Network algebra for synchronous dataflow

We develop an algebraic theory of synchronous dataflow networks. First, a basic algebraic theory of networks, called BNA (Basic Network Algebra), is introduced. This theory captures the basic algebraic properties of networks. For synchronous dataflow networks, it is subsequently extended with additional constants for the branching connections that occur between the cells of synchronous dataflow networks and axioms for these additional constants. We also give two models of the resulting theory, the one based on stream transformers and the other based on processes as considered in process algebra.Comment: 24 page

Poststructuralism against poststructuralism: Actor-network theory, organizations and economic markets

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2012 The Author.In recent years, actor-network theory (ANT) has become an increasingly influential theoretical framework through which to analyse economic markets and organizations. Indeed, with its emphasis on the power of social and natural concrete ‘things’ to become contingently enrolled in different networks, many argue that ANT successfully draws attention to the complex intermeshing of new technologies and social actors in organizations and markets across spatial divides from the local to the global. This article argues, however, that within its own method of abstraction and research methodology, ANT separates ‘concrete’ and ‘contingent’ economic markets and organizations from their abstract, necessary and virtual capitalist form. This means that ANT will tend to over-identify with how concrete-contingent actor-networks are performed in empirical economic markets and organizations at the expense of analysing how such empirical contexts are also internally mediated through abstract capitalist processes such as that of surplus value extraction. This, in turn, creates a number of difficulties in how ANT investigates economic markets and organizations. These critical points are made by recourse to the Marxist poststructuralism of Deleuze and Guattari as well as through conventional Marxist ideas

Hierarchical D ∗ algorithm with materialization of costs for robot path planning

In this paper a new hierarchical extension of the D ∗ algorithm for robot path planning is introduced. The hierarchical D ∗ algorithm uses a down-top strategy and a set of precalculated paths (materialization of path costs) in order to improve performance. This on-line path planning algorithm allows optimality and specially lower computational time. H-Graphs (hierarchical graphs) are modified and adapted to support on-line path planning with materialization of costs and multiple hierarchical levels. Traditional on-line robot path planning focused in horizontal spaces is also extended to vertical and interbuilding spaces. Some experimental results are showed and compared to other path planning algorithms

SKIRT: hybrid parallelization of radiative transfer simulations

We describe the design, implementation and performance of the new hybrid parallelization scheme in our Monte Carlo radiative transfer code SKIRT, which has been used extensively for modeling the continuum radiation of dusty astrophysical systems including late-type galaxies and dusty tori. The hybrid scheme combines distributed memory parallelization, using the standard Message Passing Interface (MPI) to communicate between processes, and shared memory parallelization, providing multiple execution threads within each process to avoid duplication of data structures. The synchronization between multiple threads is accomplished through atomic operations without high-level locking (also called lock-free programming). This improves the scaling behavior of the code and substantially simplifies the implementation of the hybrid scheme. The result is an extremely flexible solution that adjusts to the number of available nodes, processors and memory, and consequently performs well on a wide variety of computing architectures.Comment: 21 pages, 20 figure