• 한국전기화학회:학술대회논문집
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• 2001.10a
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• pp.15-15
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• 2001

• Bulletin of the Korean Chemical Society
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• v.16 no.2
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• pp.82-84
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• 1995

• Bulletin of the Korean Chemical Society
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• v.16 no.8
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• pp.699-703
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• 1995

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.571-576
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• 2011

Characteristics of bubble driven wakes were investigated in a simulated GTL process(0.102 m ${\times}$ 1.5 m in height) with viscous liquid medium. Effects of gas velocity(0.04 ~ 0.12 m/s) and liquid viscosity(0.001 ~ 0.050 $Pa{\cdot}s$) on the wake characteristics such as rising velocity, frequency, size and holdup were determined by employing a resistivity probe method. The wake phase formed behind the rising multi-bubbles as well as single bubbles were detected effectively from the conductivity fluctuations measured by the probe. Compressed, filtered and regulated air and aqueous solutions of Carboxy Methyl Cellulose(CMC) were used as a dispersed gas phase and a continuous liquid medium, respectively. It was found that the rising velocity and size of wake phase increased with an increase in gas velocity or liquid viscosity. The holdup and frequency of wake phase increased with increasing gas velocity due to the increase of gas input into the process with increasing gas velocity. However, the values of holdup and frequency of wake phase decreased with increasing liquid viscosity, since the size of bubbles and thus that of wakes increased with increasing liquid viscosity. The ratio of wake holdup to that of gas phase, which was in the range of 0.25 ~ 0.48, increased with an increase in liquid viscosity but decreased with gas velocity. The wake characteristics were well correlated in terms of operating variables within this experimental conditions.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.2
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• pp.127-135
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• 2012

The processes of chemical and physical weathering occur simultaneously. The objective of this study was to estimate the degree weathered using fractal dimension through comparison with chemical characteristic of soil samples from Pohang (PH) and Kimpo (KP). Comparing chemical characteristics with fractal dimension, $SiO_2$, $Na_2O$, $K_2O$ content decreased and loss of ignition increased as fractal dimension increased. And fractal dimension showed high correlation with CWI while ATI, STI CIW, PI, CIA and RR demonstrated different degrees of correlation with fractal dimension. The tendency of the changes in oxide content and chemical weathering index with increasing fractal dimension appeared to be similar with the chemical changes due to weathering. Therefore, fractal dimension could be a good indicator representing the extent of weathering and chemical changes.

• Clean Technology
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• v.7 no.4
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• pp.273-280
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• 2001

An absorber is a major component in the absorption refrigeration systems and its performance greatly affects the overall system performance. In this study, experimental analyses on heat transfer characteristics for removal of absorption heat in ammonia-water bubble mode absorber were performed. Heat transfer coefficients were estimated as the variations of input gas flow rate, solution flow rate, temperature, concentration, absorber diameter and height, and input flow direction. The increase of gas and solution flow rate affects positively in heat transfer. However, the increase of solution temperature and concentration affects negatively. Moreover, under the same Reynolds Numbers, countercurrent flow is superior to cocurrent flow in heat transfer performance. In addition, from these experimental data, empirical correlations which can explain easily the characteristics of heat transfer are derived.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.5
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• pp.389-395
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• 2017

In this paper, we investigate the characteristics of membrane fouling caused by water temperature in the Membrane bioreactor(MBR) process and try to derive the membrane fouling control by chemical enhanced backwashing(CEB). The extracellular polymeric substances(EPS) concentration was analyzed according to the water temperature in the MBR, and the membrane fouling characteristics were investigated according to the conditions, with sludge & without sludge, through a lab-scale reactor. As shown in the existing literature the fouling resistance rate was increased within sludge with the water temperature was lowered. However, in the lab-scale test using the synthetic wastewater, the fouling resistance increased with the water temperature. This is because that the protein of the EPS was more easily adsorbed on the membrane surface due to the increase of entropy due to the structural rearrangement of the protein inside the protein as the water temperature increases. In order to control membrane fouling, we tried to derive the cleaning characteristics of CEB by using sodium hypochlorite(NaOCl). We selected the condition with the chemicals and the retention time, and the higher the water temperature and the chemical concentration are the higher the efficiencies. It is considered that the increasing temperature accelerated the chemical reaction such as protein peptide binding and hydrolysis, so that the attached proteinaceous structure was dissolved and the frequency of the reaction collision with the protein with the chemical agent becomes higher. These results suggest that the MBRs operation focus on the fouling control of cake layer on membrane surface in low temperatures. On the other hand, the higher the water temperature is the more the operation strategies of fouling control by soluble EPS adsorption are needed.

• Asian-Australasian Journal of Animal Sciences
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• v.21 no.10
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• pp.1516-1521
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• 2008

This study was conducted to investigate the effects of different energy intake on physical and chemical composition in body fractions, growth performance and meat characteristics of finishing barrows and gilts. A total of twenty six crossbred (Landrace$\times$Yorkshire) consisting of 16 barrows and 13 gilts were used in this study. The animals were allocated by sex to two treatments to form a $2\times2$ factorial arrangement. The respective factors were sex (barrow and gilt) and dietary energy intake (1.8 and 3.0 times energy for maintenance). Pigs were kept in individual pens and had ad libitum access to feed and water from the start of the experiment at $52.4{\pm}1.9kg$ until they reached $109.9{\pm}4.4kg$ live weight. The growth performance, physical composition and meat characteristics of finishing pigs were not greatly affected by the sex. However, higher fat tissue weight in the carcass was observed in barrows compared with gilts (p<0.05). Higher proportions of water and protein (p<0.05), and lower lipid proportion (p<0.01) in the empty body and carcass were observed in gilts compared with barrows, while protein proportion in lean tissue was not affected by the sex. In fat tissue, only protein proportion was higher in gilts compared with barrows (p<0.05). Although, growth performance, physical and chemical compositions in body fractions were greatly affected, final body or carcass weight was partly affected by the energy intake In addition, loin characteristics such as shear force and loin eye area were partly influenced by energy intake levels. Therefore, the present results showed that growth performance and meat characteristics were not influenced but chemical body composition was greatly influenced by the sex. Growth performance, physical and chemical compositions in body fractions were greatly affected, whereas meat characteristics were partly affected by the energy intake levels.

• Journal of IKEEE
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• v.22 no.2
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• pp.344-349
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• 2018

Low temperature variation of electrical characteristics for AlGaN/GaN/HEMT was studied. To investigate the effect of temperatures, transistor was cool down to $-178^{\circ}C$ and electrical characteristics were measured. The drain current density of an AlGaN/GaN HEMT with a gate length of $2{\mu}m$ was increased from 264 mA/mm to 388 mA/mm and the maximum transconductance was increased from 105 mS/mm to 134 mS/mm by decreasing the temperature to $-108^{\circ}C$. Also, the threshold voltage was shifted -0.39 V with the temperature. The reason for the variations was seemed to the reduced channel resistance corresponding to the temperature. However, most of the variation of the electrical characteristics takes places above $-108^{\circ}C$.

• Elastomers and Composites
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• v.45 no.4
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• pp.298-308
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• 2010

The mechanical properties and surface characteristics of parylene thin film were improved using Xylydene-based dimers (DPX-C, DPX-D, and DPX-N). A single-parylene-C, D, N film and a hybrid chemical and physical parylene thin films in which two types are mixed were manufactured for each dimer by adjusting the deposition conditions and the thickness of the thin film by input. Parylene was deposited by chemical vapor deposition (CVD) and the thermal characteristics of the single thin film and the hybrid thin film were compared by thermal analysis. The mechanical properties of the thin films were characterized by tensile strength, elongation, and tear force tests, and the surface characteristics of the thin films were evaluated by contact angle and surface energy measurements. The hybrid chemical parylene thin film in which two types are mixed can complement the strengths and weaknesses of the different dimers, while the physical parylene thin film can freely adjust the thin film characteristics of the coated surface and the opposite surface.