3,567 research outputs found
Optimization of grazing incidence mirrors and its application to surveying X-ray telescopes
Grazing incidence mirrors for X-ray astronomy are usually designed in the
parabola-hyperbola (Wolter I) configuration. This design allows for optimal
images on-axis, which however degrade rapidly with the off-axis angle. Mirror
surfaces described by polynomia (with terms higher than order two), have been
put forward to improve the performances over the field of view. Here we present
a refined procedure aimed at optimizing wide-field grazing incidence telescopes
for X-ray astronomy. We improve the angular resolution over existing
(wide-field) designs by ~ 20%. We further consider the corrections for the
different plate scale and focal plane curvature of the mirror shells, which
sharpen by another ~ 20% the image quality. This results in a factor of ~ 2
reduction in the observing time needed to achieve the same sensitivity over
existing wide-field designs and of ~ 5 over Wolter I telescopes. We demonstrate
that such wide-field X-ray telescopes are highly advantageous for deep surveys
of the X-ray sky.Comment: 8 pages 4 figures. Accepted for publication on A&A (macro included
Bank-specific capital requirements: short and long-run determinants
This paper studies the determinants of the Pillar 2 capital requirements (P2R) of banks directly supervised by the ECB between 2016 and 2021. Drawing on the ECBâs Supervisory Review and Evaluation Process (SREP) to identify the list of potential drivers of P2R, we estimate the impact on P2R by employing a method that separates long-run from short-run determinants. Our results suggest that in (i) the long-run, the P2R is mostly driven by credit risk, funding risk, and governance, whereas (ii) profitability and market risk seem to be the main short-run determinants of P2R. Furthermore, we find evidence that suggests the supervisor incorporates proportionality in the P2R decisions. Effectively, our sensitivity analyses show considerable differences in the long-run determinants of P2R according to the level of capital, size, and access to market funding of supervised entities.info:eu-repo/semantics/publishedVersio
Preimplantation biopsy predicts delayed graft function, glomerular filtration rate and long-term graft survival of transplanted kidneys
Background
The predictive value of preimplantation biopsies for long-term graft function is often limited by conflicting results. The aim of this study was to evaluate the influence of time-zero graft biopsy histological scores on early and late graft function, graft survival and patient survival, at different time points.
Methods
We retrospectively analyzed 284 preimplantation biopsies at a single center, in a cohort of recipients with grafts from live and deceased donors (standard and nonstandard), and their impact in posttransplant renal function after a mean follow-up of 7 years (range 1â16). Implantation biopsy score (IBS), a combination score derived from 4 histopathological aspects, was determined from each sample. The correlation with incidence of delayed graft function (DGF), creatinine clearance (1st, 3rd and 5th posttransplant year) and graft and patient survival at 1 and 5 years were evaluated.
Results
Preimplantation biopsies provided somewhat of a prognostic index of early function and outcome of the transplanted kidney in the short and long term. In the immediate posttransplantation period, the degree of arteriolosclerosis and interstitial fibrosis correlated better with the presence of DGF. IBS values between 4 and 6 were predictive of worst renal function at 1st and 3rd years posttransplant and 5-year graft survival. The most important histological finding, in effectively transplanted grafts, was the grade of interstitial fibrosis. Patient survival was not influenced by IBS.
Conclusions
Higher preimplantation biopsy scores predicted an increased risk of early graft losses, especially primary nonfunction. Graft survival (at 1st and 5th years after transplant) but not patient survival was predicted by IBS
Redshift determination in the X-ray band of gamma-ray bursts
If gamma-ray bursts originate in dense stellar forming regions, the
interstellar material can imprint detectable absorption features on the
observed X-ray spectrum. Such features can be detected by existing and planned
X-ray satellites, as long as the X-ray afterglow is observed after a few
minutes from the burst. If the column density of the interstellar material
exceeds ~10^{23} cm^{-2} there exists the possibility to detect the K_alpha
fluorescent iron line, which should be visible for more than one year, long
after the X-ray afterglow continuum has faded away. Detection of these X-ray
features will make possible the determination of the redshift of gamma-ray
bursts even when their optical afterglow is severely dimmed by extinction.Comment: 15 pages with 5 figures. Submitted to Ap
SIMBOL-X : a new generation hard X-ray telescope
SIMBOL-X is a hard X-ray mission, operating in the 0.5-70 keV range, which is
proposed by a consortium of European laboratories for a launch around 2010.
Relying on two spacecraft in a formation flying configuration, SIMBOL-X uses a
30 m focal length X-ray mirror to achieve an unprecedented angular resolution
(30 arcsec HEW) and sensitivity (100 times better than INTEGRAL below 50 keV)
in the hard X-ray range. SIMBOL-X will allow to elucidate fundamental questions
in high energy astrophysics, such as the physics of accretion onto Black Holes,
of acceleration in quasar jets and in supernovae remnants, or the nature of the
hard X-ray diffuse emission. The scientific objectives and the baseline
concepts of the mission and hardware design are presented.Comment: 12 pages, 16 fig., Proc. SPIE conf. 5168, San Diego, Aug. 200
The artificial retina for track reconstruction at the LHC crossing rate
We present the results of an R&D study for a specialized processor capable of
precisely reconstructing events with hundreds of charged-particle tracks in
pixel and silicon strip detectors at , thus suitable for
processing LHC events at the full crossing frequency. For this purpose we
design and test a massively parallel pattern-recognition algorithm, inspired to
the current understanding of the mechanisms adopted by the primary visual
cortex of mammals in the early stages of visual-information processing. The
detailed geometry and charged-particle's activity of a large tracking detector
are simulated and used to assess the performance of the artificial retina
algorithm. We find that high-quality tracking in large detectors is possible
with sub-microsecond latencies when the algorithm is implemented in modern,
high-speed, high-bandwidth FPGA devices.Comment: 3 pages, 3 figures, ICHEP14. arXiv admin note: text overlap with
arXiv:1409.089
Simulation and performance of an artificial retina for 40 MHz track reconstruction
We present the results of a detailed simulation of the artificial retina
pattern-recognition algorithm, designed to reconstruct events with hundreds of
charged-particle tracks in pixel and silicon detectors at LHCb with LHC
crossing frequency of . Performances of the artificial retina
algorithm are assessed using the official Monte Carlo samples of the LHCb
experiment. We found performances for the retina pattern-recognition algorithm
comparable with the full LHCb reconstruction algorithm.Comment: Final draft of WIT proceedings modified according to JINST referee's
comment
A Specialized Processor for Track Reconstruction at the LHC Crossing Rate
We present the results of an R&D study of a specialized processor capable of
precisely reconstructing events with hundreds of charged-particle tracks in
pixel detectors at 40 MHz, thus suitable for processing LHC events at the full
crossing frequency. For this purpose we design and test a massively parallel
pattern-recognition algorithm, inspired by studies of the processing of visual
images by the brain as it happens in nature. We find that high-quality tracking
in large detectors is possible with sub-s latencies when this algorithm is
implemented in modern, high-speed, high-bandwidth FPGA devices. This opens a
possibility of making track reconstruction happen transparently as part of the
detector readout.Comment: Presented by G.Punzi at the conference on "Instrumentation for
Colliding Beam Physics" (INSTR14), 24 Feb to 1 Mar 2014, Novosibirsk, Russia.
Submitted to JINST proceeding
Simbol-X Hard X-ray Focusing Mirrors: Results Obtained During the Phase A Study
Simbol-X will push grazing incidence imaging up to 80 keV, providing a strong
improvement both in sensitivity and angular resolution compared to all
instruments that have operated so far above 10 keV. The superb hard X-ray
imaging capability will be guaranteed by a mirror module of 100 electroformed
Nickel shells with a multilayer reflecting coating. Here we will describe the
technogical development and solutions adopted for the fabrication of the mirror
module, that must guarantee an Half Energy Width (HEW) better than 20 arcsec
from 0.5 up to 30 keV and a goal of 40 arcsec at 60 keV. During the phase A,
terminated at the end of 2008, we have developed three engineering models with
two, two and three shells, respectively. The most critical aspects in the
development of the Simbol-X mirrors are i) the production of the 100 mandrels
with very good surface quality within the timeline of the mission; ii) the
replication of shells that must be very thin (a factor of 2 thinner than those
of XMM-Newton) and still have very good image quality up to 80 keV; iii) the
development of an integration process that allows us to integrate these very
thin mirrors maintaining their intrinsic good image quality. The Phase A study
has shown that we can fabricate the mandrels with the needed quality and that
we have developed a valid integration process. The shells that we have produced
so far have a quite good image quality, e.g. HEW <~30 arcsec at 30 keV, and
effective area. However, we still need to make some improvements to reach the
requirements. We will briefly present these results and discuss the possible
improvements that we will investigate during phase B.Comment: 6 pages, 3 figures, invited talk at the conference "2nd International
Simbol-X Symposium", Paris, 2-5 december, 200
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