Using a spatial overlap approach to estimate the risk of collisions between deep diving seabirds and tidal stream turbines : a review of potential methods and approaches

Peer reviewedPublisher PD

Planetary Transits Toward the Galactic Bulge

The primary difficulty with using transits to discover extrasolar planets is the low probability a planet has of transiting its parent star. One way of overcoming this difficulty is to search for transits in dense stellar fields, such as the Galactic bulge. Here I estimate the number of planets that might be detected from a monitoring campaign toward the bulge. A campaign lasting 10 nights on a 10 meter telescope (assuming 8 hours of observations per night and a 5'x5' field of view) would detect about 100 planets with radius \rp=1.5 \rjup, or about 30 planets with \rp=1.0 \rjup, if the frequency and distribution of planets in the bulge is similar to that in the solar neighborhood. Most of these planets will be discovered around stars just below the turn-off, i.e. slightly evolved G-dwarfs. Campaigns involving 1- or 4-m class telescopes are unlikely to discover any planets, unless there exists a substantial population of companions with \rp > 1.5 \rjup.Comment: 4 pages, 4 figures. Submitted to ApJ Letter

Reflections on the use of Project Wonderland as a mixed-reality environment for teaching and learning

This paper reflects on the lessons learnt from MiRTLE?a collaborative research project to create a ?mixed reality teaching and learning environment? that enables teachers and students participating in real-time mixed and online classes to interact with avatar representations of each other. The key hypothesis of the project is that avatar representations of teachers and students can help create a sense of shared presence, engendering a greater sense of community and improving student engagement in online lessons. This paper explores the technology that underpins such environments by presenting work on the use of a massively multi-user game server, based on Sun?s Project Darkstar and Project Wonderland tools, to create a shared teaching environment, illustrating the process by describing the creation of a virtual classroom. It is planned that the MiRTLE platform will be used in several trial applications ? which are described in the paper. These example applications are then used to explore some of the research issues arising from the use of virtual environments within an education environment. The research discussion initially focuses on the plans to assess this within the MiRTLE project. This includes some of the issues of designing virtual environments for teaching and learning, and how supporting pedagogical and social theories can inform this process

Negative Differential Resistivity and Positive Temperature Coefficient of Resistivity effect in the diffusion limited current of ferroelectric thin film capacitors

We present a model for the leakage current in ferroelectric thin- film capacitors which explains two of the observed phenomena that have escaped satisfactory explanation, i.e. the occurrence of either a plateau or negative differential resistivity at low voltages, and the observation of a Positive Temperature Coefficient of Resistivity (PTCR) effect in certain samples in the high-voltage regime. The leakage current is modelled by considering a diffusion-limited current process, which in the high-voltage regime recovers the diffusion-limited Schottky relationship of Simmons already shown to be applicable in these systems

Energetic Consistency and Momentum Conservation in the Gyrokinetic Description of Tokamak Plasmas

Gyrokinetic field theory is addressed in the context of a general Hamiltonian. The background magnetic geometry is static and axisymmetric, and all dependence of the Lagrangian upon dynamical variables is in the Hamiltonian or in free field terms. Equations for the fields are given by functional derivatives. The symmetry through the Hamiltonian with time and toroidal angle invariance of the geometry lead to energy and toroidal momentum conservation. In various levels of ordering against fluctuation amplitude, energetic consistency is exact. The role of this in underpinning of conservation laws is emphasised. Local transport equations for the vorticity, toroidal momentum, and energy are derived. In particular, the momentum equation is shown for any form of Hamiltonian to be well behaved and to relax to its magnetohydrodynamic (MHD) form when long wavelength approximations are taken in the Hamiltonian. Several currently used forms, those which form the basis of most global simulations, are shown to be well defined within the gyrokinetic field theory and energetic consistency.Comment: RevTeX 4, 47 pages, no figures, revised version updated following referee comments (discussion more strictly correct/consistent, 4 references added, results unchanged as they depend on consistency of the theory), resubmitted to Physics of Plasma

Atmospheric contaminant sensor. Book 2: Appendices

Appendices containing equipment specifications and performance test data of the atmospheric contaminant sensor for submarines are presented

Why do firms go public? evidence from the banking industry

The lack of data on private firms has made it difficult to empirically examine theories of why firms go public. However, both public and private banks must disclose financial information to regulators. We exploit this requirement to explore the going-public decision. Our results indicate that banks that convert to public ownership are more likely to become targets than control banks that remain private. Banks that go public are also more likely to become acquirers than control banks. IPO banks grow faster than control banks after going public, although there is some evidence that their performance deteriorates.Financial institutions

Configurations of Extremal Even Unimodular Lattices

We extend the results of Ozeki on the configurations of extremal even unimodular lattices. Specifically, we show that if L is such a lattice of rank 56, 72, or 96, then L is generated by its minimal-norm vectors.Comment: 8 pages. To appear, International Journal of Number Theor

Speed control with low armature loss for very small sensorless brushed DC motors

A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment

Effect of dopants on annealing performance of silicon solar cells

The optimum annealing parameters of time and temperature for producing cell output recovery were established. Devices made from gallium doped and boron doped silicon were investigated. The cells ranged in resistivity from 0.1 to 20 ohm-cm and in thickness from 50 to 250 micrometers. The observations can be explained in a qualitative manner by postulating a pair of competing mechanisms to account for the low temperature reverse annealing seen in most boron and gallium doped silicon solar cells. Still another mechanism dominates at higher temperatures (350 C and greater) to complete this model. One of the mechanisms, defined as B, allows migrators to couple with radiation induced recombination sites thus increasing or enhancing their capture cross sections. This would tend to reduce minority carrier diffusion length. The new recombination complex is postulated to be thermally stable up to temperatures of approximately 350 C