Task allocation in dynamic networks of satellites

The management of distributed satellite systems requires the coordination of a large number of heterogeneous spacecraft. Task allocation in such a system is complicated by limited communication and individual satellite dynamics. Previous work has shown that task allocation using a market-based mechanism can provide scalable and efficient management of static networks; in this paper we extend this work to determine the impact of dynamic topologies. We develop a Keplerian mobility model to describe the topology of the communication network over time. This movement model is then used in simulation to show that the task allocation mechanism does not show a significant decrease in effectiveness from the static case, reflecting the suitability distributed market-based control to the highly dynamic environment

Distributed and Centralized Task Allocation: When and Where to Use Them

Self-organisation is frequently advocated as the solution for managing large, dynamic systems. Distributed algorithms are implicitly designed for infinitely large problems, while small systems are regarded as being controllable using traditional, centralised approaches. Many real-world systems, however, do not fit conveniently into these "small" or "large" categories, resulting in a range of cases where the optimal solution is ambiguous. This difficulty is exacerbated by enthusiasts of either approach constructing problems that suit their preferred control architecture. We address this ambiguity by building an abstract model of task allocation in a community of specialised agents. We are inspired by the problem of work distribution in distributed satellite systems, but the model is also relevant to the resource allocation problems in distributed robotics, autonomic computing and wireless sensor networks. We compare the behaviour of a self-organising, market-based task allocation strategy to a classical approach that uses a central controller with global knowledge. The objective is not to prove one mechanism inherently superior to the other; instead we are interested in the regions of problem space where each of them dominates. Simulation is used to explore the trade-off between energy consumption and robustness in a system of intermediate size, with fixed communication costs and varying rates of component failure. We identify boundaries between regions in the parameter space where one or the other architecture will be favoured. This allows us to derive guidelines for system designers, thus contributing to the development of a disciplined approach to controlling distributed systems using self-organising mechanisms

The ENDORSE study: Research into environmental determinants of obesity related behaviors in Rotterdam schoolchildren

Background: Children and adolescents are important target groups for prevention of overweight and obesity as overweight is often developed early in life and tracks into adulthood. Research into behaviors related to overweight (energy balance-related behaviors) and the personal and environmental determinants of these behaviors is fundamental to inform prevention interventions. In the Netherlands and in other countries systematic research into environmental determinants of energy balance related behaviors in younger adolescents is largely lacking. This protocol paper describes the design, the components and the methods of the ENDORSE study (Environmental Determinants of Obesity in Rotterdam SchoolchildrEn), that aims to identify important individual and environmental determinants of behaviors related to overweight and obesity and the interactions between these determinants among adolescents. Methods: The ENDORSE study is a longitudinal study with a two-year follow-up of a cohort of adolescents aged 12–15 years. Data will be collected at baseline (2005/2006) and at two years follow-up (2007/2008). Outcome measures are body mass index (BMI), waist circumference, time spent in physical activity and sedentary behaviors, and soft drink, snack and breakfast consumption. The ENDORSE study consists of two phases, first employing qualitative research methods to inform the development of a theoretical framework to examine important energy balance related behaviors and their determinants, and to inform questionnaire development. Subsequently, the hypothetical relationships between behavioral determinants, energy balance related behaviors and BMI will be tested in a quantitative study combining school-based surveys and measurements of anthropometrical characteristics at baseline and two-year follow-up. Discussion: The ENDORSE project is a comprehensive longitudinal study that enables investigation of specific environmental and individual determinants of overweight and obesity among younger adolescents. The project will result in specific recommendations for obesity prevention interventions among younger adolescents

Objective and perceived availability of physical activity opportunities: differences in associations with physical activity behavior among urban adolescents

ABSTRACT: BACKGROUND: This study examined the associations of the perceived and objective environment with adolescent engagement in sports activities and walking and cycling in leisure time. It also explored the degree of agreement between objective and perceived availability of physical activity (PA) facilities in neighborhoods. METHODS: Cross-sectional data on physical activity, the perceived availability of physical activity opportunities (perceived physical environment) was assessed through a questionnaire and the objective availability of PA opportunities (objective physical environment) was obtained through GIS data. The final sample included 654 adolescents with a mean age of 14.1 (SD = 1.2) years. RESULTS: Perceived availability of sports facilities and parks was significantly associated with engaging in sports (OR: 1.73; 95% CI: 1.16-2.56) and with walking and cycling in leisure time (OR: 1.66; 95% CI: 1.07-2.57) respectively. Agreement between objective and perceived environment was low to moderate with Kappa values ranging from -0.005 to 0.053. CONCLUSION: The perceived environment was the stronger correlate of PA behavior among adolescents. There were substantial differences between assessments of objective and perceived physical environmen

Do individual cognitions mediate the association of socio-cultural and physical environmental factors with adolescent sports participation?

Abstract Objective To examine the associations of perceived physical environmental factors (availability of physical activity (PA) attributes at home, PA facilities in the neighbourhood, neighbourhood pleasantness and safety) and social environmental factors (parental sports behaviour and parental rule regarding sports participation) with adolescent leisure-time sports participation, and to explore whether the associations found were mediated by individual cognitions as derived from the theory of planned behaviour (TPB). Design Cross-sectional study. Setting In schoolyear 2005/2006 adolescents from seventeen schools in Rotterdam, the Netherlands, completed a questionnaire during school hours that included self-reported measures of leisure-time sports participation, perceived physical environmental factors and TPB variables. Information about parental sports behaviour and parental rule was obtained from a questionnaire that was completed by one parent of the adolescents. Subjects Data were collected from 584 adolescent-parent combinations. Results Data were analysed with multi-level logistic regression analyses. Availability of PA attributes at home (OR = 1·26), parents' sports behaviour (OR = 2·03) and parental rule (OR = 1·64) were associated with a higher likelihood of adolescents' leisure-time sports participation. These associations were partly mediated by attitude and intention. Conclusions Adolescents were more likely to engage in leisure-time sports when PA attributes were available at home, when parents participated in sports activities and had a rule about their offspring participation in sports activities. These associations were partly mediated by attitude and intention. These results suggest that parents can importantly promote sports participation among their offspring by making sports activities accessible and a family routin

Selection pressures for a theory-of-mind faculty in artificial agents

Document is itself an extended abstract

Measurement of Active Power and Energy Consumption Loads with PWM Control and Nonlinear Character

Import 22/07/2015Cílem této bakalářské práce bylo změřit činný výkon a elektrickou energii na nelineárním spotřebiči pomocí vybraných měřicích zařízení. Jako nelineární zátěž obvodu jsem zvolil úspornou zářivku a laboratorní pec. Naměřené hodnoty jsem poté graficky vykreslil a popsal. Použité přístroje jsem porovnal podle technických parametrů, jejich přesnosti a spolehlivosti. Toto měření jsem zrealizoval v laboratoři EB 116 pod dohledem vedoucího bakalářské práce.The aim of this study was to measure real power and energy on nonlinear spo-kept away by using the selected measuring device. As a nonlinear load circuit I chose saving lamp and laboratory furnace. He then measured values graphically portrayed and described. Used apparatus the I compared the technical parameters of accuracy and reliability. I realized this measurement in the laboratory EB 116 under the supervision of the thesis.410 - Katedra elektroenergetikydobř