• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.431-438
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• 2016

In this paper, a self-powered quadcopter is designed and manufactured. The quadcopter gains extra power via two types of generators which utilize the principle of electromagnetic induction. One of the types is to make use of a commercial BLDC motor which rotates together with a propeller and thus acts as a generator. The other type is to make use of a coil-wound ring around a propeller which generates electricity when small magnets embedded in a uniquely designed frame rotate together with the propeller. The proposed generators are expected to be of practical use when they are located under the propellers of a quadcopter.

• Journal of Wind Energy
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• v.15 no.2
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• pp.23-36
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• 2024

In this study, a health monitoring system was developed for the two most vulnerable parts of a wind tower support structure: the connection between steel towers (L-Flange) and the concrete foundation-steel tower connection. To select assessment parameters for health monitoring, detailed FEM analysis was conducted using the ABAQUS program. Additionally, a testbed was established near the Jeju Woljeongri wind turbine farm to evaluate the applicability of measurement data by installing sensors. Through computational analysis and relevant criteria review, we defined limits for measurement parameters by vulnerable section. We categorized the structural safety evaluation into four stages: normal, caution, warning, and danger, and selected management criteria for each stage. From this, an algorithm to evaluate safety was developed, and a visualized monitoring platform based on the established critical parts monitoring system was developed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.5
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• pp.175-181
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• 2005

Ingots of rutile single crystals were grown by the skull melting method, and their characteristics were compared in terms of melt-dwelling time for each melt. The method is based on direct inductive heating of an electrically conducted melt by an alternating RF field, and the heating is performed by absorption of RF energy. $TiO_2$ is an insulator at room temperature but its electric conductivity increases elevated temperature. Therefore, titanium metal ring(outside diameter : 6cm, inside diameter : 4cm, thickness 0.2cm) was embedded into $TiO_2$, powder (anatase phase, CERAC, 3N) for initial RF induction heating. Important factors of the skull melting method are electric resistivity of materials at their melting point, working frequency of RF generator and cold crucible size. In this study, electric resitivity of $TiO_2$, $(10^{-2}\~10^{-1}\;{\Omega}{\cdot}m)$ at its melting point was estimated by compairing the electric resitivities of alumina and zirconia. Inner diameter and height of the cold crucible was 11 and 14cm, respectively, which were determined by considering of the Penetration depth $(0.36\~1.13cm)$ and the frequency of RF generator.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.8
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• pp.185-194
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• 2014

In this paper, we proposed the clothing management system using the smart hanger. Proposed system consists of smart hanger, base module, and server, and the smart hanger consists of MCU, LED, RFID reader, RF chip, ring sensor, and battery. The smart hanger reads the RFID tag attached to the clothes and wirelessly transmitted to the server. The server associated base module communicates with the smart hanger and transmits information to the server. The server manages clothing through the DB, and can display various information through the web page and the smart phone. In order to verify the usefulness of the proposed system, we did experiment with the management system for clothing store and laundry where using a lot of hangers. Performance tests of the smart hanger are applied to check the current consumption and can be predicted the battery life with the proposed low power algorithm. The clothing store management system can be increased sales and convenience of the consumer. The laundry management system can be increased the efficiency of laundry category and convenience of the consumer.

• Steel and Composite Structures
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• v.27 no.5
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.35 no.6
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• pp.3-12
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• 2019

Current risk assessment methods typically determine accident risks embedded in construction projects by combining severity and frequency; however, they do not reflect the characteristics of construction projects. To solve the problem, this study aims to develop a novel risk assessment method that combines severity, frequency, and disaster influence factors (i.e., weather conditions and worker's characteristics) for assessing risks of activities occurring on a construction site actually. In this study, a severity was estimated by death against victims, and a frequency was estimated by the victim rate. The frequency was then converted to probability taking disaster influence factors into account. Thus, instead of considering severity and frequency for assessing the original risks (RO), the proposed method uses severity and probability to yield adjusted risks (RA) for each activity. A case study was conducted to determine if the proposed method works as intended in a real setting. The results show that RA is more sensitive to disaster influence factors than RO and, therefore, is able to assess the actual risks reflecting the working environment and conditions of a construction site. This study contributes to risk management of construction projects by offering a risk assessment method that measures a possibility of potential disasters from the probabilistic perspective. This method would help project managers assess accident risks in a more systematic and quantitative manner.

• The Korean Journal of Zoology
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• v.15 no.3
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• pp.133-147
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• 1972

Ultrastructures of spermiogeneis in other invertebrates were investigated by several workes (Anderson, et al., 1967; Bloch, et al., 1964; Christen, 1961; Gatenby, et al., 1959; Paik, et al., 1968; Silveira, 1964; Yasuzumi, 1957) but spermiogenesis of dragonfly has not been reported previously. Testes and vass deferentia of the Korean dragonfly, Crocothemis servilia, were used for electron microscopic study of spermiogenesis. Materials were prefixed for 1-2 hours at $3^{\circ}C$ in 1.25% glutaraldehyde buffered to pH 7.2 with 0.2M sodium cacodylate buffer. Fixed tissue was washed twice in 0.2M cacodylate buffer and was subsequently postfixed for 2 hours at $3^{\circ}C$ in 1% osmium tetroxide buffered to pH 7.2 with 0.4M sodium cacodylate buffer solution. Specimens were dehydrated in graded ethyl alcohol, and finally embedded in epoxy Epon resin. Thin sections prepared from all the blocks were doubly stained; first in uranyl acetate and then in lead citrate. All thin sectios were examined with a Hitachi HS-7S electron microscope. The results of this study were summarized as follows. 1. Along the condensation of chromatin in nucleus, the shpae of nucleus was changed from spherical shpae to ellipse and cone cell type. 2. During the elongation of nucleus and the migration of cytoplasm, the nucleus removed to the one side of spermatid and began to invaginate from the posterior portion of nucleus. 3. There are ring centrioles in invaginated portion and axial filaments derived from centriole extend to the tail through the tailward half of spermatid. 4. In the cross sections the axial filament consisted of a central sheath, a central fibril, and 9 peripheral doublets.

• Polymer(Korea)
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• v.30 no.3
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• pp.196-201
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• 2006

Poly (ethylene glycol)-based diblock and triblock thermo- sensitive polyester copolymers were investigated for application on tissue engineering and injectable biomaterials in drug delivery system due to their nontoxicity, biocompatibility and biodegradability. We synthesized the diblock copolymers consisting of methoxy poly (ethylene glycol) (MPEG) (Mn=750 g/mole) and poly $(\varepsilon-caprolactone)$ (PCL) by ring opening polymerization of $\varepsilon-CL$ with MPEG as an initiator in the presence of HCl $Et_2O$. The effect of diblock copolymers on in vivo osteogenic differentiation of rat bone marrow stromal cells (BMSCS) with and without the presence of osteogenic supplements (dexamethasone) was investigated. Thin sections were cut from paraffin embedded tissues and histological sections were stained by H&E, von Kossa, and immunohistochemical staining for osteocalcin. In conclusion, dexamethasone containing thermo- sensitive hydrogel might be improved osteogenic differentiation of BMSCs. We expect the osteoinduction effect to be excellent when it uses stem cell or other osteogenic materials.

• Restorative Dentistry and Endodontics
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• v.13 no.2
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• pp.337-348
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• 1988

The purpose of this study was to examine the fracture strength and characteristics of teeth with MOD cavity preparation. Freshly extracted sound maxillary premolars were cleaned and stored in normal saline solution $37^{\circ}C$ for 72 hours before experiments. The roots of teeth were embedded in a self-curing resin, and the exposed crown were maintained in a vertical position by a modelling wax in a brass ring. The MOD cavities were prepared with No. 57 carbide bur under high speed to a depth of 2.0mm and a width of 2.0mm(Fig.1). All the prepared teeth specimens were divided into 7 groups according to the mode of cavity form and restorative materials (Table 1, 2): Group I, unpreapred, intact teeth as control Group II, prepared cavity without restoration Group III, prepared teeth restored with amalgam Group IV, prepared teeth restored with composite resin (P-10) Group V, prepared teeth with beveled enamel margins restored with composite resin (P-10) Group VI, prepared teeth restored with light-cured composite resin (P-30) Group VII, prepard teeth with beveled enamel margins restored with light-cured composite resin (P-30) After placement of restorations, all of the specimens were stored in water at $37^{\circ}C$ for 72 hours before testing. All of the specimens were tested on the Instron Universal Testing machine (No. 6025) in order to evaluate the strength of fracture. One metal ball 5.0mm in diameter contacting the specimens parallel to the occlusal surface was used to in this study (Fig. 1). The fracture characteristics of the specimens were examined with naked eye and in the scanning electron microscope (JSM-20). The results obtained from this study were as follows: 1. The mean fracture strength was the highest in group VI and that in group II was the lowest. 2. The progress of crack of teeth propagated into the pulp cavity. 3. In case of the group of the restored teeth, the crack occurred to be accompanied with cuspal fracture. 4. The crack of restored teeth was initiated along the pulpo-axial line angle of the cavity.

• Journal of Gastric Cancer
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• v.1 no.2
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• pp.92-99
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• 2001

Purpose: E-cadherin is an adhesion molecule essential for tight connection between cells, forming the cadherin/catenin complex. Truncated $\beta$-catenin disrupts the interaction between E-cadherin and $\alpha$-catenin, leading to the loss of intercellular adhesion. Met protein, the hepatocyte growth factor receptor, plays important roles in signal transduction. We investigated the relationships between the expressions of E-cadherin, $\beta$-catenin, and c-met protein and the clinicopathological and prognostic parameters in gastric adenocarcinomas. Materials and Methods: The patterns of E-cadherin, $\beta$-catenin, and c-met protein expression were studied using immunohistochemistry in formalin-fixed, paraffin-embedded archival tissues from 76 surgically resected gastric adenocarcinomas. Results: Increased expressions of E-cadherin, $\beta$-catenin, and c-met were more significantly correlated in early gastric cancers (EGC) than in advanced gastric cancers (AGC) (P=0.002, P=0.003 and P=0.026). The positive immunoreactivities of all three markers were markedly lower in signet ring-cell type and poorly differentiated type lesions than in intestinal-type lesions. Decreased expression of the $\beta$-catenin protein correlated well with increased tumor invasion depth (P=0.039), and increased lymph node metastasis correlated well with reduced expression of c-met (P=0.046). Conclusion: In gastric cancers, reduced expressions of the E-cadherin, $\beta$-catenin, and c-met proteins may play some role in poorer tumor differentiation, deeper tumor invasion, and increased lymph node metastasis. Also, the c-met gene is thought to play a specific role in the mechanism of the yet unknown catenin action.