Extended Smoothed Boundary Method for Solving Partial Differential Equations with General Boundary Conditions on Complex Boundaries

In this article, we describe an approach for solving partial differential equations with general boundary conditions imposed on arbitrarily shaped boundaries. A continuous function, the domain parameter, is used to modify the original differential equations such that the equations are solved in the region where a domain parameter takes a specified value while boundary conditions are imposed on the region where the value of the domain parameter varies smoothly across a short distance. The mathematical derivations are straightforward and generically applicable to a wide variety of partial differential equations. To demonstrate the general applicability of the approach, we provide four examples herein: (1) the diffusion equation with both Neumann and Dirichlet boundary conditions; (2) the diffusion equation with both surface diffusion and reaction; (3) the mechanical equilibrium equation; and (4) the equation for phase transformation with the presence of additional boundaries. The solutions for several of these cases are validated against corresponding analytical and semi-analytical solutions. The potential of the approach is demonstrated with five applications: surface-reaction-diffusion kinetics with a complex geometry, Kirkendall-effect-induced deformation, thermal stress in a complex geometry, phase transformations affected by substrate surfaces, and a self-propelled droplet.Comment: This document is the revised version of arXiv:0912.1288v

Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO

The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1−xO heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1−xO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1−xO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth

Migration as a form of workforce attrition: a nine-country study of pharmacists

Background There is a lack of evidence to inform policy development on the reasons why health professionals migrate. Few studies have sought to empirically determine factors influencing the intention to migrate and none have explored the relationship between factors. This paper reports on the first international attempt to investigate the migration intentions of pharmacy students and identify migration factors and their relationships. Methods Responses were gathered from 791 final-year pharmacy students from nine countries: Australia, Bangladesh, Croatia, Egypt, Portugal, Nepal, Singapore, Slovenia and Zimbabwe. Data were analysed by means of Principal Components Analysis (PCA) and two-step cluster analysis to determine the relationships between factors influencing migration and the characteristics of subpopulations most likely and least likely to migrate. Results Results showed a significant difference in attitudes towards the professional and sociopolitical environment of the home country and perceptions of opportunities abroad between those who have no intention of migrating and those who intend to migrate on a long-term basis. Attitudes of students planning short-term migration were not significantly different from those of students who did not intend to migrate. These attitudes, together with gender, knowledge of other migrant pharmacists and past experiences abroad, are associated with an increased propensity for migration. Conclusion Given the influence of the country context and environment on migration intentions, research and policy should frame the issue of migration in the context of the wider human resource agenda, thus viewing migration as one form of attrition and a symptom of other root causes. Remuneration is not an independent stand-alone factor influencing migration intentions and cannot be decoupled from professional development factors. Comprehensive human resource policy development that takes into account the issues of both remuneration and professional development are necessary to encourage retention

Domains of spirituality and their importance to the health of 75 533 adolescents in 12 countries

Spirituality is considered by many to be an important domain of health. It is sometimes measured in four domains of connections: to oneself, to others, to nature and to the transcendent. While the importance of such connections is recognized as a fundamental human right for children, few interna- tional studies have studied their impacts on the health and well-being of young people. In this study of young people conducted over 4 years in 12 countries, we examined the perceived importance of each of four spiritual health domains and how they each related to positive mental health status in >75 000 adolescents. ‘Connections to self’ were consistently viewed as most important among boys and girls in all 12 countries. Fostering of strong connections to self, which involves cultivating a sense of meaning, purpose and joy in the lives of adolescents, appears most fundamental to achieving men- tal health and well-being. This may be achieved directly through a focus on connections to self, or in- directly by focusing on the indirect effects of the other three domains on mental health. This opens up many opportunities for health promotion in child populations, internationally.Brock Library Open Access Publishing Fun

Hydrogen-Enhanced Vacancy Diffusion in Metals

Copyright © 2020 American Chemical Society. Vacancy diffusion is fundamental to materials science. Hydrogen atoms bind strongly to vacancies and are often believed to retard vacancy diffusion. Here, we use a potential-of-mean-force method to study the diffusion of vacancies in Cu and Pd. We find H atoms, instead of dragging, enhance the diffusivity of vacancies due to a positive hydrogen Gibbs excess at the saddle-point: that is, the migration saddle attracts more H than the vacancy ground state, characterized by an activation excess ΓHm ≈ 1 H, together with also-positive migration activation volume ωm and activation entropy Sm. Thus, according to the Gibbs adsorption isotherm generalized to the activation path, a higher μH significantly lowers the migration free-energy barrier. This is verified by ab initio grand canonical Monte Carlo simulations and direct molecular dynamics simulations. This trend is believed to be generic for migrating dislocations, grain boundaries, and so on that also have a higher capacity for attracting H atoms due to a positive activation volume at the migration saddles

International perspectives on social media use among adolescents: Implications for mental and social well-being and substance use

In the present study, we aimed to explore the relationship between intensity of social media use (SMU), problematic SMU and well-being outcomes. Four categories of SMU were developed taking into account both intensity of use and problematic SMU simultaneously: non-active; active; intense; and problematic use. Using these four categories, we assessed associations between SMU and mental and social well-being, and substance use. Data from 190,089 respondents aged 11, 13, and 15 years from 42 countries involved in the Health Behavior in School-aged Children (HBSC) study were analyzed. With a slight cross-national variance, 78% of adolescents in the sample were classified as active or intense users, and 7% showed signs of problematic SMU. The remaining 15% belonged to the non-active users. Three-level regression analyses revealed that the problematic users showed the least favorable mental and social well-being profile and the highest level of substance use. Compared with active users, non-active users reported lower mental and social well-being, but also the lowest substance use levels. Intense non-problematic users showed the highest levels of social well-being. Our findings highlight the importance of assessing both the intensity and problematic component of SMU to reliably assess associations with mental and social well-being and substance use