Browsing by Author "Academic Press, publisher"

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Open Access
A methodology for exploiting concurrency among independent tasks in partitionable parallel processing systems
(Colorado State University. Libraries, 1993) Siegel, Howard J., author; Maciejewski, Anthony A., author; Nation, Wayne G., author; Academic Press, publisher
One benefit of partitionable parallel processing systems is their ability to execute multiple, independent tasks simultaneously. Previous work has identified conditions such that, when there are tasks to be processed, partitioning the system so that all k tasks are processed simultaneously results in a minimum overall execution time. An alternate condition is developed that provides additional insight into the effects of parallelism on execution time. This result and previous results, however, assume that execution times are data independent. It is shown that data-dependent tasks do not necessarily execute faster when processed simultaneously even if the condition is met. A model is developed that provides for the possible variability of a task's execution time and is used in a new framework to study the problem of finding an optimal mapping for identical, independent data-dependent execution time tasks onto partitionable systems. Executing one, some, or all of the k tasks simultaneously is considered. Because this new framework is general, it can also serve as a new method for the study of data-independent tasks. Extension of this framework to situations where the k tasks are nonidentical is discussed.
Open Access
Duties to endangered species (Encyclopedia of Environmental Biology)
(Colorado State University. Libraries, 1995) Rolston, Holmes, 1932-2025, author; Academic Press, publisher
Whether humans have duties to endangered species is a significant theoretical and an urgent practical question. Few doubt that we have some obligations concerning species. But these might be all obligations to persons benefitted or harmed by species as resources. Is there a human duty directly to species, additionally to obligations that humans have to fellow members of their own species? An answer is vital to the question of the conservation of biodiversity, how humans can achieve a sustainable relationship to the natural world.
Open Access
Nutrient and energy flows through soil microbial biomass
(Colorado State University. Libraries, 1980) Paul, Eldor A., author; Voroney, R. P., author; Academic Press, publisher
The recognition and recent studies of the role of living organisms (biomass) in carbon, nitrogen and phosphorus flows in nature have stressed the role of the microorganisms as sources and sinks for nutrients, in addition to their traditional role in transformation of the nutrient elements. Techniques for determining the size and activity of laboratory cultures have had to be altered for field measurements. Similarly, growth concepts developed using liquid culture studies should be applicable in the field after the effects of such factors as competition, the presence of inhibitors, physical adsorption and entrapment, and the broad variety of available energy sources have been considered. Enough information is now available on microbial biomass and activity in terrestrial soils, sediments and aquatic systems that reasonably accurate mathematical descriptions of the pool sizes and processes involved can be made. Mathematical modelling is useful in that it allows one to describe the processes. It also provides for the testing of available data and concepts and thereby points out where further research is necessary.
Open Access
Task matching and scheduling in heterogeneous computing environments using a genetic-algorithm-based approach
(Colorado State University. Libraries, 1997) Maciejewski, Anthony A., author; Roychowdhury, Vwani P., author; Siegel, Howard Jay, author; Wang, Lee, author; Academic Press, publisher
To exploit a heterogeneous computing (HC) environment, an application task may be decomposed into subtasks that have data dependencies. Subtask matching and scheduling consists of assigning subtasks to machines, ordering subtask execution for each machine, and ordering intermachine data transfers. The goal is to achieve the minimal completion time for the task. A heuristic approach based on a genetic algorithm is developed to do matching and scheduling in HC environments. It is assumed that the matcher/scheduler is in control of a dedicated HC suite of machines. The characteristics of this genetic-algorithm-based approach include: separation of the matching and the scheduling representations, independence of the chromosome structure from the details of the communication subsystem, and consideration of overlap among all computations and communications that obey subtask precedence constraints. It is applicable to the static scheduling of production jobs and can be readily used to collectively schedule a set of tasks that are decomposed into subtasks. Some parameters and the selection scheme of the genetic algorithm were chosen experimentally to achieve the best performance. Extensive simulation tests were conducted. For small-sized problems (e.g., a small number of subtasks and a small number of machines), exhaustive searches were used to verify that this genetic-algorithm-based approach found the optimal solutions. Simulation results for larger-sized problems showed that this genetic-algorithm-based approach outperformed two nonevolutionary heuristics and a random search.