LiDAR-only based navigation algorithm for an autonomous agricultural robot

The purpose of the work presented in this paper is to develop a general and robust approach for autonomous robot navigation inside a crop using LiDAR (Light Detection And Ranging) data. To be as robust as possible, the robot navigation must not need any prior information about the crop (such as the size and width of the rows). The developed approach is based on line extractions from 2D point clouds using a PEARL based method. In this paper, additional filters and refinements of the PEARL algorithm are presented in the context of crop detection. A penalization of outliers, a model elimination step, a new model search and a geometric constraint are proposed to improve the crop detection. The approach has been tested over a simulator and compared with classical PEARL and RANSAC based approaches. It appears that adding those modification improved the crop detection and thus the robot navigation. Those results are presented and discussed in this paper. It can be noticed that even if this paper presents simulated results (to ease the comparison with other algorithms), the approach also has been successfully tested using an actual Oz weeding robot, developed by the French company Naio Technologies

Recent developments in planet migration theory

Planetary migration is the process by which a forming planet undergoes a drift of its semi-major axis caused by the tidal interaction with its parent protoplanetary disc. One of the key quantities to assess the migration of embedded planets is the tidal torque between the disc and planet, which has two components: the Lindblad torque and the corotation torque. We review the latest results on both torque components for planets on circular orbits, with a special emphasis on the various processes that give rise to additional, large components of the corotation torque, and those contributing to the saturation of this torque. These additional components of the corotation torque could help address the shortcomings that have recently been exposed by models of planet population syntheses. We also review recent results concerning the migration of giant planets that carve gaps in the disc (type II migration) and the migration of sub-giant planets that open partial gaps in massive discs (type III migration).Comment: 52 pages, 18 figures. Review article to be published in "Tidal effects in Astronomy and Astrophysics", Lecture Notes in Physic

Qualité des produits et ancrage au terroir : Le cas des filières fromagères d'AOC du Massif Central

2 illus. 3 tables 2 graph. Développement dans les espaces à faible densitéNational audienc

Comparing Two Discriminant Probabilistic Interestingness Measures for Association Rules

International audiencePreliminary normalization is needed for probabilistic pairwise comparison between attributes in Data Mining. Normalization plays a very important part in preserving the discriminant property of the probability scale when the observation number becomes large. Asymmetrical associations between boolean attributes are considered in our paper. Its goal consists of comparison between two approaches. The first one is due to a normalized version of the "Likelihood Linkage Analysis" methodology. The second one is based on the notion of "Test Value" defined with respect to a hypothetical sample, sized 100 and summarizing the initial observed sample. Two facets are developed in our work: theoretical and experimental. A comparative experimental analysis is presented with the well known databases "Wages" and "Abalone"

The polarisation properties of the HD 181327 debris ring: Evidence for sub-micron particles from scattered light observations

Context: Polarisation is a powerful remote-sensing tool to study the nature of particles scattering the starlight. It is widely used to characterise interplanetary dust particles in the Solar System and increasingly employed to investigate extrasolar dust in debris discs’ systems. Aims: We aim to measure the scattering properties of the dust from the debris ring around HD 181327 at near-infrared wavelengths. Methods: We obtained high-contrast polarimetric images of HD 181327 in the H band with the SPHERE/IRDIS instrument on the Very Large Telescope (ESO). We complemented them with archival data from HST/NICMOS in the F 110W filter reprocessed in the context of the Archival Legacy Investigations of Circumstellar Environments (ALICE) project. We developed a combined forward-modelling framework to simultaneously retrieve the scattering phase function in polarisation and intensity. Results: We detected the debris disc around HD 181327 in polarised light and total intensity. We measured the scattering phase function and the degree of linear polarisation of the dust at 1.6 µm in the birth ring. The maximum polarisation is 23.6% ± 2.6% and occurs between a scattering angle of 70° and 82°. Conclusions: We show that compact spherical particles made of a highly refractive and relatively absorbing material in a differential power-law size distribution of exponent −3.5 can simultaneously reproduce the polarimetric and total intensity scattering properties of the dust. This type of material cannot be obtained with a mixture of silicates, amorphous carbon, water ice, and porosity, and requires a more refracting component such as iron-bearing minerals. We reveal a striking analogy between the near-infrared polarisation of comets and that of HD 181327. The methodology developed here combining VLT/SPHERE and HST/NICMOS may be applicable in the future to combine the polarimetric capabilities of SPHERE with the sensitivity of JWST.ISSN:0004-6361ISSN:1432-074

nuSTORM at CERN: Feasibility Study

The Neutrinos from Stored Muons, nuSTORM, facility has been designed to deliver a definitive neutrino-nucleus scattering programme using beams of $\bar{\nu}_e$ and $\bar{\nu}_\mu$ from the decay of muons confined within a storage ring. The facility is unique, it will be capable of storing $\mu^\pm$ beams with a central momentum of between 1 GeV/c and 6 GeV/c and a momentum spread of 16%. This specification will allow neutrino-scattering measurements to be made over the kinematic range of interest to the DUNE and Hyper-K collaborations. At nuSTORM, the flavour composition of the beam and the neutrino-energy spectrum are both precisely known. The storage-ring instrumentation will allow the neutrino flux to be determined to a precision of 1% or better. By exploiting sophisticated neutrino-detector techniques such as those being developed for the near detectors of DUNE and Hyper-K, the nuSTORM facility will: Serve the future long- and short-baseline neutrino-oscillation programmes by providing definitive measurements of $\bar{\nu}_e A$ and $\bar{\nu}_{\mu} A$ scattering cross-sections with percent-level precision; Provide a probe that is 100% polarised and sensitive to isospin to allow incisive studies of nuclear dynamics and collective effects in nuclei; Deliver the capability to extend the search for light sterile neutrinos beyond the sensitivities that will be provided by the FNAL Short Baseline Neutrino (SBN) programme; and Create an essential test facility for the development of muon accelerators to serve as the basis of a multi-TeV lepton-antilepton collider. To maximise its impact, nuSTORM should be implemented such that data-taking begins by $\approx 2027/28$ when the DUNE and Hyper-K collaborations will each be accumulating data sets capable of determining oscillation probabilities with percent-level precision. With its existing proton-beam infrastructure, CERN is uniquely well-placed to implement nuSTORM. The feasibility of implementing nuSTORM at CERN has been studied by a CERN Physics Beyond Colliders study group. The muon storage ring has been optimised for the neutrino-scattering programme to store muon beams with momenta in the range 1 GeV to 6 GeV. The implementation of nuSTORM exploits an existing fast-extraction from the SPS that delivers beam to the LHC and to HiRadMat. A summary of the proposed implementation of nuSTORM at CERN is presented along with an indicative cost estimate and a preliminary discussion of a possible time-line for the implementation