Abstract

This paper identifies and discusses a set of criteria relevant to assess the impact of using different media in the design of user interfaces for safety-critical systems. An evaluation of different options concerning the allocation of such media during the design of an application in the Air Traffic Control domain is shown to illustrate and clarify our approach. Particular attention is paid on how different choices in allocating tasks among air traffic controllers affect usability and safety of operators' interactions. Document type: Part of book or chapter of book

Abstract

Service-oriented computing is calling for novel computational models and languages with primitives for client-server interaction, orchestration and unexpected events handling. We present CaSPiS , a process calculus where the notions of session and pipelining play a central role. Sessions are two-sided and can be equipped with protocols executed by each side. Pipelining permits orchestrating the flow of data produced by different sessions. The calculus is also equipped with operators for handling (unexpected) termination of the partner's side of a session. Several examples are presented to provide evidence for the flexibility of the chosen set of primitives. Our main result shows that in CaSPiS it is possible to program a "graceful termination" of nested sessions, which guarantees that no session is forced to hang forever after the loss of its partner. Document type: Part of book or chapter of book

Abstract

The performance and reliability of the Internet depend, in large part, on the operation of the underlying routing protocols. Today’s IP routing protocols compute paths based on the network topology and configuration parameters, without regard to the current traffic load on the routers and links. The responsibility for adapting the paths to the prevailing traffic falls to the network operators and management systems. This chapter discusses the modeling and computational challenges of optimizing the tunable parameters, starting with conventional intradomain routing protocols that compute shortest paths as the sum of configurable link weights. Then, we consider the problem of optimizing the interdomain routing policies that control the flow of traffic from one network to another. Optimization based on local search has proven quite effective in grappling with the complexity of the routing protocols and the diversity of the performance objectives, and tools based on local search are in wide use in today’s large IP networks. Document type: Part of book or chapter of book

Abstract

In this paper we explore tramp ship routing and scheduling. Tramp ships operate much like taxies following the available demand. Tramp operators can determine some of their demand in advance by entering into long-term contracts and then try to maximise profits from optional voyages found in the spot market. Routing and scheduling a tramp fleet to best utilise fleet capacity according to current demand is therefore an ongoing and complicated problem. Here we add further complexity to the routing and scheduling problem by incorporating voyage separation requirements that enforce a minimum time spread between some voyages. The incorporation of these separation requirements helps balance the conflicting objectives of maximising profit for the tramp operator and minimising inventory costs for the charterer, since these"br/"costs increase if similar voyages are not performed with some separation in time. We have developed a new and exact branch-and-price procedure for this problem. We use a dynamic programming algorithm to generate columns and describe a time window branching scheme used to enforce the voyage separation requirements which we relax in the master problem. Computational results show that our algorithm in general finds optimal solutions very quickly and performs much faster compared to an earlier a priori path generation method. Finally, we compare our method to an earlier adaptive large neighbourhood search heuristic and find that on similar-sized instances our approach generally uses less time to find the optimal solution than the adaptive large neighbourhood search method uses to find a heuristic solution. Document type: Book

Abstract

We introduce a tool for simulation and optimization of gas pipeline networks coupled to power grids by gas-to-power plants. The model under consideration consists of the isentropic Euler equations to describe the gas flow coupled to the AC powerflow equations. A compressor station is installed to control the gas pressure such that certain bounds are satisfied. A numerical case study is presented that showcases effects of fast changes in power demand on gas pipelines and necessary operator actions. Document type: Part of book or chapter of book

Abstract

The conventional forwarding rule used by IP networks is to always choose the path with the shortest length – in terms of administrative link weights assigned to the links – to forward traffic. Lately, it has been proposed to use shortest-path-first routing to implement Traffic Engineering in IP networks, promising with a big boost in the profitability of the legacy network infrastructure. The idea is to set the link weights so that the shortest paths, and the traffic thereof, follow the paths designated by the operator. Unfortunately, traditional methods to calculate the link weights usually produce a bunch of superfluous shortest paths, often leading to congestion along the unconsidered paths. In this paper, we introduce and develop novel methods to increase the accuracy of this process and, by means of extensive simulations, we show that our proposed solution produces remarkably high quality link weights. Document type: Part of book or chapter of book

Abstract

Pipelines and other linear structures often cover large distances across topographically and geologically varied ground. In the last decade, or so, geological information has started to become available in digital form for countries and regions. This enables a wide-range of users, including pipeline operators, to access interpreted geohazard information not only for the construction of new linear infrastructure, but also to assess a range of geological risks to existing linear infrastructure that might have been constructed before such information was available. Document type: Part of book or chapter of book