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

Value-based design decision rationale documentation: Principles and empirical feasibility study

The explicit documentation of the rationale of design decisions is a practice generally encouraged, but rarely implemented in industry because of a variety of inhibitors. Methods proposed in the past for Design Decisions Rationale Documentation (DDRD) aimed to maximize benefits for the DDRD consumer by imposing on the producer of DDRD the burden to document all the potentially useful information. We propose here a compromise which consists in tailoring DDRD, based on its intended use or purpose. In our view, the adoption of a tailored DDRD, consisting only of the required set of information, would mitigate the effects of DDRD inhibitors. The aim of this paper is twofold: i) to discuss the application of Value-Based Software Engineering principles to DDRD, ii) to describe a controlled experiment to empirically analyze the feasibility of the proposed method. Results show that the level of utility related to the same category of DDRD information significantly changes depending on its purpose; such result is novel and it demonstrates the feasibility of the proposed value-based DDRD

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

Peaceful coexistence: agile developer perspectives on software architecture.

This study aims to explore the relationship between agility and architecture by surveying 72 software developers at IBM. Results suggest that software architecture and agility are not like oil and water. In particular, Agile developers perceived architectures as important and supportive (rather than in contrast or neutral) to agile values. This kind of positive perception of software architectural principles and practice bodes well for future efforts to integrate agile and architecture practices

Nonlinear interaction of Alfv\'enic instabilities and turbulence via the modification of the equilibrium profiles

Nonlinear simulations of Alfv\'en modes (AM) driven by energetic particles (EP) in the presence of turbulence are performed with the gyrokinetic particle-in-cell code ORB5. The AMs carry a heat flux, and consequently they nonlinearly modify the plasma temperature profiles. The isolated effect of this modification on the dynamics of turbulence is studied, by means of electrostatic simulations. We find that turbulence is reduced when the profiles relaxed by the AM are used, with respect to the simulation where the unperturbed profiles are used. This is an example of indirect interaction of EPs and turbulence. First, an analytic magnetic equilibrium with circular concentric flux surfaces is considered as a simplified example for this study. Then, an application to an experimentally relevant case of ASDEX Upgrade is discussed