3,731 research outputs found
Expressing Bayesian Fusion as a Product of Distributions: Application to Randomized Hough Transform
Data fusion is a common issue of mobile robotics, computer assisted
medical diagnosis or behavioral control of simulated character for instance. However
data sources are often noisy, opinion for experts are not known with absolute
precision, and motor commands do not act in the same exact manner on the environment.
In these cases, classic logic fails to manage efficiently the fusion process.
Confronting different knowledge in an uncertain environment can therefore be adequately
formalized in the bayesian framework.
Besides, bayesian fusion can be expensive in terms of memory usage and processing
time. This paper precisely aims at expressing any bayesian fusion process as a
product of probability distributions in order to reduce its complexity. We first study
both direct and inverse fusion schemes. We show that contrary to direct models,
inverse local models need a specific prior in order to allow the fusion to be computed
as a product. We therefore propose to add a consistency variable to each local
model and we show that these additional variables allow the use of a product of the
local distributions in order to compute the global probability distribution over the
fused variable. Finally, we take the example of the Randomized Hough Transform.
We rewrite it in the bayesian framework, considering that it is a fusion process
to extract lines from couples of dots in a picture. As expected, we can find back
the expression of the Randomized Hough Transform from the literature with the
appropriate assumptions
Expressing Bayesian Fusion as a Product of Distributions: Application in Robotics
More and more fields of applied computer
science involve fusion of multiple data sources, such as sensor
readings or model decision. However incompleteness of the
models prevent the programmer from having an absolute
precision over their variables. Therefore bayesian framework
can be adequate for such a process as it allows handling of
uncertainty.We will be interested in the ability to express any
fusion process as a product, for it can lead to reduction of
complexity in time and space. We study in this paper various
fusion schemes and propose to add a consistency variable to
justify the use of a product to compute distribution over the
fused variable. We will then show application of this new
fusion process to localization of a mobile robot and obstacle
avoidance
Eclipses of the inner satellites of Jupiter observed in 2015
During the 2014-2015 campaign of mutual events, we recorded ground-based
photometric observations of eclipses of Amalthea (JV) and, for the first time,
Thebe (JXIV) by the Galilean moons. We focused on estimating whether the
positioning accuracy of the inner satellites determined with photometry is
sufficient for dynamical studies. We observed two eclipses of Amalthea and one
of Thebe with the 1 m telescope at Pic du Midi Observatory using an IR filter
and a mask placed over the planetary image to avoid blooming features. A third
observation of Amalthea was taken at Saint-Sulpice Observatory with a 60 cm
telescope using a methane filter (890 nm) and a deep absorption band to
decrease the contrast between the planet and the satellites. After background
removal, we computed a differential aperture photometry to obtain the light
flux, and followed with an astrometric reduction. We provide astrometric
results with an external precision of 53 mas for the eclipse of Thebe, and 20
mas for that of Amalthea. These observation accuracies largely override
standard astrometric measurements. The (O-C)s for the eclipse of Thebe are 75
mas on the X-axis and 120 mas on the Y-axis. The (O-C)s for the total eclipses
of Amalthea are 95 mas and 22 mas, along the orbit, for two of the three
events. Taking into account the ratio of (O-C) to precision of the astrometric
results, we show a significant discrepancy with the theory established by
Avdyushev and Ban'shikova in 2008, and the JPL JUP 310 ephemeris.Comment: 7 pages, 10 figures, 4 table
GRB 110205A: Anatomy of a long gamma-ray burst
The Swift burst GRB 110205A was a very bright burst visible in the Northern
hemisphere. GRB 110205A was intrinsically long and very energetic and it
occurred in a low-density interstellar medium environment, leading to delayed
afterglow emission and a clear temporal separation of the main emitting
components: prompt emission, reverse shock, and forward shock. Our observations
show several remarkable features of GRB 110205A : the detection of prompt
optical emission strongly correlated with the BAT light curve, with no temporal
lag between the two ; the absence of correlation of the X-ray emission compared
to the optical and high energy gamma-ray ones during the prompt phase ; and a
large optical re-brightening after the end of the prompt phase, that we
interpret as a signature of the reverse shock. Beyond the pedagogical value
offered by the excellent multi-wavelength coverage of a GRB with temporally
separated radiating components, we discuss several questions raised by our
observations: the nature of the prompt optical emission and the spectral
evolution of the prompt emission at high-energies (from 0.5 keV to 150 keV) ;
the origin of an X-ray flare at the beginning of the forward shock; and the
modeling of the afterglow, including the reverse shock, in the framework of the
classical fireball model.Comment: 21 pages, 5 figure (all in colors), accepted for publication in Ap
Dark matter directional detection with MIMAC
MiMac is a project of micro-TPC matrix of gaseous (He3, CF4) chambers for
direct detection of non-baryonic dark matter. Measurement of both track and
ionization energy will allow the electron-recoil discrimination, while access
to the directionnality of the tracks will open a unique way to distinguish a
geniune WIMP signal from any background. First reconstructed tracks of 5.9 keV
electrons are presented as a proof of concept.Comment: 4 pages, proc. of the 44th Rencontres De Moriond: Electroweak
Interactions And Unified Theories, 7-14 Mar 2009, La Thuile, Ital
Impact of minority concentration on fundamental (H)D ICRF heating performance in JET-ILW
ITER will start its operation with non-activated hydrogen and helium plasmas at a reduced magnetic field of B-0 = 2.65 T. In hydrogen plasmas, the two ion cyclotron resonance frequency (ICRF) heating schemes available for central plasma heating (fundamental H majority and 2nd harmonic He-3 minority ICRF heating) are likely to suffer from relatively low RF wave absorption, as suggested by numerical modelling and confirmed by previous JET experiments conducted in conditions similar to those expected in ITER's initial phase. With He-4 plasmas, the commonly adopted fundamental H minority heating scheme will be used and its performance is expected to be much better. However, one important question that remains to be answered is whether increased levels of hydrogen (due to e. g. H pellet injection) jeopardize the high performance usually observed with this heating scheme, in particular in a full-metal environment. Recent JET experiments performed with the ITER-likewall shed some light onto this question and the main results concerning ICRF heating performance in L-mode discharges are summarized here
Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations
The prediction of stellar occultations by Transneptunian objects and Centaurs
is a difficult challenge that requires accuracy both in the occulted star
position as for the object ephemeris. Until now, the most used method of
prediction involving tens of TNOs/Centaurs was to consider a constant offset
for the right ascension and for the declination with respect to a reference
ephemeris. This offset is determined as the difference between the most recent
observations of the TNO and the reference ephemeris. This method can be
successfully applied when the offset remains constant with time. This paper
presents an alternative method of prediction based on a new accurate orbit
determination procedure, which uses all the available positions of the TNO from
the Minor Planet Center database plus sets of new astrometric positions from
unpublished observations. The orbit determination is performed through a
numerical integration procedure (NIMA), in which we develop a specific
weighting scheme. The NIMA method was applied for 51 selected TNOs/Centaurs.
For this purpose, we have performed about 2900 new observations during
2007-2014. Using NIMA, we succeed in predicting the stellar occultations of 10
TNOs and 3 Centaurs between 2013 and 2015. By comparing the NIMA and JPL
ephemerides, we highlighted the variation of the offset between them with time.
Giving examples, we show that the constant offset method could not accurately
predict 6 out of the 13 observed positive occultations successfully predicted
by NIMA. The results indicate that NIMA is capable of efficiently refine the
orbits of these bodies. Finally, we show that the astrometric positions given
by positive occultations can help to further refine the orbit of the TNO and
consequently the future predictions. We also provide the unpublished
observations of the 51 selected TNOs and their ephemeris in a usable format by
the SPICE library.Comment: 12 pages, 9 figures, accepted in A&
Component-resolved diagnosis of pollen allergy based on skin testing with profilin, polcalcin and lipid transfer protein pan-allergens
BACKGROUND Allergy diagnosis needs to be improved in patients suffering from pollen polysensitization due to the existence of possible confounding factors in this type of patients. OBJECTIVE To evaluate new diagnostic strategies by comparing skin responses to pan-allergens and conventional allergenic extracts with specific IgE (sIgE) to purified allergen molecules. METHODS One thousand three hundred and twenty-nine pollen-allergic patients were diagnosed by a combination of an in vitro method with a panel of 13 purified allergens, including major allergens and pan-allergens, using a high-capacity screening technology (ADVIA-Centaur®) and skin prick test (SPT) to pan-allergens and conventional extracts. RESULTS There was a high concordance (κ index) between in vitro (sIgE to major allergens) and in vivo (SPT to conventional extracts) methods in patients who were not sensitized to pan-allergens, but SPT with conventional extracts failed to diagnose patients with sensitization to pan-allergens. In patients who were simultaneously sensitized to polcalcins and profilins, there was a duplication both in the number of sensitizations to major allergens and in the years of disease evolution. There was a statistical association between sensitization to profilins and/or lipid transfer proteins and food allergy (P<0.0001). CONCLUSION The novel diagnostic strategy has proven to be a valuable tool in daily clinical practice. Introduction of routine SPT to pan-allergens is a simple and feasible way of improving diagnostic efficacy. Patients sensitized to pan-allergens should be tested by an adequate panel of allergenic molecules in order to identify the allergens that are responsible for the allergic disease
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