Stem hydraulic capacitance decreases with drought stress : implications for modelling tree hydraulics in the Mediterranean oak Quercus ilex

Hydraulic modelling is a primary tool to predict plant performance in future drier scenarios. However, as most tree models are validated under non-stress conditions they may fail when water becomes limiting. To simulate tree hydraulic functioning under moist and dry conditions, the current version of a water flow and storage mechanistic model was further developed by implementing equations that describe variation in xylem hydraulic resistance (RX) and stem hydraulic capacitance (CS) with predawn water potential (ΨPD). The model was applied in a Mediterranean forest experiencing intense summer drought, where six Quercus ilex trees were instrumented to monitor stem diameter variations and sap flow, concurrently with measurements of predawn and midday leaf water potential. Best model performance was observed when CS was allowed to decrease with decreasing ΨPD. Hydraulic capacitance decreased from 62 to 25 kg m-3 MPa-1 across the growing season. In parallel, tree transpiration decreased to a greater extent than the capacitive water release and the contribution of stored water to transpiration increased from 2.0% to 5.1%. Our results demonstrate the importance of stored water and seasonality in CS for tree hydraulic functioning, and they suggest that CS should be considered to predict the drought-response of trees with models

Production planning and inventory control with remanufacturing and disposal

In this paper we consider a stochastic inventory system with production, remanufacturing, and disposal operations. Customer demands must either be fulfilled from the production of new products or by the remanufacturing of used products. Used products are either remanufactured or disposed of. To coordinate production, remanufacturing and disposal operations efficiently, we extend the PUSH and PULL strategies that Van der Laan et al. developed to control a system in which all returned products are remanufactured and no planned disposals occur. The other contributions of this paper are to indicate when and why planned disposals are economically beneficial, and to compare the PUSH-disposal strategy to the PULL-disposal strategy. In addition, we investigate the robustness of the control parameters of the PUSH- and PULL-disposal strategy over the different stages of a product life-cycle

Exact and approximation algorithms for the operational fixed interval scheduling problem

The Operational Fixed Interval Scheduling Problem (OFISP) is characterized as the problem of scheduling a number of jobs, each with a fixed starting time, a fixed finishing time, a priority index, and a job class. The objective is to find an assignment of jobs to machines with maximal total priority. The problem is complicated by the restrictions that: (i) each machine can handle only one job at a time, (ii) each machine can handle only jobs from a prespecified subset of all possible job classes, and (iii) preemption is not allowed. It follows from the above that OFISP has both the character of a job scheduling problem and the character of an assignment problem. In this paper we discuss the occurrence of the problem in practice, and we present newly developed exact and approximation algorithms for solving OFISP. Finally, some computational results are shown

Product remanufacturing and disposal: A numerical comparison of alternative control strategies

In this paper we consider a single-product, single-echelon production and inventory system with product returns, product remanufacturing, and product disposal. For this system we consider three different procurement and inventor

Data Processing using Artificial Neural Networks to Improve the Simulation of Lung Motion

International audienceTo optimize the delivery in lung radiation therapy, a better understanding of the tumor motion is required. On the one hand to have a better tumor-targeting efficiency, and on the other hand to avoid as much as possible normal tissues. The 4D-CT allows to quantify tumor motion, but due to artifacts it introduces biases and errors in tumor localization. Despite of this disadvantage, we propose a method to simulate lung motion based on data provided by the 4D-CT for several patients. To reduce uncertainties introduced by the 4D-CT scan, we conveniently treated data using artificial neural networks. More precisely, our approach consists in a data augmentation technique. The data resulting from this processing step are then used to build a training set for another artificial neural network that learns the lung motion. To improve the learning accuracy, we have studied the number of phases required to precisely describe the displacement of each point. Thus, from 1118 points scattered across 5 patients and defined over 8 or 10 phases, we obtained 5800 points of 50 phases. After training, the network is used to compute the positions of 40 points from five other patients on 10 phases. These points allow to quantify the prediction performance. In comparison with the original data, the ones issued from our treatment process provide a significant increase of the prediction accuracy: an average improvement of 16% can be observed. The motion computed for several points by the neural network that has learnt the lung one exhibits an hysteresis near the one given by the 4D-CT, with an error smaller than 1 mm in the cranio-caudal axis

A DSS for capacity planning of aircraft maintenance personnel

In this paper we describe a Decision Support System (DSS) that has been developed for the aircraft maintenance department of the Dutch national airline company at the main airport in the Netherlands. The aircraft maintenance department is responsible for carrying out the regular short inspections of aircraft between their arrival at and their consecutive departure from the airport. The main resource of the aircraft maintenance department is its workforce. The DSS that has been developed can be used to support the management of the maintenance department in solving several capacity planning problems related to the size and the composition of the workforce. In this paper we give a description of the capabilities of the DSS. Furthermore, we describe the solution technique that is applied within the DSS for determining the required size and composition of the workforce

Strategic Issues in Product Recovery Management

This article examines strategic production and operations management issues in product recovery management (PRM). PRM encompasses the management of all used and discarded products, components, and materials for which a manufacturing company is legally, contractually, or otherwise responsible. The objective of PRM is to recover as much of the economic (and ecological) value of used and discarded products, components, and materials as reasonably possible, thereby reducing the ultimate quantities of waste to a minimum. This article also discusses the relevance of PRM to durable products manufacturers. It contains a categorization of PRM decisions. A case study based on the PRM system of a multinational copier manufacturer is presented to illustrate a set of specific production and operations management issues. The experiences of two other pro-active manufacturers (BMW and IBM) are also discusse

Allocation of Railway Rolling Stock for Passenger Trains

For a commercially operating railway company, providing a high level of service for the passengers is of utmost importance. The latter requires a high punctuality of the trains and an adequate rolling stock capacity. Unfortunately, the latter is currently (2002) one of the bottlenecks in the service provision by the main Dutch railway operator NS Reizigers. Especially during the morning rush hours, many passengers cannot be transported according to the usual service standards due to a shortage of the ro

An (s,Q) inventory model with remanufacturing and disposal

In this paper we analyse an (s, Q) inventory model in which used products can be remanufactured to new ones. We develop two approximations for the average costs and compare their performance with that of an approximation suggested by Muckstadt and Isaac. Next we extend the model with the option to dispose returned products and present a heuristic optimisation procedure which is checked with full enumeration