• 한국주조공학회지
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• 제10권5호
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• pp.417-425
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• 1990

The purpose of this study is to investigate the effect of Be addition on the microstructure and mechanical properties of as-cast and homogenization treated Al-Li-(Be)alloys. The ductility of as-cast Al-Li alloy was increased by the addition of Be and the fracture morphology was changed from brittle to ductile mode. Also, hardness and strength have been decreased by homogenization treatment. The morphology of eutectic structure which consists of ${\alpha}(Al)$ and ${\alpha}(Be)$ was changed from lammellae to spherical type by homogenization treatment. The shape of ${\alpha}(Be)$ phase has been revealed as hollow type by TEM observation. It consists of outer surfaces with well defined crystal facets and the core filled with ${\alpha}(Al)$. The microstructure of as-cast Al-Li-Be alloys showed coarse ${\delta}'$, fine ${\delta}'$, and coarse ${\delta}$ phases. The coarse and fine ${\delta}'$ phases were formed at Be-rich phase /matrix interfaces and in matrix, respectively. By homogenization treatment, the ${\delta}$ phase in Al-Li and Al-Li-Be alloys dissolved and the size of ${\delta}$ phase in Al-Li-Be alloys was finer than that of Al-Li alloy.

• 전력전자학회논문지
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• 제22권3호
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• pp.249-255
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• 2017

This paper presents air-gap control according to Y and Delta connections of a double-sided air-gap permanent magnet synchronous motor (DA-PMSM) with independent three-phase structure. In particular, the DA-PMSM used in this study can be applied to low-speed and high-torque applications, such as wind turbines, tidal power generations, and electric propulsion ships, because of its modular stators and a rotor with numerous permanent magnets. Unlike conventional three-phase machines, the DA-PMSM has a symmetrical configuration with double-sided air-gap. Therefore, Y/Delta winding connections and serial/parallel configurations between stator modules are possible. To identify the DA-PMSM operating characteristics, mathematical modeling is analyzed according to the Y/Delta connections. Moreover, air-gap control performances by applying the winding connection methods are verified through experimental results.

• 수산해양기술연구
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• 제31권3호
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• pp.279-286
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• 1995

As Al-Li based alloys are to find widespread use in aerospace and other structural applications in which their low-density high specific stiffness properties be exploited, their mechanical properties must adequately match those of the which they intended to replace. In order to develop these purposed, the precipitation behaviors of the rapidly solidified Al-Li-Ti alloys aged at various temperature were investigated. ${\delta}'$ phase precipitated homogeneously in the matrix during not only melt quenching but also aging at the aging temperature of $160^{\circ}C\;and\;210^{\circ}C$. The addition of the Ti in Al-Li alloy promoted the formation of $\delta$' phase. The addition of Ti on the ${\delta}'$ solvus line had a little effect over the thermodynamics ${\delta}'$ solvus line. The reason for these behavior was that the ${\delta}'$ phase was suppressed to precipitate as much as supercooling by melt quenching. The discontinuous precipitation reaction occurred by the preferential growth of ${\delta}'$ phase due to the migration of grain boundary provided the driving force dependent of solute concentration fluctuations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.456-458
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• 1991

Beacause cycloconverter requires AC power converter each phase, it has the disadvantage of complexity in main system. In this paper, the simple circulating current typed cycloconverter obtained the three variable voltage and variable frequency by delta-connceting the three natual commuatation phase controled rectifiers is constructed.

• 대한수의학회지
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• 제27권2호
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• pp.347-359
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• 1987

To investigate the changes of pituitary gland associated with ovarian cyst in Korean native cattle, pituitaries and ovaries were collected from 54 Korean native cattle at abbatoir. Pituitaries were stained with HerIant pituitary stain method and all the tissues were examined under light microscope. The results obtained were summarized as follows; 1. The delta cells and beta cells in the pars distalis were dull blue and violet in colors respeetively. Basophil size in the follicular phase and pregnant groups was larger than those of luteal phase and ovarian dysfunction groups. 2. The numbers of delta cells in the pars distalis of follicular cyst group were larger than those of remaining groups (p<0.01). 3. The distribution of delta cells in the acidophil zone was greater than that in the basophil zone of the follicular cyst and follicular phase groups. 4. The granulations of delta cells were more intensive in follicular cyst, follicular phase and pregnancy groups than in luteal phase and ovarian dysfunction groups (p<0.01). 5. The numbers of beta cells in follicular phase and ovarian dysfunction groups were larger than those in luteal phase and follicular cyst groups respectively (p<0.01). 6. In all groups, the distribution of beta cells was greater in basophilic zone than in acidophilic zone (p<0.01).

• 전기전자학회논문지
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• 제3권1호
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• pp.39-49
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• 1999

This paper describes a 1 GHz, low-phase-noise CMOS fractional-N frequency synthesizer with an integrated LC VCO. The proposed frequency synthesizer, which uses a high-order delta-sigma modulator to suppress the fractional spurious tones at all multiples of the fractional frequency resolution offset, has 64 programmable frequency channels with frequency resolution of $f_ref/64$. The measured phase noise is as low as -110 dBc/Hz at a 200 KHz offset frequency from a carrier frequency of 980 MHz. The reference sideband spurs are -73.5 dBc. The prototype is implemented in a $0.5{\mu}m$ CMOS process with triple metal layers. The active chip area is about $4mm^2$ and the prototype consumes 43 mW, including the VCO buffer power consumption, from a 3.3 V supply voltage.

• Journal of Power Electronics
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• 제11권6호
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• pp.824-836
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• 2011

A new fault-tolerant control topology for open-loop motor-drive systems with Delta-connected stator windings is introduced in this paper. This new control topology enables the operation of a three-phase induction machine as a two-phase machine fed by a three-phase inverter upon a failure in one of the motor phases. This topology utilizes the "open-Delta" configuration to independently control the current in each of the two remaining healthy phases. This new control technique leads to the alleviation of any torque pulsations resulting from the consequences of the asymmetrical conditions associated with this class of faults.

• 한국정보전자통신기술학회논문지
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• 제11권3호
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• pp.283-289
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• 2018

샘플-홀드 커패시터와 전압제어발진기 신호에 동작하는 피드포워드 루프필터를 가진 단방향 전하펌프를 가진 위상고정루프를 제안하였다. 제안된 위상고정루프는 기존의 2차 RC 필터에 비해서 저항 대신에 스위치와 작은 작은 크기의 커패시터를 사용하여 칩 크기를 줄일 수 있을 뿐만 아니라 전압제어발진기의 위상잡음에 영향을 미치는 ${\Delta}VLPF$의 변화량과, 기준신호 의사잡음에 영향을 미치는 ${\Delta}{\Delta}VLPF$의 변화량을 각각 1/5과 1/6로 줄였다. 제안된 위상고정루프는 1.8V $0.18{\mu}m$ CMOS 공정을 이용하여 시뮬레이션을 통해 위상잡음 특성이 개선된 동작을 확인하였다. 향후 시뮬레이션을 바탕으로 칩을 제작하여 성능을 검정할 계획이다.

• 열처리공학회지
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• 제4권3호
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• pp.13-20
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• 1991

The present work was aimed to examine the variation of precipitations and mechanical properties by thermomechanical treatments (TMT) in Al-2.19 wt%Li and Al-2.0 wt%Li-0.11 wt%Zr alloys. This study was performed by TEM, SEM observation, DSC, electrical resistance measurement, hardness and tensile strength measurement. First peak of resistivity aged at $90^{\circ}C$ was caused by precipitation of ${\delta}^{\prime}$-precursor phase, and second peak was caused by precipitation of ${\delta}^{\prime}$ phase. According to this result, the precipitation process of Al-2.19 wt%Li alloy was as follow : $SSSS{\rightarrow}{\delta}^{\prime}$-precursor phase ${\rightarrow}{\delta}^{\prime}$ (Coherent ${\rightarrow}$ Semi-coherent) ${\rightarrow}{\delta}$. In a Al-2.0 wt%Li-0.11 wt%Zr ternary alloy, the first peak of resistivity was appeared at initial aging heat-treatment. It is result from exsistant of ${\delta}^{\prime}$-precursor phase. The effect acceleration in a binary alloy was not appeared and the over-aging ternary alloy was accelerated with increase of the reduction rate. It is caused by combination effect of ${\delta}^{\prime}$ and composite phase.

• 대한전자공학회논문지SD
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• 제42권5호
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• pp.47-54
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• 2005

본 논문에서는 Crosstalk에 의한 coupling capacitance의 변화량, ${\Delta}Cc$이 기본값인 Cc보다 더 커질 수 있음을 제안한 테스트 회로를 이용하여 실험적으로 증명하였다. 또한 ${\Delta}Cc$가 Aggressive line의 위상에 매우 의존함을 보였으며 위상이 같은 경우보다 반대인 경우에 ${\Delta}Cc$가 크게 됨을 보였다. 실험 결과의 타당성을 검증을 위해 HSPICE 시뮬레이션을 수행하여 실험치와 잘 맞음을 나타내었다.