3,950 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
Micromegas in a Bulk
In this paper we present a novel way to manufacture the bulk Micromegas
detector. A simple process based on the PCB (Printed Circuit Board) technology
is employed to produce the entire sensitive detector. Such fabrication process
could be extended to very large area detectors made by the industry. The low
cost fabrication together with the robustness of the electrode materials will
make it extremely attractive for several applications ranging from particle
physics and astrophysics to medicineComment: 6 pages, 4 figure
First tests of a Micromegas TPC in a magnetic field
Talk given by P. ColasSince the summer of 2003, a large Micromegas TPC prototype (1000 channels, 50 cm drift, 50 cm diameter) has been operated in a 2T superconducting magnet at Saclay. A description of this apparatus and first results from cosmic ray tests are presented. Additional measurements using simpler detectors with a laser source, an X-ray gun and radio-active sources are discussed. Drift velocity and gain measurements, electron attachment and aging studies for a Micromegas TPC are presented. In particular, using simulations and measurements, it is shown that an mixture is optimal for operation at a future Linear Collider
Formation of nonlinear X-waves in condensed matter systems
X-waves are an example of a localized wave packet solution of the homogeneous wave equation, and can potentially arise in any area of physics relating to wave phenomena, such as acoustics, electromagnetism, or quantum mechanics. They have been predicted in condensed matter systems such as atomic Bose-Einstein condensates in optical lattices, and were recently observed in exciton-polariton condensates. Here we show that polariton X-waves result from an interference between two separating wave packets that arise from the combination of a locally hyperbolic dispersion relation and nonlinear interactions. We show that similar X-wave structures could also be observed in expanding spin-orbit coupled Bose-Einstein condensates.Published onlin
Ultra low energy results and their impact to dark matter and low energy neutrino physics
We present ultra low energy results taken with the novel Spherical
Proportional Counter. The energy threshold has been pushed down to about 25 eV
and single electrons are clearly collected and detected. To reach such
performance low energy calibration systems have been successfully developed: -
A pulsed UV lamp extracting photoelectrons from the inner surface of the
detector - Various radioactive sources allowing low energy peaks through
fluorescence processes. The bench mark result is the observation of a well
resolved peak at 270 eV due to carbon fluorescence which is unique performance
for such large-massive detector. It opens a new window in dark matter and low
energy neutrino search and may allow detection of neutrinos from a nuclear
reactor or from supernova via neutrino-nucleus elastic scatteringComment: 14 pages,16 figure
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
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