• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.34-40
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• 2012

In this study, effects of bonding agent, e.g. epoxy, on the behavior of fundamental guided wave modes propagated in FRP plate bonded on a concrete, are investigated. Global matrix model of multilayered FRP-epoxy-concrete system was constructed to obtain the velocity and attenuation dispersion curves of the fundamental A0 and S0 modes. Two variables, thickness and elastic modulus of epoxy layer, were considered in the dispersion analysis. It was found that both the thickness and the elastic modulus of epoxy layer greatly affect the phase velocity and attenuation of S0 mode while those are negligible for A0 mode. Based on the results, it was concluded that S0 mode is more effective than A0 mode for bonding condition assessment for FRP plate bonded concrete.

• Journal of the Korean Geographical Society
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• v.44 no.3
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• pp.323-338
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• 2009

This study analyzes the changes in commuter's mode choice between 2002 and 2006 according to the implement of the integrated public transit system in Seoul metropolitan city. Especially this study focuses on differential changes in a transit modal choice among socioeconomic status, trip purpose and spatial characteristics of origin and destination. The probability of public transit use against automobile is modeled as a function of socioeconomic variables, spatial characteristics of origin and destination and the utility of the commuter's mode. The results from conditional logit model analyses suggest that people with lower income show the larger changes in the ratio of public transit choice between 2002-06. Also both higher density, more accessible to public transit and more diverse land uses in residence zone and in work place generally increase the ratio of public transit choice between 2002-06. Car and subway have the most strong alternative relation in commuter's mode choice. The findings give an important implication that the integrated public transit system has differential impacts on commuter's mode choice in Seoul.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.2
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• pp.256-268
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• 1999

Submerged implants require secondary surgical uncovering of implants after healing period of 3-6 months. In surgical methods, there are surgical scalpel, tissue punch, electro-surgical, and laser-used uncovering, and so forth The objectives of this study are investigation and assessment of 1) thermal change in clinical application for uncovering of HA-coated implant and pure titanium implant irradiated by pulsed Nd-YAG, $CO_2$, and Er-YAG laser. 2) surface change of cover screws aaer irradiation using laser energy. The temperature of apex & side wall of implants were recorded at 10sec, 20sec, 30sec after 30sec irradiation to implant healing screw; 1) pulsed Nd-YAG laser; 2W, 20pps, contact mode 2) $CO_2$ laser; water-infused & non-water infused state, 2.5-3.5W, contibuous mode, noncontact mode 3) $CO_2$ laser ; non-water infused state, 3W, superpulse, noncontact. mode 4) Er-YAG laser; (1) non-water infused state, 10pps, 60mj, contact mode (2) water-infused state, 10pps, 60mj, 80mj, 101mj, contact mode. According to the results of this study, pulsed Nd-YAG laser is not indicated because of increased thermal change and pitting of metal surface of implant cover screw. By contrast, $CO_2$ laser & Er-YAG laser are presumed to indicate because of narrow range of thermal change & near abscence of thermal damage of metal surface. Dental laser is thought to be much helpful to surgical procedure when it is used as optimal power and time condition considering characteristics and indications of each laser. Further research is needed to verify that these techniques are safe and beneficial to implant success.

• Journal of Advanced Navigation Technology
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• v.9 no.2
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• pp.185-192
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• 2005

The aim of this paper is to analyze handling qualities of tiltrotor aircraft(TR-S4) in helicopter flight mode including hovering and forward flight. Analysis of handling qualities is composed of aircraft response to control inputs that effect on stability and controllability. In short term response analysis, bandwidth is the critical parameter for small amplitude motions since it relates to the ability of a pilot to crisply start and stop maneuver. The handling qualities of TR-S4 in helicopter mode are analyzed with a SAS and an attitude controller and are satisfied level 1 in almost criteria with simulation of TR-S4 6-DOF nonlinear model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.461-471
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• 1989

For the mixed-mode crack problems the direction of crack growth, the crack path and the rational representation of fatigue crack growth rates should be studied to predict fatigue life and safety of structures. In this study, a round specimen which produce nearly identical effects in all loading directions is proposed to make an easy measurement of initial direction of crack growth. The mode I and mode II stress intensity factors of the specimen were calculated using finite element method, in which the square root singular stresses at the crack tip are modeled by means of four rectangular quarter-point eight-noded elements surrounding the crack tip. Experimental results for high strength aluminum alloy showed that the direction of mixed-mode crack growth agree well with maximum principal stress criterion as well as minimum strain energy density criterion, but not with maximum shear stress criterion. From data of fatigue crack growth rates using crack geometry projected on the line perpendicular to the loading direction it is easily established that mixed-mode fatigue crack growth in 5083-H115 aluminum alloy goes predominantly with mode I crack growth behaviors.

• Journal of Information Technology Services
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• v.15 no.4
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• pp.97-109
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• 2016

The rapid deployment of millions of mobile sensors and smart devices has resulted in high demand for opportunistic encounter-based networking. For the cooperative video surveillance of dashboard cameras in nearby vehicles, a fast and energy-efficient asynchronous neighbor discovery protocol is indispensable because a dashboard camera is an energy-hungry device after the vehicle's engine has turned off. In the existing asynchronous neighbor discovery protocols, all nodes always try to discover all neighbors. However, a dashboard camera needs to discover nearby dashboard cameras when an event is detected. In this paper, we propose a fast and energy-efficient asynchronous neighbor discovery protocol, which enables nodes : 1) to have different roles in neighbor discovery, 2) to discover neighbors within a search range, and 3) to report promptly the exact discovery result. The proposed protocol has two modes: periodic wake-up mode and active discovery mode. A node begins with the periodic wake-up mode to be discovered by other nodes, switches to the active discovery mode on receiving a neighbor discovery request, and returns to the periodic wake-up mode when the active discovery mode finishes. In the periodic wake-up mode, a node wakes up at multiples of number ${\alpha}$, where ${\alpha}$ is determined by the node's remaining battery power. In the active discovery mode, a node wakes up for consecutive ${\gamma}$ slots. Then, the node operating in the active discovery mode can discover all neighbors waking up at multiples of ${\beta}$ for ${\beta}{\leq}{\gamma}$ within ${\gamma}$ time slots. Since the proposed protocol assigns one half of the duty cycle to each mode, it consumes equal to or less energy than the existing protocols. A performance comparison shows that the proposed protocol outperforms the existing protocols in terms of discovery latency and energy consumption, where the frequency of neighbor discovery requests by car accidents is not constantly high.

• Journal of the Korean Society of Combustion
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• v.12 no.4
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• pp.31-38
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• 2007

An numerical study was conducted on superdetonative mode ram accelerator with length extended combustor. The computation condition was based on ISL's RAMAC30 II S225 experiment. For 50% length increased combustor, flame is not sustained. For the case of 60% and 70% increase, flame is successfully sustaind. But detonation wave is oscillating and acceleration is fluctuating. Extention of combustor is helpful for sustaing detonation wave but it may cause unstart.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.12
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• pp.1296-1301
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• 1991

This paper presents a hybrid image mode Galerkin method for the analysis of the transmission line structures suspended between infinite parallel ground planes. A Green's function that consists of numerically accelerated image mode terms is developed, which is used in boundary integral equation. Transmission lines of arbitrary cross section are analyzed using Galerkin's method. Two kinds of configurations of transmission lines are studied in sample problems.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.240-243
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• 2008

Using the well-known Fokker-Planck method, this paper presents a standard way to find the joint-characteristic function for the first- and second-order polarization-mode-dispersion vectors originally derived by Foschini and Shepp. Compared with the Foschini and Shepp's approach, the Fokker-Planck approach gives a more accurate and straightforward way to find the joint-characteristic function.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.2
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• pp.107-114
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• 2009

In this paper, high efficiency amplifier configuration is proposed using the reconfigurable power divider. In order to enhance average efficiency of linear power amplifiers for wireless communication, it is required to increase efficiency in low output power region. The proposed power divider operates in two modes, high power mode and low power mode, according to output power. In each mode, it allows impedance matches and low loss, which is made possible by employing two $\lambda/4$ coupled lines and two switches. The fabricated power divider shows the return loss ($S_{11}$) and insertion loss ($S_{21}$) of -16.49 dB and -0.83 dB, respectively, in low power mode. In high power mode, the measured return loss ($S_{11}$) and insertion loss ($S_{31}$) are -16.28 dB and -0.73 dB, respectively. This result successfully demonstrates the reconfigurability of the proposed power divider.