Algebraic attacks over GF(q)

Recent algebraic attacks on LFSR-based stream ciphers and S-boxes have generated much interest as they appear to be extremely powerful. Theoretical work has been developed focusing around the Boo- lean function case. In this paper, we generalize this theory to arbitrary finite fields and extend the theory of annihilators and ideals introduced at Eurocrypt 2004 by Meier, Pasalic and Carlet. In particular, we prove that for any function f in the multivariate polynomial ring over GF(q), f has a low degree multiple precisely when two low degree functions appear in the same coset of the annihilator of f ^{q – 1} – 1. In this case, many such low degree multiples exist.

Perceptions of neighborhood safety and physical activity among youth : the CLAN study

Background: The purpose of this study was to examine associations between perceptions of neighborhood safety and physical activity among youth. Methods: We completed a cross-sectional study of children age 8 to 9 years (n = 188) and adolescents age 13 to 15 years (n = 346) in areas of varying socioeconomic status in Melbourne, Australia. Parents and adolescents completed questionnaires on perceptions of neighborhood safety. Scores were computed for perceptions of road safety, incivilities, and personal safety of the child or adolescent. Moderate-to-vigorous physical activity (MVPA) before or after school, on evenings, and on weekends was recorded using accelerometers. Results: There were no associations between parental perceptions of neighborhood safety and children’s MVPA outside school hours. Parental perception of personal safety was positively associated with adolescent boys’ MVPA after school. Adolescent girls’ concern about road safety was negatively associated with their MVPA during evenings and outside school hours. Conclusion: Perceptions of neighborhood safety might influence physical activity among youth in different ways according to age group and sex.

Neighborhood road environments and physical activity among youth : the CLAN Study

We examined associations between objective measures of the local road environment and physical activity (including active transport) among youth. There is little empirical evidence of the impact of the road environment on physical activity among children/adolescents in their neighborhoods. Most recent studies have examined perceptions rather than objective measures of the road environment. This was a cross-sectional study of children aged 8–9 years (n = 188) and adolescents aged 13–15 years (n  = 346) who were participants in the 3-year follow-up of the Children Living in Active Neighborhoods (CLAN) longitudinal study in Melbourne, Australia. At baseline (2001), they were recruited from 19 state primary schools in areas of varying socioeconomic status across Melbourne. Habitual walking/cycling to local destinations was parent-reported for children and self-reported for adolescents, while moderate-to-vigorous physical activity (MVPA) outside school hours was recorded using accelerometers. Road environment features in each participant’s neighborhood (area of radius 800 m around the home) were measured objectively using a geographical information system. Regression analyses found no associations between road environment variables and children’s likelihood of making at least seven walking/cycling trips per week to neighborhood destinations. Adolescent girls residing in neighborhoods with two to three traffic/pedestrian lights were more likely to make seven or more walking/cycling trips per week as those whose neighborhoods had fewer traffic lights (OR: 2.7; 95% CI: 1.2–6.2). For adolescent boys, residing on a cul-de-sac, compared with a through road, was associated with increases in MVPA of 9 min after school, 5 min in the evenings, and 22 min on weekend days. Speed humps were positively associated with adolescent boys’ MVPA during evenings. The road environment influences physical activity among youth in different ways, according to age group, sex and type of physical activity.

Features of public open spaces and physical activity among children : findings from the CLAN study

Objective : To examine associations between features of public open spaces, and children's physical activity.
Participants : 163 children aged 8–9 years and 334 adolescents aged 13–15 years from Melbourne, Australia participated in 2004.
Methods : A Geographic Information System was used to identify all public open spaces (POS) within 800 m of participants' homes and their closest POS. The features of all POS identified were audited in 2004/5. Accelerometers measured moderate-to-vigorous physical activity (MVPA) after school and on weekends. Linear regression analyses examined associations between features of the closest POS and participants' MVPA.
Results : Most participants had a POS within 800 m of their home. The presence of playgrounds was positively associated with younger boys' weekend MVPA (B = 24.9 min/day; p ≤ 0.05), and lighting along paths was inversely associated with weekend MVPA (B = − 54.9 min/day; p ≤ 0.05). The number of recreational facilities was inversely associated with younger girls' MVPA after school (B = − 2.6 min/day; p ≤ 0.05) and on the weekend (B = − 8.7 min/day; p ≤ 0.05). The presence of trees providing shade (5.8 min/day, p ≤ 0.01) and signage regarding dogs (B = 6.8 min/day, p ≤ 0.05) were positively associated with adolescent girls' MVPA after school.
Conclusion : Certain features of POS were associated with participants' MVPA, although mixed associations were evident. Further research is required to clarify these complex relationships.

Neighbourhood fast food outlets and obesity in children and adults : the CLAN study

Objective : We examined associations between density of and proximity to fast food outlets and body weight in a sample of children (137 aged 8-9 years and 243 aged 13-15 years) and their parents (322 fathers and 362 mothers).
Methods : Children's measured and parents' self-reported heights and weights were used to calculate body mass index (BMI). Locations of major fast food outlets were geocoded. Bivariate linear regression analyses examined associations between the presence of any fast food outlet within a 2 km buffer around participants' homes, fast food outlet density within the 2 km buffer, and distance to the nearest outlet and BMI. Each independent variable was also entered into separate bivariate logistic regression analyses to predict the odds of being overweight or obese.
Results : Among older children, those with at least one outlet within 2 km had lower BMI z-scores. The further that fathers lived from an outlet, the higher their BMI. Among 13-15-year-old girls and their fathers, the likelihood of overweight/obesity was reduced by 80% and 50%, respectively, if they had at least one fast food outlet within 2 km of their home. Among older girls, the likelihood of being overweight/obese was reduced by 14% with each additional outlet within 2 km. Fathers' odds of being overweight/obese increased by 13% for each additional kilometre to the nearest outlet.
Conclusions : While consumption of fast food has been shown to be associated with obesity, this study provides little support for the concept that exposure to fast food outlets in the local neighbourhood increases risk of obesity.

Socioeconomic position and children's physical activity and sedentary behaviors : longitudinal findings from the CLAN study

Background: This study aimed to examine cross-sectional and longitudinal associations between socioeconomic position (SEP) and physical activity and sedentary behaviors amongst children and adolescents.

Methods: Maternal education was reported by parents of 184 5-6 year-old and 358 10-12 year-old children in 2001. In 2001 and 2004, physical activity was assessed by accelerometry. Older children self-reported and parents of younger children proxy-reported physical activity and television (TV) viewing behaviors. Linear regression was used to predict physical activity and sedentary behaviors, and changes in these behaviors, from maternal education.

Results: Among all children, accelerometer-determined and self/parent-reported moderate and vigorous physical activity declined over three years. Girls of higher SEP demonstrated greater decreases in TV viewing behaviours than those of low SEP. In general, no prospective associations were evident between SEP and objectively-assessed physical activity. A small number of prospective associations were noted between SEP and self-reported physical activity, but these were generally weak and inconsistent in direction.

Conclusions: This study did not find strong evidence that maternal education was cross-sectionally or longitudinally predictive of children’s physical activity or sedentary behaviors. Given the well-documented inverse relationship of SEP with physical activity levels in adult samples, findings suggest that such disparities may emerge after adolescence.