• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.177-183
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• 2008

The sub-salt imaging technique becomes more crucial to detect the hydro-carbonates in petroleum exploration as the target reservoirs get deeper. However, the weak reflections from the sub-salt structures prevent us from obtaining high fidelity sub-salt image. As an effort to overcome this difficulty, we applied the waveform inversion by implementing multi-grid technique to the sub-salt imaging. Through the comparison between the conventional waveform inversion using fixed grid and the multi-grid technique, we confirmed that the waveform inversion using multi-grid technique has advantages over the conventional fixed grid waveform inversion. We showed that the multi-grid technique can complement he velocity estimation result of the waveform inversion for imaging the sub-salt structures, of which velocity model cannot be obtained correctly by the conventional fixed grid waveform inversion.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.4
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• pp.411-418
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• 2011

As a fish way is a structure for fish migrating well toward upper stream due to breaking river flow by a dam or dammed pool, the specific fish's swimming ability is one of the main factors in making a plan and managing it. In addition, it also needs to understand the current field in fish road to evaluate its performance. This study is aimed to analyze the swimming patterns with current velocity changes using a Particle Imaging Velocimetry (PIV) in order to understand the swimming ability of silver fish (Plecoglossus altivelis) that is one of the fishes migrating through the fish way of Nakdong River, and to analyze the 2 dimensional current field near to silver fish at swimming momentum. The results showed that average values of tail beat frequencies for continuous swimming with current velocity were 2.8 Hz at 0.3 m/s, 3.2 Hz at 0.4 m/s, 3.8 Hz at 0.5 m/s, respectively. The wake would be produced by direction turning of fish's tail fin and its magnitude would be verified by the difference of pressure. The pressure turbulent flow produced by its tail beat would be made in both sides, and then, the magnitude of wake should be the source of moving direction. The swimming momentum will help to support the primary factor in making a suitable design for specific fish species migrating toward the district river.

• Clinical and Experimental Pediatrics
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• v.53 no.1
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• pp.72-79
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• 2010

Purpose: Left ventricular (LV) hypertrophy and impaired diastolic function may occur early in systemic hypertension. Diastolic dysfunction is associated with increased cardiovascular risk. Tissue Doppler imaging (TDI)-derived tissue velocity and strain rate are new parameters for assessing diastolic dysfunction. The aim of this study is to determine whether TDI and strain rate imaging (SRI) would improve the ability to recognize early impaired diastolic and systolic functions compared with conventional echocardiography in hypertensive adolescents. Methods: We included 38 hypertensive patients with systolic blood pressure above 140 mmHg or diastolic blood pressure above 90 mmHg. Ejection fraction and myocardial performance index (MPI) were estimated by conventional echocardiography. Peak systolic myocardial velocity, early diastolic myocardial velocity (Em), and peak late diastolic myocardial velocity (Am) were obtained by using TDI and SRI. Results: In the hypertensive group, interventricular septal thickness was significantly increased on M-mode echocardiography. Em/Am was significantly decreased at the mitral valve annulus. Among hypertensive subjects, the E strain rate at basal, mid, and apex was significantly decreased. Systolic strain was significantly decreased at the septum in the hypertensive group. Conclusion: Strain rate might be a useful new parameter for the quantification of both regional and global LV functions and could be used in long-term follow up in hypertensive patients. Early identification by SRI of subjects at risk for hypertensive and ventricular dysfunction may help to stratify risk and guide therapy. Further studies, including serial assessment of LV structure and function in a larger number of adolescents with hypertension, is necessary.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3334-3343
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• 1996

A quantitative flow visualization technique was developed to measure velocity and temperature fields simultaneously in a two-dimensional cross section of thermo-fluid flows. Thermochromic liquid crystal(TLC) particles are used as temperature sensor and velocity tracers. Illuminating a thermo-fluid flow with a thin sheet of white light, the reflected colors from the TLC particles in the flow were captured simultaneously by two CCD cameras; a 3-chip CCD color camera for temperature field measurement and a black and white CCD camera for velocity field measurement. Variations of temperature field were measured by using a HSI true color image processing system and TLC solution. The relationship between the hue values of TLC color image and real temperature was obtained and this calibration curve was used to measure the true temperature under the same camera and illumination condition. The velocity field was obtained by using a 2-frame PTV technique using the concept of match-probability to track true velocity vectors from two consecutive image frames. These two techniques were applied at the same time to the unsteady thermal-fluid flow in a Hele-Shaw cell to measure the temperature and velocity field simultaneously and some results are discussed.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.87.2-87.2
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• 2013

We studied a fine-scale half ring-like structure around a pore seen from the high spectral and the high spatial resolution data. Our observations were carried out using the Fast Imaging Solar Spectrograph (FISS) and the InfraRed Imaging Magnetograph (IRIM) installed at the 1.6 meter New Solar Telescope of Big Bear Solar Observatory (BBSO) on 2012 July 19. During the observations, we found a fine-scale half ring-like structure located very close to a pore (~0.4 arcsec apart from the pore). It was seen in the far wing images of the $H{\alpha}$ and Ca II $8542{\AA}$ lines, but it was not seen in the line center images of two lines. The length of the structure is about 4200 km and the width is about 350 km. We determined its line-of-sight velocity using the Doppler shift of the centroid of the Ti II line ($6559.6{\AA}$, close to the $H{\alpha}$ line) and determined horizontal velocity using the NAVE method. we also investigated the magnetic configurations using the Stokes I, Q, U, and V maps of the IRIM. As a results, we found that it has a high blue-shift velocity (~2km) faster than the photospheric features and has a strong horizontal component of the magnetic field. Based on our findings, we suggest that it is associated with small flux emergence, which occurs very close to the pore. Even though it is very small structure, this kind of magnetic configuration can be in chare of the upper chromosphere heating, especially above the pore.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.4
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• pp.227-236
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• 1997

Quantitative analysis and imaging of elastic wave propagation are very important for the materials evaluation as well as flaw detection. The elastic wave propagation in an anisotropic media is more complex, and analysis and imaging become essential for flaw detection and materials evaluation. In the anisotropic media, the wave velocity is dependent on the propagation direction. In addition, the direction of group velocity is different from that of phase velocity, the direction of energy flow is not same as the propagation direction of wavefront (beam skewing effect). Especially, this effect becomes critical for the large anisotropic media such as fiber composite materials, and the results using elastic waves for those materials have to be analyzed considering the wave propagation mechanism. Since the analytical approach for the wave propagation in the anisotropic materials is limited, the numerical analysis such as finite difference method (FDM) have been used for these case. Therefore, 2-dimensional FDM program for the elastic wave propagation is developed, and wave propagation in anisotropic media are simulated.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.88.2-88.2
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• 2011

Fast Imaging Solar Spectrograph (FISS) is an instrument developed by Seoul National University and Korea Astronomy and Space Science Institute and installed at the 1.6 meter New Solar Telescope of Big Bear Solar Observatory. Using this instrument, we observed solar filaments and analyzed the data focusing on determining the temperature and non-thermal velocity. We inferred the Doppler absorption widths of $H{\alpha}$ and Ca II 8542$\bar{A}$ lines from the line profiles using the cloud model. From these values, we separately determined temperature and non-thermal velocity. Our first result came from a solar filament observed on 2010 July 29th. Temperature inside a small selected region of this ranges from 4500K to 12000K and non-thermal velocity, from 3.5km/s to 7km/s. We also found temperature varied a lot with time. For example temperature at a fixed point varied from 8000K to 18000K for 40 minutes, displaying an oscillating pattern with a period of about 8 minutes and amplitude of about 2000K. We will also present new results from filaments observed in 2011 summer.

• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1442-1450
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• 2017

In liquid metal fast breeder reactors, postulated failures of the plant protection system may lead to serious unprotected accidental consequences. Unprotected transients are generically categorized as transient overpower accidents and transient under cooling accidents. In both cases, core meltdown may occur and this can lead to a molten fuel coolant interaction (MFCI). The understanding of MFCI phenomena is essential for study of debris coolability and characteristics during post-accident heat removal. Sodium is used as coolant in liquid metal fast breeder reactors. Viewing inside sodium at elevated temperature is impossible because of its opaqueness. In the present study, a methodology to depict MFCI phenomena using a flat panel detector based imaging system (i.e., real time radiography) is brought out using a woods metal-water experimental facility which simulates the $UO_2-Na$ interaction. The developed imaging system can capture attributes of the MFCI process like jet breakup length, jet front velocity, fragmented particle size, and a profile of the debris bed using digital image processing methods like image filtering, segmentation, and edge detection. This paper describes the MFCI process and developed imaging methodology to capture MFCI attributes which are directly related to the safe aspects of a sodium fast reactor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.68-74
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• 2000

Experimental investigation on flame spread along suspended droplet arrays have been conducted with various droplet spacings and ambient air velocities. Especially, an opposed air stream is introduced to simulate fundamental flame spread behaviors in spray combustion. High-speed chemiluminescence imaging technique of OH radicals has been adopted to measure flame spread rates and to observe various flame spread behaviors. The fuel used is n-Decane and the air velocity varies from 0 to 17cm/s. The pattern of flame spread is grouped into two: a continuous mode and an intermittent one. It is found that there exists droplet spcings, above which flame spread does not occur. The increase of ambient air velocity causes the limit droplet spacing of flame spread to become small due to the increase of apparent flame stretch. As the ambient air velocity decreases, flame spread rate increases and then decreases after taking a maximum flame spread rate. This suggests that there exists a moderate air flowing to give a maximum flame spread rate due to enhanced chemical reaction by the increase of oxidizer concentration.

• Journal of Environmental Science International
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• v.22 no.5
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• pp.581-589
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• 2013

Surface Image Velocimetry(SIV) is an instrument to measure water surface velocity by using image processing techniques. Since SIV is a non-contact type measurement method, it is very effective and useful to measure water surface velocity for steep mountainous streams, such as streams in Jeju island. In the present study, a surface imaging velocimetry system was used to calculate the flow rate for flood event due to a typhoon. At the same time, two types of electromagnetic surface velocimetries (electromagnetic surface current meter and Kalesto) were used to observe flow velocities and compare the accuracies of each instrument. The comparison showed that for velocity distributions root mean square error(RMSE) was 0.33 and R-squared was 0.72. For discharge measurements, root mean square error(RMSE) reached 6.04 and R-squared did 0.92. It means that surface image velocimetry could be used as an alternative method for electromagnetic surface velocimetries in measuring flood discharge.