Parallel processing and expert systems

Whether it be monitoring the thermal subsystem of Space Station Freedom, or controlling the navigation of the autonomous rover on Mars, NASA missions in the 1990s cannot enjoy an increased level of autonomy without the efficient implementation of expert systems. Merely increasing the computational speed of uniprocessors may not be able to guarantee that real-time demands are met for larger systems. Speedup via parallel processing must be pursued alongside the optimization of sequential implementations. Prototypes of parallel expert systems have been built at universities and industrial laboratories in the U.S. and Japan. The state-of-the-art research in progress related to parallel execution of expert systems is surveyed. The survey discusses multiprocessors for expert systems, parallel languages for symbolic computations, and mapping expert systems to multiprocessors. Results to date indicate that the parallelism achieved for these systems is small. The main reasons are (1) the body of knowledge applicable in any given situation and the amount of computation executed by each rule firing are small, (2) dividing the problem solving process into relatively independent partitions is difficult, and (3) implementation decisions that enable expert systems to be incrementally refined hamper compile-time optimization. In order to obtain greater speedups, data parallelism and application parallelism must be exploited

An Architectural Approach to Ensuring Consistency in Hierarchical Execution

Hierarchical task decomposition is a method used in many agent systems to organize agent knowledge. This work shows how the combination of a hierarchy and persistent assertions of knowledge can lead to difficulty in maintaining logical consistency in asserted knowledge. We explore the problematic consequences of persistent assumptions in the reasoning process and introduce novel potential solutions. Having implemented one of the possible solutions, Dynamic Hierarchical Justification, its effectiveness is demonstrated with an empirical analysis

Adaptive and Reactive Rich Internet Applications

In this thesis we present the client-side approach of Adaptive and Reactive Rich Internet Applications as the main result of our research into how to bring in time adaptivity to Rich Internet Applications. Our approach leverages previous work on adaptive hypermedia, event processing and other research disciplines. We present a holistic framework covering the design-time as well as the runtime aspects of Adaptive and Reactive Rich Internet Applications focusing especially on the run-time aspects

Resilience to droughts in mammals: a conceptual framework for estimating vulnerability of a single species

The frequency and severity of droughts in certain areas is increasing as a consequence of climate change. The associated environmental challenges, including high temperatures, low food, and water availability, have affected, and will affect, many populations. Our aims are to review the behavioral, physiological, and morphological adaptations of mammals to arid environments, and to aid researchers and nature conservationists about which traits they should study to assess whether or not their study species will be able to cope with droughts. We provide a suite of traits that should be considered when making predictions about species resilience to drought. We define and differentiate between general adaptations, specialized adaptations, and exaptations, and argue that specialized adaptations are of little interest in establishing how nondesert specialists will cope with droughts. Attention should be placed on general adaptations of semidesert species and assess whether these exist as exaptations in nondesert species. We conclude that phenotypic flexibility is the most important general adaptation that may promote species resilience. Thus, to assess whether a species will be able to cope with increasing aridity, it is important to establish the degree of flexibility of traits identified in semidesert species that confer a fitness advantage under drying conditions

Expression and regulation of sex determining genes in the mouse

The aims of my thesis were to characterize the regulatory elements of the mouse gene Sry, the testes determining factor, and of the mouse gene Dax-1, a candidate for an ovary determining gene; and to analyze their function during development. The first strategy used was to map DNAse I hypersensitive sites (DHSs) in the regions flanking the open reading frame (ORF) of Sry, as it has been found that DHSs often correspond to DNA sequences that function as regulatory regions. No DHSs were found in the first four kb surrounding the ORF. Another strategy for finding regulatory regions was to use transgenic mice harbouring lac-Z reporter constructs with different amounts of flanking genomic sequence. None of the transgenic reporter constructs with Sry sequences were found to be expressed at a high enough level for the detection of β-galactosidase expression by staining with X-gal. The endogenous low levels of expression and the complex genomic structure of Sry might account for this result. Since Sry expression is tightly regulated during development, we attempted to misexpress it to see if it produced an abnormal phenotype. Three lines carrying Sry under the control of a constitutive promoter were produced. No obvious phenotype has been observed to date. Dax-1 has at least two important sites of expression: the developing gonads and the adrenal glands. Reporter constructs with Dax-1 genomic sequences allowed us to define upstream regions responsible for expression in these two tissues. Within 18 kb 5' of the ORF we have found a gonad-specific and an adrenal-specific expression element. In order to study the function of Dax-1 in the sex determining pathway, transgenic animals with extra copies of this gene have been produced. Male to female sex-reversal was expected. Up to now, no sex-reversal has been found in these animals, however the level of expression may be too low