• Journal of Welding and Joining
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• v.18 no.2
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• pp.69-76
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• 2000

Formation of the weld defect, such as a blowhole and a pit in lap-jointed fillet arc welds has been a serious problem in arc welding Zn-coated steel sheet. In this study, the relationship among welding conditions, welding materials and defect formation was investigated in order to minimize these defects in the CO₂welds. In addition, the arc stability of the commercial welding wires was evaluated for revealing their effects on defect formation. Main conclusions obtained are as follows: 1) There was no difference between shear tensile strength of the sound welds and that of the welds with blowholes whose diameters are less than 0.5mm. However, the welds with blowholes whose diameters are equal or large than 0.5mm and pits exhibited tensile strength 10∼ 20% and 30∼40% lower than that of the sound welds respectively. 2) The optimum welding condition to effectively prevent or reduce the weld defects formation are as follows: -The welding variables of 220A-23V-100cm/min and 120A-19V-30cm/min were recommended for minimizing the weld defects. -The gap between the two sheets at the lap-joint should be controlled to more than 0.2mm. -Solid wire was less susceptible to the formation of the weld defects than the flux-cored wire. -The low welding current condition produced less weld defects than the high welding current condition. 3) One of the reason why the amount of the defect was reduced at the low welding current was the gas discharging by the active agitation of the molten pool, due to an increasing in the number of the short circuit.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.505-507
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• 2014

본 연구에서는 제일원리 계산을 이용하여 $Si(100)/SiO_2$ 계면 내부에서 발생하는 point defect들의 거동에 대해 살펴보았다. Defect 계산에 앞서 안정한 $Si/SiO_2$ 계면을 찾아보았고 찾은 계면을 바탕으로 계면에서 point defect의 formation energy를 계산해 보았고 이를 통해 Si defect의 경우 Si층 쪽 보다는 $SiO_2$ 층에서, 그리고 계면 내부 보다는 계면 경계 근처에서 발생할 가능성이 높음을 보였다.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.37
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• pp.32.1-32.5
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• 2015

Background: The aims of present study were (1) to evaluate new bone formation among the 4-hexylresorcinol (4HR)-incorporated silk fabric membrane (SFM), conventional SFM, and uncovered control groups and (2) to compare the amount of residual membrane between the 4HR-incorporated SFM and conventional SFM in a rabbit parietal defect model. Methods: Nine New Zealand white rabbits were used for this animal study. After the formation of a bilateral parietal bone defect (diameter 8.0 mm), either 4HR-incorporated SFM or conventional SFM was grafted into the defect. The defect in the control was left uncovered. New bone formation and the amount of residual membrane were evaluated by histomorphometry at 8 weeks after the operation. Results: The total amount of new bone was $37.84{\pm}8.30%$ in the control, $56.64{\pm}15.74%$ in the 4HR-incorporated SFM group, and $53.35{\pm}10.52%$ in the conventional SFM group 8 weeks after the operation. The differences were significant between the control and 4HR-incorporated SFM group (P = 0.016) and between the control and conventional SFM group (P = 0.040). The residual membrane was $75.08{\pm}10.52%$ in the 4HR-incorporated SFM group and $92.23{\pm}5.46%$ in the conventional SFM group 8 weeks after the operation. The difference was significant (P = 0.039). Conclusions: The 4HR-incorporated SFM and conventional SFM groups showed more bone regeneration than the control group. The incorporated 4HR accelerated the partial degradation of the silk fabric membrane in a rabbit parietal defect model 8 weeks after the operation.

• Journal of Periodontal and Implant Science
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• v.31 no.2
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• pp.389-400
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• 2001

Previous studies have demonstrated an increase in bone mass and density with the use of bisphosphonate in osteoporosis. This agent acts as an inhibitor of osteoclastic activity, and results in increase of net osteoblastic activity. Currently, it has been reported that bisphosphonate has direct effect on osteoblast. This study was designed to evaluate the effect of alendronate on bone regeneration in defect of rat calvaria. The animals used for these experiments were 48 male rats, over 6-8 weeks old. They were divided into three groups according to the dose of alendronate($MK-217^{(R)}$, Merck, USA) administered. After the calvarial defects were surgically created, the rats received a peritoneal alendronate(0.25mg/kg) in group I, a peritoneal alendronate(1.25mg/kg) in group II, and a peritoneal normal saline injection in the control group. Three and six weeks later, blood was sampled and evaluated for alkaline phosphatase activity. The animals were sacrificed for histological observation and histometric analysis of the level of bone formation. The alkaline phosphatase activity was similar in three groups at 3 weeks of experiment. The activity at 6 weeks increased more than twice, compared to 3 weeks, and was slightly higher in group I than the other two groups. In histological observation, all the groups at 3 weeks, osteoblast rimming and new bone formation were observed along the defect margin. At 6 weeks, the defect was almost closed with new and more mature bone, but new bone is thinner than original bone in the central portion of defect. In histometric analysis, group I and II at 3 weeks showed significantly greater new bone formation than the control, and all the groups at 6 weeks showed similar amount of bone formation. These result suggest that alendronate administration in the dose of 0.25mg/kg and 1.25mg/kg promote osseous regeneration.

• Journal of Periodontal and Implant Science
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• v.38 no.2
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• pp.163-170
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• 2008

Purpose: Biphasic calcium phosphates have been of great interest recently. Mixing adequate ratios of hydroxyapatite(HA) and beta-tricalcium phosphate($\beta$-TCP) allowed to control the resorption rate without distorting its osteoconductive property. This study evaluated the bone formation effect of newly developed biphasic calcium phosphate(BCP) in calvarial defect of rabbits. Materials and Methods: 6 male New Zealand rabbits were used. Four defects with 8mm in diameter were created on each animal. BCP with HA/$\beta$-TCP ratio of 7:3 and particle size of $0.5{\sim}1.0\;mm$ was used as the test group and bovine bone with $0.25{\sim}1.0\;mm$ particle size, as the control group. Both test and control group materials were randomly implanted in the calvarial defects and were covered witha polymer membrane. The animals were sacrificed after 12, 24, and 48 weeks of implantation under general euthanasia. Resin blocks were obtained and were stained by masson's trichrome for histological observation. Results: Overall results were uneventful without any defect exposure or inflammation. The amount of new bone formation and bone maturity increased with increase in healing period at both groups. New bone in test group was mostly formed along the material particle surrounded by osteoblasts, and observation of osteoblastic stream was also present. Bone maturity increased as it was closer to thedefect margins. Under the same healing period, the test group showed more bone formation than the control group with more stable bovine bone particles remaining even after 48 weeks, whereas considerable resorption took place in BCP. Almost total defect closure was observed in test group with new bone formation in the central part of the defect. However, limited new bone formation was observed in the control group. Conclusion: Within the limits of the study, the present study reveals the newly developed BCP to be a good osteoconductive material. However, further studies are needed to be conducted in a different study model with a larger sample size.

• Journal of Periodontal and Implant Science
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• v.38 no.4
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• pp.621-628
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• 2008

Purpose: Osteopontin is one of the major non-collagenous protein of hard tissue. Use of peptide domain of biologically active protein has some advantages. The objective of this experimental study is evaluation of periodontal regenerative potency of synthetic peptide gel which containing collagen binding domain of osteopontin in the degree III periodontal defect of beagle dogs. Material and Methods: Experimental degree III furcation defect was made in the mandibular third and fourth premolar of beagles. Regenerative material was applied during flap operation. 8 weeks after regenerative surgery, all animals were sacrificed and histomorphometric measurement was performed to calculate the linear percentage of the new cementum formation and the volume percentage of new bone formation. Result: The linear percent of new cementum formation was 41.6% at control group and 67.1% at test group and there was statistically significant difference. The volume percent of new bone formation was 52.1% at control group and 58.9% at test group. Conclusion: As the results of present experiment, synthetic peptide gel containing collagen binding domain of osteopontin significantly increase new bone and cementum formation in the degree III furcation defect of canine mandible.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.4
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• pp.722-745
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• 1996

The purpose of this study is to investigate the effect of constant direct current electrical stimulation in healing the bone defects and surrounding tissues of the endo-oseous(TPS-IMZ) implants. Implants were inserted in the femur of adult dogs. Then a constrant direct current of approximately $10{\mu}A$ was applied. Artificial bone defects were prepared on one side of the implant site. Experimental groups were divided into 4 : control group : bone defect without treatment group I : bone defect filled with hydroxyapatite powders group II : bone defect, in which a negative and positive electrodes were inserted 5mm apart from both sides of the implant group III : bone defect, in which negative current was directly connected to the IMZ implant and a positive electrode was placed 10mm apart from the implant The animals were sacrificed in the 1st, 2nd, 4th and 8th week after implantation for the light microscopic examination. The results obtained were as follows : 1. In electrically stimulated experimental groups, new bone formation and osseointegration around implants were accelerated. 2. Group III showed the greatest activity in new bone formation. Osteoconductivity around HA particles was observed in group 1. 3. The defect area of the control group was healed by forming new bone, which grew from the underlying cancellous bone. The defect areas of the electrically stimulated experimental groups were healed by newly formed bone, which grew upward from the cancellous bone and downward from the periosteum. 4. 8 weeks after implantation, all the groups showed good osseointegration between the surrounding bone and implants.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.42
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• pp.34.1-34.7
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• 2020

Purpose: The purpose of this study was to evaluate the influence of biodegradable polycaprolactone membrane on new bone formation and the biodegradation of biphasic alloplastic bone substitutes using animal models. Materials and methods: In this study, bony defect was formed at the canine mandible of 8 mm in diameter, and the defects were filled with Osteon II. The experimental groups were covered with Osteoguide as barrier membrane, and the control groups were closed without membrane coverage. The proportion of new bone and residual bone graft material was measured histologically and histomorphometrically at postoperative 4 and 8 weeks. Results: At 4 weeks, the new bone proportion was similar between the groups. The proportion of remaining graft volume was 27.58 ± 6.26 and 20.01 ± 4.68% on control and experimental groups, respectively (P < 0.05). There was no significant difference between the two groups in new bone formation and the amount of residual bone graft material at 8 weeks. Conclusion: The biopolymer membrane contributes to early biodegradation of biphasic bone substitutes in the jaw defect but it does not affect the bone formation capacity of the bone graft.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.210-213
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• 1995

In this study,the effect of both process parameters (wheel velocity, friction coefficients between die and billet, etc) and die-shape (abutment height and shape, flash gap, etc.) on the surface defect on forming process is theoretically investigated. For this work, computer simulation was performed by using the DEFORM, a commercial FEM code. Through numerous simulations with different parameters and die shapes, We propose one optimal die shape for CONFORM process which can remove surface defect.

• Applied Microscopy
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• v.6 no.1
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• pp.33-38
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• 1976

Formation of crystal defects which may occur during and after the vacuum deposition of silver films on rocksalt substrates were studied by electron microscopy. To obtain defect free films, various evaporation conditions, such as evaporation rate, substrate temperature, substrate treatments and annealing of films were examined. Stacking faults and micro-twins are dominant defects in silver films.