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51.
Algebra offers an elegant and powerful approach to understand regular languages and finite automata. Such framework has been notoriously lacking for timed languages and timed automata. We introduce the notion of monoid recognizability for data languages, which includes timed languages as special case, in a way that respects the spirit of the classical situation. We study closure properties and hierarchies in this model and prove that emptiness is decidable under natural hypotheses. Our class of recognizable languages properly includes many families of deterministic timed languages that have been proposed until now, and the same holds for non-deterministic versions. 相似文献
52.
Forward Analysis of Updatable Timed Automata 总被引:1,自引:2,他引:1
Patricia Bouyer 《Formal Methods in System Design》2004,24(3):281-320
Timed automata are a widely studied model. Its decidability has been proved using the so-called region automaton construction. This construction provides a correct abstraction for the behaviours of timed automata, but it suffers from a state explosion and is thus not used in practice. Instead, algorithms based on the notion of zones are implemented using adapted data structures like DBMs. When we focus on forward analysis algorithms, the exact computation of all the successors of the initial configurations does not always terminate. Thus, some abstractions are often used to ensure termination, among which, a widening operator on zones.In this paper, we study in detail this widening operator and the corresponding forward analysis algorithm. This algorithm is most used and implemented in tools like KRONOS and UPPAAL. One of our main results is that it is hopeless to find a forward analysis algorithm for general timed automata, that uses such a widening operator, and which is correct. This goes really against what one could think. We then study in detail this algorithm in the more general framework of updatable timed automata, a model which has been introduced as a natural syntactic extension of classical timed automata. We describe subclasses of this model for which a correct widening operator can be found. 相似文献
53.
Roberto Bagnara Roberta Gori Patricia M. Hill Enea Zaffanella 《Information and Computation》2004,193(2):84-116
Logic languages based on the theory of rational, possibly infinite, trees have much appeal in that rational trees allow for faster unification (due to the safe omission of the occurs-check) and increased expressivity (cyclic terms can provide very efficient representations of grammars and other useful objects). Unfortunately, the use of infinite rational trees has problems. For instance, many of the built-in and library predicates are ill-defined for such trees and need to be supplemented by run-time checks whose cost may be significant. Moreover, some widely used program analysis and manipulation techniques are correct only for those parts of programs working over finite trees. It is thus important to obtain, automatically, a knowledge of the program variables (the finite variables) that, at the program points of interest, will always be bound to finite terms. For these reasons, we propose here a new data-flow analysis, based on abstract interpretation, that captures such information. We present a parametric domain where a simple component for recording finite variables is coupled, in the style of the open product construction of Cortesi et al., with a generic domain (the parameter of the construction) providing sharing information. The sharing domain is abstractly specified so as to guarantee the correctness of the combined domain and the generality of the approach. This finite-tree analysis domain is further enhanced by coupling it with a domain of Boolean functions, called finite-tree dependencies, that precisely captures how the finiteness of some variables influences the finiteness of other variables. We also summarize our experimental results showing how finite-tree analysis, enhanced with finite-tree dependencies, is a practical means of obtaining precise finiteness information. 相似文献
54.
Pettarin Valeria Frontini Patricia Eliçabe Guillermo Rink Marta Pavan Andrea 《Mechanics of Time-Dependent Materials》2004,8(3):269-288
This paper deals with the influence of the testing equipment on impact load measurements. A previously developed method of analysis and processing of the experimental data based on a refined analogical model of the impact event and inverse problem techniques is used. This method makes it possible to obtain the mechanical response of the material, notwithstanding the disturbance of the dynamic effects associated to the test. Results from tests carried out both on falling weight and swing pendulum instrumented testing machines are compared. It is shown that this method can give an accurate estimation of the actual bending force in impact testing independent of the testing equipment. 相似文献
55.
The corpus callosum has been proposed to contribute to attention by modulating resource allocation between the hemispheres and filtering interhemispheric signal transmission (M. T. Banich, 1998). The resource allocation hypothesis predicts that interhemispheric interactions become more advantageous with increasing resource demands. The selective filtering hypothesis predicts that interhemispheric interactions become less advantageous as filtering requirements increase. The authors tested both predictions by comparing within- and across-hemisphere letter matching under dual-task (Experiment 1) and selective attention conditions (Experiment 2). Task-specific resource demands (i.e., letter processing load) alter the bihemispheric advantage, but the general demand imposed by an unrelated secondary task does not. Filtering requirements influenced the advantage from interhemispheric interactions, providing new evidence for the role of the corpus callosum in selective attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
Blount Ronald L.; Morris Julie A. B.; Cheng Patricia S.; Campbell Robert M.; Brown Ronald T. 《Canadian Metallurgical Quarterly》2004,72(4):597
The authors examined associations among parental and child adjustment, child syncope, somatic, and school problems. Participants were children (N = 56) ages 7-18 years with syncope. Measures included syncope severity, parental distress, and children's internalizing symptoms. For children diagnosed negative for neurocardiogenic syncope (NCS), their fathers' and their own psychological symptoms were positively associated with the severity of syncope, whereas their mothers' functioning was negatively associated with the severity of syncope. Also, for the negative NCS group, fathers' psychological functioning was associated with children's nonsyncope somatic complaints but not with their school problems. For the positive NCS group, few significant father-child associations were found, but several significant positive associations were revealed between mothers' psychological symptoms and their children's syncope as well as somatic and school problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
57.
The discovery of conjunctive causes--factors that act in concert to produce or prevent an effect--has been explained by purely covariational theories. Such theories assume that concomitant variations in observable events directly license causal inferences, without postulating the existence of unobservable causal relations. This article discusses problems with these theories, proposes a causal-power theory that overcomes the problems, and reports empirical evidence favoring the new theory. Unlike earlier models, the new theory derives (a) the conditions under which covariation implies conjunctive causation and (b) functions relating observable events to unobservable conjunctive causal strength. This psychological theory, which concerns simple cases involving 2 binary candidate causes and a binary effect, raises questions about normative statistics for testing causal hypotheses regarding categorical data resulting from discrete variables. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
58.
Industrial control applications are usually developed in two phases: control design and real-time system implementation. In the control design stage a regulator is obtained and later it is translated into an algorithm in the implementation phase. Traditionally, these two phases have been developed in separate ways. Recently, some works have pointed out the necessity of the integration of the control design and its implementation. One of these works reduce the delay variance of control tasks (defined as the control action interval (CAI) and data acquisition interval (DAI) parameters) splitting every task into three parts. The CAI reduction method highly reduces the delay variance and improves the control performance. This work shows how to evaluate these delays under static and dynamic scheduling policies. A new task model is proposed in order to reduce the CAI and DAI parameters, which implies an improvement in the control performance. The new task model will be implemented in a real process, and the experimental measurements will show how, effectively, the control performance is highly improved with the methods presented in this paper. 相似文献
59.
Untreated paired helical filaments (PHFs) and pronase-digested PHF-core filaments were stereoscopically imaged with a freeze-drying vertical platinum-carbon replication preparation method for TEM. The untreated PHF have an average wide region (W) = 22.8 +/- 2.4 nm, a narrow region (T) = 10.6 +/- 1.7 nm, and a helical turn period (L) = 78.6 +/- 13.4. The surfaces of the untreated PHF's fuzzy coat appears disorganized. The widths of the pronase-treated PHF-core filaments were significantly reduced (W(d) = 14.8 +/- 1.2 nm, T(d) = 5.7 +/- 1.0 nm, and L(d) = 75.4 +/- 17 nm). The surfaces of the untreated PHF contained approximately 1.1 nm strands, the same size as tau monomer ( approximately 1.0 nm). The pronase-digested PHF cores mostly contained approximately 1.6 +/- 0.3 nm strands although strand diameters ranged from 0.6-2.5 nm. The strands sometimes appear to be wrapped around the filament axis; less often, they appear to be roughly parallel to the PHF axis, and otherwise appear to be randomly oriented. Images of pronase-digested PHF core images are discussed in relation to the core's biochemical composition, its proposed beta structure, and structural subunit models. Images of the untreated and the pronase-digested PHF support a helical ribbon morphology. 相似文献
60.
Comparison of friction measurements using the atomic force microscope and the surface forces apparatus: the issue of scale 总被引:1,自引:0,他引:1
Results are presented of lateral force measurements using the atomic force microscope (AFM) and the surface forces apparatus (SFA). Two different probes are used in the AFM measurements; a sharp silicon nitride tip (radius R20 nm) and a glass ball (R15 m). The lateral force is measured between the (silicon nitride or glass) probe and a mica surface which has been coated by a thin lubricant film. In the SFA, a thin lubricant film separates two molecularly smooth mica surfaces (R1 cm) which are slid relative to each other. Perfluoropolyether (PFPE) and polydimethylsiloxane (PDMS) were used as the lubricant films. In the SFA where the contact diameter is largest, the PFPE film shows much lower friction than PDMS. As the size of the probe decreases, the difference in the measured friction decreases. For sharp AFM tips, no clear distinction between the tribological properties of the films can be made. Hence, the measured coefficient of friction varies according to the length scale probed, at least for small dimensions. 相似文献