Multidimensional CFD Modeling of a Liquid Salt Pebble Bed Heat Transfer Loop

The Pebble Bed Advanced High Temperature Reactor (PB-AHTR) is a next generation reactor design proposed by the University of California at Berkeley. Oak Ridge National Laboratory’s Liquid Salt Test Loop (LSTL) is designed to simulate AHTR operating conditions for component testing. In this study, COMSOL Multiphysics is used to model the LSTL. Full 3D modeling of the LSTL is computationally expensive. However, COMSOL allows users to combine 1D, 2D, and 3D fluid flow physics in order to design models that are both representative and efficient. 1D pipe flow calculations are used for the piping sections. COMSOL’s porous media module is used with a 2D-axisymmetric geometry to model the fluid flow and heat transfer in the pebble bed core. The heat exchanger used to reject the loop energy to air was modeled using a 3D k-epsilon turbulence model. Modeling the LSTL in this manner requires 1D-2D and 1D-3D couplings using average operators on the 2D and 3D boundaries derived from the corresponding 1D boundary conditions. Using this strategy, a coupled model has been developed in COMSOL that provides CFD and heat transfer predictions for the LSTL. The model is presently being used to evaluate heat exchanger performance and determine potential loop operating points. The COMSOL results will be validated against experimental data once the loop is operating in 2014

Supporting Students Living Below the Poverty Line

In this article, we focus on interrelated mechanisms and practices that support students living below the poverty line. Addressing the needs of students living below the poverty line requires that educators consider both the inside- and outside-of-school realities of students and their families. Before discussing the recommendations, we define poverty and describe the complex ways it may shape student realities. We then discuss why we believe recommendations to support students must account for student realities outside of school. Finally, we outline recommendations for educators interested in becoming “poverty-responsive,” meaning that they discontinue practices that do not support students in poverty and replace them with practices responsive to student needs. We offer three recommendations: (a) promote reflection among educators as a means to identify and discard any deeply held beliefs that are not in support of students living in poverty, (b) develop partnerships between educators and communities that address key outside-of-school factors shaping the learning experience of students living in poverty, and (c) ensure that educators teach students skills in targeted areas that are likely to improve their academic success

Late-Time Behavior of Stellar Collapse and Explosions: I. Linearized Perturbations

Problem with the figures should be corrected. Apparently a broken uuencoder was the cause.Comment: 16pp, RevTex, 6 figures (included), NSF-ITP-93-8

Determinants of Childhood Adiposity: Evidence from the Australian LOOK Study

BACKGROUND To contribute to the current debate as to the relative influences of dietary intake and physical activity on the development of adiposity in community-based children. METHODS Participants were 734 boys and girls measured at age 8, 10 and 12 years for percent body fat (dual emission x-ray absorptiometry), physical activity (pedometers, accelerometers); and dietary intake (1 and 2-day records), with assessments of pubertal development and socioeconomic status. RESULTS Cross-sectional relationships revealed that boys and girls with higher percent body fat were less physically active, both in terms of steps per day and moderate and vigorous physical activity (both sexes p<0.001 for both measures). However, fatter children did not consume more energy, fat, carbohydrate or sugar; boys with higher percent body fat actually consumed less carbohydrate (p = 0.01) and energy (p = 0.05). Longitudinal analysis (combined data from both sexes) was weaker, but supported the cross-sectional findings, showing that children who reduced their PA over the four years increased their percent body fat (p = 0.04). Relationships in the 8 year-olds and also in the leanest quartile of all children, where adiposity-related underreporting was unlikely, were consistent with those of the whole group, indicating that underreporting did not influence our findings. CONCLUSIONS These data provide support for the premise that physical activity is the main source of variation in the percent body fat of healthy community-based Australian children. General community strategies involving dietary intake and physical activity to combat childhood obesity may benefit by making physical activity the foremost focus of attention.The financial support provided by the Commonwealth Education Trust (London, UK) was vital to the completion of this work, and the authors thank the Board of Trustees for supporting them over several years. The authors also thank members of The Canberra Hospital Salaried Staff Specialists Private Practice Fund for their financial contribution to the study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Responses of common diving petrel chicks (Pelecanoides urinatrix) to burrow and colony specific odours in a simple wind tunnel

Researchers have previously assumed that common diving petrels (Pelecanoides urinatrix) have a limited sense of smell since they have relatively small olfactory bulbs. A recent study, however, showed that adult diving petrels prefer the scent of their own burrow compared to burrows of other diving petrels, implying that personal scents contribute to the burrow’s odour signature. Because diving petrels appear to be adapted to use olfaction in social contexts, they could be a useful model for investigating how chemically mediated social recognition develops in birds. A first step is to determine whether diving petrel chicks can detect familiar and unfamiliar odours. We compared behavioural responses of chicks to three natural stimuli in a wind tunnel: soil collected from their burrow or colony, and a blank control. During portions of the experiment, chicks turned the least and walked the shortest distances in response to odours from the nest, which is consistent with their sedentary behaviour within the burrow. By contrast, behaviours linked to olfactory search increased when chicks were exposed to blank controls. These results suggest that common diving petrel chicks can detect natural olfactory stimuli before fledging, and lay the foundation for future studies on the role of olfaction in social contexts for this species