250 research outputs found
A cellular iterative and asynchronous motion algorithm
The growth of visual communication involves needs for image compression that are more and more important . It seems that futu r
coders will be based on the structural and semantic relevance of the image contents into play, instead of classical information -
theoretic waveform coding .
In this work we apply theoretic concept of Markov modelisation and mean field annealing to the motion analysis problem . Ou r
aim is to obtain a motion estimation algorithm highly parallelisable and dedicated, first, to error prediction minimization an d
second, to motion analysis problem . We obtain a cellular and iterative algorithm . Such an algorithm can be implemented on array
processors with locally mesh connections.
The second part of this work is based on asynchronous iteration . This iteration mode is very suitable for architectural problem . We
will see that the convergence of the algorithm in this iteration mode is verified . This part is an illustration of benefits of algorithm s
and architectures interactions .La communication visuelle est en pleine expansion, l'avènement du multimédia et ses besoins en images dynamisent fortement la recherche dans les domaines du codage et de la compression d'images. Il semble que les codeurs futurs seront basés sur des techniques de codage par modèles. Il s'agit à ce niveau essentiellement d'analyse et de synthèse d'images. Cependant toute analyse d'images dépend de primitives utilisant les caractéristiques obtenues par des traitements d'images dits de « bas-niveau » (ou niveau pixel), en particulier l'estimation de mouvement est une primitive de traitement bas-niveau extrèmement importante dans le domaine du codage d'images. Une première partie de cet article est consacrée à l'étude d'un algorithme cellulaire et itératif d'estimation de mouvement, algorithme développé à partir d'une modélisation markovienne du champs de vecteurs mouvement et d'une méthode de relaxation déterministe. Nous montrons qu'il est possible d'obtenir un champ de vecteurs mouvement apportant un très bon compromis entre la minimisation de l'erreur de prédiction et la cohérence du champ de vecteurs (critères à prendre en compte pour respectivement la réduction de l'information temporelle dans les codeurs classiques, ou l'analyse de scène dans les nouveaux codeurs). La seconde partie décrit l'étude de cet algorithme d'estimation de mouvement dans un mode de fonctionnement peu ordinaire qui est l'asynchronisme. Ce mode peut être particulièrement intéressant si on vise une implémentation massivement parallèle d'un tel algorithme. L'asynchronisme possède des atouts architecturaux irréfutables et, nous le verrons, des atouts fonctionnels intéressants, montrant ainsi que l'étroite adéquation algorithmes-architectures est très importante et souvent bénéfique
Interferometric Observatories in Earth Orbit
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76217/1/AIAA-1728-623.pd
Limits on Stellar and Planetary Companions in Microlensing Event OGLE-1998-BUL-14
We present the PLANET photometric data set for \ob14, a high magnification
() event alerted by the OGLE collaboration toward the
Galactic bulge in 1998. The PLANET data set consists a total of 461 I-band and
139 band points, the majority of which was taken over a three month period.
The median sampling interval during this period is about 1 hour, and the
scatter over the peak of the event is 1.5%. The excellent data
quality and high maximum magnification of this event make it a prime candidate
to search for the short duration, low amplitude perturbations that are
signatures of a planetary companion orbiting the primary lens. The observed
light curve for \ob14 is consistent with a single lens (no companion) within
photometric uncertainties. We calculate the detection efficiency of the light
curve to lensing companions as a function of the mass ratio and angular
separation of the two components. We find that companions of mass ratio are ruled out at the 95% confidence level for projected separations
between 0.4-2.4 \re, where \re is the Einstein ring radius of the primary
lens. Assuming that the primary is a G-dwarf with \re\sim3 {\rm AU} our
detection efficiency for this event is for a companion with the mass
and separation of Jupiter and for a companion with the mass and
separation of Saturn. Our efficiencies for planets like those around Upsilon
And and 14 Her are > 75%.Comment: Data available at http://www.astro.rug.nl/~planet/planetpapers.html
20 pages, 10 figures. Minor changes. ApJ, accepte
A Complete Set of Solutions For Caustic-Crossing Binary Microlensing Events
We present a method to analyze binary-lens microlensing light curves with one
well-sampled fold caustic crossing. In general, the surface of chi^2 shows
extremely complicated behavior over the 9-parameter space that characterizes
binary lenses. This makes it difficult to systematically search the space and
verify that a given local minimum is a global minimum. We show that for events
with well-monitored caustics, the caustic-crossing region can be isolated from
the rest of the light curve and easily fit to a 5-parameter function. Four of
these caustic-crossing parameters can then be used to constrain the search in
the larger 9-parameter space. This allows a systematic search for all solutions
and thus identification of all local minima. We illustrate this technique using
the PLANET data for MACHO 98-SMC-1, an excellent and publicly available
caustic-crossing data set. We show that a very broad range of parameter
combinations are compatible with the PLANET data set, demonstrating that
observations of binary-lens lightcurves with sampling of only one caustic
crossing do not yield unique solutions. The corollary to this is that the time
of the second caustic crossing cannot be reliably predicted on the basis of
early data including the first caustic crossing alone. We investigate the
requirements for determination of a unique solution and find that occasional
observations of the first caustic crossing may be sufficient to derive a
complete solution.Comment: 31 pages + 8 figures + 2 table
OGLE-2005-BLG-153: Microlensing Discovery and Characterization of A Very Low Mass Binary
The mass function and statistics of binaries provide important diagnostics of
the star formation process. Despite this importance, the mass function at low
masses remains poorly known due to observational difficulties caused by the
faintness of the objects. Here we report the microlensing discovery and
characterization of a binary lens composed of very low-mass stars just above
the hydrogen-burning limit. From the combined measurements of the Einstein
radius and microlens parallax, we measure the masses of the binary components
of and . This discovery
demonstrates that microlensing will provide a method to measure the mass
function of all Galactic populations of very low mass binaries that is
independent of the biases caused by the luminosity of the population.Comment: 6 pages, 3 figures, 1 tabl
OGLE-2005-BLG-071Lb, the Most Massive M-Dwarf Planetary Companion?
We combine all available information to constrain the nature of
OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first
in a high-magnification event. These include photometric and astrometric
measurements from Hubble Space Telescope, as well as constraints from higher
order effects extracted from the ground-based light curve, such as microlens
parallax, planetary orbital motion and finite-source effects. Our primary
analysis leads to the conclusion that the host of Jovian planet
OGLE-2005-BLG-071Lb is an M dwarf in the foreground disk with mass M= 0.46 +/-
0.04 Msun, distance D_l = 3.3 +/- 0.4 kpc, and thick-disk kinematics v_LSR ~
103 km/s. From the best-fit model, the planet has mass M_p = 3.8 +/- 0.4 M_Jup,
lies at a projected separation r_perp = 3.6 +/- 0.2 AU from its host and so has
an equilibrium temperature of T ~ 55 K, i.e., similar to Neptune. A degenerate
model less favored by \Delta\chi^2 = 2.1 (or 2.2, depending on the sign of the
impact parameter) gives similar planetary mass M_p = 3.4 +/- 0.4 M_Jup with a
smaller projected separation, r_\perp = 2.1 +/- 0.1 AU, and higher equilibrium
temperature T ~ 71 K. These results from the primary analysis suggest that
OGLE-2005-BLG-071Lb is likely to be the most massive planet yet discovered that
is hosted by an M dwarf. However, the formation of such high-mass planetary
companions in the outer regions of M-dwarf planetary systems is predicted to be
unlikely within the core-accretion scenario. There are a number of caveats to
this primary analysis, which assumes (based on real but limited evidence) that
the unlensed light coincident with the source is actually due to the lens, that
is, the planetary host. However, these caveats could mostly be resolved by a
single astrometric measurement a few years after the event.Comment: 51 pages, 12 figures, 3 tables, Published in Ap
H-alpha Equivalent Width Variations across the Face of a Microlensed K Giant in the Galactic Bulge
We present VLT FORS1 spectroscopy that temporally resolves the second caustic
crossing of the Bulge K giant source of microlensing event EROS 2000-BLG-5, the
first time this has been accomplished for several phases of a caustic transit.
The ~1 angstrom H-alpha equivalent width of the source star increases slightly
as the center of the star egresses the caustic and then plummets by 30% during
the final limb crossing. These changes are not seen in contemporaneous spectra
of control stars in the FORS1 slit, but are qualitatively consistent with
expectations from stellar atmosphere models as the caustic differentially
magnifies different portions of the stellar face of the target. Observations
such as these in a variety of stellar lines are equivalent to atmospheric
tomography and are expected to provide a direct test of stellar models.Comment: 15 pages, including 1 table and 4 figures. As accepted by ApJ
Letters, vol 55
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