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Search Results: 1 - 10 of 38143 matches for " Hak Jun Ahn "
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Atmospheric-Pressure Plasma Jet Induces Apoptosis Involving Mitochondria via Generation of Free Radicals
Hak Jun Ahn, Kang Il Kim, Geunyoung Kim, Eunpyo Moon, Sang Sik Yang, Jong-Soo Lee
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0028154
Abstract: The plasma jet has been proposed as a novel therapeutic method for anticancer treatment. However, its biological effects and mechanism of action remain elusive. Here, we investigated its cell death effects and underlying molecular mechanisms, using air and N2 plasma jets from a micro nozzle array. Treatment with air or N2 plasma jets caused apoptotic death in human cervical cancer HeLa cells, simultaneously with depolarization of mitochondrial membrane potential. In addition, the plasma jets were able to generate reactive oxygen species (ROS), which function as surrogate apoptotic signals by targeting the mitochondrial membrane potential. Antioxidants or caspase inhibitors ameliorated the apoptotic cell death induced by the air and N2 plasma jets, suggesting that the plasma jet may generate ROS as a proapoptotic cue, thus initiating mitochondria-mediated apoptosis. Taken together, our data suggest the potential employment of plasma jets as a novel therapy for cancer.
Forest Cover Classification by Optimal Segmentation of High Resolution Satellite Imagery
So-Ra Kim,Woo-Kyun Lee,Doo-Ahn Kwak,Greg S. Biging,Peng Gong,Jun-Hak Lee,Hyun-Kook Cho
Sensors , 2011, DOI: 10.3390/s110201943
Abstract: This study investigated whether high-resolution satellite imagery is suitable for preparing a detailed digital forest cover map that discriminates forest cover at the tree species level. First, we tried to find an optimal process for segmenting the high-resolution images using a region-growing method with the scale, color and shape factors in Definiens? Professional 5.0. The image was classified by a traditional, pixel-based, maximum likelihood classification approach using the spectral information of the pixels. The pixels in each segment were reclassified using a segment-based classification (SBC) with a majority rule. Segmentation with strongly weighted color was less sensitive to the scale parameter and led to optimal forest cover segmentation and classification. The pixel-based classification (PBC) suffered from the “salt-and-pepper effect” and performed poorly in the classification of forest cover types, whereas the SBC helped to attenuate the effect and notably improved the classification accuracy. As a whole, SBC proved to be more suitable for classifying and delineating forest cover using high-resolution satellite images.
Targeting Cancer Cells with Reactive Oxygen and Nitrogen Species Generated by Atmospheric-Pressure Air Plasma
Hak Jun Ahn, Kang Il Kim, Nguyen Ngoc Hoan, Churl Ho Kim, Eunpyo Moon, Kyeong Sook Choi, Sang Sik Yang, Jong-Soo Lee
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086173
Abstract: The plasma jet has been proposed as a novel therapeutic method for cancer. Anticancer activity of plasma has been reported to involve mitochondrial dysfunction. However, what constituents generated by plasma is linked to this anticancer process and its mechanism of action remain unclear. Here, we report that the therapeutic effects of air plasma result from generation of reactive oxygen/nitrogen species (ROS/RNS) including H2O2, Ox, OH?, ?O2, NOx, leading to depolarization of mitochondrial membrane potential and mitochondrial ROS accumulation. Simultaneously, ROS/RNS activate c-Jun NH2-terminal kinase (JNK) and p38 kinase. As a consequence, treatment with air plasma jets induces apoptotic death in human cervical cancer HeLa cells. Pretreatment of the cells with antioxidants, JNK and p38 inhibitors, or JNK and p38 siRNA abrogates the depolarization of mitochondrial membrane potential and impairs the air plasma-induced apoptotic cell death, suggesting that the ROS/RNS generated by plasma trigger signaling pathways involving JNK and p38 and promote mitochondrial perturbation, leading to apoptosis. Therefore, administration of air plasma may be a feasible strategy to eliminate cancer cells.
Effect of a Dipeptidyl Peptidase-IV Inhibitor, Des-Fluoro-Sitagliptin, on Neointimal Formation after Balloon Injury in Rats
Soo Lim, Sung Hee Choi, Hayley Shin, Bong Jun Cho, Ho Seon Park, Byung Yong Ahn, Seon Mee Kang, Ji Won Yoon, Hak Chul Jang, Young-Bum Kim, Kyong Soo Park
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035007
Abstract: Background Recently, it has been suggested that enhancement of incretin effect improves cardiac function. We investigated the effect of a DPP-IV inhibitor, des-fluoro-sitagliptin, in reducing occurrence of restenosis in carotid artery in response to balloon injury and the related mechanisms. Methods and Findings Otsuka Long-Evans Tokushima Fatty rats were grouped into four: control (normal saline) and sitagliptin 100, 250 and 500 mg/kg per day (n = 10 per group). Sitagliptin or normal saline were given orally from 1 week before to 2 weeks after carotid injury. After 3 weeks of treatment, sitagliptin treatment caused a significant and dose-dependent reduction in intima-media ratio (IMR) in obese diabetic rats. This effect was accompanied by improved glucose homeostasis, decreased circulating levels of high-sensitivity C-reactive protein (hsCRP) and increased adiponectin level. Moreover, decreased IMR was correlated significantly with reduced hsCRP, tumor necrosis factor-α and monocyte chemoattractant protein-1 levels and plasminogen activator inhibitor-1 activity. In vitro evidence with vascular smooth muscle cells (VSMCs) demonstrated that proliferation and migration were decreased significantly after sitagliptin treatment. In addition, sitagliptin increased caspase-3 activity and decreased monocyte adhesion and NFκB activation in VSMCs. Conclusions Sitagliptin has protective properties against restenosis after carotid injury and therapeutic implications for treating macrovascular complications of diabetes.
MINING TEXTS TO UNDERSTAND CUSTOMERS' IMAGE OF BRANDS
Hyung Jun Ahn
International Journal of Electronic Commerce Studies , 2013, DOI: http://dx.doi.org/10.7903/ijecs.1122
Abstract: Text mining is becoming increasingly important in understanding customers and markets these days. This paper presents a method of mining texts about customer sentiments using a network analysis technique. A data set collected about two global mobile device manufactures were used for testing the method. The analysis results show that the method can be effectively used to extract key sentiments in the customers' texts.
Possible Role of Horizontal Gene Transfer in the Colonization of Sea Ice by Algae
James A. Raymond, Hak Jun Kim
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035968
Abstract: Diatoms and other algae not only survive, but thrive in sea ice. Among sea ice diatoms, all species examined so far produce ice-binding proteins (IBPs), whereas no such proteins are found in non-ice-associated diatoms, which strongly suggests that IBPs are essential for survival in ice. The restricted occurrence also raises the question of how the IBP genes were acquired. Proteins with similar sequences and ice-binding activities are produced by ice-associated bacteria, and so it has previously been speculated that the genes were acquired by horizontal transfer (HGT) from bacteria. Here we report several new IBP sequences from three types of ice algae, which together with previously determined sequences reveal a phylogeny that is completely incongruent with algal phylogeny, and that can be most easily explained by HGT. HGT is also supported by the finding that the closest matches to the algal IBP genes are all bacterial genes and that the algal IBP genes lack introns. We also describe a highly freeze-tolerant bacterium from the bottom layer of Antarctic sea ice that produces an IBP with 47% amino acid identity to a diatom IBP from the same layer, demonstrating at least an opportunity for gene transfer. Together, these results suggest that the success of diatoms and other algae in sea ice can be at least partly attributed to their acquisition of prokaryotic IBP genes.
Development of IEC61850 Based Substation Engineering Tools with IEC61850 Schema Library  [PDF]
Yong Hak Kim, Jeon Yeol Han, You Jin Lee, Yong Ho An, In Jun Song
Smart Grid and Renewable Energy (SGRE) , 2011, DOI: 10.4236/sgre.2011.23030
Abstract: IEC 61850 allows the replacement of conventional wire based systems to communication based system with local area network. Since new engineering processes are introduced in substation, the specifications and tools are required combined with new skills across the substation engineering. In order to construct the IEC 61850 based substation automation system, the IED engineering tools as an engineering means are necessary to cope with the substation automation by full digital devices in the real power systems. Compared the configuration tools provided IEDs vendors which are able to support the operation and communication analysis between IEDs, the XML based IED integration engineering tools as substation engineering tools which are developed can build, edit and save the ICD, SCL and CID files. Particularly, the substation engineering tools are possible to apply the IEC 61850 based IEDs for the engineering process of systems and also provide the reliability and efficiency of system for the utilities and manufacturers. The developed tools are applied to test and create the SCL files for domestic-made IEDs, and then compared with the conventional tools. The reliability including accuracy of results was proved.
High Theta and Low Alpha Powers May Be Indicative of BCI-Illiteracy in Motor Imagery
Minkyu Ahn, Hohyun Cho, Sangtae Ahn, Sung Chan Jun
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0080886
Abstract: In most brain computer interface (BCI) systems, some target users have significant difficulty in using BCI systems. Such target users are called ‘BCI-illiterate’. This phenomenon has been poorly investigated, and a clear understanding of the BCI-illiteracy mechanism or a solution to this problem has not been reported to date. In this study, we sought to demonstrate the neurophysiological differences between two groups (literate, illiterate) with a total of 52 subjects. We investigated recordings under non-task related state (NTS) which is collected during subject is relaxed with eyes open. We found that high theta and low alpha waves were noticeable in the BCI-illiterate relative to the BCI-literate people. Furthermore, these high theta and low alpha wave patterns were preserved across different mental states, such as NTS, resting before motor imagery (MI), and MI states, even though the spatial distribution of both BCI-illiterate and BCI-literate groups did not differ. From these findings, an effective strategy for pre-screening subjects for BCI illiteracy has been determined, and a performance factor that reflects potential user performance has been proposed using a simple combination of band powers. Our proposed performance factor gave an r = 0.59 (r2 = 0.34) in a correlation analysis with BCI performance and yielded as much as r = 0.70 (r2 = 0.50) when seven outliers were rejected during the evaluation of whole data (N = 61), including BCI competition datasets (N = 9). These findings may be directly applicable to online BCI systems.
Prognostic Discrimination Using a 70-Gene Signature among Patients with Estrogen Receptor-Positive Breast Cancer and an Intermediate 21-Gene Recurrence Score
Sung Gwe Ahn,Hak Min Lee,Hak Woo Lee,Seung Ah Lee,Se-Ra Lee,Sun-Hee Leem,Joon Jeong,In-Sun Chu
International Journal of Molecular Sciences , 2013, DOI: 10.3390/ijms141223685
Abstract: The Oncotype DX ? recurrence score (RS) predictor has been clinically utilized to appropriately select adjuvant chemotherapy for patients with estrogen receptor (ER)-positive early breast cancer. However, the selection of chemotherapy for patients with intermediate RSs remains controversial. We assessed the prognostic value of a 70-gene signature (70GS) among patients with ER-positive breast cancer and intermediate RSs. In addition, we sought to identify genes associated with poor 70GS scores based on gene expression profiling (GEP). GEP was performed using gene expression data from 186 patients with ER-positive breast cancer. The RS and 70GS score were calculated on the basis of GEP. Among 186 patients, 82 ER-positive patients with intermediate RSs were identified. These patients were stratified by 70GS, overall survival (OS) significantly differed according to 70GS ( p = 0.013). In a supervised hierarchical analysis according to 70GS, the expression of several representative genes for cell proliferation was significantly higher in the poor 70GS cluster than in the good 70GS cluster. Furthermore, among these patients, FOXM1, AURKA, AURKB, and BIRC5 displayed prognostic significance for OS. In conclusion, 70GS can help to discriminate survival differences among ER-positive patients with intermediate RSs. FOXM1, AURKA, AURKB, and BIRC5, are associated with poor 70GS scores.
The Theory of Falling Shadows Applied to -Ideals in -Algebras
Young Bae Jun,Sun Shin Ahn
International Journal of Mathematics and Mathematical Sciences , 2012, DOI: 10.1155/2012/693090
Abstract: On the basis of the theory of a falling shadow which was first formulated by Wang (1985), the notion of falling ?-ideals in -algebras is introduced, and related properties are investigated. Characterizations of a falling ?-ideal are established. Relations among falling ?-ideals, falling -ideals, falling #-ideals, falling -subalgebras, and falling BCK-ideals are discussed.
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