2,486 research outputs found
Properties of Faint Distant Galaxies as seen through Gravitational Telescopes
This paper reviews the most recent developments related to the use of lensing
clusters of galaxies as Gravitational Telescopes in deep Universe studies. We
summarize the state of the art and the most recent results aiming at studying
the physical properties of distant galaxies beyond the limits of conventional
spectroscopy. The application of photometric redshift techniques in the context
of gravitational lensing is emphasized for the study of both lensing structures
and the background population of lensed galaxies. A presently ongoing search
for the first building blocks of galaxies behind lensing clusters is presented
and discussed.Comment: Review lecture given at "Gravitational Lensing: a unique tool for
cosmology",Aussois, France, January 2003. To appear in ASP Conf. S., eds. D.
Valls-Gabaud & J.-P. Kneib, 26 pages, 8 figure
Constraints on cosmic-ray efficiency in the supernova remnant RCW 86 using multi-wavelength observations
Several young supernova remnants (SNRs) have recently been detected in the
high-energy and very-high-energy gamma-ray domains. As exemplified by RX
J1713.7-3946, the nature of this emission has been hotly debated, and direct
evidence for the efficient acceleration of cosmic-ray protons at the SNR shocks
still remains elusive. We analyzed more than 40 months of data acquired by the
Large Area Telescope (LAT) on-board the Fermi Gamma-Ray Space Telescope in the
HE domain, and gathered all of the relevant multi-wavelength (from radio to VHE
gamma-rays) information about the broadband nonthermal emission from RCW 86.
For this purpose, we re-analyzed the archival X-ray data from the ASCA/Gas
Imaging Spectrometer (GIS), the XMM-Newton/EPIC-MOS, and the RXTE/Proportional
Counter Array (PCA). Beyond the expected Galactic diffuse background, no
significant gamma-ray emission in the direction of RCW 86 is detected in any of
the 0.1-1, 1-10 and 10-100 GeV Fermi-LAT maps. In the hadronic scenario, the
derived HE upper limits together with the HESS measurements in the VHE domain
can only be accommodated by a spectral index Gamma <= 1.8, i.e. a value
in-between the standard (test-particle) index and the asymptotic limit of
theoretical particle spectra in the case of strongly modified shocks. The
interpretation of the gamma-ray emission by inverse Compton scattering of high
energy electrons reproduces the multi-wavelength data using a reasonable value
for the average magnetic field of 15-25 muG. For these two scenarios, we
assessed the level of acceleration efficiency. We discuss these results in the
light of existing estimates of the magnetic field strength, the effective
density and the acceleration efficiency in RCW 86.Comment: Accepted for publication in A&A; 10 pages and 4 figure
Detecting stable massive neutral particles through particle lensing
Stable massive neutral particles emitted by astrophysical sources undergo
deflection under the gravitational potential of our own galaxy. The deflection
angle depends on the particle velocity and therefore non-relativistic particles
will be deflected more than relativistic ones. If these particles can be
detected through neutrino telescopes, cosmic ray detectors or directional dark
matter detectors, their arrival directions would appear aligned on the sky
along the source-lens direction. On top of this deflection, the arrival
direction of non-relativistic particles is displaced with respect to the
relativistic counterpart also due to the relative motion of the source with
respect to the observer; this induces an alignment of detections along the sky
projection of the source trajectory. The final alignment will be given by a
combination of the directions induced by lensing and source proper motion. We
derive the deflection-velocity relation for the Milky Way halo and suggest that
searching for alignments on detection maps of particle telescopes could be a
way to find new particles or new astrophysical phenomena.Comment: 17 pages, 7 figures. Accepted by PR
WMAP data and the curvature of space
Inter alia, the high precision WMAP data on Cosmic Microwave Background
Radiation marginally indicate that the universe has positively curved (and
hence spherical) spatial sections. In this paper, we take this data seriously
and consider some of the consequences for the background dynamics. In
particular, we show that this implies a limit to the number of e-foldings that
could have taken place in the inflationary epoch; however this limit is
consistent with some inflationary models that solve all the usual cosmological
problems and are consistent with standard structure formation theory.Comment: 4 pages, 2 figure
Congenital tibial deficiencies: Treatment using the Ilizarov's external fixator
SummaryIntroductionCongenital longitudinal deficiency of the tibia is a rare and often syndromic anomaly. Amputation is usually the preferred treatment option in complete absence of the tibia; however, a conservative management might be implemented in partial forms or in case of amputation refusal. Our experience with the Ilizarov fixator, convinced us this device was the best suited for progressive correction of lower limbs length discrepancies and articular or bone angular limb deformities (ALD). The aim of this study is to highlight the interest of the Ilizarov fixator in the multistage conservative treatment of congenital tibial deficiencies.Material and methodsA retrospective study was conducted in nine patients suffering from Type I or II congenital tibial deficiencies (Jones) and sequentially managed using the Ilizarov technique. The functional outcome after treatment completion was then clinically assessed.ResultsThe different stages of correction were recorded for each individual patient. Patients were assessed at a mean follow-up of 18,3 years (4–32 years). The mean maximum knee flexion was 35° (0°–90°) in type I deficiencies and 118° (90°–140°) in type II deficiencies. One patient underwent amputation and a bilateral knee arthrodesis was performed in another case.DiscussionFew series in the literature report a comparable length of follow-up period in the conservative management of severe congenital tibial deficiencies. In our study, the Ilizarov fixator provided satisfactory progressive corrections of severe congenital tibial deficiencies.Level of EvidenceLevel IV therapeutic retrospective study
A critical approach to the concept of a polar, low-altitude LARES satellite
According to very recent developments of the LARES mission, which would be
devoted to the measurement of the general relativistic Lense--Thirring effect
in the gravitational field of the Earth with Satellite Laser Ranging, it seems
that the LARES satellite might be finally launched in a polar, low--altitude
orbit by means of a relatively low--cost rocket. The observable would be the
node only. In this letter we critically analyze this scenario.Comment: LaTex2e, 11 pages, 4 figures, 1 table. Accepted for publication in
Classical and Quantum Gravit
A time frequency analysis of wave packet fractional revivals
We show that the time frequency analysis of the autocorrelation function is,
in many ways, a more appropriate tool to resolve fractional revivals of a wave
packet than the usual time domain analysis. This advantage is crucial in
reconstructing the initial state of the wave packet when its coherent structure
is short-lived and decays before it is fully revived. Our calculations are
based on the model example of fractional revivals in a Rydberg wave packet of
circular states. We end by providing an analytical investigation which fully
agrees with our numerical observations on the utility of time-frequency
analysis in the study of wave packet fractional revivals.Comment: 9 pages, 4 figure
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