Prepontine non-giant neurons drive flexible escape behavior in zebrafish

Many species execute ballistic escape reactions to avoid imminent danger. Despite fast reaction times, responses are often highly regulated, reflecting a trade-off between costly motor actions and perceived threat level. However, how sensory cues are integrated within premotor escape circuits remains poorly understood. Here, we show that in zebrafish, less precipitous threats elicit a delayed escape, characterized by flexible trajectories, which are driven by a cluster of 38 prepontine neurons that are completely separate from the fast escape pathway. Whereas neurons that initiate rapid escapes receive direct auditory input and drive motor neurons, input and output pathways for delayed escapes are indirect, facilitating integration of cross-modal sensory information. These results show that rapid decision-making in the escape system is enabled by parallel pathways for ballistic responses and flexible delayed actions and defines a neuronal substrate for hierarchical choice in the vertebrate nervous system

Maximum Entropy Linear Manifold for Learning Discriminative Low-dimensional Representation

Representation learning is currently a very hot topic in modern machine learning, mostly due to the great success of the deep learning methods. In particular low-dimensional representation which discriminates classes can not only enhance the classification procedure, but also make it faster, while contrary to the high-dimensional embeddings can be efficiently used for visual based exploratory data analysis. In this paper we propose Maximum Entropy Linear Manifold (MELM), a multidimensional generalization of Multithreshold Entropy Linear Classifier model which is able to find a low-dimensional linear data projection maximizing discriminativeness of projected classes. As a result we obtain a linear embedding which can be used for classification, class aware dimensionality reduction and data visualization. MELM provides highly discriminative 2D projections of the data which can be used as a method for constructing robust classifiers. We provide both empirical evaluation as well as some interesting theoretical properties of our objective function such us scale and affine transformation invariance, connections with PCA and bounding of the expected balanced accuracy error.Comment: submitted to ECMLPKDD 201

Models of Galaxy Clusters with Thermal Conduction

We present a simple model of hot gas in galaxy clusters, assuming hydrostatic equilibrium and energy balance between radiative cooling and thermal conduction. For five clusters, A1795, A1835, A2199, A2390 and RXJ1347.5-1145, the model gives a good description of the observed radial profiles of electron density and temperature, provided we take the thermal conductivity $\kappa$ to be about 30% of the Spitzer conductivity. Since the required $\kappa$ is consistent with the recent theoretical estimate of Narayan & Medvedev (2001) for a turbulent magnetized plasma, we consider a conduction-based equilibrium model to be viable for these clusters. We further show that the hot gas is thermally stable because of the presence of conduction. For five other clusters, A2052, A2597, Hydra A, Ser 159-03 and 3C295, the model requires unphysically large values of $\kappa$ to fit the data. These clusters must have some additional source of heat, most likely an active galactic nucleus since all the clusters have strong radio galaxies at their centers. We suggest that thermal conduction, though not dominant in these clusters, may nevertheless play a significant role by preventing the gas from becoming thermally unstable.Comment: Published in ApJ; 22 pages, including 2 tables, 4 figures; typos corrected to match the published versio

Evaluating the Australasian Consumer Fraud Awareness Month, 2007

As part of a global effort to fight mass-marketed consumer scams, consumer protection agencies in 33 western countries have participated in a month of fraud prevention activities each year to raise awareness of the problem and to provide advice to consumers on how to avoid being victimised. In Australia and New Zealand, nineteen government agencies now comprise the Australasian Consumer Fraud Taskforce (ACFT) that conducted a campaign in March 2007, the theme of which was ‘Scams Target You – Protect Yourself’. This paper provides an evaluation of the impact of the activities undertaken by the Taskforce, including the effect that the extensive publicity had on the official reporting of scams by consumers. The results of an online survey of 841 self-selected respondents are also presented. It is concluded that the campaign was highly effective in raising consumer awareness, with reporting rates increasing substantially throughout the period of the campaign

Multiscale computational fluid dynamics

This is the final version. Available on open access from MDPI via the DOI in this recordComputational Fluid Dynamics (CFD) has numerous applications in the field of energy research, in modelling the basic physics of combustion, multiphase flow and heat transfer; and in the simulation of mechanical devices such as turbines, wind wave and tidal devices, and other devices for energy generation. With the constant increase in available computing power, the fidelity and accuracy of CFD simulations have constantly improved, and the technique is now an integral part of research and development. In the past few years, the development of multiscale methods has emerged as a topic of intensive research. The variable scales may be associated with scales of turbulence, or other physical processes which operate across a range of different scales, and often lead to spatial and temporal scales crossing the boundaries of continuum and molecular mechanics. In this paper, we present a short review of multiscale CFD frameworks with potential applications to energy problems

Inhomogeneity and anisotropy in Eulerian-Eulerian near-wall modelling

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record This paper tackles the issue of image vorticity in turbulent Eulerian-Eulerian simulations. A pressure-velocity model to account for the no permeability constraint on the fluid- and particle-phase wall normal stress components is proposed. The pressure-velocity model is derived with in a Reynolds-Averaged Two-Fluid model (RA-TFM) framework and is implemented within the open-source CFD toolbox OpenFOAM. We demonstrate that this approach is capable of accounting for the strong near-wall inhomogeneity, a flow feature that hitherto has been neglected in Eulerian-Eulerian modelling. Simulation predictions are validated against benchmark Direct Numerical Simulation data and show a promising step forward in near-wall modelling in Eulerian-Eulerian simulations. The predictions reveal that the approach proposed herein can lead to a satisfactory agreement across all turbulence statistics paving the way for the correct prediction of more complex mechanisms. Finally, the source code of the recently developed solver ratfmFoam and supplementary material used in this work is made available online.University of Exete

CFD Simulations for Sensitivity Analysis of Different Parameters to the Wake Characteristics of Tidal Turbine

articleThis paper investigates the sensitivity of width proximity and mesh grid size to the wake characteristics of Momentum Reversal Lift (MRL) turbine using a new computational fluid dynamics (CFD) based Immersed Body Force (IBF) model. This model has been added as a source term into the large eddy simulation (LES), which is developed for solving two phase fluids. The open source CFD code OpenFOAM was used for the simulations. The simulation results showed that the grid size and width proximity have had massive impact on the flow characteristics and the computational cost of the tidal turbine. A fine grid size and large width inflicted longer computational time. In contrast, a coarse grid size and small width reduced the computational time but showed poor description of the flow features. In addition, a close proximity of the domain’s wall boundary to the turbine affected the free surface, the air body, and the flow characteristics at the interface between the two phases. These results showed that careful investigation of a suitable grid size and spacing between the wall boundary and the turbine is important to minimise the effect of these parameters on the simulation results.University of Exete