• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.171-177
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• 2000

Exchange coupling of Co/NiMn bilayers fabricated by RF magnetron sputtering method was studied. We investigated the variation of exchange coupling field (H$\sub$ex/) for different annealing temperature and time. The maximum exchange coupling field was obtained after 13hr annealing at 300 $^{\circ}C$. With respect to deposition sequence, it was demonstrated that NiMn-top bilayers had higher exchange coupling field than NiMn-bottom bilayers. Ta capping layer was shown to be essential in achieving exchange coupling and Auger Electron Spectroscopy (AES) proved that uncapped NiMn/Co bilayers did not have exchange coupling because of oxygen incorporation into film. We also observed the effect of Ta underlayer on exchange coupling. It was found that Ta underlayer had better not be used for attaining higher exchange coupling. XRD analysis showed that Ta underlayer helped bilayers develop texture, but it was not essential to exchange coupling of Co/NiMn bilayers, which is in contrast to NiFe/NiMn system. Furthermore, the NiMn and Co thickness dependence of exchange coupling has been investigated. The exchange coupling strength reached the maximum above 200 ${\AA}$ NiMn thickness and had inversely proportional relation with Co thickness.

• Membrane Journal
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• v.21 no.4
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• pp.389-397
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• 2011

In this study, polymer composite membranes based on sulfonated poly(arylene ether sulfone) (SPAES) were prepared using a solution casting method with different amount of vermiculite (VMT) content. The dispersion of VMT particles in the SPAES matrix was confirmed by means of a scanning electron microscopy observation. The composite membrane containing less than 1 wt% of VMT has a smooth skin on the top and bottom, which means there is a good dispersion of VMT in the matrix. The water uptake of the composite membranes gradually increases as the temperature increases, and the results confirm that all the adsorbed water is bound water because VMT has a strong water affinity on account of its high cation exchange value. A composite membrane with a VMT content of less than 1 wt% increases the proton conductivity and reduces the methanol permeability. Of all the composite membranes, the membrane SPAES/VMT 1.0 has the best fuel cell performance in terms of membrane selectivity. The performance value of SPAES/VMT 1.0 is double that of Nafion 112, which suggests that SPAES/VMT1.0 could be an excellent candidate for direct methanol fuel cells.

• Journal of Environmental Science International
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• v.11 no.10
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• pp.1109-1116
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• 2002

This study analyzed concentrations of volatile organic compounds (VOCs) produced from incineration of papers at $600^{\circ}C$. The papers used in this study included A4 papers (new, printed with ink-jet, printed with carbon), newspapers (printed with bean oil, printed with a general newspaper ink), packaging box, document envelope, single-use paper cup, and cosmetic tissue. Papers were heated from room temperature upto $600^{\circ}C$ providing air inside of the electric furnace and then they were oxidized for 80 minutes at $600^{\circ}C$ maintaining the same air supply. VOCs emitted from the incineration process were sampled using an air sampling pump and bags for 160 minutes and then the components and concentrations of the VOCs were analyzed by a CC-MS. The most prominent chemical structure of the Vous identified from incineration of the papers was furans and then furans were followed by aromatics and aliphatic alkenes. About 40% of the identified VOCs contained double bonds, which have relatively a high ozone (ground level) formation potential, within their molecular structure. Also, some cancer suspecting compounds like benzene, dichlorormethane and chloroform were identified.

• Journal of Environmental Science International
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• v.11 no.7
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• pp.627-636
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• 2002

While typhoons were passing by the coastal and offshore waters around the Korean peninsula, the variations of the sea surface temperature (SST) were studied. To study on the variation, the data related to the 22 typhoons among 346 typhoons which occurred in the western Pacific during 1990∼1999, daily measured field SSTs at coastal and offshore, and imageries from advanced very high resolution radiometer on NOAA satellite during 1990∼1999 were used. The average variations of the SSTs were -0.9℃ at coastal waters and -2℃ at offshore around the Korean peninsula while the typhoons were passing by. In very near coastal waters from the land, the SST was not changed because the bottom depth of the coastal waters was shallower than the depth of thermalcline, while the typhoon was passing. The temporal and spatial variation of SSTs at coastal waters in summer were depended on the various types of the typhoons＇paths which were passing through the Korean peninsula. When a typhoon passed by the western parts including the Yellow Sea of the Korean peninsula upwelling cold water occurred along the eastern coastal waters of the peninsula. The reason was estimated with the typhoon that was as very strong wind which blew from south toward north direction along the eastern shore of the peninsula, led to the Ekman transport from near the eastern coastal area toward the offshore. While cold water was occurring in the eastern coast, a typhoon passed over the coastal area, the cold water disappeared. The reason was estimated that the cold water was mixed up with the surrounding warm water by the effect of the typhoon. While a cold water was occurring in the eastern coast, a typhoon passed by the offshore of the eastern coast, there were the increasing of the SST as well as the disappearing of the cold water. While a typhoon was passing by the offshore of the eastern coast, the cold water which resulted from the strong tidal current in the western coast of the peninsula was horizontally spread from the onshore to the offshore. We think that the typhoon played the role of the very strong wind which was blowing from north toward south. Therefore, the Ekman transport occurred from the onshore toward the offshore of the western coast in the Korean peninsula.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.613-623
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• 2012

In this paper, we present an ultra miniaturized voltage tuned oscillator, with HMIC-type amplifier and phase shifter, using LTCC artificial dielectric resonator. ADR which consists of periodic conductor patterns and stacked layers has a smaller size than a dielectric resonator. The design specification of ADR is obtained from the design goal of oscillator. The structure of the ADR with a stacked circular disk type is chosen. The resonance characteristic, physical dimension and stack number are analyzed. For miniaturization of ADRO, the ADR is internally implemented at the upper part of the LTCC substrate and the other circuits, which are amplifier and phase shifter are integrated at the bottom side respectively. The fabricated ADRO has ultra small size of $13{\times}13{\times}3mm^3$ and is a SMT type. The designed ADRO satisfies the open-loop oscillation condition at the design frequency. As a results, the oscillation frequency range is 2.025~2.108 GHz at a tuning voltage of 0~5 V. The phase noise is $-109{\pm}4$ dBc/Hz at 100 kHz offset frequency and the power is $6.8{\pm}0.2$ dBm. The power frequency tuning normalized figure of merit is -30.88 dB.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.953-960
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• 2019

The Miller cycle is a diesel engine that has been developed in recent years that it can reduce NOx and improve fuel consumption by reducing the compression ratio through intake valve closing (IVC) time control. The Miller cycle can be divided into the early Miller method of closing the intake valve before the bottom dead center (BDC) and the late Miller method of closing the intake valve after the BDC. At low speeds, the late Miller method is advantageous as it can increase the volumetric efficiency; while at medium and high speeds, the early Miller method is advantageous because of the high internal temperature reduction effect due to the expansion of the intake air during the piston lowering from IVC to BDC. Therefore, in consideration of the ef ects of the early and late Miller methods, it is necessary to adopt the most suitable Miller method for the operating conditions. In this study, a two-stage turbo charge system was applied to four-stroke engines and the process of enhancing the Miller effect through a reduction of the intake and exhaust valve overlap as well as the valve change adjustment mechanism were considered. As a result, the ef ects of fuel consumption and Tmax reduction were confirmed by adopting the Miller cycle with a two-stage supercharge, a reduction of valve overlap, and an increase of suction valve lift.

• Journal of Navigation and Port Research
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• v.40 no.3
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• pp.159-164
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• 2016

The goal of this study is to implement a communication system that can monitor the status of the nacelle using the power cable itself, without the dedicated communication lines such as an UTP cable and optical fiber for the offshore wind turbine. An inductive coupling powerline communication system for a MW class offshore wind turbine was proposed and its communication performance was demonstrated. The inductive couplers was designed for operation at up to 500 A using a ferrite composite materials. Field test was carried out on the wind farms of Jeju island. Using the iperf communication test program, we have obtained more than 15 Mbps data transmission rate through the 100 m power cable that was installed between the nacelle and the bottom of the power converter. In the data transmission stability test for a week, there was no failure ever. The minimum transmission rate was 15 Mbps and the average data rate was about 20 Mbps. Next, we have installed an infrared camera inside the nacelle in order to measure the temperature distribution and variation of the nacelle. The real-time thermal image taken by the camera was successfully sent to the monitoring system without error.

• The Korean Journal of Quaternary Research
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• v.18 no.1 s.22
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• pp.1-20
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• 2004

A geoscientific research was performed on 12 samples of comb-pattern potteries which were excavated at Daecheonri neolithic site, Korea. The texture and compositions of 12 potteries and surrounding metrix of soil and rocks were compared with the help of petrographic microscope, XRD and REE data. As to the manufacturing techniques thick potteries are caused by the amount and number of coarse grains which are assumed to be added shards when their distributional pattern are considered. DC1, DC3, DC 7 and DC11 samples have clearly oriented textures, and the orientation of vesicles in DC3 and DC11 samples arranged in the same direction with those on the pottery surface. This indicates the use potter's wheel technique in manufacturing potteries. Burning temperature is assumed over $800^{/circ}C$, particularly under reduction environment. As to the source, raw materials of pottery matrix are derived from the bottom of excavation site, or in an extracted outcrop of the northwestern foothill from site, while the shard materials are very similar with those extracted from sandy loams near sites. Finally any use pattern of pottery may control the pottery thickness, shard addition, and matrix selection.

• Journal of the Korean Institute of Gas
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• v.2 no.1
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• pp.28-39
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• 1998

This study investigated the natural convection and radiation in a rectangular enclosure with ceiling vent experimentally and numerically. A heat source is located on the center of the bottom surface. The analysis was peformed a pure convection and is combination of natural convection and radiation. The shape of the considered two dimensional model is a square whose center of ceiling($30\%$) is opened. The numerical simulations are carried out for the pure natural convection case and the combined heat transfer case by using the SIMPLE algorithm. For the turbulent flow, Reynolds stresses are closed by the standard $k-{\epsilon}$ model and the wall function is used to determine the wall boundary conditions. The experiment was performed on the same geometrical shape as the computations. The radiative heat transfer is analized by the S-N discrete ordinates method. The results of pure natural convection are compared with those of combined heat transfer by the velocity vectors, stream lines, isothermal lines. The results obtained are as follows 1. Comparing the results of pure convection with those of the combined convection-radiation through the shape of stream lines, isothermal lines are similar to each other. 2. The temperature fields obtained by numerical method are compared to those obtained by experimental one, and it is found that they are showed mean relative error $8.5\%$. 3. Visualization bt smoke is similar to computational results.

• Food Science and Preservation
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• v.17 no.5
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• pp.581-585
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• 2010

The effects of plastic container vent ratio on fruit quality during strawberry precooling and storage were analyzed. Plastic containers ($520mm{\times}355mm{\times}182mm$) were manufactured with bottom and side vents at areal ratios of 5%, 10%, 15% and 20%. Fruit was loaded at a volume ratio of 80% prior to pressure cooling and storage at $5^{\circ}C$. The internal fruit temperature was $18^{\circ}C$ and the times taken to attain $2^{\circ}C$ after precooling were 1 hour 9 minutes, 1 hour 13 minutes, 2 hours 2 minutes, and 2 hours 51 minutes at vent ratios of 20%, 15%, 10%, and 5%, respectively. To mimic the current distribution system, precooled strawberries were packaged in tray wrapping and stored at $5^{\circ}C$. Changes in weight, bruising, extent of decay, and firmness, were measured. Weight loss, bruising, and decay were highest at a vent ratio of 20%, lowest at a vent ratio of 15%, and moderate at vent ratios of 5% and 10%. No significant among-treatment difference in fruit firmness was evident.