• Journal of international Conference on Electrical Machines and Systems
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• 제1권1호
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• pp.91-98
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• 2012

Climate change and other pollutions make a huge demand of environment friendly and high efficient motors especially Brushless DC (BLDC) motors. Generally, bidirectional energized BLDC motors are used widely; however, inverter devices used in the driver put fear of being effected by noise. This paper proposes unidirectional energized BLDC motor which utilizes asymmetrical H-bridge circuit as the driver circuit. The Minato motor is one of the pioneers in unidirectional energized system. The use of bar magnets in the rotor is one of the biggest disadvantages of the motor. We proposed using tabular magnets. The paper compares the power consumption and efficiency of the Minato motor and the proposed motor. During high speed rotation, undesirable armature current is generated that has a deceleration characteristic. This current lowers the motor's efficiency. In this paper, we propose the solutions and show comparison through equations of the copper loss ratio for the Minato and our proposed motors. The third motor, which has the highest efficiency, was discovered during examination of the equations.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권1호
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• pp.32-39
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• 2012

With the aid of genetic algorithm (GA), global optimization with multiple geometry parameters is feasible in the design of switched flux permanent magnet (SFPM) machines. To investigate the advantages of global optimization over individual optimization, which has been used extensively for the design of SFPM machines, a comparison between the two approaches is carried out for the case of fixed copper loss and volume. In the case of individual parameter optimization, the sequence in which the individual parameters are optimized is very important. In the global optimization a better design can always be achieved although the corresponding torque density is found to be only slightly better than that of individually optimized with correct design sequence. By using the obtained global optimization results, the performance in machines having two types of stator and rotor pole combinations, i.e. 12/10 and 12/14, are compared, and it is shown that higher torque is exhibited in the 12/14 SFPM machine. Finally, this paper also demonstrates that global optimization, with the restriction of equal pole width, magnet thickness and slot opening, can maximize the torque density without significantly sacrificing other performance, such as cogging torque and overload capability.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 춘계학술대회 논문집 방전 플라즈마 유기절연재료 초전도 자성체연구회
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• pp.19-22
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• 2004

The resonant planar transformer, which had power capacity of 300 W, input voltage of 220 V, output voltage of 15 V, and switching frequency of 500 kHz, was designed and manufactured by using the planar core with large effective area and the flat copper lead frames for miniaturization and high efficiency of the switching mode power supply (SMPS). As well as, a resonant converter equipped with the above mentioned planar transformer was manufactured and electromagnetic characteristics were investigated. The numerical value of turns for 1st and 2nd winding were 12 and 2 respectively. The self inductance of 1st winding was 33.2 ${\mu}H$, very low leakage inductance of 1.27 ${\mu}H$, and the coupling factor of 0.98 were obtained at switching frequency of 300 kHz. The high efficiency of 88.21 % for the SMPS equipped with planar transformer was obtained at power capacity of 300 W.

• 한국군사과학기술학회지
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• 제14권6호
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• pp.1018-1025
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• 2011

The improved properties of corrosion for 90Cu10NiFe alloy in natural seawater were explained by sodium diethyl dithio carbamate(NaDDC), namely organic compound, which is reagent for heavy metal extractions of waste water. The efficiency of NaDDC as corrosion inhibitor for 90Cu10NiFe alloy has been investigated in seawater after immersion in various concentrations of NaDDC solutions for 12~36hrs at pH 8.2 by weight loss test and electrochemical techniques including potentiodynamic polarization and SEM-EDS measurements. The results showed that the corrosion resistance of 90Cu10NiFe alloy improves with the increasing concentration of NaDDC but it did not improves with increasing time any more, so the highest inhibition efficiency was 93% at 100mg/L, 36hrs. The results obtained from weight losses and corrosion rates in polarization curve measurements were in good agreement. Therefore, it showed that NaDDC is a good inhibitor for copper corrosion of 90Cu10NiFe alloy.

• 한국전기전자재료학회논문지
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• 제20권4호
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• pp.342-347
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• 2007

$Bi_6Mg_2Nb_4O_{21}(BMN)$ thin films were deposited at various substrates by sputtering system for embedded capacitor applications. BMN thin films deposited at room temperature are manufactured as MIM(Metal/Insulator/Metal) structures. Dielectric properties and leakage current density were investigated as a function of various substrates and thickness of BMN thin films. Leakage current density of BMN thin films deposited on CCL(Copper Clad Laminates) showed relatively high value ($1{\times}10^{-3}A/cm^2$) at an applied field of 300 kV/cm on substrates, possibly due to relatively high value of roughness(rms $50{\AA}$) of CCL substrates. 100 nm-thick BMN thin films deposited on Cu/Ti/Si substrates showed the capacitance density of $300 nF/cm^2$, a dielectric constant of 32, a dielectric loss of 2 % at 100 kHz and the leakage current density of $1{\times}10^{-6}A/cm^2$ at an applied field of 300 kV/cm. BMN capacitors are expected to be promising candidates as embedded capacitors for printed circuit board(PCB).

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.185-191
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• 2020

Plant-specific analyses of an advanced reactor have been performed to assure the structural integrity of the reactor pressure vessel during transient conditions, which are expected to initiate pressurized thermal shock (PTS) events. The vessel failure probabilities from the probabilistic fracture mechanics analyses are combined with the transient frequencies to generate the through-wall cracking frequencies, which are compared to the acceptance criterion. Several sensitivity analyses are performed, focusing on the orientations and sizes of cracks, the copper content, and a flaw distribution model. The results show that the integrity of the reactor vessel is expected to be maintained for long-term operation beyond the design lifetime from the PTS perspective using the design data of the advanced reactor. Moreover, a fluence level exceeding 9×10¹⁹ n/㎠ is found to be acceptable, generating a sufficient margin beyond the design lifetime.

• 전기학회논문지
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• 제68권1호
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• pp.77-82
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• 2019

In this paper, a 0.6~6GHz quad-ridge horn antenna which can be used for the antenna measurement of 5.8GHz WiFi system from lowest frequency band of mobile LTE (Long Term Evolution) is designed and implemented. The quad-ridge horn antenna has quadruple ridges of exponential function, a back-short and a cavity. Based on this structure, we design the cavity size, ridge gap and feed gap to have broadband characteristics. For implementation, the plates material of aluminum and copper are used for the horn and four ridges, respectively. And the insulator supports are used to maintain the gap between ridges. By measurement, antenna has the gain of 6.2~13.35dBi with the return loss of less than -6dB (under VSWR 3 : 1) in the entire design band. The results of this study can be widely used to the antenna studies on the mobile communication including low frequency band of LTE, the EMI measurement and the standard calibration measurement.

• 한국전자통신학회논문지
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• 제17권6호
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• pp.1081-1088
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• 2022

동기발전기의 고조파는 철손과 동손을 증가시켜 발열의 원인이 된다. 이를 감소시키기 위하여 전기자의 권선법을 분포권, 단절권을 이용하여 고조파를 감소시키는 방법이 있으나 본 논문에서는 영구자석의 형상을 기존에 연구되었던 방법이 아닌 새로운 형상 변형을 통해 고조파를 감소시키며 기전압의 파형을 개선하고자 한다. 형상 변형 방법으로 영구자석의 양단을 절단하고 설정값에 따라 영구자석의 면적을 증가, 감소시켜 공극의 길이를 조절한다. 이때 자속밀도의 분포를 다르게 하여 이에 따른 기전압과 왜형률을 비교하였다. 이를 통해 논문에 기술된 영구자석의 형상 변화 모델들을 비교하고 가장 효과적인 변형 방법을 나타냈다.

• 한국초전도ㆍ저온공학회논문지
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• 제8권1호
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• pp.15-18
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• 2006

A new precursor solution wilt low fluorine content was synthesized for MOD processing of coated conductors. In this study, the precursor solution for MOD processing was synthesized using F-free yttrium and copper precursor. It was shown that crack-free and uniform precursor films were formed after calcination in humidified oxygen atmosphere. Less than 2 hours were required to finish the calcination process. The relatively gradual weight loss during the calcination process is attributed to the feasibility of fast calcination profile. The calcined precursor film was converted to a YBCO film without any secondary phases after annealing in wet $Ar/O_2$ atmosphere. Fully converted film shows uniform microstructure and high critical current density. $(Jc=2.7MA/cm^2) $.

• 융합경영연구
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• 제3권1호
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• pp.33-39
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• 2015

Managers are always trying to be the best internal controls in their organizations copper approximate because they know that be effective internal control over previous systems, to fulfill the mission of the organization and minimize unexpected events will be extremely difficult. On the other hand, the existence of internal controls to increase efficiency, reduce head loss, assets and achieving a reasonable assurance of the reliability of financial statements and compliance with laws and regulations will be. Internal control, not an event, but a series of operations and activities on the basis of output. Internal controls help to achieve the goal of minimizing the problems of implementing appropriate internal controls. Internal control is an integral component of corporate governance that will provide reasonable assurance of achieving the organization's objectives. preventing, detecting errors and fraud goes to work. Responsibility for the prevention and detection of fraud and error in the public sector is the responsibility of managers. Managers of internal control and consistently applying appropriate accounting systems, this responsibility will play (Lin et al., 2011). Since the public sector organizations differ from each other, thus establishing internal controls cant be the same for all organizations and agencies of the public sector. Establish specific controls on each system to factors such as size, type of operation and organizational goals that the system is designed, it depends. On the other hand, rapid advances in information technology, the need to update internal control guidelines in relation to Create a new computer system so as to ensure that the activities of managers and effective control Should be updated if necessary.