• The Korean Journal of Quaternary Research
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• v.20 no.1 s.26
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• pp.9-27
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• 2006

The East Asian (China, Korea and Japan) summer monsoon precipitation and its variability are examined from the outputs of the 22 coupled climate models performing coordinated experiments leading to the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) following the multi-model ensemble (MME) technique. Results are based on averages of all the available models. The shape of the annual cycle with maximum during the summer monsoon period is simulated by the coupled climate models. However, models fail to simulate the minimum peak in July which is associated with northward shifts of the Meiyu-Changma-Baiu precipitation band. The MME precipitation pattern is able to capture the spatial distribution of rainfall associated with the location of the north Pacific subtropical high and the Meiyu-Changma-Baiu frontal zone. However precipitation over the east coast of China, Korea-Japan peninsular and the adjoining oceanic regions is underestimated. Future projections to the radiative forcing of doubled $CO_2$ scenario are examined. The MME reveals an increase in precipitation varying from 5 to 10 %, with an average of 7.8 % over the East Asian region at the time of $CO_2$ doubling. However the increases are statistically significant only over the Korea-Japan peninsula and the adjoining north China region. The increase in precipitation may be attributed to the projected intensification of the subtropical high, and thus the associated influx of moist air from the Pacific to inland. The projected changes in the amount of precipitation are directly proportional to the changes in the strength of the subtropical high. Further a possible increase in the length of the summer monsoon precipitation period from late spring through early autumn is suggested.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.2
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• pp.92-108
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• 2017

Present work shows a numerical method to analysis of interaction analysis between solitary wave and onshore bridge. Numerical simulation is carried out by TWOPM-3D (three-dimensional one-field model for immiscible two-phase flows), which is based on Navier-Stokes solver. To do this, the solitary wave is generated numerically in numerical wave channel, and numerical results and experimental results were compared and analyzed in order to verify the applicability of force acting on an onshore bridge. From this, we discussed precisely the characteristics of horizontal and vertical forces (uplift and downward forces) changes including water level and velocity changes due to the variation of solitary wave height, water depth, onshore bridge's location and type, and number of girder. Furthermore, It is revealed that the maximum horizontal and vertical forces acting on the girder bridge show different varying properties according to the number of girder, although each maximum force acting on the girder bridge is proportional to the increasement of incident solitary wave height, and the entrained air in the fluid flow affects the vertical force highly.

• Korean Journal of Remote Sensing
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• v.15 no.2
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• pp.119-130
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• 1999

At present, many ground stations all over the world are using NORAD orbit element data in order to track and communicate with Earth orbiting satellites. The North American Aerospace Defense Command (NORAD) observes thousands of Earth orbiting objects on daily basis and provides their orbital information via internet. The orbital data provided by NORAD, which is also called two line element (TLE) sets, allows ground stations to predict the time-varying positions of satellites accurately enough to communicate with the satellites. In order to complete the mission of a high resolution remote sensing satellite which requires very high positional determination and control accuracy, however, a mission control and tracking ground station is dedicated for the observation and positional determination of the satellite rather than using NORAD orbital sets. In the case of KITSAT-3, NORAD orbital elements are currently used for image acquisition planning and for the processing of acquired images due to the absence of a dedicated KITSAT-3 tracking ground system. In this paper, we tested and analyzed the accuracy of NORAD orbital elements and the appropriate prediction model to determine how accurately a satellite acquisites an image of the location of interest and how accurately a ground processing system can generate the catalog of the images.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.18-25
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• 2000

A two-color particle image velocimetry (PIV) has been developed for measuring two dimensional velocity flowfields and applied to a Mach 2.0 supersonic nozzle. This technique is similar to a single-color PIV technique except that two different color laser beams are used to solve the directional ambiguity problem. A green-color laser sheet (532 nm: 2nd harmonic beam of YAG laser) and a red-color laser sheet (619 nm: output beam from YAG pumped Dye laser using Rhodamine 640) are employed to illuminate the seeded particles. A high resolution (3060${\times}$2036) digital color CCD camera is used to record the particle positions. This system eliminates the photographic-film processing time and subsequent digitization time as well as the complexities associated with conventional image shifting techniques for solving directional ambiguity problem. The two-color PIV also has the advantage that velocity distributions in high speed flowfields can be measured simply and accurately by varying the time interval between two different laser beams due to its high signal-to-noise ratio and thereby less requirement of panicle pair numbers for a velocity vector in one interrogation spot. The velocity distribution in the Mach 2.0 supersonic nozzle has been measured and the over-expanded shock cell structure can be predicted by the strain rate field. These results are compared and analyzed with the schlieren photograph for the velocity distributions and shock location.

• Journal of radiological science and technology
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• v.42 no.3
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• pp.167-173
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• 2019

The Cobey method and the modified Cobey method are most commonly used in clinical practice. Therefore, the purpose of this study was to investigate the radiological differences between Cobey and modified Cobey and provide radiographic information about changes of hindfoot image with X-ray entrance center and tube angle change in modified Cobey. This study was performed on foot and ankle phantom. First, for image comparison of Cobey and modified Cobey, the images obtained by applying the same X-ray entrance center to the ankle joint were compared and analyzed. Second, in the modified Cobey, the X-ray entrance center is set as ankle joint and lateral malleolus. The X-ray tube angle was varied from $10^{\circ}$ to $40^{\circ}$ at $5^{\circ}$ intervals for each X-ray entrance center. The images obtained by varying the X-ray tube angle from $10^{\circ}$ to $40^{\circ}$ at intervals of $5^{\circ}$ for each X-ray entrance center were compared and analyzed. The irradiation conditions were the same with 110 kVp, 200 mA, 10 ms, and 110 cm of source - image receptor distance (SID). Image evaluation was performed by two radiologists. Measurements were made on the lateral point, middle point, and calcaneus width based on a hypothetical line parallel to the calcaneal tuberosity. Data were analyzed by using descriptive statistics as the mean of the distance to each measurement location. The modified Cobey was longer than the Cobey by an average of 3 to 4 mm lateral and medial points, and the calcaneus width was similar (ICC = 0.939). In modified Cobey method, when the X-ray entrance center is ankle joint, the lateral point is about 3 mm and the medial point is about 4.3 mm longer than lateral malleolus. Also, when the X-ray tube angle is more than $20^{\circ}$, the degree of distortion is large. The ICCs for the lateral, medial point, and calcaneus width were 0.998, 0.961, and 0.997, respectively, as the X-ray entrance center and tube angle were changed. There was no significant difference between Modified Cobey and Cobey. Modified Cobey showed no need to compensate the $20^{\circ}$ detector angle of the Cobey. In addition, we suggest that tube angle should be limited within $20^{\circ}$ when modified Cobey is performed.

• Journal of International Area Studies (JIAS)
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• v.14 no.4
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• pp.27-52
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• 2011

The regions of Central Asia have each acquired an elevated strategic importance in the new security paradigm of post-September 1lth. Comprised of five states, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan, Central Asia's newly enhanced strategic importance stems from several other factors, ranging from trans-national threats posed by Islamic extremism, drug production and trafficking, to the geopolitical threats inherent in the region's location as a crossroads between Russia, Southwest Asia and China. Although the U.S. military presence in the region began before September 11th, the region became an important platform for the projection of U.S. military power against the Taliban in neighboring Afghanistan. The analysis goes on to warn that 'with US troops already in place to varying extents in Central Asian states, it becomes particularly important to understand the faultlines, geography, and other challenges this part of the world presents'. The Kyrgyz military remains an embryonic force with a weak chain of command, the ground force built to Cold War standards, and an almost total lack of air capabilities. Training, discipline and desertion - at over 10 per cent, the highest among the Central Asian republics - continue to present major problems for the creation of combat-effective armed forces. Kyrgyzstan has a declared policy of national defence and independence without the use of non-conventional weapons. Kyrgyzstan participates in the regional security structures, such as the Collective Security Treaty Organisation (CSTO) and the Shanghai Co-operation Organisation (SCO) but, in security matters at least, it is dependent upon Russian support. The armed forces are poorly trained and ill-equipped to fulfil an effective counter-insurgency or counter-terrorist role. The task of rebuilding is much bigger, and so are the stakes - the integrity and sovereignty of the Kyrgyz state. Only democratization, the fight against corruption, reforms in the military and educational sectors and strategic initiatives promoting internal economic integration and national cohesion hold the key to Kyrgyzstan's lasting future

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.610-620
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• 2022

An acoustic vector sensor can simultaneously receive vector quantities, such as particle velocity and acceleration, as well as acoustic pressure at one location, and thus it can be used as a single input multiple output receiver in underwater acoustic communication systems. On the other hand, vector signals received by a single vector sensor have different channel characteristics due to the azimuth angle between the source and receiver and the difference in propagation angle of multipath in each component, producing different communication performances. In this paper, we propose a channel parameter-based weighting method to improve the performance of an acoustic communication system using a single vector sensor. To verify the proposed method, we used communication data collected from the experiment conducted during the KOREX-17 (Korea Reverberation Experiment). For communication demodulation, block-based time reversal technique which is robust against time-varying channels were utilized. Finally, the communication results showed that the effectiveness of the channel parameter-based weighting method for the underwater communication system using a single vector sensor was verified.

• Journal of the Korean Society of Radiology
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• v.85 no.1
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• pp.3-23
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• 2024

Intervertebral disc herniation is frequently encountered in radiological practice. Sequestered disc herniation occurs when the disc material undergoes degeneration and completely loses continuity with the parent nucleus pulposus. Sequestered discs can reside within and outside the spinal canal, exerting a mass effect on adjacent structures, compressing nerve pathways, and eliciting a range of clinical symptoms. In particular, sequestered discs within the dura cannot be identified without durotomy. Therefore, precise preoperative localization is crucial for surgical planning. On MRI, the signal intensity of the sequestered disc may vary due to independent degeneration processes. Additionally, most sequestered disc fragments show varying degrees of peripheral enhancement depending on the degree of angiogenesis and granulation around the isolated tissue. In this article, we review various imaging findings and the location of the sequestered disc to provide patients with an accurate diagnosis and appropriate treatment direction.

• The Journal of Korean Society for Radiation Therapy
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• v.28 no.1
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• pp.47-55
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• 2016

To evaluate the position accuracy of the MLC. This study analyzed the variations of the dosimetric leaf gap(DLG) and MLC transmission factor to reflect the location of the MLC leaves according to the dose rate variation for dynamic IMRT. We used the 6 MV and 10 MV X-ray beams from linear accelerator with a Millennium 120 MLC system. We measured the variation of DLG and MLC transmission factor at depth of 10 cm for the water phantom by varying the dose rate to 200, 300, 400, 500 and 600 MU/min using the CC13 and FC-65G chambers. For 6 MV X-ray beam, a result of measuring based on a dose rate 400 MU/min by varying the dose rate to 200, 300, 400, 500 and 600 MU/min of the difference rate was respectively -2.59, -1.89, 0.00, -0.58, -2.89%. For 10 MV X-ray beam, the difference rate was respectively ?2.52, -1.69, 0.00, +1.28, -1.98%. The difference rate of MLC transmission factor was in the range of about ${\pm}1%$ of the measured values at the two types of energy and all of the dose rates. This study evaluated the variation of DLG and MLC transmission factor for the dose rate variation for dynamic IMRT. The difference of the MLC transmission factor according to the dose rate variation is negligible, but, the difference of the DLG was found to be large. Therefore, when randomly changing the dose rate dynamic IMRT, it may significantly affect the dose delivered to the tumor. Unless you change the dose rate during dynamic IMRT, it is thought that is to be the more accurate radiation therapy.

• Journal of Radiation Protection and Research
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• v.37 no.4
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• pp.181-190
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• 2012

Naturally occurring radioactive materials (NORM) in building materials are main sources of external radiation exposure to the general public. The objective of this study was to assess external radiation dose in Korean dwellings due to NORM in concrete walls. Reference room model for dose assessment was made by analyzing room structure and housing scale of Korean dwellings. In addition, dose assessments were made for varying room sizes. Absorbed doses to air and effective dose rates were calculated using radiation transport code MCNPX. Assuming a reference room of $3{\times}4{\times}2.8m^3$, absorbed dose rates in air were 0.80, 0.97, 0.08 nGy $h^{-1}$ per Bq $kg^{-1}$ for uranium series, thorium series, and $^{40}K$, respectively. Effective dose rates were 0.57, 0.69, 0.058 nSv $h^{-1}$ per Bq $kg^{-1}$, respectively. Radiation dose resulting from concrete of ceiling and floor increased with room area while radiation dose from concrete of walls decreased with room area. Therefore, total radiation doses were almost the same for the varying room area from 5 to $30m^2$. Effective dose in Korean dwellings was calculated based on measurement data of NORM concentration in concrete and occupancy fraction of Korean population by location. Annual effective dose was 0.59 mSv assuming that indoor occupancy fraction was 0.89 and concentrations of uranium series, thorium series and $^{40}K$ were 26, 39, 596 Bq $kg^{-1}$, respectively. Finally, annual effective dose in Korean dwellings can be calculated by the following equation: Effective dose=indoor occupancy fraction${\times}8760\;h\;y^{-1}{\times}(0.57C_U+0.69C_{Th}+0.058C_K)$.