• Journal of Hydrospace Technology
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• v.1 no.1
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• pp.57-65
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• 1995

For the mechanism of ship capsizing, we can generally consider that it\`s caused due to pure loss of stability, parametric oscillation(low cycle resonance) of ship in waves and the broaching phenomena. Among them, low cycle resonance occurs due to the dynamic change of righting arm with respect to the relative position of ship to waves. The dynamic change depends on the encounter period of a ship in following waves. This paper discusses the following items : (1) An analytical expression of GZ curve varying with respect to the relative position of ship to waves, (2) Non-linear equation of motion describing low cycle resonance, (3) The effects of righting arm, stability range and encounter period on low cycle resonance.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2012.06a
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• pp.184-184
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• 2012

Recently, as a result of the application of large and multi-blade propellers with high efficiency for large vessels, the vertical bending stiffness of propulsion shafting system tends to be declined. For some specific vessels, the shaft arrangement leads to the forward stern tube bearing to be omitted, decreasing vertical bending stiffness. In this respect, decreased vertical bending stiffness causes the problem which is the blade order resonance frequency to be placed within the operational range of propulsion shafting system. To verify whirling vibration, the measurement should be carried out covering the range of MCR, however, the range is un-measurable. To resolve the measurement issue, this study shows the measuring method and the estimating method of whiling vibration by using resonance frequency of sub harmonic.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.2 no.2
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• pp.73-79
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• 2001

In this paper, the transmitted noise reduction performance of piezoelectric smart panels is experimentally studied. The proposed piezoelectric smart panels are comprised of plate structure on which piezoelectric sensor/actuators are bonded and sound absorbing material is provided. It is a combination of passive and active approaches utilizing a passive effect at high frequencies and an active effect at low frequencies. To prove the concept of piezoelectric smart panels, an acoustic measurement experiment is performed. An acoustic tunnel is designed and its acoustic characteristics are tested. Below 800Hz, the tunnel exhibits a plane wave guide characteristics. When an absorbing material is bonded on a single plate, a remarkable transmitted noise reduction in mid frequency range is observed except the first resonance frequency. By enabling the active control of single smart panel with negative feedback control. about 10dB noise reduction is achieved at the resonance frequencies. The double smart panel got 4dB at the first resonance frequency and has more potential to reduce the transmitted noise in a wide range frequency. Piezoelectric smart panels incorporating passive absorbing material and active piezoelectric devices is a promising technology for noise reduction in a wide range frequency.

• Transactions on Electrical and Electronic Materials
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• v.6 no.4
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• pp.159-163
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• 2005

We analyzed the fault current limiting characteristics of a flux-lock type $high-T_c$ super­conducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element. However, the impedance of the flux lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field. From the experimental results, we investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.640-644
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• 2010

Information technology devices, such as cellular phones, MP3s and so on, due to restrictions of space, require thin and small micro-speakers to generate sound. The reduction of the size of micro-speakers has resulted in the decrease of sound quality, due to such factors as frequency range and sound pressure level. In this study, the acoustical properties of oval microspeakers has been studied as a function of pattern shape on the diaphragm. The other conditions of micro-speakers, except for the pattern, was not changed. When the pattern is present on the diaphragm and the shape of pattern was a whirlwind, the resonance frequency was reduced due to the decrease of tensile strength of diaphragm. The patterns presented in the semi-minor axis of diaphragm did not effect a change of resonance frequency. However, increasing the number of patterns in the semimajor axis of diaphragm became a reason for the decrease of resonance frequency on edge side. When the depth of pattern on edge side was increased, the resonance frequency was decreased due to reduction of geometrical stiffness. If the height of edge and dome were increased, the resonance frequency and geometrical stiffness rapidly increased. After reaching the maximum values, they began to decrease with the continuous increase of height.

• Journal of Biomedical Engineering Research
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• v.36 no.6
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• pp.241-250
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• 2015

Noninvasive temperature monitoring is feasible with Magnetic Resonance Imaging (MRI) based on temperature sensitive MR parameters such as $T_1$ and $T_2$ relaxation times, Proton Resonance Frequency shift (PRFs), diffusion, exchange process, magnetization transfer contrast, chemical exchange saturation transfer, etc. While the temperature monitoring is very useful to guide the thermal treatment such as RF hyperthermia or thermal ablation, the optimization of the MR thermometry method is essential because the range of temperature measurement depends on the choice of the measurement methods. Useful temperature range depends on the purpose of treatment methods, for example, $42^{\circ}C$ to $45^{\circ}C$ for RF hyperthermia and over $50^{\circ}C$ for thermal ablation. In this paper, MR thermometry methods using $T_1$ and $T_2$ relaxation times and PRFs-based MR thermometry are tried on a 3.0 T MRI system and their results are reported and compared. In addition, the scanning protocol and temperature calculation algorithms from $T_1$ and $T_2$ relaxation times and PRFs are optimized for the different temperature ranges for the purpose of RF hyperthermia and/or thermal ablation.

• Proceedings of the KSMRM Conference
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• 1996.10a
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• pp.18-18
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• 1996

• The Bulletin of The Korean Astronomical Society
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• v.31 no.2
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• pp.33-33
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• 2006

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.13 no.1
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• pp.19-23
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• 2007

Shock and vibration inputs are transmitted from the transporting vehicle through the packaging to the fruit. The vibration causes sustained bouncing of fruits against each other and the container wall. The steady state vibration input may cause serous fruit injury, and the damage is particularly severe if the fruits are bounced at its resonance frequency. The determination of the resonance frequencies of the fruits and vegetables may help the packaging designer to determine the proper packaging system providing adequate protection for the fruits, and to understand the complex interaction between the components of the fruits when they relate to expected transportation vibration inputs. To analyze the vibration properties of the apples for optimum packaging design during transportation, random vibration tests were carried out. In the random vibration test, the resonance frequency and PSD of the packaged freight of apples in the test were in the range of 82 to 97 Hz and 0.0013 to $0.0021G^2/Hz$ respectively and the resonance frequency and PSD of the packaged apples in the test were in the range of 13 to 71 Hz and 0.0143 to $0.0923G^2/Hz$.

• Journal of the Korean Magnetic Resonance Society
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• v.12 no.2
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• pp.96-102
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• 2008

Direct quantification of methanol in polymer electrolyte membrane (PEM) by solid-state nuclear magnetic resonance (NMR) spectroscopy was studied and the methanol concentrations in PEM produced by crossover and diffusion were compared. The error range of the quantification was not smaller than ${\pm}15%$ and the amount of the methanol crossed over in our direct methanol fuel cells (DMFCs) was less than the methanol diffused to PEM. The methanol concentration in the PEM of the DMFC operated at different current densities were equivalent.