Eutectic colony formation: A phase field study

Eutectic two-phase cells, also known as eutectic colonies, are commonly observed during the solidification of ternary alloys when the composition is close to a binary eutectic valley. In analogy with the solidification cells formed in dilute binary alloys, colony formation is triggered by a morphological instability of a macroscopically planar eutectic solidification front due to the rejection by both solid phases of a ternary impurity that diffuses in the liquid. Here we develop a phase-field model of a binary eutectic with a dilute ternary impurity and we investigate by dynamical simulations both the initial linear regime of this instability, and the subsequent highly nonlinear evolution of the interface that leads to fully developed two-phase cells with a spacing much larger than the lamellar spacing. We find a good overall agreement with our recent linear stability analysis [M. Plapp and A. Karma, Phys. Rev. E 60, 6865 (1999)], which predicts a destabilization of the front by long-wavelength modes that may be stationary or oscillatory. A fine comparison, however, reveals that the assumption commonly attributed to Cahn that lamella grow perpendicular to the envelope of the solidification front is weakly violated in the phase-field simulations. We show that, even though weak, this violation has an important quantitative effect on the stability properties of the eutectic front. We also investigate the dynamics of fully developed colonies and find that the large-scale envelope of the composite eutectic front does not converge to a steady state, but exhibits cell elimination and tip-splitting events up to the largest times simulated.Comment: 18 pages, 18 EPS figures, RevTeX twocolumn, submitted to Phys. Rev.

No mean city: adolescent health and risk behaviours in a UK urban setting

Background: The adult population of Glasgow has worse health than in the rest of Scotland, only partially explained by deprivation. Little is known about the health of young Glaswegians. Methods: The 2010 Health Behaviour in School-aged Children survey data were analysed using multilevel modelling to compare outcomes in Glasgow relative to the rest of Scotland. Results: Glasgow adolescents had similar or better self-reported health on some measures—e.g. adjusting for age and sex, OR for ‘very happy’ was 0.93 (95% CI = (0.75, 1.14))—and the beta coefficient for positive GHQ-12 was 2.79 (0.72, 4.85) compared with the rest of Scotland. However, many health aspects were worse in Glasgow especially for eating and sedentary behaviour, subjective health and aggression, e.g. the OR for ‘daily consumption of vegetables’ was 0.59 (0.46, 0.77), of reporting ‘excellent health’ was 0.66 (0.50, 0.87); headaches was 1.40 (1.09, 1.80); however drinking alcohol in the past week was lower (OR 0.71 (0.50, 0.99)) and smoking, similar. Adjustment for family affluence and school type marginally attenuated the association with Glasgow. Conclusions: The worse health experienced by Glasgow adults is only partially seen among young people in Glasgow; however, these are seen at the youngest ages in the study

Growing up in Glasgow: the social context of adolescence

The adolescent population of Glasgow, the city with the highest mortality in the UK, has a higher prevalence of risk behaviours than elsewhere in Scotland. Previous research has highlighted the importance of social context in interpreting such differences. Contextual variables from the 2010 Health Behaviour in School-aged Children Scotland survey were analysed. Glaswegian adolescents were more likely to live in low socioeconomic status, single-parent or step-families, or with neither parent in employment, less likely to share family meals, more likely to buy lunch outside school, and spend time with friends after school and in the evenings. They also had a poorer perception of their local neighbourhood. Family affluence only partially explained these differences

A preliminary study of airborne microbial biodiversity over peninsular Antarctica

This study used PCR-based molecular biological identification techniques to examine the biodiversity of air sampled over Rothera Point (Antarctic Peninsula). 16S rDNA fragments of 132 clones were sequenced and identified to reveal a range of microorganisms, including cyanobacteria, actinomycetes, diatom plastids and other uncultivated bacterial groups. Matches for microorganisms that would be considered evidence of human contamination were not found. The closest matches for many of the sequences were from Antarctic clones already in the databases or from other cold environments. Whilst the majority of the sequences are likely to be of local origin, back trajectory calculations showed that the sampled air may have travelled over the Antarctic Peninsula immediately prior to reaching the sample site. As a result, a proportion of the detected biota may be of non-local origin. Conventional identification methods based on propagule morphology or culture are often inadequate due to poor preservation of characteristic features or loss of viability during airborne transfer. The application of molecular biological techniques in describing airborne microbial biodiversity represents a major step forward in the study of airborne biota over Antarctica and in the distribution of microorganisms and propagules in the natural environment

Testing a series of causal propositions relating time in child care to children's externalizing behavior

Prior research has documented associations between hours in child care and children’s externalizing behavior. A series of longitudinal analyses were conducted to address 5 propositions, each testing the hypothesis that child care hours causes externalizing behavior. Data from the National Institute of Child Health and Human Development Early Child Care Research Network (NICHD) Study of Early Child Care and Youth Development were used in this investigation because they include repeated measures of child care experiences, externalizing behavior, and family characteristics. There were 3 main findings. First, the evidence linking child care hours with externalizing behavior was equivocal in that results varied across model specifications. Second, the association between child care hours and externalizing behavior was not due to a child effect. Third, child care quality and proportion of time spent with a large group of peers moderated the effects of child care hours on externalizing behavior. The number of hours spent in child care was more strongly related to externalizing behavior when children were in low-quality child care and when children spent a greater proportion of time with a large group of peers. The magnitude of associations between child care hours and externalizing behavior was modest. Implications are that parents and policymakers must take into account that externalizing behavior is predicted from a constellation of variables in multiple contexts

Modeling future flows of the Volta River system: impacts of climate change and socio-economic changes

As the scientific consensus concerning global climate change has increased in recent decades, research on potential impacts of climate change on water resources has been given high importance. However in Sub-Saharan Africa, few studies have fully evaluated the potential implications of climate change to their water resource systems. The Volta River is one of the major rivers in Africa covering six riparian countries (mainly Ghana and Burkina Faso). It is a principal water source for approximately 24 million people in the region. The catchment is primarily agricultural providing food supplies to rural areas, demonstrating the classic water, food, energy nexus. In this study an Integrated Catchment Model (INCA) was applied to the whole Volta River system to simulate flow in the rivers and at the outlet of the artificial Lake Volta. High-resolution climate scenarios downscaled from three different Global Climate Models (CNRM-CM5, HadGEM2-ES and CanESM2), have been used to drive the INCA model and to assess changes in flow by 2050s and 2090s under the high climate forcing scenario RCP8.5. Results show that peak flows during the monsoon months could increase into the future. The duration of high flow could become longer compared to the recent condition. In addition, we considered three different socio-economic scenarios. As an example, under the combined impact from climate change from downscaling CNRM-CM5 and medium+ (high economic growth) socio-economic changes, the extreme high flows (Q5) of the Black Volta River are projected to increase 11% and 36% at 2050s and 2090s, respectively. Lake Volta outflow would increase +1% and +5% at 2050s and 2090s, respectively, under the same scenario. The effects of changing socio-economic conditions on flow are minor compared to the climate change impact. These results will provide valuable information assisting future water resource development and adaptive strategies in the Volta Basin