784 research outputs found
(e,3e) on helium at low impact energy: the strongly correlated three-electron continuum
Double ionization of the helium atom by slow electron impact (E0=106 eV) is studied in a kinematically complete experiment. Because of a low excess energy Eexc=27 eV above the double ionization threshold, a strongly correlated three-electron continuum is realized. This is demonstrated by measuring and calculating the fully differential cross sections for equal energy sharing of the final-state electrons. While the electron emission is dominated by a strong Coulomb repulsion, also signatures of more complex dynamics of the full four-body system are identified
INTEGRAL observations of the Large Magellanic Cloud region
We present the preliminary results of the INTEGRAL survey of the Large
Magellanic Cloud. The observations have been carried out in January 2003 (about
10^6 s) and January 2004 (about 4x10^5 s). Here we concentrate on the bright
sources LMC X-1, LMC X-2, LMC X-3 located in our satellite galaxy, and on the
serendipitous detections of the Galactic Low Mass X-ray Binary EXO 0748-676 and
of the Seyfert 2 galaxy IRAS 04575-7537.Comment: 4 pages, 7 figures. To be published in the Proceedings of the 5th
INTEGRAL Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munic
The Microchannel X-ray Telescope on Board the SVOM Satellite
We present the Micro-channel X-ray Telescope (MXT), a new narrow-field (about
1{\deg}) telescope that will be flying on the Sino-French SVOM mission
dedicated to Gamma-Ray Burst science, scheduled for launch in 2021. MXT is
based on square micro pore optics (MPOs), coupled with a low noise CCD. The
optics are based on a "Lobster Eye" design, while the CCD is a focal plane
detector similar to the type developed for the seven eROSITA telescopes. MXT is
a compact and light (<35 kg) telescope with a 1 m focal length, and it will
provide an effective area of about 45 cmsq on axis at 1 keV. The MXT PSF is
expected to be better than 4.2 arc min (FWHM) ensuring a localization accuracy
of the afterglows of the SVOM GRBs to better than 1 arc min (90\% c.l. with no
systematics) provided MXT data are collected within 5 minutes after the
trigger. The MXT sensitivity will be adequate to detect the afterglows for
almost all the SVOM GRBs as well as to perform observations of non-GRB
astrophysical objects. These performances are fully adapted to the SVOM science
goals, and prove that small and light telescopes can be used for future small
X-ray missions.Comment: 6 pages, 6 figures, proceedings of the conference "Swift: 10 years of
Discovery", Rome, December 2-5, 2014. To be published by Po
The Microchannel X-ray Telescope for the Gamma-Ray Burst mission SVOM
We present the Microchannel X-ray Telescope, a new light and compact
focussing telescope that will be flying on the Sino-French SVOM mission
dedicated to Gamma-Ray Burst science. The MXT design is based on the coupling
of square pore micro-channel plates with a low noise pnCCD. MXT will provide an
effective area of about 50 cmsq, and its point spread function is expected to
be better than 3.7 arc min (FWHM) on axis. The estimated sensitivity is
adequate to detect all the afterglows of the SVOM GRBs, and to localize them to
better then 60 arc sec after five minutes of observation.Comment: 12 pages, 8 figures, to be published in SPIE Astronomical Telescopes
+ Instrumentation, Montreal, June 201
Short GRBs at the dawn of the gravitational wave era
We derive the luminosity function and redshift distribution of short Gamma
Ray Bursts (SGRBs) using (i) all the available observer-frame constraints (i.e.
peak flux, fluence, peak energy and duration distributions) of the large
population of Fermi SGRBs and (ii) the rest-frame properties of a complete
sample of Swift SGRBs. We show that a steep with a>2.0
is excluded if the full set of constraints is considered. We implement a Monte
Carlo Markov Chain method to derive the and functions
assuming intrinsic Ep-Liso and Ep-Eiso correlations or independent
distributions of intrinsic peak energy, luminosity and duration. To make our
results independent from assumptions on the progenitor (NS-NS binary mergers or
other channels) and from uncertainties on the star formation history, we assume
a parametric form for the redshift distribution of SGRBs. We find that a
relatively flat luminosity function with slope ~0.5 below a characteristic
break luminosity ~3 erg/s and a redshift distribution of SGRBs
peaking at z~1.5-2 satisfy all our constraints. These results hold also if no
Ep-Liso and Ep-Eiso correlations are assumed. We estimate that, within ~200 Mpc
(i.e. the design aLIGO range for the detection of GW produced by NS-NS merger
events), 0.007-0.03 SGRBs yr should be detectable as gamma-ray events.
Assuming current estimates of NS-NS merger rates and that all NS-NS mergers
lead to a SGRB event, we derive a conservative estimate of the average opening
angle of SGRBs: ~3-6 deg. Our luminosity function implies an
average luminosity L~1.5 erg/s, nearly two orders of magnitude
higher than previous findings, which greatly enhances the chance of observing
SGRB "orphan" afterglows. Efforts should go in the direction of finding and
identifying such orphan afterglows as counterparts of GW events.Comment: 13 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysics. Figure 5 and angle ranges corrected in revised versio
Validation of multi-body models for simulation in authorisation of rail vehicles
An application of multi-body simulations is to reduce the amount of vehicle on-track testing and present an opportunity for saving the time and costs of vehicle acceptance in regard to running characteristics. One of the objectives of the EU project DynoTRAIN was to define criteria and limits for vehicle model validation. The paper presents investigations carried out by comparing simulations with measurements from a testing campaign using a test train with 4 types of vehicles and a total of 10 force measuring wheelsets and accompanied with continuous measurement of track irregularities and rail profiles. The simulations were performed by using several vehicle models, built in different simulation tools by different partners. The results of the investigations and the criteria and limits proposed for the validation of multi-body vehicle models, intended for simulations of on-track tests, in the framework of railway vehicle authorisations are presented.Une application des simulations multi-corps consiste à réduire la quantité d'essais en ligne et à offrir une opportunité pour économiser le temps et les coûts d'acceptation des Îhicules en ce qui concerne les caractéristiques de fonctionnement dynamiques. L'un des objectifs du projet de l'UE DynoTRAIN était de définir des critères et des limites pour la validation du modèle de Îhicule. Le document présente des recherches effectuées en comparant des simulations avec des mesures à partir d'une campagne de test utilisant un train d'essai avec 4 types de Îhicules et un total de 10 essieux de mesure de force roue-rail et accompagnés d'une mesure continue des irrégularités de voie et des profils de rail. Les simulations ont été réalisées en utilisant plusieurs modèles de Îhicules, construits dans différents outils de simulation par différents partenaires. Les résultats des enquêtes et les critères et limites proposés pour la validation des modèles de Îhicules multi-corps, destinés à des simulations de tests sur voie réelle, dans le cadre des autorisations de Îhicules ferroviaires sont présentés
Genital Chlamydia Prevalence in Europe and Non-European High Income Countries: Systematic Review and Meta-Analysis
Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes
Quantum dots defined in carbon nanotubes are a platform for both basic
scientific studies and research into new device applications. In particular,
they have unique properties that make them attractive for studying the coherent
properties of single electron spins. To perform such experiments it is
necessary to confine a single electron in a quantum dot with highly tunable
barriers, but disorder has until now prevented tunable nanotube-based
quantum-dot devices from reaching the single-electron regime. Here, we use
local gate voltages applied to an ultra-clean suspended nanotube to confine a
single electron in both a single quantum dot and, for the first time, in a
tunable double quantum dot. This tunability is limited by a novel type of
tunnelling that is analogous to that in the Klein paradox of relativistic
quantum mechanics.Comment: 21 pages including supplementary informatio
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