1,646 research outputs found

    Computational Modelling of Oxygen Defects and Interfaces in Monoclinic HfO2

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    Hafnia (HfO2) is of particular interest for microelectronics applications. It is currently used as a high-k insulating dielectric in the latest generations of transistors and as the insulator in new metal-insulator-metal resistive memory devices (ReRAM). Oxygen defects within HfO2 are thought to have a signi cant impact on the performance of transistors and are seen to be a leading factor in dielectric breakdown. This same breakdown phenomenon is exploited in HfO2 ReRAM devices to form reversibly switchable conducting laments. In this work computational modelling is used to look at the properties of oxygen defects in monoclinic HfO2, to explain their mechanisms of formation and di usion, both in the bulk material and at interfaces. The properties of oxygen vacancy aggregates ranging from 2 to 4 vacancies are analysed. It is shown that the most stable aggregates form the largest void within the bulk lattice and the larger aggregates have a higher binding energy per vacancy. Negatively charged aggregates are found to be stable whereas positively charged aggregates are not. The properties of Frenkel pairs is also calculated leading to the development of a model for the formation of conductive laments in HfO2; by generation of oxygen vacancy aggregates, via Frenkel pair formation during electron ooding conditions, and oxygen interstitial out-di usion. A Pt/HfO2 interface model is created and its structural and electronic properties are analysed. The stability of oxygen defects at the interface is calculated. It is shown that at low oxygen concentrations, vacancies may be more stable at the interface however at high oxygen concentrations, oxygen interstitial ions are unlikely to penetrate the Pt electrode and so, remain within HfO2. The stability of oxygen defects across a Si/SiO2/HfO2/TiN interface are calculated and a model of oxygen scavenging process, from SiO2 and into defective TiN, is suggested

    Developing and applying heterogeneous phylogenetic models with XRate

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    Modeling sequence evolution on phylogenetic trees is a useful technique in computational biology. Especially powerful are models which take account of the heterogeneous nature of sequence evolution according to the "grammar" of the encoded gene features. However, beyond a modest level of model complexity, manual coding of models becomes prohibitively labor-intensive. We demonstrate, via a set of case studies, the new built-in model-prototyping capabilities of XRate (macros and Scheme extensions). These features allow rapid implementation of phylogenetic models which would have previously been far more labor-intensive. XRate's new capabilities for lineage-specific models, ancestral sequence reconstruction, and improved annotation output are also discussed. XRate's flexible model-specification capabilities and computational efficiency make it well-suited to developing and prototyping phylogenetic grammar models. XRate is available as part of the DART software package: http://biowiki.org/DART .Comment: 34 pages, 3 figures, glossary of XRate model terminolog

    Successful treatment with azithromycin and rifampicin of penicillin and cephalosporin insensitive pneumococcal osteomyelitis in a child with HIV infection: a case report

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    Pneumococcal infection is common in children with HIV infection, but osteomyelits is unusual. The best treatment for bone and joint infection due to antibiotic resistant pneumococci is not known, especially in immunocompromised children

    Effects of Picture Size Reduction and Blurring on Emotional Engagement

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    The activity of basic motivational systems is reflected in emotional responses to arousing stimuli, such as natural pictures. The manipulation of picture properties such as size or detail allows for investigation into the extent to which separate emotional reactions are similarly modulated by perceptual changes, or, rather, may subserve different functions. Pursuing this line of research, the present study examined the effects of two types of perceptual degradation, namely picture size reduction and blurring, on emotional responses. Both manipulations reduced picture relevance and dampened affective modulation of skin conductance, possibly because of a reduced action preparation in response to degraded or remote pictures. However, the affective modulation of the startle reflex did not vary with picture degradation, suggesting that the identification of these degraded affective cues activated the neural circuits mediating appetitive or defensive motivation

    Morphological characteristics of motor neurons do not determine their relative susceptibility to degeneration in a mouse model of severe spinal muscular atrophy

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    Spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality, resulting primarily from the degeneration and loss of lower motor neurons. Studies using mouse models of SMA have revealed widespread heterogeneity in the susceptibility of individual motor neurons to neurodegeneration, but the underlying reasons remain unclear. Data from related motor neuron diseases, such as amyotrophic lateral sclerosis (ALS), suggest that morphological properties of motor neurons may regulate susceptibility: in ALS larger motor units innervating fast-twitch muscles degenerate first. We therefore set out to determine whether intrinsic morphological characteristics of motor neurons influenced their relative vulnerability to SMA. Motor neuron vulnerability was mapped across 10 muscle groups in SMA mice. Neither the position of the muscle in the body, nor the fibre type of the muscle innervated, influenced susceptibility. Morphological properties of vulnerable and disease-resistant motor neurons were then determined from single motor units reconstructed in Thy.1-YFP-H mice. None of the parameters we investigated in healthy young adult mice - including motor unit size, motor unit arbor length, branching patterns, motor endplate size, developmental pruning and numbers of terminal Schwann cells at neuromuscular junctions - correlated with vulnerability. We conclude that morphological characteristics of motor neurons are not a major determinant of disease-susceptibility in SMA, in stark contrast to related forms of motor neuron disease such as ALS. This suggests that subtle molecular differences between motor neurons, or extrinsic factors arising from other cell types, are more likely to determine relative susceptibility in SMA

    We are all one together : peer educators\u27 views about falls prevention education for community-dwelling older adults - a qualitative study

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    Background: Falls are common in older people. Despite strong evidence for effective falls prevention strategies, there appears to be limited translation of these strategies from research to clinical practice. Use of peers in delivering falls prevention education messages has been proposed to improve uptake of falls prevention strategies and facilitate translation to practice. Volunteer peer educators often deliver educational presentations on falls prevention to community-dwelling older adults. However, research evaluating the effectiveness of peer-led education approaches in falls prevention has been limited and no known study has evaluated such a program from the perspective of peer educators involved in delivering the message. The purpose of this study was to explore peer educators’ perspective about their role in delivering peer-led falls prevention education for community-dwelling older adults. Methods: A two-stage qualitative inductive constant comparative design was used.In stage one (core component) focus group interviews involving a total of eleven participants were conducted. During stage two (supplementary component) semi-structured interviews with two participants were conducted. Data were analysed thematically by two researchers independently. Key themes were identified and findings were displayed in a conceptual framework. Results: Peer educators were motivated to deliver educational presentations and importantly, to reach an optimal peer connection with their audience. Key themes identified included both personal and organisational factors that impact on educators’ capacity to facilitate their peers’ engagement with the message. Personal factors that facilitated message delivery and engagement included peer-to-peer connection and perceived credibility, while barriers included a reluctance to accept the message that they were at risk of falling by some members in the audience. Organisational factors, including ongoing training for peer educators and formative feedback following presentations, were perceived as essential because they affect successful message delivery. Conclusions: Peer educators have the potential to effectively deliver falls prevention education to older adults and influence acceptance of the message as they possess the peer-to-peer connection that facilitates optimal engagement. There is a need to consider incorporating learnings from this research into a formal large scale evaluation of the effectiveness of the peer education approach in reducing falls in older adults
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