• Applied Chemistry for Engineering
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• v.16 no.1
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• pp.61-67
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• 2005

Zeolite membranes show better thermal, mechanical, chemical stabilities than polymer membranes. Water was separated from water/ethanol mixtures by pervaporation using the NaA and the NaY zeolite membranes synthesized in our laboratory. The effects of concentration of ethanol at the feed side and temperature were studied on the permeation flux and separation factor of water. The separation factors obtained with the NaA zeolite membrane was found to be 1000 times higher than those obtained with the NaY. However, the water flux through the NaA zeolite membrane was observed to be lower than 1/2 of that through the NaY zeolite membrane.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.279-289
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• 2017

In this study, a series of conjugate heat transfer (CHT) analyses are conducted for a stage of a fully cooled high-pressure turbine (HPT) at elevated levels of free stream turbulence (Tu = 5% and 25.7%). The goal of the analyses is to investigate the influence of high turbulence intensity on the fluid-thermal characteristics of a nozzle guide vane (NGV). The turbine inlet temperature is defined by considering a typical radial temperature distribution factor (RTDF). The Unsteady Reynolds Average Navier-Stokes (URANS) CHT simulations are carried out using CFX 15.0, a commercial CFD package. The presented CFD modeling approach for high turbulence intensity is verified with the experimental data from two types of NASA C3X NGVs with films. The computation grid is generated for both the fluid and solid domains. The fluid domain grid is created using a tetrahedral grid system with prism layers because of its complex geometry, and the solid domain grid is composed of only tetrahedral elements. The analytical results are compared to understand the effect of turbulence on flow characteristics and metal temperature distributions. The results obtained in this study provide useful insights on the effects of high free stream turbulence and unsteadiness. The results also lead to the proposal of meaningful turbine design guidelines.

• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.122-132
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• 2000

Computational fluid dynamic simulation is performed for the floating turbulent premixed flames stabilized in stagnation flows of Cho et al. [1] and Cheng and Shepherd [2]. They are both in the wrinkled flamelet regime far from the extinction limit with $u'/S^{0}_{L}$ less than unity. The turbulent flux is given in the first moment closure as a sum of the classical gradient flux due to turbulent motions and the countergradient flux due to thermal expansion. The parameter $N_{B}'s$ are greater than unity with the countergradient flux dominant over the gradient flux. The countergradient flux is assumed to be zero in $\bar{c}<0.05$. The flame surface density is modeled as a symmetric parabolic function with respect to $\bar{c}$. The product of the maximum flame surface density and the mean stretch factor is considered as a tuning constant to match the flame location. Good agreement is achieved with the measured $\tilde{w}$ and $\bar{c}$ profiles along the axis in both flames.

• Journal of the Korean Magnetic Resonance Society
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• v.5 no.1
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• pp.46-55
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• 2001

P23, a translationally controlled turner protein is involved in the interleukin-4 secretion from human basophils and is also known to be an IgE-dependent histamine-releasing factor. However, the precise physiological function and structure of P23 have not been elucidated. In the current study, we constructed the optimal expression and purification protocol of P23 and investigated the secondary structure and structural stability in various conditions. Circular dichroism (CD) investigation showed that the secondary structure of P23 adopts mainly a P-sheet conformation. CD spectroscopy and differential scanning calorimetry revealed that P23 is fairly stable in the pH range of neutral and mild-basic conditions and in the temperature range of 10 - 50$\^{C}$. Since the thermal stability and the P-sheet content of P23 were decreased by the addition of Ca$\^$2+/ ion, it could be suggested that Ca$\^$2+/ion induces structural change by partially destabilizing the structure of P23. In addition various H experiments were monitored to solve the aggregation of P23. Den results will provide the preliminary structural information about P23.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.470-473
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• 2001

In this study, 70/30 mol% P(VDF-TrFE) copolymer thin films were prepared by physical vapor deposition, and dielectric properties with frequency were investigated. From results of TA(Thermal Analysis), the Curie transition temperature and melting temperature were observed at 118.8$^{\circ}C$ and 146$^{\circ}C$, respectively. Therefore, while thin films were prepared, the substrate temperature was varied from 30$^{\circ}C$ to 90$^{\circ}C$. The dielectric constant decreased with increasing frequency. At measuring frequency of 1kHz, the relative dielectric constant increased from 3.643 to 23.998 with increasing substrate temperature from 30$^{\circ}C$ to 90$^{\circ}C$. As a result of dielectric loss factor, ${\alpha}$-relaxation and ${\beta}$-relaxation were observed near at 100Hz and 1MHz, respectively. And the magnitude of ${\alpha}$-relaxation decreased and that of ${\beta}$-relaxation increased with increasing substrate temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.817-820
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• 2002

Amorphous selenium based flat panel detectors convert incident x-ray to electric signal directly. Flat panel detectors gain more interest real time medical x-ray imaging. TFT array and electric readout circuits are used in this paper offered by LG.Philips.LCD. Detector is based on a $1536{\times}1280$ array of a-Si TFT pixels. X-ray conversion layer(a-Se) is deposited upper TFT array with a $400{\mu}m$ by thermal deposition technology. Thickness uniformity of this layer is made of thickness control system technology$({\leq}5%)$. Each $139{\mu}m{\times}139{\mu}m$ pixel is made of thin film transistor technology, a storage capacitor and collecting electrode having geometrical fill factor of 86%. This system show dynamic performance. Imaging performance is suited for digital radiography imaging substitute by conventional radiography film system.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.50.1-50.1
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• 2011

Lead-free ceramics with a composition of 0.55 mol%$K_4CuNb_8O_23-(K_{1-x}Na_x)NbO_3$ (KCN-KNNx) where $0.45{\leq}x{\leq}0.60$ were synthesized by conventional ceramic processing. Results revealed that the addition of Na was effective in changing the microstructure and relative density of KCN-KNNx. Further, the addition of Na resulted in a slight shift of the phase transition temperatures (To-t and Tc) toward low values. A high mechanical quality factor (Qm) of 1850 was found atx=0.54, which might be due to the build-up of an internal bias field (Ei) within KCN. Thermal hysteresis in KNNx was confirmed with an increase in the Na content during the heating and cooling cycles, resulting from structural changes. Thus, KCN-KNNx with x=0.54 exhibits excellent piezoelectric properties with d33 (97 pC/N), kp (36%), and Qm (1850), being promising candidates for application in high-power piezoelectric devices.

• Tribology and Lubricants
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• v.9 no.1
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• pp.62-69
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• 1993

Friction and wear behavior of a carbon/carbon composite material for aircraft brake material was experimentally investigated. Friction and wear test setup was designed and built for the experiment. Friction and wear tests were conducted under various sliding conditions. Friction coefficients were measured and processed by a data acquisition system and amount of wear measured by a balance. Stainless steel disk was used as the counterface material. Temperature was also measured by inserting thermocouple 2.5 mm beneath the sliding surface of the carbon/carbon composite specimen. Wear surfaces were observed by SEM, and analyzed by EDAX. The experimental results showed that sliding speed and normal force did not have significant effects on friction coefficient and wear factor of the composite. Temperature increase just below the surface was not large enough to cause any thermal degradation or oxidation which occurred at higher temperature when tested by TGA. Wear film was generated both on the specimen and on the counterface at relatively low sliding speed but cracks, grooves, and wear debris were observed at high sliding speed. Friction coefficient remained almost constant when the sliding speed or normal load was varied. It is believed that the adhesive and abrasive components contributed mainly to the friction coefficient. Wear behavior at low sliding speed was governed by wear film formation and adhesive wear mechanism. At high speed, fiber orientation, ploughing by counterface asperities, and fiber breakage dominated wear of the carbon/carbon composite.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.699-702
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• 2001

The increasing demand in industry to produce rectangular cans at the reduction by the rectangular backward extrusion process involves better understanding of this process. In 2-D die deflection and dimensional variation of the component during extrusion, punch retraction, component injection and cooling was conducted using a coupled thermal-mechanical approach for the forward extrusion of aluminum alloy and low-carbon steel in tools of steel. Backward extrusion FE simulation and experimental simulation by physical modeling using wax as a model material have been performed. These simulations gave good results concerning the prediction of th flow modes and the corresponding surface expansions of the material occuring at the contact surface between the can and the punch. There prediction are the limits of the can height, depending on the reduction, the punch geometry, the workpiece material and the friction factor, in order to avoid the risk of damage caused by sticking of the workpiece material to the punch face. The influence of these different parameter on the distribution of the surface expansion along the inner can wall and bottom is already determined. This paper deals with the influence of the geometry changes of the forming tool and the work material in the rectangular backward using the 3-D finite element method.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.734-741
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• 2020

A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.