Sports Participation and Physical Education in American Secondary Schools: Current Levels of Racial/Ethnic and Socioeconomic Disparities

Summarizes findings from a study of physical education requirements and school-based physical activity among American schoolchildren. Analyzes data by gender, grade, race/ethnicity and socioeconomic status

The school food environment and student body mass index and food consumption: 2004 to 2007 national data

PURPOSE: This study identifies trends in the availability of various food choices in United States' middle and high schools from 2004 to 2007, and examines the potential associations between such food availability and students' self-reported eating habits and body mass index (BMI)-related outcomes. METHODS: Data are based on nationally representative samples of 78,442 students in 684 secondary schools surveyed from 2004 to 2007 as part of the Youth, Education, and Society (YES) study and the Monitoring the Future (MTF) study. In the YES study, school administrators and food service managers completed self-administered questionnaires on their school's food environment. In the MTF study, students in the same schools completed self-administered questionnaires, providing data used to construct BMI and food consumption measures. RESULTS: Overall, there was a decrease in the availability of regular-sugar/fat food items in both middle and high schools, and some indication of an increase in high school availability of reduced-fat food items through school lunch or a la carte. Some minimal evidence was found for relationships between the school food environment and student BMI-related outcomes and food consumption measures. CONCLUSIONS: United States secondary schools are making progress in the types of foods offered to students, with food items of lower nutritional value becoming less prevalent in recent years. Continued monitoring of food environment trends may help clarify whether and how such factors relate to youth health outcomes.The Youth, Education, and Society (YES) project (part of a larger research initiative, entitled Bridging the Gap: Research Informing Policy and Practice for Healthy Youth Behavior) is funded by the Robert Wood Johnson Foundation. The Monitoring the Future study is funded by the National Institute on Drug Abuse (DA01411). The views expressed in this article are those of the authors and do not necessarily reflect the views of the funders. (Robert Wood Johnson Foundation; DA01411 - National Institute on Drug Abuse

Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission

We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both experimentally and using a three-dimensional carrier dynamics simulation. A uniform density of vacancies was formed over the optical absorption depth of bulk GaAs samples by performing multi-energy implantations of arsenic ions (1 and 2.4MeV) and subsequent thermal annealing. In a series of THz emission experiments the frequency of peak THz power was found to increase significantly from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to 10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast carrier dynamics to reproduce and explain these results. The effect of the ion-induced damage was included in the simulation by considering carrier scattering at neutral and charged impurities, as well as carrier trapping at defect sites. Higher vacancy concentrations and shorter carrier trapping times both contributed to shorter simulated THz pulses, the latter being more important over experimentally realistic parameter ranges.Comment: 6 pages, 7 figure

Polarisation-sensitive terahertz detection by multicontact photoconductive receivers

We have developed a terahertz radiation detector that measures both the amplitude and polarization of the electric field as a function of time. The device is a three-contact photoconductive receiver designed so that two orthogonal electric-field components of an arbitrary polarized electromagnetic wave may be detected simultaneously. The detector was fabricated on Fe+ ion-implanted InP. Polarization-sensitive detection is demonstrated with an extinction ratio better than 100:1. This type of device will have immediate application in studies of birefringent and optically active materials in the far-infrared region of the spectrum.Comment: 3 pages, 3 figure

Do Higher Cigarette Prices Encourage Youth to Use Marijuana?

Every major national tobacco legislation proposed in the past two years has called for significant increases in the price of cigarettes as a way to discourage youths from smoking. One argument used to oppose these bills is that increases in the price of cigarettes would cause youths to substitute marijuana for cigarettes. Although it has long been believed that cigarettes are a gateway drug,' no economic research has been done to determine whether cigarettes and marijuana are economic complements or substitutes. This paper begins to fill the void in the current research by examining the contemporaneous relationship between the demands for cigarettes and marijuana among a nationally representative sample of 8th, 10th and 12th graders from the 1992-1994 Monitoring the Future Project. Two part models are used to estimate reduced form demand equations. Examination of the cross-price effects clearly shows that higher cigarette prices will not increase marijuana use among youths. In addition to reducing youth smoking, we find that higher cigarette prices significantly reduce the average level of marijuana used by current users. Cigarette prices also have a negative effect on the probability of using marijuana findings are not significant at conventional levels.

Effects of Price and Access Laws on Teenage Smoking Initiation: A National Longitudinal Analysis

Over the past three decades a significant amount of economic research has established that increasing cigarette prices reduces cigarette smoking among both adults and adolescents. The consensus estimates for the price elasticity of adult demand from these studies fall in a narrow range of 0.3 to 0.5, suggesting that a 10% increase in the price of cigarettes would decrease adult consumption by 3%-5%. A smaller literature on youth responsiveness to cigarette prices has also emerged. A majority of these studies concluded that youth are up to three times as responsive to price as are adults. Only four econometric studies have attempted to model youth and young adult smoking initiation decisions. All four studies concluded that cigarette prices (or cigarette excise taxes) are insignificant determinants of smoking initiation. This study addresses the limitations of the previous studies on smoking initiation and examines the impact of cigarette prices and youth access laws on adolescent smoking initiation. Nationally representative longitudinal surveys of 8th and 10th graders as part of the Monitoring the Future project are employed in the analysis. State-specific prices and several measures of youth access restrictions are added to the survey data. Discrete-time hazard methods are used to model the probability of initiation. Contradicting the results of the four previous studies on smoking initiation, the results of this study clearly indicate that increases in the price of cigarettes would significantly reduce the number of adolescents who start smoking. The results are mixed with respect to youth access restrictions.

Accessibility Over Availability: Associations Between the School Food Environment and Student Fruit and Green Vegetable Consumption

Background: No national studies have examined associations between (1) school food availability and accessibility and (2) secondary student fruit and vegetable (FV) consumption. This article uses 5 years of nationally representative data from secondary school students to examine associations between the school food environment and student fruit and green vegetable consumption. Methods: From 2008 to 2012, cross-sectional, nationally representative data from US middle and high school students were collected annually on self-reported fruit and green vegetable consumption. Each year, data from administrators at each relevant school were collected on food item availability (any venue) and accessibility (total number of school sources). Data were obtained from 10,254 eighth-grade students in 317 schools and 18,898 tenth- and 12th-grade students in 518 schools. Associations were estimated by multi-level models controlling for student- and school-level characteristics. Results: Availability showed minimal association with student consumption. Candy/regular-fat snack accessibility was associated negatively with middle school fruit consumption. Salad bar availability and accessibility were positively associated with middle school green vegetable consumption; FV accessibility was associated positively with high school fruit and green vegetable consumption. Significant associations were consistent across student racial/ethnic and socioeconomic groups. Conclusions: Forthcoming USDA nutrition standards for school foods and beverages sold outside of reimbursable meal programs should result in the removal of school candy/regular-fat snacks. In deciding which items to make available under the new standards, schools should consider increasing the number of FV sources?including salad bars?thereby potentially increasing student FV consumption.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140338/1/chi.2014.0011.pd

A Chandra Study of the Dense Globular Cluster Terzan 5

We report a Chandra ACIS-I observation of the dense globular cluster Terzan 5. The previously known transient low-mass x-ray binary (LMXB) EXO 1745-248 in the cluster entered a rare high state during our August 2000 observation, complicating the analysis. Nevertheless nine additional sources clearly associated with the cluster are also detected, ranging from L_X(0.5-2.5 keV)=5.6*10^{32} down to 8.6*10^{31} ergs/s. Their X-ray colors and luminosities, and spectral fitting, indicate that five of them are probably cataclysmic variables, and four are likely quiescent LMXBs containing neutron stars. We estimate the total number of sources between L_X(0.5-2.5 keV)=10^{32} and 10^{33} ergs/s as 11.4^{+4.7}_{-1.8} by the use of artificial point source tests, and note that the numbers of X-ray sources are similar to those detected in NGC 6440. The improved X-ray position allowed us to identify a plausible infrared counterpart to EXO 1745-248 on our 1998 Hubble Space Telescope NICMOS images. This blue star (F110W=18.48, F187W=17.30) lies within 0.2'' of the boresighted LMXB position. Simultaneous Rossi X-ray Timing Explorer (RXTE) spectra, combined with the Chandra spectrum, indicate that EXO 1745-248 is an ultracompact binary system, and show a strong broad 6.55 keV iron line and an 8 keV smeared reflection edge.Comment: 18 pages, 8 figures, accepted to Ap