Metashooting: a novel tool for free energy reconstruction from polymorphic phase transition mechanisms

We introduce a novel scheme for the mechanistic investigation of solid-solid phase transitions, which we dub extit{metashooting}. Combining transition path sampling molecular dynamics and metadynamics, this scheme allows for both a complete mechanistic analysis and a detailed mapping of the free energy surface. This is illustrated by performing extit{metashooting} calculations on the pressure-induced B4/B3 $ightarrow$ B1 phase transition in ZnO. The resulting free energy map helps to clarify the role of intermediate configurations along this activated process and the competition between different mechanistic regimes with superior accuracy. We argue that extit{metashooting} can be efficiently applied to a broader class of activated processes

On the use and development of advanced computational techniques to determine the properties and behaviour of metastable materials

This thesis contains discussions and results pertaining to three distinct pieces of work, all related by an underlying theme: the use and development of computational techniques to discover and characterise novel metastable materials. Zinc oxide is a cheap and abundant material with many potential uses in the electronics and Optics industries. However, its wurtzite ground state structure gives rise to a number of undesirable properties. Thus, knowledge of how to stabilise more useful metastable phases is desirable. To that end, the mechanism of the pressure-induced phase transition between the zincblende and rocksalt polymorphs of the compound was deduced using transition path sampling. Following this, a novel technique combining TPS methods with metadynamics was applied to classify the free-energy landscape relevant to the transition pathway. This provided further information relating to the transition that would have been impossible to determine using path based analyses alone. Water ice exhibits a wealth of structural polymorphism, with at least eighteen phases known to experiment and many more configurations predicted. However, a true understanding of the transition pathways that link these structures remains elusive. Using both metadynamics techniques and a novel procedure known as rotational shooting, attempts to deduce pathways between different phases of ice have been made. The results presented include successful transformations between two crystalline phases of ice and several amorphous phases, as well as the possible elucidation of a novel ice polymorph. Crystal structure prediction remains a challenge in materials science. Using a random structure search technique, eight novel allotropes of carbon and three novel high-pressure polymorphs of zinc oxide have been found and subsequently characterised using density functional theory. Each of the materials displays its own unique array of properties, demonstrating both the variety exhibited by polymorphs of the same material and the ability of random structure prediction techniques to predict such dissimilar materials

Many-particle Li Ion dynamics in LiMPO4 olivine phosphates (M = Mn, Fe)

LiMPO4 (M = Mn, Fe) olivine phosphates are important materials for battery applications due to their stability, safety, and reliable recharge cycle. Despite continuous experimental and computational investigations, several aspects of these materials remain challenging, including conductivity dimensionality and how it maps onto Li pathways. In this work, we use a refined version of our finite temperature molecular dynamics “shooting” approach, originally designed to enhance Li hopping probability. We perform a comparative analysis of ion mobility in both materials, focused on many-particle effects. Therein, we identify main [010] diffusion channels, as well as means of interchannel couplings, in the form of Li lateral [001] hopping, which markedly impact the overall mobility efficiency as measured by self-diffusion coefficients. This clearly supports the need of many-particle approaches for reliable mechanistic investigations and for battery materials benchmarking due to the complex nature of the diffusion and transport mechanisms

Staphylococcus aureus in the oral cavity: a three-year retrospective analysis of clinical laboratory data

OBJECTIVE: A retrospective analysis of laboratory data to investigate the isolation of Staphylococcus aureus from the oral cavity and facial area in specimens submitted to a regional diagnostic oral microbiology laboratory. METHODS: A hand search of laboratory records for a three-year period (1998-2000) was performed for specimens submitted to the regional diagnostic oral microbiology laboratory based at Glasgow Dental Hospital and School. Data were collected from forms where S. aureus was isolated. These data included demographics, referral source, specimen type, methicillin susceptibility and clinical details. RESULTS: For the period 1998-2000, there were 5,005 specimens submitted to the laboratory. S. aureus was isolated from 1,017 specimens, of which 967 (95%) were sensitive to methicillin (MSSA) and 50 (5%) were resistant to methicillin (MRSA). The 1,017 specimens were provided from 615 patients. MRSA was isolated from 37 (6%) of patients. There was an increasing incidence of S. aureus with age, particularly in the greater than 70 years age group. The most common specimen from which MSSA was isolated was an oral rinse (38%) whilst for MRSA isolates this was a tongue swab (28%). The clinical condition most commonly reported for MSSA isolates was angular cheilitis (22%). Erythema, swelling, pain or burning of the oral mucosa was the clinical condition most commonly reported for MRSA isolates (16%). Patients from whom the MSSA isolates were recovered were most commonly (55%) seen in the oral medicine clinic at the dental hospital, whilst patients with MRSA were more commonly seen in primary care settings such as nursing homes, hospices and general dental practice (51%). CONCLUSION: In line with more recent surveys, this retrospective study suggests that S. aureus may be a more frequent isolate from the oral cavity than hitherto suspected. A small proportion of the S. aureus isolates were MRSA. There were insufficient data available to determine whether the S. aureus isolates were colonising or infecting the oral cavity. However, the role of S. aureus in several diseases of the oral mucosa merits further investigation

Creative learning conversations: producing living dialogic spaces

publication-status: Publishedtypes: ArticleBackground ‘Creative learning conversations’, are methodological devices developed in two co-participative qualitative research projects exploring creativity and educational futures at the University of Exeter in England. Sources of evidence Framed by Critical Theory, the projects, one on dance education partnership, the other on student voice and transformation, sought to open space between creativity and performativity to initiate emancipatory educational change. This was undertaken over the course of five years in English primary and secondary schools, prioritising humanising, wise creativity (Chappell, 2008; Craft, 2008). Purpose This paper re-analyses data and methodological processes to characterise and theorise creative learning conversations in terms of social spatiality and dialogue. The characteristics are: partiality, emancipation, working from the ‘bottom up’, participation, debate and difference, openness to action, and embodied and verbalised idea exchange. Main argument This re-analysis theoretically adapts Bronfenbrenner’s (1979) ecological model to situate layered engagement. Utilising Lefebvre’s (1991) conceptualisation of Lived space and Bakhtin’s (1984) work on open-ended dialogue, the paper theorises creative learning conversations as producing living dialogic spaces. Conclusions Creative learning conversations are a way of contributing to change which moves us towards an education future fit for the twenty-first century. From a living dialogic space perspective a creative learning conversation is the ongoing process without forced closure of those in the roles of University academic, teachers, artists, students co-participatively researching and developing knowledge of their ‘lived space’ together. Given traditional lethargy in the educational system as a whole commitment to changing education for better futures demands active involvement in living dialogic space, where our humanity both emerges from and guides our shared learning