Search

The visual search process is modeled as a sequence of fixations which may or may not partially overlap in coverage of the search field. A single expression is derived for the probability of search success which covers all overlap cases. Making the further assumption that search strategy is chosen so as to maximize expected value, yields the result that each point on the search field must be fixated an integral number of times. In an experiment where visual lobe size and fixation duration were controlled, human subjects behaved in a manner close to that predicted by the optimization model. It is concluded that further development of the model using less restrictive assumptions is warranted.

Consider the problem of achieving optimal system size, n, and threshold value, k, for {k, n-k+1}-out-of-n and majority systems with competing failure modes. Components are s-independent and identically distributed, and the two system failure modes can have different costs. The authors determine optimal k, given n; optimal n, given k; and optimal k,n. Optimal implies minimum mean system cost for the {k, n-k+1}-out-of-n or majority system. The authors study the behavior of the optimal k as a function of failure probabilities, and of maximizing the reliability of majority systems. Numerical examples illustrate the results. >

This report discusses: investigations in computational science applications at Argonne; software tools for analysis and transformation of Fortran programs; scientific visualization projects and demonstrations; and institutional strategies in advanced scientific computing.

In reliability computations for complex systems subject to two kinds of failure, analysts sometimes underestimate system reliability by using a formula that actually applies only to certain simpler structures. This error occurs several times, for example, in an otherwise instructive paper by B.W. Jenney and D.J. Sherwin (ibid., vol.R-35, p.532-8, Dec. 1986). The purpose of this work is to describe the error, illustrate how it arises in practice, and offer a correction. >