• 영어어문교육
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• 제11권4호
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• pp.21-47
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• 2005

The purpose of this study is to investigate the effectiveness of English vocabulary learning strategies such as definition-oriented/contextoriented/situated context-oriented vocabulary learning strategy according to the cognitive styles of learners and interaction effect on the achievement test score between the learners' cognitive style and vocabulary learning strategies. The results show that there is no significant difference in the achievement test scores between field-dependent learner group and field-independent learner group. And there is significant difference in the English vocabulary achievement test scores among three experimental treatment groups, definition-oriented, context-oriented, situated context-oriented vocabulary learning strategy groups. Finally, there is an interaction effect on the achievement test score between the learners' cognitive style and vocabulary learning strategies.

• 산업기술연구
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• 제17권
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• pp.79-85
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• 1997

This paper describes a control for the high performance induction motor drive system with a wide speed operating range and proposes a robust control method independent of motor parameter variation. For the operation below the rated speed, the high performance control is achieved by using the indirect field-oriented control with a speed sensor. In the high speed regain, the field weakening region with a large variation in motor parameters, the motor drive system can obtain the robustness to motor parameter variation by switchover to the direct field-oriented control. Also, the sensorless speed control using estimated speed is achieved in very high speed region that the utilization of speed sensor pulses is limited. And from experiments using high performance 32bit DSP for 2.2[kW] and 22[kW] laboratory induction motor drive systems, it is verified that the proposed opration algorithm provided a good performance.

• 기술혁신학회지
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• 제8권3호
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• pp.932-954
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• 2005

The purpose of this paper is to evaluate of The University of Science and Technology (UST) as field-oriented graduate school model. The UST is unique in world-wide because of its operating system through the synergy effect of research and education and its interdisciplinary major system differentiated from the traditional graduate school, It first deals with measuring the users satisfaction by using a five-point Likert scale to analyze the general and special factors of UST, through which some findings are pointed out as follows; the education aims and visions are highly satisfied while essential factors in field-oriented education such as curriculum composition, apprentice and tailored education system, field training are not so high level. Finally it points out some suggestions for the UST development.

• Journal of Power Electronics
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• 제14권5호
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• pp.1000-1007
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• 2014

This paper proposes an on-line rotor time constant estimation strategy for indirect field oriented induction machines. The performance of the indirect field oriented control is dependent especially on the rotor time constant whose value varies according to the temperature. The proposed method calculates the difference between the nominal rotor time constant and the real value from the d- and q-axis integration terms of a proportional integral (PI) current regulator and the demanded voltages of the induction machine to regulate the current in the steady state. Because the proposed strategy has a simple structure and is available in wide speed and torque ranges, the proposed method can be easily used in the industrial field. The effectiveness of proposed strategy is verified with simulations and a 7.5kW experimental setup.

• Journal of Power Electronics
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• 제13권4호
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• pp.656-668
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• 2013

This paper presents a wavelet-fuzzy based controller for indirect field oriented control of three-phase induction motor drives. The discrete wavelet transform is used to decompose the error between the actual speed and the command speed of the induction motor drive into different frequency components. The transformed error coefficients along with the scaling gains are used for generating the control component of the motor. Self-tuning fuzzy logic is used for online tuning of the scaling gains of the controller. The proposed controller has the ability to meet the speed tracking requirements in the closed loop system. The complete indirect field oriented control scheme incorporating the proposed wavelet-fuzzy based controller is investigated theoretically and simulated under various dynamic operating conditions. The simulation results are compared with a conventional proportional integral controller and a fuzzy based controller. The speed control scheme incorporating the proposed controller is implemented in real time using a digital processor control board. Simulation and experimental results validate the effectiveness of the proposed controller.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.227-230
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• 1993

Recently, the development of novel control methodology enables us to improve the performance of AC-machine drives by using pulse width modulation (PWM) technique. Usually, the dynamic characteristic of induction motor (IM) has been represented by the 5-th order nonlinear differential equation. This dynamics, however, can be reduced to 3-rd order dynamics by applying direct control of IM input current. This methodology concludes that it is much easier to control IM by means of the field-oriented methods employing the current controller. Therefore a precise current control is crucial to achieve a high control performance both in dynamic and steady state operations. This paper presents an adaptive fuzzy current controller with artificial neural network (ANN) for field-oriented controlled IM. This new control structure is able to adaptively minimize a current ripple while maintaining constant switching frequency. Especially the proposed controller employs neuro-computing philosophy as well as adaptive learning pattern recognizing principles with respect to variations of the system parameters. The proposed approach is applied to the IM drive system, and its performance is tested through various simulations. Simulation results show that the proposed system, compared among several known classical methods, has a superb performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권11호
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• pp.4310-4330
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• 2020

With the continuous emergence of new applications and cyberattacks and their frequent updates, the need for automatic protocol reverse engineering is gaining recognition. Although several methods for automatic protocol reverse engineering have been proposed, each method still faces major limitations in extracting clear specifications and in its universal application. In order to overcome such limitations, we propose an automatic protocol reverse engineering method using a two-pathway model based on a contiguous sequential pattern (CSP) algorithm. By using this model, the method can infer both command-oriented protocols and non-command-oriented protocols clearly and in detail. The proposed method infers all the key elements of the protocol, which are syntax, semantics, and finite state machine (FSM), and extracts clear syntax by defining fine-grained field types and three types of format: field format, message format, and flow format. We evaluated the efficacy of the proposed method over two non-command-oriented protocols and three command-oriented protocols: the former are HTTP and DNS, and the latter are FTP, SMTP, and POP3. The experimental results show that this method can reverse engineer with high coverage and correctness rates, more than 98.5% and 99.1% respectively, and be general for both command-oriented and non-command-oriented protocols.

• 한국지리정보학회지
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• 제6권2호
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• pp.33-45
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• 2003

이 연구는 객체지향 지리정보시스템을 이용하여 지리-객체와 지리-필드를 연결하는 지리-객체필드 방법을 규정하고, 수계-객체필드를 이용하여 새만금호 수량과 배수갑문수위를 조작하는 새만금수자원관리시스템의 홍수 시뮬레이션을 구현하고자 한다. 그리고 새만금 수계 수자원에 발생하는 자연현상과 인공현상을 조합하여 하나의 전체 수계-객체필드로 구성되는 객체지향 클래스 계층구조를 설계함으로써 홍수통제 알고리즘 기법을 제안하고자 한다. 동시에 UML을 이용하여 전체적인 지리-객체필드와 단계적인 부분 지리-객체필드의 클래스계층구조를 가시화하고자 하며, 각 클래스의 속성과 메소드는 ZEUS/COM과 Win32 API을 이용한 Visual Basic 6.0을 사용함으로써 각각 호환성과 재사용성 기능을 확보하고자 한다. 이 논문은 새만금수자원관리시스템을 구현함으로써 효율적인 물관리를 하는데 기여할 수 있을 것이다.

• 전기학회논문지
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• 제67권4호
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• pp.543-548
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• 2018

Ferroelectric $Bi_4Ti_3O_{12}$ films were deposited on $SrTiO_3(100)$ and Si(100) substrate by using conductive $SrRuO_3$ films as underlayer, and their ferroelectric and electrical properties were investigated depending on crystal structure and orientation. C-axis oriented $Bi_4Ti_3O_{12}$ films were grown on well lattice-matched pseudo-cubic $SrRuO_3$ films deposited on $SrTiO_3(100)$ substrate, while random-oriented polycrystalline $Bi_4Ti_3O_{12}$ films were grown on $SrRuO_3$ films deposited on Si(100) substrate. The random-oriented polycrystalline film showed a good ferroelectric hysteresis property with remanent polarization ($P_r$) of $9.4{\mu}C/cm^2$ and coercive field ($E_c$) of 84.9 kV/cm, while the c-axis oriented film showed $P_r=0.64{\mu}C/cm^2$ and $E_c=47kV/cm$ in polarizaion vs electric field curve. The c-axis oriented $Bi_4Ti_3O_{12}$ film showed a dielectric constant of about 150 and lower thickness dependence in dielectric constant compared to the random-oriented film. Furthermore, the c-axis oriented $Bi_4Ti_3O_{12}$ film showed leakage current lower than that of the polycrystalline film. The difference of ferroelectric properties in two films was explained from the viewpoint of depolarization effect due to orientation of spontaneous polarization and layered crystal structure of bismuth-base ferroelectric oxide.

• 대한전기학회논문지
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• 제43권7호
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• pp.1084-1092
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• 1994

An induction machine can be operated in the constant power region over an extended high speed range by means of field weakening. A conventional field weakening method is to set the flux reference inversely proportional to the rotor speed. With this method, however, the machines can't yield the maximum torque over the entire high speed range. In this paper, a new field weakening method for the field oriented induction machine drive by the voltage control strategy is presented. The proposed scheme ensures not only producting the maximum torque over the entire field weakening region but also the robust control independent on machine parameters. Also the smooth transition into the field weakening operation and fast dynamic response during transient operation can be obtained. Simulation and experimental results from a 3hp laboratory induction motor drive system are done to confirm the proposed control algorithm.