• Journal of Pharmaceutical Investigation
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• v.41 no.4
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• pp.239-247
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• 2011

Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, which catalyzes the conversion of HMG-CoA to mevalonate, an early and rate-limiting step in the biosynthesis of cholesterol. Simvastatin has good permeability, but it also has low solubility (BCS class II), which reduces its bioavailability. To overcome this problem, a solid dispersion is formed using a spray-dryer with polymeric material carrier to potentially enhance the dissolution rate and extend drug absorption. As carriers for solid dispersion, Gelucire$^{(R)}$44/14 and Gelucire$^{(R)}$ 50/13 are semisolid excipients that greatly improve the bioavailability of poorly-soluble drugs. To avoid any toxic effects of an organic solvent, we used aqueous medium to melt Tween$^{(R)}$ 80 and distilled water. The structural behaviors of the raw materials and the solid dispersion were analyzed by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The DSC and PXRD data indicated that the crystalline structure of simvastatin was transformed to an amorphous structure through solid dispersion. Then, solid dispersion-based tablets containing 20 mg simvastatin were prepared with excipients. Dissolution tests were performed in distilled water and artificial intestinal fluid using the USP paddle II method. Compared with that of the commercial tablet (Zocor$^{(R)}$ 20 mg), the release of simvastatin from solid dispersion based-tablet was more efficient. Although the stability study is not complete, this solid dispersion system is expected to deliver poorly water-soluble drugs with enhanced bioavailability and less toxicity.

• Journal of Advanced Navigation Technology
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• v.22 no.5
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• pp.462-466
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• 2018

Optical phase conjugation combining with dispersion management (DM) is promising technique to compensate for signal distortion due to chromatic dispersion and nonlinear Kerr effects of single mode fiber (SMF) in optical communication systems. However the fixed SMF length in every fiber spans usually used in the optical links with optical phase conjugator(OPC) and DM restricts the flexible link configuration. The goal of this paper is to investigate the possibility of the flexible configurations of the ultra-high and long-haul optical transmission systems by using the random distribution of SMF length of each fiber spans consisted of the optical link. It is confirmed that the excellent compensation for the distorted wavelength division multiplexing signals in the optical links with the randomly distribution is obtained in case of the shorter averaged SMF length over all fiber spans. It is also confirmed that the control method of net residual dispersion suitable to good compensation is postcompensation and the extent of net residual dispersion(NRD) is -10 ps/nm in DM optical link consisted of fiber spans with the randomly distributed SMF lengths.

• Journal of Environmental Science International
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• v.5 no.3
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• pp.277-284
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• 1996

The Characteristics of atmospheric flow and dispersion of air pollutants in the mountainous coastal area were studied using two-dimensional model by the combination of land-sea breezes and transport. The pollutants emitted into the simulated wind field in considering with the mesoscale local circulations. The typical effects of land-sea breezes and tophography of coastal area on the dispersion are discussed in detail, and the model is proved as an useful tool to pridict real time pollutant transport by the results of application studies in Pusan, Korea where the urbanized coastal area with mountainous topography. It was found that sulfur dioxide ($SO_2$) are differently transported and concentrated as going inland by the influence of the sea breeze with topographic changes. Key words : land-sea breezes, sulfur dioxide, dispersion, coastal area.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2014.06a
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• pp.258-259
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• 2014

It is needed the introduction of a new wave dispersion relationship considering the condition of seabed to examine closely the interaction between wave and seabed. In this study, a wave dispersion relationship is newly developed considering the condition of seabed such as permeability and displacement. Wave damping rates are compared and analysed according to the various soil parameters such as seabed soil thickness, elastic modulus, saturation, permeability, and porosity.

• Macromolecular Research
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• v.10 no.3
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• pp.140-144
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• 2002

Dispersion polymerization of acrylamide was carried out in the media of methyl alcohol/$H_2O$ mixtures using hydroxypropyl cellulose and ammonium persulfate as steric stabilizer and initiator, respectively. The effects of concentrations of initiator and steric stabilizer, amount of monomer, polymerization temperature, methyl alcohol/$H_2O$ ratio, and purification of monomer and nitrogen purge on the particle size of the latices and molecular weight of the polymers were investigated. The average particle diameter increased with increasing concentration of initiator, water content in methyl alcohol/$H_2O$ media, and polymerization temperature, but decreased with monomer and stabilizer concentrations. The viscosity average molecular weight increased with increasing concentrations of monomer, steric stabilizer, and water content in dispersion media, but decreased with initiator concentration and polymerization temperature. The PAM polymers prepared with the purified monomer and the nitrogen purging before the reaction showed the highest molecular weight.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.4
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• pp.71-73
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• 2008

The development of polymer/inorganic nanocomposites has attracted a great deal of interest due to the improved hybrid properties derived from the two different components. Various nanoscale fillers have been used to enhance polymer mechanical and thermal properties, such as toughness, stiffness, and heat resistance. The effects of the filler on the final properties of the nanocomposites are highly dependent on the filler shape, particle size, aggregate size, surface characteristics, polymer/inorganic interactions, and degree of dispersion. In this paper, we describe the influence of different $CaCO_3$ dispersion methods on the thermal properties of polyethylene terephthalate (PET)/$CaCO_3$ composites: i.e., the adsorption of $CaCO_3$ on the modified PET surface, and the hydrophobic modification of the hydrophilic $CaCO_3$ surface. We prepared PET/$CaCO_3$ nanocomposites using a twin-screw extruder, and investigated their thermal properties and morphology.

• Corrosion Science and Technology
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• v.14 no.5
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• pp.207-212
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• 2015

The purpose of this research was to synthesize fluorine modified waterborne polyurethane dispersion (F-WPU) by soap-free (internal emulsifier) emulsion polymerization techniques, to prepare coating solution based on fluorine modified waterborne polyurethane dispersion (F-WPU) and to compare the chemical and thermo-mechanical properties on the electrogalvanized steel sheet. Environmentally friendly F-WPU was prepared with a fluorinated polyol containing 60 wt% of fluorine. There are various ways of combining a wide variety of fluorinated polyols and diisocyanate to exhibit novel properties of waterborne polyurethane dispersion. Components of coating solution were largely divided into 4 kinds i.e., F-WPU, acrylic emulsion, silane coupling agent, and colloidal silicate. F-WPU coating solution on the electro-galvanized steel sheet showed excellent properties of corrosion resistance, alkali resistance and heat resistance, as compared to other coating solutions using a general waterborne resin. The F-WPU coating solution's reliable effects are possibly due to the fluorine atoms incorporated even in a small amount of F-WPU.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.11
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• pp.773-780
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• 2010

The dispersion of plume which is emitted from a chimney is governed by a lot of factors： wind, local terrain, turbulence intensity of atmosphere, and temperature, etc. In this study, we numerically investigate the plume dispersions for various altitudinal temperature gradients and wind speeds. The normal atmosphere has the temperature decrease of $0.6^{\circ}C/100m$, however, actually the real atmosphere has the various altitudinal temperature profiles according to the meteorological factors. A previous study focused on this atmospheric temperature gradient which induces a large scale vertical flow motion in the atmosphere thus makes a peculiar plume dispersion characteristics. In this paper, the effects of the atmospheric temperature gradient as well as the wind speed are investigated concurrently. The results for the developing processes in the atmosphere and the affluent's concentrations at the ambient and ground level are compared under the various altitudinal temperature gradients and wind speeds.

• Macromolecular Research
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• v.8 no.4
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• pp.186-191
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• 2000

Clay-dispersed nanocomposites have been prepared by simple melt-mixing of three components, i.e. poly (styrene co-acrylonitrile) copolymer (SAN), poly ($\xi$-caprolactone ) (PCL), and an organophilic clay(Cloisite(R) 30A). In the present study, poly($\xi$-caprolactone) was added in the mixtures in order to facilitate the intercalation of SAN into the gallery of silicate layers, and the molecular weight effects of PCL on the dispersion of silicate layers were compared by changing the amount of added PCL. The degree of dispersion of 10-$\AA$-thick silicate layers of clay in the nanocomposites was investigated by using an X-ray diffractometer and a transmission electron microscope. It was found that PCL added in the mixture facilitate the intercalation of SAN copolymers into the galleries of silicate layers modified with an organic intercalant, resulting in the better dispersion of clay. It was, also, observed that the processing temperature influences the degree of clay dispersion.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.44-52
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• 2000

The dispersion of surface oil is generally described as a break-up of oil slick into small oil droplets. These small droplets are subjected to turbulence and vertical circulation so that it can be entrained into subsurface. Sometimes they tend to be submerged into sea bottom permanently. The diameter of oil droplets is a critical parameter to determine their behavioral characteristics under water surface. At the same time the variations of droplet stability depends on the weathering of it. That is why the weathered oil has different mechanism from the unweathered one. The variability of physical properties of oil including viscosity and density contribute to interfere with effective separation of oil and emulsion droplets in water. Also in the presence of interactions among the droplets there are coalescing or coagulating effects on the dispersion process of droplets.