• Journal of Korean Society for Quality Management
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• v.27 no.1
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• pp.35-45
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• 1999

A process monitoring procedure using a correlated variable is presented when a lower specification limit is given on the performance variable. Every item is inspected with a variable correlated with the performance variable. When an item is rejected in the screening inspection, the process is checked for change using the mean and variance of measurements of the correlated variable for n preceding items including the rejected one. The performance variable is assumed to be normally distributed. A linear relationship between the performance and surrogate variables is assumed with normally distributed error term. The monitoring procedure is designed so that the prespecified outgoing quality can be attained.

• The Journal of Fisheries Business Administration
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• v.37 no.2 s.71
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• pp.1-18
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• 2006

This study analyzes the effect of exchange rate and exchange risk on the import of Korea's fisheries. The estimation models consist of the following contents. The first model consists of one dependent variable-import quantity of fisheries$(IMQ_t^{Total})$ and three independent $variables-RP_t^{Total}$, $EX_t\;and\;EXV_t$. The second one-one dependent variable-import quantity of fisheries from China$(IMQ_t^{CN})$ and three independent $variables-RP_t^{CN},\;EX_t\;and\;EXV_t$. And the last one is made up of one dependent variable - import quantity of fisheries from $Japan(IMQ_t^{JP})$ and three independent $variables-RP_t^{CN},\;EX_t\;and\;EXV_t$. The estimation results show that all of the independent variables are statistically significant. Especially, the effect of Chinese $RP_t^{CN}$ is grater than Japanese $RP/P_t^{JP}$. However, the effect of Japanese $EX_t$ is grater than Chinese $EX_t$.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.2
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• pp.165-174
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• 2007

Variable displacement type piston pump uses various controllers for controlling more than one state quantity like pressure, flow, power, and so on. These controllers need the mathematical model closely expressing dynamic behavior of pump for analyzing the stability of control systems which usually use various kinds of state variables. This paper derives the nonlinear mathematical model for variable displacement type piston pump. This model consists of two 1st oder differential equations by the continuity equations and one 2nd oder differential equation by the motion equation. To simplify the model we obtain the linear state variable model by differentiating the three nonlinear equations. And we verify this linearized model by comparison of simulation with experimentation and analyze the stability for the flow/pressure control. Finally this paper suggests the design compensation to ensure the stability of the systems.

• Structural Engineering and Mechanics
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• v.18 no.5
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• pp.591-607
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• 2004

The substance of the use of the derived non-linear creep constitutive equations under variable stress levels (see first part of the paper, Kmet 2004) is explained and the strategy of their application is outlined using the results of one-step creep tests of the steel spiral strand rope as an example. In order to investigate the creep strain increments of cables an experimental set-up was originally designed and a series of tests were carried out. Attention is turned to the individual main steps in the production and application procedure, i.e., to the one-step creep tests, definition of loading history, determination of the kernel functions, selection and definition of constitutive equation and to the comparison of the resulting values considering the product and the additive forms of the approximation of the kernel functions. To this purpose, the parametrical study is performed and the results are presented. The constitutive equations of non-linear creep of cable under variable stress history offer a strong tool for the real simulation of stochastic variable load history and prediction of realistic time-dependent response (current deflection and stress configuration) of structures with cable elements. By means of suitable stress combination and its gradual repeating various loads and times effects can be modelled.

• Journal of The Korean Association For Science Education
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• v.22 no.3
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• pp.571-585
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• 2002

This is one of the basic research for inspecting the possibility of the development of logical thinking capability to make possible formal thinking. The 5th grade students (n=306) in the elementary school were participated in this study. Performing the 6 variable-controlling activities in the 'Thinking Science' program for one semester, the SRT II test and the Variable-Controlling test were operated to examine the effects on the development of the variable-controlling ability by treatments, gender, and cognitive levels. Performing of the variable-controlling activities was highly successive on the development of students' variable-controlling ability. Although learning effect on the ability of identifying causal variable was moderate, the abilities of controlling experimental condition, measurement of variable, and identifying result variable were significantly developed. There was statistically significant difference by gender. Girls showed better performance all the time in both groups. Boys in the experimental group were getting better gradually, so the difference by gender was somewhat decreased. Examining the variable-controlling ability by cognitive levels, students in the experimental group show significant increase in all levels, especially the students in early, mid, and mature concrete level show substantial learning effects. The results of this study implied that the variable-controlling activities in the 'Thinking Science' could be effective for learning of variable-controlling and eventually for the development of logical thinking capability to make possible formal thinking.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.39-48
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• 2014

Variable valve actuation system is one of the widely used techniques to improve the fuel efficiency and power of automotive engines. 2-step variable valve actuation systems are also paid attention for the application to direct acting type valve train systems. Besides its advantages in size, weight, relatively simple structure, ets, however, 2-step variable valve actuation system has inherent disadvantages in dynamic instability of switching system to alter discontinuous lift modes. In this study, both experimental and analytical studies are performed to understand the dynamic behavior of a switching mechanism of a 2-step variable valve actuation system, and present a design method to improve its dynamic instability.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.12
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• pp.1053-1060
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• 2000

In this paper, a discrete-time variable structure control method using recursively defined switching function and a decoupled variable structure disturbance compensator is used to achieve high performance circular motion control of a CNC machining center. The discrete-time variable structure control with the decoupled disturbance compensator method developed in this paper uses a recursive switching function defined as the sum of the current tracking error vector and the previous value of the switching function multiplied by a positive constant less than one. This recursive switching function provides much improved performance compared to the method that uses a switching function defined only as a linear combination of the current tracking error. Enhancements in tracking performance are demonstrated in the circular motion control using a CNC milling machine.

• The Korean Journal of Applied Statistics
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• v.25 no.3
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• pp.471-483
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• 2012

One of the most important problems in cluster analysis is the selection of variables that truly define cluster structure, while eliminating noisy variables that mask such structure. Brusco and Cradit (2001) present VS-KM(variable-selection heuristic for K-means clustering) procedure for selecting true variables for K-means clustering based on adjusted Rand index. This procedure starts with the fixed number of clusters in K-means and adds variables sequentially based on an adjusted Rand index. This paper presents an updated procedure combining the VS-KM with the automated K-means procedure provided by Kim (2009). This automated variable selection procedure for K-means clustering calculates the cluster number and initial cluster center whenever new variable is added and adds a variable based on adjusted Rand index. Simulation result indicates that the proposed procedure is very effective at selecting true variables and at eliminating noisy variables. Implemented program using R can be obtained on the website "http://faculty.knou.ac.kr/sskim/nvarkm.r and vnvarkm.r".

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.7
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• pp.706-717
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• 1991

In order to remove the assumption of full state availability which is one of the major difficulties with the practical realization of variable structure control systems,a new switching function with a dynamic structure is proposed. And the control performances of the output feedback variable structure control systems with the dynamic switching function are evaluated through simulation studies. The proposed dynamic switching function is driven by small number of measured output and input variables while conventional static switching function requires full state information. Therefore, the proposition of the dynamic swiching function makes practical implementation of output feedback variable structure control scheme possible for the systems with unmeasurable state variables, high order systems and large scale systems that the conventional variable structure control schemes with static switching function cannot be applied. In the variable structure control systems with the dynamic switching function, desired control performance can be guaranteed by proper choice of design parameters such as poles of switching function dynamic equation and switching control gains even though small number of measured output and input variables are provided as shown in simulation resuls.

• Journal of Industrial Technology
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• v.27 no.B
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• pp.71-75
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• 2007

A cylindrical pin fin with variable diameter is analyzed by using the one dimensional analytical method. Heat loss and fin efficiency are presented as a function of the fin diameter, length and convection characteristic numbers ratio. The relationship between the fin diameter and convection characteristic number over the fin for the same amount of heat loss is shown. One of the results indicates the fin efficiency increases as the fin diameter increases while that decreases as the fin length increases.