Computation and Homotopical Applications of Induced Crossed Modules

We explain how the computation of induced crossed modules allows the computation of certain homotopy 2-types and, in particular, second homotopy groups. We discuss various issues involved in computing induced crossed modules and give some examples and applications.Comment: 15 pages, xypic, latex2

A Market Analysis of a Set-aside Program by the Five Major Grain and Oilseed Exporting Countries

Nominal grain and oilseed prices have declined dramatically from the high levels observed in the mid-1990s. As a result, it has been suggested by some industry stakeholders that measures should be taken to limit world crop supplies to raise prices. One such measure is a set-aside program involving a number of participants that would significantly reduce the quantity of land in production over a certain period of time. In fact, the European Union and the United States currently have set-aside programs that, together, already have had a positive effect on crop prices. Set-aside programs could also become relevant if the use of the World Trade Organization blue box is extended to more countries after the next round of negotiations. This analysis focuses on the quantitative aspects of a substantial multi-country, multi-commodity, set-aside program and its impact on major agricultural commodity prices. Three main conclusions can be drawn from the analysis: · A permanent set-aside program would be necessary to keep prices from returning to relatively low levels · Even with a permanent set-aside program, the results show a declining effect over time mostly because of additional production by non-participating countries and because of crop substitution in favour of cereals and oilseeds and higher yield in participating countries. · For a set-aside program to have any significant impact on prices, the program must include many commodities in many countries. A program involving Canada alone is doomed to fail. And given that the United States and the European Union-two large producers-already have their respective set-aside programs, it might be difficult to convince them to participate in an international effort.Agricultural and Food Policy, Demand and Price Analysis,

Darwinism, probability and complexity : market-based organizational transformation and change explained through the theories of evolution

The study of transformation and change is one of the most important areas of social science research. This paper synthesizes and critically reviews the emerging traditions in the study of change dynamics. Three mainstream theories of evolution are introduced to explain change: the Darwinian concept of survival of the fittest, the Probability model and the Complexity approach. The literature review provides a basis for development of research questions that search for a more comprehensive understanding of organizational change. The paper concludes by arguing for the development of a complementary research tradition, which combines an evolutionary and organizational analysis of transformation and change

A forward view on reliable computers for flight control

The requirements for fault-tolerant computers for flight control of commercial aircraft are examined; it is concluded that the reliability requirements far exceed those typically quoted for space missions. Examination of circuit technology and alternative computer architectures indicates that the desired reliability can be achieved with several different computer structures, though there are obvious advantages to those that are more economic, more reliable, and, very importantly, more certifiable as to fault tolerance. Progress in this field is expected to bring about better computer systems that are more rigorously designed and analyzed even though computational requirements are expected to increase significantly

String rewriting for Double Coset Systems

In this paper we show how string rewriting methods can be applied to give a new method of computing double cosets. Previous methods for double cosets were enumerative and thus restricted to finite examples. Our rewriting methods do not suffer this restriction and we present some examples of infinite double coset systems which can now easily be solved using our approach. Even when both enumerative and rewriting techniques are present, our rewriting methods will be competitive because they i) do not require the preliminary calculation of cosets; and ii) as with single coset problems, there are many examples for which rewriting is more effective than enumeration. Automata provide the means for identifying expressions for normal forms in infinite situations and we show how they may be constructed in this setting. Further, related results on logged string rewriting for monoid presentations are exploited to show how witnesses for the computations can be provided and how information about the subgroups and the relations between them can be extracted. Finally, we discuss how the double coset problem is a special case of the problem of computing induced actions of categories which demonstrates that our rewriting methods are applicable to a much wider class of problems than just the double coset problem.Comment: accepted for publication by the Journal of Symbolic Computatio