Rhombic Tilings and Primordia Fronts of Phyllotaxis

We introduce and study properties of phyllotactic and rhombic tilings on the cylin- der. These are discrete sets of points that generalize cylindrical lattices. Rhombic tilings appear as periodic orbits of a discrete dynamical system S that models plant pattern formation by stacking disks of equal radius on the cylinder. This system has the advantage of allowing several disks at the same level, and thus multi-jugate config- urations. We provide partial results toward proving that the attractor for S is entirely composed of rhombic tilings and is a strongly normally attracting branched manifold and conjecture that this attractor persists topologically in nearby systems. A key tool in understanding the geometry of tilings and the dynamics of S is the concept of pri- mordia front, which is a closed ring of tangent disks around the cylinder. We show how fronts determine the dynamics, including transitions of parastichy numbers, and might explain the Fibonacci number of petals often encountered in compositae.Comment: 33 pages, 10 picture

Fibonacci and quasi-symmetric phyllotaxis

The first phyllotaxis pattern formation model was proposed in 1868 by Schwendener, and consists of stacking one disk at a time on the surface of a cylinder. As simple as it is, this model exhibits plenty of geometric and dynamical richness, which are best revealed by systematic computer simulations. It helps explain the predominance of Fibonacci phyllotaxis, where the number of helixes (parastichies) in the two transverse families are successive Fibonacci numbers. It also helped us the mechanisms of formation of a type of pattern never mentioned in the literature, that we called Quasi Symmetric. In these patterns, often characterized by rapid parameter changes, the two parastichies numbers tend to be close to one another. Now go and count parastichies on a strawberry….Non UBCUnreviewedAuthor affiliation: Smith CollegeFacult

Analyse des trajets multiples dans une transmission par un radar a vision laterale bistatique

Afin de définir les caractéristiques d'un moyen d'analyse des trajets multiples dans une liaison VHF, fondé sur les principes du radar bistatique à vision latérale, on évalue les réponses à des échos de sol ponctuels et diffus. Les calculs présentés mettent en évidence les limites d'une telle méthode de cartographie, et peuvent servir à l'étude des effets d'un modèle de terrain sur les systèmes de transmission ou de localisation au voisinage du sol

Combining signal processing and machine leasing techniques for real time measurement of raindrop

International audienceThe data acquisition system for a new type of optical disdrometer is presented. As the device must measure sizes and velocities of raindrops as small as 0.1 mm diameter in real time in the presence of high noise and a variable baseline, algorithm design has been a challenge. The combining of standard signal processing techniques and machine learning methods (in this case, a neural network) has been essential to obtaining good performance