Machine Learning Chemical Guidelines for Engineering Electronic Structures in Half-Heusler Thermoelectric Materials.

Half-Heusler materials are strong candidates for thermoelectric applications due to their high weighted mobilities and power factors, which is known to be correlated to valley degeneracy in the electronic band structure. However, there are over 50 known semiconducting half-Heusler phases, and it is not clear how the chemical composition affects the electronic structure. While all the n-type electronic structures have their conduction band minimum at either the Γ- or X-point, there is more diversity in the p-type electronic structures, and the valence band maximum can be at either the Γ-, L-, or W-point. Here, we use high throughput computation and machine learning to compare the valence bands of known half-Heusler compounds and discover new chemical guidelines for promoting the highly degenerate W-point to the valence band maximum. We do this by constructing an "orbital phase diagram" to cluster the variety of electronic structures expressed by these phases into groups, based on the atomic orbitals that contribute most to their valence bands. Then, with the aid of machine learning, we develop new chemical rules that predict the location of the valence band maximum in each of the phases. These rules can be used to engineer band structures with band convergence and high valley degeneracy

Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density

An exploration of the accentuation effect: errors in memory for voice fundamental frequency (F0) and speech rate

The accentuation effect demonstrates how memory often reflects category typical representations rather than the specific features of learned items. The present study investigated the impact of manipulating fundamental frequency (F0) and speech rate (syllables per second) on immediate target matching performance (selecting a voice from a pair to match a previously heard target voice) for a range of synthesised voices. It was predicted that when participants were presented with high or low frequency target voices, voices even higher or lower in frequency would be selected. The same pattern was also predicted for speech rate. Inconsistent with the accentuation account, the results showed a general bias to select voices higher in frequency for high, moderate, and low frequency target voices. For speech rate, listeners selected voices faster in rate for slow rate target voices. Overall it seems doubtful that listeners rely solely on categorical information about voices during recognition

Earwitness memory: factors that influence voice recognition accuracy across the lifespan [poster presentation]

We aimed to explore the effect of change in frequency (F0 in Hz) and speech rate (syllables per second - SPS) on voice recognition accuracy. In part one of our experiment, participants (M=36; F=36; aged 18-30 years) were given a 2AFC voice matching task which involved hearing (binaural headphone presentation) synthesised (using NaturalReader 12) voices (uttering the phrase “spring is the season where flowers appear, summer is the warmest season of the year”). Participants had to identify whether the two voices were the ‘same’ or ‘different’ (using a key press, left/right). There were six target voices (six different identities, three male and three female) in total. In each trial the to be matched voices comprised the original voice or a modulated version (increased/decreased F0 or increased/decreased SPS) of the original voice presented in a random order. In part two of our experiment, the same participants heard the original voice and the modulated versions in a random order. After presenting each voice, participants had to decide whether the voice they heard was ‘male’ or ‘female’ (using a key press, left/right). Results from part one indicated that participants could discriminate a more subtle pitch shift than they could for speech rate. Results from part two indicated that participants correctly identified the sex of the speaker when SPS was modulated for both male and female voices, and when F0 was modulated for male voices. However, participants incorrectly identified a female voice as ‘male’ when F0 decreased. This suggests that both pitch and speech rate variations are important for accurate speaker identification and voice discrimination

Relic Neutrinos and Z-Resonance Mechanism for Highest-Energy Cosmic Rays

The origin of the highest-energy cosmic rays remains elusive. The decay of a superheavy particle (X) into an ultra-energetic neutrino which scatters from a relic (anti-)neutrino at the Z-resonance has attractive features. Given the necessary X mass of $10^{14\sim15}$ GeV, the required lifetime, $10^{15\sim16}$ y, renders model-building a serious challenge but three logical possibilities are considered: (i) X is a Higgs scalar in SU(15) belonging to high-rank representation, leading to {\it power}-enhanced lifetime; (ii) a global X quantum number has {\it exponentially}-suppressed symmetry-breaking by instantons; and (iii) with additional space dimension(s) localisation of X within the real-world brane leads to {\it gaussian} decay suppression, the most efficient of the suppression mechanisms considered.Comment: 10 page LaTeX and one postscript figure. References adde

Studying the X-ray hysteresis in GX 339-4: the disc and iron line over one decade

We report on a comprehensive and consistent investigation into the X-ray emission from GX 339-4. All public observations in the 11 year RXTE archive were analysed. Three different types of model - single powerlaw, broken powerlaw and a disc + powerlaw - were fitted to investigate the evolution of the disc, along with a fixed gaussian component at 6.4 keV to investigate any iron line in the spectrum. We show that the relative variation in flux and X-ray colour between the two best sampled outbursts are very similar. The decay of the disc temperature during the outburst is clearly seen in the soft state. The expected decay is S_Disc \propto T^4; we measure T^4.75\pm0.23. This implies that the inner disc radius is approximately constant in the soft state. We also show a significant anti-correlation between the iron line significant width and the X-ray flux in the soft state while in the hard state the EW is independent of the flux. This results in hysteresis in the relation between X-ray flux and both line flux and EW. To compare the X-ray binary outburst to the behaviour seen in AGN, we construct a Disc Fraction Luminosity Diagram for GX 339-4, the first for an X-ray binary. The shape qualitatively matches that produced for AGN. Linking this with the radio emission from GX 339-4 the change in radio spectrum between the disc and power-law dominated states is clearly visible.Comment: Accepted for publication in MNRAS, 20 pages, 17 figures. For high-res version see http://www.astro.soton.ac.uk/~r.j.dunn/publications.htm

Participation and quality of life outcomes among individuals with earthquake-related physical disability: a systematic review

Objective: A literature review to evaluate quality of life and participation outcomes of individuals with earthquake-related physical injury. Data sources: A systematic review was performed using National Health Service (NHS) Centre for Reviews and Dissemination (CRD) guidelines. MEDLINE, Embase, PsychINFO, CINAHL and AMED electronic databases were searched from 1966 to January 2014. Study selection: Studies that measured quality of life or participation outcomes among individuals who acquired a physical disability as a result of an earthquake injury were included, with no limits on research design. Data extraction: The search yielded 961 potentially relevant articles after removal of duplicates. Of these, only 8 articles met the inclusion criteria. Studies were rated for quality using the Critical Appraisal Skills Programme (CASP) guidelines. Data synthesis: A narrative synthesis was performed due to the heterogeneity of the included studies. Results: Injured earthquake survivors in developing countries experience diminished participation and reduced quality of life. Small sample sizes and lack of uniformity in outcome measurement limit generalizability. No studies from developed countries were identified. Conclusion: To maximize our understanding of quality of life and participation in injured earthquake survivors, future research should consider both the functional consequences of the injury and the environmental impact of the earthquake. The research should be based on representative samples of the injured earthquake survivors and use validated condition-specific outcome measures that are clearly defined within the publications. In addition, research should include all countries that are affected by earthquakes

Computational Culture and A.I.: Challenging human identity and curatorial practice

This paper records a half-day Symposium of invited talks on the first day of the EVA London 2020 Conference. It continues a series from the previous four EVA London Symposiums held since 2016 (Bowen & Giannini 2016; Bowen, Giannini & Polmeer 2017; Bowen, Giannini, et al. 2018; 2019)