• Proceedings of the KIEE Conference
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• 2000.11b
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• pp.235-237
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• 2000

본 연구에서는 SRM의 설계 단계에서 일반적으로 얻을 수 있는 자속 쇄교-전류 곡선으로부터 SRM의 토크-속도 특성 곡선을 예측하는 방법을 제시한다. B-스플라인 함수를 이용하여 SRM에 가해질 수 있는 상전류 파형을 모두 모델링하고 각각의 회전자의 속도에서 최대의 토크를 낼 수 있는 전류 파형을 구한다. 제안된 방법은 상전류 제어뿐만 아니라 스위칭 각도 제어까지 고려한 모든 상전류 파형을 표현할 수 있기 때문에 SRM이 최적으로 동작하는 상황에서의 토크-속도 특성임을 보장할 수 있다. 제안된 방법은 SRM의 설계 단계에서 별도의 제어기 설계 없이 간단히 성능을 평가할 수 있는 방법이다.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.55-57
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• 2020

최근 항공기 분야에서는 기존 내연기관이 아닌 배터리를 이용한 전기 추진 방식(Electric Propulsion)에 대한 연구가 활발하다. 특히 완전 전기 추진 시스템에서는 모든 전력을 배터리로부터 입력받는다. 배터리는 잔존용량에 따라 배터리의 출력전압의 크기가 변하는 특성을 갖는다. 이러한 특성은 전동기 상전류의전고조파 왜율(THD)에 영향을 준다. 본 논문에서는 배터리 잔존용량에 따른 상전류 맥동을 분석하였고, 배터리 동작 특성에 맞추어 상전류 THD 조건을 만족하고 최대 효율로 인버터를 동작하기 위한 스위칭 주파수 선정 알고리즘을 제안하였다.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.796-803
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• 1997

The PVT and $^2H$-NMR characteristic of main-chain dimer liquid crystals having structures such as ${\alpha}$, ${\omega}$-bis[4,4'-cyanobiphenyl) oxy] alkane(CBA-10) were studied. In this work, V-T curves obtained from isobaris measurements on various pressures, volume changes were observed at the nematic-isotropic and nematic-crystal phase transition. The volume changes at the transition exhibit slight odd-even effect with respect to the number of methylene unit n. The values of the$({\Delta}S_{tr})_V$ obtained at the NI transition for CBA-10 was $12.6J/mol{\cdot}K$. The values of $({\Delta}S_{CN})_V$ for the CN transition was estimated on the basis of DSC data : $65.3J/mol{\cdot}K$. For both transition, it was found that the correction about the volume change is significant, ranging from 40 to 60% of the total transition entropy observed under constant pressure. The RIS analysis of the spectra was performed so as to elucidate the conformational characteristics of the spacer in the nematic phase. The conformational entropy changes at both CN and NI interphases were estimated on the basis of the nematic conformations taken from the conformation map as well as those derived from the simulation. The estimated conformational entropy change values were then compared with the corresponding constant-volume entropies obtained from PVT measurements. The correspondence between both entropy values was found to be quite good in consideration of the uncertainties involved in both experiment and calculations.

• The korean journal of orthodontics
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• v.40 no.1
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• pp.40-49
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• 2010

Objective: The aim of this research was to evaluate the mechanical properties (MP) and degree of the phase transformation (PT) of martensitic (M-NiTi), austenitic (A-NiTi) and thermodynamic nickel-titanium wire (T-NiTi). Methods: The samples consisted of $0.016\;{\times}\;0.022$ inch M-NiTi (Nitinol Classic, NC), A-NiTi (Optimalloy, OPTI) and T-NiTi (Neo-Sentalloy, NEO). Differential scanning calorimetry (DSC), three-point bending test, X-ray diffraction (XRD), and microstructure examination were used. Statistical evaluation was undertaken using ANOVA test. Results: In DSC analysis, OPTI and NEO showed two peaks in the heating curves and one peak in the cooling curves. However, NC revealed one single broad and weak peak in the heating and cooling curves. Austenite finishing ($A_f$) temperatures were $19.7^{\circ}C$ for OPTI, $24.6^{\circ}C$ for NEO and $52.4^{\circ}C$ for NC. In the three-point bending test, residual deflection was observed for NC, OPTI and NEO. The load ranges of NC and OPTI were broader and higher than NEO. XRD and microstructure analyses showed that OPTI and NEO had a mixture of martensite and austenite at temperatures below Martensite finishing ($M_f$). NEO and OPTI showed improved MP and PT behavior than NC. Conclusions: The mechanical and thermal behaviors of NiTi wire cannot be completely explained by the expected degree of PT because of complicated martensite variants and independent PT induced by heat and stress.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.502-507
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• 2016

Vanadium dioxide, $VO_2$, is a thermochromic material that exhibits a reversible metal-insulator phase transition at $68^{\circ}C$, which accompanies rapid changes in the optical and electronic properties. To decrease the transition temperature around room temperature, a number of studies have been performed. The phase transition temperature of 1D nanowire $VO_2$ with a 100 nm diameter was reported to be approximately $29^{\circ}C$. In this study, 1D or 2D nanostructured $VO_2$ was grown using the vapor transport method. Vanadium dioxide has a different morphology with the same growth conditions for different substrates. The 1D nanowires $VO_2$ were grown on a Si substrate ($Si{\setminus}SiO_2$(300 nm), whereas the 2D & 3D nanostructured $VO_2$ were grown on an exfoliated graphene nanosheet. The crystallographic properties of the 1D or 2D & 3D nanostructured $VO_2$, which were grown by thermal CVD, and exfoliated-transferred graphene nanosheets on a Si wafer which was used as substrate for the vanadium oxide nanostructures, were analyzed by Raman spectroscopy. The as-grown vanadium oxide nanostructures have a $VO_2$ phase, which are confirmed by Raman spectroscopy.

• Journal of the Mineralogical Society of Korea
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• v.32 no.2
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• pp.79-86
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• 2019

The white aluminum phases in acid mine drainage usually precipitates when mixed with stream waters with relatively high pH. The minerals in white precipitates play important roles in controlling the behavior of heavy metals by adsorbing and coprecipitation. By the phase transition of these minerals in white precipitates, dissolution and readsorption of heavy metals may occur. This study was conducted to obtain preliminary information on the phase transition of the mineral phases in white precipitates. In this study, the mineral phase changes in the white precipitates collected from the stream around Dogye Mining Site over time were investigated with different pH values and temperatures. White precipitates consist mainly of basaluminite, amorphous $Al(OH)_3$ and a small amount of $Al_{13}$-tridecamer. During aging, the incongruent dissolution of the basaluminite occurs first, increasing the content of the amorphous $Al(OH)_3$. After that, pseudoboehmite is finally precipitated following the precursor phase of pseudoboehmite. At $80^{\circ}C$, this series of processes was clearly observed, but at relatively low temperatures, no noticeable changes were observed from the initial condition with coexisting basaluminite and amorphous $Al(OH)_3$. At high pH, the desorption of $SO{_4}^{2-}$ group in basaluminite was initiated to promote phase transition to the pseudoboehmite precursor. Over time, the solution pH decreases due to the dissolution and phase transition of the minerals, and even after the precipitation of pseudoboehmite, only the particle size slightly increased but no clear cystal form was observed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.189-196
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• 2020

When concrete member become large like in high rise buildings, hydration heat makes temperature difference inside and outside and cause cracks. The method of using latent heat material as heat reducer could be more accessible, usable and efficient than other methods. Therefore, many studies using PCM as heat reducer are being conducted. Since heat reducer have different reacting temperature, they may be affected by environmental factors like ambient and concrete mixing temperature but studies issuing this are insignificant. Therefore, this paper attempt to evaluate the hydration heat characteristics and quality of concrete using strontium-based PCM under hot weather conditions. As a result, when the strontium-based hydration heat reducer was mixed 3wt.% and 5wt.% in hot weather condition, hydration heat speed and heating rate could be reduced by 8%, 21%, and 75, 85 minutes compared to OPC, respectively. This is considered to be the phase change reaction is relatively promoted when the temperature is high and cause improve performance than room condition result. Later, comparing the efficiency of other types of P.C.M in hot weather condition, and conduct detailed reviews on the strength development in long-term age.

• Economic and Environmental Geology
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• v.56 no.1
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• pp.13-21
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• 2023

X-ray powder diffraction study was conducted on the bulk modulus and phase transition behavior of synthetic zeolite X under high temperature and high pressure. Water and HCO₃^- solution were used as a PTM. Sample was heated and pressurized up to 250 ℃ and 5.18 GPa. The change of unit cell volume and phase transition were observed by X-ray diffraction. The lattice constants and unit cell volume of zeolite X, gmelinite, natrolite, and smectite were calculated using the GSAS2 program to which Le Bail's whole powder pattern decomposition (WPPD) method was applied. The bulk modulus of each zeolite X and smectite were calculated using the EosFit program to which the Birch-Murnaghan equation was applied. The bulk modulus of zeolite X is 89(3) GPa in water run, and zeolite X is 92(3) GPa in HCO₃^- solution run. In both run, pressure induced hydration (PIH) occurred due to the inflow of PTM into the zeolite X framework at initial pressure. Zeolite X transited to gmelinite, natrolite, and smectite in water run. Zeolite X, however, transited to smectite in HCO₃^- solution run. Interzeolite transformation occurred in water run, and did not occur in HCO₃^- solution run, which is assumed that conflict between the environment to form zeolite and the pH of the HCO₃^- solution.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.235-236
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• 2011

본 논문에서는 세 개의 Shunt 저항을 이용하여 3상 인버터의 상전류를 검출하였다. Shunt 저항을 이용할 경우 전류 검출이 불가능한 제한 영역이 발생한다. 이러한 제한영역을 보상하기 위해 제한영역에 대하여 분석하였으며, 제한 영역은 추가적인 전류 추정방법을 이용하여 보상하였다. 이를 시뮬레이션을 통하여 검증하였다.

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.285-288
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• 2002

옥타데칸[$CH_3$[C $H_2$]$_{l6}$$CH_3$]은 상전이 물질(phase change material)이며, 상전이 물질은 상변화를 통해 주변의 온도가 상승하면 녹으면서 열을 흡수하고, 주변의 온도가 낮아지면 결정화(crystallization)하면서 열을 방출하는 축열ㆍ방열성을 반복적으로 나타내는 에너지 물질(enthalpic substance)이다[1, 2]. 옥타데칸은 메탄계열 탄화수소로서 파라핀류(paraffins)에 해당된다. (중략)략)