A many-body interatomic potential for ionic systems: application to MgO

An analytic representation of the short-range repulsion energy in ionic systems is described that allows for the fact that ions may change their size and shape depending on their environment. This function is extremely efficient to evaluate relative to previous methods of modeling the same physical effects. Using a well-defined parametrization procedure we have obtained parameter sets for this energy function that reproduce closely the density functional theory potential energy surface of bulk MgO. We show how excellent agreement can be obtained with experimental measurements of phonon frequencies and temperature and pressure dependences of the density by using this effective potential in conjunction with ab initio parametrization.Comment: To appear in Journal of Chemical Physics (Oct 15th 2003

Classical derivation of Bose-Einstein statistics

When its temperature is low enough, the motion of any stable classical mechanical system is a superposition of {\em quasi}-independent harmonic oscillations of its normal modes, which are standing waves if the system is a crystal or a bounded continuous medium. Without invoking quantum mechanics I prove that, at thermal equilibrium, the observed distribution of energy among these oscillations is a Bose-Einstein distribution, albeit with an unknown constant $h_?$ in place of Planck's constant, $h$. I identify characteristics of the classical independent-oscillator Hamiltonian that make my derivation of the Bose-Einstein distribution possible, and I point out that other classical physical systems, such as an ideal gas, have Hamiltonians that can be transformed canonically into forms with these characteristics. If ${h_?=h}$, among the implications of this work are that (i) there is no discrepancy between the experimentally-observed spectrum of a blackbody and what should be expected if light was a mechanical wave in a bounded medium; (ii) there is no discrepancy between the experimentally-observed temperature dependence of a crystal's heat capacity and what should be expected of classical lattice waves; and (iii) when a cluster of massive particles is cold enough, the classical expectation should be that almost all of its vibrational energy is possessed by its lowest-frequency normal mode. Therefore, below a certain temperature, all but one of its degrees of freedom are almost inactive and it is a Bose-Einstein condensate

Velocity plateaus and jumps in carbon nanotube sliding

The friction between concentric carbon nanotubes sliding one inside the other has been widely studied and simulated, but not so far using external force as the driving variable. Our molecular dynamics (MD) simulations show that as the pulling force grows, the sliding velocity increases by jumps and plateaus rather than continuously as expected. Dramatic friction peaks (similar to that recently noted by Tangney {\it et al.} in Phys. Rev. Lett. 97 (2006) 195901) which develop around some preferential sliding velocities, are at the origin of this phenomenon. The (stable) rising edge of the peak produces a velocity plateau; the (unstable) dropping edge produces a jump to the nearest stable branch. The outcome is reminiscent of conduction in ionized gases, the plateau correspon ding to a current stabilization against voltage variations, the jump corresponding to a discharge or breakdown.Comment: 9 pages, 5 color figures, format latex Elsart. Surface Science, in press, http://dx.doi.org/10.1016/j.susc.2007.05.03

An interpretive study of student-centred learning through constructivist, humanist and socio-cultural lenses

The notion of student-centred learning is ubiquitous in the pedagogic literature, in learning and teaching statements of universities, and within course documentation. However it is not often defined, and an informal investigation of university staff revealed a variety of conflicting Interpretations. This ambiguity Is problematic for academic developers, and so warranted further Investigation through literature review and interviews with academic staff from the researcher's university. The literature review revealed diversity in understanding, and on examination, ideas were underpinned by a range of perspectives on learning per se. Three different perspectives, namely constructivism, humanism and socio-culturalism were examined for their respective alignment and value in thinking about student-centred learning. Many interpretations were within a constructivist framework, others more aligned with humanist or socio-cultural perspectives. The term student-centred learning was also used in association with contemporary ideas such as employability, widening participation and social justice. A constructivist grounded approach was used to collect data through interviews with lecturers teaching in art and design, and transcripts considered from the three perspectives above. It is argued in the findings that although constructivist interpretations of student-centred learning dominate the literature, other perspectives are also evident in the conceptions and practice of the group interviewed, and incorporation of these offered a more appropriate approach to contemporary issues in higher education, especially in building a partnership approach between lecturers and students. It is suggested that technicist approaches, though often based within constructivism, may have caused the proliferation of a 'slogan' approach to the student-centred learning discourse

Factors influencing the distribution of charge in polar nanocrystals

We perform first-principles calculations of wurtzite GaAs nanorods to explore the factors determining charge distributions in polar nanostructures. We show that both the direction and magnitude of the dipole moment $\mathbf{d}$ of a nanorod, and its electic field, depend sensitively on how its surfaces are terminated and do not depend strongly on the spontaneous polarization of the underlying lattice. We identify two physical mechanisms by which $\mathbf{d}$ is controlled by the surface termination, and we show that the excess charge on the nanorod ends is not strongly localized. We discuss the implications of these results for tuning nanocrystal properties, and for their growth and assembly.Comment: Accepted for publication in Phys. Rev. B Rapid Communication

The Case of Inter-Expert Creative Collaboration in Science Gallery Dublin: A Discourse Analytical Approach

The phenomenon of creativity has been a focus of enquiry by psychologists for many years. Compared with individual creativity, much less is known about creativity in collaborative contexts (Glăveanu, 2010; Sawyer, 2010). Taking a sociocultural view of creativity, this study contributes to an emerging strand of research that focusses centrally on how creativity unfolds in the performance of creative collaboration. The research design followed an inductive path conducive to theory building and employed a single case study method (Yin, 2009). Science Gallery Dublin, part of Trinity College Dublin (TCD), is presented as a special place for creative collaboration. In response to calls for further detail about how ideas emerge in group contexts (Glăveanu, 2017; Hargadon and Beckhy, 2006; Harvey and Chia-Yu, 2013; Harvey, 2014; Kurtzberg and Amabile, 2010), this study contributes to the literature in a number of ways. It describes a kind of talk - Idea Talk - that is presented as characteristic of and instrumental in the collaborative development of ideas and solutions. It presents a ‘Creative Convergence framework’ as a model that seeks to explain how ideas emerge through interdisciplinary dialogue. Findings of the study also challenge an established doctrine of creative collaboration and brainstorming which holds that equality of participation is desirable. The implications for practice include an enhanced understanding of the organisational and contextual features that can positively contribute to creative collaborations. The Idea Talk and Creative Convergence contributions, combined with further observations relating to the hosting and facilitation of groups, provide leaders and participants with new insights into how creativity emerges in groups

Fire intensity, seasonal variation and seeds traits may influence seed fates in Banksia woodlands

This thesis presents a multifaceted approach to understanding seed survival during fire. I considered seed survival of high temperatures in the context of seed moisture content, soil temperature, and seed depth in the soil profile. I identified several seed traits associated with seed survival and seedling emergence depth. I modelled seasonal variation and interactions between these traits, fuel dynamics and soil temperatures to identify conditions and periods for burning that minimise risk of seed mortality

Bacteria and tumours: causative agents or opportunistic inhabitants?

Associations between different bacteria and various tumours have been reported in patients for decades. Studies involving characterisation of bacteria within tumour tissues have traditionally been in the context of tumourigenesis as a result of bacterial presence within healthy tissues, and in general, dogma holds that such bacteria are causative agents of malignancy (directly or indirectly). While evidence suggests that this may be the case for certain tumour types and bacterial species, it is plausible that in many cases, clinical observations of bacteria within tumours arise from spontaneous infection of established tumours. Indeed, growth of bacteria specifically within tumours following deliberate systemic administration has been demonstrated for numerous bacterial species at preclinical and clinical levels. We present the available data on links between bacteria and tumours, and propose that besides the few instances in which pathogens are playing a pathogenic role in cancer, in many instances, the prevalent relationship between solid tumours and bacteria is opportunistic rather than causative, and discuss opportunities for exploiting tumour-specific bacterial growth for cancer treatment

Proneness to Guilt, Shame, and Pride in Children with Autism Spectrum Disorders and Neurotypical Children

Self‐conscious emotions (e.g., guilt, shame, and pride) are complex emotions that require self‐reflection and self‐evaluation, and are thought to facilitate the maintenance of societal norms and personal standards. Despite the importance of self‐conscious emotions, most research has focused on basic emotion processing in children with Autism Spectrum Disorders (ASD). Therefore, in the present study, we used the Test of Self‐Conscious Affect for Children (TOSCA‐C) to assess proneness to, or propensity to experience, the self‐conscious emotions guilt, shame, and pride in children with ASD and neurotypical children. The TOSCA‐C is designed to capture a child\u27s natural tendency to experience a given emotion across a range of everyday situations [Tangney, Stuewig, & Mashek, 2007]. We also assessed how individual characteristics contribute to the development of proneness to self‐conscious emotions, including theory of mind (ToM) and ASD symptomatology. In comparison to neurotypical children, children with ASD showed less proneness to guilt, although all children showed relatively high levels of proneness to guilt. Greater ToM ability was related to more proneness to guilt and authentic pride in children with ASD. Additionally, we found that children with ASD with more severe symptomatology were more prone to hubristic pride. Our results provide evidence of differences in proneness to self‐conscious emotions in children with ASD, as well as highlight important mechanisms contributing to how children with ASD may experience self‐conscious emotions