• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.386-386
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• 2012

For white light emitting diode (LED) applications, it has been reported that Y3Al5O12:Ce3+ (YAG:Ce) in nano-sized phosphor performs better than it does in micro-sized particles. This is because nano-sized YAG:Ce can reduce internal light scattering when coated onto a blue LED surface. Recently, there have been many reports on the synthesis of nano-sized YAG particles using bottom-up method, such as co-precipitation method, sol-gel process, hydrothermal method, solvothermal method, and glycothermal method. However, there has been no report using top-down method. Top-down method has advantages than bottom-up method, such as large scale production and easy control of doping concentration and particle size. Therefore, in this study, nano-sized YAG:Ce phosphors were synthesized by a high energy beads milling process with varying beads size, milling time and milling steps. The beads milling process was performed by Laboratory Mill MINICER with ZrO2 beads. The phase identity and morphology of nano-sized YAG:Ce were characterized by X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. By controlling beads size, milling time and milling steps, we synthesized a size-tunable and uniform nano-sized YAG:Ce phosphors which average diameters were 100, 85 and 40 nm, respectively. After milling, there was no impurity and all of the peaks were in good agreement with YAG (JCPDS No. 33-0040). Luminescence and quantum efficiency (QE) of nano-sized YAG:Ce phosphors were measured by fluorescence spectrometer and QE measuring instrument, respectively. The synthesized YAG:Ce absorbed light efficiently in the visible region of 400-500 nm, and showed single broadband emission peaked at 550 nm with 50% of QE. As a result, by considering above results, high energy beads milling process could be a facile and reproducible synthesis method for nano-sized YAG:Ce phosphors.

• Clean Technology
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• v.25 no.4
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• pp.283-288
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• 2019

Monodisperse microparticles has been particularly enabling for various applications in the encapsulation and delivery of pharmaceutical agents. The microfluidic devices are attractive candidates to produce highly uniform droplets that serve as templates to form monodisperse microparticles. The microfluidic devices that have micro-scale channel allow precise control of the balance between surface tension and viscous forces in two-phase flows. One of its essential abilities is to generate highly monodisperse droplets. In this paper, a microfluidic approach for preparing monodisperse polycaprolactone (PCL) microparticles is presented. The microfluidic devices that have a flow-focusing generator are manufactured by soft-lithography using polydimethylsiloxane (PDMS). The crucial factors in the droplet generation are the controllability of size and monodispersity of the microdroplets. For this, the volumetric flow rates of the dispersed phase of oil solution and the continuous phase of water to generate monodisperse droplets are optimized. As a result, the optimal flow condition for droplet dripping region that is able to generate uniform droplet is found. Furthermore, the droplets containing PCL polymer by solvent evaporation after collection of droplet from device is solidified to generate the microparticle. The particle size can be controlled by tuning the flow rate and the size of the microchannel. The monodispersity of the PCL particles is measured by a coefficient of variation (CV) below 5%.

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.985-989
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• 1999

Silica($SiO_2$) thin film was synthesized by a low pressure metal organic chemical vapor deposition(LPMOCVD) using organic silane compound. Triethyl orthosilicate was used as a source material. Operation pressure was 1~100 torr at outlet of the reactor and deposition temperature was $600{\sim}900^{\circ}C$. The experimental results showed that the high reaction temperature and high source gas concentration led to higher growth rate of $SiO_2$. The step coverage of films on micro-scale trenches was fairly good, which resulted from the phenomena that the condensed oligomers flow into the trenches. We estimated a reaction path that the source gas polymerizes and produces oligomers (dimer, trimer, tetramer, etc.), which diffuse and condense on the solid surface. The chemical species in the gas phase at the outlet of reactor tube were analyzed by quadrapole mass spectrometer. The peaks, assigned to be monomer, dimer of source gas and geavier molecules, were observed at 650 or $700^{\circ}C$. At higher temperature($900^{\circ}C$), the peaks of the heavy molecules disappeared, because almost all the source gas and intermediate(polymerized oligomer) molecules were oxidized or condensed on colder tube wall.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.3
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• pp.332-340
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• 2007

Storm runoff from road contains significant loads of particulate and dissolved solids, organic constituents and metal elements. Micro particle is important when considering pollution mitigation because pollutant metal and organics have similar behavior with particles. The objective of this research is to evaluate the hydrodynamic filter separator performance for road storm runoff treatment. A various types of media such as perlite, granular activated carbon, zeolite were used for column test packing media and filter separator, and to determine the removal efficiency with various surface loading rate. As the results of column test, the highest SS removal efficiency was using mixed media(granular activated carbon, zeolite and perlite), and granular activated carbon mixed with zeolite has higher heavy metal removal efficiency than perlite. In laboratory scale hydrodynamic filter separator study, the operation ranges of surface loading rates were from 192 to 1,469 $m^3/m^2/day$. The estimated overall removal efficiencies of hydrodynamic filter separator for typical storm runoff were SS 48.1%, BOD 31.9%, COD 32.6%, TN 15.5%, and TP 17.3%, respectively. For the case of heavy metals, overall removal efficiencies were Fe 26.0%, Cu 19.4%, Cr 25.7, Zn 16.6%, and Pb 15.0%, respectively. The most appropriate medium for hydrodynamic filter separator was perlite mixed with granular activated carbon to treatment of road storm runoff.

• Journal of Life Science
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• v.15 no.5 s.72
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• pp.696-702
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• 2005

Ozonation is a disinfection technique of harmful mi-crobes commonly used in the treatment of drinking water. And Biological Activated Carbon (BAC) treatment also provides numerous benefits for drinking water utilities, including removal of micro- pollutants, improved treatment processes. The multiful-stage ozonation and BAC play roles as effective methods for removing several materials in raw water. Water quality variation in Nak dong river and the removal efficiency of viruses by ozonation-BAC process were investigated on pilot scale. During the period of survey, most of water quality parameters including $NH_{4}^{+}-N$ were highly improved after passing through the BAC. The removal efficiency of poliovirus type III in water treatment process using pilot-plant,$ 99.6\% $ of viruses were removed by pre-ozonation, sedimentation and sand filteration process, $ 100\% $ were removed after in BAC filteration step. In the removal survey of viruses by ozonation, ap-proximately $ 61.1\% $ or polioviruses were inactivated by ozone of 0.4 mg/l within 5 min. and $ 100\% $ were inactivated by ozone of 0.8 mg/l over 10 min.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.259-264
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• 2002

In this study, sintering properties of Artificial Lightweight aggregates(ALAs) prepared from coal ash as a function of sintering temperature (900$^{\circ}$C, 1000$^{\circ}$C, 1100$^{\circ}$C) and time (2min, 5min, 10min) when limestone added as lightweight mineral was investigated. Increasing the sintering temperature resulted simultaneously from a decline of quartz mineral as well as growth of mullite mineral. Addition of limestone to ALAs newly formed sintered minerals such as clinoptilolite and plagioclase. Sintering effect of ALAs prepared from coal ash and limestone was more affected by a sintering temperature than time. As sintering temperature and time increae, transition of macropore to micropore and formation of closed pores were happened, consequently shrank the total pore volume of ALAs. The surface of ALAs sintered at 1000$^{\circ}$C for 5min was nearly not detected open pores due toe amalgamation effect of molten slag layer but homogeneous distributions of closed pores with micro-scale were examined in cross sectional area ALAs. Sintering temperature and time which present the most adequate state, in the preparation of ALAs, are corresponded to 1000$^{\circ}$C and 5min, respectively.

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 2004.06a
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• pp.60-61
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• 2004

Metabolic engineering is now a well established discipline, used extensively to determine and execute rational strategies of strain development to improve the performance of micro-organisms employed in industrial fermentations. The basic principle of this approach is that performance of the microbial catalyst should be adequately characterised metabolically so as to clearlyidentify the metabolic network constraints, thereby identifying the most probable targets for genetic engineering and the extent to which improvements can be realistically achieved. In order to harness correctly this potential, it is clear that the physiological analysis of each strain studied needs to be undertaken under conditions as close as possible to the physico-chemical environment in which the strain evolves within the full-scale process. Furthermore, this analysis needs to be undertaken throughoutthe entire fermentation so as to take into account the changing environment in an essentially dynamic situation in which metabolic stress is accentuated by the microbial activity itself, leading to increasingly important stress response at a metabolic level. All too often these industrial fermentation constraints are overlooked, leading to identification of targets whose validity within the industrial context is at best limited. Thus the conceptual error is linked to experimental design rather than inadequate methodology. New tools are becoming available which open up new possibilities in metabolic engineering and the characterisation of complex metabolic networks. Traditionally metabolic analysis was targeted towards pre-identified genes and their corresponding enzymatic activities within pre-selected metabolic pathways. Those pathways not included at the onset were intrinsically removed from the network giving a fundamentally localised vision of pathway functionality. New tools from genome research extend this reductive approach so as to include the global characteristics of a given biological model which can now be seen as an integrated functional unit rather than a specific sub-group of biochemical reactions, thereby facilitating the resolution of complexnetworks whose exact composition cannot be estimated at the onset. This global overview of whole cell physiology enables new targets to be identified which would classically not have been suspected previously. Of course, as with all powerful analytical tools, post-genomic technology must be used carefully so as to avoid expensive errors. This is not always the case and the data obtained need to be examined carefully to avoid embarking on the study of artefacts due to poor understanding of cell biology. These basic developments and the underlying concepts will be illustrated with examples from the author's laboratory concerning the industrial production of commodity chemicals using a number of industrially important bacteria. The different levels of possibleinvestigation and the extent to which the data can be extrapolated will be highlighted together with the extent to which realistic yield targets can be attained. Genetic engineering strategies and the performance of the resulting strains will be examined within the context of the prevailing experimental conditions encountered in the industrial fermentor. Examples used will include the production of amino acids, vitamins and polysaccharides. In each case metabolic constraints can be identified and the extent to which performance can be enhanced predicted

• Tunnel and Underground Space
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• v.26 no.2
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• pp.59-67
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• 2016

In this paper, we perform a numerical analysis to evaluate the potential of fault reactivation during gas production from hydrate bearing sediments and the moment magnitude of induced seismicity. For the numerical analysis, sequential coupling of TOUGH+Hydrate and FLAC3D was used and the change in effective stress and consequent geomechanical deformation including fault reactivation was simulated by assuming that Mohr-Coulomb shear resistance criterion is valid. From the test production simulation of 30 days, we showed that pore pressure reduction as well as effective stress change hardly induces the fault reactivation in the vicinity of a production well. We also investigated the influence of stress state conditions to a fault reactivation, and showed that normal fault stress regime, where vertical stress is relatively greater than horizontal, may have the largest potential for the reactivation. We tested one simulation that earthquake can be induced during gas production and calculated the moment magnitude of the seismicity. Our calculation presented that all the magnitudes from the calculation were negative values, which indicates that induced earthquakes can be grouped into micro-seismic and as small as hardly perceived by human beings. However, it should be noted that the current simulation was carried out using the highly simplified geometric model and assumptions such that the further simulations for a scheduled test production and commercial scale production considering complex geometric conditions may produce different results.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.2169-2175
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• 2009

This research aims to evaluate the concept of eco-efficient water infrastructure and provides a list of case studies in order to help understand the applicability of eco-efficient water infrastructure to Asia and the Pacific. A set of indicators have been explored to assess eco-efficiency in water infrastructure for the region on a micro and macro scale. The core idea of eco-efficiency, 'more value with less impact (on the environment)', has proven to be applicable in management of water infrastructure. The fundamental elements in eco-efficient water infrastructure should encompass physical infrastructure and non-physical infrastructure, which is more needed particularly in Asian countries. The case studies have demonstrated the applicability of the concept of eco-efficient water infrastructure. The Republic of Korea has provided the case of the eco-friendly approaches to enhance dam management and its innovative solutions how to use water more efficiently through state-of-art technologies. The experiences of Singapore are some of the best evidence to establish eco-efficient water infrastructure, for instance, the NEWater project via application of cutting edge technologies (recycled water) and institutional reform in water tariff systems to conserve water as well as enhance water quality. A list of indicators to assess eco-efficiency in water infrastructure have been discussed, and the research presents a myriad of project cases which are good to represent eco-efficiency in water infrastructure, including multipurpose small dams, customized flood defense systems, eco-efficient ground water use, and eco-efficient desalination plants. The study has presented numerous indicators in five different categories: 1) the status of water availability and infrastructure; 2) production and consumption patterns of freshwater; 3) agricultural products and sources of environmental loads; 4) damages from water-caused natural disaster; and 5) urban water supply and sanitation. There are challenges as well as benefits in such indicators, since the indicators should be applied very carefully in accordance with specific socio-economic, political and policy contexts in different countries in Asia and the Pacific Region. The key to success of establishment of eco-efficient water infrastructure in Asia primarily depends on the extent to which each country is committed to balancing its development of physical as well as non-physical water infrastructure. Particularly, it is imperative for Asian countries to transform its policy focus from physical infrastructure to non-physical infrastructure. Such shift will help lead to implementation of sustainable in Asian countries.

• Journal of the Korean Professional Engineers Association
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• v.16 no.1
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• pp.20-34
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• 1983

A phenomenon in the unplanned urban sprawl of Cheong-ju city has to be rest-rained from disposing and to develop, though progress in urbanization inevitably decreases rural area. So, this thesis aims at reviewing, revising and guiding toward the more effective land use planning practice and zoning mechanism and system of Cheong-ju city. I proposed that land use planning should be had several factors and thereupon that Korean zoning mechanism and system including Building Code should be amended because of inducing human activities in buildings and facilities not to demarcate and plan every one of them. First, the factors of urban planning are a rather diversified approach to it than a unified, supplementation of the applicable difference in time between preparing and appling it, a solid controlling system, a micro and macro planning theory and giving serious consideration for the inertia from the existing land use. Second, the applicable amendments for our zoning mechanism including Eluding Code are as follows; a need of reorganization for Zoning Ordinance appricated to different regulation concerning a scale and peculiarity of a oily, a decision of the different earmarked confinement in area to different zone ana from Zoning Ordinance in City Planning Law, a demarcated facilities and the more detailed land use concerning human activies than the exsisting and entrusting decision on the ways and processes of it to every rural city planning committee, a settlement of zone ana area considering for block-unit and Planned Unit Development(P. U. D.), and a need of security jurisprudence in order to solve the zoning regulation rather in City Planning Law than in Building Code that our zoning regulation and controlling system are depended on. According to these applicable amendments to Cheong-ju city, I proposed the conceptions of Cheong-ju city land use planning are as follows; a reinforcement with one cored pattern of urban land use, a selection of gradual urban sprawl by way of city development and renewal, a strengthening accessibility to the core of the city with Plurizing the system of arterial roads, a choice of priority to conservation at the core of tile city and security of open spaces and parking area at the area of the city, a harmonization between development and conservation at the inner ring area that is situated between the core and periphery reserved area in order to develop in the future, a buffered open space situated at the congested area with heterogenous functions, and a completion of urban open space system. The proposal made here so far is for the hope of the better structure of Cheong-ju city that should be granted to the peculiarity developed with educational, cultural, conservative and self-sufficient city functions.