• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1157-1163
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• 2009

Complexes of Pd(btnbmtp)$Cl_2$ and Pt(btnbmptp)$Cl_2$ (btnbmtp = 2,5-bis(thiophen)-1-nonyl-3,4-bis(methylthio)- pyrrole) were prepared and their crystal structures were determined at room temperature. In the structures, the two thiophene moieties lie in cis form with an average dihedral angle of $55.26^{\circ}$ to the pyrrole frame. The luminescence properties of the free ligand and the complexes were investigated in solution and solid states. The luminescence of the compounds were not favored by substituting thiophene moieties to the pyrrole frame, compared to the unsubstituted nbmptp (nbmptp = 1-nonyl-3,4-bis(methylthio)pyrrole). In particular, thiophene substitution quenched the emission from the complexes dissolved in ,$CH_2Cl_2$ and reduced the charge transfer transitions from S atoms of the thio moieties to Pt in crystalline state, which was very characteristic of Pt(nbmptp)$Cl_2$.

• Korean Journal of Soil Science and Fertilizer
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• v.47 no.3
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• pp.191-198
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• 2014

Absorption and accumulation of heavy metals in plants were determined by phytoavailable contents rather than total contents of heavy metals. Therefore, phytoavailability-based management protocol should be prepared for safe food crop production in contaminated agricultural lands. This study was conducted to understand the distribution and phytoavailability of heavy metal in the Korean agricultural soils affected by abandoned mining sites along with investigation of soil properties (soil pH, OM, DOC, clay content, Al/Fe/Mn content) influencing on the metal phytoavailability. For this, 142 agricultural soils located nearby 39 abandoned mining sites distributed in five province in Korea, were analyzed. Among the four different heavy metals, cadmium (Cd) and zinc (Zn) appeared to exist in more phytoavailable form than cupper (Cu) and lead (Pb). Soil pH was the main factor governing phytoavailable Cd, Pb, and Zn showing positive relationship with partitioning coefficients of the corresponding metals; Cd (r = 0.66, P < 0.001), Pb (r = 0.70, P < 0.001), and Zn (r = 0.62, P < 0.001). This implied higher phytoavailability of the corresponding metals with higher soil pH. In contrast, phytoavailability of Cu (r = 0.41, p < 0.01) was only negatively related with soil DOC (dissolved organic carbon).

• Journal of the Korean Ceramic Society
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• v.35 no.11
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• pp.1171-1181
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• 1998

$SrZr_{0.95}$$Y_{0.05}$$O_{2.975}$ powder was synthesized by ultrasonic spray pyrolysis using a solution that Sr carbonate and Zr and Y nitrates were dissolved in a citric acid solution. The processes of particle formation were in-vestigated with respect to solution properties and pyrolysis temperature. With changing the solution con-centration form 0.1M to 0.01M there was a tendency that average sizes of droplets and particles were de-creased and their size distributions were narrowed. Citrate functional groups converted the droplets into gel particles which prevented an inhomogeneous precipitation of the metal ions and facilitated the diffusion of gases during thermal decomposition. As a result the powder having spherical particles without hollow par-ticles could be prepared. Low pyrolysis temperature led to amorphous particles due to incomplete pyrolysis and made the particles difficult to maintain spherical shape due to retarded gelation of the droplets. Whereas higher pyrolysis temperature produced hollow and broken particles because the droplets un-derwent rapid gelationand decomposition. The particles obtained at two pyrolysis temperature $500^{\circ}$and $1000^{\circ}C$ consisted of a perovskite phase and a very small amount of $SrCO_3$ However after calcination at $1000^{\circ}C$ the particles contained a single perovskite phase having an average particle size of 0.63${\mu}{\textrm}{m}$ and an apparent density near to the theoretical density.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.1
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• pp.70-77
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• 2001

This paper present a fuzzy mxlel of describing reacton features for ozon contactor in advanced water treatn-ent systems. Input and output variables are chosen by considenng the object of ozon processing and several parameters related to management of water quahty. Dissolved organic carbon concentration, $UV_{254}$ absorptIon and $KM_NO_4$ consumption are proposed as common variables in input and outp.lt variables. Furthermore own concentration, raw water's temperature and contact time are suggested as input variables, Membership hmctions for input variables have triangular type share and the grades in each lrembership function are determined by investigating process data gathered at pilot planl The decision parts of fuzzy model have linear combination form of input variables and coefficients included in such linear equations are computedd with process clata in the sense of least square error Also fuzzy trodel suggested in this paper is partitioned by 3 independent fuzzy rnxlels using the characteristics of having no interactions armng output variables. As a result, such fuzzy mxlel has rrerits in computation and comprehension. According to simulatIon results, fuzzy moIel's outputs give almost similar data to process output under same input conditions.

• Journal of Pharmaceutical Investigation
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• v.26 no.4
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• pp.299-308
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• 1996

In order to develop the controlled release of a drug from the suppsitories, in vitro drug release and in vivo absorption in rabbits were investigated. Various suppository forms with hollow cavities, into which drugs in the form of fine powder or solid dispersion system(SDS) could be placed, were utilized. The polyvinyl alcohol(PVA) hydrogel as a base, and propranolol HCl(PPH) as a model drug were employed. In vitro drug dissolution studies showed that the dissolved amounts(%) of PPH from PPH-methylcellulose(MC)-SDS and PPH-ethylcellulose(EC)-SDS reached 100% and 63% in 4.5-hours, respectively. In the relative strength test for PVA hydrogel, PVA hydrogel became harder and more rigid when the number of freezing-thawing cycles and the ratio of PVA 2000 were increased. In vitro drug release profile revealed that the release rate(%) of PPH from PPH-EC-SDS and PPH-MC-SDS hollow type suppositories were sustained. The release amount(%) of PPH from PPH-EC-SDS hollow type suppositories was not affected by storage time, but since the use of hydrophilic MC made PPH diffuse into the hydrogel after it absorbed the water of base, the various release patterns were appeared as the storage time went by. In vivo absorption experiments with rabbits showed that PPH-EC-SDS(PPH : EC=1:3) hollow type suppository delayed the absorption of PPH, significantly. The $C_{max}$, $AUC_{0{\rightarrow}8}$ and MRT of PPH powder hollow type suppository were $196.37{\pm}5.63\;ng/ml$, 1105.26 ng/ml/min and 8.66 min, respectively. The $C_{max}$, $AUC_{0{\rightarrow}8}$ and MRT of PPH-EC-SDS(PPH : EC=1:3) were $91.30{\pm]14.14\;ng/ml$, 554.69 ng/ml/min, 235.99 min, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.1
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• pp.136-142
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• 2007

Recent publications have paid attention on the utilization of solid reagents for the removal of substances causing eutrophication, in particular $PO_4^{3-}$ ions. The adsorption of dissolved inorganic phosphate on slag produced by the refining process of iron ore was fundamentally studied for suppressing the liberation of phosphate from wastewater. This study has been conducted in order to find a possibility to improve the phosphate removal and to evaluate the phosphate removal variation to form hydroxyapatite, when the converter slag is used for phosphate removal. The result shows that the converter slag can be applied to remove phosphate using Freundlich isotherm. The size of converter slag, $2{\sim}0.425 mm$ was more efficient than $2{\sim}4.75mm$ to remove phosphate. In particular, 1 mg/L of phosphate can be removed up to 80% of the initial concentration for the continuous column experiment.

• Journal of Soil and Groundwater Environment
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• v.21 no.2
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• pp.1-7
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• 2016

Ferrous slag is a by-product from steel making process and waste concrete is generated from construction activities. Large part of ferrous slag and waste concrete are recycled as construction materials. However, Ca²⁺ leaching out of ferrous slag and waste concrete in the water-contacting environment can cause a strength change. Strength can be reduced due to the dissolution of solid form of CaO which is one of the main contents of ferrous slag and waste concrete. On the other hand, strength can be enhanced due to the pozzolanic reaction of cementitious components with water. In this study, steelmaking slag, blast furnace slag, and waste concrete were aged by exposure to raining events, and the change of their compaction and shear strength characteristics was investigated. Optimum moisture content of all materials used in this study increased with aging period while maximum dry unit weight slightly decreased, implying that the relative contents of fine particles increased as the CaO solid particles were dissolved. Internal friction angle and shear strength of recycled materials also increased with aging period, indicating that the materials became denser by the decrease of void ratio attributed to the fine particles generated during the weathering process and the development of cementitious compounds increasing the bonding and interlocking forces between the particles. The results of this study demonstrated that mechanical strength of recycled materials used as construction materials has little chance to be deteriorated during their service life.

• Journal of Environmental Science International
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• v.28 no.10
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• pp.851-861
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• 2019

In this study, we performed a sediment elution experiment to evaluate water quality in terms of phosphorus, as influenced by the dissolved oxygen consumed by sediments. Three separate model column treatments, namely, raw, calcined, and sonicated oyster shell powders, were used in this experiment. Essential phosphorus fractions were examined to verify their roles in nutrient release from sediment based on correlation analyses. When treated with calcined or sonicated oyster shell powder, the sediment-water interface became "less anaerobic," thereby producing conditions conducive to partial oxidation and activities of aerobic bacteria. Sediment Oxygen Demand (SOD) was found to be closely correlated with the growth of algae, which confirmed an intermittent input of organic biomass at the sediment surface. SOD was positively correlated with exchangeable and loosely adsorbed phosphorus and organic phosphorus, owing to the accumulation of unbound algal biomass-derived phosphates in sediment, whereas it was negatively correlated with ferric iron-bound phosphorus or calcium fluorapatite-bound phosphorus, which were present in the form of "insoluble" complexes, thereby facilitating the free migration of sulfate-reducing bacteria or limiting the release from complexes, depending on applied local conditions. PCR-denaturing gradient gel electrophoresis revealed that iron-reducing bacteria were the dominant species in control and non-calcined oyster shell columns, whereas certain sulfur-oxidizing bacteria were identified in the column treated with calcined oyster powder.

• Archives of Pharmacal Research
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• v.24 no.6
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• pp.568-571
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• 2001

The purpose of this work was to study the effect of storage time and temperature on the in vitro release kinetics of a commercial sustained-release dosage form of theophylline, at different pHs of the dissolution medium. The formulation was stored at $35^{\circ}C$ for 16 months and at $45^{\circ}C$ for 8 months, with a relative humidity of 60%. The in vitro release tests were performed at pHs 2, 4, 6 and 7.4. The mean values of the transport coefficient n, were close to 0.5 in all the conditions tested, which indicates that the transport system is not modified after storage of the formulation at $35^{\circ}C$ and $45^{\circ}C$. The mean values of the dissolution rate constant ranged from 0.036 to 0.043 $min^{-n}$, under all the conditions tested. Significant differences (${\alpha}=0.05$) were found between pHs 2, 4 and 6, 7.4 for all the model-independent parameters studied. When the formulation was kept at $35^{\circ}C$ for 16 months, the mean percentage of drug dissolved at 8 hours was 25.61% (pHs 2, 4) and, 36.12% (pHs 6, 7.4), representing a 26% and 24% reduction, respectively. Simitar results were obtained after storing the formulation at $45^{\circ}C$ for 8 months, corresponding to 33.3% (pHs 2, 4) and, 22.5% (pHs 6, 7.4) diminution, respectively. The values of the similarity factory $f_2$, obtained were lower than 50, which indicates the lack of similarity among the dissolution profiles, after storing the formulation under the experimental Conditions tested.

• Journal of Hydrogen and New Energy
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• v.32 no.5
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• pp.315-323
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• 2021

The air-cooled proton exchange membrane fuel cells (PEMFC) stacks, which is widely used in small-sized PEMFC, have a problem in that durability is weaker than that of the water-cooled type. Because the cathode is open to the atmosphere and the structural problem of the air-cooled stack, which is difficult to maintain airtightness, is highly likely to form a hydrogen/air boundary during start-up/shut-down (SU/SD). Through the accelerated durability evaluation of the 20 W air-cooled PEMFC stack, the purpose of this study was to find out the cause of the degradation of the stack and to contribute to the improvement of the durability of the air-cooled PEMFC stack. In this study, it was possible to evaluate durability in a relatively short time by reducing 20-30% of initial performance by repeating SU/SD 1,000 to 1,200 times on an air-cooled PEMFC stack. After disassembling the stack, each cell was divided into two and the performance analysis showed that the electrode degradation was more severe in the anode outlet membrane electrode assembly (MEA), which facilitates air inflow as a whole, than in the inlet MEA. It was shown that the cathode Pt was dissolved/precipitated to deteriorate the polymer ionomer inside the membrane.