• Membrane Journal
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• v.19 no.2
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• pp.122-128
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• 2009

We prepared monodispersed spherical silica microgels by controlling various conditions of emulsification procedure using a lab-scale membrane emulsification system equipped with SPG (Shirasu porous glass) porous membrane having pore size of $1.5{\mu}m$. We determined the effects of process parameters of membrane emulsification (ratio of dispersed phase to continuous phase, sodium silicate concentration, emulsifier concentration, dispersed phase pressure, stirring speed) on the mean size and size distribution of silica microgels. The increase of the ratio of dispersed phase to continuous phase, dispersed phase pressure and sodium silicate concentration led to the increase in the mean size of microgels. On the contrary, the increase in emulsifier concentration and stirring speed of the continuous phase caused the reduction of the mean size of microgels. Through controlling these parameters, monodisperse spherical silica microgels with about $6{\mu}m$ of the mean size were finally prepared.

• Korean Chemical Engineering Research
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• v.45 no.4
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• pp.364-371
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• 2007

Effects of continuous oil phase on silver halide nanoparticles were investigated where nanoparticles were prepared using two different types of water-in-oil(W/O) microemulsions containing silver and halide, respectively. Phase behavior experiments for ternary systems containing AOT surfactant, hydrocarbon oil and aqueous solution of an inorganic salt showed that the region of one phase W/O microemulsion was found to be broadened with an increase in the alkyl chain length of a hydrocarbon mainly due to an increase in hydrophilic nature of a surfactant. With the information of phase behavior experiments, silver halide nanoparticles were prepared using different AOT-based microemulsion systems and photomicrographs obtained by transmission electron microscopy indicated that about 10 nm size particles of relatively spherical shape were obtained. It has been found that an increase in alkyl chain length of a hydrocarbon results in a decrease in particle size because of higher intermicellar exchange rate among microemulsion drops. The average particle size was also found to increase with the inorganic salt composition of initial aqueous solution.

• KSBB Journal
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• v.8 no.5
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• pp.417-423
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• 1993

The effect of moisture content of biocatalyst on the performance of a gas phase continuous bioreactor was investigated along with study on the mass transfer limitation. The biocatalysts whose moisture contents are 46.2% and 37.2%, respectively were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, following by slow dehydration method, and packed into a column. Relative production rate (RPR), acetaldehyde composition ($X_p$) and conversion (X) of biocatalysts (37.2%) are better than those of biocatalysls (46.2%), and it was considered that these are attributed to the mass transfer enhancement in the gas phase compared with the aqueous phase.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.09a
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• pp.99-107
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• 1995

The Phase-type(PH) distribution, defined as a distribution of the time until the absorption in a finite continuous-time Markov chain state with one absorbing state, has been widely used for various stochastic modelling. But great computational burdens often make us hesitate to apply PH methods. In this paper, we propose a seemingly efficient approximation method for phase type distributions. We first describe methods to bound the first passage time distribution in continuous-time Markov chains. Next, we adapt these bounding methods to approximate phase-tupe distributions. Numerical computation results are given to verify their efficiency.

• Korean Journal of Materials Research
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• v.13 no.3
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• pp.137-143
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• 2003

The air gap between the metal and mold, formed by shrinkage during solidification, causes surface and subsurface cracks in the continuous casting process. Molten crack on the surface might also occur due to improper heat transfer between them. In order to compensate the air gap in mold design, the thermal contraction is an essential factor. In this study, the thermal contraction and expansion behaviors were examined from the ($\alpha$ and pearlite)/${\gamma}$ to ${\gamma}$/$\delta$ transformations in continuous casting steels by the commercial dilatometer and the self- assembled dilatometer with laser distance measurement. It was found that the thermal contraction and expansion behaviors were very dependant on the phase transformation of the ${\gamma}$/$\delta$ as well as ($\alpha$ and pearlite)/${\gamma}$. The sudden volume change from $\delta$ to ${\gamma}$ which might cause cracks in the continuous casting process, was observed on cooling just below the melting temperature by the self-assembled dilatometer.

• Journal of the Korean Society for Heat Treatment
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• v.28 no.4
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• pp.171-180
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• 2015

The variation in microstructure and texture during continuous annealing was examined in a series of 1.6% Mn-0.1% Cr-0.3% Mo-0.005% B steels with carbon contents in the range of 0.010 to 0.030%. It was found that microstructure of hot band consisted of ferrite and pearlite as a consequence of high coiling temperature, and eutectoid carbon content was between 0.011% and 0.016%. Martensite ranged in volume fraction from 1.5% to 4.0% when annealed at $820{\circ}C$ according to the typical continuous annealing cycle. The critical martensite content for the continuous yielding was about 4% from stress-strain curves. The continuous yielding was obtained in the 0.030% carbon steel and 0.010% to 0.020% carbon steels revealed some yield point elongation ranging from 0.8% to 2.2% in as-annealed conditions. Higher tensile strength in the higher carbon steel is due to both increase in the martensite volume fraction and ferrite grain refinement. Decreasing the carbon content to 0.01% strengthened the intensities of ${\gamma}$-fiber textures, resulting in the increase in the $r_m$ value, which was caused by the lower volume fraction of martensite. The higher carbon steels showed the lower $r_m$ value of about 1.0.

• Journal of Biomedical Engineering Research
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• v.16 no.4
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• pp.415-424
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• 1995

Combined models, specified by two or more modeling formalisms, can represent a wide variety of complex systems. This paper describes a methodology for the development of combined models in two model types of discrete event and continuous process. The methodology is based on transformation of continuous state space into discrete one to homomorphically represent dynamics of continuous processes in discrete events. This paper proposes a formal structure which can combine model of the DES and the CS within a framework. The structure employs the DEVS formalism for the DES models and differential or polynomial equations for the CS models. To employ the proposed structure to specify a DEVS/CS combined model, a modeler needs to take the following steps. First, a modeler should identify events in the CS and transform the states of the CS into the DES. Second, a modular employs the formalism to specify the system as the DES. Finally, a moduler developes sub-models for the CS and continguos states of the DES and establishs one-to-one correspondence between the sub-models and such states. The proposed formal structre has been applied to develop a DEVS/CS combined model for the human cardiovascular system. For this, the cardiac cycle is partitioned into a set of phases based on events identified through observation. For each phase, a CS model has been developed and associated with the phase. To validate the DEVS/CS combined model developed, then simulate the model in the DEVSIM + + environment, which is a model simulation results with the results obtained from the CS model simulation using SPICE. The comparison shows that the DEVS/CS combined model adequately represents dynamics of the human heart system at each phase of cardiac cycle.

• Speech Sciences
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• v.14 no.4
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• pp.261-271
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• 2007

The purpose of this study was to determine the effectiveness of CPAP (Continuous Positive Airway Pressure) therapy on the treatment of hypernasality in patients with cleft lips and palates. 7 preschool children with severe hypernasality participated in the study. Acoustic measurements of nasality were done by using the NasalView (version 1.31). Results showed that the nasalance values were reduced linearly in both vowels according to the treatment period. The sharp treatment effect was observed at the beginning stage. The nasality values of the vowel /i/ showed a sharp decrease at the Evaluation Phase 1 and 2 and a small increase at the Phase 4 followed by a drop in the end. Further studies would be desirable for various patients with different disorder types.

• Clean Technology
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• v.7 no.4
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• pp.291-297
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• 2001

In this study, the stability of concentrated colloidal liquid aphrons (CLAs) containing Aliquat 336 was measured. CLAs in the continuous phase are stabilized by water-soluble surfactant and oil-soluble surfactant. To compare the stability of CLAs, half-life was introduced. According to the change of state of solution, the rate of break-up of concentrated CLAs changed rigorously at critical coagulation concentration. Critical coagulation concentration was measured with changing pH. The effects of ionic strength and concentration of Sodium Dodecyl Benzene Sulfonate (SDBS) on the stability of concentrated CLAs in the continuous phase were also investigated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.3 s.94
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• pp.286-292
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• 2005

We design and analyze the bit interleaved coded modulation(BICM) for noncoherent N-symbol continuous phase frequency shift keying(CPFSK) on the interleaved Rayleigh fading channel. In this paper, we use the equivalent normalized squared distance(ENSD) of noncoherent N-symbol CPFSK to design and analyze the BICM system. Specially, we design the BICM system for noncoherent 2-symbol 4-ary CPFSK, and analyze the performance of the system by using the ENSD. Simulation results are also provided to verify the theoretical performance analysis.