Summary, The famous Ginzburg-Landau equation describes nonlinear amplitude modulations of a wave perturbation of a basic pattern when a control parameter R lies in the unstable region O(e 2) away from the critical value Rc for which the system loses stability. Here e > 0 is a small parameter. G-Us equation is found for a general class of nonlinear evolution problems including several classical problems from hydrodynamics and other fields of physics and chemistry. Up to now, the rigorous derivation of G-Us equation for general situations is not yet completed. This was only demonstrated for special types of solutions (steady, time periodic) or for special problems (the Swift-Hohenberg equation). Here a mathematically rigorous proof of the validity of G-Us equation is given for a general situation of one space variable and a quadratic nonlinearity. Validity is meant in the following sense. For each given initial condition in a suitable Banach space there exists a unique bounded solution of the initial value problem for G-Us equation on a finite interval of the O(1/eZ)-long time scale intrinsic to the modulation. For such a finite time interval of the intrinsic modulation time scale on which the initial value problem for G-Us equation has a bounded solution, the initial value problem for the original evolution equation with corresponding initial conditions, has a unique solution O(e 2) -close to the approximation induced by the solution of G-L's equation. This property guarantees that, for rather general initial conditions on the intrinsic modulation time scale, the behavior of solutions of G-Us equation is really inherited from solutions of the original problem, and the other way around: to a solution of G-Us equation corresponds a nearby exact solution with a relatively small error.
The introduction of extended producer responsibility makes original equipment manufacturers formally responsible for take-back, recovery and reuse of discarded products. One of their key problems is to determine to what extent return products must be disassembled and which recovery and disposal options should be applied. On a tactical management level, this involves anticipating problems like meeting (legislative) recovery targets, limited secondary end markets and investments in recycling infrastructure. In this paper, a comprehensive model is presented, which determines an optimal product recovery and disposal strategy for one product type. The objective function takes into account technical, commercial and ecological criteria as well as uncertainty on these criteria due to lack of information, in particular regarding the quality level. Optimization is done on overall net pro® t and occurs using a two-phased DPalgorithm. The applicability of the model is shown in a case study.
We consider the real-time scheduling of full truckload transportation orders with time windows that arrive during schedule execution. Because a fast scheduling method is required, look-ahead heuristics are traditionally used to solve these kinds of problems. As an alternative, we introduce an agent-based approach where intelligent vehicle agents schedule their own routes. They interact with job agents, who strive for minimum transportation costs, using a Vickrey auction for each incoming order. This approach offers several advantages: it is fast, requires relatively little information and facilitates easy schedule adjustments in reaction to information updates. We compare the agent-based approach to more traditional hierarchical heuristics in an extensive simulation experiment. We find that a properly designed multiagent approach performs as good as or even better than traditional methods. Particularly, the multi-agent approach yields less empty miles and a more stable service level.
The introduction of extended producer responsibility forces Original Equipment Manufacturers to set up a logistic network for take back, processing and recovery of discarded products. In this paper, we discuss a business case study carried out at Océ, a copier firm in Venlo (NL). It concerns the installment of remanufacturing processes. There is a choice from two locations in Venlo (NL) and one in Prague (Czech Republic), where assignments are subjected to managerial constraints. The study is meant to verify whether the strategic decision of Océ to move remanufacturing activities to the Czech Republic is also economically feasible. We limit ourselves to an optimisation of the HV02-machine network. We follow our general approach, in which we first determine how return products are processed (recovery strategy) and subsequently optimise the reverse logistic network design. We optimise on total operational costs over all possibilities and also compare three pregiven managerial solutions (=network designs) with a Mixed Integer Linear Programming model. Differences in economic costs appear to be very small, hence installing recovery activities in Prague for the HV02-machine must be well motivated from a strategic point of view. Moreover, we argue that besides cost minimisation, Océ should include performance indicators, such as JIT, reliability, in logistic optimisation to support its quality oriented business strategy. In addition, we discuss aspects regarding specific modelling elements in this case situation, the definition of cost functions, the possibility of optimising the forward and reverse logistic network and the use of LP-versus MILP-models in this kind of situations.
The introduction of extended producer responsibility forces Original Equipment Manufacturers to set up a logistic network for take back, processing and recovery of discarded products. In this paper, we discuss a business case study carried out at Océ, a copier firm in Venlo (NL). It concerns the installment of remanufacturing processes. There is a choice from two locations in Venlo (NL) and one in Prague (Czech Republic), where assignments are subjected to managerial constraints. The study is meant to verify whether the strategic decision of Océ to move remanufacturing activities to the Czech Republic is also economically feasible. We limit ourselves to an optimisation of the HV02-machine network. We follow our general approach, in which we first determine how return products are processed (recovery strategy) and subsequently optimise the reverse logistic network design. We optimise on total operational costs over all possibilities and also compare three pregiven managerial solutions (=network designs) with a Mixed Integer Linear Programming model. Differences in economic costs appear to be very small, hence installing recovery activities in Prague for the HV02-machine must be well motivated from a strategic point of view. Moreover, we argue that besides cost minimisation, Océ should include performance indicators, such as JIT, reliability, in logistic optimisation to support its quality oriented business strategy. In addition, we discuss aspects regarding specific modelling elements in this case situation, the definition of cost functions, the possibility of optimising the forward and reverse logistic network and the use of LP-versus MILP-models in this kind of situations.
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