Research Publications

Summary of the discussion session on Research Publications, discussion leader, Sam Burgess

First record of an Odontaspidid shark in Ascension Island waters

The occurrence of the poorly understood shark species Odontapsis ferox is reported at an oceanic seamount in the central south Atlantic, within the Exclusive Economic Zone of Ascension Island. The presence of the species at this location is confirmed by the discovery of a tooth embedded in scientific equipment, and footage of at least one animal on autonomous underwater video. The new record of this shark species at this location demonstrates the knowledge gaps which still exist at many remote, oceanic structures and their candidacy for status as important conservation areas.info:eu-repo/semantics/publishedVersio

Generalized small-signal modelling of dual active bridge DC/DC converter

this paper presents a novel generalised approach of the small-signal modelling of dual active bridge (DAB) DC/DC converter. The adopted analysis is based on a per-unit fundamental frequency representation of the DAB. The outcome of the proposed modelling approach is a small signal, linearised, state-space DAB model; which is considered as a main building block for future control applications. The developed small signal DAB model includes all possible degrees of freedom affecting the performance of the DAB; this includes the voltage conversion ratio to allow the study of all DAB operation modes (i.e.: unity-gain and buck/boost modes.). Furthermore, since triple phase shift control (TPS) is used in this development work, the proposed model incorporates phase shift in addition to duty ratios. This feature allows for bridge voltage regulation, which is essential for efficient DAB operation in the case of buck/boost operation. Another key achievement is that the proposed small signal modelling methodology can be applied to any bidirectional DC-DC converter regardless of ratings, parameter values and number of ports. Extensive simulation is carried out to verify the proposed analysis

A Schwartz Round for Clinical Librarians – a case study

The authors, based on their involvement in supporting Schwartz Rounds at their hospital, presented and facilitateda Schwartz Round at the 9th International Clinical Librarians Conference in 2017. The paper discusses thepreparations for the Schwartz Round, and the logistical and emotional issues encountered beforehand and onthe day. They plan to hold future Schwartz Rounds on a regional basis

Successor-Predecessor Intrinsic Exploration

Exploration is essential in reinforcement learning, particularly in environments where external rewards are sparse. Here we focus on exploration with intrinsic rewards, where the agent transiently augments the external rewards with self-generated intrinsic rewards. Although the study of intrinsic rewards has a long history, existing methods focus on composing the intrinsic reward based on measures of future prospects of states, ignoring the information contained in the retrospective structure of transition sequences. Here we argue that the agent can utilise retrospective information to generate explorative behaviour with structure-awareness, facilitating efficient exploration based on global instead of local information. We propose Successor-Predecessor Intrinsic Exploration (SPIE), an exploration algorithm based on a novel intrinsic reward combining prospective and retrospective information. We show that SPIE yields more efficient and ethologically plausible exploratory behaviour in environments with sparse rewards and bottleneck states than competing methods. We also implement SPIE in deep reinforcement learning agents, and show that the resulting agent achieves stronger empirical performance than existing methods on sparse-reward Atari games

Quasinormal Modes of Optical Solitons

Quasinormal modes (QNMs) are essential for understanding the stability and resonances of open systems, with increasing prominence in black hole physics. We present here the first study of QNMs of optical potentials. We show that solitons can support QNMs, deriving a soliton perturbation equation and giving exact analytical expressions for the QNMs of fiber solitons. We discuss the boundary conditions in this intrinsically dispersive system and identify novel signatures of dispersion. From here, we discover a new analogy with astrophysical black holes and describe a regime in which the soliton is a robust black hole simulator for light-ring phenomena. Our results invite a range of applications, from the description of optical pulse propagation with QNMs to the use of state-of-the-art technology from fiber optics to address questions in black hole physics, such as QNM spectral instabilities and the role of nonlinearities in ringdown.Comment: 5 pages, 3 figure

Abnormal functional specialization within medial prefrontal cortex in high-functioning autism: a multi-voxel similarity analysis

Multi-voxel pattern analyses have proved successful in ‘decoding’ mental states from fMRI data, but have not been used to examine brain differences associated with atypical populations. We investigated a group of 16 (14 males) high-functioning participants with autism spectrum disorder (ASD) and 16 non-autistic control participants (12 males) performing two tasks (spatial/verbal) previously shown to activate medial rostral prefrontal cortex (mrPFC). Each task manipulated: (i) attention towards perceptual versus self-generated information and (ii) reflection on another person's mental state (‘mentalizing'versus ‘non-mentalizing’) in a 2 × 2 design. Behavioral performance and group-level fMRI results were similar between groups. However, multi-voxel similarity analyses revealed strong differences. In control participants, the spatial distribution of activity generalized significantly between task contexts (spatial/verbal) when examining the same function (attention/mentalizing) but not when comparing different functions. This pattern was disrupted in the ASD group, indicating abnormal functional specialization within mrPFC, and demonstrating the applicability of multi-voxel pattern analysis to investigations of atypical populations

Covalent attachment of active enzymes to upconversion phosphors allows ratiometric detection of substrates

Upconverting phosphors (UCPs) convert multiple low energy photons into higher energy emission via the process of photon upconversion and offer an attractive alternative to organic fluorophores for use as luminescent probes. Here, UCPs were capped with functionalized silica in order to provide a surface to covalently conjugate proteins with surface?accessible cysteines. Variants of green fluorescent protein (GFP) and the flavoenzyme pentaerythritol tetranitrate reductase (PETNR) were then attached via maleimide?thiol coupling in order to allow energy transfer from the UCP to the GFP or flavin cofactor of PETNR, respectively. PETNR retains its activity when coupled to the UCPs, which allows reversible detection of enzyme substrates via ratiometric sensing of the enzyme redox state