• Journal of Periodontal and Implant Science
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• v.41 no.5
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• pp.242-247
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• 2011

Purpose: The purpose of this study was to characterize the osseointegration of the fibronectin-coated implant surface. Methods: Sand-blasted, large-grit, acid-etched (SLA) surface implants, with or without a thin calcium phosphate and fibronectin coating, were placed in edentulous mandibles of dogs 8 weeks after extraction. All dogs were sacrificed forhistological and histomorphometric evaluation after 4- and 8-week healing periods. Results: All types of implants were clinically stable without any mobility. Although the bone-to-implant contact and bone density of the SLA implants coated with calcium phosphate (CaP)/fibronectin were lower than the uncoated SLA implants, there were no significant differences between the uncoated SLA surface group and the SLA surface coated with CaP/fibronectin group. Conclusions: Within the limits of this study, SLA surfaces coated with CaP/fibronectin were shown to have comparable bone-to-implant contact and bone density to uncoated SLA surfaces.

• The Journal of the Korean dental association
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• v.54 no.7
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• pp.529-540
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• 2016

Objective: The objective of this study was to evaluate the osseointegration of narrow-diameter implant with trapezoid-shape and to evaluate the effect of coronal microthreads on trapezoid-shape narrow-diameter implant. Materials and Methods: The experimental narrow-diameter implants were classified into two groups according to absence or presence of coronal microthreads: trapezoid-shape narrow diameter implant (TN group) and trapezoid-shape narrow-diameter implant with microthreads (TNM group). They were installed alternately in bilateral mandible in three dogs. After 8 weeks, the animals were sacrificed. Resonance frequency analysis, removal torque test, and histometric analysis were performed. Results: Statistically higher implant stability quotient (ISQ) values were observed in TNM group than in TN group at the time of implant installation. However, significant ISQ values difference was not observed between groups at 8 weeks. Both groups showed significantly increased ISQ values at 8 weeks, compared to the time of implant installation. There was no significant difference between groups in removal torque test. Bone-implant contact ratio also showed no significant difference between groups in total and coronal part. Conclusion: Within the limitation of this study, it could be concluded that the trapezoid-shape design on narrow-diameter implant showed successful ossointegration, and the microthreads on coronal part did not result in significant bone-implant contact and biomechanical stability at 8 weeks.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.1
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• pp.19-23
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• 2014

For the application of light-emitting diodes (LEDs) for general illumination, the development of high power LEDs chips became more essential. For these reasons, recently, modified vertical LEDs have been developed to meet various requirements such as better heat dissipation, higher light extraction and less cost of production. In this research, we investigate the effect of Size and Array of N-GaN contact on operation voltage with new structured padless vertical LED. We changed the size and array of N-electrodes and investigated how they affect the operation voltage of LEDs. We simulated the current crowding and expected operation voltage for different N-contact structures with commercial LED simulator. Also, we fabricated the padless vertical LED chips and measured the electrical property. From the simulation, we could know that the larger size and denser array of n-electrodes could make operation voltage decrease. These results are well in accordance with those measured values of real padless vertical LED chips.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.37 no.6
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• pp.448-456
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• 2011

Introduction: Condylar fractures are common in the maxillofacial region, comprising 29-40 percent of all mandibular fractures, accounting for about 20-62 percent). Previous studies reported that pediatric condylar fractures can cause disorders in facial growth and function, and the treatment methods have been controversial. Recently, conservative treatment has shown good results in skeletal growth and functional recovery but the conservative treatment of pediatric condylar fractures has shown unpredictable and undesirable results in some cases, such as facial asymmetry and temporomandibular joint disorder. This study examined the specific age groups and specific mandibular condylar fracture type in growing children treated conservatively in the past. Materials and Methods: Eighteen patients (10 men and 8 women) who received conservative treatment for unilateral condylar fractures in Dankook University Dental Hospital between 2000 to 2007 were followed up for a mean period of 7.2 years. Results: In the survey of 18 pediatric patients who received conservative treatment for condylar fractures, the incidence of temporomandibular dysfunction and growth disturbance was 45% and 35%, respectively. Conclusion: In all complications, the symptoms observed most frequently was mouth opening displacement of the mandible exceeding 2 mm. The other complications of functional and growth disturbance included facial asymmetry concentrated along specific condylar types. Complications including facial asymmetry and functional and growth disturbances showed an increasing tendency according to the specific fracture types. Functional and growth disturbances in the undisplaced condylar fracture type showed a lower incidence(P <0.05). Functional and growth disturbances differed according to the fracture type, which has poor relationship with articular fossa and condyle(P <0.05). Functional and growth disturbance in the cases of the high-level condylar fracture type showed a higher incidence(P <0.05). The functional and growth disturbances of the fracture types were similar in the fragment-contact and non-contact groups(P >0.05).

• Journal of the Korean Electrochemical Society
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• v.12 no.1
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• pp.68-74
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• 2009

The effect of physico-electrochemical properties of carbon bipolar plate(BPP) on hydrogen and formic acid fuel cell performance has been investigated. BPP made of conventional graphite and carbon fiber composite were compared with the factors of interfacial contact resistance (ICR), corrosion behaviours, and hydrophobicity. Among them, the ICR of carbon fiber composite BPP has 50% higher than conventional graphite and the surface of carbon fiber composite BPP became rougher due to weaker corrosion resistance. Fuel cell performance was strongly dependent of ICR value of carbon bipolar plate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3048-3057
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• 1996

Analysis model containing two inclined surface cracks on semi-infinite elastic body is established and analyzed on the basis of linear fracture mechanics to examine mutual interference of two surface cracks. Muskhelishvili's complex stress functions are introduced and a set of singular integral equations is obtained for a dislocation density function. The stress intensity factors at crack tip are obtained by using the Gerasoulis'method. When two surface cracks are parallel and have the same length, the values of $K_1$and $\Delta K_11$(variation of $K_11$) for crack 1 and crack 2 decrease by the mutual interference of two surface cracks as the distance between the two surface cracks shortens. The effect of mutual interference is remarkable in high friction coefficient. In case that two surface cracks are parallel, the values of $K_1$and $\Delta K_11$for crack 2 decrease as the length ratio ot crack 2 to crack 1 becomes small. As the crack inclination angle rises, the value of $K_1$ and the mutual interference of $K_1$for crack 2 increase and the value of$\Delta K_11$ for crack 1 becomes smaller than that for crack 2.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2636-2646
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• 2002

This research presents an analytical model to investigate vibration due to ball bearing waviness in a rotating system supported by two or more ball bearings, taking account of the centrifugal force and gyroscopic moment of the ball. The waviness of rolling elements is modeled by the sinusoidal function, and it is incorporated into the position vectors of the race curvature center. The Hertzian con tact theory is applied to calculate the elastic deflection and nonlinear contact force while the rotor has translational and angular motions. Both the centrifugal force and gyroscopic moment of the ball and the waviness of the rolling elements are included in the kinematic constraints and force equilibrium equations of a ball to derive the nonlinear governing equations of the rotor, which are solved by using the Runge-Kutta-Fehlberg algorithm to determine the new position of the rotor. The proposed model is validated by the comparison of the results of the prior researchers. This research shows that the centrifugal force and gyroscopic moment of the ball plays the important role in determining the bearing frequencies, i.e. the principal frequencies, their harmonics and the sideband frequencies resulting from the waviness of the rolling elements of ball bearing. It also shows that the bearing vibration frequencies are generated by the waviness interaction not only between the rolling elements of one ball bearing but also between those of two or more ball bearings constrained by the rotor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.885-894
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• 2012

A numerical study of a microchannel steam methane reforming reactor has been performed to understand the characteristics of heat and mass transfer. The integration of Rh-catalyzed steam methane reforming and Pt-catalyzed methane combustion has been simulated. The reaction rates for chemical reactions have been incorporated into the simulation. This study investigated the effect of contact time, flow pattern (parallel or counter), and channel size on the reforming performance and temperature distribution. The parallel and counter flow have opposite temperature distribution, and they show a different type of reaction rate and species mole fraction. As the contact time decreases and channel size increases, mass transfer between the catalyst layer and the flow is limited, and the reforming performance is decreased.

• Journal of the Korean Chemical Society
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• v.56 no.5
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• pp.597-602
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• 2012

The copolymerization of triacetoxyvinylsilane, EGDMA (ethylene glycol dimethacrylate as a cross-linker), HEMA (2-hydroxyethyl methacrylate), MMA (methyl methacrylate), MA (methacrylic acid) was performed in the presence of AIBN (2,2'-azobisisobutyronitrile) as an initiator. Measurement of the physical properties of the resulting copolymers showed that water content, refractive index, visible ray transmittance, and tensile strength were in the range of 35.63~32.44%, 1.4382~1.4480, 89.0~92.5% and 0.346~0.674 kgf, respectively. The values of tensile strength of copolymers-containing hexamethylene diisocyanate were higher than those of the copolymers containing triacetoxyvinylsilane. From the results we came to the conclusion that the produced copolymers are suitable for the application of ophthalmic contact lens with high tensile strength, wettability and duraility.

• Journal of the Korea Society of Computer and Information
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• v.22 no.3
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• pp.53-60
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• 2017

The purpose of this study is to provide empirical and quantitative analysis on user's perceived privacy, security, and user satisfaction when providing visualization information about objects and service provider behaviors that users can not perceive in internet service process. Through previous research, we have examined the importance of privacy and security factors as a key factor to be considered for the characteristics of the Internet of things and the Internet of things. In addition, service blueprint, which is one of the service design methodologies to examine the flow of service usage in providing Internet service of things, was examined. In the flow of things internet service utilization, it is found that the things that are out of the user's cognitive area and the behavior of the service provider take up a large part. Therefore, the hypothesis that the trust of the Internet service security and the satisfaction of the user experience can be improved by providing the security visualization information about the behavior of the object and the invisible service provider in the non-contact aspect of the user and the object. In order to verify the hypothesis, we conducted experiments and questionnaires on the use of virtual objects' internet environment and conducted statistical analysis based on them. As a result, it was analyzed that visual information feedback on non - contact and invisible objects and service provider's behaviors had a positive effect on user's perceived privacy, security, and satisfaction. In addition, we conclude that it can be used as a service design evaluation tool to eliminate psychological anxiety about security and to improve satisfaction in internet service design. We hope that this research will be a great help for the research on application method of service design method in Internet environment of objects.