• Journal of the Korean Society of Industry Convergence
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• v.4 no.3
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• pp.237-242
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• 2001

Ti-6Al-4V alloy can be obtained the stability of organization and product treasure, the evaluation of the cutting ability and the mechanical characteristics after the heat treatment of annealing, solution and aging. The difficulty in machining titanium alloy is how treat the heat generated during the process. Because the heat conductivity of titanium alloy is regardfully low, the heat generated during grinding is accumulated in workpiece. and it causes the increasing of grinding wheel grits' wear and makes the ground surface rough. So, these characteristics in grinding of titanium alloy will change the mechanical properties of the titanium alloy. From this study. the mechanical characteristics of annealed one and solution and aging one treated Ti-6Al-4V alloy after grinding was concerned with checking out the bending strength and hardness. For the result, both of bending strength and hardness were increased at the burned area on the surface. Roughness value was remarkably high at the table speed of 10m/min.

• Journal of architectural history
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• v.4 no.1
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• pp.93-112
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• 1995

The wooden pagoda was first appeared in about late 4th century in Korea. And between the late 6th century and the eary 7th centry, the multistoried wooden pagoda was replaced with the stone pagodas, in order to improve their stability and durability. In Three-kingdom and Unificated-Silla period, there are two types of stone stupas in Korea. The one is Paekche(百濟)style, and the other is Silla(新羅) style stone pagoda. These two styles are basically different in each part like podium, roof stone, body stone, structure and the others. Two types of stupas are distributed in two regions which devided into the East(Silla territory) and West(Paekche territory) in the Korean peninsular. The origin of the Korean stone pagoda can be traced to the Paekche dynasty and Silla dynasty. The former were the result of the careful study of their skillful wooden pagodas, where the latter were actualy originated from copying their sundried brick pagodas with stone. Two important pagodas of the primitive stage are the stone pagoda of Miruksa(彌勒寺) temple in Iksan and Bunhwangsa(芬皇寺) temple in Kyungju. These two pagodas are compared with each other in the style of their construction. Silla style have sharp straight lines and short distance between roof stone and eaves. They give us strong as well as intelletural feeling. Howerever, Paekche style has curved lines and dull angles of cutting area of stone, they give us soft feeling.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.3
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• pp.358-364
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• 1996

Recently, much power demand from domestic power consumer is weakening the allowable power reserve margin in summer, especially at midday for one day due to a steep increase of air cooling loads such as air conditioner. Therefore solar airconditioning system can'be considered as one of the best remedies to meet the increase of peak power. Generally in solar air conditioning system, the diode rectifier is used to build up DC link voltage from AC source. The diode rectifier is simple and cheap but it brings out the problems of low power factor and plentiful harmonics at the AC source. Also It can derate the utilization rate of solar energy because the reverse of power flow cannot be made. Hence, in this paper to overcome the peak power problem in summer and to endure good AC input characteristics, solar air conditioning system using the PWM converter is proposed. As results, obtained are the characteristics of the PWM converter such as low distorted current waveform, high power factor and bidirectional power control. And also the stability of proposed system is verified by examining the dynamics of step load change and power reversal testing. (author). refs., figs., tabs.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.988-994
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• 1997

The demands for robotic and automatic system are continually increasing in manufacturing fields. There have been many studies to monitor and predict the system, but they have mainly focused upon measuring cutting force, and current of motor spindle, and upon using acoustic sensor, etc. In this study, digital image of time series sequence was acquired by taking advantage of optical technique. Mean square error was obtained from it and was available for useful observation data. The parameter was estimated using PAA(parameter adaptation algorithm) from observation data. AR(auto regressive) model was selected for system model and fifth order was decided according to parameter estimation. Uncorrelation test was also carried out to verify convergence of parameter. Through the proceedings, it was found that there was a system stability.

• Asian Journal of Turfgrass Science
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• v.9 no.3
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• pp.173-185
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• 1995

Hydroseeding technique is a very popular method of revegetating slope areas through the control of soil erosion and stability by seeding grasses. This study was conducted to select turfgrass species and cultivars for hydroseeding. Experiment plots were established on various soil types and environmental conditions at Singar-Ansan high-way construction site. The investigation was designed in three cutting, one back-filling and other three spare sites with various seed mixtures. Results indicated that combinations of seed mixtures influenced seed germination and rates of surface cover. In a view of long term, vegetation shifts should be influenced by characters of slopes and micro-climate conditions. Hydroseeding did not show good results on rocky slope areas. Revegetation was only going on where there had soil. The combination of seed mixture with a higher rate of perennial ryegrass had relatively good revegetation with faster germination and seedling growth. Improved turf-type tall fescue Arid ⓡ and Falcon ⓡ seemed to have good environ-mental adaptation and drought tolerance. Wild or old type cultivars showed relatively slow green-up in spring and growth rates at the next year of seeding. For the harmonious landscaping with surrounding area, the combination of native grass mixture with cool-season grasses had good results. Slow and low revegetation rate at hack-filling site seemed to be caused by the poor development of capillary tubes in sub-soil. It was shown that a high correlation between seed germination and revegetation rate, and between three-month later coverage rate and final rate. The evaluation of coverage rate after three month seems to he acceptable to decide the accomplishment of hydroseeding results on rode side slopes.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.6
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• pp.841-848
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• 2021

To develop a value-added low-salt fermented seafood with a long shelf-life, we prepared seasoned low-salt fermented Omandungi Styela plicata supplemented with fermentation alcohol (SOE). The SOE was produced by washing and dewatering shelled Omandungi, followed by cutting and salting for 24 h at 0±1℃. The salted Omandungi was seasoned and fermented with garlic, ginger, monosodium glutamate, red pepper, sesame, sorbitol, and sugar, for 7-8 days at 0±1℃. After adding 3-5% fermentation alcohol, the seasoned fermented Omandungi was packed in a polyester container. The salinity, volatile basic nitrogen content, and viable cell count of SOE were 4.8%, 22.1-22.2 mg/100 g, and (1.2-1.9)×10³ CFU/g, respectively. Compared with the control, addition of 3-5% fermentation alcohol inhibited the decrease in freshness, texture degradation, and growth of residual bacteria. Additionally, the SOE showed good storage stability and organoleptic qualities when stored at 4±1℃ for 40 days. The total amino acid content of SOE was 2,186.0 mg/100 g, mainly comprising glutamic acid, aspartic acid, lysine, and phenylalanine. The free amino acid content was 189.0 mg/100 g, and mainly included taurine, glutamic acid, methionine, alanine, and proline.

• Journal of information and communication convergence engineering
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• v.17 no.2
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• pp.161-165
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• 2019

In this study, zinc tin oxide (ZTO) thin-film transistors are researched to observe the correlation between the barrier potential and electrical properties. Although much research has been conducted on the electronic radiation from Schottky contacts in semiconductor devices, research on electronic radiation that occurs at voltages above the threshold voltage is lacking. Furthermore, the current phenomena occurring below the threshold voltage need to be studied. Bidirectional transistors exhibit current flows below the threshold voltage, and studying the characteristics of these currents can help understand the problems associated with leakage current. A factor that affects the stability of bidirectional transistors is the potential barrier to the Schottky contact. It has been confirmed that Schottky contacts increase the efficiency of the element in semiconductor devices, by cutting off the leakage current, and that the recombination at the PN junction is closely related to the Schottky contacts. The bidirectional characteristics of the transistors are controlled by the space-charge limiting currents generated by the barrier potentials of the SiOC insulated film. Space-charge limiting currents caused by the tunneling phenomenon or quantum effect are new conduction mechanisms in semiconductors, and are different from the leakage current.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.4
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• pp.206-214
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• 2023

Tungsten carbide has many industrial applications due to its high electrical and thermal conductivity, high melting temperature, high hardness and good chemical stability. Because tungsten carbide is difficult to sinter, it is sintered with nickel or cobalt as a binder and is currently used in nozzles, cutting tools, and molds. Alumina is reported to be a viable binder for tungsten carbide due to its higher oxidation resistance and lower cost than nickel and cobalt. The ultrafine tungsten carbide-graphene-alumina composites were rapidly sintered in a high frequency induction heating active sintering unit. The microstructure and mechanical properties (fracture toughness and hardness) of the composites were investigated and analyzed by Vickers hardness tester and electron microscope. Since the high-frequency induction heating sintering method enables high-speed sintering, ultrafine composites can be prepared by preventing grain growth. In the tungsten carbide-graphene-alumina composites, the grain size of tungsten carbide increased with the amount of alumina participation. The hardness and fracture toughness of the tungsten carbide-5% graphene- x% alumina (x = 0, 5, 10,15) composites were 5.1, 8.6, 8.6, and 8.4 MPa-m^1/2 and 2384, 2168, 2165, and 2102 kg/mm², respectively. The fracture toughness increased without a significant decrease in hardness. Sinterability was improved by adding alumina to tungsten carbide-graphene.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.53-62
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• 2014

In Korea, in general, separation distance between existing parallel tunnels was set at two to five times as distant as the diameter of the tunnels according to ground conditions. Recently, however, actual applicability of closely spaced parallel tunnels whose distance between tunnel centers was shorter than the diameter has increased due to environmental damages resulting from massive cutting, restriction in purchase of required land, and maintenance of linear continuity. In particular, when the pillar width of tunnel decreases, the safety of pillars affects behaviors of the tunnel and therefore the need for diverse relevant studies has emerged. However, research so far has been largely confined to analysis of behavior characteristics of pillars, or parameters affecting design, and actually applicable and quantitative data have not been presented. Accordingly, in order to present a stability evaluation method which may maximally reflect construction conditions of spots, this study reflected topographical and stratigraphic characteristics of the portal part with the highest closeness between the tunnels, simulated multi-layer conditions with rock mass and complete weathering, and assessed the degree of effect the stability of pillars had on the entire tunnels through numerical analysis according to changes in pillar width by ground strength. This study also presented composite analysis result on ground surface settlement rates, interference volume rates, and average strength to stress and a formula, which may be applicable to actual work, to evaluate safety rates of closely spaced parallel tunnel pillars and minimum pillar width by ground strength based on failure criteria by Hoek-Brown (1980).

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.144.2-144.2
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• 2016

Diamond-like carbon (DLC) coatings have been widely applied to the mechanical components, cutting tools due to properties of high hardness and wear resistance. Among them, hydrogenated amorphous carbon (a-C:H) coatings are well-known for their low friction properties, stable production of thin and thick film, they were reported to be easily worn away under high temperature. Non-hydrogenated tetrahedral amorphous carbon (ta-C) is an ideal for industrial applicability due to good thermal stability from high $sp^3$-bonding fraction ranging from 70 to 80 %. However, the large compressive stress of ta-C coating limits to apply thick ta-C coating. In this study, the thick ta-C coating was deposited onto Inconel alloy disk by the FCVA technique. The thickness of the ta-C coating was about $3.5{\mu}m$. The tribological behaviors of ta-C coated disks sliding against $Si_3N_4$ balls were examined under elevated temperature divided into 23, 100, 200 and $300^{\circ}C$. The range of temperature was setting up until peel off observed. The experimental results showed that the friction coefficient was decreased from 0.14 to 0.05 with increasing temperature up to $200^{\circ}C$. At $300^{\circ}C$, the friction coefficient was dramatically increased over 5,000 cycles and then delaminated. These phenomenon was summarized two kinds of reasons: (1) Thermal degradation and (2) graphitization of ta-C coating. At first, the reason of thermal degradation was demonstrated by wear rate calculation. The wear rate of ta-C coatings showed an increasing trend with elevated temperature. For investigation of relationship between hardness and graphitization, thick ta-C coatings(2, 3 and $5{\mu}m$) were additionally deposited. As the thickness of ta-C coating was increased, hardness decreased from 58 to 49 GPa, which means that graphitization was accelerated. Therefore, now we are trying to increase $sp^3$ fraction of ta-C coating and control the coating parameters for thermal stability of thick ta-C at high temperatures.