Denis A. Nicole

A distributed scientific data archive using the Web, XML and SQL/MED

We have developed a web-based architecture and user interface for fast storage, searching and retrieval of large, distributed, files resulting from scientific simulations. We demonstrate that the new DATALINK type defined in the draft SQL Management of External Data Standard can help to overcome problems associated with limited bandwidth when trying to archive large files using the web. We also show that separating the user interface specification from the user interface processing can provide a number of advantages. We provide a tool to generate automatically a default user interface specification, in the form of an XML document, for a given database. This facilitates deployment of our system by users with little web or database development experience. The XML document can be customised to change the appearance of the interface.

Goldstone modes in vacuum decay and first-order phase transitions

The authors introduce effective Hamiltonians for Goldstone modes of the Euclidean group, representing fluctuations in the surface of a critical droplet or in the interface between two phases. The Euclidean invariance is non-linearly realised on the Goldstone fields. The Hamiltonians are non-renormalisable in more than one dimension, showing that the disappearance of a phase transition in one dimension for systems with a discrete symmetry may be interpreted in terms of the infrared instabilities induced by these modes. The existence and form of these Hamiltonians indicates the universality of the essential singularity at a first-order phase transition in models with Euclidean invariance.

Practical Parallelism using Transputer Arrays

This paper explores methods for extracting parallelism from a wide variety of numerical applications. We investigate communications overheads and load-balancing for networks of transputers. After a discussion of some practical strategies for constructing occam programs, two case studies are analysed in detail.

Named graphs as a mechanism for reasoning about provenance

Named Graphs is a simple, compatible extension to the RDF abstract syntax that enables statements to be made about RDF graphs. This approach is in contrast to earlier attempts such as RDF reification, or knowledge-base specific extensions including quads and contexts. In this paper we demonstrate the use of Named Graphs and our experiences developing new kinds of semantic web application that build on Named Graphs for digital signatures, provenance, and semantic reasoning. We present a working example based on the Named Graphs for Jena (NG4J) API, from which we developed a semantic version control system for Software Engineering capable of reasoning about Named Graph-based provenance. We go on to discuss the implications of Named Graphs for Description Logics and semantic inference strategies.

Monte Carlo Simulation on Transputer Arrays

Abstract A Monte Carlo simulation of a simple statistical physics model is decomposed onto a multi-processor (transputer) array in two essentially different ways: using ‘geometric’ and ‘algorithmic’ concurrency. The geometric decomposition (in which each processor handles a small sector of the physical system) is characterized by high efficiency in utilization of processors, and relative simplicity in programming. The algorithmic decomposition (in which each processor handles a small sub-task of the full algorithm, typically in a pipelined mode) is characterized by greater flexibility in the data-size (size of the physical system) and minimal memory requirements for a majority of the processors in the array. These assertions are made concrete in relation to our specific problem (a two-dimensional spin system simulation) which is, in many respects representative of a wide class of problems of interest to theoretical physicists.

Classical Paths and Quantum Mechanics

Abstract In the semiclassical limit, the path integral description of quantum mechanics is dominated by classical paths. A classical path method is developed to extract energy levels and wavefunctions for a one-dimensional quantum system and it is shown that this method reproduces the results of the WKB approach. The classical path method generalizes the instanton method and provides new insights into instanton interactions. It provides a convenient and intuitive approach to many problems in quantum mechanics and field theory.

Handling unbounded loops with ESBMC 1.20

We extended ESBMC to exploit the combination of context-bounded symbolic model checking and k-induction to prove safety properties in single- and multi-threaded ANSI-C programs with unbounded loops. We now first try to verify by induction that the safety property holds in the system. If that fails, we search for a bounded reachable state that constitutes a counterexample.

Context-Bounded model checking with ESBMC 1.17

ESBMC is a context-bounded symbolic model checker for single- and multi-threaded ANSI-C code. It converts the verification conditions using different background theories and passes them directly to an SMT solver.

Model checking LTL properties over ANSI-C programs with bounded traces

Context-bounded model checking has been used successfully to verify safety properties in multi-threaded systems automatically, even if they are implemented in low-level programming languages such as C. In this paper, we describe and experiment with an approach to extend context-bounded software model checking to safety and liveness properties expressed in linear-time temporal logic (LTL). Our approach checks the actual C program, rather than an extracted abstract model. It converts the LTL formulas into Büchi automata for the corresponding never claims and then further into C monitor threads that are interleaved with the execution of the program under analysis. This combined system is then checked using the ESBMC model checker. We use an extended, four-valued LTL semantics to handle the finite traces that bounded model checking explores; we thus check the combined system several times with different acceptance criteria to derive the correct truth value. In order to mitigate the state space explosion, we use a dedicated scheduler that selects the monitor thread only after updates to global variables occurring in the LTL formula. We demonstrate our approach on the analysis of the sequential firmware of a medical device and a small multi-threaded control application.

Leveraging Windows Workflow Foundation for Scientific Workflows in Wind Tunnel Applications

Scientific and engineering experiments often produce large volumes of data that must be processed and visualised in near-realtime. An example of this, described in this paper, is microphone array processing of data from wind tunnels for aeroacoustic measurements. The overall turnaround time from data acquisition and movement, to data processing and visualization is often inhibited by factors such as manual data movement, system interoperability issues, manual resource discovery for job scheduling, and disparate physical locality between the experiment and scientist or engineer post-event. Workflow frameworks and runtimes can enable rapid composition and execution of complex scientific workflows. In this paper we explore two approaches based on Windows Workflow Foundation, a component of Microsoft WinFX. In our first approach, we present a framework for users to compose sequential workflows and access Globus grid services seamlessly using a .NET-based Commodity Grid Toolkit (MyCoG.NET). We demonstrate how application specific activity sets can be developed and extended by users. In our second approach we highlight how it can be advantageous to keep databases as central to the complete workflow enactment. These two approaches are demonstrated in the context of a wind tunnel Grid system being developed to help experimental aerodynamicists orchestrate such workflows.