• Plant Journal
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• v.10 no.4
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• pp.29-34
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• 2014

In this consideration, this research investigated the piping design items and drew out key design items through interview with experts and surveys to apply them to actual project examples and look into piping design item-specific significance and cost variation ranges. Based on this investigation, the Monte-Carlo simulation was employed herein to analyze the cost variation range for the entire piping design costs with a view to presenting a way to calculate a reasonable bidding price for any similar project and verify the appropriateness of joining a bid.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.8
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• pp.901-906
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• 2006

In this paper, the power amplifier using active bias circuits for LDMOS(Lateral Diffused Metal Oxide Semiconductor) MRF-21180 is designed and fabricated. According to change the temperature, the gate voltage of LDMOS is controlled by the fabricated active bias circuits which is made of PNP transistor to suppress drain current. The driving amplifier using MRF-21125 and MRF-21060 is made to drive the LDMOS MRF-21180 power amplifier. The variation of current consumption in the fabricated 60 watt power amplifier has an excellent characteristics of less than 0.1 A, whereas a passive biasing circuit dissipates more than 0.5 A. The implemented power amplifier has the gain over 9 dB, the gain flatness of less than $\pm$0.1 dB and input and output return loss of less than -6 dB over the frequency range 2.11 $\sim$ 2.17 GHz. The DC operation point of this power amplifier at temperature variation 0 $^{\circ}C$ to 60 $^{\circ}C$ is fixed by active bias circuit.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.8
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• pp.604-612
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• 2009

Water management has been recognized as a crucial factor for achieving better performance and stability in polymer electrolyte membrane fuel cells (PEMFCs). Proper water management should provide favorable water conditions, including the local humidity, membrane water content, and liquid water saturation in PEMFCs, thereby leading to more uniform electrochemical reaction and current generation. In this study, computational fluid dynamics (CFD) simulation was conducted to investigate the effects of the cathode relative humidity (RH) on the performance of a 3 by $3\;cm^2$ PEMFC with serpentine flow fields. The CFD results showed that the best performance of the PEMFC was obtained for the cathode RH of 80%, but the performance variation was small for the cathode RH range of $60{\sim}100%$. However, the loss of the PEMFC performance was significant when the cathode RH was reduced below 40%. The reason for such performance variation was investigated through the detailed inspection of ohmic loss, activation and concentration overpotential, and water and current distributions.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.22 no.1
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• pp.1-6
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• 1977

The varietal differences of protein content in barley grain and its variation under different cultural conditions were studied. The varietal variation of protein content was significant with the range of 8～18%. The protein content of barley grain were increased by heavier nitrogen application and decreased by shading treatment and drill seeding. There was negative correlation between protein content and grain weight in hulled barley, while positive correlation between nitrogen content of plant and leaf at heading stage and protein content of barley grain was significant in Haganemugi and Buheung.

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.116-119
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• 2015

Field-effect transistor (FET)-based ion or biosensors have been intensively studied so far. Among many measurement methods, the variation of the drain current can be induced when ions or biomolecules are interacted with sensing membranes located on the gate insulator of FET. One of typical FET-type sensors is an ion-sensitive field-effect transistor (ISFET) utilized in this study. In ISFET, the voltage is usually applied to the reference electrode instead of the gate voltage. Firstly, the voltage applied to the reference electrode versus the drain current was observed, and the steepest slope in this graph was found. Using this point, the optimized condition was established for the larger variation of the drain current in the saturated region in response to the variation of the input in the dynamic range.

• Korean Journal of Ichthyology
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• v.1 no.1_2
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• pp.54-63
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• 1989

Morphological variation of the crusian carp, Carassius auratus, from Yongnam area in Korea was examined. In morphometric and meristic characters, mean values were different slightly among the polulations, whereas the range of variation was overlapped largely. In the present examination the number of spines in dorsal fin were 4-6. The majority of individuals appeared to be similar to Carassius auratus langsdorfii from Japan, but some individuals were quite different from them in having 66-83 gill rakers.

• Speech Sciences
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• v.4 no.2
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• pp.115-139
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• 1998

The aim of this study is to develop an the assessment program for the singing voice which is based on the physiological and acoustic methods. 22 sopranos, 6 mezzo sopranos, 4 tenors and 4 baritones participated to these experiments. The results measured by Visi-Pitch, spectrograph, and strobo-scope can be summarized as follows: (1) The maximum phonation time of singers must over 14 second higher with one deep inspiration (2) The parts classified by vocal range using Visi-Pitch: soprano between 167Hz $\sim$1,190Hz, mezzo soprano between 146Hz$\sim$956Hz, tenor between 75Hz$\sim$503Hz and baritone between 73 Hz and 385 Hz. (3) Longitudinal glottal size of singers decreases depending on the high-low pitch variation while lattitudinal glottal size increases depending on high-low pitch variation. (4) Well-trained singers show over 5 times the vibrato rate of untrained singers and regular pitch variation during measured periods. Vibrato's intensity do not over 3 dB. (5) Singer's formant indicates professional voice depending on the each parts: 3,207 Hz for soprano, 3,057 Hz for mezzo soprano, 2,754 Hz for tenor and 2,560 Hz for baritone.. (6) $F_1$ of singing voice is higher than that of speech while $F_2\;and\;F_3$ of singing voice are lower than those of speech.

• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.19-24
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• 2009

In order to analysis the variation in vegetation area caused by topographical change at Jinudo in the Nakdong estuary, we used aerial photographs of Jinudo from 1998 to 2006. To extract an accuracy shoreline from these aerial photographs, a tide calibration was performed. We also estimated the annual variation in topographic area and vegetation area, and then analyzed the relationship between them by a correlation analysis. The following results were obtained: 1) The calibrated shoreline distance of Jinudo from 1998 to 2006 was estimated to have a range of (-)1,927 cm to (+)4,671 cm. 2) Annual changes in the topographic area and vegetation area in Jinudo have been increasing gradually from 1998, and the correlation coefficient between topographic area and vegetation area is 0.97. 3) The estimated topographic areas were with following order: southern (III), eastern (IV), northern (II) and western (I), while for the vegetation area, the order was southern (III), northern (II), eastern (IV) and western (I). 4) The vegetation area of the southern region (III) of Jinudo had the largest size among the regions, and was calculated to be $4.3{\sim}5.4$ times larger than the eastern region (IV).

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.255-258
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• 2002

Liquid rocket engines using liquefied natural gas (LNG) or methane as a fuel is known to have several good characteristics, such as high specific impulse compared to other hydrocarbon fuels, environment-friendly exhaust gas, low production cost, and re-usability with low soot generation in the cooling channel. In this study, experimental combustion chambers capable of using LNC and $CH_{4}$ are being researched through experimental firing tests, and within easy range of eyes' inspection, there are the periodical existence of soot or discoloration in the chamber wall surface. This result means that mixture ratio of oxidizer and fuel fluctuates periodically between outer-row injectors in the mixing head in the circumferential direction. Therefore, based on this phenomenon, the variation of mixture ratio near the chamber wall caused by the spill pattern of a shear coaxial injector was analyzed quantitatively and the thermal heat flux Into the cooling channel is modified. Then, the calculated and modified results are compared with the measured ones.

• Journal of the Korean Ceramic Society
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• v.43 no.6 s.289
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• pp.383-388
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• 2006

The varistor properties and DC accelerated aging characteristics of $ZnO-Pr_{6}O_{11}-CoO-Cr_{2}O_{3}$-based varistors were investigated at different $La_{2}O_3$ contents in the range of $0{\sim}2.0mol%$. The varistors doped with 0.5 mol% $La_{2}O_3$ exhibited good nonlinearity, with 81.6 in nonlinear coefficient. Increasing the $La_{2}O_3$ content further to 2.0 mol% caused the sintered density to increase, and the breakdown voltage and nonlinearity to decrease abruptly. The varistors with 0.5 mol% $La_{2}O_3$ exhibited the high electrical stability, with -1.14% in variation rate of breakdown voltage, -3.7% in variation rate of nonlinear coefficient, and +100% in variation rate of leakage current for specified DC accelerated aging stress condition (95% of breakdown voltage/$150^{\circ}C$/24 h).