• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.1
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• pp.33-44
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• 2000

Ships in a seaway will encounter dangerous situation, such as slamming, stranding, and capsizing. The number of capsizing is small, but the loss due to them is very large from the viewpoint of human life, property, and the environmental pollution. The number of capsizing of fishing vessels is about 62% of total number of capsizing, and the half of them is originated from the operational mistake in a seaway. So the dynamics and the capsizing phenomena are to be studied, and the guide for the safe operation of a fishing vessel in a seaway are to be specified. The hydrodynamic forces consist of radiation forces (which are due to the motion of a ship), Froude-Krylov forces (which is due to the incoming waves), and diffraction forces (which is due to the wave and ship interaction). These forces are calculated by well-known strip method. Using the calculated forces, the motion of a ship in a regular sea is obtained. In the real seaway, the waves are very irregular, therefore the statistical analysis is very helpful. In this paper, using the results of the motion in a regular seaway and the wave spectrum, the motion in a irregular seaway are obtained and analyzed.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.67-75
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• 2005

For th aim of lightweight microwave absorbers, conductive and magnetic microspheres are fabricated by plating of Co films on hollow ceramic microspheres of low density. Metal plating was carried out in a two-step electroless plating process (pre-treatment of activation and plating). Uniform coating of the film with about $2{\~}3{\cal}um$ thickness was identified by SEM. High-frequency magnetic and microwave absorbing properties were determined in the rubber composites containing the Co-coated microspheres. Due to conductive and ferromagnetic behavior of the Co thin films, high dielectric constant and magnetic loss can be obtained in the microwave frequencies. Due to those electromagnetic properties, high absorption rate (25 dB) and thin matching thickness ($2.0{\~}2.5{\cal}mm$) are predicted in the composite layers containing the metal-coated microspheres of low density (about 0.84 g/cc) for the electromagnetic radiation in microwave frequencies.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.2
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• pp.265-274
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• 2011

In this paper, it is studied on wide radiating slot antenna's miniaturization for ultra wide-band(UWB) technologies and notch structure to prevent interference between UWB systems and existing wireless systems for using Wi-Fi service of IEEE standards 802.11 a/n. Proposed antenna that wide slot is decreased from $\lambda/2$ to $\lambda/4$ length of resonant frequency has decreased by 72 % compared with conventional antenna. And optimized T-shaped CPW-fed stub has satisfied UWB bandwidth for 3.0~11.8 GHz. Then, creating 2-order Hilbert curve slot line in the stub's patch area, 4.9~5.6 GHz that centered frequency is 5 GHz is eliminated. Finally, the designed antenna constructed on FR4-epoxy has $20{\times}15\;mm^2$ dimension. The measured results that are obtained return loss under -10 dB through 3.2~11.8 GHz without Wi-Fi bandwidth, a linear phase characteristic, a stable group delay, and omnidirectional radiation patterns are presented.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.11-19
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• 2013

In this paper, we designed and implemented the planar monopole antenna using the coupling effect for the multi-band characteristic. A parasitic element for the multi-band characteristic based on a rectangular patch with single resonance is inserted. Spiral shaped parasitic element is used for minimizing the antenna size and obtaining the multi-resonance characteristic. The frequency characteristics are modified and optimized by varying specific parameters. By inserting an L-shaped resonator at both sides of the feed line which connected through the via hole to the ground plane, unnecessary frequency bands are eliminated. Proposed antenna dimension is $40{\times}60{\times}1mm^3$. It is fabricated on the FR-4 substrate(${\varepsilon}_r$=4.4) using a microstrip line of $50{\Omega}$ for impedance matching. By measurement results, the characteristic of the return loss under -10 dB are 1.714~2.496 GHz, 2.977~4.301 GHz, and 4.721~6.315 GHz, and the radiation patterns have omni-directional shapes.

• Korean Journal of Food Science and Technology
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• v.21 no.5
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• pp.669-675
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• 1989

Fresh mushroom (Agaricus bisporus L.) was irradiated (0, 1, 2, 3kGy) and kept for 20 days at 9{\pm}1^{\circ}C\;and\;80{\pm}7%$ RH. Parameters of qualities were investigated on the physical and physiological characteristics. The pileus and stipe on nonirradiated mushroom were expanded and elongated from the 3rd day of storage, there by losing the acceptability as edible samples. After 5 days of storage, 2 to 3kGy of gamma irradiation were especially effective for controllong natural maturation and senescence of fresh mushrooms and so irradiated mushrooms were acceptable more than 20days storage. The texture of irradiated samples was superior to that of nonirradiated samples, even though softening of the tissue occurred during storage. Weight loss was greatest in the nonirradiated sample due to evaporation from an increased surface area resulting from expansion and ripending, which were retarded in the 2 to 3kGy irradiated samples after 5days of storage. These results suggest that the irradiation dose of 2 to 3kGy is apparently effective to extend the shelf life of fresh mushrooms stored at the above-mentioned condition.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.496-502
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• 2007

In this paper, a slotted waveguide feeder for the electric field uniformity in multi-mode cavity is designed and fabricated. In case of the conventional feeder, a mode stirrer or a turntable is used for improving electric field uniformity in the multi-mode cavity. The proposed feeder has four slots, which have uniform radiation characteristic, on broad wall and shorted terminations at both ends. The electric field uniformity is simulated by CST's MWS(Microwave Studio) for the conventional and proposed feeders, respectively. The fabricated feeder shows the return loss of less than -20 dB at 2.45 GHz. To verify the validity of our proposal, the temperature distribution of the water samples in the multi- mode cavity is observed after a few minutes' heating. The proposed feeder is confirmed to have much better field uniformity in the multi-mode cavity than the conventional feeder.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.27 no.3
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• pp.229-234
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• 1982

Environmental factors are known in general to influence much on the development of abscission layer and thereby on shedding of plant parts. The present study was carried out to determine the effect of meterological condition during ripening on the grain shatterability of rice plants at harvest. Different meteorological conditions were obtained by shifting transplanting timing of 40 days old rice seedlings 4 times with a 15 days-interval. Grain shatterability was measured as tensile strength of rice grains: it varied within a range of 214g. to 251g. in a practically non-shattering Japonica variety'Jinheung' and l27.5g. to 204g. in an easy shattering Indica \times Japonica progeny variety'Taeback'. In view of field loss of rice, the variation in tensile strength with time of transplanting and harvest did not matter in Jinheung, but was an important factor in Taeback. In Taeback the tensile strength was significantly correlated positively with mean, maximum and minimum air temperature and relative humidity during a certain period of grain ripening, especially during 30 days period before harvest, but diurnal range of air temperature showed a significant, negative correlation with it. The tensile strength seemed to be more closely related with min. air temperature than max. air temperature, and it was not significantly correlated with radiation amount during any period of pre-harvest. Meteorological effect on grain shatterability may vary with variety, but temperature regime during ripening appears to play major role among the meteorological factors in easy shattering and more thermophilic Indica \times Japonica varieties: lower the temperature, greater the shatterability.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.2
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• pp.92-103
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• 1993

A sunday system with a horizontal bin-type composter was constructed and operated to evaluate its composting performance for four days for each test in October, 1992. A sundry system is one of popular systems for composting livestock manure, of which main benefit is to utilize unlimited, clean, and free solar radiation. A rectangular concrete bin(composter) with dimension of 300cm(length) X90cm(width) X60cm(height) was bedded alternatively with four lanes of aeration pipes and heating pipes, and was insulated at three walls with 50mm styrofoam. Each aeration pipe of a diameter of 25mm had 4mm perforated holes at every 15cm longitudinally, and supplied air of about 2m$^3$/min to the composter to maintain aerobic condition . A stirrer rotating at 1 rpm made one round trip every 20 minutes on the conveying chain along the the length of the composter. Five tests (Test 1~Test 5) were implemented to evaluate the composting effectiveness of a sundry system with a horizontal bin-type composter. Treatments of two levels of the mixture ratio of swine manure and paper sludge cakes(manure : paper sludge cakes= 1 : 4 and 1 : 2) and two levels of the water content(W/C ; 70% and 50%) were made to test the significance of the physicochemical properties for decomposition of the mixture materials. Temperature, C/N ratio, water content, microbial activity of the composting materials were taken measurements to evaluate its performance with the lapse of composting time for tests. A small-scale sundry system with a bin-type composter did not appear to be an appropriate system for composting livestock manure. Since heat generation by the composting materials could not overcome heat loss due to areation in a small-scale composter, a proper thermal enviroment could not be maintained to propagate massively thermopilic microorganism relatively in a short period of time. Different from the result of Chol et al.(1992) 6), a temperature variation of the composting materials did not show the peak clearly and C/N ratio didn't lower with time as expected. Mesophilic microoragnism seemed to play an important role for decomposition of the mixture materials. A sundry system with a bin-type composter may be good for a large-scale livestock farm household which may produce enough animal manure. Therefore a decision should be made very carefully to choose a system for composting livestock waste.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.4
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• pp.489-495
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• 2018

In this paper, we designed and fabricated WLAN / UWB communication antennas operating at 3.3 [GHz] and 5 [GHz] bands in order to effectively use the high-speed communication network system that improved antenna miniaturization, gain and radiation pattern. Microstrip patch antennas were chosen to improve the bandwidth. The slot width, length, and transmission line width were calculated using the theoretical formula for each step. Simulation results show that the return loss is -14.053 [dB] at 3.3 [GHz] and -13.118 [dB] at 5 [GHz]. The gain showed a value of 2.479 [dBi] at 3.3 [GHz] and a value of 3.317 [dBi] at 5 [GHz]. After optimizing it with the CST Microwave Studio 2014 program, which can be 3D-designed, Based on these results, we investigated the performance of antennas by measuring their characteristics. In recent years, WLAN, which is a variety of wireless technologies that are continuously developing, and UWB, which is a communication technology which is increasing in frequency band due to an increase in demand of the technology users, is used for a high speed wireless communication system. Communication seems to be possible.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.320-329
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• 2021

In this paper, an empirical model of air bubble size to be applied to an air masker for reduction of underwater radiation noise is presented. The proposed model improves the divergence problem under the low-speed flow condition of the existing model derived using Rayleigh's jet instability model and simple continuity condition by introducing a jet flow velocity of air. The jet flow velocity of air is estimated using the bubble size where the liquid is quiescent. In a medium without flow, the size of the bubble is estimated by an empirical method where bubble formation regime is divided into a laminar-flow range, a transition range, and a turbulent-flow range based on the Reynolds number of the injected air. The proposed bubble size model is confirmed to be in good agreement with the Computational Fluid Dynamics (CFD) analysis result and the experimental results of the existing literature. Using the acoustic inversion method, the air bubble population is estimated from the insertion loss measured during the air injection experiment of the air- masker model in a large cavitation tunnel. The results of the experiments and the bubble size model are compared in the paper.