Volatile organic compounds (VOCs) are reported to cause adverse effects on pulmonary function in occupationally exposed workers. However, evidence is lacking on the effect in the general population. We hypothesised that VOCs impair pulmonary function through enhancing oxidative stress, especially in the elderly population.A longitudinal panel study of 154 elderly people was performed in South Korea. Repeated spirometric tests were performed up to eight times on different days for each subject. We also measured urinary concentrations of metabolites of the VOC and markers of oxidative stress (malondialdehyde and 8-oxo-29-deoxyguanosine) on the same day of spirometric tests. A mixed linear regression model was used to evaluate the association among the VOC metabolites, oxidative stress markers and spirometric tests.We found that the urinary levels of hippuric acid and methylhippuric acid, which are metabolites of toluene and xylene, respectively, were significantly associated with reduction of forced expiratory volume in 1 s (FEV1), FEV1/forced vital capacity (FVC), and forced expiratory flow at 25-75% of FVC. We also found significant associations between the metabolites of VOCs and the markers of oxidative stress. In addition, the oxidative stress markers were associated with pulmonary function parameters.This study suggests that exposure to toluene and xylene exert a harmful effect on pulmonary function by exacerbating oxidative stress in elderly people.
Changes in the carrier mobility of tensile strained Si and SiGe nanowires (NWs) were examined using an electrical push-to-pull device (E-PTP, Hysitron). The changes were found to be closely related to the chemical structure at the surface, likely defect states. As tensile strain is increased, the resistivity of SiGe NWs deceases in a linear manner. However, the corresponding values for Si NWs increased with increasing tensile strain, which is closely related to broken bonds induced by defects at the NW surface. Broken bonds at the surface, which communicate with the defect state of Si are critically altered when Ge is incorporated in Si NW. In addition, the number of defects could be significantly decreased in Si NWs by incorporating a surface passivated Al2O3 layer, which removes broken bonds, resulting in a proportional decrease in the resistivity of Si NWs with increasing strain. Moreover, the presence of a passivation layer dramatically increases the extent of fracture strain in NWs, and a significant enhancement in mobility of about 2.6 times was observed for a tensile strain of 5.7%.
The crystalline structure and interfacial reactions in HfO2 films grown on InP (001) substrates was investigated as a function of film thickness. High resolution transmission electron microscopy and x-ray diffraction measurements were used to investigate changes in the crystalline structure of the HfO2 films. As the thickness of the HfO2 increased, the crystal structure was transformed from monoclinic to tetragonal, and the interfacial layer between the HfO2 film and the InP substrate disappeared. High resolution x-ray photoelectron spectroscopy was also applied to confirm the existence of an interfacial chemical reaction in HfO2/InP. An interfacial self-cleaning effect occurred during the atomic layer deposition process, resulting in a clear interface with no indication of an interfacial layer between the HfO2 film and the InP surface. Finally, the crystallization process in the HfO2 films was found to be significantly affected by the interfacial energy.
The diffusion of Ge in Ge-rich layer (GRL) and the factors affecting on it during the oxidation of strained Si1−xGex layers were examined. Strained Si1−xGex layers, having different initial Ge concentrations (x=0.15 and 0.3), were oxidized at 800 and 900°C in a dry O2 ambient for different oxidation times. The diffusion of Ge into the underlying Si1−xGex layer having an initial constant composition and the resulting transformation to GRL were both enhanced with an increase in oxidation temperature. After complete transformation to GRL, GeO2 started to become incorporated into the resulting oxide layer. The formation of GeO2 was initiated by the Ge saturation of the GRL layer with Ge and by the differences in diffusivity of Ge atoms in Si1−xGex and Si substrate. The relaxation occurred when the Ge concentration in the GRL reached a critical value and was not affected by either oxidation time or temperature.
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