• Journal of Korean Vacuum Science & Technology
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• v.4 no.1
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• pp.23-26
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• 2000

We have fabricated by metal organic chemical vapor deposition (MOCVD) In$\_$0.13/Ga$\_$0.87/N/GaN multiple quantum well (MQW) with thickness as thin as 10 A and barriers also of th same width on (0001) sapphire substrate. We have investigated this thin MQW by steady-state and time-resolved photoluminescence(PL) in picosecond time scale in a wide temperature range from 10 to 290 K. In the PL at 10 K, we observed a broad peak at 3.134 eV which was attributed to the quantum well emission of InGaN. The full width at half maximum (FWHM) of this peak was 129 meV at 10 K and its broadening at low temperatures was considered to be due to compositional fluctuations and interfacial disorder in the alloy. The narrow width of the quantum well was mainly responsible for the broadening of the emission linewidth. We also observed an intense and sharp peak at 3.471 eV of GaN barrier. From the temperature dependent PL measurements, the activation energy of the InGaN quantum well emision peak was estimated to be 69 meV. The lifetime of the quantum well emission was found to be 720 ps at 10 K, which was explained in terms of the exciton localization arising from potential fluctuations.

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.453-458
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• 1994

$(Ba_{0.5}Sr_{0.5)/TiO_3$(BST) thin films were prepared for the application of 256 Mb DRAM by RF magnetron sputtering. The crystallinity of BST thin films increased with increasing deposition tempera lure. The composition of thin films was $(Ba_{0.48}Sr_{0.48)/TiO_{2.93}$ Pt/Ti barrier layer suppressed the diffusion of Si into BST layer. The films showed a dielectric constant of 320 and a dissipation factor of 0.022 at 100 kHz. the change of capacitance of the films with applied voltage was small, showing paraelectric property. The charge storage density and leakage current density were 40fC/$\mu \textrm{m}^{2}$ and 0.8$\mu A/\textrm{cm}^2$, respectively at a field of 0.15 MV/cm. The BST films obtained by RF magnetron sputtering appeared to be potential thin film capacitors for 256 Mb DRAM application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.980-986
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• 2009

In a triple-layered structure of ITO/N,N'-diph enyl-N,N'bis(3-methylphenyl)-1,1' - biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline)aluminum($Alq_3$)/(2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP)/Al device, we have studied the electrical and optical characteristics of organic light-emitting diodes(OLEDs) depending on the deposition condition of BCP layer. Several different sizes of holes on boat and several different deposition rates were employed in evaporating the organic materials. And then, electrical properties of the organic light-emitting diodes were measured and the performance of the devices was analyzed. It was found that the hole-size of crucible boat and the evaporation rate affect on the surface roughness of BCP layer as well as the performance of the device. When the hole-size of crucible boat and the deposition rate of BCP are 1.2 mm and $1.0\;{\AA}/s$, respectively, average surface roughness of BCP layer is lower and the efficiency of the device is higher than the ones made with other conditions. From the analysis of current density-luminance-voltage characteristics of a triple layered device, we divided the conductive mechanism by four region according to applied voltage. So we have obtained a coefficient of ${\beta}_{ST}$ in schottky region is $3.85{\times}10^{-24}$, a coefficient of ${\beta}_{PF}$ in Poole-Frenkel region is $7.35{\times}10^{-24}$, and a potential barrier of ${\phi}_{FN}$ in Fower-Nordheim region is 0.39 eV.

• Biomolecules & Therapeutics
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• v.22 no.2
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• pp.114-121
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• 2014

Refractoriness of acute myeloid leukemia (AML) cells to chemotherapeutics represents a major clinical barrier. Suicide gene therapy for cancer has been attractive but with limited clinical efficacy. In this study, we investigated the potential application of herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) based system to inhibit chemoresistant AML cells. We first generated Ara-C resistant K562 cells and doxorubicin-resistant THP-1 cells. We found that the HSV-TK/GCV anticancer system suppressed drug resistant leukemic cells in culture. Chemoresistant AML cell lines displayed similar sensitivity to HSV-TK/GCV. Moreover, HSV-TK/GCV killing of leukemic cells was augmented to a mild but significant extent by all-trans retinoic acid (ATRA) with concomitant upregulation of Connexin 43, a major component of gap junctions. Interestingly, HSV-TK/GCV killing was enhanced by expression of vesicular stomatitis virus G glycoprotein (VSV-G), a fusogenic membrane protein, which also increased leukemic cell fusion. Co-culture resistant cells expressing HSV-TK and cells stably transduced with VSV-G showed that expression of VSV-G could promote the bystander killing effect of HSV-TK/GCV. Furthermore, combination of HSV-TK/GCV with VSV-G plus ATRA produced more pronounced antileukemia effect. These results suggest that the HSV-TK/GCV system in combination with fusogenic membrane proteins and/or ATRA could provide a strategy to mitigate the chemoresistance of AML.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.515-518
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• 2007

Gas hydrates are ice-like crystalline compounds that form under low temperature and elevated pressure conditions. Recently, gas hydrates present a novel means for natural gas storage and transportation with potential applications in a wide variety of areas. An important property of hydrates that makes them attractive for use in gas storage and transportation is their very high gas-to-sol id ratio. In addition to the high gas content, gas hydrates are remarkably stable. The main barrier to development of gas hydrate technology is the lack of an effective mass production method of gas hydrate in solid form. In this study, some performance comparison among several cases classified by different volume sizes of solution were carried to identify the characteristics due to the volume increment. And it is found that one of the main reasons disturbing hydrate formation is related to the lack of cooling heat transfer due to the volume increase of the solution. So, three kinds of heat transfer plates which have different shapes and cross sectional areas were made and tested for the performance comparison following to the shape and area of each plate. Finally it is clarified that the heat transfer is one of the major factors effecting hydrate formation performance and the installation of heat transfer plate can enhance the formation performance especially not in terms of the quantity but the speed.

• Journal of the Korean Society for information Management
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• v.26 no.2
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• pp.127-147
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• 2009

The synonym issue is an inherent barrier in human-computer communication, and it is more challenging in a Web 2.0 application, especially in social tagging applications. In an effort to resolve the issue, the goal of this study is to test the feasibility of a Web 2.0 application as a potential source for synonyms. This study investigates a way of identifying similar tags from a popular collaborative tagging application, Delicious. Specifically, we propose an algorithm (FolkSim) for measuring the similarity of social tags from Delicious. We compared FolkSim to a cosine-based similarity method and observed that the top-ranked tags on the similar list generated by FolkSim tend to be among the best possible similar tags in given choices. Also, the lists appear to be relatively better than the ones created by CosSim. We also observed that tag folksonomy and similar list resemble each other to a certain degree so that it possibly serves as an alternative outcome, especially in case the FolkSim-based list is unavailable or infeasible.

• Journal of Microbiology and Biotechnology
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• v.24 no.12
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• pp.1736-1743
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• 2014

In this study, we evaluated the effect of Lactobacillus plantarum HY7714 on skin hydration in human dermal fibroblasts and in hairless mice. In Hs68 cells, L. plantarum HY7714 not only increased the serine palmitoyltransferase (SPT) mRNA level, but also decreased the ceramidase mRNA level. In order to confirm the hydrating effects of L. plantarum HY7714 in vivo, we orally administered vehicle or L. plantarum HY7714 at a dose of $1{\times}10^9CFU/day$ to hairless mice for 8 weeks. In hairless mice, L. plantarum HY7714 decreased UVB-induced epidermal thickness. In addition, we found that L. plantarum HY7714 administration suppressed the increase in transepidermal water loss and decrease in skin hydration, which reflects barrier function fluctuations following UV irradiation. In particular, L. plantarum HY7714 administration increased the ceramide level compared with that in the UVB group. In the experiment on SPT and ceramidase mRNA expressions, L. plantarum HY7714 administration improved the reduction in SPT mRNA levels and suppressed the increase in ceramidase mRNA levels caused by UVB in the hairless mice skins. Collectively, these results suggest that L. plantarum HY7714 can be a potential candidate for preserving skin hydration levels against UV irradiation.

• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.2
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• pp.27-39
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• 1998

The interaction of monochromatic incident waves with a horizontal flexible membrane is investigated in the context of two-dimensional linear hydro-elastic theory. First, analytic diffraction and radiation solutions for a submerged impermeable horizontal membrane are obtained. Second, the theoretical prediction was compared with a series of experiments conducted in a two-dimensional wave tank at Texas A&M University. The measured reflection and transmission coefficients reasonably follow the trend of predicted values. Using the developed computer program, the performance of surface-mounted or submerged horizontal membrane wave barriers is tested with various system parameters and wave characteristics. It is found that the properly designed horizontal flexible membrane can be an effective wave barrier.

• The Korean Journal of Physiology and Pharmacology
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• v.22 no.1
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• pp.43-51
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• 2018

Although cisplatin is one of the most effective antitumor drugs for ovarian cancer, the emergence of chemoresistance to cisplatin in over 80% of initially responsive patients is a major barrier to successful therapy. The precise mechanisms underlying the development of cisplatin resistance are not fully understood, but alteration of DNA methylation associated with aberrant gene silencing may play a role. To identify epigenetically regulated genes directly associated with ovarian cancer cisplatin resistance, we compared the expression and methylation profiles of cisplatin-sensitive and -resistant human ovarian cancer cell lines. We identified ${\alpha}$-N-acetylgalactosaminidase (NAGA) as one of the key candidate genes for cisplatin drug response. Interestingly, in cisplatin-resistant cell lines, NAGA was significantly down-regulated and hypermethylated at a promoter CpG site at position +251 relative to the transcriptional start site. Low NAGA expression in cisplatin-resistant cell lines was restored by treatment with a DNA demethylation agent, indicating transcriptional silencing by hyper-DNA methylation. Furthermore, overexpression of NAGA in cisplatin-resistant lines induced cytotoxicity in response to cisplatin, whereas depletion of NAGA expression increased cisplatin chemoresistance, suggesting an essential role of NAGA in sensitizing ovarian cells to cisplatin. These findings indicate that NAGA acts as a cisplatin sensitizer and its gene silencing by hypermethylation confers resistance to cisplatin in ovarian cancer. Therefore, we suggest NAGA may be a promising potential therapeutic target for improvement of sensitivity to cisplatin in ovarian cancer.

• Journal of the Korean Chemical Society
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• v.39 no.10
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• pp.806-811
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• 1995

The electrical properties for $(Ba,Sr)_{1-x}Y_xTiO_3$(x=0.001∼0.009, BSYT) with a positive temperature coefficient of resistivity(PTCR) effect were investigated. The BSYT powder was prepared by oxalate coprecipitation method. It was found that the large PTCR effect was appeared up to 0.3 mol% and decreased above 0.5 mol% of the yttrium concentration. The plot of temperature vs. $1{\varepsilon}$m(T) above Curie temperature($T_c$) was agreed with Curie-Weiss law. The potential barrier calculated from measured resistivity and dielectric constant of specimens was high up to 0.3 mol% and reduced above 0.5 mol% of yttrium concentration as the curve of PTCR effect.