• 대한두경부종양학회지
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• 제15권1호
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• pp.80-84
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• 1999

Primary hryperparathyroidism is a relatively rare disease entity in Korea. It's characterized by severe skeletal and renal changes due to hypersecretion of parathyroid hormone, and rarely shows peptic ulceration, hypertension, pancreatitis and impaired mentality. Recently the determination of the serum calcium level has become a routine laboratory test and the awareness of primary hyperparathyroidism has been incerased, the disease is being diagnosed with increasing frequency. Primary hyperparathyroidism is most commonly caused by parathyroid adenoma and rarely hyperplasia, cancer of parathyroid glands. The authors operated sucessfully a case of primary parathyroid adenoma by diagnosed by nuclear medical diagnostic work-up. The patient had anterior neck mass(soft, non tender nodule) on physical examination, multiple goiter on thyroid ultrasonogram and scan. The parathyroid lesion was difficult to find preoperatively.

• Journal of Communications and Networks
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• 제13권1호
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• pp.50-55
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• 2011

Spectrum leasing for cognitive radio (CR) networks is an effective way to improve the spectrum utilization. This paper presents an opportunistic relaying based spectrum leasing for CR networks where the primary users lease their frequency band to the cognitive users. The cognitive users act as relays for the primary users to improve the channel capacity, and this improved capacity is used for the transmission of secondary users' data. We show that the cognitive users can use a significant portion of the communication resource of primary networks while maintaining a fixed target data rate for the primary users. Moreover, the primary network is also benefited by the cooperating cognitive users in terms of outage probability. Information theoretic analysis and simulation results are presented to evaluate the performances of both primary and cognitive networks.

• Journal of Magnetics
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• 제21권3호
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• pp.374-378
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• 2016

The transformer used in an inverter type arc welding machine is designed to use high frequency in order to reduce its size and cost. Also, selecting core materials that fit frequency is important because core loss increases in a high frequency band. An inrush current can occur in the primary coil of transformer during arc welding and this inrush current can cause IGBT, the switching element, to burn out. The transformer design was carried out in $A_P$ method and amorphous core was used to reduce the size of transformer. In addition, sheet coil was used for primary winding and secondary winding coil considering the skin effect. This paper designed the transformer core with an air gap to prevent IGBT burnout due to the inrush current during welding and proposed the optimum air gap length.

• 한국정밀공학회지
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• 제13권12호
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• pp.129-135
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• 1996

This paper presents the effectiveness of the dynamic vibration absorber consisting of a single mass, coil springs and oil damper on the resonance freauency ratio and amplitude ratio for damped linear systems, that is, primary vibration system with damping. The effects of the dynamic vibration absorber are investigated numerically and experimentally for values of mass ratio, natural frequency ratio, and damping ratio. The experimental results show good agreement with calculated ones. As a result, the characteristics shown by the present work are useful in optimal tuning the dynamic vibration absorber in practice.

• 한국산학기술학회논문지
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• 제9권5호
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• pp.1150-1153
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• 2008

본 논문은 탄소 나노 튜브 (CNT)로 형성된 다중벽 탄소 나노튜브의 진동 특성을 분자 역학적 시뮬레이션 방법에 의해 해석하였다. 이로부터 이중벽 탄소 나노튜브에 비하여 다중벽 탄소 나노튜브의 경우 진동 주파수 분할이 발생됨을 분석하였다. 또한 세개의 주파수 발생자로써의 4차 벽, 5차 벽, 6차 함수 벽으로 된 오실레이터와 직경으로부터 독립적인 적합성 제안을 위해 지속적인 세 개의 정점이 나타나는 것으로 분석되었다.

• Journal of Electrical Engineering and Technology
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• 제8권2호
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• pp.262-270
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• 2013

A boundary protection method for power distribution line based on equivalent boundary effect is presented in this paper. In the proposed scheme, the equivalent resonance component with a certain central frequency is sleeve-mounted at the beginning of protected zone. The 'Line Boundary' is built by using boundary effect, which is created by introducing impedance in the primary-side of line. The 'Line Boundary' is significantly different from line wave impedance. Therefore, the boundary protection principle can be applied to power distribution line without line traps. To analyze the frequency characteristic corresponding to traveling-waves of introducing impedance in the primary-side of line, distributed parameters model of equivalent resonance component is established. The results of PSCAD/EMTDC simulation prove the obvious difference of voltage high frequency component between internal faults and external faults due to equivalent resonance component, and validate the scheme.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.218-220
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• 2005

This paper shows the analysis of the inductive power transfer system in conjunction with series resonant converter operating variable high frequency. Of particular interest is the sensitivity of the complete system to variations in operational frequency and parameters. In inductive power transfer system, electrical power is transferred from a prima교 winding in the form of a coil or track, to one or more isolated pick-up coils that may relative to the primary. The ability to transmit power without contact enables high reliability and easy maintenance that allows inductive power transfer system to be implemented in hostile environments. This technology has found application in many fields such as electric vehicles, PRT(Personal Rapid Transit) etc. The coupling between the primary and secondary is then presented to include the effects of parameter and operational frequency variation.

• Journal of Power Electronics
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• 제12권4호
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• pp.528-537
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• 2012

This paper presents an interleaved resonant converter with a parallel-series transformer connection in order to achieve ripple current reduction at the output capacitor, zero voltage turn-on for the active switches, zero current turn-off for the rectifier diodes, less voltage stress on the rectifier diodes, and less current stress on the transformer primary windings. The primary windings of the two transformers are connected in parallel in order to share the input current and to reduce the root-mean-square (rms) current on the primary windings. The secondary windings of the two transformers are connected in series in order to ensure that the transformer primary currents are balanced. A full-wave diode rectifier is used at the output side to clamp the voltage stress of the rectifier diode at the output voltage. Two circuit modules are operated with the interleaved PWM scheme so that the input and output ripple currents are reduced. Based on the resonant behavior, all of the active switches are turned on under zero voltage switching (ZVS), and the rectifier diodes are turned off under zero current switching (ZCS) if the operating switching frequency is less than the series resonant frequency. Finally, experiments with a 1kW prototype are described to verify the effectiveness of the proposed converter.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.249-254
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• 2021

As the spreading speed of electric vehicles increases rapidly, those are expected to be able to use them as flexible resources in the power system beyond the concern for the supply of its charging power. Especially when the Renewable Energy sources (RES) which have no intrinsic control capability have replaced the synchronous generators more and more, the power system needs to secure the additional frequency control resources to ensure its stability. However, the feasibility of using electric vehicles as the frequency control resources should be analyzed from the perspective of the power system operation and it requires the existing simulation frameworks for the power system. Therefore, this paper proposes the grid connected modeling of the primary frequency control provided by electric vehicles which can be integrated into the existing power system model. In addition, the proposed model is implemented considering technical performances constrained by the characteristics of the Vehicle-Grid Integration (VGI) system so that the simulation results can be accepted by the power utilities operating the power system conservatively.

• 대한지역사회영양학회지
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• 제19권5호
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• pp.415-424
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• 2014

Objectives: Vegetables are the most left over side dishes in school lunch programs. This study intended to analyze the differences in preference for vegetables among the students of different age groups in order to determine potential ways of increasing vegetable consumption in this study group. Methods: A total of 308 primary to university students in Gyeongbuk area were recruited and a questionnaire-based survey was conducted. The preference score (7-Likert scale: very much dislike (1)~so-so (4)~like very much (7)) and intake frequency (5-Likert scale) of 48 kinds of vegetables in 4 vegetable groups, such as vegetable (fruit-, root-, leaf-, and stalk-vegetable), seaweeds, mushrooms, and kimchi were investigated, and data were analyzed by SPSS WIN (ver 12.0). Results: The preference scores of vegetables except for seaweeds were significantly different among school groups, university was the highest, followed by high school. Primary and middle school students showed the lowest preference score, especially for leaf- and stalk- vegetables. The preference score for seaweeds was the highest of 5.28, followed by kimchi of 4.99. With regard to kimchis, the preference score was the highest in university', followed by high school, middle school, and primary school' was the lowest. The number of vegetables with < 4.0 preference score was the highest in primary school of 16, 15 in middle school, 11 in high school, and 7, the lowest in university. The vegetable with preference score of < 4.0 in all 4 school groups were mallow, chard, bud, radish leaf, mugwort, butterbur and sweet potato stalk. With regard to the intake frequency of vegetables, kimchis, an indispensable part of the Korean diet, was the highest of 2 times/day, followed by cooked vegetables of 1.5 times/day. The correlation coefficients between preference scores and intake frequencies were statistically significant in all groups of vegetables. As for the coefficient of variation (CV) of preference score, primary school' was the highest and university' was the lowest. The number of vegetables with high CV and high inexperience were highest in primary school students. Conclusions: Providing more opportunities for consuming a variety of vegetables, such as leaf- and stalk-vegetable, it may be possible to increase vegetable consumption, especially for the primary school students.