The Organisation of Logistic Support Systems

Journal of the Operational Research Society -     

Flow Through Symmetrically Constricted Tubes

Fluid morion through a tube is discussed when there is a moderateor severe symmetric constriction at the wall, and the oncomingflow is fully developed. The Reynolds number R is assumed large.During a moderate constriction, where the typical slope isO(R^–), upstream separation can be provoked due to thedownstream pressure being transmitted back, through the inviscidcore flow. Separation can also occur after a point of maximumconstriction. Computations and analysis indicate that the upstreamseparation point is pushed increasingly ahead as the slope israised. The implication for a severe constriction, where isO(1), is that the flow separates at a large distance O(a lnR) upstream (a being the tubewidth) and produces a shear layerwhich, on nearing the constriction, reaches O(a) distances fromthe wall.     

Travel Times Through Shock Waves

In this paper on traffic streams the author formulates the well-known principle of conservation of matter with an integral equation expressing travel times in the stream. A traffic situation is investigated where time-dependent flow rates into a bottleneck temporarily exceed its capacity. Expressions are found for queue sizes, the location and velocity of shock waves, and delays to vehicles in the stream.     

Polyhedral Separability Through Successive LP

We address the problem of discriminating between two finite point sets in the n-dimensional space by h hyperplanes generating a convex polyhedron. If the intersection of the convex hull of is empty, the two sets can be strictly separated (polyhedral separability). We introduce an error function which is piecewise linear, but not convex nor concave, and define a descent procedure based on the iterative solution of the LP descent direction finding subproblems.     

Preserving Positive Realness Through Discretization

The importance of positive real transfer functions relies on the fact that they are associated with positive linear systems. Those systems possess the property that their input-output product time-integral, which is a measure of the total enerty, is nonnegative. Such a property can be also formulated in the discrete context. It is shown that a discrete positive real transfer function is obtained from a positive real continuous one of relative order zero being strictly stable poles via discretization by a sampler and zero-order hold device provided that the direct input-output transmission gain is sufficiently large. It is also proved that a discrete positive real transfer function may be obtained from a stable continuous one of relative order zero and high direct input-output gain which posses simple complex conjugate critically stable poles even in the case that this one is not positive real. For that purpose, the use of an appropriate phase-lag or phase lead compensating network for the continuous transfer function may be required to ensure positive realness of the discrete transfer function.     

Metamorphoses Through Lie Group Action

We formally analyze a computational problem which has important applications in image understanding and shape analysis. The problem can be summarized as follows. Starting from a group action on a Riemannian manifold M, we introduce a modification of the metric by partly expressing displacements on M as an effect of the action of some group element. The study of this new structure relates to evolutions on M under the combined effect of the action and of residual displacements, called metamorphoses. This can and has been applied to image processing problems, providing in particular diffeomorphic matching algorithms for pattern recognition.