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991.
The action system formalism has been succesfully used when constructing parallel and distributed systems in a stepwise manner within the refinement calculus. Usually the derivation is carried out manually. In order to be able to produce more trustworthy software, some mechanical tool is needed. In this paper we show how action systems can be derived and refined within the B-Toolkit, which is a mechanical tool supporting a software development method, the B-Method. We describe how action systems are embedded in the B-Method. Furthermore, we show how a typical and nontrivial refinement rule, the superposition refinement rule, is formalized and applied on action systems within the B-Method. In addition to providing tool support for action system refinement we also extend the application area of the B-Method to cover parallel and distributed systems. A derivation towards a distributed load balancing algorithm is given as a case study. 相似文献
992.
Consider a given pattern H and a random text T generated by a Markovian source. We study the frequency of pattern occurrences in a random text when overlapping copies
of the pattern are counted separately. We present exact and asymptotic formulae for moments (including the variance), and
probability of r pattern occurrences for three different regions of r , namely: (i) r=O(1) , (ii) central limit regime, and (iii) large deviations regime. In order to derive these results, we first construct certain
language expressions that characterize pattern occurrences which are later translated into generating functions. We then use
analytical methods to extract asymptotic behaviors of the pattern frequency from the generating functions. These findings
are of particular interest to molecular biology problems (e.g., finding patterns with unexpectedly high or low frequencies,
and gene recognition), information theory (e.g., second-order properties of the relative frequency), and pattern matching
algorithms (e.g., q -gram algorithms). 相似文献
993.
We contrast theorem provers and computer algebra systems, pointing out the advantages and disadvantages of each, and suggest a simple way to achieve a synthesis of some of the best features of both. Our method is based on the systematic separation of search for a solution and checking the solution, using a physical connection between systems. We describe the separation of proof search and checking in some detail, relating it to proof planning and to the complexity class NP, and discuss different ways of exploiting a physical link between systems. Finally, the method is illustrated by some concrete examples of computer algebra results proved formally in the HOL theorem prover with the aid of Maple. 相似文献
994.
Muller Stéphanie Garda Patrick Muller Jean-Denis Crusem René Cansi Yves 《Neural Processing Letters》1998,8(1):83-91
This letter presents a method for modelling and processing incomplete data in connectionist systems. The approach consists in applying a neuro-fuzzy coding to the input data of a neural network. After an introduction to the different kinds of imperfections, we propose a neuro-fuzzy coding in order to take incomplete data into account. We show the efficiency of this coding on the problem of the classification of seismic events. The results show that a neuro-fuzzy coding of the inputs of a neural network increases the performance and classifies incomplete data with little affect on the results. 相似文献
995.
B Escobar-Pérez 《欧洲信息系统杂志》1998,7(3):202-209
Previous research has reviewed the foundations of the most significant methods for the evaluation of investments in information systems (IS). However, in our view, it is also necessary to provide an updated view on the evaluation methods actually used in practice by organizations. This paper offers a view on the investment in IS in business practice in Spain, analysing: (i) the evaluation methods currently used by Spanish firms; (ii) how companies make decisions concerning investments in IS; (iii) the nature and quality of the decisions; and (iv) the consequences derived from them. 相似文献
996.
基于多决策树算法的网络入侵检测 总被引:2,自引:2,他引:2
将一个大数据集分割成若干个子数据集,在每个子数据集上使用决策树算法进行挖掘,用投票的方式将多棵决策树的结果结合起来,形成全局的判断。将这种方法应用于网络入侵检测,试验表明,该方法不仅提高了数据挖掘算法对海量数据的处理能力,而且降低了误判率。 相似文献
997.
R. Sánchez-Pérez L. García-Demedices J. Palafox Ramos M. Díaz-Cruz R. D. Morales 《Metallurgical and Materials Transactions B》2004,35(1):85-99
Two-phase flows in a mold of a slab caster are studied using water modeling, particle-image velocimetry (PIV), and computational
fluid-dynamics techniques. Two-way coupled flows are observed in liquidgas systems, because both phases influence each other’s
momentum transfer. In addition to this concept, PIV measurements indicate the existence of structurally coupled flows, where
the velocity vectors of both phases observe similar orientations. When the drag forces of the liquid, exerted on the bubbles,
exceed a certain value of the inertial forces of the liquid phase, at high mass loads of gas (ratio of mass flow rates of
the gas phase and the liquid phase), the flow becomes structurally coupled. These types of flows promote large oscillations
of the meniscus level. Two jets, liquid and bubble, were identified; the latter always reported larger angles than the first,
independent of the gas load. Thus, a gas-rich jet is located closer to the lower edge of the submerged entry nozzle (SEN)
port, and the liquid-rich jet is found above this position. The liquid-jet angle approaches that of the SEN port when the
flow becomes structurally coupled. Structurally uncoupled flows report gas jets that follow torrent-type patterns which are
well explained using a multiphase fluid-dynamics model. Structurally coupled flows yield gas jets with a continuous pattern. 相似文献
998.
R. Valle M.-H. Vidal-Sétif D. Schuster P. Le Vacon 《Metallurgical and Materials Transactions A》2004,35(10):3307-3317
The mechanical behavior (tension, fatigue, and notch sensitivity) of Al-based metal matrix composite (MMC) cross-ply laminates
is investigated. The two selected laminates, K139/A357 and N610/AU2, are reinforced by continuous K139 (carbon) or N610 (alumina)
fibers. These multiplies consist in the stacking of (quasi-unidirectional) quasi-UD preforms oriented at 0, ±45, and 90 deg,
the thermomechanical behavior of the corresponding quasi-UD composites being reported independently (Part I). The investigated
cross-ply laminates exhibit attractive static and cyclic performances and a low notch (circular hole) sensitivity. High-resolution
microfractography has led to a better understanding of the fracture mechanisms of these materials. In this respect, the role
of the transverse bundles is dominant in the tensile and fatigue failure of both laminates. However, the failure surfaces
are completely different: long fiber pullout in the K139/A357 laminate and much more planar areas in the N610/AU2 laminate.
Due to the rather low notch sensitivity, a large portion of the specimen section was already highly damaged during a non-negligible
part of the fatigue life: debonded interfaces in the K139/A357 laminate and multicracked and “crumbled” matrix in the N610/AU2
laminate. These mechanisms are in good agreement with the weak interface in the first case and the very low yield stress of
the AU2 matrix, much lower than the fatigue limit of the N610/AU2 laminate, in the second case. Moreover, compared to the
quasi-UD composites, the stress concentration around the notch allows further exacerbation of the fatigue mechanisms, much
more intense than that attained in “model” composites. 相似文献
999.
In [V] the third author studied statistical properties of words generated by dynamical sources by
using generalized Ruelle operators. This erratum aims to show that a supplementary condition should be added
in Definition 2.1 of dynamical sources. This supplementary condition (called (d4) below) is closely related to
the so-called Bounded Distortion Property and should be used at two different stages of the paper: first in the
definition of the generalized operator Gs, second in the proof of Proposition 2 that deals with the Positivity
Theorem of Krasnoselskii. We also prove that this condition is actually necessary and provide an example of
a source which does not satisfy condition (d4) and for which Gs is not well-defined. 相似文献
1000.
This paper addresses the issue of improving the performance of memory management for real-time Java applications, building upon the real-time specification for Java (RTSJ) from the Real-Time Java Expert Group. In a first step, a collecting dynamic memory solution including both a real-time garbage collector and region-based memory management, is proposed. A thorough analysis of the parameters influencing the performance of write barriers in memory management, together with ways of improvement are then presented. Finally, the implementation of a memory management solution compliant with the RTSJ and integrating the proposed improvements is sketched. 相似文献