Low Mass Companions to T~Tauri Stars: a Mechanism for Rapid-rise FU~Orionis Outbursts

We show that outside-in disc instabilities, which can produce rapid-\null rise FU Orionis outbursts in T~Tauri systems, are a natural consequence of the existence of protoplanetary protostellar companions. The \pcomp{} would be formed through gravitational instability on a dynamical timescale (\sim 10^5\y), and provided it was formed at less than a few \AU{}, it would be swept in to \sim15\Rsun in less than 10^5\y. A companion of mass $10^{-2}$\Msun at this radius would act as a flood gate which stores material upstream and periodically releases it following the ignition of the thermal ionisation instability.Comment: To appear in MNRAS, 5 pages, uuencoded PostScript (figures included) also available at http://www.mpa-garching.mpg.de/~syer/papers

Data abstraction in coordination constraints

Communications in Computer and Information Science 393, 2013This paper studies complex coordination mechanisms based on constraint satisfaction. In particular, it focuses on data-sensitive connectors from the Reo coordination language. These connectors restrict how and where data can flow between loosely-coupled components taking into account the data being exchanged. Existing engines for Reo provide a very limited support for data-sensitive connectors, even though data constraints are captured by the original semantic models for Reo. When executing data-sensitive connectors, coordination constraints are not exhaustively solved at compile time but at runtime on a per-need basis, powered by an existing SMT (satisfiability modulo theories) solver.To deal with a wider range of data types and operations, we abstract data and reduce the original constraint satisfaction problem to a SAT problem, based on a variation of predicate abstraction. We show soundness and completeness of the abstraction mechanism for well-defined constraints, and validate our approach by evaluating the performance of a prototype implementation with different test cases, with and without abstraction.(undefined

Automata for context-dependent connectors

Recent approaches to component-based software engineering employ coordinating connectors to compose components into software systems. For maximum flexibility and reuse, such connectors can themselves be composed, resulting in an expressive calculus of connectors whose semantics encompasses complex combinations of synchronisation, mutual exclusion, non-deterministic choice and state-dependent behaviour. A more expressive notion of connector includes also context-dependent behaviour, namely, whenever the choices the connector can take change non-monotonically as the context, given by the pending activity on its ports, changes. Context dependency can express notions of priority and inhibition. Capturing context-dependent behaviour in formal models is non-trivial, as it is unclear how to propagate context in- formation through composition. In this paper we present an intuitive automata-based formal model of context-dependent connectors, and argue that it is superior to previous attempts at such a model for the coordination language Reo

Deconstructing Reo

AbstractCoordination in Reo emerges from the composition of the behavioural constraints of the primitives, such as channels, in a component connector. Understanding and implementing Reo, however, has been challenging due to interaction of the channel metaphor, which is an inherently local notion, and the non-local nature of constraint propagation imposed by composition. In this paper, the channel metaphor takes a back seat, and we focus on the behavioural constraints imposed by the composition of primitives, and phrase the semantics of Reo as a constraint satisfaction problem. Not only does this provide a clear intensional description of the behaviour of Reo connectors in terms of synchronisation and data flow constraints, it also paves the way for new implementation techniques based on constraint propagation and satisfaction. In fact, decomposing Reo into constraints provides a new computational model for connectors, which we extend to model interaction with an unknown external world beyond what is currently possible in Reo

Featherweight Generic Confinement

Existing approaches to object encapsulation either rely on ad hoc syntactic restrictions or require the use of specialised type systems. Syntactic restrictions are difficult to scale and to prove correct, while specialised type systems require extensive changes to programming languages. We demonstrate that confinement can be enforced cheaply in Featherweight Generic Java, with no essential change to the underlying language or type system. This result demonstrates that polymorphic type parameters can simultaneously act as ownership parameters and should facilitate the adoption of confinement and ownership type systems in general-purpose programming languages

A Procedure for Splitting Processes and its Application to Coordination

We present a procedure for splitting processes in a process algebra with multi-actions (a subset of the specification language mCRL2). This splitting procedure cuts a process into two processes along a set of actions A: roughly, one of these processes contains no actions from A, while the other process contains only actions from A. We state and prove a theorem asserting that the parallel composition of these two processes equals the original process under appropriate synchronization. We apply our splitting procedure to the process algebraic semantics of the coordination language Reo: using this procedure and its related theorem, we formally establish the soundness of splitting Reo connectors along the boundaries of their (a)synchronous regions in implementations of Reo. Such splitting can significantly improve the performance of connectors.Comment: In Proceedings FOCLASA 2012, arXiv:1208.432

Leadership and Organizational Vision ���¢�������� Hopes, Concepts and Reality.

This is an exploratory study of the challenges a particular business leader faces in bringing his organizational vision to life. It seeks to understand some of the fundamental issues relating to how the vision needs to be conceived, structured and communicated but more importantly tries to uncover some of the specific roadblocks that might be faced along the way. This involved a critique of the culture within Diageo with specific emphasis on the gaps between actual and desired and ���¢��������official���¢�������� and ���¢��������unofficial���¢�������� cultures Data gathered using focus groups, semi-structured interviews and direct observation is analyzed using a theoretical framework that critically examines the link between organizational success, vision and culture. What this study finds is that success is derived from a mixture of consistency and alignment and that a strong culture is a fundamental building block of delivering an organizational vision. Truly understanding the gaps and reasons behind the gaps is the first stage in creating a congruent and powerful culture. There are no short cuts to success and Jim Young must reevaluate his goals, timelines and action plan if he is to create his desired future for the Diageo On Trade tea