• Membrane Journal
• /
• v.33 no.6
• /
• pp.439-446
• /
• 2023

Ceramic membranes are generally used for various industrial processes operating under extreme conditions because of its high thermal and chemical stability. However, due to the trade-off phenomenon of permeability and mechanical strength, preparation of high permeability-high strength membrane is necessary. In this study, the change in characteristics and performances of ceramic membranes was analyzed depending on the type of polymer binder and its mixing ratio. Because the solubility between solvent and polymer binder was higher in PSf (polysulfone) than in PES (polyethersulfone), the viscosity and discharge pressure of the PSf-based dope solution were higher than those of PES-based dope solution. When PSf was used as a polymer binder, ceramic membrane showed high mechanical strength and low water permeability due to the dense structure. On the other hand, in case of PES, the mechanical strength was slightly reduced and the water permeability was increased. It was confirmed that the optimum mixing ratio of the PSf and PES with high water permeability and mechanical strength was 9:1.

• Journal of the Microelectronics and Packaging Society
• /
• v.29 no.4
• /
• pp.63-69
• /
• 2022

Vanadium dioxide shows a unique and interesting property of metal-insulator transition, which has attracted great attention from the viewpoints of fundamental materials science and industrial applications. In this study, the effect of Mg and W addition on the metal-insulator transition of VO₂ were investigated for the bulk materials that are prepared by spark plasma sintering. The X-ray diffraction analysis of the sintered specimens revealed that the lattice parameters barely change, and the secondary phases are present. The transition temperature of MIT appears in the range of 64.2-64.6℃, regardless of the impurity element and content. On the other hand, the addition of Mg and W alters the electrical conductivity, i.e., the electrical conductivity increases by a factor of up to 2.4 or decrease by a factor of up to 57.4 depending on the impurity type and its content. The thermal conductivity showed the values of 1.8~2.5 W/m·K below the transition temperature, and the values of 1.9~2.8 W/m·K above the transition temperature. These changes in electrical and thermal conductivities can be attributed to the combination of the change in charge carrier density, the impurities as scattering centers, and the change in microstructures.

• Korean Journal of Materials Research
• /
• v.6 no.2
• /
• pp.133-137
• /
• 1996

본연구에서는 n-type 세라믹 초전도체인 Nd2-xCexCuO4상의 산소함량에 따른 \ulcorner기적저항의 변화를 고찰하고자 하였다. 일반적인 소결과 어닐링과정을 결쳐 제조된 Nd1.85Ce0.15CuO4-x 시편을 여러 온도와 산소분압의 분위기하에서 어닐링시킴으로써 산소의 함유량이 다른 시편들을 준비하였고 각각의 시편의 산소함량은 TGA(Thermogravimetric Analysis0에 의해 측정하였다. Nd1.85Ce0.15CuO4-x시편의 전기적 저항 측정은 표준 4-탐침방법을 이용하여 액체헬륨을 주입시켜 상온으로부터 4K까지 측정하였다. Nd1.85Ce0.15CuO4-x시편의 산소함량, 3.96$\leq$4-x$\leq$4.0의 범위에서 전기적저항을 측정한 결과 초전도특성이 나타나기 시작한 임계산소함량은 4-x=3.990이었고 이때의 임계온도 Tc=12K이었다. 또한 임계온도, Tc는 산소함량 4-x=3.96에서 24K로 측정되었다. 특이할 만한 현상은 CuO/Cu2O 열역학적 상전이가 일어나는 조건이 Nd1.85Ce0.15CuO4-x 시편의 초전도가 일어나는 임계와 일치하였다. 즉, Cu2O가 안정한 영역에서는 초전도특성이 나타났고 CuO가 안정한 영역에서는 초전도특성이 나타나지 않았다.

• Physical Therapy Korea
• /
• v.5 no.4
• /
• pp.20-29
• /
• 1998

연구의 배경 앉은 자세에서 일어서기는 일상생활동작중 흔한 동작중의 하나이다. 노인들을 포함한 많은 환자들은 앉은 자세에서 일어서기에 어려움이 있고 속도가 감소한다. 이 연구의 목적은 다른 두 속도로 앉은 자세에서 일어서는 동작을 실행할 때 최대 지면반발력의 세개의 요소를 비교하는 것이다. 대상자 22명의 건강한 성인 (20-36세)을 대상으로 하였다. 실험방법 앉은 자세에서 일어서기동작 수행중 최대 지면반발력을 측정하기 위하여 힘판을 사용하였다. 대상자들은 메트로놈을 이용하여 각각 느린 속도 (3초: 총 앉은 자세에서 일어서기동작 수행시간)와 빠른 속도(1.5초)에서 앉은 자세에서 일어서기를 수행하였다. 느린 속도와 빠른 속도중 최대 지면반발력을 비교하기 위해 짝비교 t-검정을 사용하였다. 결과 빠른 속도시 최대 지면반발력의 수직(p<0.05), 전-후(p<0.05), 내-외(p<0.05) 요소에서 느린 속도시와 차이가 있었다. 최대 지면반발력의 모든 요소가 움직임의 속도의 증가에 비례하여 증가하였다. 토의 및 결론 빠른 속도의 앉은 자세에서 일어서기를 수행하기 위해서는 최대 지면반발력의 수직, 전-후요소의 추진력이 요구된다. 최대 지면반발력의 내-외요소는 상전방으로 작용하는 모멘트의 증가에 대한 제동력으로 생각된다. 또한, 빠른 속도로 앉은 자세에서 일어서기 동작을 수행하기 위하여 추진력은 일어서는 순간의 모멘트에 대한 지면반발력의 내-외요소에 영향을 미친다. 이라한 결과들은 앉은 자세에서 일어서기 동작에 어려움을 갖는 노인이나 환자들의 노력을 덜기위해 느린 속도의 움직임이 필요함을 제안한다.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.1
• /
• pp.23-28
• /
• 1999

Au fine particles dispersed $TiO_{2}$ film was prepared on silica glass substrate by sol-gel dipping and firing process. The $TiO_{2}$ films were fabricated from the system of titanium tetraisopropoxide-EtOH-HCl-$H_{2}O$-hydrogen tetrachloroaurat (III) tetrahydrate. The conditions for the formation of clear solution and dissolving high concentration of Au compound were examined. Photoreduction process was adopted to control the size of gold metal particles. Phase evolution of matrix $TiO_{2}$ and variation of Au particle with UV irradiation were investigated by XRD, SEM, TEM and UV-visible spectrophotometer. The effect of CPCl (Cetylpyridinium chloride monohydrate) as a dispersion agent was evaluated.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.1
• /
• pp.53-59
• /
• 2017

The information on the actual voltages and actual currents of the motor is required for the sensorless control of a permanent magnet synchronous motor without rotor position sensors. In the model-based rotor position estimator of a PM synchronous motor, the reference voltages, which are the outputs of the current controller, are commonly used. The reference voltages in over-modulation regions for high-speed operation differ from the actual voltages applied to the motor. Consequently, the estimated rotor position and rotor speed may fail to track the real rotor position and real rotor speed. In this paper, the sensorless control for a PM synchronous motor in over-modulation regions for high-speed operation is proposed. The three-phase voltages applied to the motor are measured by using additional voltage detection circuits, and the performance of the rotor position estimator based on the measured three-phase voltages is validated through the experimental results.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.21 no.4
• /
• pp.343-350
• /
• 2016

Generally, the average phase current is sampled at the midpoint of a PWM signal for the vector control of an AC motor. The three-phase current can also be reconstructed from a DC-link shunt resistor by sampling the shunt voltage during the active vectors of the SVPWM. However, the reconstructed current is different from the average current because of the deviation of the sampling point from the midpoint of the PWM signal. This paper proposes an algorithm to estimate the average current from the reconstructed current in a single-shunt inverter. The proposed method is derived from the phase current slopes based on switching states and corresponding switching time. In addition, the proposed method is generalized for all the six sectors of the space vector hexagon. The validity of the proposed algorithm is verified with simulations and experiments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.06a
• /
• pp.103-103
• /
• 2009

본 논문에서는 기존의 GST(GeSbTe=2:2:5)와 비교하여 상변화 재료로서의 Ga 도핑된 $Ge_2Sb_2Te_5$의 가능성을 확인하고자 하였다. 실험에 사용된 Ga 도핑된 $Ge_2Sb_2Te_5$ 박막은 전통적 melt-quenching 방법에 의해 비정질로 제작된 벌크를 Thermal evaporation을 통하여 Si(100) 및 유리 (coming glass, 7059) 기판 위에 200nm의 두께로 증착하여 제작하였다. 각 박막의 상변화 특성은 여러 온도에서 열처리된 박막을 X-ray diffraction (XRD) 측정을 통하여 확인하였다. 각 조성 박막의 비정질-결정질 상변화속도 비교를 위하여 나노-펄스 스캐너 (nano-pulse scanner)를 사용하여 power; 1~17mW, pulse duration; 10~460ns 범위에서 박막의 상변화에 따른 반사도 차이를 측정 분석하였다. Ga의 도핑농도에 따른 전기적 특성 차이를 확인하기 위하여 4-point probe를 이용하여 박막의 면 저항을 측정하였고 또한 hall 측정을 통하여 박막의 흘 계수, 흘 농도 및 이동도를 확인하고 Ga가 상전이에 미치는 영향에 대하여 분석하였다.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.22 no.3
• /
• pp.323-327
• /
• 1993

The effect of soyasaponin on the liposomal phospholipid membrane was investigated by differential scanning calorimetry (DSC). Soyasaponins were obtained and the enthalpy changes and the sizes of cooperative unit of the transition were calculated. The thermograms of L-$\alpha$-dimyristoyl phosphatidylcholine (DMPC) incorporated with soyasaponin showed that the phase transition temperature was significantly lowered and the peak was broadened. This was attributed to the possibility that incorporation of soyasaponin into the lipid bilayers reduced the cooperative unit of phospholipid bilayers. These results indicate soyasaponin might have significant effect on the fluidity of biological membrane.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.4
• /
• pp.544-549
• /
• 1998

The single crystal of $KMgCl_3$ was grown in Ar atmosphere by Czochralski method for the first time. For the stoichiometric composition, $K_2MgCl_4$ crystal was obtained, and the nonstoichiometric method was used for the $KMgCl_3$ crystal growth. The phase transition sequences of $KMgCl_3$ were investigated by the DTA, DSC and the ferroelastic properties by using the high temperature polarizing microscope and the thermomechanical system. The temperature dependences of the ferroelastic domains and the spontaneous strain obtained from the stress-strain hysteresis loops were analyzed.