• Progress in Superconductivity and Cryogenics
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• v.2 no.2
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• pp.15-19
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• 2000

The stability of variable cross-sectional area HTS current lead is considered. The cross-sectional area is varied to have a constant safety factor which is defined as the ratio of operating current and critical current of superconductor. As the constant area HTS lead, the variable cross-sectional area HTS lead also has three steady states above the bifurcation point and only one steady state below the bifurcation point. The temperature profiles and current sharing ratios for each steady state are calculated. The heat dissipation into cryogenic system for super-conducting, intermediate, and upper states are compared. For Bi-2333 sheathed with silver-gold alloy 2m length of current lead, and the maximum temperature of upper state seems to be burn-out free below 5m length.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.51.2-51.2
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• 2010

본 연구에서 우리는 casting기법을 통해 생산된 각종 귀금속 제품의 결함 및 강도 향상을 위해 다양한 조건에서 열처리를 실시하였다. casting시 일정하지 못한 온도로 냉각되어 생성된 시료내부의 결함들을 제거하기 위해 진공분위기에서 각 온도 및 시간별 조건을 달리하여 강도 및 grain의 변화를 관찰하였다. 모든 시료는 열처리 후 불안정한 grain 들이 안정화되어 경도 및 강도가 향상되는 경향을 보였으나, 특정 온도 및 시간에서는 오히려 경도가 감소하는 경향을 나타내었다. 열처리 후 모든 시료의 표면특성변화를 관찰하기 위해 OM (Optical microscope), SEM (scanning electron microscope)을 통해 분석하였고, Vickers경도계를 통해 경도 및 강도 변화를 관찰하였다. 또한 XRF(X-ray fluorescence) 분석을 통해 원소별 합금비를 정량적으로 분석하였다. 본 연구 결과를 통해 casting기법으로 생산된 귀금속 제품의 강도, 경도, 표면특성을 향상시킬 수 있는 최적조건을 얻을 수 있었다.

• The Journal of the Korean dental association
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• v.11 no.5
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• pp.353-358
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• 1973

The purpose of this study was to determine the gingival response to the various restorations for 3 weeks, 5 weeks and 8 weeks respectively after they had been inserted in 42 tooth of 5dogs. The histopathological observation was also performed to evaluate the effect of the variuos restorations on gingival tissue. They inclued gold, copper and nickel-chrome alloy. The following findings were obtained. 1. The gingivae adjacent to the well adapted and polished restorations and their margins with a level of gingival crest were grossly and histopathologically found no specific changes. 2. The gingive adjacent to the ill fitting and unpolished restorations and their margins with subgingival extension of 1 to 1.5mm were not grossly found any changes but hitopathologically, the inflammatory changes. 3. Thee wee no obvious difference in gingival response among the various alloys in histopathological observation.

• Journal of the Korean institute of surface engineering
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• v.35 no.2
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• pp.93-100
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• 2002

To better understand the codeposition mechanism of phosphorous, surface pH and potential of cathode were measured during electrodeposition of Ni-P alloys. The pH of cathode surface was measured using a flat-bottom glass pH electrode and a 500 mesh gold gauze as cathode. The cathode surface pH was increased with increasing the current density and always higher than the pH in the bulk solution. As a result of overplotting the surface pH and cathode potential on the Pourbaix diagram, it was found that cathode surface shift to the domain of predominant of $H_2$$PO3$-or $H_2$$PO_2$-. Additionally, new deposition mechanism was suggested that $H_2$ $PO_2$- and $H_2$$PO_3$- play important roles in the deposition reaction of Ni-P alloys.

• Journal of the Korean institute of surface engineering
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• v.55 no.5
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• pp.299-307
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• 2022

Gold plating is used as a coating of connector in printed circuit boards, ceramic integrated circuit packages, semiconductor devices and so on, because the film has excellent electric conductivity, solderability and chemical properties such as durability to acid and other chemicals. In most cases, internal connection between device and package and external terminals for connecting packaging and printed circuit board are electroless Ni-P plating followed by immersion Au plating (ENIG) to ensure connection reliability. The deposition behavior and film properties of electroless Au plating are affected by P content, grain size and mixed impurity components in the electroless Ni-P alloy film used as the underlayer plating. In this study, the correlation between electroless nickel plating used as a underlayer layer and cyanide-free electroless Au plating using thiomalic acid as a complexing agent and aminoethanethiol as a reducing agent was investigated.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.389-403
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• 2010

Titanium and gold-alloy abutments have been used for a long-time in the clinical situations, but the use of zirconia abutments also increased. This study was designed to compare and evaluate the microgap differences according to types of abutment and dynamic loading. Titanium abutment, zirconia abutment and gold-alloy abutment (UCLA plastic) were connected into titanium implants of external hexagonal structure US II ${\phi}$ $3.75{\times}11.5$ mm (Osstem Co., Seoul, Korea) with the tightening torque of 30 Ncm. A sine type dynamic loading of 25-250 N and $30^{\circ}$ inclination from long axis was applied for $10^5$ times. Using the SEM both before and after the loadings, implant-abutment interfaces were analyzed on the labial, palatal, mesial and distal surface. The microgaps before and after the loading were compared, no statistically significant difference was observed caused by the dynamic loading on the labial, palatal, mesial or distal surface. Statistically significant difference was observed between UCLA and titanium group and between UCLA and zirconia group on both before and after the loading(p<0.05). No statistically significant difference was found between titanium and zirconia group. Loadings for $10^5$ times did not show significant effect to the microgaps between implants and abutments.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.5
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• pp.463-476
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• 2001

Since the treatment of edentulous patients with osseointegrated implant was first introduced more than 30 years ago, implant therapy has become one of the most important dental treatment modalities today. Based on the previous experience and knowledge, $Br{\aa}nemark\;Novum^{(R)}$ protocol was introduced with the concept of simplifying surgical and prosthetic technique and reducing healing time recently. This protocol recommends the installation of three 5mm wide diameter futures in anterior mandible and the prefabricated titanium bars for superstructure fabrication. This study was designed to analyze the stress distribution at fixture and superstructure area according to changes of fixture number, diameter and superstructure materials. Four 3-dimensional finite element models were fabricated. Model 1 - 5 standard fixtures (13mm long and 3.75mm in diameter) & superstructure consisted of type IV gold alloy and resin Model 2- 3 wide diameter fixtures (13mm long and 5.0mm in diameter) & superstructure consisted of type IV gold alloy and resin Model 3-3 wide diameter fixtures (13mm long and 5.0mm in diameter) & superstructure consisted of titanium and resin Model 4-3 wide diameter fixtures (13mm long and 5.0mm in diameter) & superstructure consisted of titanium and porcelain A 150N occlusal force was applied on the 1st molar of each model in 3 directions - vertical($90^{\circ}$), horizontal($0^{\circ}$) and oblique($120^{\circ}$). After analyzing the stresses and displacements, following results were obtained. 1. There were no significant difference in stress distribution among experimental models. 2. Model 2, 3, 4 showed less amount of compressive stress than that of model 1. However, tensile stress was similar. 3. Veneer material with a high modulus of elasticity demonstrated less stress accumulation in the superstructure. Within the limites of this study, $Br{\aa}nemark\;Novum^{(R)}$ protocol demonstrated comparable biomechanical properties to conventional protocol.

• The Journal of Advanced Prosthodontics
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• v.10 no.3
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• pp.184-190
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• 2018

PURPOSE. To analyze stress distribution in premolars restored with inlays or onlays using various materials. MATERIALS AND METHODS. Three-dimensional maxillary premolar models of abutments were designed to include the following: 1) inlay with O cavity (O group), 2) inlay with MO cavity (MO group), 3) inlay with MOD cavity (MOD group), and 4) onlay (ONLAY group). A restoration of each inlay or onlay cavity was simulated using gold alloy, e.max ceramic, or composite resin for restoration. To simulate masticatory forces, a total of 140 N static axial force was applied onto the tooth at the occlusal contact areas. A finite element analysis was performed to predict the magnitude and pattern of stresses generated by occlusal loading. RESULTS. Maximum von Mises stress values generated in the abutment teeth of the ONLAY group were ranged from 26.1 to 26.8 MPa, which were significantly lower than those of inlay groups (O group: 260.3-260.7 MPa; MO group: 252.1-262.4 MPa; MOD group: 281.4-298.8 MPa). Maximum von Mises stresses generated with ceramic, gold, and composite restorations were 280.1, 269.9, and 286.6 MPa, respectively, in the MOD group. They were 252.2, 248.0, 255.1 MPa, respectively, in the ONLAY group. CONCLUSION. The onlay design (ONLAY group) protected tooth structures more effectively than inlay designs (O, MO, and MOD groups). However, stress magnitudes in restorations with various dental materials exhibited no significant difference among groups (O, MO, MOD, ONLAY).

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.2
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• pp.92-98
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• 2012

Purpose: The aim of this study was to evaluate the effects of different abutment materials on abutment screw loosening and settling-down effect in conical connection type implant system. Materials and methods: Three types of abutment, cementation, gold UCLA, and metal UCLA abutment were used. Two UCLA groups were fabricated in a similar pattern to cementation abutment. Type III gold alloy and Nickel-Chromium alloy was used for casting gold UCLA abutment and metal UCLA abutment, respectively. Fixture and abutment were tightened to 30 Ncm by using digital torque controller and re-tightening was conducted with same force after 10 minutes. Digital torque gauge was used to measure loosening torque and fixture/abutment length was measured by digital micrometer. Dynamic loads between 25 N and 250 N were applied with $0^{\circ}$ angle to the abutment axis. After loading, fixture/abutment length was re-measured and amount of settlement was calculated. Loosening torque value was also measured for comparison Results: All three groups showed significant differences of length when comparing before and after loading, but there was no significant difference of settling amount in all groups. Loosening torque values were significantly decreased when comparing before and after loading in all groups($P$<.05). However, there was no significant difference in loss of loosening torque values when compared to groups. Conclusion: In internal conical connection type implants, dynamic load affected on settlement and loosening torque of implant, but there was no differences between abutments materials. Likewise gold UCLA abutment, metal UCLA abutment might be able to withstand functional load.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.3
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• pp.45-54
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• 2000

The effect of electropolishing far stamped leadframe on the removal of the edge burr and residual stress relief was examined. The present study showed that the electropolishing could be used for enhanced surface quality of stamped leadframes. The electropolishing was performed at the condition of 60% phosphoric acid electrolyte, 5 ampere of current and 3 cm electrode gap at $70^{\circ}C$ for 2 minutes for Alloy42 type leadframe, and $50^{\circ}C$ for 1.5 minutes for C-194 type leadframe. The FWHM values from X-ray diffraction showed that residual stress of electropolished leadframe recovered to the level of as-received raw materials and surface roughness measured by using AFM tuned out to be improved by 0.079 $\mu\textrm{m}$ and 0.014 $\mu\textrm{m}$ ($R_{rms}$) far alloy 42 and C-194 type leadframes, respectively. The plated thickness using XRF showed the improved uniformity in thickness variation by 0.4~0.5 $\mu\textrm{m}$ and grain growth, which is favorable for interface adhesion, was also observed from the bake test samples. We could certify dimensional stability of leadframe with inspection by means of 3D-topography and hardness measurements.