• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.1
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• pp.57-61
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• 1998

In this study, PLZT stock solutions were prepared by Sol-Gel processing after the compositions were selected in the memory region of PLZT bulk phase diagram. PLZT solutions were deposited on the ITO glass substrate by spin-coating method. The thin films were annealed by rapid thermal processing. The electric characteristics, hysteresis loop, C-V characteristics of thin films in the memory region were measured in order to investigate the electrical characteristics of PLZT thin films. In selected compositions the decrease in Zr/Ti ratio led to an increase in dielectric constant and the decrease in remanent polarization and coercieve field which brought about slim hysteresis loop.

• Journal of Biomedical Engineering Research
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• v.28 no.3
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• pp.348-354
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• 2007

Polymer actuators, which are also called as smart materials, change their shapes when electrical, chemical, thermal, or magnetic energy is applied to them and are useful in wide variety of applications such as microelectromechanical systems (MEMS), machine components, and artificial muscles. For this study, Polyaniline/carbon-nanotube polymer actuator that is one of electroactive polymer actuators was prepared. Since the nonlinear phenomena of hysteresis and a step response are essential considerations for practical use of polymer actuators, we have investigated the movement of the Polyaniline/carbon-nanotube polymer actuator and have developed an integrated model that can be used for simulating and predicting the hysteresis and a step response during actuation. The Preisach hysteresis model, one of the most popular phenomenological models of hysteresis, were used for describing the hysteretic behavior of Polyaniline/carbon-nanotube polymer actuator while the ARX method, one of system identification techniques, were used for modeling a step response. In this paper, we first expain details in preparation of the Polyaniline/carbon-nanotube polymer then present the mathematical description of our model, the extraction of the parameters, simulation results from the model, and finally a comparison with measured data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.695-702
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• 2002

Nonlinear dynamics of striped diffusion flames, by the diffusional-thermal instability with Lewis numbers sufficiently less than unity, is numerically investigated by examining various two-dimensional flame-structure solutions. The Lewis numbers for fuel and oxidizer are assumed to be identical and an overall single-step Arrhenius-type chemical reaction rate is employed in the model. Particular attention is focused on identifying the flame-stripe solution branches corresponding to each distinct stripe pattern and hysteresis encountered during the transition. At a Damkohler number slightly greater than the extinction Damkohler number, eight-stripe solution first emerges from one dimensional solution. The eight-stripe solution survives Damkohler numbers much smaller than the extinction Damkohler number until the transition to four-stripe solution occurs at the first forward transition Damkohler number. At the second forward transition Damkohler number, somewhat smaller than the first transition Damkohler number, the transition to two-stripe solution occurs. However, anu further transition from two-stripe solution to one-stripe solution is not always possible even if one-stripe solution can be independently accessed for particular initial conditions. The Damkohler number ranges for two-stripe and one-stripe solutions are found to be virtually identical because each stripe is an independent structure if distance between stripes is sufficiently large. By increasing the Damkohler number, the backward transition can be observed. In comparison with the forward transition Damkohler numbers, the corresponding backward transition Damkohler numbers are always much greater, thereby indicating significant hysteresis between the stripe patterns of strained diffusion flames.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.122-127
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• 2000

The thermal expansion, thermal stability, mechanical strength and infrared radiative property of Al2TiO5-clay composites, prepared from synthesized Al2TiO5 and clay, were investigated to develop a material for far infrared radiators. The emittance of composites containing 10~50 wt% clay, heated at 1,20$0^{\circ}C$ for 3 h, increased with increasing clay content and emittance was about 0.3 and 0.92 in the ranges of 3,400~2,500 cm-1 and 2,500~400cm-1, respectively. The bulk density and bending strength of the Al2TiO5-clay composites increased with increasing clay content. 50 wt% Al2TiO5-50 wt% clay composite, heat-treated at 1,20$0^{\circ}C$, had an adequate strength for infrared radiators; 80 MPa. The degree of thermal expansion hysteresis decreased with increasing clay content and the mean thermal expansion coefficient increased with increasing clay content. The thermal expansion coefficient of 50 wt% Al2TiO5-50 wt% clay composite heated at 1,20$0^{\circ}C$ was 5.78$\times$10-6/$^{\circ}C$.

• The Korean Journal of Ceramics
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• v.1 no.1
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• pp.1-6
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• 1995

Submicrometer, monosized ceramic powder of $Al_2TiO_5$$Al_2O_3$ ethanolic solutions. All particles produced by sol-gel-process were amprphous, monodispersed and with a narrow particle-size distribution. Compacts fired above $1300^{\circ}C$ formed aluminium titanate. Mullite formed first at $1480^{\circ}C$. After decomposition test at $1100^{\circ}C$, and cyclic thermal decomposition test at 750-1400-$750^{\circ}C$ for 100hrs., aluminium titanate was well stablized by composition with mullite.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.65-69
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• 2004

We synthesized photoalignment material of high thermal resistance with hydroxyl aromatic polyimide, and studied the liquid crystal (LC) aligning capabilities on the photopolymer layers. Also, electro-optical (EO) performances for the twisted-nematic (TN)-liquid crystal display (LCD) photoaligned with linearly polarized UV exposure were investigated. A good LC alignment with UV exposure on the photopolymer surface can be obtained. However, the low pretilt angles were obtained below 1$^{\circ}$. The Voltage-transmittance (V-T) curve without backflow bounce in the photoaligned TN cell with UV exposure was observed. The response time of photoaligned TN cell was measured about 24 ms. Finally, The photoaligned TN cell has few hysteresis, and shows the residual DC voltage that is less.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05a
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• pp.210-213
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• 2004

We synthesized photoalignment material of high thermal resistance with hydroxyl aromatic polyimide, and studied the liquid crystal (LC) aligning capabilities on the photopolymer layers. Also, electro-optical (EO) performances for the twisted-nematic (TN)-liquid crystal display (LCD) photoaligned with linearly polarized UV exposure were investigated. A good LC alignment with UV exposure on the photopolymer surface can be obtained. However, the low pretilt angles were obtained below $1^{\circ}$. The Voltage-transmittance (V-T) curve without backflow bounce in the photoaligned TN cell with UV exposure was observed. The response time of photoaligned TN cell was measured about 24 ms. Finally, The photoaligned TN cell has few hysteresis, and shows the residual DC voltage that is less.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.5
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• pp.423-429
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• 2014

Passive attitude stabilization methods using the permanent magnet combined with hysteresis damper and the gravity gradient boom have been widely used for the attitude determination and control of cube satellite, due to its advantage of system simplicity. In this paper, on-orbit thermal characteristics of the cube satellite considering the attitude profiles obtained from the above passive attitude stabilization methods have been investigated through on-orbit thermal analysis. In addition, the effectiveness of the various thermal coatings on the panel for the communication antenna installation has been verified.

• Journal of ILASS-Korea
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• v.26 no.3
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• pp.135-141
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• 2021

High-efficient HEV Engine cooling systems reflects variable coolant temperature because it can decrease the hydrodynamic frictional losses of lubricated engine parts in light duty conditions. In order to safely raise the operating temperature of passenger cars to a constant higher level, and thus optimize combustion and all accompanying factors, a new thermostat technology was developed : the electronically map-controlled thermostat. In this work, various crystalline plastics such as polyphthalamide (PPA) and polyphenylenesulfide (PPS) mixed with various glass fiber amounts were introduced into plastic fittings of automotive electronic controlled thermostat for the purpose of suppressing influx of coolant into the element and undesirable opening during hot soaking. Skirt was installed around element frame of automotive electronic controlled thermostat for improving thermal sensitivity in terms of response time, hysteresis and melting temperature. To validate the effectiveness and optimum shape of skirt, thermal sensitivity test and three-dimensional CFD simulation have been performed. As a consequence, important improvement in thermal sensitivity with less than 3℃ of maximum coolant temperature between opening and engine inlet was obtained.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.795-801
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• 1989

The polycrystalline mullite fiber was synthesized from various combination of starting materials including metal alkoxides and colloidal sol by the sol-gel process. The best spinnability was observed in the sol which showed shear thinning and hysteresis (i.e., thixotropic flow), indicating that the network structure was broken down as the shear rate increased. The mullite fiber was polycrystalline after firing and characterized by thermal analysis, XRD, FT-IR spectroscopy, rheological measurements, and SEM.