1,721,041 research outputs found
An Improved Genetic Algorithm for the Distributed and Flexible Job-shop Scheduling problem
No full textThe Distributed and Flexible job-shop Scheduling problem (DFJS) considers the scheduling of distributed manufacturing environments, where jobs are processed by a system of several Flexible Manufacturing Units (FMUs). Distributed scheduling problems deal with the assignment of jobs to FMUs and with determining the scheduling of each FMU, in terms of assignment of each job operation to one of the machines able to work it [job-routing flexibility) and sequence of operations on each machine. The objective is to minimize the global makespan over all the FMUs. This paper proposes an Improved Genetic Algorithm to solve the Distributed and Flexible job-shop Scheduling problem. With respect to the solution representation for non-distributed job-shop scheduling, gene encoding is extended to include information on job-to-FMU assignment, and a greedy decoding procedure exploits flexibility and determines the job routings. Besides traditional crossover and mutation operators, a new local search based operator is used to improve available solutions by refining the most promising individuals of each generation. The proposed approach has been compared with other algorithms for distributed scheduling and evaluated with satisfactory results on a large set of distributed-and-flexible scheduling problems derived from classical job-shop scheduling benchmarks
On the (b, c) system contribution to superstring amplitudes
No full textWe use the sewing procedure in the operator formalism to construct explicitly the two-loop vertex for the (b, c) system of string theories in its more general form, needed to compute amplitudes involving picture-changed states. By using this operator we show that the contribution of the reparametrization ghosts to superstring amplitudes is just the same as their contribution to bosonic string ones
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