Accumulation point location on tree networks for guaranteed time distribution

Article Abstract:

The problem of guaranteed time distribution involves the implementation of a distribution system that completes movement between source-destination pairs within a guaranteed time. Movement between source and destination involves many different types of transportation at various speeds. The guaranteed time distribution problem entails decisions as to the location of accumulation points or local centers at which changes in travel modes occur. Flow from and to customers must be allocated to the local centers in such a manner as to guarantee the minimum time of travel between source-destination pairs. Flows that pass through a global center are part of a centralized sorting system (CSS) and flows that go directly between local centers are part of a decentralized sorting system (DSS). Polynomial time algorithm is presented for assigning locations to local centers so as to create a CSS in which the minimum possible time is guaranteed for a route whose points form a tree structure, and a polynomial time algorithm which is a repeated solution of a similar CSS problem is provided to solve the DSS problem.

Research, Network analysis (Planning), Distributions, Theory of (Functional analysis), Theory of distributions, Algorithms

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Garbage collection in Chicago: a dynamic scheduling model

Article Abstract:

A dynamic scheduling model has been developed for garbage collection in Chicago, IL. The weight and time required to collect garbage from a block is modeled as a random variable. A dynamic scheduling algorithm employing flexible truck routes is introduced. The selection of a truck route is modeled as a Markov decision process. The output of the model is an implementable schedule that generates daily work assignments for each truck. Comparisons between the capacity required by the model and the capacity used in the current operation show that the proposed approach can reduce truck capacity by 12%-16%, translating to a potential cost reduction of more than $9 million.

Models, Usage, Scheduling (Management), Refuse and refuse disposal, Waste disposal, Waste management, Chicago, Illinois, Markov processes

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Shared storage policies based on the duration stay of unit loads

Article Abstract:

Shared storage policies based on the duration of stay of individual unit loads are presented. These policies can considerably decrease the travel time of single-command storage and retrieval systems. The optimal policy for systems with an input-output balance involves storing unit loads based on how long they will stay in the system. Policies for systems that do not have balanced inputs and outputs can be developed by modifying the duration-of-stay principle. These policies are not optimal, but the average travel time under these policies is about 25% lower than it would be under the dedicated storage policy.

Methods, Management, Warehousing, Materials handling, Inventory control

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