11,102 research outputs found
Integer programming based solution approaches for the train dispatching problem
Railroads face the challenge of competing with the trucking industry in a fastpaced environment. In this respect, they are working toward running freight trains on schedule and reducing travel times. The planned train schedules consist of departure and arrival times at main stations on the rail network. A detailed timetable, on the other hand, consists of the departure and arrival times of each train in each track section of its route. The train dispatching problem aims to determine detailed timetables over a rail network in order to minimize deviations from the planned schedule. We provide a new integer programming formulation for this problem based on a spacetime network; we propose heuristic algorithms to solve it and present computational results of these algorithms. Our approach includes some realistic constraints that have not been previously considered as well as all the assumptions and practical issues considered by the earlier works
Dynamics of single polymers under extreme confinement
We study the dynamics of a single chain polymer confined to a two dimensional
cell. We introduce a kinetically constrained lattice gas model that preserves
the connectivity of the chain, and we use this kinetically constrained model to
study the dynamics of the polymer at varying densities through Monte Carlo
simulations. Even at densities close to the fully-packed configuration, we find
that the monomers comprising the chain manage to diffuse around the box with a
root mean square displacement of the order of the box dimensions over time
scales for which the overall geometry of the polymer is, nevertheless, largely
preserved. To capture this shape persistence, we define the local tangent field
and study the two-time tangent-tangent correlation function, which exhibits a
glass-like behavior. In both closed and open chains, we observe reptational
motion and reshaping through local fingering events which entail global monomer
displacement.Comment: 22 pages, 18 figures, slightly extended version to appear in JSTA
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