85 research outputs found
Extinction controlled adaptive phase-mask coronagraph
Context. Phase-mask coronagraphy is advantageous in terms of inner working
angle and discovery space. It is however still plagued by drawbacks such as
sensitivity to tip-tilt errors and chromatism. A nulling stellar coronagraph
based on the adaptive phase-mask concept using polarization interferometry is
presented in this paper. Aims. Our concept aims at dynamically and
achromatically optimizing the nulling efficiency of the coronagraph, making it
more immune to fast low-order aberrations (tip-tilt errors, focus, ...).
Methods. We performed numerical simulations to demonstrate the value of the
proposed method. The active control system will correct for the detrimental
effects of image instabilities on the destructive interference. The mask
adaptability both in size, phase and amplitude also compensates for
manufacturing errors of the mask itself, and potentially for chromatic effects.
Liquid-crystal properties are used to provide variable transmission of an
annulus around the phase mask, but also to achieve the achromatic {\pi} phase
shift in the core of the PSF by rotating the polarization by 180 degrees.
Results. We developed a new concept and showed its practical advantages using
numerical simulations. This new adaptive implementation of the phase-mask
coronagraph could advantageously be used on current and next-generation
adaptive optics systems, enabling small inner working angles without
compromising contrast.Comment: 7 pages, 6 figure
Robot trajectory planning using OLP and structured light 3D machine vision
This paper proposes a new methodology for robotic offline programming (OLP) addressing the issue of automatic program generation directly from 3D CAD models and verification through online 3D reconstruction. Limitations of current OLP include manufacturing tolerances between CAD and workpieces and inaccuracies in workpiece placement and modelled work cell. These issues are addressed and demonstrated through surface scanning, registration, and global and local error estimation. The method allows the robot to adjust the welding path designed from the CAD model to the actual workpiece. Alternatively, for non-repetitive tasks and where a CAD model is not available, it is possible to interactively define the path online over the scanned surface
An intelligent real time 3D vision system for robotic welding tasks
MARWIN is a top-level robot control system that has been designed for automatic robot welding tasks. It extracts welding parameters and calculates robot trajectories directly from CAD models which are then verified by real-time 3D scanning and registration. MARWIN's 3D computer vision provides a user-centred robot environment in which a task is specified by the user by simply confirming and/or adjusting suggested parameters and welding sequences. The focus of this paper is on describing a mathematical formulation for fast 3D reconstruction using structured light together with the mechanical design and testing of the 3D vision system and show how such technologies can be exploited in robot welding tasks
Extinction controlled Adaptive Mask Coronagraph Lyot and Phase Mask dual concept for wide extinction area
A dual coronagraph based on the Adaptive Mask concept is presented in this paper. A Lyot coronagraph with a variable diameter occulting disk and a nulling stellar coronagraph based on the Adaptive Phase Mask concept using polarization interferometry are presented in this work. Observations on sky and numerical simulations show the usefulness of the proposed method to optimize the nulling efficiency of the coronagraphs. In the case of the phase mask, the active control system will correct for the detrimental effects of image instabilities on the destructive interference (low-order aberrations such as tip-tilt and focus). The phase mask adaptability both in size, phase and amplitude also compensate for manufacturing errors of the mask itself, and potentially for chromatic effects. Liquid-crystal properties are used to provide variable transmission of an annulus around the phase mask, but also to achieve the achromatic π phase shift in the core of the PSF by rotating the polarization by 180°.A compressed mercury (Hg) drop is used as an occulting disk for the Lyot mask, its size control offers an adaptation to the seeing conditions and provides an optimization of the Tip-tilt correction
Preferências estabelecidas e personalidade: uma abordagem comportamental
TCC (graduação) - Universidade Federal de Santa Catarina. Centro Sócio-Econômico. Economia.Este estudo tem o objetivo de contribuir para o entendimento da dissonância cognitiva que surge quando preferências estabelecidas com relação a produtos são alteradas à medida em que os consumidores se deparam com informação mais completa do que a existente na escolha inicial. Buscou-se verificar a probabilidade de abandono da escolha preliminar na amostra de consumidores analisada. A contribuição se refere à mediação da habilidade cognitiva e da personalidade nessas decisões. No experimento, os participantes com fraca preferência na escolha inicial – e baixa habilidade cognitiva, além de baixos escores em traços de honestidade-humildade, extroversão e conscienciosidade – tendem a abandonar a escolha inicial. Já os participantes com escores mais altos em todas essas características tendem a não abandonar a sua escolha preliminar
First results from fringe tracking with the PRIMA fringe sensor unit
The fringe sensor unit (FSU) is the central element of the phase referenced
imaging and micro-arcsecond astrometry (PRIMA) dual-feed facility for the Very
Large Telescope interferometer (VLTI). It has been installed at the Paranal
observatory in August 2008 and is undergoing commissioning and preparation for
science operation. Commissioning observations began shortly after installation
and first results include the demonstration of spatially encoded fringe sensing
and the increase in VLTI limiting magnitude for fringe tracking. However,
difficulties have been encountered because the FSU does not incorporate
real-time photometric correction and its fringe encoding depends on
polarisation. These factors affect the control signals, especially their
linearity, and can disturb the tracking control loop. To account for this,
additional calibration and characterisation efforts are required. We outline
the instrument concept and give an overview of the commissioning results
obtained so far. We describe the effects of photometric variations and
beam-train polarisation on the instrument operation and propose possible
solutions. Finally, we update on the current status in view of the start of
astrometric science operation with PRIMA.Comment: 12 pages, 11 figures, SPIE 2010 conference proceeding
Rubor, calor, dolor, tumor : infections de la peau et des tissus mous [Rubor, calor, dolor, tumor : skin and soft tissue infections]
Skin infections are a frequent cause of consultation, yet the diagnosis can be challenging for physicians. Microbiological documentation is rare, and empiric antibiotic regimens should cover the most commonly identified bacteria, i.e. streptococci Staphylococcus aureus. Other pathogens should be considered in case of immunosuppression or certain exposures. Necrotizing fasciitis (NF) is a severe but rare infection. Early surgical management in parallel with antibiotics is the cornerstone of treatment. Despite the high incidence of these infections, little progress has been made in their management and some areas of uncertainty exist, especially regarding the optimal duration of treatment, the prevention of recurrences and the use of polyclonal immunoglobulins for NF. This article reviews the main aspects of diagnosis and treatment of these infections
The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations
The ESPRI project relies on the astrometric capabilities offered by the PRIMA
facility of the Very Large Telescope Interferometer for the discovery and study
of planetary systems. Our survey consists of obtaining high-precision
astrometry for a large sample of stars over several years and to detect their
barycentric motions due to orbiting planets. We present the operation
principle, the instrument's implementation, and the results of a first series
of test observations. A comprehensive overview of the instrument infrastructure
is given and the observation strategy for dual-field relative astrometry is
presented. The differential delay lines, a key component of the PRIMA facility
which was delivered by the ESPRI consortium, are described and their
performance within the facility is discussed. Observations of bright visual
binaries are used to test the observation procedures and to establish the
instrument's astrometric precision and accuracy. The data reduction strategy
for astrometry and the necessary corrections to the raw data are presented.
Adaptive optics observations with NACO are used as an independent verification
of PRIMA astrometric observations. The PRIMA facility was used to carry out
tests of astrometric observations. The astrometric performance in terms of
precision is limited by the atmospheric turbulence at a level close to the
theoretical expectations and a precision of 30 micro-arcseconds was achieved.
In contrast, the astrometric accuracy is insufficient for the goals of the
ESPRI project and is currently limited by systematic errors that originate in
the part of the interferometer beamtrain which is not monitored by the internal
metrology system. Our observations led to the definition of corrective actions
required to make the facility ready for carrying out the ESPRI search for
extrasolar planets.Comment: 32 pages, 39 figures, Accepted for publication in Astronomy and
Astrophysic
First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
To date, infrared interferometry at best achieved contrast ratios of a few
times on bright targets. GRAVITY, with its dual-field mode, is now
capable of high contrast observations, enabling the direct observation of
exoplanets. We demonstrate the technique on HR8799, a young planetary system
composed of four known giant exoplanets. We used the GRAVITY fringe tracker to
lock the fringes on the central star, and integrated off-axis on the HR8799e
planet situated at 390 mas from the star. Data reduction included
post-processing to remove the flux leaking from the central star and to extract
the coherent flux of the planet. The inferred K band spectrum of the planet has
a spectral resolution of 500. We also derive the astrometric position of the
planet relative to the star with a precision on the order of 100as. The
GRAVITY astrometric measurement disfavors perfectly coplanar stable orbital
solutions. A small adjustment of a few degrees to the orbital inclination of HR
8799 e can resolve the tension, implying that the orbits are close to, but not
strictly coplanar. The spectrum, with a signal-to-noise ratio of
per spectral channel, is compatible with a late-type L brown dwarf. Using
Exo-REM synthetic spectra, we derive a temperature of \,K and a
surface gravity of cm/s. This corresponds to a radius
of and a mass of , which is an independent confirmation of mass estimates from evolutionary
models. Our results demonstrate the power of interferometry for the direct
detection and spectroscopic study of exoplanets at close angular separations
from their stars.Comment: published in A&
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