• Journal of Power Electronics
• /
• v.6 no.1
• /
• pp.1-7
• /
• 2006

This paper is a record of the study on a high efficiency and high power chopper based on the new soft switching method QRAS (Quasi~resonant Regenerating Active Snubber) designed for a Fuel Cell Electric Vehicle (FCEV). This power chopper is basically proposed for 25kHz soft switching. To confirm the practicality and effectiveness of the converter, the fabrication of a prototype-model using IGBTs was completed. Additionally, a 8kW rating test, a light load test, a current discontinuous mode test and a stable operation resonance test was completed. The circuit geometry, the basic operation, and the 8kW one-tenth-prototype test results are reported with a $97.5\%$ efficiency measurement.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.11a
• /
• pp.264-269
• /
• 2008

This paper presents the summary of control of abnormal vibration found in the COP motors of a nuclear power plant. All six identical units of COP pump-motor assemblies showed unstable vibration pattern of which one or two showed higher vibration enough to exceed the allowable level from the installation stage. Many trials of test, measurement, overhaul and replacement had been repeated to investigate and solve the problem but only to reach unsatisfactory settlement. Recently several times of site tests are made and followed by significant diagnostic actions in which the authors group participated. It was found that the coupled shafting system of motor and pump is in close resonance with the $1^{st}$ shaft rotating speed. Redesign of topside motor bearing clearance is made to increase bearing stiffness and hence to avoid the resonance which consequently led to reduce the troubled vibration to allowable and stable status.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.22 no.8
• /
• pp.713-719
• /
• 2012

This paper deals with the natural frequency analysis and two experiments to evaluate first twisting and bending natural frequency of railway vehicle. The KS R 9228 testing method is generally performed as pseudo FRF(frequency response function) which is widely used by two accelerometers. The exciting method is utilized using the load weight(1 ton release). The modal testing is used to verify KS R 9228 testing result and the natural frequency analysis result. The first twisting and bending natural frequency should be above 10 Hz by resonance which is mostly generated between bogie and vehicle frame exciting low frequency. The first twisting and bending natural frequency of railway vehicle are successfully verified between analysis and test.

• Journal of the Korean Magnetic Resonance Society
• /
• v.15 no.1
• /
• pp.54-68
• /
• 2011

$^1H$ nuclear magnetic resonance (NMR) spectroscopy of biological samples has been proven to be an effective and nondestructive approach to probe drug toxicity within an organism. In this study, ketoprofen toxicity was investigated using $^1H$-NMR spectroscopy coupled with multivariate statistical analysis. Histopathologic test of ketoprofen-induced acute gastrointestinal damage in rats demonstrated a significant dose-dependent effect. Furthermore, principal component analysis (PCA) derived from $^1H$-NMR spectra of urinary samples showed clear separation between the vehicle-treated control and ketoprofen-treated groups. Moreover, PCA derived from endogenous metabolite concentrations through targeted profiling revealed a dose-dependent metabolic shift between the vehicle-treated control, low-dose ketoprofen-treated (10 mg/kg body weight), and high-dose ketoprofen-treated (50 mg/kg) groups coinciding with their gastric damage scores after ketoprofen administration. The resultant metabolic profiles demonstrated that the ketoprofen-induced gastric damage exhibited energy metabolism perturbations that increased urinary levels of citrate, cis-aconitate, succinate, and phosphocreatine. In addition, ketoprofen administration induced an enhancement of xenobiotic activity in fatty oxidation, which caused increase levels of N-isovalerylglycine, adipate, phenylacetylglycine, dimethylamine, betaine, hippurate, 3-indoxylsulfate, N,N-dimethylglycine, trimethyl-N-oxide, and glycine. These findings demonstrate that $^1H$-NMR-based urinary metabolic profiling can be used for noninvasive and rapid way to diagnose adverse drug effects and is suitable for explaining the possible biological pathways perturbed by nonsteroidal anti-inflammatory drug toxicity.

• Journal of Sensor Science and Technology
• /
• v.28 no.6
• /
• pp.371-376
• /
• 2019

We have developed an acoustic resonance inspection system to inspect the welding defects in the mechanical parts fabricated using friction stir welding method. The inspection system was consisted of a DAQ board, a microphone sensor, an impact hammer, and controlled by a PC software. The system was developed to collect and analyze the sound signal generated by hitting the sample with an impact hammer to determine whether it is defective. In this study, 100% welded good samples were compared with 95%, 90%, and 85% welded samples, respectively. The variation of the completeness in welding did not affect the visual appearance in the samples. As a result of analyzing the natural frequencies of the good samples, the five natural frequency peaks were identified. In the case of the defective samples, the frequency change was observed. The welding failure detection time was fast enough to be only 0.7 seconds. Employing our welding defect inspection system to the actual industrial field will maximize the efficiency of quality inspection and thus improve the productivity.

• Journal of Biomedical Engineering Research
• /
• v.28 no.1
• /
• pp.75-83
• /
• 2007

Elasticity is an important physical property of biological tissues. Differences in elasticity can help facilitate the diagnosis of tumors and their extent. Magnetic Resonance Elastography (MRE) tries to visualize images of tissue elasticity by externally applying shear stress on the surface of an imaging object. Applied shear stress induces internal displacements that can be measured from MR phase images. In order to conduct MRE imaging experiments, we need to first develop a vibrator. We found that there does not exist enough technical information to design the MRE vibrator. In this paper, we describe the theory, design and construction of an MRE vibrator. We report the performance of the developed vibrator using two different test methods. We found that the vibrator successfully induces enough internal displacements that can be imaged using an MRI scanner. We suggest future studies of numerous MRE imaging experiments using the vibrator.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.05b
• /
• pp.173-176
• /
• 2004

The piezoelectric ceramics for AE sensor piezoelectric devices are desirable to possess higher resonance vibrations. The compositions of $0.9Pb(Zr_xTi_{1-x})O_3-0.1Pb(Mn_{1/3}Nb_{1/3}Sb_{1/3})O_3$ (PZT-PMNS) in this work are selected for obtaining especially large electromechanical coupling factor, high mechanical quality factor and high Curie temperature. This ceramic has higher piezoelectric activity and higher electromechanical coupling factor, but the ceramic has lower Curie temperature. The piezoelectric and dielectric characteristics of PZT-PMNS ternary system are investigated as functions of $Ti^{2+}$, $Zi^{2+}$ mol rate. As the results, MPB(morphotropic phase boundary) in this piezoelectric ceramic is x=0.522. Resonance vibrations of PZT ceramics are investigated as ball-bearing drop test. For the use of AE sensor that driving with pre-amplifier, filter circuit after packed this ceramic and an elastic body.

• Dementia and Neurocognitive Disorders
• /
• v.16 no.2
• /
• pp.48-53
• /
• 2017

Background and Purpose Torrance Tests of Creative Thinking (TTCT) is a well-known and commonly used measure of creativity. However, the TTCT-induced creative hemodynamic brain activity is rarely revealed. The purpose of this study is to elucidate the neural correlates of creative thinking in the setting of a modified version of the figural TTCT adapted for an functional magnetic resonance imaging (fMRI) experiment. Methods We designed a blocked fMRI experiment. Twenty-five participants (11 males, 14 females, mean age $19.9{\pm}1.8$) were asked to complete the partially presented line drawing of the figural TTCT (creative drawing imagery; creative). As a control condition, subjects were asked to keep tracking the line on the screen (line tracking; control). Results Compared to the control condition, creative condition revealed greater activation in the distributed and bilateral brain regions including the left anterior cingulate, bilateral frontal, parietal, temporal and occipital regions as shown in the previous creativity studies. Conclusions The present revealed the neural basis underlying the figural TTCT using fMRI, providing an evidence of brain areas encompassing the figural TTCT. Considering the significance of a creativity test for dementia patients, the neural correlates of TTCT elucidated by this study may be valuable to evaluate the brain function of patients in the clinical field.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.21 no.7
• /
• pp.21-27
• /
• 2022

This study was conducted to evaluate the structural stability of a CNC automatic lathe structure and avoid resonance. The analysis conditions were analyzed by applying the weight of the upper assembly. From the structural analysis, the stress and deformation were low, and the safety factor was high. From the dynamic characteristic analysis, it was determined that resonance does not occur because the natural frequency is outside the driving range. The error between the dynamic characteristic analysis and vibration test results is very low; thus, the reliability of the analysis results can be secured.

• The Journal of the Acoustical Society of Korea
• /
• v.26 no.1
• /
• pp.1-7
• /
• 2007

This paper presents a study on acoustic characteristics and sound generation mechanism of Cryptotympana atratas' songs which cause noise problems in summer days. The waveforms & FFT of Cryptotympana atratas' songs in nature were analyzed, and the actions of tymbals were visualized by the high speed camera. In order to know resonance frequency of the abdominal cavity of male Cryptotympana atrata, the sine sweep test was done. It was observed from the experimental results that Cryptotympana atrata's two tymbals act asymmetrically with respect to time & shape, and make a variety of frequencies every time it vibrates. It was also shown that Cryptotympana atratas' have a structure that cause resonances sounds only in a $7{\sim}7.5 kHz$ bandwidth.