Scalar-Tensor theories from Λ(ϕ)\Lambda(\phi) Plebanski gravity

We study a modification of the Plebanski action, which generically corresponds to a bi-metric theory of gravity, and identify a subclass which is equivalent to the Bergmann-Wagoner-Nordtvedt class of scalar-tensor theories. In this manner, scalar-tensor theories are displayed as constrained BF theories. We find that in this subclass, there is no need to impose reality of the Urbantke metrics, as also the theory with real bivectors is a scalar-tensor theory with a real Lorentzian metric. Furthermore, while under the former reality conditions instabilities can arise from a wrong sign of the scalar mode kinetic term, we show that such problems do not appear if the bivectors are required to be real. Finally, we discuss how matter can be coupled to these theories. The phenomenology of scalar field dark matter arises naturally within this framework.Comment: 21 page

Force and pressure-recovery characteristics at supersonic speeds of a conical nose inlet with bypasses discharging outward from the body axis

Aerodynamic and performance characteristics of a conical spike nacelle-type inlet with two bypasses are presented at Mach numbers of 1.6, 1.8, and 2.0 for angles of attach up to 90 degrees. The bypasses were located 6 inlet diameters downstream of the inlet and were designed to discharge the bypass mass flow outward from the body axis. The inlet was designed to attain a mass-flow ratio of unity at a Mach number of 2.0. It is shown that discharging the bypass mass flow outward from the body nearly doubles the critical drag of a similar configuration but with bypass discharge in an axial direction. As a result of this greater drag, the net force on the model in the flight direction is reduced when comparison is made with the axial discharge case. The lift and pitching-moment coefficients are slightly higher than those for a configuration without bypasses. Approximately 25 % of the maximum inlet mass flow was discharged through the bypasses, and the pressure-recovery and mass-flow characteristics were in qualitative and quantitative agreement with the results of an investigation of a similar configuration with axial discharge

MULTI-OBJECTIVE SHORTEST PATH APPROACH FOR ROUTING AND SCHEDULING

Customers and goods are being transported at an ever-increasing rate, through complex and interconnected transportation systems. The need for efficiency in terms of economic and environmental aspects, to name a few, gives rise to optimisation problems that often include finding shortest paths. This is why shortest path problems are among the most studied combinatorial optimisation problems. The research presented in this thesis focuses on a class of shortest path problems that are multi-objective and where time window constraints are present. The thesis argues that such problems are best modelled through multigraphs, leading to the Multi-objective Shortest Path Problem on Multigraphs with Time Windows (MSPPMTW). The multigraph allows more detailed modelling of such problems, which is key to accessing the untapped potential for improved efficiency. Multiple aspects of the problem are investigated. The MSPPMTW has increased search space compared to the simple graph Multi-objective Shortest Path Problem, which is already NP-hard. Firstly, the increased computational complexity is investigated empirically, and a model is proposed for predicting the computational effort required, based on easily measurable metrics describing the problem instance, such as the number of parallel arcs or the size of the network. Secondly, a benchmark generation method is proposed for the MSPPMTW, based on the observations of the predictive model. Lastly, a memetic algorithm (with multiple variants based on different representation methods) is proposed to address the problem of finding solutions in short time budgets and scaling to higher numbers of parallel arcs. The memetic algorithm is tested on the proposed benchmark set and a real-world application, the airport ground movement problem. The thesis finds that the proposed memetic algorithm is comparable to the state of the art solution methods. The metaheuristic approaches also have higher promise for future applications in optimising broader transportation systems as a whol

Killing spinor space-times and constant-eigenvalue Killing tensors

A class of Petrov type D Killing spinor space-times is presented, having the peculiar property that their conformal representants can only admit Killing tensors with constant eigenvalues.Comment: 11 pages, submitted to CQ