Greening commercial air transportation by using liquid hydrogen (LH2) as a fuel

Global commercial air transportation has grown over the past two decades at a rather stable annual rate of 4.5–5% in the passenger and 6% in the cargo segment. Such developments have contributed to globalization of the economy and overall social welfare while at the same time increased impacts on the environment and society in terms of fuel consumption from non-renewable sources and related emissions of GHG (Green House Gases), land use, congestion, and local noise. In particular, further growth of emissions of GHG driven by growth of air transportation demand could contribute to global warming and consequent climate change.     

Fuzzy relation equations and reduction of fuzzy automata

We show that the state reduction problem for fuzzy automata is related to the problem of finding a solution to a particular system of fuzzy relation equations in the set of all fuzzy equivalences on its set of states. This system may consist of infinitely many equations, and finding its non-trivial solutions may be a very difficult task. For that reason we aim our attention to some instances of this system which consist of finitely many equations and are easier to solve. First, we study right invariant fuzzy equivalences, and their duals, the left invariant ones. We prove that each fuzzy automaton possesses the greatest right (resp. left) invariant fuzzy equivalence, which provides the best reduction by means of fuzzy equivalences of this type, and we give an effective procedure for computing this fuzzy equivalence, which works if the underlying structure of truth values is a locally finite residuated lattice. Moreover, we show that even better reductions can be achieved alternating reductions by means of right and left invariant fuzzy equivalences. We also study strongly right and left invariant fuzzy equivalences, which give worse reductions than right and left invariant ones, but whose computing is much easier. We give an effective procedure for computing the greatest strongly right (resp. left) invariant fuzzy equivalence, which is applicable to fuzzy automata over an arbitrary complete residuated lattice.     

Effects of access phases lengths on performance of IEEE 802.15.6 CSMA/CA

In this paper, we study interplay of prioritizing mechanisms in recently released IEEE 802.15.6 standard for Wireless Body Area Networks (WBANs). Among eight User Priorities (UPs) we study the impact of access phases lengths and CSMA/CA mechanism on the network performance. We consider a star-topology single-hop WBAN in which the hub operates in beacon mode with superframe boundaries. Our study is conducted in saturation regime and an error prone channel in order to indicate performance bounds for all UPs. We have developed an analytical model for the CSMA/CA-based Medium Access Control (MAC) layer of IEEE 802.15.6 which includes Markov chain and probabilistic models for all UPs. In order to validate the analytical model we have developed a simulation model in OPNET. We investigate the effectiveness of deploying exclusive access phases and second random access phase on the network performance. We also examine the medium utilization and normalized throughputs of all UPs. Obtained performance bounds indicate potential tradeoff between the prioritizing parameters which affect the saturation throughputs.     

Evolving priority scheduling heuristics with genetic programming

This paper investigates the use of genetic programming in automated synthesis of scheduling heuristics for an arbitrary performance measure. Genetic programming is used to evolve the priority function, which determines the priority values of certain system elements (jobs, machines). The priority function is used within an appropriate meta-algorithm for a given environment, which forms the priority scheduling heuristic. The evolved solutions are compared with existing scheduling heuristics and found to perform similarly to or better than existing algorithms. We intend to show that this approach is particularly useful for combinations of scheduling environments and performance measures for which no adequate scheduling algorithms exist.