Least fixpoints as meanings of recursive definitions.

Does knowledge of language consist of mentally-represented rules? Rumelhart and McClelland have described a connectionist (parallel distributed processing) model of the acquisition of the past tense in English which successfully maps many stems onto their past tense forms, both regular (walk/walked) and irregular (go/went), and which mimics some of the errors and sequences of development of children. Yet the model contains no explicit rules, only a set of neuron-style units which stand for trigrams of phonetic features of the stem, a set of units which stand for trigrams of phonetic features of the past form, and an array of connections between the two sets of units whose strengths are modified during learning. Rumelhart and McClelland conclude that linguistic rules may be merely convenient approximate fictions and that the real causal processes in language use and acquisition must be characterized as the transfer of activation levels among units and the modification of the weights of their connections. We analyze both the linguistic and the developmental assumptions of the model in detail and discover that (1) it cannot represent certain words, (2) it cannot learn many rules, (3) it can learn rules found in no human language, (4) it cannot explain morphological and phonological regularities, (5) it cannot explain the differences between irregular and regular forms, (6) it fails at its assigned task of mastering the past tense of English, (7) it gives an incorrect explanation for two developmental phenomena: stages of overregularization of irregular forms such as bringed, and the appearance of doubly-marked forms such as ated, and (8) it gives accounts of two others (infrequent overregularization of verbs ending in t/d, and the order of acquisition of different irregula...

We combined the CAT mixture model (Lartillot and Philippe 2004) and the non-stationary BP model (Blanquart and Lartillot 2006) into a new model, CAT-BP, accounting for variations of the evolutionary process both along the sequence and across lineages. As in CAT, the model implements a mixture of distinct Markovian processes of substitution distributed among sites, thus accommodating site-specific selective constraints induced by protein structure and function. Furthermore, as in BP, these processes are non-stationary, and their equilibrium frequencies are allowed to change along lineages in a correlated way, through discrete shifts in global amino acid composition distributed along the phylogenetic tree. We implemented the CAT-BP model in a Bayesian Markov Chain Monte Carlo framework, and compared its predictions with those of three simpler models, BP, CAT, and the site- and timehomogeneous GTR model, on a concatenation of four mitochondrial proteins of 20 arthropod species. In contrast to GTR, BP and CAT, which all display a phylogenetic reconstruction artefact positioning the bees Apis m. and Melipona b. among chelicerates, the CAT-BP model is able to recover the monophyly of insects. Using posterior predictive tests, we further show that the CAT-BP combination yields better anticipations of site- and taxon-specific amino acid

A new IGBP web site

This paper describes and compares eight heuristics that can be used in such an RMS for dynamically assigning independent tasks to machines

Although VLIW architectures offer the advantages of simplicity of design and high issue rates, a major impediment to their use is that they are not compatible with the existing software base. We describe new simple hardware features for a VLIW machine we call DAISY (Dynamically Architected Instruction Set from Yorlaown). DAISY is specifically intended to emulate existing architectures, so that all existing software for an old architecture (including operating system kernel code) runs without changes on the VLIW. Each time a new fragment of code is executed for the first time, the code is translated to VLIW primitives, parallelized and saved in a portion of main memory not visible to the old architecture, by a Firtual Machine Monitor (software) residing in read only memory. Subsequent executions of the same fragment do not require a translation (unless cast out). We discuss the architectural requirements for such a VLIW, to deal with issues including self-modifying code, precise exceptions, and aggressive reordedng of memory references in the presence of strong MP consistency and memory mapped I/O. We have implemented the dynamic parallelization algorithms for the PowerPC architecture. The initial results show high degrees of instruction level parallelism with reasonable translation overhead and memory usage.

Abstract not found

Abstract—This paper proposes LBA, a lifetime balanced data aggregation scheme for asynchronous and duty cycle sensor networks under an application-specific requirement of end-to-end data delivery delay bound. In contrast to existing aggregation schemes that focus on reducing the energy consumption

Classic binary search is extended to multidimensional search problems. These new search methods can efficiently solve several important problems of computer science. Applications of these results to an open problem in the theory of computation are discussed yielding new insight into the Lba problem

In this study we evaluate different HMM topologies in terms of recognition of handwritten numeral strings by considering the framework of the Level Building Algorithm (LBA). By including an end-state in a left-to-right HMM structure we observe a significant improvement in the string recognition