Parallel primitives (skeletons) intend to encourage programmers to build a parallel program from ready-made components for which e cient implementations are known to exist, making the parallelization process easier. However, programmers often su er from the di culty to choose a combination of proper parallel primitives so as to construct efcient parallel programs. To overcome this di culty, we ...

Abstract. We introduce an algorithm based on semidefinite programming that yields increasing (resp., decreasing) sequences of lower (resp., upper) bounds on polynomial stationary averages of di↵usions with polynomial drift vector and di↵usion coe cients. The bounds are obtained by optimizing an objective, determined by the stationary average of interest, over the set of real vectors defined by ...

Business cycle statistics di er widely across countries for some aggregates, especially for trade-related variables. Part of these variations relates to the size of the economies and to their distance from each other. This paper asks whether a three-country model is able to display the marked diversity of business cycle statistics observed across countries. The model is calibrated to two speci ...

We consider a Markovian multiserver queueing model with time dependent parameters where waiting customers may abandon and subsequently retry. We provide simple uid and di usion approximations to estimate the mean, variance, and density for both the queue length and virtual waiting time processes arising in this model. These approximations, which are generated by numerically integrating only 7 o...

We analyze the e ective di usivity of a passive scalar in a two dimensional, steady, incompressible random ow that has mean zero and a stationary stream function. We show that in the limit of small di usivity or large Peclet number, with convection dominating, there is substantial enhancement of the e ective di usivity. Our analysis is based on some new variational principles for convection di ...

|We present raster image processing algorithms for rehalftoning error di used halftones and producing interpolated error di used halftones. Rehalftoning converts a halftone created by one method into one created by another method. In interpolated halftoning, interpolation increases the image size before halftoning, e.g. for printing. Both rehalftoning and interpolated halftoning introduce blur ...

The Turing mechanism for the production of a broken spatial symmetry in an initially homogeneous system of reacting and di using substances has attracted much interest as a potential model for certain aspects of morphogenesis such as pre-patterning in the embryo, and has also served as a model for self-organization in more generic systems. The two features necessary for the formation of Turing ...

We optimize the noise shaping behavior of color error diffusion by designing an optimized error lter based on a proposed noise shaping model for color error di usion and a generalized linear spatially-invariant model of the human visual system. Our approach allows the error lter to have matrix-valued coe cients and di use quantization error across channels in an opponent color representation. T...

Voronoi cells and the notion of natural neighbours are used to develop a nite di erence method for the di usion operator on arbitrary unstructured grids. Natural neighbours are based on the Voronoi diagram, which partitions space into closest-point regions. The Sibson and the Laplace (non-Sibsonian) interpolants which are based on natural neighbours have shown promise within a Galerkin framewor...

In this thesis, I discuss two main subjects coming from biology and I propose two models that mimic the behaviours of the biological networks studied. The rst part of the thesis deals with intracellular transport of molecules. Proteins, RNA and, generally, any kind of cargo molecules move freely in the cytoplasm: intracellular transport as a consequence of Brownian motion is classically modelle...