Fast-food consumption among 17-year-olds in the Birth to Twenty cohort

Objectives: Assessment of fast-food consumption in urban black adolescents.Design: The current research was a descriptive cross-sectional study.Setting: Subjects attending the Birth to Twenty (Bt20) research facility at the Chris Hani Baragwanath Hospital in Soweto, Johannesburg between September 2007 and May 2008 were enrolled.Subjects: 655 black subjects (51.1% females) were consecutively selected to participate from the larger cohort of Bt20.Outcome measures: Fast-food item consumption and frequency of  fast-food outlet visits were assessed by interviewer-administered questionnaire.Results: Over a 7-day assessment period, participants consumed 5 026 fast-food items, with the most popular food item being an item known colloquially as a ‘quarter’. There were no gender differences in terms of preferences. Mean fast-food intake was 8.1 (4.6) items and 7.2 (4.7) items per week for males and females respectively (ρ = 0.01). A typical ‘quarter’ consists of a quarter-loaf of white bread, chips, a slice of cheese and any number of delicatessen meats and sauces. A macronutrient comparison between a ‘quarter’ and three commercially available fast-food meals was undertaken, with the ‘quarter’ providing the most energy (5 970 kJ) and being the least expensive (mean cost = R9.16).Conclusion: The average estimated daily energy requirement for a 17-year-old is approximately 10 000 kJ, thus the ‘quarter’ may make a significant contribution to daily energy intake. Further research assessing the role of fast-foods in the provision of total energy and nutrient intakes in adolescents is require

Electronic structure and total energy of interstitial hydrogen in iron: Tight binding models

An application of the tight binding approximation is presented for the description of electronic structure and interatomic force in magnetic iron, both pure and containing hydrogen impurities. We assess the simple canonical d-band description in comparison to a non orthogonal model including s and d bands. The transferability of our models is tested against known properties including the segregation energies of hydrogen to vacancies and to surfaces of iron. In many cases agreement is remarkably good, opening up the way to quantum mechanical atomistic simulation of the effects of hydrogen on mechanical properties

Block bond-order potential as a convergent moments-based method

The theory of a novel bond-order potential, which is based on the block Lanczos algorithm, is presented within an orthogonal tight-binding representation. The block scheme handles automatically the very different character of sigma and pi bonds by introducing block elements, which produces rapid convergence of the energies and forces within insulators, semiconductors, metals, and molecules. The method gives the first convergent results for vacancies in semiconductors using a moments-based method with a low number of moments. Our use of the Lanczos basis simplifies the calculations of the band energy and forces, which allows the application of the method to the molecular dynamics simulations of large systems. As an illustration of this convergent O(N) method we apply the block bond-order potential to the large scale simulation of the deformation of a carbon nanotube.Comment: revtex, 43 pages, 11 figures, submitted to Phys. Rev.

Maternal and neonatal vitamin D status at birth in black South Africans

Background. Vitamin D deficiency (VDD) in pregnant women has been associated with adverse pregnancy and neonatal outcomes. 25-hydroxyvitamin D (25(OH)D) levels are affected by numerous factors, including vitamin D intake, skin pigmentation, latitude and season of the year; they therefore vary by race and country. Vitamin D status in pregnant women and their offspring in South Africa (SA) is not well established.Objectives. To assess vitamin D status by measuring serum 25(OH)D in pregnant black SA women and their offspring in Johannesburg (latitude 26°S) and to assess whether vitamin D status is affected by maternal HIV infection.Methods. We prospectively enrolled pregnant women and their healthy neonates, and measured 25(OH)D in maternal and cord blood at delivery. Pregnant women were stratified by their HIV status. Predictors of maternal and neonatal VDD (levels <30 nmol/L) were assessed using multiple logistic regression analysis.Results. A total of 291 pregnant women and their healthy neonates were enrolled over a 21-month period. Mean (standard deviation) maternal and cord blood 25(OH)D levels were 57.0 (29.7) and 41.9 (21.0) nmol/L and the prevalence of VDD was 15.9% and 32.8%, respectively. On average, concentrations of 25(OH)D in cord blood were ~80% of those in the mother. There was no association between cord 25(OH)D and gestational age, but levels were associated with birth weight (p<0.001). There were no differences in maternal or cord blood 25(OH)D levels between those HIV-infected or uninfected. The predictor of VDD in mothers was giving birth in winter (odds ratio (OR) 2.87, 95% confidence interval (CI) 1.47 - 5.61), and in neonates the predictors were maternal age (OR 16.5, 95% CI 1.82 - 149), being born in winter (OR 3.68, 95% CI 2.05 - 6.61), being born by caesarean section (OR 4.92, 95% CI 1.56 - 15.57) and being of low birth weight (OR 1.99, 95% CI 1.13 - 3.50).Conclusions. Among black SA women delivering in Johannesburg, about one in six mothers and one in three neonates have 25(OH)D levels indicative of VDD. Maternal HIV status appears not to affect levels of 25(OH)D in either the mother or her neonate. Research on the effects of VDD on the outcomes of pregnancy and the best methods to combat the high prevalence of VDD in women of childbearing age in the SA context is required

Single-Particle Dynamics in the Vicinity of the Mott-Hubbard Metal-to-Insulator Transition

The single-particle dynamics close to a metal-to-insulator transition induced by strong repulsive interaction between the electrons is investigated. The system is described by a half-filled Hubbard model which is treated by dynamic mean-field theory evaluated by high-resolution dynamic density-matrix renormalization. We provide theoretical spectra with momentum resolution which facilitate the comparison to photoelectron spectroscopy.Comment: 22 pages, 24 figures, comprehensive high-resolution study of single electron dynamics around a Mott metal-insulator transition, with momentum resolved spectral densities; slight changes due to referees' suggestion

The emergence of leaders and followers in foraging pairs when the qualities of individuals differ.

BACKGROUND: Foraging in groups offers animals a number of advantages, such as increasing their likelihood of finding food or detecting and avoiding predators. In order for a group to remain together, there has to be some degree of coordination of behaviour and movement between its members (which may in some cases be initiated by a decision-making leader, and in other cases may emerge as an underlying property of the group). For example, behavioural synchronisation is a phenomenon where animals within a group initiate and then continue to conduct identical behaviours, and has been characterised for a wide range of species. We examine how a pair of animals should behave using a state-dependent approach, and ask what conditions are likely to lead to behavioural synchronisation occurring, and whether one of the individuals is more likely to act as a leader. RESULTS: The model we describe considers how the energetic gain, metabolic requirements and predation risks faced by the individuals affect measures of their energetic state and behaviour (such as the degree of behavioural synchronisation seen within the pair, and the value to an individual of knowing the energetic state of its colleague). We explore how predictable changes in these measures are in response to changes in physiological requirements and predation risk. We also consider how these measures should change when the members of the pair are not identical in their metabolic requirements or their susceptibility to predation. We find that many of the changes seen in these measures are complex, especially when asymmetries exist between the members of the pair. CONCLUSION: Analyses are presented that demonstrate that, although these general patterns are robust, care needs to be taken when considering the effects of individual differences, as the relationship between individual differences and the resulting qualitative changes in behaviour may be complex. We discuss how these results are related to experimental observations, and how the model and its predictions could be extended.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

HIV Prevention Interventions for Adolescents

Purpose of Review: The goal of this paper is to review recent data on biomedical, behavioral, and structural HIV prevention interventions for adolescents and young adults. Recent Findings: While it is accepted that HIV prevention interventions must take an integrated approach to achieve maximum effectiveness, to date, there have been limited, rigorously evaluated combination prevention interventions for adolescents. There are currently a range of effective biomedical, behavioral, and structural approaches that can be integrated into prevention packages to address the prevention needs of adolescents, including oral PrEP, male circumcision, rapid HIV testing, numerous behavioral interventions, and structural interventions such as cash transfers and community mobilization to address gender-based violence. Summary: There is still a need for rigorously evaluated, innovative combination prevention packages for adolescents. Prevention approaches must take into account the context of young people’s lives and address the multiple levels of influence on their lives including parents, partners, and communities