Amélioration du processus de géosimulation des phénomènes urbains complexes par l'adaptation d'une tessellation Voronoï

Similar to the intensive developments in Geographic Information Systems (GIS) and spatial databases, the field of urban geosimulation was increasingly used in recent years, with an emphasis on high-resolution applications. This recent tendency does not agree however with the traditionally homogeneous spatial representation provided by regular cellular automata which are commonly used as the spatial structures of geosimulation applications. Several issues are raised in the literature, including reports of limitations in spatial reasoning and a lack of realism related to such spatial representations. The few solutions that, so far, deviate from the ‘dogma of regularity of the spatial representation’ are also subject to recent criticism. In this context, we propose an alternative multi-scale model based on the Voronoi diagram of polygons, which matches geographic features of the urban environment. The proposed theoretical model was developed and tested in the context of a urban geosimulation using high resolution spatial data, in the form of registered parcels of irregular shapes and sizes. The first results of the approach demonstrate the potential of our model in the context of urban geosimulation. Finally, based on our extensive analysis of the main approaches of space segmentation, we propose a schematic method to choose a spatial decomposition suited to urban geosimulation

Introduction to Louis Michel’s lattice geometry through group action

Group action analysis developed and applied mainly by Louis Michel to the study of N-dimensional periodic lattices is the central subject of the book. Di¬fferent basic mathematical tools currently used for the description of lattice geometry are introduced and illustrated through applications to crystal structures in two- and three-dimensional space, to abstract multi-dimensional lattices and to lattices associated with integrable dynamical systems. Starting from general Delone sets the authors turn to di¬fferent symmetry and topological classifications including explicit construction of orbifolds for two- and three-dimensional point and space groups

Effects of therapeutic ultrasound on the nuclear envelope and nuclear pore complexes

The effects of acoustic waves on membrane structures, and any resulting consequences of this treatment on membrane subunit structures, remain poorly understood, as are the principals of related clinical effects. With a focus on morphological changes in the nuclear envelope, the current study presents detailed observations of membrane structures exposed to therapeutic ultrasound. Ultrasound treatment most commonly resulted in distinct changes in the distribution of Nuclear Pore Complexes (NPCs) and mean NPC number per unit area after 30 min of repair, as well as alterations in NPC diameters on the protoplasmic face of fractured nuclear membranes after 10 min of repair. The greatest effects of ultrasound on nuclear envelope structure and NPCs were not to appear immediately, but became evident after repair processes were initiated. Results from the current study may contribute to the general view on the biophysical effects of therapeutic ultrasound on cell morphology and, particularly, the understanding of this effect in relation to the nuclear envelope.The effects of acoustic waves on membrane structures, and any resulting consequences of this treatment on membrane subunit structures, remain poorly understood, as are the principals of related clinical effects. With a focus on morphological changes in the nuclear envelope, the current study presents detailed observations of membrane structures exposed to therapeutic ultrasound. Ultrasound treatment most commonly resulted in distinct changes in the distribution of Nuclear Pore Complexes (NPCs) and mean NPC number per unit area after 30 min of repair, as well as alterations in NPC diameters on the protoplasmic face of fractured nuclear membranes after 10 min of repair. The greatest effects of ultrasound on nuclear envelope structure and NPCs were not to appear immediately, but became evident after repair processes were initiated. Results from the current study may contribute to the general view on the biophysical effects of therapeutic ultrasound on cell morphology and, particularly, the understanding of this effect in relation to the nuclear envelope

The dynamics of finite-size settling particles

Direct numerical simulations of the gravity-induced settling of finite-size particles in triply periodic domains has been performed under dilute conditions. We consider rigid, heavy, finite-size spherical particles. Depending on the particle settling regime the particles may exhibit strong clustering. The particles inside clusters experience larger settling velocities than the average. The mean particle wake is significantly attenuated by the motion of the particles

Recurrence along directions in multidimensional words

In this paper we introduce and study new notions of uniform recurrence in multidimensional words. A d-dimensional word is called uniformly recurrent if for all s_1,...,s_d, there exists n such that each block of size (n,…,n) contains the prefix of size (s1,…,sd). We are interested in a modification of this property. Namely, we ask that for each rational direction (q_1,…,q_d), each rectangular prefix occurs along this direction in positions ℓ(q1,…,qd) with bounded gaps. Such words are called uniformly recurrent along all directions. We provide several constructions of multidimensional words satisfying this condition, and more generally, a series of four increasingly stronger conditions. In particular, we study the uniform recurrence along directions of multidimentional rotation words and of fixed points of square morphisms

The dynamics of finite-size settling particles

This book contributes to the fundamental understanding of the physical mechanisms that take place in pseudo turbulent particulate flows. In the present work we have considered the sedimentation of large numbers of spherical rigid particles in an initially quiescent flow field. We have performed direct numerical simulations employing an immersed boundary method for the representation of the fluid-solid interface. The results evidence that depending on the particle settling regime (i.e. Galileo number and particle-to-fluid density ratio) the particles may exhibit strong inhomogeneous spatial distribution. It is found that the particles are preferentially located in regions with downward fluid motion. The particles inside clusters experience larger settling velocities than the average. The flow in all flow cases is observed to exhibit characteristic features of pseudo-turbulence. The particle-induced flow field is further found to be highly anisotropic with dominant vertical components. The results indicate that, in the present flow configurations, the collective and mobility effects play significant role for the particle and fluid motion