Airline planning benchmark problems—Part II : passenger groups, utility and demand allocation

This paper is the second of two papers entitled “Airline Planning Benchmark Problems”, aimed at developing benchmark data that can be used to stimulate innovation in airline planning, in particular, in flight schedule design and fleet assignment. The former has, to date, been under-represented in the optimisation literature, due in part to the difficulty of obtaining data that adequately reflects passenger choice, and hence schedule revenue. Revenue models in airline planning optimisation only roughly approximate the passenger decision process. However, there is a growing body of literature giving empirical insights into airline passenger choice. Here we propose a new paradigm for passenger modelling, that enriches our representation of passenger revenue, in a form designed to be useful for optimisation. We divide the market demand into market segments, or passenger groups, according to characteristics that differentiate behaviour in terms of airline product selection. Each passenger group has an origin, destination, size (number of passengers), departure time window, and departure time utility curve, indicating willingness to pay for departure in time sub-windows. Taking as input market demand for each origin–destination pair, we describe a process by which we construct realistic passenger group data, based on the analysis of empirical airline data collected by our industry partner. We give the results of that analysis, and describe 33 benchmark instances produced

Influence of Vesicular-arbuscular Mycorrhizae on the Growth and Water Relations of Vegetable Crops

Onion, leek, pepper, lettuce and tomato transplants grown in a soilless medium inoculated with the VAMF Glomus aggregatum (Schenck and Smith emend. Koske) were larger and had higher tissue phosphorus (P) concentrations than non-inoculated plants if P levels in the medium were low. At higher P concentrations, inoculation had little or a slightly negative effect on transplant growth. Increasing P concentrations in the medium increased transplant growth, but decreased root infection by the VAMF. Increasing VAMF inoculvim concentrations did not affect growth or P uptake but increased VAMF infection of the transplants. Daily application of low P fertilizer solutions produced larger transplants with more extensively infected root systems than did similar amounts of P supplied less frequently but at higher concentrations. Different crops required different combinations of P concentration and application interval to produce vigorous mycorrhizal transplants. The controlled-release fertilizer Osmocote (Sierra Chemical Co., Milptas Calif.) produced predictable and stable solution P concentrations in the soilless medium used for transplant production. Growth and VAMF infection of the transplants could be manipulated by altering Osmocote P concentrations in the transplant medium. Pre-transplant inoculation of peppers subsequently planted into P deficient soil improved early P uptake, vegetative growth and total fruit yields relative to plants inoculated at transplanting. In P deficient soils, maximum pre-transplant VAMF infection of peppers increased subsequent growth and fruit yields more than maximum pre-transplant growth. Extensive pre-transplanting infection improved post-transplant P uptake earlier than in less heavily infected plants. In contrast, pre-transplant growth of lettuce was more important than mycorrhizal infection in determining subsequent growth, at all soil P levels. In pots, G. aggregatum increased total dry matter yields, promoted early fruit set and improved fruit yields of peppers at solution P concentrations below 0.3 to 0.4 mg/liter. At higher P concentrations, VAMF infection had no beneficial or harmful effects. Tissue P requirements for dry matter production by mycorrhizal plants were lower than in non-mycorrhizal plants, suggesting that mycorrhizae may influence the efficiency of utilization of absorbed P in addition to increasing P uptake efficiency. In the field, inoculation of peppers increased tissue P concentrations, growth and fruit yields by 28, 120 and 350% respectively relative to non-mycorrhizal plants in a fumigated P-fixing soil with 0.03 mg/liter solution P. Inoculation had no significant effect at 0.30 mg P/liter. Under similar conditions, VAMF infection increased yields of lettuce by 16%. Although non-mycorrhizal lettuce and peppers had similar solution P requirements for maximum growth, lettuce was more tolerant of sub-optimal solution P concentrations and was correspondingly less responsive to infection by the VAMF. Moderate water stress increased mycorrhizal responsiveness of peppers growing in P deficient soil. VAMF colonization of pepper seedlings growing in P deficient media increased the hydraulic conductivity of their roots, possibly by improving seedlings tissue P status. Mature mycorrhizal peppers had higher rates of transpiration per unit leak area than similar size non-mycorrhizal plants. At wilting, mycorrhizal transplants and mature peppers had higher leaf water potentials at lower soil water potentials than non-mycorrhizal plants. The influence of mycorrhizae on the water relations of mature peppers was apparently related to the mycorrhizae improving P uptake by their host but the change in water relations of inoculated seedlings was generally independent of host P-status

Maintenance scheduling in a railway corricdor

We investigate a novel scheduling problem which is motivated by an application in the Australian railway industry. Given a set of maintenance jobs and a set of train paths over a railway corridor with bidirectional traffic, we seek a schedule of jobs such that a minimum number of train paths are cancelled due to conflict with the job schedule. We show that the problem is NP-complete in general. In a special case of the problem when every job under any schedule just affects one train path, and the speed of trains is bounded from above and below, we show that the problem can be solved in polynomial time. Moreover, in another special case of the problem where the traffic is unidirectional, we show that the problem can be solved in time $O(n^4)$

Abscisic acid analogues for enhanced stress tolerance and size control of tomato seedlings

Non-Peer ReviewedTransplanting shock is a common problem during establishment of horticultural crops like vegetables and ornamental bedding plants. The marketing period of nursery raised seedlings is limited due to the loss of aesthetic quality associated with undesirable growth and accelerated moisture loss during storage and handling. Two synthetic analogues (PBI 365 and PBI 429) of the plant hormone abscisic acid (S. Abrams PBI/NRC) were evaluated in a number of greenhouses and field trials at the University of Saskatchewan, for their potential to alter the stress tolerance and growth of horticultural crops. Pre-planting application of analogues, at 10-4 M, enhanced the tomato transplants survival under moisture stress in field conditions. Under greenhouse conditions, the ABA analogues slowed the moisture use and growth of seedlings without deteriorating the visual quality. Thus, ABA analogues could be used in horticultural crops for enhanced stand establishment as well as to hold seedlings at a particular stage thereby allowing their storage and extending the marketing period

Capacity Alignment Planning for a Coal Chain: A Case Study

We study a capacity alignment planning problem for a coal chain. Given a set of train operators, a set of train paths, and a terminal comprising of a dump station and a set of routes from the dump station to the stockyard, we seek a feasible assignment of train operators to train paths, to time slots at the dump station, and to routes. The assignment must maximize the number of system paths in the resulting schedule and the schedule should perform well with respect to various performance criteria. We model the problem as a mixed-integer conic programme (MICP) with multiple objectives which we solve using a hierarchical optimization procedure. In each stage of this procedure we solve a single objective MICP. Depending upon whether we evaluate the associated performance criteria under a 2-or 1-norm we reformulate the MICP as either a mixed-integer second-order cone programme or as a mixed-integer linear programme respectively, and can streamline the hierarchical optimization procedure by exploiting properties of the model or observed behaviour on practical instances. We compare the performance of the procedure under the different norms on a real instance of the problem and find that the quality of the solutions found by the faster 1-norm procedure compare well to the solution found under the 2-norm

Bacterial Infection Elicits Heat Shock Protein 72 Release from Pleural Mesothelial Cells

Heat shock protein 70 (HSP70) has been implicated in infection-related processes and has been found in body fluids during infection. This study aimed to determine whether pleural mesothelial cells release HSP70 in response to bacterial infection in vitro and in mouse models of serosal infection. In addition, the in vitro cytokine effects of the HSP70 isoform, Hsp72, on mesothelial cells were examined. Further, Hsp72 was measured in human pleural effusions and levels compared between non-infectious and infectious patients to determine the diagnostic accuracy of pleural fluid Hsp72 compared to traditional pleural fluid parameters. We showed that mesothelial release of Hsp72 was significantly raised when cells were treated with live and heat-killed Streptococcus pneumoniae. In mice, intraperitoneal injection of S. pneumoniae stimulated a 2-fold increase in Hsp72 levels in peritoneal lavage (p<0.01). Extracellular Hsp72 did not induce or inhibit mediator release from cultured mesothelial cells. Hsp72 levels were significantly higher in effusions of infectious origin compared to non-infectious effusions (p<0.05). The data establish that pleural mesothelial cells can release Hsp72 in response to bacterial infection and levels are raised in infectious pleural effusions. The biological role of HSP70 in pleural infection warrants exploration

Integer programming methods for large-scale practical classroom assignment problems

In this paper we present an integer programming method for solving the Classroom Assignment Problem in University Course Timetabling. We introduce a novel formulation of the problem which generalises existing models and maintains tractability even for large instances. The model is validated through computational results based on our experiences at the University of Auckland, and on instances from the 2007 International Timetabling Competition. We also expand upon existing results into the computational difficulty of room assignment problems