• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.2 s.344
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• pp.27-38
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• 2006

When an RFID reader attempts to read tags, interference might occur if the neighboring readers also attempt to communicate with the same tag at the same time or the neighboring readers use the same frequency at the same time. These interferences cause the RFID reader collision. When the RFID reader collision occirs, either the command from the reader can not be transmitted to the tags or the response from the tags can not be received by the reader correctly. RFID reader anti-collision algorithms have been developed to reduce it. One of the best blown reader anti-collision algorithms is the Colorwave algorithm proposed by MIT. The Colorwave algorithm reduces the reader collisions by having the readers operate at different times. In Colorwave the time is divided into frames and a frame is divided into a number of slots. Each reader can access the tags using the slot time assigned to it. Depending on the probability of the interference, the colorwave adjusts the frame size to improve the efficiency. In this paper, we analyze the operations and the performance of the Colorwave algorithm and identify the problems of the algorithm. We also show that by adding some modifications to the algorithm the performance can be improved significantly.

• Journal of KIISE:Information Networking
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• v.36 no.1
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• pp.24-33
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• 2009

In patch-and-stitch localization algorithms, a flip error refers to the kind of error in which a patch is stitched to the map as being wrongly reflected. In this paper, we present an anchor-free localization algorithm which tries to detect and prevent flip errors. The flip error prevention is achieved by two filtering mechanisms: the flip-ambiguity test and the flip-conflict detection. We evaluate the performances of proposed techniques though simulations and show that they achieve significant performance improvements.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1357-1363
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• 1994

A Monte-Carlo simulation model is developed to predict size distribution produced by the coalescence of air bubbles in turbulent shear f1ow. The simulation consists of generating a population of air bubbles into the initial positions at each time step and tracking them by simulating motions and checking collisions. The radial displacement of air bubbles in the simulation model is produced by numerically solving an advective diffusion equation. Longitudinal displacements are generated from the logarithmic flow velovity distribution and the bubble rise velocity. Collision of air bubbles for each time step is detected by a geometric test using their relative positions at the beginning of the time step and relative displacements during the time step. At the end of the time step, the total number of bubbles, their positions, and sizes are updated. The computer program is coded such that minimum storages for sizes and positions of bubbles are required.

• Proceedings of KOSOMES biannual meeting
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• 2006.11a
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• pp.9-13
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• 2006

In the marine accidents judgment, investigation of truth of matters is one of important process to find out the reason of ship collision accidents. In this paper, reproduce system of ship collision accidents using ship manoeuvirng simulator technique will be introduced with which marine accidents can be easily reproduced in visual display at the case of marine accidents trial. In this system if the users select the type of ship and location of accidents, the process of ship collision will be provided in 2D and 3D display. The system also provides environmental visualizationdisplay such as fog whether and day-night view including various view angle that can be helpful to find out the reason of accidents.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.674-681
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• 2011

The increasing number of orbital debris objects is a risk for satellite operations due to space activities over past 50 years since launched Sputnik. The GEO (Geostationary Earth Orbit), where COMS-1 is being operated since last June 2010, has more and more risks that collide with space debris or another satellites. In this paper, as a preliminary study about GEO satellite collision probability and operations environment, collision probability between COMS-1 and RADUGA 1-7 that is one of Russian military communication satellites is investigated and analyzed. Indeed, the space environment including space debris of COMS-1 is presented. As a result, it is noted that collision probability between two satellites using NORAD TLEs on 14th Jan. 2011 was 2.8753E-07 in case that position uncertainty was assumed 10km. Particularly, the largest proportion of space debris around COMS-1's mission orbit is meteoroids.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.06a
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• pp.313-314
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• 2022

The intelligent maritime traffic information service provides a service to prevent collisions and stranding of ships based on the location information of ships periodically collected from ship equipment such as LTE-Maritime transceivers and AIS installed on ships. provided in real time. However, the above service may reduce the reliability of ship location information because GPS location information for measuring the ship's location may be cut off during transmission through LTE-Maritime or AIS networks, or phenomena such as location jumps and delays may occur. This study aims to estimate reliable position information to some extent even in an abnormal section through ship position prediction based on the existing received position information using the Kalman filter, which is an optimal estimation filter based on probability.

• Korean Journal of Environment and Ecology
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• v.33 no.6
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• pp.624-635
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• 2019

Bird strike accidents, a collision between aircraft and birds, have been increasing annually due to an increasing number of aircraft operating each year to meet heavier demand for air traffic. As such, many airports have conducted studies to assess and manage bird strike risks effectively by identifying and ranking bird species that can damage aircraft based on the bird strike records. This study was intended to investigate the bird species that were likely to threaten aircraft and compare and discuss the risk of each species estimated by the single-matrix and multi-matrix risk assessment models based on the Integrated Flight Information Service (IFIS) data collected in Gimpo, Gimhae and Jeju Airports in South Korea from 2005 to 2013. We found that there was a difference in the assessment results between the two models. The single-matrix model estimated 2 species and 6 taxa in Gimpo and Gimhae Airports and 2 species and 5 taxa in Jeju Airport to have the risk score above "high," whereas the multi-matrix model estimated 3 species and 5 taxa in Gimpo Airport, 4 species and 5 taxa in Gimhae Airport, and 2 species and 3 taxa in Jeju Airport to have the risk score above "very high." Although both models estimated the similar high-risk species in Gimpo and Gimhae Airports, there was a significant difference in Jeju Airport. Gimpo and Gimhae Airports are near the estuary of a river, which is an excellent habitat for large and heavy waterbirds. On the other hand, Jeju Airport is near the coast and the city center, and small and light bird species are mostly observed. Since collisions with such species have little effect on aircraft fuselage, the impact of common variables between the two models was small, and the additional variables caused a significant difference between the estimation by the two models.

• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.9-16
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• 2011

When a hydrofoil ship plies at high speed, there exist possibilities of collision with ocean mammals dwelling near the surface. An active sonar located within the immersed hydrofoil structure that provides the lift for the vessel, can be used for early warning of their presence. The proper functioning of the active sonar system depends on its ability to reject noise and pick up the target signal. In this article, we measured the noise on a hydrofoil of an operating ship with two flush-mounted hydrophones. The measurements were conducted for the purpose of (1) identifying the effect of operating state of machinery likes engine, cooler and generator (2) observing the change of noise depending on the measuring position (3) observing the change of noise with increasing ship speed. To verify our experiment, experiments were performed three times and the measured results are compared with other investigations and they show similarity to each other. The results are analyzed with frequency domain in order to apply to operating active sonar detecting system and focus on high frequency band within sonar's operating frequency region. Through these experiments and analysis, it is expected that we can identify the generated noise around hydrofoil where active sonar is installed and these results lead us to design active sonar that could distinguish target signal from noise more effectively.

• Journal of the Korean Arthroscopy Society
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• v.12 no.1
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• pp.32-39
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• 2008

Purpose: To evaluate the effectiveness of MRI after ACL reconstruction with femoral tunnel at 10 o'clock position. Materials and Methods: MRI findings of 29 patients after ACL reconstruction using hamstring tendon autograft were evaluated. The mean period from operation to MRI was 18.9 months($7{\sim}40$ months). Signal intensity, morphology and continuity of graft, femoral insertion, graft angle, roof impingement, cross pin breakage and position were evaluated. Those findings were compared with KT-2000, Lysholm knee score and pivot shift test. Results: There was no significant correlation between signal intensity of graft and the duration to MRI. Most common pattern of the morphology was straight, and the continuity was well-preserved. 13 cases of femoral tunnel insertion were zone 4 and 16 were zone 3. There were no roof impingement. 10 cases showed cross pin breakages, of which 5 were found at the outside of distal femoral posterior cortex. 9 showed cross pin directed posteriorly in axial view. There was no significant correlation between clinical results and cross pin breakage. Conclusion: MRI examinations after ACL reconstructions are useful to evaluate the graft status, position of the graft and cross pins. Since the direction of the cross pin is important especially in 10 o'clock femoral position, care should be taken to avoid cross pin breakage.

• The Journal of Korean Orthopaedic Ultrasound Society
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• v.7 no.1
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• pp.20-27
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• 2014

Purpose: The purpose of this study was to evaluate coracohumeral distance (CHD) in patients with or without subcoracoid impingement with hypothesis that patients with subcoracoid impingement would have narrower CHD. Materials and Methods: One hundred twenty-four patients with subacromial impingement were evaluated. The subjects with subcoracoid impingement which was affirmed clinically and confirmed by ultrasound guided subcoracoid injection (n=28) was compared with patients with subacromial impingement only (n=96). Patients with stiffness and rotator cuff tear were excluded. Absolute CHD was measured on magnetic resonance imaging (MRI) axial images and on ultrasound with the humerus in neutral position and internal rotation. Also relative ratio of distance difference (RRDD) defined as the difference of CHD in neutral position and internal rotation compared with absolute CHD in neutral on ultrasound was also measured. Results: The distance measured in neutral position was similar between US imaging and MRI (p>0.05) and both measurements did not have significant difference between the two groups (p>0.05). On ultrasound, the difference in CHD in internal rotation between the two groups nearly met the level of significance (p=0.07). No significant difference of CHD difference in two humeral positions was seen between the two groups. However, RRDD value was significantly greater in subcoracoid impingement group (p<0.05). Conclusion: No significant difference of CHD was seen between the subcoracoid impingement group and the control group. RRDD value was greater in subcoracoid impingement group suggesting that individualized coracohumeral distance in internal rotation should be taken into account when assessing patients with subcoracoid impingement.