Bidirectional Heuristic Search Reconsidered

The assessment of bidirectional heuristic search has been incorrect since it was first published more than a quarter of a century ago. For quite a long time, this search strategy did not achieve the expected results, and there was a major misunderstanding about the reasons behind it. Although there is still wide-spread belief that bidirectional heuristic search is afflicted by the problem of search frontiers passing each other, we demonstrate that this conjecture is wrong. Based on this finding, we present both a new generic approach to bidirectional heuristic search and a new approach to dynamically improving heuristic values that is feasible in bidirectional search only. These approaches are put into perspective with both the traditional and more recently proposed approaches in order to facilitate a better overall understanding. Empirical results of experiments with our new approaches show that bidirectional heuristic search can be performed very efficiently and also with limited memory. These results suggest that bidirectional heuristic search appears to be better for solving certain difficult problems than corresponding unidirectional search. This provides some evidence for the usefulness of a search strategy that was long neglected. In summary, we show that bidirectional heuristic search is viable and consequently propose that it be reconsidered.Comment: See http://www.jair.org/ for any accompanying file

School Literary Societies--Model Constitution, Rules of Parliamentary Procedure, and Principles of Debating

"August 22, 1913."Mode of access: Internet

Revisiting Old Ground in Light of New Dilemmas: The Need for Queensland to Reconsider the Regulation of Assisted Reproductive Technologies

In recent years, there have been many advances in assisted reproductive technology, in terms of both technological advances and changes in social attitudes. The system of regulation in Queensland is in need of review since it was last considered nearly 25 years ago. The need for review is demonstrated by examining the regulation in Australia as a whole and the impact this has on regulation in Queensland. The paper considers two specific issues. The general access criteria are examined in order to determine who is able to gain access to treatment services, together with how this impacts on gaining access to, and the regulation of, in vitro fertilisation (IVF) and pre-implantation genetic diagnosis (PGD). These issues are discussed mainly in the context of creating tissue-matched children that could act as a cure for an existing ill sibling. The recent review of assisted reproductive technologies (ART) regulation conducted by the Victorian Law Reform Commission is also considered in context of how this may impact on the future regulation of other jurisdictions. The main focus however, is on future options available for Queensland should regulation be reviewed in the future

A branch-and-bound methodology within algebraic modelling systems

Through the use of application-specific branch-and-bound directives it is possible to find solutions to combinatorial models that would otherwise be difficult or impossible to find by just using generic branch-and-bound techniques within the framework of mathematical programming. {\sc Minto} is an example of a system which offers the possibility to incorporate user-provided directives (written in {\sc C}) to guide the branch-and-bound search. Its main focus, however, remains on mathematical programming models. The aim of this paper is to present a branch-and-bound methodology for particular combinatorial structures to be embedded inside an algebraic modelling language. One advantage is the increased scope of application. Another advantage is that directives are more easily implemented at the modelling level than at the programming level

‘Genetic Coding’ Reconsidered : An Analysis of Actual Usage

I thank George Pandarakalam for research assistance; Hans-Jörg Rheinberger for hosting my stay at the Max Planck Institute for History of Science, Berlin; and Sahotra Sarkar and referees of this journal for offering detailed comments. Funded by the Wellcome Trust (WT098764MA).Peer reviewedPublisher PD

What’s a rational self-torturer to do?

This paper concerns Warren Quinn’s famous “The Puzzle of the Self-Torturer.” I argue that even if we accept his assumption that practical rationality is purely instrumental such that what he ought to do is simply a function of how the relevant options compare to each other in terms of satisfying his actual preferences that doesn’t mean that every explanation as to why he shouldn’t advance to the next level must appeal to the idea that so advancing would be suboptimal in terms of the satisfaction of his actual preferences. Rather, we can admit that his advancing would always be optimal, but argue that advancing isn’t always what he ought to do given that advancing sometimes fails to meet some necessary condition for being what he ought to do. For instance, something can be what he ought to do only if it’s an option for him. What’s more, something can be what he ought to do only if it’s something that he can do without responding inappropriately to his reasons—or, so, I argue. Thus, the solution to the puzzle is, I argue, to realize that, in certain circumstances, advancing is not what the self-torturer ought to do given that he can do so only by responding inappropriately to his reasons

School Literary Societies--Model Constitution, Rules of Parliamentary Procedure, Principles of Debating, Questions for Debate, Bibliographies and References

Mode of access: Internet

The power of natural selection

In a recent paper, Steven Horst argued that if traditional physicalist accounts of consciousness cannot explain why there are conscious phenomena in the world then teleological accounts of consciousness that appeal to the notion of natural selection cannot do so either. I agree with Horst's conclusion but his reasoning fails to address a rebuttal to his argument made by the major proponent of such theories, namely, Fred Dretske. Dretske argues that artificial selection can create new features and that, in an analogous fashion, natural selection can too. I show that Dretske's rebuttal is inadequate because crucial features of the analogy fail. Teleological accounts of consciousness that appeal to natural selection can only explain the prevalence of consciousness

Performance analysis of joint precoding and MUD techniques in multibeam satellite systems

This paper considers interference mitigation techniques in the forward link of multibeam satellite systems. In contrast to previous works, either devoted to receiver interference mitigation (e.g. multiuser detection) or transmitter interference mitigation (precoding), this work evaluates the achievable rates of the joint combination of both techniques. On the one hand, precoding cannot properly mitigate all the inter- beam interference while maintaining a sufficiently high signal-to-noise ratio. On the other hand, the receiver cost and complexity exponentially increases with the number of signals to be simultaneously detected. This highlights that the receiver cannot deal with all the interferences so that in general only 2 signals are jointly detected. As a result, the use of precoding within a coverage area jointly with multiuser detection can both benefit from each other and extremely increase the achievable rates of the system. This is numerically evaluated in a close-to-real coverage area considering simultaneous non-unique decoding strategies. The results show the benefits of this joint scheme that eventually can increase the current precoding performance a 23%.Peer ReviewedPostprint (author's final draft