• Journal of the Korean Institute of Navigation
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• v.25 no.2
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• pp.97-106
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• 2001

The purpose of this paper is to determine the expected percentage of the 'VTS addressable' casualties that could be prevented with the installation of fourth level(Automatic Dependent Surveillance) of coastal VTS. In this study, it determines the VTS benefit by multiplying casualty rate reduction factors by the effect level of causal factors. The development of casualty rate reduction factors was based on the questionnaire survey, and the evaluation of effect levels was based on the causal analysis using functional block diagram. The results of this paper are compared With the results of worldwide literature related to the VTS effectiveness. One or more of the key variable inputs of this study, casualty rate reduction factors, may be somewhat uncertain and therefore subject to sensitivity analysis.

• Korean Journal of Materials Research
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• v.14 no.10
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• pp.725-730
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• 2004

Nickel ultrafine powder have been synthesized by chemical reduction of aqueous $NiSO_4$ with hydrazine at various reaction conditions. The effect of reaction conditions such as the amount of surfactant and reductor, and reaction temperature on the particle size and shape was investigated by the mean of XRD, SEM and SEM-PSA. Experiments showed that the ratio of $N_{2}H_4/Ni$ and the reaction temperature were affected on the particle size of the nickel powder. The average particle size of synthesized nickel powder increased with increasing reaction temperature regardless of the ratio of $N_{2}H_4/Ni$. Also the surfactant could influence the size and agglomeration of ultrafine powder with the reaction temperature.

• Transactions of Materials Processing
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• v.22 no.3
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• pp.158-164
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• 2013

The spheroidization behavior of cementite in a SK85 high carbon steel was investigated in this study. Fine and coarse pearlite microstructures were obtained by appropriate heat treatments according to the TTT diagram of SK85 high carbon steel. Hot rolled plates of SK85 steel were austenitized at $800^{\circ}C$ for 2 hrs and then put directly into a salt bath at either $570^{\circ}C$ or $670^{\circ}C$ to obtain a fine pearlite (FP) structure and a coarse pearlite (CP) structure, respectively. Cold rolling was subsequently conducted on those specimens with reduction ratios from 0.2 to 0.4. Spheroidization heat treatments were conducted at the subcritical temperatures of 600 and $720^{\circ}C$ for 1 to 32 hrs to elucidate the effect of initial microstructures, heat treatment temperature, and cold reduction ratios on the cementite spheroidization rate. Spheroidization proceeded with fragmentation of cementite plates, spheroidization of the cementite platelets, and coarsening consecutively. Mechanical fragmentation of cementite by cold rolling expedited the rate of spheroidization. The spheroidization rate of FP was much more rapid than that of CP and the spheriodization rate increased with increases in the cold reduction ratio.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.10 no.S_1
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• pp.35-40
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• 2001

Effect of the addition of an enzyme/microbial additive(EMA) to enhance anaerobic digestion of the primary sludge was investigated. Two laboratory scale anaerobic digester were operated with primary sludge taken from a municipal wastewater treatment plant. The digester receiving EMA with the sludge feed performed better than the control digester, when both were operated at 10-days and 15-days Solid Retention Time(SRT). Addition of EMA to the experimental digester provided 7%(10-days SRT) and 16%(15-days SRT) higher gas production compared to the control digester when both were fed with the same amount of volatile solids. The reduction in volatile solids was 24% better in the experimental digester compared to the control ar 10-days SRT, and the improvement 10% at 15-day SRT. Improvement in COD reduction, and fecal coliform density reduction were also seen in the experimental digester due to EMA addition compared to the control both ar 10-days SRT and 15-day SRT operation. Preliminary cost benefit analysis for a wastewater treatment plant showed that approximately $115/day in gas production improvements can be realized upon addition of EMA to primary sludge anaerobic digesters operating at 10-day SRT. The value of increased gas production was $172/day if the same digesters are operated with EMA addition at 15-day SRT.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.9 no.1
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• pp.9-14
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• 2011

Purpose : The purpose of this study is to examine the influence of a core stability exercise program using Swiss Ball on muscle activity, muscle thickness, maximum muscular strength, and pain in the trunk region during a 6-weeks program involving participants who have lower back pain. Methods : A total of 21 males between the ages of 20 and 33 years old were divided into 3 Swiss Ball exercise groups. Group 1 performed isometric exercises, group 2 performed isotonic exercises, and group 3 performed mixed exercises. Measurements were taken prior to starting the exercise program and after completing the program at the 6-week period using ME6000 to measure muscle activity and VAS to measure pain reduction. Comparisons were made using a paired t-test and ANOVA on SPSS 10.0. Results : There was a statistically significant effect in muscle activity for group 1 and group 3. Secondly, there was a statistically significant effect in pain reduction for group 1, group 2, and group 3. Conclusion : We found that isometric exercises performed by group 1 were effective in improving muscle activity and pain reduction.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.3
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• pp.201-208
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• 2015

The effects of dead-time and offset error, which cause output current distortion in single-phase grid-connected inverters are investigated this paper. Offset error is typically generated by measuring phase current, including the voltage unbalance of analog devices and non-ideal characteristics in current measurement paths. Dead-time inevitably occurs during generation of the gate signal for controlling power semiconductor switches. Hence, the performance of the grid-connected inverter is significantly degraded because of the current ripples. The current and voltage, including ripple components on the synchronous reference frame and stationary reference frame, are analyzed in detail. An algorithm, which has the proportional resonant controller, is also proposed to reduce current ripple components in the synchronous PI current regulator. As a result, computational complexity of the proposed algorithm is greatly simplified, and the magnitude of the current ripples is significantly decreased. The simulation and experimental results are presented to verify the usefulness of the proposed current ripple reduction algorithm.

• Journal of the Korea Fashion and Costume Design Association
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• v.2 no.1
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• pp.113-121
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• 2000

The effect of Sunlight exposure on reducing the microorganism counts in the bedding materials was experimented by using 3 kinds of microorganisms(S. aureus, K. pnenmoniae and E. coli) and 3 kinds of fabrics (cotton, silk and polyester). Counts of the microorganism were examined before and after sunlight exposure. The sunlights were controlled U.V and Daylight D50 using MacBeth artificial light source. The specimens were exposed for 5 min, 10 min and 30 minutes under the $20^{\circ}C$ and 60% R.H, distance is 50cm from the light source. Results were as follows, 1. The reduction rate of the 3kinds of microorganisms was remarkably great under the U.V exposure. The U.V. exposure was very effective way to sterlize the bedding materials in the house care. 2. S. aureus was the most susceptible to U.V. exposure and the sunlight exposure. E. coli was the most resistant to the U.V and the sunlight exposure. 3. The reduction rate of the 3 kinds of fabrics was not significantly different. The polyester is more resistant than the silk and the cotton. Those were shown good reduction rate if all kinds of microorganism under the U.V and daylight.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.59-63
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• 2014

Object of this study is to see whether the arc-groove on a D-shape bluff body effects the drag reduction or not. To this end, the changes of the boundary layer on the surface of the object, the downstream flow field and wake flow were found by experiments. The experiments are conducted by changing number and depth of the groove, angle of the first groove and Reynolds number(Re). Groove did not effect on the surface in the downstream boundary layer of the object and was minimal impact on the time mean velocity recovery of the wake flow. Also the effects of Groove did not have a significant impact on the structure of the wake and the wake frequency. Therefore it is found that the arc-groove of the drag reduction effect on the D-shape bluff body was smaller.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.477-485
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• 2007

When Korean High Speed Train (KTX) runs over a high-speed railway bridge, the high-speed railway bridge gives quite large acceleration response. Local vibration at the large cross section, the impact from equally spaced sleepers, the vibration due to elastomeric bearings, and the vibration from the train itself are the causes of this acceleration response. Maximum peaks of the accelerations measured at the bridges are sometimes going over the limit value. Although it is smaller than 0.35G, the limit from the Korean Bridge Design Manual(BRDM), this acceleration response should be reduced for the safety of running trains with high speed. In this paper, to reduce the acceleration response by controlling excessive local vibration at the large cross section, vibration reduction method is studied. The result shows that the effect of elastomeric bearings on the vibration of the bridge is very large and that the vibration reduction device is effective against wing mode local vibration PSC box girder bridge for the high-speed railway, which usually has very large cross section, although it has little effect on global vibration modes such as flexural and twisting modes. The test of the vibration reduction device on the bridge in service has been performed in this study.

• Wind and Structures
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• v.11 no.3
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• pp.179-192
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• 2008

In a wind tunnel experiment employing a reduced scale model, Reynolds number (Re) can hardly be respected. Its effects on the aerodynamics of closed-box bridge decks have been the subject of research in recent years. Stonecutters Bridge in Hong Kong is a cable-stayed bridge having an unprecedented central span of 1018m. The issue of Re sensitivity was raised early in the design phase of the deck of Stonecutters Bridge. The objective of this study is to summarise the results of various wind tunnel experiments in order to demonstrate the effect of Re on the steady state aerodynamic force coefficients. The results may provide an insight on the choice of scale for section model experiments in bridge design projects. Computational Fluid Dynamics (CFD) analysis of forces on bridge deck section was also carried out to see how CFD results are compared with experimental results.