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BACKGROUND: Controlling for day-to-day variation is a key issue in estimating long-term dietary exposure to heavy metals using 24-hour recall (24HR) data from a relatively small number of days. OBJECTIVES: This study was conducted to estimate long-term dietary exposure to lead, cadmium and mercury among Korean children using the Iowa State University (ISU) method and to assess the contributions of different food groups to heavy metal intake. METHODS: We analyzed 2 days of 24HR data from 457 children between 0 and 6 years of age in 2010. Using bootstrapped concentration data for 118 representative foods, 93.5% of total intake was included in the exposure estimates in this study. Using the 2-day exposure data, we estimated long-term exposure by controlling for within-individual variation using the ISU method. RESULTS: The long-term dietary exposure estimates (mean [+ or -]standard deviation) for lead, cadmium, and mercury were 0.47 ± 0.14, 0.38 3 ± 0.20, and 0.22 ± 0.08 µg/kg bw/day, respectively. For lead and cadmium, the percentages of children whose exposure was greater than the reference value were 35 and 42%, respectively. Fruits were an important source of lead exposure, and cereal and fish and shellfish made the greatest contributions to the total cadmium and mercury exposure. CONCLUSIONS: Our findings also suggest that the long-term exposure to lead and cadmium was somewhat greater than the reference values, whereas mercury exposure was well below than the reference value in this population. Further studies may be necessary to evaluate the food items contributing to heavy metal exposure, and continuous monitoring is needed to ensure the safety of food intake and dietary patterns among vulnerable groups in Korea. European Journal of Clinical Nutrition (2014) 68, 1322-1326; doi: 10.1038/ejcn.2014.116; published online 25 June 2014, INTRODUCTION Heavy metals in the environment can appear as residues in foodstuffs. (1) They can be harmful for humans because they are not metabolized, and thus, they accumulate in the [...]

In this study, the rate dependent energy dissipation process and the fracture toughness of physical gels were investigated using agarose as a sample material. Both the J-integral and Essential work of Fracture (EWF) methods were examined. To assess the quasi-static fracture toughness of gels, linear regression was performed on critical J ([J.sub.c]) values at different loading rates resulting in a quasi-static [J.sub.c] value of 6.5 J/[m.sup.2] . This is close to the quasi-static EWF value of 5.3 J/[m.sup.2] obtained by performing EWF tests at a quasi-static loading rate (crosshead speed of less than 2 mm/min). Nearly constant crack propagation rates at low loading rates, regardless of crack length, suggest viscoplastic chain pull-out is the fracture mechanism. At high loading rates failure was highly brittle, which is attributed to sufficient elastic energy accumulation to precipitate failure by chain scission. We conclude that in physical gels quasi-static fracture toughness can be evaluated by both the J-integral and EWF methods provided the effects of loading rate are investigated and accounted for. POLYM. ENG. SCI., 51:1078-1086, 2011. [C] 2011 Society of Plastics Engineers, INTRODUCTION Hydrogels can be classified by the types of crosslinks joining chains together [1]. In chemical gels, the crosslinks between polymer chains are made of covalent bonds, while physical gels [...]

This study adopts the digital image correlation (DIC) method to measure the mechanical properties under tension in agarose gels. A second polynomial stress-strain equation based on a pore model is proposed in this work. It shows excellent agreement with experimental data and was verified by finite element simulation. Evaluation of the planer strain field by DIC allows measurement of strain localization and Poisson's ratio. At high stresses, Poisson's ratio is found to exceed the standard assumption of 0.5 which is shown to be a result of pore water leakage. Local failure strains are found to be approximately twice those determined by crosshead displacements. Viscous properties of agarose gels are investigated by performing the tensile tests at various loading rates. Increases in loading rate do not cause much difference in the shape of stress-strain curves, but result in increases in ultimate stress and Strain. POLYM. ENG. SCI., 50:1585-1593, 2010. [C] 2010 Society of Plastics Engineers, INTRODUCTION Polymer gels can be classified by the types of crosslinks joining chains together (1). Chemical gels are joined by permanent covalent bonds, while physical gels are linked by polymer-polymer [...]

Deformation and fracture toughness of high-density polyethylene (HDPE) in plane-stress tension was studied using the concept of essential work of fracture (EWF). Strain range for necking was determined from uniaxial tensile test, and was used to explain the deformation transition for 2-staged crack growth in double-edge-notched tensile test. Through work-partitioning, EWF values for HDPE were determined for each stage of the crack growth. Appropriateness of these EWF values to represent the material toughness is discussed. The study concludes that the EWF values for ductile polymers like HDPE may not be constant, but vary with the deformation behaviour involved in the crack growth process. POLYM. ENG. SCI., 47:1327-1337, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION The essential work of fracture (EWF) [1-5] is a concept for material toughness evaluation. Its value represents the energy consumed within the fracture process zone (FPZ) where new surface [...]

Under uniaxial tension, high-density polyethylene (HDPE) often fractures in a ductile manner. The fracture involves extensive necking that is known to occur in the plane-stress condition. However, for large-scale HDPE products like polyethylene pipe, crack can grow rapidly in a brittle manner. This type of fracture is known to be in the plane-strain condition, which has much lower toughness than that in the plane-stress condition. In this study, we extended the concept of essential work of fracture (EWF) to the plane-strain condition and evaluated the fracture toughness of extruded HDPE plate. The results show that the specific work of fracture in the plane-strain condition is also a linear function of the specimen ligament length. Therefore, the corresponding EWF value can be determined in a similar manner, that is, through linear extrapolation to zero ligament length. For HDPE, the study found that the plane-strain toughness is about one order of magnitude smaller than the plane-stress counterpart. Interestingly, the plane-strain EWF value is very close to the estimated toughness of pressurized polyethylene pipe, which was reported in the literature, predicted using numerical simulation based on data from the standard small-scale steady-state (S4) test. POLYM. ENG. SCI., 46:1428-1432, 2006. © 2006 Society of Plastics Engineers, INTRODUCTION When studying the fracture resistance of very ductile materials, where a large plastic zone develops and the energy dissipation is no longer confined to a small region around the [...]

A study on the effect of the thickness of high-temperature superconductor films on the mode resonant frequency of an axially symmetric TE01delta mode of a parallel plate dielectric resonator is presented. The analysis revealed that resonant frequency changes by under 0.4% for varying film thickness when the thickness ratio to the London penetration depth is over 10^-2. The experimental values derived were verified against the calculated values of resonant frequency.