• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.353-358
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• 2013

The ultrasonic characteristics of 2.25Cr-1Mo steel were investigated in relation to the isothermal heat treatment temperature and time. Charpy impact tests and hardness tests were conducted on individual specimens with three different heat treatment conditions. A pulse-echo method with longitudinal waves was used to measure the attenuation and velocity of ultrasonic waves. The FATT (fracture appearance transition temperature) increased with an increase in the isothermal heat treatment time, which implies that the toughness decreased. As the isothermal heat treatment time and temperature increased, the longitudinal wave velocity and ultrasonic attenuation coefficient were raised.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.213-220
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• 2020

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose design pressure was 6.0MPa. The distance between the two-cylinders was 30 millimeter measured from outer shell at the mid-length. The implosion tests were performed with water and compressed nitrogen gas as the pressurizing media. The ambient static pressure of the chamber and local dynamic pressure near the two-imploded models were measured simultaneously. It was found that the energy released during an implosion from the first, weaker cylinder triggered the instability of the second, stronger cylinders. In other words, the resulting shock wave of the first implosive impact from the weaker cylinder could cause the premature failure of the neighboring stronger cylinders. The non-contact implosion phenomena from the two-cylindrical tube were clearly observed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.6
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• pp.597-603
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• 2014

The cargo of ships and offshore structures is the number of oil of combustibility and volatile, oil processing cargo. Furthermore heavy cargo of the vehicle or container box or bulk cargo are occupied the remainder of cargo. In addition, there is a possibility to move the location of the cargo and the vessel because it is received periodic / non-periodic a load of wave and ocean current. Therefore a shipboard hazard is much greater than onshore industry hazard. Monitoring and preparation for safety are necessary things because there is always risk of accidents arise from the impact of the freight and cargo of ships and offshore structures. In this study, we conducted a study with respect to the introduction of the wireless sensor network monitoring system to ensure the safety of the crew and workers on shipboard.

• Earthquakes and Structures
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• v.14 no.6
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• pp.577-587
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• 2018

The quantitative assessment of the seismic collapse risk of a structure requires the usage of an optimal intensity measure (IM) which can adequately characterise the severity of the ground motion. Research suggests that the average spectral acceleration ($Sa_{avg}$) may be an efficient and sufficient alternate IM as compared to the more traditional first mode spectral acceleration, $Sa(T_1)$, particularly during seismic collapse risk estimation. This study primarily presents a comparative evaluation of the sufficiency of the average spectral acceleration with respect to ground motion duration, and secondarily assesses the impact of ground motion duration on collapse risk estimation. By assembling a suite of 100 historical ground motions, incremental dynamic analysis of 60 different inelastic single-degree-of-freedom (SDF) oscillators with varying periods and ductility capacities were analysed, and collapse risk estimates obtained. Linear regression models are used to comparatively quantify the sufficiency of $Sa_{avg}$ and $Sa(T_1)$ using four significant duration metrics. Results suggests that an improved sufficiency may exist for $Sa_{avg}$ when the period of the SDF system increases, particularly beyond 0.5, as compare to $Sa(T_1)$. In reference to the ground motion duration measures, results indicated that the sufficiency of $Sa_{avg}$ is more sensitive to significant duration definitions that consider almost the full wave train of an accelerogram ($SD_{a5-95}$ and $SD_{v5-95}$). In order to obtain a reduced variability of the collapse risk estimate, the 5-95% significant duration metric defined using the Arias integral ($SD_{a5-95}$) should be used for seismic collapse risk estimation in conjunction with $Sa_{avg}$.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.11 no.1
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• pp.45-52
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• 2013

Purpose : The goal of this study is to estimate the effect of SSP electrical stimulation applied to acupoints as conducted in oriental medicine on the swallowing function of patients with swallowing difficulties caused by stroke. Methods : Twenty-two hemiplegic stroke patients with swallowing difficulties were divided into an intervention-only group (Group I; n=11) and an intervention-SSP electrical stimulation group (Group II; n=11). Therapeutic intervention was performed on participants in the intervention-only group and the intervention-SSP electrical stimulation group, for 20 minutes per session, three times per week, for four weeks. In this study, SSP electrical stimulation to the acupoints (Cheondol, Yomchon, Budol, Pungji, and Sanyinjian) of stroke patients with swallowing difficulties was applied, and to investigate the effects of SSP electrical stimulation, Clinical dysphagia scale (CDS) and ultrasonography assessment was used to measure pre and post-intervention scores. Results : In the clinical dysphagia scale assessment, the post-intervention score for group II had significant enhancement unlike group I. In the ultrasonography assessment, the hyolaryngeal movement in group II showed significant increase in the swallowing function unlike group I. Conclusion : From the above results, significant effects came from SSP electrical stimulation of 3Hz, biphasic wave, continuous current when applied to the acupoints as conducted in oriental medicine to improve the swallowing function of stroke patients.

• Journal of Korean Society of Forest Science
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• v.98 no.1
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• pp.88-93
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• 2009

The overall purpose of this study was to figure out psycho-physiological variations in human bodies according to observing visual images of forests. To collect data, the authors employed 9 views each in three different environments such as cities, forests, and landscape which combines a forest with water. The experiment was conducted by showing total 27 images to 30 visitors to measure the subjects' changes of alpha waves of EEG(electroencephalogram). As measures of psychological impact of the views, PRS(Perceived Restorativeness Scale) and PANAS(Positive and Negative Affect Schedule) were used. The results of the data analyses indicated that the views of landscape with a forest and water influenced most highly on subjects' psycho-physiological responses.

• Journal of Navigation and Port Research
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• v.36 no.7
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• pp.585-590
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• 2012

On the basis of the potentials for the growth of local economy and the result of investigation of the ocean space development status, an ocean resort complex was proposed at the small harbor with a parallel beach in the east coast of Korea. As the development plan needs to reclaim the noticeable amount of coastal water area together with the applied shore facilities, it is necessary to analyze their impacts. Here, it was intended to analyze the coastal environment change such as water circulation and bottom change because of the development plan. A horizontal two-dimensional numerical model was applied to represent the combined impact of wind waves and tidal currents to sediment transport in that coastal region. Based on the result of 30 days tidal current simulations considering major four tidal components of $M_2$,$S_2$,$K_1$ and $O_1$ for the upper and lower boundaries and wind field data, bottom change was discussed. Flow velocities were not changed much at outer breakwater of Yangpo harbor. Bottom was eroded by maximum 1.7m after construction but some locations such as lee side of outer breakwater and some islets near the entrance shows isolated accretions. Although it needs more field observations for bottom change in the period of construction, the numerical calculation shows that there exist small impacts near the entrance area and coastal boundaries because of the development.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.905-910
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• 2007

As the ship is getting bigger and faster lately, ship's structure or cargoes might be often damaged and the ship might be cut in two in extreme conditions by a wave impact on its bow. In this paper, the vertical acceleration, which is one of factors for evaluating seakeeping performance, was measured under the various sea states by the hull stress monitoring system(HMS) on the bridge, and the result was compared with those of model test and theoretical studies. Then, we confirmed the seakeeping performance of T.S. HANBADA by comparing it with ITTC seakeeping criteria This result will be a great help for the safe navigation by making it possible to estimate the possibility of work and the amount of risk under the various sea conditions with which may be confronted, and the shipbuilding yard can be possible to construct the vessel with superior performance through these data measured on the actual ship.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.3
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• pp.221-233
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• 2007

In this paper, a simple but effective position profile generation algorithm for single axis high dynamic linear machine drive system is presented. In the recent industrial application fields like as LCD/PDP and semiconductor factory, requirements for the high performance positioning system with optimal position profile generator are highly increased to reduce the overall processing time. There might be various solutions for position profile generating algorithm according to the application type. A square-wave Impact quantity(Jerk) based algorithm with minimal locomotion time is argued in this paper to minimize the total time of one movement under some specific constrains such as maximum speed limit and maximum acceleration limit. In order to reduce the calculation efforts and satisfy the minimal locomotion time condition, the time variants representing each profile sector and a simple condition comparison algorithm are adopted. Also, the actual implementation method for profile generation algorithm and it's real performance results are presented through commercial linear machine drive system.

• Journal of the Korea Society of Computer and Information
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• v.24 no.10
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• pp.257-265
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• 2019

The purpose of the present study was to examine the causal relationship between aggression and mobile phone dependency among high school students and to test the mediating effect of self-esteem, and to draw out implications in order to encourage proper use of mobile phone. In this paper, we proposed a research model between aggression, self-esteem and mobile phone dependency. The present study analyzed the fourth, fifth, and sixth wave data from KCYPS 2010, using the structural equation modeling. The primary results were as follows. First, the effect of high school students' aggression on mobile phone dependency was not significant. Second, high school students' aggression had a significantly negative effect on self-esteem. Third, high school students' self-esteem had a significantly positive effect on mobile phone dependency. Fourth, high school students' self-esteem could be a significant mediator between aggression and mobile phone dependency. In conclusion, theoretical and practical suggestions were discussed in order to solve the problem of adolescents' mobile phone dependency.