Steven Phillips

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We consider variants on the Prize Collecting Steiner Tree problem and on the primal-dual 2-approximation algorithm devised for it by Goemans and Williamson. We introduce an improved pruning rule for the algorithm that is slightly faster and provides solutions that are at least as good and typically significantly better. On a selection of real-world(More)
Virtually all research in scheduling theory has been concerned with clairvoyant scheduling where it is assumed that the characteristics of a job (in particular, its execution time, release time and dependence on other jobs) are known a priori. This assumption is invalid for scheduling problems that arise in time-sharing operating systems where the scheduler(More)
What is the best paging algorithm if one has partial information about the possible sequences of page requests? We give a partial answer to this question, by presenting the analysis of strongly competitive paging algorithms in the access graph model. This model restricts page requests so that they conform to a notion of locality of reference, given by an(More)
How much can an imperfect source of randomness affect an algorithm? We examine several simple questions of this type concerning the long-term behavior of a random walk on a finite graph. In our setup, each step of the random walk a “controller” can, with a certain small probability, fix the next step, thus introducing a bias. We analyze the(More)
An 'Aha! reaction' is a brief moment of exceptional thinking where an unexpected change in one's mental perspective reveals the solution to an otherwise intractable problem. In this event-related fMRI study, subjects read incomprehensible sentences followed by solution cues that were used to evoke such a reaction by triggering an alternative interpretation(More)
Accumulating evidence on the nature, function and acquisition of relational knowledge indicates a crucial role of such knowledge in higher cognitive processes. In this review, we specify the essential properties of relational knowledge, together with the role it plays in reasoning, categorisation, planning, quantification and language. Furthermore, we(More)
When carrying Internet Protocol (IP) traffic over an Asynchronous Transfer Mode (ATM) network, the ATM adaptation layer must determine how long to hold a virtual circuit opened to carry an IP datagram. In this paper we present a formal statement of the problem and carry out a detailed empirical examination of various holding time policies taking into(More)
In this paper we consider the paging problem when the page request sequence is drawn from a distribution, and give an application to computer networking. In the IP-paging problem the page inter-request times are chosen according to independent distributions. For this model we construct a very simple deterministic algorithm whose page fault rate is at most 5(More)