• Macromolecular Research
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• 제10권4호
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• pp.204-208
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• 2002

A linear rod-like molecule, bis[4-(1,3-octadynyl)phenyl] terephthalate (2), consisting of two diacetylenic groups, was prepared. The unsymmetric diacetylene was prepared by the Cadiot-Chodkiewicz coupling reaction of 1-bromohexyne with 4-ethynylphenol and linked to a benzene core by an esterification reaction with terephthaloyl chloride in tetrahydrofuran. The thin film (200 nm thickness) of compound 2 was fabricated by the physical vapor deposition on a glass plate with a thermal evaporator. In the X-ray diffraction (XRD) study, the vapor deposited film on the glass plate showed peaks with d spacings of 19.4, 5.7, and 4.5 $\AA$. This XRD pattern was quite different from that observed for compound 2 isolated by recrystallization from methylene chloride/hexane. The vapor deposited film was polymerized by UV irradiation. Photopolymerization was carried out through a photomask, resulting in a patterned image, where the irradiated part became isotropic.

• Journal of Magnetics
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• 제8권1호
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• pp.1-6
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• 2003

The new class of $Gd_5(Si_xGe_{1-x})_4$ compounds undergoes a simultaneous magnetic/structural phase transition giving a high level of strain that can be induced either by change in temperature or by application of a magnetic field. Profound changes of structural, magnetic, and electronic changes occur in the $Gd_5(Si_xGe_{1-x})_4$ system lead to extreme behavior of the material such as the giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance. These unique material characters can be utilized for various applications including magnetic solid refrigerants, sensors, and actuators.

• 한국자기학회지
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• 제22권6호
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• pp.221-227
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• 2012

고특성 영구자석은 하이브리드 및 전기자동차의 구동모터와 풍력발전에 적용되면서 크게 주목을 받고 있다. Nd-Fe-B 영구자석은 가장 높은 최대자기에너지적을 가지고 있지만 고온(${\sim}200^{\circ}C$)의 구동환경에서는 보자력이 급격히 감소하기 때문에 사용할 수 없는 단점을 가지고 있다. 그러므로 큰 보자력을 가지는 Nd-Fe-B 영구자석에 대한 개발이 요구되고 있다. Nd-Fe-B 소결자석에서 보자력을 증가시키기 위해서는 Nd를 Dy 또는 Tb으로 치환하면 쉽게 증가시킬 수 있다. 그러나 이들 원소는 Fe와 반강자성 결합을 하여 잔류자속밀도를 낮추고, 적은 매장량과 한정된 지역에 편재되어 있어 수요급증에 따른 자원수급 및 가격 급등의 문제를 가지고 있다. 따라서, Dy 및 Tb과 같은 중희토류를 사용하지 않거나 최소한의 양을 사용하여 보자력을 증가시키고자 하는 연구가 많이 진행되고 있다. 본 논문에서는 이러한 중희토류 원소의 저감 및 대체에 대한 연구들을 소개하고자 한다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권6호
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• pp.255-261
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• 2005

Recently, the RF inductive discharge or inductively coupled plasma continues to attract growing attention as an effective plasma source in many industrial applications, the best known of which are plasma processing and lighting technology. To the point of lighting sources, the ring-shaped electrodeless fluorescent lamps utilizing an inductively coupled plasma have been objects of interest and research during the last decades, mainly because of their potential for extremely long life, high lamp efficacies, rapid power switching response. In this paper, maxwell 3D finite element analysis program (Ansoft) was used to obtain electromagnetic properties associated with the coil and nearby structures. The electromagnetic emitting properties were presented by 3D simulation software operated at 250 kHz and some specific conditions. The electromagnetic field in the ferrite core was shown to be high and symmetric. An LS-100 luminance meter and a Darsa-2000 spectrum analyzer were used in the experiment. According to data on the lamp tested using high magnetic field ferrite, the optical and thermal wave fields were shown to be high around the ring-shaped electrodeless fluorescent lamp. The optical or light field was high at the center of the bulb rather than around the ferrite core. The light conditions of the bulb were assumed to be complex, depending on the condition of the filler gas, the volume of the bulb, and the frequency of the inverter. Our results have shown coupling between the gas plasma and the field of the light emitted to be nonlinear.

• Korean Chemical Engineering Research
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• 제55권2호
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• pp.247-252
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• 2017

실란커플링제인 아미노실란을 15~20 nm의 직경을 갖는 콜로이드 실리카와 반응시킴에 의해 친수성 코팅 용액을 제조하였다. 또한 친수성 코팅 용액을 폴리카보네이트 기재 위에 담금 코팅 시킨 후 $120^{\circ}C$에서 열경화 시킴에 의해 친수성 코팅 도막이 제조되었다. 이 과정 중 아미노실란의 종류 변화가 코팅 도막의 물성에 미치는 영향을 연구하였다. 그 결과 아미노실란으로서 3-aminopropyltriethoxysilane (APTES)을 사용하여 제조된 코팅 도막은 $25{\sim}44^{\circ}$의 접촉각과 B의 좋지 못한 연필경도를 나타내었다. 반면에 아미노실란으로서 3-aminopropyltrimethoxysilane (APTMS)을 사용하여 제조된 코팅 도막은 $26{\sim}37^{\circ}$의 접촉각과 2H의 우수한 연필경도를 나타내었다.

• 항공우주기술
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• 제12권1호
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• pp.32-39
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• 2013

PZT-5 계열 압전진동자의 위성부품 활용성 연구를 위하여 CVCM(Collected Volatile Condensable Material) 및 TML(Total Mass Loss)을 측정하여 규정된 0.1% 및 1.0% 이하의 값을 얻었고, 베이크아웃 챔버를 이용하여 고온 및 고진공상태에서 $500ng/cm^2/hr$ 이하의 낮은 TQCM(Thermoelectric Quartz Crystal Microbalance) 값을 얻어 위성체 부품으로의 적합성을 재확인하였다. 압전진동자에 대한 고진공 환경 전후의 압전특성을 비교 분석한 결과 진공환경에 의한 전기-기계적 특성은 1% 미만으로 큰 변화가 없음을 확인하였다. 아울러, $-100^{\circ}C{\sim}90^{\circ}C$의 범위에 대한 PZT-5계열의 압전 진동자에 대하여 온도변화에 따른 특성변화를 조사한 결과, 공진 및 반공진주파수는 상온일 때를 중심으로 온도의 변화에 따라 증가하였고 유전상수의 경우 주어진 온도 범위에서 2500~7500의 범위에서 선형적으로 증가하였다. 기계적 손실은 0.08 ~ 0.03의 범위에서 선형적으로 감소하는 경향을 보였다.

• Nuclear Engineering and Technology
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• 제36권6호
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• pp.528-539
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• 2004

It is essential in commercial reactors that the safety limits imposed on the fuel pellets and fuel clad barriers, such as the linear power density (LPD) and the departure from nucleate boiling ratio (DNBR), are not violated during reactor operations. In order to accurately monitor the safety limits of current reactor states, a detailed three-dimensional (3D) core power distribution should be estimated from the in-core detector signals. In this paper, we propose a calculation methodology for detailed 3D core power distribution, using in-core detector signals and core monitoring constants such as the 3D Coupling Coefficients (3DCC), node power fraction, and pin-to-node factors. Also, the calculation method for several core safety parameters is introduced. The core monitoring constants for the real core state are promptly provided by the core design code and on-line MASTER (Multi-purpose Analyzer for Static and Transient Effects of Reactors), coupled with the core monitoring program. through the plant computer, core state variables, which include reactor thermal power, control rod bank position, boron concentration, inlet moderator temperature, and flow rate, are supplied as input data for MASTER. MASTER performs the core calculation based on the neutron balance equation and generates several core monitoring constants corresponding to the real core state in addition to the expected core power distribution. The accuracy of the developed method is verified through a comparison with the current CECOR method. Because in all the verification calculation cases the proposed method shows a more conservative value than the best estimated value and a less conservative one than the current CECOR and COLSS methods, it is also confirmed that this method secures a greater operating margin through the simulation of the YGN-3 Cycle-1 core from the viewpoint of the power peaking factor for the LPD and the pseudo hot pin axial power distribution for the DNBR calculation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.292-295
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• 2004

The SIT was introduced by Nishizawa. in 1972. When compared with high-voltage, power bipolar junction transistors, SITs have several advantages as power switching devices. They have a higher input impedance than do bipolar transistors and a negative temperature coefficient for the drain current that prevents thermal runaway, thus allowing the coupling of many devices in parallel to increase the current handling capability. Furthermore, the SIT is majority carrier device with a higher inherent switching speed because of the absence of minority carrier recombination, which limits the speed of bipolar transistors. This also eliminates the stringent lifetime control requirements that are essential during the fabrication of high-speed bipolar transistors. This results in a much larger safe operating area(SOA) in comparison to bipolar transistors. In this paper, vertical SIT structures are proposed to improve their electrical characteristics including the blocking voltage. Besides, the two dimensional numerical simulations were carried out using ISE-TCAD to verify the validity of the device and examine the electrical characteristics. A trench gate region oxide power SIT device is proposed to improve forward blocking characteristics. The proposed devices have superior electrical characteristics when compared to conventional device. Consequently, the fabrication of trench oxide power SIT with superior stability and electrical characteristics is simplified.

• Nuclear Engineering and Technology
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• 제45권3호
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• pp.401-414
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• 2013

HTR50S is a small modular reactor system based on HTGR. It is designed for a triad of applications to be implemented in successive stages. In the first stage, a base plant for heat and power is constructed of the fuel proven in JAEA's $950^{\circ}C$, 30MWt test reactor HTTR and a conventional steam turbine to minimize development risk. While the outlet temperature is lowered to $750^{\circ}C$ for the steam turbine, thermal power is raised to 50MWt by enabling 40% greater power density in 20% taller core than the HTTR. However the fuel temperature limit and reactor pressure vessel diameter are kept. In second stage, a new fuel that is currently under development at JAEA will allow the core outlet temperature to be raised to $900^{\circ}C$ for the purpose of demonstrating more efficient gas turbine power generation and high temperature heat supply. The third stage adds a demonstration of nuclear-heated hydrogen production by a thermochemical process. A licensing approach to coupling high temperature industrial process to nuclear reactor will be developed. The low initial risk and the high longer-term potential for performance expansion attract development of the HTR50S as a multipurpose industrial or distributed energy source.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.446-454
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• 2021

Critical heat flux (CHF) has traditionally been evaluated using look-up tables or empirical correlations for nuclear power plants. However, under complex moving condition, it is necessary to reconsider the CHF characteristics since the conventional CHF prediction methods would no longer be applicable. In this paper, the additional forces caused by motions have been added to the annular film dryout (AFD) mechanistic model to investigate the effect of moving condition on CHF. Moreover, a theoretical model of the natural circulation loop with additional forces is established to reflect the natural circulation characteristics of the loop system. By coupling the system loop with the AFD mechanistic model, a CHF prediction program called NACOM for natural circulation loop under moving condition is developed. The effects of three operating conditions, namely stationary, inclination and rolling, on the CHF of the loop are then analyzed. It can be clearly seen that the moving condition has an adverse effect on the CHF in the natural circulation system. For the calculation parameters in this paper, the CHF can be reduced by 25% compared with the static value, which indicates that it is important to consider the effects of moving condition to retain adequate safety margin in subsequent thermal-hydraulic designs.