• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.907-914
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• 2018

In this article, we conducted molecular dynamics simulations to investigate the effect of applied strain and temperature on irradiation-induced damage in alpha-zirconium. Cascade simulations were performed with primary knock-on atom energies ranging between 1 and 20 KeV, hydrostatic and uniaxial strain values ranging from -2% (compression) to 2% (tensile), and temperatures ranging from 100 to 1000 K. Results demonstrated that the number of defects increased when the displacement cascade proceeded under tensile uniaxial hydrostatic strain. In contrast, compressive strain states tended to decrease the defect production rate as compared with the reference no-strain condition. The proportions of vacancy and interstitial clustering increased by approximately 45% and 55% and 25% and 32% for 2% hydrostatic and uniaxial strain systems, respectively, as compared with the unstrained system, whereas both strain fields resulted in a 15-30% decrease in vacancy and interstitial clustering under compressive conditions. Tensile strains, specifically hydrostatic strain, tended to produce larger sized vacancy and interstitial clusters, whereas compressive strain systems did not significantly affect the size of defect clusters as compared with the reference no-strain condition. The influence of the strain system on radiation damage became more significant at lower temperatures because of less annealing than in higher temperature systems.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2298-2304
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• 2023

Titanium alloys are expected to become one of the candidate materials for nuclear-powered spacecraft due to their excellent overall performance. Nevertheless, atomistic mechanisms of the defect accumulation and evolution of the materials due to long-term exposure to irradiation remain scarcely understood by far. Here we investigate the heavy irradiation damage in a-titanium with a dose as high as 4.0 canonical displacements per atom (cDPA) using atomistic simulations of Frenkel pair accumulation. Results show that the content of surviving defects increases sharply before 0.04 cDPA and then decreases slowly to stabilize, exhibiting a strong correlation with the system energy. Under the current simulation conditions, the defect clustering fraction may be not directly dependent on the irradiation dose. Compared to vacancies, interstitials are more likely to form clusters, which may further cause the formation of 1/3<1210> interstitial-type dislocation loops extended along the (1010) plane. This study provides an important insight into the understanding of the irradiation damage behaviors for titanium.

• Archives of Plastic Surgery
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• v.50 no.5
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• pp.478-487
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• 2023

Background The outcome of alveolar grafting with synthetic bone substitute (Osteon III) in various bone defect volumes is highlighted. Methods A prospective study was accomplished on 55 patients (6-13 years of age) with unilateral alveolar bone cleft. Osteon III, consisting of hydroxyapatite and tricalcium phosphate, is used to reconstruct the defect. Alveolus defect diameter was calculated before surgery (V1), after 3 months (V2), and finally after 6 months (V3) postsurgery. In the t-test, a significant difference and correlation between V1, V2, and V3 are stated. A p-value of 0.01 is considered a significant difference between parameters. Results The degree of cleft is divided into three categories: small (9 cases), medium (20 patients), and large (26 cases).The bone volume of the clefted site is divided into three steps: volume 1: (mean 18.1091 mm³); step 2: after 3 months, volume 2 resembles the amount of unhealed defect (mean 0.5109 mm³); and the final bone volume assessment is made after 6 months (22.5455 mm³). Both show statistically significant differences in bone volume formation. Conclusion An alloplastic bone substitute can also be used as a graft material because of its unlimited bone retrieval. Osteon III can be used to reconstruct the alveolar cleft smoothly and effectively.

• Journal of Periodontal and Implant Science
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• v.27 no.1
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• pp.117-128
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• 1997

Using barrier membrane, guided bone regeneration(GBR) and guided tissue regeneration(GTR) of periodontal tissue are now widely studied and good results were reported. In bone regeneration, not all cases gained good results and in some cases using GTR, bone were less regenerated than that of control. The purpose of this study is to search for the method to improve the success rate of GBR and GTR by examination of the cause of the failure. For these study, rats and beagle dogs were used. In rat study, 5mm diameter round hole was made on parietal bone of the rat and 10mm diameter of bioresorbable membrane was placed on the bone defects and sutured. In 1 ,2, 4 weeks later, the rats were sacrificed and Masson-Trichrome staining was done and inspected under light microscope for guided bone regeneration. In dog study, $3{\times}4mm^2$ Grade III furcation defect was made at the 3rd and 1th premolar on mandible of 6 beagle dogs. The defects were covered by bioresorbable membrane extending 2-3mm from the defect margin. The membrane was sutured and buccal flap was covered the defect perfectly. In 2, 4. 8 weeks later. the animals were sacrificed and undecalcified specimens were made and stained by multiple staining method. In rats. there was much amount of new bone formation at 2 weeks. and in 4 weeks specimen, bony defect was perfectly dosed and plenty amount of new bone marrow was developed. In some cases, there were failures of guided bone regeneration. In beagle dogs, guided tissue regeneration was incomplete when the defect was collapsed by the membrane itself and when the rate of resorption was so rapid than expected. The cause of the failure in GBR and GTR procedure is that 1) the membrane was not tightly seal the bony defects. If the sealing was not perfect, fibrous connective tissue infiltrate into the defect and inhibit the new bone formation and regeneration. 2) the membrane was too tightly attached to the tissue and then there was no space to be regenerated. In conclusion, the requirements of the membrane for periodontal tissue and bone regeneration are the biocompatibility, degree of sealingness, malleability. space making and manipulation. In this animal study. space making for new bone and periodontal ligament, and sealing the space might be the most important point for successful accomplishment of GBR and GTR.

• Journal of the Korean Ceramic Society
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• v.28 no.6
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• pp.495-501
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• 1991

This study is intended to make defect-free region, denuded zone at the silicon wafer surface for semiconductor device substrates. In this experiment, initial oxygen concentration of starting material CZ-grown silicon wafer, various heat treatment combinations, denuding ambient and the amounts of oxygen reduction were measured, and then denuded zone (DZ) formation and depth were investigated. In Low/High anneal (DZ formation could be achieved), the optimum temperature for Low anneal was 700$^{\circ}C$∼750$^{\circ}C$. In case of High anneal, with the time increased, DZ depth was increased at 1000$^{\circ}C$, 1150$^{\circ}C$ respectively, but on the contrary, DZ depth was decreased at low temperature 900$^{\circ}C$. As well, out-diffusion time below 2 hours was unsuitable for effective Gettering technique even though the temperature was high, and DZ formation could be achieved when initial oxygen concentration was only above 14 ppm in silicon wafer.

• Development and Reproduction
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• v.16 no.4
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• pp.371-378
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• 2012

Notch signaling plays fundamental roles in various animal development. It has been suggested that Hr-Notch, a Notch homologue in the ascidian Halocynthia roretzi, is involved in the formation of peripheral neurons by suppressing the neural fates and promoting the epidermal differentiation. However, roles of Notch signaling remain controversial in the formation of nervous system in ascidian embryos. To precisely investigate functions of Notch signaling, we have isolated and characterized Hr-Numb, a Numb homologue which is a negative regulator of Notch signaling, in H. roretzi. Maternal expression of Hr-Numb mRNAs was detected in egg cytoplasm and the transcripts were inherited by the animal blastomeres. Its zygotic expression became evident by the early neurula stage and the transcripts were detected in dorsal neural precursor cells. Suppression of Hr-Numb function by an antisense morpholino oligonucleotide resulted in larvae with defect in brain vesicle and palps formation. Similar results have been obtained by overexpression of the constitutively activated Hr-Notch forms. Therefore, these results suggest that Hr-Numb is involved in Notch signaling during ascidian embryogenesis.

• The Journal of the Korean bone and joint tumor society
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• v.19 no.2
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• pp.56-63
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• 2013

Purpose: This study was performed to evaluate the efficiency of demineralized bone matrix (DBM, Genesis$^{(R)}$) used for bone defect after operative traetment of benign bone tumors by clinical and radiological methods. Materials and Methods: DBM was used to treat bone defect after operative treatment of benign tumor from February 2012 to May 2013. Total 25 benign bone tumor cases (15 males, and 10 females) with mean age of 30.3 were studied. The diagnoses were solitary bone cyst in 9 cases, non ossifying fibroma in 5, fibrous dysplasia in 5, aneurysmal bone cyst in 3 and enchondroma in 3. In categorization by location of tumor, there were 5 cases of distal femur, 4 of proximal tibia, 3 of proximal femur, 3 of proximal humerus, 3 of phalanx, 2 of distal radius, 2 of hip bone, 2 of calcaneus, and 1 of scapula. Autogenous bone was used with DBM in 6 cases, and only DBM used in 19 cases. Mean periods of follow up were 8.7 months (range: 6 to 14 months). Amount of graft resorption and bone formation was observed with compare of post operation radiograph and the difference was shown by percentage. Resorption level was measured by DBM level which could be observed from simple x-ray, and bone formation level by bone trabecular formation level at impaired site. Results: Twenty three cases of total 25 cases showed bone union. In the 23 cases, more than 98% DBM resorption was observed after mean 4.3 months, and more than 98% bone formation was observed after mean 6.9 months. Lesser bone defect sizes showed faster bone formation and it was statistically significant (p=0.036). But other comparative studies on other factors such as, sex, age of patients and combination of autogenous bone were no statistically significant differences in graft resorption and bone formation. And there was no significant complication in periods of follow-up. Conclusion: Demineralized Bone Matrix (Genesis$^{(R)}$) is thought to be useful treatment for bone defect after operative treatment of benign bone tumor, however longer follow-up periods appears to be needed.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.35 no.5
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• pp.294-301
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• 2013

Purpose: The purpose of this study is to assess the effectiveness of beta-tricalciumphosphate (${\beta}$-TCP) as a bone graft material on new bone formation and regeneration of mandible bone defect around dental implants. Methods: Both mandibular sites of ten rabbits were exposed. The experimental subjects were divided into two groups. Rabbits in the control group (right site of the mandible) had dental implants around cortical bone defects, without treatment, while, in the experimental group (left site of the mandible), ${\beta}$-TCP was grafted into the bone defect around the implant. Rabbits were sacrificed after one, two, three, four, and eight weeks, and histomorphometric evaluation and analysis of the bone implant contact rate were performed using an optical microscope. Results: Bone formation rates in the experimental group were greater than those in the control group from one to eight weeks, and percentages of implant surface contacted to bone were greater in the experimental group than in the control group from three weeks after implantation. Conclusion: These results suggest that the bone formation activity around dental implants was increased by osteoconduction activity of ${\beta}$-TCP.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.26 no.6
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• pp.613-619
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• 2000

The purpose of the present study was to investigate the effect of Bioactive glass on bone regeneration in the experimental mandibular bone defects. Five rabbits, weighing about 2.0kg, were used. Three artificial bone defects, $5{\times}5{\times}5mm$ in size, were made at the inferior border of the mandible. In the experimental group 1, the bone defect was grafted with $Biogran^{(R)}$ and covered with $Bio-Gide^{(R)}$ resorbable membrane. In the experimental group 2, $Biogran^{(R)}$ was grafted only. In the control group, the bone defect was filled with blood clot and was spontaneously healed. The animals were sacrificed at 1, 2, 4, and 8 weeks after the graft. Microscopic examination was performed. Results obtained were as follows: In the control group, the osteoid tissue was observed at week 1 and the bone trabeculi were connected each other and matured at week 2. The lamellar bone formation appeared at week 4, and the amount of bone tissue was increased at week 8. In the experimental group 1, the fibrous tissue was filled between the granules of Bioactive glass and the cartilage formation was found adjacent to the normal bone at week 1. The bone tissue was formed between the granules at week 2, while the amount of bone tissue increased and the lamellar bone formation was observed at week 4. The lamellar bone was increased at week 8. Histologic findings were Similar between the experimental groups 1 and 2, although the amount of Bioactive glass granules lost was increased in the latter. These results suggest that new bone formation is found around the Bioactive glass granules grafted into the bone defects, and the membrane plays a role in keeping the granules and preventing the fibrous tissue invasion.

• 대한치주과학회:학술대회논문집
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• 2004.11a
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• pp.157-158
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• 2004