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41.
Voting algorithms are used to arbitrate between the results of redundant modules in fault-tolerant systems. Inexact majority and weighted average voters have been used in many applications, although both have problems associated with them. Inexact majority voters require an application-specific 'voter threshold’ value to be specified, whereas weighted average voters are unable to produce a benign output when no agreement exists between the voter inputs. Neither voter type is able to cope with uncertainties associated with the voter inputs. This paper introduces a novel voting scheme based on fuzzy set theory. It softens the harsh behaviour of the inexact majority voter in the neighbourhood of the ‘voter threshold’, and handles uncertainty and some multiple error cases in the region defined by the fuzzy input variables. The voter assigns a fuzzy difference value to each pair of voter inputs based on their numerical distance. A set of fuzzy rules then determines a single fuzzy agreeability value for each individual input which describes how well it matches the other inputs. The agreeability of each voter input is then defuzzified to give a weighting value for that input which determines its contribution to the voter output. The weight values are then used in the weighted average algorithm for calculating the voter final output. The voter is experimentally evaluated from the point of view safety and availability, and compared with the inexact majority voter in a Triple Modular Redundant structured framework. The impact of changing some fuzzy variables on the performance of the voter is also investigated. We show that the fuzzy voter gives more correct outputs (higher availability) than the inexact majority voter with small and large errors, less incorrect outputs (higher safety) than the inexact majority voter in the presence of small errors, and less benign outputs than the inexact majority voter. The percentage of the benign outputs of the majority voter that are successfully handled by the fuzzy voter (resulting in correct outputs) is more than the percentage of those that are unsuccessfully resolved by the fuzzy voter (resulting in incorrect outputs). Our results suggest that the fuzzy voter is a viable alternative to a traditional inexact voter in cases where the benefits of a large increase in availability, and a considerable decrease in the number of benign outputs outweighs the cost of a small degradation in the safety performance of the system. The fuzzy voter is also a useful voting algorithm when arbitrating between the responses of dynamic channels of control systems incorporating uncertainties. This is the first reported use of a complete fuzzy voter in the context of fault tolerance. 相似文献
42.
Kinetics of deformation and fracture of nickel–iron alloy Inconel 718 under dynamic shear loading was measured using a split
torsional Hopkinson bar facility and high-speed photography. Tubular specimens with a reduced gage length and a starter notch
were sheared at strain rates up to 6 × 103 s−1. High-speed photographs of fiducial lines scribed on the specimen surface showed the development of local strains and cracking.
This paper describes the experimental and analytical procedures, illustrates average and local plastic strain evolution, and
presents shear crack initiation times and propagation speeds. 相似文献
43.
We study in dimension d?2 low-energy spectral and scattering asymptotics for two-body d-dimensional Schrödinger operators with a radially symmetric potential falling off like −γr−2, γ>0. We consider angular momentum sectors, labelled by l=0,1,…, for which γ>2(l+d/2−1). In each such sector the reduced Schrödinger operator has infinitely many negative eigenvalues accumulating at zero. We show that the resolvent has a non-trivial oscillatory behaviour as the spectral parameter approaches zero in cones bounded away from the negative half-axis, and we derive an asymptotic formula for the phase shift. 相似文献
44.
Yichun Chi 《Insurance: Mathematics and Economics》2011,48(3):326-337
In this paper, we generalize the Cramér-Lundberg risk model perturbed by diffusion to incorporate jumps due to surplus fluctuation and to relax the positive loading condition. Assuming that the surplus process has exponential upward and arbitrary downward jumps, we analyze the expected discounted penalty (EDP) function of Gerber and Shiu (1998) under the threshold dividend strategy. An integral equation for the EDP function is derived using the Wiener-Hopf factorization. As a result, an explicit analytical expression is obtained for the EDP function by solving the integral equation. Finally, phase-type downward jumps are considered and a matrix representation of the EDP function is presented. 相似文献
45.
Eric C.K. Cheung 《Insurance: Mathematics and Economics》2011,48(3):384-397
In a general Sparre Andersen risk model with surplus-dependent premium income, the generalization of Gerber-Shiu function proposed by Cheung et al. (2010a) is studied. A general expression for such Gerber-Shiu function is derived, and it is shown that its determination reduces to the evaluation of a transition function which is independent of the penalty function. Properties of and explicit expressions for such a transition function are derived when the surplus process is subject to (i) constant premium; (ii) a threshold dividend strategy; or (iii) credit interest. Extension of the approach is discussed for an absolute ruin model with debit interest. 相似文献
46.
Thresholds for extinction and persistence are important for assessing the risk of mortality in systems exposed to toxicant. In this paper, three single-species models with random perturbation in a polluted environment are proposed and investigated. One is the generalized logistic model and the other two are the stochastic resource–consumer models of Leslie and Gallopin. For each model, the survival threshold is obtained in some cases. In general, each threshold is determined by intensity of the random noise, the mean stress measure in organisms, the population intrinsic growth rate and the stress response rate. 相似文献
47.
48.
双阈值二元神经网络极限环的存在惟一性 总被引:3,自引:0,他引:3
研究具负反馈的双阈值二元神经网络模型的动力学性质。在一定的初始函数空间内,对设定的阈值范围证明了模型存在惟一稳定极限环。 相似文献
49.
F. Avram 《Operations Research Letters》2006,34(3):339-348
This paper deals with two M/M/1 queues served by a single server with threshold switching. Our main goal is to solve the Poisson equation and, as a result, give expressions for the long-run expected average cost of holding units and switching actions of the server, and the bias vector. 相似文献
50.
A finite element method for the analysis of nearshore current, which is one of the principal currents in coastal seas, is presented in this paper. Because the nearshore current is induced by the variable distribution of the surface waves, it is necessary to analyse two main characteristics of the wave, i.e. direction and height. The current can be computed using the resulting wave characteristics. The present method makes it possible to employ procedures for which the same methods of solution are applicable for all basic equations of wave direction, height and current flow. The linear interpolation function is used for the discretization of spatial variables and a selective lumping two step explicit scheme is employed for the numerical integration in time. The numerical solutions obtained are compared with analytical, experimental and observed ones. From these comparative studies, it is concluded that the present finite element method provide a useful tool for the analysis of nearshore current. 相似文献