• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.6
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• pp.411-418
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• 2019

Light-triggered thyristors (LTTs) are essential components in high-power applications, such as HVDC transmission and several pulsed-power applications. Generally, LTT fabrication includes a deep diffusion of aluminum as a p-type dopant to form a uniform p-base region, which needs careful concern for contamination and additional facilities in silicon semiconductor manufacturing factories. We fabricated 4-inch 5,000 V LTTs with boron implantation and diffusion process as a p-type dopant. The LTT contains a main cathode region, edge termination designed with a variation of lateral doping, breakover diode, integrated resistor, photosensitive area, and dV/dt protection region. The doping concentration of each region was adjusted with different doses of boron ion implantation. The fabricated LTTs showed good light triggering characteristics for a light pulse of 905 nm and a blocking voltage (V_DRM) of 6,500 V. They drove an average on-state current (I_TAVM) of 2,270 A, peak nonrepetitive surge current (I_TSM) of 61 kA, critical rate of rise of on-state current (di/dt) of 1,010 A/㎲, and limiting load integral (I²T) of 17 MA²s without damage to the device.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.46-55
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• 2016

Three small scale hollow circular reinforced concrete columns(4.5 aspect ratio) were tested under cyclic lateral load with constant axial load. Diameter of section is 400 mm, hollow diameter is 200 mm. The selected test variable are transverse steel ratio. Volumetric ratio of spirals of all the columns is 0.302~0.604% in the plastic hinge region. It corresponds to 45.9~91.8% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The final objectives of this study are to provide quantitative reference data and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, steel fracture, etc. In this paper, describes mainly failure behavior, strength degradation behaviour, displacement ductility of circular reinforced concrete bridge columns with respect to test variables.

• Korean Journal of Applied Biomechanics
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• v.25 no.1
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• pp.29-37
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• 2015

Objective : The purpose of this study was to investigate the biomechanical properties of shock absorption strategy and postural stability during the drop landing for each types. Methods : The motions were captured with Vicon Motion Capture System, with the fourteen infra-red cameras (100Hz) and synchronized with GRF(ground reaction force) data(1000Hz). Ten male soccer players performed a drop landing with single-leg and bi-legs on the 30cm height box. Dependent variables were the CoM trajectory and the Joint Moment. Statistical computations were performed using the paired t-test and ANOVA with Turkey HSD as post-hoc. Results : The dominant leg was confirmed to show a significant difference between the left leg and right leg as the inverted pendulum model during Drop Landing(Phase 1 & Phase 2). One-leg drop landing type had the higher CoM displacement, the peak of joint moment with the shock absorption than Bi-leg landing type. As a lower extremity joint kinetics analysis, the knee joint showed a function of shock absorption in the anterior-posterior, and the hip joint showed a function of the stability and shock absorption in the medial-lateral directions. Conclusion : These findings indicate that the instant equilibrium of posture balance(phase 1) was assessed by the passive phase as Class 1 leverage on the effect of the stability of shock absorption(phase 2) assessed by the active phase on the effect of Class 2 leverage. Application : This study shows that the cause of musculo-skeletal injuries estimated to be focused on the passive phase of landing and this findings could help the prevention of lower damage from loads involving landing related to the game of sports.

• Imaging Science in Dentistry
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• v.50 no.1
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• pp.9-14
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• 2020

Purpose: The purpose of this study was to evaluate vertical bone loss and alveolar bone thickness in the maxillary and mandibular incisors of patients with skeletal class III malocclusion. This study also aimed to evaluate the periodontal condition of class III malocclusion patients who had not undergone orthodontic treatment. Materials and Methods: The sample included cone-beam computed tomography scans of 24 Korean subjects (3 male and 21 female). Alveolar bone thickness (ABT), alveolar bone area (ABA), alveolar bone loss (ABL), and fenestration of the maxillary and mandibular incisors were measured using 3-dimensional imaging software. Results: All incisors displayed an ABT of less than 1.0 mm from the labial surface to root level 7 (70% of the root length). A statistically significant difference was observed between the mandibular labial and lingual ABAs and between the maxillary labial and mandibular labial ABAs. The lingual ABA of the mandibular lateral incisors was larger than that of the mandibular central incisors. ABL was severe on the labial surface. A statistically significant difference was observed between the maxillary and mandibular labial ABL values(21.8% and 34.4%, respectively). Mandibular lingual ABL (27.6%) was significantly more severe than maxillary lingual ABL (18.3%) (P<0.05). Eighty-two fenestrations were found on the labial surfaces of the incisors, while only 2 fenestrations were observed on the lingual surfaces. Fenestrations were most commonly observed at root level 6. Conclusion: Careful evaluation is needed before orthodontic treatment to avoid iatrogenic damage of periodontal support when treating patients with class III malocclusion.

• Korean Journal of Environmental Biology
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• v.29 no.4
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• pp.241-250
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• 2011

The safety of human exposure to an ever-increasing number and diversity of electromagnetic field (EMF) sources both at work and at home has clearly become a public health issue. To date many $in$ $vivo$ and $in$ $vitro$ studies revealed that EMF exposure can alter cellular metabolism, endocrine function, immune activity, reproductive function, and fetal development in animal system. The major parameters found to be altered in cells or individuals following EMF exposure include an increase of free radicals, DNA damage, cancer risk, developmental defect, and reproductive dysfunctions. Epidemiological studies reported EMF can increase life-threatening illnesses such as leukemia, brain cancer, amyotrophic lateral sclerosis, clinical depression, suicide, and Alzheimer's disease has been identified. These effects of EMF exposure differ according to duration of exposure, frequency of waves, and strength (energy) of EMF. In the present review, we briefly introduced the physical properties of EMF and summarized the effect of EMF on human and wildlife animals according to types of EMF, duration of exposure at cellular and organism levels.

• Archives of Reconstructive Microsurgery
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• v.5 no.1
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• pp.106-111
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• 1996

Purpose : Propose a surgical technique in donor harvesting method in free vascularized proximal fibular epiphysis. Methodology : Concerned about growth potentials of the transplanted epiphysis in our long term results of the epiphyseal transplanted 13 cases more than 4 years follow-up, anterior tibial artery which contains anterior tibial recurrent artery is most reliable vessel to proximal fibular epiphysis which is the best donor of the free vascularized epiphyseal transplantation. In vascular anatomical aspect proximal fibular epiphysis norished by latearl inferior genicular artery from popliteal, posterior tibial recurrent artery and anterior tibial recurrent artery from anterior tibial artery and peroneal artery through metaphysis. The lateral inferior genicular artery is very small and difficult to isolate, peroneal artery from metaphysis through epiphyseal plate can not give enough blood supply to epiphysis itself. The anterior tibial artery which include anterior tibial recurrent and posterior tibial recurrent artery is the best choice in this procedure. But anterior tibial recurrent artery merge from within one inch from bifucating point of the anterior and posterior tibial arteries from popliteal artery. So it is very difficult to get enough vascular pedicle length to anastomose in recipient vessel without vein graft even harvested from bifucating point from popliteal artery. Authors took recipient artery from distal direction of anterior tibial artery after ligation of the proximal popliteal side vessel, which can get unlimited pedicle length and safer dissection of the harvesting proximal fibular epiphysis. Results : This harvesting procedure can performed supine position, direct anterolateral approach to proximal tibiofibular joint. Dissect and isolate the biceps muscle insertion from fibular head, micro-dissection is needed to identify the anterior tibial recurrent arteries to proximal epiphysis, soft tissue release down to distal and deeper plane to find main anterior tibial artery which overlying on interosseous membrane. Special care is needed to protect peroneal nerve damage which across the surgical field. Conclusions : Proximal fibular epiphyseal transplantation with distally directed anterior tibial artery harvesting technique is effective and easier dissect and versatile application with much longer arterial pedicle.

• Archives of Craniofacial Surgery
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• v.11 no.1
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• pp.65-68
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• 2010

Purpose: Dermoid cysts are benign neoplasms that are derived from both ectoderm and mesoderm. Approximately 7 percent of all dermoid cysts occur in the head and neck, as most common sites are the lateral ends of the eyebrows, the midline in the nasal root and neck. Rarely they can be found in the frontal sinus, temporal bone, maxilla and the floor of the mouth. Dermoid cysts in the temporal fossa are extremely rare. We experienced a characteristic dermoid cyst that occupied the temporal fossa. Methods: A 16-year-old man had a progressive enlarging mass on the left eyebrow. Computerized tomographic scan showed a bulging mass in the temporal fossa, and it had the density similar to that of fat. The size of the mass was $3{\times}3{\times}2cm$, and it was composed of high density of fat with clear margin. There was no bony invasion, but the mass was fixed on bone. Results: We performed the surgery through coronal incision under general anesthesia. Because the mass was closely connected with temporal fat pads, we removed this mass with some portion of temporal fat pads, avoiding damage to the facial nerve. The postoperative course was ordinary without complication. Conclusion: The reports about dermoid cyst on the temporal fossa is uncommon. However, if there is a mass in the temporal fossa which has the density similar to that of fat in CT scan, we should consider the possibility of dermoid cyst. We suggest that excision through coronal incision with bewaring temporal fat pad can induce good result.

• Journal of Korean Neurosurgical Society
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• v.37 no.3
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• pp.201-206
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• 2005

Objective: To evaluate the accuracy and safety of C1-C2 transarticular screw insertion, we retrospectively review surgical records and postoperative radiological findings. Methods: From January 2001 to October 2003, the C1-C2 transarticular screw fixation and posterior wiring with iliac bone grafts was performed in 16 patients. 6 patients had rheumatoid arthritis which caused cervical instability, 3 patients had os odontoideum, 3 patients had type 2 odontoid process fracture, 3 patients had traumatic transverse ligament injury and 1 patients who had been managed with C1-C2 wire fixation had psoriatic arthritis. Results: Osseous fusion was documented in 15 patients(93.8%). Only one patient was recorded screw loosening because of postoperative infection. One patient had only one screw placed because of abnormal anatomical structure, one patients was breakage of a Kirschner wire, and one screw was medial location to lateral mass of C1, but clinical results was excellent and radiological instability was not noted. Conclusion: The author's experience demonstrates that C1-C2 transarticular screw fixation with wired bone graft is a safe procedure with higher fusion rate but precaution is needed to avoid the neural damage, vertebral artery injury, and hardware failure.

• Steel and Composite Structures
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• v.5 no.4
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• pp.271-287
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• 2005

The seismic behavior of two steel moment-resisting frames, which satisfy all the current seismic design requirements, are evaluated and compared in the presence of pre-Northridge connections denoted as BWWF and an improved post-Northridge connections denoted as BWWF-AD. Pre-Northridge connections are modeled first as fully restrained (FR) type. Then they are considered to be partially restrained (PR) to model their behavior more realistically. The improved post-Northridge connections are modeled as PR type, as proposed by the authors. A sophisticated nonlinear time-domain finite element program developed by the authors is used for the response evaluation of the frames in terms of the overall rotation of the connections and the maximum drift. The frames are excited by ten recorded earthquake time histories. These time histories are then scaled up to produce some relevant response characteristics. The behaviors of the frames are studied comprehensively with the help of 120 analyses. Following important observations are made. The frames produced essentially similar rotation and drift for the connections modeled as FR type and PR type represented by BWWF-AD indicating that the presence of slots in the web of beams in BWWF-AD is not detrimental to the overall response behavior. When the lateral displacements of the frames are significantly large, the responses are improved if BWWF-AD type connections are used in the frames. This study analytically confirms many desirable features of BWWF-AD connections. PR frames have longer periods of vibration in comparison to FR frames and may attract lower inertia forces. However, calculated periods of the frames of this study using FEMA 350 empirical equation is longer than those calculated using dynamic characteristics of the frames. This may result in even lower design forces and may adversely influence the design.

• Earthquakes and Structures
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• v.12 no.2
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• pp.237-250
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• 2017

There has been increasing attention in many countries on seismic retrofit of old fashioned RC structures in recent years. In such buildings, the joints lack transverse reinforcement and suffer inadequate seismic dimensional requirements and the reinforcement is plain bar. The behavior of the joints is governed by sliding of steel bars and diagonal shear failure is less influential. Different methods to retrofit beam-column joints have been proposed in the literature such as wrapping the joint by FRP sheets, enlargement of the beam-column joint, and strengthening the joint by steel sheets. In this study, an enlargement technique that uses external prestressed cross ties with steel angles is examined. The technique has already been used for substructures reinforced by deformed bars and has advantages such as efficient enhancement of seismic capacity and lack of damage to the joint. Three reference specimens and two retrofitted units are tested under increasing lateral cyclic load in combination with two levels of axial load. The reference specimens showed relatively low shear strength of 0.150${\surd}$($f_c$) and 0.30${\surd}$($f_c$) for the exterior and interior joints, respectively. In addition, relatively brittle behavior was observed and large deformations extended into the panel zone of the joints. The retrofit method has increased ductility ratio of the interior beam-column joints by 63%, and energy dissipation capacity by 77%, relative to the control specimen; For external joints, these values were 11%, and 94%. The retrofit method has successfully relocated the plastic joints far from the column face. The retrofit method has improved shear strength of the joints by less than 10%.