• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1193-1199
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• 2012

A cup burner experiment was performed to investigate the effect of the oxidizer velocity and concentration on flame instability near extinction. Heptane was used as a fuel and air diluted by nitrogen and carbon dioxide was used in the oxidizer stream. Two types of flame instabilities at the flame base and at axial downstream were observed near extinction. The instability at the flame base could be characterized by cell, swing, and rotation modes, and the cell mode changed to the rotation mode through the swing mode as the oxidizer velocity increased. To assess the parameters for the flame instability, the initial mixture strengths, Lewis number, and adiabatic flame temperature were investigated under each condition. The Lewis number might be the most important among them, but it is impossible to generalize because of the insufficient number of cases. Furthermore, the axial periodic flickering motion disappeared at low and high oxidizer velocities near extinction. This resulted from the fact that low oxidizer velocity induced evaporated fuel velocity below the critical velocity and high velocity made the reacting fuel velocity comparable.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.176-176
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• 2010

One of the critical issues for applications of flexible organic thin film transistors (OTFTs) for flexible electronic systems is the electrical stabilities of the OTFT devices, including variation of the current on/off ratio (Ion/Ioff), leakage current, threshold voltage, and hysteresis under repetitive mechanical deformation. In particular, repetitive mechanical deformation accelerates the degradation of device performance at the ambient environment. In this work, electrical stability of the pentacene organic thin film transistors (OTFTs) employing multi-stack hybrid encapsulation layers was investigated under mechanical cyclic bending. Flexible bottom-gated pentacene-based OTFTs fabricated on flexible polyimide substrate with poly-4-vinyl phenol (PVP) dielectric as a gate dielectric were encapsulated by the plasma-deposited organic layer and atomic-layer-deposited inorganic layer. For cyclic bending experiment of flexible OTFTs, the devices were cyclically bent up to 105 times with 5mm bending radius. In the most of the devices after 105 times of bending cycles, the off-current of the OTFT with no encapsulation layers was quickly increased due to increases in the conductivity of the pentacene caused by doping effects from $O_2$ and $H_2O$ in the atmosphere, which leads to decrease in the Ion/Ioff and increase in the hysteresis. With encapsulation layers, however, the electrical stabilities of the OTFTs were improved significantly. In particular, the OTFTs with multi-stack hybrid encapsulation layer showed the best electrical stabilities up to the bending cycles of $10^5$ times compared to the devices with single organic encapsulation layer. Changes in electrical properties of cyclically bent OTFTs with encapsulation layers will be discussed in detail.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.237.1-237.1
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• 2014

Etching is one of the most important steps in semiconductor manufacturing. In etch process control a critical task is to stop the etch process when the layer to be etched has been removed. If the etch process is allowed to continue beyond this time, the material gets over-etched and the lower layer is partially removed. On the other hand if the etch process is stopped too early, part of the layer to be etched still remains, called under-etched. Endpoint detection (EPD) is used to detect the most accurate time to stop the etch process in order to avoid over or under etch. The goal of this research is to develop a hardware and software system for EPD. The hardware consists of an Optical Plasma Monitor (OPM) sensor which is used to continuously monitor the plasma optical emission intensity during the etch process. The OPM software was developed to acquire and analyze the data to perform EPD. Our EPD algorithm is based on the following theory. As the etch process starts the plasma generated in the vacuum is added with the by-products from the etch reactions on the layer being etched. As the endpoint reaches and the layer gets completely removed the plasma constituents change gradually changing the optical intensity of the plasma. Although the change in optical intensity is not apparent, the difference in the plasma constituents when the endpoint has reached leaves a unique signature in the data gathered. Though not detectable in time domain, this signature could be obscured in the frequency spectrum of the data. By filtering and analysis of the changes in the frequency spectrum before and after the endpoint we could extract this signature. In order to do that, first, the EPD algorithm converts the time series signal into frequency domain. Next the noise in the frequency spectrum is removed to look for the useful frequency constituents of the data. Once these useful frequencies have been selected, they are monitored continuously in time and using a sub-algorithm the endpoint is detected when significant changes are observed in those signals. The experiment consisted of three kinds of etch processes; ashing, SiO2 on Si etch and metal on Si etch to develop and evaluate the EPD system.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.518-523
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• 2017

In commercial solar cells, the pattern of the front electrode is critical to effectively assemble the photo generated current. The power loss in solar cells caused by the front electrode was categorized as four types. First, losses due to the metallic resistance of the electrode. Second, losses due to the contact resistance of the electrode and emitter. Third, losses due to the emitter resistance when current flows through the emitter. Fourth, losses due to the shading effect of the front metal electrode, which has a high reflectance. In this paper, optimizing the number of finger on a $4{\times}4$ solar cell is demonstrated with known theory. We compared the short circuit current density and fill factor to evaluate the power loss from the front metal contact calculation result. By experiment, the short circuit current density($J_{sc}$), taken in each pattern as 37.61, 37.53, and $37.38mA/cm^2$ decreased as the number of fingers increased. The fill factor(FF), measured in each pattern as 0.7745, 0.7782 and 0.7843 increased as number of fingers increased. The results suggested that the efficiency(Eff) was measured in each pattern as 17.51, 17.81, and 17.84 %. Throughout this study, the short-circuit current densities($J_{sc}$) and fill factor(FF) varied according to the number of fingers in the front metal pattern. The effects on the efficiency of the two factors were also investigated.

• Korean Journal of Microbiology
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• v.45 no.1
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• pp.17-25
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• 2009

We studied soil components, methane production, the number of methanogens, and T-RFLP patterns dependent on agricultural methods with the change of seasons. There is no regular increase or decrease tendency of the most soil components followed by sampling period. And the water content in soil was higher in October than May. Also a lot of methanogens existed in soil, and acetotrophs were relatively of smaller number than hydogenotrophs and formate utilizing methanogens using MPN (most probable number) enumeration. In the experiment using the formate, it was used from the first week, and only a minute amount was detecte after four weeks. However in the acetate, it was increased until the third week, and after that was consumed. And there was higher methane production for all soil samples which administered with the hydrogen spike. The activity of methanogens was higher in the organic and low-agrichemical agricultural method samples, and the organic agricultural method had high methanogen activity among the other samples. A result of T-RFLP pattern of mcrA gene digested with Sau96I, methanogen community have a little relation with agricultural methods and seasons. This results also agreed to no critical difference the soil components dependent on agricultural methods, but some analytical data have a positive relationship with a agricultural methods. Therefor we could concluded that the comparison study of community for soil bacteria sufficiently could be useful for the microbiological indicator.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.91-99
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• 2014

The common-rail injectors are the most critical component of the CRDI diesel engines that dominantly affect engine performances through high pressure injection with exact control. Thus, from now on the advanced combustion technologies for common-rail diesel injection engine require high performance fuel injectors. Accordingly, the previous studies on the numerical and experimental analysis of the diesel injector have focused on a optimum geometry to induce proper injection rate. In this study, computational predictions of performance of the diesel injector have been performed to evaluate internal flow characteristics for various needle lift and the spray pattern at the nozzle exit. To our knowledge, three-dimensional computational fluid dynamics (CFD) model of the internal flow passage of an entire injector duct including injection and return routes has never been studied. In this study, major design parameters concerning internal routes in the injector are optimized by using a CFD analysis and Response Surface Method (RSM). The computational prediction of the internal flow characteristics of the common-rail diesel injector was carried out by using STAR-CCM+7.06 code. In this work, computations were carried out under the assumption that the internal flow passage is a steady-state condition at the maximum needle lift. The design parameters are optimized by using the L16 orthogonal array and polynomial regression, local-approximation characteristics of RSM. Meanwhile, the optimum values are confirmed to be valid in 95% confidence and 5% significance level through analysis of variance (ANOVA). In addition, optimal design and prototype design were confirmed by calculating the injection quantities, resulting in the improvement of the injection performance by more than 54%.

• Korean Journal of Organic Agriculture
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• v.20 no.2
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• pp.221-230
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• 2012

Rumen fermentative characteristic is useful indicators of the quality of ruminant feed stuffs and diets. An in vitro rumen fermentation experiment was therefore carried out to compare fermentation patterns among three forage sources. These were whole crop barley (WCBS), Italian ryegrass silage (IRGS) and rice straw silages (RSS). Rice straw (RS) was the control, making the treatments 4 in total. Forages were randomly allocated to serum bottles. The incubation times were arranged 0, 3, 6, 9, 12, 24, 48 and 72h at $39^{\circ}C$, respectively. Each forage source was replicated 3 times per incubation time. At each sampling time, total gas and pH were measured, whilst individual volatile fatty acids (VFAs), total volatile fatty acids (TVFAs) and ammonia nitrogen ($NH_3$-N) were determined later after storing samples at $-20^{\circ}C$. Acetate: Propionate ratio (A/P) was then calculated. Forage source had a significant effect (P<0.001) on pH and $NH_3$-N. RSS maintained higher pH values than the rest of the forage sources. A decreasing pH trend with increased time of incubation, in agreement with literature, was observed for all forage sources. WCBS recorded $NH_3$-N values higher than all the other treatments. Total gas, individual and total VFA and A/P ratio were not affected by forage source. However, there was a significant difference in all parameters (p<0.05) among forage sources at sampling periods at 3 to 72h. Therefore, the present results indicating that WCBS, IRGS, RS and RSS maintained in vitro rumen pH above the critical value. Also, WCBS produced the highest NH3-N and on this merit could be of better nutritive value, in vivo, in the ruminant.

• Korean Journal of Soil Science and Fertilizer
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• v.11 no.2
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• pp.61-66
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• 1979

This experiment was conducted to find out the simple and economical method to improve physical properties of the soil that was very poor for the establishment of orchard. Jeonnam clay loam soils distributed mainly on rolling and hill side slope, were treated with the explosion of two kinds of dynamite at the depth of 1 m. The change of physical properties was investigated vertically and horizontally after soil profile had settled to some extent. The results were summarized as : 1. The original soil was very high in bulk density and soil hardness. Total porosity and aeration porosities were lower than critical level providing root elongation. It was more apparent in the subsoil than in the surface soil. 2. It was recognized that soil mass destruction and cracking by dynamite explosion decreased soil bulk density and soil hardness and increased porosity, especially non-capillary pores. 3. Effective radius of the improved physical properties by explosion with two dynamites was 100cm at 60cm depth and 30cm at 80cm depth. But with the use of three dynamites it was 100cm at 80cm depth. 4. It was thought that soil mass destruction and cracking caused by explosion was uneven in the two dynamites, and three dynamites was more effective to improve physical properties evenly. 5. With the use of two dynamites, Ammonium explosive was superior to gelatin dynamite.

• Molecular & Cellular Toxicology
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• v.2 no.3
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• pp.176-184
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• 2006

The controversy on genotoxicity of molinate, an herbicide, has been reported in bacterial system, and in vitro and in vivo mammalian systems. To clarify the genotoxicity of molinate, we performed bacterial gene mutation test, in vitro chromosome aberration and mouse lymphoma $tk^{+/-}$ gene assay, and in vivo micronucleus assay using bone marrow cells and peripheral reticulocytes of mice. In bacterial gene mutation assay, no mutagenicity of molinate ($12-185{\mu}g/plate$) was observed in Salmonella typhimurium TA 98, 100, 1535 and 1537 both in the absence and in the presence of S-9 metabolic activation system. The clastogenicity of molinate was observed in the presence ($102.1-408.2\;{\mu}g/mL$) of metabolic activation system in mammalian cell system using Chinese hamster lung fibroblast. However, no clastogenicity was observed in the absence ($13.6-54.3\;{\mu}g/mL$) of metabolic activation system. It is suggested that the genotoxicity of molinate was derived some metabolites by metabolic activation. Molinate was also subjected to mouse lymphoma L5178Y $tk^{+/-}$ cells using microtiter cloning technique. In the absence of S-9 mixture, mutation frequencies (MFs) were revealed $1.4-1.9{\times}10^{-4}$ with no statistical significance. However, MFs in the presence of metabolic activation system revealed $3.2-3.4{\times}10^{-4}$ with statistical significance (p<0.05). In vivo micronucleus (MN) assay using mouse bone marrow cells, molinate revealed genotoxic potential in the dose ranges of 100-398 mg/kg of molinate when administered orally. Molinate also subjected to acridine orange MN assay with mouse peripheral reticulocytes. The frequency of micronucleated reticulocytes (MNRETs) induced 48 hr after i.p. injection at a single dose of 91, 182 and 363 mg/kg of molinate was dose-dependently increased as $10.2{\pm}4.7,\;14.6{\pm}3.9\;and\;28.6{\pm}6.3\;(mean{\pm}SD\;of\;MNRETs/2,000\;reticulocytes)$ with statistical significance (p<0.05), respectively. Consequently, genotoxic potential of molinate was observed in in vitro mammalian mutagenicity systems only in the presence of metabolic activation system and in vivo MN assay using both bone marrow cells and peripheral reticulocytes in the dose ranges used in this experiment. These results suggest that metabolic activation plays a critical role to express the genotoxicity of molinate in in vitro and in vivo mammalian system.

• Archives of design research
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• v.14 no.3
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• pp.59-68
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• 2001

The design on magazine advertisement has been developed and investigated in various fields, but the matter of properties has been inattentive in advertisement. Therefore, this study is to clarify the role of advertisement properties and the application tendency of it through the case study of the magazines for woman in Korea, and to analyze the relationship among the characteristic of manufactured goods for advertising, visual effects, copy-writing and the advertisement properties. The results of the study are as follows ; 1 . It is important to choose the discriminative property compared to the competitive company and to consider the purpose of advertisement from the beginning of idea developing. 2. Leading the photo artist to the photo working corresponding to the purpose of advertisement is critical point in advertisement design process. 3. After the photographing, it should be investigated from the designer's point of view. The presentation strategies on the application of advertisement properties are as follows, ·Conform the subject of advertisement massage. ·Choose the advertisement properties considered the relationship between manufactured goods for advertising and properties. ·Consider the properties as the supporting tool in bringing manufactured goods for advertising into relief. The pertinent application of advertisement properties is able to attract public attention and to increase the worthy of advertisement. Therefore, the prudent trial and experiment on it is needed.