• Journal of the Korean Society for Precision Engineering
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• v.16 no.6
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• pp.25-35
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• 1999

This paper presents a control gain tuning scheme for multi-axis PID control systems by Taguchi method. As an experimental set-up, a parallel mechanism machine tool has been selected. This machine has eight servodrives and each servodrive has four control gains, respectively. Therefore, total 32 control gains have to be tuned. Through a series of design of experiments, an optimal and robust set of PID control gains is tuned. The index of the sum of position error and velocity error is reduced to 61.4% after the experimental gain tuning regardless of the feedrate variation.

• Journal of KSNVE
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• v.7 no.2
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• pp.301-310
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• 1997

This paper presents active noise control method to form the near-field quiet zone for passengers in an automobile. The actuator model including interior acoustic plant, speaker and amplifier is experimentally identified in forms of auto-regressive and moving average by means of least mean square algorithm, The digital controller is composed of the regulator and Kalman filter to be designed based on LQG (linear quadratic gaussian). If the actuator model is prefiltered with digital filter to be properly designed for concentrating control performance index on the frequency band of primary noise source, LQG design approach can be effectively applied for the design of headset controller. Experimental results demonstrate that near-field quiet zone showing about 10dB noise reduction at microphone position can be formed using the headset located at passenger seat.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.1
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• pp.63-73
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• 2010

This paper presents the optimal design method of an overlapped ultrasonic sensor ring for reduced positional uncertainty, and its application to the obstacle detection with improved resolution. Basically, it is assumed that a set of ultrasonic sensors are installed to form a circle at regular intervals with their beams overlapped. First, exploiting the overlapped beam pattern, the positional uncertainty inherent to an ultrasonic sensor is shown to be significantly reduced. Second, for an ideal ultrasonic sensor ring of zero radius, the effective beam width is defined to represent the positional uncertainty, and the optimal number of ultrasonic sensors required for minimal effective beam width is obtained. Third, for an actual ultrasonic sensor ring of nonzero radius, the design index is defined to represent the degree of positional uncertainty, and an optimal design of an overlapped ultrasonic sensor ring consisting of commercial ultrasonic sensors with low directivity is given. Fourth, given measured distances from ultrasonic sensors, the geometric method is described to compute the obstacle position with reference to the center of a mobile robot. Finally, through experiments using our overlapped ultrasonic sensor ring prototype, the validity and performance of the proposed method is demonstrated.

• Korean Journal of Oriental Medicine
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• v.14 no.2
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• pp.107-112
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• 2008

Although the pulse diagnosis position, Guan is apart from Cun or Chi by only $10{\sim}20$ mm at most, traditional medical doctors applies different indent pressures and even they states different pulse images are felt at Cun, Guan and Chi, To support their clinical behaviors, in this study, we tested statistically whether there are differences in pulse waveform measured at these three positions with SphygmoCor system used world widely, A 30 years old female subject without any evidence of cardiovascular diseases was involved in this experiment. Radial pulse waves were recorded at three different positions on left lower arm 10 times at three positions-Cun, Guan and Chi. With ANOVA, we tested whether, among three different positions. there are any differences in 12 parameters of radial pulse waveform and in estimated AIx(Augmentation Index) as an arterial stiffness index extracted from radial pulse waveform. As results, differences in optimal indent pressure h0 were observed at different measuring positions(P<0.001) but not significantly different. And pulse pressure his were found to be different(Chi$22.60{\pm}3.06%,\;18.60{\pm}3.37%\;and\;26.4{\pm}5.02%$ respectively. Consequently. AIx at Gwan seems to be lowest and that at Chi seems to be highest. So. we assert the AIx at Chi is likely to be overestimated. In further studies. we want to examine what make differences in these parameters between measuring positions. And it also seems to be worthy to investigate the relationship between the depth of radial artery and AIx. And, ultimately, we need to determine the best measuring process including measuring position, hold-down pressure, signal quality validation and so on. so to achieve the optimal waveform which represents subject's health condition for both western medicine and traditional medicine.

• The Korean Journal of Financial Management
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• v.23 no.1
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• pp.243-266
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• 2006

This paper tests cross hedging performance of the KOSPI 200 stock index futures to hedge the downside risk of the KOSPI, KOSPI 200 and KOSDAQ50 spot market. For this purpose we introduce the minimum variance hedge model, bivariate GARCH(1,1) and EGARCH(1,1) model as hedge models. The main results are as follows; First, we find that the direct hedge performance of KOSPI 200 index futures is better than those of indirect hedge performance. second, in case or cross hedge performance the hedge effect of KOSPI 200 stock index futures market against KOSPI 200 stock index spot market is relatively better than those of KOSPI 200 index futures against KOSPI and KOSDAQ spot position. Third, for the out-sample, hedging effectiveness of the risk-minimization with constant hedge ratios is higher than those of the time varying bivariate GARCH(1,1) and EGARCH(1,1) model. In conclusion, investors are encouraged to use simple risk-minimization model rather than the time varying hedge models like GARCH and EGARCH model to hedge the position of the Korean stock index cash markets.

• Journal of Korean Society for Quality Management
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• v.16 no.1
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• pp.1-7
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• 1988

The most important element upon the quality of family glass products is the color of glass, which is the first object of consumers concern in purchasing. Therefore, colorless and transparent color tone can level up the additional value of the products. But we have produced the glass products in a large quantity by using the automatic tank brazier, chronic problem has been left over the color tone. By compounding and analizing the management techniques applied by peculiar technique and design of experiments pertinently, and by adjusting the decoloring composition ratio, we can contribute to improvement of color tone as well as to the cost reduction by diminishing the unnecessary decoloring agent. Intangible effect was the securing the superiority of quality home and abroad with the improvement of color tone and was taking a triangular position the factors influencing the glass decoloring which had been an unexhausted field. Tangible effect was the reduction of decoloring cost by diminishing the unnecessary oxidant. We registered the optimal composition ratio condition which was searched by applicating the design of experiments. To maintain good color tone, we manage the degree of purity, the most important thing among the items of color tone, continuously by control chart and it has maintained steady state now.

• Journal of the Korean Institute of Navigation
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• v.7 no.2
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• pp.65-113
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• 1983

A lot of studies of ship's economy are on the traditional fields such asreducing propulsion resistance, raising cargo handling rates and lessening building consts, but there are few researches on the merchant ship's economy concerning their deadweights and speeds according to shipping companies managerial cercumstances. Contrary to the contemporary trend that "the bigger, the better, if the cargo handling rate could increased sufficiently to hold down port time to that rate of smmaler vessels", this paper demonstrates the existence of certain limits in ship's size and speed according to the coditions of the freight rates, voyage distances, cargo handing rates, prices of fuel oil, interst rates etc. Fom the curves of criteria contour for various ship's deadweights and speeds which are depicted from the gird search method, one can get the costs and the yearly profit rates under the conditiions of large volume with long term contracts for the transportation of bulk cargoes. In estimating ship's transportation economy, the auther takes the position that the profit rate method is properer than the cost method, and introduces the calculation table of the voyage profit rate index. The use of the criteria contours will be of help to ship owners in determining the size and speed of the ship which will be built or purchased and serve in a certain trade route.

• Journal of Astronomy and Space Sciences
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• v.37 no.4
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• pp.219-228
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• 2020

A CubeSat platform has become a popular choice due to inexpensive commercial off-the-shelf (COTS) components and low launch cost. However, it requires more power-efficient and higher-data rate downlink capability for space applications related to remote sensing. In addition, the platform is limited by the size, weight and power (SWaP) constraints as well as the regulatory issue of licensing the radio frequency (RF) spectrum. The requirements and limitations have put optical communications on promising alternatives to RF communications for a CubeSat platform, owing to the power efficiency and high data rate as well as the license free spectrum. In this study, we analyzed the performance of optical downlink communications compatible with CubeSat platforms in terms of data rate, bit error rate (BER) and outage probability. Mathematical models of BER and outage probability were derived based on not only the log-normal model of atmospheric turbulence but also a transmitter with a finite extinction ratio. Given the fixed slot width, the optimal guard time and modulation orders were chosen to achieve the target data rate. And the two performance metrics, BER and outage data rate, were analyzed and discussed with respect to beam divergence angle, scintillation index and zenith angle.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.185-191
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• 2012

Most of Korean farms have been developed in the semi-closed bay, and its position is very vulnerable to the coastal contamination due to the long term and the high density. So, mariculture management is very essential for the sustainable aquaculture. Some of the specific ways would be the assessment of the optimal stocking density for mariculture management zone and this has to consider both the suitable site selection and the assessment of ecological carrying capacity. Habitat suitability index(0.0 totally unsuitable habitat, 1.0 optimum habitat) and ecological indicator(Filtration pressure indicator) was used to assess the stocking density for oyster farms in Geoje-Hansan Bay. Geoje Bay showed the higher habitat suitability index value 0.75 than Hansan Bay 0.53, indicating that Geoje Bay is more suitable for oyster farming. Ecological indicator showed different stocking density according to the coastal characteristics in Geoje-Hansan Bay. Consequently, it is desirable that the stocking density in Geoje Bay should reduce average 40% and Hansan Bay, average 60% than present, in order to meet the ecological carrying capacity. The assessment of the stocking density could solve various problems such as the coastal contamination, environmental aggravation and the productivity decrease and this study could be a scientific basis to establish the policies for mariculture management.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.185-190
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• 2016

Damages of the main engine aftmost bearing and the after stern tube bearing tend to increase due to misalignment. And as the shafting system becomes stiffer due to the large engine power, whereas the hull structure becomes more flexible due to optimization by using high tensile thin steel plates. And this is the reason that more sophisticated shaft alignments are required. In this study, the optimum shafting alignment calculation was carried out, considering the thermal expansion effect, exploiting the sensitivity index, which indicates the reasonable position of forward intermediate shaft bearing for shaft alignment. and as the main subject in this study, the elastic deformation on intermediate shaft and main engine bearings occurred by vertical load of shaft mass were examined thoroughly and analyzed allowable load of bearings, reaction influence numbers of all bearings. As the result, a reliable optimum shafting alignment was derived theoretically. To verify these results, they were referred to the engine maker's technical information of main engine installation and being used shafting alignment programs of both Korean Register of Shipping and Det Norske Veritas, their reliability were reviewed.