• Applied Biological Chemistry
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• v.34 no.2
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• pp.110-116
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• 1991

As the model compounds, citral and n-octanol which possess similar characteristics and structures of low molecular weight insect pheromones and $({\pm})-5-hydroxy-4-methyl-heptan-3-one$ which shows the aggregation pheromones activity of the rice weevil and the maize weevil were microencapsulated with low molecular weight polyethylene(LMPE) and urea-formaldehyde resin as wall materials. The core materials were microencapsulated as small particles in LMPE and urea-formaldehyde resin polymers and the microencapsulated polymers were white powders. And the polymer made from urea-formaldehyde resin was better than that from LMPE as wall material. The slow releasing effect and the releasing patten of the microencapsulated core materials were examined by solvent extraction method and headspace sampling method. Citral and n-octanol and $({\pm})-5-hydroxy-4-methyl-heptan-3-one$ were release more than 40 days and 15 days, respectively. The releasing pattern of urea-formaldehyde resin microcapsules showed rather smooth decrease than that of LMPE and was maintained at steady level longer.

• Journal of Biomedical Engineering Research
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• v.28 no.4
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• pp.484-493
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• 2007

Two polymeric prodrugs of PGE1 (prodrugs IVg and PNg) were newly synthesized. The drug conjugation proceeded in quantitative yield without decomposition of PGE1 to PGA1. With two types conjugates, PEG-PGE1 and PN-PGE1 with different spacer groups, we first discovered a possibility of slow release of PGE1 in blood circulatory system. PGE1 is conjugated with PEG and PN through the long alkylene spacers, and their availability as polymeric prodrugs is evaluated. Their drug-releasing behavior was examined both in phosphate buffer (pH=7.4) and rat plasma. Each prodrug was known to be highly stabile in the buffer solution. The drug-releasing rate became much faster in rat plasma than in the buffer solution due to the acceleration by the plasma enzymes. The drug-release was found to reach a plateau in rat plasma because the released PGE1 or its derivatives may be captured or decomposed by the plasma proteins. The slower drug-releasing rate of pro drug PNg in rat plasma is reasonably attributed to the molecular aggregation due to the hydrophobic bonding between the PGE1 moieties and spacers.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.354-361
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• 2001

In this paper, three kinds of poly(acrylate-co-methylacrylate) with different number average molecular weight(Mn) were synthesized and studied for the effects on the mechanical properties and the fluidities of the cement mortar admixtured with them. The physical properties of the cement mortar are more favorably enhanced by the poly(acrylate-co-methylacrylate) of Mn,, 5,000 than that of Mn, 2,000∼3,000. And the optimum dosage was decided to ca. 0.6 % of cement weight in cement mortar. However, the dispersion abilities of the polymers in cement mortar was not kept long time. This last result could not be explained by the theory that the fluidity of the cement mortar added with the slow releasing polycarboxylates is kept by the releasing of the carboxylic group of the copolymer in alkaline solution of cement paste.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.58 no.1
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• pp.8-14
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• 2013

The newly developed fertilizer is the slow-releasing fertilizer which can be used as a basal fertilizer without no additional fertilization at tillering stage. It has 30-4-6% of $N-P_2O_5-K_2O$ and was coated with mixture of LDPE (Low density polyethylene), EVA (Ethylene vinyl acetate), BDP (Bio degraded polymer), TALC and nonionic surfactant for the controlled release up to 50 days after application. Coating materials were designed to be decomposed naturally. This fertilizer can be applied directly to the seedling tray mechanically just before transplanting, resulting in significant labor saving effect. The developed slow-release fertilizer, which can replace both basal fertilization and top dressing at tillering stage by single application directly to seedling tray, showed the highest release at 14~21 days after transplanting. Considering the plant growth at different growth stages and yield, the optimal application rate of developed slow-release fertilizer was 300 g per rice nursery tray and the yield of rice at this application rate was 5.25 MT/ha. Rice quality in terms of head rice grain ratio, amylose content, whiteness, and taste value decreased as fertilization rate increased from 200 g to 500 g per nursery tray. Fertilization rate based on quantity of fertilizer ingredients (N, P, K) was reduced by 49.3% compared to the standard application rate and there was 49.2% reduction in labor input for fertilization.

• Journal of the Korea Organic Resources Recycling Association
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• v.32 no.1
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• pp.49-59
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• 2024

Biodegradable coating urea plays an important role in reducing the non-pollutants in agroecosystems, maximizing the plant nutrient utilization efficiency and slow-releasing nitrogen. Herein, the objective of this study was to investigate the nitrogen-releasing patterns and greenhouse gas emissions on different biodegradable coating urea. The treatments consisted of the control as an application of chemical fertilizers, NBCF as the non-biodegradable coating urea, NB60, and MDS as biodegradable coating urea. As a result of this study, the maximum accumulated total nitrogen (TN) concentration in the NBCF was higher at 33% than one in the NB60 during the precipitation periods. Its leaching period in the NCBF was prolonged for day 10 compared to the NB60. TN and NO₃-N releasing patterns in the NBCF and NB60 were fitted well on linear types(R²≥0.991), but their control and MDS were fitted well on Sigmoid curves(R²≥0.994) with high releasing concentration in the MDS compared to the control during leaching periods. For the greenhouse gas emissions, CH₄ emissions in the NBCF, NB60, and MDS were increased at 0.38%, 11.36%, and 5.91%, and N₂O emissions were also increased at 50.5%, 32.4%, 58.8% as compared to the control, respectively. Therefore, application of biodegradable polymer coating urea might mitigate the non-point pollutants in agro-ecosystem.

• Polymer(Korea)
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• v.33 no.4
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• pp.389-395
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• 2009

To develop the carrier of hydrophobic antifungal agents based on low molecular weight water-soluble chitosan (LMWSC), LMWSC was chemically modified with deoxycholic acid (DA) which is one of the bile acid as a hydrophobic group. The nanoparticles (WSCDA) using DA conjugated LMWSC were characterized using dynamic light scattering (DLS) and transmittance electron microscope (TEM). The particle size of WSCDA ranged from 250 to 350 nm and increased with the number of DA substitution. The loaded itraconazole as an antifungal agent WSCDA nanoparticles (WSCDA-ITCN) were prepared by solvent evaporation method. The drug content and the loading efficiency were investigated approximately $9{\sim}10%$ and $61{\sim}68%$ by UV spectrophotometer, respectively. The release of drug from nanoparticles was slow and showed sustained release characteristics. Based on the results of release study that the higher DA contents in WSCDA, the slower the releasing rate, the WSCDA-ITCN could be used as an excellent antifungal agent.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.6
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• pp.553-561
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• 2012

Existing energy sources convert chemical energy into mechanical energy, while fuel cell directly generates electricity through an electrochemical reaction between hydrogen and oxygen. Therefore, it has a lot of strong points such as high efficiency, zero emission, and etc. In addition, with the development of hydrogen preservation technique, some companies have been researching and releasing portable fuel cell power packs for specific applications like military equipment, automobile, and so on. However, there are some drawbacks to the fuel cell, high cost and slow dynamic response. In order to compensate these weak points, auxiliary energy storages could be applied to the fuel cell system. In this paper, the optimum structure for a 150W portable fuel cell power pack with a battery pack is selected considering the specification of the system, and the design process of main parts is described in detail. Here, main objectives are compact size, simple control, high efficiency, and low cost. Then, an automatic mode change algorithm, which converts the operating mode depending on the states of fuel cell stack, battery pack, and load, is introduced. Finally, performance of the designed prototype using the automatic mode change control is verified through experiments.