• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.101-104
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• 2002

Simultaneous measurement of turbulent velocity and concentration field in a stirred mixer tank is carried out by using PIV/LIF technique. Instantaneous velocity fields are measured by a $1K\times1K$ CCD camera adopting the frame straddle method while the concentration fields are obtained by measuring the fluorescence intensity of Rhodamine B tracer excited by the second pulse of Nd:Yag laser light. Image distortion due to the camera view-angle is compensated by a mapping function. It is found that the general features of the mixing pattern are quite dependent on the local flow characteristics during the rapid decay of mean concentration. However, the small scale mixing seems to be independent on the local turbulent velocity fluctuation.

• Journal of Korea Water Resources Association
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• v.38 no.12 s.161
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• pp.1039-1049
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• 2005

The objective of this study is to produce optimal radar-derived rainfall for hydrologic utilization. The ground clutter and beam blockage effects from Mt. Kwanak station (E.L 608m) are removed from radar reflectivities by POD analysis. The reflectivities are used to produce radar rainfall data in the form of rain rates (mm/h) by the application of the Marshall-Palmer reflectivity versus rainfall relationship. However, these radar-derived rainfall are underestimated in temporal and spatial scale compared with observed one, so it is necessary to hire a correction scheme based on the gauge-to-radar (G/R) statistical adjustment technique. The selected watershed for studying the real-time correction of radar-rainfall estimation is the Soyang dam site, which is located approximately 100km east of Kwanak radar station. The results indicate that adjusted radar rainfall with the gauge measurement have reasonal G/R ratio ranged on 0.95-1.32 and less uncertainty with that mean standard deviation of G/R ratio are decreased by $9-28\%$. Mean areal precipitation from adjusted radar rainfall are well agreed to the observed one on the Soyang River watershed. It is concluded that the real-time bias adjustment scheme is useful to estimate accurate basin-based radar rainfall for hydrologic application.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.5
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• pp.406-414
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• 2017

An experimental study in a recirculating water channel was carried out to investigate the effect of large coherent structures to the skin friction on a flat plate. Particle Image Velocimetry (PIV) technique was used to quantify characteristic features of coherent structures growing to the boundary layer. In the PIV measurement, it is difficult to calculate the friction velocity near the wall region due to laser deflection and uncertainty so that Clauser fitting method at the logarithmic region was adopted to compute the friction velocity and compared with the one directly measured by the dynamometer. With changing the free-stream velocity from 0.5 m/s to 1.0 m/s, the activity of coherent structures in the logarithmic region was increased over three times in terms of Reynolds stress. The flow field was separated by Variable Interval Time Averaging (VITA) technique into the weak and the strong structure case depending on the existence large coherent structures in order to validate its effectiveness. The stream-wise velocity fluctuation was scanned through at the boundary thickness whether it had a large deviation from background flow. With coherent structures connected from near-wall to the boundary layer, mean wall shear stress was higher than that of weak structure case. Proper Orthogonal Decomposition (POD) analysis was also applied to compare the energy budget between them at each free-stream velocity.

• Journal of the Korean Society of Visualization
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• v.15 no.2
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• pp.59-67
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• 2017

To verify floatability of ABB (Air bubble barrier), we compared bubble swarm behavior with and without the air-driven ejector. Experiment was conducted using the fabricated air-driven ejector with 5 mm nozzle on the bottom of 1 m3 water tank. Reynolds number of air in the nozzle was ranged 1766-13248. We analyzed data with statistical method using image processing, particle mage velocimetry (PIV) and proper orthogonal decomposition (POD) analysis. As a result of POD analysis, there was no significant eigenmode in bubbly flow generated from the ejector. It means that more complex turbulent flows were formed by the ejector, thereby (1) making bubbles finer, (2) promoting three-dimensional energy transfer between bubble and water, and (3) making evenly distributed velocity profile of water. It is concluded that the air-driven ejector could enhance the performance of ABB.

• Journal of the Korean Society of Visualization
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• v.8 no.1
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• pp.31-38
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• 2010

An experimental study to evaluate dynamic structures of flow and turbulence characteristics in bubble-driven liquid flow in a rectangular tank with a varying flow rate of compressed air is conducted. Liquid flow fields are measured by time-resolved particle image velocimetry (PIV) with fluorescent tracer particles to eliminate diffused reflections, and by an image intensifier to acquire enhanced clean particle images. Instantaneous vector fields are investigated by using the two frame cross-correlation function and bad vectors are eliminated by magnitude difference technique. By proper orthogonal decomposition (POD) analysis, the energy distributions of spatial and temporal modes are acquired. When Reynolds number increases, bubble-induced turbulent motion becomes dominant rather than the recirculating flow near the side wall. The total kinetic energy transferred to the liquid from the rising bubbles shows a nonlinear relation regarding the energy input because of the interaction between bubbles and free surface.

• Toxicological Research
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• v.26 no.4
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• pp.285-291
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• 2010

Recently, reproductive and neurobehavioral effects of bisphenol A (BPA) have been documented, and thus a review was requested for BPA management direction by the government. Therefore, this study was performed to establish a Korean tolerable daily intake (TDI) for BPA. An expert committee, consisting of specialists in fields such as toxicology, medicine, pharmacology, and statistics, was asked to evaluate BPA health based guidance values (HbGVs). Although many toxicological studies were reviewed to select a point of departure (POD) for TDI, rat and mouse reproductive studies by Tyl et al. (2002, 2006), which were performed according to GLP standards and OECD guidelines, were selected. This POD was the lowest value determined from the most sensitive toxicological test. The POD, a NOAEL of 5 mg/kg bw/day, was selected based on its systemic toxicity as critical effects. An uncertainty factor of 100 including interspecies and intraspecies differences was applied to calculate the TDI. According to the evaluation results, a TDI of BPA for Korean was suggested at 0.05 mg/kg bw/day. In addition, the BPA exposure level based on food consumption by the Korean population was estimated as 1.509 ${\mu}g/kg$ bw/day, and the HI was evaluated at 0.03 when the TDI of 0.05 mg/kg bw/day was applied. This HI value of 0.03 indicated that hazardous effects would not be expected from BPA oral exposures. Although highly uncertain, further studies on low dose neurobehavioral effects of BPA should be performed. In addition, it is recommended that the 'as low as reasonably achievable' (ALARA) principle be applied for BPA exposure from food packaging materials in newborn infants and children.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.91-99
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• 2005

Flight compatibility certification is performed to substantiate the compatibility between ALQ-X ECM pod and KF-16D/RF-4C aircraft. A certification plan for the ALQ-X flight compatibility is established. Similarity analysis, mass/inertia analysis, structural analysis/test, and ground vibration test/flutter analysis are made to support the safety of MIL-HDBK-1763 Test 250 (Captive compatibility flight profile). Aircraft flew along flight envelope boundary with representative ALQ-X configurations. Handling qualities are evaluated by comparing flight characteristics of the aircraft with and without ALQ-X. Structural integrity and endurance is evaluated using measured flight test data. Results of these flight tests showed that ALQ-X is compatible with KF-16D/RF-4C without altering the flight envelope which has originally been certified for ALQ-88 and ALQ-119 ECM pods. ALQ-X certification program made following technical achievements: Type III certification for foreign designed fighter, flutter analysis program development using GVT results, and utilization of MIL-STD-1553B data bus in flight test.

• Horticultural Science & Technology
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• v.33 no.3
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• pp.309-316
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• 2015

In this experiment, five commercial cultivars and one wild species of loquat were used to investigate frost tolerance and enzymatic activities in leaves and young fruits under cold stress at $-3^{\circ}C$. The frost injury, malondialdehyde (MDA) content, and oxygen-scavenging enzyme activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were studied. This results showed that the wild species 'Wild Oak-leaf' loquat was the most frost tolerant among accessions tested, followed by the cultivar 'Golden Block'. Other cultivars, 'Wu Gong Bai', 'Taicheng 4', 'Xiangzhong 11' and 'Zaozhong 6', were relatively weak in frost tolerance. The enzymatic activities of SOD, POD and CAT increased initially and then decreased as the exposure time increased. However, the enzymatic peak occurred later in the frost-tolerant accession than in the frost-sensitive accession. The correlation coefficients of MDA contents between leaves and immature fruits were from 0.93 to 0.99 in the five commercial loquat cultivars. For the 'Wild Oak-leaf' loquat, the correlation coefficients of MDA and POD were 0.98 and 0.95, respectively, but the coefficients for SOD, CAT and APX were relatively low. In general, there were good correlations between loquat leaves and immature fruits in MDA content and enzyme activities. These results indicate that analysis of these physiological and biochemical activities in loquat leaves could potentially be used to predict the cold tolerance in loquat at immature fruit stage and to accelerate breeding programs for cold tolerance in loquat.

• Journal of Bio-Environment Control
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• v.22 no.1
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• pp.61-64
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• 2013

This study was conducted to investigate the general characteristics of raw okra seeds and the functional components of roasted okra seeds. The number of okra seed per pod was 78 in 'Greensod' and 88 in 'Beny'. The weight of okra seed per pod of 'Greensod' and 'Beny' were 4.4 g and 6.3 g, respectively. Free amino acid contents of the stir-fry and fresh okra seeds were measured as $2.69mg{\cdot}g^{-1}$ and $0.31mg{\cdot}g^{-1}$. Total polyphenolic compound content of the stirfry okra seeds was estimated as $12.61mg\;CGA{\cdot}g^{-1}$, compared to $2.54mg\;CGA{\cdot}g^{-1}$ fresh okra seeds, Thus, free amino acid and total polyphenolic compound contents in the stir-fry okra seeds were higher than fresh one, Antioxidant activities, such as DPPH and ABTS radical scavenging in the stir-fry okra seeds was the higher than fresh okra seeds.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.720-727
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• 2019

Resonating thermal lags of solid fuel with heat transfer oscillations generated by boundary layer oscillation is the primary mechanism of the occurrence of the LFI (Low Frequency Combustion Instability) in hybrid rocket combustion. This study was experimentally attempted to confirm that how the boundary layer was perturbed and led to the LFI. Special attention was also made on oxidizer swirl injection to investigate the contribution to combustion stabilization. Also the overall behavior of fluctuating boundary layer flow and the occurrence of the LFI was monitored as swirl intensity increased. Fluctuating boundary layer was successfully monitored by the captured image and POD (Proper Orthogonal Decomposition) analysis. In the results, oscillating boundary layer became stabilized as the swirl intensity increases. And the coupling strength between high frequency p', q' diminished and periodical amplification of RI (Rayleigh Index) with similar frequency band of thermal lag was also decreased. Thus, results confirmed that oscillating axial boundary layer triggered by periodic coupling of high frequency p', q' is the primary mechanism to excite thermal resonance with thermal lag characteristics of solid fuel.