2,205 research outputs found
A focal plane detector design for a wide-band Laue-lens telescope
The energy range above 60 keV is important for the study of many open
problems in high energy astrophysics such as the role of Inverse Compton with
respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in
SNR, the study of the high energy cut-offs in AGN spectra, and the detection of
nuclear and annihilation lines. Recently the development of high energy Laue
lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a
Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of
celestial sources. The required focal plane detector should have high detection
efficiency over the entire operative range, a spatial resolution of about 1 mm,
an energy resolution of a few keV at 500 keV and a sensitivity to linear
polarization. We describe a possible configuration of the focal plane detector
based on several CdTe/CZT pixelated layers stacked together to achieve the
required detection efficiency at high energy. Each layer can operate both as a
separate position sensitive detector and polarimeter or work with other layers
to increase the overall photopeak efficiency. Each layer has a hexagonal shape
in order to minimize the detector surface required to cover the lens field of
view. The pixels would have the same geometry so as to provide the best
coupling with the lens point spread function and to increase the symmetry for
polarimetric studies.Comment: 10 pages, 9 figure
Development status of a Laue lens project for gamma-ray astronomy
We report the status of the HAXTEL project, devoted to perform a design study
and the development of a Laue lens prototype. After a summary of the major
results of the design study, the approach adopted to develop a Demonstration
Model of a Laue lens is discussed, the set up described, and some results
presented.Comment: 11 pages, 11 figures, 2007 SPIE Conference on Optics for EUV, X-Ray,
and Gamma-Ray Astronomy II
The gamma-ray burst monitor for Lobster-ISS
Lobster-ISS is an X-ray all-sky monitor experiment selected by ESA two years
ago for a Phase A study (now almost completed) for a future flight (2009)
aboard the Columbus Exposed Payload Facility of the International Space
Station. The main instrument, based on MCP optics with Lobster-eye geometry,
has an energy passband from 0.1 to 3.5 keV, an unprecedented daily sensitivity
of 2x10^{-12} erg cm^{-2}s$^{-1}, and it is capable to scan, during each orbit,
the entire sky with an angular resolution of 4--6 arcmin. This X-ray telescope
is flanked by a Gamma Ray Burst Monitor, with the minimum requirement of
recognizing true GRBs from other transient events. In this paper we describe
the GRBM. In addition to the minimum requirement, the instrument proposed is
capable to roughly localize GRBs which occur in the Lobster FOV (162x22.5
degrees) and to significantly extend the scientific capabilities of the main
instrument for the study of GRBs and X-ray transients. The combination of the
two instruments will allow an unprecedented spectral coverage (from 0.1 up to
300/700 keV) for a sensitive study of the GRB prompt emission in the passband
where GRBs and X-Ray Flashes emit most of their energy. The low-energy spectral
band (0.1-10 keV) is of key importance for the study of the GRB environment and
the search of transient absorption and emission features from GRBs, both goals
being crucial for unveiling the GRB phenomenon. The entire energy band of
Lobster-ISS is not covered by either the Swift satellite or other GRB missions
foreseen in the next decade.Comment: 6 pages, 4 figures. Paper presented at the COSPAR 2004 General
Assembly (Paris), accepted for publication in Advances in Space Research in
June 2005 and available on-line at the Journal site
(http://www.sciencedirect.com/science/journal/02731177), section "Articles in
press
Development status of the LAUE project
We present the status of LAUE, a project supported by the Italian Space
Agency (ASI), and devoted to develop Laue lenses with long focal length (up to
100 meters), for hard X--/soft gamma--ray astronomy (80-600 keV). Thanks to
their focusing capability, the design goal is to improve the sensitivity of the
current instrumention in the above energy band by 2 orders of magnitude, down
to a few times photons/(cm s keV).Comment: 9 pages, 9 figures, presented at the Space Telescopes and
Instrumentation Symposium in Amsterdam, 2012: Ultraviolet to Gamma Ray
Conference. Published in the Proceedings of the SPIE, Volume 8443, id.
84430B-84430B-9 (2012
Exploring the Hard X-/soft gamma-ray Continuum Spectra with Laue Lenses
The history of X-ray astronomy has shown that any advancement in our
knowledge of the X-ray sky is strictly related to an increase in instrument
sensitivity. At energies above 60 keV, there are interesting prospects for
greatly improving the limiting sensitivity of the current generation of direct
viewing telescopes (with or without coded masks), offered by the use of Laue
lenses. We will discuss below the development status of a Hard X-Ray focusing
Telescope (HAXTEL) based on Laue lenses with a broad bandpass (from 60 to 600
keV) for the study of the X-ray continuum of celestial sources. We show two
examplesof multi-lens configurations with expected sensitivity orders of
magnitude better ( photons cm s keV
at 200 keV) than that achieved so far. With this unprecedented sensitivity,
very exciting astrophysical prospects are opened.Comment: 4 pages, 10 figures, to be published in the Proc. of the 39th ESLAB
Symosium, 19-21 April 200
Long-term survival in patients undergoing cardiac resynchronization therapy: the importance of performing atrio-ventricular junction ablation in patients with permanent atrial fibrillation
AIMS: To investigate the effects of cardiac resynchronization therapy (CRT) on survival in heart failure (HF) patients with permanent atrial fibrillation (AF) and the role of atrio-ventricular junction (AVJ) ablation in these patients.
METHODS AND RESULTS: Data from 1285 consecutive patients implanted with CRT devices are presented: 1042 patients were in sinus rhythm (SR) and 243 (19%) in AF. Rate control in AF was achieved by either ablating the AVJ in 118 patients (AVJ-abl) or prescribing negative chronotropic drugs (AF-Drugs). Compared with SR, patients with AF were significantly older, more likely to be non-ischaemic, with higher ejection fraction, shorter QRS duration, and less often received ICD back-up. During a median follow-up of 34 months, 170/1042 patients in SR and 39/243 in AF died (mortality: 8.4 and 8.9 per 100 person-year, respectively). Adjusted hazard ratios were similar for all-cause and cardiac mortality [0.9 (0.57-1.42), P = 0.64 and 1.00 (0.60-1.66) P = 0.99, respectively]. Among AF patients, only 11/118 AVJ-abl patients died vs. 28/125 AF-Drugs patients (mortality: 4.3 and 15.2 per 100 person-year, respectively, P < 0.001). Adjusted hazard ratios of AVJ-abl vs. AF-Drugs was 0.26 [95% confidence interval (CI) 0.09-0.73, P = 0.010] for all-cause mortality, 0.31 (95% CI 0.10-0.99, P = 0.048) for cardiac mortality, and 0.15 (95% CI 0.03-0.70, P = 0.016) for HF mortality.
CONCLUSION: Patients with HF and AF treated with CRT have similar mortality compared with patients in SR. In AF, AVJ ablation in addition to CRT significantly improves overall survival compared with CRT alone, primarily by reducing HF death
Avoiding unnecessary ventricular pacing is associated with reduced incidence of heart failure hospitalizations and persistent atrial fibrillation in pacemaker patients
Aims In bradycardia patients treated with dual-chamber pacing, we aimed to evaluate whether pacing with atrioventricular (AV) delay management [AV hysteresis (AVH)], compared with standard pacing with fixed AV delays, reduces unnecessary ventricular pacing percentage (VPP) and is associated with better clinical outcomes. Main study endpoints were the incidence of heart failure hospitalizations (HFH), persistent atrial fibrillation (AF), and cardiac death. Methods Data from two identical prospective observational studies, BRADYCARE I in the USA and BRADYCARE II in Europe, Africa, and results and Asia, were pooled. Overall, 2592 patients (75 ± 10 years, 45.1% female, 50% with AVH) had complete clinical and device data at 1-year follow-up and were analysed. Primary pacing indication was sinus node disease (SND) in 1177 (45.4%), AV block (AVB) in 974 (37.6%), and other indications in 441 (17.0%) patients. Pacing with AVH, compared with standard pacing, was associated with a lower 1-year incidence of HFH [1.3% vs. 3.1%, relative risk reduction (RRR) 57.5%, P = 0.002] and of persistent AF (5.3% vs. 7.7%, RRR = 31.1%, P = 0.028). Cardiac mortality was not different between groups (1.0% vs. 1.4%, RRR = 27.8%, P = 0.366). Pacing with AVH, compared with standard pacing, was associated with a lower (P < 0.001) median VPP in all patients (7% vs. 75%), in SND (3% vs. 44%), in AVB (25% vs. 98%), and in patients with other pacing indications (3% vs. 47%).Conclusion Cardiac pacing with AV delay management via AVH is associated with reduced 1-year incidence of HFH and persistent AF, most likely due to a reduction in VPP compared to standard pacing
Scientific prospects in soft gamma-ray astronomy enabled by the LAUE project
This paper summarizes the development of a successful project, LAUE,
supported by the Italian Space Agency (ASI) and devoted to the development of
long focal length (up to 100 m) Laue lenses for hard X--/soft gamma--ray
astronomy (80-600 keV). The apparatus is ready and the assembling of a
prototype lens petal is ongoing. The great achievement of this project is the
use of bent crystals. From measurements obtained on single crystals and from
simulations, we have estimated the expected Point Spread Function and thus the
sensitivity of a lens made of petals. The expected sensitivity is a few
photons cm s keV. We discuss a number of
open astrophysical questions that can settled with such an instrument aboard a
free-flying satellite.Comment: 17 pages, 18 figures, published in Proceedings of the SPIE, Volume
8861, id. 886106 17 pp. (2013
Development and validation of a clinical index to predict survival after cardiac resynchronisation therapy
To develop and validate a prognostic risk index of cardiovascular mortality after cardiac resynchronisation therapy (CRT)
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