• Korean Journal of Materials Research
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• v.8 no.2
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• pp.135-140
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• 1998

Drag reduction produced by dilute solution of water soluble ionic polymer-surfactant complex under turbulent flow in a rotating disk apparatus(RDA) was investigated in this study. Three different molecular weights of polyacrylic acid(PAA) were adopted as drag reducing additives, and distilled water was used as a solvent. Experiments were undertaken to observe the dependence of drag reduction on various factors such as polymer molecular weight, molecular expansions and flexibility, rotating speed of the disk and polymer concentration. Specific considerations were put on conformational difference between surfactant and polymer, and effect of pH on ionic polymer possessing various molecular conformation through pH. The complex of ionic polymer and surfactant(Sodium Dodecyl Sulfate) behaves like a large polyelectrolyte. Surfactant changes the polymer conformation and then increases the dimension of the polymer. The radius of gyration, hydrodynamic volume and relative viscosity of the polymer-surfactant system are observed to be greater than those of polymer itself. Such surfactant-polymer complex has enhanced drag reduction properties.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1067-1074
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• 2001

Four different composition of autoxidation drying type waterborne coatings (WBC-1, WBC-2, WBC-3, WBC-4) were prepared by the compounding of bentonite (BEN) as a water swellable clay and organometallic soaps as a drier with acrylic binder and coating additives. The solution viscosity, solid content, rheological properties and drying rate of WBCs were investigated. Also the thermal stability, the transmittance and the water-resistance of the films casted by WBCs were measured, and the surface topology of WBC films were investigated by the scanning probe microscopy. As WBC-2, WBC-3 and WBC-4 containing BEN showed the thixotropy with the shear rate, the storage stability of WBC was a excellent. When the driers was mixed in the ratio of Mn/Zn/Ba=1/2/3, the dry ability of WBCs showed maximum as 5.0 sec at 60$\^{C}$. The initial decomposition temperature and the transmittance of WBC films containing BEN increased in range of 32.2∼54.7$\^{C}$ and 5.1∼8.6% than the commercial WBC (MC-21W), respectively. The water resistance of WBC films increased in order of MC-21W

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1008-1014
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• 2001

Nanosize YIG powders added by Cerium which is exellent element in magneto-optical effect were synthesized by Sol-Gel method using Ethylene Glycol solvent. In 120 to 150 minute reaction time, stable sol solution which showed no change in viscosity, pH, and aging time was obtained. Monolithic YIG was synthesized at 80$0^{\circ}C$ with DTA and XRD measurement and its lattice parameter had a tendency to increase from 12.3921 $\AA$. Increasing annealing temperature from 80$0^{\circ}C$ to 105$0^{\circ}C$, average particle size was in the range of 40 nm to 330 nm. Saturation magnetization (M$_{s}$) value was increased from 18.37 to 21.25 emu/g due to enhancement of YIG crystallity and decreasing of orthoferrite phase. On the other hand, coercivity (H$_{c}$) value increased up to 90$0^{\circ}C$ and then decreased above 90$0^{\circ}C$. With increasing Ce addition, coercivity was almost not changed but saturation magnetization value was maximum at Ce 0.1 mol% and then decreased because of increasing a orthoferrite amount. Also, curie temperature (T$_{c}$) of YIG were not changed with Ce addition.ion.

• Korean Chemical Engineering Research
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• v.53 no.3
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• pp.289-294
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• 2015

In this research, water and ethanol extract of Momordica charantia shells, fruits and seeds were tested to see possibility as natural functional cosmetic agent. Water and ethanol extract showed 69.45 mg/g and 70.87 mg/g polyphenol concentration, respectively. Momordica charantia water and ethanol extracts did not indicate cell toxicity up to $1,000{\mu}g/ml$ concentration in MTT assay. Tyrosinase inhibition effects of water and ethanol extract were lower than arbutin, however, ethanol extract showed better DOPA oxidation inhibition effect than arbutin. Elastase inhibition effects of ethanol extract displayed similar efficacy with adenosine at higher concentrations. Solution formulations (5% extract) were stable for 28 days in both extracts, however, lotion formulation (1% extract) showed considerable variation in viscosity whereas ethanol extraction indicated relative stability. In conclusion, water and ethanol extract of Momordica charantia shells, fruits and seeds indicated strong possibility for whitening and antiwrinkle functional cosmetic ingredient.

• Journal of the Korean Chemical Society
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• v.54 no.5
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• pp.573-578
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• 2010

In this study, iron(III)-2,4-dihydroxysalophen chloride (Fe(2,4-DHSalophen)Cl), has been synthesized by combination of 2,4-dihydroxysalophen (2,4-DHSalophen) with $FeCl_2$ in a solvent system. This complex combination was characterized using UV-vis and IR spectroscopies. Subsequently, the interaction between native calf thymus deoxyribonucleic acid (ct-DNA) and Fe(2,4-DHSalophen)Cl, was investigated in 10 mM Tris/HCl buffer solution, pH 7.2, using UV-visible absorption and fluorescence spectroscopies, thermal denaturation technique and viscosity measurements. From spectrophotometric titration experiments, the binding constant of Fe(2,4-DHSalophen)Cl with ct-DNA was found to be $(1.6{\pm}0.2){\times}10^3\;M^{-1}$. The fluorescence study represents the quenching effect of Fe(2,4-DHSalophen)Cl on bound ethidium bromide to DNA. The quenching process obeys linear Stern-Volmer equation in extended range of Fe(2,4-DHSalophen)Cl concentration. Thermal denaturation experiments represent the increasing melting temperature of DNA (about $4.3^{\circ}C$) due to binding of Fe(2,4-DHSalophen)Cl. These results are consistent with a binding mode dominated by interactions with the groove of ct-DNA.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.208-218
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• 1992

Analytic solutions for the gradient of surface elevation and vertical profiles of velocity driven by the wind stress in the one-dimensional rectangular basin were obtained under the assumption of steady-state. The approach treats the bottom frictional stress $\tau$$_{b}$ as known and includes vertically varying eddy viscosity $textsc{k}$$_{M}$, which is constant, linear and quadratic of water depth. When the $\tau$$_{b}$ is param-terized with surface stress, depth averaged velocity and bottom velocity, the result shows the relation of the no-slip bottom velocity condition and the bottom frictional stress $\tau$$_{b}$. The results of a mode splitted, (x-$\sigma$) coordinate, numerical model were compared with the derived analytic solutions. The comparison was made for the case such that $textsc{k}$$_{M}$ is the constant, linear and quadratic function of water depth. In the case of constant $textsc{k}$$_{M}$, the gradient of surface elevation and vertical profiles of velocity are discussed for a uniform depth, a mild slope and a relatively steep slope. When $textsc{k}$$_{M}$ is a linear and quadratic function of water depth, the vertical structures of velocities are discussed for various $\tau$$_{b}$. The result of the comparison shows that the vertical structure of velocities depends not only on the value of $textsc{k}$$_{M}$ but also on the profile of $textsc{k}$$_{M}$ and bottom stress $\tau$$_{b}$. Model results were in a good agreement with the analytic solutions considered in this study.his study.y.his study.

• Elastomers and Composites
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• v.47 no.4
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• pp.355-363
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• 2012

A series of poly(hydroxyamide)s (PHAs) having trifluoromethyl group were prepared by direct polycondensation of aromatic diimide-dicarboxylic acids with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane by thionyl chloride and triethyl amine in N-methyl-2-pyrrolidinone (NMP). The PHAs exhibited inherent viscosity in the range of 0.54-0.96 dL/g at $35^{\circ}C$ in DMAc solution. All PHAs were readily soluble in a variety of organic solvents, whereas the polybenzoxazoles (PBOs) were quite insoluble except partially soluble in sulfuric acid. PHAs were converted to PBOs by thermal cycling reaction with heat of endotherm. The maximum weight loss temperature of the PHAs occurred in the range of $559-567^{\circ}C$. The PBOs showed relatively high char yields in the range of 47-59%. Pyrolysis Combustion Flow Calorimeter (PCFC) results of the PBOs showed 12-19 W/g heat release rate (HRR), and 2.7-3.6 kJ/g total heat release (total HR). The HRR of PBO 1 showed the lowest value of 12 W/g, which was 37% lower than that of PBO 3 (19 W/g).

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.35-41
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• 2012

Manifold researches for carbon capture and storage (CCS) have been developed and large scale-carbon capture system can be performed recently. Hence, the technologies for $CO_2$ sequestration or storage become necessary to handle the captured $CO_2$. Among them, enhanced oil recovery using $CO_2$ can be a solution since it guarantees both oil recovery and $CO_2$ sequestration. In this study, the miscible flow of oil and $CO_2$ in porous media is modeled to analyze the effect of enhanced oil recovery and $CO_2$ sequestration. Based on Darcy-Muskat law, the equation is modified to consider miscibility of oil and $CO_2$ and the change of viscosity. Finite volume method is used for numerical modeling. As results, the pressure and oil saturation changes with time can be predicted when oil, water, and $CO_2$ are injected, respectively, and $CO_2$ injection is more efficient than water injection for oil recovery.

• Journal of Korean Ophthalmic Optics Society
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• v.14 no.3
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• pp.17-27
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• 2009

Purpose: This review article was written to determine the effects of parameters characterizing a hard contact lens (RGP included), such as BCs, diameters, edge angles, on the time interval for tight fitted lens to return to the equilibrium when it was decentered from blinking. Methods: A mathematical formulation was established to relate or calculate the restoring forces and thickness of lacrimal layer beneath the cornea with the various lens parameters when the tight fitted lens was decentered from blinking. Based on this formulation the differential equations and their numerical solution program were set up to describe the time dependence of the lens on the position and to estimate the time for the lens's return to the equilibrium after blink. Results: It is found that the time interval for the tight fitted lens to return to the equilibrium decreases as either the BC decreases or the diameter increases because both the reduction in BC and increase in diameter result in the increase in the lacrimal layer thickness between the lens and cornea increase which yielded the lowering of the viscous friction in the lens motion. As the edge angle of tight fitted lens increases the time for recentering decreases due to the increase in restoring force without change in lacrimal thickness beneath the lens. In the case of flat fitted hard lens (RGP included), the lacrimal layer thickness under the lens increases as either BC or diameter increases which results in reduction in viscous friction so that the time for the lens's return to the equilibrium were to decrease. The edge angle of flat fitted lens does not affect the lens motion. Conclusions: The effect of BCs on the lens motion (time to approach the equilibrium) was concluded to be significant with both tight and flat fitted lens where its results are contrary with each other. The edge angle of lens only affects the motion in tight fitted lenses.

• Journal of Environmental Health Sciences
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• v.47 no.5
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• pp.432-445
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• 2021

Background: The European Centre for Ecotoxicology and Toxicology of Chemicals' Targeted Risk Assessment (ECETOC TRA) tool has been recognized by EU REACH as a preferred approach for calculating worker health risks from chemicals. Objectives: The applicability of the ECETOC TRA to occupational exposure estimation from industrial uses of methanol was studied by inputting surveyed and varied parameters for TRA estimation as well as through comparison with measured data. Methods: Information on uses of methanol was collected from seven working environment monitoring reports along with the measured exposure data. Input parameters for TRA estimation such as operating conditions (OCs), risk management measures (RMMs) and process categories (PROCs) were surveyed. To compare with measured exposures, parameters from the surveyed conditions of ventilation but no use of respiratory protection were applied. Results: PROCs 4, 5, 8a, 10, and 15 were assigned to ten uses of methanol. The uses include as a solvent for manufacturing sun cream, surfactants, dyestuffs, films and adhesives. Methanol was also used as a component in a release agent, hardening media and mold wash for cast products as well as a component of hard-coating solution and a viscosity-controlling agent for manufacturing glass lenses. PROC 8a and PROC 10 of a cast product manufacturer without LEV (local exhaust ventilation) and general ventilation as well as no respiratory protection resulted in the highest exposure to methanol. Assuming the identical worst OCs and RMMs for all uses, exposures from PROC 5, 8a, and 10 were the same and the highest followed by PROC 4 and 15. The estimation resulted in higher exposures in nine uses except one use where measured exposure approximated exposures without RMMs. Conclusions: The role of ECETOC TRA as a conservative exposure assessment tool was confirmed by comparison with measured data. Moreover, it can guide which RMMs should be applied for the safe use of methanol.