From Planning Board to Welding Hall: A Case-Study in O.R./Client Involvement

Danish shipyard building supertankers was faced with a production-planning problem in one of its welding-halls, where the bow and stern sections were fabricated. The mandatory constraint of completing each section by a specified day in the production cycle was complicated by a number of other practical constraints. A trial exercise demonstrated that human skills were unbeatable in solving aspects of planning concerned with fitting shapes into spaces-and that the major planning problems were keeping track of planning-progress and computing the labour load. An interactive planning computer-system was devised which gave full rein to the complementary skills of planner and computer. This system had the merit, from management's point of view, that the fullest use could be made of existing planning expertise. The system was designed and implemented in stages over about four months: training sessions at each stage provided valuable input for the design of the next stage.     

A variational solution of the stochastic liouville model of chemically induced electron polarization in radical pairs

A variational solution is proposed for the integral equation form of the stochastic Liouville equations describing the radical pair mechanism of chemically induced electron polarization.     

Thermal stability and the behaviour in organic solvents of some poly(ester-siloxane)urethanes

Three new chemically crosslinked polyurethanes were synthesized. Their behaviour in organic solvents and in dynamic heating conditions was studied. Predictions regarding the thermal stability have been made by using the isoconversion kinetic method.     

Stochastic estimation of conditional structure: a review

Mean square estimation methods can be applied to the approximation of conditionally averaged turbulent fields to educe mean structure of the fields. The mathematical procedure is reviewed, and the results obtained by selecting events of increasing complexity are summarized.     

Singular terms of helicity amplitudes at one loop in QCD and the soft limit of the cross sections of multi-parton processes

We describe a general method that enables us to obtain all the singular terms of helicity amplitudes of n-parton processes at one loop. The algorithm uses helicity amplitudes at tree level and simple color algebra. We illustrate the method by calculating the singular part of the one-loop helicity amplitudes of all 2 → 3 parton subprocesses. The results are used to derive the soft gluon limit of the cross sections of all 2 → 4 parton scattering subprocesses which provide a useful initial condition for the angular ordering approximation to coherent multiple soft gluon emission, incorporated in existing Monte Carlo simulation programs.     

Super-Instantons, Perfect Actions, Finite-Size Scaling, and the Continuum Limit

We discuss some aspects of the continuum limit of some lattice models, in particular the 2DO(N) models. The continuum limit is taken either in an infinitevolume or in a box whose size is a fixed fraction of the infinite-volume correlation length. We point out that in this limit the fluctuations of the lattice variables must be O(1) and thus restore the symmetry which may have been broken by the boundary conditions (b.c.). This is true in particular for the socalled super-instanton b.c. introduced earlier by us. This observation leads to a criterion to assess how close a certain lattice simulation is to the continuum limit and can be applied to uncover the true lattice artefacts, present even in the so-called “perfect actions”. It also shows that David’s recent claim that superinstanton b.c. require a different renormalization must either be incorrect or an artefact of perturbation theory.     

Simulating the Kinematic Dynamo Forced by Heteroclinic Convective Velocity Fields

We report on the integration of the kinematic dynamo problem in a spherical domain forced by velocity fields that are convective fluid flows resulting from a bifurcation analysis of the spherical Bénard problem. We derive a code based on generalized spherical harmonics that ensures a divergence-free magnetic field. We determine the growth or decay of a magnetic field in the kinematic dynamo equation for various physically relevant velocity fields which are stationary as well as time-periodic and chaotic. Velocity signals that are produced by heteroclinic cycles are used as an input to an energy-saturated kinematic dynamo equation that limits the growth of the linearly unstable modes. Preliminary calculations indicate the possibility of reversals of the magnetic field for this case of forcing. Received 8 October 1996 and accepted 28 April 1997