• Journal of Korean Society of Water and Wastewater
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• v.36 no.5
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• pp.261-273
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• 2022

In this study, we collect water control valves that have had accidents due to existing cracks, etc. are collected, and propose investigation items for strengthening the valve structural safety evaluation through a series of analyzes from valve specifications to physicochemical properties are proposed. The results of this study are as follows. First, there was a large variation in the thickness of the body or flange of the valves to be investigated, which is considered to be very important factor, because it may affect the safety of the valve body against internal pressure and the flange connected with the bolt nut. Second, 60% of the valves under investigation had many voids in the valve body and flange, etc. and the decrease in thickness due to corrosion was relatively large on the inner surface in contact with water rather than the outer surface. It is judged that the investigation of depth included voids is very important factor. Third, all valves to be investigated are made of gray cast iron foam, and therefore it is judged that there is no major problem in chemical composition. It is judged that the chemical composition should be investigated. Fourth, as a physical investigation item, the analysis of metal morphology structure seems to be a very important factor for nodular cast iron from rather than a gray cast iron foam water valve with a flake structure. As it was found to be 46.7~68.8% of the standard recommended by KS, it could have a direct effect on damage such as cracks, and therefore it is judged that the evaluation of tensile strength is very important in evaluating the safety of the valve.

• Membrane and Water Treatment
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• v.14 no.2
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• pp.85-93
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• 2023

Membrane separation is widely used for several applications such as water treatment, membrane reactors and climate change. Cross-linked organic-inorganic hybrid polyvinylidene fluoride (PVDF) / Tetraethyl orthosilicate (TEOS) was adopted for the preparation of optimized hollow membrane (HFM) for membrane distillation or other low pressure separators for mechanical properties and permeability under varying pretreatment schemes. HFMs were prepared on semi-pilot membrane fabrication system. Novel adopted post-treatment schemes involved soaking in glycerol, magnesium sulphate (MgSO₄), sodium hypochlorite (NaOCl), and isopropanol for different durations. All fibers were characterized for morphology using a scanning electron microscope (SEM), surface roughness using atomic force microscope (AFM), elemental composition by examining Energy Dispersive Spectroscopy (EDS), water contact angle (CA°) and porosity. The performance of the fibers was evaluated for pure water permeation flux (PWF). Post-treatment with MgSO₄ gave the highest both tensile modulus and flux. Assessment of properties and performance revealed comparable results with other organic-inorganic separators, HF or flat. In spite of few reported data on post treatment using MgSO₄ in presence of TEOS, this proves the potential of low cost treatment without negative impact on other membrane properties. The flux is also comparable with hypochlorite which manifests substantial precaution requirements in actual industrial use.The relatively high values of flux/bar for sample treated with TEOS, post treated with MgSO₄ and hypochlorite are 88 and 82 LMH/bar respectively.

• The korean journal of orthodontics
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• v.30 no.1 s.78
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• pp.33-41
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• 2000

Although it is well known that the chincup, used to correct a skeletal class III malocclusion in growing children, reduce the mandibular prognathism by arresting the growth of the mandibular length and rotating the mandible posteroinferiorly, the majority of the studies about chincup is focused on condylar head that plays an Important role in mandibular growth. The aim of this study was to evaluate the morphologic change of the mandibular symphysis where extraoral force is applied directly during chincup treatment. The data lot this study were obtained from lateral cephalometric radiographs of 62 growing children(chincup group:32, control group:30) with mixed dentition who had been accepted lot the orthodontic treatment at Chonbuk National University Dental Hospital. The results were as follows : 1. Symphysis height was increased both in chincup therapy group and control group during treatment. Symphysis depth was decreased or maintained the initial values in chin cup therapy group, whereas increased in control group. Posterior symphysis depth was decreased both in chin cup therapy group and control group, but anterior svmphysis detph was increased in control group, whereas decreased in chincup therapy group. 2. Chin depth and chin curvature were increased in control group, whereas maintained or decreased in chincup therapy group during treatment. Chin angle, menton ang1e and symphysis angle were decreased in control group, whereas increased in chincup therapy group. It suggested that bone deposition in pogonion area that occur normally with mandibular growth was supressed by direct contact of chincup. 3. When growing children wear chincup, symphysis morphology was maintained due to inhibition of forward growth at mandibular symphysis. It may be due to the suppression of bone deposition in anterior part of symphysis.

• Applied Microscopy
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• v.36 no.3
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• pp.141-153
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• 2006

The purpose of this study is to find out how soft contact lens multi-purpose solution (MPS), often used for medical treatment, effects the inhibition on cell growth and research the result of using MPS, suspected to demage eye cells, on rabbit eye's corneal epithelium and endothelium tissue. In this treatise, $ReNu^{(R)}$ (Baush & Lomb, USA), Opti-free $express^{(R)}$ (Alcon, USA), Free-sol $plus^{(R)}$ (Hanamedicon, Korea) had been selected among the MPS. After culturing L929 roil line, cell growth inhibition rate was measured by MTT assay, and by making Hematoxylin and Eosin stain specimen. the morphology was observed by optical microscope. In the In vivo experiment,9 white rabbit eyes (18 eyes) were classified into 3 groups. The experimental group is left eyes (9 eyes) of rabbit, and MPS were dropped; however. the control group, the right eyes (9 eyes), were only used a saline solution without preservatives. After the dropping within the period, the cornea surface of rabbit eyes were stained by Rose bengal and observed. To figure out the changes of the corneal epithelium and endothelium tissue scanning electron microscopy (SEM) has been used. As the result, the rate of cell growth inhibition was 54%. 73% and 36%, respectively. Morphological changes represented that the shape has been changed into oval or round shape and those are not considered as a common formation of L929 cell line. When it comes to staining Rose bengal, each experiment group was stained red which is not shown in controls. The polygonal mosaic pattern of a corneal epithelium was disturbed in the picture taken by SEM; furthermore, the shape of the corneal endothelium was irregular. In conclusion, as we consider antimicrobial effect and the safety on living cells, it is necessary that we should improve concentration of preservatives and study continuously to develop a new preservatives without a toxic effect on the cornea surface.

• Applied Chemistry for Engineering
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• v.21 no.4
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• pp.435-439
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• 2010

Pt-$MoO_3$ electrodes were fabricated on ITO-coated glass by electrodeposition method using 20 mM hydrogen hexachloroplatinate ($H_2PtCl_6$) and 10 mM Mo-peroxo electrolyte. Deposition order was varied, and catalytic activities of synthesized electrodes were compared with that of pure Pt electrode. Scanning Electron Microscopy (SEM) was utilized to examine surface morphology. The crystallinity of synthesized films was analyzed by X-ray Diffraction (XRD), and the oxidation state of both the platinum and molybdenum were determined by X-ray Photoelectron Spectroscopy (XPS) analyses. The catalytic activity and stability for methanol oxidation were measured using cyclic voltammetry (CV) and chronoamperometry (CA) in a mixture of 0.5 M $H_2SO_4$ and 0.5 M $CH_3OH$ aqueous solution. $MoO_3$ electrodeposited on the surface of Pt showed much higher catalytic acitivity and stability than pure Pt electrode due to the good contact between Pt and $MoO_3$.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.256-263
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• 2010

A Crofer 22 APU mesh coated with a conductive ceramic material was developed as an alternative cathode current collector to Ag-based materials for solid oxide fuel cells. $(La_{0.80}Sr_{0.20})_{0.98}MnO_3$ (LSM) layer was deposited onto the Crofer mesh using a spray-coating technique, in an attempt to mitigate the degradation of electrical properties due to surface oxidation at high temperatures. The oxidation experiments at $800^{\circ}C$ in air indicated that the areaspecific resistance (ASR) of the LSM-coated Crofer mesh was strongly dependent on the wire diameter and the contact morphology between mesh and cell. In addition, the post-heat-treatment in $H_2/N_2$ resulted in a reduced thickness of Cr-containing oxide scales at the interface between Crofer mesh and LSM layer, leading to a decreased ASR.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.27 no.2
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• pp.129-134
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• 2001

Since NNK is one of the most abundant tobacco-specific alkaloids and a strong carcinogenic nitrosamine, it has been used for evaluating a potential of carcinogenicity in the animal models. The present study has attempted to examine the potential of carcinogenicity of NNK in human epithelial cells, from which the cell type the most of cancers including oral cancer and nasal cavity cancer are originated. The cellular model used for the study is a human keratinocyte cell system immortalized by Ad12-SV40 hybrid virus. The cellular system has successfully been used for the carcinogenicity studies because of its limitless life span, epithelial morphology and nontumorigenicity. When cells were treated with a variety of NNK concentrations, levels of saturation density and soft agar colony formation were increased in a dose-dependent fashion. Colonies of large cell aggregates were above 5 at the higher doses. The results indicate that exposure of human cells with NNK induced loss of contact inhibition and increases of anchorage independence and cellular adhesion, which are typical characteristics of the neoplatically transformed cells. When cells were exposed with 100uM NNK for 2hr, mRNA levels of IL-1 and PAI-2 were increased in a dose-dependent manner, but expression of TGF- 1 was not affected. While expression of growth regulatory factors were altered with a short-term exposure, there was no alteration of these factors in the NNK-transformed cells. However, mRNA levels of fibronectin were increased both in the short-term treatment and in the transformation. The results suggest that altered expression of extracellular matrix such as fibronectin following short-term exposure might be fixed in the genome and these altered properties be continuously transfered throughout the cell division. Western blot analysis showed a translocation of PKC- from cytosolic fraction to the particulate fraction, indicating a possible role of NNK in the signal transduction pathway. The present study provided an evidence that NNK in the smoking may be associated with epithelial origin cancer such as oral and nasal cavity cancers. In addition, this study suggested that altered expression of extracellular matrix and PKC may play an important role in the carcinogenic mechanism of NNK.

• Journal of the Korean Electrochemical Society
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• v.15 no.2
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• pp.95-100
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• 2012

$LiFePO_4$ is an attractive cathode material due to its low cost, good cyclability and safety. But it has low ionic conductivity and working voltage impose a limitation on its application for commercial products. In order to solve these problems, the iron($Fe^{2+}$)site in $LiFePO_4$ can be substituted with other transition metal ions such as $Mn^{2+}$ in pursuance of increase the working voltage. Also, reducing the size of electrode materials to nanometer scale can improve the power density because of a larger electrode-electrolyte contact area and shorter diffusion lengths for Li ions in crystals. Therefore, we chose electrospinning as a general method to prepare $Li[Fe_{0.9}Mn_{0.1}]PO_4$ to increase the surface area. Also, there have been very a few reports on the synthesis of cathode materials by electrospinning method for Lithium ion batteries. The morphology and nanostructure of the obtained $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers were characterized using scanning electron microscopy(SEM). X-ray diffraction(XRD) measurements were also carried out in order to determine the structure of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ nanofibers. Electrochemical properties of $Li[Fe_{0.9}Mn_{0.1}]PO_4$ were investigated with charge/discharge measurements, electrochemical impedance spectroscopy measurements(EIS).

• Applied Chemistry for Engineering
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• v.29 no.3
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• pp.330-335
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• 2018

A new approach for the fabrication of organic-organic conducting composite thin films using simultaneous co-vaporization vapor phase polymerization (SC-VPP) of two or more monomers that have different polymerization mechanisms (i.e., oxidation-coupling polymerization and radical polymerization) was reported for the first time. In this study, a PEDOT-PSMA composite thin film consisting of poly(3,4-ethylenedioxythiophene)(PEDOT) and poly(styrene-co-maleic anhydride)(PSMA) was prepared by SC-VPP process. The preparation of organic-organic conductive composite thin films was confirmed through FT-IR and $^1H-NMR$ analyses. The surface morphology analysis showed that the surface of PEDOT-PSMA thin film was rougher than that of PEDOT thin film. Therefore, PEDOT-PSMA exhibited lower electrical conductivity than that of PEDOT. But the conductivity can be improved by adding 2-ethyl-4-methyl imidazole as a weak base. The contact angle of PEDOT-PSMA was about $50^{\circ}$, as compared to $62^{\circ}$ for PEDOT. The demonstrated methodology for preparing an organic-organic conductive hybrid thin film is expected to be useful for adjusting intrinsic conductive polymer (ICP)'s surface properties such as mechanical, optical, and roughness properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.642-642
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• 2013

Graphene, two dimensional single layer of carbon atoms, has tremendous attention due to its superior property such as high electron mobility, high thermal conductivity and optical transparency. Especially, chemical vapor deposition (CVD) grown graphene has been used as a promising material for high quality and large-scale graphene film. Unfortunately, although CVD-grown graphene has strong advantages, application of the CVD-grown graphene is limited due to ineffective transfer process that delivers the graphene onto a desired substrate by using polymer support layer such as PMMA(polymethyl methacrylate). The transferred CVD-grown graphene has serious drawback due to remaining polymeric residues generated during transfer process, which induces the poor physical and electrical characteristics by a p-doping effect and impurity scattering. To solve such issue incurred during polymer transfer process of CVD-grown graphene, various approaches including thermal annealing, chemical cleaning, mechanical cleaning have been tried but were not successful in getting rid of polymeric residues. On the other hand, lithographical patterning of graphene is an essential step in any form of microelectronic processing and most of conventional lithographic techniques employ photoresist for the definition of graphene patterns on substrates. But, application of photoresist is undesirable because of the presence of residual polymers that contaminate the graphene surface consistent with the effects generated during transfer process. Therefore, in order to fully utilize the excellent properties of CVD-grown graphene, new approach of transfer and patterning techniques which can avoid polymeric residue problem needs to be developed. In this work, we carried out transfer and patterning process simultaneously with no polymeric residue by using a metal etch mask. The patterned thin gold layer was deposited on CVD-grown graphene instead of photoresists in order to make much cleaner and smoother surface and then transferred onto a desired substrate with PMMA, which does not directly contact with graphene surface. We compare the surface properties and patterning morphology of graphene by scanning electron microscopy (SEM), atomic force microscopy(AFM) and Raman spectroscopy. Comparison with the effect of residual polymer and metal on performance of graphene FET will be discussed.