Testing spatial aspects of auditory salience

Auditory salience describes the extent to which sounds attract the listener’s attention. So far, there have not been any published studies testing if the location of sound relative to the listener influences its salience. In fact, not many experiments in general test auditory attention in a fully spatialised setting, with sounds in front and behind the listener. We modified two experimental methods from the literature so that they can be used to test spatial salience - one based on oddball detection and artificially created sounds, the other based on self-reported attention tracking in a more ecologically valid scenario. Each of these methods has its advantages and each presents different challenges. However, they both seem to indicate that high frequency sounds arriving from the back are slightly less salient. We believe this result could likely be explained by loudness differences

Work minimization accounts for footfall phasing in slow quadrupedal gaits

Quadrupeds, like most bipeds, tend to walk with an even left/right footfall timing. However, the phasing between hind and forelimbs shows considerable variation. Here, we account for this variation by modeling and explaining the influence of hind-fore limb phasing on mechanical work requirements. These mechanics account for the different strategies used by: (1) slow animals (a group including crocodile, tortoise, hippopotamus and some babies); (2) normal medium to large mammals; and (3) (with an appropriate minus sign) sloths undertaking suspended locomotion across a range of speeds. While the unusual hind-fore phasing of primates does not match global work minimizing predictions, it does approach an only slightly more costly local minimum. Phases predicted to be particularly costly have not been reported in nature

Generation of tuneable 589nm radiation as a Na guide star source using an optical parametric amplifier

We describe a 5.5W 589nm source based on a passively modelocked Nd:YVO4 laser and a multi-stage Lithium Triborate optical parametric amplifier seeded by a tuneable semiconductor laser. We show this system can produce rapidly tuneable, transform-limited pulses in near diffraction-limited beams at 589nm, useful for Na guide star applications. The attraction of this scheme is that it can be assembled from commercially available hardware and is readily scalable to high average powers

Application of representation theory to magnetic and structural phase transitions

The tools of representation theory offer us a powerful insight in those terms in a system’s Hamiltonian which cause it to become ordered. Such is its power that, in many fields, the vocabulary of representations has become conventional; crystallography remains a notable exception. This thesis develops the existing methods for applying representation theory to symmetry lowering phase transitions in crystalline systems, and presents examples of its use. The opening section reviews the foundations and previous applications of representation theory to magnetic and structural phase transitions. Complimentary to the mathematical framework is a discussion of the physical interpretation of irreducible representations and basis vectors, the building blocks of any system model constructed in this way. Symmetry arguments are used to qualitatively discuss the symmetry breaking in ferroelectric materials and the role of phase factors in the loss of centro-symmetry. The body of this work is concerned with developing fast, reliable and repeatable methods for applying representation theory to displacive transitions. Calculation of a system’s basis vectors requires both a reliable method, and suitable starting resources. In this section, the first verifiable validation of the tables of Kovalev is presented, along with a strategy for determining the appropriate set of trial functions for use with the method of projection operators. Further, a new module in SARAh-Refine has been written which performs basis vector refinement of powder diffraction data to facilitate quantitative analysis using these techniques. Finally, the techniques of representation theory are applied to two experimental investigations: iron oxyborate and potassium selenate. The use of a single symmetry framework to discuss the structural, magnetic and charge-ordering transitions in these systems demonstrate the power of this technique. Representation theory provides a bridge between structure and properties; this work aims to strengthen the foundations of that bridge

Ultraviolet Cancellations in Half-Maximal Supergravity as a Consequence of the Double-Copy Structure

We show that the double-copy structure of gravity forbids divergences in pure half-maximal (16 supercharge) supergravity at four and five points at one loop in D<8 and at two loops in D<6. We link the cancellations that render these supergravity amplitudes finite to corresponding ones that eliminate forbidden color factors from the divergences of pure nonsupersymmetric Yang-Mills theory. The vanishing of the two-loop four-point divergence in D=5 half-maximal supergravity is an example where a valid counterterm satisfying the known symmetries exists, yet is not present. We also give explicit forms of divergences in half-maximal supergravity at one loop in D=8 and at two loops in D=6.Comment: 32 pages, revtex, 6 figures, v3 minor correction

'We're not like that': Crusader and Maverick Occupational Identity Resistance

This article explores the occupational identities of hairdressers and vehicle mechanics working in small and micro-firms. Using qualitative interview data from two UK cities, it examines the ways that workers expounded, reflected on and discursively reframed public perceptions of their occupation. A novel distinction between two types of identity reframing is proposed. ‘Crusaders’ are workers who reject characterisations as inappropriate for the occupation at large, whereas ‘mavericks’ accept that popular characterisations apply to other workers but differentiate themselves. The analysis identifies differences in occupational identity resistance strategies (crusader or maverick) when workers interact with two different publics: customers and trainees

Inhomogeneous Reionization Models in Cosmological Hydrodynamical Simulations

In this work we present a new hybrid method to simulate the thermal effects of the reionization in cosmological hydrodynamical simulations. The method improves upon the standard approach used in simulations of the intergalactic medium (IGM) and galaxy formation without a significant increase of the computational cost allowing for efficient exploration of the parameter space. The method uses a small set of phenomenological input parameters and combines a semi-numerical reionization model to solve for the topology of reionization and an approximate model of how reionization heats the IGM, with the massively parallel \texttt{Nyx} hydrodynamics code, specifically designed to solve for the structure of diffuse IGM gas. We have produced several large-scale high resolution cosmological hydrodynamical simulations ($2048^3$, $L_{\rm box} = 40$ Mpc/h) with different instantaneous and inhomogeneous HI reionization models that use this new methodology. We study the IGM thermal properties of these models and find that large scale temperature fluctuations extend well beyond the end of reionization. Analyzing the 1D flux power spectrum of these models, we find up to $\sim 50\%$ differences in the large scale properties (low modes, $k\lesssim0.01$ s/km) of the post-reionization power spectrum due to the thermal fluctuations. We show that these differences could allow one to distinguish between different reionization scenarios already with existing Ly$\alpha$ forest measurements. Finally, we explore the differences in the small-scale cutoff of the power spectrum and we find that, for the same heat input, models show very good agreement provided that the reionization redshift of the instantaneous reionization model happens at the midpoint of the inhomogeneous model.Comment: 24 pages, 16 figures. Accepted by MNRAS. Minor changes to match published versio

SiGMa: Simple Greedy Matching for Aligning Large Knowledge Bases

The Internet has enabled the creation of a growing number of large-scale knowledge bases in a variety of domains containing complementary information. Tools for automatically aligning these knowledge bases would make it possible to unify many sources of structured knowledge and answer complex queries. However, the efficient alignment of large-scale knowledge bases still poses a considerable challenge. Here, we present Simple Greedy Matching (SiGMa), a simple algorithm for aligning knowledge bases with millions of entities and facts. SiGMa is an iterative propagation algorithm which leverages both the structural information from the relationship graph as well as flexible similarity measures between entity properties in a greedy local search, thus making it scalable. Despite its greedy nature, our experiments indicate that SiGMa can efficiently match some of the world's largest knowledge bases with high precision. We provide additional experiments on benchmark datasets which demonstrate that SiGMa can outperform state-of-the-art approaches both in accuracy and efficiency.Comment: 10 pages + 2 pages appendix; 5 figures -- initial preprin