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System Reveals (system + reveal)

Distribution by Scientific Domains

Life Sciences	40%
Engineering	40%

Selected Abstracts

Robust nonlinear ship course-keeping control by H, I/O linearization and , -synthesis

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 1 2003
Shr-Shiung Hu
Abstract In this paper, the H, input/output (I/O) linearization formulation is applied to design an inner-loop nonlinear controller for a nonlinear ship course-keeping control problem. Due to the ship motion dynamics are non-minimum phase, it is impossible to use the ordinary feedback I/O linearization to resolve. Hence, the technique of H, I/O linearization is proposed to obtain a nonlinear H, controller such that the compensated nonlinear system approximates the linear reference model in I/O behaviour. Then a , -synthesis method is employed to design an outer-loop robust controller to address tracking, regulation, and robustness issues. The time responses of the tracking signals for the closed-loop system reveal that the overall robust nonlinear controller is able to provide robust stability and robust performance for the plant uncertainties and state measurement errors. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Complexity can enhance stability in competitive systems

ECOLOGY LETTERS, Issue 5 2001
Ian D. Rozdilsky
Empirical observations often indicate that complexity enhances stability, while most theoretical studies, such as May's (1972) classic paper, point to the opposite. Despite the wide generality of these latter theoretical analyses, our examination of the well-known competitive Lotka,Volterra system reveals that increasing complexity (measured in terms of connectance) can enhance species coexistence and persistence in model communities (measured in terms of their feasibility and stability). The high feasibility and stability found for tightly interconnected competitive subsystems might provide an explanation for the clumped structure in food webs. [source]

Input and SLA: Adults' Sensitivity to Different Sorts of Cues to French Gender

LANGUAGE LEARNING, Issue S1 2005
Susanne E. Carroll
All second language (L2) learning theories presuppose that learners learn the target language from the speech signal (or written material, when learners are reading), so an understanding of learners' ability to detect and represent novel patterns in linguistic stimuli will constitute a major building block in an adequate theory of second language acquisition (SLA) input. Pattern detection, a mainstay of current connectionist modeling of language learning, presupposes a sensitivity to particular properties of the signal. Learning abstract grammatical knowledge from the signal presupposes, as well, the capacity to map phonetic properties of the signal onto properties of another type (segments and syllables, morpheme categories, and so on). Thus, even seemingly "simple" grammatical phenomena may embody complex structural knowledge and be instantiated by a plethora of diverse cues. Moreover, cues have no a priori status; a phenomenon of a given sort takes on a value as a cue when acquisition of the grammatical system reveals it to be useful. My study deals with initial sensitivity to cues to gender attribution in French. Andersen (1984) asked: "What's gender good for anyway?" One answer comes from a number of studies, done mostly in the last 20 years, of gender processing by both monolingual and bilingual speakers (among many others, Bates, Devescovi, Hernandez, & Pizzamiglio, 1996; Bates & Liu, 1997; Friederici & Jacobsen, 1990; Grosjean, Dommergues, Cornu, Guillemon, & Besson, 1994; Guillemon & Grosjean, 2001; Taft & Meunier, 1998). These studies provide evidence that in monolinguals and early (but not late) L2 learners, prenominal morphosyntactic exponents of gender prime noun activation and speed up noun recognition. Over the same period, a growing number of studies detailing the course of L2 gender acquisition for a variety of different target languages and learner types (e.g., Bartning, 2000; Chini, 1995; Dewaele & Véronique, 2000; Granfeldt, 2003; Hawkins & Franceschina, 2004) have provided support for the hypothesis that developmental paths differ for early and later learners of gender. Yet despite its obvious importance to SLA theorizing, few studies have dealt directly with adult learners' ability to detect and analyze potential cues to gender at the initial stage of exposure to the L2 (and this despite considerable discussion in recent years of the nature of the "initial state" of L2 learning). The study reported on in this article, which was actually conducted in the late 1980s, was an attempt to shed some light on what the beginning learner can do with the gender attribution problem. This study was, at that time, and is even now, an anomaly; most research dealing with "input" provided descriptions of what people say to learners, not what learners can perceive and represent. Indeed, most studies that shed light on the initial analytical capacities of absolute beginners were concerned with "perceptual" learning, that is, with the acquisition of phonetic or phonological distinctions (e.g., Broselow, Hurtig, & Ringen's [1987] study of tone learning or various studies on the perception of the /r/ vs. /l/ phonemes in American English by Japanese speakers). In this update, it is therefore worth mentioning Rast's (2003) dissertation and Rast and Dommergues (2003), which is based on it, which examined the results of the first 8 hr of instructed learning of Polish by francophone adults. My study asked if anglophone adults, with little or no prior exposure to French, given auditory stimuli, were equally sensitive to phonological, morphosyntactic, or semantic cues to French gender classes. The issue of what learners can detect in the signal and encode is an empirical one. I presented 88 adult English speakers with highly patterned data in list form, namely, auditory sequences of [Det + N]French + translation equivalentEnglish forms. The patterns, all true generalizations, were drawn from linguistic descriptions of French. These cues are believed by grammarians of the language to be "psychologically real" to native speakers. I then measured in 3 different ways what my participants had acquired. Given the extreme limitations on the input (no visual supports to identify referents of names), the participants performed pretty well. Moreover, they proved to be highly sensitive to "natural" semantic and morphological patterns and could generalize accurately from learned instances to novel exemplars. These patterns, however, are not directly instantiated in the speech signal; they are abstractions imposed on the stimuli by human linguistic cognition. Moreover, although it would be inaccurate to describe the learning patterns as "transfer"(because English nouns have no gender feature), prior knowledge seemed to be implicated in the results. Above all, these Anglophones appear to perceive the gender learning problem as a semantic one and to make use of "top-down" information in solving it. It follows that the pattern detection that they can do when listening to speech is clearly biased by what they already know. These results, therefore, provide support for hypotheses that the initial state is to be defined in terms of the transfer of first language (L1) grammatical knowledge and/or the transfer of L1-based processing procedures. [source]

Selection of knowledge acquisition techniques based upon the problem domain characteristics of production and operations management expert systems

EXPERT SYSTEMS, Issue 2 2001
William P. Wagner
The application of expert systems to various problem domains in business has grown steadily since their introduction. Regardless of the chosen method of development, the most commonly cited problems in developing these systems are the unavailability of both the experts and knowledge engineers and difficulties with the process of acquiring knowledge from domain experts. Within the field of artificial intelligence, this has been called the ,knowledge acquisition' problem and has been identified as the greatest bottleneck in the expert system development process. Simply stated, the problem is how to acquire the specific knowledge for a well-defined problem domain efficiently from one or more experts and represent it in the appropriate computer format. Given the ,paradox of expertise', the experts have often proceduralized their knowledge to the point that they have difficulty in explaining exactly what they know and how they know it. However, empirical research in the field of expert systems reveals that certain knowledge acquisition techniques are significantly more efficient than others in helping to extract certain types of knowledge within specific problem domains. In this paper we present a mapping between these empirical studies and a generic taxonomy of expert system problem domains. In so doing, certain knowledge acquisition techniques can be prescribed based on the problem domain characteristics. With the production and operations management (P/OM) field as the pilot area for the current study, we first examine the range of problem domains and suggest a mapping of P/OM tasks to a generic taxonomy of problem domains. We then describe the most prominent knowledge acquisition techniques. Based on the examination of the existing empirical knowledge acquisition research, we present how the empirical work can be used to provide guidance to developers of expert systems in the field of P/OM. [source]

The role of soil community biodiversity in insect biodiversity

INSECT CONSERVATION AND DIVERSITY, Issue 3 2010
ALISON BENNETT
Abstract., 1.,This study demonstrates that feedback loops between plants and insects contribute to both plant and insect diversity. Synthesis of several studies reveals that both bottom-up and top-down forces are important for plant and insect communities. 2.,Feedback loops between plants and soil organisms contribute to plant and soil diversity. An analysis of multiple systems reveals that pathogens, mutualists, and a wide variety of soil fauna directly influence, and are influenced by, plant diversity. 3.,The connection of plant,insect and soil,plant feedback loops leads to the maintenance of all three groups, and the maintenance of these feedback loops crucially affects insect diversity. Examples of the influence of soil community diversity on insect diversity, and the influence of insect diversity on soil community diversity, as well as feedbacks through all three trophic levels are provided. 4.,Finally, means of conserving and restoring soil communities to influence the conservation and restoration of insect communities are discussed. [source]