• Journal of Powder Materials
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• v.17 no.3
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• pp.197-202
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• 2010

Low temperature degradation behavior in yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics was microscopically observed from the phase contrast between monoclinic surface and tetragonal matrix. The degradation behavior was dependent on the surface treatment of sintered Y-TZP, even if the sintering history is same. In the mirror polished specimen, the monoclinic layer appeared in a uniform thickness from the surface. On the contrary, for the specimen with coarse scratch, the thickness of degraded surface was more than double especially from the coarse scratch. Since the scratch results in local deformation, the residual stress should be induced around the scratch. With the transformation from tetragonal to monoclinic, the volume expansion exerts a stress on a neighboring grains and promotes a successive phase transformation. Such a autocatalytic effect can be triggered from the part of coarse scratch.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.243-247
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• 1999

We report the generation of inherently stable, high-speed, nearly transform-limited, optical pulses by chirped pulse compression, in which sinusoidally driven phase modulator generates frequency chirped pulses that are subsequently compressed by a dispersive optical fiber. Experimental results show that $sech^2$ shape pulses with a pulse width of ~14 ps and a time bandwidth product of ~0.34 are successfully generated at 10 GHz repetition rate. In contrast to other methods, such as higher order soliton compression, this approach does not depend on the optical power and thus shows promise for application to low-power lasers.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.3
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• pp.254-262
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• 1990

In the active power filter, the PWM method for controlling the power converter plays an important role for the performance and the efficiency of the filter. In this paper, a new PWM method for the single phase current source type active power filter is presented, which is intended particularly for obtaining the maximum efficiency of the compensation. This method is basically based upon the optimized injection method, but in contrast to the existing method, this method adapts the optimized injection method by putting not only the pulse width, but also the pulse position into control variables. By doing this, when the number of pulses per one cycle is N, lower order harmonics up to the Nth order can be completely eliminated by the filter. So, this method is much more efficient than any other existing method. These characteristics are well verified by the computer simulations and the experiments.

• Journal of Powder Materials
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• v.8 no.1
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• pp.42-49
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• 2001

Ti-50Ni(at%) and Ti-40Ni-10Cu(at%) alloy powders have been fabricated by ball milling method, and their microstructure and phase transformation behavior were investigated by means of scanning electron microscopy/energy dispersive spectrometry, differential scanning calorimetry (DSC), X-ray diffractions and transmission electron microscopy. In order to investigate the effect of ball milling conditions on transformation behavior, ball milling speed and time were varied. Ti-50Ni alloy powders fabricated with the milling speed more than 250 rpm were amorphous, while those done with the milling speed of 100rpm were crystalline. In contrast to Ti-50Ni alloy powders, Ti-40Ni-10Cu alloy powders were crystalline, irrespective of ball milling conditions. DSC peaks corresponding to martensitic transformation were almost discernable in alloy powders fabricated with the milling speed more than 250 rpm, while those were seen clearly in alloy powders fabricated with the milling speed of 100 rpm. This was attributed to the fact that a strain energy introduced during ball milling suppressed martensitic transformation.

• Broadcasting and Media Magazine
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• v.18 no.3
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• pp.40-56
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• 2013

본 연구 논문의 목표는 홀로그래픽 디스플레이 성능평가 항목을 구체적으로 정리하며 성능평가 정의를 기반으로 홀로그래픽 디스플레이의 화질평가 방법을 제안한다. 홀로그래픽 디스플레이를 통하여 제공되는 입체 시 인지요인의 만족지표를 설정하고 디스플레이 되는 홀로그래픽 디스플레이의 광학적 요구 사항과 관련된 성능 평가 항목을 정의 한다. 또한 본 논문에서는 위상 광변조기(Phase SLM)를 이용한 실험장치를 구성하여 획득한 홀로그래픽 재생영상을 분석함으로써 홀로그래픽 디스플레이의 영상이 갖추어야 할 평가지표를 나타낸다. 평가 항목과 관련하여 모듈레이션 전이함수(Modulation Transfer Function)를 이용한 해상도(resolution)와 대조비(contrast)에 대한 결과를 분석하였으며 마지막으로 획득된 간섭무늬(Fringe Pattern)의 랜덤 위상 노이즈(Random Phase Noise)에 따른 화질 저하에 대한 정량 분석결과를 나타낸다.

• Journal of Power Electronics
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• v.17 no.3
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• pp.664-673
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• 2017

With the development of multilevel converters, cascaded single-phase H-bridge rectifiers (CHBRs) has become widely adopted in high-voltage high-power applications. In this study, sequence pulse modulation (SPM) is proposed for CHBRs. SPM is designed to balance the dc-link voltage and maintain the smooth changes of switch states. In contrast to phase disposition modulation, SPM balances the dc-link voltage even after removing the load of one submodule. The operation principle of SPM is deduced, and the unbalance degree of SPM is analyzed. All the proposed approaches are experimentally verified through a prototype of a four-module (nine-level) CHBR. Conclusions are drawn in accordance with the results of SPM and its imbalance degree analysis.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.585-586
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• 2005

BSCCO thin films were fabricated by an ion beam sputtering method with an ultra-low growth rate, and sticking coefficients of the respective elements are evaluated. The sticking coefficient of Bi element in BSCCO film formation was observed to show a unique temperature dependence; it was almost a constant value of 0.49 below about $730^{\circ}C$ and decreased linearly over about $730^{\circ}C$. In contrast, Sr and Ca, displayed no such remarkable temperature dependence. This behavior of the sticking coefficient was explained consistently on the basis of the evaporation and sublimation processes of Bi2O3. It is considered that the liquid phase of the bismuth oxide plays an important role in the Bi 2212 phase formation in the co-deposition process.

• Journal of Korean Vacuum Science & Technology
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• v.2 no.2
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• pp.118-121
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• 1998

Diisopropylselenide (DIPSe) is employed for the metalorganic vapor phase epitaxy (MOVPE) of ZnSe in order to eliminate premature gas phase reaction while maintaining negligible carbon incorporation and preserving relatively low growth temperature. In combination with dimethylzinc, single crystalline ZnSe layers were grown on GaAs at temperature around 450$^{\circ}C$. Secondary ion mass spectrometry showed a negligible carbon incorporation in ZnSe films grown from DIPSe even at high [Ⅵ]/[II] ratios, in contrast of a carbon concentration of 1021 cm-3 in ZnSe films grown from diallyselenide (DASe). Crystalline and interface quality are demonstrated by secondary electron microscopy, secondary ion mass spectroscopy and double crystal X-ray diffraction.

• Current Applied Physics
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• v.18 no.11
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• pp.1261-1267
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• 2018

In this paper, an off-axis digital holographic microscopy compensated with self-hologram rotation is presented. The process is implemented via subtracting the unwrapped phase maps of the off-axis parabolic hologram and its rotation $180^{\circ}$ to eliminate the tilt induced by the angle between the spherical object wave O and the plane reference wave R. Merit of the proposed method is that it can be done without prior knowledge of physical parameters and hence can reconstruct a parabolic hologram of $1024{\times}768$ pixels within tens of milliseconds since it doesn't require a digital reference wave. The method is applied to characterize rough gold bumps and the obtained results were compared with those extracted from the conventional reconstruction method. The comparison showed that the proposed method can characterize rough surfaces with excellent contrast and in realtime. Merit of the proposed method is that it can be used for monitoring smaller biological cells and micro-fluidic devices.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.1242-1247
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• 2009

The sudden changes in the construction market and the progressively intensifying price wars have amplified the importance of the construction cost estimation in the initial and planning phases of construction projects. However the methodologies and process of estimating construction cost in the planning and design phase are not standardized in the domestic market, in contrast to the markets of more developed countries. Therefore this paper proposes a new approximate estimation model to be used from the initial stages of construction projects. This methodology that extracts, modifies and synthesizes comparable elements of previous cases. This will introduce the foundation for the implementation of systems with improved usability and applicability.