The final order problem for repairable spare parts under condemnation

We consider a manufacturer of complex machines that offers service contracts to her customers, committing herself to repair failed spare parts throughout a fixed service period. The suppliers of spare parts often discontinue the production of some parts as technology advances and ask the manufacturer to place a final order. We address the problem of determining final orders for such spare parts. The parts that we consider are repairable, but they are subject to the risk of condemnation. We build a transient Markovian model to represent the problem for a repairable spare part with a certain repair probability and repair lead time and we present some approximations that allow for further real life characteristics to be included. Furthermore, an approximate model that can be computed more efficiently is presented, and the sensitivity of the results obtained with respect to the problem parameters for both of the models is discussed

Inventory planning for spare parts networks with delivery time requirements

Motivated by real life, we introduce a new inventory model for spare parts where we explicitly take delivery time requirements into account. In this single-echelon, multilocation network, demand of a customer can be satisfied from multiple warehouses, but only if the customer can be reached from a warehouse within a time limit that is specified in the service contract of the customer. A delivery to a customer from a warehouse other than the closest one is referred to as a lateral transshipment. We develop a fast and accurate approximate algorithm to evaluate the performance of the network under given base stock levels and propose a fast and effective heuristic to set base stock levels. Numerical experiments show that planning with lateral transshipments can lead to cost savings up to 47% when compared to planning without lateral transshipments. Furthermore, we show the importance of taking lateral transshipments into account when designing a spare parts network

Experimental and numerical study of SiON microresonators with air and polymer cladding

A systematic experimental and numerical study of the device performance of waveguide-coupled SiON microresonators with air and polymer cladding is presented. Values of device parameters like propagation losses of the microresonator modes, the off-resonance insertion losses, and the straight waveguide to microresonator coupling are determined by applying a detailed fitting procedure to the experimental results and compared to results of detailed numerical simulations. By comparing the propagation losses of the fundamental TE polarized microresonator mode obtained by fitting to the measured spectra to the also experimentally determined propagation losses in the adjacent straight waveguide and the materials losses, it is possible to identify the loss mechanisms in the microresonator. By comparing experimental results for microresonators with air and polymethylmethacrylate cladding and a detailed numerical study, the influence of the cladding index on the bend losses is evaluated. It is demonstrated that the presence of an upper cladding can, under the right conditions, actually be beneficial for loss reduction

Mapping electronic reconstruction at the metal/insulator interfaces in \ce{LaVO_3/SrVO_3} heterostructures

A \ce{(LaVO_3)_6/(SrVO_3)_3} superlattice is studied with a combination of sub-{\AA} resolved scanning transmission electron microscopy and monochromated electron energy-loss spectroscopy. The V oxidation state is mapped with atomic spatial resolution enabling to investigate electronic reconstruction at the \ce{LaVO_3}/\ce{SrVO_3} interfaces. Surprisingly, asymmetric charge distribution is found at adjacent chemically symmetric interfaces. The local structure is proposed and simulated with double channeling calculation which agrees qualitatively with our experiment. We demonstrate that local strain asymmetry is the likely cause of the electronic asymmetry of the interfaces. The electronic reconstruction at the interfaces extends much further than the chemical composition, varying from 0.5 to 1.2 nm. This distance corresponds to the length of charge transfer previously found in the \ce{(LaVO_3)_m}/\ce{(SrVO_3)_n} metal/insulating and the \ce{(LaAlO_3)_m}/\ce{(SrTiO_3)_n} insulating/insulating interfaces.Comment: 6 pages, 5 figures. Physical Review B, 201

Effect of carbon emission regulations on transport mode selection under stochastic demand

Companies are expiriencing new and more important reasons to pay attention to their carbon footprint. In this work we consider a 'carbon-aware' company (either by choice or enforced by regulation) that is reconsidering the transport mode selection decsion. Traditionally the trade-off has been between lead time (and corresponding inventory costs) and unit transportation cost but now emission costs come into the equation. We use a carbon emission measurement methodology based on real-life data and incorporate it into an inventory model. We consider the results for different types of emission regulation (including voluntary targets). We find that even though large emission reductions can be obtained by switching to a different mode, the actual decision depends on the regulation and other practical issues

Effect of carbon emission regulations on transport mode selection in supply chains

Policy-makers are developing regulation mechanisms to drive down carbon emis- sions resulting from among others transport. We investigate what the effect of two regulation mechanisms is on the transport mode selection decision. We analyze the situation in which a single transport mode is to be selected by a decision-maker to conduct all transport (for one item). A faster transport mode typically results in lower inventory (or a higher service) at the cost of higher emissions and transport costs. We consider two possible emission regulation alternatives: an emission cost and an emission constraint. We use an accurate calculation method to determine the carbon emissions and incorporate them explicitly in our model. Our results show that the emission cost is only a small part of the total cost and we conclude that introducing an emission cost for freight transport via a direct emission tax or a market mechanism such as cap and trade are not likely to result in significant changes in transport modes and hence will not result in a large reduction of emis- sions. If policy-makers aim to reduce carbon emissions by a large fraction, they should implement a constraint on freight transport emissions

Effect of carbon emission regulations on transport mode selection under stochastic demand

Companies are expiriencing new and more important reasons to pay attention to their carbon footprint. In this work we consider a 'carbon-aware' company (either by choice or enforced by regulation) that is reconsidering the transport mode selection decsion. Traditionally the trade-off has been between lead time (and corresponding inventory costs) and unit transportation cost but now emission costs come into the equation. We use a carbon emission measurement methodology based on real-life data and incorporate it into an inventory model. We consider the results for different types of emission regulation (including voluntary targets). We find that even though large emission reductions can be obtained by switching to a different mode, the actual decision depends on the regulation and other practical issues

Switching transport modes to meet voluntary carbon emission targets

The transport sector is the second largest carbon emissions contributor in Europe and its emissions continue to increase. Many shippers are committing themselves to reducing transport emissions voluntarily, possibly in anticipation of increasing transport prices. In this paper we study a shipper that has outsourced transport and has decided to cap its carbon emissions from outbound logistics for a group of products. Setting an emission constraint for a group of products allows taking advantage of reducing emissions substantially where it is less costly and less where it is more costly. We focus on reducing emissions by switching transport modes within an existing network, since this has a large impact on emissions. In addition, the company sets the sales prices for the products, which in uences demand. We develop a solution procedure that uses Lagrange relaxation. Conditions on total logistics cost and unit emissions are derived determine which transport mode is selected for a product. It is observed that a diminishing rate of return applies in reducing emissions by switching transport modes. In a case study we apply our method to a producer of bulk liquids and find that emissions can be reduced by 10% at only a 0.7% increase in total logistics cost. Keywords: carbon emissions, green supply chains, sustainability, transport mode selection, Lagrange relaxation, pricing