Analysis of the shearing instability in nonlinear convection and magnetoconvection

Numerical experiments on two-dimensional convection with or without a vertical magnetic field reveal a bewildering variety of periodic and aperiodic oscillations. Steady rolls can develop a shearing instability, in which rolls turning over in one direction grow at the expense of rolls turning over in the other, resulting in a net shear across the layer. As the temperature difference across the fluid is increased, two-dimensional pulsating waves occur, in which the direction of shear alternates. We analyse the nonlinear dynamics of this behaviour by first constructing appropriate low-order sets of ordinary differential equations, which show the same behaviour, and then analysing the global bifurcations that lead to these oscillations by constructing one-dimensional return maps. We compare the behaviour of the partial differential equations, the models and the maps in systematic two-parameter studies of both the magnetic and the non-magnetic cases, emphasising how the symmetries of periodic solutions change as a result of global bifurcations. Much of the interesting behaviour is associated with a discontinuous change in the leading direction of a fixed point at a global bifurcation; this change occurs when the magnetic field is introduced

Parental feeding practices and child weight status in Mexican American families: a longitudinal analysis

Parental feeding practices are thought to influence children\u27s weight status, through children\u27s eating behavior and nutritional intake. However, because most studies have been cross-sectional, the direction of influence is unclear. Moreover, although obesity rates are high among Latino children, few studies of parental feeding practices have focused on this population. This 2-year longitudinal study examined mutual influences over time between parental feeding practices and children\u27s weight status, in Mexican American families with children 18 years old at baseline. Mothers (n = 322) and fathers (n = 182) reported on their feeding practices at baseline, 1-year follow-up, and 2-year follow-up. Weight status, defined by waist-height ratio (WHtR) and body mass index (BMI), was ascertained at all assessments. Cross-lagged panel models were used to examine the mutual influences of parental feeding practices and child weight status over time, controlling for covariates. Both mothers\u27 and fathers\u27 restriction of food predicted higher subsequent child weight status at Year 1, and for fathers this effect was also found at Year 2. Mothers\u27 and fathers\u27 pressure to eat predicted lower weight status among boys, but not girls, at Year 1. Child weight status also predicted some parental feeding practices: boys\u27 heavier weight predicted mothers\u27 less pressure to eat at Year 1, less use of food to control behavior at Year 2, and greater restriction at Year 2; and girls\u27 heavier weight at Year 1 predicted fathers\u27 less pressure to eat and less positive involvement in child eating at Year 2. This study provides longitudinal evidence that some parental feeding practices influence Mexican American children\u27s weight status, and that children\u27s weight status also influences some parental feeding practices. Feeding practices of both mothers and fathers were related to children\u27s weight status, underscoring the importance of including fathers in research on parental feeding practices and child obesity

Longitudinal Effects of Parental, Child and Neighborhood Factors on Moderate-Vigorous Physical Activity and Sedentary Time in Latino Children

Background: Moderate-vigorous physical activity (%MVPA) confers beneficial effects on child musculoskeletal health, cardiovascular fitness, and psychosocial well-being; in contrast, sedentary time (%SED) is emerging as a risk factor for health. This study aimed to identify parental, child and neighborhood factors influencing longitudinal assessments of body mass index (BMI) and activity patterns among Latino children, and to estimate lagged and cross-lagged effects between child BMI, %MVPA and %SED. Methods: A longitudinal design with assessments at baseline, 1 and 2 years follow-up (FU) was used to evaluate the effects of maternal and paternal factors (BMI, age, education level, acculturation, household income and household size), child factors (gender, age, BMI, pubertal status) and neighborhood factors (disorder, victimization) on child BMI, %MVPA and %SED, expressed as a percent of awake time, in 282 Latino children ages 8–10 y and their parents. This study was restricted to families with a mother and biological father or father figure in the child’s life. Results: Across time, total daily accelerometer counts (p = 0.04) and steps decreased (p = 0.0001), %SED increased (p = 0.0001), and %MVPA decreased (p = 0.02). Moderate lagged effects or tracking was seen for %MVPA and %SED (p = 0.001). %MVPA varied by gender (5.5% higher in boys than girls, p = 0.0001); child age (−0.4% per year, p = 0.03), and child BMI in boys only (−0.22%, p = 0.0002). Negative effects of paternal age, maternal education and maternal changes in BMI on %MVPA also were seen. %SED increased with child age (2.5% higher per year, p = 0.0001). Positive effects of paternal acculturation, maternal change in BMI, paternal age, and negative effects of household size on %SED were observed. A cross-lagged positive effect of BMI at FU1 on %SED at FU2 was observed for boys and girls (p = 0.03). Neighborhood disorder and victimization were not significant predictors of child BMI, %MVPA or %SED. Conclusion: The major child determinants of physical activity (age, gender and BMI) and minor parental influences (maternal BMI and education, paternal age and acculturation) should be considered in designing interventions to promote %MVPA and reduce %SED among Latino children as they approach adolescence. Keywords: Physical activity patterns, Accelerometers, Childhood obesity, Maternal factors, Paternal factors, Education level, Acculturation, Household income, Household size, Environment, Disorder, Victimizatio

Parental Feeding Practices and Child Weight Status in Mexican American Families: A Longitudinal Analysis

Parental feeding practices are thought to influence children\u27s weight status, through children\u27s eating behavior and nutritional intake. However, because most studies have been cross-sectional, the direction of influence is unclear. Moreover, although obesity rates are high among Latino children, few studies of parental feeding practices have focused on this population. This 2-year longitudinal study examined mutual influences over time between parental feeding practices and children\u27s weight status, in Mexican American families with children 18 years old at baseline. Mothers (n = 322) and fathers (n = 182) reported on their feeding practices at baseline, 1-year follow-up, and 2-year follow-up. Weight status, defined by waist-height ratio (WHtR) and body mass index (BMI), was ascertained at all assessments. Cross-lagged panel models were used to examine the mutual influences of parental feeding practices and child weight status over time, controlling for covariates. Both mothers\u27 and fathers\u27 restriction of food predicted higher subsequent child weight status at Year 1, and for fathers this effect was also found at Year 2. Mothers\u27 and fathers\u27 pressure to eat predicted lower weight status among boys, but not girls, at Year 1. Child weight status also predicted some parental feeding practices: boys\u27 heavier weight predicted mothers\u27 less pressure to eat at Year 1, less use of food to control behavior at Year 2, and greater restriction at Year 2; and girls\u27 heavier weight at Year 1 predicted fathers\u27 less pressure to eat and less positive involvement in child eating at Year 2. This study provides longitudinal evidence that some parental feeding practices influence Mexican American children\u27s weight status, and that children\u27s weight status also influences some parental feeding practices. Feeding practices of both mothers and fathers were related to children\u27s weight status, underscoring the importance of including fathers in research on parental feeding practices and child obesity

Mother-Reported Sleep, Accelerometer-Estimated Sleep, and Weight Status in Mexican American Children: Sleep Duration Is Associated with Increased Adiposity and Risk for Overweight/Obese Status

We know of no studies comparing parent-reported sleep with accelerometer-estimated sleep in their relation to pediatric adiposity. We examined: 1) the reliability of mother-reported sleep compared with accelerometer-estimated sleep, and 2) the relationship between both sleep measures and child adiposity. The current cross-sectional study included 304 Mexican American mother-child pairs recruited from Kaiser Permanente Northern California. We measured sleep duration, using maternal report and accelerometry, and child anthropometrics. Concordance between sleep measures was evaluated using the Bland-Altman method. We conducted zero-ordered correlations between mother-reported sleep, accelerometer-estimated sleep and child BMI z-scores (BMIz). Using linear regression, we examined three models to assess child BMIz with mother-reported sleep (model 1), accelerometer-estimated sleep (model 2), and both sleep measures (model 3). Children had an average age of 8.86 years (SD= .82). Mothers reported that their child slept 9.81 ± 0.74 (95% CI: 9.72, 9.89) hours, compared to 9.58 ± 0.71 (95% CI: 9.50, 9.66) hours based on accelerometry. Mother-reported sleep and accelerometer-estimated sleep were correlated (r = 0.33, p \u3c 0.001). BMIz outcomes were negatively associated with mother-reported sleep duration (model 1: β = −0.13; P = .02) and accelerometer-estimated sleep duration (model 2: β = −0.17; P \u3c .01). Accounting for both sleep measures, only accelerometer-measured sleep was related to BMIz (model 3: β = −0.14, P = .02). Each sleep measure was significantly related to adiposity, independent of covariates. Accelerometry appeared to be a more reliable measure of children’s sleep than maternal report, yet maternal report may be sufficient to examine the sleep-adiposity relationship when resources are limited

Parental Feeding Practices in Mexican American Families: Initial Test of an Expanded Measure

Background: Although obesity rates are high among Latino children, relatively few studies of parental feeding practices have examined Latino families as a separate group. Culturally-based approaches to measurement development can begin to identify parental feeding practices in specific cultural groups. This study used qualitative and quantitative methods to develop and test the Parental Feeding Practices (PFP) Questionnaire for use with Mexican American parents. Items reflected both parent’s use of control over child eating and child-centered feeding practices. Methods: In the qualitative phase of the research, 35 Latino parents participated in focus groups. Items for the PFP were developed from focus group discussions, as well as adapted from existing parent feeding practice measures. Cognitive interviews were conducted with 37 adults to evaluate items. In the quantitative phase, mothers and fathers of 174 Mexican American children ages 8–10 completed the PFP and provided demographic information. Anthropometric measures were obtained on family members. Results: Confirmatory factor analyses identified four parental feeding practice dimensions: positive involvement in child eating, pressure to eat, use of food to control behavior, and restriction of amount of food. Factorial invariance modeling suggested equivalent factor meaning and item response scaling across mothers and fathers. Mothers and fathers differed somewhat in their use of feeding practices. All four feeding practices were related to child body mass index (BMI) percentiles, for one or both parents. Mothers reporting more positive involvement had children with lower BMI percentiles. Parents using more pressure to eat had children with lower BMI percentiles, while parents using more restriction had children with higher BMI percentiles. Fathers using food to control behavior had children with lower BMI percentiles. Conclusions: Results indicate good initial validity and reliability for the PFP. It can be used to increase understanding of parental feeding practices, children’s eating, and obesity among Mexican Americans, a population at high risk of obesity

Pollutant dispersion in a developing valley cold-air pool

Pollutants are trapped and accumulate within cold-air pools, thereby affecting air quality. A numerical model is used to quantify the role of cold-air-pooling processes in the dispersion of air pollution in a developing cold-air pool within an alpine valley under decoupled stable conditions. Results indicate that the negatively buoyant downslope flows transport and mix pollutants into the valley to depths that depend on the temperature deficit of the flow and the ambient temperature structure inside the valley. Along the slopes, pollutants are generally entrained above the cold-air pool and detrained within the cold-air pool, largely above the ground-based inversion layer. The ability of the cold-air pool to dilute pollutants is quantified. The analysis shows that the downslope flows fill the valley with air from above, which is then largely trapped within the cold-air pool, and that dilution depends on where the pollutants are emitted with respect to the positions of the top of the ground-based inversion layer and cold-air pool, and on the slope wind speeds. Over the lower part of the slopes, the cold-air-pool-averaged concentrations are proportional to the slope wind speeds where the pollutants are emitted, and diminish as the cold-air pool deepens. Pollutants emitted within the ground-based inversion layer are largely trapped there. Pollutants emitted farther up the slopes detrain within the cold-air pool above the ground-based inversion layer, although some fraction, increasing with distance from the top of the slopes, penetrates into the ground-based inversion layer.Peer reviewe

Stereodivergent Synthesis of Enantioenriched 4-Hydroxy-2- cyclopentenones

Protected 4-hydroxycyclopentenones (4-HCPs) constitute an important class of intermediates in chemical synthesis. A route to this class of compound has been developed. Key steps include Noyori reduction (which establishes the stereochemistry of the product), ring-closing metathesis, and simple functional group conversions to provide a set of substituted 4-HCPs in either enantiomeric form