• The korean journal of orthodontics
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• v.28 no.2 s.67
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• pp.329-341
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• 1998

Sterilization has received much attention in orthodontic practices over the past several years. The present study was undertaken to investigate the effects of sterilization on the physical properties of orthodontic pliers-AEZ, Unitek, and Dentronix ligature cutters. This study was designed to examine the tips of ligature cutters before and after 200 and 400 sterilization cycles using the Bowmar RHT-1000, the Dentronix DDS-5000, and the Eschmann SES-2000. The tip surface and the fracture surface were observed with a scanning electron microscope. The microstructure was observed with an optical microscope. The hardness test was carried out with the mic개-Vickers hardness tester and the Rockwell C Scale hardness tester. The chemical composition was analyzed by energy dispersive X-ray spectrometer. The results of this study were as follows : 1. The number and the size of corrosion products on the tip surface and the proportion of cleavage planes in fractured specimen increased, but the hardness of the tip decreased in proportion to sterilization cycles. From these observations, it was considered that mechanical properities decreased in proportion to sterilization cycles. 2. The number and the size of chromium carbides increased in proportion to sterilization cycles. Coarse microstructure decreased mechanical properities. 3. The AEZ and Unitek ligature cutters were Fe-Cr stainless steels, but the Dentronix ligature cutter was Co-Cr alloy. There were many differences among manufactures, but the chemical composition was .not changed after sterilization cycles. 4. The tip edge of ligature cutter used in a clinic revealed microcracks with the SEM observation. Clinical experience confirmed that ligature cutters were gradually degraded by sterilization.

• Economic and Environmental Geology
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• v.31 no.3
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• pp.185-199
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• 1998

Hydrogeochemical and environmental isotope studies were undertaken for various kinds of water samples collected in 1995-1996 from the Bugok geothermal area. Physicochemical data indicate the occurrence of three distinct groups of natural water: Group I ($Na-S0_4$ type water with high temperatures up to $77^{\circ}C$, occurring from the central part of the geothermal area), Group II (warm $Na-HCO_{3}-SO_{4}$ type water, occurring from peripheral sites), Group III ($Ca-HCO_3$ type water, occurring as surface waters and/or shallow cold groundwaters). The Group I waters are further divided into two SUbtypes: Subgroup Ia and Subgroup lb. The general order of increasing degrees of hydrogeochemical evolution (due to the degrees of water-rock interaction) is: Group III$\rightarrow$Group II$\rightarrow$Group I. The Group II and III waters show smaller degrees of interaction with rocks (largely calcite and Na-plagioclase), whereas the Group I waters record the stronger interaction with plagioclase, K-feldspar, mica, chlorite and pyrite. The concentration and sulfur isotope composition of dissolved sulfate appear as a key parameter to understand the origin and evolution of geothermal waters. The sulfate was derived not only from oxidation of sedimentary pyrites in surrounding rocks (especially for the Subgroup Ib waters) but also from magmatic hydrothermal pyrites occurring in restricted fracture channels which extend down to a deep geothermal reservoir (typically for the Subgroup Ia waters). It is shown that the applicability of alkaliion geothermometer calculations for these waters is hampered by several processes (especially the mixing with Mg-rich near-surface waters) that modify the chemical composition. However, the multi-component mineral/water equilibria calculation and available fluid inclusion data indicate that geothermal waters of the Bugok area reach temperatures around $125^{\circ}C$ at deep geothermal reservoir (possibly a cooling pluton). Environmental isotope data (oxygen-18, deuterium and tritium) indicate the origin of all groups of waters from diverse meteoric waters. The Subgroup Ia waters are typically lower in O-H isotope values and tritium content, indicating their derivation from distinct meteoric waters. Combined with tritium isotope data, the Subgroup Ia waters likely represent the older (at least 45 years old) meteoric waters circuated down to the deep geothermal reservoir and record the lesser degrees of mixing with near-surface waters. We propose a model for the genesis and evolution of sulfate-rich geothermal waters.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.3
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• pp.298-307
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• 2010

The purpose of this study was to assess the effect on oxygen inhibition layer(OIL) for the interfacial bonding between resin composite layers, including shear bond strength, fracture modes and degree of conversion. The first layer of specimen was filled with Z-250(shade A3) and was cured for 40s. The second layer of specimen was filled with same composite(shade A1) and was cured for 40s. The first layer of specimens for each group were prepared by methods as followings. Control(curing in atmospheric air), Group1(curing against Mylar strip), Group2(scrubbed with a acetone-soaked cotton), Group3(using Tescera light cup), Group4(using Tescera heat cup), Group5(stored in disti1led water for 30days at $37^{\circ}C$), Group6 (using bonding agent). The results were as follows: 1. There was no statistically significant different shear bond strength between control and group 1(p>0.05). 2. Group 2 showed significantly lower shear bond strength than control and group 1(p<0.05). 3. The observation of the fracture surface leads to the evidence that a major difference occurs in the case of control, group1 and group 3 samples which break mainly cohesively while the other groups break in majority adhesively. 4. The results of FTIR showed that the degree of conversion was the highest in group 2 and the lowest in control group(p<0.05). It can be concluded that an OIL is not necessary for bonding with composite resin. But if a reduced critical amount of the unreacted monomer is present, it was detrimental to bonding additional layers of composite. Further study, such as the quantitative analysis of the unreacted monomer are required.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.171-177
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• 2001

The thermal and mechanical properties of amorphous Z $r_{62-x}$N $i_{10}$C $u_{20}$A $l_{8}$ $Ti_{x}$ (x=3, 6, 9at%) alloys were investigated. The crystallization process was confirmed as amorphous longrightarrow amorphous + Z $r_2$A $l_3$+ Zr + (Ni,Ti) longrightarrow Z $r_2$Cu + Al + (Ni,Ti) for 3at%Ti, amorphous longrightarrow amorphous + Al longrightarrow $Al_2$Ti + NiZr + CuTi for 6at%Ti and amorphous longrightarrow amorphous + Zr + Al longrightarrow Zr + $Al_2$Zr + Al $Ti_3$+ CuTi for 9at%Ti. lickers hardness ( $H_{v}$ ) increased with increasing volume fraction( $V_{f}$ ) of pricipitates for all concerned compositions. Tensile fracture strength ($\sigma_{f}$ ) showed a maximum value 1219MPa at $V_{f}$ = 38% for 3at%Ti, 1203MPa at $V_{f}$ = 2% for 6at%Ti and 1350MPa at $V_{f}$ = 5% for 9at%Ti. The $\sigma_{f}$ was rapidly decreased after showing the maximum value. The $V_{f}$ corresponding to rapidly decreased $\sigma_{f}$ coincided with the $V_{f}$ transited from ductile to brittle fracture surface.ace.

• Restorative Dentistry and Endodontics
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• v.29 no.2
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• pp.170-176
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• 2004

Objectives : In the unique metal iris method. the developing interfacial gap at the cavity floor resulting from the cavity wall property during polymerizing composite resin might affect the nominal shear bond strength values. The aim of this study is to evaluate that the iris method reduces the cohesive failure in the substrates and the cavity wall property effects on the shear bond strength tests using iris method. Materials and Methods : The occlusal dentin of 64 extracted human molars were randomly divided into 4 groups to simulate two different levels of cavity wall property (metal and dentin iris) and two different materials ($ONE-STEP^{\circledR}$ and $ALL-BOND^{\circledR}$ 2) for each wall property. After positioning the iris on the dentin surface. composite resin was packed and light-cured. After 24 hours the shear bond strength was measured at a crosshead speed of 0.5 mm/min. Fracture analysis was performed using a microscope and SEM. The data was analyzed statistically by a two-way ANOV A and t-test. Results : The shear bond strength with metal iris was significant higher than those with dentin iris (p＝0.034). Using $ONE-STEP^{\circledR}$, the shear bond strength with metal iris was significant higher than those with dentin iris (p＝0.005), but not in $ALL-BOND^{\circledR}$ 2 (p＝0.774). The incidence of cohesive failure was very lower than other shear bond strength tests that did not use iris method. Conclusions：The iris method may significantly reduce the cohesive failures in the substrates. According to the bonding agent systems. the shear bond strength was affected by the cavity wall property.

• The Korean Journal of Petroleum Geology
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• v.2 no.2 s.3
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• pp.43-50
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• 1994

The geologic structure of Gongju Basin, which is a Cretaceous sedimentary basin located on the boundary of Gyeonggi Massif and Ogcheon Belt, is modeled by using gravity data and interpreted in relation with basin forming tectonism. The electrical survey with dipole-dipole array was also conducted to uncover the development of fractures in the two fault zones which form the boundaries of the basin. In the process of gravity data reduction, the terrain correction was performed by using the conic prism model, which showed better results specially for topography having a steep slope. The gravity model of the geologic structure of Gongju basin is obtained by forward modeling based on the surface geology and density inversion. It reveals that the width of the basin at its central part is about $4{\cal}km$ and about $2.5{\cal}km$ at the southern part. The depth of crystalline basement beneath sedimentary rocks of the basin is about $700{\~}400{\cal}m$ below the sea level and it is thinner in the center than in margin. The fault of the southeastern boundary appears more clearly than that of the northwestern boundary, and its fracture zone may extended to the depth of more than $1{\cal}km$. Therefore, it is thought that the tectonic movement along the fault in the southeastern boundary was much stronger. These results coincide with the appearance of broad low resistivity anomaly at the southeastern boundary of the basin in the resistivity section. The fracture zones having low density are also recognized inside the basin from the gravity model. The swelling feature of basement and the fractures in sedimentary rocks of the basin suggest that the compressional tectonic stress had also involved after the deposition of the Cretaceous sediments.

• Journal of the Korean Orthopaedic Association
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• v.54 no.3
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• pp.227-236
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• 2019

Purpose: To evaluate the results of tibial lateral plateau fractures using arthroscopic-assisted reduction and internal fixation without cortical window or bone grafts. Materials and Methods: From March 2009 to March 2017, 27 patients with Schatzker type II tibial plateau fractures with articular depression and displacement over 5 mm on a computed tomography (CT) scan, who were treated with arthroscopic reduction and internal fixation and followed-up for at least 18 months, were enrolled in this study. Under arthroscopic guidance, the depressed fracture fragment was reduced using a freer and fixed with 5.0 or 6.5 mm cannulated screws through the inframeniscal portal without a cortical window or bone graft. The clinical and radiological results were evaluated using a Rasmussen system. Second look arthroscopy was performed in thirteen patients during the implant removal operation. Results: All fractures healed completely with a mean union time of 8.7 weeks (range from 8 to 12 weeks). Twenty four patients had good to excellent clinical results and 25 patients had good to excellent radiological results according to the Rasmussen classification. A well-healed articular surface with fibrocartilage was also found in 13 cases with second look arthroscopy. The 8 cases on CT scan at outpatient department follow-up showed bone union without bone grafting. Conclusion: Arthroscopic-assisted fixation of tibial lateral plateau fractures is a useful method without a cortical window or bone graft that produces good clinical results.

• Polymer(Korea)
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• v.39 no.3
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• pp.506-513
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• 2015

Ethylidene norbornene (ENB) and its blends with endo-dicyclopentadiene (endo-DCPD) were prepared and reacted via the ring-opening metathesis polymerization (ROMP) reaction with the $1^{st}$ and $2^{nd}$ generation Grubbs' catalysts. Dynamic exothermic behaviors during ROMP and tensile properties after ROMP were evaluated using a differential scanning calorimeter (DSC) and a universal testing machine (UTM) for the samples, respectively. It revealed that the ROMP rate was accelerated with the less contents of endo-DCPD and under the $2^{nd}$ generation catalyst. Also, the addition of endo-DCPD and the $1^{st}$ generation catalyst resulted in higher tensile modulus and strength but lower toughness. Gel fraction measurement and fracture surface observation were made to understand the tensile properties.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.51-56
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• 2015

It has been used various pad finish materials to enhance the reliability of solder joint and recently Electroless Ni Electroless Pd Immersion Gold (the following : ENEPIG) pad has been used more than others. This study is about reliability according to being used in commercial Electrolytic Ni pad and ENEPIG pad, and was observed behavior of various Cu contents. After reflow, the inter-metallic compound (IMC) between solder and pad is composed of $Cu_6Sn_5$ (Ni substituted) by using EDS, and in case of ENEPIG, between IMC and Ni layer was observed the dark layer ($Ni_3P$ layer). Additional, it could be controlled the thickness of dark layer according to Cu contents. Investigated the different fracture mode between electrolytic Ni and ENEPIG pad after drop shock test, in case of soft Ni, accelerated stress propagated along the interface between $1^{st}$ IMC and $2^{nd}$ IMC, and in case of ENEPIG pad, accelerated stress propagated along the weaken surface such as dark layer. The unstable interface exists through IMC, pad material and solder bulk by the lattice mismatch, so that the thermal and physical stress due to the continuous exterior impact is transferred to the IMC interface. Therefore, it is strongly requested to control solder morphology, IMC shape and thickness to improve the solder reliability.

• Radiation Oncology Journal
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• v.34 no.4
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• pp.265-272
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• 2016

Purpose: The purpose of this study is to evaluate the treatment outcomes of adjuvant radiotherapy using vaginal brachytherapy (VB) with a lower dose per fraction and/or external beam radiotherapy (EBRT) following surgery for patients with stage I endometrial carcinoma. Materials and Methods: The subjects were 43 patients with the International Federation of Gynecology and Obstetrics (FIGO) stage I endometrial cancer who underwent adjuvant radiotherapy following surgery between March 2000 and April 2014. Of these, 25 received postoperative VB alone, while 18 received postoperative EBRT to the whole pelvis; 3 of these were treated with EBRT plus VB. The median EBRT dose was 50.0 Gy (45.0-50.4 Gy) and the VB dose was 24 Gy in 6 fractions. Tumor dose was prescribed at a depth of 5 mm from the cylinder surface and delivered twice per week. Results: The median follow-up period for all patients was 57 months (range, 9 to 188 months). Five-year disease-free survival (DFS) and overall survival (OS) for all patients were 92.5% and 95.3%, respectively. Adjuvant radiotherapy was performed according to risk factors and stage IB, grade 3 and lymphovascular invasion were observed more frequently in the EBRT group. Five-year DFS for EBRT and VB alone were 88.1% and 96.0%, respectively (p = 0.42), and 5-year OS for EBRT and VB alone were 94.4% and 96%, respectively (p = 0.38). There was no locoregional recurrence in any patient. Two patients who received EBRT and 1 patient who received VB alone developed distant metastatic disease. Two patients who received EBRT had severe complications, one each of grade 3 gastrointestinal complication and pelvic bone insufficiency fracture. Conclusion: Adjuvant radiotherapy achieved high DFS and OS with acceptable toxicity in stage I endometrial cancer. VB (with a lower dose per fraction) may be a viable option for selected patients with early-stage endometrial cancer following surgery.