342 research outputs found

    Reconstruction of 2D Al Ti on TiB in an aluminium melt

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    It has been widely considered that Al Ti is involved in the aluminium nucleation on TiB , although the mechanism has not been fully understood. In this paper molecular dynamics has been conducted to investigate this phenomenon at an atomistic scale. It was found that a two-dimensional Al Ti layer may remain on TiB above the aluminium liquidus. In addition, the results showed that this 2D Al Ti undergoes interface reconstruction by forming a triangular pattern. This triangular pattern consists of different alternative stacking sequences. The transition region between the triangles forms an area of strain concentration. By means of this mechanism, this interfacial Al Ti layer stabilizes itself by localizing the large misfit strain between TiB and Al Ti This reconstruction is similar to the hdp-fcc interface reconstruction in other systems which has been observed experimentally.EPSR

    Contrasting effects of hemiparasites on ecosystem processes: can positive litter effects offset the negative effects of parasitism?

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    Hemiparasites are known to influence community structure and ecosystem functioning, but the underlying mechanisms are not well studied. Variation in the impacts of hemiparasites on diversity and production could be due to the difference in the relative strength of two interacting pathways: direct negative effects of parasitism and positive effects on N availability via litter. Strong effects of parasitism should result in substantial changes in diversity and declines in productivity. Conversely, strong litter effects should result in minor changes in diversity and increased productivity. We conducted field-based surveys to determine the association of Castillejaoccidentalis with diversity and productivity in the alpine tundra. To examine litter effects, we compared the decomposition of Castilleja litter with litter of four other abundant plant species, and examined the decomposition of those four species when mixed with Castilleja. Castilleja was associated with minor changes in diversity but almost a twofold increase in productivity and greater foliar N in co-occurring species. Our decomposition trials suggest litter effects are due to both the rapid N loss of Castilleja litter and the effects of mixing Castilleja litter with co-occurring species. Castilleja produces litter that accelerates decomposition in the alpine tundra, which could accelerate the slow N cycle and boost productivity. We speculate that these positive effects of litter outweigh the effects of parasitism in nutrient-poor systems with long-lived hemiparasites. Determining the relative importance of parasitism and litter effects of this functional group is crucial to understand the strong but variable roles hemiparasites play in affecting community structure and ecosystem processes

    An epitaxial model for heterogeneous nucleation on potent substrates

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    © The Minerals, Metals & Materials Society and ASM International 2012In this article, we present an epitaxial model for heterogeneous nucleation on potent substrates. It is proposed that heterogeneous nucleation of the solid phase (S) on a potent substrate (N) occurs by epitaxial growth of a pseudomorphic solid (PS) layer on the substrate surface under a critical undercooling (ΔT ). The PS layer with a coherent PS/N interface mimics the atomic arrangement of the substrate, giving rise to a linear increase of misfit strain energy with layer thickness. At a critical thickness (h ), elastic strain energy reaches a critical level, at which point, misfit dislocations are created to release the elastic strain energy in the PS layer. This converts the strained PS layer to a strainless solid (S), and changes the initial coherent PS/N interface into a semicoherent S/N interface. Beyond this critical thickness, further growth will be strainless, and solidification enters the growth stage. It is shown analytically that the lattice misfit (f) between the solid and the substrate has a strong influence on both h and ΔT ; h decreases; and ΔT increases with increasing lattice misfit. This epitaxial nucleation model will be used to explain qualitatively the generally accepted experimental findings on grain refinement in the literature and to analyze the general approaches to effective grain refinement.EPSRC Centre for Innovative Manufacturing in Liquid Metal Engineerin

    Trial feasibility and process evaluation of a motivationally-embellished group peer led walking intervention in retirement villages using the RE-AIM framework: The Residents in Action Trial (RiAT)

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    Objective: The Residents in Action Trial (RiAT; ACTRN12616001177448) was a 16-week motivationally-embellished peer-led walking intervention designed to increase walking, reduce sitting, and improve mental health and well-being in insufficiently active residents in retirement villages. In this paper we report on 1) trial feasibility and acceptability, and 2) evaluate the processes involved in the implementation of the intervention using the RE-AIM framework. Method: A mixed methods design was employed, consisting of data from accelerometers, surveys, (individual, pair-based and focus group) interviews, and participant logbooks. Participants included 116 walkers (M(SD) age = 78.37(8.30); 92% female), 8 peer leaders (i.e. ambassadors) and 3 retirement village managers from 14 retirement villages. Descriptives and linear mixed modelling were used to analyse the quantitative data and inductive thematic analyses were employed to analyse the interview data. Results: The intended cluster randomised controlled design became quasi-experimental due to insufficient numbers of recruited ambassadors. The perceived burden of the number and frequency of research assessments was a frequently mentioned reason for a poor recruitment. Facilitators to walking maintenance were the use of self-monitoring, goal setting, social support, and having a routine. Reach was modest (about 14% of eligible participants were recruited from each village), but retention was excellent (92%). The motivational strategies taught appeared to have been implemented, at least in part, by the ambassadors. The walkers in the main experimental condition increased marginally their step counts, but there were no group differences on mental health and well-being outcomes, partly because of low statistical power. Conclusions: Walkers and ambassadors who did take part in the study suggested that they enjoyed the programme and found it useful in terms of becoming more active and making social connections. However, the group format was not appealing to some participants, hence, other delivery options should be explored in the future

    Comparative efficacy and acceptability of pharmacological treatments for insomnia in adults: A systematic review and network meta-analysis

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    This is the protocol for a review and there is no abstract. The objectives are as follows: 1) To compare individual pharmacological treatments for insomnia in adults in terms of: efficacy, measured as self-rated quality of sleep or satisfaction with sleep; and acceptability of treatment. 2) To generate a clinically-useful hierarchy of available pharmacological treatments for insomnia in adults, according to their efficacy and acceptability

    Patients with paroxysmal nocturnal hemoglobinuria demonstrate a prothrombotic clotting phenotype which is improved by complement inhibition with eculizumab

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    Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder, characterized by complement‐mediated intravascular hemolysis and thrombosis. The increased incidence of PNH‐driven thrombosis is still poorly understood, but unlike other thrombotic disorders, is thought to largely occur through complement‐mediated mechanisms. Treatment with a C5 inhibitor, eculizumab, has been shown to significantly reduce the number of thromboembolic events in these patients. Based on previously described links between changes in fibrin clot structure and thrombosis in other disorders, our aim was to investigate clot structure as a possible mechanism of thrombosis in patients with PNH and the anti‐thrombotic effects of eculizumab treatment on clot structure. Clot structure, fibrinogen levels and thrombin generation were examined in plasma samples from 82 patients from the National PNH Service in Leeds, UK. Untreated PNH patients were found to have increased levels of fibrinogen and thrombin generation, with subsequent prothrombotic changes in clot structure. No link was found between increasing disease severity and fibrinogen levels, thrombin generation, clot formation or structure. However, eculizumab treated patients showed decreased fibrinogen levels, thrombin generation and clot density, with increasing time spent on treatment augmenting these antithrombotic effects. These data suggest that PNH patients have a prothrombotic clot phenotype due to increased fibrinogen levels and thrombin generation, and that the antithrombotic effects of eculizumab are, in‐part, due to reductions in fibrinogen and thrombin generation with downstream effects on clot structure

    Relationship between solidification microstructure and hot cracking susceptibility for continuous casting of low-carbon and high-strength low-alloyed steels: A phase-field study

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    © The Minerals, Metals & Materials Society and ASM International 2013Hot cracking is one of the major defects in continuous casting of steels, frequently limiting the productivity. To understand the factors leading to this defect, microstructure formation is simulated for a low-carbon and two high-strength low-alloyed steels. 2D simulation of the initial stage of solidification is performed in a moving slice of the slab using proprietary multiphase-field software and taking into account all elements which are expected to have a relevant effect on the mechanical properties and structure formation during solidification. To account for the correct thermodynamic and kinetic properties of the multicomponent alloy grades, the simulation software is online coupled to commercial thermodynamic and mobility databases. A moving-frame boundary condition allows traveling through the entire solidification history starting from the slab surface, and tracking the morphology changes during growth of the shell. From the simulation results, significant microstructure differences between the steel grades are quantitatively evaluated and correlated with their hot cracking behavior according to the Rappaz-Drezet-Gremaud (RDG) hot cracking criterion. The possible role of the microalloying elements in hot cracking, in particular of traces of Ti, is analyzed. With the assumption that TiN precipitates trigger coalescence of the primary dendrites, quantitative evaluation of the critical strain rates leads to a full agreement with the observed hot cracking behavior. © 2013 The Minerals, Metals & Materials Society and ASM International

    Culture change in elite sport performance teams: Examining and advancing effectiveness in the new era

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    Reflecting the importance of optimizing culture for elite teams, Fletcher and Arnold (2011) recently suggested the need for expertise in culture change. Acknowledging the dearth of literature on the specific process, however, the potential effectiveness of practitioners in this area is unknown. The present paper examines the activity's precise demands and the validity of understanding in sport psychology and organizational research to support its delivery. Recognizing that sport psychologists are being increasingly utilized by elite team management, initial evidence-based guidelines are presented. Finally, to stimulate the development of ecologically valid, practically meaningful knowledge, the paper identifies a number of future research directions
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