). One hundred and fifty acid- and bile-resistant strains were selected, avoiding preliminary and time-consuming isolation steps. Strains were further characterized for survival at pH 2.5 for 3 h in phosphate-buffered saline and for growth in the presence of 0.3% bile salts with and without pre-exposure at low pH. Twentyeight strains showed a survival >80% at pH 2.5 for 3 h; moreover, most of the strains were able to grow in the presence of 0.3% bile salts. Low pH and bile resistance was shown to be dependent on both the species, identified by phenotypic and molecular methods, and the strain tested. This is the first report on the direct selection of potentially probiotic lactobacilli from dry fermented sausages. Technologically interesting strains may be used in the future as probiotic starter cultures for novel fermented sausage manufacture
Strutture organizzative e risorse manageriali nella governance delle imprese internazionalizzate
Nella dimensione globale il concetto sistemico dell'impresa si deve aprire a una molteplicit\ue0 di contesti; la governance si trasferisce al sistema internazionale, mantenendo forti le sue radici nell'ambiente originario, ma allo stesso tempo confrontandosi con nuovi stakeholders, nuove regole, nuove dimensioni statuali. L'attivit\ue0 di governance deve quindi affrontare tutti gli aspetti critici dell'ampliamento e della complessit\ue0 delle attivit\ue0 aziendali, mirando all'efficacia complessiva del sistema attraverso la guida strategica e il coordinamento del vertice, l'autonomia e la valorizzazione delle unit\ue0 periferiche e il loro contributo all'innovazione, l'efficacia del trasferimento delle conoscenze in tutte le direzioni e la gestione delle risorse umane centrali e locali in una prospettiva multiculturale. Si rende quindi fondamentale la gestione e la valorizzazione di quei manager capaci di interpretare il multiculturalismo, rimanendo fedeli all'organizzazione, vivendo pi\uf9 dimensioni dell'organizzazione internazionalizzata, coniugando le esigenze dell'unit\ue0 centrale con quelle delle unit\ue0 periferiche
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