Modelling diffusion in crystals under high internal stress gradients

Diffusion of vacancies and impurities in metals is important in many processes occurring in structural materials. This diffusion often takes place in the presence of spatially rapidly varying stresses. Diffusion under stress is frequently modelled by local approximations to the vacancy formation and diffusion activation enthalpies which are linear in the stress, in order to account for its dependence on the local stress state and its gradient. Here, more accurate local approximations to the vacancy formation and diffusion activation enthalpies, and the simulation methods needed to implement them, are introduced. The accuracy of both these approximations and the linear approximations are assessed via comparison to full atomistic studies for the problem of vacancies around a Lomer dislocation in Aluminium. Results show that the local and linear approximations for the vacancy formation enthalpy and diffusion activation enthalpy are accurate to within 0.05 eV outside a radius of about 13 Å (local) and 17 Å (linear) from the centre of the dislocation core or, more generally, for a strain gradient of roughly up to 6 × 10^6 m^-1 and 3 × 10^6 m^-1, respectively. These results provide a basis for the development of multiscale models of diffusion under highly non-uniform stress

Nine-month-olds use frequency of onset clusters to segment novel words

Before their first birthday, infants have started to identify and use information about their native language, such as frequent words, transitional probabilities, and co-occurrence of segments (phonotactics), to identify viable word boundaries. These cues can then be used to segment new words from running speech. We explored whether infants are capable of detecting a novel word form using the frequency of occurrence of the onset alone to further characterize the role of phonotactics in speech segmentation. Experiment 1 shows that English-learning 9-month-olds can successfully segment a word from natural speech if the onset is legal in English (i.e., pleet) but not if the onset is illegal (i.e., tleet). Experiment 2 shows that English-learning 9-month-olds are successful at word segmentation when presented with two onset clusters that vary in statistical frequency. Infants familiarized to a high-frequency onset (i.e., trom) were successful at segmenting the target word embedded in speech, but those familiarized to the low-frequency onset (i.e., drom) were unsuccessful. Together, these results show that infants use statistical information from the speech input and that low levels of exposure to onset phonotactics alone might not be sufficient in identifying word boundaries

Examining Mental Health and Well-being Provision in Schools in Europe: Methodological Approach

Schools are considered an ideal setting for community-based mental health and well-being interventions for young people. However, in spite of extensive literature examining the effectiveness of such interventions, very few studies have investigated existing mental health and well-being provision in schools. The current study aims to extend such previous research by surveying primary and secondary schools to investigate the nature of available provision in nine European countries (Germany, Ireland, the Netherlands, Poland, Serbia, Spain, Sweden, the UK and Ukraine). Furthermore, the study aims to investigate potential barriers to mental health and well-being provision and compare provision within and between countries

Weighted-density approximation for general nonuniform fluid mixtures

In order to construct a general density-functional theory for nonuniform fluid mixtures, we propose an extension to multicomponent systems of the weighted-density approximation (WDA) of Curtin and Ashcroft [Phys. Rev. A 32, 2909 (1985)]. This extension corrects a deficiency in a similar extension proposed earlier by Denton and Ashcroft [Phys. Rev. A 42, 7312 (1990)], in that that functional cannot be applied to the multi-component nonuniform fluid systems with spatially varying composition, such as solid-fluid interfaces. As a test of the accuracy of our new functional, we apply it to the calculation of the freezing phase diagram of a binary hard-sphere fluid, and compare the results to simulation and the Denton-Ashcroft extension.Comment: 4 pages, 4 figures, to appear in Phys. Rev. E as Brief Repor

Cu/Ag EAM Potential Optimized for Heteroepitaxial Diffusion from ab initio Data

A binary embedded-atom method (EAM) potential is optimized for Cu on Ag(111) by fitting to ab initio data. The fitting database consists of DFT calculations of Cu monomers and dimers on Ag(111), specifically their relative energies, adatom heights, and dimer separations. We start from the Mishin Cu-Ag EAM potential and first modify the Cu-Ag pair potential to match the FCC/HCP site energy difference then include Cu-Cu pair potential optimization for the entire database. The optimized EAM potential reproduce DFT monomer and dimer relative energies and geometries correctly. In trimer calculations, the potential produces the DFT relative energy between FCC and HCP trimers, though a different ground state is predicted. We use the optimized potential to calculate diffusion barriers for Cu monomers, dimers, and trimers. The predicted monomer barrier is the same as DFT, while experimental barriers for monomers and dimers are both lower than predicted here. We attribute the difference with experiment to the overestimation of surface adsorption energies by DFT and a simple correction is presented. Our results show that the optimized Cu-Ag EAM can be applied in the study of larger Cu islands on Ag(111).Comment: 15 pages, 7 figure

Tree-Independent Dual-Tree Algorithms

Dual-tree algorithms are a widely used class of branch-and-bound algorithms. Unfortunately, developing dual-tree algorithms for use with different trees and problems is often complex and burdensome. We introduce a four-part logical split: the tree, the traversal, the point-to-point base case, and the pruning rule. We provide a meta-algorithm which allows development of dual-tree algorithms in a tree-independent manner and easy extension to entirely new types of trees. Representations are provided for five common algorithms; for k-nearest neighbor search, this leads to a novel, tighter pruning bound. The meta-algorithm also allows straightforward extensions to massively parallel settings.Comment: accepted in ICML 201

Bursts in a fiber bundle model with continuous damage

We study the constitutive behaviour, the damage process, and the properties of bursts in the continuous damage fiber bundle model introduced recently. Depending on its two parameters, the model provides various types of constitutive behaviours including also macroscopic plasticity. Analytic results are obtained to characterize the damage process along the plastic plateau under strain controlled loading, furthermore, for stress controlled experiments we develop a simulation technique and explore numerically the distribution of bursts of fiber breaks assuming infinite range of interaction. Simulations revealed that under certain conditions power law distribution of bursts arises with an exponent significantly different from the mean field exponent 5/2. A phase diagram of the model characterizing the possible burst distributions is constructed.Comment: 9 pages, 11 figures, APS style, submitted for publicatio

The association between ADHD and eating disorders/pathology in adolescents: A systematic review

Background: Attention-Deficit/Hyperactivity Disorder (ADHD), one of the most common neurodevelopmental conditions of childhood, is associated with high rates of mood and behavioral disorders. Preliminary evidence suggests that ADHD may also be associated with eating disorders (ED) or eating pathology (EP). This systematic review synthesizes the extant published literature on this association among youth ages 12 - 21 years. Methods: Literature searches were performed using Medline, Ovid/Psych Info, Google Scholar, and via manual inspection of bibliographies. Crosssectional, case-control, and prospective studies published in English with sample sizes larger than 50, participant ages 12 - 21 years, and assessed ADHD and ED or EP, were considered for review. Case reports, feeding, and drug studies were excluded. Results: Preliminary searches yielded 337 articles; eight articles met inclusion/exclusion criteria. Two studies documented an association between ADHD and ED, and three studies found an association between ADHD and EP. Youth with ADHD were nearly 3 to 6 times more likely to develop an ED than youth without ADHD, and were also more likely to have higher rates of EP, body dissatisfaction, and desire to lose weight/ drive for thinness. Impulsivity was predictive of EP, and ADHD youth with co-occurring mood/behavioral disorders and punitive parental relationships were at higher risk. Conclusions: Five of eight studies documented an association between ADHD and ED or EP in adolescents. Future research is needed to confirm and refine further these findings. The findings have clinical implications, including the inclusion of ED/EP in screening and anticipatory guidance efforts. Evaluating whether medical management of ADHD may be efficacious in preventing and/or treating ED/EP is also warranted

CpG Island Methylation in Colorectal Cancer: Past, Present and Future

The concept of a CpG island methylator phenotype, or CIMP, quickly became the focus of several colorectal cancer studies describing its clinical and pathological features after its introduction in 1999 by Toyota and colleagues. Further characterization of CIMP in tumors lead to widespread acceptance of the concept, as expressed by Shen and Issa in their 2005 editorial, “CIMP, at last.” Since that time, extensive research efforts have brought great insights into the epidemiology and prognosis of CIMP+ tumors and other epigenetic mechanisms underlying tumorigenesis. With the advances in technology and subsequent cataloging of the human methylome in cancer and normal tissue, new directions in research to understand CIMP and its role in complex biological systems yield hope for future epigenetically based diagnostics and treatments