354 research outputs found
Path-Tree Optimization in Partially Observable Environments using Rapidly-Exploring Belief-Space Graphs
Robots often need to solve path planning problems where essential and
discrete aspects of the environment are partially observable. This introduces a
multi-modality, where the robot must be able to observe and infer the state of
its environment. To tackle this problem, we introduce the Path-Tree
Optimization (PTO) algorithm which plans a path-tree in belief-space. A
path-tree is a tree-like motion with branching points where the robot receives
an observation leading to a belief-state update. The robot takes different
branches depending on the observation received. The algorithm has three main
steps. First, a rapidly-exploring random graph (RRG) on the state space is
grown. Second, the RRG is expanded to a belief-space graph by querying the
observation model. In a third step, dynamic programming is performed on the
belief-space graph to extract a path-tree. The resulting path-tree combines
exploration with exploitation i.e. it balances the need for gaining knowledge
about the environment with the need for reaching the goal. We demonstrate the
algorithm capabilities on navigation and mobile manipulation tasks, and show
its advantage over a baseline using a task and motion planning approach (TAMP)
both in terms of optimality and runtime.Comment: Also submitted to IROS 2022 and RA-
Head-to-head domain walls in one-dimensional nanostructures: an extended phase diagram ranging from strips to cylindrical wires
International audienceSo far magnetic domain walls in one-dimensional structures have been described theoretically only in the cases of flat strips, or cylindrical structures with a compact cross-section, either square or disk. Here we describe an extended phase diagram unifying the two pictures, extensively covering the (width,thickness) space. It is derived on the basis of symmetry and phase-transition arguments, and micromagnetic simulations. A simple classification of all domain walls in two varieties is proposed on the basis of their topology: either with a combined transverse/vortex character, or of the Bloch-point type. The exact arrangement of magnetization within each variety results mostly from the need to decrease dipolar energy, giving rise to asymmetric and curling structures. Numerical evaluators are introduced to quantify curling, and scaling laws are derived analytically for some of the iso-energy lines of the phase diagram
Asymmetric hysteresis of N\'eel caps in flux-closure magnetic dots
We investigated with XMCD-PEEM magnetic imaging the magnetization reversal
processes of N\'eel caps inside Bloch walls in self-assembled, micron-sized
Fe(110) dots with flux-closure magnetic state. In most cases the
magnetic-dependent processes are symmetric in field, as expected. However, some
dots show pronounced asymmetric behaviors. Micromagnetic simulations suggest
that the geometrical features (and their asymmetry) of the dots strongly affect
the switching mechanism of the N\'eel caps.Comment: Proceeding for MMM-Intermag 2010 (Washington
Observation of Bloch-point domain walls in cylindrical magnetic nanowires
Topological protection is an elegant way of warranting the integrity of
quantum and nanosized systems. In magnetism one example is the Bloch-point, a
peculiar object implying the local vanishing of magnetization within a
ferromagnet. Its existence had been postulated and described theoretically
since several decades, however it has never been observed. We con rm
experimentally the existence of Bloch points, imaged within domain walls in
cylindrical magnetic nanowires, combining surface and transmission XMCD-PEEM
magnetic microscopy. This opens the way to the experimental search for peculiar
phenomena predicted during the motion of Bloch-point-based domain walls
EchoFusion: Tracking and Reconstruction of Objects in 4D Freehand Ultrasound Imaging without External Trackers
Ultrasound (US) is the most widely used fetal imaging technique. However, US
images have limited capture range, and suffer from view dependent artefacts
such as acoustic shadows. Compounding of overlapping 3D US acquisitions into a
high-resolution volume can extend the field of view and remove image artefacts,
which is useful for retrospective analysis including population based studies.
However, such volume reconstructions require information about relative
transformations between probe positions from which the individual volumes were
acquired. In prenatal US scans, the fetus can move independently from the
mother, making external trackers such as electromagnetic or optical tracking
unable to track the motion between probe position and the moving fetus. We
provide a novel methodology for image-based tracking and volume reconstruction
by combining recent advances in deep learning and simultaneous localisation and
mapping (SLAM). Tracking semantics are established through the use of a
Residual 3D U-Net and the output is fed to the SLAM algorithm. As a proof of
concept, experiments are conducted on US volumes taken from a whole body fetal
phantom, and from the heads of real fetuses. For the fetal head segmentation,
we also introduce a novel weak annotation approach to minimise the required
manual effort for ground truth annotation. We evaluate our method
qualitatively, and quantitatively with respect to tissue discrimination
accuracy and tracking robustness.Comment: MICCAI Workshop on Perinatal, Preterm and Paediatric Image analysis
(PIPPI), 201
Chapitre 5 - Croiser enjeux de durabilité et leviers des politiques urbaines
L’élaboration de politiques alimentaires urbaines ne repose pas sur des démarches unifiées. Cet exercice est relativement récent et l’on dispose encore de peu de recul pour voir émerger d’éventuelles démarches aptes à appréhender la complexité des systèmes alimentaires. Les chapitres précédents ont montré que les initiatives sont nombreuses de par le monde et qu’elles ont recours à des démarches disparates. Dans ce contexte, outiller..
Voyage dans l'Empire de Flore ou Élémens d'histoire naturelle végétale : ouvrage ou l'on trouve l'analyse des Leçons du savant auteur de la "Flore atlantique"
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