• KSBB Journal
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• v.16 no.4
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• pp.370-375
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• 2001

For the production of new exo-biopolymers from microorganisms, an exe-biopolymer producing bacterial strain was isolated from the composter used in composting of organic wastes. Bacteriological properties of this strain and physicochemical properties of producing exo-biopolymer were investigated. The isolated strain was identified as Enterobacter sp. through its morphological, cultural and physiological characteristics. The results of color reactions, CPC (cetyl pyridinium chloride) precipitation and infra red absorption spectral analysis indicated that this exo-biopolymer was presumed as an acidic polysaccharide with uronic acid. This polysaccharide was identified as hetero-polysaccharide consisting of galactose, mannose and galacturonic acid by gas chromatography, and the molecular weight of exopolysaccharide purified by gel chromatography were about 370,000 daltons. The polysaccharide solutions(0.50-2.0%, w/v) exhibited non-Newtonian flow behavior with pseudoplastic property and showed the ability of gel formation at above 1.5% (w/v) of polysaccharide concentration.

• Journal of the Korean Society of Food Science and Nutrition
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• v.29 no.2
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• pp.198-203
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• 2000

A highly viscous biopolymer from Bacillus coagulans CE-74 was purified and its rheological properties were studied The rheological properties of biopolymers produced by Bacillus coagulans CE-74 were studied at the temperature ranges with 20~8$0^{\circ}C$, at the concentration of 0.5~4.0%, at the pH ranges from 3 to 1 and at the shear rate fo 7.34~73.38 sec-1. The apparent viscosity of biopolymer was decreased with increasing shear rate, and thereby biopolymer showed pseudoplastic characteristics. Biopolymer solution showed a characteristic of non-Newtonian fluid properties. At the concentration of 1%, the consistency index and the flow behavior index were shown at 2.64 poise. sec11 and 0.8571, respectively. All dispersions were pseudoplastic fluids described accurately by Herschel-Bulkley model. The change of the biopolymer viscosity on pH showed the highest value at the pH 7.0 and it showed lower at acidic conditon that at alkaline condition comparatively.

• YAKHAK HOEJI
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• v.39 no.5
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• pp.495-505
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• 1995

The O/W microemulsion systems were made from 2 or 4% (w/w) oil (soybean oil, olive oil or isopropyl myristate) and 10, 15 or 20% (w/w) Brij 96. They were compared with micellar solution of equivalent surfactant concentration m therms of physicochemical properties, and the solubilization of sudan IV. They were characterized by dynamic light scattering, stability, surface tension, viscosity and rheogram. The mean diameters of O/W microemulsion systems were 10-15nm, and those of Brij 96 micellar solutions were 18-19 nm. Both of them were monodisperse systems. The O/W microemulsion systems showed Newtonian flow and their apparent viscosities were lower than those of micellar solutions. The surface tensions of O/W microemulsion systems were increased or decreased depending on the types of oil used, when compared with those of micellar solutions. The O/W microemulsion systems were very stable, and did not show any flocculation or aggregation. Their mean diameters were not changed after three months. But oxidation was observed in microemulsions without nitrogen gas at high temperature. There was a significant improvement in the sudan IV solubffimtion in micromulsion compared with that m the micellar solution containing equivalent concentration of surfactant. The size distribution and mean diameters of O/W micromulsions were not changed when sudan IV was solubilized.

• KSBB Journal
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• v.11 no.3
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• pp.340-346
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• 1996

Variations of rheological properties of culture broth during the production of biopolymer by an alkali tolerant Bacillus sp. were investigated. Correlations among the rheological characteristics of culture broth, cell growth and biopolymer production were examined. Rheology of the culture broth changed in the course of fermentation. The culture broth showed a non-Newtonian flow behavior, as the viscosity and pseudoplasticsity increased during the cultivation. The rheological parameters such as flow index, consistency index, yield stress and apparent viscosity during the cultivation were not influenced by the cell growth, but significantly related to the biopolymer synthesis. Changes in the rheological parameters of the broth were affected not only by the biopolymer concentration, but also by the progress of fermentation. Some rheological parameters showed maximum values just before the completion of biopolymer production and substrate consumption. Hence, it was shown that the rheological characteristics of the culture broth could be used as a good indicator for the detection of the progress or completion of fermentation.

• Journal of Microbiology and Biotechnology
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• v.20 no.4
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• pp.844-851
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• 2010

Controlling the dissolved oxygen (DO) in the fed-batch culture of the medicinal mushroom Ganoderma lucidum led to a 2-fold increase of the maximum biomass productivity compared with uncontrolled DO conditions. By contrast, extracellular polysaccharide (EPS) production was two times higher under oxygen limitation (uncontrolled DO) than under increased oxygen availability (controlled DO). Morphologically, dispersed mycelium was predominant under controlled DO conditions, with highly branched hyphae, consistent with the enhanced culture growth noted under these conditions, whereas in the uncontrolled DO process mycelial clumps were the most common morphology throughout the culture. However, in both cultures, clamp connections were found. This is an exciting new finding, which widens the applicability of this basidiomycete in submerged fermentation. In rheological terms, broths demonstrated shear-thinning behavior with a yield stress under both DO conditions. The flow curves were best described by the Herschel-Bulkley model: flow index down to 0.6 and consistency coefficient up to 0.2 and 0.6 Pa $s^n$ in uncontrolled and controlled cultures DO, respectively. The pseudoplastic behavior was entirely due to the fungal biomass, and not to the presence of EPS (rheological analysis of the filtered broth showed Newtonian behavior). It is clear from this study that dissolved oxygen tension is a critical process parameter that distinctly influences G. lucidum morphology and rheology, affecting the overall performance of the process. This study contributes to an improved understanding of the process physiology of submerged fermentation of G. lucidum.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.599-605
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• 2013

The characteristics of centrifugal pump performance according to fluid viscosity change were studied experimentally. A small volute pump with low specific speed was tested by changing the viscosity of an aqueous solution of sugar and glycerin, which is considered a Newtonian fluid. After finishing the test, the total head, shaft horsepower, and pump efficiency were compared with those of a water pump. The results are summarized as follows: (1) when the fluid viscosity is increased, the shut-off head shows very little change but the total head decreases gradually as the flow increases, and this makes the H-Q curve leaning rapidly, and (2) when the fluid viscosity is increased, the shaft horsepower shows very little change at the shutoff condition; however, the shaft horsepower increases more rapidly with an increase in the flow and viscosity.

• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.80-93
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• 2023

We performed numerical simulations of blood flow in an arterial cerebral artery aneurysm to investigate the hemodynamic behavior after coil embolization. A patient-specific model was created based on CTA data. We also conducted the coil embolization simulation to obtain the coil placement within the aneurysm. Blood was assumed to be an incompressible Newtonian fluid, and both the vessel and coil were considered rigid walls. The pulsatile boundary condition was applied at the inlet, and the outflow boundary conditions were used at the outlets. Our findings demonstrated that the coil embolization significantly reduces the blood volume flowrate entering the aneurysm by effectively blocking the inflow jet, leading to a decrease in both TAWSS and WSS, especially at the systolic peak in the impingement zone. While several high OSI regions disappeared over the aneurysm surface, we observed high OSI regions with a relatively small area where the coil did not completely occlude the aneurysm. Overall, these results quantitatively analyzed the effectiveness of coil embolization by focusing on hemodynamic indicators, potentially preventing aneurysm rupture. The present work could contribute to the development of patient-specific coil embolization.

• Microbiology and Biotechnology Letters
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• v.20 no.3
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• pp.316-323
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• 1992

Studies on the changes in rheological properties, molecular weight distribution and dextran yield after being reacted in lO%(w/w) sucrose concentration were performed with crude dextransucrase produced from Leuconostoc mesenteroides isolated from Sikhae. The reaction rate of dextran formation was monitored by sugar analysis with HPLC and by the changes in apparent viscosity. According to the periodate oxidation test, the dextran produced in this experiment was estimated to have 89% $\alpha$-(1->6) main linkages and 11% $\alpha$-(1->) side linkages. The rheological properties of the dextran solution formed changed with reaction time, and it was related to the changes in molecular weight distribution of dextran as determined by GPC analysis. As the reaction proceeded, the rheological behavior changed from Newtonian to non-Newtonian, showing Binghampseudoplastic and thixothropic flow behavior. The apparent viscosity of dextran formed solution increased with increasing reaction time, reached a maximum value of 2680 cP ($\gamma$=$33.75s^{-1}$, $25^{\circ}C$) by enzyme reaction for 8 hours, and then decreased. The temperature dependency of dextran formed solutions was well expressed by the Arrhenius equation and the activation energy reached a maximum value of 1.69 kcal/mole by enzyme reaction for 8 hours.

• Korean Journal of Food Science and Technology
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• v.27 no.6
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• pp.845-851
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• 1995

To improve the utilization of pear in its processing, the cloudy and clear juice concentrates were prepared and their rheological properties were investigated in the range of temperatures($5{\sim}60^{\circ}C$) and concentrations($15{\sim}60^{\circ}Brix$). Pear juice concentrates showed flow behavior close to Newtonian fluids. Their flow behavior was also explained by applying Power law model and Herschel-Bulkley model. Flow behavior index did not have good correlation with concentration, but decreased with the increase of temperature, showing pseudoplastic properties. Consistency index increased with the increase of concentration and with the decrease of temperature. The effect of temperature and concentration on the apparent viscosity at 1500 1/s shear rate was examined by applying Arrhenius equation. The activation energy for flow of the cloudy and clear pear juice concentrates increased from $1.5140{\times}10^4\;to\;3.4141{\times}10^4\;J/kg{\cdot}mol$, and from $1.4762{\times}10^4\;to\;3.4963{\times}10^4\;J/kg{\cdot}mol$ with the increase of concentration, respectively. The influence of temperature on the apparent viscosity was more pronounced at higher concentration. And the concentration-dependent constant A decreased from $0.0789\;to\;0.0484^{\circ}Brix^{-1}$, and from $0.0786\;to\;0.0476^{\circ}Brix^1$ with the increase of temperature, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.513-518
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• 2019

Friction Stir Welding is a welding technique for metal materials that utilizes the heat generated by friction between the material to be welded and the welding tool that rotates at high speed. In this study, a numerical analysis method was used to analyze the change in the internal temperature of the welded material during friction stir welding. As the welding target material, AZ31 magnesium alloy was applied and the welding phenomenon was considered a flow characteristic, in which a melting-pool was formed. FLUENT was used as the numerical tool to perform the flow analysis. For flow analysis of the welding process, the welding material was assumed to be a high viscosity Newtonian fluid, and the boundary condition of the welding tool and the material was considered to be the condition that friction and slippage occur simultaneously. Analyses were carried out for various rotational speeds and the translational moving speed of the welding tool as variables. The analysis results showed that the higher the rotational speed of the welding tool and the slower the welding tool movement speed, the higher the maximum temperature in the material increases. Moreover, the difference in the rotational speed of the welding tool has a greater effect on the temperature change.