Yoon Ho Cho

Grain-Boundary Conduction in Gadolinia-Doped Ceria: The Effect of SrO Addition

This study examined the effect of adding SrO on the grain-boundary conduction of Ce0.9Gd0.1O1.95 gadolinia-doped ceria containing 500 ppm SiO2. The apparent grain-boundary resistivity at 300°C decreased drastically from 746.7 to 0.90–1.97 k cm upon doping with 1 mol % SrO, while the grain-interior resistivity increased gradually from 3.1 to 11.6 k cm as the SrO concentration was increased up to 5 mol %. Therefore, doping with 1 mol % SrO resulted in the minimum total resistivity. The electron probe X-ray microanalysis and the analysis of the lattice parameters suggest that the 140–500-fold enhancement in the grain-boundary conduction is attributed to the scavenging of the highly resistive siliceous phase by the SrO-containing phase.

SiO2-Tolerant Grain-Boundary Conduction in Sr- and Mg-Doped Lanthanum Gallate

The effect of SiO 2 impurity on the grain-boundary conduction in Sr- and Mg-doped lanthanum gallate (La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ , LSGM) was studied. The grain-boundary conduction of LSGM was slightly affected, even by the addition of 500-2000 ppm SiO 2 , while the apparent grain-boundary resistivity was increased up to ∼780 times in gadolinia-doped ceria by the doping of 500-2000 ppm SiO 2 . The high tolerance of the grain-boundary conduction against siliceous impurity in the LSGM specimen was explained by the gathering of the acidic siliceous phase near the basic SrO component.

Effects of oxygen incorporation in GeSbTe films on electrical properties and thermal stability

Oxygen incorporated Ge2Sb2Te5 (GST) films were prepared by an ion beam sputtering deposition method. I-V curves of the oxygen incorporated GST active layer showed that the threshold voltage (Vth) varied, depending on the level of incorporated oxygen. In the case of a GST film with an elevated oxygen content of 30.8%, the GST layer melted at 9.02 V due to the instability conferred by the high oxygen content. The formation of Ge-deficient hexagonal phases such as GeSb2Te4 and Sb2Te3 appear to be responsible for the Vth variation. Impedance analyses indicated that the resistance in GST films with oxygen contents of 16.7% and 21.7% had different origins. Thermal desorption spectroscopy data indicate that moisture and hydrocarbons were more readily desorbed at higher oxygen content because the oxygen incorporated GST films are more hydrophilic than undoped GST films.

Toxicogenomic analysis of the pulmonary toxic effects of hexanal in F344 rat

Hexanal is a major component of indoor air pollutants and is a kind of aldehydes; it has adverse effects on human health. We performed an in vivo inhalation study and transcriptomic analysis to determine the mode of toxic actions in response to hexanal. Fischer 344 rats of both sexes were exposed by inhalation to hexanal aerosol for 4 h day−1, 5 days week−1 for 4 weeks at 0, 600, 1000, and 1500 ppm. Throughout our microarray‐based genome‐wide expression analysis, we identified 56 differentially expressed genes in three doses of hexanal; among these genes, 11 genes showed dose‐dependent expression patterns (10 downregulated and 1 upregulated, 1.5‐fold, p < 0.05). Through a comparative toxicogenomics database (CTD) analysis of 11 genes, we determined that five genes (CCL12, DDIT4, KLF2, CEBPD, and ADH6) are linked to diverse disease categories such as cancer, respiratory tract disease, and immune system disease. These diseases were previously known for being induced by volatile organic compounds (VOCs). Our data demonstrated that the hexanal‐induced dose‐dependent altered genes could be valuable quantitative biomarkers to predict hexanal exposure and to perform relative risk assessments, including pulmonary toxicity.

MicroRNA response of inhalation exposure to hexanal in lung tissues from Fischer 344 rats

In previous studies, we have investigated the relationships between environmental chemicals and health risk based on omics analysis and identified significant biomarkers. Our current findings indicate that hexanal may be an important toxicant of the pulmonary system in epigenetic insights. MicroRNA (miRNA) is an important indicator of biomedical risk assessment and target identification. Hexanal is highly detectable in the exhaled breath of patients with chronic obstructive pulmonary disease (COPD) and chronic inflammatory lung disease. In this study, we aimed to identify hexanal‐characterized miRNA‐mRNA correlations involved in lung toxicity. Microarray analysis identified 56 miRNAs that commonly changed their expression more than 1.3‐fold in three doses (600, 1000, and 1500 ppm) within hexanal‐exposed Fischer 344 rats by inhalation, and 226 genes were predicted to be target genes of miRNAs through TargetScan analysis. By integrating analyses of miRNA and mRNA expression profiles, we identified one anti‐correlated target gene (Chga; chromogranin A; parathyroid secretory protein 1). Comparative toxicogenomics database (CTD) analysis of this gene showed that Chga is involved with several disease categories such as cancer, respiratory tract disease, nervous system disease, and cardiovascular disease. Further research is necessary to elucidate the mechanisms of hexanal‐responsive toxicologic pathways at the molecular level. This study concludes that our integrated approach to miRNA and mRNA enables us to identify molecular events in disease development induced by hexanal in an in vivo rat model.

Preparation of Ni-GDC Powders by the Solution Reduction Method Using Hydrazine and Its Electrical Properties

Ni-GDC (gadolinia-doped ceria) composite powders, the anode material for the application of solid oxide fuel cells, were prepared by a solution reduction method using hydrazine. The distribution of Ni particles in the composite powders was homogeneous. The Ni-GDC powders were sintered at 1400˚C for 2 h and then reduced at 800˚C for 24 h in 3% H2. The percolation limit of Ni of the sintered composite was 20 vol%, which was significantly lower than these values in the literature (30-35 vol%). The marked decrease of percolation limit is attributed to the small size of the Ni particles and the high degree of dispersion. The hydrazine method suggests a facile chemical route to prepare well-dispersed Ni-GDC composite powders.

DNA Methylome Analysis of Saturated Aliphatic Aldehydes in Pulmonary Toxicity

Recent studies have investigated the epigenetic effects of environmental exposure to chemicals on human health. The associations of DNA methylation, environmental exposure and human diseases have been widely demonstrated. However, the use of gene methylation patterns as a predictive biomarker for exposure to environmental toxicants is relatively poorly understood. Here, we focused on low-molecular-weight saturated aliphatic aldehydes (LSAAs), which are important environmental risk factors in humans as major indoor air pollutants. Based on DNA methylation profiling in gene promoter regions, we analysed DNA methylation profiles following exposure of A549 cells to seven LSAAs (propanal, butanal, pentanal, hexanal, heptanal, octanal, and nonanal) to identify LSAA-characterized methylated sites and target genes, as well as to investigate whether exposure to LSAAs contributes to inducing of pulmonary toxicity. Additionally, by integrating DNA methylation and mRNA expression profile analyses, we identified core anti-correlated target genes. Gene ontology analysis of these target genes revealed several key biological processes. These findings suggest that alterations in DNA methylation by exposure to LSAAs provide novel epigenetic biomarkers for risk assessments. This DNA methylation-mRNA approach also reveals potential new mechanistic insights into the epigenetic actions of pulmonary toxicity.

PhraseRank for document clustering: reweighting the weight of phrase

Given a document collection, a hierarchical clustering algorithm groups several clusters. Recent works have identified the set of overlap phrases as useful features in hierarchical document clustering. However, they did not consider the relationship between co-occurred overlap phrases in a document and degrees of opposite relationships between overlap phrases. In this paper, we propose new algorithms for effective similarity measure before working hierarchical clustering algorithm. There are two important features in the proposed methods: the ranking list of top-k phrases for each particular overlap phrase and the opposite significances between two overlap phrases with each other. Experiment result shows that proposed method improves the results of clustering.