1,077 research outputs found
Coupling MOAO with Integral Field Spectroscopy: specifications for the VLT and the E-ELT
[Abridged] We have developed an end-to-end simulation to specify the science
requirements of a MOAO-fed integral field spectrograph on either an 8m or 42m
telescope. Our simulations re-scales observations of local galaxies or results
from numerical simulations of disk or interacting galaxies. For the current
analysis, we limit ourselves to a local disk galaxy which exhibits simple
rotation and a simulation of a merger. We have attempted to generalize our
results by introducing the simple concepts of "PSF contrast" which is the
amount of light polluting adjacent spectra which we find drives the smallest EE
at a given spatial scale. The choice of the spatial sampling is driven by the
"scale-coupling", i.e., the relationship between the IFU pixel scale and the
size of the features that need to be recovered by 3D spectroscopy in order to
understand the nature of the galaxy and its substructure. Because the dynamical
nature of galaxies are mostly reflected in their large-scale motions, a
relatively coarse spatial resolution is enough to distinguish between a
rotating disk and a major merger. Although we used a limited number of
morpho-kinematic cases, our simulations suggest that, on a 42m telescope, the
choice of an IFU pixel scale of 50-75 mas seems to be sufficient. Such a coarse
sampling has the benefit of lowering the exposure time to reach a specific
signal-to-noise as well as relaxing the performance of the MOAO system. On the
other hand, recovering the full 2D-kinematics of z~4 galaxies requires high
signal-to-noise and at least an EE of 34% in 150 mas (2 pixels of 75 mas).
Finally, we carried out a similar study at z=1.6 with a MOAO-fed spectrograph
for an 8m, and find that at least an EE of 30% at 0.25 arcsec spatial sampling
is required to understand the nature of disks and mergers.Comment: 17 pages, 20 figures, accepted for publication in the MNRA
The Physics and Mass Assembly of distant galaxies with the E-ELT
One of the main science goal of the future European Extremely Large Telescope
will be to understand the mass assembly process in galaxies as a function of
cosmic time. To this aim, a multi-object, AO-assisted integral field
spectrograph will be required to map the physical and chemical properties of
very distant galaxies. In this paper, we examine the ability of such an
instrument to obtain spatially resolved spectroscopy of a large sample of
massive (0.1<Mstellar<5e11Mo) galaxies at 2<z<6, selected from future large
area optical-near IR surveys. We produced a set of about one thousand numerical
simulations of 3D observations using reasonable assumptions about the site,
telescope, and instrument, and about the physics of distant galaxies. These
data-cubes were analysed as real data to produce realistic kinematic
measurements of very distant galaxies. We then studied how sensible the
scientific goals are to the observational (i.e., site-, telescope-, and
instrument-related) and physical (i.e., galaxy-related) parameters. We
specifically investigated the impact of AO performance on the science goal. We
did not identify any breaking points with respect to the parameters (e.g., the
telescope diameter), with the exception of the telescope thermal background,
which strongly limits the performance in the highest (z>5) redshift bin. We
find that a survey of Ngal galaxies that fulfil the range of science goals can
be achieved with a ~90 nights program on the E-ELT, provided a multiplex
capability M Ngal/8.Comment: 21 pages, 13 figures, 7 tables. Accepted for publication in MNRA
Hydrologie et météorologie de méso-échelle dans HAPEX-Sahel : dispositif de mesures au sol et premiers résultats
Cet article décrit les mesures météorologiques d'encadrement de l'expérience HAPEX-Sahel. Il s'agit principalement : a) des moyens de radiosondages venant compléter la station OMM de Niamey, destinés à suivre l'évolution de la structure de la couche limite, et à dériver les paramètres nécessaires aux corrections atmosphériques des données télédétectées ; b) d'un réseau de douze stations automatiques, permettant d'estimer la variabilité des paramètres météorologiques et d'interpréter les flux à méso-échelle. (Résumé d'auteur
Remote sensing techniques in the mapping of vegetation and their application to runoff evolution in burnt areas
South of experimental forested catchments named "Réal Collo- brier" was destroyed by fire in August 1990. Partially or entirely bumt catchments became an interesting field to study links between vegetation and runoff. An experimental program was built on two axis : - use of remote sensing techniques to map limits of bumt areas and recovery of vegetation, year after year.- link between vegetation and runoff. The first investigations were done on two bumt catchments (Rimbaud and Meffrey), using a runoff model fitted with data before fire. This model has permitted to compare new data (observed after fire) with the ones we would have observed without fire, for the months just after fire (1990, direct effect of fire) and the year after (1991, effect of vegetation recovery
Remote sensing techniques in the mapping of vegetation and their application to runoff evolution in burnt areas
South of experimental forested catchments named "Réal Collo- brier" was destroyed by fire in August 1990. Partially or entirely bumt catchments became an interesting field to study links between vegetation and runoff. An experimental program was built on two axis : - use of remote sensing techniques to map limits of bumt areas and recovery of vegetation, year after year.- link between vegetation and runoff. The first investigations were done on two bumt catchments (Rimbaud and Meffrey), using a runoff model fitted with data before fire. This model has permitted to compare new data (observed after fire) with the ones we would have observed without fire, for the months just after fire (1990, direct effect of fire) and the year after (1991, effect of vegetation recovery
Update on the ICUD-SIU consultation on multi-parametric magnetic resonance imaging in localised prostate cancer
Introduction: Prostate cancer (PCa) imaging is a rapidly evolving field. Dramatic improvements in prostate MRI during the last decade will probably change the accuracy of diagnosis. This chapter reviews recent current evidence about MRI diagnostic performance and impact on PCa management. Materials and methods: The International Consultation on Urological Diseases nominated a committee to review the literature on prostate MRI. A search of the PubMed database was conducted to identify articles focussed on MP-MRI detection and staging protocols, reporting and scoring systems, the role of MP-MRI in diagnosing PCa prior to biopsy, in active surveillance, in focal therapy and in detecting local recurrence after treatment. Results: Differences in opinion were reported in the use of the strength of magnets [1.5 Tesla (T) vs. 3T] and coils. More agreement was found regarding the choice of pulse sequences; diffusion-weighted MRI (DW-MRI), dynamic contrast-enhanced MRI (DCE MRI), and/or MR spectroscopy imaging (MRSI) are recommended in addition to conventional T2-weighted anatomical sequences. In 2015, the Prostate Imaging Reporting and Data System (PI-RADS version 2) was described to standardize image acquisition and interpretation. MP-MRI improves detection of clinically significant PCa (csPCa) in the repeat biopsy setting or before the confirmatory biopsy in patients considering active surveillance. It is useful to guide focal treatment and to detect local recurrences after treatment. Its role in biopsy-naive patients or during the course of active surveillance remains debated. Conclusion: MP-MRI is increasingly used to improve detection of csPCa and for the selection of a suitable therapeutic approach
Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data
About two-thirds of present-day, large galaxies are spirals such as the Milky
Way or Andromeda, but the way their thin rotating disks formed remains
uncertain. Observations have revealed that half of their progenitors, six
billion years ago, had peculiar morphologies and/or kinematics, which exclude
them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of
similar mass, are found to be the likeliest driver for such strong
peculiarities. However, thin disks are fragile and easily destroyed by such
violent collisions, which creates a critical tension between the observed
fraction of thin disks and their survival within the L-CDM paradigm. Here we
show that the observed high occurrence of mergers amongst their progenitors is
only apparent and is resolved when using morpho-kinematic observations which
are sensitive to all the phases of the merging process. This provides an
original way of narrowing down observational estimates of the galaxy merger
rate and leads to a perfect match with predictions by state-of-the-art L-CDM
semi-empirical models with no particular fine-tuning needed. These results
imply that half of local thin disks do not survive but are actually rebuilt
after a gas-rich major merger occurring in the past nine billion years, i.e.,
two-thirds of the lifetime of the Universe. This emphasizes the need to study
how thin disks can form in halos with a more active merger history than
previously considered, and to investigate what is the origin of the gas
reservoir from which local disks would reform.Comment: 19 pages, 7 figures, 2 tables. Accepted in ApJ. V2 to match proof
corrections and added reference
Preparation and characterization of electrolytic alumina deposit on austenitic stainless steel
Conversion coating modified by alumina has been studied as a way for improving the resistance to thermal oxidation of an austenitic stainless steel. Conversion coating, characterized by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. The influence of the current density and treatment time on alumina deposit was studied using statistical experimental designs like Doehlert uniform shell design. After heating, coatings present a continuous composition gradient with refractory compounds at the surface. The behavior at high temperature (1000 8C) of the alumina coating was investigated. The presence of alumina increases the oxidation resistance of an austenitic stainless steel at 1000 8C. The morphology and the chemical composition of the deposit are analyzed. Results on the thermal stability of coating on austenitic stainless steel are presented
Prostate MRI: Can we do without DCE sequences in 2013?
AbstractMultiparametric MRI (mp-MRI) of the prostate currently provides stable and reproducible performances. The usefulness of dynamic contrast-enhanced (DCE) sequences is currently challenged, as they sometimes only confirm what has already been observed on diffusion-weighted imaging (DWI) and require the additional purchase of a contrast agent. Eliminating these sequences may help accelerate the use of MRI in addition to, or in lieu of, prostate biopsies in selected patients. However, many studies show that these sequences can detect lesions invisible on T2-weighted and diffusion-weighted images, better assess cancer extension and aggressiveness, and finally help detecting recurrence after treatment. We present the various applications of dynamic MRI and discuss the possible consequences of its omission from the current protocol
Remote ischemic preconditioning in patients with intermittent claudication
OBJECTIVE: Remote ischemic preconditioning (RIPC) is a phenomenon in which a short period of sub-lethal ischemia in one organ protects against subsequent bouts of ischemia in another organ. We hypothesized that RIPC in patients with intermittent claudication would increase muscle tissue resistance to ischemia, thereby resulting in an increased ability to walk.
METHODS: In a claudication clinic, 52 ambulatory patients who presented with complaints of intermittent claudication in the lower limbs associated with an absent or reduced arterial pulse in the symptomatic limb and/or an ankle-brachial index <0.90 were recruited for this study. The patients were randomly divided into three groups (A, B and C). All of the patients underwent two tests on a treadmill according to the Gardener protocol. Group A was tested first without RIPC. Group A was subjected to RIPC prior to the second treadmill test. Group B was subjected to RIPC prior to the first treadmill test and then was subjected to a treadmill test without RIPC. In Group C (control group), both treadmill tests were performed without RIPC. The first and second tests were conducted seven days apart. Brazilian Clinical Trials: RBR-7TF6TM.
RESULTS: Group A showed a significant increase in the initial claudication distance in the second test compared to the first test.
CONCLUSION: RIPC increased the initial claudication distance in patients with intermittent claudication; however, RIPC did not affect the total walking distance of the patients
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