Parallel Performance for a Real Time Lattice Boltzmann Code

The paper will present the details of a Lattice Boltzmann solver running in real time for unsteady wake computations. In addition to algorithmic implementation, computational results, single core and parallel optimization of the methods are also discussed

XMM-Newton observations of UW CrB -- detection of X-ray bursts and evidence for accretion disc evolution

UW CrB (MS1603+2600) is a peculiar short period X-ray binary that exhibits extraordinary optical behaviour. The optical light curve shape of the system changes drastically from night to night, without any changes in overall brightness. Here we report X-ray observations of UW CrB obtained with {\it XMM-Newton}. We find evidence for several X-ray bursts confirming a neutron star primary. This considerably strengthens the case that UW CrB is an Accretion Disc Corona (ADC) system located at a distance of at least 5--7 kpc, (3--5 kpc above the galactic plane). The X-ray and optical monitor (UV+optical) light curves show remarkable shape variation from one observing run to another, which we suggest are due to large scale variations in the accretion disc shape resulting from a warp which periodically obscures the optical and soft X-ray emission. This is also supported by the changes in phase-resolved X-ray spectra.Comment: Accepted for publication in MNRA

Coupled atomistic–continuum simulations of nucleate boiling

Boiling is a striking example of a multiscale process, where the dynamics of bubbles is governed by the interplay between the molecular interactions responsible for nucleation, and the macroscale hydrodynamic and thermal boundary layers. A complete description of this phenomenon requires coupling molecular- and continuum-scale fluid mechanics into a single modelling framework. This article presents a hybrid atomistic–continuum computational model for coupled simulations of nucleate boiling. A domain decomposition coupling method is utilised, where the near-wall region is solved by a Molecular Dynamics description, which handles nucleation and the moving contact lines, while the bulk flow region is solved by a continuum-scale description based on the Navier–Stokes equations. The latter employs a Volume Of Fluid method to track the evolution of the liquid–vapour interface and the interphase mass transfer is computed via the Hertz–Knudsen–Schrage relationship. Boiling of a Lennard-Jones fluid over a heated wall is simulated and the hybrid solution is validated against a fully molecular solution. The results obtained with the coupled framework in terms of time-dependent bubble volume, phase-change rates, bubble dynamics and evolution of the temperature field agree quantitatively with those achieved by a MD-only simulation. The coupled framework reproduces the bubble growth rate over time from nucleation until a bubble diameter of about 70 nm, demonstrating the accuracy and robustness of the coupling architecture. This also demonstrates that the fluid dynamics description based on the Navier–Stokes equations is capable of correctly capturing the main heat and mass transfer mechanisms responsible for bubble growth at the nanoscale. The proposed modelling framework paves the way towards multiscale simulations of boiling, where the necessary molecular-level physics is retained in a computational fluid dynamics solver

Using Simulation for Decision Support: Lessons Learned from FireGrid

This paper describes some of the lessons learned from the FireGrid project. It starts with a brief overview of the project. The discussion of the lessons learned that follows is intended for others attempting to develop a similar system, where sensor data is used to steer a super-real time simulation in order to generate predictions that will provide decision support for emergency responders

An Architecture for an Integrated Fire Emergency Response System for the Built Environment

Peer-reviewed article published in the Proceedings of the 9th International Symposium on Fire Safety Science, Karlsruhe, 2008.FireGrid is a modern concept that aims to leverage a number of modern technologies to aid fire emergency response. In this paper we provide a brief introduction to the FireGrid project. A number of different technologies such as wireless sensor networks, grid-enabled High Performance Computing (HPC) implementation of fire models, and artificial intelligence tools need to be integrated to build up a modern fire emergency response system. We propose a system architecture that provides the framework for integration of the various technologies. We describe the components of the generic FireGrid system architecture in detail. Finally we present a small-scale demonstration experiment which has been completed to highlight the concept and application of the FireGrid system to an actual fire. Although our proposed system architecture provides a versatile framework for integration, a number of new and interesting research problems need to be solved before actual deployment of the system. We outline some of the challenges involved which require significant interdisciplinary collaborations

FireGrid: An e-infrastructure for next-generation emergency response support

Peer reviewed paper published in Journal of Parallel and Distributed Computing.The FireGrid project aims to harness the potential of advanced forms of computation to support the response to large-scale emergencies (with an initial focus on the response to fires in the built environment). Computational models of physical phenomena are developed, and then deployed and computed on High Performance Computing resources to infer incident conditions by assimilating live sensor data from an emergency in real time–or, in the case of predictive models, faster-than-real time. The results of these models are then interpreted by a knowledge-based reasoning scheme to provide decision support information in appropriate terms for the emergency responder. These models are accessed over a Grid from an agent-based system, of which the human responders form an integral part. This paper proposes a novel FireGrid architecture, and describes the rationale behind this architecture and the research results of its application to a large-scale fire experiment.Emergency response, Grid, High performance computing, Multi-agent system, Knowledge-based reasoning, Fire simulation mode

Species’ traits as predictors of avoidance towards roads and traffic

Road-networks and their associated motorized traffic pose a threat to biodiversity and ecosystems, with different groups of species exhibiting different avoidance responses. The often species-specific nature of these behavioural responses to roads and traffic suggest that morphological, ecological, life-history and behavioural traits could be useful in explaining and predicting these responses. Trait-based predictive models have been used to assess extinction risk, land use impacts, and road mortality. Here we present the first, to our knowledge, test of their potential to address animal road avoidance. We studied the fleeing responses and spatial distribution in relation to roads of diverse ungulate species across three South African protected areas. Our results show that smaller, solitary species with non-grazing food habits are more likely to flee in response to presence of a vehicle. None of the tested traits showed a clear relationship based on biological hypotheses with initial distance to roads and tolerance distance to vehicles (used to describe behavioural avoidance towards roads and vehicles, respectively). However, we found significant effects that supported proposed methodological hypotheses. Our results show the potential to use traits as indicators of vehicle and traffic avoidance. Obtaining behavioural avoidance data in the field for many species and areas can be time consuming, but here we show it may be possible to use available trait data to generally predict species responses. This could be useful for initial species risk assessments

A Systematic Analysis of Cell Cycle Regulators in Yeast Reveals That Most Factors Act Independently of Cell Size to Control Initiation of Division

Upstream events that trigger initiation of cell division, at a point called START in yeast, determine the overall rates of cell proliferation. The identity and complete sequence of those events remain unknown. Previous studies relied mainly on cell size changes to identify systematically genes required for the timely completion of START. Here, we evaluated panels of non-essential single gene deletion strains for altered DNA content by flow cytometry. This analysis revealed that most gene deletions that altered cell cycle progression did not change cell size. Our results highlight a strong requirement for ribosomal biogenesis and protein synthesis for initiation of cell division. We also identified numerous factors that have not been previously implicated in cell cycle control mechanisms. We found that CBS, which catalyzes the synthesis of cystathionine from serine and homocysteine, advances START in two ways: by promoting cell growth, which requires CBS's catalytic activity, and by a separate function, which does not require CBS's catalytic activity. CBS defects cause disease in humans, and in animals CBS has vital, non-catalytic, unknown roles. Hence, our results may be relevant for human biology. Taken together, these findings significantly expand the range of factors required for the timely initiation of cell division. The systematic identification of non-essential regulators of cell division we describe will be a valuable resource for analysis of cell cycle progression in yeast and other organisms