• Journal of Korean Society for Quality Management
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• v.28 no.3
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• pp.18-30
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• 2000

Recent studies have shown that the $\bar{X}$ chart with variable sampling intervals(VSI) and the $\bar{X}$ chart with variable sample size(VSS) are much quicker than Shewhart $\bar{X}$ chart in detecting shiks in the process. Shewhart $\bar{X}$ chart has been beneficial to detect large shifts but it is hard to apply Shewhart $\bar{X}$ chart in detecting moderate shifts in the process mean. In this article the $\bar{X}$ chart using variable sample size(VSS) and variable sampling Intervals(VSI) has been proposed to supplement the weak point mentioned above. So the purpose of this paper is to consider finding the design parameters which minimize expected loss costs for unit process time and measure the performance of VSSI(variable sample size and sampling interval) $\bar{X}$ chart. It is important that assignable causes be detected to maintain the process controlled. This paper has been studied under the assumption that one cycle is from starting of the process to eliminating the assignable causes in the process. The other purpose of this article is to represent the expected loss costs in one cycle with three process parameters(sample size, sampling interval and control limits) function and find the three parameters.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.08a
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• pp.142-147
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• 1998

Recently, 8 kb/s CS-ACELP coder of G.729 is atandardized by ITU-T SG15 and it has been reported that the speech quality of G729 is better than or equal to that of 32kb/s ADPCM. However G.729 is the fixed rate speech coder, and it does not consider the property of voice activity in mutual conversation. If we use the voice activity, we can reduce the average bit rate in half without any degradations of the speech quality. In this paper, we propose an efficient variable rate algorithm for G.729. The variable rate algorithm consists of two main subjects, the rate determination algorithm and algorithm, we combine the energy-thresholding method, the phonetic segmentation method by integration of various feature parameters obtained through the analysis procedure, and the variable hangover period method. Through the analysis of noise features, the 1 kb/s sub rate coder is designed for coding the background noise signal. So, we design the 4 kb/s sub rate coder for the unvoiced parts. The performance of the variable rate algorithm is evaluated by the comparison of speed quality and average bit rate with G.729. Subjective quality test is also done by MOS test. Conclusively, it is verified that the proposed variable rate CS-ACELP coder produced the same speech quality as G.729, at the average bit rate of 4.4 kb/s.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.4
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• pp.321-328
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• 2008

In this paper, variable gain amplifier(VGA) with a gain slope controller has been proposed and verified by circuit simulations and measurements. The proposed VGA has a gain control, gain slope switch and variable gain range. The input source coupled pair with diode connected load is used for VGA gain stage. The gain slope controller with switch can control VGA gain slope. The proposed VGA is fabricated in $0.18{\mu}m$ CMOS process for multi -standard wireless receiver. The proposed two stage VGA consumes min. 2.0 mW to max. 2.6 mW in gain control range and gives input IP3 of -3.77 dBm and NF of 28.7 dB at 1.8 V power supply under -25 dBm, 1 MHz input. The proposed VGA has 37 dB(-16 dB $\sim$ 21 dB) variable gain range, and 8 dB gain range control per 0.3 V control voltage, and can provide variable gain, positive and negative gain slope control, and gain range control. This VGA characteristics provide design flexibility in multi-standard wireless receiver.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.3-11
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• 1999

Optimum design of mooring dolphin is numerically investigated. Design optimization problem of moring dolphin is first formulated. Geometry and cross sections of piles are used as design variables. Design objective is the total weight of steel piles of mooring dolphin, and the constraints of stress, penetration depth, lower and upper bounds on design variables are imposed. Based on the design variable linking and fixing, several class of design variations are sought. For the numerical optimization, both PLBA(Pshenichny - Lim - Belegundu - Arora) program and DNCONF subroutine code in IMSL library are used. For a dolphin structure with 20 steel piles, vertical and inclined, optimum designs for different cases are successfully obtained, which can be applied for the mooring of a very large floating structure.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.335-342
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• 2002

A continuum-based design sensitivity analysis (DSA) method fur non-shape problems is developed for geometrically nonlinear elastic structures. The non-shape problem is characterized by the design variables that are not associated with the domain of system like sizing, material property, loading, and so on. Total Lagrangian formulation with the Green-Lagrange strain and the second Piola-Kirchhoff stress is employed to describe the geometrically nonlinear structures. The spatial domain is discretized using the 4-node isoparametric plane stress/strain elements. The resulting nonlinear system is solved using the Newton-Raphson iterative method. To take advantage of the derived analytical sensitivity In topology optimization, a fast and efficient design sensitivity analysis method, adjoint variable method, is employed and the material property of each element is selected as non-shape design variable. Combining the design sensitivity analysis method and a gradient-based design optimization algorithm, an automated design optimization method is developed. The comparison of the analytical sensitivity with the finite difference results shows excellent agreement. Also application to the topology design optimization problem suggests a very good insight for the layout design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.3
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• pp.175-185
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• 2006

This study performed the optimum design of balanced and unbalanced span length bridges with many variable Girder types by using the optimum design program to minimize the cost for PSC box girder bridge of the full staging method. The objective of this study is to present tendon's application direction about complicated construction hereafter by studying about optimum tendon arrangement that is worked in each variable Girder type. This program used SUMT procedure and Kavlie's extended penalty function to allow infeasible design points in the process. Powell's direct method was used in searching design points and Gradient Approximate Method was used to reduce design hours.

• Journal of Korean Society for Quality Management
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• v.40 no.2
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• pp.186-198
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• 2012

Since Duncan(1956) first proposed an economic design of $\bar{X}$-control charts, most of the succeeding works on economic design of control charts assumed the exponential failure model like Duncan. Hu(1984), however, assumed a more versatile Weibull failure model to develop an economic design of $\bar{X}$-control charts and Banerjee and Rahim(1988) further improved Hu's design by changing the assumption of fixed-length sampling intervals to variable-length ones. In this article we follow the approach of Banerjee and Rahim(1988) but include a pair of warning limits inside the control limits in order to search for a failure without stopping the process when the sample mean falls between warning and control limits. The computational results indicate that the proposed model gives a lower cost than Banerjee and Rahim's model unless the early failure probability of a Weibull distribution is relatively large. The reduction in cost is shown to become larger as the cost of production loss outweighs the cost of searches for a failure.

• Journal of Korean Institute of Industrial Engineers
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• v.32 no.1
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• pp.51-60
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• 2006

When the nature of measuring a performance variable is destructive or very expensive, it is attractive to use a surrogate variable which is highly correlated with the performance variable and less expensive to measure. In this paper, we propose rectifying screening procedures using the performance and surrogate variables. Two screening procedures are considered; a statistically-based screening procedure to reduce the current proportion of nonconforming items to a specified lower value after screening, and an economically-based screening procedure where the screening limit is determined so that the expected cost is minimized. It is assumed that the surrogate variable given the performance variable is normally distributed with known mean and standard deviation. For two screening procedures, methods of finding the optimal solutions are presented and numerical examples are also given.

• Journal of Korean Institute of Industrial Engineers
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• v.19 no.3
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• pp.25-35
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• 1993

Economic screening procedures using a correlated variable are proposed to assure that the proportion of conforming items is above a desired level after screening. It is assumed that the performance variable and the screening variable are jointly normally distributed. Two screening procedures are considered. In the first screening procedure, all of the items are inspected on the screening variable. If an item fails to meet the screening specifications, it is rejected and excluded from shipment without inspection of the performance variable. In the second screening procedure, the item which fails to meet the screening specifications is inspected on the performance variable. If the value of the performance variable is within specifications the item is accepted, and the item is rejected otherwise. Cost models are constructed which involve cast from an accepted nonconforming item, cost from a rejected item, and quality inspection cost. Methods of finding optimal cutoff value on a screening variable are presented and numerical examples are given.

• Journal of Power Electronics
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• v.12 no.1
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• pp.164-171
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• 2012

Variable step size maximum power point trackers (MPPTs) are widely used in photovoltaic (PV) systems to extract the peak array power which depends on solar irradiation and array temperature. One essential factor which judges system dynamics and steady state performances is the scaling factor (N), which is used to update the controlling equation in the tracking algorithm to determine a new duty cycle. This paper proposes a novel stability study of variable step size incremental resistance maximum power point tracking (INR MPPT). The main contribution of this analysis appears when developing the overall small signal model of the PV system. Therefore, by using linear control theory, the boundary value of the scaling factor can be determined. The theoretical analysis and the design principle of the proposed stability analysis have been validated using MATLAB simulations, and experimentally using a fixed point digital signal processor (TMS320F2808).