• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.575-585
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• 2006

In Orthogonal Frequency Division Multiple Access (OFDMA) systems, timing synchronization in uplink is accomplished by an initial uplink synchronization called an initial ranging process. The Base Station's receiver synchronizes the symbol timing to specific user's symbol and the other user's symbols have some Symbol Timing Offset (STO). Linear phase shift is occurred by each user's STO in an OFDMA symbol. The Multiple Access Interference (MAI) caused by the summation of each user's linear phase shift degrades the performance of ranging code detection. In this paper, we propose an initial ranging symbol structure with common ranging code for phase shift estimation and compensation. We car estimate the average of phase shift that is generated by each user's STO and compensate this phase shift by using common ranging code. This scheme will suppress the MAI and provide better detection performance than conventional process.

• KSBB Journal
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• v.10 no.4
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• pp.421-427
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• 1995

A fungal strain, designated Aspevgillus sp. JS-42, was isolated and shown to produce an extracellular polysaccharide used as a bioflocsulant. The optimal medium composition for the production of flocculant with Aspergillus sp. JS-42 was glucose 3.0%, yeast extract 0.2%, $(NH_4)_2S0_4 0.1%, CaCI_2.2H_2 0.05%$ in distilled water. The optimum culture temperature and optimum culture pH for the production of the flocculant were $25^{\circ}C$ and pH 7.0, respectively. The highest production of flocculant was observed after 90 hours of cultivation at the optimal condition. The flocculant could efficiently flocculaled the tested solids suspended in aqueous solution and was stable at high temperature($100^{\circ}C$) and to pH range of from 2 to 10. The flocculant seems to be a kind of high viscous polysaccharide.

• KSBB Journal
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• v.9 no.3
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• pp.287-293
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• 1994

A bacterium isolated from waste coal mine water around Hawsun had an ability for the degradation of hydrogen sulfide. The isolate was identified as Thiobacillus sp. IW. on the basis of its morphological, physiological and chemotaxonomical characteristics. The optimum pH and temperature were 7 and $30^{\circ}C$, respectively. Growth occurred in a pH range of 3 to 9. Due to the sulfate accumulated in liquid medium, the pH decreased. As a consequence the cell growth was inhibited. Potasium nitrate and glutamic acid were utilized as a nitrogen source but urea and ammonium chloride not consumed. Denitrification occurred in a basal medium containing the glucose but did not in a basal medium containing the malate. The maximum specific growth rate of cell was 0.78h-1 and generation time was 0.9 hour. The cell productivity was 6.25mg/1$.$h and the isolate grew logarithmically up to 18 hour. These results indicate that the isolate can be a suitable bacterium responsible for degradation of hydrogen sulfide as malodorous compounds.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.23-36
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• 2008

Polymer-clay nanocomposites, a novel organic-inorganic hybrid, attract much attention from both scientific fields and engineering fields due to their balanced improvements in mechanical properties as well as diffusion behaviors, including flame-retarding and barrier properties, with small amounts of clay. Preparation of polymer-clay nanocomposites, summarized as a process for uniform dispersion of hydrophilic layered clays in hydrophobic polymer matrixes, includes several technologies and scientific phenomena, such as surface-modifications of clay layers, physical properties of clays in liquids and dried states, polymer synthesis, polymer rheology, behaviors of polymer solutions/or monomers in the confined geometry, mechanical properties of polymers and clays. To comprehend complicated physical/chemical phenomena involved in the fabrication of nanocomposites, we reviewed physical properties of clays, structures of clays in nanocomposites, characterization of nanocomposites, the relation between morphology and physical property of nanocomposites, surveyed recent research trends, and then suggested a few strategies or methods for fabrication of nanocomposites reflecting future research directions.

• Journal of the Korean Chemical Society
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• v.36 no.3
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• pp.351-359
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• 1992

Interaction of xenon with alkaline-earth cations in Y zeolite supercage was studied by xenon adsorption and $^{129}Xe$ NMR experiments. The CaY and the BaY samples were prepared by exchanging $Ca^{2+}$ and $Ba^{2+}$ into a high-purity NaY zeolite. Xenon adsorption isotherms of these samples were obtained by using a conventional volummetric gas adsorption apparatus in the range of 260 to 320 K and the chemical shift in the $^{129}Xe$ NMR spectrum of the adsorbed xenon was measured at 296 K. The chemical shift against pressure was quantitatively explained assuming that the xenon gas exchanged very rapidly between various adsorption sites consisting of zeolite-framework surface and alkaline-earth ion. From this analysis, it was found that the alkaline-earth ion adsorbed xenon more strongly than $Na^+$ ion and zeolite-framework surface. Baring on the difference of the adsorption strength, the number of the alkaline-earth cations present in the zeolite supercage could be estimated by analyzing the adsorption isotherm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1153-1159
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• 2015

Recently, synthetic biopolymers and bioceramics such as poly (${\varepsilon}$-caprolactone)(PCL), hydroxyapatite, tricalcium phosphate, biphasic calcium phosphate(BCP), and zirconia have been used as substrates to generate various tissues or organs in tissue engineering. Thus, the purpose of this study was the characterization of $ZrO_2$/BCP/PCL(ZBP) scaffold for bone tissue regeneration. Based on the result of single-line test, blended 3D ZBP scaffolds with fully interconnected pores and new complex pore pattern of $45^{\circ}+135^{\circ}$-type and staggered-type were successfully fabricated using a polymer deposition system. Furthermore, the effect of ZBP scaffold on mechanical property was analyzed. In addition, in vitro cell interaction of ZBP scaffold on MG63 cells was evaluated using a cell counting kit-8(CCK-8) assay.

• Elastomers and Composites
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• v.48 no.1
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• pp.30-38
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• 2013

Polyolefin is one of the most important commodity polymers having excellent physical properties and cost competitiveness, which has continuously broadened their market in response to a heavy demand from industry. However, the lack of polarity in polyolefin has limited its applications, especially where interactions with other materials are important. In view of the above, the incorporation of polar functional groups in polyolefin has been widely attempted. Especially, the preparations of segmented modified polyolefin copolymers, such as block and graft copolymers have been extensively investigated, since the loss of the original properties of polyolefin can be minimized while the polar segments can endow interactions with other materials. Living radical polymerization (LRP) method can be one of the most attractive synthetic tools for the preparation of the modified polyolefin block or graft copolymers. In this review, progress on the preparation of the polyolefin based block or graft copolymers through LRP technique is briefly summarized.

• The Korean Journal of Zoology
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• v.22 no.2
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• pp.81-93
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• 1979

Metabolic changes of early mouse embryos treated with progesterone were investigated in order to elucidate the mode of action of progesterone on embryogenesis in vitro. The embryos were cultured, and labelled with radioactive precursors of macromolecules for certain periods in the absence or presence of various concentrations of progesterone by employing the microtube culture technique. The changes of transport and macromolecular synthesis systems of the embryos were examined by measuring the amounts of uptake and incorporation of the precursors. The results obtained were as follows: 1. Progesterone stimulated markedly the uptake of amino acids, but rather suppressed their incorporation by embryonic cells. 2. Progesterone suppressed both the uptake and incorporation of nucleotide precursors (uridine and thymidine) by embryonic cells. 3. Progesterone penetrated into the embryonic cell membranes and was taken up by them. The present results seem to indicate that the inhibition of the progesterone on the mammalian embryogenesis in vitro may not be directly related to the membrane transport system. They seem to imply that progesterone would penetrate into the embryonic cells and may directly block the biosynethetic pathways of macromolecules, and so lead to the inhibition of the embryogenesis in vitro.

• Food Science and Preservation
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• v.10 no.4
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• pp.574-583
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• 2003

There have been a lot of research efforts on development of active food packaging structures and materials in the form of plastic films and containers, along with investigating novel polymers and bioactive compounds for packaging purpose, in order to improve storage stability and safety of foods during distribution and sale. Recently, great interests focus on antimicrobial package films, as an active packaging system, made from synthetic plastic polymer% and natural biopolymers containing various antimicrobial substances for food packaging applications. In this active system, substances are slowly released onto the food surface. However, antimicrobial activity as well as physical properties of the films can be significantly influenced by several factors such as polymer matrix, antimicrobial compounds, and interactions between polymers and compounds. Thus, this study reviews present status of antimicrobial food packaging films in overall performance aspects including types of polymers and active substances, test for antimicrobial activity, and changes in mechanical and antimicrobial properties by preparation method.

• Journal of the Korean Chemical Society
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• v.40 no.4
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• pp.254-263
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• 1996

Five cobalt(Ⅲ) complexes were synthesized from bi- or tridentate nitrogen ligands. Catalytic actions of these complexes for hydrolyses of p-nitrophenyl picolinate, p-nitrophenyl nicotinate, and p-nitrophenyl isonicotinate were investigated by a spectrophotometric method. p-Nitrophenyl picolinate showed the most senstive reaction among three substrates by these catalysts. Aquohydroxo Co(Ⅲ) complexes raised as much as 21∼40 times the rate of hydrolysis of p-nitrophenyl picolinate at pH 6.5. Activities of complexes were in the order: Co(ibpn)(OH)2(OH2) > Co(aepn)(OH)2(OH2) > Co(tn)2(OH)(OH2) > Co (bpy)2(OH)(OH2) > Co(dien)(OH)2(OH2). Catalytic hydrolysis was postulated to proceed through a intramolecular general base catalysis path which is mixed by a partial intramolecular nucleophilic catalysis.