• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.262-270
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• 2004

Basic experiments were carried out using the THT-IV low-power Hall thruster to examine the influences of magnetic field shape and strength, and acceleration channel length on thruster performance and to establish guidelines for design of high-performance Hall thrusters. Thrusts were measured with varying magnetic field and channel structure. Exhaust plasma diagnostic measurement was also made to evaluate plume divergent angles and voltage utilization efficiencies. Ion current spatial profiles were measured with a Faraday cup, and ion energy distribution functions were estimated from data with a retarding potential analyzer. The thruster was stably operated with a highest performance under an optimum acceleration channel length of 20 mm and an optimum magnetic field with a maximum strength of about 150 Gauss near the channel exit and with some shape considering ion acceleration directions. Accordingly, an optimum magnetic field and channel structure is considered to exist under an operational condition, related to inner physical phenomena of plasma production, ion acceleration and exhaust plasma feature. A new Hall thruster was designed with basic research data of the THT-IV thruster. With the thruster with many considerations, long stable operations were achieved. In all experiments at 200-400 V with 1.5-3 mg/s, the thrust and the specific impulse ranged from 15 to 70 mN and from 1100 to 2300 see, respectively, in a low electric power range of 300~1300 W. The thrust efficiency reached 55 %. Hence, a large map of the thruster performance was successfully made. The thermal characteristics were also examined with data of both measured and calculated temperatures in the thruster body. Thermally safe conditions were achieved with all input powers.

• Journal of the Korean Electrochemical Society
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• v.16 no.3
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• pp.157-161
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• 2013

Porous $LiMn_{0.6}Fe_{0.4}PO_4$ (LMFP) was synthesized by a sol-gel process. Uniform dispersion of the conductive carbon source throughout LMFP with uniform carbon coating was achieved by heating a stoichiometric mixture of raw materials at $600^{\circ}C$ for 10 h. The crystal structure of LMFP was investigated by Rietveld refinement. The surface structure and pore properties were investigated by SEM, TEM and BET. The LMFP so obtained has a high specific surface area with a uniform, porous, and web-like nano-sized carbon layer at the surface. The initial discharge capacity and energy density were 152 mAh/g and 570 Wh/kg, respectively, at 0.1 C current density, and showed stable cycle performance. The combined effect of high porosity and uniform carbon coating leads to fast lithium ion diffusion and enhanced electrochemical performance.

• Journal of Information Technology Services
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• v.15 no.4
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• pp.63-72
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• 2016

Critical infrastructure has been operating in a closed environment with a completely separate information system and in the private area. However, with the current ICT environment changes due to convergence and open platforms it has increased the threats and risks to critical infrastructure. The importance of cyber security is increasing in the infrastructure control system, such as the outbreak of Ukraine blackout in 2015 by a malicious code called 'black energy'. This thesis aims to recognize the importance and necessity of protecting the critical infrastructure service, designing a security framework reflecting environmental and characteristic changes, and analyzing the management system suitable for a security framework. We also propose a theoretical basis for constructing a new security framework by comparing and analyzing seven international security management system standards, such as NIST 800-82 and IEC 62443-2-1, which are used in the control system. As a result, the environment surrounding critical infrastructure changes with the characteristics of connectivity, openness, and finality was studied, and as a response to this, many scholars and institutions present critical infrastructure security frameworks as cycle enhancement type structures, risk management structures, and management domain expansion structures. In response, the security framework encompassing these structures, CISF (Critical Infrastructure Security Framework), was designed. Additionally, through the security related international standard and criterion analysis, as a newly designed security standard suitable for CISF, IEC 62443-2-1 is reviewed and suggestions are made.

• Electrical & Electronic Materials
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• v.9 no.1
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• pp.30-37
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• 1996

Previously, crystallization of a-Si:H films on glass substrates were limited to anneal temperature below 600.deg. C, over 10 hours to avoid glass shrinkage. Our study indicates that the crystallization is strongly influenced by anneal temperature and weakly affected by anneal duration time. Because of the high temperature process and nonconducting substrate requirements for poly-Si TFTs, the employed substrates were limited to quartz, sapphire, and oxidized Si wafer. We report on poly-Si TFT's using high temperature anneal on a Si:H/Mo structures. The metal Mo substrate was stable enough to allow 1000.deg. C anneal. A novel TFT fabrication was achieved by using part of the Mo substrate as drain and source ohmic contact electrode. The as-grown a-Si:H TFT was compared to anneal treated poly-Si TFT'S. Defect induced trap states of TFT's were examined using the thermally stimulated current (TSC) method. In some case, the poly-Si grain boundaries were passivated by hydrogen. A-SI:H and poly-Si TFT characteristics were investigated using an inverted staggered type TFT. The poly -Si films were achieved by various anneal techniques; isothermal, RTA, and excimer laser anneal. The TFT on as grown a-Si:H exhibited a low field effect mobility, transconductance, and high gate threshold voltage. Some films were annealed at temperatures from 200 to >$1000^{\circ}C$ The TFT on poly-Si showed an improved $I_on$$I_off$ ratio of $10_6$, reduced gate threshold voltage, and increased field effect mobility by three orders. Inverter operation was examined to verify logic circuit application using the poly Si TFTs.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.11a
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• pp.1-2
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• 2000

In chip plating, several parameters must be taken into consideration. Current density, solution concentration, pH, solution temperature, components volume, chip and media ratio, barrel geometrical shape were most likely found to have an effect to the process yields. The 3 types of barrels utilized in chip plating industry are the onventional rotating barrel, vibrational barrel(vibarrel), and the centrifugal type. Conventional rotating barrel is a close type and is commonly used. The components inside the barrel are circulated by the barrel's rotation at a horizontal axis. Process yield has known to have higher thickness deviation. The vibrational barrel is an open type which offers a wide exposure to electrolyte resulting to a stable thickness deviation. It rotates in a vertical axis coupled with multi-vibration action to facilitate mixed up and easy transportation of components. The centrifugal barrel has its plated work centrifugally compacted against the cathode ring for superior electrical contact with simultaneous rotary motion. This experiment has determined the effect of barrel vibration intensity to the plating thickness distribution. The procedures carried out in the experiment involved the overall plating process., cleaning, rinse, Nickel plating, Tin-Lead plating. Plating time was adjusted to meet the required specification. All other parameters were maintained constant. Two trials were performed to confirm the consistency of the result. The thickness data of the experiment conducted showed thatbthe average mean value obtained from higher vibrational intensity is nearer to the standard mean. The distribution curve shown has a narrower specification limits and it has a reduced variation around the target value. Generally, intensity control in vi-barrel facilitates mixed up and easy transportation of components. However, it is desirable to maintain an optimum vibration intensity to prevent solution intrusion into the chips' internal electrode. A cathodic reaction can occur in the interface of the external and internal electrode. 2H20 + e $\rightarrow$M/TEX> 20H + H2.. Hydrogen can penetrate into the body and create pressure which can cause cracks. At high intensity, the chip's motion becomes stronger, its contact between each other is delayed and so plating action is being controlled. However, the strong impact created by its collision can damage the external electrode's structure there by resulting to bad plating condition.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1532-1534
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• 2003

We attempted to fabricate a dendrimer Langmuir-Blodgett(LB) films containing 48 pyridinepropanol functional end group. As the pyridinepropanol functional group could form a complex structure with metal ions. In this study the samples for electrical measurement were fabricated to two types metal complexes with $Pt^{4+}$ ions by LB method. And we have investigated the surface activity at the air-water interface as well as the electrical properties for the monolayers of G4-48PyP dendrimer complex with metal ions($Pt^{4+}$ ions) by different method. In the surface pressure-area(${\pi}$-A) isotherms of the dendrimers, the stable condensed films formed at the air-water interface and the different method of metal complex showed the difference on molecular behavior. We have studied the electrical properties of the ultra thin dendrimer LB films investigated by the current-voltage (I-V) characteristics of metal/dendrimer LB films/metal(MIM) structure. In conclusion, it is demonstrated that the metal ion around G4-48PyP dendrimer can contribute to make formation of network structure among dendrimers and it result from the change of electrical properties.

• Journal of Conservation Science
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• v.6 no.2 s.8
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• pp.141-148
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• 1997

When we have entered high economic growth since 1970s, many archaeological excavations were performed all over the country. Excavated objects composed of variable materials are inevitably subjected to deformations owing to surrounding environments and storage conditions. Although the importance of conservation treatment of the objects is greatly increased, a few conservation laboratories are there comparing with excavation groups. The metallic objects excavated are very unstable and deformable state. So it is important not to allow iron objects, especially cast iron, to dry out once excavated. Because the corrosion reactions on the surface proceed rapidly, the objects may be destroyed at the moment. The conservation procedures of the excavated metallic objects are as follows: (1)It is stable on-site storage method for objects to keep vinyl film with envelop or to immerse alkaline solution to prevent the environmental changes. (2)The objects must be treated at once under suitable methods in the conservation laboratory after excavation. (3)The continued existence of objects depends on environmental factors such as relative humidities, regular inspection, light etc.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.3
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• pp.130-141
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• 2009

The spatial range of EIA is mainly related to landscape ecological factors such as topography, geology, animals, and plants. Problems were detected involved land, soil, noise, oscillation, the atmosphere, animals, and plants in the natural-environment. First of all, the current EIA lacks explicit spatial ranges and sections in terms of scientific exactitude and objectivity for assessment. Secondly, there are overlapping influence-area problems resulting in cumulative impacts of unit developments that accumulate. Finally, some developments have no regard for ecological and conservational value in relation to determining which effect ecological stability, and which should be regarded as Regional Ecological Resources. Therefore, this study suggests that EIA should be improved in the following manner. First, the standard classification of landscape unit for analysis should be established 10 regulate each spatial range on a wide-landscape scale. Secondly, the impacts resulting from the interaction of overlapping influence-area developments between individual development should be assessed. Third, Minimization of the of the environmental effects is needed by applying the cumulative effects to the influence-area where developments occur in the same time or in a sequence. Fourth, individual characteristics of landscape elements such as roads, rivers, and green networks need to be considered separately in the analysis. Finally, regional ecological habitats should be included in the analysis in order to achieve stable ecosystems.

• Journal of Microbiology and Biotechnology
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• v.11 no.5
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• pp.763-771
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• 2001

Biphenyl dioxygenase (BPDO), which catalyzes the first step in the bacterial degradation of biphenyl and polychlorinated biphenyls, was characterized in Pseudomonas sp. B4. The bphA locus containing the four structural genes encoding BPDO were cloned and sequenced. A regulatory gene as well as a putative regulatory sequence were identified upstream of this locus. A transposase-like gene was found within a 1-kb region further upstream, thereby suggesting that the bphA locus may be carried on a transposable element. The three components of the BPDO enzyme have been separately overexpressed and purified from E. coli. The ferredoxin and terminal dioxygenase components showed biochemical properties comparable to those of two previously characterized BPDOs, whereas the ferredoxin reductase exhibited an unusually high lability. The substrate selectivity of BPDO was examined in vivo using resting cell assays performed with mixtures of selected polychlorinated biphenyls. The results indicated that para-substituted congeners were the preferred substrates. In vitro studies were carried out on a BPDO complex where the reductase from strain B4 we replaced by the more stable isoform from Comamonas testosteroni B-356. The BPDO enzyme had a specific activity of $0.26{\pm}0.02 {\mu}mol {min^-1}{mg^-1}\;of\;ISP_{BPH}$ with biphenyl as the substrate. The 2,3-, 4,4'-, and 2,4,4'-chlorobiphenyls were converted to single dihydrodiols, while 2,4'-dichlorobiphenyl gave rise to two dihydrodiols. The current data also indicated that 2,4,4'-trichlorobiphenyl was a better substrate than the 4,4'-dichlorinated congener.

• Journal of the Society of Disaster Information
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• v.15 no.4
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• pp.514-523
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• 2019

Purpose: This study was designed to provide necessary institutional improvements for job security for foreign workers in the domestic construction sector. Method: I analyzed the National Statistical Office and related reports to investigate the status of foreign workers. Based on this, the government came up with measures to improve the system. Results: Based on the current comparative advantage index (RCA) analysis, the technology standard of foreign workers compared to Korean workers was evaluated, and the results were analyzed in order of moldwork, rebar, concrete work, stone work, and waterproof work. Conclusion: A foreign worker's work system was introduced to solve the problem of local Lunar New Year's Day field manpower. To ensure stable implementation of the system, there is a need to improve the operation of the employment permit system at construction sites and limit the size of the construction industry that introduces the employment permit system.