• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1164-1171
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• 2020

T-junction structures play an important role in nuclear power plant systems. Research on liquid entrainment is mostly based on small-scale branch pipes (d/D ≤ 0.2) and attention paid to large-scale branch pipes (0.33 < d/D < 1) is insufficient. Accordingly, this study implements a series of experiments on the liquid entrainment of T-junction with different angles (32.2°,47.9°,62.3°,90°) through a large-scale branch (d/D = 0.675). The onset liquid entrainment is related to the gas phase Froude number Fr_g, the dimensionless gas chamber height h_b/d and the branch pipe angle 𝜃. As Fr_g increases, h_b/d also rises. With a constant h_b/d, the onset liquid entrainment changes from droplets entrainment by the gas phase to that by the rising liquid film. The steady-state liquid entrainment is related to w_3g, h/d and 𝜃. With constant w_3g and h/d, the branch quality grows as the branch angle increases. With a certain h/d, the branch quality increases, as the w_3g number increases.

• Geotechnical Engineering
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• v.14 no.2
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• pp.67-78
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• 1998

Microtunnelling is a technique applied to install a small-size tunnel in a soft cohesionless ground. In microtunnelling, a series of concrete tubular segments are pushed from a starting pit to power-line tunnel under a runway of JFK international airport at New York. During the microtunneling process, bentonite is jetted with very hyh pressure through a nozzle to advance disturbance in the subgrade caused by the pressurized bentonite in the aspects of subgrade stiffness. SASW measurements were performed on the runway above the center line of the shear wave velocity profiles. Besides the change of subgrade stiffness, the change of subgrade strength was also evaluated by the site-specific relationships between shear wave velocity and N value, which was determined by N values. The estimated N values gave a clue to the understanding of the change of subgrade strength.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.967-973
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• 2009

In this paper, X-band satellite communication oscillator of double phase locked is implemented by constructing a couple of phased-locked loop, and then we have analyzed the phase noise of designed PLL-DRO. The designed phase-locked oscillator is consist of series feedback DRO, frequency divider, phase detector, loop filter and programmable PLL-IC. By dividing oscillation frequency of 12.6 GHz into two frequencies, it exhibits output power of 15.32 dBm at 6.3 GHz. Phase noises of implemented oscillator are -81 dBc/Hz@100Hz, -100.86 dBc/Hz@1 kHz, -111.12 dBc/Hz@10 kHz, -116 dBc/Hz@100 kHz and -140.49 dBc/Hz@1 MHz respectively. These indicate excellent stable operation of oscillator and very good phase noise characteristics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.900-905
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• 2009

A common drain feedback CMOS wideband LNA with current bleeding and input inductive series-peaking techniques is presented in this paper. DC coupling is adopted between cascode and feedback amplifiers, so that the gain and NF of the LNA can be dynamically controlled by adjusting the bleeding current. The fabricated LNA shows the bandwidth of 2.5 GHz. The high gain mode shows 17.5 dB gain with $1.7{\sim}2.8\;dB$ NF and consumes 27 mW power and the low gain mode has 14 dB gain with $2.7{\sim}4.0\;dB$ NF and dissipates 1.8 mW from 1.8 V supply.

• Journal of Korean Biological Nursing Science
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• v.15 no.4
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• pp.202-209
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• 2013

Purpose: The purpose of this study is to investigate relationships among sun-screening agents use, bone health promotion behavior, and bone mineral density. Methods: The participants of this study were 105 female college students. The data were collected using a questionnaire about sun-screening agent use and bone health promotion behavior. Bone mineral density was measured with Ultrasound Bone Densitometer/Osteo Pro Series. Data were analyzed with the SPSS/Win 18.0 program. Results: The mean Z-score in female college students was $-1.04{\pm}1.26$, and the T-score was $-1.16{\pm}1.22$, 21.39% of the participants have osteopenia. Bone mineral density showed a significant correlation with weight. Bone mineral density showed no significant correlation between sun-screening agent use, and bone health promotion behavior. There was a significant correlation between protection power of sun-screening agents and the protection by clothes. Conclusion: According to the results of this study, we need to develop an intervention program for bone health promotion of female college students.

• Journal of The Korean Association of Information Education
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• v.14 no.4
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• pp.651-658
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• 2010

This paper is to study adequacy of developing tutorial series for primary school students regarding MOS certification and to analyze a validity. In order to analyze a level of difficulty, current primary teaching materials being used after class, in comparison with ICT discretionary hour materials being used through primary discretionary class, were evaluated. It was done by primary teachers with in- depth understanding of a level of difficulty and after class instructors using Likert scale through quantitative analysis. As a result, level of PowerPoint has a satisfactory fit (76%), however, the degree of difficulty of Word and Excel is quite high. On its subject matter, there is quite a dispute with present curriculum. Therefore, in order to introduce MS-Word or Excel, it is necessary to adjust a level of difficulty or related subjects according to the level of students.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1133-1138
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• 2005

In this study, we have prepared, as the pluse power source, a commercially supplied Li-ion battery with a capacity of 700 mAh and AC resistivity of 60 md at 1 kHz and nonaqeous asymmetric hybrid capacitor composed of an activated carbon cathode and MCMB anode, and have examined the electrochemical characteristics of hybrid capacitor and the pulse performances of parallel connected hybrid capacitor/Li-ion battery source. The nonaqueous asymmetric hybrid capacitors constituted with each stack number of pairs composed of the cathode, the porous separator and the anode electrode were housed in Al-laminated film cell. The 10 stacked hybrid capacitor, which was charged and discharged at a constant current at 0.25 $mA/cm^2$ between 3 and 4.3 V, has exhibited the capacitance of 108F and the lowest equivalent series resistance was 32 $m{\Omega}$ at 1 kHz. On the other hand, the enhanced run time of Li-ion battery assisted by the hybrid capacitor was obtained with increasing of current density and pulse width in Pulse mode. The best improvement, $84\;\%$ for hybrid capacitor/Li-ion battery was obtained in the condition of a 7C-rate pulse (100 msec)/0.5C-rate standby/$10\;\%$ duty cycle.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.159-159
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• 2010

We conducted bum-in test by current stress to evaluate acceleration reliability characteristics about p-resistivity influence of GaN-based light-emitting diodes. The LEDs used in this study are the polarization field-induced LED(PF-LED) having low p-resistivity and the highly resistive LED(HR-LED) having high p-resistivity. The result of high stress experiment shows that current crowding phenomenon is occurred from the center of between p-bonding pad and n-bonding pad to either electrodes. In addition, series resistance and optical power decrease dramatically. These results means that the resistance of between p-bonding pad and p-GaN affect reliability. That's why we need to consider the ohmic contact of p-bonding pad when design the high efficiency and high reliability LEDs.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.4
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• pp.153-161
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• 2017

Liquid storage tank is one of the major infrastructures and generally used to store gases, drinking and utilizing water, dangerous fluids, fire water and so on. According to the recent reports and experiences, the tank structures are damaged in many earthquakes due to their low energy dissipating capacity. Therefore, many researchers have been tried to know the dynamic properties of the tanks including liquids. However, vary limited experimental studies are carried out using relatively small tank models. In this study, a series of shaking table tests are performed with maximum 2 m cubic rectangular liquid storage tanks made of steel to measure the natural frequency and estimate damping coefficient of impulsive and convective mode of the tanks. Especially, the damping values under different shapes and excitation methods are estimated by logarithmic decrement method and half power band-pass method and compared with current design code and standards such as ASCE 7, Eurocode 8 and NZS. Test results show that the impulsive mode damping is around 2% which is proposed by general standards and codes but the impulsive mode damping is 0.13% average that is slightly lower than the code recommendation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.357-365
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• 2013

The 4 by 4 series slot sub-array antenna is proposed using substrate integrated waveguide(SIW) technology for 35 GHz of Ka band application. The proposed antenna is realized with multi-layered structure for compact size and easy integration features. 4 by 4 radiating slots are arrayed on top PCB with equal spacing and the feeding SIWs are arranged on middle and bottom PCBs for uniform power distribution. The multi-layered antenna is realized using RT/Duroid 5880 that has dielectric constant of 2.2 and the total antenna size is $750.76mm^2$. The individual parts such as radiators and feeding networks are simulated using full-wave simulator CST MWS. Furthermore, the total sub-array antenna also fabricated and measured the electrical performances such as impedance bandwidth under the criteria of -10 dB(490 MHz), maximum gain(18.02 dBi), sidelobe level(SLL)(-11.0 dB), and cross polarization discrimination (XPD)(-20.16 dB).