We propose a multilevel preconditioning strategy for the iterative solution of large sparse linear systems arising from a nite element discretization of the radiation di usion equations. In particular, these equations are solved using a mixed nite element scheme in order to make the discretization discontinuous, which is imposed by the application in which the di usion equation will be embedded...

Di usion magnetic resonance imaging (dMRI) is the reference in vivo modality to study the connectivity of the brain white matter. Images obtained through dMRI are indeed related to the probability density function (pdf) of displacement of water molecules subject to restricted di usion in the brain white matter. The knowledge of this di usion pdf is therefore of primary importance. Several metho...

Existing state-of-the-art schemes for dynamic repartitioning of adaptive meshes can be classi ed as either di usion-based schemes or scratch-remap schemes. We present a new scratch-remap scheme called Locally-Matched Multilevel Scratch-Remap (or simply LMSR). The LMSR scheme tries to compute a partitioning that has a high overlap with the existing partitioning. We show that LMSR decreases the a...

A framework that naturally uni es smoothing and enhancement processes is presented. We generalize the linear and nonlinear scale spaces in the complex domain, by combining the di usion equation with the simpli ed schrodinger equation. A fundamental solution for the linear case is developed. Preliminary analysis of the complex di usion shows that the generalized di usion has properties of both ...

We explore the determinants of research specialization and examine the e ects of technology di usion and trade on the incentives for innovation. To some extent, di usion substitutes for trade. If trade costs are low relative to di erences in comparative advantage in doing research, rapid di usion implies specialization in research activity. Country size has an ambiguous e ect on specialization ...

This study aims to explain what drives innovation di€usion in management accounting during its various phases. Based on Abrahamson [Abrahamson, E. (1991). Managerial fads and fashions: the di€usion and rejection of innovations. Academy of Management Review, 16, 586±612], four perspectives with potential to explain the di€usion of accounting innovations are identi®ed: the ecient-choice, forced ...

We compare two load balancing techniques for Cayley graphs based on information and load exchange between neighboring vertices. In the rst scheme, called natural di usion, each vertex gives (or receives) a xed part of the load di erence to (from) its direct neighbors. In the second scheme, called Cayley di usion, each vertex successively gives (or receives) a part of the load di erence to (or f...

We consider di usion processes on a class of R{trees. The processes are de ned in a manner similar to that of Le Gall's Brownian snake. Each point in the tree has a real{valued \height" or \generation", and the height of the di usion process evolves as a Brownian motion. When the height process decreases the di usion retreats back along a lineage, whereas when the height process increases the d...

Water pollution by industrial and agricultural waste is an increasingly major public health issue. It is therefore important for water engineers and managers to be able to predict accurately the local behaviour of water-borne pollutants. This paper describes the novel and ecient coupling of dynamically adaptive hierarchical grids with standard solvers of the advection±di€usion equation. Adapti...

Grayscale error di usion introduces nonlinear distortion (directional artifacts and false textures), linear distortion (sharpening), and additive noise. In color error di usion what color to render is a major concern in addition to nding optimal dot patterns. This article presents a survey of key methods for artifact reduction in grayscale and color error di usion. The linear gain model by Kite...