• The Journal of the Acoustical Society of Korea
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• v.17 no.1E
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• pp.44-53
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• 1998

Bolt degradation has become a major issue in the nuclear industry since the 1980's due to failure during operation. If small cracks in stud bolt are not detected early enough, they grow rapidly and cause catastrophic disasters. Their detection, despite its importance, is known to be a very difficult problem due to the complicated structures of the stud bolts. This paper presents a method of detecting and sizing a small crack in the root between two adjacent crests in threads. The key idea is from the fact that the Rayleigh wave propagates slowly along a crack from the tip to the opening and is reflected from the opening mouth. When there exists a crack, a small delayed pulse due to the Rayleigh wave is detected between large regularly spaced pulses from the thread. The delay time is the same as the propagation delay time of the slow Rayleigh wave and is proportional to the size of the crack. To efficiently detect the slow Rayleigh wave, three methods based on digital signal processing are proposed : modified wave shaping, dynamic predictive deconvolution, and dynamic predictive deconvolution combined with wave shaping.

• Korean Journal of Materials Research
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• v.24 no.7
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• pp.344-350
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• 2014

Metal films (i.e., Ti, Al and SUH310S) were prepared in a magnetron sputtering apparatus, and their cross-sectional structures were investigated using scanning electron microscopy. The apparatus used consisted of a cylindrical metal target which was electrically grounded, and two anode rings attached to the top and to the bottom of the target. A wire was placed along the center-line of the cylindrical target to provide a substrate. When the electrical potential of the substrate was varied, the metal-film formation rate depended on both the discharge voltage and the electrical potential of the substrate. As we made the magnetic field stronger, the plasma which appeared near the target collected on the plasma wall surface and thereby decreased the bias current. The bias current on the conducting wire was different from that for cation collection. The bias current decreased because the collection of cations decreased when we increased the magnetic-coil current. When the substrate was electrically isolated, the films deposited showed a slightly coarse columnar structure with thin voids between adjacent columns. In contrast, in the case of the grounded substrate, the deposited film did not show any clear columns but instead, showed a densely-packed granular structure. No peeling region was observed between the film and substrate, indicating good adhesion.

• Journal of KIBIM
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• v.6 no.3
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• pp.42-48
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• 2016

Structural members are designed to maintain the load-carrying capacity as well as structural strength, and the structural serviceability such as the deflection, cracks, and vibration to give the occupants uncomfortable environment should be checked. Recently, the importance of the vibration has been issued since the Techno Mart accident due to vibration resonance. This study provides a passive vibration control system using the repulsion force of magnets to reduce dynamic vibrations. The systems is devised by importing the constraint condition by a hinge to operate magnets installed at two adjacent locations. The effectiveness of the proposed system is investigated by the vibration control test of a steel beam with and without the control system. It is illustrated in the test that the system is activated by the control forces executed by the magnets and can be utilized in reducing the dynamic responses. The system can be applied to pedestrian bridge and traffic bridge. The applicability is expected in the future by optimizing the factors to affect the dynamic responses like the intensity, mass, locations of magnets.

• Bulletin of the Korean Chemical Society
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• v.20 no.1
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• pp.42-48
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• 1999

We have performed a quantum-chemical investigation on the conformations and electronic properties of a variety of methoxy-substituted poly(p-phenylenevinylenes) (PPVs) to elucidate the effects of alkoxy substitution. Geometrical parameters for the polymers were fully optimized through Austin Model I (AM I) semi-empirical Hartree-Fock (HF) band calculations. Electronic properties of the polymers were obtained by applying the AM I optimized structures to the modified extended Huckel method. To confirm validity of the AM I conformational results, we also carried out ab initio HF calculations with the 6-31G (d) basis set for a variety of methoxy-substituted divinylbenzenes. It is found that the potential energy surfaces of alkoxy-substituted PPVs are quite shallow around the planar conformations, suggesting that the prepared films possess a variety of conformations with different torsion angle in the solid state, depending on the synthetic conditions. When two alkoxy groups are concurrently substituted at the adjacent sites in the phenylene ring, these groups are subject to rotating around the C(sp2)-O bonds by 70-80° to avoid the strong steric repulsion between them. Consequently, the overlap between the π-type p orbital of oxygen and the π molecular orbitals of the polymer decreases. This leads to a wide gap and a high oxidation potential for tetramethoxy-substituted PPV, compared to those of dialkoxy-substituted PPV.

• Animal Systematics, Evolution and Diversity
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• v.33 no.2
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• pp.65-72
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• 2017

This study reports three species in the genus Tubastraea from Korea: Tubastraea coccinea Lesson, 1829; Tubastraea faulkneri Wells, 1982; and Tubastraea micranthus (Ehrenberg, 1834). Tubastraea faulkneri and T. micranthus are newly recorded in Korea. The specimens of three species were collected in the subtidal zones off Jeju-do between 1991 and 2010. The two newly recorded species were described in detail based upon the morphological characters of skeletal structures. The previous records of T. coccinea in Korea were supplemented with additional data in the remarks. These three species have a straight septal arrangement or irregular septal fusion in common as a main character for the genus Tubastraea, but they differ with respect to the growth form, intercorallite distance, exsertness from common coenosteum, and the detailed characters of septal arrangement. Tubastraea faulkneri is similar to T. coccinea in its plocoid growth form, well developed common coenosteum, and corallite size. However, unlike the latter species, the former species is characterized by rare or absent budding adjacent to the corallite edges, wider intercorallite distance, and irregularly developed septal fusion near the columella. In particular, T. micranthus is distinguished by an axial dendroid growth form, and the smallest corallites in this genus.

• Structural Engineering and Mechanics
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• v.68 no.5
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• pp.621-632
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• 2018

Soft-story buildings have bottom stories much less rigid than the top stories and are susceptible to earthquake damage. Therefore, the seismic design specifications need strict design considerations in such cases. In this paper, a four-story building was investigated as a case study and the effects of X-braces elimination in its lower stories studied. In addition, the possibility of replacement of the X-braces in soft-stories with equivalent moment resisting frame inspected in two different phases. In first phase, the stiffness of X-braces and equivalent moment-resisting frames evaluated using classic equations. In final phase, diagonals removed from the lowest story to develop a soft-story and replaced with moment resisting frames. Then, the seismic stiffness variation of moment-resisting frame evaluated using nonlinear static and dynamic analyses. The results show that substitution of braced frames with an equivalent moment-resisting frame of the same stiffness increases story drift and reduces energy absorption capacity. However, it is enough to consider the needs of building codes, even using equivalent moment resisting frame instead of X-Braces, to avoid soft-story stiffness irregularity in seismic design of buildings. Besides, soft-story development in the second story may be more critical under strong ground excitations, because of interaction of adjacent stories.

• Structural Engineering and Mechanics
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• v.82 no.3
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• pp.385-400
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• 2022

Sky-bridges between adjacent buildings can enhance lateral stiffness and limit the impact of lateral forces. This study analysed the structural capabilities and dynamic performances of sky-bridge-coupled buildings under various sets of ground motions. Finite Element (FE) analyses were carried out with the link being iteratively repositioned along the full height of the structures. Incremental dynamic analysis (IDA) and probabilistic damage distribution were also applied. The results indicated that the establishment of sky-bridges caused a slight change in the natural frequency and mode shapes. The sky-bridge system was shown to be efficient in controlling displacement and Inter-Storey Drift Ratio (%ISDR) and reducing the probability of damage in the higher floors. The most efficient location of the sky-bridge, for improving its rigidity, was found to be at 88% of the building height. Finally, the effects of two types of materials (steel and concrete) and end conditions (hinged and fixed) were studied. The outcomes showed that coupled buildings with a sky-bridge made of steel with hinged connection could withstand ground motions longer than those made of concrete with fixed connection.

• Geomechanics and Engineering
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• v.32 no.6
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• pp.653-671
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• 2023

In practice, the interference influence caused by adjacent footings of structures on geo-reinforced loose soil has a considerable impact on their behavior. Thus, the goal of this study is to evaluate the behavior of two strip footings in close proximity on both geocell and geogrid reinforced soil with different reinforcement layers. Geocell was made from geogrid material used to compare the performance of cellular and planar reinforcement on the bearing pressure of twin footings. Extensive experimental tests have been performed to attain the optimum embedment depth and vertical distance between reinforcement layers. Particle image velocimetry (PIV) analysis has been conducted to monitor the deformation, tilting and movement of soil particles beneath and between twin footings. Results of tests and PIV technique were verified using finite element modeling (FEM) and the results of both PIV and FEM were used to utilize failure mechanisms and influenced shear strain around the loading region. The results show that the performance of twin footings on geocell-reinforced sand at allowable and ultimate settlement ranges are almost 4% and 25% greater than the same twin footings on the same geogrid-reinforced sand, respectively. By increasing the distance between twin footings, soil particle displacements become smaller than the settlement of the foundations.

• Journal of the korean academy of Pediatric Dentistry
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• v.50 no.1
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• pp.121-130
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• 2023

In children, large odontogenic cysts affect adjacent anatomical structures as well as displace developing permanent teeth. Odontogenic cysts are treated via enucleation or marsupialization. This case reports a 5-year-old boy and a 10-year-old boy who have not only displaced 3 or more permanent teeth but also elevated the maxillary sinus floor due to the large size of the cyst in the maxillary anterior region. In both cases, marsupialization was selected to minimize complications. After marsupialization, a customized acrylic obturator, window opening, and orthodontic traction for eruption guidance were gradually attempted, and it showed a good prognosis, so we report these cases.

• Smart Structures and Systems
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• v.21 no.5
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• pp.623-635
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• 2018

In order to study the mechanical behavior of shield tunnel segments during assembly stage, the in-situ tests and FDM numerical simulation were conducted based on the Foguan Shiziyang Tunnel with large cross-section. Analysis for the load state of the assembling segments in different assembly steps as well as the investigation for the changing of inner forces and longitudinal stress of segments with assembling steps were carried out in this paper. By comparing the tested results with the simulated results, the conclusions and suggestions could be drawn as follows: (1) It is the most significant for the effects on axial force and bending moment caused by the assembly of adjacent segment, followed by the insertion of key segment while the effects in the other assembly steps are relative smaller. With the increasing value of axial force, the negative bending moment turns into positive and remains increasing in most monitored sections, while the bending moment of segment B1and B6 are negative and keeping increasing; (2) The closer the monitored section to the adjacent segments or the key segment, the more significant the internal forces response, and the monitored effects of key segment insertion are more obvious than that of calculation; (3) The axial forces are all in compression during assembling and the monitored values are about 1.5~1.75 times larger than the calculated values, and the monitored values of bending moment are about 2 times the numerical calculation. The bending moment is more sensitive to the segments assembly process compared with axial force, and it will result in the large bending moment of segments during assembling when the construction parameters are not suitable or the assembly error is too large. However, the internal forces in assembly stage are less than those in normal service stage; (4) The distribution of longitudinal stress has strong influence on the changing of the internal forces. The segment side surface and intrados in the middle of two adjacent jacks are the crack-sensitive positions in the early assembly stage, and subsequently segment corners far away from the jacks become the crack-sensitive parts either.