• Restorative Dentistry and Endodontics
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• v.35 no.6
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• pp.429-435
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• 2010

Objectives: The aim of this study was to investigate average working lengths of Korean posterior teeth and evaluate validity of endodontic file length. Materials and Methods: The endodontic working length of the posterior teeth of 670 Korean patients were measured than each mean value and standard deviation were investigated than the frequency deviation and standard deviation per each length were calculated. Results: Among the canals of premolar, 66.5% of canal length was marked under 20 mm by endodontic working length and 95.4% could be measured under 22 mm and Among the canals of molars, 95.5% of canal length was marked under 20 mm endodontic working length. Conclusions: With the result of measurement of endodontic working length of premolars of Korean, it suggested that 23 mm endodontic file is more proper than the 21 mm and 25 mm file on the market.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.118-121
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• 2007

Bulk metallic glass (BMG)/crystalline composites comprising a copper based BMG alloy and crystalline nickel were produced by means of eloctroless plating of nickel on $Cu_{54}Zr_{22}Ti_{18}Ni_6$ BMG powder and subsequent consolidation using spark plasma sintering. The plastic deformation behavior of BMG/crystalline composites was examined by uniaxial compression test at various temperatures in the supercooled liquid region (SLR) of the BMG alloy. The evolution of strain states during uniaxial compression was tackled by microstructure observations. Deformation temperature played an important role in the deformation behavior of BMG/crystalline composites, which was attributed to a strong temperature dependence of the flow stress of the BMG alloy in the SLR. BMG/crystalline composites deformed homogenously in the temperature range where the flow stress of the BMG alloy was close to that of crystalline nickel. In contrast, inhomogeneous deformation was observed in the temperature range where the flow stress of the BMG alloy largely differs from that of crystalline nickel.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.1
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• pp.20-25
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• 2001

To develop the piezoelectric actuator, the structural, dielectric and piezoelectric properties and electric fieldinduced strain of the ceramics(Pb$\_$1-2/Ba$\_$x/)[Mg$\_$1/2/W$\_$1/2/)$\_$0.03/-Ni$\_$1/3/Nb$\_$2/3/)$\_$0.12/-(Zr$\_$0.5/Ti$\_$0.5/)$\_$0.85/]O$_3$(x=0, 0.01, 0.03, 0.05, 0.07, 0.1) were investigated with the substitution of Ba. The tetragonality of crystal structure and grain size decreased by the substitution of Ba. Curie temperature decreased due to the decrease of the tetragonality, and dielectric constants increased with the substitution of Ba. The coercive field, remnant polarization and electromechanical coupling factor also decreased, whereas the piezoelectric constatns d$\_$33/ and d$\_$31/ were showed the highest value of 430 and 209(x10$\^$-12/C/N), respectively, because of the increase of dielectric constant. The strain induced by 60Hz AC electric field had the maximum value of 204x10$\^$-6/Δℓ/ℓ at the substitution of Ba 3mol%. As the applied electric field approaches to the coercive field, the piezoelectric element is depolarized and the electric field induced strain revealed non-linearity.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.647-653
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• 2020

Stainless steel is used commonly in nuclear applications for shielding radiation, so in this study, three different types of new stainless steel samples were designed and developed. New stainless steel compound ratios were determined by using Monte Carlo Simulation program Geant 4 code. In the sample production, iron (Fe), nickel (Ni), chromium (Cr), silicium (Si), sulphur (S), carbon (C), molybdenum (Mo), manganese (Mn), wolfram (W), rhenium (Re), titanium (Ti) and vanadium (V), powder materials were used with powder metallurgy method. Total macroscopic cross sections, mean free path and transmission number were calculated for the fast neutron radiation shielding by using (Geant 4) code. In addition to neutron shielding, the gamma absorption parameters such as mass attenuation coefficients (MACs) and half value layer (HVL) were calculated using Win-XCOM software. Sulfuric acid abrasion and compressive strength tests were carried out and all samples showed good resistance to acid wear and pressure force. The neutron equivalent dose was measured using an average 4.5 MeV energy fast neutron source. Results were compared to 316LN type stainless steel, which commonly used in shielding radiation. New stainless steel samples were found to absorb neutron better than 316LN stainless steel at both low and high temperatures.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.52-59
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• 2002

The thermo-mechanical characteristics of high temperature NITINOL shape memory alloy were evaluated using DSC with small samples and DMA with three-point bending specimens. The shape memory alloy of 54.4Ni/45.5Ti wt.% was used so that the phase transformation temperatures were in the range of 50~11$0^{\circ}C$. Two types of sample were tested in the experiments corresponding to as-received and annealed conditions. Simple beam bending theory was used to calculate the dynamic moduli of the shape memory alloy. According to the results, a large discrepancy in transformation temperatures was found between DSC and DMA techniques. Annealing treatment was found to suppress the R-phase transformation during cooling and the secondary plateau in the austenite transformation. Such a heat treatment was also significantly influenced to raise the transformation temperatures and the moduli of the shape memory alloy.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.148-148
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• 2011

일반적으로 LED 제작에 사용되는 c-plane GaN는 c축 방향으로 발생하는 분극의 영향을 받게 된다. 분극은 LED내 양자우물의 밴드를 기울게 하여 그 결과 전자와 홀의 재결합 확률을 감소시켜 낮은 내부양자효율을 가지게 된다. 이러한 문제를 해결하기 위한 여러 가지 방법들이 제시되었는데 그 중에서도 특히 a-plane 혹은 m-plane면과 같은 무분극 면을 사용하는 GaN LED가 주목받고 있다. 그 이유는 무분극 면은 분극이 발생하는 c축과 수직이기 때문에 분극의 영향을 받지 않아 높은 내부 양자효율을 가질수 있다. 본 연구에서는 MOCVD 장비를 사용하여 2인치 r-plane 사파이어 기판위에 3um두께의 a-plane GaN을 성장하였다. 그위에 2um정도로 Si을 도핑하여 n-type GaN 형성한후 단일 양자우물, 그리고 Mg을 도핑하여 p-type GaN을 성장하였다. 장파장대역의 a-plane LED의 특성을 알아보기 위해서 양자우물 형성시 In의 조성비를 높였다. 일반적인 포토리소그래피 공정과 Dry etching 공정을 사용하여 메사구조를 형성하였으며 Ti/Al/Pt/Au와 Ni/Au를 각각 n-type과 p-type의 전극 물질로 사용하였다. 제작된 LED의 특성을 파악하기 위해서 인가전류를 0부터 100mA까지 출력 스펙트럼을 측정하였으며 orange대역의 파장을 갖는 LED를 얻었다. 인가전류별 Peak 파장의 변화와 반측폭의 변화를 파악하여 장파장 대역의 a-plane LED의 특성을 확인하였다.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1444-1445
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• 2006

Carbon nanotubes (CNTs) are grown on TiN-Coated silicon substrates at $700^{\circ}C$ using an ICP-CVD method. Ni catalysts for CNT growth are formed using an RF magnetron sputtering system. Post-treatment using hydrogen ions has been performed in the ICP reactor by varying the treatment period. The characterization using various techniques, such as FESEM, HRTEM, and Raman spectroscopy, show that the physical dimension as well as the crystal quality of CNTs are changed by the post-treatment process. It is also seen that the hydrogen ion-bombardment may change the surface structure of CNTs, which may lead to produce better electron emission properties. The physical reason for all the measured data obtained are discussed to establish the relationship between the structural property and the electron emission characteristic of CNTs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.847-851
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• 2000

In this study, contour-vibration-mode Pb($Ni_{1/2}$,$W_{1/2}$)$O_3$-Pb(Zr,Ti)$O_3$ piezoelectric transformers for driving a 28W(T5) fluorescent lamp were fabricated to the modified filter structure with ring and dot electrodes which has been developed for application in 455kHz AM radios. The piezoelectric transformers were fabricated to the size of $31.5$\times$31.5$\times$2.5$mm^3$ with the variations of ring/dot electrode area ratio. Driving of piezoelectric transformer was carried out with input region for the ring electrode and output region for the dot electrode. The electrical properties and characteristic temperature rises caused by the vibration were measured at various load resistances. A 28 W fluorescent lamp, T5, was successfully driven by the fabricated transformer. The transformer with ring/dot electrode area ratio of 1.83 exhibited the best properties in terms of output power, efficiency and characteristic temperature rise, 30.95 W, 97.57% and8.3$^{\circ}C$ respectively.

• 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.

• Current Research on Agriculture and Life Sciences
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• v.30 no.2
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• pp.76-81
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• 2012

In this study the natural colorant was extracted from black bean seed coat in aqueous solution and used to dye silk and cotton fabrics. To obtain the optimal dyeing conditions it was examined at various dyeing condition (temperature, pH, time and liquor ratio). The dyeing behavior and the depths of shade which were evaluated in terms of K/S and CIELAB color difference values of the dyed and mordanted fabrics were also investigated. The dyeing fastness evaluated standard light and wash fastness tests. The obtained results were as follows ; The most K/S value of silk and cotton fabrics were obtained when the pH was 4.0 and 4.8, respectively and it increased slightly with dyeing time passes when the dyeing temperatures were at $40^{\circ}C$ and $60^{\circ}C$ but, it increased at $80^{\circ}C$. The color of silk fabrics changed from yellowish red to yellow at only Fe mordanting among various mordanting. Sn and Ti mordanting of silk fabric and only Ni mordanting of cotton fabric increased the $L^*$ values, but the others decreased. The light fastness of silk fabrics showed 4-6 grade without mordant, 4-5 grade with Al, 3-4 grade with Cu and Sn, and 2-3 grade with Fe as mordant, and that of cotton fabrics showed 1-2 grade without mordant, 2-3 grade with Fe, 2 grade with Cu, 1-2 grade with Al and Sn as mordants. All mordanting coluld not improve the light fastness of fabrics. Washing fastness(fade) of silk fabrics showed 2 grade without mordants and 2-3 grade with mordants and those of cotton fabrics showed 4 grade with Cu, 3 grade without mordant and with Al, Sn and Fe. All of the washing fastness(stain) of both fabrics showed 4-5 grade.