Double exponential stability of quasi-periodic motion in Hamiltonian systems

We prove that generically, both in a topological and measure-theoretical sense, an invariant Lagrangian Diophantine torus of a Hamiltonian system is doubly exponentially stable in the sense that nearby solutions remain close to the torus for an interval of time which is doubly exponentially large with respect to the inverse of the distance to the torus. We also prove that for an arbitrary small perturbation of a generic integrable Hamiltonian system, there is a set of almost full positive Lebesgue measure of KAM tori which are doubly exponentially stable. Our results hold true for real-analytic but more generally for Gevrey smooth systems

Okapi: a prototype online catalogue

This article is a continuation and expansion of, which reported on an early stage of 'Microcomputer networking in libraries', a project funded by the British Library Research and Development Department and the Department of Trade and Industry. The work was carried out at the Polytechnic of Central London (PCL) by Mitev, Venner and Walker; its main aim was to construct a prototype online public access catalogue (OPAC) using local area network (LAN) hardware. The hardware was a Nestar PLAN 4000 network, using Apple IIe microcomputers as work stations and a 137 megabyte Winchester disc controlled by a 68000-based file server

Convergence and divergence in information systems and knowledge based systems development methodologies: a case for integrated strategic planning

There is a need to integrate knowledge based systems (KBS) with information systems (IS) technical solutions, which implies that KBS and IS development methodologies should be less isolated from each other. KBS and IS development methodologies are generally examined in terms of their similarities and differences. There is divergence at the feasibility and analysis stages, convergence at the design and coding stages, divergence during testing, convergence at the implementation stage, and divergence during maintenance. There are more similarities than there are differences between IS and KBS methodologies, particularly during the strategic planning stage. It is argued that linking KBS strategic planning to the planning element of an IS methodology will go further towards ensuring that the whole of the business is considered, leading to better integrated IS/KBS solutions. Application selection activities of two well-known KBS methodologies are briefly analysed. We show that these activities, which precede the feasibility study, do not consider the strategic aspects of the use of KBS (and IS in general) in business organizations. It is argued that a KBS strategy should be formulated in relation to the IS strategy and the business strategy, therefore increasing the convergence between IS and KBS methodologies

Information systems failure, politics and the sociology of translation The problematic introduction of an American computerised reservation system and yield management at French Railways

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