A formal analysis of blockchain consensus

In this thesis, we analyse these protocols using PRISM+, our extension of the probabilistic model checker PRISM with blockchain types and operations upon them. This allows us to model the behaviour of key participants in the protocols and describe the protocols as a parallel composition of PRISM+ processes. Through our analysis of the Bitcoin model, we are able to understand how forks (where different nodes have different versions of the blockchain) occur and how they depend on specific parameters of the protocol, such as the difficulty of the cryptopuzzle and network communication delays. Our results corroborate the statement that considering confirmed the transactions in blocks at depth larger than 5 is reasonable because the majority of miners have consistent blockchains up-to that depth with probability of almost 1. We also study the behaviour of the Bitcoin network with churn miners (nodes that leave and rejoin the network) and with different topologies (linear topology, ring topology, tree topology and fully connected topology). PRISM+ is therefore used to analyse the resilience of Hybrid Casper when changing various basic parameters of the protocol, such as block creation rates and penalty determination strategies. We also study the robustness of Hybrid Casper against two known attacks: the Eclipse attack (where an attacker controls a significant portion of the network's nodes and can prevent other nodes from receiving new transactions) and the majority attack (where an attacker controls a majority of the network's nodes and can manipulate the blockchain to their advantage).

A new global wheat marketmodel (GLOWMM) for the analysis of wheat export prices

Food commodity prices fluctuations have important impacts on poverty and food insecurity across the world. Conventional models have not provided a complete picture of recent price spikes in agricultural commodity markets, while there is an urgent need for appropriate policy responses. Perhaps new approaches are needed in order to better understand international spill-overs, the feedback between the real and the financial sectors and also the link between food and energy prices. In this paper, we present results from a new worldwide dynamic model that provides short and long-run impulse responses of wheat international prices to various real shocks.

Discrete Event Systems based Design Patterns for Diagnosability Analysis of Automated Manufacturing Systems

The main goal of this thesis is to facilitate the process of industrial automated systems development applying formal methods to ensure the reliability of systems. A new formulation of distributed diagnosability problem in terms of Discrete Event Systems theory and automata framework is presented, which is then used to enforce the desired property of the system, rather then just verifying it. This approach tackles the state explosion problem with modeling patterns and new algorithms, aimed for verification of diagnosability property in the context of the distributed diagnosability problem. The concepts are validated with a newly developed software tool.