• Korean Journal of Materials Research
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• v.11 no.3
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• pp.221-226
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• 2001

The basal slip (0001)1/3<1120 > dislocation velocity in sapphire ($\alpha$-$Al_2$$O_3$) single crystals was measured by four-point bending test. The bending experiment was carried out in the temperature range from 120$0^{\circ}C$ to $1400^{\circ}C$ at various engineering stresses 90MPa, 120MPa, and 150MPa. The velocity of such dislocations was estimated from the bending displacement rate of the four-point bend sample. The dependence of temperature and stress in dislocation velocity was investigated. The activation energy for dislocation velocity was determined to be about 2.2$\pm$0.4eV. In addition, the stress exponent (m) describing the stress dependence of dislocation velocities was in the range of 2.0$\pm$0.2.

• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.343-348
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• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• Clinics in Shoulder and Elbow
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• v.12 no.1
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• pp.98-101
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• 2009

Purpose: These case reports have been prepared to highlight the uncommon occurrence of anterior shoulder dislocation after an epileptic seizure, the recognition of which is important as this type of injury is associated with bony lesions and a high incidence of recurrence. Materials and Methods: We report two cases of recurrent anterior dislocation of the shoulder due to grand mal epilepsy. These cases were treated as usual anterior dislocations of the shoulder, and were regularly followed to detect any recurrence of shoulder instability. Results: Outcome of the surgery in the two cases was different because of the differences in seizure control. In the patient in whom seizures were well-controlled, there was no recurrence of instability, while the patient with poorly controlled seizures developed a recurrence of the dislocation following shoulder repair. Conclusion: The authors emphasize the need to control seizures in order to prevent injury recurrence in this subset of patients.

• Journal of Korea Foundry Society
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• v.40 no.4
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• pp.118-127
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• 2020

Microstructural evolution during a heat treatment and high-temperature tensile properties have been investigated in conventionally cast CM247LC. In as-cast specimens, MC carbides with high amounts of Ta, Ti, Hf, and W were found to exist in the interdendritic regions, and γ' was observed in the form of cubes and octocubes prior to decomposition into cubes. In the heat-treated condition, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in both interdendritic regions and dendrite core. Three types of carbides with different stoichiometries and compositions were found at the grain boundaries. MC carbides with high Hf contents were observed in the vicinity of eutectic γ-γ'. The highest tensile strength value was found at 750℃, whereas the greatest ductility appeared at 649℃. The effect of the temperature on the tensile properties was closely related to the dislocation structure. With increase in the test temperature, the density of dislocations inside γ' decreased, whereas that in the γ matrix increased. Stacking faults generated in γ' at 750℃ had a strengthening effect, whereas thermally activated dislocation motion at a high temperature was considered to have the opposite effect.

• Journal of the Korean Vacuum Society
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• v.4 no.S2
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• pp.100-105
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• 1995

Nitrogen implantation process has been applied for improvement of wear resistance of Zircaloy-4 fuel cladding materials. Nitrogen was implanted at 120keV to a total dose range of $1\times 10^{17}$ions/$\textrm{cm}^2$ to $1\times 10^{18}$ions/$\textrm{cm}^2$ at various temperatures between $270^{\circ}C$ and $671^{\circ}C$. The microstructure changes by nitrogen implantation were analyzed by XRD and AES and wear behavior was evaluated by performing ball-on-disc type wear testing at various loads and sliding velocities under unlubricated condition. Nitrogen implantation produced ZrNx nitride above $3\times 10^{17}$ions/$\textrm{cm}^2$ as well as heavy dislocations, which resluted in an increase in microhardness of the implanted surface of up to 1400 $H_k$ from 200 $H_k$ of unimplanted substrate. Hardness was also found to be increased with increasing implantation temperature up to 1760 $H_k$ at $620^{\circ}C$. The wear resistance was greatly improved as total ion dose and implantation temperature increased. The effective enhancement of wear resistance at high dose and temperature is believed to be due to the significant hardening associated with high degree of precipitation of Zr nitrides and generation of prismatic dislocation loops.

• Journal of Trauma and Injury
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• v.21 no.2
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• pp.91-99
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• 2008

Purpose: Multiple rib fracture (MRF) and a hemopneumothorax accompany with most blunt chest traumas. We aimed to analyze the factors increasing the probability of a hemopneumothorax. In addition, other injuries accompanying MRF were analyzed. Methods: We retrospectively reviewed the medical records of 154 mutiple rib fracture patients who visited our hospital between January 2005 and December 2007. The medical records were reviewed for sex, age, mechanism of injury, location, number of fractures, distance of dislocated rib fragments, and presence of complications. We measured the distance of bony dislocations by using the PACS (Picture Archiving and Communication System). Results: The average number of rib fractures was $3.7{\pm}2.1$, and the number of rib fractures significantly influenced the incidence of a hemothorax (p<0.001). The risk of a hemothorax was increased in a bilateral MRF compared to a unilateral MRF (p=0.027). The distance of dislocated rib fragments influenced the probability of a hemothorax significantly (p=0.018), and subcutaneous emphysema and lung contusion were significantly associated with a pneumothorax (p=0.021, p=0.036). Conclusion: The number of MRFs did not influence the risk for a pneumothorax, but did influence the risk for a hemothorax. The laterality, distance of dislocation, also had an influence on the risk for a hemothorax. Also, subcutaneous emphysema and lung contusion were increased in cases with a pneumothorax. We must consider the possibility of a hemothorax even when the initial chest X-ray shows no evidence of a hemothorax. If a lung contusion is present, then an occult pneumothorax must be considered.

• Journal of Korean Neurosurgical Society
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• v.30 no.sup2
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• pp.322-327
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• 2001

Objectives : There are many kinds of method to evaluate neural decompression during operation. They are direct visual and manual inspection, intraoperative ultrasound, endoscope, intraoperative computed tomography and intraoperative myelography. We used intraoperative myelography to evaluate the proper decompression of neural elements during the decompressive surgery. Methods : We injected 10-20cc of nonionic water-soluble contrast materials through direct puncture site of exposed dura during operation or lower lumbar level or lumbar drain inserted preoperatively. 12 patients were included in this study. They were 7 patients of centrally herniated lumbar disc disease, 1 patient of multiple lumbar spinal stenosis, 2 patients of thoracic extradural tumor and 2 cervical fracture & dislocations. Results : 5 of 12 patients showed remained neural compression through intraoperative myelography, so they were operated further through other approach. Myelographic dye is heavier than CSF, so the dependent side of subarachnoid space was visualized only. In one case, CSF leakage through hemovac was detected, but it was treated only bed rest for 5 days after hemovac removal. Conclusion :Intraoperative myelography is an effective method to evaluate neural decompression during spinal surgery. This technique is easy and familiar to us, neurosurgeons.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.2
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• pp.401-406
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• 2008

Fall event detection is one of the most common problems for elderly people, especially those living alone because falls result in serious injuries such as joint dislocations, fractures, severe head injuries or even death. In order to prevent falls or fall-related injuries, several previous methods based on video sensor showed low fall detection rates in recent years. To improve this problem and outperform the system performance, this paper presented a novel approach for fall event detection in the elderly using a subtraction between successive difference images and temporal templates in real time environment. The proposed algorithm obtained the successful detection rate of 96.43% and the low false positive rate of 3.125% even though the low-quality video sequences are obtained by a USB PC camera sensor. The experimental results have shown very promising performance in terms of high detection rate and low false positive rate.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.6
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• pp.263-269
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• 2019

The mechanism of microstructure and hardness changes during mill annealing of Ti-6Al-4V alloy was investigated. The annealing heat treatments were performed at $675{\sim}795^{\circ}C$ in vacuum for 2 hours, followed by air cooling. The microstructure was observed by using an optical microscope and X-ray diffraction, and hardness was measured by using a Rockwell hardness tester and micro Vickers hardness tester. The average grain size becomes smaller at $675^{\circ}C$ to $735^{\circ}C$ due to the formation of new grains rather than grain growth, but becomes larger at $735^{\circ}C$ to $795^{\circ}C$ due to growth of the already-formed grains rather than formation of new grains. The mill annealing temperature becomes higher, the ${\beta}$ phase fraction decreases and ${\alpha}$ phase fraction increases at room temperature. This is because the higher annealing temperature, the smaller amount of V present in the ${\beta}$ phase, and thus the ${\beta}$ to ${\alpha}$ transformation occurs more easily when cooled to room temperature. As the mill annealing temperature increases, the hardness value tends to decrease, mainly due to resolution of defects such as dislocations from $675^{\circ}C$ to $735^{\circ}C$ and due to grain growth from $735^{\circ}C$ to $795^{\circ}C$, respectively.

• Nuclear Engineering and Technology
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• v.8 no.1
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• pp.19-27
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• 1976

The strain ageing behaviour of Zircaloy-4 has been studied in the temperature range 175$^{\circ}C$ to 575$^{\circ}C$ for both quenched and annealed specimens. The strain ageing in quenched Zircaloy-4 was found in the temperature range 175$^{\circ}C$ to 50$0^{\circ}C$ and its Peak occured at 3$25^{\circ}C$ while the strain ageing in annealed specimens occured in the temperature range 175-575$^{\circ}C$, showing two peaks, one at 323$^{\circ}C$ and a higher one at 45$0^{\circ}C$. The peak at 3$25^{\circ}C$ in both quenched and annealed specimens is considered to be due to the segregation of interstitial oxygen atoms to cell walls during ageing. The peak at 45$0^{\circ}C$ in annealed specimens is considered to he due to the interaction of dislocations with Fe atoms. It has been found that strain ageing stress at ~30$0^{\circ}C$ in zirconium alloys is proportional to the square root of oxygen content.