• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.63-69
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• 2011

In this study, we report on the novel lithographic patterning method to fabricate organic thin film field effect transistors (OTFTs) based on photo and e-beam lithography with well-known silicon technology. The method is applied to fabricate pentacene-based organic field effect transistors. Owing to their solubility, sub-micron sized patterning of P3HT and PEDOT has been well established via micromolding in capillaries and inkjet printing techniques. Since the thermally deposited pentacene cannot be dissolved in solvents, other approach was done to fabricate pentacene FETs with a very short channel length (~30 nm), or in-plane orientation of pentacene molecules by using nanometer-scale periodic groove patterns as an alignment layer for high-performance pentacene devices. Here, we introduce $Al_2O_3$ film grown via atomic layer deposition method onto pentacene as a passivation layer. $Al_2O_3$ passivation layer on OTFTs has some advantages in preventing the penetration of water and oxygen and obtaining the long-term stability of electrical properties. AZ5214 and ma N-2402 were used as a photo and e-beam resist, respectively. A few micrometer sized lithography patterns were transferred by wet and dry etching processes. Finally, we fabricated micron sized pentacene FETs and measured their electrical characteristics.

• Journal of Korean Society for Geospatial Information Science
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• v.24 no.1
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• pp.9-16
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• 2016

As the need of eco-friendly transportation systems for sustainable development increases, public transport accessibility has been considered as an important element of transportation system design. When analyzing the accessibility, shortest path algorithms can be utilized to reflect the actual movement and we can obtain high resolution accessibility for all other stations on the network with shortest distance and time. This study used the algorithm improved by reflecting the penalty of number of transfers and waiting time of overlapped routes to get the accessibility. KTX Seoul Station is a target place and this algorithm is applied to multi-layer subway bus network of Seoul to calculate the accessibility, therefore this study presented the accessibility of KTX Seoul station by stations.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.595-609
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• 2017

Due to high in-situ stress and brittleness of rock mass, the surrounding rock masses of underground caverns are prone to appear splitting failure. In this paper, a kind of loading-unloading variable elastic modulus model has been initially proposed and developed based on energy dissipation principle, and the stress state of elements has been determined by a splitting failure criterion. Then the underground caverns of Dagangshan hydropower station is analyzed using the above model. For comparing with the monitoring results, the entire process of rock splitting failure has been achieved through monitoring the splitting failure on side walls of large-scale caverns in Dagangshan via borehole TV, micro-meter and deformation resistivity instrument. It shows that the maximum depth of splitting area in the downstream sidewall of the main power house is approximately 14 m, which is close to the numerical results, about 12.5 m based on the energy dissipation model. As monitoring result, the calculation indicates that the key point displacement of caverns decreases firstly with the distance from main powerhouse downstream side wall rising, and then increases, because this area gets close to the side wall of main transformer house and another smaller splitting zone formed here. Therefore it is concluded that the energy dissipation model can preferably present deformation and fracture zones in engineering, and be very useful for similar projects.

• Journal of Powder Materials
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• v.18 no.2
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• pp.122-128
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• 2011

This study investigated the high temperature oxidation behavior of Ni-22.4%Fe-22%Cr-6%Al (wt.%) porous metal. Two types of open porous metals with different pore sizes of 30 PPI and 40 PPI (pore per inch) were used. A 24-hour TGA test was conducted at three different temperatures of $900^{\circ}C$, $1000^{\circ}C$ and $1100^{\circ}C$. The results of the BET analysis revealed that the specific surface area increased as the pore size decreased from 30 PPI to 40 PPI. The oxidation resistance of porous metal decreased with decreasing pore size. As the temperature increased, the oxidation weight gain of the porous metal also increased. Porous metals mainly created oxides such as $Al_2O_3$, $Cr_2O_3$, $NiAl_2O_4$, and $NiCr_2O_4$. In the 40 PPI porous metal with small pore size and larger specific surface area, the depletion of stabilizing elements such as Al and Cr occurred more quickly during oxidation compared to the 30 PPI porous metal. Ni-Fe-Cr-Al porous metal's high-temperature oxidation micro-mechanism was also discussed.

• Journal of Korean Neurosurgical Society
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• v.42 no.4
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• pp.281-285
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• 2007

Objective : Distal anterior cerebral artery (DACA) aneurysms are fragile and known to have high risks for intraoperative premature rupture and a relatively high associated morbidity. To improve surgical outcomes of DACA aneurysms, we reviewed our surgical strategy and its results postoperatively. Methods : A total of 845 patients with ruptured cerebral aneurysms were operated in our hospital from January 1991 to December 2005. Twenty-three of 845 patients had ruptured DACA aneurysms which were operated on according to our surgical strategy. Our surgical strategy was as follows; early surgery, appropriate releasing of CSF, appropriate surgical approach, using neuronavigating system, securing the bridging veins, using temporary clipping and/or tentative clipping, meticulous manipulation of aneurysm, and using micro-Doppler flow probe. Twenty of 23 patients who had complete medical records were studied retrospectively. We observed the postoperative radiographic findings and checked Glasgow Outcome Scale score sixth months after the operation. Results : Nineteen DACA aneurysms were clipped through a unilateral interhemispheric approach and one DACA aneurysm was clipped through a pterional approach. Postoperative radiographic findings revealed complete clipping of aneurysmal neck without stenosis or occlusion of parent arteries. In two patients, a residual neck of aneurysm was visualized. Seventeen patients showed good recovery, one patient resulted in moderate disability, while 2 patients died. Conclusion : With our surgical strategy it was possible to achieve acceptable surgical morbidity and mortality rates in patients with DACA aneurysms. Appropriate use of tentative clipping, temporary clipping and neuro-navigating systems can give great help for safe approach and clipping of DACA aneurysm.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.2
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• pp.104-113
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• 2012

Crab-like flavorants (CFs) were made from snow crab cooker effluent (SCCE) using response surface methodology (RSM) and reaction flavoring technology (RFT). Type A CF was made from SCCE via RSM, RFT, adding starch syrup, centrifugation, and microfiltration. Type B was made from type A by adding the food additives dimethyl sulfide, ethyl valerate and fish sauce. The stability of the CFs was evaluated in terms of the color values, sensory evaluation, and flavor profiles after storage for 90 days at three different temperatures: 10, 20, and $30^{\circ}C$. The compounds, ethanol and 3-methyl-1-butanol, were considered key components of off-flavor and a decrease in dimethyl-2-vinylpyrazine affected the occurrence of off-flavor. It may be a microbial metabolite arising from contamination and lab-scale micro-filtration. At the lowest temperature ($10^{\circ}C$), the decrease in volatile compounds, such as pyrazines, was not as dramatic as at $20^{\circ}C$ and $30^{\circ}C$ and alcohol formation was prevented or delayed. Therefore, it is necessary to store CFs at < $10^{\circ}C$ with suitable sterilization to preserve volatile flavor compounds and prevent off-flavor from occurring.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.3.1-3.1
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• 2011

Over the past decade, the major efforts for lowering the cost of electronics has been devoted to increasing the packaging efficiency of the integrated circuits (ICs), which is defined by the ratio of all devices on system-level board compared to the area of the board, and to working on a larger but cheaper substrates. Especially, in flexible electronics, the latter has been the favorable way along with using novel nanomaterials that have excellent mechanical flexibility and electrical properties as active channel materials and conductive films. Here, the tool for achieving large area patterning is by printing methods. Although diverse printing methods have been investigated to produce highly-aligned structures of the nanomaterials with desired patterns, many require laborious processes that need to be further optimized for practical applications, showing a clear limit to the design of the nanomaterial patterns in a large scale assembly. Here, we demonstrate the alignment of highly ordered and dense silicon (Si) NW arrays to anisotropically etched micro-engraved structures using a simple evaporation process. During evaporation, entropic attraction combined with the internal flow of the NW solution induced the alignment of NWs at the corners of pre-defined structures. The assembly characteristics of the NWs were highly dependent on the polarity of the NW solutions. After complete evaporation, the aligned NW arrays were subsequently transferred onto a flexible substrate with 95% selectivity using a direct gravure printing technique. As proof-of-concept, flexible back-gated NW field effect transistors (FETs) were fabricated. The fabricated FETs had an effective hole mobility of 0.17 $cm2/V{\cdot}s$ and an on/off ratio of ${\sim}1.4{\times}104$. These results demonstrate that our NW gravure printing technique is a simple and effective method that can be used to fabricate high-performance flexible electronics based on inorganic materials.

• Transactions of Materials Processing
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• v.29 no.2
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• pp.103-112
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• 2020

This study explores the effects of different pre-machining conditions on the deposition characteristics and mechanical properties of austenitic stainless steel samples repaired using direct energy deposition (DED). In the DED repair process, defects such as pores and cracks can occur at the interface between the substrate and deposited material. In this study, we varied the shape of the pre-machined zone for repair in order to prevent cracks from occurring at the slope surface. After repairs by the DED process, macro-scale cracks were observed in samples that had been pre-machined with elliptic and trapezoidal grooves. In addition, it was not possible to completely prevent micro-crack generation on the sloped interfaces, even in the capsule-type grooved sample. From observation of the fracture surfaces, it was found that the cracks around the inclined interface were due to a lack of fusion between the substrate and the powder material, which led to low tensile properties. The specimen with the capsule-type groove provided the highest tensile strength and elongation (respective of 46% and 571% compared to the trapezoidal grooved specimen). However, the tensile properties were degraded compared to the non-repaired specimen (as-hot rolled material). The fracture characteristics of the repaired specimens were determined by the cracks at the sloped interfaces. These cracks grew and coalesced with each other to form macro-cracks, they then coalesced with other cracks and propagated to the substrate, causing final fracture.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.53-58
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• 2002

Electrical insulation and mechanical properties of the plasma sprayed oxide ceramic coatings were studied before and after the sealing treatment of the ceramic coatings. Plasma sprayed A1$_2$O$_3$-TiO$_2$ coating as the reference coating was sealed using three commercial sealants based on polymer. Penetration depth of the sealants to the ceramic coating was evaluated directly from the optical microscope using a fluorescent dye. It is estimated that the penetration depth of the sealants to the ceramic coating is from 0.2 to 0.5 mm depending on the sealants used. The preliminary test results with a DC puncture tester imply that the dielectric breakdown voltage mechanism of plasma sprayed ceramic coatings has been determined to be a corona mechanism. Dielectric breakdown voltage of the as-sprayed and as-ground samples have shown a linear trend with regard to the thickness showing an average dielectric strength of 20 kV/mm for the thickness scale studied. It is also shown that grinding the coating before sealing and adding fluorescent dye do not agent the penetration depth of sealants. All of the microhardness, two-body abrasive wear resistance, bond strength, and surface roughness of the ceramic coating after the sealing treatment are improved. The extent of improvement is different from the sealants used. However, three-point bending stress of the ceramic coating after the sealing treatment is decreased. This is attributed to the reduced micro-crack toughening effect since the cracks propagate easily through the lamellar of the coating without crack deflection and/or branching after the sealing treatment.

• Journal of Wetlands Research
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• v.19 no.4
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• pp.501-507
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• 2017

The heavy metal such as Nikel (Ni) in industrial wastewater is one of the major reasons of decreasing nitrification efficiency in municipal wastewater treatment plants (MWTPs). In this study, laboratory scale reactors were operated in order to analyse of nitrification efficiency and improvement measures. As a result, nitrification efficiency during high Ni concentration (0.295 mg/L) was about 20%. However nitrification efficiency during low Ni concentration (0.114 mg/L) was over 70%. The changes of the micro-organism activity according to Ni concentration was investigated as being the major reason behind the gap of nitrification efficiency through analysing AUR and SNR. Increasing the HRT in high Ni concentration also increased the nitrification efficiency. Thus, maintenance of microorganisms and increasing the HRT in nitrification reactors suggests that measures taken to treat wastewater is positively correlated with high concentration of heavy metal.