• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1650-1658
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• 1998

This paper describes how to remove echoes effectively using speech parameter information provided form speech coder. More specially, the proposed adaptive echo canceller utilizes the excitation signal or linearly predicted error signal instead of output speech signal of vocoder as the input signal for adaptation algorithm. The normalized least mean ssquare(NLMS) algorithm is used for the adaptive echo canceller. The proposed algorithm showed a fast convergece charactersitcis in the sinulatio compared to the conventional method. Specially, the proposed echo canceller utilizing the excitation signal of speech coder showed about four times fast convergence speed over the echo canceller utilizing the output speech signal of the speech coder for the adaptation input.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.345-352
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• 2008

The motion of a projectile initiated by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one. The effects of water compressibility on projectile movements are investigated, comparing results based on the Fluent VOF model where water is treated as an incompressible medium with those from the presently developed VOF scheme. The present model considers compressibility of both air and water. The Fluent results show that the body moves farther and at higher speeds than the present ones. As time proceeds, the relative difference of speed and displacement between the two results drops substantially, after acoustic waves in water traverse and return the full length of the tube several times. To estimate instantaneous accelerations, however, requires implementation of the water compressibility effect as discrepancies between them do not decrease even after several pressure wave cycles.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.85-92
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• 2011

Main characteristic in railroad is the guided movement of the wheel by the track through a metal-to-metal contact, conferring to the rail vehicle a single degree of freedom. There are defects such as head check, shelling, corrugation, squats etc in surface of the rail by interface between the wheel and rail. These defects bring about reducing the life-cycle of rails and track components and increasing noises. In case of bad conditions, it is possible to happen to full-scale accident such as derailment. Recently, the track capacity has been increased for increasing speed and operation efficiency. So, maintenance and indirect cost have been increased. Currently, a coating method of rail construction is proposed by using the ceramics in Korea. Rails are used as the earth in electrical railroad systems. Currently traction return current is flowed through wheels of trains. In case of rails coated, problems are caused in the contact power between wheel and coating material of spray. In this paper, electric model is presented in the AT feeding method. In case of rails coated, electric model is presented. Also, standard resistance of the ceramic is demonstrated by contact power between wheel and coating material of spray.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.1
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• pp.63-70
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• 2009

The air sterilization systems are investigated experimentally in this paper. The goal is to reduce bacteria, mold and viruses in office air by using a UV sterilizer installed inside a partition panel and wall-mounted unit. These systems allow occupants to turn the system on/off and to control the incoming air speed and direction. The partition air sterilization system conditions and sterilizes the air, and then delivers the clean air into the personal task area through the partition panels, which are connected to the pressurized under-floor plenum. Room air exits through the return grills mounted on the ceiling. The wall-mounted air sterilization system sterilizes the air, and then delivers the clean air to the personal task area from the wall. In this study a full-size experimental environment is established to investigate the immunization performance of these air sterilization systems. A typical office space scale is used in this study in order to find an optimal system to achieve a sterilized healthy micro-environment. Multiple system parameters, including volume flow rate and velocity of supplied air, were regulated during the experiments. The more air contact these air sterilization systems had, the better disinfection performance. Over 90% of eradication ratios were obtained by these two air sterilization systems. The results indicate that these systems can efficiently disinfect office air contamination.

• Journal of Construction Engineering and Project Management
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• v.1 no.3
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• pp.28-37
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• 2011

Domestic construction companies are suffering from financing difficulties in the wake of the economic slump in Korea and abroad. During this economic slump, real estate investment trusts (REITs), facilitators for improving financing and stimulating construction businesses, have increasingly expanded since their introduction in 2001. However, in terms of growth speed and marketing size, Korean REITs are falling behind those of other nations. The purpose of this study is to suggest a method for composing a portfolio using the Markowitz portfolio selection model to stimulate REITs. The main contents are as follows. First, a comparative analysis was conducted of increased REIT profit with the application of the Markowitz model and the average REIT profit rate from July 3, 2007, to July 21, 2008, during the investment analysis periods. The results showed that the total profit rate from the Markowitz model was about 10% higher than the average REIT profit rate. Second, the sensitivity was analyzed according to the portfolio's data-gathering and replacement cycle to measure the optimum cycle and yield. The six-mouth profit data collection period showed about 16% higher profits with the Markowitz model than with the REITs. The two-week portfolio change period resulted in about 11% higher profits with the Markowitz model than with the REITs.

• International Journal of Automotive Technology
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• v.7 no.3
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• pp.369-375
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• 2006

This paper describes a simple proportional and integral control algorithm for a swirl motor controller and its application. The control algorithm may be complicated in order to have desired performance, such as low steady state errors, fast response time, and relatively low overshoot. At the same time, it should be compact so that it can be easily implemented on a low cost microcontroller, which has no floating-point calculation capability and low computing speed. These conflicting requirements are fulfilled by the proposed control algorithm which consists of a gain scheduling proportional controller and an anti-windup integral controller. The mechanical friction, which is caused by gears and a return spring, varies very nonlinearly according to the angular position of the system. This nonlinear static friction is overcome by the proportional controller, which has a two-dimensional look up gain table. It has error axis and angular position axis. The integral controller is designed not only to minimize the steady state error but also to avoid the windup effect, which may be caused by the saturation of a motor driver. The proposed control algorithm is verified by use of a commercial product to prove the feasibility of the algorithm.

• 사회경제평론
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• no.38
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• pp.129-161
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• 2012

This paper suggests that, in contrast to main argument of Efficient Market Hypothesis, hedge funds's financial speculation activity in the commodity markets are tending to generate a malfunction of making future price diverge from fundamental price. For this reason, we insist that stricter regulation on commodity derivative markets, including position limitation, is needed. Using some statistic analysis tools, we show that derivative transaction volume is getting so larger that financial speculation by hedge funds dominates price movement in commodity market and eventually slackens the speed of price's return to the fundamental price.

• PNF and Movement
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• v.10 no.1
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• pp.25-33
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• 2012

Purpose : The purpose of this study was to compare the effect of treadmill training and cognitive task with in the course of treadmill training at the same time with chronic stroke patients. Methods : Fourteen chronic stroke patients participated. Participants were randomly assigned to the control and experimental group(7 experimental, 7 control). All of participants were in-patients at local hospital and had been receiving a traditional rehabilitation program, five days a week. The both groups have undergone 4weeks. The experimental group trained in treadmill and cognitive task at the same time, but control group trained only treadmill. 10m walking test, Timed Up & Go (TUG) test and 6 Minutes walking(6M walking) test to measure the walking speed, dynamic balance and waling endurance ability were carried out before and after the training. Results : The result of the study were as follow:10m walking test were significantly increased both groups(p<.01), but not significant between groups(p>.05). TUG test were significantly increased both groups(p<.001) and between groups(p<.01). 6M walking test were significantly increased both groups(p<.001), but not significant between groups(p>.05). Conclusion : Ahead of return to the community to patients with stroke, cognitive task with in the course of treadmill training at the same time was effective in improving the dynamic balance ability.

• Journal of the Semiconductor & Display Technology
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• v.22 no.1
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• pp.94-98
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• 2023

In the case of high-speed data transmission on high multilayer boards, signal coherence is a problem, especially due to the via hole, and a solution to improve return loss or insertion loss by applying a back drill to the via hole is being proposed. In this paper, Near-Field Electromagnetic measurements were made on a high multilayer board to determine how the presence or absence of back drill affects signal consistency. For this purpose, we used a signal generator, spectrum analyzer, and EMC scanner on a test board to determine if it is possible to distinguish between areas with and without back drill in the via holes of the stubs on the board. Also, we analyzed the measured value of S11, S21 and EMC etc. for how much it improves the signal attenuation of the stub with back drill. Through this, we knew that less electromagnetic waves are generated the stub via with back drill. At future research, we will analyze how much it improves the signal loss and electromagnetic waves due to the depth of back drill.

• Publications of The Korean Astronomical Society
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• v.38 no.2
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• pp.25-36
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• 2023

Since interstellar objects like 1I/'Oumuamua and 2I/Borisov originate from exoplanetary systems, even if we do not visit the exoplanetary systems, flyby, rendezvous, and sample return missions of interstellar objects can provide clues to solve the mysteries of cosmic life phenomena such as the origin of exoplanetary systems, galactic evolution, biosignatures (or even technosignatures), and panspermia. In this paper, we review space missions for interstellar object exploration in the stage of mission design or concept study such as Project Lyra, Bridge, Comet Interceptors, and Lightcraft^TM. We also review space missions, OSIRIS-REx and NEA Scout, designed for Near Earth Asteroids(NEA) explorations, to investigate the current state of basic technologies that can be extended to explore interstellar objects in a velocity of ~ 6AU/year. One of the technologies that needs to be developed for interstellar object exploration is a spacecraft propulsion method such as solar sail, which can catch up with the fast speed of interstellar objects. If this kind of propulsion becomes practical for space explorations, interstellar object explorations will mark a new era and serve as a driving force to provide evidences of cosmic life.