• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.26 no.2
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• pp.181-189
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• 1996

Ameloblastic odontoma is a mixed odontogenic tumor, which is characterized as being extremely rare, displaying aggressive clinical behavior, resembling a mixed radiopaque and radiolucent radiographic appearance and containing both ameloblastoma and a composite odontoma. Seven-year-old boy complaining of delayed eruption of the left lower permanent 1st molar came to the department of Oral & Maxillofacial Radiology at Chonbuk National University Hospital. The list of our radiographic differential diagnosis included the dental follicle, compound odontoma, complex odontoma and cystic odontoma. The microscopic analysis showed the lesion with the characteristics of an ameloblastic odontoma. The obtained results were as follows; 1. The area was asymptomatic, but the delayed eruption of the left lower permanent 1st molar was observed. Radiographically, well-defined widened pericoronal radiolucency containing several tooth-like radiopacities involving the impacted left lower permanent 1st molar and well-defined round radiolucency containing irregular radiopaque mass were observed. 3. Histopathologically, several tooth-like structures, odontoma components with the area of typical enamel, dentin and pulp, and ameloblastic components with typical follicular ameloblastoma were observed.

• Journal of ILASS-Korea
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• v.3 no.4
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• pp.58-64
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• 1998

In the gasoline engine of fuel injection type, atomization of fuel droplet and its distribution has directly influenced the performance of engine and harmful emission. To investigate atomization characteristics of fuel spray, in this paper fuel spray of air-assisted injector is observed at the various initial conditions of ambient air temperature and air assisted pressure. Behavior of fuel spray is photographed with microscopic visualization system. The SMD of fuel droplet is measured with PMAS (Particle Motion Analysis System). The effect of air-assisted pressure and temperature of ambient air resulted in the decrement of SMD and its variation. Finally, It was found that It was found that from spray angle at the two-hole injector had measured $20{\pm}4$ degree the result of photographs by shadow graphy. The mean diameter of suns decreased and the of droplets increased with increasing the temperature in the spray fields by the results of PMAS measurement. It was found that the characteristics of sprays became finer by increasing the temperature of spray fields about 373K without the delivery of air-assistance.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.247-253
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• 2010

The characteristics of selective oxidation prior to hot-dip galvanizing with the annealing atmosphere dew point and chemical composition in dual-phase steels and their effect on the inhibition layer formation relevant to coating adhesion have been studied using a combination of electron microscopic and surface analytical techniques. The annealed and also galvanized samples of 3 kinds of Si/Mn ratios with varied amounts of Si addition were prepared by galvanizing simulator. The dew point was controlled at soaking temperature $800^{\circ}C$ in 15%$H_2$ -85%$N_2$ atmosphere. It was shown that good adhesion factors were mainly uniformity of oxide particle distribution of low number density and low Si/Mn ratio prior to hot-dip galvanizing. Their effect was the greatly reduced coating bare spots and the formation of uniform inhibition layer leading to good adhesion of Zn overlay. The mechanism of good adhesion is suggested by two processes: the formation of inhibition layer on the oxide free surface uncovered with no $SiO_2$-containing particles in particular, and the inhibition layer bridging of oxide particles. The growth of inhibition layer was enhanced markedly by the delayed reaction of Fe and Al with the increase of Si/Mn ratio.

• Corrosion Science and Technology
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• v.19 no.3
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• pp.138-145
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• 2020

Immersion tests of Alloy 600 were conducted in simulated primary water environments of a pressurized water reactor at 325 ℃ for 10, 100, and 1000 h to obtain insight into effects of surface deformation on internal and intergranular (IG) oxidation behavior through precise characterization using various microscopic equipment. Oxidized samples after immersion tests were covered with polyhedral and filamentous oxides. It was found that oxides were abundant in mechanically ground (MG) samples the most. The number density of surface oxides increased with time irrespective of the method of surface finish. IG oxidation occurred in mechanically polished (MP) and chemically polished (CP) samples with thin internal oxidation layers. However, IG oxidation was suppressed with relatively thick internal oxidation layers in MG samples compared to MP and CP samples, suggesting that MG treatment could increase resistance to primary water stress corrosion cracking (PWSCC) from the standpoint of IG oxidation. As a result, appropriate surface treatment for Alloy 600 could prevent oxygen diffusion into grain boundaries, inhibit IG oxidation, and finally induce its high PWSCC resistance.

• Korean Journal of Materials Research
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• v.10 no.11
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• pp.725-731
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• 2000

Recrystallization behaviors of cold-worked and $\beta$-quenched Zr-Zn alloys were investigated by the microhardness tests and microscopic examinations. The recrystallization of the $\beta$-quenched alloys was retarded in comparison with that of the cold-worked alloys, suggesting that the stored energy of the cold-worked alloys is larger than that of the $\beta$-quenched alloys. Although initial hardness for the cold-worked and the $\beta$-quenched specimens had an equal value, the recrystallization behaviors were observed to be quite different. Based on the transmission electron microscope(TEM) studies, it was suggested that the recrystallization of the cold-worked specimen would have occurred by subgrain coalescence while that of $\beta$-quenched specimen by strain-induced grain boundary migration.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.32 no.5
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• pp.1-7
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• 2000

Alkaline Sizing behavior and mechanism of handsheets, which were prepared from thermomechanical pulp (TMP) with alkylketene dimer (AKD), were studied in terms of the conditions of the handsheet-making. AKD content in the TMP handsheets was increased with increasing of AKD addition level and the addition of a polyamideamine-epichlorohydrin resin (PAE) clearly enhanced AKD retention as well as the resultant sizing performance of TMP handsheets. Although drying of the AKD sized TMP webs at $20^{\circ}C$ led to no or quite low sizing level, but TMP handsheets sized with AKD had higher sizing degrees with increasing of the temperature of heat treatment. Scanning electron microscopic observations of the AKD-sized TMP handsheets showed that AKD emulsion particles were present on pulp fiber surfaces independently without coagulation in the TMP handsheets dried at $20^{\circ}C$. Heat treatment of the AKD-sized handsheets resulted in disappearance of the AKD emulsion particles because of their melting and spreading. The addition of calcium carbonate filler to the TMP suspensions did not influence on AKD content in the TMP handsheets. Nevertheless, their sizing degrees clearly increased by the addition of $CaCO_3$filler. Probably, AKD molecules adsorbed on the $CaCO_3$filler particles contribute to the enhancement of sizing performance. Thus, AKD can give sizing features effectively to the TMP handsheets, when they are made under suitable conditions.

• Tribology and Lubricants
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• v.31 no.6
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• pp.287-293
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• 2015

Laser surface texturing (LST), a surface engineering modification, has been considered as one of the new processes used to improve tribological characteristics of materials by creating artificially patterned microstructure on the contact surface of mechanical components. In LST technology, the laser is optimized to obtain or manufacture the dimples with maximum precision. The micro-dimples reduce the coefficients of friction and also improve the wear resistance of materials. This study investigates the effect of dimple density is investigated. For this purpose, a ball-on-disc type tester is used with AISI 52100 bearing steel as the test material. Discs are textured with a 5% and 10% dimple density. Experimental work is performed with normal loads of 5 N, 10 N, and 15 N under a fixed speed of 150 rpm at room temperature. The effect of the textured surface is compared to that of the untextured one. Experimental results show that the textured surface yields lower friction coefficients compared to those of untextured surfaces. Specifically, the 10% dimple density textured surface shows better friction reduction behavior than the 5% dimple density textured sample, and has an 18% improvement in friction reduction compared with the untextured samples. Microscopic observation using a scanning electron microscope (SEM) shows that the major friction mechanisms of the AISI 52100 bearing steel are adhesion, plastic deformation, and ploughing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.938-946
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• 1989

Using the CT specimen of carbon steel(SM45C), we estimated the fatigue crack propagation behavior in stable crack propagation range. Furthermore the fatigue crack propagation rate, Acoustic Emission(AE) count rate, and fractography characteristics were also compared among others. The following results were confirmed by experimental observation. Near-threshold stress intensity factor range(.DELTA. $K_{th}$) is influenced by stress ratio but not at the upper limit of stable crack propagation range. As stress intensity factor range(.DELTA.K) and(or) stress amplitude increase (s), both crack propagation rate(da/dN) and AE count rate(dn/dN) increase. Effective stress intensity factor range(.DELTA. $K_{off}$) determined from the crack closure point measurement by AE method is useful for the evaluation of fatigue crack propagation rate. Fractography in stable crack propagation range showed striation, and agreed with the crack propagation rate obtained either by experiment of by the results of microscopic measurements.s.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.541-549
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• 2007

This work describes an investigation into the feasibility of using an acoustic emission (AE) technique to evaluate the integrity of a composite actuator with a PZT ceramic under electromechanical cyclic loading. AE characteristics have been analyzed in terms of the behavior of the AE count rate and signal waveform in association with the performance degradation of the composite actuator during the cyclic tests. The results showed that the fatigue cracking of the composite actuator with a PZT ceramic occurred only in the PZT ceramic layer, and that the performance degradation caused by the fatigue damage varied immensely depending on the existence of a protecting composite bottom layer. We confirmed the correlations between the fatigue damage mechanisms and AE signal types for the actuators that exhibited multiple modes of fatigue damage; transgranular micro damage, intergranular fatigue cracking, and breakdown by a short circuiting were related to a burst type signal showing a shortly rising and slowly decaying waveform with a comparably low voltage, a continuous type signal showing a gradual rising and slowly decaying waveform with a very high voltage and a burst and continuous type signal with a high voltage, respectively. Results from the present work showed that the evolution of fatigue damage in the composite actuator with a PZT ceramic can be nondestructively identified via in situ AE monitoring and microscopic observations.

• International Journal of Reliability and Applications
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• v.17 no.2
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• pp.137-147
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• 2016

The engine mount of a car subjected to a pre-load related to the weight of the engine, and acts to insulate the vibration coming from the engine by moving on large or small displacement depending on the driving condition of the car. The vibration insulation of the engine mount is an effect obtained by dissipating the mechanical energy into heat by the viscosity characteristic of the rubber and the microscopic behavior of the additive carbon black. Therefore, dynamic stiffness from the intrinsic properties of rubber filled with carbon black at the design stage is an important design consideration. In this paper, we introduced a hyper-elastic, visco-elastic and elasto-plastic model to predict the dynamic characteristics of rubber, and developed a fitting program to determine the material model parameters using MATLAB. The dynamic characteristics analysis of the rubber insulator of the ACTIVE MOUNT was carried out by using MSC.MARC nonlinear structural analysis software, which provides the dynamic characteristics material model. The analysis results were compared with the dynamic characteristics test results of the rubber insulator, which is one of the active mount components, and the analysis results were confirmed to be valid.