Nuno Loureiro

Intrinsic momentum transport in up–down asymmetric tokamaks

Recent work has demonstrated that breaking the up–down symmetry of tokamak flux surfaces removes a constraint that limits intrinsic momentum transport, and hence toroidal rotation, to be small. We show, through MHD analysis, that ellipticity is most effective at introducing up–down asymmetry throughout the plasma. We detail an extension to GS2, a local δf gyrokinetic code that self-consistently calculates momentum transport, to permit up–down asymmetric configurations. Tokamaks with tilted elliptical poloidal cross-sections were simulated to determine nonlinear momentum transport. The results, which are consistent with the experiment in magnitude, suggest that a toroidal velocity gradient, (∂uζi/∂ρ)/vthi, of 5% of the temperature gradient, (∂Ti/∂ρ)/Ti, is sustainable. Here vthi is the ion thermal speed, uζi is the ion toroidal mean flow, ρ is the minor radial coordinate normalized to the tokamak minor radius, and Ti is the ion temperature. Though other known core intrinsic momentum transport mechanisms scale poorly to larger machines, these results indicate that up–down asymmetry may be a feasible method to generate the current experimentally measured rotation levels in reactor-sized devices.

Health related behaviours: grouped risks across adolescence

Purpose: Adolescence can be associated with a tendency to engage in health damaging behaviour. The purpose of this study is to test whether cardiovascular disease (CVD) risk factors are present in this age group, and to explore possible moderator variables. Methods: The database of the Portuguese Health Behaviour in School-Aged Children (HBSC; Currie, Hurrelmann, Settertobulte, Smith & Todd, 2000) study was used comprising a nationally representative sample of 6131 adolescents attending the 6th, 8th and 10th grades (M = 14 years, SD = 1.85). Students answered a self-report questionnaire concerning health behaviours. Results: An Exploratory Factor Analysis with Promax Rotation yielded a factor solution consisting of four types of risk behaviours: psychological symptoms, substance use, weight inducers, and body concerns and inactivity. Younger students demonstrated the least risky behaviours. Females scored highest in psychological symptoms and body concerns, whereas males scored highest in substance abuse and weight inducers.Psychological symptoms and body concerns are higher among overweight and obese adolescents compared to normal weight adolescents. Conclusions: Adolescents already present a number of risk behaviours associated with CVD. This association is moderated by gender, age and Body Mass Index (BMI). Implications are discussed

Associations Between Health Compromising Behaviorsand Sleep Patterns in Portuguese Adolescents

Introduction: The pattern of sleep plays an important role in protecting the adolescents’ health. The main objective of this research is to determine the relationship between sufficient sleep (≥ 8 hours of sleep per night on school days) and health-risk behaviours in Portuguese adolescents. Methods: 5,050 participants with an average age of 13.98 (DP ± 1.85), 52.3% of which were female. The instrument used was the Health Behaviour in School-aged Children 2010 (HBSC) questionnaire. The associations were studied by applying χ² tests and the multivariate logistic regression models. Results: A significant percentage of adolescents (39%) get less than 8 hours sleep on weekdays. Sufficient sleep (≥ 8 h) is associated with younger age: adolescents between the ages of 13 and 15 (OR=0.549, p<.05) and those aged 16 or older (OR=0.291, p<.05) sleep less, as well as with less consumption of tobacco (OR=0.728, p<.05) and alcohol (OR=0.837, p<.05), a lower level of sadness (OR=0.786, p<.05) and a lower tendency to use the computer for 3 hours or more a day (OR=0.829, p<.05). Conclusion: The adolescents’ pattern of sleep is an important feature in adolescents lifestyles being associated to a large range of health and health compromising behaviours.