654 research outputs found
Hybrid-procedures for the Treatment of Thoracoabdominal Aortic Aneurysms and Dissections
AimThe conventional open repair of thoracoabdominal aneurysms and dissections remains complex and demanding and is associated with significant morbidity and mortality. We present our experience of hybrid open and endovascular treatment of thoracoabdominal aneurysms and dissections.MethodsWithin an experience of 226 aortic stent-grafts between 1998 and April 2006, 6 of the patients (median age 60 years, range 35 to 68 years) with thoracoabdominal aneurysms (Crawford type I, II, III, and V) were treated with a combined endovascular and open surgical approach. Five men and one woman, with median aneurysm diameter of 75mm (range 70â100mm), received revascularization of the renal arteries, the superior mesenteric artery, and the coeliac trunk accomplished via transperitoneal bypass grafting. Aneurysmal exclusion was then performed by stent-graft deployment.ResultsThe entire procedure was technically successful in all patients. The patients were discharged a median of 9 days after the operation, while the postoperative studies revealed the patency of the vessels and no evidence of type I endoleak or secondary rupture of the aneurysm. During follow up (1 to 22 months) spiral-CT scanning revealed distinct shrinkage of the aneurysm, no graft migration or endoleak and patency of all revascularised vessels, except one renal artery in two patients. No patient experienced any temporary or permanent neurological deficit, and no dialysis was necessary.ConclusionThe combined endovascular and open surgical approach is feasible, without cross clamping of the aorta and with minimized ischemia time for renal and visceral arteries, and seems to be an appropriate strategy for patients with a thoraco-abdominal aortic aneurysm or dissection
X-ray spectral curvature of High Frequency Peaked BL Lacs: a predictor for the TeV flux
Most of the extragalactic sources detected at TeV energies are BL Lac
objects. They belong to the subclass of "high frequency peaked BL Lacs" (HBLs)
exhibiting spectral energy distributions with a lower energy peak in the X-ray
band; this is widely interpreted as synchrotron emission from relativistic
electrons. The X-ray spectra are generally curved, and well described in terms
of a log-parabolic shape. In a previous investigation of TeV HBLs (TBLs) we
found two correlations between their spectral parameters. (1) The synchrotron
peak luminosity L_p increases with its peak energy E_p; (2) the curvature
parameter b decreases as E_p increases. The first is consistent with the
synchrotron scenario, while the second is expected from statistical/stochastic
acceleration mechanisms for the emitting electrons. Here we present an
extensive X-ray analysis of a sample of HBLs observed with XMM-Newton and SWIFT
but undetected at TeV energies (UBLs), to compare their spectral behavior with
that of TBLs. Investigating the distributions of their spectral parameters and
comparing the TBL X-ray spectra with that of UBLs, we develop a criterion to
select the best HBLs candidates for future TeV observations.Comment: 25 pages, 6 figures, Astrophysical Journal publishe
Fractal and stereological analyses of insulin-induced rat exocrine pancreas remodelling
Background: The effect of insulin on the endocrine pancreas has been the subject of extensive study, but quantitative morphometric investigations of the exocrine pancreas are scarce. This study was therefore undertaken to investigate the effect of acute and chronic insulin administration (two doses, 0.4 IU and 4 IU) on the morphology of rat pancreas acini. Materials and methods: Semi-fine sections stained with methylene blue and basic fuchsine or haematoxylin and eosin-stained 5-micrometer thick paraffin sections were used for fractal and stereological analysis of exocrine acini. Acute insulin treatment, independent of applied doses increased fractal dimension in line with decreased lacunarity of pancreas acini. Chronic low dose insulin decreased fractal dimension and increased lacunarity of pancreas acini, but a high dose had the opposite effect. The volume densities (Vv) of cytoplasm, granules and nucleus are affected differently: acute low dose and high chronic dose significantly decreased granules Vv, and in line increased cytoplasmic Vv, whereas other examined structures showed slight changes without statistical significance. Results: The results obtained from this investigation indicate that insulin treatment induced structural remodelling of the exocrine pancreas suggesting a substantial role of insulin in its functioning. Conclusions: Additionally, we showed that fine architectural changes in acini could be detected by fractal analysis, suggesting this method as an alternative or addition to routine stereology
Simultaneous multi-frequency observation of the unknown redshift blazar PG1553+113 in March-April 2008
5 pĂĄginas, 2 figuras, 3 tablas.-- El Pdf del artĂculo es la versiĂłn pre-print: arXiv: arXiv:0911.1088.-- MAGIC Collaboration: et al.The blazar PGâ1553+113 is a well known TeV Îł-ray emitter. In this paper we determine its spectral energy distribution through simultaneous multi-frequency data to study its emission processes. An extensive campaign was carried out between March and April 2008, where optical, X-ray, high-energy (HE) Îł-ray, and very-high-energy (VHE) Îł-ray data were obtained with the KVA, Abastumani, REM, RossiXTE/ASM, AGILE and MAGIC telescopes, respectively. We combine the data to derive the source's spectral energy distribution and interpret its double-peaked shape within the framework of a synchrotron self-Compton model.Major support
from Germanyâs Bundesministerium fšur Bildung, Wissenschaft, Forschung
und Technologie and Max-Planck-Gesellschaft, Italyâs Istituto Nazionale di
Fisica Nucleare (INFN) and Istituto Nazionale di Astrofisica (INAF), and
Spainâs Ministerio de Ciencia e Innovacion is gratefully acknowledged. The
work was also supported by Switzerlandâs ETH Research grant TH34/043,
Polandâs Ministertwo Nauki i Szkolnictwa WyËzszego grant N N203 390834,
and Germanyâs Young Investigator Program of the Helmholtz Gemeinschaft.
This work was also supported by Georgian National Science Foundation grant
GNSF/ST07/4-180. EP acknowledges support from the Italian Space Agency
through grants ASI-INAF I/023/05/0 and ASI I/088/06/0.Peer reviewe
The near-infrared detection of PSR B0540-69 and its nebula
The ~1700 year old PSR B0540-69 in the LMC is considered the twin of the Crab
pulsar because of its similar spin parameters, magnetic field, and energetics.
Its optical spectrum is fit by a power-law, ascribed to synchrotron radiation,
like for the young Crab and Vela pulsars. nIR observations, never performed for
PSR B0540-69, are crucial to determine whether the optical power-law spectrum
extends to longer wavelengths or a new break occurs, like it happens for both
the Crab and Vela pulsars in the mIR, hinting at an even more complex particle
energy and density distribution in the pulsar magnetosphere. We observed PSR
B0540-69 in the J, H, and Ks bands with the VLT to detect it, for the first
time, in the nIR and characterise its optical-to-nIR spectrum. To disentangle
the pulsar emission from that of its pulsar wind nebula (PWN), we obtained
high-spatial resolution adaptive optics images with NACO. We could clearly
identify PSR B0540-69 in our J, H, and Ks-band images and measure its flux
(J=20.14, H=19.33, Ks=18.55, with an overall error of +/- 0.1 magnitudes in
each band). The joint fit to the available optical and nIR photometry with a
power-law spectrum gives a spectral index alpha=0.70 +/-0.04. The comparison
between our NACO images and HST optical ones does not reveal any apparent
difference in the PWN morphology as a function of wavelength. The PWN
optical-to-nIR spectrum is also fit by a single power-law, with spectral index
alpha=0.56+/- 0.03, slightly flatter than the pulsar's. Using NACO at the VLT,
we obtained the first detection of PSR B0540-69 and its PWN in the nIR. Due to
the small angular scale of the PWN (~4") only the spatial resolution of the
JWST will make it possible to extend the study of the pulsar and PWN spectrum
towards the mid-IR.Comment: 11 pages, 10 figures, Accepted for publication on Astronomy and
Astrophysic
MAGIC observation of the GRBâ080430 afterglow
6 pĂĄginas, 1 figura.-- El Pdf del artĂculo es la versiĂłn pre-print: arXiv:1004.3665v2.-- MAGIC Collaboration: et al.[Context]: Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the long-lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment.
[Aims]: Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, being satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ~100âGeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies.
[Methods]: We used the results of the MAGIC telescope observation of the moderate resdhift (z ~ 0.76) GRBâ080430 at energies above about 80âGeV, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes.
[Results]: We obtained an upper limit of F95% CL = 5.5 Ă 10-11âergâcm-2 s-1 for the very-high energy emission of GRBâ080430, which cannot set further constraints on the theoretical scenarios proposed for this object also due to the difficulties in modeling the low-energy afterglow. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z âČ 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase.The support of the German BMBF and MPG,
the Italian INFN and Spanish MICINN is gratefully acknowledged. This work
was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW
Grant N N203 390834, and by the YIP of the Helmholtz Gemeinschaft.Peer reviewe
Acceleration and radiation of ultra-high energy protons in galaxy clusters
Clusters of galaxies are believed to be capable to accelerate protons at
accretion shocks to energies exceeding 10^18 eV. At these energies, the losses
caused by interactions of cosmic rays with photons of the Cosmic Microwave
Background Radiation (CMBR) become effective and determine the maximum energy
of protons and the shape of the energy spectrum in the cutoff region. The aim
of this work is the study of the formation of the energy spectrum of
accelerated protons at accretion shocks of galaxy clusters and of the
characteristics of their broad band emission. The proton energy distribution is
calculated self-consistently via a time-dependent numerical treatment of the
shock acceleration process which takes into account the proton energy losses
due to interactions with the CMBR. We calculate the energy distribution of
accelerated protons, as well as the flux of broad-band emission produced by
secondary electrons and positrons via synchrotron and inverse Compton
scattering processes. We find that the downstream and upstream regions
contribute almost at the same level to the emission. For the typical parameters
characterising galaxy clusters, the synchrotron and IC peaks in the spectral
energy distributions appear at comparable flux levels. For an efficient
acceleration, the expected emission components in the X-ray and gamma-ray band
are close to the detection threshold of current generation instruments, and
will be possibly detected with the future generation of detectors.Comment: 9 pages, 13 figures, submitted to Astronomy & Astrophysic
Studies of active galactic nuclei with CTA
In this paper, we review the prospects for studies of active galactic nuclei
(AGN) using the envisioned future Cherenkov Telescope Array (CTA). This review
focuses on jetted AGN, which constitute the vast majority of AGN detected at
gamma-ray energies. Future progress will be driven by the planned lower energy
threshold for very high energy (VHE) gamma-ray detections to ~10 GeV and
improved flux sensitivity compared to current-generation Cherenkov Telescope
facilities. We argue that CTA will enable substantial progress on gamma-ray
population studies by deepening existing surveys both through increased flux
sensitivity and by improving the chances of detecting a larger number of
low-frequency peaked blazars because of the lower energy threshold. More
detailed studies of the VHE gamma-ray spectral shape and variability might
furthermore yield insight into unsolved questions concerning jet formation and
composition, the acceleration of particles within relativistic jets, and the
microphysics of the radiation mechanisms leading to the observable high-energy
emission. The broad energy range covered by CTA includes energies where
gamma-rays are unaffected from absorption while propagating in the
extragalactic background light (EBL), and extends to an energy regime where VHE
spectra are strongly distorted. This will help to reduce systematic effects in
the spectra from different instruments, leading to a more reliable EBL
determination, and hence will make it possible to constrain blazar models up to
the highest energies with less ambiguity.Comment: invited review article, 15 pages, 9 figures, Astroparticle Physics,
Special Issue on Physics with the Cherenkov Telescope Array, in pres
Prospects for a Dark Matter annihilation signal towards the Sagittarius dwarf galaxy with ground based Cherenkov telescopes
Dwarf galaxies are widely believed to be among the best targets for indirect
dark matter searches using high-energy gamma rays; and indeed gamma-ray
emission from these objects has long been a subject of detailed study for
ground-based atmospheric Cherenkov telescopes. Here, we update current
exclusion limits obtained on the closest dwarf, the Sagittarius dwarf galaxy,
in light of recent realistic dark matter halo models. The constraints on the
velocity-weighted annihilation cross section of the dark matter particle are of
a few 10 cms in the TeV energy range for a 50 h exposure.
The limits are extrapolated to the sensitivities of future Cherenkov Telescope
Arrays. For 200 h of observation time, the sensitivity at 95% C.L. reaches
10 cms. Possible astrophysical backgrounds from gamma-ray
sources dissembled in Sagittarius dwarf are studied. It is shown that with
long-enough observation times, gamma-ray background from millisecond pulsars in
a globular cluster contained within Sagittarius dwarf may limit the sensitivity
to dark matter annihilations.Comment: 12 pages, 5 figures, 2 tables, accepted for publication in Ap
Dark Energy Survey year 1 results: Cosmological constraints from galaxy clustering and weak lensing
We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321ââdeg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric-redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while âblindâ to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat ÎCDM and wCDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for ÎCDM) or 7 (for wCDM) cosmological parameters including the neutrino mass density and including the 457Ă457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions and from their combination obtain S8âĄÏ8(Ωm/0.3)0.5=0.773+0.026â0.020 and Ωm=0.267+0.030â0.017 for ÎCDM; for wCDM, we find S8=0.782+0.036â0.024, Ωm=0.284+0.033â0.030, and w=â0.82+0.21â0.20 at 68% C.L. The precision of these DES Y1 constraints rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for S8 and Ωm are lower than the central values from Planck for both ÎCDM and wCDM, the Bayes factor indicates that the DES Y1 and Planck data sets are consistent with each other in the context of ÎCDM. Combining DES Y1 with Planck, baryonic acoustic oscillation measurements from SDSS, 6dF, and BOSS and type Ia supernovae from the Joint Lightcurve Analysis data set, we derive very tight constraints on cosmological parameters: S8=0.802±0.012 and Ωm=0.298±0.007 in ÎCDM and w=â1.00+0.05â0.04 in wCDM. Upcoming Dark Energy Survey analyses will provide more stringent tests of the ÎCDM model and extensions such as a time-varying equation of state of dark energy or modified gravity
- âŠ