Lagrangian coherent structures and plasma transport processes

A dynamical system framework is used to describe transport processes in plasmas embedded in a magnetic field. For periodic systems with one degree of freedom the Poincar\'e map provides a splitting of the phase space into regions where particles have different kinds of motion: periodic, quasi-periodic or chaotic. The boundaries of these regions are transport barriers; i.e., a trajectory cannot cross such boundaries during the whole evolution of the system. Lagrangian Coherent Structure (LCS) generalize this method to systems with the most general time dependence, splitting the phase space into regions with different qualitative behaviours. This leads to the definition of finite-time transport barriers, i.e. trajectories cannot cross the barrier for a finite amount of time. This methodology can be used to identify fast recirculating regions in the dynamical system and to characterize the transport between them

Coherent transport structures in magnetized plasmas II: Numerical results

In a pair of linked articles (called Article I and II respectively) we apply the concept of Lagrangian Coherent Structures borrowed from the study of Dynamical Systems to magnetic field configurations in order to separate regions where field lines have different kind of behavior. In the present article, article II, by means of a numerical procedure we investigate the Lagrangian Coherent Structures in the case of a two-dimensional magnetic configuration with two island chains that are generated by magnetic reconnection and evolve nonlinearly in time. The comparison with previous results, obtained by assuming a fixed magnetic field configuration, allows us to explore the dependence of transport barriers on the particle velocity

Documenting design decision rationale to improve individual and team design decision making: An experimental evaluation

Individual and team decision-making have crucial influence on the level of success of every software project. Even though several studies were already conducted, which concerned design decision rationale documentation approaches, a few of them focused on performances and evaluated them in laboratory. This paper proposes a technique to document design decision rationale, and evaluates experimentally the impact such a technique has on effectiveness and efficiency of individual/team decision-making in presence of requirement changes. The study was conducted as a controlled experiment. Fifty post-graduate Master students performed in the role of experiment subjects. Documented design decisions regarding the Ambient Intelligence paradigm constituted the experiment objects. Main results of the experiment show that, for both individual and team-based decision-making, effectiveness significantly improves, while efficiency remains unaltered, when decision-makers are allowed to use, rather not use, the proposed design rationale documentation technique. Copyright 2006 ACM

Coherent transport structures in magnetized plasmas, I : Theory

In a pair of linked articles (called Article I and II respectively) we apply the concept of Lagrangian Coherent Structures (LCSs) borrowed from the study of Dynamical Systems to magnetic field configurations in order to separate regions where field lines have different kind of behaviour. In the present article, article I, after recalling the definition and the properties of the LCSs, we show how this conceptual framework can be applied to the study of particle transport in a magnetized plasma. Futhermore we introduce a simplified model that allows us to consider explicitly the case where the magnetic configuration evolves in time on timescales comparable to the particle transit time through the configuration. In contrast with previous works on this topic, this analysis requires that a system that is aperiodic in time be investigated. In this case the Poincar\'e map technique cannot be applied and LCSs remain the only viable tool

SafeSlice: A model slicing and design safety inspection tool for SysML

Software safety certification involves checking that the software design meets the (software) safety requirements. In practice, inspections are one of the primary vehicles for ensuring that safety requirements are satisfied by the design. Unless the safety-related aspects of the design are clearly delineated, the inspections conducted by safety assessors would have to consider the entire design, although only small fragments of the design may be related to safety. In a model-driven development context, this means that the assessors have to browse through large models, understand them, and identify the safety-related fragments. This is time-consuming and error-prone, specially noting that the assessors are often third-party regulatory bodies who were not involved in the design. To address this problem, we describe in this paper a prototype tool called, SafeSlice, that enables one to automatically extract the safety-related slices (fragments) of design models. The main enabler for our slicing technique is the traceability between the safety requirements and the design, established by following a structured design methodology that we propose. Our work is grounded on SysML, which is being increasingly used for expressing the design of safety-critical systems. We have validated our work through two case studies and a control experiment which we briefly outline in the paper. © 2011 ACM