• Journal of Periodontal and Implant Science
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• v.27 no.2
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• pp.317-328
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• 1997

Since laser therapy has been applied to dentistry, many dental practitioners are very interested in laser therapy on various intraoral soft tissue lesions including gingival hyperplasia and aphthous ulcer. The purpose of the present study was to determine the therapeutic effect and the harmful effect of a pulsed-Nd:YAG laser irradiation on human gingival tissue. In twenty periodontal patients with gingival enlargement, the facial gingival surface of maxillary anterior teeth was randomly irradiated at various power of 1.0W(100mJ, 10Hz), 3.0W(100mJ, 30Hz) and 6.0W(l50mJ, 40Hz) for 60 seconds by contact delivery of a pulsed-Nd:YAG laser(EN.EL.EN060, Italy). Immediately after laser irradiation, the gingival tissues were surgically excised and prepared in size of 1mm3. Subsequently the specimens were processed for prefixation and postfixation, embedded with epon mixture, sectioned in $1{\mu}$ thickness, stained with uranyl acetate and lead citrate, and observed under transmission electron microscope(JEM 100 CXII). Following findings were observed; l. In the gingival specimens irradiated with l.OW power, widening of intercelluar space and minute vesicle formation along the widened intercellular space were noted at the epithelial cells adjacent to irradiated area. 2. In the gingival specimens irradiated with 3.0W power, the disruption of cellular membrane, aggregation of cytoplasm, and loss of intercellular space were observed at the epithelial cells adjacent to irradiated area. 3. In the gingival specimens irradiated with 6.0W power, the disruption of nuclear and cellular membrane was observed at the epithelial cells adjacent to irradiated area. The ultrastructural findings of this study suggest that surgical application of a pulsed-Nd:YAG laser on human gingival tissue may lead somewhat delayed wound healing due to damage of epithelial cells adjacent to irradiated area.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.373-388
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• 2010

Fracture causes serious problems in many instance of prosthetic failures. But it is hard to find the definite causes when fractures occur. Fractography encompasses the examination of fracture surfaces that contain features resulting from the interaction of the advancing crack with the microstructure of the material and the stress fields. All fractured specimens(implant retaining screw) retrieved from Gangneung-Wonju national university dental hospital for 3 years(from 2007 to 2009). After pretreatment of samples, the scanning electon microscope were used for surface examination and fracture analysis. In case of most of the fractured specimens, fracture took place by fatigue fracture and fractured surface represents fatigue striation. Fatigue striation indicate the progression of the crack front under cyclic loading, are characteristic of stage 2 crack growth. The site of crack initiation and stage 1 crack growth were not easily identified in any of the failure, presumably because of the complex microstructural features of the polycrystalline sample. In case of fractured by overload, dimpled or cleavage surface were observed. Using the interpretation of characteristic markings(ratchet mark, fatigue striation, dimple, cleavage et al) in fracture surfaces, failure events containing the crack origin, crack propagation, material deficiency could be understand. Using the interpretation of characteristic markings in fracture surfaces, cause and mechanism of fractures could be analyzed.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.214-219
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• 1997

The mechanical seals, which are installed in rotating machines like pump and compressor, are generally used as sealing devices in the many fields of industries. The failure of mechanical seals such as leakage, crack, breakage, fast and severe wear, excessive torque, and squeaking results in big problems. To identify abnormal phenomena on mechanical seals and to propose the proper monitoring parameter for the failure of mechanical seals, sliding wear experiments were conducted. Acoustic emission, torque, and temperature were measured during experiments. Optical microstructure was observed for the wear processing after every 10 minute sliding at rotation speed of 1750 rpm and scanning electron microscopy was also observed. Except for the initial part of every experiment, the variation of acoustic emission was well coincided with torque variation during the experiments. This study concludes that acoustic emission and torque are proper monitoring parameters for the failure of mechanical seals. The intensity of acoustic emission signals is measured in root mean square voltage. Temperature of sealing face will be used as a parallel parameter for increasing the reliability of monitoring system.

• Asian Pacific Journal of Cancer Prevention
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• v.14 no.10
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• pp.6007-6012
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• 2013

ANXA2, a member of the annexin family, is overexpressed and plays important roles in tumor development. However, the significance of ANXA2 expression in gastric carcinoma has not been clarified.To elucidate its roles in growth of gastric cancer, ANXA2 expression in SGC-7901 cells was inhibited with a designated siRNA, then cell proliferation, cell cycling, apoptosis and motility were determined by MTT assay, flow cytometry, Hoechst 33342 staining and wound healing assay, respectively. To further assess the behavior of ANXA2 deleted SGC-7901 cells, changes of microstructures were observed under fluorescence microscopy, laser scanning confocal microscopy and electron microscopy. We found that inhibition of ANXA2 expression caused cell proliferation to decrease significantly with G1 arrest, motility to be reduced with changes in pseudopodia/filopodia structure and F-actin and ${\beta}$-tubulin expression, and apoptosis to be enhanced albeit without significance. At the same time, ANXA2 deletion resulted in fewer pseudopodia/filopodia, non-stained areas were increased, contact inhibition among cells reappeared, and expression of F-actin and ${\beta}$-tubulin was decreased, with induction of polymerized disassembled forms. Taken together, these data suggest that ANXA2 overexpression is important to maintain the malignancy of cancer cells, and this member of the annexin family has potential to be considered as a target for the gene therapy of gastric carcinoma.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.877-885
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• 2013

A seawater pipe of the engine room in the ships is being surrounded with severely corrosive environments caused by fast flowing of the seawater, containing aggressive chloride ion and high conductivity etc.. Therefore, the leakage of the seawater from its pipe have been often occurred due to its local corrosion by aggressive chloride ions. Subsequently, its leakage area is usually welded by AC shielded metal arc welding with various electrodes. In this study, when the sea water pipe is welded with several types of electrodes such as E4301, E4311, E4313 and E4316, a difference of the corrosion resistance on the welding metal zones was investigated using an electrochemical method, observing microstructure, measuring polarization behaviors and hardness. The weld metal zone welded with E4313 electrode exhibited the lowest value of hardness compared to other weld metal zones. In addition, its zone indicated also the best corrosion resistance than those of other weld metal zones. Furthermore, all of the weld metal zones revealed a relatively better corrosion resistance than those of the base metal zones. and also showed higher hardness than the base metal zones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1421-1426
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• 2014

To improve the inherent safety of the sodium-cooled fast reactor (SFR), the supercritical $CO_2$ ($S-CO_2$) Brayton cycle is being considered as an alternative power conversion system to steam the Rankine cycle. In the $S-CO_2$ system, a PCHE (printed circuit heat exchanger) is being considered. In this type of heat exchangers, diffusion bonding is used for joining the thin plates. In this study, the diffusion bonding characteristics of various austenitic alloys were evaluated. The tensile properties were measured at temperatures starting from the room temperature up to $650^{\circ}C$. For the 316H and 347H types of stainless steel, the tensile ductility was well maintained up to $550^{\circ}C$. However, the Incoloy 800HT showed lower strength and ductility at all temperatures. The microstructure near the bond line was examined to understand the reason for the loss of ductility at high temperatures.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.49 no.3
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• pp.301-309
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• 2016

To facilitate the effective use of butter clam shell as a natural calcium resource, we determined the optimal conditions for calcium lactate (BCCL) preparation with high solubility using response surface methodology (RSM). The polynomial models developed by RSM for pH, solubility and yield were highly effective in describing the relationships between factors (P<0.05). Increased molar ratios of calcined powder (BCCP) from butter clam shell led to reduced solubility, yield, color values and overall quality. The critical values of multiple response optimization to independent variables were 1.75 M and 0.94 M for lactic acid and BCCP, respectively. The actual values (pH 7.23, 97.42% for solubility and 423.22% for yield) under optimization conditions were similar to the predicted values. White indices of BCCLs were in the range of 86.70–90.86. Therefore, organic acid treatment improved color value. The buffering capacity of BCCLs was strong, at pH 2.82 to 3.80, upon the addition of less than 2 mL of 1 N HCl. The calcium content and solubility of BCCLs were 6.2–16.7 g/100 g and 93.6-98.5%, respectively. Fourier transform analysis of infrared spectroscopy data identified BCCL as calcium lactate pentahydrate, and the analysis of microstructure by field emission scanning electron microscopy revealed an irregular form.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.6
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• pp.493-498
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• 2016

In the present study, graphene oxide based polyurethane foams were manufactured as a part of the development process of mechanically strengthened polyurethane foam insulation material. This material is used in a liquefied natural gas carrier cargo containment system. The temperature of the containment system is $-163^{\circ}C$. First, graphene oxide was synthesized using the Hummers' method, and it was supplemented into polyol-isocyanate reagent by considering a different amount of graphene oxide weight percent. Then, a bulk form of graphene-oxide-polyurethane foam was manufactured. In order to investigate the cell stability of the graphene-oxide-polyurethane foam, its microstructural morphology was observed, and the effect of graphene oxide on microstructure of the polyurethane foam was investigated. In addition, the compressive strength of graphene-oxide-polyurethane foam was measured at ambient and cryogenic temperatures. The cryogenic tests were conducted in a cryogenic chamber equipped with universal testing machine to investigate mechanical and failure characteristics of the graphene-oxide-polyurethane foam. The results revealed that the additions of graphene oxide enhanced the mechanical characteristics of polyurethane foam. However, cell stability and mechanical strength of graphene-oxide-polyurethane foam decreased as the weight percent of graphene oxide was increased.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.327.1-327.1
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• 2014

Nitrides-on-silicon structures are considered to be an excellent candidate for unique design architectures and creating devices for high-power applications. Therefore, a lot of effort has been concentrating on growing high-quality III-nitrides on Si substrates, mostly Si(111) and Si(001) substrates. However, there are several fundamental problems in the growth of nitride compound semiconductors on silicon. First, the large difference in lattice constants and thermal expansion coefficients will lead to misfit dislocation and stress in the epitaxial films. Second, the growth of polar compounds on a non-polar substrate can lead to antiphase domains or other defective structures. Even though the lattice mismatches are reached to 16.9 % to GaN and 19 % to AlN and a number of dislocations are originated, Si(111) has been selected as the substrate for the epitaxial growth of nitrides because it is always favored due to its three-fold symmetry at the surface, which gives a good rotational matching for the six-fold symmetry of the wurtzite structure of nitrides. Also, Si(001) has been used for the growth of nitrides due to a possible integration of nitride devices with silicon technology despite a four-fold symmetry and a surface reconstruction. Moreover, Si(110), one of surface orientations used in the silicon technology, begins to attract attention as a substrate for the epitaxial growth of nitrides due to an interesting interface structure. In this system, the close lattice match along the [-1100]AlN/[001]Si direction promotes the faster growth along a particular crystal orientation. However, there are insufficient until now on the studies for the growth of nitride compound semiconductors on Si(110) substrate from a microstructural point of view. In this work, the microstructural properties of nitride thin layers grown on Si(110) have been characterized using various TEM techniques. The main purpose of this study was to understand the atomic structure and the strain behavior of III-nitrides grown on Si(110) substrate by molecular beam epitaxy (MBE). Insight gained at the microscopic level regarding how thin layer grows at the interface is essential for the growth of high quality thin films for various applications.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.654-660
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• 2010

The influences of Na and K content on the crystal phase, the microstructure and the electrical property of $BaTiO_3$-based thermistors was found to show typical PTC effects. The crystal phase of powder calcined at $1000^{\circ}C$ for 4hrs showed a single phase with $BaTiO_3$, and the crystal structure was transformed from tetragonal to cubic phase according to added amounts of Na and K. In XRD results at $43^{\circ}\sim47^{\circ}$, the $(Ba_{0.858}Na_{0.071}K_{0.071})(Ti_{0.9985}Nb_{0.0015})O_{3-\delta}$ showed (002) and (200) peaks but the $(Ba_{0.762}Na_{0.119}K_{0.119})(Ti_{0.9975}Nb_{0.0025})O_{3-\delta}$ showed (002), (020) and (200) peaks. In sintered bodies, those calcined at $600^{\circ}C$ rather than at $1000^{\circ}C$ were dense, and for certain amounts of Na and K showed rapid decreases in grain size. In relative permittivity, the curie temperature due to the transformation of ferroelectric phase rose with added Na and K but decreased in terms of relative permittivity. In the result of the R-T curve, the sintered bodies have curie temperatures of about $140^{\circ}C$ and the resistivity of sintered bodies have scores of $\Omega{\cdot}cm$; the jump order of sintered bodies was shown to be more than $10^4$ in powder calcined at $1000^{\circ}C$.