• Archives of Pharmacal Research
• /
• v.28 no.3
• /
• pp.370-375
• /
• 2005

The objective of this study was to develop a new reverse micelle-based microencapsulation technique to load tetracycline hydrochloride into PLGA microspheres. To do so, a reverse micellar system was formulated to dissolve tetracycline hydrochloride and water in ethyl formate with the aid of cetyltrimethylammonium bromide. The resultant micellar solution was used to dissolve 0.3 to 0.75 g of PLGA, and microspheres were prepared following a modified solvent quenching technique. As a control experiment, the drug was encapsulated into PLGA microspheres via a conventional methylene chloride-based emulsion procedure. The micro­spheres were then characterized with regard to drug loading efficiency, their size distribution and morphology. The reverse micellar procedure led to the formation of free-flowing, spherical microspheres with the size mode of 88 ~m. When PLGA microspheres were prepared follow­ing the conventional methylene chloride-based procedure, most of tetracycline hydrochloride leached to the aqueous external phase: A maximal loading efficiency observed our experimental conditions was below $5\%$. Their surfaces had numerous pores, while their internal architecture was honey-combed. In sharp contrast, the new reverse micellar encapsulation technique permitted the attainment of a maximal loading efficiency of 63.19 $\pm$$0.64\%$. Also, the microspheres had smooth and pore-free surfaces, and hollow cavities were absent from their internal matrices. The results of this study demonstrated that PLGA microspheres could be successfully prepared following the new reverse micellar encapsulation technique.

• Nuclear Engineering and Technology
• /
• v.17 no.2
• /
• pp.116-128
• /
• 1985

Considering vacancy generation and migration in grain and sink at grain boundary, a mechanistic densification model which is dependent on UO$_2$ temperature and microstructure has been developed. This densification model is a function of time, fission rate, temperature, density, pore size distribution and grain size. The resultant equation derived in this model which is different from Assmann and Stehle's resultant equations for four temperature regions, can be applied directly for all the pellet temperatures. The predictions of the present densification model very well agreed with the experimental data. This model well predicts absolute magnitude and trend in comparison with the empirical algorithm used in KFEDA code.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.4 s.71
• /
• pp.43-49
• /
• 2006

Detailed investigations were carried out on the stability of the dredged soil bed against wave actions, aimedat establishing the design method of artificial tidal flats using dredged soil. The soil was dredged at Nagoya port, Japan, and has a mean grain size of 0.013mm. Basic features of artificial dredged soil bed against wave actions were explained from a series of model experiments in a wave flume. The two types of section shapes were employed; one is a horizontal bed and the other is a sloped one. Changes of the bed profile, shear strength, grain size distribution and water content, according to the wave actions, were measured in detail. The cumulative effect of the wave actions, over about one week, was investigated. A dredged soil bed moves withthe wave actions with relatively small wave height. It should be especially. noted that the clay component is dissolved and flown out, away from the surface layer, and consequently the surface layer hardens, as if it is covered with sand. Wren the wave height is gradually increased, the bed is not liquefied and the shear strength of the dredged bed is increased by a wave-induced dissipation of pore pressures in the bed and a decrease of clay component by the wave-induced leakage.

• Tunnel and Underground Space
• /
• v.29 no.6
• /
• pp.542-557
• /
• 2019

The behavior of rock mass is influenced by its microscopic feature of internal structure generating from forming and metamorphic process. This study investigated a new methodology for characterization of rock based on the X-ray CT (computed tomography) images reflecting the spatial distribution characteristics of internal constituent materials. The X-ray image based analysis is capable of quantification of heterogeneity and anisotropy of rock fabric, size distribution and shape parameter analysis of rock mineral grains, fluid flow simulation based on pore geometry image and roughness evaluation of unexposed joint surface which are hardly acquired by conventional rock testing methods.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.35 no.4
• /
• pp.372-376
• /
• 2022

Since the ZnO varistor is a semiconductor device, the internal thermal distribution during the varistor operation is recognized as an important factor in the performance and deterioration of the varistor. For an optimal varistor structure design, the thermal runaway phenomenon during the varistor operation was interpreted using the Comsol 5.2 analysis program by a finite element analysis. The maximum temperature of the center measured in the cross section of the ZnO varistor was confirmed to increase as the temperature moved from the lower electrode to the center towards the upper electrode up to 572.6 K. The electrodes are thinned so that the influence of the Schottky barrier is not great. The heat gradient balance is determined to be improved when the electrode of the hybrid form is introduced. The thickness, density, pore distribution, impurity uniformity, and particle size of the ZnO varistor are required, and it is determined that the pyrolysis gradient will be improved regardless of the electrode thickness. When these results are applied to design the ZnO varistor, the optimal structure of the ZnO varistor can be obtained.

• Korean Journal of Materials Research
• /
• v.22 no.5
• /
• pp.243-248
• /
• 2012

ZrN nanoparticles were prepared by an exothermic reduction of $ZrCl_4$ with $NaN_3$ in the presence of NaCl flux in a nitrogen atmosphere. Using a solid-state combustion approach, we have demonstrated that the zirconium nitride nanoparticles synthesis process can be completed in only several minutes compared with a few hours for previous synthesis approaches. The chemistry of the combustion process is not complex and is based on a metathesis reaction between $ZrCl_4$ and $NaN_3$. Because of the low melting and boiling points of the raw materials it was possible to synthesize the ZrN phase at low combustion temperatures. It was shown that the combustion temperature and the size of the particles can be readily controlled by tuning the concentration of the NaCl flux. The results show that an increase in the NaCl concentration (from 2 to 13 M) results in a temperature decrease from 1280 to $750^{\circ}C$. ZrN nanoparticles have a high surface area (50-70 $m^2/g$), narrow pore size distribution, and nano-particle size between 10 and 30 nm. The activation energy, which can be extracted from the experimental combustion temperature data, is: E = 20 kcal/mol. The method reported here is self-sustaining, rapid, and can be scaled up for a large scale production of a transition metal nitride nanoparticle system (TiN, TaN, HfN, etc.) with suitable halide salts and alkali metal azide.

• Membrane Journal
• /
• v.17 no.3
• /
• pp.174-183
• /
• 2007

The manufacturing process of metal membrane made of only metal mesh and both metal mesh and powder with using rolling process have been studied. In the rolling of metal mesh, selected metal meshes were rolled with the reduction ratio of 10%, 20%, and 30%, respectively. Such rolling process resulted in the decrease of mesh pore size through reduction the cross sectional area of mesh and changing the diameter of mesh wires. Also, it enhanced the filtration ratio of rolled mesh which is almost same as the filtration ratio of upper grade unrolled mesh and the reliability of membrane by making pore size distribution become more uniform. In fabricating metal powder layer onto metal mesh, using PVA(polyvinyl alcohol) as a binder of powder, drying the metal powder layer at $100^{\circ}C$ for 1 hr, and sintering it at $1,000^{\circ}C$ for 3 hr in vacuum were to be optimum conditions for obtaining good quality of metal powder layer on metal mesh with high pore density but no crack. With additional rolling of metal powder layer on metal mesh with 30% reduction before sintering, metal membrane which filtration ratio is about $0.7{\mu}m$ has been successfully manufactured.

• Korean Journal of Soil Science and Fertilizer
• /
• v.43 no.4
• /
• pp.407-414
• /
• 2010

Until now, the pore size distribution, PSD, of soil profile has been calculated from soil moisture characteristic data by water release method or mercury porosimetry using the capillary rise equation. But the current methods are often difficult to use and time consuming. Thus, in this work, theoretical framework for an easy and fast technique was suggested to estimate the PSD from unsaturated hydraulic conductivity data in an undisturbed field soil profile. In this study, unsaturated hydraulic conductivity data were collected and simulated by the variation of soil parameters in the given boundary conditions (Brooks and Corey soil parameters, ${\alpha}_{BC}=1-5L^{-1}$, b = 1 - 10; van Genuchten soil parameters, ${\alpha}_{VG}=0.001-1.0L^{-1}$, m = 0.1 - 0.9). Then, $K_s$ (1.0 cm $h^{-1})$ was used as the fixed input parameter for the simulation of each models. The PSDs were estimated from the collected K(h) data by model simulation. In the simulation of Brooks-Corey parameter, the saturated hydraulic conductivity, $K_s$, played a role of scaling factor for unsaturated hydraulic conductivity, K(h) Changes of parameter b explained the shape of PSD curve of soil intimately, and a ${\alpha}_{BC}$ affected on the sensitivity of PSD curve. In the case of van Genuchten model, $K_s$ and ${\alpha}_{VG}$ played the role of scaling factor for a vertical axis and a horizontal axis, respectively. Parameter m described the shape of PSD curve and K(h) systematically. This study suggests that the new theoretical technique can be applied to the in situ prediction of PSD in undisturbed field soil.

• Journal of Korean Society of Environmental Engineers
• /
• v.22 no.6
• /
• pp.1037-1044
• /
• 2000

The objective of this study is the preparation of activated carbon for BAC(biological activated carbon). Prepared activated carbon was measured iodine adsorption(mg/g). methylene blue adsorption(mg/g), B.E.T($m^2/g$), PSD(Pore Size Distribution) and 'Picabiol' which in commercial activated carbon for BAC. Activation method for this study was a chemical activation used the phosphoric acid. In the method, two important factors affected activation characterized in preparation were temperature and impregnated phosphoric acid concentration. Activation temperature and impregnated phosphoric acid concentration were changed the $600{\sim}800^{\circ}C$ and 35~50wt% respectively. Activation time was fixed for 3 hour. Optimal activation temperature was $800^{\circ}C$ and impregnated phosphoric acid concentrations was about 50wt%. By the above condition specific surface area, iodine adsorption number and methylene blue adsorption number resulted $1643.3m^2/g$, 1093 mg/g, 445.6 mg/g, respectively.

• Membrane Journal
• /
• v.19 no.2
• /
• pp.136-144
• /
• 2009

In this study, sodium dedocyl sulfate (SDS), which was anionic surfactant, was added for forming micelles to remove ferrous ions that could be contained with a small amount in industrial water. Then aggregates were formed by adsorption or binding of ferrous ions on the surface of micelles, and then rejected by ceramic membranes to remove ferrous ions. Ferrous concentration was fixed at 1mM and SDS was changed as $0{\sim}10mM$ to investigate the effect of the anionic surfactant. As a result, rejection rate of ferrous was the highest to 88.97% at 6mM. And we used ELS (Electrophoretic Light Scattering Spectrometer) to investigate particle size distribution of micellar aggregates depending on SDS concentration. Then distribution of large aggregates was the highest at 6mM. And we investigated effects of $N_2$-back-flushing time (BT) during periodic $N_2$-back-flushing on ceramic membranes. Finally optimal $N_2$-BT for NCMT-723l (pore size $0.10{\mu}m$) membrane was 20 sec.