On-line decision support for take-off runway scheduling with uncertain taxi times at London Heathrow airport

This paper addresses the challenge of building an automated decision support methodology to tackle the complex problem faced every day by runway controllers at London Heathrow Airport. Aircraft taxi from stands to holding areas at the end of the take-off runway where they wait in queues for permission to take off. A runway controller attempts to find the best order for aircraft to take off. Sequence-dependent separation rules that depend upon aircraft size, departure route and speed group ensure that this is not a simple problem to solve. Take-off time slots on some aircraft and the need to avoid excessive delay for any aircraft make this an even more complicated problem. Making this decision at the holding area helps to avoid the problems of unpredictable push-back and taxi times, but introduces a number of complex spatial constraints that would not otherwise exist. The holding area allows some flexibility for interchange of aircraft between queues, but this is limited by its physical layout. These physical constraints are not usually included in academic models of the departure problem. However, any decision support system to support the take-off runway controller must include them. We show, in this paper, that a decision support system could help the controllers to significantly improve the departure sequence at busy times of the day, by considering the taxiing aircraft in addition to those already at the holding area. However, undertaking this re-introduces the issue of taxi time uncertainty, the effect of which we explicitly measure in these experiments. Empirical results are presented for experiments using real data from different times of the day, showing how the performance of the system varies depending upon the volume of traffic and the accuracy of the provided taxi time estimations. We conclude that the development of a good taxi time prediction system is key to maximising the benefits, although benefits can be observed even without this.     

Least-cost planning: issues and methods

Electric utility least-cost planning is formulated in terms of supply- and demand-side options, irreducible uncertainties, and stakeholders' objectives. Planning methods include constrained optimization, tradeoff analysis, and game theory. Constrained optimization is the traditional and still most popular approach. Tradeoff analysis, which seeks good compromises, seems most appropriate for today's least-cost planning environment. It is suggested that game theory, which is particularly useful in a competitive and noncooperative environment, may play a role in least-cost planning     

Fossils, molecules and embryos: new perspectives on the Cambrian explosion

The Cambrian explosion is named for the geologically sudden appearance of numerous metazoan body plans (many of living phyla) between about 530 and 520 million years ago, only 1.7% of the duration of the fossil record of animals. Earlier indications of metazoans are found in the Neoproterozic; minute trails suggesting bilaterian activity date from about 600 million years ago. Larger and more elaborate fossil burrows appear near 543 million years ago, the beginning of the Cambrian Period. Evidence of metazoan activity in both trace and body fossils then increased during the 13 million years leading to the explosion. All living phyla may have originated by the end of the explosion. Molecular divergences among lineages leading to phyla record speciation events that have been earlier than the origins of the new body plans, which can arise many tens of millions of years after an initial branching. Various attempts to date those branchings by using molecular clocks have disagreed widely. While the timing of the evolution of the developmental systems of living metazoan body plans is still uncertain, the distribution of Hox and other developmental control genes among metazoans indicates that an extensive patterning system was in place prior to the Cambrian. However, it is likely that much genomic repatterning occurred during the Early Cambrian, involving both key control genes and regulators within their downstream cascades, as novel body plans evolved.     

Management of upper urinary tract calculi with ureteroscopic techniques

Frequent loss of heterozygosity on chromosome 8p in a variety of human malignancies, including head and neck cancers, has suggested the presence of a tumor suppressor gene (or genes) associated with the pathogenesis of these cancers. To test the role of genetic alterations at 8p23 in oral carcinogenesis, we studied 51 squamous cell carcinomas of the head and neck and 29 oral squamous cell carcinoma cell lines for allelic loss using 7 microsatellite markers spanning approximately 5 cM of chromosome band 8p23. Twenty-three of 51 tumors (45%) and 23 of 29 cell lines (79%) showed allelic loss at 1 or more loci. Three cell lines showed homozygous deletion of loci within a 3 cM region defined by the markers D8S1781 and D8S262. Our results suggest that a tumor suppressor gene (or genes) is located in 8p23 and is associated with the development and/or progression of oral carcinomas.     

Posttraumatic elbow arthritis and arthroplasty

Elbow contractures without significant articular injury can be treated with soft-tissue procedures, such as joint capsular releases, resection of heterotropic ossification, and joint debridement. Elbows with significant intra-articular injuries or posttraumatic arthritis require some form of joint reconstruction, such as a distraction arthroplasty, interposition arthroplasty, or implant replacement arthroplasty. With a better understanding of the surgical indications for elbow arthroplasty, improvements in surgical technique, improvements in elbow implants, and increased surgical experience, the results of implant arthroplasty for the posttraumatic elbow continue to improve.