3,524 research outputs found
Electromagnetic Corrections in Partially Quenched Chiral Perturbation Theory
We introduce photons in Partially Quenched Chiral Perturbation Theory and
calculate the resulting electromagnetic loop-corrections at NLO for the charged
meson masses and decay constants. We also present a numerical analysis to
indicate the size of the different corrections. We show that several
phenomenologically relevant quantities can be calculated consistently with
photons which couple only to the valence quarks, allowing the use of gluon
configurations produced without dynamical photons.Comment: 11 page
First orbital solution for the non-thermal emitter Cyg OB2 #9
After the first detection of its binary nature, the spectroscopic monitoring
of the non-thermal radio emitter Cyg OB2 #9 (P=2.4yrs) has continued, doubling
the number of available spectra of the star. Since the discovery paper of 2008,
a second periastron passage has occurred in February 2009. Using a variety of
techniques, the radial velocities could be estimated and a first, preliminary
orbital solution was derived from the HeI5876 line. The mass ratio appears
close to unity and the eccentricity is large, 0.7--0.75. X-ray data from 2004
and 2007 are also analyzed in quest of peculiarities linked to binarity. The
observations reveal no large overluminosity nor strong hardness, but it must be
noted that the high-energy data were taken after the periastron passage, at a
time where colliding wind emission may be low. Some unusual X-ray variability
is however detected, with a 10% flux decrease between 2004 and 2007. To clarify
their origin and find a more obvious signature of the wind-wind collision,
additional data, taken at periastron and close to it, are needed.Comment: 15 pages, 4 figures, accepted by Ap
The Kaon B-parameter from Quenched Domain-Wall QCD
We present numerical results for the kaon B-parameter, B_K, determined in the
quenched approximation of lattice QCD. Our simulations are performed using
domain-wall fermions and the renormalization group improved, DBW2 gauge action
which combine to give quarks with good chiral symmetry at finite lattice
spacing. Operators are renormalized non-perturbatively using the RI/MOM scheme.
We study scaling by performing the simulation on two different lattices with
a^{-1} = 1.982(30) and 2.914(54) GeV. We combine this quenched scaling study
with an earlier calculation of B_K using two flavors of dynamical, domain-wall
quarks at a single lattice spacing to obtain
B_K(MS,NDR,mu=2GeV)=0.563(21)(39)(30), were the first error is statistical, the
second systematic (without quenching errors) and the third estimates the error
due to quenching.Comment: 77 pages, 44 figures, to be published in Phys. Rev.
Component Separation for Spectral X-Ray Imaging Using the XPAD3 Hybrid Pixel Camera
The advent of hybrid pixel cameras in X-ray imaging opens the way to the acquisition of spectral measurements. These new devices for which photon counting replaces charge integration incorporate a dedicated readout electronic for each pixel including a capability of selecting energies via the setup of an energy threshold. This ability is of uppermost importance for the development of new polychromatic X-ray imaging approaches that will exploit spectral information on the detected X-rays. Spectral measurements in X-ray imaging pave the way to the separation of images in several components of physical and biological interest: the photoelectric and the Compton contributions can be separated while several contrast agents can be simultaneously localized. We investigate the capability to perform component separation by using the newly developed XPAD3 hybrid pixel camera incorporated in the micro-CT demonstrator PIXSCAN. Firstly, we propose an approach to configure the acquisition setup in order to optimize the component separation problem with respect to the robustness to the photon noise. The method is based on the Cramer-Rao Bound (CRB) that indicates the lowest reachable variance for the estimation of each component whatever the algorithm. Secondly, we investigate the separation problem with two components namely the photoelectric and the Compton ones. We show on noisy simulated data that such a separation with optimized setup i) enhances the contrast and the Contrast to Noise Ratio (CNR) between biological materials (adipose, soft tissues) and water; ii) cancels the artifacts of the beam-hardening effect that may strongly degrade the image quality. On going work involves two steps: first, dealing with Monte Carlo simulations and real data acquired with the PIXSCAN demonstrator; second, dealing with component separation with more than two components by adding several contrast agents, for which PIXSCAN has already proved its ability to separate them
Results from percutaneous drainage of Hinchey stage II diverticulitis guided by computed tomography scan
Background: Percutaneous abscess drainage guided by computed tomography scan is considered the initial step in the management of patients presenting with Hinchey II diverticulitis. The rationale behind this approach is to manage the septic complication conservatively and to follow this later using elective sigmoidectomy with primary anastomosis. Methods: The clinical outcomes for Hinchey II patients who underwent percutaneous abscess drainage in our institution were reviewed. Drainage was considered a failure when signs of continuing sepsis developed, abscess or fistula recurred within 4 weeks of drainage, and emergency surgical resection with or without a colostomy had to be performed. Results: A total of 34 patients (17 men and 17 women; median age, 71 years; range, 34-90 years) were considered for analysis. The median abscess size was 6 cm (range, 3-18 cm), and the median duration of drainage was 8 days (range, 1-18 days). Drainage was considered successful for 23 patients (67%). The causes of failure for the remaining 11 patients included continuing sepsis (n = 5), abscess recurrence (n = 5), and fistula formation (n = 1). Ten patients who failed percutaneous abscess drainage underwent an emergency Hartmann procedure, with a median delay of 14 days (range, 1-65 days) between drainage and surgery. Three patients in this group (33%) died in the immediate postoperative period. Among the 23 patients successfully drained, 12 underwent elective sigmoid resection with a primary anastomosis. The median delay between drainage and surgery was 101 days (range, 40-420 days). In this group, there were no anastomotic leaks and no mortality. Conclusion: Drainage of Hinchey II diverticulitis guided by computed scan was successful in two-thirds of the cases, and 35% of the patients eventually underwent a safe elective sigmoid resection with primary anastomosis. By contrast, failure of percutaneous abscess drainage to control sepsis is associated with a high mortality rate when an emergency resection is performed. The current results demonstrate that percutaneous abscess drainage is an effective initial therapeutic approach for patients with Hinchey II diverticulitis, and that emergency surgery should be avoided whenever possibl
A Preliminary Seismic Analysis of 51 Peg: Large and Small Spacings from Standard Models
We present a preliminary theoretical seismic study of the astronomically
famous star 51 Peg. This is done by first performing a detailed analysis within
the Hertzsprung-Russell diagram (HRD). Using the Yale stellar evolution code
(YREC), a grid of stellar evolutionary tracks has been constructed for the
masses 1.00 M_sun, 1.05 M_sun and 1.10 M_sun, in the metallicity range
Z=0.024-0.044, and for values of the Galactic helium enrichment ratio DY/DZ in
the range 0-2.5. Along these evolutionary tracks, we select 75 stellar model
candidates that fall within the 51 Peg observational error box in the HRD (all
turn out to have masses of 1.05 M_sun and 1.10 M_sun. The corresponding
allowable age range for these models, which depends sensitively on the
parameters of the model, is relatively large and is ~2.5 - 5.5 Gyr. For each of
the 75 models, a non-radial pulsation analysis is carried out, and the large
and small frequency spacings are calculated. The results show that just
measuring the large and small frequency spacings will greatly reduce the
present uncertainties in the derived physical parameters and in the age of 51
Peg. Finally we discuss briefly refinements in the physics of the models and in
the method of analysis which will have to be included in future models to make
the best of the precise frequency determinations expected from space
observations.Comment: 22 pages, 5 figures, 3 tables. Accepted for publicaton by Ap
Modelling a high-mass red giant observed by CoRoT
The G6 giant HR\,2582 (HD\,50890) was observed by CoRoT for approximately 55
days. Mode frequencies are extracted from the observed Fourier spectrum of the
light curve. Numerical stellar models are then computed to determine the
characteristics of the star (mass, age, etc...) from the comparison with
observational constraints. We provide evidence for the presence of solar-like
oscillations at low frequency, between 10 and 20\,Hz, with a regular
spacing of Hz between consecutive radial orders. Only radial
modes are clearly visible. From the models compatible with the observational
constraints used here, We find that HR\,2582 (HD\,50890) is a massive star with
a mass in the range (3--\,5\,), clearly above the red clump. It
oscillates with rather low radial order ( = 5\,--\,12) modes. Its
evolutionary stage cannot be determined with precision: the star could be on
the ascending red giant branch (hydrogen shell burning) with an age of
approximately 155 Myr or in a later phase (helium burning). In order to obtain
a reasonable helium amount, the metallicity of the star must be quite subsolar.
Our best models are obtained with a mixing length significantly smaller than
that obtained for the Sun with the same physical description (except
overshoot). The amount of core overshoot during the main-sequence phase is
found to be mild, of the order of 0.1\,.Comment: Accepted in A&
Seismic diagnostics for transport of angular momentum in stars 1. Rotational splittings from the PMS to the RGB
Rotational splittings are currently measured for several main sequence stars
and a large number of red giants with the space mission Kepler. This will
provide stringent constraints on rotation profiles. Our aim is to obtain
seismic constraints on the internal transport and surface loss of angular
momentum of oscillating solar-like stars. To this end, we study the evolution
of rotational splittings from the pre-main sequence to the red-giant branch for
stochastically excited oscillation modes. We modified the evolutionary code
CESAM2K to take rotationally induced transport in radiative zones into account.
Linear rotational splittings were computed for a sequence of
models. Rotation profiles were derived from our evolutionary models and
eigenfunctions from linear adiabatic oscillation calculations. We find that
transport by meridional circulation and shear turbulence yields far too high a
core rotation rate for red-giant models compared with recent seismic
observations. We discuss several uncertainties in the physical description of
stars that could have an impact on the rotation profiles. For instance, we find
that the Goldreich-Schubert-Fricke instability does not extract enough angular
momentum from the core to account for the discrepancy. In contrast, an increase
of the horizontal turbulent viscosity by 2 orders of magnitude is able to
significantly decrease the central rotation rate on the red-giant branch. Our
results indicate that it is possible that the prescription for the horizontal
turbulent viscosity largely underestimates its actual value or else a mechanism
not included in current stellar models of low mass stars is needed to slow down
the rotation in the radiative core of red-giant stars.Comment: 15 pages, 13 figures, accepted for publication in A&
Impact of the new solar abundances on the calibration of the PMS binary system RS Cha
Context: In a recent work, we tried to obtain a calibration of the two
components of the pre-main sequence binary system RS Cha by means of
theoretical stellar models. We found that the only way to reproduce the
observational parameters of RS Cha with standard stellar models is to decrease
the initial abundances of carbon and nitrogen derived from the GN93 solar
mixture of heavy elements by a few tenths of dex.
Aims: In this work, we aim to reproduce the observational properties of the
RS Cha stars with stellar evolution models based on the new AGS05 solar mixture
recently derived from a three-dimensional solar model atmosphere. The AGS05
mixture is depleted in carbon, nitrogen and oxygen with respect to the GN93
mixture.
Methods: We calculated new stellar models of the RS Cha components using the
AGS05 mixture and appropriate opacity tables. We sought models that
simultaneously satisfy the observations of the two components (masses, radii,
luminosities, effective temperatures and metallicity).
Results: We find that it is possible to reproduce the observational data of
the RS Cha stars with AGS05 models based on standard input physics. From these
models, the initial helium content of the system is Y~0.255 and its age is
~9.13 +- 0.12 Myr.Comment: Research note accepted in A&A, 5 pages, 2 figure
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