• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.446-454
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• 2008

The purpose of this paper is to analyze two-phase flows of the hydrogen recirculation system. Two-phase flow modeling is one of the great challenges in the classical sciences. As with most problems in engineering, the interest in two-phase flow is due to its extreme importance in various industrial applications. In hydrogen recirculation systems of fuel cell, the changes in pressure and temperature affect the phase change of mixture. Therefore, two-phase flow analysis of the hydrogen recirculation system is very important. Two-phase computation fluid dynamics (CFD) calculations, using a commercial CFD package FLUENT 6.2, were employed to calculate the gas-liquid flow. A two-phase flow calculation was conducted to solve continuity, momentum, energy equation for each phase. Then, the mass transfer between water vapor and liquid water was calculated. Through an experiment to measure production of liquid water with change of pressure, the analysis model was verified. The predictions of rate of condensed liquid water with change of pressure were within an average error of about 5%. A comparison of experimental and computed data was found to be in good agreement. The variations of performance, properties, mass fraction and two-phase flow characteristic of mixture with resepct to the fuel cell power were investigated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.3
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• pp.245-252
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• 2007

The important problems from the point of view of preventing global warming are to save the power consumption of automotive air-conditioning systems and reduce the refrigerant amount filled. To achieve such requirements, integral receiver/dryer (R/D) condensers were developed recently. Typical integral R/D condensers have extra headers that play the role of R/D. Except an extra header and somewhat complex tube array resulting from the extra header, the most integral R/D condensers have almost the same specification that tube has multi channels, fin has louvers, flow in tube is parallel, etc. When integral condensers are applied, it is known that the refrigerating effect increases, resulting from the increase of subcooling degree in condenser, and the refrigerant amount used saves. In spite of several merits, integral condensers have not been applied a lot. That is why there is an uncertainty in performance, using integral condensers. The objective of this study is to theoretically optimize the tube array in an integral R/D condenser that is really being applied to some vehicles. The tube array has a great effect on the performance of the integral condenser as well as common ones. Through computer simulation, we could see that the tube array, 14-6-3-5-3-4, in the same condenser was the best, comparing heat release rate, pressure drop, etc. to the real array, 17-5-3-3-2-5. It should be noted that the optimization is based on the condenser performance only.

• Korean Journal of Optics and Photonics
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• v.26 no.1
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• pp.30-37
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• 2015

The design and implementation of a radiative temperature measurement system for a flash light are carried out. Since a massive amount of energy is emitted within a very short time, it is impossible to measure the temperature of a flash with a conventional method. It is also irrelevant to measure one with an optical noncontact method. In this paper, a radiative temperature measurement system using the ratio of spectral radiances over mid- and long-wavelength infrared (IR) is designed and implemented. The implemented system utilizes optical bandpass filters to divide the wavelengths within the mid- and long-wavelength IR ranges, and pyroelectric IR detectors to measure the incident optical power of each wavelength-divided channel. It is shown that the measured radiative temperature of a flash is in the range of 1393 to 1455 K. This temperature-measurement system can be utilized to obtain information about the spectral radiance of a flash as a light source, which is of crucial importance to approaching the modeling and simulation of the various effects of a flash.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.6
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• pp.19-26
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• 2005

Image interpolation in the wavelet domain usually takes advantage of the probabilistic models for the intrascale statistics and the interscale dependency. In this paper, we adopt the linear model for the absolute values of wavelet coefficients of interpolated image across scale to estimate the variances of extrapolated bands. The proposed algorithm uses randomly generated wavelet coefficients based on the estimated parameters for probabilistic model. Random number generation according to the estimated probabilistic model may induce the 'salt and pepper' noise in subbands. We reduce the noise power by Wiener filtering. We observe that the proposed method generates the histogram of the subband coefficients similar to the that of original image. Experimental results show that our method outperforms the previous wavelet-domain interpolation method as well as the conventional bicubic method.

• Journal of The Korean Association of Information Education
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• v.8 no.3
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• pp.365-372
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• 2004

The purpose of this study is to develop FVU, which enables teachers effectively to construct self-page on the screen, to reduce the size of file for teaching, and to correct many different kinds of event which was already made in the previous. The instrument used in the development of this Editor is UML(Unified Modeling Language), which is object-oriented methodology. The Authoring tool developed in this study is named FVU. The first page which is needed in class can be constructed by using VUEditor in FVU. Using VUEditor can get Instructional Syllabus exported into VUAuthor through Vector-transformation. Through this procedure, the size of image file comes to be reduced into forming low band width, which results in solving the problem of network traffic. Also, Instructor can create image, shape and text, and delete and correct errors or mistakes which make in the course of constructing materials for teaching. In conclusion, this VUEditor enables program designer to construct the first page, even without using such applied program as Image Tool and Power Point. This VUEditor makes instructor to make some contents for teaching easily.

• The Journal of Information Systems
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• v.17 no.3
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• pp.205-233
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• 2008

This study suggests the dynamic value chain model, that will be able to not only show changing processes to organization's significant capital by integrating an individual, implicit, and explicit knowledge which affect organizational decision making, but also distinguish the key driver for raising organizational competitive power because it makes possible to analyze sensitivity of performance along with decision making alternatives and policy changes from dynamic view by connecting knowledge management capability, knowledge management activity, and relations with organizational performance with specific strategic map. Recently, a lot of organizations show interest in measuring and evaluating their performance synthetically. In organizations taking knowledge management, they introduce effective value chain model like a dynamic balanced scorecard (DBSC), and therefore they can reflect their knowledge management condition as well as show their changes by checking performance of established vision and strategy periodically. Furthermore, they can ask for their inner members' understanding and participation by communicating with and inspiring their members with awareness that members are one of their group, present a base of benchmarking, and offer significant information for later decision making. The BSC has been a successful framework for measuring an organization's performance in various perspectives through translating an organization's vision and strategy into an interrelated set of key performance indicators and specific actions. The BSC, while having significant strengths over traditional performance measurement methods, however, has its own limitations, due to its static nature, such as overlooking two-way causation between performance indicators and neglecting the impact of delayed feedback flowing from the adoption of new strategies or policy changes. To overcome these limitations, this study employs SD, a methodology for understanding complex systems where dynamic feedback among the interrelated system components significantly impact on the system outcomes. The SD simulation model in the form of DBSC would serve as a useful strategic teaming tool for facilitating an organization's communication process through various scenario analyses as well as predicting the dynamic behavior pattern of their key performance measures over a future time frame. For the demonstration purpose, this study applied the DBSC model to Prototype of Korea manufacturing and service firm.

• Journal of Digital Convergence
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• v.16 no.7
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• pp.79-88
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• 2018

Previously, there have been many studies on the fraud of employees, internal customers of the company, but there have been a lot of studies on military affairs that are closely related to the improvement of army's combat power. Therefore, this study investigates how communication satisfaction is influenced by the characteristics of SNS. For empirical verification, 240 soldiers were surveyed in this study. The analysis method was to investigate the correlation between each variable using the Structural Equation Model (SEM). The results of this study show that the SNS characteristics have a positive effect on the overall model related to organizational communication satisfaction. Organizational communication satisfaction has a positive impact on military fraud and organizational communication satisfaction has been shown to mediate between army and SNS traits. Through this research, we intend to promote the morale of soldiers by activating communication among group members using appropriate level of social networking.

• Journal of Radiation Protection and Research
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• v.28 no.1
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• pp.1-8
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• 2003

The periodic safety review of operational nuclear power plants requires that the plants should keep a well organized environmental monitoring program. The past records of environment monitoring data were analyzed. and the tritium concentrations of the samples in the surface and ground water around Kori site were measured. It was shown that the tritium concentrations around the Kori site were slightly higher than that of natural background. The change of background tritium concentration was estimated through a numerical modeling. Two different versions of 7 compartments model - the world and the northern hemisphere - defined in NCRP-62 were modeled for the global tritium cycling. The numerical solution of the model was obtained using a computer program, AMBER. The four cases of tritium source-terms into the atmosphere were considered. The results showed that the tritium concentration in the surface soil water was higher than that in sea water or surface stream water. Also, it was shown that the tritium produced by the interaction between cosmic rays and the gases were the major source of tritium, and the tritium produced by nuclear weapon test decreased considerably.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.110-124
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• 1993

A Nonlinear model-based Hybrid Controller (NHC) is developed which consists of the adaptive proportional-integral-feedforward (PIF) gains and variable structure controller. The controller has the robustness against modeling uncertainty and is applied to the trajectory tracking control of single-input, single-output nonlinear systems. The essence of the scheme is to divide the control into four different terms. Namely, the adaptive P-I-F gains and variable structure controller are used to accomplish the specific control actions by each terms. The robustness of the controller is guaranteed by the feedback of estimated uncertainty and the performance specification given by the adaptation of PIF gains using the second method of Lyapunov. The variable structure controller is incorporated to regulate the initial peak of the tracking error during the parameter adaptation is not settled yet. The newly developed NHC method is applied to the power tracking control of a nuclear reactor and the simulation results show great improvement in tracking performance compared with the conventional model-based control methods.

• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.59-69
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• 2001

Five kinds of modified electrode arrays were proposed to overcome the weak points of the commonly used arrays using dipole and/or pole in two-dimensional resistivity surveys. The modified pole-pole array was suggested to overcome the inefficiency caused by distant earthing in pole-pole array. Four kinds of modified arrays using dipole were designed to enhance the signal-to-noise ratio of the conventional dipole-dipole and pole-dipole arrays through boosting up the measured potential difference. In the numerical experiments using the two-dimensional modeling and inversion, the effects of the ambient electrical noise and the resolving power were examined and the results showed the validity of the modified arrays proposed in this study.