The bakony growth study. By Éva BodzsÁr. 210 pp. Budapest: Humanbiologia Budapestinensis. 1991

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38554/1/1310050318_ftp.pd

Maternal short stature does not predict their children's fatness indicators in a nutritional dual-burden sample of urban Mexican Maya

The co-existence of very short stature due to poor chronic environment in early life and obesity is becoming a public health concern in rapidly transitioning populations with high levels of poverty. Individuals who have very short stature seem to be at an increased risk of obesity in times of relative caloric abundance. Increasing evidence shows that an individual is influenced by exposures in previous generations. This study assesses whether maternal poor early life environment predicts her child's adiposity using cross sectional design on Maya schoolchildren aged 7–9 and their mothers (n = 57 pairs). We compared maternal chronic early life environment (stature) with her child's adiposity (body mass index [BMI] z-score, waist circumference z-score, and percentage body fat) using multiple linear regression, controlling for the child's own environmental exposures (household sanitation and maternal parity). The research was performed in the south of Merida, Yucatan, Mexico, a low socioeconomic urban area in an upper middle income country. The Maya mothers were very short, with a mean stature of 147 cm. The children had fairly high adiposity levels, with BMI and waist circumference z-scores above the reference median. Maternal stature did not significantly predict any child adiposity indicator. There does not appear to be an intergenerational component of maternal early life chronic under-nutrition on her child's obesity risk within this free living population living in poverty. These results suggest that the co-existence of very short stature and obesity appears to be primarily due to exposures and experiences within a generation rather than across generations

Modeling the Fuel Spray and Combustion Process of the Ignition Quality Tester with KIVA-3V Modeling the Fuel Spray and Combustion Process of the Ignition Quality Tester with KIVA-3V

Development of advanced compression ignition and low-temperature combustion engines is increasingly dependent on chemical kinetic ignition models. However, rigorous experimental validation of kinetic models has been limited as a result of several factors. For example, shock tubes and rapid compression machines are often limited to premixed gas-phase studies, precluding the use of more realistic, low-volatility diesel or biodiesel surrogates. The Ignition Quality Tester (IQT) constant-volume spray combustion system measures ignition delay of low-volatility fuels; therefore, the IQT has the potential to validate ignition models experimentally. However, a better understanding of the IQT's fuel spray and combustion processes is necessary to facilitate chemical kinetic studies. KIVA-3V is utilized in developing a three-dimensional computational fluid dynamics (CFD) model that accurately and efficiently reproduces ignition behavior and temporally resolves temperature and equivalence ratio regions inside the IQT. The model's fuel spray characteristics (e.g., velocity, cone-angle, oscillations) are experimentally validated; n-heptane is initially studied because of the simplicity of its chemical kinetics and use as IQT calibration fuel. Reduced/skeletal n-heptane chemical mechanisms (60, 42, and 33 species) and one-step chemistry are employed. The CFD results indicate combustion is governed by autoignition kinetics, and perturbations/oscillations in the fuel spray have significant effects on the combustion process, as verified experimentally. The CFD model provides insight into the complex interaction between the fuel spray and combustion processes, which is vital to expanding the fuel research capabilities of the IQT

Experiments and Computational Fluid Dynamics Modeling Analysis of Large <i>n</i>‑Alkane Ignition Kinetics in the Ignition Quality Tester

This paper presents experimental measurements of ignition delays from low- to high-volatility <i>n</i>-alkanes representative of diesel and jet fuel compounds that are supplemented with a computational fluid dynamics (CFD) analysis. The ignition quality tester (IQT) is shown to be effective for studying ignition of low-volatility fuels, such as <i>n</i>-hexadecane, which are typically difficult to measure. Ignition delays, both experimental and modeled, are presented using an eight-point experimental design matrix (1.5 and 3.0 MPa, 823 and 723 K, and 15 and 21% O₂). A detailed <i>n</i>-alkane mechanism (C₈–C₁₆ with a total of 2115 species) was reduced to a skeletal 237 species <i>n</i>-hexadecane mechanism using a targeted search algorithm. A CFD model of the IQT (developed using KIVA-3V) coupled with skeletal mechanisms predicted ignition delays of <i>n</i>-heptane and <i>n</i>-hexadecane with reasonable accuracy over the eight-point matrix, with the exception of the highest temperature, lowest pressure, and oxygen concentration conditions. Temperature sweeps across a range of pressures (0.1–1.0 MPa) and temperatures (673–973 K) were performed for <i>n</i>-heptane, <i>n</i>-decane, <i>n</i>-dodecane, and <i>n</i>-hexadecane. The negative temperature coefficient (NTC) region was observed experimentally for the first time for <i>n</i>-hexadecane. The NTC region for <i>n</i>-dodecane and <i>n</i>-decane has previously been observed in shock tubes and rapid compression machines and is reported here for the first time in the IQT. The IQT is thus capable of capturing NTC behavior for large alkanes and can serve as an additional experimental validation tool for chemical kinetic mechanisms of low-volatility surrogates for diesel and jet fuels

Investigation of Iso-octane Ignition and Validation of a Multizone Modeling Method in an Ignition Quality Tester

An ignition quality tester was used to characterize the autoignition delay times of iso-octane. The experimental data were characterized between temperatures of 653 and 996 K, pressures of 1.0 and 1.5 MPa, and global equivalence ratios of 0.7 and 1.05. A clear negative temperature coefficient behavior was seen at both pressures in the experimental data. These data were used to characterize the effectiveness of three modeling methods: a single-zone homogeneous batch reactor, a multizone engine model, and a three-dimensional computational fluid dynamics (CFD) model. A detailed 874 species iso-octane ignition mechanism (Mehl, M.; Curran, H. J.; Pitz, W. J.; Westbrook, C. K. Chemical kinetic modeling of component mixtures relevant to gasoline. Proceedings of the European Combustion Meeting; Vienna, Austria, April 14–17, 2009) was reduced to 89 species for use in these models, and the predictions of the reduced mechanism were consistent with ignition delay times predicted by the detailed chemical mechanism across a broad range of temperatures, pressures, and equivalence ratios. The CFD model was also run without chemistry to characterize the extent of mixing of fuel and air in the chamber. The calculations predicted that the main part of the combustion chamber was fairly well-mixed at longer times (> ∼30 ms), suggesting that the simpler models might be applicable in this quasi-homogeneous region. The multizone predictions, where the combustion chamber was divided into 20 zones of temperature and equivalence ratio, were quite close to the coupled CFD–kinetics results, but the calculation time was ∼11 times faster than the coupled CFD–kinetics model. Although the coupled CFD–kinetics model captured the observed negative temperature coefficient behavior and pressure dependence, discrepancies remain between the predictions and the observed ignition time delays, suggesting improvements are still needed in the kinetic mechanism and/or the CFD model. This approach suggests a combined modeling approach, wherein the CFD calculations (without chemistry) can be used to examine the sensitivity of various model inputs to in-cylinder temperature and equivalence ratios. These values can be used as inputs to the multizone model to examine the impact on ignition delay. The speed of the multizone model also makes it feasible to quickly test more detailed kinetic mechanisms for comparison to experimental data and sensitivity analysis