• Restorative Dentistry and Endodontics
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• v.33 no.1
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• pp.54-65
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• 2008

The purpose of this study was to determine the effect of sodium hypochlorite and steam autoclaving on the cyclic fatigue of nickel-titanium endodontic files. Two types of files with a .06 taper and #30 were used, $K3^{(R)}$ (SybronEndo, Glendora, California, USA) and Hero $642^{(R)}$(Micro-Mega, BesanCon, France). The files were divided into 6 experimental groups containing 10 files each group depending the soaking time in 6% sodium hypochlorite solution and number of cycles of steam autoclave. After sterilization, a cyclic fatigue test was performed on each file, and the fracture time was recorded in seconds. The control group underwent the cyclic fatigue test only. After the test, the surface characteristics of the files were observed using scanning electron microscopy (SEM). All groups containing the Hero 64~ files showed a similar cyclic fatigue fracture time. However, the cyclic fatigue fracture time with the $K3^{(R)}$ files was significantly shorter in groups which were treated with sodium hypochlorite than in the control group (P < 0.05), SEM revealed both Hero $642^{(R)}$ and $K3^{(R)}$ files to have significant corrosion on the file surface in groups treated with sodium hypochlorite, compared with the sharp and regular blades of the control group. $K3^{(R)}$ files showed more corrosion than the Hero $642^{(R)}$ files. Bluntness of the blades of the $K3^{(R)}$ file was observed in groups treated with steam autoclave. Although there was no obvious destruction on the surface of steam autoclaved Hero $642^{(R)}$ files, slight bluntness was observed. Sterilizing with a steam autoclave is much less destructive to $K3^{(R)}$ files than sodium hypochlorite. The longer time exposed to sodium hypochlorite, the more destructive pattern was shown on the blades of the files. Therefore, when using sodium hypochlorite solution, the exposure time should be as short as possible in order to prevent corrosion and increase the cyclic fatigue fracture time.

• Journal of the Korean Vacuum Society
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• v.18 no.2
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• pp.85-91
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• 2009

There has been a rapid progress for flexible polymer-based MEMS(Microelectromechanical Systems) technology. Polycarbonate (PC) and Poly Methyl Methacrylate (PMMA), so-called acrylic, have many advantages for optical, non-toxic and micro-device application. We studied dry etching of PC and PMMA as a function of % gas ratio in the $O_2/SF_6/CH_4$ temary plasma. A photoresist pattern was defined on the polymer samples with a mask using a conventional lithography. Plasma etching was done at 100 W RIE chuck power and 10 sccm total gas flow rate. The etch rates of PMMA were typically 2 times higher than those of PC in the whole experimental range. The result would be related to higher melting point of PC compared to that of PMMA. The highest etch rates of PMMA and PC were found in the $O_2/SF_6$ discharges among $O_2/SF_6$, $O_2/CH_4$ and $SF_6/CH_4$ and $O_2/SF_6/CH_4$ plasma composition (PC: ${\sim}350\;nm/min$ at 5 sccm $O_2/5$ sccm $SF_6$, PMMA: ${\sim}570\;nm/min$ at 2.5 sccm $O_2/7.5$ sccm $SF_6$). PC has smoother surface morphology than PMMA after etching in the $O_2/SF_6/CH_4$ discharges. The surface roughness of PC was in the range of 1.9$\sim$3.88 nm. However, that of PMMA was 17.3$\sim$26.1 nm.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.21 no.1
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• pp.24-35
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• 2016

To assess the relationship between environmental factors and seasonal phytoplankton community structure, we investigated abiotic and biotic factors in Ulsan Bay, Korea. We divided the bay into two areas based on geographical characteristics and compared the difference in each factor between inner and outer bay with t-test statistics. As a result, temperature in the outer bay was higher than that of the inner bay during winter (t = -5.833, p < 0.01) and autumn (p > 0.05). However, opposite trend was observed during spring (t = 4.247, p < 0.01) and summer (t = 2.876, p < 0.05). Salinity was significantly lower in the inner bay than in the outer bay in winter, spring, and summer (p < 0.01). However, the salinity was not significantly different between the inner and the outer bay in the autumn (p > 0.05). In particular, high nutrient concentration was observed in most stations during winter season due to vertical well mixing. The nutrient concentration was significantly higher in surface layers of inner bay after rainfall, particularly in the summer. The relative contribution (approximately 70%) of < $20{\mu}m$ (nano and pico) size phytoplankton was increased in all seasons with continuously low nutrients from the offshore water due to their adaption to low nutrient without other large competitors. Interestingly, high population of Eutreptiella gymnastica was kept in the inner bay during the spring and summer associated with high DIN (nitrate+nitrite, ammonium) after river discharge following rainfall, suggesting that DIN supply might have triggered the increase of Eutreptiella gymnastica population. In addition, high density of freshwater species Oscillatoria sp. and Microcystis sp. were found in several stations of the inner bay that were provided with large amounts of freshwater from the Tae-wha River. Diatom and cryptophyta species were found to be dominant species in the autumn and winter. Of these, centric diatom Chaetoceros genus was occupied in the outer bay in the autumn. Cryptophyta species known as opportunistic micro-algae were found to have high biomass without competitors in the inner bay. Our results demonstrated that Ulsan Bay was strongly affected by freshwater from Tae-wha River during the rainy season and by the surface warm water current from the offshore of the bay during dry season. These two external factors might play important roles in regulating the seasonal phytoplankton community structures.

• Journal of the Mineralogical Society of Korea
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• v.23 no.2
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• pp.125-139
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• 2010

Behavior of heavy metals and arsenic in the tailings of Songcheon Au-Ag mine was characterized via both mineralogical and geochemical methods. Mineral composition of the tailings was investigated by X-ray diffractometry, energy-dispersive spectroscopy, and electron probe micro-analyzer (EPMA) and total concentrations of heavy metals and arsenic and their chemical forms were analyzed by total digestion of aqua regia and sequential extraction method, respectively. The results of mineralogical study indicate that the tailings included mineral particles of resinous shape mainly consisting of galena, sphalerite, pyrite, quartz, and scorodite, and specifically socordite was identified in the form of matrix. EPMA quantitative analyses were performed to evaluate the weatherability of each mineral, and the results suggest that it decreased in the sequence of arsenopyrite > galena > sphalerite > pyrite. The weathering pattern of galena was observed to show distinctive zonal structure consisting of secondary minerals such as anglesite and beudantite. In addition, almost all of arsenopyrite has been altered to scorodite existing asmatrix and galena, sphalerite, and pyrite which have lower weatherability than arsenopyrite were identified within the matrix of scorodite. During the process of alteration of arsenopyrite into scorodite, it is likely that a portion of arsenic was lixiviated and caused a great deal of detrimental effects to surrounding environment. The results of EPMA quantitative analyses verify that the stability of scorodite was relatively high and this stable scorodite has restrained the weathering of other primary minerals within tailings as a result of its coating of mineral surfaces. For this reason, Songcheon tailings show the characteristics of the first weathering stage, although they have been exposed to the surface environment for a long time. Based on the overall results of mineralogical and geochemical studies undertaken in this research, if the tailings are kept to be exposed to the surface environment and the weathering process is continuous, not only hazardous heavy metals, such as lead and arsenic seem to be significantly leached out because their larger portions are being partitioned in weakly-bound (highly-mobile) fractions, but the potential of arsenic leaching is likely to be high as the stability of scorodite is gradually decreased. Consequently, it is speculated that the environmental hazard of Songcheon mine is significantly high.

• Journal of Chest Surgery
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• v.39 no.1 s.258
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• pp.1-11
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• 2006

Background: CD44 is a glycoprotein on the cell surface which is involved in the cell-to-cell and cell-to-matrix interaction. The standard form, CD44s and multiple isoforms are determined by alternative splicing of 10 exons. Recent studies have suggested that CD44 may help invasion and metastasis of various epithelial tumors as well as activation of Iymphocytes and monocytes. The expression pattern of CD44 can be different according to tumor types. The author studied the expression pattern of CD44s and one of its variants, CD44v6 in non-small cell lung carcinomas (NSCLC) to find their implications on clinicopathologic aspects, including the survival of the patients. Material and Method: A total of 89 primary NSCLSs (48 squamous cell carcinomas, 33 adenocarcinomas, and 8 undifferentiated large cell carcinomas) were retrieved during the years between 1985 to 1994. The immunohisto chemistry was done by using monoclonal antibodies and the CD44 expression for angiogenesis was evaluated by counting the number of tumor microvessels. Result: Seventy-one (79.8$\%$) and 64 (71 .9$\%$) among 89 NSCLSs revealed the expression of CD44s and CD44v6, respectively. The expression of CD44s was well correlated with that of CD44v6 (r=0.710, p < 0.0001). The expression of CD44s and CD44v6 was associated with the histopathologic type of the NSCLCs, and squamous cell carcinoma was the type that showed the highest expression of CD44s and CD44v6 (p < 0.0001). Microvessel count was the highest in adenocarcinomas (113.6$\pm$69.7 on 200-fold magnification and 54.8$\pm$41.1 on 400-fold magnification) and correlated with the tumor size of TNM system (r=0.217, p=0.043) and CD44s expression (r=0.218, p=0.040). In adenocarcinoma, the patients with higher CD44s expression survived shorter than those with lower CD44s expression (p=0.0194) but there was no statistical significance on multivariate analysis(p=0.3298). Conclusion: The expression of both CD44s and CD44v6 may be associated with the squamous differentiation in non-small cell lung carcinomas. The relationship of CD44s expression with micro-vessel density of the tumor suggests an involvement of CD44s in tumor angiogenesis, which in turn would help tumor growth.

• Korean Journal of Environment and Ecology
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• v.32 no.4
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• pp.425-439
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• 2018

W investigated the environmental factors and inhabiting biota such as macrophytes and zooplankton in 43 sites located on Jeju Island from May and June 2017 to evaluate the spread and ecosystem risk of dotted duckweed (landoltia punctata) which was recently found for the first time in Jeju Island. Dotted duckweeds were found in a total of 18 sites which tended to show low biomass of aquatic macrophyte species other than the dotted duckweed. We conducted a pattern analysis using SOM (Self-Organizing Map), which extracts information through competitive and adaptive properties, to analyze the effect of inhabiting biota on aquatic macrophytes such as the dotted duckweed and environmental factors. The SOM analysis showed that the inhabiting biota such as the zooplankton affected the biomass of aquatic macrophytes than they did the environmental factors. In particular, the biomass of dotted duckweed was positively related to plant-attached species (Alona, Chydorus, and Pleuroxus). Considering that low density of aquatic macrophytes covers the streams and wetlands on Jeju Island because of irregular water source and sharp change of water depth, the dotted duckweeds are likely to play an essential role as the vital habitat for micro-biota including zooplankton in wetlands and streams on Jeju Island. Furthermore, considering that organic matters are utilized as the primary food source in the areas occupied by dotted duckweed, dotted duckweeds have the role of being both habitat and food source. Although the dense growth of dotted duckweed adversely affects growth and development of some aquatic plants due to the shadow effect, it is due to the dominance of floating plants on the water surface should not be regarded as the risk of the dotted duckweed. In conclusion, the dotted duckweeds have spread and settled in most of the water systems on Jeju Island, their impact on inhabiting biota and the aquatic environment was minor. It is necessary to monitor the distribution and spread of dotted duckweeds in the inland areas outside of Jeju Island in the future.