Susceptibility of optimal train schedules to stochastic disturbances of process times

This work focuses on the stochastic evaluation of train schedules computed by a microscopic scheduler of railway operations based on deterministic information. The research question is to assess the degree of sensitivity of various rescheduling algorithms to variations in process times (running and dwell times). In fact, the objective of railway traffic management is to reduce delay propagation and to increase disturbance robustness of train schedules at a network scale. We present a quantitative study of traffic disturbances and their effects on the schedules computed by simple and advanced rescheduling algorithms. Computational results are based on a complex and densely occupied Dutch railway area; train delays are computed based on accepted statistical distributions, and dwell and running times of trains are subject to additional stochastic variations. From the results obtained on a real case study, an advanced branch and bound algorithm, on average, outperforms a First In First Out scheduling rule both in deterministic and stochastic traffic scenarios. However, the characteristic of the stochastic processes and the way a stochastic instance is handled turn out to have a serious impact on the scheduler performance

Effects of dried Portulaca oleracea supplementation to the laying hen diet on productive performance, egg physical traits, fatty acid composition, and cholesterol content

Portulaca oleracea is a widespread herbaceous plant particularly rich in polyunsaturated fatty acids (PUFA), antioxidant compounds and characterised by a healthy omega-6/omega-3 ratio. The focus of this research was to evaluate the effects of Portulaca oleracea supplementation to the diet of laying hens on productive performance, egg physical traits, fatty acid composition and cholesterol content. Twenty-six 24-week-old Warren strain layers were randomly assigned to two different groups of 18 and eight birds, respectively: one group received a commercial diet (C) whereas the other group was given the same control diet supplemented with 20% of dried Portulaca oleracea (PO). Hens were fed for 21 days. Feed and water were provided ad libitum. The poor palatability of the PO diet compromised the optimisation of the productive performance, with a significant reduction of the oviposition efficiency (0.69 vs 0.88 for PO and C, respectively; P < 0.05) and egg physical traits. Considering the egg nutritional traits, dietary PO significantly decreased the yolk proportion of saturated fatty acid (43.0% vs 44.1%, P < 0.05), while it increased the content of PUFA (19.4% vs 17.8%, P < 0.001), and within the latter, both omega-6 and omega-3 proportion significantly increased in comparison with C group (16.4% vs 17.6%, P < 0.001 and 1.46% vs 1.80%, P < 0.001, for n-6 and n-3, respectively). This resulted in an improvement of the omega-6/omega-3 ratio (10.4 vs 11.3 for PO and C, respectively; P < 0.05). Egg yolk cholesterol content did not vary between dietary treatments. It could be concluded that the use of Portulaca oleracea for producing omega3-enriched eggs is feasible once the problem of palatability has been overcome and the energy requirements of the hens have been covered

Risk-Aware Scheduling of Elective Surgeries

This paper addresses Operating Room scheduling problems in elective surgery. In particular, we study a model for determining the surgical schedule when uncertainty on surgery duration is taken into account in order to consider and evaluate the risk of overtime and the possible waste of operating time. Surgical cases are selected from the waiting lists according to several parameters, including surgery duration, waiting time and priority class of the operations. We apply the proposed approach to the operating theatre of a public, medium-size hospital in Italy, using Mathematical Programming formulations and Monte Carlo simulations, assuring the scalability of the approach on larger hospitals. © Springer International Publishing Switzerland 2014

A rollout algorithmic approach for complex parallel machine scheduling in healthcare operations

Healthcare Operations Management calls to tackle different scheduling problems. Often the environment to consider can be modeled with a set of parallel resources to be scheduled and is characterized by one or more application-specific constraints or objectives. Rollout methodology is effortless to implement and able to easy incorporate human experience inside its research patterns to fulfill complex scheduling requirements as those of interest in healthcare applications. A drawback is represented by the high computation time often required to terminate the algorithm. We analyze a deterministic parallel machine scheduling problem showing how a rollout framework can be extended and adapted to tackle several additional specific constraints arising in healthcare operations, such as surgery block scheduling. We also describe simple methodologies that can be used to address the uncertainties in the problem by iterating the solution of deterministic models. A lower bound is used to certify the quality of the generated solutions for complex parallel machines scheduling problems. A preliminary campaign of computational experiments, shows the behavior of different algorithmic variants of this approach

Expected Shortfall for the Makespan in Activity Networks with Fuzzy Durations

The paper deals with the evaluation of the Expected Shortfall or the Conditional Value-at-Risk for the makespan in scheduling problems represented as temporal activity networks where we assume that only a type-1 fuzzy representation for the activity integer valued durations is known to the scheduler. More precisely, we address the evaluation of the Expected Shortfall associated to a feasible schedule, and we extend the approach recently proposed for the case of interval valued durations. We develop and analyze a suitable computational method to obtain the fuzzy evaluation of the Expected Shortfall of the makespan of a given schedule. The proposed method enables to use the Expected Shortfall as quality criterion for wide classes of scheduling approaches considering risk-aversion in different practical contexts when only a fuzzy representation of activity durations is known